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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, rfc4443, rfc8201 (if A. Whyman 5 approved) MWA Ltd c/o Inmarsat Global Ltd 6 Intended status: Standards Track December 7, 2020 7 Expires: June 10, 2021 9 Transmission of IP Packets over Overlay Multilink Network (OMNI) 10 Interfaces 11 draft-templin-6man-omni-interface-54 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 June 10, 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 . . . . . . . . . . . . . . . . . . . . . . . . 8 61 4. Overlay Multilink Network (OMNI) Interface Model . . . . . . 8 62 5. The OMNI Adaptation Layer (OAL) . . . . . . . . . . . . . . . 13 63 5.1. Fragmentation Security Implications . . . . . . . . . . . 17 64 6. Frame Format . . . . . . . . . . . . . . . . . . . . . . . . 18 65 7. Link-Local Addresses (LLAs) . . . . . . . . . . . . . . . . . 18 66 8. Domain-Local Addresses (DLAs) . . . . . . . . . . . . . . . . 20 67 9. Address Mapping - Unicast . . . . . . . . . . . . . . . . . . 21 68 9.1. Sub-Options . . . . . . . . . . . . . . . . . . . . . . . 23 69 9.1.1. Pad1 . . . . . . . . . . . . . . . . . . . . . . . . 24 70 9.1.2. PadN . . . . . . . . . . . . . . . . . . . . . . . . 24 71 9.1.3. Interface Attributes . . . . . . . . . . . . . . . . 24 72 9.1.4. Traffic Selector . . . . . . . . . . . . . . . . . . 28 73 9.1.5. MS-Register . . . . . . . . . . . . . . . . . . . . . 29 74 9.1.6. MS-Release . . . . . . . . . . . . . . . . . . . . . 29 75 9.1.7. Network Access Identifier (NAI) . . . . . . . . . . . 30 76 9.1.8. Geo Coordinates . . . . . . . . . . . . . . . . . . . 31 77 9.1.9. DHCP Unique Identifier (DUID) . . . . . . . . . . . . 31 78 9.1.10. DHCPv6 Message . . . . . . . . . . . . . . . . . . . 32 79 10. Address Mapping - Multicast . . . . . . . . . . . . . . . . . 32 80 11. Multilink Conceptual Sending Algorithm . . . . . . . . . . . 33 81 11.1. Multiple OMNI Interfaces . . . . . . . . . . . . . . . . 33 82 11.2. MN<->AR Traffic Loop Prevention . . . . . . . . . . . . 34 83 12. Router Discovery and Prefix Registration . . . . . . . . . . 34 84 12.1. Router Discovery in IP Multihop and IPv4-Only Access 85 Networks . . . . . . . . . . . . . . . . . . . . . . . . 38 86 12.2. MS-Register and MS-Release List Processing . . . . . . . 40 87 12.3. DHCPv6-based Prefix Registration . . . . . . . . . . . . 41 88 13. Secure Redirection . . . . . . . . . . . . . . . . . . . . . 42 89 14. AR and MSE Resilience . . . . . . . . . . . . . . . . . . . . 43 90 15. Detecting and Responding to MSE Failures . . . . . . . . . . 43 91 16. Transition Considerations . . . . . . . . . . . . . . . . . . 44 92 17. OMNI Interfaces on the Open Internet . . . . . . . . . . . . 44 93 18. Time-Varying MNPs . . . . . . . . . . . . . . . . . . . . . . 45 94 19. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 46 95 20. Security Considerations . . . . . . . . . . . . . . . . . . . 47 96 21. Implementation Status . . . . . . . . . . . . . . . . . . . . 47 97 22. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 48 98 23. References . . . . . . . . . . . . . . . . . . . . . . . . . 48 99 23.1. Normative References . . . . . . . . . . . . . . . . . . 48 100 23.2. Informative References . . . . . . . . . . . . . . . . . 50 101 Appendix A. Interface Attribute Preferences Bitmap Encoding . . 55 102 Appendix B. VDL Mode 2 Considerations . . . . . . . . . . . . . 57 103 Appendix C. MN / AR Isolation Through L2 Address Mapping . . . . 58 104 Appendix D. Change Log . . . . . . . . . . . . . . . . . . . . . 58 105 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 61 107 1. Introduction 109 Mobile Nodes (MNs) (e.g., aircraft of various configurations, 110 terrestrial vehicles, seagoing vessels, enterprise wireless devices, 111 etc.) often have multiple data links for communicating with networked 112 correspondents. These data links may have diverse performance, cost 113 and availability properties that can change dynamically according to 114 mobility patterns, flight phases, proximity to infrastructure, etc. 115 MNs coordinate their data links in a discipline known as "multilink", 116 in which a single virtual interface is configured over the underlying 117 data links. 119 The MN configures a virtual interface (termed the "Overlay Multilink 120 Network (OMNI) interface") as a thin layer over the underlying Access 121 Network (ANET) interfaces. The OMNI interface is therefore the only 122 interface abstraction exposed to the IP layer and behaves according 123 to the Non-Broadcast, Multiple Access (NBMA) interface principle, 124 while underlying interfaces appear as link layer communication 125 channels in the architecture. The OMNI interface connects to a 126 virtual overlay service known as the "OMNI link". The OMNI link 127 spans one or more Internetworks that may include private-use 128 infrastructures and/or the global public Internet itself. 130 Each MN receives a Mobile Network Prefix (MNP) for numbering 131 downstream-attached End User Networks (EUNs) independently of the 132 access network data links selected for data transport. The MN 133 performs router discovery over the OMNI interface (i.e., similar to 134 IPv6 customer edge routers [RFC7084]) and acts as a mobile router on 135 behalf of its EUNs. The router discovery process is iterated over 136 each of the OMNI interface's underlying interfaces in order to 137 register per-link parameters (see Section 12). 139 The OMNI interface provides a multilink nexus for exchanging inbound 140 and outbound traffic via the correct underlying interface(s). The IP 141 layer sees the OMNI interface as a point of connection to the OMNI 142 link. Each OMNI link has one or more associated Mobility Service 143 Prefixes (MSPs) from which OMNI link MNPs are derived. If there are 144 multiple OMNI links, the IPv6 layer will see multiple OMNI 145 interfaces. 147 MNs may connect to multiple distinct OMNI links by configuring 148 multiple OMNI interfaces, e.g., omni0, omni1, omni2, etc. Each OMNI 149 interface is configured over a set of underlying interfaces and 150 provides a nexus for Safety-Based Multilink (SBM) operation. The IP 151 layer selects an OMNI interface based on SBM routing considerations, 152 then the selected interface applies Performance-Based Multilink (PBM) 153 to select the correct underlying interface. Applications can apply 154 Segment Routing [RFC8402] to select independent SBM topologies for 155 fault tolerance. 157 The OMNI interface interacts with a network-based Mobility Service 158 (MS) through IPv6 Neighbor Discovery (ND) control message exchanges 159 [RFC4861]. The MS provides Mobility Service Endpoints (MSEs) that 160 track MN movements and represent their MNPs in a global routing or 161 mapping system. 163 Many OMNI use cases are currently under active consideration. In 164 particular, the International Civil Aviation Organization (ICAO) 165 Working Group-I Mobility Subgroup is developing a future Aeronautical 166 Telecommunications Network with Internet Protocol Services (ATN/IPS) 167 and has issued a liaison statement requesting IETF adoption [ATN]. 168 The IETF IP Wireless Access in Vehicular Environments (ipwave) 169 working group has further included problem statement and use case 170 analysis for OMNI in a document now in AD evaluation for RFC 171 publication [I-D.ietf-ipwave-vehicular-networking]. Still other 172 communities of interest include AEEC, RTCA Special Committee 228 (SC- 173 228) and NASA programs that examine commercial aviation, Urban Air 174 Mobility (UAM) and Unmanned Air Systems (UAS). Pedestrians with 175 handheld devices represent another large class of potential OMNI 176 users. 178 This document specifies the transmission of IP packets and MN/MS 179 control messages over OMNI interfaces. The OMNI interface supports 180 either IP protocol version (i.e., IPv4 [RFC0791] or IPv6 [RFC8200]) 181 as the network layer in the data plane, while using IPv6 ND messaging 182 as the control plane independently of the data plane IP protocol(s). 183 The OMNI Adaptation Layer (OAL) which operates as a mid-layer between 184 L3 and L2 is based on IP-in-IPv6 encapsulation per [RFC2473] as 185 discussed in the following sections. 187 2. Terminology 189 The terminology in the normative references applies; especially, the 190 terms "link" and "interface" are the same as defined in the IPv6 191 [RFC8200] and IPv6 Neighbor Discovery (ND) [RFC4861] specifications. 193 Additionally, this document assumes the following IPv6 ND message 194 types: Router Solicitation (RS), Router Advertisement (RA), Neighbor 195 Solicitation (NS), Neighbor Advertisement (NA) and Redirect. 197 The Protocol Constants defined in Section 10 of [RFC4861] are used in 198 their same format and meaning in this document. The terms "All- 199 Routers multicast", "All-Nodes multicast" and "Subnet-Router anycast" 200 are the same as defined in [RFC4291] (with Link-Local scope assumed). 202 The term "IP" is used to refer collectively to either Internet 203 Protocol version (i.e., IPv4 [RFC0791] or IPv6 [RFC8200]) when a 204 specification at the layer in question applies equally to either 205 version. 207 The following terms are defined within the scope of this document: 209 Mobile Node (MN) 210 an end system with a mobile router having multiple distinct 211 upstream data link connections that are grouped together in one or 212 more logical units. The MN's data link connection parameters can 213 change over time due to, e.g., node mobility, link quality, etc. 214 The MN further connects a downstream-attached End User Network 215 (EUN). The term MN used here is distinct from uses in other 216 documents, and does not imply a particular mobility protocol. 218 End User Network (EUN) 219 a simple or complex downstream-attached mobile network that 220 travels with the MN as a single logical unit. The IP addresses 221 assigned to EUN devices remain stable even if the MN's upstream 222 data link connections change. 224 Mobility Service (MS) 225 a mobile routing service that tracks MN movements and ensures that 226 MNs remain continuously reachable even across mobility events. 227 Specific MS details are out of scope for this document. 229 Mobility Service Endpoint (MSE) 230 an entity in the MS (either singular or aggregate) that 231 coordinates the mobility events of one or more MN. 233 Mobility Service Prefix (MSP) 234 an aggregated IP prefix (e.g., 2001:db8::/32, 192.0.2.0/24, etc.) 235 advertised to the rest of the Internetwork by the MS, and from 236 which more-specific Mobile Network Prefixes (MNPs) are derived. 238 Mobile Network Prefix (MNP) 239 a longer IP prefix taken from an MSP (e.g., 240 2001:db8:1000:2000::/56, 192.0.2.8/30, etc.) and assigned to a MN. 241 MNs sub-delegate the MNP to devices located in EUNs. 243 Access Network (ANET) 244 a data link service network (e.g., an aviation radio access 245 network, satellite service provider network, cellular operator 246 network, wifi network, etc.) that connects MNs. Physical and/or 247 data link level security between the MN and ANET are assumed. 249 Access Router (AR) 250 a first-hop router in the ANET for connecting MNs to 251 correspondents in outside Internetworks. 253 ANET interface 254 a MN's attachment to a link in an ANET. 256 Internetwork (INET) 257 a connected network region with a coherent IP addressing plan that 258 provides transit forwarding services for ANET MNs and INET 259 correspondents. Examples include private enterprise networks, 260 ground domain aviation service networks and the global public 261 Internet itself. 263 INET interface 264 a node's attachment to a link in an INET. 266 OMNI link 267 a Non-Broadcast, Multiple Access (NBMA) virtual overlay configured 268 over one or more INETs and their connected ANETs. An OMNI link 269 can comprise multiple INET segments joined by bridges the same as 270 for any link; the addressing plans in each segment may be mutually 271 exclusive and managed by different administrative entities. 273 OMNI domain 274 a set of affiliated OMNI links that collectively provide services 275 under a common (set of) Mobility Service Prefixes (MSPs). 277 OMNI interface 278 a node's attachment to an OMNI link, and configured over one or 279 more underlying ANET/INET interfaces. If there are multiple OMNI 280 links in an OMNI domain, a separate OMNI interface is configured 281 for each link. 283 OMNI Adaptation Layer (OAL) 284 an OMNI interface process whereby packets admitted into the 285 interface are wrapped in a mid-layer IPv6 header and fragmented/ 286 reassembled if necessary to support the OMNI link Maximum 287 Transmission Unit (MTU). The OAL is also responsible for 288 generating MTU-related control messages as necessary, and for 289 providing addressing context for spanning multiple segments of a 290 bridged OMNI link. 292 OMNI Link-Local Address (LLA) 293 a link local IPv6 address per [RFC4291] constructed as specified 294 in Section 7. 296 OMNI Domain-Local Address (DLA) 297 an IPv6 address from the prefix [DLA]::/48 constructed as 298 specified in Section 8. OMNI DLAs are statelessly derived from 299 OMNI LLAs, and vice-versa. 301 OMNI Option 302 an IPv6 Neighbor Discovery option providing multilink parameters 303 for the OMNI interface as specified in Section 9. 305 Multilink 306 an OMNI interface's manner of managing diverse underlying data 307 link interfaces as a single logical unit. The OMNI interface 308 provides a single unified interface to upper layers, while 309 underlying data link selections are performed on a per-packet 310 basis considering factors such as DSCP, flow label, application 311 policy, signal quality, cost, etc. Multilinking decisions are 312 coordinated in both the outbound (i.e. MN to correspondent) and 313 inbound (i.e., correspondent to MN) directions. 315 L2 316 The second layer in the OSI network model. Also known as "layer- 317 2", "link-layer", "sub-IP layer", "data link layer", etc. 319 L3 320 The third layer in the OSI network model. Also known as "layer- 321 3", "network-layer", "IP layer", etc. 323 underlying interface 324 an ANET/INET interface over which an OMNI interface is configured. 325 The OMNI interface is seen as a L3 interface by the IP layer, and 326 each underlying interface is seen as a L2 interface by the OMNI 327 interface. 329 Mobility Service Identification (MSID) 330 Each MSE and AR is assigned a unique 32-bit Identification (MSID) 331 as specified in Section 7. 333 Safety-Based Multilink (SBM) 334 A means for ensuring fault tolerance through redundancy by 335 connecting multiple independent OMNI interfaces to independent 336 routing topologies (i.e., multiple independent OMNI links). 338 Performance Based Multilink (PBM) 339 A means for selecting underlying interface(s) for packet 340 transmission and reception within a single OMNI interface. 342 3. Requirements 344 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 345 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 346 "OPTIONAL" in this document are to be interpreted as described in BCP 347 14 [RFC2119][RFC8174] when, and only when, they appear in all 348 capitals, as shown here. 350 OMNI links maintain a constant value "MAX_MSID" selected to provide 351 MNs with an acceptable level of MSE redundancy while minimizing 352 control message amplification. It is RECOMMENDED that MAX_MSID be 353 set to the default value 5; if a different value is chosen, it should 354 be set uniformly by all nodes on the OMNI link. 356 An implementation is not required to internally use the architectural 357 constructs described here so long as its external behavior is 358 consistent with that described in this document. 360 4. Overlay Multilink Network (OMNI) Interface Model 362 An OMNI interface is a MN virtual interface configured over one or 363 more underlying interfaces, which may be physical (e.g., an 364 aeronautical radio link) or virtual (e.g., an Internet or higher- 365 layer "tunnel"). The MN receives a MNP from the MS, and coordinates 366 with the MS through IPv6 ND message exchanges. The MN uses the MNP 367 to construct a unique OMNI LLA through the algorithmic derivation 368 specified in Section 7 and assigns the LLA to the OMNI interface. 370 The OMNI interface architectural layering model is the same as in 371 [RFC5558][RFC7847], and augmented as shown in Figure 1. The IP layer 372 therefore sees the OMNI interface as a single L3 interface with 373 multiple underlying interfaces that appear as L2 communication 374 channels in the architecture. 376 +----------------------------+ 377 | Upper Layer Protocol | 378 Session-to-IP +---->| | 379 Address Binding | +----------------------------+ 380 +---->| IP (L3) | 381 IP Address +---->| | 382 Binding | +----------------------------+ 383 +---->| OMNI Interface | 384 Logical-to- +---->| (OMNI LLA) | 385 Physical | +----------------------------+ 386 Interface +---->| L2 | L2 | | L2 | 387 Binding |(IF#1)|(IF#2)| ..... |(IF#n)| 388 +------+------+ +------+ 389 | L1 | L1 | | L1 | 390 | | | | | 391 +------+------+ +------+ 393 Figure 1: OMNI Interface Architectural Layering Model 395 Each underlying interface provides an L2/L1 abstraction according to 396 one of the following models: 398 o INET interfaces connect to an INET either natively or through one 399 or several IPv4 Network Address Translators (NATs). Native INET 400 interfaces have global IP addresses that are reachable from any 401 INET correspondent. NATed INET interfaces typically have private 402 IP addresses and connect to a private network behind one or more 403 NATs that provide INET access. 405 o ANET interfaces connect to a protected ANET that is separated from 406 the open INET by an AR acting as a proxy. The ANET interface may 407 be either on the same L2 link segment as the AR, or separated from 408 the AR by multiple IP hops. 410 o VPNed interfaces use security encapsulation over an INET/ANET to a 411 Virtual Private Network (VPN) gateway. Other than the link-layer 412 encapsulation format, VPNed interfaces behave the same as for 413 Direct interfaces. 415 o Direct (aka "point-to-point") interfaces connect directly to a 416 peer without crossing any ANET/INET paths. An example is a line- 417 of-sight link between a remote pilot and an unmanned aircraft. 419 The OMNI virtual interface model gives rise to a number of 420 opportunities: 422 o since MN OMNI LLAs are uniquely derived from an MNP, no Duplicate 423 Address Detection (DAD) or Multicast Listener Discovery (MLD) 424 messaging is necessary. 426 o since Temporary OMNI LLAs are statistically unique, they can be 427 used without DAD for short-term purposes, e.g. until an MN OMNI 428 LLA is obtained. 430 o ANET interfaces on the same L2 link segment as an AR do not 431 require any L3 addresses (i.e., not even link-local) in 432 environments where communications are coordinated entirely over 433 the OMNI interface. (An alternative would be to also assign the 434 same OMNI LLA to all ANET interfaces.) 436 o as underlying interface properties change (e.g., link quality, 437 cost, availability, etc.), any active interface can be used to 438 update the profiles of multiple additional interfaces in a single 439 message. This allows for timely adaptation and service continuity 440 under dynamically changing conditions. 442 o coordinating underlying interfaces in this way allows them to be 443 represented in a unified MS profile with provisions for mobility 444 and multilink operations. 446 o exposing a single virtual interface abstraction to the IPv6 layer 447 allows for multilink operation (including QoS based link 448 selection, packet replication, load balancing, etc.) at L2 while 449 still permitting L3 traffic shaping based on, e.g., DSCP, flow 450 label, etc. 452 o the OMNI interface allows inter-INET traversal when nodes located 453 in different INETs need to communicate with one another. This 454 mode of operation would not be possible via direct communications 455 over the underlying interfaces themselves. 457 o the OMNI Adaptation Layer (OAL) within the OMNI interface supports 458 lossless and adaptive path MTU mitigations not available for 459 communications directly over the underlying interfaces themselves. 461 o L3 sees the OMNI interface as a point of connection to the OMNI 462 link; if there are multiple OMNI links (i.e., multiple MS's), L3 463 will see multiple OMNI interfaces. 465 o Multiple independent OMNI interfaces can be used for increased 466 fault tolerance through Safety-Based Multilink (SBM), with 467 Performance-Based Multilink (PBM) applied within each interface. 469 Other opportunities are discussed in [RFC7847]. Note that even when 470 the OMNI virtual interface is present, applications can still access 471 underlying interfaces either through the network protocol stack using 472 an Internet socket or directly using a raw socket. This allows for 473 intra-network (or point-to-point) communications without invoking the 474 OMNI interface and/or OAL. For example, when an IPv6 OMNI interface 475 is configured over an underlying IPv4 interface, applications can 476 still invoke IPv4 intra-network communications as long as the 477 communicating endpoints are not subject to mobility dynamics. 478 However, the opportunities discussed above are not available when the 479 architectural layering is bypassed in this way. 481 Figure 2 depicts the architectural model for a MN with an attached 482 EUN connecting to the MS via multiple independent ANETs. When an 483 underlying interface becomes active, the MN's OMNI interface sends 484 IPv6 ND messages without encapsulation if the first-hop Access Router 485 (AR) is on the same underlying link; otherwise, the interface uses 486 IP-in-IP encapsulation. The IPv6 ND messages traverse the ground 487 domain ANETs until they reach an AR (AR#1, AR#2, ..., AR#n), which 488 then coordinates with a Mobility Service Endpoint (MSE#1, MSE#2, ..., 489 MSE#m) in the INET and returns an IPv6 ND message response to the MN. 490 The Hop Limit in IPv6 ND messages is not decremented due to 491 encapsulation; hence, the OMNI interface appears to be attached to an 492 ordinary link. 494 +--------------+ (:::)-. 495 | MN |<-->.-(::EUN:::) 496 +--------------+ `-(::::)-' 497 |OMNI interface| 498 +----+----+----+ 499 +--------|IF#1|IF#2|IF#n|------ + 500 / +----+----+----+ \ 501 / | \ 502 / | \ 503 v v v 504 (:::)-. (:::)-. (:::)-. 505 .-(::ANET:::) .-(::ANET:::) .-(::ANET:::) 506 `-(::::)-' `-(::::)-' `-(::::)-' 507 +----+ +----+ +----+ 508 ... |AR#1| .......... |AR#2| ......... |AR#n| ... 509 . +-|--+ +-|--+ +-|--+ . 510 . | | | 511 . v v v . 512 . <----- INET Encapsulation -----> . 513 . . 514 . +-----+ (:::)-. . 515 . |MSE#2| .-(::::::::) +-----+ . 516 . +-----+ .-(::: INET :::)-. |MSE#m| . 517 . (::::: Routing ::::) +-----+ . 518 . `-(::: System :::)-' . 519 . +-----+ `-(:::::::-' . 520 . |MSE#1| +-----+ +-----+ . 521 . +-----+ |MSE#3| |MSE#4| . 522 . +-----+ +-----+ . 523 . . 524 . . 525 . <----- Worldwide Connected Internetwork ----> . 526 ........................................................... 528 Figure 2: MN/MS Coordination via Multiple ANETs 530 After the initial IPv6 ND message exchange, the MN (and/or any nodes 531 on its attached EUNs) can send and receive IP data packets over the 532 OMNI interface. OMNI interface multilink services will forward the 533 packets via ARs in the correct underlying ANETs. The AR encapsulates 534 the packets according to the capabilities provided by the MS and 535 forwards them to the next hop within the worldwide connected 536 Internetwork via optimal routes. 538 OMNI links span one or more underlying Internetwork via the OMNI 539 Adaptation Layer (OAL) which is based on a mid-layer overlay 540 encapsulation using [RFC2473]. Each OMNI link corresponds to a 541 different overlay (differentiated by an address codepoint) which may 542 be carried over a completely separate underlying topology. Each MN 543 can facilitate SBM by connecting to multiple OMNI links using a 544 distinct OMNI interface for each link. 546 5. The OMNI Adaptation Layer (OAL) 548 The OMNI interface observes the link nature of tunnels, including the 549 Maximum Transmission Unit (MTU), Maximum Reassembly Unit (MRU) and 550 the role of fragmentation and reassembly [I-D.ietf-intarea-tunnels]. 551 The OMNI interface is configured over one or more underlying 552 interfaces that may have diverse MTUs. OMNI interfaces accommodate 553 MTU diversity through the use of the OMNI Adaptation Layer (OAL) as 554 discussed in this section. 556 IPv6 underlying interfaces are REQUIRED to configure a minimum MTU of 557 1280 bytes and a minimum MRU of 1500 bytes [RFC8200]. Therefore, the 558 minimum IPv6 path MTU is 1280 bytes since routers on the path are not 559 permitted to perform network fragmentation even though the 560 destination is required to reassemble more. The network therefore 561 MUST forward packets of at least 1280 bytes without generating an 562 IPv6 Path MTU Discovery (PMTUD) Packet Too Big (PTB) message 563 [RFC8201]. (Note: the source can apply "source fragmentation" for 564 locally-generated IPv6 packets up to 1500 bytes and larger still if 565 it if has a way to determine that the destination configures a larger 566 MRU, but this does not affect the minimum IPv6 path MTU.) 568 IPv4 underlying interfaces are REQUIRED to configure a minimum MTU of 569 68 bytes [RFC0791] and a minimum MRU of 576 bytes [RFC0791][RFC1122]. 570 Therefore, when the Don't Fragment (DF) bit in the IPv4 header is set 571 to 0 the minimum IPv4 path MTU is 576 bytes since routers on the path 572 support network fragmentation and the destination is required to 573 reassemble at least that much. The DF bit in the IPv4 encapsulation 574 headers of packets sent over IPv4 underlying interfaces therefore 575 MUST be set to 0. (Note: even if the encapsulation source has a way 576 to determine that the encapsulation destination configures an MRU 577 larger than 576 bytes, it should not assume a larger minimum IPv4 578 path MTU without careful consideration of the issues discussed in 579 Section 5.1.) 581 The OMNI interface configures both an MTU and MRU of 9180 bytes 582 [RFC2492]; the size is therefore not a reflection of the underlying 583 interface MTUs, but rather determines the largest packet the OMNI 584 interface can forward or reassemble. The OMNI interface uses the 585 OMNI Adaptation Layer (OAL) to admit packets from the network layer 586 that are no larger than the OMNI interface MTU while generating 587 ICMPv4 Fragmentation Needed [RFC1191] or ICMPv6 Path MTU Discovery 588 (PMTUD) Packet Too Big (PTB) [RFC8201] messages as necessary. This 589 document refers to both of these ICMPv4/ICMPv6 message types simply 590 as "PTBs", and introduces a distinction between PTB "hard" and "soft" 591 errors as discussed below. 593 For IPv4 packets with DF=0, the network layer performs IPv4 594 fragmentation if necessary then admits the packets/fragments into the 595 OMNI interface; these fragments will be reassembled by the final 596 destination. For IPv4 packets with DF=1 and IPv6 packets, the 597 network layer admits the packet if it is no larger than the OMNI 598 interface MTU; otherwise, it drops the packet and returns a PTB hard 599 error message to the source. 601 For each admitted IP packet/fragment, the OMNI interface internally 602 employs the OAL when necessary by inserting a mid-layer IPv6 header 603 between the inner IP packet/fragment and any outer IP encapsulation 604 headers per [RFC2473]. (The OAL does not decrement the inner IP Hop 605 Limit/TTL during enapsulation since the insertion occurs at a layer 606 below IP forwarding.) The OAL then calculates the 32-bit CRC over 607 the entire mid-layer packet and writes the value in a trailing 608 4-octet field at the end of the packet. Next, the OAL fragments this 609 mid-layer IPv6 packet, forwards the fragments (using outer IP 610 encapsulation if necessary), and returns an internally-generated PTB 611 soft error message (subject to rate limiting) if it deems the packet 612 too large according to factors such as link performance 613 characteristics, reassembly congestion, etc. This ensures that the 614 path MTU is adaptive and reflects the current path used for a given 615 data flow. 617 The OAL operates with respect to both the minimum IPv6 and IPv4 path 618 MTUs as follows: 620 o When an OMNI interface sends a packet toward a final destination 621 via an ANET peer, it sends without OAL encapsulation if the packet 622 (including any outer-layer ANET encapsulations) is no larger than 623 the underlying interface MTU for on-link ANET peers or the minimum 624 ANET path MTU for peers separated by multiple IP hops. Otherwise, 625 the OAL inserts an IPv6 header per [RFC2473] with source address 626 set to the node's own OMNI Domain-Local Address (DLA) (see: 627 Section 8) and destination set to the OMNI DLA of the ANET peer. 628 The OAL then calculates and appends the trailing 32-bit CRC, then 629 uses IPv6 fragmentation to break the packet into a minimum number 630 of non-overlapping fragments where the largest fragment size 631 (including both the OMNI and any outer-layer ANET encapsulations) 632 is determined by the underlying interface MTU for on-link ANET 633 peers or the minimum ANET path MTU for peers separated by multiple 634 IP hops. The OAL then encapsulates the fragments in any ANET 635 headers and sends them to the ANET peer, which reassembles before 636 forwarding toward the final destination. 638 o When an OMNI interface sends a packet toward a final destination 639 via an INET interface, it sends packets (including any outer-layer 640 INET encapsulations) no larger than the minimum INET path MTU 641 without OAL encapsulation if the destination is reached via an 642 INET address within the same OMNI link segment. Otherwise, the 643 OAL inserts an IPv6 header per [RFC2473] with source address set 644 to the node's OMNI DLA, destination set to the DLA of the next hop 645 OMNI node toward the final destination and (if necessary) with a 646 Segment Routing Header with the remaining Segment IDs on the path 647 to the final destination. The OAL then calculates and appends the 648 trailing 32-bit CRC, then uses IPv6 fragmentation to break the 649 packet into a minimum number of non-overlapping fragments where 650 the largest fragment size (including both the OMNI and outer-layer 651 INET encapsulations) is the minimum INET path MTU, and the 652 smallest fragment size is no smaller than 256 bytes (i.e., 653 slightly less than half the minimum IPv4 path MTU). The OAL then 654 encapsulates the fragments in any INET headers and sends them to 655 the OMNI link neighbor, which reassembles before forwarding toward 656 the final destination. 658 The OAL unconditionally drops all OAL fragments received from an INET 659 peer that are smaller than 256 bytes (note that no minimum fragment 660 size is specified for ANET peers since the underlying ANET is secured 661 against tiny fragment attacks). In order to set the correct context 662 for reassembly, the OAL of the OMNI interface that inserts the IPv6 663 header MUST also be the one that inserts the IPv6 Fragment Header 664 Identification value. While not strictly required, sending all 665 fragments of the same fragmented OAL packet consecutively over the 666 same underlying interface with minimal inter-fragment delay may 667 increase the likelihood of successful reassembly. 669 Ordinary PTB messages with ICMPv4 header "unused" field or ICMPv6 670 header Code field value 0 are hard errors that always indicate that a 671 packet has been dropped due to a real MTU restriction. However, the 672 OAL can also forward large packets via encapsulation and 673 fragmentation while at the same time returning PTB soft error 674 messages (subject to rate limiting) indicating that a forwarded 675 packet was uncomfortably large. The OMNI interface can therefore 676 continuously forward large packets without loss while returning PTB 677 soft error messages recommending a smaller size. Original sources 678 that receive the soft errors in turn reduce the size of the packets 679 they send, i.e., the same as for hard errors. 681 The OAL sets the ICMPv4 header "unused" field or ICMPv6 header Code 682 field to the value 1 in PTB soft error messages. The OAL sets the 683 PTB destination address to the source address of the original packet, 684 and sets the source address to the MNP Subnet Router Anycast address 685 of the MN (i.e., whether the MN was the source or target of the 686 original packet). When the original source receives the PTB, it 687 reduces its path MTU estimate the same as for hard errors but does 688 not regard the message as a loss indication. (If the original source 689 does not recognize the soft error code, it regards the PTB the same 690 as a hard error but should heed the retransmission advice given in 691 [RFC8201] suggesting retransmission based on normal packetization 692 layer retransmission timers.) This document therefore updates 693 [RFC1191][RFC4443] and [RFC8201]. Furthermore, implementations of 694 [RFC4821] must be aware that PTB hard or soft errors may arrive at 695 any time even if after a successful MTU probe (this is the same 696 consideration as for an ordinary path fluctuation following a 697 successful probe). 699 In summary, the OAL supports continuous transmission and reception of 700 packets of various sizes in the face of dynamically changing network 701 conditions. Moreover, since PTB soft errors do not indicate loss, 702 original sources that receive soft errors can quickly scan for path 703 MTU increases without waiting for the minimum 10 minutes specified 704 for loss-oriented PTB hard errors [RFC1191][RFC8201]. The OAL 705 therefore provides a lossless and adaptive service that accommodates 706 MTU diversity especially well-suited for dynamic multilink 707 environments. 709 Note: In network paths where IPv6/IPv4 protocol translation or IPv6- 710 in-IPv4 encapsulation may be prevalent, it may be prudent for the OAL 711 to always assume the IPv4 minimum path MTU (i.e., 576 bytes) 712 regardless of the underlying interface IP protocol version. Always 713 assuming the IPv4 minimum path MTU even for IPv6 underlying 714 interfaces may produce more fragments and additional header overhead, 715 but will always interoperate and never run the risk of presenting an 716 IPv4 interface with a packet that exceeds its MRU. 718 Note: An OMNI interface that reassembles OAL fragments may experience 719 congestion-oriented loss in its reassembly cache and can optionally 720 send PTB soft errors to the original source and/or ICMP "Time 721 Exceeded" messages to the source of the OAL fragments. In 722 environments where the messages may contribute to unacceptable 723 additional congestion, however, the OMNI interface can simply regard 724 the loss as an ordinary unreported congestion event for which the 725 original source will eventually compensate. 727 Note: When the network layer forwards an IPv4 packet/fragment with 728 DF=0 into the OMNI interface, the interface can optionally perform 729 (further) IPv4 fragmentation before invoking the OAL so that the 730 fragments will be reassembled by the final destination. When the 731 network layer performs IPv6 fragmentation for locally-generated IPv6 732 packets, the OMNI interface typically invokes the OAL without first 733 applying (further) IPv6 fragmentation; the network layer should 734 therefore fragment to the minimum IPv6 path MTU (or smaller still) to 735 push the reassembly burden to the final destination and avoid 736 receiving PTB soft errors from the OMNI interface. Aside from these 737 non-normative guidelines, the manner in which any IP fragmentation is 738 invoked prior to OAL encapsulation/fragmentation is an implementation 739 matter. 741 Note: Inclusion of the 32-bit CRC prior to fragmentation assumes that 742 the receiving OAL will discard any packets with incorrect CRC values 743 following reassembly. The 32-bit CRC is sufficient to detect 744 reassembly misassociations for packet sizes up to the OMNI interface 745 MTU 9180 but may not be sufficient to detect errors for larger sizes 746 [CRC]. 748 Note: Some underlying interface types (e.g., VPNs) may already 749 provide their own robust fragmentation and reassembly services even 750 without OAL encapsulation. In those cases, the OAL can invoke the 751 inherent underlying interface schemes instead while employing PTB 752 soft errors in the same fashion as described above. Other underlying 753 interface properties such as header/message compression can also be 754 harnessed in a similar fashion. 756 Note: Applications can dynamically tune the size of the packets they 757 to send to produce the best possible throughput and latency, with the 758 understanding that these parameters may change over time due to 759 factors such as congestion, mobility, network path changes, etc. The 760 receipt or absence of soft errors should be seen as hints of when 761 increasing or decreasing packet sizes may be beneficial. 763 5.1. Fragmentation Security Implications 765 As discussed in Section 3.7 of [RFC8900], there are four basic 766 threats concerning IPv6 fragmentation; each of which is addressed by 767 effective mitigations as follows: 769 1. Overlapping fragment attacks - reassembly of overlapping 770 fragments is forbidden by [RFC8200]; therefore, this threat does 771 not apply to the OAL. 773 2. Resource exhaustion attacks - this threat is mitigated by 774 providing a sufficiently large OAL reassembly cache and 775 instituting "fast discard" of incomplete reassemblies that may be 776 part of a buffer exhaustion attack. The reassembly cache should 777 be sufficiently large so that a sustained attack does not cause 778 excessive loss of good reassemblies but not so large that (timer- 779 based) data structure management becomes computationally 780 expensive. The cache should also be indexed based on the arrival 781 underlying interface such that congestion experienced over a 782 first underlying interface does not cause discard of incomplete 783 reassemblies for uncongested underlying interfaces. 785 3. Attacks based on predictable fragment identification values - 786 this threat is mitigated by selecting a suitably random ID value 787 per [RFC7739]. 789 4. Evasion of Network Intrusion Detection Systems (NIDS) - this 790 threat is mitigated by disallowing "tiny fragments" per the OAL 791 fragmentation procedures specified above. 793 Additionally, IPv4 fragmentation includes a 16-bit Identification (IP 794 ID) field with only 65535 unique values such that at high data rates 795 the field could wrap and apply to new packets while the fragments of 796 old packets using the same ID are still alive in the network 797 [RFC4963]. However, since the largest OAL fragment that will be sent 798 via an IPv4 INET path is 576 bytes any IPv4 fragmentation would occur 799 only on links with an IPv4 MTU smaller than this size, and [RFC3819] 800 recommendations suggest that such links will have low data rates. 801 Since IPv6 provides a 32-bit Identification value, IP ID wraparound 802 at high data rates is not a concern for IPv6 fragmentation. 804 6. Frame Format 806 The OMNI interface transmits IPv6 packets according to the native 807 frame format of each underlying interface. For example, for 808 Ethernet-compatible interfaces the frame format is specified in 809 [RFC2464], for aeronautical radio interfaces the frame format is 810 specified in standards such as ICAO Doc 9776 (VDL Mode 2 Technical 811 Manual), for tunnels over IPv6 the frame format is specified in 812 [RFC2473], etc. 814 7. Link-Local Addresses (LLAs) 816 OMNI nodes are assigned OMNI interface IPv6 Link-Local Addresses 817 (i.e., "OMNI LLAs") through pre-service administrative actions. MN 818 OMNI LLAs embed the MNP assigned to the mobile node, while MS OMNI 819 LLAs include an administratively-unique ID that is guaranteed to be 820 unique on the link. OMNI LLAs are configured as follows: 822 o IPv6 MN OMNI LLAs encode the most-significant 64 bits of a MNP 823 within the least-significant 64 bits of the IPv6 link-local prefix 824 fe80::/64, i.e., in the LLA "interface identifier" portion. The 825 prefix length for the LLA is determined by adding 64 to the MNP 826 prefix length. For example, for the MNP 2001:db8:1000:2000::/56 827 the corresponding MN OMNI LLA is fe80::2001:db8:1000:2000/120. 829 o IPv4-compatible MN OMNI LLAs are constructed as fe80::ffff:[IPv4], 830 i.e., the interface identifier consists of 16 '0' bits, followed 831 by 16 '1' bits, followed by a 32bit IPv4 address/prefix. The 832 prefix length for the LLA is determined by adding 96 to the MNP 833 prefix length. For example, the IPv4-Compatible MN OMNI LLA for 834 192.0.2.0/24 is fe80::ffff:192.0.2.0/120 (also written as 835 fe80::ffff:c000:0200/120). 837 o MS OMNI LLAs are assigned to ARs and MSEs and MUST be managed for 838 uniqueness. The lower 32 bits of the LLA includes a unique 839 integer "MSID" value between 0x00000001 and 0xfeffffff, e.g., as 840 in fe80::1, fe80::2, fe80::3, etc., fe80::feff:ffff. The MS OMNI 841 LLA prefix length is determined by adding 96 to the MSID prefix 842 length. For example, if the MSID '0x10002000' prefix length is 16 843 then the MS OMNI LLA prefix length is set to 112 and the LLA is 844 written as fe80::1000:2000/112. The MSID 0x00000000 is the 845 "Anycast" MSID and corresponds to the link-local Subnet-Router 846 anycast address (fe80::) [RFC4291]; the MSID range 0xff000000 847 through 0xffffffff is reserved for future use. 849 o Temporary OMNI LLAs are constructed per [I-D.ietf-6man-rfc4941bis] 850 and used by MNs for the short-term purpose of procuring an actual 851 MN OMNI LLA upon startup or (re)connecting to the network. MNs 852 may use Temporary OMNI LLAs as the IPv6 source address of an RS 853 message in order to request a MN OMNI LLA from the MS. 855 Since the prefix 0000::/8 is "Reserved by the IETF" [RFC4291], no 856 MNPs can be allocated from that block ensuring that there is no 857 possibility for overlap between the various OMNI LLA constructs 858 discussed above. 860 Since MN OMNI LLAs are based on the distribution of administratively 861 assured unique MNPs, and since MS OMNI LLAs are guaranteed unique 862 through administrative assignment, OMNI interfaces set the 863 autoconfiguration variable DupAddrDetectTransmits to 0 [RFC4862]. 865 Temporary OMNI LLAs employ optimistic DAD principles [RFC4429] since 866 they are probabilistically unique and their use is short-duration in 867 nature. 869 Note: If future extensions of the IPv6 protocol permit extension of 870 the /64 boundary, the additional prefix bits of IPv6 MN OMNI LLAs 871 would be encoded in bits 16 through 63 of the LLA. (The most- 872 significant 64 bits would therefore still be in LLA bits 64-127, and 873 the remaining bits would be in bits 16 through 48 of the LLA. This 874 would permit encoding of IPv6 prefix lengths up to /112.) 876 8. Domain-Local Addresses (DLAs) 878 OMNI links use IPv6 Domain-Local Addresses (i.e., "OMNI DLAs") as the 879 source and destination addresses in OAL IPv6 encapsulation headers. 880 This document assumes availability of a prefix [DLA]::/48 for mapping 881 OMNI LLAs to routable OMNI DLAs. Since DLAs are only routable within 882 the scope of an OMNI domain, [DLA]::/48 could be taken from either an 883 IPv6 Globally Unique Address (GUA) prefix or from the IPv6 Unique 884 Local Address (ULA) prefix [RFC4193]. 886 Each OMNI link instance is identified by a value between 0x0000 and 887 0xfeff in bits 48-63 of the OMNI service prefix [DLA]::/48 (the 888 values 0xff00 through 0xfffe are reserved for future use and the 889 value 0xffff denotes a Temporary OMNI DLA). For example, OMNI DLAs 890 associated with instance 0 are configured from the prefix 891 [DLA]:0000::/64, instance 1 from [DLA]:0001::/64, instance 2 from 892 [DLA]:0002::/64, etc. OMNI DLAs and their associated prefix lengths 893 are configured in correspondence with OMNI LLAs through stateless 894 prefix translation. For example, for OMNI link instance 895 [DLA]:1010::/64: 897 o the OMNI DLA corresponding to the MN OMNI LLA fe80::2001:db8:1:2 898 with a 56-bit MNP length is derived by copying the lower 64 bits 899 of the LLA into the lower 64 bits of the DLA as 900 [DLA]:1010:2001:db8:1:2/120 (where, the DLA prefix length becomes 901 64 plus the IPv6 MNP length). 903 o the OMNI DLA corresponding to fe80::ffff:192.0.2.0 with a 28-bit 904 MNP length is derived by simply writing the LLA interface ID into 905 the lower 64 bits as [DLA]:1010:0:ffff:192.0.2.0/124 (where, the 906 DLA prefix length is 64 plus 32 plus the IPv4 MNP length). 908 o the OMNI DLA corresponding to fe80::1000/112 is simply 909 [DLA]:1010::1000/112. 911 o the OMNI DLA corresponding to fe80::/128 is simply 912 [DLA]:1010::/128. 914 o the OMNI DLA corresponding to a Temporary OMNI LLA is simply 915 [DLA]:ffff:[64-bit Temporary Interface ID]/128. 917 o etc. 919 Each OMNI interface assigns the Anycast OMNI DLA specific to the OMNI 920 link instance. For example, the OMNI interface connected to instance 921 3 assigns the Anycast OMNI DLA [DLA]:0003::/128. Routers that 922 configure OMNI interfaces advertise the OMNI service prefix (e.g., 924 [DLA]:0003::/64) into the local routing system so that applications 925 can direct traffic according to SBM requirements. 927 The OMNI DLA presents an IPv6 address format that is routable within 928 the OMNI domain routing system and can be used to convey link-scoped 929 IPv6 ND messages across multiple hops using IPv6 encapsulation 930 [RFC2473]. The OMNI link extends across one or more underling 931 Internetworks to include all ARs and MSEs. All MNs are also 932 considered to be connected to the OMNI link, however OAL 933 encapsulation is omitted over ANET links when possible to conserve 934 bandwidth (see: Section 11). 936 Each OMNI link can be subdivided into "segments" that often 937 correspond to different administrative domains or physical 938 partitions. OMNI nodes can use IPv6 Segment Routing [RFC8402] when 939 necessary to support efficient packet forwarding to destinations 940 located in other OMNI link segments. A full discussion of Segment 941 Routing over the OMNI link appears in [I-D.templin-intarea-6706bis]. 943 9. Address Mapping - Unicast 945 OMNI interfaces maintain a neighbor cache for tracking per-neighbor 946 state and use the link-local address format specified in Section 7. 947 OMNI interface IPv6 Neighbor Discovery (ND) [RFC4861] messages sent 948 over physical underlying interfaces without encapsulation observe the 949 native underlying interface Source/Target Link-Layer Address Option 950 (S/TLLAO) format (e.g., for Ethernet the S/TLLAO is specified in 951 [RFC2464]). OMNI interface IPv6 ND messages sent over underlying 952 interfaces via encapsulation do not include S/TLLAOs which were 953 intended for encoding physical L2 media address formats and not 954 encapsulation IP addresses. Furthermore, S/TLLAOs are not intended 955 for encoding additional interface attributes needed for multilink 956 coordination. Hence, this document does not define an S/TLLAO format 957 but instead defines a new option type termed the "OMNI option" 958 designed for these purposes. 960 MNs such as aircraft typically have many wireless data link types 961 (e.g. satellite-based, cellular, terrestrial, air-to-air directional, 962 etc.) with diverse performance, cost and availability properties. 963 The OMNI interface would therefore appear to have multiple L2 964 connections, and may include information for multiple underlying 965 interfaces in a single IPv6 ND message exchange. OMNI interfaces use 966 an IPv6 ND option called the OMNI option formatted as shown in 967 Figure 3: 969 0 1 2 3 970 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 1 971 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 972 | Type | Length |T| Preflen | S/T-ifIndex | 973 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 974 | | 975 ~ Sub-Options ~ 976 | | 977 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 979 Figure 3: OMNI Option Format 981 In this format: 983 o Type is set to TBD. If multiple OMNI option instances appear in 984 the same IPv6 ND message, the first instance is processed and all 985 other instances are ignored. 987 o Length is set to the number of 8 octet blocks in the option. 989 o T is a 1-bit flag set to 1 for Temporary OMNI LLAs (otherwise, set 990 to 0) and Preflen is a 7 bit field that determines the length of 991 prefix associated with an MN OMNI LLA. Values 1 through 127 992 specify a prefix length, while the value 0 indicates 993 "unspecified". For IPv6 ND messages sent from a MN to the MS, T 994 and Preflen apply to the IPv6 source LLA and provide the length 995 that the MN is requesting or asserting to the MS. For IPv6 ND 996 messages sent from the MS to the MN, T and Preflen apply to the 997 IPv6 destination LLA and indicate the length that the MS is 998 granting to the MN. For IPv6 ND messages sent between MS 999 endpoints, T is set to 0 and Preflen provides the length 1000 associated with the source/target MN that is subject of the ND 1001 message. 1003 o S/T-ifIndex corresponds to the ifIndex value for source or target 1004 underlying interface used to convey this IPv6 ND message. OMNI 1005 interfaces MUST number each distinct underlying interface with an 1006 ifIndex value between '1' and '255' that represents a MN-specific 1007 8-bit mapping for the actual ifIndex value assigned by network 1008 management [RFC2863] (the ifIndex value '0' is reserved for use by 1009 the MS). For RS and NS messages, S/T-ifIndex corresponds to the 1010 source underlying interface the message originated from. For RA 1011 and NA messages, S/T-ifIndex corresponds to the target underlying 1012 interface that the message is destined to. 1014 o Sub-Options is a Variable-length field, of length such that the 1015 complete OMNI Option is an integer multiple of 8 octets long. 1016 Contains one or more Sub-Options, as described in Section 9.1. 1018 9.1. Sub-Options 1020 The OMNI option includes zero or more Sub-Options. Each consecutive 1021 Sub-Option is concatenated immediately after its predecessor. All 1022 Sub-Options except Pad1 (see below) are in type-length-value (TLV) 1023 encoded in the following format: 1025 0 1 2 1026 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 1027 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1028 | Sub-Type | Sub-length | Sub-Option Data ... 1029 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1031 Figure 4: Sub-Option Format 1033 o Sub-Type is a 1-octet field that encodes the Sub-Option type. 1034 Sub-Options defined in this document are: 1036 Option Name Sub-Type 1037 Pad1 0 1038 PadN 1 1039 Interface Attributes 2 1040 Traffic Selector 3 1041 MS-Register 4 1042 MS-Release 5 1043 Network Access Identifier 6 1044 Geo Coordinates 7 1045 DHCP Unique Identifier (DUID) 8 1046 DHCPv6 Message 9 1048 Figure 5 1050 Sub-Types 253 and 254 are reserved for experimentation, as 1051 recommended in [RFC3692]. 1053 o Sub-Length is a 1-octet field that encodes the length of the Sub- 1054 Option Data (i.e., ranging from 0 to 255 octets). 1056 o Sub-Option Data is a block of data with format determined by Sub- 1057 Type. 1059 During processing, unrecognized Sub-Options are ignored and the next 1060 Sub-Option processed until the end of the OMNI option is reached. 1062 The following Sub-Option types and formats are defined in this 1063 document: 1065 9.1.1. Pad1 1067 0 1068 0 1 2 3 4 5 6 7 1069 +-+-+-+-+-+-+-+-+ 1070 | Sub-Type=0 | 1071 +-+-+-+-+-+-+-+-+ 1073 Figure 6: Pad1 1075 o Sub-Type is set to 0. If multiple instances appear in the same 1076 OMNI option all are processed. 1078 o No Sub-Length or Sub-Option Data follows (i.e., the "Sub-Option" 1079 consists of a single zero octet). 1081 9.1.2. PadN 1083 0 1 2 1084 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 1085 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1086 | Sub-Type=1 | Sub-length=N | N padding octets ... 1087 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1089 Figure 7: PadN 1091 o Sub-Type is set to 1. If multiple instances appear in the same 1092 OMNI option all are processed. 1094 o Sub-Length is set to N (from 0 to 255) being the number of padding 1095 octets that follow. 1097 o Sub-Option Data consists of N zero-valued octets. 1099 9.1.3. Interface Attributes 1101 The Interface Attributes sub-option provides L2 forwarding 1102 information for the multilink conceptual sending algorithm discussed 1103 in Section 11. The L2 information is used for selecting among 1104 potentially multiple candidate underlying interfaces that can be used 1105 to forward packets to the neighbor based on factors such as DSCP 1106 preferences and link quality. Interface Attributes further include 1107 link-layer address information to be used for either OAL 1108 encapsulation or direct UDP/IP encapsulation (when OAL encapsulation 1109 can be avoided). The Interface Attributes format and contents are 1110 given in Figure 8 below: 1112 0 1 2 3 1113 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 1114 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1115 | Sub-Type=2 | Sub-length=N | ifIndex | ifType | 1116 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1117 | Provider ID | Link |R| API | SRT | FMT | LHS (0 - 7) | 1118 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1119 | LHS (bits 8 - 31) | ~ 1120 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ 1121 ~ ~ 1122 ~ Link Layer Address (L2ADDR) ~ 1123 ~ ~ 1124 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1125 | Bitmap(0)=0xff|P00|P01|P02|P03|P04|P05|P06|P07|P08|P09|P10|P11| 1126 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1127 |P12|P13|P14|P15|P16|P17|P18|P19|P20|P21|P22|P23|P24|P25|P26|P27| 1128 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1129 |P28|P29|P30|P31| Bitmap(1)=0xff|P32|P33|P34|P35|P36| ... 1130 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1132 Figure 8: Interface Attributes 1134 o Sub-Type is set to 2. If multiple instances with different 1135 ifIndex values appear in the same OMNI option all are processed; 1136 if multiple instances with the same ifIndex value appear, the 1137 first is processed and all others are ignored. 1139 o Sub-Length is set to N (from 4 to 255) that encodes the number of 1140 Sub-Option Data octets that follow. 1142 o Sub-Option Data contains an "Interface Attribute" option encoded 1143 as follows (note that the first four octets must be present): 1145 * ifIndex is set to an 8-bit integer value corresponding to a 1146 specific underlying interface the same as specified above for 1147 the OMNI option header S/T-ifIndex. An OMNI option may include 1148 multiple Interface Attributes Sub-Options, with each distinct 1149 ifIndex value pertaining to a different underlying interface. 1150 The OMNI option will often include an Interface Attributes Sub- 1151 Option with the same ifIndex value that appears in the S/ 1152 T-ifIndex. In that case, the actual encapsulation address of 1153 the received IPv6 ND message should be compared with the L2ADDR 1154 encoded in the Sub-Option (see below); if the addresses are 1155 different (or, if L2ADDR absent) the presence of a Network 1156 Address Translator (NAT) is indicated. 1158 * ifType is set to an 8-bit integer value corresponding to the 1159 underlying interface identified by ifIndex. The value 1160 represents an OMNI interface-specific 8-bit mapping for the 1161 actual IANA ifType value registered in the 'IANAifType-MIB' 1162 registry [http://www.iana.org]. 1164 * Provider ID is set to an OMNI interface-specific 8-bit ID value 1165 for the network service provider associated with this ifIndex. 1167 * Link encodes a 4-bit link metric. The value '0' means the link 1168 is DOWN, and the remaining values mean the link is UP with 1169 metric ranging from '1' ("lowest") to '15' ("highest"). 1171 * R is reserved for future use. 1173 * API - a 3-bit "Address/Preferences/Indexed" code that 1174 determines the contents of the remainder of the sub-option as 1175 follows: 1177 + When the most significant bit (i.e., "Address") is set to 1, 1178 the SRT, FMT, LHS and L2ADDR fields are included immediately 1179 following the API code; else, they are omitted. 1181 + When the next most significant bit (i.e., "Preferences") is 1182 set to 1, a preferences block is included next; else, it is 1183 omitted. (Note that if "Address" is set the preferences 1184 block immediately follows L2ADDR; else, it immediately 1185 follows the API code.) 1187 + When a preferences block is present and the least 1188 significant bit (i.e., "Indexed") is set to 0, the block is 1189 encoded in "Simplex" form as shown in Figure 8; else it is 1190 encoded in "Indexed" form as discussed below. 1192 * When API indicates that an "Address" is included, the following 1193 fields appear in consecutive order (else, they are omitted): 1195 + SRT - a 5-bit Segment Routing Topology prefix length value 1196 that (when added to 96) determines the prefix length to 1197 apply to the DLA formed from concatenating fe*::/96 with the 1198 32 bit LHS MSID value that follows. For example, the value 1199 16 corresponds to the prefix length 112. 1201 + FMT - a 3-bit "Framework/Mode/Type" code corresponding to 1202 the included Link Layer Address as follows: 1204 - When the most significant bit (i.e., "Framework") is set 1205 to 0, L2ADDR is the INET encapsulation address of a 1206 Proxy/Server; otherwise, it is the address for the 1207 Source/Target itself 1209 - When the next most significant bit (i.e., "Mode") is set 1210 to 0, the Source/Target L2ADDR is on the open INET; 1211 otherwise, it is (likely) located behind a Network 1212 Address Translator (NAT). 1214 - When the least significant bit (i.e., "Type") is set to 1215 0, L2ADDR includes a UDP Port Number followed by an IPv4 1216 address; else, a UDP Port Number followed by an IPv6 1217 address. 1219 + LHS - the 32 bit MSID of the Last Hop Server/Proxy on the 1220 path to the target. When SRT and LHS are both set to 0, the 1221 LHS is considered unspecified in this IPv6 ND message. When 1222 SRT is set to 0 and LHS is non-zero, the prefix length is 1223 set to 128. SRT and LHS provide guidance to the OMNI 1224 interface forwarding algorithm. Specifically, if SRT/LHS is 1225 located in the local OMNI link segment then the OMNI 1226 interface can encapsulate according to FMT/L2ADDR; else, it 1227 must forward according to the OMNI link spanning tree. See 1228 [I-D.templin-intarea-6706bis] for further discussion. 1230 + Link Layer Address (L2ADDR) - Formatted according to FMT, 1231 and identifies the link-layer address (i.e., the 1232 encapsulation address) of the source/target. The UDP Port 1233 Number appears in the first two octets and the IP address 1234 appears in the next 4 octets for IPv4 or 16 octets for IPv6. 1235 The Port Number and IP address are recorded in ones- 1236 compliment "obfuscated" form per [RFC4380]. The OMNI 1237 interface forwarding algorithm uses FMT/L2ADDR to determine 1238 the encapsulation address for forwarding when SRT/LHS is 1239 located in the local OMNI link segment. 1241 * When API indicates that "Preferences" are included, a 1242 preferences block appears as the remainder of the Sub-Option as 1243 a series of Bitmaps and P[*] values. In "Simplex" form, the 1244 index for each singleton Bitmap octet is inferred from its 1245 sequential position (i.e., 0, 1, 2, ...) as shown in Figure 8. 1246 In "Indexed" form, each Bitmap is preceded by an Index octet 1247 that encodes a value "i" = (0 - 255) as the index for its 1248 companion Bitmap as follows: 1250 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1251 | Index=i | Bitmap(i) |P[*] values ... 1252 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1254 Figure 9 1256 * The preferences consist of a first (simplex/indexed) Bitmap 1257 (i.e., "Bitmap(i)") followed by 0-8 single-octet blocks of 1258 2-bit P[*] values, followed by a second Bitmap (i), followed by 1259 0-8 blocks of P[*] values, etc. Reading from bit 0 to bit 7, 1260 the bits of each Bitmap(i) that are set to '1'' indicate the 1261 P[*] blocks from the range P[(i*32)] through P[(i*32) + 31] 1262 that follow; if any Bitmap(i) bits are '0', then the 1263 corresponding P[*] block is instead omitted. For example, if 1264 Bitmap(0) contains 0xff then the block with P[00]-P[03], 1265 followed by the block with P[04]-P[07], etc., and ending with 1266 the block with P[28]-P[31] are included (as shown in Figure 8). 1267 The next Bitmap(i) is then consulted with its bits indicating 1268 which P[*] blocks follow, etc. out to the end of the Sub- 1269 Option. 1271 * Each 2-bit P[*] field is set to the value '0' ("disabled"), '1' 1272 ("low"), '2' ("medium") or '3' ("high") to indicate a QoS 1273 preference for underlying interface selection purposes. Not 1274 all P[*] values need to be included in the OMNI option of each 1275 IPv6 ND message received. Any P[*] values represented in an 1276 earlier OMNI option but omitted in the current OMNI option 1277 remain unchanged. Any P[*] values not yet represented in any 1278 OMNI option default to "medium". 1280 * The first 16 P[*] blocks correspond to the 64 Differentiated 1281 Service Code Point (DSCP) values P[00] - P[63] [RFC2474]. Any 1282 additional P[*] blocks that follow correspond to "pseudo-DSCP" 1283 traffic classifier values P[64], P[65], P[66], etc. See 1284 Appendix A for further discussion and examples. 1286 9.1.4. Traffic Selector 1288 0 1 2 3 1289 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 1290 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1291 | Sub-Type=3 | Sub-length=N | ifIndex | ~ 1292 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ 1293 ~ ~ 1294 ~ RFC 6088 Format Traffic Selector ~ 1295 ~ ~ 1296 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1298 Figure 10: Traffic Selector 1300 o Sub-Type is set to 3. If multiple instances appear in the same 1301 OMNI option all are processed, i.e., even if the same ifIndex 1302 value appears multiple times. 1304 o Sub-Length is set to N (the number of Sub-Option Data octets that 1305 follow). 1307 o Sub-Option Data contains a 1-octet ifIndex encoded exactly as 1308 specified in Section 9.1.3, followed by an N-1 octet traffic 1309 selector formatted per [RFC6088] beginning with the "TS Format" 1310 field. The largest traffic selector for a given ifIndex is 1311 therefore 254 octets. 1313 9.1.5. MS-Register 1315 0 1 2 3 1316 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 1317 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1318 | Sub-Type=4 | Sub-length=4n | MSID[1] (bits 0 - 15) | 1319 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1320 | MSID [1] (bits 16 - 32) | MSID[2] (bits 0 - 15) | 1321 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1322 | MSID [2] (bits 16 - 32) | MSID[3] (bits 0 - 15) | 1323 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1324 ... ... ... ... ... ... 1325 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1326 | MSID [n] (bits 16 - 32) | 1327 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1329 Figure 11: MS-Register Sub-option 1331 o Sub-Type is set to 4. If multiple instances appear in the same 1332 OMNI option all are processed. Only the first MAX_MSID values 1333 processed (whether in a single instance or multiple) are retained 1334 and all other MSIDs are ignored. 1336 o Sub-Length is set to 4n. 1338 o A list of n 4-octet MSIDs is included in the following 4n octets. 1339 The Anycast MSID value '0' in an RS message MS-Register sub-option 1340 requests the recipient to return the MSID of a nearby MSE in a 1341 corresponding RA response. 1343 9.1.6. MS-Release 1344 0 1 2 3 1345 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 1346 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1347 | Sub-Type=5 | Sub-length=4n | MSID[1] (bits 0 - 15) | 1348 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1349 | MSID [1] (bits 16 - 32) | MSID[2] (bits 0 - 15) | 1350 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1351 | MSID [2] (bits 16 - 32) | MSID[3] (bits 0 - 15) | 1352 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1353 ... ... ... ... ... ... 1354 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1355 | MSID [n] (bits 16 - 32) | 1356 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1358 Figure 12: MS-Release Sub-option 1360 o Sub-Type is set to 5. If multiple instances appear in the same 1361 IPv6 OMNI option all are processed. Only the first MAX_MSID 1362 values processed (whether in a single instance or multiple) are 1363 retained and all other MSIDs are ignored. 1365 o Sub-Length is set to 4n. 1367 o A list of n 4 octet MSIDs is included in the following 4n octets. 1368 The Anycast MSID value '0' is ignored in MS-Release sub-options, 1369 i.e., only non-zero values are processed. 1371 9.1.7. Network Access Identifier (NAI) 1373 0 1 2 3 1374 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 1375 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1376 | Sub-Type=6 | Sub-length=N |Network Access Identifier (NAI) 1377 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... 1379 Figure 13: Network Access Identifier (NAI) Sub-option 1381 o Sub-Type is set to 6. If multiple instances appear in the same 1382 OMNI option the first is processed and all others are ignored. 1384 o Sub-Length is set to N. 1386 o A Network Access Identifier (NAI) up to 255 octets in length is 1387 coded per [RFC7542]. 1389 9.1.8. Geo Coordinates 1391 0 1 2 3 1392 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 1393 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1394 | Sub-Type=7 | Sub-length=N | Geo Coordinates 1395 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... 1397 Figure 14: Geo Coordinates Sub-option 1399 o Sub-Type is set to 7. If multiple instances appear in the same 1400 OMNI option the first is processed and all others are ignored. 1402 o Sub-Length is set to N. 1404 o A set of Geo Coordinates up to 255 octets in length (format TBD). 1405 Includes Latitude/Longitude at a minimum; may also include 1406 additional attributes such as altitude, heading, speed, etc.). 1408 9.1.9. DHCP Unique Identifier (DUID) 1410 0 1 2 3 1411 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 1412 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1413 | Sub-Type=8 | Sub-length=N | DUID-Type | 1414 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1415 . . 1416 . type-specific DUID body (variable length) . 1417 . . 1418 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1420 Figure 15: DHCP Unique Identifier (DUID) Sub-option 1422 o Sub-Type is set to 8. If multiple instances appear in the same 1423 OMNI option the first is processed and all others are ignored. 1425 o Sub-Length is set to N (i.e., the length of the option beginning 1426 with the DUID-Type and continuing to the end of the type-specific 1427 body). 1429 o DUID-Type is a two-octet field coded in network byte order that 1430 determines the format and contents of the type-specific body 1431 according to Section 11 of [RFC8415]. DUID-Type 4 in particular 1432 corresponds to the Universally Unique Identifier (UUID) [RFC6355] 1433 which will occur in common operational practice. 1435 o A type-specific DUID body up to 253 octets in length follows, 1436 formatted according to DUID-type. For example, for type 4 the 1437 body consists of a 128-bit UUID selected according to [RFC6355]. 1439 9.1.10. DHCPv6 Message 1441 0 1 2 3 1442 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 1443 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1444 | Sub-Type=9 | Sub-length=N | msg-type | id (octet 0) | 1445 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1446 | transaction-id (octets 1-2) | | 1447 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 1448 | | 1449 . DHCPv6 options . 1450 . (variable number and length) . 1451 | | 1452 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1454 Figure 16: DHCPv6 Message Sub-option 1456 o Sub-Type is set to 9. If multiple instances appear in the same 1457 OMNI option the first is processed and all others are ignored. 1459 o Sub-Length is set to N (i.e., the length of the DHCPv6 message 1460 beginning with 'msg-type' and continuing to the end of the DHCPv6 1461 options). The length of the entire DHCPv6 message is therefore 1462 restricted to 255 octets. 1464 o 'msg-type' and 'transaction-id' are coded according to Section 8 1465 of [RFC8415]. 1467 o A set of DHCPv6 options coded according to Section 21 of [RFC8415] 1468 follows. 1470 10. Address Mapping - Multicast 1472 The multicast address mapping of the native underlying interface 1473 applies. The mobile router on board the MN also serves as an IGMP/ 1474 MLD Proxy for its EUNs and/or hosted applications per [RFC4605] while 1475 using the L2 address of the AR as the L2 address for all multicast 1476 packets. 1478 The MN uses Multicast Listener Discovery (MLDv2) [RFC3810] to 1479 coordinate with the AR, and ANET L2 elements use MLD snooping 1480 [RFC4541]. 1482 11. Multilink Conceptual Sending Algorithm 1484 The MN's IPv6 layer selects the outbound OMNI interface according to 1485 SBM considerations when forwarding data packets from local or EUN 1486 applications to external correspondents. Each OMNI interface 1487 maintains a neighbor cache the same as for any IPv6 interface, but 1488 with additional state for multilink coordination. Each OMNI 1489 interface maintains default routes via ARs discovered as discussed in 1490 Section 12, and may configure more-specific routes discovered through 1491 means outside the scope of this specification. 1493 After a packet enters the OMNI interface, one or more outbound 1494 underlying interfaces are selected based on PBM traffic attributes, 1495 and one or more neighbor underlying interfaces are selected based on 1496 the receipt of Interface Attributes sub-options in IPv6 ND messages 1497 (see: Figure 8). Underlying interface selection for the nodes own 1498 local interfaces are based on attributes such as DSCP, application 1499 port number, cost, performance, message size, etc. OMNI interface 1500 multilink selections could also be configured to perform replication 1501 across multiple underlying interfaces for increased reliability at 1502 the expense of packet duplication. The set of all Interface 1503 Attributes received in IPv6 ND messages determine the multilink 1504 forwarding profile for selecting the neighbor's underlying 1505 interfaces. 1507 When the OMNI interface sends a packet over a selected outbound 1508 underlying interface, the OAL includes or omits a mid-layer 1509 encapsulation header as necessary as discussed in Section 5 and as 1510 determined by the L2 address information received in Interface 1511 Attributes. The OAL also performs encapsulation when the nearest AR 1512 is located multiple hops away as discussed in Section 12.1. 1514 OMNI interface multilink service designers MUST observe the BCP 1515 guidance in Section 15 [RFC3819] in terms of implications for 1516 reordering when packets from the same flow may be spread across 1517 multiple underlying interfaces having diverse properties. 1519 11.1. Multiple OMNI Interfaces 1521 MNs may connect to multiple independent OMNI links concurrently in 1522 support of SBM. Each OMNI interface is distinguished by its Anycast 1523 OMNI DLA (e.g., [DLA]:0002::, [DLA]:1000::, [DLA]:7345::, etc.). The 1524 MN configures a separate OMNI interface for each link so that 1525 multiple interfaces (e.g., omni0, omni1, omni2, etc.) are exposed to 1526 the IPv6 layer. A different Anycast OMNI DLA is assigned to each 1527 interface, and the MN injects the service prefixes for the OMNI link 1528 instances into the EUN routing system. 1530 Applications in EUNs can use Segment Routing to select the desired 1531 OMNI interface based on SBM considerations. The Anycast OMNI DLA is 1532 written into the IPv6 destination address, and the actual destination 1533 (along with any additional intermediate hops) is written into the 1534 Segment Routing Header. Standard IP routing directs the packets to 1535 the MN's mobile router entity, and the Anycast OMNI DLA identifies 1536 the OMNI interface to be used for transmission to the next hop. When 1537 the MN receives the message, it replaces the IPv6 destination address 1538 with the next hop found in the routing header and transmits the 1539 message over the OMNI interface identified by the Anycast OMNI DLA. 1541 Multiple distinct OMNI links can therefore be used to support fault 1542 tolerance, load balancing, reliability, etc. The architectural model 1543 is similar to Layer 2 Virtual Local Area Networks (VLANs). 1545 11.2. MN<->AR Traffic Loop Prevention 1547 After an AR has registered an MNP for a MN (see: Section 12), the AR 1548 will forward packets destined to an address within the MNP to the MN. 1549 The MN will under normal circumstances then forward the packet to the 1550 correct destination within its internal networks. 1552 If at some later time the MN loses state (e.g., after a reboot), it 1553 may begin returning packets destined to an MNP address to the AR as 1554 its default router. The AR therefore must drop any packets 1555 originating from the MN and destined to an address within the MN's 1556 registered MNP. To do so, the AR institutes the following check: 1558 o if the IP destination address belongs to a neighbor on the same 1559 OMNI interface, and if the link-layer source address is the same 1560 as one of the neighbor's link-layer addresses, drop the packet. 1562 12. Router Discovery and Prefix Registration 1564 MNs interface with the MS by sending RS messages with OMNI options 1565 under the assumption that one or more AR on the ANET will process the 1566 message and respond. The MN then configures default routes for the 1567 OMNI interface via the discovered ARs as the next hop. The manner in 1568 which the ANET ensures AR coordination is link-specific and outside 1569 the scope of this document (however, considerations for ANETs that do 1570 not provide ARs that recognize the OMNI option are discussed in 1571 Section 17). 1573 For each underlying interface, the MN sends an RS message with an 1574 OMNI option to coordinate with MSEs identified by MSID values. 1575 Example MSID discovery methods are given in [RFC5214] and include 1576 data link login parameters, name service lookups, static 1577 configuration, a static "hosts" file, etc. The MN can also send an 1578 RS with an MS-Register suboption that includes the Anycast MSID value 1579 '0', i.e., instead of or in addition to any non-zero MSIDs. When the 1580 AR receives an RS with a MSID '0', it selects a nearby MSE (which may 1581 be itself) and returns an RA with the selected MSID in an MS-Register 1582 suboption. The AR selects only a single wildcard MSE (i.e., even if 1583 the RS MS-Register suboption included multiple '0' MSIDs) while also 1584 soliciting the MSEs corresponding to any non-zero MSIDs. 1586 MNs configure OMNI interfaces that observe the properties discussed 1587 in the previous section. The OMNI interface and its underlying 1588 interfaces are said to be in either the "UP" or "DOWN" state 1589 according to administrative actions in conjunction with the interface 1590 connectivity status. An OMNI interface transitions to UP or DOWN 1591 through administrative action and/or through state transitions of the 1592 underlying interfaces. When a first underlying interface transitions 1593 to UP, the OMNI interface also transitions to UP. When all 1594 underlying interfaces transition to DOWN, the OMNI interface also 1595 transitions to DOWN. 1597 When an OMNI interface transitions to UP, the MN sends RS messages to 1598 register its MNP and an initial set of underlying interfaces that are 1599 also UP. The MN sends additional RS messages to refresh lifetimes 1600 and to register/deregister underlying interfaces as they transition 1601 to UP or DOWN. The MN sends initial RS messages over an UP 1602 underlying interface with its MN OMNI LLA as the source and with 1603 destination set to All-Routers multicast (ff02::2) [RFC4291]. The RS 1604 messages include an OMNI option per Section 9 with a Preflen 1605 assertion, Interface Attributes appropriate for underlying 1606 interfaces, MS-Register/Release sub-options containing MSID values, 1607 and with any other necessary OMNI sub-options (e.g., a DUID suboption 1608 as an identity for the MN). The S/T-ifIndex field is set to the 1609 index of the underlying interface over which the RS message is sent. 1611 ARs process IPv6 ND messages with OMNI options and act as an MSE 1612 themselves and/or as a proxy for other MSEs. ARs receive RS messages 1613 and create a neighbor cache entry for the MN, then coordinate with 1614 any MSEs named in the Register/Release lists in a manner outside the 1615 scope of this document. When an MSE processes the OMNI information, 1616 it first validates the prefix registration information then injects/ 1617 withdraws the MNP in the routing/mapping system and caches/discards 1618 the new Preflen, MNP and Interface Attributes. The MSE then informs 1619 the AR of registration success/failure, and the AR returns an RA 1620 message to the MN with an OMNI option per Section 9. 1622 The AR returns the RA message via the same underlying interface of 1623 the MN over which the RS was received, and with destination address 1624 set to the MN OMNI LLA (i.e., unicast), with source address set to 1625 its own OMNI LLA, and with an OMNI option with S/T-ifIndex set to the 1626 value included in the RS. The OMNI option also includes a Preflen 1627 confirmation, Interface Attributes, MS-Register/Release and any other 1628 necessary OMNI sub-options (e.g., a DUID suboption as an identity for 1629 the AR). The RA also includes any information for the link, 1630 including RA Cur Hop Limit, M and O flags, Router Lifetime, Reachable 1631 Time and Retrans Timer values, and includes any necessary options 1632 such as: 1634 o PIOs with (A; L=0) that include MSPs for the link [RFC8028]. 1636 o RIOs [RFC4191] with more-specific routes. 1638 o an MTU option that specifies the maximum acceptable packet size 1639 for this ANET interface. 1641 The AR MAY also send periodic and/or event-driven unsolicited RA 1642 messages per [RFC4861]. In that case, the S/T-ifIndex field in the 1643 OMNI header of the unsolicited RA message identifies the target 1644 underlying interface of the destination MN. 1646 The AR can combine the information from multiple MSEs into one or 1647 more "aggregate" RAs sent to the MN in order conserve ANET bandwidth. 1648 Each aggregate RA includes an OMNI option with MS-Register/Release 1649 sub-options with the MSEs represented by the aggregate. If an 1650 aggregate is sent, the RA message contents must consistently 1651 represent the combined information advertised by all represented 1652 MSEs. Note that since the AR uses its own OMNI LLA as the RA source 1653 address, the MN determines the addresses of the represented MSEs by 1654 examining the MS-Register/Release OMNI sub-options. 1656 When the MN receives the RA message, it creates an OMNI interface 1657 neighbor cache entry for each MSID that has confirmed MNP 1658 registration via the L2 address of this AR. If the MN connects to 1659 multiple ANETs, it records the additional L2 AR addresses in each 1660 MSID neighbor cache entry (i.e., as multilink neighbors). The MN 1661 then configures a default route via the MSE that returned the RA 1662 message, and assigns the Subnet Router Anycast address corresponding 1663 to the MNP (e.g., 2001:db8:1:2::) to the OMNI interface. The MN then 1664 manages its underlying interfaces according to their states as 1665 follows: 1667 o When an underlying interface transitions to UP, the MN sends an RS 1668 over the underlying interface with an OMNI option. The OMNI 1669 option contains at least one Interface Attribute sub-option with 1670 values specific to this underlying interface, and may contain 1671 additional Interface Attributes specific to other underlying 1672 interfaces. The option also includes any MS-Register/Release sub- 1673 options. 1675 o When an underlying interface transitions to DOWN, the MN sends an 1676 RS or unsolicited NA message over any UP underlying interface with 1677 an OMNI option containing an Interface Attribute sub-option for 1678 the DOWN underlying interface with Link set to '0'. The MN sends 1679 an RS when an acknowledgement is required, or an unsolicited NA 1680 when reliability is not thought to be a concern (e.g., if 1681 redundant transmissions are sent on multiple underlying 1682 interfaces). 1684 o When the Router Lifetime for a specific AR nears expiration, the 1685 MN sends an RS over the underlying interface to receive a fresh 1686 RA. If no RA is received, the MN can send RS messages to an 1687 alternate MSID in case the current MSID has failed. If no RS 1688 messages are received even after trying to contact alternate 1689 MSIDs, the MN marks the underlying interface as DOWN. 1691 o When a MN wishes to release from one or more current MSIDs, it 1692 sends an RS or unsolicited NA message over any UP underlying 1693 interfaces with an OMNI option with a Release MSID. Each MSID 1694 then withdraws the MNP from the routing/mapping system and informs 1695 the AR that the release was successful. 1697 o When all of a MNs underlying interfaces have transitioned to DOWN 1698 (or if the prefix registration lifetime expires), any associated 1699 MSEs withdraw the MNP the same as if they had received a message 1700 with a release indication. 1702 The MN is responsible for retrying each RS exchange up to 1703 MAX_RTR_SOLICITATIONS times separated by RTR_SOLICITATION_INTERVAL 1704 seconds until an RA is received. If no RA is received over an UP 1705 underlying interface (i.e., even after attempting to contact 1706 alternate MSEs), the MN declares this underlying interface as DOWN. 1708 The IPv6 layer sees the OMNI interface as an ordinary IPv6 interface. 1709 Therefore, when the IPv6 layer sends an RS message the OMNI interface 1710 returns an internally-generated RA message as though the message 1711 originated from an IPv6 router. The internally-generated RA message 1712 contains configuration information that is consistent with the 1713 information received from the RAs generated by the MS. Whether the 1714 OMNI interface IPv6 ND messaging process is initiated from the 1715 receipt of an RS message from the IPv6 layer is an implementation 1716 matter. Some implementations may elect to defer the IPv6 ND 1717 messaging process until an RS is received from the IPv6 layer, while 1718 others may elect to initiate the process proactively. Still other 1719 deployments may elect to administratively disable the ordinary RS/RA 1720 messaging used by the IPv6 layer over the OMNI interface, since they 1721 are not required to drive the internal RS/RA processing. (Note that 1722 this same logic applies to IPv4 implementations that employ ICMP- 1723 based Router Discovery per [RFC1256].) 1725 Note: The Router Lifetime value in RA messages indicates the time 1726 before which the MN must send another RS message over this underlying 1727 interface (e.g., 600 seconds), however that timescale may be 1728 significantly longer than the lifetime the MS has committed to retain 1729 the prefix registration (e.g., REACHABLETIME seconds). ARs are 1730 therefore responsible for keeping MS state alive on a shorter 1731 timescale than the MN is required to do on its own behalf. 1733 Note: On multicast-capable underlying interfaces, MNs should send 1734 periodic unsolicited multicast NA messages and ARs should send 1735 periodic unsolicited multicast RA messages as "beacons" that can be 1736 heard by other nodes on the link. If a node fails to receive a 1737 beacon after a timeout value specific to the link, it can initiate a 1738 unicast exchange to test reachability. 1740 Note: if an AR acting as a proxy forwards a MN's RS message to 1741 another node acting as an MSE using UDP/IP encapsulation, it must use 1742 a distinct UDP source port number for each MN. This allows the MSE 1743 to distinguish different MNs behind the same AR at the link-layer, 1744 whereas the link-layer addresses would otherwise be 1745 indistinguishable. 1747 12.1. Router Discovery in IP Multihop and IPv4-Only Access Networks 1749 On some ANET types a MN may be located multiple IP hops away from the 1750 nearest AR. Forwarding through IP multihop ANETs is conducted 1751 through the application of a routing protocol (e.g., a Mobile Ad-hoc 1752 Network (MANET) routing protocol over omni-directional wireless 1753 interfaces, an inter-domain routing protocol in an enterprise 1754 network, etc.). These ANETs could be either IPv6-enabled or 1755 IPv4-only, while IPv4-only ANETs could be either multicast-capable or 1756 unicast-only (note that for IPv4-only ANETs the following procedures 1757 apply for both single-hop and multihop cases). 1759 A MN located potentially multiple ANET hops away from the nearest AR 1760 prepares an RS message with source address set to either its MN OMNI 1761 LLA or a Temporary OMNI LLA, and with destination set to link-scoped 1762 All-Routers multicast the same as discussed above. For IPv6-enabled 1763 ANETs, the MN then encapsulates the message in an IPv6 header with 1764 source address set to the DLA corresponding to the LLA source address 1765 and with destination set to either a unicast or anycast DLA. For 1766 IPv4-only ANETs, the MN instead encapsulates the RS message in an 1767 IPv4 header with source address set to the node's own IPv4 address 1768 and with destination address set to either the unicast IPv4 address 1769 of an AR [RFC5214] or an IPv4 anycast address reserved for OMNI. The 1770 MN then sends the encapsulated RS message via the ANET interface, 1771 where it will be forwarded by zero or more intermediate ANET hops. 1773 When an intermediate ANET hop that participates in the routing 1774 protocol receives the encapsulated RS, it forwards the message 1775 according to its routing tables (note that an intermediate node could 1776 be a fixed infrastructure element or another MN). This process 1777 repeats iteratively until the RS message is received by a penultimate 1778 ANET hop within single-hop communications range of an AR, which 1779 forwards the message to the AR. 1781 When the AR receives the message, it decapsulates the RS and 1782 coordinates with the MS the same as for an ordinary link-local RS, 1783 since the inner Hop Limit will not have been decremented by the 1784 multihop forwarding process. The AR then prepares an RA message with 1785 source address set to its own LLA and destination address set to the 1786 LLA of the original MN, then encapsulates the message in an IPv4/IPv6 1787 header with source address set to its own IPv4/DLA address and with 1788 destination set to the encapsulation source of the RS. 1790 The AR then forwards the message to an ANET node within 1791 communications range, which forwards the message according to its 1792 routing tables to an intermediate node. The multihop forwarding 1793 process within the ANET continues repetitively until the message is 1794 delivered to the original MN, which decapsulates the message and 1795 performs autoconfiguration the same as if it had received the RA 1796 directly from the AR as an on-link neighbor. 1798 Note: An alternate approach to multihop forwarding via IPv6 1799 encapsulation would be to statelessly translate the IPv6 LLAs into 1800 DLAs and forward the messages without encapsulation. This would 1801 violate the [RFC4861] requirement that certain IPv6 ND messages must 1802 use link-local addresses and must not be accepted if received with 1803 Hop Limit less than 255. This document therefore advocates 1804 encapsulation since the overhead is nominal considering the 1805 infrequent nature and small size of IPv6 ND messages. Future 1806 documents may consider encapsulation avoidance through translation 1807 while updating [RFC4861]. 1809 Note: An alternate approach to multihop forwarding via IPv4 1810 encapsulation would be to employ IPv6/IPv4 protocol translation. 1811 However, for IPv6 ND messages the OMNI LLA addresses would be 1812 truncated due to translation and the OMNI Router and Prefix Discovery 1813 services would not be able to function. The use of IPv4 1814 encapsulation is therefore indicated. 1816 Note: An IPv4 anycast address for OMNI in IPv4 networks could be part 1817 of a new IPv4 /24 prefix allocation, but this may be difficult to 1818 obtain given IPv4 address exhaustion. An alternative would be to re- 1819 purpose the prefix 192.88.99.0 which has been set aside from its 1820 former use by [RFC7526]. 1822 12.2. MS-Register and MS-Release List Processing 1824 When a MN sends an RS message with an OMNI option via an underlying 1825 interface to an AR, the MN must convey its knowledge of its 1826 currently-associated MSEs. Initially, the MN will have no associated 1827 MSEs and should therefore include an MS-Register sub-option with the 1828 single MSID value 0 which requests the AR to select and assign an 1829 MSE. The AR will then return an RA message with source address set 1830 to the OMNI LLA containing the MSE of the selected MSE. 1832 As the MN activates additional underlying interfaces, it can 1833 optionally include an MS-Register sub-option with MSID value 0, or 1834 with non-zero MSIDs for MSEs discovered from previous RS/RA 1835 exchanges. The MN will thus eventually begin to learn and manage its 1836 currently active set of MSEs, and can register with new MSEs or 1837 release from former MSEs with each successive RS/RA exchange. As the 1838 MN's MSE constituency grows, it alone is responsible for including or 1839 omitting MSIDs in the MS-Register/Release lists it sends in RS 1840 messages. The inclusion or omission of MSIDs determines the MN's 1841 interface to the MS and defines the manner in which MSEs will 1842 respond. The only limiting factor is that the MN should include no 1843 more than MAX_MSID values in each list per each IPv6 ND message, and 1844 should avoid duplication of entries in each list unless it wants to 1845 increase likelihood of control message delivery. 1847 When an AR receives an RS message sent by a MN with an OMNI option, 1848 the option will contain zero or more MS-Register and MS-Release sub- 1849 options containing MSIDs. After processing the OMNI option, the AR 1850 will have a list of zero or more MS-Register MSIDs and a list of zero 1851 or more of MS-Release MSIDs. The AR then processes the lists as 1852 follows: 1854 o For each list, retain the first MAX_MSID values in the list and 1855 discard any additional MSIDs (i.e., even if there are duplicates 1856 within a list). 1858 o Next, for each MSID in the MS-Register list, remove all matching 1859 MSIDs from the MS-Release list. 1861 o Next, proceed according to whether the AR's own MSID or the value 1862 0 appears in the MS-Register list as follows: 1864 * If yes, send an RA message directly back to the MN and send a 1865 proxy copy of the RS message to each additional MSID in the MS- 1866 Register list with the MS-Register/Release lists omitted. 1867 Then, send a uNA message to each MSID in the MS-Release list 1868 with the MS-Register/Release lists omitted and with an OMNI 1869 header with S/T-ifIndex set to 0. 1871 * If no, send a proxy copy of the RS message to each additional 1872 MSID in the MS-Register list with the MS-Register list omitted. 1873 For the first MSID, include the original MS-Release list; for 1874 all other MSIDs, omit the MS-Release list. 1876 Each proxy copy of the RS message will include an OMNI option and 1877 encapsulation header with the DLA of the AR as the source and the DLA 1878 of the Register MSE as the destination. When the Register MSE 1879 receives the proxy RS message, if the message includes an MS-Release 1880 list the MSE sends a uNA message to each additional MSID in the 1881 Release list. The Register MSE then sends an RA message back to the 1882 (Proxy) AR wrapped in an OMNI encapsulation header with source and 1883 destination addresses reversed, and with RA destination set to the 1884 LLA of the MN. When the AR receives this RA message, it sends a 1885 proxy copy of the RA to the MN. 1887 Each uNA message (whether send by the first-hop AR or by a Register 1888 MSE) will include an OMNI option and an encapsulation header with the 1889 DLA of the Register MSE as the source and the DLA of the Release ME 1890 as the destination. The uNA informs the Release MSE that its 1891 previous relationship with the MN has been released and that the 1892 source of the uNA message is now registered. The Release MSE must 1893 then note that the subject MN of the uNA message is now "departed", 1894 and forward any subsequent packets destined to the MN to the Register 1895 MSE. 1897 Note that it is not an error for the MS-Register/Release lists to 1898 include duplicate entries. If duplicates occur within a list, the AR 1899 will generate multiple proxy RS and/or uNA messages - one for each 1900 copy of the duplicate entries. 1902 12.3. DHCPv6-based Prefix Registration 1904 When a MN is not pre-provisioned with an OMNI LLA containing a MNP 1905 (or, when multiple MNPs are needed), it will require the AR to select 1906 MNPs on its behalf and set up the correct routing state within the 1907 MS. The DHCPv6 service [RFC8415] supports this requirement. 1909 When an MN needs to have the AR select MNPs, it sends an RS message 1910 with a DHCPv6 Message suboption containing a Client Identifier, one 1911 or more IA_PD options and a Rapid Commit option. The MN also sets 1912 the 'msg-type' field to "Solicit", and includes a 3-octet 1913 'transaction-id'. 1915 When the AR receives the RS message, it extracts the DHCPv6 message 1916 from the OMNI option. The AR then acts as a "Proxy DHCPv6 Client" in 1917 a message exchange with the locally-resident DHCPv6 server, which 1918 delegates MNPs and returns a DHCPv6 Reply message with PD parameters. 1919 (If the AR wishes to defer creation of MN state until the DHCPv6 1920 Reply is received, it can instead act as a Lightweight DHCPv6 Relay 1921 Agent per [RFC6221] by encapsulating the DHCPv6 message in a Relay- 1922 forward/reply exchange with Relay Message and Interface ID options.) 1924 When the AR receives the DHCPv6 Reply, it adds routes to the routing 1925 system and creates MN OMNI LLAs based on the delegated MNPs. The AR 1926 then sends an RA back to the MN with the DHCPv6 Reply message 1927 included in an OMNI DHCPv6 message sub-option. If the RS message 1928 source address was a Temporary address, the AR includes one of the 1929 (newly-created) MN OMNI LLAs as the RA destination address. The MN 1930 then creates a default route, assigns Subnet Router Anycast addresses 1931 and uses the RA destination address as its primary MN OMNI LLA. The 1932 MN will then use this primary MN OMNI LLA as the source address of 1933 any IPv6 ND messages it sends as long as it retains ownership of the 1934 MNP. 1936 Note: The single-octet OMNI sub-option length field restricts the 1937 DHCPv6 Message sub-option to a maximum of 255 octets for both the RS 1938 and RA messages. This provides sufficient room for the DHCPv6 1939 message header, a Client/Server Identifier option, a Rapid Commit 1940 option, at least 3 Identity Association for Prefix Delegation (IA_PD) 1941 options and any other supporting DHCPv6 options. A MN requiring more 1942 DHCPv6-based configuration information than this can either perform 1943 multiple independent RS/RA exchanges (with each exchange providing a 1944 subset of the total configuration information) or simply perform an 1945 actual DHCPv6 message exchange in addition to any RS/RA exchanges. 1947 Note: After a MN performs a DHCPv6-based prefix registration exchange 1948 with a first AR, it would need to repeat the exchange with each 1949 additional MSE it registers with. In that case, the MN supplies the 1950 MNP delegations received from the first AR in the IA_PD fields of a 1951 DHCPv6 message when it engages the additonal MSEs. 1953 13. Secure Redirection 1955 If the ANET link model is multiple access, the AR is responsible for 1956 assuring that address duplication cannot corrupt the neighbor caches 1957 of other nodes on the link. When the MN sends an RS message on a 1958 multiple access ANET link, the AR verifies that the MN is authorized 1959 to use the address and returns an RA with a non-zero Router Lifetime 1960 only if the MN is authorized. 1962 After verifying MN authorization and returning an RA, the AR MAY 1963 return IPv6 ND Redirect messages to direct MNs located on the same 1964 ANET link to exchange packets directly without transiting the AR. In 1965 that case, the MNs can exchange packets according to their unicast L2 1966 addresses discovered from the Redirect message instead of using the 1967 dogleg path through the AR. In some ANET links, however, such direct 1968 communications may be undesirable and continued use of the dogleg 1969 path through the AR may provide better performance. In that case, 1970 the AR can refrain from sending Redirects, and/or MNs can ignore 1971 them. 1973 14. AR and MSE Resilience 1975 ANETs SHOULD deploy ARs in Virtual Router Redundancy Protocol (VRRP) 1976 [RFC5798] configurations so that service continuity is maintained 1977 even if one or more ARs fail. Using VRRP, the MN is unaware which of 1978 the (redundant) ARs is currently providing service, and any service 1979 discontinuity will be limited to the failover time supported by VRRP. 1980 Widely deployed public domain implementations of VRRP are available. 1982 MSEs SHOULD use high availability clustering services so that 1983 multiple redundant systems can provide coordinated response to 1984 failures. As with VRRP, widely deployed public domain 1985 implementations of high availability clustering services are 1986 available. Note that special-purpose and expensive dedicated 1987 hardware is not necessary, and public domain implementations can be 1988 used even between lightweight virtual machines in cloud deployments. 1990 15. Detecting and Responding to MSE Failures 1992 In environments where fast recovery from MSE failure is required, ARs 1993 SHOULD use proactive Neighbor Unreachability Detection (NUD) in a 1994 manner that parallels Bidirectional Forwarding Detection (BFD) 1995 [RFC5880] to track MSE reachability. ARs can then quickly detect and 1996 react to failures so that cached information is re-established 1997 through alternate paths. Proactive NUD control messaging is carried 1998 only over well-connected ground domain networks (i.e., and not low- 1999 end ANET links such as aeronautical radios) and can therefore be 2000 tuned for rapid response. 2002 ARs perform proactive NUD for MSEs for which there are currently 2003 active MNs on the ANET. If an MSE fails, ARs can quickly inform MNs 2004 of the outage by sending multicast RA messages on the ANET interface. 2005 The AR sends RA messages to MNs via the ANET interface with an OMNI 2006 option with a Release ID for the failed MSE, and with destination 2007 address set to All-Nodes multicast (ff02::1) [RFC4291]. 2009 The AR SHOULD send MAX_FINAL_RTR_ADVERTISEMENTS RA messages separated 2010 by small delays [RFC4861]. Any MNs on the ANET interface that have 2011 been using the (now defunct) MSE will receive the RA messages and 2012 associate with a new MSE. 2014 16. Transition Considerations 2016 When a MN connects to an ANET link for the first time, it sends an RS 2017 message with an OMNI option. If the first hop AR recognizes the 2018 option, it returns an RA with its MS OMNI LLA as the source, the MN 2019 OMNI LLA as the destination and with an OMNI option included. The MN 2020 then engages the AR according to the OMNI link model specified above. 2021 If the first hop AR is a legacy IPv6 router, however, it instead 2022 returns an RA message with no OMNI option and with a non-OMNI unicast 2023 source LLA as specified in [RFC4861]. In that case, the MN engages 2024 the ANET according to the legacy IPv6 link model and without the OMNI 2025 extensions specified in this document. 2027 If the ANET link model is multiple access, there must be assurance 2028 that address duplication cannot corrupt the neighbor caches of other 2029 nodes on the link. When the MN sends an RS message on a multiple 2030 access ANET link with an OMNI LLA source address and an OMNI option, 2031 ARs that recognize the option ensure that the MN is authorized to use 2032 the address and return an RA with a non-zero Router Lifetime only if 2033 the MN is authorized. ARs that do not recognize the option instead 2034 return an RA that makes no statement about the MN's authorization to 2035 use the source address. In that case, the MN should perform 2036 Duplicate Address Detection to ensure that it does not interfere with 2037 other nodes on the link. 2039 An alternative approach for multiple access ANET links to ensure 2040 isolation for MN / AR communications is through L2 address mappings 2041 as discussed in Appendix C. This arrangement imparts a (virtual) 2042 point-to-point link model over the (physical) multiple access link. 2044 17. OMNI Interfaces on the Open Internet 2046 OMNI interfaces configured over IPv6-enabled underlying interfaces on 2047 the open Internet without an OMNI-aware first-hop AR receive RA 2048 messages that do not include an OMNI option, while OMNI interfaces 2049 configured over IPv4-only underlying interfaces do not receive any 2050 (IPv6) RA messages at all. OMNI interfaces that receive RA messages 2051 without an OMNI option configure addresses, on-link prefixes, etc. on 2052 the underlying interface that received the RA according to standard 2053 IPv6 ND and address resolution conventions [RFC4861] [RFC4862]. OMNI 2054 interfaces configured over IPv4-only underlying interfaces configure 2055 IPv4 address information on the underlying interfaces using 2056 mechanisms such as DHCPv4 [RFC2131]. 2058 OMNI interfaces configured over underlying interfaces that connect to 2059 the open Internet can apply security services such as VPNs to connect 2060 to an MSE or establish a direct link to an MSE through some other 2061 means (see Section 4). In environments where an explicit VPN or 2062 direct link may be impractical, OMNI interfaces can instead use UDP/ 2063 IP encapsulation and HMAC-based message authentication per 2064 [RFC6081][RFC4380]. 2066 After establishing a VPN or preparing for UDP/IP encapsulation, OMNI 2067 interfaces send control plane messages to interface with the MS, 2068 including Neighbor Solicitation (NS) and Neighbor Advertisement (NA) 2069 messages used for address resolution / route optimization (see: 2070 [I-D.templin-intarea-6706bis]). The control plane messages must be 2071 authenticated while data plane messages are delivered the same as for 2072 ordinary best-effort Internet traffic with basic source address-based 2073 data origin verification. Data plane communications via OMNI 2074 interfaces that connect over the open Internet without an explicit 2075 VPN should therefore employ transport- or higher-layer security to 2076 ensure integrity and/or confidentiality. 2078 OMNI interfaces in the open Internet are often located behind Network 2079 Address Translators (NATs). The OMNI interface accommodates NAT 2080 traversal using UDP/IP encapsulation and the mechanisms discussed in 2081 [RFC6081][RFC4380][I-D.templin-intarea-6706bis]. 2083 18. Time-Varying MNPs 2085 In some use cases, it is desirable, beneficial and efficient for the 2086 MN to receive a constant MNP that travels with the MN wherever it 2087 moves. For example, this would allow air traffic controllers to 2088 easily track aircraft, etc. In other cases, however (e.g., 2089 intelligent transportation systems), the MN may be willing to 2090 sacrifice a modicum of efficiency in order to have time-varying MNPs 2091 that can be changed every so often to defeat adversarial tracking. 2093 The prefix delegation services discussed in Section 12.3 allows OMNI 2094 MNs that desire time-varying MNPs to obtain short-lived prefixes to 2095 use a Temporary OMNI LLA as the source address of an RS message with 2096 an OMNI option with DHCPv6 Option sub-options. The MN would then be 2097 obligated to renumber its internal networks whenever its MNP (and 2098 therefore also its OMNI address) changes. This should not present a 2099 challenge for MNs with automated network renumbering services, 2100 however presents limits for the durations of ongoing sessions that 2101 would prefer to use a constant address. 2103 19. IANA Considerations 2105 The IANA is instructed to allocate an official Type number TBD from 2106 the registry "IPv6 Neighbor Discovery Option Formats" for the OMNI 2107 option. Implementations set Type to 253 as an interim value 2108 [RFC4727]. 2110 The IANA is instructed to assign a new Code value "1" in the "ICMPv6 2111 Code Fields: Type 2 - Packet Too Big" registry. The registry should 2112 read as follows: 2114 Code Name Reference 2115 --- ---- --------- 2116 0 Diagnostic Packet Too Big [RFC4443] 2117 1 Advisory Packet Too Big [RFCXXXX] 2119 Figure 17: OMNI Option Sub-Type Values 2121 The IANA is instructed to allocate one Ethernet unicast address TBD2 2122 (suggest 00-00-5E-00-52-14 [RFC5214]) in the registry "IANA Ethernet 2123 Address Block - Unicast Use". 2125 The OMNI option also defines an 8-bit Sub-Type field, for which IANA 2126 is instructed to create and maintain a new registry entitled "OMNI 2127 option Sub-Type values". Initial values for the OMNI option Sub-Type 2128 values registry are given below; future assignments are to be made 2129 through Expert Review [RFC8126]. 2131 Value Sub-Type name Reference 2132 ----- ------------- ---------- 2133 0 Pad1 [RFCXXXX] 2134 1 PadN [RFCXXXX] 2135 2 Interface Attributes [RFCXXXX] 2136 3 Traffic Selector [RFCXXXX] 2137 4 MS-Register [RFCXXXX] 2138 5 MS-Release [RFCXXXX] 2139 6 Network Access Identifier [RFCXXXX] 2140 7 Geo Coordinates [RFCXXXX] 2141 8 DHCP Unique Identifier (DUID) [RFCXXXX] 2142 9 DHCPv6 Message [RFCXXXX] 2143 10-252 Unassigned 2144 253-254 Experimental [RFCXXXX] 2145 255 Reserved [RFCXXXX] 2147 Figure 18: OMNI Option Sub-Type Values 2149 20. Security Considerations 2151 Security considerations for IPv4 [RFC0791], IPv6 [RFC8200] and IPv6 2152 Neighbor Discovery [RFC4861] apply. OMNI interface IPv6 ND messages 2153 SHOULD include Nonce and Timestamp options [RFC3971] when transaction 2154 confirmation and/or time synchronization is needed. 2156 OMNI interfaces configured over secured ANET interfaces inherit the 2157 physical and/or link-layer security properties of the connected 2158 ANETs. OMNI interfaces configured over open INET interfaces can use 2159 symmetric securing services such as VPNs or can by some other means 2160 establish a direct link. When a VPN or direct link may be 2161 impractical, however, an asymmetric security service such as the 2162 authentication option specified in [RFC4380] or other protocol 2163 control message security mechanisms may be necessary. While the OMNI 2164 link protects control plane messaging, applications must still employ 2165 end-to-end transport- or higher-layer security services to protect 2166 the data plane. 2168 The Mobility Service MUST provide strong network layer security for 2169 control plane messages and forwarding path integrity for data plane 2170 messages. In one example, the AERO service 2171 [I-D.templin-intarea-6706bis] constructs a spanning tree between 2172 mobility service elements and secures the links in the spanning tree 2173 with network layer security mechanisms such as IPsec [RFC4301] or 2174 Wireguard. Control plane messages are then constrained to travel 2175 only over the secured spanning tree paths and are therefore protected 2176 from attack or eavesdropping. Since data plane messages can travel 2177 over route optimized paths that do not strictly follow the spanning 2178 tree, however, end-to-end transport- or higher-layer security 2179 services are still required. 2181 Security considerations for specific access network interface types 2182 are covered under the corresponding IP-over-(foo) specification 2183 (e.g., [RFC2464], [RFC2492], etc.). 2185 Security considerations for IPv6 fragmentation and reassembly are 2186 discussed in Section 5.1. 2188 21. Implementation Status 2190 Draft -29 is implemented in the recently tagged AERO/OMNI 3.0.0 2191 internal release, and Draft -30 is now tagged as the AERO/OMNI 3.0.1. 2192 Newer specification versions will be tagged in upcoming releases. 2193 First public release expected before the end of 2020. 2195 22. Acknowledgements 2197 The first version of this document was prepared per the consensus 2198 decision at the 7th Conference of the International Civil Aviation 2199 Organization (ICAO) Working Group-I Mobility Subgroup on March 22, 2200 2019. Consensus to take the document forward to the IETF was reached 2201 at the 9th Conference of the Mobility Subgroup on November 22, 2019. 2202 Attendees and contributors included: Guray Acar, Danny Bharj, 2203 Francois D'Humieres, Pavel Drasil, Nikos Fistas, Giovanni Garofolo, 2204 Bernhard Haindl, Vaughn Maiolla, Tom McParland, Victor Moreno, Madhu 2205 Niraula, Brent Phillips, Liviu Popescu, Jacky Pouzet, Aloke Roy, Greg 2206 Saccone, Robert Segers, Michal Skorepa, Michel Solery, Stephane 2207 Tamalet, Fred Templin, Jean-Marc Vacher, Bela Varkonyi, Tony Whyman, 2208 Fryderyk Wrobel and Dongsong Zeng. 2210 The following individuals are acknowledged for their useful comments: 2211 Michael Matyas, Madhu Niraula, Michael Richardson, Greg Saccone, 2212 Stephane Tamalet, Eric Vyncke. Pavel Drasil, Zdenek Jaron and Michal 2213 Skorepa are recognized for their many helpful ideas and suggestions. 2214 Madhuri Madhava Badgandi, Katherine Tran, and Vijayasarathy 2215 Rajagopalan are acknowledged for their hard work on the 2216 implementation and insights that led to improvements to the spec. 2218 Discussions on the IETF 6man and atn mailing lists during the fall of 2219 2020 suggested additional points to consider. The authors gratefully 2220 acknowledge the list members who contributed valuable insights 2221 through those discussions. 2223 This work is aligned with the NASA Safe Autonomous Systems Operation 2224 (SASO) program under NASA contract number NNA16BD84C. 2226 This work is aligned with the FAA as per the SE2025 contract number 2227 DTFAWA-15-D-00030. 2229 23. References 2231 23.1. Normative References 2233 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, 2234 DOI 10.17487/RFC0791, September 1981, 2235 . 2237 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 2238 Requirement Levels", BCP 14, RFC 2119, 2239 DOI 10.17487/RFC2119, March 1997, 2240 . 2242 [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black, 2243 "Definition of the Differentiated Services Field (DS 2244 Field) in the IPv4 and IPv6 Headers", RFC 2474, 2245 DOI 10.17487/RFC2474, December 1998, 2246 . 2248 [RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander, 2249 "SEcure Neighbor Discovery (SEND)", RFC 3971, 2250 DOI 10.17487/RFC3971, March 2005, 2251 . 2253 [RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and 2254 More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191, 2255 November 2005, . 2257 [RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast 2258 Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005, 2259 . 2261 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 2262 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 2263 2006, . 2265 [RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet 2266 Control Message Protocol (ICMPv6) for the Internet 2267 Protocol Version 6 (IPv6) Specification", STD 89, 2268 RFC 4443, DOI 10.17487/RFC4443, March 2006, 2269 . 2271 [RFC4727] Fenner, B., "Experimental Values In IPv4, IPv6, ICMPv4, 2272 ICMPv6, UDP, and TCP Headers", RFC 4727, 2273 DOI 10.17487/RFC4727, November 2006, 2274 . 2276 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 2277 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 2278 DOI 10.17487/RFC4861, September 2007, 2279 . 2281 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 2282 Address Autoconfiguration", RFC 4862, 2283 DOI 10.17487/RFC4862, September 2007, 2284 . 2286 [RFC6088] Tsirtsis, G., Giarreta, G., Soliman, H., and N. Montavont, 2287 "Traffic Selectors for Flow Bindings", RFC 6088, 2288 DOI 10.17487/RFC6088, January 2011, 2289 . 2291 [RFC8028] Baker, F. and B. Carpenter, "First-Hop Router Selection by 2292 Hosts in a Multi-Prefix Network", RFC 8028, 2293 DOI 10.17487/RFC8028, November 2016, 2294 . 2296 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2297 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2298 May 2017, . 2300 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 2301 (IPv6) Specification", STD 86, RFC 8200, 2302 DOI 10.17487/RFC8200, July 2017, 2303 . 2305 [RFC8201] McCann, J., Deering, S., Mogul, J., and R. Hinden, Ed., 2306 "Path MTU Discovery for IP version 6", STD 87, RFC 8201, 2307 DOI 10.17487/RFC8201, July 2017, 2308 . 2310 [RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A., 2311 Richardson, M., Jiang, S., Lemon, T., and T. Winters, 2312 "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", 2313 RFC 8415, DOI 10.17487/RFC8415, November 2018, 2314 . 2316 23.2. Informative References 2318 [ATN] Maiolla, V., "The OMNI Interface - An IPv6 Air/Ground 2319 Interface for Civil Aviation, IETF Liaison Statement 2320 #1676, https://datatracker.ietf.org/liaison/1676/", March 2321 2020. 2323 [CRC] Jain, R., "Error Characteristics of Fiber Distributed Data 2324 Interface (FDDI), IEEE Transactions on Communications", 2325 August 1990. 2327 [I-D.ietf-6man-rfc4941bis] 2328 Gont, F., Krishnan, S., Narten, T., and R. Draves, 2329 "Temporary Address Extensions for Stateless Address 2330 Autoconfiguration in IPv6", draft-ietf-6man-rfc4941bis-12 2331 (work in progress), November 2020. 2333 [I-D.ietf-intarea-tunnels] 2334 Touch, J. and M. Townsley, "IP Tunnels in the Internet 2335 Architecture", draft-ietf-intarea-tunnels-10 (work in 2336 progress), September 2019. 2338 [I-D.ietf-ipwave-vehicular-networking] 2339 Jeong, J., "IPv6 Wireless Access in Vehicular Environments 2340 (IPWAVE): Problem Statement and Use Cases", draft-ietf- 2341 ipwave-vehicular-networking-19 (work in progress), July 2342 2020. 2344 [I-D.templin-6man-dhcpv6-ndopt] 2345 Templin, F., "A Unified Stateful/Stateless Configuration 2346 Service for IPv6", draft-templin-6man-dhcpv6-ndopt-10 2347 (work in progress), June 2020. 2349 [I-D.templin-6man-lla-type] 2350 Templin, F., "The IPv6 Link-Local Address Type Field", 2351 draft-templin-6man-lla-type-02 (work in progress), 2352 November 2020. 2354 [I-D.templin-intarea-6706bis] 2355 Templin, F., "Asymmetric Extended Route Optimization 2356 (AERO)", draft-templin-intarea-6706bis-71 (work in 2357 progress), December 2020. 2359 [RFC1122] Braden, R., Ed., "Requirements for Internet Hosts - 2360 Communication Layers", STD 3, RFC 1122, 2361 DOI 10.17487/RFC1122, October 1989, 2362 . 2364 [RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191, 2365 DOI 10.17487/RFC1191, November 1990, 2366 . 2368 [RFC1256] Deering, S., Ed., "ICMP Router Discovery Messages", 2369 RFC 1256, DOI 10.17487/RFC1256, September 1991, 2370 . 2372 [RFC2131] Droms, R., "Dynamic Host Configuration Protocol", 2373 RFC 2131, DOI 10.17487/RFC2131, March 1997, 2374 . 2376 [RFC2225] Laubach, M. and J. Halpern, "Classical IP and ARP over 2377 ATM", RFC 2225, DOI 10.17487/RFC2225, April 1998, 2378 . 2380 [RFC2464] Crawford, M., "Transmission of IPv6 Packets over Ethernet 2381 Networks", RFC 2464, DOI 10.17487/RFC2464, December 1998, 2382 . 2384 [RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in 2385 IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473, 2386 December 1998, . 2388 [RFC2492] Armitage, G., Schulter, P., and M. Jork, "IPv6 over ATM 2389 Networks", RFC 2492, DOI 10.17487/RFC2492, January 1999, 2390 . 2392 [RFC2529] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4 2393 Domains without Explicit Tunnels", RFC 2529, 2394 DOI 10.17487/RFC2529, March 1999, 2395 . 2397 [RFC2863] McCloghrie, K. and F. Kastenholz, "The Interfaces Group 2398 MIB", RFC 2863, DOI 10.17487/RFC2863, June 2000, 2399 . 2401 [RFC3692] Narten, T., "Assigning Experimental and Testing Numbers 2402 Considered Useful", BCP 82, RFC 3692, 2403 DOI 10.17487/RFC3692, January 2004, 2404 . 2406 [RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener 2407 Discovery Version 2 (MLDv2) for IPv6", RFC 3810, 2408 DOI 10.17487/RFC3810, June 2004, 2409 . 2411 [RFC3819] Karn, P., Ed., Bormann, C., Fairhurst, G., Grossman, D., 2412 Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J., and L. 2413 Wood, "Advice for Internet Subnetwork Designers", BCP 89, 2414 RFC 3819, DOI 10.17487/RFC3819, July 2004, 2415 . 2417 [RFC3879] Huitema, C. and B. Carpenter, "Deprecating Site Local 2418 Addresses", RFC 3879, DOI 10.17487/RFC3879, September 2419 2004, . 2421 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 2422 Internet Protocol", RFC 4301, DOI 10.17487/RFC4301, 2423 December 2005, . 2425 [RFC4380] Huitema, C., "Teredo: Tunneling IPv6 over UDP through 2426 Network Address Translations (NATs)", RFC 4380, 2427 DOI 10.17487/RFC4380, February 2006, 2428 . 2430 [RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery 2431 Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April 2432 2006, . 2434 [RFC4429] Moore, N., "Optimistic Duplicate Address Detection (DAD) 2435 for IPv6", RFC 4429, DOI 10.17487/RFC4429, April 2006, 2436 . 2438 [RFC4541] Christensen, M., Kimball, K., and F. Solensky, 2439 "Considerations for Internet Group Management Protocol 2440 (IGMP) and Multicast Listener Discovery (MLD) Snooping 2441 Switches", RFC 4541, DOI 10.17487/RFC4541, May 2006, 2442 . 2444 [RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick, 2445 "Internet Group Management Protocol (IGMP) / Multicast 2446 Listener Discovery (MLD)-Based Multicast Forwarding 2447 ("IGMP/MLD Proxying")", RFC 4605, DOI 10.17487/RFC4605, 2448 August 2006, . 2450 [RFC4821] Mathis, M. and J. Heffner, "Packetization Layer Path MTU 2451 Discovery", RFC 4821, DOI 10.17487/RFC4821, March 2007, 2452 . 2454 [RFC4963] Heffner, J., Mathis, M., and B. Chandler, "IPv4 Reassembly 2455 Errors at High Data Rates", RFC 4963, 2456 DOI 10.17487/RFC4963, July 2007, 2457 . 2459 [RFC5175] Haberman, B., Ed. and R. Hinden, "IPv6 Router 2460 Advertisement Flags Option", RFC 5175, 2461 DOI 10.17487/RFC5175, March 2008, 2462 . 2464 [RFC5213] Gundavelli, S., Ed., Leung, K., Devarapalli, V., 2465 Chowdhury, K., and B. Patil, "Proxy Mobile IPv6", 2466 RFC 5213, DOI 10.17487/RFC5213, August 2008, 2467 . 2469 [RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site 2470 Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214, 2471 DOI 10.17487/RFC5214, March 2008, 2472 . 2474 [RFC5558] Templin, F., Ed., "Virtual Enterprise Traversal (VET)", 2475 RFC 5558, DOI 10.17487/RFC5558, February 2010, 2476 . 2478 [RFC5798] Nadas, S., Ed., "Virtual Router Redundancy Protocol (VRRP) 2479 Version 3 for IPv4 and IPv6", RFC 5798, 2480 DOI 10.17487/RFC5798, March 2010, 2481 . 2483 [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 2484 (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, 2485 . 2487 [RFC6081] Thaler, D., "Teredo Extensions", RFC 6081, 2488 DOI 10.17487/RFC6081, January 2011, 2489 . 2491 [RFC6221] Miles, D., Ed., Ooghe, S., Dec, W., Krishnan, S., and A. 2492 Kavanagh, "Lightweight DHCPv6 Relay Agent", RFC 6221, 2493 DOI 10.17487/RFC6221, May 2011, 2494 . 2496 [RFC6355] Narten, T. and J. Johnson, "Definition of the UUID-Based 2497 DHCPv6 Unique Identifier (DUID-UUID)", RFC 6355, 2498 DOI 10.17487/RFC6355, August 2011, 2499 . 2501 [RFC6543] Gundavelli, S., "Reserved IPv6 Interface Identifier for 2502 Proxy Mobile IPv6", RFC 6543, DOI 10.17487/RFC6543, May 2503 2012, . 2505 [RFC7084] Singh, H., Beebee, W., Donley, C., and B. Stark, "Basic 2506 Requirements for IPv6 Customer Edge Routers", RFC 7084, 2507 DOI 10.17487/RFC7084, November 2013, 2508 . 2510 [RFC7421] Carpenter, B., Ed., Chown, T., Gont, F., Jiang, S., 2511 Petrescu, A., and A. Yourtchenko, "Analysis of the 64-bit 2512 Boundary in IPv6 Addressing", RFC 7421, 2513 DOI 10.17487/RFC7421, January 2015, 2514 . 2516 [RFC7526] Troan, O. and B. Carpenter, Ed., "Deprecating the Anycast 2517 Prefix for 6to4 Relay Routers", BCP 196, RFC 7526, 2518 DOI 10.17487/RFC7526, May 2015, 2519 . 2521 [RFC7542] DeKok, A., "The Network Access Identifier", RFC 7542, 2522 DOI 10.17487/RFC7542, May 2015, 2523 . 2525 [RFC7739] Gont, F., "Security Implications of Predictable Fragment 2526 Identification Values", RFC 7739, DOI 10.17487/RFC7739, 2527 February 2016, . 2529 [RFC7847] Melia, T., Ed. and S. Gundavelli, Ed., "Logical-Interface 2530 Support for IP Hosts with Multi-Access Support", RFC 7847, 2531 DOI 10.17487/RFC7847, May 2016, 2532 . 2534 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 2535 Writing an IANA Considerations Section in RFCs", BCP 26, 2536 RFC 8126, DOI 10.17487/RFC8126, June 2017, 2537 . 2539 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 2540 Decraene, B., Litkowski, S., and R. Shakir, "Segment 2541 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 2542 July 2018, . 2544 [RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J., 2545 Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header 2546 (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020, 2547 . 2549 [RFC8900] Bonica, R., Baker, F., Huston, G., Hinden, R., Troan, O., 2550 and F. Gont, "IP Fragmentation Considered Fragile", 2551 BCP 230, RFC 8900, DOI 10.17487/RFC8900, September 2020, 2552 . 2554 Appendix A. Interface Attribute Preferences Bitmap Encoding 2556 Adaptation of the OMNI option Interface Attributes Preferences Bitmap 2557 encoding to specific Internetworks such as the Aeronautical 2558 Telecommunications Network with Internet Protocol Services (ATN/IPS) 2559 may include link selection preferences based on other traffic 2560 classifiers (e.g., transport port numbers, etc.) in addition to the 2561 existing DSCP-based preferences. Nodes on specific Internetworks 2562 maintain a map of traffic classifiers to additional P[*] preference 2563 fields beyond the first 64. For example, TCP port 22 maps to P[67], 2564 TCP port 443 maps to P[70], UDP port 8060 maps to P[76], etc. 2566 Implementations use Simplex or Indexed encoding formats for P[*] 2567 encoding in order to encode a given set of traffic classifiers in the 2568 most efficient way. Some use cases may be more efficiently coded 2569 using Simplex form, while others may be more efficient using Indexed. 2570 Once a format is selected for preparation of a single Interface 2571 Attribute the same format must be used for the entire Interface 2572 Attribute sub-option. Different sub-options may use different 2573 formats. 2575 The following figures show coding examples for various Simplex and 2576 Indexed formats: 2578 0 1 2 3 2579 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 2580 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2581 | Sub-Type=2 | Sub-length=N | ifIndex | ifType | 2582 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2583 | Provider ID | Link |R| API | Bitmap(0)=0xff|P00|P01|P02|P03| 2584 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2585 |P04|P05|P06|P07|P08|P09|P10|P11|P12|P13|P14|P15|P16|P17|P18|P19| 2586 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2587 |P20|P21|P22|P23|P24|P25|P26|P27|P28|P29|P30|P31| Bitmap(1)=0xff| 2588 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2589 |P32|P33|P34|P35|P36|P37|P38|P39|P40|P41|P42|P43|P44|P45|P46|P47| 2590 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2591 |P48|P49|P50|P51|P52|P53|P54|P55|P56|P57|P58|P59|P60|P61|P62|P63| 2592 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2593 | Bitmap(2)=0xff|P64|P65|P67|P68| ... 2594 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 2596 Figure 19: Example 1: Dense Simplex Encoding 2598 0 1 2 3 2599 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 2600 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2601 | Sub-Type=2 | Sub-length=N | ifIndex | ifType | 2602 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2603 | Provider ID | Link |R| API | Bitmap(0)=0x00| Bitmap(1)=0x0f| 2604 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2605 |P48|P49|P50|P51|P52|P53|P54|P55|P56|P57|P58|P59|P60|P61|P62|P63| 2606 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2607 | Bitmap(2)=0x00| Bitmap(3)=0x00| Bitmap(4)=0x00| Bitmap(5)=0x00| 2608 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2609 | Bitmap(6)=0xf0|192|193|194|195|196|197|198|199|200|201|202|203| 2610 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2611 |204|205|206|207| Bitmap(7)=0x00| Bitmap(8)=0x0f|272|273|274|275| 2612 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2613 |276|277|278|279|280|281|282|283|284|285|286|287| Bitmap(9)=0x00| 2614 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2615 |Bitmap(10)=0x00| ... 2616 +-+-+-+-+-+-+-+-+-+-+- 2618 Figure 20: Example 2: Sparse Simplex Encoding 2620 0 1 2 3 2621 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 2622 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2623 | Sub-Type=2 | Sub-length=N | ifIndex | ifType | 2624 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2625 | Provider ID | Link |R| API | Index = 0x00 | Bitmap = 0x80 | 2626 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2627 |P00|P01|P02|P03| Index = 0x01 | Bitmap = 0x01 |P60|P61|P62|P63| 2628 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2629 | Index = 0x10 | Bitmap = 0x80 |512|513|514|515| Index = 0x18 | 2630 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2631 | Bitmap = 0x01 |796|797|798|799| ... 2632 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 2634 Figure 21: Example 3: Indexed Encoding 2636 Appendix B. VDL Mode 2 Considerations 2638 ICAO Doc 9776 is the "Technical Manual for VHF Data Link Mode 2" 2639 (VDLM2) that specifies an essential radio frequency data link service 2640 for aircraft and ground stations in worldwide civil aviation air 2641 traffic management. The VDLM2 link type is "multicast capable" 2642 [RFC4861], but with considerable differences from common multicast 2643 links such as Ethernet and IEEE 802.11. 2645 First, the VDLM2 link data rate is only 31.5Kbps - multiple orders of 2646 magnitude less than most modern wireless networking gear. Second, 2647 due to the low available link bandwidth only VDLM2 ground stations 2648 (i.e., and not aircraft) are permitted to send broadcasts, and even 2649 so only as compact layer 2 "beacons". Third, aircraft employ the 2650 services of ground stations by performing unicast RS/RA exchanges 2651 upon receipt of beacons instead of listening for multicast RA 2652 messages and/or sending multicast RS messages. 2654 This beacon-oriented unicast RS/RA approach is necessary to conserve 2655 the already-scarce available link bandwidth. Moreover, since the 2656 numbers of beaconing ground stations operating within a given spatial 2657 range must be kept as sparse as possible, it would not be feasible to 2658 have different classes of ground stations within the same region 2659 observing different protocols. It is therefore highly desirable that 2660 all ground stations observe a common language of RS/RA as specified 2661 in this document. 2663 Note that links of this nature may benefit from compression 2664 techniques that reduce the bandwidth necessary for conveying the same 2665 amount of data. The IETF lpwan working group is considering possible 2666 alternatives: [https://datatracker.ietf.org/wg/lpwan/documents]. 2668 Appendix C. MN / AR Isolation Through L2 Address Mapping 2670 Per [RFC4861], IPv6 ND messages may be sent to either a multicast or 2671 unicast link-scoped IPv6 destination address. However, IPv6 ND 2672 messaging should be coordinated between the MN and AR only without 2673 invoking other nodes on the ANET. This implies that MN / AR control 2674 messaging should be isolated and not overheard by other nodes on the 2675 link. 2677 To support MN / AR isolation on some ANET links, ARs can maintain an 2678 OMNI-specific unicast L2 address ("MSADDR"). For Ethernet-compatible 2679 ANETs, this specification reserves one Ethernet unicast address TBD2 2680 (see: Section 19). For non-Ethernet statically-addressed ANETs, 2681 MSADDR is reserved per the assigned numbers authority for the ANET 2682 addressing space. For still other ANETs, MSADDR may be dynamically 2683 discovered through other means, e.g., L2 beacons. 2685 MNs map the L3 addresses of all IPv6 ND messages they send (i.e., 2686 both multicast and unicast) to MSADDR instead of to an ordinary 2687 unicast or multicast L2 address. In this way, all of the MN's IPv6 2688 ND messages will be received by ARs that are configured to accept 2689 packets destined to MSADDR. Note that multiple ARs on the link could 2690 be configured to accept packets destined to MSADDR, e.g., as a basis 2691 for supporting redundancy. 2693 Therefore, ARs must accept and process packets destined to MSADDR, 2694 while all other devices must not process packets destined to MSADDR. 2695 This model has well-established operational experience in Proxy 2696 Mobile IPv6 (PMIP) [RFC5213][RFC6543]. 2698 Appendix D. Change Log 2700 << RFC Editor - remove prior to publication >> 2702 Differences from draft-templin-6man-omni-interface-35 to draft- 2703 templin-6man-omni-interface-36: 2705 o Major clarifications on aspects such as "hard/soft" PTB error 2706 messages 2708 o Made generic so that either IP protocol version (IPv4 or IPv6) can 2709 be used in the data plane. 2711 Differences from draft-templin-6man-omni-interface-31 to draft- 2712 templin-6man-omni-interface-32: 2714 o MTU 2715 o Support for multi-hop ANETS such as ISATAP. 2717 Differences from draft-templin-6man-omni-interface-29 to draft- 2718 templin-6man-omni-interface-30: 2720 o Moved link-layer addressing information into the OMNI option on a 2721 per-ifIndex basis 2723 o Renamed "ifIndex-tuple" to "Interface Attributes" 2725 Differences from draft-templin-6man-omni-interface-27 to draft- 2726 templin-6man-omni-interface-28: 2728 o Updates based on implementation expereince. 2730 Differences from draft-templin-6man-omni-interface-25 to draft- 2731 templin-6man-omni-interface-26: 2733 o Further clarification on "aggregate" RA messages. 2735 o Expanded Security Considerations to discuss expectations for 2736 security in the Mobility Service. 2738 Differences from draft-templin-6man-omni-interface-20 to draft- 2739 templin-6man-omni-interface-21: 2741 o Safety-Based Multilink (SBM) and Performance-Based Multilink 2742 (PBM). 2744 Differences from draft-templin-6man-omni-interface-18 to draft- 2745 templin-6man-omni-interface-19: 2747 o SEND/CGA. 2749 Differences from draft-templin-6man-omni-interface-17 to draft- 2750 templin-6man-omni-interface-18: 2752 o Teredo 2754 Differences from draft-templin-6man-omni-interface-14 to draft- 2755 templin-6man-omni-interface-15: 2757 o Prefix length discussions removed. 2759 Differences from draft-templin-6man-omni-interface-12 to draft- 2760 templin-6man-omni-interface-13: 2762 o Teredo 2763 Differences from draft-templin-6man-omni-interface-11 to draft- 2764 templin-6man-omni-interface-12: 2766 o Major simplifications and clarifications on MTU and fragmentation. 2768 o Document now updates RFC4443 and RFC8201. 2770 Differences from draft-templin-6man-omni-interface-10 to draft- 2771 templin-6man-omni-interface-11: 2773 o Removed /64 assumption, resulting in new OMNI address format. 2775 Differences from draft-templin-6man-omni-interface-07 to draft- 2776 templin-6man-omni-interface-08: 2778 o OMNI MNs in the open Internet 2780 Differences from draft-templin-6man-omni-interface-06 to draft- 2781 templin-6man-omni-interface-07: 2783 o Brought back L2 MSADDR mapping text for MN / AR isolation based on 2784 L2 addressing. 2786 o Expanded "Transition Considerations". 2788 Differences from draft-templin-6man-omni-interface-05 to draft- 2789 templin-6man-omni-interface-06: 2791 o Brought back OMNI option "R" flag, and discussed its use. 2793 Differences from draft-templin-6man-omni-interface-04 to draft- 2794 templin-6man-omni-interface-05: 2796 o Transition considerations, and overhaul of RS/RA addressing with 2797 the inclusion of MSE addresses within the OMNI option instead of 2798 as RS/RA addresses (developed under FAA SE2025 contract number 2799 DTFAWA-15-D-00030). 2801 Differences from draft-templin-6man-omni-interface-02 to draft- 2802 templin-6man-omni-interface-03: 2804 o Added "advisory PTB messages" under FAA SE2025 contract number 2805 DTFAWA-15-D-00030. 2807 Differences from draft-templin-6man-omni-interface-01 to draft- 2808 templin-6man-omni-interface-02: 2810 o Removed "Primary" flag and supporting text. 2812 o Clarified that "Router Lifetime" applies to each ANET interface 2813 independently, and that the union of all ANET interface Router 2814 Lifetimes determines MSE lifetime. 2816 Differences from draft-templin-6man-omni-interface-00 to draft- 2817 templin-6man-omni-interface-01: 2819 o "All-MSEs" OMNI LLA defined. Also reserved fe80::ff00:0000/104 2820 for future use (most likely as "pseudo-multicast"). 2822 o Non-normative discussion of alternate OMNI LLA construction form 2823 made possible if the 64-bit assumption were relaxed. 2825 First draft version (draft-templin-atn-aero-interface-00): 2827 o Draft based on consensus decision of ICAO Working Group I Mobility 2828 Subgroup March 22, 2019. 2830 Authors' Addresses 2832 Fred L. Templin (editor) 2833 The Boeing Company 2834 P.O. Box 3707 2835 Seattle, WA 98124 2836 USA 2838 Email: fltemplin@acm.org 2840 Tony Whyman 2841 MWA Ltd c/o Inmarsat Global Ltd 2842 99 City Road 2843 London EC1Y 1AX 2844 England 2846 Email: tony.whyman@mccallumwhyman.com