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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 May 25, 2021 5 Expires: November 26, 2021 7 Asymmetric Extended Route Optimization (AERO) 8 draft-templin-6man-aero-06 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 November 26, 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) . . . . . . . . . . 23 69 3.2.6. Segment Routing For OMNI Link Selection . . . . . . . 24 70 3.2.7. Segment Routing Within the OMNI Link . . . . . . . . 24 71 3.3. OMNI Interface Characteristics . . . . . . . . . . . . . 25 72 3.4. OMNI Interface Initialization . . . . . . . . . . . . . . 27 73 3.4.1. AERO Proxy/Server and Relay Behavior . . . . . . . . 27 74 3.4.2. AERO Client Behavior . . . . . . . . . . . . . . . . 27 75 3.4.3. AERO Bridge Behavior . . . . . . . . . . . . . . . . 28 76 3.5. OMNI Interface Neighbor Cache Maintenance . . . . . . . . 28 77 3.5.1. OMNI Neighbor Interface Attributes . . . . . . . . . 29 78 3.5.2. OMNI Neighbor Advertisement Message Flags . . . . . . 30 79 3.5.3. OMNI Neighbor Window Synchronization . . . . . . . . 30 80 3.6. OMNI Interface Encapsulation and Re-encapsulation . . . . 31 81 3.7. OMNI Interface Decapsulation . . . . . . . . . . . . . . 31 82 3.8. OMNI Interface Data Origin Authentication . . . . . . . . 31 83 3.9. OMNI Interface MTU . . . . . . . . . . . . . . . . . . . 32 84 3.10. OMNI Interface Forwarding Algorithm . . . . . . . . . . . 33 85 3.10.1. Client Forwarding Algorithm . . . . . . . . . . . . 34 86 3.10.2. Proxy/Server and Relay Forwarding Algorithm . . . . 35 87 3.10.3. Bridge Forwarding Algorithm . . . . . . . . . . . . 38 88 3.11. OMNI Interface Error Handling . . . . . . . . . . . . . . 39 89 3.12. AERO Router Discovery, Prefix Delegation and 90 Autoconfiguration . . . . . . . . . . . . . . . . . . . . 42 91 3.12.1. AERO Service Model . . . . . . . . . . . . . . . . . 42 92 3.12.2. AERO Client Behavior . . . . . . . . . . . . . . . . 42 93 3.12.3. AERO Proxy/Server Behavior . . . . . . . . . . . . . 44 94 3.13. The AERO Proxy Function . . . . . . . . . . . . . . . . . 47 95 3.13.1. Detecting and Responding to Proxy/Server Failures . 50 96 3.13.2. Point-to-Multipoint Proxy/Server Coordination . . . 51 98 3.14. AERO Route Optimization . . . . . . . . . . . . . . . . . 52 99 3.14.1. Route Optimization Initiation . . . . . . . . . . . 52 100 3.14.2. Relaying the NS(AR) *NET Packet(s) . . . . . . . . . 53 101 3.14.3. Processing the NS(AR) and Sending the NA(AR) . . . . 53 102 3.14.4. Relaying the NA(AR) . . . . . . . . . . . . . . . . 55 103 3.14.5. Processing the NA(AR) . . . . . . . . . . . . . . . 56 104 3.14.6. Route Optimization Maintenance . . . . . . . . . . . 56 105 3.15. Neighbor Unreachability Detection (NUD) . . . . . . . . . 58 106 3.16. Mobility Management and Quality of Service (QoS) . . . . 60 107 3.16.1. Mobility Update Messaging . . . . . . . . . . . . . 60 108 3.16.2. Announcing Link-Layer Address and/or QoS Preference 109 Changes . . . . . . . . . . . . . . . . . . . . . . 61 110 3.16.3. Bringing New Links Into Service . . . . . . . . . . 62 111 3.16.4. Deactivating Existing Links . . . . . . . . . . . . 62 112 3.16.5. Moving Between Proxy/Servers . . . . . . . . . . . . 62 113 3.17. Multicast . . . . . . . . . . . . . . . . . . . . . . . . 64 114 3.17.1. Source-Specific Multicast (SSM) . . . . . . . . . . 64 115 3.17.2. Any-Source Multicast (ASM) . . . . . . . . . . . . . 65 116 3.17.3. Bi-Directional PIM (BIDIR-PIM) . . . . . . . . . . . 66 117 3.18. Operation over Multiple OMNI Links . . . . . . . . . . . 66 118 3.19. DNS Considerations . . . . . . . . . . . . . . . . . . . 67 119 3.20. Transition/Coexistence Considerations . . . . . . . . . . 67 120 3.21. Detecting and Reacting to Proxy/Server and Bridge 121 Failures . . . . . . . . . . . . . . . . . . . . . . . . 68 122 3.22. AERO Clients on the Open Internet . . . . . . . . . . . . 68 123 3.23. Time-Varying MNPs . . . . . . . . . . . . . . . . . . . . 71 124 4. Implementation Status . . . . . . . . . . . . . . . . . . . . 72 125 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 72 126 6. Security Considerations . . . . . . . . . . . . . . . . . . . 72 127 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 74 128 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 76 129 8.1. Normative References . . . . . . . . . . . . . . . . . . 76 130 8.2. Informative References . . . . . . . . . . . . . . . . . 78 131 Appendix A. Non-Normative Considerations . . . . . . . . . . . . 84 132 A.1. Implementation Strategies for Route Optimization . . . . 84 133 A.2. Implicit Mobility Management . . . . . . . . . . . . . . 85 134 A.3. Direct Underlying Interfaces . . . . . . . . . . . . . . 85 135 A.4. AERO Critical Infrastructure Considerations . . . . . . . 85 136 A.5. AERO Server Failure Implications . . . . . . . . . . . . 86 137 A.6. AERO Client / Server Architecture . . . . . . . . . . . . 87 138 Appendix B. Change Log . . . . . . . . . . . . . . . . . . . . . 89 139 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 90 141 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 messages toward 864 AERO destination nodes located in different OMNI link segments over 865 the spanning tree. The OMNI interface uses the OMNI Adaptation Layer 866 (OAL) encapsulation service [I-D.templin-6man-omni], and includes an 867 OMNI Routing Header (ORH) as an extension to the OAL header if final 868 segment forwarding information is available, e.g., in the neighbor 869 cache. (For nodes located in the same OMNI link segment, or when no 870 final segment forwarding information is available, the ORH may be 871 omitted.) The ORH is 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 | SRT | FMT | 877 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 878 | Last Hop Segment-id (LHS) | 879 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 880 ~ Link Layer Address (L2ADDR) ~ 881 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 882 ~ Destination Suffix (if necessary) ~ 883 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 884 ~ Null Padding (if necessary) ~ 885 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 887 Figure 3: OMNI Routing Header (ORH) Format 889 In this format: 891 o Next Header identifies the type of header immediately following 892 the ORH. 894 o Hdr Ext Len is the length of the Routing header in 8-octet units 895 (not including the first 8 octets), with trailing padding added if 896 necessary to produce an integral number of 8-octet units. 898 o Routing Type is set to TBD1 (see IANA Considerations). 900 o Segments Left is omitted, and replaced by a 5-bit SRT and 3-bit 901 FMT field. 903 o SRT - a 5-bit Segment Routing Topology prefix length value that 904 (when added to 96) determines the prefix length to apply to the 905 ADM-ULA formed from concatenating [ULA*]::/96 with the 32 bit LHS 906 value that follows (for example, the value 16 corresponds to the 907 prefix length 112). 909 o FMT - a 3-bit "Framework/Mode/Type" code corresponding to the 910 included Link Layer Address as follows: 912 * When the most significant bit (i.e., "Framework") is set to 1, 913 L2ADDR is the *NET encapsulation address for the target Client 914 itself; otherwise L2ADDR is the address of the Proxy/Server 915 named in the LHS. 917 * When the next most significant bit (i.e., "Mode") is set to 1, 918 the Framework node is (likely) located behind a *NET Network 919 Address Translator (NAT); otherwise, it is on the open *NET. 921 * When the least significant bit (i.e., "Type") is set to 0, 922 L2ADDR includes a UDP Port Number followed by an IPv4 address; 923 otherwise, it includes a UDP Port Number followed by an IPv6 924 address. 926 o LHS - the 32 bit ID of a node in the Last Hop Segment that 927 services the target. When SRT and LHS are both set to 0, the LHS 928 is considered unspecified. When SRT is set to 0 and LHS is non- 929 zero, the prefix length is set to 128. SRT and LHS provide 930 guidance to the OMNI interface forwarding algorithm. 931 Specifically, if SRT/LHS is located in the local OMNI link 932 segment, the OAL source can omit the ORH and (following any 933 necessary NAT traversal messaging) send directly to the OAL 934 destination according to FMT/L2ADDR. Otherwise, it includes the 935 ORH and forwards according to the OMNI link spanning tree. 937 o Link Layer Address (L2ADDR) - Formatted according to FMT, and 938 identifies the link-layer address (i.e., the encapsulation 939 address) of the target. The UDP Port Number appears in the first 940 two octets and the IP address appears in the next 4 octets for 941 IPv4 or 16 octets for IPv6. The Port Number and IP address are 942 recorded in network byte order, and in ones-compliment 943 "obfuscated" form per [RFC4380]. The OMNI interface forwarding 944 algorithm uses FMT/L2ADDR to determine the *NET encapsulation 945 address for local forwarding when SRT/LHS is located in the same 946 OMNI link segment. Note that if the target is behind a NAT, 947 L2ADDR will contain the mapped *NET address stored in the NAT; 948 otherwise, L2ADDR will contain the native *NET information of the 949 target itself. 951 o Destination Suffix is a 64-bit field included only for OAL non- 952 first-fragments. Present only when Hdr Ext Len indicates that at 953 least 8 octets follow L2ADDR. When present, encodes the 64-bit 954 MNP-ULA suffix for the target Client. 956 o Null Padding contains zero-valued octets as necessary to pad the 957 ORH to an integral number of 8-octet units. 959 AERO neighbors use OAL encapsulation and fragmentation to exchange 960 OAL packets as specified in [I-D.templin-6man-omni]. When an AERO 961 node's OMNI interface (acting as an OAL source) uses OAL 962 encapsulation for an original IP packet with source address 963 2001:db8:1:2::1 and destination address 2001:db8:1234:5678::1, it 964 sets the OAL header source address to its own ULA (e.g., 965 [ULA*]::2001:db8:1:2), sets the destination address to the MNP-ULA 966 corresponding to the IP destination address (e.g., 967 [ULA*]::2001:db8:1234:5678), sets the Traffic Class, Flow Label, Hop 968 Limit and Payload Length as discussed in [I-D.templin-6man-omni], 969 then finally selects an Identification and appends an OAL checksum. 971 If the neighbor cache information indicates that the target is in a 972 different segment, the OAL source next inserts an ORH immediately 973 following the OAL header while including the correct SRT, FMT, LHS, 974 L2ADDR and Destination Suffix if fragmentation if needed (in this 975 case, the Destination Suffix is 2001:db8:1234:5678). Next, the OAL 976 source overwrites the OAL header destination address with the LHS 977 Subnet Router Anycast address (for example, for LHS 3000:4567 with 978 SRT 16, the Subnet Router Anycast address is [ULA*]::3000:0000). 979 (Note: if the ADM-ULA of the last-hop Proxy/Server is known but the 980 SRT, FMT, LHS and L2ADDR are not (yet) known, the OAL source instead 981 overwrites the OAL header destination address with the ADM-ULA.) 983 The OAL source then fragments the OAL packet, with each resulting OAL 984 fragment including the OAL/ORH headers while only the first fragment 985 includes the original IPv6 header. (Note that if no actual 986 fragmentation is required the OAL packet is still prepared as an 987 "atomic" fragment that includes a Fragment Header with Offset and 988 More Fragments both set to 0.) The OAL source finally encapsulates 989 each resulting OAL fragment in an *NET header to form an OAL carrier 990 packet, with source address set to its own *NET address (e.g., 991 192.0.2.100) and destination set to the *NET address of a Bridge 992 (e.g., 192.0.2.1). 994 The carrier packet encapsulation format in the above example is shown 995 in Figure 4: 997 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 998 | *NET Header | 999 | src = 192.0.2.100 | 1000 | dst = 192.0.2.1 | 1001 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1002 | OAL IPv6 Header | 1003 | src = [ULA*]::2001:db8:1:2 | 1004 | dst= [ULA*]::3000:0000 | 1005 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1006 | ORH (if necessary) | 1007 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1008 | OAL Fragment Header | 1009 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1010 | Original IP Header | 1011 | (first-fragment only) | 1012 | src = 2001:db8:1:2::1 | 1013 | dst = 2001:db8:1234:5678::1 | 1014 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1015 | | 1016 ~ ~ 1017 ~ Original Packet Body/Fragment ~ 1018 ~ ~ 1019 | | 1020 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1022 Figure 4: Carrier Packet Format 1024 In this format, the original IP header and packet body/fragment are 1025 from the original IP packet, the OAL header is an IPv6 header 1026 prepared according to [RFC2473], the ORH is a Routing Header 1027 extension of the OAL header, the Fragment Header identifies each 1028 fragment, and the INET header is prepared as discussed in 1029 Section 3.6. When the OAL source transmits the resulting carrier 1030 packets, they are forwarded over possibly multiple OAL intermediate 1031 nodes in the OMNI link spanning tree until they arrive at the OAL 1032 destination. 1034 This gives rise to a routing system that contains both Client MNP-ULA 1035 routes that may change dynamically due to regional node mobility and 1036 per-partition ADM-ULA routes that rarely if ever change. The Bridges 1037 can therefore provide link-layer bridging by sending carrier packets 1038 over the spanning tree instead of network-layer routing according to 1039 MNP routes. As a result, opportunities for loss due to node mobility 1040 between different segments are mitigated. 1042 Note: When the OAL source and destination are on the same INET 1043 segment, the ORH is not needed and OAL header compression can be used 1044 to significantly reduce encapsulation overhead 1045 [I-D.templin-6man-omni]. 1047 Note: When the OAL source has multiple original IP packets to send to 1048 the same OAL destination, it can perform "packing" to generate a 1049 "super-packet" [I-D.templin-6man-omni]. In that case, the OAL/ORH 1050 super-packet may include up to N original IP packets as long as the 1051 total length of the super-packet does not exceed the OMNI interface 1052 MTU. 1054 Note: Use of an IPv6 "minimal encapsulation" format (i.e., an IPv6 1055 variant of [RFC2004]) based on extensions to the ORH was considered 1056 and abandoned. In the approach, the ORH would be inserted as an 1057 extension header to the original IPv6 packet header. The IPv6 1058 destination address would then be written into the ORH, and the ULA 1059 corresponding to the destination would be overwritten in the IPv6 1060 destination address. This would seemingly convey enough forwarding 1061 information so that OAL encapsulation could be avoided. However, 1062 this "minimal encapsulation" IPv6 packet would then have a non-ULA 1063 source address and ULA destination address, an incorrect value in 1064 upper layer protocol checksums, and a Hop Limit that is decremented 1065 within the spanning tree when it should not be. The insertion and 1066 removal of the ORH would also entail rewriting the Payload Length and 1067 Next Header fields - again, invalidating upper layer checksums. 1068 These irregularities would result in implementation challenges and 1069 the potential for operational issues, e.g., since actionable ICMPv6 1070 error reports could not be delivered to the original source. In 1071 order to address the issues, still more information such as the 1072 original IPv6 source address could be written into the ORH. However, 1073 with the additional information the benefit of the "minimal 1074 encapsulation" savings quickly diminishes, and becomes overshadowed 1075 by the implementation and operational irregularities. 1077 3.2.5. Segment Routing Topologies (SRTs) 1079 The 64-bit sub-prefixes of [ULA]::/48 identify up to 2^16 distinct 1080 Segment Routing Topologies (SRTs). Each SRT is a mutually-exclusive 1081 OMNI link overlay instance using a distinct set of ULAs, and emulates 1082 a Virtual LAN (VLAN) service for the OMNI link. In some cases (e.g., 1083 when redundant topologies are needed for fault tolerance and 1084 reliability) it may be beneficial to deploy multiple SRTs that act as 1085 independent overlay instances. A communication failure in one 1086 instance therefore will not affect communications in other instances. 1088 Each SRT is identified by a distinct value in bits 48-63 of 1089 [ULA]::/48, i.e., as [ULA0]::/64, [ULA1]::/64, [ULA2]::/64, etc. 1090 Each OMNI interface is identified by a unique interface name (e.g., 1091 omni0, omni1, omni2, etc.) and assigns an anycast ADM-ULA 1092 corresponding to its SRT prefix length. The anycast ADM-ULA is used 1093 for OMNI interface determination in Safety-Based Multilink (SBM) as 1094 discussed in [I-D.templin-6man-omni]. Each OMNI interface further 1095 applies Performance-Based Multilink (PBM) internally. 1097 3.2.6. Segment Routing For OMNI Link Selection 1099 An original IPv6 source can direct an IPv6 packet to an AERO node by 1100 including a standard IPv6 Segment Routing Header (SRH) [RFC8754] with 1101 the anycast ADM-ULA for the selected SRT as either the IPv6 1102 destination or as an intermediate hop within the SRH. This allows 1103 the original source to determine the specific OMNI link topology an 1104 original IPv6 packet will traverse when there may be multiple 1105 alternatives. 1107 When the AERO node processes the SRH and forwards the original IPv6 1108 packet to the correct OMNI interface, the OMNI interface writes the 1109 next IPv6 address from the SRH into the IPv6 destination address and 1110 decrements Segments Left. If decrementing would cause Segments Left 1111 to become 0, the OMNI interface deletes the SRH before forwarding. 1112 This form of Segment Routing supports Safety-Based Multilink (SBM). 1114 3.2.7. Segment Routing Within the OMNI Link 1116 OAL sources can insert an ORH for Segment Routing within the OMNI 1117 link to influence the paths of OAL packets sent to OAL destinations 1118 in remote segments without requiring all carrier packets to traverse 1119 strict spanning tree paths. 1121 When an AERO node's OMNI interface has an original IP packet to send 1122 to a target discovered through route optimization located in the same 1123 OMNI link segment, it acts as an OAL source to perform OAL 1124 encapsulation and fragmentation. The node then uses the target's 1125 Link Layer Address (L2ADDR) information for *NET encapsulation. 1127 When an AERO node's OMNI interface has an original IP packet to send 1128 to a route optimization target located in a remote OMNI link segment, 1129 it acts as an OAL source the same as above but also includes an ORH 1130 while setting the OAL destination to the Subnet Router Anycast 1131 address for the final OMNI link segment, then forwards the resulting 1132 carrier packets to a Bridge. 1134 When a Bridge receives a carrier packet destined to its Subnet Router 1135 Anycast address with an ORH with SRT/LHS values corresponding to the 1136 local segment, it examines the L2ADDR according to FMT and removes 1137 the ORH from the carrier packet. The Bridge then writes the MNP-ULA 1138 corresponding to the ORH Destination Suffix into the OAL destination 1139 address, decrements the OAL IPv6 header Hop Limit (and discards the 1140 packet if the Hop Limit reaches 0), re-encapsulates the carrier 1141 packet according to L2ADDR and forwards the carrier packet either to 1142 the LHS Proxy/Server or directly to the target Client itself. In 1143 this way, the Bridge participates in route optimization to reduce 1144 traffic load and suboptimal routing through strict spanning tree 1145 paths. 1147 3.3. OMNI Interface Characteristics 1149 OMNI interfaces are virtual interfaces configured over one or more 1150 underlying interfaces classified as follows: 1152 o INET interfaces connect to an INET either natively or through one 1153 or more NATs. Native INET interfaces have global IP addresses 1154 that are reachable from any INET correspondent. The INET-facing 1155 interfaces of Proxy/Servers are native interfaces, as are Relay 1156 and Bridge interfaces. NATed INET interfaces connect to a private 1157 network behind one or more NATs that provide INET access. Clients 1158 that are behind a NAT are required to send periodic keepalive 1159 messages to keep NAT state alive when there are no carrier packets 1160 flowing. 1162 o ANET interfaces connect to an ANET that is separated from the open 1163 INET by a Proxy/Server. Proxy/Servers can actively issue control 1164 messages over the INET on behalf of the Client to reduce ANET 1165 congestion. 1167 o VPNed interfaces use security encapsulation over the INET to a 1168 Virtual Private Network (VPN) server that also acts as a Proxy/ 1169 Server. Other than the link-layer encapsulation format, VPNed 1170 interfaces behave the same as Direct interfaces. 1172 o Direct (i.e., single-hop point-to-point) interfaces connect a 1173 Client directly to a Proxy/Server without crossing any ANET/INET 1174 paths. An example is a line-of-sight link between a remote pilot 1175 and an unmanned aircraft. The same Client considerations apply as 1176 for VPNed interfaces. 1178 OMNI interfaces use OAL encapsulation and fragmentation as discussed 1179 in Section 3.2.4. OMNI interfaces use *NET encapsulation (see: 1180 Section 3.6) to exchange carrier packets with OMNI link neighbors 1181 over INET or VPNed interfaces as well as over ANET interfaces for 1182 which the Client and Proxy/Server may be multiple IP hops away. OMNI 1183 interfaces do not use link-layer encapsulation over Direct underlying 1184 interfaces or ANET interfaces when the Client and Proxy/Server are 1185 known to be on the same underlying link. 1187 OMNI interfaces maintain a neighbor cache for tracking per-neighbor 1188 state the same as for any interface. OMNI interfaces use ND messages 1189 including Router Solicitation (RS), Router Advertisement (RA), 1190 Neighbor Solicitation (NS) and Neighbor Advertisement (NA) for 1191 neighbor cache management. In environments where spoofing may be a 1192 threat, OMNI neighbors should employ OAL Identification window 1193 synchronization in their ND message exchanges. 1195 OMNI interfaces send ND messages with an OMNI option formatted as 1196 specified in [I-D.templin-6man-omni]. The OMNI option includes 1197 prefix registration information and Interface Attributes containing 1198 link information parameters for the OMNI interface's underlying 1199 interfaces. Each OMNI option may include multiple Interface 1200 Attributes sub-options, each identified by an omIndex value. 1202 A Client's OMNI interface may be configured over multiple underlying 1203 interface connections. For example, common mobile handheld devices 1204 have both wireless local area network ("WLAN") and cellular wireless 1205 links. These links are often used "one at a time" with low-cost WLAN 1206 preferred and highly-available cellular wireless as a standby, but a 1207 simultaneous-use capability could provide benefits. In a more 1208 complex example, aircraft frequently have many wireless data link 1209 types (e.g. satellite-based, cellular, terrestrial, air-to-air 1210 directional, etc.) with diverse performance and cost properties. 1212 If a Client's multiple underlying interfaces are used "one at a time" 1213 (i.e., all other interfaces are in standby mode while one interface 1214 is active), then ND message OMNI options include Interface Attributes 1215 sub-options with the same underlying interface index. In that case, 1216 the Client would appear to have a single interface but with a 1217 dynamically changing link-layer address. 1219 If the Client has multiple active underlying interfaces, then from 1220 the perspective of ND it would appear to have multiple link-layer 1221 addresses. In that case, ND message OMNI options MAY include 1222 Interface Attributes sub-options with different underlying interface 1223 indexes. Every ND message need not include Interface Attributes for 1224 all underlying interfaces; for any attributes not included, the 1225 neighbor considers the status as unchanged. 1227 Bridge and Proxy/Server OMNI interfaces are configured over secured 1228 tunnel underlying interfaces for carrying IPv6 ND and BGP protocol 1229 control plane messages, plus open INET underlying interfaces for 1230 carrying unsecured messages. The OMNI interface configures both an 1231 ADM-LLA and its corresponding ADM-ULA, and acts as an OAL source to 1232 encapsulate and fragment original IP packets while presenting the 1233 resulting carrier packets to a secured or unsecured underlying 1234 interface. Note that Bridge and Proxy/Server BGP protocol TCP 1235 sessions are run directly over the OMNI interface using ADM-ULA 1236 source and destination addresses. The OMNI interface will 1237 encapsulate these as carrier packets even though the OAL header may 1238 use the same ADM-ULAs as the original IP header; these carrier 1239 packets must then be sent over a secured underlying interface. 1241 3.4. OMNI Interface Initialization 1243 AERO Proxy/Servers and Clients configure OMNI interfaces as their 1244 point of attachment to the OMNI link. AERO nodes assign the MSPs for 1245 the link to their OMNI interfaces (i.e., as a "route-to-interface") 1246 to ensure that original IP packets with destination addresses covered 1247 by an MNP not explicitly assigned to a non-OMNI interface are 1248 directed to the OMNI interface. 1250 OMNI interface initialization procedures for Proxy/Servers, Clients 1251 and Bridges are discussed in the following sections. 1253 3.4.1. AERO Proxy/Server and Relay Behavior 1255 When a Proxy/Server enables an OMNI interface, it assigns an 1256 ADM-{LLA,ULA} appropriate for the given OMNI link segment. The 1257 Proxy/Server also configures secured tunnels with one or more 1258 neighboring Bridges and engages in a BGP routing protocol session 1259 with each Bridge. 1261 The OMNI interface provides a single interface abstraction to the IP 1262 layer, but internally includes an NBMA nexus for sending carrier 1263 packets to OMNI interface neighbors over underlying INET interfaces 1264 and secured tunnels. The Proxy/Server further configures a service 1265 to facilitate ND exchanges with AERO Clients and manages per-Client 1266 neighbor cache entries and IP forwarding table entries based on 1267 control message exchanges. 1269 Relays are simply Proxy/Servers that run a dynamic routing protocol 1270 to redistribute routes between the OMNI interface and INET/EUN 1271 interfaces (see: Section 3.2.3). The Relay provisions MNPs to 1272 networks on the INET/EUN interfaces (i.e., the same as a Client would 1273 do) and advertises the MSP(s) for the OMNI link over the INET/EUN 1274 interfaces. The Relay further provides an attachment point of the 1275 OMNI link to a non-MNP-based global topology. 1277 3.4.2. AERO Client Behavior 1279 When a Client enables an OMNI interface, it assigns either an 1280 MNP-{LLA, ULA} or a Temporary ULA and sends RS messages with ND 1281 parameters over its underlying interfaces to a Proxy/Server, which 1282 returns an RA message with corresponding parameters. The RS/RA 1283 messages may pass through one or more NATs in the case of a Client's 1284 INET interface. (Note: if the Client used a Temporary ULA in its 1285 initial RS message, it will discover an MNP-{LLA, ULA} in the 1286 corresponding RA that it receives from the Proxy/Server and begin 1287 using these new addresses. If the Client is operating outside the 1288 context of AERO infrastructure such as in a Mobile Ad-hoc Network 1289 (MANET), however, it may continue using Temporary ULAs for Client-to- 1290 Client communications until it encounters an infrastructure element 1291 that can provide an MNP.) 1293 3.4.3. AERO Bridge Behavior 1295 AERO Bridges configure an OMNI interface and assign the ADM-ULA 1296 Subnet Router Anycast address for each OMNI link segment they connect 1297 to. Bridges configure secured tunnels with Proxy/Servers and other 1298 Bridges, and engage in a BGP routing protocol session with neighbors 1299 on the spanning tree (see: Section 3.2.3). 1301 3.5. OMNI Interface Neighbor Cache Maintenance 1303 Each OMNI interface maintains a conceptual neighbor cache that 1304 includes an entry for each neighbor it communicates with on the OMNI 1305 link per [RFC4861]. In addition to ordinary neighbor cache entries, 1306 proxy neighbor cache entries are created and maintained by AERO 1307 Proxy/Servers when they proxy Client ND message exchanges [RFC4389]. 1308 AERO Proxy/Servers maintain proxy neighbor cache entries for each of 1309 their associated Clients. 1311 To the list of neighbor cache entry states in Section 7.3.2 of 1312 [RFC4861], Proxy/Server OMNI interfaces add an additional state 1313 DEPARTED that applies to Clients that have recently departed. The 1314 interface sets a "DepartTime" variable for the neighbor cache entry 1315 to "DEPART_TIME" seconds. DepartTime is decremented unless a new ND 1316 message causes the state to return to REACHABLE. While a neighbor 1317 cache entry is in the DEPARTED state, the Proxy/Server forwards 1318 carrier packets destined to the target Client to the Client's new 1319 location instead. When DepartTime decrements to 0, the neighbor 1320 cache entry is deleted. It is RECOMMENDED that DEPART_TIME be set to 1321 the default constant value REACHABLE_TIME plus 10 seconds (40 seconds 1322 by default) to allow a window for carrier packets in flight to be 1323 delivered while stale route optimization state may be present. 1325 Proxy/Servers can act as RORs on behalf of dependent Clients 1326 according to the Proxy Neighbor Advertisement specification in 1327 Section 7.2.8 of [RFC4861], while well-connected Clients can act as 1328 an ROR on their own behalf. When a Proxy/Server ROR receives an 1329 authentic NS message used for route optimization, it first searches 1330 for a proxy neighbor cache entry for the target Client and accepts 1331 the message only if there is an entry. The Proxy/Server then returns 1332 a solicited NA message while creating a neighbor cache entry for the 1333 ROS. Proxy/Server RORs also create or update a "Report List" entry 1334 for the ROS in the target Client's neighbor cache entry with a 1335 "ReportTime" variable set to REPORT_TIME seconds. The ROR resets 1336 ReportTime when it receives a new authentic NS message, and otherwise 1337 decrements ReportTime while no authentic NS messages have been 1338 received. It is RECOMMENDED that REPORT_TIME be set to the default 1339 constant value REACHABLE_TIME plus 10 seconds (40 seconds by default) 1340 to allow a window for route optimization to converge before 1341 ReportTime decrements below REACHABLE_TIME. 1343 When the ROS receives a solicited NA message response to its NS 1344 message used for route optimization, it creates or updates a neighbor 1345 cache entry for the target network-layer and link-layer addresses. 1346 The ROS then (re)sets ReachableTime for the neighbor cache entry to 1347 REACHABLE_TIME seconds and uses this value to determine whether 1348 carrier packets can be forwarded directly to the target, i.e., 1349 instead of via a default route. The ROS otherwise decrements 1350 ReachableTime while no further solicited NA messages arrive. It is 1351 RECOMMENDED that REACHABLE_TIME be set to the default constant value 1352 30 seconds as specified in [RFC4861]. 1354 AERO nodes also use the value MAX_UNICAST_SOLICIT to limit the number 1355 of NS keepalives sent when a correspondent may have gone unreachable, 1356 the value MAX_RTR_SOLICITATIONS to limit the number of RS messages 1357 sent without receiving an RA and the value MAX_NEIGHBOR_ADVERTISEMENT 1358 to limit the number of unsolicited NAs that can be sent based on a 1359 single event. It is RECOMMENDED that MAX_UNICAST_SOLICIT, 1360 MAX_RTR_SOLICITATIONS and MAX_NEIGHBOR_ADVERTISEMENT be set to 3 the 1361 same as specified in [RFC4861]. 1363 Different values for DEPART_TIME, REPORT_TIME, REACHABLE_TIME, 1364 MAX_UNICAST_SOLICIT, MAX_RTR_SOLCITATIONS and 1365 MAX_NEIGHBOR_ADVERTISEMENT MAY be administratively set; however, if 1366 different values are chosen, all nodes on the link MUST consistently 1367 configure the same values. Most importantly, DEPART_TIME and 1368 REPORT_TIME SHOULD be set to a value that is sufficiently longer than 1369 REACHABLE_TIME to avoid packet loss due to stale route optimization 1370 state. 1372 3.5.1. OMNI Neighbor Interface Attributes 1374 OMNI interface IPv6 ND messages include OMNI options 1375 [I-D.templin-6man-omni] with Interface Attributes that provide Link- 1376 Layer Address and traffic selector information for the neighbor's 1377 underlying interfaces. This information is stored in the neighbor 1378 cache and provides the basis for the forwarding algorithm specified 1379 in Section 3.10. The information is cumulative and reflects the 1380 union of the OMNI information from the most recent ND messages 1381 received from the neighbor; it is therefore not required that each ND 1382 message contain all neighbor information. 1384 The OMNI option Interface Attributes for each underlying interface 1385 includes a two-part "Link-Layer Address" consisting of a simple IP 1386 encapsulation address determined by the FMT and L2ADDR fields and an 1387 ADM-ULA determined by the SRT and LHS fields. Underlying interfaces 1388 are further selected based on their associated preference values 1389 "high", "medium", "low" or "disabled". 1391 Note: the OMNI option is distinct from any Source/Target Link-Layer 1392 Address Options (S/TLLAOs) that may appear in an ND message according 1393 to the appropriate IPv6 over specific link layer specification (e.g., 1394 [RFC2464]). If both an OMNI option and S/TLLAO appear, the former 1395 pertains to encapsulation addresses while the latter pertains to the 1396 native L2 address format of the underlying media. 1398 3.5.2. OMNI Neighbor Advertisement Message Flags 1400 As discussed in Section 4.4 of [RFC4861] NA messages include three 1401 flag bits R, S and O. OMNI interface NA messages treat the flags as 1402 follows: 1404 o R: The R ("Router") flag is set to 1 in the NA messages sent by 1405 all AERO/OMNI node types. Simple hosts that would set R to 0 do 1406 not occur on the OMNI link itself, but may occur on the downstream 1407 links of Clients and Relays. 1409 o S: The S ("Solicited") flag is set exactly as specified in 1410 Section 4.4. of [RFC4861], i.e., it is set to 1 for Solicited NAs 1411 and set to 0 for Unsolicited NAs (both unicast and multicast). 1413 o O: The O ("Override") flag is set to 0 for solicited proxy NAs 1414 returned by a Proxy/Server ROR and set to 1 for all other 1415 solicited and unsolicited NAs. For further study is whether 1416 solicited NAs for anycast targets apply for OMNI links. Since 1417 MNP-LLAs must be uniquely assigned to Clients to support correct 1418 ND protocol operation, however, no role is currently seen for 1419 assigning the same MNP-LLA to multiple Clients. 1421 3.5.3. OMNI Neighbor Window Synchronization 1423 In environments where spoofing is considered a threat, OMNI interface 1424 neighbors invoke window synchronization in ND message exchanges and 1425 maintain send/receive window state in their respective neighbor cache 1426 entries as specified in [I-D.templin-6man-omni]. In the asymmetric 1427 case, the initial ND message exchange establishes only the 1428 initiator's send window and the responder's receive window such that 1429 a corresponding NS/NA exchange would be needed to establish the 1430 reverse direction. In the symmetric case, the initiator and 1431 responder engage in a three-way handshake to symmetrically establish 1432 the send/receive windows of both parties. 1434 3.6. OMNI Interface Encapsulation and Re-encapsulation 1436 The OMNI interface admits original IP packets then (acting as an OAL 1437 source) performs OAL encapsulation and fragmentation as specified in 1438 [I-D.templin-6man-omni] while including an ORH if necessary as 1439 specified in Section 3.2.4. OAL encapsulation produces OAL packets, 1440 while OAL fragmentation turns them into OAL fragments which are then 1441 encapsulated in *NET headers as carrier packets. 1443 For carrier packets undergoing re-encapsulation at an OAL 1444 intermediate node, the OMNI interface decrements the OAL IPv6 header 1445 Hop Limit and discards the carrier packet if the Hop Limit reaches 0. 1446 The intermediate node next removes the *NET encapsulation headers 1447 from the first segment and re-encapsulates the packet in new *NET 1448 encapsulation headers for the next segment. 1450 When a Proxy/Server or Relay re-encapsulates a carrier packet 1451 received from a Client that includes an OAL but no ORH, it inserts an 1452 ORH immediately following the OAL header and adjusts the OAL payload 1453 length and destination address field. The inserted ORH will be 1454 removed by the final-hop Bridge, but its insertion and removal will 1455 not interfere with reassembly at the final destination. For this 1456 reason, Clients must reserve 40 bytes for a maximum-length ORH when 1457 they perform OAL encapsulation (see: Section 3.9). 1459 3.7. OMNI Interface Decapsulation 1461 OMNI interfaces (acting as OAL destinations) decapsulate and 1462 reassemble OAL packets into original IP packets destined either to 1463 the AERO node itself or to a destination reached via an interface 1464 other than the OMNI interface the original IP packet was received on. 1465 When carrier packets containing OAL fragments arrive, the OMNI 1466 interface reassembles as discussed in Section 3.9. 1468 3.8. OMNI Interface Data Origin Authentication 1470 AERO nodes employ simple data origin authentication procedures. In 1471 particular: 1473 o AERO Bridges and Proxy/Servers accept carrier packets received 1474 from secured underlying interfaces. 1476 o AERO Proxy/Servers and Clients accept carrier packets and original 1477 IP packets that originate from within the same secured ANET. 1479 o AERO Clients and Relays accept original IP packets from downstream 1480 network correspondents based on ingress filtering. 1482 o AERO Clients, Relays and Proxy/Servers verify carrier packet UDP/ 1483 IP encapsulation addresses according to [I-D.templin-6man-omni]. 1485 o AERO Clients (as well as Proxy/Servers and Relays when acting as 1486 OAL destinations) accept only carrier packets with Identification 1487 values within the current window for the OAL source neighbor when 1488 window synchronization is employed. 1490 AERO nodes silently drop any packets that do not satisfy the above 1491 data origin authentication procedures. Further security 1492 considerations are discussed in Section 6. 1494 3.9. OMNI Interface MTU 1496 The OMNI interface observes the link nature of tunnels, including the 1497 Maximum Transmission Unit (MTU), Maximum Reassembly Unit (MRU) and 1498 the role of fragmentation and reassembly [I-D.ietf-intarea-tunnels]. 1499 The OMNI interface employs an OMNI Adaptation Layer (OAL) that 1500 accommodates multiple underlying links with diverse MTUs while 1501 observing both a minimum and per-path Maximum Payload Size (MPS). 1502 The functions of the OAL and the OMNI interface MTU/MRU/MPS are 1503 specified in [I-D.templin-6man-omni] with MTU/MRU both set to the 1504 constant value 9180 bytes, with minimum MPS set to 400 bytes, and 1505 with per-path MPS set to potentially larger values depending on the 1506 underlying path. 1508 When the network layer presents an original IP packet to the OMNI 1509 interface, the OAL source encapsulates and fragments the original IP 1510 packet if necessary. When the network layer presents the OMNI 1511 interface with multiple original IP packets bound to the same OAL 1512 destination, the OAL source can concatenate them together into a 1513 single OAL super-packet as discussed in [I-D.templin-6man-omni]. The 1514 OAL source then fragments the OAL packet if necessary according to 1515 the minimum/path MPS such that the OAL headers appear in each 1516 fragment while the original IP packet header appears only in the 1517 first fragment. The OAL source then encapsulates each OAL fragment 1518 in *NET headers for transmission as carrier packets over an 1519 underlying interface connected to either a physical link such as 1520 Ethernet, WiFi and the like or a virtual link such as an Internet or 1521 higher-layer tunnel (see the definition of link in [RFC8200]). 1523 Note: A Client that does not (yet) have neighbor cache state for a 1524 target may omit the ORH in carrier packets with the understanding 1525 that a Proxy/Server may insert an ORH on its behalf. For this 1526 reason, Clients reserve 40 bytes for the largest possible ORH in 1527 their OAL fragment size calculations. 1529 Note: Although the ORH may be removed by a Bridge on the path (see: 1530 Section 3.10.3), this does not interfere with the destination's 1531 ability to reassemble. This is due to the fact that the ORH is not 1532 included in the fragmentable part; therefore, its removal does not 1533 invalidate the offset values in any fragment headers. 1535 3.10. OMNI Interface Forwarding Algorithm 1537 Original IP packets enter a node's OMNI interface either from the 1538 network layer (i.e., from a local application or the IP forwarding 1539 system) while carrier packets enter from the link layer (i.e., from 1540 an OMNI interface neighbor). All original IP packets and carrier 1541 packets entering a node's OMNI interface first undergo data origin 1542 authentication as discussed in Section 3.8. Those that satisfy data 1543 origin authentication are processed further, while all others are 1544 dropped silently. 1546 Original IP packets that enter the OMNI interface from the network 1547 layer are forwarded to an OMNI interface neighbor using OAL 1548 encapsulation and fragmentation to produce carrier packets for 1549 transmission over underlying interfaces. (If routing indicates that 1550 the original IP packet should instead be forwarded back to the 1551 network layer, the packet is dropped to avoid looping). Carrier 1552 packets that enter the OMNI interface from the link layer are either 1553 re-encapsulated and re-admitted into the OMNI link, or reassembled 1554 and forwarded to the network layer where they are subject to either 1555 local delivery or IP forwarding. In all cases, the OAL MUST NOT 1556 decrement the network layer TTL/Hop-count since its forwarding 1557 actions occur below the network layer. 1559 OMNI interfaces may have multiple underlying interfaces and/or 1560 neighbor cache entries for neighbors with multiple underlying 1561 interfaces (see Section 3.3). The OAL uses Interface Attribute 1562 traffic selectors (e.g., port number, flow specification, etc.) to 1563 select an outgoing underlying interface for each OAL packet based on 1564 the node's own interface attributes, and also to select a destination 1565 link-layer address based on the neighbor's underlying interface 1566 attributes. AERO implementations SHOULD allow for traffic selector 1567 values to be modified at runtime through network management. 1569 If multiple outgoing interfaces and/or neighbor interfaces match the 1570 traffic selectors, the AERO node replicates the OAL packet and sends 1571 one copy via each of the (outgoing / neighbor) interface pairs; 1572 otherwise, the node sends a single copy of the OAL packet via an 1573 interface with a matching traffic selector. (While not strictly 1574 required, successful delivery may be more likely when all fragments 1575 of the same OAL packet are sent over the same underlying interface.) 1576 AERO nodes keep track of which underlying interfaces are currently 1577 "reachable" or "unreachable", and only use "reachable" interfaces for 1578 forwarding purposes. 1580 The following sections discuss the OMNI interface forwarding 1581 algorithms for Clients, Proxy/Servers and Bridges. In the following 1582 discussion, an original IP packet's destination address is said to 1583 "match" if it is the same as a cached address, or if it is covered by 1584 a cached prefix (which may be encoded in an MNP-LLA). 1586 3.10.1. Client Forwarding Algorithm 1588 When an original IP packet enters a Client's OMNI interface from the 1589 network layer the Client searches for a neighbor cache entry that 1590 matches the destination. If there is a match, the Client selects one 1591 or more "reachable" neighbor interfaces in the entry for forwarding 1592 purposes. If there is no neighbor cache entry, the Client instead 1593 either enqueues the original IP packet and invokes route optimization 1594 or forwards the original IP packet toward a Proxy/Server. The Client 1595 (acting as an OAL source) performs OAL encapsulation and sets the OAL 1596 destination address to the MNP-ULA if there is a matching neighbor 1597 cache entry; otherwise, it sets the OAL destination to the ADM-ULA of 1598 the Proxy/Server. If the Client has multiple original IP packets to 1599 send to the same neighbor, it can concatenate them in a single super- 1600 packet [I-D.templin-6man-omni]. The OAL source then performs 1601 fragmentation to create OAL fragments (see: Section 3.9), appends any 1602 *NET encapsulation, and sends the resulting carrier packets over 1603 underlying interfaces to the neighbor acting as an OAL destination. 1605 If the neighbor interface selected for forwarding is located on the 1606 same OMNI link segment and not behind a NAT, the Client forwards the 1607 carrier packets directly according to the L2ADDR information for the 1608 neighbor. If the neighbor interface is behind a NAT on the same OMNI 1609 link segment, the Client instead forwards the initial carrier packets 1610 to its Proxy/Server and initiates NAT traversal procedures. If the 1611 Client's intended source underlying interface is also behind a NAT 1612 and located on the same OMNI link segment, it sends a "direct bubble" 1613 over the interface per [RFC6081][RFC4380] to the L2ADDR found in the 1614 neighbor cache in order to establish state in its own NAT by 1615 generating traffic toward the neighbor (note that no response to the 1616 bubble is expected). 1618 The Client next sends an NS(NUD) message toward the MNP-ULA of the 1619 neighbor via its Proxy/Server as discussed in Section 3.15. If the 1620 Client receives an NA(NUD) from the neighbor over the underlying 1621 interface, it marks the neighbor interface as "trusted" and sends 1622 future carrier packets directly to the L2ADDR information for the 1623 neighbor instead of indirectly via the Proxy/Server. The Client must 1624 honor the neighbor cache maintenance procedure by sending additional 1625 direct bubbles and/or NS/NA(NUD) messages as discussed in 1626 [RFC6081][RFC4380] in order to keep NAT state alive as long as 1627 carrier packets are still flowing. 1629 When a carrier packet enters a Client's OMNI interface from the link- 1630 layer, if the OAL destination matches one of the Client's ULAs the 1631 Client (acting as an OAL destination) reassembles and decapsulates as 1632 necessary and delivers the original IP packet to the network layer. 1633 Otherwise, the Client drops the original IP packet and MAY return a 1634 network-layer ICMP Destination Unreachable message subject to rate 1635 limiting (see: Section 3.11). 1637 Note: Clients and their Proxy/Server (and other Client) peers can 1638 exchange original IP packets over ANET underlying interfaces without 1639 invoking the OAL, since the ANET is secured at the link and physical 1640 layers. By forwarding original IP packets without invoking the OAL, 1641 however, the ANET peers can engage only in classical path MTU 1642 discovery since the packets are subject to loss and/or corruption due 1643 to the various per-link MTU limitations that may occur within the 1644 ANET. Moreover, the original IP packets do not include either the 1645 OAL integrity check or per-packet Identification values that can be 1646 used for data origin authentication and link-layer retransmissions. 1647 The tradeoff therefore involves an assessment of the per-packet 1648 encapsulation overhead saved by bypassing the OAL vs. inheritance of 1649 classical network "brittleness". (Note however that ANET peers can 1650 send small original IP packets without invoking the OAL, while 1651 invoking the OAL for larger packets. This presents the beneficial 1652 aspects of both small packet efficiency and large packet robustness.) 1654 3.10.2. Proxy/Server and Relay Forwarding Algorithm 1656 When the Proxy/Server receives an original IP packet from the network 1657 layer, it drops the packet if routing indicates that it should be 1658 forwarded back to the network layer to avoid looping. Otherwise, the 1659 Proxy/Server regards the original IP packet the same as if it had 1660 arrived as carrier packets with OAL destination set to its own ADM- 1661 ULA. When the Proxy/Server receives carrier packets on underlying 1662 interfaces with OAL destination set to its own ADM-ULA, it performs 1663 OAL reassembly if necessary to obtain the original IP packet. 1665 The Proxy/Server next searches for a neighbor cache entry that 1666 matches the original IP destination and proceeds as follows: 1668 o if the original IP packet destination matches a neighbor cache 1669 entry, the Proxy/Sever uses one or more "reachable" neighbor 1670 interfaces in the entry for packet forwarding using OAL 1671 encapsulation and fragmentation according to the cached link-layer 1672 address information. If the neighbor interface is in a different 1673 OMNI link segment, the Proxy/Server forwards the resulting carrier 1674 packets via the spanning tree to a Bridge; otherwise, it forwards 1675 the carrier packets directly to the neighbor. If the neighbor is 1676 behind a NAT, the Proxy/Server instead forwards initial carrier 1677 packets via a Bridge while sending an NS(NUD) to the neighbor. 1678 When the Proxy/Server receives the NA(NUD), it can begin 1679 forwarding carrier packets directly to the neighbor the same as 1680 discussed in Section 3.10.1 while sending additional NS(NUD) 1681 messages as necessary to maintain NAT state. Note that no direct 1682 bubbles are necessary since the Proxy/Server is by definition not 1683 located behind a NAT. 1685 o else, if the original IP destination matches a non-MNP route in 1686 the IP forwarding table or an ADM-LLA assigned to the Proxy/ 1687 Server's OMNI interface, the Proxy/Server acting as a Relay 1688 presents the original IP packet to the network layer for local 1689 delivery or IP forwarding. 1691 o else, the Proxy/Server initiates address resolution as discussed 1692 in Section 3.14, while retaining initial original IP packets in a 1693 small queue awaiting address resolution completion. 1695 When the Proxy/Server receives a carrier packet with OAL destination 1696 set to an MNP-ULA that does not match the MSP, it accepts the carrier 1697 packet only if data origin authentication succeeds and if there is a 1698 network layer routing table entry for a GUA route that matches the 1699 MNP-ULA. If there is no route, the Proxy/Server drops the carrier 1700 packet; otherwise, it reassembles and decapsulates to obtain the 1701 original IP packet and acts as a Relay to present it to the network 1702 layer where it will be delivered according to standard IP forwarding. 1704 When the Proxy/Server receives a carrier packet from one of its 1705 Client neighbors with OAL destination set to another node, it 1706 forwards the packets via a matching neighbor cache entry or via the 1707 spanning tree if there is no matching entry. When the Proxy/Server 1708 receives a carrier packet with OAL destination set to the MNP-ULA of 1709 one of its Client neighbors established through RS/RA exchanges, it 1710 accepts the carrier packet only if data origin authentication 1711 succeeds. If the neighbor cache entry state is DEPARTED, the Proxy/ 1712 Server inserts an ORH that encodes the MNP-ULA destination suffix and 1713 changes the OAL destination address to the ADM-ULA of the new Proxy/ 1714 Server, then re-encapsulates the carrier packet and forwards it to a 1715 Bridge which will eventually deliver it to the new Proxy/Server. 1717 If the neighbor cache state for the MNP-ULA is REACHABLE, the Proxy/ 1718 Server forwards the carrier packets to the Client which then must 1719 reassemble. (Note that the Proxy/Server does not reassemble carrier 1720 packets not explicitly addressed to its own ADM-ULA, since routing 1721 could direct some of the carrier packet of the same original IP 1722 packet through a different Proxy/Server.) In that case, the Client 1723 may receive fragments that are smaller than its link MTU but can 1724 still be reassembled. 1726 Note: Clients and their Proxy/Server peers can exchange original IP 1727 packets over ANET underlying interfaces without invoking the OAL, 1728 since the ANET is secured at the link and physical layers. By 1729 forwarding original IP packets without invoking the OAL, however, the 1730 Client and Proxy/Server can engage only in classical path MTU 1731 discovery since the packets are subject to loss and/or corruption due 1732 to the various per-link MTU limitations that may occur within the 1733 ANET. Moreover, the original IP packets do not include either the 1734 OAL integrity check or per-packet Identification values that can be 1735 used for data origin authentication and link-layer retransmissions. 1736 The tradeoff therefore involves an assessment of the per-packet 1737 encapsulation overhead saved by bypassing the OAL vs. inheritance of 1738 classical network "brittleness". (Note however that ANET peers can 1739 send small original IP packets without invoking the OAL, while 1740 invoking the OAL for larger packets. This presents the beneficial 1741 aspects of both small packet efficiency and large packet robustness.) 1743 Note: When a Proxy/Server receives a (non-OAL) original IP packet 1744 from an ANET Client, or a carrier packet with OAL destination set to 1745 its own ADM-ULA from any Client, the Proxy/Server reassembles if 1746 necessary then performs ROS functions on behalf of the Client. The 1747 Client may at some later time begin sending carrier packets to the 1748 OAL address of the actual target instead of the Proxy/Server, at 1749 which point it may begin functioning as an ROS on its own behalf and 1750 thereby "override" the Proxy/Server's ROS role. 1752 Note: Proxy/Servers forward secure control plane carrier packets via 1753 the secured spanning tree and forwards other carrier packets via the 1754 unsecured spanning tree. When a Proxy/Server receives a carrier 1755 packet from the secured spanning tree, it considers the message as 1756 authentic without having to verify upper layer authentication 1757 signatures. When a Proxy/Server receives a carrier packet from the 1758 unsecured spanning tree, it verifies any upper layer authentication 1759 signatures and/or forwards the unsecured message toward the 1760 destination which must apply data origin authentication. 1762 Note: If the Proxy/Server has multiple original IP packets to send to 1763 the same neighbor, it can concatenate them in a single OAL super- 1764 packet [I-D.templin-6man-omni]. 1766 3.10.3. Bridge Forwarding Algorithm 1768 Bridges forward carrier packets the same as any IPv6 router. Bridges 1769 convey carrier packets that encapsulate IPv6 ND control messages or 1770 routing protocol control messages using security encapsulations, and 1771 may convey carrier packets that encapsulate ordinary data without 1772 including security encapsulations. When the Bridge receives a 1773 carrier packet, it removes the outer *NET header and searches for a 1774 forwarding table entry that matches the OAL destination address. The 1775 Bridge then processes the packet as follows: 1777 o if the carrier packet destination matches its ADM-ULA or the 1778 corresponding ADM-ULA Subnet Router Anycast address and the OAL 1779 header is followed by an ORH, the Bridge removes and sets aside 1780 the ORH then processes the carrier packet locally before 1781 forwarding. If the encapsulated packet is an atomic fragment 1782 containing an NA(NUD) message, the Bridge replaces the OMNI option 1783 Interface Attributes sub-option with information for its own 1784 interface while retaining the omIndex value supplied by the 1785 NA(NUD) message source. The Bridge next examines the ORH FMT 1786 code. If the code indicates the destination is a Client on the 1787 open *NET (or, a Client behind a NAT for which NAT traversal 1788 procedures have already converged) the Bridge writes the MNP-ULA 1789 formed from the ORH Destination Suffix into the OAL destination. 1790 The Bridge then re-encapsulates the carrier packet and forwards it 1791 to the ORH L2ADDR. For all other cases, the Bridge instead writes 1792 the ADM-ULA formed from the ORH SRT/LHS into the OAL destination 1793 address and forwards the carrier packet to the ADM-ULA Proxy/ 1794 Server while invoking NAT traversal procedures the same as for 1795 Proxy/Servers if necessary, noting that no direct bubbles are 1796 necessary since only the target Client and not the Bridge is 1797 behind a NAT 1799 o else, if the carrier packet destination matches its ADM-ULA or the 1800 corresponding ADM-ULA Subnet Router Anycast address and the OAL 1801 header is not followed by an ORH, the Bridge submits the packet 1802 for reassembly. When reassembly is complete, the Bridge submits 1803 the original packet to the IP layer to support local applications 1804 such as BGP routing protocol sessions. 1806 o else, if the carrier packet destination matches a forwarding table 1807 entry the Bridge forwards the carrier packet to the next hop. (If 1808 the destination matches an MSP without matching an MNP, however, 1809 the Bridge instead drops the packet and returns an ICMP 1810 Destination Unreachable message subject to rate limiting - see: 1811 Section 3.11). 1813 o else, the Bridge drops the packet and returns an ICMP Destination 1814 Unreachable as above. 1816 As for any IP router, the Bridge decrements the OAL IPv6 header Hop 1817 Limit when it forwards the carrier packet and drops the packet if the 1818 Hop Limit reaches 0. Therefore, only the Hop Limit in the OAL header 1819 is decremented and not the TTL/Hop Limit in the original IP packet 1820 header. Bridges do not insert OAL/ORH headers themselves; instead, 1821 they act as IPv6 routers and forward carrier packets based on their 1822 destination addresses. 1824 Bridges forward carrier packets received from a first segment via the 1825 unsecured spanning tree to the next segment also via the unsecured 1826 spanning tree. Bridges forward carrier packets received from a first 1827 segment via the secured spanning tree to the next segment also via 1828 the secured spanning tree. Bridges use a single IPv6 routing table 1829 that always determines the same next hop for a given OAL destination, 1830 where the secured/unsecured spanning tree is determined through the 1831 selection of the underlying interface to be used for transmission 1832 (i.e., a secured tunnel or an open INET interface). 1834 3.11. OMNI Interface Error Handling 1836 When an AERO node admits an original IP packet into the OMNI 1837 interface, it may receive link-layer or network-layer error 1838 indications. 1840 A link-layer error indication is an ICMP error message generated by a 1841 router in the INET on the path to the neighbor or by the neighbor 1842 itself. The message includes an IP header with the address of the 1843 node that generated the error as the source address and with the 1844 link-layer address of the AERO node as the destination address. 1846 The IP header is followed by an ICMP header that includes an error 1847 Type, Code and Checksum. Valid type values include "Destination 1848 Unreachable", "Time Exceeded" and "Parameter Problem" 1849 [RFC0792][RFC4443]. (OMNI interfaces ignore link-layer IPv4 1850 "Fragmentation Needed" and IPv6 "Packet Too Big" messages for carrier 1851 packets that are no larger than the minimum/path MPS as discussed in 1852 Section 3.9, however these messages may provide useful hints of probe 1853 failures during path MPS probing.) 1855 The ICMP header is followed by the leading portion of the carrier 1856 packet that generated the error, also known as the "packet-in-error". 1857 For ICMPv6, [RFC4443] specifies that the packet-in-error includes: 1859 "As much of invoking packet as possible without the ICMPv6 packet 1860 exceeding the minimum IPv6 MTU" (i.e., no more than 1280 bytes). For 1861 ICMPv4, [RFC0792] specifies that the packet-in-error includes: 1862 "Internet Header + 64 bits of Original Data Datagram", however 1863 [RFC1812] Section 4.3.2.3 updates this specification by stating: "the 1864 ICMP datagram SHOULD contain as much of the original datagram as 1865 possible without the length of the ICMP datagram exceeding 576 1866 bytes". 1868 The link-layer error message format is shown in Figure 5 (where, "L2" 1869 and "L3" refer to link-layer and network-layer, respectively): 1871 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1872 ~ ~ 1873 | L2 IP Header of | 1874 | error message | 1875 ~ ~ 1876 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1877 | L2 ICMP Header | 1878 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 1879 ~ ~ P 1880 | carrier packet *NET and OAL | a 1881 | encapsulation headers | c 1882 ~ ~ k 1883 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ e 1884 ~ ~ t 1885 | original IP packet headers | 1886 | (first-fragment only) | i 1887 ~ ~ n 1888 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1889 ~ ~ e 1890 | Portion of the body of | r 1891 | the original IP packet | r 1892 | (all fragments) | o 1893 ~ ~ r 1894 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 1896 Figure 5: OMNI Interface Link-Layer Error Message Format 1898 The AERO node rules for processing these link-layer error messages 1899 are as follows: 1901 o When an AERO node receives a link-layer Parameter Problem message, 1902 it processes the message the same as described as for ordinary 1903 ICMP errors in the normative references [RFC0792][RFC4443]. 1905 o When an AERO node receives persistent link-layer Time Exceeded 1906 messages, the IP ID field may be wrapping before earlier fragments 1907 awaiting reassembly have been processed. In that case, the node 1908 should begin including integrity checks and/or institute rate 1909 limits for subsequent packets. 1911 o When an AERO node receives persistent link-layer Destination 1912 Unreachable messages in response to carrier packets that it sends 1913 to one of its neighbor correspondents, the node should process the 1914 message as an indication that a path may be failing, and 1915 optionally initiate NUD over that path. If it receives 1916 Destination Unreachable messages over multiple paths, the node 1917 should allow future carrier packets destined to the correspondent 1918 to flow through a default route and re-initiate route 1919 optimization. 1921 o When an AERO Client receives persistent link-layer Destination 1922 Unreachable messages in response to carrier packets that it sends 1923 to one of its neighbor Proxy/Servers, the Client should mark the 1924 path as unusable and use another path. If it receives Destination 1925 Unreachable messages on many or all paths, the Client should 1926 associate with a new Proxy/Server and release its association with 1927 the old Proxy/Server as specified in Section 3.16.5. 1929 o When an AERO Proxy/Server receives persistent link-layer 1930 Destination Unreachable messages in response to carrier packets 1931 that it sends to one of its neighbor Clients, the Proxy/Server 1932 should mark the underlying path as unusable and use another 1933 underlying path. 1935 o When an AERO Proxy/Server receives link-layer Destination 1936 Unreachable messages in response to a carrier packet that it sends 1937 to one of its permanent neighbors, it treats the messages as an 1938 indication that the path to the neighbor may be failing. However, 1939 the dynamic routing protocol should soon reconverge and correct 1940 the temporary outage. 1942 When an AERO Bridge receives a carrier packet for which the network- 1943 layer destination address is covered by an MSP, the Bridge drops the 1944 packet if there is no more-specific routing information for the 1945 destination and returns a network-layer Destination Unreachable 1946 message subject to rate limiting. The Bridge writes the network- 1947 layer source address of the original IP packet as the destination 1948 address and uses one of its non link-local addresses as the source 1949 address of the message. 1951 When an AERO node receives a carrier packet for which reassembly is 1952 currently congested, it returns a network-layer Packet Too Big (PTB) 1953 message as discussed in [I-D.templin-6man-omni] (note that the PTB 1954 messages could indicate either "hard" or "soft" errors). 1956 3.12. AERO Router Discovery, Prefix Delegation and Autoconfiguration 1958 AERO Router Discovery, Prefix Delegation and Autoconfiguration are 1959 coordinated as discussed in the following Sections. 1961 3.12.1. AERO Service Model 1963 Each AERO Proxy/Server on the OMNI link is configured to facilitate 1964 Client prefix delegation/registration requests. Each Proxy/Server is 1965 provisioned with a database of MNP-to-Client ID mappings for all 1966 Clients enrolled in the AERO service, as well as any information 1967 necessary to authenticate each Client. The Client database is 1968 maintained by a central administrative authority for the OMNI link 1969 and securely distributed to all Proxy/Servers, e.g., via the 1970 Lightweight Directory Access Protocol (LDAP) [RFC4511], via static 1971 configuration, etc. Clients receive the same service regardless of 1972 the Proxy/Servers they select. 1974 AERO Clients and Proxy/Servers use ND messages to maintain neighbor 1975 cache entries. AERO Proxy/Servers configure their OMNI interfaces as 1976 advertising NBMA interfaces, and therefore send unicast RA messages 1977 with a short Router Lifetime value (e.g., ReachableTime seconds) in 1978 response to a Client's RS message. Thereafter, Clients send 1979 additional RS messages to keep Proxy/Server state alive. 1981 AERO Clients and Proxy/Servers include prefix delegation and/or 1982 registration parameters in RS/RA messages (see 1983 [I-D.templin-6man-omni]). The ND messages are exchanged between 1984 Client and Proxy/Server according to the prefix management schedule 1985 required by the service. If the Client knows its MNP in advance, it 1986 can employ prefix registration by including its MNP-LLA as the source 1987 address of an RS message and with an OMNI option with valid prefix 1988 registration information for the MNP. If the Proxy/Server accepts 1989 the Client's MNP assertion, it injects the MNP into the routing 1990 system and establishes the necessary neighbor cache state. If the 1991 Client does not have a pre-assigned MNP, it can instead employ prefix 1992 delegation by including the unspecified address (::) as the source 1993 address of an RS message and with an OMNI option with prefix 1994 delegation parameters to request an MNP. 1996 The following sections specify the Client and Proxy/Server behavior. 1998 3.12.2. AERO Client Behavior 2000 AERO Clients discover the addresses of Proxy/Servers in a similar 2001 manner as described in [RFC5214]. Discovery methods include static 2002 configuration (e.g., from a flat-file map of Proxy/Server addresses 2003 and locations), or through an automated means such as Domain Name 2004 System (DNS) name resolution [RFC1035]. Alternatively, the Client 2005 can discover Proxy/Server addresses through a layer 2 data link login 2006 exchange, or through a unicast RA response to a multicast/anycast RS 2007 as described below. In the absence of other information, the Client 2008 can resolve the DNS Fully-Qualified Domain Name (FQDN) 2009 "linkupnetworks.[domainname]" where "linkupnetworks" is a constant 2010 text string and "[domainname]" is a DNS suffix for the OMNI link 2011 (e.g., "example.com"). 2013 To associate with a Proxy/Server, the Client acts as a requesting 2014 router to request MNPs. The Client prepares an RS message with 2015 prefix management parameters and includes a Nonce and Timestamp 2016 option if the Client needs them to correlate RA replies. If the 2017 Client already knows the Proxy/Server's ADM-LLA, it includes the LLA 2018 as the network-layer destination address; otherwise, the Client 2019 includes the (link-local) All-Routers multicast as the network-layer 2020 destination. If the Client already knows its own MNP-LLA, it can use 2021 the MNP-LLA as the network-layer source address and include an OMNI 2022 option with prefix registration information. Otherwise, the Client 2023 uses the unspecified address (::) as the network-layer source address 2024 and includes prefix delegation parameters in the OMNI option (see: 2025 [I-D.templin-6man-omni]). 2027 The Client next includes Interface Attributes corresponding to the 2028 underlying interface over which it will send the RS message, and MAY 2029 include additional Interface Attributes specific to other underlying 2030 interfaces. Next, the Client submits the RS for OAL encapsulation 2031 and fragmentation if necessary with its own MNP-ULA and the Proxy/ 2032 Server's ADM-ULA as the OAL addresses while selecting an 2033 Identification value and optionally invoking window synchronization 2034 as specified in [I-D.templin-6man-omni]. 2036 The Client then sends the RS (either directly via Direct interfaces, 2037 via a VPN for VPNed interfaces, via an access router for ANET 2038 interfaces or via INET encapsulation for INET interfaces) then waits 2039 up to RetransTimer milliseconds for an RA message reply (see 2040 Section 3.12.3) (retrying up to MAX_RTR_SOLICITATIONS). If the 2041 Client receives no RAs, or if it receives an RA with Router Lifetime 2042 set to 0, the Client SHOULD abandon attempts through the first Proxy/ 2043 Server and try another Proxy/Server. Otherwise, the Client processes 2044 the prefix information found in the RA message. 2046 When the Client processes an RA, it first performs OAL reassembly and 2047 decapsulation if necessary then creates a neighbor cache entry with 2048 the Proxy/Server's ADM-LLA as the network-layer address and the 2049 Proxy/Server's encapsulation and/or link-layer addresses as the link- 2050 layer address. The Client next records the RA Router Lifetime field 2051 value in the neighbor cache entry as the time for which the Proxy/ 2052 Server has committed to maintaining the MNP in the routing system via 2053 this underlying interface, and caches the other RA configuration 2054 information including Cur Hop Limit, M and O flags, Reachable Time 2055 and Retrans Timer. The Client then autoconfigures MNP-LLAs for any 2056 delegated MNPs and assigns them to the OMNI interface. The Client 2057 also caches any MSPs included in Route Information Options (RIOs) 2058 [RFC4191] as MSPs to associate with the OMNI link, and assigns the 2059 MTU value in the MTU option to the underlying interface. 2061 The Client then registers additional underlying interfaces with the 2062 Proxy/Server by sending RS messages via each additional interface as 2063 described above. The RS messages include the same parameters as for 2064 the initial RS/RA exchange, but with destination address set to the 2065 Proxy/Server's ADM-LLA. The Client finally sub-delegates the MNPs to 2066 its attached EUNs and/or the Client's own internal virtual interfaces 2067 as described in [I-D.templin-v6ops-pdhost] to support the Client's 2068 downstream attached "Internet of Things (IoT)". The Client then 2069 sends additional RS messages over each underlying interface before 2070 the Router Lifetime received for that interface expires. 2072 After the Client registers its underlying interfaces, it may wish to 2073 change one or more registrations, e.g., if an interface changes 2074 address or becomes unavailable, if traffic selectors change, etc. To 2075 do so, the Client prepares an RS message to send over any available 2076 underlying interface as above. The RS includes an OMNI option with 2077 prefix registration/delegation information, with Interface Attributes 2078 specific to the selected underlying interface, and with any 2079 additional Interface Attributes specific to other underlying 2080 interfaces. When the Client receives the Proxy/Server's RA response, 2081 it has assurance that the Proxy/Server has been updated with the new 2082 information. 2084 If the Client wishes to discontinue use of a Proxy/Server it issues 2085 an RS message over any underlying interface with an OMNI option with 2086 a prefix release indication. When the Proxy/Server processes the 2087 message, it releases the MNP, sets the neighbor cache entry state for 2088 the Client to DEPARTED and returns an RA reply with Router Lifetime 2089 set to 0. After a short delay (e.g., 2 seconds), the Proxy/Server 2090 withdraws the MNP from the routing system. 2092 3.12.3. AERO Proxy/Server Behavior 2094 AERO Proxy/Servers act as IP routers and support a prefix delegation/ 2095 registration service for Clients. Proxy/Servers arrange to add their 2096 ADM-LLAs to a static map of Proxy/Server addresses for the link and/ 2097 or the DNS resource records for the FQDN 2098 "linkupnetworks.[domainname]" before entering service. Proxy/Server 2099 addresses should be geographically and/or topologically referenced, 2100 and made available for discovery by Clients on the OMNI link. 2102 When a Proxy/Server receives a prospective Client's RS message on its 2103 OMNI interface, it SHOULD return an immediate RA reply with Router 2104 Lifetime set to 0 if it is currently too busy or otherwise unable to 2105 service the Client. Otherwise, the Proxy/Server performs OAL 2106 reassembly and decapsulation if necessary, then authenticates the RS 2107 message and processes the prefix delegation/registration parameters. 2108 The Proxy/Server first determines the correct MNPs to provide to the 2109 Client by processing the MNP-LLA prefix parameters and/or the DHCPv6 2110 OMNI sub-option. When the Proxy/Server returns the MNPs, it also 2111 creates a forwarding table entry for the MNP-ULA corresponding to 2112 each MNP so that the MNPs are propagated into the routing system 2113 (see: Section 3.2.3). For IPv6, the Proxy/Server creates an IPv6 2114 forwarding table entry for each MNP. For IPv4, the Proxy/Server 2115 creates an IPv6 forwarding table entry with the IPv4-compatibility 2116 MNP-ULA prefix corresponding to the IPv4 address. 2118 The Proxy/Server next creates a neighbor cache entry for the Client 2119 using the base MNP-LLA as the network-layer address and with lifetime 2120 set to no more than the smallest prefix lifetime. Next, the Proxy/ 2121 Server updates the neighbor cache entry by recording the information 2122 in each Interface Attributes sub-option in the RS OMNI option. The 2123 Proxy/Server also records the actual OAL/*NET addresses and RS 2124 message window synchronization parameters (if any) in the neighbor 2125 cache entry. 2127 Next, the Proxy/Server prepares an RA message using its ADM-LLA as 2128 the network-layer source address and the network-layer source address 2129 of the RS message as the network-layer destination address. The 2130 Proxy/Server sets the Router Lifetime to the time for which it will 2131 maintain both this underlying interface individually and the neighbor 2132 cache entry as a whole. The Proxy/Server also sets Cur Hop Limit, M 2133 and O flags, Reachable Time and Retrans Timer to values appropriate 2134 for the OMNI link. The Proxy/Server includes the MNPs, any other 2135 prefix management parameters and an OMNI option with no Interface 2136 Attributes but with an Origin Indication sub-option per 2137 [I-D.templin-6man-omni] with the mapped and obfuscated Port Number 2138 and IP address corresponding to the Client's own INET address in the 2139 case of INET Clients or to the Proxy/Server's INET-facing address for 2140 all other Clients. The Proxy/Server then includes one or more RIOs 2141 that encode the MSPs for the OMNI link, plus an MTU option (see 2142 Section 3.9). The Proxy/Server finally forwards the message to the 2143 Client using OAL encapsulation/fragmentation if necessary while 2144 including an acknowledgement if the RS invoked window 2145 synchronization. 2147 After the initial RS/RA exchange, the Proxy/Server maintains a 2148 ReachableTime timer for each of the Client's underlying interfaces 2149 individually (and for the Client's neighbor cache entry collectively) 2150 set to expire after ReachableTime seconds. If the Client (or Proxy) 2151 issues additional RS messages, the Proxy/Server sends an RA response 2152 and resets ReachableTime. If the Proxy/Server receives an ND message 2153 with a prefix release indication it sets the Client's neighbor cache 2154 entry to the DEPARTED state and withdraws the MNP from the routing 2155 system after a short delay (e.g., 2 seconds). If ReachableTime 2156 expires before a new RS is received on an individual underlying 2157 interface, the Proxy/Server marks the interface as DOWN. If 2158 ReachableTime expires before any new RS is received on any individual 2159 underlying interface, the Proxy/Server sets the neighbor cache entry 2160 state to STALE and sets a 10 second timer. If the Proxy/Server has 2161 not received a new RS or ND message with a prefix release indication 2162 before the 10 second timer expires, it deletes the neighbor cache 2163 entry and withdraws the MNP from the routing system. 2165 The Proxy/Server processes any ND messages pertaining to the Client 2166 and returns an NA/RA reply in response to solicitations. The Proxy/ 2167 Server may also issue unsolicited RA messages, e.g., with reconfigure 2168 parameters to cause the Client to renegotiate its prefix delegation/ 2169 registrations, with Router Lifetime set to 0 if it can no longer 2170 service this Client, etc. Finally, If the neighbor cache entry is in 2171 the DEPARTED state, the Proxy/Server deletes the entry after 2172 DepartTime expires. 2174 Note: Clients SHOULD notify former Proxy/Servers of their departures, 2175 but Proxy/Servers are responsible for expiring neighbor cache entries 2176 and withdrawing routes even if no departure notification is received 2177 (e.g., if the Client leaves the network unexpectedly). Proxy/Servers 2178 SHOULD therefore set Router Lifetime to ReachableTime seconds in 2179 solicited RA messages to minimize persistent stale cache information 2180 in the absence of Client departure notifications. A short Router 2181 Lifetime also ensures that proactive RS/RA messaging between Clients 2182 and Proxy/Servers will keep any NAT state alive (see above). 2184 Note: All Proxy/Servers on an OMNI link MUST advertise consistent 2185 values in the RA Cur Hop Limit, M and O flags, Reachable Time and 2186 Retrans Timer fields the same as for any link, since unpredictable 2187 behavior could result if different Proxy/Servers on the same link 2188 advertised different values. 2190 3.12.3.1. DHCPv6-Based Prefix Registration 2192 When a Client is not pre-provisioned with an MNP-LLA, it will need 2193 for the Proxy/Server to select one or more MNPs on its behalf and set 2194 up the correct state in the AERO routing service. (A Client with a 2195 pre-provisioned MNP may also request the Proxy/Server to select 2196 additional MNPs.) The DHCPv6 service [RFC8415] is used to support 2197 this requirement. 2199 When a Client needs to have the Proxy/Server select MNPs, it sends an 2200 RS message with source address set to the unspecified address (::) 2201 and with an OMNI option that includes a DHCPv6 message sub-option 2202 with DHCPv6 Prefix Delegation (DHCPv6-PD) parameters. When the 2203 Proxy/Server receives the RS message, it extracts the DHCPv6-PD 2204 message from the OMNI option. 2206 The Proxy/Server then acts as a "Proxy DHCPv6 Client" in a message 2207 exchange with the locally-resident DHCPv6 server, which delegates 2208 MNPs and returns a DHCPv6-PD Reply message. (If the Proxy/Server 2209 wishes to defer creation of MN state until the DHCPv6-PD Reply is 2210 received, it can instead act as a Lightweight DHCPv6 Relay Agent per 2211 [RFC6221] by encapsulating the DHCPv6-PD message in a Relay-forward/ 2212 reply exchange with Relay Message and Interface ID options.) 2214 When the Proxy/Server receives the DHCPv6-PD Reply, it adds a route 2215 to the routing system and creates an MNP-LLA based on the delegated 2216 MNP. The Proxy/Server then sends an RA back to the Client with the 2217 (newly-created) MNP-LLA as the destination address and with the 2218 DHCPv6-PD Reply message coded in the OMNI option. When the Client 2219 receives the RA, it creates a default route, assigns the Subnet 2220 Router Anycast address and sets its MNP-LLA based on the delegated 2221 MNP. 2223 Note: See [I-D.templin-6man-omni] for an MNP delegation alternative 2224 that avoids including a DHCPv6 message sub-option in the RS. Namely, 2225 when the Client requests a single MNP it can set the RS source to the 2226 unspecified address (::) and include a Node Identification sub-option 2227 and Preflen in the OMNI option (but with no DHCPv6 message sub- 2228 option). When the Proxy/Server receives the RS message, it forwards 2229 a self-generated DHCPv6 Solicit message to the DHCPv6 server on 2230 behalf of the Client. When the Proxy/Server receives the DHCPv6 2231 Reply, it prepares an RA message with an OMNI option with Preflen 2232 information (but with no DHCPv6 message sub-option), then places the 2233 (newly-created) MNP-LLA in the RA destination address and returns the 2234 message to the Client. 2236 3.13. The AERO Proxy Function 2238 Clients connect to the OMNI link via Proxy/Servers, with one Proxy/ 2239 Server for each underlying interface. Each of the Client's Proxy/ 2240 Servers must be informed of all of the Client's additional underlying 2241 interfaces. For Clients on Direct and VPNed underlying interfaces 2242 the Proxy/Server "A" for that interface is directly connected, for 2243 Clients on ANET underlying interfaces Proxy/Server "A" is located on 2244 the ANET/INET boundary, and for Clients on INET underlying interfaces 2245 Proxy/Server "A" is located somewhere in the connected Internetwork. 2246 When the Client registers with Proxy/Server "A", it must also report 2247 the registration to any other Proxy/Servers for other underlying 2248 interfaces "B", "C", "D", etc. for which an underlying interface 2249 relationship has already been established. The Proxy/Server 2250 satisfies these requirements as follows: 2252 o when Proxy/Server "A" receives an RS message from a new Client, it 2253 first authenticates the message then examines the network-layer 2254 destination address. If the destination address is Proxy/Server 2255 "A"'s ADM-LLA or (link-local) All-Routers multicast, Proxy/Server 2256 "A" creates a proxy neighbor cache entry and caches the Client 2257 link-layer addresses along with the OMNI option information and 2258 any other identifying information including OAL Identification 2259 values, Client Identifiers, Nonce values, etc. If the RS message 2260 destination was the ADM-LLA of a different Proxy/Server "B" (or, 2261 if the OMNI option included an MS-Register sub-option with the 2262 ADM-LLA of a different Proxy/Server "B"), Proxy/Server "A" 2263 encapsulates a proxyed version of the RS message in an OAL header 2264 with source set to Proxy/Server "A"'s ADM-ULA and destination set 2265 to Proxy/Server "B"'s ADM-ULA. Proxy/Server "A" also includes an 2266 OMNI header with an Interface Attributes option that includes its 2267 own INET address plus a unique UDP Port Number for this Client, 2268 then forwards the message into the OMNI link spanning tree. 2269 (Note: including a unique Port Number allows Proxy/Server "B" to 2270 distinguish different Clients located behind the same Proxy/Server 2271 "A" at the link-layer, whereas the link-layer addresses would 2272 otherwise be indistinguishable.) 2274 o when the Proxy/Server "B" receives the RS, it authenticates the 2275 message then creates or updates a neighbor cache entry for the 2276 Client with Proxy/Server "A"'s ADM-ULA, INET address and UDP Port 2277 Number as the link-layer address information. Proxy/Server "B" 2278 then sends an RA message back to Proxy/Server "A" via the spanning 2279 tree. 2281 o when Proxy/Server "A" receives the RA, it authenticates the 2282 message and matches it with the proxy neighbor cache entry created 2283 by the RS. Proxy/Server "A" then caches the prefix information as 2284 a mapping from the Client's MNPs to the Client's link-layer 2285 address, caches the Proxy/Server's advertised Router Lifetime and 2286 sets the neighbor cache entry state to REACHABLE. The Proxy/ 2287 Server then optionally rewrites the Router Lifetime and forwards 2288 the (proxyed) message to the Client. The Proxy/Server finally 2289 includes an MTU option (if necessary) with an MTU to use for the 2290 underlying ANET interface. 2292 o The Client repeats this process with each Proxy/Server "B", "C", 2293 "D" for each of its additional underlying interfaces. 2295 After the initial RS/RA exchanges each Proxy/Server forwards any of 2296 the Client's carrier packets for which there is no matching neighbor 2297 cache entry to a Bridge using OAL encapsulation with its own ADM-ULA 2298 as the source and the MNP-ULA corresponding to the Client as the 2299 destination. The Proxy/Server instead forwards any carrier packets 2300 destined to a neighbor cache target directly to the target according 2301 to the OAL/link-layer information - the process of establishing 2302 neighbor cache entries is specified in Section 3.14. 2304 While the Client is still associated with each Proxy/Server "A", "A" 2305 can send NS, RS and/or unsolicited NA messages to update the neighbor 2306 cache entries of other AERO nodes on behalf of the Client and/or to 2307 convey Interface Attribute updates. This allows for higher-frequency 2308 Proxy-initiated RS/RA messaging over well-connected INET 2309 infrastructure supplemented by lower-frequency Client-initiated RS/RA 2310 messaging over constrained ANET data links. 2312 If any Proxy/Server "B", "C", "D" ceases to send solicited 2313 advertisements, Proxy/Server "A" sends unsolicited RAs to the Client 2314 with destination set to (link-local) All-Nodes multicast and with 2315 Router Lifetime set to zero to inform Clients that a Proxy/Server has 2316 failed. Although Proxy/Server "A" can engage in ND exchanges on 2317 behalf of the Client, the Client can also send ND messages on its own 2318 behalf, e.g., if it is in a better position than "A" to convey 2319 Interface Attribute changes, etc. The ND messages sent by the Client 2320 include the Client's MNP-LLA as the source in order to differentiate 2321 them from the ND messages sent by Proxy/Server "A". 2323 If the Client becomes unreachable over an underlying interface, 2324 Proxy/Server "A" sets the neighbor cache entry state to DEPARTED and 2325 retains the entry for DepartTime seconds. While the state is 2326 DEPARTED, Proxy/Server "A" forwards any carrier packets destined to 2327 the Client to a Bridge via OAL/ORH encapsulation. When DepartTime 2328 expires, Proxy/Server "A" deletes the neighbor cache entry and 2329 discards any further carrier packets destined to the former Client. 2331 In some ANETs that employ a Proxy/Server, the Client's MNP can be 2332 injected into the ANET routing system. In that case, the Client can 2333 send original IP packets without invoking the OAL so that the ANET 2334 routing system transports the original IP packets to the Proxy. This 2335 can be very beneficial, e.g., if the Client connects to the ANET via 2336 low-end data links such as some aviation wireless links. 2338 If the ANET first-hop access router is on the same underlying link as 2339 the Client and recognizes the AERO/OMNI protocol, the Client can 2340 avoid OAL encapsulation for both its control and data messages. When 2341 the Client connects to the link, it can send an unencapsulated RS 2342 message with source address set to its own MNP-LLA (or to a Temporary 2343 LLA), and with destination address set to the ADM-LLA of the Client's 2344 selected Proxy/Server or to (link-local) All-Routers multicast. The 2345 Client includes an OMNI option formatted as specified in 2346 [I-D.templin-6man-omni]. The Client then sends the unencapsulated RS 2347 message, which will be intercepted by the AERO-Aware access router. 2349 The ANET access router then performs OAL encapsulation on the RS 2350 message and forwards it to a Proxy/Server at the ANET/INET boundary. 2351 When the access router and Proxy/Server are one and the same node, 2352 the Proxy/Server would share and underlying link with the Client but 2353 its message exchanges with outside correspondents would need to pass 2354 through a security gateway at the ANET/INET border. The method for 2355 deploying access routers and Proxys (i.e. as a single node or 2356 multiple nodes) is an ANET-local administrative consideration. 2358 Note: The Proxy/Server can apply packing as discussed in 2359 [I-D.templin-6man-omni] if an opportunity arises to concatenate 2360 multiple original IP packets that will be destined to the same 2361 neighbor. 2363 3.13.1. Detecting and Responding to Proxy/Server Failures 2365 In environments where fast recovery from Proxy/Server failure is 2366 required, Proxy/Server "A" SHOULD use proactive Neighbor 2367 Unreachability Detection (NUD) to track peer Proxy/Server "B" 2368 reachability in a similar fashion as for Bidirectional Forwarding 2369 Detection (BFD) [RFC5880]. Proxy/Server "A" can then quickly detect 2370 and react to failures so that cached information is re-established 2371 through alternate paths. The NUD control messaging is carried only 2372 over well-connected ground domain networks (i.e., and not low-end 2373 aeronautical radio links) and can therefore be tuned for rapid 2374 response. 2376 Proxy/Server "A" performs proactive NUD with peer Proxy/Server "B" 2377 for which there are currently active Clients by sending continuous NS 2378 messages in rapid succession, e.g., one message per second. Proxy/ 2379 Server "A" sends the NS message via the spanning tree with its own 2380 ADM-LLA as the source and the ADM-LLA of the peer Proxy/Server "B" as 2381 the destination. When Proxy/Server "A" is also sending RS messages 2382 to the peer Proxy/Server "B" on behalf of ANET Clients, the resulting 2383 RA responses can be considered as equivalent hints of forward 2384 progress. This means that Proxy/Server "B" need not also send a 2385 periodic NS if it has already sent an RS within the same period. If 2386 the peer Proxy/Server "B" fails (i.e., if "A" ceases to receive 2387 advertisements), Proxy/Server "A" can quickly inform Clients by 2388 sending multicast RA messages on the ANET interface. 2390 Proxy/Server "A" sends RA messages on the ANET interface with source 2391 address set to Proxy/Server "B"'s address, destination address set to 2392 (link-local) All-Nodes multicast, and Router Lifetime set to 0. 2393 Proxy/Server "A" SHOULD send MAX_FINAL_RTR_ADVERTISEMENTS RA messages 2394 separated by small delays [RFC4861]. Any Clients on the ANET that 2395 had been using the failed Proxy/Server "B" will receive the RA 2396 messages and associate with a new Proxy/Server. 2398 3.13.2. Point-to-Multipoint Proxy/Server Coordination 2400 In environments where Client messaging over ANETs is bandwidth- 2401 limited and/or expensive, Clients can enlist the services of Proxy/ 2402 Server "A" to coordinate with multiple Proxy/Servers "B", "C", "D" 2403 etc. in a single RS/RA message exchange. The Client can send a 2404 single RS message to (link-local) All-Routers multicast that includes 2405 the ID's of multiple Proxy/Servers in MS-Register sub-options of the 2406 OMNI option. 2408 When Proxy/Server "A" receives the RS and processes the OMNI option, 2409 it sends a separate RS to each MS-Register Proxy/Server ID. When 2410 Proxy/Server "A" receives an RA, it can optionally return an 2411 immediate "singleton" RA to the Client or record the Proxy/Server's 2412 ID for inclusion in a pending "aggregate" RA message. Proxy/Server 2413 "A" can then return aggregate RA messages to the Client including 2414 multiple Proxy/Server IDs in order to conserve bandwidth. Each RA 2415 includes a proper subset of the Proxy/Server IDs from the original RS 2416 message, and Proxy/Server "A" must ensure that the message contents 2417 of each RA are consistent with the information received from the 2418 (aggregated) additional Proxy/Servers. 2420 Clients can thereafter employ efficient point-to-multipoint Proxy/ 2421 Server coordination under the assistance of Proxy/Server "A" to 2422 reduce the number of messages sent over the ANET while enlisting the 2423 support of multiple Proxy/Servers for fault tolerance. Clients can 2424 further include MS-Release sub-options in IPv6 ND messages to request 2425 Proxy/Server "A" to release from former Proxy/Servers via the 2426 procedures discussed in Section 3.16.5. 2428 The OMNI interface specification [I-D.templin-6man-omni] provides 2429 further discussion of the RS/RA messaging involved in point-to- 2430 multipoint coordination. 2432 3.14. AERO Route Optimization 2434 While AERO nodes can always send data packets over strict spanning 2435 tree paths, route optimization should be performed while carrier 2436 packets are flowing between a source and target node. Route 2437 optimization is based on asymmetric IPv6 ND Address Resolution 2438 messaging between a Route Optimization Source (ROS) and Route 2439 Optimization Responder (ROR), then extended to the target using IPv6 2440 ND Neighbor Unreachability Detection messaging. Route optimization 2441 is initiated by the first eligible ROS closest to the source as 2442 follows: 2444 o For Clients on VPNed and Direct interfaces, the Proxy/Server is 2445 the ROS. 2447 o For Clients on ANET interfaces, either the Client or the Proxy/ 2448 Server may be the ROS. 2450 o For Clients on INET interfaces, the Client itself is the ROS. 2452 o For correspondent nodes on INET/EUN interfaces serviced by a 2453 Relay, the Relay is the ROS. 2455 The route optimization procedure is conducted between the ROS and the 2456 target Proxy/Server/Relay acting as an ROR (the target may either be 2457 a MNP Client serviced by a Proxy/Server or a non-MNP correspondent 2458 reachable via a Relay). Note that in this arrangement the ROS is 2459 always the Client or Proxy/Server/Relay nearest the source over the 2460 selected source underlying interface, while the ROR is always a 2461 Proxy/Server/Relay that services the target regardless of the target 2462 underlying interface. 2464 The procedures are specified in the following sections. 2466 3.14.1. Route Optimization Initiation 2468 When an original IP packet from a source node destined to a target 2469 node arrives, the ROS checks for a neighbor cache entry with an MNP- 2470 LLA that matches the target destination. If there is a neighbor 2471 cache entry in the REACHABLE state, the ROS invokes the OAL and 2472 forwards the resulting carrier packets according to the cached state 2473 and returns from processing. Otherwise, if there is no neighbor 2474 cache entry the ROS creates one in the INCOMPLETE state. 2476 The ROS next places the original IP packet on a short queue then 2477 sends an NS message for Address Resolution (NS(AR)) to receive a 2478 solicited NA(AR) message from a ROR. The NS(AR) message must be no 2479 larger than the minimum/path MPS so that its entire contents will fit 2480 in an OAL first fragment (i.e., as an atomic fragment). The ROS 2481 prepares an NS(AR) that includes: 2483 o the LLA of the ROS as the source address. 2485 o the MNP-LLA corresponding to the original IP packet's destination 2486 as the Target Address, e.g., for 2001:db8:1:2::10:2000 the Target 2487 Address is fe80::2001:db8:1:2. 2489 o the Solicited-Node multicast address [RFC4291] formed from the 2490 lower 24 bits of the original IP packet's destination as the 2491 destination address, e.g., for 2001:db8:1:2::10:2000 the NS 2492 destination address is ff02:0:0:0:0:1:ff10:2000. 2494 The NS(AR) message also includes an OMNI option with an Interface 2495 Attributes entry for the sending interface, with S/T-omIndex set to 0 2496 and with Preflen set to the prefix length associated with the NS(AR) 2497 source. The ROS then selects an Identification value and invokes OAL 2498 window synchronization (if necessary) and submits the NS(AR) message 2499 for OAL encapsulation as an atomic fragment, with OAL source set to 2500 its own ULA and OAL destination set to the ULA corresponding to the 2501 target. 2503 The ROS then sends the resulting carrier packet into the spanning 2504 tree without decrementing the network-layer TTL/Hop Limit field. 2505 (When the ROS is an INET Client, it instead must first sign the 2506 NS(AR) message and send the resulting carrier packet to the ADM-ULA 2507 of one of its current Proxy/Servers which then verifies the NS(AR) 2508 signature and forwards the carrier packet over the secured spanning 2509 tree on behalf of the Client.) 2511 3.14.2. Relaying the NS(AR) *NET Packet(s) 2513 When the Bridge receives the carrier packet containing the RS from 2514 the ROS, it discards the *NET headers and determines the next hop by 2515 consulting its standard IPv6 forwarding table for the OAL header 2516 destination address. The Bridge then decrements the OAL header Hop- 2517 Limit, re-encapsulates the carrier packet and forwards it via the 2518 secured spanning tree the same as for any IPv6 router, where it may 2519 traverse multiple OMNI link segments. The final-hop Bridge will 2520 deliver the carrier packet via the secured spanning tree to a Proxy/ 2521 Server or Relay that services the target. 2523 3.14.3. Processing the NS(AR) and Sending the NA(AR) 2525 When the target Proxy/Server (or Relay) receives the carrier packet, 2526 it examines the enclosed atomic fragment to determine that it 2527 contains an NS(AR) then examines the NS(AR) target to determine 2528 whether it has a matching neighbor cache entry and/or non-MNP route. 2529 If there is no match, the Proxy/Server drops the message. Otherwise, 2530 the Proxy/Server/Relay continues processing as follows: 2532 o if the NS(AR) target matches a Client neighbor cache entry in the 2533 DEPARTED state, the Proxy/Server inserts an ORH with destination 2534 prefix set to the lower 64 bits of the Client's MNP-ULA and sets 2535 the destination address to the ADM-ULA of the Client's new Proxy/ 2536 Server. The (old) Proxy/Server then re-encapsulates the carrier 2537 packet, forwards it over the secured spanning tree and returns 2538 from processing. 2540 o If the NS(AR) target matches the MNP-LLA of a Client neighbor 2541 cache entry in the REACHABLE state, the Proxy/Server makes note of 2542 whether the NS arrived from the secured or unsecured spanning 2543 tree, then acts as an ROR to provide route optimization 2544 information on behalf of the Client. (Note that if the message 2545 arrived via the secured spanning tree the ROR need not perform 2546 further authentication, but if it arrived over an open INET 2547 underlying interface it must check for and verify the message 2548 authentication signature before accepting.) 2550 o If the NS(AR) target matches one of its non-MNP routes, the Relay 2551 acts as an ROR since it serves as a router to forward IP packets 2552 toward the (fixed network) target at the network layer. 2554 The ROR next checks the target neighbor cache entry for a Report List 2555 entry that matches the NS(AR) source LLA/ULA of the ROS. If there is 2556 a Report List entry, the ROR accepts the NS(AR) only if the OAL 2557 Identification value is within the receive window for this ROS or if 2558 the NS(AR) is determined to be authentic. If the NS(AR) is authentic 2559 and requests window synchronization, the ROS caches the new window 2560 parameters. If the NS(AR) is authentic but the target neighbor cache 2561 entry does not already include a Report List entry for this ROS, the 2562 ROR creates a new entry and caches the ROS information. The Report 2563 List cache entry therefore includes the ROS LLA, ULA and window state 2564 information. 2566 The ROR then prepares a (solicited) NA(AR) message to send back to 2567 the ROS with an asymmetric acknowledgement of the window 2568 synchronization. The ROR sets the NA(AR) source address to the 2569 target's MNP-LLA, sets the destination address to the NS(AR) LLA 2570 source address and sets the Target Address to the same value that 2571 appeared in the NS(AR). The ROR then includes an OMNI option with 2572 Preflen set to the prefix length associated with the NA(AR) source 2573 address. If the NS(AR) target was an MNP Client, the ROR next 2574 includes Interface Attributes in the OMNI option for each of the 2575 target's underlying interfaces with current information for each 2576 interface and includes an authentication signature if necessary. The 2577 ROR then sets the S/T-omIndex field in the OMNI header to 0. 2579 For each Interface Attributes sub-option, the ROR sets the L2ADDR 2580 according to the Proxy/Server's INET address for VPNed or Direct 2581 interfaces, to the INET address of the Proxy/Server for proxyed 2582 interfaces or to the Client's INET address for INET interfaces. The 2583 ROR then includes the lower 32 bits of the Proxy/Server's ADM-ULA as 2584 the LHS, encodes the ADM-ULA prefix length code in the SRT field and 2585 sets the FMT code accordingly as specified in Section 3.3. 2587 The ROR then sets the NA(AR) message R flag to 1 (as a router) and S 2588 flag to 1 (as a response to a solicitation) and sets the O flag to 0 2589 (as a proxy). The ROR finally submits the NA(AR) for OAL 2590 encapsulation with source set to its own ULA and destination set to 2591 the ULA of the ROS, then performs OAL fragmentation using the same 2592 Identification value that appeared in the NS(AR) and forwards the 2593 resulting (*NET-encapsulated) carrier packets via the secured 2594 spanning tree without decrementing the network-layer TTL/Hop Limit 2595 field. 2597 While sending the NA(AR), the ROR also performs extended route 2598 optimization by sending an NS(NUD) to each of the target's underlying 2599 interfaces by changing the NS(AR) destination address to the address 2600 of the target and sending a distinct copy of the message according to 2601 each of the target's Link-Layer addresses (while setting S/T-omIndex 2602 to the index of the target underlying interface). Each NS(NUD) also 2603 includes the window synchronization parameters that were included in 2604 the NS(AR). The process for sending NS(NUD) messages is discussed in 2605 greater detail in Section 3.15. 2607 It is therefore often the case that the ROS may receive multiple NA 2608 responses to a single NS(AR) message - one from the ROR plus zero or 2609 more from each of the target's underlying interfaces. (Note: when 2610 sending the NS(NUD) on open INET interfaces, the ROR must include an 2611 OMNI authentication using its own security parameters and not those 2612 that it may have received from the ROS NS(AR) message. Therefore, 2613 the NS(NUD) must be prepared as a new IPv6 ND message from-scratch 2614 instead of simply copying the information received in the NS(AR).) 2616 3.14.4. Relaying the NA(AR) 2618 When the Bridge receives the NA(AR) carrier packets from the ROR, it 2619 discards the *NET header and determines the next hop by consulting 2620 its standard IPv6 forwarding table for the OAL header destination 2621 address. The Bridge then decrements the OAL header Hop-Limit, re- 2622 encapsulates the carrier packet and forwards it via a spanning tree 2623 secured tunnel the same as for any IPv6 router, where it may traverse 2624 multiple OMNI link segments. The final-hop Bridge will deliver the 2625 carrier packet via the secured spanning tree to a Proxy/Server for 2626 the ROS. 2628 3.14.5. Processing the NA(AR) 2630 When the ROS receives the NA(AR) message, it first searches for a 2631 neighbor cache entry that matches the NA(AR) LLA source address. If 2632 there is an entry in the INCOMPLETE or STALE state, the ROS matches 2633 the OAL Identification value with the value it had included in the 2634 corresponding NS(AR). If the values match, the ROS processes the 2635 message the same as for standard IPv6 Address Resolution [RFC4861]. 2636 In the process, it caches the NA(AR) LLA source address and all 2637 information found in the OMNI option in the neighbor cache entry for 2638 the target. The ROS finally sets the neighbor cache entry state to 2639 REACHABLE and sets its lifetime to ReachableTime seconds. (When the 2640 ROS is a Client, the solicited NA(AR) message will first be delivered 2641 via the secured spanning tree to one of its current Proxy/Servers, 2642 which then securely forwards the message to the Client. If the 2643 Client is on an ANET, ANET physical security and protected spectrum 2644 ensures security; if the Client is on the open ANET, the Proxy/Server 2645 must re-format the NA(AR) message to include its own authentication 2646 signature.) 2648 The ROS may also receive zero or more NA(NUD) messages appearing to 2649 be responses to NS(NUD) messages sent by itself, but these messages 2650 will have been triggered by the ROR's actions. Each NA(NUD) message 2651 includes information for only one of the target's underlying 2652 interfaces, and has the O flag set to 1 such that it will override 2653 any information previously received from the ROR's NA(AR). The 2654 Identification value in the message will match the value included in 2655 the original NS(AR) sent by the ROS. The ROS caches the NA(NUD) 2656 information, and marks each underlying interface as reachable. 2658 3.14.6. Route Optimization Maintenance 2660 Following route optimization, the ROS forwards future carrier packets 2661 with user data destined to the target via the addresses found in the 2662 cached link-layer information and with a monotonically-incrementing 2663 Identification value for each OAL packet. The route optimization is 2664 shared by all sources that send original IP packets to the target via 2665 the ROS, i.e., and not just the source on behalf of which the route 2666 optimization was initiated. Note that route optimization is 2667 performed only for original IP packets that contain user data, and 2668 not for those that contain other IPv6 ND control messages. 2670 While the ROS continues to forward additional original IP packets 2671 destined to the target, it sends additional NS(AR) messages to the 2672 ROR before ReachableTime expires to receive fresh NA messages the 2673 same as described in the previous sections (route optimization 2674 refreshment strategies are an implementation matter, with a non- 2675 normative example given in Appendix A.1). The ROS includes new 2676 window synchronization parameters if the current window is nearing 2677 exhaustion or if ReachableTime is nearing expiration. If the ROS is 2678 an INET Client, it must include an authentication signature with the 2679 NS(AR) message so that the Proxy/Server can authenticate. 2681 The ROS uses its own ULA as the NS(AR) OAL source address and the ULA 2682 of the ROR as the NS(AR) OAL destination address, and sends up to 2683 MAX_MULTICAST_SOLICIT NS(AR) messages separated by 1 second until an 2684 NA(AR) is received. If no NA(AR) is received, the ROS assumes that 2685 the current ROR has become unreachable and deletes the target 2686 neighbor cache entry. Subsequent original IP packets will trigger a 2687 new route optimization event (see: Section 3.14.1) which may discover 2688 a different ROR that services the same target. 2690 If an NA(AR) is received, the ROS then updates the neighbor cache 2691 entry for the target to refresh ReachableTime, while (for MNP 2692 targets) the ROR adds or updates the ROS address to the target's 2693 Report List and with time set to ReportTime. While no carrier 2694 packets are flowing, the ROS instead allows ReachableTime for the 2695 target neighbor cache entry to expire. When ReachableTime expires, 2696 the ROS places the target neighbor cache entry back in the STALE 2697 state. Any future carrier packets flowing through the ROS will again 2698 trigger a new route optimization. 2700 The ROS may also receive unsolicited NA (uNA) messages from the ROR 2701 at any time (see: Section 3.16). If there is a neighbor cache entry 2702 for the target and the carrier packet(s) containing the uNA is 2703 received securely, the ROS updates the link-layer information but 2704 does not update ReachableTime since the receipt of a uNA does not 2705 confirm that any forward paths are working. If there is no neighbor 2706 cache entry or the message cannot be authenticated, the ROS simply 2707 discards the uNA. 2709 In this arrangement, the ROS holds a neighbor cache entry for the 2710 target in the REACHABLE state with send window information, while the 2711 ROR's target neighbor cache entry holds a Report List entry for the 2712 ROS with receive window information for the ULA of the ROS. The 2713 target node also holds a neighbor cache entry for the ROS in the 2714 STALE state with receive window information due to extended route 2715 optimization. 2717 The route optimization neighbor relationship is therefore asymmetric 2718 and unidirectional. If the target node also has carrier packets to 2719 send back to the source node, it performs a separate asymmetric route 2720 optimization in the reverse direction. But, there is no requirement 2721 that the forward and reverse paths be symmetric. 2723 3.15. Neighbor Unreachability Detection (NUD) 2725 AERO nodes perform Neighbor Unreachability Detection (NUD) per 2726 [RFC4861] either reactively in response to persistent link-layer 2727 errors (see Section 3.11) or on-demand to confirm reachability and/or 2728 extend route optimizations from the ROS to the target. The NUD 2729 algorithm is based on periodic control message exchanges. The 2730 algorithm may further be seeded by ND hints of forward progress, but 2731 care must be taken to avoid inferring reachability based on spoofed 2732 information. For example, authentic IPv6 ND message exchanges may be 2733 considered as acceptable hints of forward progress, while spurious 2734 random packets should not be. 2736 AERO nodes can use standard NS/NA(NUD) exchanges sent over the OMNI 2737 link spanning tree to securely test reachability without risk of DoS 2738 attacks from nodes pretending to be a neighbor. These NS/NA(NUD) 2739 messages use the unicast LLAs and ULAs of the two parties involved in 2740 the NUD test the same as for standard IPv6 ND over the secured 2741 spanning tree, however a means for an ROS to test the unsecured 2742 target route optimized paths is also necessary. 2744 When an ROR directs an ROS to a target neighbor with one or more 2745 link-layer addresses, the ROS probes each unsecured target underlying 2746 interface either proactively or on-demand of carrier packets directed 2747 to the path by multilink forwarding to maintain the interface's state 2748 as reachable. Probing is performed through secured NS(NUD) messages 2749 over the spanning tree in the forward path that invoke an unsecured 2750 NA(NUD) reply over the target underlying interface on return path. 2751 (The NS(NUD) messages must therefore include Identification values 2752 (and optionally Nonce and Timestamp options) that will be echoed in 2753 the unsecured NA(NUD) replies.) While testing a target underlying 2754 interface, the ROS can optionally continue to send carrier packets 2755 via alternate interfaces and/or the ROR or maintain a small queue of 2756 carrier packets until target reachability is confirmed. 2758 When the ROS sends an NS(NUD) message, it sets the IPv6 source to its 2759 own LLA and sets both the destination and Target Address to the LLA 2760 of the target. The ROS also includes an OMNI option with S/T-omIndex 2761 set to the index of the target underlying interface and with a single 2762 Interface Attributes sub-option with the SRT, FMT, LHS and L2ADDR 2763 information for its own underlying interface. The ROS includes an 2764 Identification value within the current send window for this target 2765 neighbor (and optionally Nonce and Timestamp options), then 2766 encapsulates the message in OAL/INET headers with its own ULA as the 2767 source and the ULA formed from the SRT/LHS values for this target 2768 interface as the destination. The ROS then forwards the NS(NUD) 2769 message toward the destination ULA via the spanning tree. 2771 When the destination ULA node receives the NS(NUD) message, it 2772 examines the S/T-omIndex. If the corresponding underlying interface 2773 is a Direct or VPNed interface, the node acts as the target. If the 2774 underlying interface is a Proxyed interface, the node either acts as 2775 the target itself or forwards the message to the target Client. If 2776 the underlying interface is an INET interface, the node changes the 2777 OAL destination address to the ULA of the target Client and forwards 2778 the NS(NUD) over the underlying interface to the target Client while 2779 including an authentication signature. 2781 The target then creates a neighbor cache entry for the ROS LLA 2782 address if necessary and caches receive window information for this 2783 ROS. The target then creates an NA(NUD) by reversing the OAL and 2784 IPv6 addresses from the NS(NUD) while copying the Identification 2785 value, and next including an Interface Attributes sub-option with 2786 attributes for its own interface identified by the NS(NUD) S/ 2787 T-omIndex. The target sets the NA(NUD) S/T-omIndex to the index of 2788 the ROS, sets the Target Address to the same value that was in the 2789 NS(NUD), sets R flag to 1, the S flag to 1 and the O flag to 1, and 2790 returns the message using its own underlying interface identified by 2791 NS(NUD) S/T-omIndex and destined to the ROS's interface identified by 2792 the original Interface Attributes sub-option. 2794 When the ROS receives the NA(NUD) message, it can determine from the 2795 Identification value and Target Address (and optionally the Nonce and 2796 Timestamp) that the message matched its NS(NUD) and that it transited 2797 the direct path using the selected underlying interface pair. The 2798 ROS marks route optimization target paths that pass these NUD tests 2799 as "reachable", and those that do not as "unreachable". These 2800 markings inform the OMNI interface forwarding algorithm specified in 2801 Section 3.10. Following the initial NA(NUD), the ROS sends 2802 additional NS(NUDs) as necessary, but may send them via the cached 2803 SRT, FMT, LHS and L2ADDR for the target via each underlying interface 2804 to be tested. 2806 Note: If the target determines that the OMNI option Interface 2807 Attributes in the NS(NUD) is located in a different OMNI link segment 2808 than its own interface named in the S/T-omIndex, it instead returns 2809 the NA(NUD) via the spanning tree while including an ORH and setting 2810 the OAL destination address to the Subnet Router Anycast address used 2811 by Bridges on the ROS segment. When a Bridge on the ROS segment 2812 receives the NA(NUD), it replaces the Interface Attributes with 2813 information for its own interface while using the omIndex value 2814 specific to the target. 2816 3.16. Mobility Management and Quality of Service (QoS) 2818 AERO is a Distributed Mobility Management (DMM) service. Each Proxy/ 2819 Server is responsible for only a subset of the Clients on the OMNI 2820 link, as opposed to a Centralized Mobility Management (CMM) service 2821 where there is a single network mobility collective entity for all 2822 Clients. Clients coordinate with their associated Proxy/Servers via 2823 RS/RA exchanges to maintain the DMM profile, and the AERO routing 2824 system tracks all current Client/Proxy/Server peering relationships. 2826 Proxy/Servers provide default routing and mobility/multilink services 2827 for their dependent Clients. Clients are responsible for maintaining 2828 neighbor relationships with their Proxy/Servers through periodic RS/ 2829 RA exchanges, which also serves to confirm neighbor reachability. 2830 When a Client's underlying Interface Attributes change, the Client is 2831 responsible for updating the Proxy/Server with this new information. 2832 Note that when there is a Proxy/Server in the path, the Proxy 2833 function can also perform some RS/RA exchanges on the Client's 2834 behalf. 2836 Mobility management messaging is based on the transmission and 2837 reception of unsolicited Neighbor Advertisement (uNA) messages. Each 2838 uNA message sets the IPv6 destination address to (link-local) All- 2839 Nodes multicast to convey a general update of Interface Attributes to 2840 (possibly) multiple recipients, or to a specific unicast LLA to 2841 announce a departure event to a specific recipient. Implementations 2842 must therefore examine the destination address to determine the 2843 nature of the mobility event (i.e., update vs departure). 2845 Mobility management considerations are specified in the following 2846 sections. 2848 3.16.1. Mobility Update Messaging 2850 RORs accommodate Client mobility and/or multilink change events by 2851 sending unsolicited NA (uNA) messages to each ROS in the target 2852 Client's Report List. When an ROR sends a uNA message, it sets the 2853 IPv6 source address to the its own LLA, sets the destination address 2854 to (link-local) All-Nodes multicast and sets the Target Address to 2855 the Client's MNP-LLA. The ROR also includes an OMNI option with 2856 Preflen set to the prefix length associated with the Client's MNP- 2857 LLA, with Interface Attributes for the target Client's underlying 2858 interfaces and with the OMNI header S/T-omIndex set to 0. The ROR 2859 then sets the NA R flag to 1, the S flag to 0 and the O flag to 1, 2860 then encapsulates the message in an OAL header with source set to its 2861 own ULA and destination set to the ULA of the ROS and sends the 2862 message into the spanning tree. 2864 As discussed in Section 7.2.6 of [RFC4861], the transmission and 2865 reception of uNA messages is unreliable but provides a useful 2866 optimization. In well-connected Internetworks with robust data links 2867 uNA messages will be delivered with high probability, but in any case 2868 the Proxy/Server can optionally send up to MAX_NEIGHBOR_ADVERTISEMENT 2869 uNAs to each ROS to increase the likelihood that at least one will be 2870 received. Alternatively, the Proxy/Server can set the PNG flag in 2871 the uNA OMNI option header to request a solicited NA acknowledgement 2872 as specified in [I-D.templin-6man-omni]. 2874 When the ROS receives a uNA message prepared as above, it ignores the 2875 message if there is no existing neighbor cache entry for the target 2876 Client. Otherwise, it uses the included OMNI option information to 2877 update the neighbor cache entry, but does not reset ReachableTime 2878 since the receipt of an unsolicited NA message from the ROR does not 2879 provide confirmation that any forward paths to the target Client are 2880 working. (If the uNA message PNG flag was set, the ROS then returns 2881 a solicited NA acknowledgement as specified in 2882 [I-D.templin-6man-omni]. 2884 In addition to sending uNA messages to the current set of ROSs for 2885 the Client, the ROR also sends uNAs to the MNP-ULA associated with 2886 the link-layer address for any underlying interface for which the 2887 link-layer address has changed. These uNA messages update an old 2888 Proxy/Server that cannot easily detect (e.g., without active probing) 2889 when a formerly-active Client has departed. When the ROR sends the 2890 uNA, it sets the IPv6 source address to its LLA, sets the destination 2891 address to the old Proxy/Server's ADM-LLA, and sets the Target 2892 Address to the Client's MNP-LLA. The ROR also includes an OMNI 2893 option with Preflen set to the prefix length associated with the 2894 Client's MNP-LLA, with Interface Attributes for the changed 2895 underlying interface, and with the OMNI header S/T-omIndex set to its 2896 own omIndex if the ROR is a Client or 0 if the ROR is a Proxy/Server. 2897 The ROR then sets the uNA R flag to 1, the S flag to 0 and the O flag 2898 to 1, then encapsulates the message in an OAL header with source set 2899 to its own ULA and destination set to the ADM-ULA of the old Proxy/ 2900 Server and sends the message into the spanning tree. 2902 3.16.2. Announcing Link-Layer Address and/or QoS Preference Changes 2904 When a Client needs to change its underlying Interface Attributes 2905 (e.g., due to a mobility event), the Client requests one of its 2906 Proxy/Servers to send RS messages to all of its other Proxy/Servers 2907 via the spanning tree with an OMNI option that includes Interface 2908 attributes with the new link quality and address information. 2910 Up to MAX_RTR_SOLICITATIONS RS messages MAY be sent in parallel with 2911 sending carrier packets containing user data in case one or more RAs 2912 are lost. If all RAs are lost, the Client SHOULD re-associate with a 2913 new Proxy/Server. 2915 When the Proxy/Server receives the Client's changes, it sends uNA 2916 messages to all nodes in the Report List the same as described in the 2917 previous section. 2919 3.16.3. Bringing New Links Into Service 2921 When a Client needs to bring new underlying interfaces into service 2922 (e.g., when it activates a new data link), it sends an RS message to 2923 the Proxy/Server via the underlying interface with an OMNI option 2924 that includes Interface Attributes with appropriate link quality 2925 values and with link-layer address information for the new link. 2927 3.16.4. Deactivating Existing Links 2929 When a Client needs to deactivate an existing underlying interface, 2930 it sends an RS or uNA message to its Proxy/Server with an OMNI option 2931 with appropriate Interface Attribute values - in particular, the link 2932 quality value 0 assures that neighbors will cease to use the link. 2934 If the Client needs to send RS/uNA messages over an underlying 2935 interface other than the one being deactivated, it MUST include 2936 Interface Attributes with appropriate link quality values for any 2937 underlying interfaces being deactivated. 2939 Note that when a Client deactivates an underlying interface, 2940 neighbors that have received the RS/uNA messages need not purge all 2941 references for the underlying interface from their neighbor cache 2942 entries. The Client may reactivate or reuse the underlying interface 2943 and/or its omIndex at a later point in time, when it will send RS/uNA 2944 messages with fresh Interface Attributes to update any neighbors. 2946 3.16.5. Moving Between Proxy/Servers 2948 The Client performs the procedures specified in Section 3.12.2 when 2949 it first associates with a new Proxy/Server or renews its association 2950 with an existing Proxy/Server. The Client also includes MS-Release 2951 identifiers in the RS message OMNI option per [I-D.templin-6man-omni] 2952 if it wants the new Proxy/Server to notify any old Proxy/Servers from 2953 which the Client is departing. 2955 When the new Proxy/Server receives the Client's RS message, it 2956 returns an RA as specified in Section 3.12.3 and sends uNA messages 2957 to any old Proxy/Servers listed in OMNI option MS-Release 2958 identifiers. When the new Proxy/Server sends a uNA message, it sets 2959 the IPv6 source address to the Client's MNP-LLA, sets the destination 2960 address to the old Proxy/Server's ADM-LLA, and sets the Target 2961 Address to the Client's LLA. The new Proxy/Server also includes an 2962 OMNI option with Preflen set to the prefix length associated with the 2963 Client's MNP-LLA, with Interface Attributes for its own underlying 2964 interface, and with the OMNI header S/T-omIndex set to 0. The new 2965 Proxy/Server then sets the NA R flag to 1, the S flag to 0 and the O 2966 flag to 1, then encapsulates the message in an OAL header with source 2967 set to its own ADM-ULA and destination set to the ADM-ULA of the old 2968 Proxy/Server and sends the message into the spanning tree. 2970 When an old Proxy/Server receives the uNA, it changes the Client's 2971 neighbor cache entry state to DEPARTED, sets the link-layer address 2972 of the Client to the new Proxy/Server's ADM-ULA, and resets 2973 DepartTime. After a short delay (e.g., 2 seconds) the old Proxy/ 2974 Server withdraws the Client's MNP from the routing system. After 2975 DepartTime expires, the old Proxy/Server deletes the Client's 2976 neighbor cache entry. 2978 The old Proxy/Server also iteratively forwards a copy of the uNA 2979 message to each ROS in the Client's Report List by changing the OAL 2980 destination address to the ULA of the ROS while leaving all other 2981 fields of the message unmodified. When the ROS receives the uNA, it 2982 examines the Target address to determine the correct neighbor cache 2983 entry and verifies that the IPv6 destination address matches the old 2984 Proxy/Server. The ROS then caches the IPv6 source address as the new 2985 Proxy/Server for the existing neighbor cache entry and marks the 2986 entry as STALE. While in the STALE state, the ROS allows new carrier 2987 packets to flow according to any existing cached link-layer 2988 information and sends new NS(AR) messages using its own ULA as the 2989 OAL source and the ADM-ULA of the new Proxy/Server as the OAL 2990 destination address to elicit NA messages that reset the neighbor 2991 cache entry state to REACHABLE. If no new NA message is received for 2992 10 seconds while in the STALE state, the ROS deletes the neighbor 2993 cache entry. 2995 Clients SHOULD NOT move rapidly between Proxy/Servers in order to 2996 avoid causing excessive oscillations in the AERO routing system. 2997 Examples of when a Client might wish to change to a different Proxy/ 2998 Server include a Proxy/Server that has gone unreachable, topological 2999 movements of significant distance, movement to a new geographic 3000 region, movement to a new OMNI link segment, etc. 3002 When a Client moves to a new Proxy/Server, some of the carrier 3003 packets of a multiple fragment OAL packet may have already arrived at 3004 the old Proxy/Server while others are en route to the new Proxy/ 3005 Server, however no special attention in the reassembly algorithm is 3006 necessary since all carrier packets will eventually arrive at the 3007 Client which can then reassemble. 3009 3.17. Multicast 3011 The AERO Client provides an IGMP (IPv4) [RFC2236] or MLD (IPv6) 3012 [RFC3810] proxy service for its EUNs and/or hosted applications 3013 [RFC4605]. The Client forwards IGMP/MLD messages over any of its 3014 underlying interfaces for which group membership is required. The 3015 IGMP/MLD messages may be further forwarded by a first-hop ANET access 3016 router acting as an IGMP/MLD-snooping switch [RFC4541], then 3017 ultimately delivered to an AERO Proxy/Server acting as a Protocol 3018 Independent Multicast - Sparse-Mode (PIM-SM, or simply "PIM") 3019 Designated Router (DR) [RFC7761]. AERO Relays also act as PIM 3020 routers (i.e., the same as AERO Proxys/Servers) on behalf of nodes on 3021 INET/EUN networks. The behaviors identified in the following 3022 sections correspond to Source-Specific Multicast (SSM) and Any-Source 3023 Multicast (ASM) operational modes. 3025 3.17.1. Source-Specific Multicast (SSM) 3027 When an ROS "X" acting as PIM router receives a Join/Prune message 3028 from a node on its downstream interfaces containing one or more 3029 ((S)ource, (G)roup) pairs, it updates its Multicast Routing 3030 Information Base (MRIB) accordingly. For each S belonging to a 3031 prefix reachable via X's non-OMNI interfaces, X then forwards the (S, 3032 G) Join/Prune to any PIM routers on those interfaces per [RFC7761]. 3034 For each S belonging to a prefix reachable via X's OMNI interface, X 3035 includes a PIM Join/Prune for each (S,G) in the OMNI option of an 3036 NS(AR) message (see: Section 3.14) using its own LLA as the source 3037 address and ALL-PIM-ROUTERS as the destination address. X then 3038 encapsulates the NS(AR) in an OAL header with source address set to 3039 the ULA of X and destination address set to S then forwards the 3040 message into the spanning tree, which delivers it to ROR "Y" that 3041 services S. The resulting NA(AR) will return the LLA for the prefix 3042 that matches S as the network-layer source address and with an OMNI 3043 option with the ULA corresponding to any underlying interfaces that 3044 are currently servicing S. 3046 When Y processes the NS(AR) it examines the PIM Join/Prune message. 3047 If S is located behind any INET, Direct, or VPNed interfaces Y acts 3048 as a PIM router and updates its MRIB to list X as the next hop in the 3049 reverse path. If S is located behind any Proxys "Z"*, Y then sends 3050 an NS(NUD) message containing the PIM message to each Z* with 3051 addressing and encapsulation details the same as specified in 3052 Section 3.15. Each Z* then updates its MRIB accordingly and 3053 maintains the LLA of X as the next hop in the reverse path. Since 3054 the Bridges do not examine network layer control messages, this means 3055 that the (reverse) multicast tree path is simply from each Z* (and/or 3056 Y) to X with no other multicast-aware routers in the path. 3058 Following the initial combined Join/Prune and NS/NA messaging, X 3059 maintains a neighbor cache entry for each S the same as if X was 3060 sending unicast data traffic to S. In particular, X performs 3061 additional NS/NA exchanges to keep the neighbor cache entry alive for 3062 up to t_periodic seconds [RFC7761]. If no new Joins are received 3063 within t_periodic seconds, X allows the neighbor cache entry to 3064 expire. Finally, if X receives any additional Join/Prune messages 3065 for (S,G) it forwards the messages in NS/NA exchanges with each Y and 3066 Z* in the neighbor cache entry over the spanning tree. 3068 At some later time, Client C that holds an MNP for source S may 3069 depart from a first Proxy/Server Z1 and/or connect via a new Proxy/ 3070 Server Z2. In that case, Y sends a uNA message to X the same as 3071 specified for unicast mobility in Section 3.16. When X receives the 3072 uNA message, it updates its neighbor cache entry for the LLA for 3073 source S and sends new Join messages to any new Proxys Z2. There is 3074 no requirement to send any Prune messages to old Proxy/Server Z1 3075 since source S will no longer source any multicast data traffic via 3076 Z1. Instead, the multicast state for (S,G) in Proxy/Server Z1 will 3077 soon time out since no new Joins will arrive. 3079 After some later time, C may move to a new Proxy/Server Y2 and depart 3080 from old Sever Y1. In that case, Y1 sends Join messages for any of 3081 C's active (S,G) groups to Y2 while including its own LLA as the 3082 source address. This causes Y2 to include Y1 in the multicast 3083 forwarding tree during the interim time that Y1's neighbor cache 3084 entry for C is in the DEPARTED state. At the same time, Y1 sends a 3085 uNA message to X with an OMNI option with S/T-omIndex in the header 3086 set to 0 and a release indication to cause X to release its neighbor 3087 cache entry for S. X then sends a new Join message to S via the 3088 spanning tree and re-initiates route optimization the same as if it 3089 were receiving a fresh Join message from a node on a downstream link. 3091 3.17.2. Any-Source Multicast (ASM) 3093 When an ROS X acting as a PIM router receives a Join/Prune from a 3094 node on its downstream interfaces containing one or more (*,G) pairs, 3095 it updates its Multicast Routing Information Base (MRIB) accordingly. 3096 X then forwards a copy of the message within the OMNI option of an 3097 NS(AR) message to the Rendezvous Point (RP) R for each G over the 3098 spanning tree. X uses its own LLA as the source address and ALL-PIM- 3099 ROUTERS as the destination address, then encapsulates the NS(AR) 3100 message in an OAL header with source address set to the ULA of X and 3101 destination address set to R, then sends the message into the 3102 spanning tree. 3104 For each source S that sends multicast traffic to group G via R, the 3105 Proxy/Server Z* for the Client that aggregates S encapsulates the 3106 original IP packets in PIM Register messages and forwards them to R 3107 via the spanning tree, which may then elect to send a PIM Join to Z*. 3108 This will result in an (S,G) tree rooted at Z* with R as the next hop 3109 so that R will begin to receive two copies of the original IP packet; 3110 one native copy from the (S, G) tree and a second copy from the pre- 3111 existing (*, G) tree that still uses PIM Register encapsulation. R 3112 can then issue a PIM Register-stop message to suppress the Register- 3113 encapsulated stream. At some later time, if C moves to a new Proxy/ 3114 Server Z*, it resumes sending original IP packets via PIM Register 3115 encapsulation via the new Z*. 3117 At the same time, as multicast listeners discover individual S's for 3118 a given G, they can initiate an (S,G) Join for each S under the same 3119 procedures discussed in Section 3.17.1. Once the (S,G) tree is 3120 established, the listeners can send (S, G) Prune messages to R so 3121 that multicast original IP packets for group G sourced by S will only 3122 be delivered via the (S, G) tree and not from the (*, G) tree rooted 3123 at R. All mobility considerations discussed for SSM apply. 3125 3.17.3. Bi-Directional PIM (BIDIR-PIM) 3127 Bi-Directional PIM (BIDIR-PIM) [RFC5015] provides an alternate 3128 approach to ASM that treats the Rendezvous Point (RP) as a Designated 3129 Forwarder (DF). Further considerations for BIDIR-PIM are out of 3130 scope. 3132 3.18. Operation over Multiple OMNI Links 3134 An AERO Client can connect to multiple OMNI links the same as for any 3135 data link service. In that case, the Client maintains a distinct 3136 OMNI interface for each link, e.g., 'omni0' for the first link, 3137 'omni1' for the second, 'omni2' for the third, etc. Each OMNI link 3138 would include its own distinct set of Bridges and Proxy/Servers, 3139 thereby providing redundancy in case of failures. 3141 Each OMNI link could utilize the same or different ANET connections. 3142 The links can be distinguished at the link-layer via the SRT prefix 3143 in a similar fashion as for Virtual Local Area Network (VLAN) tagging 3144 (e.g., IEEE 802.1Q) and/or through assignment of distinct sets of 3145 MSPs on each link. This gives rise to the opportunity for supporting 3146 multiple redundant networked paths, with each VLAN distinguished by a 3147 different SRT "color" (see: Section 3.2.5). 3149 The Client's IP layer can select the outgoing OMNI interface 3150 appropriate for a given traffic profile while (in the reverse 3151 direction) correspondent nodes must have some way of steering their 3152 original IP packets destined to a target via the correct OMNI link. 3154 In a first alternative, if each OMNI link services different MSPs, 3155 then the Client can receive a distinct MNP from each of the links. 3156 IP routing will therefore assure that the correct OMNI link is used 3157 for both outbound and inbound traffic. This can be accomplished 3158 using existing technologies and approaches, and without requiring any 3159 special supporting code in correspondent nodes or Bridges. 3161 In a second alternative, if each OMNI link services the same MSP(s) 3162 then each link could assign a distinct "OMNI link Anycast" address 3163 that is configured by all Bridges on the link. Correspondent nodes 3164 can then perform Segment Routing to select the correct SRT, which 3165 will then direct the original IP packet over multiple hops to the 3166 target. 3168 3.19. DNS Considerations 3170 AERO Client MNs and INET correspondent nodes consult the Domain Name 3171 System (DNS) the same as for any Internetworking node. When 3172 correspondent nodes and Client MNs use different IP protocol versions 3173 (e.g., IPv4 correspondents and IPv6 MNs), the INET DNS must maintain 3174 A records for IPv4 address mappings to MNs which must then be 3175 populated in Relay NAT64 mapping caches. In that way, an IPv4 3176 correspondent node can send original IPv4 packets to the IPv4 address 3177 mapping of the target MN, and the Relay will translate the IPv4 3178 header and destination address into an IPv6 header and IPv6 3179 destination address of the MN. 3181 When an AERO Client registers with an AERO Proxy/Server, the Proxy/ 3182 Server can return the address(es) of DNS servers in RDNSS options 3183 [RFC6106]. The DNS server provides the IP addresses of other MNs and 3184 correspondent nodes in AAAA records for IPv6 or A records for IPv4. 3186 3.20. Transition/Coexistence Considerations 3188 OAL encapsulation ensures that dissimilar INET partitions can be 3189 joined into a single unified OMNI link, even though the partitions 3190 themselves may have differing protocol versions and/or incompatible 3191 addressing plans. However, a commonality can be achieved by 3192 incrementally distributing globally routable (i.e., native) IP 3193 prefixes to eventually reach all nodes (both mobile and fixed) in all 3194 OMNI link segments. This can be accomplished by incrementally 3195 deploying AERO Bridges on each INET partition, with each Bridge 3196 distributing its MNPs and/or discovering non-MNP IP GUA prefixes on 3197 its INET links. 3199 This gives rise to the opportunity to eventually distribute native IP 3200 addresses to all nodes, and to present a unified OMNI link view even 3201 if the INET partitions remain in their current protocol and 3202 addressing plans. In that way, the OMNI link can serve the dual 3203 purpose of providing a mobility/multilink service and a transition/ 3204 coexistence service. Or, if an INET partition is transitioned to a 3205 native IP protocol version and addressing scheme that is compatible 3206 with the OMNI link MNP-based addressing scheme, the partition and 3207 OMNI link can be joined by Bridges. 3209 Relays that connect INETs/EUNs with dissimilar IP protocol versions 3210 may need to employ a network address and protocol translation 3211 function such as NAT64 [RFC6146]. 3213 3.21. Detecting and Reacting to Proxy/Server and Bridge Failures 3215 In environments where rapid failure recovery is required, Proxy/ 3216 Servers and Bridges SHOULD use Bidirectional Forwarding Detection 3217 (BFD) [RFC5880]. Nodes that use BFD can quickly detect and react to 3218 failures so that cached information is re-established through 3219 alternate nodes. BFD control messaging is carried only over well- 3220 connected ground domain networks (i.e., and not low-end radio links) 3221 and can therefore be tuned for rapid response. 3223 Proxy/Servers and Bridges maintain BFD sessions in parallel with 3224 their BGP peerings. If a Proxy/Server or Bridge fails, BGP peers 3225 will quickly re-establish routes through alternate paths the same as 3226 for common BGP deployments. Similarly, Proxys maintain BFD sessions 3227 with their associated Bridges even though they do not establish BGP 3228 peerings with them. 3230 3.22. AERO Clients on the Open Internet 3232 AERO Clients that connect to the open Internet via INET interfaces 3233 can establish a VPN or direct link to securely connect to a Proxy/ 3234 Server in a "tethered" arrangement with all of the Client's traffic 3235 transiting the Proxy/Server. Alternatively, the Client can associate 3236 with an INET Proxy/Server using UDP/IP encapsulation and control 3237 message securing services as discussed in the following sections. 3239 When a Client's OMNI interface enables an INET underlying interface, 3240 it first determines whether the interface is likely to be behind a 3241 NAT. For IPv4, the Client assumes it is on the open Internet if the 3242 INET address is not a special-use IPv4 address per [RFC3330]. 3243 Similarly for IPv6, the Client assumes it is on the open Internet if 3244 the INET address is a Global Unicast Address (GUA) [RFC4291]. 3245 Otherwise, the Client assumes it may be behind one or several NATs. 3247 The Client then prepares an RS message with IPv6 source address set 3248 to its MNP-LLA, with IPv6 destination set to (link-local) All-Routers 3249 multicast and with an OMNI option with underlying interface 3250 attributes. If the Client believes that it is on the open Internet, 3251 it SHOULD include an L2ADDR in the Interface Attributes sub-option 3252 corresponding to the underlying interface; otherwise, it MAY omit 3253 L2ADDR. If the underlying address is IPv4, the Client includes the 3254 Port Number and IPv4 address written in obfuscated form [RFC4380] as 3255 discussed in Section 3.3. If the underlying interface address is 3256 IPv6, the Client instead includes the Port Number and IPv6 address in 3257 obfuscated form. The Client finally includes an authentication 3258 signature sub-option in the OMNI option [I-D.templin-6man-omni] to 3259 provide message authentication, selects an Identification value and 3260 window synchronization parameters, and submits the RS for OAL 3261 encapsulation. The Client then encapsulates the OAL fragment in UDP/ 3262 IP headers to form a carrier packet, sets the UDP/IP source to its 3263 INET address and UDP port, sets the UDP/IP destination to the Proxy/ 3264 Server's INET address and the AERO service port number (8060), then 3265 sends the carrier packet to the Proxy/Server. 3267 When the Proxy/Server receives the RS, it discards the OAL 3268 encapsulation, authenticates the RS message, creates a neighbor cache 3269 entry and registers the Client's MNP, window synchronization state 3270 and INET interface information according to the OMNI option 3271 parameters. If the RS message OMNI option includes Interface 3272 Attributes with an L2ADDR, the Proxy/Server compares the 3273 encapsulation IP address and UDP port number with the (unobfuscated) 3274 values. If the values are the same, the Proxy/Server caches the 3275 Client's information as "INET" addresses meaning that the Client is 3276 likely to accept direct messages without requiring NAT traversal 3277 exchanges. If the values are different (or, if the OMNI option did 3278 not include an L2ADDR) the Proxy/Server instead caches the Client's 3279 information as "mapped" addresses meaning that NAT traversal 3280 exchanges may be necessary. 3282 The Proxy/Server then prepares an RA message with IPv6 source and 3283 destination set corresponding to the addresses in the RS, and with an 3284 OMNI option with an Origin Indication sub-option per 3285 [I-D.templin-6man-omni] with the mapped and obfuscated Port Number 3286 and IP address observed in the encapsulation headers. The Proxy/ 3287 Server also includes an authentication signature sub-option per 3288 [I-D.templin-6man-omni] and a symmetric window synchronization/ 3289 acknowledgement. The Proxy/Server then performs OAL encapsulation 3290 and fragmentation if necessary and encapsulates each fragment in UDP/ 3291 IP headers with addresses set per the L2ADDR information in the 3292 neighbor cache entry for the Client. 3294 When the Client receives the RA, it authenticates the message then 3295 process the window synchronization/acknowledgement and compares the 3296 mapped Port Number and IP address from the Origin Indication sub- 3297 option with its own address. If the addresses are the same, the 3298 Client assumes the open Internet / Cone NAT principle; if the 3299 addresses are different, the Client instead assumes that further 3300 qualification procedures are necessary to detect the type of NAT and 3301 proceeds according to standard procedures [RFC6081][RFC4380]. The 3302 Client finally arranges to return an explicit/implicit 3303 acknowledgement, and sends periodic RS messages to receive fresh RA 3304 messages before the Router Lifetime received on each INET interface 3305 expires. 3307 When the Client sends messages to target IP addresses, it also 3308 invokes route optimization per Section 3.14. The Client first 3309 creates a neighbor cache entry for the target in the INCOMPLETE 3310 state, then sends the NS(AR) message to the Proxy/Server with an OMNI 3311 option with an authentication signature sub-option. The Client sets 3312 the NS source address to its own MNP-LLA, destination address to the 3313 target solicited node multicast address and target address to the LLA 3314 of the target. The Client then includes window synchronization 3315 parameters and wraps the NS message in OAL headers (i.e., as an 3316 atomic fragment) with source address set to its own MNP-ULA and 3317 destination address set to the target's MNP-ULA. The Client then 3318 wraps the atomic fragment in a UDP/IP header and sends the resulting 3319 carrier packet to the Proxy/Server. 3321 When the Client's Proxy/Server receives the OAL-encapsulated NS, it 3322 authenticates the message by processing the authentication signature 3323 sub-option and forwards the message over the secured spanning tree on 3324 behalf of the Client. When the ROR receives the NS(AR), it adds an 3325 entry for the ROS to the target neighbor cache entry Report List and 3326 caches the receive window information for this ROS. The ROR then 3327 returns an NA(AR) with OMNI option information for the target 3328 including all of the target's Interface Attributes and sends extended 3329 route optimization NS(NUD) messages to the target the same as 3330 specified in Section 3.14. 3332 When the Proxy/Sever for the ROS Client receives the resulting NA 3333 messages, it verifies the OAL Identifications match the same value 3334 that was used in the NS(AR) then reassembles if necessary. When 3335 reassembly is complete, the Proxy/Server includes an authentication 3336 signature and forwards the NAs to the ROS Client. The ROS Client 3337 then verifies the authentication signature and changes the neighbor 3338 cache entry state for this target to REACHABLE. 3340 Following route optimization, the ROR may return uNAs via the ROS 3341 Proxy/Server if the target moves and the Proxy/Server will forward 3342 corresponding uNAs to the Client with an OMNI authentication sub- 3343 option. The Client can also send NUD messages to test forward path 3344 reachability even though there is no security association between the 3345 Client and the target. 3347 For route optimized targets in the same OMNI link segment, if the 3348 target's L2ADDR is on the open INET, the Client forwards carrier 3349 packets directly to the target INET address. If the target is behind 3350 a NAT, the Client first establishes NAT state for the L2ADDR using 3351 the "direct bubble" and NUD mechanisms discussed in Section 3.10.1. 3352 The Client continues to send carrier packets via its Proxy/Server 3353 until NAT state is populated, then begins forwarding carrier packets 3354 via the direct path through the NAT to the target. For targets in 3355 different OMNI link segments, the Client uses OAL/ORH encapsulation 3356 and forwards carrier packets to the Bridge that returned the NA 3357 message. 3359 The Client can send original IP packets to route-optimized neighbors 3360 in the same OMNI link segment no larger than the minimum/path MPS in 3361 one piece and with OAL encapsulation as atomic fragments. For larger 3362 original IP packets, the Client applies OAL encapsulation and 3363 fragmentation if necessary according to Section 3.9, with OAL header 3364 with source set to its own MNP-ULA and destination set to the MNP-ULA 3365 of the target. The Client then encapsulates each resulting carrier 3366 packet in UDP/IP *NET headers and sends them to the next hop. 3368 Note: The NAT traversal procedures specified in this document are 3369 applicable for Cone, Address-Restricted and Port-Restricted NATs 3370 only. While future updates to this document may specify procedures 3371 for other NAT variations (e.g., hairpinning and various forms of 3372 Symmetric NATs), it should be noted that continuous communications 3373 are always possible through forwarding via a Proxy/Server even if NAT 3374 traversal is not employed. 3376 3.23. Time-Varying MNPs 3378 In some use cases, it is desirable, beneficial and efficient for the 3379 Client to receive a constant MNP that travels with the Client 3380 wherever it moves. For example, this would allow air traffic 3381 controllers to easily track aircraft, etc. In other cases, however 3382 (e.g., intelligent transportation systems), the MN may be willing to 3383 sacrifice a modicum of efficiency in order to have time-varying MNPs 3384 that can be changed every so often to defeat adversarial tracking. 3386 The DHCPv6 service offers a way for Clients that desire time-varying 3387 MNPs to obtain short-lived prefixes (e.g., on the order of a small 3388 number of minutes). In that case, the identity of the Client would 3389 not be bound to the MNP but rather to a Node Identification value 3390 (see: [I-D.templin-6man-omni]) to be used as the Client ID seed for 3391 MNP prefix delegation. The Client would then be obligated to 3392 renumber its internal networks whenever its MNP (and therefore also 3393 its MNP-LLA) changes. This should not present a challenge for 3394 Clients with automated network renumbering services, however presents 3395 limits for the durations of ongoing sessions that would prefer to use 3396 a constant address. 3398 4. Implementation Status 3400 An early AERO implementation based on OpenVPN (https://openvpn.net/) 3401 was announced on the v6ops mailing list on January 10, 2018 and an 3402 initial public release of the AERO proof-of-concept source code was 3403 announced on the intarea mailing list on August 21, 2015. 3405 AERO Release-3.2 was tagged on March 30, 2021, and is undergoing 3406 internal testing. Additional internal releases expected within the 3407 coming months, with first public release expected end of 1H2021. 3409 5. IANA Considerations 3411 The IANA is instructed to assign a new type value TBD1 in the IPv6 3412 Routing Types registry (IANA registration procedure is IETF Review or 3413 IESG Approval). 3415 The IANA has assigned the UDP port number "8060" for an earlier 3416 experimental first version of AERO [RFC6706]. This document 3417 obsoletes [RFC6706], and together with [I-D.templin-6man-omni] 3418 reclaims the UDP port number "8060" for 'aero' as the service port 3419 for UDP/IP encapsulation. (Note that, although [RFC6706] was not 3420 widely implemented or deployed, any messages coded to that 3421 specification can be easily distinguished and ignored since they use 3422 the invalid ICMPv6 message type number '0'.) This document makes no 3423 request of IANA, since [I-D.templin-6man-omni] already provides 3424 instructions. 3426 No further IANA actions are required. 3428 6. Security Considerations 3430 AERO Bridges configure secured tunnels with AERO Proxy/Servers and 3431 Relays within their local OMNI link segments. Applicable secured 3432 tunnel alternatives include IPsec [RFC4301], TLS/SSL [RFC8446], DTLS 3433 [RFC6347], WireGuard [WG], etc. The AERO Bridges of all OMNI link 3434 segments in turn configure secured tunnels for their neighboring AERO 3435 Bridges in a spanning tree topology. Therefore, control messages 3436 exchanged between any pair of OMNI link neighbors on the spanning 3437 tree are already secured. 3439 AERO nodes acting as Route Optimization Responders (RORs) may also 3440 receive packets directly from arbitrary nodes in INET partitions 3441 instead of via the secured spanning tree. For INET partitions that 3442 apply effective ingress filtering to defeat source address spoofing, 3443 the simple data origin authentication procedures in Section 3.8 can 3444 be applied. 3446 For INET partitions that require strong security in the data plane, 3447 two options for securing communications include 1) disable route 3448 optimization so that all traffic is conveyed over secured tunnels, or 3449 2) enable on-demand secure tunnel creation between Client neighbors. 3450 Option 1) would result in longer routes than necessary and impose 3451 traffic concentration on critical infrastructure elements. Option 2) 3452 could be coordinated between Clients using NS/NA messages with OMNI 3453 Host Identity Protocol (HIP) "Initiator/Responder" message sub- 3454 options [RFC7401][I-D.templin-6man-omni] to create a secured tunnel 3455 on-demand. 3457 AERO Clients that connect to secured ANETs need not apply security to 3458 their ND messages, since the messages will be intercepted by a 3459 perimeter Proxy/Server that applies security on its INET-facing 3460 interface as part of the spanning tree (see above). AERO Clients 3461 connected to the open INET can use network and/or transport layer 3462 security services such as VPNs or can by some other means establish a 3463 direct link to a Proxy/Server. When a VPN or direct link may be 3464 impractical, however, INET Clients and Proxy/Servers SHOULD include 3465 and verify authentication signatures for their IPv6 ND messages as 3466 specified in [I-D.templin-6man-omni]. 3468 Application endpoints SHOULD use transport-layer (or higher-layer) 3469 security services such as TLS/SSL, DTLS or SSH [RFC4251] to assure 3470 the same level of protection as for critical secured Internet 3471 services. AERO Clients that require host-based VPN services SHOULD 3472 use network and/or transport layer security services such as IPsec, 3473 TLS/SSL, DTLS, etc. AERO Proxys and Proxy/Servers can also provide a 3474 network-based VPN service on behalf of the Client, e.g., if the 3475 Client is located within a secured enclave and cannot establish a VPN 3476 on its own behalf. 3478 AERO Proxy/Servers and Bridges present targets for traffic 3479 amplification Denial of Service (DoS) attacks. This concern is no 3480 different than for widely-deployed VPN security gateways in the 3481 Internet, where attackers could send spoofed packets to the gateways 3482 at high data rates. This can be mitigated through the AERO/OMNI data 3483 origin authentication procedures, as well as connecting Proxy/Servers 3484 and Bridges over dedicated links with no connections to the Internet 3485 and/or when connections to the Internet are only permitted through 3486 well-managed firewalls. Traffic amplification DoS attacks can also 3487 target an AERO Client's low data rate links. This is a concern not 3488 only for Clients located on the open Internet but also for Clients in 3489 secured enclaves. AERO Proxy/Servers and Proxys can institute rate 3490 limits that protect Clients from receiving packet floods that could 3491 DoS low data rate links. 3493 AERO Relays must implement ingress filtering to avoid a spoofing 3494 attack in which spurious messages with ULA addresses are injected 3495 into an OMNI link from an outside attacker. AERO Clients MUST ensure 3496 that their connectivity is not used by unauthorized nodes on their 3497 EUNs to gain access to a protected network, i.e., AERO Clients that 3498 act as routers MUST NOT provide routing services for unauthorized 3499 nodes. (This concern is no different than for ordinary hosts that 3500 receive an IP address delegation but then "share" the address with 3501 other nodes via some form of Internet connection sharing such as 3502 tethering.) 3504 The MAP list MUST be well-managed and secured from unauthorized 3505 tampering, even though the list contains only public information. 3506 The MAP list can be conveyed to the Client in a similar fashion as in 3507 [RFC5214] (e.g., through layer 2 data link login messaging, secure 3508 upload of a static file, DNS lookups, etc.). 3510 The AERO service for open INET Clients depends on a public key 3511 distribution service in which Client public keys and identities are 3512 maintained in a shared database accessible to all open INET Proxy/ 3513 Servers. Similarly, each Client must be able to determine the public 3514 key of each Proxy/Server, e.g. by consulting an online database. 3515 When AERO nodes register their public keys indexed by a unique Host 3516 Identity Tag (HIT) [RFC7401] in a distributed database such as the 3517 DNS, and use the HIT as an identity for applying IPv6 ND message 3518 authentication signatures, a means for determining public key 3519 attestation is available. 3521 Security considerations for IPv6 fragmentation and reassembly are 3522 discussed in [I-D.templin-6man-omni]. In environments where spoofing 3523 is considered a threat, OMNI nodes SHOULD employ Identification 3524 window synchronization and OAL destinations SHOULD configure an (end- 3525 system-based) firewall. 3527 SRH authentication facilities are specified in [RFC8754]. Security 3528 considerations for accepting link-layer ICMP messages and reflected 3529 packets are discussed throughout the document. 3531 7. Acknowledgements 3533 Discussions in the IETF, aviation standards communities and private 3534 exchanges helped shape some of the concepts in this work. 3535 Individuals who contributed insights include Mikael Abrahamsson, Mark 3536 Andrews, Fred Baker, Bob Braden, Stewart Bryant, Brian Carpenter, 3537 Wojciech Dec, Pavel Drasil, Ralph Droms, Adrian Farrel, Nick Green, 3538 Sri Gundavelli, Brian Haberman, Bernhard Haindl, Joel Halpern, Tom 3539 Herbert, Sascha Hlusiak, Lee Howard, Zdenek Jaron, Andre Kostur, 3540 Hubert Kuenig, Ted Lemon, Andy Malis, Satoru Matsushima, Tomek 3541 Mrugalski, Madhu Niraula, Alexandru Petrescu, Behcet Saikaya, Michal 3542 Skorepa, Joe Touch, Bernie Volz, Ryuji Wakikawa, Tony Whyman, Lloyd 3543 Wood and James Woodyatt. Members of the IESG also provided valuable 3544 input during their review process that greatly improved the document. 3545 Special thanks go to Stewart Bryant, Joel Halpern and Brian Haberman 3546 for their shepherding guidance during the publication of the AERO 3547 first edition. 3549 This work has further been encouraged and supported by Boeing 3550 colleagues including Kyle Bae, M. Wayne Benson, Dave Bernhardt, Cam 3551 Brodie, John Bush, Balaguruna Chidambaram, Irene Chin, Bruce Cornish, 3552 Claudiu Danilov, Don Dillenburg, Joe Dudkowski, Wen Fang, Samad 3553 Farooqui, Anthony Gregory, Jeff Holland, Seth Jahne, Brian Jaury, 3554 Greg Kimberly, Ed King, Madhuri Madhava Badgandi, Laurel Matthew, 3555 Gene MacLean III, Kyle Mikos, Rob Muszkiewicz, Sean O'Sullivan, Vijay 3556 Rajagopalan, Greg Saccone, Rod Santiago, Kent Shuey, Brian Skeen, 3557 Mike Slane, Carrie Spiker, Katie Tran, Brendan Williams, Amelia 3558 Wilson, Julie Wulff, Yueli Yang, Eric Yeh and other members of the 3559 Boeing mobility, networking and autonomy teams. Kyle Bae, Wayne 3560 Benson, Madhuri Madhava Badgandi, Vijayasarathy Rajagopalan, Katie 3561 Tran and Eric Yeh are especially acknowledged for implementing the 3562 AERO functions as extensions to the public domain OpenVPN 3563 distribution. Chuck Klabunde is honored and remembered for his early 3564 leadership, and we mourn his untimely loss. 3566 Earlier works on NBMA tunneling approaches are found in 3567 [RFC2529][RFC5214][RFC5569]. 3569 Many of the constructs presented in this second edition of AERO are 3570 based on the author's earlier works, including: 3572 o The Internet Routing Overlay Network (IRON) 3573 [RFC6179][I-D.templin-ironbis] 3575 o Virtual Enterprise Traversal (VET) 3576 [RFC5558][I-D.templin-intarea-vet] 3578 o The Subnetwork Encapsulation and Adaptation Layer (SEAL) 3579 [RFC5320][I-D.templin-intarea-seal] 3581 o AERO, First Edition [RFC6706] 3583 Note that these works cite numerous earlier efforts that are not also 3584 cited here due to space limitations. The authors of those earlier 3585 works are acknowledged for their insights. 3587 This work is aligned with the NASA Safe Autonomous Systems Operation 3588 (SASO) program under NASA contract number NNA16BD84C. 3590 This work is aligned with the FAA as per the SE2025 contract number 3591 DTFAWA-15-D-00030. 3593 This work is aligned with the Boeing Commercial Airplanes (BCA) 3594 Internet of Things (IoT) and autonomy programs. 3596 This work is aligned with the Boeing Information Technology (BIT) 3597 MobileNet program. 3599 8. References 3601 8.1. Normative References 3603 [I-D.templin-6man-omni] 3604 Templin, F. L. and T. Whyman, "Transmission of IP Packets 3605 over Overlay Multilink Network (OMNI) Interfaces", draft- 3606 templin-6man-omni-03 (work in progress), April 2021. 3608 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, 3609 DOI 10.17487/RFC0791, September 1981, 3610 . 3612 [RFC0792] Postel, J., "Internet Control Message Protocol", STD 5, 3613 RFC 792, DOI 10.17487/RFC0792, September 1981, 3614 . 3616 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 3617 Requirement Levels", BCP 14, RFC 2119, 3618 DOI 10.17487/RFC2119, March 1997, 3619 . 3621 [RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in 3622 IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473, 3623 December 1998, . 3625 [RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander, 3626 "SEcure Neighbor Discovery (SEND)", RFC 3971, 3627 DOI 10.17487/RFC3971, March 2005, 3628 . 3630 [RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)", 3631 RFC 3972, DOI 10.17487/RFC3972, March 2005, 3632 . 3634 [RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and 3635 More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191, 3636 November 2005, . 3638 [RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast 3639 Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005, 3640 . 3642 [RFC4380] Huitema, C., "Teredo: Tunneling IPv6 over UDP through 3643 Network Address Translations (NATs)", RFC 4380, 3644 DOI 10.17487/RFC4380, February 2006, 3645 . 3647 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 3648 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 3649 DOI 10.17487/RFC4861, September 2007, 3650 . 3652 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 3653 Address Autoconfiguration", RFC 4862, 3654 DOI 10.17487/RFC4862, September 2007, 3655 . 3657 [RFC6081] Thaler, D., "Teredo Extensions", RFC 6081, 3658 DOI 10.17487/RFC6081, January 2011, 3659 . 3661 [RFC7401] Moskowitz, R., Ed., Heer, T., Jokela, P., and T. 3662 Henderson, "Host Identity Protocol Version 2 (HIPv2)", 3663 RFC 7401, DOI 10.17487/RFC7401, April 2015, 3664 . 3666 [RFC7739] Gont, F., "Security Implications of Predictable Fragment 3667 Identification Values", RFC 7739, DOI 10.17487/RFC7739, 3668 February 2016, . 3670 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 3671 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 3672 May 2017, . 3674 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 3675 (IPv6) Specification", STD 86, RFC 8200, 3676 DOI 10.17487/RFC8200, July 2017, 3677 . 3679 [RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A., 3680 Richardson, M., Jiang, S., Lemon, T., and T. Winters, 3681 "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", 3682 RFC 8415, DOI 10.17487/RFC8415, November 2018, 3683 . 3685 8.2. Informative References 3687 [BGP] Huston, G., "BGP in 2015, http://potaroo.net", January 3688 2016. 3690 [I-D.bonica-6man-comp-rtg-hdr] 3691 Bonica, R., Kamite, Y., Alston, A., Henriques, D., and L. 3692 Jalil, "The IPv6 Compact Routing Header (CRH)", draft- 3693 bonica-6man-comp-rtg-hdr-24 (work in progress), January 3694 2021. 3696 [I-D.bonica-6man-crh-helper-opt] 3697 Li, X., Bao, C., Ruan, E., and R. Bonica, "Compressed 3698 Routing Header (CRH) Helper Option", draft-bonica-6man- 3699 crh-helper-opt-03 (work in progress), April 2021. 3701 [I-D.ietf-intarea-frag-fragile] 3702 Bonica, R., Baker, F., Huston, G., Hinden, R. M., Troan, 3703 O., and F. Gont, "IP Fragmentation Considered Fragile", 3704 draft-ietf-intarea-frag-fragile-17 (work in progress), 3705 September 2019. 3707 [I-D.ietf-intarea-tunnels] 3708 Touch, J. and M. Townsley, "IP Tunnels in the Internet 3709 Architecture", draft-ietf-intarea-tunnels-10 (work in 3710 progress), September 2019. 3712 [I-D.ietf-ipwave-vehicular-networking] 3713 (editor), J. (. J., "IPv6 Wireless Access in Vehicular 3714 Environments (IPWAVE): Problem Statement and Use Cases", 3715 draft-ietf-ipwave-vehicular-networking-20 (work in 3716 progress), March 2021. 3718 [I-D.ietf-rtgwg-atn-bgp] 3719 Templin, F. L., Saccone, G., Dawra, G., Lindem, A., and V. 3720 Moreno, "A Simple BGP-based Mobile Routing System for the 3721 Aeronautical Telecommunications Network", draft-ietf- 3722 rtgwg-atn-bgp-10 (work in progress), January 2021. 3724 [I-D.templin-6man-dhcpv6-ndopt] 3725 Templin, F. L., "A Unified Stateful/Stateless 3726 Configuration Service for IPv6", draft-templin-6man- 3727 dhcpv6-ndopt-11 (work in progress), January 2021. 3729 [I-D.templin-intarea-seal] 3730 Templin, F. L., "The Subnetwork Encapsulation and 3731 Adaptation Layer (SEAL)", draft-templin-intarea-seal-68 3732 (work in progress), January 2014. 3734 [I-D.templin-intarea-vet] 3735 Templin, F. L., "Virtual Enterprise Traversal (VET)", 3736 draft-templin-intarea-vet-40 (work in progress), May 2013. 3738 [I-D.templin-ipwave-uam-its] 3739 Templin, F. L., "Urban Air Mobility Implications for 3740 Intelligent Transportation Systems", draft-templin-ipwave- 3741 uam-its-04 (work in progress), January 2021. 3743 [I-D.templin-ironbis] 3744 Templin, F. L., "The Interior Routing Overlay Network 3745 (IRON)", draft-templin-ironbis-16 (work in progress), 3746 March 2014. 3748 [I-D.templin-v6ops-pdhost] 3749 Templin, F. L., "IPv6 Prefix Delegation and Multi- 3750 Addressing Models", draft-templin-v6ops-pdhost-27 (work in 3751 progress), January 2021. 3753 [OVPN] OpenVPN, O., "http://openvpn.net", October 2016. 3755 [RFC1035] Mockapetris, P., "Domain names - implementation and 3756 specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, 3757 November 1987, . 3759 [RFC1812] Baker, F., Ed., "Requirements for IP Version 4 Routers", 3760 RFC 1812, DOI 10.17487/RFC1812, June 1995, 3761 . 3763 [RFC2003] Perkins, C., "IP Encapsulation within IP", RFC 2003, 3764 DOI 10.17487/RFC2003, October 1996, 3765 . 3767 [RFC2004] Perkins, C., "Minimal Encapsulation within IP", RFC 2004, 3768 DOI 10.17487/RFC2004, October 1996, 3769 . 3771 [RFC2236] Fenner, W., "Internet Group Management Protocol, Version 3772 2", RFC 2236, DOI 10.17487/RFC2236, November 1997, 3773 . 3775 [RFC2464] Crawford, M., "Transmission of IPv6 Packets over Ethernet 3776 Networks", RFC 2464, DOI 10.17487/RFC2464, December 1998, 3777 . 3779 [RFC2529] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4 3780 Domains without Explicit Tunnels", RFC 2529, 3781 DOI 10.17487/RFC2529, March 1999, 3782 . 3784 [RFC2983] Black, D., "Differentiated Services and Tunnels", 3785 RFC 2983, DOI 10.17487/RFC2983, October 2000, 3786 . 3788 [RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition 3789 of Explicit Congestion Notification (ECN) to IP", 3790 RFC 3168, DOI 10.17487/RFC3168, September 2001, 3791 . 3793 [RFC3330] IANA, "Special-Use IPv4 Addresses", RFC 3330, 3794 DOI 10.17487/RFC3330, September 2002, 3795 . 3797 [RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener 3798 Discovery Version 2 (MLDv2) for IPv6", RFC 3810, 3799 DOI 10.17487/RFC3810, June 2004, 3800 . 3802 [RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally 3803 Unique IDentifier (UUID) URN Namespace", RFC 4122, 3804 DOI 10.17487/RFC4122, July 2005, 3805 . 3807 [RFC4251] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH) 3808 Protocol Architecture", RFC 4251, DOI 10.17487/RFC4251, 3809 January 2006, . 3811 [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A 3812 Border Gateway Protocol 4 (BGP-4)", RFC 4271, 3813 DOI 10.17487/RFC4271, January 2006, 3814 . 3816 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 3817 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 3818 2006, . 3820 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 3821 Internet Protocol", RFC 4301, DOI 10.17487/RFC4301, 3822 December 2005, . 3824 [RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery 3825 Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April 3826 2006, . 3828 [RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet 3829 Control Message Protocol (ICMPv6) for the Internet 3830 Protocol Version 6 (IPv6) Specification", STD 89, 3831 RFC 4443, DOI 10.17487/RFC4443, March 2006, 3832 . 3834 [RFC4511] Sermersheim, J., Ed., "Lightweight Directory Access 3835 Protocol (LDAP): The Protocol", RFC 4511, 3836 DOI 10.17487/RFC4511, June 2006, 3837 . 3839 [RFC4541] Christensen, M., Kimball, K., and F. Solensky, 3840 "Considerations for Internet Group Management Protocol 3841 (IGMP) and Multicast Listener Discovery (MLD) Snooping 3842 Switches", RFC 4541, DOI 10.17487/RFC4541, May 2006, 3843 . 3845 [RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick, 3846 "Internet Group Management Protocol (IGMP) / Multicast 3847 Listener Discovery (MLD)-Based Multicast Forwarding 3848 ("IGMP/MLD Proxying")", RFC 4605, DOI 10.17487/RFC4605, 3849 August 2006, . 3851 [RFC4982] Bagnulo, M. and J. Arkko, "Support for Multiple Hash 3852 Algorithms in Cryptographically Generated Addresses 3853 (CGAs)", RFC 4982, DOI 10.17487/RFC4982, July 2007, 3854 . 3856 [RFC5015] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano, 3857 "Bidirectional Protocol Independent Multicast (BIDIR- 3858 PIM)", RFC 5015, DOI 10.17487/RFC5015, October 2007, 3859 . 3861 [RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site 3862 Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214, 3863 DOI 10.17487/RFC5214, March 2008, 3864 . 3866 [RFC5320] Templin, F., Ed., "The Subnetwork Encapsulation and 3867 Adaptation Layer (SEAL)", RFC 5320, DOI 10.17487/RFC5320, 3868 February 2010, . 3870 [RFC5522] Eddy, W., Ivancic, W., and T. Davis, "Network Mobility 3871 Route Optimization Requirements for Operational Use in 3872 Aeronautics and Space Exploration Mobile Networks", 3873 RFC 5522, DOI 10.17487/RFC5522, October 2009, 3874 . 3876 [RFC5558] Templin, F., Ed., "Virtual Enterprise Traversal (VET)", 3877 RFC 5558, DOI 10.17487/RFC5558, February 2010, 3878 . 3880 [RFC5569] Despres, R., "IPv6 Rapid Deployment on IPv4 3881 Infrastructures (6rd)", RFC 5569, DOI 10.17487/RFC5569, 3882 January 2010, . 3884 [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 3885 (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, 3886 . 3888 [RFC6106] Jeong, J., Park, S., Beloeil, L., and S. Madanapalli, 3889 "IPv6 Router Advertisement Options for DNS Configuration", 3890 RFC 6106, DOI 10.17487/RFC6106, November 2010, 3891 . 3893 [RFC6139] Russert, S., Ed., Fleischman, E., Ed., and F. Templin, 3894 Ed., "Routing and Addressing in Networks with Global 3895 Enterprise Recursion (RANGER) Scenarios", RFC 6139, 3896 DOI 10.17487/RFC6139, February 2011, 3897 . 3899 [RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful 3900 NAT64: Network Address and Protocol Translation from IPv6 3901 Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146, 3902 April 2011, . 3904 [RFC6179] Templin, F., Ed., "The Internet Routing Overlay Network 3905 (IRON)", RFC 6179, DOI 10.17487/RFC6179, March 2011, 3906 . 3908 [RFC6221] Miles, D., Ed., Ooghe, S., Dec, W., Krishnan, S., and A. 3909 Kavanagh, "Lightweight DHCPv6 Relay Agent", RFC 6221, 3910 DOI 10.17487/RFC6221, May 2011, 3911 . 3913 [RFC6273] Kukec, A., Krishnan, S., and S. Jiang, "The Secure 3914 Neighbor Discovery (SEND) Hash Threat Analysis", RFC 6273, 3915 DOI 10.17487/RFC6273, June 2011, 3916 . 3918 [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer 3919 Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, 3920 January 2012, . 3922 [RFC6355] Narten, T. and J. Johnson, "Definition of the UUID-Based 3923 DHCPv6 Unique Identifier (DUID-UUID)", RFC 6355, 3924 DOI 10.17487/RFC6355, August 2011, 3925 . 3927 [RFC6438] Carpenter, B. and S. Amante, "Using the IPv6 Flow Label 3928 for Equal Cost Multipath Routing and Link Aggregation in 3929 Tunnels", RFC 6438, DOI 10.17487/RFC6438, November 2011, 3930 . 3932 [RFC6706] Templin, F., Ed., "Asymmetric Extended Route Optimization 3933 (AERO)", RFC 6706, DOI 10.17487/RFC6706, August 2012, 3934 . 3936 [RFC6935] Eubanks, M., Chimento, P., and M. Westerlund, "IPv6 and 3937 UDP Checksums for Tunneled Packets", RFC 6935, 3938 DOI 10.17487/RFC6935, April 2013, 3939 . 3941 [RFC6936] Fairhurst, G. and M. Westerlund, "Applicability Statement 3942 for the Use of IPv6 UDP Datagrams with Zero Checksums", 3943 RFC 6936, DOI 10.17487/RFC6936, April 2013, 3944 . 3946 [RFC7333] Chan, H., Ed., Liu, D., Seite, P., Yokota, H., and J. 3947 Korhonen, "Requirements for Distributed Mobility 3948 Management", RFC 7333, DOI 10.17487/RFC7333, August 2014, 3949 . 3951 [RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I., 3952 Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent 3953 Multicast - Sparse Mode (PIM-SM): Protocol Specification 3954 (Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March 3955 2016, . 3957 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 3958 Decraene, B., Litkowski, S., and R. Shakir, "Segment 3959 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 3960 July 2018, . 3962 [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol 3963 Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, 3964 . 3966 [RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J., 3967 Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header 3968 (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020, 3969 . 3971 [WG] Wireguard, "WireGuard, https://www.wireguard.com", August 3972 2020. 3974 Appendix A. Non-Normative Considerations 3976 AERO can be applied to a multitude of Internetworking scenarios, with 3977 each having its own adaptations. The following considerations are 3978 provided as non-normative guidance: 3980 A.1. Implementation Strategies for Route Optimization 3982 Route optimization as discussed in Section 3.14 results in the route 3983 optimization source (ROS) creating a neighbor cache entry for the 3984 target neighbor. The neighbor cache entry state is set to REACHABLE 3985 for at most ReachableTime seconds. In order to refresh the neighbor 3986 cache entry lifetime before the ReachableTime timer expires, the 3987 specification requires implementations to issue a new NS/NA exchange 3988 to reset ReachableTime while data packets are still flowing. 3989 However, the decision of when to initiate a new NS/NA exchange and to 3990 perpetuate the process is left as an implementation detail. 3992 One possible strategy may be to monitor the neighbor cache entry 3993 watching for data packets for (ReachableTime - 5) seconds. If any 3994 data packets have been sent to the neighbor within this timeframe, 3995 then send an NS to receive a new NA. If no data packets have been 3996 sent, wait for 5 additional seconds and send an immediate NS if any 3997 data packets are sent within this "expiration pending" 5 second 3998 window. If no additional data packets are sent within the 5 second 3999 window, reset the neighbor cache entry state to STALE. 4001 The monitoring of the neighbor data packet traffic therefore becomes 4002 an ongoing process during the neighbor cache entry lifetime. If the 4003 neighbor cache entry expires, future data packets will trigger a new 4004 NS/NA exchange while the packets themselves are delivered over a 4005 longer path until route optimization state is re-established. 4007 A.2. Implicit Mobility Management 4009 OMNI interface neighbors MAY provide a configuration option that 4010 allows them to perform implicit mobility management in which no ND 4011 messaging is used. In that case, the Client only transmits packets 4012 over a single interface at a time, and the neighbor always observes 4013 packets arriving from the Client from the same link-layer source 4014 address. 4016 If the Client's underlying interface address changes (either due to a 4017 readdressing of the original interface or switching to a new 4018 interface) the neighbor immediately updates the neighbor cache entry 4019 for the Client and begins accepting and sending packets according to 4020 the Client's new address. This implicit mobility method applies to 4021 use cases such as cellphones with both WiFi and Cellular interfaces 4022 where only one of the interfaces is active at a given time, and the 4023 Client automatically switches over to the backup interface if the 4024 primary interface fails. 4026 A.3. Direct Underlying Interfaces 4028 When a Client's OMNI interface is configured over a Direct interface, 4029 the neighbor at the other end of the Direct link can receive packets 4030 without any encapsulation. In that case, the Client sends packets 4031 over the Direct link according to traffic selectors. If the Direct 4032 interface is selected, then the Client's IP packets are transmitted 4033 directly to the peer without going through an ANET/INET. If other 4034 interfaces are selected, then the Client's IP packets are transmitted 4035 via a different interface, which may result in the inclusion of 4036 Proxy/Servers and Bridges in the communications path. Direct 4037 interfaces must be tested periodically for reachability, e.g., via 4038 NUD. 4040 A.4. AERO Critical Infrastructure Considerations 4042 AERO Bridges can be either Commercial off-the Shelf (COTS) standard 4043 IP routers or virtual machines in the cloud. Bridges must be 4044 provisioned, supported and managed by the INET administrative 4045 authority, and connected to the Bridges of other INETs via inter- 4046 domain peerings. Cost for purchasing, configuring and managing 4047 Bridges is nominal even for very large OMNI links. 4049 AERO cloud Proxy/Servers can be standard dedicated server platforms, 4050 but most often will be deployed as virtual machines in the cloud. 4051 The only requirements for cloud Proxy/Servers are that they can run 4052 the AERO user-level code and have at least one network interface 4053 connection to the INET. Cloud Proxy/Servers must be provisioned, 4054 supported and managed by the INET administrative authority. Cost for 4055 purchasing, configuring and managing cloud Proxy/Servers is nominal 4056 especially for virtual machines. 4058 AERO ANET Proxy/Servers are most often standard dedicated server 4059 platforms with one underlying interface connected to the ANET and a 4060 second interface connected to an INET. As with cloud Proxy/Servers, 4061 the only requirements are that they can run the AERO user-level code 4062 and have at least one interface connection to the INET. ANET Proxy/ 4063 Servers must be provisioned, supported and managed by the ANET 4064 administrative authority. Cost for purchasing, configuring and 4065 managing Proxys is nominal, and borne by the ANET administrative 4066 authority. 4068 AERO Relays are simply Proxy/Servers connected to INETs and/or EUNs 4069 that provide forwarding services for non-MNP destinations. The Relay 4070 connects to the OMNI link and engages in eBGP peering with one or 4071 more Bridges as a stub AS. The Relay then injects its MNPs and/or 4072 non-MNP prefixes into the BGP routing system, and provisions the 4073 prefixes to its downstream-attached networks. The Relay can perform 4074 ROS/ROR services the same as for any Proxy/Server, and can route 4075 between the MNP and non-MNP address spaces. 4077 A.5. AERO Server Failure Implications 4079 AERO Proxy/Servers may appear as a single point of failure in the 4080 architecture, but such is not the case since all Proxy/Servers on the 4081 link provide identical services and loss of a Proxy/Server does not 4082 imply immediate and/or comprehensive communication failures. Proxy/ 4083 Server failure is quickly detected and conveyed by Bidirectional 4084 Forward Detection (BFD) and/or proactive NUD allowing Clients to 4085 migrate to new Proxy/Servers. 4087 If a Proxy/Server fails, ongoing packet forwarding to Clients will 4088 continue by virtue of the neighbor cache entries that have already 4089 been established in route optimization sources (ROSs). If a Client 4090 also experiences mobility events at roughly the same time the Proxy/ 4091 Server fails, unsolicited NA messages may be lost but neighbor cache 4092 entries in the DEPARTED state will ensure that packet forwarding to 4093 the Client's new locations will continue for up to DepartTime 4094 seconds. 4096 If a Client is left without a Proxy/Server for a considerable length 4097 of time (e.g., greater than ReachableTime seconds) then existing 4098 neighbor cache entries will eventually expire and both ongoing and 4099 new communications will fail. The original source will continue to 4100 retransmit until the Client has established a new Proxy/Server 4101 relationship, after which time continuous communications will resume. 4103 Therefore, providing many Proxy/Servers on the link with high 4104 availability profiles provides resilience against loss of individual 4105 Proxy/Servers and assurance that Clients can establish new Proxy/ 4106 Server relationships quickly in event of a Proxy/Server failure. 4108 A.6. AERO Client / Server Architecture 4110 The AERO architectural model is client / server in the control plane, 4111 with route optimization in the data plane. The same as for common 4112 Internet services, the AERO Client discovers the addresses of AERO 4113 Proxy/Servers and connects to one or more of them. The AERO service 4114 is analogous to common Internet services such as google.com, 4115 yahoo.com, cnn.com, etc. However, there is only one AERO service for 4116 the link and all Proxy/Servers provide identical services. 4118 Common Internet services provide differing strategies for advertising 4119 server addresses to clients. The strategy is conveyed through the 4120 DNS resource records returned in response to name resolution queries. 4121 As of January 2020 Internet-based 'nslookup' services were used to 4122 determine the following: 4124 o When a client resolves the domainname "google.com", the DNS always 4125 returns one A record (i.e., an IPv4 address) and one AAAA record 4126 (i.e., an IPv6 address). The client receives the same addresses 4127 each time it resolves the domainname via the same DNS resolver, 4128 but may receive different addresses when it resolves the 4129 domainname via different DNS resolvers. But, in each case, 4130 exactly one A and one AAAA record are returned. 4132 o When a client resolves the domainname "ietf.org", the DNS always 4133 returns one A record and one AAAA record with the same addresses 4134 regardless of which DNS resolver is used. 4136 o When a client resolves the domainname "yahoo.com", the DNS always 4137 returns a list of 4 A records and 4 AAAA records. Each time the 4138 client resolves the domainname via the same DNS resolver, the same 4139 list of addresses are returned but in randomized order (i.e., 4140 consistent with a DNS round-robin strategy). But, interestingly, 4141 the same addresses are returned (albeit in randomized order) when 4142 the domainname is resolved via different DNS resolvers. 4144 o When a client resolves the domainname "amazon.com", the DNS always 4145 returns a list of 3 A records and no AAAA records. As with 4146 "yahoo.com", the same three A records are returned from any 4147 worldwide Internet connection point in randomized order. 4149 The above example strategies show differing approaches to Internet 4150 resilience and service distribution offered by major Internet 4151 services. The Google approach exposes only a single IPv4 and a 4152 single IPv6 address to clients. Clients can then select whichever IP 4153 protocol version offers the best response, but will always use the 4154 same IP address according to the current Internet connection point. 4155 This means that the IP address offered by the network must lead to a 4156 highly-available server and/or service distribution point. In other 4157 words, resilience is predicated on high availability within the 4158 network and with no client-initiated failovers expected (i.e., it is 4159 all-or-nothing from the client's perspective). However, Google does 4160 provide for worldwide distributed service distribution by virtue of 4161 the fact that each Internet connection point responds with a 4162 different IPv6 and IPv4 address. The IETF approach is like google 4163 (all-or-nothing from the client's perspective), but provides only a 4164 single IPv4 or IPv6 address on a worldwide basis. This means that 4165 the addresses must be made highly-available at the network level with 4166 no client failover possibility, and if there is any worldwide service 4167 distribution it would need to be conducted by a network element that 4168 is reached via the IP address acting as a service distribution point. 4170 In contrast to the Google and IETF philosophies, Yahoo and Amazon 4171 both provide clients with a (short) list of IP addresses with Yahoo 4172 providing both IP protocol versions and Amazon as IPv4-only. The 4173 order of the list is randomized with each name service query 4174 response, with the effect of round-robin load balancing for service 4175 distribution. With a short list of addresses, there is still 4176 expectation that the network will implement high availability for 4177 each address but in case any single address fails the client can 4178 switch over to using a different address. The balance then becomes 4179 one of function in the network vs function in the end system. 4181 The same implications observed for common highly-available services 4182 in the Internet apply also to the AERO client/server architecture. 4183 When an AERO Client connects to one or more ANETs, it discovers one 4184 or more AERO Proxy/Server addresses through the mechanisms discussed 4185 in earlier sections. Each Proxy/Server address presumably leads to a 4186 fault-tolerant clustering arrangement such as supported by Linux-HA, 4187 Extended Virtual Synchrony or Paxos. Such an arrangement has 4188 precedence in common Internet service deployments in lightweight 4189 virtual machines without requiring expensive hardware deployment. 4190 Similarly, common Internet service deployments set service IP 4191 addresses on service distribution points that may relay requests to 4192 many different servers. 4194 For AERO, the expectation is that a combination of the Google/IETF 4195 and Yahoo/Amazon philosophies would be employed. The AERO Client 4196 connects to different ANET access points and can receive 1-2 Proxy/ 4197 Server ADM-LLAs at each point. It then selects one AERO Proxy/Server 4198 address, and engages in RS/RA exchanges with the same Proxy/Server 4199 from all ANET connections. The Client remains with this Proxy/Server 4200 unless or until the Proxy/Server fails, in which case it can switch 4201 over to an alternate Proxy/Server. The Client can likewise switch 4202 over to a different Proxy/Server at any time if there is some reason 4203 for it to do so. So, the AERO expectation is for a balance of 4204 function in the network and end system, with fault tolerance and 4205 resilience at both levels. 4207 Appendix B. Change Log 4209 << RFC Editor - remove prior to publication >> 4211 Changes from draft-templin-6man-aero-05 to draft-templin-6man-aero- 4212 06: 4214 o Final editorial review pass resulting in multiple changes. 4215 Document now submit for final approval. 4217 Changes from draft-templin-6man-aero-04 to draft-templin-6man-aero- 4218 05: 4220 o Changed to use traffic selectors instead of the former multilink 4221 selection strategy. 4223 Changes from draft-templin-6man-aero-03 to draft-templin-6man-aero- 4224 04: 4226 o Removed documents from "Obsoletes" list. 4228 o Introduced the concept of "secured" and "unsecured" spanning tree. 4230 o Additional security considerations. 4232 o Additional route optimization considerations. 4234 Changes from draft-templin-6man-aero-02 to draft-templin-6man-aero- 4235 03: 4237 o Support for extended route optimization from ROR to target over 4238 target's underlying interfaces. 4240 Changes from draft-templin-6man-aero-01 to draft-templin-6man-aero- 4241 02: 4243 o Changed reference citations to "draft-templin-6man-omni". 4245 o Several important updates to IPv6 ND cache states and route 4246 optimization message addressing. 4248 o Included introductory description of the "6M's". 4250 o Updated Multicast specification. 4252 Changes from draft-templin-6man-aero-00 to draft-templin-6man-aero- 4253 01: 4255 o Changed category to "Informational". 4257 o Updated implementation status. 4259 Changes from earlier versions to draft-templin-6man-aero-00: 4261 o Established working baseline reference. 4263 Author's Address 4265 Fred L. Templin (editor) 4266 Boeing Research & Technology 4267 P.O. Box 3707 4268 Seattle, WA 98124 4269 USA 4271 Email: fltemplin@acm.org