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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, February 3, 2021 5 rfc6179, rfc6706 (if 6 approved) 7 Intended status: Standards Track 8 Expires: August 7, 2021 10 Asymmetric Extended Route Optimization (AERO) 11 draft-templin-intarea-6706bis-90 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 August 7, 2021. 47 Copyright Notice 49 Copyright (c) 2021 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) . . . . . . . . 11 67 3.1. AERO Node Types . . . . . . . . . . . . . . . . . . . . . 11 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), Unique Local Addresses 71 (ULAs) and Global Unicast Addresses (GUA) . . . . . . 15 72 3.2.3. Node Identification . . . . . . . . . . . . . . . . . 16 73 3.2.4. AERO Routing System . . . . . . . . . . . . . . . . . 16 74 3.2.5. OMNI Link Encapsulation . . . . . . . . . . . . . . . 18 75 3.2.6. Segment Routing Topologies (SRTs) . . . . . . . . . . 22 76 3.2.7. Segment Routing For OMNI Link Selection . . . . . . . 23 77 3.2.8. Segment Routing Within the OMNI Link . . . . . . . . 23 78 3.3. OMNI Interface Characteristics . . . . . . . . . . . . . 24 79 3.4. OMNI Interface Initialization . . . . . . . . . . . . . . 26 80 3.4.1. AERO Server/Relay Behavior . . . . . . . . . . . . . 26 81 3.4.2. AERO Proxy Behavior . . . . . . . . . . . . . . . . . 26 82 3.4.3. AERO Client Behavior . . . . . . . . . . . . . . . . 27 83 3.4.4. AERO Bridge Behavior . . . . . . . . . . . . . . . . 27 84 3.5. OMNI Interface Neighbor Cache Maintenance . . . . . . . . 27 85 3.5.1. OMNI Neighbor Interface Attributes . . . . . . . . . 29 86 3.5.2. OMNI Neighbor Advertisement Message Flags . . . . . . 30 87 3.6. OMNI Interface Encapsulation and Re-encapsulation . . . . 30 88 3.7. OMNI Interface Decapsulation . . . . . . . . . . . . . . 32 89 3.8. OMNI Interface Data Origin Authentication . . . . . . . . 32 90 3.9. OMNI Adaptation Layer and OMNI Interface MTU . . . . . . 32 91 3.10. OMNI Interface Forwarding Algorithm . . . . . . . . . . . 33 92 3.10.1. Client Forwarding Algorithm . . . . . . . . . . . . 34 93 3.10.2. Proxy Forwarding Algorithm . . . . . . . . . . . . . 35 94 3.10.3. Server/Relay Forwarding Algorithm . . . . . . . . . 36 95 3.10.4. Bridge Forwarding Algorithm . . . . . . . . . . . . 38 96 3.11. OMNI Interface Error Handling . . . . . . . . . . . . . . 39 97 3.12. AERO Router Discovery, Prefix Delegation and 98 Autoconfiguration . . . . . . . . . . . . . . . . . . . . 41 99 3.12.1. AERO Service Model . . . . . . . . . . . . . . . . . 41 100 3.12.2. AERO Client Behavior . . . . . . . . . . . . . . . . 42 101 3.12.3. AERO Server Behavior . . . . . . . . . . . . . . . . 44 102 3.13. The AERO Proxy . . . . . . . . . . . . . . . . . . . . . 47 103 3.13.1. Combined Proxy/Servers . . . . . . . . . . . . . . . 49 104 3.13.2. Detecting and Responding to Server Failures . . . . 49 105 3.13.3. Point-to-Multipoint Server Coordination . . . . . . 50 106 3.14. AERO Route Optimization / Address Resolution . . . . . . 51 107 3.14.1. Route Optimization Initiation . . . . . . . . . . . 51 108 3.14.2. Relaying the NS(AR) . . . . . . . . . . . . . . . . 52 109 3.14.3. Processing the NS(AR) and Sending the NA(AR) . . . . 52 110 3.14.4. Relaying the NA(AR) . . . . . . . . . . . . . . . . 53 111 3.14.5. Processing the NA(AR) . . . . . . . . . . . . . . . 54 112 3.14.6. Route Optimization Maintenance . . . . . . . . . . . 54 113 3.15. Neighbor Unreachability Detection (NUD) . . . . . . . . . 55 114 3.16. Mobility Management and Quality of Service (QoS) . . . . 56 115 3.16.1. Mobility Update Messaging . . . . . . . . . . . . . 57 116 3.16.2. Announcing Link-Layer Address and/or QoS Preference 117 Changes . . . . . . . . . . . . . . . . . . . . . . 58 118 3.16.3. Bringing New Links Into Service . . . . . . . . . . 59 119 3.16.4. Deactivating Existing Links . . . . . . . . . . . . 59 120 3.16.5. Moving Between Servers . . . . . . . . . . . . . . . 59 121 3.17. Multicast . . . . . . . . . . . . . . . . . . . . . . . . 60 122 3.17.1. Source-Specific Multicast (SSM) . . . . . . . . . . 61 123 3.17.2. Any-Source Multicast (ASM) . . . . . . . . . . . . . 62 124 3.17.3. Bi-Directional PIM (BIDIR-PIM) . . . . . . . . . . . 63 125 3.18. Operation over Multiple OMNI Links . . . . . . . . . . . 63 126 3.19. DNS Considerations . . . . . . . . . . . . . . . . . . . 64 127 3.20. Transition Considerations . . . . . . . . . . . . . . . . 64 128 3.21. Detecting and Reacting to Server and Bridge Failures . . 65 129 3.22. AERO Clients on the Open Internet . . . . . . . . . . . . 66 130 3.23. Time-Varying MNPs . . . . . . . . . . . . . . . . . . . . 69 131 4. Implementation Status . . . . . . . . . . . . . . . . . . . . 69 132 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 69 133 6. Security Considerations . . . . . . . . . . . . . . . . . . . 70 134 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 71 135 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 73 136 8.1. Normative References . . . . . . . . . . . . . . . . . . 73 137 8.2. Informative References . . . . . . . . . . . . . . . . . 74 138 Appendix A. Non-Normative Considerations . . . . . . . . . . . . 81 139 A.1. Implementation Strategies for Route Optimization . . . . 81 140 A.2. Implicit Mobility Management . . . . . . . . . . . . . . 81 141 A.3. Direct Underlying Interfaces . . . . . . . . . . . . . . 82 142 A.4. AERO Critical Infrastructure Considerations . . . . . . . 82 143 A.5. AERO Server Failure Implications . . . . . . . . . . . . 83 144 A.6. AERO Client / Server Architecture . . . . . . . . . . . . 83 145 Appendix B. Change Log . . . . . . . . . . . . . . . . . . . . . 85 146 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 86 148 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 that employs 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 as single-hop neighbors via 160 encapsulation. The OMNI Adaptation Layer (OAL) supports multilink 161 operation for increased reliability, bandwidth optimization and 162 traffic path selection while accommodating Maximum Transmission Unit 163 (MTU) diversity. 165 The AERO service comprises Clients, Proxys, Servers and Relays that 166 are seen as OMNI link neighbors as well as Bridges that interconnect 167 OMNI link segments. Each node's OMNI interface uses an IPv6 link- 168 local address format that supports operation of the IPv6 Neighbor 169 Discovery (ND) protocol [RFC4861] and links ND to IP forwarding. A 170 node's OMNI interface can be configured over multiple underlying 171 interfaces, and may therefore appear as a single interface with 172 multiple link-layer addresses. Each link-layer address is subject to 173 change due to mobility and/or QoS fluctuations, and link-layer 174 address changes are signaled by ND messaging the same as for any IPv6 175 link. 177 AERO provides a cloud-based service where mobile node Clients may use 178 any Server acting as a Mobility Anchor Point (MAP) and fixed nodes 179 may use any Relay on the link for efficient communications. Fixed 180 nodes forward packets destined to other AERO nodes via the nearest 181 Relay, which forwards them through the cloud. A mobile node's 182 initial packets are forwarded through the Server, while direct 183 routing is supported through asymmetric extended route optimization 184 while data packets are flowing. Both unicast and multicast 185 communications are supported, and mobile nodes may efficiently move 186 between locations while maintaining continuous communications with 187 correspondents and without changing their IP Address. 189 AERO Bridges are interconnected in a secured private BGP overlay 190 routing instance using encapsulation to provide a hybrid routing/ 191 bridging service that joins the underlying Internetworks of multiple 192 disjoint administrative domains into a single unified OMNI link. 193 Each OMNI link instance is characterized by the set of Mobility 194 Service Prefixes (MSPs) common to all mobile nodes. The link extends 195 to the point where a Relay/Server is on the optimal route from any 196 correspondent node on the link, and provides a conduit between the 197 underlying Internetwork and the OMNI link. To the underlying 198 Internetwork, the Relay/Server is the source of a route to the MSP, 199 and hence uplink traffic to the mobile node is naturally routed to 200 the nearest Relay/Server. 202 AERO can be used with OMNI links that span private-use Internetworks 203 and/or public Internetworks such as the global Internet. In the 204 latter case, some end systems may be located behind global Internet 205 Network Address Translators (NATs). A means for robust traversal of 206 NATs while avoiding "triangle routing" is therefore provided. 208 AERO assumes the use of PIM Sparse Mode in support of multicast 209 communication. In support of Source Specific Multicast (SSM) when a 210 Mobile Node is the source, AERO route optimization ensures that a 211 shortest-path multicast tree is established with provisions for 212 mobility and multilink operation. In all other multicast scenarios 213 there are no AERO dependencies. 215 AERO was designed for aeronautical networking for both manned and 216 unmanned aircraft, where the aircraft is treated as a mobile node 217 that can connect an Internet of Things (IoT). AERO is also 218 applicable to a wide variety of other use cases. For example, it can 219 be used to coordinate the links of mobile nodes (e.g., cellphones, 220 tablets, laptop computers, etc.) that connect into a home enterprise 221 network via public access networks using tunneling software such as 222 OpenVPN [OVPN] with VPN or non-VPN services enabled according to the 223 appropriate security model. AERO can also be used to facilitate 224 terrestrial vehicular and urban air mobility (as well as pedestrian 225 communication services) for future intelligent transportation systems 226 [I-D.ietf-ipwave-vehicular-networking][I-D.templin-ipwave-uam-its]. 227 Other applicable use cases are also in scope. 229 The following numbered sections present the AERO specification. The 230 appendices at the end of the document are non-normative. 232 2. Terminology 234 The terminology in the normative references applies; especially, the 235 terminology in the OMNI specification 236 [I-D.templin-6man-omni-interface] is used extensively throughout. 237 The following terms are defined within the scope of this document: 239 IPv6 Neighbor Discovery (ND) 240 an IPv6 control message service for coordinating neighbor 241 relationships between nodes connected to a common link. AERO uses 242 the ND service specified in [RFC4861]. 244 IPv6 Prefix Delegation 245 a networking service for delegating IPv6 prefixes to nodes on the 246 link. The nominal service is DHCPv6 [RFC8415], however alternate 247 services (e.g., based on ND messaging) are also in scope. Most 248 notably, a minimal form of prefix delegation known as "prefix 249 registration" can be used if the Client knows its prefix in 250 advance and can represent it in the IPv6 source address of an ND 251 message. 253 Access Network (ANET) 254 a node's first-hop data link service network (e.g., a radio access 255 network, cellular service provider network, corporate enterprise 256 network, etc.) that often provides link-layer security services 257 such as IEEE 802.1X and physical-layer security prevent 258 unauthorized access internally and with border network-layer 259 security services such as firewalls and proxies that prevent 260 unauthorized outside access. 262 ANET interface 263 a node's attachment to a link in an ANET. 265 Internetwork (INET) 266 a connected IP network topology with a coherent routing and 267 addressing plan and that provides a transit backbone service for 268 ANET end systems. INETs also provide an underlay service over 269 which the AERO virtual link is configured. Example INETs include 270 corporate enterprise networks, aviation networks, and the public 271 Internet itself. When there is no administrative boundary between 272 an ANET and the INET, the ANET and INET are one and the same. 274 INET Partition 275 frequently, INETs such as large corporate enterprise networks are 276 sub-divided internally into separate isolated partitions. Each 277 partition is fully connected internally but disconnected from 278 other partitions, and there is no requirement that separate 279 partitions maintain consistent Internet Protocol and/or addressing 280 plans. (Each INET partition is seen as a separate OMNI link 281 segment as discussed below.) 283 INET interface 284 a node's attachment to a link in an INET. 286 INET address 287 an IP address assigned to a node's interface connection to an 288 INET. 290 INET encapsulation 291 the encapsulation of a packet in an outer header or headers that 292 can be routed within the scope of the local INET partition. 294 OMNI link 295 the same as defined in [I-D.templin-6man-omni-interface], and 296 manifested by IPv6 encapsulation [RFC2473]. The OMNI link spans 297 underlying INET segments joined by virtual bridges in a spanning 298 tree the same as a bridged campus LAN. AERO nodes on the OMNI 299 link appear as single-hop neighbors even though they may be 300 separated by multiple underlying INET hops, and can use Segment 301 Routing [RFC8402] to cause packets to visit selected waypoints on 302 the link. 304 OMNI Interface 305 a node's attachment to an OMNI link. Since the addresses assigned 306 to an OMNI interface are managed for uniqueness, OMNI interfaces 307 do not require Duplicate Address Detection (DAD) and therefore set 308 the administrative variable 'DupAddrDetectTransmits' to zero 309 [RFC4862]. 311 OMNI Adaptation Layer (OAL) 312 an OMNI interface process whereby packets admitted into the 313 interface are wrapped in a mid-layer IPv6 header and fragmented/ 314 reassembled if necessary to support the OMNI link Maximum 315 Transmission Unit (MTU). The OAL is also responsible for 316 generating MTU-related control messages as necessary, and for 317 providing addressing context for spanning multiple segments of a 318 bridged OMNI link. 320 underlying interface 321 an ANET or INET interface over which an OMNI interface is 322 configured. 324 Mobility Service Prefix (MSP) 325 an aggregated IP Global Unicast Address (GUA) prefix (e.g., 326 2001:db8::/32, 192.0.2.0/24, etc.) assigned to the OMNI link and 327 from which more-specific Mobile Network Prefixes (MNPs) are 328 delegated. OMNI link administrators typically obtain MSPs from an 329 Internet address registry, however private-use prefixes can 330 alternatively be used subject to certain limitations (see: 331 [I-D.templin-6man-omni-interface]). OMNI links that connect to 332 the global Internet advertise their MSPs to their interdomain 333 routing peers. 335 Mobile Network Prefix (MNP) 336 a longer IP prefix delegated from an MSP (e.g., 337 2001:db8:1000:2000::/56, 192.0.2.8/30, etc.) and assigned to an 338 AERO Client or Relay. 340 Mobile Network Prefix Link Local Address (MNP-LLA) 341 an IPv6 Link Local Address that embeds the most significant 64 342 bits of an MNP in the lower 64 bits of fe80::/64, as specified in 343 [I-D.templin-6man-omni-interface]. 345 Mobile Network Prefix Unique Local Address (MNP-ULA) 346 an IPv6 Unique-Local Address derived from an MNP-LLA. 348 Administrative Link Local Address (ADM-LLA) 349 an IPv6 Link Local Address that embeds a 32-bit administratively- 350 assigned identification value in the lower 32 bits of fe80::/96, 351 as specified in [I-D.templin-6man-omni-interface]. 353 Administrative Unique Local Address (ADM-ULA) 354 an IPv6 Unique-Local Address derived from an ADM-LLA. 356 AERO node 357 a node that is connected to an OMNI link and participates in the 358 AERO internetworking and mobility service. 360 AERO Client ("Client") 361 an AERO node that connects over one or more underlying interfaces 362 and requests MNP delegation/registration service from AERO 363 Servers. The Client assigns an MNP-LLA to the OMNI interface for 364 use in ND exchanges with other AERO nodes and forwards packets to 365 correspondents according to OMNI interface neighbor cache state. 367 AERO Server ("Server") 368 an INET node that configures an OMNI interface to provide default 369 forwarding and mobility/multilink services for AERO Clients. The 370 Server assigns an ADM-LLA to its OMNI interface to support the 371 operation of the ND services, and advertises all of its associated 372 MNPs via BGP peerings with Bridges. 374 AERO Relay ("Relay") 375 an AERO Server that also provides forwarding services between 376 nodes reached via the OMNI link and correspondents on other links. 377 AERO Relays are provisioned with MNPs (i.e., the same as for an 378 AERO Client) and run a dynamic routing protocol to discover any 379 non-MNP IP GUA routes in service on its connected INET links. In 380 both cases, the Relay advertises the MSP(s) to its downstream 381 networks, and distributes all of its associated MNPs and non-MNP 382 IP GUA routes via BGP peerings with Bridges (i.e., the same as for 383 an AERO Server). 385 AERO Bridge ("Bridge") 386 a node that provides hybrid routing/bridging services (as well as 387 a security trust anchor) for nodes on an OMNI link. As a router, 388 the Bridge forwards packets using standard IP forwarding. As a 389 bridge, the Bridge forwards packets over the OMNI link without 390 decrementing the IPv6 Hop Limit. AERO Bridges peer with Servers 391 and other Bridges to discover the full set of MNPs for the link as 392 well as any non-MNP IP GUA routes that are reachable via Relays. 394 AERO Proxy ("Proxy") 395 a node that provides proxying services between Clients in an ANET 396 and Servers in external INETs. The AERO Proxy is a conduit 397 between the ANET and external INETs in the same manner as for 398 common web proxies, and behaves in a similar fashion as for ND 399 proxies [RFC4389]. A node may be configured to act as either a 400 Proxy and/or a Server, depending on Client Server selection 401 criteria. 403 ingress tunnel endpoint (ITE) 404 an OMNI interface endpoint that injects encapsulated packets into 405 an OMNI link. 407 egress tunnel endpoint (ETE) 408 an OMNI interface endpoint that receives encapsulated packets from 409 an OMNI link. 411 link-layer address 412 an IP address used as an encapsulation header source or 413 destination address from the perspective of the OMNI interface. 414 When an upper layer protocol (e.g., UDP) is used as part of the 415 encapsulation, the port number is also considered as part of the 416 link-layer address. 418 network layer address 419 the source or destination address of an encapsulated IP packet 420 presented to the OMNI interface. 422 end user network (EUN) 423 an internal virtual or external edge IP network that an AERO 424 Client or Relay connects to the rest of the network via the OMNI 425 interface. The Client/Relay sees each EUN as a "downstream" 426 network, and sees the OMNI interface as the point of attachment to 427 the "upstream" network. 429 Mobile Node (MN) 430 an AERO Client and all of its downstream-attached networks that 431 move together as a single unit, i.e., an end system that connects 432 an Internet of Things. 434 Mobile Router (MR) 435 a MN's on-board router that forwards packets between any 436 downstream-attached networks and the OMNI link. The MR is the MN 437 entity that hosts the AERO Client. 439 Route Optimization Source (ROS) 440 the AERO node nearest the source that initiates route 441 optimization. The ROS may be a Server or Proxy acting on behalf 442 of the source Client, or may be the Client itself if the Client is 443 connected to the INET either directly or through a NAT. 445 Route Optimization responder (ROR) 446 the AERO node nearest the target destination that responds to 447 route optimization requests. The ROR may be a Server acting on 448 behalf of a target MNP Client, or a Relay for a non-MNP 449 destination. 451 MAP List 452 a geographically and/or topologically referenced list of addresses 453 of all Servers within the same OMNI link. There is a single MAP 454 list for the entire OMNI link. 456 Distributed Mobility Management (DMM) 457 a BGP-based overlay routing service coordinated by Servers and 458 Bridges that tracks all Server-to-Client associations. 460 Mobility Service (MS) 461 the collective set of all Servers, Proxys, Bridges and Relays that 462 provide the AERO Service to Clients. 464 Mobility Service Endpoint MSE) 465 an individual Server, Proxy, Bridge or Relay in the Mobility 466 Service. 468 Throughout the document, the simple terms "Client", "Server", 469 "Bridge", "Proxy" and "Relay" refer to "AERO Client", "AERO Server", 470 "AERO Bridge", "AERO Proxy" and "AERO Relay", respectively. 471 Capitalization is used to distinguish these terms from other common 472 Internetworking uses in which they appear without capitalization. 474 The terminology of DHCPv6 [RFC8415] and IPv6 ND [RFC4861] (including 475 the names of node variables, messages and protocol constants) is used 476 throughout this document. The terms "All-Routers multicast", "All- 477 Nodes multicast", "Solicited-Node multicast" and "Subnet-Router 478 anycast" are defined in [RFC4291]. Also, the term "IP" is used to 479 generically refer to either Internet Protocol version, i.e., IPv4 480 [RFC0791] or IPv6 [RFC8200]. 482 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 483 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 484 "OPTIONAL" in this document are to be interpreted as described in BCP 485 14 [RFC2119][RFC8174] when, and only when, they appear in all 486 capitals, as shown here. 488 3. Asymmetric Extended Route Optimization (AERO) 490 The following sections specify the operation of IP over OMNI links 491 using the AERO service: 493 3.1. AERO Node Types 495 AERO Clients are Mobile Nodes (MNs) that connect via underlying 496 interfaces with addresses that may change when the Client moves to a 497 new network connection point. AERO Clients register their Mobile 498 Network Prefixes (MNPs) with the AERO service, and distribute the 499 MNPs to nodes on EUNs. AERO Bridges, Servers, Proxys and Relays are 500 critical infrastructure elements in fixed (i.e., non-mobile) INET 501 deployments and hence have permanent and unchanging INET addresses. 502 Together, they constitute the AERO service which provides an OMNI 503 link virtual overlay for connecting AERO Clients. 505 AERO Bridges provide hybrid routing/bridging services (as well as a 506 security trust anchor) for nodes on an OMNI link. Bridges use 507 standard IPv6 routing to forward packets both within the same INET 508 partition and between disjoint INET partitions based on an IPv6 509 encapsulation mid-layer known as the OMNI Adaptation Layer (OAL) 510 [I-D.templin-6man-omni-interface]. During forwarding, the inner IP 511 layer experiences a virtual bridging service since the inner IP TTL/ 512 Hop Limit is not decremented. Each Bridge also peers with Servers 513 and other Bridges in a dynamic routing protocol instance to provide a 514 Distributed Mobility Management (DMM) service for the list of active 515 MNPs (see Section 3.2.4). Bridges present the OMNI link as a set of 516 one or more Mobility Service Prefixes (MSPs) and configure secured 517 tunnels with Servers, Relays, Proxys and other Bridges; they further 518 maintain IP forwarding table entries for each MNP and any other 519 reachable non-MNP prefixes. 521 AERO Servers in distributed INET locations provide default forwarding 522 and mobility/multilink services for AERO Client Mobile Nodes (MNs). 523 Each Server also peers with Bridges in a dynamic routing protocol 524 instance to advertise its list of associated MNPs (see 525 Section 3.2.4). Servers facilitate prefix delegation/registration 526 exchanges with Clients, where each delegated prefix becomes an MNP 527 taken from an MSP. Servers forward packets between OMNI interface 528 neighbors and track each Client's mobility profiles. Servers may 529 further act as Servers for some sets of Clients and as Proxies for 530 others. 532 AERO Proxys provide a conduit for ANET Clients to associate with 533 Servers in external INETs. Client and Servers exchange control plane 534 messages via the Proxy acting as a bridge between the ANET/INET 535 boundary. The Proxy forwards data packets between Clients and the 536 OMNI link according to forwarding information in the neighbor cache. 537 The Proxy function is specified in Section 3.13. Proxys may further 538 act as Proxys for some sets of Clients and as Servers for others. 540 AERO Relays are Servers that provide forwarding services between the 541 OMNI interface and INET/EUN interfaces. Relays are provisioned with 542 MNPs the same as for an AERO Client, and also run a dynamic routing 543 protocol to discover any non-MNP IP routes. The Relay advertises the 544 MSP(s) to its connected networks, and distributes all of its 545 associated MNPs and non-MNP IP GUA routes via BGP peerings with 546 Bridges 548 3.2. The AERO Service over OMNI Links 550 3.2.1. AERO/OMNI Reference Model 552 Figure 1 presents the basic OMNI link reference model: 554 +----------------+ 555 | AERO Bridge B1 | 556 | Nbr: S1, S2, P1| 557 |(X1->S1; X2->S2)| 558 | MSP M1 | 559 +-+---------+--+-+ 560 +--------------+ | Secured | | +--------------+ 561 |AERO Server S1| | tunnels | | |AERO Server S2| 562 | Nbr: C1, B1 +-----+ | +-----+ Nbr: C2, B1 | 563 | default->B1 | | | default->B1 | 564 | X1->C1 | | | X2->C2 | 565 +-------+------+ | +------+-------+ 566 | OMNI link | | 567 X===+===+===================+==)===============+===+===X 568 | | | | 569 +-----+--------+ +--------+--+-----+ +--------+-----+ 570 |AERO Client C1| | AERO Proxy P1 | |AERO Client C2| 571 | Nbr: S1 | |(Proxy Nbr Cache)| | Nbr: S2 | 572 | default->S1 | +--------+--------+ | default->S2 | 573 | MNP X1 | | | MNP X2 | 574 +------+-------+ .--------+------. +-----+--------+ 575 | (- Proxyed Clients -) | 576 .-. `---------------' .-. 577 ,-( _)-. ,-( _)-. 578 .-(_ IP )-. +-------+ +-------+ .-(_ IP )-. 579 (__ EUN )--|Host H1| |Host H2|--(__ EUN ) 580 `-(______)-' +-------+ +-------+ `-(______)-' 582 Figure 1: AERO/OMNI Reference Model 584 In this model: 586 o the OMNI link is an overlay network service configured over one or 587 more underlying INET partitions which may be managed by different 588 administrative authorities and have incompatible protocols and/or 589 addressing plans. 591 o AERO Bridge B1 aggregates Mobility Service Prefix (MSP) M1, 592 discovers Mobile Network Prefixes (MNPs) X* and advertises the MSP 593 via BGP peerings over secured tunnels to Servers (S1, S2). 594 Bridges connect the disjoint segments of a partitioned OMNI link. 596 o AERO Servers/Relays S1 and S2 configure secured tunnels with 597 Bridge B1 and also provide mobility, multilink and default router 598 services for their associated Clients C1 and C2. 600 o AERO Clients C1 and C2 associate with Servers S1 and S2, 601 respectively. They receive Mobile Network Prefix (MNP) 602 delegations X1 and X2, and also act as default routers for their 603 associated physical or internal virtual EUNs. Simple hosts H1 and 604 H2 attach to the EUNs served by Clients C1 and C2, respectively. 606 o AERO Proxy P1 configures a secured tunnel with Bridge B1 and 607 provides proxy services for AERO Clients in secured enclaves that 608 cannot associate directly with other OMNI link neighbors. 610 An OMNI link configured over a single INET appears as a single 611 unified link with a consistent underlying network addressing plan. 612 In that case, all nodes on the link can exchange packets via simple 613 INET encapsulation, since the underlying INET is connected. In 614 common practice, however, an OMNI link may be partitioned into 615 multiple "segments", where each segment is a distinct INET 616 potentially managed under a different administrative authority (e.g., 617 as for worldwide aviation service providers such as ARINC, SITA, 618 Inmarsat, etc.). Individual INETs may also themselves be partitioned 619 internally, in which case each internal partition is seen as a 620 separate segment. 622 The addressing plan of each segment is consistent internally but will 623 often bear no relation to the addressing plans of other segments. 624 Each segment is also likely to be separated from others by network 625 security devices (e.g., firewalls, proxies, packet filtering 626 gateways, etc.), and in many cases disjoint segments may not even 627 have any common physical link connections. Therefore, nodes can only 628 be assured of exchanging packets directly with correspondents in the 629 same segment, and not with those in other segments. The only means 630 for joining the segments therefore is through inter-domain peerings 631 between AERO Bridges. 633 The same as for traditional campus LANs, multiple OMNI link segments 634 can be joined into a single unified link via a virtual bridging 635 service using the OMNI Adaptation Layer (OAL) 636 [I-D.templin-6man-omni-interface] which inserts a mid-layer IPv6 637 encapsulation header that supports inter-segment forwarding (i.e., 638 bridging) without decrementing the network-layer TTL/Hop Limit. This 639 bridging of OMNI link segments is shown in Figure 2: 641 . . . . . . . . . . . . . . . . . . . . . . . 642 . . 643 . .-(::::::::) . 644 . .-(::::::::::::)-. +-+ . 645 . (:::: Segment A :::)--|B|---+ . 646 . `-(::::::::::::)-' +-+ | . 647 . `-(::::::)-' | . 648 . | . 649 . .-(::::::::) | . 650 . .-(::::::::::::)-. +-+ | . 651 . (:::: Segment B :::)--|B|---+ . 652 . `-(::::::::::::)-' +-+ | . 653 . `-(::::::)-' | . 654 . | . 655 . .-(::::::::) | . 656 . .-(::::::::::::)-. +-+ | . 657 . (:::: Segment C :::)--|B|---+ . 658 . `-(::::::::::::)-' +-+ | . 659 . `-(::::::)-' | . 660 . | . 661 . ..(etc).. x . 662 . . 663 . . 664 . <- OMNI link Bridged by encapsulation -> . 665 . . . . . . . . . . . . . .. . . . . . . . . 667 Figure 2: Bridging OMNI Link Segments 669 Bridges, Servers, Relays and Proxys connect via secured INET tunnels 670 over their respective segments in a spanning tree topology rooted at 671 the Bridges. The secured spanning tree supports strong 672 authentication for IPv6 ND control messages and may also be used to 673 convey the initial data packets in a flow. Route optimization can 674 then be employed to cause data packets to take more direct paths 675 between OMNI link neighbors without having to strictly follow the 676 spanning tree. 678 3.2.2. Link-Local Addresses (LLAs), Unique Local Addresses (ULAs) and 679 Global Unicast Addresses (GUA) 681 AERO nodes on OMNI links use the Link-Local Address (LLA) prefix 682 fe80::/64 [RFC4291] to assign LLAs used for network-layer addresses 683 in link-scoped IPv6 ND and data messages. AERO Clients use LLAs 684 constructed from MNPs (i.e., "MNP-LLAs") while other AERO nodes use 685 LLAs constructed from administrative identification values ("ADM- 686 LLAs") as specified in [I-D.templin-6man-omni-interface]. 688 AERO nodes also use the Unique Local Address (ULA) prefix fd00::/8 689 followed by a pseudo-random 40-bit OMNI domain identifier to form the 690 prefix [ULA]::/48, then include a 16-bit OMNI link identifier '*' to 691 form the prefix [ULA*]::/64 [RFC4291]. The AERO node then uses the 692 prefix [ULA*]::/64 to form "MNP-ULAs" or "ADM-ULA"s as specified in 693 [I-D.templin-6man-omni-interface] to support OAL addressing. 695 AERO Clients also use Temporary LLAs/ULAs constructed per 696 [I-D.templin-6man-omni-interface], where the addresses are typically 697 used only in initial control message exchanges until a stable MNP- 698 LLA/ULA is assigned. 700 Finally, the MSPs and MNPs used by AERO nodes are typically based on 701 Global Unicast Addresses (GUAs), but in some cases may be based on 702 private-use addresses. See [I-D.templin-6man-omni-interface] for a 703 full specification of LLAs, ULAs and GUAs used by AERO nodes on OMNI 704 links. 706 3.2.3. Node Identification 708 AERO Clients and Servers configure node identification values as 709 specified in [I-D.templin-6man-omni-interface]. 711 3.2.4. AERO Routing System 713 The AERO routing system comprises a private instance of the Border 714 Gateway Protocol (BGP) [RFC4271] that is coordinated between Bridges 715 and Servers and does not interact with either the public Internet BGP 716 routing system or any underlying INET routing systems. 718 In a reference deployment, each Server is configured as an Autonomous 719 System Border Router (ASBR) for a stub Autonomous System (AS) using a 720 32-bit AS Number (ASN) [RFC4271] that is unique within the BGP 721 instance, and each Server further uses eBGP to peer with one or more 722 Bridges but does not peer with other Servers. Each INET of a multi- 723 segment OMNI link must include one or more Bridges, which peer with 724 the Servers and Proxys within that INET. All Bridges within the same 725 INET are members of the same hub AS, and use iBGP to maintain a 726 consistent view of all active MNPs currently in service. The Bridges 727 of different INETs peer with one another using eBGP. 729 Bridges advertise the OMNI link's MSPs and any non-MNP routes to each 730 of their Servers. This means that any aggregated non-MNPs (including 731 "default") are advertised to all Servers. Each Bridge configures a 732 black-hole route for each of its MSPs. By black-holing the MSPs, the 733 Bridge will maintain forwarding table entries only for the MNPs that 734 are currently active, and packets destined to all other MNPs will 735 correctly incur Destination Unreachable messages due to the black- 736 hole route. In this way, Servers have only partial topology 737 knowledge (i.e., they know only about the MNPs of their directly 738 associated Clients) and they forward all other packets to Bridges 739 which have full topology knowledge. 741 Each OMNI link segment assigns a unique ADM-ULA sub-prefix of 742 [ULA*]::/96. For example, a first segment could assign 743 [ULA*]::1000/116, a second could assign [ULA*]::2000/116, a third 744 could assign [ULA*]::3000/116, etc. Within each segment, each Proxy/ 745 Server configures an ADM-ULA within the segment's prefix, e.g., the 746 Proxy/Servers within [ULA*]::2000/116 could assign the ADM-ULAs 747 [ULA*]::2011/116, [ULA*]::2026/116, [ULA*]::2003/116, etc. 749 The administrative authorities for each segment must therefore 750 coordinate to assure mutually-exclusive ADM-ULA prefix assignments, 751 but internal provisioning of ADM-ULAs an independent local 752 consideration for each administrative authority. For each ADM-ULA 753 prefix, the Bridge(s) that connect that segment assign the all-zero's 754 address of the prefix as a Subnet Router Anycast address. For 755 example, the Subnet Router Anycast address for [ULA*]::1023/116 is 756 simply [ULA*]::1000. 758 ADM-ULA prefixes are statically represented in Bridge forwarding 759 tables. Bridges join multiple segments into a unified OMNI link over 760 multiple diverse administrative domains. They support a bridging 761 function by first establishing forwarding table entries for their 762 ADM-ULA prefixes either via standard BGP routing or static routes. 763 For example, if three Bridges ('A', 'B' and 'C') from different 764 segments serviced [ULA*]::1000/116, [ULA*]::2000/116 and 765 [ULA*]::3000/116 respectively, then the forwarding tables in each 766 Bridge are as follows: 768 A: [ULA*]::1000/116->local, [ULA*]::2000/116->B, [ULA*]::3000/116->C 770 B: [ULA*]::1000/116->A, [ULA*]::2000/116->local, [ULA*]::3000/116->C 772 C: [ULA*]::1000/116->A, [ULA*]::2000/116->B, [ULA*]::3000/116->local 774 These forwarding table entries are permanent and never change, since 775 they correspond to fixed infrastructure elements in their respective 776 segments. 778 MNP ULAs are instead dynamically advertised in the AERO routing 779 system by Servers and Relays that provide service for their 780 corresponding MNPs. For example, if three Servers ('D', 'E' and 'F') 781 service the MNPs 2001:db8:1000:2000::/56, 2001:db8:3000:4000::/56 and 782 2001:db8:5000:6000::/56 then the routing system would include: 784 D: [ULA*]:2001:db8:1000:2000/120 786 E: [ULA*]:2001:db8:3000:4000/120 788 F: [ULA*]:2001:db8:5000:6000/120 790 A full discussion of the BGP-based routing system used by AERO is 791 found in [I-D.ietf-rtgwg-atn-bgp]. 793 3.2.5. OMNI Link Encapsulation 795 With the Client and partition prefixes in place in Bridge forwarding 796 tables, the OMNI interface sends control and data packets toward AERO 797 destination nodes located in different OMNI link segments over the 798 spanning tree via mid-layer encapsulation using the IPv6 OMNI 799 Adaptation Layer (OAL) header [I-D.templin-6man-omni-interface]. 800 When necessary, the OMNI interface also includes an OMNI Routing 801 Header (ORH) as an extension to the OAL header if final segment 802 forwarding information is available, e.g., in the neighbor cache. 803 The ORH is formatted as shown in Figure 3: 805 0 1 2 3 806 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 1 807 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 808 | Next Header | Hdr Ext Len | Routing Type | SRT | FMT | 809 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 810 | Last Hop Segment-id (LHS) | 811 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 812 ~ Link Layer Address (L2ADDR) ~ 813 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 814 ~ Destination Suffix (if necessary) ~ 815 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 816 ~ Null Padding (if necessary) ~ 817 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 819 Figure 3: OMNI Routing Header (ORH) Format 821 In this format: 823 o Next Header identifies the type of header immediately following 824 the ORH. 826 o Hdr Ext Len is the length of the Routing header in 8-octet units 827 (not including the first 8 octets), with trailing padding added if 828 necessary to produce an integral number of 8-octet units. 830 o Routing Type is set to TBD (see IANA Considerations). 832 o Segments Left is omitted, and replaced by a 5-bit SRT and 3-bit 833 FMT field. 835 o SRT - a 5-bit Segment Routing Topology prefix length value that 836 (when added to 96) determines the prefix length to apply to the 837 ADM-ULA formed from concatenating [ULA*]::/96 with the 32 bit LHS 838 value that follows. For example, the value 16 corresponds to the 839 prefix length 112. 841 o FMT - a 3-bit "Framework/Mode/Type" code corresponding to the 842 included Link Layer Address as follows: 844 * When the most significant bit (i.e., "Framework") is set to 1, 845 L2ADDR is the INET encapsulation address for the target Client 846 itself; otherwise is the address of the Server/Proxy named in 847 the LHS. 849 * When the next most significant bit (i.e., "Mode") is set to 1, 850 the target Client is (likely) located behind an INET Network 851 Address Translator (NAT); otherwise, L2ADDR encodes the native 852 INET address of the target's Server/Proxy or of the target 853 itself. 855 * When the least significant bit (i.e., "Type") is set to 0, 856 L2ADDR includes a UDP Port Number followed by an IPv4 address; 857 otherwise, it includes a UDP Port Number followed by an IPv6 858 address. 860 o LHS - the 32 bit ID of a node in the Last Hop Segment that 861 services the target. When SRT and LHS are both set to 0, the LHS 862 is considered unspecified. When SRT is set to 0 and LHS is non- 863 zero, the prefix length is set to 128. SRT and LHS provide 864 guidance to the OMNI interface forwarding algorithm. 865 Specifically, if SRT/LHS is located in the local OMNI link segment 866 then the OMNI interface can omit OAL/ORH encapsulation and 867 (following any necessary NAT traversal messaging) send directly to 868 the target using INET encapsulation according to FMT/L2ADDR. 869 Otherwise, it must perform INET/OAL/ORH encapsulation and forward 870 according to the OMNI link spanning tree. 872 o Link Layer Address (L2ADDR) - Formatted according to FMT, and 873 identifies the link-layer address (i.e., the encapsulation 874 address) of the target. The UDP Port Number appears in the first 875 two octets and the IP address appears in the next 4 octets for 876 IPv4 or 16 octets for IPv6. The Port Number and IP address are 877 recorded in ones-compliment "obfuscated" form per [RFC4380]. The 878 OMNI interface forwarding algorithm uses FMT/L2ADDR to determine 879 the INET encapsulation address for local forwarding when SRT/LHS 880 is located in the same OMNI link segment. Note that if the target 881 is behind a NAT, L2ADDR will contain the mapped INET address 882 stored in the NAT; otherwise, L2ADDR will contain the native INET 883 information of the target itself. 885 o Destination Suffix is a 64-bit field included only for OAL- 886 encapsulated packets that require OAL fragmentation. Present only 887 when Hdr Ext Len indicates that at least 8 bytes follow L2ADDR. 888 When present, encodes the 64-bit MNP-ULA suffix for the target 889 Client. For example, if the MNP-ULA is [ULA*]:2001:db8:1:2 then 890 the Destination suffix encodes the value 2001:db8:1:2. 892 o Null Padding contains zero-valued octets as necessary to pad the 893 ORH to an integral number of 8-octet units. 895 AERO nodes use OAL encapsulation when the target destination is 896 located in a different OMNI link segment, or when OAL fragmentation 897 is necessary (otherwise, OAL encapsulation is omitted and simple INET 898 encapsulation is used). When an AERO node uses OAL encapsulation for 899 a packet with source address 2001:db8:1:2::1 and destination address 900 2001:db8:1234:5678::1, it sets the OAL header source address to its 901 own ULA (e.g., [ULA*]::1000:2000) and sets the destination address to 902 the MNP-ULA corresponding to the IP destination address (e.g., 903 [ULA*]::2001:db8:1234:5678). 905 If the neighbor cache information indicates that the target is in a 906 different segment, the node next inserts an ORH immediately following 907 the OAL header while including the correct SRT, FMT, LHS, L2ADDR and 908 Destination Suffix if fragmentation is needed (in this case, the 909 Destination Suffix is 2001:db8:1234:5678). Next, the node overwrites 910 the OAL header destination address with the LHS Subnet Router Anycast 911 address (for example, for LHS 3000:4567 with SRT 16, the Subnet 912 Router Anycast address is [ULA*]::3000:0000). (Note: if ADM-ULA of 913 the last-hop Proxy/Server is known but the SRT, FMT, LHS and L2ADDR 914 are not (yet) known, the node instead overwrites the OAL header 915 destination address with the ADM-ULA.) 917 The node then fragments the OAL/ORH packet if necessary, with each 918 resulting fragment including the OAL/ORH headers while only the first 919 fragment includes the original IPv6 header. The node finally 920 encapsulates each resulting OAL/ORH packet/fragment in an INET header 921 with source address set to its own INET address (e.g., 192.0.2.100) 922 and destination set to the INET address of a Bridge (e.g., 923 192.0.2.1). 925 The encapsulation format in the above example is shown in Figure 4: 927 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 928 | INET Header | 929 | src = 192.0.2.100 | 930 | dst = 192.0.2.1 | 931 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 932 | OAL Header (if necessary) | 933 | src = [ULA*]::1000:2000 | 934 | dst= [ULA*]::3000:0000 | 935 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 936 | ORH Header (if necessary) | 937 | Destination Suffix: | 938 | 2001:db8:1234:5678 | 939 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 940 | Inner IP Header | 941 | src = 2001:db8:1:2::1 | 942 | dst = 2001:db8:1234:5678::1 | 943 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 944 | | 945 ~ ~ 946 ~ Inner Packet Body ~ 947 ~ ~ 948 | | 949 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 951 Figure 4: OAL/ORH Encapsulation 953 In this format, the inner IP header and packet body are the original 954 IP packet, the OAL header is an IPv6 header prepared according to 955 [RFC2473], the ORH is a Routing Header extension of the OAL header, 956 and the INET header is prepared as discussed in Section 3.6. 958 This gives rise to a routing system that contains both Client prefix 959 routes that may change dynamically due to regional node mobility and 960 partition prefix routes that rarely if ever change. The Bridges can 961 therefore provide link-layer bridging by sending packets over the 962 spanning tree instead of network-layer routing according to MNP 963 routes. As a result, opportunities for packet loss due to node 964 mobility between different segments are mitigated. 966 In normal operations, IPv6 ND messages are conveyed over secured 967 paths between OMNI link neighbors so that specific Proxys, Servers or 968 Relays can be addressed without being subject to mobility events. 969 Conversely, only the first few packets destined to Clients need to 970 traverse secured paths until route optimization can determine a more 971 direct path. 973 Note: When the source OAL has multiple inner IP packets to send to 974 the same destination, it can perform "packing" to generate a "super- 975 packet" as discussed in Section 5.2 of 976 [I-D.templin-6man-omni-interface]. In that case, the OAL/ORH super- 977 packet may include up to N inner packets as long as the total length 978 of the super-packet does not exceed the OMNI interface MTU. 980 Note: Use of an IPv6 "minimal encapsulation" format (i.e., an IPv6 981 variant of [RFC2004]) based on extensions to the ORH was considered 982 and abandoned. In the approach, the ORH would be inserted as an 983 extension header to the original IPv6 packet header. The IPv6 984 destination address would then be written into the ORH, and the ULA 985 corresponding to the destination would be overwritten in the IPv6 986 destination address. This would seemingly convey enough forwarding 987 information so that OAL encapsulation could be avoided. However, 988 this "minimal encapsulation" IPv6 packet would then have a non-ULA 989 source address and ULA destination address, an incorrect value in 990 upper layer protocol checksums, and a Hop Limit that is decremented 991 within the spanning tree when it should not be. The insertion and 992 removal of the ORH would also entail rewriting the Payload Length and 993 Next Header fields - again, invalidating upper layer checksums. 994 These irregularities would result in implementation challenges and 995 the potential for operational issues, e.g., since actionable ICMPv6 996 error reports could not be delivered to the original source. In 997 order to address the issues, still more information such as the 998 original IPv6 source address could be written into the ORH. However, 999 with the additional information the benefit of the "minimal 1000 encapsulation" savings quickly diminishes, and becomes overshadowed 1001 by the implementation and operational irregularities. 1003 3.2.6. Segment Routing Topologies (SRTs) 1005 The 64-bit sub-prefixes of [ULA]::/48 identify up to 2^16 distinct 1006 Segment Routing Topologies (SRTs). Each SRT is a mutually-exclusive 1007 OMNI link overlay instance using a distinct set of ULAs, and emulates 1008 a Virtual LAN (VLAN) service for the OMNI link. In some cases (e.g., 1009 when redundant topologies are needed for fault tolerance and 1010 reliability) it may be beneficial to deploy multiple SRTs that act as 1011 independent overlay instances. A communication failure in one 1012 instance therefore will not affect communications in other instances. 1014 Each SRT is identified by a distinct value in bits 48-63 of 1015 [ULA]::/48, i.e., as [ULA0]::/64, [ULA1]::/64, [ULA2]::/64, etc. 1016 Each OMNI interface is identified by a unique interface name (e.g., 1017 omni0, omni1, omni2, etc.) and assigns an anycast ADM-ULA 1018 corresponding to its SRT prefix length. The anycast ADM-ULA is used 1019 for OMNI interface determination in Safety-Based Multilink (SBM) as 1020 discussed in [I-D.templin-6man-omni-interface]. Each OMNI interface 1021 further applies Performance-Based Multilink (PBM) internally. 1023 3.2.7. Segment Routing For OMNI Link Selection 1025 An original IPv6 source can direct an IPv6 packet to an AERO node by 1026 including a standard IPv6 Segment Routing Header (SRH) [RFC8754] with 1027 the anycast ADM-ULA for the selected SRT as either the IPv6 1028 destination or as an intermediate hop within the SRH. This allows 1029 the original source to determine the specific OMNI link topology a 1030 packet will traverse when there may be multiple alternatives. 1032 When the AERO node processes the SRH and forwards the packet to the 1033 correct OMNI interface, the OMNI interface writes the next IPv6 1034 address from the SRH into the IPv6 destination address and decrements 1035 Segments Left. If decrementing would cause Segments Left to become 1036 0, the OMNI interface deletes the SRH before forwarding. This form 1037 of Segment Routing supports Safety-Based Multilink (SBM). 1039 3.2.8. Segment Routing Within the OMNI Link 1041 AERO node OMNI interfaces can insert OAL/ORH headers for Segment 1042 Routing within the OMNI link to influence the paths of packets 1043 destined to targets in remote segments without requiring all packets 1044 to traverse strict spanning tree paths. 1046 When an AERO node's OMNI interface has a packet to send to a target 1047 discovered through route optimization located in the same OMNI link 1048 segment, it encapsulates the packet in OAL/ORH headers if necessary 1049 as discussed above. The node then uses the target's Link Layer 1050 Address (L2ADDR) information for INET encapsulation. 1052 When an AERO node's OMNI interface has a packet to send to a route 1053 optimization target located in a remote OMNI link segment, it 1054 encapsulates the packet in OAL/ORH headers as discussed above while 1055 forwarding the packet to a Bridge with destination set to the Subnet 1056 Router Anycast address for the final OMNI link segment. 1058 When a Bridge receives a packet destined to its Subnet Router Anycast 1059 address with an OAL/ORH with SRT/LHS values corresponding to the 1060 local segment, it examines the L2ADDR according to FMT and removes 1061 the ORH from the packet; if the packet is not a fragment, the Bridge 1062 also removes the OAL header. If the packet was a fragment, the 1063 Bridge instead writes the MNP-ULA corresponding to the ORH 1064 Destination Suffix into the OAL destination address. The Bridge then 1065 encapsulates the packet/fragment in an INET header according to 1066 L2ADDR and forwards the packet within the INET either to the LHS 1067 Server/Proxy or directly to the target Client itself. In this way, 1068 the Bridge participates in route optimization to reduce traffic load 1069 and suboptimal routing through strict spanning tree paths. 1071 3.3. OMNI Interface Characteristics 1073 OMNI interfaces are virtual interfaces configured over one or more 1074 underlying interfaces classified as follows: 1076 o INET interfaces connect to an INET either natively or through one 1077 or several IPv4 NATs. Native INET interfaces have global IP 1078 addresses that are reachable from any INET correspondent. All 1079 Server, Relay and Bridge interfaces are native interfaces, as are 1080 INET-facing interfaces of Proxys. NATed INET interfaces connect 1081 to a private network behind one or more NATs that provide INET 1082 access. Clients that are behind a NAT are required to send 1083 periodic keepalive messages to keep NAT state alive when there are 1084 no data packets flowing. 1086 o ANET interfaces connect to an ANET that is separated from the open 1087 INET by a Proxy. Proxys can actively issue control messages over 1088 the INET on behalf of the Client to reduce ANET congestion. 1090 o VPNed interfaces use security encapsulation over the INET to a 1091 Virtual Private Network (VPN) server that also acts as a Server or 1092 Proxy. Other than the link-layer encapsulation format, VPNed 1093 interfaces behave the same as Direct interfaces. 1095 o Direct (i.e., single-hop point-to-point) interfaces connect a 1096 Client directly to a Server or Proxy without crossing any ANET/ 1097 INET paths. An example is a line-of-sight link between a remote 1098 pilot and an unmanned aircraft. The same Client considerations 1099 apply as for VPNed interfaces. 1101 OMNI interfaces use OAL/ORH encapsulation as necessary as discussed 1102 in Section 3.2.5. OMNI interfaces use link-layer encapsulation (see: 1103 Section 3.6) to exchange packets with OMNI link neighbors over INET 1104 or VPNed interfaces as well as over ANET interfaces for which the 1105 Client and Proxy may be multiple IP hops away. OMNI interfaces do 1106 not use link-layer encapsulation over Direct underlying interfaces or 1107 ANET interfaces when the Client and Proxy are known to be on the same 1108 underlying link. 1110 OMNI interfaces maintain a neighbor cache for tracking per-neighbor 1111 state the same as for any interface. OMNI interfaces use ND messages 1112 including Router Solicitation (RS), Router Advertisement (RA), 1113 Neighbor Solicitation (NS) and Neighbor Advertisement (NA) for 1114 neighbor cache management. 1116 OMNI interfaces send ND messages with an OMNI option formatted as 1117 specified in [I-D.templin-6man-omni-interface]. The OMNI option 1118 includes prefix registration information and Interface Attributes 1119 containing link information parameters for the OMNI interface's 1120 underlying interfaces. Each OMNI option may include multiple 1121 Interface Attributes sub-options, each identified by an ifIndex 1122 value. 1124 A Client's OMNI interface may be configured over multiple underlying 1125 interface connections. For example, common mobile handheld devices 1126 have both wireless local area network ("WLAN") and cellular wireless 1127 links. These links are often used "one at a time" with low-cost WLAN 1128 preferred and highly-available cellular wireless as a standby, but a 1129 simultaneous-use capability could provide benefits. In a more 1130 complex example, aircraft frequently have many wireless data link 1131 types (e.g. satellite-based, cellular, terrestrial, air-to-air 1132 directional, etc.) with diverse performance and cost properties. 1134 If a Client's multiple underlying interfaces are used "one at a time" 1135 (i.e., all other interfaces are in standby mode while one interface 1136 is active), then ND message OMNI options include only a single 1137 Interface Attributes sub-option set to constant values. In that 1138 case, the Client would appear to have a single interface but with a 1139 dynamically changing link-layer address. 1141 If the Client has multiple active underlying interfaces, then from 1142 the perspective of ND it would appear to have multiple link-layer 1143 addresses. In that case, ND message OMNI options MAY include 1144 multiple Interface Attributes sub-options - each with values that 1145 correspond to a specific interface. Every ND message need not 1146 include Interface Attributes for all underlying interfaces; for any 1147 attributes not included, the neighbor considers the status as 1148 unchanged. 1150 Bridge, Server and Proxy OMNI interfaces may be configured over one 1151 or more secured tunnel interfaces. The OMNI interface configures 1152 both an ADM-LLA and its corresponding ADM-ULA, while the underlying 1153 secured tunnel interfaces are either unnumbered or configure the same 1154 ULA. The OMNI interface encapsulates each IP packet in OAL/ORH 1155 headers and presents the packet to the underlying secured tunnel 1156 interface. Routing protocols such as BGP that run over the OMNI 1157 interface do not employ OAL/ORH encapsulation, but rather present the 1158 routing protocol messages directly to the underlying secured tunnels 1159 while using the ULA as the source address. This distinction must be 1160 honored consistently according to each node's configuration so that 1161 the IP forwarding table will associate discovered IP routes with the 1162 correct interface. 1164 3.4. OMNI Interface Initialization 1166 AERO Servers, Proxys and Clients configure OMNI interfaces as their 1167 point of attachment to the OMNI link. AERO nodes assign the MSPs for 1168 the link to their OMNI interfaces (i.e., as a "route-to-interface") 1169 to ensure that packets with destination addresses covered by an MNP 1170 not explicitly assigned to a non-OMNI interface are directed to the 1171 OMNI interface. 1173 OMNI interface initialization procedures for Servers, Proxys, Clients 1174 and Bridges are discussed in the following sections. 1176 3.4.1. AERO Server/Relay Behavior 1178 When a Server enables an OMNI interface, it assigns an ADM-{LLA,ULA} 1179 appropriate for the given OMNI link segment. The Server also 1180 configures secured tunnels with one or more neighboring Bridges and 1181 engages in a BGP routing protocol session with each Bridge. 1183 The OMNI interface provides a single interface abstraction to the IP 1184 layer, but internally comprises multiple secured tunnels as well as 1185 an NBMA nexus for sending encapsulated data packets to OMNI interface 1186 neighbors. The Server further configures a service to facilitate ND 1187 exchanges with AERO Clients and manages per-Client neighbor cache 1188 entries and IP forwarding table entries based on control message 1189 exchanges. 1191 Relays are simply Servers that run a dynamic routing protocol to 1192 redistribute routes between the OMNI interface and INET/EUN 1193 interfaces (see: Section 3.2.4). The Relay provisions MNPs to 1194 networks on the INET/EUN interfaces (i.e., the same as a Client would 1195 do) and advertises the MSP(s) for the OMNI link over the INET/EUN 1196 interfaces. The Relay further provides an attachment point of the 1197 OMNI link to a non-MNP-based global topology. 1199 3.4.2. AERO Proxy Behavior 1201 When a Proxy enables an OMNI interface, it assigns an ADM-{LLA, ULA} 1202 and configures permanent neighbor cache entries the same as for 1203 Servers. The Proxy also configures secured tunnels with one or more 1204 neighboring Bridges and maintains per-Client neighbor cache entries 1205 based on control message exchanges. Importantly Proxys are often 1206 configured to act as Servers, and vice-versa. 1208 3.4.3. AERO Client Behavior 1210 When a Client enables an OMNI interface, it assigns either an 1211 MNP-{LLA, ULA} or a Temporary {LLA, ULA} and sends RS messages with 1212 ND parameters over its underlying interfaces to a Server, which 1213 returns an RA message with corresponding parameters. The RS/RA 1214 messages may pass through a Proxy in the case of a Client's ANET 1215 interface, or through one or more NATs in the case of a Client's INET 1216 interface. (Note: if the Client used a Temporary {LLA, ULA} in its 1217 initial RS message, it will discover an MNP-{LLA, ULA} in the 1218 corresponding RA that it receives from the Server and begin using 1219 these new addresses while deprecating the Temporary addresses.) 1221 3.4.4. AERO Bridge Behavior 1223 AERO Bridges configure an OMNI interface and assign the ADM-ULA 1224 Subnet Router Anycast address for each OMNI link segment they connect 1225 to. Bridges configure secured tunnels with Servers, Proxys and other 1226 Bridges, and engage in a BGP routing protocol session with neighbors 1227 on the spanning tree (see: Section 3.2.4). 1229 3.5. OMNI Interface Neighbor Cache Maintenance 1231 Each OMNI interface maintains a conceptual neighbor cache that 1232 includes an entry for each neighbor it communicates with on the OMNI 1233 link per [RFC4861]. OMNI interface neighbor cache entries are said 1234 to be one of "permanent", "symmetric", "asymmetric" or "proxy". 1236 Permanent neighbor cache entries are created through explicit 1237 administrative action; they have no timeout values and remain in 1238 place until explicitly deleted. AERO Bridges maintain permanent 1239 neighbor cache entries for their associated Proxys/Servers (and vice- 1240 versa). Each entry maintains the mapping between the neighbor's 1241 network-layer LLA and corresponding INET address. 1243 Symmetric neighbor cache entries are created and maintained through 1244 RS/RA exchanges as specified in Section 3.12, and remain in place for 1245 durations bounded by prefix lifetimes. AERO Servers maintain 1246 symmetric neighbor cache entries for each of their associated 1247 Clients, and AERO Clients maintain symmetric neighbor cache entries 1248 for each of their associated Servers. 1250 Asymmetric neighbor cache entries are created or updated based on 1251 route optimization messaging as specified in Section 3.14, and are 1252 garbage-collected when keepalive timers expire. AERO ROSs maintain 1253 asymmetric neighbor cache entries for active targets with lifetimes 1254 based on ND messaging constants. Asymmetric neighbor cache entries 1255 are unidirectional since only the ROS (and not the ROR) creates an 1256 entry. 1258 Proxy neighbor cache entries are created and maintained by AERO 1259 Proxys when they process Client/Server ND exchanges, and remain in 1260 place for durations bounded by ND and prefix lifetimes. AERO Proxys 1261 maintain proxy neighbor cache entries for each of their associated 1262 Clients. Proxy neighbor cache entries track the Client state and the 1263 address of the Client's associated Server(s). 1265 To the list of neighbor cache entry states in Section 7.3.2 of 1266 [RFC4861], Proxy and Server OMNI interfaces add an additional state 1267 DEPARTED that applies to symmetric and proxy neighbor cache entries 1268 for Clients that have recently departed. The interface sets a 1269 "DepartTime" variable for the neighbor cache entry to "DEPART_TIME" 1270 seconds. DepartTime is decremented unless a new ND message causes 1271 the state to return to REACHABLE. While a neighbor cache entry is in 1272 the DEPARTED state, packets destined to the target Client are 1273 forwarded to the Client's new location instead of being dropped. 1274 When DepartTime decrements to 0, the neighbor cache entry is deleted. 1275 It is RECOMMENDED that DEPART_TIME be set to the default constant 1276 value REACHABLE_TIME plus 10 seconds (40 seconds by default) to allow 1277 a window for packets in flight to be delivered while stale route 1278 optimization state may be present. 1280 When an ROR receives an authentic NS message used for route 1281 optimization, it searches for a symmetric neighbor cache entry for 1282 the target Client. The ROR then returns a solicited NA message 1283 without creating a neighbor cache entry for the ROS, but creates or 1284 updates a target Client "Report List" entry for the ROS and sets a 1285 "ReportTime" variable for the entry to REPORT_TIME seconds. The ROR 1286 resets ReportTime when it receives a new authentic NS message, and 1287 otherwise decrements ReportTime while no authentic NS messages have 1288 been received. It is RECOMMENDED that REPORT_TIME be set to the 1289 default constant value REACHABLE_TIME plus 10 seconds (40 seconds by 1290 default) to allow a window for route optimization to converge before 1291 ReportTime decrements below REACHABLE_TIME. 1293 When the ROS receives a solicited NA message response to its NS 1294 message used for route optimization, it creates or updates an 1295 asymmetric neighbor cache entry for the target network-layer and 1296 link-layer addresses. The ROS then (re)sets ReachableTime for the 1297 neighbor cache entry to REACHABLE_TIME seconds and uses this value to 1298 determine whether packets can be forwarded directly to the target, 1299 i.e., instead of via a default route. The ROS otherwise decrements 1300 ReachableTime while no further solicited NA messages arrive. It is 1301 RECOMMENDED that REACHABLE_TIME be set to the default constant value 1302 30 seconds as specified in [RFC4861]. 1304 AERO nodes also use the value MAX_UNICAST_SOLICIT to limit the number 1305 of NS keepalives sent when a correspondent may have gone unreachable, 1306 the value MAX_RTR_SOLICITATIONS to limit the number of RS messages 1307 sent without receiving an RA and the value MAX_NEIGHBOR_ADVERTISEMENT 1308 to limit the number of unsolicited NAs that can be sent based on a 1309 single event. It is RECOMMENDED that MAX_UNICAST_SOLICIT, 1310 MAX_RTR_SOLICITATIONS and MAX_NEIGHBOR_ADVERTISEMENT be set to 3 the 1311 same as specified in [RFC4861]. 1313 Different values for DEPART_TIME, REPORT_TIME, REACHABLE_TIME, 1314 MAX_UNICAST_SOLICIT, MAX_RTR_SOLCITATIONS and 1315 MAX_NEIGHBOR_ADVERTISEMENT MAY be administratively set; however, if 1316 different values are chosen, all nodes on the link MUST consistently 1317 configure the same values. Most importantly, DEPART_TIME and 1318 REPORT_TIME SHOULD be set to a value that is sufficiently longer than 1319 REACHABLE_TIME to avoid packet loss due to stale route optimization 1320 state. 1322 3.5.1. OMNI Neighbor Interface Attributes 1324 OMNI interface IPv6 ND messages include OMNI options 1325 [I-D.templin-6man-omni-interface] with Interface Attributes that 1326 provide Link-Layer Address and QoS Preference information for the 1327 neighbor's underlying interfaces. This information is stored in the 1328 neighbor cache and provides the basis for the forwarding algorithm 1329 specified in Section 3.10. The information is cumulative and 1330 reflects the union of the OMNI information from the most recent ND 1331 messages received from the neighbor; it is therefore not required 1332 that each ND message contain all neighbor information. 1334 The OMNI option Interface Attributes for each underlying interface 1335 includes a two-part "Link-Layer Address" consisting of a simple IP 1336 encapsulation address determined by the FMT and L2ADDR fields and an 1337 ADM-ULA determined by the SRT and LHS fields. If the neighbor is 1338 located in the local OMNI link segment (and, if any necessary NAT 1339 state has been established) forwarding via simple IP encapsulation 1340 can be used; otherwise, OAL encapsulation must be used. Underlying 1341 interfaces are further selected based on their associated preference 1342 values "high", "medium", "low" or "disabled". 1344 Note: the OMNI option is distinct from any Source/Target Link-Layer 1345 Address Options (S/TLLAOs) that may appear in an ND message according 1346 to the appropriate IPv6 over specific link layer specification (e.g., 1347 [RFC2464]). If both an OMNI option and S/TLLAO appear, the former 1348 pertains to encapsulation addresses while the latter pertains to the 1349 native L2 address format of the underlying media. 1351 3.5.2. OMNI Neighbor Advertisement Message Flags 1353 As discussed in Section 4.4 of [RFC4861] NA messages include three 1354 flag bits R, S and O. OMNI interface NA messages treat the flags as 1355 follows: 1357 o R: The R ("Router") flag is set to 1 in the NA messages sent by 1358 all AERO/OMNI node types. Simple hosts that would set R to 0 do 1359 not occur on the OMNI link itself, but may occur on the downstream 1360 links of Clients and Relays. 1362 o S: The S ("Solicited") flag is set exactly as specified in 1363 Section 4.4. of [RFC4861], i.e., it is set to 1 for Solicited NAs 1364 and set to 0 for Unsolicited NAs (both unicast and multicast). 1366 o O: The O ("Override") flag is set to 0 for solicited proxy NAs and 1367 set to 1 for all other solicited and unsolicited NAs. For further 1368 study is whether solicited NAs for anycast targets apply for OMNI 1369 links. Since MNP-LLAs must be uniquely assigned to Clients to 1370 support correct ND protocol operation, however, no role is 1371 currently seen for assigning the same MNP-LLA to multiple Clients. 1373 3.6. OMNI Interface Encapsulation and Re-encapsulation 1375 The OMNI Adaptation Layer (OAL) inserts mid-layer IPv6 headers known 1376 as the OAL/ORH headers when necessary as discussed in the following 1377 sections. After either inserting or omitting the OAL/ORH headers, 1378 the OMNI interface also inserts or omits an outer ANET/INET 1379 encapsulation header as discussed below. 1381 OMNI interfaces avoid outer encapsulation over Direct underlying 1382 interfaces and ANET underlying interfaces for which the Client and 1383 Proxy are connected to the same underlying link. Otherwise, OMNI 1384 interfaces encapsulate packets according to whether they are entering 1385 the OMNI interface from the network layer or if they are being re- 1386 admitted into the same OMNI link they arrived on. This latter form 1387 of encapsulation is known as "re-encapsulation". 1389 For packets entering the OMNI interface from the network layer, the 1390 OMNI interface copies the "TTL/Hop Limit", "Type of Service/Traffic 1391 Class" [RFC2983], "Flow Label"[RFC6438] (for IPv6) and "Congestion 1392 Experienced" [RFC3168] values in the inner packet's IP header into 1393 the corresponding fields in the OAL and outer encapsulation 1394 header(s). 1396 For packets undergoing re-encapsulation, the OMNI interface instead 1397 copies these values from the original encapsulation header into the 1398 new encapsulation header, i.e., the values are transferred between 1399 encapsulation headers and *not* copied from the encapsulated packet's 1400 network-layer header. (Note especially that by copying the TTL/Hop 1401 Limit between encapsulation headers the value will eventually 1402 decrement to 0 if there is a (temporary) routing loop.) 1404 OMNI interfaces configured over ANET underlying interfaces which 1405 employ a different IP protocol version (and/or when the Client and 1406 Proxy may be separated by multiple ANET IP hops) use IP-in-IP 1407 encapsulation so that the inner packet can traverse the ANET without 1408 decrementing the TTL/Hop-Limit. IPv6 underlying ANET interfaces use 1409 [RFC2473] encapsulation, while IPv4 interfaces use the appropriate 1410 encapsulation per one of [RFC5214][RFC2003]. 1412 OMNI interfaces configured over INET underlying interfaces 1413 encapsulate packets in INET headers according to the next hop 1414 determined in the forwarding algorithm in Section 3.10. If the next 1415 hop is reached via a secured tunnel, the OMNI interface uses an 1416 encapsulation format specific to the secured tunnel type (see: 1417 Section 6). If the next hop is reached via an unsecured INET 1418 interface, the OMNI interface instead uses UDP/IP encapsulation per 1419 [RFC4380] and as extended in [RFC6081]. 1421 When UDP/IP encapsulation is used, the OMNI interface next sets the 1422 UDP source port to a constant value that it will use in each 1423 successive packet it sends, and sets the UDP length field to the 1424 length of the encapsulated packet plus 8 bytes for the UDP header 1425 itself plus the length of any included extension headers or trailers. 1426 The encapsulated packet may be either IPv6 or IPv4, as distinguished 1427 by the version number found in the first four bits. 1429 For UDP/IP-encapsulated packets sent to a Server, Relay or Bridge, 1430 the OMNI interface sets the UDP destination port to 8060, i.e., the 1431 IANA-registered port number for AERO. For packets sent to a Client, 1432 the OMNI interface sets the UDP destination port to the port value 1433 stored in the neighbor cache entry for this Client. The OMNI 1434 interface finally includes/omits the UDP checksum according to 1435 [RFC6935][RFC6936]. 1437 When a Proxy, Relay or Server re-encapsulates a packet received from 1438 a Client that includes an OAL but no ORH, it inserts an ORH 1439 immediately following the OAL header and adjusts the OAL payload 1440 length and destination address field. The inserted ORH will be 1441 removed by the final-hop Bridge, but its insertion and removal will 1442 not interfere with reassembly at the final destination. 1444 3.7. OMNI Interface Decapsulation 1446 OMNI interfaces decapsulate packets destined either to the AERO node 1447 itself or to a destination reached via an interface other than the 1448 OMNI interface the packet was received on. When the encapsulated 1449 packet arrives in multiple OAL fragments, the OMNI interface 1450 reassembles as discussed in Section 3.9. Further decapsulation steps 1451 are performed according to the appropriate encapsulation format 1452 specification. 1454 3.8. OMNI Interface Data Origin Authentication 1456 AERO nodes employ simple data origin authentication procedures. In 1457 particular: 1459 o AERO Bridges, Servers and Proxys accept encapsulated data packets 1460 and control messages received from the (secured) spanning tree. 1462 o AERO Proxys and Clients accept packets that originate from within 1463 the same secured ANET. 1465 o AERO Clients and Relays accept packets from downstream network 1466 correspondents based on ingress filtering. 1468 o AERO Clients, Relays and Servers verify the outer UDP/IP 1469 encapsulation addresses according to [RFC4380]. 1471 AERO nodes silently drop any packets that do not satisfy the above 1472 data origin authentication procedures. Further security 1473 considerations are discussed in Section 6. 1475 3.9. OMNI Adaptation Layer and OMNI Interface MTU 1477 The OMNI interface observes the link nature of tunnels, including the 1478 Maximum Transmission Unit (MTU), Maximum Reassembly Unit (MRU) and 1479 the role of fragmentation and reassembly [I-D.ietf-intarea-tunnels]. 1480 The OMNI interface employs an OMNI Adaptation Layer (OAL) for 1481 accommodating multiple underlying links with diverse MTUs. The 1482 functions of the OAL and the OMNI interface MTU/MRU are specified in 1483 Section 5 of [I-D.templin-6man-omni-interface], with MTU/MRU both set 1484 to the constant value 9180 bytes. 1486 When the network layer presents an IP packet to the OMNI interface, 1487 the OAL encapsulates the packet in OAL/ORH headers. When the network 1488 layer presents the OMNI interface with multiple IP packets bound to 1489 the same destination, the OAL can concatenate multiple IP packets 1490 together into a single OAL super-packet as discussed in Section 5.2 1491 of [I-D.templin-6man-omni-interface]. The OAL then fragments the 1492 encapsulated packet if necessary such that the OAL/ORH headers appear 1493 in each fragment while the original IP packet header appears only in 1494 the first fragment. The OAL then transmits each OAL/ORH packet/ 1495 fragment over an underlying interface connected to either a physical 1496 link such as Ethernet, WiFi and the like or a virtual link such as an 1497 Internet or higher-layer tunnel (see the definition of link in 1498 [RFC8200]). 1500 Note: Although the ORH may be removed by a Bridge on the path (see: 1501 Section 3.10.4), this does not interfere with the destination's 1502 ability to reassemble in the event that the packet was fragmented. 1503 This is due to the fact that the ORH is not included in the 1504 fragmentable part; therefore, its removal does not invalidate the 1505 offset values in any fragment headers. 1507 3.10. OMNI Interface Forwarding Algorithm 1509 IP packets enter a node's OMNI interface either from the network 1510 layer (i.e., from a local application or the IP forwarding system) or 1511 from the link layer (i.e., from an OMNI interface neighbor). All 1512 packets entering a node's OMNI interface first undergo data origin 1513 authentication as discussed in Section 3.8. Packets that satisfy 1514 data origin authentication are processed further, while all others 1515 are dropped silently. The OMNI interface OAL wraps accepted packets 1516 in OAL/ORH headers if necessary as discussed above. 1518 Packets that enter the OMNI interface from the network layer are 1519 forwarded to an OMNI interface neighbor. Packets that enter the OMNI 1520 interface from the link layer are either re-admitted into the OMNI 1521 link or forwarded to the network layer where they are subject to 1522 either local delivery or IP forwarding. In all cases, the OMNI 1523 interface itself MUST NOT decrement the network layer TTL/Hop-count 1524 since its forwarding actions occur below the network layer. 1526 OMNI interfaces may have multiple underlying interfaces and/or 1527 neighbor cache entries for neighbors with multiple underlying 1528 interfaces (see Section 3.3). The OMNI interface uses interface 1529 attributes and/or traffic classifiers (e.g., DSCP value, port number, 1530 flow specification, etc.) to select an outgoing underlying interface 1531 for each packet based on the node's own QoS preferences, and also to 1532 select a destination link-layer address based on the neighbor's 1533 underlying interface with the highest preference. AERO 1534 implementations SHOULD allow for QoS preference values to be modified 1535 at runtime through network management. 1537 If multiple outgoing interfaces and/or neighbor interfaces have a 1538 preference of "high", the AERO node replicates the packet and sends 1539 one copy via each of the (outgoing / neighbor) interface pairs; 1540 otherwise, the node sends a single copy of the packet via an 1541 interface with the highest preference. AERO nodes keep track of 1542 which underlying interfaces are currently "reachable" or 1543 "unreachable", and only use "reachable" interfaces for forwarding 1544 purposes. 1546 The following sections discuss the OMNI interface forwarding 1547 algorithms for Clients, Proxys, Servers and Bridges. In the 1548 following discussion, a packet's destination address is said to 1549 "match" if it is the same as a cached address, or if it is covered by 1550 a cached prefix (which may be encoded in an MNP-LLA). 1552 3.10.1. Client Forwarding Algorithm 1554 When an IP packet enters a Client's OMNI interface from the network 1555 layer the Client searches for an asymmetric neighbor cache entry that 1556 matches the destination. If there is a match, the Client uses one or 1557 more "reachable" neighbor interfaces in the entry for packet 1558 forwarding. If there is no asymmetric neighbor cache entry, the 1559 Client instead forwards the packet toward a Server (the packet is 1560 intercepted by a Proxy if there is a Proxy on the path). The Client 1561 encapsulates the packet in OAL/ORH headers if necessary and fragments 1562 according to MTU requirements (see: Section 3.9). If the Client has 1563 multiple IP packets to send to the same destination, it can 1564 concatenate them in a single super-packet as discussed in Section 5.2 1565 of [I-D.templin-6man-omni-interface]. 1567 If there is an asymmetric neighbor cache entry and the neighbor 1568 interface selected for forwarding is located on the same OMNI link 1569 segment and not behind a NAT, the Client forwards the packet/ 1570 fragments directly according to the L2ADDR information for the 1571 neighbor. If the neighbor interface is behind a NAT on the same OMNI 1572 link segment, the Client instead forwards the initial packet/ 1573 fragments to its Server and initiates NAT traversal procedures. If 1574 the Client's intended source underlying interface is also behind a 1575 NAT and located on the same OMNI link segment, it sends a "direct 1576 bubble" over the interface per [RFC6081][RFC4380] to the L2ADDR found 1577 in the neighbor cache in order to establish state in its own NAT by 1578 generating traffic toward the neighbor (note that no response to the 1579 bubble is expected). 1581 The Client next sends an NS(NUD) message toward the MNP-ULA of the 1582 neighbor via its Server as discussed in Section 3.15. If the Client 1583 receives an NA(NUD) from the neighbor over the underlying interface, 1584 it marks the neighbor interface as "trusted" and sends future 1585 packets/fragments directly to the L2ADDR information for the neighbor 1586 instead of indirectly via the Server. The Client must honor the 1587 neighbor cache maintenance procedure by sending additional direct 1588 bubbles and/or NS/NA(NUD) messages as discussed in [RFC6081][RFC4380] 1589 in order to keep NAT state alive as long as packets are still 1590 flowing. 1592 When an IP packet enters a Client's OMNI interface from the link- 1593 layer, if the destination matches one of the Client's MNPs or link- 1594 local addresses the Client reassembles and decapsulates as necessary 1595 and delivers the inner packet to the network layer. Otherwise, the 1596 Client drops the packet and MAY return a network-layer ICMP 1597 Destination Unreachable message subject to rate limiting (see: 1598 Section 3.11). 1600 3.10.2. Proxy Forwarding Algorithm 1602 For control messages originating from or destined to a Client, the 1603 Proxy intercepts the message and updates its proxy neighbor cache 1604 entry for the Client. The Proxy then forwards a (proxyed) copy of 1605 the control message. (For example, the Proxy forwards a proxied 1606 version of a Client's NS/RS message to the target neighbor, and 1607 forwards a proxied version of the neighbor's NA/RA reply to the 1608 Client.) 1610 When the Proxy receives a data packet from a Client within the ANET, 1611 the Proxy reassembles and re-fragments if necessary then searches for 1612 an asymmetric neighbor cache entry that matches the destination and 1613 forwards as follows: 1615 o if the destination matches an asymmetric neighbor cache entry, the 1616 Proxy uses one or more "reachable" neighbor interfaces in the 1617 entry for packet forwarding using OAL/ORH encapsulation if 1618 necessary according to the cached link-layer address information. 1619 If the neighbor interface is in a different OMNI link segment, the 1620 Proxy forwards the packet to a Bridge; otherwise, it forwards the 1621 packet directly to the neighbor. If the neighbor is behind a NAT, 1622 the Proxy instead forwards initial packets via a Bridge while 1623 sending an NS(NUD) to the neighbor. When the Proxy receives the 1624 NA(NUD), it can begin forwarding packets directly to the neighbor 1625 the same as discussed in Section 3.10.1 while sending additional 1626 NUD messages as necessary to maintain NAT state. Note that no 1627 direct bubbles are necessary since the Proxy is by definition not 1628 located behind a NAT. 1630 o else, the Proxy uses OAL/ORH encapsulation and forwards the packet 1631 to a Bridge while using the MNP-ULA corresponding to the packet's 1632 destination as the destination address. 1634 When the Proxy receives an encapsulated data packet from an INET 1635 neighbor or from a secured tunnel from a Bridge, it accepts the 1636 packet only if data origin authentication succeeds and if there is a 1637 proxy neighbor cache entry that matches the inner destination. Next, 1638 the Proxy reassembles the packet (if necessary) and continues 1639 processing. If the reassembly is complete and the neighbor cache 1640 state is REACHABLE, the Proxy then returns a PTB if necessary (see: 1641 Section 3.9) then either drops or forwards the packet to the Client 1642 while performing OAL/ORH re-encapsulation and re-fragmentation if 1643 necessary. If the neighbor cache entry state is DEPARTED, the Proxy 1644 instead changes the destination address to the address of the new 1645 Server and forwards it to a Bridge while performing OAL/ORH re- 1646 encapsulation if necessary. 1648 Note: When the Proxy receives fragmented OAL packets with destination 1649 address set to the MNP-ULA of the Client, it can either reassemble 1650 first and then re-encapsulate/re-fragment before forwarding to the 1651 Client or forward the raw fragments on to the Client which then must 1652 reassemble. In the former case, the Proxy can re-fragment to a size 1653 that better matches the link MTU for the Client, which may be 1654 important for low-end links with large MTUs. In the latter case, the 1655 Client may receive fragments that are smaller than its link MTU but 1656 can still be reassembled; this case may provide an important 1657 performance benefit to Proxys by permitting them to avoid excessive 1658 reassembly and re-fragmentation overhead.) 1660 Note: If the Proxy has multiple IP packets to send to the same 1661 destination, it can concatenate them in a single super-packet as 1662 discussed in Section 5.2 of [I-D.templin-6man-omni-interface]. 1664 3.10.3. Server/Relay Forwarding Algorithm 1666 For control messages destined to a target Client's MNP-LLA that are 1667 received from a secured tunnel, the Server intercepts the message and 1668 returns a Proxyed response on behalf of the Client. (For example, 1669 the Server sends a Proxyed NA message reply in response to an NS 1670 message directed to one of its associated Clients.) If the Client's 1671 neighbor cache entry is in the DEPARTED state, however, the Server 1672 instead forwards the packet to the Client's new Server using OAL/ORH 1673 re-encapsulation the same as discussed for Proxys in Section 3.10.2. 1675 When the Server receives an encapsulated data packet from an INET 1676 neighbor or from a secured tunnel, it accepts the packet only if data 1677 origin authentication succeeds. If the packet was an OAL fragment 1678 with destination set to the Server's ADM-ULA, the Server submits the 1679 packet for reassembly (if the destination was the MNP-ULA of one of 1680 its Clients, the Server instead either submits the packet for 1681 reassembly or forwards the fragment directly to the target Client). 1682 If reassembly is complete (or if no reassembly was required), the 1683 Server then (re)fragments if necessary and forwards as follows: 1685 o if the network layer destination matches a symmetric neighbor 1686 cache entry in the REACHABLE state the Server prepares the packet 1687 for forwarding to the destination Client. The Server then 1688 forwards the packet as specified in Section 3.9. 1690 o else, if the destination matches a symmetric neighbor cache entry 1691 in the DEPARETED state the Server re-encapsulates the packet and 1692 forwards it using the ADM-ULA of the Client's new Server as the 1693 destination. 1695 o else, if the destination matches an asymmetric neighbor cache 1696 entry, the Server proceeds the same as specified for a Proxy in 1697 Section 3.10.2. Again, the Server need not send direct bubbles 1698 since it is not located behind a NAT. 1700 o else, if the destination matches a non-MNP route in the IP 1701 forwarding table or an ADM-LLA assigned to the Server's OMNI 1702 interface, the Server decapsulates the packet and releases it to 1703 the network layer for local delivery or IP forwarding. 1705 o else, the Server drops the packet. 1707 When the Server's OMNI interface receives a data packet from the 1708 network layer or from a VPNed or Direct Client, it performs OAL/ORH 1709 encapsulation and fragmentation if necessary, then processes the 1710 packet according to the network-layer destination address as follows: 1712 o if the destination matches a symmetric or asymmetric neighbor 1713 cache entry the Server processes the packet as above. 1715 o else, the Server encapsulates the packet in OLA/ORH headers and 1716 forwards it to a Bridge using its own ADM-ULA as the source and 1717 the MNP-ULA corresponding to the destination as the destination. 1719 Note: The same as for Proxys, when the Server receives fragmented OAL 1720 packets with destination address set to the MNP-ULA of the target, it 1721 can either reassemble first and then re-encapsulate/re-fragment 1722 before sending or forward the raw fragments on to the target which 1723 then must reassemble. In the former case, the Server can re-fragment 1724 to a size that better matches the link MTU for the Client, which may 1725 be important for low-end links with large MTUs. In the latter case, 1726 the target may receive fragments that are smaller than its link MTU 1727 but can still be reassembled; this case may provide an important 1728 performance benefit to Servers by permitting them to avoid excessive 1729 reassembly and re-fragmentation overhead.) 1730 Note: If the Server has multiple IP packets to send to the same 1731 destination, it can concatenate them in a single super-packet as 1732 discussed in Section 5.2 of [I-D.templin-6man-omni-interface]. 1734 3.10.4. Bridge Forwarding Algorithm 1736 Bridges forward OAL/ORH-encapsulated packets over secured tunnels the 1737 same as any IP router. When the Bridge receives an OAL/ORH- 1738 encapsulated packet via a secured tunnel, it removes the outer INET 1739 header and searches for a forwarding table entry that matches the OAL 1740 destination address. The Bridge then processes the packet as 1741 follows: 1743 o if the destination matches its ADM-ULA Subnet Router Anycast 1744 address the Bridge processes the packet locally before forwarding. 1745 The Bridge drops the packet if the next header is not an ORH; 1746 otherwise, for NA(NUD) messages the Bridge replaces the OMNI 1747 option Interface Attributes sub-option with information for its 1748 own interface while retaining the ifIndex value supplied by the 1749 NA(NUD) message source. For all packet types, the Bridge next 1750 examines the ORH FMT code. If the code indicates the destination 1751 is a Client on the open INET (or, a Client behind a NAT for which 1752 NAT traversal procedures have already converged) the Bridge 1753 removes the ORH then writes the MNP-ULA formed from the ORH 1754 Destination Suffix into the OAL destination if the packet is a 1755 fragment (otherwise, the Bridge also removes the OAL header). The 1756 Bridge then forwards the packet/fragment via INET encapsulation to 1757 the ORH L2ADDR. For all other destination cases, the Bridge 1758 instead writes the ADM-ULA formed from the ORH SRT/LHS into the 1759 OAL destination address and forwards the OAL/ORH encapsulated 1760 packet to the ADM-ULA Server while invoking NAT traversal 1761 procedures the same as for Proxys and Servers if necessary, noting 1762 that no direct bubbles are necessary since only the Client and not 1763 the Bridge is behind a NAT. 1765 o else, if the destination matches one of the Bridge's own 1766 addresses, the Bridge submits the packet for local delivery. 1768 o else, if the destination matches a forwarding table entry the 1769 Bridge forwards the packet via a secured tunnel to the next hop. 1770 If the destination matches an MSP without matching an MNP, 1771 however, the Bridge instead drops the packet and returns an ICMP 1772 Destination Unreachable message subject to rate limiting (see: 1773 Section 3.11). 1775 o else, the Bridge drops the packet and returns an ICMP Destination 1776 Unreachable as above. 1778 As for any IP router, the Bridge decrements the TTL/Hop Limit when it 1779 forwards the packet. Therefore, when an OAL header is present only 1780 the Hop Limit in the OAL header is decremented and not the TTL/Hop 1781 Limit in the inner packet header. Bridges do not insert OAL/ORH 1782 headers themselves; instead, they act as IPv6 routers and forward 1783 packets based on the destination address found in the headers of 1784 packets they receive. 1786 3.11. OMNI Interface Error Handling 1788 When an AERO node admits a packet into the OMNI interface, it may 1789 receive link-layer or network-layer error indications. 1791 A link-layer error indication is an ICMP error message generated by a 1792 router in the INET on the path to the neighbor or by the neighbor 1793 itself. The message includes an IP header with the address of the 1794 node that generated the error as the source address and with the 1795 link-layer address of the AERO node as the destination address. 1797 The IP header is followed by an ICMP header that includes an error 1798 Type, Code and Checksum. Valid type values include "Destination 1799 Unreachable", "Time Exceeded" and "Parameter Problem" 1800 [RFC0792][RFC4443]. (OMNI interfaces ignore all link-layer IPv4 1801 "Fragmentation Needed" and IPv6 "Packet Too Big" messages since they 1802 only emit packets that are guaranteed to be no larger than the IP 1803 minimum link MTU as discussed in Section 3.9.) 1805 The ICMP header is followed by the leading portion of the packet that 1806 generated the error, also known as the "packet-in-error". For 1807 ICMPv6, [RFC4443] specifies that the packet-in-error includes: "As 1808 much of invoking packet as possible without the ICMPv6 packet 1809 exceeding the minimum IPv6 MTU" (i.e., no more than 1280 bytes). For 1810 ICMPv4, [RFC0792] specifies that the packet-in-error includes: 1811 "Internet Header + 64 bits of Original Data Datagram", however 1812 [RFC1812] Section 4.3.2.3 updates this specification by stating: "the 1813 ICMP datagram SHOULD contain as much of the original datagram as 1814 possible without the length of the ICMP datagram exceeding 576 1815 bytes". 1817 The link-layer error message format is shown in Figure 5 (where, "L2" 1818 and "L3" refer to link-layer and network-layer, respectively): 1820 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1821 ~ ~ 1822 | L2 IP Header of | 1823 | error message | 1824 ~ ~ 1825 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1826 | L2 ICMP Header | 1827 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 1828 ~ ~ P 1829 | IP and other encapsulation | a 1830 | headers of original L3 packet | c 1831 ~ ~ k 1832 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ e 1833 ~ ~ t 1834 | IP header of | 1835 | original L3 packet | i 1836 ~ ~ n 1837 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1838 ~ ~ e 1839 | Upper layer headers and | r 1840 | leading portion of body | r 1841 | of the original L3 packet | o 1842 ~ ~ r 1843 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 1845 Figure 5: OMNI Interface Link-Layer Error Message Format 1847 The AERO node rules for processing these link-layer error messages 1848 are as follows: 1850 o When an AERO node receives a link-layer Parameter Problem message, 1851 it processes the message the same as described as for ordinary 1852 ICMP errors in the normative references [RFC0792][RFC4443]. 1854 o When an AERO node receives persistent link-layer Time Exceeded 1855 messages, the IP ID field may be wrapping before earlier fragments 1856 awaiting reassembly have been processed. In that case, the node 1857 should begin including integrity checks and/or institute rate 1858 limits for subsequent packets. 1860 o When an AERO node receives persistent link-layer Destination 1861 Unreachable messages in response to encapsulated packets that it 1862 sends to one of its asymmetric neighbor correspondents, the node 1863 should process the message as an indication that a path may be 1864 failing, and optionally initiate NUD over that path. If it 1865 receives Destination Unreachable messages over multiple paths, the 1866 node should allow future packets destined to the correspondent to 1867 flow through a default route and re-initiate route optimization. 1869 o When an AERO Client receives persistent link-layer Destination 1870 Unreachable messages in response to encapsulated packets that it 1871 sends to one of its symmetric neighbor Servers, the Client should 1872 mark the path as unusable and use another path. If it receives 1873 Destination Unreachable messages on many or all paths, the Client 1874 should associate with a new Server and release its association 1875 with the old Server as specified in Section 3.16.5. 1877 o When an AERO Server receives persistent link-layer Destination 1878 Unreachable messages in response to encapsulated packets that it 1879 sends to one of its symmetric neighbor Clients, the Server should 1880 mark the underlying path as unusable and use another underlying 1881 path. 1883 o When an AERO Server or Proxy receives link-layer Destination 1884 Unreachable messages in response to an encapsulated packet that it 1885 sends to one of its permanent neighbors, it treats the messages as 1886 an indication that the path to the neighbor may be failing. 1887 However, the dynamic routing protocol should soon reconverge and 1888 correct the temporary outage. 1890 When an AERO Bridge receives a packet for which the network-layer 1891 destination address is covered by an MSP, the Bridge drops the packet 1892 if there is no more-specific routing information for the destination 1893 and returns a network-layer Destination Unreachable message subject 1894 to rate limiting. The Bridge writes the network-layer source address 1895 of the original packet as the destination address and uses one of its 1896 non link-local addresses as the source address of the message. 1898 When an AERO node receives an encapsulated packet for which the 1899 reassembly buffer it too small, it drops the packet and returns a 1900 network-layer Packet Too Big (PTB) message. The node first writes 1901 the MRU value into the PTB message MTU field, writes the network- 1902 layer source address of the original packet as the destination 1903 address and writes one of its non link-local addresses as the source 1904 address. 1906 3.12. AERO Router Discovery, Prefix Delegation and Autoconfiguration 1908 AERO Router Discovery, Prefix Delegation and Autoconfiguration are 1909 coordinated as discussed in the following Sections. 1911 3.12.1. AERO Service Model 1913 Each AERO Server on the OMNI link is configured to facilitate Client 1914 prefix delegation/registration requests. Each Server is provisioned 1915 with a database of MNP-to-Client ID mappings for all Clients enrolled 1916 in the AERO service, as well as any information necessary to 1917 authenticate each Client. The Client database is maintained by a 1918 central administrative authority for the OMNI link and securely 1919 distributed to all Servers, e.g., via the Lightweight Directory 1920 Access Protocol (LDAP) [RFC4511], via static configuration, etc. 1921 Clients receive the same service regardless of the Servers they 1922 select. 1924 AERO Clients and Servers use ND messages to maintain neighbor cache 1925 entries. AERO Servers configure their OMNI interfaces as advertising 1926 NBMA interfaces, and therefore send unicast RA messages with a short 1927 Router Lifetime value (e.g., ReachableTime seconds) in response to a 1928 Client's RS message. Thereafter, Clients send additional RS messages 1929 to keep Server state alive. 1931 AERO Clients and Servers include prefix delegation and/or 1932 registration parameters in RS/RA messages (see 1933 [I-D.templin-6man-omni-interface]). The ND messages are exchanged 1934 between Client and Server according to the prefix management schedule 1935 required by the service. If the Client knows its MNP in advance, it 1936 can employ prefix registration by including its MNP-LLA as the source 1937 address of an RS message and with an OMNI option with valid prefix 1938 registration information for the MNP. If the Server (and Proxy) 1939 accept the Client's MNP assertion, they inject the prefix into the 1940 routing system and establish the necessary neighbor cache state. 1942 The following sections specify the Client and Server behavior. 1944 3.12.2. AERO Client Behavior 1946 AERO Clients discover the addresses of Servers in a similar manner as 1947 described in [RFC5214]. Discovery methods include static 1948 configuration (e.g., from a flat-file map of Server addresses and 1949 locations), or through an automated means such as Domain Name System 1950 (DNS) name resolution [RFC1035]. Alternatively, the Client can 1951 discover Server addresses through a layer 2 data link login exchange, 1952 or through a unicast RA response to a multicast/anycast RS as 1953 described below. In the absence of other information, the Client can 1954 resolve the DNS Fully-Qualified Domain Name (FQDN) 1955 "linkupnetworks.[domainname]" where "linkupnetworks" is a constant 1956 text string and "[domainname]" is a DNS suffix for the OMNI link 1957 (e.g., "example.com"). 1959 To associate with a Server, the Client acts as a requesting router to 1960 request MNPs. The Client prepares an RS message with prefix 1961 management parameters and includes a Nonce and Timestamp option if 1962 the Client needs to correlate RA replies. If the Client already 1963 knows the Server's ADM-LLA, it includes the LLA as the network-layer 1964 destination address; otherwise, it includes (link-local) All-Routers 1965 multicast as the network-layer destination. If the Client already 1966 knows its own MNP-LLA, it uses the LLA as the network-layer source 1967 address; otherwise, it uses a Temporary LLA as the network-layer 1968 source address and includes a DHCP Unique Identifier (DUID) sub- 1969 option in the OMNI option (see: [I-D.templin-6man-omni-interface]). 1971 The Client next includes an OMNI option in the RS message to register 1972 its link-layer information with the Server. The Client sets the OMNI 1973 option prefix registration information according to the MNP, and 1974 includes Interface Attributes corresponding to the underlying 1975 interface over which the Client will send the RS message. The Client 1976 MAY include additional Interface Attributes specific to other 1977 underlying interfaces. 1979 The Client then sends the RS message (either directly via Direct 1980 interfaces, via a VPN for VPNed interfaces, via a Proxy for ANET 1981 interfaces or via INET encapsulation for INET interfaces) and waits 1982 for an RA message reply (see Section 3.12.3). The Client retries up 1983 to MAX_RTR_SOLICITATIONS times until an RA is received. If the 1984 Client receives no RAs, or if it receives an RA with Router Lifetime 1985 set to 0, the Client SHOULD abandon this Server and try another 1986 Server. Otherwise, the Client processes the prefix information found 1987 in the RA message. 1989 Next, the Client creates a symmetric neighbor cache entry with the 1990 Server's ADM-LLA as the network-layer address and the Server's 1991 encapsulation and/or link-layer addresses as the link-layer address. 1992 The Client records the RA Router Lifetime field value in the neighbor 1993 cache entry as the time for which the Server has committed to 1994 maintaining the MNP in the routing system via this underlying 1995 interface, and caches the other RA configuration information 1996 including Cur Hop Limit, M and O flags, Reachable Time and Retrans 1997 Timer. The Client then autoconfigures MNP-LLAs for each of the 1998 delegated MNPs and assigns them to the OMNI interface. The Client 1999 also caches any MSPs included in Route Information Options (RIOs) 2000 [RFC4191] as MSPs to associate with the OMNI link, and assigns the 2001 MTU value in the MTU option to the underlying interface. 2003 The Client then registers additional underlying interfaces with the 2004 Server by sending RS messages via each additional interface. The RS 2005 messages include the same parameters as for the initial RS/RA 2006 exchange, but with destination address set to the Server's ADM-LLA. 2008 Following autoconfiguration, the Client sub-delegates the MNPs to its 2009 attached EUNs and/or the Client's own internal virtual interfaces as 2010 described in [I-D.templin-v6ops-pdhost] to support the Client's 2011 downstream attached "Internet of Things (IoT)". The Client 2012 subsequently sends additional RS messages over each underlying 2013 interface before the Router Lifetime received for that interface 2014 expires. 2016 After the Client registers its underlying interfaces, it may wish to 2017 change one or more registrations, e.g., if an interface changes 2018 address or becomes unavailable, if QoS preferences change, etc. To 2019 do so, the Client prepares an RS message to send over any available 2020 underlying interface. The RS includes an OMNI option with prefix 2021 registration information specific to its MNP, with Interface 2022 Attributes specific to the selected underlying interface, and with 2023 any additional Interface Attributes specific to other underlying 2024 interfaces. When the Client receives the Server's RA response, it 2025 has assurance that the Server has been updated with the new 2026 information. 2028 If the Client wishes to discontinue use of a Server it issues an RS 2029 message over any underlying interface with an OMNI option with a 2030 prefix release indication. When the Server processes the message, it 2031 releases the MNP, sets the symmetric neighbor cache entry state for 2032 the Client to DEPARTED and returns an RA reply with Router Lifetime 2033 set to 0. After a short delay (e.g., 2 seconds), the Server 2034 withdraws the MNP from the routing system. 2036 3.12.3. AERO Server Behavior 2038 AERO Servers act as IP routers and support a prefix delegation/ 2039 registration service for Clients. Servers arrange to add their ADM- 2040 LLAs to a static map of Server addresses for the link and/or the DNS 2041 resource records for the FQDN "linkupnetworks.[domainname]" before 2042 entering service. Server addresses should be geographically and/or 2043 topologically referenced, and made available for discovery by Clients 2044 on the OMNI link. 2046 When a Server receives a prospective Client's RS message on its OMNI 2047 interface, it SHOULD return an immediate RA reply with Router 2048 Lifetime set to 0 if it is currently too busy or otherwise unable to 2049 service the Client. Otherwise, the Server authenticates the RS 2050 message and processes the prefix delegation/registration parameters. 2051 The Server first determines the correct MNPs to provide to the Client 2052 by searching the Client database. When the Server returns the MNPs, 2053 it also creates a forwarding table entry for the MNP-ULA 2054 corresponding to each MNP so that the MNPs are propagated into the 2055 routing system (see: Section 3.2.4). For IPv6, the Server creates an 2056 IPv6 forwarding table entry for each MNP. For IPv4, the Server 2057 creates an IPv6 forwarding table entry with the IPv4-compatibility 2058 MNP-ULA prefix corresponding to the IPv4 address. 2060 The Server next creates a symmetric neighbor cache entry for the 2061 Client using the base MNP-LLA as the network-layer address and with 2062 lifetime set to no more than the smallest prefix lifetime. Next, the 2063 Server updates the neighbor cache entry by recording the information 2064 in each Interface Attributes sub-option in the RS OMNI option. The 2065 Server also records the actual OAL/INET addresses in the neighbor 2066 cache entry. 2068 Next, the Server prepares an RA message using its ADM-LLA as the 2069 network-layer source address and the network-layer source address of 2070 the RS message as the network-layer destination address. The Server 2071 sets the Router Lifetime to the time for which it will maintain both 2072 this underlying interface individually and the symmetric neighbor 2073 cache entry as a whole. The Server also sets Cur Hop Limit, M and O 2074 flags, Reachable Time and Retrans Timer to values appropriate for the 2075 OMNI link. The Server includes the MNPs, any other prefix management 2076 parameters and an OMNI option with no Interface Attributes. The 2077 Server then includes one or more RIOs that encode the MSPs for the 2078 OMNI link, plus an MTU option (see Section 3.9). The Server finally 2079 forwards the message to the Client using OAL/INET, INET, or NULL 2080 encapsulation as necessary. 2082 After the initial RS/RA exchange, the Server maintains a 2083 ReachableTime timer for each of the Client's underlying interfaces 2084 individually (and for the Client's symmetric neighbor cache entry 2085 collectively) set to expire after ReachableTime seconds. If the 2086 Client (or Proxy) issues additional RS messages, the Server sends an 2087 RA response and resets ReachableTime. If the Server receives an ND 2088 message with a prefix release indication it sets the Client's 2089 symmetric neighbor cache entry to the DEPARTED state and withdraws 2090 the MNP from the routing system after a short delay (e.g., 2 2091 seconds). If ReachableTime expires before a new RS is received on an 2092 individual underlying interface, the Server marks the interface as 2093 DOWN. If ReachableTime expires before any new RS is received on any 2094 individual underlying interface, the Server sets the symmetric 2095 neighbor cache entry state to STALE and sets a 10 second timer. If 2096 the Server has not received a new RS or ND message with a prefix 2097 release indication before the 10 second timer expires, it deletes the 2098 neighbor cache entry and withdraws the MNP from the routing system. 2100 The Server processes any ND messages pertaining to the Client and 2101 returns an NA/RA reply in response to solicitations. The Server may 2102 also issue unsolicited RA messages, e.g., with reconfigure parameters 2103 to cause the Client to renegotiate its prefix delegation/ 2104 registrations, with Router Lifetime set to 0 if it can no longer 2105 service this Client, etc. Finally, If the symmetric neighbor cache 2106 entry is in the DEPARTED state, the Server deletes the entry after 2107 DepartTime expires. 2109 Note: Clients SHOULD notify former Servers of their departures, but 2110 Servers are responsible for expiring neighbor cache entries and 2111 withdrawing routes even if no departure notification is received 2112 (e.g., if the Client leaves the network unexpectedly). Servers 2113 SHOULD therefore set Router Lifetime to ReachableTime seconds in 2114 solicited RA messages to minimize persistent stale cache information 2115 in the absence of Client departure notifications. A short Router 2116 Lifetime also ensures that proactive Client/Server RS/RA messaging 2117 will keep any NAT state alive (see above). 2119 Note: All Servers on an OMNI link MUST advertise consistent values in 2120 the RA Cur Hop Limit, M and O flags, Reachable Time and Retrans Timer 2121 fields the same as for any link, since unpredictable behavior could 2122 result if different Servers on the same link advertised different 2123 values. 2125 3.12.3.1. DHCPv6-Based Prefix Registration 2127 When a Client is not pre-provisioned with an MNP-LLA, it will need 2128 for the Server to select one or more MNPs on its behalf and set up 2129 the correct state in the AERO routing service. (A Client with a pre- 2130 provisioned MNP may also request the Server to select additional 2131 MNPs.) The DHCPv6 service [RFC8415] is used to support this 2132 requirement. 2134 When a Client needs to have the Server select MNPs, it sends an RS 2135 message with a Temporary LLA and with an OMNI option that includes a 2136 DHCPv6 message sub-option with DHCPv6 Prefix Delegation (DHCPv6-PD) 2137 parameters. When the Server receives the RS message, it extracts the 2138 DHCPv6-PD message from the OMNI option. 2140 The Server then acts as a "Proxy DHCPv6 Client" in a message exchange 2141 with the locally-resident DHCPv6 server, which delegates MNPs and 2142 returns a DHCPv6-PD Reply message. (If the Server wishes to defer 2143 creation of MN state until the DHCPv6-PD Reply is received, it can 2144 instead act as a Lightweight DHCPv6 Relay Agent per [RFC6221] by 2145 encapsulating the DHCPv6-PD message in a Relay-forward/reply exchange 2146 with Relay Message and Interface ID options.) 2148 When the Server receives the DHCPv6-PD Reply, it adds a route to the 2149 routing system and creates an MNP-LLA based on the delegated MNP. 2150 The Server then sends an RA back to the Client with the (newly- 2151 created) MNP-LLA as the destination address and with the DHCPv6-PD 2152 Reply message coded in the OMNI option. When the Client receives the 2153 RA, it creates a default route, assigns the Subnet Router Anycast 2154 address and sets its MNP-LLA based on the delegated MNP. 2156 3.13. The AERO Proxy 2158 Clients may connect to protected-spectrum ANETs that employ physical 2159 and/or link-layer security services to facilitate communications to 2160 Servers in outside INETs. In that case, the ANET can employ an AERO 2161 Proxy. The Proxy is located at the ANET/INET border and listens for 2162 RS messages originating from or RA messages destined to ANET Clients. 2163 The Proxy acts on these control messages as follows: 2165 o when the Proxy receives an RS message from a new ANET Client, it 2166 first authenticates the message then examines the network-layer 2167 destination address. If the destination address is a Server's 2168 ADM-LLA, the Proxy proceeds to the next step. Otherwise, if the 2169 destination is (link-local) All-Routers multicast, the Proxy 2170 selects a "nearby" Server that is likely to be a good candidate to 2171 serve the Client and replaces the destination address with the 2172 Server's ADM-LLA. Next, the Proxy creates a proxy neighbor cache 2173 entry and caches the Client and Server link-layer addresses along 2174 with the OMNI option information and any other identifying 2175 information including Transaction IDs, Client Identifiers, Nonce 2176 values, etc. The Proxy finally encapsulates the (proxyed) RS 2177 message in an OAL header with source set to the Proxy's ADM-ULA 2178 and destination set to the Server's ADM-ULA. The Proxy also 2179 includes an OMNI header with an Interface Attributes option that 2180 includes its own INET address plus a unique Port Number for this 2181 Client, then forwards the message into the OMNI link spanning 2182 tree. (Note: including a unique Port Number allows the Server to 2183 distinguish different Clients located behind the same Proxy at the 2184 link-layer, whereas the link-layer addresses would otherwise be 2185 indistinguishable) 2187 o when the Server receives the RS, it authenticates the message then 2188 creates or updates a symmetric neighbor cache entry for the Client 2189 with the Proxy's ADM-ULA, INET address and Port Number as the 2190 link-layer address information. The Server then sends an RA 2191 message back to the Proxy via the spanning tree. 2193 o when the Proxy receives the RA, it authenticates the message and 2194 matches it with the proxy neighbor cache entry created by the RS. 2195 The Proxy then caches the prefix information as a mapping from the 2196 Client's MNPs to the Client's link-layer address, caches the 2197 Server's advertised Router Lifetime and sets the neighbor cache 2198 entry state to REACHABLE. The Proxy then optionally rewrites the 2199 Router Lifetime and forwards the (proxyed) message to the Client. 2200 The Proxy finally includes an MTU option (if necessary) with an 2201 MTU to use for the underlying ANET interface. 2203 After the initial RS/RA exchange, the Proxy forwards any Client data 2204 packets for which there is no matching asymmetric neighbor cache 2205 entry to a Bridge using OAL encapsulation with its own ADM-ULA as the 2206 source and the MNP-ULA corresponding to the Client as the 2207 destination. The Proxy instead forwards any Client data destined to 2208 an asymmetric neighbor cache target directly to the target according 2209 to the OAL/link-layer information - the process of establishing 2210 asymmetric neighbor cache entries is specified in Section 3.14. 2212 While the Client is still attached to the ANET, the Proxy sends NS, 2213 RS and/or unsolicited NA messages to update the Server's symmetric 2214 neighbor cache entries on behalf of the Client and/or to convey QoS 2215 updates. This allows for higher-frequency Proxy-initiated RS/RA 2216 messaging over well-connected INET infrastructure supplemented by 2217 lower-frequency Client-initiated RS/RA messaging over constrained 2218 ANET data links. 2220 If the Server ceases to send solicited advertisements, the Proxy 2221 sends unsolicited RAs on the ANET interface with destination set to 2222 (link-local) All-Nodes multicast and with Router Lifetime set to zero 2223 to inform Clients that the Server has failed. Although the Proxy 2224 engages in ND exchanges on behalf of the Client, the Client can also 2225 send ND messages on its own behalf, e.g., if it is in a better 2226 position than the Proxy to convey QoS changes, etc. For this reason, 2227 the Proxy marks any Client-originated solicitation messages (e.g. by 2228 inserting a Nonce option) so that it can return the solicited 2229 advertisement to the Client instead of processing it locally. 2231 If the Client becomes unreachable, the Proxy sets the neighbor cache 2232 entry state to DEPARTED and retains the entry for DepartTime seconds. 2233 While the state is DEPARTED, the Proxy forwards any packets destined 2234 to the Client to a Bridge via OAL/ORH encapsulation. When DepartTime 2235 expires, the Proxy deletes the neighbor cache entry and discards any 2236 further packets destined to this (now forgotten) Client. 2238 In some ANETs that employ a Proxy, the Client's MNP can be injected 2239 into the ANET routing system. In that case, the Client can send data 2240 messages without encapsulation so that the ANET routing system 2241 transports the unencapsulated packets to the Proxy. This can be very 2242 beneficial, e.g., if the Client connects to the ANET via low-end data 2243 links such as some aviation wireless links. 2245 If the first-hop ANET access router is on the same underlying link 2246 and recognizes the AERO/OMNI protocol, the Client can avoid 2247 encapsulation for both its control and data messages. When the 2248 Client connects to the link, it can send an unencapsulated RS message 2249 with source address set to its own MNP-LLA (or to a Temporary LLA), 2250 and with destination address set to the ADM-LLA of the Client's 2251 selected Server or to (link-local) All-Routers multicast. The Client 2252 includes an OMNI option formatted as specified in 2253 [I-D.templin-6man-omni-interface]. 2255 The Client then sends the unencapsulated RS message, which will be 2256 intercepted by the AERO-Aware access router. The access router then 2257 encapsulates the RS message in an ANET header with its own address as 2258 the source address and the address of a Proxy as the destination 2259 address. The access router further remembers the address of the 2260 Proxy so that it can encapsulate future data packets from the Client 2261 via the same Proxy. If the access router needs to change to a new 2262 Proxy, it simply sends another RS message toward the Server via the 2263 new Proxy on behalf of the Client. 2265 In some cases, the access router and Proxy may be one and the same 2266 node. In that case, the node would be located on the same physical 2267 link as the Client, but its message exchanges with the Server would 2268 need to pass through a security gateway at the ANET/INET border. The 2269 method for deploying access routers and Proxys (i.e. as a single node 2270 or multiple nodes) is an ANET-local administrative consideration. 2272 Note: The Proxy can apply packing as discussed in Section 5.2 of 2273 [I-D.templin-6man-omni-interface] if an opportunity arises to 2274 concatenate multiple payload packets that will be destined to the 2275 same destination. 2277 3.13.1. Combined Proxy/Servers 2279 Clients may need to connect directly to Servers via INET, Direct and 2280 VPNed interfaces (i.e., non-ANET interfaces). If the Client's 2281 underlying interfaces all connect via the same INET partition, then 2282 it can connect to a single controlling Server via all interfaces. 2284 If some Client interfaces connect via different INET partitions, 2285 however, the Client still selects a set of controlling Servers and 2286 sends RS messages via their directly-connected Servers while using 2287 the ADM-LLA of the controlling Server as the destination. 2289 When a Server receives an RS with destination set to the ADM-LLA of a 2290 controlling Server, it acts as a Proxy to forward the message to the 2291 controlling Server while forwarding the corresponding RA reply to the 2292 Client. 2294 3.13.2. Detecting and Responding to Server Failures 2296 In environments where fast recovery from Server failure is required, 2297 Proxys SHOULD use proactive Neighbor Unreachability Detection (NUD) 2298 to track Server reachability in a similar fashion as for 2299 Bidirectional Forwarding Detection (BFD) [RFC5880]. Proxys can then 2300 quickly detect and react to failures so that cached information is 2301 re-established through alternate paths. The NUD control messaging is 2302 carried only over well-connected ground domain networks (i.e., and 2303 not low-end aeronautical radio links) and can therefore be tuned for 2304 rapid response. 2306 Proxys perform proactive NUD with Servers for which there are 2307 currently active ANET Clients by sending continuous NS messages in 2308 rapid succession, e.g., one message per second. The Proxy sends the 2309 NS message via the spanning tree with the Proxy's ADM-LLA as the 2310 source and the ADM-LLA of the Server as the destination. When the 2311 Proxy is also sending RS messages to the Server on behalf of ANET 2312 Clients, the resulting RA responses can be considered as equivalent 2313 hints of forward progress. This means that the Proxy need not also 2314 send a periodic NS if it has already sent an RS within the same 2315 period. If the Server fails (i.e., if the Proxy ceases to receive 2316 advertisements), the Proxy can quickly inform Clients by sending 2317 multicast RA messages on the ANET interface. 2319 The Proxy sends RA messages on the ANET interface with source address 2320 set to the Server's address, destination address set to (link-local) 2321 All-Nodes multicast, and Router Lifetime set to 0. The Proxy SHOULD 2322 send MAX_FINAL_RTR_ADVERTISEMENTS RA messages separated by small 2323 delays [RFC4861]. Any Clients on the ANET that had been using the 2324 failed Server will receive the RA messages and associate with a new 2325 Server. 2327 3.13.3. Point-to-Multipoint Server Coordination 2329 In environments where Client messaging over ANETs is bandwidth- 2330 limited and/or expensive, Clients can enlist the services of the 2331 Proxy to coordinate with multiple Servers in a single RS/RA message 2332 exchange. The Client can send a single RS message to (link-local) 2333 All-Routers multicast that includes the ID's of multiple Servers in 2334 MS-Register sub-options of the OMNI option. 2336 When the Proxy receives the RS and processes the OMNI option, it 2337 sends a separate RS to each MS-Register Server ID. When the Proxy 2338 receives an RA, it can optionally return an immediate "singleton" RA 2339 to the Client or record the Server's ID for inclusion in a pending 2340 "aggregate" RA message. The Proxy can then return aggregate RA 2341 messages to the Client including multiple Server IDs in order to 2342 conserve bandwidth. Each RA includes a proper subset of the Server 2343 IDs from the original RS message, and the Proxy must ensure that the 2344 message contents of each RA are consistent with the information 2345 received from the (aggregated) Servers. 2347 Clients can thereafter employ efficient point-to-multipoint Server 2348 coordination under the assistance of the Proxy to reduce the number 2349 of messages sent over the ANET while enlisting the support of 2350 multiple Servers for fault tolerance. Clients can further include 2351 MS-Release sub-options in IPv6 ND messages to request the Proxy to 2352 release from former Servers via the procedures discussed in 2353 Section 3.16.5. 2355 The OMNI interface specification [I-D.templin-6man-omni-interface] 2356 provides further discussion of the Client/Proxy RS/RA messaging 2357 involved in point-to-multipoint coordination. 2359 3.14. AERO Route Optimization / Address Resolution 2361 While data packets are flowing between a source and target node, 2362 route optimization SHOULD be used. Route optimization is initiated 2363 by the first eligible Route Optimization Source (ROS) closest to the 2364 source as follows: 2366 o For Clients on VPNed and Direct interfaces, the Server is the ROS. 2368 o For Clients on ANET interfaces, the Proxy is the ROS. 2370 o For Clients on INET interfaces, the Client itself is the ROS. 2372 o For correspondent nodes on INET/EUN interfaces serviced by a 2373 Relay, the Relay is the ROS. 2375 The route optimization procedure is conducted between the ROS and the 2376 target Server/Relay acting as a Route Optimization Responder (ROR) in 2377 the same manner as for IPv6 ND Address Resolution and using the same 2378 NS/NA messaging. The target may either be a MNP Client serviced by a 2379 Server, or a non-MNP correspondent reachable via a Relay. 2381 The procedures are specified in the following sections. 2383 3.14.1. Route Optimization Initiation 2385 While data packets are flowing from the source node toward a target 2386 node, the ROS performs address resolution by sending an NS message 2387 for Address Resolution (NS(AR)) to receive a solicited NA(AR) message 2388 from the ROR. When the ROS sends an NS(AR), it includes: 2390 o the LLA of the ROS as the source address. 2392 o the data packet's destination as the Target Address. 2394 o the Solicited-Node multicast address [RFC4291] formed from the 2395 lower 24 bits of the data packet's destination as the destination 2396 address, e.g., for 2001:db8:1:2::10:2000 the NS destination 2397 address is ff02:0:0:0:0:1:ff10:2000. 2399 The NS(AR) message includes an OMNI option with no Interface 2400 Attributes, such that the target will not create a neighbor cache 2401 entry. The Prefix Length in the OMNI option is set to the Prefix 2402 Length associated with the ROS's LLA. 2404 The ROS then encapsulates the NS(AR) message in an OAL header with 2405 source set to its own ULA and destination set to the MNP-ULA 2406 corresponding to the target, then sends the message into the spanning 2407 tree without decrementing the network-layer TTL/Hop Limit field. 2408 (When the ROS is a Client, it instead securely sends the NS(AR) to 2409 one of its current Servers as specified in Section 3.22. The Server 2410 then forwards an adapted version of the NS(AR) into the spanning tree 2411 on behalf of the Client.) 2413 Note: The ROS can apply packing as discussed in Section 5.2 of 2414 [I-D.templin-6man-omni-interface] to concatenate the NS(AR) onto the 2415 same OAL packet used to carry a data packet that triggered route 2416 optimization. 2418 3.14.2. Relaying the NS(AR) 2420 When the Bridge receives the NS(AR) message from the ROS, it discards 2421 the INET header and determines that the ROR is the next hop by 2422 consulting its standard IPv6 forwarding table for the OAL header 2423 destination address. The Bridge then forwards the message toward the 2424 ROR via the spanning tree the same as for any IPv6 router. The 2425 final-hop Bridge in the spanning tree will deliver the message via a 2426 secured tunnel to the ROR. 2428 3.14.3. Processing the NS(AR) and Sending the NA(AR) 2430 When the ROR receives the NS(AR) message, it examines the Target 2431 Address to determine whether it has a neighbor cache entry and/or 2432 route that matches the target. If there is no match, the ROR drops 2433 the message. Otherwise, the ROR continues processing as follows: 2435 o if the target belongs to an MNP Client neighbor in the DEPARTED 2436 state the ROR changes the NS(AR) message OAL destination address 2437 to the ADM-ULA of the Client's new Server, forwards the message 2438 into the spanning tree and returns from processing. 2440 o If the target belongs to an MNP Client neighbor in the REACHABLE 2441 state, the ROR instead adds the AERO source address to the target 2442 Client's Report List with time set to ReportTime. 2444 o If the target belongs to a non-MNP route, the ROR continues 2445 processing without adding an entry to the Report List. 2447 The ROR then prepares a (solicited) NA(AR) message to send back to 2448 the ROS but does not create a neighbor cache entry. The ROR sets the 2449 NA(AR) source address to the MNP-LLA corresponding to the target, 2450 sets the Target Address to the target of the solicitation, and sets 2451 the destination address to the source of the solicitation. The ROR 2452 then includes an OMNI option with Prefix Length set to the length 2453 associated with the MNP-LLA. 2455 If the target is an MNP Client, the ROR next includes Interface 2456 Attributes in the OMNI option for each of the target Client's 2457 underlying interfaces with current information for each interface and 2458 with the S/T-ifIndex field in the OMNI header set to 0 to indicate 2459 that the message originated from the ROR and not the Client. 2461 For each Interface Attributes sub-option, the ROR sets the L2ADDR 2462 according to its own INET address for VPNed or Direct interfaces, to 2463 the INET address of the Proxy or to the Client's INET address for 2464 INET interfaces. The ROR then includes the lower 32 bits of its own 2465 ADM-ULA (or the ADM-ULA of the Proxy) as the LHS, encodes the ADM-ULA 2466 prefix length code in the SRT field and sets the FMT code accordingly 2467 as specified in Section 3.3. 2469 The ROR then sets the NA(AR) message R flag to 1 (as a router), S 2470 flag to 1 (as a response to a solicitation), and O flag to 0 (as a 2471 proxy). The ROR finally encapsulates the NA(AR) message in an OAL 2472 header with source set to its own ULA and destination set to the 2473 source ULA of the NS(AR) message, then forwards the message into the 2474 spanning tree without decrementing the network-layer TTL/Hop Limit 2475 field. 2477 3.14.4. Relaying the NA(AR) 2479 When the Bridge receives the NA(AR) message from the ROR, it discards 2480 the INET header and determines that the ROS is the next hop by 2481 consulting its standard IPv6 forwarding table for the OAL header 2482 destination address. The Bridge then forwards the OAL-encapsulated 2483 NA(AR) message toward the ROS the same as for any IPv6 router. The 2484 final-hop Bridge in the spanning tree will deliver the message via a 2485 secured tunnel to the ROS. 2487 3.14.5. Processing the NA(AR) 2489 When the ROS receives the NA(AR) message, it processes the message 2490 the same as for standard IPv6 Address Resolution [RFC4861]. In the 2491 process, it caches the source MNP-ULA then creates an asymmetric 2492 neighbor cache entry for the target and caches all information found 2493 in the OMNI option. The ROS finally sets the asymmetric neighbor 2494 cache entry lifetime to ReachableTime seconds. (When the ROS is a 2495 Client, the solicited NA(AR) message will first be delivered via the 2496 spanning tree to one of its current Servers, which then securely 2497 forwards the message to the Client as discussed in Section 3.22.) 2499 3.14.6. Route Optimization Maintenance 2501 Following route optimization, the ROS forwards future data packets 2502 destined to the target via the addresses found in the cached link- 2503 layer information. The route optimization is shared by all sources 2504 that send packets to the target via the ROS, i.e., and not just the 2505 source on behalf of which the route optimization was initiated. 2507 While new data packets destined to the target are flowing through the 2508 ROS, it sends additional NS(AR) messages to the ROR before 2509 ReachableTime expires to receive a fresh NA(AR) message the same as 2510 described in the previous sections (route optimization refreshment 2511 strategies are an implementation matter, with a non-normative example 2512 given in Appendix A.1). The ROS uses the cached ADM-ULA of the ROR 2513 as the NS(AR) OAL destination address (i.e., instead of using the ULA 2514 corresponding to the target as was the case for the initial NS(AR)), 2515 and sends up to MAX_MULTICAST_SOLICIT NS(AR) messages separated by 1 2516 second until an NA(AR) is received. If no NA(AR) is received, the 2517 ROS assumes that the current ROR has become unreachable and deletes 2518 the target neighbor cache entry. Subsequent data packets will 2519 trigger a new route optimization with an NS with OAL destination 2520 address set to the MNP-ULA corresponding to the target per 2521 Section 3.14.1 to discover a new ROR while initial data packets 2522 travel over a suboptimal route. 2524 If an NA(AR) is received, the ROS then updates the asymmetric 2525 neighbor cache entry to refresh ReachableTime, while (for MNP 2526 destinations) the ROR adds or updates the ROS address to the target's 2527 Report List and with time set to ReportTime. While no data packets 2528 are flowing, the ROS instead allows ReachableTime for the asymmetric 2529 neighbor cache entry to expire. When ReachableTime expires, the ROS 2530 deletes the asymmetric neighbor cache entry. Any future data packets 2531 flowing through the ROS will again trigger a new route optimization. 2533 The ROS may also receive unsolicited NA messages from the ROR at any 2534 time (see: Section 3.16). If there is an asymmetric neighbor cache 2535 entry for the target, the ROS updates the link-layer information but 2536 does not update ReachableTime since the receipt of an unsolicited NA 2537 does not confirm that any forward paths are working. If there is no 2538 asymmetric neighbor cache entry, the ROS simply discards the 2539 unsolicited NA. 2541 In this arrangement, the ROS holds an asymmetric neighbor cache entry 2542 for the target via the ROR, but the ROR does not hold an asymmetric 2543 neighbor cache entry for the ROS. The route optimization neighbor 2544 relationship is therefore asymmetric and unidirectional. If the 2545 target node also has packets to send back to the source node, then a 2546 separate route optimization procedure is performed in the reverse 2547 direction. But, there is no requirement that the forward and reverse 2548 paths be symmetric. 2550 3.15. Neighbor Unreachability Detection (NUD) 2552 AERO nodes perform Neighbor Unreachability Detection (NUD) per 2553 [RFC4861] either reactively in response to persistent link-layer 2554 errors (see Section 3.11) or proactively to confirm reachability and/ 2555 or establish NAT state. The NUD algorithm is based on periodic 2556 control message exchanges. The algorithm may further be seeded by ND 2557 hints of forward progress, but care must be taken to avoid inferring 2558 reachability based on spoofed information. For example, authentic 2559 IPv6 ND message exchanges may be considered as acceptable hints of 2560 forward progress, while spurious data packets should not be. 2562 AERO nodes can use (OAL/ORH-encapsulated) standard NS/NA exchanges 2563 sent over the OMNI link spanning tree to securely test reachability 2564 without risk of DoS attacks from nodes pretending to be a neighbor 2565 (these NS/NA(NUD) messages use the unicast LLAs and ULAs of the two 2566 parties involved in the NUD test the same as for standard IPv6 ND, 2567 and both messages flow over the spanning tree). Proxys can further 2568 perform NUD to securely verify Server reachability on behalf of their 2569 proxyed Clients. However, a means for an ROS to test the unsecured 2570 target route optimized paths is also necessary. 2572 When an ROR directs an ROS to a target neighbor with one or more 2573 link-layer addresses, the ROS can proactively test each such 2574 unsecured route optimized path through secured NS(NUD) messages over 2575 the spanning tree that invoke an unsecured NA(NUD) reply that travels 2576 over the route optimized path.. (The NS(NUD) messages must therefore 2577 include Nonce and Timestamp options that will be echoed in the 2578 unsecured NA(NUD) replies.) While testing the paths, the ROS can 2579 optionally continue to send packets via the spanning tree, maintain a 2580 small queue of packets until target reachability is confirmed, or 2581 (optimistically) allow packets to flow via the route optimized paths. 2583 When the ROS sends an NS(NUD) message, it sets the IPv6 source to its 2584 own address, sets the destination to the MNP-LLA of the target, and 2585 sets the target's MNP Subnet-Router anycast address as the Target 2586 Address. The ROS also includes an OMNI option with a single 2587 Interface Attributes sub-option with the L2ADDR information for its 2588 own underlying interface it wishes to test, but sets the S/T-ifIndex 2589 field to the index for target's underlying interface to be tested. 2590 The ROS includes a Nonce and Timestamp option, then encapsulates the 2591 message in OAL/INET headers with its own ULA as the source and the 2592 ULA of the target as the destination. The ROS then forwards the 2593 NS(NUD) message toward the target via a Server or Bridge. 2595 When the target receives the NS(NUD) message, it creates an NA(NUD) 2596 by reversing the OAL and IPv6 addresses and including an Interface 2597 Attributes sub-option with attributes for its own interface 2598 identified by the NS(NUD) S/T-ifIndex. The target sets the NA(NUD) 2599 S/T-ifIndex to the index of the ROS, sets the Target Address to the 2600 same value that was in the NS(NUD), and returns the message using its 2601 own underlying interface identified by S/T-ifIndex and destined to 2602 the ROS's interface identified by the original Interface Attributes 2603 sub-option. 2605 When the ROS receives the NA(NUD) message, it can determine from the 2606 Nonce, Timestamp and Target Address that the message matched its 2607 NS(NUD) and that it transited the direct path from the ROR using the 2608 selected underlying interface pair. The ROS marks route optimization 2609 target paths that pass these NUD tests as "reachable", and those that 2610 do not as "unreachable". These markings inform the OMNI interface 2611 forwarding algorithm specified in Section 3.10. 2613 Note: If the target determines that the OMNI option Interface 2614 Attributes in the NS(NUD) is located in a different OMNI link segment 2615 than its own interface named in the S/T-ifIndex, it instead returns 2616 the NA(NUD) via the spanning tree while including an ORH and setting 2617 the OAL destination address to the Subnet Router Anycast address used 2618 by Bridges on the ROS segment. When a Bridge on the ROS segment 2619 receives the NA(NUD), it replaces the Interface Attributes with 2620 information for its own interface while using the ifIndex value 2621 specific to the target. 2623 3.16. Mobility Management and Quality of Service (QoS) 2625 AERO is a Distributed Mobility Management (DMM) service. Each Server 2626 is responsible for only a subset of the Clients on the OMNI link, as 2627 opposed to a Centralized Mobility Management (CMM) service where 2628 there is a single network mobility collective entity for all Clients. 2629 Clients coordinate with their associated Servers via RS/RA exchanges 2630 to maintain the DMM profile, and the AERO routing system tracks all 2631 current Client/Server peering relationships. 2633 Servers provide default routing and mobility/multilink services for 2634 their dependent Clients. Clients are responsible for maintaining 2635 neighbor relationships with their Servers through periodic RS/RA 2636 exchanges, which also serves to confirm neighbor reachability. When 2637 a Client's underlying interface address and/or QoS information 2638 changes, the Client is responsible for updating the Server with this 2639 new information. Note that when there is a Proxy in the path, the 2640 Proxy can also perform some RS/RA exchanges on the Client's behalf. 2642 Mobility management messaging is based on the transmission and 2643 reception of unsolicited Neighbor Advertisement (uNA) messages. Each 2644 uNA message sets the IPv6 destination address to (link-local) All- 2645 Nodes multicast to convey a general update of Interface Attributes to 2646 (possibly) multiple recipients, or to a specific unicast LLA to 2647 announce a departure event to a specific recipient. Implementations 2648 must therefore examine the destination address to determine the 2649 nature of the mobility event (i.e., update vs departure). 2651 Mobility management considerations are specified in the following 2652 sections. 2654 3.16.1. Mobility Update Messaging 2656 Servers accommodate Client mobility, multilink and/or QoS change 2657 events by sending unsolicited NA (uNA) messages to each ROS in the 2658 target Client's Report List. When a Server sends a uNA message, it 2659 sets the IPv6 source address to the Client's MNP-LLA, sets the 2660 destination address to (link-local) All-Nodes multicast and sets the 2661 Target Address to the Client's Subnet-Router anycast address. The 2662 Server also includes an OMNI option with Prefix Length set to the 2663 length associated with the Client's MNP-LLA, with Interface 2664 Attributes for the target Client's underlying interfaces and with the 2665 OMNI header S/T-ifIndex set to 0. The Server then sets the NA R flag 2666 to 1, the S flag to 0 and the O flag to 1, then encapsulates the 2667 message in an OAL header with source set to its own ADM-ULA and 2668 destination set to the ULA of the ROS and sends the message into the 2669 spanning tree. 2671 As discussed in Section 7.2.6 of [RFC4861], the transmission and 2672 reception of uNA messages is unreliable but provides a useful 2673 optimization. In well-connected Internetworks with robust data links 2674 uNA messages will be delivered with high probability, but in any case 2675 the Server can optionally send up to MAX_NEIGHBOR_ADVERTISEMENT uNAs 2676 to each ROS to increase the likelihood that at least one will be 2677 received. 2679 When the ROS receives a uNA message prepared as above, it ignores the 2680 message if there is no existing neighbor cache entry for the Client. 2681 Otherwise, it uses the included OMNI option information to update the 2682 neighbor cache entry, but does not reset ReachableTime since the 2683 receipt of an unsolicited NA message from the target Server does not 2684 provide confirmation that any forward paths to the target Client are 2685 working. 2687 If uNA messages are lost, the ROS may be left with stale address and/ 2688 or QoS information for the Client for up to ReachableTime seconds. 2689 During this time, the ROS can continue sending packets according to 2690 its stale neighbor cache information. When ReachableTime is close to 2691 expiring, the ROS will re-initiate route optimization and receive 2692 fresh link-layer address information. 2694 In addition to sending uNA messages to the current set of ROSs for 2695 the Client, the Server also sends uNAs to the MNP-ULA associated with 2696 the link-layer address for any underlying interface for which the 2697 link-layer address has changed. These uNA messages update an old 2698 Proxy/Server that cannot easily detect (e.g., without active probing) 2699 when a formerly-active Client has departed. When the Server sends 2700 the uNA, it sets the IPv6 source address to the Client's MNP-LLA, 2701 sets the destination address to the old Proxy/Server's ADM-LLA, and 2702 sets the Target Address to the Client's Subnet-Router anycast 2703 address. The Server also includes an OMNI option with Prefix Length 2704 set to the length associated with the Client's MNP-LLA, with 2705 Interface Attributes for the changed underlying interface, and with 2706 the OMNI header S/T-ifIndex set to 0. The Server then sets the NA R 2707 flag to 1, the S flag to 0 and the O flag to 1, then encapsulates the 2708 message in an OAL header with source set to its own ADM-ULA and 2709 destination set to the ADM-ULA of the old Proxy/Server and sends the 2710 message into the spanning tree. 2712 3.16.2. Announcing Link-Layer Address and/or QoS Preference Changes 2714 When a Client needs to change its underlying interface addresses and/ 2715 or QoS preferences (e.g., due to a mobility event), either the Client 2716 or its Proxys send RS messages to the Server via the spanning tree 2717 with an OMNI option that includes Interface attributes with the new 2718 link quality and address information. 2720 Up to MAX_RTR_SOLICITATIONS RS messages MAY be sent in parallel with 2721 sending actual data packets in case one or more RAs are lost. If all 2722 RAs are lost, the Client SHOULD re-associate with a new Server. 2724 When the Server receives the Client's changes, it sends uNA messages 2725 to all nodes in the Report List the same as described in the previous 2726 section. 2728 3.16.3. Bringing New Links Into Service 2730 When a Client needs to bring new underlying interfaces into service 2731 (e.g., when it activates a new data link), it sends an RS message to 2732 the Server via the underlying interface with an OMNI option that 2733 includes Interface Attributes with appropriate link quality values 2734 and with link-layer address information for the new link. 2736 3.16.4. Deactivating Existing Links 2738 When a Client needs to deactivate an existing underlying interface, 2739 it sends an RS or uNA message to its Server with an OMNI option with 2740 appropriate Interface Attribute values - in particular, the link 2741 quality value 0 assures that neighbors will cease to use the link. 2743 If the Client needs to send RS/uNA messages over an underlying 2744 interface other than the one being deactivated, it MUST include 2745 Interface Attributes with appropriate link quality values for any 2746 underlying interfaces being deactivated. 2748 Note that when a Client deactivates an underlying interface, 2749 neighbors that have received the RS/uNA messages need not purge all 2750 references for the underlying interface from their neighbor cache 2751 entries. The Client may reactivate or reuse the underlying interface 2752 and/or its ifIndex at a later point in time, when it will send RS/uNA 2753 messages with fresh Interface Attributes to update any neighbors. 2755 3.16.5. Moving Between Servers 2757 The Client performs the procedures specified in Section 3.12.2 when 2758 it first associates with a new Server or renews its association with 2759 an existing Server. The Client also includes MS-Release identifiers 2760 in the RS message OMNI option per [I-D.templin-6man-omni-interface] 2761 if it wants the new Server to notify any old Servers from which the 2762 Client is departing. 2764 When the new Server receives the Client's RS message, it returns an 2765 RA as specified in Section 3.12.3 and sends up to 2766 MAX_NEIGHBOR_ADVERTIISEMENT uNA messages to any old Servers listed in 2767 OMNI option MS-Release identifiers. When the new Server sends a uNA 2768 message, it sets the IPv6 source address to the Client's MNP-LLA, 2769 sets the destination address to the old Server's ADM-LLA, and sets 2770 the Target Address to the Client's Subnet-Router anycast address. 2771 The new Server also includes an OMNI option with Prefix Length set to 2772 the length associated with the Client's MNP-LLA, with Interface 2773 Attributes for its own underlying interface, and with the OMNI header 2774 S/T-ifIndex set to 0. The new Server then sets the NA R flag to 1, 2775 the S flag to 0 and the O flag to 1, then encapsulates the message in 2776 an OAL header with source set to its own ADM-ULA and destination set 2777 to the ADM-ULA of the old Server and sends the message into the 2778 spanning tree. 2780 When an old Server receives the uNA, it changes the Client's neighbor 2781 cache entry state to DEPARTED, sets the link-layer address of the 2782 Client to the new Server's ADM-ULA, and resets DepartTime. After a 2783 short delay (e.g., 2 seconds) the old Server withdraws the Client's 2784 MNP from the routing system. After DepartTime expires, the old 2785 Server deletes the Client's neighbor cache entry. 2787 The old Server also iteratively forwards a copy of the uNA message to 2788 each ROS in the Client's Report List by changing the OAL destination 2789 address to the ULA of the ROS while leaving all other fields of the 2790 message unmodified. When the ROS receives the uNA, it examines the 2791 Target address to determine the correct asymmetric neighbor cache 2792 entry and verifies that the IPv6 destination address matches the old 2793 Server. The ROS then caches the IPv6 source address as the new 2794 Server for the existing asymmetric neighbor cache entry and marks the 2795 entry as STALE. While in the STALE state, the ROS allows new data 2796 packets to flow according to any existing cached link-layer 2797 information and sends new NS(AR) messages using its own ULA as the 2798 OAL source and the ADM-ULA of the new Server as the OAL destination 2799 address to elicit NA messages that reset the asymmetric neighbor 2800 cache entry state to REACHABLE. If no new NA message is received for 2801 10 seconds while in the STALE state, the ROS deletes the neighbor 2802 cache entry. 2804 Clients SHOULD NOT move rapidly between Servers in order to avoid 2805 causing excessive oscillations in the AERO routing system. Examples 2806 of when a Client might wish to change to a different Server include a 2807 Server that has gone unreachable, topological movements of 2808 significant distance, movement to a new geographic region, movement 2809 to a new OMNI link segment, etc. 2811 When a Client moves to a new Server, some of the fragments of a 2812 multiple fragment packet may have already arrived at the old Server 2813 while others are en route to the new Server, however no special 2814 attention in the reassembly algorithm is necessary when re-routed 2815 fragments are simply treated as loss. 2817 3.17. Multicast 2819 The AERO Client provides an IGMP (IPv4) [RFC2236] or MLD (IPv6) 2820 [RFC3810] proxy service for its EUNs and/or hosted applications 2821 [RFC4605]. The Client forwards IGMP/MLD messages over any of its 2822 underlying interfaces for which group membership is required. The 2823 IGMP/MLD messages may be further forwarded by a first-hop ANET access 2824 router acting as an IGMP/MLD-snooping switch [RFC4541], then 2825 ultimately delivered to an AERO Proxy/Server acting as a Protocol 2826 Independent Multicast - Sparse-Mode (PIM-SM, or simply "PIM") 2827 Designated Router (DR) [RFC7761]. AERO Relays also act as PIM 2828 routers (i.e., the same as AERO Proxys/Servers) on behalf of nodes on 2829 INET/EUN networks. The behaviors identified in the following 2830 sections correspond to Source-Specific Multicast (SSM) and Any-Source 2831 Multicast (ASM) operational modes. 2833 3.17.1. Source-Specific Multicast (SSM) 2835 When an ROS (i.e., an AERO Proxy/Server/Relay) "X" acting as PIM 2836 router receives a Join/Prune message from a node on its downstream 2837 interfaces containing one or more ((S)ource, (G)roup) pairs, it 2838 updates its Multicast Routing Information Base (MRIB) accordingly. 2839 For each S belonging to a prefix reachable via X's non-OMNI 2840 interfaces, X then forwards the (S, G) Join/Prune to any PIM routers 2841 on those interfaces per [RFC7761]. 2843 For each S belonging to a prefix reachable via X's OMNI interface, X 2844 originates a separate copy of the Join/Prune for each (S,G) in the 2845 message using its own LLA as the source address and ALL-PIM-ROUTERS 2846 as the destination address. X then encapsulates each message in an 2847 OAL header with source address set to the ULA of X and destination 2848 address set to S then forwards the message into the spanning tree, 2849 which delivers it to AERO Server/Relay "Y" that services S. At the 2850 same time, if the message was a Join, X sends a route-optimization NS 2851 message toward each S the same as discussed in Section 3.14. The 2852 resulting NAs will return the LLA for the prefix that matches S as 2853 the network-layer source address and with an OMNI option with the ULA 2854 corresponding to any underlying interfaces that are currently 2855 servicing S. 2857 When Y processes the Join/Prune message, if S located behind any 2858 INET, Direct, or VPNed interfaces Y acts as a PIM router and updates 2859 its MRIB to list X as the next hop in the reverse path. If S is 2860 located behind any Proxys "Z"*, Y also forwards the message to each 2861 Z* over the spanning tree while continuing to use the LLA of X as the 2862 source address. Each Z* then updates its MRIB accordingly and 2863 maintains the LLA of X as the next hop in the reverse path. Since 2864 the Bridges do not examine network layer control messages, this means 2865 that the (reverse) multicast tree path is simply from each Z* (and/or 2866 Y) to X with no other multicast-aware routers in the path. If any Z* 2867 (and/or Y) is located on the same OMNI link segment as X, the 2868 multicast data traffic sent to X directly using OAL/INET 2869 encapsulation instead of via a Bridge. 2871 Following the initial Join/Prune and NS/NA messaging, X maintains an 2872 asymmetric neighbor cache entry for each S the same as if X was 2873 sending unicast data traffic to S. In particular, X performs 2874 additional NS/NA exchanges to keep the neighbor cache entry alive for 2875 up to t_periodic seconds [RFC7761]. If no new Joins are received 2876 within t_periodic seconds, X allows the neighbor cache entry to 2877 expire. Finally, if X receives any additional Join/Prune messages 2878 for (S,G) it forwards the messages to each Y and Z* in the neighbor 2879 cache entry over the spanning tree. 2881 At some later time, Client C that holds an MNP for source S may 2882 depart from a first Proxy Z1 and/or connect via a new Proxy Z2. In 2883 that case, Y sends an unsolicited NA message to X the same as 2884 specified for unicast mobility in Section 3.16. When X receives the 2885 unsolicited NA message, it updates its asymmetric neighbor cache 2886 entry for the LLA for source S and sends new Join messages to any new 2887 Proxys Z2. There is no requirement to send any Prune messages to old 2888 Proxys Z1 since source S will no longer source any multicast data 2889 traffic via Z1. Instead, the multicast state for (S,G) in Proxy Z1 2890 will soon time out since no new Joins will arrive. 2892 After some later time, C may move to a new Server Y2 and depart from 2893 old Sever Y1. In that case, Y1 sends Join messages for any of C's 2894 active (S,G) groups to Y2 while including its own LLA as the source 2895 address. This causes Y2 to include Y1 in the multicast forwarding 2896 tree during the interim time that Y1's symmetric neighbor cache entry 2897 for C is in the DEPARTED state. At the same time, Y1 sends an 2898 unsolicited NA message to X with an OMNI option with S/T-ifIndex in 2899 the header set to 0 and a release indication to cause X to release 2900 its asymmetric neighbor cache entry. X then sends a new Join message 2901 to S via the spanning tree and re-initiates route optimization the 2902 same as if it were receiving a fresh Join message from a node on a 2903 downstream link. 2905 3.17.2. Any-Source Multicast (ASM) 2907 When an ROS X acting as a PIM router receives a Join/Prune from a 2908 node on its downstream interfaces containing one or more (*,G) pairs, 2909 it updates its Multicast Routing Information Base (MRIB) accordingly. 2910 X then forwards a copy of the message to the Rendezvous Point (RP) R 2911 for each G over the spanning tree. X uses its own LLA as the source 2912 address and ALL-PIM-ROUTERS as the destination address, then 2913 encapsulates each message in an OAL header with source address set to 2914 the ULA of X and destination address set to R, then sends the message 2915 into the spanning tree. At the same time, if the message was a Join 2916 X initiates NS/NA route optimization the same as for the SSM case 2917 discussed in Section 3.17.1. 2919 For each source S that sends multicast traffic to group G via R, the 2920 Proxy/Server Z* for the Client that aggregates S encapsulates the 2921 packets in PIM Register messages and forwards them to R via the 2922 spanning tree, which may then elect to send a PIM Join to Z*. This 2923 will result in an (S,G) tree rooted at Z* with R as the next hop so 2924 that R will begin to receive two copies of the packet; one native 2925 copy from the (S, G) tree and a second copy from the pre-existing (*, 2926 G) tree that still uses PIM Register encapsulation. R can then issue 2927 a PIM Register-stop message to suppress the Register-encapsulated 2928 stream. At some later time, if C moves to a new Proxy/Server Z*, it 2929 resumes sending packets via PIM Register encapsulation via the new 2930 Z*. 2932 At the same time, as multicast listeners discover individual S's for 2933 a given G, they can initiate an (S,G) Join for each S under the same 2934 procedures discussed in Section 3.17.1. Once the (S,G) tree is 2935 established, the listeners can send (S, G) Prune messages to R so 2936 that multicast packets for group G sourced by S will only be 2937 delivered via the (S, G) tree and not from the (*, G) tree rooted at 2938 R. All mobility considerations discussed for SSM apply. 2940 3.17.3. Bi-Directional PIM (BIDIR-PIM) 2942 Bi-Directional PIM (BIDIR-PIM) [RFC5015] provides an alternate 2943 approach to ASM that treats the Rendezvous Point (RP) as a Designated 2944 Forwarder (DF). Further considerations for BIDIR-PIM are out of 2945 scope. 2947 3.18. Operation over Multiple OMNI Links 2949 An AERO Client can connect to multiple OMNI links the same as for any 2950 data link service. In that case, the Client maintains a distinct 2951 OMNI interface for each link, e.g., 'omni0' for the first link, 2952 'omni1' for the second, 'omni2' for the third, etc. Each OMNI link 2953 would include its own distinct set of Bridges, Servers and Proxys, 2954 thereby providing redundancy in case of failures. 2956 Each OMNI link could utilize the same or different ANET connections. 2957 The links can be distinguished at the link-layer via the SRT prefix 2958 in a similar fashion as for Virtual Local Area Network (VLAN) tagging 2959 (e.g., IEEE 802.1Q) and/or through assignment of distinct sets of 2960 MSPs on each link. This gives rise to the opportunity for supporting 2961 multiple redundant networked paths, with each VLAN distinguished by a 2962 different SRT "color" (see: Section 3.2.6). 2964 The Client's IP layer can select the outgoing OMNI interface 2965 appropriate for a given traffic profile while (in the reverse 2966 direction) correspondent nodes must have some way of steering their 2967 packets destined to a target via the correct OMNI link. 2969 In a first alternative, if each OMNI link services different MSPs, 2970 then the Client can receive a distinct MNP from each of the links. 2971 IP routing will therefore assure that the correct OMNI link is used 2972 for both outbound and inbound traffic. This can be accomplished 2973 using existing technologies and approaches, and without requiring any 2974 special supporting code in correspondent nodes or Bridges. 2976 In a second alternative, if each OMNI link services the same MSP(s) 2977 then each link could assign a distinct "OMNI link Anycast" address 2978 that is configured by all Bridges on the link. Correspondent nodes 2979 can then perform Segment Routing to select the correct SRT, which 2980 will then direct the packet over multiple hops to the target. 2982 3.19. DNS Considerations 2984 AERO Client MNs and INET correspondent nodes consult the Domain Name 2985 System (DNS) the same as for any Internetworking node. When 2986 correspondent nodes and Client MNs use different IP protocol versions 2987 (e.g., IPv4 correspondents and IPv6 MNs), the INET DNS must maintain 2988 A records for IPv4 address mappings to MNs which must then be 2989 populated in Relay NAT64 mapping caches. In that way, an IPv4 2990 correspondent node can send packets to the IPv4 address mapping of 2991 the target MN, and the Relay will translate the IPv4 header and 2992 destination address into an IPv6 header and IPv6 destination address 2993 of the MN. 2995 When an AERO Client registers with an AERO Server, the Server can 2996 return the address(es) of DNS servers in RDNSS options [RFC6106]. 2997 The DNS server provides the IP addresses of other MNs and 2998 correspondent nodes in AAAA records for IPv6 or A records for IPv4. 3000 3.20. Transition Considerations 3002 OAL encapsulation ensures that dissimilar INET partitions can be 3003 joined into a single unified OMNI link, even though the partitions 3004 themselves may have differing protocol versions and/or incompatible 3005 addressing plans. However, a commonality can be achieved by 3006 incrementally distributing globally routable (i.e., native) IP 3007 prefixes to eventually reach all nodes (both mobile and fixed) in all 3008 OMNI link segments. This can be accomplished by incrementally 3009 deploying AERO Relays on each INET partition, with each Relay 3010 distributing its MNPs and/or discovering non-MNP IP GUA prefixes on 3011 its INET links. 3013 This gives rise to the opportunity to eventually distribute native IP 3014 addresses to all nodes, and to present a unified OMNI link view even 3015 if the INET partitions remain in their current protocol and 3016 addressing plans. In that way, the OMNI link can serve the dual 3017 purpose of providing a mobility/multilink service and a transition 3018 service. Or, if an INET partition is transitioned to a native IP 3019 protocol version and addressing scheme that is compatible with the 3020 OMNI link MNP-based addressing scheme, the partition and OMNI link 3021 can be joined by Relays. 3023 Relays that connect INETs/EUNs with dissimilar IP protocol versions 3024 may need to employ a network address and protocol translation 3025 function such as NAT64 [RFC6146]. 3027 3.21. Detecting and Reacting to Server and Bridge Failures 3029 In environments where rapid failure recovery is required, Servers and 3030 Bridges SHOULD use Bidirectional Forwarding Detection (BFD) 3031 [RFC5880]. Nodes that use BFD can quickly detect and react to 3032 failures so that cached information is re-established through 3033 alternate nodes. BFD control messaging is carried only over well- 3034 connected ground domain networks (i.e., and not low-end radio links) 3035 and can therefore be tuned for rapid response. 3037 Servers and Bridges maintain BFD sessions in parallel with their BGP 3038 peerings. If a Server or Bridge fails, BGP peers will quickly re- 3039 establish routes through alternate paths the same as for common BGP 3040 deployments. Similarly, Proxys maintain BFD sessions with their 3041 associated Bridges even though they do not establish BGP peerings 3042 with them. 3044 Proxys SHOULD use proactive NUD for Servers for which there are 3045 currently active ANET Clients in a manner that parallels BFD, i.e., 3046 by sending unicast NS messages in rapid succession to receive 3047 solicited NA messages. When the Proxy is also sending RS messages on 3048 behalf of ANET Clients, the RS/RA messaging can be considered as 3049 equivalent hints of forward progress. This means that the Proxy need 3050 not also send a periodic NS if it has already sent an RS within the 3051 same period. If a Server fails, the Proxy will cease to receive 3052 advertisements and can quickly inform Clients of the outage by 3053 sending multicast RA messages on the ANET interface. 3055 The Proxy sends multicast RA messages with source address set to the 3056 Server's address, destination address set to (link-local) All-Nodes 3057 multicast, and Router Lifetime set to 0. The Proxy SHOULD send 3058 MAX_FINAL_RTR_ADVERTISEMENTS RA messages separated by small delays 3059 [RFC4861]. Any Clients on the ANET interface that have been using 3060 the (now defunct) Server will receive the RA messages and associate 3061 with a new Server. 3063 3.22. AERO Clients on the Open Internet 3065 AERO Clients that connect to the open Internet via INET interfaces 3066 can establish a VPN or direct link to securely connect to a Server in 3067 a "tethered" arrangement with all of the Client's traffic transiting 3068 the Server. Alternatively, the Client can associate with an INET 3069 Server using UDP/IP encapsulation and asymmetric securing services as 3070 discussed in the following sections. 3072 When a Client's OMNI interface enables an INET underlying interface, 3073 it first determines whether the interface is likely to be behind a 3074 NAT. For IPv4, the Client assumes it is on the open Internet if the 3075 INET address is not a special-use IPv4 address per [RFC3330]. 3076 Similarly for IPv6, the Client assumes it is on the open Internet if 3077 the INET address is not a link-local [RFC4291] or unique-local 3078 [RFC4193] IPv6 address. 3080 The Client then prepares a UDP/IP-encapsulated RS message with IPv6 3081 source address set to its MNP-LLA, with IPv6 destination set to 3082 (link-local) All-Routers multicast and with an OMNI option with 3083 underlying interface attributes. If the Client believes that it is 3084 on the open Internet, it SHOULD include Interface Attributes with the 3085 L2ADDR used for INET encapsulation (otherwise, it MAY omit L2ADDR). 3086 If the underlying address is IPv4, the Client includes the Port 3087 Number and IPv4 address written in obfuscated form [RFC4380] as 3088 discussed in Section 3.3. If the underlying interface address is 3089 IPv6, the Client instead includes the Port Number and IPv6 address in 3090 obfuscated form. The Client finally includes a HIP "Initiator" 3091 message sub-option in the OMNI option 3092 [I-D.templin-6man-omni-interface] to provide message authentication, 3093 sets the UDP/IP source to its INET address and UDP port, sets the 3094 UDP/IP destination to the Server's INET address and the AERO service 3095 port number (8060), then sends the message to the Server. 3097 When the Server receives the RS, it authenticates the message and 3098 registers the Client's MNP and INET interface information according 3099 to the OMNI option parameters. If the RS message OMNI option 3100 includes Interface Attributes with an L2ADDR, the Server compares the 3101 encapsulation IP address and UDP port number with the (unobfuscated) 3102 values. If the values are the same, the Server caches the Client's 3103 information as "INET" addresses meaning that the Client is likely to 3104 accept direct messages without requiring NAT traversal exchanges. If 3105 the values are different (or, if the OMNI option did not include an 3106 L2ADDR) the Server instead caches the Client's information as 3107 "mapped" addresses meaning that NAT traversal exchanges may be 3108 necessary. 3110 The Server then returns an RA message with IPv6 source and 3111 destination set corresponding to the addresses in the RS, and with an 3112 OMNI option with a HIP "Responder" message sub-option per 3113 [I-D.templin-6man-omni-interface] that contains an acknowledgement of 3114 the update sent by the Client. For IPv4, the Server also includes an 3115 Origin Indication sub-option per [I-D.templin-6man-omni-interface] 3116 with the mapped and obfuscated Port Number and IPv4 address observed 3117 in the encapsulation headers. 3119 When the Client receives the RA message, it compares the mapped Port 3120 Number and IP address from the Origin sub-option with its own 3121 address. If the addresses are the same, the Client assumes the open 3122 Internet / Cone NAT principle; if the addresses are different, the 3123 Client instead assumes that further qualification procedures are 3124 necessary to detect the type of NAT and proceeds according to 3125 standard [RFC4380] procedures. 3127 After the Client has registered its INET interfaces in such RS/RA 3128 exchanges it sends periodic RS messages to receive fresh RA messages 3129 before the Router Lifetime received on each INET interface expires. 3130 The Client also maintains default routes via its Servers, i.e., the 3131 same as described in earlier sections. 3133 When the Client sends messages to target IP addresses, it also 3134 invokes route optimization per Section 3.14 using IPv6 ND address 3135 resolution messaging. The Client sends the NS(AR) message to the 3136 Server with an OMNI option with a HIP "Update/Sequence" message sub- 3137 option. The Client sets the NS source address to the Client's MNP- 3138 LLA and destination address to the target solicited node multicast 3139 address. The Client wraps the NS message in an OAL header with 3140 source address set to its own MNP-ULA and destination address set to 3141 the Server's ADM-ULA. The Client then wraps the OAL message in a 3142 UDP/IP header and sends it to the Server. 3144 When the Server receives the OAL-encapsulated NS, it authenticates 3145 the message by processing the HIP message sub-option and sends a 3146 corresponding NS(AR) message over the spanning tree the same as if it 3147 were the ROS, but with the OAL source address set to the Server's 3148 ADM-ULA, with destination set to the MNP-ULA of the target, and with 3149 an OMNI option that includes no sub-options. When the ROR receives 3150 the NS(AR), it adds the Server's ADM-ULA and Client's MNP-LLA to the 3151 target's Report List, and returns an NA(AR) with OMNI option 3152 information for the target including all of the target's Interface 3153 Attributes. The ROR sets the NA(AR) source address to the target's 3154 MNP-LLA and sets the destination address to the Client's MNP-LLA, 3155 then sets the OAL source address to the ADM-ULA of the ROR and the 3156 destination to the ADM-ULA of the Server. When the Server receives 3157 the NA(AR) message, it rewrites the OAL source address to its own 3158 ADM-ULA and the destination address to the MNP-ULA of the Client, 3159 then includes a HIP "Update/Acknowledge" message sub-option in the 3160 OMNI option, wraps the message in UDP/IP headers, and sends it to the 3161 Client. 3163 Following route optimization for targets in the same OMNI link 3164 segment, if the target's L2ADDR is on the open INET, the Client 3165 forwards data packets directly to the target INET address. If the 3166 target is behind a NAT, the Client first establishes NAT state for 3167 the L2ADDR using the "direct bubble" and NUD mechanisms discussed in 3168 Section 3.10.1. The Client continues to send data packets via its 3169 Server until NAT state is populated, then begins forwarding packets 3170 via the direct path through the NAT to the target. For targets in 3171 different OMNI link segments, the Client uses OAL/ORH encapsulation 3172 and forwards data packets to the Bridge that returned the NA message. 3174 The ROR may return uNAs via the Server if the target moves, and the 3175 Server will send corresponding authentication-protected uNAs to the 3176 Client. The Client can also send NUD messages to test forward path 3177 reachability even though there is no security association between the 3178 Client and the target. 3180 The Client sends UDP/IP encapsulated IPv6 packets to route-optimized 3181 neighbors in the same OMNI link segment no larger than 576 bytes in 3182 one piece and without OAL encapsulation. Otherwise, the Client 3183 inserts an OAL header with source set to its own MNP-ULA and 3184 destination set to the MNP-ULA of the target and uses OAL 3185 fragmentation if necessary according to Section 3.9. The Client then 3186 encapsulates each fragment in a UDP/IP header and sends the fragments 3187 to the next hop. 3189 Note: The NAT traversal procedures specified in this document are 3190 applicable for Cone, Address-Restricted and Port-Restricted NATs 3191 only. While future updates to this document may specify procedures 3192 for other NAT variations (e.g., hairpinning and various forms of 3193 Symmetric NATs), it should be noted that continuous communications 3194 are always possible through forwarding via a Server even if NAT 3195 traversal is not employed. 3197 Note: Following the initial HIP Initiator/Responder exchange, AERO 3198 Clients with OMNI interfaces configured over the open Internet 3199 maintain HIP associations through the transmission of IPv6 ND 3200 messages that include OMNI options with HIP "Update" and "Notify" 3201 messages. OMNI interfaces use the HIP "Update" message when an 3202 acknowledgement is required, and use the "Notify" message in 3203 unacknowledged isolated IPv6 ND messages (e.g., unsolicited NAs). 3205 3.23. Time-Varying MNPs 3207 In some use cases, it is desirable, beneficial and efficient for the 3208 Client to receive a constant MNP that travels with the Client 3209 wherever it moves. For example, this would allow air traffic 3210 controllers to easily track aircraft, etc. In other cases, however 3211 (e.g., intelligent transportation systems), the MN may be willing to 3212 sacrifice a modicum of efficiency in order to have time-varying MNPs 3213 that can be changed every so often to defeat adversarial tracking. 3215 The DHCPv6 service offers a way for Clients that desire time-varying 3216 MNPs to obtain short-lived prefixes (e.g., on the order of a small 3217 number of minutes). In that case, the identity of the Client would 3218 not be bound to the MNP but rather the Client's identity would be 3219 bound to the DHCPv6 Device Unique Identifier (DUID) and used as the 3220 seed for Prefix Delegation. The Client would then be obligated to 3221 renumber its internal networks whenever its MNP (and therefore also 3222 its MNP-LLA) changes. This should not present a challenge for 3223 Clients with automated network renumbering services, however presents 3224 limits for the durations of ongoing sessions that would prefer to use 3225 a constant address. 3227 4. Implementation Status 3229 An early AERO implementation based on OpenVPN (https://openvpn.net/) 3230 was announced on the v6ops mailing list on January 10, 2018 and an 3231 initial public release of the AERO proof-of-concept source code was 3232 announced on the intarea mailing list on August 21, 2015. 3234 AERO Release-3.0.2 was tagged on October 15, 2020, and is undergoing 3235 internal testing. Additional internal releases expected within the 3236 coming months, with first public release expected end of 1H2021. 3238 5. IANA Considerations 3240 The IANA has assigned the UDP port number "8060" for an earlier 3241 experimental version of AERO [RFC6706]. This document obsoletes 3242 [RFC6706] and claims the UDP port number "8060" for all future use. 3244 The IANA is instructed to assign a new type value TBD in the IPv6 3245 Routing Types registry. 3247 No further IANA actions are required. 3249 6. Security Considerations 3251 AERO Bridges configure secured tunnels with AERO Servers, Relays and 3252 Proxys within their local OMNI link segments. Applicable secured 3253 tunnel alternatives include IPsec [RFC4301], TLS/SSL [RFC8446], DTLS 3254 [RFC6347], WireGuard [WG], etc. The AERO Bridges of all OMNI link 3255 segments in turn configure secured tunnels for their neighboring AERO 3256 Bridges in a spanning tree topology. Therefore, control messages 3257 exchanged between any pair of OMNI link neighbors on the spanning 3258 tree are already secured. 3260 AERO Servers, Relays and Proxys targeted by a route optimization may 3261 also receive data packets directly from arbitrary nodes in INET 3262 partitions instead of via the spanning tree. For INET partitions 3263 that apply effective ingress filtering to defeat source address 3264 spoofing, the simple data origin authentication procedures in 3265 Section 3.8 can be applied. 3267 For INET partitions that require strong security in the data plane, 3268 two options for securing communications include 1) disable route 3269 optimization so that all traffic is conveyed over secured tunnels, or 3270 2) enable on-demand secure tunnel creation between INET partition 3271 neighbors. Option 1) would result in longer routes than necessary 3272 and traffic concentration on critical infrastructure elements. 3273 Option 2) could be coordinated by establishing a secured tunnel on- 3274 demand instead of performing an NS/NA exchange in the route 3275 optimization procedures. Procedures for establishing on-demand 3276 secured tunnels are out of scope. 3278 AERO Clients that connect to secured ANETs need not apply security to 3279 their ND messages, since the messages will be intercepted by a 3280 perimeter Proxy that applies security on its INET-facing interface as 3281 part of the spanning tree (see above). AERO Clients connected to the 3282 open INET can use symmetric network and/or transport layer security 3283 services such as VPNs or can by some other means establish a direct 3284 link. When a VPN or direct link may be impractical, however, the 3285 HIP-based authentication services specified in [RFC7401] should be 3286 applied. 3288 Application endpoints SHOULD use application-layer security services 3289 such as TLS/SSL, DTLS or SSH [RFC4251] to assure the same level of 3290 protection as for critical secured Internet services. AERO Clients 3291 that require host-based VPN services SHOULD use symmetric network 3292 and/or transport layer security services such as IPsec, TLS/SSL, 3293 DTLS, etc. AERO Proxys and Servers can also provide a network-based 3294 VPN service on behalf of the Client, e.g., if the Client is located 3295 within a secured enclave and cannot establish a VPN on its own 3296 behalf. 3298 AERO Servers and Bridges present targets for traffic amplification 3299 Denial of Service (DoS) attacks. This concern is no different than 3300 for widely-deployed VPN security gateways in the Internet, where 3301 attackers could send spoofed packets to the gateways at high data 3302 rates. This can be mitigated by connecting Servers and Bridges over 3303 dedicated links with no connections to the Internet and/or when 3304 connections to the Internet are only permitted through well-managed 3305 firewalls. Traffic amplification DoS attacks can also target an AERO 3306 Client's low data rate links. This is a concern not only for Clients 3307 located on the open Internet but also for Clients in secured 3308 enclaves. AERO Servers and Proxys can institute rate limits that 3309 protect Clients from receiving packet floods that could DoS low data 3310 rate links. 3312 AERO Relays must implement ingress filtering to avoid a spoofing 3313 attack in which spurious messages with ULA addresses are injected 3314 into an OMNI link from an outside attacker. AERO Clients MUST ensure 3315 that their connectivity is not used by unauthorized nodes on their 3316 EUNs to gain access to a protected network, i.e., AERO Clients that 3317 act as routers MUST NOT provide routing services for unauthorized 3318 nodes. (This concern is no different than for ordinary hosts that 3319 receive an IP address delegation but then "share" the address with 3320 other nodes via some form of Internet connection sharing such as 3321 tethering.) 3323 The MAP list MUST be well-managed and secured from unauthorized 3324 tampering, even though the list contains only public information. 3325 The MAP list can be conveyed to the Client in a similar fashion as in 3326 [RFC5214] (e.g., through layer 2 data link login messaging, secure 3327 upload of a static file, DNS lookups, etc.). 3329 SRH authentication facilities are specified in [RFC8754]. 3331 Security considerations for accepting link-layer ICMP messages and 3332 reflected packets are discussed throughout the document. 3334 Security considerations for IPv6 fragmentation and reassembly are 3335 discussed in [I-D.templin-6man-omni-interface]. 3337 7. Acknowledgements 3339 Discussions in the IETF, aviation standards communities and private 3340 exchanges helped shape some of the concepts in this work. 3341 Individuals who contributed insights include Mikael Abrahamsson, Mark 3342 Andrews, Fred Baker, Bob Braden, Stewart Bryant, Brian Carpenter, 3343 Wojciech Dec, Pavel Drasil, Ralph Droms, Adrian Farrel, Nick Green, 3344 Sri Gundavelli, Brian Haberman, Bernhard Haindl, Joel Halpern, Tom 3345 Herbert, Sascha Hlusiak, Lee Howard, Zdenek Jaron, Andre Kostur, 3346 Hubert Kuenig, Ted Lemon, Andy Malis, Satoru Matsushima, Tomek 3347 Mrugalski, Madhu Niraula, Alexandru Petrescu, Behcet Saikaya, Michal 3348 Skorepa, Joe Touch, Bernie Volz, Ryuji Wakikawa, Tony Whyman, Lloyd 3349 Wood and James Woodyatt. Members of the IESG also provided valuable 3350 input during their review process that greatly improved the document. 3351 Special thanks go to Stewart Bryant, Joel Halpern and Brian Haberman 3352 for their shepherding guidance during the publication of the AERO 3353 first edition. 3355 This work has further been encouraged and supported by Boeing 3356 colleagues including Kyle Bae, M. Wayne Benson, Dave Bernhardt, Cam 3357 Brodie, John Bush, Balaguruna Chidambaram, Irene Chin, Bruce Cornish, 3358 Claudiu Danilov, Don Dillenburg, Joe Dudkowski, Wen Fang, Samad 3359 Farooqui, Anthony Gregory, Jeff Holland, Seth Jahne, Brian Jaury, 3360 Greg Kimberly, Ed King, Madhuri Madhava Badgandi, Laurel Matthew, 3361 Gene MacLean III, Rob Muszkiewicz, Sean O'Sullivan, Vijay 3362 Rajagopalan, Greg Saccone, Rod Santiago, Kent Shuey, Brian Skeen, 3363 Mike Slane, Carrie Spiker, Katie Tran, Brendan Williams, Amelia 3364 Wilson, Julie Wulff, Yueli Yang, Eric Yeh and other members of the 3365 Boeing mobility, networking and autonomy teams. Kyle Bae, Wayne 3366 Benson, Katie Tran and Eric Yeh are especially acknowledged for 3367 implementing the AERO functions as extensions to the public domain 3368 OpenVPN distribution. 3370 Earlier works on NBMA tunneling approaches are found in 3371 [RFC2529][RFC5214][RFC5569]. 3373 Many of the constructs presented in this second edition of AERO are 3374 based on the author's earlier works, including: 3376 o The Internet Routing Overlay Network (IRON) 3377 [RFC6179][I-D.templin-ironbis] 3379 o Virtual Enterprise Traversal (VET) 3380 [RFC5558][I-D.templin-intarea-vet] 3382 o The Subnetwork Encapsulation and Adaptation Layer (SEAL) 3383 [RFC5320][I-D.templin-intarea-seal] 3385 o AERO, First Edition [RFC6706] 3387 Note that these works cite numerous earlier efforts that are not also 3388 cited here due to space limitations. The authors of those earlier 3389 works are acknowledged for their insights. 3391 This work is aligned with the NASA Safe Autonomous Systems Operation 3392 (SASO) program under NASA contract number NNA16BD84C. 3394 This work is aligned with the FAA as per the SE2025 contract number 3395 DTFAWA-15-D-00030. 3397 This work is aligned with the Boeing Commercial Airplanes (BCA) 3398 Internet of Things (IoT) and autonomy programs. 3400 This work is aligned with the Boeing Information Technology (BIT) 3401 MobileNet program. 3403 8. References 3405 8.1. Normative References 3407 [I-D.templin-6man-omni-interface] 3408 Templin, F. and T. Whyman, "Transmission of IP Packets 3409 over Overlay Multilink Network (OMNI) Interfaces", draft- 3410 templin-6man-omni-interface-69 (work in progress), January 3411 2021. 3413 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, 3414 DOI 10.17487/RFC0791, September 1981, 3415 . 3417 [RFC0792] Postel, J., "Internet Control Message Protocol", STD 5, 3418 RFC 792, DOI 10.17487/RFC0792, September 1981, 3419 . 3421 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 3422 Requirement Levels", BCP 14, RFC 2119, 3423 DOI 10.17487/RFC2119, March 1997, 3424 . 3426 [RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in 3427 IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473, 3428 December 1998, . 3430 [RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander, 3431 "SEcure Neighbor Discovery (SEND)", RFC 3971, 3432 DOI 10.17487/RFC3971, March 2005, 3433 . 3435 [RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)", 3436 RFC 3972, DOI 10.17487/RFC3972, March 2005, 3437 . 3439 [RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and 3440 More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191, 3441 November 2005, . 3443 [RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast 3444 Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005, 3445 . 3447 [RFC4380] Huitema, C., "Teredo: Tunneling IPv6 over UDP through 3448 Network Address Translations (NATs)", RFC 4380, 3449 DOI 10.17487/RFC4380, February 2006, 3450 . 3452 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 3453 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 3454 DOI 10.17487/RFC4861, September 2007, 3455 . 3457 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 3458 Address Autoconfiguration", RFC 4862, 3459 DOI 10.17487/RFC4862, September 2007, 3460 . 3462 [RFC6081] Thaler, D., "Teredo Extensions", RFC 6081, 3463 DOI 10.17487/RFC6081, January 2011, 3464 . 3466 [RFC7401] Moskowitz, R., Ed., Heer, T., Jokela, P., and T. 3467 Henderson, "Host Identity Protocol Version 2 (HIPv2)", 3468 RFC 7401, DOI 10.17487/RFC7401, April 2015, 3469 . 3471 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 3472 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 3473 May 2017, . 3475 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 3476 (IPv6) Specification", STD 86, RFC 8200, 3477 DOI 10.17487/RFC8200, July 2017, 3478 . 3480 [RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A., 3481 Richardson, M., Jiang, S., Lemon, T., and T. Winters, 3482 "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", 3483 RFC 8415, DOI 10.17487/RFC8415, November 2018, 3484 . 3486 8.2. Informative References 3488 [BGP] Huston, G., "BGP in 2015, http://potaroo.net", January 3489 2016. 3491 [I-D.bonica-6man-comp-rtg-hdr] 3492 Bonica, R., Kamite, Y., Alston, A., Henriques, D., and L. 3493 Jalil, "The IPv6 Compact Routing Header (CRH)", draft- 3494 bonica-6man-comp-rtg-hdr-24 (work in progress), January 3495 2021. 3497 [I-D.bonica-6man-crh-helper-opt] 3498 Li, X., Bao, C., Ruan, E., and R. Bonica, "Compressed 3499 Routing Header (CRH) Helper Option", draft-bonica-6man- 3500 crh-helper-opt-02 (work in progress), October 2020. 3502 [I-D.ietf-intarea-frag-fragile] 3503 Bonica, R., Baker, F., Huston, G., Hinden, R., Troan, O., 3504 and F. Gont, "IP Fragmentation Considered Fragile", draft- 3505 ietf-intarea-frag-fragile-17 (work in progress), September 3506 2019. 3508 [I-D.ietf-intarea-tunnels] 3509 Touch, J. and M. Townsley, "IP Tunnels in the Internet 3510 Architecture", draft-ietf-intarea-tunnels-10 (work in 3511 progress), September 2019. 3513 [I-D.ietf-ipwave-vehicular-networking] 3514 Jeong, J., "IPv6 Wireless Access in Vehicular Environments 3515 (IPWAVE): Problem Statement and Use Cases", draft-ietf- 3516 ipwave-vehicular-networking-19 (work in progress), July 3517 2020. 3519 [I-D.ietf-rtgwg-atn-bgp] 3520 Templin, F., Saccone, G., Dawra, G., Lindem, A., and V. 3521 Moreno, "A Simple BGP-based Mobile Routing System for the 3522 Aeronautical Telecommunications Network", draft-ietf- 3523 rtgwg-atn-bgp-10 (work in progress), January 2021. 3525 [I-D.templin-6man-dhcpv6-ndopt] 3526 Templin, F., "A Unified Stateful/Stateless Configuration 3527 Service for IPv6", draft-templin-6man-dhcpv6-ndopt-11 3528 (work in progress), January 2021. 3530 [I-D.templin-intarea-seal] 3531 Templin, F., "The Subnetwork Encapsulation and Adaptation 3532 Layer (SEAL)", draft-templin-intarea-seal-68 (work in 3533 progress), January 2014. 3535 [I-D.templin-intarea-vet] 3536 Templin, F., "Virtual Enterprise Traversal (VET)", draft- 3537 templin-intarea-vet-40 (work in progress), May 2013. 3539 [I-D.templin-ipwave-uam-its] 3540 Templin, F., "Urban Air Mobility Implications for 3541 Intelligent Transportation Systems", draft-templin-ipwave- 3542 uam-its-04 (work in progress), January 2021. 3544 [I-D.templin-ironbis] 3545 Templin, F., "The Interior Routing Overlay Network 3546 (IRON)", draft-templin-ironbis-16 (work in progress), 3547 March 2014. 3549 [I-D.templin-v6ops-pdhost] 3550 Templin, F., "IPv6 Prefix Delegation and Multi-Addressing 3551 Models", draft-templin-v6ops-pdhost-27 (work in progress), 3552 January 2021. 3554 [OVPN] OpenVPN, O., "http://openvpn.net", October 2016. 3556 [RFC1035] Mockapetris, P., "Domain names - implementation and 3557 specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, 3558 November 1987, . 3560 [RFC1812] Baker, F., Ed., "Requirements for IP Version 4 Routers", 3561 RFC 1812, DOI 10.17487/RFC1812, June 1995, 3562 . 3564 [RFC2003] Perkins, C., "IP Encapsulation within IP", RFC 2003, 3565 DOI 10.17487/RFC2003, October 1996, 3566 . 3568 [RFC2004] Perkins, C., "Minimal Encapsulation within IP", RFC 2004, 3569 DOI 10.17487/RFC2004, October 1996, 3570 . 3572 [RFC2236] Fenner, W., "Internet Group Management Protocol, Version 3573 2", RFC 2236, DOI 10.17487/RFC2236, November 1997, 3574 . 3576 [RFC2464] Crawford, M., "Transmission of IPv6 Packets over Ethernet 3577 Networks", RFC 2464, DOI 10.17487/RFC2464, December 1998, 3578 . 3580 [RFC2529] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4 3581 Domains without Explicit Tunnels", RFC 2529, 3582 DOI 10.17487/RFC2529, March 1999, 3583 . 3585 [RFC2983] Black, D., "Differentiated Services and Tunnels", 3586 RFC 2983, DOI 10.17487/RFC2983, October 2000, 3587 . 3589 [RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition 3590 of Explicit Congestion Notification (ECN) to IP", 3591 RFC 3168, DOI 10.17487/RFC3168, September 2001, 3592 . 3594 [RFC3330] IANA, "Special-Use IPv4 Addresses", RFC 3330, 3595 DOI 10.17487/RFC3330, September 2002, 3596 . 3598 [RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener 3599 Discovery Version 2 (MLDv2) for IPv6", RFC 3810, 3600 DOI 10.17487/RFC3810, June 2004, 3601 . 3603 [RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally 3604 Unique IDentifier (UUID) URN Namespace", RFC 4122, 3605 DOI 10.17487/RFC4122, July 2005, 3606 . 3608 [RFC4251] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH) 3609 Protocol Architecture", RFC 4251, DOI 10.17487/RFC4251, 3610 January 2006, . 3612 [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A 3613 Border Gateway Protocol 4 (BGP-4)", RFC 4271, 3614 DOI 10.17487/RFC4271, January 2006, 3615 . 3617 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 3618 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 3619 2006, . 3621 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 3622 Internet Protocol", RFC 4301, DOI 10.17487/RFC4301, 3623 December 2005, . 3625 [RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery 3626 Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April 3627 2006, . 3629 [RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet 3630 Control Message Protocol (ICMPv6) for the Internet 3631 Protocol Version 6 (IPv6) Specification", STD 89, 3632 RFC 4443, DOI 10.17487/RFC4443, March 2006, 3633 . 3635 [RFC4511] Sermersheim, J., Ed., "Lightweight Directory Access 3636 Protocol (LDAP): The Protocol", RFC 4511, 3637 DOI 10.17487/RFC4511, June 2006, 3638 . 3640 [RFC4541] Christensen, M., Kimball, K., and F. Solensky, 3641 "Considerations for Internet Group Management Protocol 3642 (IGMP) and Multicast Listener Discovery (MLD) Snooping 3643 Switches", RFC 4541, DOI 10.17487/RFC4541, May 2006, 3644 . 3646 [RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick, 3647 "Internet Group Management Protocol (IGMP) / Multicast 3648 Listener Discovery (MLD)-Based Multicast Forwarding 3649 ("IGMP/MLD Proxying")", RFC 4605, DOI 10.17487/RFC4605, 3650 August 2006, . 3652 [RFC4982] Bagnulo, M. and J. Arkko, "Support for Multiple Hash 3653 Algorithms in Cryptographically Generated Addresses 3654 (CGAs)", RFC 4982, DOI 10.17487/RFC4982, July 2007, 3655 . 3657 [RFC5015] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano, 3658 "Bidirectional Protocol Independent Multicast (BIDIR- 3659 PIM)", RFC 5015, DOI 10.17487/RFC5015, October 2007, 3660 . 3662 [RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site 3663 Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214, 3664 DOI 10.17487/RFC5214, March 2008, 3665 . 3667 [RFC5320] Templin, F., Ed., "The Subnetwork Encapsulation and 3668 Adaptation Layer (SEAL)", RFC 5320, DOI 10.17487/RFC5320, 3669 February 2010, . 3671 [RFC5522] Eddy, W., Ivancic, W., and T. Davis, "Network Mobility 3672 Route Optimization Requirements for Operational Use in 3673 Aeronautics and Space Exploration Mobile Networks", 3674 RFC 5522, DOI 10.17487/RFC5522, October 2009, 3675 . 3677 [RFC5558] Templin, F., Ed., "Virtual Enterprise Traversal (VET)", 3678 RFC 5558, DOI 10.17487/RFC5558, February 2010, 3679 . 3681 [RFC5569] Despres, R., "IPv6 Rapid Deployment on IPv4 3682 Infrastructures (6rd)", RFC 5569, DOI 10.17487/RFC5569, 3683 January 2010, . 3685 [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 3686 (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, 3687 . 3689 [RFC6106] Jeong, J., Park, S., Beloeil, L., and S. Madanapalli, 3690 "IPv6 Router Advertisement Options for DNS Configuration", 3691 RFC 6106, DOI 10.17487/RFC6106, November 2010, 3692 . 3694 [RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful 3695 NAT64: Network Address and Protocol Translation from IPv6 3696 Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146, 3697 April 2011, . 3699 [RFC6179] Templin, F., Ed., "The Internet Routing Overlay Network 3700 (IRON)", RFC 6179, DOI 10.17487/RFC6179, March 2011, 3701 . 3703 [RFC6221] Miles, D., Ed., Ooghe, S., Dec, W., Krishnan, S., and A. 3704 Kavanagh, "Lightweight DHCPv6 Relay Agent", RFC 6221, 3705 DOI 10.17487/RFC6221, May 2011, 3706 . 3708 [RFC6273] Kukec, A., Krishnan, S., and S. Jiang, "The Secure 3709 Neighbor Discovery (SEND) Hash Threat Analysis", RFC 6273, 3710 DOI 10.17487/RFC6273, June 2011, 3711 . 3713 [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer 3714 Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, 3715 January 2012, . 3717 [RFC6355] Narten, T. and J. Johnson, "Definition of the UUID-Based 3718 DHCPv6 Unique Identifier (DUID-UUID)", RFC 6355, 3719 DOI 10.17487/RFC6355, August 2011, 3720 . 3722 [RFC6438] Carpenter, B. and S. Amante, "Using the IPv6 Flow Label 3723 for Equal Cost Multipath Routing and Link Aggregation in 3724 Tunnels", RFC 6438, DOI 10.17487/RFC6438, November 2011, 3725 . 3727 [RFC6706] Templin, F., Ed., "Asymmetric Extended Route Optimization 3728 (AERO)", RFC 6706, DOI 10.17487/RFC6706, August 2012, 3729 . 3731 [RFC6935] Eubanks, M., Chimento, P., and M. Westerlund, "IPv6 and 3732 UDP Checksums for Tunneled Packets", RFC 6935, 3733 DOI 10.17487/RFC6935, April 2013, 3734 . 3736 [RFC6936] Fairhurst, G. and M. Westerlund, "Applicability Statement 3737 for the Use of IPv6 UDP Datagrams with Zero Checksums", 3738 RFC 6936, DOI 10.17487/RFC6936, April 2013, 3739 . 3741 [RFC7333] Chan, H., Ed., Liu, D., Seite, P., Yokota, H., and J. 3742 Korhonen, "Requirements for Distributed Mobility 3743 Management", RFC 7333, DOI 10.17487/RFC7333, August 2014, 3744 . 3746 [RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I., 3747 Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent 3748 Multicast - Sparse Mode (PIM-SM): Protocol Specification 3749 (Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March 3750 2016, . 3752 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 3753 Decraene, B., Litkowski, S., and R. Shakir, "Segment 3754 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 3755 July 2018, . 3757 [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol 3758 Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, 3759 . 3761 [RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J., 3762 Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header 3763 (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020, 3764 . 3766 [WG] Wireguard, "Wireguard, https://www.wireguard.com", August 3767 2020. 3769 Appendix A. Non-Normative Considerations 3771 AERO can be applied to a multitude of Internetworking scenarios, with 3772 each having its own adaptations. The following considerations are 3773 provided as non-normative guidance: 3775 A.1. Implementation Strategies for Route Optimization 3777 Route optimization as discussed in Section 3.14 results in the route 3778 optimization source (ROS) creating an asymmetric neighbor cache entry 3779 for the target neighbor. The neighbor cache entry is maintained for 3780 at most ReachableTime seconds and then deleted unless updated. In 3781 order to refresh the neighbor cache entry lifetime before the 3782 ReachableTime timer expires, the specification requires 3783 implementations to issue a new NS/NA exchange to reset ReachableTime 3784 while data packets are still flowing. However, the decision of when 3785 to initiate a new NS/NA exchange and to perpetuate the process is 3786 left as an implementation detail. 3788 One possible strategy may be to monitor the neighbor cache entry 3789 watching for data packets for (ReachableTime - 5) seconds. If any 3790 data packets have been sent to the neighbor within this timeframe, 3791 then send an NS to receive a new NA. If no data packets have been 3792 sent, wait for 5 additional seconds and send an immediate NS if any 3793 data packets are sent within this "expiration pending" 5 second 3794 window. If no additional data packets are sent within the 5 second 3795 window, delete the neighbor cache entry. 3797 The monitoring of the neighbor data packet traffic therefore becomes 3798 an asymmetric ongoing process during the neighbor cache entry 3799 lifetime. If the neighbor cache entry expires, future data packets 3800 will trigger a new NS/NA exchange while the packets themselves are 3801 delivered over a longer path until route optimization state is re- 3802 established. 3804 A.2. Implicit Mobility Management 3806 OMNI interface neighbors MAY provide a configuration option that 3807 allows them to perform implicit mobility management in which no ND 3808 messaging is used. In that case, the Client only transmits packets 3809 over a single interface at a time, and the neighbor always observes 3810 packets arriving from the Client from the same link-layer source 3811 address. 3813 If the Client's underlying interface address changes (either due to a 3814 readdressing of the original interface or switching to a new 3815 interface) the neighbor immediately updates the neighbor cache entry 3816 for the Client and begins accepting and sending packets according to 3817 the Client's new address. This implicit mobility method applies to 3818 use cases such as cellphones with both WiFi and Cellular interfaces 3819 where only one of the interfaces is active at a given time, and the 3820 Client automatically switches over to the backup interface if the 3821 primary interface fails. 3823 A.3. Direct Underlying Interfaces 3825 When a Client's OMNI interface is configured over a Direct interface, 3826 the neighbor at the other end of the Direct link can receive packets 3827 without any encapsulation. In that case, the Client sends packets 3828 over the Direct link according to QoS preferences. If the Direct 3829 interface has the highest QoS preference, then the Client's IP 3830 packets are transmitted directly to the peer without going through an 3831 ANET/INET. If other interfaces have higher QoS preferences, then the 3832 Client's IP packets are transmitted via a different interface, which 3833 may result in the inclusion of Proxys, Servers and Bridges in the 3834 communications path. Direct interfaces must be tested periodically 3835 for reachability, e.g., via NUD. 3837 A.4. AERO Critical Infrastructure Considerations 3839 AERO Bridges can be either Commercial off-the Shelf (COTS) standard 3840 IP routers or virtual machines in the cloud. Bridges must be 3841 provisioned, supported and managed by the INET administrative 3842 authority, and connected to the Bridges of other INETs via inter- 3843 domain peerings. Cost for purchasing, configuring and managing 3844 Bridges is nominal even for very large OMNI links. 3846 AERO Servers can be standard dedicated server platforms, but most 3847 often will be deployed as virtual machines in the cloud. The only 3848 requirements for Servers are that they can run the AERO user-level 3849 code and have at least one network interface connection to the INET. 3850 As with Bridges, Servers must be provisioned, supported and managed 3851 by the INET administrative authority. Cost for purchasing, 3852 configuring and managing Servers is nominal especially for virtual 3853 Servers hosted in the cloud. 3855 AERO Proxys are most often standard dedicated server platforms with 3856 one network interface connected to the ANET and a second interface 3857 connected to an INET. As with Servers, the only requirements are 3858 that they can run the AERO user-level code and have at least one 3859 interface connection to the INET. Proxys must be provisioned, 3860 supported and managed by the ANET administrative authority. Cost for 3861 purchasing, configuring and managing Proxys is nominal, and borne by 3862 the ANET administrative authority. 3864 AERO Relays can be any dedicated server or COTS router platform 3865 connected to INETs and/or EUNs. The Relay connects to the OMNI link 3866 and engages in eBGP peering with one or more Bridges as a stub AS. 3867 The Relay then injects its MNPs and/or non-MNP prefixes into the BGP 3868 routing system, and provisions the prefixes to its downstream- 3869 attached networks. The Relay can perform ROS/ROR services the same 3870 as for any Server, and can route between the MNP and non-MNP address 3871 spaces. 3873 A.5. AERO Server Failure Implications 3875 AERO Servers may appear as a single point of failure in the 3876 architecture, but such is not the case since all Servers on the link 3877 provide identical services and loss of a Server does not imply 3878 immediate and/or comprehensive communication failures. Although 3879 Clients typically associate with a single Server at a time, Server 3880 failure is quickly detected and conveyed by Bidirectional Forward 3881 Detection (BFD) and/or proactive NUD allowing Clients to migrate to 3882 new Servers. 3884 If a Server fails, ongoing packet forwarding to Clients will continue 3885 by virtue of the asymmetric neighbor cache entries that have already 3886 been established in route optimization sources (ROSs). If a Client 3887 also experiences mobility events at roughly the same time the Server 3888 fails, unsolicited NA messages may be lost but proxy neighbor cache 3889 entries in the DEPARTED state will ensure that packet forwarding to 3890 the Client's new locations will continue for up to DepartTime 3891 seconds. 3893 If a Client is left without a Server for an extended timeframe (e.g., 3894 greater than ReachableTime seconds) then existing asymmetric neighbor 3895 cache entries will eventually expire and both ongoing and new 3896 communications will fail. The original source will continue to 3897 retransmit until the Client has established a new Server 3898 relationship, after which time continuous communications will resume. 3900 Therefore, providing many Servers on the link with high availability 3901 profiles provides resilience against loss of individual Servers and 3902 assurance that Clients can establish new Server relationships quickly 3903 in event of a Server failure. 3905 A.6. AERO Client / Server Architecture 3907 The AERO architectural model is client / server in the control plane, 3908 with route optimization in the data plane. The same as for common 3909 Internet services, the AERO Client discovers the addresses of AERO 3910 Servers and selects one Server to connect to. The AERO service is 3911 analogous to common Internet services such as google.com, yahoo.com, 3912 cnn.com, etc. However, there is only one AERO service for the link 3913 and all Servers provide identical services. 3915 Common Internet services provide differing strategies for advertising 3916 server addresses to clients. The strategy is conveyed through the 3917 DNS resource records returned in response to name resolution queries. 3918 As of January 2020 Internet-based 'nslookup' services were used to 3919 determine the following: 3921 o When a client resolves the domainname "google.com", the DNS always 3922 returns one A record (i.e., an IPv4 address) and one AAAA record 3923 (i.e., an IPv6 address). The client receives the same addresses 3924 each time it resolves the domainname via the same DNS resolver, 3925 but may receive different addresses when it resolves the 3926 domainname via different DNS resolvers. But, in each case, 3927 exactly one A and one AAAA record are returned. 3929 o When a client resolves the domainname "ietf.org", the DNS always 3930 returns one A record and one AAAA record with the same addresses 3931 regardless of which DNS resolver is used. 3933 o When a client resolves the domainname "yahoo.com", the DNS always 3934 returns a list of 4 A records and 4 AAAA records. Each time the 3935 client resolves the domainname via the same DNS resolver, the same 3936 list of addresses are returned but in randomized order (i.e., 3937 consistent with a DNS round-robin strategy). But, interestingly, 3938 the same addresses are returned (albeit in randomized order) when 3939 the domainname is resolved via different DNS resolvers. 3941 o When a client resolves the domainname "amazon.com", the DNS always 3942 returns a list of 3 A records and no AAAA records. As with 3943 "yahoo.com", the same three A records are returned from any 3944 worldwide Internet connection point in randomized order. 3946 The above example strategies show differing approaches to Internet 3947 resilience and service distribution offered by major Internet 3948 services. The Google approach exposes only a single IPv4 and a 3949 single IPv6 address to clients. Clients can then select whichever IP 3950 protocol version offers the best response, but will always use the 3951 same IP address according to the current Internet connection point. 3952 This means that the IP address offered by the network must lead to a 3953 highly-available server and/or service distribution point. In other 3954 words, resilience is predicated on high availability within the 3955 network and with no client-initiated failovers expected (i.e., it is 3956 all-or-nothing from the client's perspective). However, Google does 3957 provide for worldwide distributed service distribution by virtue of 3958 the fact that each Internet connection point responds with a 3959 different IPv6 and IPv4 address. The IETF approach is like google 3960 (all-or-nothing from the client's perspective), but provides only a 3961 single IPv4 or IPv6 address on a worldwide basis. This means that 3962 the addresses must be made highly-available at the network level with 3963 no client failover possibility, and if there is any worldwide service 3964 distribution it would need to be conducted by a network element that 3965 is reached via the IP address acting as a service distribution point. 3967 In contrast to the Google and IETF philosophies, Yahoo and Amazon 3968 both provide clients with a (short) list of IP addresses with Yahoo 3969 providing both IP protocol versions and Amazon as IPv4-only. The 3970 order of the list is randomized with each name service query 3971 response, with the effect of round-robin load balancing for service 3972 distribution. With a short list of addresses, there is still 3973 expectation that the network will implement high availability for 3974 each address but in case any single address fails the client can 3975 switch over to using a different address. The balance then becomes 3976 one of function in the network vs function in the end system. 3978 The same implications observed for common highly-available services 3979 in the Internet apply also to the AERO client/server architecture. 3980 When an AERO Client connects to one or more ANETs, it discovers one 3981 or more AERO Server addresses through the mechanisms discussed in 3982 earlier sections. Each Server address presumably leads to a fault- 3983 tolerant clustering arrangement such as supported by Linux-HA, 3984 Extended Virtual Synchrony or Paxos. Such an arrangement has 3985 precedence in common Internet service deployments in lightweight 3986 virtual machines without requiring expensive hardware deployment. 3987 Similarly, common Internet service deployments set service IP 3988 addresses on service distribution points that may relay requests to 3989 many different servers. 3991 For AERO, the expectation is that a combination of the Google/IETF 3992 and Yahoo/Amazon philosophies would be employed. The AERO Client 3993 connects to different ANET access points and can receive 1-2 Server 3994 ADM-LLAs at each point. It then selects one AERO Server address, and 3995 engages in RS/RA exchanges with the same Server from all ANET 3996 connections. The Client remains with this Server unless or until the 3997 Server fails, in which case it can switch over to an alternate 3998 Server. The Client can likewise switch over to a different Server at 3999 any time if there is some reason for it to do so. So, the AERO 4000 expectation is for a balance of function in the network and end 4001 system, with fault tolerance and resilience at both levels. 4003 Appendix B. Change Log 4005 << RFC Editor - remove prior to publication >> 4006 Changes from draft-templin-intarea-6706bis-61 to draft-templin- 4007 intrea-6706bis-62: 4009 o New sub-section on OMNI Neighbor Interface Attributes 4011 Changes from draft-templin-intarea-6706bis-59 to draft-templin- 4012 intrea-6706bis-60: 4014 o Removed all references to S/TLLAO - all Interface Attributes are 4015 now maintained completely in the OMNI option. 4017 Changes from draft-templin-intarea-6706bis-58 to draft-templin- 4018 intrea-6706bis-59: 4020 o The term "Relay" used in older draft versions is now "Bridge". 4021 "Relay" now refers to what was formally called: "Gateway". 4023 o Fine-grained cleanup of Forwarding Algorithm; IPv6 ND message 4024 addressing; OMNI Prefix Lengths, etc. 4026 Changes from draft-templin-intarea-6706bis-54 to draft-templin- 4027 intrea-6706bis-55: 4029 o Updates on Segment Routing and S/TLLAO contents. 4031 o Various editorials and addressing cleanups. 4033 Changes from draft-templin-intarea-6706bis-52 to draft-templin- 4034 intrea-6706bis-53: 4036 o Normative reference to the OMNI spec, and remove portions that are 4037 already specified in OMNI. 4039 o Renamed "AERO interface/link" to "OMIN interface/link" throughout 4040 the document. 4042 o Truncated obsolete back section matter. 4044 Author's Address 4046 Fred L. Templin (editor) 4047 Boeing Research & Technology 4048 P.O. Box 3707 4049 Seattle, WA 98124 4050 USA 4052 Email: fltemplin@acm.org