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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 Boeing Research & Technology 4 Intended status: Informational June 23, 2021 5 Expires: December 25, 2021 7 Automatic Extended Route Optimization (AERO) 8 draft-templin-6man-aero-20 10 Abstract 12 This document specifies an Automatic Extended Route Optimization 13 (AERO) service for IP internetworking over Overlay Multilink Network 14 (OMNI) interfaces. AERO/OMNI use an IPv6 link-local address format 15 that supports operation of the IPv6 Neighbor Discovery (IPv6 ND) 16 protocol. Prefix delegation/registration services are employed for 17 network admission and to manage the IP forwarding and routing 18 systems. Secure multilink operation, mobility management, multicast, 19 traffic selector signaling and route optimization are naturally 20 supported through dynamic neighbor cache updates. AERO is a widely- 21 applicable mobile internetworking service especially well-suited to 22 aviation services, intelligent transportation systems, mobile end 23 user devices and many other applications. 25 Status of This Memo 27 This Internet-Draft is submitted in full conformance with the 28 provisions of BCP 78 and BCP 79. 30 Internet-Drafts are working documents of the Internet Engineering 31 Task Force (IETF). Note that other groups may also distribute 32 working documents as Internet-Drafts. The list of current Internet- 33 Drafts is at https://datatracker.ietf.org/drafts/current/. 35 Internet-Drafts are draft documents valid for a maximum of six months 36 and may be updated, replaced, or obsoleted by other documents at any 37 time. It is inappropriate to use Internet-Drafts as reference 38 material or to cite them other than as "work in progress." 40 This Internet-Draft will expire on December 25, 2021. 42 Copyright Notice 44 Copyright (c) 2021 IETF Trust and the persons identified as the 45 document authors. All rights reserved. 47 This document is subject to BCP 78 and the IETF Trust's Legal 48 Provisions Relating to IETF Documents 49 (https://trustee.ietf.org/license-info) in effect on the date of 50 publication of this document. Please review these documents 51 carefully, as they describe your rights and restrictions with respect 52 to this document. Code Components extracted from this document must 53 include Simplified BSD License text as described in Section 4.e of 54 the Trust Legal Provisions and are provided without warranty as 55 described in the Simplified BSD License. 57 Table of Contents 59 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 60 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6 61 3. Automatic Extended Route Optimization (AERO) . . . . . . . . 13 62 3.1. AERO Node Types . . . . . . . . . . . . . . . . . . . . . 13 63 3.2. The AERO Service over OMNI Links . . . . . . . . . . . . 15 64 3.2.1. AERO/OMNI Reference Model . . . . . . . . . . . . . . 15 65 3.2.2. Addressing and Node Identification . . . . . . . . . 17 66 3.2.3. AERO Routing System . . . . . . . . . . . . . . . . . 18 67 3.2.4. OMNI Link Forwarding . . . . . . . . . . . . . . . . 20 68 3.2.5. Segment Routing Topologies (SRTs) . . . . . . . . . . 22 69 3.2.6. Segment Routing For OMNI Link Selection . . . . . . . 22 70 3.2.7. OMNI Multilink Forwarding . . . . . . . . . . . . . . 23 71 3.3. OMNI Interface Characteristics . . . . . . . . . . . . . 33 72 3.4. OMNI Interface Initialization . . . . . . . . . . . . . . 35 73 3.4.1. AERO Proxy/Server and Relay Behavior . . . . . . . . 35 74 3.4.2. AERO Client Behavior . . . . . . . . . . . . . . . . 36 75 3.4.3. AERO Bridge Behavior . . . . . . . . . . . . . . . . 36 76 3.5. OMNI Interface Neighbor Cache Maintenance . . . . . . . . 36 77 3.5.1. OMNI ND Messages . . . . . . . . . . . . . . . . . . 38 78 3.5.2. OMNI Neighbor Advertisement Message Flags . . . . . . 40 79 3.5.3. OMNI Neighbor Window Synchronization . . . . . . . . 41 80 3.6. OMNI Interface Encapsulation and Re-encapsulation . . . . 41 81 3.7. OMNI Interface Decapsulation . . . . . . . . . . . . . . 42 82 3.8. OMNI Interface Data Origin Authentication . . . . . . . . 42 83 3.9. OMNI Interface MTU . . . . . . . . . . . . . . . . . . . 43 84 3.10. OMNI Interface Forwarding Algorithm . . . . . . . . . . . 43 85 3.10.1. Client Forwarding Algorithm . . . . . . . . . . . . 45 86 3.10.2. Proxy/Server and Relay Forwarding Algorithm . . . . 46 87 3.10.3. Bridge Forwarding Algorithm . . . . . . . . . . . . 49 88 3.11. OMNI Interface Error Handling . . . . . . . . . . . . . . 50 89 3.12. AERO Router Discovery, Prefix Delegation and 90 Autoconfiguration . . . . . . . . . . . . . . . . . . . . 52 91 3.12.1. AERO Service Model . . . . . . . . . . . . . . . . . 53 92 3.12.2. AERO Client Behavior . . . . . . . . . . . . . . . . 53 93 3.12.3. AERO Proxy/Server Behavior . . . . . . . . . . . . . 55 94 3.13. AERO Proxy/Server Coordination . . . . . . . . . . . . . 58 95 3.13.1. Detecting and Responding to Proxy/Server Failures . 61 96 3.13.2. Point-to-Multipoint Proxy/Server Coordination . . . 62 98 3.14. AERO Route Optimization . . . . . . . . . . . . . . . . . 63 99 3.14.1. Route Optimization Initiation . . . . . . . . . . . 64 100 3.14.2. Relaying the NS(AR) *NET Packet(s) . . . . . . . . . 65 101 3.14.3. Processing the NS(AR) and Sending the NA(AR) . . . . 65 102 3.14.4. Relaying the NA(AR) . . . . . . . . . . . . . . . . 66 103 3.14.5. Processing the NA(AR) . . . . . . . . . . . . . . . 66 104 3.14.6. Forwarding Packets to Route Optimized Targets . . . 67 105 3.15. Neighbor Unreachability Detection (NUD) . . . . . . . . . 68 106 3.16. Mobility Management and Quality of Service (QoS) . . . . 70 107 3.16.1. Mobility Update Messaging . . . . . . . . . . . . . 70 108 3.16.2. Announcing Link-Layer Address and/or QoS Preference 109 Changes . . . . . . . . . . . . . . . . . . . . . . 71 110 3.16.3. Bringing New Links Into Service . . . . . . . . . . 72 111 3.16.4. Deactivating Existing Links . . . . . . . . . . . . 72 112 3.16.5. Moving Between Proxy/Servers . . . . . . . . . . . . 72 113 3.17. Multicast . . . . . . . . . . . . . . . . . . . . . . . . 74 114 3.17.1. Source-Specific Multicast (SSM) . . . . . . . . . . 74 115 3.17.2. Any-Source Multicast (ASM) . . . . . . . . . . . . . 75 116 3.17.3. Bi-Directional PIM (BIDIR-PIM) . . . . . . . . . . . 76 117 3.18. Operation over Multiple OMNI Links . . . . . . . . . . . 76 118 3.19. DNS Considerations . . . . . . . . . . . . . . . . . . . 77 119 3.20. Transition/Coexistence Considerations . . . . . . . . . . 77 120 3.21. Detecting and Reacting to Proxy/Server and Bridge 121 Failures . . . . . . . . . . . . . . . . . . . . . . . . 78 122 3.22. AERO Clients on the Open Internet . . . . . . . . . . . . 78 123 3.23. Time-Varying MNPs . . . . . . . . . . . . . . . . . . . . 81 124 4. Implementation Status . . . . . . . . . . . . . . . . . . . . 81 125 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 82 126 6. Security Considerations . . . . . . . . . . . . . . . . . . . 82 127 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 84 128 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 86 129 8.1. Normative References . . . . . . . . . . . . . . . . . . 86 130 8.2. Informative References . . . . . . . . . . . . . . . . . 88 131 Appendix A. Non-Normative Considerations . . . . . . . . . . . . 94 132 A.1. Implementation Strategies for Route Optimization . . . . 94 133 A.2. Implicit Mobility Management . . . . . . . . . . . . . . 95 134 A.3. Direct Underlying Interfaces . . . . . . . . . . . . . . 95 135 A.4. AERO Critical Infrastructure Considerations . . . . . . . 95 136 A.5. AERO Server Failure Implications . . . . . . . . . . . . 96 137 A.6. AERO Client / Server Architecture . . . . . . . . . . . . 97 138 Appendix B. Change Log . . . . . . . . . . . . . . . . . . . . . 99 139 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 102 141 1. Introduction 143 Automatic Extended Route Optimization (AERO) fulfills the 144 requirements of Distributed Mobility Management (DMM) [RFC7333] and 145 route optimization [RFC5522] for aeronautical networking and other 146 network mobility use cases including intelligent transportation 147 systems and enterprise mobile device users. AERO is a secure 148 internetworking and mobility management service that employs the 149 Overlay Multilink Network Interface (OMNI) [I-D.templin-6man-omni] 150 Non-Broadcast, Multiple Access (NBMA) virtual link model. The OMNI 151 link is a virtual overlay configured over one or more underlying 152 Internetworks, and nodes on the link can exchange original IP packets 153 as single-hop neighbors. The OMNI Adaptation Layer (OAL) supports 154 multilink operation for increased reliability and path optimization 155 while providing fragmentation and reassembly services to support 156 Maximum Transmission Unit (MTU) diversity. In terms of precedence, 157 this specification may provide first-principle insights into a 158 representative mobility service architecture as context for 159 understanding the OMNI specification. 161 The AERO service comprises Clients, Proxy/Servers and Relays that are 162 seen as OMNI link neighbors as well as Bridges that interconnect 163 diverse Internetworks as OMNI link segments through OAL forwarding at 164 a layer below IP. Each node's OMNI interface uses an IPv6 link-local 165 address format that supports operation of the IPv6 Neighbor Discovery 166 (IPv6 ND) protocol [RFC4861]. A node's OMNI interface can be 167 configured over multiple underlying interfaces, and therefore appears 168 as a single interface with multiple link-layer addresses. Each link- 169 layer address is subject to change due to mobility and/or multilink 170 fluctuations, and link-layer address changes are signaled by ND 171 messaging the same as for any IPv6 link. 173 AERO provides a secure cloud-based service where mobile node Clients 174 may use any Proxy/Server acting as a mobility anchor point and fixed 175 nodes may use any Relay on the link for efficient communications. 176 Fixed nodes forward original IP packets destined to other AERO nodes 177 via the nearest Relay, which forwards them through the cloud. Mobile 178 node Clients discover shortest paths to OMNI link neighbors through 179 AERO route optimization. Both unicast and multicast communications 180 are supported, and Clients may efficiently move between locations 181 while maintaining continuous communications with correspondents and 182 without changing their IP Address. 184 AERO Bridges peer with Proxy/Servers in a secured private BGP overlay 185 routing instance to establish a Segment Routing Topology (SRT) 186 spanning tree over the underlying Internetworks of multiple disjoint 187 administrative domains as a single unified OMNI link. Each OMNI link 188 instance is characterized by the set of Mobility Service Prefixes 189 (MSPs) common to all mobile nodes. Relays provide an optimal route 190 from (fixed) correspondent nodes on the underlying Internetwork to 191 (mobile or fixed) nodes on the OMNI link. To the underlying 192 Internetwork, the Relay is the source of a route to the MSP; hence 193 uplink traffic to the mobile node is naturally routed to the nearest 194 Relay. 196 AERO can be used with OMNI links that span private-use Internetworks 197 and/or public Internetworks such as the global Internet. In the 198 latter case, some end systems may be located behind global Internet 199 Network Address Translators (NATs). A means for robust traversal of 200 NATs while avoiding "triangle routing" and Proxy/Server traffic 201 concentration is therefore provided. 203 AERO assumes the use of PIM Sparse Mode in support of multicast 204 communication. In support of Source Specific Multicast (SSM) when a 205 Mobile Node is the source, AERO route optimization ensures that a 206 shortest-path multicast tree is established with provisions for 207 mobility and multilink operation. In all other multicast scenarios 208 there are no AERO dependencies. 210 AERO provides a secure aeronautical internetworking service for both 211 manned and unmanned aircraft, where the aircraft is treated as a 212 mobile node that can connect an Internet of Things (IoT). AERO is 213 also applicable to a wide variety of other use cases. For example, 214 it can be used to coordinate the links of mobile nodes (e.g., 215 cellphones, tablets, laptop computers, etc.) that connect into a home 216 enterprise network via public access networks with VPN or non-VPN 217 services enabled according to the appropriate security model. AERO 218 can also be used to facilitate terrestrial vehicular and urban air 219 mobility (as well as pedestrian communication services) for future 220 intelligent transportation systems 221 [I-D.ietf-ipwave-vehicular-networking][I-D.templin-ipwave-uam-its]. 222 Other applicable use cases are also in scope. 224 Along with OMNI, AERO provides secured optimal routing support for 225 the "6M's" of modern Internetworking, including: 227 1. Multilink - a mobile node's ability to coordinate multiple 228 diverse underlying data links as a single logical unit (i.e., the 229 OMNI interface) to achieve the required communications 230 performance and reliability objectives. 232 2. Multinet - the ability to span the OMNI link over a segment 233 routing topology with multiple diverse network administrative 234 domains while maintaining seamless end-to-end communications 235 between mobile Clients and correspondents such as air traffic 236 controllers, fleet administrators, etc. 238 3. Mobility - a mobile node's ability to change network points of 239 attachment (e.g., moving between wireless base stations) which 240 may result in an underlying interface address change, but without 241 disruptions to ongoing communication sessions with peers over the 242 OMNI link. 244 4. Multicast - the ability to send a single network transmission 245 that reaches multiple nodes belonging to the same interest group, 246 but without disturbing other nodes not subscribed to the interest 247 group. 249 5. Multihop - a mobile node vehicle-to-vehicle relaying capability 250 useful when multiple forwarding hops between vehicles may be 251 necessary to "reach back" to an infrastructure access point 252 connection to the OMNI link. 254 6. MTU assurance - the ability to deliver packets of various robust 255 sizes between peers without loss due to a link size restriction, 256 and to dynamically adjust packets sizes to achieve the optimal 257 performance for each independent traffic flow. 259 The following numbered sections present the AERO specification. The 260 appendices at the end of the document are non-normative. 262 2. Terminology 264 The terminology in the normative references applies; especially, the 265 terminology in the OMNI specification [I-D.templin-6man-omni] is used 266 extensively throughout. The following terms are defined within the 267 scope of this document: 269 IPv6 Neighbor Discovery (IPv6 ND) 270 a control message service for coordinating neighbor relationships 271 between nodes connected to a common link. AERO uses the IPv6 ND 272 messaging service specified in [RFC4861]. 274 IPv6 Prefix Delegation 275 a networking service for delegating IPv6 prefixes to nodes on the 276 link. The nominal service is DHCPv6 [RFC8415], however alternate 277 services (e.g., based on IPv6 ND messaging) are also in scope. A 278 minimal form of prefix delegation known as "prefix registration" 279 can be used if the Client knows its prefix in advance and can 280 represent it in the source address of an IPv6 ND message. 282 Access Network (ANET) 283 a node's first-hop data link service network (e.g., a radio access 284 network, cellular service provider network, corporate enterprise 285 network, etc.) that often provides link-layer security services 286 such as IEEE 802.1X and physical-layer security (e.g., "protected 287 spectrum") to prevent unauthorized access internally and with 288 border network-layer security services such as firewalls and 289 proxys that prevent unauthorized outside access. 291 ANET interface 292 a node's attachment to a link in an ANET. 294 Internetwork (INET) 295 a network topology with a coherent IP routing and addressing plan 296 and that provides a transit backbone service for its connected end 297 systems. INETs also provide an underlay service over which the 298 AERO virtual link is configured. Example INETs include corporate 299 enterprise networks, aviation networks, and the public Internet 300 itself. When there is no administrative boundary between an ANET 301 and the INET, the ANET and INET are one and the same. 303 INET interface 304 a node's attachment to a link in an INET. 306 *NET 307 a "wildcard" term referring to either ANET or INET when it is not 308 necessary to draw a distinction between the two. 310 *NET interface 311 a node's attachment to a link in a *NET. 313 *NET Partition 314 frequently, *NETs such as large corporate enterprise networks are 315 sub-divided internally into separate isolated partitions (a 316 technique also known as "network segmentation"). Each partition 317 is fully connected internally but disconnected from other 318 partitions, and there is no requirement that separate partitions 319 maintain consistent Internet Protocol and/or addressing plans. 320 (Each *NET partition is seen as a separate OMNI link segment as 321 discussed below.) 323 *NET address 324 an IP address assigned to a node's interface connection to a *NET. 326 *NET encapsulation 327 the encapsulation of a packet in an outer header or headers that 328 can be routed within the scope of the local *NET partition. 330 OMNI link 331 the same as defined in [I-D.templin-6man-omni]. The OMNI link 332 employs IPv6 encapsulation [RFC2473] to traverse intermediate 333 nodes in a spanning tree over underlying *NET segments the same as 334 a bridged campus LAN. AERO nodes on the OMNI link appear as 335 single-hop neighbors at the network layer even though they may be 336 separated by many underlying *NET hops; AERO nodes can employ 337 Segment Routing [RFC8402] to navigate between different OMNI 338 links, and/or to cause packets to visit selected waypoints within 339 the same OMNI link. 341 OMNI Interface 342 a node's attachment to an OMNI link. Since OMNI interface 343 addresses are managed for uniqueness, OMNI interfaces do not 344 require Duplicate Address Detection (DAD) and therefore set the 345 administrative variable 'DupAddrDetectTransmits' to zero 346 [RFC4862]. 348 OMNI Adaptation Layer (OAL) 349 an OMNI interface service that subjects original IP packets 350 admitted into the interface to mid-layer IPv6 header encapsulation 351 followed by fragmentation and reassembly. The OAL is also 352 responsible for generating MTU-related control messages as 353 necessary, and for providing addressing context for spanning 354 multiple segments of a bridged OMNI link. 356 original IP packet 357 a whole IP packet or fragment admitted into the OMNI interface by 358 the network layer prior to OAL encapsulation and fragmentation, or 359 an IP packet delivered to the network layer by the OMNI interface 360 following OAL decapsulation and reassembly. 362 OAL packet 363 an original IP packet encapsulated in OAL headers and trailers 364 before OAL fragmentation, or following OAL reassembly. 366 OAL fragment 367 a portion of an OAL packet following fragmentation but prior to 368 *NET encapsulation, or following *NET encapsulation but prior to 369 OAL reassembly. 371 (OAL) atomic fragment 372 an OAL packet that can be forwarded without fragmentation, but 373 still includes a Fragment Header with a valid Identification value 374 and with Fragment Offset and More Fragments both set to 0. 376 (OAL) carrier packet 377 an encapsulated OAL fragment following *NET encapsulation or prior 378 to *NET decapsulation. OAL sources and destinations exchange 379 carrier packets over underlying interfaces, and may be separated 380 by one or more OAL intermediate nodes. OAL intermediate nodes re- 381 encapsulate carrier packets during forwarding by removing the *NET 382 headers of the previous hop underlying network and replacing them 383 with new *NET headers for the next hop underlying network. 385 OAL source 386 an OMNI interface acts as an OAL source when it encapsulates 387 original IP packets to form OAL packets, then performs OAL 388 fragmentation and *NET encapsulation to create carrier packets. 390 OAL destination 391 an OMNI interface acts as an OAL destination when it decapsulates 392 carrier packets, then performs OAL reassembly and decapsulation to 393 derive the original IP packet. 395 OAL intermediate node 396 an OMNI interface acts as an OAL intermediate node when it removes 397 the *NET headers of carrier packets received from a first hop, 398 then re-encapsulates the carrier packets in new *NET headers and 399 forwards them to the next hop. OAL intermediate nodes decrement 400 the Hop Limit of the OAL IPv6 header during re-encapsulation, and 401 discard the packet if the Hop Limit reaches 0. OAL intermediate 402 nodes do not decrement the Hop Limit/TTL of the original IP 403 packet. 405 underlying interface 406 a *NET interface over which an OMNI interface is configured. 408 Mobility Service Prefix (MSP) 409 an aggregated IP Global Unicast Address (GUA) prefix (e.g., 410 2001:db8::/32, 192.0.2.0/24, etc.) assigned to the OMNI link and 411 from which more-specific Mobile Network Prefixes (MNPs) are 412 delegated. OMNI link administrators typically obtain MSPs from an 413 Internet address registry, however private-use prefixes can 414 alternatively be used subject to certain limitations (see: 415 [I-D.templin-6man-omni]). OMNI links that connect to the global 416 Internet advertise their MSPs to their interdomain routing peers. 418 Mobile Network Prefix (MNP) 419 a longer IP prefix delegated from an MSP (e.g., 420 2001:db8:1000:2000::/56, 192.0.2.8/30, etc.) and delegated to an 421 AERO Client or Relay. 423 Mobile Network Prefix Link Local Address (MNP-LLA) 424 an IPv6 Link Local Address that embeds the most significant 64 425 bits of an MNP in the lower 64 bits of fe80::/64, as specified in 426 [I-D.templin-6man-omni]. 428 Mobile Network Prefix Unique Local Address (MNP-ULA) 429 an IPv6 Unique-Local Address derived from an MNP-LLA. 431 Administrative Link Local Address (ADM-LLA) 432 an IPv6 Link Local Address that embeds a 32-bit administratively- 433 assigned identification value in the lower 32 bits of fe80::/96, 434 as specified in [I-D.templin-6man-omni]. 436 Administrative Unique Local Address (ADM-ULA) 437 an IPv6 Unique-Local Address derived from an ADM-LLA. 439 AERO node 440 a node that is connected to an OMNI link and participates in the 441 AERO internetworking and mobility service. 443 AERO Client ("Client") 444 an AERO node that connects over one or more underlying interfaces 445 and requests MNP delegation/registration service from AERO Proxy/ 446 Servers. The Client assigns an MNP-LLA to the OMNI interface for 447 use in IPv6 ND exchanges with other AERO nodes and forwards 448 original IP packets to correspondents according to OMNI interface 449 neighbor cache state. 451 AERO Proxy/Server ("Proxy/Server") 452 a node that provides a proxying service between AERO Clients and 453 external peers on its Client-facing ANET interfaces (i.e., in the 454 same fashion as for an enterprise network proxy) as well as 455 default forwarding and mobility anchor point services for 456 coordination with correspondents on its INET-facing interfaces. 457 (Proxy/Servers in the open INET instead configure only an INET 458 interface and no ANET interfaces.) The Proxy/Server configures an 459 OMNI interface and assigns an ADM-LLA to support the operation of 460 IPv6 ND services, while advertising all of its associated MNPs via 461 BGP peerings with Bridges. 463 AERO Relay ("Relay") 464 a Proxy/Server that provides forwarding services between nodes 465 reached via the OMNI link and correspondents on other links/ 466 networks. AERO Relays configure an OMNI interface and assign an 467 ADM-LLA the same as Proxy/Servers, and also run a dynamic routing 468 protocol to discover any non-MNP IP GUA routes in service on its 469 other links/networks. The Relay advertises the MSP(s) to its 470 other links/networks, and redistributes routes discovered on other 471 links/networks into the OMNI link routing system the same as for 472 Proxy/Servers. 474 AERO Bridge ("Bridge") 475 a BGP hub autonomous system node that also provides OAL forwarding 476 services for nodes on an OMNI link. Bridges forwards carrier 477 packets between OMNI link segments as OAL intermediate nodes while 478 decrementing the OAL IPv6 header Hop Limit but without 479 decrementing the network layer IP TTL/Hop Limit. Bridges peer 480 with Proxy/Servers and other Bridges to form a spanning tree over 481 all OMNI link segments and to discover the set of all MNP and non- 482 MNP prefixes in service. Bridges process carrier packets received 483 over the secured spanning tree that are addressed to themselves, 484 while forwarding all other carrier packets to the next hop also 485 via the secured spanning tree. Bridges forward carrier packets 486 received over the unsecured spanning tree to the next hop either 487 via the unsecured spanning tree or via direct encapsulation if the 488 next hop is on the same OMNI link segment. 490 First-Hop Segment (FHS) Proxy/Server 491 a Proxy/Server for an underlying interface of the source Client 492 that forwards packets sent by the source Client over that 493 interface into the segment routing topology. 495 Last-Hop Segment (LHS) Proxy/Server 496 a Proxy/Server for an underlying interface of the target Client 497 that forwards packets received from the segment routing topology 498 to the target Client over that interface. 500 Segment Routing Topology (SRT) 501 a multinet OMNI link forwarding region between the FHS Proxy/ 502 Server and LHS Proxy/Server. FHS/LHS Proxy/Servers and SRT 503 Bridges span the OMNI link on behalf of source/target Client 504 pairs. The SRT maintains a spanning tree established through BGP 505 peerings between Bridges and Proxy/Servers. Each SRT segment 506 includes Bridges in a "hub" and Proxy/Servers in "spokes", while 507 adjacent segments are interconnected by Bridge-Bridge peerings. 508 The BGP peerings are configured over both secured and unsecured 509 underlying network paths such that a secured spanning tree is 510 available for critical control messages while other messages can 511 use the unsecured spanning tree. 513 link-layer address 514 an IP address used as an encapsulation header source or 515 destination address from the perspective of the OMNI interface. 516 When an upper layer protocol (e.g., UDP) is used as part of the 517 encapsulation, the port number is also considered as part of the 518 link-layer address. 520 network layer address 521 the source or destination address of an original IP packet 522 presented to the OMNI interface. 524 end user network (EUN) 525 an internal virtual or external edge IP network that an AERO 526 Client or Relay connects to the rest of the network via the OMNI 527 interface. The Client/Relay sees each EUN as a "downstream" 528 network, and sees the OMNI interface as the point of attachment to 529 the "upstream" network. 531 Mobile Node (MN) 532 an AERO Client and all of its downstream-attached networks that 533 move together as a single unit, i.e., an end system that connects 534 an Internet of Things. 536 Mobile Router (MR) 537 a MN's on-board router that forwards original IP packets between 538 any downstream-attached networks and the OMNI link. The MR is the 539 MN entity that hosts the AERO Client. 541 Route Optimization Source (ROS) 542 the AERO node nearest the source that initiates route 543 optimization. The ROS may be a FHS Proxy/Server or Relay for the 544 source, or may be the source Client itself. 546 Route Optimization responder (ROR) 547 the AERO node that responds to route optimization requests on 548 behalf of the target. The ROR may be a Proxy/Server for a target 549 MNP Client or a Relay for a non-MNP target. 551 Potential Router List (PRL) 552 a geographically and/or topologically referenced list of addresses 553 of all Proxy/Servers within the same OMNI link. Each OMNI link 554 has its own PRL. 556 Distributed Mobility Management (DMM) 557 a BGP-based overlay routing service coordinated by Proxy/Servers 558 and Bridges that tracks all Proxy/Server-to-Client associations. 560 Mobility Service (MS) 561 the collective set of all Proxy/Servers, Bridges and Relays that 562 provide the AERO Service to Clients. 564 Mobility Service Endpoint MSE) 565 an individual Proxy/Server, Bridge or Relay in the Mobility 566 Service. 568 Multilink Forwarding Information Base (MFIB) 569 A forwarding table on each AERO/OMNI source, destination and 570 intermediate node that includes Multilink Forwarding Vectors (MFV) 571 with both next hop forwarding instructions and context for 572 reconstructing compressed headers for specific underlying 573 interface pairs used to communicate with peers. 575 Multilink Forwarding Vector (MFV) 576 An MFIB entry that includes soft state for each underlying 577 interface pairwise communication session between peer OMNI nodes. 578 MFVs are identified by both a next-hop and previous-hop MFV Index 579 (MFVI), with the next-hop established based on an IPv6 ND 580 solicitation and the previous hop established based on the 581 solicited IPv6 ND advertisement response. 583 Multilink Forwarding Vector Index (MVFI) 584 A 4 octet value selected by an AERO/OMNI node when it creates an 585 MFV, then advertised to either a next-hop or previous-hop. AERO/ 586 OMNI intermediate nodes assign two distinct local MFVIs for each 587 MFV and advertise one to the next-hop and the other to the 588 previous-hop. AERO/OMNI end systems assign and advertise a single 589 MFVI. AERO/OMNI nodes also discover the remote MFVIs advertised 590 by other nodes that indicate a value the other node is willing to 591 accept. 593 Throughout the document, the simple terms "Client", "Proxy/Server", 594 "Bridge" and "Relay" refer to "AERO Client", "AERO Proxy/Server", 595 "AERO Bridge" and "AERO Relay", respectively. Capitalization is used 596 to distinguish these terms from other common Internetworking uses in 597 which they appear without capitalization. 599 The terminology of IPv6 ND [RFC4861] and DHCPv6 [RFC8415] (including 600 the names of node variables, messages and protocol constants) is used 601 throughout this document. The terms "All-Routers multicast", "All- 602 Nodes multicast", "Solicited-Node multicast" and "Subnet-Router 603 anycast" are defined in [RFC4291]. Also, the term "IP" is used to 604 generically refer to either Internet Protocol version, i.e., IPv4 605 [RFC0791] or IPv6 [RFC8200]. 607 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 608 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 609 "OPTIONAL" in this document are to be interpreted as described in BCP 610 14 [RFC2119][RFC8174] when, and only when, they appear in all 611 capitals, as shown here. 613 3. Automatic Extended Route Optimization (AERO) 615 The following sections specify the operation of IP over OMNI links 616 using the AERO service: 618 3.1. AERO Node Types 620 AERO Clients can be deployed as fixed infrastructure nodes close to 621 end systems, or as Mobile Nodes (MNs) that can change their network 622 attachment points dynamically. AERO Clients configure OMNI 623 interfaces over underlying interfaces with addresses that may change 624 due to mobility. AERO Clients register their Mobile Network Prefixes 625 (MNPs) with the AERO service, and distribute the MNPs to nodes on 626 EUNs. AERO Bridges, Proxy/Servers and Relays are critical 627 infrastructure elements in fixed (i.e., non-mobile) INET deployments 628 and hence have permanent and unchanging INET addresses. Together, 629 they constitute the AERO service which provides an OMNI link virtual 630 overlay for connecting AERO Clients. 632 AERO Bridges (together with Proxy/Servers) provide the secured 633 backbone supporting infrastructure for a Segment Routing Topology 634 (SRT) spanning tree for the OMNI link. Bridges forward carrier 635 packets both within the same SRT segment and between disjoint SRT 636 segments based on an IPv6 encapsulation mid-layer known as the OMNI 637 Adaptation Layer (OAL) [I-D.templin-6man-omni]. The OMNI interface 638 and OAL provide a virtual bridging service, since the inner IP TTL/ 639 Hop Limit is not decremented. Each Bridge also peers with Proxy/ 640 Servers and other Bridges in a dynamic routing protocol instance to 641 provide a Distributed Mobility Management (DMM) service for the list 642 of active MNPs (see Section 3.2.3). Bridges present the OMNI link as 643 a set of one or more Mobility Service Prefixes (MSPs) and configure 644 secured tunnels with Proxy/Servers, Relays and other Bridges; they 645 further maintain forwarding table entries for each MNP or non-MNP 646 prefix in service on the OMNI link. 648 AERO Proxy/Servers in distributed SRT segments provide default 649 forwarding and mobility/multilink services for AERO Client mobile 650 nodes. Each Proxy/Server also peers with Bridges in a dynamic 651 routing protocol instance to advertise its list of associated MNPs 652 (see Section 3.2.3). Proxy/Servers provide prefix delegation/ 653 registration services and track the mobility/multilink profiles of 654 each of their associated Clients, where each delegated prefix becomes 655 an MNP taken from an MSP. Proxy/Servers at ANET/INET boundaries 656 provide a forwarding service for ANET Clients to communicate with 657 peers in external INETs while Proxy/Servers in the open INET provide 658 an authentication for INET Client IPv6 ND messages but limited 659 forwarding services. Source Clients securely coordinate with target 660 Clients by sending control messages via a First-Hop Segment (FHS) 661 Proxy/Server which forwards them over the SRT spanning tree to a 662 Last-Hop Segment (LHS) Proxy/Server which finally forwards them to 663 the target. 665 AERO Relays are Proxy/Servers that provide forwarding services to 666 exchange original IP packets between the OMNI link and other links/ 667 networks. Relays run a dynamic routing protocol to discover any non- 668 MNP prefixes in service on other links/networks. The Relay 669 redistributes OMNI link MSP(s) into other links/networks, and 670 redistributes non-MNP prefixes via OMNI link Bridge BGP peerings. 672 3.2. The AERO Service over OMNI Links 674 3.2.1. AERO/OMNI Reference Model 676 Figure 1 presents the basic OMNI link reference model: 678 +----------------+ 679 | AERO Bridge B1 | 680 | Nbr: S1, S2, P1| 681 |(X1->S1; X2->S2)| 682 | MSP M1 | 683 +-------+--------+ 684 +--------------+ | +--------------+ 685 | AERO P/S S1 | | | AERO P/S S2 | 686 | Nbr: C1, B1 | | | Nbr: C2, B1 | 687 | default->B1 | | | default->B1 | 688 | X1->C1 | | | X2->C2 | 689 +-------+------+ | +------+-------+ 690 | OMNI link | | 691 X===+===+==================+===================+===+===X 692 | | 693 +-----+--------+ +--------+-----+ 694 |AERO Client C1| |AERO Client C2| 695 | Nbr: S1 | | Nbr: S2 | 696 | default->S1 | | default->S2 | 697 | MNP X1 | | MNP X2 | 698 +------+-------+ +-----+--------+ 699 | | 700 .-. .-. 701 ,-( _)-. ,-( _)-. 702 .-(_ IP )-. +-------+ +-------+ .-(_ IP )-. 703 (__ EUN )--|Host H1| |Host H2|--(__ EUN ) 704 `-(______)-' +-------+ +-------+ `-(______)-' 706 Figure 1: AERO/OMNI Reference Model 708 In this model: 710 o the OMNI link is an overlay network service configured over one or 711 more underlying SRT segments which may be managed by different 712 administrative authorities and have incompatible protocols and/or 713 addressing plans. 715 o AERO Bridge B1 aggregates Mobility Service Prefix (MSP) M1, 716 discovers Mobile Network Prefixes (MNPs) X* and advertises the MSP 717 via BGP peerings over secured tunnels to Proxy/Servers (S1, S2). 718 Bridges provide the backbone for an SRT spanning tree for the OMNI 719 link. 721 o AERO Proxy/Servers S1 and S2 configure secured tunnels with Bridge 722 B1 and also provide mobility, multilink, multicast and default 723 router services for the MNPs of their associated Clients C1 and 724 C2. (Proxy/Servers that act as Relays can also advertise non-MNP 725 routes for non-mobile correspondent nodes the same as for MNP 726 Clients.) 728 o AERO Clients C1 and C2 associate with Proxy/Servers S1 and S2, 729 respectively. They receive MNP delegations X1 and X2, and also 730 act as default routers for their associated physical or internal 731 virtual EUNs. Simple hosts H1 and H2 attach to the EUNs served by 732 Clients C1 and C2, respectively. 734 An OMNI link configured over a single *NET appears as a single 735 unified link with a consistent underlying network addressing plan; 736 all nodes on the link can exchange carrier packets via simple *NET 737 encapsulation (i.e., following any necessary NAT traversal) since the 738 underlying *NET is connected. In common practice, however, OMNI 739 links are often configured over an SRT spanning tree that bridges 740 multiple distinct *NET segments managed under different 741 administrative authorities (e.g., as for worldwide aviation service 742 providers such as ARINC, SITA, Inmarsat, etc.). Individual *NETs may 743 also be partitioned internally, in which case each internal partition 744 appears as a separate segment. 746 The addressing plan of each SRT segment is consistent internally but 747 will often bear no relation to the addressing plans of other 748 segments. Each segment is also likely to be separated from others by 749 network security devices (e.g., firewalls, proxys, packet filtering 750 gateways, etc.), and disjoint segments often have no common physical 751 link connections. Therefore, nodes can only be assured of exchanging 752 carrier packets directly with correspondents in the same segment, and 753 not with those in other segments. The only means for joining the 754 segments therefore is through inter-domain peerings between AERO 755 Bridges. 757 The OMNI link spans multi-segment SRT topologies using the OMNI 758 Adaptation Layer (OAL) [I-D.templin-6man-omni] to provide the network 759 layer with a virtual abstraction similar to a bridged campus LAN. 760 The OAL is an OMNI interface sublayer that inserts a mid-layer IPv6 761 encapsulation header for inter-segment forwarding (i.e., bridging) 762 without decrementing the network-layer TTL/Hop Limit of the original 763 IP packet. An example OMNI link SRT is shown in Figure 2: 765 . . . . . . . . . . . . . . . . . . . . . . . 766 . . 767 . .-(::::::::) . 768 . .-(::::::::::::)-. +-+ . 769 . (:::: Segment A :::)--|B|---+ . 770 . `-(::::::::::::)-' +-+ | . 771 . `-(::::::)-' | . 772 . | . 773 . .-(::::::::) | . 774 . .-(::::::::::::)-. +-+ | . 775 . (:::: Segment B :::)--|B|---+ . 776 . `-(::::::::::::)-' +-+ | . 777 . `-(::::::)-' | . 778 . | . 779 . .-(::::::::) | . 780 . .-(::::::::::::)-. +-+ | . 781 . (:::: Segment C :::)--|B|---+ . 782 . `-(::::::::::::)-' +-+ | . 783 . `-(::::::)-' | . 784 . | . 785 . ..(etc).. x . 786 . . 787 . . 788 . <- Segment Routing Topology (SRT) -> . 789 . . . . . . . . . . . . . .. . . . . . . . . 791 Figure 2: OMNI Link Segment Routing Topology (SRT) 793 Bridge, Proxy/Server and Relay OMNI interfaces are configured over 794 both secured tunnels and open INET underlying interfaces within their 795 respective SRT segments. Within each segment, Bridges configure 796 "hub-and-spokes" BGP peerings with Proxy/Server/Relays as "spokes". 797 Adjacent SRT segments are joined by Bridge-to-Bridge peerings to 798 collectively form a spanning tree over the entire SRT. The "secured" 799 spanning tree supports authentication and integrity for critical 800 control plane messages. The "unsecured" spanning tree conveys 801 ordinary carrier packets without security codes and that must be 802 treated by destinations according to data origin authentication 803 procedures. AERO nodes can employ route optimization to cause 804 carrier packets to take more direct paths between OMNI link neighbors 805 without having to follow strict spanning tree paths. 807 3.2.2. Addressing and Node Identification 809 AERO nodes on OMNI links use the Link-Local Address (LLA) prefix 810 fe80::/64 [RFC4291] to assign LLAs used for network-layer addresses 811 in link-scoped IPv6 ND and data messages. AERO Clients use LLAs 812 constructed from MNPs (i.e., "MNP-LLAs") while other AERO nodes use 813 LLAs constructed from administrative identification values ("ADM- 814 LLAs") as specified in [I-D.templin-6man-omni]. Non-MNP routes are 815 also represented the same as for MNP-LLAs, but may include a prefix 816 that is not properly covered by the MSP. 818 AERO nodes also use the Unique Local Address (ULA) prefix fd00::/8 819 followed by a pseudo-random 40-bit OMNI domain identifier to form the 820 prefix [ULA]::/48, then include a 16-bit OMNI link identifier '*' to 821 form the prefix [ULA*]::/64 [RFC4291]. The AERO node then uses the 822 prefix [ULA*]::/64 to form "MNP-ULAs" or "ADM-ULA"s as specified in 823 [I-D.templin-6man-omni] to support OAL addressing. (The prefix 824 [ULA*]::/64 appearing alone and with no suffix represents "default".) 825 AERO Clients also use Temporary ULAs constructed per 826 [I-D.templin-6man-omni], where the addresses are typically used only 827 in initial control message exchanges until a stable MNP-LLA/ULA is 828 assigned. 830 AERO MSPs, MNPs and non-MNP routes are typically based on Global 831 Unicast Addresses (GUAs), but in some cases may be based on private- 832 use addresses. See [I-D.templin-6man-omni] for a full specification 833 of LLAs, ULAs and GUAs used by AERO nodes on OMNI links. 835 Finally, AERO Clients and Proxy/Servers configure node identification 836 values as specified in [I-D.templin-6man-omni]. 838 3.2.3. AERO Routing System 840 The AERO routing system comprises a private Border Gateway Protocol 841 (BGP) [RFC4271] service coordinated between Bridges and Proxy/ 842 Servers. The service supports carrier packet forwarding at a layer 843 below IP and does not interact with the public Internet BGP routing 844 system, but supports redistribution of information for other links 845 and networks discovered by Relays. 847 In a reference deployment, each Proxy/Server is configured as an 848 Autonomous System Border Router (ASBR) for a stub Autonomous System 849 (AS) using a 32-bit AS Number (ASN) [RFC4271] that is unique within 850 the BGP instance, and each Proxy/Server further uses eBGP to peer 851 with one or more Bridges but does not peer with other Proxy/Servers. 852 Each SRT segment in the OMNI link must include one or more Bridges in 853 a "hub" AS, which peer with the Proxy/Servers within that segment as 854 "spoke" ASes. All Bridges within the same segment are members of the 855 same hub AS, and use iBGP to maintain a consistent view of all active 856 routes currently in service. The Bridges of different segments peer 857 with one another using eBGP. 859 Bridges maintain forwarding table entries only for the MNP-ULAs 860 corresponding to MNP and non-MNP routes that are currently active, 861 while carrier packets destined to all other MNP-ULAs are dropped with 862 a Destination Unreachable message returned due to the black-hole 863 route. In this way, Proxy/Servers and Relays have only partial 864 topology knowledge (i.e., they only maintain routing information for 865 their directly associated Clients and non-AERO links) and they 866 forward all other carrier packets to Bridges which have full topology 867 knowledge. 869 Each OMNI link segment assigns a unique ADM-ULA sub-prefix of 870 [ULA*]::/96 known as the "SRT prefix". For example, a first segment 871 could assign [ULA*]::1000/116, a second could assign 872 [ULA*]::2000/116, a third could assign [ULA*]::3000/116, etc. Within 873 each segment, each Proxy/Server configures an ADM-ULA within the 874 segment's SRT prefix, e.g., the Proxy/Servers within [ULA*]::2000/116 875 could assign the ADM-ULAs [ULA*]::2011/116, [ULA*]::2026/116, 876 [ULA*]::2003/116, etc. 878 The administrative authorities for each segment must therefore 879 coordinate to assure mutually-exclusive ADM-ULA prefix assignments, 880 but internal provisioning of ADM-ULAs an independent local 881 consideration for each administrative authority. For each ADM-ULA 882 prefix, the Bridge(s) that connect that segment assign the all-zero's 883 address of the prefix as a Subnet Router Anycast address. For 884 example, the Subnet Router Anycast address for [ULA*]::1023/116 is 885 simply [ULA*]::1000. 887 ADM-ULA prefixes are statically represented in Bridge forwarding 888 tables. Bridges join multiple SRT segments into a unified OMNI link 889 over multiple diverse network administrative domains. They support a 890 virtual bridging service by first establishing forwarding table 891 entries for their ADM-ULA prefixes either via standard BGP routing or 892 static routes. For example, if three Bridges ('A', 'B' and 'C') from 893 different segments serviced [ULA*]::1000/116, [ULA*]::2000/116 and 894 [ULA*]::3000/116 respectively, then the forwarding tables in each 895 Bridge are as follows: 897 A: [ULA*]::1000/116->local, [ULA*]::2000/116->B, [ULA*]::3000/116->C 899 B: [ULA*]::1000/116->A, [ULA*]::2000/116->local, [ULA*]::3000/116->C 901 C: [ULA*]::1000/116->A, [ULA*]::2000/116->B, [ULA*]::3000/116->local 903 These forwarding table entries rarely change, since they correspond 904 to fixed infrastructure elements in their respective segments. 906 MNP (and non-MNP) ULAs are instead dynamically advertised in the AERO 907 routing system by Proxy/Servers and Relays that provide service for 908 their corresponding MNPs. For example, if three Proxy/Servers ('D', 909 'E' and 'F') service the MNPs 2001:db8:1000:2000::/56, 910 2001:db8:3000:4000::/56 and 2001:db8:5000:6000::/56 then the routing 911 system would include: 913 D: [ULA*]:2001:db8:1000:2000/120 915 E: [ULA*]:2001:db8:3000:4000/120 917 F: [ULA*]:2001:db8:5000:6000/120 919 A full discussion of the BGP-based routing system used by AERO is 920 found in [I-D.ietf-rtgwg-atn-bgp]. 922 3.2.4. OMNI Link Forwarding 924 When the network layer forwards an original IP packet into an OMNI 925 interface, the OMNI Adaptation Layer (OAL) encapsulates the packet to 926 produce an OAL packet [I-D.templin-6man-omni]. This OAL source then 927 fragments the OAL packet while including an identical Identification 928 value for each fragment that must be within the window for the LHS 929 Proxy/Server or the target Client itself. The OAL source also 930 includes an identical Compressed Routing Header with 32-bit ID fields 931 (CRH-32) [I-D.bonica-6man-comp-rtg-hdr] with each fragment if 932 necessary as discussed in Section 3.2.7 and Section 3.14. The OAL 933 source finally encapsulates each resulting OAL fragment in *NET 934 headers to form an OAL carrier packet, with source address set to its 935 own *NET address (e.g., 192.0.2.100) and destination set to the *NET 936 address of the next hop OAL intermediate node or destination (e.g., 937 192.0.2.1). 939 The carrier packet encapsulation format in the above example is shown 940 in Figure 3: 942 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 943 | *NET Header | 944 | src = 192.0.2.100 | 945 | dst = 192.0.2.1 | 946 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 947 | OAL IPv6 Header | 948 | src = [ULA*]::2001:db8:1:2 | 949 | dst= [ULA*]::3000:0000 | 950 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 951 | CRH-32 (if necessary) | 952 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 953 | OAL Fragment Header | 954 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 955 | Original IP Header | 956 | (first-fragment only) | 957 | src = 2001:db8:1:2::1 | 958 | dst = 2001:db8:1234:5678::1 | 959 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 960 | | 961 ~ ~ 962 ~ Original Packet Body/Fragment ~ 963 ~ ~ 964 | | 965 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 967 Figure 3: Carrier Packet Format 969 In this format, the original IP header and packet body/fragment are 970 encapsulated in an OAL IPv6 header prepared according to [RFC2473], 971 the CRH-32 is a Routing Header extension of the OAL header, the 972 Fragment Header identifies each fragment, and the *NET header is 973 prepared as discussed in Section 3.6. The OAL source transmits each 974 such carrier packet into the SRT spanning tree, where they are 975 forwarded over possibly multiple OAL intermediate nodes until they 976 arrive at the OAL destination. 978 The OMNI link control plane service distributes both Client MNP-ULA 979 prefix information that may change dynamically due to regional node 980 mobility and per-segment ADM-ULA prefix information that rarely 981 changes. OMNI link Bridges and Proxy/Servers use the information to 982 establish and maintain a forwarding plane spanning tree that connects 983 all nodes on the link. The spanning tree supports a carrier packet 984 virtual bridging service according to link-layer (instead of network- 985 layer) information, but may often include longer paths than 986 necessary. Each OMNI interface therefore also includes a Multilink 987 Forwarding Information Base (MFIB) with Multilink Forwarding Vectors 988 (MFVs) that can often provide "shortcuts" instead of always following 989 strict spanning tree paths. As a result, the spanning tree is always 990 available but OMNI interfaces can often use the MFIB to greatly 991 improve performance and reduce load on critical infrastructure 992 elements. 994 3.2.5. Segment Routing Topologies (SRTs) 996 The 64-bit sub-prefixes of [ULA]::/48 identify up to 2^16 distinct 997 Segment Routing Topologies (SRTs). Each SRT is a mutually-exclusive 998 OMNI link overlay instance using a distinct set of ULAs, and emulates 999 a bridged campus LAN service for the OMNI link. In some cases (e.g., 1000 when redundant topologies are needed for fault tolerance and 1001 reliability) it may be beneficial to deploy multiple SRTs that act as 1002 independent overlay instances. A communication failure in one 1003 instance therefore will not affect communications in other instances. 1005 Each SRT is identified by a distinct value in bits 48-63 of 1006 [ULA]::/48, i.e., as [ULA0]::/64, [ULA1]::/64, [ULA2]::/64, etc. 1007 Each OMNI interface is identified by a unique interface name (e.g., 1008 omni0, omni1, omni2, etc.) and assigns an anycast ADM-ULA 1009 corresponding to its SRT prefix length. The anycast ADM-ULA is used 1010 for OMNI interface determination in Safety-Based Multilink (SBM) as 1011 discussed in [I-D.templin-6man-omni]. Each OMNI interface further 1012 applies Performance-Based Multilink (PBM) internally. 1014 The Bridges and Proxy/Servers of each independent SRT engage in BGP 1015 peerings to form a spanning tree with the Bridges in non-leaf nodes 1016 and the Proxy/Servers in leaf nodes. The spanning tree is configured 1017 over both secured and unsecured underlying network paths. The 1018 secured spanning tree is used to convey secured control messages 1019 between FHS and LHS Proxy/Servers, while the unsecured spanning tree 1020 forwards data messages and/or unsecured control messages. 1022 Each SRT segment is identified by a unique ADM-ULA prefix used by all 1023 Proxy/Servers and Bridges in the segment. Each AERO node must 1024 therefore discover an SRT prefix that correspondents can use to 1025 determine the correct segment, and must publish the SRT prefix in 1026 IPv6 ND messages. 1028 3.2.6. Segment Routing For OMNI Link Selection 1030 Original IPv6 source can direct IPv6 packets to an AERO node by 1031 including a standard IPv6 Segment Routing Header (SRH) [RFC8754] with 1032 the anycast ADM-ULA for the selected OMNI link as either the IPv6 1033 destination or as an intermediate hop within the SRH. This allows 1034 the original source to determine the specific OMNI link SRT an 1035 original IPv6 packet will traverse when there may be multiple 1036 alternatives. 1038 When an AERO node processes the SRH and forwards the original IPv6 1039 packet to the correct OMNI interface, the OMNI interface writes the 1040 next IPv6 address from the SRH into the IPv6 destination address and 1041 decrements Segments Left. If decrementing would cause Segments Left 1042 to become 0, the OMNI interface deletes the SRH before forwarding. 1043 This form of Segment Routing supports Safety-Based Multilink (SBM). 1045 3.2.7. OMNI Multilink Forwarding 1047 OMNI interfaces include a supplemental forwarding table termed the 1048 Multilink Forwarding Information Base (MFIB) that provides shorter 1049 paths for carrier packet forwarding based on OMNI neighbor underlying 1050 interface pairs. The MFIB contains Multilink Forwarding Vectors 1051 (MFVs) indexed by 4-octet values known as MFV Indexes (MFVIs). 1053 OMNI interface "OAL source", "OAL intermediate" and "OAL destination" 1054 nodes create MFVs/MFVIs when they process an IPv6 ND solicitation 1055 message with Job code "00" or a solicited advertisement with Job code 1056 "01" (see: [I-D.templin-6man-omni]).. The OAL source of the 1057 solicitation (and OAL destination of the solicited advertisement) are 1058 considered to reside in the "First Hop Segment (FHS)", while the OAL 1059 destination of the solicitation (and OAL source of the solicited 1060 advertisement) are considered to reside in the "Last Hop Segment 1061 (LHS)". 1063 When an OAL node processes a solicitation with Job code "00", it 1064 creates an MFV, records the solicitation's source and destination 1065 LLAs and assigns a "B" MFVI. When the "B" MVFI is referenced, the 1066 MVF presents the LLAs in (dst,src) order the opposite of how they 1067 appeared in the original solicitation. 1069 When an OAL node processes a solicited advertisement with Job code 1070 "01", it locates the MFV created by the solicitation and assigns an 1071 "A" MFVI. When the "B" MFVI is referenced, the MFV presents the LLAs 1072 in (src,dst) order the same as they appeared in the original 1073 solicitation. 1075 OAL nodes generate random 32-bit values as candidate A/B MFVIs which 1076 must first be tested for local uniqueness. If a candidate MFVI s 1077 already in use (or if the value is 0), the OAL node repeats the 1078 process until it obtains a unique non-zero value. (Since the number 1079 of MFVs in service at each OAL node is likely to be much smaller than 1080 2**32, the process will generate a unique value after a small number 1081 of tries.) An MFVI generated by a first OAL node SHOULD NOT be 1082 tested for uniqueness on other OAL nodes, since the uniqueness 1083 property is node-local only. 1085 OAL nodes maintain A/B MFVIs as follows: 1087 o "B1" - a locally-unique MFVI maintained independently by each OAL 1088 node on the path from the FHS OAL source to the last LHS 1089 intermediate node before the OAL destination. The OAL node 1090 generates and assigns a "B1" MFVI to a newly-created MFV when it 1091 processes a solicitation message with Job code "00". When the OAL 1092 node receives future carrier packets that include this value, it 1093 can unambiguously locate the correct MFV and determine 1094 directionality without examining addresses. 1096 o "A1" - a locally unique MFVI maintained independently by each OAL 1097 node on the path from the LHS OAL source to the last FHS 1098 intermediate node before the OAL destination. The OAL node 1099 generates and assigns an "A1" MFVI to the MVF that configures the 1100 corresponding "B1" MFVI when it processes a solicited 1101 advertisement message with Job code "01". The local OAL node can 1102 use unambiguously locate the correct MFV and determine 1103 directionality without examining addresses. 1105 o "A2" - the A1 MFVI of a remote OAL node discovered by an FHS OAL 1106 source or OAL intermediate node when it processes an advertisement 1107 message with Job code "01" that originated from an LHS OAL source. 1108 A2 values MUST NOT be tested for uniqueness within the OAL node's 1109 local context. 1111 o "B2" - the B1 MFVI of a remote OAL node discovered by an LHS OAL 1112 source or OAL intermediate node when it processes a solicitation 1113 message with Job code "00" that originated from an FHS OAL source. 1114 B2 values MUST NOT be tested for uniqueness within the OAL node's 1115 local context. 1117 When an FHS OAL source has an original IP packet to send to an LHS 1118 OAL destination, (i.e., one for which there is no existing NCE) it 1119 first selects a source and target underlying interface pair. The OAL 1120 source uses its cached information for the source underlying 1121 interface as FHS information and its cached information for the 1122 target underlying interface as LHS information. The OAL source then 1123 prepares a solicitation message with an OMNI Multilink Forwarding 1124 Parameters sub-option with Job code "00" and with source set to its 1125 own {ADM,MNP}-LLA. If the LHS FMT-Forward and FMT-Mode bits are both 1126 clear, the OAL source sets the destination to the ADM-LLA of the LHS 1127 Proxy/Server; otherwise, it sets the destination to the MNP-LLA of 1128 the target Client. The OAL source then sets window synchronization 1129 information in the OMNI header, creates a NCE for the selected 1130 destination {ADM,MNP}-LLA in the INCOMPLETE state and places the 1131 original IP packet on a short queue. The OAL source next creates an 1132 MFV based on the solicitation source and destination LLAs, then 1133 generates a "B1" MFVI and assigns it to the MFV while also including 1134 it as the first B entry in the MFVI List. The OAL source then 1135 populates the solicitation Multilink Forwarding Parameters based on 1136 the FHS/LHS information. 1138 If the OAL source is the FHS Proxy/Server, it then performs OAL 1139 encapsulation/fragmentation while setting the source to its own ADM- 1140 ULA and setting the destination to the FHS Subnet Router Anycast ULA 1141 determined by applying the FHS SRT prefix length to its ADM-ULA. The 1142 FHS Proxy/Server next examines the LHS FMT code. If FMT-Forward is 1143 clear and FMT-Mode is set, the FHS Proxy/Server checks for a NCE for 1144 the ADM-LLA of the LHS Proxy/Server. If there is no NCE, the LHS 1145 Proxy/Server creates one in the INCOMPLETE state. If a new NCE was 1146 created (or if the existing NCE requires fresh window 1147 synchronization), the FHS Proxy/Server then writes window 1148 synchronization parameters into the OMNI Multilink Forwarding 1149 Parameters Tunnel Window Synchronization fields. The FHS Proxy/ 1150 Server then selects an appropriate Identification value and *NET 1151 headers and forwards the resulting carrier packets into the secured 1152 spanning tree which will deliver them to a Bridge interface that 1153 assigns the FHS Subnet Router Anycast ULA.. 1155 If the OAL source is the FHS Client, it instead includes an 1156 authentication signature if necessary, performs OAL encapsulation/ 1157 fragmentation, sets the source to its own ADM-ULA and sets the 1158 destination to the ADM-ULA of the FHS Proxy/Server. The FHS Client 1159 then selects an appropriate Identification value and *NET headers and 1160 forwards the carrier packets to the FHS Proxy/Server. When the FHS 1161 Proxy/Server receives the carrier packets, it verifies the 1162 Identification, reassembles/decapsulates to obtain the solicitation 1163 then verifies the authentication signature. The FHS Proxy/Server 1164 then creates an MFV (i.e., the same as the FHS Client had done) while 1165 assigning the current B entry in the MFVI List (i.e., the one 1166 included by the FHS Client) as the "B2" MFVI for this MVF. The FHS 1167 Proxy/Server then generates a new unique "B1" MFVI, then both assigns 1168 it to the MFV and writes it as the next B entry in the OMNI Multilink 1169 Forwarding Parameters MFVI List. The FHS Proxy/Server then checks 1170 LHS FMT-Forward/Mode to determine whether to create a NCE for the LHS 1171 Proxy/Server ADM-LLA and include Tunnel Window Synchronization 1172 parameters the same as above. The FHS Proxy/Server then re- 1173 encapsulates/re-fragments while setting the source to its own ADM-ULA 1174 and destination address to the FHS Subnet Router Anycast ULA. The 1175 FHS Proxy/Server finally includes an appropriate Identification value 1176 and *NET headers and forwards the carrier packets into the secured 1177 spanning tree the same as above. 1179 Bridges in the spanning tree forward carrier packets not explicitly 1180 addressed to themselves, while forwarding those that arrived via the 1181 secured spanning tree to the next hop also via the secured spanning 1182 tree and forwarding all others via the unsecured spanning tree. When 1183 an FHS Bridge receives a carrier packet over the secured spanning 1184 tree addressed to its ADM-ULA or the FHS Subnet Router Anycast ULA, 1185 it instead reassembles/decapsulates to obtain the solicitation. The 1186 FHS Bridge next creates an MFV (i.e., the same as the FHS Proxy/ 1187 Server had done) while assigning the current B entry in the MFVI List 1188 as the MFV "B2" index. The FHS Bridge also caches the solicitation 1189 Multilink Forwarding Parameters FHS information in the MFV, and also 1190 caches the first B entry in the MFVI List as "FHS-Client" when FHS 1191 FMT-Forward/Mode are both set to enable future direct forwarding to 1192 this FHS Client. The FHS Bridge then generates a "B1" MFVI for the 1193 MFV and also writes it as the next B entry in the solicitation's MFVI 1194 List. 1196 The FHS Bridge then examines the SRT prefixes corresponding to both 1197 FHS and LHS. If the FHS Bridge has a local interface connection to 1198 both the FHS and LHS (whether they are the same or different 1199 segments), the FHS/LHS Bridge caches the solicitation LHS information 1200 and writes its ADM-ULA suffix and LHS INET address into the 1201 solicitation OMNI Multilink Forwarding Parameters LHS fields. The 1202 FHS/LHS Bridge then re-encapsulates the solicitation with its own 1203 ADM-ULA as the source and with the ADM-ULA of the LHS Proxy/Server as 1204 the destination. If the FHS and LHS prefixes are different, the FHS 1205 Bridge instead re-encapsulates with its own ADM-ULA as the source and 1206 with the LHS Subnet Router Anycast ULA as the destination. The FHS 1207 Bridge selects an appropriate Identification and *NET headers as 1208 above then forwards the carrier packets into the secured spanning 1209 tree. 1211 When the FHS and LHS Bridges are different, the LHS Bridge will 1212 receive carrier packets over the secured spanning tree from the FHS 1213 Bridge. The LHS Bridge reassembles/decapsulates to obtain the 1214 solicitation then creates an MFV (i.e., the same as the FHS Bridge 1215 had done) while assigning the current B entry in the MFVI List as the 1216 MFV "B2" index. The LHS Bridge also caches the ADM-ULA of the FHS 1217 Bridge as the spanning tree address for "B2", caches the solicitation 1218 Multilink Forwarding Parameters LHS information then generates a "B1" 1219 MFVI for the MFV while also writing it as the next B entry in the 1220 MFVI List. The LHS Bridge also writes its own ADM-ULA suffix and LHS 1221 INET address into the OMNI Multilink Forwarding Parameters. The LHS 1222 Bridge then re-encapsulates with its own ADM-ULA as the source and 1223 the ADM-ULA of the LHS Proxy/Server as the destination, then selects 1224 an appropriate Identification and *NET headers and forwards the 1225 carrier packets into the secured spanning tree. 1227 When the LHS Proxy/Server receives the carrier packets from the 1228 secured spanning tree, it reassembles/decapsulates to obtain the 1229 solicitation then creates an MFV and assigns the current B entry in 1230 the MFVI List as the "B2" MFVI the same as for the prior hop. If the 1231 solicitation destination is the MNP-LLA of the target Client, the LHS 1232 Proxy/Server also generates a "B1" MFVI and assigns it both to the 1233 MFVI and as the next B entry in the MFVI List. The LHS Proxy/Server 1234 then examines FHS FMT; if FMT-Forward is clear and FMT-Mode is set, 1235 the LHS Proxy/Server creates a NCE for the ADM-LLA of the FHS Proxy/ 1236 Server (if necessary) and sets the state to STALE, then caches any 1237 Tunnel Window Synchronization parameters. 1239 If the solicitation destination is its own ADM-LLA, the LHS Proxy/ 1240 Server next prepares to return a solicited advertisement with Job 1241 code "01". If the solicitation source was the MNP-LLA of the FHS 1242 Client, the LHS Proxy/Server first creates or updates an NCE for the 1243 MNP-LLA with state set to STALE. The LHS Proxy/Server next caches 1244 the solicitation OMNI header window synchronization parameters and 1245 Multilink Forwarding Parameters information (including the MFVI List) 1246 in the NCE corresponding to the LLA source. When the LHS Proxy/ 1247 Server forwards future carrier packets based on the NCE, it can 1248 populate reverse-path forwarding information in a CRH-32 routing 1249 header to enable forwarding based on the cached MFVI List B entries 1250 instead of ULA addresses. 1252 The LHS Proxy/Server then creates an advertisement with Job code "01" 1253 while copying the solicitation OMNI Multilink Forwarding Parameters 1254 FHS/LHS information into the corresponding fields in the 1255 advertisement. The LHS Proxy/Server then generates an "A1" MFVI and 1256 both assigns it to the MFV and includes it as the first A entry in 1257 advertisement's MFVI List (see: [I-D.templin-6man-omni] for details 1258 on MFVI List A/B processing). The LHS Proxy/Server then includes 1259 end-to-end window synchronization parameters in the OMIN header (if 1260 necessary) and also tunnel window synchronization parameters in the 1261 Multilink Forwarding Parameters Tunnel block (if necessary). The LHS 1262 Proxy/Server then encapsulates the advertisement, sets the source to 1263 its own ADM-ULA, sets the destination to the ADM-ULA of the LHS 1264 Bridge, selects an appropriate Identification value and *NET headers 1265 then forwards the carrier packets into the secured spanning tree. 1267 If the solicitation destination was the MNP-LLA of the LHS Client, 1268 the LHS Proxy/Server instead includes an authentication signature in 1269 the solicitation, then re-encapsulates/re-fragments with its own ADM- 1270 ULA as the source and the MNP-ULA of the LHS Client as the 1271 destination. The LHS Proxy/Server then selects an appropriate 1272 Identification value and *NET headers and forwards the carrier 1273 packets to the LHS Client. When the LHS Client receives the carrier 1274 packets, it verifies the Identification and reassembles/decapsulates 1275 to obtain the solicitation. The LHS Client then creates a NCE for 1276 the solicitation LLA source address in the STALE state. If LHS FMT- 1277 Forward is set, FHS FMT-Forward is clear and the solicitation source 1278 was an MNP-LLA, the Client also creates a NCE for the ADM-LLA of the 1279 FHS Proxy/Server in the STALE state and caches any Tunnel Window 1280 Synchronization parameters. The Client then caches the solicitation 1281 OMNI header window synchronization parameters and Multilink 1282 Forwarding Parameters in the NCE corresponding to the solicitation 1283 LLA source, then creates an MFV and assigns both the current MFVI 1284 List B entry as "B2" and a locally generated "A1" MFVI the same as 1285 for previous hops (the LHS Client also includes the "A1" value in the 1286 solicited advertisement - see above and below). The LHS Client also 1287 caches the previous MFVI List B entry as "LHS-Bridge" since it can 1288 include this value when it sends future carrier packets directly to 1289 the Bridge. 1291 The LHS Client then prepares an advertisement using exactly the same 1292 procedures as for the LHS Proxy/Server above, except that it uses its 1293 MNP-LLA as the source. The LHS Client also includes an 1294 authentication signature, then encapsulates the advertisement with 1295 source set to its own ADM-ULA and destination set to the ADM-ULA of 1296 the LHS Proxy/Server. The LHS Client then includes an appropriate 1297 Identification and *NET headers and forwards the carrier packets to 1298 the LHS Proxy/Server. When the LHS Proxy/Server receives the carrier 1299 packets, it verifies the Identifications, reassembles/decapsulates to 1300 obtain the advertisement, verifies the authentication signature, then 1301 uses the current MVFI List B entry to locate the MFV. The LHS Proxy/ 1302 Server then writes the current MFVI List A entry as the "A2" value 1303 for the MVF, generates an "A1" MFVI and both assigns it to the MFV 1304 and writes it as the next MFVI List A entry. The LHS Proxy/Server 1305 then examines the FHS/LHS FMT codes to determine if it needs to 1306 include Tunnel window synchronization parameters. The LHS Proxy/ 1307 Server then re-encapsulates/re-fragments the advertisement, sets the 1308 OAL source to its own ADM-ULA and destination to the ADM-ULA of the 1309 LHS Bridge, includes an appropriate Identification and *NET headers 1310 and forwards the carrier packets into the secured spanning tree. 1312 When the LHS Bridge receives the carrier packets, it reassembles/ 1313 decapsulates to obtain the advertisement then uses the current MFVI 1314 List B entry to locate the MFV. The LHS Bridge then writes the 1315 current MFVI List A entry as the MFV "A2" index and generates a new 1316 "A1" value which it both assigns the MFV and writes as the next MFVI 1317 List A entry. If the LHS Bridge is connected directly to both the 1318 FHS and LHS segments (whether the segments are the same or 1319 different), the FHS/LHS Bridge will have already cached the FHS/LHS 1320 information based on the original solicitation. The FHS/LHS Bridge 1321 then re-encapsulates the solicitation with its own ADM-ULA as the 1322 source and with the ADM-ULA of the FHS Proxy/Server as the 1323 destination. If the FHS and LHS prefixes are different, the FHS 1324 Bridge instead re-encapsulates/re-fragments with its own ADM-ULA as 1325 the source and with the ADM-ULA of the FHS Bridge as the destination. 1327 The LHS Bridge selects an appropriate Identification and *NET headers 1328 then forwards the carrier packets into the secured spanning tree. 1330 When the FHS and LHS Bridges are different, the FHS Bridge will 1331 receive the carrier packets from the LHS Bridge over the secured 1332 spanning tree. The FHS Bridge reassembles/decapsulates to obtain the 1333 advertisement, then locates the MFV based on the current MFVI List B 1334 entry. The FHS Bridge then assigns the current MFVI List A entry as 1335 the as the MFV "A2" index and caches the ADM-ULA of the LHS Bridge as 1336 the spanning tree address for "A2". The FHS Bridge then generates an 1337 "A1" MVFI and both assigns it to the MVF and writes it as the next 1338 MFVI List A entry while also writing its ADM-ULA and INET address in 1339 the NA(WIN) FHS Bridge fields. The FHS Bridge then re-encapsulates/ 1340 re-fragments with its own ADM-ULA as the source, with the ADM-ULA of 1341 the FHS Proxy/Server as the destination, then selects an appropriate 1342 Identification value and *NET headers and forwards the carrier 1343 packets into the secured spanning tree. 1345 When the FHS Proxy/Server receives the carrier packets from the 1346 secured spanning tree, it reassembles/decapsulates to obtain the 1347 advertisement then locates the MFV based on the current MFVI List B 1348 entry. The FHS Proxy/Server then assigns the current MFVI List A 1349 entry as the "A2" MFVI the same as for the prior hop. If the 1350 advertisement destination is its own ADM-LLA, the FHS Proxy/Server 1351 then caches the advertisement Multilink Forwarding Parameters with 1352 the MFV and examines LHS FMT. If FMT-Forward is clear, the FHS 1353 Proxy/Server locates the NCE for the ADM-LLA of the LHS Proxy/Server 1354 and sets the state to REACHABLE then caches any Tunnel Window 1355 Synchronization parameters. If the advertisement source is the MNP- 1356 LLA of the LHS Client, the FHS Proxy/Server then locates the LHS 1357 Client NCE and sets the state to REACHABLE then caches the OMNI 1358 header window synchronization parameters and prepares to return an NA 1359 acknowledgement, if necessary. 1361 If the advertisement destination is the MNP-LLA of the FHS Client, 1362 the FHS Proxy/Server also searches for and updates the NCE for the 1363 ADM-LLA of the LHS Proxy/Server if necessary the same as above. The 1364 FHS Proxy/Server then generates an "A1" MFVI and assigns it both to 1365 the MFVI and as the next MFVI List A entry, then includes an 1366 authentication signature in the advertisement message. The FHS 1367 Proxy/Server then re-encapsulates/re-fragment with its own ADM-ULA as 1368 the source, with the MNP-ULA of the FHS Client as the destination, 1369 then selects an appropriate Identification value and *NET headers and 1370 forwards the carrier packets to the FHS Client. 1372 When the FHS Client receives the carrier packets, it verifies the 1373 Identification, reassembles/decapsulates to obtain the advertisement 1374 then locates the MFV based on the current MFVI List B entry. The FHS 1375 Client then assigns the current MFVI List A entry as the "A2" MFVI 1376 the same as for the prior hop. The FHS Client then caches the 1377 advertisement Multilink Forwarding Parameters (including the MFVI 1378 List) with the MFV and examines LHS FMT. If FMT-Forward is clear, 1379 the FHS Client locates the NCE for the ADM-LLA of the LHS Proxy/ 1380 Server and sets the state to REACHABLE then caches any Tunnel Window 1381 Synchronization parameters. If the advertisement source is the MNP- 1382 LLA of the LHS Client, the FHS Proxy/Server then locates the LHS 1383 Client NCE and sets the state to REACHABLE then caches the OMNI 1384 header window synchronization parameters and prepares to return an NA 1385 acknowledgement, if necessary. 1387 When either the FHS Client or FHS Proxy/Server needs to return an NA 1388 acknowledgement to complete window synchronization, it prepares an 1389 acknowledgement message with an OMNI Multilink Forwarding Parameters 1390 sub-option with Job code set to "10" (Follow A; Record B). The FHS 1391 node then includes Tunnel Window Synchronization parameters if 1392 necessary and sets the MFVI List to the cached list of A entries 1393 received in the LHS advertisement, but need not set any other FHS/LHS 1394 information. If the FHS node is the Client, it next includes an 1395 authentication signature then encapsulates/fragments with its own 1396 MNP-ULA as the source and the ADM-ULA of the FHS Proxy/Server as the 1397 destination, then selects an appropriate Identification value and 1398 *NET headers and forwards the carrier packets to the FHS Proxy/ 1399 Server. The FHS Proxy/Server then verifies the Identification, 1400 reassembles/decapsulates, verifies the authentication signature and 1401 uses the current MFVI List A entry to locate the MFV. The FHS Proxy/ 1402 Server then writes its "B1" MFVI as the next MFVI List B entry and 1403 determines whether it needs to include Tunnel Window Synchronization 1404 parameters the same as it had done when it forwarded the original 1405 solicitation. 1407 The FHS Proxy/Server then re-encapsulates/re-fragments with its own 1408 ADM-ULA as the source and the ADM-ULA of the FHS Bridge as the 1409 destination, then selects an appropriate Identification and *NET 1410 headers and forwards the carrier packets into the secured spanning 1411 tree. When the FHS Bridge receives the carrier packets, it 1412 reassembles/decapsulates then uses the current MFVI List A entry to 1413 locate the MFV. The FHS Bridge then writes its "B1" MFVI as the next 1414 MFVI List B entry. The FHS Bridge then re-encapsulates/re-fragments 1415 with its own ADM-ULA as the source and the ADM-ULA of the LHS Proxy/ 1416 Server as the destination. If the FHS Bridge is also the LHS Bridge, 1417 it sets the ADM-ULA of the LHS Proxy/Server as the destination; 1418 otherwise it sets the ADM-ULA of the LHS Bridge. The FHS Bridge then 1419 selects an appropriate Identification and *NET headers and forwards 1420 the carrier packets into the secured spanning tree. If an LHS Bridge 1421 receives the carrier packets, it processes them exactly the same as 1422 the FHS Bridge had done while setting the carrier packet source to 1423 its own ADM-ULA and destination to the ADM-ULA of the LHS Proxy/ 1424 Server. 1426 When the LHS Proxy/Server receives the carrier packets, it 1427 reassembles/decapsulates to obtain the NA acknowledgement message. 1428 The LHS Proxy/Server then locates the MFV based on the current MFVI 1429 List A entry then determines whether it is a tunnel ingress the same 1430 as for the original solicitation. If it is a tunnel ingress, the LHS 1431 Proxy/Server updates the NCE for the tunnel far-end based on the 1432 Tunnel Window Synchronization parameters in the NA. If the NA 1433 destination is its own ADM-LLA, the LHS Proxy/Server next updates the 1434 NCE for the NA source LLA based on the OMNI header Window 1435 Synchronization parameters and MAY compare the MVFI List to the 1436 version it had cached in the MFV based on the original solicitation. 1438 If the NA destination is the MNP-LLA of the LHS Client, the LHS 1439 Proxy/Server instead writes its "B1" MFV as the next MFVI List B 1440 entry, includes an authentication signature, re-encapsulates/re- 1441 fragments with its own ADM-ULA as the source and the MNP-ULA of the 1442 Client as the destination then selects an appropriate Identification 1443 and *NET headers and forwards the resulting carrier packets to the 1444 LHS Client. When the LHS Client receives the carrier packets, it 1445 verifies the Identification, reassembles/decapsulates to obtain the 1446 NA acknowledgement, verifies the authentication signature then 1447 processes the message exactly the same as for the LHS Proxy/Server 1448 case above. 1450 Following the solicitation/advertisement/acknowledgement exchange, 1451 OAL end systems and tunnel endpoints can begin exchanging ordinary 1452 carrier packets with Identification values within their respective 1453 send/receive windows without requiring security signatures and/or 1454 secured spanning tree traversal. Either peer can refresh window 1455 synchronization parameters and/or send other carrier packets 1456 requiring security at any time using the same secured procedures 1457 described above. OAL end systems and intermediate nodes can also use 1458 their own A1/B1 MFVIs when they receive carrier packets to 1459 unambiguously locate the correct MFV and determine directionality and 1460 can use any discovered A2/B2 MFVIs to forward carrier packets to 1461 other OAL nodes that configure the corresponding A1/B1 MFVIs. When 1462 an OAL node uses an MFVI included in a carrier packet to locate an 1463 MFV, it need not also examine the carrier packet addresses. 1465 OAL sources can also begin including CRH-32s in carrier packets with 1466 a list of A/B MFVIs that OAL intermediate nodes can use for shortest- 1467 path carrier packet forwarding based on MFVIs instead of spanning 1468 tree addresses. OAL sources and intermediate nodes can also begin 1469 forwarding carrier packets with compressed headers (see: 1470 [I-D.templin-6man-omni]) that include only a single A/B MFVI 1471 meaningful to the next hop, since all nodes in the path up to (and 1472 sometimes including) the OAL destination have already established MFV 1473 forwarding information. Note that when an FHS OAL source receives a 1474 solicited advertisement with Job code "01', the message will contain 1475 an MFVI List with A entries populated in the reverse order needed for 1476 populating a CRH-32 routing header. The FHS OAL source must 1477 therefore write the MFVI List A entries last-to-first when it 1478 populates a CRH-32, or must select the correct A entry to include in 1479 a compressed OAL header based on the intended OAL intermediate node 1480 or destination. 1482 When a Bridge receives unsecured carrier packets destined to a local 1483 segment Client that has asserted direct reachability, the Bridge 1484 employs NAT traversal procedures to enable direct carrier packet 1485 forwarding while bypassing the local Proxy/Server based on the 1486 Client's advertised MFVIs and discovered NATed L2ADDR information. 1487 If the Client cannot be reached directly (or if NAT traversal has not 1488 yet converged), the Bridge instead forwards carrier packets directly 1489 to the local Proxy/Server. 1491 When a Proxy/Server receives carrier packets destined to a local 1492 Client or forwards carrier packets received from a local Client, it 1493 first locates the correct MFV. If the carrier packets include a 1494 secured IPv6 ND message, the Proxy/Server uses the Client's MVF 1495 established through RS/RA exchanges to re-encapsulate/re-fragment 1496 while forwarding outbound secured carrier packets via the secured 1497 spanning tree and forwarding inbound secured carrier packets while 1498 including an authentication signature. For ordinary carrier packets, 1499 the Proxy/Server uses the same MFV if directed by MFVI and/or OAL 1500 addressing. Otherwise it locates an MFV established through an NS/NA 1501 exchange between the Client and the remote peer, and forwards the 1502 carrier packets without first reassembling/decapsulating. 1504 When a Proxy/Server or Client configured as a tunnel ingress receives 1505 a carrier packet with a full header with an MNP-ULA source or a 1506 compressed header with an MFVI that matches an MFV, the ingress 1507 encapsulates the carrier packet in a new OAL full or compressed 1508 header with the inner header containing Identification values 1509 appropriate for the end-to-end window and the outer header containing 1510 an Identification value appropriate for the tunnel endpoints. When a 1511 Proxy/Server or Client configured as a tunnel egress receives an 1512 encapsulated carrier packet, it verifies the Identification in the 1513 outer header, then discards the outer header and forwards the inner 1514 carrier packet to the final destination. 1516 When a source Client forwards carrier packets it can employ header 1517 compression according to the MFVIs established through an NS/NA 1518 exchange with a remote or local peer. When the source Client 1519 forwards to a remote peer, it can forward carrier packets to a local 1520 SRT Bridge while bypassing the Proxy/Server. When a target Client 1521 receives carrier packets that match a local MFV, the Client first 1522 verifies the Identification then decompresses the headers if 1523 necessary, reassembles if necessary to obtain the OAL packet then 1524 decapsulates and delivers the IP packet to upper layers. 1526 When synchronized peer Clients in the same SRT segment with FMT- 1527 Forward and FMT-Mode set discover each other's NATed L2ADDR addresses 1528 through NAT traversal, they can exchange carrier packets directly 1529 with header compression using MFVIs discovered as above. 1531 3.3. OMNI Interface Characteristics 1533 OMNI interfaces are virtual interfaces configured over one or more 1534 underlying interfaces classified as follows: 1536 o INET interfaces connect to an INET either natively or through one 1537 or more NATs. Native INET interfaces have global IP addresses 1538 that are reachable from any INET correspondent. The INET-facing 1539 interfaces of Proxy/Servers are native interfaces, as are Relay 1540 and Bridge interfaces. NATed INET interfaces connect to a private 1541 network behind one or more NATs that provide INET access. Clients 1542 that are behind a NAT are required to send periodic keepalive 1543 messages to keep NAT state alive when there are no carrier packets 1544 flowing. 1546 o ANET interfaces connect to an ANET that is separated from the open 1547 INET by an FHS Proxy/Server. Clients can issue control messages 1548 over the ANET without including an authentication signature since 1549 the ANET is secured at the network layer or below. Proxy/Servers 1550 can actively issue control messages over the INET on behalf of 1551 ANET Clients to reduce ANET congestion. 1553 o VPNed interfaces use security encapsulation over the INET to a 1554 Virtual Private Network (VPN) server that also acts as an FHS 1555 Proxy/Server. Other than the link-layer encapsulation format, 1556 VPNed interfaces behave the same as Direct interfaces. 1558 o Direct (i.e., single-hop point-to-point) interfaces connect a 1559 Client directly to an FHS Proxy/Server without crossing any ANET/ 1560 INET paths. An example is a line-of-sight link between a remote 1561 pilot and an unmanned aircraft. The same Client considerations 1562 apply as for VPNed interfaces. 1564 OMNI interfaces use OAL encapsulation and fragmentation as discussed 1565 in Section 3.2.4. OMNI interfaces use *NET encapsulation (see: 1566 Section 3.6) to exchange carrier packets with OMNI link neighbors 1567 over INET or VPNed interfaces as well as over ANET interfaces for 1568 which the Client and FHS Proxy/Server may be multiple IP hops away. 1569 OMNI interfaces do not use link-layer encapsulation over Direct 1570 underlying interfaces or ANET interfaces when the Client and FHS 1571 Proxy/Server are known to be on the same underlying link. 1573 OMNI interfaces maintain a neighbor cache for tracking per-neighbor 1574 state the same as for any interface. OMNI interfaces use IPv6 ND 1575 messages including Router Solicitation (RS), Router Advertisement 1576 (RA), Neighbor Solicitation (NS) and Neighbor Advertisement (NA) for 1577 neighbor cache management. In environments where spoofing may be a 1578 threat, OMNI neighbors should employ OAL Identification window 1579 synchronization in their IPv6 ND message exchanges. 1581 OMNI interfaces send IPv6 ND messages with an OMNI option formatted 1582 as specified in [I-D.templin-6man-omni]. The OMNI option includes 1583 prefix registration information, Interface Attributes containing link 1584 information parameters for the OMNI interface's underlying interfaces 1585 and any other per-neighbor information. Each OMNI option may include 1586 multiple Interface Attributes sub-options identified by omIndex 1587 values. 1589 A Client's OMNI interface may be configured over multiple underlying 1590 interfaces. For example, common mobile handheld devices have both 1591 wireless local area network ("WLAN") and cellular wireless links. 1592 These links are often used "one at a time" with low-cost WLAN 1593 preferred and highly-available cellular wireless as a standby, but a 1594 simultaneous-use capability could provide benefits. In a more 1595 complex example, aircraft frequently have many wireless data link 1596 types (e.g. satellite-based, cellular, terrestrial, air-to-air 1597 directional, etc.) with diverse performance and cost properties. 1599 If a Client's multiple underlying interfaces are used "one at a time" 1600 (i.e., all other interfaces are in standby mode while one interface 1601 is active), then successive IPv6 ND messages all include OMNI option 1602 Interface Attributes sub-options with the same underlying interface 1603 index. In that case, the Client would appear to have a single 1604 underlying interface but with a dynamically changing link-layer 1605 address. 1607 If the Client has multiple active underlying interfaces, then from 1608 the perspective of IPv6 ND it would appear to have multiple link- 1609 layer addresses. In that case, IPv6 ND message OMNI options MAY 1610 include Interface Attributes sub-options with different underlying 1611 interface indexes. Every IPv6 ND message need not include Interface 1612 Attributes for all underlying interfaces; for any attributes not 1613 included, the neighbor considers the status as unchanged. 1615 Bridge and Proxy/Server OMNI interfaces are configured over 1616 underlying interfaces that provide both secured tunnels for carrying 1617 IPv6 ND and BGP protocol control plane messages and open INET access 1618 for carrying unsecured messages. The OMNI interface configures both 1619 an ADM-LLA and its corresponding ADM-ULA, and acts as an OAL source 1620 to encapsulate and fragment original IP packets while presenting the 1621 resulting carrier packets over the secured or unsecured underlying 1622 paths. Note that Bridge and Proxy/Server BGP protocol TCP sessions 1623 are run directly over the OMNI interface and use ADM-ULA source and 1624 destination addresses. The OMNI interface employs the OAL to 1625 encapsulate the original IP packets for these sessions as carrier 1626 packets (i.e., even though the OAL header may use the same ADM-ULAs 1627 as the original IP header) and forwards them over the secured 1628 underlying path. 1630 3.4. OMNI Interface Initialization 1632 AERO Proxy/Servers and Clients configure OMNI interfaces as their 1633 point of attachment to the OMNI link. AERO nodes assign the MSPs for 1634 the link to their OMNI interfaces (i.e., as a "route-to-interface") 1635 to ensure that original IP packets with destination addresses covered 1636 by an MNP not explicitly associated with another interface are 1637 directed to an OMNI interface. 1639 OMNI interface initialization procedures for Proxy/Servers, Clients 1640 and Bridges are discussed in the following sections. 1642 3.4.1. AERO Proxy/Server and Relay Behavior 1644 When a Proxy/Server enables an OMNI interface, it assigns an 1645 ADM-{LLA,ULA} appropriate for the given OMNI link SRT segment. The 1646 Proxy/Server also configures secured tunnels with one or more 1647 neighboring Bridges and engages in a BGP routing protocol session 1648 with each Bridge. 1650 The OMNI interface provides a single interface abstraction to the IP 1651 layer, but internally includes an NBMA nexus for sending carrier 1652 packets to OMNI interface neighbors over underlying INET interfaces 1653 and secured tunnels. The Proxy/Server further configures a service 1654 to facilitate IPv6 ND exchanges with AERO Clients and manages per- 1655 Client neighbor cache entries and IP forwarding table entries based 1656 on control message exchanges. 1658 Relays are simply Proxy/Servers that run a dynamic routing protocol 1659 to redistribute routes between the OMNI interface and INET/EUN 1660 interfaces (see: Section 3.2.3). The Relay provisions MNPs to 1661 networks on the INET/EUN interfaces (i.e., the same as a Client would 1662 do) and advertises the MSP(s) for the OMNI link over the INET/EUN 1663 interfaces. The Relay further provides an attachment point of the 1664 OMNI link to a non-MNP-based global topology. 1666 3.4.2. AERO Client Behavior 1668 When a Client enables an OMNI interface, it assigns either an 1669 MNP-{LLA, ULA} or a Temporary ULA and sends RS messages over its 1670 underlying interfaces to an FHS Proxy/Server, which returns an RA 1671 message with corresponding parameters. The RS/RA messages may pass 1672 through one or more NATs in the case of a Client's INET interface. 1673 (Note: if the Client used a Temporary ULA in its initial RS message, 1674 it will discover an MNP-{LLA, ULA} in the corresponding RA that it 1675 receives from the FHS Proxy/Server and begin using these new 1676 addresses. If the Client is operating outside the context of AERO 1677 infrastructure such as in a Mobile Ad-hoc Network (MANET), however, 1678 it may continue using Temporary ULAs for Client-to-Client 1679 communications until it encounters an infrastructure element that can 1680 provide an MNP.) 1682 3.4.3. AERO Bridge Behavior 1684 AERO Bridges configure an OMNI interface and assign an ADM-ULA and 1685 corresponding Subnet Router Anycast address for each OMNI link SRT 1686 segment they connect to. Bridges configure secured tunnels with 1687 Proxy/Servers in the same SRT segment and other Bridges in the same 1688 (or an adjacent) SRT segment. Bridges then engage in a BGP routing 1689 protocol session with neighbors over the secured spanning tree (see: 1690 Section 3.2.3). 1692 3.5. OMNI Interface Neighbor Cache Maintenance 1694 Each OMNI interface maintains a conceptual neighbor cache that 1695 includes a Neighbor Cache Entry (NCE) for each of its active 1696 neighbors on the OMNI link per [RFC4861]. Each NCE is indexed by the 1697 LLA of the neighbor, while the OAL encapsulation ULA determines the 1698 context for Identification verification. Clients and Proxy/Servers 1699 maintain NCEs through RS/RA exchanges, and also maintain NCEs for any 1700 active correspondent peers through NS/NA exchanges. 1702 Bridges also maintain NCEs for Clients within their local segments 1703 based on NS/NA(WIN) route optimization. When a Bridge creates/ 1704 updates a NCE for a local segment Client based on NS/NA(WIN) route 1705 optimization, it also maintains a "Peer List" for the NCE with an 1706 entry for the ULA, window state and FMT/SRT/LHS/L2ADDR information 1707 for the source of each NS/NA(WIN) message destined to this local 1708 segment Client. The Bridge also assigns a unique "Peer Index" value 1709 for each (NCE, Peer List entry)-tuple. The Bridge maintains a 1710 separate ReachableTime timer for each NCE Peer List entry 1711 individually. When ReachableTime for an NCE Peer List entry expires, 1712 the Bridge deletes the Peer List entry and frees the associated Peer 1713 Index. When ReachableTime for all of an NCE's Peer List entries 1714 expire, the Bridge deletes the NCE. Proxy/Servers also create/update 1715 a Peer List entry for the NCE of a local Client when they forward an 1716 NA(WIN) that was not processed by a Bridge. Proxy/Servers maintain 1717 the Peer List and Peer Index values the same as for Bridges, except 1718 that they do not delete the NCE when all Peer List entries expire. 1720 Proxy/Servers add an additional state DEPARTED to the list of NCE 1721 states found in Section 7.3.2 of [RFC4861]. When a Client terminates 1722 its association, the Proxy/Server OMNI interface sets a "DepartTime" 1723 variable for the NCE to "DEPART_TIME" seconds. DepartTime is 1724 decremented unless a new IPv6 ND message causes the state to return 1725 to REACHABLE. While a NCE is in the DEPARTED state, the Proxy/Server 1726 forwards carrier packets destined to the target Client to the 1727 Client's new location instead. When DepartTime decrements to 0, the 1728 NCE is deleted. It is RECOMMENDED that DEPART_TIME be set to the 1729 default constant value REACHABLE_TIME plus 10 seconds (40 seconds by 1730 default) to allow a window for carrier packets in flight to be 1731 delivered while stale route optimization state may be present. 1733 Proxy/Servers can act as RORs on behalf of their associated Clients 1734 according to the Proxy Neighbor Advertisement specification in 1735 Section 7.2.8 of [RFC4861]. When a Proxy/Server ROR receives an 1736 authentic NS(AR) message, it first searches for a NCE for the target 1737 Client and accepts the message only if there is an entry. The Proxy/ 1738 Server then returns a solicited NA(AR) message while creating or 1739 updating a "Report List" entry in the target Client's NCE that caches 1740 both the LLA and ULA of ROS with a "ReportTime" variable set to 1741 REPORT_TIME seconds. The ROR resets ReportTime when it receives a 1742 new authentic NS(AR) message, and otherwise decrements ReportTime 1743 while no authentic NS(AR) messages have been received. It is 1744 RECOMMENDED that REPORT_TIME be set to the default constant value 1745 REACHABLE_TIME plus 10 seconds (40 seconds by default) to allow a 1746 window for route optimization to converge before ReportTime 1747 decrements below REACHABLE_TIME. 1749 When the ROS receives a solicited NA(AR) message response to its 1750 NS(AR), it creates or updates a NCE for the target network-layer and 1751 link-layer addresses. The ROS then (re)sets ReachableTime for the 1752 NCE to REACHABLE_TIME seconds and performs reachability tests over 1753 specific underlying interface pairs to determine paths for forwarding 1754 carrier packets directly to the target. The ROS otherwise decrements 1755 ReachableTime while no further solicited NA messages arrive. It is 1756 RECOMMENDED that REACHABLE_TIME be set to the default constant value 1757 30 seconds as specified in [RFC4861]. 1759 AERO nodes also use the value MAX_UNICAST_SOLICIT to limit the number 1760 of NS messages sent when a correspondent may have gone unreachable, 1761 the value MAX_RTR_SOLICITATIONS to limit the number of RS messages 1762 sent without receiving an RA and the value MAX_NEIGHBOR_ADVERTISEMENT 1763 to limit the number of unsolicited NAs that can be sent based on a 1764 single event. It is RECOMMENDED that MAX_UNICAST_SOLICIT, 1765 MAX_RTR_SOLICITATIONS and MAX_NEIGHBOR_ADVERTISEMENT be set to 3 the 1766 same as specified in [RFC4861]. 1768 Different values for the above constants MAY be administratively set; 1769 however, if different values are chosen, all nodes on the link MUST 1770 consistently configure the same values. Most importantly, 1771 DEPART_TIME and REPORT_TIME SHOULD be set to a value that is 1772 sufficiently longer than REACHABLE_TIME to avoid packet loss due to 1773 stale route optimization state. 1775 3.5.1. OMNI ND Messages 1777 OMNI interfaces prepare IPv6 ND messages the same as for standard 1778 IPv6 ND, but also include a new option type termed the OMNI option 1779 [I-D.templin-6man-omni]. OMNI interfaces prepare IPv6 ND messages 1780 the same as for standard IPv6 ND, and include one or more OMNI 1781 options and any other options then completely populate all option 1782 information. If the OMNI interface includes an authentication 1783 signature, it sets the IPv6 ND message Checksum field to 0 and 1784 calculates the authentication signature over the entire length of the 1785 message (beginning with a pseudo-header of the IPv6 header) but does 1786 not then proceed to calculate the IPv6 ND message checksum itself. 1787 If the OMNI interface forwards the message to a next hop over the 1788 secured spanning tree path, it omits both the authentication 1789 signature an checksum since lower layers already ensure 1790 authentication and integrity. In all other cases, the OMNI interface 1791 calculates the standard IPv6 ND message checksum and writes the value 1792 in the Checksum field. OMNI interfaces verify authentication and 1793 integrity of each IPv6 ND message received according to the specific 1794 check(s) included, and process the message further only following 1795 verification. 1797 OMNI options include per-neighbor information such as Interface 1798 Attributes that provide segment routing, link-layer address and 1799 traffic selector information for the neighbor's underlying 1800 interfaces. This information is stored in the neighbor cache and 1801 provides the basis for the forwarding algorithm specified in 1802 Section 3.10. The information is cumulative and reflects the union 1803 of the OMNI information from the most recent IPv6 ND messages 1804 received from the neighbor; it is therefore not required that each 1805 IPv6 ND message contain all neighbor information. 1807 The OMNI option Interface Attributes for each underlying interface 1808 includes a two-part "Link-Layer Address" consisting of an INET 1809 encapsulation address determined by the FMT and L2ADDR fields and a 1810 Proxy/Server or Bridge spanning tree address determined by the SRT 1811 and LHS fields. Underlying interfaces are further selected based on 1812 their associated traffic selectors. When the SRT is 0, LHS instead 1813 includes a Peer Index value meaningful to the node identified by FMT 1814 and L2ADDR. 1816 The OMNI option is distinct from any Source/Target Link-Layer Address 1817 Options (S/TLLAOs) that may appear in an IPv6 ND message according to 1818 the appropriate IPv6 over specific link layer specification (e.g., 1819 [RFC2464]). If both an OMNI option and S/TLLAO appear, the former 1820 pertains to encapsulation addresses while the latter pertains to the 1821 native L2 address format of the underlying media 1823 OMNI interface IPv6 ND messages may also include other IPv6 ND 1824 options. In particular, solicitation messages may include Nonce and/ 1825 or Timestamp options if required for verification of advertisement 1826 replies. If an OMNI IPv6 ND solicitation message includes a Nonce 1827 option, the advertisement reply must echo the same Nonce. If an OMNI 1828 IPv6 ND solicitation message includes a Timestamp option, the 1829 advertisement reply should also include a Timestamp option. 1831 AERO Clients send RS messages to the All-Routers multicast address 1832 while using unicast link-layer addresses. AERO Proxy/Servers respond 1833 by returning unicast RA messages. During the RS/RA exchange, AERO 1834 Clients and Servers include state synchronization parameters to 1835 establish Identification windows and other state. 1837 AERO nodes use NS/NA messages for the following purposes: 1839 o NS/NA(AR) messages are used for address resolution only. The ROS 1840 sends an NS(AR) to the solicited-node multicast address of the 1841 target, and an ROR in the network with addressing information for 1842 the target returns a unicast NA(AR). The NA(AR) contains current, 1843 consistent and authentic target address resolution information, 1844 but only an implicit third-party assertion of target reachability. 1845 NS/NA(AR) messages must be secured. 1847 o NS/NA(WIN) messages are used for establishing and maintaining 1848 window synchronization state (and/or any other state such as 1849 Interface Attributes). The source sends an NS(WIN) to the unicast 1850 address of the target, and the target returns a unicast NA(WIN). 1851 The NS/NA(WIN) exchange synchronizes the sequence number windows 1852 for Identification values the neighbors will include in subsequent 1853 carrier packets, and asserts reachability for the target without 1854 necessarily testing a specific underlying interface pair. NS/ 1855 NA(WIN) messages must be secured. 1857 o NS/NA(NUD) messages are used for determining target reachability. 1858 The source sends an NS(NUD) to the unicast address of the target 1859 while naming a specific underlying interface pair, and the target 1860 returns a unicast NA(NUD). NS/NA(NUD) messages that use an in- 1861 window sequence number and do not update any other state need not 1862 be secured but should include an IPv6 ND message checksum. NS/ 1863 NA(NUD) messages may also be used in combination with window 1864 synchronization (i.e., NUD+WIN), in which case the messages must 1865 be secured. 1867 o Unsolicited NA (uNA) messages are used to signal addressing and/or 1868 other neighbor state changes (e.g., address changes due to 1869 mobility, signal degradation, traffic selector updates, etc.). uNA 1870 messages that include state update information must be secured. 1872 o NS/NA(DAD) messages are not used in AERO, since Duplicate Address 1873 Detection is not required. 1875 Additionally, nodes may send NA/RA messages with the OMNI option PNG 1876 flag set to receive a solicited NA response from the neighbor. The 1877 solicited NA response MUST set the ACK flag (without also setting the 1878 SYN or PNG flags) and include the Identification used in the PNG 1879 message in the Acknowledgement. 1881 3.5.2. OMNI Neighbor Advertisement Message Flags 1883 As discussed in Section 4.4 of [RFC4861] NA messages include three 1884 flag bits R, S and O. OMNI interface NA messages treat the flags as 1885 follows: 1887 o R: The R ("Router") flag is set to 1 in the NA messages sent by 1888 all AERO/OMNI node types. Simple hosts that would set R to 0 do 1889 not occur on the OMNI link itself, but may occur on the downstream 1890 links of Clients and Relays. 1892 o S: The S ("Solicited") flag is set exactly as specified in 1893 Section 4.4. of [RFC4861], i.e., it is set to 1 for Solicited NAs 1894 and set to 0 for uNAs (both unicast and multicast). 1896 o O: The O ("Override") flag is set to 0 for solicited NAs returned 1897 by a Proxy/Server ROR and set to 1 for all other solicited and 1898 unsolicited NAs. For further study is whether solicited NAs for 1899 anycast targets apply for OMNI links. Since MNP-LLAs must be 1900 uniquely assigned to Clients to support correct IPv6 ND protocol 1901 operation, however, no role is currently seen for assigning the 1902 same MNP-LLA to multiple Clients. 1904 3.5.3. OMNI Neighbor Window Synchronization 1906 In secured environments (e.g., such as between nodes on the same 1907 secured ANET), OMNI interface neighbors can exchange OAL packets 1908 using randomly-initialized and monotonically-increasing 1909 Identification values (modulo 2*32) without window synchronization. 1910 In environments where spoofing is considered a threat, OMNI interface 1911 neighbors instead invoke window synchronization in NS/NA(WIN) message 1912 exchanges to maintain send/receive window state in their respective 1913 neighbor cache entries as specified in [I-D.templin-6man-omni]. 1915 In the asymmetric window synchronization case, the initial NS/NA(WN) 1916 message exchange establishes only the initiator's send window and the 1917 responder's receive window such that a corresponding exchange would 1918 be needed to establish the reverse direction. In the symmetric case, 1919 the initiator and responder engage in a symmetric three-way handshake 1920 to establish the send/receive windows of both parties. 1922 When Bridges and Proxy/Servers forward and NS/NA(WIN) exchange 1923 between Client peers, they also cache window state in a Peer List 1924 entry maintained by a NCE for the local segment Client. This allows 1925 Bridges and Proxy/Servers to maintain forwarding information and 1926 verify that the Identifications included in carrier packets exchanged 1927 between the peers are within the current window. 1929 3.6. OMNI Interface Encapsulation and Re-encapsulation 1931 The OMNI interface admits original IP packets then acts as an OAL 1932 source to perform OAL encapsulation and fragmentation as specified in 1933 [I-D.templin-6man-omni] while including a CRH-32 if necessary as 1934 specified in Section 3.2.4. The OAL encapsulates original IP packets 1935 to form OAL packets subject to fragmentation, then encapsulates the 1936 resulting OAL fragments in *NET headers as carrier packets. 1938 For carrier packets undergoing re-encapsulation at an OAL 1939 intermediate node, the OMNI interface decrements the OAL IPv6 header 1940 Hop Limit and discards the carrier packet if the Hop Limit reaches 0. 1941 The intermediate node next removes the *NET encapsulation headers 1942 from the first segment and re-encapsulates the packet in new *NET 1943 encapsulation headers for the next segment. 1945 When an FHS Bridge receives a carrier packet with a compressed header 1946 that must be forwarded to an LHS Bridge over the unsecured spanning 1947 tree, it reconstructs the headers based on MFV state, inserts a 1948 CRH-32 immediately following the OAL header and adjusts the OAL 1949 payload length and destination address field. The FHS Bridge 1950 includes a single MFVI in the CRH-32 that will be meaningful to the 1951 LHS Bridge. When the LHS Bridge receives the carrier packet, it 1952 locates the MFV for the next hop based on the CRH-32 MFVI then re- 1953 applies header compression (resulting in the removal of the CRH-32) 1954 and forwards the carrier packet to the next hop. 1956 3.7. OMNI Interface Decapsulation 1958 OMNI interfaces (acting as OAL destinations) decapsulate and 1959 reassemble OAL packets into original IP packets destined either to 1960 the AERO node itself or to a destination reached via an interface 1961 other than the OMNI interface the original IP packet was received on. 1962 When carrier packets containing OAL fragments addressed to itself 1963 arrive, the OMNI interface discards the NET encapsulation headers and 1964 reassembles as discussed in Section 3.9. 1966 3.8. OMNI Interface Data Origin Authentication 1968 AERO nodes employ simple data origin authentication procedures. In 1969 particular: 1971 o AERO Bridges and Proxy/Servers accept carrier packets received 1972 from secured underlying interfaces. 1974 o AERO Proxy/Servers and Clients accept carrier packets and original 1975 IP packets that originate from within the same secured ANET. 1977 o AERO Clients and Relays accept original IP packets from downstream 1978 network correspondents based on ingress filtering. 1980 o AERO Clients, Relays and Proxy/Servers verify carrier packet UDP/ 1981 IP encapsulation addresses according to [I-D.templin-6man-omni]. 1983 o AERO nodes accept carrier packets addressed to themselves with 1984 Identification values within the current window for the OAL source 1985 neighbor (when window synchronization is used) and drop any 1986 carrier packets with out-of-window Identification values. (AERO 1987 nodes may forward carrier packets not addressed to themselves 1988 without verifying the Identification value.) 1990 AERO nodes silently drop any packets that do not satisfy the above 1991 data origin authentication procedures. Further security 1992 considerations are discussed in Section 6. 1994 3.9. OMNI Interface MTU 1996 The OMNI interface observes the link nature of tunnels, including the 1997 Maximum Transmission Unit (MTU), Maximum Reassembly Unit (MRU) and 1998 the role of fragmentation and reassembly [I-D.ietf-intarea-tunnels]. 1999 The OMNI interface employs an OMNI Adaptation Layer (OAL) that 2000 accommodates multiple underlying links with diverse MTUs while 2001 observing both a minimum and per-path Maximum Payload Size (MPS). 2002 The functions of the OAL and the OMNI interface MTU/MRU/MPS are 2003 specified in [I-D.templin-6man-omni] with MTU/MRU both set to the 2004 constant value 9180 bytes, with minimum MPS set to 400 bytes, and 2005 with potentially larger per-path MPS values depending on the 2006 underlying path. 2008 When the network layer presents an original IP packet to the OMNI 2009 interface, the OAL source encapsulates and fragments the original IP 2010 packet if necessary. When the network layer presents the OMNI 2011 interface with multiple original IP packets bound to the same OAL 2012 destination, the OAL source can concatenate them together into a 2013 single OAL super-packet as discussed in [I-D.templin-6man-omni]. The 2014 OAL source then fragments the OAL packet if necessary according to 2015 the minimum/path MPS such that the OAL headers appear in each 2016 fragment while the original IP packet header appears only in the 2017 first fragment. The OAL source then encapsulates each OAL fragment 2018 in *NET headers for transmission as carrier packets over an 2019 underlying interface connected to either a physical link (such as 2020 Ethernet, WiFi and the like) or a virtual link such as an Internet or 2021 higher-layer tunnel (see the definition of link in [RFC8200]). 2023 Note: Although a CRH-32 may be inserted or removed by a Bridge in the 2024 path (see: Section 3.10.3), this does not interfere with the 2025 destination's ability to reassemble since the CRH-32 is not included 2026 in the fragmentable part and its removal/transformation does not 2027 invalidate fragment header information. 2029 3.10. OMNI Interface Forwarding Algorithm 2031 NOTE (6/23/20201): This section is scheduled for significant overhaul 2032 and reduction to harmonize with the new text found in Section 3.2.7. 2033 Please refer to that section until further notice. 2035 Original IP packets enter a node's OMNI interface either from the 2036 network layer (i.e., from a local application or the IP forwarding 2037 system) while carrier packets enter from the link layer (i.e., from 2038 an OMNI interface neighbor). All original IP packets and carrier 2039 packets entering a node's OMNI interface first undergo data origin 2040 authentication as discussed in Section 3.8. Those that satisfy data 2041 origin authentication are processed further, while all others are 2042 dropped silently. 2044 Original IP packets that enter the OMNI interface from the network 2045 layer are forwarded to an OMNI interface neighbor using OAL 2046 encapsulation and fragmentation to produce carrier packets for 2047 transmission over underlying interfaces. (If routing indicates that 2048 the original IP packet should instead be forwarded back to the 2049 network layer, the packet is dropped to avoid looping). Carrier 2050 packets that enter the OMNI interface from the link layer are either 2051 re-encapsulated and re-admitted into the OMNI link, or reassembled 2052 and forwarded to the network layer where they are subject to either 2053 local delivery or IP forwarding. In all cases, the OAL MUST NOT 2054 decrement the original IP packet TTL/Hop-count since its forwarding 2055 actions occur below the network layer. 2057 OMNI interfaces may have multiple underlying interfaces and/or 2058 neighbor cache entries for neighbors with multiple underlying 2059 interfaces (see Section 3.3). The OAL uses Interface Attributes 2060 traffic selectors (e.g., port number, flow specification, etc.) to 2061 select an outbound underlying interface for each OAL packet based on 2062 the node's own interface attributes, and also to select segment 2063 routing and/or link-layer destination addresses based on the 2064 neighbor's underlying interface attributes. AERO implementations 2065 SHOULD permit network management to dynamically adjust traffic 2066 selector values at runtime. 2068 If an OAL packet matches the traffic selectors of multiple outgoing 2069 interfaces and/or neighbor interfaces, the OMNI interface replicates 2070 the packet and sends one copy via each of the (outgoing / neighbor) 2071 interface pairs; otherwise, it sends a single copy of the OAL packet 2072 via an interface with the best matching traffic selector. (While not 2073 strictly required, the likelihood of successful reassembly may 2074 improve when the OMNI interface sends all fragments of the same 2075 fragmented OAL packet consecutively over the same underlying 2076 interface pair to avoid complicating factors such as delay variance 2077 and reordering.) AERO nodes keep track of which underlying 2078 interfaces are currently "reachable" or "unreachable", and only use 2079 "reachable" interfaces for forwarding purposes. 2081 The following sections discuss the OMNI interface forwarding 2082 algorithms for Clients, Proxy/Servers and Bridges. In the following 2083 discussion, an original IP packet's destination address is said to 2084 "match" if it is the same as a cached address, or if it is covered by 2085 a cached prefix (which may be encoded in an MNP-LLA). 2087 3.10.1. Client Forwarding Algorithm 2089 When an original IP packet enters a Client's OMNI interface from the 2090 network layer the Client searches for a NCE that matches the 2091 destination. If there is a match, the Client selects one or more 2092 "reachable" neighbor interfaces in the entry for forwarding purposes. 2093 If there is no NCE, the Client instead either enqueues the original 2094 IP packet and invokes route optimization or forwards the original IP 2095 packet toward a Proxy/Server. The Client (acting as an OAL source) 2096 performs OAL encapsulation and sets the OAL destination address to 2097 the MNP-ULA of the target if there is a matching NCE; otherwise, it 2098 sets the OAL destination to the ADM-ULA of the Proxy/Server. If the 2099 Client has multiple original IP packets to send to the same neighbor, 2100 it can concatenate them in a single super-packet 2101 [I-D.templin-6man-omni]. The OAL source then performs fragmentation 2102 to create OAL fragments (see: Section 3.9), appends any *NET 2103 encapsulation, and sends the resulting carrier packets over 2104 underlying interfaces to the neighbor acting as an OAL destination. 2106 If the neighbor interface selected for forwarding is located on the 2107 same OMNI link segment and not behind a NAT, the Client forwards the 2108 carrier packets directly according to the L2ADDR information for the 2109 neighbor. If the neighbor interface is behind a NAT on the same OMNI 2110 link segment, the Client instead forwards the initial carrier packets 2111 to the LHS Proxy/Server (while inserting an CRH-32 if necessary) and 2112 initiates NAT traversal procedures. If the Client's intended source 2113 underlying interface is also behind a NAT and located on the same 2114 OMNI link segment, it sends a "direct bubble" over the interface per 2115 [RFC6081][RFC4380] to the L2ADDR found in the neighbor cache in order 2116 to establish state in its own NAT by generating traffic toward the 2117 neighbor (note that no response to the bubble is expected). 2119 The Client next sends an NS(NUD) message toward the MNP-ULA of the 2120 neighbor via the LHS Proxy/Server as discussed in Section 3.15. If 2121 the Client receives an NA(NUD) from the neighbor over the underlying 2122 interface, it marks the neighbor interface as "trusted" and sends 2123 future carrier packets directly to the L2ADDR information for the 2124 neighbor instead of indirectly via the LHS Proxy/Server. The Client 2125 must honor the neighbor cache maintenance procedure by sending 2126 additional direct bubbles and/or NS/NA(NUD) messages as discussed in 2127 [RFC6081][RFC4380] in order to keep NAT state alive as long as 2128 carrier packets are still flowing. 2130 When a carrier packet enters a Client's OMNI interface from the link- 2131 layer, if the OAL destination matches one of the Client's ULAs the 2132 Client (acting as an OAL destination) verifies that the 2133 Identification is in-window for this OAL source, then reassembles and 2134 decapsulates as necessary and delivers the original IP packet to the 2135 network layer. If the OAL destination does not match, the Client 2136 drops the original IP packet and MAY return a network-layer ICMP 2137 Destination Unreachable message subject to rate limiting (see: 2138 Section 3.11). 2140 Note: When an LHS Bridge or Proxy/Server forwards an NA(WIN), it 2141 overwrites its own link-layer address and a Peer Index value in the 2142 Interface Attribute option. When the local Client updates the NCE 2143 for this ROS, it caches the link-layer address and Peer Index 2144 information as the FHS encapsulation values to use when sending 2145 return carrier packets to the ROS. 2147 Note: Clients and their FHS Proxy/Server (and other Client) peers can 2148 exchange original IP packets over ANET underlying interfaces without 2149 invoking the OAL, since the ANET is secured at the link and physical 2150 layers. By forwarding original IP packets without invoking the OAL, 2151 however, the ANET peers can engage only in classical path MTU 2152 discovery since the packets are subject to loss and/or corruption due 2153 to the various per-link MTU limitations that may occur within the 2154 ANET. Moreover, the original IP packets do not include either the 2155 OAL integrity check or per-packet Identification values that can be 2156 used for data origin authentication and link-layer retransmissions. 2157 The tradeoff therefore involves an assessment of the per-packet 2158 encapsulation overhead saved by bypassing the OAL vs. inheritance of 2159 classical network "brittleness". (Note however that ANET peers can 2160 send small original IP packets without invoking the OAL, while 2161 invoking the OAL for larger packets. This presents the beneficial 2162 aspects of both small packet efficiency and large packet robustness, 2163 with delay variance and reordering as possible side effects.) 2165 3.10.2. Proxy/Server and Relay Forwarding Algorithm 2167 When the Proxy/Server receives an original IP packet from the network 2168 layer, it drops the packet if routing indicates that it should be 2169 forwarded back to the network layer to avoid looping. Otherwise, the 2170 Proxy/Server regards the original IP packet the same as if it had 2171 arrived as carrier packets with OAL destination set to its own ADM- 2172 ULA. When the Proxy/Server receives carrier packets on underlying 2173 interfaces with OAL destination set to its own ADM-ULA, it performs 2174 OAL reassembly if necessary to obtain the original IP packet. 2176 The Proxy/Server next searches for a NCE that matches the original IP 2177 destination and proceeds as follows: 2179 o if the packet is an NA(WIN) message for a local Client NCE, the 2180 Proxy/Server examines the Interface Attributes information and 2181 rewrites the fields if the NA(WIN) was not already processed by a 2182 (local segment) Bridge as discussed in Section 3.2.7. 2184 o else, if the original IP packet destination matches a NCE, the 2185 Proxy/Sever uses one or more "reachable" neighbor interfaces in 2186 the entry for packet forwarding using OAL encapsulation and 2187 fragmentation according to the cached link-layer address 2188 information. If the neighbor interface is in a different OMNI 2189 link segment, the Proxy/Server performs OAL encapsulation and 2190 fragmentation, inserts an CRH-32 if necessary and forwards the 2191 resulting carrier packets via the spanning tree to a Bridge; 2192 otherwise, it forwards the carrier packets directly to the 2193 neighbor via INET encapsulation. If the neighbor is behind a NAT, 2194 this FHS Proxy/Server instead forwards initial carrier packets via 2195 a Bridge (or more directly via an LHS Proxy/Server) while sending 2196 an NS(NUD) to the neighbor. When the Proxy/Server receives the 2197 NA(NUD), it can begin forwarding carrier packets directly to the 2198 neighbor the same as discussed in Section 3.10.1 while sending 2199 additional NS(NUD) messages as necessary to maintain NAT state. 2200 Note that no direct bubbles are necessary since the Proxy/Server 2201 is by definition not located behind a NAT. 2203 o else, if the original IP destination matches a non-MNP route in 2204 the IP forwarding table or an ADM-LLA assigned to the Proxy/ 2205 Server's OMNI interface, the Proxy/Server acting as a Relay 2206 presents the original IP packet to the network layer for local 2207 delivery or IP forwarding. 2209 o else, the Proxy/Server initiates address resolution as discussed 2210 in Section 3.14, while retaining initial original IP packets in a 2211 small queue awaiting address resolution completion. 2213 When the Proxy/Server receives a carrier packet with OAL destination 2214 set to an MNP-ULA that does not match the MSP, it accepts the carrier 2215 packet only if data origin authentication succeeds and if there is a 2216 network layer routing table entry for a GUA route that matches the 2217 MNP-ULA. If there is no route, the Proxy/Server drops the carrier 2218 packet; otherwise, it reassembles and decapsulates to obtain the 2219 original IP packet then acts as a Relay to present it to the network 2220 layer where it will be delivered according to standard IP forwarding. 2222 When a Proxy/Server receives a carrier packet from one of its Client 2223 neighbors with OAL destination set to another node, it forwards the 2224 packets via a matching NCE or via the spanning tree if there is no 2225 matching entry. When the Proxy/Server receives a carrier packet with 2226 OAL destination set to the MNP-ULA of one of its Client neighbors 2227 established through RS/RA exchanges, it accepts the carrier packet 2228 only if data origin authentication succeeds. If the NCE state is 2229 DEPARTED, the Proxy/Server changes the OAL destination address to the 2230 ADM-ULA of the new Proxy/Server, then re-encapsulates the carrier 2231 packet and forwards it to a Bridge which will eventually deliver it 2232 to the new Proxy/Server. 2234 If the neighbor cache state for the MNP-ULA is REACHABLE, the Proxy/ 2235 Server forwards the carrier packets to the Client which then must 2236 reassemble. (Note that the Proxy/Server does not reassemble carrier 2237 packets not explicitly addressed to its own ADM-ULA, since some of 2238 the carrier packets of the same original IP packet could be forwarded 2239 through a different Proxy/Server.) In that case, the Client may 2240 receive fragments that are smaller than its link MTU but that can 2241 still be reassembled. 2243 Note: Proxy/Servers may receive carrier packets with CRH-32s that 2244 include additional forwarding information. Proxy/Servers use the 2245 forwarding information to determine the correct NCE and underlying 2246 interface for forwarding to the target Client, then remove the CRH-32 2247 and forward the carrier packet. If necessary, the Proxy/Server 2248 reassembles first before re-encapsulating (and possibly also re- 2249 fragmenting) then forwards to the target Client. For a full 2250 discussion see: Section 3.14.6. 2252 Note: Clients and their FHS Proxy/Server peers can exchange original 2253 IP packets over ANET underlying interfaces without invoking the OAL, 2254 since the ANET is secured at the link and physical layers. By 2255 forwarding original IP packets without invoking the OAL, however, the 2256 Client and Proxy/Server can engage only in classical path MTU 2257 discovery since the packets are subject to loss and/or corruption due 2258 to the various per-link MTU limitations that may occur within the 2259 ANET. Moreover, the original IP packets do not include either the 2260 OAL integrity check or per-packet Identification values that can be 2261 used for data origin authentication and link-layer retransmissions. 2262 The tradeoff therefore involves an assessment of the per-packet 2263 encapsulation overhead saved by bypassing the OAL vs. inheritance of 2264 classical network "brittleness". (Note however that ANET peers can 2265 send small original IP packets without invoking the OAL, while 2266 invoking the OAL for larger packets. This presents the beneficial 2267 aspects of both small packet efficiency and large packet robustness.) 2269 Note: When a Proxy/Server receives a (non-OAL) original IP packet 2270 from an ANET Client, or a carrier packet with OAL destination set to 2271 its own ADM-ULA from any Client, the Proxy/Server reassembles if 2272 necessary then performs ROS functions on behalf of the Client. The 2273 Client may at some later time begin sending carrier packets to the 2274 OAL address of the actual target instead of the Proxy/Server, at 2275 which point it may begin functioning as an ROS on its own behalf and 2276 thereby "override" the Proxy/Server's ROS role. 2278 Note; Proxy/Servers drop any original IP packets (received either 2279 directly from an ANET Client or following reassembly of carrier 2280 packets received from an ANET/INET Client) with a destination that 2281 corresponds to the Client's delegated MNP. Similarly, Proxy/Servers 2282 drop any carrier packet received with both a source and destination 2283 that correspond to the Client's delegated MNP regardless of their 2284 OMNI link point of origin. These checks are necessary to prevent 2285 Clients from either accidentally or intentionally establishing 2286 endless loops that could congest Proxy/Servers and/or ANET/INET 2287 links. 2289 Note: Proxy/Servers forward secure control plane carrier packets via 2290 the SRT secured spanning tree and forward other carrier packets via 2291 the unsecured spanning tree. When a Proxy/Server receives a carrier 2292 packet from the secured spanning tree, it considers the message as 2293 authentic without having to verify upper layer authentication 2294 signatures. When a Proxy/Server receives a carrier packet from the 2295 unsecured spanning tree, it verifies any upper layer authentication 2296 signatures and/or forwards the unsecured message toward the 2297 destination which must apply data origin authentication. 2299 Note: If the Proxy/Server has multiple original IP packets to send to 2300 the same neighbor, it can concatenate them in a single OAL super- 2301 packet [I-D.templin-6man-omni]. 2303 3.10.3. Bridge Forwarding Algorithm 2305 Bridges forward spanning tree carrier packets while decrementing the 2306 OAL header Hop Count but not the original IP header Hop Count/TTL. 2307 Bridges convey carrier packets that encapsulate critical IPv6 ND 2308 control messages or routing protocol control messages via the secured 2309 spanning tree, and may convey other carrier packets via the unsecured 2310 spanning tree or via more direct paths according to MFIB information. 2311 When the Bridge receives a carrier packet, it removes the outer *NET 2312 header and searches for an MFIB entry that matches an MFVI or an IP 2313 forwarding table entry that matches the OAL destination address. 2315 Bridges forward carrier packets received from a first segment via the 2316 SRT secured spanning tree to the next segment also via the secured 2317 spanning tree. Bridges forward carrier packets received from a first 2318 segment via the unsecured spanning tree to the next segment also via 2319 the unsecured spanning tree. Bridges use a single IPv6 routing table 2320 that always determines the same next hop for a given OAL destination, 2321 where the secured/unsecured spanning tree is determined through the 2322 selection of the underlying interface to be used for transmission 2323 (i.e., a secured tunnel or an open INET interface). 2325 3.11. OMNI Interface Error Handling 2327 When an AERO node admits an original IP packet into the OMNI 2328 interface, it may receive link-layer or network-layer error 2329 indications. The AERO node may also receive OMNI link error 2330 indications in OAL-encapsulated uNA messages that include 2331 authentication signatures. 2333 A link-layer error indication is an ICMP error message generated by a 2334 router in the INET on the path to the neighbor or by the neighbor 2335 itself. The message includes an IP header with the address of the 2336 node that generated the error as the source address and with the 2337 link-layer address of the AERO node as the destination address. 2339 The IP header is followed by an ICMP header that includes an error 2340 Type, Code and Checksum. Valid type values include "Destination 2341 Unreachable", "Time Exceeded" and "Parameter Problem" 2342 [RFC0792][RFC4443]. (OMNI interfaces ignore link-layer IPv4 2343 "Fragmentation Needed" and IPv6 "Packet Too Big" messages for carrier 2344 packets that are no larger than the minimum/path MPS as discussed in 2345 Section 3.9, however these messages may provide useful hints of probe 2346 failures during path MPS probing.) 2348 The ICMP header is followed by the leading portion of the carrier 2349 packet that generated the error, also known as the "packet-in-error". 2350 For ICMPv6, [RFC4443] specifies that the packet-in-error includes: 2351 "As much of invoking packet as possible without the ICMPv6 packet 2352 exceeding the minimum IPv6 MTU" (i.e., no more than 1280 bytes). For 2353 ICMPv4, [RFC0792] specifies that the packet-in-error includes: 2354 "Internet Header + 64 bits of Original Data Datagram", however 2355 [RFC1812] Section 4.3.2.3 updates this specification by stating: "the 2356 ICMP datagram SHOULD contain as much of the original datagram as 2357 possible without the length of the ICMP datagram exceeding 576 2358 bytes". 2360 The link-layer error message format is shown in Figure 4: 2362 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2363 ~ ~ 2364 | IP Header of link layer | 2365 | error message | 2366 ~ ~ 2367 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2368 | ICMP Header | 2369 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 2370 ~ ~ P 2371 | carrier packet *NET and OAL | a 2372 | encapsulation headers | c 2373 ~ ~ k 2374 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ e 2375 ~ ~ t 2376 | original IP packet headers | 2377 | (first-fragment only) | i 2378 ~ ~ n 2379 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2380 ~ ~ e 2381 | Portion of the body of | r 2382 | the original IP packet | r 2383 | (all fragments) | o 2384 ~ ~ r 2385 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 2387 Figure 4: OMNI Interface Link-Layer Error Message Format 2389 The AERO node rules for processing these link-layer error messages 2390 are as follows: 2392 o When an AERO node receives a link-layer Parameter Problem message, 2393 it processes the message the same as described as for ordinary 2394 ICMP errors in the normative references [RFC0792][RFC4443]. 2396 o When an AERO node receives persistent link-layer Time Exceeded 2397 messages, the IP ID field may be wrapping before earlier fragments 2398 awaiting reassembly have been processed. In that case, the node 2399 should begin including integrity checks and/or institute rate 2400 limits for subsequent packets. 2402 o When an AERO node receives persistent link-layer Destination 2403 Unreachable messages in response to carrier packets that it sends 2404 to one of its neighbor correspondents, the node should process the 2405 message as an indication that a path may be failing, and 2406 optionally initiate NUD over that path. If it receives 2407 Destination Unreachable messages over multiple paths, the node 2408 should allow future carrier packets destined to the correspondent 2409 to flow through a default route and re-initiate route 2410 optimization. 2412 o When an AERO Client receives persistent link-layer Destination 2413 Unreachable messages in response to carrier packets that it sends 2414 to one of its neighbor Proxy/Servers, the Client should mark the 2415 path as unusable and use another path. If it receives Destination 2416 Unreachable messages on many or all paths, the Client should 2417 associate with a new Proxy/Server and release its association with 2418 the old Proxy/Server as specified in Section 3.16.5. 2420 o When an AERO Proxy/Server receives persistent link-layer 2421 Destination Unreachable messages in response to carrier packets 2422 that it sends to one of its neighbor Clients, the Proxy/Server 2423 should mark the underlying path as unusable and use another 2424 underlying path. 2426 o When an AERO Proxy/Server receives link-layer Destination 2427 Unreachable messages in response to a carrier packet that it sends 2428 to one of its permanent neighbors, it treats the messages as an 2429 indication that the path to the neighbor may be failing. However, 2430 the dynamic routing protocol should soon reconverge and correct 2431 the temporary outage. 2433 When an AERO Bridge receives a carrier packet for which the network- 2434 layer destination address is covered by an MSP, the Bridge drops the 2435 packet if there is no more-specific routing information for the 2436 destination and returns an OMNI interface Destination Unreachable 2437 message subject to rate limiting. 2439 When an AERO node receives a carrier packet for which reassembly is 2440 currently congested, it returns an OMNI interface Packet Too Big 2441 (PTB) message as discussed in [I-D.templin-6man-omni] (note that the 2442 PTB messages could indicate either "hard" or "soft" errors). 2444 AERO nodes include ICMPv6 error messages intended for the OAL source 2445 as sub-options in the OMNI option of secured uNA messages. When the 2446 OAL source receives the uNA message, it can extract the ICMPv6 error 2447 message enclosed in the OMNI option and either process it locally or 2448 translate it into a network-layer error to return to the original 2449 source. 2451 3.12. AERO Router Discovery, Prefix Delegation and Autoconfiguration 2453 AERO Router Discovery, Prefix Delegation and Autoconfiguration are 2454 coordinated as discussed in the following Sections. 2456 3.12.1. AERO Service Model 2458 Each AERO Proxy/Server on the OMNI link is configured to facilitate 2459 Client prefix delegation/registration requests. Each Proxy/Server is 2460 provisioned with a database of MNP-to-Client ID mappings for all 2461 Clients enrolled in the AERO service, as well as any information 2462 necessary to authenticate each Client. The Client database is 2463 maintained by a central administrative authority for the OMNI link 2464 and securely distributed to all Proxy/Servers, e.g., via the 2465 Lightweight Directory Access Protocol (LDAP) [RFC4511], via static 2466 configuration, etc. Clients receive the same service regardless of 2467 the Proxy/Servers they select. 2469 AERO Clients and Proxy/Servers use IPv6 ND messages to maintain 2470 neighbor cache entries. AERO Proxy/Servers configure their OMNI 2471 interfaces as advertising NBMA interfaces, and therefore send unicast 2472 RA messages with a short Router Lifetime value (e.g., ReachableTime 2473 seconds) in response to a Client's RS message. Thereafter, Clients 2474 send additional RS messages to keep Proxy/Server state alive. 2476 AERO Clients and Proxy/Servers include prefix delegation and/or 2477 registration parameters in RS/RA messages (see 2478 [I-D.templin-6man-omni]). The IPv6 ND messages are exchanged between 2479 Client and FHS Proxy/Servers according to the prefix management 2480 schedule required by the service. If the Client knows its MNP in 2481 advance, it can employ prefix registration by including its MNP-LLA 2482 as the source address of an RS message and with an OMNI option with 2483 valid prefix registration information for the MNP. If the Proxy/ 2484 Server accepts the Client's MNP assertion, it injects the MNP into 2485 the routing system and establishes the necessary neighbor cache 2486 state. If the Client does not have a pre-assigned MNP, it can 2487 instead employ prefix delegation by including the unspecified address 2488 (::) as the source address of an RS message and with an OMNI option 2489 with prefix delegation parameters to request an MNP. 2491 The following sections specify the Client and Proxy/Server behavior. 2493 3.12.2. AERO Client Behavior 2495 AERO Clients discover the addresses of candidate FHS Proxy/Servers by 2496 resolving the Potential Router List (PRL) in a similar manner as 2497 described in [RFC5214]. Discovery methods include static 2498 configuration (e.g., a flat-file map of Proxy/Server addresses and 2499 locations), or through an automated means such as Domain Name System 2500 (DNS) name resolution [RFC1035]. Alternatively, the Client can 2501 discover Proxy/Server addresses through a layer 2 data link login 2502 exchange, or through a unicast RA response to a multicast/anycast RS 2503 as described below. In the absence of other information, the Client 2504 can resolve the DNS Fully-Qualified Domain Name (FQDN) 2505 "linkupnetworks.[domainname]" where "linkupnetworks" is a constant 2506 text string and "[domainname]" is a DNS suffix for the OMNI link 2507 (e.g., "example.com"). 2509 To associate with a FHS Proxy/Server over an underlying interface, 2510 the Client acts as a requesting router to request MNPs by preparing 2511 an RS message with prefix management parameters. If the Client 2512 already knows the Proxy/Server's ADM-LLA, it includes the LLA as the 2513 network-layer destination address; otherwise, the Client includes the 2514 (link-local) All-Routers multicast as the network-layer destination. 2515 The Client can use its MNP-LLA as the network-layer source address 2516 and include an OMNI option with prefix registration information. If 2517 the Client does not yet have an MNP-LLA, it instead sets the network- 2518 layer source address to unspecified (::) and includes prefix 2519 delegation parameters in the OMNI option (see: 2520 [I-D.templin-6man-omni]). 2522 The Client next includes an authentication sub-option if necessary, 2523 Interface Attributes corresponding to the underlying interface over 2524 which it will send the RS message, and optionally any additional 2525 Interface Attributes corresponding to other underlying interfaces. 2526 Next, the Client submits the RS for OAL encapsulation and 2527 fragmentation if necessary with its own MNP-ULA and the Proxy/ 2528 Server's ADM-ULA or (site-scoped) All-Routers multicast as the OAL 2529 addresses while selecting an Identification value and invoking window 2530 synchronization as specified in [I-D.templin-6man-omni]. 2532 The Client then sends the RS (either directly via Direct interfaces, 2533 via a VPN for VPNed interfaces, via an access router for ANET 2534 interfaces or via INET encapsulation for INET interfaces) then waits 2535 up to RetransTimer milliseconds for an RA message reply (see 2536 Section 3.12.3) (retrying up to MAX_RTR_SOLICITATIONS). If the 2537 Client receives no RAs, or if it receives an RA with Router Lifetime 2538 set to 0, the Client SHOULD abandon attempts through the first 2539 candidate FHS Proxy/Server and try another Proxy/Server. Otherwise, 2540 the Client processes the prefix information found in the RA message. 2542 When the Client processes an RA, it first performs OAL reassembly and 2543 decapsulation if necessary then creates a NCE with the Proxy/Server's 2544 ADM-LLA as the network-layer address and the Proxy/Server's 2545 encapsulation and/or link-layer addresses as the link-layer address. 2546 The Client then caches the FMT/SRT/LHS/L2ADDR information from the 2547 Interface Attributes for omIndex 0 included in the RA as an SRT local 2548 segment reference point for this Proxy/Server. The Client next 2549 records the RA Router Lifetime field value in the NCE as the time for 2550 which the Proxy/Server has committed to maintaining the MNP in the 2551 routing system via this underlying interface, and caches the other RA 2552 configuration information including Cur Hop Limit, M and O flags, 2553 Reachable Time and Retrans Timer. The Client then autoconfigures 2554 MNP-LLAs for any delegated MNPs and assigns them to the OMNI 2555 interface. The Client also caches any MSPs included in Route 2556 Information Options (RIOs) [RFC4191] as MSPs to associate with the 2557 OMNI link, and assigns the MTU value in the MTU option to the 2558 underlying interface. 2560 The Client then registers its additional underlying interfaces with 2561 FHS Proxy/Servers for those interfaces discovered by sending RS 2562 messages via each additional interface as described above. The RS 2563 messages include the same parameters as for the initial RS/RA 2564 exchange, but with destination address set to the Proxy/Server's ADM- 2565 LLA. The Client finally sub-delegates the MNPs to its attached EUNs 2566 and/or the Client's own internal virtual interfaces as described in 2567 [I-D.templin-v6ops-pdhost] to support the Client's downstream 2568 attached "Internet of Things (IoT)". The Client then sends 2569 additional RS messages over each underlying interface before the 2570 Router Lifetime received for that interface expires. 2572 After the Client registers its underlying interfaces, it may wish to 2573 change one or more registrations, e.g., if an interface changes 2574 address or becomes unavailable, if traffic selectors change, etc. To 2575 do so, the Client prepares an RS message to send over any available 2576 underlying interface as above. The RS includes an OMNI option with 2577 prefix registration/delegation information, with Interface Attributes 2578 specific to the selected underlying interface, and with any 2579 additional Interface Attributes specific to other underlying 2580 interfaces. When the Client receives the Proxy/Server's RA response, 2581 it has assurance that the Proxy/Server has been updated with the new 2582 information. 2584 If the Client wishes to discontinue use of a Proxy/Server it issues 2585 an RS message over any underlying interface with an OMNI option with 2586 a prefix release indication. When the Proxy/Server processes the 2587 message, it releases the MNP, sets the NCE state for the Client to 2588 DEPARTED and returns an RA reply with Router Lifetime set to 0. 2589 After a short delay (e.g., 2 seconds), the Proxy/Server withdraws the 2590 MNP from the routing system. 2592 3.12.3. AERO Proxy/Server Behavior 2594 AERO Proxy/Servers act as both IP routers and IPv6 ND proxies, and 2595 support a prefix delegation/registration service for Clients. Proxy/ 2596 Servers arrange to add their ADM-LLAs to the PRL maintained in a 2597 static map of Proxy/Server addresses for the link, the DNS resource 2598 records for the FQDN "linkupnetworks.[domainname]", etc. before 2599 entering service. The PRL should be arranged such that Clients can 2600 discover the addresses of Proxy/Servers that are geographically and/ 2601 or topologically "close" to their underlying network connections. 2603 When an FHS Proxy/Server receives a prospective Client's RS message, 2604 it SHOULD return an immediate RA reply with Router Lifetime set to 0 2605 if it is currently too busy or otherwise unable to service the 2606 Client. Otherwise, the Proxy/Server performs OAL reassembly if 2607 necessary, then decapsulates and authenticates the RS message before 2608 processing the prefix delegation/registration parameters. The Proxy/ 2609 Server then determines the correct MNPs to provide to the Client by 2610 processing the MNP-LLA prefix parameters and/or the DHCPv6 OMNI sub- 2611 option. When the Proxy/Server returns the MNPs, it also creates a 2612 forwarding table entry for the MNP-ULA corresponding to each MNP 2613 resulting in a BGP update (see: Section 3.2.3). For IPv6, the Proxy/ 2614 Server creates an IPv6 forwarding table entry for each MNP. For 2615 IPv4, the Proxy/Server creates an IPv6 forwarding table entry with 2616 the IPv4-compatibility MNP-ULA prefix corresponding to the IPv4 2617 address. 2619 The Proxy/Server next creates a NCE for the Client using the base 2620 MNP-LLA as the network-layer address. Next, the Proxy/Server updates 2621 the NCE by recording the information in each Interface Attributes 2622 sub-option in the RS OMNI option. The Proxy/Server also records the 2623 actual OAL/*NET addresses and RS message window synchronization 2624 parameters (if any) in the NCE. 2626 Next, the Proxy/Server prepares an RA message using its ADM-LLA as 2627 the network-layer source address and the network-layer source address 2628 of the RS message as the network-layer destination address. The 2629 Proxy/Server sets the Router Lifetime to the time for which it will 2630 maintain both this underlying interface individually and the NCE as a 2631 whole. The Proxy/Server also sets Cur Hop Limit, M and O flags, 2632 Reachable Time and Retrans Timer to values appropriate for the OMNI 2633 link. The Proxy/Server includes the MNPs, any other prefix 2634 management parameters and an OMNI option with an Interface Attributes 2635 sub-option with omIndex 0 and FMT/SRT/LHS/L2ADDR information for its 2636 INET interface and an Origin Indication sub-option with the mapped 2637 and obfuscated Port Number and IP address corresponding to the 2638 Client's RS encapsulation addresses. The Proxy/Server then includes 2639 one or more RIOs that encode the MSPs for the OMNI link, plus an MTU 2640 option (see Section 3.9). The Proxy/Server finally forwards the 2641 message to the Client using OAL encapsulation/fragmentation if 2642 necessary while including an acknowledgement if the RS invoked window 2643 synchronization. 2645 After the initial RS/RA exchange, the Proxy/Server maintains a 2646 ReachableTime timer for each of the Client's underlying interfaces 2647 individually (and for the Client's NCE collectively) set to expire 2648 after ReachableTime seconds. If the Client (or Proxy) issues 2649 additional RS messages, the Proxy/Server sends an RA response and 2650 resets ReachableTime. If the Proxy/Server receives an IPv6 ND 2651 message with a prefix release indication it sets the Client's NCE to 2652 the DEPARTED state and withdraws the MNP from the routing system 2653 after a short delay (e.g., 2 seconds). If ReachableTime expires 2654 before a new RS is received on an individual underlying interface, 2655 the Proxy/Server marks the interface as DOWN. If ReachableTime 2656 expires before any new RS is received on any individual underlying 2657 interface, the Proxy/Server sets the NCE state to STALE and sets a 10 2658 second timer. If the Proxy/Server has not received a new RS or uNA 2659 message with a prefix release indication before the 10 second timer 2660 expires, it deletes the NCE and withdraws the MNP from the routing 2661 system. 2663 The Proxy/Server processes any IPv6 ND messages pertaining to the 2664 Client and returns an NA/RA reply in response to solicitations. The 2665 Proxy/Server may also issue unsolicited RA messages, e.g., with 2666 reconfigure parameters to cause the Client to renegotiate its prefix 2667 delegation/registrations, with Router Lifetime set to 0 if it can no 2668 longer service this Client, etc. Finally, If the NCE is in the 2669 DEPARTED state, the Proxy/Server deletes the entry after DepartTime 2670 expires. 2672 Note: Clients SHOULD notify former Proxy/Servers of their departures, 2673 but Proxy/Servers are responsible for expiring neighbor cache entries 2674 and withdrawing routes even if no departure notification is received 2675 (e.g., if the Client leaves the network unexpectedly). Proxy/Servers 2676 SHOULD therefore set Router Lifetime to ReachableTime seconds in 2677 solicited RA messages to minimize persistent stale cache information 2678 in the absence of Client departure notifications. A short Router 2679 Lifetime also ensures that proactive RS/RA messaging between Clients 2680 and Proxy/Servers will keep any NAT state alive (see above). 2682 Note: All Proxy/Servers on an OMNI link MUST advertise consistent 2683 values in the RA Cur Hop Limit, M and O flags, Reachable Time and 2684 Retrans Timer fields the same as for any link, since unpredictable 2685 behavior could result if different Proxy/Servers on the same link 2686 advertised different values. 2688 3.12.3.1. DHCPv6-Based Prefix Registration 2690 When a Client is not pre-provisioned with an MNP-LLA, it will need 2691 for the FHS Proxy/Server to select one or more MNPs on its behalf and 2692 set up the correct state in the AERO routing service. (A Client with 2693 a pre-provisioned MNP may also request the Proxy/Server to select 2694 additional MNPs.) The DHCPv6 service [RFC8415] is used to support 2695 this requirement. 2697 When a Client needs to have the FHS Proxy/Server select MNPs, it 2698 sends an RS message with source address set to the unspecified 2699 address (::) and with an OMNI option that includes a DHCPv6 message 2700 sub-option with DHCPv6 Prefix Delegation (DHCPv6-PD) parameters. 2701 When the Proxy/Server receives the RS message, it extracts the 2702 DHCPv6-PD message from the OMNI option. 2704 The Proxy/Server then acts as a "Proxy DHCPv6 Client" in a message 2705 exchange with the locally-resident DHCPv6 server, which delegates 2706 MNPs and returns a DHCPv6-PD Reply message. (If the Proxy/Server 2707 wishes to defer creation of MN state until the DHCPv6-PD Reply is 2708 received, it can instead act as a Lightweight DHCPv6 Relay Agent per 2709 [RFC6221] by encapsulating the DHCPv6-PD message in a Relay-forward/ 2710 reply exchange with Relay Message and Interface ID options.) 2712 When the Proxy/Server receives the DHCPv6-PD Reply, it adds a route 2713 to the routing system and creates an MNP-LLA based on the delegated 2714 MNP. The Proxy/Server then sends an RA back to the Client with the 2715 (newly-created) MNP-LLA as the destination address and with the 2716 DHCPv6-PD Reply message coded in the OMNI option. When the Client 2717 receives the RA, it creates a default route, assigns the Subnet 2718 Router Anycast address and sets its MNP-LLA based on the delegated 2719 MNP. 2721 Note: See [I-D.templin-6man-omni] for an MNP delegation alternative 2722 that avoids including a DHCPv6 message sub-option in the RS. Namely, 2723 when the Client requests a single MNP it can set the RS source to the 2724 unspecified address (::) and include a Node Identification sub-option 2725 and Preflen in the OMNI option (but with no DHCPv6 message sub- 2726 option). When the Proxy/Server receives the RS message, it forwards 2727 a self-generated DHCPv6 Solicit message to the DHCPv6 server on 2728 behalf of the Client. When the Proxy/Server receives the DHCPv6 2729 Reply, it prepares an RA message with an OMNI option with Preflen 2730 information (but with no DHCPv6 message sub-option), then places the 2731 (newly-created) MNP-LLA in the RA destination address and returns the 2732 message to the Client. 2734 3.13. AERO Proxy/Server Coordination 2736 OMNI link Clients register with one or more FHS Proxy/Servers for 2737 each underlying interface. Each of the Client's FHS Proxy/Servers 2738 must be informed of all of the Client's additional underlying 2739 interfaces. For Clients on Direct and VPNed underlying interfaces, 2740 the FHS Proxy/Server for each interface is directly connected, for 2741 Clients on ANET underlying interfaces the Proxy/Server is located on 2742 the ANET/INET boundary, and for Clients on INET underlying interfaces 2743 the FHS Proxy/Server is located somewhere in the connected 2744 Internetwork. When FHS Proxy/Server "A" processes a Client 2745 registration, it must also forward a proxyed registration to any 2746 Proxy/Servers "B", "C", "D", etc. for the Client's other underlying 2747 interfaces, which it perceives as LHS Proxy/Servers (i.e., and not 2748 FHS) from its own reference point. Proxy/Servers satisfies these 2749 requirements as follows: 2751 o when FHS Proxy/Server "A" receives a Client RS message, it first 2752 verifies that the OAL Identification is within the window for the 2753 NCE that matches the MNP-ULA for this Client neighbor and 2754 authenticates the message. (If no NCE was found, Proxy/Server "A 2755 instead creates one in the STALE state and returns an RA message 2756 with an authentication signature if necessary and any window 2757 synchronization parameters.) Proxy/Server "A" then examines the 2758 network-layer destination address. If the destination address is 2759 the ADM-LLA of a different Proxy/Server "B" (or, if the OMNI 2760 option included MS-Register/Release sub-options with the ADM-LLAs 2761 of one or more different LHS Proxy/Servers "B", "C", "D", etc.), 2762 Proxy/Server "A" prepares a separate proxyed version of the RS 2763 message with an OAL header with source set to its own ADM-ULA and 2764 destination set to the LHS Proxy/Server's ADM-ULA. Proxy/Server 2765 "A" also writes its own FMT/SRT/LHS/L2ADDR information over the 2766 first Interface Attributes supplied by the Client (i.e., by 2767 inserting the FMT/SRT/LHS/L2ADDR fields if not already present, or 2768 increasing/decreasing the L2ADDR field size if the IP version of 2769 the Client underlying interface differs from its own INET 2770 interface). Proxy/Server "A" then sets the S/T-omIndex to the 2771 value for this Client underlying interface, then forwards the 2772 message into the OMNI link secured spanning tree. 2774 o when LHS Proxy/Server "B" receives the RS, it authenticates the 2775 message then creates or updates a NCE for the Client with FHS 2776 Proxy/Server "A"'s Interface Attributes as the link-layer address 2777 information for this S/T-omIndex and caches any window 2778 synchronization parameters supplied by the Client. LHS Proxy/ 2779 Server "B" then prepares an RA message with source set to its own 2780 LLA and destination set to the Client's MNP-LLA, and with any 2781 window synchronization acknowledgements. Proxy/Server "B" then 2782 encapsulates the RA in an OAL header with source set to its own 2783 ADM-ULA and destination set to the ADM-ULA of Proxy/Server "A, 2784 performs fragmentation if necessary, then sends the resulting 2785 carrier packets into the secured spanning tree. 2787 o when Proxy/Server "A" reassembles the RA, it locates the Client 2788 NCE based on the RA destination LLA. Proxy/Server "A" then re- 2789 encapsulates the RA message with OAL source set to its own ADM-ULA 2790 and OAL destination set to the MNP-ULA of the Client, includes an 2791 authentication signature if necessary, and includes an Interface 2792 Attributes sub-option with omIndex 0 and with FMT/SRT/LHS/L2ADDR 2793 information for its INET interface. Proxy/Server "A" then 2794 fragments if necessary and returns the fragments to the Client. 2796 o The Client repeats this process over each of its additional 2797 underlying interfaces while treating each "B", "C", "D" as a FHS 2798 Proxy/Server while providing MS-Register//Release information for 2799 the others as LHS Proxy/Servers. 2801 After the initial RS/RA exchanges each Proxy/Server forwards any of 2802 the Client's carrier packets with OAL destinations for which there is 2803 no matching NCE to a Bridge using OAL encapsulation with its own ADM- 2804 ULA as the source and with destination determined by the Client. The 2805 Proxy/Server instead forwards any carrier packets destined to a 2806 neighbor cache target directly to the target according to the OAL/ 2807 link-layer information - the process of establishing neighbor cache 2808 entries is specified in Section 3.14. 2810 While the Client is still associated with each Proxy/Server "A", "A" 2811 can send NS, RS and/or unsolicited NA messages to update the neighbor 2812 cache entries of other AERO nodes on behalf of the Client and/or to 2813 convey Interface Attributes updates. This allows for higher- 2814 frequency Proxy-initiated RS/RA messaging over well-connected INET 2815 infrastructure supplemented by lower-frequency Client-initiated RS/RA 2816 messaging over constrained ANET data links. 2818 If any Proxy/Server "B", "C", "D" ceases to send solicited RAs, 2819 Proxy/Server "A" sends unsolicited RAs over the Client's underlying 2820 interface with destination set to (link-local) All-Nodes multicast 2821 and with Router Lifetime set to zero to inform Clients that another 2822 Proxy/Server has failed. Although Proxy/Server "A" can engage in 2823 IPv6 ND exchanges on behalf of the Client, the Client can also send 2824 IPv6 ND messages on its own behalf, e.g., if it is in a better 2825 position than "A" to convey Interface Attribute changes, etc. The 2826 IPv6 ND messages sent by the Client include the Client's MNP-LLA as 2827 the source in order to differentiate them from the IPv6 ND messages 2828 sent by Proxy/Server "A". 2830 If the Client becomes unreachable over all underlying interface it 2831 serves, Proxy/Server "A" sets the NCE state to DEPARTED and retains 2832 the entry for DepartTime seconds. While the state is DEPARTED, 2833 Proxy/Server "A" forwards any carrier packets destined to the Client 2834 to a Bridge via OAL encapsulation. When DepartTime expires, Proxy/ 2835 Server "A" deletes the NCE and discards any further carrier packets 2836 destined to the former Client. 2838 In some ANETs that employ a Proxy/Server, the Client's MNP can be 2839 injected into the ANET routing system. In that case, the Client can 2840 send original IP packets without invoking the OAL so that the ANET 2841 routing system transports the original IP packets to the Proxy. This 2842 can be very beneficial, e.g., if the Client connects to the ANET via 2843 low-end data links such as some aviation wireless links. 2845 If the ANET first-hop access router is on the same underlying link as 2846 the Client and recognizes the AERO/OMNI protocol, the Client can 2847 avoid OAL encapsulation for both its control and data messages. When 2848 the Client connects to the link, it can send an unencapsulated RS 2849 message with source address set to its own MNP-LLA (or to a Temporary 2850 LLA), and with destination address set to the ADM-LLA of the Client's 2851 selected Proxy/Server or to (link-local) All-Routers multicast. The 2852 Client includes an OMNI option formatted as specified in 2853 [I-D.templin-6man-omni]. The Client then sends the unencapsulated RS 2854 message, which will be intercepted by the AERO-Aware access router. 2856 The ANET access router then performs OAL encapsulation on the RS 2857 message and forwards it to a Proxy/Server at the ANET/INET boundary. 2858 When the access router and Proxy/Server are one and the same node, 2859 the Proxy/Server would share and underlying link with the Client but 2860 its message exchanges with outside correspondents would need to pass 2861 through a security gateway at the ANET/INET border. The method for 2862 deploying access routers and Proxys (i.e. as a single node or 2863 multiple nodes) is an ANET-local administrative consideration. 2865 Note: When a Proxy/Server alters the IPv6 ND message contents before 2866 forwarding (e.g., such as altering the OMNI option contents), the 2867 IPv6 ND message checksum and/or authentication signature are 2868 invalidated. If the Proxy/Server forwards the message over the 2869 secured spanning tree, however, it need not re-calculate the 2870 checksum/signature since they will not be examined by the next hop. 2872 Note: When a Proxy/Server receives a secured Client NS message, it 2873 performs the same proxying procedures as for described for RS 2874 messages above. The proxying procedures for NS/NA message exchanges 2875 is specified in Section 3.14. 2877 3.13.1. Detecting and Responding to Proxy/Server Failures 2879 In environments where fast recovery from Proxy/Server failure is 2880 required, Proxy/Server "A" SHOULD use proactive Neighbor 2881 Unreachability Detection (NUD) to track each peer Proxy/Server "B" 2882 reachability in a similar fashion as for Bidirectional Forwarding 2883 Detection (BFD) [RFC5880]. Proxy/Server "A" can then quickly detect 2884 and react to failures so that cached information is re-established 2885 through alternate paths. The NS/NA(NUD) control messaging is carried 2886 only over well-connected ground domain networks (i.e., and not low- 2887 end aeronautical radio links) and can therefore be tuned for rapid 2888 response. 2890 Proxy/Server "A" performs continuous NS/NA(NUD) exchanges with peer 2891 Proxy/Server "B" for which there are currently active Clients in 2892 rapid succession, e.g., one exchange per second. Proxy/Server "A" 2893 sends the NS(NUD) message via the spanning tree with its own ADM-LLA 2894 as the source and the ADM-LLA of the peer Proxy/Server "B" as the 2895 destination, and Proxy/Server "B" responds with an NA(NUD). When 2896 Proxy/Server "A" is also sending RS messages to the peer Proxy/Server 2897 "B" on behalf of Clients, the resulting RA responses can be 2898 considered as equivalent hints of forward progress. This means that 2899 Proxy/Server "B" need not also send a periodic NS(NUD) if it has 2900 already sent an RS within the same period. If the peer Proxy/Server 2901 "B" fails (i.e., if "A" ceases to receive advertisements), Proxy/ 2902 Server "A" can quickly inform Clients by sending unsolicited RA 2903 messages 2905 Proxy/Server "A" sends unsolicited RA messages with source address 2906 set to Proxy/Server "B"'s address, destination address set to (link- 2907 local) All-Nodes multicast, and Router Lifetime set to 0. Proxy/ 2908 Server "A" SHOULD send MAX_FINAL_RTR_ADVERTISEMENTS RA messages 2909 separated by small delays [RFC4861]. Any Clients that had been using 2910 the failed Proxy/Server "B" will receive the RA messages and 2911 associate with a new Proxy/Server. 2913 3.13.2. Point-to-Multipoint Proxy/Server Coordination 2915 In environments where Client messaging over ANETs is bandwidth- 2916 limited and/or expensive, Clients can enlist the services of FHS 2917 Proxy/Server "A" to coordinate with multiple LHS Proxy/Servers "B", 2918 "C", "D" etc. in a single RS/RA message exchange. The Client can 2919 send a single RS message to (link-local) All-Routers multicast that 2920 includes the ID's of multiple Proxy/Servers in MS-Register/MS-Release 2921 OMNI sub-options. 2923 When FHS Proxy/Server "A" receives the RS and processes the OMNI 2924 option, it sends a separate RS to each MS-Register/MS-Release LHS 2925 Proxy/Server "B", "C", "D", etc. When FHS Proxy/Server "A" receives 2926 an LHS Proxy/Server RA, it can optionally return an immediate 2927 "singleton" RA to the Client or record the LHS Proxy/Server's MSID 2928 for inclusion in a pending "aggregate" RA message. FHS Proxy/Server 2929 "A" can then return aggregate RA messages to the Client including 2930 multiple LHS Proxy/Server MSIDs in order to conserve bandwidth. Each 2931 RA includes a proper subset of the LHS Proxy/Server MSIDs from the 2932 original RS message, and FHS Proxy/Server "A" must ensure that the 2933 message contents of each RA are consistent with the information 2934 received from the (aggregated) LHS Proxy/Servers. 2936 Clients can thereafter employ efficient point-to-multipoint LHS 2937 Proxy/Server coordination under the assistance of FHS Proxy/Server 2938 "A" to reduce the number of messages sent over the *NET. Clients can 2939 further include MS-Release sub-options in IPv6 ND messages to request 2940 FHS Proxy/Server "A" to release from former LHS Proxy/Servers via the 2941 procedures discussed in Section 3.16.5. 2943 The OMNI interface specification [I-D.templin-6man-omni] provides 2944 further discussion of the RS/RA messaging involved in point-to- 2945 multipoint coordination. 2947 3.14. AERO Route Optimization 2949 AERO nodes invoke route optimization when they need to forward 2950 packets to new target destinations. Route optimization is based on 2951 IPv6 ND Address Resolution messaging between a Route Optimization 2952 Source (ROS) and Route Optimization Responder (ROR). Route 2953 optimization is initiated by the first eligible ROS closest to the 2954 source as follows: 2956 o For Clients on VPNed and Direct interfaces, the Client's FHS 2957 Proxy/Server is the ROS. 2959 o For Clients on ANET interfaces, either the Client or the FHS 2960 Proxy/Server may be the ROS. 2962 o For Clients on INET interfaces, the Client itself is the ROS. 2964 o For correspondent nodes on INET/EUN interfaces serviced by a 2965 Relay, the Relay is the ROS. 2967 The route optimization procedure is conducted between the ROS and an 2968 LHS Proxy/Server/Relay for the target selected by routing as the ROR. 2969 In this arrangement, the ROS is always the Client or Proxy/Server (or 2970 Relay) nearest the source over the selected source underlying 2971 interface, while the ROR may be any of the target's Proxy/Servers 2972 that can provide comprehensive information. 2974 The AERO routing system directs a route optimization request sent by 2975 the ROS to the nearest available ROR, which returns a route 2976 optimization reply. The exact ROR selected is unimportant as long as 2977 the information returned is current, consistent and authentic. The 2978 ROS is responsible for periodically refreshing the route 2979 optimization, and the ROR is responsible for quickly informing the 2980 ROS of any changes. 2982 The procedures are specified in the following sections. 2984 3.14.1. Route Optimization Initiation 2986 When an original IP packet from a source node destined to a target 2987 node arrives, the ROS checks for a NCE with an MNP-LLA that matches 2988 the target destination. If there is a NCE in the REACHABLE state, 2989 the ROS invokes the OAL and forwards the resulting carrier packets 2990 according to the cached state then returns from processing. 2991 Otherwise, if there is no NCE the ROS creates one in the INCOMPLETE 2992 state. 2994 The ROS next places the original IP packet on a short queue then 2995 sends an NS message for Address Resolution (NS(AR)) to receive a 2996 solicited NA(AR) message from an ROR. The NS(AR) message must be 2997 sent securely, and includes: 2999 o the LLA of the ROS as the source address. 3001 o the MNP-LLA corresponding to the original IP packet's destination 3002 as the Target Address, e.g., for 2001:db8:1:2::10:2000 the Target 3003 Address is fe80::2001:db8:1:2. 3005 o the Solicited-Node multicast address [RFC4291] formed from the 3006 lower 24 bits of the original IP packet's destination as the 3007 destination address, e.g., for 2001:db8:1:2::10:2000 the NS(AR) 3008 destination address is ff02:0:0:0:0:1:ff10:2000. 3010 The NS(AR) message also includes an OMNI option with an 3011 authentication sub-option if necessary, an Interface Attributes sub- 3012 option for the underlying interface, with S/T-omIndex set to the 3013 underlying interface index and with Preflen set to the prefix length 3014 associated with the NS(AR) source. The ROS then selects an 3015 Identification value and submits the NS(AR) message for OAL 3016 encapsulation with OAL source set to its own ULA and OAL destination 3017 set to the ULA corresponding to the target. (The ROS does not 3018 include any window synchronization parameters, since it will not 3019 exchange other packet types with the ROR.) The ROS then sends the 3020 resulting carrier packet into the SRT secured spanning tree without 3021 decrementing the network-layer TTL/Hop Limit field. 3023 When the ROS is an INET Client, it must instead forward the resulting 3024 carrier packet to the ADM-ULA of one of its current Proxy/Servers. 3025 The Proxy/Server then verifies the NS(AR) authentication signature 3026 and writes its FMT/SRT/LHS/L2ADDR information into the Interface 3027 Attributes sub-option the same as described for RS messages in 3028 Section 3.13. The Proxy/Server then re-encapsulates the NS(AR) with 3029 the OAL source set to its own ADM-ULA and OAL destination set to the 3030 ULA corresponding to the target and forwards the resulting carrier 3031 packets into the secured spanning tree on behalf of the Client. 3033 3.14.2. Relaying the NS(AR) *NET Packet(s) 3035 When the Bridge receives the carrier packet containing the RS from 3036 the ROS, it discards the *NET headers and determines the next hop by 3037 consulting its standard IPv6 forwarding table for the OAL header 3038 destination address. The Bridge then decrements the OAL header Hop- 3039 Limit, then re-encapsulates and forwards the carrier packet(s) via 3040 the secured spanning tree the same as for any IPv6 router, where it 3041 may traverse multiple OMNI link segments. The final-hop Bridge will 3042 deliver the carrier packet via the secured spanning tree to the 3043 closest ROR Proxy/Server for the target. 3045 3.14.3. Processing the NS(AR) and Sending the NA(AR) 3047 When an ROR for the target receives the secured carrier packet, it 3048 examines the NS(AR) target to determine whether it has a matching NCE 3049 and/or non-MNP route. If there is no match, the ROR drops the 3050 message. Otherwise, the ROR continues processing as follows: 3052 o if the NS(AR) target matches a Client NCE in the DEPARTED state, 3053 the ROR re-encapsulates while setting the OAL source to the ULA of 3054 the ROS and OAL destination address to the ADM-ULA of the Client's 3055 new Proxy/Server. The ROR then forwards the resulting carrier 3056 packet over the secured spanning tree then returns from 3057 processing. 3059 o If the NS(AR) target matches the MNP-LLA of a Client NCE in the 3060 REACHABLE state, the ROR notes whether the NS (AR) arrived from 3061 the secured spanning tree then provides route optimization 3062 information on behalf of the Client. If the message arrived via 3063 the secured spanning tree the ROR need not perform further 3064 authentication; otherwise, it must verify the message 3065 authentication signature before accepting. 3067 o If the NS(AR) target matches one of its non-MNP routes, the ROR 3068 serves as both a Relay and a route optimization target, since the 3069 Relay forwards IP packets toward the (fixed network) target at the 3070 network layer. 3072 The ROR next checks the target NCE for a Report List entry that 3073 matches the NS(AR) source LLA/ULA of the ROS. If there is a Report 3074 List entry, the ROR refreshes ReportTime for this ROR; otherwise, the 3075 ROR creates a new entry for the ROS and records both the LLA and ULA. 3077 The ROR then prepares a (solicited) NA(AR) message to return to the 3078 ROS with the source address set to its own ADM-LLA, the destination 3079 address set to the NS(AR) LLA source address and the Target Address 3080 set to the target Client's MNP-LLA. The ROR includes an OMNI option 3081 with Preflen set to the prefix length associated with the NA(AR) 3082 source address, with S/T-omIndex set to the value that appeared in 3083 the NS(AR) and with Interface Attributes sub-options for all of the 3084 target's underlying interfaces with current information for each 3085 interface. 3087 For each Interface Attributes sub-option, the ROR sets the L2ADDR 3088 according to its own INET address for VPNed, Direct, ANET and NATed 3089 Client interfaces, or to the Client's INET address for native Client 3090 interfaces. The ROR then includes the lower 32 bits of its ADM-ULA 3091 as the LHS, encodes the ADM-ULA SRT prefix length in the SRT field 3092 and sets FMT as specified in Section 3.3. 3094 The ROR then sets the NA(AR) message R flag to 1 (as a router) and S 3095 flag to 1 (as a response to a solicitation) and sets the O flag to 0 3096 (as a proxy). The ROR finally submits the NA(AR) for OAL 3097 encapsulation with source set to its own ULA and destination set to 3098 the same ULA that appeared in the NS(AR) OAL source, then performs 3099 OAL encapsulation using the same Identification value that appeared 3100 in the NS(AR) and finally forwards the resulting (*NET-encapsulated) 3101 carrier packet via the secured spanning tree without decrementing the 3102 network-layer TTL/Hop Limit field. 3104 3.14.4. Relaying the NA(AR) 3106 When the Bridge receives NA(AR) carrier packet from the ROR, it 3107 discards the *NET header and determines the next hop by consulting 3108 its standard IPv6 forwarding table for the OAL header destination 3109 address. The Bridge then decrements the OAL header Hop-Limit, re- 3110 encapsulates the carrier packet and forwards it via the SRT secured 3111 spanning tree, where it may traverse multiple OMNI link segments. 3112 The final-hop Bridge will deliver the carrier packet via the secured 3113 spanning tree to a Proxy/Server for the ROS. 3115 3.14.5. Processing the NA(AR) 3117 When the ROS receives the NA(AR) message, it first searches for a NCE 3118 that matches the NA(AR) target address. The ROS then processes the 3119 message the same as for standard IPv6 Address Resolution [RFC4861]. 3120 In the process, it caches all OMNI option information in the target 3121 NCE (including all Interface Attributes), and caches the NA(AR) 3122 ADM-{LLA,ULA} source addresses as the addresses of the ROR. If the 3123 ROS receives additional NA(AR) or uNA messages for this target Client 3124 with the same ADM-LLA source address but a different ADM-ULA source 3125 address, it configures the ADM-LLA corresponding to the new ADM-ULA, 3126 then caches the new ADM-{LLA,ULA} and deprecates the former 3127 ADM-{LLA,ULA}. 3129 When the ROS is a Client, the SRT secured spanning tree will first 3130 deliver the solicited NA(AR) message to the local Proxy/Server, which 3131 re-encapsulates and forwards the message to the Client. If the 3132 Client is on a well-managed ANET, physical security and protected 3133 spectrum ensures security for the unmodified NA(AR); if the Client is 3134 on the open INET the Proxy/Server must instead include an 3135 authentication signature (while adjusting the OMNI option size, if 3136 necessary). The Proxy/Server uses its own ADM-ULA as the OAL source 3137 and the MNP-ULA of the Client as the OAL destination. 3139 3.14.6. Forwarding Packets to Route Optimized Targets 3141 After the ROS receives the route optimization NA(AR) and updates the 3142 target NCE, it sends additional NS(AR) messages to the ADM-ULA of the 3143 ROR to refresh the NCE ReachableTime before expiration while it still 3144 has sustained interest in this target. While the NCE remains 3145 REACHABLE, the ROS can forward packets along paths that use best 3146 underlying interface pairs based on local preferences and target 3147 Interface Attributes. The ROS selects target underlying interfaces 3148 according to traffic selectors and/or any other traffic 3149 discriminators, but must first establish window synchronization state 3150 for each target if necessary. 3152 The ROS initiates window synchronization through a secured uncast NS/ 3153 NA(WIN) exchange as specified in Section 3.2.7. The NS/NA(WIN) 3154 exchange is conducted over a first underlying interface pair and 3155 registers only those interfaces. If the ROS and target have 3156 additional underlying interface pairs serviced by the same source/ 3157 destination LLAs, they may register new interfaces by sending 3158 additional NS/NA(WIN) messages but need not include window 3159 synchronization parameters. If the ROS and target have additional 3160 underlying interface pairs services by different source/destination 3161 LLAs, they must include window synchronization parameters when they 3162 send NS/NA(WIN) messages to establish NCE state for the new source/ 3163 destination LLAs. 3165 After window synchronization state has been established, the ROS and 3166 target Client can begin forwarding carrier packets while performing 3167 additional NS/NA(WIN) exchanges as above to update window state, 3168 register new interfaces and/or test reachability. The ROS sends 3169 carrier packets to the FHS Bridge discovered through the NS/NA(WIN) 3170 exchange which verifies the Identification is in window for the 3171 target Client. The FHS Bridge then forwards the carrier packets over 3172 the unsecured spanning tree to the LHS Bridge, which forwards them 3173 via LHS encapsulation to the LHS Proxy/Server or directly to the 3174 target Client itself. The target Client in turn sends packets to the 3175 ROS in the reverse direction while forwarding through the Bridges to 3176 minimize Proxy/Server load whenever possible. 3178 While the ROS continues to actively forward packets to the target 3179 Client, it is responsible for updating window synchronization state 3180 and per-interface reachability before expiration. Window 3181 synchronization state is shared by all underlying interfaces in the 3182 ROS' NCE that use the same destination LLA so that a single NS/ 3183 NA(WIN) exchange applies for all interfaces regardless of the 3184 (single) interface used to conduct the exchange. However, the window 3185 synchronization exchange only confirms target Client reachability 3186 over the specific interface used to conduct the exchange. 3187 Reachability for other underlying interfaces that share the same 3188 window synchronization state must be determined individually using 3189 NS/NA(NUD) messages which need not be secured as long as they use in- 3190 window Identifications and do not update other state information. 3192 3.15. Neighbor Unreachability Detection (NUD) 3194 AERO nodes perform Neighbor Unreachability Detection (NUD) per 3195 [RFC4861] either reactively in response to persistent link-layer 3196 errors (see Section 3.11) or proactively to confirm reachability. 3197 The NUD algorithm is based on periodic control message exchanges and 3198 may further be seeded by IPv6 ND hints of forward progress, but care 3199 must be taken to avoid inferring reachability based on spoofed 3200 information. For example, IPv6 ND message exchanges that include 3201 authentication codes and/or in-window Identifications may be 3202 considered as acceptable hints of forward progress, while spurious 3203 random carrier packets should be ignored. 3205 AERO nodes can perform NS/NA(NUD) exchanges over the OMNI link 3206 secured spanning tree (i.e. the same as described above for NS/ 3207 NA(WIN)) to test reachability without risk of DoS attacks from nodes 3208 pretending to be a neighbor. These NS/NA(NUD) messages use the 3209 unicast LLAs and ULAs of the parties involved in the NUD test. When 3210 only reachability information is required without updating any other 3211 NCE state, AERO nodes can instead perform NS/NA(NUD) exchanges 3212 directly between neighbors without employing the secured spanning 3213 tree as long as they include in-window Identifications and either an 3214 authentication signature or checksum. 3216 When an ROR directs an ROS to a target neighbor with one or more 3217 link-layer addresses, the ROS probes each unsecured target underlying 3218 interface either proactively or on-demand of carrier packets directed 3219 to the path by multilink forwarding to maintain the interface's state 3220 as reachable. Probing is performed through NS(NUD) messages over the 3221 SRT secured or unsecured spanning tree, or through NS(NUD) messages 3222 sent directly to an underlying interface of the target itself. While 3223 testing a target underlying interface, the ROS can optionally 3224 continue to forward carrier packets via alternate interfaces and/or 3225 maintain a small queue of carrier packets until target reachability 3226 is confirmed. 3228 NS(NUD) messages are encapsulated, fragmented and transmitted as 3229 carrier packets the same as for ordinary original IP data packets, 3230 however the encapsulated destinations are the LLA of the ROS and 3231 either the ADM-LLA of the LHS Proxy/Server or the MNP-LLA of the 3232 target itself. The ROS encapsulates the NS(NUD) message the same as 3233 described in Section 3.2.7, however Destination Trailers (if present) 3234 are set according to the LLA destination suffix (i.e., and not the 3235 ULA/GUA destination). The ROS sets the NS(NUD) OMNI header S/ 3236 T-omIndex to identify the underlying interface used for forwarding 3237 (or to 0 if any underlying interface can be used). The ROS then 3238 fragments the OAL packet and forwards the resulting carrier packets 3239 into the unsecured spanning tree or via direct encapsulation for 3240 local segment targets. 3242 When the target receives the NS(NUD) carrier packets, it verifies 3243 that it has a NCE for this ROS and that the Identification is in- 3244 window, then submits the carrier packets for reassembly. The node 3245 then verifies the authentication signature or checksum, then searches 3246 for Interface Attributes in its NCE for the ROS that match the 3247 NS(NUD) S/T-omIndex for the NA(NUD) reply. The node then prepares 3248 the NA(NUD) with the source and destination LLAs reversed, 3249 encapsulates and sets the OAL source and destination, sets the 3250 NA(NUD) S/T-omIndex to the index of the underlying interface the 3251 NS(NUD) arrived on and sets the Target Address to the same value 3252 included in the NS(NUD). The target next sets the R flag to 1, the S 3253 flag to 1 and the O flag to 1, then selects an in-window 3254 Identification for the ROS and performs fragmentation. The node then 3255 forwards the carrier packets into the unsecured spanning tree, 3256 directly to the ROS if it is in the local segment or directly to a 3257 Bridge in the local segment. 3259 When the ROS receives the NA(NUD), it marks the target underlying 3260 interface tested as "reachable". Note that underlying interface 3261 states are maintained independently of the overall NCE REACHABLE 3262 state, and that a single NCE may have multiple target underlying 3263 interfaces in various states "reachable" and otherwise while the NCE 3264 state as a whole remains REACHABLE. 3266 Note also that the exchange of NS/NA(NUD) messages has the useful 3267 side-benefit of opening holes in NATs that may be useful for NAT 3268 traversal. 3270 3.16. Mobility Management and Quality of Service (QoS) 3272 AERO is a Distributed Mobility Management (DMM) service. Each Proxy/ 3273 Server is responsible for only a subset of the Clients on the OMNI 3274 link, as opposed to a Centralized Mobility Management (CMM) service 3275 where there is a single network mobility collective entity for all 3276 Clients. Clients coordinate with their associated Proxy/Servers via 3277 RS/RA exchanges to maintain the DMM profile, and the AERO routing 3278 system tracks all current Client/Proxy/Server peering relationships. 3280 Proxy/Servers provide default routing and mobility/multilink services 3281 for their dependent Clients. Clients are responsible for maintaining 3282 neighbor relationships with their Proxy/Servers through periodic RS/ 3283 RA exchanges, which also serves to confirm neighbor reachability. 3284 When a Client's underlying Interface Attributes change, the Client is 3285 responsible for updating the Proxy/Server with this new information. 3286 The Proxy/Server can also act as a proxy to perform some IPv6 ND 3287 exchanges on the Client's behalf without consuming bandwidth on the 3288 Client underlying interface. 3290 Mobility update messaging is based on the transmission and reception 3291 of unsolicited Neighbor Advertisement (uNA) messages. Each uNA 3292 message sets the IPv6 source address to the ADM-LLA of the ROR and 3293 the destination address to the unicast LLA of the ROS. 3295 Mobility management considerations are specified in the following 3296 sections. 3298 3.16.1. Mobility Update Messaging 3300 RORs accommodate Client mobility and/or multilink change events by 3301 sending secured uNA messages to each ROS in the target Client's 3302 Report List. When an ROR sends a uNA message, it sets the IPv6 3303 source address to the its own ADM-LLA, sets the destination address 3304 to the ROS LLA (i.e., an MNP-LLA if the ROS is a Client and an ADM- 3305 LLA if the ROS is a Proxy/Server) and sets the Target Address to the 3306 Client's MNP-LLA. The ROR also includes an OMNI option with Preflen 3307 set to the prefix length associated with the Client's MNP-LLA, with 3308 Interface Attributes for the target Client's underlying interfaces 3309 and with the OMNI header S/T-omIndex set to 0. The ROR then sets the 3310 uNA R flag to 1, S flag to 0 and O flag to 1, then encapsulates the 3311 message in an OAL header with source set to its own ADM-ULA and 3312 destination set to the ROS ULA (i.e., the ADM-ULA of the ROS Proxy/ 3313 Server) and sends the message into the secured spanning tree. 3315 As discussed in Section 7.2.6 of [RFC4861], the transmission and 3316 reception of uNA messages is unreliable but provides a useful 3317 optimization. In well-connected Internetworks with robust data links 3318 uNA messages will be delivered with high probability, but in any case 3319 the ROR can optionally send up to MAX_NEIGHBOR_ADVERTISEMENT uNAs to 3320 each ROS to increase the likelihood that at least one will be 3321 received. Alternatively, the ROR can set the PNG flag in the uNA 3322 OMNI option header to request a solicited NA acknowledgement as 3323 specified in [I-D.templin-6man-omni]. 3325 When the ROS Proxy/Server receives a uNA message prepared as above, 3326 it ignores the message if the OAL destination is not its own ADM-ULA. 3327 If the uNA destination was its own ADM-LLA, the ROS Proxy/Server uses 3328 the included OMNI option information to update its NCE for the target 3329 but does not reset ReachableTime since the receipt of an unsolicited 3330 NA message from the ROR does not provide confirmation that any 3331 forward paths to the target Client are working. If the destination 3332 was the MNP-LLA of the ROS Client, the Proxy/Server instead re- 3333 encapsulates with the OAL source set to its own ADM-ULA, OAL 3334 destination set to the MNP-ULA of the ROS Client with an 3335 authentication signature if necessary, and with an in-window 3336 Identification for this Client. Finally, if the uNA message PNG flag 3337 was set, the ROS returns a solicited NA acknowledgement as specified 3338 in [I-D.templin-6man-omni]. 3340 In addition to sending uNA messages to the current set of ROSs for 3341 the target Client, the ROR also sends uNAs to the former Proxy/Server 3342 associated with the underlying interface for which the link-layer 3343 address has changed. These uNA messages update former Proxy/Servers 3344 that cannot easily detect (e.g., without active probing) when a 3345 formerly-active Client has departed. When the ROR sends the uNA, it 3346 sets the source address to its ADM-LLA, sets the destination address 3347 to the former Proxy/Server's ADM-LLA, and sets the Target Address to 3348 the Client's MNP-LLA. The ROR also includes an OMNI option with 3349 Preflen set to the prefix length associated with the Client's MNP- 3350 LLA, with Interface Attributes for the changed underlying interface, 3351 and with the OMNI header S/T-omIndex set to 0. The ROR then sets the 3352 uNA R flag to 1, S flag to 0 and O flag to 1, then encapsulates the 3353 message in an OAL header with source set to its own ADM-ULA and 3354 destination set to the ADM-ULA of the former Proxy/Server and sends 3355 the message into the secured spanning tree. 3357 3.16.2. Announcing Link-Layer Address and/or QoS Preference Changes 3359 When a Client needs to change its underlying Interface Attributes 3360 (e.g., due to a mobility event), the Client requests one of its 3361 Proxy/Servers to send RS messages to all of its other Proxy/Servers 3362 via the secured spanning tree with an OMNI option that includes 3363 Interface Attributes with the new link quality and address 3364 information. 3366 Up to MAX_RTR_SOLICITATIONS RS messages MAY be sent in parallel with 3367 sending carrier packets containing user data in case one or more RAs 3368 are lost. If all RAs are lost, the Client SHOULD re-associate with a 3369 new Proxy/Server. 3371 When the Proxy/Server receives the Client's changes, it sends uNA 3372 messages to all nodes in the Report List the same as described in the 3373 previous section. 3375 3.16.3. Bringing New Links Into Service 3377 When a Client needs to bring new underlying interfaces into service 3378 (e.g., when it activates a new data link), it sends an RS message to 3379 the Proxy/Server via the underlying interface with an OMNI option 3380 that includes Interface Attributes with appropriate link quality 3381 values and with link-layer address information for the new link. 3383 3.16.4. Deactivating Existing Links 3385 When a Client needs to deactivate an existing underlying interface, 3386 it sends an RS message to an FHS Proxy/Server with an OMNI option 3387 with appropriate Interface Attribute values for the deactivated link 3388 - in particular, the link quality value 0 assures that neighbors will 3389 cease to use the link. 3391 If the Client needs to send RS messages over an underlying interface 3392 other than the one being deactivated, it MUST include Interface 3393 Attributes with appropriate link quality values for any underlying 3394 interfaces being deactivated. 3396 Note that when a Client deactivates an underlying interface, 3397 neighbors that have received the RS/uNA messages need not purge all 3398 references for the underlying interface from their neighbor cache 3399 entries. The Client may reactivate or reuse the underlying interface 3400 and/or its omIndex at a later point in time, when it will send new RS 3401 messages to an FHS Proxy/Server with fresh Interface Attributes to 3402 update any neighbors. 3404 3.16.5. Moving Between Proxy/Servers 3406 The Client performs the procedures specified in Section 3.12.2 when 3407 it first associates with a new FHS Proxy/Server or renews its 3408 association with an existing Proxy/Server. The Client also includes 3409 MS-Release identifiers in the RS message OMNI option per 3410 [I-D.templin-6man-omni] if it wants the new Proxy/Server to notify 3411 any old Proxy/Servers from which the Client is departing. 3413 When the new FHS Proxy/Server receives the Client's RS message, it 3414 sends RS messages to any old Proxy/Servers listed in OMNI option MS- 3415 Release identifiers and returns an RA (either immediate or deferred) 3416 as specified in Section 3.12.3. The new Proxy/Server sends each RS 3417 message with source set to the MNP-LLA of the Client and destination 3418 set to the ADM-LLA of the old Proxy/Server. The new Proxy/Server 3419 also includes an OMNI option with Preflen set to the prefix length 3420 associated with the Client's MNP-LLA, with Interface Attributes for 3421 its INET underlying interface, and with the OMNI header S/T-omIndex 3422 set to 0. The new Proxy/Server then encapsulates the message in an 3423 OAL header with source set to its own ADM-ULA and destination set to 3424 the ADM-ULA of the old Proxy/Server and sends the message into the 3425 secured spanning tree. 3427 When an old Proxy/Server receives the RS, it notices that the message 3428 appears to have originated from the Client's MNP-LLA but that it 3429 includes an Interface Attributes sub-option for the new Proxy/Server 3430 and with S/T-omIndex set to 0. The old Proxy/Server then changes the 3431 Client's NCE state to DEPARTED, sets the FMT/SRT/LHS/L2ADDR 3432 information for the Client to point to the new Proxy/Server, and 3433 resets DepartTime. The old Proxy/Server then returns an RA message 3434 with zero Router Lifetime via the secured spanning tree by reversing 3435 the LLA and ULA addresses found in the RS message. After a short 3436 delay (e.g., 2 seconds) the old Proxy/Server withdraws the Client's 3437 MNP from the routing system. After DepartTime expires, the old 3438 Proxy/Server deletes the Client's NCE. 3440 The old Proxy/Server also iteratively sends uNA messages to each ROS 3441 in the Client's Report List with its own ADM-LLA as the source and 3442 the LLA of the ROS as the destination. The old Proxy/Server then 3443 encapsulates the uNA with OAL source address set to the ADM-ULA of 3444 the new Proxy/Server and OAL destination address set to the ADM-ULA 3445 of the ROS Proxy/Server and sends the carrier packets over the 3446 secured spanning tree. When the ROS Proxy/Server receives the uNA, 3447 it forwards the message to the ROS Client if the destination is an 3448 MNP-LLA. The ROS then examines the uNA Target Address to locate the 3449 target Client's NCE and the ADM-LLA source address to identify the 3450 old Proxy/Server. The ROS then caches the ULA source address as the 3451 ADM-{LLA/ULA} for the new Proxy/Server for this target NCE and marks 3452 the entry as STALE. While in the STALE state, the ROS sends new 3453 NS(AR) messages using its own ULA as the OAL source and the ADM-ULA 3454 of the new Proxy/Server as the OAL destination address. The new 3455 Proxy/Server will then process the NS(AR) and return an NA(AR) 3456 response. 3458 Clients SHOULD NOT move rapidly between Proxy/Servers in order to 3459 avoid causing excessive oscillations in the AERO routing system. 3460 Examples of when a Client might wish to change to a different Proxy/ 3461 Server include a Proxy/Server that has gone unreachable, topological 3462 movements of significant distance, movement to a new geographic 3463 region, movement to a new OMNI link segment, etc. 3465 3.17. Multicast 3467 Clients provide an IGMP (IPv4) [RFC2236] or MLD (IPv6) [RFC3810] 3468 proxy service for its EUNs and/or hosted applications [RFC4605] and 3469 act as a Protocol Independent Multicast - Sparse-Mode (PIM-SM, or 3470 simply "PIM") Designated Router (DR) [RFC7761] on the OMNI link. 3471 Proxy/Servers act as OMNI link PIM routers for Clients on ANET, VPNed 3472 or Direct interfaces, and Relays also act as OMNI link PIM routers on 3473 behalf of nodes on other links/networks. 3475 Clients on VPNed, Direct or ANET underlying interfaces for which the 3476 ANET has deployed native multicast services forward IGMP/MLD messages 3477 into the ANET. The IGMP/MLD messages may be further forwarded by a 3478 first-hop ANET access router acting as an IGMP/MLD-snooping switch 3479 [RFC4541], then ultimately delivered to an ANET Proxy/Server. The 3480 Proxy/Server then acts as an ROS to send NS(AR) messages to an ROR. 3481 Clients on INET and ANET underlying interfaces without native 3482 multicast services instead send NS(AR) messages as an ROS to cause 3483 their Proxy/Server forward the message to an ROR. When the ROR 3484 receives an NA(AR) response, it initiates PIM protocol messaging 3485 according to the Source-Specific Multicast (SSM) and Any-Source 3486 Multicast (ASM) operational modes as discussed in the following 3487 sections. 3489 3.17.1. Source-Specific Multicast (SSM) 3491 When an ROS "X" (i.e., either a Client or Proxy Server) acting as PIM 3492 router receives a Join/Prune message from a node on its downstream 3493 interfaces containing one or more ((S)ource, (G)roup) pairs, it 3494 updates its Multicast Routing Information Base (MRIB) accordingly. 3495 For each S belonging to a prefix reachable via X's non-OMNI 3496 interfaces, X then forwards the (S, G) Join/Prune to any PIM routers 3497 on those interfaces per [RFC7761]. 3499 For each S belonging to a prefix reachable via X's OMNI interface, X 3500 sends an NS(AR) message (see: Section 3.14) using its own LLA as the 3501 source address, the solicited node multicast address corresponding to 3502 S as the destination and the LLA of S as the target address. X then 3503 encapsulates the NS(AR) in an OAL header with source address set to 3504 its own ULA and destination address set to the ULA for S, then 3505 forwards the message into the secured spanning tree which delivers it 3506 to ROR "Y" that services S. The resulting NA(AR) will return an OMNI 3507 option with Interface Attributes for any underlying interfaces that 3508 are currently servicing S. 3510 When X processes the NA(AR) it selects one or more underlying 3511 interfaces for S and performs an NS/NA(WIN) exchange over the secured 3512 spanning tree while including a PIM Join/Prune message for each 3513 multicast group of interest in the OMNI option. If S is located 3514 behind any Proxys "Z"*, each Z* then updates its MRIB accordingly and 3515 maintains the LLA of X as the next hop in the reverse path. Since 3516 Bridges forward messages not addressed to themselves without 3517 examining them, this means that the (reverse) multicast tree path is 3518 simply from each Z* (and/or S) to X with no other multicast-aware 3519 routers in the path. 3521 Following the initial combined Join/Prune and NS/NA(WIN) messaging, X 3522 maintains a NCE for each S the same as if X was sending unicast data 3523 traffic to S. In particular, X performs additional NS/NA(WIN) 3524 exchanges to keep the NCE alive for up to t_periodic seconds 3525 [RFC7761]. If no new Joins are received within t_periodic seconds, X 3526 allows the NCE to expire. Finally, if X receives any additional 3527 Join/Prune messages for (S,G) it forwards the messages over the 3528 secured spanning tree. 3530 Client C that holds an MNP for source S may later depart from a first 3531 Proxy/Server Z1 and/or connect via a new Proxy/Server Z2. In that 3532 case, Y sends a uNA message to X the same as specified for unicast 3533 mobility in Section 3.16. When X receives the uNA message, it 3534 updates its NCE for the LLA for source S and sends new Join messages 3535 in NS/NA(WIN) exchanges addressed to the new target Client underlying 3536 interface connection for S. There is no requirement to send any 3537 Prune messages to old Proxy/Server Z1 since source S will no longer 3538 source any multicast data traffic via Z1. Instead, the multicast 3539 state for (S,G) in Proxy/Server Z1 will soon expire since no new 3540 Joins will arrive. 3542 3.17.2. Any-Source Multicast (ASM) 3544 When an ROS X acting as a PIM router receives Join/Prune messages 3545 from a node on its downstream interfaces containing one or more (*,G) 3546 pairs, it updates its Multicast Routing Information Base (MRIB) 3547 accordingly. X first performs an NS/NA(AR) exchange to receive route 3548 optimization information for Rendezvous Point (RP) R for each G. X 3549 then includes a copy of each Join/Prune message in the OMNI option of 3550 an NS(WIN) message with its own LLA as the source address and the LLA 3551 for R as the destination address, then encapsulates the NS(WIN) 3552 message in an OAL header with its own ULA as the source and the ADM- 3553 ULA of R's Proxy/Server as the destination then sends the message 3554 into the secured spanning tree. 3556 For each source S that sends multicast traffic to group G via R, 3557 Client S* that aggregates S (or its Proxy/Server) encapsulates the 3558 original IP packets in PIM Register messages, includes the PIM 3559 Register messages in the OMNI options of uNA messages, performs OAL 3560 encapsulation and fragmentation then forwards the resulting carrier 3561 packets with Identification values within the receive window for 3562 Client R* that aggregates R. Client R* may then elect to send a PIM 3563 Join to S* in the OMNI option of a uNA over the secured spanning 3564 tree. This will result in an (S,G) tree rooted at S* with R as the 3565 next hop so that R will begin to receive two copies of the original 3566 IP packet; one native copy from the (S, G) tree and a second copy 3567 from the pre-existing (*, G) tree that still uses uNA PIM Register 3568 encapsulation. R can then issue a uNA PIM Register-stop message over 3569 the secured spanning tree to suppress the Register-encapsulated 3570 stream. At some later time, if Client S* moves to a new Proxy/ 3571 Server, it resumes sending original IP packets via uNA PIM Register 3572 encapsulation via the new Proxy/Server. 3574 At the same time, as multicast listeners discover individual S's for 3575 a given G, they can initiate an (S,G) Join for each S under the same 3576 procedures discussed in Section 3.17.1. Once the (S,G) tree is 3577 established, the listeners can send (S, G) Prune messages to R so 3578 that multicast original IP packets for group G sourced by S will only 3579 be delivered via the (S, G) tree and not from the (*, G) tree rooted 3580 at R. All mobility considerations discussed for SSM apply. 3582 3.17.3. Bi-Directional PIM (BIDIR-PIM) 3584 Bi-Directional PIM (BIDIR-PIM) [RFC5015] provides an alternate 3585 approach to ASM that treats the Rendezvous Point (RP) as a Designated 3586 Forwarder (DF). Further considerations for BIDIR-PIM are out of 3587 scope. 3589 3.18. Operation over Multiple OMNI Links 3591 An AERO Client can connect to multiple OMNI links the same as for any 3592 data link service. In that case, the Client maintains a distinct 3593 OMNI interface for each link, e.g., 'omni0' for the first link, 3594 'omni1' for the second, 'omni2' for the third, etc. Each OMNI link 3595 would include its own distinct set of Bridges and Proxy/Servers, 3596 thereby providing redundancy in case of failures. 3598 Each OMNI link could utilize the same or different ANET connections. 3599 The links can be distinguished at the link-layer via the SRT prefix 3600 in a similar fashion as for Virtual Local Area Network (VLAN) tagging 3601 (e.g., IEEE 802.1Q) and/or through assignment of distinct sets of 3602 MSPs on each link. This gives rise to the opportunity for supporting 3603 multiple redundant networked paths (see: Section 3.2.5). 3605 The Client's IP layer can select the outgoing OMNI interface 3606 appropriate for a given traffic profile while (in the reverse 3607 direction) correspondent nodes must have some way of steering their 3608 original IP packets destined to a target via the correct OMNI link. 3610 In a first alternative, if each OMNI link services different MSPs the 3611 Client can receive a distinct MNP from each of the links. IP routing 3612 will therefore assure that the correct OMNI link is used for both 3613 outbound and inbound traffic. This can be accomplished using 3614 existing technologies and approaches, and without requiring any 3615 special supporting code in correspondent nodes or Bridges. 3617 In a second alternative, if each OMNI link services the same MSP(s) 3618 then each link could assign a distinct "OMNI link Anycast" address 3619 that is configured by all Bridges on the link. Correspondent nodes 3620 can then perform Segment Routing to select the correct SRT, which 3621 will then direct the original IP packet over multiple hops to the 3622 target. 3624 3.19. DNS Considerations 3626 AERO Client MNs and INET correspondent nodes consult the Domain Name 3627 System (DNS) the same as for any Internetworking node. When 3628 correspondent nodes and Client MNs use different IP protocol versions 3629 (e.g., IPv4 correspondents and IPv6 MNs), the INET DNS must maintain 3630 A records for IPv4 address mappings to MNs which must then be 3631 populated in Relay NAT64 mapping caches. In that way, an IPv4 3632 correspondent node can send original IPv4 packets to the IPv4 address 3633 mapping of the target MN, and the Relay will translate the IPv4 3634 header and destination address into an IPv6 header and IPv6 3635 destination address of the MN. 3637 When an AERO Client registers with an AERO Proxy/Server, the Proxy/ 3638 Server can return the address(es) of DNS servers in RDNSS options 3639 [RFC6106]. The DNS server provides the IP addresses of other MNs and 3640 correspondent nodes in AAAA records for IPv6 or A records for IPv4. 3642 3.20. Transition/Coexistence Considerations 3644 OAL encapsulation ensures that dissimilar INET partitions can be 3645 joined into a single unified OMNI link, even though the partitions 3646 themselves may have differing protocol versions and/or incompatible 3647 addressing plans. However, a commonality can be achieved by 3648 incrementally distributing globally routable (i.e., native) IP 3649 prefixes to eventually reach all nodes (both mobile and fixed) in all 3650 OMNI link segments. This can be accomplished by incrementally 3651 deploying AERO Bridges on each INET partition, with each Bridge 3652 distributing its MNPs and/or discovering non-MNP IP GUA prefixes on 3653 its INET links. 3655 This gives rise to the opportunity to eventually distribute native IP 3656 addresses to all nodes, and to present a unified OMNI link view even 3657 if the INET partitions remain in their current protocol and 3658 addressing plans. In that way, the OMNI link can serve the dual 3659 purpose of providing a mobility/multilink service and a transition/ 3660 coexistence service. Or, if an INET partition is transitioned to a 3661 native IP protocol version and addressing scheme that is compatible 3662 with the OMNI link MNP-based addressing scheme, the partition and 3663 OMNI link can be joined by Bridges. 3665 Relays that connect INETs/EUNs with dissimilar IP protocol versions 3666 may need to employ a network address and protocol translation 3667 function such as NAT64 [RFC6146]. 3669 3.21. Detecting and Reacting to Proxy/Server and Bridge Failures 3671 In environments where rapid failure recovery is required, Proxy/ 3672 Servers and Bridges SHOULD use Bidirectional Forwarding Detection 3673 (BFD) [RFC5880]. Nodes that use BFD can quickly detect and react to 3674 failures so that cached information is re-established through 3675 alternate nodes. BFD control messaging is carried only over well- 3676 connected ground domain networks (i.e., and not low-end radio links) 3677 and can therefore be tuned for rapid response. 3679 Proxy/Servers and Bridges maintain BFD sessions in parallel with 3680 their BGP peerings. If a Proxy/Server or Bridge fails, BGP peers 3681 will quickly re-establish routes through alternate paths the same as 3682 for common BGP deployments. Similarly, Proxys maintain BFD sessions 3683 with their associated Bridges even though they do not establish BGP 3684 peerings with them. 3686 3.22. AERO Clients on the Open Internet 3688 AERO Clients that connect to the open Internet via INET interfaces 3689 can establish a VPN or direct link to securely connect to a FHS 3690 Proxy/Server in a "tethered" arrangement with all of the Client's 3691 traffic transiting the Proxy/Server which acts as a router. 3692 Alternatively, the Client can associate with an INET FHS Proxy/Server 3693 using UDP/IP encapsulation and control message securing services as 3694 discussed in the following sections. 3696 When a Client's OMNI interface enables an INET underlying interface, 3697 it first examines the INET address. For IPv4, the Client assumes it 3698 is on the open Internet if the INET address is not a special-use IPv4 3699 address per [RFC3330]. Similarly for IPv6, the Client assumes it is 3700 on the open Internet if the INET address is a Global Unicast Address 3701 (GUA) [RFC4291]. Otherwise, the Client should assume it is behind 3702 one or several NATs. 3704 The Client then prepares an RS message with IPv6 source address set 3705 to its MNP-LLA, with IPv6 destination set to (link-local) All-Routers 3706 multicast and with an OMNI option with underlying interface 3707 attributes. If the Client believes that it is on the open Internet, 3708 it SHOULD include its IP address and UDP port number in the Interface 3709 Attributes sub-option corresponding to the underlying interface 3710 (otherwise it may omit the FMT/SRT/LHS/L2ADDR fields). If the 3711 underlying address is IPv4, the Client includes the Port Number and 3712 IPv4 address written in obfuscated form [RFC4380] as discussed in 3713 Section 3.3. If the underlying interface address is IPv6, the Client 3714 instead includes the Port Number and IPv6 address in obfuscated form. 3715 The Client finally includes an authentication signature per 3716 [I-D.templin-6man-omni] to provide message authentication, selects an 3717 Identification value and window synchronization parameters, and 3718 submits the RS for OAL encapsulation. The Client then encapsulates 3719 the OAL atomic fragment in UDP/IP headers to form a carrier packet, 3720 sets the UDP/IP source to its INET address and UDP port, sets the 3721 UDP/IP destination to the FHS Proxy/Server's INET address and the 3722 AERO service port number (8060), then sends the carrier packet to the 3723 Proxy/Server. 3725 When the FHS Proxy/Server receives the RS, it discards the OAL 3726 encapsulation, authenticates the RS message, creates a NCE and 3727 registers the Client's MNP, window synchronization state and INET 3728 interface information according to the OMNI option parameters. If 3729 the Interface Attributes sub-option includes an L2ADDR, the Proxy/ 3730 Server compares the encapsulation IP address and UDP port number with 3731 the (unobfuscated) values. If the values are the same, the Proxy/ 3732 Server caches the Client's information as an "INET" address meaning 3733 that the Client is likely to accept direct messages without requiring 3734 NAT traversal exchanges. If the values are different (or, if the 3735 OMNI option did not include an L2ADDR) the Proxy/Server instead 3736 caches the Client's information as a "mapped" address meaning that 3737 NAT traversal exchanges may be necessary. 3739 The FHS Proxy/Server then prepares an RA message with IPv6 source and 3740 destination set corresponding to the addresses in the RS, and with an 3741 OMNI option with an Origin Indication sub-option per 3742 [I-D.templin-6man-omni] with the mapped and obfuscated Port Number 3743 and IP address observed in the encapsulation headers. The Proxy/ 3744 Server also includes an Interface Attributes sub-option with omIndex 3745 0 and FMT/SRT/LHS/L2ADDR information appropriate for its INET 3746 interface, an authentication signature sub-option per 3747 [I-D.templin-6man-omni] and/or a symmetric window synchronization/ 3748 acknowledgement if necessary. The Proxy/Server then performs OAL 3749 encapsulation then encapsulates the carrier packet in UDP/IP headers 3750 with addresses set per the L2ADDR information in the NCE for the 3751 Client. 3753 When the Client receives the RA, it authenticates the message then 3754 process the window synchronization/acknowledgement and compares the 3755 mapped Port Number and IP address from the Origin Indication sub- 3756 option with its own address. If the addresses are the same, the 3757 Client assumes the open Internet / Cone NAT principle; if the 3758 addresses are different, the Client instead assumes that further 3759 qualification procedures are necessary to detect the type of NAT and 3760 performs NAT traversal on-demand according to standard procedures 3761 [RFC6081][RFC4380]. The Client also caches the RA Interface 3762 Attributes FMT/SRT/LHS/L2ADDR information to discover the Proxy/ 3763 Server's local spanning tree segment. The Client finally arranges to 3764 return an explicit/implicit acknowledgement, and sends periodic RS 3765 messages to receive fresh RA messages before the Router Lifetime 3766 received on each INET interface expires. 3768 When the Client sends messages to target IP addresses, it also 3769 invokes route optimization per Section 3.14. For route optimized 3770 targets in the same OMNI link segment, if the target's L2ADDR is on 3771 the open INET, the Client forwards carrier packets directly to the 3772 target INET address. If the target is behind a NAT, the Client first 3773 establishes NAT state for the L2ADDR using the "direct bubble" and 3774 NS/NA(NUD) mechanisms discussed in Section 3.10.1. The Client 3775 continues to send carrier packets via the local Bridge discovered 3776 during window synchronization until NAT state is populated, then 3777 begins forwarding carrier packets via the direct path through the NAT 3778 to the target. For targets in different OMNI link segments, the 3779 Client forwards carrier packets to the local Bridge. 3781 The Client can send original IP packets to route-optimized neighbors 3782 in the same OMNI link segment no larger than the minimum/path MPS in 3783 one piece and with OAL encapsulation as atomic fragments. For larger 3784 original IP packets, the Client applies OAL encapsulation then 3785 fragments if necessary according to Section 3.9, with OAL header with 3786 source set to its own MNP-ULA and destination set to the MNP-ULA of 3787 the target, and with an in-window Identification value. The Client 3788 then encapsulates each resulting carrier packet in UDP/IP *NET 3789 headers and sends them to the neighbor. 3791 INET Clients exchange NS/NA(WIN) messages to associate with a new 3792 peer as discussed in Section 3.2.7. The local segment Bridge that 3793 delivers an NA(WIN) to the Client will supply a Peer Index that can 3794 be used for header compression. When the Client receives the 3795 NA(WIN), it can begin exchanging header-compressed carrier packets 3796 with the Bridge while supplying the Peer Index. If the peer is also 3797 in the local segment, the Client can begin exchanging header- 3798 compressed carrier packets directly with the peer following NAT 3799 traversal using the Peer Index supplied by the Bridge and the peer's 3800 NATed L2ADDR. The Client can instead forward carrier packets with 3801 uncompressed headers to the peer via its Proxy/Server, however the 3802 Client will experience better performance by forwarding directly to 3803 the Bridge and other local segment Clients and should avoid 3804 overburdening the Proxy/Server in this way. 3806 Note: The NAT traversal procedures specified in this document are 3807 applicable for Cone, Address-Restricted and Port-Restricted NATs 3808 only. While future updates to this document may specify procedures 3809 for other NAT variations (e.g., hairpinning and various forms of 3810 Symmetric NATs), it should be noted that continuous communications 3811 are always possible through Proxy/Server forwarding even for these 3812 other NAT variations. 3814 3.23. Time-Varying MNPs 3816 In some use cases, it is desirable, beneficial and efficient for the 3817 Client to receive a constant MNP that travels with the Client 3818 wherever it moves. For example, this would allow air traffic 3819 controllers to easily track aircraft, etc. In other cases, however 3820 (e.g., intelligent transportation systems), the MN may be willing to 3821 sacrifice a modicum of efficiency in order to have time-varying MNPs 3822 that can be changed every so often to defeat adversarial tracking. 3824 The DHCPv6 service offers a way for Clients that desire time-varying 3825 MNPs to obtain short-lived prefixes (e.g., on the order of a small 3826 number of minutes). In that case, the identity of the Client would 3827 not be bound to the MNP but rather to a Node Identification value 3828 (see: [I-D.templin-6man-omni]) to be used as the Client ID seed for 3829 MNP prefix delegation. The Client would then be obligated to 3830 renumber its internal networks whenever its MNP (and therefore also 3831 its MNP-LLA) changes. This should not present a challenge for 3832 Clients with automated network renumbering services, however presents 3833 limits for the durations of ongoing sessions that would prefer to use 3834 a constant address. 3836 4. Implementation Status 3838 An early AERO implementation based on OpenVPN (https://openvpn.net/) 3839 was announced on the v6ops mailing list on January 10, 2018 and an 3840 initial public release of the AERO proof-of-concept source code was 3841 announced on the intarea mailing list on August 21, 2015. 3843 AERO Release-3.2 was tagged on March 30, 2021, and is undergoing 3844 internal testing. Additional internal releases expected within the 3845 coming months, with first public release expected end of 1H2021. 3847 Many AERO/OMNI functions are implemented and undergoing final 3848 integration. OAL fragmentation/reassembly buffer management code has 3849 been cleared for public release and will be presented at the June 3850 2021 ICAO mobility subgroup meeting. 3852 5. IANA Considerations 3854 The IANA has assigned the UDP port number "8060" for an earlier 3855 experimental first version of AERO [RFC6706]. This document together 3856 with [I-D.templin-6man-omni] reclaims UDP port number "8060" as the 3857 service port for UDP/IP encapsulation. This document makes no 3858 request of IANA, since [I-D.templin-6man-omni] already provides 3859 instructions. (Note: although [RFC6706] was not widely implemented 3860 or deployed, it need not be obsoleted since its messages use the 3861 invalid ICMPv6 message type number '0' which implementations of this 3862 specification can easily distinguish and ignore.) 3864 No further IANA actions are required. 3866 6. Security Considerations 3868 AERO Bridges configure secured tunnels with AERO Proxy/Servers and 3869 Relays within their local OMNI link segments. Applicable secured 3870 tunnel alternatives include IPsec [RFC4301], TLS/SSL [RFC8446], DTLS 3871 [RFC6347], WireGuard [WG], etc. The AERO Bridges of all OMNI link 3872 segments in turn configure secured tunnels for their neighboring AERO 3873 Bridges in a secured spanning tree topology. Therefore, control 3874 messages exchanged between any pair of OMNI link neighbors over the 3875 secured spanning tree are already protected. 3877 To prevent spoofing vectors, Proxy/Servers MUST discard without 3878 responding to any unsecured NS(AR) messages. Also, Proxy/Servers 3879 MUST discard without forwarding any original IP packets received from 3880 one of their own Clients (whether directly or following OAL 3881 reassembly) with a source address that does not match the Client's 3882 MNP and/or a destination address that does match the Client's MNP. 3883 Finally, Proxy/Servers MUST discard without forwarding any carrier 3884 packets with an OAL source and destination that both match the same 3885 MNP. 3887 For INET partitions that require strong security in the data plane, 3888 two options for securing communications include 1) disable route 3889 optimization so that all traffic is conveyed over secured tunnels, or 3890 2) enable on-demand secure tunnel creation between Client neighbors. 3892 Option 1) would result in longer routes than necessary and impose 3893 traffic concentration on critical infrastructure elements. Option 2) 3894 could be coordinated between Clients using NS/NA messages with OMNI 3895 Host Identity Protocol (HIP) "Initiator/Responder" message sub- 3896 options [RFC7401][I-D.templin-6man-omni] to create a secured tunnel 3897 on-demand. 3899 AERO Clients that connect to secured ANETs need not apply security to 3900 their IPv6 ND messages, since the messages will be authenticated and 3901 forwarded by a perimeter Proxy/Server that applies security on its 3902 INET-facing interface as part of the spanning tree (see above). AERO 3903 Clients connected to the open INET can use network and/or transport 3904 layer security services such as VPNs or can by some other means 3905 establish a direct link to a Proxy/Server. When a VPN or direct link 3906 may be impractical, however, INET Clients and Proxy/Servers SHOULD 3907 include and verify authentication signatures for their IPv6 ND 3908 messages as specified in [I-D.templin-6man-omni]. 3910 Application endpoints SHOULD use transport-layer (or higher-layer) 3911 security services such as TLS/SSL, DTLS or SSH [RFC4251] to assure 3912 the same level of protection as for critical secured Internet 3913 services. AERO Clients that require host-based VPN services SHOULD 3914 use network and/or transport layer security services such as IPsec, 3915 TLS/SSL, DTLS, etc. AERO Proxys and Proxy/Servers can also provide a 3916 network-based VPN service on behalf of the Client, e.g., if the 3917 Client is located within a secured enclave and cannot establish a VPN 3918 on its own behalf. 3920 AERO Proxy/Servers and Bridges present targets for traffic 3921 amplification Denial of Service (DoS) attacks. This concern is no 3922 different than for widely-deployed VPN security gateways in the 3923 Internet, where attackers could send spoofed packets to the gateways 3924 at high data rates. This can be mitigated through the AERO/OMNI data 3925 origin authentication procedures, as well as connecting Proxy/Servers 3926 and Bridges over dedicated links with no connections to the Internet 3927 and/or when connections to the Internet are only permitted through 3928 well-managed firewalls. Traffic amplification DoS attacks can also 3929 target an AERO Client's low data rate links. This is a concern not 3930 only for Clients located on the open Internet but also for Clients in 3931 secured enclaves. AERO Proxy/Servers and Proxys can institute rate 3932 limits that protect Clients from receiving packet floods that could 3933 DoS low data rate links. 3935 AERO Relays must implement ingress filtering to avoid a spoofing 3936 attack in which spurious messages with ULA addresses are injected 3937 into an OMNI link from an outside attacker. AERO Clients MUST ensure 3938 that their connectivity is not used by unauthorized nodes on their 3939 EUNs to gain access to a protected network, i.e., AERO Clients that 3940 act as routers MUST NOT provide routing services for unauthorized 3941 nodes. (This concern is no different than for ordinary hosts that 3942 receive an IP address delegation but then "share" the address with 3943 other nodes via some form of Internet connection sharing such as 3944 tethering.) 3946 The PRL MUST be well-managed and secured from unauthorized tampering, 3947 even though the list contains only public information. The PRL can 3948 be conveyed to the Client in a similar fashion as in [RFC5214] (e.g., 3949 through layer 2 data link login messaging, secure upload of a static 3950 file, DNS lookups, etc.). 3952 The AERO service for open INET Clients depends on a public key 3953 distribution service in which Client public keys and identities are 3954 maintained in a shared database accessible to all open INET Proxy/ 3955 Servers. Similarly, each Client must be able to determine the public 3956 key of each Proxy/Server, e.g. by consulting an online database. 3957 When AERO nodes register their public keys indexed by a unique Host 3958 Identity Tag (HIT) [RFC7401] in a distributed database such as the 3959 DNS, and use the HIT as an identity for applying IPv6 ND message 3960 authentication signatures, a means for determining public key 3961 attestation is available. 3963 Security considerations for IPv6 fragmentation and reassembly are 3964 discussed in [I-D.templin-6man-omni]. In environments where spoofing 3965 is considered a threat, OMNI nodes SHOULD employ Identification 3966 window synchronization and OAL destinations SHOULD configure an (end- 3967 system-based) firewall. 3969 SRH authentication facilities are specified in [RFC8754]. Security 3970 considerations for accepting link-layer ICMP messages and reflected 3971 packets are discussed throughout the document. 3973 7. Acknowledgements 3975 Discussions in the IETF, aviation standards communities and private 3976 exchanges helped shape some of the concepts in this work. 3977 Individuals who contributed insights include Mikael Abrahamsson, Mark 3978 Andrews, Fred Baker, Bob Braden, Stewart Bryant, Scott Burleigh, 3979 Brian Carpenter, Wojciech Dec, Pavel Drasil, Ralph Droms, Adrian 3980 Farrel, Nick Green, Sri Gundavelli, Brian Haberman, Bernhard Haindl, 3981 Joel Halpern, Tom Herbert, Bob Hinden, Sascha Hlusiak, Lee Howard, 3982 Christian Huitema, Zdenek Jaron, Andre Kostur, Hubert Kuenig, Ted 3983 Lemon, Andy Malis, Satoru Matsushima, Tomek Mrugalski, Thomas Narten, 3984 Madhu Niraula, Alexandru Petrescu, Behcet Saikaya, Michal Skorepa, 3985 Dave Thaler, Joe Touch, Bernie Volz, Ryuji Wakikawa, Tony Whyman, 3986 Lloyd Wood and James Woodyatt. Members of the IESG also provided 3987 valuable input during their review process that greatly improved the 3988 document. Special thanks go to Stewart Bryant, Joel Halpern and 3989 Brian Haberman for their shepherding guidance during the publication 3990 of the AERO first edition. 3992 This work has further been encouraged and supported by Boeing 3993 colleagues including Kyle Bae, M. Wayne Benson, Dave Bernhardt, Cam 3994 Brodie, John Bush, Balaguruna Chidambaram, Irene Chin, Bruce Cornish, 3995 Claudiu Danilov, Don Dillenburg, Joe Dudkowski, Wen Fang, Samad 3996 Farooqui, Anthony Gregory, Jeff Holland, Seth Jahne, Brian Jaury, 3997 Greg Kimberly, Ed King, Madhuri Madhava Badgandi, Laurel Matthew, 3998 Gene MacLean III, Kyle Mikos, Rob Muszkiewicz, Sean O'Sullivan, Vijay 3999 Rajagopalan, Greg Saccone, Rod Santiago, Kent Shuey, Brian Skeen, 4000 Mike Slane, Carrie Spiker, Katie Tran, Brendan Williams, Amelia 4001 Wilson, Julie Wulff, Yueli Yang, Eric Yeh and other members of the 4002 Boeing mobility, networking and autonomy teams. Kyle Bae, Wayne 4003 Benson, Madhuri Madhava Badgandi, Vijayasarathy Rajagopalan, Katie 4004 Tran and Eric Yeh are especially acknowledged for their work on the 4005 AERO implementation. Chuck Klabunde is honored and remembered for 4006 his early leadership, and we mourn his untimely loss. 4008 This work was inspired by the support and encouragement of countless 4009 outstanding colleagues, managers and program directors over the span 4010 of many decades. Beginning in the late 1980s,' the Digital Equipment 4011 Corporation (DEC) Ultrix Engineering and DECnet Architects groups 4012 identified early issues with fragmentation and bridging links with 4013 diverse MTUs. In the early 1990s, engagements at DEC Project Sequoia 4014 at UC Berkeley and the DEC Western Research Lab in Palo Alto included 4015 investigations into large-scale networked filesystems, ATM vs 4016 Internet and network security proxies. In the mid-1990s to early 4017 2000s employment at the NASA Ames Research Center (Sterling Software) 4018 and SRI International supported early investigations of IPv6, ONR UAV 4019 Communications and the IETF. An employment at Nokia where important 4020 IETF documents were published gave way to a present-day engagement 4021 with The Boeing Company. The work matured at Boeing through major 4022 programs including Future Combat Systems, Advanced Airplane Program, 4023 DTN for the International Space Station, Mobility Vision Lab, CAST, 4024 Caravan, Airplane Internet of Things, the NASA UAS/CNS program, the 4025 FAA/ICAO ATN/IPS program and many others. An attempt to name all who 4026 gave support and encouragement would double the current document size 4027 and result in many unintentional omissions - but to all a humble 4028 thanks. 4030 Earlier works on NBMA tunneling approaches are found in 4031 [RFC2529][RFC5214][RFC5569]. 4033 Many of the constructs presented in this second edition of AERO are 4034 based on the author's earlier works, including: 4036 o The Internet Routing Overlay Network (IRON) 4037 [RFC6179][I-D.templin-ironbis] 4039 o Virtual Enterprise Traversal (VET) 4040 [RFC5558][I-D.templin-intarea-vet] 4042 o The Subnetwork Encapsulation and Adaptation Layer (SEAL) 4043 [RFC5320][I-D.templin-intarea-seal] 4045 o AERO, First Edition [RFC6706] 4047 Note that these works cite numerous earlier efforts that are not also 4048 cited here due to space limitations. The authors of those earlier 4049 works are acknowledged for their insights. 4051 This work is aligned with the NASA Safe Autonomous Systems Operation 4052 (SASO) program under NASA contract number NNA16BD84C. 4054 This work is aligned with the FAA as per the SE2025 contract number 4055 DTFAWA-15-D-00030. 4057 This work is aligned with the Boeing Commercial Airplanes (BCA) 4058 Internet of Things (IoT) and autonomy programs. 4060 This work is aligned with the Boeing Information Technology (BIT) 4061 MobileNet program. 4063 8. References 4065 8.1. Normative References 4067 [I-D.templin-6man-omni] 4068 Templin, F. L. and T. Whyman, "Transmission of IP Packets 4069 over Overlay Multilink Network (OMNI) Interfaces", draft- 4070 templin-6man-omni-03 (work in progress), April 2021. 4072 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, 4073 DOI 10.17487/RFC0791, September 1981, 4074 . 4076 [RFC0792] Postel, J., "Internet Control Message Protocol", STD 5, 4077 RFC 792, DOI 10.17487/RFC0792, September 1981, 4078 . 4080 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 4081 Requirement Levels", BCP 14, RFC 2119, 4082 DOI 10.17487/RFC2119, March 1997, 4083 . 4085 [RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in 4086 IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473, 4087 December 1998, . 4089 [RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander, 4090 "SEcure Neighbor Discovery (SEND)", RFC 3971, 4091 DOI 10.17487/RFC3971, March 2005, 4092 . 4094 [RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)", 4095 RFC 3972, DOI 10.17487/RFC3972, March 2005, 4096 . 4098 [RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and 4099 More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191, 4100 November 2005, . 4102 [RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast 4103 Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005, 4104 . 4106 [RFC4380] Huitema, C., "Teredo: Tunneling IPv6 over UDP through 4107 Network Address Translations (NATs)", RFC 4380, 4108 DOI 10.17487/RFC4380, February 2006, 4109 . 4111 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 4112 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 4113 DOI 10.17487/RFC4861, September 2007, 4114 . 4116 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 4117 Address Autoconfiguration", RFC 4862, 4118 DOI 10.17487/RFC4862, September 2007, 4119 . 4121 [RFC6081] Thaler, D., "Teredo Extensions", RFC 6081, 4122 DOI 10.17487/RFC6081, January 2011, 4123 . 4125 [RFC7401] Moskowitz, R., Ed., Heer, T., Jokela, P., and T. 4126 Henderson, "Host Identity Protocol Version 2 (HIPv2)", 4127 RFC 7401, DOI 10.17487/RFC7401, April 2015, 4128 . 4130 [RFC7739] Gont, F., "Security Implications of Predictable Fragment 4131 Identification Values", RFC 7739, DOI 10.17487/RFC7739, 4132 February 2016, . 4134 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 4135 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 4136 May 2017, . 4138 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 4139 (IPv6) Specification", STD 86, RFC 8200, 4140 DOI 10.17487/RFC8200, July 2017, 4141 . 4143 [RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A., 4144 Richardson, M., Jiang, S., Lemon, T., and T. Winters, 4145 "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", 4146 RFC 8415, DOI 10.17487/RFC8415, November 2018, 4147 . 4149 8.2. Informative References 4151 [BGP] Huston, G., "BGP in 2015, http://potaroo.net", January 4152 2016. 4154 [I-D.bonica-6man-comp-rtg-hdr] 4155 Bonica, R., Kamite, Y., Alston, A., Henriques, D., and L. 4156 Jalil, "The IPv6 Compact Routing Header (CRH)", draft- 4157 bonica-6man-comp-rtg-hdr-24 (work in progress), January 4158 2021. 4160 [I-D.bonica-6man-crh-helper-opt] 4161 Li, X., Bao, C., Ruan, E., and R. Bonica, "Compressed 4162 Routing Header (CRH) Helper Option", draft-bonica-6man- 4163 crh-helper-opt-03 (work in progress), April 2021. 4165 [I-D.ietf-intarea-frag-fragile] 4166 Bonica, R., Baker, F., Huston, G., Hinden, R. M., Troan, 4167 O., and F. Gont, "IP Fragmentation Considered Fragile", 4168 draft-ietf-intarea-frag-fragile-17 (work in progress), 4169 September 2019. 4171 [I-D.ietf-intarea-tunnels] 4172 Touch, J. and M. Townsley, "IP Tunnels in the Internet 4173 Architecture", draft-ietf-intarea-tunnels-10 (work in 4174 progress), September 2019. 4176 [I-D.ietf-ipwave-vehicular-networking] 4177 (editor), J. (. J., "IPv6 Wireless Access in Vehicular 4178 Environments (IPWAVE): Problem Statement and Use Cases", 4179 draft-ietf-ipwave-vehicular-networking-20 (work in 4180 progress), March 2021. 4182 [I-D.ietf-rtgwg-atn-bgp] 4183 Templin, F. L., Saccone, G., Dawra, G., Lindem, A., and V. 4184 Moreno, "A Simple BGP-based Mobile Routing System for the 4185 Aeronautical Telecommunications Network", draft-ietf- 4186 rtgwg-atn-bgp-10 (work in progress), January 2021. 4188 [I-D.templin-6man-dhcpv6-ndopt] 4189 Templin, F. L., "A Unified Stateful/Stateless 4190 Configuration Service for IPv6", draft-templin-6man- 4191 dhcpv6-ndopt-11 (work in progress), January 2021. 4193 [I-D.templin-intarea-seal] 4194 Templin, F. L., "The Subnetwork Encapsulation and 4195 Adaptation Layer (SEAL)", draft-templin-intarea-seal-68 4196 (work in progress), January 2014. 4198 [I-D.templin-intarea-vet] 4199 Templin, F. L., "Virtual Enterprise Traversal (VET)", 4200 draft-templin-intarea-vet-40 (work in progress), May 2013. 4202 [I-D.templin-ipwave-uam-its] 4203 Templin, F. L., "Urban Air Mobility Implications for 4204 Intelligent Transportation Systems", draft-templin-ipwave- 4205 uam-its-04 (work in progress), January 2021. 4207 [I-D.templin-ironbis] 4208 Templin, F. L., "The Interior Routing Overlay Network 4209 (IRON)", draft-templin-ironbis-16 (work in progress), 4210 March 2014. 4212 [I-D.templin-v6ops-pdhost] 4213 Templin, F. L., "IPv6 Prefix Delegation and Multi- 4214 Addressing Models", draft-templin-v6ops-pdhost-27 (work in 4215 progress), January 2021. 4217 [OVPN] OpenVPN, O., "http://openvpn.net", October 2016. 4219 [RFC1035] Mockapetris, P., "Domain names - implementation and 4220 specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, 4221 November 1987, . 4223 [RFC1812] Baker, F., Ed., "Requirements for IP Version 4 Routers", 4224 RFC 1812, DOI 10.17487/RFC1812, June 1995, 4225 . 4227 [RFC2003] Perkins, C., "IP Encapsulation within IP", RFC 2003, 4228 DOI 10.17487/RFC2003, October 1996, 4229 . 4231 [RFC2004] Perkins, C., "Minimal Encapsulation within IP", RFC 2004, 4232 DOI 10.17487/RFC2004, October 1996, 4233 . 4235 [RFC2236] Fenner, W., "Internet Group Management Protocol, Version 4236 2", RFC 2236, DOI 10.17487/RFC2236, November 1997, 4237 . 4239 [RFC2464] Crawford, M., "Transmission of IPv6 Packets over Ethernet 4240 Networks", RFC 2464, DOI 10.17487/RFC2464, December 1998, 4241 . 4243 [RFC2529] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4 4244 Domains without Explicit Tunnels", RFC 2529, 4245 DOI 10.17487/RFC2529, March 1999, 4246 . 4248 [RFC2983] Black, D., "Differentiated Services and Tunnels", 4249 RFC 2983, DOI 10.17487/RFC2983, October 2000, 4250 . 4252 [RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition 4253 of Explicit Congestion Notification (ECN) to IP", 4254 RFC 3168, DOI 10.17487/RFC3168, September 2001, 4255 . 4257 [RFC3330] IANA, "Special-Use IPv4 Addresses", RFC 3330, 4258 DOI 10.17487/RFC3330, September 2002, 4259 . 4261 [RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener 4262 Discovery Version 2 (MLDv2) for IPv6", RFC 3810, 4263 DOI 10.17487/RFC3810, June 2004, 4264 . 4266 [RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally 4267 Unique IDentifier (UUID) URN Namespace", RFC 4122, 4268 DOI 10.17487/RFC4122, July 2005, 4269 . 4271 [RFC4251] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH) 4272 Protocol Architecture", RFC 4251, DOI 10.17487/RFC4251, 4273 January 2006, . 4275 [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A 4276 Border Gateway Protocol 4 (BGP-4)", RFC 4271, 4277 DOI 10.17487/RFC4271, January 2006, 4278 . 4280 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 4281 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 4282 2006, . 4284 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 4285 Internet Protocol", RFC 4301, DOI 10.17487/RFC4301, 4286 December 2005, . 4288 [RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery 4289 Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April 4290 2006, . 4292 [RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet 4293 Control Message Protocol (ICMPv6) for the Internet 4294 Protocol Version 6 (IPv6) Specification", STD 89, 4295 RFC 4443, DOI 10.17487/RFC4443, March 2006, 4296 . 4298 [RFC4511] Sermersheim, J., Ed., "Lightweight Directory Access 4299 Protocol (LDAP): The Protocol", RFC 4511, 4300 DOI 10.17487/RFC4511, June 2006, 4301 . 4303 [RFC4541] Christensen, M., Kimball, K., and F. Solensky, 4304 "Considerations for Internet Group Management Protocol 4305 (IGMP) and Multicast Listener Discovery (MLD) Snooping 4306 Switches", RFC 4541, DOI 10.17487/RFC4541, May 2006, 4307 . 4309 [RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick, 4310 "Internet Group Management Protocol (IGMP) / Multicast 4311 Listener Discovery (MLD)-Based Multicast Forwarding 4312 ("IGMP/MLD Proxying")", RFC 4605, DOI 10.17487/RFC4605, 4313 August 2006, . 4315 [RFC4982] Bagnulo, M. and J. Arkko, "Support for Multiple Hash 4316 Algorithms in Cryptographically Generated Addresses 4317 (CGAs)", RFC 4982, DOI 10.17487/RFC4982, July 2007, 4318 . 4320 [RFC5015] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano, 4321 "Bidirectional Protocol Independent Multicast (BIDIR- 4322 PIM)", RFC 5015, DOI 10.17487/RFC5015, October 2007, 4323 . 4325 [RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site 4326 Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214, 4327 DOI 10.17487/RFC5214, March 2008, 4328 . 4330 [RFC5320] Templin, F., Ed., "The Subnetwork Encapsulation and 4331 Adaptation Layer (SEAL)", RFC 5320, DOI 10.17487/RFC5320, 4332 February 2010, . 4334 [RFC5522] Eddy, W., Ivancic, W., and T. Davis, "Network Mobility 4335 Route Optimization Requirements for Operational Use in 4336 Aeronautics and Space Exploration Mobile Networks", 4337 RFC 5522, DOI 10.17487/RFC5522, October 2009, 4338 . 4340 [RFC5558] Templin, F., Ed., "Virtual Enterprise Traversal (VET)", 4341 RFC 5558, DOI 10.17487/RFC5558, February 2010, 4342 . 4344 [RFC5569] Despres, R., "IPv6 Rapid Deployment on IPv4 4345 Infrastructures (6rd)", RFC 5569, DOI 10.17487/RFC5569, 4346 January 2010, . 4348 [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 4349 (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, 4350 . 4352 [RFC6106] Jeong, J., Park, S., Beloeil, L., and S. Madanapalli, 4353 "IPv6 Router Advertisement Options for DNS Configuration", 4354 RFC 6106, DOI 10.17487/RFC6106, November 2010, 4355 . 4357 [RFC6139] Russert, S., Ed., Fleischman, E., Ed., and F. Templin, 4358 Ed., "Routing and Addressing in Networks with Global 4359 Enterprise Recursion (RANGER) Scenarios", RFC 6139, 4360 DOI 10.17487/RFC6139, February 2011, 4361 . 4363 [RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful 4364 NAT64: Network Address and Protocol Translation from IPv6 4365 Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146, 4366 April 2011, . 4368 [RFC6179] Templin, F., Ed., "The Internet Routing Overlay Network 4369 (IRON)", RFC 6179, DOI 10.17487/RFC6179, March 2011, 4370 . 4372 [RFC6221] Miles, D., Ed., Ooghe, S., Dec, W., Krishnan, S., and A. 4373 Kavanagh, "Lightweight DHCPv6 Relay Agent", RFC 6221, 4374 DOI 10.17487/RFC6221, May 2011, 4375 . 4377 [RFC6273] Kukec, A., Krishnan, S., and S. Jiang, "The Secure 4378 Neighbor Discovery (SEND) Hash Threat Analysis", RFC 6273, 4379 DOI 10.17487/RFC6273, June 2011, 4380 . 4382 [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer 4383 Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, 4384 January 2012, . 4386 [RFC6355] Narten, T. and J. Johnson, "Definition of the UUID-Based 4387 DHCPv6 Unique Identifier (DUID-UUID)", RFC 6355, 4388 DOI 10.17487/RFC6355, August 2011, 4389 . 4391 [RFC6438] Carpenter, B. and S. Amante, "Using the IPv6 Flow Label 4392 for Equal Cost Multipath Routing and Link Aggregation in 4393 Tunnels", RFC 6438, DOI 10.17487/RFC6438, November 2011, 4394 . 4396 [RFC6706] Templin, F., Ed., "Asymmetric Extended Route Optimization 4397 (AERO)", RFC 6706, DOI 10.17487/RFC6706, August 2012, 4398 . 4400 [RFC6935] Eubanks, M., Chimento, P., and M. Westerlund, "IPv6 and 4401 UDP Checksums for Tunneled Packets", RFC 6935, 4402 DOI 10.17487/RFC6935, April 2013, 4403 . 4405 [RFC6936] Fairhurst, G. and M. Westerlund, "Applicability Statement 4406 for the Use of IPv6 UDP Datagrams with Zero Checksums", 4407 RFC 6936, DOI 10.17487/RFC6936, April 2013, 4408 . 4410 [RFC7333] Chan, H., Ed., Liu, D., Seite, P., Yokota, H., and J. 4411 Korhonen, "Requirements for Distributed Mobility 4412 Management", RFC 7333, DOI 10.17487/RFC7333, August 2014, 4413 . 4415 [RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I., 4416 Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent 4417 Multicast - Sparse Mode (PIM-SM): Protocol Specification 4418 (Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March 4419 2016, . 4421 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 4422 Decraene, B., Litkowski, S., and R. Shakir, "Segment 4423 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 4424 July 2018, . 4426 [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol 4427 Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, 4428 . 4430 [RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J., 4431 Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header 4432 (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020, 4433 . 4435 [WG] Wireguard, "WireGuard, https://www.wireguard.com", August 4436 2020. 4438 Appendix A. Non-Normative Considerations 4440 AERO can be applied to a multitude of Internetworking scenarios, with 4441 each having its own adaptations. The following considerations are 4442 provided as non-normative guidance: 4444 A.1. Implementation Strategies for Route Optimization 4446 Route optimization as discussed in Section 3.14 results in the route 4447 optimization source (ROS) creating a NCE for the target neighbor. 4448 The NCE state is set to REACHABLE for at most ReachableTime seconds. 4449 In order to refresh the NCE lifetime before the ReachableTime timer 4450 expires, the specification requires implementations to issue a new 4451 NS/NA(AR) exchange to reset ReachableTime while data packets are 4452 still flowing. However, the decision of when to initiate a new NS/ 4453 NA(AR) exchange and to perpetuate the process is left as an 4454 implementation detail. 4456 One possible strategy may be to monitor the NCE watching for data 4457 packets for (ReachableTime - 5) seconds. If any data packets have 4458 been sent to the neighbor within this timeframe, then send an NS(AR) 4459 to receive a new NA(AR). If no data packets have been sent, wait for 4460 5 additional seconds and send an immediate NS(AR) if any data packets 4461 are sent within this "expiration pending" 5 second window. If no 4462 additional data packets are sent within the 5 second window, reset 4463 the NCE state to STALE. 4465 The monitoring of the neighbor data packet traffic therefore becomes 4466 an ongoing process during the NCE lifetime. If the NCE expires, 4467 future data packets will trigger a new NS/NA(AR) exchange while the 4468 packets themselves are delivered over a longer path until route 4469 optimization state is re-established. 4471 A.2. Implicit Mobility Management 4473 OMNI interface neighbors MAY provide a configuration option that 4474 allows them to perform implicit mobility management in which no IPv6 4475 ND messaging is used. In that case, the Client only transmits 4476 packets over a single interface at a time, and the neighbor always 4477 observes packets arriving from the Client from the same link-layer 4478 source address. 4480 If the Client's underlying interface address changes (either due to a 4481 readdressing of the original interface or switching to a new 4482 interface) the neighbor immediately updates the NCE for the Client 4483 and begins accepting and sending packets according to the Client's 4484 new address. This implicit mobility method applies to use cases such 4485 as cellphones with both WiFi and Cellular interfaces where only one 4486 of the interfaces is active at a given time, and the Client 4487 automatically switches over to the backup interface if the primary 4488 interface fails. 4490 A.3. Direct Underlying Interfaces 4492 When a Client's OMNI interface is configured over a Direct interface, 4493 the neighbor at the other end of the Direct link can receive packets 4494 without any encapsulation. In that case, the Client sends packets 4495 over the Direct link according to traffic selectors. If the Direct 4496 interface is selected, then the Client's IP packets are transmitted 4497 directly to the peer without going through an ANET/INET. If other 4498 interfaces are selected, then the Client's IP packets are transmitted 4499 via a different interface, which may result in the inclusion of 4500 Proxy/Servers and Bridges in the communications path. Direct 4501 interfaces must be tested periodically for reachability, e.g., via 4502 NUD. 4504 A.4. AERO Critical Infrastructure Considerations 4506 AERO Bridges can be either Commercial off-the Shelf (COTS) standard 4507 IP routers or virtual machines in the cloud. Bridges must be 4508 provisioned, supported and managed by the INET administrative 4509 authority, and connected to the Bridges of other INETs via inter- 4510 domain peerings. Cost for purchasing, configuring and managing 4511 Bridges is nominal even for very large OMNI links. 4513 AERO INET Proxy/Servers can be standard dedicated server platforms, 4514 but most often will be deployed as virtual machines in the cloud. 4515 The only requirements for INET Proxy/Servers are that they can run 4516 the AERO/OMNI code and have at least one network interface connection 4517 to the INET. INET Proxy/Servers must be provisioned, supported and 4518 managed by the INET administrative authority. Cost for purchasing, 4519 configuring and managing cloud Proxy/Servers is nominal especially 4520 for virtual machines. 4522 AERO ANET Proxy/Servers are most often standard dedicated server 4523 platforms with one underlying interface connected to the ANET and a 4524 second interface connected to an INET. As with INET Proxy/Servers, 4525 the only requirements are that they can run the AERO/OMNI code and 4526 have at least one interface connection to the INET. ANET Proxy/ 4527 Servers must be provisioned, supported and managed by the ANET 4528 administrative authority. Cost for purchasing, configuring and 4529 managing Proxys is nominal, and borne by the ANET administrative 4530 authority. 4532 AERO Relays are simply Proxy/Servers connected to INETs and/or EUNs 4533 that provide forwarding services for non-MNP destinations. The Relay 4534 connects to the OMNI link and engages in eBGP peering with one or 4535 more Bridges as a stub AS. The Relay then injects its MNPs and/or 4536 non-MNP prefixes into the BGP routing system, and provisions the 4537 prefixes to its downstream-attached networks. The Relay can perform 4538 ROS/ROR services the same as for any Proxy/Server, and can route 4539 between the MNP and non-MNP address spaces. 4541 A.5. AERO Server Failure Implications 4543 AERO Proxy/Servers may appear as a single point of failure in the 4544 architecture, but such is not the case since all Proxy/Servers on the 4545 link provide identical services and loss of a Proxy/Server does not 4546 imply immediate and/or comprehensive communication failures. Proxy/ 4547 Server failure is quickly detected and conveyed by Bidirectional 4548 Forward Detection (BFD) and/or proactive NUD allowing Clients to 4549 migrate to new Proxy/Servers. 4551 If a Proxy/Server fails, ongoing packet forwarding to Clients will 4552 continue by virtue of the neighbor cache entries that have already 4553 been established in route optimization sources (ROSs). If a Client 4554 also experiences mobility events at roughly the same time the Proxy/ 4555 Server fails, uNA messages may be lost but neighbor cache entries in 4556 the DEPARTED state will ensure that packet forwarding to the Client's 4557 new locations will continue for up to DepartTime seconds. 4559 If a Client is left without a Proxy/Server for a considerable length 4560 of time (e.g., greater than ReachableTime seconds) then existing 4561 neighbor cache entries will eventually expire and both ongoing and 4562 new communications will fail. The original source will continue to 4563 retransmit until the Client has established a new Proxy/Server 4564 relationship, after which time continuous communications will resume. 4566 Therefore, providing many Proxy/Servers on the link with high 4567 availability profiles provides resilience against loss of individual 4568 Proxy/Servers and assurance that Clients can establish new Proxy/ 4569 Server relationships quickly in event of a Proxy/Server failure. 4571 A.6. AERO Client / Server Architecture 4573 The AERO architectural model is client / server in the control plane, 4574 with route optimization in the data plane. The same as for common 4575 Internet services, the AERO Client discovers the addresses of AERO 4576 Proxy/Servers and connects to one or more of them. The AERO service 4577 is analogous to common Internet services such as google.com, 4578 yahoo.com, cnn.com, etc. However, there is only one AERO service for 4579 the link and all Proxy/Servers provide identical services. 4581 Common Internet services provide differing strategies for advertising 4582 server addresses to clients. The strategy is conveyed through the 4583 DNS resource records returned in response to name resolution queries. 4584 As of January 2020 Internet-based 'nslookup' services were used to 4585 determine the following: 4587 o When a client resolves the domainname "google.com", the DNS always 4588 returns one A record (i.e., an IPv4 address) and one AAAA record 4589 (i.e., an IPv6 address). The client receives the same addresses 4590 each time it resolves the domainname via the same DNS resolver, 4591 but may receive different addresses when it resolves the 4592 domainname via different DNS resolvers. But, in each case, 4593 exactly one A and one AAAA record are returned. 4595 o When a client resolves the domainname "ietf.org", the DNS always 4596 returns one A record and one AAAA record with the same addresses 4597 regardless of which DNS resolver is used. 4599 o When a client resolves the domainname "yahoo.com", the DNS always 4600 returns a list of 4 A records and 4 AAAA records. Each time the 4601 client resolves the domainname via the same DNS resolver, the same 4602 list of addresses are returned but in randomized order (i.e., 4603 consistent with a DNS round-robin strategy). But, interestingly, 4604 the same addresses are returned (albeit in randomized order) when 4605 the domainname is resolved via different DNS resolvers. 4607 o When a client resolves the domainname "amazon.com", the DNS always 4608 returns a list of 3 A records and no AAAA records. As with 4609 "yahoo.com", the same three A records are returned from any 4610 worldwide Internet connection point in randomized order. 4612 The above example strategies show differing approaches to Internet 4613 resilience and service distribution offered by major Internet 4614 services. The Google approach exposes only a single IPv4 and a 4615 single IPv6 address to clients. Clients can then select whichever IP 4616 protocol version offers the best response, but will always use the 4617 same IP address according to the current Internet connection point. 4618 This means that the IP address offered by the network must lead to a 4619 highly-available server and/or service distribution point. In other 4620 words, resilience is predicated on high availability within the 4621 network and with no client-initiated failovers expected (i.e., it is 4622 all-or-nothing from the client's perspective). However, Google does 4623 provide for worldwide distributed service distribution by virtue of 4624 the fact that each Internet connection point responds with a 4625 different IPv6 and IPv4 address. The IETF approach is like google 4626 (all-or-nothing from the client's perspective), but provides only a 4627 single IPv4 or IPv6 address on a worldwide basis. This means that 4628 the addresses must be made highly-available at the network level with 4629 no client failover possibility, and if there is any worldwide service 4630 distribution it would need to be conducted by a network element that 4631 is reached via the IP address acting as a service distribution point. 4633 In contrast to the Google and IETF philosophies, Yahoo and Amazon 4634 both provide clients with a (short) list of IP addresses with Yahoo 4635 providing both IP protocol versions and Amazon as IPv4-only. The 4636 order of the list is randomized with each name service query 4637 response, with the effect of round-robin load balancing for service 4638 distribution. With a short list of addresses, there is still 4639 expectation that the network will implement high availability for 4640 each address but in case any single address fails the client can 4641 switch over to using a different address. The balance then becomes 4642 one of function in the network vs function in the end system. 4644 The same implications observed for common highly-available services 4645 in the Internet apply also to the AERO client/server architecture. 4646 When an AERO Client connects to one or more ANETs, it discovers one 4647 or more AERO Proxy/Server addresses through the mechanisms discussed 4648 in earlier sections. Each Proxy/Server address presumably leads to a 4649 fault-tolerant clustering arrangement such as supported by Linux-HA, 4650 Extended Virtual Synchrony or Paxos. Such an arrangement has 4651 precedence in common Internet service deployments in lightweight 4652 virtual machines without requiring expensive hardware deployment. 4653 Similarly, common Internet service deployments set service IP 4654 addresses on service distribution points that may relay requests to 4655 many different servers. 4657 For AERO, the expectation is that a combination of the Google/IETF 4658 and Yahoo/Amazon philosophies would be employed. The AERO Client 4659 connects to different ANET access points and can receive 1-2 Proxy/ 4660 Server ADM-LLAs at each point. It then selects one AERO Proxy/Server 4661 address, and engages in RS/RA exchanges with the same Proxy/Server 4662 from all ANET connections. The Client remains with this Proxy/Server 4663 unless or until the Proxy/Server fails, in which case it can switch 4664 over to an alternate Proxy/Server. The Client can likewise switch 4665 over to a different Proxy/Server at any time if there is some reason 4666 for it to do so. So, the AERO expectation is for a balance of 4667 function in the network and end system, with fault tolerance and 4668 resilience at both levels. 4670 Appendix B. Change Log 4672 << RFC Editor - remove prior to publication >> 4674 Changes from draft-templin-6man-aero-19 to draft-templin-6man-aero- 4675 20: 4677 o Major updates especially in Section 3.2.7. 4679 Changes from draft-templin-6man-aero-18 to draft-templin-6man-aero- 4680 19: 4682 o Major revision update for review. 4684 Changes from draft-templin-6man-aero-17 to draft-templin-6man-aero- 4685 18: 4687 o Interim version with extensive new text - cleanup planned for next 4688 release. 4690 Changes from draft-templin-6man-aero-16 to draft-templin-6man-aero- 4691 17: 4693 o Final editorial review pass resulting in multiple changes. 4694 Document now submit for final approval (with reference to rfcdiff 4695 from previous version). 4697 Changes from draft-templin-6man-aero-15 to draft-templin-6man-aero- 4698 16: 4700 o Final editorial review pass resulting in multiple changes. 4701 Document now submit for final approval (with reference to rfcdiff 4702 from previous version). 4704 Changes from draft-templin-6man-aero-14 to draft-templin-6man-aero- 4705 15: 4707 o Final editorial review pass resulting in multiple changes. 4708 Document now submit for final approval (with reference to rfcdiff 4709 from previous version). 4711 Changes from draft-templin-6man-aero-13 to draft-templin-6man-aero- 4712 14: 4714 o Final editorial review pass resulting in multiple changes. 4715 Document now submit for final approval (with reference to rfcdiff 4716 from previous version). 4718 Changes from draft-templin-6man-aero-12 to draft-templin-6man-aero- 4719 13: 4721 o Final editorial review pass resulting in multiple changes. 4722 Document now submit for final approval (with reference to rfcdiff 4723 from previous version). 4725 Changes from draft-templin-6man-aero-11 to draft-templin-6man-aero- 4726 12: 4728 o Final editorial review pass resulting in multiple changes. 4729 Document now submit for final approval (with reference to rfcdiff 4730 from previous version). 4732 Changes from draft-templin-6man-aero-10 to draft-templin-6man-aero- 4733 11: 4735 o Final editorial review pass resulting in multiple changes. 4736 Document now submit for final approval (with reference to rfcdiff 4737 from previous version). 4739 Changes from draft-templin-6man-aero-09 to draft-templin-6man-aero- 4740 10: 4742 o Final editorial review pass resulting in multiple changes. 4743 Document now submit for final approval (with reference to rfcdiff 4744 from previous version). 4746 Changes from draft-templin-6man-aero-08 to draft-templin-6man-aero- 4747 09: 4749 o Final editorial review pass resulting in multiple changes. 4750 Document now submit for final approval (with reference to rfcdiff 4751 from previous version). 4753 Changes from draft-templin-6man-aero-07 to draft-templin-6man-aero- 4754 08: 4756 o Final editorial review pass resulting in multiple changes. 4757 Document now submit for final approval (with reference to rfcdiff 4758 from previous version). 4760 Changes from draft-templin-6man-aero-06 to draft-templin-6man-aero- 4761 07: 4763 o Final editorial review pass resulting in multiple changes. 4764 Document now submit for final approval (with reference to rfcdiff 4765 from previous version). 4767 Changes from draft-templin-6man-aero-05 to draft-templin-6man-aero- 4768 06: 4770 o Final editorial review pass resulting in multiple changes. 4771 Document now submit for final approval. 4773 Changes from draft-templin-6man-aero-04 to draft-templin-6man-aero- 4774 05: 4776 o Changed to use traffic selectors instead of the former multilink 4777 selection strategy. 4779 Changes from draft-templin-6man-aero-03 to draft-templin-6man-aero- 4780 04: 4782 o Removed documents from "Obsoletes" list. 4784 o Introduced the concept of "secured" and "unsecured" spanning tree. 4786 o Additional security considerations. 4788 o Additional route optimization considerations. 4790 Changes from draft-templin-6man-aero-02 to draft-templin-6man-aero- 4791 03: 4793 o Support for extended route optimization from ROR to target over 4794 target's underlying interfaces. 4796 Changes from draft-templin-6man-aero-01 to draft-templin-6man-aero- 4797 02: 4799 o Changed reference citations to "draft-templin-6man-omni". 4801 o Several important updates to IPv6 ND cache states and route 4802 optimization message addressing. 4804 o Included introductory description of the "6M's". 4806 o Updated Multicast specification. 4808 Changes from draft-templin-6man-aero-00 to draft-templin-6man-aero- 4809 01: 4811 o Changed category to "Informational". 4813 o Updated implementation status. 4815 Changes from earlier versions to draft-templin-6man-aero-00: 4817 o Established working baseline reference. 4819 Author's Address 4821 Fred L. Templin (editor) 4822 Boeing Research & Technology 4823 P.O. Box 3707 4824 Seattle, WA 98124 4825 USA 4827 Email: fltemplin@acm.org