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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-69 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 For OMNI Link Selection . . . . . . . 21 76 3.2.7. Segment Routing Within the OMNI Link . . . . . . . . 21 77 3.3. OMNI Interface Characteristics . . . . . . . . . . . . . 22 78 3.4. OMNI Interface Initialization . . . . . . . . . . . . . . 24 79 3.4.1. AERO Server/Relay Behavior . . . . . . . . . . . . . 24 80 3.4.2. AERO Proxy Behavior . . . . . . . . . . . . . . . . . 25 81 3.4.3. AERO Client Behavior . . . . . . . . . . . . . . . . 25 82 3.4.4. AERO Bridge Behavior . . . . . . . . . . . . . . . . 25 83 3.5. OMNI Interface Neighbor Cache Maintenance . . . . . . . . 25 84 3.5.1. OMNI Neighbor Interface Attributes . . . . . . . . . 27 85 3.5.2. OMNI Neighbor Advertisement Message Flags . . . . . . 28 86 3.6. OMNI Interface Encapsulation and Re-encapsulation . . . . 28 87 3.7. OMNI Interface Decapsulation . . . . . . . . . . . . . . 30 88 3.8. OMNI Interface Data Origin Authentication . . . . . . . . 30 89 3.9. OMNI Adaptation Layer and OMNI Interface MTU . . . . . . 30 90 3.10. OMNI Interface Forwarding Algorithm . . . . . . . . . . . 31 91 3.10.1. Client Forwarding Algorithm . . . . . . . . . . . . 32 92 3.10.2. Proxy Forwarding Algorithm . . . . . . . . . . . . . 32 93 3.10.3. Server/Relay Forwarding Algorithm . . . . . . . . . 33 94 3.10.4. Bridge Forwarding Algorithm . . . . . . . . . . . . 34 96 3.11. OMNI Interface Error Handling . . . . . . . . . . . . . . 35 97 3.12. AERO Router Discovery, Prefix Delegation and 98 Autoconfiguration . . . . . . . . . . . . . . . . . . . . 37 99 3.12.1. AERO Service Model . . . . . . . . . . . . . . . . . 37 100 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 . . . . 45 105 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 . . . . . . . . . . . . . . . . . 49 112 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 . . . . . . . . . . . . 54 120 3.16.5. Moving Between Servers . . . . . . . . . . . . . . . 55 121 3.17. Multicast . . . . . . . . . . . . . . . . . . . . . . . . 56 122 3.17.1. Source-Specific Multicast (SSM) . . . . . . . . . . 56 123 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 . . . . . . . . . . . . . . . . . . . 59 127 3.20. Transition Considerations . . . . . . . . . . . . . . . . 60 128 3.21. Detecting and Reacting to Server and Bridge Failures . . 60 129 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 . . . . . . . . . . . . . . . . . . . . 65 133 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 66 134 6. Security Considerations . . . . . . . . . . . . . . . . . . . 66 135 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 68 136 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 69 137 8.1. Normative References . . . . . . . . . . . . . . . . . . 69 138 8.2. Informative References . . . . . . . . . . . . . . . . . 71 139 Appendix A. Non-Normative Considerations . . . . . . . . . . . . 76 140 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 . . . . . . . . . . . . 79 146 Appendix B. Change Log . . . . . . . . . . . . . . . . . . . . . 81 147 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 82 149 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 OMNI link segments can be carried over the spanning tree 751 via mid-layer encapsulations using the OMNI Adaptation Layer (OAL) 752 header and/or the OMNI Routing Header (ORH). OAL encapsulation is 753 used for all IPv4 packets, for IPv6 packets for which route 754 optimization addressing information for the final segment is not yet 755 known, for transportation of IPv6 ND messages, and when fragmentation 756 is necessary (see Section 5 of [I-D.templin-6man-omni-interface]). 757 OAL encapsulation is based on Generic Packet Tunneling in IPv6 758 [RFC2473], with the inclusion of an ORH as an extension to the OAL 759 header if final segment link-layer address and/or final IPv6 760 destination address information is necessary. 762 The ORH is formatted as shown in Figure 3: 764 0 1 2 3 765 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 1 766 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 767 | Next Header | Hdr Ext Len | Routing Type | Segments Left | 768 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 769 | Reserved | SRT | FMT | LHS (bits 0 - 15) | 770 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 771 | LHS (bits 16 - 31) | ~ 772 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ 773 ~ Link Layer Address (L2ADDR) ~ 774 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 775 ~ IPv6 Destination Address ~ 776 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 777 ~ Null Padding ~ 778 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 780 Figure 3: OMNI Routing Header (ORH) Format 782 In this format: 784 o Next Header identifies the type of header immediately following 785 the ORH. 787 o Hdr Ext Len is the length of the Routing header in 8-octet units, 788 not including the first 8 octets. 790 o Routing Type is set to TBD (see IANA Considerations). 792 o Segments Left is set to the value 1 if an IPv6 Destination Address 793 is included, or the value 0 if no IPv6 Destination Address is 794 included. If Segments Left encodes any other value, the entire 795 ORH is ignored and the next header is processed. 797 o Reserved is set to 0 on transmission and ignored on reception. 799 o SRT - a 5-bit Segment Routing Topology prefix length value that 800 (when added to 96) determines the prefix length to apply to the 801 DLA formed from concatenating [DLA*]::/96 with the 32 bit LHS MSID 802 value that follows. For example, the value 16 corresponds to the 803 prefix length 112. 805 o FMT - a 3-bit "Framework/Mode/Type" code corresponding to the 806 included Link Layer Address as follows: 808 * When the most significant bit (i.e., "Framework") is set to 0, 809 L2ADDR is the INET encapsulation address of a Server/Proxy; 810 otherwise, it is the address for the Source/Target itself. 812 * When the next most significant bit (i.e., "Mode") is set to 0, 813 the Source/Target L2ADDR is on the open INET; otherwise, it is 814 (likely) located behind a Network Address Translator (NAT). 816 * When the least significant bit (i.e., "Type") is set to 0, 817 L2ADDR includes a UDP Port Number followed by an IPv4 address; 818 else, a UDP Port Number followed by an IPv6 address. 820 o LHS - the 32 bit MSID of the Last Hop Server/Proxy on the path to 821 the target. When SRT and LHS are both set to 0, the LHS is 822 considered unspecified in this IPv6 ND message. When SRT is set 823 to 0 and LHS is non-zero, the prefix length is set to 128. SRT 824 and LHS provide guidance to the OMNI interface forwarding 825 algorithm. Specifically, if SRT/LHS is located in the local OMNI 826 link segment then the OMNI interface can encapsulate according to 827 FMT/L2ADDR; else, it must forward according to the OMNI link 828 spanning tree. 830 o Link Layer Address (L2ADDR) - Formatted according to FMT, and 831 identifies the link-layer address (i.e., the encapsulation 832 address) of the source/target. The UDP Port Number appears in the 833 first two octets and the IP address appears in the next 4 octets 834 for IPv4 or 16 octets for IPv6. The Port Number and IP address 835 are recorded in ones-compliment "obfuscated" form per [RFC4380]. 836 The OMNI interface forwarding algorithm uses FMT/L2ADDR to 837 determine the encapsulation address for forwarding when SRT/LHS is 838 located in the local OMNI link segment. 840 o IPv6 Destination Address is a 16-octet IPv6 address included only 841 when Segments Left is 1, and omitted otherwise. 843 o Null Padding contains 0/4 zero-valued octets as necessary to pad 844 the ORH to an integral number of 8-octet units. 846 When an AERO node uses OAL encapsulation for a packet with IPv6 847 source address 2001:db8:1:2::1 and IPv6 destination address 848 2001:db8:1000:2000::1 and the LHS is not yet known, it sets the OAL 849 header source address to its own DLA address (e.g., [DLA]::1000:2000) 850 and sets the destination address to [DLA]:2001:db8:1000:2000::. The 851 node also includes an ORH header as an extension to the OAL header if 852 necessary, then fragments the mid-layer packet if necessary (note 853 that the ORH header need not include an IPv6 destination address, 854 since the address is already included in the encapsulated IPv6 855 packet). Next, the node encapsulates each resulting OAL packet in an 856 INET header with source address set to its own INET address (e.g., 857 192.0.2.100) and destination set to the INET address of a Bridge 858 (e.g., 192.0.2.1). The encapsulation format in the above example is 859 shown in Figure 4: 861 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 862 | INET Header | 863 | src = 192.0.2.100 | 864 | dst = 192.0.2.1 | 865 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 866 | OAL Header | 867 | src = [DLA]::1000:2000 | 868 | dst=[DLA]:2001:db8:1000:2000::| 869 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 870 | ORH Header | 871 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 872 | Inner IP Header | 873 | src = 2001:db8:1:2::1 | 874 | dst = 2001:db8:1000:2000::1 | 875 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 876 | | 877 ~ ~ 878 ~ Inner Packet Body ~ 879 ~ ~ 880 | | 881 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 883 Figure 4: OAL/ORH Encapsulation 885 In this format, the inner IP header and packet body are the original 886 IP packet, the OAL header is an IPv6 header prepared according to 887 [RFC2473], the ORH is a Routing Header extension of the OAL header, 888 and the INET header is prepared as discussed in Section 3.6. 890 For IPv6 packets with non-link-local addresses for which the LHS is 891 known, the AERO node can avoid OAL encapsulation while inserting an 892 ORH as an extension to the existing IPv6 header of the packet. The 893 node further changes the IPv6 destination address to the Subnet 894 Router Anycast address corresponding to the LHS DLA address (for 895 example, for LHS [DLA]::1000:2000 and with SRT prefix length 16, the 896 Subnet Router Anycast address is [DLA]::1000:0000). When the node 897 changes the IPv6 destination address, it places the original 898 destination address in the ORH header so that it can be restored upon 899 OMNI link egress. The 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 is identified by a unqiue interface name (e.g., 966 omni0, omni1, omni2, etc.) and assigns an anycast DLA corresponding 967 to its SRT prefix. For example, the anycast DLA for the Green SRT is 968 simply [DLA1]::. The anycast DLA is used for OMNI interface 969 determination in Safety-Based Multilink (SBM) as discussed in 970 [I-D.templin-6man-omni-interface]. Each OMNI interface further 971 applies Performance-Based Multilink (PBM) internally. 973 3.2.6. Segment Routing For OMNI Link Selection 975 An original IPv6 source can direct an IPv6 packet to an AERO node by 976 including a standard IPv6 Segment Routing Header (SRH) [RFC8754] with 977 the anycast DLA for the selected SRT as either the IPv6 destination 978 or as an intermediate hop within the SRH. This allows the original 979 source to determine the specific OMNI link topology a packet will 980 traverse when there may be multiple alternatives. 982 When the AERO node processes the SRH and forwards the packet to the 983 correct OMNI interface, the OMNI interface writes the next IPv6 984 address from the SRH into the IPv6 desination address and decrements 985 Segments Left. If decrementing would cause Segments Left to become 986 0, the OMNI interface deletes the SRH before forwarding. This form 987 of Segment Routing supports Safety-Based Multilink (SBM). 989 3.2.7. Segment Routing Within the OMNI Link 991 AERO node OMNI interfaces can insert an OAL and/or ORH header for 992 Segment Routing within the OMNI link to influence the paths of 993 packets destined to targets in remote segments without requiring all 994 packets to traverse strict spanning tree paths. 996 When an AERO node's OMNI interface has a packet to send to a target 997 discovered through route optimization located in the same OMNI link 998 segment, it encapsulates the packet in OAL/ORH headers if necessary 999 as discussed above. The node then uses the target's Link Layer 1000 Address (L2ADDR) information for INET encapsulation. 1002 When an AERO node's OMNI interface has a packet to send to a route 1003 optimization target located in a remote OMNI link segment, it 1004 encapsulates the packet in OAL/ORH headers as discussed above while 1005 forwarding the packet to a Bridge with destination set to the Subnet 1006 Router Anycast address for the final OMNI link segment. 1008 When a Bridge receives a packet destined to its Subnet Router Anycast 1009 address with an ORH with SRT/LHS values corresponding to the local 1010 segment, it examines the L2ADDR according to FMT and removes the ORH 1011 from the packet. If the packet did not include an OAL header, the 1012 Bridge writes the saved IPv6 address from the ORH into the packet's 1013 IPv6 destination address; otherwise, the Bridge writes the DLA 1014 corresponding to the inner packet IPv6 destination addresss into the 1015 OAL header destination. Next, the Bridge encapsulates the packet in 1016 an INET header according to L2ADDR and forwards the packet within the 1017 INET either to the LHS Server/Proxy or directly to the destination 1018 itself. In this way, the Bridge participates in route optimization 1019 to reduce traffic load and suboptimal routing through strict spanning 1020 tree paths. 1022 3.3. OMNI Interface Characteristics 1024 OMNI interfaces are virtual interfaces configured over one or more 1025 underlying interfaces classified as follows: 1027 o INET interfaces connect to an INET either natively or through one 1028 or several IPv4 Network Address Translators (NATs). Native INET 1029 interfaces have global IP addresses that are reachable from any 1030 INET correspondent. All Server, Relay and Bridge interfaces are 1031 native interfaces, as are INET-facing interfaces of Proxys. NATed 1032 INET interfaces connect to a private network behind one or more 1033 NATs that provide INET access. Clients that are behind a NAT are 1034 required to send periodic keepalive messages to keep NAT state 1035 alive when there are no data packets flowing. 1037 o ANET interfaces connect to an ANET that is separated from the open 1038 INET by a Proxy. Proxys can actively issue control messages over 1039 the INET on behalf of the Client to reduce ANET congestion. 1041 o VPNed interfaces use security encapsulation over the INET to a 1042 Virtual Private Network (VPN) server that also acts as a Server or 1043 Proxy. Other than the link-layer encapsulation format, VPNed 1044 interfaces behave the same as Direct interfaces. 1046 o Direct interfaces connect a Client directly to a Server or Proxy 1047 without crossing any ANET/INET paths. An example is a line-of- 1048 sight link between a remote pilot and an unmanned aircraft. The 1049 same Client considerations apply as for VPNed interfaces. 1051 OMNI interfaces use OAL/ORH encapsulation as necessary as discussed 1052 in Section 3.2.4. OMNI interfaces use link-layer encapsulation (see: 1053 Section 3.6) to exchange packets with OMNI link neighbors over INET 1054 or VPNed interfaces. OMNI interfaces do not use link-layer 1055 encapsulation over ANET and Direct underlying interfaces. 1057 OMNI interfaces maintain a neighbor cache for tracking per-neighbor 1058 state the same as for any interface. OMNI interfaces use ND messages 1059 including Router Solicitation (RS), Router Advertisement (RA), 1060 Neighbor Solicitation (NS) and Neighbor Advertisement (NA) for 1061 neighbor cache management. 1063 OMNI interfaces send ND messages with an OMNI option formatted as 1064 specified in [I-D.templin-6man-omni-interface]. The OMNI option 1065 includes prefix registration information and Interface Attributes 1066 containing link information parameters for the OMNI interface's 1067 underlying interfaces. Each OMNI option may include multiple 1068 Interface Attributes sub-options, each identified by an ifIndex 1069 value. 1071 A Client's OMNI interface may be configured over multiple underlying 1072 interface connections. For example, common mobile handheld devices 1073 have both wireless local area network ("WLAN") and cellular wireless 1074 links. These links are often used "one at a time" with low-cost WLAN 1075 preferred and highly-available cellular wireless as a standby, but a 1076 simultaneous-use capability could provide benefits. In a more 1077 complex example, aircraft frequently have many wireless data link 1078 types (e.g. satellite-based, cellular, terrestrial, air-to-air 1079 directional, etc.) with diverse performance and cost properties. 1081 If a Client's multiple underlying interfaces are used "one at a time" 1082 (i.e., all other interfaces are in standby mode while one interface 1083 is active), then ND message OMNI options include only a single 1084 Interface Attributes sub-option set to constant values. In that 1085 case, the Client would appear to have a single interface but with a 1086 dynamically changing link-layer address. 1088 If the Client has multiple active underlying interfaces, then from 1089 the perspective of ND it would appear to have multiple link-layer 1090 addresses. In that case, ND message OMNI options MAY include 1091 multiple Interface Attributes sub-options - each with values that 1092 correspond to a specific interface. Every ND message need not 1093 include Interface Attributes for all underlying interfaces; for any 1094 attributes not included, the neighbor considers the status as 1095 unchanged. 1097 Bridge, Server and Proxy OMNI interfaces may be configured over one 1098 or more secured tunnel interfaces. The OMNI interface configures 1099 both an LLA and its corresponding DLA, while the underlying secured 1100 tunnel interfaces are either unnumbered or configure the same DLA. 1101 The OMNI interface encapsulates each IP packet in OAL/ORH headers and 1102 presents the packet to the underlying secured tunnel interface. 1103 Routing protocols such as BGP that run over the OMNI interface do not 1104 employ OAL/ORH encapsulation, but rather present the routing protocol 1105 messages directly to the underlying secured tunnels while using the 1106 DLA as the source address. This distinction must be honored 1107 consistently according to each node's configuration so that the IP 1108 forwarding table will associate discovered IP routes with the correct 1109 interface. 1111 3.4. OMNI Interface Initialization 1113 AERO Servers, Proxys and Clients configure OMNI interfaces as their 1114 point of attachment to the OMNI link. AERO nodes assign the MSPs for 1115 the link to their OMNI interfaces (i.e., as a "route-to-interface") 1116 to ensure that packets with destination addresses covered by an MNP 1117 not explicitly assigned to a non-OMNI interface are directed to the 1118 OMNI interface. 1120 OMNI interface initialization procedures for Servers, Proxys, Clients 1121 and Bridges are discussed in the following sections. 1123 3.4.1. AERO Server/Relay Behavior 1125 When a Server enables an OMNI interface, it assigns an LLA/DLA 1126 appropriate for the given OMNI link segment. The Server also 1127 configures secured tunnels with one or more neighboring Bridges and 1128 engages in a BGP routing protocol session with each Bridge. 1130 The OMNI interface provides a single interface abstraction to the IP 1131 layer, but internally comprises multiple secured tunnels as well as 1132 an NBMA nexus for sending encapsulated data packets to OMNI interface 1133 neighbors. The Server further configures a service to facilitate ND 1134 exchanges with AERO Clients and manages per-Client neighbor cache 1135 entries and IP forwarding table entries based on control message 1136 exchanges. 1138 Relays are simply Servers that run a dynamic routing protocol to 1139 redistribute routes between the OMNI interface and INET/EUN 1140 interfaces (see: Section 3.2.3). The Relay provisions MNPs to 1141 networks on the INET/EUN interfaces (i.e., the same as a Client would 1142 do) and advertises the MSP(s) for the OMNI link over the INET/EUN 1143 interfaces. The Relay further provides an attachment point of the 1144 OMNI link to a non-MNP-based global topology. 1146 3.4.2. AERO Proxy Behavior 1148 When a Proxy enables an OMNI interface, it assigns an LLA/DLA and 1149 configures permanent neighbor cache entries the same as for Servers. 1150 The Proxy also configures secured tunnels with one or more 1151 neighboring Bridges and maintains per-Client neighbor cache entries 1152 based on control message exchanges. Importantly Proxys are often 1153 configured to act as Servers, and vice-versa. 1155 3.4.3. AERO Client Behavior 1157 When a Client enables an OMNI interface, it sends RS messages with ND 1158 parameters over its underlying interfaces to a Server, which returns 1159 an RA message with corresponding parameters. (The RS/RA messages may 1160 pass through a Proxy in the case of a Client's ANET interface, or 1161 through one or more NATs in the case of a Client's INET interface.) 1163 3.4.4. AERO Bridge Behavior 1165 AERO Bridges configure an OMNI interface and assign the DLA Subnet 1166 Router Anycast address for each OMNI link segment they connect to. 1167 Bridges configure secured tunnels with Servers, Proxys and other 1168 Bridges; they also configure LLAs/DLAs and permanent neighbor cache 1169 entries the same as Servers. Bridges engage in a BGP routing 1170 protocol session with a subset of the Servers and other Bridges on 1171 the spanning tree (see: Section 3.2.3). 1173 3.5. OMNI Interface Neighbor Cache Maintenance 1175 Each OMNI interface maintains a conceptual neighbor cache that 1176 includes an entry for each neighbor it communicates with on the OMNI 1177 link per [RFC4861]. OMNI interface neighbor cache entries are said 1178 to be one of "permanent", "symmetric", "asymmetric" or "proxy". 1180 Permanent neighbor cache entries are created through explicit 1181 administrative action; they have no timeout values and remain in 1182 place until explicitly deleted. AERO Bridges maintain permanent 1183 neighbor cache entries for their associated Proxys/Servers (and vice- 1184 versa). Each entry maintains the mapping between the neighbor's 1185 network-layer LLA and corresponding INET address. 1187 Symmetric neighbor cache entries are created and maintained through 1188 RS/RA exchanges as specified in Section 3.12, and remain in place for 1189 durations bounded by prefix lifetimes. AERO Servers maintain 1190 symmetric neighbor cache entries for each of their associated 1191 Clients, and AERO Clients maintain symmetric neighbor cache entries 1192 for each of their associated Servers. 1194 Asymmetric neighbor cache entries are created or updated based on 1195 route optimization messaging as specified in Section 3.14, and are 1196 garbage-collected when keepalive timers expire. AERO ROSs maintain 1197 asymmetric neighbor cache entries for active targets with lifetimes 1198 based on ND messaging constants. Asymmetric neighbor cache entries 1199 are unidirectional since only the ROS (and not the ROR) creates an 1200 entry. 1202 Proxy neighbor cache entries are created and maintained by AERO 1203 Proxys when they process Client/Server ND exchanges, and remain in 1204 place for durations bounded by ND and prefix lifetimes. AERO Proxys 1205 maintain proxy neighbor cache entries for each of their associated 1206 Clients. Proxy neighbor cache entries track the Client state and the 1207 address of the Client's associated Server(s). 1209 To the list of neighbor cache entry states in Section 7.3.2 of 1210 [RFC4861], Proxy and Server OMNI interfaces add an additional state 1211 DEPARTED that applies to symmetric and proxy neighbor cache entries 1212 for Clients that have recently departed. The interface sets a 1213 "DepartTime" variable for the neighbor cache entry to "DEPART_TIME" 1214 seconds. DepartTime is decremented unless a new ND message causes 1215 the state to return to REACHABLE. While a neighbor cache entry is in 1216 the DEPARTED state, packets destined to the target Client are 1217 forwarded to the Client's new location instead of being dropped. 1218 When DepartTime decrements to 0, the neighbor cache entry is deleted. 1219 It is RECOMMENDED that DEPART_TIME be set to the default constant 1220 value REACHABLE_TIME plus 10 seconds (40 seconds by default) to allow 1221 a window for packets in flight to be delivered while stale route 1222 optimization state may be present. 1224 When an ROR receives an authentic NS message used for route 1225 optimization, it searches for a symmetric neighbor cache entry for 1226 the target Client. The ROR then returns a solicited NA message 1227 without creating a neighbor cache entry for the ROS, but creates or 1228 updates a target Client "Report List" entry for the ROS and sets a 1229 "ReportTime" variable for the entry to REPORT_TIME seconds. The ROR 1230 resets ReportTime when it receives a new authentic NS message, and 1231 otherwise decrements ReportTime while no authentic NS messages have 1232 been received. It is RECOMMENDED that REPORT_TIME be set to the 1233 default constant value REACHABLE_TIME plus 10 seconds (40 seconds by 1234 default) to allow a window for route optimization to converge before 1235 ReportTime decrements below REACHABLE_TIME. 1237 When the ROS receives a solicited NA message response to its NS 1238 message used for route optimization, it creates or updates an 1239 asymmetric neighbor cache entry for the target network-layer and 1240 link-layer addresses. The ROS then (re)sets ReachableTime for the 1241 neighbor cache entry to REACHABLE_TIME seconds and uses this value to 1242 determine whether packets can be forwarded directly to the target, 1243 i.e., instead of via a default route. The ROS otherwise decrements 1244 ReachableTime while no further solicited NA messages arrive. It is 1245 RECOMMENDED that REACHABLE_TIME be set to the default constant value 1246 30 seconds as specified in [RFC4861]. 1248 AERO nodes also use the value MAX_UNICAST_SOLICIT to limit the number 1249 of NS keepalives sent when a correspondent may have gone unreachable, 1250 the value MAX_RTR_SOLICITATIONS to limit the number of RS messages 1251 sent without receiving an RA and the value MAX_NEIGHBOR_ADVERTISEMENT 1252 to limit the number of unsolicited NAs that can be sent based on a 1253 single event. It is RECOMMENDED that MAX_UNICAST_SOLICIT, 1254 MAX_RTR_SOLICITATIONS and MAX_NEIGHBOR_ADVERTISEMENT be set to 3 the 1255 same as specified in [RFC4861]. 1257 Different values for DEPART_TIME, REPORT_TIME, REACHABLE_TIME, 1258 MAX_UNICAST_SOLICIT, MAX_RTR_SOLCITATIONS and 1259 MAX_NEIGHBOR_ADVERTISEMENT MAY be administratively set; however, if 1260 different values are chosen, all nodes on the link MUST consistently 1261 configure the same values. Most importantly, DEPART_TIME and 1262 REPORT_TIME SHOULD be set to a value that is sufficiently longer than 1263 REACHABLE_TIME to avoid packet loss due to stale route optimization 1264 state. 1266 3.5.1. OMNI Neighbor Interface Attributes 1268 OMNI interface IPv6 ND messages include OMNI options 1269 [I-D.templin-6man-omni-interface] with Interface Attributes that 1270 provide Link-Layer Address and QoS Preference information for the 1271 neighbor's underlying interfaces. This information is stored in the 1272 neighbor cache and provides the basis for the forwarding algorithm 1273 specified in Section 3.10. The information is cumulative and 1274 reflects the union of the OMNI information from the most recent ND 1275 messages received from the neighbor; it is therefore not required 1276 that each ND message contain all neighbor information. 1278 The OMNI option Interface Attributes for each underlying interface 1279 includes a two-part "Link-Layer Address" consisting of a simple IP 1280 encapsulation address determined by the FMT and L2ADDR fields and an 1281 OAL DLA determined by the SRT and LHS fields. If the neighbor is 1282 located in the local OMNI link segment (and, if any necessary NAT 1283 state has been established) forwarding via simple IP encapsulation 1284 can be used; otherwise, OAL encapsulation must be used. Underlying 1285 interfaces are further selected based on their associated preference 1286 values "high", "medium", "low" or "disabled". 1288 Note: the OMNI option is distinct from any Source/Target Link-Layer 1289 Address Options (S/TLLAOs) that may appear in an ND message according 1290 to the appropriate IPv6 over specific link layer specification (e.g., 1291 [RFC2464]). If both an OMNI option and S/TLLAO appear, the former 1292 pertains to encapsulation addresses while the latter pertains to the 1293 native L2 address format of the underlying media. 1295 3.5.2. OMNI Neighbor Advertisement Message Flags 1297 As discussed in Section 4.4 of [RFC4861] NA messages include three 1298 flag bits R, S and O. OMNI interface NA messages treat the flags as 1299 follows: 1301 o R: The R ("Router") flag is set to 1 in the NA messages sent by 1302 all AERO/OMNI node types. Simple hosts that would set R to 0 do 1303 not occur on the OMNI link itself, but may occur on the downstream 1304 links of Clients and Relays. 1306 o S: The S ("Solicited") flag is set exactly as specified in 1307 Section 4.4. of [RFC4861], i.e., it is set to 1 for Solicited NAs 1308 and set to 0 for Unsolicited NAs (both unicast and multicast). 1310 o O: The O ("Override") flag is set to 0 for solicited proxy NAs and 1311 set to 1 for all other solicited and unsolicited NAs. For further 1312 study is whether solicited NAs for anycast targets apply for OMNI 1313 links. Since OMNI LLAs must be uniquely assigned to Clients to 1314 support correct ND protocol operation, however, no role is 1315 currently seen for assigning the same OMNI LLA to multiple 1316 Clients. 1318 3.6. OMNI Interface Encapsulation and Re-encapsulation 1320 The OMNI Adaptation Layer (OAL) inserts mid-layer IPv6 headers known 1321 as the OAL/ORH headers when necessary as discussed in the following 1322 sections. After either inserting or omitting the OAL/ORH headers, 1323 the OMNI interface also inserts or omits an outer encapsulation 1324 header as discussed below. 1326 OMNI interfaces avoid outer encapsulation over Direct underlying 1327 interfaces and ANET underlying interfaces for which the first-hop 1328 access router is connected to the same underlying link. Otherwise, 1329 OMNI interfaces encapsulate packets according to whether they are 1330 entering the OMNI interface from the network layer or if they are 1331 being re-admitted into the same OMNI link they arrived on. This 1332 latter form of encapsulation is known as "re-encapsulation". 1334 For packets entering the OMNI interface from the network layer, the 1335 OMNI interface copies the "TTL/Hop Limit", "Type of Service/Traffic 1336 Class" [RFC2983], "Flow Label"[RFC6438] (for IPv6) and "Congestion 1337 Experienced" [RFC3168] values in the inner packet's IP header into 1338 the corresponding fields in the OAL and outer encapsulation 1339 header(s). 1341 For packets undergoing re-encapsulation, the OMNI interface instead 1342 copies these values from the original encapsulation header into the 1343 new encapsulation header, i.e., the values are transferred between 1344 encapsulation headers and *not* copied from the encapsulated packet's 1345 network-layer header. (Note especially that by copying the TTL/Hop 1346 Limit between encapsulation headers the value will eventually 1347 decrement to 0 if there is a (temporary) routing loop.) 1349 OMNI interfaces configured over ANET underlying interfaces which 1350 employ a different IP protocol version and/or may be located multiple 1351 IP hops from the nearest Proxy/Server use IP-in-IP encapsulation so 1352 that the inner packet can traverse the ANET. IPv6 underlying ANET 1353 interfaces use [RFC2473] encapsulation, while IPv4 interfaces use the 1354 appropriate encapsulation per one of [RFC2529][RFC5214][RFC2003]. 1356 OMNI interfaces configured over INET underlying interfaces 1357 encapsulate packets in INET headers according to the next hop 1358 determined in the forwarding algorithm in Section 3.10. If the next 1359 hop is reached via a secured tunnel, the OMNI interface uses an 1360 encapsulation format specific to the secured tunnel type (see: 1361 Section 6). If the next hop is reached via an unsecured INET 1362 interface, the OMNI interface instead uses UDP/IP encapsulation per 1363 [RFC4380] and as extended in [RFC6081]. 1365 When UDP/IP encapsulation is used, the OMNI interface next sets the 1366 UDP source port to a constant value that it will use in each 1367 successive packet it sends, and sets the UDP length field to the 1368 length of the encapsulated packet plus 8 bytes for the UDP header 1369 itself plus the length of any included extension headers or trailers. 1370 The encapsulated packet may be either IPv6 or IPv4, as distinguished 1371 by the version number found in the first four bits. 1373 For UDP/IP-encapsulated packets sent to a Server, Relay or Bridge, 1374 the OMNI interface sets the UDP destination port to 8060, i.e., the 1375 IANA-registered port number for AERO. For packets sent to a Client, 1376 the OMNI interface sets the UDP destination port to the port value 1377 stored in the neighbor cache entry for this Client. The OMNI 1378 interface finally includes/omits the UDP checksum according to 1379 [RFC6935][RFC6936]. 1381 3.7. OMNI Interface Decapsulation 1383 OMNI interfaces decapsulate packets destined either to the AERO node 1384 itself or to a destination reached via an interface other than the 1385 OMNI interface the packet was received on. When the encapsulated 1386 packet arrives in multiple OAL fragments, the OMNI interface 1387 reassembles as discussed in Section 3.9. Further decapsulation steps 1388 are performed according to the appropriate encapsulation format 1389 specification. 1391 3.8. OMNI Interface Data Origin Authentication 1393 AERO nodes employ simple data origin authentication procedures. In 1394 particular: 1396 o AERO Bridges, Servers and Proxys accept encapsulated data packets 1397 and control messages received from the (secured) spanning tree. 1399 o AERO Proxys and Clients accept packets that originate from within 1400 the same secured ANET. 1402 o AERO Clients and Relays accept packets from downstream network 1403 correspondents based on ingress filtering. 1405 o AERO Clients, Relays and Servers verify the outer UDP/IP 1406 encapsulation addresses according to [RFC4380]. 1408 AERO nodes silently drop any packets that do not satisfy the above 1409 data origin authentication procedures. Further security 1410 considerations are discussed in Section 6. 1412 3.9. OMNI Adaptation Layer and OMNI Interface MTU 1414 The OMNI interface observes the link nature of tunnels, including the 1415 Maximum Transmission Unit (MTU), Maximum Reassembly Unit (MRU) and 1416 the role of fragmentation and reassembly [I-D.ietf-intarea-tunnels]. 1417 The OMNI interface employs an OMNI Adaptation Layer (OAL) for 1418 accommodating multiple underlying links with diverse MTUs. The 1419 functions of the OAL and the OMNI interface MTU/MRU are specified in 1420 Section 5 of [I-D.templin-6man-omni-interface], with MTU/MRU both set 1421 to the constant value 9180 bytes. 1423 3.10. OMNI Interface Forwarding Algorithm 1425 IP packets enter a node's OMNI interface either from the network 1426 layer (i.e., from a local application or the IP forwarding system) or 1427 from the link layer (i.e., from an OMNI interface neighbor). All 1428 packets entering a node's OMNI interface first undergo data origin 1429 authentication as discussed in Section 3.8. Packets that satisfy 1430 data origin authentication are processed further, while all others 1431 are dropped silently. The OMNI interface OAL wraps accepted packets 1432 in OAL/ORH headers if necessary as discussed above. 1434 Packets that enter the OMNI interface from the network layer are 1435 forwarded to an OMNI interface neighbor. Packets that enter the OMNI 1436 interface from the link layer are either re-admitted into the OMNI 1437 link or forwarded to the network layer where they are subject to 1438 either local delivery or IP forwarding. In all cases, the OMNI 1439 interface itself MUST NOT decrement the network layer TTL/Hop-count 1440 since its forwarding actions occur below the network layer. 1442 OMNI interfaces may have multiple underlying interfaces and/or 1443 neighbor cache entries for neighbors with multiple underlying 1444 interfaces (see Section 3.3). The OMNI interface uses interface 1445 attributes and/or traffic classifiers (e.g., DSCP value, port number, 1446 etc.) to select an outgoing underlying interface for each packet 1447 based on the node's own QoS preferences, and also to select a 1448 destination link-layer address based on the neighbor's underlying 1449 interface with the highest preference. AERO implementations SHOULD 1450 allow for QoS preference values to be modified at runtime through 1451 network management. 1453 If multiple outgoing interfaces and/or neighbor interfaces have a 1454 preference of "high", the AERO node replicates the packet and sends 1455 one copy via each of the (outgoing / neighbor) interface pairs; 1456 otherwise, the node sends a single copy of the packet via an 1457 interface with the highest preference. AERO nodes keep track of 1458 which underlying interfaces are currently "reachable" or 1459 "unreachable", and only use "reachable" interfaces for forwarding 1460 purposes. 1462 The following sections discuss the OMNI interface forwarding 1463 algorithms for Clients, Proxys, Servers and Bridges. In the 1464 following discussion, a packet's destination address is said to 1465 "match" if it is the same as a cached address, or if it is covered by 1466 a cached prefix (which may be encoded in an LLA). 1468 3.10.1. Client Forwarding Algorithm 1470 When an IP packet enters a Client's OMNI interface from the network 1471 layer the Client searches for an asymmetric neighbor cache entry that 1472 matches the destination. If there is a match, the Client uses one or 1473 more "reachable" neighbor interfaces in the entry for packet 1474 forwarding. If there is no asymmetric neighbor cache entry, the 1475 Client instead forwards the packet toward a Server (the packet is 1476 intercepted by a Proxy if there is a Proxy on the path). The Client 1477 encapsulates the packet in OAL/ORH headers if necessary and fragments 1478 according to MTU requirements (see: Section 3.9). 1480 When an IP packet enters a Client's OMNI interface from the link- 1481 layer, if the destination matches one of the Client's MNPs or link- 1482 local addresses the Client reassembles and decapsulates as necessary 1483 and delivers the inner packet to the network layer. Otherwise, the 1484 Client drops the packet and MAY return a network-layer ICMP 1485 Destination Unreachable message subject to rate limiting (see: 1486 Section 3.11). 1488 3.10.2. Proxy Forwarding Algorithm 1490 For control messages originating from or destined to a Client, the 1491 Proxy intercepts the message and updates its proxy neighbor cache 1492 entry for the Client. The Proxy then forwards a (proxyed) copy of 1493 the control message. (For example, the Proxy forwards a proxied 1494 version of a Client's NS/RS message to the target neighbor, and 1495 forwards a proxied version of the NA/RA reply to the Client.) 1497 When the Proxy receives a data packet from a Client within the ANET, 1498 the Proxy reassembles and re-fragments if necessary then searches for 1499 an asymmetric neighbor cache entry that matches the destination and 1500 forwards as follows: 1502 o if the destination matches an asymmetric neighbor cache entry, the 1503 Proxy uses one or more "reachable" neighbor interfaces in the 1504 entry for packet forwarding using OAL/ORH encapsulation if 1505 necessary according to the cached link-layer address information. 1506 If the neighbor interface is in the same OMNI link segment, the 1507 Proxy forwards the packet directly to the neighbor; otherwise, it 1508 forwards the packet to a Bridge. 1510 o else, the Proxy uses OAL/ORH encapsulation and forwards the packet 1511 to a Bridge while using the DLA corresponding to the packet's 1512 destination as the destination address. 1514 When the Proxy receives an encapsulated data packet from an INET 1515 neighbor or from a secured tunnel from a Bridge, it accepts the 1516 packet only if data origin authentication succeeds and if there is a 1517 proxy neighbor cache entry that matches the inner destination. Next, 1518 the Proxy reassembles the packet (if necessary) and continues 1519 processing. If the reassembly is complete and the neighbor cache 1520 state is REACHABLE, the Proxy then returns a PTB if necessary (see: 1521 Section 3.9) then either drops or forwards the packet to the Client 1522 while performing OAL/ORH encapsulation and re-fragmentation if 1523 necessary. If the neighbor cache entry state is DEPARTED, the Proxy 1524 instead changes the destination address to the address of the new 1525 Server and forwards it to a Bridge while performing OAL/ORH re- 1526 fragmentation if necessary. 1528 3.10.3. Server/Relay Forwarding Algorithm 1530 For control messages destined to a target Client's LLA that are 1531 received from a secured tunnel, the Server intercepts the message and 1532 sends a Proxyed response on behalf of the Client. (For example, the 1533 Server sends a Proxyed NA message reply in response to an NS message 1534 directed to one of its associated Clients.) If the Client's neighbor 1535 cache entry is in the DEPARTED state, however, the Server instead 1536 forwards the packet to the Client's new Server as discussed in 1537 Section 3.16. 1539 When the Server receives an encapsulated data packet from an INET 1540 neighbor or from a secured tunnel, it accepts the packet only if data 1541 origin authentication succeeds. The Server then continues processing 1542 as follows: 1544 o if the network layer destination matches a symmetric neighbor 1545 cache entry in the REACHABLE state the Server prepares the packet 1546 for forwarding to the destination Client. The Server first 1547 reassembles (if necessary) and forwards the packet (while re- 1548 fragmenting if necessary) as specified in Section 3.9. 1550 o else, if the destination matches a symmetric neighbor cache entry 1551 in the DEPARETED state the Server re-encapsulates the packet and 1552 forwards it using the DLA of the Client's new Server as the 1553 destination. 1555 o else, if the destination matches an asymmetric neighbor cache 1556 entry, the Server uses one or more "reachable" neighbor interfaces 1557 in the entry for packet forwarding via the local INET if the 1558 neighbor is in the same OMNI link segment or using OAL/ORH 1559 encapsulation if necessary with the final destination set to the 1560 neighbor's DLA otherwise. 1562 o else, if the destination matches a non-MNP route in the IP 1563 forwarding table or an LLA assigned to the Server's OMNI 1564 interface, the Server reassembles if necessary, decapsulates the 1565 packet and releases it to the network layer for local delivery or 1566 IP forwarding. 1568 o else, the Server drops the packet. 1570 When the Server's OMNI interface receives a data packet from the 1571 network layer or from a VPNed or Direct Client, it performs OAL/ORH 1572 encapsulation and fragmentation if necessary, then processes the 1573 packet according to the network-layer destination address as follows: 1575 o if the destination matches a symmetric or asymmetric neighbor 1576 cache entry the Server processes the packet as above. 1578 o else, the Server encapsulates the packet in OLA/ORH headers and 1579 forwards it to a Bridge using its own DLA as the source and the 1580 DLA corresponding to the destination as the destination. 1582 3.10.4. Bridge Forwarding Algorithm 1584 Bridges forward OAL/ORH-encapsulated packets over secured tunnels the 1585 same as any IP router. When the Bridge receives an OAL/ORH- 1586 encapsulated packet via a secured tunnel, it removes the outer INET 1587 header and searches for a forwarding table entry that matches the 1588 destination address. The Bridge then processes the packet as 1589 follows: 1591 o if the destination matches its DLA Subnet Router Anycast address, 1592 the Bridge checks for an ORH. If there is an ORH with SRT/LHS 1593 located on the local segment, the Bridge removes the ORH from the 1594 packet. (If there is no OAL header, the Bridge also writes the 1595 saved IPv6 destination address from the ORH into the packet's IPv6 1596 destination address.) Next, the Bridge examines the FMT to 1597 determine if the target is behind a NAT. If no NAT is indicated, 1598 the Bridge forwards the packet directly to the L2ADDR using link- 1599 layer (UDP/IP) encapsulation. If a NAT is indicated, the Bridge 1600 MAY perform NAT traversal procedures by sending bubbles per 1601 [RFC4380]. The Bridge then either applies AERO route optimization 1602 if NAT traversal procedures have been successfully applied, or 1603 forwards the packet directly to the Server indicated by the SR/LHS 1604 values. 1606 o if the destination matches one of the Bridge's own addresses, the 1607 Bridge submits the packet for local delivery. 1609 o else, if the destination matches a forwarding table entry the 1610 Bridge forwards the packet via a secured tunnel to the next hop. 1611 If the destination matches an MSP without matching an MNP, 1612 however, the Bridge instead drops the packet and returns an ICMP 1613 Destination Unreachable message subject to rate limiting (see: 1614 Section 3.11). 1616 o else, the Bridge drops the packet and returns an ICMP Destination 1617 Unreachable as above. 1619 As for any IP router, the Bridge decrements the TTL/Hop Limit when it 1620 forwards the packet. Therefore, when an OAL header is present only 1621 the Hop Limit in the OAL header is decremented and not the TTL/Hop 1622 Limit in the inner packet header. Bridges do not insert OAL/ORH 1623 headers themselves; instead, they act as IPv6 routers and forward 1624 packets based on the destination address found in the headers of 1625 packets they receive. 1627 3.11. OMNI Interface Error Handling 1629 When an AERO node admits a packet into the OMNI interface, it may 1630 receive link-layer or network-layer error indications. 1632 A link-layer error indication is an ICMP error message generated by a 1633 router in the INET on the path to the neighbor or by the neighbor 1634 itself. The message includes an IP header with the address of the 1635 node that generated the error as the source address and with the 1636 link-layer address of the AERO node as the destination address. 1638 The IP header is followed by an ICMP header that includes an error 1639 Type, Code and Checksum. Valid type values include "Destination 1640 Unreachable", "Time Exceeded" and "Parameter Problem" 1641 [RFC0792][RFC4443]. (OMNI interfaces ignore all link-layer IPv4 1642 "Fragmentation Needed" and IPv6 "Packet Too Big" messages since they 1643 only emit packets that are guaranteed to be no larger than the IP 1644 minimum link MTU as discussed in Section 3.9.) 1646 The ICMP header is followed by the leading portion of the packet that 1647 generated the error, also known as the "packet-in-error". For 1648 ICMPv6, [RFC4443] specifies that the packet-in-error includes: "As 1649 much of invoking packet as possible without the ICMPv6 packet 1650 exceeding the minimum IPv6 MTU" (i.e., no more than 1280 bytes). For 1651 ICMPv4, [RFC0792] specifies that the packet-in-error includes: 1652 "Internet Header + 64 bits of Original Data Datagram", however 1653 [RFC1812] Section 4.3.2.3 updates this specification by stating: "the 1654 ICMP datagram SHOULD contain as much of the original datagram as 1655 possible without the length of the ICMP datagram exceeding 576 1656 bytes". 1658 The link-layer error message format is shown in Figure 6 (where, "L2" 1659 and "L3" refer to link-layer and network-layer, respectively): 1661 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1662 ~ ~ 1663 | L2 IP Header of | 1664 | error message | 1665 ~ ~ 1666 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1667 | L2 ICMP Header | 1668 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 1669 ~ ~ P 1670 | IP and other encapsulation | a 1671 | headers of original L3 packet | c 1672 ~ ~ k 1673 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ e 1674 ~ ~ t 1675 | IP header of | 1676 | original L3 packet | i 1677 ~ ~ n 1678 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1679 ~ ~ e 1680 | Upper layer headers and | r 1681 | leading portion of body | r 1682 | of the original L3 packet | o 1683 ~ ~ r 1684 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 1686 Figure 6: OMNI Interface Link-Layer Error Message Format 1688 The AERO node rules for processing these link-layer error messages 1689 are as follows: 1691 o When an AERO node receives a link-layer Parameter Problem message, 1692 it processes the message the same as described as for ordinary 1693 ICMP errors in the normative references [RFC0792][RFC4443]. 1695 o When an AERO node receives persistent link-layer Time Exceeded 1696 messages, the IP ID field may be wrapping before earlier fragments 1697 awaiting reassembly have been processed. In that case, the node 1698 should begin including integrity checks and/or institute rate 1699 limits for subsequent packets. 1701 o When an AERO node receives persistent link-layer Destination 1702 Unreachable messages in response to encapsulated packets that it 1703 sends to one of its asymmetric neighbor correspondents, the node 1704 should process the message as an indication that a path may be 1705 failing, and optionally initiate NUD over that path. If it 1706 receives Destination Unreachable messages over multiple paths, the 1707 node should allow future packets destined to the correspondent to 1708 flow through a default route and re-initiate route optimization. 1710 o When an AERO Client receives persistent link-layer Destination 1711 Unreachable messages in response to encapsulated packets that it 1712 sends to one of its symmetric neighbor Servers, the Client should 1713 mark the path as unusable and use another path. If it receives 1714 Destination Unreachable messages on many or all paths, the Client 1715 should associate with a new Server and release its association 1716 with the old Server as specified in Section 3.16.5. 1718 o When an AERO Server receives persistent link-layer Destination 1719 Unreachable messages in response to encapsulated packets that it 1720 sends to one of its symmetric neighbor Clients, the Server should 1721 mark the underlying path as unusable and use another underlying 1722 path. 1724 o When an AERO Server or Proxy receives link-layer Destination 1725 Unreachable messages in response to an encapsulated packet that it 1726 sends to one of its permanent neighbors, it treats the messages as 1727 an indication that the path to the neighbor may be failing. 1728 However, the dynamic routing protocol should soon reconverge and 1729 correct the temporary outage. 1731 When an AERO Bridge receives a packet for which the network-layer 1732 destination address is covered by an MSP, if there is no more- 1733 specific routing information for the destination the Bridge drops the 1734 packet and returns a network-layer Destination Unreachable message 1735 subject to rate limiting. The Bridge writes the network-layer source 1736 address of the original packet as the destination address and uses 1737 one of its non link-local addresses as the source address of the 1738 message. 1740 When an AERO node receives an encapsulated packet for which the 1741 reassembly buffer it too small, it drops the packet and returns a 1742 network-layer Packet Too Big (PTB) message. The node first writes 1743 the MRU value into the PTB message MTU field, writes the network- 1744 layer source address of the original packet as the destination 1745 address and writes one of its non link-local addresses as the source 1746 address. 1748 3.12. AERO Router Discovery, Prefix Delegation and Autoconfiguration 1750 AERO Router Discovery, Prefix Delegation and Autoconfiguration are 1751 coordinated as discussed in the following Sections. 1753 3.12.1. AERO Service Model 1755 Each AERO Server on the OMNI link is configured to facilitate Client 1756 prefix delegation/registration requests. Each Server is provisioned 1757 with a database of MNP-to-Client ID mappings for all Clients enrolled 1758 in the AERO service, as well as any information necessary to 1759 authenticate each Client. The Client database is maintained by a 1760 central administrative authority for the OMNI link and securely 1761 distributed to all Servers, e.g., via the Lightweight Directory 1762 Access Protocol (LDAP) [RFC4511], via static configuration, etc. 1763 Clients receive the same service regardless of the Servers they 1764 select. 1766 AERO Clients and Servers use ND messages to maintain neighbor cache 1767 entries. AERO Servers configure their OMNI interfaces as advertising 1768 NBMA interfaces, and therefore send unicast RA messages with a short 1769 Router Lifetime value (e.g., ReachableTime seconds) in response to a 1770 Client's RS message. Thereafter, Clients send additional RS messages 1771 to keep Server state alive. 1773 AERO Clients and Servers include prefix delegation and/or 1774 registration parameters in RS/RA messages (see 1775 [I-D.templin-6man-omni-interface]). The ND messages are exchanged 1776 between Client and Server according to the prefix management schedule 1777 required by the service. If the Client knows its MNP in advance, it 1778 can employ prefix registration by including its LLA as the source 1779 address of an RS message and with an OMNI option with valid prefix 1780 registration information for the MNP. If the Server (and Proxy) 1781 accept the Client's MNP assertion, they inject the prefix into the 1782 routing system and establish the necessary neighbor cache state. 1784 The following sections specify the Client and Server behavior. 1786 3.12.2. AERO Client Behavior 1788 AERO Clients discover the addresses of Servers in a similar manner as 1789 described in [RFC5214]. Discovery methods include static 1790 configuration (e.g., from a flat-file map of Server addresses and 1791 locations), or through an automated means such as Domain Name System 1792 (DNS) name resolution [RFC1035]. Alternatively, the Client can 1793 discover Server addresses through a layer 2 data link login exchange, 1794 or through a unicast RA response to a multicast/anycast RS as 1795 described below. In the absence of other information, the Client can 1796 resolve the DNS Fully-Qualified Domain Name (FQDN) 1797 "linkupnetworks.[domainname]" where "linkupnetworks" is a constant 1798 text string and "[domainname]" is a DNS suffix for the OMNI link 1799 (e.g., "example.com"). 1801 To associate with a Server, the Client acts as a requesting router to 1802 request MNPs. The Client prepares an RS message with prefix 1803 management parameters and includes a Nonce and Timestamp option if 1804 the Client needs to correlate RA replies. If the Client already 1805 knows the Server's LLA, it includes the LLA as the network-layer 1806 destination address; otherwise, it includes (link-local) All-Routers 1807 multicast as the network-layer destination. If the Client already 1808 knows its own LLA, it uses the LLA as the network-layer source 1809 address; otherwise, it uses an OMNI Temporary LLA as the network- 1810 layer source address and includes a DHCP Unique Identifier (DUID) 1811 sub-option in the OMNI option (see: 1812 [I-D.templin-6man-omni-interface]). 1814 The Client next includes an OMNI option in the RS message to register 1815 its link-layer information with the Server. The Client sets the OMNI 1816 option prefix registration information according to the MNP, and 1817 includes Interface Attributes corresponding to the underlying 1818 interface over which the Client will send the RS message. The Client 1819 MAY include additional Interface Attributes specific to other 1820 underlying interfaces. 1822 The Client then sends the RS message (either directly via Direct 1823 interfaces, via a VPN for VPNed interfaces, via a Proxy for ANET 1824 interfaces or via INET encapsulation for INET interfaces) and waits 1825 for an RA message reply (see Section 3.12.3). The Client retries up 1826 to MAX_RTR_SOLICITATIONS times until an RA is received. If the 1827 Client receives no RAs, or if it receives an RA with Router Lifetime 1828 set to 0, the Client SHOULD abandon this Server and try another 1829 Server. Otherwise, the Client processes the prefix information found 1830 in the RA message. 1832 Next, the Client creates a symmetric neighbor cache entry with the 1833 Server's LLA as the network-layer address and the Server's 1834 encapsulation and/or link-layer addresses as the link-layer address. 1835 The Client records the RA Router Lifetime field value in the neighbor 1836 cache entry as the time for which the Server has committed to 1837 maintaining the MNP in the routing system via this underlying 1838 interface, and caches the other RA configuration information 1839 including Cur Hop Limit, M and O flags, Reachable Time and Retrans 1840 Timer. The Client then autoconfigures LLAs for each of the delegated 1841 MNPs and assigns them to the OMNI interface. The Client also caches 1842 any MSPs included in Route Information Options (RIOs) [RFC4191] as 1843 MSPs to associate with the OMNI link, and assigns the MTU value in 1844 the MTU option to the underlying interface. 1846 The Client then registers additional underlying interfaces with the 1847 Server by sending RS messages via each additional interface. The RS 1848 messages include the same parameters as for the initial RS/RA 1849 exchange, but with destination address set to the Server's LLA. 1851 Following autoconfiguration, the Client sub-delegates the MNPs to its 1852 attached EUNs and/or the Client's own internal virtual interfaces as 1853 described in [I-D.templin-v6ops-pdhost] to support the Client's 1854 downstream attached "Internet of Things (IoT)". The Client 1855 subsequently sends additional RS messages over each underlying 1856 interface before the Router Lifetime received for that interface 1857 expires. 1859 After the Client registers its underlying interfaces, it may wish to 1860 change one or more registrations, e.g., if an interface changes 1861 address or becomes unavailable, if QoS preferences change, etc. To 1862 do so, the Client prepares an RS message to send over any available 1863 underlying interface. The RS includes an OMNI option with prefix 1864 registration information specific to its MNP, with Interface 1865 Attributes specific to the selected underlying interface, and with 1866 any additional Interface Attributes specific to other underlying 1867 interfaces. When the Client receives the Server's RA response, it 1868 has assurance that the Server has been updated with the new 1869 information. 1871 If the Client wishes to discontinue use of a Server it issues an RS 1872 message over any underlying interface with an OMNI option with a 1873 prefix release indication. When the Server processes the message, it 1874 releases the MNP, sets the symmetric neighbor cache entry state for 1875 the Client to DEPARTED and returns an RA reply with Router Lifetime 1876 set to 0. After a short delay (e.g., 2 seconds), the Server 1877 withdraws the MNP from the routing system. 1879 3.12.3. AERO Server Behavior 1881 AERO Servers act as IP routers and support a prefix delegation/ 1882 registration service for Clients. Servers arrange to add their LLAs 1883 to a static map of Server addresses for the link and/or the DNS 1884 resource records for the FQDN "linkupnetworks.[domainname]" before 1885 entering service. Server addresses should be geographically and/or 1886 topologically referenced, and made available for discovery by Clients 1887 on the OMNI link. 1889 When a Server receives a prospective Client's RS message on its OMNI 1890 interface, it SHOULD return an immediate RA reply with Router 1891 Lifetime set to 0 if it is currently too busy or otherwise unable to 1892 service the Client. Otherwise, the Server authenticates the RS 1893 message and processes the prefix delegation/registration parameters. 1894 The Server first determines the correct MNPs to provide to the Client 1895 by searching the Client database. When the Server returns the MNPs, 1896 it also creates a forwarding table entry for the DLA corresponding to 1897 each MNP so that the MNPs are propagated into the routing system 1898 (see: Section 3.2.3). For IPv6, the Server creates an IPv6 1899 forwarding table entry for each MNP. For IPv4, the Server creates an 1900 IPv6 forwarding table entry with the IPv4-compatibility DLA prefix 1901 corresponding to the IPv4 address. 1903 The Server next creates a symmetric neighbor cache entry for the 1904 Client using the base LLA as the network-layer address and with 1905 lifetime set to no more than the smallest prefix lifetime. Next, the 1906 Server updates the neighbor cache entry by recording the information 1907 in each Interface Attributes sub-option in the RS OMNI option. The 1908 Server also records the actual OAL/INET addresses in the neighbor 1909 cache entry. 1911 Next, the Server prepares an RA message using its LLA as the network- 1912 layer source address and the network-layer source address of the RS 1913 message as the network-layer destination address. The Server sets 1914 the Router Lifetime to the time for which it will maintain both this 1915 underlying interface individually and the symmetric neighbor cache 1916 entry as a whole. The Server also sets Cur Hop Limit, M and O flags, 1917 Reachable Time and Retrans Timer to values appropriate for the OMNI 1918 link. The Server includes the MNPs, any other prefix management 1919 parameters and an OMNI option with no Interface Attributes. The 1920 Server then includes one or more RIOs that encode the MSPs for the 1921 OMNI link, plus an MTU option (see Section 3.9). The Server finally 1922 forwards the message to the Client using OAL/INET, INET, or NULL 1923 encapsulation as necessary. 1925 After the initial RS/RA exchange, the Server maintains a 1926 ReachableTime timer for each of the Client's underlying interfaces 1927 individually (and for the Client's symmetric neighbor cache entry 1928 collectively) set to expire after ReachableTime seconds. If the 1929 Client (or Proxy) issues additional RS messages, the Server sends an 1930 RA response and resets ReachableTime. If the Server receives an ND 1931 message with a prefix release indication it sets the Client's 1932 symmetric neighbor cache entry to the DEPARTED state and withdraws 1933 the MNP from the routing system after a short delay (e.g., 2 1934 seconds). If ReachableTime expires before a new RS is received on an 1935 individual underlying interface, the Server marks the interface as 1936 DOWN. If ReachableTime expires before any new RS is received on any 1937 individual underlying interface, the Server sets the symmetric 1938 neighbor cache entry state to STALE and sets a 10 second timer. If 1939 the Server has not received a new RS or ND message with a prefix 1940 release indication before the 10 second timer expires, it deletes the 1941 neighbor cache entry and withdraws the MNP from the routing system. 1943 The Server processes any ND messages pertaining to the Client and 1944 returns an NA/RA reply in response to solicitations. The Server may 1945 also issue unsolicited RA messages, e.g., with reconfigure parameters 1946 to cause the Client to renegotiate its prefix delegation/ 1947 registrations, with Router Lifetime set to 0 if it can no longer 1948 service this Client, etc. Finally, If the symmetric neighbor cache 1949 entry is in the DEPARTED state, the Server deletes the entry after 1950 DepartTime expires. 1952 Note: Clients SHOULD notify former Servers of their departures, but 1953 Servers are responsible for expiring neighbor cache entries and 1954 withdrawing routes even if no departure notification is received 1955 (e.g., if the Client leaves the network unexpectedly). Servers 1956 SHOULD therefore set Router Lifetime to ReachableTime seconds in 1957 solicited RA messages to minimize persistent stale cache information 1958 in the absence of Client departure notifications. A short Router 1959 Lifetime also ensures that proactive Client/Server RS/RA messaging 1960 will keep any NAT state alive (see above). 1962 Note: All Servers on an OMNI link MUST advertise consistent values in 1963 the RA Cur Hop Limit, M and O flags, Reachable Time and Retrans Timer 1964 fields the same as for any link, since unpredictable behavior could 1965 result if different Servers on the same link advertised different 1966 values. 1968 3.12.3.1. DHCPv6-Based Prefix Registration 1970 When a Client is not pre-provisioned with an OMNI LLA containing a 1971 MNP, it will need for the Server to select an MNP on its behalf and 1972 set up the correct state in the AERO routing service. The DHCPv6 1973 service [RFC8415] is used to support this requirement. 1975 When a Client without a pre-provisioned OMNI MN LLA needs to have the 1976 Server select an MNP, it sends an RS message with source address set 1977 to an OMNI Temporary LLA. The RS message includes an OMNI option 1978 with a DUID sub-option that contains a unique DUID value for the MN, 1979 and a Prefix Length value corresponding to the length of MNP it 1980 wishes to receive. 1982 When the Server receives the RS message, it notes that the source was 1983 a Temporary LLA and derives the DUID and Prefix Length from the OMNI 1984 option. The Server (acting as a "proxy DHCP client") then crafts a 1985 well-formed DHCPv6 Solicit message with Prefix Delegation (PD) 1986 parameters, and forwards the message to a locally-resident DHCPv6 1987 server. The DHCPv6 server then delegates an MNP and returns a DHCPv6 1988 Reply message with PD parameters. (Note: the Solicit message should 1989 contain enough identifying information for the MN so that the AR can 1990 correlate the server's Reply with the original Solicit.) 1992 When the Server receives the DHCPv6 Reply, it adds a route to the 1993 routing system and creates an OMNI MN LLA based on the delegated MNP. 1994 The Server then sends an RA back to the Client with the (newly- 1995 created) OMNI MN LLA as the destination address and with Prefix 1996 Length set in the OMNI option. When the Client receives the RA, it 1997 creates a default route, assigns the Subnet Router Anycast address 1998 and sets its OMNI LLA based on the delegated MNP. 2000 3.13. The AERO Proxy 2002 Clients may connect to protected-spectrum ANETs that employ physical 2003 and/or link-layer security services to facilitate communications to 2004 Servers in outside INETs. In that case, the ANET can employ an AERO 2005 Proxy. The Proxy is located at the ANET/INET border and listens for 2006 RS messages originating from or RA messages destined to ANET Clients. 2007 The Proxy acts on these control messages as follows: 2009 o when the Proxy receives an RS message from a new ANET Client, it 2010 first authenticates the message then examines the network-layer 2011 destination address. If the destination address is a Server's 2012 LLA, the Proxy proceeds to the next step. Otherwise, if the 2013 destination is (link-local) All-Routers multicast, the Proxy 2014 selects a "nearby" Server that is likely to be a good candidate to 2015 serve the Client and replaces the destination address with the 2016 Server's LLA. Next, the Proxy creates a proxy neighbor cache 2017 entry and caches the Client and Server link-layer addresses along 2018 with the OMNI option information and any other identifying 2019 information including Transaction IDs, Client Identifiers, Nonce 2020 values, etc. The Proxy finally encapsulates the (proxyed) RS 2021 message in an OAL header with source set to the Proxy's DLA and 2022 destination set to the Server's DLA. The Proxy also includes an 2023 OMNI header with an Interface Attributes option that includes its 2024 own INET address plus a unique Port Number for this Client, then 2025 forwards the message into the OMNI link spanning tree. 2027 o when the Server receives the RS, it authenticates the message then 2028 creates or updates a symmetric neighbor cache entry for the Client 2029 with the Proxy's DLA, INET address and Port Number as the link- 2030 layer address information. The Server then sends an RA message 2031 back to the Proxy via the spanning tree. 2033 o when the Proxy receives the RA, it authenticates the message and 2034 matches it with the proxy neighbor cache entry created by the RS. 2035 The Proxy then caches the prefix information as a mapping from the 2036 Client's MNPs to the Client's link-layer address, caches the 2037 Server's advertised Router Lifetime and sets the neighbor cache 2038 entry state to REACHABLE. The Proxy then optionally rewrites the 2039 Router Lifetime and forwards the (proxyed) message to the Client. 2040 The Proxy finally includes an MTU option (if necessary) with an 2041 MTU to use for the underlying ANET interface. 2043 After the initial RS/RA exchange, the Proxy forwards any Client data 2044 packets for which there is no matching asymmetric neighbor cache 2045 entry to a Bridge using OAL encapsulation with its own DLA as the 2046 source and the DLA corresponding to the Client as the destination. 2047 The Proxy instead forwards any Client data destined to an asymmetric 2048 neighbor cache target directly to the target according to the OAL/ 2049 link-layer information - the process of establishing asymmetric 2050 neighbor cache entries is specified in Section 3.14. 2052 While the Client is still attached to the ANET, the Proxy sends NS, 2053 RS and/or unsolicited NA messages to update the Server's symmetric 2054 neighbor cache entries on behalf of the Client and/or to convey QoS 2055 updates. This allows for higher-frequency Proxy-initiated RS/RA 2056 messaging over well-connected INET infrastructure supplemented by 2057 lower-frequency Client-initiated RS/RA messaging over constrained 2058 ANET data links. 2060 If the Server ceases to send solicited advertisements, the Proxy 2061 sends unsolicited RAs on the ANET interface with destination set to 2062 (link-local) All-Nodes multicast and with Router Lifetime set to zero 2063 to inform Clients that the Server has failed. Although the Proxy 2064 engages in ND exchanges on behalf of the Client, the Client can also 2065 send ND messages on its own behalf, e.g., if it is in a better 2066 position than the Proxy to convey QoS changes, etc. For this reason, 2067 the Proxy marks any Client-originated solicitation messages (e.g. by 2068 inserting a Nonce option) so that it can return the solicited 2069 advertisement to the Client instead of processing it locally. 2071 If the Client becomes unreachable, the Proxy sets the neighbor cache 2072 entry state to DEPARTED and retains the entry for DepartTime seconds. 2073 While the state is DEPARTED, the Proxy forwards any packets destined 2074 to the Client to a Bridge via OAL encapsulation with the Client's 2075 current Server as the destination. The Bridge in turn forwards the 2076 packets to the Client's current Server. When DepartTime expires, the 2077 Proxy deletes the neighbor cache entry and discards any further 2078 packets destined to this (now forgotten) Client. 2080 In some ANETs that employ a Proxy, the Client's MNP can be injected 2081 into the ANET routing system. In that case, the Client can send data 2082 messages without encapsulation so that the ANET routing system 2083 transports the unencapsulated packets to the Proxy. This can be very 2084 beneficial, e.g., if the Client connects to the ANET via low-end data 2085 links such as some aviation wireless links. 2087 If the first-hop ANET access router is on the same underlying link 2088 and recognizes the AERO/OMNI protocol, the Client can avoid 2089 encapsulation for both its control and data messages. When the 2090 Client connects to the link, it can send an unencapsulated RS message 2091 with source address set to its LLA and with destination address set 2092 to the LLA of the Client's selected Server or to (link-local) All- 2093 Routers multicast. The Client includes an OMNI option formatted as 2094 specified in [I-D.templin-6man-omni-interface]. 2096 The Client then sends the unencapsulated RS message, which will be 2097 intercepted by the AERO-Aware access router. The access router then 2098 encapsulates the RS message in an ANET header with its own address as 2099 the source address and the address of a Proxy as the destination 2100 address. The access router further remembers the address of the 2101 Proxy so that it can encapsulate future data packets from the Client 2102 via the same Proxy. If the access router needs to change to a new 2103 Proxy, it simply sends another RS message toward the Server via the 2104 new Proxy on behalf of the Client. 2106 In some cases, the access router and Proxy may be one and the same 2107 node. In that case, the node would be located on the same physical 2108 link as the Client, but its message exchanges with the Server would 2109 need to pass through a security gateway at the ANET/INET border. The 2110 method for deploying access routers and Proxys (i.e. as a single node 2111 or multiple nodes) is an ANET-local administrative consideration. 2113 3.13.1. Combined Proxy/Servers 2115 Clients may need to connect directly to Servers via INET, Direct and 2116 VPNed interfaces (i.e., non-ANET interfaces). If the Client's 2117 underlying interfaces all connect via the same INET partition, then 2118 it can connect to a single controlling Server via all interfaces. 2120 If some Client interfaces connect via different INET partitions, 2121 however, the Client still selects a set of controlling Servers and 2122 sends RS messages via their directly-connected Servers while using 2123 the LLA of the controlling Server as the destination. 2125 When a Server receives an RS with destination set to the LLA of a 2126 controlling Server, it acts as a Proxy to forward the message to the 2127 controlling Server while forwarding the corresponding RA reply to the 2128 Client. 2130 3.13.2. Detecting and Responding to Server Failures 2132 In environments where fast recovery from Server failure is required, 2133 Proxys SHOULD use proactive Neighbor Unreachability Detection (NUD) 2134 to track Server reachability in a similar fashion as for 2135 Bidirectional Forwarding Detection (BFD) [RFC5880]. Proxys can then 2136 quickly detect and react to failures so that cached information is 2137 re-established through alternate paths. The NUD control messaging is 2138 carried only over well-connected ground domain networks (i.e., and 2139 not low-end aeronautical radio links) and can therefore be tuned for 2140 rapid response. 2142 Proxys perform proactive NUD with Servers for which there are 2143 currently active ANET Clients by sending continuous NS messages in 2144 rapid succession, e.g., one message per second. The Proxy sends the 2145 NS message via the spanning tree with the Proxy's LLA as the source 2146 and the LLA of the Server as the destination. When the Proxy is also 2147 sending RS messages to the Server on behalf of ANET Clients, the 2148 resulting RA responses can be considered as equivalent hints of 2149 forward progress. This means that the Proxy need not also send a 2150 periodic NS if it has already sent an RS within the same period. If 2151 the Server fails (i.e., if the Proxy ceases to receive 2152 advertisements), the Proxy can quickly inform Clients by sending 2153 multicast RA messages on the ANET interface. 2155 The Proxy sends RA messages on the ANET interface with source address 2156 set to the Server's address, destination address set to (link-local) 2157 All-Nodes multicast, and Router Lifetime set to 0. The Proxy SHOULD 2158 send MAX_FINAL_RTR_ADVERTISEMENTS RA messages separated by small 2159 delays [RFC4861]. Any Clients on the ANET that had been using the 2160 failed Server will receive the RA messages and associate with a new 2161 Server. 2163 3.13.3. Point-to-Multipoint Server Coordination 2165 In environments where Client messaging over ANETs is bandwidth- 2166 limited and/or expensive, Clients can enlist the services of the 2167 Proxy to coordinate with multiple Servers in a single RS/RA message 2168 exchange. The Client can send a single RS message to (link-local) 2169 All-Routers multicast that includes the ID's of multiple Servers in 2170 MS-Register sub-options of the OMNI option. 2172 When the Proxy receives the RS and processes the OMNI option, it 2173 sends a separate RS to each MS-Register Server ID. When the Proxy 2174 receives an RA, it can optionally return an immediate "singleton" RA 2175 to the Client or record the Server's ID for inclusion in a pending 2176 "aggregate" RA message. The Proxy can then return aggregate RA 2177 messages to the Client including multiple Server IDs in order to 2178 conserve bandwidth. Each RA includes a proper subset of the Server 2179 IDs from the original RS message, and the Proxy must ensure that the 2180 message contents of each RA are consistent with the information 2181 received from the (aggregated) Servers. 2183 Clients can thereafter employ efficient point-to-multipoint Server 2184 coordination under the assistance of the Proxy to reduce the number 2185 of messages sent over the ANET while enlisting the support of 2186 multiple Servers for fault tolerance. Clients can further include 2187 MS-Release sub-options in IPv6 ND messages to request the Proxy to 2188 release from former Servers via the procedures discussed in 2189 Section 3.16.5. 2191 The OMNI interface specification [I-D.templin-6man-omni-interface] 2192 provides further discussion of the Client/Proxy RS/RA messaging 2193 involved in point-to-multipoint coordination. 2195 3.14. AERO Route Optimization / Address Resolution 2197 While data packets are flowing between a source and target node, 2198 route optimization SHOULD be used. Route optimization is initiated 2199 by the first eligible Route Optimization Source (ROS) closest to the 2200 source as follows: 2202 o For Clients on VPNed and Direct interfaces, the Server is the ROS. 2204 o For Clients on ANET interfaces, the Proxy is the ROS. 2206 o For Clients on INET interfaces, the Client itself is the ROS. 2208 o For correspondent nodes on INET/EUN interfaces serviced by a 2209 Relay, the Relay is the ROS. 2211 The route optimization procedure is conducted between the ROS and the 2212 target Server/Relay acting as a Route Optimization Responder (ROR) in 2213 the same manner as for IPv6 ND Address Resolution and using the same 2214 NS/NA messaging. The target may either be a MNP Client serviced by a 2215 Server, or a non-MNP correspondent reachable via a Relay. 2217 The procedures are specified in the following sections. 2219 3.14.1. Route Optimization Initiation 2221 While data packets are flowing from the source node toward a target 2222 node, the ROS performs address resolution by sending an NS message 2223 for Address Resolution (NS(AR)) to receive a solicited NA message 2224 from the ROR. When the ROS sends an NS(AR), it includes: 2226 o the LLA of the ROS as the source address. 2228 o the data packet's destination as the Target Address. 2230 o the Solicited-Node multicast address [RFC4291] formed from the 2231 lower 24 bits of the data packet's destination as the destination 2232 address, e.g., for 2001:db8:1:2::10:2000 the NS destination 2233 address is ff02:0:0:0:0:1:ff10:2000. 2235 The NS(AR) message includes an OMNI option with no Interface 2236 Attributes, such that the target will not create a neighbor cache 2237 entry. The Prefix Length in the OMNI option is set to the Prefix 2238 Length associated with the ROS's LLA. 2240 The ROS then encapsulates the NS(AR) message in an OAL header with 2241 source set to its own DLA and destination set to the DLA 2242 corresponding to the target, then sends the message into the spanning 2243 tree without decrementing the network-layer TTL/Hop Limit field. 2244 (When the ROS is a Client, it instead securely sends the NS(AR) per 2245 Section 3.22.1 to one of its current Servers, which forwards the 2246 message into the spanning tree on behalf of the Client. When the 2247 Server forwards the NS(AR), it sets the IPv6 source address and the 2248 OAL source address to the LLA and DLA of the Client, respectively.) 2250 3.14.2. Relaying the NS 2252 When the Bridge receives the NS(AR) message from the ROS, it discards 2253 the INET header and determines that the ROR is the next hop by 2254 consulting its standard IPv6 forwarding table for the OAL header 2255 destination address. The Bridge then forwards the message toward the 2256 ROR via the spanning tree the same as for any IPv6 router. The 2257 final-hop Bridge in the spanning tree will deliver the message via a 2258 secured tunnel to the ROR. 2260 3.14.3. Processing the NS and Sending the NA 2262 When the ROR receives the NS(AR) message, it examines the Target 2263 Address to determine whether it has a neighbor cache entry and/or 2264 route that matches the target. If there is no match, the ROR drops 2265 the message. Otherwise, the ROR continues processing as follows: 2267 o if the target belongs to an MNP Client neighbor in the DEPARTED 2268 state the ROR changes the NS(AR) message OAL destination address 2269 to the DLA of the Client's new Server, forwards the message into 2270 the spanning tree and returns from processing. 2272 o If the target belongs to an MNP Client neighbor in the REACHABLE 2273 state, the ROR instead adds the AERO source address to the target 2274 Client's Report List with time set to ReportTime. 2276 o If the target belongs to a non-MNP route, the ROR continues 2277 processing without adding an entry to the Report List. 2279 The ROR then prepares a solicited NA message to send back to the ROS 2280 but does not create a neighbor cache entry. The ROR sets the NA 2281 source address to the LLA corresponding to the target, sets the 2282 Target Address to the target of the solicitation, and sets the 2283 destination address to the source of the solicitation. The ROR then 2284 includes an OMNI option with Prefix Length set to the length 2285 associated with the LLA. 2287 If the target is an MNP Client, the ROR next includes Interface 2288 Attributes in the OMNI option for each of the target Client's 2289 underlying interfaces with current information for each interface and 2290 with the S/T-ifIndex field in the OMNI header set to 0 to indicate 2291 that the message originated from the ROR and not the Client. 2293 For each Interface Attributes sub-option, the ROR sets the L2ADDR 2294 according to its own INET address for VPNed or Direct interfaces, to 2295 the INET address of the Proxy or to the Client's INET address for 2296 INET interfaces. The ROR then includes the lower 32 bits of its own 2297 DLA (or the DLA of the Proxy) as the LHS, encodes the DLA prefix 2298 length code in the SRT field and sets the FMT code accordingly as 2299 specified in Section 3.3. 2301 The ROR then sets the NA message R flag to 1 (as a router), S flag to 2302 1 (as a response to a solicitation), and O flag to 0 (as a proxy). 2303 The ROR finally encapsulates the NA message in an OAL header with 2304 source set to its own DLA and destination set to the source DLA of 2305 the NS(AR) message, then forwards the message into the spanning tree 2306 without decrementing the network-layer TTL/Hop Limit field. 2308 3.14.4. Relaying the NA 2310 When the Bridge receives the NA message from the ROR, it discards the 2311 INET header and determines that the ROS is the next hop by consulting 2312 its standard IPv6 forwarding table for the OAL header destination 2313 address. The Bridge then forwards the OAL-encapsulated NA message 2314 toward the ROS the same as for any IPv6 router. The final-hop Bridge 2315 in the spanning tree will deliver the message via a secured tunnel to 2316 the ROS. 2318 3.14.5. Processing the NA 2320 When the ROS receives the solicited NA message, it processes the 2321 message the same as for standard IPv6 Address Resolution [RFC4861]. 2322 In the process, it caches the source DLA then creates an asymmetric 2323 neighbor cache entry for the target and caches all information found 2324 in the OMNI option. The ROS finally sets the asymmetric neighbor 2325 cache entry lifetime to ReachableTime seconds. (When the ROS is a 2326 Client, the solicited NA message will first be delivered via the 2327 spanning tree to one of its current Servers, which then securely 2328 forwards the message to the Client per Section 3.22.1. When the 2329 Server forwards the NS(AR), it sets the IPv6 source address to its 2330 own Cryptographically-Generated Address (CGA) and sets the OAL source 2331 address to its own DLA.) 2333 3.14.6. Route Optimization Maintenance 2335 Following route optimization, the ROS forwards future data packets 2336 destined to the target via the addresses found in the cached link- 2337 layer information. The route optimization is shared by all sources 2338 that send packets to the target via the ROS, i.e., and not just the 2339 source on behalf of which the route optimization was initiated. 2341 While new data packets destined to the target are flowing through the 2342 ROS, it sends additional NS(AR) messages to the ROR before 2343 ReachableTime expires to receive a fresh solicited NA message the 2344 same as described in the previous sections (route optimization 2345 refreshment strategies are an implementation matter, with a non- 2346 normative example given in Appendix A.1). The ROS uses the cached 2347 DLA of the ROR as the NS(AR) OAL destination address (i.e., instead 2348 of using the DLA corresponding to the target as was the case for the 2349 initial NS(AR)), and sends up to MAX_MULTICAST_SOLICIT NS(AR) 2350 messages separated by 1 second until an NA is received. If no NA is 2351 received, the ROS assumes that the current ROR has become unreachable 2352 and deletes the target neighbor cache entry. Subsequent data packets 2353 will trigger a new route optimization with an NS with OAL destination 2354 address set to the DLA corresponding to the target per Section 3.14.1 2355 to discover a new ROR while initial data packets travel over a 2356 suboptimal route. 2358 If an NA is received, the ROS then updates the asymmetric neighbor 2359 cache entry to refresh ReachableTime, while (for MNP destinations) 2360 the ROR adds or updates the ROS address to the target's Report List 2361 and with time set to ReportTime. While no data packets are flowing, 2362 the ROS instead allows ReachableTime for the asymmetric neighbor 2363 cache entry to expire. When ReachableTime expires, the ROS deletes 2364 the asymmetric neighbor cache entry. Any future data packets flowing 2365 through the ROS will again trigger a new route optimization. 2367 The ROS may also receive unsolicited NA messages from the ROR at any 2368 time (see: Section 3.16). If there is an asymmetric neighbor cache 2369 entry for the target, the ROS updates the link-layer information but 2370 does not update ReachableTime since the receipt of an unsolicited NA 2371 does not confirm that any forward paths are working. If there is no 2372 asymmetric neighbor cache entry, the ROS simply discards the 2373 unsolicited NA. 2375 In this arrangement, the ROS holds an asymmetric neighbor cache entry 2376 for the target via the ROR, but the ROR does not hold an asymmetric 2377 neighbor cache entry for the ROS. The route optimization neighbor 2378 relationship is therefore asymmetric and unidirectional. If the 2379 target node also has packets to send back to the source node, then a 2380 separate route optimization procedure is performed in the reverse 2381 direction. But, there is no requirement that the forward and reverse 2382 paths be symmetric. 2384 3.15. Neighbor Unreachability Detection (NUD) 2386 AERO nodes perform Neighbor Unreachability Detection (NUD) per 2387 [RFC4861] either reactively in response to persistent link-layer 2388 errors (see Section 3.11) or proactively to confirm reachability. 2389 The NUD algorithm is based on periodic control message exchanges. 2390 The algorithm may further be seeded by ND hints of forward progress, 2391 but care must be taken to avoid inferring reachability based on 2392 spoofed information. For example, authentic IPv6 ND message 2393 exchanges may be considered as acceptable hints of forward progress, 2394 while spurious data packets should not be. 2396 AERO Servers, Proxys and Relays can use (OAL-encapsulated) standard 2397 NS/NA NUD exchanges sent over the OMNI link spanning tree to securely 2398 test reachability without risk of DoS attacks from nodes pretending 2399 to be a neighbor (these NS/NA(NUD) messages use the unicast LLAs and 2400 DLAs of the two parties involved in the NUD test the same as for 2401 standard IPv6 ND). Proxys can further perform NUD to securely verify 2402 Server reachability on behalf of their proxyed Clients. However, a 2403 means for an ROS to test the unsecured forward directions of target 2404 route optimized paths is also necessary. 2406 When an ROR directs an ROS to a neighbor with one or more target 2407 link-layer addresses, the ROS can proactively test each such 2408 unsecured route optimized path by sending "loopback" NS(NUD) 2409 messages. While testing the paths, the ROS can optionally continue 2410 to send packets via the spanning tree, maintain a small queue of 2411 packets until target reachability is confirmed, or (optimistically) 2412 allow packets to flow via the route optimized paths. 2414 When the ROS sends a loopback NS(NUD) message, it uses its own LLA as 2415 both the IPv6 source and destination address, and the MNP Subnet- 2416 Router anycast address as the Target Address. The ROS includes a 2417 Nonce and Timestamp option, then encapsulates the message in OAL/INET 2418 headers with its own DLA as the source and the DLA of the route 2419 optimization target as the destination. The ROS then forwards the 2420 message to the target (either directly to the L2ADDR of the target if 2421 the target is in the same OMNI link segment, or via a Bridge if the 2422 target is in a different OMNI link segment). 2424 When the route optimization target receives the NS(NUD) message, it 2425 notices that the IPv6 destination address is the same as the source 2426 address. It then reverses the OAL header source and destination 2427 addresses and returns the message to the ROS (either directly or via 2428 the spanning tree). The route optimization target does not decrement 2429 the NS(NUD) message IPv6 Hop-Limit in the process, since the message 2430 has not exited the OMNI link. 2432 When the ROS receives the NS(NUD) message, it can determine from the 2433 Nonce, Timestamp and Target Address that the message originated from 2434 itself and that it transited the forward path. The ROS need not 2435 prepare an NA response, since the destination of the response would 2436 be itself and testing the route optimization path again would be 2437 redundant. 2439 The ROS marks route optimization target paths that pass these NUD 2440 tests as "reachable", and those that do not as "unreachable". These 2441 markings inform the OMNI interface forwarding algorithm specified in 2442 Section 3.10. 2444 Note that to avoid a DoS vector nodes MUST NOT return loopback 2445 NS(NUD) messages received from an unsecured link-layer source via the 2446 spanning tree. 2448 3.16. Mobility Management and Quality of Service (QoS) 2450 AERO is a Distributed Mobility Management (DMM) service. Each Server 2451 is responsible for only a subset of the Clients on the OMNI link, as 2452 opposed to a Centralized Mobility Management (CMM) service where 2453 there is a single network mobility collective entity for all Clients. 2454 Clients coordinate with their associated Servers via RS/RA exchanges 2455 to maintain the DMM profile, and the AERO routing system tracks all 2456 current Client/Server peering relationships. 2458 Servers provide default routing and mobility/multilink services for 2459 their dependent Clients. Clients are responsible for maintaining 2460 neighbor relationships with their Servers through periodic RS/RA 2461 exchanges, which also serves to confirm neighbor reachability. When 2462 a Client's underlying interface address and/or QoS information 2463 changes, the Client is responsible for updating the Server with this 2464 new information. Note that when there is a Proxy in the path, the 2465 Proxy can also perform some RS/RA exchanges on the Client's behalf. 2467 Mobility management messaging is based on the transmission and 2468 reception of unsolicited Neighbor Advertisement (uNA) messages. Each 2469 uNA message sets the IPv6 destination address to (link-local) All- 2470 Nodes multicast to convey a general update of Interface Attributes to 2471 (possibly) multiple recipients, or to a specific unicast LLA to 2472 announce a departure event to a specific recipient. Implementations 2473 must therefore examine the destination address to determine the 2474 nature of the mobility event (i.e., update vs departure). 2476 Mobility management considerations are specified in the following 2477 sections. 2479 3.16.1. Mobility Update Messaging 2481 Servers accommodate Client mobility, multilink and/or QoS change 2482 events by sending unsolicited NA (uNA) messages to each ROS in the 2483 target Client's Report List. When a Server sends a uNA message, it 2484 sets the IPv6 source address to the Client's LLA, sets the 2485 destination address to (link-local) All-Nodes multicast and sets the 2486 Target Address to the Client's Subnet-Router anycast address. The 2487 Server also includes an OMNI option with Prefix Length set to the 2488 length associated with the Client's LLA, with Interface Attributes 2489 for the target Client's underlying interfaces and with the OMNI 2490 header S/T-ifIndex set to 0. The Server then sets the NA R flag to 2491 1, the S flag to 0 and the O flag to 1, then encapsulates the message 2492 in an OAL header with source set to its own DLA and destination set 2493 to the DLA of the ROS and sends the message into the spanning tree. 2495 As discussed in Section 7.2.6 of [RFC4861], the transmission and 2496 reception of uNA messages is unreliable but provides a useful 2497 optimization. In well-connected Internetworks with robust data links 2498 uNA messages will be delivered with high probability, but in any case 2499 the Server can optionally send up to MAX_NEIGHBOR_ADVERTISEMENT uNAs 2500 to each ROS to increase the likelihood that at least one will be 2501 received. 2503 When the ROS receives a uNA message prepared as above, it ignores the 2504 message if there is no existing neighbor cache entry for the Client. 2505 Otherwise, it uses the included OMNI option information to update the 2506 neighbor cache entry, but does not reset ReachableTime since the 2507 receipt of an unsolicited NA message from the target Server does not 2508 provide confirmation that any forward paths to the target Client are 2509 working. 2511 If uNA messages are lost, the ROS may be left with stale address and/ 2512 or QoS information for the Client for up to ReachableTime seconds. 2513 During this time, the ROS can continue sending packets according to 2514 its stale neighbor cache information. When ReachableTime is close to 2515 expiring, the ROS will re-initiate route optimization and receive 2516 fresh link-layer address information. 2518 In addition to sending uNA messages to the current set of ROSs for 2519 the Client, the Server also sends uNAs to the DLA associated with the 2520 link-layer address for any underlying interface for which the link- 2521 layer address has changed. These uNA messages update an old Proxy/ 2522 Server that cannot easily detect (e.g., without active probing) when 2523 a formerly-active Client has departed. When the Server sends the 2524 uNA, it sets the IPv6 source address to the Client's LLA, sets the 2525 destination address to the old Proxy/Server's LLA, and sets the 2526 Target Address to the Client's Subnet-Router anycast address. The 2527 Server also includes an OMNI option with Prefix Length set to the 2528 length associated with the Client's LLA, with Interface Attributes 2529 for the changed underlying interface, and with the OMNI header S/ 2530 T-ifIndex set to 0. The Server then sets the NA R flag to 1, the S 2531 flag to 0 and the O flag to 1, then encapsulates the message in an 2532 OAL header with source set to its own DLA and destination set to the 2533 DLA of the old Proxy/Server and sends the message into the spanning 2534 tree. 2536 3.16.2. Announcing Link-Layer Address and/or QoS Preference Changes 2538 When a Client needs to change its underlying interface addresses and/ 2539 or QoS preferences (e.g., due to a mobility event), either the Client 2540 or its Proxys send RS messages to the Server via the spanning tree 2541 with an OMNI option that includes Interface attributes with the new 2542 link quality and address information. 2544 Up to MAX_RTR_SOLICITATIONS RS messages MAY be sent in parallel with 2545 sending actual data packets in case one or more RAs are lost. If all 2546 RAs are lost, the Client SHOULD re-associate with a new Server. 2548 When the Server receives the Client's changes, it sends uNA messages 2549 to all nodes in the Report List the same as described in the previous 2550 section. 2552 3.16.3. Bringing New Links Into Service 2554 When a Client needs to bring new underlying interfaces into service 2555 (e.g., when it activates a new data link), it sends an RS message to 2556 the Server via the underlying interface with an OMNI option that 2557 includes Interface Attributes with appropriate link quality values 2558 and with link-layer address information for the new link. 2560 3.16.4. Deactivating Existing Links 2562 When a Client needs to deactivate an existing underlying interface, 2563 it sends an RS or uNA message to its Server with an OMNI option with 2564 appropriate Interface Attribute values - in particular, the link 2565 quality value 0 assures that neighbors will cease to use the link. 2567 If the Client needs to send RS/uNA messages over an underlying 2568 interface other than the one being deactivated, it MUST include 2569 Interface Attributes with appropriate link quality values for any 2570 underlying interfaces being deactivated. 2572 Note that when a Client deactivates an underlying interface, 2573 neighbors that have received the RS/uNA messages need not purge all 2574 references for the underlying interface from their neighbor cache 2575 entries. The Client may reactivate or reuse the underlying interface 2576 and/or its ifIndex at a later point in time, when it will send RS/uNA 2577 messages with fresh Interface Attributes to update any neighbors. 2579 3.16.5. Moving Between Servers 2581 The Client performs the procedures specified in Section 3.12.2 when 2582 it first associates with a new Server or renews its association with 2583 an existing Server. The Client also includes MS-Release identifiers 2584 in the RS message OMNI option per [I-D.templin-6man-omni-interface] 2585 if it wants the new Server to notify any old Servers from which the 2586 Client is departing. 2588 When the new Server receives the Client's RS message, it returns an 2589 RA as specified in Section 3.12.3 and sends up to 2590 MAX_NEIGHBOR_ADVERTIISEMENT uNA messages to any old Servers listed in 2591 OMNI option MS-Release identifiers. When the new Server sends a uNA 2592 message, it sets the IPv6 source address to the Client's LLA, sets 2593 the destination address to the old Server's LLA, and sets the Target 2594 Address to the Client's Subnet-Router anycast address. The new 2595 Server also includes an OMNI option with Prefix Length set to the 2596 length associated with the Client's LLA, with Interface Attributes 2597 for its own underlying interface, and with the OMNI header S/ 2598 T-ifIndex set to 0. The new Server then sets the NA R flag to 1, the 2599 S flag to 0 and the O flag to 1, then encapsulates the message in an 2600 OAL header with source set to its own DLA and destination set to the 2601 DLA of the old Server and sends the message into the spanning tree. 2603 When an old Server receives the uNA, it changes the Client's neighbor 2604 cache entry state to DEPARTED, sets the link-layer address of the 2605 Client to the new Server's DLA, and resets DepartTime. After a short 2606 delay (e.g., 2 seconds) the old Server withdraws the Client's MNP 2607 from the routing system. After DepartTime expires, the old Server 2608 deletes the Client's neighbor cache entry. 2610 The old Server also iteratively forwards a copy of the uNA message to 2611 each ROS in the Client's Report List by changing the OAL destination 2612 address to the DLA of the ROS while leaving all other fields of the 2613 message unmodified. When the ROS receives the uNA, it examines the 2614 Target address to determine the correct asymmetric neighbor cache 2615 entry and verifies that the IPv6 destination address matches the old 2616 Server. The ROS then caches the IPv6 source address as the new 2617 Server for the existing asymmetric neighbor cache entry and marks the 2618 entry as STALE. While in the STALE state, the ROS allows new data 2619 packets to flow according to any existing cached link-layer 2620 information and sends new NS(AR) messages using its own DLA as the 2621 OAL source and the DLA of the new Server as the OAL destination 2622 address to elicit NA messages that reset the asymmetric neighbor 2623 cache entry state to REACHABLE. If no new NA message is received for 2624 10 seconds while in the STALE state, the ROS deletes the neighbor 2625 cache entry. 2627 Clients SHOULD NOT move rapidly between Servers in order to avoid 2628 causing excessive oscillations in the AERO routing system. Examples 2629 of when a Client might wish to change to a different Server include a 2630 Server that has gone unreachable, topological movements of 2631 significant distance, movement to a new geographic region, movement 2632 to a new OMNI link segment, etc. 2634 When a Client moves to a new Server, some of the fragments of a 2635 multiple fragment packet may have already arrived at the old Server 2636 while others are en route to the new Server, however no special 2637 attention in the reassembly algorithm is necessary when re-routed 2638 fragments are simply treated as loss. 2640 3.17. Multicast 2642 The AERO Client provides an IGMP (IPv4) [RFC2236] or MLD (IPv6) 2643 [RFC3810] proxy service for its EUNs and/or hosted applications 2644 [RFC4605]. The Client forwards IGMP/MLD messages over any of its 2645 underlying interfaces for which group membership is required. The 2646 IGMP/MLD messages may be further forwarded by a first-hop ANET access 2647 router acting as an IGMP/MLD-snooping switch [RFC4541], then 2648 ultimately delivered to an AERO Proxy/Server acting as a Protocol 2649 Independent Multicast - Sparse-Mode (PIM-SM, or simply "PIM") 2650 Designated Router (DR) [RFC7761]. AERO Relays also act as PIM 2651 routers (i.e., the same as AERO Proxys/Servers) on behalf of nodes on 2652 INET/EUN networks. The behaviors identified in the following 2653 sections correspond to Source-Specific Multicast (SSM) and Any-Source 2654 Multicast (ASM) operational modes. 2656 3.17.1. Source-Specific Multicast (SSM) 2658 When an ROS (i.e., an AERO Proxy/Server/Relay) "X" acting as PIM 2659 router receives a Join/Prune message from a node on its downstream 2660 interfaces containing one or more ((S)ource, (G)roup) pairs, it 2661 updates its Multicast Routing Information Base (MRIB) accordingly. 2662 For each S belonging to a prefix reachable via X's non-OMNI 2663 interfaces, X then forwards the (S, G) Join/Prune to any PIM routers 2664 on those interfaces per [RFC7761]. 2666 For each S belonging to a prefix reachable via X's OMNI interface, X 2667 originates a separate copy of the Join/Prune for each (S,G) in the 2668 message using its own LLA as the source address and ALL-PIM-ROUTERS 2669 as the destination address. X then encapsulates each message in an 2670 OAL header with source address set to the DLA of X and destination 2671 address set to S then forwards the message into the spanning tree, 2672 which delivers it to AERO Server/Relay "Y" that services S. At the 2673 same time, if the message was a Join, X sends a route-optimization NS 2674 message toward each S the same as discussed in Section 3.14. The 2675 resulting NAs will return the LLA for the prefix that matches S as 2676 the network-layer source address and with an OMNI option with the DLA 2677 corresponding to any underlying interfaces that are currently 2678 servicing S. 2680 When Y processes the Join/Prune message, if S located behind any 2681 INET, Direct, or VPNed interfaces Y acts as a PIM router and updates 2682 its MRIB to list X as the next hop in the reverse path. If S is 2683 located behind any Proxys "Z"*, Y also forwards the message to each 2684 Z* over the spanning tree while continuing to use the LLA of X as the 2685 source address. Each Z* then updates its MRIB accordingly and 2686 maintains the LLA of X as the next hop in the reverse path. Since 2687 the Bridges do not examine network layer control messages, this means 2688 that the (reverse) multicast tree path is simply from each Z* (and/or 2689 Y) to X with no other multicast-aware routers in the path. If any Z* 2690 (and/or Y) is located on the same OMNI link segment as X, the 2691 multicast data traffic sent to X directly using OAL/INET 2692 encapsulation instead of via a Bridge. 2694 Following the initial Join/Prune and NS/NA messaging, X maintains an 2695 asymmetric neighbor cache entry for each S the same as if X was 2696 sending unicast data traffic to S. In particular, X performs 2697 additional NS/NA exchanges to keep the neighbor cache entry alive for 2698 up to t_periodic seconds [RFC7761]. If no new Joins are received 2699 within t_periodic seconds, X allows the neighbor cache entry to 2700 expire. Finally, if X receives any additional Join/Prune messages 2701 for (S,G) it forwards the messages to each Y and Z* in the neighbor 2702 cache entry over the spanning tree. 2704 At some later time, Client C that holds an MNP for source S may 2705 depart from a first Proxy Z1 and/or connect via a new Proxy Z2. In 2706 that case, Y sends an unsolicited NA message to X the same as 2707 specified for unicast mobility in Section 3.16. When X receives the 2708 unsolicited NA message, it updates its asymmetric neighbor cache 2709 entry for the LLA for source S and sends new Join messages to any new 2710 Proxys Z2. There is no requirement to send any Prune messages to old 2711 Proxys Z1 since source S will no longer source any multicast data 2712 traffic via Z1. Instead, the multicast state for (S,G) in Proxy Z1 2713 will soon time out since no new Joins will arrive. 2715 After some later time, C may move to a new Server Y2 and depart from 2716 old Sever Y1. In that case, Y1 sends Join messages for any of C's 2717 active (S,G) groups to Y2 while including its own LLA as the source 2718 address. This causes Y2 to include Y1 in the multicast forwarding 2719 tree during the interim time that Y1's symmetric neighbor cache entry 2720 for C is in the DEPARTED state. At the same time, Y1 sends an 2721 unsolicited NA message to X with an OMNI option with S/T-ifIndex in 2722 the header set to 0 and a release indication to cause X to release 2723 its asymmetric neighbor cache entry. X then sends a new Join message 2724 to S via the spanning tree and re-initiates route optimization the 2725 same as if it were receiving a fresh Join message from a node on a 2726 downstream link. 2728 3.17.2. Any-Source Multicast (ASM) 2730 When an ROS X acting as a PIM router receives a Join/Prune from a 2731 node on its downstream interfaces containing one or more (*,G) pairs, 2732 it updates its Multicast Routing Information Base (MRIB) accordingly. 2733 X then forwards a copy of the message to the Rendezvous Point (RP) R 2734 for each G over the spanning tree. X uses its own LLA as the source 2735 address and ALL-PIM-ROUTERS as the destination address, then 2736 encapsulates each message in an OAL header with source address set to 2737 the DLA of X and destination address set to R, then sends the message 2738 into the spanning tree. At the same time, if the message was a Join 2739 X initiates NS/NA route optimization the same as for the SSM case 2740 discussed in Section 3.17.1. 2742 For each source S that sends multicast traffic to group G via R, the 2743 Proxy/Server Z* for the Client that aggregates S encapsulates the 2744 packets in PIM Register messages and forwards them to R via the 2745 spanning tree, which may then elect to send a PIM Join to Z*. This 2746 will result in an (S,G) tree rooted at Z* with R as the next hop so 2747 that R will begin to receive two copies of the packet; one native 2748 copy from the (S, G) tree and a second copy from the pre-existing (*, 2749 G) tree that still uses PIM Register encapsulation. R can then issue 2750 a PIM Register-stop message to suppress the Register-encapsulated 2751 stream. At some later time, if C moves to a new Proxy/Server Z*, it 2752 resumes sending packets via PIM Register encapsulation via the new 2753 Z*. 2755 At the same time, as multicast listeners discover individual S's for 2756 a given G, they can initiate an (S,G) Join for each S under the same 2757 procedures discussed in Section 3.17.1. Once the (S,G) tree is 2758 established, the listeners can send (S, G) Prune messages to R so 2759 that multicast packets for group G sourced by S will only be 2760 delivered via the (S, G) tree and not from the (*, G) tree rooted at 2761 R. All mobility considerations discussed for SSM apply. 2763 3.17.3. Bi-Directional PIM (BIDIR-PIM) 2765 Bi-Directional PIM (BIDIR-PIM) [RFC5015] provides an alternate 2766 approach to ASM that treats the Rendezvous Point (RP) as a Designated 2767 Forwarder (DF). Further considerations for BIDIR-PIM are out of 2768 scope. 2770 3.18. Operation over Multiple OMNI Links 2772 An AERO Client can connect to multiple OMNI links the same as for any 2773 data link service. In that case, the Client maintains a distinct 2774 OMNI interface for each link, e.g., 'omni0' for the first link, 2775 'omni1' for the second, 'omni2' for the third, etc. Each OMNI link 2776 would include its own distinct set of Bridges, Servers and Proxys, 2777 thereby providing redundancy in case of failures. 2779 Each OMNI link could utilize the same or different ANET connections. 2780 The links can be distinguished at the link-layer via the SRT prefix 2781 in a similar fashion as for Virtual Local Area Network (VLAN) tagging 2782 (e.g., IEEE 802.1Q) and/or through assignment of distinct sets of 2783 MSPs on each link. This gives rise to the opportunity for supporting 2784 multiple redundant networked paths, with each VLAN distinguished by a 2785 different SRT "color" (see: Section 3.2.5). 2787 The Client's IP layer can select the outgoing OMNI interface 2788 appropriate for a given traffic profile while (in the reverse 2789 direction) correspondent nodes must have some way of steering their 2790 packets destined to a target via the correct OMNI link. 2792 In a first alternative, if each OMNI link services different MSPs, 2793 then the Client can receive a distinct MNP from each of the links. 2794 IP routing will therefore assure that the correct Red/Green/Blue/etc. 2795 network is used for both outbound and inbound traffic. This can be 2796 accomplished using existing technologies and approaches, and without 2797 requiring any special supporting code in correspondent nodes or 2798 Bridges. 2800 In a second alternative, if each OMNI link services the same MSP(s) 2801 then each link could assign a distinct "OMNI link Anycast" address 2802 that is configured by all Bridges on the link. Correspondent nodes 2803 can then perform Segment Routing to select the correct SRT, which 2804 will then direct the packet over multiple hops to the target. 2806 3.19. DNS Considerations 2808 AERO Client MNs and INET correspondent nodes consult the Domain Name 2809 System (DNS) the same as for any Internetworking node. When 2810 correspondent nodes and Client MNs use different IP protocol versions 2811 (e.g., IPv4 correspondents and IPv6 MNs), the INET DNS must maintain 2812 A records for IPv4 address mappings to MNs which must then be 2813 populated in Relay NAT64 mapping caches. In that way, an IPv4 2814 correspondent node can send packets to the IPv4 address mapping of 2815 the target MN, and the Relay will translate the IPv4 header and 2816 destination address into an IPv6 header and IPv6 destination address 2817 of the MN. 2819 When an AERO Client registers with an AERO Server, the Server can 2820 return the address(es) of DNS servers in RDNSS options [RFC6106]. 2821 The DNS server provides the IP addresses of other MNs and 2822 correspondent nodes in AAAA records for IPv6 or A records for IPv4. 2824 3.20. Transition Considerations 2826 OAL encapsulation ensures that dissimilar INET partitions can be 2827 joined into a single unified OMNI link, even though the partitions 2828 themselves may have differing protocol versions and/or incompatible 2829 addressing plans. However, a commonality can be achieved by 2830 incrementally distributing globally routable (i.e., native) IP 2831 prefixes to eventually reach all nodes (both mobile and fixed) in all 2832 OMNI link segments. This can be accomplished by incrementally 2833 deploying AERO Relays on each INET partition, with each Relay 2834 distributing its MNPs and/or discovering non-MNP prefixes on its INET 2835 links. 2837 This gives rise to the opportunity to eventually distribute native IP 2838 addresses to all nodes, and to present a unified OMNI link view even 2839 if the INET partitions remain in their current protocol and 2840 addressing plans. In that way, the OMNI link can serve the dual 2841 purpose of providing a mobility/multilink service and a transition 2842 service. Or, if an INET partition is transitioned to a native IP 2843 protocol version and addressing scheme that is compatible with the 2844 OMNI link MNP-based addressing scheme, the partition and OMNI link 2845 can be joined by Relays. 2847 Relays that connect INETs/EUNs with dissimilar IP protocol versions 2848 may need to employ a network address and protocol translation 2849 function such as NAT64 [RFC6146]. 2851 3.21. Detecting and Reacting to Server and Bridge Failures 2853 In environments where rapid failure recovery is required, Servers and 2854 Bridges SHOULD use Bidirectional Forwarding Detection (BFD) 2855 [RFC5880]. Nodes that use BFD can quickly detect and react to 2856 failures so that cached information is re-established through 2857 alternate nodes. BFD control messaging is carried only over well- 2858 connected ground domain networks (i.e., and not low-end radio links) 2859 and can therefore be tuned for rapid response. 2861 Servers and Bridges maintain BFD sessions in parallel with their BGP 2862 peerings. If a Server or Bridge fails, BGP peers will quickly re- 2863 establish routes through alternate paths the same as for common BGP 2864 deployments. Similarly, Proxys maintain BFD sessions with their 2865 associated Bridges even though they do not establish BGP peerings 2866 with them. 2868 Proxys SHOULD use proactive NUD for Servers for which there are 2869 currently active ANET Clients in a manner that parallels BFD, i.e., 2870 by sending unicast NS messages in rapid succession to receive 2871 solicited NA messages. When the Proxy is also sending RS messages on 2872 behalf of ANET Clients, the RS/RA messaging can be considered as 2873 equivalent hints of forward progress. This means that the Proxy need 2874 not also send a periodic NS if it has already sent an RS within the 2875 same period. If a Server fails, the Proxy will cease to receive 2876 advertisements and can quickly inform Clients of the outage by 2877 sending multicast RA messages on the ANET interface. 2879 The Proxy sends multicast RA messages with source address set to the 2880 Server's address, destination address set to (link-local) All-Nodes 2881 multicast, and Router Lifetime set to 0. The Proxy SHOULD send 2882 MAX_FINAL_RTR_ADVERTISEMENTS RA messages separated by small delays 2883 [RFC4861]. Any Clients on the ANET interface that have been using 2884 the (now defunct) Server will receive the RA messages and associate 2885 with a new Server. 2887 3.22. AERO Clients on the Open Internet 2889 AERO Clients that connect to the open Internet via INET interfaces 2890 can establish a VPN or direct link to securely connect to a Server in 2891 a "tethered" arrangement with all of the Client's traffic transiting 2892 the Server. Alternatively, the Client can associate with an INET 2893 Server using UDP/IP encapsulation and asymmetric securing services as 2894 discussed in the following sections. 2896 When a Client's OMNI interface enables an INET underlying interface, 2897 it first determines whether the interface is likely to be behind a 2898 NAT. For IPv4, the Client assumes it is on the open Internet if the 2899 INET address is not a special-use IPv4 address per [RFC3330]. 2900 Similarly for IPv6, the Client assumes it is on the open Internet if 2901 the INET address is not a link-local [RFC4291] or unique-local 2902 [RFC4193] IPv6 address. 2904 The Client then prepares a UDP/IP-encapsulated RS message with IPv6 2905 source address set to its LLA, with IPv6 destination set to (link- 2906 local) All-Routers multicast and with an OMNI option with underlying 2907 interface parameters. If the Client believes that it is on the open 2908 Internet, it SHOULD include Interface Attributes with the L2ADDR used 2909 for INET encapsulation (otherwise, it MAY omit L2ADDR). If the 2910 underlying address is IPv4, the Client includes the Port Number and 2911 IPv4 address written in obfuscated form [RFC4380] as discussed in 2912 Section 3.3. If the underlying interface address is IPv6, the Client 2913 instead includes the Port Number and IPv6 address in obfuscated form. 2914 The Client finally includes an Authentication option per [RFC4380] to 2915 provide message authentication, sets the UDP/IP source to its INET 2916 address and UDP port, sets the UDP/IP destination to the Server's 2917 INET address and the AERO service port number (8060), then sends the 2918 message to the Server. 2920 When the Server receives the RS, it authenticates the message and 2921 registers the Client's MNP and INET interface information according 2922 to the OMNI option parameters. If the RS message includes an L2ADDR 2923 in the OMNI option, the Server compares the encapsulation IP address 2924 and UDP port number with the (unobfuscated) values. If the values 2925 are the same, the Server caches the Client's information as "INET" 2926 addresses meaning that the Client is likely to accept direct messages 2927 without requiring NAT traversal exchanges. If the values are 2928 different (or, if the OMNI option did not include an L2ADDR) the 2929 Server instead caches the Client's information as "NAT" addresses 2930 meaning that NAT traversal exchanges may be necessary. 2932 The Server then returns an RA message with IPv6 source and 2933 destination set corresponding to the addresses in the RS, and with an 2934 Authentication option per [RFC4380]. For IPv4, the Server also 2935 includes an Origin option per [RFC4380] with the mapped and 2936 obfuscated Port Number and IPv4 address observed in the encapsulation 2937 headers. For IPv6, the Server instead includes an IPv6 Origin option 2938 per Figure 7 with the mapped and obfuscated observed Port Number and 2939 IPv6 address (note that the value 0x02 in the second octet 2940 differentiates from other [RFC4380] option types). 2942 +--------+--------+-----------------+ 2943 | 0x00 | 0x02 | Origin port # | 2944 +--------+--------+-----------------+ 2945 ~ Origin IPv6 address ~ 2946 +-----------------------------------+ 2948 Figure 7: IPv6 Origin Option 2950 When the Client receives the RA message, it compares the mapped Port 2951 Number and IP address from the Origin option with its own address. 2952 If the addresses are the same, the Client assumes the open Internet / 2953 Cone NAT principle; if the addresses are different, the Client 2954 instead assumes that further qualification procedures are necessary 2955 to detect the type of NAT and proceeds according to standard 2956 [RFC4380] procedures. 2958 After the Client has registered its INET interfaces in such RS/RA 2959 exchanges it sends periodic RS messages to receive fresh RA messages 2960 before the Router Lifetime received on each INET interface expires. 2961 The Client also maintains default routes via its Servers, i.e., the 2962 same as described in earlier sections. 2964 When the Client sends messages to target IP addresses, it also 2965 invokes route optimization per Section 3.14 using IPv6 ND address 2966 resolution messaging. The Client sends the NS(AR) message to the 2967 Server wrapped in a UDP/IP header with an Authentication option with 2968 the NS source address set to the Client's LLA and destination address 2969 set to the target solicited node multicast address. The Server 2970 authenticates the message and sends a corresponding NS(AR) message 2971 over the spanning tree the same as if it were the ROS, but with the 2972 OAL source address set to the Server's DLA and destination set to the 2973 DLA of the target. When the ROR receives the NS(AR), it adds the 2974 Server's DLA and Client's LLA to the target's Report List, and 2975 returns an NA with OMNI option information for the target. The 2976 Server then returns a UDP/IP encapsulated NA message with an 2977 Authentication option to the Client. 2979 Following route optimization for targets in the same OMNI link 2980 segment, if the target's L2ADDR is on the open INET, the Client 2981 forwards data packets directly to the target INET address. If the 2982 target is behind a NAT, the Client first establishes NAT state for 2983 the L2ADDR using the "bubble" mechanisms specified in 2984 [RFC6081][RFC4380]. The Client continues to send data packets via 2985 its Server until NAT state is populated, then begins forwarding 2986 packets via the direct path through the NAT to the target. For 2987 targets in different OMNI link segments, the Client inserts an ORH 2988 and forwards data packets to the Bridge that returned the NA message. 2990 The ROR may return uNAs via the Server if the target moves, and the 2991 Server will send corresponding Authentication-protected uNAs to the 2992 Client. The Client can also send "loopback" NS(NUD) messages to test 2993 forward path reachability even though there is no security 2994 association between the Client and the target. 2996 The Client sends UDP/IP encapsulated IPv6 packets no larger than 1280 2997 bytes in one piece. In order to accommodate larger IPv6 packets (up 2998 to the OMNI interface MTU), the Client inserts an OAL header with 2999 source set to its own DLA and destination set to the DLA of the 3000 target and uses IPv6 fragmentation according to Section 3.9. The 3001 Client then encapsulates each fragment in a UDP/IP header and sends 3002 the fragments to the next hop. 3004 3.22.1. Use of SEND and CGA 3006 In some environments, use of the [RFC4380] Authentication option 3007 alone may be sufficient for assuring IPv6 ND message authentication 3008 between Clients and Servers. When additional protection is 3009 necessary, nodes should employ SEcure Neighbor Discovery (SEND) 3010 [RFC3971] with Cryptographically-Generated Addresses (CGA) [RFC3972]. 3012 When SEND/CGA are used, the Client prepares RS messages with its 3013 link-local CGA as the IPv6 source and (link-local) All-Routers 3014 multicast as the IPv6 Destination, includes any SEND options and 3015 wraps the message in an OAL header. The Client sets the OAL source 3016 address to its own DLA and sets the OAL destination address to (site- 3017 local) All-Routers multicast. The Client then wraps the RS message 3018 in UDP/IP headers according to [RFC4380] and sends the message to the 3019 Server. 3021 When the Server receives the message, it first verifies the 3022 Authentication option (if present) then uses the OAL source address 3023 to determine the MNP of the Client. The Server then processes the 3024 SEND options to authenticate the RS message and prepares an RA 3025 message response. The Server prepares the RA with its own link-local 3026 CGA as the IPv6 source and the CGA of the Client as the IPv6 3027 destination, includes any SEND options and wraps the message in an 3028 OAL header. The Server sets the OAL source address to its own DLA 3029 and sets the OAL destination address to the Client's DLA. The Server 3030 then wraps the RA message in UDP/IP headers according to [RFC4380] 3031 and sends the message to the Client. Thereafter, the Client/Server 3032 send additional RS/RA messages to maintain their association and any 3033 NAT state. 3035 The Client and Server also may exchange NS/NA messages using their 3036 own CGA as the source and with OAL encapsulation as above. When a 3037 Client sends an NS(AR), it sets the IPv6 source to its CGA and sets 3038 the IPv6 destination to the Solicited-Node Multicast address of the 3039 target. The Client then wraps the message in an OAL header with its 3040 own DLA as the source and the DLA of the target as the destination 3041 and sends it to the Server. The Server authenticates the message, 3042 then changes the IPv6 source address to the Client's LLA, removes the 3043 SEND options, and sends a corresponding NS(AR) into the spanning 3044 tree. When the Server receives the corresponding OAL-encapsulated 3045 NA, it changes the IPv6 destination address to the Client's CGA, 3046 inserts SEND options, then wraps the message in UDP/IP headers and 3047 sends it to the Client. 3049 When a Client sends a uNA, it sets the IPv6 source address to its own 3050 CGA and sets the IPv6 destination address to (link-local) All-Nodes 3051 multicast, includes SEND options, wraps the message in OAL and UDP/IP 3052 headers and sends the message to the Server. The Server 3053 authenticates the message, then changes the IPv6 address to the 3054 Client's LLA, removes the SEND options and forwards the message the 3055 same as discussed in Section 3.16.1. In the reverse direction, when 3056 the Server forwards a uNA to the Client, it changes the IPv6 address 3057 to its own CGA and inserts SEND options then forwards the message to 3058 the Client. 3060 When a Client sends an NS(NUD), it sets both the IPv6 source and 3061 destination address to its own LLA, wraps the message in an OAL 3062 header and UDP/IP headers, then sends the message directly to the 3063 peer which will loop the message back. In this case alone, the 3064 Client does not use the Server as a trust broker for forwarding the 3065 ND message. 3067 3.23. Time-Varying MNPs 3069 In some use cases, it is desirable, beneficial and efficient for the 3070 Client to receive a constant MNP that travels with the Client 3071 wherever it moves. For example, this would allow air traffic 3072 controllers to easily track aircraft, etc. In other cases, however 3073 (e.g., intelligent transportation systems), the MN may be willing to 3074 sacrifice a modicum of efficiency in order to have time-varying MNPs 3075 that can be changed every so often to defeat adversarial tracking. 3077 The DHCPv6 service offers a way for Clients that desire time-varying 3078 MNPs to obtain short-lived prefixes (e.g., on the order of a small 3079 number of minutes). In that case, the identity of the Client would 3080 not be bound to the MNP but rather the Client's identity would be 3081 bound to the DHCPv6 Device Unique Identifier (DUID) and used as the 3082 seed for Prefix Delegation. The Client would then be obligated to 3083 renumber its internal networks whenever its MNP (and therefore also 3084 its LLA) changes. This should not present a challenge for Clients 3085 with automated network renumbering services, however presents limits 3086 for the durations of ongoing sessions that would prefer to use a 3087 constant address. 3089 4. Implementation Status 3091 An early AERO implementation based on OpenVPN (https://openvpn.net/) 3092 was announced on the v6ops mailing list on January 10, 2018 and an 3093 initial public release of the AERO proof-of-concept source code was 3094 announced on the intarea mailing list on August 21, 2015. 3096 AERO Release-3.0.2 was tagged on October 15, 2020, and is undergoing 3097 internal testing. Additional releases expected Q42020, with first 3098 public release expected before year-end. 3100 5. IANA Considerations 3102 The IANA has assigned a 4-octet Private Enterprise Number "45282" for 3103 AERO in the "enterprise-numbers" registry. 3105 The IANA has assigned the UDP port number "8060" for an earlier 3106 experimental version of AERO [RFC6706]. This document obsoletes 3107 [RFC6706] and claims the UDP port number "8060" for all future use. 3109 The IANA is instructed to assign a new type value TBD in the IPv6 3110 Routing Types registry. 3112 No further IANA actions are required. 3114 6. Security Considerations 3116 AERO Bridges configure secured tunnels with AERO Servers, Relays and 3117 Proxys within their local OMNI link segments. Applicable secured 3118 tunnel alternatives include IPsec [RFC4301], TLS/SSL [RFC8446], DTLS 3119 [RFC6347], WireGuard [WG], etc. The AERO Bridges of all OMNI link 3120 segments in turn configure secured tunnels for their neighboring AERO 3121 Bridges in a spanning tree topology. Therefore, control messages 3122 exchanged between any pair of OMNI link neighbors on the spanning 3123 tree are already secured. 3125 AERO Servers, Relays and Proxys targeted by a route optimization may 3126 also receive data packets directly from arbitrary nodes in INET 3127 partitions instead of via the spanning tree. For INET partitions 3128 that apply effective ingress filtering to defeat source address 3129 spoofing, the simple data origin authentication procedures in 3130 Section 3.8 can be applied. 3132 For INET partitions that require strong security in the data plane, 3133 two options for securing communications include 1) disable route 3134 optimization so that all traffic is conveyed over secured tunnels, or 3135 2) enable on-demand secure tunnel creation between INET partition 3136 neighbors. Option 1) would result in longer routes than necessary 3137 and traffic concentration on critical infrastructure elements. 3138 Option 2) could be coordinated by establishing a secured tunnel on- 3139 demand instead of performing an NS/NA exchange in the route 3140 optimization procedures. Procedures for establishing on-demand 3141 secured tunnels are out of scope. 3143 AERO Clients that connect to secured ANETs need not apply security to 3144 their ND messages, since the messages will be intercepted by a 3145 perimeter Proxy that applies security on its INET-facing interface as 3146 part of the spanning tree (see above). AERO Clients connected to the 3147 open INET can use symmetric network and/or transport layer security 3148 services such as VPNs or can by some other means establish a direct 3149 link. When a VPN or direct link may be impractical, however, an 3150 asymmetric security service such as SEcure Neighbor Discovery (SEND) 3151 [RFC3971] with Cryptographically Generated Addresses (CGAs) [RFC3972] 3152 and/or the Authentication option [RFC4380] can be applied. 3154 Application endpoints SHOULD use application-layer security services 3155 such as TLS/SSL, DTLS or SSH [RFC4251] to assure the same level of 3156 protection as for critical secured Internet services. AERO Clients 3157 that require host-based VPN services SHOULD use symmetric network 3158 and/or transport layer security services such as IPsec, TLS/SSL, 3159 DTLS, etc. AERO Proxys and Servers can also provide a network-based 3160 VPN service on behalf of the Client, e.g., if the Client is located 3161 within a secured enclave and cannot establish a VPN on its own 3162 behalf. 3164 AERO Servers and Bridges present targets for traffic amplification 3165 Denial of Service (DoS) attacks. This concern is no different than 3166 for widely-deployed VPN security gateways in the Internet, where 3167 attackers could send spoofed packets to the gateways at high data 3168 rates. This can be mitigated by connecting Servers and Bridges over 3169 dedicated links with no connections to the Internet and/or when 3170 connections to the Internet are only permitted through well-managed 3171 firewalls. Traffic amplification DoS attacks can also target an AERO 3172 Client's low data rate links. This is a concern not only for Clients 3173 located on the open Internet but also for Clients in secured 3174 enclaves. AERO Servers and Proxys can institute rate limits that 3175 protect Clients from receiving packet floods that could DoS low data 3176 rate links. 3178 AERO Relays must implement ingress filtering to avoid a spoofing 3179 attack in which spurious messages with DLA addresses are injected 3180 into an OMNI link from an outside attacker. AERO Clients MUST ensure 3181 that their connectivity is not used by unauthorized nodes on their 3182 EUNs to gain access to a protected network, i.e., AERO Clients that 3183 act as routers MUST NOT provide routing services for unauthorized 3184 nodes. (This concern is no different than for ordinary hosts that 3185 receive an IP address delegation but then "share" the address with 3186 other nodes via some form of Internet connection sharing such as 3187 tethering.) 3189 The MAP list MUST be well-managed and secured from unauthorized 3190 tampering, even though the list contains only public information. 3192 The MAP list can be conveyed to the Client in a similar fashion as in 3193 [RFC5214] (e.g., through layer 2 data link login messaging, secure 3194 upload of a static file, DNS lookups, etc.). 3196 Although public domain and commercial SEND implementations exist, 3197 concerns regarding the strength of the cryptographic hash algorithm 3198 have been documented [RFC6273] [RFC4982]. 3200 SRH authentication facilities are specified in [RFC8754]. 3202 Security considerations for accepting link-layer ICMP messages and 3203 reflected packets are discussed throughout the document. 3205 Security considerations for IPv6 fragmentation and reassembly are 3206 discussed in [I-D.templin-6man-omni-interface]. 3208 7. Acknowledgements 3210 Discussions in the IETF, aviation standards communities and private 3211 exchanges helped shape some of the concepts in this work. 3212 Individuals who contributed insights include Mikael Abrahamsson, Mark 3213 Andrews, Fred Baker, Bob Braden, Stewart Bryant, Brian Carpenter, 3214 Wojciech Dec, Pavel Drasil, Ralph Droms, Adrian Farrel, Nick Green, 3215 Sri Gundavelli, Brian Haberman, Bernhard Haindl, Joel Halpern, Tom 3216 Herbert, Sascha Hlusiak, Lee Howard, Zdenek Jaron, Andre Kostur, 3217 Hubert Kuenig, Ted Lemon, Andy Malis, Satoru Matsushima, Tomek 3218 Mrugalski, Madhu Niraula, Alexandru Petrescu, Behcet Saikaya, Michal 3219 Skorepa, Joe Touch, Bernie Volz, Ryuji Wakikawa, Tony Whyman, Lloyd 3220 Wood and James Woodyatt. Members of the IESG also provided valuable 3221 input during their review process that greatly improved the document. 3222 Special thanks go to Stewart Bryant, Joel Halpern and Brian Haberman 3223 for their shepherding guidance during the publication of the AERO 3224 first edition. 3226 This work has further been encouraged and supported by Boeing 3227 colleagues including Kyle Bae, M. Wayne Benson, Dave Bernhardt, Cam 3228 Brodie, John Bush, Balaguruna Chidambaram, Irene Chin, Bruce Cornish, 3229 Claudiu Danilov, Don Dillenburg, Joe Dudkowski, Wen Fang, Samad 3230 Farooqui, Anthony Gregory, Jeff Holland, Seth Jahne, Brian Jaury, 3231 Greg Kimberly, Ed King, Madhuri Madhava Badgandi, Laurel Matthew, 3232 Gene MacLean III, Rob Muszkiewicz, Sean O'Sullivan, Vijay 3233 Rajagopalan, Greg Saccone, Rod Santiago, Kent Shuey, Brian Skeen, 3234 Mike Slane, Carrie Spiker, Katie Tran, Brendan Williams, Amelia 3235 Wilson, Julie Wulff, Yueli Yang, Eric Yeh and other members of the 3236 Boeing mobility, networking and autonomy teams. Kyle Bae, Wayne 3237 Benson, Katie Tran and Eric Yeh are especially acknowledged for 3238 implementing the AERO functions as extensions to the public domain 3239 OpenVPN distribution. 3241 Earlier works on NBMA tunneling approaches are found in 3242 [RFC2529][RFC5214][RFC5569]. 3244 Many of the constructs presented in this second edition of AERO are 3245 based on the author's earlier works, including: 3247 o The Internet Routing Overlay Network (IRON) 3248 [RFC6179][I-D.templin-ironbis] 3250 o Virtual Enterprise Traversal (VET) 3251 [RFC5558][I-D.templin-intarea-vet] 3253 o The Subnetwork Encapsulation and Adaptation Layer (SEAL) 3254 [RFC5320][I-D.templin-intarea-seal] 3256 o AERO, First Edition [RFC6706] 3258 Note that these works cite numerous earlier efforts that are not also 3259 cited here due to space limitations. The authors of those earlier 3260 works are acknowledged for their insights. 3262 This work is aligned with the NASA Safe Autonomous Systems Operation 3263 (SASO) program under NASA contract number NNA16BD84C. 3265 This work is aligned with the FAA as per the SE2025 contract number 3266 DTFAWA-15-D-00030. 3268 This work is aligned with the Boeing Commercial Airplanes (BCA) 3269 Internet of Things (IoT) and autonomy programs. 3271 This work is aligned with the Boeing Information Technology (BIT) 3272 MobileNet program. 3274 8. References 3276 8.1. Normative References 3278 [I-D.templin-6man-omni-interface] 3279 Templin, F. and T. Whyman, "Transmission of IP Packets 3280 over Overlay Multilink Network (OMNI) Interfaces", draft- 3281 templin-6man-omni-interface-50 (work in progress), October 3282 2020. 3284 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, 3285 DOI 10.17487/RFC0791, September 1981, 3286 . 3288 [RFC0792] Postel, J., "Internet Control Message Protocol", STD 5, 3289 RFC 792, DOI 10.17487/RFC0792, September 1981, 3290 . 3292 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 3293 Requirement Levels", BCP 14, RFC 2119, 3294 DOI 10.17487/RFC2119, March 1997, 3295 . 3297 [RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in 3298 IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473, 3299 December 1998, . 3301 [RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander, 3302 "SEcure Neighbor Discovery (SEND)", RFC 3971, 3303 DOI 10.17487/RFC3971, March 2005, 3304 . 3306 [RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)", 3307 RFC 3972, DOI 10.17487/RFC3972, March 2005, 3308 . 3310 [RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and 3311 More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191, 3312 November 2005, . 3314 [RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast 3315 Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005, 3316 . 3318 [RFC4380] Huitema, C., "Teredo: Tunneling IPv6 over UDP through 3319 Network Address Translations (NATs)", RFC 4380, 3320 DOI 10.17487/RFC4380, February 2006, 3321 . 3323 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 3324 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 3325 DOI 10.17487/RFC4861, September 2007, 3326 . 3328 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 3329 Address Autoconfiguration", RFC 4862, 3330 DOI 10.17487/RFC4862, September 2007, 3331 . 3333 [RFC6081] Thaler, D., "Teredo Extensions", RFC 6081, 3334 DOI 10.17487/RFC6081, January 2011, 3335 . 3337 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 3338 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 3339 May 2017, . 3341 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 3342 (IPv6) Specification", STD 86, RFC 8200, 3343 DOI 10.17487/RFC8200, July 2017, 3344 . 3346 [RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A., 3347 Richardson, M., Jiang, S., Lemon, T., and T. Winters, 3348 "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", 3349 RFC 8415, DOI 10.17487/RFC8415, November 2018, 3350 . 3352 8.2. Informative References 3354 [BGP] Huston, G., "BGP in 2015, http://potaroo.net", January 3355 2016. 3357 [I-D.bonica-6man-comp-rtg-hdr] 3358 Bonica, R., Kamite, Y., Alston, A., Henriques, D., and L. 3359 Jalil, "The IPv6 Compact Routing Header (CRH)", draft- 3360 bonica-6man-comp-rtg-hdr-23 (work in progress), October 3361 2020. 3363 [I-D.bonica-6man-crh-helper-opt] 3364 Li, X., Bao, C., Ruan, E., and R. Bonica, "Compressed 3365 Routing Header (CRH) Helper Option", draft-bonica-6man- 3366 crh-helper-opt-02 (work in progress), October 2020. 3368 [I-D.ietf-intarea-frag-fragile] 3369 Bonica, R., Baker, F., Huston, G., Hinden, R., Troan, O., 3370 and F. Gont, "IP Fragmentation Considered Fragile", draft- 3371 ietf-intarea-frag-fragile-17 (work in progress), September 3372 2019. 3374 [I-D.ietf-intarea-tunnels] 3375 Touch, J. and M. Townsley, "IP Tunnels in the Internet 3376 Architecture", draft-ietf-intarea-tunnels-10 (work in 3377 progress), September 2019. 3379 [I-D.ietf-rtgwg-atn-bgp] 3380 Templin, F., Saccone, G., Dawra, G., Lindem, A., and V. 3381 Moreno, "A Simple BGP-based Mobile Routing System for the 3382 Aeronautical Telecommunications Network", draft-ietf- 3383 rtgwg-atn-bgp-06 (work in progress), June 2020. 3385 [I-D.templin-6man-dhcpv6-ndopt] 3386 Templin, F., "A Unified Stateful/Stateless Configuration 3387 Service for IPv6", draft-templin-6man-dhcpv6-ndopt-10 3388 (work in progress), June 2020. 3390 [I-D.templin-intarea-seal] 3391 Templin, F., "The Subnetwork Encapsulation and Adaptation 3392 Layer (SEAL)", draft-templin-intarea-seal-68 (work in 3393 progress), January 2014. 3395 [I-D.templin-intarea-vet] 3396 Templin, F., "Virtual Enterprise Traversal (VET)", draft- 3397 templin-intarea-vet-40 (work in progress), May 2013. 3399 [I-D.templin-ironbis] 3400 Templin, F., "The Interior Routing Overlay Network 3401 (IRON)", draft-templin-ironbis-16 (work in progress), 3402 March 2014. 3404 [I-D.templin-v6ops-pdhost] 3405 Templin, F., "IPv6 Prefix Delegation and Multi-Addressing 3406 Models", draft-templin-v6ops-pdhost-26 (work in progress), 3407 June 2020. 3409 [OVPN] OpenVPN, O., "http://openvpn.net", October 2016. 3411 [RFC1035] Mockapetris, P., "Domain names - implementation and 3412 specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, 3413 November 1987, . 3415 [RFC1812] Baker, F., Ed., "Requirements for IP Version 4 Routers", 3416 RFC 1812, DOI 10.17487/RFC1812, June 1995, 3417 . 3419 [RFC2003] Perkins, C., "IP Encapsulation within IP", RFC 2003, 3420 DOI 10.17487/RFC2003, October 1996, 3421 . 3423 [RFC2236] Fenner, W., "Internet Group Management Protocol, Version 3424 2", RFC 2236, DOI 10.17487/RFC2236, November 1997, 3425 . 3427 [RFC2464] Crawford, M., "Transmission of IPv6 Packets over Ethernet 3428 Networks", RFC 2464, DOI 10.17487/RFC2464, December 1998, 3429 . 3431 [RFC2529] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4 3432 Domains without Explicit Tunnels", RFC 2529, 3433 DOI 10.17487/RFC2529, March 1999, 3434 . 3436 [RFC2983] Black, D., "Differentiated Services and Tunnels", 3437 RFC 2983, DOI 10.17487/RFC2983, October 2000, 3438 . 3440 [RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition 3441 of Explicit Congestion Notification (ECN) to IP", 3442 RFC 3168, DOI 10.17487/RFC3168, September 2001, 3443 . 3445 [RFC3330] IANA, "Special-Use IPv4 Addresses", RFC 3330, 3446 DOI 10.17487/RFC3330, September 2002, 3447 . 3449 [RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener 3450 Discovery Version 2 (MLDv2) for IPv6", RFC 3810, 3451 DOI 10.17487/RFC3810, June 2004, 3452 . 3454 [RFC4251] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH) 3455 Protocol Architecture", RFC 4251, DOI 10.17487/RFC4251, 3456 January 2006, . 3458 [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A 3459 Border Gateway Protocol 4 (BGP-4)", RFC 4271, 3460 DOI 10.17487/RFC4271, January 2006, 3461 . 3463 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 3464 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 3465 2006, . 3467 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 3468 Internet Protocol", RFC 4301, DOI 10.17487/RFC4301, 3469 December 2005, . 3471 [RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery 3472 Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April 3473 2006, . 3475 [RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet 3476 Control Message Protocol (ICMPv6) for the Internet 3477 Protocol Version 6 (IPv6) Specification", STD 89, 3478 RFC 4443, DOI 10.17487/RFC4443, March 2006, 3479 . 3481 [RFC4511] Sermersheim, J., Ed., "Lightweight Directory Access 3482 Protocol (LDAP): The Protocol", RFC 4511, 3483 DOI 10.17487/RFC4511, June 2006, 3484 . 3486 [RFC4541] Christensen, M., Kimball, K., and F. Solensky, 3487 "Considerations for Internet Group Management Protocol 3488 (IGMP) and Multicast Listener Discovery (MLD) Snooping 3489 Switches", RFC 4541, DOI 10.17487/RFC4541, May 2006, 3490 . 3492 [RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick, 3493 "Internet Group Management Protocol (IGMP) / Multicast 3494 Listener Discovery (MLD)-Based Multicast Forwarding 3495 ("IGMP/MLD Proxying")", RFC 4605, DOI 10.17487/RFC4605, 3496 August 2006, . 3498 [RFC4982] Bagnulo, M. and J. Arkko, "Support for Multiple Hash 3499 Algorithms in Cryptographically Generated Addresses 3500 (CGAs)", RFC 4982, DOI 10.17487/RFC4982, July 2007, 3501 . 3503 [RFC5015] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano, 3504 "Bidirectional Protocol Independent Multicast (BIDIR- 3505 PIM)", RFC 5015, DOI 10.17487/RFC5015, October 2007, 3506 . 3508 [RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site 3509 Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214, 3510 DOI 10.17487/RFC5214, March 2008, 3511 . 3513 [RFC5320] Templin, F., Ed., "The Subnetwork Encapsulation and 3514 Adaptation Layer (SEAL)", RFC 5320, DOI 10.17487/RFC5320, 3515 February 2010, . 3517 [RFC5522] Eddy, W., Ivancic, W., and T. Davis, "Network Mobility 3518 Route Optimization Requirements for Operational Use in 3519 Aeronautics and Space Exploration Mobile Networks", 3520 RFC 5522, DOI 10.17487/RFC5522, October 2009, 3521 . 3523 [RFC5558] Templin, F., Ed., "Virtual Enterprise Traversal (VET)", 3524 RFC 5558, DOI 10.17487/RFC5558, February 2010, 3525 . 3527 [RFC5569] Despres, R., "IPv6 Rapid Deployment on IPv4 3528 Infrastructures (6rd)", RFC 5569, DOI 10.17487/RFC5569, 3529 January 2010, . 3531 [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 3532 (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, 3533 . 3535 [RFC6106] Jeong, J., Park, S., Beloeil, L., and S. Madanapalli, 3536 "IPv6 Router Advertisement Options for DNS Configuration", 3537 RFC 6106, DOI 10.17487/RFC6106, November 2010, 3538 . 3540 [RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful 3541 NAT64: Network Address and Protocol Translation from IPv6 3542 Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146, 3543 April 2011, . 3545 [RFC6179] Templin, F., Ed., "The Internet Routing Overlay Network 3546 (IRON)", RFC 6179, DOI 10.17487/RFC6179, March 2011, 3547 . 3549 [RFC6221] Miles, D., Ed., Ooghe, S., Dec, W., Krishnan, S., and A. 3550 Kavanagh, "Lightweight DHCPv6 Relay Agent", RFC 6221, 3551 DOI 10.17487/RFC6221, May 2011, 3552 . 3554 [RFC6273] Kukec, A., Krishnan, S., and S. Jiang, "The Secure 3555 Neighbor Discovery (SEND) Hash Threat Analysis", RFC 6273, 3556 DOI 10.17487/RFC6273, June 2011, 3557 . 3559 [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer 3560 Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, 3561 January 2012, . 3563 [RFC6438] Carpenter, B. and S. Amante, "Using the IPv6 Flow Label 3564 for Equal Cost Multipath Routing and Link Aggregation in 3565 Tunnels", RFC 6438, DOI 10.17487/RFC6438, November 2011, 3566 . 3568 [RFC6706] Templin, F., Ed., "Asymmetric Extended Route Optimization 3569 (AERO)", RFC 6706, DOI 10.17487/RFC6706, August 2012, 3570 . 3572 [RFC6935] Eubanks, M., Chimento, P., and M. Westerlund, "IPv6 and 3573 UDP Checksums for Tunneled Packets", RFC 6935, 3574 DOI 10.17487/RFC6935, April 2013, 3575 . 3577 [RFC6936] Fairhurst, G. and M. Westerlund, "Applicability Statement 3578 for the Use of IPv6 UDP Datagrams with Zero Checksums", 3579 RFC 6936, DOI 10.17487/RFC6936, April 2013, 3580 . 3582 [RFC7333] Chan, H., Ed., Liu, D., Seite, P., Yokota, H., and J. 3583 Korhonen, "Requirements for Distributed Mobility 3584 Management", RFC 7333, DOI 10.17487/RFC7333, August 2014, 3585 . 3587 [RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I., 3588 Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent 3589 Multicast - Sparse Mode (PIM-SM): Protocol Specification 3590 (Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March 3591 2016, . 3593 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 3594 Decraene, B., Litkowski, S., and R. Shakir, "Segment 3595 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 3596 July 2018, . 3598 [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol 3599 Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, 3600 . 3602 [RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J., 3603 Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header 3604 (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020, 3605 . 3607 [WG] Wireguard, "Wireguard, https://www.wireguard.com", August 3608 2020. 3610 Appendix A. Non-Normative Considerations 3612 AERO can be applied to a multitude of Internetworking scenarios, with 3613 each having its own adaptations. The following considerations are 3614 provided as non-normative guidance: 3616 A.1. Implementation Strategies for Route Optimization 3618 Route optimization as discussed in Section 3.14 results in the route 3619 optimization source (ROS) creating an asymmetric neighbor cache entry 3620 for the target neighbor. The neighbor cache entry is maintained for 3621 at most ReachableTime seconds and then deleted unless updated. In 3622 order to refresh the neighbor cache entry lifetime before the 3623 ReachableTime timer expires, the specification requires 3624 implementations to issue a new NS/NA exchange to reset ReachableTime 3625 while data packets are still flowing. However, the decision of when 3626 to initiate a new NS/NA exchange and to perpetuate the process is 3627 left as an implementation detail. 3629 One possible strategy may be to monitor the neighbor cache entry 3630 watching for data packets for (ReachableTime - 5) seconds. If any 3631 data packets have been sent to the neighbor within this timeframe, 3632 then send an NS to receive a new NA. If no data packets have been 3633 sent, wait for 5 additional seconds and send an immediate NS if any 3634 data packets are sent within this "expiration pending" 5 second 3635 window. If no additional data packets are sent within the 5 second 3636 window, delete the neighbor cache entry. 3638 The monitoring of the neighbor data packet traffic therefore becomes 3639 an asymmetric ongoing process during the neighbor cache entry 3640 lifetime. If the neighbor cache entry expires, future data packets 3641 will trigger a new NS/NA exchange while the packets themselves are 3642 delivered over a longer path until route optimization state is re- 3643 established. 3645 A.2. Implicit Mobility Management 3647 OMNI interface neighbors MAY provide a configuration option that 3648 allows them to perform implicit mobility management in which no ND 3649 messaging is used. In that case, the Client only transmits packets 3650 over a single interface at a time, and the neighbor always observes 3651 packets arriving from the Client from the same link-layer source 3652 address. 3654 If the Client's underlying interface address changes (either due to a 3655 readdressing of the original interface or switching to a new 3656 interface) the neighbor immediately updates the neighbor cache entry 3657 for the Client and begins accepting and sending packets according to 3658 the Client's new address. This implicit mobility method applies to 3659 use cases such as cellphones with both WiFi and Cellular interfaces 3660 where only one of the interfaces is active at a given time, and the 3661 Client automatically switches over to the backup interface if the 3662 primary interface fails. 3664 A.3. Direct Underlying Interfaces 3666 When a Client's OMNI interface is configured over a Direct interface, 3667 the neighbor at the other end of the Direct link can receive packets 3668 without any encapsulation. In that case, the Client sends packets 3669 over the Direct link according to QoS preferences. If the Direct 3670 interface has the highest QoS preference, then the Client's IP 3671 packets are transmitted directly to the peer without going through an 3672 ANET/INET. If other interfaces have higher QoS preferences, then the 3673 Client's IP packets are transmitted via a different interface, which 3674 may result in the inclusion of Proxys, Servers and Bridges in the 3675 communications path. Direct interfaces must be tested periodically 3676 for reachability, e.g., via NUD. 3678 A.4. AERO Critical Infrastructure Considerations 3680 AERO Bridges can be either Commercial off-the Shelf (COTS) standard 3681 IP routers or virtual machines in the cloud. Bridges must be 3682 provisioned, supported and managed by the INET administrative 3683 authority, and connected to the Bridges of other INETs via inter- 3684 domain peerings. Cost for purchasing, configuring and managing 3685 Bridges is nominal even for very large OMNI links. 3687 AERO Servers can be standard dedicated server platforms, but most 3688 often will be deployed as virtual machines in the cloud. The only 3689 requirements for Servers are that they can run the AERO user-level 3690 code and have at least one network interface connection to the INET. 3691 As with Bridges, Servers must be provisioned, supported and managed 3692 by the INET administrative authority. Cost for purchasing, 3693 configuring and managing Servers is nominal especially for virtual 3694 Servers hosted in the cloud. 3696 AERO Proxys are most often standard dedicated server platforms with 3697 one network interface connected to the ANET and a second interface 3698 connected to an INET. As with Servers, the only requirements are 3699 that they can run the AERO user-level code and have at least one 3700 interface connection to the INET. Proxys must be provisioned, 3701 supported and managed by the ANET administrative authority. Cost for 3702 purchasing, configuring and managing Proxys is nominal, and borne by 3703 the ANET administrative authority. 3705 AERO Relays can be any dedicated server or COTS router platform 3706 connected to INETs and/or EUNs. The Relay connects to the OMNI link 3707 and engages in eBGP peering with one or more Bridges as a stub AS. 3708 The Relay then injects its MNPs and/or non-MNP prefixes into the BGP 3709 routing system, and provisions the prefixes to its downstream- 3710 attached networks. The Relay can perform ROS/ROR services the same 3711 as for any Server, and can route between the MNP and non-MNP address 3712 spaces. 3714 A.5. AERO Server Failure Implications 3716 AERO Servers may appear as a single point of failure in the 3717 architecture, but such is not the case since all Servers on the link 3718 provide identical services and loss of a Server does not imply 3719 immediate and/or comprehensive communication failures. Although 3720 Clients typically associate with a single Server at a time, Server 3721 failure is quickly detected and conveyed by Bidirectional Forward 3722 Detection (BFD) and/or proactive NUD allowing Clients to migrate to 3723 new Servers. 3725 If a Server fails, ongoing packet forwarding to Clients will continue 3726 by virtue of the asymmetric neighbor cache entries that have already 3727 been established in route optimization sources (ROSs). If a Client 3728 also experiences mobility events at roughly the same time the Server 3729 fails, unsolicited NA messages may be lost but proxy neighbor cache 3730 entries in the DEPARTED state will ensure that packet forwarding to 3731 the Client's new locations will continue for up to DepartTime 3732 seconds. 3734 If a Client is left without a Server for an extended timeframe (e.g., 3735 greater than ReachableTime seconds) then existing asymmetric neighbor 3736 cache entries will eventually expire and both ongoing and new 3737 communications will fail. The original source will continue to 3738 retransmit until the Client has established a new Server 3739 relationship, after which time continuous communications will resume. 3741 Therefore, providing many Servers on the link with high availability 3742 profiles provides resilience against loss of individual Servers and 3743 assurance that Clients can establish new Server relationships quickly 3744 in event of a Server failure. 3746 A.6. AERO Client / Server Architecture 3748 The AERO architectural model is client / server in the control plane, 3749 with route optimization in the data plane. The same as for common 3750 Internet services, the AERO Client discovers the addresses of AERO 3751 Servers and selects one Server to connect to. The AERO service is 3752 analogous to common Internet services such as google.com, yahoo.com, 3753 cnn.com, etc. However, there is only one AERO service for the link 3754 and all Servers provide identical services. 3756 Common Internet services provide differing strategies for advertising 3757 server addresses to clients. The strategy is conveyed through the 3758 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