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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, November 2, 2020 5 rfc6179, rfc6706 (if 6 approved) 7 Intended status: Standards Track 8 Expires: May 6, 2021 10 Asymmetric Extended Route Optimization (AERO) 11 draft-templin-intarea-6706bis-68 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 May 6, 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 To the OMNI Link . . . . . . . . . . 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 . . . . 29 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 . . . . . . 31 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 . . . . . . . . . . . 47 108 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 . . . . . . . . . . 54 119 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 . . . . . . . . . . . . 61 130 3.22.1. Use of SEND and CGA . . . . . . . . . . . . . . . . 64 131 3.23. Time-Varying MNPs . . . . . . . . . . . . . . . . . . . . 65 132 4. Implementation Status . . . . . . . . . . . . . . . . . . . . 66 133 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 66 134 6. Security Considerations . . . . . . . . . . . . . . . . . . . 66 135 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 68 136 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 69 137 8.1. Normative References . . . . . . . . . . . . . . . . . . 70 138 8.2. Informative References . . . . . . . . . . . . . . . . . 71 139 Appendix A. Non-Normative Considerations . . . . . . . . . . . . 77 140 A.1. Implementation Strategies for Route Optimization . . . . 77 141 A.2. Implicit Mobility Management . . . . . . . . . . . . . . 77 142 A.3. Direct Underlying Interfaces . . . . . . . . . . . . . . 78 143 A.4. AERO Critical Infrastructure Considerations . . . . . . . 78 144 A.5. AERO Server Failure Implications . . . . . . . . . . . . 79 145 A.6. AERO Client / Server Architecture . . . . . . . . . . . . 80 146 Appendix B. Change Log . . . . . . . . . . . . . . . . . . . . . 82 147 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 83 149 1. Introduction 151 Asymmetric Extended Route Optimization (AERO) fulfills the 152 requirements of Distributed Mobility Management (DMM) [RFC7333] and 153 route optimization [RFC5522] for aeronautical networking and other 154 network mobility use cases such as intelligent transportation 155 systems. AERO is an internetworking and mobility management service 156 based on the Overlay Multilink Network Interface (OMNI) 157 [I-D.templin-6man-omni-interface] Non-Broadcast, Multiple Access 158 (NBMA) virtual link model. The OMNI link is a virtual overlay 159 configured over one or more underlying Internetworks, and nodes on 160 the link can exchange IP packets via tunneling. The OMNI Adaptation 161 Layer (OAL) supports multilink operation for increased reliability, 162 bandwidth optimization and traffic path selection while accommodating 163 Maximum Transmission Unit (MTU) diversity. 165 The AERO service comprises Clients, Proxys, Servers and Relays that 166 are seen as OMNI link neighbors as well as Bridges that interconnect 167 OMNI link segments. Each node's OMNI interface uses an IPv6 link- 168 local address format that supports operation of the IPv6 Neighbor 169 Discovery (ND) protocol [RFC4861] and links ND to IP forwarding. A 170 node's OMNI interface can be configured over multiple underlying 171 interfaces, and may therefore appear as a single interface with 172 multiple link-layer addresses. Each link-layer address is subject to 173 change due to mobility and/or QoS fluctuations, and link-layer 174 address changes are signaled by ND messaging the same as for any IPv6 175 link. 177 AERO provides a cloud-based service where mobile nodes may use any 178 Server acting as a Mobility Anchor Point (MAP) and fixed nodes may 179 use any Relay on the link for efficient communications. Fixed nodes 180 forward packets destined to other AERO nodes to the nearest Relay, 181 which forwards them through the cloud. A mobile node's initial 182 packets are forwarded through the Server, while direct routing is 183 supported through asymmetric extended route optimization while data 184 packets are flowing. Both unicast and multicast communications are 185 supported, and mobile nodes may efficiently move between locations 186 while maintaining continuous communications with correspondents and 187 without changing their IP Address. 189 AERO Bridges are interconnected in a secured private BGP overlay 190 routing instance using encapsulation to provide a hybrid routing/ 191 bridging service that joins the underlying Internetworks of multiple 192 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::/10 [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]::/10 to form DLAs used for OAL header source and 661 destination addresses. See [I-D.templin-6man-omni-interface] for a 662 full specification of the LLAs and DLAs used by AERO nodes on OMNI 663 links. 665 For routing system organization (see Section 3.2.3), DLAs are 666 organized in partition prefixes, e.g., [DLA]::1000/116. For each 667 such partition prefix, the Bridge(s) that connect that segment assign 668 the all-zero's address of the prefix as a Subnet Router Anycast 669 address. For example, the Subnet Router Anycast address for 670 [DLA]::1000/116 is simply [DLA]::1000. 672 3.2.3. AERO Routing System 674 The AERO routing system comprises a private instance of the Border 675 Gateway Protocol (BGP) [RFC4271] that is coordinated between Bridges 676 and Servers and does not interact with either the public Internet BGP 677 routing system or any underlying INET routing systems. 679 In a reference deployment, each Server is configured as an Autonomous 680 System Border Router (ASBR) for a stub Autonomous System (AS) using 681 an AS Number (ASN) that is unique within the BGP instance, and each 682 Server further uses eBGP to peer with one or more Bridges but does 683 not peer with other Servers. Each INET of a multi-segment OMNI link 684 must include one or more Bridges, which peer with the Servers and 685 Proxys within that INET. All Bridges within the same INET are 686 members of the same hub AS using a common ASN, and use iBGP to 687 maintain a consistent view of all active MNPs currently in service. 688 The Bridges of different INETs peer with one another using eBGP. 690 Bridges advertise the OMNI link's MSPs and any non-MNP routes to each 691 of their Servers. This means that any aggregated non-MNPs (including 692 "default") are advertised to all Servers. Each Bridge configures a 693 black-hole route for each of its MSPs. By black-holing the MSPs, the 694 Bridge will maintain forwarding table entries only for the MNPs that 695 are currently active, and packets destined to all other MNPs will 696 correctly incur Destination Unreachable messages due to the black- 697 hole route. In this way, Servers have only partial topology 698 knowledge (i.e., they know only about the MNPs of their directly 699 associated Clients) and they forward all other packets to Bridges 700 which have full topology knowledge. 702 Each OMNI link segment assigns a unique sub-prefix of [DLA]::/96 703 known as the DLA partition prefix. For example, a first segment 704 could assign [DLA]::1000/116, a second could assign [DLA]::2000/116, 705 a third could assign [DLA]::3000/116, etc. The administrative 706 authorities for each segment must therefore coordinate to assure 707 mutually-exclusive partition prefix assignments, but internal 708 provisioning of each prefix is an independent local consideration for 709 each administrative authority. 711 DLA partition prefixes are statically represented in Bridge 712 forwarding tables. Bridges join multiple segments into a unified 713 OMNI link over multiple diverse administrative domains. They support 714 a bridging function by first establishing forwarding table entries 715 for their partition prefixes either via standard BGP routing or 716 static routes. For example, if three Bridges ('A', 'B' and 'C') from 717 different segments serviced [DLA]::1000/116, [DLA]::2000/116 and 718 [DLA]::3000/116 respectively, then the forwarding tables in each 719 Bridge are as follows: 721 A: [DLA]::1000/116->local, [DLA]::2000/116->B, [DLA]::3000/116->C 723 B: [DLA]::1000/116->A, [DLA]::2000/116->local, [DLA]::3000/116->C 725 C: [DLA]::1000/116->A, [DLA]::2000/116->B, [DLA]::3000/116->local 727 These forwarding table entries are permanent and never change, since 728 they correspond to fixed infrastructure elements in their respective 729 segments. 731 DLA Client prefixes are instead dynamically advertised in the AERO 732 routing system by Servers and Relays that provide service for their 733 corresponding MNPs. For example, if three Servers ('D', 'E' and 'F') 734 service the MNPs 2001:db8:1000:2000::/56, 2001:db8:3000:4000::/56 and 735 2001:db8:5000:6000::/56 then the routing system would include: 737 D: [DLA]:2001:db8:1000:2000::/72 739 E: [DLA]:2001:db8:3000:4000::/72 741 F: [DLA]:2001:db8:5000:6000::/72 743 A full discussion of the BGP-based routing system used by AERO is 744 found in [I-D.ietf-rtgwg-atn-bgp]. 746 3.2.4. OMNI Link Encapsulation 748 With the Client and partition prefixes in place in each Bridge's 749 forwarding table, control and data packets sent between AERO nodes in 750 different segments can be carried over the spanning tree via mid- 751 layer encapsulations using the OMNI Adaptation Layer (OAL) header 752 and/or the OMNI Routing Header (ORH) formatted as shown in Figure 3: 754 0 1 2 3 755 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 1 756 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 757 | Next Header | Hdr Ext Len | Routing Type | Segments Left | 758 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 759 | Reserved | SRT | FMT | LHS (bits 0 - 15) | 760 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 761 | LHS (bits 16 - 31) | ~ 762 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ 763 ~ Link Layer Address (L2ADDR) ~ 764 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 765 ~ IPv6 Destination Address ~ 766 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 767 ~ Null Padding ~ 768 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 770 Figure 3: OMNI Routing Header (ORH) Format 772 In this format: 774 o Next Header identifies the type of header immediately following 775 the ORH. 777 o Hdr Ext Len is the length of the Routing header in 8-octet units, 778 not including the first 8 octets. 780 o Routing Type is set to TBD (see IANA Considerations). 782 o Segments Left is set to the value 1 if an IPv6 Destination Address 783 is included, or the value 0 if no IPv6 Destination Address is 784 included. If Segments Left encodes any other value, the entire 785 ORH is ignored and the next header is processed. 787 o Reserved is set to 0 on transmission and ignored on reception. 789 o SRT - a 5-bit Segment Routing Topology prefix length value that 790 (when added to 96) determines the prefix length to apply to the 791 DLA formed from concatenating [DLA*]::/96 with the 32 bit LHS MSID 792 value that follows. For example, the value 16 corresponds to the 793 prefix length 112. 795 o FMT - a 3-bit "Framework/Mode/Type" code corresponding to the 796 included Link Layer Address as follows: 798 * When the most significant bit (i.e., "Framework") is set to 0, 799 L2ADDR is the INET encapsulation address of a Server/Proxy; 800 otherwise, it is the address for the Source/Target itself. 802 * When the next most significant bit (i.e., "Mode") is set to 0, 803 the Source/Target L2ADDR is on the open INET; otherwise, it is 804 (likely) located behind a Network Address Translator (NAT). 806 * When the least significant bit (i.e., "Type") is set to 0, 807 L2ADDR includes a UDP Port Number followed by an IPv4 address; 808 else, a UDP Port Number followed by an IPv6 address. 810 o LHS - the 32 bit MSID of the Last Hop Server/Proxy on the path to 811 the target. When SRT and LHS are both set to 0, the LHS is 812 considered unspecified in this IPv6 ND message. When SRT is set 813 to 0 and LHS is non-zero, the prefix length is set to 128. SRT 814 and LHS provide guidance to the OMNI interface forwarding 815 algorithm. Specifically, if SRT/LHS is located in the local OMNI 816 link segment then the OMNI interface can encapsulate according to 817 FMT/L2ADDR; else, it must forward according to the OMNI link 818 spanning tree. 820 o Link Layer Address (L2ADDR) - Formatted according to FMT, and 821 identifies the link-layer address (i.e., the encapsulation 822 address) of the source/target. The UDP Port Number appears in the 823 first two octets and the IP address appears in the next 4 octets 824 for IPv4 or 16 octets for IPv6. The Port Number and IP address 825 are recorded in ones-compliment "obfuscated" form per [RFC4380]. 826 The OMNI interface forwarding algorithm uses FMT/L2ADDR to 827 determine the encapsulation address for forwarding when SRT/LHS is 828 located in the local OMNI link segment. 830 o IPv6 Destination Address is a 16-octet IPv6 address included only 831 when Segments Left is 1, and omitted otherwise. 833 o Null Padding contains 0/4 zero-valued octets as necessary to pad 834 the ORH to an integral number of 8-octet units. 836 The OAL header is inserted for all IPv4 packets, for IPv6 packets for 837 which the LHS ID is not yet known, for transportation of IPv6 ND 838 messages, and when fragmentation (see Section 5 of 839 [I-D.templin-6man-omni-interface]) is necessary. When an OAL header 840 is necessary, encapsulation is based on Generic Packet Tunneling in 841 IPv6 [RFC2473] with the inclusion of an ORH as an extension to the 842 OAL header if final hop link-layer address and/or final IPv6 843 destination address information is necessary. 845 For example, when an AERO service node encapsulates a packet with 846 IPv6 source address 2001:db8:1:2::1 and IPv6 destination address 847 2001:db8:1000:2000::1 and the LHS is not yet known, it can first 848 encapsulate the packet in an OAL header with source address set to 849 its own DLA address (e.g., [DLA]::1000:2000) and destination address 850 set to [DLA]:2001:db8:1000:2000::. The service node also includes an 851 ORH header as an extension to the OAL header if necessary, then 852 fragments the mid-layer packet if necessary. Next, the service node 853 encapsulates each resulting OAL packet in an INET header with source 854 address set to its own INET address (e.g., 192.0.2.100) and 855 destination set to the INET address of a Bridge (e.g., 192.0.2.1). 856 The encapsulation format in the above example is shown in Figure 4: 858 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 859 | INET Header | 860 | src = 192.0.2.100 | 861 | dst = 192.0.2.1 | 862 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 863 | OAL Header | 864 | src = [DLA]::1000:2000 | 865 | dst=[DLA]:2001:db8:1000:2000::| 866 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 867 | ORH Header | 868 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 869 | Inner IP Header | 870 | src = 2001:db8:1:2::1 | 871 | dst = 2001:db8:1000:2000::1 | 872 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 873 | | 874 ~ ~ 875 ~ Inner Packet Body ~ 876 ~ ~ 877 | | 878 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 880 Figure 4: OAL/ORH Encapsulation 882 In this format, the inner IP header and packet body are the original 883 IP packet, the OAL header is an IPv6 header prepared according to 884 [RFC2473], the ORH is a Routing Header extension of the OAL header, 885 and the INET header is prepared as discussed in Section 3.6. 887 For IPv6 packets with non-link-local addresses for which the LHS is 888 known, the AERO service node can avoid OAL encapsulation while 889 inserting an ORH as an extension to the existing IPv6 header of the 890 packet. The service node further changes the IPv6 destination 891 address to the Subnet Router Anycast address corresponding to the 892 Last Hop Server/Proxy DLA address (for example, for the LHS 893 [DLA]::1000:2000 and with SRT prefix length 16, the Subnet Router 894 Anycast address is [DLA]::1000:0000). When the service node changes 895 the IPv6 destination address, it places the original destination 896 address in the ORH header unless the address already appears in a 897 different IPv6 Routing Header already included in the packet. The 898 ORH-only encapsulation is shown in 900 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 901 | INET Header | 902 | src = 192.0.2.100 | 903 | dst = 192.0.2.1 | 904 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 905 | Inner IP Header | 906 | src = 2001:db8:1:2::1 | 907 | dst = [DLA]::1000:0000 | 908 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 909 | ORH Header | 910 | dst = 2001:db8:1000:2000::1 | 911 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 912 | | 913 ~ ~ 914 ~ Inner Packet Body ~ 915 ~ ~ 916 | | 917 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 919 Figure 5: ORH-Only Encapsulation 921 This gives rise to a routing system that contains both Client prefix 922 routes that may change dynamically due to regional node mobility and 923 partition prefix routes that rarely if ever change. The Bridges can 924 therefore provide link-layer bridging by sending packets over the 925 spanning tree instead of network-layer routing according to MNP 926 routes. As a result, opportunities for packet loss due to node 927 mobility between different segments are mitigated. 929 In normal operations, IPv6 ND messages are conveyed over secured 930 paths between OMNI link neighbors so that specific Proxys, Servers or 931 Relays can be addressed without being subject to mobility events. 932 Conversely, only the first few packets destined to Clients need to 933 traverse secured paths until route optimization can determine a more 934 direct path. 936 3.2.5. Segment Routing Topologies (SRTs) 938 The 16-bit sub-prefixes of [DLA]::/10 identify up to 64 distinct 939 Segment Routing Topologies (SRTs). Each SRT is a mutually-exclusive 940 OMNI link overlay instance using a distinct set of DLAs, and emulates 941 a Virtual LAN (VLAN) service for the OMNI link. In some cases (e.g., 942 when redundant topologies are needed for fault tolerance and 943 reliability) it may be beneficial to deploy multiple SRTs that act as 944 independent overlay instances. A communication failure in one 945 instance therefore will not affect communications in other instances. 947 Each SRT is identified by a distinct value in bits 10-15 of 948 [DLA]::10, i.e., as [DLA0]::/16, [DLA1]::/16, [DLA2]::/16, etc. This 949 document asserts that up to four SRTs provide a level of safety 950 sufficient for critical communications such as civil aviation. Each 951 SRT is designated with a color that identifies a different OMNI link 952 instance as follows: 954 o Red - corresponds to [DLA0]::/16 956 o Green - corresponds to [DLA1]::/16 958 o Blue-1 - corresponds to [DLA2]::/16 960 o Blue-2 - corresponds to [DLA3]::/16 962 o [DLA4]::/16 through [DLA63]::/16 are available for additional 963 SRTs. 965 Each OMNI interface assigns an anycast DLA corresponding to its SRT 966 prefix. For example, the anycast DLA for the Green SRT is simply 967 [DLA1]::. The anycast DLA is used for OMNI interface determination in 968 Safety-Based Multilink (SBM) as discussed in 969 [I-D.templin-6man-omni-interface]. Each OMNI interface further 970 applies Performance-Based Multilink (PBM) internally. 972 3.2.6. Segment Routing To the OMNI Link 974 An original IPv6 source can direct a packet to an OMNI link Client by 975 including a standard IPv6 Segment Routing Header (SRH) with the 976 anycast DLA for the selected SRT as either the IPv6 destination or as 977 an intermediate hop within the SRH. This allows the original source 978 to determine the specific topology a packet will traverse when there 979 may be multiple alternatives to choose from. Since the SRH contains 980 no useful information for the destination, the Client may elect to 981 delete the SRH before forwarding in order to reduce overhead. This 982 form of Segment Routing supports Safety-Based Multilink (SBM), and 983 can be exercised through general-purpose SRH types such as [RFC8754]. 985 3.2.7. Segment Routing Within the OMNI Link 987 AERO nodes that insert an OAL and/or ORH header can use Segment 988 Routing within the OMNI link when necessary to influence the path of 989 packets destined to targets in remote segments without requiring all 990 packets to traverse strict spanning tree paths. 992 When a Client, Proxy or Server has a packet to send to a target 993 discovered through route optimization located in the same OMNI link 994 segment, it encapsulates the packet in an OAL/ORH header if 995 necessary; otherwise, it may omit the OAL/ORH headers. The node then 996 uses the target's Link Layer Address (L2ADDR) information for INET 997 encapsulation. 999 When a Client, Proxy or Server has a packet to send to a route 1000 optimization target located in a remote OMNI link segment, it 1001 encapsulates the packet in OAL/ORH headers as discussed above while 1002 forwarding the packet to a Bridge with destination set to the Subnet 1003 Router Anycast address for the final OMNI link segment. 1005 When a Bridge receives a packet destined to its Subnet Router Anycast 1006 address with an ORH with SRT/LHS on the local segment, it examines 1007 the L2ADDR according to FMT, saves the actual IPv6 destination 1008 address, and removes the ORH from the packet. If the packet included 1009 an OAL header, the Bridge rewrites the destination address of the OAL 1010 header to the saved actual IPv6 destination address. If the packet 1011 did not include an OAL header, the Bridge rewrites the destination 1012 address of the native IPv6 packet header to the saved actual IPv6 1013 destination address. Next, the Bridge encapsulates the packet in an 1014 INET header according to L2ADDR and forwards the packet within the 1015 INET either to the LHS Server/Proxy or directly to the destination 1016 itself. 1018 In this way, the Bridge participates in route optimization to reduce 1019 traffic load and suboptimal routing through strict spanning tree 1020 paths. Note that if the Bridge does not recognize the AERO Route 1021 Optimization TLV, it instead places the SRT [DLA*]::/96 prefix 1022 concatenated with the 32 bit LHS in the IPv6 destination address and 1023 forwards according to the spanning tree. (Note that this is the same 1024 behavior that would occur if the AERO Route Optimization TLV were not 1025 present). 1027 3.3. OMNI Interface Characteristics 1029 OMNI interfaces are virtual interfaces configured over one or more 1030 underlying interfaces classified as follows: 1032 o INET interfaces connect to an INET either natively or through one 1033 or several IPv4 Network Address Translators (NATs). Native INET 1034 interfaces have global IP addresses that are reachable from any 1035 INET correspondent. All Server, Relay and Bridge interfaces are 1036 native interfaces, as are INET-facing interfaces of Proxys. NATed 1037 INET interfaces connect to a private network behind one or more 1038 NATs that provide INET access. Clients that are behind a NAT are 1039 required to send periodic keepalive messages to keep NAT state 1040 alive when there are no data packets flowing. 1042 o ANET interfaces connect to an ANET that is separated from the open 1043 INET by a Proxy. Proxys can actively issue control messages over 1044 the INET on behalf of the Client to reduce ANET congestion. 1046 o VPNed interfaces use security encapsulation over the INET to a 1047 Virtual Private Network (VPN) server that also acts as a Server or 1048 Proxy. Other than the link-layer encapsulation format, VPNed 1049 interfaces behave the same as Direct interfaces. 1051 o Direct interfaces connect a Client directly to a Server or Proxy 1052 without crossing any ANET/INET paths. An example is a line-of- 1053 sight link between a remote pilot and an unmanned aircraft. The 1054 same Client considerations apply as for VPNed interfaces. 1056 OMNI interfaces use OAL/ORH encapsulation as necessary as discussed 1057 in Section 3.2.4. OMNI interfaces use link-layer encapsulation (see: 1058 Section 3.6) to exchange packets with OMNI link neighbors over INET 1059 or VPNed interfaces. OMNI interfaces do not use link-layer 1060 encapsulation over ANET and Direct underlying interfaces. 1062 OMNI interfaces maintain a neighbor cache for tracking per-neighbor 1063 state the same as for any interface. OMNI interfaces use ND messages 1064 including Router Solicitation (RS), Router Advertisement (RA), 1065 Neighbor Solicitation (NS) and Neighbor Advertisement (NA) for 1066 neighbor cache management. 1068 OMNI interfaces send ND messages with an OMNI option formatted as 1069 specified in [I-D.templin-6man-omni-interface]. The OMNI option 1070 includes prefix registration information and Interface Attributes 1071 containing link information parameters for the OMNI interface's 1072 underlying interfaces. Each OMNI option may include multiple 1073 Interface Attributes sub-options, each identified by an ifIndex 1074 value. 1076 A Client's OMNI interface may be configured over multiple underlying 1077 interface connections. For example, common mobile handheld devices 1078 have both wireless local area network ("WLAN") and cellular wireless 1079 links. These links are often used "one at a time" with low-cost WLAN 1080 preferred and highly-available cellular wireless as a standby, but a 1081 simultaneous-use capability could provide benefits. In a more 1082 complex example, aircraft frequently have many wireless data link 1083 types (e.g. satellite-based, cellular, terrestrial, air-to-air 1084 directional, etc.) with diverse performance and cost properties. 1086 If a Client's multiple underlying interfaces are used "one at a time" 1087 (i.e., all other interfaces are in standby mode while one interface 1088 is active), then ND message OMNI options include only a single 1089 Interface Attributes sub-option set to constant values. In that 1090 case, the Client would appear to have a single interface but with a 1091 dynamically changing link-layer address. 1093 If the Client has multiple active underlying interfaces, then from 1094 the perspective of ND it would appear to have multiple link-layer 1095 addresses. In that case, ND message OMNI options MAY include 1096 multiple Interface Attributes sub-options - each with values that 1097 correspond to a specific interface. Every ND message need not 1098 include Interface Attributes for all underlying interfaces; for any 1099 attributes not included, the neighbor considers the status as 1100 unchanged. 1102 Bridge, Server and Proxy OMNI interfaces may be configured over one 1103 or more secured tunnel interfaces. The OMNI interface configures 1104 both an LLA and its corresponding DLA, while the underlying secured 1105 tunnel interfaces are either unnumbered or configure the same DLA. 1106 The OMNI interface encapsulates each IP packet in OAL/ORH headers and 1107 presents the packet to the underlying secured tunnel interface. 1108 Routing protocols such as BGP that run over the OMNI interface do not 1109 employ OAL/ORH encapsulation, but rather present the routing protocol 1110 messages directly to the underlying secured tunnels while using the 1111 DLA as the source address. This distinction must be honored 1112 consistently according to each node's configuration so that the IP 1113 forwarding table will associate discovered IP routes with the correct 1114 interface. 1116 3.4. OMNI Interface Initialization 1118 AERO Servers, Proxys and Clients configure OMNI interfaces as their 1119 point of attachment to the OMNI link. AERO nodes assign the MSPs for 1120 the link to their OMNI interfaces (i.e., as a "route-to-interface") 1121 to ensure that packets with destination addresses covered by an MNP 1122 not explicitly assigned to a non-OMNI interface are directed to the 1123 OMNI interface. 1125 OMNI interface initialization procedures for Servers, Proxys, Clients 1126 and Bridges are discussed in the following sections. 1128 3.4.1. AERO Server/Relay Behavior 1130 When a Server enables an OMNI interface, it assigns an LLA/DLA 1131 appropriate for the given OMNI link segment. The Server also 1132 configures secured tunnels with one or more neighboring Bridges and 1133 engages in a BGP routing protocol session with each Bridge. 1135 The OMNI interface provides a single interface abstraction to the IP 1136 layer, but internally comprises multiple secured tunnels as well as 1137 an NBMA nexus for sending encapsulated data packets to OMNI interface 1138 neighbors. The Server further configures a service to facilitate ND 1139 exchanges with AERO Clients and manages per-Client neighbor cache 1140 entries and IP forwarding table entries based on control message 1141 exchanges. 1143 Relays are simply Servers that run a dynamic routing protocol to 1144 redistribute routes between the OMNI interface and INET/EUN 1145 interfaces (see: Section 3.2.3). The Relay provisions MNPs to 1146 networks on the INET/EUN interfaces (i.e., the same as a Client would 1147 do) and advertises the MSP(s) for the OMNI link over the INET/EUN 1148 interfaces. The Relay further provides an attachment point of the 1149 OMNI link to a non-MNP-based global topology. 1151 3.4.2. AERO Proxy Behavior 1153 When a Proxy enables an OMNI interface, it assigns an LLA/DLA and 1154 configures permanent neighbor cache entries the same as for Servers. 1155 The Proxy also configures secured tunnels with one or more 1156 neighboring Bridges and maintains per-Client neighbor cache entries 1157 based on control message exchanges. Importantly Proxys are often 1158 configured to act as Servers, and vice-versa. 1160 3.4.3. AERO Client Behavior 1162 When a Client enables an OMNI interface, it sends RS messages with ND 1163 parameters over its underlying interfaces to a Server, which returns 1164 an RA message with corresponding parameters. (The RS/RA messages may 1165 pass through a Proxy in the case of a Client's ANET interface, or 1166 through one or more NATs in the case of a Client's INET interface.) 1168 3.4.4. AERO Bridge Behavior 1170 AERO Bridges configure an OMNI interface and assign the DLA Subnet 1171 Router Anycast address for each OMNI link segment they connect to. 1172 Bridges configure secured tunnels with Servers, Proxys and other 1173 Bridges; they also configure LLAs/DLAs and permanent neighbor cache 1174 entries the same as Servers. Bridges engage in a BGP routing 1175 protocol session with a subset of the Servers and other Bridges on 1176 the spanning tree (see: Section 3.2.3). 1178 3.5. OMNI Interface Neighbor Cache Maintenance 1180 Each OMNI interface maintains a conceptual neighbor cache that 1181 includes an entry for each neighbor it communicates with on the OMNI 1182 link per [RFC4861]. OMNI interface neighbor cache entries are said 1183 to be one of "permanent", "symmetric", "asymmetric" or "proxy". 1185 Permanent neighbor cache entries are created through explicit 1186 administrative action; they have no timeout values and remain in 1187 place until explicitly deleted. AERO Bridges maintain permanent 1188 neighbor cache entries for their associated Proxys/Servers (and vice- 1189 versa). Each entry maintains the mapping between the neighbor's 1190 network-layer LLA and corresponding INET address. 1192 Symmetric neighbor cache entries are created and maintained through 1193 RS/RA exchanges as specified in Section 3.12, and remain in place for 1194 durations bounded by prefix lifetimes. AERO Servers maintain 1195 symmetric neighbor cache entries for each of their associated 1196 Clients, and AERO Clients maintain symmetric neighbor cache entries 1197 for each of their associated Servers. 1199 Asymmetric neighbor cache entries are created or updated based on 1200 route optimization messaging as specified in Section 3.14, and are 1201 garbage-collected when keepalive timers expire. AERO ROSs maintain 1202 asymmetric neighbor cache entries for active targets with lifetimes 1203 based on ND messaging constants. Asymmetric neighbor cache entries 1204 are unidirectional since only the ROS (and not the ROR) creates an 1205 entry. 1207 Proxy neighbor cache entries are created and maintained by AERO 1208 Proxys when they process Client/Server ND exchanges, and remain in 1209 place for durations bounded by ND and prefix lifetimes. AERO Proxys 1210 maintain proxy neighbor cache entries for each of their associated 1211 Clients. Proxy neighbor cache entries track the Client state and the 1212 address of the Client's associated Server(s). 1214 To the list of neighbor cache entry states in Section 7.3.2 of 1215 [RFC4861], Proxy and Server OMNI interfaces add an additional state 1216 DEPARTED that applies to symmetric and proxy neighbor cache entries 1217 for Clients that have recently departed. The interface sets a 1218 "DepartTime" variable for the neighbor cache entry to "DEPART_TIME" 1219 seconds. DepartTime is decremented unless a new ND message causes 1220 the state to return to REACHABLE. While a neighbor cache entry is in 1221 the DEPARTED state, packets destined to the target Client are 1222 forwarded to the Client's new location instead of being dropped. 1223 When DepartTime decrements to 0, the neighbor cache entry is deleted. 1224 It is RECOMMENDED that DEPART_TIME be set to the default constant 1225 value REACHABLE_TIME plus 10 seconds (40 seconds by default) to allow 1226 a window for packets in flight to be delivered while stale route 1227 optimization state may be present. 1229 When an ROR receives an authentic NS message used for route 1230 optimization, it searches for a symmetric neighbor cache entry for 1231 the target Client. The ROR then returns a solicited NA message 1232 without creating a neighbor cache entry for the ROS, but creates or 1233 updates a target Client "Report List" entry for the ROS and sets a 1234 "ReportTime" variable for the entry to REPORT_TIME seconds. The ROR 1235 resets ReportTime when it receives a new authentic NS message, and 1236 otherwise decrements ReportTime while no authentic NS messages have 1237 been received. It is RECOMMENDED that REPORT_TIME be set to the 1238 default constant value REACHABLE_TIME plus 10 seconds (40 seconds by 1239 default) to allow a window for route optimization to converge before 1240 ReportTime decrements below REACHABLE_TIME. 1242 When the ROS receives a solicited NA message response to its NS 1243 message used for route optimization, it creates or updates an 1244 asymmetric neighbor cache entry for the target network-layer and 1245 link-layer addresses. The ROS then (re)sets ReachableTime for the 1246 neighbor cache entry to REACHABLE_TIME seconds and uses this value to 1247 determine whether packets can be forwarded directly to the target, 1248 i.e., instead of via a default route. The ROS otherwise decrements 1249 ReachableTime while no further solicited NA messages arrive. It is 1250 RECOMMENDED that REACHABLE_TIME be set to the default constant value 1251 30 seconds as specified in [RFC4861]. 1253 AERO nodes also use the value MAX_UNICAST_SOLICIT to limit the number 1254 of NS keepalives sent when a correspondent may have gone unreachable, 1255 the value MAX_RTR_SOLICITATIONS to limit the number of RS messages 1256 sent without receiving an RA and the value MAX_NEIGHBOR_ADVERTISEMENT 1257 to limit the number of unsolicited NAs that can be sent based on a 1258 single event. It is RECOMMENDED that MAX_UNICAST_SOLICIT, 1259 MAX_RTR_SOLICITATIONS and MAX_NEIGHBOR_ADVERTISEMENT be set to 3 the 1260 same as specified in [RFC4861]. 1262 Different values for DEPART_TIME, REPORT_TIME, REACHABLE_TIME, 1263 MAX_UNICAST_SOLICIT, MAX_RTR_SOLCITATIONS and 1264 MAX_NEIGHBOR_ADVERTISEMENT MAY be administratively set; however, if 1265 different values are chosen, all nodes on the link MUST consistently 1266 configure the same values. Most importantly, DEPART_TIME and 1267 REPORT_TIME SHOULD be set to a value that is sufficiently longer than 1268 REACHABLE_TIME to avoid packet loss due to stale route optimization 1269 state. 1271 3.5.1. OMNI Neighbor Interface Attributes 1273 OMNI interface IPv6 ND messages include OMNI options 1274 [I-D.templin-6man-omni-interface] with Interface Attributes that 1275 provide Link-Layer Address and QoS Preference information for the 1276 neighbor's underlying interfaces. This information is stored in the 1277 neighbor cache and provides the basis for the forwarding algorithm 1278 specified in Section 3.10. The information is cumulative and 1279 reflects the union of the OMNI information from the most recent ND 1280 messages received from the neighbor; it is therefore not required 1281 that each ND message contain all neighbor information. 1283 The OMNI option Interface Attributes for each underlying interface 1284 includes a two-part "Link-Layer Address" consisting of a simple IP 1285 encapsulation address determined by the FMT and L2ADDR fields and an 1286 OAL DLA determined by the SRT and LHS fields. If the neighbor is 1287 located in the local OMNI link segment (and, if any necessary NAT 1288 state has been established) forwarding via simple IP encapsulation 1289 can be used; otherwise, OAL encapsulation must be used. Underlying 1290 interfaces are further selected based on their associated preference 1291 values "high", "medium", "low" or "disabled". 1293 Note: the OMNI option is distinct from any Source/Target Link-Layer 1294 Address Options (S/TLLAOs) that may appear in an ND message according 1295 to the appropriate IPv6 over specific link layer specification (e.g., 1296 [RFC2464]). If both an OMNI option and S/TLLAO appear, the former 1297 pertains to encapsulation addresses while the latter pertains to the 1298 native L2 address format of the underlying media. 1300 3.5.2. OMNI Neighbor Advertisement Message Flags 1302 As discussed in Section 4.4 of [RFC4861] NA messages include three 1303 flag bits R, S and O. OMNI interface NA messages treat the flags as 1304 follows: 1306 o R: The R ("Router") flag is set to 1 in the NA messages sent by 1307 all AERO/OMNI node types. Simple hosts that would set R to 0 do 1308 not occur on the OMNI link itself, but may occur on the downstream 1309 links of Clients and Relays. 1311 o S: The S ("Solicited") flag is set exactly as specified in 1312 Section 4.4. of [RFC4861], i.e., it is set to 1 for Solicited NAs 1313 and set to 0 for Unsolicited NAs (both unicast and multicast). 1315 o O: The O ("Override") flag is set to 0 for solicited proxy NAs and 1316 set to 1 for all other solicited and unsolicited NAs. For further 1317 study is whether solicited NAs for anycast targets apply for OMNI 1318 links. Since OMNI LLAs must be uniquely assigned to Clients to 1319 support correct ND protocol operation, however, no role is 1320 currently seen for assigning the same OMNI LLA to multiple 1321 Clients. 1323 3.6. OMNI Interface Encapsulation and Re-encapsulation 1325 The OMNI Adaptation Layer (OAL) inserts mid-layer IPv6 headers known 1326 as the OAL/ORH headers when necessary as discussed in the following 1327 sections. After either inserting or omitting the OAL/ORH headers, 1328 the OMNI interface also inserts or omits an outer encapsulation 1329 header as discussed below. 1331 OMNI interfaces avoid outer encapsulation over Direct underlying 1332 interfaces and ANET underlying interfaces for which the first-hop 1333 access router is connected to the same underlying link. Otherwise, 1334 OMNI interfaces encapsulate packets according to whether they are 1335 entering the OMNI interface from the network layer or if they are 1336 being re-admitted into the same OMNI link they arrived on. This 1337 latter form of encapsulation is known as "re-encapsulation". 1339 For packets entering the OMNI interface from the network layer, the 1340 OMNI interface copies the "TTL/Hop Limit", "Type of Service/Traffic 1341 Class" [RFC2983], "Flow Label"[RFC6438] (for IPv6) and "Congestion 1342 Experienced" [RFC3168] values in the inner packet's IP header into 1343 the corresponding fields in the OAL and outer encapsulation 1344 header(s). 1346 For packets undergoing re-encapsulation, the OMNI interface instead 1347 copies these values from the original encapsulation header into the 1348 new encapsulation header, i.e., the values are transferred between 1349 encapsulation headers and *not* copied from the encapsulated packet's 1350 network-layer header. (Note especially that by copying the TTL/Hop 1351 Limit between encapsulation headers the value will eventually 1352 decrement to 0 if there is a (temporary) routing loop.) 1354 OMNI interfaces configured over ANET underlying interfaces which 1355 employ a different IP protocol version and/or may be located multiple 1356 IP hops from the nearest Proxy/Server use IP-in-IP encapsulation so 1357 that the inner packet can traverse the ANET. IPv6 underlying ANET 1358 interfaces use [RFC2473] encapsulation, while IPv4 interfaces use the 1359 appropriate encapsulation per one of [RFC2529][RFC5214][RFC2003]. 1361 OMNI interfaces configured over INET underlying interfaces 1362 encapsulate packets in INET headers according to the next hop 1363 determined in the forwarding algorithm in Section 3.10. If the next 1364 hop is reached via a secured tunnel, the OMNI interface uses an 1365 encapsulation format specific to the secured tunnel type (see: 1366 Section 6). If the next hop is reached via an unsecured INET 1367 interface, the OMNI interface instead uses UDP/IP encapsulation per 1368 [RFC4380] and as extended in [RFC6081]. 1370 When UDP/IP encapsulation is used, the OMNI interface next sets the 1371 UDP source port to a constant value that it will use in each 1372 successive packet it sends, and sets the UDP length field to the 1373 length of the encapsulated packet plus 8 bytes for the UDP header 1374 itself plus the length of any included extension headers or trailers. 1375 The encapsulated packet may be either IPv6 or IPv4, as distinguished 1376 by the version number found in the first four bits. 1378 For UDP/IP-encapsulated packets sent to a Server, Relay or Bridge, 1379 the OMNI interface sets the UDP destination port to 8060, i.e., the 1380 IANA-registered port number for AERO. For packets sent to a Client, 1381 the OMNI interface sets the UDP destination port to the port value 1382 stored in the neighbor cache entry for this Client. The OMNI 1383 interface finally includes/omits the UDP checksum according to 1384 [RFC6935][RFC6936]. 1386 3.7. OMNI Interface Decapsulation 1388 OMNI interfaces decapsulate packets destined either to the AERO node 1389 itself or to a destination reached via an interface other than the 1390 OMNI interface the packet was received on. When the encapsulated 1391 packet arrives in multiple OAL fragments, the OMNI interface 1392 reassembles as discussed in Section 3.9. Further decapsulation steps 1393 are performed according to the appropriate encapsulation format 1394 specification. 1396 3.8. OMNI Interface Data Origin Authentication 1398 AERO nodes employ simple data origin authentication procedures. In 1399 particular: 1401 o AERO Bridges, Servers and Proxys accept encapsulated data packets 1402 and control messages received from the (secured) spanning tree. 1404 o AERO Proxys and Clients accept packets that originate from within 1405 the same secured ANET. 1407 o AERO Clients and Relays accept packets from downstream network 1408 correspondents based on ingress filtering. 1410 o AERO Clients, Relays and Servers verify the outer UDP/IP 1411 encapsulation addresses according to [RFC4380]. 1413 AERO nodes silently drop any packets that do not satisfy the above 1414 data origin authentication procedures. Further security 1415 considerations are discussed in Section 6. 1417 3.9. OMNI Adaptation Layer and OMNI Interface MTU 1419 The OMNI interface observes the link nature of tunnels, including the 1420 Maximum Transmission Unit (MTU), Maximum Reassembly Unit (MRU) and 1421 the role of fragmentation and reassembly [I-D.ietf-intarea-tunnels]. 1422 The OMNI interface employs an OMNI Adaptation Layer (OAL) for 1423 accommodating multiple underlying links with diverse MTUs. The 1424 functions of the OAL and the OMNI interface MTU/MRU are specified in 1425 Section 5 of [I-D.templin-6man-omni-interface], with MTU/MRU both set 1426 to the constant value 9180 bytes. 1428 3.10. OMNI Interface Forwarding Algorithm 1430 IP packets enter a node's OMNI interface either from the network 1431 layer (i.e., from a local application or the IP forwarding system) or 1432 from the link layer (i.e., from an OMNI interface neighbor). All 1433 packets entering a node's OMNI interface first undergo data origin 1434 authentication as discussed in Section 3.8. Packets that satisfy 1435 data origin authentication are processed further, while all others 1436 are dropped silently. The OMNI interface OAL wraps accepted packets 1437 in OAL/ORH headers if necessary as discussed above. 1439 Packets that enter the OMNI interface from the network layer are 1440 forwarded to an OMNI interface neighbor. Packets that enter the OMNI 1441 interface from the link layer are either re-admitted into the OMNI 1442 link or forwarded to the network layer where they are subject to 1443 either local delivery or IP forwarding. In all cases, the OMNI 1444 interface itself MUST NOT decrement the network layer TTL/Hop-count 1445 since its forwarding actions occur below the network layer. 1447 OMNI interfaces may have multiple underlying interfaces and/or 1448 neighbor cache entries for neighbors with multiple underlying 1449 interfaces (see Section 3.3). The OMNI interface uses interface 1450 attributes and/or traffic classifiers (e.g., DSCP value, port number, 1451 etc.) to select an outgoing underlying interface for each packet 1452 based on the node's own QoS preferences, and also to select a 1453 destination link-layer address based on the neighbor's underlying 1454 interface with the highest preference. AERO implementations SHOULD 1455 allow for QoS preference values to be modified at runtime through 1456 network management. 1458 If multiple outgoing interfaces and/or neighbor interfaces have a 1459 preference of "high", the AERO node replicates the packet and sends 1460 one copy via each of the (outgoing / neighbor) interface pairs; 1461 otherwise, the node sends a single copy of the packet via an 1462 interface with the highest preference. AERO nodes keep track of 1463 which underlying interfaces are currently "reachable" or 1464 "unreachable", and only use "reachable" interfaces for forwarding 1465 purposes. 1467 The following sections discuss the OMNI interface forwarding 1468 algorithms for Clients, Proxys, Servers and Bridges. In the 1469 following discussion, a packet's destination address is said to 1470 "match" if it is the same as a cached address, or if it is covered by 1471 a cached prefix (which may be encoded in an LLA). 1473 3.10.1. Client Forwarding Algorithm 1475 When an IP packet enters a Client's OMNI interface from the network 1476 layer the Client searches for an asymmetric neighbor cache entry that 1477 matches the destination. If there is a match, the Client uses one or 1478 more "reachable" neighbor interfaces in the entry for packet 1479 forwarding. If there is no asymmetric neighbor cache entry, the 1480 Client instead forwards the packet toward a Server (the packet is 1481 intercepted by a Proxy if there is a Proxy on the path). The Client 1482 encapsulates the packet in OAL/ORH headers if necessary and fragments 1483 according to MTU requirements (see: Section 3.9). 1485 When an IP packet enters a Client's OMNI interface from the link- 1486 layer, if the destination matches one of the Client's MNPs or link- 1487 local addresses the Client reassembles and decapsulates as necessary 1488 and delivers the inner packet to the network layer. Otherwise, the 1489 Client drops the packet and MAY return a network-layer ICMP 1490 Destination Unreachable message subject to rate limiting (see: 1491 Section 3.11). 1493 3.10.2. Proxy Forwarding Algorithm 1495 For control messages originating from or destined to a Client, the 1496 Proxy intercepts the message and updates its proxy neighbor cache 1497 entry for the Client. The Proxy then forwards a (proxyed) copy of 1498 the control message. (For example, the Proxy forwards a proxied 1499 version of a Client's NS/RS message to the target neighbor, and 1500 forwards a proxied version of the NA/RA reply to the Client.) 1502 When the Proxy receives a data packet from a Client within the ANET, 1503 the Proxy reassembles and re-fragments if necessary then searches for 1504 an asymmetric neighbor cache entry that matches the destination and 1505 forwards as follows: 1507 o if the destination matches an asymmetric neighbor cache entry, the 1508 Proxy uses one or more "reachable" neighbor interfaces in the 1509 entry for packet forwarding using OAL/ORH encapsulation if 1510 necessary according to the cached link-layer address information. 1511 If the neighbor interface is in the same OMNI link segment, the 1512 Proxy forwards the packet directly to the neighbor; otherwise, it 1513 forwards the packet to a Bridge. 1515 o else, the Proxy uses OAL/ORH encapsulation and forwards the packet 1516 to a Bridge while using the DLA corresponding to the packet's 1517 destination as the destination address. 1519 When the Proxy receives an encapsulated data packet from an INET 1520 neighbor or from a secured tunnel from a Bridge, it accepts the 1521 packet only if data origin authentication succeeds and if there is a 1522 proxy neighbor cache entry that matches the inner destination. Next, 1523 the Proxy reassembles the packet (if necessary) and continues 1524 processing. If the reassembly is complete and the neighbor cache 1525 state is REACHABLE, the Proxy then returns a PTB if necessary (see: 1526 Section 3.9) then either drops or forwards the packet to the Client 1527 while performing OAL/ORH encapsulation and re-fragmentation if 1528 necessary. If the neighbor cache entry state is DEPARTED, the Proxy 1529 instead changes the destination address to the address of the new 1530 Server and forwards it to a Bridge while performing OAL/ORH re- 1531 fragmentation if necessary. 1533 3.10.3. Server/Relay Forwarding Algorithm 1535 For control messages destined to a target Client's LLA that are 1536 received from a secured tunnel, the Server intercepts the message and 1537 sends a Proxyed response on behalf of the Client. (For example, the 1538 Server sends a Proxyed NA message reply in response to an NS message 1539 directed to one of its associated Clients.) If the Client's neighbor 1540 cache entry is in the DEPARTED state, however, the Server instead 1541 forwards the packet to the Client's new Server as discussed in 1542 Section 3.16. 1544 When the Server receives an encapsulated data packet from an INET 1545 neighbor or from a secured tunnel, it accepts the packet only if data 1546 origin authentication succeeds. The Server then continues processing 1547 as follows: 1549 o if the network layer destination matches a symmetric neighbor 1550 cache entry in the REACHABLE state the Server prepares the packet 1551 for forwarding to the destination Client. The Server first 1552 reassembles (if necessary) and forwards the packet (while re- 1553 fragmenting if necessary) as specified in Section 3.9. 1555 o else, if the destination matches a symmetric neighbor cache entry 1556 in the DEPARETED state the Server re-encapsulates the packet and 1557 forwards it using the DLA of the Client's new Server as the 1558 destination. 1560 o else, if the destination matches an asymmetric neighbor cache 1561 entry, the Server uses one or more "reachable" neighbor interfaces 1562 in the entry for packet forwarding via the local INET if the 1563 neighbor is in the same OMNI link segment or using OAL/ORH 1564 encapsulation if necessary with the final destination set to the 1565 neighbor's DLA otherwise. 1567 o else, if the destination matches a non-MNP route in the IP 1568 forwarding table or an LLA assigned to the Server's OMNI 1569 interface, the Server reassembles if necessary, decapsulates the 1570 packet and releases it to the network layer for local delivery or 1571 IP forwarding. 1573 o else, the Server drops the packet. 1575 When the Server's OMNI interface receives a data packet from the 1576 network layer or from a VPNed or Direct Client, it performs OAL/ORH 1577 encapsulation and fragmentation if necessary, then processes the 1578 packet according to the network-layer destination address as follows: 1580 o if the destination matches a symmetric or asymmetric neighbor 1581 cache entry the Server processes the packet as above. 1583 o else, the Server encapsulates the packet in OLA/ORH headers and 1584 forwards it to a Bridge using its own DLA as the source and the 1585 DLA corresponding to the destination as the destination. 1587 3.10.4. Bridge Forwarding Algorithm 1589 Bridges forward OAL/ORH-encapsulated packets over secured tunnels the 1590 same as any IP router. When the Bridge receives an OAL/ORH- 1591 encapsulated packet via a secured tunnel, it removes the outer INET 1592 header and searches for a forwarding table entry that matches the 1593 destination address. The Bridge then processes the packet as 1594 follows: 1596 o if the destination matches its DLA Subnet Router Anycast address, 1597 the Bridge checks for an ORH. If there is an ORH with SRT/LHS 1598 located on the local segment, the Bridge removes the ORH from the 1599 packet and examines the FMT to determine if the target is behind a 1600 NAT. If no NAT is indicated, the Bridge copies the actual 1601 destination address into the IPv6 destination then forwards the 1602 packet directly to the L2ADDR using link-layer (UDP/IP) 1603 encapsulation. If a NAT is indicated, the Bridge MAY perform NAT 1604 traversal procedures by sending bubbles per [RFC4380]. The Bridge 1605 then either applies AERO route optimization if NAT traversal 1606 procedures have been successfully applied, or forwards the packet 1607 directly to the Server. 1609 o if the destination matches one of the Bridge's own addresses, the 1610 Bridge submits the packet for local delivery. 1612 o else, if the destination matches a forwarding table entry the 1613 Bridge forwards the packet via a secured tunnel to the next hop. 1614 If the destination matches an MSP without matching an MNP, 1615 however, the Bridge instead drops the packet and returns an ICMP 1616 Destination Unreachable message subject to rate limiting (see: 1617 Section 3.11). 1619 o else, the Bridge drops the packet and returns an ICMP Destination 1620 Unreachable as above. 1622 As for any IP router, the Bridge decrements the TTL/Hop Limit when it 1623 forwards the packet. Therefore, only the Hop Limit in the OAL header 1624 is decremented, and not the TTL/Hop Limit in the inner packet header. 1625 Bridges do not insert OAL/ORH headers themselves; instead, they act 1626 as IPv6 routers and forward packets based on the destination address 1627 found in the headers of packets they receive. 1629 3.11. OMNI Interface Error Handling 1631 When an AERO node admits a packet into the OMNI interface, it may 1632 receive link-layer or network-layer error indications. 1634 A link-layer error indication is an ICMP error message generated by a 1635 router in the INET on the path to the neighbor or by the neighbor 1636 itself. The message includes an IP header with the address of the 1637 node that generated the error as the source address and with the 1638 link-layer address of the AERO node as the destination address. 1640 The IP header is followed by an ICMP header that includes an error 1641 Type, Code and Checksum. Valid type values include "Destination 1642 Unreachable", "Time Exceeded" and "Parameter Problem" 1643 [RFC0792][RFC4443]. (OMNI interfaces ignore all link-layer IPv4 1644 "Fragmentation Needed" and IPv6 "Packet Too Big" messages since they 1645 only emit packets that are guaranteed to be no larger than the IP 1646 minimum link MTU as discussed in Section 3.9.) 1648 The ICMP header is followed by the leading portion of the packet that 1649 generated the error, also known as the "packet-in-error". For 1650 ICMPv6, [RFC4443] specifies that the packet-in-error includes: "As 1651 much of invoking packet as possible without the ICMPv6 packet 1652 exceeding the minimum IPv6 MTU" (i.e., no more than 1280 bytes). For 1653 ICMPv4, [RFC0792] specifies that the packet-in-error includes: 1654 "Internet Header + 64 bits of Original Data Datagram", however 1655 [RFC1812] Section 4.3.2.3 updates this specification by stating: "the 1656 ICMP datagram SHOULD contain as much of the original datagram as 1657 possible without the length of the ICMP datagram exceeding 576 1658 bytes". 1660 The link-layer error message format is shown in Figure 6 (where, "L2" 1661 and "L3" refer to link-layer and network-layer, respectively): 1663 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1664 ~ ~ 1665 | L2 IP Header of | 1666 | error message | 1667 ~ ~ 1668 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1669 | L2 ICMP Header | 1670 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 1671 ~ ~ P 1672 | IP and other encapsulation | a 1673 | headers of original L3 packet | c 1674 ~ ~ k 1675 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ e 1676 ~ ~ t 1677 | IP header of | 1678 | original L3 packet | i 1679 ~ ~ n 1680 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1681 ~ ~ e 1682 | Upper layer headers and | r 1683 | leading portion of body | r 1684 | of the original L3 packet | o 1685 ~ ~ r 1686 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 1688 Figure 6: OMNI Interface Link-Layer Error Message Format 1690 The AERO node rules for processing these link-layer error messages 1691 are as follows: 1693 o When an AERO node receives a link-layer Parameter Problem message, 1694 it processes the message the same as described as for ordinary 1695 ICMP errors in the normative references [RFC0792][RFC4443]. 1697 o When an AERO node receives persistent link-layer Time Exceeded 1698 messages, the IP ID field may be wrapping before earlier fragments 1699 awaiting reassembly have been processed. In that case, the node 1700 should begin including integrity checks and/or institute rate 1701 limits for subsequent packets. 1703 o When an AERO node receives persistent link-layer Destination 1704 Unreachable messages in response to encapsulated packets that it 1705 sends to one of its asymmetric neighbor correspondents, the node 1706 should process the message as an indication that a path may be 1707 failing, and optionally initiate NUD over that path. If it 1708 receives Destination Unreachable messages over multiple paths, the 1709 node should allow future packets destined to the correspondent to 1710 flow through a default route and re-initiate route optimization. 1712 o When an AERO Client receives persistent link-layer Destination 1713 Unreachable messages in response to encapsulated packets that it 1714 sends to one of its symmetric neighbor Servers, the Client should 1715 mark the path as unusable and use another path. If it receives 1716 Destination Unreachable messages on many or all paths, the Client 1717 should associate with a new Server and release its association 1718 with the old Server as specified in Section 3.16.5. 1720 o When an AERO Server receives persistent link-layer Destination 1721 Unreachable messages in response to encapsulated packets that it 1722 sends to one of its symmetric neighbor Clients, the Server should 1723 mark the underlying path as unusable and use another underlying 1724 path. 1726 o When an AERO Server or Proxy receives link-layer Destination 1727 Unreachable messages in response to an encapsulated packet that it 1728 sends to one of its permanent neighbors, it treats the messages as 1729 an indication that the path to the neighbor may be failing. 1730 However, the dynamic routing protocol should soon reconverge and 1731 correct the temporary outage. 1733 When an AERO Bridge receives a packet for which the network-layer 1734 destination address is covered by an MSP, if there is no more- 1735 specific routing information for the destination the Bridge drops the 1736 packet and returns a network-layer Destination Unreachable message 1737 subject to rate limiting. The Bridge writes the network-layer source 1738 address of the original packet as the destination address and uses 1739 one of its non link-local addresses as the source address of the 1740 message. 1742 When an AERO node receives an encapsulated packet for which the 1743 reassembly buffer it too small, it drops the packet and returns a 1744 network-layer Packet Too Big (PTB) message. The node first writes 1745 the MRU value into the PTB message MTU field, writes the network- 1746 layer source address of the original packet as the destination 1747 address and writes one of its non link-local addresses as the source 1748 address. 1750 3.12. AERO Router Discovery, Prefix Delegation and Autoconfiguration 1752 AERO Router Discovery, Prefix Delegation and Autoconfiguration are 1753 coordinated as discussed in the following Sections. 1755 3.12.1. AERO Service Model 1757 Each AERO Server on the OMNI link is configured to facilitate Client 1758 prefix delegation/registration requests. Each Server is provisioned 1759 with a database of MNP-to-Client ID mappings for all Clients enrolled 1760 in the AERO service, as well as any information necessary to 1761 authenticate each Client. The Client database is maintained by a 1762 central administrative authority for the OMNI link and securely 1763 distributed to all Servers, e.g., via the Lightweight Directory 1764 Access Protocol (LDAP) [RFC4511], via static configuration, etc. 1765 Clients receive the same service regardless of the Servers they 1766 select. 1768 AERO Clients and Servers use ND messages to maintain neighbor cache 1769 entries. AERO Servers configure their OMNI interfaces as advertising 1770 NBMA interfaces, and therefore send unicast RA messages with a short 1771 Router Lifetime value (e.g., ReachableTime seconds) in response to a 1772 Client's RS message. Thereafter, Clients send additional RS messages 1773 to keep Server state alive. 1775 AERO Clients and Servers include prefix delegation and/or 1776 registration parameters in RS/RA messages (see 1777 [I-D.templin-6man-omni-interface]). The ND messages are exchanged 1778 between Client and Server according to the prefix management schedule 1779 required by the service. If the Client knows its MNP in advance, it 1780 can employ prefix registration by including its LLA as the source 1781 address of an RS message and with an OMNI option with valid prefix 1782 registration information for the MNP. If the Server (and Proxy) 1783 accept the Client's MNP assertion, they inject the prefix into the 1784 routing system and establish the necessary neighbor cache state. 1786 The following sections specify the Client and Server behavior. 1788 3.12.2. AERO Client Behavior 1790 AERO Clients discover the addresses of Servers in a similar manner as 1791 described in [RFC5214]. Discovery methods include static 1792 configuration (e.g., from a flat-file map of Server addresses and 1793 locations), or through an automated means such as Domain Name System 1794 (DNS) name resolution [RFC1035]. Alternatively, the Client can 1795 discover Server addresses through a layer 2 data link login exchange, 1796 or through a unicast RA response to a multicast/anycast RS as 1797 described below. In the absence of other information, the Client can 1798 resolve the DNS Fully-Qualified Domain Name (FQDN) 1799 "linkupnetworks.[domainname]" where "linkupnetworks" is a constant 1800 text string and "[domainname]" is a DNS suffix for the OMNI link 1801 (e.g., "example.com"). 1803 To associate with a Server, the Client acts as a requesting router to 1804 request MNPs. The Client prepares an RS message with prefix 1805 management parameters and includes a Nonce and Timestamp option if 1806 the Client needs to correlate RA replies. If the Client already 1807 knows the Server's LLA, it includes the LLA as the network-layer 1808 destination address; otherwise, it includes (link-local) All-Routers 1809 multicast as the network-layer destination. If the Client already 1810 knows its own LLA, it uses the LLA as the network-layer source 1811 address; otherwise, it uses an OMNI Temporary LLA as the network- 1812 layer source address and includes a DHCP Unique Identifier (DUID) 1813 sub-option in the OMNI option (see: 1814 [I-D.templin-6man-omni-interface]). 1816 The Client next includes an OMNI option in the RS message to register 1817 its link-layer information with the Server. The Client sets the OMNI 1818 option prefix registration information according to the MNP, and 1819 includes Interface Attributes corresponding to the underlying 1820 interface over which the Client will send the RS message. The Client 1821 MAY include additional Interface Attributes specific to other 1822 underlying interfaces. 1824 The Client then sends the RS message (either directly via Direct 1825 interfaces, via a VPN for VPNed interfaces, via a Proxy for ANET 1826 interfaces or via INET encapsulation for INET interfaces) and waits 1827 for an RA message reply (see Section 3.12.3). The Client retries up 1828 to MAX_RTR_SOLICITATIONS times until an RA is received. If the 1829 Client receives no RAs, or if it receives an RA with Router Lifetime 1830 set to 0, the Client SHOULD abandon this Server and try another 1831 Server. Otherwise, the Client processes the prefix information found 1832 in the RA message. 1834 Next, the Client creates a symmetric neighbor cache entry with the 1835 Server's LLA as the network-layer address and the Server's 1836 encapsulation and/or link-layer addresses as the link-layer address. 1837 The Client records the RA Router Lifetime field value in the neighbor 1838 cache entry as the time for which the Server has committed to 1839 maintaining the MNP in the routing system via this underlying 1840 interface, and caches the other RA configuration information 1841 including Cur Hop Limit, M and O flags, Reachable Time and Retrans 1842 Timer. The Client then autoconfigures LLAs for each of the delegated 1843 MNPs and assigns them to the OMNI interface. The Client also caches 1844 any MSPs included in Route Information Options (RIOs) [RFC4191] as 1845 MSPs to associate with the OMNI link, and assigns the MTU value in 1846 the MTU option to the underlying interface. 1848 The Client then registers additional underlying interfaces with the 1849 Server by sending RS messages via each additional interface. The RS 1850 messages include the same parameters as for the initial RS/RA 1851 exchange, but with destination address set to the Server's LLA. 1853 Following autoconfiguration, the Client sub-delegates the MNPs to its 1854 attached EUNs and/or the Client's own internal virtual interfaces as 1855 described in [I-D.templin-v6ops-pdhost] to support the Client's 1856 downstream attached "Internet of Things (IoT)". The Client 1857 subsequently sends additional RS messages over each underlying 1858 interface before the Router Lifetime received for that interface 1859 expires. 1861 After the Client registers its underlying interfaces, it may wish to 1862 change one or more registrations, e.g., if an interface changes 1863 address or becomes unavailable, if QoS preferences change, etc. To 1864 do so, the Client prepares an RS message to send over any available 1865 underlying interface. The RS includes an OMNI option with prefix 1866 registration information specific to its MNP, with Interface 1867 Attributes specific to the selected underlying interface, and with 1868 any additional Interface Attributes specific to other underlying 1869 interfaces. When the Client receives the Server's RA response, it 1870 has assurance that the Server has been updated with the new 1871 information. 1873 If the Client wishes to discontinue use of a Server it issues an RS 1874 message over any underlying interface with an OMNI option with a 1875 prefix release indication. When the Server processes the message, it 1876 releases the MNP, sets the symmetric neighbor cache entry state for 1877 the Client to DEPARTED and returns an RA reply with Router Lifetime 1878 set to 0. After a short delay (e.g., 2 seconds), the Server 1879 withdraws the MNP from the routing system. 1881 3.12.3. AERO Server Behavior 1883 AERO Servers act as IP routers and support a prefix delegation/ 1884 registration service for Clients. Servers arrange to add their LLAs 1885 to a static map of Server addresses for the link and/or the DNS 1886 resource records for the FQDN "linkupnetworks.[domainname]" before 1887 entering service. Server addresses should be geographically and/or 1888 topologically referenced, and made available for discovery by Clients 1889 on the OMNI link. 1891 When a Server receives a prospective Client's RS message on its OMNI 1892 interface, it SHOULD return an immediate RA reply with Router 1893 Lifetime set to 0 if it is currently too busy or otherwise unable to 1894 service the Client. Otherwise, the Server authenticates the RS 1895 message and processes the prefix delegation/registration parameters. 1896 The Server first determines the correct MNPs to provide to the Client 1897 by searching the Client database. When the Server returns the MNPs, 1898 it also creates a forwarding table entry for the DLA corresponding to 1899 each MNP so that the MNPs are propagated into the routing system 1900 (see: Section 3.2.3). For IPv6, the Server creates an IPv6 1901 forwarding table entry for each MNP. For IPv4, the Server creates an 1902 IPv6 forwarding table entry with the IPv4-compatibility DLA prefix 1903 corresponding to the IPv4 address. 1905 The Server next creates a symmetric neighbor cache entry for the 1906 Client using the base LLA as the network-layer address and with 1907 lifetime set to no more than the smallest prefix lifetime. Next, the 1908 Server updates the neighbor cache entry by recording the information 1909 in each Interface Attributes sub-option in the RS OMNI option. The 1910 Server also records the actual OAL/INET addresses in the neighbor 1911 cache entry. 1913 Next, the Server prepares an RA message using its LLA as the network- 1914 layer source address and the network-layer source address of the RS 1915 message as the network-layer destination address. The Server sets 1916 the Router Lifetime to the time for which it will maintain both this 1917 underlying interface individually and the symmetric neighbor cache 1918 entry as a whole. The Server also sets Cur Hop Limit, M and O flags, 1919 Reachable Time and Retrans Timer to values appropriate for the OMNI 1920 link. The Server includes the MNPs, any other prefix management 1921 parameters and an OMNI option with no Interface Attributes. The 1922 Server then includes one or more RIOs that encode the MSPs for the 1923 OMNI link, plus an MTU option (see Section 3.9). The Server finally 1924 forwards the message to the Client using OAL/INET, INET, or NULL 1925 encapsulation as necessary. 1927 After the initial RS/RA exchange, the Server maintains a 1928 ReachableTime timer for each of the Client's underlying interfaces 1929 individually (and for the Client's symmetric neighbor cache entry 1930 collectively) set to expire after ReachableTime seconds. If the 1931 Client (or Proxy) issues additional RS messages, the Server sends an 1932 RA response and resets ReachableTime. If the Server receives an ND 1933 message with a prefix release indication it sets the Client's 1934 symmetric neighbor cache entry to the DEPARTED state and withdraws 1935 the MNP from the routing system after a short delay (e.g., 2 1936 seconds). If ReachableTime expires before a new RS is received on an 1937 individual underlying interface, the Server marks the interface as 1938 DOWN. If ReachableTime expires before any new RS is received on any 1939 individual underlying interface, the Server sets the symmetric 1940 neighbor cache entry state to STALE and sets a 10 second timer. If 1941 the Server has not received a new RS or ND message with a prefix 1942 release indication before the 10 second timer expires, it deletes the 1943 neighbor cache entry and withdraws the MNP from the routing system. 1945 The Server processes any ND messages pertaining to the Client and 1946 returns an NA/RA reply in response to solicitations. The Server may 1947 also issue unsolicited RA messages, e.g., with reconfigure parameters 1948 to cause the Client to renegotiate its prefix delegation/ 1949 registrations, with Router Lifetime set to 0 if it can no longer 1950 service this Client, etc. Finally, If the symmetric neighbor cache 1951 entry is in the DEPARTED state, the Server deletes the entry after 1952 DepartTime expires. 1954 Note: Clients SHOULD notify former Servers of their departures, but 1955 Servers are responsible for expiring neighbor cache entries and 1956 withdrawing routes even if no departure notification is received 1957 (e.g., if the Client leaves the network unexpectedly). Servers 1958 SHOULD therefore set Router Lifetime to ReachableTime seconds in 1959 solicited RA messages to minimize persistent stale cache information 1960 in the absence of Client departure notifications. A short Router 1961 Lifetime also ensures that proactive Client/Server RS/RA messaging 1962 will keep any NAT state alive (see above). 1964 Note: All Servers on an OMNI link MUST advertise consistent values in 1965 the RA Cur Hop Limit, M and O flags, Reachable Time and Retrans Timer 1966 fields the same as for any link, since unpredictable behavior could 1967 result if different Servers on the same link advertised different 1968 values. 1970 3.12.3.1. DHCPv6-Based Prefix Registration 1972 When a Client is not pre-provisioned with an OMNI LLA containing a 1973 MNP, it will need for the Server to select an MNP on its behalf and 1974 set up the correct state in the AERO routing service. The DHCPv6 1975 service [RFC8415] is used to support this requirement. 1977 When a Client without a pre-provisioned OMNI MN LLA needs to have the 1978 Server select an MNP, it sends an RS message with source address set 1979 to an OMNI Temporary LLA. The RS message includes an OMNI option 1980 with a DUID sub-option that contains a unique DUID value for the MN, 1981 and a Prefix Length value corresponding to the length of MNP it 1982 wishes to receive. 1984 When the Server receives the RS message, it notes that the source was 1985 a Temporary LLA and derives the DUID and Prefix Length from the OMNI 1986 option. The Server (acting as a "proxy DHCP client") then crafts a 1987 well-formed DHCPv6 Solicit message with Prefix Delegation (PD) 1988 parameters, and forwards the message to a locally-resident DHCPv6 1989 server. The DHCPv6 server then delegates an MNP and returns a DHCPv6 1990 Reply message with PD parameters. (Note: the Solicit message should 1991 contain enough identifying information for the MN so that the AR can 1992 correlate the server's Reply with the original Solicit.) 1994 When the Server receives the DHCPv6 Reply, it adds a route to the 1995 routing system and creates an OMNI MN LLA based on the delegated MNP. 1996 The Server then sends an RA back to the Client with the (newly- 1997 created) OMNI MN LLA as the destination address and with Prefix 1998 Length set in the OMNI option. When the Client receives the RA, it 1999 creates a default route, assigns the Subnet Router Anycast address 2000 and sets its OMNI LLA based on the delegated MNP. 2002 3.13. The AERO Proxy 2004 Clients may connect to protected-spectrum ANETs that employ physical 2005 and/or link-layer security services to facilitate communications to 2006 Servers in outside INETs. In that case, the ANET can employ an AERO 2007 Proxy. The Proxy is located at the ANET/INET border and listens for 2008 RS messages originating from or RA messages destined to ANET Clients. 2009 The Proxy acts on these control messages as follows: 2011 o when the Proxy receives an RS message from a new ANET Client, it 2012 first authenticates the message then examines the network-layer 2013 destination address. If the destination address is a Server's 2014 LLA, the Proxy proceeds to the next step. Otherwise, if the 2015 destination is (link-local) All-Routers multicast, the Proxy 2016 selects a "nearby" Server that is likely to be a good candidate to 2017 serve the Client and replaces the destination address with the 2018 Server's LLA. Next, the Proxy creates a proxy neighbor cache 2019 entry and caches the Client and Server link-layer addresses along 2020 with the OMNI option information and any other identifying 2021 information including Transaction IDs, Client Identifiers, Nonce 2022 values, etc. The Proxy finally encapsulates the (proxyed) RS 2023 message in an OAL header with source set to the Proxy's DLA and 2024 destination set to the Server's DLA. The Proxy also includes an 2025 OMNI header with an Interface Attributes option that includes its 2026 own INET address plus a unique Port Number for this Client, then 2027 forwards the message into the OMNI link spanning tree. 2029 o when the Server receives the RS, it authenticates the message then 2030 creates or updates a symmetric neighbor cache entry for the Client 2031 with the Proxy's DLA, INET address and Port Number as the link- 2032 layer address information. The Server then sends an RA message 2033 back to the Proxy via the spanning tree. 2035 o when the Proxy receives the RA, it authenticates the message and 2036 matches it with the proxy neighbor cache entry created by the RS. 2038 The Proxy then caches the prefix information as a mapping from the 2039 Client's MNPs to the Client's link-layer address, caches the 2040 Server's advertised Router Lifetime and sets the neighbor cache 2041 entry state to REACHABLE. The Proxy then optionally rewrites the 2042 Router Lifetime and forwards the (proxyed) message to the Client. 2043 The Proxy finally includes an MTU option (if necessary) with an 2044 MTU to use for the underlying ANET interface. 2046 After the initial RS/RA exchange, the Proxy forwards any Client data 2047 packets for which there is no matching asymmetric neighbor cache 2048 entry to a Bridge using OAL encapsulation with its own DLA as the 2049 source and the DLA corresponding to the Client as the destination. 2050 The Proxy instead forwards any Client data destined to an asymmetric 2051 neighbor cache target directly to the target according to the OAL/ 2052 link-layer information - the process of establishing asymmetric 2053 neighbor cache entries is specified in Section 3.14. 2055 While the Client is still attached to the ANET, the Proxy sends NS, 2056 RS and/or unsolicited NA messages to update the Server's symmetric 2057 neighbor cache entries on behalf of the Client and/or to convey QoS 2058 updates. This allows for higher-frequency Proxy-initiated RS/RA 2059 messaging over well-connected INET infrastructure supplemented by 2060 lower-frequency Client-initiated RS/RA messaging over constrained 2061 ANET data links. 2063 If the Server ceases to send solicited advertisements, the Proxy 2064 sends unsolicited RAs on the ANET interface with destination set to 2065 (link-local) All-Nodes multicast and with Router Lifetime set to zero 2066 to inform Clients that the Server has failed. Although the Proxy 2067 engages in ND exchanges on behalf of the Client, the Client can also 2068 send ND messages on its own behalf, e.g., if it is in a better 2069 position than the Proxy to convey QoS changes, etc. For this reason, 2070 the Proxy marks any Client-originated solicitation messages (e.g. by 2071 inserting a Nonce option) so that it can return the solicited 2072 advertisement to the Client instead of processing it locally. 2074 If the Client becomes unreachable, the Proxy sets the neighbor cache 2075 entry state to DEPARTED and retains the entry for DepartTime seconds. 2076 While the state is DEPARTED, the Proxy forwards any packets destined 2077 to the Client to a Bridge via OAL encapsulation with the Client's 2078 current Server as the destination. The Bridge in turn forwards the 2079 packets to the Client's current Server. When DepartTime expires, the 2080 Proxy deletes the neighbor cache entry and discards any further 2081 packets destined to this (now forgotten) Client. 2083 In some ANETs that employ a Proxy, the Client's MNP can be injected 2084 into the ANET routing system. In that case, the Client can send data 2085 messages without encapsulation so that the ANET routing system 2086 transports the unencapsulated packets to the Proxy. This can be very 2087 beneficial, e.g., if the Client connects to the ANET via low-end data 2088 links such as some aviation wireless links. 2090 If the first-hop ANET access router is on the same underlying link 2091 and recognizes the AERO/OMNI protocol, the Client can avoid 2092 encapsulation for both its control and data messages. When the 2093 Client connects to the link, it can send an unencapsulated RS message 2094 with source address set to its LLA and with destination address set 2095 to the LLA of the Client's selected Server or to (link-local) All- 2096 Routers multicast. The Client includes an OMNI option formatted as 2097 specified in [I-D.templin-6man-omni-interface]. 2099 The Client then sends the unencapsulated RS message, which will be 2100 intercepted by the AERO-Aware access router. The access router then 2101 encapsulates the RS message in an ANET header with its own address as 2102 the source address and the address of a Proxy as the destination 2103 address. The access router further remembers the address of the 2104 Proxy so that it can encapsulate future data packets from the Client 2105 via the same Proxy. If the access router needs to change to a new 2106 Proxy, it simply sends another RS message toward the Server via the 2107 new Proxy on behalf of the Client. 2109 In some cases, the access router and Proxy may be one and the same 2110 node. In that case, the node would be located on the same physical 2111 link as the Client, but its message exchanges with the Server would 2112 need to pass through a security gateway at the ANET/INET border. The 2113 method for deploying access routers and Proxys (i.e. as a single node 2114 or multiple nodes) is an ANET-local administrative consideration. 2116 3.13.1. Combined Proxy/Servers 2118 Clients may need to connect directly to Servers via INET, Direct and 2119 VPNed interfaces (i.e., non-ANET interfaces). If the Client's 2120 underlying interfaces all connect via the same INET partition, then 2121 it can connect to a single controlling Server via all interfaces. 2123 If some Client interfaces connect via different INET partitions, 2124 however, the Client still selects a set of controlling Servers and 2125 sends RS messages via their directly-connected Servers while using 2126 the LLA of the controlling Server as the destination. 2128 When a Server receives an RS with destination set to the LLA of a 2129 controlling Server, it acts as a Proxy to forward the message to the 2130 controlling Server while forwarding the corresponding RA reply to the 2131 Client. 2133 3.13.2. Detecting and Responding to Server Failures 2135 In environments where fast recovery from Server failure is required, 2136 Proxys SHOULD use proactive Neighbor Unreachability Detection (NUD) 2137 to track Server reachability in a similar fashion as for 2138 Bidirectional Forwarding Detection (BFD) [RFC5880]. Proxys can then 2139 quickly detect and react to failures so that cached information is 2140 re-established through alternate paths. The NUD control messaging is 2141 carried only over well-connected ground domain networks (i.e., and 2142 not low-end aeronautical radio links) and can therefore be tuned for 2143 rapid response. 2145 Proxys perform proactive NUD with Servers for which there are 2146 currently active ANET Clients by sending continuous NS messages in 2147 rapid succession, e.g., one message per second. The Proxy sends the 2148 NS message via the spanning tree with the Proxy's LLA as the source 2149 and the LLA of the Server as the destination. When the Proxy is also 2150 sending RS messages to the Server on behalf of ANET Clients, the 2151 resulting RA responses can be considered as equivalent hints of 2152 forward progress. This means that the Proxy need not also send a 2153 periodic NS if it has already sent an RS within the same period. If 2154 the Server fails (i.e., if the Proxy ceases to receive 2155 advertisements), the Proxy can quickly inform Clients by sending 2156 multicast RA messages on the ANET interface. 2158 The Proxy sends RA messages on the ANET interface with source address 2159 set to the Server's address, destination address set to (link-local) 2160 All-Nodes multicast, and Router Lifetime set to 0. The Proxy SHOULD 2161 send MAX_FINAL_RTR_ADVERTISEMENTS RA messages separated by small 2162 delays [RFC4861]. Any Clients on the ANET that had been using the 2163 failed Server will receive the RA messages and associate with a new 2164 Server. 2166 3.13.3. Point-to-Multipoint Server Coordination 2168 In environments where Client messaging over ANETs is bandwidth- 2169 limited and/or expensive, Clients can enlist the services of the 2170 Proxy to coordinate with multiple Servers in a single RS/RA message 2171 exchange. The Client can send a single RS message to (link-local) 2172 All-Routers multicast that includes the ID's of multiple Servers in 2173 MS-Register sub-options of the OMNI option. 2175 When the Proxy receives the RS and processes the OMNI option, it 2176 sends a separate RS to each MS-Register Server ID. When the Proxy 2177 receives an RA, it can optionally return an immediate "singleton" RA 2178 to the Client or record the Server's ID for inclusion in a pending 2179 "aggregate" RA message. The Proxy can then return aggregate RA 2180 messages to the Client including multiple Server IDs in order to 2181 conserve bandwidth. Each RA includes a proper subset of the Server 2182 IDs from the original RS message, and the Proxy must ensure that the 2183 message contents of each RA are consistent with the information 2184 received from the (aggregated) Servers. 2186 Clients can thereafter employ efficient point-to-multipoint Server 2187 coordination under the assistance of the Proxy to reduce the number 2188 of messages sent over the ANET while enlisting the support of 2189 multiple Servers for fault tolerance. Clients can further include 2190 MS-Release sub-options in IPv6 ND messages to request the Proxy to 2191 release from former Servers via the procedures discussed in 2192 Section 3.16.5. 2194 The OMNI interface specification [I-D.templin-6man-omni-interface] 2195 provides further discussion of the Client/Proxy RS/RA messaging 2196 involved in point-to-multipoint coordination. 2198 3.14. AERO Route Optimization / Address Resolution 2200 While data packets are flowing between a source and target node, 2201 route optimization SHOULD be used. Route optimization is initiated 2202 by the first eligible Route Optimization Source (ROS) closest to the 2203 source as follows: 2205 o For Clients on VPNed and Direct interfaces, the Server is the ROS. 2207 o For Clients on ANET interfaces, the Proxy is the ROS. 2209 o For Clients on INET interfaces, the Client itself is the ROS. 2211 o For correspondent nodes on INET/EUN interfaces serviced by a 2212 Relay, the Relay is the ROS. 2214 The route optimization procedure is conducted between the ROS and the 2215 target Server/Relay acting as a Route Optimization Responder (ROR) in 2216 the same manner as for IPv6 ND Address Resolution and using the same 2217 NS/NA messaging. The target may either be a MNP Client serviced by a 2218 Server, or a non-MNP correspondent reachable via a Relay. 2220 The procedures are specified in the following sections. 2222 3.14.1. Route Optimization Initiation 2224 While data packets are flowing from the source node toward a target 2225 node, the ROS performs address resolution by sending an NS message 2226 for Address Resolution (NS(AR)) to receive a solicited NA message 2227 from the ROR. When the ROS sends an NS(AR), it includes: 2229 o the LLA of the ROS as the source address. 2231 o the data packet's destination as the Target Address. 2233 o the Solicited-Node multicast address [RFC4291] formed from the 2234 lower 24 bits of the data packet's destination as the destination 2235 address, e.g., for 2001:db8:1:2::10:2000 the NS destination 2236 address is ff02:0:0:0:0:1:ff10:2000. 2238 The NS(AR) message includes an OMNI option with no Interface 2239 Attributes, such that the target will not create a neighbor cache 2240 entry. The Prefix Length in the OMNI option is set to the Prefix 2241 Length associated with the ROS's LLA. 2243 The ROS then encapsulates the NS(AR) message in an OAL header with 2244 source set to its own DLA and destination set to the DLA 2245 corresponding to the target, then sends the message into the spanning 2246 tree without decrementing the network-layer TTL/Hop Limit field. 2247 (When the ROS is a Client, it instead securely sends the NS(AR) per 2248 Section 3.22.1 to one of its current Servers, which forwards the 2249 message into the spanning tree on behalf of the Client. When the 2250 Server forwards the NS(AR), it sets the IPv6 source address and the 2251 OAL source address to the LLA and DLA of the Client, respectively.) 2253 3.14.2. Relaying the NS 2255 When the Bridge receives the NS(AR) message from the ROS, it discards 2256 the INET header and determines that the ROR is the next hop by 2257 consulting its standard IPv6 forwarding table for the OAL header 2258 destination address. The Bridge then forwards the message toward the 2259 ROR via the spanning tree the same as for any IPv6 router. The 2260 final-hop Bridge in the spanning tree will deliver the message via a 2261 secured tunnel to the ROR. 2263 3.14.3. Processing the NS and Sending the NA 2265 When the ROR receives the NS(AR) message, it examines the Target 2266 Address to determine whether it has a neighbor cache entry and/or 2267 route that matches the target. If there is no match, the ROR drops 2268 the message. Otherwise, the ROR continues processing as follows: 2270 o if the target belongs to an MNP Client neighbor in the DEPARTED 2271 state the ROR changes the NS(AR) message OAL destination address 2272 to the DLA of the Client's new Server, forwards the message into 2273 the spanning tree and returns from processing. 2275 o If the target belongs to an MNP Client neighbor in the REACHABLE 2276 state, the ROR instead adds the AERO source address to the target 2277 Client's Report List with time set to ReportTime. 2279 o If the target belongs to a non-MNP route, the ROR continues 2280 processing without adding an entry to the Report List. 2282 The ROR then prepares a solicited NA message to send back to the ROS 2283 but does not create a neighbor cache entry. The ROR sets the NA 2284 source address to the LLA corresponding to the target, sets the 2285 Target Address to the target of the solicitation, and sets the 2286 destination address to the source of the solicitation. The ROR then 2287 includes an OMNI option with Prefix Length set to the length 2288 associated with the LLA. 2290 If the target is an MNP Client, the ROR next includes Interface 2291 Attributes in the OMNI option for each of the target Client's 2292 underlying interfaces with current information for each interface and 2293 with the S/T-ifIndex field in the OMNI header set to 0 to indicate 2294 that the message originated from the ROR and not the Client. 2296 For each Interface Attributes sub-option, the ROR sets the L2ADDR 2297 according to its own INET address for VPNed or Direct interfaces, to 2298 the INET address of the Proxy or to the Client's INET address for 2299 INET interfaces. The ROR then includes the lower 32 bits of its own 2300 DLA (or the DLA of the Proxy) as the LHS, encodes the DLA prefix 2301 length code in the SRT field and sets the FMT code accordingly as 2302 specified in Section 3.3. 2304 The ROR then sets the NA message R flag to 1 (as a router), S flag to 2305 1 (as a response to a solicitation), and O flag to 0 (as a proxy). 2306 The ROR finally encapsulates the NA message in an OAL header with 2307 source set to its own DLA and destination set to the source DLA of 2308 the NS(AR) message, then forwards the message into the spanning tree 2309 without decrementing the network-layer TTL/Hop Limit field. 2311 3.14.4. Relaying the NA 2313 When the Bridge receives the NA message from the ROR, it discards the 2314 INET header and determines that the ROS is the next hop by consulting 2315 its standard IPv6 forwarding table for the OAL header destination 2316 address. The Bridge then forwards the OAL-encapsulated NA message 2317 toward the ROS the same as for any IPv6 router. The final-hop Bridge 2318 in the spanning tree will deliver the message via a secured tunnel to 2319 the ROS. 2321 3.14.5. Processing the NA 2323 When the ROS receives the solicited NA message, it processes the 2324 message the same as for standard IPv6 Address Resolution [RFC4861]. 2325 In the process, it caches the source DLA then creates an asymmetric 2326 neighbor cache entry for the target and caches all information found 2327 in the OMNI option. The ROS finally sets the asymmetric neighbor 2328 cache entry lifetime to ReachableTime seconds. (When the ROS is a 2329 Client, the solicited NA message will first be delivered via the 2330 spanning tree to one of its current Servers, which then securely 2331 forwards the message to the Client per Section 3.22.1. When the 2332 Server forwards the NS(AR), it sets the IPv6 source address to its 2333 own Cryptographically-Generated Address (CGA) and sets the OAL source 2334 address to its own DLA.) 2336 3.14.6. Route Optimization Maintenance 2338 Following route optimization, the ROS forwards future data packets 2339 destined to the target via the addresses found in the cached link- 2340 layer information. The route optimization is shared by all sources 2341 that send packets to the target via the ROS, i.e., and not just the 2342 source on behalf of which the route optimization was initiated. 2344 While new data packets destined to the target are flowing through the 2345 ROS, it sends additional NS(AR) messages to the ROR before 2346 ReachableTime expires to receive a fresh solicited NA message the 2347 same as described in the previous sections (route optimization 2348 refreshment strategies are an implementation matter, with a non- 2349 normative example given in Appendix A.1). The ROS uses the cached 2350 DLA of the ROR as the NS(AR) OAL destination address (i.e., instead 2351 of using the DLA corresponding to the target as was the case for the 2352 initial NS(AR)), and sends up to MAX_MULTICAST_SOLICIT NS(AR) 2353 messages separated by 1 second until an NA is received. If no NA is 2354 received, the ROS assumes that the current ROR has become unreachable 2355 and deletes the target neighbor cache entry. Subsequent data packets 2356 will trigger a new route optimization with an NS with OAL destination 2357 address set to the DLA corresponding to the target per Section 3.14.1 2358 to discover a new ROR while initial data packets travel over a 2359 suboptimal route. 2361 If an NA is received, the ROS then updates the asymmetric neighbor 2362 cache entry to refresh ReachableTime, while (for MNP destinations) 2363 the ROR adds or updates the ROS address to the target's Report List 2364 and with time set to ReportTime. While no data packets are flowing, 2365 the ROS instead allows ReachableTime for the asymmetric neighbor 2366 cache entry to expire. When ReachableTime expires, the ROS deletes 2367 the asymmetric neighbor cache entry. Any future data packets flowing 2368 through the ROS will again trigger a new route optimization. 2370 The ROS may also receive unsolicited NA messages from the ROR at any 2371 time (see: Section 3.16). If there is an asymmetric neighbor cache 2372 entry for the target, the ROS updates the link-layer information but 2373 does not update ReachableTime since the receipt of an unsolicited NA 2374 does not confirm that any forward paths are working. If there is no 2375 asymmetric neighbor cache entry, the ROS simply discards the 2376 unsolicited NA. 2378 In this arrangement, the ROS holds an asymmetric neighbor cache entry 2379 for the target via the ROR, but the ROR does not hold an asymmetric 2380 neighbor cache entry for the ROS. The route optimization neighbor 2381 relationship is therefore asymmetric and unidirectional. If the 2382 target node also has packets to send back to the source node, then a 2383 separate route optimization procedure is performed in the reverse 2384 direction. But, there is no requirement that the forward and reverse 2385 paths be symmetric. 2387 3.15. Neighbor Unreachability Detection (NUD) 2389 AERO nodes perform Neighbor Unreachability Detection (NUD) per 2390 [RFC4861] either reactively in response to persistent link-layer 2391 errors (see Section 3.11) or proactively to confirm reachability. 2392 The NUD algorithm is based on periodic control message exchanges. 2393 The algorithm may further be seeded by ND hints of forward progress, 2394 but care must be taken to avoid inferring reachability based on 2395 spoofed information. For example, authentic IPv6 ND message 2396 exchanges may be considered as acceptable hints of forward progress, 2397 while spurious data packets should not be. 2399 AERO Servers, Proxys and Relays can use (OAL-encapsulated) standard 2400 NS/NA NUD exchanges sent over the OMNI link spanning tree to securely 2401 test reachability without risk of DoS attacks from nodes pretending 2402 to be a neighbor (these NS/NA(NUD) messages use the unicast LLAs and 2403 DLAs of the two parties involved in the NUD test the same as for 2404 standard IPv6 ND). Proxys can further perform NUD to securely verify 2405 Server reachability on behalf of their proxyed Clients. However, a 2406 means for an ROS to test the unsecured forward directions of target 2407 route optimized paths is also necessary. 2409 When an ROR directs an ROS to a neighbor with one or more target 2410 link-layer addresses, the ROS can proactively test each such 2411 unsecured route optimized path by sending "loopback" NS(NUD) 2412 messages. While testing the paths, the ROS can optionally continue 2413 to send packets via the spanning tree, maintain a small queue of 2414 packets until target reachability is confirmed, or (optimistically) 2415 allow packets to flow via the route optimized paths. 2417 When the ROS sends a loopback NS(NUD) message, it uses its own LLA as 2418 both the IPv6 source and destination address, and the MNP Subnet- 2419 Router anycast address as the Target Address. The ROS includes a 2420 Nonce and Timestamp option, then encapsulates the message in OAL/INET 2421 headers with its own DLA as the source and the DLA of the route 2422 optimization target as the destination. The ROS then forwards the 2423 message to the target (either directly to the L2ADDR of the target if 2424 the target is in the same OMNI link segment, or via a Bridge if the 2425 target is in a different OMNI link segment). 2427 When the route optimization target receives the NS(NUD) message, it 2428 notices that the IPv6 destination address is the same as the source 2429 address. It then reverses the OAL header source and destination 2430 addresses and returns the message to the ROS (either directly or via 2431 the spanning tree). The route optimization target does not decrement 2432 the NS(NUD) message IPv6 Hop-Limit in the process, since the message 2433 has not exited the OMNI link. 2435 When the ROS receives the NS(NUD) message, it can determine from the 2436 Nonce, Timestamp and Target Address that the message originated from 2437 itself and that it transited the forward path. The ROS need not 2438 prepare an NA response, since the destination of the response would 2439 be itself and testing the route optimization path again would be 2440 redundant. 2442 The ROS marks route optimization target paths that pass these NUD 2443 tests as "reachable", and those that do not as "unreachable". These 2444 markings inform the OMNI interface forwarding algorithm specified in 2445 Section 3.10. 2447 Note that to avoid a DoS vector nodes MUST NOT return loopback 2448 NS(NUD) messages received from an unsecured link-layer source via the 2449 spanning tree. 2451 3.16. Mobility Management and Quality of Service (QoS) 2453 AERO is a Distributed Mobility Management (DMM) service. Each Server 2454 is responsible for only a subset of the Clients on the OMNI link, as 2455 opposed to a Centralized Mobility Management (CMM) service where 2456 there is a single network mobility collective entity for all Clients. 2457 Clients coordinate with their associated Servers via RS/RA exchanges 2458 to maintain the DMM profile, and the AERO routing system tracks all 2459 current Client/Server peering relationships. 2461 Servers provide default routing and mobility/multilink services for 2462 their dependent Clients. Clients are responsible for maintaining 2463 neighbor relationships with their Servers through periodic RS/RA 2464 exchanges, which also serves to confirm neighbor reachability. When 2465 a Client's underlying interface address and/or QoS information 2466 changes, the Client is responsible for updating the Server with this 2467 new information. Note that when there is a Proxy in the path, the 2468 Proxy can also perform some RS/RA exchanges on the Client's behalf. 2470 Mobility management messaging is based on the transmission and 2471 reception of unsolicited Neighbor Advertisement (uNA) messages. Each 2472 uNA message sets the IPv6 destination address to (link-local) All- 2473 Nodes multicast to convey a general update of Interface Attributes to 2474 (possibly) multiple recipients, or to a specific unicast LLA to 2475 announce a departure event to a specific recipient. Implementations 2476 must therefore examine the destination address to determine the 2477 nature of the mobility event (i.e., update vs departure). 2479 Mobility management considerations are specified in the following 2480 sections. 2482 3.16.1. Mobility Update Messaging 2484 Servers accommodate Client mobility, multilink and/or QoS change 2485 events by sending unsolicited NA (uNA) messages to each ROS in the 2486 target Client's Report List. When a Server sends a uNA message, it 2487 sets the IPv6 source address to the Client's LLA, sets the 2488 destination address to (link-local) All-Nodes multicast and sets the 2489 Target Address to the Client's Subnet-Router anycast address. The 2490 Server also includes an OMNI option with Prefix Length set to the 2491 length associated with the Client's LLA, with Interface Attributes 2492 for the target Client's underlying interfaces and with the OMNI 2493 header S/T-ifIndex set to 0. The Server then sets the NA R flag to 2494 1, the S flag to 0 and the O flag to 1, then encapsulates the message 2495 in an OAL header with source set to its own DLA and destination set 2496 to the DLA of the ROS and sends the message into the spanning tree. 2498 As discussed in Section 7.2.6 of [RFC4861], the transmission and 2499 reception of uNA messages is unreliable but provides a useful 2500 optimization. In well-connected Internetworks with robust data links 2501 uNA messages will be delivered with high probability, but in any case 2502 the Server can optionally send up to MAX_NEIGHBOR_ADVERTISEMENT uNAs 2503 to each ROS to increase the likelihood that at least one will be 2504 received. 2506 When the ROS receives a uNA message prepared as above, it ignores the 2507 message if there is no existing neighbor cache entry for the Client. 2508 Otherwise, it uses the included OMNI option information to update the 2509 neighbor cache entry, but does not reset ReachableTime since the 2510 receipt of an unsolicited NA message from the target Server does not 2511 provide confirmation that any forward paths to the target Client are 2512 working. 2514 If uNA messages are lost, the ROS may be left with stale address and/ 2515 or QoS information for the Client for up to ReachableTime seconds. 2516 During this time, the ROS can continue sending packets according to 2517 its stale neighbor cache information. When ReachableTime is close to 2518 expiring, the ROS will re-initiate route optimization and receive 2519 fresh link-layer address information. 2521 In addition to sending uNA messages to the current set of ROSs for 2522 the Client, the Server also sends uNAs to the DLA associated with the 2523 link-layer address for any underlying interface for which the link- 2524 layer address has changed. These uNA messages update an old Proxy/ 2525 Server that cannot easily detect (e.g., without active probing) when 2526 a formerly-active Client has departed. When the Server sends the 2527 uNA, it sets the IPv6 source address to the Client's LLA, sets the 2528 destination address to the old Proxy/Server's LLA, and sets the 2529 Target Address to the Client's Subnet-Router anycast address. The 2530 Server also includes an OMNI option with Prefix Length set to the 2531 length associated with the Client's LLA, with Interface Attributes 2532 for the changed underlying interface, and with the OMNI header S/ 2533 T-ifIndex set to 0. The Server then sets the NA R flag to 1, the S 2534 flag to 0 and the O flag to 1, then encapsulates the message in an 2535 OAL header with source set to its own DLA and destination set to the 2536 DLA of the old Proxy/Server and sends the message into the spanning 2537 tree. 2539 3.16.2. Announcing Link-Layer Address and/or QoS Preference Changes 2541 When a Client needs to change its underlying interface addresses and/ 2542 or QoS preferences (e.g., due to a mobility event), either the Client 2543 or its Proxys send RS messages to the Server via the spanning tree 2544 with an OMNI option that includes Interface attributes with the new 2545 link quality and address information. 2547 Up to MAX_RTR_SOLICITATIONS RS messages MAY be sent in parallel with 2548 sending actual data packets in case one or more RAs are lost. If all 2549 RAs are lost, the Client SHOULD re-associate with a new Server. 2551 When the Server receives the Client's changes, it sends uNA messages 2552 to all nodes in the Report List the same as described in the previous 2553 section. 2555 3.16.3. Bringing New Links Into Service 2557 When a Client needs to bring new underlying interfaces into service 2558 (e.g., when it activates a new data link), it sends an RS message to 2559 the Server via the underlying interface with an OMNI option that 2560 includes Interface Attributes with appropriate link quality values 2561 and with link-layer address information for the new link. 2563 3.16.4. Deactivating Existing Links 2565 When a Client needs to deactivate an existing underlying interface, 2566 it sends an RS or uNA message to its Server with an OMNI option with 2567 appropriate Interface Attribute values - in particular, the link 2568 quality value 0 assures that neighbors will cease to use the link. 2570 If the Client needs to send RS/uNA messages over an underlying 2571 interface other than the one being deactivated, it MUST include 2572 Interface Attributes with appropriate link quality values for any 2573 underlying interfaces being deactivated. 2575 Note that when a Client deactivates an underlying interface, 2576 neighbors that have received the RS/uNA messages need not purge all 2577 references for the underlying interface from their neighbor cache 2578 entries. The Client may reactivate or reuse the underlying interface 2579 and/or its ifIndex at a later point in time, when it will send RS/uNA 2580 messages with fresh Interface Attributes to update any neighbors. 2582 3.16.5. Moving Between Servers 2584 The Client performs the procedures specified in Section 3.12.2 when 2585 it first associates with a new Server or renews its association with 2586 an existing Server. The Client also includes MS-Release identifiers 2587 in the RS message OMNI option per [I-D.templin-6man-omni-interface] 2588 if it wants the new Server to notify any old Servers from which the 2589 Client is departing. 2591 When the new Server receives the Client's RS message, it returns an 2592 RA as specified in Section 3.12.3 and sends up to 2593 MAX_NEIGHBOR_ADVERTIISEMENT uNA messages to any old Servers listed in 2594 OMNI option MS-Release identifiers. When the new Server sends a uNA 2595 message, it sets the IPv6 source address to the Client's LLA, sets 2596 the destination address to the old Server's LLA, and sets the Target 2597 Address to the Client's Subnet-Router anycast address. The new 2598 Server also includes an OMNI option with Prefix Length set to the 2599 length associated with the Client's LLA, with Interface Attributes 2600 for its own underlying interface, and with the OMNI header S/ 2601 T-ifIndex set to 0. The new Server then sets the NA R flag to 1, the 2602 S flag to 0 and the O flag to 1, then encapsulates the message in an 2603 OAL header with source set to its own DLA and destination set to the 2604 DLA of the old Server and sends the message into the spanning tree. 2606 When an old Server receives the uNA, it changes the Client's neighbor 2607 cache entry state to DEPARTED, sets the link-layer address of the 2608 Client to the new Server's DLA, and resets DepartTime. After a short 2609 delay (e.g., 2 seconds) the old Server withdraws the Client's MNP 2610 from the routing system. After DepartTime expires, the old Server 2611 deletes the Client's neighbor cache entry. 2613 The old Server also iteratively forwards a copy of the uNA message to 2614 each ROS in the Client's Report List by changing the OAL destination 2615 address to the DLA of the ROS while leaving all other fields of the 2616 message unmodified. When the ROS receives the uNA, it examines the 2617 Target address to determine the correct asymmetric neighbor cache 2618 entry and verifies that the IPv6 destination address matches the old 2619 Server. The ROS then caches the IPv6 source address as the new 2620 Server for the existing asymmetric neighbor cache entry and marks the 2621 entry as STALE. While in the STALE state, the ROS allows new data 2622 packets to flow according to any existing cached link-layer 2623 information and sends new NS(AR) messages using its own DLA as the 2624 OAL source and the DLA of the new Server as the OAL destination 2625 address to elicit NA messages that reset the asymmetric neighbor 2626 cache entry state to REACHABLE. If no new NA message is received for 2627 10 seconds while in the STALE state, the ROS deletes the neighbor 2628 cache entry. 2630 Clients SHOULD NOT move rapidly between Servers in order to avoid 2631 causing excessive oscillations in the AERO routing system. Examples 2632 of when a Client might wish to change to a different Server include a 2633 Server that has gone unreachable, topological movements of 2634 significant distance, movement to a new geographic region, movement 2635 to a new OMNI link segment, etc. 2637 When a Client moves to a new Server, some of the fragments of a 2638 multiple fragment packet may have already arrived at the old Server 2639 while others are en route to the new Server, however no special 2640 attention in the reassembly algorithm is necessary when re-routed 2641 fragments are simply treated as loss. 2643 3.17. Multicast 2645 The AERO Client provides an IGMP (IPv4) [RFC2236] or MLD (IPv6) 2646 [RFC3810] proxy service for its EUNs and/or hosted applications 2647 [RFC4605]. The Client forwards IGMP/MLD messages over any of its 2648 underlying interfaces for which group membership is required. The 2649 IGMP/MLD messages may be further forwarded by a first-hop ANET access 2650 router acting as an IGMP/MLD-snooping switch [RFC4541], then 2651 ultimately delivered to an AERO Proxy/Server acting as a Protocol 2652 Independent Multicast - Sparse-Mode (PIM-SM, or simply "PIM") 2653 Designated Router (DR) [RFC7761]. AERO Relays also act as PIM 2654 routers (i.e., the same as AERO Proxys/Servers) on behalf of nodes on 2655 INET/EUN networks. The behaviors identified in the following 2656 sections correspond to Source-Specific Multicast (SSM) and Any-Source 2657 Multicast (ASM) operational modes. 2659 3.17.1. Source-Specific Multicast (SSM) 2661 When an ROS (i.e., an AERO Proxy/Server/Relay) "X" acting as PIM 2662 router receives a Join/Prune message from a node on its downstream 2663 interfaces containing one or more ((S)ource, (G)roup) pairs, it 2664 updates its Multicast Routing Information Base (MRIB) accordingly. 2665 For each S belonging to a prefix reachable via X's non-OMNI 2666 interfaces, X then forwards the (S, G) Join/Prune to any PIM routers 2667 on those interfaces per [RFC7761]. 2669 For each S belonging to a prefix reachable via X's OMNI interface, X 2670 originates a separate copy of the Join/Prune for each (S,G) in the 2671 message using its own LLA as the source address and ALL-PIM-ROUTERS 2672 as the destination address. X then encapsulates each message in an 2673 OAL header with source address set to the DLA of X and destination 2674 address set to S then forwards the message into the spanning tree, 2675 which delivers it to AERO Server/Relay "Y" that services S. At the 2676 same time, if the message was a Join, X sends a route-optimization NS 2677 message toward each S the same as discussed in Section 3.14. The 2678 resulting NAs will return the LLA for the prefix that matches S as 2679 the network-layer source address and with an OMNI option with the DLA 2680 corresponding to any underlying interfaces that are currently 2681 servicing S. 2683 When Y processes the Join/Prune message, if S located behind any 2684 INET, Direct, or VPNed interfaces Y acts as a PIM router and updates 2685 its MRIB to list X as the next hop in the reverse path. If S is 2686 located behind any Proxys "Z"*, Y also forwards the message to each 2687 Z* over the spanning tree while continuing to use the LLA of X as the 2688 source address. Each Z* then updates its MRIB accordingly and 2689 maintains the LLA of X as the next hop in the reverse path. Since 2690 the Bridges do not examine network layer control messages, this means 2691 that the (reverse) multicast tree path is simply from each Z* (and/or 2692 Y) to X with no other multicast-aware routers in the path. If any Z* 2693 (and/or Y) is located on the same OMNI link segment as X, the 2694 multicast data traffic sent to X directly using OAL/INET 2695 encapsulation instead of via a Bridge. 2697 Following the initial Join/Prune and NS/NA messaging, X maintains an 2698 asymmetric neighbor cache entry for each S the same as if X was 2699 sending unicast data traffic to S. In particular, X performs 2700 additional NS/NA exchanges to keep the neighbor cache entry alive for 2701 up to t_periodic seconds [RFC7761]. If no new Joins are received 2702 within t_periodic seconds, X allows the neighbor cache entry to 2703 expire. Finally, if X receives any additional Join/Prune messages 2704 for (S,G) it forwards the messages to each Y and Z* in the neighbor 2705 cache entry over the spanning tree. 2707 At some later time, Client C that holds an MNP for source S may 2708 depart from a first Proxy Z1 and/or connect via a new Proxy Z2. In 2709 that case, Y sends an unsolicited NA message to X the same as 2710 specified for unicast mobility in Section 3.16. When X receives the 2711 unsolicited NA message, it updates its asymmetric neighbor cache 2712 entry for the LLA for source S and sends new Join messages to any new 2713 Proxys Z2. There is no requirement to send any Prune messages to old 2714 Proxys Z1 since source S will no longer source any multicast data 2715 traffic via Z1. Instead, the multicast state for (S,G) in Proxy Z1 2716 will soon time out since no new Joins will arrive. 2718 After some later time, C may move to a new Server Y2 and depart from 2719 old Sever Y1. In that case, Y1 sends Join messages for any of C's 2720 active (S,G) groups to Y2 while including its own LLA as the source 2721 address. This causes Y2 to include Y1 in the multicast forwarding 2722 tree during the interim time that Y1's symmetric neighbor cache entry 2723 for C is in the DEPARTED state. At the same time, Y1 sends an 2724 unsolicited NA message to X with an OMNI option with S/T-ifIndex in 2725 the header set to 0 and a release indication to cause X to release 2726 its asymmetric neighbor cache entry. X then sends a new Join message 2727 to S via the spanning tree and re-initiates route optimization the 2728 same as if it were receiving a fresh Join message from a node on a 2729 downstream link. 2731 3.17.2. Any-Source Multicast (ASM) 2733 When an ROS X acting as a PIM router receives a Join/Prune from a 2734 node on its downstream interfaces containing one or more (*,G) pairs, 2735 it updates its Multicast Routing Information Base (MRIB) accordingly. 2736 X then forwards a copy of the message to the Rendezvous Point (RP) R 2737 for each G over the spanning tree. X uses its own LLA as the source 2738 address and ALL-PIM-ROUTERS as the destination address, then 2739 encapsulates each message in an OAL header with source address set to 2740 the DLA of X and destination address set to R, then sends the message 2741 into the spanning tree. At the same time, if the message was a Join 2742 X initiates NS/NA route optimization the same as for the SSM case 2743 discussed in Section 3.17.1. 2745 For each source S that sends multicast traffic to group G via R, the 2746 Proxy/Server Z* for the Client that aggregates S encapsulates the 2747 packets in PIM Register messages and forwards them to R via the 2748 spanning tree, which may then elect to send a PIM Join to Z*. This 2749 will result in an (S,G) tree rooted at Z* with R as the next hop so 2750 that R will begin to receive two copies of the packet; one native 2751 copy from the (S, G) tree and a second copy from the pre-existing (*, 2752 G) tree that still uses PIM Register encapsulation. R can then issue 2753 a PIM Register-stop message to suppress the Register-encapsulated 2754 stream. At some later time, if C moves to a new Proxy/Server Z*, it 2755 resumes sending packets via PIM Register encapsulation via the new 2756 Z*. 2758 At the same time, as multicast listeners discover individual S's for 2759 a given G, they can initiate an (S,G) Join for each S under the same 2760 procedures discussed in Section 3.17.1. Once the (S,G) tree is 2761 established, the listeners can send (S, G) Prune messages to R so 2762 that multicast packets for group G sourced by S will only be 2763 delivered via the (S, G) tree and not from the (*, G) tree rooted at 2764 R. All mobility considerations discussed for SSM apply. 2766 3.17.3. Bi-Directional PIM (BIDIR-PIM) 2768 Bi-Directional PIM (BIDIR-PIM) [RFC5015] provides an alternate 2769 approach to ASM that treats the Rendezvous Point (RP) as a Designated 2770 Forwarder (DF). Further considerations for BIDIR-PIM are out of 2771 scope. 2773 3.18. Operation over Multiple OMNI Links 2775 An AERO Client can connect to multiple OMNI links the same as for any 2776 data link service. In that case, the Client maintains a distinct 2777 OMNI interface for each link, e.g., 'omni0' for the first link, 2778 'omni1' for the second, 'omni2' for the third, etc. Each OMNI link 2779 would include its own distinct set of Bridges, Servers and Proxys, 2780 thereby providing redundancy in case of failures. 2782 Each OMNI link could utilize the same or different ANET connections. 2783 The links can be distinguished at the link-layer via the SRT prefix 2784 in a similar fashion as for Virtual Local Area Network (VLAN) tagging 2785 (e.g., IEEE 802.1Q) and/or through assignment of distinct sets of 2786 MSPs on each link. This gives rise to the opportunity for supporting 2787 multiple redundant networked paths, with each VLAN distinguished by a 2788 different SRT "color" (see: Section 3.2.5). 2790 The Client's IP layer can select the outgoing OMNI interface 2791 appropriate for a given traffic profile while (in the reverse 2792 direction) correspondent nodes must have some way of steering their 2793 packets destined to a target via the correct OMNI link. 2795 In a first alternative, if each OMNI link services different MSPs, 2796 then the Client can receive a distinct MNP from each of the links. 2797 IP routing will therefore assure that the correct Red/Green/Blue/etc. 2798 network is used for both outbound and inbound traffic. This can be 2799 accomplished using existing technologies and approaches, and without 2800 requiring any special supporting code in correspondent nodes or 2801 Bridges. 2803 In a second alternative, if each OMNI link services the same MSP(s) 2804 then each link could assign a distinct "OMNI link Anycast" address 2805 that is configured by all Bridges on the link. Correspondent nodes 2806 can then perform Segment Routing to select the correct SRT, which 2807 will then direct the packet over multiple hops to the target. 2809 3.19. DNS Considerations 2811 AERO Client MNs and INET correspondent nodes consult the Domain Name 2812 System (DNS) the same as for any Internetworking node. When 2813 correspondent nodes and Client MNs use different IP protocol versions 2814 (e.g., IPv4 correspondents and IPv6 MNs), the INET DNS must maintain 2815 A records for IPv4 address mappings to MNs which must then be 2816 populated in Relay NAT64 mapping caches. In that way, an IPv4 2817 correspondent node can send packets to the IPv4 address mapping of 2818 the target MN, and the Relay will translate the IPv4 header and 2819 destination address into an IPv6 header and IPv6 destination address 2820 of the MN. 2822 When an AERO Client registers with an AERO Server, the Server can 2823 return the address(es) of DNS servers in RDNSS options [RFC6106]. 2824 The DNS server provides the IP addresses of other MNs and 2825 correspondent nodes in AAAA records for IPv6 or A records for IPv4. 2827 3.20. Transition Considerations 2829 OAL encapsulation ensures that dissimilar INET partitions can be 2830 joined into a single unified OMNI link, even though the partitions 2831 themselves may have differing protocol versions and/or incompatible 2832 addressing plans. However, a commonality can be achieved by 2833 incrementally distributing globally routable (i.e., native) IP 2834 prefixes to eventually reach all nodes (both mobile and fixed) in all 2835 OMNI link segments. This can be accomplished by incrementally 2836 deploying AERO Relays on each INET partition, with each Relay 2837 distributing its MNPs and/or discovering non-MNP prefixes on its INET 2838 links. 2840 This gives rise to the opportunity to eventually distribute native IP 2841 addresses to all nodes, and to present a unified OMNI link view even 2842 if the INET partitions remain in their current protocol and 2843 addressing plans. In that way, the OMNI link can serve the dual 2844 purpose of providing a mobility/multilink service and a transition 2845 service. Or, if an INET partition is transitioned to a native IP 2846 protocol version and addressing scheme that is compatible with the 2847 OMNI link MNP-based addressing scheme, the partition and OMNI link 2848 can be joined by Relays. 2850 Relays that connect INETs/EUNs with dissimilar IP protocol versions 2851 may need to employ a network address and protocol translation 2852 function such as NAT64 [RFC6146]. 2854 3.21. Detecting and Reacting to Server and Bridge Failures 2856 In environments where rapid failure recovery is required, Servers and 2857 Bridges SHOULD use Bidirectional Forwarding Detection (BFD) 2858 [RFC5880]. Nodes that use BFD can quickly detect and react to 2859 failures so that cached information is re-established through 2860 alternate nodes. BFD control messaging is carried only over well- 2861 connected ground domain networks (i.e., and not low-end radio links) 2862 and can therefore be tuned for rapid response. 2864 Servers and Bridges maintain BFD sessions in parallel with their BGP 2865 peerings. If a Server or Bridge fails, BGP peers will quickly re- 2866 establish routes through alternate paths the same as for common BGP 2867 deployments. Similarly, Proxys maintain BFD sessions with their 2868 associated Bridges even though they do not establish BGP peerings 2869 with them. 2871 Proxys SHOULD use proactive NUD for Servers for which there are 2872 currently active ANET Clients in a manner that parallels BFD, i.e., 2873 by sending unicast NS messages in rapid succession to receive 2874 solicited NA messages. When the Proxy is also sending RS messages on 2875 behalf of ANET Clients, the RS/RA messaging can be considered as 2876 equivalent hints of forward progress. This means that the Proxy need 2877 not also send a periodic NS if it has already sent an RS within the 2878 same period. If a Server fails, the Proxy will cease to receive 2879 advertisements and can quickly inform Clients of the outage by 2880 sending multicast RA messages on the ANET interface. 2882 The Proxy sends multicast RA messages with source address set to the 2883 Server's address, destination address set to (link-local) All-Nodes 2884 multicast, and Router Lifetime set to 0. The Proxy SHOULD send 2885 MAX_FINAL_RTR_ADVERTISEMENTS RA messages separated by small delays 2886 [RFC4861]. Any Clients on the ANET interface that have been using 2887 the (now defunct) Server will receive the RA messages and associate 2888 with a new Server. 2890 3.22. AERO Clients on the Open Internet 2892 AERO Clients that connect to the open Internet via INET interfaces 2893 can establish a VPN or direct link to securely connect to a Server in 2894 a "tethered" arrangement with all of the Client's traffic transiting 2895 the Server. Alternatively, the Client can associate with an INET 2896 Server using UDP/IP encapsulation and asymmetric securing services as 2897 discussed in the following sections. 2899 When a Client's OMNI interface enables an INET underlying interface, 2900 it first determines whether the interface is likely to be behind a 2901 NAT. For IPv4, the Client assumes it is on the open Internet if the 2902 INET address is not a special-use IPv4 address per [RFC3330]. 2903 Similarly for IPv6, the Client assumes it is on the open Internet if 2904 the INET address is not a link-local [RFC4291] or unique-local 2905 [RFC4193] IPv6 address. 2907 The Client then prepares a UDP/IP-encapsulated RS message with IPv6 2908 source address set to its LLA, with IPv6 destination set to (link- 2909 local) All-Routers multicast and with an OMNI option with underlying 2910 interface parameters. If the Client believes that it is on the open 2911 Internet, it SHOULD include Interface Attributes with the L2ADDR used 2912 for INET encapsulation (otherwise, it MAY omit L2ADDR). If the 2913 underlying address is IPv4, the Client includes the Port Number and 2914 IPv4 address written in obfuscated form [RFC4380] as discussed in 2915 Section 3.3. If the underlying interface address is IPv6, the Client 2916 instead includes the Port Number and IPv6 address in obfuscated form. 2917 The Client finally includes an Authentication option per [RFC4380] to 2918 provide message authentication, sets the UDP/IP source to its INET 2919 address and UDP port, sets the UDP/IP destination to the Server's 2920 INET address and the AERO service port number (8060), then sends the 2921 message to the Server. 2923 When the Server receives the RS, it authenticates the message and 2924 registers the Client's MNP and INET interface information according 2925 to the OMNI option parameters. If the RS message includes an L2ADDR 2926 in the OMNI option, the Server compares the encapsulation IP address 2927 and UDP port number with the (unobfuscated) values. If the values 2928 are the same, the Server caches the Client's information as "INET" 2929 addresses meaning that the Client is likely to accept direct messages 2930 without requiring NAT traversal exchanges. If the values are 2931 different (or, if the OMNI option did not include an L2ADDR) the 2932 Server instead caches the Client's information as "NAT" addresses 2933 meaning that NAT traversal exchanges may be necessary. 2935 The Server then returns an RA message with IPv6 source and 2936 destination set corresponding to the addresses in the RS, and with an 2937 Authentication option per [RFC4380]. For IPv4, the Server also 2938 includes an Origin option per [RFC4380] with the mapped and 2939 obfuscated Port Number and IPv4 address observed in the encapsulation 2940 headers. For IPv6, the Server instead includes an IPv6 Origin option 2941 per Figure 7 with the mapped and obfuscated observed Port Number and 2942 IPv6 address (note that the value 0x02 in the second octet 2943 differentiates from other [RFC4380] option types). 2945 +--------+--------+-----------------+ 2946 | 0x00 | 0x02 | Origin port # | 2947 +--------+--------+-----------------+ 2948 ~ Origin IPv6 address ~ 2949 +-----------------------------------+ 2951 Figure 7: IPv6 Origin Option 2953 When the Client receives the RA message, it compares the mapped Port 2954 Number and IP address from the Origin option with its own address. 2955 If the addresses are the same, the Client assumes the open Internet / 2956 Cone NAT principle; if the addresses are different, the Client 2957 instead assumes that further qualification procedures are necessary 2958 to detect the type of NAT and proceeds according to standard 2959 [RFC4380] procedures. 2961 After the Client has registered its INET interfaces in such RS/RA 2962 exchanges it sends periodic RS messages to receive fresh RA messages 2963 before the Router Lifetime received on each INET interface expires. 2964 The Client also maintains default routes via its Servers, i.e., the 2965 same as described in earlier sections. 2967 When the Client sends messages to target IP addresses, it also 2968 invokes route optimization per Section 3.14 using IPv6 ND address 2969 resolution messaging. The Client sends the NS(AR) message to the 2970 Server wrapped in a UDP/IP header with an Authentication option with 2971 the NS source address set to the Client's LLA and destination address 2972 set to the target solicited node multicast address. The Server 2973 authenticates the message and sends a corresponding NS(AR) message 2974 over the spanning tree the same as if it were the ROS, but with the 2975 OAL source address set to the Server's DLA and destination set to the 2976 DLA of the target. When the ROR receives the NS(AR), it adds the 2977 Server's DLA and Client's LLA to the target's Report List, and 2978 returns an NA with OMNI option information for the target. The 2979 Server then returns a UDP/IP encapsulated NA message with an 2980 Authentication option to the Client. 2982 Following route optimization for targets in the same OMNI link 2983 segment, if the target's L2ADDR is on the open INET, the Client 2984 forwards data packets directly to the target INET address. If the 2985 target is behind a NAT, the Client first establishes NAT state for 2986 the L2ADDR using the "bubble" mechanisms specified in 2987 [RFC6081][RFC4380]. The Client continues to send data packets via 2988 its Server until NAT state is populated, then begins forwarding 2989 packets via the direct path through the NAT to the target. For 2990 targets in different OMNI link segments, the Client inserts an ORH 2991 and forwards data packets to the Bridge that returned the NA message. 2993 The ROR may return uNAs via the Server if the target moves, and the 2994 Server will send corresponding Authentication-protected uNAs to the 2995 Client. The Client can also send "loopback" NS(NUD) messages to test 2996 forward path reachability even though there is no security 2997 association between the Client and the target. 2999 The Client sends UDP/IP encapsulated IPv6 packets no larger than 1280 3000 bytes in one piece. In order to accommodate larger IPv6 packets (up 3001 to the OMNI interface MTU), the Client inserts an OAL header with 3002 source set to its own DLA and destination set to the DLA of the 3003 target and uses IPv6 fragmentation according to Section 3.9. The 3004 Client then encapsulates each fragment in a UDP/IP header and sends 3005 the fragments to the next hop. 3007 3.22.1. Use of SEND and CGA 3009 In some environments, use of the [RFC4380] Authentication option 3010 alone may be sufficient for assuring IPv6 ND message authentication 3011 between Clients and Servers. When additional protection is 3012 necessary, nodes should employ SEcure Neighbor Discovery (SEND) 3013 [RFC3971] with Cryptographically-Generated Addresses (CGA) [RFC3972]. 3015 When SEND/CGA are used, the Client prepares RS messages with its 3016 link-local CGA as the IPv6 source and (link-local) All-Routers 3017 multicast as the IPv6 Destination, includes any SEND options and 3018 wraps the message in an OAL header. The Client sets the OAL source 3019 address to its own DLA and sets the OAL destination address to (site- 3020 local) All-Routers multicast. The Client then wraps the RS message 3021 in UDP/IP headers according to [RFC4380] and sends the message to the 3022 Server. 3024 When the Server receives the message, it first verifies the 3025 Authentication option (if present) then uses the OAL source address 3026 to determine the MNP of the Client. The Server then processes the 3027 SEND options to authenticate the RS message and prepares an RA 3028 message response. The Server prepares the RA with its own link-local 3029 CGA as the IPv6 source and the CGA of the Client as the IPv6 3030 destination, includes any SEND options and wraps the message in an 3031 OAL header. The Server sets the OAL source address to its own DLA 3032 and sets the OAL destination address to the Client's DLA. The Server 3033 then wraps the RA message in UDP/IP headers according to [RFC4380] 3034 and sends the message to the Client. Thereafter, the Client/Server 3035 send additional RS/RA messages to maintain their association and any 3036 NAT state. 3038 The Client and Server also may exchange NS/NA messages using their 3039 own CGA as the source and with OAL encapsulation as above. When a 3040 Client sends an NS(AR), it sets the IPv6 source to its CGA and sets 3041 the IPv6 destination to the Solicited-Node Multicast address of the 3042 target. The Client then wraps the message in an OAL header with its 3043 own DLA as the source and the DLA of the target as the destination 3044 and sends it to the Server. The Server authenticates the message, 3045 then changes the IPv6 source address to the Client's LLA, removes the 3046 SEND options, and sends a corresponding NS(AR) into the spanning 3047 tree. When the Server receives the corresponding OAL-encapsulated 3048 NA, it changes the IPv6 destination address to the Client's CGA, 3049 inserts SEND options, then wraps the message in UDP/IP headers and 3050 sends it to the Client. 3052 When a Client sends a uNA, it sets the IPv6 source address to its own 3053 CGA and sets the IPv6 destination address to (link-local) All-Nodes 3054 multicast, includes SEND options, wraps the message in OAL and UDP/IP 3055 headers and sends the message to the Server. The Server 3056 authenticates the message, then changes the IPv6 address to the 3057 Client's LLA, removes the SEND options and forwards the message the 3058 same as discussed in Section 3.16.1. In the reverse direction, when 3059 the Server forwards a uNA to the Client, it changes the IPv6 address 3060 to its own CGA and inserts SEND options then forwards the message to 3061 the Client. 3063 When a Client sends an NS(NUD), it sets both the IPv6 source and 3064 destination address to its own LLA, wraps the message in an OAL 3065 header and UDP/IP headers, then sends the message directly to the 3066 peer which will loop the message back. In this case alone, the 3067 Client does not use the Server as a trust broker for forwarding the 3068 ND message. 3070 3.23. Time-Varying MNPs 3072 In some use cases, it is desirable, beneficial and efficient for the 3073 Client to receive a constant MNP that travels with the Client 3074 wherever it moves. For example, this would allow air traffic 3075 controllers to easily track aircraft, etc. In other cases, however 3076 (e.g., intelligent transportation systems), the MN may be willing to 3077 sacrifice a modicum of efficiency in order to have time-varying MNPs 3078 that can be changed every so often to defeat adversarial tracking. 3080 The DHCPv6 service offers a way for Clients that desire time-varying 3081 MNPs to obtain short-lived prefixes (e.g., on the order of a small 3082 number of minutes). In that case, the identity of the Client would 3083 not be bound to the MNP but rather the Client's identity would be 3084 bound to the DHCPv6 Device Unique Identifier (DUID) and used as the 3085 seed for Prefix Delegation. The Client would then be obligated to 3086 renumber its internal networks whenever its MNP (and therefore also 3087 its LLA) changes. This should not present a challenge for Clients 3088 with automated network renumbering services, however presents limits 3089 for the durations of ongoing sessions that would prefer to use a 3090 constant address. 3092 4. Implementation Status 3094 An early AERO implementation based on OpenVPN (https://openvpn.net/) 3095 was announced on the v6ops mailing list on January 10, 2018 and an 3096 initial public release of the AERO proof-of-concept source code was 3097 announced on the intarea mailing list on August 21, 2015. 3099 AERO Release-3.0.2 was tagged on October 15, 2020, and is undergoing 3100 internal testing. Additional releases expected Q42020, with first 3101 public release expected before year-end. 3103 5. IANA Considerations 3105 The IANA has assigned a 4-octet Private Enterprise Number "45282" for 3106 AERO in the "enterprise-numbers" registry. 3108 The IANA has assigned the UDP port number "8060" for an earlier 3109 experimental version of AERO [RFC6706]. This document obsoletes 3110 [RFC6706] and claims the UDP port number "8060" for all future use. 3112 The IANA is instructed to assign a new type value TBD in the IPv6 3113 Routing Types registry. 3115 No further IANA actions are required. 3117 6. Security Considerations 3119 AERO Bridges configure secured tunnels with AERO Servers, Relays and 3120 Proxys within their local OMNI link segments. Applicable secured 3121 tunnel alternatives include IPsec [RFC4301], TLS/SSL [RFC8446], DTLS 3122 [RFC6347], WireGuard [WG], etc. The AERO Bridges of all OMNI link 3123 segments in turn configure secured tunnels for their neighboring AERO 3124 Bridges in a spanning tree topology. Therefore, control messages 3125 exchanged between any pair of OMNI link neighbors on the spanning 3126 tree are already secured. 3128 AERO Servers, Relays and Proxys targeted by a route optimization may 3129 also receive data packets directly from arbitrary nodes in INET 3130 partitions instead of via the spanning tree. For INET partitions 3131 that apply effective ingress filtering to defeat source address 3132 spoofing, the simple data origin authentication procedures in 3133 Section 3.8 can be applied. 3135 For INET partitions that require strong security in the data plane, 3136 two options for securing communications include 1) disable route 3137 optimization so that all traffic is conveyed over secured tunnels, or 3138 2) enable on-demand secure tunnel creation between INET partition 3139 neighbors. Option 1) would result in longer routes than necessary 3140 and traffic concentration on critical infrastructure elements. 3141 Option 2) could be coordinated by establishing a secured tunnel on- 3142 demand instead of performing an NS/NA exchange in the route 3143 optimization procedures. Procedures for establishing on-demand 3144 secured tunnels are out of scope. 3146 AERO Clients that connect to secured ANETs need not apply security to 3147 their ND messages, since the messages will be intercepted by a 3148 perimeter Proxy that applies security on its INET-facing interface as 3149 part of the spanning tree (see above). AERO Clients connected to the 3150 open INET can use symmetric network and/or transport layer security 3151 services such as VPNs or can by some other means establish a direct 3152 link. When a VPN or direct link may be impractical, however, an 3153 asymmetric security service such as SEcure Neighbor Discovery (SEND) 3154 [RFC3971] with Cryptographically Generated Addresses (CGAs) [RFC3972] 3155 and/or the Authentication option [RFC4380] can be applied. 3157 Application endpoints SHOULD use application-layer security services 3158 such as TLS/SSL, DTLS or SSH [RFC4251] to assure the same level of 3159 protection as for critical secured Internet services. AERO Clients 3160 that require host-based VPN services SHOULD use symmetric network 3161 and/or transport layer security services such as IPsec, TLS/SSL, 3162 DTLS, etc. AERO Proxys and Servers can also provide a network-based 3163 VPN service on behalf of the Client, e.g., if the Client is located 3164 within a secured enclave and cannot establish a VPN on its own 3165 behalf. 3167 AERO Servers and Bridges present targets for traffic amplification 3168 Denial of Service (DoS) attacks. This concern is no different than 3169 for widely-deployed VPN security gateways in the Internet, where 3170 attackers could send spoofed packets to the gateways at high data 3171 rates. This can be mitigated by connecting Servers and Bridges over 3172 dedicated links with no connections to the Internet and/or when 3173 connections to the Internet are only permitted through well-managed 3174 firewalls. Traffic amplification DoS attacks can also target an AERO 3175 Client's low data rate links. This is a concern not only for Clients 3176 located on the open Internet but also for Clients in secured 3177 enclaves. AERO Servers and Proxys can institute rate limits that 3178 protect Clients from receiving packet floods that could DoS low data 3179 rate links. 3181 AERO Relays must implement ingress filtering to avoid a spoofing 3182 attack in which spurious messages with DLA addresses are injected 3183 into an OMNI link from an outside attacker. AERO Clients MUST ensure 3184 that their connectivity is not used by unauthorized nodes on their 3185 EUNs to gain access to a protected network, i.e., AERO Clients that 3186 act as routers MUST NOT provide routing services for unauthorized 3187 nodes. (This concern is no different than for ordinary hosts that 3188 receive an IP address delegation but then "share" the address with 3189 other nodes via some form of Internet connection sharing such as 3190 tethering.) 3192 The MAP list MUST be well-managed and secured from unauthorized 3193 tampering, even though the list contains only public information. 3194 The MAP list can be conveyed to the Client in a similar fashion as in 3195 [RFC5214] (e.g., through layer 2 data link login messaging, secure 3196 upload of a static file, DNS lookups, etc.). 3198 Although public domain and commercial SEND implementations exist, 3199 concerns regarding the strength of the cryptographic hash algorithm 3200 have been documented [RFC6273] [RFC4982]. 3202 SRH authentication facilities are specified in [RFC8754]. 3204 Security considerations for accepting link-layer ICMP messages and 3205 reflected packets are discussed throughout the document. 3207 Security considerations for IPv6 fragmentation and reassembly are 3208 discussed in [I-D.templin-6man-omni-interface]. 3210 7. Acknowledgements 3212 Discussions in the IETF, aviation standards communities and private 3213 exchanges helped shape some of the concepts in this work. 3214 Individuals who contributed insights include Mikael Abrahamsson, Mark 3215 Andrews, Fred Baker, Bob Braden, Stewart Bryant, Brian Carpenter, 3216 Wojciech Dec, Pavel Drasil, Ralph Droms, Adrian Farrel, Nick Green, 3217 Sri Gundavelli, Brian Haberman, Bernhard Haindl, Joel Halpern, Tom 3218 Herbert, Sascha Hlusiak, Lee Howard, Zdenek Jaron, Andre Kostur, 3219 Hubert Kuenig, Ted Lemon, Andy Malis, Satoru Matsushima, Tomek 3220 Mrugalski, Madhu Niraula, Alexandru Petrescu, Behcet Saikaya, Michal 3221 Skorepa, Joe Touch, Bernie Volz, Ryuji Wakikawa, Tony Whyman, Lloyd 3222 Wood and James Woodyatt. Members of the IESG also provided valuable 3223 input during their review process that greatly improved the document. 3224 Special thanks go to Stewart Bryant, Joel Halpern and Brian Haberman 3225 for their shepherding guidance during the publication of the AERO 3226 first edition. 3228 This work has further been encouraged and supported by Boeing 3229 colleagues including Kyle Bae, M. Wayne Benson, Dave Bernhardt, Cam 3230 Brodie, John Bush, Balaguruna Chidambaram, Irene Chin, Bruce Cornish, 3231 Claudiu Danilov, Don Dillenburg, Joe Dudkowski, Wen Fang, Samad 3232 Farooqui, Anthony Gregory, Jeff Holland, Seth Jahne, Brian Jaury, 3233 Greg Kimberly, Ed King, Madhuri Madhava Badgandi, Laurel Matthew, 3234 Gene MacLean III, Rob Muszkiewicz, Sean O'Sullivan, Vijay 3235 Rajagopalan, Greg Saccone, Rod Santiago, Kent Shuey, Brian Skeen, 3236 Mike Slane, Carrie Spiker, Katie Tran, Brendan Williams, Amelia 3237 Wilson, Julie Wulff, Yueli Yang, Eric Yeh and other members of the 3238 Boeing mobility, networking and autonomy teams. Kyle Bae, Wayne 3239 Benson, Katie Tran and Eric Yeh are especially acknowledged for 3240 implementing the AERO functions as extensions to the public domain 3241 OpenVPN distribution. 3243 Earlier works on NBMA tunneling approaches are found in 3244 [RFC2529][RFC5214][RFC5569]. 3246 Many of the constructs presented in this second edition of AERO are 3247 based on the author's earlier works, including: 3249 o The Internet Routing Overlay Network (IRON) 3250 [RFC6179][I-D.templin-ironbis] 3252 o Virtual Enterprise Traversal (VET) 3253 [RFC5558][I-D.templin-intarea-vet] 3255 o The Subnetwork Encapsulation and Adaptation Layer (SEAL) 3256 [RFC5320][I-D.templin-intarea-seal] 3258 o AERO, First Edition [RFC6706] 3260 Note that these works cite numerous earlier efforts that are not also 3261 cited here due to space limitations. The authors of those earlier 3262 works are acknowledged for their insights. 3264 This work is aligned with the NASA Safe Autonomous Systems Operation 3265 (SASO) program under NASA contract number NNA16BD84C. 3267 This work is aligned with the FAA as per the SE2025 contract number 3268 DTFAWA-15-D-00030. 3270 This work is aligned with the Boeing Commercial Airplanes (BCA) 3271 Internet of Things (IoT) and autonomy programs. 3273 This work is aligned with the Boeing Information Technology (BIT) 3274 MobileNet program. 3276 8. References 3277 8.1. Normative References 3279 [I-D.templin-6man-omni-interface] 3280 Templin, F. and T. Whyman, "Transmission of IP Packets 3281 over Overlay Multilink Network (OMNI) Interfaces", draft- 3282 templin-6man-omni-interface-50 (work in progress), October 3283 2020. 3285 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, 3286 DOI 10.17487/RFC0791, September 1981, 3287 . 3289 [RFC0792] Postel, J., "Internet Control Message Protocol", STD 5, 3290 RFC 792, DOI 10.17487/RFC0792, September 1981, 3291 . 3293 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 3294 Requirement Levels", BCP 14, RFC 2119, 3295 DOI 10.17487/RFC2119, March 1997, 3296 . 3298 [RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in 3299 IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473, 3300 December 1998, . 3302 [RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander, 3303 "SEcure Neighbor Discovery (SEND)", RFC 3971, 3304 DOI 10.17487/RFC3971, March 2005, 3305 . 3307 [RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)", 3308 RFC 3972, DOI 10.17487/RFC3972, March 2005, 3309 . 3311 [RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and 3312 More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191, 3313 November 2005, . 3315 [RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast 3316 Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005, 3317 . 3319 [RFC4380] Huitema, C., "Teredo: Tunneling IPv6 over UDP through 3320 Network Address Translations (NATs)", RFC 4380, 3321 DOI 10.17487/RFC4380, February 2006, 3322 . 3324 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 3325 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 3326 DOI 10.17487/RFC4861, September 2007, 3327 . 3329 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 3330 Address Autoconfiguration", RFC 4862, 3331 DOI 10.17487/RFC4862, September 2007, 3332 . 3334 [RFC6081] Thaler, D., "Teredo Extensions", RFC 6081, 3335 DOI 10.17487/RFC6081, January 2011, 3336 . 3338 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 3339 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 3340 May 2017, . 3342 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 3343 (IPv6) Specification", STD 86, RFC 8200, 3344 DOI 10.17487/RFC8200, July 2017, 3345 . 3347 [RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A., 3348 Richardson, M., Jiang, S., Lemon, T., and T. Winters, 3349 "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", 3350 RFC 8415, DOI 10.17487/RFC8415, November 2018, 3351 . 3353 8.2. Informative References 3355 [BGP] Huston, G., "BGP in 2015, http://potaroo.net", January 3356 2016. 3358 [I-D.bonica-6man-comp-rtg-hdr] 3359 Bonica, R., Kamite, Y., Alston, A., Henriques, D., and L. 3360 Jalil, "The IPv6 Compact Routing Header (CRH)", draft- 3361 bonica-6man-comp-rtg-hdr-23 (work in progress), October 3362 2020. 3364 [I-D.bonica-6man-crh-helper-opt] 3365 Li, X., Bao, C., Ruan, E., and R. Bonica, "Compressed 3366 Routing Header (CRH) Helper Option", draft-bonica-6man- 3367 crh-helper-opt-02 (work in progress), October 2020. 3369 [I-D.ietf-intarea-frag-fragile] 3370 Bonica, R., Baker, F., Huston, G., Hinden, R., Troan, O., 3371 and F. Gont, "IP Fragmentation Considered Fragile", draft- 3372 ietf-intarea-frag-fragile-17 (work in progress), September 3373 2019. 3375 [I-D.ietf-intarea-tunnels] 3376 Touch, J. and M. Townsley, "IP Tunnels in the Internet 3377 Architecture", draft-ietf-intarea-tunnels-10 (work in 3378 progress), September 2019. 3380 [I-D.ietf-rtgwg-atn-bgp] 3381 Templin, F., Saccone, G., Dawra, G., Lindem, A., and V. 3382 Moreno, "A Simple BGP-based Mobile Routing System for the 3383 Aeronautical Telecommunications Network", draft-ietf- 3384 rtgwg-atn-bgp-06 (work in progress), June 2020. 3386 [I-D.templin-6man-dhcpv6-ndopt] 3387 Templin, F., "A Unified Stateful/Stateless Configuration 3388 Service for IPv6", draft-templin-6man-dhcpv6-ndopt-10 3389 (work in progress), June 2020. 3391 [I-D.templin-intarea-seal] 3392 Templin, F., "The Subnetwork Encapsulation and Adaptation 3393 Layer (SEAL)", draft-templin-intarea-seal-68 (work in 3394 progress), January 2014. 3396 [I-D.templin-intarea-vet] 3397 Templin, F., "Virtual Enterprise Traversal (VET)", draft- 3398 templin-intarea-vet-40 (work in progress), May 2013. 3400 [I-D.templin-ironbis] 3401 Templin, F., "The Interior Routing Overlay Network 3402 (IRON)", draft-templin-ironbis-16 (work in progress), 3403 March 2014. 3405 [I-D.templin-v6ops-pdhost] 3406 Templin, F., "IPv6 Prefix Delegation and Multi-Addressing 3407 Models", draft-templin-v6ops-pdhost-26 (work in progress), 3408 June 2020. 3410 [OVPN] OpenVPN, O., "http://openvpn.net", October 2016. 3412 [RFC1035] Mockapetris, P., "Domain names - implementation and 3413 specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, 3414 November 1987, . 3416 [RFC1812] Baker, F., Ed., "Requirements for IP Version 4 Routers", 3417 RFC 1812, DOI 10.17487/RFC1812, June 1995, 3418 . 3420 [RFC2003] Perkins, C., "IP Encapsulation within IP", RFC 2003, 3421 DOI 10.17487/RFC2003, October 1996, 3422 . 3424 [RFC2236] Fenner, W., "Internet Group Management Protocol, Version 3425 2", RFC 2236, DOI 10.17487/RFC2236, November 1997, 3426 . 3428 [RFC2464] Crawford, M., "Transmission of IPv6 Packets over Ethernet 3429 Networks", RFC 2464, DOI 10.17487/RFC2464, December 1998, 3430 . 3432 [RFC2529] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4 3433 Domains without Explicit Tunnels", RFC 2529, 3434 DOI 10.17487/RFC2529, March 1999, 3435 . 3437 [RFC2983] Black, D., "Differentiated Services and Tunnels", 3438 RFC 2983, DOI 10.17487/RFC2983, October 2000, 3439 . 3441 [RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition 3442 of Explicit Congestion Notification (ECN) to IP", 3443 RFC 3168, DOI 10.17487/RFC3168, September 2001, 3444 . 3446 [RFC3330] IANA, "Special-Use IPv4 Addresses", RFC 3330, 3447 DOI 10.17487/RFC3330, September 2002, 3448 . 3450 [RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener 3451 Discovery Version 2 (MLDv2) for IPv6", RFC 3810, 3452 DOI 10.17487/RFC3810, June 2004, 3453 . 3455 [RFC4251] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH) 3456 Protocol Architecture", RFC 4251, DOI 10.17487/RFC4251, 3457 January 2006, . 3459 [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A 3460 Border Gateway Protocol 4 (BGP-4)", RFC 4271, 3461 DOI 10.17487/RFC4271, January 2006, 3462 . 3464 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 3465 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 3466 2006, . 3468 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 3469 Internet Protocol", RFC 4301, DOI 10.17487/RFC4301, 3470 December 2005, . 3472 [RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery 3473 Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April 3474 2006, . 3476 [RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet 3477 Control Message Protocol (ICMPv6) for the Internet 3478 Protocol Version 6 (IPv6) Specification", STD 89, 3479 RFC 4443, DOI 10.17487/RFC4443, March 2006, 3480 . 3482 [RFC4511] Sermersheim, J., Ed., "Lightweight Directory Access 3483 Protocol (LDAP): The Protocol", RFC 4511, 3484 DOI 10.17487/RFC4511, June 2006, 3485 . 3487 [RFC4541] Christensen, M., Kimball, K., and F. Solensky, 3488 "Considerations for Internet Group Management Protocol 3489 (IGMP) and Multicast Listener Discovery (MLD) Snooping 3490 Switches", RFC 4541, DOI 10.17487/RFC4541, May 2006, 3491 . 3493 [RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick, 3494 "Internet Group Management Protocol (IGMP) / Multicast 3495 Listener Discovery (MLD)-Based Multicast Forwarding 3496 ("IGMP/MLD Proxying")", RFC 4605, DOI 10.17487/RFC4605, 3497 August 2006, . 3499 [RFC4982] Bagnulo, M. and J. Arkko, "Support for Multiple Hash 3500 Algorithms in Cryptographically Generated Addresses 3501 (CGAs)", RFC 4982, DOI 10.17487/RFC4982, July 2007, 3502 . 3504 [RFC5015] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano, 3505 "Bidirectional Protocol Independent Multicast (BIDIR- 3506 PIM)", RFC 5015, DOI 10.17487/RFC5015, October 2007, 3507 . 3509 [RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site 3510 Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214, 3511 DOI 10.17487/RFC5214, March 2008, 3512 . 3514 [RFC5320] Templin, F., Ed., "The Subnetwork Encapsulation and 3515 Adaptation Layer (SEAL)", RFC 5320, DOI 10.17487/RFC5320, 3516 February 2010, . 3518 [RFC5522] Eddy, W., Ivancic, W., and T. Davis, "Network Mobility 3519 Route Optimization Requirements for Operational Use in 3520 Aeronautics and Space Exploration Mobile Networks", 3521 RFC 5522, DOI 10.17487/RFC5522, October 2009, 3522 . 3524 [RFC5558] Templin, F., Ed., "Virtual Enterprise Traversal (VET)", 3525 RFC 5558, DOI 10.17487/RFC5558, February 2010, 3526 . 3528 [RFC5569] Despres, R., "IPv6 Rapid Deployment on IPv4 3529 Infrastructures (6rd)", RFC 5569, DOI 10.17487/RFC5569, 3530 January 2010, . 3532 [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 3533 (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, 3534 . 3536 [RFC6106] Jeong, J., Park, S., Beloeil, L., and S. Madanapalli, 3537 "IPv6 Router Advertisement Options for DNS Configuration", 3538 RFC 6106, DOI 10.17487/RFC6106, November 2010, 3539 . 3541 [RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful 3542 NAT64: Network Address and Protocol Translation from IPv6 3543 Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146, 3544 April 2011, . 3546 [RFC6179] Templin, F., Ed., "The Internet Routing Overlay Network 3547 (IRON)", RFC 6179, DOI 10.17487/RFC6179, March 2011, 3548 . 3550 [RFC6221] Miles, D., Ed., Ooghe, S., Dec, W., Krishnan, S., and A. 3551 Kavanagh, "Lightweight DHCPv6 Relay Agent", RFC 6221, 3552 DOI 10.17487/RFC6221, May 2011, 3553 . 3555 [RFC6273] Kukec, A., Krishnan, S., and S. Jiang, "The Secure 3556 Neighbor Discovery (SEND) Hash Threat Analysis", RFC 6273, 3557 DOI 10.17487/RFC6273, June 2011, 3558 . 3560 [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer 3561 Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, 3562 January 2012, . 3564 [RFC6438] Carpenter, B. and S. Amante, "Using the IPv6 Flow Label 3565 for Equal Cost Multipath Routing and Link Aggregation in 3566 Tunnels", RFC 6438, DOI 10.17487/RFC6438, November 2011, 3567 . 3569 [RFC6706] Templin, F., Ed., "Asymmetric Extended Route Optimization 3570 (AERO)", RFC 6706, DOI 10.17487/RFC6706, August 2012, 3571 . 3573 [RFC6935] Eubanks, M., Chimento, P., and M. Westerlund, "IPv6 and 3574 UDP Checksums for Tunneled Packets", RFC 6935, 3575 DOI 10.17487/RFC6935, April 2013, 3576 . 3578 [RFC6936] Fairhurst, G. and M. Westerlund, "Applicability Statement 3579 for the Use of IPv6 UDP Datagrams with Zero Checksums", 3580 RFC 6936, DOI 10.17487/RFC6936, April 2013, 3581 . 3583 [RFC7333] Chan, H., Ed., Liu, D., Seite, P., Yokota, H., and J. 3584 Korhonen, "Requirements for Distributed Mobility 3585 Management", RFC 7333, DOI 10.17487/RFC7333, August 2014, 3586 . 3588 [RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I., 3589 Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent 3590 Multicast - Sparse Mode (PIM-SM): Protocol Specification 3591 (Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March 3592 2016, . 3594 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 3595 Decraene, B., Litkowski, S., and R. Shakir, "Segment 3596 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 3597 July 2018, . 3599 [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol 3600 Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, 3601 . 3603 [RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J., 3604 Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header 3605 (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020, 3606 . 3608 [WG] Wireguard, "Wireguard, https://www.wireguard.com", August 3609 2020. 3611 Appendix A. Non-Normative Considerations 3613 AERO can be applied to a multitude of Internetworking scenarios, with 3614 each having its own adaptations. The following considerations are 3615 provided as non-normative guidance: 3617 A.1. Implementation Strategies for Route Optimization 3619 Route optimization as discussed in Section 3.14 results in the route 3620 optimization source (ROS) creating an asymmetric neighbor cache entry 3621 for the target neighbor. The neighbor cache entry is maintained for 3622 at most ReachableTime seconds and then deleted unless updated. In 3623 order to refresh the neighbor cache entry lifetime before the 3624 ReachableTime timer expires, the specification requires 3625 implementations to issue a new NS/NA exchange to reset ReachableTime 3626 while data packets are still flowing. However, the decision of when 3627 to initiate a new NS/NA exchange and to perpetuate the process is 3628 left as an implementation detail. 3630 One possible strategy may be to monitor the neighbor cache entry 3631 watching for data packets for (ReachableTime - 5) seconds. If any 3632 data packets have been sent to the neighbor within this timeframe, 3633 then send an NS to receive a new NA. If no data packets have been 3634 sent, wait for 5 additional seconds and send an immediate NS if any 3635 data packets are sent within this "expiration pending" 5 second 3636 window. If no additional data packets are sent within the 5 second 3637 window, delete the neighbor cache entry. 3639 The monitoring of the neighbor data packet traffic therefore becomes 3640 an asymmetric ongoing process during the neighbor cache entry 3641 lifetime. If the neighbor cache entry expires, future data packets 3642 will trigger a new NS/NA exchange while the packets themselves are 3643 delivered over a longer path until route optimization state is re- 3644 established. 3646 A.2. Implicit Mobility Management 3648 OMNI interface neighbors MAY provide a configuration option that 3649 allows them to perform implicit mobility management in which no ND 3650 messaging is used. In that case, the Client only transmits packets 3651 over a single interface at a time, and the neighbor always observes 3652 packets arriving from the Client from the same link-layer source 3653 address. 3655 If the Client's underlying interface address changes (either due to a 3656 readdressing of the original interface or switching to a new 3657 interface) the neighbor immediately updates the neighbor cache entry 3658 for the Client and begins accepting and sending packets according to 3659 the Client's new address. This implicit mobility method applies to 3660 use cases such as cellphones with both WiFi and Cellular interfaces 3661 where only one of the interfaces is active at a given time, and the 3662 Client automatically switches over to the backup interface if the 3663 primary interface fails. 3665 A.3. Direct Underlying Interfaces 3667 When a Client's OMNI interface is configured over a Direct interface, 3668 the neighbor at the other end of the Direct link can receive packets 3669 without any encapsulation. In that case, the Client sends packets 3670 over the Direct link according to QoS preferences. If the Direct 3671 interface has the highest QoS preference, then the Client's IP 3672 packets are transmitted directly to the peer without going through an 3673 ANET/INET. If other interfaces have higher QoS preferences, then the 3674 Client's IP packets are transmitted via a different interface, which 3675 may result in the inclusion of Proxys, Servers and Bridges in the 3676 communications path. Direct interfaces must be tested periodically 3677 for reachability, e.g., via NUD. 3679 A.4. AERO Critical Infrastructure Considerations 3681 AERO Bridges can be either Commercial off-the Shelf (COTS) standard 3682 IP routers or virtual machines in the cloud. Bridges must be 3683 provisioned, supported and managed by the INET administrative 3684 authority, and connected to the Bridges of other INETs via inter- 3685 domain peerings. Cost for purchasing, configuring and managing 3686 Bridges is nominal even for very large OMNI links. 3688 AERO Servers can be standard dedicated server platforms, but most 3689 often will be deployed as virtual machines in the cloud. The only 3690 requirements for Servers are that they can run the AERO user-level 3691 code and have at least one network interface connection to the INET. 3692 As with Bridges, Servers must be provisioned, supported and managed 3693 by the INET administrative authority. Cost for purchasing, 3694 configuring and managing Servers is nominal especially for virtual 3695 Servers hosted in the cloud. 3697 AERO Proxys are most often standard dedicated server platforms with 3698 one network interface connected to the ANET and a second interface 3699 connected to an INET. As with Servers, the only requirements are 3700 that they can run the AERO user-level code and have at least one 3701 interface connection to the INET. Proxys must be provisioned, 3702 supported and managed by the ANET administrative authority. Cost for 3703 purchasing, configuring and managing Proxys is nominal, and borne by 3704 the ANET administrative authority. 3706 AERO Relays can be any dedicated server or COTS router platform 3707 connected to INETs and/or EUNs. The Relay connects to the OMNI link 3708 and engages in eBGP peering with one or more Bridges as a stub AS. 3709 The Relay then injects its MNPs and/or non-MNP prefixes into the BGP 3710 routing system, and provisions the prefixes to its downstream- 3711 attached networks. The Relay can perform ROS/ROR services the same 3712 as for any Server, and can route between the MNP and non-MNP address 3713 spaces. 3715 A.5. AERO Server Failure Implications 3717 AERO Servers may appear as a single point of failure in the 3718 architecture, but such is not the case since all Servers on the link 3719 provide identical services and loss of a Server does not imply 3720 immediate and/or comprehensive communication failures. Although 3721 Clients typically associate with a single Server at a time, Server 3722 failure is quickly detected and conveyed by Bidirectional Forward 3723 Detection (BFD) and/or proactive NUD allowing Clients to migrate to 3724 new Servers. 3726 If a Server fails, ongoing packet forwarding to Clients will continue 3727 by virtue of the asymmetric neighbor cache entries that have already 3728 been established in route optimization sources (ROSs). If a Client 3729 also experiences mobility events at roughly the same time the Server 3730 fails, unsolicited NA messages may be lost but proxy neighbor cache 3731 entries in the DEPARTED state will ensure that packet forwarding to 3732 the Client's new locations will continue for up to DepartTime 3733 seconds. 3735 If a Client is left without a Server for an extended timeframe (e.g., 3736 greater than ReachableTime seconds) then existing asymmetric neighbor 3737 cache entries will eventually expire and both ongoing and new 3738 communications will fail. The original source will continue to 3739 retransmit until the Client has established a new Server 3740 relationship, after which time continuous communications will resume. 3742 Therefore, providing many Servers on the link with high availability 3743 profiles provides resilience against loss of individual Servers and 3744 assurance that Clients can establish new Server relationships quickly 3745 in event of a Server failure. 3747 A.6. AERO Client / Server Architecture 3749 The AERO architectural model is client / server in the control plane, 3750 with route optimization in the data plane. The same as for common 3751 Internet services, the AERO Client discovers the addresses of AERO 3752 Servers and selects one Server to connect to. The AERO service is 3753 analogous to common Internet services such as google.com, yahoo.com, 3754 cnn.com, etc. However, there is only one AERO service for the link 3755 and all Servers provide identical services. 3757 Common Internet services provide differing strategies for advertising 3758 server addresses to clients. The strategy is conveyed through the 3759 DNS resource records returned in response to name resolution queries. 3760 As of January 2020 Internet-based 'nslookup' services were used to 3761 determine the following: 3763 o When a client resolves the domainname "google.com", the DNS always 3764 returns one A record (i.e., an IPv4 address) and one AAAA record 3765 (i.e., an IPv6 address). The client receives the same addresses 3766 each time it resolves the domainname via the same DNS resolver, 3767 but may receive different addresses when it resolves the 3768 domainname via different DNS resolvers. But, in each case, 3769 exactly one A and one AAAA record are returned. 3771 o When a client resolves the domainname "ietf.org", the DNS always 3772 returns one A record and one AAAA record with the same addresses 3773 regardless of which DNS resolver is used. 3775 o When a client resolves the domainname "yahoo.com", the DNS always 3776 returns a list of 4 A records and 4 AAAA records. Each time the 3777 client resolves the domainname via the same DNS resolver, the same 3778 list of addresses are returned but in randomized order (i.e., 3779 consistent with a DNS round-robin strategy). But, interestingly, 3780 the same addresses are returned (albeit in randomized order) when 3781 the domainname is resolved via different DNS resolvers. 3783 o When a client resolves the domainname "amazon.com", the DNS always 3784 returns a list of 3 A records and no AAAA records. As with 3785 "yahoo.com", the same three A records are returned from any 3786 worldwide Internet connection point in randomized order. 3788 The above example strategies show differing approaches to Internet 3789 resilience and service distribution offered by major Internet 3790 services. The Google approach exposes only a single IPv4 and a 3791 single IPv6 address to clients. Clients can then select whichever IP 3792 protocol version offers the best response, but will always use the 3793 same IP address according to the current Internet connection point. 3794 This means that the IP address offered by the network must lead to a 3795 highly-available server and/or service distribution point. In other 3796 words, resilience is predicated on high availability within the 3797 network and with no client-initiated failovers expected (i.e., it is 3798 all-or-nothing from the client's perspective). However, Google does 3799 provide for worldwide distributed service distribution by virtue of 3800 the fact that each Internet connection point responds with a 3801 different IPv6 and IPv4 address. The IETF approach is like google 3802 (all-or-nothing from the client's perspective), but provides only a 3803 single IPv4 or IPv6 address on a worldwide basis. This means that 3804 the addresses must be made highly-available at the network level with 3805 no client failover possibility, and if there is any worldwide service 3806 distribution it would need to be conducted by a network element that 3807 is reached via the IP address acting as a service distribution point. 3809 In contrast to the Google and IETF philosophies, Yahoo and Amazon 3810 both provide clients with a (short) list of IP addresses with Yahoo 3811 providing both IP protocol versions and Amazon as IPv4-only. The 3812 order of the list is randomized with each name service query 3813 response, with the effect of round-robin load balancing for service 3814 distribution. With a short list of addresses, there is still 3815 expectation that the network will implement high availability for 3816 each address but in case any single address fails the client can 3817 switch over to using a different address. The balance then becomes 3818 one of function in the network vs function in the end system. 3820 The same implications observed for common highly-available services 3821 in the Internet apply also to the AERO client/server architecture. 3822 When an AERO Client connects to one or more ANETs, it discovers one 3823 or more AERO Server addresses through the mechanisms discussed in 3824 earlier sections. Each Server address presumably leads to a fault- 3825 tolerant clustering arrangement such as supported by Linux-HA, 3826 Extended Virtual Synchrony or Paxos. Such an arrangement has 3827 precedence in common Internet service deployments in lightweight 3828 virtual machines without requiring expensive hardware deployment. 3829 Similarly, common Internet service deployments set service IP 3830 addresses on service distribution points that may relay requests to 3831 many different servers. 3833 For AERO, the expectation is that a combination of the Google/IETF 3834 and Yahoo/Amazon philosophies would be employed. The AERO Client 3835 connects to different ANET access points and can receive 1-2 Server 3836 LLAs at each point. It then selects one AERO Server address, and 3837 engages in RS/RA exchanges with the same Server from all ANET 3838 connections. The Client remains with this Server unless or until the 3839 Server fails, in which case it can switch over to an alternate 3840 Server. The Client can likewise switch over to a different Server at 3841 any time if there is some reason for it to do so. So, the AERO 3842 expectation is for a balance of function in the network and end 3843 system, with fault tolerance and resilience at both levels. 3845 Appendix B. Change Log 3847 << RFC Editor - remove prior to publication >> 3849 Changes from draft-templin-intarea-6706bis-61 to draft-templin- 3850 intrea-6706bis-62: 3852 o New sub-section on OMNI Neighbor Interface Attributes 3854 Changes from draft-templin-intarea-6706bis-59 to draft-templin- 3855 intrea-6706bis-60: 3857 o Removed all references to S/TLLAO - all Interface Attributes are 3858 now maintained completely in the OMNI option. 3860 Changes from draft-templin-intarea-6706bis-58 to draft-templin- 3861 intrea-6706bis-59: 3863 o The term "Relay" used in older draft versions is now "Bridge". 3864 "Relay" now refers to what was formally called: "Gateway". 3866 o Fine-grained cleanup of Forwarding Algorithm; IPv6 ND message 3867 addressing; OMNI Prefix Lengths, etc. 3869 Changes from draft-templin-intarea-6706bis-54 to draft-templin- 3870 intrea-6706bis-55: 3872 o Updates on Segment Routing and S/TLLAO contents. 3874 o Various editorials and addressing cleanups. 3876 Changes from draft-templin-intarea-6706bis-52 to draft-templin- 3877 intrea-6706bis-53: 3879 o Normative reference to the OMNI spec, and remove portions that are 3880 already specified in OMNI. 3882 o Renamed "AERO interface/link" to "OMIN interface/link" throughout 3883 the document. 3885 o Truncated obsolete back section matter. 3887 Author's Address 3889 Fred L. Templin (editor) 3890 Boeing Research & Technology 3891 P.O. Box 3707 3892 Seattle, WA 98124 3893 USA 3895 Email: fltemplin@acm.org