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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, rfc3879, rfc4291, A. Whyman 5 rfc4443, rfc8201 (if approved) MWA Ltd c/o Inmarsat Global Ltd 6 Intended status: Standards Track October 6, 2020 7 Expires: April 9, 2021 9 Transmission of IP Packets over Overlay Multilink Network (OMNI) 10 Interfaces 11 draft-templin-6man-omni-interface-46 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 9, 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) . . . . . . . . . . . . . . . 12 63 5.1. Fragmentation Security Implications . . . . . . . . . . . 16 64 6. Frame Format . . . . . . . . . . . . . . . . . . . . . . . . 17 65 7. Link-Local Addresses (LLAs) . . . . . . . . . . . . . . . . . 17 66 8. Segment-Local Addresses (SLAs) . . . . . . . . . . . . . . . 18 67 9. Address Mapping - Unicast . . . . . . . . . . . . . . . . . . 19 68 9.1. Sub-Options . . . . . . . . . . . . . . . . . . . . . . . 21 69 9.1.1. Pad1 . . . . . . . . . . . . . . . . . . . . . . . . 22 70 9.1.2. PadN . . . . . . . . . . . . . . . . . . . . . . . . 22 71 9.1.3. Interface Attributes . . . . . . . . . . . . . . . . 22 72 9.1.4. Traffic Selector . . . . . . . . . . . . . . . . . . 26 73 9.1.5. MS-Register . . . . . . . . . . . . . . . . . . . . . 27 74 9.1.6. MS-Release . . . . . . . . . . . . . . . . . . . . . 27 75 9.1.7. Network Access Identifier (NAI) . . . . . . . . . . . 28 76 9.1.8. Geo Coordinates . . . . . . . . . . . . . . . . . . . 29 77 9.1.9. DHCP Unique Identifier (DUID) . . . . . . . . . . . . 29 78 10. Address Mapping - Multicast . . . . . . . . . . . . . . . . . 30 79 11. Conceptual Sending Algorithm . . . . . . . . . . . . . . . . 30 80 11.1. Multiple OMNI Interfaces . . . . . . . . . . . . . . . . 30 81 12. Router Discovery and Prefix Registration . . . . . . . . . . 31 82 12.1. Router Discovery in IP Multihop and IPv4-Only Access 83 Networks . . . . . . . . . . . . . . . . . . . . . . . . 35 84 12.2. MS-Register and MS-Release List Processing . . . . . . . 36 85 13. Secure Redirection . . . . . . . . . . . . . . . . . . . . . 38 86 14. AR and MSE Resilience . . . . . . . . . . . . . . . . . . . . 38 87 15. Detecting and Responding to MSE Failures . . . . . . . . . . 39 88 16. Transition Considerations . . . . . . . . . . . . . . . . . . 39 89 17. OMNI Interfaces on the Open Internet . . . . . . . . . . . . 40 90 18. Time-Varying MNPs . . . . . . . . . . . . . . . . . . . . . . 41 91 19. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 41 92 20. Security Considerations . . . . . . . . . . . . . . . . . . . 42 93 21. Implementation Status . . . . . . . . . . . . . . . . . . . . 43 94 22. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 43 95 23. References . . . . . . . . . . . . . . . . . . . . . . . . . 44 96 23.1. Normative References . . . . . . . . . . . . . . . . . . 44 97 23.2. Informative References . . . . . . . . . . . . . . . . . 46 98 Appendix A. Interface Attribute Heuristic Bitmap Encoding . . . 50 99 Appendix B. VDL Mode 2 Considerations . . . . . . . . . . . . . 52 100 Appendix C. MN / AR Isolation Through L2 Address Mapping . . . . 53 101 Appendix D. Change Log . . . . . . . . . . . . . . . . . . . . . 53 102 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 56 104 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 Segment-Local Address (SLA) 272 an IPv6 address from the prefix fec0::/10 (see: Section 2.5.7 of 273 [RFC4291]) constructed as specified in Section 8. OMNI SLAs are 274 statelessly derived from OMNI LLAs, 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 Each underlying interface provides an L2/L1 abstraction according to 371 one of the following models: 373 o INET interfaces connect to an INET either natively or through one 374 or several IPv4 Network Address Translators (NATs). Native INET 375 interfaces have global IP addresses that are reachable from any 376 INET correspondent. NATed INET interfaces typically have private 377 IP addresses and connect to a private network behind one or more 378 NATs that provide INET access. 380 o ANET interfaces connect to a protected ANET that is separated from 381 the open INET by an AR acting as a proxy. The ANET interface may 382 be either on the same L2 link segment as the AR, or separated from 383 the AR by multiple IP hops. 385 o VPNed interfaces use security encapsulation over an INET/ANET to a 386 Virtual Private Network (VPN) gateway. Other than the link-layer 387 encapsulation format, VPNed interfaces behave the same as for 388 Direct interfaces. 390 o Direct (aka "point-to-point") interfaces connect directly to a 391 peer without crossing any ANET/INET paths. An example is a line- 392 of-sight link between a remote pilot and an unmanned aircraft. 394 The OMNI virtual interface model gives rise to a number of 395 opportunities: 397 o since OMNI LLAs are uniquely derived from an MNP, no Duplicate 398 Address Detection (DAD) or Muticast Listener Discovery (MLD) 399 messaging is necessary. 401 o ANET interfaces on the same L2 link segment as an AR do not 402 require any L3 addresses (i.e., not even link-local) in 403 environments where communications are coordinated entirely over 404 the OMNI interface. (An alternative would be to also assign the 405 same OMNI LLA to all ANET interfaces.) 407 o as underlying interface properties change (e.g., link quality, 408 cost, availability, etc.), any active interface can be used to 409 update the profiles of multiple additional interfaces in a single 410 message. This allows for timely adaptation and service continuity 411 under dynamically changing conditions. 413 o coordinating underlying interfaces in this way allows them to be 414 represented in a unified MS profile with provisions for mobility 415 and multilink operations. 417 o exposing a single virtual interface abstraction to the IPv6 layer 418 allows for multilink operation (including QoS based link 419 selection, packet replication, load balancing, etc.) at L2 while 420 still permitting L3 traffic shaping based on, e.g., DSCP, flow 421 label, etc. 423 o the OMNI interface allows inter-INET traversal when nodes located 424 in different INETs need to communicate with one another. This 425 mode of operation would not be possible via direct communications 426 over the underlying interfaces themselves. 428 o the OMNI Adaptation Layer (OAL) within the OMNI interface supports 429 lossless and adaptive path MTU mitigations not available for 430 communications directly over the underlying interfaces themselves. 432 o L3 sees the OMNI interface as a point of connection to the OMNI 433 link; if there are multiple OMNI links (i.e., multiple MS's), L3 434 will see multiple OMNI interfaces. 436 o Multiple independent OMNI interfaces can be used for increased 437 fault tolerance through Safety-Based Multilink (SBM), with 438 Performance-Based Multilink (PBM) applied within each interface. 440 Other opportunities are discussed in [RFC7847]. Note that even when 441 the OMNI virtual interface is present, applications can still access 442 underlying interfaces either through the network protocol stack using 443 an Internet socket or directly using a raw socket. This allows for 444 intra-network (or point-to-point) communications without invoking the 445 OMNI interface and/or OAL. For example, when an IPv6 OMNI interface 446 is configured over an underlying IPv4 interface, applications can 447 still invoke IPv4 intra-network communications as long as the 448 communicating endpoints are not subject to mobility dynamics. 449 However, the opportunities discussed above are not available when the 450 architectural layering is bypassed in this way. 452 Figure 2 depicts the architectural model for a MN connecting to the 453 MS via multiple independent ANETs. When an underlying interface 454 becomes active, the MN's OMNI interface sends native (i.e., 455 unencapsulated) IPv6 ND messages via the underlying interface. IPv6 456 ND messages traverse the ground domain ANETs until they reach an 457 Access Router (AR#1, AR#2, .., AR#n). The AR then coordinates with a 458 Mobility Service Endpoint (MSE#1, MSE#2, ..., MSE#m) in the INET and 459 returns an IPv6 ND message response to the MN. IPv6 ND messages 460 traverse the ANET at layer 2; hence, the Hop Limit is not 461 decremented. 463 +--------------+ 464 | MN | 465 +--------------+ 466 |OMNI interface| 467 +----+----+----+ 468 +--------|IF#1|IF#2|IF#n|------ + 469 / +----+----+----+ \ 470 / | \ 471 / <---- Native | IP ----> \ 472 v v v 473 (:::)-. (:::)-. (:::)-. 474 .-(::ANET:::) .-(::ANET:::) .-(::ANET:::) 475 `-(::::)-' `-(::::)-' `-(::::)-' 476 +----+ +----+ +----+ 477 ... |AR#1| .......... |AR#2| ......... |AR#n| ... 478 . +-|--+ +-|--+ +-|--+ . 479 . | | | 480 . v v v . 481 . <----- Encapsulation -----> . 482 . . 483 . +-----+ (:::)-. . 484 . |MSE#2| .-(::::::::) +-----+ . 485 . +-----+ .-(::: INET :::)-. |MSE#m| . 486 . (::::: Routing ::::) +-----+ . 487 . `-(::: System :::)-' . 488 . +-----+ `-(:::::::-' . 489 . |MSE#1| +-----+ +-----+ . 490 . +-----+ |MSE#3| |MSE#4| . 491 . +-----+ +-----+ . 492 . . 493 . . 494 . <----- Worldwide Connected Internetwork ----> . 495 ........................................................... 497 Figure 2: MN/MS Coordination via Multiple ANETs 499 After the initial IPv6 ND message exchange, the MN can send and 500 receive unencapsulated IP data packets over the OMNI interface. OMNI 501 interface multilink services will forward the packets via ARs in the 502 correct underlying ANETs. The AR encapsulates the packets according 503 to the capabilities provided by the MS and forwards them to the next 504 hop within the worldwide connected Internetwork via optimal routes. 506 OMNI links span one or more underlying Internetwork via the OMNI 507 Adaptation Layer (OAL) which is based on a mid-layer overlay 508 encapsulation using [RFC2473]. Each OMNI link corresponds to a 509 different overlay (differentiated by an address codepoint) which may 510 be carried over a completely separate underlying topology. Each MN 511 can facilitate SBM by connecting to multiple OMNI links using a 512 distinct OMNI interface for each link. 514 5. The OMNI Adaptation Layer (OAL) 516 The OMNI interface observes the link nature of tunnels, including the 517 Maximum Transmission Unit (MTU), Maximum Reassembly Unit (MRU) and 518 the role of fragmentation and reassembly [I-D.ietf-intarea-tunnels]. 519 The OMNI interface is configured over one or more underlying 520 interfaces that may have diverse MTUs. OMNI interfaces accommodate 521 MTU diversity through the use of the OMNI Adpatation Layer (OAL) as 522 discussed in this section. 524 IPv6 underlying interfaces are REQUIRED to configure a minimum MTU of 525 1280 bytes and a minimum MRU of 1500 bytes [RFC8200], meaning that 526 the minimum IPv6 path MTU is 1280 bytes since routers on the path are 527 not permitted to perform network fragmentation even though the 528 destination is required to reassemble more. The network therefore 529 MUST forward packets of at least 1280 bytes without generating an 530 IPv6 Path MTU Discovery (PMTUD) Packet Too Big (PTB) message 531 [RFC8201]. (Note: the source can apply "source fragmentation" for 532 locally-generated IPv6 packets up to 1500 bytes and larger still if 533 it if has a way to determine that the destination configures a larger 534 MRU, but this does not affect the minimum IPv6 path MTU.) 536 IPv4 underlying interfaces are REQUIRED to configure a minimum MTU of 537 68 bytes [RFC0791] and a minimum MRU of 576 bytes [RFC0791][RFC1122]. 538 Therefore, when the Don't Fragment (DF) bit in the IPv4 header is set 539 to 0 the minimum IPv4 path MTU is 576 bytes since routers on the path 540 support network fragmentation and the destination is required to 541 reassemble at least that much. The DF bit in the IPv4 encapsulation 542 headers of packets sent over IPv4 underlying interfaces therefore 543 MUST be set to 0. (Note: even if the encapsulation source has a way 544 to determine that the encapsulation destination configures an MRU 545 larger than 576 bytes, it should not assume a larger minimum IPv4 546 path MTU without careful consderation of the issues discussed in 547 Section 5.1.) 549 The OMNI interface configures both an MTU and MRU of 9180 bytes 550 [RFC2492]; the size is therefore not a reflection of the underlying 551 interface MTUs, but rather determines the largest packet the OMNI 552 interface can forward or reassemble. The OMNI interface uses the 553 OMNI Adaptation Layer (OAL) to admit packets from the network layer 554 that are no larger than the OMNI interface MTU while generating 555 ICMPv4 Fragmentation Needed [RFC1191] or ICMPv6 Path MTU Discovery 556 (PMTUD) Packet Too Big (PTB) [RFC8201] messages as necessary. This 557 document refers to both of these ICMPv4/ICMPv6 message types simply 558 as "PTBs", and introduces a distinction between PTB "hard" and "soft" 559 errors as discussed below. 561 For IPv4 packets with DF=0, the network layer performs IPv4 562 fragmentation if necessary then admits the packets/fragments into the 563 OMNI interface; these fragments will be reassembled by the final 564 destination. For IPv4 packets with DF=1 and IPv6 packets, the 565 network layer admits the packet if it is no larger than the OMNI 566 interface MTU; otherwise, it drops the packet and returns a PTB hard 567 error message to the source. 569 For each admitted IP packet/fragment, the OMNI interface internally 570 employs the OAL when necessary by inserting a mid-layer IPv6 header 571 between the inner IP packet/fragment and any outer IP encapsulation 572 headers per [RFC2473] (but without decrementing the inner IP Hop 573 Limit/TTL since the insertion occurs at a layer below IP forwarding). 574 The OAL then calculates the 32-bit CRC over the entire mid-layer 575 packet and writes the value in a trailing 4-octet field at the end of 576 the packet. Next, the OAL fragments this mid-layer IPv6 packet, 577 forwards the fragments (using outer IP encapsulation if necessary), 578 and returns an internally-generated PTB soft error message (subject 579 to rate limitiing) if it deems the packet too large according to 580 factors such as link performance characteristics, reassembly 581 congestion, etc. This ensures that the path MTU is adaptive and 582 reflects the current path used for a given data flow. 584 The OAL operates with respect to both the minimum IPv6 and IPv4 path 585 MTUs as follows: 587 o When an OMNI interface sends a packet toward a final destination 588 via an ANET peer, it sends without OAL encapsulation if the packet 589 (including any outer-layer ANET encapsulations) is no larger than 590 the underlying interface MTU for on-link ANET peers or the minimum 591 ANET path MTU for peers separated by multiple IP hops. Otherwise, 592 the OAL inserts an IPv6 header per [RFC2473] with source address 593 set to the node's own OMNI Segment-Local Address (SLA) (see: 594 Section 8) and destination set to the OMNI SLA of the ANET peer. 595 The OAL then calculates and appends the trailing 32-bit CRC, then 596 uses IPv6 fragmentation to break the packet into a minimum number 597 of non-overlapping fragments where the largest fragment size 598 (including both the OMNI and any outer-layer ANET encapsulations) 599 is determined by the underlying interface MTU for on-link ANET 600 peers or the minimum ANET path MTU for peers separated by multiple 601 IP hops. The OAL then encapsulates the fragements in any ANET 602 headers and sends them to the ANET peer, which reassembles before 603 forwarding toward the final destination. 605 o When an OMNI interface sends a packet toward a final destination 606 via an INET interface, it sends packets (including any outer-layer 607 INET encapsulations) no larger than the minimum INET path MTU 608 without OAL encapsulation if the destination is reached via an 609 INET address within the same OMNI link segment. Otherwise, the 610 OAL inserts an IPv6 header per [RFC2473] with source address set 611 to the node's OMNI SLA, destination set to the SLA of the next hop 612 OMNI node toward the final destination and (if necessary) with a 613 Segment Routing Header with the remaining Segment IDs on the path 614 to the final destination. The OAL then calculates and appends the 615 trailing 32-bit CRC, then uses IPv6 fragmentation to break the 616 packet into a minimum number of non-overlapping fragments where 617 the largest fragment size (including both the OMNI and outer-layer 618 INET encapsulations) is the minimum INET path MTU, and the 619 smallest fragment size is no smaller than 256 bytes (i.e., 620 slightly less than half the minimum IPv4 path MTU). The OAL then 621 encapsulates the fragments in any INET headers and sends them to 622 the OMNI link neighbor, which reassembles before forwarding toward 623 the final destination. 625 The OAL unconditionally drops all OAL fragments received from an INET 626 peer that are smaller than 256 bytes (note that no minimum fragment 627 size is specified for ANET peers since the underlying ANET is secured 628 against tiny fragment attacks). In order to set the correct context 629 for reassembly, the OAL of the OMNI interface that inserts the IPv6 630 header MUST also be the one that inserts the IPv6 Fragment Header 631 Identification value. While not strictly required, sending all 632 fragments of the same fragmented OAL packet consecutively over the 633 same underlying interface with minimal inter-fragment delay may 634 increase the likelihood of successful reassembly. 636 Ordinary PTB messages with ICMPv4 header "unused" field or ICMPv6 637 header Code field value 0 are hard errors that always indicate that a 638 packet has been dropped due to a real MTU restriction. However, the 639 OAL can also forward large packets via encapsulation and 640 fragmentation while at the same time returning PTB soft error 641 messages (subject to rate limiting) indicating that a forwarded 642 packet was uncomfortably large. The OMNI interface can therefore 643 continuously forward large packets without loss while returning PTB 644 soft error messages recommending a smaller size. Original sources 645 that receive the soft errors in turn reduce the size of the packets 646 they send, i.e., the same as for hard errors. 648 The OAL sets the ICMPv4 header "unused" field or ICMPv6 header Code 649 field to the value 1 in PTB soft error messages. The OAL sets the 650 PTB destination address to the source address of the original packet, 651 and sets the source address to the MNP Subnet Router Anycast address 652 of the MN (i.e., whether the MN was the source or target of the 653 original packet). When the original source receives the PTB, it 654 reduces its path MTU estimate the same as for hard errors but does 655 not regard the message as a loss indication. (If the original source 656 does not recognize the soft error code, it regards the PTB the same 657 as a hard error but should heed the retransmission advice given in 658 [RFC8201] suggesting retransmission based on normal packetization 659 layer retransmission timers.) This document therefore updates 660 [RFC1191][RFC4443] and [RFC8201]. Furthermore, implementations of 661 [RFC4821] must be aware that PTB hard or soft errors may arrive at 662 any time even if after a successful MTU probe (this is the same 663 consideration as for an ordinary path fluctuation following a 664 successful probe). 666 In summary, the OAL supports continuous transmission and reception of 667 packets of various sizes in the face of dynamically changing network 668 conditions. Moreover, since PTB soft errors do not indicate loss, 669 original sources that receive soft errors can quickly scan for path 670 MTU increases without waiting for the minimum 10 minutes specified 671 for loss-oriented PTB hard errors [RFC1191][RFC8201]. The OAL 672 therefore provides a lossless and adaptive service that accommodates 673 MTU diversity especially well suited for dynamic multilink 674 environments. 676 Note: In network paths where IPv6/IPv4 protocol translation or IPv6- 677 in-IPv4 encapsulation may be prevalent, it may be prudent for the OAL 678 to always assume the IPv4 minimum path MTU (i.e., 576 bytes) 679 regardless of the underlying interface IP protocol version. Always 680 assuming the IPv4 minimum path MTU even for IPv6 underlying 681 interfaces may produce more fragments and additional header overhead, 682 but will always interoperate and never run the risk of presenting an 683 IPv4 node with a packet that exceeds its MRU. 685 Note: An OMNI interface that reassembles OAL fragments may experience 686 congestion-oriented loss in its reassembly cache and can optionally 687 send PTB soft errors to the original source and/or ICMP "Time 688 Exceeded" messages to the source of the OAL fragments. In 689 environments where the messages may contribute to unacceptable 690 additional congestion, however, the OMNI interface can simply regard 691 the loss as an ordinary unreported congestion event for which the 692 original source will eventually compensate. 694 Note: When the network layer forwards an IPv4 packet/fragment with 695 DF=0 into the OMNI interface, the interface can optionally perform 696 (further) IPv4 fragmentation before invoking the OAL so that the 697 fragments will be reassembled by the final destination. When the 698 network layer performs IPv6 fragmentation for locally-generated IPv6 699 packets, the OMNI interface typically invokes the OAL without first 700 applying (further) IPv6 fragmentation; the network layer should 701 therefore fragment to the minimum IPv6 path MTU (or smaller still) to 702 push the reassembly burden to the final destination and avoid 703 receiving PTB soft errors from the OMNI interface. Aside from these 704 non-normative guidelines, the manner in which any IP fragmentation is 705 invoked prior to OAL encapsulation/fragmentation is an implementation 706 matter. 708 Note: Inclusion of the 32-bit CRC prior to fragmentation assumes that 709 the receiving OAL will discard any packets with incorrect CRC values 710 following reassembly. The 32-bit CRC is sufficient to detect 711 reassembly misassociations for packet sizes up to the OMNI interface 712 MTU 9180 but may not be sufficient to detect errors for larger sizes 713 [CRC]. 715 Note: Some underlying interface types (e.g., VPNs) may already 716 provide their own robust fragmentation and reassembly services even 717 without OAL encapsulation. In those cases, the OAL can invoke the 718 inherent underlying interface schemes instead while employing PTB 719 soft errors in the same fashion as described above. Other underlying 720 interface properties such as header/message compression can also be 721 harnessed in a similar fashion. 723 5.1. Fragmentation Security Implications 725 As discussed in Section 3.7 of [RFC8900], there are four basic 726 threats concerning IPv6 fragmentation; each of which is addressed by 727 effective mitigations as follows: 729 1. Overlapping fragment attacks - reassembly of overlapping 730 fragments is forbidden by [RFC8200]; therefore, this threat does 731 not apply to the OAL. 733 2. Resource exhaustion attacks - this threat is mitigated by 734 providing a sufficiently large OAL reassembly cache and 735 instituting "fast discard" of incomplete reassemblies that may be 736 part of a buffer exhaustion attack. The reassembly cache should 737 be sufficiently large so that a sustained attack does not cause 738 excessive loss of good reassemblies but not so large that (timer- 739 based) data structure management becomes computationally 740 expensive. The cache should also be indexed based on the arrival 741 underlying interface such that congestion experienced over a 742 first underlying interface does not cause discard of incomplete 743 reassemblies for uncongested underlying interfaces. 745 3. Attacks based on predictable fragment identification values - 746 this threat is mitigated by selecting a suitably random ID value 747 per [RFC7739]. 749 4. Evasion of Network Intrusion Detection Systems (NIDS) - this 750 threat is mitigated by disallowing "tiny fragments" per the OAL 751 fragmentation procedures specified above. 753 Additionally, IPv4 fragmentation includes a 16-bit Identification (IP 754 ID) field with only 65535 unique values such that at high data rates 755 the field could wrap and apply to new packets while the fragments of 756 old packets using the same ID are still alive in the network 757 [RFC4963]. However, since the largest OAL fragment that will be sent 758 via an IPv4 INET path is 576 bytes any IPv4 fragmentation would occur 759 only on links with an IPv4 MTU smaller than this size, and [RFC3819] 760 recommendations suggest that such links will have low data rates. 761 Since IPv6 provides a 32-bit Identification value, IP ID wraparound 762 at high data rates is not a concern for IPv6 fragmentation. 764 6. Frame Format 766 The OMNI interface transmits IPv6 packets according to the native 767 frame format of each underlying interface. For example, for 768 Ethernet-compatible interfaces the frame format is specified in 769 [RFC2464], for aeronautical radio interfaces the frame format is 770 specified in standards such as ICAO Doc 9776 (VDL Mode 2 Technical 771 Manual), for tunnels over IPv6 the frame format is specified in 772 [RFC2473], etc. 774 7. Link-Local Addresses (LLAs) 776 OMNI interfaces construct IPv6 Link-Local Addresses (i.e., "OMNI 777 LLAs") as follows: 779 o IPv6 MN OMNI LLAs encode the most-significant 112 bits of a MNP 780 within the least-significant 112 bits of the IPv6 link-local 781 prefix fe80::/16. The Prefix Length is determined by adding 16 to 782 the length of the embedded MNP. For example, for the MNP 783 2001:db8:1000:2000::/56 the corresponding MN OMNI LLA is 784 fe80:2001:db8:1000:2000::/72. This specification updates the IPv6 785 link-local address format specified in Section 2.5.6 of [RFC4291] 786 by defining a use for bits 11 - 63. 788 o IPv4-compatible MN OMNI LLAs are constructed as fe80::ffff:[IPv4], 789 i.e., the most significant 16 bits of the prefix fe80::/16, 790 followed by 64 '0' bits, followed by 16 '1' bits, followed by a 791 32bit IPv4 address/prefix. The Prefix Length is determined by 792 adding 96 to the length of the embedded IPv4 address/prefix. For 793 example, the IPv4-Compatible MN OMNI LLA for 192.0.2.0/24 is 794 fe80::ffff:192.0.2.0/120 (also written as 795 fe80::ffff:c000:0200/120). 797 o MS OMNI LLAs are assigned to ARs and MSEs from the range 798 fe80::/96, and MUST be managed for uniqueness. The lower 32 bits 799 of the LLA includes a unique integer "MSID" value between 800 0x00000001 and 0xfeffffff, e.g., as in fe80::1, fe80::2, fe80::3, 801 etc., fe80::feff:ffff. The MS OMNI LLA Prefix Length is 802 determined by adding 96 to the MSID prefix length. For example, 803 if the MSID '0x10002000' prefix length is 16 then the MS OMNI LLA 804 Prefix Length is set to 112 and the LLA is written as 805 fe80::1000:2000/112. Finally, the MSID 0x00000000 is the 806 "Anycast" MSID and corresponds to the link-local Subnet-Router 807 anycast address (fe80::) [RFC4291]; the MSID range 0xff000000 808 through 0xffffffff is reserved for future use. 810 o The OMNI LLA range fe80::/32 is used as the service prefix for the 811 address format specified in Section 4 of [RFC4380] (see Section 17 812 for further discussion). 814 Since the prefix 0000::/8 is "Reserved by the IETF" [RFC4291], no 815 MNPs can be allocated from that block ensuring that there is no 816 possibility for overlap between the above OMNI LLA constructs. 818 Since MN OMNI LLAs are based on the distribution of administratively 819 assured unique MNPs, and since MS OMNI LLAs are guaranteed unique 820 through administrative assignment, OMNI interfaces set the 821 autoconfiguration variable DupAddrDetectTransmits to 0 [RFC4862]. 823 8. Segment-Local Addresses (SLAs) 825 OMNI links use IPv6 Segment-Local Addresses (i.e., "OMNI SLAs") as 826 the source and destination addresses in OAL IPv6 encapsulation 827 headers. This document uses the prefix fec0::/10 for mapping OMNI 828 LLAs to routable OMNI SLAs, and therefore updates Section 2.5.7 of 829 [RFC4291] by re-purposing the (deprecated) IPv6 "site-local" address 830 block. 832 Each OMNI link instance is identified by bits 10-15 of the OMNI 833 service prefix fec0::/10. For example, OMNI SLAs associated with 834 instance 0 are configured from the prefix fec0::/16, instance 1 from 835 fec1::/16, etc., up to instance 63 from feff::/16. OMNI SLAs and 836 their associated prefix lengths are configured in one-to-one 837 correspondence with OMNI LLAs through stateless prefix translation. 838 For example, for OMNI link instance fec0::/16: 840 o the OMNI SLA corresponding to fe80:2001:db8:1:2::/80 is simply 841 fec0:2001:db8:1:2::/80 843 o the OMNI SLA corresponding to fe80::ffff:192.0.2.0/120 is simply 844 fec0::ffff:192.0.2.0/120 846 o the OMNI SLA corresponding to fe80::1000/112 is simply 847 fec0::1000/112 849 o the OMNI SLA corresponding to fe80::/128 is simply fec0::/128. 851 Each OMNI interface assigns the Anycast OMNI SLA specific to the OMNI 852 link instance, e.g., the OMNI interface connected to instance 3 853 assigns the Anycast OMNI SLA fec3:. Routers that configure OMNI 854 interfaces advertise the OMNI service prefix (e.g., fec3::/16) into 855 the local routing system so that applications can direct traffic 856 according to SBM requirements. 858 The OMNI SLA presents an IPv6 address format that is routable within 859 the OMNI link routing system and can be used to convey link-scoped 860 messages across multiple hops using IPv6 encapsulation [RFC2473]. 861 The OMNI link extends across one or more underling Internetworks to 862 include all ARs and MSEs. All MNs are also considered to be 863 connected to the OMNI link, however OAL encapsulation is omitted over 864 ANET links when possible to conserve bandwidth (see: Section 11). 866 The OMNI link can be subdivided into "segments" that often correspond 867 to different administrative domains or physical partitions. OMNI 868 nodes can use IPv6 Segment Routing [RFC8402] when necessary to 869 support efficient packet forwarding to destinations located in other 870 OMNI link segments. A full discussion of Segment Routing over the 871 OMNI link appears in [I-D.templin-intarea-6706bis]. 873 NOTE: Re-purposing the (deprectated) IPv6 "site-local" address block 874 as OMNI SLAs is a natural fit since both LLA and SLA prefix lengths 875 are ::/10, the prefixes fe80:: and fec0:: differ only in a single bit 876 setting, and LLAs and SLAs can be unambiguously allocated in one-to- 877 one correspondence with one another. This would also make good use 878 of an otherwise-wasted address range that has been "parked" since the 879 2004 deprecation. However, re-purposing the block will require an 880 IETF standards action acknowledging this document as obsoleting 881 [RFC3879] and updating [RFC4291]. 883 9. Address Mapping - Unicast 885 OMNI interfaces maintain a neighbor cache for tracking per-neighbor 886 state and use the link-local address format specified in Section 7. 887 OMNI interface IPv6 Neighbor Discovery (ND) [RFC4861] messages sent 888 over physical underlying interfaces without encapsulation observe the 889 native underlying interface Source/Target Link-Layer Address Option 890 (S/TLLAO) format (e.g., for Ethernet the S/TLLAO is specified in 891 [RFC2464]). OMNI interface IPv6 ND messages sent over underlying 892 interfaces via encapsulation do not include S/TLLAOs which were 893 intended for encoding physical L2 media address formats and not 894 encapsulation IP addresses. Furthermore S/TLLAOs are not intended 895 for encoding additional interface attributes. Hence, this document 896 does not define an S/TLLAO format but instead defines a new option 897 type termed the "OMNI option" designed for these purposes. 899 MNs such as aircraft typically have many wireless data link types 900 (e.g. satellite-based, cellular, terrestrial, air-to-air directional, 901 etc.) with diverse performance, cost and availability properties. 902 The OMNI interface would therefore appear to have multiple L2 903 connections, and may include information for multiple underlying 904 interfaces in a single IPv6 ND message exchange. OMNI interfaces use 905 an IPv6 ND option called the OMNI option formatted as shown in 906 Figure 3: 908 0 1 2 3 909 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 1 910 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 911 | Type | Length | Prefix Length | S/T-ifIndex | 912 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 913 | | 914 ~ Sub-Options ~ 915 | | 916 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 918 Figure 3: OMNI Option Format 920 In this format: 922 o Type is set to TBD. If multiple OMNI option instances appear in 923 the same IPv6 ND message, the first instance is processed and all 924 other instances are ignored. 926 o Length is set to the number of 8 octet blocks in the option. 928 o Prefix Length is determines the length of prefix to be applied to 929 an OMNI MN LLA/SLA. For IPv6 ND messages sent from a MN to the 930 MS, Prefix Length is the length that the MN is requesting or 931 asserting to the MS. For IPv6 ND messages sent from the MS to the 932 MN, Prefix Length indicates the length that the MS is granting to 933 the MN. For IPv6 ND messages sent between MS endpoints, Prefix 934 Length indicates the length associated with the target MN that is 935 subject of the ND message. 937 o S/T-ifIndex corresponds to the ifIndex value for source or target 938 underlying interface used to convey this IPv6 ND message. OMNI 939 interfaces MUST number each distinct underlying interface with an 940 ifIndex value between '1' and '255' that represents a MN-specific 941 8-bit mapping for the actual ifIndex value assigned by network 942 management [RFC2863] (the ifIndex value '0' is reserved for use by 943 the MS). For RS and NS messages,S/T-ifIndex corresponds to the 944 source underlying interface the message originated from. For RA 945 and NA messages, S/T-ifIndex corresponds to the target underlying 946 interface that the message is destined to. 948 o Sub-Options is a Variable-length field, of length such that the 949 complete OMNI Option is an integer multiple of 8 octets long. 950 Contains one or more Sub-Options, as described in Section 9.1. 952 9.1. Sub-Options 954 The OMNI option includes zero or more Sub-Options. Each consecutive 955 Sub-Option is concatenated immediately after its predecessor. All 956 Sub-Options except Pad1 (see below) are in type-length-value (TLV) 957 encoded in the following format: 959 0 1 2 960 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 5 961 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 962 | Sub-Type | Sub-length | Sub-Option Data ... 963 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 965 Figure 4: Sub-Option Format 967 o Sub-Type is a 1-octet field that encodes the Sub-Option type. 968 Sub-Options defined in this document are: 970 Option Name Sub-Type 971 Pad1 0 972 PadN 1 973 Interface Attributes 2 974 Traffic Selector 3 975 MS-Register 4 976 MS-Release 5 977 Network Access Identifier 6 978 Geo Coordinates 7 979 DHCP Unique Identifier (DUID) 8 981 Figure 5 983 Sub-Types 253 and 254 are reserved for experimentation, as 984 recommended in [RFC3692]. 986 o Sub-Length is a 1-octet field that encodes the length of the Sub- 987 Option Data (i.e., ranging from 0 to 255 octets). 989 o Sub-Option Data is a block of data with format determined by Sub- 990 Type. 992 During processing, unrecognized Sub-Options are ignored and the next 993 Sub-Option processed until the end of the OMNI option is reached. 995 The following Sub-Option types and formats are defined in this 996 document: 998 9.1.1. Pad1 1000 0 1001 0 1 2 3 4 5 6 7 1002 +-+-+-+-+-+-+-+-+ 1003 | Sub-Type=0 | 1004 +-+-+-+-+-+-+-+-+ 1006 Figure 6: Pad1 1008 o Sub-Type is set to 0. If multiple instances appear in the same 1009 OMNI option all are processed. 1011 o No Sub-Length or Sub-Option Data follows (i.e., the "Sub-Option" 1012 consists of a single zero octet). 1014 9.1.2. PadN 1016 0 1 2 1017 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 1018 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1019 | Sub-Type=1 | Sub-length=N | N padding octets ... 1020 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1022 Figure 7: PadN 1024 o Sub-Type is set to 1. If multiple instances appear in the same 1025 OMNI option all are processed. 1027 o Sub-Length is set to N (from 0 to 255) being the number of padding 1028 octets that follow. 1030 o Sub-Option Data consists of N zero-valued octets. 1032 9.1.3. Interface Attributes 1033 0 1 2 3 1034 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 1035 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1036 | Sub-Type=2 | Sub-length=N | ifIndex | ifType | 1037 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1038 | Provider ID | Link |R| APS | SRT | FMT | LHS (0 - 7) | 1039 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1040 | LHS (bits 8 - 31) | ~ 1041 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ 1042 ~ ~ 1043 ~ Link Layer Address (L2ADDR) ~ 1044 ~ ~ 1045 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1046 | Bitmap(0)=0xff|P00|P01|P02|P03|P04|P05|P06|P07|P08|P09|P10|P11| 1047 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1048 |P12|P13|P14|P15|P16|P17|P18|P19|P20|P21|P22|P23|P24|P25|P26|P27| 1049 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1050 |P28|P29|P30|P31| Bitmap(1)=0xff|P32|P33|P34|P35|P36| ... 1051 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1053 Figure 8: Interface Attributes 1055 o Sub-Type is set to 2. If multiple instances with different 1056 ifIndex values appear in the same OMNI option all are processed; 1057 if multiple instances with the same ifIndex value appear, the 1058 first is processed and all others are ignored. 1060 o Sub-Length is set to N (from 4 to 255) that encodes the number of 1061 Sub-Option Data octets that follow. 1063 o Sub-Option Data contains an "Interface Attribute" option encoded 1064 as follows (note that the first four octets must be present): 1066 * ifIndex is set to an 8-bit integer value corresponding to a 1067 specific underlying interface the same as specified above for 1068 the OMNI option header S/T-ifIndex. An OMNI option may include 1069 multiple Interface Attributes Sub-Options, with each distinct 1070 ifIndex value pertaining to a different underlying interface. 1071 The OMNI option will often include an Interface Attributes Sub- 1072 Option with the same ifIndex value that appears in the S/ 1073 T-ifIndex. In that case, the actual encapsulation address of 1074 the received IPv6 ND message should be compared with the L2ADDR 1075 encoded in the Sub-Option (see below); if the addresses are 1076 different (or, if L2ADDR absent) the presence of a Network 1077 Address Translator (NAT) is indicated. 1079 * ifType is set to an 8-bit integer value corresponding to the 1080 underlying interface identified by ifIndex. The value 1081 represents an OMNI interface-specific 8-bit mapping for the 1082 actual IANA ifType value registered in the 'IANAifType-MIB' 1083 registry [http://www.iana.org]. 1085 * Provider ID is set to an OMNI interface-specific 8-bit ID value 1086 for the network service provider associated with this ifIndex. 1088 * Link encodes a 4-bit link metric. The value '0' means the link 1089 is DOWN, and the remaining values mean the link is UP with 1090 metric ranging from '1' ("lowest") to '15' ("highest"). 1092 * R is reserved for future use. 1094 * APS - a 3-bit "Address/Preferences/Simplex" code that 1095 determines the contents of the remainder of the sub-option as 1096 follows: 1098 + When the most significant bit (i.e., "Address") is set to 1, 1099 the SRT, FMT, LHS and L2ADDR fields are included immediately 1100 following the APS code; else, they are omitted. 1102 + When the next most significant bit (i.e., "Preferences") is 1103 set to 1, a preferences block is included next; else, it is 1104 omitted. (Note that if "Address" is set the preferences 1105 block immediately follows L2ADDR; else, it immediately 1106 follows the APS code.) 1108 + When a preferences block is present and the least 1109 significant bit (i.e., "Simplex") is set to 1, the block is 1110 encoded in "Simplex" form as shown in Figure 8; else it is 1111 encoded in "Indexed" form as discussed below. 1113 * When APS indicates that an "Address" is included, the following 1114 fields appear in consecutive order (else, they are omitted): 1116 + SRT - a 5-bit Segment Routing Topology prefix length value 1117 that (when added to 96) determines the prefix length to 1118 apply to the SLA formed from concatenating fe*::/96 with the 1119 32 bit LHS MSID value that follows. For example, the value 1120 16 corresponds to the prefix length 112. 1122 + FMT - a 3-bit "Framework/Mode/Type" code corresponding to 1123 the included Link Layer Address as follows: 1125 - When the most significant bit (i.e., "Framework") is set 1126 to 0, L2ADDR is the INET encapsulation address of a 1127 Proxy/Server; otherwise, it is the addresss for the 1128 Source/Target itself 1130 - When the next most significant bit (i.e., "Mode") is set 1131 to 0, the Source/Target L2ADDR is on the open INET; 1132 otherwise, it is (likely) located behind a Network 1133 Address Translator (NAT). 1135 - When the least significant bit (i.e., "Type") is set to 1136 0, L2ADDR includes a UDP Port Number followed by an IPv4 1137 address; else, a UDP Port Number followed by an IPv6 1138 address. 1140 + LHS - the 32 bit MSID of the Last Hop Server/Proxy on the 1141 path to the target. When SRT and LHS are both set to 0, the 1142 LHS is considered unspecified in this IPv6 ND message. When 1143 SRT is set to 0 and LHS is non-zero, the prefix length is 1144 set to 128. SRT and LHS provide guidance to the OMNI 1145 interface forwarding algorithm. Specifically, if SRT/LHS is 1146 located in the local OMNI link segment then the OMNI 1147 interface can encapsulate according to FMT/L2ADDR; else, it 1148 must forward according to the OMNI link spanning tree. See 1149 [I-D.templin-intarea-6706bis] for further discussion. 1151 + Link Layer Address (L2ADDR) - Formatted according to FMT, 1152 and identifies the link-layer address (i.e., the 1153 encapsulation address) of the source/target. The UDP Port 1154 Number appears in the first two octets and the IP address 1155 appears in the next 4 octets for IPv4 or 16 octets for IPv6. 1156 The Port Number and IP address are recorded in ones- 1157 compliment "obfuscated" form per [RFC4380]. The OMNI 1158 interface forwarding algoritherm uses FMT/L2ADDR to 1159 determine the encapsulation address for forwarding when SRT/ 1160 LHS is located in the local OMNI link segment. 1162 * When APS indicates that "Preferences" are included, a 1163 preferences block appears as the remainder of the Sub-Option as 1164 a series of Bitmaps and P[*] values. In "Simplex" form, the 1165 index for each singleton Bitmap octet is inferred from its 1166 sequential position (i.e., 0, 1, 2, ...) as shown in Figure 8. 1167 In "Indexed" form, each Bitmap is preceded by an Index octet 1168 that encodes a value "i" = (0 - 255) as the index for its 1169 companion Bitmap as follows: 1171 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1172 | Index=i | Bitmap(i) |P[*] values ... 1173 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1175 Figure 9 1177 * The preferences consist of a first (simplex/indexed) Bitmap 1178 (i.e., "Bitmap(i)") followed by 0-8 single-octet blocks of 1179 2-bit P[*] values, followed by a second Bitmap (i), followed by 1180 0-8 blocks of P[*] values, etc. Reading from bit 0 to bit 7, 1181 the bits of each Bitmap(i) that are set to '1'' indicate the 1182 P[*] blocks from the range P[(i*32)] through P[(i*32) + 31] 1183 that follow; if any Bitmap(i) bits are '0', then the 1184 corresponding P[*] block is instead omitted. For example, if 1185 Bitmap(0) contains 0xff then the block with P[00]-P[03], 1186 followed by the block with P[04]-P[07], etc., and ending with 1187 the block with P[28]-P[31] are included (as shown in Figure 8). 1188 The next Bitmap(i) is then consulted with its bits indicating 1189 which P[*] blocks follow, etc. out to the end of the Sub- 1190 Option. 1192 * Each 2-bit P[*] field is set to the value '0' ("disabled"), '1' 1193 ("low"), '2' ("medium") or '3' ("high") to indicate a QoS 1194 preference for underlying interface selection purposes. Not 1195 all P[*] values need to be included in the OMNI option of each 1196 IPv6 ND message received. Any P[*] values represented in an 1197 earlier OMNI option but omitted in the current OMNI option 1198 remain unchanged. Any P[*] values not yet represented in any 1199 OMNI option default to "medium". 1201 * The first 16 P[*] blocks correspond to the 64 Differentiated 1202 Service Code Point (DSCP) values P[00] - P[63] [RFC2474]. Any 1203 additional P[*] blocks that follow correspond to "pseudo-DSCP" 1204 traffic classifier values P[64], P[65], P[66], etc. See 1205 Appendix A for further discussion and examples. 1207 9.1.4. Traffic Selector 1209 0 1 2 3 1210 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 1211 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1212 | Sub-Type=3 | Sub-length=N | ifIndex | ~ 1213 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ 1214 ~ ~ 1215 ~ RFC 6088 Format Traffic Selector ~ 1216 ~ ~ 1217 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1219 Figure 10: Traffic Selector 1221 o Sub-Type is set to 3. If multiple instances appear in the same 1222 OMNI option all are processed, i.e., even if the same ifIndex 1223 value appears multiple times. 1225 o Sub-Length is set to N (the number of Sub-Option Data octets that 1226 follow). 1228 o Sub-Option Data contains a 1-octet ifIndex encoded exactly as 1229 specified in Section 9.1.3, followed by an N-1 octet traffic 1230 selector formatted per [RFC6088] beginning with the "TS Format" 1231 field. The largest traffic selector for a given ifIndex is 1232 therefore 254 octets. 1234 9.1.5. MS-Register 1236 0 1 2 3 1237 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 1238 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1239 | Sub-Type=4 | Sub-length=4n | MSID[1] (bits 0 - 15) | 1240 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1241 | MSID [1] (bits 16 - 32) | MSID[2] (bits 0 - 15) | 1242 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1243 | MSID [2] (bits 16 - 32) | MSID[3] (bits 0 - 15) | 1244 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1245 ... ... ... ... ... ... 1246 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1247 | MSID [n] (bits 16 - 32) | 1248 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1250 Figure 11: MS-Register Sub-option 1252 o Sub-Type is set to 4. If multiple instances appear in the same 1253 OMNI option all are processed. Only the first MAX_MSID values 1254 processed (whether in a single instance or multiple) are retained 1255 and all other MSIDs are ignored. 1257 o Sub-Length is set to 4n. 1259 o A list of n 4-octet MSIDs is included in the following 4n octets. 1260 The Anycast MSID value '0' in an RS message MS-Register sub-option 1261 requests the recipient to return the MSID of a nearby MSE in a 1262 corresponding RA response. 1264 9.1.6. MS-Release 1265 0 1 2 3 1266 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 1267 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1268 | Sub-Type=5 | Sub-length=4n | MSID[1] (bits 0 - 15) | 1269 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1270 | MSID [1] (bits 16 - 32) | MSID[2] (bits 0 - 15) | 1271 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1272 | MSID [2] (bits 16 - 32) | MSID[3] (bits 0 - 15) | 1273 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1274 ... ... ... ... ... ... 1275 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1276 | MSID [n] (bits 16 - 32) | 1277 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1279 Figure 12: MS-Release Sub-option 1281 o Sub-Type is set to 5. If multiple instances appear in the same 1282 IPv6 OMNI option all are processed. Only the first MAX_MSID 1283 values processed (whether in a single instance or multiple) are 1284 retained and all other MSIDs are ignored. 1286 o Sub-Length is set to 4n. 1288 o A list of n 4 octet MSIDs is included in the following 4n octets. 1289 The Anycast MSID value '0' is ignored in MS-Release sub-options, 1290 i.e., only non-zero values are processed. 1292 9.1.7. Network Access Identifier (NAI) 1294 0 1 2 3 1295 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 1296 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1297 | Sub-Type=6 | Sub-length=N |Network Access Identifier (NAI) 1298 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... 1300 Figure 13: Network Access Identifier (NAI) Sub-option 1302 o Sub-Type is set to 6. If multiple instances appear in the same 1303 OMNI option the first is processed and all others are ignored. 1305 o Sub-Length is set to N. 1307 o A Network Access Identifier (NAI) up to 255 octets in length is 1308 coded per [RFC7542]. 1310 9.1.8. Geo Coordinates 1312 0 1 2 3 1313 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 1314 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1315 | Sub-Type=7 | Sub-length=N | Geo Coordinates 1316 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... 1318 Figure 14: Geo Coordinates Sub-option 1320 o Sub-Type is set to 7. If multiple instances appear in the same 1321 OMNI option the first is processed and all others are ignored. 1323 o Sub-Length is set to N. 1325 o A set of Geo Coordinates up to 255 octets in length (format TBD). 1326 Includes Latitude/Longitude at a minimum; may also include 1327 additional attributes such as altitude, heading, speed, etc.). 1329 9.1.9. DHCP Unique Identifier (DUID) 1331 0 1 2 3 1332 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 1333 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1334 | Sub-Type=8 | Sub-length=N | DUID-Type | 1335 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1336 . . 1337 . type-specific DUID body (variable length) . 1338 . . 1339 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1341 Figure 15: DHCP Unique Identifier (DUID) Sub-option 1343 o Sub-Type is set to 8. If multiple instances appear in the same 1344 OMNI option the first is processed and all others are ignored. 1346 o Sub-Length is set to N (i.e., the length of the option beginning 1347 with the DUID-Type and continuing to the end of the type-specific 1348 body). 1350 o DUID-Type is a two-octet field coded in network byte order that 1351 determines the format and contents of the type-specific body 1352 according to Section 11 of [RFC8415]. DUID-Type 4 in particular 1353 corresponds to the Universally Unique Identifier (UUID) [RFC6355] 1354 which will occur in common operational practice. 1356 o A type-specific DUID body up to 253 octets in length follows, 1357 formatted according to DUID-type. For example, for type 4 the 1358 body consists of a 128-bit UUID selected according to [RFC6355]. 1360 10. Address Mapping - Multicast 1362 The multicast address mapping of the native underlying interface 1363 applies. The mobile router on board the MN also serves as an IGMP/ 1364 MLD Proxy for its EUNs and/or hosted applications per [RFC4605] while 1365 using the L2 address of the AR as the L2 address for all multicast 1366 packets. 1368 The MN uses Multicast Listener Discovery (MLDv2) [RFC3810] to 1369 coordinate with the AR, and ANET L2 elements use MLD snooping 1370 [RFC4541]. 1372 11. Conceptual Sending Algorithm 1374 The MN's IPv6 layer selects the outbound OMNI interface according to 1375 SBM considerations when forwarding data packets from local or EUN 1376 applications to external correspondents. Each OMNI interface 1377 maintains a neighbor cache the same as for any IPv6 interface, but 1378 with additional state for multilink coordination. 1380 After a packet enters the OMNI interface, an outbound underlying 1381 interface is selected based on PBM traffic attributes such as DSCP, 1382 application port number, cost, performance, message size, etc. OMNI 1383 interface multilink selections could also be configured to perform 1384 replication across multiple underlying interfaces for increased 1385 reliability at the expense of packet duplication. 1387 When the OMNI interface sends a packet over a selected outbound 1388 underlying interface, the OAL includes or omits a mid-layer 1389 encapsulation header as necessary as discussed in Section 5. The OAL 1390 also performs encapsulation when the nearest AR is located multiple 1391 hops away as discussed in Section 12.1. 1393 OMNI interface multilink service designers MUST observe the BCP 1394 guidance in Section 15 [RFC3819] in terms of implications for 1395 reordering when packets from the same flow may be spread across 1396 multiple underlying interfaces having diverse properties. 1398 11.1. Multiple OMNI Interfaces 1400 MNs may connect to multiple independent OMNI links concurrently in 1401 support of SBM. Each OMNI interface is distinguished by its Anycast 1402 OMNI SLA (e.g., fec0::, fec1::, fec2::). The MN configures a 1403 separate OMNI interface for each link so that multiple interfaces 1404 (e.g., omni0, omni1, omni2, etc.) are exposed to the IPv6 layer. A 1405 different Anycast OMNI SLA is assigned to each interface, and the MN 1406 injects the service prefixes for the OMNI link instances into the EUN 1407 routing system. 1409 Applications in EUNs can use Segment Routing to select the desired 1410 OMNI interface based on SBM considerations. The Anycast OMNI SLA is 1411 written into the IPv6 destination address, and the actual destination 1412 (along with any additional intermediate hops) is written into the 1413 Segment Routing Header. Standard IP routing directs the packets to 1414 the MN's mobile router entity, and the Anycast OMNI SLA identifies 1415 the OMNI interface to be used for transmission to the next hop. When 1416 the MN receives the message, it replaces the IPv6 destination address 1417 with the next hop found in the routing header and transmits the 1418 message over the OMNI interface identified by the Anycast OMNI SLA. 1420 Multiple distinct OMNI links can therefore be used to support fault 1421 tolerance, load balancing, reliability, etc. The architectural model 1422 is similar to Layer 2 Virtual Local Area Networks (VLANs). 1424 12. Router Discovery and Prefix Registration 1426 MNs interface with the MS by sending RS messages with OMNI options 1427 under the assumption that one or more AR on the ANET will process the 1428 message and respond. The manner in which the ANET ensures AR 1429 coordination is link-specific and outside the scope of this document 1430 (however, considerations for ANETs that do not provide ARs that 1431 recognize the OMNI option are discussed in Section 17). 1433 For each underlying interface, the MN sends an RS message with an 1434 OMNI option to coordinate with MSEs identified by MSID values. 1435 Example MSID discovery methods are given in [RFC5214] and include 1436 data link login parameters, name service lookups, static 1437 configuration, a static "hosts" file, etc. The MN can also send an 1438 RS with an MS-Register suboption that includes the Anycast MSID value 1439 '0', i.e., instead of or in addition to any non-zero MSIDs. When the 1440 AR receives an RS with a MSID '0', it selects a nearby MSE (which may 1441 be itself) and returns an RA with the selected MSID in an MS-Register 1442 suboption. The AR selects only a single wildcard MSE (i.e., even if 1443 the RS MS-Register suboption included multiple '0' MSIDs) while also 1444 soliciting the MSEs corresponding to any non-zero MSIDs. 1446 MNs configure OMNI interfaces that observe the properties discussed 1447 in the previous section. The OMNI interface and its underlying 1448 interfaces are said to be in either the "UP" or "DOWN" state 1449 according to administrative actions in conjunction with the interface 1450 connectivity status. An OMNI interface transitions to UP or DOWN 1451 through administrative action and/or through state transitions of the 1452 underlying interfaces. When a first underlying interface transitions 1453 to UP, the OMNI interface also transitions to UP. When all 1454 underlying interfaces transition to DOWN, the OMNI interface also 1455 transitions to DOWN. 1457 When an OMNI interface transitions to UP, the MN sends RS messages to 1458 register its MNP and an initial set of underlying interfaces that are 1459 also UP. The MN sends additional RS messages to refresh lifetimes 1460 and to register/deregister underlying interfaces as they transition 1461 to UP or DOWN. The MN sends initial RS messages over an UP 1462 underlying interface with its OMNI LLA as the source and with 1463 destination set to All-Routers multicast (ff02::2) [RFC4291]. The RS 1464 messages include an OMNI option per Section 9 with valid prefix 1465 registration information, Interface Attributes appropriate for 1466 underlying interfaces, MS-Register/Release sub-options containing 1467 MSID values, and with any other necessary OMNI sub-options. The S/ 1468 T-ifIndex field is set to the index of the underlying interface over 1469 which the RS message is sent. 1471 ARs process IPv6 ND messages with OMNI options and act as an MSE 1472 themselves and/or as a proxy for other MSEs. ARs receive RS messages 1473 and create a neighbor cache entry for the MN, then coordinate with 1474 any MSEs named in the Register/Release lists in a manner outside the 1475 scope of this document. When an MSE processes the OMNI information, 1476 it first validates the prefix registration information then injects/ 1477 withdraws the MNP in the routing/mapping system and caches/discards 1478 the new Prefix Length, MNP and Interface Attributes. The MSE then 1479 informs the AR of registration success/failure, and the AR returns an 1480 RA message to the MN with an OMNI option per Section 9. 1482 The AR returns the RA message via the same underlying interface of 1483 the MN over which the RS was received, and with destination address 1484 set to the MN OMNI LLA (i.e., unicast), with source address set to 1485 its own OMNI LLA, and with an OMNI option with S/T-ifIndex set to the 1486 value included in the RS. The OMNI option also includes valid prefix 1487 registration information, Interface Attributes, MS-Register/Release 1488 and any other necessary OMNI sub-options. The RA also includes any 1489 information for the link, including RA Cur Hop Limit, M and O flags, 1490 Router Lifetime, Reachable Time and Retrans Timer values, and 1491 includes any necessary options such as: 1493 o PIOs with (A; L=0) that include MSPs for the link [RFC8028]. 1495 o RIOs [RFC4191] with more-specific routes. 1497 o an MTU option that specifies the maximum acceptable packet size 1498 for this ANET interface. 1500 The AR MAY also send periodic and/or event-driven unsolicited RA 1501 messages per [RFC4861]. In that case, the S/T-ifIndex field in the 1502 OMNI header of the unsolicited RA message identifies the target 1503 underlying interface of the destination MN. 1505 The AR can combine the information from multiple MSEs into one or 1506 more "aggregate" RAs sent to the MN in order conserve ANET bandwidth. 1507 Each aggregate RA includes an OMNI option with MS-Register/Release 1508 sub-options with the MSEs represented by the aggregate. If an 1509 aggregate is sent, the RA message contents must consistently 1510 represent the combined information advertised by all represented 1511 MSEs. Note that since the AR uses its own OMNI LLA as the RA source 1512 address, the MN determines the addresses of the represented MSEs by 1513 examining the MS-Register/Release OMNI sub-options. 1515 When the MN receives the RA message, it creates an OMNI interface 1516 neighbor cache entry for each MSID that has confirmed MNP 1517 registration via the L2 address of this AR. If the MN connects to 1518 multiple ANETs, it records the additional L2 AR addresses in each 1519 MSID neighbor cache entry (i.e., as multilink neighbors). The MN 1520 then manages its underlying interfaces according to their states as 1521 follows: 1523 o When an underlying interface transitions to UP, the MN sends an RS 1524 over the underlying interface with an OMNI option. The OMNI 1525 option contains at least one Interface Attribute sub-option with 1526 values specific to this underlying interface, and may contain 1527 additional Interface Attributes specific to other underlying 1528 interfaces. The option also includes any MS-Register/Release sub- 1529 options. 1531 o When an underlying interface transitions to DOWN, the MN sends an 1532 RS or unsolicited NA message over any UP underlying interface with 1533 an OMNI option containing an Interface Attribute sub-option for 1534 the DOWN underlying interface with Link set to '0'. The MN sends 1535 an RS when an acknowledgement is required, or an unsolicited NA 1536 when reliability is not thought to be a concern (e.g., if 1537 redundant transmissions are sent on multiple underlying 1538 interfaces). 1540 o When the Router Lifetime for a specific AR nears expiration, the 1541 MN sends an RS over the underlying interface to receive a fresh 1542 RA. If no RA is received, the MN can send RS messages to an 1543 alternate MSID in case the current MSID has failed. If no RS 1544 messages are received even after trying to contact alternate 1545 MSIDs, the MN marks the underlying interface as DOWN. 1547 o When a MN wishes to release from one or more current MSIDs, it 1548 sends an RS or unsolicited NA message over any UP underlying 1549 interfaces with an OMNI option with a Release MSID. Each MSID 1550 then withdraws the MNP from the routing/mapping system and informs 1551 the AR that the release was successful. 1553 o When all of a MNs underlying interfaces have transitioned to DOWN 1554 (or if the prefix registration lifetime expires), any associated 1555 MSEs withdraw the MNP the same as if they had received a message 1556 with a release indication. 1558 The MN is responsible for retrying each RS exchange up to 1559 MAX_RTR_SOLICITATIONS times separated by RTR_SOLICITATION_INTERVAL 1560 seconds until an RA is received. If no RA is received over a an UP 1561 underlying interface (i.e., even after attempting to contact 1562 alternate MSEs), the MN declares this underlying interface as DOWN. 1564 The IPv6 layer sees the OMNI interface as an ordinary IPv6 interface. 1565 Therefore, when the IPv6 layer sends an RS message the OMNI interface 1566 returns an internally-generated RA message as though the message 1567 originated from an IPv6 router. The internally-generated RA message 1568 contains configuration information that is consistent with the 1569 information received from the RAs generated by the MS. Whether the 1570 OMNI interface IPv6 ND messaging process is initiated from the 1571 receipt of an RS message from the IPv6 layer is an implementation 1572 matter. Some implementations may elect to defer the IPv6 ND 1573 messaging process until an RS is received from the IPv6 layer, while 1574 others may elect to initiate the process proactively. Still other 1575 deployments may elect to administratively disable the ordinary RS/RA 1576 messaging used by the IPv6 layer over the OMNI interface, since they 1577 are not required to drive the internal RS/RA processing. (Note that 1578 this same logic applies to IPv4 implementations that employ ICMP- 1579 based Router Discovery per [RFC1256].) 1581 Note: The Router Lifetime value in RA messages indicates the time 1582 before which the MN must send another RS message over this underlying 1583 interface (e.g., 600 seconds), however that timescale may be 1584 significantly longer than the lifetime the MS has committed to retain 1585 the prefix registration (e.g., REACHABLETIME seconds). ARs are 1586 therefore responsible for keeping MS state alive on a shorter 1587 timescale than the MN is required to do on its own behalf. 1589 Note: On multicast-capable underlying interfaces, MNs should send 1590 periodic unsolicited multicast NA messages and ARs should send 1591 periodic unsolicited multicast RA messages as "beacons" that can be 1592 heard by other nodes on the link. If a node fails to receive a 1593 beacon after a timeout value specific to the link, it can initiate a 1594 unicast exchange to test reachability. 1596 12.1. Router Discovery in IP Multihop and IPv4-Only Access Networks 1598 On some ANET types a MN may be located multiple IP hops away from the 1599 nearest AR. Forwarding through IP multihop ANETs is conducted 1600 through the application of a routing protocol (e.g., a Mobile Ad-hoc 1601 Network (MANET) routing protocol over omni-directional wireless 1602 interfaces, an inter-domain routing protocol in an enterprise 1603 network, etc.). These ANETs could be either IPv6-enabled or 1604 IPv4-only, while IPv4-only ANETs could be either multicast-capable or 1605 unicast-only (note that for IPv4-only ANETs the following procedures 1606 apply for both single-hop and multhop cases). 1608 A MN located potentially multiple ANET hops away from the nearst AR 1609 prepares an RS message with source address set to its OMNI LLA and 1610 with destination set to link-scoped All-Routers multicast the same as 1611 discussed above. For IPv6-enabled ANETs, the MN then encapsulates 1612 the message in an IPv6 header with source address set to the SLA 1613 corresponding to the LLA source address and with destination set to 1614 site-scoped All-Routers multicast (ff05::2)[RFC4291]. For IPv4-only 1615 ANETs, the MN instead encapsulates the RS message in an IPv4 header 1616 with source address set to the node's own IPv4 address. For 1617 multicast-capable IPv4-only ANETs, the MN then sets the destination 1618 address to the site-scoped IPv4 multicast address corresponding to 1619 link-scoped IPv6 All-Routers multicast [RFC2529]; for unicast-only 1620 IPv4-only ANETs, the MN instead sets the destination address to the 1621 unicast IPv4 adddress of an AR [RFC5214]. The MN then sends the 1622 encapsulated RS message via the ANET interface, where it will be 1623 forwarded by zero or more intermediate ANET hops. 1625 When an intermediate ANET hop that particpates in the routing 1626 protocol receives the encapsulated RS, it forwards the message 1627 according to its routing tables (note that an intermediate node could 1628 be a fixed infrastructure element or another MN). This process 1629 repeats iteratively until the RS message is received by a penultimate 1630 ANET hop within single-hop communications range of an AR, which 1631 forwards the message to the AR. 1633 When the AR receives the message, it decapsulates the RS and 1634 coordinates with the MS the same as for an ordinary link-local RS, 1635 since the inner Hop Limit will not have been decremented by the 1636 multihop forwarding process. The AR then prepares an RA message with 1637 source address set to its own LLA and destination address set to the 1638 LLA of the original MN, then encapsulates the message in an IPv4/IPv6 1639 header with source address set to its own IPv4/SLA address and with 1640 destination set to the encapsulation source of the RS. 1642 The AR then forwards the message to an ANET node within 1643 communications range, which forwards the message according to its 1644 routing tables to an intermediate node. The multihop forwarding 1645 process within the ANET continues repetitively until the message is 1646 delivered to the original MN, which decapsulates the message and 1647 performs autoconfiguration the same as if it had received the RA 1648 directly from the AR as an on-link neighbor. 1650 Note: An alternate approach to multihop forwarding via IPv6 1651 encapsulation would be to statelessly translate the IPv6 LLAs into 1652 SLAs and forward the messages without encapsulation. This would 1653 violate the [RFC4861] requirement that certain IPv6 ND messages must 1654 use link-local addresses and must not be accepted if received with 1655 Hop Limit less than 255. This document therefore advocates 1656 encapsulation since the overhead is nominal considering the 1657 infrequent nature and small size of IPv6 ND messages. Future 1658 documents may consider encapsulation avoidance through translation 1659 while updating [RFC4861]. 1661 Note: An alternate approach to multihop forwarding via IPv4 1662 encapsulation would be to employ IPv6/IPv4 protocol translation. 1663 However, for IPv6 ND messages the OMNI LLA addresses would be 1664 truncated due to translation and the OMNI Router and Prefix Discovery 1665 services would not be able to function. The use of IPv4 1666 encapsulation is therefore indicated. 1668 12.2. MS-Register and MS-Release List Processing 1670 When a MN sends an RS message with an OMNI option via an underlying 1671 interface to an AR, the MN must convey its knowledge of its 1672 currently-associated MSEs. Initially, the MN will have no associated 1673 MSEs and should therefore include an MS-Register sub-option with the 1674 single MSID value 0 which requests the AR to select and assign an 1675 MSE. The AR will then return an RA message with source address set 1676 to the OMNI LLA containing the MSE of the selected MSE. 1678 As the MN activates additional underlying interfaces, it can 1679 optionally include an MS-Register sub-option with MSID value 0, or 1680 with non-zero MSIDs for MSEs discovered from previous RS/RA 1681 exchanges. The MN will thus eventually begin to learn and manage its 1682 currently active set of MSEs, and can register with new MSEs or 1683 release from former MSEs with each successive RS/RA exchange. As the 1684 MN's MSE constituency grows, it alone is responsible for including or 1685 omitting MSIDs in the MS-Register/Release lists it sends in RS 1686 messages. The inclusion or omission of MSIDs determines the MN's 1687 interface to the MS and defines the manner in which MSEs will 1688 respond. The only limiting factor is that the MN should include no 1689 more than MAX_MSID values in each list per each IPv6 ND message, and 1690 should avoid duplication of entries in each list unless it wants to 1691 increase likelihood of control message delivery. 1693 When an AR receives an RS message sent by a MN with an OMNI option, 1694 the option will contain zero or more MS-Register and MS-Release sub- 1695 options containing MSIDs. After processing the OMNI option, the AR 1696 will have a list of zero or more MS-Register MSIDs and a list of zero 1697 or more of MS-Release MSIDs. The AR then processes the lists as 1698 follows: 1700 o For each list, retain the first MAX_MSID values in the list and 1701 discard any additional MSIDs (i.e., even if there are duplicates 1702 within a list). 1704 o Next, for each MSID in the MS-Register list, remove all matching 1705 MSIDs from the MS-Release list. 1707 o Next, proceed according to whether the AR's own MSID or the value 1708 0 appears in the MS-Register list as folllows: 1710 * If yes, send an RA message directly back to the MN and send a 1711 proxy copy of the RS message to each additional MSID in the MS- 1712 Register list with the MS-Register/Release lists omitted. 1713 Then, send a uNA message to each MSID in the MS-Release list 1714 with the MS-Register/Release lists omitted and with an OMNI 1715 header with S/T-ifIndex set to 0. 1717 * If no, send a proxy copy of the RS message to each additional 1718 MSID in the MS-Register list with the MS-Register list omitted. 1719 For the first MSID, include the original MS-Release list; for 1720 all other MSIDs, omit the MS-Release list. 1722 Each proxy copy of the RS message will include an OMNI option and 1723 encapsulation header with the SLA of the AR as the source and the SLA 1724 of the Register MSE as the destination. When the Register MSE 1725 receives the proxy RS message, if the message includes an MS-Release 1726 list the MSE sends a uNA message to each additional MSID in the 1727 Release list. The Register MSE then sends an RA message back to the 1728 (Proxy) AR wrapped in an OMNI encapsulation header with source and 1729 destination addresses reversed, and with RA destination set to the 1730 LLA of the MN. When the AR receives this RA message, it sends a 1731 proxy copy of the RA to the MN. 1733 Each uNA message (whether send by the first-hop AR or by a Register 1734 MSE) will include an OMNI option and an encapsulation header with the 1735 SLA of the Register MSE as the source and the SLA of the Release ME 1736 as the destination. The uNA informs the Release MSE that its 1737 previous relationship with the MN has been released and that the 1738 source of the uNA message is now registered. The Release MSE must 1739 then note that the subject MN of the uNA message is now "departed", 1740 and forward any subsequent packets destined to the MN to the Register 1741 MSE. 1743 Note that it is not an error for the MS-Register/Release lists to 1744 include duplicate entries. If duplicates occur within a list, the 1745 the AR will generate multiple proxy RS and/or uNA messages - one for 1746 each copy of the duplicate entries. 1748 13. Secure Redirection 1750 If the ANET link model is multiple access, the AR is responsible for 1751 assuring that address duplication cannot corrupt the neighbor caches 1752 of other nodes on the link. When the MN sends an RS message on a 1753 multiple access ANET link, the AR verifies that the MN is authorized 1754 to use the address and returns an RA with a non-zero Router Lifetime 1755 only if the MN is authorized. 1757 After verifying MN authorization and returning an RA, the AR MAY 1758 return IPv6 ND Redirect messages to direct MNs located on the same 1759 ANET link to exchange packets directly without transiting the AR. In 1760 that case, the MNs can exchange packets according to their unicast L2 1761 addresses discovered from the Redirect message instead of using the 1762 dogleg path through the AR. In some ANET links, however, such direct 1763 communications may be undesirable and continued use of the dogleg 1764 path through the AR may provide better performance. In that case, 1765 the AR can refrain from sending Redirects, and/or MNs can ignore 1766 them. 1768 14. AR and MSE Resilience 1770 ANETs SHOULD deploy ARs in Virtual Router Redundancy Protocol (VRRP) 1771 [RFC5798] configurations so that service continuity is maintained 1772 even if one or more ARs fail. Using VRRP, the MN is unaware which of 1773 the (redundant) ARs is currently providing service, and any service 1774 discontinuity will be limited to the failover time supported by VRRP. 1775 Widely deployed public domain implementations of VRRP are available. 1777 MSEs SHOULD use high availability clustering services so that 1778 multiple redundant systems can provide coordinated response to 1779 failures. As with VRRP, widely deployed public domain 1780 implementations of high availability clustering services are 1781 available. Note that special-purpose and expensive dedicated 1782 hardware is not necessary, and public domain implementations can be 1783 used even between lightweight virtual machines in cloud deployments. 1785 15. Detecting and Responding to MSE Failures 1787 In environments where fast recovery from MSE failure is required, ARs 1788 SHOULD use proactive Neighbor Unreachability Detection (NUD) in a 1789 manner that parallels Bidirectional Forwarding Detection (BFD) 1790 [RFC5880] to track MSE reachability. ARs can then quickly detect and 1791 react to failures so that cached information is re-established 1792 through alternate paths. Proactive NUD control messaging is carried 1793 only over well-connected ground domain networks (i.e., and not low- 1794 end ANET links such as aeronautical radios) and can therefore be 1795 tuned for rapid response. 1797 ARs perform proactive NUD for MSEs for which there are currently 1798 active MNs on the ANET. If an MSE fails, ARs can quickly inform MNs 1799 of the outage by sending multicast RA messages on the ANET interface. 1800 The AR sends RA messages to MNs via the ANET interface with an OMNI 1801 option with a Release ID for the failed MSE, and with destination 1802 address set to All-Nodes multicast (ff02::1) [RFC4291]. 1804 The AR SHOULD send MAX_FINAL_RTR_ADVERTISEMENTS RA messages separated 1805 by small delays [RFC4861]. Any MNs on the ANET interface that have 1806 been using the (now defunct) MSE will receive the RA messages and 1807 associate with a new MSE. 1809 16. Transition Considerations 1811 When a MN connects to an ANET link for the first time, it sends an RS 1812 message with an OMNI option. If the first hop AR recognizes the 1813 option, it returns an RA with its MS OMNI LLA as the source, the MN 1814 OMNI LLA as the destination and with an OMNI option included. The MN 1815 then engages the AR according to the OMNI link model specified above. 1816 If the first hop AR is a legacy IPv6 router, however, it instead 1817 returns an RA message with no OMNI option and with a non-OMNI unicast 1818 source LLA as specified in [RFC4861]. In that case, the MN engages 1819 the ANET according to the legacy IPv6 link model and without the OMNI 1820 extensions specified in this document. 1822 If the ANET link model is multiple access, there must be assurance 1823 that address duplication cannot corrupt the neighbor caches of other 1824 nodes on the link. When the MN sends an RS message on a multiple 1825 access ANET link with an OMNI LLA source address and an OMNI option, 1826 ARs that recognize the option ensure that the MN is authorized to use 1827 the address and return an RA with a non-zero Router Lifetime only if 1828 the MN is authorized. ARs that do not recognize the option instead 1829 return an RA that makes no statement about the MN's authorization to 1830 use the source address. In that case, the MN should perform 1831 Duplicate Address Detection to ensure that it does not interfere with 1832 other nodes on the link. 1834 An alternative approach for multiple access ANET links to ensure 1835 isolation for MN / AR communications is through L2 address mappings 1836 as discussed in Appendix C. This arrangement imparts a (virtual) 1837 point-to-point link model over the (physical) multiple access link. 1839 17. OMNI Interfaces on the Open Internet 1841 OMNI interfaces configured over IPv6-enabled underlying interfaces on 1842 the open Internet without an OMNI-aware first-hop AR receive RA 1843 messages that do not include an OMNI option, while OMNI interfaces 1844 configured over IPv4-only underlying interfaces do not receive any 1845 (IPv6) RA messages at all. OMNI interfaces that receive RA messages 1846 without an OMNI option configure addresses, on-link prefxies, etc. on 1847 the underlying interface that received the RA according to standard 1848 IPv6 ND and address resolution conventions [RFC4861] [RFC4862]. OMNI 1849 interfaces configured over IPv4-only underlying interfaces configure 1850 IPv4 address information on the underlying interfaces using 1851 mechanisms such as DHCPv4 [RFC2131]. 1853 OMNI interfaces configured over underlying interfaces that connect to 1854 the open Internet can apply security services such as VPNs to connect 1855 to an MSE or establish a direct link to an MSE through some other 1856 means. In environments where an explicit VPN or direct link may be 1857 impractical, OMNI interfaces can instead use UDP/IP encapsulation per 1858 [RFC6081][RFC4380]. (SEcure Neighbor Discovery (SEND) and 1859 Cryptographically Generated Addresses (CGA) [RFC3971][RFC3972] or 1860 other protocol-specific security services can can also be used if 1861 additional authentication is necessary.) 1863 After estabishing a VPN or preparing for UDP/IP encapsulation, OMNI 1864 interfaces send control plane messages to interface with the MS. The 1865 control plane messages must be authenticated while data plane 1866 messages are delivered the same as for ordinary best-effort Internet 1867 traffic with basic source address-based data origin verification. 1868 Data plane communications via OMNI interfaces that connect over the 1869 open Internet without an explicit VPN should therefore employ 1870 transport- or higher-layer security to ensure integrity and/or 1871 confidentiality. 1873 When SEND/CGA are used over an open Internet underlying interfaces, 1874 each OMNI node configures a link-local CGA for use as the source 1875 address of IPv6 ND messages. The node then employs OMNI link 1876 encapsualation and sets the IPv6 source address of the OMNI header to 1877 the SLA corresponding to its OMNI LLA. Any Prefix Length values in 1878 the IPv6 ND message OMNI option then apply to the SLA found in the 1879 OMNI header, i.e., and not to the CGA found in the IPv6 ND message 1880 source address. 1882 OMNI interfaces in the open Internet are often located behind Network 1883 Address Translators (NATs). The OMNI interface accommodates NAT 1884 traversal using UDP/IP encapsulation and the mechanisms discussed in 1885 [RFC6081][RFC4380][I-D.templin-intarea-6706bis]. 1887 18. Time-Varying MNPs 1889 In some use cases, it is desirable, beneficial and efficient for the 1890 MN to receive a constant MNP that travels with the MN wherever it 1891 moves. For example, this would allow air traffic controllers to 1892 easily track aircraft, etc. In other cases, however (e.g., 1893 intelligent transportation systems), the MN may be willing to 1894 sacrifice a modicum of efficiency in order to have time-varying MNPs 1895 that can be changed every so often to defeat adversarial tracking. 1897 Prefix delegation services such as those discussed in 1898 [I-D.templin-6man-dhcpv6-ndopt] and [I-D.templin-intarea-6706bis] 1899 allow OMNI MNs that desire time-varying MNPs to obtain short-lived 1900 prefixes. In that case, the identity of the MN can be used as a 1901 prefix delegation seed (e.g., a DHCPv6 Device Unique IDentifier 1902 (DUID) [RFC8415]). The MN would then be obligated to renumber its 1903 internal networks whenever its MNP (and therefore also its OMNI 1904 address) changes. This should not present a challenge for MNs with 1905 automated network renumbering services, however presents limits for 1906 the durations of ongoing sessions that would prefer to use a constant 1907 address. 1909 When a MN wishes to invoke DHCPv6 Prefix Delegation (PD) services, it 1910 sets the source address of an RS message to fe80:: and includes a 1911 DUID sub-option and a desired Prefix Length value in the RS message 1912 OMNI option. When the first-hop AR receives the RS message, it 1913 performs a PD exchange with the DHCPv6 service to obtain an IPv6 MNP 1914 of the requested length then returns an RA message with the OMNI LLA 1915 corresponding to the MNP as the destination address. When the MN 1916 receives the RA message, it provisons the PD to its downstream- 1917 attached networks and begins using the OMNI LLA in subsequent IPv6 ND 1918 messaging. 1920 19. IANA Considerations 1922 The IANA is instructed to allocate an official Type number TBD from 1923 the registry "IPv6 Neighbor Discovery Option Formats" for the OMNI 1924 option. Implementations set Type to 253 as an interim value 1925 [RFC4727]. 1927 The IANA is instructed to assign a new Code value "1" in the "ICMPv6 1928 Code Fields: Type 2 - Packet Too Big" registry. The registry should 1929 read as follows: 1931 Code Name Reference 1932 --- ---- --------- 1933 0 Diagnostic Packet Too Big [RFC4443] 1934 1 Advisory Packet Too Big [RFCXXXX] 1936 Figure 16: OMNI Option Sub-Type Values 1938 The IANA is instructed to allocate one Ethernet unicast address TBD2 1939 (suggest 00-00-5E-00-52-14 [RFC5214]) in the registry "IANA Ethernet 1940 Address Block - Unicast Use". 1942 The OMNI option also defines an 8-bit Sub-Type field, for which IANA 1943 is instructed to create and maintain a new registry entitled "OMNI 1944 option Sub-Type values". Initial values for the OMNI option Sub-Type 1945 values registry are given below; future assignments are to be made 1946 through Expert Review [RFC8126]. 1948 Value Sub-Type name Reference 1949 ----- ------------- ---------- 1950 0 Pad1 [RFCXXXX] 1951 1 PadN [RFCXXXX] 1952 2 Interface Attributes [RFCXXXX] 1953 3 Traffic Selector [RFCXXXX] 1954 4 MS-Register [RFCXXXX] 1955 5 MS-Release [RFCXXXX] 1956 6 Network Acceess Identifier [RFCXXXX] 1957 7 Geo Coordinates [RFCXXXX] 1958 8 DHCP Unique Identifier (DUID) [RFCXXXX] 1959 9-252 Unassigned 1960 253-254 Experimental [RFCXXXX] 1961 255 Reserved [RFCXXXX] 1963 Figure 17: OMNI Option Sub-Type Values 1965 20. Security Considerations 1967 Security considerations for IPv4 [RFC0791], IPv6 [RFC8200] and IPv6 1968 Neighbor Discovery [RFC4861] apply. OMNI interface IPv6 ND messages 1969 SHOULD include Nonce and Timestamp options [RFC3971] when transaction 1970 confirmation and/or time synchronization is needed. 1972 OMNI interfaces configured over secured ANET interfaces inherit the 1973 physical and/or link-layer security properties of the connected 1974 ANETs. OMNI interfaces configured over open INET interfaces can use 1975 symmetric securing services such as VPNs or can by some other means 1976 establish a direct link. When a VPN or direct link may be 1977 impractical, however, an asymmetric security service such as SEcure 1978 Neighbor Discovery (SEND) [RFC3971] with Cryptographically Generated 1979 Addresses (CGAs) [RFC3972], the authentication option specified in 1980 [RFC4380] or other protocol control message security mechanisms may 1981 be necessary. While the OMNI link protects control plane messaging, 1982 applications must still employ end-to-end transport- or higher-layer 1983 security services to protect the data plane. 1985 The Mobility Service MUST provide strong network layer security for 1986 control plane messages and forwading path integrity for data plane 1987 messages. In one example, the AERO service 1988 [I-D.templin-intarea-6706bis] constructs a spanning tree between 1989 mobility service elements and secures the links in the spanning tree 1990 with network layer security mechanisms such as IPsec [RFC4301] or 1991 Wireguard. Control plane messages are then constrained to travel 1992 only over the secured spanning tree paths and are therefore protected 1993 from attack or eavesdropping. Since data plane messages can travel 1994 over route optimized paths that do not strictly follow the spanning 1995 tree, however, end-to-end transport- or higher-layer security 1996 services are still required. 1998 Security considerations for specific access network interface types 1999 are covered under the corresponding IP-over-(foo) specification 2000 (e.g., [RFC2464], [RFC2492], etc.). 2002 Security considerations for IPv6 fragmentation and reassembly are 2003 discussed in Section 5.1. 2005 21. Implementation Status 2007 Draft -29 is implemented in the recently tagged AERO/OMNI 3.0.0 2008 internal release, and Draft -30 is now tagged as the AERO/OMNI 3.0.1. 2009 Newer specification versions will be tagged in upcoming releases. 2010 First public release expected before the end of 2020. 2012 22. Acknowledgements 2014 The first version of this document was prepared per the consensus 2015 decision at the 7th Conference of the International Civil Aviation 2016 Organization (ICAO) Working Group-I Mobility Subgroup on March 22, 2017 2019. Consensus to take the document forward to the IETF was reached 2018 at the 9th Conference of the Mobility Subgroup on November 22, 2019. 2019 Attendees and contributors included: Guray Acar, Danny Bharj, 2020 Francois D'Humieres, Pavel Drasil, Nikos Fistas, Giovanni Garofolo, 2021 Bernhard Haindl, Vaughn Maiolla, Tom McParland, Victor Moreno, Madhu 2022 Niraula, Brent Phillips, Liviu Popescu, Jacky Pouzet, Aloke Roy, Greg 2023 Saccone, Robert Segers, Michal Skorepa, Michel Solery, Stephane 2024 Tamalet, Fred Templin, Jean-Marc Vacher, Bela Varkonyi, Tony Whyman, 2025 Fryderyk Wrobel and Dongsong Zeng. 2027 The following individuals are acknowledged for their useful comments: 2028 Michael Matyas, Madhu Niraula, Michael Richardson, Greg Saccone, 2029 Stephane Tamalet, Eric Vyncke. Pavel Drasil, Zdenek Jaron and Michal 2030 Skorepa are recognized for their many helpful ideas and suggestions. 2031 Madhuri Madhava Badgandi, Katherine Tran, and Vijayasarathy 2032 Rajagopalan are acknowledged for their hard work on the 2033 implementation and insights that led to improvements to the spec. 2035 This work is aligned with the NASA Safe Autonomous Systems Operation 2036 (SASO) program under NASA contract number NNA16BD84C. 2038 This work is aligned with the FAA as per the SE2025 contract number 2039 DTFAWA-15-D-00030. 2041 23. References 2043 23.1. Normative References 2045 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, 2046 DOI 10.17487/RFC0791, September 1981, 2047 . 2049 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 2050 Requirement Levels", BCP 14, RFC 2119, 2051 DOI 10.17487/RFC2119, March 1997, 2052 . 2054 [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black, 2055 "Definition of the Differentiated Services Field (DS 2056 Field) in the IPv4 and IPv6 Headers", RFC 2474, 2057 DOI 10.17487/RFC2474, December 1998, 2058 . 2060 [RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander, 2061 "SEcure Neighbor Discovery (SEND)", RFC 3971, 2062 DOI 10.17487/RFC3971, March 2005, 2063 . 2065 [RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)", 2066 RFC 3972, DOI 10.17487/RFC3972, March 2005, 2067 . 2069 [RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and 2070 More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191, 2071 November 2005, . 2073 [RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast 2074 Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005, 2075 . 2077 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 2078 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 2079 2006, . 2081 [RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet 2082 Control Message Protocol (ICMPv6) for the Internet 2083 Protocol Version 6 (IPv6) Specification", STD 89, 2084 RFC 4443, DOI 10.17487/RFC4443, March 2006, 2085 . 2087 [RFC4727] Fenner, B., "Experimental Values In IPv4, IPv6, ICMPv4, 2088 ICMPv6, UDP, and TCP Headers", RFC 4727, 2089 DOI 10.17487/RFC4727, November 2006, 2090 . 2092 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 2093 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 2094 DOI 10.17487/RFC4861, September 2007, 2095 . 2097 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 2098 Address Autoconfiguration", RFC 4862, 2099 DOI 10.17487/RFC4862, September 2007, 2100 . 2102 [RFC6088] Tsirtsis, G., Giarreta, G., Soliman, H., and N. Montavont, 2103 "Traffic Selectors for Flow Bindings", RFC 6088, 2104 DOI 10.17487/RFC6088, January 2011, 2105 . 2107 [RFC8028] Baker, F. and B. Carpenter, "First-Hop Router Selection by 2108 Hosts in a Multi-Prefix Network", RFC 8028, 2109 DOI 10.17487/RFC8028, November 2016, 2110 . 2112 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2113 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2114 May 2017, . 2116 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 2117 (IPv6) Specification", STD 86, RFC 8200, 2118 DOI 10.17487/RFC8200, July 2017, 2119 . 2121 [RFC8201] McCann, J., Deering, S., Mogul, J., and R. Hinden, Ed., 2122 "Path MTU Discovery for IP version 6", STD 87, RFC 8201, 2123 DOI 10.17487/RFC8201, July 2017, 2124 . 2126 [RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A., 2127 Richardson, M., Jiang, S., Lemon, T., and T. Winters, 2128 "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", 2129 RFC 8415, DOI 10.17487/RFC8415, November 2018, 2130 . 2132 23.2. Informative References 2134 [CRC] Jain, R., "Error Characteristics of Fiber Distributed Data 2135 Interface (FDDI), IEEE Transactions on Communications", 2136 August 1990. 2138 [I-D.ietf-intarea-tunnels] 2139 Touch, J. and M. Townsley, "IP Tunnels in the Internet 2140 Architecture", draft-ietf-intarea-tunnels-10 (work in 2141 progress), September 2019. 2143 [I-D.templin-6man-dhcpv6-ndopt] 2144 Templin, F., "A Unified Stateful/Stateless Configuration 2145 Service for IPv6", draft-templin-6man-dhcpv6-ndopt-10 2146 (work in progress), June 2020. 2148 [I-D.templin-intarea-6706bis] 2149 Templin, F., "Asymmetric Extended Route Optimization 2150 (AERO)", draft-templin-intarea-6706bis-66 (work in 2151 progress), October 2020. 2153 [RFC1122] Braden, R., Ed., "Requirements for Internet Hosts - 2154 Communication Layers", STD 3, RFC 1122, 2155 DOI 10.17487/RFC1122, October 1989, 2156 . 2158 [RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191, 2159 DOI 10.17487/RFC1191, November 1990, 2160 . 2162 [RFC1256] Deering, S., Ed., "ICMP Router Discovery Messages", 2163 RFC 1256, DOI 10.17487/RFC1256, September 1991, 2164 . 2166 [RFC2131] Droms, R., "Dynamic Host Configuration Protocol", 2167 RFC 2131, DOI 10.17487/RFC2131, March 1997, 2168 . 2170 [RFC2225] Laubach, M. and J. Halpern, "Classical IP and ARP over 2171 ATM", RFC 2225, DOI 10.17487/RFC2225, April 1998, 2172 . 2174 [RFC2464] Crawford, M., "Transmission of IPv6 Packets over Ethernet 2175 Networks", RFC 2464, DOI 10.17487/RFC2464, December 1998, 2176 . 2178 [RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in 2179 IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473, 2180 December 1998, . 2182 [RFC2492] Armitage, G., Schulter, P., and M. Jork, "IPv6 over ATM 2183 Networks", RFC 2492, DOI 10.17487/RFC2492, January 1999, 2184 . 2186 [RFC2529] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4 2187 Domains without Explicit Tunnels", RFC 2529, 2188 DOI 10.17487/RFC2529, March 1999, 2189 . 2191 [RFC2863] McCloghrie, K. and F. Kastenholz, "The Interfaces Group 2192 MIB", RFC 2863, DOI 10.17487/RFC2863, June 2000, 2193 . 2195 [RFC3692] Narten, T., "Assigning Experimental and Testing Numbers 2196 Considered Useful", BCP 82, RFC 3692, 2197 DOI 10.17487/RFC3692, January 2004, 2198 . 2200 [RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener 2201 Discovery Version 2 (MLDv2) for IPv6", RFC 3810, 2202 DOI 10.17487/RFC3810, June 2004, 2203 . 2205 [RFC3819] Karn, P., Ed., Bormann, C., Fairhurst, G., Grossman, D., 2206 Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J., and L. 2207 Wood, "Advice for Internet Subnetwork Designers", BCP 89, 2208 RFC 3819, DOI 10.17487/RFC3819, July 2004, 2209 . 2211 [RFC3879] Huitema, C. and B. Carpenter, "Deprecating Site Local 2212 Addresses", RFC 3879, DOI 10.17487/RFC3879, September 2213 2004, . 2215 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 2216 Internet Protocol", RFC 4301, DOI 10.17487/RFC4301, 2217 December 2005, . 2219 [RFC4380] Huitema, C., "Teredo: Tunneling IPv6 over UDP through 2220 Network Address Translations (NATs)", RFC 4380, 2221 DOI 10.17487/RFC4380, February 2006, 2222 . 2224 [RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery 2225 Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April 2226 2006, . 2228 [RFC4541] Christensen, M., Kimball, K., and F. Solensky, 2229 "Considerations for Internet Group Management Protocol 2230 (IGMP) and Multicast Listener Discovery (MLD) Snooping 2231 Switches", RFC 4541, DOI 10.17487/RFC4541, May 2006, 2232 . 2234 [RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick, 2235 "Internet Group Management Protocol (IGMP) / Multicast 2236 Listener Discovery (MLD)-Based Multicast Forwarding 2237 ("IGMP/MLD Proxying")", RFC 4605, DOI 10.17487/RFC4605, 2238 August 2006, . 2240 [RFC4821] Mathis, M. and J. Heffner, "Packetization Layer Path MTU 2241 Discovery", RFC 4821, DOI 10.17487/RFC4821, March 2007, 2242 . 2244 [RFC4963] Heffner, J., Mathis, M., and B. Chandler, "IPv4 Reassembly 2245 Errors at High Data Rates", RFC 4963, 2246 DOI 10.17487/RFC4963, July 2007, 2247 . 2249 [RFC5175] Haberman, B., Ed. and R. Hinden, "IPv6 Router 2250 Advertisement Flags Option", RFC 5175, 2251 DOI 10.17487/RFC5175, March 2008, 2252 . 2254 [RFC5213] Gundavelli, S., Ed., Leung, K., Devarapalli, V., 2255 Chowdhury, K., and B. Patil, "Proxy Mobile IPv6", 2256 RFC 5213, DOI 10.17487/RFC5213, August 2008, 2257 . 2259 [RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site 2260 Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214, 2261 DOI 10.17487/RFC5214, March 2008, 2262 . 2264 [RFC5558] Templin, F., Ed., "Virtual Enterprise Traversal (VET)", 2265 RFC 5558, DOI 10.17487/RFC5558, February 2010, 2266 . 2268 [RFC5798] Nadas, S., Ed., "Virtual Router Redundancy Protocol (VRRP) 2269 Version 3 for IPv4 and IPv6", RFC 5798, 2270 DOI 10.17487/RFC5798, March 2010, 2271 . 2273 [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 2274 (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, 2275 . 2277 [RFC6081] Thaler, D., "Teredo Extensions", RFC 6081, 2278 DOI 10.17487/RFC6081, January 2011, 2279 . 2281 [RFC6355] Narten, T. and J. Johnson, "Definition of the UUID-Based 2282 DHCPv6 Unique Identifier (DUID-UUID)", RFC 6355, 2283 DOI 10.17487/RFC6355, August 2011, 2284 . 2286 [RFC6543] Gundavelli, S., "Reserved IPv6 Interface Identifier for 2287 Proxy Mobile IPv6", RFC 6543, DOI 10.17487/RFC6543, May 2288 2012, . 2290 [RFC7084] Singh, H., Beebee, W., Donley, C., and B. Stark, "Basic 2291 Requirements for IPv6 Customer Edge Routers", RFC 7084, 2292 DOI 10.17487/RFC7084, November 2013, 2293 . 2295 [RFC7421] Carpenter, B., Ed., Chown, T., Gont, F., Jiang, S., 2296 Petrescu, A., and A. Yourtchenko, "Analysis of the 64-bit 2297 Boundary in IPv6 Addressing", RFC 7421, 2298 DOI 10.17487/RFC7421, January 2015, 2299 . 2301 [RFC7542] DeKok, A., "The Network Access Identifier", RFC 7542, 2302 DOI 10.17487/RFC7542, May 2015, 2303 . 2305 [RFC7739] Gont, F., "Security Implications of Predictable Fragment 2306 Identification Values", RFC 7739, DOI 10.17487/RFC7739, 2307 February 2016, . 2309 [RFC7847] Melia, T., Ed. and S. Gundavelli, Ed., "Logical-Interface 2310 Support for IP Hosts with Multi-Access Support", RFC 7847, 2311 DOI 10.17487/RFC7847, May 2016, 2312 . 2314 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 2315 Writing an IANA Considerations Section in RFCs", BCP 26, 2316 RFC 8126, DOI 10.17487/RFC8126, June 2017, 2317 . 2319 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 2320 Decraene, B., Litkowski, S., and R. Shakir, "Segment 2321 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 2322 July 2018, . 2324 [RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J., 2325 Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header 2326 (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020, 2327 . 2329 [RFC8900] Bonica, R., Baker, F., Huston, G., Hinden, R., Troan, O., 2330 and F. Gont, "IP Fragmentation Considered Fragile", 2331 BCP 230, RFC 8900, DOI 10.17487/RFC8900, September 2020, 2332 . 2334 Appendix A. Interface Attribute Heuristic Bitmap Encoding 2336 Adaptation of the OMNI option Interface Attributes Heuristic Bitmap 2337 encoding to specific Internetworks such as the Aeronautical 2338 Telecommunications Network with Internet Protocol Services (ATN/IPS) 2339 may include link selection preferences based on other traffic 2340 classifiers (e.g., transport port numbers, etc.) in addition to the 2341 existing DSCP-based preferences. Nodes on specific Internetworks 2342 maintain a map of traffic classifiers to additional P[*] preference 2343 fields beyond the first 64. For example, TCP port 22 maps to P[67], 2344 TCP port 443 maps to P[70], UDP port 8060 maps to P[76], etc. 2346 Implementations use Simplex or Indexed encoding formats for P[*] 2347 encoding in order to encode a given set of traffic classifiers in the 2348 most efficient way. Some use cases may be more efficiently coded 2349 using Simplex form, while others may be more efficient using Indexed. 2350 Once a format is selected for preparation of a single Interface 2351 Attribute the same format must be used for the entire Interface 2352 Attribute sub-option. Different sub-options may use different 2353 formats. 2355 The following figures show coding examples for various Simplex and 2356 Indexed formats: 2358 0 1 2 3 2359 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 2360 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2361 | Sub-Type=2 | Sub-length=N | ifIndex | ifType | 2362 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2363 | Provider ID | Link |R| APS | Bitmap(0)=0xff|P00|P01|P02|P03| 2364 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2365 |P04|P05|P06|P07|P08|P09|P10|P11|P12|P13|P14|P15|P16|P17|P18|P19| 2366 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2367 |P20|P21|P22|P23|P24|P25|P26|P27|P28|P29|P30|P31| Bitmap(1)=0xff| 2368 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2369 |P32|P33|P34|P35|P36|P37|P38|P39|P40|P41|P42|P43|P44|P45|P46|P47| 2370 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2371 |P48|P49|P50|P51|P52|P53|P54|P55|P56|P57|P58|P59|P60|P61|P62|P63| 2372 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2373 | Bitmap(2)=0xff|P64|P65|P67|P68| ... 2374 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 2376 Figure 18: Example 1: Dense Simplex Encoding 2378 0 1 2 3 2379 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 2380 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2381 | Sub-Type=2 | Sub-length=N | ifIndex | ifType | 2382 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2383 | Provider ID | Link |R| APS | Bitmap(0)=0x00| Bitmap(1)=0x0f| 2384 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2385 |P48|P49|P50|P51|P52|P53|P54|P55|P56|P57|P58|P59|P60|P61|P62|P63| 2386 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2387 | Bitmap(2)=0x00| Bitmap(3)=0x00| Bitmap(4)=0x00| Bitmap(5)=0x00| 2388 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2389 | Bitmap(6)=0xf0|192|193|194|195|196|197|198|199|200|201|202|203| 2390 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2391 |204|205|206|207| Bitmap(7)=0x00| Bitmap(8)=0x0f|272|273|274|275| 2392 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2393 |276|277|278|279|280|281|282|283|284|285|286|287| Bitmap(9)=0x00| 2394 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2395 |Bitmap(10)=0x00| ... 2396 +-+-+-+-+-+-+-+-+-+-+- 2398 Figure 19: Example 2: Sparse Simplex Encoding 2400 0 1 2 3 2401 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 2402 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2403 | Sub-Type=2 | Sub-length=N | ifIndex | ifType | 2404 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2405 | Provider ID | Link |R| APS | Index = 0x00 | Bitmap = 0x80 | 2406 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2407 |P00|P01|P02|P03| Index = 0x01 | Bitmap = 0x01 |P60|P61|P62|P63| 2408 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2409 | Index = 0x10 | Bitmap = 0x80 |512|513|514|515| Index = 0x18 | 2410 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2411 | Bitmap = 0x01 |796|797|798|799| ... 2412 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 2414 Figure 20: Example 3: Indexed Encoding 2416 Appendix B. VDL Mode 2 Considerations 2418 ICAO Doc 9776 is the "Technical Manual for VHF Data Link Mode 2" 2419 (VDLM2) that specifies an essential radio frequency data link service 2420 for aircraft and ground stations in worldwide civil aviation air 2421 traffic management. The VDLM2 link type is "multicast capable" 2422 [RFC4861], but with considerable differences from common multicast 2423 links such as Ethernet and IEEE 802.11. 2425 First, the VDLM2 link data rate is only 31.5Kbps - multiple orders of 2426 magnitude less than most modern wireless networking gear. Second, 2427 due to the low available link bandwidth only VDLM2 ground stations 2428 (i.e., and not aircraft) are permitted to send broadcasts, and even 2429 so only as compact layer 2 "beacons". Third, aircraft employ the 2430 services of ground stations by performing unicast RS/RA exchanges 2431 upon receipt of beacons instead of listening for multicast RA 2432 messages and/or sending multicast RS messages. 2434 This beacon-oriented unicast RS/RA approach is necessary to conserve 2435 the already-scarce available link bandwidth. Moreover, since the 2436 numbers of beaconing ground stations operating within a given spatial 2437 range must be kept as sparse as possible, it would not be feasible to 2438 have different classes of ground stations within the same region 2439 observing different protocols. It is therefore highly desirable that 2440 all ground stations observe a common language of RS/RA as specified 2441 in this document. 2443 Note that links of this nature may benefit from compression 2444 techniques that reduce the bandwidth necessary for conveying the same 2445 amount of data. The IETF lpwan working group is considering possible 2446 alternatives: [https://datatracker.ietf.org/wg/lpwan/documents]. 2448 Appendix C. MN / AR Isolation Through L2 Address Mapping 2450 Per [RFC4861], IPv6 ND messages may be sent to either a multicast or 2451 unicast link-scoped IPv6 destination address. However, IPv6 ND 2452 messaging should be coordinated between the MN and AR only without 2453 invoking other nodes on the ANET. This implies that MN / AR control 2454 messaging should be isolated and not overheard by other nodes on the 2455 link. 2457 To support MN / AR isolation on some ANET links, ARs can maintain an 2458 OMNI-specific unicast L2 address ("MSADDR"). For Ethernet-compatible 2459 ANETs, this specification reserves one Ethernet unicast address TBD2 2460 (see: Section 19). For non-Ethernet statically-addressed ANETs, 2461 MSADDR is reserved per the assigned numbers authority for the ANET 2462 addressing space. For still other ANETs, MSADDR may be dynamically 2463 discovered through other means, e.g., L2 beacons. 2465 MNs map the L3 addresses of all IPv6 ND messages they send (i.e., 2466 both multicast and unicast) to MSADDR instead of to an ordinary 2467 unicast or multicast L2 address. In this way, all of the MN's IPv6 2468 ND messages will be received by ARs that are configured to accept 2469 packets destined to MSADDR. Note that multiple ARs on the link could 2470 be configured to accept packets destined to MSADDR, e.g., as a basis 2471 for supporting redundancy. 2473 Therefore, ARs must accept and process packets destined to MSADDR, 2474 while all other devices must not process packets destined to MSADDR. 2475 This model has well-established operational experience in Proxy 2476 Mobile IPv6 (PMIP) [RFC5213][RFC6543]. 2478 Appendix D. Change Log 2480 << RFC Editor - remove prior to publication >> 2482 Differences from draft-templin-6man-omni-interface-35 to draft- 2483 templin-6man-omni-interface-36: 2485 o Major clarifications on aspects such as "hard/soft" PTB error 2486 messages 2488 o Made generic so that either IP protocol version (IPv4 or IPv6) can 2489 be used in the data plane. 2491 Differences from draft-templin-6man-omni-interface-31 to draft- 2492 templin-6man-omni-interface-32: 2494 o MTU 2495 o Support for multi-hop ANETS such as ISATAP. 2497 Differences from draft-templin-6man-omni-interface-29 to draft- 2498 templin-6man-omni-interface-30: 2500 o Moved link-layer addressing information into the OMNI option on a 2501 per-ifIndex basis 2503 o Renamed "ifIndex-tuple" to "Interface Attributes" 2505 Differences from draft-templin-6man-omni-interface-27 to draft- 2506 templin-6man-omni-interface-28: 2508 o Updates based on implementation expereince. 2510 Differences from draft-templin-6man-omni-interface-25 to draft- 2511 templin-6man-omni-interface-26: 2513 o Further clarification on "aggregate" RA messages. 2515 o Expanded Security Considerations to discuss expectations for 2516 security in the Mobility Service. 2518 Differences from draft-templin-6man-omni-interface-20 to draft- 2519 templin-6man-omni-interface-21: 2521 o Safety-Based Multilink (SBM) and Performance-Based Multilink 2522 (PBM). 2524 Differences from draft-templin-6man-omni-interface-18 to draft- 2525 templin-6man-omni-interface-19: 2527 o SEND/CGA. 2529 Differences from draft-templin-6man-omni-interface-17 to draft- 2530 templin-6man-omni-interface-18: 2532 o Teredo 2534 Differences from draft-templin-6man-omni-interface-14 to draft- 2535 templin-6man-omni-interface-15: 2537 o Prefix length discussions removed. 2539 Differences from draft-templin-6man-omni-interface-12 to draft- 2540 templin-6man-omni-interface-13: 2542 o Teredo 2543 Differences from draft-templin-6man-omni-interface-11 to draft- 2544 templin-6man-omni-interface-12: 2546 o Major simplifications and clarifications on MTU and fragmentation. 2548 o Document now updates RFC4443 and RFC8201. 2550 Differences from draft-templin-6man-omni-interface-10 to draft- 2551 templin-6man-omni-interface-11: 2553 o Removed /64 assumption, resulting in new OMNI address format. 2555 Differences from draft-templin-6man-omni-interface-07 to draft- 2556 templin-6man-omni-interface-08: 2558 o OMNI MNs in the open Internet 2560 Differences from draft-templin-6man-omni-interface-06 to draft- 2561 templin-6man-omni-interface-07: 2563 o Brought back L2 MSADDR mapping text for MN / AR isolation based on 2564 L2 addressing. 2566 o Expanded "Transition Considerations". 2568 Differences from draft-templin-6man-omni-interface-05 to draft- 2569 templin-6man-omni-interface-06: 2571 o Brought back OMNI option "R" flag, and discussed its use. 2573 Differences from draft-templin-6man-omni-interface-04 to draft- 2574 templin-6man-omni-interface-05: 2576 o Transition considerations, and overhaul of RS/RA addressing with 2577 the inclusion of MSE addresses within the OMNI option instead of 2578 as RS/RA addresses (developed under FAA SE2025 contract number 2579 DTFAWA-15-D-00030). 2581 Differences from draft-templin-6man-omni-interface-02 to draft- 2582 templin-6man-omni-interface-03: 2584 o Added "advisory PTB messages" under FAA SE2025 contract number 2585 DTFAWA-15-D-00030. 2587 Differences from draft-templin-6man-omni-interface-01 to draft- 2588 templin-6man-omni-interface-02: 2590 o Removed "Primary" flag and supporting text. 2592 o Clarified that "Router Lifetime" applies to each ANET interface 2593 independently, and that the union of all ANET interface Router 2594 Lifetimes determines MSE lifetime. 2596 Differences from draft-templin-6man-omni-interface-00 to draft- 2597 templin-6man-omni-interface-01: 2599 o "All-MSEs" OMNI LLA defined. Also reserved fe80::ff00:0000/104 2600 for future use (most likely as "pseudo-multicast"). 2602 o Non-normative discussion of alternate OMNI LLA construction form 2603 made possible if the 64-bit assumption were relaxed. 2605 First draft version (draft-templin-atn-aero-interface-00): 2607 o Draft based on consensus decision of ICAO Working Group I Mobility 2608 Subgroup March 22, 2019. 2610 Authors' Addresses 2612 Fred L. Templin (editor) 2613 The Boeing Company 2614 P.O. Box 3707 2615 Seattle, WA 98124 2616 USA 2618 Email: fltemplin@acm.org 2620 Tony Whyman 2621 MWA Ltd c/o Inmarsat Global Ltd 2622 99 City Road 2623 London EC1Y 1AX 2624 England 2626 Email: tony.whyman@mccallumwhyman.com