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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 1, 2021 5 Expires: December 3, 2021 7 Asymmetric Extended Route Optimization (AERO) 8 draft-templin-6man-aero-09 10 Abstract 12 This document specifies an Asymmetric 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 (ND) protocol 16 and links ND to IP forwarding. Prefix delegation/registration 17 services are employed for network admission and to manage the routing 18 system. 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 Virtual 23 Private Networks (VPNs) 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 3, 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. Asymmetric Extended Route Optimization (AERO) . . . . . . . . 12 62 3.1. AERO Node Types . . . . . . . . . . . . . . . . . . . . . 12 63 3.2. The AERO Service over OMNI Links . . . . . . . . . . . . 13 64 3.2.1. AERO/OMNI Reference Model . . . . . . . . . . . . . . 13 65 3.2.2. Addressing and Node Identification . . . . . . . . . 16 66 3.2.3. AERO Routing System . . . . . . . . . . . . . . . . . 17 67 3.2.4. OMNI Link Segment Routing . . . . . . . . . . . . . . 19 68 3.2.5. Segment Routing Topologies (SRTs) . . . . . . . . . . 25 69 3.2.6. Segment Routing For OMNI Link Selection . . . . . . . 25 70 3.2.7. Segment Routing Within the OMNI Link . . . . . . . . 25 71 3.3. OMNI Interface Characteristics . . . . . . . . . . . . . 27 72 3.4. OMNI Interface Initialization . . . . . . . . . . . . . . 29 73 3.4.1. AERO Proxy/Server and Relay Behavior . . . . . . . . 30 74 3.4.2. AERO Client Behavior . . . . . . . . . . . . . . . . 30 75 3.4.3. AERO Bridge Behavior . . . . . . . . . . . . . . . . 30 76 3.5. OMNI Interface Neighbor Cache Maintenance . . . . . . . . 31 77 3.5.1. OMNI ND Messages . . . . . . . . . . . . . . . . . . 32 78 3.5.2. OMNI Neighbor Advertisement Message Flags . . . . . . 34 79 3.5.3. OMNI Neighbor Window Synchronization . . . . . . . . 34 80 3.6. OMNI Interface Encapsulation and Re-encapsulation . . . . 35 81 3.7. OMNI Interface Decapsulation . . . . . . . . . . . . . . 35 82 3.8. OMNI Interface Data Origin Authentication . . . . . . . . 35 83 3.9. OMNI Interface MTU . . . . . . . . . . . . . . . . . . . 36 84 3.10. OMNI Interface Forwarding Algorithm . . . . . . . . . . . 37 85 3.10.1. Client Forwarding Algorithm . . . . . . . . . . . . 38 86 3.10.2. Proxy/Server and Relay Forwarding Algorithm . . . . 39 87 3.10.3. Bridge Forwarding Algorithm . . . . . . . . . . . . 42 88 3.11. OMNI Interface Error Handling . . . . . . . . . . . . . . 43 89 3.12. AERO Router Discovery, Prefix Delegation and 90 Autoconfiguration . . . . . . . . . . . . . . . . . . . . 46 91 3.12.1. AERO Service Model . . . . . . . . . . . . . . . . . 47 92 3.12.2. AERO Client Behavior . . . . . . . . . . . . . . . . 47 93 3.12.3. AERO Proxy/Server Behavior . . . . . . . . . . . . . 49 94 3.13. The AERO Proxy Function . . . . . . . . . . . . . . . . . 52 95 3.13.1. Detecting and Responding to Proxy/Server Failures . 55 96 3.13.2. Point-to-Multipoint Proxy/Server Coordination . . . 56 98 3.14. AERO Route Optimization . . . . . . . . . . . . . . . . . 57 99 3.14.1. Route Optimization Initiation . . . . . . . . . . . 57 100 3.14.2. Relaying the NS(AR) *NET Packet(s) . . . . . . . . . 58 101 3.14.3. Processing the NS(AR) and Sending the NA(AR) . . . . 59 102 3.14.4. Relaying the NA(AR) . . . . . . . . . . . . . . . . 60 103 3.14.5. Processing the NA(AR) . . . . . . . . . . . . . . . 60 104 3.14.6. Forwarding Packets to Route Optimized Targets . . . 61 105 3.15. Neighbor Unreachability Detection (NUD) . . . . . . . . . 63 106 3.16. Mobility Management and Quality of Service (QoS) . . . . 65 107 3.16.1. Mobility Update Messaging . . . . . . . . . . . . . 65 108 3.16.2. Announcing Link-Layer Address and/or QoS Preference 109 Changes . . . . . . . . . . . . . . . . . . . . . . 67 110 3.16.3. Bringing New Links Into Service . . . . . . . . . . 67 111 3.16.4. Deactivating Existing Links . . . . . . . . . . . . 67 112 3.16.5. Moving Between Proxy/Servers . . . . . . . . . . . . 68 113 3.17. Multicast . . . . . . . . . . . . . . . . . . . . . . . . 69 114 3.17.1. Source-Specific Multicast (SSM) . . . . . . . . . . 69 115 3.17.2. Any-Source Multicast (ASM) . . . . . . . . . . . . . 71 116 3.17.3. Bi-Directional PIM (BIDIR-PIM) . . . . . . . . . . . 71 117 3.18. Operation over Multiple OMNI Links . . . . . . . . . . . 72 118 3.19. DNS Considerations . . . . . . . . . . . . . . . . . . . 72 119 3.20. Transition/Coexistence Considerations . . . . . . . . . . 73 120 3.21. Detecting and Reacting to Proxy/Server and Bridge 121 Failures . . . . . . . . . . . . . . . . . . . . . . . . 73 122 3.22. AERO Clients on the Open Internet . . . . . . . . . . . . 74 123 3.23. Time-Varying MNPs . . . . . . . . . . . . . . . . . . . . 76 124 4. Implementation Status . . . . . . . . . . . . . . . . . . . . 76 125 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 77 126 6. Security Considerations . . . . . . . . . . . . . . . . . . . 77 127 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 79 128 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 81 129 8.1. Normative References . . . . . . . . . . . . . . . . . . 81 130 8.2. Informative References . . . . . . . . . . . . . . . . . 82 131 Appendix A. Non-Normative Considerations . . . . . . . . . . . . 89 132 A.1. Implementation Strategies for Route Optimization . . . . 89 133 A.2. Implicit Mobility Management . . . . . . . . . . . . . . 89 134 A.3. Direct Underlying Interfaces . . . . . . . . . . . . . . 90 135 A.4. AERO Critical Infrastructure Considerations . . . . . . . 90 136 A.5. AERO Server Failure Implications . . . . . . . . . . . . 91 137 A.6. AERO Client / Server Architecture . . . . . . . . . . . . 91 138 Appendix B. Change Log . . . . . . . . . . . . . . . . . . . . . 93 139 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 95 141 1. Introduction 143 Asymmetric 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 end system multilink operation for increased reliability, bandwidth 155 optimization and traffic path selection while performing 156 fragmentation and reassembly to support Internetwork segment routing 157 and Maximum Transmission Unit (MTU) diversity. 159 The AERO service comprises Clients, Proxy/Servers and Relays that are 160 seen as OMNI link neighbors as well as Bridges that interconnect 161 diverse Internetworks as OMNI link segments through OAL forwarding at 162 a layer below IP. Each node's OMNI interface uses an IPv6 link-local 163 address format that supports operation of the IPv6 Neighbor Discovery 164 (ND) protocol [RFC4861] and links ND to IP forwarding. A node's OMNI 165 interface can be configured over multiple underlying interfaces, and 166 therefore appears as a single interface with multiple link-layer 167 addresses. Each link-layer address is subject to change due to 168 mobility and/or multilink fluctuations, and link-layer address 169 changes are signaled by ND messaging the same as for any IPv6 link. 171 AERO provides a secure cloud-based service where mobile node Clients 172 may use any Proxy/Server acting as a Mobility Anchor Point (MAP) and 173 fixed nodes may use any Relay on the link for efficient 174 communications. Fixed nodes forward original IP packets destined to 175 other AERO nodes via the nearest Relay, which forwards them through 176 the cloud. A mobile node's initial packets are forwarded through the 177 Proxy/Server, and direct routing is supported through route 178 optimization while packets are flowing. Both unicast and multicast 179 communications are supported, and mobile nodes may efficiently move 180 between locations while maintaining continuous communications with 181 correspondents and without changing their IP Address. 183 AERO Bridges are interconnected in a secured private BGP overlay 184 routing instance to provide an OAL routing/bridging service that 185 joins the underlying Internetworks of multiple disjoint 186 administrative domains into a single unified OMNI link at a layer 187 below IP. Each OMNI link instance is characterized by the set of 188 Mobility Service Prefixes (MSPs) common to all mobile nodes. Relays 189 provide an optimal route from correspondent nodes on the underlying 190 Internetwork to nodes on the OMNI link. To the underlying 191 Internetwork, the Relay is the source of a route to the MSP, and 192 hence uplink traffic to the mobile node is naturally routed to the 193 nearest Relay. 195 AERO can be used with OMNI links that span private-use Internetworks 196 and/or public Internetworks such as the global Internet. In the 197 latter case, some end systems may be located behind global Internet 198 Network Address Translators (NATs). A means for robust traversal of 199 NATs while avoiding "triangle routing" is therefore provided. 201 AERO assumes the use of PIM Sparse Mode in support of multicast 202 communication. In support of Source Specific Multicast (SSM) when a 203 Mobile Node is the source, AERO route optimization ensures that a 204 shortest-path multicast tree is established with provisions for 205 mobility and multilink operation. In all other multicast scenarios 206 there are no AERO dependencies. 208 AERO was designed as a secure aeronautical internetworking service 209 for both manned and unmanned aircraft, where the aircraft is treated 210 as a mobile node that can connect an Internet of Things (IoT). AERO 211 is also applicable to a wide variety of other use cases. For 212 example, it can be used to coordinate the links of mobile nodes 213 (e.g., cellphones, tablets, laptop computers, etc.) that connect into 214 a home enterprise network via public access networks using tunneling 215 software such as OpenVPN [OVPN] with VPN or non-VPN services enabled 216 according to the appropriate security model. AERO can also be used 217 to facilitate terrestrial vehicular and urban air mobility (as well 218 as pedestrian communication services) for future intelligent 219 transportation systems 220 [I-D.ietf-ipwave-vehicular-networking][I-D.templin-ipwave-uam-its]. 221 Other applicable use cases are also in scope. 223 Along with OMNI, AERO provides secured optimal routing support for 224 the "6M's" of modern Internetworking, including: 226 1. Multilink - a mobile node's ability to coordinate multiple 227 diverse underlying data links as a single logical unit (i.e., the 228 OMNI interface) to achieve the required communications 229 performance and reliability objectives. 231 2. Multinet - the ability to span the OMNI link across multiple 232 diverse network administrative segments while maintaining 233 seamless end-to-end communications between mobile nodes and 234 correspondents such as air traffic controllers, fleet 235 administrators, etc. 237 3. Mobility - a mobile node's ability to change network points of 238 attachment (e.g., moving between wireless base stations) which 239 may result in an underlying interface address change, but without 240 disruptions to ongoing communication sessions with peers over the 241 OMNI link. 243 4. Multicast - the ability to send a single network transmission 244 that reaches multiple nodes belonging to the same interest group, 245 but without disturbing other nodes not subscribed to the interest 246 group. 248 5. Multihop - a mobile node vehicle-to-vehicle relaying capability 249 useful when multiple forwarding hops between vehicles may be 250 necessary to "reach back" to an infrastructure access point 251 connection to the OMNI link. 253 6. MTU assurance - the ability to deliver packets of various robust 254 sizes between peers without loss due to a link size restriction, 255 and to dynamically adjust packets sizes to achieve the optimal 256 performance for each independent traffic flow. 258 The following numbered sections present the AERO specification. The 259 appendices at the end of the document are non-normative. 261 2. Terminology 263 The terminology in the normative references applies; especially, the 264 terminology in the OMNI specification [I-D.templin-6man-omni] is used 265 extensively throughout. The following terms are defined within the 266 scope of this document: 268 IPv6 Neighbor Discovery (ND) 269 a control message service for coordinating neighbor relationships 270 between nodes connected to a common link. AERO uses the IPv6 ND 271 messaging service specified in [RFC4861]. 273 IPv6 Prefix Delegation 274 a networking service for delegating IPv6 prefixes to nodes on the 275 link. The nominal service is DHCPv6 [RFC8415], however alternate 276 services (e.g., based on ND messaging) are also in scope. Most 277 notably, a minimal form of prefix delegation known as "prefix 278 registration" can be used if the Client knows its prefix in 279 advance and can represent it in the IPv6 source address of an ND 280 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 connected IP network topology with a coherent routing and 296 addressing plan and that provides a transit backbone service for 297 ANET end systems. INETs also provide an underlay service over 298 which the AERO virtual link is configured. Example INETs include 299 corporate enterprise networks, aviation networks, and the public 300 Internet itself. When there is no administrative boundary between 301 an ANET 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], and manifested by 332 IPv6 encapsulation [RFC2473]. The OMNI link spans underlying *NET 333 segments joined by virtual bridges in a spanning tree the same as 334 a bridged campus LAN. AERO nodes on the OMNI link appear as 335 single-hop neighbors even though they may be separated by multiple 336 underlying *NET hops, and can use Segment Routing [RFC8402] to 337 cause packets to visit selected waypoints on the link. 339 OMNI Interface 340 a node's attachment to an OMNI link. Since the addresses assigned 341 to an OMNI interface are managed for uniqueness, OMNI interfaces 342 do not require Duplicate Address Detection (DAD) and therefore set 343 the administrative variable 'DupAddrDetectTransmits' to zero 344 [RFC4862]. 346 OMNI Adaptation Layer (OAL) 347 an OMNI interface process whereby original IP packets admitted 348 into the interface are wrapped in a mid-layer IPv6 header and 349 subject to fragmentation and reassembly. The OAL is also 350 responsible for generating MTU-related control messages as 351 necessary, and for providing addressing context for spanning 352 multiple segments of a bridged OMNI link. 354 original IP packet 355 a whole IP packet or fragment admitted into the OMNI interface by 356 the network layer prior to OAL encapsulation and fragmentation, or 357 an IP packet delivered to the network layer by the OMNI interface 358 following OAL decapsulation and reassembly. 360 OAL packet 361 an original IP packet encapsulated in OAL headers and trailers 362 before OAL fragmentation, or following OAL reassembly. 364 OAL fragment 365 a portion of an OAL packet following fragmentation but prior to 366 *NET encapsulation, or following *NET encapsulation but prior to 367 OAL reassembly. 369 (OAL) atomic fragment 370 an OAL packet that does not require fragmentation is always 371 encapsulated as an "atomic fragment" with a Fragment Header with 372 Fragment Offset and More Fragments both set to 0, but with a valid 373 Identification value. 375 (OAL) carrier packet 376 an encapsulated OAL fragment following *NET encapsulation or prior 377 to *NET decapsulation. OAL sources and destinations exchange 378 carrier packets over underlying interfaces, and may be separated 379 by one or more OAL intermediate nodes. OAL intermediate nodes may 380 perform re-encapsulation on carrier packets by removing the *NET 381 headers of the first hop network and replacing them with new *NET 382 headers for the next hop network. 384 OAL source 385 an OMNI interface acts as an OAL source when it encapsulates 386 original IP packets to form OAL packets, then performs OAL 387 fragmentation and *NET encapsulation to create carrier packets. 389 OAL destination 390 an OMNI interface acts as an OAL destination when it decapsulates 391 carrier packets, then performs OAL reassembly and decapsulation to 392 derive the original IP packet. 394 OAL intermediate node 395 an OMNI interface acts as an OAL intermediate node when it removes 396 the *NET headers of carrier packets received on a first segment, 397 then re-encapsulates the carrier packets in new *NET headers and 398 forwards them into the next segment. OAL intermediate nodes 399 decrement the Hop Limit of the OAL IPv6 header during re- 400 encapsulation, and discard the packet if the Hop Limit reaches 0. 402 underlying interface 403 a *NET interface over which an OMNI interface is configured. 405 Mobility Service Prefix (MSP) 406 an aggregated IP Global Unicast Address (GUA) prefix (e.g., 407 2001:db8::/32, 192.0.2.0/24, etc.) assigned to the OMNI link and 408 from which more-specific Mobile Network Prefixes (MNPs) are 409 delegated. OMNI link administrators typically obtain MSPs from an 410 Internet address registry, however private-use prefixes can 411 alternatively be used subject to certain limitations (see: 412 [I-D.templin-6man-omni]). OMNI links that connect to the global 413 Internet advertise their MSPs to their interdomain routing peers. 415 Mobile Network Prefix (MNP) 416 a longer IP prefix delegated from an MSP (e.g., 417 2001:db8:1000:2000::/56, 192.0.2.8/30, etc.) and delegated to an 418 AERO Client or Relay. 420 Mobile Network Prefix Link Local Address (MNP-LLA) 421 an IPv6 Link Local Address that embeds the most significant 64 422 bits of an MNP in the lower 64 bits of fe80::/64, as specified in 423 [I-D.templin-6man-omni]. 425 Mobile Network Prefix Unique Local Address (MNP-ULA) 426 an IPv6 Unique-Local Address derived from an MNP-LLA. 428 Administrative Link Local Address (ADM-LLA) 429 an IPv6 Link Local Address that embeds a 32-bit administratively- 430 assigned identification value in the lower 32 bits of fe80::/96, 431 as specified in [I-D.templin-6man-omni]. 433 Administrative Unique Local Address (ADM-ULA) 434 an IPv6 Unique-Local Address derived from an ADM-LLA. 436 AERO node 437 a node that is connected to an OMNI link and participates in the 438 AERO internetworking and mobility service. 440 AERO Client ("Client") 441 an AERO node that connects over one or more underlying interfaces 442 and requests MNP delegation/registration service from AERO Proxy/ 443 Servers. The Client assigns an MNP-LLA to the OMNI interface for 444 use in ND exchanges with other AERO nodes and forwards original IP 445 packets to correspondents according to OMNI interface neighbor 446 cache state. 448 AERO Proxy/Server ("Proxy/Server") 449 a dual-function node that provides a proxying service between AERO 450 Clients and external peers on its Client-facing ANET interfaces 451 (i.e., in the same fashion as for an enterprise network proxy) as 452 well as default forwarding and Mobility Anchor Point (MAP) 453 services for coordination with correspondents on its INET-facing 454 interfaces. (Proxy/Servers in the open INET instead configure 455 only an INET interface and no ANET interfaces.) The Proxy/Server 456 configures an OMNI interface and assigns an ADM-LLA to support the 457 operation of IPv6 ND services, while advertising all of its 458 associated MNPs via BGP peerings with Bridges. Note that the 459 Proxy and Server functions can be considered logically separable, 460 but since each Proxy/Server must be informed of all of the 461 Client's other multilink Proxy/Server affiliations the AERO 462 service is best supported when the two functions are coresident on 463 the same physical or logical platform. 465 AERO Relay ("Relay") 466 a Proxy/Server that provides forwarding services between nodes 467 reached via the OMNI link and correspondents on connected 468 downstream links. AERO Relays configure an OMNI interface and 469 assign an ADM-LLA the same as Proxy/Servers. AERO Relays also run 470 a dynamic routing protocol to discover any non-MNP IP GUA routes 471 in service on its connected downstream network links. In both 472 cases, the Relay advertises the MSP(s) to its downstream networks, 473 and distributes all of its associated non-MNP IP GUA routes via 474 BGP peerings with Bridges (i.e., the same as for Proxy/Servers). 476 AERO Bridge ("Bridge") 477 a node that provides hybrid routing/bridging services (as well as 478 a security trust anchor) for nodes on an OMNI link. The Bridge 479 forwards carrier packets between OMNI link segments as OAL 480 intermediate nodes while decrementing the OAL IPv6 header Hop 481 Limit but without decrementing the network layer IP TTL/Hop Limit. 482 AERO Bridges peer with Proxy/Servers and other Bridges over 483 secured tunnels to discover the full set of MNPs for the link as 484 well as any non-MNP IP GUA routes that are reachable via Relays. 486 link-layer address 487 an IP address used as an encapsulation header source or 488 destination address from the perspective of the OMNI interface. 489 When an upper layer protocol (e.g., UDP) is used as part of the 490 encapsulation, the port number is also considered as part of the 491 link-layer address. 493 network layer address 494 the source or destination address of an original IP packet 495 presented to the OMNI interface. 497 end user network (EUN) 498 an internal virtual or external edge IP network that an AERO 499 Client or Relay connects to the rest of the network via the OMNI 500 interface. The Client/Relay sees each EUN as a "downstream" 501 network, and sees the OMNI interface as the point of attachment to 502 the "upstream" network. 504 Mobile Node (MN) 505 an AERO Client and all of its downstream-attached networks that 506 move together as a single unit, i.e., an end system that connects 507 an Internet of Things. 509 Mobile Router (MR) 510 a MN's on-board router that forwards original IP packets between 511 any downstream-attached networks and the OMNI link. The MR is the 512 MN entity that hosts the AERO Client. 514 Route Optimization Source (ROS) 515 the AERO node nearest the source that initiates route 516 optimization. The ROS may be a Proxy/Server or Relay acting on 517 behalf of the source, or may be the source Client itself. 519 Route Optimization responder (ROR) 520 the AERO node nearest the target destination that responds to 521 route optimization requests. The ROR may be a Proxy/Server acting 522 on behalf of a target MNP Client or a Relay for a non-MNP 523 destination. 525 MAP List 526 a geographically and/or topologically referenced list of addresses 527 of all Proxy/Servers within the same OMNI link. Each OMNI link 528 has its own MAP list. 530 Distributed Mobility Management (DMM) 531 a BGP-based overlay routing service coordinated by Proxy/Servers 532 and Bridges that tracks all Proxy/Server-to-Client associations. 534 Mobility Service (MS) 535 the collective set of all Proxy/Servers, Bridges and Relays that 536 provide the AERO Service to Clients. 538 Mobility Service Endpoint MSE) 539 an individual Proxy/Server, Bridge or Relay in the Mobility 540 Service. 542 Throughout the document, the simple terms "Client", "Proxy/Server", 543 "Bridge" and "Relay" refer to "AERO Client", "AERO Proxy/Server", 544 "AERO Bridge" and "AERO Relay", respectively. Capitalization is used 545 to distinguish these terms from other common Internetworking uses in 546 which they appear without capitalization. 548 The terminology of DHCPv6 [RFC8415] and IPv6 ND [RFC4861] (including 549 the names of node variables, messages and protocol constants) is used 550 throughout this document. The terms "All-Routers multicast", "All- 551 Nodes multicast", "Solicited-Node multicast" and "Subnet-Router 552 anycast" are defined in [RFC4291]. Also, the term "IP" is used to 553 generically refer to either Internet Protocol version, i.e., IPv4 554 [RFC0791] or IPv6 [RFC8200]. 556 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 557 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 558 "OPTIONAL" in this document are to be interpreted as described in BCP 559 14 [RFC2119][RFC8174] when, and only when, they appear in all 560 capitals, as shown here. 562 3. Asymmetric Extended Route Optimization (AERO) 564 The following sections specify the operation of IP over OMNI links 565 using the AERO service: 567 3.1. AERO Node Types 569 AERO Clients are Mobile Nodes (MNs) that configure OMNI interfaces 570 over underlying interfaces with addresses that may change when the 571 Client moves to a new network connection point. AERO Clients 572 register their Mobile Network Prefixes (MNPs) with the AERO service, 573 and distribute the MNPs to nodes on EUNs. AERO Bridges, Proxy/ 574 Servers and Relays are critical infrastructure elements in fixed 575 (i.e., non-mobile) INET deployments and hence have permanent and 576 unchanging INET addresses. Together, they constitute the AERO 577 service which provides an OMNI link virtual overlay for connecting 578 AERO Clients. 580 AERO Bridges provide hybrid routing/bridging services (as well as a 581 security trust anchor) for nodes on an OMNI link. Bridges use 582 standard IPv6 routing to forward carrier packets both within the same 583 *NET partition and between disjoint *NET partitions based on an IPv6 584 encapsulation mid-layer known as the OMNI Adaptation Layer (OAL) 585 [I-D.templin-6man-omni]. During forwarding, the inner IP layer 586 experiences a virtual bridging service since the inner IP TTL/Hop 587 Limit is not decremented. Each Bridge also peers with Proxy/Servers 588 and other Bridges in a dynamic routing protocol instance to provide a 589 Distributed Mobility Management (DMM) service for the list of active 590 MNPs (see Section 3.2.3). Bridges present the OMNI link as a set of 591 one or more Mobility Service Prefixes (MSPs) and configure secured 592 tunnels with Proxy/Servers, Relays and other Bridges; they further 593 maintain IP forwarding table entries for each MNP and any other 594 reachable non-MNP prefixes. 596 AERO Proxy/Servers in distributed *NET locations provide default 597 forwarding and mobility/multilink services for AERO Client Mobile 598 Nodes (MNs). Each Proxy/Server also peers with Bridges in a dynamic 599 routing protocol instance to advertise its list of associated MNPs 600 (see Section 3.2.3). Proxy/Servers facilitate prefix delegation/ 601 registration exchanges with Clients, where each delegated prefix 602 becomes an MNP taken from an MSP. Proxy/Servers forward carrier 603 packets between OMNI interface neighbors and track each Client's 604 mobility profiles. Proxy/Servers at ANET/INET boundaries provide a 605 conduit for ANET Clients to associate with peers reached through 606 external INETs. Proxy/Servers in the open INET support INET Clients 607 through authenticated IPv6 ND message exchanges. 609 AERO Relays are Proxy/Servers that provide forwarding services to 610 exchange original IP packets between the OMNI interface and INET/EUN 611 interfaces. Relays are provisioned with MNPs the same as for an AERO 612 Client, and also run a dynamic routing protocol to discover any non- 613 MNP IP routes. The Relay advertises the MSP(s) to its connected 614 networks, and distributes all of its associated MNP and non-MNP 615 routes via BGP peerings with Bridges 617 3.2. The AERO Service over OMNI Links 619 3.2.1. AERO/OMNI Reference Model 621 Figure 1 presents the basic OMNI link reference model: 623 +----------------+ 624 | AERO Bridge B1 | 625 | Nbr: S1, S2, P1| 626 |(X1->S1; X2->S2)| 627 | MSP M1 | 628 +-+------------+-+ 629 +--------------+ | Secured | +--------------+ 630 | AERO P/S S1 | | tunnels | | AERO P/S S2 | 631 | Nbr: C1, B1 +-----+ +-----+ Nbr: C2, B1 | 632 | default->B1 | | default->B1 | 633 | X1->C1 | | X2->C2 | 634 +-------+------+ +------+-------+ 635 | OMNI link | 636 X===+===+======================================+===+===X 637 | | 638 +-----+--------+ +--------+-----+ 639 |AERO Client C1| |AERO Client C2| 640 | Nbr: S1 | | Nbr: S2 | 641 | default->S1 | | default->S2 | 642 | MNP X1 | | MNP X2 | 643 +------+-------+ +-----+--------+ 644 | | 645 .-. .-. 646 ,-( _)-. ,-( _)-. 647 .-(_ IP )-. +-------+ +-------+ .-(_ IP )-. 648 (__ EUN )--|Host H1| |Host H2|--(__ EUN ) 649 `-(______)-' +-------+ +-------+ `-(______)-' 651 Figure 1: AERO/OMNI Reference Model 653 In this model: 655 o the OMNI link is an overlay network service configured over one or 656 more underlying *NET partitions which may be managed by different 657 administrative authorities and have incompatible protocols and/or 658 addressing plans. 660 o AERO Bridge B1 aggregates Mobility Service Prefix (MSP) M1, 661 discovers Mobile Network Prefixes (MNPs) X* and advertises the MSP 662 via BGP peerings over secured tunnels to Proxy/Servers (S1, S2). 663 Bridges connect the disjoint segments of a partitioned OMNI link. 665 o AERO Proxy/Servers S1 and S2 configure secured tunnels with Bridge 666 B1 and also provide mobility, multilink, multicast and default 667 router services for the MNPs of their associated Clients C1 and 668 C2. (AERO Proxy/Servers that act as Relays can also advertise 669 non-MNP routes for non-mobile correspondent nodes the same as for 670 MNP Clients.) 672 o AERO Clients C1 and C2 associate with Proxy/Servers S1 and S2, 673 respectively. They receive MNP delegations X1 and X2, and also 674 act as default routers for their associated physical or internal 675 virtual EUNs. Simple hosts H1 and H2 attach to the EUNs served by 676 Clients C1 and C2, respectively. 678 An OMNI link configured over a single *NET appears as a single 679 unified link with a consistent underlying network addressing plan. 680 In that case, all nodes on the link can exchange carrier packets via 681 simple *NET encapsulation, since the underlying *NET is connected. 682 In common practice, however, an OMNI link may be partitioned into 683 multiple "segments", where each segment is a distinct *NET 684 potentially managed under a different administrative authority (e.g., 685 as for worldwide aviation service providers such as ARINC, SITA, 686 Inmarsat, etc.). Individual *NETs may also themselves be partitioned 687 internally, in which case each internal partition is seen as a 688 separate segment. 690 The addressing plan of each segment is consistent internally but will 691 often bear no relation to the addressing plans of other segments. 692 Each segment is also likely to be separated from others by network 693 security devices (e.g., firewalls, proxys, packet filtering gateways, 694 etc.), and in many cases disjoint segments may not even have any 695 common physical link connections. Therefore, nodes can only be 696 assured of exchanging carrier packets directly with correspondents in 697 the same segment, and not with those in other segments. The only 698 means for joining the segments therefore is through inter-domain 699 peerings between AERO Bridges. 701 The same as for traditional campus LANs, multiple OMNI link segments 702 can be joined into a single unified link via a virtual bridging 703 service using the OMNI Adaptation Layer (OAL) [I-D.templin-6man-omni] 704 which inserts a mid-layer IPv6 encapsulation header that supports 705 inter-segment forwarding (i.e., bridging) without decrementing the 706 network-layer TTL/Hop Limit. This bridging of OMNI link segments is 707 shown in Figure 2: 709 . . . . . . . . . . . . . . . . . . . . . . . 710 . . 711 . .-(::::::::) . 712 . .-(::::::::::::)-. +-+ . 713 . (:::: Segment A :::)--|B|---+ . 714 . `-(::::::::::::)-' +-+ | . 715 . `-(::::::)-' | . 716 . | . 717 . .-(::::::::) | . 718 . .-(::::::::::::)-. +-+ | . 719 . (:::: Segment B :::)--|B|---+ . 720 . `-(::::::::::::)-' +-+ | . 721 . `-(::::::)-' | . 722 . | . 723 . .-(::::::::) | . 724 . .-(::::::::::::)-. +-+ | . 725 . (:::: Segment C :::)--|B|---+ . 726 . `-(::::::::::::)-' +-+ | . 727 . `-(::::::)-' | . 728 . | . 729 . ..(etc).. x . 730 . . 731 . . 732 . <- OMNI link Bridged by encapsulation -> . 733 . . . . . . . . . . . . . .. . . . . . . . . 735 Figure 2: Bridging OMNI Link Segments 737 Bridges, Proxy/Servers and Relay OMNI interfaces are configured over 738 both secured tunnels and open INET underlying interfaces over their 739 respective segments in a spanning tree topology rooted at the 740 Bridges. The "secured" spanning tree supports strong authentication 741 for control plane messages and may also be used to convey the initial 742 carrier packets in a flow. The "unsecured" spanning tree conveys 743 ordinary carrier packets without security codes and that must be 744 treated by destinations according to data origin authentication 745 procedures. Route optimization can be employed to cause carrier 746 packets to take more direct paths between OMNI link neighbors without 747 having to follow strict spanning tree paths. 749 3.2.2. Addressing and Node Identification 751 AERO nodes on OMNI links use the Link-Local Address (LLA) prefix 752 fe80::/64 [RFC4291] to assign LLAs used for network-layer addresses 753 in link-scoped IPv6 ND and data messages. AERO Clients use LLAs 754 constructed from MNPs (i.e., "MNP-LLAs") while other AERO nodes use 755 LLAs constructed from administrative identification values ("ADM- 756 LLAs") as specified in [I-D.templin-6man-omni]. Non-MNP routes are 757 also represented the same as for MNP-LLAs, but may include a prefix 758 that is not properly covered by the MSP. 760 AERO nodes also use the Unique Local Address (ULA) prefix fd00::/8 761 followed by a pseudo-random 40-bit OMNI domain identifier to form the 762 prefix [ULA]::/48, then include a 16-bit OMNI link identifier '*' to 763 form the prefix [ULA*]::/64 [RFC4291]. The AERO node then uses the 764 prefix [ULA*]::/64 to form "MNP-ULAs" or "ADM-ULA"s as specified in 765 [I-D.templin-6man-omni] to support OAL addressing. (The prefix 766 [ULA*]::/64 appearing alone and with no suffix represents "default".) 767 AERO Clients also use Temporary ULAs constructed per 768 [I-D.templin-6man-omni], where the addresses are typically used only 769 in initial control message exchanges until a stable MNP-LLA/ULA is 770 assigned. 772 AERO MSPs, MNPs and non-MNP routes are typically based on Global 773 Unicast Addresses (GUAs), but in some cases may be based on private- 774 use addresses. See [I-D.templin-6man-omni] for a full specification 775 of LLAs, ULAs and GUAs used by AERO nodes on OMNI links. 777 Finally, AERO Clients and Proxy/Servers configure node identification 778 values as specified in [I-D.templin-6man-omni]. 780 3.2.3. AERO Routing System 782 The AERO routing system comprises a private instance of the Border 783 Gateway Protocol (BGP) [RFC4271] that is coordinated between Bridges 784 and Proxy/Servers and does not interact with either the public 785 Internet BGP routing system or any underlying INET routing systems. 787 In a reference deployment, each Proxy/Server is configured as an 788 Autonomous System Border Router (ASBR) for a stub Autonomous System 789 (AS) using a 32-bit AS Number (ASN) [RFC4271] that is unique within 790 the BGP instance, and each Proxy/Server further uses eBGP to peer 791 with one or more Bridges but does not peer with other Proxy/Servers. 792 Each *NET of a multi-segment OMNI link must include one or more 793 Bridges, which peer with the Proxy/Servers within that *NET. All 794 Bridges within the same *NET are members of the same hub AS, and use 795 iBGP to maintain a consistent view of all active routes currently in 796 service. The Bridges of different *NETs peer with one another using 797 eBGP. 799 Bridges maintain forwarding table entries only for the MNP-ULAs 800 corresponding to MNP and non-MNP routes that are currently active, 801 and carrier packets destined to all other MNP-ULAs will correctly 802 incur Destination Unreachable messages due to the black-hole route. 803 In this way, Proxy/Servers and Relays have only partial topology 804 knowledge (i.e., they know only about the routes their directly 805 associated Clients and non-AERO links) and they forward all other 806 carrier packets to Bridges which have full topology knowledge. 808 Each OMNI link segment assigns a unique ADM-ULA sub-prefix of 809 [ULA*]::/96. For example, a first segment could assign 810 [ULA*]::1000/116, a second could assign [ULA*]::2000/116, a third 811 could assign [ULA*]::3000/116, etc. Within each segment, each Proxy/ 812 Server configures an ADM-ULA within the segment's prefix, e.g., the 813 Proxy/Servers within [ULA*]::2000/116 could assign the ADM-ULAs 814 [ULA*]::2011/116, [ULA*]::2026/116, [ULA*]::2003/116, etc. 816 The administrative authorities for each segment must therefore 817 coordinate to assure mutually-exclusive ADM-ULA prefix assignments, 818 but internal provisioning of ADM-ULAs an independent local 819 consideration for each administrative authority. For each ADM-ULA 820 prefix, the Bridge(s) that connect that segment assign the all-zero's 821 address of the prefix as a Subnet Router Anycast address. For 822 example, the Subnet Router Anycast address for [ULA*]::1023/116 is 823 simply [ULA*]::1000. 825 ADM-ULA prefixes are statically represented in Bridge forwarding 826 tables. Bridges join multiple segments into a unified OMNI link over 827 multiple diverse administrative domains. They support a bridging 828 function by first establishing forwarding table entries for their 829 ADM-ULA prefixes either via standard BGP routing or static routes. 830 For example, if three Bridges ('A', 'B' and 'C') from different 831 segments serviced [ULA*]::1000/116, [ULA*]::2000/116 and 832 [ULA*]::3000/116 respectively, then the forwarding tables in each 833 Bridge are as follows: 835 A: [ULA*]::1000/116->local, [ULA*]::2000/116->B, [ULA*]::3000/116->C 837 B: [ULA*]::1000/116->A, [ULA*]::2000/116->local, [ULA*]::3000/116->C 839 C: [ULA*]::1000/116->A, [ULA*]::2000/116->B, [ULA*]::3000/116->local 841 These forwarding table entries are permanent and never change, since 842 they correspond to fixed infrastructure elements in their respective 843 segments. 845 MNP ULAs are instead dynamically advertised in the AERO routing 846 system by Proxy/Servers and Relays that provide service for their 847 corresponding MNPs. For example, if three Proxy/Servers ('D', 'E' 848 and 'F') service the MNPs 2001:db8:1000:2000::/56, 849 2001:db8:3000:4000::/56 and 2001:db8:5000:6000::/56 then the routing 850 system would include: 852 D: [ULA*]:2001:db8:1000:2000/120 853 E: [ULA*]:2001:db8:3000:4000/120 855 F: [ULA*]:2001:db8:5000:6000/120 857 A full discussion of the BGP-based routing system used by AERO is 858 found in [I-D.ietf-rtgwg-atn-bgp]. 860 3.2.4. OMNI Link Segment Routing 862 With the Client and partition prefixes in place in Bridge forwarding 863 tables, the OMNI interface sends control and data carrier packets 864 toward AERO destination nodes located in different OMNI link segments 865 over the spanning tree. The OMNI interface uses the OMNI Adaptation 866 Layer (OAL) encapsulation service [I-D.templin-6man-omni], and 867 includes an OMNI Routing Header (ORH) as an extension to the OAL 868 header if final segment forwarding information is available, e.g., in 869 the neighbor cache. (For nodes located in the same OMNI link segment 870 the ORH may instead be omitted.) In its full form, the ORH is 871 formatted as shown in Figure 3: 873 0 1 2 3 874 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 875 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 876 | Next Header | Hdr Ext Len | Routing Type | Segments Left | 877 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 878 | FMT | SRT | omIndex | LHS (bits 0 -15) | 879 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 880 | LHS (bits 0 -15) | ~ 881 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ 882 ~ Link Layer Address (L2ADDR) ~ 883 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 884 | Null Padding (if necessary) | 885 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 886 ~ Destination Suffix ~ 887 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 889 Figure 3: OMNI Routing Header (ORH) Format 891 In this format: 893 o Next Header identifies the type of header immediately following 894 the ORH. 896 o Hdr Ext Len is the length of the Routing header in 8-octet units 897 (not including the first 8 octets). The field must encode a value 898 between 0 and 4 (all other values are treated as a parameter 899 problem). 901 o Routing Type is set to TBD1 (see IANA Considerations). 903 o Segments Left encodes the value 0 or 1 (all other values are 904 treated as a parameter problem). 906 o FMT - a 3-bit "Forward/Mode/Trailer" code corresponding to the 907 included Link Layer Address as follows: 909 * When the most significant bit (i.e., "FMT-Forward") is clear, 910 the Last Hop Segment (LHS) Proxy/Server must reassemble. When 911 FMT-Forward is set, the LHS Proxy/Server must forward the 912 fragments to the Client (while changing the OAL destination 913 address to the MNP-ULA of the Client if necessary) without 914 reassembling. 916 * When the next most significant bit (i.e., "FMT-Mode") is clear, 917 L2ADDR is the INET address of the LHS Proxy/Server and the 918 Client must be reached through the LHS Proxy/Server. When FMT- 919 Mode is set, the Client is eligible for route optimization over 920 the open INET where it may be located behind one or more NATs, 921 and L2ADDR is either the INET address of the LHS Proxy/Server 922 (when FMT-Forward is set) or the native INET address of the 923 Client itself (when FMT-Forward is clear). 925 * When the least significant bit (i.e., "FMT-Trailer") is set and 926 Hdr Ext Len is 1, a trailing 8-octet Destination Suffix is 927 included; otherwise, an LHS with L2ADDR for IPv4 is included. 928 FMT-Trailer is otherwise ignored (see below). 930 o SRT - a 5-bit Segment Routing Topology prefix length consulted 931 only when Segments Left is 1, and encodes a value that (when added 932 to 96) determines the prefix length to apply to the ADM-ULA formed 933 from concatenating [ULA*]::/96 with the 32 bit LHS value (for 934 example, the value 16 corresponds to the prefix length 112). 936 o omIndex - a 1-octet field consulted only when Segments Left is 0; 937 encodes the index for the target Client underlying interface and 938 informs the LHS Proxy-Server of the specific interface for 939 forwarding when there are multiple alternatives. When FMT-Forward 940 is clear, omIndex determines the interface for forwarding the ORH 941 packet following reassembly; when FMT-Forward is set, omIndex 942 determines the interface for forwarding the raw carrier packets 943 without first reassembling. 945 o LHS - a 4-octet field present only when indicated by the ORH 946 length (see below) and consulted only when Segments Left is 1. 947 The field encodes the 32-bit ADM-ULA suffix of a Last Hop Segment 948 (LHS) Proxy/Server for the target. When SRT and LHS are both set 949 to 0, the LHS must be reached directly via INET encapsulation 950 instead of over the spanning tree. When SRT is set to 0 and LHS 951 is non-zero, the prefix length is set to 128. SRT and LHS 952 determine the ADM-ULA of the LHS Proxy/Server over the spanning 953 tree. 955 o Link Layer Address (L2ADDR) - an IP encapsulation address present 956 only when indicated by the ORH length (see below) and consulted 957 only when Segments Left is 1. The L2ADDR IP version is determined 958 by consulting the ORH length (see below), since the field will 959 always contain exactly 6 octets for UDP/IPv4 or 18 octets for UDP/ 960 IPv6. When present, provides the link-layer address (i.e., the 961 encapsulation address) of the Proxy/Server or the target Client 962 itself. The UDP Port Number appears in the first two octets and 963 the IP address appears in the remaining octets. The Port Number 964 and IP address are recorded in network byte order, and in ones- 965 compliment "obfuscated" form per [RFC4380]. The OMNI interface 966 forwarding algorithm uses L2ADDR as the INET encapsulation address 967 for forwarding when SRT/LHS is located in the same OMNI link 968 segment. If direct INET encapsulation is not permitted, L2ADDR is 969 instead set to all-zeros and the packet must be forwarded to the 970 LHS Proxy-Server via the spanning tree. 972 o Null Padding - zero-valued octets added as necessary to pad the 973 portion of the ORH included up to this point to an even 8-octet 974 boundary. 976 o Destination Suffix - a trailing 8-octet field present only when 977 indicated by the ORH length (see below). When ORH length is 1, 978 FMT-Trailer determines whether the option includes a Destination 979 Suffix or an LHS/L2ADDR since there is only enough space available 980 for one. When present, encodes the 64-bit MNP-ULA suffix for the 981 target Client. 983 The ORH Hdr Ext Len field value also serves as an implicit ORH "Type" 984 such that 5 distinct Types (i.e., ORH-0 through ORH-4) are supported. 985 All Types include the same 6-octet preamble beginning with the Next 986 Header field up to and including the omIndex field. The Types are 987 defined as follows: 989 o ORH-0 - The preamble Hdr Ext Len and Segments Left fields must 990 both be 0. Two null padding octets follow the preamble, and all 991 other fields are omitted. 993 o ORH-1 - The preamble Hdr Ext Len is set to 1. When FMT-Trailer is 994 clear, the LHS and L2ADDR for IPv4 fields are included and the 995 Destination Suffix is omitted. When FMT-Trailer is set, the LHS 996 and L2ADDR fields are omitted, the Destination Suffix field is 997 included and Segments Left must be 0. 999 o ORH-2 - The preamble Hdr Ext Len is set to 2. The LHS, L2ADDR for 1000 IPv4 and Destination Suffix fields are all included. 1002 o ORH-3 - The preamble Hdr Ext Len is set to 3. The LHS and L2ADDR 1003 for IPv6 fields are included and the Destination Suffix field is 1004 omitted. 1006 o ORH-4 - The preamble Hdr Ext Len is set to 4. The LHS, L2ADDR for 1007 IPv6 and Destination Suffix fields are all included. 1009 AERO neighbors use OAL encapsulation and fragmentation to exchange 1010 OAL packets as specified in [I-D.templin-6man-omni]. When an AERO 1011 node's OMNI interface (acting as an OAL source) uses OAL 1012 encapsulation for an original IP packet with source address 1013 2001:db8:1:2::1 and destination address 2001:db8:1234:5678::1, it 1014 sets the OAL header source address to its own ULA (e.g., 1015 [ULA*]::2001:db8:1:2), sets the destination address to the MNP-ULA 1016 corresponding to the IP destination address (e.g., 1017 [ULA*]::2001:db8:1234:5678), sets the Traffic Class, Flow Label, Hop 1018 Limit and Payload Length as discussed in [I-D.templin-6man-omni], 1019 then finally selects an Identification and appends an OAL checksum. 1021 If the neighbor cache information indicates that the target is in a 1022 different segment, the OAL source next inserts an ORH immediately 1023 following the OAL header while including Destination Suffix for non- 1024 first-fragments only when necessary (in this case, the Destination 1025 Suffix is 2001:db8:1234:5678). Next, to direct the packet to a 1026 first-hop Proxy/Server or a Bridge, the source prepares an ORH with 1027 Segments Left set to 1 and with LHS/L2ADDR included, then overwrites 1028 the OAL header destination address with the LHS Subnet Router Anycast 1029 address (for example, for LHS 3000:4567 with SRT 16, the Subnet 1030 Router Anycast address is [ULA*]::3000:0000). To send the packet to 1031 the LHS Proxy/Server either directly or via the spanning tree, the 1032 OAL source instead includes an ORH (Type 0 or 1) with Segments Left 1033 set to 0 and LHS/L2ADDR omitted, and overwrites the OAL header 1034 destination address with either the LHS Proxy/Server ADM-ULA or the 1035 MNP-ULA of the Client itself.) 1037 The OAL source then fragments the OAL packet, with each resulting OAL 1038 fragment including the OAL/ORH headers while only the first fragment 1039 includes the original IPv6 header. If FMT-Forward is set, the 1040 Identification used for fragmentation must be within the window for 1041 the Client and a Destination Suffix must be included with each non- 1042 first-fragment when necessary; otherwise the Identification must be 1043 within the window for the Client's Proxy/Server and no Destination 1044 Suffix is needed. (Note that if no actual fragmentation is required 1045 the OAL source still prepares the packet as an "atomic" fragment that 1046 includes a Fragment Header with Offset and More Fragments both set to 1047 0.) The OAL source finally encapsulates each resulting OAL fragment 1048 in an *NET header to form an OAL carrier packet, with source address 1049 set to its own *NET address (e.g., 192.0.2.100) and destination set 1050 to the *NET address of the last hop itself or the next hop in the 1051 spanning tree (e.g., 192.0.2.1). 1053 The carrier packet encapsulation format in the above example is shown 1054 in Figure 4: 1056 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1057 | *NET Header | 1058 | src = 192.0.2.100 | 1059 | dst = 192.0.2.1 | 1060 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1061 | OAL IPv6 Header | 1062 | src = [ULA*]::2001:db8:1:2 | 1063 | dst= [ULA*]::3000:0000 | 1064 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1065 | ORH (if necessary) | 1066 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1067 | OAL Fragment Header | 1068 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1069 | Original IP Header | 1070 | (first-fragment only) | 1071 | src = 2001:db8:1:2::1 | 1072 | dst = 2001:db8:1234:5678::1 | 1073 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1074 | | 1075 ~ ~ 1076 ~ Original Packet Body/Fragment ~ 1077 ~ ~ 1078 | | 1079 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1081 Figure 4: Carrier Packet Format 1083 In this format, the original IP header and packet body/fragment are 1084 from the original IP packet, the OAL header is an IPv6 header 1085 prepared according to [RFC2473], the ORH is a Routing Header 1086 extension of the OAL header, the Fragment Header identifies each 1087 fragment, and the INET header is prepared as discussed in 1088 Section 3.6. When the OAL source transmits the resulting carrier 1089 packets, they are forwarded over possibly multiple OAL intermediate 1090 nodes in the OMNI link spanning tree until they arrive at the OAL 1091 destination. 1093 This gives rise to a routing system that contains both Client MNP-ULA 1094 routes that may change dynamically due to regional node mobility and 1095 per-partition ADM-ULA routes that rarely if ever change. The 1096 spanning tree can therefore provide link-layer bridging by sending 1097 carrier packets over the spanning tree instead of network-layer 1098 routing according to MNP routes. As a result, opportunities for loss 1099 due to node mobility between different segments are mitigated. 1101 Note: The document suggests in several places that AERO nodes 1102 transform ORHs with Segments Left set to 1 into ORH-0 during 1103 forwarding. While this may yield a substantial savings in 1104 encapsulation overhead in some cases, the AERO node may instead 1105 simply set Segments Left to 0 and leave the original ORH in place. 1106 The LHS Proxy/Server or target Client that processes the ORH will 1107 receive the same information in both cases. 1109 Note: When the OAL source and destination are on the same INET 1110 segment, OAL header compression can be used to significantly reduce 1111 encapsulation overhead [I-D.templin-6man-omni]. 1113 Note: When the OAL source has multiple original IP packets to send to 1114 the same OAL destination, it can perform "packing" to generate a 1115 "super-packet" [I-D.templin-6man-omni]. In that case, the OAL/ORH 1116 super-packet may include up to N original IP packets as long as the 1117 total length of the super-packet does not exceed the OMNI interface 1118 MTU. 1120 Note: Use of an IPv6 "minimal encapsulation" format (i.e., an IPv6 1121 variant of [RFC2004]) based on extensions to the ORH was considered 1122 and abandoned. In the approach, the ORH would be inserted as an 1123 extension header to the original IPv6 packet header. The IPv6 1124 destination address would then be written into the ORH, and the ULA 1125 corresponding to the destination would be overwritten in the IPv6 1126 destination address. This would seemingly convey enough forwarding 1127 information so that OAL encapsulation could be avoided. However, 1128 this "minimal encapsulation" IPv6 packet would then have a non-ULA 1129 source address and ULA destination address, an incorrect value in 1130 upper layer protocol checksums, and a Hop Limit that is decremented 1131 within the spanning tree when it should not be. The insertion and 1132 removal of the ORH would also entail rewriting the Payload Length and 1133 Next Header fields - again, invalidating upper layer checksums. 1134 These irregularities would result in implementation challenges and 1135 the potential for operational issues, e.g., since actionable ICMPv6 1136 error reports could not be delivered to the original source. In 1137 order to address the issues, still more information such as the 1138 original IPv6 source address could be written into the ORH. However, 1139 with the additional information the benefit of the "minimal 1140 encapsulation" savings quickly diminishes, and becomes overshadowed 1141 by the implementation and operational irregularities. 1143 3.2.5. Segment Routing Topologies (SRTs) 1145 The 64-bit sub-prefixes of [ULA]::/48 identify up to 2^16 distinct 1146 Segment Routing Topologies (SRTs). Each SRT is a mutually-exclusive 1147 OMNI link overlay instance using a distinct set of ULAs, and emulates 1148 a Virtual LAN (VLAN) service for the OMNI link. In some cases (e.g., 1149 when redundant topologies are needed for fault tolerance and 1150 reliability) it may be beneficial to deploy multiple SRTs that act as 1151 independent overlay instances. A communication failure in one 1152 instance therefore will not affect communications in other instances. 1154 Each SRT is identified by a distinct value in bits 48-63 of 1155 [ULA]::/48, i.e., as [ULA0]::/64, [ULA1]::/64, [ULA2]::/64, etc. 1156 Each OMNI interface is identified by a unique interface name (e.g., 1157 omni0, omni1, omni2, etc.) and assigns an anycast ADM-ULA 1158 corresponding to its SRT prefix length. The anycast ADM-ULA is used 1159 for OMNI interface determination in Safety-Based Multilink (SBM) as 1160 discussed in [I-D.templin-6man-omni]. Each OMNI interface further 1161 applies Performance-Based Multilink (PBM) internally. 1163 3.2.6. Segment Routing For OMNI Link Selection 1165 An original IPv6 source can direct an IPv6 packet to an AERO node by 1166 including a standard IPv6 Segment Routing Header (SRH) [RFC8754] with 1167 the anycast ADM-ULA for the selected SRT as either the IPv6 1168 destination or as an intermediate hop within the SRH. This allows 1169 the original source to determine the specific OMNI link topology an 1170 original IPv6 packet will traverse when there may be multiple 1171 alternatives. 1173 When the AERO node processes the SRH and forwards the original IPv6 1174 packet to the correct OMNI interface, the OMNI interface writes the 1175 next IPv6 address from the SRH into the IPv6 destination address and 1176 decrements Segments Left. If decrementing would cause Segments Left 1177 to become 0, the OMNI interface deletes the SRH before forwarding. 1178 This form of Segment Routing supports Safety-Based Multilink (SBM). 1180 3.2.7. Segment Routing Within the OMNI Link 1182 OAL sources can insert an ORH for Segment Routing within the OMNI 1183 link to influence the paths of OAL packets sent to OAL destinations 1184 in remote segments without requiring all carrier packets to traverse 1185 strict spanning tree paths. 1187 When an AERO node's OMNI interface has an original IP packet to send 1188 to a target discovered through route optimization located in the same 1189 OMNI link segment, it acts as an OAL source to perform OAL 1190 encapsulation and fragmentation. The node then uses L2ADDR for INET 1191 encapsulation while including an ORH-0 when sending the resulting 1192 carrier packets to the LHS Proxy/Server, or omitting the ORH-0 when 1193 sending directly to the target Client itself. When the node sends 1194 carrier packets with an ORH-0 to the LHS Proxy/Server, it sets the 1195 OAL destination to the ADM-ULA of the Proxy/Server if the Proxy/ 1196 Server is responsible for reassembly; otherwise, it sets the OAL 1197 destination to the MNP-ULA of the target Client to cause the Proxy/ 1198 Server to forward without reassembling. The node also sets omIndex 1199 to identify a specific target Client underlying interface. 1201 When an AERO node's OMNI interface has an original IP packet to send 1202 to a route optimization target located in a remote OMNI link segment, 1203 it acts as an OAL source the same as above but also includes an 1204 appropriate ORH type with Segments Left set to 1 and with SRT/LHS/ 1205 L2ADDR information while setting the OAL destination to the Subnet 1206 Router Anycast address for the LHS OMNI link segment. The OAL source 1207 can alternatively include an ORH with Segments Left set to 0 while 1208 setting the OAL destination to the ADM-ULA of the LHS Proxy/Server, 1209 but this would cause the carrier packets to follow strict spanning 1210 tree paths all the way to the LHS Proxy/Server. The OMNI interface 1211 then forwards the resulting carrier packets into the spanning tree. 1213 When a Bridge receives a carrier packet destined to its Subnet Router 1214 Anycast address with any ORH type with Segments Left set to 1 and 1215 SRT/LHS/L2ADDR values corresponding to the local segment, it examines 1216 FMT-Mode to determine whether the target Client can accept packets 1217 directly (i.e., following any NAT traversal procedures necessary) 1218 while bypassing the LHS Proxy/Server. If the Client can be reached 1219 directly and NAT traversal has converged, the Bridge then writes the 1220 MNP-ULA (found in the inner IPv6 header for first fragments or the 1221 ORH Destination Suffix for non-first fragments) into the OAL 1222 destination address, decrements the OAL IPv6 header Hop Limit (and 1223 discards the packet if Hop Limit reaches 0), removes the ORH, re- 1224 encapsulates the carrier packet according to L2ADDR then forwards the 1225 carrier packet directly to the target Client. If the Client cannot 1226 be reached directly (or if NAT traversal has not yet converged), the 1227 Bridge instead transforms the ORH into an ORH-0, re-encapsulates the 1228 packet according to L2ADDR, changes the OAL destination to the ADM- 1229 ULA of the LHS Proxy/Server if FMT-Forward is clear or the MNP-ULA of 1230 the Client if FMT-Forward is set and forwards the carrier packet to 1231 the LHS Proxy/Server. 1233 When a Bridge receives a carrier packet destined to its Subnet Router 1234 Anycast address with any ORH type with Segments Left set to 1 and 1235 L2ADDR set to 0, the Bridge instead forwards the packet toward the 1236 LHS Proxy/Server via the spanning tree. The Bridge changes the OAL 1237 destination to the ADM-ULA of the LHS Proxy/Server, transforms the 1238 ORH into an ORH-0 (or an ORH-1 with FMT-Trailer set and Segments Left 1239 0), then forwards the packet to the next hop in the spanning tree. 1240 The Bridge may also elect to forward via the spanning tree as above 1241 even when it receives a carrier packet with any ORH even if it 1242 includes a valid L2ADDR Port Number and IP address, however this may 1243 result in a longer path than necessary. If the carrier packet 1244 arrived via the secured spanning tree, the Bridge forwards to the 1245 next hop also via the secured spanning tree. If the carrier packet 1246 arrived via the unsecured spanning tree, the Bridge forwards to the 1247 next hop also via the unsecured spanning tree. 1249 When an LHS Proxy/Server receives carrier packets with any ORH type 1250 with Segments Left set to 0 and with OAL destination set to its own 1251 ADM-ULA, it proceeds according to FMT-Forward and omIndex. If FMT- 1252 Forward is set, the LHS Proxy/Server changes the OAL destination to 1253 the MNP-ULA of the target Client found in the IPv6 header for first 1254 fragments or in the ORH Destination Suffix for non-first-fragments, 1255 removes the ORH and forwards to the target Client interface 1256 identified by omIndex. If FMT-Forward is clear, the LHS Proxy/Server 1257 instead reassembles then re-encapsulates while refragmenting if 1258 necessary, removes the ORH and forwards to the target Client 1259 according to omIndex. 1261 When an LHS Proxy/Server receives carrier packets with any ORH type 1262 with Segments Left set to 0 and with OAL destination set to the MNP- 1263 ULA of the target Client, it removes the ORH and forwards to the 1264 target Client according to omIndex. 1266 When a target Client receives carrier packets with OAL destination 1267 set to is MNP-ULA, it reassembles to obtain the OAL packet, then 1268 decapsulates and delivers the original IP packet to upper layers. 1270 Note: Special handling procedures are employed for the exchange of 1271 IPv6 ND messages used to establish neighbor cache state as discussed 1272 in Section 3.14. The procedures call for hop-by-hop authentication 1273 and neighbor cache state establishment based on the encapsulation 1274 ULA, with next-hop determination based on the IPv6 ND message LLA. 1276 3.3. OMNI Interface Characteristics 1278 OMNI interfaces are virtual interfaces configured over one or more 1279 underlying interfaces classified as follows: 1281 o INET interfaces connect to an INET either natively or through one 1282 or more NATs. Native INET interfaces have global IP addresses 1283 that are reachable from any INET correspondent. The INET-facing 1284 interfaces of Proxy/Servers are native interfaces, as are Relay 1285 and Bridge interfaces. NATed INET interfaces connect to a private 1286 network behind one or more NATs that provide INET access. Clients 1287 that are behind a NAT are required to send periodic keepalive 1288 messages to keep NAT state alive when there are no carrier packets 1289 flowing. 1291 o ANET interfaces connect to an ANET that is separated from the open 1292 INET by a Proxy/Server. Proxy/Servers can actively issue control 1293 messages over the INET on behalf of the Client to reduce ANET 1294 congestion. 1296 o VPNed interfaces use security encapsulation over the INET to a 1297 Virtual Private Network (VPN) server that also acts as a Proxy/ 1298 Server. Other than the link-layer encapsulation format, VPNed 1299 interfaces behave the same as Direct interfaces. 1301 o Direct (i.e., single-hop point-to-point) interfaces connect a 1302 Client directly to a Proxy/Server without crossing any ANET/INET 1303 paths. An example is a line-of-sight link between a remote pilot 1304 and an unmanned aircraft. The same Client considerations apply as 1305 for VPNed interfaces. 1307 OMNI interfaces use OAL encapsulation and fragmentation as discussed 1308 in Section 3.2.4. OMNI interfaces use *NET encapsulation (see: 1309 Section 3.6) to exchange carrier packets with OMNI link neighbors 1310 over INET or VPNed interfaces as well as over ANET interfaces for 1311 which the Client and Proxy/Server may be multiple IP hops away. OMNI 1312 interfaces do not use link-layer encapsulation over Direct underlying 1313 interfaces or ANET interfaces when the Client and Proxy/Server are 1314 known to be on the same underlying link. 1316 OMNI interfaces maintain a neighbor cache for tracking per-neighbor 1317 state the same as for any interface. OMNI interfaces use ND messages 1318 including Router Solicitation (RS), Router Advertisement (RA), 1319 Neighbor Solicitation (NS) and Neighbor Advertisement (NA) for 1320 neighbor cache management. In environments where spoofing may be a 1321 threat, OMNI neighbors should employ OAL Identification window 1322 synchronization in their ND message exchanges. 1324 OMNI interfaces send ND messages with an OMNI option formatted as 1325 specified in [I-D.templin-6man-omni]. The OMNI option includes 1326 prefix registration information and Interface Attributes containing 1327 link information parameters for the OMNI interface's underlying 1328 interfaces. Each OMNI option may include multiple Interface 1329 Attributes sub-options, each identified by an omIndex value. 1331 A Client's OMNI interface may be configured over multiple underlying 1332 interface connections. For example, common mobile handheld devices 1333 have both wireless local area network ("WLAN") and cellular wireless 1334 links. These links are often used "one at a time" with low-cost WLAN 1335 preferred and highly-available cellular wireless as a standby, but a 1336 simultaneous-use capability could provide benefits. In a more 1337 complex example, aircraft frequently have many wireless data link 1338 types (e.g. satellite-based, cellular, terrestrial, air-to-air 1339 directional, etc.) with diverse performance and cost properties. 1341 If a Client's multiple underlying interfaces are used "one at a time" 1342 (i.e., all other interfaces are in standby mode while one interface 1343 is active), then ND message OMNI options include Interface Attributes 1344 sub-options with the same underlying interface index. In that case, 1345 the Client would appear to have a single interface but with a 1346 dynamically changing link-layer address. 1348 If the Client has multiple active underlying interfaces, then from 1349 the perspective of ND it would appear to have multiple link-layer 1350 addresses. In that case, ND message OMNI options MAY include 1351 Interface Attributes sub-options with different underlying interface 1352 indexes. Every ND message need not include Interface Attributes for 1353 all underlying interfaces; for any attributes not included, the 1354 neighbor considers the status as unchanged. 1356 Bridge and Proxy/Server OMNI interfaces are configured over secured 1357 tunnel underlying interfaces for carrying IPv6 ND and BGP protocol 1358 control plane messages, plus open INET underlying interfaces for 1359 carrying unsecured messages. The OMNI interface configures both an 1360 ADM-LLA and its corresponding ADM-ULA, and acts as an OAL source to 1361 encapsulate and fragment original IP packets while presenting the 1362 resulting carrier packets to a secured or unsecured underlying 1363 interface. Note that Bridge and Proxy/Server BGP protocol TCP 1364 sessions are run directly over the OMNI interface using ADM-ULA 1365 source and destination addresses. The OMNI interface will 1366 encapsulate these as carrier packets even though the OAL header may 1367 use the same ADM-ULAs as the original IP header; these carrier 1368 packets must then be sent over a secured underlying interface. 1370 3.4. OMNI Interface Initialization 1372 AERO Proxy/Servers and Clients configure OMNI interfaces as their 1373 point of attachment to the OMNI link. AERO nodes assign the MSPs for 1374 the link to their OMNI interfaces (i.e., as a "route-to-interface") 1375 to ensure that original IP packets with destination addresses covered 1376 by an MNP not explicitly assigned to a non-OMNI interface are 1377 directed to the OMNI interface. 1379 OMNI interface initialization procedures for Proxy/Servers, Clients 1380 and Bridges are discussed in the following sections. 1382 3.4.1. AERO Proxy/Server and Relay Behavior 1384 When a Proxy/Server enables an OMNI interface, it assigns an 1385 ADM-{LLA,ULA} appropriate for the given OMNI link segment. The 1386 Proxy/Server also configures secured tunnels with one or more 1387 neighboring Bridges and engages in a BGP routing protocol session 1388 with each Bridge. 1390 The OMNI interface provides a single interface abstraction to the IP 1391 layer, but internally includes an NBMA nexus for sending carrier 1392 packets to OMNI interface neighbors over underlying INET interfaces 1393 and secured tunnels. The Proxy/Server further configures a service 1394 to facilitate ND exchanges with AERO Clients and manages per-Client 1395 neighbor cache entries and IP forwarding table entries based on 1396 control message exchanges. 1398 Relays are simply Proxy/Servers that run a dynamic routing protocol 1399 to redistribute routes between the OMNI interface and INET/EUN 1400 interfaces (see: Section 3.2.3). The Relay provisions MNPs to 1401 networks on the INET/EUN interfaces (i.e., the same as a Client would 1402 do) and advertises the MSP(s) for the OMNI link over the INET/EUN 1403 interfaces. The Relay further provides an attachment point of the 1404 OMNI link to a non-MNP-based global topology. 1406 3.4.2. AERO Client Behavior 1408 When a Client enables an OMNI interface, it assigns either an 1409 MNP-{LLA, ULA} or a Temporary ULA and sends RS messages with ND 1410 parameters over its underlying interfaces to a Proxy/Server, which 1411 returns an RA message with corresponding parameters. The RS/RA 1412 messages may pass through one or more NATs in the case of a Client's 1413 INET interface. (Note: if the Client used a Temporary ULA in its 1414 initial RS message, it will discover an MNP-{LLA, ULA} in the 1415 corresponding RA that it receives from the Proxy/Server and begin 1416 using these new addresses. If the Client is operating outside the 1417 context of AERO infrastructure such as in a Mobile Ad-hoc Network 1418 (MANET), however, it may continue using Temporary ULAs for Client-to- 1419 Client communications until it encounters an infrastructure element 1420 that can provide an MNP.) 1422 3.4.3. AERO Bridge Behavior 1424 AERO Bridges configure an OMNI interface and assign the ADM-ULA 1425 Subnet Router Anycast address for each OMNI link segment they connect 1426 to. Bridges configure secured tunnels with Proxy/Servers and other 1427 Bridges, and engage in a BGP routing protocol session with neighbors 1428 on the spanning tree (see: Section 3.2.3). 1430 3.5. OMNI Interface Neighbor Cache Maintenance 1432 Each OMNI interface maintains a conceptual neighbor cache that 1433 includes a Neighbor Cache Entry (NCE) for each neighbor it 1434 communicates with on the OMNI link per [RFC4861]. Each route 1435 optimization source NCE is indexed by the LLA of the neighbor, which 1436 must match the ULA used during OAL encapsulation. In addition to 1437 ordinary neighbor cache entries, proxy neighbor cache entries are 1438 created and maintained by AERO Proxy/Servers when they proxy Client 1439 ND message exchanges [RFC4389]. AERO Proxy/Servers maintain proxy 1440 neighbor cache entries for each of their associated Clients. 1442 To the list of NCE states in Section 7.3.2 of [RFC4861], Proxy/Server 1443 OMNI interfaces add an additional state DEPARTED that applies to 1444 Clients that have recently departed. The interface sets a 1445 "DepartTime" variable for the NCE to "DEPART_TIME" seconds. 1446 DepartTime is decremented unless a new ND message causes the state to 1447 return to REACHABLE. While a NCE is in the DEPARTED state, the 1448 Proxy/Server forwards carrier packets destined to the target Client 1449 to the Client's new location instead. When DepartTime decrements to 1450 0, the NCE is deleted. It is RECOMMENDED that DEPART_TIME be set to 1451 the default constant value REACHABLE_TIME plus 10 seconds (40 seconds 1452 by default) to allow a window for carrier packets in flight to be 1453 delivered while stale route optimization state may be present. 1455 Proxy/Servers can act as RORs on behalf of dependent Clients 1456 according to the Proxy Neighbor Advertisement specification in 1457 Section 7.2.8 of [RFC4861], while well-connected Clients can act as 1458 an ROR on their own behalf. When a Proxy/Server ROR receives an 1459 authentic NS message used for route optimization, it first searches 1460 for a proxy NCE for the target Client and accepts the message only if 1461 there is an entry. The Proxy/Server then returns a solicited NA 1462 message while creating a NCE for the ROS. Proxy/Server RORs also 1463 create or update a "Report List" entry for the ROS in the target 1464 Client's NCE with a "ReportTime" variable set to REPORT_TIME seconds. 1465 The ROR resets ReportTime when it receives a new authentic NS 1466 message, and otherwise decrements ReportTime while no authentic NS 1467 messages have been received. It is RECOMMENDED that REPORT_TIME be 1468 set to the default constant value REACHABLE_TIME plus 10 seconds (40 1469 seconds by default) to allow a window for route optimization to 1470 converge before ReportTime decrements below REACHABLE_TIME. 1472 When the ROS receives a solicited NA message response to its NS 1473 message used for route optimization, it creates or updates a NCE for 1474 the target network-layer and link-layer addresses. The ROS then 1475 (re)sets ReachableTime for the NCE to REACHABLE_TIME seconds and uses 1476 this value to determine whether carrier packets can be forwarded 1477 directly to the target, i.e., instead of via a default route. The 1478 ROS otherwise decrements ReachableTime while no further solicited NA 1479 messages arrive. It is RECOMMENDED that REACHABLE_TIME be set to the 1480 default constant value 30 seconds as specified in [RFC4861]. 1482 AERO nodes also use the value MAX_UNICAST_SOLICIT to limit the number 1483 of NS messages sent when a correspondent may have gone unreachable, 1484 the value MAX_RTR_SOLICITATIONS to limit the number of RS messages 1485 sent without receiving an RA and the value MAX_NEIGHBOR_ADVERTISEMENT 1486 to limit the number of unsolicited NAs that can be sent based on a 1487 single event. It is RECOMMENDED that MAX_UNICAST_SOLICIT, 1488 MAX_RTR_SOLICITATIONS and MAX_NEIGHBOR_ADVERTISEMENT be set to 3 the 1489 same as specified in [RFC4861]. 1491 Different values for DEPART_TIME, REPORT_TIME, REACHABLE_TIME, 1492 MAX_UNICAST_SOLICIT, MAX_RTR_SOLCITATIONS and 1493 MAX_NEIGHBOR_ADVERTISEMENT MAY be administratively set; however, if 1494 different values are chosen, all nodes on the link MUST consistently 1495 configure the same values. Most importantly, DEPART_TIME and 1496 REPORT_TIME SHOULD be set to a value that is sufficiently longer than 1497 REACHABLE_TIME to avoid packet loss due to stale route optimization 1498 state. 1500 3.5.1. OMNI ND Messages 1502 OMNI interface IPv6 ND messages include OMNI options 1503 [I-D.templin-6man-omni] with per-neighbor information including 1504 Interface Attributes that provide Link-Layer Address and traffic 1505 selector information for the neighbor's underlying interfaces. This 1506 information is stored in the neighbor cache and provides the basis 1507 for the forwarding algorithm specified in Section 3.10. The 1508 information is cumulative and reflects the union of the OMNI 1509 information from the most recent ND messages received from the 1510 neighbor; it is therefore not required that each ND message contain 1511 all neighbor information. 1513 The OMNI option Interface Attributes for each underlying interface 1514 includes a two-part "Link-Layer Address" consisting of a simple IP 1515 encapsulation address determined by the FMT and L2ADDR fields and an 1516 ADM-ULA determined by the SRT and LHS fields. Underlying interfaces 1517 are further selected based on their associated traffic selectors. 1519 The OMNI option is distinct from any Source/Target Link-Layer Address 1520 Options (S/TLLAOs) that may appear in an ND message according to the 1521 appropriate IPv6 over specific link layer specification (e.g., 1522 [RFC2464]). If both an OMNI option and S/TLLAO appear, the former 1523 pertains to encapsulation addresses while the latter pertains to the 1524 native L2 address format of the underlying media 1526 OMNI interface IPv6 ND messages may also include other IPv6 ND 1527 options. In particular, solicitation messages may include Nonce and/ 1528 or Timestamp options if required for verification of advertisement 1529 replies. If an OMNI ND solicitation message includes a Nonce option, 1530 the advertisement reply must echo the same Nonce. If an OMNI ND 1531 solicitation message includes a Timestamp option, the advertisement 1532 reply should also include a Timestamp option. 1534 AERO Clients send RS messages to the All-Routers multicast address 1535 while using unicast link-layer addresses. AERO Proxy/Servers respond 1536 by returning unicast RA messages. During the RS/RA exchange, AERO 1537 Clients and Servers include state synchronization parameters to 1538 establish Identification windows and other state. 1540 AERO nodes use NS/NA messages for the following purposes: 1542 o NS/NA(AR) messages are used for address resolution only. The ROS 1543 sends an NS(AR) to the solicited-node multicast address of the 1544 target, and an ROR in the network with addressing information for 1545 the target returns a unicast NA(AR). The NA(AR) contains 1546 authentic and current target address resolution information, but 1547 only an implicit third-party assertion of target reachability. 1548 NS/NA(AR) messages must be secured. 1550 o NS/NA(WIN) messages are used for establishing and maintaining 1551 window synchronization (and any other) state. The source sends an 1552 NS(WIN) to the unicast address of the target, and the target 1553 returns a unicast NA(WIN). The NS/NA(WIN) exchange synchronizes 1554 the sequence numbers the neighbors will include in subsequent 1555 packets, and asserts reachability for the target without 1556 necessarily testing a specific underlying interface pair. NS/ 1557 NA(WIN) messages must be secured. 1559 o NS/NA(NUD) messages are used for determining target reachability. 1560 The source sends an NS(NUD) to the unicast address of the target 1561 over a specific underlying interface pair, and the target returns 1562 a unicast NA(NUD). NS/NA(NUD) messages that use an in-window 1563 sequence number and do not update any other state need not be 1564 secured. NS/NA(NUD) messages may also be used in combination with 1565 window synchronization (i.e., NUD+WIN), in which case the messages 1566 must be secured. 1568 o Unsolicited NA (uNA) messages are used to signal addressing and/or 1569 other neighbor state changes (e.g., due to mobility, signal 1570 degradation, traffic selector updates, etc.). uNA messages that 1571 include state update information must be secured. 1573 o NS/NA(DAD) messages are not used in AERO, since Duplicate Address 1574 Detection is not required. 1576 Additionally, nodes may send NA/RA messages with the OMNI option PNG 1577 flag set to receive a solicited NA response from the neighbor. The 1578 solicited NA response MUST set the ACK flag (without also setting the 1579 SYN or PNG flags) and include the Identification used in the PNG 1580 message in the Acknowledgement. 1582 3.5.2. OMNI Neighbor Advertisement Message Flags 1584 As discussed in Section 4.4 of [RFC4861] NA messages include three 1585 flag bits R, S and O. OMNI interface NA messages treat the flags as 1586 follows: 1588 o R: The R ("Router") flag is set to 1 in the NA messages sent by 1589 all AERO/OMNI node types. Simple hosts that would set R to 0 do 1590 not occur on the OMNI link itself, but may occur on the downstream 1591 links of Clients and Relays. 1593 o S: The S ("Solicited") flag is set exactly as specified in 1594 Section 4.4. of [RFC4861], i.e., it is set to 1 for Solicited NAs 1595 and set to 0 for uNAs (both unicast and multicast). 1597 o O: The O ("Override") flag is set to 0 for solicited NAs returned 1598 by a Proxy/Server ROR and set to 1 for all other solicited and 1599 unsolicited NAs. For further study is whether solicited NAs for 1600 anycast targets apply for OMNI links. Since MNP-LLAs must be 1601 uniquely assigned to Clients to support correct ND protocol 1602 operation, however, no role is currently seen for assigning the 1603 same MNP-LLA to multiple Clients. 1605 3.5.3. OMNI Neighbor Window Synchronization 1607 In secured environments (e.g., such as between nodes on the same 1608 secured ANET), OMNI interface neighbors can exchange OAL packets 1609 using randomly-initialized and monotonically-increasing 1610 Identification values (modulo 2*32) without window synchronization. 1611 In environments where spoofing is considered a threat, OMNI interface 1612 neighbors instead invoke window synchronization in ND message 1613 exchanges to maintain send/receive window state in their respective 1614 neighbor cache entries as specified in [I-D.templin-6man-omni]. 1616 In the asymmetric window synchronization case, the initial ND message 1617 exchange establishes only the initiator's send window and the 1618 responder's receive window such that a corresponding exchange would 1619 be needed to establish the reverse direction. In the symmetric case, 1620 the initiator and responder engage in a three-way handshake to 1621 symmetrically establish the send/receive windows of both parties. 1623 3.6. OMNI Interface Encapsulation and Re-encapsulation 1625 The OMNI interface admits original IP packets then (acting as an OAL 1626 source) performs OAL encapsulation and fragmentation as specified in 1627 [I-D.templin-6man-omni] while including an ORH if necessary as 1628 specified in Section 3.2.4. OAL encapsulation produces OAL packets, 1629 while OAL fragmentation turns them into OAL fragments which are then 1630 encapsulated in *NET headers as carrier packets. 1632 For carrier packets undergoing re-encapsulation at an OAL 1633 intermediate node, the OMNI interface decrements the OAL IPv6 header 1634 Hop Limit and discards the carrier packet if the Hop Limit reaches 0. 1635 The intermediate node next removes the *NET encapsulation headers 1636 from the first segment and re-encapsulates the packet in new *NET 1637 encapsulation headers for the next segment. 1639 When a Proxy/Server or Relay re-encapsulates a carrier packet 1640 received from a Client that includes an OAL but no ORH, it inserts an 1641 ORH immediately following the OAL header and adjusts the OAL payload 1642 length and destination address field. The inserted ORH will be 1643 removed by the LHS Bridge or Proxy/Server, but its insertion and 1644 removal will not interfere with reassembly at the final destination. 1645 For this reason, Clients must reserve 40 bytes for a maximum-length 1646 ORH when they perform OAL encapsulation (see: Section 3.9). 1648 3.7. OMNI Interface Decapsulation 1650 OMNI interfaces (acting as OAL destinations) decapsulate and 1651 reassemble OAL packets into original IP packets destined either to 1652 the AERO node itself or to a destination reached via an interface 1653 other than the OMNI interface the original IP packet was received on. 1654 When carrier packets containing OAL fragments arrive, the OMNI 1655 interface reassembles as discussed in Section 3.9. 1657 3.8. OMNI Interface Data Origin Authentication 1659 AERO nodes employ simple data origin authentication procedures. In 1660 particular: 1662 o AERO Bridges and Proxy/Servers accept carrier packets received 1663 from secured underlying interfaces. 1665 o AERO Proxy/Servers and Clients accept carrier packets and original 1666 IP packets that originate from within the same secured ANET. 1668 o AERO Clients and Relays accept original IP packets from downstream 1669 network correspondents based on ingress filtering. 1671 o AERO Clients, Relays and Proxy/Servers verify carrier packet UDP/ 1672 IP encapsulation addresses according to [I-D.templin-6man-omni]. 1674 o AERO Clients (as well as Proxy/Servers and Relays when acting as 1675 OAL destinations) accept only carrier packets with Identification 1676 values within the current window for the OAL source neighbor when 1677 window synchronization is employed. 1679 AERO nodes silently drop any packets that do not satisfy the above 1680 data origin authentication procedures. Further security 1681 considerations are discussed in Section 6. 1683 3.9. OMNI Interface MTU 1685 The OMNI interface observes the link nature of tunnels, including the 1686 Maximum Transmission Unit (MTU), Maximum Reassembly Unit (MRU) and 1687 the role of fragmentation and reassembly [I-D.ietf-intarea-tunnels]. 1688 The OMNI interface employs an OMNI Adaptation Layer (OAL) that 1689 accommodates multiple underlying links with diverse MTUs while 1690 observing both a minimum and per-path Maximum Payload Size (MPS). 1691 The functions of the OAL and the OMNI interface MTU/MRU/MPS are 1692 specified in [I-D.templin-6man-omni] with MTU/MRU both set to the 1693 constant value 9180 bytes, with minimum MPS set to 400 bytes, and 1694 with per-path MPS set to potentially larger values depending on the 1695 underlying path. 1697 When the network layer presents an original IP packet to the OMNI 1698 interface, the OAL source encapsulates and fragments the original IP 1699 packet if necessary. When the network layer presents the OMNI 1700 interface with multiple original IP packets bound to the same OAL 1701 destination, the OAL source can concatenate them together into a 1702 single OAL super-packet as discussed in [I-D.templin-6man-omni]. The 1703 OAL source then fragments the OAL packet if necessary according to 1704 the minimum/path MPS such that the OAL headers appear in each 1705 fragment while the original IP packet header appears only in the 1706 first fragment. The OAL source then encapsulates each OAL fragment 1707 in *NET headers for transmission as carrier packets over an 1708 underlying interface connected to either a physical link such as 1709 Ethernet, WiFi and the like or a virtual link such as an Internet or 1710 higher-layer tunnel (see the definition of link in [RFC8200]). 1712 Note: A Client that does not (yet) have neighbor cache state for a 1713 target may omit the ORH in carrier packets with the understanding 1714 that a Proxy/Server may insert an ORH on its behalf. For this 1715 reason, Clients reserve 40 bytes for the largest possible ORH in 1716 their OAL fragment size calculations. 1718 Note: Although the ORH may be removed or replaced by a Bridge on the 1719 path (see: Section 3.10.3), this does not interfere with the 1720 destination's ability to reassemble. This is due to the fact that 1721 the ORH is not included in the fragmentable part; therefore, its 1722 removal does not invalidate the offset values in any fragment 1723 headers. 1725 3.10. OMNI Interface Forwarding Algorithm 1727 Original IP packets enter a node's OMNI interface either from the 1728 network layer (i.e., from a local application or the IP forwarding 1729 system) while carrier packets enter from the link layer (i.e., from 1730 an OMNI interface neighbor). All original IP packets and carrier 1731 packets entering a node's OMNI interface first undergo data origin 1732 authentication as discussed in Section 3.8. Those that satisfy data 1733 origin authentication are processed further, while all others are 1734 dropped silently. 1736 Original IP packets that enter the OMNI interface from the network 1737 layer are forwarded to an OMNI interface neighbor using OAL 1738 encapsulation and fragmentation to produce carrier packets for 1739 transmission over underlying interfaces. (If routing indicates that 1740 the original IP packet should instead be forwarded back to the 1741 network layer, the packet is dropped to avoid looping). Carrier 1742 packets that enter the OMNI interface from the link layer are either 1743 re-encapsulated and re-admitted into the OMNI link, or reassembled 1744 and forwarded to the network layer where they are subject to either 1745 local delivery or IP forwarding. In all cases, the OAL MUST NOT 1746 decrement the network layer TTL/Hop-count since its forwarding 1747 actions occur below the network layer. 1749 OMNI interfaces may have multiple underlying interfaces and/or 1750 neighbor cache entries for neighbors with multiple underlying 1751 interfaces (see Section 3.3). The OAL uses Interface Attribute 1752 traffic selectors (e.g., port number, flow specification, etc.) to 1753 select an outbound underlying interface for each OAL packet based on 1754 the node's own interface attributes, and also to select a destination 1755 link-layer address based on the neighbor's underlying interface 1756 attributes. AERO implementations SHOULD allow for traffic selector 1757 values to be modified at runtime through network management. 1759 If multiple outgoing interfaces and/or neighbor interfaces match the 1760 traffic selectors, the AERO node replicates the OAL packet and sends 1761 one copy via each of the (outgoing / neighbor) interface pairs; 1762 otherwise, the node sends a single copy of the OAL packet via an 1763 interface with a matching traffic selector. (While not strictly 1764 required, successful delivery may be more likely when all fragments 1765 of the same OAL packet are sent over the same underlying interface.) 1766 AERO nodes keep track of which underlying interfaces are currently 1767 "reachable" or "unreachable", and only use "reachable" interfaces for 1768 forwarding purposes. 1770 The following sections discuss the OMNI interface forwarding 1771 algorithms for Clients, Proxy/Servers and Bridges. In the following 1772 discussion, an original IP packet's destination address is said to 1773 "match" if it is the same as a cached address, or if it is covered by 1774 a cached prefix (which may be encoded in an MNP-LLA). 1776 3.10.1. Client Forwarding Algorithm 1778 When an original IP packet enters a Client's OMNI interface from the 1779 network layer the Client searches for a NCE that matches the 1780 destination. If there is a match, the Client selects one or more 1781 "reachable" neighbor interfaces in the entry for forwarding purposes. 1782 If there is no NCE, the Client instead either enqueues the original 1783 IP packet and invokes route optimization or forwards the original IP 1784 packet toward a Proxy/Server. The Client (acting as an OAL source) 1785 performs OAL encapsulation and sets the OAL destination address to 1786 the MNP-ULA of the target if there is a matching NCE; otherwise, it 1787 sets the OAL destination to the ADM-ULA of the Proxy/Server. If the 1788 Client has multiple original IP packets to send to the same neighbor, 1789 it can concatenate them in a single super-packet 1790 [I-D.templin-6man-omni]. The OAL source then performs fragmentation 1791 to create OAL fragments (see: Section 3.9), appends any *NET 1792 encapsulation, and sends the resulting carrier packets over 1793 underlying interfaces to the neighbor acting as an OAL destination. 1795 If the neighbor interface selected for forwarding is located on the 1796 same OMNI link segment and not behind a NAT, the Client forwards the 1797 carrier packets directly according to the L2ADDR information for the 1798 neighbor. If the neighbor interface is behind a NAT on the same OMNI 1799 link segment, the Client instead forwards the initial carrier packets 1800 to its Proxy/Server (while inserting an ORH-0) and initiates NAT 1801 traversal procedures. If the Client's intended source underlying 1802 interface is also behind a NAT and located on the same OMNI link 1803 segment, it sends a "direct bubble" over the interface per 1804 [RFC6081][RFC4380] to the L2ADDR found in the neighbor cache in order 1805 to establish state in its own NAT by generating traffic toward the 1806 neighbor (note that no response to the bubble is expected). 1808 The Client next sends an NS(NUD) message toward the MNP-ULA of the 1809 neighbor via its Proxy/Server as discussed in Section 3.15. If the 1810 Client receives an NA(NUD) from the neighbor over the underlying 1811 interface, it marks the neighbor interface as "trusted" and sends 1812 future carrier packets directly to the L2ADDR information for the 1813 neighbor instead of indirectly via the Proxy/Server. The Client must 1814 honor the neighbor cache maintenance procedure by sending additional 1815 direct bubbles and/or NS/NA(NUD) messages as discussed in 1816 [RFC6081][RFC4380] in order to keep NAT state alive as long as 1817 carrier packets are still flowing. 1819 When a carrier packet enters a Client's OMNI interface from the link- 1820 layer, if the OAL destination matches one of the Client's ULAs the 1821 Client (acting as an OAL destination) verifies that the 1822 Identification is in-window for this OAL source, then reassembles and 1823 decapsulates as necessary and delivers the original IP packet to the 1824 network layer. Otherwise, the Client drops the original IP packet 1825 and MAY return a network-layer ICMP Destination Unreachable message 1826 subject to rate limiting (see: Section 3.11). 1828 Note: Clients and their Proxy/Server (and other Client) peers can 1829 exchange original IP packets over ANET underlying interfaces without 1830 invoking the OAL, since the ANET is secured at the link and physical 1831 layers. By forwarding original IP packets without invoking the OAL, 1832 however, the ANET peers can engage only in classical path MTU 1833 discovery since the packets are subject to loss and/or corruption due 1834 to the various per-link MTU limitations that may occur within the 1835 ANET. Moreover, the original IP packets do not include either the 1836 OAL integrity check or per-packet Identification values that can be 1837 used for data origin authentication and link-layer retransmissions. 1838 The tradeoff therefore involves an assessment of the per-packet 1839 encapsulation overhead saved by bypassing the OAL vs. inheritance of 1840 classical network "brittleness". (Note however that ANET peers can 1841 send small original IP packets without invoking the OAL, while 1842 invoking the OAL for larger packets. This presents the beneficial 1843 aspects of both small packet efficiency and large packet robustness.) 1845 3.10.2. Proxy/Server and Relay Forwarding Algorithm 1847 When the Proxy/Server receives an original IP packet from the network 1848 layer, it drops the packet if routing indicates that it should be 1849 forwarded back to the network layer to avoid looping. Otherwise, the 1850 Proxy/Server regards the original IP packet the same as if it had 1851 arrived as carrier packets with OAL destination set to its own ADM- 1852 ULA. When the Proxy/Server receives carrier packets on underlying 1853 interfaces with OAL destination set to its own ADM-ULA, it performs 1854 OAL reassembly if necessary to obtain the original IP packet. 1856 The Proxy/Server next searches for a NCE that matches the original IP 1857 destination and proceeds as follows: 1859 o if the original IP packet destination matches a NCE, the Proxy/ 1860 Sever uses one or more "reachable" neighbor interfaces in the 1861 entry for packet forwarding using OAL encapsulation and 1862 fragmentation according to the cached link-layer address 1863 information. If the neighbor interface is in a different OMNI 1864 link segment, the Proxy/Server performs OAL encapsulation and 1865 fragmentation, inserts an appropriate ORH and forwards the 1866 resulting carrier packets via the spanning tree to a Bridge; 1867 otherwise, it forwards the carrier packets directly to the 1868 neighbor. If the neighbor is behind a NAT, the Proxy/Server 1869 instead forwards initial carrier packets via a Bridge while 1870 sending an NS(NUD) to the neighbor. When the Proxy/Server 1871 receives the NA(NUD), it can begin forwarding carrier packets 1872 directly to the neighbor the same as discussed in Section 3.10.1 1873 while sending additional NS(NUD) messages as necessary to maintain 1874 NAT state. Note that no direct bubbles are necessary since the 1875 Proxy/Server is by definition not located behind a NAT. 1877 o else, if the original IP destination matches a non-MNP route in 1878 the IP forwarding table or an ADM-LLA assigned to the Proxy/ 1879 Server's OMNI interface, the Proxy/Server acting as a Relay 1880 presents the original IP packet to the network layer for local 1881 delivery or IP forwarding. 1883 o else, the Proxy/Server initiates address resolution as discussed 1884 in Section 3.14, while retaining initial original IP packets in a 1885 small queue awaiting address resolution completion. 1887 When the Proxy/Server receives a carrier packet with OAL destination 1888 set to an MNP-ULA that does not match the MSP, it accepts the carrier 1889 packet only if data origin authentication succeeds and if there is a 1890 network layer routing table entry for a GUA route that matches the 1891 MNP-ULA. If there is no route, the Proxy/Server drops the carrier 1892 packet; otherwise, it reassembles and decapsulates to obtain the 1893 original IP packet and acts as a Relay to present it to the network 1894 layer where it will be delivered according to standard IP forwarding. 1896 When the Proxy/Server receives a carrier packet from one of its 1897 Client neighbors with OAL destination set to another node, it 1898 forwards the packets via a matching NCE or via the spanning tree if 1899 there is no matching entry. When the Proxy/Server receives a carrier 1900 packet with OAL destination set to the MNP-ULA of one of its Client 1901 neighbors established through RS/RA exchanges, it accepts the carrier 1902 packet only if data origin authentication succeeds. If the NCE state 1903 is DEPARTED, the Proxy/Server inserts an ORH that encodes the MNP-ULA 1904 destination suffix and changes the OAL destination address to the 1905 ADM-ULA of the new Proxy/Server, then re-encapsulates the carrier 1906 packet and forwards it to a Bridge which will eventually deliver it 1907 to the new Proxy/Server. 1909 If the neighbor cache state for the MNP-ULA is REACHABLE, the Proxy/ 1910 Server forwards the carrier packets to the Client which then must 1911 reassemble. (Note that the Proxy/Server does not reassemble carrier 1912 packets not explicitly addressed to its own ADM-ULA, since routing 1913 could direct some of the carrier packet of the same original IP 1914 packet through a different Proxy/Server.) In that case, the Client 1915 may receive fragments that are smaller than its link MTU but can 1916 still be reassembled. 1918 Note: Proxy/Servers may receive carrier packets with ORHs that 1919 include additional forwarding information. Proxy/Servers use the 1920 forwarding information to determine the correct interface for 1921 forwarding to the target destination Client, then remove the ORH and 1922 forward the carrier packet. If the ORH information instead indicates 1923 that the Proxy/Server is responsible for reassembly, the Proxy/Server 1924 reassembles first before re-encapsulating (and possibly also re- 1925 fragmenting) then forwards to the target Client. For a full 1926 discussion of cases when the Proxy/Server may receive carrier packets 1927 with ORHs, see: Section 3.14.6. 1929 Note: Clients and their Proxy/Server peers can exchange original IP 1930 packets over ANET underlying interfaces without invoking the OAL, 1931 since the ANET is secured at the link and physical layers. By 1932 forwarding original IP packets without invoking the OAL, however, the 1933 Client and Proxy/Server can engage only in classical path MTU 1934 discovery since the packets are subject to loss and/or corruption due 1935 to the various per-link MTU limitations that may occur within the 1936 ANET. Moreover, the original IP packets do not include either the 1937 OAL integrity check or per-packet Identification values that can be 1938 used for data origin authentication and link-layer retransmissions. 1939 The tradeoff therefore involves an assessment of the per-packet 1940 encapsulation overhead saved by bypassing the OAL vs. inheritance of 1941 classical network "brittleness". (Note however that ANET peers can 1942 send small original IP packets without invoking the OAL, while 1943 invoking the OAL for larger packets. This presents the beneficial 1944 aspects of both small packet efficiency and large packet robustness.) 1946 Note: When a Proxy/Server receives a (non-OAL) original IP packet 1947 from an ANET Client, or a carrier packet with OAL destination set to 1948 its own ADM-ULA from any Client, the Proxy/Server reassembles if 1949 necessary then performs ROS functions on behalf of the Client. The 1950 Client may at some later time begin sending carrier packets to the 1951 OAL address of the actual target instead of the Proxy/Server, at 1952 which point it may begin functioning as an ROS on its own behalf and 1953 thereby "override" the Proxy/Server's ROS role. 1955 Note: Proxy/Servers forward secure control plane carrier packets via 1956 the secured spanning tree and forwards other carrier packets via the 1957 unsecured spanning tree. When a Proxy/Server receives a carrier 1958 packet from the secured spanning tree, it considers the message as 1959 authentic without having to verify upper layer authentication 1960 signatures. When a Proxy/Server receives a carrier packet from the 1961 unsecured spanning tree, it verifies any upper layer authentication 1962 signatures and/or forwards the unsecured message toward the 1963 destination which must apply data origin authentication. 1965 Note: If the Proxy/Server has multiple original IP packets to send to 1966 the same neighbor, it can concatenate them in a single OAL super- 1967 packet [I-D.templin-6man-omni]. 1969 3.10.3. Bridge Forwarding Algorithm 1971 Bridges forward carrier packets the same as any IPv6 router. Bridges 1972 convey carrier packets that encapsulate IPv6 ND control messages or 1973 routing protocol control messages using security encapsulations, and 1974 may convey carrier packets that encapsulate ordinary data without 1975 including security encapsulations. When the Bridge receives a 1976 carrier packet, it removes the outer *NET header and searches for a 1977 forwarding table entry that matches the OAL destination address. The 1978 Bridge then processes the packet as follows: 1980 o if the carrier packet destination matches its ADM-ULA or the 1981 corresponding ADM-ULA Subnet Router Anycast address and the OAL 1982 header is followed by an ORH, the Bridge reassembles if necessary 1983 then sets aside the ORH and processes the carrier packet locally 1984 before forwarding. If the OAL packet contains an NA(NUD) message, 1985 the Bridge replaces the OMNI option Interface Attributes sub- 1986 option with information for its own interface while retaining the 1987 omIndex value supplied by the NA(NUD) message source. The Bridge 1988 next examines the ORH FMT code. If FMT-Mode indicates the 1989 destination is a Client on the open *NET (or, a Client behind a 1990 NAT for which NAT traversal procedures have already converged) the 1991 Bridge writes the MNP-ULA formed from the ORH Destination Suffix 1992 into the OAL destination. The Bridge then removes the ORH and 1993 forwards the packet using encapsulation based on L2ADDR. If the 1994 LHS Proxy/Server will forward to the Client without reassembly, 1995 the Bridge also writes the MNP-ULA into the OAL destination, then 1996 replaces the ORH with an ORH-0 and forwards the carrier packet to 1997 the LHS Proxy/Server, while also invoking NAT traversal procedures 1998 if necessary noting that no direct bubbles are necessary since 1999 only the target Client and not the Bridge is behind a NAT. If the 2000 LHS Proxy/Server must perform reassembly before forwarding to the 2001 Client, the Bridge instead writes the ADM-ULA formed from the ORH 2002 SRT/LHS into the OAL destination address, replaces the ORH with an 2003 ORH-0 and forwards the carrier packet to the LHS Proxy/Server. 2005 o else, if the carrier packet destination matches its ADM-ULA or the 2006 corresponding ADM-ULA Subnet Router Anycast address and the OAL 2007 header is not followed by an ORH with Segments Left set to 1, the 2008 Bridge submits the packet for reassembly. When reassembly is 2009 complete, the Bridge submits the original packet to the IP layer 2010 to support local applications such as BGP routing protocol 2011 sessions. 2013 o else, if the carrier packet destination matches a forwarding table 2014 entry the Bridge forwards the carrier packet to the next hop. (If 2015 the destination matches an MSP without matching an MNP, however, 2016 the Bridge instead drops the packet and returns an ICMP 2017 Destination Unreachable message subject to rate limiting - see: 2018 Section 3.11). 2020 o else, the Bridge drops the packet and returns an ICMP Destination 2021 Unreachable as above. 2023 As for any IP router, the Bridge decrements the OAL IPv6 header Hop 2024 Limit when it forwards the carrier packet and drops the packet if the 2025 Hop Limit reaches 0. Therefore, only the Hop Limit in the OAL header 2026 is decremented and not the TTL/Hop Limit in the original IP packet 2027 header. Bridges do not insert OAL/ORH headers themselves; instead, 2028 they act as IPv6 routers and forward carrier packets based on their 2029 destination addresses while also possibly transforming larger ORHs 2030 into an ORH-0. 2032 Bridges forward carrier packets received from a first segment via the 2033 unsecured spanning tree to the next segment also via the unsecured 2034 spanning tree. Bridges forward carrier packets received from a first 2035 segment via the secured spanning tree to the next segment also via 2036 the secured spanning tree. Bridges use a single IPv6 routing table 2037 that always determines the same next hop for a given OAL destination, 2038 where the secured/unsecured spanning tree is determined through the 2039 selection of the underlying interface to be used for transmission 2040 (i.e., a secured tunnel or an open INET interface). 2042 3.11. OMNI Interface Error Handling 2044 When an AERO node admits an original IP packet into the OMNI 2045 interface, it may receive link-layer or network-layer error 2046 indications. 2048 A link-layer error indication is an ICMP error message generated by a 2049 router in the INET on the path to the neighbor or by the neighbor 2050 itself. The message includes an IP header with the address of the 2051 node that generated the error as the source address and with the 2052 link-layer address of the AERO node as the destination address. 2054 The IP header is followed by an ICMP header that includes an error 2055 Type, Code and Checksum. Valid type values include "Destination 2056 Unreachable", "Time Exceeded" and "Parameter Problem" 2057 [RFC0792][RFC4443]. (OMNI interfaces ignore link-layer IPv4 2058 "Fragmentation Needed" and IPv6 "Packet Too Big" messages for carrier 2059 packets that are no larger than the minimum/path MPS as discussed in 2060 Section 3.9, however these messages may provide useful hints of probe 2061 failures during path MPS probing.) 2063 The ICMP header is followed by the leading portion of the carrier 2064 packet that generated the error, also known as the "packet-in-error". 2065 For ICMPv6, [RFC4443] specifies that the packet-in-error includes: 2066 "As much of invoking packet as possible without the ICMPv6 packet 2067 exceeding the minimum IPv6 MTU" (i.e., no more than 1280 bytes). For 2068 ICMPv4, [RFC0792] specifies that the packet-in-error includes: 2069 "Internet Header + 64 bits of Original Data Datagram", however 2070 [RFC1812] Section 4.3.2.3 updates this specification by stating: "the 2071 ICMP datagram SHOULD contain as much of the original datagram as 2072 possible without the length of the ICMP datagram exceeding 576 2073 bytes". 2075 The link-layer error message format is shown in Figure 5 (where, "L2" 2076 and "L3" refer to link-layer and network-layer, respectively): 2078 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2079 ~ ~ 2080 | L2 IP Header of | 2081 | error message | 2082 ~ ~ 2083 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2084 | L2 ICMP Header | 2085 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 2086 ~ ~ P 2087 | carrier packet *NET and OAL | a 2088 | encapsulation headers | c 2089 ~ ~ k 2090 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ e 2091 ~ ~ t 2092 | original IP packet headers | 2093 | (first-fragment only) | i 2094 ~ ~ n 2095 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2096 ~ ~ e 2097 | Portion of the body of | r 2098 | the original IP packet | r 2099 | (all fragments) | o 2100 ~ ~ r 2101 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 2103 Figure 5: OMNI Interface Link-Layer Error Message Format 2105 The AERO node rules for processing these link-layer error messages 2106 are as follows: 2108 o When an AERO node receives a link-layer Parameter Problem message, 2109 it processes the message the same as described as for ordinary 2110 ICMP errors in the normative references [RFC0792][RFC4443]. 2112 o When an AERO node receives persistent link-layer Time Exceeded 2113 messages, the IP ID field may be wrapping before earlier fragments 2114 awaiting reassembly have been processed. In that case, the node 2115 should begin including integrity checks and/or institute rate 2116 limits for subsequent packets. 2118 o When an AERO node receives persistent link-layer Destination 2119 Unreachable messages in response to carrier packets that it sends 2120 to one of its neighbor correspondents, the node should process the 2121 message as an indication that a path may be failing, and 2122 optionally initiate NUD over that path. If it receives 2123 Destination Unreachable messages over multiple paths, the node 2124 should allow future carrier packets destined to the correspondent 2125 to flow through a default route and re-initiate route 2126 optimization. 2128 o When an AERO Client receives persistent link-layer Destination 2129 Unreachable messages in response to carrier packets that it sends 2130 to one of its neighbor Proxy/Servers, the Client should mark the 2131 path as unusable and use another path. If it receives Destination 2132 Unreachable messages on many or all paths, the Client should 2133 associate with a new Proxy/Server and release its association with 2134 the old Proxy/Server as specified in Section 3.16.5. 2136 o When an AERO Proxy/Server receives persistent link-layer 2137 Destination Unreachable messages in response to carrier packets 2138 that it sends to one of its neighbor Clients, the Proxy/Server 2139 should mark the underlying path as unusable and use another 2140 underlying path. 2142 o When an AERO Proxy/Server receives link-layer Destination 2143 Unreachable messages in response to a carrier packet that it sends 2144 to one of its permanent neighbors, it treats the messages as an 2145 indication that the path to the neighbor may be failing. However, 2146 the dynamic routing protocol should soon reconverge and correct 2147 the temporary outage. 2149 When an AERO Bridge receives a carrier packet for which the network- 2150 layer destination address is covered by an MSP, the Bridge drops the 2151 packet if there is no more-specific routing information for the 2152 destination and returns a network-layer Destination Unreachable 2153 message subject to rate limiting. The Bridge writes the network- 2154 layer source address of the original IP packet as the destination 2155 address and uses one of its non link-local addresses as the source 2156 address of the message. 2158 When an AERO node receives a carrier packet for which reassembly is 2159 currently congested, it returns a network-layer Packet Too Big (PTB) 2160 message as discussed in [I-D.templin-6man-omni] (note that the PTB 2161 messages could indicate either "hard" or "soft" errors). 2163 AERO nodes that act as OAL destinations include ICMPv6 error messages 2164 intended for the OAL source as sub-options in the OMNI option of 2165 secured uNA messages. When the OAL source receives the uNA message, 2166 it can extract the ICMPv6 error message enclosed in the OMNI option. 2168 3.12. AERO Router Discovery, Prefix Delegation and Autoconfiguration 2170 AERO Router Discovery, Prefix Delegation and Autoconfiguration are 2171 coordinated as discussed in the following Sections. 2173 3.12.1. AERO Service Model 2175 Each AERO Proxy/Server on the OMNI link is configured to facilitate 2176 Client prefix delegation/registration requests. Each Proxy/Server is 2177 provisioned with a database of MNP-to-Client ID mappings for all 2178 Clients enrolled in the AERO service, as well as any information 2179 necessary to authenticate each Client. The Client database is 2180 maintained by a central administrative authority for the OMNI link 2181 and securely distributed to all Proxy/Servers, e.g., via the 2182 Lightweight Directory Access Protocol (LDAP) [RFC4511], via static 2183 configuration, etc. Clients receive the same service regardless of 2184 the Proxy/Servers they select. 2186 AERO Clients and Proxy/Servers use ND messages to maintain neighbor 2187 cache entries. AERO Proxy/Servers configure their OMNI interfaces as 2188 advertising NBMA interfaces, and therefore send unicast RA messages 2189 with a short Router Lifetime value (e.g., ReachableTime seconds) in 2190 response to a Client's RS message. Thereafter, Clients send 2191 additional RS messages to keep Proxy/Server state alive. 2193 AERO Clients and Proxy/Servers include prefix delegation and/or 2194 registration parameters in RS/RA messages (see 2195 [I-D.templin-6man-omni]). The ND messages are exchanged between 2196 Client and Proxy/Server according to the prefix management schedule 2197 required by the service. If the Client knows its MNP in advance, it 2198 can employ prefix registration by including its MNP-LLA as the source 2199 address of an RS message and with an OMNI option with valid prefix 2200 registration information for the MNP. If the Proxy/Server accepts 2201 the Client's MNP assertion, it injects the MNP into the routing 2202 system and establishes the necessary neighbor cache state. If the 2203 Client does not have a pre-assigned MNP, it can instead employ prefix 2204 delegation by including the unspecified address (::) as the source 2205 address of an RS message and with an OMNI option with prefix 2206 delegation parameters to request an MNP. 2208 The following sections specify the Client and Proxy/Server behavior. 2210 3.12.2. AERO Client Behavior 2212 AERO Clients discover the addresses of Proxy/Servers in a similar 2213 manner as described in [RFC5214]. Discovery methods include static 2214 configuration (e.g., from a flat-file map of Proxy/Server addresses 2215 and locations), or through an automated means such as Domain Name 2216 System (DNS) name resolution [RFC1035]. Alternatively, the Client 2217 can discover Proxy/Server addresses through a layer 2 data link login 2218 exchange, or through a unicast RA response to a multicast/anycast RS 2219 as described below. In the absence of other information, the Client 2220 can resolve the DNS Fully-Qualified Domain Name (FQDN) 2221 "linkupnetworks.[domainname]" where "linkupnetworks" is a constant 2222 text string and "[domainname]" is a DNS suffix for the OMNI link 2223 (e.g., "example.com"). 2225 To associate with a Proxy/Server, the Client acts as a requesting 2226 router to request MNPs by preparing an RS message with prefix 2227 management parameters. If the Client already knows the Proxy/ 2228 Server's ADM-LLA, it includes the LLA as the network-layer 2229 destination address; otherwise, the Client includes the (link-local) 2230 All-Routers multicast as the network-layer destination. If the 2231 Client already knows its own MNP-LLA, it can use the MNP-LLA as the 2232 network-layer source address and include an OMNI option with prefix 2233 registration information. Otherwise, the Client uses the unspecified 2234 address (::) as the network-layer source address and includes prefix 2235 delegation parameters in the OMNI option (see: 2236 [I-D.templin-6man-omni]). 2238 The Client next includes Interface Attributes corresponding to the 2239 underlying interface over which it will send the RS message, and MAY 2240 include additional Interface Attributes specific to other underlying 2241 interfaces. Next, the Client submits the RS for OAL encapsulation 2242 and fragmentation if necessary with its own MNP-ULA and the Proxy/ 2243 Server's ADM-ULA as the OAL addresses while selecting an 2244 Identification value and invoking window synchronization as specified 2245 in [I-D.templin-6man-omni]. 2247 The Client then sends the RS (either directly via Direct interfaces, 2248 via a VPN for VPNed interfaces, via an access router for ANET 2249 interfaces or via INET encapsulation for INET interfaces) then waits 2250 up to RetransTimer milliseconds for an RA message reply (see 2251 Section 3.12.3) (retrying up to MAX_RTR_SOLICITATIONS). If the 2252 Client receives no RAs, or if it receives an RA with Router Lifetime 2253 set to 0, the Client SHOULD abandon attempts through the first Proxy/ 2254 Server and try another Proxy/Server. Otherwise, the Client processes 2255 the prefix information found in the RA message. 2257 When the Client processes an RA, it first performs OAL reassembly and 2258 decapsulation if necessary then creates a NCE with the Proxy/Server's 2259 ADM-LLA as the network-layer address and the Proxy/Server's 2260 encapsulation and/or link-layer addresses as the link-layer address. 2261 The Client next records the RA Router Lifetime field value in the NCE 2262 as the time for which the Proxy/Server has committed to maintaining 2263 the MNP in the routing system via this underlying interface, and 2264 caches the other RA configuration information including Cur Hop 2265 Limit, M and O flags, Reachable Time and Retrans Timer. The Client 2266 then autoconfigures MNP-LLAs for any delegated MNPs and assigns them 2267 to the OMNI interface. The Client also caches any MSPs included in 2268 Route Information Options (RIOs) [RFC4191] as MSPs to associate with 2269 the OMNI link, and assigns the MTU value in the MTU option to the 2270 underlying interface. 2272 The Client then registers additional underlying interfaces with the 2273 Proxy/Server by sending RS messages via each additional interface as 2274 described above. The RS messages include the same parameters as for 2275 the initial RS/RA exchange, but with destination address set to the 2276 Proxy/Server's ADM-LLA. The Client finally sub-delegates the MNPs to 2277 its attached EUNs and/or the Client's own internal virtual interfaces 2278 as described in [I-D.templin-v6ops-pdhost] to support the Client's 2279 downstream attached "Internet of Things (IoT)". The Client then 2280 sends additional RS messages over each underlying interface before 2281 the Router Lifetime received for that interface expires. 2283 After the Client registers its underlying interfaces, it may wish to 2284 change one or more registrations, e.g., if an interface changes 2285 address or becomes unavailable, if traffic selectors change, etc. To 2286 do so, the Client prepares an RS message to send over any available 2287 underlying interface as above. The RS includes an OMNI option with 2288 prefix registration/delegation information, with Interface Attributes 2289 specific to the selected underlying interface, and with any 2290 additional Interface Attributes specific to other underlying 2291 interfaces. When the Client receives the Proxy/Server's RA response, 2292 it has assurance that the Proxy/Server has been updated with the new 2293 information. 2295 If the Client wishes to discontinue use of a Proxy/Server it issues 2296 an RS message over any underlying interface with an OMNI option with 2297 a prefix release indication. When the Proxy/Server processes the 2298 message, it releases the MNP, sets the NCE state for the Client to 2299 DEPARTED and returns an RA reply with Router Lifetime set to 0. 2300 After a short delay (e.g., 2 seconds), the Proxy/Server withdraws the 2301 MNP from the routing system. 2303 3.12.3. AERO Proxy/Server Behavior 2305 AERO Proxy/Servers act as IP routers and support a prefix delegation/ 2306 registration service for Clients. Proxy/Servers arrange to add their 2307 ADM-LLAs to a static map of Proxy/Server addresses for the link and/ 2308 or the DNS resource records for the FQDN 2309 "linkupnetworks.[domainname]" before entering service. Proxy/Server 2310 addresses should be geographically and/or topologically referenced, 2311 and made available for discovery by Clients on the OMNI link. 2313 When a Proxy/Server receives a prospective Client's RS message on its 2314 OMNI interface, it SHOULD return an immediate RA reply with Router 2315 Lifetime set to 0 if it is currently too busy or otherwise unable to 2316 service the Client. Otherwise, the Proxy/Server performs OAL 2317 reassembly and decapsulation if necessary, then authenticates the RS 2318 message and processes the prefix delegation/registration parameters. 2319 The Proxy/Server first determines the correct MNPs to provide to the 2320 Client by processing the MNP-LLA prefix parameters and/or the DHCPv6 2321 OMNI sub-option. When the Proxy/Server returns the MNPs, it also 2322 creates a forwarding table entry for the MNP-ULA corresponding to 2323 each MNP so that the MNPs are propagated into the routing system 2324 (see: Section 3.2.3). For IPv6, the Proxy/Server creates an IPv6 2325 forwarding table entry for each MNP. For IPv4, the Proxy/Server 2326 creates an IPv6 forwarding table entry with the IPv4-compatibility 2327 MNP-ULA prefix corresponding to the IPv4 address. 2329 The Proxy/Server next creates a NCE for the Client using the base 2330 MNP-LLA as the network-layer address and with lifetime set to no more 2331 than the smallest prefix lifetime. Next, the Proxy/Server updates 2332 the NCE by recording the information in each Interface Attributes 2333 sub-option in the RS OMNI option. The Proxy/Server also records the 2334 actual OAL/*NET addresses and RS message window synchronization 2335 parameters (if any) in the NCE. 2337 Next, the Proxy/Server prepares an RA message using its ADM-LLA as 2338 the network-layer source address and the network-layer source address 2339 of the RS message as the network-layer destination address. The 2340 Proxy/Server sets the Router Lifetime to the time for which it will 2341 maintain both this underlying interface individually and the NCE as a 2342 whole. The Proxy/Server also sets Cur Hop Limit, M and O flags, 2343 Reachable Time and Retrans Timer to values appropriate for the OMNI 2344 link. The Proxy/Server includes the MNPs, any other prefix 2345 management parameters and an OMNI option with no Interface Attributes 2346 but with an Origin Indication sub-option per [I-D.templin-6man-omni] 2347 with the mapped and obfuscated Port Number and IP address 2348 corresponding to the Client's own INET address in the case of INET 2349 Clients or to the Proxy/Server's INET-facing address for all other 2350 Clients. The Proxy/Server then includes one or more RIOs that encode 2351 the MSPs for the OMNI link, plus an MTU option (see Section 3.9). 2352 The Proxy/Server finally forwards the message to the Client using OAL 2353 encapsulation/fragmentation if necessary while including an 2354 acknowledgement if the RS invoked window synchronization. 2356 After the initial RS/RA exchange, the Proxy/Server maintains a 2357 ReachableTime timer for each of the Client's underlying interfaces 2358 individually (and for the Client's NCE collectively) set to expire 2359 after ReachableTime seconds. If the Client (or Proxy) issues 2360 additional RS messages, the Proxy/Server sends an RA response and 2361 resets ReachableTime. If the Proxy/Server receives an ND message 2362 with a prefix release indication it sets the Client's NCE to the 2363 DEPARTED state and withdraws the MNP from the routing system after a 2364 short delay (e.g., 2 seconds). If ReachableTime expires before a new 2365 RS is received on an individual underlying interface, the Proxy/ 2366 Server marks the interface as DOWN. If ReachableTime expires before 2367 any new RS is received on any individual underlying interface, the 2368 Proxy/Server sets the NCE state to STALE and sets a 10 second timer. 2369 If the Proxy/Server has not received a new RS or ND message with a 2370 prefix release indication before the 10 second timer expires, it 2371 deletes the NCE and withdraws the MNP from the routing system. 2373 The Proxy/Server processes any ND messages pertaining to the Client 2374 and returns an NA/RA reply in response to solicitations. The Proxy/ 2375 Server may also issue unsolicited RA messages, e.g., with reconfigure 2376 parameters to cause the Client to renegotiate its prefix delegation/ 2377 registrations, with Router Lifetime set to 0 if it can no longer 2378 service this Client, etc. Finally, If the NCE is in the DEPARTED 2379 state, the Proxy/Server deletes the entry after DepartTime expires. 2381 Note: Clients SHOULD notify former Proxy/Servers of their departures, 2382 but Proxy/Servers are responsible for expiring neighbor cache entries 2383 and withdrawing routes even if no departure notification is received 2384 (e.g., if the Client leaves the network unexpectedly). Proxy/Servers 2385 SHOULD therefore set Router Lifetime to ReachableTime seconds in 2386 solicited RA messages to minimize persistent stale cache information 2387 in the absence of Client departure notifications. A short Router 2388 Lifetime also ensures that proactive RS/RA messaging between Clients 2389 and Proxy/Servers will keep any NAT state alive (see above). 2391 Note: All Proxy/Servers on an OMNI link MUST advertise consistent 2392 values in the RA Cur Hop Limit, M and O flags, Reachable Time and 2393 Retrans Timer fields the same as for any link, since unpredictable 2394 behavior could result if different Proxy/Servers on the same link 2395 advertised different values. 2397 3.12.3.1. DHCPv6-Based Prefix Registration 2399 When a Client is not pre-provisioned with an MNP-LLA, it will need 2400 for the Proxy/Server to select one or more MNPs on its behalf and set 2401 up the correct state in the AERO routing service. (A Client with a 2402 pre-provisioned MNP may also request the Proxy/Server to select 2403 additional MNPs.) The DHCPv6 service [RFC8415] is used to support 2404 this requirement. 2406 When a Client needs to have the Proxy/Server select MNPs, it sends an 2407 RS message with source address set to the unspecified address (::) 2408 and with an OMNI option that includes a DHCPv6 message sub-option 2409 with DHCPv6 Prefix Delegation (DHCPv6-PD) parameters. When the 2410 Proxy/Server receives the RS message, it extracts the DHCPv6-PD 2411 message from the OMNI option. 2413 The Proxy/Server then acts as a "Proxy DHCPv6 Client" in a message 2414 exchange with the locally-resident DHCPv6 server, which delegates 2415 MNPs and returns a DHCPv6-PD Reply message. (If the Proxy/Server 2416 wishes to defer creation of MN state until the DHCPv6-PD Reply is 2417 received, it can instead act as a Lightweight DHCPv6 Relay Agent per 2418 [RFC6221] by encapsulating the DHCPv6-PD message in a Relay-forward/ 2419 reply exchange with Relay Message and Interface ID options.) 2421 When the Proxy/Server receives the DHCPv6-PD Reply, it adds a route 2422 to the routing system and creates an MNP-LLA based on the delegated 2423 MNP. The Proxy/Server then sends an RA back to the Client with the 2424 (newly-created) MNP-LLA as the destination address and with the 2425 DHCPv6-PD Reply message coded in the OMNI option. When the Client 2426 receives the RA, it creates a default route, assigns the Subnet 2427 Router Anycast address and sets its MNP-LLA based on the delegated 2428 MNP. 2430 Note: See [I-D.templin-6man-omni] for an MNP delegation alternative 2431 that avoids including a DHCPv6 message sub-option in the RS. Namely, 2432 when the Client requests a single MNP it can set the RS source to the 2433 unspecified address (::) and include a Node Identification sub-option 2434 and Preflen in the OMNI option (but with no DHCPv6 message sub- 2435 option). When the Proxy/Server receives the RS message, it forwards 2436 a self-generated DHCPv6 Solicit message to the DHCPv6 server on 2437 behalf of the Client. When the Proxy/Server receives the DHCPv6 2438 Reply, it prepares an RA message with an OMNI option with Preflen 2439 information (but with no DHCPv6 message sub-option), then places the 2440 (newly-created) MNP-LLA in the RA destination address and returns the 2441 message to the Client. 2443 3.13. The AERO Proxy Function 2445 Clients connect to the OMNI link via Proxy/Servers, with one Proxy/ 2446 Server for each underlying interface. Each of the Client's Proxy/ 2447 Servers must be informed of all of the Client's additional underlying 2448 interfaces. For Clients on Direct and VPNed underlying interfaces 2449 the Proxy/Server "A" for that interface is directly connected, for 2450 Clients on ANET underlying interfaces Proxy/Server "A" is located on 2451 the ANET/INET boundary, and for Clients on INET underlying interfaces 2452 Proxy/Server "A" is located somewhere in the connected Internetwork. 2453 When the Client registers with Proxy/Server "A", it must also report 2454 the registration to any other Proxy/Servers for other underlying 2455 interfaces "B", "C", "D", etc. for which an underlying interface 2456 relationship has already been established. The Proxy/Server 2457 satisfies these requirements as follows: 2459 o when Proxy/Server "A" receives an RS message from a new Client, it 2460 first verifies that the OAL Identification is within the window 2461 for the NCE that matches the MNP-ULA for this Client neighbor and 2462 authenticates the message. (If no NCE was found, Proxy/Server "A 2463 instead creates one in the STALE state and returns an RA message 2464 with an authentication signature and any window synchronization 2465 parameters.) Proxy/Server "A" then examines the network-layer 2466 destination address. If the destination address is the ADM-LLA of 2467 a different Proxy/Server "B" (or, if the OMNI option included an 2468 MS-Register sub-option with the ADM-LLAs of one or more different 2469 Proxy/Servers "B", "C", "D", etc.), Proxy/Server "A" prepares a 2470 separate proxyed version of the RS message with an OAL header with 2471 source set to its own ADM-ULA and destination set to Proxy/Server 2472 "B"'s ADM-ULA for each such "B". Proxy/Server "A" also includes 2473 an OMNI header with an Interface Attributes option that includes 2474 its own INET address, a unique UDP Port Number for this Client, 2475 and SRT/LHS information. Proxy/Server "A" then sets the S/ 2476 T-omIndex to the appropriate value for this Client underlying 2477 interface, then forwards the message into the OMNI link secured 2478 spanning tree. (Note: including a unique Port Number allows 2479 Proxy/Server "B" to distinguish different Clients located behind 2480 the same Proxy/Server "A" at the link-layer, whereas the link- 2481 layer addresses would otherwise be indistinguishable.) 2483 o when Proxy/Server "B" receives the RS, it authenticates the 2484 message then creates or updates a NCE for the Client with Proxy/ 2485 Server "A"'s Interface Attributes as the link-layer address 2486 information for this S/T-omIndex and caches any window 2487 synchronization parameters supplied by the Client. Proxy/Server 2488 "B" then prepares an RA message with source set to its own LLA and 2489 destination set to the Client's MNP-LLA, and with any window 2490 synchronization acknowledgements. Proxy/Server "B" then 2491 encapsulates the RA in an OAL header with source set to its own 2492 ADM-ULA and destination set to the ADM-ULA of Proxy/Server "A, 2493 performs fragmentation if necessary, then sends the resulting 2494 carrier packets into the secured spanning tree. 2496 o when Proxy/Server "A" reassembles the RA, it locates the Client 2497 NCE based on the RA destination LLA. Proxy/Server "A" then re- 2498 encapsulates the RA message with OAL source set to its own ADM-ULA 2499 and OAL destination set to the MNP-ULA of the Client, includes an 2500 authentication signature if necessary, fragments if necessary and 2501 returns the fragments to the Client. 2503 o The Client repeats this process with each Proxy/Server "B", "C", 2504 "D" for each of its additional underlying interfaces. When the 2505 Client includes multiple Proxy/Server IDs in the MS-Register 2506 option, it may receive multiple RAs - each with identical window 2507 acknowledgements. The Client can then create an independent NCE 2508 for each responding Proxy/Server and complete the window 2509 synchronization even though all Proxy/Servers received the same 2510 ISS. 2512 After the initial RS/RA exchanges each Proxy/Server forwards any of 2513 the Client's carrier packets with OAL destinations for which there is 2514 no matching NCE to a Bridge using OAL encapsulation with its own ADM- 2515 ULA as the source and the destination determined by the ORH supplied 2516 by the Client. The Proxy/Server instead forwards any carrier packets 2517 destined to a neighbor cache target directly to the target according 2518 to the OAL/link-layer information - the process of establishing 2519 neighbor cache entries is specified in Section 3.14. 2521 While the Client is still associated with each Proxy/Server "A", "A" 2522 can send NS, RS and/or unsolicited NA messages to update the neighbor 2523 cache entries of other AERO nodes on behalf of the Client and/or to 2524 convey Interface Attribute updates. This allows for higher-frequency 2525 Proxy-initiated RS/RA messaging over well-connected INET 2526 infrastructure supplemented by lower-frequency Client-initiated RS/RA 2527 messaging over constrained ANET data links. 2529 If any Proxy/Server "B", "C", "D" ceases to send solicited 2530 advertisements, Proxy/Server "A" sends unsolicited RAs to the Client 2531 with destination set to (link-local) All-Nodes multicast and with 2532 Router Lifetime set to zero to inform Clients that a Proxy/Server has 2533 failed. Although Proxy/Server "A" can engage in ND exchanges on 2534 behalf of the Client, the Client can also send ND messages on its own 2535 behalf, e.g., if it is in a better position than "A" to convey 2536 Interface Attribute changes, etc. The ND messages sent by the Client 2537 include the Client's MNP-LLA as the source in order to differentiate 2538 them from the ND messages sent by Proxy/Server "A". 2540 If the Client becomes unreachable over an underlying interface, 2541 Proxy/Server "A" sets the NCE state to DEPARTED and retains the entry 2542 for DepartTime seconds. While the state is DEPARTED, Proxy/Server 2543 "A" forwards any carrier packets destined to the Client to a Bridge 2544 via OAL/ORH encapsulation. When DepartTime expires, Proxy/Server "A" 2545 deletes the NCE and discards any further carrier packets destined to 2546 the former Client. 2548 In some ANETs that employ a Proxy/Server, the Client's MNP can be 2549 injected into the ANET routing system. In that case, the Client can 2550 send original IP packets without invoking the OAL so that the ANET 2551 routing system transports the original IP packets to the Proxy. This 2552 can be very beneficial, e.g., if the Client connects to the ANET via 2553 low-end data links such as some aviation wireless links. 2555 If the ANET first-hop access router is on the same underlying link as 2556 the Client and recognizes the AERO/OMNI protocol, the Client can 2557 avoid OAL encapsulation for both its control and data messages. When 2558 the Client connects to the link, it can send an unencapsulated RS 2559 message with source address set to its own MNP-LLA (or to a Temporary 2560 LLA), and with destination address set to the ADM-LLA of the Client's 2561 selected Proxy/Server or to (link-local) All-Routers multicast. The 2562 Client includes an OMNI option formatted as specified in 2563 [I-D.templin-6man-omni]. The Client then sends the unencapsulated RS 2564 message, which will be intercepted by the AERO-Aware access router. 2566 The ANET access router then performs OAL encapsulation on the RS 2567 message and forwards it to a Proxy/Server at the ANET/INET boundary. 2568 When the access router and Proxy/Server are one and the same node, 2569 the Proxy/Server would share and underlying link with the Client but 2570 its message exchanges with outside correspondents would need to pass 2571 through a security gateway at the ANET/INET border. The method for 2572 deploying access routers and Proxys (i.e. as a single node or 2573 multiple nodes) is an ANET-local administrative consideration. 2575 Note: The Proxy/Server can apply packing as discussed in 2576 [I-D.templin-6man-omni] if an opportunity arises to concatenate 2577 multiple original IP packets that will be destined to the same 2578 neighbor. 2580 3.13.1. Detecting and Responding to Proxy/Server Failures 2582 In environments where fast recovery from Proxy/Server failure is 2583 required, Proxy/Server "A" SHOULD use proactive Neighbor 2584 Unreachability Detection (NUD) to track peer Proxy/Server "B" 2585 reachability in a similar fashion as for Bidirectional Forwarding 2586 Detection (BFD) [RFC5880]. Proxy/Server "A" can then quickly detect 2587 and react to failures so that cached information is re-established 2588 through alternate paths. The NUD control messaging is carried only 2589 over well-connected ground domain networks (i.e., and not low-end 2590 aeronautical radio links) and can therefore be tuned for rapid 2591 response. 2593 Proxy/Server "A" performs proactive NUD with peer Proxy/Server "B" 2594 for which there are currently active Clients by sending continuous NS 2595 messages in rapid succession, e.g., one message per second. Proxy/ 2596 Server "A" sends the NS message via the spanning tree with its own 2597 ADM-LLA as the source and the ADM-LLA of the peer Proxy/Server "B" as 2598 the destination. When Proxy/Server "A" is also sending RS messages 2599 to the peer Proxy/Server "B" on behalf of ANET Clients, the resulting 2600 RA responses can be considered as equivalent hints of forward 2601 progress. This means that Proxy/Server "B" need not also send a 2602 periodic NS if it has already sent an RS within the same period. If 2603 the peer Proxy/Server "B" fails (i.e., if "A" ceases to receive 2604 advertisements), Proxy/Server "A" can quickly inform Clients by 2605 sending multicast RA messages on the ANET interface. 2607 Proxy/Server "A" sends RA messages on the ANET interface with source 2608 address set to Proxy/Server "B"'s address, destination address set to 2609 (link-local) All-Nodes multicast, and Router Lifetime set to 0. 2610 Proxy/Server "A" SHOULD send MAX_FINAL_RTR_ADVERTISEMENTS RA messages 2611 separated by small delays [RFC4861]. Any Clients on the ANET that 2612 had been using the failed Proxy/Server "B" will receive the RA 2613 messages and associate with a new Proxy/Server. 2615 3.13.2. Point-to-Multipoint Proxy/Server Coordination 2617 In environments where Client messaging over ANETs is bandwidth- 2618 limited and/or expensive, Clients can enlist the services of Proxy/ 2619 Server "A" to coordinate with multiple Proxy/Servers "B", "C", "D" 2620 etc. in a single RS/RA message exchange. The Client can send a 2621 single RS message to (link-local) All-Routers multicast that includes 2622 the ID's of multiple Proxy/Servers in MS-Register sub-options of the 2623 OMNI option. 2625 When Proxy/Server "A" receives the RS and processes the OMNI option, 2626 it sends a separate RS to each MS-Register Proxy/Server ID. When 2627 Proxy/Server "A" receives an RA, it can optionally return an 2628 immediate "singleton" RA to the Client or record the Proxy/Server's 2629 ID for inclusion in a pending "aggregate" RA message. Proxy/Server 2630 "A" can then return aggregate RA messages to the Client including 2631 multiple Proxy/Server IDs in order to conserve bandwidth. Each RA 2632 includes a proper subset of the Proxy/Server IDs from the original RS 2633 message, and Proxy/Server "A" must ensure that the message contents 2634 of each RA are consistent with the information received from the 2635 (aggregated) additional Proxy/Servers. 2637 Clients can thereafter employ efficient point-to-multipoint Proxy/ 2638 Server coordination under the assistance of Proxy/Server "A" to 2639 reduce the number of messages sent over the ANET while enlisting the 2640 support of multiple Proxy/Servers for fault tolerance. Clients can 2641 further include MS-Release sub-options in IPv6 ND messages to request 2642 Proxy/Server "A" to release from former Proxy/Servers via the 2643 procedures discussed in Section 3.16.5. 2645 The OMNI interface specification [I-D.templin-6man-omni] provides 2646 further discussion of the RS/RA messaging involved in point-to- 2647 multipoint coordination. 2649 3.14. AERO Route Optimization 2651 AERO nodes invoke route optimization when they need to forward 2652 packets to new target destinations. Route optimization is based on 2653 IPv6 ND Address Resolution messaging between a Route Optimization 2654 Source (ROS) and Route Optimization Responder (ROR). Route 2655 optimization is initiated by the first eligible ROS closest to the 2656 source as follows: 2658 o For Clients on VPNed and Direct interfaces, the Proxy/Server is 2659 the ROS. 2661 o For Clients on ANET interfaces, either the Client or the Proxy/ 2662 Server may be the ROS. 2664 o For Clients on INET interfaces, the Client itself is the ROS. 2666 o For correspondent nodes on INET/EUN interfaces serviced by a 2667 Relay, the Relay is the ROS. 2669 The route optimization procedure is conducted between the ROS and the 2670 nearest Proxy/Server/Relay for the target selected by routing as the 2671 ROR. In this arrangement, the ROS is always the Client or 2672 Proxy/Server/Relay nearest the source over the selected source 2673 underlying interface, while the ROR is always a Proxy/Server/Relay 2674 that services the target regardless of the target underlying 2675 interface. 2677 The AERO routing system directs a route optimization solicitation 2678 sent by the ROS to the nearest available ROR, which returns a route 2679 optimization reply. The exact ROR selected is unimportant; all that 2680 matters is that the route optimization information returned must be 2681 current and authentic. The ROS is responsible for periodically 2682 refreshing the route optimization, and the ROR is responsible for 2683 quickly informing the ROS of any changes. 2685 The procedures are specified in the following sections. 2687 3.14.1. Route Optimization Initiation 2689 When an original IP packet from a source node destined to a target 2690 node arrives, the ROS checks for a NCE with an MNP-LLA that matches 2691 the target destination. If there is a NCE in the REACHABLE state, 2692 the ROS invokes the OAL and forwards the resulting carrier packets 2693 according to the cached state then returns from processing. 2694 Otherwise, if there is no NCE the ROS creates one in the INCOMPLETE 2695 state. 2697 The ROS next places the original IP packet on a short queue then 2698 sends an NS message for Address Resolution (NS(AR)) to receive a 2699 solicited NA(AR) message from an ROR. The NS(AR) message must be 2700 sent securely, and includes: 2702 o the LLA of the ROS as the source address. 2704 o the MNP-LLA corresponding to the original IP packet's destination 2705 as the Target Address, e.g., for 2001:db8:1:2::10:2000 the Target 2706 Address is fe80::2001:db8:1:2. 2708 o the Solicited-Node multicast address [RFC4291] formed from the 2709 lower 24 bits of the original IP packet's destination as the 2710 destination address, e.g., for 2001:db8:1:2::10:2000 the NS(AR) 2711 destination address is ff02:0:0:0:0:1:ff10:2000. 2713 The NS(AR) message also includes an OMNI option with an Interface 2714 Attributes entry for the sending interface, with S/T-omIndex set to 0 2715 and with Preflen set to the prefix length associated with the NS(AR) 2716 source. The ROS then selects an Identification value submits the 2717 NS(AR) message for OAL encapsulation with OAL source set to its own 2718 ULA and OAL destination set to the ULA corresponding to the target. 2719 (The ROS does not include any window synchronization parameters, 2720 since it will never forward OAL packets directly to the ROR). 2722 The ROS then sends the resulting carrier packet(s) into the secured 2723 spanning tree without decrementing the network-layer TTL/Hop Limit 2724 field. (When the ROS is an INET Client, it instead sends the 2725 resulting carrier packets to the ADM-ULA of one of its current Proxy/ 2726 Servers. The Proxy/Server then reassembles if necessary, verifies 2727 the NS(AR) signature, then re-encapsulates with the OAL source set to 2728 its own ADM-ULA and OAL destination set to the ULA corresponding to 2729 the target. The Proxy/Server then fragments if necessary and sends 2730 the resulting carrier packets into the secured spanning tree on 2731 behalf of the Client.) 2733 3.14.2. Relaying the NS(AR) *NET Packet(s) 2735 When the Bridge receives the carrier packet(s) containing the RS from 2736 the ROS, it discards the *NET headers and determines the next hop by 2737 consulting its standard IPv6 forwarding table for the OAL header 2738 destination address. The Bridge then decrements the OAL header Hop- 2739 Limit, then re-encapsulates and forwards the carrier packet(s) via 2740 the secured spanning tree the same as for any IPv6 router, where it 2741 may traverse multiple OMNI link segments. The final-hop Bridge will 2742 deliver the carrier packet(s) via the secured spanning tree to a 2743 Proxy/Server or Relay that services the target. 2745 3.14.3. Processing the NS(AR) and Sending the NA(AR) 2747 When the target Proxy/Server (or Relay) receives the secured carrier 2748 packet(s), it reassembles if necessary then examines the NS(AR) 2749 target to determine whether it has a matching NCE and/or non-MNP 2750 route. If there is no match, the Proxy/Server drops the message. 2751 Otherwise, the Proxy/Server/Relay continues processing as follows: 2753 o if the NS(AR) target matches a Client NCE in the DEPARTED state, 2754 the Proxy/Server re-encapsulates while setting the OAL source to 2755 the ULA of the ROS and OAL destination address to the ADM-ULA of 2756 the Client's new Proxy/Server. The (old) Proxy/Server then 2757 fragments if necessary and forwards the resulting carrier 2758 packet(s) over the secured spanning tree then returns from 2759 processing. 2761 o If the NS(AR) target matches the MNP-LLA of a Client NCE in the 2762 REACHABLE state, the Proxy/Server makes note of whether the NS 2763 (AR) arrived from the secured or unsecured spanning tree then acts 2764 as an ROR to provide route optimization information on behalf of 2765 the Client. (Note that if the message arrived via the secured 2766 spanning tree the ROR need not perform further authentication, but 2767 if it arrived over an open INET underlying interface it must check 2768 for and verify the message authentication signature before 2769 accepting.) 2771 o If the NS(AR) target matches one of its non-MNP routes, the Relay 2772 acts as both an ROR and a route optimization target, since the 2773 Relay forwards IP packets toward the (fixed network) target at the 2774 network layer. 2776 The ROR next checks the target NCE for a Report List entry that 2777 matches the NS(AR) source LLA/ULA of the ROS. If there is a Report 2778 List entry, the ROR refreshes ReportTime for this ROR; otherwise, the 2779 ROR creates a new entry for the ROS and records both the LLA and ULA. 2781 The ROR then prepares a (solicited) NA(AR) message to return to the 2782 ROS with the source address set to the target's MNP-LLA, the 2783 destination address set to the NS(AR) LLA source address and the 2784 Target Address set to the same value that appeared in the NS(AR). 2785 The ROR then includes an OMNI option with Preflen set to the prefix 2786 length associated with the NA(AR) source address. The ROR next 2787 includes Interface Attributes in the OMNI option for all of the 2788 target's underlying interfaces with current information for each 2789 interface. 2791 For each Interface Attributes sub-option, the ROR sets the L2ADDR 2792 according to the Proxy/Server's INET address for VPNed or Direct 2793 interfaces, to the INET address of the Proxy/Server for proxyed 2794 interfaces or to the Client's INET address for INET interfaces. The 2795 ROR then includes the lower 32 bits of the Proxy/Server's ADM-ULA as 2796 the LHS, encodes the ADM-ULA prefix length code in the SRT field and 2797 sets FMT as specified in Section 3.3. 2799 The ROR then sets the NA(AR) message R flag to 1 (as a router) and S 2800 flag to 1 (as a response to a solicitation) and sets the O flag to 0 2801 (as a proxy) and sets the OMNI header S/T-omIndex to 0. The ROR 2802 finally submits the NA(AR) for OAL encapsulation with source set to 2803 its own ULA and destination set to the same ULA that appeared in the 2804 NS(AR) OAL source, then performs OAL encapsulation and fragmentation 2805 using the same Identification value that appeared in the NS(AR) and 2806 finally forwards the resulting (*NET-encapsulated) carrier packets 2807 via the secured spanning tree without decrementing the network-layer 2808 TTL/Hop Limit field. 2810 3.14.4. Relaying the NA(AR) 2812 When the Bridge receives NA(AR) carrier packets from the ROR, it 2813 discards the *NET header and determines the next hop by consulting 2814 its standard IPv6 forwarding table for the OAL header destination 2815 address. The Bridge then decrements the OAL header Hop-Limit, re- 2816 encapsulates the carrier packet and forwards it via the secured 2817 spanning tree the same as for any IPv6 router, where it may traverse 2818 multiple OMNI link segments. The final-hop Bridge will deliver the 2819 carrier packet via the secured spanning tree to a Proxy/Server for 2820 the ROS. 2822 3.14.5. Processing the NA(AR) 2824 When the ROS receives the NA(AR) message from the ROR, it first 2825 searches for a NCE that matches the NA(AR) LLA source address. The 2826 ROS then processes the message the same as for standard IPv6 Address 2827 Resolution [RFC4861]. In the process, it caches all OMNI option 2828 information in the target NCE (including all Interface Attributes). 2830 When the ROS is a Client, the solicited NA(AR) message will first be 2831 delivered via the secured spanning tree to the Proxy/Server that 2832 forwarded the NS(AR), which reassembles if necessary. The Proxy/ 2833 Server then forwards the message to the Client while re-encapsulating 2834 and re-fragmenting if necessary. If the Client is on an ANET, ANET 2835 physical security and protected spectrum ensures security for the 2836 unmodified NA(AR); if the Client is on the open INET the Proxy/Server 2837 must instead insert an authentication signature. The Proxy/Server 2838 uses its own ADM-ULA as the OAL source and the MNP-ULA of the Client 2839 as the OAL destination. 2841 3.14.6. Forwarding Packets to Route Optimized Targets 2843 After the ROS receives the route optimization NA(AR) and updates the 2844 target NCE, it can begin forwarding packets along the best paths 2845 based on the target's Interface Attributes. The ROS selects target 2846 underlying interfaces according to traffic selectors and/or any other 2847 traffic discriminators, however each underlying interface selected 2848 must first establish window synchronization state if necessary. 2850 To establish window synchronization state, the ROS performs a secured 2851 unicast NS/NA(WIN) exchange with window synchronization parameters 2852 according to Interface Attribute FMTs. The ROS prepares an NS(WIN) 2853 with its own LLA as the source and the MNP-LLA of the target Client 2854 as the destination if FMT-Forward is set; otherwise, it sets the ADM- 2855 LLA of the LHS Proxy/Server as the destination. The ROS then 2856 encapsulates the NS(WIN) in an OAL header with its own ULA as the 2857 source. If the ROS is the Client, it sets the OAL destination to the 2858 ADM-ULA of its Proxy/Server, includes an authentication signature if 2859 necessary, and includes an ORH-1 with Trailer Clear. The Client sets 2860 the ORH Segments Left to 1 and includes valid SRT/LHS information for 2861 the LHS Proxy/Server with L2ADDR set to 0, then forwards the NS(WIN) 2862 to its own Proxy/Server which must reassemble and verify the 2863 authentication signature if necessary. The Proxy/Server then re- 2864 encapsulates, re-fragments and forwards the NS(WIN) carrier packets 2865 into the secured spanning tree with its own ADM-ULA as the OAL source 2866 and the ADM-ULA of the LHS Proxy/Server as the OAL destination while 2867 replacing the ORH-1 with an ORH-0. (If the ROS was the Proxy/Server 2868 itself, it instead includes an ORH-0, and forwards the carrier 2869 packets into the secured spanning tree.) 2871 When an LHS Proxy/Server receives the NS(WIN) it first reassembles if 2872 necessary. If the NS(WIN) destination is its own ADM-LLA, the LHS 2873 Proxy/Server creates an NCE based on the NS(WIN) source LLA, caches 2874 the window synchronization information, and prepares an NA(WIN) while 2875 using its own ADM-LLA as the source and the ROS LLA as the 2876 destination. The LHS Proxy/Server then encapsulates the NA(WIN) in 2877 an OAL header with source set to its own ADM-ULA and destination set 2878 to the NS(WIN) OAL source. The LHS Proxy/Server then fragments if 2879 necessary includes an ORH-0 with omIndex set to the S/T-omIndex value 2880 found in the NS(WIN) OMNI option, then forwards the resulting carrier 2881 packets into the secured spanning tree which will deliver them to the 2882 ROS Proxy/Server. 2884 If the NS(WIN) destination is the MNP-LLA of the target Client, the 2885 LHS Proxy/Server instead includes an authentication signature if 2886 necessary then re-encapsulates using the same OAL source and the MNP- 2887 ULA of the target as the OAL destination while removing the ORH-0. 2888 The LHS Proxy/Server then forwards the NS(WIN) to the target over the 2889 underlying interface identified by the ORH-0 omIndex (or, over any 2890 underlying interface if the omIndex is 0). When the target receives 2891 the NS(WIN), it verifies the authentication signature if necessary 2892 then creates an NCE for the ROS LLA, caches the window 2893 synchronization information and prepares an NA(WIN) to return to the 2894 ROS with its MNP-LLA as the source and the LLA of the ROS as the 2895 destination, and with an authentication signature if necessary. The 2896 target Client then encapsulates the NA(WIN) in an OAL header with its 2897 own MNP-ULA as the source, the ADM-ULA of the LHS Proxy/Server as the 2898 destination, and with an ORH-1 with SRT/LHS information copied from 2899 the ADM-ULA of the ROS Proxy/Server found in the NS(WIN) OAL source 2900 address. The target Client then sets the ORH-1 omIndex to the S/ 2901 T-omIndex value found in the NS(WIN) OMNI option, then forward the 2902 message to the LHS Proxy/Server. 2904 When the LHS Proxy/Server receives the message, it reassembles if 2905 necessary, verifies the authentication signature if necessary then 2906 re-encapsulates using its own ADM-ULA as the source and the ADM-ULA 2907 of the ROS Proxy/Server as the destination The LHS Proxy/Server then 2908 re-fragments and forwards the NS(WIN) carrier packets into the 2909 spanning tree while replacing the ORH-1 with an ORH-0. When the ROS 2910 Proxy/Server receives the NA(WIN), it reassembles if necessary then 2911 updates the target NCE based on the message contents if the Proxy/ 2912 Server itself is the ROS. If the NS(WIN) source was the ADM-LLA of 2913 the LHS Proxy/Server, the ROS must create and maintain a NCE for the 2914 LHS Proxy/Server which it must regard as a companion to the existing 2915 MNP-LLA NCE for the target Client. (The NCE for the LHS Proxy/Server 2916 can also be shared by multiple target Client NCEs if the ROS 2917 communicates with multiple active targets located behind the same LHS 2918 Proxy/Server.) If the ROS is the Client, the Proxy/Server instead 2919 inserts an authentication signature if necessary, removes the ORH-0 2920 then re-encapsulates and re-fragments if necessary while changing the 2921 OAL destination to the MNP-ULA of the ROS Client. The Proxy/Server 2922 then forwards the NA(WIN) to the ROS Client over the underlying 2923 interface identified by the ORH-0 omIndex which then updates its own 2924 NCE based on the target Client MNP-LLA or LHS Proxy/Server ADM-LLA. 2925 The ROS (whether the Proxy/Server or the Client itself) finally 2926 arranges to return an acknowledgement if requested by the NA(WIN). 2928 After window synchronization state has been established, the ROS can 2929 begin forwarding packets while performing additional NS/NA(WIN) 2930 exchanges as above to update window state and/or test reachability. 2931 When the ROS forwards carrier packets, it proceeds as specified in 2932 Section 3.2.7. These forwarding procedures apply to the case where 2933 the selected target interface SRT/LHS codes indicate that the 2934 interface is located in a foreign OMNI link segment. In that case, 2935 the ROS must include ORHs and send the resulting carrier packets into 2936 the spanning tree. 2938 If the SRT/LHS codes indicate that the interface is in the local OMNI 2939 link segment, the ROS can instead forward carrier packets directly to 2940 the LHS Proxy/Server using the L2ADDR for encapsulation, or even to 2941 the target Client itself while invoking NAT traversal if necessary. 2942 When the ROS sends packets directly to the LHS Proxy/Server, it must 2943 still include an ORH-0 so the Proxy/Server can determine the correct 2944 target Client interface for (re)forwarding. If the LHS Proxy/Server 2945 is required to reassemble, the ROS sets the OAL destination to the 2946 ADM-ULA of the LHS Proxy/Server; otherwise, it sets the OAL 2947 destination to the MNP-ULA of the target Client itself. When the ROS 2948 sends packets directly to the target Client, it need not include an 2949 ORH. In both cases, the ROS can also begin applying OAL header 2950 compression as specified in [I-D.templin-6man-omni], since the OAL 2951 header is not examined by any forwarding nodes in the path. 2953 While the ROS continues to actively forward packets to the target 2954 Client, it is responsible for updating window synchronization state 2955 and per-interface reachability before expiration. Window 2956 synchronization state is shared by all underlying interfaces in the 2957 ROS' NCE that use the same destination LLA so that a single NS/ 2958 NA(NUD) exchange applies for all interfaces regardless of the 2959 (single) interface used to conduct the exchange. However, the window 2960 synchronization exchange only confirms target Client reachability 2961 over the specific interface used to conduct the exchange. 2962 Reachability for other underlying interfaces that share the same 2963 window synchronization state must be determined individually using 2964 NS/NA(NUD) messages which need not be secured as long as they use in- 2965 window Identifications and do not update other state information. 2967 3.15. Neighbor Unreachability Detection (NUD) 2969 AERO nodes perform Neighbor Unreachability Detection (NUD) per 2970 [RFC4861] either reactively in response to persistent link-layer 2971 errors (see Section 3.11) or proactively to confirm reachability. 2972 The NUD algorithm is based on periodic control message exchanges and 2973 may further be seeded by ND hints of forward progress, but care must 2974 be taken to avoid inferring reachability based on spoofed 2975 information. For example, IPv6 ND message exchanges that include 2976 authentication codes and/or in-window Identifications may be 2977 considered as acceptable hints of forward progress, while spurious 2978 random carrier packets should be ignored. 2980 AERO nodes can use standard NS/NA(NUD) exchanges sent over the OMNI 2981 link secured spanning tree (i.e. the same as described above for NS/ 2982 NA(WIN)) to test reachability without risk of DoS attacks from nodes 2983 pretending to be a neighbor. These NS/NA(NUD) messages use the 2984 unicast LLAs and ULAs of the parties involved in the NUD test the 2985 same as for standard IPv6 ND over the secured spanning tree. When 2986 only reachability information is required without updating any other 2987 NCE state, unsecured NS/NA(NUD) messages may instead be exchanged 2988 directly between neighbors as long as they include in-window 2989 Identifications. 2991 When an ROR directs an ROS to a target neighbor with one or more 2992 link-layer addresses, the ROS probes each unsecured target underlying 2993 interface either proactively or on-demand of carrier packets directed 2994 to the path by multilink forwarding to maintain the interface's state 2995 as reachable. Probing is performed through NS(NUD) messages over 2996 either the secured or unsecured spanning tree, or through NS(NUD) 2997 messages sent directly to an underlying interface of the target 2998 itself. While testing a target underlying interface, the ROS can 2999 optionally continue to forward carrier packets via alternate 3000 interfaces and/or maintain a small queue of carrier packets until 3001 target reachability is confirmed. 3003 NS(NUD) messages are encapsulated, fragmented and transmitted as 3004 carrier packets the same as for ordinary original IP data packets, 3005 however the encapsulated destinations are the LLA of the ROS and 3006 either the ADM-LLA of the LHS Proxy/Server or the MNP-LLA of the 3007 target itself. The ROS encapsulates the NS(NUD) message the same as 3008 described in Section 3.2.7, however Destination Suffixes (if present) 3009 are set according to the LLA destination (i.e., and not a ULA/GUA 3010 destination). The ROS sets the S/T-omIndex in the NS(NUD) OMNI 3011 header to identify the underlying interface used for forwarding. The 3012 ROS also includes an ORH with SRT/LHS/LLADDR information the same as 3013 for ordinary data packets, but no authentication signatures are 3014 included. The ROS then fragments the OAL packet and forwards the 3015 resulting carrier packets into the unsecured spanning tree or 3016 directly to the target (or LHS Proxy/Server) if it is in the local 3017 segment. 3019 When the target (or LHS Proxy/Server) receives the NS(NUD) carrier 3020 packets, it verifies that it has a NCE for this ROS and that the 3021 Identification is in-window, then submits the carrier packets for 3022 reassembly. The node then searches for Interface Attributes in its 3023 NCE for the ROS that match the NS(NUD) S/T-omIndex and uses the 3024 SRT/LHS/L2ADDR and FMT information to prepare an ORH for the NA(NUD) 3025 reply. The node then prepare the NA(NUD) with the source and 3026 destination LLAs reversed, encapsulates and sets the OAL source and 3027 destination, sets the NA(NUD) S/T-omIndex to the index of the 3028 underlying interface the NS(NUD) arrived on and sets the Target 3029 Address to the same value included in the NS(NUD). The target next 3030 sets the R flag to 1, the S flag to 1 and the O flag to 1, then 3031 selects an in-window Identification for the ROS and performs 3032 fragmentation. The node then forwards the carrier packets into the 3033 unsecured spanning tree, directly to the ROS if it is in the local 3034 segment or directly to a Bridge in the local segment. 3036 When the ROS receives the NA(NUD), it marks the target underlying 3037 interface tested as "reachable". Note that underlying interface 3038 states are maintained independently of the overall NCE REACHABLE 3039 state, and that a single NCE may have multiple target underlying 3040 interfaces in various states "reachable" and otherwise while the NCE 3041 state as a whole remains REACHABLE. 3043 Note also that the exchange of NS/NA(NUD) messages has the useful 3044 side-benefit of opening holes in NATs that may be useful for NAT 3045 traversal. 3047 3.16. Mobility Management and Quality of Service (QoS) 3049 AERO is a Distributed Mobility Management (DMM) service. Each Proxy/ 3050 Server is responsible for only a subset of the Clients on the OMNI 3051 link, as opposed to a Centralized Mobility Management (CMM) service 3052 where there is a single network mobility collective entity for all 3053 Clients. Clients coordinate with their associated Proxy/Servers via 3054 RS/RA exchanges to maintain the DMM profile, and the AERO routing 3055 system tracks all current Client/Proxy/Server peering relationships. 3057 Proxy/Servers provide default routing and mobility/multilink services 3058 for their dependent Clients. Clients are responsible for maintaining 3059 neighbor relationships with their Proxy/Servers through periodic RS/ 3060 RA exchanges, which also serves to confirm neighbor reachability. 3061 When a Client's underlying Interface Attributes change, the Client is 3062 responsible for updating the Proxy/Server with this new information. 3063 Note that when there is a Proxy/Server in the path, the Proxy 3064 function can also perform some RS/RA exchanges on the Client's 3065 behalf. 3067 Mobility management messaging is based on the transmission and 3068 reception of unsolicited Neighbor Advertisement (uNA) messages. Each 3069 uNA message sets the IPv6 source address to the LLA of the ROR and 3070 the destination address to the unicast LLA of the ROS. 3072 Mobility management considerations are specified in the following 3073 sections. 3075 3.16.1. Mobility Update Messaging 3077 RORs accommodate Client mobility and/or multilink change events by 3078 sending secured uNA messages to each ROS in the target Client's 3079 Report List. When an ROR sends a uNA message, it sets the IPv6 3080 source address to the its own LLA, sets the destination address to 3081 the ROS LLA (i.e., an MNP-LLA if the ROS is a Client and an ADM-LLA 3082 if the ROS is a Proxy/Server) and sets the Target Address to the 3083 Client's MNP-LLA. The ROR also includes an OMNI option with Preflen 3084 set to the prefix length associated with the Client's MNP-LLA, with 3085 Interface Attributes for the target Client's underlying interfaces 3086 and with the OMNI header S/T-omIndex set to 0. The ROR then sets the 3087 uNA R flag to 1, S flag to 0 and O flag to 1, then encapsulates the 3088 message in an OAL header with source set to its own ADM-ULA and 3089 destination set to the ROS ULA (i.e., the ADM-ULA of the ROS Proxy/ 3090 Server) and sends the message into the secured spanning tree. 3092 As discussed in Section 7.2.6 of [RFC4861], the transmission and 3093 reception of uNA messages is unreliable but provides a useful 3094 optimization. In well-connected Internetworks with robust data links 3095 uNA messages will be delivered with high probability, but in any case 3096 the Proxy/Server can optionally send up to MAX_NEIGHBOR_ADVERTISEMENT 3097 uNAs to each ROS to increase the likelihood that at least one will be 3098 received. Alternatively, the Proxy/Server can set the PNG flag in 3099 the uNA OMNI option header to request a solicited NA acknowledgement 3100 as specified in [I-D.templin-6man-omni]. 3102 When the ROS Proxy/Server receives a uNA message prepared as above, 3103 it ignores the message if the destination is not its own ADM-ULA or 3104 the MNP-ULA of the Client ROS. In the former case, it uses the 3105 included OMNI option information to update its NCE for the target, 3106 but does not reset ReachableTime since the receipt of an unsolicited 3107 NA message from the ROR does not provide confirmation that any 3108 forward paths to the target Client are working. If the destination 3109 was the MNP-ULA of the ROS Client, the ROS Proxy/Server instead re- 3110 encapsulates with the OAL source set to its own ADM-ULA, OAL 3111 destination set to the MNP-ULA of the ROS Client with an 3112 authentication signature if necessary, and with an in-window 3113 Identification for this Client. Finally, if the uNA message PNG flag 3114 was set, the ROS returns a solicited NA acknowledgement as specified 3115 in [I-D.templin-6man-omni]. 3117 In addition to sending uNA messages to the current set of ROSs for 3118 the target Client, the ROR also sends uNAs to the MNP-ULA associated 3119 with the link-layer address for any underlying interface for which 3120 the link-layer address has changed. These uNA messages update an old 3121 Proxy/Server that cannot easily detect (e.g., without active probing) 3122 when a formerly-active Client has departed. When the ROR sends the 3123 uNA, it sets the IPv6 source address to its LLA, sets the destination 3124 address to the old Proxy/Server's ADM-LLA, and sets the Target 3125 Address to the Client's MNP-LLA. The ROR also includes an OMNI 3126 option with Preflen set to the prefix length associated with the 3127 Client's MNP-LLA, with Interface Attributes for the changed 3128 underlying interface, and with the OMNI header S/T-omIndex set to 0. 3130 The ROR then sets the uNA R flag to 1, S flag to 0 and O flag to 1, 3131 then encapsulates the message in an OAL header with source set to its 3132 own ULA and destination set to the ADM-ULA of the old Proxy/Server 3133 and sends the message into the secured spanning tree. 3135 3.16.2. Announcing Link-Layer Address and/or QoS Preference Changes 3137 When a Client needs to change its underlying Interface Attributes 3138 (e.g., due to a mobility event), the Client requests one of its 3139 Proxy/Servers to send RS messages to all of its other Proxy/Servers 3140 via the secured spanning tree with an OMNI option that includes 3141 Interface attributes with the new link quality and address 3142 information. 3144 Up to MAX_RTR_SOLICITATIONS RS messages MAY be sent in parallel with 3145 sending carrier packets containing user data in case one or more RAs 3146 are lost. If all RAs are lost, the Client SHOULD re-associate with a 3147 new Proxy/Server. 3149 When the Proxy/Server receives the Client's changes, it sends uNA 3150 messages to all nodes in the Report List the same as described in the 3151 previous section. 3153 3.16.3. Bringing New Links Into Service 3155 When a Client needs to bring new underlying interfaces into service 3156 (e.g., when it activates a new data link), it sends an RS message to 3157 the Proxy/Server via the underlying interface with an OMNI option 3158 that includes Interface Attributes with appropriate link quality 3159 values and with link-layer address information for the new link. 3161 3.16.4. Deactivating Existing Links 3163 When a Client needs to deactivate an existing underlying interface, 3164 it sends an RS or uNA message to its Proxy/Server with an OMNI option 3165 with appropriate Interface Attribute values - in particular, the link 3166 quality value 0 assures that neighbors will cease to use the link. 3168 If the Client needs to send RS/uNA messages over an underlying 3169 interface other than the one being deactivated, it MUST include 3170 Interface Attributes with appropriate link quality values for any 3171 underlying interfaces being deactivated. 3173 Note that when a Client deactivates an underlying interface, 3174 neighbors that have received the RS/uNA messages need not purge all 3175 references for the underlying interface from their neighbor cache 3176 entries. The Client may reactivate or reuse the underlying interface 3177 and/or its omIndex at a later point in time, when it will send RS/uNA 3178 messages with fresh Interface Attributes to update any neighbors. 3180 3.16.5. Moving Between Proxy/Servers 3182 The Client performs the procedures specified in Section 3.12.2 when 3183 it first associates with a new Proxy/Server or renews its association 3184 with an existing Proxy/Server. The Client also includes MS-Release 3185 identifiers in the RS message OMNI option per [I-D.templin-6man-omni] 3186 if it wants the new Proxy/Server to notify any old Proxy/Servers from 3187 which the Client is departing. 3189 When the new Proxy/Server receives the Client's RS message, it 3190 returns an RA as specified in Section 3.12.3 and sends uNA messages 3191 to any old Proxy/Servers listed in OMNI option MS-Release 3192 identifiers. When the new Proxy/Server sends a uNA message, it sets 3193 the IPv6 source address to the Client's MNP-LLA, sets the destination 3194 address to the old Proxy/Server's ADM-LLA, and sets the Target 3195 Address to 0. The new Proxy/Server also includes an OMNI option with 3196 Preflen set to the prefix length associated with the Client's MNP- 3197 LLA, with Interface Attributes for its own underlying interface, and 3198 with the OMNI header S/T-omIndex set to 0. The new Proxy/Server then 3199 sets the uNA R flag to 1, S flag to 0 and O flag to 1, then 3200 encapsulates the message in an OAL header with source set to its own 3201 ADM-ULA and destination set to the ADM-ULA of the old Proxy/Server 3202 and sends the message into the secured spanning tree. 3204 When an old Proxy/Server receives the uNA, it notices that the 3205 message appears to have originated from the Client's MNP-LLA but that 3206 the Target Address is 0. The old Proxy/Server then changes the 3207 Client's NCE state to DEPARTED, sets the link-layer address of the 3208 Client to the new Proxy/Server's ADM-ULA, and resets DepartTime. 3209 After a short delay (e.g., 2 seconds) the old Proxy/Server withdraws 3210 the Client's MNP from the routing system. After DepartTime expires, 3211 the old Proxy/Server deletes the Client's NCE. 3213 The old Proxy/Server also iteratively forwards a copy of the uNA 3214 message to each ROS in the Client's Report List by changing the OAL 3215 destination address to the ULA of the ROS while leaving all other 3216 fields of the message unmodified. When the ROS receives the uNA, it 3217 examines the source address to determine the target Client NCE and 3218 verifies that the destination address matches the old Proxy/Server. 3219 The ROS then caches the ULA source address as the new Proxy/Server 3220 for the existing NCE and marks the entry as STALE. While in the 3221 STALE state, the ROS allows new carrier packets to flow according to 3222 any alternate reachable underlying interfaces and sends new NS(WIN) 3223 messages using its own ULA as the OAL source and the ADM-ULA of the 3224 new Proxy/Server as the OAL destination address to elicit NA(WIN) 3225 messages that reset the NCE state to REACHABLE. 3227 Clients SHOULD NOT move rapidly between Proxy/Servers in order to 3228 avoid causing excessive oscillations in the AERO routing system. 3229 Examples of when a Client might wish to change to a different Proxy/ 3230 Server include a Proxy/Server that has gone unreachable, topological 3231 movements of significant distance, movement to a new geographic 3232 region, movement to a new OMNI link segment, etc. 3234 When a Client moves to a new Proxy/Server, some of the carrier 3235 packets of a multiple fragment OAL packet may have already arrived at 3236 the old Proxy/Server while others are en route to the new Proxy/ 3237 Server, however no special attention in the reassembly algorithm is 3238 necessary since all carrier packets will eventually arrive at the 3239 Client which can then reassemble. However, any carrier packets that 3240 are somehow lost can often be recovered through retransmissions. 3242 3.17. Multicast 3244 The AERO Client provides an IGMP (IPv4) [RFC2236] or MLD (IPv6) 3245 [RFC3810] proxy service for its EUNs and/or hosted applications 3246 [RFC4605]. The Client forwards IGMP/MLD messages over any of its 3247 underlying interfaces for which group membership is required. The 3248 IGMP/MLD messages may be further forwarded by a first-hop ANET access 3249 router acting as an IGMP/MLD-snooping switch [RFC4541], then 3250 ultimately delivered to an AERO Proxy/Server acting as a Protocol 3251 Independent Multicast - Sparse-Mode (PIM-SM, or simply "PIM") 3252 Designated Router (DR) [RFC7761]. AERO Relays also act as PIM 3253 routers (i.e., the same as AERO Proxys/Servers) on behalf of nodes on 3254 INET/EUN networks. The behaviors identified in the following 3255 sections correspond to Source-Specific Multicast (SSM) and Any-Source 3256 Multicast (ASM) operational modes. 3258 3.17.1. Source-Specific Multicast (SSM) 3260 When an ROS "X" acting as PIM router receives a Join/Prune message 3261 from a node on its downstream interfaces containing one or more 3262 ((S)ource, (G)roup) pairs, it updates its Multicast Routing 3263 Information Base (MRIB) accordingly. For each S belonging to a 3264 prefix reachable via X's non-OMNI interfaces, X then forwards the (S, 3265 G) Join/Prune to any PIM routers on those interfaces per [RFC7761]. 3267 For each S belonging to a prefix reachable via X's OMNI interface, X 3268 includes a PIM Join/Prune for each (S,G) in the OMNI option of an 3269 NS(AR) message (see: Section 3.14) using its own LLA as the source 3270 address and ALL-PIM-ROUTERS as the destination address. X then 3271 encapsulates the NS(AR) in an OAL header with source address set to 3272 the ULA of X and destination address set to S then forwards the 3273 message into the secured spanning tree, which delivers it to ROR "Y" 3274 that services S. The resulting NA(AR) will return the LLA for the 3275 prefix that matches S as the network-layer source address and with an 3276 OMNI option with the ULA corresponding to any underlying interfaces 3277 that are currently servicing S. 3279 When Y processes the NS(AR) it examines the PIM Join/Prune message. 3280 If S is located behind any INET, Direct, or VPNed interfaces Y acts 3281 as a PIM router and updates its MRIB to list X as the next hop in the 3282 reverse path. If S is located behind any Proxys "Z"*, Y then sends 3283 an NS(NUD) message containing the PIM message to each Z* with 3284 addressing and encapsulation details the same as specified in 3285 Section 3.15. Each Z* then updates its MRIB accordingly and 3286 maintains the LLA of X as the next hop in the reverse path. Since 3287 the Bridges do not examine network layer control messages, this means 3288 that the (reverse) multicast tree path is simply from each Z* (and/or 3289 Y) to X with no other multicast-aware routers in the path. 3291 Following the initial combined Join/Prune and NS/NA messaging, X 3292 maintains a NCE for each S the same as if X was sending unicast data 3293 traffic to S. In particular, X performs additional NS/NA exchanges 3294 to keep the NCE alive for up to t_periodic seconds [RFC7761]. If no 3295 new Joins are received within t_periodic seconds, X allows the NCE to 3296 expire. Finally, if X receives any additional Join/Prune messages 3297 for (S,G) it forwards the messages in NS/NA exchanges with each Y and 3298 Z* in the NCE over the secured spanning tree. 3300 At some later time, Client C that holds an MNP for source S may 3301 depart from a first Proxy/Server Z1 and/or connect via a new Proxy/ 3302 Server Z2. In that case, Y sends a uNA message to X the same as 3303 specified for unicast mobility in Section 3.16. When X receives the 3304 uNA message, it updates its NCE for the LLA for source S and sends 3305 new Join messages to any new Proxys Z2. There is no requirement to 3306 send any Prune messages to old Proxy/Server Z1 since source S will no 3307 longer source any multicast data traffic via Z1. Instead, the 3308 multicast state for (S,G) in Proxy/Server Z1 will soon time out since 3309 no new Joins will arrive. 3311 After some later time, C may move to a new Proxy/Server Y2 and depart 3312 from old Sever Y1. In that case, Y1 sends Join messages for any of 3313 C's active (S,G) groups to Y2 while including its own LLA as the 3314 source address. This causes Y2 to include Y1 in the multicast 3315 forwarding tree during the interim time that Y1's NCE for C is in the 3316 DEPARTED state. At the same time, Y1 sends a uNA message to X with 3317 an OMNI option with S/T-omIndex in the header set to 0 and a release 3318 indication to cause X to release its NCE for S. X then sends a new 3319 Join message to S via the secured spanning tree and re-initiates 3320 route optimization the same as if it were receiving a fresh Join 3321 message from a node on a downstream link. 3323 3.17.2. Any-Source Multicast (ASM) 3325 When an ROS X acting as a PIM router receives a Join/Prune from a 3326 node on its downstream interfaces containing one or more (*,G) pairs, 3327 it updates its Multicast Routing Information Base (MRIB) accordingly. 3328 X then forwards a copy of the message within the OMNI option of an 3329 NS(AR) message to the Rendezvous Point (RP) R for each G over the 3330 secured spanning tree. X uses its own LLA as the source address and 3331 ALL-PIM-ROUTERS as the destination address, then encapsulates the 3332 NS(AR) message in an OAL header with source address set to the ULA of 3333 X and destination address set to R, then sends the message into the 3334 secured spanning tree. 3336 For each source S that sends multicast traffic to group G via R, the 3337 Proxy/Server Z* for the Client that aggregates S encapsulates the 3338 original IP packets in PIM Register messages and forwards them to R 3339 via the secured spanning tree, which may then elect to send a PIM 3340 Join to Z*. This will result in an (S,G) tree rooted at Z* with R as 3341 the next hop so that R will begin to receive two copies of the 3342 original IP packet; one native copy from the (S, G) tree and a second 3343 copy from the pre-existing (*, G) tree that still uses PIM Register 3344 encapsulation. R can then issue a PIM Register-stop message to 3345 suppress the Register-encapsulated stream. At some later time, if C 3346 moves to a new Proxy/Server Z*, it resumes sending original IP 3347 packets via PIM Register encapsulation via the new Z*. 3349 At the same time, as multicast listeners discover individual S's for 3350 a given G, they can initiate an (S,G) Join for each S under the same 3351 procedures discussed in Section 3.17.1. Once the (S,G) tree is 3352 established, the listeners can send (S, G) Prune messages to R so 3353 that multicast original IP packets for group G sourced by S will only 3354 be delivered via the (S, G) tree and not from the (*, G) tree rooted 3355 at R. All mobility considerations discussed for SSM apply. 3357 3.17.3. Bi-Directional PIM (BIDIR-PIM) 3359 Bi-Directional PIM (BIDIR-PIM) [RFC5015] provides an alternate 3360 approach to ASM that treats the Rendezvous Point (RP) as a Designated 3361 Forwarder (DF). Further considerations for BIDIR-PIM are out of 3362 scope. 3364 3.18. Operation over Multiple OMNI Links 3366 An AERO Client can connect to multiple OMNI links the same as for any 3367 data link service. In that case, the Client maintains a distinct 3368 OMNI interface for each link, e.g., 'omni0' for the first link, 3369 'omni1' for the second, 'omni2' for the third, etc. Each OMNI link 3370 would include its own distinct set of Bridges and Proxy/Servers, 3371 thereby providing redundancy in case of failures. 3373 Each OMNI link could utilize the same or different ANET connections. 3374 The links can be distinguished at the link-layer via the SRT prefix 3375 in a similar fashion as for Virtual Local Area Network (VLAN) tagging 3376 (e.g., IEEE 802.1Q) and/or through assignment of distinct sets of 3377 MSPs on each link. This gives rise to the opportunity for supporting 3378 multiple redundant networked paths, with each VLAN distinguished by a 3379 different SRT "color" (see: Section 3.2.5). 3381 The Client's IP layer can select the outgoing OMNI interface 3382 appropriate for a given traffic profile while (in the reverse 3383 direction) correspondent nodes must have some way of steering their 3384 original IP packets destined to a target via the correct OMNI link. 3386 In a first alternative, if each OMNI link services different MSPs, 3387 then the Client can receive a distinct MNP from each of the links. 3388 IP routing will therefore assure that the correct OMNI link is used 3389 for both outbound and inbound traffic. This can be accomplished 3390 using existing technologies and approaches, and without requiring any 3391 special supporting code in correspondent nodes or Bridges. 3393 In a second alternative, if each OMNI link services the same MSP(s) 3394 then each link could assign a distinct "OMNI link Anycast" address 3395 that is configured by all Bridges on the link. Correspondent nodes 3396 can then perform Segment Routing to select the correct SRT, which 3397 will then direct the original IP packet over multiple hops to the 3398 target. 3400 3.19. DNS Considerations 3402 AERO Client MNs and INET correspondent nodes consult the Domain Name 3403 System (DNS) the same as for any Internetworking node. When 3404 correspondent nodes and Client MNs use different IP protocol versions 3405 (e.g., IPv4 correspondents and IPv6 MNs), the INET DNS must maintain 3406 A records for IPv4 address mappings to MNs which must then be 3407 populated in Relay NAT64 mapping caches. In that way, an IPv4 3408 correspondent node can send original IPv4 packets to the IPv4 address 3409 mapping of the target MN, and the Relay will translate the IPv4 3410 header and destination address into an IPv6 header and IPv6 3411 destination address of the MN. 3413 When an AERO Client registers with an AERO Proxy/Server, the Proxy/ 3414 Server can return the address(es) of DNS servers in RDNSS options 3415 [RFC6106]. The DNS server provides the IP addresses of other MNs and 3416 correspondent nodes in AAAA records for IPv6 or A records for IPv4. 3418 3.20. Transition/Coexistence Considerations 3420 OAL encapsulation ensures that dissimilar INET partitions can be 3421 joined into a single unified OMNI link, even though the partitions 3422 themselves may have differing protocol versions and/or incompatible 3423 addressing plans. However, a commonality can be achieved by 3424 incrementally distributing globally routable (i.e., native) IP 3425 prefixes to eventually reach all nodes (both mobile and fixed) in all 3426 OMNI link segments. This can be accomplished by incrementally 3427 deploying AERO Bridges on each INET partition, with each Bridge 3428 distributing its MNPs and/or discovering non-MNP IP GUA prefixes on 3429 its INET links. 3431 This gives rise to the opportunity to eventually distribute native IP 3432 addresses to all nodes, and to present a unified OMNI link view even 3433 if the INET partitions remain in their current protocol and 3434 addressing plans. In that way, the OMNI link can serve the dual 3435 purpose of providing a mobility/multilink service and a transition/ 3436 coexistence service. Or, if an INET partition is transitioned to a 3437 native IP protocol version and addressing scheme that is compatible 3438 with the OMNI link MNP-based addressing scheme, the partition and 3439 OMNI link can be joined by Bridges. 3441 Relays that connect INETs/EUNs with dissimilar IP protocol versions 3442 may need to employ a network address and protocol translation 3443 function such as NAT64 [RFC6146]. 3445 3.21. Detecting and Reacting to Proxy/Server and Bridge Failures 3447 In environments where rapid failure recovery is required, Proxy/ 3448 Servers and Bridges SHOULD use Bidirectional Forwarding Detection 3449 (BFD) [RFC5880]. Nodes that use BFD can quickly detect and react to 3450 failures so that cached information is re-established through 3451 alternate nodes. BFD control messaging is carried only over well- 3452 connected ground domain networks (i.e., and not low-end radio links) 3453 and can therefore be tuned for rapid response. 3455 Proxy/Servers and Bridges maintain BFD sessions in parallel with 3456 their BGP peerings. If a Proxy/Server or Bridge fails, BGP peers 3457 will quickly re-establish routes through alternate paths the same as 3458 for common BGP deployments. Similarly, Proxys maintain BFD sessions 3459 with their associated Bridges even though they do not establish BGP 3460 peerings with them. 3462 3.22. AERO Clients on the Open Internet 3464 AERO Clients that connect to the open Internet via INET interfaces 3465 can establish a VPN or direct link to securely connect to a Proxy/ 3466 Server in a "tethered" arrangement with all of the Client's traffic 3467 transiting the Proxy/Server which acts as a router. Alternatively, 3468 the Client can associate with an INET Proxy/Server using UDP/IP 3469 encapsulation and control message securing services as discussed in 3470 the following sections. 3472 When a Client's OMNI interface enables an INET underlying interface, 3473 it first determines whether the interface is likely to be behind a 3474 NAT. For IPv4, the Client assumes it is on the open Internet if the 3475 INET address is not a special-use IPv4 address per [RFC3330]. 3476 Similarly for IPv6, the Client assumes it is on the open Internet if 3477 the INET address is a Global Unicast Address (GUA) [RFC4291]. 3478 Otherwise, the Client assumes it may be behind one or several NATs. 3480 The Client then prepares an RS message with IPv6 source address set 3481 to its MNP-LLA, with IPv6 destination set to (link-local) All-Routers 3482 multicast and with an OMNI option with underlying interface 3483 attributes. If the Client believes that it is on the open Internet, 3484 it SHOULD include an L2ADDR in the Interface Attributes sub-option 3485 corresponding to the underlying interface; otherwise, it MAY set 3486 L2ADDR to 0. If the underlying address is IPv4, the Client includes 3487 the Port Number and IPv4 address written in obfuscated form [RFC4380] 3488 as discussed in Section 3.3. If the underlying interface address is 3489 IPv6, the Client instead includes the Port Number and IPv6 address in 3490 obfuscated form. The Client finally includes an authentication 3491 signature sub-option in the OMNI option [I-D.templin-6man-omni] to 3492 provide message authentication, selects an Identification value and 3493 window synchronization parameters, and submits the RS for OAL 3494 encapsulation. The Client then encapsulates the OAL fragment in UDP/ 3495 IP headers to form a carrier packet, sets the UDP/IP source to its 3496 INET address and UDP port, sets the UDP/IP destination to the Proxy/ 3497 Server's INET address and the AERO service port number (8060), then 3498 sends the carrier packet to the Proxy/Server. 3500 When the Proxy/Server receives the RS, it discards the OAL 3501 encapsulation, authenticates the RS message, creates a NCE and 3502 registers the Client's MNP, window synchronization state and INET 3503 interface information according to the OMNI option parameters. If 3504 the RS message OMNI option includes Interface Attributes with an 3505 L2ADDR, the Proxy/Server compares the encapsulation IP address and 3506 UDP port number with the (unobfuscated) values. If the values are 3507 the same, the Proxy/Server caches the Client's information as "INET" 3508 addresses meaning that the Client is likely to accept direct messages 3509 without requiring NAT traversal exchanges. If the values are 3510 different (or, if the OMNI option did not include an L2ADDR) the 3511 Proxy/Server instead caches the Client's information as "mapped" 3512 addresses meaning that NAT traversal exchanges may be necessary. 3514 The Proxy/Server then prepares an RA message with IPv6 source and 3515 destination set corresponding to the addresses in the RS, and with an 3516 OMNI option with an Origin Indication sub-option per 3517 [I-D.templin-6man-omni] with the mapped and obfuscated Port Number 3518 and IP address observed in the encapsulation headers. The Proxy/ 3519 Server also includes an authentication signature sub-option per 3520 [I-D.templin-6man-omni] and a symmetric window synchronization/ 3521 acknowledgement. The Proxy/Server then performs OAL encapsulation 3522 and fragmentation if necessary and encapsulates each fragment in UDP/ 3523 IP headers with addresses set per the L2ADDR information in the NCE 3524 for the Client. 3526 When the Client receives the RA, it authenticates the message then 3527 process the window synchronization/acknowledgement and compares the 3528 mapped Port Number and IP address from the Origin Indication sub- 3529 option with its own address. If the addresses are the same, the 3530 Client assumes the open Internet / Cone NAT principle; if the 3531 addresses are different, the Client instead assumes that further 3532 qualification procedures are necessary to detect the type of NAT and 3533 proceeds according to standard procedures [RFC6081][RFC4380]. The 3534 Client finally arranges to return an explicit/implicit 3535 acknowledgement, and sends periodic RS messages to receive fresh RA 3536 messages before the Router Lifetime received on each INET interface 3537 expires. 3539 When the Client sends messages to target IP addresses, it also 3540 invokes route optimization per Section 3.14. For route optimized 3541 targets in the same OMNI link segment, if the target's L2ADDR is on 3542 the open INET, the Client forwards carrier packets directly to the 3543 target INET address. If the target is behind a NAT, the Client first 3544 establishes NAT state for the L2ADDR using the "direct bubble" and 3545 NUD mechanisms discussed in Section 3.10.1. The Client continues to 3546 send carrier packets via its Proxy/Server until NAT state is 3547 populated, then begins forwarding carrier packets via the direct path 3548 through the NAT to the target. For targets in different OMNI link 3549 segments, the Client uses OAL/ORH encapsulation and forwards carrier 3550 packets to the Bridge that returned the NA(AR) message. 3552 The Client can send original IP packets to route-optimized neighbors 3553 in the same OMNI link segment no larger than the minimum/path MPS in 3554 one piece and with OAL encapsulation as atomic fragments. For larger 3555 original IP packets, the Client applies OAL encapsulation and 3556 fragmentation if necessary according to Section 3.9, with OAL header 3557 with source set to its own MNP-ULA and destination set to the MNP-ULA 3558 of the target, and with an in-window Identification value. The 3559 Client then encapsulates each resulting carrier packet in UDP/IP *NET 3560 headers and sends them to the next hop. 3562 Note: The NAT traversal procedures specified in this document are 3563 applicable for Cone, Address-Restricted and Port-Restricted NATs 3564 only. While future updates to this document may specify procedures 3565 for other NAT variations (e.g., hairpinning and various forms of 3566 Symmetric NATs), it should be noted that continuous communications 3567 are always possible through forwarding via a Proxy/Server even if NAT 3568 traversal is not employed. 3570 3.23. Time-Varying MNPs 3572 In some use cases, it is desirable, beneficial and efficient for the 3573 Client to receive a constant MNP that travels with the Client 3574 wherever it moves. For example, this would allow air traffic 3575 controllers to easily track aircraft, etc. In other cases, however 3576 (e.g., intelligent transportation systems), the MN may be willing to 3577 sacrifice a modicum of efficiency in order to have time-varying MNPs 3578 that can be changed every so often to defeat adversarial tracking. 3580 The DHCPv6 service offers a way for Clients that desire time-varying 3581 MNPs to obtain short-lived prefixes (e.g., on the order of a small 3582 number of minutes). In that case, the identity of the Client would 3583 not be bound to the MNP but rather to a Node Identification value 3584 (see: [I-D.templin-6man-omni]) to be used as the Client ID seed for 3585 MNP prefix delegation. The Client would then be obligated to 3586 renumber its internal networks whenever its MNP (and therefore also 3587 its MNP-LLA) changes. This should not present a challenge for 3588 Clients with automated network renumbering services, however presents 3589 limits for the durations of ongoing sessions that would prefer to use 3590 a constant address. 3592 4. Implementation Status 3594 An early AERO implementation based on OpenVPN (https://openvpn.net/) 3595 was announced on the v6ops mailing list on January 10, 2018 and an 3596 initial public release of the AERO proof-of-concept source code was 3597 announced on the intarea mailing list on August 21, 2015. 3599 AERO Release-3.2 was tagged on March 30, 2021, and is undergoing 3600 internal testing. Additional internal releases expected within the 3601 coming months, with first public release expected end of 1H2021. 3603 5. IANA Considerations 3605 The IANA is instructed to assign a new type value TBD1 in the IPv6 3606 Routing Types registry (IANA registration procedure is IETF Review or 3607 IESG Approval). 3609 The IANA has assigned the UDP port number "8060" for an earlier 3610 experimental first version of AERO [RFC6706]. This document 3611 obsoletes [RFC6706], and together with [I-D.templin-6man-omni] 3612 reclaims the UDP port number "8060" for 'aero' as the service port 3613 for UDP/IP encapsulation. (Note that, although [RFC6706] was not 3614 widely implemented or deployed, any messages coded to that 3615 specification can be easily distinguished and ignored since they use 3616 the invalid ICMPv6 message type number '0'.) This document makes no 3617 request of IANA, since [I-D.templin-6man-omni] already provides 3618 instructions. 3620 No further IANA actions are required. 3622 6. Security Considerations 3624 AERO Bridges configure secured tunnels with AERO Proxy/Servers and 3625 Relays within their local OMNI link segments. Applicable secured 3626 tunnel alternatives include IPsec [RFC4301], TLS/SSL [RFC8446], DTLS 3627 [RFC6347], WireGuard [WG], etc. The AERO Bridges of all OMNI link 3628 segments in turn configure secured tunnels for their neighboring AERO 3629 Bridges in a secured spanning tree topology. Therefore, control 3630 messages exchanged between any pair of OMNI link neighbors over the 3631 secured spanning tree are already protected. 3633 AERO nodes acting as Route Optimization Responders (RORs) may also 3634 receive packets directly from arbitrary nodes in INET partitions 3635 instead of via the secured spanning tree. For INET partitions that 3636 apply effective ingress filtering to defeat source address spoofing, 3637 the simple data origin authentication procedures in Section 3.8 can 3638 be applied. 3640 For INET partitions that require strong security in the data plane, 3641 two options for securing communications include 1) disable route 3642 optimization so that all traffic is conveyed over secured tunnels, or 3643 2) enable on-demand secure tunnel creation between Client neighbors. 3644 Option 1) would result in longer routes than necessary and impose 3645 traffic concentration on critical infrastructure elements. Option 2) 3646 could be coordinated between Clients using NS/NA messages with OMNI 3647 Host Identity Protocol (HIP) "Initiator/Responder" message sub- 3648 options [RFC7401][I-D.templin-6man-omni] to create a secured tunnel 3649 on-demand. 3651 AERO Clients that connect to secured ANETs need not apply security to 3652 their ND messages, since the messages will be intercepted by a 3653 perimeter Proxy/Server that applies security on its INET-facing 3654 interface as part of the spanning tree (see above). AERO Clients 3655 connected to the open INET can use network and/or transport layer 3656 security services such as VPNs or can by some other means establish a 3657 direct link to a Proxy/Server. When a VPN or direct link may be 3658 impractical, however, INET Clients and Proxy/Servers SHOULD include 3659 and verify authentication signatures for their IPv6 ND messages as 3660 specified in [I-D.templin-6man-omni]. 3662 Application endpoints SHOULD use transport-layer (or higher-layer) 3663 security services such as TLS/SSL, DTLS or SSH [RFC4251] to assure 3664 the same level of protection as for critical secured Internet 3665 services. AERO Clients that require host-based VPN services SHOULD 3666 use network and/or transport layer security services such as IPsec, 3667 TLS/SSL, DTLS, etc. AERO Proxys and Proxy/Servers can also provide a 3668 network-based VPN service on behalf of the Client, e.g., if the 3669 Client is located within a secured enclave and cannot establish a VPN 3670 on its own behalf. 3672 AERO Proxy/Servers and Bridges present targets for traffic 3673 amplification Denial of Service (DoS) attacks. This concern is no 3674 different than for widely-deployed VPN security gateways in the 3675 Internet, where attackers could send spoofed packets to the gateways 3676 at high data rates. This can be mitigated through the AERO/OMNI data 3677 origin authentication procedures, as well as connecting Proxy/Servers 3678 and Bridges over dedicated links with no connections to the Internet 3679 and/or when connections to the Internet are only permitted through 3680 well-managed firewalls. Traffic amplification DoS attacks can also 3681 target an AERO Client's low data rate links. This is a concern not 3682 only for Clients located on the open Internet but also for Clients in 3683 secured enclaves. AERO Proxy/Servers and Proxys can institute rate 3684 limits that protect Clients from receiving packet floods that could 3685 DoS low data rate links. 3687 AERO Relays must implement ingress filtering to avoid a spoofing 3688 attack in which spurious messages with ULA addresses are injected 3689 into an OMNI link from an outside attacker. AERO Clients MUST ensure 3690 that their connectivity is not used by unauthorized nodes on their 3691 EUNs to gain access to a protected network, i.e., AERO Clients that 3692 act as routers MUST NOT provide routing services for unauthorized 3693 nodes. (This concern is no different than for ordinary hosts that 3694 receive an IP address delegation but then "share" the address with 3695 other nodes via some form of Internet connection sharing such as 3696 tethering.) 3697 The MAP list MUST be well-managed and secured from unauthorized 3698 tampering, even though the list contains only public information. 3699 The MAP list can be conveyed to the Client in a similar fashion as in 3700 [RFC5214] (e.g., through layer 2 data link login messaging, secure 3701 upload of a static file, DNS lookups, etc.). 3703 The AERO service for open INET Clients depends on a public key 3704 distribution service in which Client public keys and identities are 3705 maintained in a shared database accessible to all open INET Proxy/ 3706 Servers. Similarly, each Client must be able to determine the public 3707 key of each Proxy/Server, e.g. by consulting an online database. 3708 When AERO nodes register their public keys indexed by a unique Host 3709 Identity Tag (HIT) [RFC7401] in a distributed database such as the 3710 DNS, and use the HIT as an identity for applying IPv6 ND message 3711 authentication signatures, a means for determining public key 3712 attestation is available. 3714 Security considerations for IPv6 fragmentation and reassembly are 3715 discussed in [I-D.templin-6man-omni]. In environments where spoofing 3716 is considered a threat, OMNI nodes SHOULD employ Identification 3717 window synchronization and OAL destinations SHOULD configure an (end- 3718 system-based) firewall. 3720 SRH authentication facilities are specified in [RFC8754]. Security 3721 considerations for accepting link-layer ICMP messages and reflected 3722 packets are discussed throughout the document. 3724 7. Acknowledgements 3726 Discussions in the IETF, aviation standards communities and private 3727 exchanges helped shape some of the concepts in this work. 3728 Individuals who contributed insights include Mikael Abrahamsson, Mark 3729 Andrews, Fred Baker, Bob Braden, Stewart Bryant, Brian Carpenter, 3730 Wojciech Dec, Pavel Drasil, Ralph Droms, Adrian Farrel, Nick Green, 3731 Sri Gundavelli, Brian Haberman, Bernhard Haindl, Joel Halpern, Tom 3732 Herbert, Sascha Hlusiak, Lee Howard, Zdenek Jaron, Andre Kostur, 3733 Hubert Kuenig, Ted Lemon, Andy Malis, Satoru Matsushima, Tomek 3734 Mrugalski, Madhu Niraula, Alexandru Petrescu, Behcet Saikaya, Michal 3735 Skorepa, Joe Touch, Bernie Volz, Ryuji Wakikawa, Tony Whyman, Lloyd 3736 Wood and James Woodyatt. Members of the IESG also provided valuable 3737 input during their review process that greatly improved the document. 3738 Special thanks go to Stewart Bryant, Joel Halpern and Brian Haberman 3739 for their shepherding guidance during the publication of the AERO 3740 first edition. 3742 This work has further been encouraged and supported by Boeing 3743 colleagues including Kyle Bae, M. Wayne Benson, Dave Bernhardt, Cam 3744 Brodie, John Bush, Balaguruna Chidambaram, Irene Chin, Bruce Cornish, 3745 Claudiu Danilov, Don Dillenburg, Joe Dudkowski, Wen Fang, Samad 3746 Farooqui, Anthony Gregory, Jeff Holland, Seth Jahne, Brian Jaury, 3747 Greg Kimberly, Ed King, Madhuri Madhava Badgandi, Laurel Matthew, 3748 Gene MacLean III, Kyle Mikos, Rob Muszkiewicz, Sean O'Sullivan, Vijay 3749 Rajagopalan, Greg Saccone, Rod Santiago, Kent Shuey, Brian Skeen, 3750 Mike Slane, Carrie Spiker, Katie Tran, Brendan Williams, Amelia 3751 Wilson, Julie Wulff, Yueli Yang, Eric Yeh and other members of the 3752 Boeing mobility, networking and autonomy teams. Kyle Bae, Wayne 3753 Benson, Madhuri Madhava Badgandi, Vijayasarathy Rajagopalan, Katie 3754 Tran and Eric Yeh are especially acknowledged for implementing the 3755 AERO functions as extensions to the public domain OpenVPN 3756 distribution. Chuck Klabunde is honored and remembered for his early 3757 leadership, and we mourn his untimely loss. 3759 Earlier works on NBMA tunneling approaches are found in 3760 [RFC2529][RFC5214][RFC5569]. 3762 Many of the constructs presented in this second edition of AERO are 3763 based on the author's earlier works, including: 3765 o The Internet Routing Overlay Network (IRON) 3766 [RFC6179][I-D.templin-ironbis] 3768 o Virtual Enterprise Traversal (VET) 3769 [RFC5558][I-D.templin-intarea-vet] 3771 o The Subnetwork Encapsulation and Adaptation Layer (SEAL) 3772 [RFC5320][I-D.templin-intarea-seal] 3774 o AERO, First Edition [RFC6706] 3776 Note that these works cite numerous earlier efforts that are not also 3777 cited here due to space limitations. The authors of those earlier 3778 works are acknowledged for their insights. 3780 This work is aligned with the NASA Safe Autonomous Systems Operation 3781 (SASO) program under NASA contract number NNA16BD84C. 3783 This work is aligned with the FAA as per the SE2025 contract number 3784 DTFAWA-15-D-00030. 3786 This work is aligned with the Boeing Commercial Airplanes (BCA) 3787 Internet of Things (IoT) and autonomy programs. 3789 This work is aligned with the Boeing Information Technology (BIT) 3790 MobileNet program. 3792 8. References 3794 8.1. Normative References 3796 [I-D.templin-6man-omni] 3797 Templin, F. L. and T. Whyman, "Transmission of IP Packets 3798 over Overlay Multilink Network (OMNI) Interfaces", draft- 3799 templin-6man-omni-03 (work in progress), April 2021. 3801 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, 3802 DOI 10.17487/RFC0791, September 1981, 3803 . 3805 [RFC0792] Postel, J., "Internet Control Message Protocol", STD 5, 3806 RFC 792, DOI 10.17487/RFC0792, September 1981, 3807 . 3809 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 3810 Requirement Levels", BCP 14, RFC 2119, 3811 DOI 10.17487/RFC2119, March 1997, 3812 . 3814 [RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in 3815 IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473, 3816 December 1998, . 3818 [RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander, 3819 "SEcure Neighbor Discovery (SEND)", RFC 3971, 3820 DOI 10.17487/RFC3971, March 2005, 3821 . 3823 [RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)", 3824 RFC 3972, DOI 10.17487/RFC3972, March 2005, 3825 . 3827 [RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and 3828 More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191, 3829 November 2005, . 3831 [RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast 3832 Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005, 3833 . 3835 [RFC4380] Huitema, C., "Teredo: Tunneling IPv6 over UDP through 3836 Network Address Translations (NATs)", RFC 4380, 3837 DOI 10.17487/RFC4380, February 2006, 3838 . 3840 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 3841 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 3842 DOI 10.17487/RFC4861, September 2007, 3843 . 3845 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 3846 Address Autoconfiguration", RFC 4862, 3847 DOI 10.17487/RFC4862, September 2007, 3848 . 3850 [RFC6081] Thaler, D., "Teredo Extensions", RFC 6081, 3851 DOI 10.17487/RFC6081, January 2011, 3852 . 3854 [RFC7401] Moskowitz, R., Ed., Heer, T., Jokela, P., and T. 3855 Henderson, "Host Identity Protocol Version 2 (HIPv2)", 3856 RFC 7401, DOI 10.17487/RFC7401, April 2015, 3857 . 3859 [RFC7739] Gont, F., "Security Implications of Predictable Fragment 3860 Identification Values", RFC 7739, DOI 10.17487/RFC7739, 3861 February 2016, . 3863 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 3864 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 3865 May 2017, . 3867 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 3868 (IPv6) Specification", STD 86, RFC 8200, 3869 DOI 10.17487/RFC8200, July 2017, 3870 . 3872 [RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A., 3873 Richardson, M., Jiang, S., Lemon, T., and T. Winters, 3874 "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", 3875 RFC 8415, DOI 10.17487/RFC8415, November 2018, 3876 . 3878 8.2. Informative References 3880 [BGP] Huston, G., "BGP in 2015, http://potaroo.net", January 3881 2016. 3883 [I-D.bonica-6man-comp-rtg-hdr] 3884 Bonica, R., Kamite, Y., Alston, A., Henriques, D., and L. 3885 Jalil, "The IPv6 Compact Routing Header (CRH)", draft- 3886 bonica-6man-comp-rtg-hdr-24 (work in progress), January 3887 2021. 3889 [I-D.bonica-6man-crh-helper-opt] 3890 Li, X., Bao, C., Ruan, E., and R. Bonica, "Compressed 3891 Routing Header (CRH) Helper Option", draft-bonica-6man- 3892 crh-helper-opt-03 (work in progress), April 2021. 3894 [I-D.ietf-intarea-frag-fragile] 3895 Bonica, R., Baker, F., Huston, G., Hinden, R. M., Troan, 3896 O., and F. Gont, "IP Fragmentation Considered Fragile", 3897 draft-ietf-intarea-frag-fragile-17 (work in progress), 3898 September 2019. 3900 [I-D.ietf-intarea-tunnels] 3901 Touch, J. and M. Townsley, "IP Tunnels in the Internet 3902 Architecture", draft-ietf-intarea-tunnels-10 (work in 3903 progress), September 2019. 3905 [I-D.ietf-ipwave-vehicular-networking] 3906 (editor), J. (. J., "IPv6 Wireless Access in Vehicular 3907 Environments (IPWAVE): Problem Statement and Use Cases", 3908 draft-ietf-ipwave-vehicular-networking-20 (work in 3909 progress), March 2021. 3911 [I-D.ietf-rtgwg-atn-bgp] 3912 Templin, F. L., Saccone, G., Dawra, G., Lindem, A., and V. 3913 Moreno, "A Simple BGP-based Mobile Routing System for the 3914 Aeronautical Telecommunications Network", draft-ietf- 3915 rtgwg-atn-bgp-10 (work in progress), January 2021. 3917 [I-D.templin-6man-dhcpv6-ndopt] 3918 Templin, F. L., "A Unified Stateful/Stateless 3919 Configuration Service for IPv6", draft-templin-6man- 3920 dhcpv6-ndopt-11 (work in progress), January 2021. 3922 [I-D.templin-intarea-seal] 3923 Templin, F. L., "The Subnetwork Encapsulation and 3924 Adaptation Layer (SEAL)", draft-templin-intarea-seal-68 3925 (work in progress), January 2014. 3927 [I-D.templin-intarea-vet] 3928 Templin, F. L., "Virtual Enterprise Traversal (VET)", 3929 draft-templin-intarea-vet-40 (work in progress), May 2013. 3931 [I-D.templin-ipwave-uam-its] 3932 Templin, F. L., "Urban Air Mobility Implications for 3933 Intelligent Transportation Systems", draft-templin-ipwave- 3934 uam-its-04 (work in progress), January 2021. 3936 [I-D.templin-ironbis] 3937 Templin, F. L., "The Interior Routing Overlay Network 3938 (IRON)", draft-templin-ironbis-16 (work in progress), 3939 March 2014. 3941 [I-D.templin-v6ops-pdhost] 3942 Templin, F. L., "IPv6 Prefix Delegation and Multi- 3943 Addressing Models", draft-templin-v6ops-pdhost-27 (work in 3944 progress), January 2021. 3946 [OVPN] OpenVPN, O., "http://openvpn.net", October 2016. 3948 [RFC1035] Mockapetris, P., "Domain names - implementation and 3949 specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, 3950 November 1987, . 3952 [RFC1812] Baker, F., Ed., "Requirements for IP Version 4 Routers", 3953 RFC 1812, DOI 10.17487/RFC1812, June 1995, 3954 . 3956 [RFC2003] Perkins, C., "IP Encapsulation within IP", RFC 2003, 3957 DOI 10.17487/RFC2003, October 1996, 3958 . 3960 [RFC2004] Perkins, C., "Minimal Encapsulation within IP", RFC 2004, 3961 DOI 10.17487/RFC2004, October 1996, 3962 . 3964 [RFC2236] Fenner, W., "Internet Group Management Protocol, Version 3965 2", RFC 2236, DOI 10.17487/RFC2236, November 1997, 3966 . 3968 [RFC2464] Crawford, M., "Transmission of IPv6 Packets over Ethernet 3969 Networks", RFC 2464, DOI 10.17487/RFC2464, December 1998, 3970 . 3972 [RFC2529] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4 3973 Domains without Explicit Tunnels", RFC 2529, 3974 DOI 10.17487/RFC2529, March 1999, 3975 . 3977 [RFC2983] Black, D., "Differentiated Services and Tunnels", 3978 RFC 2983, DOI 10.17487/RFC2983, October 2000, 3979 . 3981 [RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition 3982 of Explicit Congestion Notification (ECN) to IP", 3983 RFC 3168, DOI 10.17487/RFC3168, September 2001, 3984 . 3986 [RFC3330] IANA, "Special-Use IPv4 Addresses", RFC 3330, 3987 DOI 10.17487/RFC3330, September 2002, 3988 . 3990 [RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener 3991 Discovery Version 2 (MLDv2) for IPv6", RFC 3810, 3992 DOI 10.17487/RFC3810, June 2004, 3993 . 3995 [RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally 3996 Unique IDentifier (UUID) URN Namespace", RFC 4122, 3997 DOI 10.17487/RFC4122, July 2005, 3998 . 4000 [RFC4251] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH) 4001 Protocol Architecture", RFC 4251, DOI 10.17487/RFC4251, 4002 January 2006, . 4004 [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A 4005 Border Gateway Protocol 4 (BGP-4)", RFC 4271, 4006 DOI 10.17487/RFC4271, January 2006, 4007 . 4009 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 4010 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 4011 2006, . 4013 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 4014 Internet Protocol", RFC 4301, DOI 10.17487/RFC4301, 4015 December 2005, . 4017 [RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery 4018 Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April 4019 2006, . 4021 [RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet 4022 Control Message Protocol (ICMPv6) for the Internet 4023 Protocol Version 6 (IPv6) Specification", STD 89, 4024 RFC 4443, DOI 10.17487/RFC4443, March 2006, 4025 . 4027 [RFC4511] Sermersheim, J., Ed., "Lightweight Directory Access 4028 Protocol (LDAP): The Protocol", RFC 4511, 4029 DOI 10.17487/RFC4511, June 2006, 4030 . 4032 [RFC4541] Christensen, M., Kimball, K., and F. Solensky, 4033 "Considerations for Internet Group Management Protocol 4034 (IGMP) and Multicast Listener Discovery (MLD) Snooping 4035 Switches", RFC 4541, DOI 10.17487/RFC4541, May 2006, 4036 . 4038 [RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick, 4039 "Internet Group Management Protocol (IGMP) / Multicast 4040 Listener Discovery (MLD)-Based Multicast Forwarding 4041 ("IGMP/MLD Proxying")", RFC 4605, DOI 10.17487/RFC4605, 4042 August 2006, . 4044 [RFC4982] Bagnulo, M. and J. Arkko, "Support for Multiple Hash 4045 Algorithms in Cryptographically Generated Addresses 4046 (CGAs)", RFC 4982, DOI 10.17487/RFC4982, July 2007, 4047 . 4049 [RFC5015] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano, 4050 "Bidirectional Protocol Independent Multicast (BIDIR- 4051 PIM)", RFC 5015, DOI 10.17487/RFC5015, October 2007, 4052 . 4054 [RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site 4055 Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214, 4056 DOI 10.17487/RFC5214, March 2008, 4057 . 4059 [RFC5320] Templin, F., Ed., "The Subnetwork Encapsulation and 4060 Adaptation Layer (SEAL)", RFC 5320, DOI 10.17487/RFC5320, 4061 February 2010, . 4063 [RFC5522] Eddy, W., Ivancic, W., and T. Davis, "Network Mobility 4064 Route Optimization Requirements for Operational Use in 4065 Aeronautics and Space Exploration Mobile Networks", 4066 RFC 5522, DOI 10.17487/RFC5522, October 2009, 4067 . 4069 [RFC5558] Templin, F., Ed., "Virtual Enterprise Traversal (VET)", 4070 RFC 5558, DOI 10.17487/RFC5558, February 2010, 4071 . 4073 [RFC5569] Despres, R., "IPv6 Rapid Deployment on IPv4 4074 Infrastructures (6rd)", RFC 5569, DOI 10.17487/RFC5569, 4075 January 2010, . 4077 [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 4078 (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, 4079 . 4081 [RFC6106] Jeong, J., Park, S., Beloeil, L., and S. Madanapalli, 4082 "IPv6 Router Advertisement Options for DNS Configuration", 4083 RFC 6106, DOI 10.17487/RFC6106, November 2010, 4084 . 4086 [RFC6139] Russert, S., Ed., Fleischman, E., Ed., and F. Templin, 4087 Ed., "Routing and Addressing in Networks with Global 4088 Enterprise Recursion (RANGER) Scenarios", RFC 6139, 4089 DOI 10.17487/RFC6139, February 2011, 4090 . 4092 [RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful 4093 NAT64: Network Address and Protocol Translation from IPv6 4094 Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146, 4095 April 2011, . 4097 [RFC6179] Templin, F., Ed., "The Internet Routing Overlay Network 4098 (IRON)", RFC 6179, DOI 10.17487/RFC6179, March 2011, 4099 . 4101 [RFC6221] Miles, D., Ed., Ooghe, S., Dec, W., Krishnan, S., and A. 4102 Kavanagh, "Lightweight DHCPv6 Relay Agent", RFC 6221, 4103 DOI 10.17487/RFC6221, May 2011, 4104 . 4106 [RFC6273] Kukec, A., Krishnan, S., and S. Jiang, "The Secure 4107 Neighbor Discovery (SEND) Hash Threat Analysis", RFC 6273, 4108 DOI 10.17487/RFC6273, June 2011, 4109 . 4111 [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer 4112 Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, 4113 January 2012, . 4115 [RFC6355] Narten, T. and J. Johnson, "Definition of the UUID-Based 4116 DHCPv6 Unique Identifier (DUID-UUID)", RFC 6355, 4117 DOI 10.17487/RFC6355, August 2011, 4118 . 4120 [RFC6438] Carpenter, B. and S. Amante, "Using the IPv6 Flow Label 4121 for Equal Cost Multipath Routing and Link Aggregation in 4122 Tunnels", RFC 6438, DOI 10.17487/RFC6438, November 2011, 4123 . 4125 [RFC6706] Templin, F., Ed., "Asymmetric Extended Route Optimization 4126 (AERO)", RFC 6706, DOI 10.17487/RFC6706, August 2012, 4127 . 4129 [RFC6935] Eubanks, M., Chimento, P., and M. Westerlund, "IPv6 and 4130 UDP Checksums for Tunneled Packets", RFC 6935, 4131 DOI 10.17487/RFC6935, April 2013, 4132 . 4134 [RFC6936] Fairhurst, G. and M. Westerlund, "Applicability Statement 4135 for the Use of IPv6 UDP Datagrams with Zero Checksums", 4136 RFC 6936, DOI 10.17487/RFC6936, April 2013, 4137 . 4139 [RFC7333] Chan, H., Ed., Liu, D., Seite, P., Yokota, H., and J. 4140 Korhonen, "Requirements for Distributed Mobility 4141 Management", RFC 7333, DOI 10.17487/RFC7333, August 2014, 4142 . 4144 [RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I., 4145 Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent 4146 Multicast - Sparse Mode (PIM-SM): Protocol Specification 4147 (Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March 4148 2016, . 4150 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 4151 Decraene, B., Litkowski, S., and R. Shakir, "Segment 4152 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 4153 July 2018, . 4155 [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol 4156 Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, 4157 . 4159 [RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J., 4160 Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header 4161 (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020, 4162 . 4164 [WG] Wireguard, "WireGuard, https://www.wireguard.com", August 4165 2020. 4167 Appendix A. Non-Normative Considerations 4169 AERO can be applied to a multitude of Internetworking scenarios, with 4170 each having its own adaptations. The following considerations are 4171 provided as non-normative guidance: 4173 A.1. Implementation Strategies for Route Optimization 4175 Route optimization as discussed in Section 3.14 results in the route 4176 optimization source (ROS) creating a NCE for the target neighbor. 4177 The NCE state is set to REACHABLE for at most ReachableTime seconds. 4178 In order to refresh the NCE lifetime before the ReachableTime timer 4179 expires, the specification requires implementations to issue a new 4180 NS/NA exchange to reset ReachableTime while data packets are still 4181 flowing. However, the decision of when to initiate a new NS/NA 4182 exchange and to perpetuate the process is left as an implementation 4183 detail. 4185 One possible strategy may be to monitor the NCE watching for data 4186 packets for (ReachableTime - 5) seconds. If any data packets have 4187 been sent to the neighbor within this timeframe, then send an NS to 4188 receive a new NA. If no data packets have been sent, wait for 5 4189 additional seconds and send an immediate NS if any data packets are 4190 sent within this "expiration pending" 5 second window. If no 4191 additional data packets are sent within the 5 second window, reset 4192 the NCE state to STALE. 4194 The monitoring of the neighbor data packet traffic therefore becomes 4195 an ongoing process during the NCE lifetime. If the NCE expires, 4196 future data packets will trigger a new NS/NA exchange while the 4197 packets themselves are delivered over a longer path until route 4198 optimization state is re-established. 4200 A.2. Implicit Mobility Management 4202 OMNI interface neighbors MAY provide a configuration option that 4203 allows them to perform implicit mobility management in which no ND 4204 messaging is used. In that case, the Client only transmits packets 4205 over a single interface at a time, and the neighbor always observes 4206 packets arriving from the Client from the same link-layer source 4207 address. 4209 If the Client's underlying interface address changes (either due to a 4210 readdressing of the original interface or switching to a new 4211 interface) the neighbor immediately updates the NCE for the Client 4212 and begins accepting and sending packets according to the Client's 4213 new address. This implicit mobility method applies to use cases such 4214 as cellphones with both WiFi and Cellular interfaces where only one 4215 of the interfaces is active at a given time, and the Client 4216 automatically switches over to the backup interface if the primary 4217 interface fails. 4219 A.3. Direct Underlying Interfaces 4221 When a Client's OMNI interface is configured over a Direct interface, 4222 the neighbor at the other end of the Direct link can receive packets 4223 without any encapsulation. In that case, the Client sends packets 4224 over the Direct link according to traffic selectors. If the Direct 4225 interface is selected, then the Client's IP packets are transmitted 4226 directly to the peer without going through an ANET/INET. If other 4227 interfaces are selected, then the Client's IP packets are transmitted 4228 via a different interface, which may result in the inclusion of 4229 Proxy/Servers and Bridges in the communications path. Direct 4230 interfaces must be tested periodically for reachability, e.g., via 4231 NUD. 4233 A.4. AERO Critical Infrastructure Considerations 4235 AERO Bridges can be either Commercial off-the Shelf (COTS) standard 4236 IP routers or virtual machines in the cloud. Bridges must be 4237 provisioned, supported and managed by the INET administrative 4238 authority, and connected to the Bridges of other INETs via inter- 4239 domain peerings. Cost for purchasing, configuring and managing 4240 Bridges is nominal even for very large OMNI links. 4242 AERO cloud Proxy/Servers can be standard dedicated server platforms, 4243 but most often will be deployed as virtual machines in the cloud. 4244 The only requirements for cloud Proxy/Servers are that they can run 4245 the AERO user-level code and have at least one network interface 4246 connection to the INET. Cloud Proxy/Servers must be provisioned, 4247 supported and managed by the INET administrative authority. Cost for 4248 purchasing, configuring and managing cloud Proxy/Servers is nominal 4249 especially for virtual machines. 4251 AERO ANET Proxy/Servers are most often standard dedicated server 4252 platforms with one underlying interface connected to the ANET and a 4253 second interface connected to an INET. As with cloud Proxy/Servers, 4254 the only requirements are that they can run the AERO user-level code 4255 and have at least one interface connection to the INET. ANET Proxy/ 4256 Servers must be provisioned, supported and managed by the ANET 4257 administrative authority. Cost for purchasing, configuring and 4258 managing Proxys is nominal, and borne by the ANET administrative 4259 authority. 4261 AERO Relays are simply Proxy/Servers connected to INETs and/or EUNs 4262 that provide forwarding services for non-MNP destinations. The Relay 4263 connects to the OMNI link and engages in eBGP peering with one or 4264 more Bridges as a stub AS. The Relay then injects its MNPs and/or 4265 non-MNP prefixes into the BGP routing system, and provisions the 4266 prefixes to its downstream-attached networks. The Relay can perform 4267 ROS/ROR services the same as for any Proxy/Server, and can route 4268 between the MNP and non-MNP address spaces. 4270 A.5. AERO Server Failure Implications 4272 AERO Proxy/Servers may appear as a single point of failure in the 4273 architecture, but such is not the case since all Proxy/Servers on the 4274 link provide identical services and loss of a Proxy/Server does not 4275 imply immediate and/or comprehensive communication failures. Proxy/ 4276 Server failure is quickly detected and conveyed by Bidirectional 4277 Forward Detection (BFD) and/or proactive NUD allowing Clients to 4278 migrate to new Proxy/Servers. 4280 If a Proxy/Server fails, ongoing packet forwarding to Clients will 4281 continue by virtue of the neighbor cache entries that have already 4282 been established in route optimization sources (ROSs). If a Client 4283 also experiences mobility events at roughly the same time the Proxy/ 4284 Server fails, unsolicited NA messages may be lost but neighbor cache 4285 entries in the DEPARTED state will ensure that packet forwarding to 4286 the Client's new locations will continue for up to DepartTime 4287 seconds. 4289 If a Client is left without a Proxy/Server for a considerable length 4290 of time (e.g., greater than ReachableTime seconds) then existing 4291 neighbor cache entries will eventually expire and both ongoing and 4292 new communications will fail. The original source will continue to 4293 retransmit until the Client has established a new Proxy/Server 4294 relationship, after which time continuous communications will resume. 4296 Therefore, providing many Proxy/Servers on the link with high 4297 availability profiles provides resilience against loss of individual 4298 Proxy/Servers and assurance that Clients can establish new Proxy/ 4299 Server relationships quickly in event of a Proxy/Server failure. 4301 A.6. AERO Client / Server Architecture 4303 The AERO architectural model is client / server in the control plane, 4304 with route optimization in the data plane. The same as for common 4305 Internet services, the AERO Client discovers the addresses of AERO 4306 Proxy/Servers and connects to one or more of them. The AERO service 4307 is analogous to common Internet services such as google.com, 4308 yahoo.com, cnn.com, etc. However, there is only one AERO service for 4309 the link and all Proxy/Servers provide identical services. 4311 Common Internet services provide differing strategies for advertising 4312 server addresses to clients. The strategy is conveyed through the 4313 DNS resource records returned in response to name resolution queries. 4314 As of January 2020 Internet-based 'nslookup' services were used to 4315 determine the following: 4317 o When a client resolves the domainname "google.com", the DNS always 4318 returns one A record (i.e., an IPv4 address) and one AAAA record 4319 (i.e., an IPv6 address). The client receives the same addresses 4320 each time it resolves the domainname via the same DNS resolver, 4321 but may receive different addresses when it resolves the 4322 domainname via different DNS resolvers. But, in each case, 4323 exactly one A and one AAAA record are returned. 4325 o When a client resolves the domainname "ietf.org", the DNS always 4326 returns one A record and one AAAA record with the same addresses 4327 regardless of which DNS resolver is used. 4329 o When a client resolves the domainname "yahoo.com", the DNS always 4330 returns a list of 4 A records and 4 AAAA records. Each time the 4331 client resolves the domainname via the same DNS resolver, the same 4332 list of addresses are returned but in randomized order (i.e., 4333 consistent with a DNS round-robin strategy). But, interestingly, 4334 the same addresses are returned (albeit in randomized order) when 4335 the domainname is resolved via different DNS resolvers. 4337 o When a client resolves the domainname "amazon.com", the DNS always 4338 returns a list of 3 A records and no AAAA records. As with 4339 "yahoo.com", the same three A records are returned from any 4340 worldwide Internet connection point in randomized order. 4342 The above example strategies show differing approaches to Internet 4343 resilience and service distribution offered by major Internet 4344 services. The Google approach exposes only a single IPv4 and a 4345 single IPv6 address to clients. Clients can then select whichever IP 4346 protocol version offers the best response, but will always use the 4347 same IP address according to the current Internet connection point. 4348 This means that the IP address offered by the network must lead to a 4349 highly-available server and/or service distribution point. In other 4350 words, resilience is predicated on high availability within the 4351 network and with no client-initiated failovers expected (i.e., it is 4352 all-or-nothing from the client's perspective). However, Google does 4353 provide for worldwide distributed service distribution by virtue of 4354 the fact that each Internet connection point responds with a 4355 different IPv6 and IPv4 address. The IETF approach is like google 4356 (all-or-nothing from the client's perspective), but provides only a 4357 single IPv4 or IPv6 address on a worldwide basis. This means that 4358 the addresses must be made highly-available at the network level with 4359 no client failover possibility, and if there is any worldwide service 4360 distribution it would need to be conducted by a network element that 4361 is reached via the IP address acting as a service distribution point. 4363 In contrast to the Google and IETF philosophies, Yahoo and Amazon 4364 both provide clients with a (short) list of IP addresses with Yahoo 4365 providing both IP protocol versions and Amazon as IPv4-only. The 4366 order of the list is randomized with each name service query 4367 response, with the effect of round-robin load balancing for service 4368 distribution. With a short list of addresses, there is still 4369 expectation that the network will implement high availability for 4370 each address but in case any single address fails the client can 4371 switch over to using a different address. The balance then becomes 4372 one of function in the network vs function in the end system. 4374 The same implications observed for common highly-available services 4375 in the Internet apply also to the AERO client/server architecture. 4376 When an AERO Client connects to one or more ANETs, it discovers one 4377 or more AERO Proxy/Server addresses through the mechanisms discussed 4378 in earlier sections. Each Proxy/Server address presumably leads to a 4379 fault-tolerant clustering arrangement such as supported by Linux-HA, 4380 Extended Virtual Synchrony or Paxos. Such an arrangement has 4381 precedence in common Internet service deployments in lightweight 4382 virtual machines without requiring expensive hardware deployment. 4383 Similarly, common Internet service deployments set service IP 4384 addresses on service distribution points that may relay requests to 4385 many different servers. 4387 For AERO, the expectation is that a combination of the Google/IETF 4388 and Yahoo/Amazon philosophies would be employed. The AERO Client 4389 connects to different ANET access points and can receive 1-2 Proxy/ 4390 Server ADM-LLAs at each point. It then selects one AERO Proxy/Server 4391 address, and engages in RS/RA exchanges with the same Proxy/Server 4392 from all ANET connections. The Client remains with this Proxy/Server 4393 unless or until the Proxy/Server fails, in which case it can switch 4394 over to an alternate Proxy/Server. The Client can likewise switch 4395 over to a different Proxy/Server at any time if there is some reason 4396 for it to do so. So, the AERO expectation is for a balance of 4397 function in the network and end system, with fault tolerance and 4398 resilience at both levels. 4400 Appendix B. Change Log 4402 << RFC Editor - remove prior to publication >> 4404 Changes from draft-templin-6man-aero-08 to draft-templin-6man-aero- 4405 09: 4407 o Final editorial review pass resulting in multiple changes. 4408 Document now submit for final approval (with reference to rfcdiff 4409 from previous version). 4411 Changes from draft-templin-6man-aero-07 to draft-templin-6man-aero- 4412 08: 4414 o Final editorial review pass resulting in multiple changes. 4415 Document now submit for final approval (with reference to rfcdiff 4416 from previous version). 4418 Changes from draft-templin-6man-aero-06 to draft-templin-6man-aero- 4419 07: 4421 o Final editorial review pass resulting in multiple changes. 4422 Document now submit for final approval (with reference to rfcdiff 4423 from previous version). 4425 Changes from draft-templin-6man-aero-05 to draft-templin-6man-aero- 4426 06: 4428 o Final editorial review pass resulting in multiple changes. 4429 Document now submit for final approval. 4431 Changes from draft-templin-6man-aero-04 to draft-templin-6man-aero- 4432 05: 4434 o Changed to use traffic selectors instead of the former multilink 4435 selection strategy. 4437 Changes from draft-templin-6man-aero-03 to draft-templin-6man-aero- 4438 04: 4440 o Removed documents from "Obsoletes" list. 4442 o Introduced the concept of "secured" and "unsecured" spanning tree. 4444 o Additional security considerations. 4446 o Additional route optimization considerations. 4448 Changes from draft-templin-6man-aero-02 to draft-templin-6man-aero- 4449 03: 4451 o Support for extended route optimization from ROR to target over 4452 target's underlying interfaces. 4454 Changes from draft-templin-6man-aero-01 to draft-templin-6man-aero- 4455 02: 4457 o Changed reference citations to "draft-templin-6man-omni". 4459 o Several important updates to IPv6 ND cache states and route 4460 optimization message addressing. 4462 o Included introductory description of the "6M's". 4464 o Updated Multicast specification. 4466 Changes from draft-templin-6man-aero-00 to draft-templin-6man-aero- 4467 01: 4469 o Changed category to "Informational". 4471 o Updated implementation status. 4473 Changes from earlier versions to draft-templin-6man-aero-00: 4475 o Established working baseline reference. 4477 Author's Address 4479 Fred L. Templin (editor) 4480 Boeing Research & Technology 4481 P.O. Box 3707 4482 Seattle, WA 98124 4483 USA 4485 Email: fltemplin@acm.org