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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 4, 2020 MWA Ltd c/o Inmarsat Global Ltd 6 April 2, 2020 8 Transmission of IPv6 Packets over Overlay Multilink Network (OMNI) 9 Interfaces 10 draft-templin-6man-omni-interface-09 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 4, 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) . . . . . . . . . . . . . . . 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 . . . . . . . . . . . . . . . . . 19 74 11. Conceptual Sending Algorithm . . . . . . . . . . . . . . . . 20 75 11.1. Multiple OMNI Interfaces . . . . . . . . . . . . . . . . 20 76 12. Router Discovery and Prefix Registration . . . . . . . . . . 21 77 13. AR and MSE Resilience . . . . . . . . . . . . . . . . . . . . 23 78 14. Detecting and Responding to MSE Failures . . . . . . . . . . 24 79 15. Transition Considerations . . . . . . . . . . . . . . . . . . 24 80 16. OMNI Interfaces on the Open Internet . . . . . . . . . . . . 25 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 . . . . . . . . . . . . . . . . . . . . . . 31 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 AERO 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 simple 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 outbound underlying interfaces (e.g., according to underlying 420 interface performance characteristics, MTU, etc). For all other 421 packets, the OMNI interface performs PMTUD even if the destination 422 appears to be on the same link since an OMNI link node on the path 423 could return a PTB message. This ensures that the path MTU is 424 adaptive and reflects the current path used for a given data flow. 426 The MN's OMNI interface forwards packets that are no larger than the 427 MTUs of selected underlying interfaces according to the ANET L2 frame 428 format. When the OMNI interface forwards a packet that is larger 429 than an underlying interface MTU, it encapsulates the packet in an 430 IPv6 header with source set to the SPAN address corresponding to the 431 packet's source and destination set to the SPAN address corresponding 432 to the packet's destination (see: Section 8). The OMNI interface 433 then uses IPv6 fragmentation to break the encapsulated packet into 434 fragments that are no larger than the underlying interface MTU and 435 sends the fragments over the ANET where they will be intercepted by 436 the AR. The AR then conveys the fragments toward the final 437 destination. (Note that the outbound fragments can further be spread 438 across multiple underlying ANET interfaces, since they will be 439 reassembled by the OMNI interface closest to the final destination.) 441 When an AR receives a fragmented or whole packet from the INET 442 destined to an ANET MN, it first determines whether to forward or 443 drop and return a PTB. If the AR deems the packet to be of 444 acceptable size, it first re-adjusts fragment sizes (if necessary) 445 then forwards the packet/fragments to the MN. If the packet is no 446 larger than the ANET MTU, the AR forwards according to the ANET L2 447 frame format. If the packet is larger than the ANET MTU, the AR 448 instead uses IPv6 encapsulation and fragmentation as above if the MN 449 accepts fragments or drops and returns a PTB otherwise. The MN then 450 reassembles and discards the encapsulation header, then forwards the 451 whole packet to the final destination. 453 Applications that cannot tolerate loss due to MTU restrictions SHOULD 454 avoid sending packets larger than 1280 bytes, since dynamic path 455 changes can reduce the path MTU at any time. Applications that may 456 benefit from sending larger packets even though the path MTU may 457 change dynamically MAY use larger sizes (i.e., up to the OMNI 458 interface MTU). 460 Note that when a Proxy/Server forwards a fragmented packet received 461 from the INET to a Client, it realigns fragments if necessary instead 462 of blindly forwarding fragments directly to the Client to avoid 463 attacks such as tiny fragments, overlapping fragments, etc. In any 464 case, however, the node that inserts the SPAN header MUST also the 465 node that inserts the Identification value in the IPv6 Fragment 466 Header. 468 Note also that the OMNI interface can forward large packets via 469 encapsulation and fragmentation while at the same time returning 470 advisory PTB messages, e.g., subject to rate limiting. The receiving 471 node that performs reassembly can also send advisory PTB messages if 472 reassembly conditions become unfavorable. The OMNI interface can 473 therefore continuously forward large packets without loss while 474 returning advisory messages recommending a smaller size. 476 6. Frame Format 478 The OMNI interface transmits IPv6 packets according to the native 479 frame format of each underlying interface. For example, for 480 Ethernet-compatible interfaces the frame format is specified in 481 [RFC2464], for aeronautical radio interfaces the frame format is 482 specified in standards such as ICAO Doc 9776 (VDL Mode 2 Technical 483 Manual), for tunnels over IPv6 the frame format is specified in 484 [RFC2473], etc. 486 7. Link-Local Addresses 488 OMNI interfaces assign IPv6 Link-Local Addresses (i.e., "OMNI LLAs") 489 using the following constructs: 491 o IPv6 MN OMNI LLAs encode the most-significant 64 bits of a MNP 492 within the least-significant 64 bits (i.e., the interface ID) of a 493 Link-Local IPv6 Unicast Address (see: [RFC4291], Section 2.5.6). 494 For example, for the MNP 2001:db8:1000:2000::/56 the corresponding 495 LLA is fe80::2001:db8:1000:2000. 497 o IPv4-compatible MN OMNI LLAs are assigned as fe80::ffff:[v4addr], 498 i.e., the most significant 10 bits of the prefix fe80::/10, 499 followed by 70 '0' bits, followed by 16 '1' bits, followed by a 500 32bit IPv4 address. For example, the IPv4-Compatible MN OMNI LLA 501 for 192.0.2.1 is fe80::ffff:192.0.2.1 (also written as 502 fe80::ffff:c000:0201). 504 o MS OMNI LLAs are assigned to ARs and MSEs from the range 505 fe80::/96, and MUST be managed for uniqueness. The lower 32 bits 506 of the LLA includes a unique integer "MSID" value between 507 0x00000001 and 0xfeffffff, e.g., as in fe80::1, fe80::2, fe80::3, 508 etc., fe80::feff:ffff. The MSID 0x00000000 corresponds to the 509 link-local Subnet-Router anycast address (fe80::) [RFC4291] and 510 the MSID 0xffffffff corresponds to the "All-MSEs" address 511 (fe80::ffff:ffff). The MSID range 0xff00000000 through 0xfffffffe 512 is reserved for future use. (Note that distinct OMNI link 513 segments can avoid overlap by assigning MS OMNI LLAs from unique 514 fe80::/96 sub-prefixes. For example, a first segment could assign 515 from fe80::1000/116, a second from fe80::2000/116, a third from 516 fe80::3000/116, etc.) 518 Since the prefix 0000::/8 is "Reserved by the IETF" [RFC4291], no 519 MNPs can be allocated from that block ensuring that there is no 520 possibility for overlap between the above OMNI LLA constructs. 522 Since MN OMNI LLAs are based on the distribution of administratively 523 assured unique MNPs, and since MS OMNI LLAs are guaranteed unique 524 through administrative assignment, OMNI interfaces set the 525 autoconfiguration variable DupAddrDetectTransmits to 0 [RFC4862]. 527 8. SPAN Addresses 529 OMNI links employ an overlay network instance called the SPAN 530 (Spanning Partitioned Administrative Networks) that supports 531 forwarding of link-local messages over a private IPv6 routing 532 instance that spans the entire link without decrementing the (link- 533 local) Hop Limit. The OMNI link reserves the Unique Local Address 534 (ULA) prefix fd80::/10 [RFC4193] known as the SPAN Service Prefix 535 (SSP) and used for mapping OMNI LLAs to IPv6 addresses that are 536 routable via the SPAN. 538 SPAN addresses are configured in one-to-one correspondence with MN/MS 539 OMNI LLAs by simply zeroing bit 7 of the LLA. For example: 541 o the SPAN address corresponding to fe80::2001:db8:1:2 is simply 542 fd80::2001:db8:1:2 544 o the SPAN address corresponding to fe80::ffff:192.0.2.1 is simply 545 fd80::ffff:192.0.2.1 547 o the SPAN address corresponding to fe80::1000 is simply fd80::1000 549 Note that for MNPs longer than 64 bits (see: Appendix B), the 550 resulting OMNI LLA would include non-routable bits when converted to 551 a SPAN address. For this reason, the Subnet-Router anycast address 552 for an IPv6 MNP is used as a "pseudo-SPAN" address instead of the 553 fd80::/10 expansion (e.g., 2001:db8:1:2:: insteadl of 554 fd80::2001:db8:1:2). This implies that the SPAN routing system needs 555 to maintain multiple types of IPv6 routes (i.e. a mix of ULA and GUA 556 routes), which would not be necessary if a mandate naming /64 as the 557 longest IPv6 prefix length were issued. 559 Further details of the SPAN are out of scope for this document. A 560 full discussion of the SPAN appears in [I-D.templin-intarea-6706bis]. 562 9. Address Mapping - Unicast 564 OMNI interfaces maintain a neighbor cache for tracking per-neighbor 565 state and use the link-local address format specified in Section 7. 566 IPv6 Neighbor Discovery (ND) [RFC4861] messages on MN OMNI interfaces 567 observe the native Source/Target Link-Layer Address Option (S/TLLAO) 568 formats of the underlying interfaces (e.g., for Ethernet the S/TLLAO 569 is specified in [RFC2464]). 571 MNs such as aircraft typically have many wireless data link types 572 (e.g. satellite-based, cellular, terrestrial, air-to-air directional, 573 etc.) with diverse performance, cost and availability properties. 574 The OMNI interface would therefore appear to have multiple L2 575 connections, and may include information for multiple underlying 576 interfaces in a single IPv6 ND message exchange. 578 OMNI interfaces use an IPv6 ND option called the "OMNI option" 579 formatted as shown in Figure 3: 581 0 1 2 3 582 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 1 583 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 584 | Type | Length | Prefix Length |R| Reserved | 585 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 586 | | 587 ~ Sub-Options ~ 588 | | 589 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 591 Figure 3: OMNI Option Format 593 In this format: 595 o Type is set to TBD. 597 o Length is set to the number of 8 octet blocks in the option. 599 o Prefix Length is set according to the IPv6 source address type. 600 For MN OMNI LLAs, the value is set to the length of the embedded 601 MNP. For IPv4-compatible MN OMNI LLAs, the value is set to 96 602 plus the length of the embedded IPv4 prefix. For MS OMNI LLAs, 603 the value is set to 128. 605 o R (the "Register/Release" bit) is set to 1/0 to request the 606 message recipient to register/release a MN's MNP. The OMNI option 607 may additionally include MSIDs for the recipient to contact to 608 also register/release the MNP. 610 o Reserved is set to the value '0' on transmission and ignored on 611 reception. 613 o Sub-Options is a Variable-length field, of length such that the 614 complete OMNI Option is an integer multiple of 8 octets long. 615 Contains one or more options, as described in Section 8.1. 617 9.1. Sub-Options 619 The OMNI option includes zero or more Sub-Options, some of which may 620 appear multiple times in the same message. Each consecutive Sub- 621 Option is concatenated immediately after its predecessor. All Sub- 622 Options except Pad1 (see below) are type-length-value (TLV) encoded 623 in the following format: 625 0 1 2 626 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 5 627 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 628 | Sub-Type | Sub-length | Sub-Option Data ... 629 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 631 Figure 4: Sub-Option Format 633 o Sub-Type is a 1-byte field that encodes the Sub-Option type. Sub- 634 Options defined in this document are: 636 Option Name Sub-Type 637 Pad1 0 638 PadN 1 639 ifIndex-tuple (Type 1) 2 640 ifIndex-tuple (Type 2) 3 641 MS-Register 4 642 MS-Release 5 644 Figure 5 646 Sub-Types 253 and 254 are reserved for experimentation, as 647 recommended in[RFC3692]]. 649 o Sub-Length is a 1-byte field that encodes the length of the Sub- 650 Option Data, in bytes 652 o Sub-Option Data is a byte string with format determined by Sub- 653 Type 655 During processing, unrecognized Sub-Options are ignored and the next 656 Sub-Option processed until the end of the OMNI option. 658 The following Sub-Option types and formats are defined in this 659 document: 661 9.1.1. Pad1 663 0 664 0 1 2 3 4 5 6 7 665 +-+-+-+-+-+-+-+-+ 666 | Sub-Type=0 | 667 +-+-+-+-+-+-+-+-+ 669 Figure 6: Pad1 671 o Sub-Type is set to 0. 673 o No Sub-Length or Sub-Option Data follows (i.e., the "Sub-Option" 674 consists of a single zero octet). 676 9.1.2. PadN 677 0 1 2 678 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 5 679 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 680 | Sub-Type=1 |Sub-length=N-2 | N-2 padding bytes ... 681 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 683 Figure 7: PadN 685 o Sub-Type is set to 1. 687 o Sub-Length is set to N-2 being the number of padding bytes that 688 follow. 690 o Sub-Option Data consists of N-2 zero-valued octets. 692 9.1.3. ifIndex-tuple (Type 1) 694 0 1 2 3 695 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 1 696 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 697 | Sub-Type=2 | Sub-length=4+N| ifIndex | ifType | 698 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 699 | Provider ID | Link |S|I|RSV| Bitmap(0)=0xff|P00|P01|P02|P03| 700 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 701 |P04|P05|P06|P07|P08|P09|P10|P11|P12|P13|P14|P15|P16|P17|P18|P19| 702 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 703 |P20|P21|P22|P23|P24|P25|P26|P27|P28|P29|P30|P31| Bitmap(1)=0xff| 704 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 705 |P32|P33|P34|P35|P36|P37|P38|P39| ... 706 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 708 Figure 8: ifIndex-tuple (Type 1) 710 o Sub-Type is set to 2. 712 o Sub-Length is set to 4+N (the number of Sub-Option Data bytes that 713 follow). 715 o Sub-Option Data contains an "ifIndex-tuple" (Type 1) encoded as 716 follows (note that the first four bytes must be present): 718 * ifIndex is set to an 8-bit integer value corresponding to a 719 specific underlying interface. OMNI options MAY include 720 multiple ifIndex-tuples, and MUST number each with an ifIndex 721 value between '1' and '255' that represents a MN-specific 8-bit 722 mapping for the actual ifIndex value assigned to the underlying 723 interface by network management [RFC2863] (the ifIndex value 724 '0' is reserved for use by the MS). Multiple ifIndex-tuples 725 with the same ifIndex value MAY appear in the same OMNI option. 727 * ifType is set to an 8-bit integer value corresponding to the 728 underlying interface identified by ifIndex. The value 729 represents an OMNI interface-specific 8-bit mapping for the 730 actual IANA ifType value registered in the 'IANAifType-MIB' 731 registry [http://www.iana.org]. 733 * Provider ID is set to an OMNI interface-specific 8-bit ID value 734 for the network service provider associated with this ifIndex. 736 * Link encodes a 4-bit link metric. The value '0' means the link 737 is DOWN, and the remaining values mean the link is UP with 738 metric ranging from '1' ("lowest") to '15' ("highest"). 740 * S is set to '1' if this ifIndex-tuple corresponds to the 741 underlying interface that is the source of the ND message. Set 742 to '0' otherwise. 744 * I is set to '0' ("Simplex") if the index for each singleton 745 Bitmap byte in the Sub-Option Data is inferred from its 746 sequential position (i.e., 0, 1, 2, ...), or set to '1' 747 ("Indexed") if each Bitmap is preceded by an Index byte. 748 Figure 8 shows the simplex case for I set to '0'. For I set to 749 '1', each Bitmap is instead preceded by an Index byte that 750 encodes a value "i" = (0 - 255) as the index for its companion 751 Bitmap as follows: 753 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 754 | Index=i | Bitmap(i) |P[*] values ... 755 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 757 Figure 9 759 * RSV is set to the value 0 on transmission and ignored on 760 reception. 762 * The remainder of the Sub-Option Data contains N = (0 - 251) 763 bytes of traffic classifier preferences consisting of a first 764 (indexed) Bitmap (i.e., "Bitmap(i)") followed by 0-8 1-byte 765 blocks of 2-bit P[*] values, followed by a second Bitmap (i), 766 followed by 0-8 blocks of P[*] values, etc. Reading from bit 0 767 to bit 7, the bits of each Bitmap(i) that are set to '1'' 768 indicate the P[*] blocks from the range P[(i*32)] through 769 P[(i*32) + 31] that follow; if any Bitmap(i) bits are '0', then 770 the corresponding P[*] block is instead omitted. For example, 771 if Bitmap(0) contains 0xff then the block with P[00]-P[03], 772 followed by the block with P[04]-P[07], etc., and ending with 773 the block with P[28]-P[31] are included (as showin in 774 Figure 8). The next Bitmap(i) is then consulted with its bits 775 indicating which P[*] blocks follow, etc. out to the end of the 776 Sub-Option. The first 16 P[*] blocks correspond to the 64 777 Differentiated Service Code Point (DSCP) values P[00] - P[63] 778 [RFC2474]. If additional P[*] blocks follow, their values 779 correspond to "pseudo-DSCP" traffic classifier values P[64], 780 P[65], P[66], etc. See Appendix A for further discussion and 781 examples. 783 * Each 2-bit P[*] field is set to the value '0' ("disabled"), '1' 784 ("low"), '2' ("medium") or '3' ("high") to indicate a QoS 785 preference level for underlying interface selection purposes. 786 Not all P[*] values need to be included in all OMNI option 787 instances of a given ifIndex-tuple. Any P[*] values 788 represented in an earlier OMNI option but ommitted in the 789 current OMNI option remain unchanged. Any P[*] values not yet 790 represented in any OMNI option default to "medium". 792 9.1.4. ifIndex-tuple (Type 2) 794 0 1 2 3 795 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 1 796 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 797 | Sub-Type=3 | Sub-length=4+N| ifIndex | ifType | 798 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 799 | Provider ID | Link |S|Resvd| ~ 800 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ 801 ~ ~ 802 ~ RFC 6088 Format Traffic Selector ~ 803 ~ ~ 804 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 806 Figure 10: ifIndex-tuple (Type 2) 808 o Sub-Type is set to 3. 810 o Sub-Length is set to 4+N (the number of Sub-Option Data bytes that 811 follow). 813 o Sub-Option Data contains an "ifIndex-tuple" (Type 2) encoded as 814 follows (note that the first four bytes must be present): 816 * ifIndex, ifType, Provider ID, Link and S are set exactly as for 817 Type 1 ifIndex-tuples as specified in Section 9.1.3. 819 * the remainder of the Sub-Option body encodes a variable-length 820 traffic selector formatted per [RFC6088], beginning with the 821 "TS Format" field. 823 9.1.5. MS-Register 825 0 1 2 3 826 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 1 827 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 828 | Sub-Type=4 | Sub-length=4 | MSID (bits 0 - 15) | 829 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 830 | MSID (bits 16 - 32) | 831 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 833 Figure 11: MS-Register Sub-option 835 o Sub-Type is set to 4. 837 o Sub-Length is set to 4. 839 o MSID contains the 32 bit ID of an MSE or AR, in network byte 840 order. OMNI options contain zero or more MS-Register sub-options. 842 9.1.6. MS-Release 844 0 1 2 3 845 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 1 846 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 847 | Sub-Type=5 | Sub-length=4 | MSID (bits 0 - 15) | 848 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 849 | MSID (bits 16 - 32) | 850 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 852 Figure 12: MS-Release Sub-option 854 o Sub-Type is set to 5. 856 o Sub-Length is set to 4. 858 o MSIID contains the 32 bit ID of an MS or AR, in network byte 859 order. OMNI options contain zero or more MS-Release sub-options. 861 10. Address Mapping - Multicast 863 The multicast address mapping of the native underlying interface 864 applies. The mobile router on board the aircraft also serves as an 865 IGMP/MLD Proxy for its EUNs and/or hosted applications per [RFC4605] 866 while using the L2 address of the router as the L2 address for all 867 multicast packets. 869 11. Conceptual Sending Algorithm 871 The MN's IPv6 layer selects the outbound OMNI interface according to 872 standard IPv6 requirements when forwarding data packets from local or 873 EUN applications to external correspondents. The OMNI interface 874 maintains a neighbor cache the same as for any IPv6 interface, but 875 with additional state for multilink coordination. 877 After a packet enters the OMNI interface, an outbound underlying 878 interface is selected based on multilink parameters such as DSCP, 879 application port number, cost, performance, message size, etc. OMNI 880 interface multilink selections could also be configured to perform 881 replication across multiple underlying interfaces for increased 882 reliability at the expense of packet duplication. 884 OMNI interface multilink service designers MUST observe the BCP 885 guidance in Section 15 [RFC3819] in terms of implications for 886 reordering when packets from the same flow may be spread across 887 multiple underlying interfaces having diverse properties. 889 11.1. Multiple OMNI Interfaces 891 MNs may associate with multiple MS instances concurrently. Each MS 892 instance represents a distinct OMNI link distinguished by its 893 associated MSPs. The MN configures a separate OMNI interface for 894 each link so that multiple interfaces (e.g., omni0, omni1, omni2, 895 etc.) are exposed to the IPv6 layer. 897 Depending on local policy and configuration, an MN may choose between 898 alternative active OMNI interfaces using a packet's DSCP, routing 899 information or static configuration. Interface selection based on 900 per-packet source addresses is also enabled when the MSPs for each 901 OMNI interface are known (e.g., discovered through Prefix Information 902 Options (PIOs) and/or Route Information Options (RIOs)). 904 Each OMNI interface can be configured over the same or different sets 905 of underlying interfaces. Each ANET distinguishes between the 906 different OMNI links based on the MSPs represented in per-packet IPv6 907 addresses. 909 Multiple distinct OMNI links can therefore be used to support fault 910 tolerance, load balancing, reliability, etc. The architectural model 911 parallels Layer 2 Virtual Local Area Networks (VLANs), where the MSPs 912 serve as (virtual) VLAN tags. 914 12. Router Discovery and Prefix Registration 916 MNs interface with the MS by sending RS messages with OMNI options 917 that include MSIDs. For each underlying interface, the MN sends an 918 RS message with an OMNI option with (R,A) flags, wth MS-Register/ 919 Release suboptions, and with destination address set to All-Routers 920 multicast (ff02::2) [RFC4291]. Example MSID discovery methods are 921 given in [RFC5214], including data link login parameters, name 922 service lookups, static configuration, etc. Alternatively, MNs can 923 discover indiviual MSIDs by sending an initial RS with MS-Register 924 MSID set to 0x00000000, or associate with all MSEs by sending an RS 925 with MS-Register MSID set to 0xffffffff. 927 MNs configure OMNI interfaces that observe the properties discussed 928 in the previous section. The OMNI interface and its underlying 929 interfaces are said to be in either the "UP" or "DOWN" state 930 according to administrative actions in conjunction with the interface 931 connectivity status. An OMNI interface transitions to UP or DOWN 932 through administrative action and/or through state transitions of the 933 underlying interfaces. When a first underlying interface transitions 934 to UP, the OMNI interface also transitions to UP. When all 935 underlying interfaces transition to DOWN, the OMNI interface also 936 transitions to DOWN. 938 When an OMNI interface transitions to UP, the MN sends RS messages to 939 register its MNP and an initial set of underlying interfaces that are 940 also UP. The MN sends additional RS messages to refresh lifetimes 941 and to register/deregister underlying interfaces as they transition 942 to UP or DOWN. The MN sends initial RS messages over an UP 943 underlying interface with its OMNI LLA as the source and with 944 destination set to All-Routers multicast. The RS messages include an 945 OMNI option per Section 9 with a valid Prefix Length, (R, A) flags, 946 ifIndex-tuples appropriate for underlying interfaces and with MS- 947 Register/Release sub-options. 949 ARs process IPv6 ND messages with OMNI options and act as a proxy for 950 MSEs. ARs receive RS messages and create a neighbor cache entry for 951 the MN, then coordinate with any named MSIDs in a manner outside the 952 scope of this document. The AR returns an RA message with 953 destination address set to the MN OMNI LLA (i.e., unicast), with 954 source address set to its MS OMNI LLA, with the P(roxy) bit set in 955 the RA flags [RFC4389], with an OMNI option with (R, A) flags, 956 ifIndex tuples and MS-Register/Release sub-options, and with any 957 information for the link that would normally be delivered in a 958 solicited RA message. ARs return RA messages with configuration 959 information in response to a MN's RS messages. The AR sets the RA 960 Cur Hop Limit, M and O flags, Router Lifetime, Reachable Time and 961 Retrans Timer values, and includes any necessary options such as: 963 o PIOs with (A; L=0) that include MSPs for the link [RFC8028]. 965 o RIOs [RFC4191] with more-specific routes. 967 o an MTU option that specifies the maximum acceptable packet size 968 for this ANET interface. 970 The AR coordinates with each Register/Release MSID then sends an 971 immediate unicast RA response without delay; therefore, the IPv6 ND 972 MAX_RA_DELAY_TIME and MIN_DELAY_BETWEEN_RAS constants for multicast 973 RAs do not apply. The AR MAY send periodic and/or event-driven 974 unsolicited RA messages according to the standard [RFC4861]. 976 When the MSE processes the OMNI information, it first validates the 977 prefix registration information. The MSE then injects/withdraws the 978 MNP in the routing/mapping system and caches/discards the new Prefix 979 Length, MNP and ifIndex-tuples. The MSE then informs the AR of 980 registration success/failure, and the AR adds the MSE to the list of 981 Register/Release MSIDs to return in an RA message OMNI option per 982 Section 9. 984 When the MN receives the RA message, it creates an OMNI interface 985 neighbor cache entry with the AR's address as an L2 address and 986 records the MSIDs that have confirmed MNP registration via this AR. 987 If the MN connects to multiple ANETs, it establishes additional AR L2 988 addresses (i.e., as a Multilink neighbor). The MN then manages its 989 underlying interfaces according to their states as follows: 991 o When an underlying interface transitions to UP, the MN sends an RS 992 over the underlying interface with an OMNI option with R set to 1. 993 The OMNI option contains at least one ifIndex-tuple with values 994 specific to this underlying interface, and may contain additional 995 ifIndex-tuples specific to this and/or other underlying 996 interfaces. The option also includes any Register/Release MSIDs. 998 o When an underlying interface transitions to DOWN, the MN sends an 999 RS or unsolicited NA message over any UP underlying interface with 1000 an OMNI option containing an ifIndex-tuple for the DOWN underlying 1001 interface with Link set to '0'. The MN sends an RS when an 1002 acknowledgement is required, or an unsolicited NA when reliability 1003 is not thought to be a concern (e.g., if redundant transmissions 1004 are sent on multiple underlying interfaces). 1006 o When the Router Lifetime for a specific AR nears expiration, the 1007 MN sends an RS over the underlying interface to receive a fresh 1008 RA. If no RA is received, the MN marks the underlying interface 1009 as DOWN. 1011 o When a MN wishes to release from one or more current MSIDs, it 1012 sends an RS or unsolicited NA message over any UP underlying 1013 interfaces with an OMNI option with a Release MSID. Each MSID 1014 then withdraws the MNP from the routing/mapping system and informs 1015 the AR that the release was successful. 1017 o When all of a MNs underlying interfaces have transitioned to DOWN 1018 (or if the prefix registration lifetime expires), any associated 1019 MSEs withdraw the MNP the same as if they had received a message 1020 with a release indication. 1022 The MN is responsible for retrying each RS exchange up to 1023 MAX_RTR_SOLICITATIONS times separated by RTR_SOLICITATION_INTERVAL 1024 seconds until an RA is received. If no RA is received over a an UP 1025 underlying interface, the MN declares this underlying interface as 1026 DOWN. 1028 The IPv6 layer sees the OMNI interface as an ordinary IPv6 interface. 1029 Therefore, when the IPv6 layer sends an RS message the OMNI interface 1030 returns an internally-generated RA message as though the message 1031 originated from an IPv6 router. The internally-generated RA message 1032 contains configuration information that is consistent with the 1033 information received from the RAs generated by the MS. Whether the 1034 OMNI interface IPv6 ND messaging process is initiated from the 1035 receipt of an RS message from the IPv6 layer is an implementation 1036 matter. Some implementations may elect to defer the IPv6 ND 1037 messaging process until an RS is received from the IPv6 layer, while 1038 others may elect to initiate the process proactively. 1040 Note: The Router Lifetime value in RA messages indicates the time 1041 before which the MN must send another RS message over this underlying 1042 interface (e.g., 600 seconds), however that timescale may be 1043 significantly longer than the lifetime the MS has committed to retain 1044 the prefix registration (e.g., REACHABLETIME seconds). ARs are 1045 therefore responsible for keeping MS state alive on a finer-grained 1046 timescale than the MN is required to do on its own behalf. 1048 13. AR and MSE Resilience 1050 ANETs SHOULD deploy ARs in Virtual Router Redundancy Protocol (VRRP) 1051 [RFC5798] configurations so that service continuity is maintained 1052 even if one or more ARs fail. Using VRRP, the MN is unaware which of 1053 the (redundant) ARs is currently providing service, and any service 1054 discontinuity will be limited to the failover time supported by VRRP. 1055 Widely deployed public domain implementations of VRRP are available. 1057 MSEs SHOULD use high availability clustering services so that 1058 multiple redundant systems can provide coordinated response to 1059 failures. As with VRRP, widely deployed public domain 1060 implementations of high availability clustering services are 1061 available. Note that special-purpose and expensive dedicated 1062 hardware is not necessary, and public domain implementations can be 1063 used even between lightweight virtual machines in cloud deployments. 1065 14. Detecting and Responding to MSE Failures 1067 In environments where fast recovery from MSE failure is required, ARs 1068 SHOULD use proactive Neighbor Unreachability Detection (NUD) in a 1069 manner that parallels Bidirectional Forwarding Detection (BFD) 1070 [RFC5880] to track MSE reachability. ARs can then quickly detect and 1071 react to failures so that cached information is re-established 1072 through alternate paths. Proactive NUD control messaging is carried 1073 only over well-connected ground domain networks (i.e., and not low- 1074 end ANET links such as aeronautical radios) and can therefore be 1075 tuned for rapid response. 1077 ARs perform proactive NUD for MSEs for which there are currently 1078 active MNs on the ANET. If an MSE fails, ARs can quickly inform MNs 1079 of the outage by sending multicast RA messages on the ANET interface. 1080 The AR sends RA messages to the MN via the ANET interface with an 1081 OMNI option with a Release ID for the failed MSE, and with 1082 destination address set to All-Nodes multicast (ff02::1) [RFC4291]. 1084 The AR SHOULD send MAX_FINAL_RTR_ADVERTISEMENTS RA messages separated 1085 by small delays [RFC4861]. Any MNs on the ANET interface that have 1086 been using the (now defunct) MSE will receive the RA messages and 1087 associate with a new MSE. 1089 15. Transition Considerations 1091 When a MN connects to an ANET link for the first time, it sends an RS 1092 message with an OMNI option. If the first hop AR recognizes the 1093 option, it returns an RA with its MS OMNI LLA as the source, the MN 1094 OMNI LLA as the destination, the P(roxy) bit set in the RA flags and 1095 with an OMNI option included. The MN then engages the AR according 1096 to the OMNI link model specified above. If the first hop AR is a 1097 legacy IPv6 router, however, it instead returns an RA message with no 1098 OMNI option and with a non-OMNI unicast source LLA as specified in 1099 [RFC4861]. In that case, the MN engages the ANET according to the 1100 legacy IPv6 link model and without the OMNI extensions specified in 1101 this document. 1103 If the ANET link model is multiple access, there must be assurance 1104 that address duplication cannot corrupt the neighbor caches of other 1105 nodes on the link. When the MN sends an RS message on a multiple 1106 access ANET link with an OMNI LLA source address and an OMNI option, 1107 ARs that recognize the option ensure that the MN is authorized to use 1108 the address and return an RA with a non-zero Router Lifetime only if 1109 the MN is authorized. ARs that do not recognize the option instead 1110 return an RA that makes no statement about the MN's authorization to 1111 use the source address. In that case, the MN should perform 1112 Duplicate Address Detection to ensure that it does not interfere with 1113 other nodes on the link. 1115 An alternative approach for multiple access ANET links to ensure 1116 isolation for MN / AR communications is through L2 address mappings 1117 as discussed in Appendix D. This arrangement imparts a (virtual) 1118 point-to-point link model over the (physical) multiple access link. 1120 16. OMNI Interfaces on the Open Internet 1122 OMNI interfaces that connect to the open Internet via native and/or 1123 NATed underlying interfaces can apply symmetric security services 1124 such as VPNs to establish secured tunnels to MSEs. In environments 1125 where an explicit VPN may be too restrictive, OMNI interfaces can 1126 instead ensure neighbor cache integrity using SEcure Neighbor 1127 Discovery (SEND) [RFC3971] and Cryptographically Generated Addresses 1128 (CGAs) [RFC3972]. 1130 When SEND/CGA are used, the IPv6 ND control plane messages used to 1131 establish neighbor cache state are authenticated while data plane 1132 messages are delivered the same as for ordinary best-effort Internet 1133 traffic. Instead, data plane communications via OMNI interfaces that 1134 connect over the open Internet without an explicit VPN must emply 1135 transport- or higher-layer security to ensure integrity and/or 1136 confidentiality. 1138 In addition to secured OMNI interface RS/RA exchanges, SEND/CGA 1139 supports safe address resolution and neighbor unreachability 1140 detection as discused in Asymmetric Extended Route Optimization 1141 (AERO) [I-D.templin-intarea-6706bis]. This allows for efficient 1142 multilink operations over the open Internet with assured neighbor 1143 cache integrity. 1145 17. IANA Considerations 1147 The IANA is instructed to allocate an official Type number TBD from 1148 the registry "IPv6 Neighbor Discovery Option Formats" for the OMNI 1149 option. Implementations set Type to 253 as an interim value 1150 [RFC4727]. 1152 The OMNI option also defines an 8-bit Sub-Type field, for which IANA 1153 is instructed to create and maintain a new registry entitled "OMNI 1154 option Sub-Type values". Initial values for the OMNI option Sub-Type 1155 values registry are given below; future assignments are to be made 1156 through Expert Review [RFC8126]. 1158 Value Sub-Type name Reference 1159 ----- ------------- ---------- 1160 0 Pad1 [RFCXXXX] 1161 1 PadN [RFCXXXX] 1162 2 ifIndex-tuple (Type 1) [RFCXXXX] 1163 3 ifIndex-tuple (Type 2) [RFCXXXX] 1164 4 MS-Register [RFCXXXX] 1165 5 MS-Release [RFCXXXX] 1166 6-252 Unassigned 1167 253-254 Experimental [RFCXXXX] 1168 255 Reserved [RFCXXXX] 1170 Figure 13: OMNI Option Sub-Type Values 1172 The IANA is instructed to allocate one Ethernet unicast address TBD2 1173 (suggest 00-00-5E-00-52-14 [RFC5214]) in the registry "IANA Ethernet 1174 Address Block - Unicast Use". 1176 18. Security Considerations 1178 Security considerations for IPv6 [RFC8200] and IPv6 Neighbor 1179 Discovery [RFC4861] apply. OMNI interface IPv6 ND messages SHOULD 1180 include Nonce and Timestamp options [RFC3971] when synchronized 1181 transaction confirmation is needed. 1183 OMNI interfaces configured over secured underlying ANET interfaces 1184 inherit the physical and/or link-layer security aspects of the 1185 connected ANETs. OMNI interfaces configured over open Internet 1186 interfaces must use symmetric securing services such as VPNs or 1187 asymmetric services such as SEND/CGA [RFC3971][RFC3972]. 1189 Security considerations for specific access network interface types 1190 are covered under the corresponding IP-over-(foo) specification 1191 (e.g., [RFC2464], [RFC2492], etc.). 1193 19. Acknowledgements 1195 The first version of this document was prepared per the consensus 1196 decision at the 7th Conference of the International Civil Aviation 1197 Organization (ICAO) Working Group-I Mobility Subgroup on March 22, 1198 2019. Consensus to take the document forward to the IETF was reached 1199 at the 9th Conference of the Mobility Subgroup on November 22, 2019. 1200 Attendees and contributors included: Guray Acar, Danny Bharj, 1201 Francois D'Humieres, Pavel Drasil, Nikos Fistas, Giovanni Garofolo, 1202 Bernhard Haindl, Vaughn Maiolla, Tom McParland, Victor Moreno, Madhu 1203 Niraula, Brent Phillips, Liviu Popescu, Jacky Pouzet, Aloke Roy, Greg 1204 Saccone, Robert Segers, Michal Skorepa, Michel Solery, Stephane 1205 Tamalet, Fred Templin, Jean-Marc Vacher, Bela Varkonyi, Tony Whyman, 1206 Fryderyk Wrobel and Dongsong Zeng. 1208 The following individuals are acknowledged for their useful comments: 1209 Michael Matyas, Madhu Niraula, Greg Saccone, Stephane Tamalet, Eric 1210 Vyncke. Pavel Drasil, Zdenek Jaron and Michal Skorepa are recognized 1211 for their many helpful ideas and suggestions. 1213 This work is aligned with the NASA Safe Autonomous Systems Operation 1214 (SASO) program under NASA contract number NNA16BD84C. 1216 This work is aligned with the FAA as per the SE2025 contract number 1217 DTFAWA-15-D-00030. 1219 20. References 1221 20.1. Normative References 1223 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1224 Requirement Levels", BCP 14, RFC 2119, 1225 DOI 10.17487/RFC2119, March 1997, 1226 . 1228 [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black, 1229 "Definition of the Differentiated Services Field (DS 1230 Field) in the IPv4 and IPv6 Headers", RFC 2474, 1231 DOI 10.17487/RFC2474, December 1998, 1232 . 1234 [RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander, 1235 "SEcure Neighbor Discovery (SEND)", RFC 3971, 1236 DOI 10.17487/RFC3971, March 2005, 1237 . 1239 [RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)", 1240 RFC 3972, DOI 10.17487/RFC3972, March 2005, 1241 . 1243 [RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and 1244 More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191, 1245 November 2005, . 1247 [RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast 1248 Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005, 1249 . 1251 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 1252 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 1253 2006, . 1255 [RFC4727] Fenner, B., "Experimental Values In IPv4, IPv6, ICMPv4, 1256 ICMPv6, UDP, and TCP Headers", RFC 4727, 1257 DOI 10.17487/RFC4727, November 2006, 1258 . 1260 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 1261 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 1262 DOI 10.17487/RFC4861, September 2007, 1263 . 1265 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 1266 Address Autoconfiguration", RFC 4862, 1267 DOI 10.17487/RFC4862, September 2007, 1268 . 1270 [RFC6088] Tsirtsis, G., Giarreta, G., Soliman, H., and N. Montavont, 1271 "Traffic Selectors for Flow Bindings", RFC 6088, 1272 DOI 10.17487/RFC6088, January 2011, 1273 . 1275 [RFC8028] Baker, F. and B. Carpenter, "First-Hop Router Selection by 1276 Hosts in a Multi-Prefix Network", RFC 8028, 1277 DOI 10.17487/RFC8028, November 2016, 1278 . 1280 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 1281 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 1282 May 2017, . 1284 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 1285 (IPv6) Specification", STD 86, RFC 8200, 1286 DOI 10.17487/RFC8200, July 2017, 1287 . 1289 [RFC8201] McCann, J., Deering, S., Mogul, J., and R. Hinden, Ed., 1290 "Path MTU Discovery for IP version 6", STD 87, RFC 8201, 1291 DOI 10.17487/RFC8201, July 2017, 1292 . 1294 20.2. Informative References 1296 [I-D.templin-intarea-6706bis] 1297 Templin, F., "Asymmetric Extended Route Optimization 1298 (AERO)", draft-templin-intarea-6706bis-36 (work in 1299 progress), April 2020. 1301 [RFC2225] Laubach, M. and J. Halpern, "Classical IP and ARP over 1302 ATM", RFC 2225, DOI 10.17487/RFC2225, April 1998, 1303 . 1305 [RFC2464] Crawford, M., "Transmission of IPv6 Packets over Ethernet 1306 Networks", RFC 2464, DOI 10.17487/RFC2464, December 1998, 1307 . 1309 [RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in 1310 IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473, 1311 December 1998, . 1313 [RFC2492] Armitage, G., Schulter, P., and M. Jork, "IPv6 over ATM 1314 Networks", RFC 2492, DOI 10.17487/RFC2492, January 1999, 1315 . 1317 [RFC2863] McCloghrie, K. and F. Kastenholz, "The Interfaces Group 1318 MIB", RFC 2863, DOI 10.17487/RFC2863, June 2000, 1319 . 1321 [RFC3692] Narten, T., "Assigning Experimental and Testing Numbers 1322 Considered Useful", BCP 82, RFC 3692, 1323 DOI 10.17487/RFC3692, January 2004, 1324 . 1326 [RFC3819] Karn, P., Ed., Bormann, C., Fairhurst, G., Grossman, D., 1327 Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J., and L. 1328 Wood, "Advice for Internet Subnetwork Designers", BCP 89, 1329 RFC 3819, DOI 10.17487/RFC3819, July 2004, 1330 . 1332 [RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery 1333 Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April 1334 2006, . 1336 [RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick, 1337 "Internet Group Management Protocol (IGMP) / Multicast 1338 Listener Discovery (MLD)-Based Multicast Forwarding 1339 ("IGMP/MLD Proxying")", RFC 4605, DOI 10.17487/RFC4605, 1340 August 2006, . 1342 [RFC5213] Gundavelli, S., Ed., Leung, K., Devarapalli, V., 1343 Chowdhury, K., and B. Patil, "Proxy Mobile IPv6", 1344 RFC 5213, DOI 10.17487/RFC5213, August 2008, 1345 . 1347 [RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site 1348 Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214, 1349 DOI 10.17487/RFC5214, March 2008, 1350 . 1352 [RFC5798] Nadas, S., Ed., "Virtual Router Redundancy Protocol (VRRP) 1353 Version 3 for IPv4 and IPv6", RFC 5798, 1354 DOI 10.17487/RFC5798, March 2010, 1355 . 1357 [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 1358 (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, 1359 . 1361 [RFC6543] Gundavelli, S., "Reserved IPv6 Interface Identifier for 1362 Proxy Mobile IPv6", RFC 6543, DOI 10.17487/RFC6543, May 1363 2012, . 1365 [RFC7084] Singh, H., Beebee, W., Donley, C., and B. Stark, "Basic 1366 Requirements for IPv6 Customer Edge Routers", RFC 7084, 1367 DOI 10.17487/RFC7084, November 2013, 1368 . 1370 [RFC7421] Carpenter, B., Ed., Chown, T., Gont, F., Jiang, S., 1371 Petrescu, A., and A. Yourtchenko, "Analysis of the 64-bit 1372 Boundary in IPv6 Addressing", RFC 7421, 1373 DOI 10.17487/RFC7421, January 2015, 1374 . 1376 [RFC7847] Melia, T., Ed. and S. Gundavelli, Ed., "Logical-Interface 1377 Support for IP Hosts with Multi-Access Support", RFC 7847, 1378 DOI 10.17487/RFC7847, May 2016, 1379 . 1381 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 1382 Writing an IANA Considerations Section in RFCs", BCP 26, 1383 RFC 8126, DOI 10.17487/RFC8126, June 2017, 1384 . 1386 Appendix A. Type 1 ifIndex-tuple Traffic Classifier Preference Encoding 1388 Adaptation of the OMNI option Type 1 ifIndex-tuple's traffic 1389 classifier Bitmap to specific Internetworks such as the Aeronautical 1390 Telecommunications Network with Internet Protocol Services (ATN/IPS) 1391 may include link selection preferences based on other traffic 1392 classifiers (e.g., transport port numbers, etc.) in addition to the 1393 existing DSCP-based preferences. Nodes on specific Internetworks 1394 maintain a map of traffic classifiers to additional P[*] preference 1395 fields beyond the first 64. For example, TCP port 22 maps to P[67], 1396 TCP port 443 maps to P[70], UDP port 8060 maps to P[76], etc. 1398 Implementations use Simplex or Indexed encoding formats for P[*] 1399 encoding in order to encode a given set of traffic classifiers in the 1400 most efficient way. Some use cases may be more efficiently coded 1401 using Simplex form, while others may be more efficient using Indexed. 1402 Once a format is selected for preparation of a single ifIndex-tuple 1403 the same format must be used for the entire Sub-Option. Different 1404 Sub-Options may use different formats. 1406 The following figures show coding examples for various Simplex and 1407 Indexed formats: 1409 0 1 2 3 1410 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 1411 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1412 | Sub-Type=2 | Sub-length=4+N| ifIndex | ifType | 1413 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1414 | Provider ID | Link |S|0|RSV| Bitmap(0)=0xff|P00|P01|P02|P03| 1415 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1416 |P04|P05|P06|P07|P08|P09|P10|P11|P12|P13|P14|P15|P16|P17|P18|P19| 1417 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1418 |P20|P21|P22|P23|P24|P25|P26|P27|P28|P29|P30|P31| Bitmap(1)=0xff| 1419 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1420 |P32|P33|P34|P35|P36|P37|P38|P39|P40|P41|P42|P43|P44|P45|P46|P47| 1421 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1422 |P48|P49|P50|P51|P52|P53|P54|P55|P56|P57|P58|P59|P60|P61|P62|P63| 1423 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1424 | Bitmap(2)=0xff|P64|P65|P67|P68| ... 1425 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1427 Figure 14: Example 1: Dense Simplex Encoding 1429 0 1 2 3 1430 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 1431 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1432 | Sub-Type=2 | Sub-length=4+N| ifIndex | ifType | 1433 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1434 | Provider ID | Link |S|0|RSV| Bitmap(0)=0x00| Bitmap(1)=0x0f| 1435 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1436 |P48|P49|P50|P51|P52|P53|P54|P55|P56|P57|P58|P59|P60|P61|P62|P63| 1437 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1438 | Bitmap(2)=0x00| Bitmap(3)=0x00| Bitmap(4)=0x00| Bitmap(5)=0x00| 1439 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1440 | Bitmap(6)=0xf0|192|193|194|195|196|197|198|199|200|201|202|203| 1441 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1442 |204|205|206|207| Bitmap(7)=0x00| Bitmap(8)=0x0f|272|273|274|275| 1443 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1444 |276|277|278|279|280|281|282|283|284|285|286|287| Bitmap(9)=0x00| 1445 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1446 |Bitmap(10)=0x00| ... 1447 +-+-+-+-+-+-+-+-+-+-+- 1449 Figure 15: Example 2: Sparse Simplex Encoding 1451 0 1 2 3 1452 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 1453 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1454 | Sub-Type=2 | Sub-length=4+N| ifIndex | ifType | 1455 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1456 | Provider ID | Link |S|1|RSV| Index = 0x00 | Bitmap = 0x80 | 1457 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1458 |P00|P01|P02|P03| Index = 0x01 | Bitmap = 0x01 |P60|P61|P62|P63| 1459 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1460 | Index = 0x10 | Bitmap = 0x80 |512|513|514|515| Index = 0x18 | 1461 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1462 | Bitmap = 0x01 |796|797|798|799| ... 1463 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1465 Figure 16: Example 3: Indexed Encoding 1467 Appendix B. Prefix Length Considerations 1469 The 64-bit boundary in IPv6 addresses [RFC7421] determines the MN 1470 OMNI LLA format for encoding the most-significant 64 MNP bits into 1471 the least-significant 64 bits of the prefix fe80::/64 as discussed in 1472 Section 7. 1474 [RFC4291] defines the link-local address format as the most 1475 significant 10 bits of the prefix fe80::/10, followed by 54 unused 1476 bits, followed by the least-significant 64 bits of the address. If 1477 the 64-bit boundary is relaxed through future standards activity, 1478 then the 54 unused bits can be employed for extended coding of MNPs 1479 of length /65 up to /118. 1481 The extended coding format would continue to encode MNP bits 0-63 in 1482 bits 64-127 of the OMNI LLA, while including MNP bits 64-117 in bits 1483 10-63. For example, the OMNI LLA corresponding to the MNP 1484 2001:db8:1111:2222:3333:4444:5555::/112 would be 1485 fe8c:ccd1:1115:5540:2001:db8:1111:2222/128, and would still be a 1486 valid IPv6 LLA per [RFC4291]. However, a prefix length shorter than 1487 /128 cannot be applied due to the non-sequential byte ordering. 1489 Note that if the 64-bit boundary were relaxed an alternate form of 1490 OMNI LLA construction could be employed by embedding the MNP 1491 beginning with the most significant bit immediately following bit 10 1492 of the prefix fe80::/10. For example, the OMNI LLA corresponding to 1493 the MNP 2001:db8:1111:2222:3333:4444:5555::/112 would be written as 1494 fe88:0043:6e04:4448:888c:ccd1:1115:5540/122. This alternate form may 1495 provide a more natural coding for the MS along with the ability to 1496 apply a fully-qualified prefix length. It has the disadvantages of 1497 requiring an unweildy 10-bit right-shift of a 16byte address, as well 1498 as presenting a non-human-readable form. 1500 Appendix C. VDL Mode 2 Considerations 1502 ICAO Doc 9776 is the "Technical Manual for VHF Data Link Mode 2" 1503 (VDLM2) that specifies an essential radio frequency data link service 1504 for aircraft and ground stations in worldwide civil aviation air 1505 traffic management. The VDLM2 link type is "multicast capable" 1506 [RFC4861], but with considerable differences from common multicast 1507 links such as Ethernet and IEEE 802.11. 1509 First, the VDLM2 link data rate is only 31.5Kbps - multiple orders of 1510 magnitude less than most modern wireless networking gear. Second, 1511 due to the low available link bandwidth only VDLM2 ground stations 1512 (i.e., and not aircraft) are permitted to send broadcasts, and even 1513 so only as compact layer 2 "beacons". Third, aircraft employ the 1514 services of ground stations by performing unicast RS/RA exchanges 1515 upon receipt of beacons instead of listening for multicast RA 1516 messages and/or sending multicast RS messages. 1518 This beacon-oriented unicast RS/RA approach is necessary to conserve 1519 the already-scarce available link bandwidth. Moreover, since the 1520 numbers of beaconing ground stations operating within a given spatial 1521 range must be kept as sparse as possible, it would not be feasible to 1522 have different classes of ground stations within the same region 1523 observing different protocols. It is therefore highly desirable that 1524 all ground stations observe a common language of RS/RA as specified 1525 in this document. 1527 Note that links of this nature may benefit from compression 1528 techniques that reduce the bandwidth necessary for conveying the same 1529 amount of data. The IETF lpwan working group is considering possible 1530 alternatives: [https://datatracker.ietf.org/wg/lpwan/documents]. 1532 Appendix D. MN / AR Isolation Through L2 Address Mapping 1534 Per [RFC4861], IPv6 ND messages may be sent to either a multicast or 1535 unicast link-scoped IPv6 destination address. However, IPv6 ND 1536 messaging should be coordinated between the MN and AR only without 1537 invoking other nodes on the ANET. This implies that MN / AR 1538 coordinations should be isolated and not overheard by other nodes on 1539 the link. 1541 To support MN / AR isolation on some ANET links, ARs can maintain an 1542 OMNI-specific unicast L2 address ("MSADDR"). For Ethernet-compatible 1543 ANETs, this specification reserves one Ethernet unicast address TBD2 1544 (see: Section 17). For non-Ethernet statically-addressed ANETs, 1545 MSADDR is reserved per the assigned numbers authority for the ANET 1546 addressing space. For still other ANETs, MSADDR may be dynamically 1547 discovered through other means, e.g., L2 beacons. 1549 MNs map the L3 addresses of all IPv6 ND messages they send (i.e., 1550 both multicast and unicast) to MSADDR instead of to an ordinary 1551 unicast or multicast L2 address. In this way, all of the MN's IPv6 1552 ND messages will be received by ARs that are configured to accept 1553 packets destined to MSADDR. Note that multiple ARs on the link could 1554 be configured to accept packets destined to MSADDR, e.g., as a basis 1555 for supporting redundancy. 1557 Therefore, ARs must accept and process packets destined to MSADDR, 1558 while all other devices must not process packets destined to MSADDR. 1559 This model has well-established operational experience in Proxy 1560 Mobile IPv6 (PMIP) [RFC5213][RFC6543]. 1562 Appendix E. Change Log 1564 << RFC Editor - remove prior to publication >> 1566 Differences from draft-templin-6man-omni-interface-07 to draft- 1567 templin-6man-omni-interface-08: 1569 o OMNI MNs in the open Internet 1570 Differences from draft-templin-6man-omni-interface-06 to draft- 1571 templin-6man-omni-interface-07: 1573 o Brought back L2 MSADDR mapping text for MN / AR isolation based on 1574 L2 addressing. 1576 o Explanded "Transition Considerations". 1578 Differences from draft-templin-6man-omni-interface-05 to draft- 1579 templin-6man-omni-interface-06: 1581 o Brought back OMNI option "R" flag, and dicussed its use. 1583 Differences from draft-templin-6man-omni-interface-04 to draft- 1584 templin-6man-omni-interface-05: 1586 o Transition considerations, and overhaul of RS/RA addressing with 1587 the inclusion of MSE addresses within the OMNI option instead of 1588 as RS/RA addresses (developed under FAA SE2025 contract number 1589 DTFAWA-15-D-00030). 1591 Differences from draft-templin-6man-omni-interface-02 to draft- 1592 templin-6man-omni-interface-03: 1594 o Added "advisory PTB messages" under FAA SE2025 contract number 1595 DTFAWA-15-D-00030. 1597 Differences from draft-templin-6man-omni-interface-01 to draft- 1598 templin-6man-omni-interface-02: 1600 o Removed "Primary" flag and supporting text. 1602 o Clarified that "Router Lifetime" applies to each ANET interface 1603 independently, and that the union of all ANET interface Router 1604 Lifetimes determines MSE lifetime. 1606 Differences from draft-templin-6man-omni-interface-00 to draft- 1607 templin-6man-omni-interface-01: 1609 o "All-MSEs" OMNI LLA defined. Also reserverd fe80::ff00:0000/104 1610 for future use (most likely as "pseudo-multicast"). 1612 o Non-normative discussion of alternate OMNI LLA construction form 1613 made possible if the 64-bit assumption were relaxed. 1615 Differences from draft-templin-atn-aero-interface-21 to draft- 1616 templin-6man-omni-interface-00: 1618 o Minor clarification on Type-2 ifIndex-tuple encoding. 1620 o Draft filename change (replaces draft-templin-atn-aero-interface). 1622 Differences from draft-templin-atn-aero-interface-20 to draft- 1623 templin-atn-aero-interface-21: 1625 o OMNI option format 1627 o MTU 1629 Differences from draft-templin-atn-aero-interface-19 to draft- 1630 templin-atn-aero-interface-20: 1632 o MTU 1634 Differences from draft-templin-atn-aero-interface-18 to draft- 1635 templin-atn-aero-interface-19: 1637 o MTU 1639 Differences from draft-templin-atn-aero-interface-17 to draft- 1640 templin-atn-aero-interface-18: 1642 o MTU and RA configuration information updated. 1644 Differences from draft-templin-atn-aero-interface-16 to draft- 1645 templin-atn-aero-interface-17: 1647 o New "Primary" flag in OMNI option. 1649 Differences from draft-templin-atn-aero-interface-15 to draft- 1650 templin-atn-aero-interface-16: 1652 o New note on MSE OMNI LLA uniqueness assurance. 1654 o General cleanup. 1656 Differences from draft-templin-atn-aero-interface-14 to draft- 1657 templin-atn-aero-interface-15: 1659 o General cleanup. 1661 Differences from draft-templin-atn-aero-interface-13 to draft- 1662 templin-atn-aero-interface-14: 1664 o General cleanup. 1666 Differences from draft-templin-atn-aero-interface-12 to draft- 1667 templin-atn-aero-interface-13: 1669 o Minor re-work on "Notify-MSE" (changed to Notification ID). 1671 Differences from draft-templin-atn-aero-interface-11 to draft- 1672 templin-atn-aero-interface-12: 1674 o Removed "Request/Response" OMNI option formats. Now, there is 1675 only one OMNI option format that applies to all ND messages. 1677 o Added new OMNI option field and supporting text for "Notify-MSE". 1679 Differences from draft-templin-atn-aero-interface-10 to draft- 1680 templin-atn-aero-interface-11: 1682 o Changed name from "aero" to "OMNI" 1684 o Resolved AD review comments from Eric Vyncke (posted to atn list) 1686 Differences from draft-templin-atn-aero-interface-09 to draft- 1687 templin-atn-aero-interface-10: 1689 o Renamed ARO option to AERO option 1691 o Re-worked Section 13 text to discuss proactive NUD. 1693 Differences from draft-templin-atn-aero-interface-08 to draft- 1694 templin-atn-aero-interface-09: 1696 o Version and reference update 1698 Differences from draft-templin-atn-aero-interface-07 to draft- 1699 templin-atn-aero-interface-08: 1701 o Removed "Classic" and "MS-enabled" link model discussion 1703 o Added new figure for MN/AR/MSE model. 1705 o New Section on "Detecting and responding to MSE failure". 1707 Differences from draft-templin-atn-aero-interface-06 to draft- 1708 templin-atn-aero-interface-07: 1710 o Removed "nonce" field from AR option format. Applications that 1711 require a nonce can include a standard nonce option if they want 1712 to. 1714 o Various editorial cleanups. 1716 Differences from draft-templin-atn-aero-interface-05 to draft- 1717 templin-atn-aero-interface-06: 1719 o New Appendix C on "VDL Mode 2 Considerations" 1721 o New Appendix D on "RS/RA Messaging as a Single Standard API" 1723 o Various significant updates in Section 5, 10 and 12. 1725 Differences from draft-templin-atn-aero-interface-04 to draft- 1726 templin-atn-aero-interface-05: 1728 o Introduced RFC6543 precedent for focusing IPv6 ND messaging to a 1729 reserved unicast link-layer address 1731 o Introduced new IPv6 ND option for Aero Registration 1733 o Specification of MN-to-MSE message exchanges via the ANET access 1734 router as a proxy 1736 o IANA Considerations updated to include registration requests and 1737 set interim RFC4727 option type value. 1739 Differences from draft-templin-atn-aero-interface-03 to draft- 1740 templin-atn-aero-interface-04: 1742 o Removed MNP from aero option format - we already have RIOs and 1743 PIOs, and so do not need another option type to include a Prefix. 1745 o Clarified that the RA message response must include an aero option 1746 to indicate to the MN that the ANET provides a MS. 1748 o MTU interactions with link adaptation clarified. 1750 Differences from draft-templin-atn-aero-interface-02 to draft- 1751 templin-atn-aero-interface-03: 1753 o Sections re-arranged to match RFC4861 structure. 1755 o Multiple aero interfaces 1757 o Conceptual sending algorithm 1759 Differences from draft-templin-atn-aero-interface-01 to draft- 1760 templin-atn-aero-interface-02: 1762 o Removed discussion of encapsulation (out of scope) 1764 o Simplified MTU section 1766 o Changed to use a new IPv6 ND option (the "aero option") instead of 1767 S/TLLAO 1769 o Explained the nature of the interaction between the mobility 1770 management service and the air interface 1772 Differences from draft-templin-atn-aero-interface-00 to draft- 1773 templin-atn-aero-interface-01: 1775 o Updates based on list review comments on IETF 'atn' list from 1776 4/29/2019 through 5/7/2019 (issue tracker established) 1778 o added list of opportunities afforded by the single virtual link 1779 model 1781 o added discussion of encapsulation considerations to Section 6 1783 o noted that DupAddrDetectTransmits is set to 0 1785 o removed discussion of IPv6 ND options for prefix assertions. The 1786 aero address already includes the MNP, and there are many good 1787 reasons for it to continue to do so. Therefore, also including 1788 the MNP in an IPv6 ND option would be redundant. 1790 o Significant re-work of "Router Discovery" section. 1792 o New Appendix B on Prefix Length considerations 1794 First draft version (draft-templin-atn-aero-interface-00): 1796 o Draft based on consensus decision of ICAO Working Group I Mobility 1797 Subgroup March 22, 2019. 1799 Authors' Addresses 1801 Fred L. Templin (editor) 1802 The Boeing Company 1803 P.O. Box 3707 1804 Seattle, WA 98124 1805 USA 1807 Email: fltemplin@acm.org 1808 Tony Whyman 1809 MWA Ltd c/o Inmarsat Global Ltd 1810 99 City Road 1811 London EC1Y 1AX 1812 England 1814 Email: tony.whyman@mccallumwhyman.com