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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 Obsoletes: rfc5320, rfc5558, rfc5720, December 10, 2020 5 rfc6179, rfc6706 (if 6 approved) 7 Intended status: Standards Track 8 Expires: June 13, 2021 10 Asymmetric Extended Route Optimization (AERO) 11 draft-templin-intarea-6706bis-75 13 Abstract 15 This document specifies the operation of IP over Overlay Multilink 16 Network (OMNI) interfaces using the Asymmetric Extended Route 17 Optimization (AERO) internetworking and mobility management service. 18 AERO/OMNI use an IPv6 link-local address format that supports 19 operation of the IPv6 Neighbor Discovery (ND) protocol and links ND 20 to IP forwarding. Prefix delegation/registration services are 21 employed for network admission and to manage the routing system. 22 Multilink operation, mobility management, quality of service (QoS) 23 signaling and route optimization are naturally supported through 24 dynamic neighbor cache updates. Standard IP multicasting services 25 are also supported. AERO is a widely-applicable mobile 26 internetworking service especially well-suited to aviation services, 27 intelligent transportation systems, mobile Virtual Private Networks 28 (VPNs) and many other applications. 30 Status of This Memo 32 This Internet-Draft is submitted in full conformance with the 33 provisions of BCP 78 and BCP 79. 35 Internet-Drafts are working documents of the Internet Engineering 36 Task Force (IETF). Note that other groups may also distribute 37 working documents as Internet-Drafts. The list of current Internet- 38 Drafts is at https://datatracker.ietf.org/drafts/current/. 40 Internet-Drafts are draft documents valid for a maximum of six months 41 and may be updated, replaced, or obsoleted by other documents at any 42 time. It is inappropriate to use Internet-Drafts as reference 43 material or to cite them other than as "work in progress." 45 This Internet-Draft will expire on June 13, 2021. 47 Copyright Notice 49 Copyright (c) 2020 IETF Trust and the persons identified as the 50 document authors. All rights reserved. 52 This document is subject to BCP 78 and the IETF Trust's Legal 53 Provisions Relating to IETF Documents 54 (https://trustee.ietf.org/license-info) in effect on the date of 55 publication of this document. Please review these documents 56 carefully, as they describe your rights and restrictions with respect 57 to this document. Code Components extracted from this document must 58 include Simplified BSD License text as described in Section 4.e of 59 the Trust Legal Provisions and are provided without warranty as 60 described in the Simplified BSD License. 62 Table of Contents 64 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 65 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 66 3. Asymmetric Extended Route Optimization (AERO) . . . . . . . . 10 67 3.1. AERO Node Types . . . . . . . . . . . . . . . . . . . . . 10 68 3.2. The AERO Service over OMNI Links . . . . . . . . . . . . 12 69 3.2.1. AERO/OMNI Reference Model . . . . . . . . . . . . . . 12 70 3.2.2. Link-Local Addresses (LLAs) and Domain Local 71 Addresses (DLAs) . . . . . . . . . . . . . . . . . . 14 72 3.2.3. AERO Routing System . . . . . . . . . . . . . . . . . 15 73 3.2.4. OMNI Link Encapsulation . . . . . . . . . . . . . . . 16 74 3.2.5. Segment Routing Topologies (SRTs) . . . . . . . . . . 20 75 3.2.6. Segment Routing For OMNI Link Selection . . . . . . . 21 76 3.2.7. Segment Routing Within the OMNI Link . . . . . . . . 21 77 3.3. OMNI Interface Characteristics . . . . . . . . . . . . . 22 78 3.4. OMNI Interface Initialization . . . . . . . . . . . . . . 24 79 3.4.1. AERO Server/Relay Behavior . . . . . . . . . . . . . 24 80 3.4.2. AERO Proxy Behavior . . . . . . . . . . . . . . . . . 25 81 3.4.3. AERO Client Behavior . . . . . . . . . . . . . . . . 25 82 3.4.4. AERO Bridge Behavior . . . . . . . . . . . . . . . . 25 83 3.5. OMNI Interface Neighbor Cache Maintenance . . . . . . . . 25 84 3.5.1. OMNI Neighbor Interface Attributes . . . . . . . . . 27 85 3.5.2. OMNI Neighbor Advertisement Message Flags . . . . . . 28 86 3.6. OMNI Interface Encapsulation and Re-encapsulation . . . . 28 87 3.7. OMNI Interface Decapsulation . . . . . . . . . . . . . . 30 88 3.8. OMNI Interface Data Origin Authentication . . . . . . . . 30 89 3.9. OMNI Adaptation Layer and OMNI Interface MTU . . . . . . 30 90 3.10. OMNI Interface Forwarding Algorithm . . . . . . . . . . . 31 91 3.10.1. Client Forwarding Algorithm . . . . . . . . . . . . 32 92 3.10.2. Proxy Forwarding Algorithm . . . . . . . . . . . . . 32 93 3.10.3. Server/Relay Forwarding Algorithm . . . . . . . . . 33 94 3.10.4. Bridge Forwarding Algorithm . . . . . . . . . . . . 34 96 3.11. OMNI Interface Error Handling . . . . . . . . . . . . . . 35 97 3.12. AERO Router Discovery, Prefix Delegation and 98 Autoconfiguration . . . . . . . . . . . . . . . . . . . . 38 99 3.12.1. AERO Service Model . . . . . . . . . . . . . . . . . 38 100 3.12.2. AERO Client Behavior . . . . . . . . . . . . . . . . 38 101 3.12.3. AERO Server Behavior . . . . . . . . . . . . . . . . 40 102 3.13. The AERO Proxy . . . . . . . . . . . . . . . . . . . . . 43 103 3.13.1. Combined Proxy/Servers . . . . . . . . . . . . . . . 45 104 3.13.2. Detecting and Responding to Server Failures . . . . 46 105 3.13.3. Point-to-Multipoint Server Coordination . . . . . . 46 106 3.14. AERO Route Optimization / Address Resolution . . . . . . 47 107 3.14.1. Route Optimization Initiation . . . . . . . . . . . 48 108 3.14.2. Relaying the NS . . . . . . . . . . . . . . . . . . 48 109 3.14.3. Processing the NS and Sending the NA . . . . . . . . 48 110 3.14.4. Relaying the NA . . . . . . . . . . . . . . . . . . 49 111 3.14.5. Processing the NA . . . . . . . . . . . . . . . . . 50 112 3.14.6. Route Optimization Maintenance . . . . . . . . . . . 50 113 3.15. Neighbor Unreachability Detection (NUD) . . . . . . . . . 51 114 3.16. Mobility Management and Quality of Service (QoS) . . . . 52 115 3.16.1. Mobility Update Messaging . . . . . . . . . . . . . 53 116 3.16.2. Announcing Link-Layer Address and/or QoS Preference 117 Changes . . . . . . . . . . . . . . . . . . . . . . 54 118 3.16.3. Bringing New Links Into Service . . . . . . . . . . 55 119 3.16.4. Deactivating Existing Links . . . . . . . . . . . . 55 120 3.16.5. Moving Between Servers . . . . . . . . . . . . . . . 55 121 3.17. Multicast . . . . . . . . . . . . . . . . . . . . . . . . 56 122 3.17.1. Source-Specific Multicast (SSM) . . . . . . . . . . 57 123 3.17.2. Any-Source Multicast (ASM) . . . . . . . . . . . . . 58 124 3.17.3. Bi-Directional PIM (BIDIR-PIM) . . . . . . . . . . . 59 125 3.18. Operation over Multiple OMNI Links . . . . . . . . . . . 59 126 3.19. DNS Considerations . . . . . . . . . . . . . . . . . . . 60 127 3.20. Transition Considerations . . . . . . . . . . . . . . . . 60 128 3.21. Detecting and Reacting to Server and Bridge Failures . . 61 129 3.22. AERO Clients on the Open Internet . . . . . . . . . . . . 62 130 3.23. Time-Varying MNPs . . . . . . . . . . . . . . . . . . . . 64 131 4. Implementation Status . . . . . . . . . . . . . . . . . . . . 65 132 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 65 133 6. Security Considerations . . . . . . . . . . . . . . . . . . . 65 134 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 67 135 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 68 136 8.1. Normative References . . . . . . . . . . . . . . . . . . 68 137 8.2. Informative References . . . . . . . . . . . . . . . . . 70 138 Appendix A. Non-Normative Considerations . . . . . . . . . . . . 76 139 A.1. Implementation Strategies for Route Optimization . . . . 76 140 A.2. Implicit Mobility Management . . . . . . . . . . . . . . 76 141 A.3. Direct Underlying Interfaces . . . . . . . . . . . . . . 77 142 A.4. AERO Critical Infrastructure Considerations . . . . . . . 77 143 A.5. AERO Server Failure Implications . . . . . . . . . . . . 78 144 A.6. AERO Client / Server Architecture . . . . . . . . . . . . 79 145 Appendix B. Change Log . . . . . . . . . . . . . . . . . . . . . 81 146 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 82 148 1. Introduction 150 Asymmetric Extended Route Optimization (AERO) fulfills the 151 requirements of Distributed Mobility Management (DMM) [RFC7333] and 152 route optimization [RFC5522] for aeronautical networking and other 153 network mobility use cases such as intelligent transportation 154 systems. AERO is an internetworking and mobility management service 155 based on the Overlay Multilink Network Interface (OMNI) 156 [I-D.templin-6man-omni-interface] Non-Broadcast, Multiple Access 157 (NBMA) virtual link model. The OMNI link is a virtual overlay 158 configured over one or more underlying Internetworks, and nodes on 159 the link can exchange IP packets via tunneling. The OMNI Adaptation 160 Layer (OAL) supports multilink operation for increased reliability, 161 bandwidth optimization and traffic path selection while accommodating 162 Maximum Transmission Unit (MTU) diversity. 164 The AERO service comprises Clients, Proxys, Servers and Relays that 165 are seen as OMNI link neighbors as well as Bridges that interconnect 166 OMNI link segments. Each node's OMNI interface uses an IPv6 link- 167 local address format that supports operation of the IPv6 Neighbor 168 Discovery (ND) protocol [RFC4861] and links ND to IP forwarding. A 169 node's OMNI interface can be configured over multiple underlying 170 interfaces, and may therefore appear as a single interface with 171 multiple link-layer addresses. Each link-layer address is subject to 172 change due to mobility and/or QoS fluctuations, and link-layer 173 address changes are signaled by ND messaging the same as for any IPv6 174 link. 176 AERO provides a cloud-based service where mobile nodes may use any 177 Server acting as a Mobility Anchor Point (MAP) and fixed nodes may 178 use any Relay on the link for efficient communications. Fixed nodes 179 forward packets destined to other AERO nodes to the nearest Relay, 180 which forwards them through the cloud. A mobile node's initial 181 packets are forwarded through the Server, while direct routing is 182 supported through asymmetric extended route optimization while data 183 packets are flowing. Both unicast and multicast communications are 184 supported, and mobile nodes may efficiently move between locations 185 while maintaining continuous communications with correspondents and 186 without changing their IP Address. 188 AERO Bridges are interconnected in a secured private BGP overlay 189 routing instance using encapsulation to provide a hybrid routing/ 190 bridging service that joins the underlying Internetworks of multiple 191 disjoint administrative domains into a single unified OMNI link. 193 Each OMNI link instance is characterized by the set of Mobility 194 Service Prefixes (MSPs) common to all mobile nodes. The link extends 195 to the point where a Relay/Server is on the optimal route from any 196 correspondent node on the link, and provides a conduit between the 197 underlying Internetwork and the OMNI link. To the underlying 198 Internetwork, the Relay/Server is the source of a route to the MSP, 199 and hence uplink traffic to the mobile node is naturally routed to 200 the nearest Relay/Server. 202 AERO assumes the use of PIM Sparse Mode in support of multicast 203 communication. In support of Source Specific Multicast (SSM) when a 204 Mobile Node is the source, AERO route optimization ensures that a 205 shortest-path multicast tree is established with provisions for 206 mobility and multilink operation. In all other multicast scenarios 207 there are no AERO dependencies. 209 AERO was designed for aeronautical networking for both manned and 210 unmanned aircraft, where the aircraft is treated as a mobile node 211 that can connect an Internet of Things (IoT). AERO is also 212 applicable to a wide variety of other use cases. For example, it can 213 be used to coordinate the Virtual Private Network (VPN) links of 214 mobile nodes (e.g., cellphones, tablets, laptop computers, etc.) that 215 connect into a home enterprise network via public access networks 216 using services such as OpenVPN [OVPN]. It can also be used to 217 facilitate vehicular and pedestrian communications services for 218 intelligent transportation systems. Other applicable use cases are 219 also in scope. 221 The following numbered sections present the AERO specification. The 222 appendices at the end of the document are non-normative. 224 2. Terminology 226 The terminology in the normative references applies; especially, the 227 terminology in the OMNI specification 228 [I-D.templin-6man-omni-interface] is used extensively throughout. 229 The following terms are defined within the scope of this document: 231 IPv6 Neighbor Discovery (ND) 232 an IPv6 control message service for coordinating neighbor 233 relationships between nodes connected to a common link. AERO uses 234 the ND service specified in [RFC4861]. 236 IPv6 Prefix Delegation 237 a networking service for delegating IPv6 prefixes to nodes on the 238 link. The nominal service is DHCPv6 [RFC8415], however alternate 239 services (e.g., based on ND messaging) are also in scope. Most 240 notably, a minimal form of prefix delegation known as "prefix 241 registration" can be used if the Client knows its prefix in 242 advance and can represent it in the IPv6 source address of an ND 243 message. 245 Access Network (ANET) 246 a node's first-hop data link service network (e.g., a radio access 247 network, cellular service provider network, corporate enterprise 248 network, etc.) that often provides link-layer security services 249 such as IEEE 802.1X and physical-layer security prevent 250 unauthorized access internally and with border network-layer 251 security services such as firewalls and proxies that prevent 252 unauthorized outside access. 254 ANET interface 255 a node's attachment to a link in an ANET. 257 Internetwork (INET) 258 a connected IP network topology with a coherent routing and 259 addressing plan and that provides a transit backbone service for 260 ANET end systems. INETs also provide an underlay service over 261 which the AERO virtual link is configured. Example INETs include 262 corporate enterprise networks, aviation networks, and the public 263 Internet itself. When there is no administrative boundary between 264 an ANET and the INET, the ANET and INET are one and the same. 266 INET Partition 267 frequently, INETs such as large corporate enterprise networks are 268 sub-divided internally into separate isolated partitions. Each 269 partition is fully connected internally but disconnected from 270 other partitions, and there is no requirement that separate 271 partitions maintain consistent Internet Protocol and/or addressing 272 plans. (Each INET partition is seen as a separate OMNI link 273 segment as discussed below.) 275 INET interface 276 a node's attachment to a link in an INET. 278 INET address 279 an IP address assigned to a node's interface connection to an 280 INET. 282 INET encapsulation 283 the encapsulation of a packet in an outer header or headers that 284 can be routed within the scope of the local INET partition. 286 OMNI link 287 the same as defined in [I-D.templin-6man-omni-interface], and 288 manifested by IPv6 encapsulation [RFC2473]. The OMNI link spans 289 underlying INET segments joined by virtual bridges in a spanning 290 tree the same as a bridged campus LAN. AERO nodes on the OMNI 291 link appear as single-hop neighbors even though they may be 292 separated by multiple underlying INET hops, and can use Segment 293 Routing [RFC8402] to cause packets to visit selected waypoints on 294 the link. 296 OMNI domain 297 a set of affiliated OMNI links that collectively provide services 298 under a common (set of) Mobility Service Prefixes (MSPs). 300 OMNI Interface 301 a node's attachment to an OMNI link. Since the addresses assigned 302 to an OMNI interface are managed for uniqueness, OMNI interfaces 303 do not require Duplicate Address Detection (DAD) and therefore set 304 the administrative variable 'DupAddrDetectTransmits' to zero 305 [RFC4862]. 307 OMNI Adaptation Layer (OAL) 308 an OMNI interface process whereby packets admitted into the 309 interface are wrapped in a mid-layer IPv6 header and fragmented/ 310 reassembled if necessary to support the OMNI link Maximum 311 Transmission Unit (MTU). The OAL is also responsible for 312 generating MTU-related control messages as necessary, and for 313 providing addressing context for spanning multiple segments of a 314 bridged OMNI link. 316 OMNI Link-Local Address (LLA) 317 a link local IPv6 address per [RFC4291] constructed as specified 318 in Section 3.2.2. 320 OMNI Domain-Local Address (DLA) 321 an IPv6 address from the prefix [DLA]::/10 constructed as 322 specified in [I-D.templin-6man-omni-interface]. OMNI DLAs are 323 statelessly derived from OMNI LLAs, and vice-versa. 325 underlying interface 326 an ANET or INET interface over which an OMNI interface is 327 configured. 329 Mobility Service Prefix (MSP) 330 an IP prefix assigned to the OMNI link and from which more- 331 specific Mobile Network Prefixes (MNPs) are derived. 333 Mobile Network Prefix (MNP) 334 an IP prefix allocated from an MSP and delegated to an AERO Client 335 or Relay. 337 AERO node 338 a node that is connected to an OMNI link and participates in the 339 AERO internetworking and mobility service. 341 AERO Client ("Client") 342 an AERO node that connects over one or more underlying interfaces 343 and requests MNP delegation/registration service from AERO 344 Servers. The Client assigns a Client LLA to the OMNI interface 345 for use in ND exchanges with other AERO nodes and forwards packets 346 to correspondents according to OMNI interface neighbor cache 347 state. 349 AERO Server ("Server") 350 an INET node that configures an OMNI interface to provide default 351 forwarding and mobility/multilink services for AERO Clients. The 352 Server assigns an administratively-provisioned LLA to its OMNI 353 interface to support the operation of the ND services, and 354 advertises all of its associated MNPs via BGP peerings with 355 Bridges. 357 AERO Relay ("Relay") 358 an AERO Server that also provides forwarding services between 359 nodes reached via the OMNI link and correspondents on other links. 360 AERO Relays are provisioned with MNPs (i.e., the same as for an 361 AERO Client) and run a dynamic routing protocol to discover any 362 non-MNP IP routes. In both cases, the Relay advertises the MSP(s) 363 to its downstream networks, and distributes all of its associated 364 MNPs and non-MNP IP routes via BGP peerings with Bridges (i.e., 365 the same as for an AERO Server). 367 AERO Bridge ("Bridge") 368 a node that provides hybrid routing/bridging services (as well as 369 a security trust anchor) for nodes on an OMNI link. As a router, 370 the Bridge forwards packets using standard IP forwarding. As a 371 bridge, the Bridge forwards packets over the OMNI link without 372 decrementing the IPv6 Hop Limit. AERO Bridges peer with Servers 373 and other Bridges to discover the full set of MNPs for the link as 374 well as any non-MNPs that are reachable via Relays. 376 AERO Proxy ("Proxy") 377 a node that provides proxying services between Clients in an ANET 378 and Servers in external INETs. The AERO Proxy is a conduit 379 between the ANET and external INETs in the same manner as for 380 common web proxies, and behaves in a similar fashion as for ND 381 proxies [RFC4389]. A node may be configured to act as either a 382 Proxy and/or a Server, depending on Client Server selection 383 criteria. 385 ingress tunnel endpoint (ITE) 386 an OMNI interface endpoint that injects encapsulated packets into 387 an OMNI link. 389 egress tunnel endpoint (ETE) 390 an OMNI interface endpoint that receives encapsulated packets from 391 an OMNI link. 393 link-layer address 394 an IP address used as an encapsulation header source or 395 destination address from the perspective of the OMNI interface. 396 When an upper layer protocol (e.g., UDP) is used as part of the 397 encapsulation, the port number is also considered as part of the 398 link-layer address. 400 network layer address 401 the source or destination address of an encapsulated IP packet 402 presented to the OMNI interface. 404 end user network (EUN) 405 an internal virtual or external edge IP network that an AERO 406 Client or Relay connects to the rest of the network via the OMNI 407 interface. The Client/Relay sees each EUN as a "downstream" 408 network, and sees the OMNI interface as the point of attachment to 409 the "upstream" network. 411 Mobile Node (MN) 412 an AERO Client and all of its downstream-attached networks that 413 move together as a single unit, i.e., an end system that connects 414 an Internet of Things. 416 Mobile Router (MR) 417 a MN's on-board router that forwards packets between any 418 downstream-attached networks and the OMNI link. 420 Route Optimization Source (ROS) 421 the AERO node nearest the source that initiates route 422 optimization. The ROS may be a Server or Proxy acting on behalf 423 of the source Client. 425 Route Optimization responder (ROR) 426 the AERO node nearest the target destination that responds to 427 route optimization requests. The ROR may be a Server acting on 428 behalf of a target MNP Client, or a Relay for a non-MNP 429 destination. 431 MAP List 432 a geographically and/or topologically referenced list of addresses 433 of all Servers within the same OMNI link. There is a single MAP 434 list for the entire OMNI link. 436 Distributed Mobility Management (DMM) 437 a BGP-based overlay routing service coordinated by Servers and 438 Bridges that tracks all Server-to-Client associations. 440 Mobility Service (MS) 441 the collective set of all Servers, Proxys, Bridges and Relays that 442 provide the AERO Service to Clients. 444 Mobility Service Endpoint MSE) 445 an individual Server, Proxy, Bridge or Relay in the Mobility 446 Service. 448 Throughout the document, the simple terms "Client", "Server", 449 "Bridge", "Proxy" and "Relay" refer to "AERO Client", "AERO Server", 450 "AERO Bridge", "AERO Proxy" and "AERO Relay", respectively. 451 Capitalization is used to distinguish these terms from other common 452 Internetworking uses in which they appear without capitalization. 454 The terminology of DHCPv6 [RFC8415] and IPv6 ND [RFC4861] (including 455 the names of node variables, messages and protocol constants) is used 456 throughout this document. The terms "All-Routers multicast", "All- 457 Nodes multicast", "Solicited-Node multicast" and "Subnet-Router 458 anycast" are defined in [RFC4291]. Also, the term "IP" is used to 459 generically refer to either Internet Protocol version, i.e., IPv4 460 [RFC0791] or IPv6 [RFC8200]. 462 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 463 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 464 "OPTIONAL" in this document are to be interpreted as described in BCP 465 14 [RFC2119][RFC8174] when, and only when, they appear in all 466 capitals, as shown here. 468 3. Asymmetric Extended Route Optimization (AERO) 470 The following sections specify the operation of IP over OMNI links 471 using the AERO service: 473 3.1. AERO Node Types 475 AERO Clients are Mobile Nodes (MNs) that connect via underlying 476 interfaces with addresses that may change when the Client moves to a 477 new network connection point. AERO Clients register their Mobile 478 Network Prefixes (MNPs) with the AERO service, and distribute the 479 MNPs to nodes on EUNs. AERO Bridges, Servers, Proxys and Relays are 480 critical infrastructure elements in fixed (i.e., non-mobile) INET 481 deployments and hence have permanent and unchanging INET addresses. 482 Together, they constitute the AERO service which provides an OMNI 483 link virtual overlay for connecting AERO Clients. 485 AERO Bridges provide hybrid routing/bridging services (as well as a 486 security trust anchor) for nodes on an OMNI link. Bridges use 487 standard IPv6 routing to forward packets both within the same INET 488 partitions and between disjoint INET partitions based on a mid-layer 489 IPv6 encapsulation per [RFC2473]. The inner IP layer experiences a 490 virtual bridging service since the inner IP TTL/Hop Limit is not 491 decremented during forwarding. Each Bridge also peers with Servers 492 and other Bridges in a dynamic routing protocol instance to provide a 493 Distributed Mobility Management (DMM) service for the list of active 494 MNPs (see Section 3.2.3). Bridges present the OMNI link as a set of 495 one or more Mobility Service Prefixes (MSPs) and configure secured 496 tunnels with Servers, Relays, Proxys and other Bridges; they further 497 maintain IP forwarding table entries for each MNP and any other 498 reachable non-MNP prefixes. 500 AERO Servers provide default forwarding and mobility/multilink 501 services for AERO Client Mobile Nodes (MNs). Each Server also peers 502 with Bridges in a dynamic routing protocol instance to advertise its 503 list of associated MNPs (see Section 3.2.3). Servers facilitate 504 prefix delegation/registration exchanges with Clients, where each 505 delegated prefix becomes an MNP taken from an MSP. Servers forward 506 packets between OMNI interface neighbors and track each Client's 507 mobility profiles. Servers may further act as Servers for some sets 508 of Clients and as Proxies for others. 510 AERO Proxys provide a conduit for ANET Clients to associate with 511 Servers in external INETs. Client and Servers exchange control plane 512 messages via the Proxy acting as a bridge between the ANET/INET 513 boundary. The Proxy forwards data packets between Clients and the 514 OMNI link according to forwarding information in the neighbor cache. 515 The Proxy function is specified in Section 3.13. Proxys may further 516 act as Proxys for some sets of Clients and as Servers for others. 518 AERO Relays are Servers that provide forwarding services between the 519 OMNI interface and INET/EUN interfaces. Relays are provisioned with 520 MNPs the same as for an AERO Client, and also run a dynamic routing 521 protocol to discover any non-MNP IP routes. The Relay advertises the 522 MSP(s) to its connected networks, and distributes all of its 523 associated MNPs and non-MNP IP routes via BGP peerings with Bridges 525 3.2. The AERO Service over OMNI Links 527 3.2.1. AERO/OMNI Reference Model 529 Figure 1 presents the basic OMNI link reference model: 531 +----------------+ 532 | AERO Bridge B1 | 533 | Nbr: S1, S2, P1| 534 |(X1->S1; X2->S2)| 535 | MSP M1 | 536 +-+---------+--+-+ 537 +--------------+ | Secured | | +--------------+ 538 |AERO Server S1| | tunnels | | |AERO Server S2| 539 | Nbr: C1, B1 +-----+ | +-----+ Nbr: C2, B1 | 540 | default->B1 | | | default->B1 | 541 | X1->C1 | | | X2->C2 | 542 +-------+------+ | +------+-------+ 543 | OMNI link | | 544 X===+===+===================+==)===============+===+===X 545 | | | | 546 +-----+--------+ +--------+--+-----+ +--------+-----+ 547 |AERO Client C1| | AERO Proxy P1 | |AERO Client C2| 548 | Nbr: S1 | |(Proxy Nbr Cache)| | Nbr: S2 | 549 | default->S1 | +--------+--------+ | default->S2 | 550 | MNP X1 | | | MNP X2 | 551 +------+-------+ .--------+------. +-----+--------+ 552 | (- Proxyed Clients -) | 553 .-. `---------------' .-. 554 ,-( _)-. ,-( _)-. 555 .-(_ IP )-. +-------+ +-------+ .-(_ IP )-. 556 (__ EUN )--|Host H1| |Host H2|--(__ EUN ) 557 `-(______)-' +-------+ +-------+ `-(______)-' 559 Figure 1: AERO/OMNI Reference Model 561 In this model: 563 o the OMNI link is an overlay network service configured over one or 564 more underlying INET partitions which may be managed by different 565 administrative authorities and have incompatible protocols and/or 566 addressing plans. 568 o AERO Bridge B1 aggregates Mobility Service Prefix (MSP) M1, 569 discovers Mobile Network Prefixes (MNPs) X* and advertises the MSP 570 via BGP peerings over secured tunnels to Servers (S1, S2). 571 Bridges connect the disjoint segments of a partitioned OMNI link. 573 o AERO Servers/Relays S1 and S2 configure secured tunnels with 574 Bridge B1 and also provide mobility, multilink and default router 575 services for their associated Clients C1 and C2. 577 o AERO Clients C1 and C2 associate with Servers S1 and S2, 578 respectively. They receive Mobile Network Prefix (MNP) 579 delegations X1 and X2, and also act as default routers for their 580 associated physical or internal virtual EUNs. Simple hosts H1 and 581 H2 attach to the EUNs served by Clients C1 and C2, respectively. 583 o AERO Proxy P1 configures a secured tunnel with Bridge B1 and 584 provides proxy services for AERO Clients in secured enclaves that 585 cannot associate directly with other OMNI link neighbors. 587 An OMNI link configured over a single INET appears as a single 588 unified link with a consistent underlying network addressing plan. 589 In that case, all nodes on the link can exchange packets via simple 590 INET encapsulation, since the underlying INET is connected. In 591 common practice, however, an OMNI link may be partitioned into 592 multiple "segments", where each segment is a distinct INET 593 potentially managed under a different administrative authority (e.g., 594 as for worldwide aviation service providers such as ARINC, SITA, 595 Inmarsat, etc.). Individual INETs may also themselves be partitioned 596 internally, in which case each internal partition is seen as a 597 separate segment. 599 The addressing plan of each segment is consistent internally but will 600 often bear no relation to the addressing plans of other segments. 601 Each segment is also likely to be separated from others by network 602 security devices (e.g., firewalls, proxies, packet filtering 603 gateways, etc.), and in many cases disjoint segments may not even 604 have any common physical link connections. Therefore, nodes can only 605 be assured of exchanging packets directly with correspondents in the 606 same segment, and not with those in other segments. The only means 607 for joining the segments therefore is through inter-domain peerings 608 between AERO Bridges. 610 The same as for traditional campus LANs, multiple OMNI link segments 611 can be joined into a single unified link via a virtual bridging 612 service using the OMNI Adaptation Layer (OAL) which inserts a mid- 613 layer IPv6 encapsulation per [RFC2473] that supports inter-segment 614 forwarding (i.e., bridging) without decrementing the network-layer 615 TTL/Hop Limit. This bridging of OMNI link segments is shown in 616 Figure 2: 618 . . . . . . . . . . . . . . . . . . . . . . . 619 . . 620 . .-(::::::::) . 621 . .-(::::::::::::)-. +-+ . 622 . (:::: Segment A :::)--|B|---+ . 623 . `-(::::::::::::)-' +-+ | . 624 . `-(::::::)-' | . 625 . | . 626 . .-(::::::::) | . 627 . .-(::::::::::::)-. +-+ | . 628 . (:::: Segment B :::)--|B|---+ . 629 . `-(::::::::::::)-' +-+ | . 630 . `-(::::::)-' | . 631 . | . 632 . .-(::::::::) | . 633 . .-(::::::::::::)-. +-+ | . 634 . (:::: Segment C :::)--|B|---+ . 635 . `-(::::::::::::)-' +-+ | . 636 . `-(::::::)-' | . 637 . | . 638 . ..(etc).. x . 639 . . 640 . . 641 . <- OMNI link Bridged by encapsulation -> . 642 . . . . . . . . . . . . . .. . . . . . . . . 644 Figure 2: Bridging OMNI Link Segments 646 Bridges, Servers, Relays and Proxys connect via secured INET tunnels 647 over their respective segments in a spanning tree topology rooted at 648 the Bridges. The secured spanning tree supports strong 649 authentication for IPv6 ND control messages and may also be used to 650 convey the initial data packets in a flow. Route optimization can 651 then be employed to cause data packets to take more direct paths 652 between OMNI link neighbors without having to strictly follow the 653 spanning tree. 655 3.2.2. Link-Local Addresses (LLAs) and Domain Local Addresses (DLAs) 657 AERO nodes on OMNI links use the Link-Local Address (LLA) prefix 658 fe80::/64 [RFC4291] to assign LLAs used for network-layer addresses 659 in IPv6 ND and data messages. They also use the Domain Local Address 660 (DLA) prefix [DLA]::/48 to form per-link DLA sub-prefixes of the form 661 [DLA*]::/64, where '*' is a 16-bit OMNI link identifier. Each per- 662 link DLA sub-prefix is in turn used to form DLAs used for OAL header 663 source and destination addresses. See 664 [I-D.templin-6man-omni-interface] for a full specification of the 665 LLAs and DLAs used by AERO nodes on OMNI links. 667 IPv6 routers are not permitted to forward packets with LLA addresses. 668 Therefore, IPv6 packets with LLA addresses must be encapsulated in 669 IPv6 headers with DLA addresses in order to traverse the OMNI link. 670 DLA addresses therefore must be routable within the OMNI link domain- 671 local area. 673 For routing system organization (see Section 3.2.3), DLAs are 674 organized in partition prefixes, e.g., [DLA]::1000/116. For each 675 such partition prefix, the Bridge(s) that connect that segment assign 676 the all-zero's address of the prefix as a Subnet Router Anycast 677 address. For example, the Subnet Router Anycast address for 678 [DLA*]::1000/116 is simply [DLA*]::1000. 680 3.2.3. AERO Routing System 682 The AERO routing system comprises a private instance of the Border 683 Gateway Protocol (BGP) [RFC4271] that is coordinated between Bridges 684 and Servers and does not interact with either the public Internet BGP 685 routing system or any underlying INET routing systems. 687 In a reference deployment, each Server is configured as an Autonomous 688 System Border Router (ASBR) for a stub Autonomous System (AS) using 689 an AS Number (ASN) that is unique within the BGP instance, and each 690 Server further uses eBGP to peer with one or more Bridges but does 691 not peer with other Servers. Each INET of a multi-segment OMNI link 692 must include one or more Bridges, which peer with the Servers and 693 Proxys within that INET. All Bridges within the same INET are 694 members of the same hub AS using a common ASN, and use iBGP to 695 maintain a consistent view of all active MNPs currently in service. 696 The Bridges of different INETs peer with one another using eBGP. 698 Bridges advertise the OMNI link's MSPs and any non-MNP routes to each 699 of their Servers. This means that any aggregated non-MNPs (including 700 "default") are advertised to all Servers. Each Bridge configures a 701 black-hole route for each of its MSPs. By black-holing the MSPs, the 702 Bridge will maintain forwarding table entries only for the MNPs that 703 are currently active, and packets destined to all other MNPs will 704 correctly incur Destination Unreachable messages due to the black- 705 hole route. In this way, Servers have only partial topology 706 knowledge (i.e., they know only about the MNPs of their directly 707 associated Clients) and they forward all other packets to Bridges 708 which have full topology knowledge. 710 Each OMNI link segment assigns a unique sub-prefix of [DLA*]::/96 711 known as the DLA partition prefix. For example, a first segment 712 could assign [DLA*]::1000/116, a second could assign 713 [DLA*]::2000/116, a third could assign [DLA*]::3000/116, etc. The 714 administrative authorities for each segment must therefore coordinate 715 to assure mutually-exclusive partition prefix assignments, but 716 internal provisioning of each prefix is an independent local 717 consideration for each administrative authority. 719 DLA partition prefixes are statically represented in Bridge 720 forwarding tables. Bridges join multiple segments into a unified 721 OMNI link over multiple diverse administrative domains. They support 722 a bridging function by first establishing forwarding table entries 723 for their partition prefixes either via standard BGP routing or 724 static routes. For example, if three Bridges ('A', 'B' and 'C') from 725 different segments serviced [DLA*]::1000/116, [DLA*]::2000/116 and 726 [DLA*]::3000/116 respectively, then the forwarding tables in each 727 Bridge are as follows: 729 A: [DLA*]::1000/116->local, [DLA*]::2000/116->B, [DLA*]::3000/116->C 731 B: [DLA*]::1000/116->A, [DLA*]::2000/116->local, [DLA*]::3000/116->C 733 C: [DLA*]::1000/116->A, [DLA*]::2000/116->B, [DLA*]::3000/116->local 735 These forwarding table entries are permanent and never change, since 736 they correspond to fixed infrastructure elements in their respective 737 segments. 739 DLA Client prefixes are instead dynamically advertised in the AERO 740 routing system by Servers and Relays that provide service for their 741 corresponding MNPs. For example, if three Servers ('D', 'E' and 'F') 742 service the MNPs 2001:db8:1000:2000::/56, 2001:db8:3000:4000::/56 and 743 2001:db8:5000:6000::/56 then the routing system would include: 745 D: [DLA*]:2001:db8:1000:2000/120 747 E: [DLA*]:2001:db8:3000:4000/120 749 F: [DLA*]:2001:db8:5000:6000/120 751 A full discussion of the BGP-based routing system used by AERO is 752 found in [I-D.ietf-rtgwg-atn-bgp]. 754 3.2.4. OMNI Link Encapsulation 756 With the Client and partition prefixes in place in Bridge forwarding 757 tables, the OMNI interface sends control and data packets toward AERO 758 destination nodes located in different OMNI link segments over the 759 spanning tree via mid-layer encapsulation using the OMNI Adaptation 760 Layer (OAL) header based on Generic Packet Tunneling in IPv6 761 [RFC2473]. When necessary, the OMNI interface also includes an OMNI 762 Routing Header (ORH) as an extension to the OAL header if final 763 segment forwarding information is available, e.g., in the neighbor 764 cache. The ORH is formatted as shown in Figure 3: 766 0 1 2 3 767 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 1 768 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 769 | Next Header | Hdr Ext Len | Routing Type | SRT | FMT | 770 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 771 | Last Hop Segment-id (LHS) | 772 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 773 ~ Link Layer Address (L2ADDR) ~ 774 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 775 ~ Destination Suffix (if necessary) ~ 776 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 777 ~ Null Padding (if necessary) ~ 778 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 780 Figure 3: OMNI Routing Header (ORH) Format 782 In this format: 784 o Next Header identifies the type of header immediately following 785 the ORH. 787 o Hdr Ext Len is the length of the Routing header in 8-octet units 788 (not including the first 8 octets), with trailing padding added if 789 necessary to produce an integral number of 8-octet units. 791 o Routing Type is set to TBD (see IANA Considerations). 793 o Segments Left is omitted, and replaced by a 5-bit SRT and 3-bit 794 FMT field. 796 o SRT - a 5-bit Segment Routing Topology prefix length value that 797 (when added to 96) determines the prefix length to apply to the 798 DLA formed from concatenating [DLA*]::/96 with the 32 bit LHS MSID 799 value that follows. For example, the value 16 corresponds to the 800 prefix length 112. 802 o FMT - a 3-bit "Framework/Mode/Type" code corresponding to the 803 included Link Layer Address as follows: 805 * When the most significant bit (i.e., "Framework") is set to 0, 806 L2ADDR is the INET encapsulation address of the Server/Proxy 807 named in the LHS; otherwise, it is the address for the target 808 Client, and the Destination Suffix is included. 810 * When the next most significant bit (i.e., "Mode") is set to 0, 811 the Source/Target L2ADDR is on the open INET; otherwise, it is 812 (likely) located behind a Network Address Translator (NAT). 814 * When the least significant bit (i.e., "Type") is set to 0, 815 L2ADDR includes a UDP Port Number followed by an IPv4 address; 816 otherwise, it includes a UDP Port Number followed by an IPv6 817 address. 819 o LHS - the 32 bit MSID of a service node in the Last Hop Segment on 820 the path to the target. When SRT and LHS are both set to 0, the 821 LHS is considered unspecified. When SRT is set to 0 and LHS is 822 non-zero, the prefix length is set to 128. SRT and LHS provide 823 guidance to the OMNI interface forwarding algorithm. 824 Specifically, if SRT/LHS is located in the local OMNI link segment 825 then the OMNI interface can omit OAL/ORH encapsualtion and send 826 directly to the target using INET encapsulation according to FMT/ 827 L2ADDR; else, it must perform INET/OAL/ORH encapsulation and 828 forward according to the OMNI link spanning tree. 830 o Link Layer Address (L2ADDR) - Formatted according to FMT, and 831 identifies the link-layer address (i.e., the encapsulation 832 address) of the source/target. The UDP Port Number appears in the 833 first two octets and the IP address appears in the next 4 octets 834 for IPv4 or 16 octets for IPv6. The Port Number and IP address 835 are recorded in ones-compliment "obfuscated" form per [RFC4380]. 836 The OMNI interface forwarding algorithm uses FMT/L2ADDR to 837 determine the INET encapsulation address for local forwarding when 838 SRT/LHS is located in the same OMNI link segment. 840 o Destination Suffix is a 64-bit field included only for OAL- 841 encapsulated packets that are destined directly to the DLA of the 842 Client (i.e., according to the FMT code). When present, 843 Destination Suffix encodes the 64-bit DLA suffix for the Client 844 that will receive packet. For example, if the Client DLA is 845 [DLA*]:2001:db8:1:2 then the Destination suffix encodes the value 846 2001:db8:1:2. 848 o Null Padding contains zero-valued octets as necessary to pad the 849 ORH to an integral number of 8-octet units. 851 When an AERO node uses OAL encapsulation for a packet with addresses 852 such as 2001:db8:1:2::1 and 2001:db8:1234:5678::1, it sets the OAL 853 header source address to its own DLA address (e.g., 854 [DLA*]::1000:2000). The node also sets the destination address to 855 the DLA of the Client (e.g., [DLA*]::2001:db8:1234:5678) when the 856 Client is addressed directly; otherwise, it sets the destination 857 address to the DLA of the Client's Proxy/Server (e.g., 859 [DLA*]::4321:9876). If the neighbor cache includes Last Hop Segment 860 information for the target destination, the node next inserts an ORH 861 immediately following the OAL header while including the correct SRT, 862 FMT, LHS, L2ADDR and (if necessary) Destination Suffix information. 863 Next, the node overwrites the OAL header destination address with the 864 LHS Subnet Router Anycast address (for example, for LHS 1000:2000 865 with SRT 16, the Subnet Router Anycast address is [DLA*]::1000:0000). 867 The node then fragments the OAL/ORH packet if necessary, with each 868 resulting fragment including the OAL/ORH headers while only the first 869 fragment includes the original IPv6 header. The node finally 870 encapsulates each resulting OAL/ORH packet/fragment in an INET header 871 with source address set to its own INET address (e.g., 192.0.2.100) 872 and destination set to the INET address of a Bridge (e.g., 873 192.0.2.1). 875 The encapsulation format in the above example is shown in Figure 4: 877 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 878 | INET Header | 879 | src = 192.0.2.100 | 880 | dst = 192.0.2.1 | 881 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 882 | OAL Header | 883 | src = [DLA*]::1000:2000 | 884 | dst= DLA for inner IP dst | 885 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 886 | ORH Header | 887 | (if necessary) | 888 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 889 | Inner IP Header | 890 | src = 2001:db8:1:2::1 | 891 | dst = 2001:db8:1234:5678::1 | 892 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 893 | | 894 ~ ~ 895 ~ Inner Packet Body ~ 896 ~ ~ 897 | | 898 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 900 Figure 4: OAL/ORH Encapsulation 902 In this format, the inner IP header and packet body are the original 903 IP packet, the OAL header is an IPv6 header prepared according to 904 [RFC2473], the ORH is a Routing Header extension of the OAL header, 905 and the INET header is prepared as discussed in Section 3.6. 907 This gives rise to a routing system that contains both Client prefix 908 routes that may change dynamically due to regional node mobility and 909 partition prefix routes that rarely if ever change. The Bridges can 910 therefore provide link-layer bridging by sending packets over the 911 spanning tree instead of network-layer routing according to MNP 912 routes. As a result, opportunities for packet loss due to node 913 mobility between different segments are mitigated. 915 In normal operations, IPv6 ND messages are conveyed over secured 916 paths between OMNI link neighbors so that specific Proxys, Servers or 917 Relays can be addressed without being subject to mobility events. 918 Conversely, only the first few packets destined to Clients need to 919 traverse secured paths until route optimization can determine a more 920 direct path. 922 Note: An IPv6 "minimal encapsulation" format (i.e., an IPv6 variant 923 of [RFC2004]) based on extensions to the ORH was considered, analyzed 924 and rejected. In the approach, the ORH would be inserted as an 925 extension header to the original IPv6 packet header. The IPv6 926 destination address would then be written into the ORH, and the DLA 927 corresponding to the destination would be overwritten in the IPv6 928 destination address. This would seemingly convey enough forwarding 929 information so that OAL encapsulation could be avoided. However, 930 this "minimal encapsulation" IPv6 packet would then have a non-DLA 931 source address and DLA destination address, an incorrect value in 932 upper layer protocol checksums, and a Hop Limit that is decremented 933 within the spanning tree when it should not be. The insertion and 934 removal of the ORH would also entail rewriting the Payload Length and 935 Next Header fields - again, invalidating upper layer checksums. 936 These irregularities would result in implementation challenges and 937 the potential for operational issues, e.g., since actionable ICMPv6 938 error reports could not be delivered to the original source. In 939 order to address the issues, still more information such as the 940 original IPv6 source address could be written into the ORH. However, 941 with the additional information the benefit of the "minimal 942 encapsulation" savings quickly diminishes, and becomes overshadowed 943 by the implementation and operational irregularities. 945 3.2.5. Segment Routing Topologies (SRTs) 947 The 64-bit sub-prefixes of [DLA]::/48 identify up to 2^16 distinct 948 Segment Routing Topologies (SRTs). Each SRT is a mutually-exclusive 949 OMNI link overlay instance using a distinct set of DLAs, and emulates 950 a Virtual LAN (VLAN) service for the OMNI link. In some cases (e.g., 951 when redundant topologies are needed for fault tolerance and 952 reliability) it may be beneficial to deploy multiple SRTs that act as 953 independent overlay instances. A communication failure in one 954 instance therefore will not affect communications in other instances. 956 Each SRT is identified by a distinct value in bits 48-63 of 957 [DLA]::/48, i.e., as [DLA0]::/64, [DLA1]::/64, [DLA2]::/64, etc. 958 This document asserts that up to four SRTs provide a level of safety 959 sufficient for critical communications such as civil aviation. Each 960 SRT is designated with a color that identifies a different OMNI link 961 instance as follows: 963 o Red - corresponds to [DLA0]::/64 965 o Green - corresponds to [DLA1]::/64 967 o Blue-1 - corresponds to [DLA2]::/64 969 o Blue-2 - corresponds to [DLA3]::/64 971 o the remaining [DLA*]::/64 sub prefixes are available for 972 additional SRTs. 974 Each OMNI interface is identified by a unique interface name (e.g., 975 omni0, omni1, omni2, etc.) and assigns an anycast DLA corresponding 976 to its SRT prefix. For example, the anycast DLA for the Green SRT is 977 simply [DLA1]::. The anycast DLA is used for OMNI interface 978 determination in Safety-Based Multilink (SBM) as discussed in 979 [I-D.templin-6man-omni-interface]. Each OMNI interface further 980 applies Performance-Based Multilink (PBM) internally. 982 3.2.6. Segment Routing For OMNI Link Selection 984 An original IPv6 source can direct an IPv6 packet to an AERO node by 985 including a standard IPv6 Segment Routing Header (SRH) [RFC8754] with 986 the anycast DLA for the selected SRT as either the IPv6 destination 987 or as an intermediate hop within the SRH. This allows the original 988 source to determine the specific OMNI link topology a packet will 989 traverse when there may be multiple alternatives. 991 When the AERO node processes the SRH and forwards the packet to the 992 correct OMNI interface, the OMNI interface writes the next IPv6 993 address from the SRH into the IPv6 destination address and decrements 994 Segments Left. If decrementing would cause Segments Left to become 995 0, the OMNI interface deletes the SRH before forwarding. This form 996 of Segment Routing supports Safety-Based Multilink (SBM). 998 3.2.7. Segment Routing Within the OMNI Link 1000 AERO node OMNI interfaces can insert OAL/ORH headers for Segment 1001 Routing within the OMNI link to influence the paths of packets 1002 destined to targets in remote segments without requiring all packets 1003 to traverse strict spanning tree paths. 1005 When an AERO node's OMNI interface has a packet to send to a target 1006 discovered through route optimization located in the same OMNI link 1007 segment, it encapsulates the packet in OAL/ORH headers if necessary 1008 as discussed above. The node then uses the target's Link Layer 1009 Address (L2ADDR) information for INET encapsulation. 1011 When an AERO node's OMNI interface has a packet to send to a route 1012 optimization target located in a remote OMNI link segment, it 1013 encapsulates the packet in OAL/ORH headers as discussed above while 1014 forwarding the packet to a Bridge with destination set to the Subnet 1015 Router Anycast address for the final OMNI link segment. 1017 When a Bridge receives a packet destined to its Subnet Router Anycast 1018 address with an OAL/ORH with SRT/LHS values corresponding to the 1019 local segment, it examines the L2ADDR according to FMT and removes 1020 the ORH from the packet. If the ORH includes a saved Destination 1021 Suffix, the Bridge then writes the corresponding DLA into the OAL 1022 destination address; otherwise, it writes the DLA corresponding to 1023 the SRT/LHS fields into the destination. The Bridge then 1024 encapsulates the packet in an INET header according to L2ADDR and 1025 forwards the packet within the INET either to the LHS Server/Proxy or 1026 directly to the destination itself. In this way, the Bridge 1027 participates in route optimization to reduce traffic load and 1028 suboptimal routing through strict spanning tree paths. 1030 3.3. OMNI Interface Characteristics 1032 OMNI interfaces are virtual interfaces configured over one or more 1033 underlying interfaces classified as follows: 1035 o INET interfaces connect to an INET either natively or through one 1036 or several IPv4 Network Address Translators (NATs). Native INET 1037 interfaces have global IP addresses that are reachable from any 1038 INET correspondent. All Server, Relay and Bridge interfaces are 1039 native interfaces, as are INET-facing interfaces of Proxys. NATed 1040 INET interfaces connect to a private network behind one or more 1041 NATs that provide INET access. Clients that are behind a NAT are 1042 required to send periodic keepalive messages to keep NAT state 1043 alive when there are no data packets flowing. 1045 o ANET interfaces connect to an ANET that is separated from the open 1046 INET by a Proxy. Proxys can actively issue control messages over 1047 the INET on behalf of the Client to reduce ANET congestion. 1049 o VPNed interfaces use security encapsulation over the INET to a 1050 Virtual Private Network (VPN) server that also acts as a Server or 1051 Proxy. Other than the link-layer encapsulation format, VPNed 1052 interfaces behave the same as Direct interfaces. 1054 o Direct interfaces connect a Client directly to a Server or Proxy 1055 without crossing any ANET/INET paths. An example is a line-of- 1056 sight link between a remote pilot and an unmanned aircraft. The 1057 same Client considerations apply as for VPNed interfaces. 1059 OMNI interfaces use OAL/ORH encapsulation as necessary as discussed 1060 in Section 3.2.4. OMNI interfaces use link-layer encapsulation (see: 1061 Section 3.6) to exchange packets with OMNI link neighbors over INET 1062 or VPNed interfaces as well as over ANET interfaces for which the 1063 Client and Proxy may be multiple IP hops away. OMNI interfaces do 1064 not use link-layer encapsulation over Direct underlying interfaces or 1065 ANET interfaces when the Client and Proxy are known to be on the same 1066 underlying link. 1068 OMNI interfaces maintain a neighbor cache for tracking per-neighbor 1069 state the same as for any interface. OMNI interfaces use ND messages 1070 including Router Solicitation (RS), Router Advertisement (RA), 1071 Neighbor Solicitation (NS) and Neighbor Advertisement (NA) for 1072 neighbor cache management. 1074 OMNI interfaces send ND messages with an OMNI option formatted as 1075 specified in [I-D.templin-6man-omni-interface]. The OMNI option 1076 includes prefix registration information and Interface Attributes 1077 containing link information parameters for the OMNI interface's 1078 underlying interfaces. Each OMNI option may include multiple 1079 Interface Attributes sub-options, each identified by an ifIndex 1080 value. 1082 A Client's OMNI interface may be configured over multiple underlying 1083 interface connections. For example, common mobile handheld devices 1084 have both wireless local area network ("WLAN") and cellular wireless 1085 links. These links are often used "one at a time" with low-cost WLAN 1086 preferred and highly-available cellular wireless as a standby, but a 1087 simultaneous-use capability could provide benefits. In a more 1088 complex example, aircraft frequently have many wireless data link 1089 types (e.g. satellite-based, cellular, terrestrial, air-to-air 1090 directional, etc.) with diverse performance and cost properties. 1092 If a Client's multiple underlying interfaces are used "one at a time" 1093 (i.e., all other interfaces are in standby mode while one interface 1094 is active), then ND message OMNI options include only a single 1095 Interface Attributes sub-option set to constant values. In that 1096 case, the Client would appear to have a single interface but with a 1097 dynamically changing link-layer address. 1099 If the Client has multiple active underlying interfaces, then from 1100 the perspective of ND it would appear to have multiple link-layer 1101 addresses. In that case, ND message OMNI options MAY include 1102 multiple Interface Attributes sub-options - each with values that 1103 correspond to a specific interface. Every ND message need not 1104 include Interface Attributes for all underlying interfaces; for any 1105 attributes not included, the neighbor considers the status as 1106 unchanged. 1108 Bridge, Server and Proxy OMNI interfaces may be configured over one 1109 or more secured tunnel interfaces. The OMNI interface configures 1110 both an LLA and its corresponding DLA, while the underlying secured 1111 tunnel interfaces are either unnumbered or configure the same DLA. 1112 The OMNI interface encapsulates each IP packet in OAL/ORH headers and 1113 presents the packet to the underlying secured tunnel interface. 1114 Routing protocols such as BGP that run over the OMNI interface do not 1115 employ OAL/ORH encapsulation, but rather present the routing protocol 1116 messages directly to the underlying secured tunnels while using the 1117 DLA as the source address. This distinction must be honored 1118 consistently according to each node's configuration so that the IP 1119 forwarding table will associate discovered IP routes with the correct 1120 interface. 1122 3.4. OMNI Interface Initialization 1124 AERO Servers, Proxys and Clients configure OMNI interfaces as their 1125 point of attachment to the OMNI link. AERO nodes assign the MSPs for 1126 the link to their OMNI interfaces (i.e., as a "route-to-interface") 1127 to ensure that packets with destination addresses covered by an MNP 1128 not explicitly assigned to a non-OMNI interface are directed to the 1129 OMNI interface. 1131 OMNI interface initialization procedures for Servers, Proxys, Clients 1132 and Bridges are discussed in the following sections. 1134 3.4.1. AERO Server/Relay Behavior 1136 When a Server enables an OMNI interface, it assigns an LLA/DLA 1137 appropriate for the given OMNI link segment. The Server also 1138 configures secured tunnels with one or more neighboring Bridges and 1139 engages in a BGP routing protocol session with each Bridge. 1141 The OMNI interface provides a single interface abstraction to the IP 1142 layer, but internally comprises multiple secured tunnels as well as 1143 an NBMA nexus for sending encapsulated data packets to OMNI interface 1144 neighbors. The Server further configures a service to facilitate ND 1145 exchanges with AERO Clients and manages per-Client neighbor cache 1146 entries and IP forwarding table entries based on control message 1147 exchanges. 1149 Relays are simply Servers that run a dynamic routing protocol to 1150 redistribute routes between the OMNI interface and INET/EUN 1151 interfaces (see: Section 3.2.3). The Relay provisions MNPs to 1152 networks on the INET/EUN interfaces (i.e., the same as a Client would 1153 do) and advertises the MSP(s) for the OMNI link over the INET/EUN 1154 interfaces. The Relay further provides an attachment point of the 1155 OMNI link to a non-MNP-based global topology. 1157 3.4.2. AERO Proxy Behavior 1159 When a Proxy enables an OMNI interface, it assigns an LLA/DLA and 1160 configures permanent neighbor cache entries the same as for Servers. 1161 The Proxy also configures secured tunnels with one or more 1162 neighboring Bridges and maintains per-Client neighbor cache entries 1163 based on control message exchanges. Importantly Proxys are often 1164 configured to act as Servers, and vice-versa. 1166 3.4.3. AERO Client Behavior 1168 When a Client enables an OMNI interface, it sends RS messages with ND 1169 parameters over its underlying interfaces to a Server, which returns 1170 an RA message with corresponding parameters. (The RS/RA messages may 1171 pass through a Proxy in the case of a Client's ANET interface, or 1172 through one or more NATs in the case of a Client's INET interface.) 1174 3.4.4. AERO Bridge Behavior 1176 AERO Bridges configure an OMNI interface and assign the DLA Subnet 1177 Router Anycast address for each OMNI link segment they connect to. 1178 Bridges configure secured tunnels with Servers, Proxys and other 1179 Bridges; they also configure LLAs/DLAs and permanent neighbor cache 1180 entries the same as Servers. Bridges engage in a BGP routing 1181 protocol session with a subset of the Servers and other Bridges on 1182 the spanning tree (see: Section 3.2.3). 1184 3.5. OMNI Interface Neighbor Cache Maintenance 1186 Each OMNI interface maintains a conceptual neighbor cache that 1187 includes an entry for each neighbor it communicates with on the OMNI 1188 link per [RFC4861]. OMNI interface neighbor cache entries are said 1189 to be one of "permanent", "symmetric", "asymmetric" or "proxy". 1191 Permanent neighbor cache entries are created through explicit 1192 administrative action; they have no timeout values and remain in 1193 place until explicitly deleted. AERO Bridges maintain permanent 1194 neighbor cache entries for their associated Proxys/Servers (and vice- 1195 versa). Each entry maintains the mapping between the neighbor's 1196 network-layer LLA and corresponding INET address. 1198 Symmetric neighbor cache entries are created and maintained through 1199 RS/RA exchanges as specified in Section 3.12, and remain in place for 1200 durations bounded by prefix lifetimes. AERO Servers maintain 1201 symmetric neighbor cache entries for each of their associated 1202 Clients, and AERO Clients maintain symmetric neighbor cache entries 1203 for each of their associated Servers. 1205 Asymmetric neighbor cache entries are created or updated based on 1206 route optimization messaging as specified in Section 3.14, and are 1207 garbage-collected when keepalive timers expire. AERO ROSs maintain 1208 asymmetric neighbor cache entries for active targets with lifetimes 1209 based on ND messaging constants. Asymmetric neighbor cache entries 1210 are unidirectional since only the ROS (and not the ROR) creates an 1211 entry. 1213 Proxy neighbor cache entries are created and maintained by AERO 1214 Proxys when they process Client/Server ND exchanges, and remain in 1215 place for durations bounded by ND and prefix lifetimes. AERO Proxys 1216 maintain proxy neighbor cache entries for each of their associated 1217 Clients. Proxy neighbor cache entries track the Client state and the 1218 address of the Client's associated Server(s). 1220 To the list of neighbor cache entry states in Section 7.3.2 of 1221 [RFC4861], Proxy and Server OMNI interfaces add an additional state 1222 DEPARTED that applies to symmetric and proxy neighbor cache entries 1223 for Clients that have recently departed. The interface sets a 1224 "DepartTime" variable for the neighbor cache entry to "DEPART_TIME" 1225 seconds. DepartTime is decremented unless a new ND message causes 1226 the state to return to REACHABLE. While a neighbor cache entry is in 1227 the DEPARTED state, packets destined to the target Client are 1228 forwarded to the Client's new location instead of being dropped. 1229 When DepartTime decrements to 0, the neighbor cache entry is deleted. 1230 It is RECOMMENDED that DEPART_TIME be set to the default constant 1231 value REACHABLE_TIME plus 10 seconds (40 seconds by default) to allow 1232 a window for packets in flight to be delivered while stale route 1233 optimization state may be present. 1235 When an ROR receives an authentic NS message used for route 1236 optimization, it searches for a symmetric neighbor cache entry for 1237 the target Client. The ROR then returns a solicited NA message 1238 without creating a neighbor cache entry for the ROS, but creates or 1239 updates a target Client "Report List" entry for the ROS and sets a 1240 "ReportTime" variable for the entry to REPORT_TIME seconds. The ROR 1241 resets ReportTime when it receives a new authentic NS message, and 1242 otherwise decrements ReportTime while no authentic NS messages have 1243 been received. It is RECOMMENDED that REPORT_TIME be set to the 1244 default constant value REACHABLE_TIME plus 10 seconds (40 seconds by 1245 default) to allow a window for route optimization to converge before 1246 ReportTime decrements below REACHABLE_TIME. 1248 When the ROS receives a solicited NA message response to its NS 1249 message used for route optimization, it creates or updates an 1250 asymmetric neighbor cache entry for the target network-layer and 1251 link-layer addresses. The ROS then (re)sets ReachableTime for the 1252 neighbor cache entry to REACHABLE_TIME seconds and uses this value to 1253 determine whether packets can be forwarded directly to the target, 1254 i.e., instead of via a default route. The ROS otherwise decrements 1255 ReachableTime while no further solicited NA messages arrive. It is 1256 RECOMMENDED that REACHABLE_TIME be set to the default constant value 1257 30 seconds as specified in [RFC4861]. 1259 AERO nodes also use the value MAX_UNICAST_SOLICIT to limit the number 1260 of NS keepalives sent when a correspondent may have gone unreachable, 1261 the value MAX_RTR_SOLICITATIONS to limit the number of RS messages 1262 sent without receiving an RA and the value MAX_NEIGHBOR_ADVERTISEMENT 1263 to limit the number of unsolicited NAs that can be sent based on a 1264 single event. It is RECOMMENDED that MAX_UNICAST_SOLICIT, 1265 MAX_RTR_SOLICITATIONS and MAX_NEIGHBOR_ADVERTISEMENT be set to 3 the 1266 same as specified in [RFC4861]. 1268 Different values for DEPART_TIME, REPORT_TIME, REACHABLE_TIME, 1269 MAX_UNICAST_SOLICIT, MAX_RTR_SOLCITATIONS and 1270 MAX_NEIGHBOR_ADVERTISEMENT MAY be administratively set; however, if 1271 different values are chosen, all nodes on the link MUST consistently 1272 configure the same values. Most importantly, DEPART_TIME and 1273 REPORT_TIME SHOULD be set to a value that is sufficiently longer than 1274 REACHABLE_TIME to avoid packet loss due to stale route optimization 1275 state. 1277 3.5.1. OMNI Neighbor Interface Attributes 1279 OMNI interface IPv6 ND messages include OMNI options 1280 [I-D.templin-6man-omni-interface] with Interface Attributes that 1281 provide Link-Layer Address and QoS Preference information for the 1282 neighbor's underlying interfaces. This information is stored in the 1283 neighbor cache and provides the basis for the forwarding algorithm 1284 specified in Section 3.10. The information is cumulative and 1285 reflects the union of the OMNI information from the most recent ND 1286 messages received from the neighbor; it is therefore not required 1287 that each ND message contain all neighbor information. 1289 The OMNI option Interface Attributes for each underlying interface 1290 includes a two-part "Link-Layer Address" consisting of a simple IP 1291 encapsulation address determined by the FMT and L2ADDR fields and an 1292 OAL DLA determined by the SRT and LHS fields. If the neighbor is 1293 located in the local OMNI link segment (and, if any necessary NAT 1294 state has been established) forwarding via simple IP encapsulation 1295 can be used; otherwise, OAL encapsulation must be used. Underlying 1296 interfaces are further selected based on their associated preference 1297 values "high", "medium", "low" or "disabled". 1299 Note: the OMNI option is distinct from any Source/Target Link-Layer 1300 Address Options (S/TLLAOs) that may appear in an ND message according 1301 to the appropriate IPv6 over specific link layer specification (e.g., 1302 [RFC2464]). If both an OMNI option and S/TLLAO appear, the former 1303 pertains to encapsulation addresses while the latter pertains to the 1304 native L2 address format of the underlying media. 1306 3.5.2. OMNI Neighbor Advertisement Message Flags 1308 As discussed in Section 4.4 of [RFC4861] NA messages include three 1309 flag bits R, S and O. OMNI interface NA messages treat the flags as 1310 follows: 1312 o R: The R ("Router") flag is set to 1 in the NA messages sent by 1313 all AERO/OMNI node types. Simple hosts that would set R to 0 do 1314 not occur on the OMNI link itself, but may occur on the downstream 1315 links of Clients and Relays. 1317 o S: The S ("Solicited") flag is set exactly as specified in 1318 Section 4.4. of [RFC4861], i.e., it is set to 1 for Solicited NAs 1319 and set to 0 for Unsolicited NAs (both unicast and multicast). 1321 o O: The O ("Override") flag is set to 0 for solicited proxy NAs and 1322 set to 1 for all other solicited and unsolicited NAs. For further 1323 study is whether solicited NAs for anycast targets apply for OMNI 1324 links. Since OMNI LLAs must be uniquely assigned to Clients to 1325 support correct ND protocol operation, however, no role is 1326 currently seen for assigning the same OMNI LLA to multiple 1327 Clients. 1329 3.6. OMNI Interface Encapsulation and Re-encapsulation 1331 The OMNI Adaptation Layer (OAL) inserts mid-layer IPv6 headers known 1332 as the OAL/ORH headers when necessary as discussed in the following 1333 sections. After either inserting or omitting the OAL/ORH headers, 1334 the OMNI interface also inserts or omits an outer encapsulation 1335 header as discussed below. 1337 OMNI interfaces avoid outer encapsulation over Direct underlying 1338 interfaces and ANET underlying interfaces for which the Client and 1339 Proxy are connected to the same underlying link. Otherwise, OMNI 1340 interfaces encapsulate packets according to whether they are entering 1341 the OMNI interface from the network layer or if they are being re- 1342 admitted into the same OMNI link they arrived on. This latter form 1343 of encapsulation is known as "re-encapsulation". 1345 For packets entering the OMNI interface from the network layer, the 1346 OMNI interface copies the "TTL/Hop Limit", "Type of Service/Traffic 1347 Class" [RFC2983], "Flow Label"[RFC6438] (for IPv6) and "Congestion 1348 Experienced" [RFC3168] values in the inner packet's IP header into 1349 the corresponding fields in the OAL and outer encapsulation 1350 header(s). 1352 For packets undergoing re-encapsulation, the OMNI interface instead 1353 copies these values from the original encapsulation header into the 1354 new encapsulation header, i.e., the values are transferred between 1355 encapsulation headers and *not* copied from the encapsulated packet's 1356 network-layer header. (Note especially that by copying the TTL/Hop 1357 Limit between encapsulation headers the value will eventually 1358 decrement to 0 if there is a (temporary) routing loop.) 1360 OMNI interfaces configured over ANET underlying interfaces which 1361 employ a different IP protocol version (and/or when the Client and 1362 Proxy may be separated by multiple ANET IP hops) use IP-in-IP 1363 encapsulation so that the inner packet can traverse the ANET without 1364 decrementing the TTL/Hop-Limit. IPv6 underlying ANET interfaces use 1365 [RFC2473] encapsulation, while IPv4 interfaces use the appropriate 1366 encapsulation per one of [RFC5214][RFC2003]. 1368 OMNI interfaces configured over INET underlying interfaces 1369 encapsulate packets in INET headers according to the next hop 1370 determined in the forwarding algorithm in Section 3.10. If the next 1371 hop is reached via a secured tunnel, the OMNI interface uses an 1372 encapsulation format specific to the secured tunnel type (see: 1373 Section 6). If the next hop is reached via an unsecured INET 1374 interface, the OMNI interface instead uses UDP/IP encapsulation per 1375 [RFC4380] and as extended in [RFC6081]. 1377 When UDP/IP encapsulation is used, the OMNI interface next sets the 1378 UDP source port to a constant value that it will use in each 1379 successive packet it sends, and sets the UDP length field to the 1380 length of the encapsulated packet plus 8 bytes for the UDP header 1381 itself plus the length of any included extension headers or trailers. 1382 The encapsulated packet may be either IPv6 or IPv4, as distinguished 1383 by the version number found in the first four bits. 1385 For UDP/IP-encapsulated packets sent to a Server, Relay or Bridge, 1386 the OMNI interface sets the UDP destination port to 8060, i.e., the 1387 IANA-registered port number for AERO. For packets sent to a Client, 1388 the OMNI interface sets the UDP destination port to the port value 1389 stored in the neighbor cache entry for this Client. The OMNI 1390 interface finally includes/omits the UDP checksum according to 1391 [RFC6935][RFC6936]. 1393 3.7. OMNI Interface Decapsulation 1395 OMNI interfaces decapsulate packets destined either to the AERO node 1396 itself or to a destination reached via an interface other than the 1397 OMNI interface the packet was received on. When the encapsulated 1398 packet arrives in multiple OAL fragments, the OMNI interface 1399 reassembles as discussed in Section 3.9. Further decapsulation steps 1400 are performed according to the appropriate encapsulation format 1401 specification. 1403 3.8. OMNI Interface Data Origin Authentication 1405 AERO nodes employ simple data origin authentication procedures. In 1406 particular: 1408 o AERO Bridges, Servers and Proxys accept encapsulated data packets 1409 and control messages received from the (secured) spanning tree. 1411 o AERO Proxys and Clients accept packets that originate from within 1412 the same secured ANET. 1414 o AERO Clients and Relays accept packets from downstream network 1415 correspondents based on ingress filtering. 1417 o AERO Clients, Relays and Servers verify the outer UDP/IP 1418 encapsulation addresses according to [RFC4380]. 1420 AERO nodes silently drop any packets that do not satisfy the above 1421 data origin authentication procedures. Further security 1422 considerations are discussed in Section 6. 1424 3.9. OMNI Adaptation Layer and OMNI Interface MTU 1426 The OMNI interface observes the link nature of tunnels, including the 1427 Maximum Transmission Unit (MTU), Maximum Reassembly Unit (MRU) and 1428 the role of fragmentation and reassembly [I-D.ietf-intarea-tunnels]. 1429 The OMNI interface employs an OMNI Adaptation Layer (OAL) for 1430 accommodating multiple underlying links with diverse MTUs. The 1431 functions of the OAL and the OMNI interface MTU/MRU are specified in 1432 Section 5 of [I-D.templin-6man-omni-interface], with MTU/MRU both set 1433 to the constant value 9180 bytes. 1435 When the network layer presents an IP packet to the OMNI interface, 1436 the OAL encapsulates the packet in OAL/ORH headers. The OAL then 1437 fragments the encapsulated packet if necessary such that the OAL/ORH 1438 headers appear in each fragment while the original IP packet header 1439 appears only in the first fragment. The OAL then transmits each OAL/ 1440 ORH packet/fragment over an underlying linterface connected to either 1441 a physical link such as Ethernet, WiFi and the like or a virtual link 1442 such as an Internet or higher-layer tunnel (see the definition of 1443 link in [RFC8200]). 1445 Note: Although the ORH may be removed by a Bridge on the path (see: 1446 Section 3.10.4), this does not interfere with the destination's 1447 ability to reassemble in the event that the packet was fragmented. 1448 This is due to the fact that the ORH is not included in the 1449 fragmentabe part; therefore, its removal does not invalidate the 1450 offset values in any fragment headers. 1452 3.10. OMNI Interface Forwarding Algorithm 1454 IP packets enter a node's OMNI interface either from the network 1455 layer (i.e., from a local application or the IP forwarding system) or 1456 from the link layer (i.e., from an OMNI interface neighbor). All 1457 packets entering a node's OMNI interface first undergo data origin 1458 authentication as discussed in Section 3.8. Packets that satisfy 1459 data origin authentication are processed further, while all others 1460 are dropped silently. The OMNI interface OAL wraps accepted packets 1461 in OAL/ORH headers if necessary as discussed above. 1463 Packets that enter the OMNI interface from the network layer are 1464 forwarded to an OMNI interface neighbor. Packets that enter the OMNI 1465 interface from the link layer are either re-admitted into the OMNI 1466 link or forwarded to the network layer where they are subject to 1467 either local delivery or IP forwarding. In all cases, the OMNI 1468 interface itself MUST NOT decrement the network layer TTL/Hop-count 1469 since its forwarding actions occur below the network layer. 1471 OMNI interfaces may have multiple underlying interfaces and/or 1472 neighbor cache entries for neighbors with multiple underlying 1473 interfaces (see Section 3.3). The OMNI interface uses interface 1474 attributes and/or traffic classifiers (e.g., DSCP value, port number, 1475 etc.) to select an outgoing underlying interface for each packet 1476 based on the node's own QoS preferences, and also to select a 1477 destination link-layer address based on the neighbor's underlying 1478 interface with the highest preference. AERO implementations SHOULD 1479 allow for QoS preference values to be modified at runtime through 1480 network management. 1482 If multiple outgoing interfaces and/or neighbor interfaces have a 1483 preference of "high", the AERO node replicates the packet and sends 1484 one copy via each of the (outgoing / neighbor) interface pairs; 1485 otherwise, the node sends a single copy of the packet via an 1486 interface with the highest preference. AERO nodes keep track of 1487 which underlying interfaces are currently "reachable" or 1488 "unreachable", and only use "reachable" interfaces for forwarding 1489 purposes. 1491 The following sections discuss the OMNI interface forwarding 1492 algorithms for Clients, Proxys, Servers and Bridges. In the 1493 following discussion, a packet's destination address is said to 1494 "match" if it is the same as a cached address, or if it is covered by 1495 a cached prefix (which may be encoded in an LLA). 1497 3.10.1. Client Forwarding Algorithm 1499 When an IP packet enters a Client's OMNI interface from the network 1500 layer the Client searches for an asymmetric neighbor cache entry that 1501 matches the destination. If there is a match, the Client uses one or 1502 more "reachable" neighbor interfaces in the entry for packet 1503 forwarding. If there is no asymmetric neighbor cache entry, the 1504 Client instead forwards the packet toward a Server (the packet is 1505 intercepted by a Proxy if there is a Proxy on the path). The Client 1506 encapsulates the packet in OAL/ORH headers if necessary and fragments 1507 according to MTU requirements (see: Section 3.9). 1509 When an IP packet enters a Client's OMNI interface from the link- 1510 layer, if the destination matches one of the Client's MNPs or link- 1511 local addresses the Client reassembles and decapsulates as necessary 1512 and delivers the inner packet to the network layer. Otherwise, the 1513 Client drops the packet and MAY return a network-layer ICMP 1514 Destination Unreachable message subject to rate limiting (see: 1515 Section 3.11). 1517 3.10.2. Proxy Forwarding Algorithm 1519 For control messages originating from or destined to a Client, the 1520 Proxy intercepts the message and updates its proxy neighbor cache 1521 entry for the Client. The Proxy then forwards a (proxyed) copy of 1522 the control message. (For example, the Proxy forwards a proxied 1523 version of a Client's NS/RS message to the target neighbor, and 1524 forwards a proxied version of the NA/RA reply to the Client.) 1526 When the Proxy receives a data packet from a Client within the ANET, 1527 the Proxy reassembles and re-fragments if necessary then searches for 1528 an asymmetric neighbor cache entry that matches the destination and 1529 forwards as follows: 1531 o if the destination matches an asymmetric neighbor cache entry, the 1532 Proxy uses one or more "reachable" neighbor interfaces in the 1533 entry for packet forwarding using OAL/ORH encapsulation if 1534 necessary according to the cached link-layer address information. 1535 If the neighbor interface is in the same OMNI link segment, the 1536 Proxy forwards the packet directly to the neighbor; otherwise, it 1537 forwards the packet to a Bridge. 1539 o else, the Proxy uses OAL/ORH encapsulation and forwards the packet 1540 to a Bridge while using the DLA corresponding to the packet's 1541 destination as the destination address. 1543 When the Proxy receives an encapsulated data packet from an INET 1544 neighbor or from a secured tunnel from a Bridge, it accepts the 1545 packet only if data origin authentication succeeds and if there is a 1546 proxy neighbor cache entry that matches the inner destination. Next, 1547 the Proxy reassembles the packet (if necessary) and continues 1548 processing. If the reassembly is complete and the neighbor cache 1549 state is REACHABLE, the Proxy then returns a PTB if necessary (see: 1550 Section 3.9) then either drops or forwards the packet to the Client 1551 while performing OAL/ORH encapsulation and re-fragmentation if 1552 necessary. If the neighbor cache entry state is DEPARTED, the Proxy 1553 instead changes the destination address to the address of the new 1554 Server and forwards it to a Bridge while performing OAL/ORH re- 1555 fragmentation if necessary. 1557 3.10.3. Server/Relay Forwarding Algorithm 1559 For control messages destined to a target Client's LLA that are 1560 received from a secured tunnel, the Server intercepts the message and 1561 sends a Proxyed response on behalf of the Client. (For example, the 1562 Server sends a Proxyed NA message reply in response to an NS message 1563 directed to one of its associated Clients.) If the Client's neighbor 1564 cache entry is in the DEPARTED state, however, the Server instead 1565 forwards the packet to the Client's new Server as discussed in 1566 Section 3.16. 1568 When the Server receives an encapsulated data packet from an INET 1569 neighbor or from a secured tunnel, it accepts the packet only if data 1570 origin authentication succeeds. The Server then continues processing 1571 as follows: 1573 o if the network layer destination matches a symmetric neighbor 1574 cache entry in the REACHABLE state the Server prepares the packet 1575 for forwarding to the destination Client. The Server first 1576 reassembles (if necessary) and forwards the packet (while re- 1577 fragmenting if necessary) as specified in Section 3.9. 1579 o else, if the destination matches a symmetric neighbor cache entry 1580 in the DEPARETED state the Server re-encapsulates the packet and 1581 forwards it using the DLA of the Client's new Server as the 1582 destination. 1584 o else, if the destination matches an asymmetric neighbor cache 1585 entry, the Server uses one or more "reachable" neighbor interfaces 1586 in the entry for packet forwarding via the local INET if the 1587 neighbor is in the same OMNI link segment or using OAL/ORH 1588 encapsulation if necessary with the final destination set to the 1589 neighbor's DLA otherwise. 1591 o else, if the destination matches a non-MNP route in the IP 1592 forwarding table or an LLA assigned to the Server's OMNI 1593 interface, the Server reassembles if necessary, decapsulates the 1594 packet and releases it to the network layer for local delivery or 1595 IP forwarding. 1597 o else, the Server drops the packet. 1599 When the Server's OMNI interface receives a data packet from the 1600 network layer or from a VPNed or Direct Client, it performs OAL/ORH 1601 encapsulation and fragmentation if necessary, then processes the 1602 packet according to the network-layer destination address as follows: 1604 o if the destination matches a symmetric or asymmetric neighbor 1605 cache entry the Server processes the packet as above. 1607 o else, the Server encapsulates the packet in OLA/ORH headers and 1608 forwards it to a Bridge using its own DLA as the source and the 1609 DLA corresponding to the destination as the destination. 1611 3.10.4. Bridge Forwarding Algorithm 1613 Bridges forward OAL/ORH-encapsulated packets over secured tunnels the 1614 same as any IP router. When the Bridge receives an OAL/ORH- 1615 encapsulated packet via a secured tunnel, it removes the outer INET 1616 header and searches for a forwarding table entry that matches the 1617 destination address. The Bridge then processes the packet as 1618 follows: 1620 o if the destination matches its DLA Subnet Router Anycast address, 1621 the Bridge determines if the next header is an ORH. If so, the 1622 Bridge removes the ORH from the packet while decrementing the OAL 1623 header Payload Length field. If the ORH includes a Destination 1624 Suffix the Bridge also writes the DLA formed from the Destination 1625 Suffix into the OAL header destination address; otherwise, it 1626 writes the DLA formed from the SRT/LHS values. Next, the Bridge 1627 examines the FMT to determine if the target is behind a NAT. If 1628 no NAT is indicated, the Bridge forwards the packet directly to 1629 the L2ADDR using link-layer (UDP/IP) encapsulation. If a NAT is 1630 indicated, the Bridge MAY perform NAT traversal procedures by 1631 sending bubbles per [RFC4380]. The Bridge then either applies 1632 AERO route optimization after NAT traversal procedures have 1633 converged, or simply forwards the packet directly to the Server 1634 indicated by SRT/LHS. 1636 o if the destination matches one of the Bridge's own addresses, the 1637 Bridge submits the packet for local delivery. 1639 o else, if the destination matches a forwarding table entry the 1640 Bridge forwards the packet via a secured tunnel to the next hop. 1641 If the destination matches an MSP without matching an MNP, 1642 however, the Bridge instead drops the packet and returns an ICMP 1643 Destination Unreachable message subject to rate limiting (see: 1644 Section 3.11). 1646 o else, the Bridge drops the packet and returns an ICMP Destination 1647 Unreachable as above. 1649 As for any IP router, the Bridge decrements the TTL/Hop Limit when it 1650 forwards the packet. Therefore, when an OAL header is present only 1651 the Hop Limit in the OAL header is decremented and not the TTL/Hop 1652 Limit in the inner packet header. Bridges do not insert OAL/ORH 1653 headers themselves; instead, they act as IPv6 routers and forward 1654 packets based on the destination address found in the headers of 1655 packets they receive. 1657 3.11. OMNI Interface Error Handling 1659 When an AERO node admits a packet into the OMNI interface, it may 1660 receive link-layer or network-layer error indications. 1662 A link-layer error indication is an ICMP error message generated by a 1663 router in the INET on the path to the neighbor or by the neighbor 1664 itself. The message includes an IP header with the address of the 1665 node that generated the error as the source address and with the 1666 link-layer address of the AERO node as the destination address. 1668 The IP header is followed by an ICMP header that includes an error 1669 Type, Code and Checksum. Valid type values include "Destination 1670 Unreachable", "Time Exceeded" and "Parameter Problem" 1671 [RFC0792][RFC4443]. (OMNI interfaces ignore all link-layer IPv4 1672 "Fragmentation Needed" and IPv6 "Packet Too Big" messages since they 1673 only emit packets that are guaranteed to be no larger than the IP 1674 minimum link MTU as discussed in Section 3.9.) 1675 The ICMP header is followed by the leading portion of the packet that 1676 generated the error, also known as the "packet-in-error". For 1677 ICMPv6, [RFC4443] specifies that the packet-in-error includes: "As 1678 much of invoking packet as possible without the ICMPv6 packet 1679 exceeding the minimum IPv6 MTU" (i.e., no more than 1280 bytes). For 1680 ICMPv4, [RFC0792] specifies that the packet-in-error includes: 1681 "Internet Header + 64 bits of Original Data Datagram", however 1682 [RFC1812] Section 4.3.2.3 updates this specification by stating: "the 1683 ICMP datagram SHOULD contain as much of the original datagram as 1684 possible without the length of the ICMP datagram exceeding 576 1685 bytes". 1687 The link-layer error message format is shown in Figure 5 (where, "L2" 1688 and "L3" refer to link-layer and network-layer, respectively): 1690 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1691 ~ ~ 1692 | L2 IP Header of | 1693 | error message | 1694 ~ ~ 1695 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1696 | L2 ICMP Header | 1697 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 1698 ~ ~ P 1699 | IP and other encapsulation | a 1700 | headers of original L3 packet | c 1701 ~ ~ k 1702 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ e 1703 ~ ~ t 1704 | IP header of | 1705 | original L3 packet | i 1706 ~ ~ n 1707 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1708 ~ ~ e 1709 | Upper layer headers and | r 1710 | leading portion of body | r 1711 | of the original L3 packet | o 1712 ~ ~ r 1713 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 1715 Figure 5: OMNI Interface Link-Layer Error Message Format 1717 The AERO node rules for processing these link-layer error messages 1718 are as follows: 1720 o When an AERO node receives a link-layer Parameter Problem message, 1721 it processes the message the same as described as for ordinary 1722 ICMP errors in the normative references [RFC0792][RFC4443]. 1724 o When an AERO node receives persistent link-layer Time Exceeded 1725 messages, the IP ID field may be wrapping before earlier fragments 1726 awaiting reassembly have been processed. In that case, the node 1727 should begin including integrity checks and/or institute rate 1728 limits for subsequent packets. 1730 o When an AERO node receives persistent link-layer Destination 1731 Unreachable messages in response to encapsulated packets that it 1732 sends to one of its asymmetric neighbor correspondents, the node 1733 should process the message as an indication that a path may be 1734 failing, and optionally initiate NUD over that path. If it 1735 receives Destination Unreachable messages over multiple paths, the 1736 node should allow future packets destined to the correspondent to 1737 flow through a default route and re-initiate route optimization. 1739 o When an AERO Client receives persistent link-layer Destination 1740 Unreachable messages in response to encapsulated packets that it 1741 sends to one of its symmetric neighbor Servers, the Client should 1742 mark the path as unusable and use another path. If it receives 1743 Destination Unreachable messages on many or all paths, the Client 1744 should associate with a new Server and release its association 1745 with the old Server as specified in Section 3.16.5. 1747 o When an AERO Server receives persistent link-layer Destination 1748 Unreachable messages in response to encapsulated packets that it 1749 sends to one of its symmetric neighbor Clients, the Server should 1750 mark the underlying path as unusable and use another underlying 1751 path. 1753 o When an AERO Server or Proxy receives link-layer Destination 1754 Unreachable messages in response to an encapsulated packet that it 1755 sends to one of its permanent neighbors, it treats the messages as 1756 an indication that the path to the neighbor may be failing. 1757 However, the dynamic routing protocol should soon reconverge and 1758 correct the temporary outage. 1760 When an AERO Bridge receives a packet for which the network-layer 1761 destination address is covered by an MSP, if there is no more- 1762 specific routing information for the destination the Bridge drops the 1763 packet and returns a network-layer Destination Unreachable message 1764 subject to rate limiting. The Bridge writes the network-layer source 1765 address of the original packet as the destination address and uses 1766 one of its non link-local addresses as the source address of the 1767 message. 1769 When an AERO node receives an encapsulated packet for which the 1770 reassembly buffer it too small, it drops the packet and returns a 1771 network-layer Packet Too Big (PTB) message. The node first writes 1772 the MRU value into the PTB message MTU field, writes the network- 1773 layer source address of the original packet as the destination 1774 address and writes one of its non link-local addresses as the source 1775 address. 1777 3.12. AERO Router Discovery, Prefix Delegation and Autoconfiguration 1779 AERO Router Discovery, Prefix Delegation and Autoconfiguration are 1780 coordinated as discussed in the following Sections. 1782 3.12.1. AERO Service Model 1784 Each AERO Server on the OMNI link is configured to facilitate Client 1785 prefix delegation/registration requests. Each Server is provisioned 1786 with a database of MNP-to-Client ID mappings for all Clients enrolled 1787 in the AERO service, as well as any information necessary to 1788 authenticate each Client. The Client database is maintained by a 1789 central administrative authority for the OMNI link and securely 1790 distributed to all Servers, e.g., via the Lightweight Directory 1791 Access Protocol (LDAP) [RFC4511], via static configuration, etc. 1792 Clients receive the same service regardless of the Servers they 1793 select. 1795 AERO Clients and Servers use ND messages to maintain neighbor cache 1796 entries. AERO Servers configure their OMNI interfaces as advertising 1797 NBMA interfaces, and therefore send unicast RA messages with a short 1798 Router Lifetime value (e.g., ReachableTime seconds) in response to a 1799 Client's RS message. Thereafter, Clients send additional RS messages 1800 to keep Server state alive. 1802 AERO Clients and Servers include prefix delegation and/or 1803 registration parameters in RS/RA messages (see 1804 [I-D.templin-6man-omni-interface]). The ND messages are exchanged 1805 between Client and Server according to the prefix management schedule 1806 required by the service. If the Client knows its MNP in advance, it 1807 can employ prefix registration by including its LLA as the source 1808 address of an RS message and with an OMNI option with valid prefix 1809 registration information for the MNP. If the Server (and Proxy) 1810 accept the Client's MNP assertion, they inject the prefix into the 1811 routing system and establish the necessary neighbor cache state. 1813 The following sections specify the Client and Server behavior. 1815 3.12.2. AERO Client Behavior 1817 AERO Clients discover the addresses of Servers in a similar manner as 1818 described in [RFC5214]. Discovery methods include static 1819 configuration (e.g., from a flat-file map of Server addresses and 1820 locations), or through an automated means such as Domain Name System 1821 (DNS) name resolution [RFC1035]. Alternatively, the Client can 1822 discover Server addresses through a layer 2 data link login exchange, 1823 or through a unicast RA response to a multicast/anycast RS as 1824 described below. In the absence of other information, the Client can 1825 resolve the DNS Fully-Qualified Domain Name (FQDN) 1826 "linkupnetworks.[domainname]" where "linkupnetworks" is a constant 1827 text string and "[domainname]" is a DNS suffix for the OMNI link 1828 (e.g., "example.com"). 1830 To associate with a Server, the Client acts as a requesting router to 1831 request MNPs. The Client prepares an RS message with prefix 1832 management parameters and includes a Nonce and Timestamp option if 1833 the Client needs to correlate RA replies. If the Client already 1834 knows the Server's LLA, it includes the LLA as the network-layer 1835 destination address; otherwise, it includes (link-local) All-Routers 1836 multicast as the network-layer destination. If the Client already 1837 knows its own LLA, it uses the LLA as the network-layer source 1838 address; otherwise, it uses an OMNI Temporary LLA as the network- 1839 layer source address and includes a DHCP Unique Identifier (DUID) 1840 sub-option in the OMNI option (see: 1841 [I-D.templin-6man-omni-interface]). 1843 The Client next includes an OMNI option in the RS message to register 1844 its link-layer information with the Server. The Client sets the OMNI 1845 option prefix registration information according to the MNP, and 1846 includes Interface Attributes corresponding to the underlying 1847 interface over which the Client will send the RS message. The Client 1848 MAY include additional Interface Attributes specific to other 1849 underlying interfaces. 1851 The Client then sends the RS message (either directly via Direct 1852 interfaces, via a VPN for VPNed interfaces, via a Proxy for ANET 1853 interfaces or via INET encapsulation for INET interfaces) and waits 1854 for an RA message reply (see Section 3.12.3). The Client retries up 1855 to MAX_RTR_SOLICITATIONS times until an RA is received. If the 1856 Client receives no RAs, or if it receives an RA with Router Lifetime 1857 set to 0, the Client SHOULD abandon this Server and try another 1858 Server. Otherwise, the Client processes the prefix information found 1859 in the RA message. 1861 Next, the Client creates a symmetric neighbor cache entry with the 1862 Server's LLA as the network-layer address and the Server's 1863 encapsulation and/or link-layer addresses as the link-layer address. 1864 The Client records the RA Router Lifetime field value in the neighbor 1865 cache entry as the time for which the Server has committed to 1866 maintaining the MNP in the routing system via this underlying 1867 interface, and caches the other RA configuration information 1868 including Cur Hop Limit, M and O flags, Reachable Time and Retrans 1869 Timer. The Client then autoconfigures LLAs for each of the delegated 1870 MNPs and assigns them to the OMNI interface. The Client also caches 1871 any MSPs included in Route Information Options (RIOs) [RFC4191] as 1872 MSPs to associate with the OMNI link, and assigns the MTU value in 1873 the MTU option to the underlying interface. 1875 The Client then registers additional underlying interfaces with the 1876 Server by sending RS messages via each additional interface. The RS 1877 messages include the same parameters as for the initial RS/RA 1878 exchange, but with destination address set to the Server's LLA. 1880 Following autoconfiguration, the Client sub-delegates the MNPs to its 1881 attached EUNs and/or the Client's own internal virtual interfaces as 1882 described in [I-D.templin-v6ops-pdhost] to support the Client's 1883 downstream attached "Internet of Things (IoT)". The Client 1884 subsequently sends additional RS messages over each underlying 1885 interface before the Router Lifetime received for that interface 1886 expires. 1888 After the Client registers its underlying interfaces, it may wish to 1889 change one or more registrations, e.g., if an interface changes 1890 address or becomes unavailable, if QoS preferences change, etc. To 1891 do so, the Client prepares an RS message to send over any available 1892 underlying interface. The RS includes an OMNI option with prefix 1893 registration information specific to its MNP, with Interface 1894 Attributes specific to the selected underlying interface, and with 1895 any additional Interface Attributes specific to other underlying 1896 interfaces. When the Client receives the Server's RA response, it 1897 has assurance that the Server has been updated with the new 1898 information. 1900 If the Client wishes to discontinue use of a Server it issues an RS 1901 message over any underlying interface with an OMNI option with a 1902 prefix release indication. When the Server processes the message, it 1903 releases the MNP, sets the symmetric neighbor cache entry state for 1904 the Client to DEPARTED and returns an RA reply with Router Lifetime 1905 set to 0. After a short delay (e.g., 2 seconds), the Server 1906 withdraws the MNP from the routing system. 1908 3.12.3. AERO Server Behavior 1910 AERO Servers act as IP routers and support a prefix delegation/ 1911 registration service for Clients. Servers arrange to add their LLAs 1912 to a static map of Server addresses for the link and/or the DNS 1913 resource records for the FQDN "linkupnetworks.[domainname]" before 1914 entering service. Server addresses should be geographically and/or 1915 topologically referenced, and made available for discovery by Clients 1916 on the OMNI link. 1918 When a Server receives a prospective Client's RS message on its OMNI 1919 interface, it SHOULD return an immediate RA reply with Router 1920 Lifetime set to 0 if it is currently too busy or otherwise unable to 1921 service the Client. Otherwise, the Server authenticates the RS 1922 message and processes the prefix delegation/registration parameters. 1923 The Server first determines the correct MNPs to provide to the Client 1924 by searching the Client database. When the Server returns the MNPs, 1925 it also creates a forwarding table entry for the DLA corresponding to 1926 each MNP so that the MNPs are propagated into the routing system 1927 (see: Section 3.2.3). For IPv6, the Server creates an IPv6 1928 forwarding table entry for each MNP. For IPv4, the Server creates an 1929 IPv6 forwarding table entry with the IPv4-compatibility DLA prefix 1930 corresponding to the IPv4 address. 1932 The Server next creates a symmetric neighbor cache entry for the 1933 Client using the base LLA as the network-layer address and with 1934 lifetime set to no more than the smallest prefix lifetime. Next, the 1935 Server updates the neighbor cache entry by recording the information 1936 in each Interface Attributes sub-option in the RS OMNI option. The 1937 Server also records the actual OAL/INET addresses in the neighbor 1938 cache entry. 1940 Next, the Server prepares an RA message using its LLA as the network- 1941 layer source address and the network-layer source address of the RS 1942 message as the network-layer destination address. The Server sets 1943 the Router Lifetime to the time for which it will maintain both this 1944 underlying interface individually and the symmetric neighbor cache 1945 entry as a whole. The Server also sets Cur Hop Limit, M and O flags, 1946 Reachable Time and Retrans Timer to values appropriate for the OMNI 1947 link. The Server includes the MNPs, any other prefix management 1948 parameters and an OMNI option with no Interface Attributes. The 1949 Server then includes one or more RIOs that encode the MSPs for the 1950 OMNI link, plus an MTU option (see Section 3.9). The Server finally 1951 forwards the message to the Client using OAL/INET, INET, or NULL 1952 encapsulation as necessary. 1954 After the initial RS/RA exchange, the Server maintains a 1955 ReachableTime timer for each of the Client's underlying interfaces 1956 individually (and for the Client's symmetric neighbor cache entry 1957 collectively) set to expire after ReachableTime seconds. If the 1958 Client (or Proxy) issues additional RS messages, the Server sends an 1959 RA response and resets ReachableTime. If the Server receives an ND 1960 message with a prefix release indication it sets the Client's 1961 symmetric neighbor cache entry to the DEPARTED state and withdraws 1962 the MNP from the routing system after a short delay (e.g., 2 1963 seconds). If ReachableTime expires before a new RS is received on an 1964 individual underlying interface, the Server marks the interface as 1965 DOWN. If ReachableTime expires before any new RS is received on any 1966 individual underlying interface, the Server sets the symmetric 1967 neighbor cache entry state to STALE and sets a 10 second timer. If 1968 the Server has not received a new RS or ND message with a prefix 1969 release indication before the 10 second timer expires, it deletes the 1970 neighbor cache entry and withdraws the MNP from the routing system. 1972 The Server processes any ND messages pertaining to the Client and 1973 returns an NA/RA reply in response to solicitations. The Server may 1974 also issue unsolicited RA messages, e.g., with reconfigure parameters 1975 to cause the Client to renegotiate its prefix delegation/ 1976 registrations, with Router Lifetime set to 0 if it can no longer 1977 service this Client, etc. Finally, If the symmetric neighbor cache 1978 entry is in the DEPARTED state, the Server deletes the entry after 1979 DepartTime expires. 1981 Note: Clients SHOULD notify former Servers of their departures, but 1982 Servers are responsible for expiring neighbor cache entries and 1983 withdrawing routes even if no departure notification is received 1984 (e.g., if the Client leaves the network unexpectedly). Servers 1985 SHOULD therefore set Router Lifetime to ReachableTime seconds in 1986 solicited RA messages to minimize persistent stale cache information 1987 in the absence of Client departure notifications. A short Router 1988 Lifetime also ensures that proactive Client/Server RS/RA messaging 1989 will keep any NAT state alive (see above). 1991 Note: All Servers on an OMNI link MUST advertise consistent values in 1992 the RA Cur Hop Limit, M and O flags, Reachable Time and Retrans Timer 1993 fields the same as for any link, since unpredictable behavior could 1994 result if different Servers on the same link advertised different 1995 values. 1997 3.12.3.1. DHCPv6-Based Prefix Registration 1999 When a Client is not pre-provisioned with an OMNI LLA containing a 2000 MNP, it will need for the Server to select one or more MNPs on its 2001 behalf and set up the correct state in the AERO routing service. (A 2002 Client with a pre-provisioned MNP may also request the Server to 2003 select additional MNPs.) The DHCPv6 service [RFC8415] is used to 2004 support this requirement. 2006 When a Client needs to have the Server select MNPs, it sends an RS 2007 message with an OMNI option that includes a DHCPv6 message suboption 2008 with DHCPv6 Prefix Delegation (DHCPv6-PD) parameters. When the 2009 Server receives the RS message, it extracts the DHCPv6-PD message 2010 from the OMNI option. 2012 The Server then acts as a "Proxy DHCPv6 Client" in a message exchange 2013 with the locally-resident DHCPv6 server, which delegates MNPs and 2014 returns a DHCPv6-PD Reply message. (If the Server wishes to defer 2015 creation of MN state until the DHCPv6-PD Reply is received, it can 2016 instead act as a Lightweight DHCPv6 Relay Agent per [RFC6221] by 2017 encapsulating the DHCPv6-PD message in a Relay-forward/reply exchange 2018 with Relay Message and Interface ID options.) 2020 When the Server receives the DHCPv6-PD Reply, it adds a route to the 2021 routing system and creates an OMNI MN LLA based on the delegated MNP. 2022 The Server then sends an RA back to the Client with the (newly- 2023 created) OMNI MN LLA as the destination address and with the 2024 DHCPv6-PD Reply message coded in the OMNI option. When the Client 2025 receives the RA, it creates a default route, assigns the Subnet 2026 Router Anycast address and sets its OMNI LLA based on the delegated 2027 MNP. 2029 3.13. The AERO Proxy 2031 Clients may connect to protected-spectrum ANETs that employ physical 2032 and/or link-layer security services to facilitate communications to 2033 Servers in outside INETs. In that case, the ANET can employ an AERO 2034 Proxy. The Proxy is located at the ANET/INET border and listens for 2035 RS messages originating from or RA messages destined to ANET Clients. 2036 The Proxy acts on these control messages as follows: 2038 o when the Proxy receives an RS message from a new ANET Client, it 2039 first authenticates the message then examines the network-layer 2040 destination address. If the destination address is a Server's 2041 LLA, the Proxy proceeds to the next step. Otherwise, if the 2042 destination is (link-local) All-Routers multicast, the Proxy 2043 selects a "nearby" Server that is likely to be a good candidate to 2044 serve the Client and replaces the destination address with the 2045 Server's LLA. Next, the Proxy creates a proxy neighbor cache 2046 entry and caches the Client and Server link-layer addresses along 2047 with the OMNI option information and any other identifying 2048 information including Transaction IDs, Client Identifiers, Nonce 2049 values, etc. The Proxy finally encapsulates the (proxyed) RS 2050 message in an OAL header with source set to the Proxy's DLA and 2051 destination set to the Server's DLA. The Proxy also includes an 2052 OMNI header with an Interface Attributes option that includes its 2053 own INET address plus a unique Port Number for this Client, then 2054 forwards the message into the OMNI link spanning tree. 2056 o when the Server receives the RS, it authenticates the message then 2057 creates or updates a symmetric neighbor cache entry for the Client 2058 with the Proxy's DLA, INET address and Port Number as the link- 2059 layer address information. The Server then sends an RA message 2060 back to the Proxy via the spanning tree. 2062 o when the Proxy receives the RA, it authenticates the message and 2063 matches it with the proxy neighbor cache entry created by the RS. 2064 The Proxy then caches the prefix information as a mapping from the 2065 Client's MNPs to the Client's link-layer address, caches the 2066 Server's advertised Router Lifetime and sets the neighbor cache 2067 entry state to REACHABLE. The Proxy then optionally rewrites the 2068 Router Lifetime and forwards the (proxyed) message to the Client. 2069 The Proxy finally includes an MTU option (if necessary) with an 2070 MTU to use for the underlying ANET interface. 2072 After the initial RS/RA exchange, the Proxy forwards any Client data 2073 packets for which there is no matching asymmetric neighbor cache 2074 entry to a Bridge using OAL encapsulation with its own DLA as the 2075 source and the DLA corresponding to the Client as the destination. 2076 The Proxy instead forwards any Client data destined to an asymmetric 2077 neighbor cache target directly to the target according to the OAL/ 2078 link-layer information - the process of establishing asymmetric 2079 neighbor cache entries is specified in Section 3.14. 2081 While the Client is still attached to the ANET, the Proxy sends NS, 2082 RS and/or unsolicited NA messages to update the Server's symmetric 2083 neighbor cache entries on behalf of the Client and/or to convey QoS 2084 updates. This allows for higher-frequency Proxy-initiated RS/RA 2085 messaging over well-connected INET infrastructure supplemented by 2086 lower-frequency Client-initiated RS/RA messaging over constrained 2087 ANET data links. 2089 If the Server ceases to send solicited advertisements, the Proxy 2090 sends unsolicited RAs on the ANET interface with destination set to 2091 (link-local) All-Nodes multicast and with Router Lifetime set to zero 2092 to inform Clients that the Server has failed. Although the Proxy 2093 engages in ND exchanges on behalf of the Client, the Client can also 2094 send ND messages on its own behalf, e.g., if it is in a better 2095 position than the Proxy to convey QoS changes, etc. For this reason, 2096 the Proxy marks any Client-originated solicitation messages (e.g. by 2097 inserting a Nonce option) so that it can return the solicited 2098 advertisement to the Client instead of processing it locally. 2100 If the Client becomes unreachable, the Proxy sets the neighbor cache 2101 entry state to DEPARTED and retains the entry for DepartTime seconds. 2102 While the state is DEPARTED, the Proxy forwards any packets destined 2103 to the Client to a Bridge via OAL encapsulation with the Client's 2104 current Server as the destination. The Bridge in turn forwards the 2105 packets to the Client's current Server. When DepartTime expires, the 2106 Proxy deletes the neighbor cache entry and discards any further 2107 packets destined to this (now forgotten) Client. 2109 In some ANETs that employ a Proxy, the Client's MNP can be injected 2110 into the ANET routing system. In that case, the Client can send data 2111 messages without encapsulation so that the ANET routing system 2112 transports the unencapsulated packets to the Proxy. This can be very 2113 beneficial, e.g., if the Client connects to the ANET via low-end data 2114 links such as some aviation wireless links. 2116 If the first-hop ANET access router is on the same underlying link 2117 and recognizes the AERO/OMNI protocol, the Client can avoid 2118 encapsulation for both its control and data messages. When the 2119 Client connects to the link, it can send an unencapsulated RS message 2120 with source address set to its LLA and with destination address set 2121 to the LLA of the Client's selected Server or to (link-local) All- 2122 Routers multicast. The Client includes an OMNI option formatted as 2123 specified in [I-D.templin-6man-omni-interface]. 2125 The Client then sends the unencapsulated RS message, which will be 2126 intercepted by the AERO-Aware access router. The access router then 2127 encapsulates the RS message in an ANET header with its own address as 2128 the source address and the address of a Proxy as the destination 2129 address. The access router further remembers the address of the 2130 Proxy so that it can encapsulate future data packets from the Client 2131 via the same Proxy. If the access router needs to change to a new 2132 Proxy, it simply sends another RS message toward the Server via the 2133 new Proxy on behalf of the Client. 2135 In some cases, the access router and Proxy may be one and the same 2136 node. In that case, the node would be located on the same physical 2137 link as the Client, but its message exchanges with the Server would 2138 need to pass through a security gateway at the ANET/INET border. The 2139 method for deploying access routers and Proxys (i.e. as a single node 2140 or multiple nodes) is an ANET-local administrative consideration. 2142 3.13.1. Combined Proxy/Servers 2144 Clients may need to connect directly to Servers via INET, Direct and 2145 VPNed interfaces (i.e., non-ANET interfaces). If the Client's 2146 underlying interfaces all connect via the same INET partition, then 2147 it can connect to a single controlling Server via all interfaces. 2149 If some Client interfaces connect via different INET partitions, 2150 however, the Client still selects a set of controlling Servers and 2151 sends RS messages via their directly-connected Servers while using 2152 the LLA of the controlling Server as the destination. 2154 When a Server receives an RS with destination set to the LLA of a 2155 controlling Server, it acts as a Proxy to forward the message to the 2156 controlling Server while forwarding the corresponding RA reply to the 2157 Client. 2159 3.13.2. Detecting and Responding to Server Failures 2161 In environments where fast recovery from Server failure is required, 2162 Proxys SHOULD use proactive Neighbor Unreachability Detection (NUD) 2163 to track Server reachability in a similar fashion as for 2164 Bidirectional Forwarding Detection (BFD) [RFC5880]. Proxys can then 2165 quickly detect and react to failures so that cached information is 2166 re-established through alternate paths. The NUD control messaging is 2167 carried only over well-connected ground domain networks (i.e., and 2168 not low-end aeronautical radio links) and can therefore be tuned for 2169 rapid response. 2171 Proxys perform proactive NUD with Servers for which there are 2172 currently active ANET Clients by sending continuous NS messages in 2173 rapid succession, e.g., one message per second. The Proxy sends the 2174 NS message via the spanning tree with the Proxy's LLA as the source 2175 and the LLA of the Server as the destination. When the Proxy is also 2176 sending RS messages to the Server on behalf of ANET Clients, the 2177 resulting RA responses can be considered as equivalent hints of 2178 forward progress. This means that the Proxy need not also send a 2179 periodic NS if it has already sent an RS within the same period. If 2180 the Server fails (i.e., if the Proxy ceases to receive 2181 advertisements), the Proxy can quickly inform Clients by sending 2182 multicast RA messages on the ANET interface. 2184 The Proxy sends RA messages on the ANET interface with source address 2185 set to the Server's address, destination address set to (link-local) 2186 All-Nodes multicast, and Router Lifetime set to 0. The Proxy SHOULD 2187 send MAX_FINAL_RTR_ADVERTISEMENTS RA messages separated by small 2188 delays [RFC4861]. Any Clients on the ANET that had been using the 2189 failed Server will receive the RA messages and associate with a new 2190 Server. 2192 3.13.3. Point-to-Multipoint Server Coordination 2194 In environments where Client messaging over ANETs is bandwidth- 2195 limited and/or expensive, Clients can enlist the services of the 2196 Proxy to coordinate with multiple Servers in a single RS/RA message 2197 exchange. The Client can send a single RS message to (link-local) 2198 All-Routers multicast that includes the ID's of multiple Servers in 2199 MS-Register sub-options of the OMNI option. 2201 When the Proxy receives the RS and processes the OMNI option, it 2202 sends a separate RS to each MS-Register Server ID. When the Proxy 2203 receives an RA, it can optionally return an immediate "singleton" RA 2204 to the Client or record the Server's ID for inclusion in a pending 2205 "aggregate" RA message. The Proxy can then return aggregate RA 2206 messages to the Client including multiple Server IDs in order to 2207 conserve bandwidth. Each RA includes a proper subset of the Server 2208 IDs from the original RS message, and the Proxy must ensure that the 2209 message contents of each RA are consistent with the information 2210 received from the (aggregated) Servers. 2212 Clients can thereafter employ efficient point-to-multipoint Server 2213 coordination under the assistance of the Proxy to reduce the number 2214 of messages sent over the ANET while enlisting the support of 2215 multiple Servers for fault tolerance. Clients can further include 2216 MS-Release sub-options in IPv6 ND messages to request the Proxy to 2217 release from former Servers via the procedures discussed in 2218 Section 3.16.5. 2220 The OMNI interface specification [I-D.templin-6man-omni-interface] 2221 provides further discussion of the Client/Proxy RS/RA messaging 2222 involved in point-to-multipoint coordination. 2224 3.14. AERO Route Optimization / Address Resolution 2226 While data packets are flowing between a source and target node, 2227 route optimization SHOULD be used. Route optimization is initiated 2228 by the first eligible Route Optimization Source (ROS) closest to the 2229 source as follows: 2231 o For Clients on VPNed and Direct interfaces, the Server is the ROS. 2233 o For Clients on ANET interfaces, the Proxy is the ROS. 2235 o For Clients on INET interfaces, the Client itself is the ROS. 2237 o For correspondent nodes on INET/EUN interfaces serviced by a 2238 Relay, the Relay is the ROS. 2240 The route optimization procedure is conducted between the ROS and the 2241 target Server/Relay acting as a Route Optimization Responder (ROR) in 2242 the same manner as for IPv6 ND Address Resolution and using the same 2243 NS/NA messaging. The target may either be a MNP Client serviced by a 2244 Server, or a non-MNP correspondent reachable via a Relay. 2246 The procedures are specified in the following sections. 2248 3.14.1. Route Optimization Initiation 2250 While data packets are flowing from the source node toward a target 2251 node, the ROS performs address resolution by sending an NS message 2252 for Address Resolution (NS(AR)) to receive a solicited NA message 2253 from the ROR. When the ROS sends an NS(AR), it includes: 2255 o the LLA of the ROS as the source address. 2257 o the data packet's destination as the Target Address. 2259 o the Solicited-Node multicast address [RFC4291] formed from the 2260 lower 24 bits of the data packet's destination as the destination 2261 address, e.g., for 2001:db8:1:2::10:2000 the NS destination 2262 address is ff02:0:0:0:0:1:ff10:2000. 2264 The NS(AR) message includes an OMNI option with no Interface 2265 Attributes, such that the target will not create a neighbor cache 2266 entry. The Prefix Length in the OMNI option is set to the Prefix 2267 Length associated with the ROS's LLA. 2269 The ROS then encapsulates the NS(AR) message in an OAL header with 2270 source set to its own DLA and destination set to the DLA 2271 corresponding to the target, then sends the message into the spanning 2272 tree without decrementing the network-layer TTL/Hop Limit field. 2273 (When the ROS is a Client, it instead securely sends the NS(AR) to 2274 one of its current Servers by including an Authentication option per 2275 [RFC4380]. The Server then forwards the message into the spanning 2276 tree on behalf of the Client, while setting the IPv6 source address 2277 and the OAL source address to the LLA and DLA of the Client, 2278 respectively.) 2280 3.14.2. Relaying the NS 2282 When the Bridge receives the NS(AR) message from the ROS, it discards 2283 the INET header and determines that the ROR is the next hop by 2284 consulting its standard IPv6 forwarding table for the OAL header 2285 destination address. The Bridge then forwards the message toward the 2286 ROR via the spanning tree the same as for any IPv6 router. The 2287 final-hop Bridge in the spanning tree will deliver the message via a 2288 secured tunnel to the ROR. 2290 3.14.3. Processing the NS and Sending the NA 2292 When the ROR receives the NS(AR) message, it examines the Target 2293 Address to determine whether it has a neighbor cache entry and/or 2294 route that matches the target. If there is no match, the ROR drops 2295 the message. Otherwise, the ROR continues processing as follows: 2297 o if the target belongs to an MNP Client neighbor in the DEPARTED 2298 state the ROR changes the NS(AR) message OAL destination address 2299 to the DLA of the Client's new Server, forwards the message into 2300 the spanning tree and returns from processing. 2302 o If the target belongs to an MNP Client neighbor in the REACHABLE 2303 state, the ROR instead adds the AERO source address to the target 2304 Client's Report List with time set to ReportTime. 2306 o If the target belongs to a non-MNP route, the ROR continues 2307 processing without adding an entry to the Report List. 2309 The ROR then prepares a solicited NA message to send back to the ROS 2310 but does not create a neighbor cache entry. The ROR sets the NA 2311 source address to the LLA corresponding to the target, sets the 2312 Target Address to the target of the solicitation, and sets the 2313 destination address to the source of the solicitation. The ROR then 2314 includes an OMNI option with Prefix Length set to the length 2315 associated with the LLA. 2317 If the target is an MNP Client, the ROR next includes Interface 2318 Attributes in the OMNI option for each of the target Client's 2319 underlying interfaces with current information for each interface and 2320 with the S/T-ifIndex field in the OMNI header set to 0 to indicate 2321 that the message originated from the ROR and not the Client. 2323 For each Interface Attributes sub-option, the ROR sets the L2ADDR 2324 according to its own INET address for VPNed or Direct interfaces, to 2325 the INET address of the Proxy or to the Client's INET address for 2326 INET interfaces. The ROR then includes the lower 32 bits of its own 2327 DLA (or the DLA of the Proxy) as the LHS, encodes the DLA prefix 2328 length code in the SRT field and sets the FMT code accordingly as 2329 specified in Section 3.3. 2331 The ROR then sets the NA message R flag to 1 (as a router), S flag to 2332 1 (as a response to a solicitation), and O flag to 0 (as a proxy). 2333 The ROR finally encapsulates the NA message in an OAL header with 2334 source set to its own DLA and destination set to the source DLA of 2335 the NS(AR) message, then forwards the message into the spanning tree 2336 without decrementing the network-layer TTL/Hop Limit field. 2338 3.14.4. Relaying the NA 2340 When the Bridge receives the NA message from the ROR, it discards the 2341 INET header and determines that the ROS is the next hop by consulting 2342 its standard IPv6 forwarding table for the OAL header destination 2343 address. The Bridge then forwards the OAL-encapsulated NA message 2344 toward the ROS the same as for any IPv6 router. The final-hop Bridge 2345 in the spanning tree will deliver the message via a secured tunnel to 2346 the ROS. 2348 3.14.5. Processing the NA 2350 When the ROS receives the solicited NA message, it processes the 2351 message the same as for standard IPv6 Address Resolution [RFC4861]. 2352 In the process, it caches the source DLA then creates an asymmetric 2353 neighbor cache entry for the target and caches all information found 2354 in the OMNI option. The ROS finally sets the asymmetric neighbor 2355 cache entry lifetime to ReachableTime seconds. (When the ROS is a 2356 Client, the solicited NA message will first be delivered via the 2357 spanning tree to one of its current Servers, which then securely 2358 forwards the message to the Client by including an Authentication 2359 option per [RFC4380]. 2361 3.14.6. Route Optimization Maintenance 2363 Following route optimization, the ROS forwards future data packets 2364 destined to the target via the addresses found in the cached link- 2365 layer information. The route optimization is shared by all sources 2366 that send packets to the target via the ROS, i.e., and not just the 2367 source on behalf of which the route optimization was initiated. 2369 While new data packets destined to the target are flowing through the 2370 ROS, it sends additional NS(AR) messages to the ROR before 2371 ReachableTime expires to receive a fresh solicited NA message the 2372 same as described in the previous sections (route optimization 2373 refreshment strategies are an implementation matter, with a non- 2374 normative example given in Appendix A.1). The ROS uses the cached 2375 DLA of the ROR as the NS(AR) OAL destination address (i.e., instead 2376 of using the DLA corresponding to the target as was the case for the 2377 initial NS(AR)), and sends up to MAX_MULTICAST_SOLICIT NS(AR) 2378 messages separated by 1 second until an NA is received. If no NA is 2379 received, the ROS assumes that the current ROR has become unreachable 2380 and deletes the target neighbor cache entry. Subsequent data packets 2381 will trigger a new route optimization with an NS with OAL destination 2382 address set to the DLA corresponding to the target per Section 3.14.1 2383 to discover a new ROR while initial data packets travel over a 2384 suboptimal route. 2386 If an NA is received, the ROS then updates the asymmetric neighbor 2387 cache entry to refresh ReachableTime, while (for MNP destinations) 2388 the ROR adds or updates the ROS address to the target's Report List 2389 and with time set to ReportTime. While no data packets are flowing, 2390 the ROS instead allows ReachableTime for the asymmetric neighbor 2391 cache entry to expire. When ReachableTime expires, the ROS deletes 2392 the asymmetric neighbor cache entry. Any future data packets flowing 2393 through the ROS will again trigger a new route optimization. 2395 The ROS may also receive unsolicited NA messages from the ROR at any 2396 time (see: Section 3.16). If there is an asymmetric neighbor cache 2397 entry for the target, the ROS updates the link-layer information but 2398 does not update ReachableTime since the receipt of an unsolicited NA 2399 does not confirm that any forward paths are working. If there is no 2400 asymmetric neighbor cache entry, the ROS simply discards the 2401 unsolicited NA. 2403 In this arrangement, the ROS holds an asymmetric neighbor cache entry 2404 for the target via the ROR, but the ROR does not hold an asymmetric 2405 neighbor cache entry for the ROS. The route optimization neighbor 2406 relationship is therefore asymmetric and unidirectional. If the 2407 target node also has packets to send back to the source node, then a 2408 separate route optimization procedure is performed in the reverse 2409 direction. But, there is no requirement that the forward and reverse 2410 paths be symmetric. 2412 3.15. Neighbor Unreachability Detection (NUD) 2414 AERO nodes perform Neighbor Unreachability Detection (NUD) per 2415 [RFC4861] either reactively in response to persistent link-layer 2416 errors (see Section 3.11) or proactively to confirm reachability. 2417 The NUD algorithm is based on periodic control message exchanges. 2418 The algorithm may further be seeded by ND hints of forward progress, 2419 but care must be taken to avoid inferring reachability based on 2420 spoofed information. For example, authentic IPv6 ND message 2421 exchanges may be considered as acceptable hints of forward progress, 2422 while spurious data packets should not be. 2424 AERO Servers, Proxys and Relays can use (OAL-encapsulated) standard 2425 NS/NA NUD exchanges sent over the OMNI link spanning tree to securely 2426 test reachability without risk of DoS attacks from nodes pretending 2427 to be a neighbor (these NS/NA(NUD) messages use the unicast LLAs and 2428 DLAs of the two parties involved in the NUD test the same as for 2429 standard IPv6 ND). Proxys can further perform NUD to securely verify 2430 Server reachability on behalf of their proxyed Clients. However, a 2431 means for an ROS to test the unsecured forward directions of target 2432 route optimized paths is also necessary. 2434 When an ROR directs an ROS to a neighbor with one or more target 2435 link-layer addresses, the ROS can proactively test each such 2436 unsecured route optimized path by sending "loopback" NS(NUD) 2437 messages. While testing the paths, the ROS can optionally continue 2438 to send packets via the spanning tree, maintain a small queue of 2439 packets until target reachability is confirmed, or (optimistically) 2440 allow packets to flow via the route optimized paths. 2442 When the ROS sends a loopback NS(NUD) message, it uses its own LLA as 2443 both the IPv6 source and destination address, and the MNP Subnet- 2444 Router anycast address as the Target Address. The ROS includes a 2445 Nonce and Timestamp option, then encapsulates the message in OAL/INET 2446 headers with its own DLA as the source and the DLA of the route 2447 optimization target as the destination. The ROS then forwards the 2448 message to the target (either directly to the L2ADDR of the target if 2449 the target is in the same OMNI link segment, or via a Bridge if the 2450 target is in a different OMNI link segment). 2452 When the route optimization target receives the NS(NUD) message, it 2453 notices that the IPv6 destination address is the same as the source 2454 address. It then reverses the OAL header source and destination 2455 addresses and returns the message to the ROS (either directly or via 2456 the spanning tree). The route optimization target does not decrement 2457 the NS(NUD) message IPv6 Hop-Limit in the process, since the message 2458 has not exited the OMNI link. 2460 When the ROS receives the NS(NUD) message, it can determine from the 2461 Nonce, Timestamp and Target Address that the message originated from 2462 itself and that it transited the forward path. The ROS need not 2463 prepare an NA response, since the destination of the response would 2464 be itself and testing the route optimization path again would be 2465 redundant. 2467 The ROS marks route optimization target paths that pass these NUD 2468 tests as "reachable", and those that do not as "unreachable". These 2469 markings inform the OMNI interface forwarding algorithm specified in 2470 Section 3.10. 2472 Note that to avoid a DoS vector nodes MUST NOT return loopback 2473 NS(NUD) messages received from an unsecured link-layer source via the 2474 (secured) spanning tree. 2476 3.16. Mobility Management and Quality of Service (QoS) 2478 AERO is a Distributed Mobility Management (DMM) service. Each Server 2479 is responsible for only a subset of the Clients on the OMNI link, as 2480 opposed to a Centralized Mobility Management (CMM) service where 2481 there is a single network mobility collective entity for all Clients. 2482 Clients coordinate with their associated Servers via RS/RA exchanges 2483 to maintain the DMM profile, and the AERO routing system tracks all 2484 current Client/Server peering relationships. 2486 Servers provide default routing and mobility/multilink services for 2487 their dependent Clients. Clients are responsible for maintaining 2488 neighbor relationships with their Servers through periodic RS/RA 2489 exchanges, which also serves to confirm neighbor reachability. When 2490 a Client's underlying interface address and/or QoS information 2491 changes, the Client is responsible for updating the Server with this 2492 new information. Note that when there is a Proxy in the path, the 2493 Proxy can also perform some RS/RA exchanges on the Client's behalf. 2495 Mobility management messaging is based on the transmission and 2496 reception of unsolicited Neighbor Advertisement (uNA) messages. Each 2497 uNA message sets the IPv6 destination address to (link-local) All- 2498 Nodes multicast to convey a general update of Interface Attributes to 2499 (possibly) multiple recipients, or to a specific unicast LLA to 2500 announce a departure event to a specific recipient. Implementations 2501 must therefore examine the destination address to determine the 2502 nature of the mobility event (i.e., update vs departure). 2504 Mobility management considerations are specified in the following 2505 sections. 2507 3.16.1. Mobility Update Messaging 2509 Servers accommodate Client mobility, multilink and/or QoS change 2510 events by sending unsolicited NA (uNA) messages to each ROS in the 2511 target Client's Report List. When a Server sends a uNA message, it 2512 sets the IPv6 source address to the Client's LLA, sets the 2513 destination address to (link-local) All-Nodes multicast and sets the 2514 Target Address to the Client's Subnet-Router anycast address. The 2515 Server also includes an OMNI option with Prefix Length set to the 2516 length associated with the Client's LLA, with Interface Attributes 2517 for the target Client's underlying interfaces and with the OMNI 2518 header S/T-ifIndex set to 0. The Server then sets the NA R flag to 2519 1, the S flag to 0 and the O flag to 1, then encapsulates the message 2520 in an OAL header with source set to its own DLA and destination set 2521 to the DLA of the ROS and sends the message into the spanning tree. 2523 As discussed in Section 7.2.6 of [RFC4861], the transmission and 2524 reception of uNA messages is unreliable but provides a useful 2525 optimization. In well-connected Internetworks with robust data links 2526 uNA messages will be delivered with high probability, but in any case 2527 the Server can optionally send up to MAX_NEIGHBOR_ADVERTISEMENT uNAs 2528 to each ROS to increase the likelihood that at least one will be 2529 received. 2531 When the ROS receives a uNA message prepared as above, it ignores the 2532 message if there is no existing neighbor cache entry for the Client. 2533 Otherwise, it uses the included OMNI option information to update the 2534 neighbor cache entry, but does not reset ReachableTime since the 2535 receipt of an unsolicited NA message from the target Server does not 2536 provide confirmation that any forward paths to the target Client are 2537 working. 2539 If uNA messages are lost, the ROS may be left with stale address and/ 2540 or QoS information for the Client for up to ReachableTime seconds. 2541 During this time, the ROS can continue sending packets according to 2542 its stale neighbor cache information. When ReachableTime is close to 2543 expiring, the ROS will re-initiate route optimization and receive 2544 fresh link-layer address information. 2546 In addition to sending uNA messages to the current set of ROSs for 2547 the Client, the Server also sends uNAs to the DLA associated with the 2548 link-layer address for any underlying interface for which the link- 2549 layer address has changed. These uNA messages update an old Proxy/ 2550 Server that cannot easily detect (e.g., without active probing) when 2551 a formerly-active Client has departed. When the Server sends the 2552 uNA, it sets the IPv6 source address to the Client's LLA, sets the 2553 destination address to the old Proxy/Server's LLA, and sets the 2554 Target Address to the Client's Subnet-Router anycast address. The 2555 Server also includes an OMNI option with Prefix Length set to the 2556 length associated with the Client's LLA, with Interface Attributes 2557 for the changed underlying interface, and with the OMNI header S/ 2558 T-ifIndex set to 0. The Server then sets the NA R flag to 1, the S 2559 flag to 0 and the O flag to 1, then encapsulates the message in an 2560 OAL header with source set to its own DLA and destination set to the 2561 DLA of the old Proxy/Server and sends the message into the spanning 2562 tree. 2564 3.16.2. Announcing Link-Layer Address and/or QoS Preference Changes 2566 When a Client needs to change its underlying interface addresses and/ 2567 or QoS preferences (e.g., due to a mobility event), either the Client 2568 or its Proxys send RS messages to the Server via the spanning tree 2569 with an OMNI option that includes Interface attributes with the new 2570 link quality and address information. 2572 Up to MAX_RTR_SOLICITATIONS RS messages MAY be sent in parallel with 2573 sending actual data packets in case one or more RAs are lost. If all 2574 RAs are lost, the Client SHOULD re-associate with a new Server. 2576 When the Server receives the Client's changes, it sends uNA messages 2577 to all nodes in the Report List the same as described in the previous 2578 section. 2580 3.16.3. Bringing New Links Into Service 2582 When a Client needs to bring new underlying interfaces into service 2583 (e.g., when it activates a new data link), it sends an RS message to 2584 the Server via the underlying interface with an OMNI option that 2585 includes Interface Attributes with appropriate link quality values 2586 and with link-layer address information for the new link. 2588 3.16.4. Deactivating Existing Links 2590 When a Client needs to deactivate an existing underlying interface, 2591 it sends an RS or uNA message to its Server with an OMNI option with 2592 appropriate Interface Attribute values - in particular, the link 2593 quality value 0 assures that neighbors will cease to use the link. 2595 If the Client needs to send RS/uNA messages over an underlying 2596 interface other than the one being deactivated, it MUST include 2597 Interface Attributes with appropriate link quality values for any 2598 underlying interfaces being deactivated. 2600 Note that when a Client deactivates an underlying interface, 2601 neighbors that have received the RS/uNA messages need not purge all 2602 references for the underlying interface from their neighbor cache 2603 entries. The Client may reactivate or reuse the underlying interface 2604 and/or its ifIndex at a later point in time, when it will send RS/uNA 2605 messages with fresh Interface Attributes to update any neighbors. 2607 3.16.5. Moving Between Servers 2609 The Client performs the procedures specified in Section 3.12.2 when 2610 it first associates with a new Server or renews its association with 2611 an existing Server. The Client also includes MS-Release identifiers 2612 in the RS message OMNI option per [I-D.templin-6man-omni-interface] 2613 if it wants the new Server to notify any old Servers from which the 2614 Client is departing. 2616 When the new Server receives the Client's RS message, it returns an 2617 RA as specified in Section 3.12.3 and sends up to 2618 MAX_NEIGHBOR_ADVERTIISEMENT uNA messages to any old Servers listed in 2619 OMNI option MS-Release identifiers. When the new Server sends a uNA 2620 message, it sets the IPv6 source address to the Client's LLA, sets 2621 the destination address to the old Server's LLA, and sets the Target 2622 Address to the Client's Subnet-Router anycast address. The new 2623 Server also includes an OMNI option with Prefix Length set to the 2624 length associated with the Client's LLA, with Interface Attributes 2625 for its own underlying interface, and with the OMNI header S/ 2626 T-ifIndex set to 0. The new Server then sets the NA R flag to 1, the 2627 S flag to 0 and the O flag to 1, then encapsulates the message in an 2628 OAL header with source set to its own DLA and destination set to the 2629 DLA of the old Server and sends the message into the spanning tree. 2631 When an old Server receives the uNA, it changes the Client's neighbor 2632 cache entry state to DEPARTED, sets the link-layer address of the 2633 Client to the new Server's DLA, and resets DepartTime. After a short 2634 delay (e.g., 2 seconds) the old Server withdraws the Client's MNP 2635 from the routing system. After DepartTime expires, the old Server 2636 deletes the Client's neighbor cache entry. 2638 The old Server also iteratively forwards a copy of the uNA message to 2639 each ROS in the Client's Report List by changing the OAL destination 2640 address to the DLA of the ROS while leaving all other fields of the 2641 message unmodified. When the ROS receives the uNA, it examines the 2642 Target address to determine the correct asymmetric neighbor cache 2643 entry and verifies that the IPv6 destination address matches the old 2644 Server. The ROS then caches the IPv6 source address as the new 2645 Server for the existing asymmetric neighbor cache entry and marks the 2646 entry as STALE. While in the STALE state, the ROS allows new data 2647 packets to flow according to any existing cached link-layer 2648 information and sends new NS(AR) messages using its own DLA as the 2649 OAL source and the DLA of the new Server as the OAL destination 2650 address to elicit NA messages that reset the asymmetric neighbor 2651 cache entry state to REACHABLE. If no new NA message is received for 2652 10 seconds while in the STALE state, the ROS deletes the neighbor 2653 cache entry. 2655 Clients SHOULD NOT move rapidly between Servers in order to avoid 2656 causing excessive oscillations in the AERO routing system. Examples 2657 of when a Client might wish to change to a different Server include a 2658 Server that has gone unreachable, topological movements of 2659 significant distance, movement to a new geographic region, movement 2660 to a new OMNI link segment, etc. 2662 When a Client moves to a new Server, some of the fragments of a 2663 multiple fragment packet may have already arrived at the old Server 2664 while others are en route to the new Server, however no special 2665 attention in the reassembly algorithm is necessary when re-routed 2666 fragments are simply treated as loss. 2668 3.17. Multicast 2670 The AERO Client provides an IGMP (IPv4) [RFC2236] or MLD (IPv6) 2671 [RFC3810] proxy service for its EUNs and/or hosted applications 2672 [RFC4605]. The Client forwards IGMP/MLD messages over any of its 2673 underlying interfaces for which group membership is required. The 2674 IGMP/MLD messages may be further forwarded by a first-hop ANET access 2675 router acting as an IGMP/MLD-snooping switch [RFC4541], then 2676 ultimately delivered to an AERO Proxy/Server acting as a Protocol 2677 Independent Multicast - Sparse-Mode (PIM-SM, or simply "PIM") 2678 Designated Router (DR) [RFC7761]. AERO Relays also act as PIM 2679 routers (i.e., the same as AERO Proxys/Servers) on behalf of nodes on 2680 INET/EUN networks. The behaviors identified in the following 2681 sections correspond to Source-Specific Multicast (SSM) and Any-Source 2682 Multicast (ASM) operational modes. 2684 3.17.1. Source-Specific Multicast (SSM) 2686 When an ROS (i.e., an AERO Proxy/Server/Relay) "X" acting as PIM 2687 router receives a Join/Prune message from a node on its downstream 2688 interfaces containing one or more ((S)ource, (G)roup) pairs, it 2689 updates its Multicast Routing Information Base (MRIB) accordingly. 2690 For each S belonging to a prefix reachable via X's non-OMNI 2691 interfaces, X then forwards the (S, G) Join/Prune to any PIM routers 2692 on those interfaces per [RFC7761]. 2694 For each S belonging to a prefix reachable via X's OMNI interface, X 2695 originates a separate copy of the Join/Prune for each (S,G) in the 2696 message using its own LLA as the source address and ALL-PIM-ROUTERS 2697 as the destination address. X then encapsulates each message in an 2698 OAL header with source address set to the DLA of X and destination 2699 address set to S then forwards the message into the spanning tree, 2700 which delivers it to AERO Server/Relay "Y" that services S. At the 2701 same time, if the message was a Join, X sends a route-optimization NS 2702 message toward each S the same as discussed in Section 3.14. The 2703 resulting NAs will return the LLA for the prefix that matches S as 2704 the network-layer source address and with an OMNI option with the DLA 2705 corresponding to any underlying interfaces that are currently 2706 servicing S. 2708 When Y processes the Join/Prune message, if S located behind any 2709 INET, Direct, or VPNed interfaces Y acts as a PIM router and updates 2710 its MRIB to list X as the next hop in the reverse path. If S is 2711 located behind any Proxys "Z"*, Y also forwards the message to each 2712 Z* over the spanning tree while continuing to use the LLA of X as the 2713 source address. Each Z* then updates its MRIB accordingly and 2714 maintains the LLA of X as the next hop in the reverse path. Since 2715 the Bridges do not examine network layer control messages, this means 2716 that the (reverse) multicast tree path is simply from each Z* (and/or 2717 Y) to X with no other multicast-aware routers in the path. If any Z* 2718 (and/or Y) is located on the same OMNI link segment as X, the 2719 multicast data traffic sent to X directly using OAL/INET 2720 encapsulation instead of via a Bridge. 2722 Following the initial Join/Prune and NS/NA messaging, X maintains an 2723 asymmetric neighbor cache entry for each S the same as if X was 2724 sending unicast data traffic to S. In particular, X performs 2725 additional NS/NA exchanges to keep the neighbor cache entry alive for 2726 up to t_periodic seconds [RFC7761]. If no new Joins are received 2727 within t_periodic seconds, X allows the neighbor cache entry to 2728 expire. Finally, if X receives any additional Join/Prune messages 2729 for (S,G) it forwards the messages to each Y and Z* in the neighbor 2730 cache entry over the spanning tree. 2732 At some later time, Client C that holds an MNP for source S may 2733 depart from a first Proxy Z1 and/or connect via a new Proxy Z2. In 2734 that case, Y sends an unsolicited NA message to X the same as 2735 specified for unicast mobility in Section 3.16. When X receives the 2736 unsolicited NA message, it updates its asymmetric neighbor cache 2737 entry for the LLA for source S and sends new Join messages to any new 2738 Proxys Z2. There is no requirement to send any Prune messages to old 2739 Proxys Z1 since source S will no longer source any multicast data 2740 traffic via Z1. Instead, the multicast state for (S,G) in Proxy Z1 2741 will soon time out since no new Joins will arrive. 2743 After some later time, C may move to a new Server Y2 and depart from 2744 old Sever Y1. In that case, Y1 sends Join messages for any of C's 2745 active (S,G) groups to Y2 while including its own LLA as the source 2746 address. This causes Y2 to include Y1 in the multicast forwarding 2747 tree during the interim time that Y1's symmetric neighbor cache entry 2748 for C is in the DEPARTED state. At the same time, Y1 sends an 2749 unsolicited NA message to X with an OMNI option with S/T-ifIndex in 2750 the header set to 0 and a release indication to cause X to release 2751 its asymmetric neighbor cache entry. X then sends a new Join message 2752 to S via the spanning tree and re-initiates route optimization the 2753 same as if it were receiving a fresh Join message from a node on a 2754 downstream link. 2756 3.17.2. Any-Source Multicast (ASM) 2758 When an ROS X acting as a PIM router receives a Join/Prune from a 2759 node on its downstream interfaces containing one or more (*,G) pairs, 2760 it updates its Multicast Routing Information Base (MRIB) accordingly. 2761 X then forwards a copy of the message to the Rendezvous Point (RP) R 2762 for each G over the spanning tree. X uses its own LLA as the source 2763 address and ALL-PIM-ROUTERS as the destination address, then 2764 encapsulates each message in an OAL header with source address set to 2765 the DLA of X and destination address set to R, then sends the message 2766 into the spanning tree. At the same time, if the message was a Join 2767 X initiates NS/NA route optimization the same as for the SSM case 2768 discussed in Section 3.17.1. 2770 For each source S that sends multicast traffic to group G via R, the 2771 Proxy/Server Z* for the Client that aggregates S encapsulates the 2772 packets in PIM Register messages and forwards them to R via the 2773 spanning tree, which may then elect to send a PIM Join to Z*. This 2774 will result in an (S,G) tree rooted at Z* with R as the next hop so 2775 that R will begin to receive two copies of the packet; one native 2776 copy from the (S, G) tree and a second copy from the pre-existing (*, 2777 G) tree that still uses PIM Register encapsulation. R can then issue 2778 a PIM Register-stop message to suppress the Register-encapsulated 2779 stream. At some later time, if C moves to a new Proxy/Server Z*, it 2780 resumes sending packets via PIM Register encapsulation via the new 2781 Z*. 2783 At the same time, as multicast listeners discover individual S's for 2784 a given G, they can initiate an (S,G) Join for each S under the same 2785 procedures discussed in Section 3.17.1. Once the (S,G) tree is 2786 established, the listeners can send (S, G) Prune messages to R so 2787 that multicast packets for group G sourced by S will only be 2788 delivered via the (S, G) tree and not from the (*, G) tree rooted at 2789 R. All mobility considerations discussed for SSM apply. 2791 3.17.3. Bi-Directional PIM (BIDIR-PIM) 2793 Bi-Directional PIM (BIDIR-PIM) [RFC5015] provides an alternate 2794 approach to ASM that treats the Rendezvous Point (RP) as a Designated 2795 Forwarder (DF). Further considerations for BIDIR-PIM are out of 2796 scope. 2798 3.18. Operation over Multiple OMNI Links 2800 An AERO Client can connect to multiple OMNI links the same as for any 2801 data link service. In that case, the Client maintains a distinct 2802 OMNI interface for each link, e.g., 'omni0' for the first link, 2803 'omni1' for the second, 'omni2' for the third, etc. Each OMNI link 2804 would include its own distinct set of Bridges, Servers and Proxys, 2805 thereby providing redundancy in case of failures. 2807 Each OMNI link could utilize the same or different ANET connections. 2808 The links can be distinguished at the link-layer via the SRT prefix 2809 in a similar fashion as for Virtual Local Area Network (VLAN) tagging 2810 (e.g., IEEE 802.1Q) and/or through assignment of distinct sets of 2811 MSPs on each link. This gives rise to the opportunity for supporting 2812 multiple redundant networked paths, with each VLAN distinguished by a 2813 different SRT "color" (see: Section 3.2.5). 2815 The Client's IP layer can select the outgoing OMNI interface 2816 appropriate for a given traffic profile while (in the reverse 2817 direction) correspondent nodes must have some way of steering their 2818 packets destined to a target via the correct OMNI link. 2820 In a first alternative, if each OMNI link services different MSPs, 2821 then the Client can receive a distinct MNP from each of the links. 2822 IP routing will therefore assure that the correct Red/Green/Blue/etc. 2823 network is used for both outbound and inbound traffic. This can be 2824 accomplished using existing technologies and approaches, and without 2825 requiring any special supporting code in correspondent nodes or 2826 Bridges. 2828 In a second alternative, if each OMNI link services the same MSP(s) 2829 then each link could assign a distinct "OMNI link Anycast" address 2830 that is configured by all Bridges on the link. Correspondent nodes 2831 can then perform Segment Routing to select the correct SRT, which 2832 will then direct the packet over multiple hops to the target. 2834 3.19. DNS Considerations 2836 AERO Client MNs and INET correspondent nodes consult the Domain Name 2837 System (DNS) the same as for any Internetworking node. When 2838 correspondent nodes and Client MNs use different IP protocol versions 2839 (e.g., IPv4 correspondents and IPv6 MNs), the INET DNS must maintain 2840 A records for IPv4 address mappings to MNs which must then be 2841 populated in Relay NAT64 mapping caches. In that way, an IPv4 2842 correspondent node can send packets to the IPv4 address mapping of 2843 the target MN, and the Relay will translate the IPv4 header and 2844 destination address into an IPv6 header and IPv6 destination address 2845 of the MN. 2847 When an AERO Client registers with an AERO Server, the Server can 2848 return the address(es) of DNS servers in RDNSS options [RFC6106]. 2849 The DNS server provides the IP addresses of other MNs and 2850 correspondent nodes in AAAA records for IPv6 or A records for IPv4. 2852 3.20. Transition Considerations 2854 OAL encapsulation ensures that dissimilar INET partitions can be 2855 joined into a single unified OMNI link, even though the partitions 2856 themselves may have differing protocol versions and/or incompatible 2857 addressing plans. However, a commonality can be achieved by 2858 incrementally distributing globally routable (i.e., native) IP 2859 prefixes to eventually reach all nodes (both mobile and fixed) in all 2860 OMNI link segments. This can be accomplished by incrementally 2861 deploying AERO Relays on each INET partition, with each Relay 2862 distributing its MNPs and/or discovering non-MNP prefixes on its INET 2863 links. 2865 This gives rise to the opportunity to eventually distribute native IP 2866 addresses to all nodes, and to present a unified OMNI link view even 2867 if the INET partitions remain in their current protocol and 2868 addressing plans. In that way, the OMNI link can serve the dual 2869 purpose of providing a mobility/multilink service and a transition 2870 service. Or, if an INET partition is transitioned to a native IP 2871 protocol version and addressing scheme that is compatible with the 2872 OMNI link MNP-based addressing scheme, the partition and OMNI link 2873 can be joined by Relays. 2875 Relays that connect INETs/EUNs with dissimilar IP protocol versions 2876 may need to employ a network address and protocol translation 2877 function such as NAT64 [RFC6146]. 2879 3.21. Detecting and Reacting to Server and Bridge Failures 2881 In environments where rapid failure recovery is required, Servers and 2882 Bridges SHOULD use Bidirectional Forwarding Detection (BFD) 2883 [RFC5880]. Nodes that use BFD can quickly detect and react to 2884 failures so that cached information is re-established through 2885 alternate nodes. BFD control messaging is carried only over well- 2886 connected ground domain networks (i.e., and not low-end radio links) 2887 and can therefore be tuned for rapid response. 2889 Servers and Bridges maintain BFD sessions in parallel with their BGP 2890 peerings. If a Server or Bridge fails, BGP peers will quickly re- 2891 establish routes through alternate paths the same as for common BGP 2892 deployments. Similarly, Proxys maintain BFD sessions with their 2893 associated Bridges even though they do not establish BGP peerings 2894 with them. 2896 Proxys SHOULD use proactive NUD for Servers for which there are 2897 currently active ANET Clients in a manner that parallels BFD, i.e., 2898 by sending unicast NS messages in rapid succession to receive 2899 solicited NA messages. When the Proxy is also sending RS messages on 2900 behalf of ANET Clients, the RS/RA messaging can be considered as 2901 equivalent hints of forward progress. This means that the Proxy need 2902 not also send a periodic NS if it has already sent an RS within the 2903 same period. If a Server fails, the Proxy will cease to receive 2904 advertisements and can quickly inform Clients of the outage by 2905 sending multicast RA messages on the ANET interface. 2907 The Proxy sends multicast RA messages with source address set to the 2908 Server's address, destination address set to (link-local) All-Nodes 2909 multicast, and Router Lifetime set to 0. The Proxy SHOULD send 2910 MAX_FINAL_RTR_ADVERTISEMENTS RA messages separated by small delays 2911 [RFC4861]. Any Clients on the ANET interface that have been using 2912 the (now defunct) Server will receive the RA messages and associate 2913 with a new Server. 2915 3.22. AERO Clients on the Open Internet 2917 AERO Clients that connect to the open Internet via INET interfaces 2918 can establish a VPN or direct link to securely connect to a Server in 2919 a "tethered" arrangement with all of the Client's traffic transiting 2920 the Server. Alternatively, the Client can associate with an INET 2921 Server using UDP/IP encapsulation and asymmetric securing services as 2922 discussed in the following sections. 2924 When a Client's OMNI interface enables an INET underlying interface, 2925 it first determines whether the interface is likely to be behind a 2926 NAT. For IPv4, the Client assumes it is on the open Internet if the 2927 INET address is not a special-use IPv4 address per [RFC3330]. 2928 Similarly for IPv6, the Client assumes it is on the open Internet if 2929 the INET address is not a link-local [RFC4291] or unique-local 2930 [RFC4193] IPv6 address. 2932 The Client then prepares a UDP/IP-encapsulated RS message with IPv6 2933 source address set to its LLA, with IPv6 destination set to (link- 2934 local) All-Routers multicast and with an OMNI option with underlying 2935 interface attributes. If the Client believes that it is on the open 2936 Internet, it SHOULD include Interface Attributes with the L2ADDR used 2937 for INET encapsulation (otherwise, it MAY omit L2ADDR). If the 2938 underlying address is IPv4, the Client includes the Port Number and 2939 IPv4 address written in obfuscated form [RFC4380] as discussed in 2940 Section 3.3. If the underlying interface address is IPv6, the Client 2941 instead includes the Port Number and IPv6 address in obfuscated form. 2942 The Client finally includes an Authentication option per [RFC4380] to 2943 provide message authentication, sets the UDP/IP source to its INET 2944 address and UDP port, sets the UDP/IP destination to the Server's 2945 INET address and the AERO service port number (8060), then sends the 2946 message to the Server. 2948 When the Server receives the RS, it authenticates the message and 2949 registers the Client's MNP and INET interface information according 2950 to the OMNI option parameters. If the RS message includes an L2ADDR 2951 in the OMNI option, the Server compares the encapsulation IP address 2952 and UDP port number with the (unobfuscated) values. If the values 2953 are the same, the Server caches the Client's information as "INET" 2954 addresses meaning that the Client is likely to accept direct messages 2955 without requiring NAT traversal exchanges. If the values are 2956 different (or, if the OMNI option did not include an L2ADDR) the 2957 Server instead caches the Client's information as "NAT" addresses 2958 meaning that NAT traversal exchanges may be necessary. 2960 The Server then returns an RA message with IPv6 source and 2961 destination set corresponding to the addresses in the RS, and with an 2962 Authentication option per [RFC4380]. For IPv4, the Server also 2963 includes an Origin option per [RFC4380] with the mapped and 2964 obfuscated Port Number and IPv4 address observed in the encapsulation 2965 headers. For IPv6, the Server instead includes an IPv6 Origin option 2966 per Figure 6 with the mapped and obfuscated observed Port Number and 2967 IPv6 address (note that the value 0x02 in the second octet 2968 differentiates from other [RFC4380] option types). 2970 +--------+--------+-----------------+ 2971 | 0x00 | 0x02 | Origin port # | 2972 +--------+--------+-----------------+ 2973 ~ Origin IPv6 address ~ 2974 +-----------------------------------+ 2976 Figure 6: IPv6 Origin Option 2978 When the Client receives the RA message, it compares the mapped Port 2979 Number and IP address from the Origin option with its own address. 2980 If the addresses are the same, the Client assumes the open Internet / 2981 Cone NAT principle; if the addresses are different, the Client 2982 instead assumes that further qualification procedures are necessary 2983 to detect the type of NAT and proceeds according to standard 2984 [RFC4380] procedures. 2986 After the Client has registered its INET interfaces in such RS/RA 2987 exchanges it sends periodic RS messages to receive fresh RA messages 2988 before the Router Lifetime received on each INET interface expires. 2989 The Client also maintains default routes via its Servers, i.e., the 2990 same as described in earlier sections. 2992 When the Client sends messages to target IP addresses, it also 2993 invokes route optimization per Section 3.14 using IPv6 ND address 2994 resolution messaging. The Client sends the NS(AR) message to the 2995 Server wrapped in a UDP/IP header with an Authentication option with 2996 the NS source address set to the Client's LLA and destination address 2997 set to the target solicited node multicast address. The Server 2998 authenticates the message and sends a corresponding NS(AR) message 2999 over the spanning tree the same as if it were the ROS, but with the 3000 OAL source address set to the Server's DLA and destination set to the 3001 DLA of the target. When the ROR receives the NS(AR), it adds the 3002 Server's DLA and Client's LLA to the target's Report List, and 3003 returns an NA with OMNI option information for the target. The 3004 Server then returns a UDP/IP encapsulated NA message with an 3005 Authentication option to the Client. 3007 Following route optimization for targets in the same OMNI link 3008 segment, if the target's L2ADDR is on the open INET, the Client 3009 forwards data packets directly to the target INET address. If the 3010 target is behind a NAT, the Client first establishes NAT state for 3011 the L2ADDR using the "bubble" mechanisms specified in 3012 [RFC6081][RFC4380]. The Client continues to send data packets via 3013 its Server until NAT state is populated, then begins forwarding 3014 packets via the direct path through the NAT to the target. For 3015 targets in different OMNI link segments, the Client uses OAL/ORH 3016 encapsulation and forwards data packets to the Bridge that returned 3017 the NA message. 3019 The ROR may return uNAs via the Server if the target moves, and the 3020 Server will send corresponding Authentication-protected uNAs to the 3021 Client. The Client can also send "loopback" NS(NUD) messages to test 3022 forward path reachability even though there is no security 3023 association between the Client and the target. 3025 The Client sends UDP/IP encapsulated IPv6 packets no larger than 1280 3026 bytes in one piece. In order to accommodate larger IPv6 packets (up 3027 to the OMNI interface MTU), the Client inserts an OAL header with 3028 source set to its own DLA and destination set to the DLA of the 3029 target and uses IPv6 fragmentation according to Section 3.9. The 3030 Client then encapsulates each fragment in a UDP/IP header and sends 3031 the fragments to the next hop. 3033 3.23. Time-Varying MNPs 3035 In some use cases, it is desirable, beneficial and efficient for the 3036 Client to receive a constant MNP that travels with the Client 3037 wherever it moves. For example, this would allow air traffic 3038 controllers to easily track aircraft, etc. In other cases, however 3039 (e.g., intelligent transportation systems), the MN may be willing to 3040 sacrifice a modicum of efficiency in order to have time-varying MNPs 3041 that can be changed every so often to defeat adversarial tracking. 3043 The DHCPv6 service offers a way for Clients that desire time-varying 3044 MNPs to obtain short-lived prefixes (e.g., on the order of a small 3045 number of minutes). In that case, the identity of the Client would 3046 not be bound to the MNP but rather the Client's identity would be 3047 bound to the DHCPv6 Device Unique Identifier (DUID) and used as the 3048 seed for Prefix Delegation. The Client would then be obligated to 3049 renumber its internal networks whenever its MNP (and therefore also 3050 its LLA) changes. This should not present a challenge for Clients 3051 with automated network renumbering services, however presents limits 3052 for the durations of ongoing sessions that would prefer to use a 3053 constant address. 3055 4. Implementation Status 3057 An early AERO implementation based on OpenVPN (https://openvpn.net/) 3058 was announced on the v6ops mailing list on January 10, 2018 and an 3059 initial public release of the AERO proof-of-concept source code was 3060 announced on the intarea mailing list on August 21, 2015. 3062 AERO Release-3.0.2 was tagged on October 15, 2020, and is undergoing 3063 internal testing. Additional releases expected Q42020, with first 3064 public release expected before year-end. 3066 5. IANA Considerations 3068 The IANA has assigned a 4-octet Private Enterprise Number "45282" for 3069 AERO in the "enterprise-numbers" registry. 3071 The IANA has assigned the UDP port number "8060" for an earlier 3072 experimental version of AERO [RFC6706]. This document obsoletes 3073 [RFC6706] and claims the UDP port number "8060" for all future use. 3075 The IANA is instructed to assign a new type value TBD in the IPv6 3076 Routing Types registry. 3078 No further IANA actions are required. 3080 6. Security Considerations 3082 AERO Bridges configure secured tunnels with AERO Servers, Relays and 3083 Proxys within their local OMNI link segments. Applicable secured 3084 tunnel alternatives include IPsec [RFC4301], TLS/SSL [RFC8446], DTLS 3085 [RFC6347], WireGuard [WG], etc. The AERO Bridges of all OMNI link 3086 segments in turn configure secured tunnels for their neighboring AERO 3087 Bridges in a spanning tree topology. Therefore, control messages 3088 exchanged between any pair of OMNI link neighbors on the spanning 3089 tree are already secured. 3091 AERO Servers, Relays and Proxys targeted by a route optimization may 3092 also receive data packets directly from arbitrary nodes in INET 3093 partitions instead of via the spanning tree. For INET partitions 3094 that apply effective ingress filtering to defeat source address 3095 spoofing, the simple data origin authentication procedures in 3096 Section 3.8 can be applied. 3098 For INET partitions that require strong security in the data plane, 3099 two options for securing communications include 1) disable route 3100 optimization so that all traffic is conveyed over secured tunnels, or 3101 2) enable on-demand secure tunnel creation between INET partition 3102 neighbors. Option 1) would result in longer routes than necessary 3103 and traffic concentration on critical infrastructure elements. 3104 Option 2) could be coordinated by establishing a secured tunnel on- 3105 demand instead of performing an NS/NA exchange in the route 3106 optimization procedures. Procedures for establishing on-demand 3107 secured tunnels are out of scope. 3109 AERO Clients that connect to secured ANETs need not apply security to 3110 their ND messages, since the messages will be intercepted by a 3111 perimeter Proxy that applies security on its INET-facing interface as 3112 part of the spanning tree (see above). AERO Clients connected to the 3113 open INET can use symmetric network and/or transport layer security 3114 services such as VPNs or can by some other means establish a direct 3115 link. When a VPN or direct link may be impractical, however, an 3116 asymmetric security service such as the Authentication option 3117 specified in [RFC4380] should be applied. The Authentication option 3118 requires a unique Client identifier, which can be obtained per the 3119 Universally Unique IDentifier (UUID) [RFC4122] service and also used 3120 as a DHCP Unique Identifier (DUID) per [RFC6355]. 3122 Application endpoints SHOULD use application-layer security services 3123 such as TLS/SSL, DTLS or SSH [RFC4251] to assure the same level of 3124 protection as for critical secured Internet services. AERO Clients 3125 that require host-based VPN services SHOULD use symmetric network 3126 and/or transport layer security services such as IPsec, TLS/SSL, 3127 DTLS, etc. AERO Proxys and Servers can also provide a network-based 3128 VPN service on behalf of the Client, e.g., if the Client is located 3129 within a secured enclave and cannot establish a VPN on its own 3130 behalf. 3132 AERO Servers and Bridges present targets for traffic amplification 3133 Denial of Service (DoS) attacks. This concern is no different than 3134 for widely-deployed VPN security gateways in the Internet, where 3135 attackers could send spoofed packets to the gateways at high data 3136 rates. This can be mitigated by connecting Servers and Bridges over 3137 dedicated links with no connections to the Internet and/or when 3138 connections to the Internet are only permitted through well-managed 3139 firewalls. Traffic amplification DoS attacks can also target an AERO 3140 Client's low data rate links. This is a concern not only for Clients 3141 located on the open Internet but also for Clients in secured 3142 enclaves. AERO Servers and Proxys can institute rate limits that 3143 protect Clients from receiving packet floods that could DoS low data 3144 rate links. 3146 AERO Relays must implement ingress filtering to avoid a spoofing 3147 attack in which spurious messages with DLA addresses are injected 3148 into an OMNI link from an outside attacker. AERO Clients MUST ensure 3149 that their connectivity is not used by unauthorized nodes on their 3150 EUNs to gain access to a protected network, i.e., AERO Clients that 3151 act as routers MUST NOT provide routing services for unauthorized 3152 nodes. (This concern is no different than for ordinary hosts that 3153 receive an IP address delegation but then "share" the address with 3154 other nodes via some form of Internet connection sharing such as 3155 tethering.) 3157 The MAP list MUST be well-managed and secured from unauthorized 3158 tampering, even though the list contains only public information. 3159 The MAP list can be conveyed to the Client in a similar fashion as in 3160 [RFC5214] (e.g., through layer 2 data link login messaging, secure 3161 upload of a static file, DNS lookups, etc.). 3163 SRH authentication facilities are specified in [RFC8754]. 3165 Security considerations for accepting link-layer ICMP messages and 3166 reflected packets are discussed throughout the document. 3168 Security considerations for IPv6 fragmentation and reassembly are 3169 discussed in [I-D.templin-6man-omni-interface]. 3171 7. Acknowledgements 3173 Discussions in the IETF, aviation standards communities and private 3174 exchanges helped shape some of the concepts in this work. 3175 Individuals who contributed insights include Mikael Abrahamsson, Mark 3176 Andrews, Fred Baker, Bob Braden, Stewart Bryant, Brian Carpenter, 3177 Wojciech Dec, Pavel Drasil, Ralph Droms, Adrian Farrel, Nick Green, 3178 Sri Gundavelli, Brian Haberman, Bernhard Haindl, Joel Halpern, Tom 3179 Herbert, Sascha Hlusiak, Lee Howard, Zdenek Jaron, Andre Kostur, 3180 Hubert Kuenig, Ted Lemon, Andy Malis, Satoru Matsushima, Tomek 3181 Mrugalski, Madhu Niraula, Alexandru Petrescu, Behcet Saikaya, Michal 3182 Skorepa, Joe Touch, Bernie Volz, Ryuji Wakikawa, Tony Whyman, Lloyd 3183 Wood and James Woodyatt. Members of the IESG also provided valuable 3184 input during their review process that greatly improved the document. 3185 Special thanks go to Stewart Bryant, Joel Halpern and Brian Haberman 3186 for their shepherding guidance during the publication of the AERO 3187 first edition. 3189 This work has further been encouraged and supported by Boeing 3190 colleagues including Kyle Bae, M. Wayne Benson, Dave Bernhardt, Cam 3191 Brodie, John Bush, Balaguruna Chidambaram, Irene Chin, Bruce Cornish, 3192 Claudiu Danilov, Don Dillenburg, Joe Dudkowski, Wen Fang, Samad 3193 Farooqui, Anthony Gregory, Jeff Holland, Seth Jahne, Brian Jaury, 3194 Greg Kimberly, Ed King, Madhuri Madhava Badgandi, Laurel Matthew, 3195 Gene MacLean III, Rob Muszkiewicz, Sean O'Sullivan, Vijay 3196 Rajagopalan, Greg Saccone, Rod Santiago, Kent Shuey, Brian Skeen, 3197 Mike Slane, Carrie Spiker, Katie Tran, Brendan Williams, Amelia 3198 Wilson, Julie Wulff, Yueli Yang, Eric Yeh and other members of the 3199 Boeing mobility, networking and autonomy teams. Kyle Bae, Wayne 3200 Benson, Katie Tran and Eric Yeh are especially acknowledged for 3201 implementing the AERO functions as extensions to the public domain 3202 OpenVPN distribution. 3204 Earlier works on NBMA tunneling approaches are found in 3205 [RFC2529][RFC5214][RFC5569]. 3207 Many of the constructs presented in this second edition of AERO are 3208 based on the author's earlier works, including: 3210 o The Internet Routing Overlay Network (IRON) 3211 [RFC6179][I-D.templin-ironbis] 3213 o Virtual Enterprise Traversal (VET) 3214 [RFC5558][I-D.templin-intarea-vet] 3216 o The Subnetwork Encapsulation and Adaptation Layer (SEAL) 3217 [RFC5320][I-D.templin-intarea-seal] 3219 o AERO, First Edition [RFC6706] 3221 Note that these works cite numerous earlier efforts that are not also 3222 cited here due to space limitations. The authors of those earlier 3223 works are acknowledged for their insights. 3225 This work is aligned with the NASA Safe Autonomous Systems Operation 3226 (SASO) program under NASA contract number NNA16BD84C. 3228 This work is aligned with the FAA as per the SE2025 contract number 3229 DTFAWA-15-D-00030. 3231 This work is aligned with the Boeing Commercial Airplanes (BCA) 3232 Internet of Things (IoT) and autonomy programs. 3234 This work is aligned with the Boeing Information Technology (BIT) 3235 MobileNet program. 3237 8. References 3239 8.1. Normative References 3241 [I-D.templin-6man-omni-interface] 3242 Templin, F. and T. Whyman, "Transmission of IP Packets 3243 over Overlay Multilink Network (OMNI) Interfaces", draft- 3244 templin-6man-omni-interface-54 (work in progress), 3245 December 2020. 3247 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, 3248 DOI 10.17487/RFC0791, September 1981, 3249 . 3251 [RFC0792] Postel, J., "Internet Control Message Protocol", STD 5, 3252 RFC 792, DOI 10.17487/RFC0792, September 1981, 3253 . 3255 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 3256 Requirement Levels", BCP 14, RFC 2119, 3257 DOI 10.17487/RFC2119, March 1997, 3258 . 3260 [RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in 3261 IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473, 3262 December 1998, . 3264 [RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander, 3265 "SEcure Neighbor Discovery (SEND)", RFC 3971, 3266 DOI 10.17487/RFC3971, March 2005, 3267 . 3269 [RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)", 3270 RFC 3972, DOI 10.17487/RFC3972, March 2005, 3271 . 3273 [RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and 3274 More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191, 3275 November 2005, . 3277 [RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast 3278 Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005, 3279 . 3281 [RFC4380] Huitema, C., "Teredo: Tunneling IPv6 over UDP through 3282 Network Address Translations (NATs)", RFC 4380, 3283 DOI 10.17487/RFC4380, February 2006, 3284 . 3286 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 3287 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 3288 DOI 10.17487/RFC4861, September 2007, 3289 . 3291 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 3292 Address Autoconfiguration", RFC 4862, 3293 DOI 10.17487/RFC4862, September 2007, 3294 . 3296 [RFC6081] Thaler, D., "Teredo Extensions", RFC 6081, 3297 DOI 10.17487/RFC6081, January 2011, 3298 . 3300 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 3301 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 3302 May 2017, . 3304 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 3305 (IPv6) Specification", STD 86, RFC 8200, 3306 DOI 10.17487/RFC8200, July 2017, 3307 . 3309 [RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A., 3310 Richardson, M., Jiang, S., Lemon, T., and T. Winters, 3311 "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", 3312 RFC 8415, DOI 10.17487/RFC8415, November 2018, 3313 . 3315 8.2. Informative References 3317 [BGP] Huston, G., "BGP in 2015, http://potaroo.net", January 3318 2016. 3320 [I-D.bonica-6man-comp-rtg-hdr] 3321 Bonica, R., Kamite, Y., Alston, A., Henriques, D., and L. 3322 Jalil, "The IPv6 Compact Routing Header (CRH)", draft- 3323 bonica-6man-comp-rtg-hdr-23 (work in progress), October 3324 2020. 3326 [I-D.bonica-6man-crh-helper-opt] 3327 Li, X., Bao, C., Ruan, E., and R. Bonica, "Compressed 3328 Routing Header (CRH) Helper Option", draft-bonica-6man- 3329 crh-helper-opt-02 (work in progress), October 2020. 3331 [I-D.ietf-intarea-frag-fragile] 3332 Bonica, R., Baker, F., Huston, G., Hinden, R., Troan, O., 3333 and F. Gont, "IP Fragmentation Considered Fragile", draft- 3334 ietf-intarea-frag-fragile-17 (work in progress), September 3335 2019. 3337 [I-D.ietf-intarea-tunnels] 3338 Touch, J. and M. Townsley, "IP Tunnels in the Internet 3339 Architecture", draft-ietf-intarea-tunnels-10 (work in 3340 progress), September 2019. 3342 [I-D.ietf-rtgwg-atn-bgp] 3343 Templin, F., Saccone, G., Dawra, G., Lindem, A., and V. 3344 Moreno, "A Simple BGP-based Mobile Routing System for the 3345 Aeronautical Telecommunications Network", draft-ietf- 3346 rtgwg-atn-bgp-06 (work in progress), June 2020. 3348 [I-D.templin-6man-dhcpv6-ndopt] 3349 Templin, F., "A Unified Stateful/Stateless Configuration 3350 Service for IPv6", draft-templin-6man-dhcpv6-ndopt-10 3351 (work in progress), June 2020. 3353 [I-D.templin-intarea-seal] 3354 Templin, F., "The Subnetwork Encapsulation and Adaptation 3355 Layer (SEAL)", draft-templin-intarea-seal-68 (work in 3356 progress), January 2014. 3358 [I-D.templin-intarea-vet] 3359 Templin, F., "Virtual Enterprise Traversal (VET)", draft- 3360 templin-intarea-vet-40 (work in progress), May 2013. 3362 [I-D.templin-ironbis] 3363 Templin, F., "The Interior Routing Overlay Network 3364 (IRON)", draft-templin-ironbis-16 (work in progress), 3365 March 2014. 3367 [I-D.templin-v6ops-pdhost] 3368 Templin, F., "IPv6 Prefix Delegation and Multi-Addressing 3369 Models", draft-templin-v6ops-pdhost-26 (work in progress), 3370 June 2020. 3372 [OVPN] OpenVPN, O., "http://openvpn.net", October 2016. 3374 [RFC1035] Mockapetris, P., "Domain names - implementation and 3375 specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, 3376 November 1987, . 3378 [RFC1812] Baker, F., Ed., "Requirements for IP Version 4 Routers", 3379 RFC 1812, DOI 10.17487/RFC1812, June 1995, 3380 . 3382 [RFC2003] Perkins, C., "IP Encapsulation within IP", RFC 2003, 3383 DOI 10.17487/RFC2003, October 1996, 3384 . 3386 [RFC2004] Perkins, C., "Minimal Encapsulation within IP", RFC 2004, 3387 DOI 10.17487/RFC2004, October 1996, 3388 . 3390 [RFC2236] Fenner, W., "Internet Group Management Protocol, Version 3391 2", RFC 2236, DOI 10.17487/RFC2236, November 1997, 3392 . 3394 [RFC2464] Crawford, M., "Transmission of IPv6 Packets over Ethernet 3395 Networks", RFC 2464, DOI 10.17487/RFC2464, December 1998, 3396 . 3398 [RFC2529] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4 3399 Domains without Explicit Tunnels", RFC 2529, 3400 DOI 10.17487/RFC2529, March 1999, 3401 . 3403 [RFC2983] Black, D., "Differentiated Services and Tunnels", 3404 RFC 2983, DOI 10.17487/RFC2983, October 2000, 3405 . 3407 [RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition 3408 of Explicit Congestion Notification (ECN) to IP", 3409 RFC 3168, DOI 10.17487/RFC3168, September 2001, 3410 . 3412 [RFC3330] IANA, "Special-Use IPv4 Addresses", RFC 3330, 3413 DOI 10.17487/RFC3330, September 2002, 3414 . 3416 [RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener 3417 Discovery Version 2 (MLDv2) for IPv6", RFC 3810, 3418 DOI 10.17487/RFC3810, June 2004, 3419 . 3421 [RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally 3422 Unique IDentifier (UUID) URN Namespace", RFC 4122, 3423 DOI 10.17487/RFC4122, July 2005, 3424 . 3426 [RFC4251] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH) 3427 Protocol Architecture", RFC 4251, DOI 10.17487/RFC4251, 3428 January 2006, . 3430 [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A 3431 Border Gateway Protocol 4 (BGP-4)", RFC 4271, 3432 DOI 10.17487/RFC4271, January 2006, 3433 . 3435 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 3436 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 3437 2006, . 3439 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 3440 Internet Protocol", RFC 4301, DOI 10.17487/RFC4301, 3441 December 2005, . 3443 [RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery 3444 Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April 3445 2006, . 3447 [RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet 3448 Control Message Protocol (ICMPv6) for the Internet 3449 Protocol Version 6 (IPv6) Specification", STD 89, 3450 RFC 4443, DOI 10.17487/RFC4443, March 2006, 3451 . 3453 [RFC4511] Sermersheim, J., Ed., "Lightweight Directory Access 3454 Protocol (LDAP): The Protocol", RFC 4511, 3455 DOI 10.17487/RFC4511, June 2006, 3456 . 3458 [RFC4541] Christensen, M., Kimball, K., and F. Solensky, 3459 "Considerations for Internet Group Management Protocol 3460 (IGMP) and Multicast Listener Discovery (MLD) Snooping 3461 Switches", RFC 4541, DOI 10.17487/RFC4541, May 2006, 3462 . 3464 [RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick, 3465 "Internet Group Management Protocol (IGMP) / Multicast 3466 Listener Discovery (MLD)-Based Multicast Forwarding 3467 ("IGMP/MLD Proxying")", RFC 4605, DOI 10.17487/RFC4605, 3468 August 2006, . 3470 [RFC4982] Bagnulo, M. and J. Arkko, "Support for Multiple Hash 3471 Algorithms in Cryptographically Generated Addresses 3472 (CGAs)", RFC 4982, DOI 10.17487/RFC4982, July 2007, 3473 . 3475 [RFC5015] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano, 3476 "Bidirectional Protocol Independent Multicast (BIDIR- 3477 PIM)", RFC 5015, DOI 10.17487/RFC5015, October 2007, 3478 . 3480 [RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site 3481 Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214, 3482 DOI 10.17487/RFC5214, March 2008, 3483 . 3485 [RFC5320] Templin, F., Ed., "The Subnetwork Encapsulation and 3486 Adaptation Layer (SEAL)", RFC 5320, DOI 10.17487/RFC5320, 3487 February 2010, . 3489 [RFC5522] Eddy, W., Ivancic, W., and T. Davis, "Network Mobility 3490 Route Optimization Requirements for Operational Use in 3491 Aeronautics and Space Exploration Mobile Networks", 3492 RFC 5522, DOI 10.17487/RFC5522, October 2009, 3493 . 3495 [RFC5558] Templin, F., Ed., "Virtual Enterprise Traversal (VET)", 3496 RFC 5558, DOI 10.17487/RFC5558, February 2010, 3497 . 3499 [RFC5569] Despres, R., "IPv6 Rapid Deployment on IPv4 3500 Infrastructures (6rd)", RFC 5569, DOI 10.17487/RFC5569, 3501 January 2010, . 3503 [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 3504 (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, 3505 . 3507 [RFC6106] Jeong, J., Park, S., Beloeil, L., and S. Madanapalli, 3508 "IPv6 Router Advertisement Options for DNS Configuration", 3509 RFC 6106, DOI 10.17487/RFC6106, November 2010, 3510 . 3512 [RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful 3513 NAT64: Network Address and Protocol Translation from IPv6 3514 Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146, 3515 April 2011, . 3517 [RFC6179] Templin, F., Ed., "The Internet Routing Overlay Network 3518 (IRON)", RFC 6179, DOI 10.17487/RFC6179, March 2011, 3519 . 3521 [RFC6221] Miles, D., Ed., Ooghe, S., Dec, W., Krishnan, S., and A. 3522 Kavanagh, "Lightweight DHCPv6 Relay Agent", RFC 6221, 3523 DOI 10.17487/RFC6221, May 2011, 3524 . 3526 [RFC6273] Kukec, A., Krishnan, S., and S. Jiang, "The Secure 3527 Neighbor Discovery (SEND) Hash Threat Analysis", RFC 6273, 3528 DOI 10.17487/RFC6273, June 2011, 3529 . 3531 [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer 3532 Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, 3533 January 2012, . 3535 [RFC6355] Narten, T. and J. Johnson, "Definition of the UUID-Based 3536 DHCPv6 Unique Identifier (DUID-UUID)", RFC 6355, 3537 DOI 10.17487/RFC6355, August 2011, 3538 . 3540 [RFC6438] Carpenter, B. and S. Amante, "Using the IPv6 Flow Label 3541 for Equal Cost Multipath Routing and Link Aggregation in 3542 Tunnels", RFC 6438, DOI 10.17487/RFC6438, November 2011, 3543 . 3545 [RFC6706] Templin, F., Ed., "Asymmetric Extended Route Optimization 3546 (AERO)", RFC 6706, DOI 10.17487/RFC6706, August 2012, 3547 . 3549 [RFC6935] Eubanks, M., Chimento, P., and M. Westerlund, "IPv6 and 3550 UDP Checksums for Tunneled Packets", RFC 6935, 3551 DOI 10.17487/RFC6935, April 2013, 3552 . 3554 [RFC6936] Fairhurst, G. and M. Westerlund, "Applicability Statement 3555 for the Use of IPv6 UDP Datagrams with Zero Checksums", 3556 RFC 6936, DOI 10.17487/RFC6936, April 2013, 3557 . 3559 [RFC7333] Chan, H., Ed., Liu, D., Seite, P., Yokota, H., and J. 3560 Korhonen, "Requirements for Distributed Mobility 3561 Management", RFC 7333, DOI 10.17487/RFC7333, August 2014, 3562 . 3564 [RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I., 3565 Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent 3566 Multicast - Sparse Mode (PIM-SM): Protocol Specification 3567 (Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March 3568 2016, . 3570 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 3571 Decraene, B., Litkowski, S., and R. Shakir, "Segment 3572 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 3573 July 2018, . 3575 [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol 3576 Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, 3577 . 3579 [RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J., 3580 Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header 3581 (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020, 3582 . 3584 [WG] Wireguard, "Wireguard, https://www.wireguard.com", August 3585 2020. 3587 Appendix A. Non-Normative Considerations 3589 AERO can be applied to a multitude of Internetworking scenarios, with 3590 each having its own adaptations. The following considerations are 3591 provided as non-normative guidance: 3593 A.1. Implementation Strategies for Route Optimization 3595 Route optimization as discussed in Section 3.14 results in the route 3596 optimization source (ROS) creating an asymmetric neighbor cache entry 3597 for the target neighbor. The neighbor cache entry is maintained for 3598 at most ReachableTime seconds and then deleted unless updated. In 3599 order to refresh the neighbor cache entry lifetime before the 3600 ReachableTime timer expires, the specification requires 3601 implementations to issue a new NS/NA exchange to reset ReachableTime 3602 while data packets are still flowing. However, the decision of when 3603 to initiate a new NS/NA exchange and to perpetuate the process is 3604 left as an implementation detail. 3606 One possible strategy may be to monitor the neighbor cache entry 3607 watching for data packets for (ReachableTime - 5) seconds. If any 3608 data packets have been sent to the neighbor within this timeframe, 3609 then send an NS to receive a new NA. If no data packets have been 3610 sent, wait for 5 additional seconds and send an immediate NS if any 3611 data packets are sent within this "expiration pending" 5 second 3612 window. If no additional data packets are sent within the 5 second 3613 window, delete the neighbor cache entry. 3615 The monitoring of the neighbor data packet traffic therefore becomes 3616 an asymmetric ongoing process during the neighbor cache entry 3617 lifetime. If the neighbor cache entry expires, future data packets 3618 will trigger a new NS/NA exchange while the packets themselves are 3619 delivered over a longer path until route optimization state is re- 3620 established. 3622 A.2. Implicit Mobility Management 3624 OMNI interface neighbors MAY provide a configuration option that 3625 allows them to perform implicit mobility management in which no ND 3626 messaging is used. In that case, the Client only transmits packets 3627 over a single interface at a time, and the neighbor always observes 3628 packets arriving from the Client from the same link-layer source 3629 address. 3631 If the Client's underlying interface address changes (either due to a 3632 readdressing of the original interface or switching to a new 3633 interface) the neighbor immediately updates the neighbor cache entry 3634 for the Client and begins accepting and sending packets according to 3635 the Client's new address. This implicit mobility method applies to 3636 use cases such as cellphones with both WiFi and Cellular interfaces 3637 where only one of the interfaces is active at a given time, and the 3638 Client automatically switches over to the backup interface if the 3639 primary interface fails. 3641 A.3. Direct Underlying Interfaces 3643 When a Client's OMNI interface is configured over a Direct interface, 3644 the neighbor at the other end of the Direct link can receive packets 3645 without any encapsulation. In that case, the Client sends packets 3646 over the Direct link according to QoS preferences. If the Direct 3647 interface has the highest QoS preference, then the Client's IP 3648 packets are transmitted directly to the peer without going through an 3649 ANET/INET. If other interfaces have higher QoS preferences, then the 3650 Client's IP packets are transmitted via a different interface, which 3651 may result in the inclusion of Proxys, Servers and Bridges in the 3652 communications path. Direct interfaces must be tested periodically 3653 for reachability, e.g., via NUD. 3655 A.4. AERO Critical Infrastructure Considerations 3657 AERO Bridges can be either Commercial off-the Shelf (COTS) standard 3658 IP routers or virtual machines in the cloud. Bridges must be 3659 provisioned, supported and managed by the INET administrative 3660 authority, and connected to the Bridges of other INETs via inter- 3661 domain peerings. Cost for purchasing, configuring and managing 3662 Bridges is nominal even for very large OMNI links. 3664 AERO Servers can be standard dedicated server platforms, but most 3665 often will be deployed as virtual machines in the cloud. The only 3666 requirements for Servers are that they can run the AERO user-level 3667 code and have at least one network interface connection to the INET. 3668 As with Bridges, Servers must be provisioned, supported and managed 3669 by the INET administrative authority. Cost for purchasing, 3670 configuring and managing Servers is nominal especially for virtual 3671 Servers hosted in the cloud. 3673 AERO Proxys are most often standard dedicated server platforms with 3674 one network interface connected to the ANET and a second interface 3675 connected to an INET. As with Servers, the only requirements are 3676 that they can run the AERO user-level code and have at least one 3677 interface connection to the INET. Proxys must be provisioned, 3678 supported and managed by the ANET administrative authority. Cost for 3679 purchasing, configuring and managing Proxys is nominal, and borne by 3680 the ANET administrative authority. 3682 AERO Relays can be any dedicated server or COTS router platform 3683 connected to INETs and/or EUNs. The Relay connects to the OMNI link 3684 and engages in eBGP peering with one or more Bridges as a stub AS. 3685 The Relay then injects its MNPs and/or non-MNP prefixes into the BGP 3686 routing system, and provisions the prefixes to its downstream- 3687 attached networks. The Relay can perform ROS/ROR services the same 3688 as for any Server, and can route between the MNP and non-MNP address 3689 spaces. 3691 A.5. AERO Server Failure Implications 3693 AERO Servers may appear as a single point of failure in the 3694 architecture, but such is not the case since all Servers on the link 3695 provide identical services and loss of a Server does not imply 3696 immediate and/or comprehensive communication failures. Although 3697 Clients typically associate with a single Server at a time, Server 3698 failure is quickly detected and conveyed by Bidirectional Forward 3699 Detection (BFD) and/or proactive NUD allowing Clients to migrate to 3700 new Servers. 3702 If a Server fails, ongoing packet forwarding to Clients will continue 3703 by virtue of the asymmetric neighbor cache entries that have already 3704 been established in route optimization sources (ROSs). If a Client 3705 also experiences mobility events at roughly the same time the Server 3706 fails, unsolicited NA messages may be lost but proxy neighbor cache 3707 entries in the DEPARTED state will ensure that packet forwarding to 3708 the Client's new locations will continue for up to DepartTime 3709 seconds. 3711 If a Client is left without a Server for an extended timeframe (e.g., 3712 greater than ReachableTime seconds) then existing asymmetric neighbor 3713 cache entries will eventually expire and both ongoing and new 3714 communications will fail. The original source will continue to 3715 retransmit until the Client has established a new Server 3716 relationship, after which time continuous communications will resume. 3718 Therefore, providing many Servers on the link with high availability 3719 profiles provides resilience against loss of individual Servers and 3720 assurance that Clients can establish new Server relationships quickly 3721 in event of a Server failure. 3723 A.6. AERO Client / Server Architecture 3725 The AERO architectural model is client / server in the control plane, 3726 with route optimization in the data plane. The same as for common 3727 Internet services, the AERO Client discovers the addresses of AERO 3728 Servers and selects one Server to connect to. The AERO service is 3729 analogous to common Internet services such as google.com, yahoo.com, 3730 cnn.com, etc. However, there is only one AERO service for the link 3731 and all Servers provide identical services. 3733 Common Internet services provide differing strategies for advertising 3734 server addresses to clients. The strategy is conveyed through the 3735 DNS resource records returned in response to name resolution queries. 3736 As of January 2020 Internet-based 'nslookup' services were used to 3737 determine the following: 3739 o When a client resolves the domainname "google.com", the DNS always 3740 returns one A record (i.e., an IPv4 address) and one AAAA record 3741 (i.e., an IPv6 address). The client receives the same addresses 3742 each time it resolves the domainname via the same DNS resolver, 3743 but may receive different addresses when it resolves the 3744 domainname via different DNS resolvers. But, in each case, 3745 exactly one A and one AAAA record are returned. 3747 o When a client resolves the domainname "ietf.org", the DNS always 3748 returns one A record and one AAAA record with the same addresses 3749 regardless of which DNS resolver is used. 3751 o When a client resolves the domainname "yahoo.com", the DNS always 3752 returns a list of 4 A records and 4 AAAA records. Each time the 3753 client resolves the domainname via the same DNS resolver, the same 3754 list of addresses are returned but in randomized order (i.e., 3755 consistent with a DNS round-robin strategy). But, interestingly, 3756 the same addresses are returned (albeit in randomized order) when 3757 the domainname is resolved via different DNS resolvers. 3759 o When a client resolves the domainname "amazon.com", the DNS always 3760 returns a list of 3 A records and no AAAA records. As with 3761 "yahoo.com", the same three A records are returned from any 3762 worldwide Internet connection point in randomized order. 3764 The above example strategies show differing approaches to Internet 3765 resilience and service distribution offered by major Internet 3766 services. The Google approach exposes only a single IPv4 and a 3767 single IPv6 address to clients. Clients can then select whichever IP 3768 protocol version offers the best response, but will always use the 3769 same IP address according to the current Internet connection point. 3770 This means that the IP address offered by the network must lead to a 3771 highly-available server and/or service distribution point. In other 3772 words, resilience is predicated on high availability within the 3773 network and with no client-initiated failovers expected (i.e., it is 3774 all-or-nothing from the client's perspective). However, Google does 3775 provide for worldwide distributed service distribution by virtue of 3776 the fact that each Internet connection point responds with a 3777 different IPv6 and IPv4 address. The IETF approach is like google 3778 (all-or-nothing from the client's perspective), but provides only a 3779 single IPv4 or IPv6 address on a worldwide basis. This means that 3780 the addresses must be made highly-available at the network level with 3781 no client failover possibility, and if there is any worldwide service 3782 distribution it would need to be conducted by a network element that 3783 is reached via the IP address acting as a service distribution point. 3785 In contrast to the Google and IETF philosophies, Yahoo and Amazon 3786 both provide clients with a (short) list of IP addresses with Yahoo 3787 providing both IP protocol versions and Amazon as IPv4-only. The 3788 order of the list is randomized with each name service query 3789 response, with the effect of round-robin load balancing for service 3790 distribution. With a short list of addresses, there is still 3791 expectation that the network will implement high availability for 3792 each address but in case any single address fails the client can 3793 switch over to using a different address. The balance then becomes 3794 one of function in the network vs function in the end system. 3796 The same implications observed for common highly-available services 3797 in the Internet apply also to the AERO client/server architecture. 3798 When an AERO Client connects to one or more ANETs, it discovers one 3799 or more AERO Server addresses through the mechanisms discussed in 3800 earlier sections. Each Server address presumably leads to a fault- 3801 tolerant clustering arrangement such as supported by Linux-HA, 3802 Extended Virtual Synchrony or Paxos. Such an arrangement has 3803 precedence in common Internet service deployments in lightweight 3804 virtual machines without requiring expensive hardware deployment. 3805 Similarly, common Internet service deployments set service IP 3806 addresses on service distribution points that may relay requests to 3807 many different servers. 3809 For AERO, the expectation is that a combination of the Google/IETF 3810 and Yahoo/Amazon philosophies would be employed. The AERO Client 3811 connects to different ANET access points and can receive 1-2 Server 3812 LLAs at each point. It then selects one AERO Server address, and 3813 engages in RS/RA exchanges with the same Server from all ANET 3814 connections. The Client remains with this Server unless or until the 3815 Server fails, in which case it can switch over to an alternate 3816 Server. The Client can likewise switch over to a different Server at 3817 any time if there is some reason for it to do so. So, the AERO 3818 expectation is for a balance of function in the network and end 3819 system, with fault tolerance and resilience at both levels. 3821 Appendix B. Change Log 3823 << RFC Editor - remove prior to publication >> 3825 Changes from draft-templin-intarea-6706bis-61 to draft-templin- 3826 intrea-6706bis-62: 3828 o New sub-section on OMNI Neighbor Interface Attributes 3830 Changes from draft-templin-intarea-6706bis-59 to draft-templin- 3831 intrea-6706bis-60: 3833 o Removed all references to S/TLLAO - all Interface Attributes are 3834 now maintained completely in the OMNI option. 3836 Changes from draft-templin-intarea-6706bis-58 to draft-templin- 3837 intrea-6706bis-59: 3839 o The term "Relay" used in older draft versions is now "Bridge". 3840 "Relay" now refers to what was formally called: "Gateway". 3842 o Fine-grained cleanup of Forwarding Algorithm; IPv6 ND message 3843 addressing; OMNI Prefix Lengths, etc. 3845 Changes from draft-templin-intarea-6706bis-54 to draft-templin- 3846 intrea-6706bis-55: 3848 o Updates on Segment Routing and S/TLLAO contents. 3850 o Various editorials and addressing cleanups. 3852 Changes from draft-templin-intarea-6706bis-52 to draft-templin- 3853 intrea-6706bis-53: 3855 o Normative reference to the OMNI spec, and remove portions that are 3856 already specified in OMNI. 3858 o Renamed "AERO interface/link" to "OMIN interface/link" throughout 3859 the document. 3861 o Truncated obsolete back section matter. 3863 Author's Address 3865 Fred L. Templin (editor) 3866 Boeing Research & Technology 3867 P.O. Box 3707 3868 Seattle, WA 98124 3869 USA 3871 Email: fltemplin@acm.org