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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group F. Templin, Ed. 3 Internet-Draft The Boeing Company 4 Updates: rfc1191, rfc4193, rfc4291, A. Whyman 5 rfc4443, rfc8201 (if approved) MWA Ltd c/o Inmarsat Global Ltd 6 Intended status: Standards Track October 2, 2020 7 Expires: April 5, 2021 9 Transmission of IP Packets over Overlay Multilink Network (OMNI) 10 Interfaces 11 draft-templin-6man-omni-interface-44 13 Abstract 15 Mobile nodes (e.g., aircraft of various configurations, terrestrial 16 vehicles, seagoing vessels, enterprise wireless devices, etc.) 17 communicate with networked correspondents over multiple access 18 network data links and configure mobile routers to connect end user 19 networks. A multilink interface specification is therefore needed 20 for coordination with the network-based mobility service. This 21 document specifies the transmission of IP packets over Overlay 22 Multilink Network (OMNI) Interfaces. 24 Status of This Memo 26 This Internet-Draft is submitted in full conformance with the 27 provisions of BCP 78 and BCP 79. 29 Internet-Drafts are working documents of the Internet Engineering 30 Task Force (IETF). Note that other groups may also distribute 31 working documents as Internet-Drafts. The list of current Internet- 32 Drafts is at https://datatracker.ietf.org/drafts/current/. 34 Internet-Drafts are draft documents valid for a maximum of six months 35 and may be updated, replaced, or obsoleted by other documents at any 36 time. It is inappropriate to use Internet-Drafts as reference 37 material or to cite them other than as "work in progress." 39 This Internet-Draft will expire on April 5, 2021. 41 Copyright Notice 43 Copyright (c) 2020 IETF Trust and the persons identified as the 44 document authors. All rights reserved. 46 This document is subject to BCP 78 and the IETF Trust's Legal 47 Provisions Relating to IETF Documents 48 (https://trustee.ietf.org/license-info) in effect on the date of 49 publication of this document. Please review these documents 50 carefully, as they describe your rights and restrictions with respect 51 to this document. Code Components extracted from this document must 52 include Simplified BSD License text as described in Section 4.e of 53 the Trust Legal Provisions and are provided without warranty as 54 described in the Simplified BSD License. 56 Table of Contents 58 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 59 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 60 3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 7 61 4. Overlay Multilink Network (OMNI) Interface Model . . . . . . 8 62 5. The OMNI Adaptation Layer (OAL) . . . . . . . . . . . . . . . 11 63 5.1. Fragmentation Security Implications . . . . . . . . . . . 15 64 6. Frame Format . . . . . . . . . . . . . . . . . . . . . . . . 16 65 7. Link-Local Addresses (LLAs) . . . . . . . . . . . . . . . . . 16 66 8. Unique-Local Addresses (ULAs) . . . . . . . . . . . . . . . . 17 67 9. Address Mapping - Unicast . . . . . . . . . . . . . . . . . . 18 68 9.1. Sub-Options . . . . . . . . . . . . . . . . . . . . . . . 20 69 9.1.1. Pad1 . . . . . . . . . . . . . . . . . . . . . . . . 21 70 9.1.2. PadN . . . . . . . . . . . . . . . . . . . . . . . . 21 71 9.1.3. Interface Attributes . . . . . . . . . . . . . . . . 21 72 9.1.4. Traffic Selector . . . . . . . . . . . . . . . . . . 25 73 9.1.5. MS-Register . . . . . . . . . . . . . . . . . . . . . 26 74 9.1.6. MS-Release . . . . . . . . . . . . . . . . . . . . . 26 75 9.1.7. Network Access Identifier (NAI) . . . . . . . . . . . 27 76 9.1.8. Geo Coordinates . . . . . . . . . . . . . . . . . . . 28 77 9.1.9. DHCP Unique Identifier (DUID) . . . . . . . . . . . . 28 78 10. Address Mapping - Multicast . . . . . . . . . . . . . . . . . 29 79 11. Conceptual Sending Algorithm . . . . . . . . . . . . . . . . 29 80 11.1. Multiple OMNI Interfaces . . . . . . . . . . . . . . . . 29 81 12. Router Discovery and Prefix Registration . . . . . . . . . . 30 82 12.1. Router Discovery in IP Multihop and IPv4-Only Access 83 Networks . . . . . . . . . . . . . . . . . . . . . . . . 34 84 12.2. MS-Register and MS-Release List Processing . . . . . . . 35 85 13. Secure Redirection . . . . . . . . . . . . . . . . . . . . . 37 86 14. AR and MSE Resilience . . . . . . . . . . . . . . . . . . . . 37 87 15. Detecting and Responding to MSE Failures . . . . . . . . . . 38 88 16. Transition Considerations . . . . . . . . . . . . . . . . . . 38 89 17. OMNI Interfaces on the Open Internet . . . . . . . . . . . . 39 90 18. Time-Varying MNPs . . . . . . . . . . . . . . . . . . . . . . 40 91 19. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 40 92 20. Security Considerations . . . . . . . . . . . . . . . . . . . 41 93 21. Implementation Status . . . . . . . . . . . . . . . . . . . . 42 94 22. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 42 95 23. References . . . . . . . . . . . . . . . . . . . . . . . . . 43 96 23.1. Normative References . . . . . . . . . . . . . . . . . . 43 97 23.2. Informative References . . . . . . . . . . . . . . . . . 45 98 Appendix A. Interface Attribute Heuristic Bitmap Encoding . . . 49 99 Appendix B. VDL Mode 2 Considerations . . . . . . . . . . . . . 51 100 Appendix C. MN / AR Isolation Through L2 Address Mapping . . . . 52 101 Appendix D. Change Log . . . . . . . . . . . . . . . . . . . . . 52 102 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 55 104 1. Introduction 106 Mobile Nodes (MNs) (e.g., aircraft of various configurations, 107 terrestrial vehicles, seagoing vessels, enterprise wireless devices, 108 etc.) often have multiple data links for communicating with networked 109 correspondents. These data links may have diverse performance, cost 110 and availability properties that can change dynamically according to 111 mobility patterns, flight phases, proximity to infrastructure, etc. 112 MNs coordinate their data links in a discipline known as "multilink", 113 in which a single virtual interface is configured over the underlying 114 data links. 116 The MN configures a virtual interface (termed the "Overlay Multilink 117 Network (OMNI) interface") as a thin layer over the underlying Access 118 Network (ANET) interfaces. The OMNI interface is therefore the only 119 interface abstraction exposed to the IP layer and behaves according 120 to the Non-Broadcast, Multiple Access (NBMA) interface principle, 121 while underlying interfaces appear as link layer communication 122 channels in the architecture. The OMNI interface connects to a 123 virtual overlay service known as the "OMNI link". The OMNI link 124 spans one or more Internetworks that may include private-use 125 infrastructures and/or the global public Internet itself. 127 Each MN receives a Mobile Network Prefix (MNP) for numbering 128 downstream-attached End User Networks (EUNs) independently of the 129 access network data links selected for data transport. The MN 130 performs router discovery over the OMNI interface (i.e., similar to 131 IPv6 customer edge routers [RFC7084]) and acts as a mobile router on 132 behalf of its EUNs. The router discovery process is iterated over 133 each of the OMNI interface's underlying interfaces in order to 134 register per-link parameters (see Section 12). 136 The OMNI interface provides a multilink nexus for exchanging inbound 137 and outbound traffic via the correct underlying interface(s). The IP 138 layer sees the OMNI interface as a point of connection to the OMNI 139 link. Each OMNI link has one or more associated Mobility Service 140 Prefixes (MSPs) from which OMNI link MNPs are derived. If there are 141 multiple OMNI links, the IPv6 layer will see multiple OMNI 142 interfaces. 144 MNs may connect to multiple distinct OMNI links by configuring 145 multiple OMNI interfaces, e.g., omni0, omni1, omni2, etc. Each OMNI 146 interface is configured over a set of underlying interfaces and 147 provides a nexus for Safety-Based Multilink (SBM) operation. The IP 148 layer selects an OMNI interface based on SBM routing considerations, 149 then the selected interface applies Performance-Based Multilink (PBM) 150 to select the correct underlying interface. Applications can apply 151 Segment Routing [RFC8402] to select independent SBM topologies for 152 fault tolerance. 154 The OMNI interface interacts with a network-based Mobility Service 155 (MS) through IPv6 Neighbor Discovery (ND) control message exchanges 156 [RFC4861]. The MS provides Mobility Service Endpoints (MSEs) that 157 track MN movements and represent their MNPs in a global routing or 158 mapping system. 160 This document specifies the transmission of IP packets and MN/MS 161 control messages over OMNI interfaces. The OMNI interface supports 162 either IP protocol version (i.e., IPv4 [RFC0791] or IPv6 [RFC8200]) 163 as the network layer in the data plane, while using IPv6 ND messaging 164 as the control plane independently of the data plane IP protocol(s). 165 The OMNI Adaptation Layer (OAL) which operates as a mid-layer between 166 L3 and L2 is based on IP-in-IPv6 encapsulation per [RFC2473] as 167 discussed in the following sections. 169 2. Terminology 171 The terminology in the normative references applies; especially, the 172 terms "link" and "interface" are the same as defined in the IPv6 173 [RFC8200] and IPv6 Neighbor Discovery (ND) [RFC4861] specifications. 174 Additionally, this document assumes the following IPv6 ND message 175 types: Router Solicitation (RS), Router Advertisement (RA), Neighbor 176 Solicitation (NS), Neighbor Advertisement (NA) and Redirect. 178 The Protocol Constants defined in Section 10 of [RFC4861] are used in 179 their same format and meaning in this document. The terms "All- 180 Routers multicast", "All-Nodes multicast" and "Subnet-Router anycast" 181 are the same as defined in [RFC4291] (with Link-Local scope assumed). 183 The term "IP" is used to refer collectively to either Internet 184 Protocol version (i.e., IPv4 [RFC0791] or IPv6 [RFC8200]) when a 185 specification at the layer in question applies equally to either 186 version. 188 The following terms are defined within the scope of this document: 190 Mobile Node (MN) 191 an end system with a mobile router having multiple distinct 192 upstream data link connections that are grouped together in one or 193 more logical units. The MN's data link connection parameters can 194 change over time due to, e.g., node mobility, link quality, etc. 195 The MN further connects a downstream-attached End User Network 196 (EUN). The term MN used here is distinct from uses in other 197 documents, and does not imply a particular mobility protocol. 199 End User Network (EUN) 200 a simple or complex downstream-attached mobile network that 201 travels with the MN as a single logical unit. The IP addresses 202 assigned to EUN devices remain stable even if the MN's upstream 203 data link connections change. 205 Mobility Service (MS) 206 a mobile routing service that tracks MN movements and ensures that 207 MNs remain continuously reachable even across mobility events. 208 Specific MS details are out of scope for this document. 210 Mobility Service Endpoint (MSE) 211 an entity in the MS (either singular or aggregate) that 212 coordinates the mobility events of one or more MN. 214 Mobility Service Prefix (MSP) 215 an aggregated IP prefix (e.g., 2001:db8::/32, 192.0.2.0/24, etc.) 216 advertised to the rest of the Internetwork by the MS, and from 217 which more-specific Mobile Network Prefixes (MNPs) are derived. 219 Mobile Network Prefix (MNP) 220 a longer IP prefix taken from an MSP (e.g., 221 2001:db8:1000:2000::/56, 192.0.2.8/30, etc.) and assigned to a MN. 222 MNs sub-delegate the MNP to devices located in EUNs. 224 Access Network (ANET) 225 a data link service network (e.g., an aviation radio access 226 network, satellite service provider network, cellular operator 227 network, wifi network, etc.) that connects MNs. Physical and/or 228 data link level security between the MN and ANET are assumed. 230 Access Router (AR) 231 a first-hop router in the ANET for connecting MNs to 232 correspondents in outside Internetworks. 234 ANET interface 235 a MN's attachment to a link in an ANET. 237 Internetwork (INET) 238 a connected network region with a coherent IP addressing plan that 239 provides transit forwarding services for ANET MNs and INET 240 correspondents. Examples include private enterprise networks, 241 ground domain aviation service networks and the global public 242 Internet itself. 244 INET interface 245 a node's attachment to a link in an INET. 247 OMNI link 248 a Non-Broadcast, Multiple Access (NBMA) virtual overlay configured 249 over one or more INETs and their connected ANETs. An OMNI link 250 can comprise multiple INET segments joined by bridges the same as 251 for any link; the addressing plans in each segment may be mutually 252 exclusive and managed by different administrative entities. 254 OMNI interface 255 a node's attachment to an OMNI link, and configured over one or 256 more underlying ANET/INET interfaces. 258 OMNI Adaptation Layer (OAL) 259 an OMNI interface process whereby packets admitted into the 260 interface are wrapped in a mid-layer IPv6 header and fragmented/ 261 reassembled if necessary to support the OMNI link Maximum 262 Transmission Unit (MTU). The OAL is also responsible for 263 generating MTU-related control messages as necessary, and for 264 providing addressing context for spanning multiple segments of a 265 bridged OMNI link. 267 OMNI Link-Local Address (LLA) 268 a link local IPv6 address per [RFC4291] constructed as specified 269 in Section 7. 271 OMNI Unique-Local Address (ULA) 272 a unique local IPv6 address per [RFC4193] constructed as specified 273 in Section 8. OMNI ULAs are statelessly derived from OMNI LLAs, 274 and vice-versa. 276 OMNI Option 277 an IPv6 Neighbor Discovery option providing multilink parameters 278 for the OMNI interface as specified in Section 9. 280 Multilink 281 an OMNI interface's manner of managing diverse underlying data 282 link interfaces as a single logical unit. The OMNI interface 283 provides a single unified interface to upper layers, while 284 underlying data link selections are performed on a per-packet 285 basis considering factors such as DSCP, flow label, application 286 policy, signal quality, cost, etc. Multilinking decisions are 287 coordinated in both the outbound (i.e. MN to correspondent) and 288 inbound (i.e., correspondent to MN) directions. 290 L2 291 The second layer in the OSI network model. Also known as "layer- 292 2", "link-layer", "sub-IP layer", "data link layer", etc. 294 L3 295 The third layer in the OSI network model. Also known as "layer- 296 3", "network-layer", "IP layer", etc. 298 underlying interface 299 an ANET/INET interface over which an OMNI interface is configured. 300 The OMNI interface is seen as a L3 interface by the IP layer, and 301 each underlying interface is seen as a L2 interface by the OMNI 302 interface. 304 Mobility Service Identification (MSID) 305 Each MSE and AR is assigned a unique 32-bit Identification (MSID) 306 as specified in Section 7. 308 Safety-Based Multilink (SBM) 309 A means for ensuring fault tolerance through redundancy by 310 connecting multiple independent OMNI interfaces to independent 311 routing topologies (i.e., multiple independent OMNI links). 313 Performance Based Multilink (PBM) 314 A means for selecting underlying interface(s) for packet 315 trasnmission and reception within a single OMNI interface. 317 3. Requirements 319 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 320 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 321 "OPTIONAL" in this document are to be interpreted as described in BCP 322 14 [RFC2119][RFC8174] when, and only when, they appear in all 323 capitals, as shown here. 325 OMNI links maintain a constant value "MAX_MSID" selected to provide 326 MNs with an acceptable level of MSE redundancy while minimizing 327 control message amplificaiton. It is RECOMMENDED that MAX_MSID be 328 set to the default value 5; if a different value is chosen, it should 329 be set uniformly by all nodes on the OMNI link. 331 An implementation is not required to internally use the architectural 332 constructs described here so long as its external behavior is 333 consistent with that described in this document. 335 4. Overlay Multilink Network (OMNI) Interface Model 337 An OMNI interface is a MN virtual interface configured over one or 338 more underlying interfaces, which may be physical (e.g., an 339 aeronautical radio link) or virtual (e.g., an Internet or higher- 340 layer "tunnel"). The MN receives a MNP from the MS, and coordinates 341 with the MS through IPv6 ND message exchanges. The MN uses the MNP 342 to construct a unique OMNI LLA through the algorithmic derivation 343 specified in Section 7 and assigns the LLA to the OMNI interface. 345 The OMNI interface architectural layering model is the same as in 346 [RFC5558][RFC7847], and augmented as shown in Figure 1. The IP layer 347 therefore sees the OMNI interface as a single L3 interface with 348 multiple underlying interfaces that appear as L2 communication 349 channels in the architecture. 351 +----------------------------+ 352 | Upper Layer Protocol | 353 Session-to-IP +---->| | 354 Address Binding | +----------------------------+ 355 +---->| IP (L3) | 356 IP Address +---->| | 357 Binding | +----------------------------+ 358 +---->| OMNI Interface | 359 Logical-to- +---->| (OMNI LLA) | 360 Physical | +----------------------------+ 361 Interface +---->| L2 | L2 | | L2 | 362 Binding |(IF#1)|(IF#2)| ..... |(IF#n)| 363 +------+------+ +------+ 364 | L1 | L1 | | L1 | 365 | | | | | 366 +------+------+ +------+ 368 Figure 1: OMNI Interface Architectural Layering Model 370 The OMNI virtual interface model gives rise to a number of 371 opportunities: 373 o since OMNI LLAs are uniquely derived from an MNP, no Duplicate 374 Address Detection (DAD) or Muticast Listener Discovery (MLD) 375 messaging is necessary. 377 o ANET interfaces do not require any L3 addresses (i.e., not even 378 link-local) in environments where communications are coordinated 379 entirely over the OMNI interface. (An alternative would be to 380 also assign the same OMNI LLA to all ANET interfaces.) 382 o as ANET interface properties change (e.g., link quality, cost, 383 availability, etc.), any active ANET interface can be used to 384 update the profiles of multiple additional ANET interfaces in a 385 single message. This allows for timely adaptation and service 386 continuity under dynamically changing conditions. 388 o coordinating ANET interfaces in this way allows them to be 389 represented in a unified MS profile with provisions for mobility 390 and multilink operations. 392 o exposing a single virtual interface abstraction to the IPv6 layer 393 allows for multilink operation (including QoS based link 394 selection, packet replication, load balancing, etc.) at L2 while 395 still permitting L3 traffic shaping based on, e.g., DSCP, flow 396 label, etc. 398 o L3 sees the OMNI interface as a point of connection to the OMNI 399 link; if there are multiple OMNI links (i.e., multiple MS's), L3 400 will see multiple OMNI interfaces. 402 o Multiple independent OMNI interfaces can be used for increased 403 fault tolerance through Safety-Based Multilink (SBM), with 404 Performance-Based Multilink (PBM) applied within each interface. 406 Other opportunities are discussed in [RFC7847]. 408 Figure 2 depicts the architectural model for a MN connecting to the 409 MS via multiple independent ANETs. When an underlying interface 410 becomes active, the MN's OMNI interface sends native (i.e., 411 unencapsulated) IPv6 ND messages via the underlying interface. IPv6 412 ND messages traverse the ground domain ANETs until they reach an 413 Access Router (AR#1, AR#2, .., AR#n). The AR then coordinates with a 414 Mobility Service Endpoint (MSE#1, MSE#2, ..., MSE#m) in the INET and 415 returns an IPv6 ND message response to the MN. IPv6 ND messages 416 traverse the ANET at layer 2; hence, the Hop Limit is not 417 decremented. 419 +--------------+ 420 | MN | 421 +--------------+ 422 |OMNI interface| 423 +----+----+----+ 424 +--------|IF#1|IF#2|IF#n|------ + 425 / +----+----+----+ \ 426 / | \ 427 / <---- Native | IP ----> \ 428 v v v 429 (:::)-. (:::)-. (:::)-. 430 .-(::ANET:::) .-(::ANET:::) .-(::ANET:::) 431 `-(::::)-' `-(::::)-' `-(::::)-' 432 +----+ +----+ +----+ 433 ... |AR#1| .......... |AR#2| ......... |AR#n| ... 434 . +-|--+ +-|--+ +-|--+ . 435 . | | | 436 . v v v . 437 . <----- Encapsulation -----> . 438 . . 439 . +-----+ (:::)-. . 440 . |MSE#2| .-(::::::::) +-----+ . 441 . +-----+ .-(::: INET :::)-. |MSE#m| . 442 . (::::: Routing ::::) +-----+ . 443 . `-(::: System :::)-' . 444 . +-----+ `-(:::::::-' . 445 . |MSE#1| +-----+ +-----+ . 446 . +-----+ |MSE#3| |MSE#4| . 447 . +-----+ +-----+ . 448 . . 449 . . 450 . <----- Worldwide Connected Internetwork ----> . 451 ........................................................... 453 Figure 2: MN/MS Coordination via Multiple ANETs 455 After the initial IPv6 ND message exchange, the MN can send and 456 receive unencapsulated IP data packets over the OMNI interface. OMNI 457 interface multilink services will forward the packets via ARs in the 458 correct underlying ANETs. The AR encapsulates the packets according 459 to the capabilities provided by the MS and forwards them to the next 460 hop within the worldwide connected Internetwork via optimal routes. 462 OMNI links span one or more underlying Internetwork via the OMNI 463 Adaptation Layer (OAL) which is based on a mid-layer overlay 464 encapsulation using [RFC2473] with [RFC4193] addressing. Each OMNI 465 link corresponds to a different overlay (differentiated by an address 466 codepoint) which may be carried over a completely separate underlying 467 topology. Each MN can facilitate SBM by connecting to multiple OMNI 468 links using a distinct OMNI interface for each link. 470 5. The OMNI Adaptation Layer (OAL) 472 The OMNI interface observes the link nature of tunnels, including the 473 Maximum Transmission Unit (MTU), Maximum Reassembly Unit (MRU) and 474 the role of fragmentation and reassembly [I-D.ietf-intarea-tunnels]. 475 The OMNI interface is configured over one or more underlying 476 interfaces that may have diverse MTUs. OMNI interfaces accommodate 477 MTU diversity through the use of the OMNI Adpatation Layer (OAL) as 478 discussed in this section. 480 IPv6 underlying interfaces are REQUIRED to configure a minimum MTU of 481 1280 bytes and a minimum MRU of 1500 bytes [RFC8200], meaning that 482 the minimum IPv6 path MTU is 1280 bytes since routers on the path are 483 not permitted to perform network fragmentation even though the 484 destination is required to reassemble more. The network therefore 485 MUST forward packets of at least 1280 bytes without generating an 486 IPv6 Path MTU Discovery (PMTUD) Packet Too Big (PTB) message 487 [RFC8201]. (Note: the source can apply "source fragmentation" for 488 locally-generated IPv6 packets up to 1500 bytes and larger still if 489 it if has a way to determine that the destination configures a larger 490 MRU, but this does not affect the minimum IPv6 path MTU.) 492 IPv4 underlying interfaces are REQUIRED to configure a minimum MTU of 493 68 bytes [RFC0791] and a minimum MRU of 576 bytes [RFC0791][RFC1122]. 494 Therefore, when the Don't Fragment (DF) bit in the IPv4 header is set 495 to 0 the minimum IPv4 path MTU is 576 bytes since routers on the path 496 support network fragmentation and the destination is required to 497 reassemble at least that much. The DF bit in the IPv4 encapsulation 498 headers of packets sent over IPv4 underlying interfaces therefore 499 MUST be set to 0. (Note: even if the encapsulation source has a way 500 to determine that the encapsulation destination configures an MRU 501 larger than 576 bytes, it should not assume a larger minimum IPv4 502 path MTU without careful consderation of the issues discussed in 503 Section 5.1.) 505 The OMNI interface configures both an MTU and MRU of 9180 bytes 506 [RFC2492]; the size is therefore not a reflection of the underlying 507 interface MTUs, but rather determines the largest packet the OMNI 508 interface can forward or reassemble. The OMNI interface uses the 509 OMNI Adaptation Layer (OAL) to admit packets from the network layer 510 that are no larger than the OMNI interface MTU while generating 511 ICMPv4 Fragmentation Needed [RFC1191] or ICMPv6 Path MTU Discovery 512 (PMTUD) Packet Too Big (PTB) [RFC8201] messages as necessary. This 513 document refers to both of these ICMPv4/ICMPv6 message types simply 514 as "PTBs", and introduces a distinction between PTB "hard" and "soft" 515 errors as discussed below. 517 For IPv4 packets with DF=0, the network layer performs IPv4 518 fragmentation if necessary then admits the packets/fragments into the 519 OMNI interface; these fragments will be reassembled by the final 520 destination. For IPv4 packets with DF=1 and IPv6 packets, the 521 network layer admits the packet if it is no larger than the OMNI 522 interface MTU; otherwise, it drops the packet and returns a PTB hard 523 error message to the source. 525 For each admitted IP packet/fragment, the OMNI interface internally 526 employs the OAL by either inserting or omitting a mid-layer IPv6 527 header between the inner IP packet/fragment and any outer IP 528 encapsulation headers per [RFC2473]. When the OAL inserts a mid- 529 layer IPv6 header, it calculates the 32-bit CRC over the entire 530 packet and writes the value in a trailing 4-octet field at the end of 531 the packet. The OAL then fragments this mid-layer IPv6 packet when 532 necessary, and returns internally-generated PTB soft error messages 533 for packets that it deems too large (e.g., according to link 534 performance characteristics, reassembly congestion, etc.) while 535 forwarding the packets/fragments without loss. This ensures that the 536 path MTU is adaptive and reflects the current path used for a given 537 data flow. 539 The OAL operates with respect to both the minimum IPv6 and IPv4 path 540 MTUs as follows: 542 o When an OMNI interface sends a packet toward a final destination 543 via an ANET peer, it sends without OAL encapsulation if the packet 544 (including any outer-layer ANET encapsulations) is no larger than 545 the underlying interface MTU for on-link ANET peers or the minimum 546 ANET path MTU for peers separated by multiple IP hops. Otherwise, 547 the OAL inserts an IPv6 header per [RFC2473] with source address 548 set to the node's own OMNI Unique Local Address (ULA) (see: 549 Section 8) and destination set to the OMNI ULA of the ANET peer. 550 The OAL then calculates and appends the trailing 32-bit CRC, then 551 uses IPv6 fragmentation to break the packet into a minimum number 552 of non-overlapping fragments where the largest fragment size 553 (including both the OMNI and any outer-layer ANET encapsulations) 554 is determined by the underlying interface MTU for on-link ANET 555 peers or the minimum ANET path MTU for peers separated by multiple 556 IP hops. The OAL then encapsulates the fragements in any ANET 557 headers and sends them to the ANET peer, which reassembles before 558 forwarding toward the final destination. 560 o When an OMNI interface sends a packet toward a final destination 561 via an INET interface, it sends packets (including any outer-layer 562 INET encapsulations) no larger than the minimum INET path MTU 563 without OAL encapsulation if the destination is reached via an 564 INET address within the same OMNI link segment. Otherwise, the 565 OAL inserts an IPv6 header per [RFC2473] with source address set 566 to the node's OMNI ULA, destination set to the ULA of the next hop 567 OMNI node toward the final destination and (if necessary) with a 568 Segment Routing Header with the remaining Segment IDs on the path 569 to the final destination. The OAL then calculates and appends the 570 trailing 32-bit CRC, then uses IPv6 fragmentation to break the 571 packet into a minimum number of non-overlapping fragments where 572 the largest fragment size (including both the OMNI and outer-layer 573 INET encapsulations) is the minimum INET path MTU, and the 574 smallest fragment size is no smaller than 256 bytes (i.e., 575 slightly less than half the minimum IPv4 path MTU). The OAL then 576 encapsulates the fragments in any INET headers and sends them to 577 the OMNI link neighbor, which reassembles before forwarding toward 578 the final destination. 580 The OAL unconditionally drops all OAL fragments received from an INET 581 peer that are smaller than 256 bytes (note that no minimum fragment 582 size is specified for ANET peers since the underlying ANET is secured 583 against tiny fragment attacks). In order to set the correct context 584 for reassembly, the OAL of the OMNI interface that inserts the IPv6 585 header MUST also be the one that inserts the IPv6 Fragment Header 586 Identification value. While not strictly required, sending all 587 fragments of the same fragmented OAL packet consecutively over the 588 same underlying interface with minimal inter-fragment delay may 589 increase the likelihood of successful reassembly. 591 Ordinary PTB messages with ICMPv4 header "unused" field or ICMPv6 592 header Code field value 0 are hard errors that always indicate that a 593 packet has been dropped due to a real MTU restriction. However, the 594 OAL can also forward large packets via encapsulation and 595 fragmentation while at the same time returning PTB soft error 596 messages (subject to rate limiting) indicating that a forwarded 597 packet was uncomfortably large. The OMNI interface can therefore 598 continuously forward large packets without loss while returning PTB 599 soft error messages recommending a smaller size. Original sources 600 that receive the soft errors in turn reduce the size of the packets 601 they send, i.e., the same as for hard errors. 603 The OAL sets the ICMPv4 header "unused" field or ICMPv6 header Code 604 field to the value 1 in PTB soft error messages. Receiving nodes 605 that recognize the code reduce their estimate of the path MTU the 606 same as for hard errors but do not regard the message as a loss 607 indication. Nodes that do not recognize the code treat the message 608 the same as a hard error, but should heed the retransmission advice 609 given in [RFC8201] which suggests retransmission based on normal 610 packetization layer retransmission timers. This document therefore 611 updates [RFC1191][RFC4443] and [RFC8201]. Furthermore, 612 implementations of [RFC4821] must be aware that PTB hard or soft 613 errors may arrive at any time even if after a successful MTU probe 614 (this is the same consideration as for an ordinary path fluctuation 615 following a successful probe). 617 In summary, the OAL supports continuous transmission and reception of 618 packets of various sizes in the face of dynamically changing network 619 conditions. Moreover, since PTB soft errors do not indicate loss, 620 original sources that receive soft errors can quickly scan for path 621 MTU increases without waiting for the minimum 10 minutes specified 622 for loss-oriented PTB hard errors [RFC1191][RFC8201]. The OAL 623 therefore provides a lossless and adaptive service that accommodates 624 MTU diversity especially well suited for dynamic multilink 625 environments. 627 Note: In network paths where IPv6/IPv4 protocol translation or IPv6- 628 in-IPv4 encapsulation may be prevalent, it may be prudent for the OAL 629 to always assume the IPv4 minimum path MTU (i.e., 576 bytes) 630 regardless of the underlying interface IP protocol version. Always 631 assuming the IPv4 minimum path MTU even for IPv6 underlying 632 interfaces may produce more fragments and additional header overhead, 633 but will always interoperate and never run the risk of presenting an 634 IPv4 node with a packet that exceeds its MRU. 636 Note: An OMNI interface that reassembles OAL fragments may experience 637 congestion-oriented loss in its reassembly cache and can optionally 638 send PTB soft errors to the original source and/or ICMP "Time 639 Exceeded" messages to the source of the OAL fragments. In 640 environments where the messages may contribute to unacceptable 641 additional congestion, however, the OMNI interface can simply regard 642 the loss as an ordinary unreported congestion event for which the 643 original source will eventually compensate. 645 Note: When the network layer forwards an IPv4 packet/fragment with 646 DF=0 into the OMNI interface, the interface can optionally perform 647 (further) IPv4 fragmentation before invoking the OAL so that the 648 fragments will be reassembled by the final destination. When the 649 network layer performs IPv6 fragmentation for locally-generated IPv6 650 packets, the OMNI interface typically invokes the OAL without first 651 applying (further) IPv6 fragmentation; the network layer should 652 therefore fragment to the minimum IPv6 path MTU (or smaller still) to 653 push the reassembly burden to the final destination and avoid 654 receiving PTB soft errors from the OMNI interface. Aside from these 655 non-normative guidelines, the manner in which any IP fragmentation is 656 invoked prior to OAL encapsulation/fragmentation is an implementation 657 matter. 659 Note: Inclusion of the 32-bit CRC prior to fragmentation assumes that 660 the receiving OAL will discard any packets with incorrect CRC values 661 following reassembly. The 32-bit CRC is sufficient to detect 662 reassembly misassociations for packet sizes up to the OMNI interface 663 MTU 9180 but may not be sufficient to detect errors for larger sizes 664 [CRC]. 666 5.1. Fragmentation Security Implications 668 As discussed in Section 3.7 of [RFC8900], there are four basic 669 threats concerning IPv6 fragmentation; each of which is addressed by 670 effective mitigations as follows: 672 1. Overlapping fragment attacks - reassembly of overlapping 673 fragments is forbidden by [RFC8200]; therefore, this threat does 674 not apply to the OAL. 676 2. Resource exhaustion attacks - this threat is mitigated by 677 providing a sufficiently large OAL reassembly cache and 678 instituting "fast discard" of incomplete reassemblies that may be 679 part of a buffer exhaustion attack. The reassembly cache should 680 be sufficiently large so that a sustained attack does not cause 681 excessive loss of good reassemblies but not so large that (timer- 682 based) data structure management becomes computationally 683 expensive. The cache should also be indexed based on the arrival 684 underlying interface such that congestion experienced over a 685 first underlying interface does not cause discard of incomplete 686 reassemblies for uncongested underlying interfaces. 688 3. Attacks based on predictable fragment identification values - 689 this threat is mitigated by selecting a suitably random ID value 690 per [RFC7739]. 692 4. Evasion of Network Intrusion Detection Systems (NIDS) - this 693 threat is mitigated by disallowing "tiny fragments" per the OAL 694 fragmentation procedures specified above. 696 Additionally, IPv4 fragmentation includes a 16-bit Identification (IP 697 ID) field with only 65535 unique values such that at high data rates 698 the field could wrap and apply to new packets while the fragments of 699 old packets using the same ID are still alive in the network 700 [RFC4963]. However, since the largest OAL fragment that will be sent 701 via an IPv4 INET path is 576 bytes any IPv4 fragmentation would occur 702 only on links with an IPv4 MTU smaller than this size, and [RFC3819] 703 recommendations suggest that such links will have low data rates. 704 Since IPv6 provides a 32-bit Identification value, IP ID wraparound 705 at high data rates is not a concern for IPv6 fragmentation. 707 6. Frame Format 709 The OMNI interface transmits IPv6 packets according to the native 710 frame format of each underlying interface. For example, for 711 Ethernet-compatible interfaces the frame format is specified in 712 [RFC2464], for aeronautical radio interfaces the frame format is 713 specified in standards such as ICAO Doc 9776 (VDL Mode 2 Technical 714 Manual), for tunnels over IPv6 the frame format is specified in 715 [RFC2473], etc. 717 7. Link-Local Addresses (LLAs) 719 OMNI interfaces construct IPv6 Link-Local Addresses (i.e., "OMNI 720 LLAs") as follows: 722 o IPv6 MN OMNI LLAs encode the most-significant 112 bits of a MNP 723 within the least-significant 112 bits of the IPv6 link-local 724 prefix fe80::/16. The Prefix Length is determined by adding 16 to 725 the length of the embedded MNP. For example, for the MNP 726 2001:db8:1000:2000::/56 the corresponding MN OMNI LLA is 727 fe80:2001:db8:1000:2000::/72. This specification updates the IPv6 728 link-local address format specified in Section 2.5.6 of [RFC4291] 729 by defining a use for bits 11 - 63. 731 o IPv4-compatible MN OMNI LLAs are constructed as fe80::ffff:[IPv4], 732 i.e., the most significant 16 bits of the prefix fe80::/16, 733 followed by 64 '0' bits, followed by 16 '1' bits, followed by a 734 32bit IPv4 address/prefix. The Prefix Length is determined by 735 adding 96 to the length of the embedded IPv4 address/prefix. For 736 example, the IPv4-Compatible MN OMNI LLA for 192.0.2.0/24 is 737 fe80::ffff:192.0.2.0/120 (also written as 738 fe80::ffff:c000:0200/120). 740 o MS OMNI LLAs are assigned to ARs and MSEs from the range 741 fe80::/96, and MUST be managed for uniqueness. The lower 32 bits 742 of the LLA includes a unique integer "MSID" value between 743 0x00000001 and 0xfeffffff, e.g., as in fe80::1, fe80::2, fe80::3, 744 etc., fe80::feff:ffff. The MS OMNI LLA Prefix Length is 745 determined by adding 96 to the MSID prefix length. For example, 746 if the MSID '0x10002000' prefix length is 16 then the MS OMNI LLA 747 Prefix Length is set to 112 and the LLA is written as 748 fe80::1000:2000/112. Finally, the MSID 0x00000000 is the 749 "Anycast" MSID and corresponds to the link-local Subnet-Router 750 anycast address (fe80::) [RFC4291]; the MSID range 0xff000000 751 through 0xffffffff is reserved for future use. 753 o The OMNI LLA range fe80::/32 is used as the service prefix for the 754 address format specified in Section 4 of [RFC4380] (see Section 17 755 for further discussion). 757 Since the prefix 0000::/8 is "Reserved by the IETF" [RFC4291], no 758 MNPs can be allocated from that block ensuring that there is no 759 possibility for overlap between the above OMNI LLA constructs. 761 Since MN OMNI LLAs are based on the distribution of administratively 762 assured unique MNPs, and since MS OMNI LLAs are guaranteed unique 763 through administrative assignment, OMNI interfaces set the 764 autoconfiguration variable DupAddrDetectTransmits to 0 [RFC4862]. 766 8. Unique-Local Addresses (ULAs) 768 OMNI links use IPv6 Unique Local Addresses (i.e., "OMNI ULAs") 769 [RFC4193] as the source and destination addresses in OAL IPv6 770 encapsulation headers. This document currently assumes use of the 771 ULA prefix fc80::/10 for mapping OMNI LLAs to routable OMNI ULAs 772 (however, see the note at the end of this section). 774 Each OMNI link instance is identified by bits 10-15 of the OMNI 775 service prefix fc80::/10. For example, OMNI ULAs associated with 776 instance 0 are configured from the prefix fc80::/16, instance 1 from 777 fc81::/16, etc., up to instance 63 from fcbf::/16. OMNI ULAs and 778 their associated prefix lengths are configured in one-to-one 779 correspondence with OMNI LLAs through stateless prefix translation. 780 For example, for OMNI link instance fc80::/16: 782 o the OMNI ULA corresponding to fe80:2001:db8:1:2::/80 is simply 783 fc80:2001:db8:1:2::/80 785 o the OMNI ULA corresponding to fe80::ffff:192.0.2.0/120 is simply 786 fc80::ffff:192.0.2.0/120 788 o the OMNI ULA corresponding to fe80::1000/112 is simply 789 fc80::1000/112 791 o the OMNI ULA corresponding to fe80::/128 is simply fc80:/128. 793 Each OMNI interface assigns the Anycast OMNI ULA specific to the OMNI 794 link instance, e.g., the OMNI interface connected to instance 3 795 assigns the Anycast OMNI ULA fc83:. Routers that configure OMNI 796 interfaces advertise the OMNI service prefix (e.g., fc83::/16) into 797 the local routing system so that applications can direct traffic 798 according to SBM requirements. 800 The OMNI ULA presents an IPv6 address format that is routable within 801 the OMNI link routing system and can be used to convey link-scoped 802 messages across multiple hops using IPv6 encapsulation [RFC2473]. 803 The OMNI link extends across one or more underling Internetworks to 804 include all ARs and MSEs. All MNs are also considered to be 805 connected to the OMNI link, however OAL encapsulation is omitted over 806 ANET links when possible to conserve bandwidth (see: Section 11). 808 The OMNI link can be subdivided into "segments" that often correspond 809 to different administrative domains or physical partitions. OMNI 810 nodes can use IPv6 Segment Routing [RFC8402] when necessary to 811 support efficient packet forwarding to destinations located in other 812 OMNI link segments. A full discussion of Segment Routing over the 813 OMNI link appears in [I-D.templin-intarea-6706bis]. 815 NOTE: An alternative to the application of ULAs as discussed in this 816 document would be to re-purpose the deprectated IPv6 Site-Local 817 Address (SLA) range fec0::/10 [RFC3879]. In many ways, re-purposing 818 SLAs would be a more natural fit since both LLA and SLA prefix 819 lengths are ::/10, the prefixes fe80:: and fec0:: differ only in a 820 single bit setting, and LLAs and SLAs can be unambiguously allocated 821 in one-to-one correspondence with one another. Re-purposing SLAs 822 would also make good use of an otherwise-wasted address range that 823 has been "parked" since the 2004 deprecation. However, moving from 824 ULAs to SLAs would require an IETF standards action acknowledging 825 this document as obsoleting [RFC3879] and updating [RFC4291]. The 826 authors therefore defer to IETF consensus as to the proper way 827 forward. 829 9. Address Mapping - Unicast 831 OMNI interfaces maintain a neighbor cache for tracking per-neighbor 832 state and use the link-local address format specified in Section 7. 833 OMNI interface IPv6 Neighbor Discovery (ND) [RFC4861] messages sent 834 over physical underlying interfaces without encapsulation observe the 835 native underlying interface Source/Target Link-Layer Address Option 836 (S/TLLAO) format (e.g., for Ethernet the S/TLLAO is specified in 837 [RFC2464]). OMNI interface IPv6 ND messages sent over underlying 838 interfaces via encapsulation do not include S/TLLAOs which were 839 intended for encoding physical L2 media address formats and not 840 encapsulation IP addresses. Furthermore S/TLLAOs are not intended 841 for encoding additional interface attributes. Hence, this document 842 does not define an S/TLLAO format but instead defines a new option 843 type termed the "OMNI option" designed for these purposes. 845 MNs such as aircraft typically have many wireless data link types 846 (e.g. satellite-based, cellular, terrestrial, air-to-air directional, 847 etc.) with diverse performance, cost and availability properties. 849 The OMNI interface would therefore appear to have multiple L2 850 connections, and may include information for multiple underlying 851 interfaces in a single IPv6 ND message exchange. OMNI interfaces use 852 an IPv6 ND option called the OMNI option formatted as shown in 853 Figure 3: 855 0 1 2 3 856 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 1 857 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 858 | Type | Length | Prefix Length | S/T-ifIndex | 859 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 860 | | 861 ~ Sub-Options ~ 862 | | 863 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 865 Figure 3: OMNI Option Format 867 In this format: 869 o Type is set to TBD. If multiple OMNI option instances appear in 870 the same IPv6 ND message, the first instance is processed and all 871 other instances are ignored. 873 o Length is set to the number of 8 octet blocks in the option. 875 o Prefix Length is determines the length of prefix to be applied to 876 an OMNI MN LLA/ULA. For IPv6 ND messages sent from a MN to the 877 MS, Prefix Length is the length that the MN is requesting or 878 asserting to the MS. For IPv6 ND messages sent from the MS to the 879 MN, Prefix Length indicates the length that the MS is granting to 880 the MN. For IPv6 ND messages sent between MS endpoints, Prefix 881 Length indicates the length associated with the target MN that is 882 subject of the ND message. 884 o S/T-ifIndex corresponds to the ifIndex value for source or target 885 underlying interface used to convey this IPv6 ND message. OMNI 886 interfaces MUST number each distinct underlying interface with an 887 ifIndex value between '1' and '255' that represents a MN-specific 888 8-bit mapping for the actual ifIndex value assigned by network 889 management [RFC2863] (the ifIndex value '0' is reserved for use by 890 the MS). For RS and NS messages,S/T-ifIndex corresponds to the 891 source underlying interface the message originated from. For RA 892 and NA messages, S/T-ifIndex corresponds to the target underlying 893 interface that the message is destined to. 895 o Sub-Options is a Variable-length field, of length such that the 896 complete OMNI Option is an integer multiple of 8 octets long. 897 Contains one or more Sub-Options, as described in Section 9.1. 899 9.1. Sub-Options 901 The OMNI option includes zero or more Sub-Options. Each consecutive 902 Sub-Option is concatenated immediately after its predecessor. All 903 Sub-Options except Pad1 (see below) are in type-length-value (TLV) 904 encoded in the following format: 906 0 1 2 907 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 5 908 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 909 | Sub-Type | Sub-length | Sub-Option Data ... 910 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 912 Figure 4: Sub-Option Format 914 o Sub-Type is a 1-octet field that encodes the Sub-Option type. 915 Sub-Options defined in this document are: 917 Option Name Sub-Type 918 Pad1 0 919 PadN 1 920 Interface Attributes 2 921 Traffic Selector 3 922 MS-Register 4 923 MS-Release 5 924 Network Access Identifier 6 925 Geo Coordinates 7 926 DHCP Unique Identifier (DUID) 8 928 Figure 5 930 Sub-Types 253 and 254 are reserved for experimentation, as 931 recommended in [RFC3692]. 933 o Sub-Length is a 1-octet field that encodes the length of the Sub- 934 Option Data (i.e., ranging from 0 to 255 octets). 936 o Sub-Option Data is a block of data with format determined by Sub- 937 Type. 939 During processing, unrecognized Sub-Options are ignored and the next 940 Sub-Option processed until the end of the OMNI option is reached. 942 The following Sub-Option types and formats are defined in this 943 document: 945 9.1.1. Pad1 947 0 948 0 1 2 3 4 5 6 7 949 +-+-+-+-+-+-+-+-+ 950 | Sub-Type=0 | 951 +-+-+-+-+-+-+-+-+ 953 Figure 6: Pad1 955 o Sub-Type is set to 0. If multiple instances appear in the same 956 OMNI option all are processed. 958 o No Sub-Length or Sub-Option Data follows (i.e., the "Sub-Option" 959 consists of a single zero octet). 961 9.1.2. PadN 963 0 1 2 964 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 5 965 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 966 | Sub-Type=1 | Sub-length=N | N padding octets ... 967 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 969 Figure 7: PadN 971 o Sub-Type is set to 1. If multiple instances appear in the same 972 OMNI option all are processed. 974 o Sub-Length is set to N (from 0 to 255) being the number of padding 975 octets that follow. 977 o Sub-Option Data consists of N zero-valued octets. 979 9.1.3. Interface Attributes 980 0 1 2 3 981 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 1 982 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 983 | Sub-Type=2 | Sub-length=N | ifIndex | ifType | 984 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 985 | Provider ID | Link |R| APS | SRT | FMT | LHS (0 - 7) | 986 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 987 | LHS (bits 8 - 31) | ~ 988 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ 989 ~ ~ 990 ~ Link Layer Address (L2ADDR) ~ 991 ~ ~ 992 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 993 | Bitmap(0)=0xff|P00|P01|P02|P03|P04|P05|P06|P07|P08|P09|P10|P11| 994 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 995 |P12|P13|P14|P15|P16|P17|P18|P19|P20|P21|P22|P23|P24|P25|P26|P27| 996 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 997 |P28|P29|P30|P31| Bitmap(1)=0xff|P32|P33|P34|P35|P36| ... 998 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1000 Figure 8: Interface Attributes 1002 o Sub-Type is set to 2. If multiple instances with different 1003 ifIndex values appear in the same OMNI option all are processed; 1004 if multiple instances with the same ifIndex value appear, the 1005 first is processed and all others are ignored. 1007 o Sub-Length is set to N (from 4 to 255) that encodes the number of 1008 Sub-Option Data octets that follow. 1010 o Sub-Option Data contains an "Interface Attribute" option encoded 1011 as follows (note that the first four octets must be present): 1013 * ifIndex is set to an 8-bit integer value corresponding to a 1014 specific underlying interface the same as specified above for 1015 the OMNI option header S/T-ifIndex. An OMNI option may include 1016 multiple Interface Attributes Sub-Options, with each distinct 1017 ifIndex value pertaining to a different underlying interface. 1018 The OMNI option will often include an Interface Attributes Sub- 1019 Option with the same ifIndex value that appears in the S/ 1020 T-ifIndex. In that case, the actual encapsulation address of 1021 the received IPv6 ND message should be compared with the L2ADDR 1022 encoded in the Sub-Option (see below); if the addresses are 1023 different (or, if L2ADDR absent) the presence of a Network 1024 Address Translator (NAT) is indicated. 1026 * ifType is set to an 8-bit integer value corresponding to the 1027 underlying interface identified by ifIndex. The value 1028 represents an OMNI interface-specific 8-bit mapping for the 1029 actual IANA ifType value registered in the 'IANAifType-MIB' 1030 registry [http://www.iana.org]. 1032 * Provider ID is set to an OMNI interface-specific 8-bit ID value 1033 for the network service provider associated with this ifIndex. 1035 * Link encodes a 4-bit link metric. The value '0' means the link 1036 is DOWN, and the remaining values mean the link is UP with 1037 metric ranging from '1' ("lowest") to '15' ("highest"). 1039 * R is reserved for future use. 1041 * APS - a 3-bit "Address/Preferences/Simplex" code that 1042 determines the contents of the remainder of the sub-option as 1043 follows: 1045 + When the most significant bit (i.e., "Address") is set to 1, 1046 the SRT, FMT, LHS and L2ADDR fields are included immediately 1047 following the APS code; else, they are omitted. 1049 + When the next most significant bit (i.e., "Preferences") is 1050 set to 1, a preferences block is included next; else, it is 1051 omitted. (Note that if "Address" is set the preferences 1052 block immediately follows L2ADDR; else, it immediately 1053 follows the APS code.) 1055 + When a preferences block is present and the least 1056 significant bit (i.e., "Simplex") is set to 1, the block is 1057 encoded in "Simplex" form as shown in Figure 8; else it is 1058 encoded in "Indexed" form as discussed below. 1060 * When APS indicates that an "Address" is included, the following 1061 fields appear in consecutive order (else, they are omitted): 1063 + SRT - a 5-bit Segment Routing Topology prefix length value 1064 that (when added to 96) determines the prefix length to 1065 apply to the ULA formed from concatenating fc*::/96 with the 1066 32 bit LHS MSID value that follows. For example, the value 1067 16 corresponds to the prefix length 112. 1069 + FMT - a 3-bit "Framework/Mode/Type" code corresponding to 1070 the included Link Layer Address as follows: 1072 - When the most significant bit (i.e., "Framework") is set 1073 to 0, L2ADDR is the INET encapsulation address of a 1074 Proxy/Server; otherwise, it is the addresss for the 1075 Source/Target itself 1077 - When the next most significant bit (i.e., "Mode") is set 1078 to 0, the Source/Target L2ADDR is on the open INET; 1079 otherwise, it is (likely) located behind a Network 1080 Address Translator (NAT). 1082 - When the least significant bit (i.e., "Type") is set to 1083 0, L2ADDR includes a UDP Port Number followed by an IPv4 1084 address; else, a UDP Port Number followed by an IPv6 1085 address. 1087 + LHS - the 32 bit MSID of the Last Hop Server/Proxy on the 1088 path to the target. When SRT and LHS are both set to 0, the 1089 LHS is considered unspecified in this IPv6 ND message. When 1090 SRT is set to 0 and LHS is non-zero, the prefix length is 1091 set to 128. SRT and LHS provide guidance to the OMNI 1092 interface forwarding algorithm. Specifically, if SRT/LHS is 1093 located in the local OMNI link segment then the OMNI 1094 interface can encapsulate according to FMT/L2ADDR; else, it 1095 must forward according to the OMNI link spanning tree. See 1096 [I-D.templin-intarea-6706bis] for further discussion. 1098 + Link Layer Address (L2ADDR) - Formatted according to FMT, 1099 and identifies the link-layer address (i.e., the 1100 encapsulation address) of the source/target. The UDP Port 1101 Number appears in the first two octets and the IP address 1102 appears in the next 4 octets for IPv4 or 16 octets for IPv6. 1103 The Port Number and IP address are recorded in ones- 1104 compliment "obfuscated" form per [RFC4380]. The OMNI 1105 interface forwarding algoritherm uses FMT/L2ADDR to 1106 determine the encapsulation address for forwarding when SRT/ 1107 LHS is located in the local OMNI link segment. 1109 * When APS indicates that "Preferences" are included, a 1110 preferences block appears as the remainder of the Sub-Option as 1111 a series of Bitmaps and P[*] values. In "Simplex" form, the 1112 index for each singleton Bitmap octet is inferred from its 1113 sequential position (i.e., 0, 1, 2, ...) as shown in Figure 8. 1114 In "Indexed" form, each Bitmap is preceded by an Index octet 1115 that encodes a value "i" = (0 - 255) as the index for its 1116 companion Bitmap as follows: 1118 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1119 | Index=i | Bitmap(i) |P[*] values ... 1120 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1122 Figure 9 1124 * The preferences consist of a first (simplex/indexed) Bitmap 1125 (i.e., "Bitmap(i)") followed by 0-8 single-octet blocks of 1126 2-bit P[*] values, followed by a second Bitmap (i), followed by 1127 0-8 blocks of P[*] values, etc. Reading from bit 0 to bit 7, 1128 the bits of each Bitmap(i) that are set to '1'' indicate the 1129 P[*] blocks from the range P[(i*32)] through P[(i*32) + 31] 1130 that follow; if any Bitmap(i) bits are '0', then the 1131 corresponding P[*] block is instead omitted. For example, if 1132 Bitmap(0) contains 0xff then the block with P[00]-P[03], 1133 followed by the block with P[04]-P[07], etc., and ending with 1134 the block with P[28]-P[31] are included (as shown in Figure 8). 1135 The next Bitmap(i) is then consulted with its bits indicating 1136 which P[*] blocks follow, etc. out to the end of the Sub- 1137 Option. 1139 * Each 2-bit P[*] field is set to the value '0' ("disabled"), '1' 1140 ("low"), '2' ("medium") or '3' ("high") to indicate a QoS 1141 preference for underlying interface selection purposes. Not 1142 all P[*] values need to be included in the OMNI option of each 1143 IPv6 ND message received. Any P[*] values represented in an 1144 earlier OMNI option but omitted in the current OMNI option 1145 remain unchanged. Any P[*] values not yet represented in any 1146 OMNI option default to "medium". 1148 * The first 16 P[*] blocks correspond to the 64 Differentiated 1149 Service Code Point (DSCP) values P[00] - P[63] [RFC2474]. Any 1150 additional P[*] blocks that follow correspond to "pseudo-DSCP" 1151 traffic classifier values P[64], P[65], P[66], etc. See 1152 Appendix A for further discussion and examples. 1154 9.1.4. Traffic Selector 1156 0 1 2 3 1157 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 1158 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1159 | Sub-Type=3 | Sub-length=N | ifIndex | ~ 1160 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ 1161 ~ ~ 1162 ~ RFC 6088 Format Traffic Selector ~ 1163 ~ ~ 1164 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1166 Figure 10: Traffic Selector 1168 o Sub-Type is set to 3. If multiple instances appear in the same 1169 OMNI option all are processed, i.e., even if the same ifIndex 1170 value appears multiple times. 1172 o Sub-Length is set to N (the number of Sub-Option Data octets that 1173 follow). 1175 o Sub-Option Data contains a 1-octet ifIndex encoded exactly as 1176 specified in Section 9.1.3, followed by an N-1 octet traffic 1177 selector formatted per [RFC6088] beginning with the "TS Format" 1178 field. The largest traffic selector for a given ifIndex is 1179 therefore 254 octets. 1181 9.1.5. MS-Register 1183 0 1 2 3 1184 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 1185 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1186 | Sub-Type=4 | Sub-length=4n | MSID[1] (bits 0 - 15) | 1187 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1188 | MSID [1] (bits 16 - 32) | MSID[2] (bits 0 - 15) | 1189 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1190 | MSID [2] (bits 16 - 32) | MSID[3] (bits 0 - 15) | 1191 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1192 ... ... ... ... ... ... 1193 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1194 | MSID [n] (bits 16 - 32) | 1195 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1197 Figure 11: MS-Register Sub-option 1199 o Sub-Type is set to 4. If multiple instances appear in the same 1200 OMNI option all are processed. Only the first MAX_MSID values 1201 processed (whether in a single instance or multiple) are retained 1202 and all other MSIDs are ignored. 1204 o Sub-Length is set to 4n. 1206 o A list of n 4-octet MSIDs is included in the following 4n octets. 1207 The Anycast MSID value '0' in an RS message MS-Register sub-option 1208 requests the recipient to return the MSID of a nearby MSE in a 1209 corresponding RA response. 1211 9.1.6. MS-Release 1212 0 1 2 3 1213 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 1214 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1215 | Sub-Type=5 | Sub-length=4n | MSID[1] (bits 0 - 15) | 1216 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1217 | MSID [1] (bits 16 - 32) | MSID[2] (bits 0 - 15) | 1218 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1219 | MSID [2] (bits 16 - 32) | MSID[3] (bits 0 - 15) | 1220 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1221 ... ... ... ... ... ... 1222 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1223 | MSID [n] (bits 16 - 32) | 1224 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1226 Figure 12: MS-Release Sub-option 1228 o Sub-Type is set to 5. If multiple instances appear in the same 1229 IPv6 OMNI option all are processed. Only the first MAX_MSID 1230 values processed (whether in a single instance or multiple) are 1231 retained and all other MSIDs are ignored. 1233 o Sub-Length is set to 4n. 1235 o A list of n 4 octet MSIDs is included in the following 4n octets. 1236 The Anycast MSID value '0' is ignored in MS-Release sub-options, 1237 i.e., only non-zero values are processed. 1239 9.1.7. Network Access Identifier (NAI) 1241 0 1 2 3 1242 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 1243 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1244 | Sub-Type=6 | Sub-length=N |Network Access Identifier (NAI) 1245 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... 1247 Figure 13: Network Access Identifier (NAI) Sub-option 1249 o Sub-Type is set to 6. If multiple instances appear in the same 1250 OMNI option the first is processed and all others are ignored. 1252 o Sub-Length is set to N. 1254 o A Network Access Identifier (NAI) up to 255 octets in length is 1255 coded per [RFC7542]. 1257 9.1.8. Geo Coordinates 1259 0 1 2 3 1260 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 1261 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1262 | Sub-Type=7 | Sub-length=N | Geo Coordinates 1263 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... 1265 Figure 14: Geo Coordinates Sub-option 1267 o Sub-Type is set to 7. If multiple instances appear in the same 1268 OMNI option the first is processed and all others are ignored. 1270 o Sub-Length is set to N. 1272 o A set of Geo Coordinates up to 255 octets in length (format TBD). 1273 Includes Latitude/Longitude at a minimum; may also include 1274 additional attributes such as altitude, heading, speed, etc.). 1276 9.1.9. DHCP Unique Identifier (DUID) 1278 0 1 2 3 1279 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 1280 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1281 | Sub-Type=8 | Sub-length=N | DUID-Type | 1282 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1283 . . 1284 . type-specific DUID body (variable length) . 1285 . . 1286 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1288 Figure 15: DHCP Unique Identifier (DUID) Sub-option 1290 o Sub-Type is set to 8. If multiple instances appear in the same 1291 OMNI option the first is processed and all others are ignored. 1293 o Sub-Length is set to N (i.e., the length of the option beginning 1294 with the DUID-Type and continuing to the end of the type-specifc 1295 body). 1297 o DUID-Type is a two-octet field coded in network byte order that 1298 determines the format and contents of the type-specific body 1299 according to Section 11 of [RFC8415]. DUID-Type 4 in particular 1300 corresponds to the Universally Unique Identifier (UUID) [RFC6355] 1301 which will occur in common operational practice. 1303 o A type-specific DUID body up to 253 octets in length follows, 1304 formatted according to DUID-type. For example, for type 4 the 1305 body consists of a 128-bit UUID selected according to [RFC6355]. 1307 10. Address Mapping - Multicast 1309 The multicast address mapping of the native underlying interface 1310 applies. The mobile router on board the MN also serves as an IGMP/ 1311 MLD Proxy for its EUNs and/or hosted applications per [RFC4605] while 1312 using the L2 address of the AR as the L2 address for all multicast 1313 packets. 1315 The MN uses Multicast Listener Discovery (MLDv2) [RFC3810] to 1316 coordinate with the AR, and ANET L2 elements use MLD snooping 1317 [RFC4541]. 1319 11. Conceptual Sending Algorithm 1321 The MN's IPv6 layer selects the outbound OMNI interface according to 1322 SBM considerations when forwarding data packets from local or EUN 1323 applications to external correspondents. Each OMNI interface 1324 maintains a neighbor cache the same as for any IPv6 interface, but 1325 with additional state for multilink coordination. 1327 After a packet enters the OMNI interface, an outbound underlying 1328 interface is selected based on PBM traffic attributes such as DSCP, 1329 application port number, cost, performance, message size, etc. OMNI 1330 interface multilink selections could also be configured to perform 1331 replication across multiple underlying interfaces for increased 1332 reliability at the expense of packet duplication. 1334 When the OMNI interface sends a packet over a selected outbound 1335 underlying interface, the OAL includes or omits a mid-layer 1336 encapsulation header as necessary as discussed in Section 5. The OAL 1337 also performs encapsulation when the nearest AR is located multiple 1338 hops away as discussed in Section 12.1. 1340 OMNI interface multilink service designers MUST observe the BCP 1341 guidance in Section 15 [RFC3819] in terms of implications for 1342 reordering when packets from the same flow may be spread across 1343 multiple underlying interfaces having diverse properties. 1345 11.1. Multiple OMNI Interfaces 1347 MNs may connect to multiple independent OMNI links concurrently in 1348 support of SBM. Each OMNI interface is distinguished by its Anycast 1349 OMNI ULA (e.g., fc80::, fc81::, fc82::). The MN configures a 1350 separate OMNI interface for each link so that multiple interfaces 1351 (e.g., omni0, omni1, omni2, etc.) are exposed to the IPv6 layer. A 1352 different Anycast OMNI ULA is assigned to each interface, and the MN 1353 injects the service prefixes for the OMNI link instances into the EUN 1354 routing system. 1356 Applications in EUNs can use Segment Routing to select the desired 1357 OMNI interface based on SBM considerations. The Anycast OMNI ULA is 1358 written into the IPv6 destination address, and the actual destination 1359 (along with any additional intermediate hops) is written into the 1360 Segment Routing Header. Standard IP routing directs the packets to 1361 the MN's mobile router entity, and the Anycast OMNI ULA identifies 1362 the OMNI interface to be used for transmission to the next hop. When 1363 the MN receives the message, it replaces the IPv6 destination address 1364 with the next hop found in the routing header and transmits the 1365 message over the OMNI interface identified by the Anycast OMNI ULA. 1367 Multiple distinct OMNI links can therefore be used to support fault 1368 tolerance, load balancing, reliability, etc. The architectural model 1369 is similar to Layer 2 Virtual Local Area Networks (VLANs). 1371 12. Router Discovery and Prefix Registration 1373 MNs interface with the MS by sending RS messages with OMNI options 1374 under the assumption that one or more AR on the ANET will process the 1375 message and respond. The manner in which the ANET ensures AR 1376 coordination is link-specific and outside the scope of this document 1377 (however, considerations for ANETs that do not provide ARs that 1378 recognize the OMNI option are discussed in Section 17). 1380 For each underlying interface, the MN sends an RS message with an 1381 OMNI option to coordinate with MSEs identified by MSID values. 1382 Example MSID discovery methods are given in [RFC5214] and include 1383 data link login parameters, name service lookups, static 1384 configuration, a static "hosts" file, etc. The MN can also send an 1385 RS with an MS-Register suboption that includes the Anycast MSID value 1386 '0', i.e., instead of or in addition to any non-zero MSIDs. When the 1387 AR receives an RS with a MSID '0', it selects a nearby MSE (which may 1388 be itself) and returns an RA with the selected MSID in an MS-Register 1389 suboption. The AR selects only a single wildcard MSE (i.e., even if 1390 the RS MS-Register suboption included multiple '0' MSIDs) while also 1391 soliciting the MSEs corresponding to any non-zero MSIDs. 1393 MNs configure OMNI interfaces that observe the properties discussed 1394 in the previous section. The OMNI interface and its underlying 1395 interfaces are said to be in either the "UP" or "DOWN" state 1396 according to administrative actions in conjunction with the interface 1397 connectivity status. An OMNI interface transitions to UP or DOWN 1398 through administrative action and/or through state transitions of the 1399 underlying interfaces. When a first underlying interface transitions 1400 to UP, the OMNI interface also transitions to UP. When all 1401 underlying interfaces transition to DOWN, the OMNI interface also 1402 transitions to DOWN. 1404 When an OMNI interface transitions to UP, the MN sends RS messages to 1405 register its MNP and an initial set of underlying interfaces that are 1406 also UP. The MN sends additional RS messages to refresh lifetimes 1407 and to register/deregister underlying interfaces as they transition 1408 to UP or DOWN. The MN sends initial RS messages over an UP 1409 underlying interface with its OMNI LLA as the source and with 1410 destination set to All-Routers multicast (ff02::2) [RFC4291]. The RS 1411 messages include an OMNI option per Section 9 with valid prefix 1412 registration information, Interface Attributes appropriate for 1413 underlying interfaces, MS-Register/Release sub-options containing 1414 MSID values, and with any other necessary OMNI sub-options. The S/ 1415 T-ifIndex field is set to the index of the underlying interface over 1416 which the RS message is sent. 1418 ARs process IPv6 ND messages with OMNI options and act as an MSE 1419 themselves and/or as a proxy for other MSEs. ARs receive RS messages 1420 and create a neighbor cache entry for the MN, then coordinate with 1421 any MSEs named in the Register/Release lists in a manner outside the 1422 scope of this document. When an MSE processes the OMNI information, 1423 it first validates the prefix registration information then injects/ 1424 withdraws the MNP in the routing/mapping system and caches/discards 1425 the new Prefix Length, MNP and Interface Attributes. The MSE then 1426 informs the AR of registration success/failure, and the AR returns an 1427 RA message to the MN with an OMNI option per Section 9. 1429 The AR returns the RA message via the same underlying interface of 1430 the MN over which the RS was received, and with destination address 1431 set to the MN OMNI LLA (i.e., unicast), with source address set to 1432 its own OMNI LLA, and with an OMNI option with S/T-ifIndex set to the 1433 value included in the RS. The OMNI option also includes valid prefix 1434 registration information, Interface Attributes, MS-Register/Release 1435 and any other necessary OMNI sub-options. The RA also includes any 1436 information for the link, including RA Cur Hop Limit, M and O flags, 1437 Router Lifetime, Reachable Time and Retrans Timer values, and 1438 includes any necessary options such as: 1440 o PIOs with (A; L=0) that include MSPs for the link [RFC8028]. 1442 o RIOs [RFC4191] with more-specific routes. 1444 o an MTU option that specifies the maximum acceptable packet size 1445 for this ANET interface. 1447 The AR MAY also send periodic and/or event-driven unsolicited RA 1448 messages per [RFC4861]. In that case, the S/T-ifIndex field in the 1449 OMNI header of the unsolicited RA message identifies the target 1450 underlying interface of the destination MN. 1452 The AR can combine the information from multiple MSEs into one or 1453 more "aggregate" RAs sent to the MN in order conserve ANET bandwidth. 1454 Each aggregate RA includes an OMNI option with MS-Register/Release 1455 sub-options with the MSEs represented by the aggregate. If an 1456 aggregate is sent, the RA message contents must consistently 1457 represent the combined information advertised by all represented 1458 MSEs. Note that since the AR uses its own OMNI LLA as the RA source 1459 address, the MN determines the addresses of the represented MSEs by 1460 examining the MS-Register/Release OMNI sub-options. 1462 When the MN receives the RA message, it creates an OMNI interface 1463 neighbor cache entry for each MSID that has confirmed MNP 1464 registration via the L2 address of this AR. If the MN connects to 1465 multiple ANETs, it records the additional L2 AR addresses in each 1466 MSID neighbor cache entry (i.e., as multilink neighbors). The MN 1467 then manages its underlying interfaces according to their states as 1468 follows: 1470 o When an underlying interface transitions to UP, the MN sends an RS 1471 over the underlying interface with an OMNI option. The OMNI 1472 option contains at least one Interface Attribute sub-option with 1473 values specific to this underlying interface, and may contain 1474 additional Interface Attributes specific to other underlying 1475 interfaces. The option also includes any MS-Register/Release sub- 1476 options. 1478 o When an underlying interface transitions to DOWN, the MN sends an 1479 RS or unsolicited NA message over any UP underlying interface with 1480 an OMNI option containing an Interface Attribute sub-option for 1481 the DOWN underlying interface with Link set to '0'. The MN sends 1482 an RS when an acknowledgement is required, or an unsolicited NA 1483 when reliability is not thought to be a concern (e.g., if 1484 redundant transmissions are sent on multiple underlying 1485 interfaces). 1487 o When the Router Lifetime for a specific AR nears expiration, the 1488 MN sends an RS over the underlying interface to receive a fresh 1489 RA. If no RA is received, the MN can send RS messages to an 1490 alternate MSID in case the current MSID has failed. If no RS 1491 messages are received even after trying to contact alternate 1492 MSIDs, the MN marks the underlying interface as DOWN. 1494 o When a MN wishes to release from one or more current MSIDs, it 1495 sends an RS or unsolicited NA message over any UP underlying 1496 interfaces with an OMNI option with a Release MSID. Each MSID 1497 then withdraws the MNP from the routing/mapping system and informs 1498 the AR that the release was successful. 1500 o When all of a MNs underlying interfaces have transitioned to DOWN 1501 (or if the prefix registration lifetime expires), any associated 1502 MSEs withdraw the MNP the same as if they had received a message 1503 with a release indication. 1505 The MN is responsible for retrying each RS exchange up to 1506 MAX_RTR_SOLICITATIONS times separated by RTR_SOLICITATION_INTERVAL 1507 seconds until an RA is received. If no RA is received over a an UP 1508 underlying interface (i.e., even after attempting to contact 1509 alternate MSEs), the MN declares this underlying interface as DOWN. 1511 The IPv6 layer sees the OMNI interface as an ordinary IPv6 interface. 1512 Therefore, when the IPv6 layer sends an RS message the OMNI interface 1513 returns an internally-generated RA message as though the message 1514 originated from an IPv6 router. The internally-generated RA message 1515 contains configuration information that is consistent with the 1516 information received from the RAs generated by the MS. Whether the 1517 OMNI interface IPv6 ND messaging process is initiated from the 1518 receipt of an RS message from the IPv6 layer is an implementation 1519 matter. Some implementations may elect to defer the IPv6 ND 1520 messaging process until an RS is received from the IPv6 layer, while 1521 others may elect to initiate the process proactively. Still other 1522 deployments may elect to administratively disable the ordinary RS/RA 1523 messaging used by the IPv6 layer over the OMNI interface, since they 1524 are not required to drive the internal RS/RA processing. (Note that 1525 this same logic applies to IPv4 implementations that employ ICMP- 1526 based Router Discovery per [RFC1256].) 1528 Note: The Router Lifetime value in RA messages indicates the time 1529 before which the MN must send another RS message over this underlying 1530 interface (e.g., 600 seconds), however that timescale may be 1531 significantly longer than the lifetime the MS has committed to retain 1532 the prefix registration (e.g., REACHABLETIME seconds). ARs are 1533 therefore responsible for keeping MS state alive on a shorter 1534 timescale than the MN is required to do on its own behalf. 1536 Note: On multicast-capable underlying interfaces, MNs should send 1537 periodic unsolicited multicast NA messages and ARs should send 1538 periodic unsolicited multicast RA messages as "beacons" that can be 1539 heard by other nodes on the link. If a node fails to receive a 1540 beacon after a timeout value specific to the link, it can initiate a 1541 unicast exchange to test reachability. 1543 12.1. Router Discovery in IP Multihop and IPv4-Only Access Networks 1545 On some ANET types a MN may be located multiple IP hops away from the 1546 nearest AR. Forwarding through IP multihop ANETs is conducted 1547 through the application of a routing protocol (e.g., a Mobile Ad-hoc 1548 Network (MANET) routing protocol over omni-directional wireless 1549 interfaces, an inter-domain routing protocol in an enterprise 1550 network, etc.). These ANETs could be either IPv6-enabled or 1551 IPv4-only, while IPv4-only ANETs could be either multicast-capable or 1552 unicast-only (note that for IPv4-only ANETs the following procedures 1553 apply for both single-hop and multhop cases). 1555 A MN located potentially multiple ANET hops away from the nearst AR 1556 prepares an RS message with source address set to its OMNI LLA and 1557 with destination set to link-scoped All-Routers multicast the same as 1558 discussed above. For IPv6-enabled ANETs, the MN then encapsulates 1559 the message in an IPv6 header with source address set to the ULA 1560 corresponding to the LLA source address and with destination set to 1561 site-scoped All-Routers multicast (ff05::2)[RFC4291]. For IPv4-only 1562 ANETs, the MN instead encapsulates the RS message in an IPv4 header 1563 with source address set to the node's own IPv4 address. For 1564 multicast-capable IPv4-only ANETs, the MN then sets the destination 1565 address to the site-scoped IPv4 multicast address corresponding to 1566 link-scoped IPv6 All-Routers multicast [RFC2529]; for unicast-only 1567 IPv4-only ANETs, the MN instead sets the destination address to the 1568 unicast IPv4 adddress of an AR [RFC5214]. The MN then sends the 1569 encapsulated RS message via the ANET interface, where it will be 1570 forwarded by zero or more intermediate ANET hops. 1572 When an intermediate ANET hop that particpates in the routing 1573 protocol receives the encapsulated RS, it forwards the message 1574 according to its routing tables (note that an intermediate node could 1575 be a fixed infrastructure element or another MN). This process 1576 repeats iteratively until the RS message is received by a penultimate 1577 ANET hop within single-hop communications range of an AR, which 1578 forwards the message to the AR. 1580 When the AR receives the message, it decapsulates the RS and 1581 coordinates with the MS the same as for an ordinary link-local RS, 1582 since the inner Hop Limit will not have been decremented by the 1583 multihop forwarding process. The AR then prepares an RA message with 1584 source address set to its own LLA and destination address set to the 1585 LLA of the original MN, then encapsulates the message in an IPv4/IPv6 1586 header with source address set to its own IPv4/ULA address and with 1587 destination set to the encapsulation source of the RS. 1589 The AR then forwards the message to an ANET node within 1590 communications range, which forwards the message according to its 1591 routing tables to an intermediate node. The multihop forwarding 1592 process within the ANET continues repetitively until the message is 1593 delivered to the original MN, which decapsulates the message and 1594 performs autoconfiguration the same as if it had received the RA 1595 directly from the AR as an on-link neighbor. 1597 Note: An alternate approach to multihop forwarding via IPv6 1598 encapsulation would be to statelessly translate the IPv6 LLAs into 1599 ULAs and forward the messages without encapsulation. This would 1600 violate the [RFC4861] requirement that certain IPv6 ND messages must 1601 use link-local addresses and must not be accepted if received with 1602 Hop Limit less than 255. This document therefore advocates 1603 encapsulation since the overhead is nominal considering the 1604 infrequent nature and small size of IPv6 ND messages. Future 1605 documents may consider encapsulation avoidance through translation 1606 while updating [RFC4861]. 1608 Note: An alternate approach to multihop forwarding via IPv4 1609 encapsulation would be to employ IPv6/IPv4 protocol translation. 1610 However, for IPv6 ND messages the OMNI LLA addresses would be 1611 truncated due to translation and the OMNI Router and Prefix Discovery 1612 services would not be able to function. The use of IPv4 1613 encapsulation is therefore indicated. 1615 12.2. MS-Register and MS-Release List Processing 1617 When a MN sends an RS message with an OMNI option via an underlying 1618 interface to an AR, the MN must convey its knowledge of its 1619 currently-associated MSEs. Initially, the MN will have no associated 1620 MSEs and should therefore include an MS-Register sub-option with the 1621 single MSID value 0 which requests the AR to select and assign an 1622 MSE. The AR will then return an RA message with source address set 1623 to the OMNI LLA containing the MSE of the selected MSE. 1625 As the MN activates additional underlying interfaces, it can 1626 optionally include an MS-Register sub-option with MSID value 0, or 1627 with non-zero MSIDs for MSEs discovered from previous RS/RA 1628 exchanges. The MN will thus eventually begin to learn and manage its 1629 currently active set of MSEs, and can register with new MSEs or 1630 release from former MSEs with each successive RS/RA exchange. As the 1631 MN's MSE constituency grows, it alone is responsible for including or 1632 omitting MSIDs in the MS-Register/Release lists it sends in RS 1633 messages. The inclusion or omission of MSIDs determines the MN's 1634 interface to the MS and defines the manner in which MSEs will 1635 respond. The only limiting factor is that the MN should include no 1636 more than MAX_MSID values in each list per each IPv6 ND message, and 1637 should avoid duplication of entries in each list unless it wants to 1638 increase likelihood of control message delivery. 1640 When an AR receives an RS message sent by a MN with an OMNI option, 1641 the option will contain zero or more MS-Register and MS-Release sub- 1642 options containing MSIDs. After processing the OMNI option, the AR 1643 will have a list of zero or more MS-Register MSIDs and a list of zero 1644 or more of MS-Release MSIDs. The AR then processes the lists as 1645 follows: 1647 o For each list, retain the first MAX_MSID values in the list and 1648 discard any additional MSIDs (i.e., even if there are duplicates 1649 within a list). 1651 o Next, for each MSID in the MS-Register list, remove all matching 1652 MSIDs from the MS-Release list. 1654 o Next, proceed according to whether the AR's own MSID or the value 1655 0 appears in the MS-Register list as folllows: 1657 * If yes, send an RA message directly back to the MN and send a 1658 proxy copy of the RS message to each additional MSID in the MS- 1659 Register list with the MS-Register/Release lists omitted. 1660 Then, send a uNA message to each MSID in the MS-Release list 1661 with the MS-Register/Release lists omitted and with an OMNI 1662 header with S/T-ifIndex set to 0. 1664 * If no, send a proxy copy of the RS message to each additional 1665 MSID in the MS-Register list with the MS-Register list omitted. 1666 For the first MSID, include the original MS-Release list; for 1667 all other MSIDs, omit the MS-Release list. 1669 Each proxy copy of the RS message will include an OMNI option and 1670 encapsulation header with the ULA of the AR as the source and the ULA 1671 of the Register MSE as the destination. When the Register MSE 1672 receives the proxy RS message, if the message includes an MS-Release 1673 list the MSE sends a uNA message to each additional MSID in the 1674 Release list. The Register MSE then sends an RA message back to the 1675 (Proxy) AR wrapped in an OMNI encapsulation header with source and 1676 destination addresses reversed, and with RA destination set to the 1677 LLA of the MN. When the AR receives this RA message, it sends a 1678 proxy copy of the RA to the MN. 1680 Each uNA message (whether send by the first-hop AR or by a Register 1681 MSE) will include an OMNI option and an encapsulation header with the 1682 ULA of the Register MSE as the source and the ULA of the Release ME 1683 as the destination. The uNA informs the Release MSE that its 1684 previous relationship with the MN has been released and that the 1685 source of the uNA message is now registered. The Release MSE must 1686 then note that the subject MN of the uNA message is now "departed", 1687 and forward any subsequent packets destined to the MN to the Register 1688 MSE. 1690 Note that it is not an error for the MS-Register/Release lists to 1691 include duplicate entries. If duplicates occur within a list, the 1692 the AR will generate multiple proxy RS and/or uNA messages - one for 1693 each copy of the duplicate entries. 1695 13. Secure Redirection 1697 If the ANET link model is multiple access, the AR is responsible for 1698 assuring that address duplication cannot corrupt the neighbor caches 1699 of other nodes on the link. When the MN sends an RS message on a 1700 multiple access ANET link, the AR verifies that the MN is authorized 1701 to use the address and returns an RA with a non-zero Router Lifetime 1702 only if the MN is authorized. 1704 After verifying MN authorization and returning an RA, the AR MAY 1705 return IPv6 ND Redirect messages to direct MNs located on the same 1706 ANET link to exchange packets directly without transiting the AR. In 1707 that case, the MNs can exchange packets according to their unicast L2 1708 addresses discovered from the Redirect message instead of using the 1709 dogleg path through the AR. In some ANET links, however, such direct 1710 communications may be undesirable and continued use of the dogleg 1711 path through the AR may provide better performance. In that case, 1712 the AR can refrain from sending Redirects, and/or MNs can ignore 1713 them. 1715 14. AR and MSE Resilience 1717 ANETs SHOULD deploy ARs in Virtual Router Redundancy Protocol (VRRP) 1718 [RFC5798] configurations so that service continuity is maintained 1719 even if one or more ARs fail. Using VRRP, the MN is unaware which of 1720 the (redundant) ARs is currently providing service, and any service 1721 discontinuity will be limited to the failover time supported by VRRP. 1722 Widely deployed public domain implementations of VRRP are available. 1724 MSEs SHOULD use high availability clustering services so that 1725 multiple redundant systems can provide coordinated response to 1726 failures. As with VRRP, widely deployed public domain 1727 implementations of high availability clustering services are 1728 available. Note that special-purpose and expensive dedicated 1729 hardware is not necessary, and public domain implementations can be 1730 used even between lightweight virtual machines in cloud deployments. 1732 15. Detecting and Responding to MSE Failures 1734 In environments where fast recovery from MSE failure is required, ARs 1735 SHOULD use proactive Neighbor Unreachability Detection (NUD) in a 1736 manner that parallels Bidirectional Forwarding Detection (BFD) 1737 [RFC5880] to track MSE reachability. ARs can then quickly detect and 1738 react to failures so that cached information is re-established 1739 through alternate paths. Proactive NUD control messaging is carried 1740 only over well-connected ground domain networks (i.e., and not low- 1741 end ANET links such as aeronautical radios) and can therefore be 1742 tuned for rapid response. 1744 ARs perform proactive NUD for MSEs for which there are currently 1745 active MNs on the ANET. If an MSE fails, ARs can quickly inform MNs 1746 of the outage by sending multicast RA messages on the ANET interface. 1747 The AR sends RA messages to MNs via the ANET interface with an OMNI 1748 option with a Release ID for the failed MSE, and with destination 1749 address set to All-Nodes multicast (ff02::1) [RFC4291]. 1751 The AR SHOULD send MAX_FINAL_RTR_ADVERTISEMENTS RA messages separated 1752 by small delays [RFC4861]. Any MNs on the ANET interface that have 1753 been using the (now defunct) MSE will receive the RA messages and 1754 associate with a new MSE. 1756 16. Transition Considerations 1758 When a MN connects to an ANET link for the first time, it sends an RS 1759 message with an OMNI option. If the first hop AR recognizes the 1760 option, it returns an RA with its MS OMNI LLA as the source, the MN 1761 OMNI LLA as the destination and with an OMNI option included. The MN 1762 then engages the AR according to the OMNI link model specified above. 1763 If the first hop AR is a legacy IPv6 router, however, it instead 1764 returns an RA message with no OMNI option and with a non-OMNI unicast 1765 source LLA as specified in [RFC4861]. In that case, the MN engages 1766 the ANET according to the legacy IPv6 link model and without the OMNI 1767 extensions specified in this document. 1769 If the ANET link model is multiple access, there must be assurance 1770 that address duplication cannot corrupt the neighbor caches of other 1771 nodes on the link. When the MN sends an RS message on a multiple 1772 access ANET link with an OMNI LLA source address and an OMNI option, 1773 ARs that recognize the option ensure that the MN is authorized to use 1774 the address and return an RA with a non-zero Router Lifetime only if 1775 the MN is authorized. ARs that do not recognize the option instead 1776 return an RA that makes no statement about the MN's authorization to 1777 use the source address. In that case, the MN should perform 1778 Duplicate Address Detection to ensure that it does not interfere with 1779 other nodes on the link. 1781 An alternative approach for multiple access ANET links to ensure 1782 isolation for MN / AR communications is through L2 address mappings 1783 as discussed in Appendix C. This arrangement imparts a (virtual) 1784 point-to-point link model over the (physical) multiple access link. 1786 17. OMNI Interfaces on the Open Internet 1788 OMNI interfaces configured over IPv6-enabled underlying interfaces on 1789 the open Internet without an OMNI-aware first-hop AR receive RA 1790 messages that do not include an OMNI option, while OMNI interfaces 1791 configured over IPv4-only underlying interfaces do not receive any 1792 (IPv6) RA messages at all. OMNI interfaces that receive RA messages 1793 without an OMNI option configure addresses, on-link prefxies, etc. on 1794 the underlying interface that received the RA according to standard 1795 IPv6 ND and address resolution conventions [RFC4861] [RFC4862]. OMNI 1796 interfaces configured over IPv4-only underlying interfaces configure 1797 IPv4 address information on the underlying interfaces using 1798 mechanisms such as DHCPv4 [RFC2131]. 1800 OMNI interfaces configured over underlying interfaces that connect to 1801 the open Internet can apply security services such as VPNs to connect 1802 to an MSE or establish a direct link to an MSE through some other 1803 means. In environments where an explicit VPN or direct link may be 1804 impractical, OMNI interfaces can instead use UDP/IP encapsulation per 1805 [RFC6081][RFC4380]. (SEcure Neighbor Discovery (SEND) and 1806 Cryptographically Generated Addresses (CGA) [RFC3971][RFC3972] or 1807 other protocol-specific security services can can also be used if 1808 additional authentication is necessary.) 1810 After estabishing a VPN or preparing for UDP/IP encapsulation, OMNI 1811 interfaces send control plane messages to interface with the MS. The 1812 control plane messages must be authenticated while data plane 1813 messages are delivered the same as for ordinary best-effort Internet 1814 traffic with basic source address-based data origin verification. 1815 Data plane communications via OMNI interfaces that connect over the 1816 open Internet without an explicit VPN should therefore employ 1817 transport- or higher-layer security to ensure integrity and/or 1818 confidentiality. 1820 When SEND/CGA are used over an open Internet underlying interfaces, 1821 each OMNI node configures a link-local CGA for use as the source 1822 address of IPv6 ND messages. The node then employs OMNI link 1823 encapsualation and sets the IPv6 source address of the OMNI header to 1824 the ULA corresponding to its OMNI LLA. Any Prefix Length values in 1825 the IPv6 ND message OMNI option then apply to the ULA found in the 1826 OMNI header, i.e., and not to the CGA found in the IPv6 ND message 1827 source address. 1829 OMNI interfaces in the open Internet are often located behind Network 1830 Address Translators (NATs). The OMNI interface accommodates NAT 1831 traversal using UDP/IP encapsulation and the mechanisms discussed in 1832 [RFC6081][RFC4380][I-D.templin-intarea-6706bis]. 1834 18. Time-Varying MNPs 1836 In some use cases, it is desirable, beneficial and efficient for the 1837 MN to receive a constant MNP that travels with the MN wherever it 1838 moves. For example, this would allow air traffic controllers to 1839 easily track aircraft, etc. In other cases, however (e.g., 1840 intelligent transportation systems), the MN may be willing to 1841 sacrifice a modicum of efficiency in order to have time-varying MNPs 1842 that can be changed every so often to defeat adversarial tracking. 1844 Prefix delegation services such as those discussed in 1845 [I-D.templin-6man-dhcpv6-ndopt] and [I-D.templin-intarea-6706bis] 1846 allow OMNI MNs that desire time-varying MNPs to obtain short-lived 1847 prefixes. In that case, the identity of the MN can be used as a 1848 prefix delegation seed (e.g., a DHCPv6 Device Unique IDentifier 1849 (DUID) [RFC8415]). The MN would then be obligated to renumber its 1850 internal networks whenever its MNP (and therefore also its OMNI 1851 address) changes. This should not present a challenge for MNs with 1852 automated network renumbering services, however presents limits for 1853 the durations of ongoing sessions that would prefer to use a constant 1854 address. 1856 When a MN wishes to invoke DHCPv6 Prefix Delegation (PD) services, it 1857 sets the source address of an RS message to fe80:: and includes a 1858 DUID sub-option and a desired Prefix Length value in the RS message 1859 OMNI option. When the first-hop AR receives the RS message, it 1860 performs a PD exchange with the DHCPv6 service to obtain an IPv6 MNP 1861 of the requested length then returns an RA message with the OMNI LLA 1862 corresponding to the MNP as the destination address. When the MN 1863 receives the RA message, it provisons the PD to its downstream- 1864 attached networks and begins using the OMNI LLA in subsequent IPv6 ND 1865 messaging. 1867 19. IANA Considerations 1869 The IANA is instructed to allocate an official Type number TBD from 1870 the registry "IPv6 Neighbor Discovery Option Formats" for the OMNI 1871 option. Implementations set Type to 253 as an interim value 1872 [RFC4727]. 1874 The IANA is instructed to assign a new Code value "1" in the "ICMPv6 1875 Code Fields: Type 2 - Packet Too Big" registry. The registry should 1876 read as follows: 1878 Code Name Reference 1879 --- ---- --------- 1880 0 Diagnostic Packet Too Big [RFC4443] 1881 1 Advisory Packet Too Big [RFCXXXX] 1883 Figure 16: OMNI Option Sub-Type Values 1885 The IANA is instructed to allocate one Ethernet unicast address TBD2 1886 (suggest 00-00-5E-00-52-14 [RFC5214]) in the registry "IANA Ethernet 1887 Address Block - Unicast Use". 1889 The OMNI option also defines an 8-bit Sub-Type field, for which IANA 1890 is instructed to create and maintain a new registry entitled "OMNI 1891 option Sub-Type values". Initial values for the OMNI option Sub-Type 1892 values registry are given below; future assignments are to be made 1893 through Expert Review [RFC8126]. 1895 Value Sub-Type name Reference 1896 ----- ------------- ---------- 1897 0 Pad1 [RFCXXXX] 1898 1 PadN [RFCXXXX] 1899 2 Interface Attributes [RFCXXXX] 1900 3 Traffic Selector [RFCXXXX] 1901 4 MS-Register [RFCXXXX] 1902 5 MS-Release [RFCXXXX] 1903 6 Network Acceess Identifier [RFCXXXX] 1904 7 Geo Coordinates [RFCXXXX] 1905 8 DHCP Unique Identifier (DUID) [RFCXXXX] 1906 9-252 Unassigned 1907 253-254 Experimental [RFCXXXX] 1908 255 Reserved [RFCXXXX] 1910 Figure 17: OMNI Option Sub-Type Values 1912 20. Security Considerations 1914 Security considerations for IPv4 [RFC0791], IPv6 [RFC8200] and IPv6 1915 Neighbor Discovery [RFC4861] apply. OMNI interface IPv6 ND messages 1916 SHOULD include Nonce and Timestamp options [RFC3971] when transaction 1917 confirmation and/or time synchronization is needed. 1919 OMNI interfaces configured over secured ANET interfaces inherit the 1920 physical and/or link-layer security properties of the connected 1921 ANETs. OMNI interfaces configured over open INET interfaces can use 1922 symmetric securing services such as VPNs or can by some other means 1923 establish a direct link. When a VPN or direct link may be 1924 impractical, however, an asymmetric security service such as SEcure 1925 Neighbor Discovery (SEND) [RFC3971] with Cryptographically Generated 1926 Addresses (CGAs) [RFC3972], the authentication option specified in 1927 [RFC4380] or other protocol control message security mechanisms may 1928 be necessary. While the OMNI link protects control plane messaging, 1929 applications must still employ end-to-end transport- or higher-layer 1930 security services to protect the data plane. 1932 The Mobility Service MUST provide strong network layer security for 1933 control plane messages and forwading path integrity for data plane 1934 messages. In one example, the AERO service 1935 [I-D.templin-intarea-6706bis] constructs a spanning tree between 1936 mobility service elements and secures the links in the spanning tree 1937 with network layer security mechanisms such as IPsec [RFC4301] or 1938 Wireguard. Control plane messages are then constrained to travel 1939 only over the secured spanning tree paths and are therefore protected 1940 from attack or eavesdropping. Since data plane messages can travel 1941 over route optimized paths that do not strictly follow the spanning 1942 tree, however, end-to-end transport- or higher-layer security 1943 services are still required. 1945 Security considerations for specific access network interface types 1946 are covered under the corresponding IP-over-(foo) specification 1947 (e.g., [RFC2464], [RFC2492], etc.). 1949 Security considerations for IPv6 fragmentation and reassembly are 1950 discussed in Section 5.1. 1952 21. Implementation Status 1954 Draft -29 is implemented in the recently tagged AERO/OMNI 3.0.0 1955 internal release, and Draft -30 is now tagged as the AERO/OMNI 3.0.1. 1956 Newer specification versions will be tagged in upcoming releases. 1957 First public release expected before the end of 2020. 1959 22. Acknowledgements 1961 The first version of this document was prepared per the consensus 1962 decision at the 7th Conference of the International Civil Aviation 1963 Organization (ICAO) Working Group-I Mobility Subgroup on March 22, 1964 2019. Consensus to take the document forward to the IETF was reached 1965 at the 9th Conference of the Mobility Subgroup on November 22, 2019. 1966 Attendees and contributors included: Guray Acar, Danny Bharj, 1967 Francois D'Humieres, Pavel Drasil, Nikos Fistas, Giovanni Garofolo, 1968 Bernhard Haindl, Vaughn Maiolla, Tom McParland, Victor Moreno, Madhu 1969 Niraula, Brent Phillips, Liviu Popescu, Jacky Pouzet, Aloke Roy, Greg 1970 Saccone, Robert Segers, Michal Skorepa, Michel Solery, Stephane 1971 Tamalet, Fred Templin, Jean-Marc Vacher, Bela Varkonyi, Tony Whyman, 1972 Fryderyk Wrobel and Dongsong Zeng. 1974 The following individuals are acknowledged for their useful comments: 1975 Michael Matyas, Madhu Niraula, Michael Richardson, Greg Saccone, 1976 Stephane Tamalet, Eric Vyncke. Pavel Drasil, Zdenek Jaron and Michal 1977 Skorepa are recognized for their many helpful ideas and suggestions. 1978 Madhuri Madhava Badgandi, Katherine Tran, and Vijayasarathy 1979 Rajagopalan are acknowledged for their hard work on the 1980 implementation and insights that led to improvements to the spec. 1982 This work is aligned with the NASA Safe Autonomous Systems Operation 1983 (SASO) program under NASA contract number NNA16BD84C. 1985 This work is aligned with the FAA as per the SE2025 contract number 1986 DTFAWA-15-D-00030. 1988 23. References 1990 23.1. Normative References 1992 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, 1993 DOI 10.17487/RFC0791, September 1981, 1994 . 1996 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1997 Requirement Levels", BCP 14, RFC 2119, 1998 DOI 10.17487/RFC2119, March 1997, 1999 . 2001 [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black, 2002 "Definition of the Differentiated Services Field (DS 2003 Field) in the IPv4 and IPv6 Headers", RFC 2474, 2004 DOI 10.17487/RFC2474, December 1998, 2005 . 2007 [RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander, 2008 "SEcure Neighbor Discovery (SEND)", RFC 3971, 2009 DOI 10.17487/RFC3971, March 2005, 2010 . 2012 [RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)", 2013 RFC 3972, DOI 10.17487/RFC3972, March 2005, 2014 . 2016 [RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and 2017 More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191, 2018 November 2005, . 2020 [RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast 2021 Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005, 2022 . 2024 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 2025 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 2026 2006, . 2028 [RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet 2029 Control Message Protocol (ICMPv6) for the Internet 2030 Protocol Version 6 (IPv6) Specification", STD 89, 2031 RFC 4443, DOI 10.17487/RFC4443, March 2006, 2032 . 2034 [RFC4727] Fenner, B., "Experimental Values In IPv4, IPv6, ICMPv4, 2035 ICMPv6, UDP, and TCP Headers", RFC 4727, 2036 DOI 10.17487/RFC4727, November 2006, 2037 . 2039 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 2040 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 2041 DOI 10.17487/RFC4861, September 2007, 2042 . 2044 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 2045 Address Autoconfiguration", RFC 4862, 2046 DOI 10.17487/RFC4862, September 2007, 2047 . 2049 [RFC6088] Tsirtsis, G., Giarreta, G., Soliman, H., and N. Montavont, 2050 "Traffic Selectors for Flow Bindings", RFC 6088, 2051 DOI 10.17487/RFC6088, January 2011, 2052 . 2054 [RFC8028] Baker, F. and B. Carpenter, "First-Hop Router Selection by 2055 Hosts in a Multi-Prefix Network", RFC 8028, 2056 DOI 10.17487/RFC8028, November 2016, 2057 . 2059 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2060 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2061 May 2017, . 2063 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 2064 (IPv6) Specification", STD 86, RFC 8200, 2065 DOI 10.17487/RFC8200, July 2017, 2066 . 2068 [RFC8201] McCann, J., Deering, S., Mogul, J., and R. Hinden, Ed., 2069 "Path MTU Discovery for IP version 6", STD 87, RFC 8201, 2070 DOI 10.17487/RFC8201, July 2017, 2071 . 2073 [RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A., 2074 Richardson, M., Jiang, S., Lemon, T., and T. Winters, 2075 "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", 2076 RFC 8415, DOI 10.17487/RFC8415, November 2018, 2077 . 2079 23.2. Informative References 2081 [CRC] Jain, R., "Error Characteristics of Fiber Distributed Data 2082 Interface (FDDI), IEEE Transactions on Communications", 2083 August 1990. 2085 [I-D.ietf-intarea-tunnels] 2086 Touch, J. and M. Townsley, "IP Tunnels in the Internet 2087 Architecture", draft-ietf-intarea-tunnels-10 (work in 2088 progress), September 2019. 2090 [I-D.templin-6man-dhcpv6-ndopt] 2091 Templin, F., "A Unified Stateful/Stateless Configuration 2092 Service for IPv6", draft-templin-6man-dhcpv6-ndopt-10 2093 (work in progress), June 2020. 2095 [I-D.templin-intarea-6706bis] 2096 Templin, F., "Asymmetric Extended Route Optimization 2097 (AERO)", draft-templin-intarea-6706bis-65 (work in 2098 progress), September 2020. 2100 [RFC1122] Braden, R., Ed., "Requirements for Internet Hosts - 2101 Communication Layers", STD 3, RFC 1122, 2102 DOI 10.17487/RFC1122, October 1989, 2103 . 2105 [RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191, 2106 DOI 10.17487/RFC1191, November 1990, 2107 . 2109 [RFC1256] Deering, S., Ed., "ICMP Router Discovery Messages", 2110 RFC 1256, DOI 10.17487/RFC1256, September 1991, 2111 . 2113 [RFC2131] Droms, R., "Dynamic Host Configuration Protocol", 2114 RFC 2131, DOI 10.17487/RFC2131, March 1997, 2115 . 2117 [RFC2225] Laubach, M. and J. Halpern, "Classical IP and ARP over 2118 ATM", RFC 2225, DOI 10.17487/RFC2225, April 1998, 2119 . 2121 [RFC2464] Crawford, M., "Transmission of IPv6 Packets over Ethernet 2122 Networks", RFC 2464, DOI 10.17487/RFC2464, December 1998, 2123 . 2125 [RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in 2126 IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473, 2127 December 1998, . 2129 [RFC2492] Armitage, G., Schulter, P., and M. Jork, "IPv6 over ATM 2130 Networks", RFC 2492, DOI 10.17487/RFC2492, January 1999, 2131 . 2133 [RFC2529] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4 2134 Domains without Explicit Tunnels", RFC 2529, 2135 DOI 10.17487/RFC2529, March 1999, 2136 . 2138 [RFC2863] McCloghrie, K. and F. Kastenholz, "The Interfaces Group 2139 MIB", RFC 2863, DOI 10.17487/RFC2863, June 2000, 2140 . 2142 [RFC3692] Narten, T., "Assigning Experimental and Testing Numbers 2143 Considered Useful", BCP 82, RFC 3692, 2144 DOI 10.17487/RFC3692, January 2004, 2145 . 2147 [RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener 2148 Discovery Version 2 (MLDv2) for IPv6", RFC 3810, 2149 DOI 10.17487/RFC3810, June 2004, 2150 . 2152 [RFC3819] Karn, P., Ed., Bormann, C., Fairhurst, G., Grossman, D., 2153 Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J., and L. 2154 Wood, "Advice for Internet Subnetwork Designers", BCP 89, 2155 RFC 3819, DOI 10.17487/RFC3819, July 2004, 2156 . 2158 [RFC3879] Huitema, C. and B. Carpenter, "Deprecating Site Local 2159 Addresses", RFC 3879, DOI 10.17487/RFC3879, September 2160 2004, . 2162 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 2163 Internet Protocol", RFC 4301, DOI 10.17487/RFC4301, 2164 December 2005, . 2166 [RFC4380] Huitema, C., "Teredo: Tunneling IPv6 over UDP through 2167 Network Address Translations (NATs)", RFC 4380, 2168 DOI 10.17487/RFC4380, February 2006, 2169 . 2171 [RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery 2172 Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April 2173 2006, . 2175 [RFC4541] Christensen, M., Kimball, K., and F. Solensky, 2176 "Considerations for Internet Group Management Protocol 2177 (IGMP) and Multicast Listener Discovery (MLD) Snooping 2178 Switches", RFC 4541, DOI 10.17487/RFC4541, May 2006, 2179 . 2181 [RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick, 2182 "Internet Group Management Protocol (IGMP) / Multicast 2183 Listener Discovery (MLD)-Based Multicast Forwarding 2184 ("IGMP/MLD Proxying")", RFC 4605, DOI 10.17487/RFC4605, 2185 August 2006, . 2187 [RFC4821] Mathis, M. and J. Heffner, "Packetization Layer Path MTU 2188 Discovery", RFC 4821, DOI 10.17487/RFC4821, March 2007, 2189 . 2191 [RFC4963] Heffner, J., Mathis, M., and B. Chandler, "IPv4 Reassembly 2192 Errors at High Data Rates", RFC 4963, 2193 DOI 10.17487/RFC4963, July 2007, 2194 . 2196 [RFC5175] Haberman, B., Ed. and R. Hinden, "IPv6 Router 2197 Advertisement Flags Option", RFC 5175, 2198 DOI 10.17487/RFC5175, March 2008, 2199 . 2201 [RFC5213] Gundavelli, S., Ed., Leung, K., Devarapalli, V., 2202 Chowdhury, K., and B. Patil, "Proxy Mobile IPv6", 2203 RFC 5213, DOI 10.17487/RFC5213, August 2008, 2204 . 2206 [RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site 2207 Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214, 2208 DOI 10.17487/RFC5214, March 2008, 2209 . 2211 [RFC5558] Templin, F., Ed., "Virtual Enterprise Traversal (VET)", 2212 RFC 5558, DOI 10.17487/RFC5558, February 2010, 2213 . 2215 [RFC5798] Nadas, S., Ed., "Virtual Router Redundancy Protocol (VRRP) 2216 Version 3 for IPv4 and IPv6", RFC 5798, 2217 DOI 10.17487/RFC5798, March 2010, 2218 . 2220 [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 2221 (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, 2222 . 2224 [RFC6081] Thaler, D., "Teredo Extensions", RFC 6081, 2225 DOI 10.17487/RFC6081, January 2011, 2226 . 2228 [RFC6355] Narten, T. and J. Johnson, "Definition of the UUID-Based 2229 DHCPv6 Unique Identifier (DUID-UUID)", RFC 6355, 2230 DOI 10.17487/RFC6355, August 2011, 2231 . 2233 [RFC6543] Gundavelli, S., "Reserved IPv6 Interface Identifier for 2234 Proxy Mobile IPv6", RFC 6543, DOI 10.17487/RFC6543, May 2235 2012, . 2237 [RFC7084] Singh, H., Beebee, W., Donley, C., and B. Stark, "Basic 2238 Requirements for IPv6 Customer Edge Routers", RFC 7084, 2239 DOI 10.17487/RFC7084, November 2013, 2240 . 2242 [RFC7421] Carpenter, B., Ed., Chown, T., Gont, F., Jiang, S., 2243 Petrescu, A., and A. Yourtchenko, "Analysis of the 64-bit 2244 Boundary in IPv6 Addressing", RFC 7421, 2245 DOI 10.17487/RFC7421, January 2015, 2246 . 2248 [RFC7542] DeKok, A., "The Network Access Identifier", RFC 7542, 2249 DOI 10.17487/RFC7542, May 2015, 2250 . 2252 [RFC7739] Gont, F., "Security Implications of Predictable Fragment 2253 Identification Values", RFC 7739, DOI 10.17487/RFC7739, 2254 February 2016, . 2256 [RFC7847] Melia, T., Ed. and S. Gundavelli, Ed., "Logical-Interface 2257 Support for IP Hosts with Multi-Access Support", RFC 7847, 2258 DOI 10.17487/RFC7847, May 2016, 2259 . 2261 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 2262 Writing an IANA Considerations Section in RFCs", BCP 26, 2263 RFC 8126, DOI 10.17487/RFC8126, June 2017, 2264 . 2266 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 2267 Decraene, B., Litkowski, S., and R. Shakir, "Segment 2268 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 2269 July 2018, . 2271 [RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J., 2272 Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header 2273 (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020, 2274 . 2276 [RFC8900] Bonica, R., Baker, F., Huston, G., Hinden, R., Troan, O., 2277 and F. Gont, "IP Fragmentation Considered Fragile", 2278 BCP 230, RFC 8900, DOI 10.17487/RFC8900, September 2020, 2279 . 2281 Appendix A. Interface Attribute Heuristic Bitmap Encoding 2283 Adaptation of the OMNI option Interface Attributes Heuristic Bitmap 2284 encoding to specific Internetworks such as the Aeronautical 2285 Telecommunications Network with Internet Protocol Services (ATN/IPS) 2286 may include link selection preferences based on other traffic 2287 classifiers (e.g., transport port numbers, etc.) in addition to the 2288 existing DSCP-based preferences. Nodes on specific Internetworks 2289 maintain a map of traffic classifiers to additional P[*] preference 2290 fields beyond the first 64. For example, TCP port 22 maps to P[67], 2291 TCP port 443 maps to P[70], UDP port 8060 maps to P[76], etc. 2293 Implementations use Simplex or Indexed encoding formats for P[*] 2294 encoding in order to encode a given set of traffic classifiers in the 2295 most efficient way. Some use cases may be more efficiently coded 2296 using Simplex form, while others may be more efficient using Indexed. 2297 Once a format is selected for preparation of a single Interface 2298 Attribute the same format must be used for the entire Interface 2299 Attribute sub-option. Different sub-options may use different 2300 formats. 2302 The following figures show coding examples for various Simplex and 2303 Indexed formats: 2305 0 1 2 3 2306 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 2307 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2308 | Sub-Type=2 | Sub-length=N | ifIndex | ifType | 2309 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2310 | Provider ID | Link |R| APS | Bitmap(0)=0xff|P00|P01|P02|P03| 2311 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2312 |P04|P05|P06|P07|P08|P09|P10|P11|P12|P13|P14|P15|P16|P17|P18|P19| 2313 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2314 |P20|P21|P22|P23|P24|P25|P26|P27|P28|P29|P30|P31| Bitmap(1)=0xff| 2315 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2316 |P32|P33|P34|P35|P36|P37|P38|P39|P40|P41|P42|P43|P44|P45|P46|P47| 2317 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2318 |P48|P49|P50|P51|P52|P53|P54|P55|P56|P57|P58|P59|P60|P61|P62|P63| 2319 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2320 | Bitmap(2)=0xff|P64|P65|P67|P68| ... 2321 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 2323 Figure 18: Example 1: Dense Simplex Encoding 2325 0 1 2 3 2326 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 2327 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2328 | Sub-Type=2 | Sub-length=N | ifIndex | ifType | 2329 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2330 | Provider ID | Link |R| APS | Bitmap(0)=0x00| Bitmap(1)=0x0f| 2331 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2332 |P48|P49|P50|P51|P52|P53|P54|P55|P56|P57|P58|P59|P60|P61|P62|P63| 2333 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2334 | Bitmap(2)=0x00| Bitmap(3)=0x00| Bitmap(4)=0x00| Bitmap(5)=0x00| 2335 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2336 | Bitmap(6)=0xf0|192|193|194|195|196|197|198|199|200|201|202|203| 2337 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2338 |204|205|206|207| Bitmap(7)=0x00| Bitmap(8)=0x0f|272|273|274|275| 2339 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2340 |276|277|278|279|280|281|282|283|284|285|286|287| Bitmap(9)=0x00| 2341 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2342 |Bitmap(10)=0x00| ... 2343 +-+-+-+-+-+-+-+-+-+-+- 2345 Figure 19: Example 2: Sparse Simplex Encoding 2347 0 1 2 3 2348 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 2349 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2350 | Sub-Type=2 | Sub-length=N | ifIndex | ifType | 2351 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2352 | Provider ID | Link |R| APS | Index = 0x00 | Bitmap = 0x80 | 2353 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2354 |P00|P01|P02|P03| Index = 0x01 | Bitmap = 0x01 |P60|P61|P62|P63| 2355 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2356 | Index = 0x10 | Bitmap = 0x80 |512|513|514|515| Index = 0x18 | 2357 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2358 | Bitmap = 0x01 |796|797|798|799| ... 2359 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 2361 Figure 20: Example 3: Indexed Encoding 2363 Appendix B. VDL Mode 2 Considerations 2365 ICAO Doc 9776 is the "Technical Manual for VHF Data Link Mode 2" 2366 (VDLM2) that specifies an essential radio frequency data link service 2367 for aircraft and ground stations in worldwide civil aviation air 2368 traffic management. The VDLM2 link type is "multicast capable" 2369 [RFC4861], but with considerable differences from common multicast 2370 links such as Ethernet and IEEE 802.11. 2372 First, the VDLM2 link data rate is only 31.5Kbps - multiple orders of 2373 magnitude less than most modern wireless networking gear. Second, 2374 due to the low available link bandwidth only VDLM2 ground stations 2375 (i.e., and not aircraft) are permitted to send broadcasts, and even 2376 so only as compact layer 2 "beacons". Third, aircraft employ the 2377 services of ground stations by performing unicast RS/RA exchanges 2378 upon receipt of beacons instead of listening for multicast RA 2379 messages and/or sending multicast RS messages. 2381 This beacon-oriented unicast RS/RA approach is necessary to conserve 2382 the already-scarce available link bandwidth. Moreover, since the 2383 numbers of beaconing ground stations operating within a given spatial 2384 range must be kept as sparse as possible, it would not be feasible to 2385 have different classes of ground stations within the same region 2386 observing different protocols. It is therefore highly desirable that 2387 all ground stations observe a common language of RS/RA as specified 2388 in this document. 2390 Note that links of this nature may benefit from compression 2391 techniques that reduce the bandwidth necessary for conveying the same 2392 amount of data. The IETF lpwan working group is considering possible 2393 alternatives: [https://datatracker.ietf.org/wg/lpwan/documents]. 2395 Appendix C. MN / AR Isolation Through L2 Address Mapping 2397 Per [RFC4861], IPv6 ND messages may be sent to either a multicast or 2398 unicast link-scoped IPv6 destination address. However, IPv6 ND 2399 messaging should be coordinated between the MN and AR only without 2400 invoking other nodes on the ANET. This implies that MN / AR control 2401 messaging should be isolated and not overheard by other nodes on the 2402 link. 2404 To support MN / AR isolation on some ANET links, ARs can maintain an 2405 OMNI-specific unicast L2 address ("MSADDR"). For Ethernet-compatible 2406 ANETs, this specification reserves one Ethernet unicast address TBD2 2407 (see: Section 19). For non-Ethernet statically-addressed ANETs, 2408 MSADDR is reserved per the assigned numbers authority for the ANET 2409 addressing space. For still other ANETs, MSADDR may be dynamically 2410 discovered through other means, e.g., L2 beacons. 2412 MNs map the L3 addresses of all IPv6 ND messages they send (i.e., 2413 both multicast and unicast) to MSADDR instead of to an ordinary 2414 unicast or multicast L2 address. In this way, all of the MN's IPv6 2415 ND messages will be received by ARs that are configured to accept 2416 packets destined to MSADDR. Note that multiple ARs on the link could 2417 be configured to accept packets destined to MSADDR, e.g., as a basis 2418 for supporting redundancy. 2420 Therefore, ARs must accept and process packets destined to MSADDR, 2421 while all other devices must not process packets destined to MSADDR. 2422 This model has well-established operational experience in Proxy 2423 Mobile IPv6 (PMIP) [RFC5213][RFC6543]. 2425 Appendix D. Change Log 2427 << RFC Editor - remove prior to publication >> 2429 Differences from draft-templin-6man-omni-interface-35 to draft- 2430 templin-6man-omni-interface-36: 2432 o Major clarifications on aspects such as "hard/soft" PTB error 2433 messages 2435 o Made generic so that either IP protocol version (IPv4 or IPv6) can 2436 be used in the data plane. 2438 Differences from draft-templin-6man-omni-interface-31 to draft- 2439 templin-6man-omni-interface-32: 2441 o MTU 2442 o Support for multi-hop ANETS such as ISATAP. 2444 Differences from draft-templin-6man-omni-interface-29 to draft- 2445 templin-6man-omni-interface-30: 2447 o Moved link-layer addressing information into the OMNI option on a 2448 per-ifIndex basis 2450 o Renamed "ifIndex-tuple" to "Interface Attributes" 2452 Differences from draft-templin-6man-omni-interface-27 to draft- 2453 templin-6man-omni-interface-28: 2455 o Updates based on implementation expereince. 2457 Differences from draft-templin-6man-omni-interface-25 to draft- 2458 templin-6man-omni-interface-26: 2460 o Further clarification on "aggregate" RA messages. 2462 o Expanded Security Considerations to discuss expectations for 2463 security in the Mobility Service. 2465 Differences from draft-templin-6man-omni-interface-20 to draft- 2466 templin-6man-omni-interface-21: 2468 o Safety-Based Multilink (SBM) and Performance-Based Multilink 2469 (PBM). 2471 Differences from draft-templin-6man-omni-interface-18 to draft- 2472 templin-6man-omni-interface-19: 2474 o SEND/CGA. 2476 Differences from draft-templin-6man-omni-interface-17 to draft- 2477 templin-6man-omni-interface-18: 2479 o Teredo 2481 Differences from draft-templin-6man-omni-interface-14 to draft- 2482 templin-6man-omni-interface-15: 2484 o Prefix length discussions removed. 2486 Differences from draft-templin-6man-omni-interface-12 to draft- 2487 templin-6man-omni-interface-13: 2489 o Teredo 2490 Differences from draft-templin-6man-omni-interface-11 to draft- 2491 templin-6man-omni-interface-12: 2493 o Major simplifications and clarifications on MTU and fragmentation. 2495 o Document now updates RFC4443 and RFC8201. 2497 Differences from draft-templin-6man-omni-interface-10 to draft- 2498 templin-6man-omni-interface-11: 2500 o Removed /64 assumption, resulting in new OMNI address format. 2502 Differences from draft-templin-6man-omni-interface-07 to draft- 2503 templin-6man-omni-interface-08: 2505 o OMNI MNs in the open Internet 2507 Differences from draft-templin-6man-omni-interface-06 to draft- 2508 templin-6man-omni-interface-07: 2510 o Brought back L2 MSADDR mapping text for MN / AR isolation based on 2511 L2 addressing. 2513 o Expanded "Transition Considerations". 2515 Differences from draft-templin-6man-omni-interface-05 to draft- 2516 templin-6man-omni-interface-06: 2518 o Brought back OMNI option "R" flag, and discussed its use. 2520 Differences from draft-templin-6man-omni-interface-04 to draft- 2521 templin-6man-omni-interface-05: 2523 o Transition considerations, and overhaul of RS/RA addressing with 2524 the inclusion of MSE addresses within the OMNI option instead of 2525 as RS/RA addresses (developed under FAA SE2025 contract number 2526 DTFAWA-15-D-00030). 2528 Differences from draft-templin-6man-omni-interface-02 to draft- 2529 templin-6man-omni-interface-03: 2531 o Added "advisory PTB messages" under FAA SE2025 contract number 2532 DTFAWA-15-D-00030. 2534 Differences from draft-templin-6man-omni-interface-01 to draft- 2535 templin-6man-omni-interface-02: 2537 o Removed "Primary" flag and supporting text. 2539 o Clarified that "Router Lifetime" applies to each ANET interface 2540 independently, and that the union of all ANET interface Router 2541 Lifetimes determines MSE lifetime. 2543 Differences from draft-templin-6man-omni-interface-00 to draft- 2544 templin-6man-omni-interface-01: 2546 o "All-MSEs" OMNI LLA defined. Also reserved fe80::ff00:0000/104 2547 for future use (most likely as "pseudo-multicast"). 2549 o Non-normative discussion of alternate OMNI LLA construction form 2550 made possible if the 64-bit assumption were relaxed. 2552 First draft version (draft-templin-atn-aero-interface-00): 2554 o Draft based on consensus decision of ICAO Working Group I Mobility 2555 Subgroup March 22, 2019. 2557 Authors' Addresses 2559 Fred L. Templin (editor) 2560 The Boeing Company 2561 P.O. Box 3707 2562 Seattle, WA 98124 2563 USA 2565 Email: fltemplin@acm.org 2567 Tony Whyman 2568 MWA Ltd c/o Inmarsat Global Ltd 2569 99 City Road 2570 London EC1Y 1AX 2571 England 2573 Email: tony.whyman@mccallumwhyman.com