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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group F. Templin, Ed. 3 Internet-Draft Boeing Research & Technology 4 Obsoletes: rfc5320, rfc5558, rfc5720, December 7, 2020 5 rfc6179, rfc6706 (if 6 approved) 7 Intended status: Standards Track 8 Expires: June 10, 2021 10 Asymmetric Extended Route Optimization (AERO) 11 draft-templin-intarea-6706bis-72 13 Abstract 15 This document specifies the operation of IP over Overlay Multilink 16 Network (OMNI) interfaces using the Asymmetric Extended Route 17 Optimization (AERO) internetworking and mobility management service. 18 AERO/OMNI use an IPv6 link-local address format that supports 19 operation of the IPv6 Neighbor Discovery (ND) protocol and links ND 20 to IP forwarding. Prefix delegation/registration services are 21 employed for network admission and to manage the routing system. 22 Multilink operation, mobility management, quality of service (QoS) 23 signaling and route optimization are naturally supported through 24 dynamic neighbor cache updates. Standard IP multicasting services 25 are also supported. AERO is a widely-applicable mobile 26 internetworking service especially well-suited to aviation services, 27 intelligent transportation systems, mobile Virtual Private Networks 28 (VPNs) and many other applications. 30 Status of This Memo 32 This Internet-Draft is submitted in full conformance with the 33 provisions of BCP 78 and BCP 79. 35 Internet-Drafts are working documents of the Internet Engineering 36 Task Force (IETF). Note that other groups may also distribute 37 working documents as Internet-Drafts. The list of current Internet- 38 Drafts is at https://datatracker.ietf.org/drafts/current/. 40 Internet-Drafts are draft documents valid for a maximum of six months 41 and may be updated, replaced, or obsoleted by other documents at any 42 time. It is inappropriate to use Internet-Drafts as reference 43 material or to cite them other than as "work in progress." 45 This Internet-Draft will expire on June 10, 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) . . . . . . . . . . 21 75 3.2.6. Segment Routing For OMNI Link Selection . . . . . . . 21 76 3.2.7. Segment Routing Within the OMNI Link . . . . . . . . 22 77 3.3. OMNI Interface Characteristics . . . . . . . . . . . . . 22 78 3.4. OMNI Interface Initialization . . . . . . . . . . . . . . 24 79 3.4.1. AERO Server/Relay Behavior . . . . . . . . . . . . . 25 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 . . . . . . . . 26 84 3.5.1. OMNI Neighbor Interface Attributes . . . . . . . . . 28 85 3.5.2. OMNI Neighbor Advertisement Message Flags . . . . . . 28 86 3.6. OMNI Interface Encapsulation and Re-encapsulation . . . . 29 87 3.7. OMNI Interface Decapsulation . . . . . . . . . . . . . . 30 88 3.8. OMNI Interface Data Origin Authentication . . . . . . . . 30 89 3.9. OMNI Adaptation Layer and OMNI Interface MTU . . . . . . 31 90 3.10. OMNI Interface Forwarding Algorithm . . . . . . . . . . . 31 91 3.10.1. Client Forwarding Algorithm . . . . . . . . . . . . 32 92 3.10.2. Proxy Forwarding Algorithm . . . . . . . . . . . . . 32 93 3.10.3. Server/Relay Forwarding Algorithm . . . . . . . . . 33 94 3.10.4. Bridge Forwarding Algorithm . . . . . . . . . . . . 34 96 3.11. OMNI Interface Error Handling . . . . . . . . . . . . . . 35 97 3.12. AERO Router Discovery, Prefix Delegation and 98 Autoconfiguration . . . . . . . . . . . . . . . . . . . . 38 99 3.12.1. AERO Service Model . . . . . . . . . . . . . . . . . 38 100 3.12.2. AERO Client Behavior . . . . . . . . . . . . . . . . 38 101 3.12.3. AERO Server Behavior . . . . . . . . . . . . . . . . 40 102 3.13. The AERO Proxy . . . . . . . . . . . . . . . . . . . . . 43 103 3.13.1. Combined Proxy/Servers . . . . . . . . . . . . . . . 45 104 3.13.2. Detecting and Responding to Server Failures . . . . 46 105 3.13.3. Point-to-Multipoint Server Coordination . . . . . . 46 106 3.14. AERO Route Optimization / Address Resolution . . . . . . 47 107 3.14.1. Route Optimization Initiation . . . . . . . . . . . 48 108 3.14.2. Relaying the NS . . . . . . . . . . . . . . . . . . 48 109 3.14.3. Processing the NS and Sending the NA . . . . . . . . 48 110 3.14.4. Relaying the NA . . . . . . . . . . . . . . . . . . 49 111 3.14.5. Processing the NA . . . . . . . . . . . . . . . . . 50 112 3.14.6. Route Optimization Maintenance . . . . . . . . . . . 50 113 3.15. Neighbor Unreachability Detection (NUD) . . . . . . . . . 51 114 3.16. Mobility Management and Quality of Service (QoS) . . . . 52 115 3.16.1. Mobility Update Messaging . . . . . . . . . . . . . 53 116 3.16.2. Announcing Link-Layer Address and/or QoS Preference 117 Changes . . . . . . . . . . . . . . . . . . . . . . 54 118 3.16.3. Bringing New Links Into Service . . . . . . . . . . 55 119 3.16.4. Deactivating Existing Links . . . . . . . . . . . . 55 120 3.16.5. Moving Between Servers . . . . . . . . . . . . . . . 55 121 3.17. Multicast . . . . . . . . . . . . . . . . . . . . . . . . 56 122 3.17.1. Source-Specific Multicast (SSM) . . . . . . . . . . 57 123 3.17.2. Any-Source Multicast (ASM) . . . . . . . . . . . . . 58 124 3.17.3. Bi-Directional PIM (BIDIR-PIM) . . . . . . . . . . . 59 125 3.18. Operation over Multiple OMNI Links . . . . . . . . . . . 59 126 3.19. DNS Considerations . . . . . . . . . . . . . . . . . . . 60 127 3.20. Transition Considerations . . . . . . . . . . . . . . . . 60 128 3.21. Detecting and Reacting to Server and Bridge Failures . . 61 129 3.22. AERO Clients on the Open Internet . . . . . . . . . . . . 62 130 3.23. Time-Varying MNPs . . . . . . . . . . . . . . . . . . . . 64 131 4. Implementation Status . . . . . . . . . . . . . . . . . . . . 65 132 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 65 133 6. Security Considerations . . . . . . . . . . . . . . . . . . . 65 134 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 67 135 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 68 136 8.1. Normative References . . . . . . . . . . . . . . . . . . 68 137 8.2. Informative References . . . . . . . . . . . . . . . . . 70 138 Appendix A. Non-Normative Considerations . . . . . . . . . . . . 76 139 A.1. Implementation Strategies for Route Optimization . . . . 76 140 A.2. Implicit Mobility Management . . . . . . . . . . . . . . 76 141 A.3. Direct Underlying Interfaces . . . . . . . . . . . . . . 77 142 A.4. AERO Critical Infrastructure Considerations . . . . . . . 77 143 A.5. AERO Server Failure Implications . . . . . . . . . . . . 78 144 A.6. AERO Client / Server Architecture . . . . . . . . . . . . 79 145 Appendix B. Change Log . . . . . . . . . . . . . . . . . . . . . 81 146 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 82 148 1. Introduction 150 Asymmetric Extended Route Optimization (AERO) fulfills the 151 requirements of Distributed Mobility Management (DMM) [RFC7333] and 152 route optimization [RFC5522] for aeronautical networking and other 153 network mobility use cases such as intelligent transportation 154 systems. AERO is an internetworking and mobility management service 155 based on the Overlay Multilink Network Interface (OMNI) 156 [I-D.templin-6man-omni-interface] Non-Broadcast, Multiple Access 157 (NBMA) virtual link model. The OMNI link is a virtual overlay 158 configured over one or more underlying Internetworks, and nodes on 159 the link can exchange IP packets via tunneling. The OMNI Adaptation 160 Layer (OAL) supports multilink operation for increased reliability, 161 bandwidth optimization and traffic path selection while accommodating 162 Maximum Transmission Unit (MTU) diversity. 164 The AERO service comprises Clients, Proxys, Servers and Relays that 165 are seen as OMNI link neighbors as well as Bridges that interconnect 166 OMNI link segments. Each node's OMNI interface uses an IPv6 link- 167 local address format that supports operation of the IPv6 Neighbor 168 Discovery (ND) protocol [RFC4861] and links ND to IP forwarding. A 169 node's OMNI interface can be configured over multiple underlying 170 interfaces, and may therefore appear as a single interface with 171 multiple link-layer addresses. Each link-layer address is subject to 172 change due to mobility and/or QoS fluctuations, and link-layer 173 address changes are signaled by ND messaging the same as for any IPv6 174 link. 176 AERO provides a cloud-based service where mobile nodes may use any 177 Server acting as a Mobility Anchor Point (MAP) and fixed nodes may 178 use any Relay on the link for efficient communications. Fixed nodes 179 forward packets destined to other AERO nodes to the nearest Relay, 180 which forwards them through the cloud. A mobile node's initial 181 packets are forwarded through the Server, while direct routing is 182 supported through asymmetric extended route optimization while data 183 packets are flowing. Both unicast and multicast communications are 184 supported, and mobile nodes may efficiently move between locations 185 while maintaining continuous communications with correspondents and 186 without changing their IP Address. 188 AERO Bridges are interconnected in a secured private BGP overlay 189 routing instance using encapsulation to provide a hybrid routing/ 190 bridging service that joins the underlying Internetworks of multiple 191 disjoint administrative domains into a single unified OMNI link. 193 Each OMNI link instance is characterized by the set of Mobility 194 Service Prefixes (MSPs) common to all mobile nodes. The link extends 195 to the point where a Relay/Server is on the optimal route from any 196 correspondent node on the link, and provides a conduit between the 197 underlying Internetwork and the OMNI link. To the underlying 198 Internetwork, the Relay/Server is the source of a route to the MSP, 199 and hence uplink traffic to the mobile node is naturally routed to 200 the nearest Relay/Server. 202 AERO assumes the use of PIM Sparse Mode in support of multicast 203 communication. In support of Source Specific Multicast (SSM) when a 204 Mobile Node is the source, AERO route optimization ensures that a 205 shortest-path multicast tree is established with provisions for 206 mobility and multilink operation. In all other multicast scenarios 207 there are no AERO dependencies. 209 AERO was designed for aeronautical networking for both manned and 210 unmanned aircraft, where the aircraft is treated as a mobile node 211 that can connect an Internet of Things (IoT). AERO is also 212 applicable to a wide variety of other use cases. For example, it can 213 be used to coordinate the Virtual Private Network (VPN) links of 214 mobile nodes (e.g., cellphones, tablets, laptop computers, etc.) that 215 connect into a home enterprise network via public access networks 216 using services such as OpenVPN [OVPN]. It can also be used to 217 facilitate vehicular and pedestrian communications services for 218 intelligent transportation systems. Other applicable use cases are 219 also in scope. 221 The following numbered sections present the AERO specification. The 222 appendices at the end of the document are non-normative. 224 2. Terminology 226 The terminology in the normative references applies; especially, the 227 terminology in the OMNI specification 228 [I-D.templin-6man-omni-interface] is used extensively throughout. 229 The following terms are defined within the scope of this document: 231 IPv6 Neighbor Discovery (ND) 232 an IPv6 control message service for coordinating neighbor 233 relationships between nodes connected to a common link. AERO uses 234 the ND service specified in [RFC4861]. 236 IPv6 Prefix Delegation 237 a networking service for delegating IPv6 prefixes to nodes on the 238 link. The nominal service is DHCPv6 [RFC8415], however alternate 239 services (e.g., based on ND messaging) are also in scope. Most 240 notably, a minimal form of prefix delegation known as "prefix 241 registration" can be used if the Client knows its prefix in 242 advance and can represent it in the IPv6 source address of an ND 243 message. 245 Access Network (ANET) 246 a node's first-hop data link service network (e.g., a radio access 247 network, cellular service provider network, corporate enterprise 248 network, etc.) that often provides link-layer security services 249 such as IEEE 802.1X and physical-layer security prevent 250 unauthorized access internally and with border network-layer 251 security services such as firewalls and proxies that prevent 252 unauthorized outside access. 254 ANET interface 255 a node's attachment to a link in an ANET. 257 Internetwork (INET) 258 a connected IP network topology with a coherent routing and 259 addressing plan and that provides a transit backbone service for 260 ANET end systems. INETs also provide an underlay service over 261 which the AERO virtual link is configured. Example INETs include 262 corporate enterprise networks, aviation networks, and the public 263 Internet itself. When there is no administrative boundary between 264 an ANET and the INET, the ANET and INET are one and the same. 266 INET Partition 267 frequently, INETs such as large corporate enterprise networks are 268 sub-divided internally into separate isolated partitions. Each 269 partition is fully connected internally but disconnected from 270 other partitions, and there is no requirement that separate 271 partitions maintain consistent Internet Protocol and/or addressing 272 plans. (Each INET partition is seen as a separate OMNI link 273 segment as discussed below.) 275 INET interface 276 a node's attachment to a link in an INET. 278 INET address 279 an IP address assigned to a node's interface connection to an 280 INET. 282 INET encapsulation 283 the encapsulation of a packet in an outer header or headers that 284 can be routed within the scope of the local INET partition. 286 OMNI link 287 the same as defined in [I-D.templin-6man-omni-interface], and 288 manifested by IPv6 encapsulation [RFC2473]. The OMNI link spans 289 underlying INET segments joined by virtual bridges in a spanning 290 tree the same as a bridged campus LAN. AERO nodes on the OMNI 291 link appear as single-hop neighbors even though they may be 292 separated by multiple underlying INET hops, and can use Segment 293 Routing [RFC8402] to cause packets to visit selected waypoints on 294 the link. 296 OMNI domain 297 a set of affiliated OMNI links that collectively provide services 298 under a common (set of) Mobility Service Prefixes (MSPs). 300 OMNI Interface 301 a node's attachment to an OMNI link. Since the addresses assigned 302 to an OMNI interface are managed for uniqueness, OMNI interfaces 303 do not require Duplicate Address Detection (DAD) and therefore set 304 the administrative variable 'DupAddrDetectTransmits' to zero 305 [RFC4862]. 307 OMNI Adaptation Layer (OAL) 308 an OMNI interface process whereby packets admitted into the 309 interface are wrapped in a mid-layer IPv6 header and fragmented/ 310 reassembled if necessary to support the OMNI link Maximum 311 Transmission Unit (MTU). The OAL is also responsible for 312 generating MTU-related control messages as necessary, and for 313 providing addressing context for spanning multiple segments of a 314 bridged OMNI link. 316 OMNI Link-Local Address (LLA) 317 a link local IPv6 address per [RFC4291] constructed as specified 318 in Section 3.2.2. 320 OMNI Domain-Local Address (DLA) 321 an IPv6 address from the prefix [DLA]::/10 constructed as 322 specified in [I-D.templin-6man-omni-interface]. OMNI DLAs are 323 statelessly derived from OMNI LLAs, and vice-versa. 325 underlying interface 326 an ANET or INET interface over which an OMNI interface is 327 configured. 329 Mobility Service Prefix (MSP) 330 an IP prefix assigned to the OMNI link and from which more- 331 specific Mobile Network Prefixes (MNPs) are derived. 333 Mobile Network Prefix (MNP) 334 an IP prefix allocated from an MSP and delegated to an AERO Client 335 or Relay. 337 AERO node 338 a node that is connected to an OMNI link and participates in the 339 AERO internetworking and mobility service. 341 AERO Client ("Client") 342 an AERO node that connects over one or more underlying interfaces 343 and requests MNP delegation/registration service from AERO 344 Servers. The Client assigns a Client LLA to the OMNI interface 345 for use in ND exchanges with other AERO nodes and forwards packets 346 to correspondents according to OMNI interface neighbor cache 347 state. 349 AERO Server ("Server") 350 an INET node that configures an OMNI interface to provide default 351 forwarding and mobility/multilink services for AERO Clients. The 352 Server assigns an administratively-provisioned LLA to its OMNI 353 interface to support the operation of the ND services, and 354 advertises all of its associated MNPs via BGP peerings with 355 Bridges. 357 AERO Relay ("Relay") 358 an AERO Server that also provides forwarding services between 359 nodes reached via the OMNI link and correspondents on other links. 360 AERO Relays are provisioned with MNPs (i.e., the same as for an 361 AERO Client) and run a dynamic routing protocol to discover any 362 non-MNP IP routes. In both cases, the Relay advertises the MSP(s) 363 to its downstream networks, and distributes all of its associated 364 MNPs and non-MNP IP routes via BGP peerings with Bridges (i.e., 365 the same as for an AERO Server). 367 AERO Bridge ("Bridge") 368 a node that provides hybrid routing/bridging services (as well as 369 a security trust anchor) for nodes on an OMNI link. As a router, 370 the Bridge forwards packets using standard IP forwarding. As a 371 bridge, the Bridge forwards packets over the OMNI link without 372 decrementing the IPv6 Hop Limit. AERO Bridges peer with Servers 373 and other Bridges to discover the full set of MNPs for the link as 374 well as any non-MNPs that are reachable via Relays. 376 AERO Proxy ("Proxy") 377 a node that provides proxying services between Clients in an ANET 378 and Servers in external INETs. The AERO Proxy is a conduit 379 between the ANET and external INETs in the same manner as for 380 common web proxies, and behaves in a similar fashion as for ND 381 proxies [RFC4389]. A node may be configured to act as either a 382 Proxy and/or a Server, depending on Client Server selection 383 criteria. 385 ingress tunnel endpoint (ITE) 386 an OMNI interface endpoint that injects encapsulated packets into 387 an OMNI link. 389 egress tunnel endpoint (ETE) 390 an OMNI interface endpoint that receives encapsulated packets from 391 an OMNI link. 393 link-layer address 394 an IP address used as an encapsulation header source or 395 destination address from the perspective of the OMNI interface. 396 When an upper layer protocol (e.g., UDP) is used as part of the 397 encapsulation, the port number is also considered as part of the 398 link-layer address. 400 network layer address 401 the source or destination address of an encapsulated IP packet 402 presented to the OMNI interface. 404 end user network (EUN) 405 an internal virtual or external edge IP network that an AERO 406 Client or Relay connects to the rest of the network via the OMNI 407 interface. The Client/Relay sees each EUN as a "downstream" 408 network, and sees the OMNI interface as the point of attachment to 409 the "upstream" network. 411 Mobile Node (MN) 412 an AERO Client and all of its downstream-attached networks that 413 move together as a single unit, i.e., an end system that connects 414 an Internet of Things. 416 Mobile Router (MR) 417 a MN's on-board router that forwards packets between any 418 downstream-attached networks and the OMNI link. 420 Route Optimization Source (ROS) 421 the AERO node nearest the source that initiates route 422 optimization. The ROS may be a Server or Proxy acting on behalf 423 of the source Client. 425 Route Optimization responder (ROR) 426 the AERO node nearest the target destination that responds to 427 route optimization requests. The ROR may be a Server acting on 428 behalf of a target MNP Client, or a Relay for a non-MNP 429 destination. 431 MAP List 432 a geographically and/or topologically referenced list of addresses 433 of all Servers within the same OMNI link. There is a single MAP 434 list for the entire OMNI link. 436 Distributed Mobility Management (DMM) 437 a BGP-based overlay routing service coordinated by Servers and 438 Bridges that tracks all Server-to-Client associations. 440 Mobility Service (MS) 441 the collective set of all Servers, Proxys, Bridges and Relays that 442 provide the AERO Service to Clients. 444 Mobility Service Endpoint MSE) 445 an individual Server, Proxy, Bridge or Relay in the Mobility 446 Service. 448 Throughout the document, the simple terms "Client", "Server", 449 "Bridge", "Proxy" and "Relay" refer to "AERO Client", "AERO Server", 450 "AERO Bridge", "AERO Proxy" and "AERO Relay", respectively. 451 Capitalization is used to distinguish these terms from other common 452 Internetworking uses in which they appear without capitalization. 454 The terminology of DHCPv6 [RFC8415] and IPv6 ND [RFC4861] (including 455 the names of node variables, messages and protocol constants) is used 456 throughout this document. The terms "All-Routers multicast", "All- 457 Nodes multicast", "Solicited-Node multicast" and "Subnet-Router 458 anycast" are defined in [RFC4291]. Also, the term "IP" is used to 459 generically refer to either Internet Protocol version, i.e., IPv4 460 [RFC0791] or IPv6 [RFC8200]. 462 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 463 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 464 "OPTIONAL" in this document are to be interpreted as described in BCP 465 14 [RFC2119][RFC8174] when, and only when, they appear in all 466 capitals, as shown here. 468 3. Asymmetric Extended Route Optimization (AERO) 470 The following sections specify the operation of IP over OMNI links 471 using the AERO service: 473 3.1. AERO Node Types 475 AERO Clients are Mobile Nodes (MNs) that connect via underlying 476 interfaces with addresses that may change when the Client moves to a 477 new network connection point. AERO Clients register their Mobile 478 Network Prefixes (MNPs) with the AERO service, and distribute the 479 MNPs to nodes on EUNs. AERO Bridges, Servers, Proxys and Relays are 480 critical infrastructure elements in fixed (i.e., non-mobile) INET 481 deployments and hence have permanent and unchanging INET addresses. 482 Together, they constitute the AERO service which provides an OMNI 483 link virtual overlay for connecting AERO Clients. 485 AERO Bridges provide hybrid routing/bridging services (as well as a 486 security trust anchor) for nodes on an OMNI link. Bridges use 487 standard IPv6 routing to forward packets both within the same INET 488 partitions and between disjoint INET partitions based on a mid-layer 489 IPv6 encapsulation per [RFC2473]. The inner IP layer experiences a 490 virtual bridging service since the inner IP TTL/Hop Limit is not 491 decremented during forwarding. Each Bridge also peers with Servers 492 and other Bridges in a dynamic routing protocol instance to provide a 493 Distributed Mobility Management (DMM) service for the list of active 494 MNPs (see Section 3.2.3). Bridges present the OMNI link as a set of 495 one or more Mobility Service Prefixes (MSPs) and configure secured 496 tunnels with Servers, Relays, Proxys and other Bridges; they further 497 maintain IP forwarding table entries for each MNP and any other 498 reachable non-MNP prefixes. 500 AERO Servers provide default forwarding and mobility/multilink 501 services for AERO Client Mobile Nodes (MNs). Each Server also peers 502 with Bridges in a dynamic routing protocol instance to advertise its 503 list of associated MNPs (see Section 3.2.3). Servers facilitate 504 prefix delegation/registration exchanges with Clients, where each 505 delegated prefix becomes an MNP taken from an MSP. Servers forward 506 packets between OMNI interface neighbors and track each Client's 507 mobility profiles. Servers may further act as Servers for some sets 508 of Clients and as Proxies for others. 510 AERO Proxys provide a conduit for ANET Clients to associate with 511 Servers in external INETs. Client and Servers exchange control plane 512 messages via the Proxy acting as a bridge between the ANET/INET 513 boundary. The Proxy forwards data packets between Clients and the 514 OMNI link according to forwarding information in the neighbor cache. 515 The Proxy function is specified in Section 3.13. Proxys may further 516 act as Proxys for some sets of Clients and as Servers for others. 518 AERO Relays are Servers that provide forwarding services between the 519 OMNI interface and INET/EUN interfaces. Relays are provisioned with 520 MNPs the same as for an AERO Client, and also run a dynamic routing 521 protocol to discover any non-MNP IP routes. The Relay advertises the 522 MSP(s) to its connected networks, and distributes all of its 523 associated MNPs and non-MNP IP routes via BGP peerings with Bridges 525 3.2. The AERO Service over OMNI Links 527 3.2.1. AERO/OMNI Reference Model 529 Figure 1 presents the basic OMNI link reference model: 531 +----------------+ 532 | AERO Bridge B1 | 533 | Nbr: S1, S2, P1| 534 |(X1->S1; X2->S2)| 535 | MSP M1 | 536 +-+---------+--+-+ 537 +--------------+ | Secured | | +--------------+ 538 |AERO Server S1| | tunnels | | |AERO Server S2| 539 | Nbr: C1, B1 +-----+ | +-----+ Nbr: C2, B1 | 540 | default->B1 | | | default->B1 | 541 | X1->C1 | | | X2->C2 | 542 +-------+------+ | +------+-------+ 543 | OMNI link | | 544 X===+===+===================+==)===============+===+===X 545 | | | | 546 +-----+--------+ +--------+--+-----+ +--------+-----+ 547 |AERO Client C1| | AERO Proxy P1 | |AERO Client C2| 548 | Nbr: S1 | |(Proxy Nbr Cache)| | Nbr: S2 | 549 | default->S1 | +--------+--------+ | default->S2 | 550 | MNP X1 | | | MNP X2 | 551 +------+-------+ .--------+------. +-----+--------+ 552 | (- Proxyed Clients -) | 553 .-. `---------------' .-. 554 ,-( _)-. ,-( _)-. 555 .-(_ IP )-. +-------+ +-------+ .-(_ IP )-. 556 (__ EUN )--|Host H1| |Host H2|--(__ EUN ) 557 `-(______)-' +-------+ +-------+ `-(______)-' 559 Figure 1: AERO/OMNI Reference Model 561 In this model: 563 o the OMNI link is an overlay network service configured over one or 564 more underlying INET partitions which may be managed by different 565 administrative authorities and have incompatible protocols and/or 566 addressing plans. 568 o AERO Bridge B1 aggregates Mobility Service Prefix (MSP) M1, 569 discovers Mobile Network Prefixes (MNPs) X* and advertises the MSP 570 via BGP peerings over secured tunnels to Servers (S1, S2). 571 Bridges connect the disjoint segments of a partitioned OMNI link. 573 o AERO Servers/Relays S1 and S2 configure secured tunnels with 574 Bridge B1 and also provide mobility, multilink and default router 575 services for their associated Clients C1 and C2. 577 o AERO Clients C1 and C2 associate with Servers S1 and S2, 578 respectively. They receive Mobile Network Prefix (MNP) 579 delegations X1 and X2, and also act as default routers for their 580 associated physical or internal virtual EUNs. Simple hosts H1 and 581 H2 attach to the EUNs served by Clients C1 and C2, respectively. 583 o AERO Proxy P1 configures a secured tunnel with Bridge B1 and 584 provides proxy services for AERO Clients in secured enclaves that 585 cannot associate directly with other OMNI link neighbors. 587 An OMNI link configured over a single INET appears as a single 588 unified link with a consistent underlying network addressing plan. 589 In that case, all nodes on the link can exchange packets via simple 590 INET encapsulation, since the underlying INET is connected. In 591 common practice, however, an OMNI link may be partitioned into 592 multiple "segments", where each segment is a distinct INET 593 potentially managed under a different administrative authority (e.g., 594 as for worldwide aviation service providers such as ARINC, SITA, 595 Inmarsat, etc.). Individual INETs may also themselves be partitioned 596 internally, in which case each internal partition is seen as a 597 separate segment. 599 The addressing plan of each segment is consistent internally but will 600 often bear no relation to the addressing plans of other segments. 601 Each segment is also likely to be separated from others by network 602 security devices (e.g., firewalls, proxies, packet filtering 603 gateways, etc.), and in many cases disjoint segments may not even 604 have any common physical link connections. Therefore, nodes can only 605 be assured of exchanging packets directly with correspondents in the 606 same segment, and not with those in other segments. The only means 607 for joining the segments therefore is through inter-domain peerings 608 between AERO Bridges. 610 The same as for traditional campus LANs, multiple OMNI link segments 611 can be joined into a single unified link via a virtual bridging 612 service using the OMNI Adaptation Layer (OAL) which inserts a mid- 613 layer IPv6 encapsulation per [RFC2473] that supports inter-segment 614 forwarding (i.e., bridging) without decrementing the network-layer 615 TTL/Hop Limit. This bridging of OMNI link segments is shown in 616 Figure 2: 618 . . . . . . . . . . . . . . . . . . . . . . . 619 . . 620 . .-(::::::::) . 621 . .-(::::::::::::)-. +-+ . 622 . (:::: Segment A :::)--|B|---+ . 623 . `-(::::::::::::)-' +-+ | . 624 . `-(::::::)-' | . 625 . | . 626 . .-(::::::::) | . 627 . .-(::::::::::::)-. +-+ | . 628 . (:::: Segment B :::)--|B|---+ . 629 . `-(::::::::::::)-' +-+ | . 630 . `-(::::::)-' | . 631 . | . 632 . .-(::::::::) | . 633 . .-(::::::::::::)-. +-+ | . 634 . (:::: Segment C :::)--|B|---+ . 635 . `-(::::::::::::)-' +-+ | . 636 . `-(::::::)-' | . 637 . | . 638 . ..(etc).. x . 639 . . 640 . . 641 . <- OMNI link Bridged by encapsulation -> . 642 . . . . . . . . . . . . . .. . . . . . . . . 644 Figure 2: Bridging OMNI Link Segments 646 Bridges, Servers, Relays and Proxys connect via secured INET tunnels 647 over their respective segments in a spanning tree topology rooted at 648 the Bridges. The secured spanning tree supports strong 649 authentication for IPv6 ND control messages and may also be used to 650 convey the initial data packets in a flow. Route optimization can 651 then be employed to cause data packets to take more direct paths 652 between OMNI link neighbors without having to strictly follow the 653 spanning tree. 655 3.2.2. Link-Local Addresses (LLAs) and Domain Local Addresses (DLAs) 657 AERO nodes on OMNI links use the Link-Local Address (LLA) prefix 658 fe80::/64 [RFC4291] to assign LLAs used for network-layer addresses 659 in IPv6 ND and data messages. They also use the Domain Local Address 660 (DLA) prefix [DLA]::/48 to form per-link DLA sub-prefixes of the form 661 [DLA*]::/64, where '*' is a 16-bit OMNI link identitier. Each per- 662 link DLA sub-prefix is in turn used to form DLAs used for OAL header 663 source and destination addresses. See 664 [I-D.templin-6man-omni-interface] for a full specification of the 665 LLAs and DLAs used by AERO nodes on OMNI links. 667 IPv6 routers are not permitted to forward packets with LLA addresses. 668 Therefore, IPv6 packets with LLA addresses must be encapsulated in 669 IPv6 headers with DLA addresses in order to traverse the OMNI link. 670 DLA addresses therefore must be routable within the OMNI link domain- 671 local area. 673 For routing system organization (see Section 3.2.3), DLAs are 674 organized in partition prefixes, e.g., [DLA]::1000/116. For each 675 such partition prefix, the Bridge(s) that connect that segment assign 676 the all-zero's address of the prefix as a Subnet Router Anycast 677 address. For example, the Subnet Router Anycast address for 678 [DLA*]::1000/116 is simply [DLA*]::1000. 680 3.2.3. AERO Routing System 682 The AERO routing system comprises a private instance of the Border 683 Gateway Protocol (BGP) [RFC4271] that is coordinated between Bridges 684 and Servers and does not interact with either the public Internet BGP 685 routing system or any underlying INET routing systems. 687 In a reference deployment, each Server is configured as an Autonomous 688 System Border Router (ASBR) for a stub Autonomous System (AS) using 689 an AS Number (ASN) that is unique within the BGP instance, and each 690 Server further uses eBGP to peer with one or more Bridges but does 691 not peer with other Servers. Each INET of a multi-segment OMNI link 692 must include one or more Bridges, which peer with the Servers and 693 Proxys within that INET. All Bridges within the same INET are 694 members of the same hub AS using a common ASN, and use iBGP to 695 maintain a consistent view of all active MNPs currently in service. 696 The Bridges of different INETs peer with one another using eBGP. 698 Bridges advertise the OMNI link's MSPs and any non-MNP routes to each 699 of their Servers. This means that any aggregated non-MNPs (including 700 "default") are advertised to all Servers. Each Bridge configures a 701 black-hole route for each of its MSPs. By black-holing the MSPs, the 702 Bridge will maintain forwarding table entries only for the MNPs that 703 are currently active, and packets destined to all other MNPs will 704 correctly incur Destination Unreachable messages due to the black- 705 hole route. In this way, Servers have only partial topology 706 knowledge (i.e., they know only about the MNPs of their directly 707 associated Clients) and they forward all other packets to Bridges 708 which have full topology knowledge. 710 Each OMNI link segment assigns a unique sub-prefix of [DLA*]::/96 711 known as the DLA partition prefix. For example, a first segment 712 could assign [DLA*]::1000/116, a second could assign 713 [DLA*]::2000/116, a third could assign [DLA*]::3000/116, etc. The 714 administrative authorities for each segment must therefore coordinate 715 to assure mutually-exclusive partition prefix assignments, but 716 internal provisioning of each prefix is an independent local 717 consideration for each administrative authority. 719 DLA partition prefixes are statically represented in Bridge 720 forwarding tables. Bridges join multiple segments into a unified 721 OMNI link over multiple diverse administrative domains. They support 722 a bridging function by first establishing forwarding table entries 723 for their partition prefixes either via standard BGP routing or 724 static routes. For example, if three Bridges ('A', 'B' and 'C') from 725 different segments serviced [DLA*]::1000/116, [DLA*]::2000/116 and 726 [DLA*]::3000/116 respectively, then the forwarding tables in each 727 Bridge are as follows: 729 A: [DLA*]::1000/116->local, [DLA*]::2000/116->B, [DLA*]::3000/116->C 731 B: [DLA*]::1000/116->A, [DLA*]::2000/116->local, [DLA*]::3000/116->C 733 C: [DLA*]::1000/116->A, [DLA*]::2000/116->B, [DLA*]::3000/116->local 735 These forwarding table entries are permanent and never change, since 736 they correspond to fixed infrastructure elements in their respective 737 segments. 739 DLA Client prefixes are instead dynamically advertised in the AERO 740 routing system by Servers and Relays that provide service for their 741 corresponding MNPs. For example, if three Servers ('D', 'E' and 'F') 742 service the MNPs 2001:db8:1000:2000::/56, 2001:db8:3000:4000::/56 and 743 2001:db8:5000:6000::/56 then the routing system would include: 745 D: [DLA*]:2001:db8:1000:2000/120 747 E: [DLA*]:2001:db8:3000:4000/120 749 F: [DLA*]:2001:db8:5000:6000/120 751 A full discussion of the BGP-based routing system used by AERO is 752 found in [I-D.ietf-rtgwg-atn-bgp]. 754 3.2.4. OMNI Link Encapsulation 756 With the Client and partition prefixes in place in Bridge forwarding 757 tables, control and data packets sent between AERO nodes in different 758 OMNI link segments can be carried over the spanning tree via mid- 759 layer encapsulations using the OMNI Adaptation Layer (OAL) header 760 and/or the OMNI Routing Header (ORH). OAL encapsulation is used for 761 all IPv4 packets, for IPv6 packets for which no route optimization 762 addressing information for the final segment is available, for 763 transportation of IPv6 ND messages with LLAs, and when fragmentation 764 is necessary (see Section 5 of [I-D.templin-6man-omni-interface]). 765 OAL encapsulation is based on Generic Packet Tunneling in IPv6 766 [RFC2473], with the inclusion of an ORH as an extension to the OAL 767 header if final segment link-layer address and/or final IPv6 768 destination address information is necessary. 770 The ORH is formatted as shown in Figure 3: 772 0 1 2 3 773 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 1 774 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 775 | Next Header | Hdr Ext Len | Routing Type | Segments Left | 776 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 777 |Saved Hop Limit| SRT | FMT | LHS (bits 0 - 15) | 778 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 779 | LHS (bits 16 - 31) | ~ 780 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ 781 ~ Link Layer Address (L2ADDR) ~ 782 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 783 ~ IPv6 Destination Address ~ 784 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 785 ~ Null Padding ~ 786 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 788 Figure 3: OMNI Routing Header (ORH) Format 790 In this format: 792 o Next Header identifies the type of header immediately following 793 the ORH. 795 o Hdr Ext Len is the length of the Routing header in 8-octet units, 796 not including the first 8 octets. 798 o Routing Type is set to TBD (see IANA Considerations). 800 o Segments Left is set to the value 1 if an IPv6 Destination Address 801 is included, or the value 0 if no IPv6 Destination Address is 802 included. If Segments Left encodes any other value, the entire 803 ORH is ignored and the next header is processed. 805 o Saved Hop Limit is used only for ORH-Only encapsulation (see 806 below), and otherwise set to 0. When ORH-Only encapsulation is 807 applied, the Hop Limit value found in the IPv6 header is 808 decremented and also written into the Saved Hop Limit field. When 809 the ORH-Only encapsulation is removed, the value found in the 810 Saved Hop Limit field is written into the IPv6 header Hop Limit 811 field. 813 o SRT - a 5-bit Segment Routing Topology prefix length value that 814 (when added to 96) determines the prefix length to apply to the 815 DLA formed from concatenating [DLA*]::/96 with the 32 bit LHS MSID 816 value that follows. For example, the value 16 corresponds to the 817 prefix length 112. 819 o FMT - a 3-bit "Framework/Mode/Type" code corresponding to the 820 included Link Layer Address as follows: 822 * When the most significant bit (i.e., "Framework") is set to 0, 823 L2ADDR is the INET encapsulation address of a Server/Proxy; 824 otherwise, it is the address for the Source/Target itself. 826 * When the next most significant bit (i.e., "Mode") is set to 0, 827 the Source/Target L2ADDR is on the open INET; otherwise, it is 828 (likely) located behind a Network Address Translator (NAT). 830 * When the least significant bit (i.e., "Type") is set to 0, 831 L2ADDR includes a UDP Port Number followed by an IPv4 address; 832 else, a UDP Port Number followed by an IPv6 address. 834 o LHS - the 32 bit MSID of the Last Hop Server/Proxy on the path to 835 the target. When SRT and LHS are both set to 0, the LHS is 836 considered unspecified in this IPv6 ND message. When SRT is set 837 to 0 and LHS is non-zero, the prefix length is set to 128. SRT 838 and LHS provide guidance to the OMNI interface forwarding 839 algorithm. Specifically, if SRT/LHS is located in the local OMNI 840 link segment then the OMNI interface can encapsulate according to 841 FMT/L2ADDR; else, it must forward according to the OMNI link 842 spanning tree. 844 o Link Layer Address (L2ADDR) - Formatted according to FMT, and 845 identifies the link-layer address (i.e., the encapsulation 846 address) of the source/target. The UDP Port Number appears in the 847 first two octets and the IP address appears in the next 4 octets 848 for IPv4 or 16 octets for IPv6. The Port Number and IP address 849 are recorded in ones-compliment "obfuscated" form per [RFC4380]. 850 The OMNI interface forwarding algorithm uses FMT/L2ADDR to 851 determine the encapsulation address for forwarding when SRT/LHS is 852 located in the local OMNI link segment. 854 o IPv6 Destination Address is a 16-octet IPv6 address included only 855 when Segments Left is 1, and omitted otherwise. 857 o Null Padding contains 0/4 zero-valued octets as necessary to pad 858 the ORH to an integral number of 8-octet units. 860 When an AERO node uses OAL encapsulation for an IPv4 packet, an IPv6 861 packet with link-local source/destination addresses, or an IPv6 862 packet with GUA source/destination addresses such as 2001:db8:1:2::1 863 and 2001:db8:1000:2000::1, it sets the OAL header source address to 864 its own DLA address (e.g., [DLA*]::1000:2000) and sets the 865 destination address to the DLA corresponding to the IP destination 866 address. The node then fragments the mid-layer packet if necessary 867 then encapsulates each resulting OAL packet in an INET header with 868 source address set to its own INET address (e.g., 192.0.2.100) and 869 destination set to the INET address of a Bridge (e.g., 192.0.2.1). 871 If the final segment LHS is known, the node next inserts an ORH 872 immediately following the OAL header of each packet/fragment with the 873 correct SRT, FMT and LHS information. The node then copies the OAL 874 header destination into the ORH destination, then writes the Subnet 875 Router Anycast address corresponding to the LHS DLA address (for 876 example, for LHS [DLA]::1000:2000 and with SRT prefix length 16, the 877 Subnet Router Anycast address is [DLA*]::1000:0000) into the OAL 878 header destination. The encapsulation format in the above example is 879 shown in Figure 4: 881 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 882 | INET Header | 883 | src = 192.0.2.100 | 884 | dst = 192.0.2.1 | 885 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 886 | OAL Header | 887 | src = [DLA*]::1000:2000 | 888 | dst= DLA for inner IP dst | 889 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 890 | ORH Header | 891 | (if necessary) | 892 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 893 | Inner IP Header | 894 | src = 2001:db8:1:2::1 | 895 | dst = 2001:db8:1000:2000::1 | 896 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 897 | | 898 ~ ~ 899 ~ Inner Packet Body ~ 900 ~ ~ 901 | | 902 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 904 Figure 4: OAL/ORH Encapsulation 906 In this format, the inner IP header and packet body are the original 907 IP packet, the OAL header is an IPv6 header prepared according to 908 [RFC2473], the ORH is a Routing Header extension of the OAL header, 909 and the INET header is prepared as discussed in Section 3.6. 911 For IPv6 packets with non-link-local IPv6 addresses for which the LHS 912 is known and no fragmentation is required, the AERO node can avoid 913 OAL encapsulation while inserting an ORH as an extension to the 914 actual IPv6 header of the packet. The node further changes the IPv6 915 destination address to the Subnet Router Anycast address 916 corresponding to the LHS DLA address (for example, for LHS 917 [DLA]::1000:2000 and with SRT prefix length 16, the Subnet Router 918 Anycast address is [DLA*]::1000:0000). When the node changes the 919 IPv6 destination address, it places the original destination address 920 in the ORH header so that it can be restored upon OMNI link egress. 921 The ORH-only encapsulation is shown in 923 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 924 | INET Header | 925 | src = 192.0.2.100 | 926 | dst = 192.0.2.1 | 927 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 928 | Inner IP Header | 929 | src = 2001:db8:1:2::1 | 930 | dst = [DLA*]::1000:0000 | 931 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 932 | ORH Header | 933 | dst = 2001:db8:1000:2000::1 | 934 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 935 | | 936 ~ ~ 937 ~ Inner Packet Body ~ 938 ~ ~ 939 | | 940 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 942 Figure 5: ORH-Only Encapsulation 944 This gives rise to a routing system that contains both Client prefix 945 routes that may change dynamically due to regional node mobility and 946 partition prefix routes that rarely if ever change. The Bridges can 947 therefore provide link-layer bridging by sending packets over the 948 spanning tree instead of network-layer routing according to MNP 949 routes. As a result, opportunities for packet loss due to node 950 mobility between different segments are mitigated. 952 In normal operations, IPv6 ND messages are conveyed over secured 953 paths between OMNI link neighbors so that specific Proxys, Servers or 954 Relays can be addressed without being subject to mobility events. 955 Conversely, only the first few packets destined to Clients need to 956 traverse secured paths until route optimization can determine a more 957 direct path. 959 3.2.5. Segment Routing Topologies (SRTs) 961 The 64-bit sub-prefixes of [DLA]::/48 identify up to 2^16 distinct 962 Segment Routing Topologies (SRTs). Each SRT is a mutually-exclusive 963 OMNI link overlay instance using a distinct set of DLAs, and emulates 964 a Virtual LAN (VLAN) service for the OMNI link. In some cases (e.g., 965 when redundant topologies are needed for fault tolerance and 966 reliability) it may be beneficial to deploy multiple SRTs that act as 967 independent overlay instances. A communication failure in one 968 instance therefore will not affect communications in other instances. 970 Each SRT is identified by a distinct value in bits 48-63 of 971 [DLA]::/48, i.e., as [DLA0]::/64, [DLA1]::/64, [DLA2]::/64, etc. 972 This document asserts that up to four SRTs provide a level of safety 973 sufficient for critical communications such as civil aviation. Each 974 SRT is designated with a color that identifies a different OMNI link 975 instance as follows: 977 o Red - corresponds to [DLA0]::/64 979 o Green - corresponds to [DLA1]::/64 981 o Blue-1 - corresponds to [DLA2]::/64 983 o Blue-2 - corresponds to [DLA3]::/64 985 o the remaining [DLA*]::/64 sub prefixes are available for 986 additional SRTs. 988 Each OMNI interface is identified by a unqiue interface name (e.g., 989 omni0, omni1, omni2, etc.) and assigns an anycast DLA corresponding 990 to its SRT prefix. For example, the anycast DLA for the Green SRT is 991 simply [DLA1]::. The anycast DLA is used for OMNI interface 992 determination in Safety-Based Multilink (SBM) as discussed in 993 [I-D.templin-6man-omni-interface]. Each OMNI interface further 994 applies Performance-Based Multilink (PBM) internally. 996 3.2.6. Segment Routing For OMNI Link Selection 998 An original IPv6 source can direct an IPv6 packet to an AERO node by 999 including a standard IPv6 Segment Routing Header (SRH) [RFC8754] with 1000 the anycast DLA for the selected SRT as either the IPv6 destination 1001 or as an intermediate hop within the SRH. This allows the original 1002 source to determine the specific OMNI link topology a packet will 1003 traverse when there may be multiple alternatives. 1005 When the AERO node processes the SRH and forwards the packet to the 1006 correct OMNI interface, the OMNI interface writes the next IPv6 1007 address from the SRH into the IPv6 desination address and decrements 1008 Segments Left. If decrementing would cause Segments Left to become 1009 0, the OMNI interface deletes the SRH before forwarding. This form 1010 of Segment Routing supports Safety-Based Multilink (SBM). 1012 3.2.7. Segment Routing Within the OMNI Link 1014 AERO node OMNI interfaces can insert an OAL and/or ORH header for 1015 Segment Routing within the OMNI link to influence the paths of 1016 packets destined to targets in remote segments without requiring all 1017 packets to traverse strict spanning tree paths. 1019 When an AERO node's OMNI interface has a packet to send to a target 1020 discovered through route optimization located in the same OMNI link 1021 segment, it encapsulates the packet in OAL/ORH headers if necessary 1022 as discussed above. The node then uses the target's Link Layer 1023 Address (L2ADDR) information for INET encapsulation. 1025 When an AERO node's OMNI interface has a packet to send to a route 1026 optimization target located in a remote OMNI link segment, it 1027 encapsulates the packet in OAL/ORH headers as discussed above while 1028 forwarding the packet to a Bridge with destination set to the Subnet 1029 Router Anycast address for the final OMNI link segment. 1031 When a Bridge receives a packet destined to its Subnet Router Anycast 1032 address with an ORH with SRT/LHS values corresponding to the local 1033 segment, it examines the L2ADDR according to FMT and removes the ORH 1034 from the packet. The Bridge writes the saved IPv6 address from the 1035 ORH into the OAL header destination address if an OAL header is 1036 present; else it writes the address in the packet's IPv6 destination 1037 address. The Bridge then encapsulates the packet in an INET header 1038 according to L2ADDR and forwards the packet within the INET either to 1039 the LHS Server/Proxy or directly to the destination itself. In this 1040 way, the Bridge participates in route optimization to reduce traffic 1041 load and suboptimal routing through strict spanning tree paths. 1043 3.3. OMNI Interface Characteristics 1045 OMNI interfaces are virtual interfaces configured over one or more 1046 underlying interfaces classified as follows: 1048 o INET interfaces connect to an INET either natively or through one 1049 or several IPv4 Network Address Translators (NATs). Native INET 1050 interfaces have global IP addresses that are reachable from any 1051 INET correspondent. All Server, Relay and Bridge interfaces are 1052 native interfaces, as are INET-facing interfaces of Proxys. NATed 1053 INET interfaces connect to a private network behind one or more 1054 NATs that provide INET access. Clients that are behind a NAT are 1055 required to send periodic keepalive messages to keep NAT state 1056 alive when there are no data packets flowing. 1058 o ANET interfaces connect to an ANET that is separated from the open 1059 INET by a Proxy. Proxys can actively issue control messages over 1060 the INET on behalf of the Client to reduce ANET congestion. 1062 o VPNed interfaces use security encapsulation over the INET to a 1063 Virtual Private Network (VPN) server that also acts as a Server or 1064 Proxy. Other than the link-layer encapsulation format, VPNed 1065 interfaces behave the same as Direct interfaces. 1067 o Direct interfaces connect a Client directly to a Server or Proxy 1068 without crossing any ANET/INET paths. An example is a line-of- 1069 sight link between a remote pilot and an unmanned aircraft. The 1070 same Client considerations apply as for VPNed interfaces. 1072 OMNI interfaces use OAL/ORH encapsulation as necessary as discussed 1073 in Section 3.2.4. OMNI interfaces use link-layer encapsulation (see: 1074 Section 3.6) to exchange packets with OMNI link neighbors over INET 1075 or VPNed interfaces as well aso over ANET interfaces for which the 1076 Client and Proxy may be multiple IP hops away. OMNI interfaces do 1077 not use link-layer encapsulation over Direct underlying interfaces or 1078 ANET interfaces when the Client and Proxy are known to be on the same 1079 underlying link. 1081 OMNI interfaces maintain a neighbor cache for tracking per-neighbor 1082 state the same as for any interface. OMNI interfaces use ND messages 1083 including Router Solicitation (RS), Router Advertisement (RA), 1084 Neighbor Solicitation (NS) and Neighbor Advertisement (NA) for 1085 neighbor cache management. 1087 OMNI interfaces send ND messages with an OMNI option formatted as 1088 specified in [I-D.templin-6man-omni-interface]. The OMNI option 1089 includes prefix registration information and Interface Attributes 1090 containing link information parameters for the OMNI interface's 1091 underlying interfaces. Each OMNI option may include multiple 1092 Interface Attributes sub-options, each identified by an ifIndex 1093 value. 1095 A Client's OMNI interface may be configured over multiple underlying 1096 interface connections. For example, common mobile handheld devices 1097 have both wireless local area network ("WLAN") and cellular wireless 1098 links. These links are often used "one at a time" with low-cost WLAN 1099 preferred and highly-available cellular wireless as a standby, but a 1100 simultaneous-use capability could provide benefits. In a more 1101 complex example, aircraft frequently have many wireless data link 1102 types (e.g. satellite-based, cellular, terrestrial, air-to-air 1103 directional, etc.) with diverse performance and cost properties. 1105 If a Client's multiple underlying interfaces are used "one at a time" 1106 (i.e., all other interfaces are in standby mode while one interface 1107 is active), then ND message OMNI options include only a single 1108 Interface Attributes sub-option set to constant values. In that 1109 case, the Client would appear to have a single interface but with a 1110 dynamically changing link-layer address. 1112 If the Client has multiple active underlying interfaces, then from 1113 the perspective of ND it would appear to have multiple link-layer 1114 addresses. In that case, ND message OMNI options MAY include 1115 multiple Interface Attributes sub-options - each with values that 1116 correspond to a specific interface. Every ND message need not 1117 include Interface Attributes for all underlying interfaces; for any 1118 attributes not included, the neighbor considers the status as 1119 unchanged. 1121 Bridge, Server and Proxy OMNI interfaces may be configured over one 1122 or more secured tunnel interfaces. The OMNI interface configures 1123 both an LLA and its corresponding DLA, while the underlying secured 1124 tunnel interfaces are either unnumbered or configure the same DLA. 1125 The OMNI interface encapsulates each IP packet in OAL/ORH headers and 1126 presents the packet to the underlying secured tunnel interface. 1127 Routing protocols such as BGP that run over the OMNI interface do not 1128 employ OAL/ORH encapsulation, but rather present the routing protocol 1129 messages directly to the underlying secured tunnels while using the 1130 DLA as the source address. This distinction must be honored 1131 consistently according to each node's configuration so that the IP 1132 forwarding table will associate discovered IP routes with the correct 1133 interface. 1135 3.4. OMNI Interface Initialization 1137 AERO Servers, Proxys and Clients configure OMNI interfaces as their 1138 point of attachment to the OMNI link. AERO nodes assign the MSPs for 1139 the link to their OMNI interfaces (i.e., as a "route-to-interface") 1140 to ensure that packets with destination addresses covered by an MNP 1141 not explicitly assigned to a non-OMNI interface are directed to the 1142 OMNI interface. 1144 OMNI interface initialization procedures for Servers, Proxys, Clients 1145 and Bridges are discussed in the following sections. 1147 3.4.1. AERO Server/Relay Behavior 1149 When a Server enables an OMNI interface, it assigns an LLA/DLA 1150 appropriate for the given OMNI link segment. The Server also 1151 configures secured tunnels with one or more neighboring Bridges and 1152 engages in a BGP routing protocol session with each Bridge. 1154 The OMNI interface provides a single interface abstraction to the IP 1155 layer, but internally comprises multiple secured tunnels as well as 1156 an NBMA nexus for sending encapsulated data packets to OMNI interface 1157 neighbors. The Server further configures a service to facilitate ND 1158 exchanges with AERO Clients and manages per-Client neighbor cache 1159 entries and IP forwarding table entries based on control message 1160 exchanges. 1162 Relays are simply Servers that run a dynamic routing protocol to 1163 redistribute routes between the OMNI interface and INET/EUN 1164 interfaces (see: Section 3.2.3). The Relay provisions MNPs to 1165 networks on the INET/EUN interfaces (i.e., the same as a Client would 1166 do) and advertises the MSP(s) for the OMNI link over the INET/EUN 1167 interfaces. The Relay further provides an attachment point of the 1168 OMNI link to a non-MNP-based global topology. 1170 3.4.2. AERO Proxy Behavior 1172 When a Proxy enables an OMNI interface, it assigns an LLA/DLA and 1173 configures permanent neighbor cache entries the same as for Servers. 1174 The Proxy also configures secured tunnels with one or more 1175 neighboring Bridges and maintains per-Client neighbor cache entries 1176 based on control message exchanges. Importantly Proxys are often 1177 configured to act as Servers, and vice-versa. 1179 3.4.3. AERO Client Behavior 1181 When a Client enables an OMNI interface, it sends RS messages with ND 1182 parameters over its underlying interfaces to a Server, which returns 1183 an RA message with corresponding parameters. (The RS/RA messages may 1184 pass through a Proxy in the case of a Client's ANET interface, or 1185 through one or more NATs in the case of a Client's INET interface.) 1187 3.4.4. AERO Bridge Behavior 1189 AERO Bridges configure an OMNI interface and assign the DLA Subnet 1190 Router Anycast address for each OMNI link segment they connect to. 1191 Bridges configure secured tunnels with Servers, Proxys and other 1192 Bridges; they also configure LLAs/DLAs and permanent neighbor cache 1193 entries the same as Servers. Bridges engage in a BGP routing 1194 protocol session with a subset of the Servers and other Bridges on 1195 the spanning tree (see: Section 3.2.3). 1197 3.5. OMNI Interface Neighbor Cache Maintenance 1199 Each OMNI interface maintains a conceptual neighbor cache that 1200 includes an entry for each neighbor it communicates with on the OMNI 1201 link per [RFC4861]. OMNI interface neighbor cache entries are said 1202 to be one of "permanent", "symmetric", "asymmetric" or "proxy". 1204 Permanent neighbor cache entries are created through explicit 1205 administrative action; they have no timeout values and remain in 1206 place until explicitly deleted. AERO Bridges maintain permanent 1207 neighbor cache entries for their associated Proxys/Servers (and vice- 1208 versa). Each entry maintains the mapping between the neighbor's 1209 network-layer LLA and corresponding INET address. 1211 Symmetric neighbor cache entries are created and maintained through 1212 RS/RA exchanges as specified in Section 3.12, and remain in place for 1213 durations bounded by prefix lifetimes. AERO Servers maintain 1214 symmetric neighbor cache entries for each of their associated 1215 Clients, and AERO Clients maintain symmetric neighbor cache entries 1216 for each of their associated Servers. 1218 Asymmetric neighbor cache entries are created or updated based on 1219 route optimization messaging as specified in Section 3.14, and are 1220 garbage-collected when keepalive timers expire. AERO ROSs maintain 1221 asymmetric neighbor cache entries for active targets with lifetimes 1222 based on ND messaging constants. Asymmetric neighbor cache entries 1223 are unidirectional since only the ROS (and not the ROR) creates an 1224 entry. 1226 Proxy neighbor cache entries are created and maintained by AERO 1227 Proxys when they process Client/Server ND exchanges, and remain in 1228 place for durations bounded by ND and prefix lifetimes. AERO Proxys 1229 maintain proxy neighbor cache entries for each of their associated 1230 Clients. Proxy neighbor cache entries track the Client state and the 1231 address of the Client's associated Server(s). 1233 To the list of neighbor cache entry states in Section 7.3.2 of 1234 [RFC4861], Proxy and Server OMNI interfaces add an additional state 1235 DEPARTED that applies to symmetric and proxy neighbor cache entries 1236 for Clients that have recently departed. The interface sets a 1237 "DepartTime" variable for the neighbor cache entry to "DEPART_TIME" 1238 seconds. DepartTime is decremented unless a new ND message causes 1239 the state to return to REACHABLE. While a neighbor cache entry is in 1240 the DEPARTED state, packets destined to the target Client are 1241 forwarded to the Client's new location instead of being dropped. 1243 When DepartTime decrements to 0, the neighbor cache entry is deleted. 1244 It is RECOMMENDED that DEPART_TIME be set to the default constant 1245 value REACHABLE_TIME plus 10 seconds (40 seconds by default) to allow 1246 a window for packets in flight to be delivered while stale route 1247 optimization state may be present. 1249 When an ROR receives an authentic NS message used for route 1250 optimization, it searches for a symmetric neighbor cache entry for 1251 the target Client. The ROR then returns a solicited NA message 1252 without creating a neighbor cache entry for the ROS, but creates or 1253 updates a target Client "Report List" entry for the ROS and sets a 1254 "ReportTime" variable for the entry to REPORT_TIME seconds. The ROR 1255 resets ReportTime when it receives a new authentic NS message, and 1256 otherwise decrements ReportTime while no authentic NS messages have 1257 been received. It is RECOMMENDED that REPORT_TIME be set to the 1258 default constant value REACHABLE_TIME plus 10 seconds (40 seconds by 1259 default) to allow a window for route optimization to converge before 1260 ReportTime decrements below REACHABLE_TIME. 1262 When the ROS receives a solicited NA message response to its NS 1263 message used for route optimization, it creates or updates an 1264 asymmetric neighbor cache entry for the target network-layer and 1265 link-layer addresses. The ROS then (re)sets ReachableTime for the 1266 neighbor cache entry to REACHABLE_TIME seconds and uses this value to 1267 determine whether packets can be forwarded directly to the target, 1268 i.e., instead of via a default route. The ROS otherwise decrements 1269 ReachableTime while no further solicited NA messages arrive. It is 1270 RECOMMENDED that REACHABLE_TIME be set to the default constant value 1271 30 seconds as specified in [RFC4861]. 1273 AERO nodes also use the value MAX_UNICAST_SOLICIT to limit the number 1274 of NS keepalives sent when a correspondent may have gone unreachable, 1275 the value MAX_RTR_SOLICITATIONS to limit the number of RS messages 1276 sent without receiving an RA and the value MAX_NEIGHBOR_ADVERTISEMENT 1277 to limit the number of unsolicited NAs that can be sent based on a 1278 single event. It is RECOMMENDED that MAX_UNICAST_SOLICIT, 1279 MAX_RTR_SOLICITATIONS and MAX_NEIGHBOR_ADVERTISEMENT be set to 3 the 1280 same as specified in [RFC4861]. 1282 Different values for DEPART_TIME, REPORT_TIME, REACHABLE_TIME, 1283 MAX_UNICAST_SOLICIT, MAX_RTR_SOLCITATIONS and 1284 MAX_NEIGHBOR_ADVERTISEMENT MAY be administratively set; however, if 1285 different values are chosen, all nodes on the link MUST consistently 1286 configure the same values. Most importantly, DEPART_TIME and 1287 REPORT_TIME SHOULD be set to a value that is sufficiently longer than 1288 REACHABLE_TIME to avoid packet loss due to stale route optimization 1289 state. 1291 3.5.1. OMNI Neighbor Interface Attributes 1293 OMNI interface IPv6 ND messages include OMNI options 1294 [I-D.templin-6man-omni-interface] with Interface Attributes that 1295 provide Link-Layer Address and QoS Preference information for the 1296 neighbor's underlying interfaces. This information is stored in the 1297 neighbor cache and provides the basis for the forwarding algorithm 1298 specified in Section 3.10. The information is cumulative and 1299 reflects the union of the OMNI information from the most recent ND 1300 messages received from the neighbor; it is therefore not required 1301 that each ND message contain all neighbor information. 1303 The OMNI option Interface Attributes for each underlying interface 1304 includes a two-part "Link-Layer Address" consisting of a simple IP 1305 encapsulation address determined by the FMT and L2ADDR fields and an 1306 OAL DLA determined by the SRT and LHS fields. If the neighbor is 1307 located in the local OMNI link segment (and, if any necessary NAT 1308 state has been established) forwarding via simple IP encapsulation 1309 can be used; otherwise, OAL encapsulation must be used. Underlying 1310 interfaces are further selected based on their associated preference 1311 values "high", "medium", "low" or "disabled". 1313 Note: the OMNI option is distinct from any Source/Target Link-Layer 1314 Address Options (S/TLLAOs) that may appear in an ND message according 1315 to the appropriate IPv6 over specific link layer specification (e.g., 1316 [RFC2464]). If both an OMNI option and S/TLLAO appear, the former 1317 pertains to encapsulation addresses while the latter pertains to the 1318 native L2 address format of the underlying media. 1320 3.5.2. OMNI Neighbor Advertisement Message Flags 1322 As discussed in Section 4.4 of [RFC4861] NA messages include three 1323 flag bits R, S and O. OMNI interface NA messages treat the flags as 1324 follows: 1326 o R: The R ("Router") flag is set to 1 in the NA messages sent by 1327 all AERO/OMNI node types. Simple hosts that would set R to 0 do 1328 not occur on the OMNI link itself, but may occur on the downstream 1329 links of Clients and Relays. 1331 o S: The S ("Solicited") flag is set exactly as specified in 1332 Section 4.4. of [RFC4861], i.e., it is set to 1 for Solicited NAs 1333 and set to 0 for Unsolicited NAs (both unicast and multicast). 1335 o O: The O ("Override") flag is set to 0 for solicited proxy NAs and 1336 set to 1 for all other solicited and unsolicited NAs. For further 1337 study is whether solicited NAs for anycast targets apply for OMNI 1338 links. Since OMNI LLAs must be uniquely assigned to Clients to 1339 support correct ND protocol operation, however, no role is 1340 currently seen for assigning the same OMNI LLA to multiple 1341 Clients. 1343 3.6. OMNI Interface Encapsulation and Re-encapsulation 1345 The OMNI Adaptation Layer (OAL) inserts mid-layer IPv6 headers known 1346 as the OAL/ORH headers when necessary as discussed in the following 1347 sections. After either inserting or omitting the OAL/ORH headers, 1348 the OMNI interface also inserts or omits an outer encapsulation 1349 header as discussed below. 1351 OMNI interfaces avoid outer encapsulation over Direct underlying 1352 interfaces and ANET underlying interfaces for which the Client and 1353 Proxy are connected to the same underlying link. Otherwise, OMNI 1354 interfaces encapsulate packets according to whether they are entering 1355 the OMNI interface from the network layer or if they are being re- 1356 admitted into the same OMNI link they arrived on. This latter form 1357 of encapsulation is known as "re-encapsulation". 1359 For packets entering the OMNI interface from the network layer, the 1360 OMNI interface copies the "TTL/Hop Limit", "Type of Service/Traffic 1361 Class" [RFC2983], "Flow Label"[RFC6438] (for IPv6) and "Congestion 1362 Experienced" [RFC3168] values in the inner packet's IP header into 1363 the corresponding fields in the OAL and outer encapsulation 1364 header(s). 1366 For packets undergoing re-encapsulation, the OMNI interface instead 1367 copies these values from the original encapsulation header into the 1368 new encapsulation header, i.e., the values are transferred between 1369 encapsulation headers and *not* copied from the encapsulated packet's 1370 network-layer header. (Note especially that by copying the TTL/Hop 1371 Limit between encapsulation headers the value will eventually 1372 decrement to 0 if there is a (temporary) routing loop.) 1374 OMNI interfaces configured over ANET underlying interfaces which 1375 employ a different IP protocol version (and/or when the Client and 1376 Proxy may be separated by multiple ANET IP hops) use IP-in-IP 1377 encapsulation so that the inner packet can traverse the ANET without 1378 decrementing the TTL/Hop-Limit. IPv6 underlying ANET interfaces use 1379 [RFC2473] encapsulation, while IPv4 interfaces use the appropriate 1380 encapsulation per one of [RFC5214][RFC2003]. 1382 OMNI interfaces configured over INET underlying interfaces 1383 encapsulate packets in INET headers according to the next hop 1384 determined in the forwarding algorithm in Section 3.10. If the next 1385 hop is reached via a secured tunnel, the OMNI interface uses an 1386 encapsulation format specific to the secured tunnel type (see: 1388 Section 6). If the next hop is reached via an unsecured INET 1389 interface, the OMNI interface instead uses UDP/IP encapsulation per 1390 [RFC4380] and as extended in [RFC6081]. 1392 When UDP/IP encapsulation is used, the OMNI interface next sets the 1393 UDP source port to a constant value that it will use in each 1394 successive packet it sends, and sets the UDP length field to the 1395 length of the encapsulated packet plus 8 bytes for the UDP header 1396 itself plus the length of any included extension headers or trailers. 1397 The encapsulated packet may be either IPv6 or IPv4, as distinguished 1398 by the version number found in the first four bits. 1400 For UDP/IP-encapsulated packets sent to a Server, Relay or Bridge, 1401 the OMNI interface sets the UDP destination port to 8060, i.e., the 1402 IANA-registered port number for AERO. For packets sent to a Client, 1403 the OMNI interface sets the UDP destination port to the port value 1404 stored in the neighbor cache entry for this Client. The OMNI 1405 interface finally includes/omits the UDP checksum according to 1406 [RFC6935][RFC6936]. 1408 3.7. OMNI Interface Decapsulation 1410 OMNI interfaces decapsulate packets destined either to the AERO node 1411 itself or to a destination reached via an interface other than the 1412 OMNI interface the packet was received on. When the encapsulated 1413 packet arrives in multiple OAL fragments, the OMNI interface 1414 reassembles as discussed in Section 3.9. Further decapsulation steps 1415 are performed according to the appropriate encapsulation format 1416 specification. 1418 3.8. OMNI Interface Data Origin Authentication 1420 AERO nodes employ simple data origin authentication procedures. In 1421 particular: 1423 o AERO Bridges, Servers and Proxys accept encapsulated data packets 1424 and control messages received from the (secured) spanning tree. 1426 o AERO Proxys and Clients accept packets that originate from within 1427 the same secured ANET. 1429 o AERO Clients and Relays accept packets from downstream network 1430 correspondents based on ingress filtering. 1432 o AERO Clients, Relays and Servers verify the outer UDP/IP 1433 encapsulation addresses according to [RFC4380]. 1435 AERO nodes silently drop any packets that do not satisfy the above 1436 data origin authentication procedures. Further security 1437 considerations are discussed in Section 6. 1439 3.9. OMNI Adaptation Layer and OMNI Interface MTU 1441 The OMNI interface observes the link nature of tunnels, including the 1442 Maximum Transmission Unit (MTU), Maximum Reassembly Unit (MRU) and 1443 the role of fragmentation and reassembly [I-D.ietf-intarea-tunnels]. 1444 The OMNI interface employs an OMNI Adaptation Layer (OAL) for 1445 accommodating multiple underlying links with diverse MTUs. The 1446 functions of the OAL and the OMNI interface MTU/MRU are specified in 1447 Section 5 of [I-D.templin-6man-omni-interface], with MTU/MRU both set 1448 to the constant value 9180 bytes. 1450 3.10. OMNI Interface Forwarding Algorithm 1452 IP packets enter a node's OMNI interface either from the network 1453 layer (i.e., from a local application or the IP forwarding system) or 1454 from the link layer (i.e., from an OMNI interface neighbor). All 1455 packets entering a node's OMNI interface first undergo data origin 1456 authentication as discussed in Section 3.8. Packets that satisfy 1457 data origin authentication are processed further, while all others 1458 are dropped silently. The OMNI interface OAL wraps accepted packets 1459 in OAL/ORH headers if necessary as discussed above. 1461 Packets that enter the OMNI interface from the network layer are 1462 forwarded to an OMNI interface neighbor. Packets that enter the OMNI 1463 interface from the link layer are either re-admitted into the OMNI 1464 link or forwarded to the network layer where they are subject to 1465 either local delivery or IP forwarding. In all cases, the OMNI 1466 interface itself MUST NOT decrement the network layer TTL/Hop-count 1467 since its forwarding actions occur below the network layer. 1469 OMNI interfaces may have multiple underlying interfaces and/or 1470 neighbor cache entries for neighbors with multiple underlying 1471 interfaces (see Section 3.3). The OMNI interface uses interface 1472 attributes and/or traffic classifiers (e.g., DSCP value, port number, 1473 etc.) to select an outgoing underlying interface for each packet 1474 based on the node's own QoS preferences, and also to select a 1475 destination link-layer address based on the neighbor's underlying 1476 interface with the highest preference. AERO implementations SHOULD 1477 allow for QoS preference values to be modified at runtime through 1478 network management. 1480 If multiple outgoing interfaces and/or neighbor interfaces have a 1481 preference of "high", the AERO node replicates the packet and sends 1482 one copy via each of the (outgoing / neighbor) interface pairs; 1483 otherwise, the node sends a single copy of the packet via an 1484 interface with the highest preference. AERO nodes keep track of 1485 which underlying interfaces are currently "reachable" or 1486 "unreachable", and only use "reachable" interfaces for forwarding 1487 purposes. 1489 The following sections discuss the OMNI interface forwarding 1490 algorithms for Clients, Proxys, Servers and Bridges. In the 1491 following discussion, a packet's destination address is said to 1492 "match" if it is the same as a cached address, or if it is covered by 1493 a cached prefix (which may be encoded in an LLA). 1495 3.10.1. Client Forwarding Algorithm 1497 When an IP packet enters a Client's OMNI interface from the network 1498 layer the Client searches for an asymmetric neighbor cache entry that 1499 matches the destination. If there is a match, the Client uses one or 1500 more "reachable" neighbor interfaces in the entry for packet 1501 forwarding. If there is no asymmetric neighbor cache entry, the 1502 Client instead forwards the packet toward a Server (the packet is 1503 intercepted by a Proxy if there is a Proxy on the path). The Client 1504 encapsulates the packet in OAL/ORH headers if necessary and fragments 1505 according to MTU requirements (see: Section 3.9). 1507 When an IP packet enters a Client's OMNI interface from the link- 1508 layer, if the destination matches one of the Client's MNPs or link- 1509 local addresses the Client reassembles and decapsulates as necessary 1510 and delivers the inner packet to the network layer. Otherwise, the 1511 Client drops the packet and MAY return a network-layer ICMP 1512 Destination Unreachable message subject to rate limiting (see: 1513 Section 3.11). 1515 3.10.2. Proxy Forwarding Algorithm 1517 For control messages originating from or destined to a Client, the 1518 Proxy intercepts the message and updates its proxy neighbor cache 1519 entry for the Client. The Proxy then forwards a (proxyed) copy of 1520 the control message. (For example, the Proxy forwards a proxied 1521 version of a Client's NS/RS message to the target neighbor, and 1522 forwards a proxied version of the NA/RA reply to the Client.) 1524 When the Proxy receives a data packet from a Client within the ANET, 1525 the Proxy reassembles and re-fragments if necessary then searches for 1526 an asymmetric neighbor cache entry that matches the destination and 1527 forwards as follows: 1529 o if the destination matches an asymmetric neighbor cache entry, the 1530 Proxy uses one or more "reachable" neighbor interfaces in the 1531 entry for packet forwarding using OAL/ORH encapsulation if 1532 necessary according to the cached link-layer address information. 1533 If the neighbor interface is in the same OMNI link segment, the 1534 Proxy forwards the packet directly to the neighbor; otherwise, it 1535 forwards the packet to a Bridge. 1537 o else, the Proxy uses OAL/ORH encapsulation and forwards the packet 1538 to a Bridge while using the DLA corresponding to the packet's 1539 destination as the destination address. 1541 When the Proxy receives an encapsulated data packet from an INET 1542 neighbor or from a secured tunnel from a Bridge, it accepts the 1543 packet only if data origin authentication succeeds and if there is a 1544 proxy neighbor cache entry that matches the inner destination. Next, 1545 the Proxy reassembles the packet (if necessary) and continues 1546 processing. If the reassembly is complete and the neighbor cache 1547 state is REACHABLE, the Proxy then returns a PTB if necessary (see: 1548 Section 3.9) then either drops or forwards the packet to the Client 1549 while performing OAL/ORH encapsulation and re-fragmentation if 1550 necessary. If the neighbor cache entry state is DEPARTED, the Proxy 1551 instead changes the destination address to the address of the new 1552 Server and forwards it to a Bridge while performing OAL/ORH re- 1553 fragmentation if necessary. 1555 3.10.3. Server/Relay Forwarding Algorithm 1557 For control messages destined to a target Client's LLA that are 1558 received from a secured tunnel, the Server intercepts the message and 1559 sends a Proxyed response on behalf of the Client. (For example, the 1560 Server sends a Proxyed NA message reply in response to an NS message 1561 directed to one of its associated Clients.) If the Client's neighbor 1562 cache entry is in the DEPARTED state, however, the Server instead 1563 forwards the packet to the Client's new Server as discussed in 1564 Section 3.16. 1566 When the Server receives an encapsulated data packet from an INET 1567 neighbor or from a secured tunnel, it accepts the packet only if data 1568 origin authentication succeeds. The Server then continues processing 1569 as follows: 1571 o if the network layer destination matches a symmetric neighbor 1572 cache entry in the REACHABLE state the Server prepares the packet 1573 for forwarding to the destination Client. The Server first 1574 reassembles (if necessary) and forwards the packet (while re- 1575 fragmenting if necessary) as specified in Section 3.9. 1577 o else, if the destination matches a symmetric neighbor cache entry 1578 in the DEPARETED state the Server re-encapsulates the packet and 1579 forwards it using the DLA of the Client's new Server as the 1580 destination. 1582 o else, if the destination matches an asymmetric neighbor cache 1583 entry, the Server uses one or more "reachable" neighbor interfaces 1584 in the entry for packet forwarding via the local INET if the 1585 neighbor is in the same OMNI link segment or using OAL/ORH 1586 encapsulation if necessary with the final destination set to the 1587 neighbor's DLA otherwise. 1589 o else, if the destination matches a non-MNP route in the IP 1590 forwarding table or an LLA assigned to the Server's OMNI 1591 interface, the Server reassembles if necessary, decapsulates the 1592 packet and releases it to the network layer for local delivery or 1593 IP forwarding. 1595 o else, the Server drops the packet. 1597 When the Server's OMNI interface receives a data packet from the 1598 network layer or from a VPNed or Direct Client, it performs OAL/ORH 1599 encapsulation and fragmentation if necessary, then processes the 1600 packet according to the network-layer destination address as follows: 1602 o if the destination matches a symmetric or asymmetric neighbor 1603 cache entry the Server processes the packet as above. 1605 o else, the Server encapsulates the packet in OLA/ORH headers and 1606 forwards it to a Bridge using its own DLA as the source and the 1607 DLA corresponding to the destination as the destination. 1609 3.10.4. Bridge Forwarding Algorithm 1611 Bridges forward OAL/ORH-encapsulated packets over secured tunnels the 1612 same as any IP router. When the Bridge receives an OAL/ORH- 1613 encapsulated packet via a secured tunnel, it removes the outer INET 1614 header and searches for a forwarding table entry that matches the 1615 destination address. The Bridge then processes the packet as 1616 follows: 1618 o if the destination matches its DLA Subnet Router Anycast address, 1619 the Bridge checks for an ORH. If there is an ORH with SRT/LHS 1620 located on the local segment, the Bridge removes the ORH from the 1621 packet. The Bridge also writes the saved IPv6 destination address 1622 from the ORH into the OAL header destination address if the OAL 1623 header is present, else, into the packet's IPv6 destination 1624 address. Next, the Bridge examines the FMT to determine if the 1625 target is behind a NAT. If no NAT is indicated, the Bridge 1626 forwards the packet directly to the L2ADDR using link-layer (UDP/ 1627 IP) encapsulation. If a NAT is indicated, the Bridge MAY perform 1628 NAT traversal procedures by sending bubbles per [RFC4380]. The 1629 Bridge then either applies AERO route optimization if NAT 1630 traversal procedures have been successfully applied, or forwards 1631 the packet directly to the Server indicated by the SR/LHS values. 1633 o if the destination matches one of the Bridge's own addresses, the 1634 Bridge submits the packet for local delivery. 1636 o else, if the destination matches a forwarding table entry the 1637 Bridge forwards the packet via a secured tunnel to the next hop. 1638 If the destination matches an MSP without matching an MNP, 1639 however, the Bridge instead drops the packet and returns an ICMP 1640 Destination Unreachable message subject to rate limiting (see: 1641 Section 3.11). 1643 o else, the Bridge drops the packet and returns an ICMP Destination 1644 Unreachable as above. 1646 As for any IP router, the Bridge decrements the TTL/Hop Limit when it 1647 forwards the packet. Therefore, when an OAL header is present only 1648 the Hop Limit in the OAL header is decremented and not the TTL/Hop 1649 Limit in the inner packet header. Bridges do not insert OAL/ORH 1650 headers themselves; instead, they act as IPv6 routers and forward 1651 packets based on the destination address found in the headers of 1652 packets they receive. 1654 3.11. OMNI Interface Error Handling 1656 When an AERO node admits a packet into the OMNI interface, it may 1657 receive link-layer or network-layer error indications. 1659 A link-layer error indication is an ICMP error message generated by a 1660 router in the INET on the path to the neighbor or by the neighbor 1661 itself. The message includes an IP header with the address of the 1662 node that generated the error as the source address and with the 1663 link-layer address of the AERO node as the destination address. 1665 The IP header is followed by an ICMP header that includes an error 1666 Type, Code and Checksum. Valid type values include "Destination 1667 Unreachable", "Time Exceeded" and "Parameter Problem" 1668 [RFC0792][RFC4443]. (OMNI interfaces ignore all link-layer IPv4 1669 "Fragmentation Needed" and IPv6 "Packet Too Big" messages since they 1670 only emit packets that are guaranteed to be no larger than the IP 1671 minimum link MTU as discussed in Section 3.9.) 1673 The ICMP header is followed by the leading portion of the packet that 1674 generated the error, also known as the "packet-in-error". For 1675 ICMPv6, [RFC4443] specifies that the packet-in-error includes: "As 1676 much of invoking packet as possible without the ICMPv6 packet 1677 exceeding the minimum IPv6 MTU" (i.e., no more than 1280 bytes). For 1678 ICMPv4, [RFC0792] specifies that the packet-in-error includes: 1679 "Internet Header + 64 bits of Original Data Datagram", however 1680 [RFC1812] Section 4.3.2.3 updates this specification by stating: "the 1681 ICMP datagram SHOULD contain as much of the original datagram as 1682 possible without the length of the ICMP datagram exceeding 576 1683 bytes". 1685 The link-layer error message format is shown in Figure 6 (where, "L2" 1686 and "L3" refer to link-layer and network-layer, respectively): 1688 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1689 ~ ~ 1690 | L2 IP Header of | 1691 | error message | 1692 ~ ~ 1693 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1694 | L2 ICMP Header | 1695 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 1696 ~ ~ P 1697 | IP and other encapsulation | a 1698 | headers of original L3 packet | c 1699 ~ ~ k 1700 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ e 1701 ~ ~ t 1702 | IP header of | 1703 | original L3 packet | i 1704 ~ ~ n 1705 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1706 ~ ~ e 1707 | Upper layer headers and | r 1708 | leading portion of body | r 1709 | of the original L3 packet | o 1710 ~ ~ r 1711 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 1713 Figure 6: OMNI Interface Link-Layer Error Message Format 1715 The AERO node rules for processing these link-layer error messages 1716 are as follows: 1718 o When an AERO node receives a link-layer Parameter Problem message, 1719 it processes the message the same as described as for ordinary 1720 ICMP errors in the normative references [RFC0792][RFC4443]. 1722 o When an AERO node receives persistent link-layer Time Exceeded 1723 messages, the IP ID field may be wrapping before earlier fragments 1724 awaiting reassembly have been processed. In that case, the node 1725 should begin including integrity checks and/or institute rate 1726 limits for subsequent packets. 1728 o When an AERO node receives persistent link-layer Destination 1729 Unreachable messages in response to encapsulated packets that it 1730 sends to one of its asymmetric neighbor correspondents, the node 1731 should process the message as an indication that a path may be 1732 failing, and optionally initiate NUD over that path. If it 1733 receives Destination Unreachable messages over multiple paths, the 1734 node should allow future packets destined to the correspondent to 1735 flow through a default route and re-initiate route optimization. 1737 o When an AERO Client receives persistent link-layer Destination 1738 Unreachable messages in response to encapsulated packets that it 1739 sends to one of its symmetric neighbor Servers, the Client should 1740 mark the path as unusable and use another path. If it receives 1741 Destination Unreachable messages on many or all paths, the Client 1742 should associate with a new Server and release its association 1743 with the old Server as specified in Section 3.16.5. 1745 o When an AERO Server receives persistent link-layer Destination 1746 Unreachable messages in response to encapsulated packets that it 1747 sends to one of its symmetric neighbor Clients, the Server should 1748 mark the underlying path as unusable and use another underlying 1749 path. 1751 o When an AERO Server or Proxy receives link-layer Destination 1752 Unreachable messages in response to an encapsulated packet that it 1753 sends to one of its permanent neighbors, it treats the messages as 1754 an indication that the path to the neighbor may be failing. 1755 However, the dynamic routing protocol should soon reconverge and 1756 correct the temporary outage. 1758 When an AERO Bridge receives a packet for which the network-layer 1759 destination address is covered by an MSP, if there is no more- 1760 specific routing information for the destination the Bridge drops the 1761 packet and returns a network-layer Destination Unreachable message 1762 subject to rate limiting. The Bridge writes the network-layer source 1763 address of the original packet as the destination address and uses 1764 one of its non link-local addresses as the source address of the 1765 message. 1767 When an AERO node receives an encapsulated packet for which the 1768 reassembly buffer it too small, it drops the packet and returns a 1769 network-layer Packet Too Big (PTB) message. The node first writes 1770 the MRU value into the PTB message MTU field, writes the network- 1771 layer source address of the original packet as the destination 1772 address and writes one of its non link-local addresses as the source 1773 address. 1775 3.12. AERO Router Discovery, Prefix Delegation and Autoconfiguration 1777 AERO Router Discovery, Prefix Delegation and Autoconfiguration are 1778 coordinated as discussed in the following Sections. 1780 3.12.1. AERO Service Model 1782 Each AERO Server on the OMNI link is configured to facilitate Client 1783 prefix delegation/registration requests. Each Server is provisioned 1784 with a database of MNP-to-Client ID mappings for all Clients enrolled 1785 in the AERO service, as well as any information necessary to 1786 authenticate each Client. The Client database is maintained by a 1787 central administrative authority for the OMNI link and securely 1788 distributed to all Servers, e.g., via the Lightweight Directory 1789 Access Protocol (LDAP) [RFC4511], via static configuration, etc. 1790 Clients receive the same service regardless of the Servers they 1791 select. 1793 AERO Clients and Servers use ND messages to maintain neighbor cache 1794 entries. AERO Servers configure their OMNI interfaces as advertising 1795 NBMA interfaces, and therefore send unicast RA messages with a short 1796 Router Lifetime value (e.g., ReachableTime seconds) in response to a 1797 Client's RS message. Thereafter, Clients send additional RS messages 1798 to keep Server state alive. 1800 AERO Clients and Servers include prefix delegation and/or 1801 registration parameters in RS/RA messages (see 1802 [I-D.templin-6man-omni-interface]). The ND messages are exchanged 1803 between Client and Server according to the prefix management schedule 1804 required by the service. If the Client knows its MNP in advance, it 1805 can employ prefix registration by including its LLA as the source 1806 address of an RS message and with an OMNI option with valid prefix 1807 registration information for the MNP. If the Server (and Proxy) 1808 accept the Client's MNP assertion, they inject the prefix into the 1809 routing system and establish the necessary neighbor cache state. 1811 The following sections specify the Client and Server behavior. 1813 3.12.2. AERO Client Behavior 1815 AERO Clients discover the addresses of Servers in a similar manner as 1816 described in [RFC5214]. Discovery methods include static 1817 configuration (e.g., from a flat-file map of Server addresses and 1818 locations), or through an automated means such as Domain Name System 1819 (DNS) name resolution [RFC1035]. Alternatively, the Client can 1820 discover Server addresses through a layer 2 data link login exchange, 1821 or through a unicast RA response to a multicast/anycast RS as 1822 described below. In the absence of other information, the Client can 1823 resolve the DNS Fully-Qualified Domain Name (FQDN) 1824 "linkupnetworks.[domainname]" where "linkupnetworks" is a constant 1825 text string and "[domainname]" is a DNS suffix for the OMNI link 1826 (e.g., "example.com"). 1828 To associate with a Server, the Client acts as a requesting router to 1829 request MNPs. The Client prepares an RS message with prefix 1830 management parameters and includes a Nonce and Timestamp option if 1831 the Client needs to correlate RA replies. If the Client already 1832 knows the Server's LLA, it includes the LLA as the network-layer 1833 destination address; otherwise, it includes (link-local) All-Routers 1834 multicast as the network-layer destination. If the Client already 1835 knows its own LLA, it uses the LLA as the network-layer source 1836 address; otherwise, it uses an OMNI Temporary LLA as the network- 1837 layer source address and includes a DHCP Unique Identifier (DUID) 1838 sub-option in the OMNI option (see: 1839 [I-D.templin-6man-omni-interface]). 1841 The Client next includes an OMNI option in the RS message to register 1842 its link-layer information with the Server. The Client sets the OMNI 1843 option prefix registration information according to the MNP, and 1844 includes Interface Attributes corresponding to the underlying 1845 interface over which the Client will send the RS message. The Client 1846 MAY include additional Interface Attributes specific to other 1847 underlying interfaces. 1849 The Client then sends the RS message (either directly via Direct 1850 interfaces, via a VPN for VPNed interfaces, via a Proxy for ANET 1851 interfaces or via INET encapsulation for INET interfaces) and waits 1852 for an RA message reply (see Section 3.12.3). The Client retries up 1853 to MAX_RTR_SOLICITATIONS times until an RA is received. If the 1854 Client receives no RAs, or if it receives an RA with Router Lifetime 1855 set to 0, the Client SHOULD abandon this Server and try another 1856 Server. Otherwise, the Client processes the prefix information found 1857 in the RA message. 1859 Next, the Client creates a symmetric neighbor cache entry with the 1860 Server's LLA as the network-layer address and the Server's 1861 encapsulation and/or link-layer addresses as the link-layer address. 1862 The Client records the RA Router Lifetime field value in the neighbor 1863 cache entry as the time for which the Server has committed to 1864 maintaining the MNP in the routing system via this underlying 1865 interface, and caches the other RA configuration information 1866 including Cur Hop Limit, M and O flags, Reachable Time and Retrans 1867 Timer. The Client then autoconfigures LLAs for each of the delegated 1868 MNPs and assigns them to the OMNI interface. The Client also caches 1869 any MSPs included in Route Information Options (RIOs) [RFC4191] as 1870 MSPs to associate with the OMNI link, and assigns the MTU value in 1871 the MTU option to the underlying interface. 1873 The Client then registers additional underlying interfaces with the 1874 Server by sending RS messages via each additional interface. The RS 1875 messages include the same parameters as for the initial RS/RA 1876 exchange, but with destination address set to the Server's LLA. 1878 Following autoconfiguration, the Client sub-delegates the MNPs to its 1879 attached EUNs and/or the Client's own internal virtual interfaces as 1880 described in [I-D.templin-v6ops-pdhost] to support the Client's 1881 downstream attached "Internet of Things (IoT)". The Client 1882 subsequently sends additional RS messages over each underlying 1883 interface before the Router Lifetime received for that interface 1884 expires. 1886 After the Client registers its underlying interfaces, it may wish to 1887 change one or more registrations, e.g., if an interface changes 1888 address or becomes unavailable, if QoS preferences change, etc. To 1889 do so, the Client prepares an RS message to send over any available 1890 underlying interface. The RS includes an OMNI option with prefix 1891 registration information specific to its MNP, with Interface 1892 Attributes specific to the selected underlying interface, and with 1893 any additional Interface Attributes specific to other underlying 1894 interfaces. When the Client receives the Server's RA response, it 1895 has assurance that the Server has been updated with the new 1896 information. 1898 If the Client wishes to discontinue use of a Server it issues an RS 1899 message over any underlying interface with an OMNI option with a 1900 prefix release indication. When the Server processes the message, it 1901 releases the MNP, sets the symmetric neighbor cache entry state for 1902 the Client to DEPARTED and returns an RA reply with Router Lifetime 1903 set to 0. After a short delay (e.g., 2 seconds), the Server 1904 withdraws the MNP from the routing system. 1906 3.12.3. AERO Server Behavior 1908 AERO Servers act as IP routers and support a prefix delegation/ 1909 registration service for Clients. Servers arrange to add their LLAs 1910 to a static map of Server addresses for the link and/or the DNS 1911 resource records for the FQDN "linkupnetworks.[domainname]" before 1912 entering service. Server addresses should be geographically and/or 1913 topologically referenced, and made available for discovery by Clients 1914 on the OMNI link. 1916 When a Server receives a prospective Client's RS message on its OMNI 1917 interface, it SHOULD return an immediate RA reply with Router 1918 Lifetime set to 0 if it is currently too busy or otherwise unable to 1919 service the Client. Otherwise, the Server authenticates the RS 1920 message and processes the prefix delegation/registration parameters. 1921 The Server first determines the correct MNPs to provide to the Client 1922 by searching the Client database. When the Server returns the MNPs, 1923 it also creates a forwarding table entry for the DLA corresponding to 1924 each MNP so that the MNPs are propagated into the routing system 1925 (see: Section 3.2.3). For IPv6, the Server creates an IPv6 1926 forwarding table entry for each MNP. For IPv4, the Server creates an 1927 IPv6 forwarding table entry with the IPv4-compatibility DLA prefix 1928 corresponding to the IPv4 address. 1930 The Server next creates a symmetric neighbor cache entry for the 1931 Client using the base LLA as the network-layer address and with 1932 lifetime set to no more than the smallest prefix lifetime. Next, the 1933 Server updates the neighbor cache entry by recording the information 1934 in each Interface Attributes sub-option in the RS OMNI option. The 1935 Server also records the actual OAL/INET addresses in the neighbor 1936 cache entry. 1938 Next, the Server prepares an RA message using its LLA as the network- 1939 layer source address and the network-layer source address of the RS 1940 message as the network-layer destination address. The Server sets 1941 the Router Lifetime to the time for which it will maintain both this 1942 underlying interface individually and the symmetric neighbor cache 1943 entry as a whole. The Server also sets Cur Hop Limit, M and O flags, 1944 Reachable Time and Retrans Timer to values appropriate for the OMNI 1945 link. The Server includes the MNPs, any other prefix management 1946 parameters and an OMNI option with no Interface Attributes. The 1947 Server then includes one or more RIOs that encode the MSPs for the 1948 OMNI link, plus an MTU option (see Section 3.9). The Server finally 1949 forwards the message to the Client using OAL/INET, INET, or NULL 1950 encapsulation as necessary. 1952 After the initial RS/RA exchange, the Server maintains a 1953 ReachableTime timer for each of the Client's underlying interfaces 1954 individually (and for the Client's symmetric neighbor cache entry 1955 collectively) set to expire after ReachableTime seconds. If the 1956 Client (or Proxy) issues additional RS messages, the Server sends an 1957 RA response and resets ReachableTime. If the Server receives an ND 1958 message with a prefix release indication it sets the Client's 1959 symmetric neighbor cache entry to the DEPARTED state and withdraws 1960 the MNP from the routing system after a short delay (e.g., 2 1961 seconds). If ReachableTime expires before a new RS is received on an 1962 individual underlying interface, the Server marks the interface as 1963 DOWN. If ReachableTime expires before any new RS is received on any 1964 individual underlying interface, the Server sets the symmetric 1965 neighbor cache entry state to STALE and sets a 10 second timer. If 1966 the Server has not received a new RS or ND message with a prefix 1967 release indication before the 10 second timer expires, it deletes the 1968 neighbor cache entry and withdraws the MNP from the routing system. 1970 The Server processes any ND messages pertaining to the Client and 1971 returns an NA/RA reply in response to solicitations. The Server may 1972 also issue unsolicited RA messages, e.g., with reconfigure parameters 1973 to cause the Client to renegotiate its prefix delegation/ 1974 registrations, with Router Lifetime set to 0 if it can no longer 1975 service this Client, etc. Finally, If the symmetric neighbor cache 1976 entry is in the DEPARTED state, the Server deletes the entry after 1977 DepartTime expires. 1979 Note: Clients SHOULD notify former Servers of their departures, but 1980 Servers are responsible for expiring neighbor cache entries and 1981 withdrawing routes even if no departure notification is received 1982 (e.g., if the Client leaves the network unexpectedly). Servers 1983 SHOULD therefore set Router Lifetime to ReachableTime seconds in 1984 solicited RA messages to minimize persistent stale cache information 1985 in the absence of Client departure notifications. A short Router 1986 Lifetime also ensures that proactive Client/Server RS/RA messaging 1987 will keep any NAT state alive (see above). 1989 Note: All Servers on an OMNI link MUST advertise consistent values in 1990 the RA Cur Hop Limit, M and O flags, Reachable Time and Retrans Timer 1991 fields the same as for any link, since unpredictable behavior could 1992 result if different Servers on the same link advertised different 1993 values. 1995 3.12.3.1. DHCPv6-Based Prefix Registration 1997 When a Client is not pre-provisioned with an OMNI LLA containing a 1998 MNP, it will need for the Server to select one or more MNPs on its 1999 behalf and set up the correct state in the AERO routing service. (A 2000 Client with a pre-provisioned MNP may also request the Server to 2001 select additional MNPs.) The DHCPv6 service [RFC8415] is used to 2002 support this requirement. 2004 When a Client needs to have the Server select MNPs, it sends an RS 2005 message with an OMNI option that includes a DHCPv6 message suboption 2006 with DHCPv6 Prefix Delegation (DHCPv6-PD) parameters. When the 2007 Server receives the RS message, it extracts the DHCPv6-PD message 2008 from the OMNI option. 2010 The Server then acts as a "Proxy DHCPv6 Client" in a message exchange 2011 with the locally-resident DHCPv6 server, which delegates MNPs and 2012 returns a DHCPv6-PD Reply message. (If the Server wishes to defer 2013 creation of MN state until the DHCPv6-PD Reply is received, it can 2014 instead act as a Lightweight DHCPv6 Relay Agent per [RFC6221] by 2015 encapsulating the DHCPv6-PD message in a Relay-forward/reply exchange 2016 with Relay Message and Interface ID options.) 2018 When the Server receives the DHCPv6-PD Reply, it adds a route to the 2019 routing system and creates an OMNI MN LLA based on the delegated MNP. 2020 The Server then sends an RA back to the Client with the (newly- 2021 created) OMNI MN LLA as the destination address and with the 2022 DHCPv6-PD Reply message coded in the OMNI option. When the Client 2023 receives the RA, it creates a default route, assigns the Subnet 2024 Router Anycast address and sets its OMNI LLA based on the delegated 2025 MNP. 2027 3.13. The AERO Proxy 2029 Clients may connect to protected-spectrum ANETs that employ physical 2030 and/or link-layer security services to facilitate communications to 2031 Servers in outside INETs. In that case, the ANET can employ an AERO 2032 Proxy. The Proxy is located at the ANET/INET border and listens for 2033 RS messages originating from or RA messages destined to ANET Clients. 2034 The Proxy acts on these control messages as follows: 2036 o when the Proxy receives an RS message from a new ANET Client, it 2037 first authenticates the message then examines the network-layer 2038 destination address. If the destination address is a Server's 2039 LLA, the Proxy proceeds to the next step. Otherwise, if the 2040 destination is (link-local) All-Routers multicast, the Proxy 2041 selects a "nearby" Server that is likely to be a good candidate to 2042 serve the Client and replaces the destination address with the 2043 Server's LLA. Next, the Proxy creates a proxy neighbor cache 2044 entry and caches the Client and Server link-layer addresses along 2045 with the OMNI option information and any other identifying 2046 information including Transaction IDs, Client Identifiers, Nonce 2047 values, etc. The Proxy finally encapsulates the (proxyed) RS 2048 message in an OAL header with source set to the Proxy's DLA and 2049 destination set to the Server's DLA. The Proxy also includes an 2050 OMNI header with an Interface Attributes option that includes its 2051 own INET address plus a unique Port Number for this Client, then 2052 forwards the message into the OMNI link spanning tree. 2054 o when the Server receives the RS, it authenticates the message then 2055 creates or updates a symmetric neighbor cache entry for the Client 2056 with the Proxy's DLA, INET address and Port Number as the link- 2057 layer address information. The Server then sends an RA message 2058 back to the Proxy via the spanning tree. 2060 o when the Proxy receives the RA, it authenticates the message and 2061 matches it with the proxy neighbor cache entry created by the RS. 2062 The Proxy then caches the prefix information as a mapping from the 2063 Client's MNPs to the Client's link-layer address, caches the 2064 Server's advertised Router Lifetime and sets the neighbor cache 2065 entry state to REACHABLE. The Proxy then optionally rewrites the 2066 Router Lifetime and forwards the (proxyed) message to the Client. 2067 The Proxy finally includes an MTU option (if necessary) with an 2068 MTU to use for the underlying ANET interface. 2070 After the initial RS/RA exchange, the Proxy forwards any Client data 2071 packets for which there is no matching asymmetric neighbor cache 2072 entry to a Bridge using OAL encapsulation with its own DLA as the 2073 source and the DLA corresponding to the Client as the destination. 2074 The Proxy instead forwards any Client data destined to an asymmetric 2075 neighbor cache target directly to the target according to the OAL/ 2076 link-layer information - the process of establishing asymmetric 2077 neighbor cache entries is specified in Section 3.14. 2079 While the Client is still attached to the ANET, the Proxy sends NS, 2080 RS and/or unsolicited NA messages to update the Server's symmetric 2081 neighbor cache entries on behalf of the Client and/or to convey QoS 2082 updates. This allows for higher-frequency Proxy-initiated RS/RA 2083 messaging over well-connected INET infrastructure supplemented by 2084 lower-frequency Client-initiated RS/RA messaging over constrained 2085 ANET data links. 2087 If the Server ceases to send solicited advertisements, the Proxy 2088 sends unsolicited RAs on the ANET interface with destination set to 2089 (link-local) All-Nodes multicast and with Router Lifetime set to zero 2090 to inform Clients that the Server has failed. Although the Proxy 2091 engages in ND exchanges on behalf of the Client, the Client can also 2092 send ND messages on its own behalf, e.g., if it is in a better 2093 position than the Proxy to convey QoS changes, etc. For this reason, 2094 the Proxy marks any Client-originated solicitation messages (e.g. by 2095 inserting a Nonce option) so that it can return the solicited 2096 advertisement to the Client instead of processing it locally. 2098 If the Client becomes unreachable, the Proxy sets the neighbor cache 2099 entry state to DEPARTED and retains the entry for DepartTime seconds. 2100 While the state is DEPARTED, the Proxy forwards any packets destined 2101 to the Client to a Bridge via OAL encapsulation with the Client's 2102 current Server as the destination. The Bridge in turn forwards the 2103 packets to the Client's current Server. When DepartTime expires, the 2104 Proxy deletes the neighbor cache entry and discards any further 2105 packets destined to this (now forgotten) Client. 2107 In some ANETs that employ a Proxy, the Client's MNP can be injected 2108 into the ANET routing system. In that case, the Client can send data 2109 messages without encapsulation so that the ANET routing system 2110 transports the unencapsulated packets to the Proxy. This can be very 2111 beneficial, e.g., if the Client connects to the ANET via low-end data 2112 links such as some aviation wireless links. 2114 If the first-hop ANET access router is on the same underlying link 2115 and recognizes the AERO/OMNI protocol, the Client can avoid 2116 encapsulation for both its control and data messages. When the 2117 Client connects to the link, it can send an unencapsulated RS message 2118 with source address set to its LLA and with destination address set 2119 to the LLA of the Client's selected Server or to (link-local) All- 2120 Routers multicast. The Client includes an OMNI option formatted as 2121 specified in [I-D.templin-6man-omni-interface]. 2123 The Client then sends the unencapsulated RS message, which will be 2124 intercepted by the AERO-Aware access router. The access router then 2125 encapsulates the RS message in an ANET header with its own address as 2126 the source address and the address of a Proxy as the destination 2127 address. The access router further remembers the address of the 2128 Proxy so that it can encapsulate future data packets from the Client 2129 via the same Proxy. If the access router needs to change to a new 2130 Proxy, it simply sends another RS message toward the Server via the 2131 new Proxy on behalf of the Client. 2133 In some cases, the access router and Proxy may be one and the same 2134 node. In that case, the node would be located on the same physical 2135 link as the Client, but its message exchanges with the Server would 2136 need to pass through a security gateway at the ANET/INET border. The 2137 method for deploying access routers and Proxys (i.e. as a single node 2138 or multiple nodes) is an ANET-local administrative consideration. 2140 3.13.1. Combined Proxy/Servers 2142 Clients may need to connect directly to Servers via INET, Direct and 2143 VPNed interfaces (i.e., non-ANET interfaces). If the Client's 2144 underlying interfaces all connect via the same INET partition, then 2145 it can connect to a single controlling Server via all interfaces. 2147 If some Client interfaces connect via different INET partitions, 2148 however, the Client still selects a set of controlling Servers and 2149 sends RS messages via their directly-connected Servers while using 2150 the LLA of the controlling Server as the destination. 2152 When a Server receives an RS with destination set to the LLA of a 2153 controlling Server, it acts as a Proxy to forward the message to the 2154 controlling Server while forwarding the corresponding RA reply to the 2155 Client. 2157 3.13.2. Detecting and Responding to Server Failures 2159 In environments where fast recovery from Server failure is required, 2160 Proxys SHOULD use proactive Neighbor Unreachability Detection (NUD) 2161 to track Server reachability in a similar fashion as for 2162 Bidirectional Forwarding Detection (BFD) [RFC5880]. Proxys can then 2163 quickly detect and react to failures so that cached information is 2164 re-established through alternate paths. The NUD control messaging is 2165 carried only over well-connected ground domain networks (i.e., and 2166 not low-end aeronautical radio links) and can therefore be tuned for 2167 rapid response. 2169 Proxys perform proactive NUD with Servers for which there are 2170 currently active ANET Clients by sending continuous NS messages in 2171 rapid succession, e.g., one message per second. The Proxy sends the 2172 NS message via the spanning tree with the Proxy's LLA as the source 2173 and the LLA of the Server as the destination. When the Proxy is also 2174 sending RS messages to the Server on behalf of ANET Clients, the 2175 resulting RA responses can be considered as equivalent hints of 2176 forward progress. This means that the Proxy need not also send a 2177 periodic NS if it has already sent an RS within the same period. If 2178 the Server fails (i.e., if the Proxy ceases to receive 2179 advertisements), the Proxy can quickly inform Clients by sending 2180 multicast RA messages on the ANET interface. 2182 The Proxy sends RA messages on the ANET interface with source address 2183 set to the Server's address, destination address set to (link-local) 2184 All-Nodes multicast, and Router Lifetime set to 0. The Proxy SHOULD 2185 send MAX_FINAL_RTR_ADVERTISEMENTS RA messages separated by small 2186 delays [RFC4861]. Any Clients on the ANET that had been using the 2187 failed Server will receive the RA messages and associate with a new 2188 Server. 2190 3.13.3. Point-to-Multipoint Server Coordination 2192 In environments where Client messaging over ANETs is bandwidth- 2193 limited and/or expensive, Clients can enlist the services of the 2194 Proxy to coordinate with multiple Servers in a single RS/RA message 2195 exchange. The Client can send a single RS message to (link-local) 2196 All-Routers multicast that includes the ID's of multiple Servers in 2197 MS-Register sub-options of the OMNI option. 2199 When the Proxy receives the RS and processes the OMNI option, it 2200 sends a separate RS to each MS-Register Server ID. When the Proxy 2201 receives an RA, it can optionally return an immediate "singleton" RA 2202 to the Client or record the Server's ID for inclusion in a pending 2203 "aggregate" RA message. The Proxy can then return aggregate RA 2204 messages to the Client including multiple Server IDs in order to 2205 conserve bandwidth. Each RA includes a proper subset of the Server 2206 IDs from the original RS message, and the Proxy must ensure that the 2207 message contents of each RA are consistent with the information 2208 received from the (aggregated) Servers. 2210 Clients can thereafter employ efficient point-to-multipoint Server 2211 coordination under the assistance of the Proxy to reduce the number 2212 of messages sent over the ANET while enlisting the support of 2213 multiple Servers for fault tolerance. Clients can further include 2214 MS-Release sub-options in IPv6 ND messages to request the Proxy to 2215 release from former Servers via the procedures discussed in 2216 Section 3.16.5. 2218 The OMNI interface specification [I-D.templin-6man-omni-interface] 2219 provides further discussion of the Client/Proxy RS/RA messaging 2220 involved in point-to-multipoint coordination. 2222 3.14. AERO Route Optimization / Address Resolution 2224 While data packets are flowing between a source and target node, 2225 route optimization SHOULD be used. Route optimization is initiated 2226 by the first eligible Route Optimization Source (ROS) closest to the 2227 source as follows: 2229 o For Clients on VPNed and Direct interfaces, the Server is the ROS. 2231 o For Clients on ANET interfaces, the Proxy is the ROS. 2233 o For Clients on INET interfaces, the Client itself is the ROS. 2235 o For correspondent nodes on INET/EUN interfaces serviced by a 2236 Relay, the Relay is the ROS. 2238 The route optimization procedure is conducted between the ROS and the 2239 target Server/Relay acting as a Route Optimization Responder (ROR) in 2240 the same manner as for IPv6 ND Address Resolution and using the same 2241 NS/NA messaging. The target may either be a MNP Client serviced by a 2242 Server, or a non-MNP correspondent reachable via a Relay. 2244 The procedures are specified in the following sections. 2246 3.14.1. Route Optimization Initiation 2248 While data packets are flowing from the source node toward a target 2249 node, the ROS performs address resolution by sending an NS message 2250 for Address Resolution (NS(AR)) to receive a solicited NA message 2251 from the ROR. When the ROS sends an NS(AR), it includes: 2253 o the LLA of the ROS as the source address. 2255 o the data packet's destination as the Target Address. 2257 o the Solicited-Node multicast address [RFC4291] formed from the 2258 lower 24 bits of the data packet's destination as the destination 2259 address, e.g., for 2001:db8:1:2::10:2000 the NS destination 2260 address is ff02:0:0:0:0:1:ff10:2000. 2262 The NS(AR) message includes an OMNI option with no Interface 2263 Attributes, such that the target will not create a neighbor cache 2264 entry. The Prefix Length in the OMNI option is set to the Prefix 2265 Length associated with the ROS's LLA. 2267 The ROS then encapsulates the NS(AR) message in an OAL header with 2268 source set to its own DLA and destination set to the DLA 2269 corresponding to the target, then sends the message into the spanning 2270 tree without decrementing the network-layer TTL/Hop Limit field. 2271 (When the ROS is a Client, it instead securely sends the NS(AR) to 2272 one of its current Servers by including an Authentication option per 2273 [RFC4380]. The Server then forwards the message into the spanning 2274 tree on behalf of the Client, while setting the IPv6 source address 2275 and the OAL source address to the LLA and DLA of the Client, 2276 respectively.) 2278 3.14.2. Relaying the NS 2280 When the Bridge receives the NS(AR) message from the ROS, it discards 2281 the INET header and determines that the ROR is the next hop by 2282 consulting its standard IPv6 forwarding table for the OAL header 2283 destination address. The Bridge then forwards the message toward the 2284 ROR via the spanning tree the same as for any IPv6 router. The 2285 final-hop Bridge in the spanning tree will deliver the message via a 2286 secured tunnel to the ROR. 2288 3.14.3. Processing the NS and Sending the NA 2290 When the ROR receives the NS(AR) message, it examines the Target 2291 Address to determine whether it has a neighbor cache entry and/or 2292 route that matches the target. If there is no match, the ROR drops 2293 the message. Otherwise, the ROR continues processing as follows: 2295 o if the target belongs to an MNP Client neighbor in the DEPARTED 2296 state the ROR changes the NS(AR) message OAL destination address 2297 to the DLA of the Client's new Server, forwards the message into 2298 the spanning tree and returns from processing. 2300 o If the target belongs to an MNP Client neighbor in the REACHABLE 2301 state, the ROR instead adds the AERO source address to the target 2302 Client's Report List with time set to ReportTime. 2304 o If the target belongs to a non-MNP route, the ROR continues 2305 processing without adding an entry to the Report List. 2307 The ROR then prepares a solicited NA message to send back to the ROS 2308 but does not create a neighbor cache entry. The ROR sets the NA 2309 source address to the LLA corresponding to the target, sets the 2310 Target Address to the target of the solicitation, and sets the 2311 destination address to the source of the solicitation. The ROR then 2312 includes an OMNI option with Prefix Length set to the length 2313 associated with the LLA. 2315 If the target is an MNP Client, the ROR next includes Interface 2316 Attributes in the OMNI option for each of the target Client's 2317 underlying interfaces with current information for each interface and 2318 with the S/T-ifIndex field in the OMNI header set to 0 to indicate 2319 that the message originated from the ROR and not the Client. 2321 For each Interface Attributes sub-option, the ROR sets the L2ADDR 2322 according to its own INET address for VPNed or Direct interfaces, to 2323 the INET address of the Proxy or to the Client's INET address for 2324 INET interfaces. The ROR then includes the lower 32 bits of its own 2325 DLA (or the DLA of the Proxy) as the LHS, encodes the DLA prefix 2326 length code in the SRT field and sets the FMT code accordingly as 2327 specified in Section 3.3. 2329 The ROR then sets the NA message R flag to 1 (as a router), S flag to 2330 1 (as a response to a solicitation), and O flag to 0 (as a proxy). 2331 The ROR finally encapsulates the NA message in an OAL header with 2332 source set to its own DLA and destination set to the source DLA of 2333 the NS(AR) message, then forwards the message into the spanning tree 2334 without decrementing the network-layer TTL/Hop Limit field. 2336 3.14.4. Relaying the NA 2338 When the Bridge receives the NA message from the ROR, it discards the 2339 INET header and determines that the ROS is the next hop by consulting 2340 its standard IPv6 forwarding table for the OAL header destination 2341 address. The Bridge then forwards the OAL-encapsulated NA message 2342 toward the ROS the same as for any IPv6 router. The final-hop Bridge 2343 in the spanning tree will deliver the message via a secured tunnel to 2344 the ROS. 2346 3.14.5. Processing the NA 2348 When the ROS receives the solicited NA message, it processes the 2349 message the same as for standard IPv6 Address Resolution [RFC4861]. 2350 In the process, it caches the source DLA then creates an asymmetric 2351 neighbor cache entry for the target and caches all information found 2352 in the OMNI option. The ROS finally sets the asymmetric neighbor 2353 cache entry lifetime to ReachableTime seconds. (When the ROS is a 2354 Client, the solicited NA message will first be delivered via the 2355 spanning tree to one of its current Servers, which then securely 2356 forwards the message to the Client by including an Authentication 2357 option per [RFC4380]. 2359 3.14.6. Route Optimization Maintenance 2361 Following route optimization, the ROS forwards future data packets 2362 destined to the target via the addresses found in the cached link- 2363 layer information. The route optimization is shared by all sources 2364 that send packets to the target via the ROS, i.e., and not just the 2365 source on behalf of which the route optimization was initiated. 2367 While new data packets destined to the target are flowing through the 2368 ROS, it sends additional NS(AR) messages to the ROR before 2369 ReachableTime expires to receive a fresh solicited NA message the 2370 same as described in the previous sections (route optimization 2371 refreshment strategies are an implementation matter, with a non- 2372 normative example given in Appendix A.1). The ROS uses the cached 2373 DLA of the ROR as the NS(AR) OAL destination address (i.e., instead 2374 of using the DLA corresponding to the target as was the case for the 2375 initial NS(AR)), and sends up to MAX_MULTICAST_SOLICIT NS(AR) 2376 messages separated by 1 second until an NA is received. If no NA is 2377 received, the ROS assumes that the current ROR has become unreachable 2378 and deletes the target neighbor cache entry. Subsequent data packets 2379 will trigger a new route optimization with an NS with OAL destination 2380 address set to the DLA corresponding to the target per Section 3.14.1 2381 to discover a new ROR while initial data packets travel over a 2382 suboptimal route. 2384 If an NA is received, the ROS then updates the asymmetric neighbor 2385 cache entry to refresh ReachableTime, while (for MNP destinations) 2386 the ROR adds or updates the ROS address to the target's Report List 2387 and with time set to ReportTime. While no data packets are flowing, 2388 the ROS instead allows ReachableTime for the asymmetric neighbor 2389 cache entry to expire. When ReachableTime expires, the ROS deletes 2390 the asymmetric neighbor cache entry. Any future data packets flowing 2391 through the ROS will again trigger a new route optimization. 2393 The ROS may also receive unsolicited NA messages from the ROR at any 2394 time (see: Section 3.16). If there is an asymmetric neighbor cache 2395 entry for the target, the ROS updates the link-layer information but 2396 does not update ReachableTime since the receipt of an unsolicited NA 2397 does not confirm that any forward paths are working. If there is no 2398 asymmetric neighbor cache entry, the ROS simply discards the 2399 unsolicited NA. 2401 In this arrangement, the ROS holds an asymmetric neighbor cache entry 2402 for the target via the ROR, but the ROR does not hold an asymmetric 2403 neighbor cache entry for the ROS. The route optimization neighbor 2404 relationship is therefore asymmetric and unidirectional. If the 2405 target node also has packets to send back to the source node, then a 2406 separate route optimization procedure is performed in the reverse 2407 direction. But, there is no requirement that the forward and reverse 2408 paths be symmetric. 2410 3.15. Neighbor Unreachability Detection (NUD) 2412 AERO nodes perform Neighbor Unreachability Detection (NUD) per 2413 [RFC4861] either reactively in response to persistent link-layer 2414 errors (see Section 3.11) or proactively to confirm reachability. 2415 The NUD algorithm is based on periodic control message exchanges. 2416 The algorithm may further be seeded by ND hints of forward progress, 2417 but care must be taken to avoid inferring reachability based on 2418 spoofed information. For example, authentic IPv6 ND message 2419 exchanges may be considered as acceptable hints of forward progress, 2420 while spurious data packets should not be. 2422 AERO Servers, Proxys and Relays can use (OAL-encapsulated) standard 2423 NS/NA NUD exchanges sent over the OMNI link spanning tree to securely 2424 test reachability without risk of DoS attacks from nodes pretending 2425 to be a neighbor (these NS/NA(NUD) messages use the unicast LLAs and 2426 DLAs of the two parties involved in the NUD test the same as for 2427 standard IPv6 ND). Proxys can further perform NUD to securely verify 2428 Server reachability on behalf of their proxyed Clients. However, a 2429 means for an ROS to test the unsecured forward directions of target 2430 route optimized paths is also necessary. 2432 When an ROR directs an ROS to a neighbor with one or more target 2433 link-layer addresses, the ROS can proactively test each such 2434 unsecured route optimized path by sending "loopback" NS(NUD) 2435 messages. While testing the paths, the ROS can optionally continue 2436 to send packets via the spanning tree, maintain a small queue of 2437 packets until target reachability is confirmed, or (optimistically) 2438 allow packets to flow via the route optimized paths. 2440 When the ROS sends a loopback NS(NUD) message, it uses its own LLA as 2441 both the IPv6 source and destination address, and the MNP Subnet- 2442 Router anycast address as the Target Address. The ROS includes a 2443 Nonce and Timestamp option, then encapsulates the message in OAL/INET 2444 headers with its own DLA as the source and the DLA of the route 2445 optimization target as the destination. The ROS then forwards the 2446 message to the target (either directly to the L2ADDR of the target if 2447 the target is in the same OMNI link segment, or via a Bridge if the 2448 target is in a different OMNI link segment). 2450 When the route optimization target receives the NS(NUD) message, it 2451 notices that the IPv6 destination address is the same as the source 2452 address. It then reverses the OAL header source and destination 2453 addresses and returns the message to the ROS (either directly or via 2454 the spanning tree). The route optimization target does not decrement 2455 the NS(NUD) message IPv6 Hop-Limit in the process, since the message 2456 has not exited the OMNI link. 2458 When the ROS receives the NS(NUD) message, it can determine from the 2459 Nonce, Timestamp and Target Address that the message originated from 2460 itself and that it transited the forward path. The ROS need not 2461 prepare an NA response, since the destination of the response would 2462 be itself and testing the route optimization path again would be 2463 redundant. 2465 The ROS marks route optimization target paths that pass these NUD 2466 tests as "reachable", and those that do not as "unreachable". These 2467 markings inform the OMNI interface forwarding algorithm specified in 2468 Section 3.10. 2470 Note that to avoid a DoS vector nodes MUST NOT return loopback 2471 NS(NUD) messages received from an unsecured link-layer source via the 2472 (secured) spanning tree. 2474 3.16. Mobility Management and Quality of Service (QoS) 2476 AERO is a Distributed Mobility Management (DMM) service. Each Server 2477 is responsible for only a subset of the Clients on the OMNI link, as 2478 opposed to a Centralized Mobility Management (CMM) service where 2479 there is a single network mobility collective entity for all Clients. 2480 Clients coordinate with their associated Servers via RS/RA exchanges 2481 to maintain the DMM profile, and the AERO routing system tracks all 2482 current Client/Server peering relationships. 2484 Servers provide default routing and mobility/multilink services for 2485 their dependent Clients. Clients are responsible for maintaining 2486 neighbor relationships with their Servers through periodic RS/RA 2487 exchanges, which also serves to confirm neighbor reachability. When 2488 a Client's underlying interface address and/or QoS information 2489 changes, the Client is responsible for updating the Server with this 2490 new information. Note that when there is a Proxy in the path, the 2491 Proxy can also perform some RS/RA exchanges on the Client's behalf. 2493 Mobility management messaging is based on the transmission and 2494 reception of unsolicited Neighbor Advertisement (uNA) messages. Each 2495 uNA message sets the IPv6 destination address to (link-local) All- 2496 Nodes multicast to convey a general update of Interface Attributes to 2497 (possibly) multiple recipients, or to a specific unicast LLA to 2498 announce a departure event to a specific recipient. Implementations 2499 must therefore examine the destination address to determine the 2500 nature of the mobility event (i.e., update vs departure). 2502 Mobility management considerations are specified in the following 2503 sections. 2505 3.16.1. Mobility Update Messaging 2507 Servers accommodate Client mobility, multilink and/or QoS change 2508 events by sending unsolicited NA (uNA) messages to each ROS in the 2509 target Client's Report List. When a Server sends a uNA message, it 2510 sets the IPv6 source address to the Client's LLA, sets the 2511 destination address to (link-local) All-Nodes multicast and sets the 2512 Target Address to the Client's Subnet-Router anycast address. The 2513 Server also includes an OMNI option with Prefix Length set to the 2514 length associated with the Client's LLA, with Interface Attributes 2515 for the target Client's underlying interfaces and with the OMNI 2516 header S/T-ifIndex set to 0. The Server then sets the NA R flag to 2517 1, the S flag to 0 and the O flag to 1, then encapsulates the message 2518 in an OAL header with source set to its own DLA and destination set 2519 to the DLA of the ROS and sends the message into the spanning tree. 2521 As discussed in Section 7.2.6 of [RFC4861], the transmission and 2522 reception of uNA messages is unreliable but provides a useful 2523 optimization. In well-connected Internetworks with robust data links 2524 uNA messages will be delivered with high probability, but in any case 2525 the Server can optionally send up to MAX_NEIGHBOR_ADVERTISEMENT uNAs 2526 to each ROS to increase the likelihood that at least one will be 2527 received. 2529 When the ROS receives a uNA message prepared as above, it ignores the 2530 message if there is no existing neighbor cache entry for the Client. 2531 Otherwise, it uses the included OMNI option information to update the 2532 neighbor cache entry, but does not reset ReachableTime since the 2533 receipt of an unsolicited NA message from the target Server does not 2534 provide confirmation that any forward paths to the target Client are 2535 working. 2537 If uNA messages are lost, the ROS may be left with stale address and/ 2538 or QoS information for the Client for up to ReachableTime seconds. 2539 During this time, the ROS can continue sending packets according to 2540 its stale neighbor cache information. When ReachableTime is close to 2541 expiring, the ROS will re-initiate route optimization and receive 2542 fresh link-layer address information. 2544 In addition to sending uNA messages to the current set of ROSs for 2545 the Client, the Server also sends uNAs to the DLA associated with the 2546 link-layer address for any underlying interface for which the link- 2547 layer address has changed. These uNA messages update an old Proxy/ 2548 Server that cannot easily detect (e.g., without active probing) when 2549 a formerly-active Client has departed. When the Server sends the 2550 uNA, it sets the IPv6 source address to the Client's LLA, sets the 2551 destination address to the old Proxy/Server's LLA, and sets the 2552 Target Address to the Client's Subnet-Router anycast address. The 2553 Server also includes an OMNI option with Prefix Length set to the 2554 length associated with the Client's LLA, with Interface Attributes 2555 for the changed underlying interface, and with the OMNI header S/ 2556 T-ifIndex set to 0. The Server then sets the NA R flag to 1, the S 2557 flag to 0 and the O flag to 1, then encapsulates the message in an 2558 OAL header with source set to its own DLA and destination set to the 2559 DLA of the old Proxy/Server and sends the message into the spanning 2560 tree. 2562 3.16.2. Announcing Link-Layer Address and/or QoS Preference Changes 2564 When a Client needs to change its underlying interface addresses and/ 2565 or QoS preferences (e.g., due to a mobility event), either the Client 2566 or its Proxys send RS messages to the Server via the spanning tree 2567 with an OMNI option that includes Interface attributes with the new 2568 link quality and address information. 2570 Up to MAX_RTR_SOLICITATIONS RS messages MAY be sent in parallel with 2571 sending actual data packets in case one or more RAs are lost. If all 2572 RAs are lost, the Client SHOULD re-associate with a new Server. 2574 When the Server receives the Client's changes, it sends uNA messages 2575 to all nodes in the Report List the same as described in the previous 2576 section. 2578 3.16.3. Bringing New Links Into Service 2580 When a Client needs to bring new underlying interfaces into service 2581 (e.g., when it activates a new data link), it sends an RS message to 2582 the Server via the underlying interface with an OMNI option that 2583 includes Interface Attributes with appropriate link quality values 2584 and with link-layer address information for the new link. 2586 3.16.4. Deactivating Existing Links 2588 When a Client needs to deactivate an existing underlying interface, 2589 it sends an RS or uNA message to its Server with an OMNI option with 2590 appropriate Interface Attribute values - in particular, the link 2591 quality value 0 assures that neighbors will cease to use the link. 2593 If the Client needs to send RS/uNA messages over an underlying 2594 interface other than the one being deactivated, it MUST include 2595 Interface Attributes with appropriate link quality values for any 2596 underlying interfaces being deactivated. 2598 Note that when a Client deactivates an underlying interface, 2599 neighbors that have received the RS/uNA messages need not purge all 2600 references for the underlying interface from their neighbor cache 2601 entries. The Client may reactivate or reuse the underlying interface 2602 and/or its ifIndex at a later point in time, when it will send RS/uNA 2603 messages with fresh Interface Attributes to update any neighbors. 2605 3.16.5. Moving Between Servers 2607 The Client performs the procedures specified in Section 3.12.2 when 2608 it first associates with a new Server or renews its association with 2609 an existing Server. The Client also includes MS-Release identifiers 2610 in the RS message OMNI option per [I-D.templin-6man-omni-interface] 2611 if it wants the new Server to notify any old Servers from which the 2612 Client is departing. 2614 When the new Server receives the Client's RS message, it returns an 2615 RA as specified in Section 3.12.3 and sends up to 2616 MAX_NEIGHBOR_ADVERTIISEMENT uNA messages to any old Servers listed in 2617 OMNI option MS-Release identifiers. When the new Server sends a uNA 2618 message, it sets the IPv6 source address to the Client's LLA, sets 2619 the destination address to the old Server's LLA, and sets the Target 2620 Address to the Client's Subnet-Router anycast address. The new 2621 Server also includes an OMNI option with Prefix Length set to the 2622 length associated with the Client's LLA, with Interface Attributes 2623 for its own underlying interface, and with the OMNI header S/ 2624 T-ifIndex set to 0. The new Server then sets the NA R flag to 1, the 2625 S flag to 0 and the O flag to 1, then encapsulates the message in an 2626 OAL header with source set to its own DLA and destination set to the 2627 DLA of the old Server and sends the message into the spanning tree. 2629 When an old Server receives the uNA, it changes the Client's neighbor 2630 cache entry state to DEPARTED, sets the link-layer address of the 2631 Client to the new Server's DLA, and resets DepartTime. After a short 2632 delay (e.g., 2 seconds) the old Server withdraws the Client's MNP 2633 from the routing system. After DepartTime expires, the old Server 2634 deletes the Client's neighbor cache entry. 2636 The old Server also iteratively forwards a copy of the uNA message to 2637 each ROS in the Client's Report List by changing the OAL destination 2638 address to the DLA of the ROS while leaving all other fields of the 2639 message unmodified. When the ROS receives the uNA, it examines the 2640 Target address to determine the correct asymmetric neighbor cache 2641 entry and verifies that the IPv6 destination address matches the old 2642 Server. The ROS then caches the IPv6 source address as the new 2643 Server for the existing asymmetric neighbor cache entry and marks the 2644 entry as STALE. While in the STALE state, the ROS allows new data 2645 packets to flow according to any existing cached link-layer 2646 information and sends new NS(AR) messages using its own DLA as the 2647 OAL source and the DLA of the new Server as the OAL destination 2648 address to elicit NA messages that reset the asymmetric neighbor 2649 cache entry state to REACHABLE. If no new NA message is received for 2650 10 seconds while in the STALE state, the ROS deletes the neighbor 2651 cache entry. 2653 Clients SHOULD NOT move rapidly between Servers in order to avoid 2654 causing excessive oscillations in the AERO routing system. Examples 2655 of when a Client might wish to change to a different Server include a 2656 Server that has gone unreachable, topological movements of 2657 significant distance, movement to a new geographic region, movement 2658 to a new OMNI link segment, etc. 2660 When a Client moves to a new Server, some of the fragments of a 2661 multiple fragment packet may have already arrived at the old Server 2662 while others are en route to the new Server, however no special 2663 attention in the reassembly algorithm is necessary when re-routed 2664 fragments are simply treated as loss. 2666 3.17. Multicast 2668 The AERO Client provides an IGMP (IPv4) [RFC2236] or MLD (IPv6) 2669 [RFC3810] proxy service for its EUNs and/or hosted applications 2670 [RFC4605]. The Client forwards IGMP/MLD messages over any of its 2671 underlying interfaces for which group membership is required. The 2672 IGMP/MLD messages may be further forwarded by a first-hop ANET access 2673 router acting as an IGMP/MLD-snooping switch [RFC4541], then 2674 ultimately delivered to an AERO Proxy/Server acting as a Protocol 2675 Independent Multicast - Sparse-Mode (PIM-SM, or simply "PIM") 2676 Designated Router (DR) [RFC7761]. AERO Relays also act as PIM 2677 routers (i.e., the same as AERO Proxys/Servers) on behalf of nodes on 2678 INET/EUN networks. The behaviors identified in the following 2679 sections correspond to Source-Specific Multicast (SSM) and Any-Source 2680 Multicast (ASM) operational modes. 2682 3.17.1. Source-Specific Multicast (SSM) 2684 When an ROS (i.e., an AERO Proxy/Server/Relay) "X" acting as PIM 2685 router receives a Join/Prune message from a node on its downstream 2686 interfaces containing one or more ((S)ource, (G)roup) pairs, it 2687 updates its Multicast Routing Information Base (MRIB) accordingly. 2688 For each S belonging to a prefix reachable via X's non-OMNI 2689 interfaces, X then forwards the (S, G) Join/Prune to any PIM routers 2690 on those interfaces per [RFC7761]. 2692 For each S belonging to a prefix reachable via X's OMNI interface, X 2693 originates a separate copy of the Join/Prune for each (S,G) in the 2694 message using its own LLA as the source address and ALL-PIM-ROUTERS 2695 as the destination address. X then encapsulates each message in an 2696 OAL header with source address set to the DLA of X and destination 2697 address set to S then forwards the message into the spanning tree, 2698 which delivers it to AERO Server/Relay "Y" that services S. At the 2699 same time, if the message was a Join, X sends a route-optimization NS 2700 message toward each S the same as discussed in Section 3.14. The 2701 resulting NAs will return the LLA for the prefix that matches S as 2702 the network-layer source address and with an OMNI option with the DLA 2703 corresponding to any underlying interfaces that are currently 2704 servicing S. 2706 When Y processes the Join/Prune message, if S located behind any 2707 INET, Direct, or VPNed interfaces Y acts as a PIM router and updates 2708 its MRIB to list X as the next hop in the reverse path. If S is 2709 located behind any Proxys "Z"*, Y also forwards the message to each 2710 Z* over the spanning tree while continuing to use the LLA of X as the 2711 source address. Each Z* then updates its MRIB accordingly and 2712 maintains the LLA of X as the next hop in the reverse path. Since 2713 the Bridges do not examine network layer control messages, this means 2714 that the (reverse) multicast tree path is simply from each Z* (and/or 2715 Y) to X with no other multicast-aware routers in the path. If any Z* 2716 (and/or Y) is located on the same OMNI link segment as X, the 2717 multicast data traffic sent to X directly using OAL/INET 2718 encapsulation instead of via a Bridge. 2720 Following the initial Join/Prune and NS/NA messaging, X maintains an 2721 asymmetric neighbor cache entry for each S the same as if X was 2722 sending unicast data traffic to S. In particular, X performs 2723 additional NS/NA exchanges to keep the neighbor cache entry alive for 2724 up to t_periodic seconds [RFC7761]. If no new Joins are received 2725 within t_periodic seconds, X allows the neighbor cache entry to 2726 expire. Finally, if X receives any additional Join/Prune messages 2727 for (S,G) it forwards the messages to each Y and Z* in the neighbor 2728 cache entry over the spanning tree. 2730 At some later time, Client C that holds an MNP for source S may 2731 depart from a first Proxy Z1 and/or connect via a new Proxy Z2. In 2732 that case, Y sends an unsolicited NA message to X the same as 2733 specified for unicast mobility in Section 3.16. When X receives the 2734 unsolicited NA message, it updates its asymmetric neighbor cache 2735 entry for the LLA for source S and sends new Join messages to any new 2736 Proxys Z2. There is no requirement to send any Prune messages to old 2737 Proxys Z1 since source S will no longer source any multicast data 2738 traffic via Z1. Instead, the multicast state for (S,G) in Proxy Z1 2739 will soon time out since no new Joins will arrive. 2741 After some later time, C may move to a new Server Y2 and depart from 2742 old Sever Y1. In that case, Y1 sends Join messages for any of C's 2743 active (S,G) groups to Y2 while including its own LLA as the source 2744 address. This causes Y2 to include Y1 in the multicast forwarding 2745 tree during the interim time that Y1's symmetric neighbor cache entry 2746 for C is in the DEPARTED state. At the same time, Y1 sends an 2747 unsolicited NA message to X with an OMNI option with S/T-ifIndex in 2748 the header set to 0 and a release indication to cause X to release 2749 its asymmetric neighbor cache entry. X then sends a new Join message 2750 to S via the spanning tree and re-initiates route optimization the 2751 same as if it were receiving a fresh Join message from a node on a 2752 downstream link. 2754 3.17.2. Any-Source Multicast (ASM) 2756 When an ROS X acting as a PIM router receives a Join/Prune from a 2757 node on its downstream interfaces containing one or more (*,G) pairs, 2758 it updates its Multicast Routing Information Base (MRIB) accordingly. 2759 X then forwards a copy of the message to the Rendezvous Point (RP) R 2760 for each G over the spanning tree. X uses its own LLA as the source 2761 address and ALL-PIM-ROUTERS as the destination address, then 2762 encapsulates each message in an OAL header with source address set to 2763 the DLA of X and destination address set to R, then sends the message 2764 into the spanning tree. At the same time, if the message was a Join 2765 X initiates NS/NA route optimization the same as for the SSM case 2766 discussed in Section 3.17.1. 2768 For each source S that sends multicast traffic to group G via R, the 2769 Proxy/Server Z* for the Client that aggregates S encapsulates the 2770 packets in PIM Register messages and forwards them to R via the 2771 spanning tree, which may then elect to send a PIM Join to Z*. This 2772 will result in an (S,G) tree rooted at Z* with R as the next hop so 2773 that R will begin to receive two copies of the packet; one native 2774 copy from the (S, G) tree and a second copy from the pre-existing (*, 2775 G) tree that still uses PIM Register encapsulation. R can then issue 2776 a PIM Register-stop message to suppress the Register-encapsulated 2777 stream. At some later time, if C moves to a new Proxy/Server Z*, it 2778 resumes sending packets via PIM Register encapsulation via the new 2779 Z*. 2781 At the same time, as multicast listeners discover individual S's for 2782 a given G, they can initiate an (S,G) Join for each S under the same 2783 procedures discussed in Section 3.17.1. Once the (S,G) tree is 2784 established, the listeners can send (S, G) Prune messages to R so 2785 that multicast packets for group G sourced by S will only be 2786 delivered via the (S, G) tree and not from the (*, G) tree rooted at 2787 R. All mobility considerations discussed for SSM apply. 2789 3.17.3. Bi-Directional PIM (BIDIR-PIM) 2791 Bi-Directional PIM (BIDIR-PIM) [RFC5015] provides an alternate 2792 approach to ASM that treats the Rendezvous Point (RP) as a Designated 2793 Forwarder (DF). Further considerations for BIDIR-PIM are out of 2794 scope. 2796 3.18. Operation over Multiple OMNI Links 2798 An AERO Client can connect to multiple OMNI links the same as for any 2799 data link service. In that case, the Client maintains a distinct 2800 OMNI interface for each link, e.g., 'omni0' for the first link, 2801 'omni1' for the second, 'omni2' for the third, etc. Each OMNI link 2802 would include its own distinct set of Bridges, Servers and Proxys, 2803 thereby providing redundancy in case of failures. 2805 Each OMNI link could utilize the same or different ANET connections. 2806 The links can be distinguished at the link-layer via the SRT prefix 2807 in a similar fashion as for Virtual Local Area Network (VLAN) tagging 2808 (e.g., IEEE 802.1Q) and/or through assignment of distinct sets of 2809 MSPs on each link. This gives rise to the opportunity for supporting 2810 multiple redundant networked paths, with each VLAN distinguished by a 2811 different SRT "color" (see: Section 3.2.5). 2813 The Client's IP layer can select the outgoing OMNI interface 2814 appropriate for a given traffic profile while (in the reverse 2815 direction) correspondent nodes must have some way of steering their 2816 packets destined to a target via the correct OMNI link. 2818 In a first alternative, if each OMNI link services different MSPs, 2819 then the Client can receive a distinct MNP from each of the links. 2820 IP routing will therefore assure that the correct Red/Green/Blue/etc. 2821 network is used for both outbound and inbound traffic. This can be 2822 accomplished using existing technologies and approaches, and without 2823 requiring any special supporting code in correspondent nodes or 2824 Bridges. 2826 In a second alternative, if each OMNI link services the same MSP(s) 2827 then each link could assign a distinct "OMNI link Anycast" address 2828 that is configured by all Bridges on the link. Correspondent nodes 2829 can then perform Segment Routing to select the correct SRT, which 2830 will then direct the packet over multiple hops to the target. 2832 3.19. DNS Considerations 2834 AERO Client MNs and INET correspondent nodes consult the Domain Name 2835 System (DNS) the same as for any Internetworking node. When 2836 correspondent nodes and Client MNs use different IP protocol versions 2837 (e.g., IPv4 correspondents and IPv6 MNs), the INET DNS must maintain 2838 A records for IPv4 address mappings to MNs which must then be 2839 populated in Relay NAT64 mapping caches. In that way, an IPv4 2840 correspondent node can send packets to the IPv4 address mapping of 2841 the target MN, and the Relay will translate the IPv4 header and 2842 destination address into an IPv6 header and IPv6 destination address 2843 of the MN. 2845 When an AERO Client registers with an AERO Server, the Server can 2846 return the address(es) of DNS servers in RDNSS options [RFC6106]. 2847 The DNS server provides the IP addresses of other MNs and 2848 correspondent nodes in AAAA records for IPv6 or A records for IPv4. 2850 3.20. Transition Considerations 2852 OAL encapsulation ensures that dissimilar INET partitions can be 2853 joined into a single unified OMNI link, even though the partitions 2854 themselves may have differing protocol versions and/or incompatible 2855 addressing plans. However, a commonality can be achieved by 2856 incrementally distributing globally routable (i.e., native) IP 2857 prefixes to eventually reach all nodes (both mobile and fixed) in all 2858 OMNI link segments. This can be accomplished by incrementally 2859 deploying AERO Relays on each INET partition, with each Relay 2860 distributing its MNPs and/or discovering non-MNP prefixes on its INET 2861 links. 2863 This gives rise to the opportunity to eventually distribute native IP 2864 addresses to all nodes, and to present a unified OMNI link view even 2865 if the INET partitions remain in their current protocol and 2866 addressing plans. In that way, the OMNI link can serve the dual 2867 purpose of providing a mobility/multilink service and a transition 2868 service. Or, if an INET partition is transitioned to a native IP 2869 protocol version and addressing scheme that is compatible with the 2870 OMNI link MNP-based addressing scheme, the partition and OMNI link 2871 can be joined by Relays. 2873 Relays that connect INETs/EUNs with dissimilar IP protocol versions 2874 may need to employ a network address and protocol translation 2875 function such as NAT64 [RFC6146]. 2877 3.21. Detecting and Reacting to Server and Bridge Failures 2879 In environments where rapid failure recovery is required, Servers and 2880 Bridges SHOULD use Bidirectional Forwarding Detection (BFD) 2881 [RFC5880]. Nodes that use BFD can quickly detect and react to 2882 failures so that cached information is re-established through 2883 alternate nodes. BFD control messaging is carried only over well- 2884 connected ground domain networks (i.e., and not low-end radio links) 2885 and can therefore be tuned for rapid response. 2887 Servers and Bridges maintain BFD sessions in parallel with their BGP 2888 peerings. If a Server or Bridge fails, BGP peers will quickly re- 2889 establish routes through alternate paths the same as for common BGP 2890 deployments. Similarly, Proxys maintain BFD sessions with their 2891 associated Bridges even though they do not establish BGP peerings 2892 with them. 2894 Proxys SHOULD use proactive NUD for Servers for which there are 2895 currently active ANET Clients in a manner that parallels BFD, i.e., 2896 by sending unicast NS messages in rapid succession to receive 2897 solicited NA messages. When the Proxy is also sending RS messages on 2898 behalf of ANET Clients, the RS/RA messaging can be considered as 2899 equivalent hints of forward progress. This means that the Proxy need 2900 not also send a periodic NS if it has already sent an RS within the 2901 same period. If a Server fails, the Proxy will cease to receive 2902 advertisements and can quickly inform Clients of the outage by 2903 sending multicast RA messages on the ANET interface. 2905 The Proxy sends multicast RA messages with source address set to the 2906 Server's address, destination address set to (link-local) All-Nodes 2907 multicast, and Router Lifetime set to 0. The Proxy SHOULD send 2908 MAX_FINAL_RTR_ADVERTISEMENTS RA messages separated by small delays 2909 [RFC4861]. Any Clients on the ANET interface that have been using 2910 the (now defunct) Server will receive the RA messages and associate 2911 with a new Server. 2913 3.22. AERO Clients on the Open Internet 2915 AERO Clients that connect to the open Internet via INET interfaces 2916 can establish a VPN or direct link to securely connect to a Server in 2917 a "tethered" arrangement with all of the Client's traffic transiting 2918 the Server. Alternatively, the Client can associate with an INET 2919 Server using UDP/IP encapsulation and asymmetric securing services as 2920 discussed in the following sections. 2922 When a Client's OMNI interface enables an INET underlying interface, 2923 it first determines whether the interface is likely to be behind a 2924 NAT. For IPv4, the Client assumes it is on the open Internet if the 2925 INET address is not a special-use IPv4 address per [RFC3330]. 2926 Similarly for IPv6, the Client assumes it is on the open Internet if 2927 the INET address is not a link-local [RFC4291] or unique-local 2928 [RFC4193] IPv6 address. 2930 The Client then prepares a UDP/IP-encapsulated RS message with IPv6 2931 source address set to its LLA, with IPv6 destination set to (link- 2932 local) All-Routers multicast and with an OMNI option with underlying 2933 interface attributes. If the Client believes that it is on the open 2934 Internet, it SHOULD include Interface Attributes with the L2ADDR used 2935 for INET encapsulation (otherwise, it MAY omit L2ADDR). If the 2936 underlying address is IPv4, the Client includes the Port Number and 2937 IPv4 address written in obfuscated form [RFC4380] as discussed in 2938 Section 3.3. If the underlying interface address is IPv6, the Client 2939 instead includes the Port Number and IPv6 address in obfuscated form. 2940 The Client finally includes an Authentication option per [RFC4380] to 2941 provide message authentication, sets the UDP/IP source to its INET 2942 address and UDP port, sets the UDP/IP destination to the Server's 2943 INET address and the AERO service port number (8060), then sends the 2944 message to the Server. 2946 When the Server receives the RS, it authenticates the message and 2947 registers the Client's MNP and INET interface information according 2948 to the OMNI option parameters. If the RS message includes an L2ADDR 2949 in the OMNI option, the Server compares the encapsulation IP address 2950 and UDP port number with the (unobfuscated) values. If the values 2951 are the same, the Server caches the Client's information as "INET" 2952 addresses meaning that the Client is likely to accept direct messages 2953 without requiring NAT traversal exchanges. If the values are 2954 different (or, if the OMNI option did not include an L2ADDR) the 2955 Server instead caches the Client's information as "NAT" addresses 2956 meaning that NAT traversal exchanges may be necessary. 2958 The Server then returns an RA message with IPv6 source and 2959 destination set corresponding to the addresses in the RS, and with an 2960 Authentication option per [RFC4380]. For IPv4, the Server also 2961 includes an Origin option per [RFC4380] with the mapped and 2962 obfuscated Port Number and IPv4 address observed in the encapsulation 2963 headers. For IPv6, the Server instead includes an IPv6 Origin option 2964 per Figure 7 with the mapped and obfuscated observed Port Number and 2965 IPv6 address (note that the value 0x02 in the second octet 2966 differentiates from other [RFC4380] option types). 2968 +--------+--------+-----------------+ 2969 | 0x00 | 0x02 | Origin port # | 2970 +--------+--------+-----------------+ 2971 ~ Origin IPv6 address ~ 2972 +-----------------------------------+ 2974 Figure 7: IPv6 Origin Option 2976 When the Client receives the RA message, it compares the mapped Port 2977 Number and IP address from the Origin option with its own address. 2978 If the addresses are the same, the Client assumes the open Internet / 2979 Cone NAT principle; if the addresses are different, the Client 2980 instead assumes that further qualification procedures are necessary 2981 to detect the type of NAT and proceeds according to standard 2982 [RFC4380] procedures. 2984 After the Client has registered its INET interfaces in such RS/RA 2985 exchanges it sends periodic RS messages to receive fresh RA messages 2986 before the Router Lifetime received on each INET interface expires. 2987 The Client also maintains default routes via its Servers, i.e., the 2988 same as described in earlier sections. 2990 When the Client sends messages to target IP addresses, it also 2991 invokes route optimization per Section 3.14 using IPv6 ND address 2992 resolution messaging. The Client sends the NS(AR) message to the 2993 Server wrapped in a UDP/IP header with an Authentication option with 2994 the NS source address set to the Client's LLA and destination address 2995 set to the target solicited node multicast address. The Server 2996 authenticates the message and sends a corresponding NS(AR) message 2997 over the spanning tree the same as if it were the ROS, but with the 2998 OAL source address set to the Server's DLA and destination set to the 2999 DLA of the target. When the ROR receives the NS(AR), it adds the 3000 Server's DLA and Client's LLA to the target's Report List, and 3001 returns an NA with OMNI option information for the target. The 3002 Server then returns a UDP/IP encapsulated NA message with an 3003 Authentication option to the Client. 3005 Following route optimization for targets in the same OMNI link 3006 segment, if the target's L2ADDR is on the open INET, the Client 3007 forwards data packets directly to the target INET address. If the 3008 target is behind a NAT, the Client first establishes NAT state for 3009 the L2ADDR using the "bubble" mechanisms specified in 3010 [RFC6081][RFC4380]. The Client continues to send data packets via 3011 its Server until NAT state is populated, then begins forwarding 3012 packets via the direct path through the NAT to the target. For 3013 targets in different OMNI link segments, the Client inserts an ORH 3014 and forwards data packets to the Bridge that returned the NA message. 3016 The ROR may return uNAs via the Server if the target moves, and the 3017 Server will send corresponding Authentication-protected uNAs to the 3018 Client. The Client can also send "loopback" NS(NUD) messages to test 3019 forward path reachability even though there is no security 3020 association between the Client and the target. 3022 The Client sends UDP/IP encapsulated IPv6 packets no larger than 1280 3023 bytes in one piece. In order to accommodate larger IPv6 packets (up 3024 to the OMNI interface MTU), the Client inserts an OAL header with 3025 source set to its own DLA and destination set to the DLA of the 3026 target and uses IPv6 fragmentation according to Section 3.9. The 3027 Client then encapsulates each fragment in a UDP/IP header and sends 3028 the fragments to the next hop. 3030 3.23. Time-Varying MNPs 3032 In some use cases, it is desirable, beneficial and efficient for the 3033 Client to receive a constant MNP that travels with the Client 3034 wherever it moves. For example, this would allow air traffic 3035 controllers to easily track aircraft, etc. In other cases, however 3036 (e.g., intelligent transportation systems), the MN may be willing to 3037 sacrifice a modicum of efficiency in order to have time-varying MNPs 3038 that can be changed every so often to defeat adversarial tracking. 3040 The DHCPv6 service offers a way for Clients that desire time-varying 3041 MNPs to obtain short-lived prefixes (e.g., on the order of a small 3042 number of minutes). In that case, the identity of the Client would 3043 not be bound to the MNP but rather the Client's identity would be 3044 bound to the DHCPv6 Device Unique Identifier (DUID) and used as the 3045 seed for Prefix Delegation. The Client would then be obligated to 3046 renumber its internal networks whenever its MNP (and therefore also 3047 its LLA) changes. This should not present a challenge for Clients 3048 with automated network renumbering services, however presents limits 3049 for the durations of ongoing sessions that would prefer to use a 3050 constant address. 3052 4. Implementation Status 3054 An early AERO implementation based on OpenVPN (https://openvpn.net/) 3055 was announced on the v6ops mailing list on January 10, 2018 and an 3056 initial public release of the AERO proof-of-concept source code was 3057 announced on the intarea mailing list on August 21, 2015. 3059 AERO Release-3.0.2 was tagged on October 15, 2020, and is undergoing 3060 internal testing. Additional releases expected Q42020, with first 3061 public release expected before year-end. 3063 5. IANA Considerations 3065 The IANA has assigned a 4-octet Private Enterprise Number "45282" for 3066 AERO in the "enterprise-numbers" registry. 3068 The IANA has assigned the UDP port number "8060" for an earlier 3069 experimental version of AERO [RFC6706]. This document obsoletes 3070 [RFC6706] and claims the UDP port number "8060" for all future use. 3072 The IANA is instructed to assign a new type value TBD in the IPv6 3073 Routing Types registry. 3075 No further IANA actions are required. 3077 6. Security Considerations 3079 AERO Bridges configure secured tunnels with AERO Servers, Relays and 3080 Proxys within their local OMNI link segments. Applicable secured 3081 tunnel alternatives include IPsec [RFC4301], TLS/SSL [RFC8446], DTLS 3082 [RFC6347], WireGuard [WG], etc. The AERO Bridges of all OMNI link 3083 segments in turn configure secured tunnels for their neighboring AERO 3084 Bridges in a spanning tree topology. Therefore, control messages 3085 exchanged between any pair of OMNI link neighbors on the spanning 3086 tree are already secured. 3088 AERO Servers, Relays and Proxys targeted by a route optimization may 3089 also receive data packets directly from arbitrary nodes in INET 3090 partitions instead of via the spanning tree. For INET partitions 3091 that apply effective ingress filtering to defeat source address 3092 spoofing, the simple data origin authentication procedures in 3093 Section 3.8 can be applied. 3095 For INET partitions that require strong security in the data plane, 3096 two options for securing communications include 1) disable route 3097 optimization so that all traffic is conveyed over secured tunnels, or 3098 2) enable on-demand secure tunnel creation between INET partition 3099 neighbors. Option 1) would result in longer routes than necessary 3100 and traffic concentration on critical infrastructure elements. 3101 Option 2) could be coordinated by establishing a secured tunnel on- 3102 demand instead of performing an NS/NA exchange in the route 3103 optimization procedures. Procedures for establishing on-demand 3104 secured tunnels are out of scope. 3106 AERO Clients that connect to secured ANETs need not apply security to 3107 their ND messages, since the messages will be intercepted by a 3108 perimeter Proxy that applies security on its INET-facing interface as 3109 part of the spanning tree (see above). AERO Clients connected to the 3110 open INET can use symmetric network and/or transport layer security 3111 services such as VPNs or can by some other means establish a direct 3112 link. When a VPN or direct link may be impractical, however, an 3113 asymmetric security service such as the Authentication option 3114 specified in [RFC4380] should be applied. The Authentication option 3115 requires a unique Client identifier, which can be obtained per the 3116 Universally Unique IDentifier (UUID) [RFC4122] service and also used 3117 as a DHCP Unique Identifier (DUID) per [RFC6355]. 3119 Application endpoints SHOULD use application-layer security services 3120 such as TLS/SSL, DTLS or SSH [RFC4251] to assure the same level of 3121 protection as for critical secured Internet services. AERO Clients 3122 that require host-based VPN services SHOULD use symmetric network 3123 and/or transport layer security services such as IPsec, TLS/SSL, 3124 DTLS, etc. AERO Proxys and Servers can also provide a network-based 3125 VPN service on behalf of the Client, e.g., if the Client is located 3126 within a secured enclave and cannot establish a VPN on its own 3127 behalf. 3129 AERO Servers and Bridges present targets for traffic amplification 3130 Denial of Service (DoS) attacks. This concern is no different than 3131 for widely-deployed VPN security gateways in the Internet, where 3132 attackers could send spoofed packets to the gateways at high data 3133 rates. This can be mitigated by connecting Servers and Bridges over 3134 dedicated links with no connections to the Internet and/or when 3135 connections to the Internet are only permitted through well-managed 3136 firewalls. Traffic amplification DoS attacks can also target an AERO 3137 Client's low data rate links. This is a concern not only for Clients 3138 located on the open Internet but also for Clients in secured 3139 enclaves. AERO Servers and Proxys can institute rate limits that 3140 protect Clients from receiving packet floods that could DoS low data 3141 rate links. 3143 AERO Relays must implement ingress filtering to avoid a spoofing 3144 attack in which spurious messages with DLA addresses are injected 3145 into an OMNI link from an outside attacker. AERO Clients MUST ensure 3146 that their connectivity is not used by unauthorized nodes on their 3147 EUNs to gain access to a protected network, i.e., AERO Clients that 3148 act as routers MUST NOT provide routing services for unauthorized 3149 nodes. (This concern is no different than for ordinary hosts that 3150 receive an IP address delegation but then "share" the address with 3151 other nodes via some form of Internet connection sharing such as 3152 tethering.) 3154 The MAP list MUST be well-managed and secured from unauthorized 3155 tampering, even though the list contains only public information. 3156 The MAP list can be conveyed to the Client in a similar fashion as in 3157 [RFC5214] (e.g., through layer 2 data link login messaging, secure 3158 upload of a static file, DNS lookups, etc.). 3160 SRH authentication facilities are specified in [RFC8754]. 3162 Security considerations for accepting link-layer ICMP messages and 3163 reflected packets are discussed throughout the document. 3165 Security considerations for IPv6 fragmentation and reassembly are 3166 discussed in [I-D.templin-6man-omni-interface]. 3168 7. Acknowledgements 3170 Discussions in the IETF, aviation standards communities and private 3171 exchanges helped shape some of the concepts in this work. 3172 Individuals who contributed insights include Mikael Abrahamsson, Mark 3173 Andrews, Fred Baker, Bob Braden, Stewart Bryant, Brian Carpenter, 3174 Wojciech Dec, Pavel Drasil, Ralph Droms, Adrian Farrel, Nick Green, 3175 Sri Gundavelli, Brian Haberman, Bernhard Haindl, Joel Halpern, Tom 3176 Herbert, Sascha Hlusiak, Lee Howard, Zdenek Jaron, Andre Kostur, 3177 Hubert Kuenig, Ted Lemon, Andy Malis, Satoru Matsushima, Tomek 3178 Mrugalski, Madhu Niraula, Alexandru Petrescu, Behcet Saikaya, Michal 3179 Skorepa, Joe Touch, Bernie Volz, Ryuji Wakikawa, Tony Whyman, Lloyd 3180 Wood and James Woodyatt. Members of the IESG also provided valuable 3181 input during their review process that greatly improved the document. 3182 Special thanks go to Stewart Bryant, Joel Halpern and Brian Haberman 3183 for their shepherding guidance during the publication of the AERO 3184 first edition. 3186 This work has further been encouraged and supported by Boeing 3187 colleagues including Kyle Bae, M. Wayne Benson, Dave Bernhardt, Cam 3188 Brodie, John Bush, Balaguruna Chidambaram, Irene Chin, Bruce Cornish, 3189 Claudiu Danilov, Don Dillenburg, Joe Dudkowski, Wen Fang, Samad 3190 Farooqui, Anthony Gregory, Jeff Holland, Seth Jahne, Brian Jaury, 3191 Greg Kimberly, Ed King, Madhuri Madhava Badgandi, Laurel Matthew, 3192 Gene MacLean III, Rob Muszkiewicz, Sean O'Sullivan, Vijay 3193 Rajagopalan, Greg Saccone, Rod Santiago, Kent Shuey, Brian Skeen, 3194 Mike Slane, Carrie Spiker, Katie Tran, Brendan Williams, Amelia 3195 Wilson, Julie Wulff, Yueli Yang, Eric Yeh and other members of the 3196 Boeing mobility, networking and autonomy teams. Kyle Bae, Wayne 3197 Benson, Katie Tran and Eric Yeh are especially acknowledged for 3198 implementing the AERO functions as extensions to the public domain 3199 OpenVPN distribution. 3201 Earlier works on NBMA tunneling approaches are found in 3202 [RFC2529][RFC5214][RFC5569]. 3204 Many of the constructs presented in this second edition of AERO are 3205 based on the author's earlier works, including: 3207 o The Internet Routing Overlay Network (IRON) 3208 [RFC6179][I-D.templin-ironbis] 3210 o Virtual Enterprise Traversal (VET) 3211 [RFC5558][I-D.templin-intarea-vet] 3213 o The Subnetwork Encapsulation and Adaptation Layer (SEAL) 3214 [RFC5320][I-D.templin-intarea-seal] 3216 o AERO, First Edition [RFC6706] 3218 Note that these works cite numerous earlier efforts that are not also 3219 cited here due to space limitations. The authors of those earlier 3220 works are acknowledged for their insights. 3222 This work is aligned with the NASA Safe Autonomous Systems Operation 3223 (SASO) program under NASA contract number NNA16BD84C. 3225 This work is aligned with the FAA as per the SE2025 contract number 3226 DTFAWA-15-D-00030. 3228 This work is aligned with the Boeing Commercial Airplanes (BCA) 3229 Internet of Things (IoT) and autonomy programs. 3231 This work is aligned with the Boeing Information Technology (BIT) 3232 MobileNet program. 3234 8. References 3236 8.1. Normative References 3238 [I-D.templin-6man-omni-interface] 3239 Templin, F. and T. Whyman, "Transmission of IP Packets 3240 over Overlay Multilink Network (OMNI) Interfaces", draft- 3241 templin-6man-omni-interface-54 (work in progress), 3242 December 2020. 3244 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, 3245 DOI 10.17487/RFC0791, September 1981, 3246 . 3248 [RFC0792] Postel, J., "Internet Control Message Protocol", STD 5, 3249 RFC 792, DOI 10.17487/RFC0792, September 1981, 3250 . 3252 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 3253 Requirement Levels", BCP 14, RFC 2119, 3254 DOI 10.17487/RFC2119, March 1997, 3255 . 3257 [RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in 3258 IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473, 3259 December 1998, . 3261 [RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander, 3262 "SEcure Neighbor Discovery (SEND)", RFC 3971, 3263 DOI 10.17487/RFC3971, March 2005, 3264 . 3266 [RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)", 3267 RFC 3972, DOI 10.17487/RFC3972, March 2005, 3268 . 3270 [RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and 3271 More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191, 3272 November 2005, . 3274 [RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast 3275 Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005, 3276 . 3278 [RFC4380] Huitema, C., "Teredo: Tunneling IPv6 over UDP through 3279 Network Address Translations (NATs)", RFC 4380, 3280 DOI 10.17487/RFC4380, February 2006, 3281 . 3283 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 3284 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 3285 DOI 10.17487/RFC4861, September 2007, 3286 . 3288 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 3289 Address Autoconfiguration", RFC 4862, 3290 DOI 10.17487/RFC4862, September 2007, 3291 . 3293 [RFC6081] Thaler, D., "Teredo Extensions", RFC 6081, 3294 DOI 10.17487/RFC6081, January 2011, 3295 . 3297 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 3298 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 3299 May 2017, . 3301 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 3302 (IPv6) Specification", STD 86, RFC 8200, 3303 DOI 10.17487/RFC8200, July 2017, 3304 . 3306 [RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A., 3307 Richardson, M., Jiang, S., Lemon, T., and T. Winters, 3308 "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", 3309 RFC 8415, DOI 10.17487/RFC8415, November 2018, 3310 . 3312 8.2. Informative References 3314 [BGP] Huston, G., "BGP in 2015, http://potaroo.net", January 3315 2016. 3317 [I-D.bonica-6man-comp-rtg-hdr] 3318 Bonica, R., Kamite, Y., Alston, A., Henriques, D., and L. 3319 Jalil, "The IPv6 Compact Routing Header (CRH)", draft- 3320 bonica-6man-comp-rtg-hdr-23 (work in progress), October 3321 2020. 3323 [I-D.bonica-6man-crh-helper-opt] 3324 Li, X., Bao, C., Ruan, E., and R. Bonica, "Compressed 3325 Routing Header (CRH) Helper Option", draft-bonica-6man- 3326 crh-helper-opt-02 (work in progress), October 2020. 3328 [I-D.ietf-intarea-frag-fragile] 3329 Bonica, R., Baker, F., Huston, G., Hinden, R., Troan, O., 3330 and F. Gont, "IP Fragmentation Considered Fragile", draft- 3331 ietf-intarea-frag-fragile-17 (work in progress), September 3332 2019. 3334 [I-D.ietf-intarea-tunnels] 3335 Touch, J. and M. Townsley, "IP Tunnels in the Internet 3336 Architecture", draft-ietf-intarea-tunnels-10 (work in 3337 progress), September 2019. 3339 [I-D.ietf-rtgwg-atn-bgp] 3340 Templin, F., Saccone, G., Dawra, G., Lindem, A., and V. 3341 Moreno, "A Simple BGP-based Mobile Routing System for the 3342 Aeronautical Telecommunications Network", draft-ietf- 3343 rtgwg-atn-bgp-06 (work in progress), June 2020. 3345 [I-D.templin-6man-dhcpv6-ndopt] 3346 Templin, F., "A Unified Stateful/Stateless Configuration 3347 Service for IPv6", draft-templin-6man-dhcpv6-ndopt-10 3348 (work in progress), June 2020. 3350 [I-D.templin-intarea-seal] 3351 Templin, F., "The Subnetwork Encapsulation and Adaptation 3352 Layer (SEAL)", draft-templin-intarea-seal-68 (work in 3353 progress), January 2014. 3355 [I-D.templin-intarea-vet] 3356 Templin, F., "Virtual Enterprise Traversal (VET)", draft- 3357 templin-intarea-vet-40 (work in progress), May 2013. 3359 [I-D.templin-ironbis] 3360 Templin, F., "The Interior Routing Overlay Network 3361 (IRON)", draft-templin-ironbis-16 (work in progress), 3362 March 2014. 3364 [I-D.templin-v6ops-pdhost] 3365 Templin, F., "IPv6 Prefix Delegation and Multi-Addressing 3366 Models", draft-templin-v6ops-pdhost-26 (work in progress), 3367 June 2020. 3369 [OVPN] OpenVPN, O., "http://openvpn.net", October 2016. 3371 [RFC1035] Mockapetris, P., "Domain names - implementation and 3372 specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, 3373 November 1987, . 3375 [RFC1812] Baker, F., Ed., "Requirements for IP Version 4 Routers", 3376 RFC 1812, DOI 10.17487/RFC1812, June 1995, 3377 . 3379 [RFC2003] Perkins, C., "IP Encapsulation within IP", RFC 2003, 3380 DOI 10.17487/RFC2003, October 1996, 3381 . 3383 [RFC2236] Fenner, W., "Internet Group Management Protocol, Version 3384 2", RFC 2236, DOI 10.17487/RFC2236, November 1997, 3385 . 3387 [RFC2464] Crawford, M., "Transmission of IPv6 Packets over Ethernet 3388 Networks", RFC 2464, DOI 10.17487/RFC2464, December 1998, 3389 . 3391 [RFC2529] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4 3392 Domains without Explicit Tunnels", RFC 2529, 3393 DOI 10.17487/RFC2529, March 1999, 3394 . 3396 [RFC2983] Black, D., "Differentiated Services and Tunnels", 3397 RFC 2983, DOI 10.17487/RFC2983, October 2000, 3398 . 3400 [RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition 3401 of Explicit Congestion Notification (ECN) to IP", 3402 RFC 3168, DOI 10.17487/RFC3168, September 2001, 3403 . 3405 [RFC3330] IANA, "Special-Use IPv4 Addresses", RFC 3330, 3406 DOI 10.17487/RFC3330, September 2002, 3407 . 3409 [RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener 3410 Discovery Version 2 (MLDv2) for IPv6", RFC 3810, 3411 DOI 10.17487/RFC3810, June 2004, 3412 . 3414 [RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally 3415 Unique IDentifier (UUID) URN Namespace", RFC 4122, 3416 DOI 10.17487/RFC4122, July 2005, 3417 . 3419 [RFC4251] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH) 3420 Protocol Architecture", RFC 4251, DOI 10.17487/RFC4251, 3421 January 2006, . 3423 [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A 3424 Border Gateway Protocol 4 (BGP-4)", RFC 4271, 3425 DOI 10.17487/RFC4271, January 2006, 3426 . 3428 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 3429 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 3430 2006, . 3432 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 3433 Internet Protocol", RFC 4301, DOI 10.17487/RFC4301, 3434 December 2005, . 3436 [RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery 3437 Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April 3438 2006, . 3440 [RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet 3441 Control Message Protocol (ICMPv6) for the Internet 3442 Protocol Version 6 (IPv6) Specification", STD 89, 3443 RFC 4443, DOI 10.17487/RFC4443, March 2006, 3444 . 3446 [RFC4511] Sermersheim, J., Ed., "Lightweight Directory Access 3447 Protocol (LDAP): The Protocol", RFC 4511, 3448 DOI 10.17487/RFC4511, June 2006, 3449 . 3451 [RFC4541] Christensen, M., Kimball, K., and F. Solensky, 3452 "Considerations for Internet Group Management Protocol 3453 (IGMP) and Multicast Listener Discovery (MLD) Snooping 3454 Switches", RFC 4541, DOI 10.17487/RFC4541, May 2006, 3455 . 3457 [RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick, 3458 "Internet Group Management Protocol (IGMP) / Multicast 3459 Listener Discovery (MLD)-Based Multicast Forwarding 3460 ("IGMP/MLD Proxying")", RFC 4605, DOI 10.17487/RFC4605, 3461 August 2006, . 3463 [RFC4982] Bagnulo, M. and J. Arkko, "Support for Multiple Hash 3464 Algorithms in Cryptographically Generated Addresses 3465 (CGAs)", RFC 4982, DOI 10.17487/RFC4982, July 2007, 3466 . 3468 [RFC5015] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano, 3469 "Bidirectional Protocol Independent Multicast (BIDIR- 3470 PIM)", RFC 5015, DOI 10.17487/RFC5015, October 2007, 3471 . 3473 [RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site 3474 Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214, 3475 DOI 10.17487/RFC5214, March 2008, 3476 . 3478 [RFC5320] Templin, F., Ed., "The Subnetwork Encapsulation and 3479 Adaptation Layer (SEAL)", RFC 5320, DOI 10.17487/RFC5320, 3480 February 2010, . 3482 [RFC5522] Eddy, W., Ivancic, W., and T. Davis, "Network Mobility 3483 Route Optimization Requirements for Operational Use in 3484 Aeronautics and Space Exploration Mobile Networks", 3485 RFC 5522, DOI 10.17487/RFC5522, October 2009, 3486 . 3488 [RFC5558] Templin, F., Ed., "Virtual Enterprise Traversal (VET)", 3489 RFC 5558, DOI 10.17487/RFC5558, February 2010, 3490 . 3492 [RFC5569] Despres, R., "IPv6 Rapid Deployment on IPv4 3493 Infrastructures (6rd)", RFC 5569, DOI 10.17487/RFC5569, 3494 January 2010, . 3496 [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 3497 (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, 3498 . 3500 [RFC6106] Jeong, J., Park, S., Beloeil, L., and S. Madanapalli, 3501 "IPv6 Router Advertisement Options for DNS Configuration", 3502 RFC 6106, DOI 10.17487/RFC6106, November 2010, 3503 . 3505 [RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful 3506 NAT64: Network Address and Protocol Translation from IPv6 3507 Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146, 3508 April 2011, . 3510 [RFC6179] Templin, F., Ed., "The Internet Routing Overlay Network 3511 (IRON)", RFC 6179, DOI 10.17487/RFC6179, March 2011, 3512 . 3514 [RFC6221] Miles, D., Ed., Ooghe, S., Dec, W., Krishnan, S., and A. 3515 Kavanagh, "Lightweight DHCPv6 Relay Agent", RFC 6221, 3516 DOI 10.17487/RFC6221, May 2011, 3517 . 3519 [RFC6273] Kukec, A., Krishnan, S., and S. Jiang, "The Secure 3520 Neighbor Discovery (SEND) Hash Threat Analysis", RFC 6273, 3521 DOI 10.17487/RFC6273, June 2011, 3522 . 3524 [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer 3525 Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, 3526 January 2012, . 3528 [RFC6355] Narten, T. and J. Johnson, "Definition of the UUID-Based 3529 DHCPv6 Unique Identifier (DUID-UUID)", RFC 6355, 3530 DOI 10.17487/RFC6355, August 2011, 3531 . 3533 [RFC6438] Carpenter, B. and S. Amante, "Using the IPv6 Flow Label 3534 for Equal Cost Multipath Routing and Link Aggregation in 3535 Tunnels", RFC 6438, DOI 10.17487/RFC6438, November 2011, 3536 . 3538 [RFC6706] Templin, F., Ed., "Asymmetric Extended Route Optimization 3539 (AERO)", RFC 6706, DOI 10.17487/RFC6706, August 2012, 3540 . 3542 [RFC6935] Eubanks, M., Chimento, P., and M. Westerlund, "IPv6 and 3543 UDP Checksums for Tunneled Packets", RFC 6935, 3544 DOI 10.17487/RFC6935, April 2013, 3545 . 3547 [RFC6936] Fairhurst, G. and M. Westerlund, "Applicability Statement 3548 for the Use of IPv6 UDP Datagrams with Zero Checksums", 3549 RFC 6936, DOI 10.17487/RFC6936, April 2013, 3550 . 3552 [RFC7333] Chan, H., Ed., Liu, D., Seite, P., Yokota, H., and J. 3553 Korhonen, "Requirements for Distributed Mobility 3554 Management", RFC 7333, DOI 10.17487/RFC7333, August 2014, 3555 . 3557 [RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I., 3558 Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent 3559 Multicast - Sparse Mode (PIM-SM): Protocol Specification 3560 (Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March 3561 2016, . 3563 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 3564 Decraene, B., Litkowski, S., and R. Shakir, "Segment 3565 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 3566 July 2018, . 3568 [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol 3569 Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, 3570 . 3572 [RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J., 3573 Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header 3574 (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020, 3575 . 3577 [WG] Wireguard, "Wireguard, https://www.wireguard.com", August 3578 2020. 3580 Appendix A. Non-Normative Considerations 3582 AERO can be applied to a multitude of Internetworking scenarios, with 3583 each having its own adaptations. The following considerations are 3584 provided as non-normative guidance: 3586 A.1. Implementation Strategies for Route Optimization 3588 Route optimization as discussed in Section 3.14 results in the route 3589 optimization source (ROS) creating an asymmetric neighbor cache entry 3590 for the target neighbor. The neighbor cache entry is maintained for 3591 at most ReachableTime seconds and then deleted unless updated. In 3592 order to refresh the neighbor cache entry lifetime before the 3593 ReachableTime timer expires, the specification requires 3594 implementations to issue a new NS/NA exchange to reset ReachableTime 3595 while data packets are still flowing. However, the decision of when 3596 to initiate a new NS/NA exchange and to perpetuate the process is 3597 left as an implementation detail. 3599 One possible strategy may be to monitor the neighbor cache entry 3600 watching for data packets for (ReachableTime - 5) seconds. If any 3601 data packets have been sent to the neighbor within this timeframe, 3602 then send an NS to receive a new NA. If no data packets have been 3603 sent, wait for 5 additional seconds and send an immediate NS if any 3604 data packets are sent within this "expiration pending" 5 second 3605 window. If no additional data packets are sent within the 5 second 3606 window, delete the neighbor cache entry. 3608 The monitoring of the neighbor data packet traffic therefore becomes 3609 an asymmetric ongoing process during the neighbor cache entry 3610 lifetime. If the neighbor cache entry expires, future data packets 3611 will trigger a new NS/NA exchange while the packets themselves are 3612 delivered over a longer path until route optimization state is re- 3613 established. 3615 A.2. Implicit Mobility Management 3617 OMNI interface neighbors MAY provide a configuration option that 3618 allows them to perform implicit mobility management in which no ND 3619 messaging is used. In that case, the Client only transmits packets 3620 over a single interface at a time, and the neighbor always observes 3621 packets arriving from the Client from the same link-layer source 3622 address. 3624 If the Client's underlying interface address changes (either due to a 3625 readdressing of the original interface or switching to a new 3626 interface) the neighbor immediately updates the neighbor cache entry 3627 for the Client and begins accepting and sending packets according to 3628 the Client's new address. This implicit mobility method applies to 3629 use cases such as cellphones with both WiFi and Cellular interfaces 3630 where only one of the interfaces is active at a given time, and the 3631 Client automatically switches over to the backup interface if the 3632 primary interface fails. 3634 A.3. Direct Underlying Interfaces 3636 When a Client's OMNI interface is configured over a Direct interface, 3637 the neighbor at the other end of the Direct link can receive packets 3638 without any encapsulation. In that case, the Client sends packets 3639 over the Direct link according to QoS preferences. If the Direct 3640 interface has the highest QoS preference, then the Client's IP 3641 packets are transmitted directly to the peer without going through an 3642 ANET/INET. If other interfaces have higher QoS preferences, then the 3643 Client's IP packets are transmitted via a different interface, which 3644 may result in the inclusion of Proxys, Servers and Bridges in the 3645 communications path. Direct interfaces must be tested periodically 3646 for reachability, e.g., via NUD. 3648 A.4. AERO Critical Infrastructure Considerations 3650 AERO Bridges can be either Commercial off-the Shelf (COTS) standard 3651 IP routers or virtual machines in the cloud. Bridges must be 3652 provisioned, supported and managed by the INET administrative 3653 authority, and connected to the Bridges of other INETs via inter- 3654 domain peerings. Cost for purchasing, configuring and managing 3655 Bridges is nominal even for very large OMNI links. 3657 AERO Servers can be standard dedicated server platforms, but most 3658 often will be deployed as virtual machines in the cloud. The only 3659 requirements for Servers are that they can run the AERO user-level 3660 code and have at least one network interface connection to the INET. 3661 As with Bridges, Servers must be provisioned, supported and managed 3662 by the INET administrative authority. Cost for purchasing, 3663 configuring and managing Servers is nominal especially for virtual 3664 Servers hosted in the cloud. 3666 AERO Proxys are most often standard dedicated server platforms with 3667 one network interface connected to the ANET and a second interface 3668 connected to an INET. As with Servers, the only requirements are 3669 that they can run the AERO user-level code and have at least one 3670 interface connection to the INET. Proxys must be provisioned, 3671 supported and managed by the ANET administrative authority. Cost for 3672 purchasing, configuring and managing Proxys is nominal, and borne by 3673 the ANET administrative authority. 3675 AERO Relays can be any dedicated server or COTS router platform 3676 connected to INETs and/or EUNs. The Relay connects to the OMNI link 3677 and engages in eBGP peering with one or more Bridges as a stub AS. 3678 The Relay then injects its MNPs and/or non-MNP prefixes into the BGP 3679 routing system, and provisions the prefixes to its downstream- 3680 attached networks. The Relay can perform ROS/ROR services the same 3681 as for any Server, and can route between the MNP and non-MNP address 3682 spaces. 3684 A.5. AERO Server Failure Implications 3686 AERO Servers may appear as a single point of failure in the 3687 architecture, but such is not the case since all Servers on the link 3688 provide identical services and loss of a Server does not imply 3689 immediate and/or comprehensive communication failures. Although 3690 Clients typically associate with a single Server at a time, Server 3691 failure is quickly detected and conveyed by Bidirectional Forward 3692 Detection (BFD) and/or proactive NUD allowing Clients to migrate to 3693 new Servers. 3695 If a Server fails, ongoing packet forwarding to Clients will continue 3696 by virtue of the asymmetric neighbor cache entries that have already 3697 been established in route optimization sources (ROSs). If a Client 3698 also experiences mobility events at roughly the same time the Server 3699 fails, unsolicited NA messages may be lost but proxy neighbor cache 3700 entries in the DEPARTED state will ensure that packet forwarding to 3701 the Client's new locations will continue for up to DepartTime 3702 seconds. 3704 If a Client is left without a Server for an extended timeframe (e.g., 3705 greater than ReachableTime seconds) then existing asymmetric neighbor 3706 cache entries will eventually expire and both ongoing and new 3707 communications will fail. The original source will continue to 3708 retransmit until the Client has established a new Server 3709 relationship, after which time continuous communications will resume. 3711 Therefore, providing many Servers on the link with high availability 3712 profiles provides resilience against loss of individual Servers and 3713 assurance that Clients can establish new Server relationships quickly 3714 in event of a Server failure. 3716 A.6. AERO Client / Server Architecture 3718 The AERO architectural model is client / server in the control plane, 3719 with route optimization in the data plane. The same as for common 3720 Internet services, the AERO Client discovers the addresses of AERO 3721 Servers and selects one Server to connect to. The AERO service is 3722 analogous to common Internet services such as google.com, yahoo.com, 3723 cnn.com, etc. However, there is only one AERO service for the link 3724 and all Servers provide identical services. 3726 Common Internet services provide differing strategies for advertising 3727 server addresses to clients. The strategy is conveyed through the 3728 DNS resource records returned in response to name resolution queries. 3729 As of January 2020 Internet-based 'nslookup' services were used to 3730 determine the following: 3732 o When a client resolves the domainname "google.com", the DNS always 3733 returns one A record (i.e., an IPv4 address) and one AAAA record 3734 (i.e., an IPv6 address). The client receives the same addresses 3735 each time it resolves the domainname via the same DNS resolver, 3736 but may receive different addresses when it resolves the 3737 domainname via different DNS resolvers. But, in each case, 3738 exactly one A and one AAAA record are returned. 3740 o When a client resolves the domainname "ietf.org", the DNS always 3741 returns one A record and one AAAA record with the same addresses 3742 regardless of which DNS resolver is used. 3744 o When a client resolves the domainname "yahoo.com", the DNS always 3745 returns a list of 4 A records and 4 AAAA records. Each time the 3746 client resolves the domainname via the same DNS resolver, the same 3747 list of addresses are returned but in randomized order (i.e., 3748 consistent with a DNS round-robin strategy). But, interestingly, 3749 the same addresses are returned (albeit in randomized order) when 3750 the domainname is resolved via different DNS resolvers. 3752 o When a client resolves the domainname "amazon.com", the DNS always 3753 returns a list of 3 A records and no AAAA records. As with 3754 "yahoo.com", the same three A records are returned from any 3755 worldwide Internet connection point in randomized order. 3757 The above example strategies show differing approaches to Internet 3758 resilience and service distribution offered by major Internet 3759 services. The Google approach exposes only a single IPv4 and a 3760 single IPv6 address to clients. Clients can then select whichever IP 3761 protocol version offers the best response, but will always use the 3762 same IP address according to the current Internet connection point. 3763 This means that the IP address offered by the network must lead to a 3764 highly-available server and/or service distribution point. In other 3765 words, resilience is predicated on high availability within the 3766 network and with no client-initiated failovers expected (i.e., it is 3767 all-or-nothing from the client's perspective). However, Google does 3768 provide for worldwide distributed service distribution by virtue of 3769 the fact that each Internet connection point responds with a 3770 different IPv6 and IPv4 address. The IETF approach is like google 3771 (all-or-nothing from the client's perspective), but provides only a 3772 single IPv4 or IPv6 address on a worldwide basis. This means that 3773 the addresses must be made highly-available at the network level with 3774 no client failover possibility, and if there is any worldwide service 3775 distribution it would need to be conducted by a network element that 3776 is reached via the IP address acting as a service distribution point. 3778 In contrast to the Google and IETF philosophies, Yahoo and Amazon 3779 both provide clients with a (short) list of IP addresses with Yahoo 3780 providing both IP protocol versions and Amazon as IPv4-only. The 3781 order of the list is randomized with each name service query 3782 response, with the effect of round-robin load balancing for service 3783 distribution. With a short list of addresses, there is still 3784 expectation that the network will implement high availability for 3785 each address but in case any single address fails the client can 3786 switch over to using a different address. The balance then becomes 3787 one of function in the network vs function in the end system. 3789 The same implications observed for common highly-available services 3790 in the Internet apply also to the AERO client/server architecture. 3791 When an AERO Client connects to one or more ANETs, it discovers one 3792 or more AERO Server addresses through the mechanisms discussed in 3793 earlier sections. Each Server address presumably leads to a fault- 3794 tolerant clustering arrangement such as supported by Linux-HA, 3795 Extended Virtual Synchrony or Paxos. Such an arrangement has 3796 precedence in common Internet service deployments in lightweight 3797 virtual machines without requiring expensive hardware deployment. 3798 Similarly, common Internet service deployments set service IP 3799 addresses on service distribution points that may relay requests to 3800 many different servers. 3802 For AERO, the expectation is that a combination of the Google/IETF 3803 and Yahoo/Amazon philosophies would be employed. The AERO Client 3804 connects to different ANET access points and can receive 1-2 Server 3805 LLAs at each point. It then selects one AERO Server address, and 3806 engages in RS/RA exchanges with the same Server from all ANET 3807 connections. The Client remains with this Server unless or until the 3808 Server fails, in which case it can switch over to an alternate 3809 Server. The Client can likewise switch over to a different Server at 3810 any time if there is some reason for it to do so. So, the AERO 3811 expectation is for a balance of function in the network and end 3812 system, with fault tolerance and resilience at both levels. 3814 Appendix B. Change Log 3816 << RFC Editor - remove prior to publication >> 3818 Changes from draft-templin-intarea-6706bis-61 to draft-templin- 3819 intrea-6706bis-62: 3821 o New sub-section on OMNI Neighbor Interface Attributes 3823 Changes from draft-templin-intarea-6706bis-59 to draft-templin- 3824 intrea-6706bis-60: 3826 o Removed all references to S/TLLAO - all Interface Attributes are 3827 now maintained completely in the OMNI option. 3829 Changes from draft-templin-intarea-6706bis-58 to draft-templin- 3830 intrea-6706bis-59: 3832 o The term "Relay" used in older draft versions is now "Bridge". 3833 "Relay" now refers to what was formally called: "Gateway". 3835 o Fine-grained cleanup of Forwarding Algorithm; IPv6 ND message 3836 addressing; OMNI Prefix Lengths, etc. 3838 Changes from draft-templin-intarea-6706bis-54 to draft-templin- 3839 intrea-6706bis-55: 3841 o Updates on Segment Routing and S/TLLAO contents. 3843 o Various editorials and addressing cleanups. 3845 Changes from draft-templin-intarea-6706bis-52 to draft-templin- 3846 intrea-6706bis-53: 3848 o Normative reference to the OMNI spec, and remove portions that are 3849 already specified in OMNI. 3851 o Renamed "AERO interface/link" to "OMIN interface/link" throughout 3852 the document. 3854 o Truncated obsolete back section matter. 3856 Author's Address 3858 Fred L. Templin (editor) 3859 Boeing Research & Technology 3860 P.O. Box 3707 3861 Seattle, WA 98124 3862 USA 3864 Email: fltemplin@acm.org