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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group F. Templin, Ed. 3 Internet-Draft Boeing Research & Technology 4 Obsoletes: rfc5320, rfc5558, rfc5720, December 31, 2020 5 rfc6179, rfc6706 (if 6 approved) 7 Intended status: Standards Track 8 Expires: July 4, 2021 10 Asymmetric Extended Route Optimization (AERO) 11 draft-templin-intarea-6706bis-86 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 July 4, 2021. 47 Copyright Notice 49 Copyright (c) 2020 IETF Trust and the persons identified as the 50 document authors. All rights reserved. 52 This document is subject to BCP 78 and the IETF Trust's Legal 53 Provisions Relating to IETF Documents 54 (https://trustee.ietf.org/license-info) in effect on the date of 55 publication of this document. Please review these documents 56 carefully, as they describe your rights and restrictions with respect 57 to this document. Code Components extracted from this document must 58 include Simplified BSD License text as described in Section 4.e of 59 the Trust Legal Provisions and are provided without warranty as 60 described in the Simplified BSD License. 62 Table of Contents 64 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 65 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 66 3. Asymmetric Extended Route Optimization (AERO) . . . . . . . . 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. AERO Routing System . . . . . . . . . . . . . . . . . 16 73 3.2.4. OMNI Link Encapsulation . . . . . . . . . . . . . . . 18 74 3.2.5. Segment Routing Topologies (SRTs) . . . . . . . . . . 22 75 3.2.6. Segment Routing For OMNI Link Selection . . . . . . . 22 76 3.2.7. Segment Routing Within the OMNI Link . . . . . . . . 23 77 3.3. OMNI Interface Characteristics . . . . . . . . . . . . . 23 78 3.4. OMNI Interface Initialization . . . . . . . . . . . . . . 25 79 3.4.1. AERO Server/Relay Behavior . . . . . . . . . . . . . 26 80 3.4.2. AERO Proxy Behavior . . . . . . . . . . . . . . . . . 26 81 3.4.3. AERO Client Behavior . . . . . . . . . . . . . . . . 26 82 3.4.4. AERO Bridge Behavior . . . . . . . . . . . . . . . . 27 83 3.5. OMNI Interface Neighbor Cache Maintenance . . . . . . . . 27 84 3.5.1. OMNI Neighbor Interface Attributes . . . . . . . . . 29 85 3.5.2. OMNI Neighbor Advertisement Message Flags . . . . . . 29 86 3.6. OMNI Interface Encapsulation and Re-encapsulation . . . . 30 87 3.7. OMNI Interface Decapsulation . . . . . . . . . . . . . . 31 88 3.8. OMNI Interface Data Origin Authentication . . . . . . . . 31 89 3.9. OMNI Adaptation Layer and OMNI Interface MTU . . . . . . 32 90 3.10. OMNI Interface Forwarding Algorithm . . . . . . . . . . . 32 91 3.10.1. Client Forwarding Algorithm . . . . . . . . . . . . 33 92 3.10.2. Proxy Forwarding Algorithm . . . . . . . . . . . . . 34 93 3.10.3. Server/Relay Forwarding Algorithm . . . . . . . . . 36 94 3.10.4. Bridge Forwarding Algorithm . . . . . . . . . . . . 37 96 3.11. OMNI Interface Error Handling . . . . . . . . . . . . . . 38 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 . . . . . . . . . . . . . . . . 41 101 3.12.3. AERO Server Behavior . . . . . . . . . . . . . . . . 43 102 3.13. The AERO Proxy . . . . . . . . . . . . . . . . . . . . . 46 103 3.13.1. Combined Proxy/Servers . . . . . . . . . . . . . . . 48 104 3.13.2. Detecting and Responding to Server Failures . . . . 49 105 3.13.3. Point-to-Multipoint Server Coordination . . . . . . 49 106 3.14. AERO Route Optimization / Address Resolution . . . . . . 50 107 3.14.1. Route Optimization Initiation . . . . . . . . . . . 51 108 3.14.2. Relaying the NS . . . . . . . . . . . . . . . . . . 51 109 3.14.3. Processing the NS and Sending the NA . . . . . . . . 51 110 3.14.4. Relaying the NA . . . . . . . . . . . . . . . . . . 52 111 3.14.5. Processing the NA . . . . . . . . . . . . . . . . . 53 112 3.14.6. Route Optimization Maintenance . . . . . . . . . . . 53 113 3.15. Neighbor Unreachability Detection (NUD) . . . . . . . . . 54 114 3.16. Mobility Management and Quality of Service (QoS) . . . . 56 115 3.16.1. Mobility Update Messaging . . . . . . . . . . . . . 56 116 3.16.2. Announcing Link-Layer Address and/or QoS Preference 117 Changes . . . . . . . . . . . . . . . . . . . . . . 57 118 3.16.3. Bringing New Links Into Service . . . . . . . . . . 58 119 3.16.4. Deactivating Existing Links . . . . . . . . . . . . 58 120 3.16.5. Moving Between Servers . . . . . . . . . . . . . . . 58 121 3.17. Multicast . . . . . . . . . . . . . . . . . . . . . . . . 60 122 3.17.1. Source-Specific Multicast (SSM) . . . . . . . . . . 60 123 3.17.2. Any-Source Multicast (ASM) . . . . . . . . . . . . . 61 124 3.17.3. Bi-Directional PIM (BIDIR-PIM) . . . . . . . . . . . 62 125 3.18. Operation over Multiple OMNI Links . . . . . . . . . . . 62 126 3.19. DNS Considerations . . . . . . . . . . . . . . . . . . . 63 127 3.20. Transition Considerations . . . . . . . . . . . . . . . . 63 128 3.21. Detecting and Reacting to Server and Bridge Failures . . 64 129 3.22. AERO Clients on the Open Internet . . . . . . . . . . . . 65 130 3.23. Time-Varying MNPs . . . . . . . . . . . . . . . . . . . . 67 131 4. Implementation Status . . . . . . . . . . . . . . . . . . . . 68 132 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 68 133 6. Security Considerations . . . . . . . . . . . . . . . . . . . 68 134 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 70 135 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 72 136 8.1. Normative References . . . . . . . . . . . . . . . . . . 72 137 8.2. Informative References . . . . . . . . . . . . . . . . . 73 138 Appendix A. Non-Normative Considerations . . . . . . . . . . . . 79 139 A.1. Implementation Strategies for Route Optimization . . . . 79 140 A.2. Implicit Mobility Management . . . . . . . . . . . . . . 80 141 A.3. Direct Underlying Interfaces . . . . . . . . . . . . . . 80 142 A.4. AERO Critical Infrastructure Considerations . . . . . . . 81 143 A.5. AERO Server Failure Implications . . . . . . . . . . . . 81 144 A.6. AERO Client / Server Architecture . . . . . . . . . . . . 82 145 Appendix B. Change Log . . . . . . . . . . . . . . . . . . . . . 84 146 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 85 148 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 to 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 partitions and between disjoint INET partitions based on a mid-layer 509 IPv6 encapsulation per [RFC2473]. The inner IP layer experiences a 510 virtual bridging service since the inner IP TTL/Hop Limit is not 511 decremented during forwarding. Each Bridge also peers with Servers 512 and other Bridges in a dynamic routing protocol instance to provide a 513 Distributed Mobility Management (DMM) service for the list of active 514 MNPs (see Section 3.2.3). Bridges present the OMNI link as a set of 515 one or more Mobility Service Prefixes (MSPs) and configure secured 516 tunnels with Servers, Relays, Proxys and other Bridges; they further 517 maintain IP forwarding table entries for each MNP and any other 518 reachable non-MNP prefixes. 520 AERO Servers provide default forwarding and mobility/multilink 521 services for AERO Client Mobile Nodes (MNs). Each Server also peers 522 with Bridges in a dynamic routing protocol instance to advertise its 523 list of associated MNPs (see Section 3.2.3). Servers facilitate 524 prefix delegation/registration exchanges with Clients, where each 525 delegated prefix becomes an MNP taken from an MSP. Servers forward 526 packets between OMNI interface neighbors and track each Client's 527 mobility profiles. Servers may further act as Servers for some sets 528 of Clients and as Proxies for others. 530 AERO Proxys provide a conduit for ANET Clients to associate with 531 Servers in external INETs. Client and Servers exchange control plane 532 messages via the Proxy acting as a bridge between the ANET/INET 533 boundary. The Proxy forwards data packets between Clients and the 534 OMNI link according to forwarding information in the neighbor cache. 535 The Proxy function is specified in Section 3.13. Proxys may further 536 act as Proxys for some sets of Clients and as Servers for others. 538 AERO Relays are Servers that provide forwarding services between the 539 OMNI interface and INET/EUN interfaces. Relays are provisioned with 540 MNPs the same as for an AERO Client, and also run a dynamic routing 541 protocol to discover any non-MNP IP routes. The Relay advertises the 542 MSP(s) to its connected networks, and distributes all of its 543 associated MNPs and non-MNP IP GUA routes via BGP peerings with 544 Bridges 546 3.2. The AERO Service over OMNI Links 548 3.2.1. AERO/OMNI Reference Model 550 Figure 1 presents the basic OMNI link reference model: 552 +----------------+ 553 | AERO Bridge B1 | 554 | Nbr: S1, S2, P1| 555 |(X1->S1; X2->S2)| 556 | MSP M1 | 557 +-+---------+--+-+ 558 +--------------+ | Secured | | +--------------+ 559 |AERO Server S1| | tunnels | | |AERO Server S2| 560 | Nbr: C1, B1 +-----+ | +-----+ Nbr: C2, B1 | 561 | default->B1 | | | default->B1 | 562 | X1->C1 | | | X2->C2 | 563 +-------+------+ | +------+-------+ 564 | OMNI link | | 565 X===+===+===================+==)===============+===+===X 566 | | | | 567 +-----+--------+ +--------+--+-----+ +--------+-----+ 568 |AERO Client C1| | AERO Proxy P1 | |AERO Client C2| 569 | Nbr: S1 | |(Proxy Nbr Cache)| | Nbr: S2 | 570 | default->S1 | +--------+--------+ | default->S2 | 571 | MNP X1 | | | MNP X2 | 572 +------+-------+ .--------+------. +-----+--------+ 573 | (- Proxyed Clients -) | 574 .-. `---------------' .-. 575 ,-( _)-. ,-( _)-. 576 .-(_ IP )-. +-------+ +-------+ .-(_ IP )-. 577 (__ EUN )--|Host H1| |Host H2|--(__ EUN ) 578 `-(______)-' +-------+ +-------+ `-(______)-' 580 Figure 1: AERO/OMNI Reference Model 582 In this model: 584 o the OMNI link is an overlay network service configured over one or 585 more underlying INET partitions which may be managed by different 586 administrative authorities and have incompatible protocols and/or 587 addressing plans. 589 o AERO Bridge B1 aggregates Mobility Service Prefix (MSP) M1, 590 discovers Mobile Network Prefixes (MNPs) X* and advertises the MSP 591 via BGP peerings over secured tunnels to Servers (S1, S2). 592 Bridges connect the disjoint segments of a partitioned OMNI link. 594 o AERO Servers/Relays S1 and S2 configure secured tunnels with 595 Bridge B1 and also provide mobility, multilink and default router 596 services for their associated Clients C1 and C2. 598 o AERO Clients C1 and C2 associate with Servers S1 and S2, 599 respectively. They receive Mobile Network Prefix (MNP) 600 delegations X1 and X2, and also act as default routers for their 601 associated physical or internal virtual EUNs. Simple hosts H1 and 602 H2 attach to the EUNs served by Clients C1 and C2, respectively. 604 o AERO Proxy P1 configures a secured tunnel with Bridge B1 and 605 provides proxy services for AERO Clients in secured enclaves that 606 cannot associate directly with other OMNI link neighbors. 608 An OMNI link configured over a single INET appears as a single 609 unified link with a consistent underlying network addressing plan. 610 In that case, all nodes on the link can exchange packets via simple 611 INET encapsulation, since the underlying INET is connected. In 612 common practice, however, an OMNI link may be partitioned into 613 multiple "segments", where each segment is a distinct INET 614 potentially managed under a different administrative authority (e.g., 615 as for worldwide aviation service providers such as ARINC, SITA, 616 Inmarsat, etc.). Individual INETs may also themselves be partitioned 617 internally, in which case each internal partition is seen as a 618 separate segment. 620 The addressing plan of each segment is consistent internally but will 621 often bear no relation to the addressing plans of other segments. 622 Each segment is also likely to be separated from others by network 623 security devices (e.g., firewalls, proxies, packet filtering 624 gateways, etc.), and in many cases disjoint segments may not even 625 have any common physical link connections. Therefore, nodes can only 626 be assured of exchanging packets directly with correspondents in the 627 same segment, and not with those in other segments. The only means 628 for joining the segments therefore is through inter-domain peerings 629 between AERO Bridges. 631 The same as for traditional campus LANs, multiple OMNI link segments 632 can be joined into a single unified link via a virtual bridging 633 service using the OMNI Adaptation Layer (OAL) which inserts a mid- 634 layer IPv6 encapsulation per [RFC2473] that supports inter-segment 635 forwarding (i.e., bridging) without decrementing the network-layer 636 TTL/Hop Limit. This bridging of OMNI link segments is shown in 637 Figure 2: 639 . . . . . . . . . . . . . . . . . . . . . . . 640 . . 641 . .-(::::::::) . 642 . .-(::::::::::::)-. +-+ . 643 . (:::: Segment A :::)--|B|---+ . 644 . `-(::::::::::::)-' +-+ | . 645 . `-(::::::)-' | . 646 . | . 647 . .-(::::::::) | . 648 . .-(::::::::::::)-. +-+ | . 649 . (:::: Segment B :::)--|B|---+ . 650 . `-(::::::::::::)-' +-+ | . 651 . `-(::::::)-' | . 652 . | . 653 . .-(::::::::) | . 654 . .-(::::::::::::)-. +-+ | . 655 . (:::: Segment C :::)--|B|---+ . 656 . `-(::::::::::::)-' +-+ | . 657 . `-(::::::)-' | . 658 . | . 659 . ..(etc).. x . 660 . . 661 . . 662 . <- OMNI link Bridged by encapsulation -> . 663 . . . . . . . . . . . . . .. . . . . . . . . 665 Figure 2: Bridging OMNI Link Segments 667 Bridges, Servers, Relays and Proxys connect via secured INET tunnels 668 over their respective segments in a spanning tree topology rooted at 669 the Bridges. The secured spanning tree supports strong 670 authentication for IPv6 ND control messages and may also be used to 671 convey the initial data packets in a flow. Route optimization can 672 then be employed to cause data packets to take more direct paths 673 between OMNI link neighbors without having to strictly follow the 674 spanning tree. 676 3.2.2. Link-Local Addresses (LLAs), Unique Local Addresses (ULAs) and 677 Global Unicast Addresses (GUA) 679 AERO nodes on OMNI links use the Link-Local Address (LLA) prefix 680 fe80::/64 [RFC4291] to assign LLAs used for network-layer addresses 681 in link-scoped IPv6 ND and data messages. AERO Clients use LLAs 682 constructed from MNPs (i.e., "MNP-LLAs") while other AERO nodes use 683 LLAs constructed from administrative identification values ("ADM- 684 LLAs") as specified in [I-D.templin-6man-omni-interface]. 686 AERO nodes also use the Unique Local Address (ULA) prefix fd00::/8 687 followed by a pseudo-random 40-bit global ID to form the prefix 688 [ULA]::/48, then include a 16-bit OMNI link identifier '*' to form 689 the prefix [ULA*]::/64 [RFC4291]. The AERO node then uses the prefix 690 [ULA*]::/64 to form "MNP-ULAs" or "ADM-ULA"s as specified in 691 [I-D.templin-6man-omni-interface] to support OAL addressing. 693 AERO Clients also use Temporary LLAs/ULAs constructed per 694 [I-D.templin-6man-omni-interface], where the addresses are typically 695 used only in initial control message exchanges until a stable MNP- 696 LLA/ULA is assigned. 698 Finally, the MSPs and MNPs used by AERO nodes are typically based on 699 Global Unicast Addresses (GUAs), but in some cases may be based on 700 private-use addresses. See for a full specification of LLAs, ULAs 701 and GUAs used by AERO nodes on OMNI links. 703 3.2.3. AERO Routing System 705 The AERO routing system comprises a private instance of the Border 706 Gateway Protocol (BGP) [RFC4271] that is coordinated between Bridges 707 and Servers and does not interact with either the public Internet BGP 708 routing system or any underlying INET routing systems. 710 In a reference deployment, each Server is configured as an Autonomous 711 System Border Router (ASBR) for a stub Autonomous System (AS) using a 712 32-bit AS Number (ASN) [RFC4271] that is unique within the BGP 713 instance, and each Server further uses eBGP to peer with one or more 714 Bridges but does not peer with other Servers. Each INET of a multi- 715 segment OMNI link must include one or more Bridges, which peer with 716 the Servers and Proxys within that INET. All Bridges within the same 717 INET are members of the same hub AS, and use iBGP to maintain a 718 consistent view of all active MNPs currently in service. The Bridges 719 of different INETs peer with one another using eBGP. 721 Bridges advertise the OMNI link's MSPs and any non-MNP routes to each 722 of their Servers. This means that any aggregated non-MNPs (including 723 "default") are advertised to all Servers. Each Bridge configures a 724 black-hole route for each of its MSPs. By black-holing the MSPs, the 725 Bridge will maintain forwarding table entries only for the MNPs that 726 are currently active, and packets destined to all other MNPs will 727 correctly incur Destination Unreachable messages due to the black- 728 hole route. In this way, Servers have only partial topology 729 knowledge (i.e., they know only about the MNPs of their directly 730 associated Clients) and they forward all other packets to Bridges 731 which have full topology knowledge. 733 Each OMNI link segment assigns a unique ADM-ULA sub-prefix of 734 [ULA*]::/96. For example, a first segment could assign 735 [ULA*]::1000/116, a second could assign [ULA*]::2000/116, a third 736 could assign [ULA*]::3000/116, etc. Within each segment, each Proxy/ 737 Server configures an ADM-ULA within the segment's prefix, e.g., the 738 Proxy/Servers within [ULA*]::2000/116 could assign the ADM-ULAs 739 [ULA*]::2011/116, [ULA*]::2026/116, [ULA*]::2003/116, etc. 741 The administrative authorities for each segment must therefore 742 coordinate to assure mutually-exclusive ADM-ULA prefix assignments, 743 but internal provisioning of ADM-ULAs an independent local 744 consideration for each administrative authority. For each ADM-ULA 745 prefix, the Bridge(s) that connect that segment assign the all-zero's 746 address of the prefix as a Subnet Router Anycast address. For 747 example, the Subnet Router Anycast address for [ULA*]::1023/116 is 748 simply [ULA*]::1000. 750 ADM-ULA prefixes are statically represented in Bridge forwarding 751 tables. Bridges join multiple segments into a unified OMNI link over 752 multiple diverse administrative domains. They support a bridging 753 function by first establishing forwarding table entries for their 754 ADM-ULA prefixes either via standard BGP routing or static routes. 755 For example, if three Bridges ('A', 'B' and 'C') from different 756 segments serviced [ULA*]::1000/116, [ULA*]::2000/116 and 757 [ULA*]::3000/116 respectively, then the forwarding tables in each 758 Bridge are as follows: 760 A: [ULA*]::1000/116->local, [ULA*]::2000/116->B, [ULA*]::3000/116->C 762 B: [ULA*]::1000/116->A, [ULA*]::2000/116->local, [ULA*]::3000/116->C 764 C: [ULA*]::1000/116->A, [ULA*]::2000/116->B, [ULA*]::3000/116->local 766 These forwarding table entries are permanent and never change, since 767 they correspond to fixed infrastructure elements in their respective 768 segments. 770 MNP ULAs are instead dynamically advertised in the AERO routing 771 system by Servers and Relays that provide service for their 772 corresponding MNPs. For example, if three Servers ('D', 'E' and 'F') 773 service the MNPs 2001:db8:1000:2000::/56, 2001:db8:3000:4000::/56 and 774 2001:db8:5000:6000::/56 then the routing system would include: 776 D: [ULA*]:2001:db8:1000:2000/120 778 E: [ULA*]:2001:db8:3000:4000/120 780 F: [ULA*]:2001:db8:5000:6000/120 781 A full discussion of the BGP-based routing system used by AERO is 782 found in [I-D.ietf-rtgwg-atn-bgp]. 784 3.2.4. OMNI Link Encapsulation 786 With the Client and partition prefixes in place in Bridge forwarding 787 tables, the OMNI interface sends control and data packets toward AERO 788 destination nodes located in different OMNI link segments over the 789 spanning tree via mid-layer encapsulation using the OMNI Adaptation 790 Layer (OAL) header based on Generic Packet Tunneling in IPv6 791 [RFC2473]. When necessary, the OMNI interface also includes an OMNI 792 Routing Header (ORH) as an extension to the OAL header if final 793 segment forwarding information is available, e.g., in the neighbor 794 cache. The ORH is formatted as shown in Figure 3: 796 0 1 2 3 797 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 1 798 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 799 | Next Header | Hdr Ext Len | Routing Type | SRT | FMT | 800 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 801 | Last Hop Segment-id (LHS) | 802 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 803 ~ Link Layer Address (L2ADDR) ~ 804 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 805 ~ Destination Suffix (if necessary) ~ 806 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 807 ~ Null Padding (if necessary) ~ 808 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 810 Figure 3: OMNI Routing Header (ORH) Format 812 In this format: 814 o Next Header identifies the type of header immediately following 815 the ORH. 817 o Hdr Ext Len is the length of the Routing header in 8-octet units 818 (not including the first 8 octets), with trailing padding added if 819 necessary to produce an integral number of 8-octet units. 821 o Routing Type is set to TBD (see IANA Considerations). 823 o Segments Left is omitted, and replaced by a 5-bit SRT and 3-bit 824 FMT field. 826 o SRT - a 5-bit Segment Routing Topology prefix length value that 827 (when added to 96) determines the prefix length to apply to the 828 ADM-ULA formed from concatenating [ULA*]::/96 with the 32 bit LHS 829 value that follows. For example, the value 16 corresponds to the 830 prefix length 112. 832 o FMT - a 3-bit "Framework/Mode/Type" code corresponding to the 833 included Link Layer Address as follows: 835 * When the most significant bit (i.e., "Framework") is set to 1, 836 L2ADDR is the INET encapsulation address for the target Client 837 itself; otherwise is the address of the Server/Proxy named in 838 the LHS. 840 * When the next most significant bit (i.e., "Mode") is set to 1, 841 the target Client is (likely) located behind an INET Network 842 Address Translator (NAT); otherwise, it is reachable only via 843 the Server/Proxy or directly addressable via INET addressing. 845 * When the least significant bit (i.e., "Type") is set to 0, 846 L2ADDR includes a UDP Port Number followed by an IPv4 address; 847 otherwise, it includes a UDP Port Number followed by an IPv6 848 address. 850 o LHS - the 32 bit ID of a node in the Last Hop Segment that 851 services the target. When SRT and LHS are both set to 0, the LHS 852 is considered unspecified. When SRT is set to 0 and LHS is non- 853 zero, the prefix length is set to 128. SRT and LHS provide 854 guidance to the OMNI interface forwarding algorithm. 855 Specifically, if SRT/LHS is located in the local OMNI link segment 856 then the OMNI interface can omit OAL/ORH encapsulation and 857 (following any necessary NAT traversal messaging) send directly to 858 the target using INET encapsulation according to FMT/L2ADDR. 859 Otherwise, it must perform INET/OAL/ORH encapsulation and forward 860 according to the OMNI link spanning tree. 862 o Link Layer Address (L2ADDR) - Formatted according to FMT, and 863 identifies the link-layer address (i.e., the encapsulation 864 address) of the target. The UDP Port Number appears in the first 865 two octets and the IP address appears in the next 4 octets for 866 IPv4 or 16 octets for IPv6. The Port Number and IP address are 867 recorded in ones-compliment "obfuscated" form per [RFC4380]. The 868 OMNI interface forwarding algorithm uses FMT/L2ADDR to determine 869 the INET encapsulation address for local forwarding when SRT/LHS 870 is located in the same OMNI link segment. Note that if the target 871 is behind a NAT, L2ADDR will contain the mapped INET address 872 stored in the NAT; otherwise, L2ADDR will contain the native INET 873 information of the target itself. 875 o Destination Suffix is a 64-bit field included only for OAL- 876 encapsulated packets that require OAL fragmentation. Present only 877 when Hdr Ext Len indicates that at least 8 bytes follow L2ADDR. 878 When present, encodes the 64-bit MNP-ULA suffix for the target 879 Client. For example, if the MNP-ULA is [ULA*]:2001:db8:1:2 then 880 the Destination suffix encodes the value 2001:db8:1:2. 882 o Null Padding contains zero-valued octets as necessary to pad the 883 ORH to an integral number of 8-octet units. 885 AERO nodes use OAL encapsulation when the target destination is 886 located in a different OMNI link segment, or when fragmentation is 887 necessary (otherwise, OAL encapsulation is omitted and simple INET 888 encapsulation is used). When an AERO node uses OAL encapsulation for 889 a packet with source address 2001:db8:1:2::1 and destination address 890 2001:db8:1234:5678::1, it sets the OAL header source address to its 891 own ULA (e.g., [ULA*]::1000:2000) and sets the destination address to 892 the MNP-ULA corresponding to the IP destination address (e.g., 893 [ULA*]::2001:db8:1234:5678). 895 If the neighbor cache information indicates that the target is in a 896 different segment, the node next inserts an ORH immediately following 897 the OAL header while including the correct SRT, FMT, LHS, L2ADDR and 898 Destination Suffix if fragmentation is needed (in this case, the 899 Destination Suffix is 2001:db8:1234:5678). Next, the node overwrites 900 the OAL header destination address with the LHS Subnet Router Anycast 901 address (for example, for LHS 3000:4567 with SRT 16, the Subnet 902 Router Anycast address is [ULA*]::3000:0000). (Note: if ADM-ULA of 903 the last-hop Proxy/Server is known but the SRT, FMT, LHS and L2ADDR 904 are not (yet) known, the node instead overwrites the OAL header 905 destination address with the ADM-ULA.) 907 The node then fragments the OAL/ORH packet if necessary, with each 908 resulting fragment including the OAL/ORH headers while only the first 909 fragment includes the original IPv6 header. The node finally 910 encapsulates each resulting OAL/ORH packet/fragment in an INET header 911 with source address set to its own INET address (e.g., 192.0.2.100) 912 and destination set to the INET address of a Bridge (e.g., 913 192.0.2.1). 915 The encapsulation format in the above example is shown in Figure 4: 917 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 918 | INET Header | 919 | src = 192.0.2.100 | 920 | dst = 192.0.2.1 | 921 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 922 | OAL Header (if necessary) | 923 | src = [ULA*]::1000:2000 | 924 | dst= [ULA*]::3000:0000 | 925 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 926 | ORH Header (if necessary) | 927 | Destination Suffix: | 928 | 2001:db8:1234:5678 | 929 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 930 | Inner IP Header | 931 | src = 2001:db8:1:2::1 | 932 | dst = 2001:db8:1234:5678::1 | 933 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 934 | | 935 ~ ~ 936 ~ Inner Packet Body ~ 937 ~ ~ 938 | | 939 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 941 Figure 4: OAL/ORH Encapsulation 943 In this format, the inner IP header and packet body are the original 944 IP packet, the OAL header is an IPv6 header prepared according to 945 [RFC2473], the ORH is a Routing Header extension of the OAL header, 946 and the INET header is prepared as discussed in Section 3.6. 948 This gives rise to a routing system that contains both Client prefix 949 routes that may change dynamically due to regional node mobility and 950 partition prefix routes that rarely if ever change. The Bridges can 951 therefore provide link-layer bridging by sending packets over the 952 spanning tree instead of network-layer routing according to MNP 953 routes. As a result, opportunities for packet loss due to node 954 mobility between different segments are mitigated. 956 In normal operations, IPv6 ND messages are conveyed over secured 957 paths between OMNI link neighbors so that specific Proxys, Servers or 958 Relays can be addressed without being subject to mobility events. 959 Conversely, only the first few packets destined to Clients need to 960 traverse secured paths until route optimization can determine a more 961 direct path. 963 Note: Use of an IPv6 "minimal encapsulation" format (i.e., an IPv6 964 variant of [RFC2004]) based on extensions to the ORH was considered 965 and abandoned. In the approach, the ORH would be inserted as an 966 extension header to the original IPv6 packet header. The IPv6 967 destination address would then be written into the ORH, and the ULA 968 corresponding to the destination would be overwritten in the IPv6 969 destination address. This would seemingly convey enough forwarding 970 information so that OAL encapsulation could be avoided. However, 971 this "minimal encapsulation" IPv6 packet would then have a non-ULA 972 source address and ULA destination address, an incorrect value in 973 upper layer protocol checksums, and a Hop Limit that is decremented 974 within the spanning tree when it should not be. The insertion and 975 removal of the ORH would also entail rewriting the Payload Length and 976 Next Header fields - again, invalidating upper layer checksums. 977 These irregularities would result in implementation challenges and 978 the potential for operational issues, e.g., since actionable ICMPv6 979 error reports could not be delivered to the original source. In 980 order to address the issues, still more information such as the 981 original IPv6 source address could be written into the ORH. However, 982 with the additional information the benefit of the "minimal 983 encapsulation" savings quickly diminishes, and becomes overshadowed 984 by the implementation and operational irregularities. 986 3.2.5. Segment Routing Topologies (SRTs) 988 The 64-bit sub-prefixes of [ULA]::/48 identify up to 2^16 distinct 989 Segment Routing Topologies (SRTs). Each SRT is a mutually-exclusive 990 OMNI link overlay instance using a distinct set of ULAs, and emulates 991 a Virtual LAN (VLAN) service for the OMNI link. In some cases (e.g., 992 when redundant topologies are needed for fault tolerance and 993 reliability) it may be beneficial to deploy multiple SRTs that act as 994 independent overlay instances. A communication failure in one 995 instance therefore will not affect communications in other instances. 997 Each SRT is identified by a distinct value in bits 48-63 of 998 [ULA]::/48, i.e., as [ULA0]::/64, [ULA1]::/64, [ULA2]::/64, etc. 999 Each OMNI interface is identified by a unique interface name (e.g., 1000 omni0, omni1, omni2, etc.) and assigns an anycast ADM-ULA 1001 corresponding to its SRT prefix length. The anycast ADM-ULA is used 1002 for OMNI interface determination in Safety-Based Multilink (SBM) as 1003 discussed in [I-D.templin-6man-omni-interface]. Each OMNI interface 1004 further applies Performance-Based Multilink (PBM) internally. 1006 3.2.6. Segment Routing For OMNI Link Selection 1008 An original IPv6 source can direct an IPv6 packet to an AERO node by 1009 including a standard IPv6 Segment Routing Header (SRH) [RFC8754] with 1010 the anycast ADM-ULA for the selected SRT as either the IPv6 1011 destination or as an intermediate hop within the SRH. This allows 1012 the original source to determine the specific OMNI link topology a 1013 packet will traverse when there may be multiple alternatives. 1015 When the AERO node processes the SRH and forwards the packet to the 1016 correct OMNI interface, the OMNI interface writes the next IPv6 1017 address from the SRH into the IPv6 destination address and decrements 1018 Segments Left. If decrementing would cause Segments Left to become 1019 0, the OMNI interface deletes the SRH before forwarding. This form 1020 of Segment Routing supports Safety-Based Multilink (SBM). 1022 3.2.7. Segment Routing Within the OMNI Link 1024 AERO node OMNI interfaces can insert OAL/ORH headers for Segment 1025 Routing within the OMNI link to influence the paths of packets 1026 destined to targets in remote segments without requiring all packets 1027 to traverse strict spanning tree paths. 1029 When an AERO node's OMNI interface has a packet to send to a target 1030 discovered through route optimization located in the same OMNI link 1031 segment, it encapsulates the packet in OAL/ORH headers if necessary 1032 as discussed above. The node then uses the target's Link Layer 1033 Address (L2ADDR) information for INET encapsulation. 1035 When an AERO node's OMNI interface has a packet to send to a route 1036 optimization target located in a remote OMNI link segment, it 1037 encapsulates the packet in OAL/ORH headers as discussed above while 1038 forwarding the packet to a Bridge with destination set to the Subnet 1039 Router Anycast address for the final OMNI link segment. 1041 When a Bridge receives a packet destined to its Subnet Router Anycast 1042 address with an OAL/ORH with SRT/LHS values corresponding to the 1043 local segment, it examines the L2ADDR according to FMT and removes 1044 the ORH from the packet; if the packet is not a fragment, the Bridge 1045 also removes the OAL header. If the packet was a fragment, the 1046 Bridge instead writes the MNP-ULA corresponding to the ORH 1047 Destination Suffix into the OAL destination address. The Bridge then 1048 encapsulates the packet/fragment in an INET header according to 1049 L2ADDR and forwards the packet within the INET either to the LHS 1050 Server/Proxy or directly to the target Client itself. In this way, 1051 the Bridge participates in route optimization to reduce traffic load 1052 and suboptimal routing through strict spanning tree paths. 1054 3.3. OMNI Interface Characteristics 1056 OMNI interfaces are virtual interfaces configured over one or more 1057 underlying interfaces classified as follows: 1059 o INET interfaces connect to an INET either natively or through one 1060 or several IPv4 NATs. Native INET interfaces have global IP 1061 addresses that are reachable from any INET correspondent. All 1062 Server, Relay and Bridge interfaces are native interfaces, as are 1063 INET-facing interfaces of Proxys. NATed INET interfaces connect 1064 to a private network behind one or more NATs that provide INET 1065 access. Clients that are behind a NAT are required to send 1066 periodic keepalive messages to keep NAT state alive when there are 1067 no data packets flowing. 1069 o ANET interfaces connect to an ANET that is separated from the open 1070 INET by a Proxy. Proxys can actively issue control messages over 1071 the INET on behalf of the Client to reduce ANET congestion. 1073 o VPNed interfaces use security encapsulation over the INET to a 1074 Virtual Private Network (VPN) server that also acts as a Server or 1075 Proxy. Other than the link-layer encapsulation format, VPNed 1076 interfaces behave the same as Direct interfaces. 1078 o Direct interfaces connect a Client directly to a Server or Proxy 1079 without crossing any ANET/INET paths. An example is a line-of- 1080 sight link between a remote pilot and an unmanned aircraft. The 1081 same Client considerations apply as for VPNed interfaces. 1083 OMNI interfaces use OAL/ORH encapsulation as necessary as discussed 1084 in Section 3.2.4. OMNI interfaces use link-layer encapsulation (see: 1085 Section 3.6) to exchange packets with OMNI link neighbors over INET 1086 or VPNed interfaces as well as over ANET interfaces for which the 1087 Client and Proxy may be multiple IP hops away. OMNI interfaces do 1088 not use link-layer encapsulation over Direct underlying interfaces or 1089 ANET interfaces when the Client and Proxy are known to be on the same 1090 underlying link. 1092 OMNI interfaces maintain a neighbor cache for tracking per-neighbor 1093 state the same as for any interface. OMNI interfaces use ND messages 1094 including Router Solicitation (RS), Router Advertisement (RA), 1095 Neighbor Solicitation (NS) and Neighbor Advertisement (NA) for 1096 neighbor cache management. 1098 OMNI interfaces send ND messages with an OMNI option formatted as 1099 specified in [I-D.templin-6man-omni-interface]. The OMNI option 1100 includes prefix registration information and Interface Attributes 1101 containing link information parameters for the OMNI interface's 1102 underlying interfaces. Each OMNI option may include multiple 1103 Interface Attributes sub-options, each identified by an ifIndex 1104 value. 1106 A Client's OMNI interface may be configured over multiple underlying 1107 interface connections. For example, common mobile handheld devices 1108 have both wireless local area network ("WLAN") and cellular wireless 1109 links. These links are often used "one at a time" with low-cost WLAN 1110 preferred and highly-available cellular wireless as a standby, but a 1111 simultaneous-use capability could provide benefits. In a more 1112 complex example, aircraft frequently have many wireless data link 1113 types (e.g. satellite-based, cellular, terrestrial, air-to-air 1114 directional, etc.) with diverse performance and cost properties. 1116 If a Client's multiple underlying interfaces are used "one at a time" 1117 (i.e., all other interfaces are in standby mode while one interface 1118 is active), then ND message OMNI options include only a single 1119 Interface Attributes sub-option set to constant values. In that 1120 case, the Client would appear to have a single interface but with a 1121 dynamically changing link-layer address. 1123 If the Client has multiple active underlying interfaces, then from 1124 the perspective of ND it would appear to have multiple link-layer 1125 addresses. In that case, ND message OMNI options MAY include 1126 multiple Interface Attributes sub-options - each with values that 1127 correspond to a specific interface. Every ND message need not 1128 include Interface Attributes for all underlying interfaces; for any 1129 attributes not included, the neighbor considers the status as 1130 unchanged. 1132 Bridge, Server and Proxy OMNI interfaces may be configured over one 1133 or more secured tunnel interfaces. The OMNI interface configures 1134 both an ADM-LLA and its corresponding ADM-ULA, while the underlying 1135 secured tunnel interfaces are either unnumbered or configure the same 1136 ULA. The OMNI interface encapsulates each IP packet in OAL/ORH 1137 headers and presents the packet to the underlying secured tunnel 1138 interface. Routing protocols such as BGP that run over the OMNI 1139 interface do not employ OAL/ORH encapsulation, but rather present the 1140 routing protocol messages directly to the underlying secured tunnels 1141 while using the ULA as the source address. This distinction must be 1142 honored consistently according to each node's configuration so that 1143 the IP forwarding table will associate discovered IP routes with the 1144 correct interface. 1146 3.4. OMNI Interface Initialization 1148 AERO Servers, Proxys and Clients configure OMNI interfaces as their 1149 point of attachment to the OMNI link. AERO nodes assign the MSPs for 1150 the link to their OMNI interfaces (i.e., as a "route-to-interface") 1151 to ensure that packets with destination addresses covered by an MNP 1152 not explicitly assigned to a non-OMNI interface are directed to the 1153 OMNI interface. 1155 OMNI interface initialization procedures for Servers, Proxys, Clients 1156 and Bridges are discussed in the following sections. 1158 3.4.1. AERO Server/Relay Behavior 1160 When a Server enables an OMNI interface, it assigns an ADM-{LLA,ULA} 1161 appropriate for the given OMNI link segment. The Server also 1162 configures secured tunnels with one or more neighboring Bridges and 1163 engages in a BGP routing protocol session with each Bridge. 1165 The OMNI interface provides a single interface abstraction to the IP 1166 layer, but internally comprises multiple secured tunnels as well as 1167 an NBMA nexus for sending encapsulated data packets to OMNI interface 1168 neighbors. The Server further configures a service to facilitate ND 1169 exchanges with AERO Clients and manages per-Client neighbor cache 1170 entries and IP forwarding table entries based on control message 1171 exchanges. 1173 Relays are simply Servers that run a dynamic routing protocol to 1174 redistribute routes between the OMNI interface and INET/EUN 1175 interfaces (see: Section 3.2.3). The Relay provisions MNPs to 1176 networks on the INET/EUN interfaces (i.e., the same as a Client would 1177 do) and advertises the MSP(s) for the OMNI link over the INET/EUN 1178 interfaces. The Relay further provides an attachment point of the 1179 OMNI link to a non-MNP-based global topology. 1181 3.4.2. AERO Proxy Behavior 1183 When a Proxy enables an OMNI interface, it assigns an ADM-{LLA, ULA} 1184 and configures permanent neighbor cache entries the same as for 1185 Servers. The Proxy also configures secured tunnels with one or more 1186 neighboring Bridges and maintains per-Client neighbor cache entries 1187 based on control message exchanges. Importantly Proxys are often 1188 configured to act as Servers, and vice-versa. 1190 3.4.3. AERO Client Behavior 1192 When a Client enables an OMNI interface, it assigns either an 1193 MNP-{LLA, ULA} or a Temporary {LLA, ULA} and sends RS messages with 1194 ND parameters over its underlying interfaces to a Server, which 1195 returns an RA message with corresponding parameters. The RS/RA 1196 messages may pass through a Proxy in the case of a Client's ANET 1197 interface, or through one or more NATs in the case of a Client's INET 1198 interface. (Note: if the Client used a Temporary {LLA, ULA} in its 1199 initial RS message, it will discover an MNP-{LLA, ULA} in the 1200 corresponding RA that it receives from the Server and begin using 1201 these new addresses while deprecating the Temporary addresses.) 1203 3.4.4. AERO Bridge Behavior 1205 AERO Bridges configure an OMNI interface and assign the ADM-ULA 1206 Subnet Router Anycast address for each OMNI link segment they connect 1207 to. Bridges configure secured tunnels with Servers, Proxys and other 1208 Bridges, and engage in a BGP routing protocol session with neighbors 1209 on the spanning tree (see: Section 3.2.3). 1211 3.5. OMNI Interface Neighbor Cache Maintenance 1213 Each OMNI interface maintains a conceptual neighbor cache that 1214 includes an entry for each neighbor it communicates with on the OMNI 1215 link per [RFC4861]. OMNI interface neighbor cache entries are said 1216 to be one of "permanent", "symmetric", "asymmetric" or "proxy". 1218 Permanent neighbor cache entries are created through explicit 1219 administrative action; they have no timeout values and remain in 1220 place until explicitly deleted. AERO Bridges maintain permanent 1221 neighbor cache entries for their associated Proxys/Servers (and vice- 1222 versa). Each entry maintains the mapping between the neighbor's 1223 network-layer LLA and corresponding INET address. 1225 Symmetric neighbor cache entries are created and maintained through 1226 RS/RA exchanges as specified in Section 3.12, and remain in place for 1227 durations bounded by prefix lifetimes. AERO Servers maintain 1228 symmetric neighbor cache entries for each of their associated 1229 Clients, and AERO Clients maintain symmetric neighbor cache entries 1230 for each of their associated Servers. 1232 Asymmetric neighbor cache entries are created or updated based on 1233 route optimization messaging as specified in Section 3.14, and are 1234 garbage-collected when keepalive timers expire. AERO ROSs maintain 1235 asymmetric neighbor cache entries for active targets with lifetimes 1236 based on ND messaging constants. Asymmetric neighbor cache entries 1237 are unidirectional since only the ROS (and not the ROR) creates an 1238 entry. 1240 Proxy neighbor cache entries are created and maintained by AERO 1241 Proxys when they process Client/Server ND exchanges, and remain in 1242 place for durations bounded by ND and prefix lifetimes. AERO Proxys 1243 maintain proxy neighbor cache entries for each of their associated 1244 Clients. Proxy neighbor cache entries track the Client state and the 1245 address of the Client's associated Server(s). 1247 To the list of neighbor cache entry states in Section 7.3.2 of 1248 [RFC4861], Proxy and Server OMNI interfaces add an additional state 1249 DEPARTED that applies to symmetric and proxy neighbor cache entries 1250 for Clients that have recently departed. The interface sets a 1251 "DepartTime" variable for the neighbor cache entry to "DEPART_TIME" 1252 seconds. DepartTime is decremented unless a new ND message causes 1253 the state to return to REACHABLE. While a neighbor cache entry is in 1254 the DEPARTED state, packets destined to the target Client are 1255 forwarded to the Client's new location instead of being dropped. 1256 When DepartTime decrements to 0, the neighbor cache entry is deleted. 1257 It is RECOMMENDED that DEPART_TIME be set to the default constant 1258 value REACHABLE_TIME plus 10 seconds (40 seconds by default) to allow 1259 a window for packets in flight to be delivered while stale route 1260 optimization state may be present. 1262 When an ROR receives an authentic NS message used for route 1263 optimization, it searches for a symmetric neighbor cache entry for 1264 the target Client. The ROR then returns a solicited NA message 1265 without creating a neighbor cache entry for the ROS, but creates or 1266 updates a target Client "Report List" entry for the ROS and sets a 1267 "ReportTime" variable for the entry to REPORT_TIME seconds. The ROR 1268 resets ReportTime when it receives a new authentic NS message, and 1269 otherwise decrements ReportTime while no authentic NS messages have 1270 been received. It is RECOMMENDED that REPORT_TIME be set to the 1271 default constant value REACHABLE_TIME plus 10 seconds (40 seconds by 1272 default) to allow a window for route optimization to converge before 1273 ReportTime decrements below REACHABLE_TIME. 1275 When the ROS receives a solicited NA message response to its NS 1276 message used for route optimization, it creates or updates an 1277 asymmetric neighbor cache entry for the target network-layer and 1278 link-layer addresses. The ROS then (re)sets ReachableTime for the 1279 neighbor cache entry to REACHABLE_TIME seconds and uses this value to 1280 determine whether packets can be forwarded directly to the target, 1281 i.e., instead of via a default route. The ROS otherwise decrements 1282 ReachableTime while no further solicited NA messages arrive. It is 1283 RECOMMENDED that REACHABLE_TIME be set to the default constant value 1284 30 seconds as specified in [RFC4861]. 1286 AERO nodes also use the value MAX_UNICAST_SOLICIT to limit the number 1287 of NS keepalives sent when a correspondent may have gone unreachable, 1288 the value MAX_RTR_SOLICITATIONS to limit the number of RS messages 1289 sent without receiving an RA and the value MAX_NEIGHBOR_ADVERTISEMENT 1290 to limit the number of unsolicited NAs that can be sent based on a 1291 single event. It is RECOMMENDED that MAX_UNICAST_SOLICIT, 1292 MAX_RTR_SOLICITATIONS and MAX_NEIGHBOR_ADVERTISEMENT be set to 3 the 1293 same as specified in [RFC4861]. 1295 Different values for DEPART_TIME, REPORT_TIME, REACHABLE_TIME, 1296 MAX_UNICAST_SOLICIT, MAX_RTR_SOLCITATIONS and 1297 MAX_NEIGHBOR_ADVERTISEMENT MAY be administratively set; however, if 1298 different values are chosen, all nodes on the link MUST consistently 1299 configure the same values. Most importantly, DEPART_TIME and 1300 REPORT_TIME SHOULD be set to a value that is sufficiently longer than 1301 REACHABLE_TIME to avoid packet loss due to stale route optimization 1302 state. 1304 3.5.1. OMNI Neighbor Interface Attributes 1306 OMNI interface IPv6 ND messages include OMNI options 1307 [I-D.templin-6man-omni-interface] with Interface Attributes that 1308 provide Link-Layer Address and QoS Preference information for the 1309 neighbor's underlying interfaces. This information is stored in the 1310 neighbor cache and provides the basis for the forwarding algorithm 1311 specified in Section 3.10. The information is cumulative and 1312 reflects the union of the OMNI information from the most recent ND 1313 messages received from the neighbor; it is therefore not required 1314 that each ND message contain all neighbor information. 1316 The OMNI option Interface Attributes for each underlying interface 1317 includes a two-part "Link-Layer Address" consisting of a simple IP 1318 encapsulation address determined by the FMT and L2ADDR fields and an 1319 ADM-ULA determined by the SRT and LHS fields. If the neighbor is 1320 located in the local OMNI link segment (and, if any necessary NAT 1321 state has been established) forwarding via simple IP encapsulation 1322 can be used; otherwise, OAL encapsulation must be used. Underlying 1323 interfaces are further selected based on their associated preference 1324 values "high", "medium", "low" or "disabled". 1326 Note: the OMNI option is distinct from any Source/Target Link-Layer 1327 Address Options (S/TLLAOs) that may appear in an ND message according 1328 to the appropriate IPv6 over specific link layer specification (e.g., 1329 [RFC2464]). If both an OMNI option and S/TLLAO appear, the former 1330 pertains to encapsulation addresses while the latter pertains to the 1331 native L2 address format of the underlying media. 1333 3.5.2. OMNI Neighbor Advertisement Message Flags 1335 As discussed in Section 4.4 of [RFC4861] NA messages include three 1336 flag bits R, S and O. OMNI interface NA messages treat the flags as 1337 follows: 1339 o R: The R ("Router") flag is set to 1 in the NA messages sent by 1340 all AERO/OMNI node types. Simple hosts that would set R to 0 do 1341 not occur on the OMNI link itself, but may occur on the downstream 1342 links of Clients and Relays. 1344 o S: The S ("Solicited") flag is set exactly as specified in 1345 Section 4.4. of [RFC4861], i.e., it is set to 1 for Solicited NAs 1346 and set to 0 for Unsolicited NAs (both unicast and multicast). 1348 o O: The O ("Override") flag is set to 0 for solicited proxy NAs and 1349 set to 1 for all other solicited and unsolicited NAs. For further 1350 study is whether solicited NAs for anycast targets apply for OMNI 1351 links. Since MNP-LLAs must be uniquely assigned to Clients to 1352 support correct ND protocol operation, however, no role is 1353 currently seen for assigning the same MNP-LLA to multiple Clients. 1355 3.6. OMNI Interface Encapsulation and Re-encapsulation 1357 The OMNI Adaptation Layer (OAL) inserts mid-layer IPv6 headers known 1358 as the OAL/ORH headers when necessary as discussed in the following 1359 sections. After either inserting or omitting the OAL/ORH headers, 1360 the OMNI interface also inserts or omits an outer ANET/INET 1361 encapsulation header as discussed below. 1363 OMNI interfaces avoid outer encapsulation over Direct underlying 1364 interfaces and ANET underlying interfaces for which the Client and 1365 Proxy are connected to the same underlying link. Otherwise, OMNI 1366 interfaces encapsulate packets according to whether they are entering 1367 the OMNI interface from the network layer or if they are being re- 1368 admitted into the same OMNI link they arrived on. This latter form 1369 of encapsulation is known as "re-encapsulation". 1371 For packets entering the OMNI interface from the network layer, the 1372 OMNI interface copies the "TTL/Hop Limit", "Type of Service/Traffic 1373 Class" [RFC2983], "Flow Label"[RFC6438] (for IPv6) and "Congestion 1374 Experienced" [RFC3168] values in the inner packet's IP header into 1375 the corresponding fields in the OAL and outer encapsulation 1376 header(s). 1378 For packets undergoing re-encapsulation, the OMNI interface instead 1379 copies these values from the original encapsulation header into the 1380 new encapsulation header, i.e., the values are transferred between 1381 encapsulation headers and *not* copied from the encapsulated packet's 1382 network-layer header. (Note especially that by copying the TTL/Hop 1383 Limit between encapsulation headers the value will eventually 1384 decrement to 0 if there is a (temporary) routing loop.) 1386 OMNI interfaces configured over ANET underlying interfaces which 1387 employ a different IP protocol version (and/or when the Client and 1388 Proxy may be separated by multiple ANET IP hops) use IP-in-IP 1389 encapsulation so that the inner packet can traverse the ANET without 1390 decrementing the TTL/Hop-Limit. IPv6 underlying ANET interfaces use 1391 [RFC2473] encapsulation, while IPv4 interfaces use the appropriate 1392 encapsulation per one of [RFC5214][RFC2003]. 1394 OMNI interfaces configured over INET underlying interfaces 1395 encapsulate packets in INET headers according to the next hop 1396 determined in the forwarding algorithm in Section 3.10. If the next 1397 hop is reached via a secured tunnel, the OMNI interface uses an 1398 encapsulation format specific to the secured tunnel type (see: 1399 Section 6). If the next hop is reached via an unsecured INET 1400 interface, the OMNI interface instead uses UDP/IP encapsulation per 1401 [RFC4380] and as extended in [RFC6081]. 1403 When UDP/IP encapsulation is used, the OMNI interface next sets the 1404 UDP source port to a constant value that it will use in each 1405 successive packet it sends, and sets the UDP length field to the 1406 length of the encapsulated packet plus 8 bytes for the UDP header 1407 itself plus the length of any included extension headers or trailers. 1408 The encapsulated packet may be either IPv6 or IPv4, as distinguished 1409 by the version number found in the first four bits. 1411 For UDP/IP-encapsulated packets sent to a Server, Relay or Bridge, 1412 the OMNI interface sets the UDP destination port to 8060, i.e., the 1413 IANA-registered port number for AERO. For packets sent to a Client, 1414 the OMNI interface sets the UDP destination port to the port value 1415 stored in the neighbor cache entry for this Client. The OMNI 1416 interface finally includes/omits the UDP checksum according to 1417 [RFC6935][RFC6936]. 1419 When a Proxy, Relay or Server re-encapsulates a packet received from 1420 a Client that includes an OAL but no ORH, it inserts an ORH 1421 immediately following the OAL header and adjusts the OAL payload 1422 length and destination address field. The inserted ORH will be 1423 removed by the final-hop Bridge, but its insertion and removal will 1424 not interfere with reassembly at the final destination. 1426 3.7. OMNI Interface Decapsulation 1428 OMNI interfaces decapsulate packets destined either to the AERO node 1429 itself or to a destination reached via an interface other than the 1430 OMNI interface the packet was received on. When the encapsulated 1431 packet arrives in multiple OAL fragments, the OMNI interface 1432 reassembles as discussed in Section 3.9. Further decapsulation steps 1433 are performed according to the appropriate encapsulation format 1434 specification. 1436 3.8. OMNI Interface Data Origin Authentication 1438 AERO nodes employ simple data origin authentication procedures. In 1439 particular: 1441 o AERO Bridges, Servers and Proxys accept encapsulated data packets 1442 and control messages received from the (secured) spanning tree. 1444 o AERO Proxys and Clients accept packets that originate from within 1445 the same secured ANET. 1447 o AERO Clients and Relays accept packets from downstream network 1448 correspondents based on ingress filtering. 1450 o AERO Clients, Relays and Servers verify the outer UDP/IP 1451 encapsulation addresses according to [RFC4380]. 1453 AERO nodes silently drop any packets that do not satisfy the above 1454 data origin authentication procedures. Further security 1455 considerations are discussed in Section 6. 1457 3.9. OMNI Adaptation Layer and OMNI Interface MTU 1459 The OMNI interface observes the link nature of tunnels, including the 1460 Maximum Transmission Unit (MTU), Maximum Reassembly Unit (MRU) and 1461 the role of fragmentation and reassembly [I-D.ietf-intarea-tunnels]. 1462 The OMNI interface employs an OMNI Adaptation Layer (OAL) for 1463 accommodating multiple underlying links with diverse MTUs. The 1464 functions of the OAL and the OMNI interface MTU/MRU are specified in 1465 Section 5 of [I-D.templin-6man-omni-interface], with MTU/MRU both set 1466 to the constant value 9180 bytes. 1468 When the network layer presents an IP packet to the OMNI interface, 1469 the OAL encapsulates the packet in OAL/ORH headers. The OAL then 1470 fragments the encapsulated packet if necessary such that the OAL/ORH 1471 headers appear in each fragment while the original IP packet header 1472 appears only in the first fragment. The OAL then transmits each OAL/ 1473 ORH packet/fragment over an underlying interface connected to either 1474 a physical link such as Ethernet, WiFi and the like or a virtual link 1475 such as an Internet or higher-layer tunnel (see the definition of 1476 link in [RFC8200]). 1478 Note: Although the ORH may be removed by a Bridge on the path (see: 1479 Section 3.10.4), this does not interfere with the destination's 1480 ability to reassemble in the event that the packet was fragmented. 1481 This is due to the fact that the ORH is not included in the 1482 fragmentable part; therefore, its removal does not invalidate the 1483 offset values in any fragment headers. 1485 3.10. OMNI Interface Forwarding Algorithm 1487 IP packets enter a node's OMNI interface either from the network 1488 layer (i.e., from a local application or the IP forwarding system) or 1489 from the link layer (i.e., from an OMNI interface neighbor). All 1490 packets entering a node's OMNI interface first undergo data origin 1491 authentication as discussed in Section 3.8. Packets that satisfy 1492 data origin authentication are processed further, while all others 1493 are dropped silently. The OMNI interface OAL wraps accepted packets 1494 in OAL/ORH headers if necessary as discussed above. 1496 Packets that enter the OMNI interface from the network layer are 1497 forwarded to an OMNI interface neighbor. Packets that enter the OMNI 1498 interface from the link layer are either re-admitted into the OMNI 1499 link or forwarded to the network layer where they are subject to 1500 either local delivery or IP forwarding. In all cases, the OMNI 1501 interface itself MUST NOT decrement the network layer TTL/Hop-count 1502 since its forwarding actions occur below the network layer. 1504 OMNI interfaces may have multiple underlying interfaces and/or 1505 neighbor cache entries for neighbors with multiple underlying 1506 interfaces (see Section 3.3). The OMNI interface uses interface 1507 attributes and/or traffic classifiers (e.g., DSCP value, port number, 1508 flow specification, etc.) to select an outgoing underlying interface 1509 for each packet based on the node's own QoS preferences, and also to 1510 select a destination link-layer address based on the neighbor's 1511 underlying interface with the highest preference. AERO 1512 implementations SHOULD allow for QoS preference values to be modified 1513 at runtime through network management. 1515 If multiple outgoing interfaces and/or neighbor interfaces have a 1516 preference of "high", the AERO node replicates the packet and sends 1517 one copy via each of the (outgoing / neighbor) interface pairs; 1518 otherwise, the node sends a single copy of the packet via an 1519 interface with the highest preference. AERO nodes keep track of 1520 which underlying interfaces are currently "reachable" or 1521 "unreachable", and only use "reachable" interfaces for forwarding 1522 purposes. 1524 The following sections discuss the OMNI interface forwarding 1525 algorithms for Clients, Proxys, Servers and Bridges. In the 1526 following discussion, a packet's destination address is said to 1527 "match" if it is the same as a cached address, or if it is covered by 1528 a cached prefix (which may be encoded in an MNP-LLA). 1530 3.10.1. Client Forwarding Algorithm 1532 When an IP packet enters a Client's OMNI interface from the network 1533 layer the Client searches for an asymmetric neighbor cache entry that 1534 matches the destination. If there is a match, the Client uses one or 1535 more "reachable" neighbor interfaces in the entry for packet 1536 forwarding. If there is no asymmetric neighbor cache entry, the 1537 Client instead forwards the packet toward a Server (the packet is 1538 intercepted by a Proxy if there is a Proxy on the path). The Client 1539 encapsulates the packet in OAL/ORH headers if necessary and fragments 1540 according to MTU requirements (see: Section 3.9). 1542 If there is an asymmetric neighbor cache entry and the neighbor 1543 interface selected for forwarding is located on the same OMNI link 1544 segment and not behind a NAT, the Client forwards the packet/ 1545 fragments directly according to the L2ADDR information for the 1546 neighbor. If the neighbor interface is behind a NAT on the same OMNI 1547 link segment, the Client instead forwards the initial packet/ 1548 fragments to its Server and initiates NAT traversal procedures. If 1549 the Client's intended source underlying interface is also behind a 1550 NAT and located on the same OMNI link segment, it sends a "direct 1551 bubble" over the interface per [RFC6081][RFC4380] to the L2ADDR found 1552 in the neighbor cache in order to establish state in its own NAT by 1553 generating traffic toward the neighbor (note that no response to the 1554 bubble is expected). 1556 The Client next sends an NS(NUD) message toward the MNP-ULA of the 1557 neighbor via its Server as discussed in Section 3.15. If the Client 1558 receives an NA(NUD) from the neighbor over the underlying interface, 1559 it marks the neighbor interface as "trusted" and sends future 1560 packets/fragments directly to the L2ADDR information for the neighbor 1561 instead of indirectly via the Server. The Client must honor the 1562 neighbor cache maintenance procedure by sending additional direct 1563 bubbles and/or NS/NA(NUD) messages as discussed in [RFC6081][RFC4380] 1564 in order to keep NAT state alive as long as packets are still 1565 flowing. 1567 When an IP packet enters a Client's OMNI interface from the link- 1568 layer, if the destination matches one of the Client's MNPs or link- 1569 local addresses the Client reassembles and decapsulates as necessary 1570 and delivers the inner packet to the network layer. Otherwise, the 1571 Client drops the packet and MAY return a network-layer ICMP 1572 Destination Unreachable message subject to rate limiting (see: 1573 Section 3.11). 1575 3.10.2. Proxy Forwarding Algorithm 1577 For control messages originating from or destined to a Client, the 1578 Proxy intercepts the message and updates its proxy neighbor cache 1579 entry for the Client. The Proxy then forwards a (proxyed) copy of 1580 the control message. (For example, the Proxy forwards a proxied 1581 version of a Client's NS/RS message to the target neighbor, and 1582 forwards a proxied version of the neighbor's NA/RA reply to the 1583 Client.) 1585 When the Proxy receives a data packet from a Client within the ANET, 1586 the Proxy reassembles and re-fragments if necessary then searches for 1587 an asymmetric neighbor cache entry that matches the destination and 1588 forwards as follows: 1590 o if the destination matches an asymmetric neighbor cache entry, the 1591 Proxy uses one or more "reachable" neighbor interfaces in the 1592 entry for packet forwarding using OAL/ORH encapsulation if 1593 necessary according to the cached link-layer address information. 1594 If the neighbor interface is in a different OMNI link segment, the 1595 Proxy forwards the packet to a Bridge; otherwise, it forwards the 1596 packet directly to the neighbor. If the neighbor is behind a NAT, 1597 the Proxy instead forwards initial packets via a Bridge while 1598 sending an NS(NUD) to the neighbor. When the Proxy receives the 1599 NA(NUD), it can begin forwarding packets directly to the neighbor 1600 the same as discussed in Section 3.10.1 while sending additional 1601 NUD messages as necessary to maintain NAT state. Note that no 1602 direct bubbles are necessary since the Proxy is by definition not 1603 located behind a NAT. 1605 o else, the Proxy uses OAL/ORH encapsulation and forwards the packet 1606 to a Bridge while using the MNP-ULA corresponding to the packet's 1607 destination as the destination address. 1609 When the Proxy receives an encapsulated data packet from an INET 1610 neighbor or from a secured tunnel from a Bridge, it accepts the 1611 packet only if data origin authentication succeeds and if there is a 1612 proxy neighbor cache entry that matches the inner destination. Next, 1613 the Proxy reassembles the packet (if necessary) and continues 1614 processing. If the reassembly is complete and the neighbor cache 1615 state is REACHABLE, the Proxy then returns a PTB if necessary (see: 1616 Section 3.9) then either drops or forwards the packet to the Client 1617 while performing OAL/ORH re-encapsulation and re-fragmentation if 1618 necessary. If the neighbor cache entry state is DEPARTED, the Proxy 1619 instead changes the destination address to the address of the new 1620 Server and forwards it to a Bridge while performing OAL/ORH re- 1621 encapsulation if necessary. 1623 Note: When the Proxy receives fragmented OAL packets with destination 1624 address set to the MNP-ULA of the Client, it can either reassemble 1625 first and then re-encapsulate/re-fragment before forwarding to the 1626 Client or forward the raw fragments on to the Client which then must 1627 reassemble. In the former case, the Proxy can re-fragment to a size 1628 that better matches the link MTU for the Client, which may be 1629 important for low-end links with large MTUs. In the latter case, the 1630 Client may receive fragments that are smaller than its link MTU but 1631 can still be reassembled; this case may provide an important 1632 performance benefit to Proxys by permitting them to avoid excessive 1633 reassembly and re-fragmentation overhead.) 1635 3.10.3. Server/Relay Forwarding Algorithm 1637 For control messages destined to a target Client's MNP-LLA that are 1638 received from a secured tunnel, the Server intercepts the message and 1639 returns a Proxyed response on behalf of the Client. (For example, 1640 the Server sends a Proxyed NA message reply in response to an NS 1641 message directed to one of its associated Clients.) If the Client's 1642 neighbor cache entry is in the DEPARTED state, however, the Server 1643 instead forwards the packet to the Client's new Server as discussed 1644 in Section 3.16. 1646 When the Server receives an encapsulated data packet from an INET 1647 neighbor or from a secured tunnel, it accepts the packet only if data 1648 origin authentication succeeds. If the packet was an OAL fragment 1649 with destination set to the Server's ADM-ULA, the Server submits the 1650 packet for reassembly (if the destination was the MNP-ULA of one of 1651 its Clients, the Server instead either submits the packet for 1652 reassembly or forwards the fragment directly to the target Client). 1653 If reassembly is complete (or if no reassembly was required), the 1654 Server then (re)fragments if necessary and forwards as follows: 1656 o if the network layer destination matches a symmetric neighbor 1657 cache entry in the REACHABLE state the Server prepares the packet 1658 for forwarding to the destination Client. The Server then 1659 forwards the packet as specified in Section 3.9. 1661 o else, if the destination matches a symmetric neighbor cache entry 1662 in the DEPARETED state the Server re-encapsulates the packet and 1663 forwards it using the ADM-ULA of the Client's new Server as the 1664 destination. 1666 o else, if the destination matches an asymmetric neighbor cache 1667 entry, the Server proceeds the same as specified for a Proxy in 1668 Section 3.10.2. Again, the Server need not send direct bubbles 1669 since it is not located behind a NAT. 1671 o else, if the destination matches a non-MNP route in the IP 1672 forwarding table or an ADM-LLA assigned to the Server's OMNI 1673 interface, the Server decapsulates the packet and releases it to 1674 the network layer for local delivery or IP forwarding. 1676 o else, the Server drops the packet. 1678 When the Server's OMNI interface receives a data packet from the 1679 network layer or from a VPNed or Direct Client, it performs OAL/ORH 1680 encapsulation and fragmentation if necessary, then processes the 1681 packet according to the network-layer destination address as follows: 1683 o if the destination matches a symmetric or asymmetric neighbor 1684 cache entry the Server processes the packet as above. 1686 o else, the Server encapsulates the packet in OLA/ORH headers and 1687 forwards it to a Bridge using its own ADM-ULA as the source and 1688 the MNP-ULA corresponding to the destination as the destination. 1690 Note: The same as for Proxys, when the Server receives fragmented OAL 1691 packets with destination address set to the MNP-ULA of the target, it 1692 can either reassemble first and then re-encapsulate/re-fragment 1693 before sending or forward the raw fragments on to the target which 1694 then must reassemble. In the former case, the Server can re-fragment 1695 to a size that better matches the link MTU for the Client, which may 1696 be important for low-end links with large MTUs. In the latter case, 1697 the target may receive fragments that are smaller than its link MTU 1698 but can still be reassembled; this case may provide an important 1699 performance benefit to Servers by permitting them to avoid excessive 1700 reassembly and re-fragmentation overhead.) 1702 3.10.4. Bridge Forwarding Algorithm 1704 Bridges forward OAL/ORH-encapsulated packets over secured tunnels the 1705 same as any IP router. When the Bridge receives an OAL/ORH- 1706 encapsulated packet via a secured tunnel, it removes the outer INET 1707 header and searches for a forwarding table entry that matches the OAL 1708 destination address. The Bridge then processes the packet as 1709 follows: 1711 o if the destination matches its ADM-ULA Subnet Router Anycast 1712 address the Bridge drops the packet if the next header is not an 1713 ORH; otherwise, the Bridge removes the ORH and saves it for 1714 reference while processing the packet further. If the packet is 1715 an NA(NUD) with source and destination both belonging to a local 1716 segment Client, the Bridge replaces the OMNI option Interface 1717 Attributes sub-option with information for its own interface while 1718 retaining the ifIndex value for the target. The Bridge next 1719 writes the MNP-ULA formed from the ORH Destination Suffix if 1720 present into the OAL destination address; otherwise, it writes the 1721 ADM-ULA formed from the ORH SRT/LHS information and forwards the 1722 packet via the spanning tree. For packets with MNP-ULA 1723 destinations, the Bridge next examines the ORH FMT to determine if 1724 the local Client is behind a NAT. If not (or, if NAT traversal 1725 procedures have already converged) the Bridge removes the OAL 1726 header and forwards the packet via INET encapsulation to the ORH 1727 L2ADDR. If this is a new target located behind a NAT, the Bridge 1728 instead forwards according to NAT traversal procedures the same as 1729 for Proxys and Servers, noting that no direct bubbles are 1730 necessary since only the target and not the Bridge is behind a 1731 NAT. 1733 o else, if the destination matches one of the Bridge's own 1734 addresses, the Bridge submits the packet for local delivery. 1736 o else, if the destination matches a forwarding table entry the 1737 Bridge forwards the packet via a secured tunnel to the next hop. 1738 If the destination matches an MSP without matching an MNP, 1739 however, the Bridge instead drops the packet and returns an ICMP 1740 Destination Unreachable message subject to rate limiting (see: 1741 Section 3.11). 1743 o else, the Bridge drops the packet and returns an ICMP Destination 1744 Unreachable as above. 1746 As for any IP router, the Bridge decrements the TTL/Hop Limit when it 1747 forwards the packet. Therefore, when an OAL header is present only 1748 the Hop Limit in the OAL header is decremented and not the TTL/Hop 1749 Limit in the inner packet header. Bridges do not insert OAL/ORH 1750 headers themselves; instead, they act as IPv6 routers and forward 1751 packets based on the destination address found in the headers of 1752 packets they receive. 1754 3.11. OMNI Interface Error Handling 1756 When an AERO node admits a packet into the OMNI interface, it may 1757 receive link-layer or network-layer error indications. 1759 A link-layer error indication is an ICMP error message generated by a 1760 router in the INET on the path to the neighbor or by the neighbor 1761 itself. The message includes an IP header with the address of the 1762 node that generated the error as the source address and with the 1763 link-layer address of the AERO node as the destination address. 1765 The IP header is followed by an ICMP header that includes an error 1766 Type, Code and Checksum. Valid type values include "Destination 1767 Unreachable", "Time Exceeded" and "Parameter Problem" 1768 [RFC0792][RFC4443]. (OMNI interfaces ignore all link-layer IPv4 1769 "Fragmentation Needed" and IPv6 "Packet Too Big" messages since they 1770 only emit packets that are guaranteed to be no larger than the IP 1771 minimum link MTU as discussed in Section 3.9.) 1773 The ICMP header is followed by the leading portion of the packet that 1774 generated the error, also known as the "packet-in-error". For 1775 ICMPv6, [RFC4443] specifies that the packet-in-error includes: "As 1776 much of invoking packet as possible without the ICMPv6 packet 1777 exceeding the minimum IPv6 MTU" (i.e., no more than 1280 bytes). For 1778 ICMPv4, [RFC0792] specifies that the packet-in-error includes: 1779 "Internet Header + 64 bits of Original Data Datagram", however 1780 [RFC1812] Section 4.3.2.3 updates this specification by stating: "the 1781 ICMP datagram SHOULD contain as much of the original datagram as 1782 possible without the length of the ICMP datagram exceeding 576 1783 bytes". 1785 The link-layer error message format is shown in Figure 5 (where, "L2" 1786 and "L3" refer to link-layer and network-layer, respectively): 1788 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1789 ~ ~ 1790 | L2 IP Header of | 1791 | error message | 1792 ~ ~ 1793 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1794 | L2 ICMP Header | 1795 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 1796 ~ ~ P 1797 | IP and other encapsulation | a 1798 | headers of original L3 packet | c 1799 ~ ~ k 1800 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ e 1801 ~ ~ t 1802 | IP header of | 1803 | original L3 packet | i 1804 ~ ~ n 1805 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1806 ~ ~ e 1807 | Upper layer headers and | r 1808 | leading portion of body | r 1809 | of the original L3 packet | o 1810 ~ ~ r 1811 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 1813 Figure 5: OMNI Interface Link-Layer Error Message Format 1815 The AERO node rules for processing these link-layer error messages 1816 are as follows: 1818 o When an AERO node receives a link-layer Parameter Problem message, 1819 it processes the message the same as described as for ordinary 1820 ICMP errors in the normative references [RFC0792][RFC4443]. 1822 o When an AERO node receives persistent link-layer Time Exceeded 1823 messages, the IP ID field may be wrapping before earlier fragments 1824 awaiting reassembly have been processed. In that case, the node 1825 should begin including integrity checks and/or institute rate 1826 limits for subsequent packets. 1828 o When an AERO node receives persistent link-layer Destination 1829 Unreachable messages in response to encapsulated packets that it 1830 sends to one of its asymmetric neighbor correspondents, the node 1831 should process the message as an indication that a path may be 1832 failing, and optionally initiate NUD over that path. If it 1833 receives Destination Unreachable messages over multiple paths, the 1834 node should allow future packets destined to the correspondent to 1835 flow through a default route and re-initiate route optimization. 1837 o When an AERO Client receives persistent link-layer Destination 1838 Unreachable messages in response to encapsulated packets that it 1839 sends to one of its symmetric neighbor Servers, the Client should 1840 mark the path as unusable and use another path. If it receives 1841 Destination Unreachable messages on many or all paths, the Client 1842 should associate with a new Server and release its association 1843 with the old Server as specified in Section 3.16.5. 1845 o When an AERO Server receives persistent link-layer Destination 1846 Unreachable messages in response to encapsulated packets that it 1847 sends to one of its symmetric neighbor Clients, the Server should 1848 mark the underlying path as unusable and use another underlying 1849 path. 1851 o When an AERO Server or Proxy receives link-layer Destination 1852 Unreachable messages in response to an encapsulated packet that it 1853 sends to one of its permanent neighbors, it treats the messages as 1854 an indication that the path to the neighbor may be failing. 1855 However, the dynamic routing protocol should soon reconverge and 1856 correct the temporary outage. 1858 When an AERO Bridge receives a packet for which the network-layer 1859 destination address is covered by an MSP, if there is no more- 1860 specific routing information for the destination the Bridge drops the 1861 packet and returns a network-layer Destination Unreachable message 1862 subject to rate limiting. The Bridge writes the network-layer source 1863 address of the original packet as the destination address and uses 1864 one of its non link-local addresses as the source address of the 1865 message. 1867 When an AERO node receives an encapsulated packet for which the 1868 reassembly buffer it too small, it drops the packet and returns a 1869 network-layer Packet Too Big (PTB) message. The node first writes 1870 the MRU value into the PTB message MTU field, writes the network- 1871 layer source address of the original packet as the destination 1872 address and writes one of its non link-local addresses as the source 1873 address. 1875 3.12. AERO Router Discovery, Prefix Delegation and Autoconfiguration 1877 AERO Router Discovery, Prefix Delegation and Autoconfiguration are 1878 coordinated as discussed in the following Sections. 1880 3.12.1. AERO Service Model 1882 Each AERO Server on the OMNI link is configured to facilitate Client 1883 prefix delegation/registration requests. Each Server is provisioned 1884 with a database of MNP-to-Client ID mappings for all Clients enrolled 1885 in the AERO service, as well as any information necessary to 1886 authenticate each Client. The Client database is maintained by a 1887 central administrative authority for the OMNI link and securely 1888 distributed to all Servers, e.g., via the Lightweight Directory 1889 Access Protocol (LDAP) [RFC4511], via static configuration, etc. 1890 Clients receive the same service regardless of the Servers they 1891 select. 1893 AERO Clients and Servers use ND messages to maintain neighbor cache 1894 entries. AERO Servers configure their OMNI interfaces as advertising 1895 NBMA interfaces, and therefore send unicast RA messages with a short 1896 Router Lifetime value (e.g., ReachableTime seconds) in response to a 1897 Client's RS message. Thereafter, Clients send additional RS messages 1898 to keep Server state alive. 1900 AERO Clients and Servers include prefix delegation and/or 1901 registration parameters in RS/RA messages (see 1902 [I-D.templin-6man-omni-interface]). The ND messages are exchanged 1903 between Client and Server according to the prefix management schedule 1904 required by the service. If the Client knows its MNP in advance, it 1905 can employ prefix registration by including its MNP-LLA as the source 1906 address of an RS message and with an OMNI option with valid prefix 1907 registration information for the MNP. If the Server (and Proxy) 1908 accept the Client's MNP assertion, they inject the prefix into the 1909 routing system and establish the necessary neighbor cache state. 1911 The following sections specify the Client and Server behavior. 1913 3.12.2. AERO Client Behavior 1915 AERO Clients discover the addresses of Servers in a similar manner as 1916 described in [RFC5214]. Discovery methods include static 1917 configuration (e.g., from a flat-file map of Server addresses and 1918 locations), or through an automated means such as Domain Name System 1919 (DNS) name resolution [RFC1035]. Alternatively, the Client can 1920 discover Server addresses through a layer 2 data link login exchange, 1921 or through a unicast RA response to a multicast/anycast RS as 1922 described below. In the absence of other information, the Client can 1923 resolve the DNS Fully-Qualified Domain Name (FQDN) 1924 "linkupnetworks.[domainname]" where "linkupnetworks" is a constant 1925 text string and "[domainname]" is a DNS suffix for the OMNI link 1926 (e.g., "example.com"). 1928 To associate with a Server, the Client acts as a requesting router to 1929 request MNPs. The Client prepares an RS message with prefix 1930 management parameters and includes a Nonce and Timestamp option if 1931 the Client needs to correlate RA replies. If the Client already 1932 knows the Server's ADM-LLA, it includes the LLA as the network-layer 1933 destination address; otherwise, it includes (link-local) All-Routers 1934 multicast as the network-layer destination. If the Client already 1935 knows its own MNP-LLA, it uses the LLA as the network-layer source 1936 address; otherwise, it uses a Temporary LLA as the network-layer 1937 source address and includes a DHCP Unique Identifier (DUID) sub- 1938 option in the OMNI option (see: [I-D.templin-6man-omni-interface]). 1940 The Client next includes an OMNI option in the RS message to register 1941 its link-layer information with the Server. The Client sets the OMNI 1942 option prefix registration information according to the MNP, and 1943 includes Interface Attributes corresponding to the underlying 1944 interface over which the Client will send the RS message. The Client 1945 MAY include additional Interface Attributes specific to other 1946 underlying interfaces. 1948 The Client then sends the RS message (either directly via Direct 1949 interfaces, via a VPN for VPNed interfaces, via a Proxy for ANET 1950 interfaces or via INET encapsulation for INET interfaces) and waits 1951 for an RA message reply (see Section 3.12.3). The Client retries up 1952 to MAX_RTR_SOLICITATIONS times until an RA is received. If the 1953 Client receives no RAs, or if it receives an RA with Router Lifetime 1954 set to 0, the Client SHOULD abandon this Server and try another 1955 Server. Otherwise, the Client processes the prefix information found 1956 in the RA message. 1958 Next, the Client creates a symmetric neighbor cache entry with the 1959 Server's ADM-LLA as the network-layer address and the Server's 1960 encapsulation and/or link-layer addresses as the link-layer address. 1961 The Client records the RA Router Lifetime field value in the neighbor 1962 cache entry as the time for which the Server has committed to 1963 maintaining the MNP in the routing system via this underlying 1964 interface, and caches the other RA configuration information 1965 including Cur Hop Limit, M and O flags, Reachable Time and Retrans 1966 Timer. The Client then autoconfigures MNP-LLAs for each of the 1967 delegated MNPs and assigns them to the OMNI interface. The Client 1968 also caches any MSPs included in Route Information Options (RIOs) 1969 [RFC4191] as MSPs to associate with the OMNI link, and assigns the 1970 MTU value in the MTU option to the underlying interface. 1972 The Client then registers additional underlying interfaces with the 1973 Server by sending RS messages via each additional interface. The RS 1974 messages include the same parameters as for the initial RS/RA 1975 exchange, but with destination address set to the Server's ADM-LLA. 1977 Following autoconfiguration, the Client sub-delegates the MNPs to its 1978 attached EUNs and/or the Client's own internal virtual interfaces as 1979 described in [I-D.templin-v6ops-pdhost] to support the Client's 1980 downstream attached "Internet of Things (IoT)". The Client 1981 subsequently sends additional RS messages over each underlying 1982 interface before the Router Lifetime received for that interface 1983 expires. 1985 After the Client registers its underlying interfaces, it may wish to 1986 change one or more registrations, e.g., if an interface changes 1987 address or becomes unavailable, if QoS preferences change, etc. To 1988 do so, the Client prepares an RS message to send over any available 1989 underlying interface. The RS includes an OMNI option with prefix 1990 registration information specific to its MNP, with Interface 1991 Attributes specific to the selected underlying interface, and with 1992 any additional Interface Attributes specific to other underlying 1993 interfaces. When the Client receives the Server's RA response, it 1994 has assurance that the Server has been updated with the new 1995 information. 1997 If the Client wishes to discontinue use of a Server it issues an RS 1998 message over any underlying interface with an OMNI option with a 1999 prefix release indication. When the Server processes the message, it 2000 releases the MNP, sets the symmetric neighbor cache entry state for 2001 the Client to DEPARTED and returns an RA reply with Router Lifetime 2002 set to 0. After a short delay (e.g., 2 seconds), the Server 2003 withdraws the MNP from the routing system. 2005 3.12.3. AERO Server Behavior 2007 AERO Servers act as IP routers and support a prefix delegation/ 2008 registration service for Clients. Servers arrange to add their ADM- 2009 LLAs to a static map of Server addresses for the link and/or the DNS 2010 resource records for the FQDN "linkupnetworks.[domainname]" before 2011 entering service. Server addresses should be geographically and/or 2012 topologically referenced, and made available for discovery by Clients 2013 on the OMNI link. 2015 When a Server receives a prospective Client's RS message on its OMNI 2016 interface, it SHOULD return an immediate RA reply with Router 2017 Lifetime set to 0 if it is currently too busy or otherwise unable to 2018 service the Client. Otherwise, the Server authenticates the RS 2019 message and processes the prefix delegation/registration parameters. 2020 The Server first determines the correct MNPs to provide to the Client 2021 by searching the Client database. When the Server returns the MNPs, 2022 it also creates a forwarding table entry for the MNP-ULA 2023 corresponding to each MNP so that the MNPs are propagated into the 2024 routing system (see: Section 3.2.3). For IPv6, the Server creates an 2025 IPv6 forwarding table entry for each MNP. For IPv4, the Server 2026 creates an IPv6 forwarding table entry with the IPv4-compatibility 2027 MNP-ULA prefix corresponding to the IPv4 address. 2029 The Server next creates a symmetric neighbor cache entry for the 2030 Client using the base MNP-LLA as the network-layer address and with 2031 lifetime set to no more than the smallest prefix lifetime. Next, the 2032 Server updates the neighbor cache entry by recording the information 2033 in each Interface Attributes sub-option in the RS OMNI option. The 2034 Server also records the actual OAL/INET addresses in the neighbor 2035 cache entry. 2037 Next, the Server prepares an RA message using its ADM-LLA as the 2038 network-layer source address and the network-layer source address of 2039 the RS message as the network-layer destination address. The Server 2040 sets the Router Lifetime to the time for which it will maintain both 2041 this underlying interface individually and the symmetric neighbor 2042 cache entry as a whole. The Server also sets Cur Hop Limit, M and O 2043 flags, Reachable Time and Retrans Timer to values appropriate for the 2044 OMNI link. The Server includes the MNPs, any other prefix management 2045 parameters and an OMNI option with no Interface Attributes. The 2046 Server then includes one or more RIOs that encode the MSPs for the 2047 OMNI link, plus an MTU option (see Section 3.9). The Server finally 2048 forwards the message to the Client using OAL/INET, INET, or NULL 2049 encapsulation as necessary. 2051 After the initial RS/RA exchange, the Server maintains a 2052 ReachableTime timer for each of the Client's underlying interfaces 2053 individually (and for the Client's symmetric neighbor cache entry 2054 collectively) set to expire after ReachableTime seconds. If the 2055 Client (or Proxy) issues additional RS messages, the Server sends an 2056 RA response and resets ReachableTime. If the Server receives an ND 2057 message with a prefix release indication it sets the Client's 2058 symmetric neighbor cache entry to the DEPARTED state and withdraws 2059 the MNP from the routing system after a short delay (e.g., 2 2060 seconds). If ReachableTime expires before a new RS is received on an 2061 individual underlying interface, the Server marks the interface as 2062 DOWN. If ReachableTime expires before any new RS is received on any 2063 individual underlying interface, the Server sets the symmetric 2064 neighbor cache entry state to STALE and sets a 10 second timer. If 2065 the Server has not received a new RS or ND message with a prefix 2066 release indication before the 10 second timer expires, it deletes the 2067 neighbor cache entry and withdraws the MNP from the routing system. 2069 The Server processes any ND messages pertaining to the Client and 2070 returns an NA/RA reply in response to solicitations. The Server may 2071 also issue unsolicited RA messages, e.g., with reconfigure parameters 2072 to cause the Client to renegotiate its prefix delegation/ 2073 registrations, with Router Lifetime set to 0 if it can no longer 2074 service this Client, etc. Finally, If the symmetric neighbor cache 2075 entry is in the DEPARTED state, the Server deletes the entry after 2076 DepartTime expires. 2078 Note: Clients SHOULD notify former Servers of their departures, but 2079 Servers are responsible for expiring neighbor cache entries and 2080 withdrawing routes even if no departure notification is received 2081 (e.g., if the Client leaves the network unexpectedly). Servers 2082 SHOULD therefore set Router Lifetime to ReachableTime seconds in 2083 solicited RA messages to minimize persistent stale cache information 2084 in the absence of Client departure notifications. A short Router 2085 Lifetime also ensures that proactive Client/Server RS/RA messaging 2086 will keep any NAT state alive (see above). 2088 Note: All Servers on an OMNI link MUST advertise consistent values in 2089 the RA Cur Hop Limit, M and O flags, Reachable Time and Retrans Timer 2090 fields the same as for any link, since unpredictable behavior could 2091 result if different Servers on the same link advertised different 2092 values. 2094 3.12.3.1. DHCPv6-Based Prefix Registration 2096 When a Client is not pre-provisioned with an MNP-LLA, it will need 2097 for the Server to select one or more MNPs on its behalf and set up 2098 the correct state in the AERO routing service. (A Client with a pre- 2099 provisioned MNP may also request the Server to select additional 2100 MNPs.) The DHCPv6 service [RFC8415] is used to support this 2101 requirement. 2103 When a Client needs to have the Server select MNPs, it sends an RS 2104 message with a Temporary LLA and with an OMNI option that includes a 2105 DHCPv6 message sub-option with DHCPv6 Prefix Delegation (DHCPv6-PD) 2106 parameters. When the Server receives the RS message, it extracts the 2107 DHCPv6-PD message from the OMNI option. 2109 The Server then acts as a "Proxy DHCPv6 Client" in a message exchange 2110 with the locally-resident DHCPv6 server, which delegates MNPs and 2111 returns a DHCPv6-PD Reply message. (If the Server wishes to defer 2112 creation of MN state until the DHCPv6-PD Reply is received, it can 2113 instead act as a Lightweight DHCPv6 Relay Agent per [RFC6221] by 2114 encapsulating the DHCPv6-PD message in a Relay-forward/reply exchange 2115 with Relay Message and Interface ID options.) 2117 When the Server receives the DHCPv6-PD Reply, it adds a route to the 2118 routing system and creates an MNP-LLA based on the delegated MNP. 2119 The Server then sends an RA back to the Client with the (newly- 2120 created) MNP-LLA as the destination address and with the DHCPv6-PD 2121 Reply message coded in the OMNI option. When the Client receives the 2122 RA, it creates a default route, assigns the Subnet Router Anycast 2123 address and sets its MNP-LLA based on the delegated MNP. 2125 3.13. The AERO Proxy 2127 Clients may connect to protected-spectrum ANETs that employ physical 2128 and/or link-layer security services to facilitate communications to 2129 Servers in outside INETs. In that case, the ANET can employ an AERO 2130 Proxy. The Proxy is located at the ANET/INET border and listens for 2131 RS messages originating from or RA messages destined to ANET Clients. 2132 The Proxy acts on these control messages as follows: 2134 o when the Proxy receives an RS message from a new ANET Client, it 2135 first authenticates the message then examines the network-layer 2136 destination address. If the destination address is a Server's 2137 ADM-LLA, the Proxy proceeds to the next step. Otherwise, if the 2138 destination is (link-local) All-Routers multicast, the Proxy 2139 selects a "nearby" Server that is likely to be a good candidate to 2140 serve the Client and replaces the destination address with the 2141 Server's ADM-LLA. Next, the Proxy creates a proxy neighbor cache 2142 entry and caches the Client and Server link-layer addresses along 2143 with the OMNI option information and any other identifying 2144 information including Transaction IDs, Client Identifiers, Nonce 2145 values, etc. The Proxy finally encapsulates the (proxyed) RS 2146 message in an OAL header with source set to the Proxy's ADM-ULA 2147 and destination set to the Server's ADM-ULA. The Proxy also 2148 includes an OMNI header with an Interface Attributes option that 2149 includes its own INET address plus a unique Port Number for this 2150 Client, then forwards the message into the OMNI link spanning 2151 tree. (Note: including a unique Port Number allows the Server to 2152 distinguish different Clients located behind the same Proxy at the 2153 link-layer, whereas the link-layer addresses would otherwise be 2154 indistinguishable) 2156 o when the Server receives the RS, it authenticates the message then 2157 creates or updates a symmetric neighbor cache entry for the Client 2158 with the Proxy's ADM-ULA, INET address and Port Number as the 2159 link-layer address information. The Server then sends an RA 2160 message back to the Proxy via the spanning tree. 2162 o when the Proxy receives the RA, it authenticates the message and 2163 matches it with the proxy neighbor cache entry created by the RS. 2164 The Proxy then caches the prefix information as a mapping from the 2165 Client's MNPs to the Client's link-layer address, caches the 2166 Server's advertised Router Lifetime and sets the neighbor cache 2167 entry state to REACHABLE. The Proxy then optionally rewrites the 2168 Router Lifetime and forwards the (proxyed) message to the Client. 2169 The Proxy finally includes an MTU option (if necessary) with an 2170 MTU to use for the underlying ANET interface. 2172 After the initial RS/RA exchange, the Proxy forwards any Client data 2173 packets for which there is no matching asymmetric neighbor cache 2174 entry to a Bridge using OAL encapsulation with its own ADM-ULA as the 2175 source and the MNP-ULA corresponding to the Client as the 2176 destination. The Proxy instead forwards any Client data destined to 2177 an asymmetric neighbor cache target directly to the target according 2178 to the OAL/link-layer information - the process of establishing 2179 asymmetric neighbor cache entries is specified in Section 3.14. 2181 While the Client is still attached to the ANET, the Proxy sends NS, 2182 RS and/or unsolicited NA messages to update the Server's symmetric 2183 neighbor cache entries on behalf of the Client and/or to convey QoS 2184 updates. This allows for higher-frequency Proxy-initiated RS/RA 2185 messaging over well-connected INET infrastructure supplemented by 2186 lower-frequency Client-initiated RS/RA messaging over constrained 2187 ANET data links. 2189 If the Server ceases to send solicited advertisements, the Proxy 2190 sends unsolicited RAs on the ANET interface with destination set to 2191 (link-local) All-Nodes multicast and with Router Lifetime set to zero 2192 to inform Clients that the Server has failed. Although the Proxy 2193 engages in ND exchanges on behalf of the Client, the Client can also 2194 send ND messages on its own behalf, e.g., if it is in a better 2195 position than the Proxy to convey QoS changes, etc. For this reason, 2196 the Proxy marks any Client-originated solicitation messages (e.g. by 2197 inserting a Nonce option) so that it can return the solicited 2198 advertisement to the Client instead of processing it locally. 2200 If the Client becomes unreachable, the Proxy sets the neighbor cache 2201 entry state to DEPARTED and retains the entry for DepartTime seconds. 2202 While the state is DEPARTED, the Proxy forwards any packets destined 2203 to the Client to a Bridge via OAL/ORH encapsulation. When DepartTime 2204 expires, the Proxy deletes the neighbor cache entry and discards any 2205 further packets destined to this (now forgotten) Client. 2207 In some ANETs that employ a Proxy, the Client's MNP can be injected 2208 into the ANET routing system. In that case, the Client can send data 2209 messages without encapsulation so that the ANET routing system 2210 transports the unencapsulated packets to the Proxy. This can be very 2211 beneficial, e.g., if the Client connects to the ANET via low-end data 2212 links such as some aviation wireless links. 2214 If the first-hop ANET access router is on the same underlying link 2215 and recognizes the AERO/OMNI protocol, the Client can avoid 2216 encapsulation for both its control and data messages. When the 2217 Client connects to the link, it can send an unencapsulated RS message 2218 with source address set to its own MNP-LLA (or to a Temporary LLA), 2219 and with destination address set to the ADM-LLA of the Client's 2220 selected Server or to (link-local) All-Routers multicast. The Client 2221 includes an OMNI option formatted as specified in 2222 [I-D.templin-6man-omni-interface]. 2224 The Client then sends the unencapsulated RS message, which will be 2225 intercepted by the AERO-Aware access router. The access router then 2226 encapsulates the RS message in an ANET header with its own address as 2227 the source address and the address of a Proxy as the destination 2228 address. The access router further remembers the address of the 2229 Proxy so that it can encapsulate future data packets from the Client 2230 via the same Proxy. If the access router needs to change to a new 2231 Proxy, it simply sends another RS message toward the Server via the 2232 new Proxy on behalf of the Client. 2234 In some cases, the access router and Proxy may be one and the same 2235 node. In that case, the node would be located on the same physical 2236 link as the Client, but its message exchanges with the Server would 2237 need to pass through a security gateway at the ANET/INET border. The 2238 method for deploying access routers and Proxys (i.e. as a single node 2239 or multiple nodes) is an ANET-local administrative consideration. 2241 3.13.1. Combined Proxy/Servers 2243 Clients may need to connect directly to Servers via INET, Direct and 2244 VPNed interfaces (i.e., non-ANET interfaces). If the Client's 2245 underlying interfaces all connect via the same INET partition, then 2246 it can connect to a single controlling Server via all interfaces. 2248 If some Client interfaces connect via different INET partitions, 2249 however, the Client still selects a set of controlling Servers and 2250 sends RS messages via their directly-connected Servers while using 2251 the ADM-LLA of the controlling Server as the destination. 2253 When a Server receives an RS with destination set to the ADM-LLA of a 2254 controlling Server, it acts as a Proxy to forward the message to the 2255 controlling Server while forwarding the corresponding RA reply to the 2256 Client. 2258 3.13.2. Detecting and Responding to Server Failures 2260 In environments where fast recovery from Server failure is required, 2261 Proxys SHOULD use proactive Neighbor Unreachability Detection (NUD) 2262 to track Server reachability in a similar fashion as for 2263 Bidirectional Forwarding Detection (BFD) [RFC5880]. Proxys can then 2264 quickly detect and react to failures so that cached information is 2265 re-established through alternate paths. The NUD control messaging is 2266 carried only over well-connected ground domain networks (i.e., and 2267 not low-end aeronautical radio links) and can therefore be tuned for 2268 rapid response. 2270 Proxys perform proactive NUD with Servers for which there are 2271 currently active ANET Clients by sending continuous NS messages in 2272 rapid succession, e.g., one message per second. The Proxy sends the 2273 NS message via the spanning tree with the Proxy's ADM-LLA as the 2274 source and the ADM-LLA of the Server as the destination. When the 2275 Proxy is also sending RS messages to the Server on behalf of ANET 2276 Clients, the resulting RA responses can be considered as equivalent 2277 hints of forward progress. This means that the Proxy need not also 2278 send a periodic NS if it has already sent an RS within the same 2279 period. If the Server fails (i.e., if the Proxy ceases to receive 2280 advertisements), the Proxy can quickly inform Clients by sending 2281 multicast RA messages on the ANET interface. 2283 The Proxy sends RA messages on the ANET interface with source address 2284 set to the Server's address, destination address set to (link-local) 2285 All-Nodes multicast, and Router Lifetime set to 0. The Proxy SHOULD 2286 send MAX_FINAL_RTR_ADVERTISEMENTS RA messages separated by small 2287 delays [RFC4861]. Any Clients on the ANET that had been using the 2288 failed Server will receive the RA messages and associate with a new 2289 Server. 2291 3.13.3. Point-to-Multipoint Server Coordination 2293 In environments where Client messaging over ANETs is bandwidth- 2294 limited and/or expensive, Clients can enlist the services of the 2295 Proxy to coordinate with multiple Servers in a single RS/RA message 2296 exchange. The Client can send a single RS message to (link-local) 2297 All-Routers multicast that includes the ID's of multiple Servers in 2298 MS-Register sub-options of the OMNI option. 2300 When the Proxy receives the RS and processes the OMNI option, it 2301 sends a separate RS to each MS-Register Server ID. When the Proxy 2302 receives an RA, it can optionally return an immediate "singleton" RA 2303 to the Client or record the Server's ID for inclusion in a pending 2304 "aggregate" RA message. The Proxy can then return aggregate RA 2305 messages to the Client including multiple Server IDs in order to 2306 conserve bandwidth. Each RA includes a proper subset of the Server 2307 IDs from the original RS message, and the Proxy must ensure that the 2308 message contents of each RA are consistent with the information 2309 received from the (aggregated) Servers. 2311 Clients can thereafter employ efficient point-to-multipoint Server 2312 coordination under the assistance of the Proxy to reduce the number 2313 of messages sent over the ANET while enlisting the support of 2314 multiple Servers for fault tolerance. Clients can further include 2315 MS-Release sub-options in IPv6 ND messages to request the Proxy to 2316 release from former Servers via the procedures discussed in 2317 Section 3.16.5. 2319 The OMNI interface specification [I-D.templin-6man-omni-interface] 2320 provides further discussion of the Client/Proxy RS/RA messaging 2321 involved in point-to-multipoint coordination. 2323 3.14. AERO Route Optimization / Address Resolution 2325 While data packets are flowing between a source and target node, 2326 route optimization SHOULD be used. Route optimization is initiated 2327 by the first eligible Route Optimization Source (ROS) closest to the 2328 source as follows: 2330 o For Clients on VPNed and Direct interfaces, the Server is the ROS. 2332 o For Clients on ANET interfaces, the Proxy is the ROS. 2334 o For Clients on INET interfaces, the Client itself is the ROS. 2336 o For correspondent nodes on INET/EUN interfaces serviced by a 2337 Relay, the Relay is the ROS. 2339 The route optimization procedure is conducted between the ROS and the 2340 target Server/Relay acting as a Route Optimization Responder (ROR) in 2341 the same manner as for IPv6 ND Address Resolution and using the same 2342 NS/NA messaging. The target may either be a MNP Client serviced by a 2343 Server, or a non-MNP correspondent reachable via a Relay. 2345 The procedures are specified in the following sections. 2347 3.14.1. Route Optimization Initiation 2349 While data packets are flowing from the source node toward a target 2350 node, the ROS performs address resolution by sending an NS message 2351 for Address Resolution (NS(AR)) to receive a solicited NA message 2352 from the ROR. When the ROS sends an NS(AR), it includes: 2354 o the LLA of the ROS as the source address. 2356 o the data packet's destination as the Target Address. 2358 o the Solicited-Node multicast address [RFC4291] formed from the 2359 lower 24 bits of the data packet's destination as the destination 2360 address, e.g., for 2001:db8:1:2::10:2000 the NS destination 2361 address is ff02:0:0:0:0:1:ff10:2000. 2363 The NS(AR) message includes an OMNI option with no Interface 2364 Attributes, such that the target will not create a neighbor cache 2365 entry. The Prefix Length in the OMNI option is set to the Prefix 2366 Length associated with the ROS's LLA. 2368 The ROS then encapsulates the NS(AR) message in an OAL header with 2369 source set to its own ULA and destination set to the MNP-ULA 2370 corresponding to the target, then sends the message into the spanning 2371 tree without decrementing the network-layer TTL/Hop Limit field. 2372 (When the ROS is a Client, it instead securely sends the NS(AR) to 2373 one of its current Servers by including an Authentication option per 2374 [RFC4380]. The Server then forwards the message into the spanning 2375 tree on behalf of the Client, while setting the IPv6 source address 2376 and the OAL source address to the MNP-LLA and MNP-ULA of the Client, 2377 respectively.) 2379 3.14.2. Relaying the NS 2381 When the Bridge receives the NS(AR) message from the ROS, it discards 2382 the INET header and determines that the ROR is the next hop by 2383 consulting its standard IPv6 forwarding table for the OAL header 2384 destination address. The Bridge then forwards the message toward the 2385 ROR via the spanning tree the same as for any IPv6 router. The 2386 final-hop Bridge in the spanning tree will deliver the message via a 2387 secured tunnel to the ROR. 2389 3.14.3. Processing the NS and Sending the NA 2391 When the ROR receives the NS(AR) message, it examines the Target 2392 Address to determine whether it has a neighbor cache entry and/or 2393 route that matches the target. If there is no match, the ROR drops 2394 the message. Otherwise, the ROR continues processing as follows: 2396 o if the target belongs to an MNP Client neighbor in the DEPARTED 2397 state the ROR changes the NS(AR) message OAL destination address 2398 to the ADM-ULA of the Client's new Server, forwards the message 2399 into the spanning tree and returns from processing. 2401 o If the target belongs to an MNP Client neighbor in the REACHABLE 2402 state, the ROR instead adds the AERO source address to the target 2403 Client's Report List with time set to ReportTime. 2405 o If the target belongs to a non-MNP route, the ROR continues 2406 processing without adding an entry to the Report List. 2408 The ROR then prepares a solicited NA message to send back to the ROS 2409 but does not create a neighbor cache entry. The ROR sets the NA 2410 source address to the MNP-LLA corresponding to the target, sets the 2411 Target Address to the target of the solicitation, and sets the 2412 destination address to the source of the solicitation. The ROR then 2413 includes an OMNI option with Prefix Length set to the length 2414 associated with the MNP-LLA. 2416 If the target is an MNP Client, the ROR next includes Interface 2417 Attributes in the OMNI option for each of the target Client's 2418 underlying interfaces with current information for each interface and 2419 with the S/T-ifIndex field in the OMNI header set to 0 to indicate 2420 that the message originated from the ROR and not the Client. 2422 For each Interface Attributes sub-option, the ROR sets the L2ADDR 2423 according to its own INET address for VPNed or Direct interfaces, to 2424 the INET address of the Proxy or to the Client's INET address for 2425 INET interfaces. The ROR then includes the lower 32 bits of its own 2426 ADM-ULA (or the ADM-ULA of the Proxy) as the LHS, encodes the ADM-ULA 2427 prefix length code in the SRT field and sets the FMT code accordingly 2428 as specified in Section 3.3. 2430 The ROR then sets the NA message R flag to 1 (as a router), S flag to 2431 1 (as a response to a solicitation), and O flag to 0 (as a proxy). 2432 The ROR finally encapsulates the NA message in an OAL header with 2433 source set to its own ULA and destination set to the source ULA of 2434 the NS(AR) message, then forwards the message into the spanning tree 2435 without decrementing the network-layer TTL/Hop Limit field. 2437 3.14.4. Relaying the NA 2439 When the Bridge receives the NA message from the ROR, it discards the 2440 INET header and determines that the ROS is the next hop by consulting 2441 its standard IPv6 forwarding table for the OAL header destination 2442 address. The Bridge then forwards the OAL-encapsulated NA message 2443 toward the ROS the same as for any IPv6 router. The final-hop Bridge 2444 in the spanning tree will deliver the message via a secured tunnel to 2445 the ROS. 2447 3.14.5. Processing the NA 2449 When the ROS receives the solicited NA message, it processes the 2450 message the same as for standard IPv6 Address Resolution [RFC4861]. 2451 In the process, it caches the source MNP-ULA then creates an 2452 asymmetric neighbor cache entry for the target and caches all 2453 information found in the OMNI option. The ROS finally sets the 2454 asymmetric neighbor cache entry lifetime to ReachableTime seconds. 2455 (When the ROS is a Client, the solicited NA message will first be 2456 delivered via the spanning tree to one of its current Servers, which 2457 then securely forwards the message to the Client by including an 2458 Authentication option per [RFC4380]. 2460 3.14.6. Route Optimization Maintenance 2462 Following route optimization, the ROS forwards future data packets 2463 destined to the target via the addresses found in the cached link- 2464 layer information. The route optimization is shared by all sources 2465 that send packets to the target via the ROS, i.e., and not just the 2466 source on behalf of which the route optimization was initiated. 2468 While new data packets destined to the target are flowing through the 2469 ROS, it sends additional NS(AR) messages to the ROR before 2470 ReachableTime expires to receive a fresh solicited NA message the 2471 same as described in the previous sections (route optimization 2472 refreshment strategies are an implementation matter, with a non- 2473 normative example given in Appendix A.1). The ROS uses the cached 2474 ADM-ULA of the ROR as the NS(AR) OAL destination address (i.e., 2475 instead of using the ULA corresponding to the target as was the case 2476 for the initial NS(AR)), and sends up to MAX_MULTICAST_SOLICIT NS(AR) 2477 messages separated by 1 second until an NA is received. If no NA is 2478 received, the ROS assumes that the current ROR has become unreachable 2479 and deletes the target neighbor cache entry. Subsequent data packets 2480 will trigger a new route optimization with an NS with OAL destination 2481 address set to the MNP-ULA corresponding to the target per 2482 Section 3.14.1 to discover a new ROR while initial data packets 2483 travel over a suboptimal route. 2485 If an NA is received, the ROS then updates the asymmetric neighbor 2486 cache entry to refresh ReachableTime, while (for MNP destinations) 2487 the ROR adds or updates the ROS address to the target's Report List 2488 and with time set to ReportTime. While no data packets are flowing, 2489 the ROS instead allows ReachableTime for the asymmetric neighbor 2490 cache entry to expire. When ReachableTime expires, the ROS deletes 2491 the asymmetric neighbor cache entry. Any future data packets flowing 2492 through the ROS will again trigger a new route optimization. 2494 The ROS may also receive unsolicited NA messages from the ROR at any 2495 time (see: Section 3.16). If there is an asymmetric neighbor cache 2496 entry for the target, the ROS updates the link-layer information but 2497 does not update ReachableTime since the receipt of an unsolicited NA 2498 does not confirm that any forward paths are working. If there is no 2499 asymmetric neighbor cache entry, the ROS simply discards the 2500 unsolicited NA. 2502 In this arrangement, the ROS holds an asymmetric neighbor cache entry 2503 for the target via the ROR, but the ROR does not hold an asymmetric 2504 neighbor cache entry for the ROS. The route optimization neighbor 2505 relationship is therefore asymmetric and unidirectional. If the 2506 target node also has packets to send back to the source node, then a 2507 separate route optimization procedure is performed in the reverse 2508 direction. But, there is no requirement that the forward and reverse 2509 paths be symmetric. 2511 3.15. Neighbor Unreachability Detection (NUD) 2513 AERO nodes perform Neighbor Unreachability Detection (NUD) per 2514 [RFC4861] either reactively in response to persistent link-layer 2515 errors (see Section 3.11) or proactively to confirm reachability and/ 2516 or establish NAT state. The NUD algorithm is based on periodic 2517 control message exchanges. The algorithm may further be seeded by ND 2518 hints of forward progress, but care must be taken to avoid inferring 2519 reachability based on spoofed information. For example, authentic 2520 IPv6 ND message exchanges may be considered as acceptable hints of 2521 forward progress, while spurious data packets should not be. 2523 AERO nodes can use (OAL-encapsulated) standard NS/NA exchanges sent 2524 over the OMNI link spanning tree to securely test reachability 2525 without risk of DoS attacks from nodes pretending to be a neighbor 2526 (these NS/NA(NUD) messages use the unicast LLAs and ULAs of the two 2527 parties involved in the NUD test the same as for standard IPv6 ND, 2528 and both messages flow over the spanning tree). Proxys can further 2529 perform NUD to securely verify Server reachability on behalf of their 2530 proxyed Clients. However, a means for an ROS to test the unsecured 2531 target route optimized paths is also necessary. 2533 When an ROR directs an ROS to a target neighbor with one or more 2534 link-layer addresses, the ROS can proactively test each such 2535 unsecured route optimized path through secured NS(NUD) messages over 2536 the spanning tree that invoke an unsecured NA(NUD) reply that travels 2537 over the route optimized path.. (The NS(NUD) messages must therefore 2538 include Nonce and Timestamp options that will be echoed in the 2539 unsecured NA(NUD) replies.) While testing the paths, the ROS can 2540 optionally continue to send packets via the spanning tree, maintain a 2541 small queue of packets until target reachability is confirmed, or 2542 (optimistically) allow packets to flow via the route optimized paths. 2544 When the ROS sends an NS(NUD) message, it sets the IPv6 source to its 2545 own address, sets the destination to the MNP-LLA of the target, and 2546 sets the target's MNP Subnet-Router anycast address as the Target 2547 Address. The ROS also includes an OMNI option with a single 2548 Interface Attributes sub-option with the L2ADDR information for its 2549 own underlying interface it wishes to test, but sets the S/T-ifIndex 2550 field to the index for target's underlying interface to be tested. 2551 The ROS includes a Nonce and Timestamp option, then encapsulates the 2552 message in OAL/INET headers with its own ULA as the source and the 2553 ULA of the target as the destination. The ROS then forwards the 2554 NS(NUD) message toward the target via a Server or Bridge. 2556 When the target receives the NS(NUD) message, it creates an NA(NUD) 2557 by reversing the OAL and IPv6 addresses and including an Interface 2558 Attributes sub-option with attributes for its own interface 2559 identified by the NS(NUD) S/T-ifIndex. The target sets the NA(NUD) 2560 S/T-ifIndex to the index of the ROS, sets the Target Address to the 2561 same value that was in the NS(NUD), and returns the message using its 2562 own underlying interface identified by S/T-ifIndex and destined to 2563 the ROS's interface identified by the original Interface Attributes 2564 sub-option. 2566 When the ROS receives the NA(NUD) message, it can determine from the 2567 Nonce, Timestamp and Target Address that the message matched its 2568 NS(NUD) and that it transited the direct path from the ROR using the 2569 selected underlying interface pair. The ROS marks route optimization 2570 target paths that pass these NUD tests as "reachable", and those that 2571 do not as "unreachable". These markings inform the OMNI interface 2572 forwarding algorithm specified in Section 3.10. 2574 Note: If the target determines that the OMNI option Interface 2575 Attributes in the NS(NUD) is located in a different OMNI link segment 2576 than its own interface named in the S/T-ifIndex, it instead returns 2577 the NA(NUD) via the spanning tree while including an ORH and setting 2578 the OAL destination address to the Subnet Router Anycast address used 2579 by Bridges on the ROS segment. When a Bridge on the ROS segment 2580 receives the NA(NUD), it replaces the Interface Attributes with 2581 information for its own interface while using the ifIndex value 2582 specific to the target. 2584 3.16. Mobility Management and Quality of Service (QoS) 2586 AERO is a Distributed Mobility Management (DMM) service. Each Server 2587 is responsible for only a subset of the Clients on the OMNI link, as 2588 opposed to a Centralized Mobility Management (CMM) service where 2589 there is a single network mobility collective entity for all Clients. 2590 Clients coordinate with their associated Servers via RS/RA exchanges 2591 to maintain the DMM profile, and the AERO routing system tracks all 2592 current Client/Server peering relationships. 2594 Servers provide default routing and mobility/multilink services for 2595 their dependent Clients. Clients are responsible for maintaining 2596 neighbor relationships with their Servers through periodic RS/RA 2597 exchanges, which also serves to confirm neighbor reachability. When 2598 a Client's underlying interface address and/or QoS information 2599 changes, the Client is responsible for updating the Server with this 2600 new information. Note that when there is a Proxy in the path, the 2601 Proxy can also perform some RS/RA exchanges on the Client's behalf. 2603 Mobility management messaging is based on the transmission and 2604 reception of unsolicited Neighbor Advertisement (uNA) messages. Each 2605 uNA message sets the IPv6 destination address to (link-local) All- 2606 Nodes multicast to convey a general update of Interface Attributes to 2607 (possibly) multiple recipients, or to a specific unicast LLA to 2608 announce a departure event to a specific recipient. Implementations 2609 must therefore examine the destination address to determine the 2610 nature of the mobility event (i.e., update vs departure). 2612 Mobility management considerations are specified in the following 2613 sections. 2615 3.16.1. Mobility Update Messaging 2617 Servers accommodate Client mobility, multilink and/or QoS change 2618 events by sending unsolicited NA (uNA) messages to each ROS in the 2619 target Client's Report List. When a Server sends a uNA message, it 2620 sets the IPv6 source address to the Client's MNP-LLA, sets the 2621 destination address to (link-local) All-Nodes multicast and sets the 2622 Target Address to the Client's Subnet-Router anycast address. The 2623 Server also includes an OMNI option with Prefix Length set to the 2624 length associated with the Client's MNP-LLA, with Interface 2625 Attributes for the target Client's underlying interfaces and with the 2626 OMNI header S/T-ifIndex set to 0. The Server then sets the NA R flag 2627 to 1, the S flag to 0 and the O flag to 1, then encapsulates the 2628 message in an OAL header with source set to its own ADM-ULA and 2629 destination set to the ULA of the ROS and sends the message into the 2630 spanning tree. 2632 As discussed in Section 7.2.6 of [RFC4861], the transmission and 2633 reception of uNA messages is unreliable but provides a useful 2634 optimization. In well-connected Internetworks with robust data links 2635 uNA messages will be delivered with high probability, but in any case 2636 the Server can optionally send up to MAX_NEIGHBOR_ADVERTISEMENT uNAs 2637 to each ROS to increase the likelihood that at least one will be 2638 received. 2640 When the ROS receives a uNA message prepared as above, it ignores the 2641 message if there is no existing neighbor cache entry for the Client. 2642 Otherwise, it uses the included OMNI option information to update the 2643 neighbor cache entry, but does not reset ReachableTime since the 2644 receipt of an unsolicited NA message from the target Server does not 2645 provide confirmation that any forward paths to the target Client are 2646 working. 2648 If uNA messages are lost, the ROS may be left with stale address and/ 2649 or QoS information for the Client for up to ReachableTime seconds. 2650 During this time, the ROS can continue sending packets according to 2651 its stale neighbor cache information. When ReachableTime is close to 2652 expiring, the ROS will re-initiate route optimization and receive 2653 fresh link-layer address information. 2655 In addition to sending uNA messages to the current set of ROSs for 2656 the Client, the Server also sends uNAs to the MNP-ULA associated with 2657 the link-layer address for any underlying interface for which the 2658 link-layer address has changed. These uNA messages update an old 2659 Proxy/Server that cannot easily detect (e.g., without active probing) 2660 when a formerly-active Client has departed. When the Server sends 2661 the uNA, it sets the IPv6 source address to the Client's MNP-LLA, 2662 sets the destination address to the old Proxy/Server's ADM-LLA, and 2663 sets the Target Address to the Client's Subnet-Router anycast 2664 address. The Server also includes an OMNI option with Prefix Length 2665 set to the length associated with the Client's MNP-LLA, with 2666 Interface Attributes for the changed underlying interface, and with 2667 the OMNI header S/T-ifIndex set to 0. The Server then sets the NA R 2668 flag to 1, the S flag to 0 and the O flag to 1, then encapsulates the 2669 message in an OAL header with source set to its own ADM-ULA and 2670 destination set to the ADM-ULA of the old Proxy/Server and sends the 2671 message into the spanning tree. 2673 3.16.2. Announcing Link-Layer Address and/or QoS Preference Changes 2675 When a Client needs to change its underlying interface addresses and/ 2676 or QoS preferences (e.g., due to a mobility event), either the Client 2677 or its Proxys send RS messages to the Server via the spanning tree 2678 with an OMNI option that includes Interface attributes with the new 2679 link quality and address information. 2681 Up to MAX_RTR_SOLICITATIONS RS messages MAY be sent in parallel with 2682 sending actual data packets in case one or more RAs are lost. If all 2683 RAs are lost, the Client SHOULD re-associate with a new Server. 2685 When the Server receives the Client's changes, it sends uNA messages 2686 to all nodes in the Report List the same as described in the previous 2687 section. 2689 3.16.3. Bringing New Links Into Service 2691 When a Client needs to bring new underlying interfaces into service 2692 (e.g., when it activates a new data link), it sends an RS message to 2693 the Server via the underlying interface with an OMNI option that 2694 includes Interface Attributes with appropriate link quality values 2695 and with link-layer address information for the new link. 2697 3.16.4. Deactivating Existing Links 2699 When a Client needs to deactivate an existing underlying interface, 2700 it sends an RS or uNA message to its Server with an OMNI option with 2701 appropriate Interface Attribute values - in particular, the link 2702 quality value 0 assures that neighbors will cease to use the link. 2704 If the Client needs to send RS/uNA messages over an underlying 2705 interface other than the one being deactivated, it MUST include 2706 Interface Attributes with appropriate link quality values for any 2707 underlying interfaces being deactivated. 2709 Note that when a Client deactivates an underlying interface, 2710 neighbors that have received the RS/uNA messages need not purge all 2711 references for the underlying interface from their neighbor cache 2712 entries. The Client may reactivate or reuse the underlying interface 2713 and/or its ifIndex at a later point in time, when it will send RS/uNA 2714 messages with fresh Interface Attributes to update any neighbors. 2716 3.16.5. Moving Between Servers 2718 The Client performs the procedures specified in Section 3.12.2 when 2719 it first associates with a new Server or renews its association with 2720 an existing Server. The Client also includes MS-Release identifiers 2721 in the RS message OMNI option per [I-D.templin-6man-omni-interface] 2722 if it wants the new Server to notify any old Servers from which the 2723 Client is departing. 2725 When the new Server receives the Client's RS message, it returns an 2726 RA as specified in Section 3.12.3 and sends up to 2727 MAX_NEIGHBOR_ADVERTIISEMENT uNA messages to any old Servers listed in 2728 OMNI option MS-Release identifiers. When the new Server sends a uNA 2729 message, it sets the IPv6 source address to the Client's MNP-LLA, 2730 sets the destination address to the old Server's ADM-LLA, and sets 2731 the Target Address to the Client's Subnet-Router anycast address. 2732 The new Server also includes an OMNI option with Prefix Length set to 2733 the length associated with the Client's MNP-LLA, with Interface 2734 Attributes for its own underlying interface, and with the OMNI header 2735 S/T-ifIndex set to 0. The new Server then sets the NA R flag to 1, 2736 the S flag to 0 and the O flag to 1, then encapsulates the message in 2737 an OAL header with source set to its own ADM-ULA and destination set 2738 to the ADM-ULA of the old Server and sends the message into the 2739 spanning tree. 2741 When an old Server receives the uNA, it changes the Client's neighbor 2742 cache entry state to DEPARTED, sets the link-layer address of the 2743 Client to the new Server's ADM-ULA, and resets DepartTime. After a 2744 short delay (e.g., 2 seconds) the old Server withdraws the Client's 2745 MNP from the routing system. After DepartTime expires, the old 2746 Server deletes the Client's neighbor cache entry. 2748 The old Server also iteratively forwards a copy of the uNA message to 2749 each ROS in the Client's Report List by changing the OAL destination 2750 address to the ULA of the ROS while leaving all other fields of the 2751 message unmodified. When the ROS receives the uNA, it examines the 2752 Target address to determine the correct asymmetric neighbor cache 2753 entry and verifies that the IPv6 destination address matches the old 2754 Server. The ROS then caches the IPv6 source address as the new 2755 Server for the existing asymmetric neighbor cache entry and marks the 2756 entry as STALE. While in the STALE state, the ROS allows new data 2757 packets to flow according to any existing cached link-layer 2758 information and sends new NS(AR) messages using its own ULA as the 2759 OAL source and the ADM-ULA of the new Server as the OAL destination 2760 address to elicit NA messages that reset the asymmetric neighbor 2761 cache entry state to REACHABLE. If no new NA message is received for 2762 10 seconds while in the STALE state, the ROS deletes the neighbor 2763 cache entry. 2765 Clients SHOULD NOT move rapidly between Servers in order to avoid 2766 causing excessive oscillations in the AERO routing system. Examples 2767 of when a Client might wish to change to a different Server include a 2768 Server that has gone unreachable, topological movements of 2769 significant distance, movement to a new geographic region, movement 2770 to a new OMNI link segment, etc. 2772 When a Client moves to a new Server, some of the fragments of a 2773 multiple fragment packet may have already arrived at the old Server 2774 while others are en route to the new Server, however no special 2775 attention in the reassembly algorithm is necessary when re-routed 2776 fragments are simply treated as loss. 2778 3.17. Multicast 2780 The AERO Client provides an IGMP (IPv4) [RFC2236] or MLD (IPv6) 2781 [RFC3810] proxy service for its EUNs and/or hosted applications 2782 [RFC4605]. The Client forwards IGMP/MLD messages over any of its 2783 underlying interfaces for which group membership is required. The 2784 IGMP/MLD messages may be further forwarded by a first-hop ANET access 2785 router acting as an IGMP/MLD-snooping switch [RFC4541], then 2786 ultimately delivered to an AERO Proxy/Server acting as a Protocol 2787 Independent Multicast - Sparse-Mode (PIM-SM, or simply "PIM") 2788 Designated Router (DR) [RFC7761]. AERO Relays also act as PIM 2789 routers (i.e., the same as AERO Proxys/Servers) on behalf of nodes on 2790 INET/EUN networks. The behaviors identified in the following 2791 sections correspond to Source-Specific Multicast (SSM) and Any-Source 2792 Multicast (ASM) operational modes. 2794 3.17.1. Source-Specific Multicast (SSM) 2796 When an ROS (i.e., an AERO Proxy/Server/Relay) "X" acting as PIM 2797 router receives a Join/Prune message from a node on its downstream 2798 interfaces containing one or more ((S)ource, (G)roup) pairs, it 2799 updates its Multicast Routing Information Base (MRIB) accordingly. 2800 For each S belonging to a prefix reachable via X's non-OMNI 2801 interfaces, X then forwards the (S, G) Join/Prune to any PIM routers 2802 on those interfaces per [RFC7761]. 2804 For each S belonging to a prefix reachable via X's OMNI interface, X 2805 originates a separate copy of the Join/Prune for each (S,G) in the 2806 message using its own LLA as the source address and ALL-PIM-ROUTERS 2807 as the destination address. X then encapsulates each message in an 2808 OAL header with source address set to the ULA of X and destination 2809 address set to S then forwards the message into the spanning tree, 2810 which delivers it to AERO Server/Relay "Y" that services S. At the 2811 same time, if the message was a Join, X sends a route-optimization NS 2812 message toward each S the same as discussed in Section 3.14. The 2813 resulting NAs will return the LLA for the prefix that matches S as 2814 the network-layer source address and with an OMNI option with the ULA 2815 corresponding to any underlying interfaces that are currently 2816 servicing S. 2818 When Y processes the Join/Prune message, if S located behind any 2819 INET, Direct, or VPNed interfaces Y acts as a PIM router and updates 2820 its MRIB to list X as the next hop in the reverse path. If S is 2821 located behind any Proxys "Z"*, Y also forwards the message to each 2822 Z* over the spanning tree while continuing to use the LLA of X as the 2823 source address. Each Z* then updates its MRIB accordingly and 2824 maintains the LLA of X as the next hop in the reverse path. Since 2825 the Bridges do not examine network layer control messages, this means 2826 that the (reverse) multicast tree path is simply from each Z* (and/or 2827 Y) to X with no other multicast-aware routers in the path. If any Z* 2828 (and/or Y) is located on the same OMNI link segment as X, the 2829 multicast data traffic sent to X directly using OAL/INET 2830 encapsulation instead of via a Bridge. 2832 Following the initial Join/Prune and NS/NA messaging, X maintains an 2833 asymmetric neighbor cache entry for each S the same as if X was 2834 sending unicast data traffic to S. In particular, X performs 2835 additional NS/NA exchanges to keep the neighbor cache entry alive for 2836 up to t_periodic seconds [RFC7761]. If no new Joins are received 2837 within t_periodic seconds, X allows the neighbor cache entry to 2838 expire. Finally, if X receives any additional Join/Prune messages 2839 for (S,G) it forwards the messages to each Y and Z* in the neighbor 2840 cache entry over the spanning tree. 2842 At some later time, Client C that holds an MNP for source S may 2843 depart from a first Proxy Z1 and/or connect via a new Proxy Z2. In 2844 that case, Y sends an unsolicited NA message to X the same as 2845 specified for unicast mobility in Section 3.16. When X receives the 2846 unsolicited NA message, it updates its asymmetric neighbor cache 2847 entry for the LLA for source S and sends new Join messages to any new 2848 Proxys Z2. There is no requirement to send any Prune messages to old 2849 Proxys Z1 since source S will no longer source any multicast data 2850 traffic via Z1. Instead, the multicast state for (S,G) in Proxy Z1 2851 will soon time out since no new Joins will arrive. 2853 After some later time, C may move to a new Server Y2 and depart from 2854 old Sever Y1. In that case, Y1 sends Join messages for any of C's 2855 active (S,G) groups to Y2 while including its own LLA as the source 2856 address. This causes Y2 to include Y1 in the multicast forwarding 2857 tree during the interim time that Y1's symmetric neighbor cache entry 2858 for C is in the DEPARTED state. At the same time, Y1 sends an 2859 unsolicited NA message to X with an OMNI option with S/T-ifIndex in 2860 the header set to 0 and a release indication to cause X to release 2861 its asymmetric neighbor cache entry. X then sends a new Join message 2862 to S via the spanning tree and re-initiates route optimization the 2863 same as if it were receiving a fresh Join message from a node on a 2864 downstream link. 2866 3.17.2. Any-Source Multicast (ASM) 2868 When an ROS X acting as a PIM router receives a Join/Prune from a 2869 node on its downstream interfaces containing one or more (*,G) pairs, 2870 it updates its Multicast Routing Information Base (MRIB) accordingly. 2871 X then forwards a copy of the message to the Rendezvous Point (RP) R 2872 for each G over the spanning tree. X uses its own LLA as the source 2873 address and ALL-PIM-ROUTERS as the destination address, then 2874 encapsulates each message in an OAL header with source address set to 2875 the ULA of X and destination address set to R, then sends the message 2876 into the spanning tree. At the same time, if the message was a Join 2877 X initiates NS/NA route optimization the same as for the SSM case 2878 discussed in Section 3.17.1. 2880 For each source S that sends multicast traffic to group G via R, the 2881 Proxy/Server Z* for the Client that aggregates S encapsulates the 2882 packets in PIM Register messages and forwards them to R via the 2883 spanning tree, which may then elect to send a PIM Join to Z*. This 2884 will result in an (S,G) tree rooted at Z* with R as the next hop so 2885 that R will begin to receive two copies of the packet; one native 2886 copy from the (S, G) tree and a second copy from the pre-existing (*, 2887 G) tree that still uses PIM Register encapsulation. R can then issue 2888 a PIM Register-stop message to suppress the Register-encapsulated 2889 stream. At some later time, if C moves to a new Proxy/Server Z*, it 2890 resumes sending packets via PIM Register encapsulation via the new 2891 Z*. 2893 At the same time, as multicast listeners discover individual S's for 2894 a given G, they can initiate an (S,G) Join for each S under the same 2895 procedures discussed in Section 3.17.1. Once the (S,G) tree is 2896 established, the listeners can send (S, G) Prune messages to R so 2897 that multicast packets for group G sourced by S will only be 2898 delivered via the (S, G) tree and not from the (*, G) tree rooted at 2899 R. All mobility considerations discussed for SSM apply. 2901 3.17.3. Bi-Directional PIM (BIDIR-PIM) 2903 Bi-Directional PIM (BIDIR-PIM) [RFC5015] provides an alternate 2904 approach to ASM that treats the Rendezvous Point (RP) as a Designated 2905 Forwarder (DF). Further considerations for BIDIR-PIM are out of 2906 scope. 2908 3.18. Operation over Multiple OMNI Links 2910 An AERO Client can connect to multiple OMNI links the same as for any 2911 data link service. In that case, the Client maintains a distinct 2912 OMNI interface for each link, e.g., 'omni0' for the first link, 2913 'omni1' for the second, 'omni2' for the third, etc. Each OMNI link 2914 would include its own distinct set of Bridges, Servers and Proxys, 2915 thereby providing redundancy in case of failures. 2917 Each OMNI link could utilize the same or different ANET connections. 2918 The links can be distinguished at the link-layer via the SRT prefix 2919 in a similar fashion as for Virtual Local Area Network (VLAN) tagging 2920 (e.g., IEEE 802.1Q) and/or through assignment of distinct sets of 2921 MSPs on each link. This gives rise to the opportunity for supporting 2922 multiple redundant networked paths, with each VLAN distinguished by a 2923 different SRT "color" (see: Section 3.2.5). 2925 The Client's IP layer can select the outgoing OMNI interface 2926 appropriate for a given traffic profile while (in the reverse 2927 direction) correspondent nodes must have some way of steering their 2928 packets destined to a target via the correct OMNI link. 2930 In a first alternative, if each OMNI link services different MSPs, 2931 then the Client can receive a distinct MNP from each of the links. 2932 IP routing will therefore assure that the correct OMNI link is used 2933 for both outbound and inbound traffic. This can be accomplished 2934 using existing technologies and approaches, and without requiring any 2935 special supporting code in correspondent nodes or Bridges. 2937 In a second alternative, if each OMNI link services the same MSP(s) 2938 then each link could assign a distinct "OMNI link Anycast" address 2939 that is configured by all Bridges on the link. Correspondent nodes 2940 can then perform Segment Routing to select the correct SRT, which 2941 will then direct the packet over multiple hops to the target. 2943 3.19. DNS Considerations 2945 AERO Client MNs and INET correspondent nodes consult the Domain Name 2946 System (DNS) the same as for any Internetworking node. When 2947 correspondent nodes and Client MNs use different IP protocol versions 2948 (e.g., IPv4 correspondents and IPv6 MNs), the INET DNS must maintain 2949 A records for IPv4 address mappings to MNs which must then be 2950 populated in Relay NAT64 mapping caches. In that way, an IPv4 2951 correspondent node can send packets to the IPv4 address mapping of 2952 the target MN, and the Relay will translate the IPv4 header and 2953 destination address into an IPv6 header and IPv6 destination address 2954 of the MN. 2956 When an AERO Client registers with an AERO Server, the Server can 2957 return the address(es) of DNS servers in RDNSS options [RFC6106]. 2958 The DNS server provides the IP addresses of other MNs and 2959 correspondent nodes in AAAA records for IPv6 or A records for IPv4. 2961 3.20. Transition Considerations 2963 OAL encapsulation ensures that dissimilar INET partitions can be 2964 joined into a single unified OMNI link, even though the partitions 2965 themselves may have differing protocol versions and/or incompatible 2966 addressing plans. However, a commonality can be achieved by 2967 incrementally distributing globally routable (i.e., native) IP 2968 prefixes to eventually reach all nodes (both mobile and fixed) in all 2969 OMNI link segments. This can be accomplished by incrementally 2970 deploying AERO Relays on each INET partition, with each Relay 2971 distributing its MNPs and/or discovering non-MNP IP GUA prefixes on 2972 its INET links. 2974 This gives rise to the opportunity to eventually distribute native IP 2975 addresses to all nodes, and to present a unified OMNI link view even 2976 if the INET partitions remain in their current protocol and 2977 addressing plans. In that way, the OMNI link can serve the dual 2978 purpose of providing a mobility/multilink service and a transition 2979 service. Or, if an INET partition is transitioned to a native IP 2980 protocol version and addressing scheme that is compatible with the 2981 OMNI link MNP-based addressing scheme, the partition and OMNI link 2982 can be joined by Relays. 2984 Relays that connect INETs/EUNs with dissimilar IP protocol versions 2985 may need to employ a network address and protocol translation 2986 function such as NAT64 [RFC6146]. 2988 3.21. Detecting and Reacting to Server and Bridge Failures 2990 In environments where rapid failure recovery is required, Servers and 2991 Bridges SHOULD use Bidirectional Forwarding Detection (BFD) 2992 [RFC5880]. Nodes that use BFD can quickly detect and react to 2993 failures so that cached information is re-established through 2994 alternate nodes. BFD control messaging is carried only over well- 2995 connected ground domain networks (i.e., and not low-end radio links) 2996 and can therefore be tuned for rapid response. 2998 Servers and Bridges maintain BFD sessions in parallel with their BGP 2999 peerings. If a Server or Bridge fails, BGP peers will quickly re- 3000 establish routes through alternate paths the same as for common BGP 3001 deployments. Similarly, Proxys maintain BFD sessions with their 3002 associated Bridges even though they do not establish BGP peerings 3003 with them. 3005 Proxys SHOULD use proactive NUD for Servers for which there are 3006 currently active ANET Clients in a manner that parallels BFD, i.e., 3007 by sending unicast NS messages in rapid succession to receive 3008 solicited NA messages. When the Proxy is also sending RS messages on 3009 behalf of ANET Clients, the RS/RA messaging can be considered as 3010 equivalent hints of forward progress. This means that the Proxy need 3011 not also send a periodic NS if it has already sent an RS within the 3012 same period. If a Server fails, the Proxy will cease to receive 3013 advertisements and can quickly inform Clients of the outage by 3014 sending multicast RA messages on the ANET interface. 3016 The Proxy sends multicast RA messages with source address set to the 3017 Server's address, destination address set to (link-local) All-Nodes 3018 multicast, and Router Lifetime set to 0. The Proxy SHOULD send 3019 MAX_FINAL_RTR_ADVERTISEMENTS RA messages separated by small delays 3020 [RFC4861]. Any Clients on the ANET interface that have been using 3021 the (now defunct) Server will receive the RA messages and associate 3022 with a new Server. 3024 3.22. AERO Clients on the Open Internet 3026 AERO Clients that connect to the open Internet via INET interfaces 3027 can establish a VPN or direct link to securely connect to a Server in 3028 a "tethered" arrangement with all of the Client's traffic transiting 3029 the Server. Alternatively, the Client can associate with an INET 3030 Server using UDP/IP encapsulation and asymmetric securing services as 3031 discussed in the following sections. 3033 When a Client's OMNI interface enables an INET underlying interface, 3034 it first determines whether the interface is likely to be behind a 3035 NAT. For IPv4, the Client assumes it is on the open Internet if the 3036 INET address is not a special-use IPv4 address per [RFC3330]. 3037 Similarly for IPv6, the Client assumes it is on the open Internet if 3038 the INET address is not a link-local [RFC4291] or unique-local 3039 [RFC4193] IPv6 address. 3041 The Client then prepares a UDP/IP-encapsulated RS message with IPv6 3042 source address set to its MNP-LLA, with IPv6 destination set to 3043 (link-local) All-Routers multicast and with an OMNI option with 3044 underlying interface attributes. If the Client believes that it is 3045 on the open Internet, it SHOULD include Interface Attributes with the 3046 L2ADDR used for INET encapsulation (otherwise, it MAY omit L2ADDR). 3047 If the underlying address is IPv4, the Client includes the Port 3048 Number and IPv4 address written in obfuscated form [RFC4380] as 3049 discussed in Section 3.3. If the underlying interface address is 3050 IPv6, the Client instead includes the Port Number and IPv6 address in 3051 obfuscated form. The Client finally includes an Authentication 3052 option per [RFC4380] to provide message authentication, sets the UDP/ 3053 IP source to its INET address and UDP port, sets the UDP/IP 3054 destination to the Server's INET address and the AERO service port 3055 number (8060), then sends the message to the Server. 3057 When the Server receives the RS, it authenticates the message and 3058 registers the Client's MNP and INET interface information according 3059 to the OMNI option parameters. If the RS message includes an L2ADDR 3060 in the OMNI option, the Server compares the encapsulation IP address 3061 and UDP port number with the (unobfuscated) values. If the values 3062 are the same, the Server caches the Client's information as "INET" 3063 addresses meaning that the Client is likely to accept direct messages 3064 without requiring NAT traversal exchanges. If the values are 3065 different (or, if the OMNI option did not include an L2ADDR) the 3066 Server instead caches the Client's information as "mapped" addresses 3067 meaning that NAT traversal exchanges may be necessary. 3069 The Server then returns an RA message with IPv6 source and 3070 destination set corresponding to the addresses in the RS, and with an 3071 Authentication option per [RFC4380]. For IPv4, the Server also 3072 includes an Origin option per [RFC4380] with the mapped and 3073 obfuscated Port Number and IPv4 address observed in the encapsulation 3074 headers. For IPv6, the Server instead includes an IPv6 Origin option 3075 per Figure 6 with the mapped and obfuscated observed Port Number and 3076 IPv6 address (note that the value 0x02 in the second octet 3077 differentiates from other [RFC4380] option types). 3079 +--------+--------+-----------------+ 3080 | 0x00 | 0x02 | Origin port # | 3081 +--------+--------+-----------------+ 3082 ~ Origin IPv6 address ~ 3083 +-----------------------------------+ 3085 Figure 6: IPv6 Origin Option 3087 When the Client receives the RA message, it compares the mapped Port 3088 Number and IP address from the Origin option with its own address. 3089 If the addresses are the same, the Client assumes the open Internet / 3090 Cone NAT principle; if the addresses are different, the Client 3091 instead assumes that further qualification procedures are necessary 3092 to detect the type of NAT and proceeds according to standard 3093 [RFC4380] procedures. 3095 After the Client has registered its INET interfaces in such RS/RA 3096 exchanges it sends periodic RS messages to receive fresh RA messages 3097 before the Router Lifetime received on each INET interface expires. 3098 The Client also maintains default routes via its Servers, i.e., the 3099 same as described in earlier sections. 3101 When the Client sends messages to target IP addresses, it also 3102 invokes route optimization per Section 3.14 using IPv6 ND address 3103 resolution messaging. The Client sends the NS(AR) message to the 3104 Server wrapped in a UDP/IP header with an Authentication option with 3105 the NS source address set to the Client's MNP-LLA and destination 3106 address set to the target solicited node multicast address. The 3107 Server authenticates the message and sends a corresponding NS(AR) 3108 message over the spanning tree the same as if it were the ROS, but 3109 with the OAL source address set to the Server's ADM-ULA and 3110 destination set to the MNP-ULA of the target. When the ROR receives 3111 the NS(AR), it adds the Server's ADM-ULA and Client's MNP-LLA to the 3112 target's Report List, and returns an NA with OMNI option information 3113 for the target. The Server then returns a UDP/IP encapsulated NA 3114 message with an Authentication option to the Client. 3116 Following route optimization for targets in the same OMNI link 3117 segment, if the target's L2ADDR is on the open INET, the Client 3118 forwards data packets directly to the target INET address. If the 3119 target is behind a NAT, the Client first establishes NAT state for 3120 the L2ADDR using the "direct bubble" and NUD mechanisms discussed in 3121 Section 3.10.1. The Client continues to send data packets via its 3122 Server until NAT state is populated, then begins forwarding packets 3123 via the direct path through the NAT to the target. For targets in 3124 different OMNI link segments, the Client uses OAL/ORH encapsulation 3125 and forwards data packets to the Bridge that returned the NA message. 3127 The ROR may return uNAs via the Server if the target moves, and the 3128 Server will send corresponding Authentication-protected uNAs to the 3129 Client. The Client can also send NUD messages to test forward path 3130 reachability even though there is no security association between the 3131 Client and the target. 3133 The Client sends UDP/IP encapsulated IPv6 packets no larger than 1280 3134 bytes in one piece. In order to accommodate larger IPv6 packets (up 3135 to the OMNI interface MTU), the Client inserts an OAL header with 3136 source set to its own MNP-ULA and destination set to the MNP-ULA of 3137 the target and uses IPv6 fragmentation according to Section 3.9. The 3138 Client then encapsulates each fragment in a UDP/IP header and sends 3139 the fragments to the next hop. 3141 Note: The NAT traversal procedures specified in this document are 3142 applicable for Cone, Address-Restricted and Port-Restricted NATs 3143 only. While future updates to this document may specify procedures 3144 for other NAT variations (e.g., hairpinning and various forms of 3145 Symmetric NATs), it should be noted that continuous communications 3146 are always possible through forwarding via a Server even if NAT 3147 traversal is not employed. 3149 3.23. Time-Varying MNPs 3151 In some use cases, it is desirable, beneficial and efficient for the 3152 Client to receive a constant MNP that travels with the Client 3153 wherever it moves. For example, this would allow air traffic 3154 controllers to easily track aircraft, etc. In other cases, however 3155 (e.g., intelligent transportation systems), the MN may be willing to 3156 sacrifice a modicum of efficiency in order to have time-varying MNPs 3157 that can be changed every so often to defeat adversarial tracking. 3159 The DHCPv6 service offers a way for Clients that desire time-varying 3160 MNPs to obtain short-lived prefixes (e.g., on the order of a small 3161 number of minutes). In that case, the identity of the Client would 3162 not be bound to the MNP but rather the Client's identity would be 3163 bound to the DHCPv6 Device Unique Identifier (DUID) and used as the 3164 seed for Prefix Delegation. The Client would then be obligated to 3165 renumber its internal networks whenever its MNP (and therefore also 3166 its MNP-LLA) changes. This should not present a challenge for 3167 Clients with automated network renumbering services, however presents 3168 limits for the durations of ongoing sessions that would prefer to use 3169 a constant address. 3171 4. Implementation Status 3173 An early AERO implementation based on OpenVPN (https://openvpn.net/) 3174 was announced on the v6ops mailing list on January 10, 2018 and an 3175 initial public release of the AERO proof-of-concept source code was 3176 announced on the intarea mailing list on August 21, 2015. 3178 AERO Release-3.0.2 was tagged on October 15, 2020, and is undergoing 3179 internal testing. Additional releases expected Q42020, with first 3180 public release expected before year-end. 3182 5. IANA Considerations 3184 The IANA has assigned a 4-octet Private Enterprise Number "45282" for 3185 AERO in the "enterprise-numbers" registry. 3187 The IANA has assigned the UDP port number "8060" for an earlier 3188 experimental version of AERO [RFC6706]. This document obsoletes 3189 [RFC6706] and claims the UDP port number "8060" for all future use. 3191 The IANA is instructed to assign a new type value TBD in the IPv6 3192 Routing Types registry. 3194 No further IANA actions are required. 3196 6. Security Considerations 3198 AERO Bridges configure secured tunnels with AERO Servers, Relays and 3199 Proxys within their local OMNI link segments. Applicable secured 3200 tunnel alternatives include IPsec [RFC4301], TLS/SSL [RFC8446], DTLS 3201 [RFC6347], WireGuard [WG], etc. The AERO Bridges of all OMNI link 3202 segments in turn configure secured tunnels for their neighboring AERO 3203 Bridges in a spanning tree topology. Therefore, control messages 3204 exchanged between any pair of OMNI link neighbors on the spanning 3205 tree are already secured. 3207 AERO Servers, Relays and Proxys targeted by a route optimization may 3208 also receive data packets directly from arbitrary nodes in INET 3209 partitions instead of via the spanning tree. For INET partitions 3210 that apply effective ingress filtering to defeat source address 3211 spoofing, the simple data origin authentication procedures in 3212 Section 3.8 can be applied. 3214 For INET partitions that require strong security in the data plane, 3215 two options for securing communications include 1) disable route 3216 optimization so that all traffic is conveyed over secured tunnels, or 3217 2) enable on-demand secure tunnel creation between INET partition 3218 neighbors. Option 1) would result in longer routes than necessary 3219 and traffic concentration on critical infrastructure elements. 3220 Option 2) could be coordinated by establishing a secured tunnel on- 3221 demand instead of performing an NS/NA exchange in the route 3222 optimization procedures. Procedures for establishing on-demand 3223 secured tunnels are out of scope. 3225 AERO Clients that connect to secured ANETs need not apply security to 3226 their ND messages, since the messages will be intercepted by a 3227 perimeter Proxy that applies security on its INET-facing interface as 3228 part of the spanning tree (see above). AERO Clients connected to the 3229 open INET can use symmetric network and/or transport layer security 3230 services such as VPNs or can by some other means establish a direct 3231 link. When a VPN or direct link may be impractical, however, an 3232 asymmetric security service such as the Authentication option 3233 specified in [RFC4380] should be applied. The Authentication option 3234 requires a unique Client identifier, which can be obtained per the 3235 Universally Unique IDentifier (UUID) [RFC4122] service and also used 3236 as a DHCP Unique Identifier (DUID) per [RFC6355]. 3238 Application endpoints SHOULD use application-layer security services 3239 such as TLS/SSL, DTLS or SSH [RFC4251] to assure the same level of 3240 protection as for critical secured Internet services. AERO Clients 3241 that require host-based VPN services SHOULD use symmetric network 3242 and/or transport layer security services such as IPsec, TLS/SSL, 3243 DTLS, etc. AERO Proxys and Servers can also provide a network-based 3244 VPN service on behalf of the Client, e.g., if the Client is located 3245 within a secured enclave and cannot establish a VPN on its own 3246 behalf. 3248 AERO Servers and Bridges present targets for traffic amplification 3249 Denial of Service (DoS) attacks. This concern is no different than 3250 for widely-deployed VPN security gateways in the Internet, where 3251 attackers could send spoofed packets to the gateways at high data 3252 rates. This can be mitigated by connecting Servers and Bridges over 3253 dedicated links with no connections to the Internet and/or when 3254 connections to the Internet are only permitted through well-managed 3255 firewalls. Traffic amplification DoS attacks can also target an AERO 3256 Client's low data rate links. This is a concern not only for Clients 3257 located on the open Internet but also for Clients in secured 3258 enclaves. AERO Servers and Proxys can institute rate limits that 3259 protect Clients from receiving packet floods that could DoS low data 3260 rate links. 3262 AERO Relays must implement ingress filtering to avoid a spoofing 3263 attack in which spurious messages with ULA addresses are injected 3264 into an OMNI link from an outside attacker. AERO Clients MUST ensure 3265 that their connectivity is not used by unauthorized nodes on their 3266 EUNs to gain access to a protected network, i.e., AERO Clients that 3267 act as routers MUST NOT provide routing services for unauthorized 3268 nodes. (This concern is no different than for ordinary hosts that 3269 receive an IP address delegation but then "share" the address with 3270 other nodes via some form of Internet connection sharing such as 3271 tethering.) 3273 The MAP list MUST be well-managed and secured from unauthorized 3274 tampering, even though the list contains only public information. 3275 The MAP list can be conveyed to the Client in a similar fashion as in 3276 [RFC5214] (e.g., through layer 2 data link login messaging, secure 3277 upload of a static file, DNS lookups, etc.). 3279 SRH authentication facilities are specified in [RFC8754]. 3281 Security considerations for accepting link-layer ICMP messages and 3282 reflected packets are discussed throughout the document. 3284 Security considerations for IPv6 fragmentation and reassembly are 3285 discussed in [I-D.templin-6man-omni-interface]. 3287 7. Acknowledgements 3289 Discussions in the IETF, aviation standards communities and private 3290 exchanges helped shape some of the concepts in this work. 3291 Individuals who contributed insights include Mikael Abrahamsson, Mark 3292 Andrews, Fred Baker, Bob Braden, Stewart Bryant, Brian Carpenter, 3293 Wojciech Dec, Pavel Drasil, Ralph Droms, Adrian Farrel, Nick Green, 3294 Sri Gundavelli, Brian Haberman, Bernhard Haindl, Joel Halpern, Tom 3295 Herbert, Sascha Hlusiak, Lee Howard, Zdenek Jaron, Andre Kostur, 3296 Hubert Kuenig, Ted Lemon, Andy Malis, Satoru Matsushima, Tomek 3297 Mrugalski, Madhu Niraula, Alexandru Petrescu, Behcet Saikaya, Michal 3298 Skorepa, Joe Touch, Bernie Volz, Ryuji Wakikawa, Tony Whyman, Lloyd 3299 Wood and James Woodyatt. Members of the IESG also provided valuable 3300 input during their review process that greatly improved the document. 3301 Special thanks go to Stewart Bryant, Joel Halpern and Brian Haberman 3302 for their shepherding guidance during the publication of the AERO 3303 first edition. 3305 This work has further been encouraged and supported by Boeing 3306 colleagues including Kyle Bae, M. Wayne Benson, Dave Bernhardt, Cam 3307 Brodie, John Bush, Balaguruna Chidambaram, Irene Chin, Bruce Cornish, 3308 Claudiu Danilov, Don Dillenburg, Joe Dudkowski, Wen Fang, Samad 3309 Farooqui, Anthony Gregory, Jeff Holland, Seth Jahne, Brian Jaury, 3310 Greg Kimberly, Ed King, Madhuri Madhava Badgandi, Laurel Matthew, 3311 Gene MacLean III, Rob Muszkiewicz, Sean O'Sullivan, Vijay 3312 Rajagopalan, Greg Saccone, Rod Santiago, Kent Shuey, Brian Skeen, 3313 Mike Slane, Carrie Spiker, Katie Tran, Brendan Williams, Amelia 3314 Wilson, Julie Wulff, Yueli Yang, Eric Yeh and other members of the 3315 Boeing mobility, networking and autonomy teams. Kyle Bae, Wayne 3316 Benson, Katie Tran and Eric Yeh are especially acknowledged for 3317 implementing the AERO functions as extensions to the public domain 3318 OpenVPN distribution. 3320 Earlier works on NBMA tunneling approaches are found in 3321 [RFC2529][RFC5214][RFC5569]. 3323 Many of the constructs presented in this second edition of AERO are 3324 based on the author's earlier works, including: 3326 o The Internet Routing Overlay Network (IRON) 3327 [RFC6179][I-D.templin-ironbis] 3329 o Virtual Enterprise Traversal (VET) 3330 [RFC5558][I-D.templin-intarea-vet] 3332 o The Subnetwork Encapsulation and Adaptation Layer (SEAL) 3333 [RFC5320][I-D.templin-intarea-seal] 3335 o AERO, First Edition [RFC6706] 3337 Note that these works cite numerous earlier efforts that are not also 3338 cited here due to space limitations. The authors of those earlier 3339 works are acknowledged for their insights. 3341 This work is aligned with the NASA Safe Autonomous Systems Operation 3342 (SASO) program under NASA contract number NNA16BD84C. 3344 This work is aligned with the FAA as per the SE2025 contract number 3345 DTFAWA-15-D-00030. 3347 This work is aligned with the Boeing Commercial Airplanes (BCA) 3348 Internet of Things (IoT) and autonomy programs. 3350 This work is aligned with the Boeing Information Technology (BIT) 3351 MobileNet program. 3353 8. References 3355 8.1. Normative References 3357 [I-D.templin-6man-omni-interface] 3358 Templin, F. and T. Whyman, "Transmission of IP Packets 3359 over Overlay Multilink Network (OMNI) Interfaces", draft- 3360 templin-6man-omni-interface-66 (work in progress), 3361 December 2020. 3363 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, 3364 DOI 10.17487/RFC0791, September 1981, 3365 . 3367 [RFC0792] Postel, J., "Internet Control Message Protocol", STD 5, 3368 RFC 792, DOI 10.17487/RFC0792, September 1981, 3369 . 3371 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 3372 Requirement Levels", BCP 14, RFC 2119, 3373 DOI 10.17487/RFC2119, March 1997, 3374 . 3376 [RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in 3377 IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473, 3378 December 1998, . 3380 [RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander, 3381 "SEcure Neighbor Discovery (SEND)", RFC 3971, 3382 DOI 10.17487/RFC3971, March 2005, 3383 . 3385 [RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)", 3386 RFC 3972, DOI 10.17487/RFC3972, March 2005, 3387 . 3389 [RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and 3390 More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191, 3391 November 2005, . 3393 [RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast 3394 Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005, 3395 . 3397 [RFC4380] Huitema, C., "Teredo: Tunneling IPv6 over UDP through 3398 Network Address Translations (NATs)", RFC 4380, 3399 DOI 10.17487/RFC4380, February 2006, 3400 . 3402 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 3403 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 3404 DOI 10.17487/RFC4861, September 2007, 3405 . 3407 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 3408 Address Autoconfiguration", RFC 4862, 3409 DOI 10.17487/RFC4862, September 2007, 3410 . 3412 [RFC6081] Thaler, D., "Teredo Extensions", RFC 6081, 3413 DOI 10.17487/RFC6081, January 2011, 3414 . 3416 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 3417 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 3418 May 2017, . 3420 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 3421 (IPv6) Specification", STD 86, RFC 8200, 3422 DOI 10.17487/RFC8200, July 2017, 3423 . 3425 [RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A., 3426 Richardson, M., Jiang, S., Lemon, T., and T. Winters, 3427 "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", 3428 RFC 8415, DOI 10.17487/RFC8415, November 2018, 3429 . 3431 8.2. Informative References 3433 [BGP] Huston, G., "BGP in 2015, http://potaroo.net", January 3434 2016. 3436 [I-D.bonica-6man-comp-rtg-hdr] 3437 Bonica, R., Kamite, Y., Alston, A., Henriques, D., and L. 3438 Jalil, "The IPv6 Compact Routing Header (CRH)", draft- 3439 bonica-6man-comp-rtg-hdr-23 (work in progress), October 3440 2020. 3442 [I-D.bonica-6man-crh-helper-opt] 3443 Li, X., Bao, C., Ruan, E., and R. Bonica, "Compressed 3444 Routing Header (CRH) Helper Option", draft-bonica-6man- 3445 crh-helper-opt-02 (work in progress), October 2020. 3447 [I-D.ietf-intarea-frag-fragile] 3448 Bonica, R., Baker, F., Huston, G., Hinden, R., Troan, O., 3449 and F. Gont, "IP Fragmentation Considered Fragile", draft- 3450 ietf-intarea-frag-fragile-17 (work in progress), September 3451 2019. 3453 [I-D.ietf-intarea-tunnels] 3454 Touch, J. and M. Townsley, "IP Tunnels in the Internet 3455 Architecture", draft-ietf-intarea-tunnels-10 (work in 3456 progress), September 2019. 3458 [I-D.ietf-ipwave-vehicular-networking] 3459 Jeong, J., "IPv6 Wireless Access in Vehicular Environments 3460 (IPWAVE): Problem Statement and Use Cases", draft-ietf- 3461 ipwave-vehicular-networking-19 (work in progress), July 3462 2020. 3464 [I-D.ietf-rtgwg-atn-bgp] 3465 Templin, F., Saccone, G., Dawra, G., Lindem, A., and V. 3466 Moreno, "A Simple BGP-based Mobile Routing System for the 3467 Aeronautical Telecommunications Network", draft-ietf- 3468 rtgwg-atn-bgp-09 (work in progress), December 2020. 3470 [I-D.templin-6man-dhcpv6-ndopt] 3471 Templin, F., "A Unified Stateful/Stateless Configuration 3472 Service for IPv6", draft-templin-6man-dhcpv6-ndopt-10 3473 (work in progress), June 2020. 3475 [I-D.templin-intarea-seal] 3476 Templin, F., "The Subnetwork Encapsulation and Adaptation 3477 Layer (SEAL)", draft-templin-intarea-seal-68 (work in 3478 progress), January 2014. 3480 [I-D.templin-intarea-vet] 3481 Templin, F., "Virtual Enterprise Traversal (VET)", draft- 3482 templin-intarea-vet-40 (work in progress), May 2013. 3484 [I-D.templin-ipwave-uam-its] 3485 Templin, F., "Urban Air Mobility Implications for 3486 Intelligent Transportation Systems", draft-templin-ipwave- 3487 uam-its-03 (work in progress), July 2020. 3489 [I-D.templin-ironbis] 3490 Templin, F., "The Interior Routing Overlay Network 3491 (IRON)", draft-templin-ironbis-16 (work in progress), 3492 March 2014. 3494 [I-D.templin-v6ops-pdhost] 3495 Templin, F., "IPv6 Prefix Delegation and Multi-Addressing 3496 Models", draft-templin-v6ops-pdhost-26 (work in progress), 3497 June 2020. 3499 [OVPN] OpenVPN, O., "http://openvpn.net", October 2016. 3501 [RFC1035] Mockapetris, P., "Domain names - implementation and 3502 specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, 3503 November 1987, . 3505 [RFC1812] Baker, F., Ed., "Requirements for IP Version 4 Routers", 3506 RFC 1812, DOI 10.17487/RFC1812, June 1995, 3507 . 3509 [RFC2003] Perkins, C., "IP Encapsulation within IP", RFC 2003, 3510 DOI 10.17487/RFC2003, October 1996, 3511 . 3513 [RFC2004] Perkins, C., "Minimal Encapsulation within IP", RFC 2004, 3514 DOI 10.17487/RFC2004, October 1996, 3515 . 3517 [RFC2236] Fenner, W., "Internet Group Management Protocol, Version 3518 2", RFC 2236, DOI 10.17487/RFC2236, November 1997, 3519 . 3521 [RFC2464] Crawford, M., "Transmission of IPv6 Packets over Ethernet 3522 Networks", RFC 2464, DOI 10.17487/RFC2464, December 1998, 3523 . 3525 [RFC2529] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4 3526 Domains without Explicit Tunnels", RFC 2529, 3527 DOI 10.17487/RFC2529, March 1999, 3528 . 3530 [RFC2983] Black, D., "Differentiated Services and Tunnels", 3531 RFC 2983, DOI 10.17487/RFC2983, October 2000, 3532 . 3534 [RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition 3535 of Explicit Congestion Notification (ECN) to IP", 3536 RFC 3168, DOI 10.17487/RFC3168, September 2001, 3537 . 3539 [RFC3330] IANA, "Special-Use IPv4 Addresses", RFC 3330, 3540 DOI 10.17487/RFC3330, September 2002, 3541 . 3543 [RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener 3544 Discovery Version 2 (MLDv2) for IPv6", RFC 3810, 3545 DOI 10.17487/RFC3810, June 2004, 3546 . 3548 [RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally 3549 Unique IDentifier (UUID) URN Namespace", RFC 4122, 3550 DOI 10.17487/RFC4122, July 2005, 3551 . 3553 [RFC4251] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH) 3554 Protocol Architecture", RFC 4251, DOI 10.17487/RFC4251, 3555 January 2006, . 3557 [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A 3558 Border Gateway Protocol 4 (BGP-4)", RFC 4271, 3559 DOI 10.17487/RFC4271, January 2006, 3560 . 3562 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 3563 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 3564 2006, . 3566 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 3567 Internet Protocol", RFC 4301, DOI 10.17487/RFC4301, 3568 December 2005, . 3570 [RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery 3571 Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April 3572 2006, . 3574 [RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet 3575 Control Message Protocol (ICMPv6) for the Internet 3576 Protocol Version 6 (IPv6) Specification", STD 89, 3577 RFC 4443, DOI 10.17487/RFC4443, March 2006, 3578 . 3580 [RFC4511] Sermersheim, J., Ed., "Lightweight Directory Access 3581 Protocol (LDAP): The Protocol", RFC 4511, 3582 DOI 10.17487/RFC4511, June 2006, 3583 . 3585 [RFC4541] Christensen, M., Kimball, K., and F. Solensky, 3586 "Considerations for Internet Group Management Protocol 3587 (IGMP) and Multicast Listener Discovery (MLD) Snooping 3588 Switches", RFC 4541, DOI 10.17487/RFC4541, May 2006, 3589 . 3591 [RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick, 3592 "Internet Group Management Protocol (IGMP) / Multicast 3593 Listener Discovery (MLD)-Based Multicast Forwarding 3594 ("IGMP/MLD Proxying")", RFC 4605, DOI 10.17487/RFC4605, 3595 August 2006, . 3597 [RFC4982] Bagnulo, M. and J. Arkko, "Support for Multiple Hash 3598 Algorithms in Cryptographically Generated Addresses 3599 (CGAs)", RFC 4982, DOI 10.17487/RFC4982, July 2007, 3600 . 3602 [RFC5015] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano, 3603 "Bidirectional Protocol Independent Multicast (BIDIR- 3604 PIM)", RFC 5015, DOI 10.17487/RFC5015, October 2007, 3605 . 3607 [RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site 3608 Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214, 3609 DOI 10.17487/RFC5214, March 2008, 3610 . 3612 [RFC5320] Templin, F., Ed., "The Subnetwork Encapsulation and 3613 Adaptation Layer (SEAL)", RFC 5320, DOI 10.17487/RFC5320, 3614 February 2010, . 3616 [RFC5522] Eddy, W., Ivancic, W., and T. Davis, "Network Mobility 3617 Route Optimization Requirements for Operational Use in 3618 Aeronautics and Space Exploration Mobile Networks", 3619 RFC 5522, DOI 10.17487/RFC5522, October 2009, 3620 . 3622 [RFC5558] Templin, F., Ed., "Virtual Enterprise Traversal (VET)", 3623 RFC 5558, DOI 10.17487/RFC5558, February 2010, 3624 . 3626 [RFC5569] Despres, R., "IPv6 Rapid Deployment on IPv4 3627 Infrastructures (6rd)", RFC 5569, DOI 10.17487/RFC5569, 3628 January 2010, . 3630 [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 3631 (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, 3632 . 3634 [RFC6106] Jeong, J., Park, S., Beloeil, L., and S. Madanapalli, 3635 "IPv6 Router Advertisement Options for DNS Configuration", 3636 RFC 6106, DOI 10.17487/RFC6106, November 2010, 3637 . 3639 [RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful 3640 NAT64: Network Address and Protocol Translation from IPv6 3641 Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146, 3642 April 2011, . 3644 [RFC6179] Templin, F., Ed., "The Internet Routing Overlay Network 3645 (IRON)", RFC 6179, DOI 10.17487/RFC6179, March 2011, 3646 . 3648 [RFC6221] Miles, D., Ed., Ooghe, S., Dec, W., Krishnan, S., and A. 3649 Kavanagh, "Lightweight DHCPv6 Relay Agent", RFC 6221, 3650 DOI 10.17487/RFC6221, May 2011, 3651 . 3653 [RFC6273] Kukec, A., Krishnan, S., and S. Jiang, "The Secure 3654 Neighbor Discovery (SEND) Hash Threat Analysis", RFC 6273, 3655 DOI 10.17487/RFC6273, June 2011, 3656 . 3658 [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer 3659 Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, 3660 January 2012, . 3662 [RFC6355] Narten, T. and J. Johnson, "Definition of the UUID-Based 3663 DHCPv6 Unique Identifier (DUID-UUID)", RFC 6355, 3664 DOI 10.17487/RFC6355, August 2011, 3665 . 3667 [RFC6438] Carpenter, B. and S. Amante, "Using the IPv6 Flow Label 3668 for Equal Cost Multipath Routing and Link Aggregation in 3669 Tunnels", RFC 6438, DOI 10.17487/RFC6438, November 2011, 3670 . 3672 [RFC6706] Templin, F., Ed., "Asymmetric Extended Route Optimization 3673 (AERO)", RFC 6706, DOI 10.17487/RFC6706, August 2012, 3674 . 3676 [RFC6935] Eubanks, M., Chimento, P., and M. Westerlund, "IPv6 and 3677 UDP Checksums for Tunneled Packets", RFC 6935, 3678 DOI 10.17487/RFC6935, April 2013, 3679 . 3681 [RFC6936] Fairhurst, G. and M. Westerlund, "Applicability Statement 3682 for the Use of IPv6 UDP Datagrams with Zero Checksums", 3683 RFC 6936, DOI 10.17487/RFC6936, April 2013, 3684 . 3686 [RFC7333] Chan, H., Ed., Liu, D., Seite, P., Yokota, H., and J. 3687 Korhonen, "Requirements for Distributed Mobility 3688 Management", RFC 7333, DOI 10.17487/RFC7333, August 2014, 3689 . 3691 [RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I., 3692 Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent 3693 Multicast - Sparse Mode (PIM-SM): Protocol Specification 3694 (Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March 3695 2016, . 3697 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 3698 Decraene, B., Litkowski, S., and R. Shakir, "Segment 3699 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 3700 July 2018, . 3702 [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol 3703 Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, 3704 . 3706 [RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J., 3707 Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header 3708 (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020, 3709 . 3711 [WG] Wireguard, "Wireguard, https://www.wireguard.com", August 3712 2020. 3714 Appendix A. Non-Normative Considerations 3716 AERO can be applied to a multitude of Internetworking scenarios, with 3717 each having its own adaptations. The following considerations are 3718 provided as non-normative guidance: 3720 A.1. Implementation Strategies for Route Optimization 3722 Route optimization as discussed in Section 3.14 results in the route 3723 optimization source (ROS) creating an asymmetric neighbor cache entry 3724 for the target neighbor. The neighbor cache entry is maintained for 3725 at most ReachableTime seconds and then deleted unless updated. In 3726 order to refresh the neighbor cache entry lifetime before the 3727 ReachableTime timer expires, the specification requires 3728 implementations to issue a new NS/NA exchange to reset ReachableTime 3729 while data packets are still flowing. However, the decision of when 3730 to initiate a new NS/NA exchange and to perpetuate the process is 3731 left as an implementation detail. 3733 One possible strategy may be to monitor the neighbor cache entry 3734 watching for data packets for (ReachableTime - 5) seconds. If any 3735 data packets have been sent to the neighbor within this timeframe, 3736 then send an NS to receive a new NA. If no data packets have been 3737 sent, wait for 5 additional seconds and send an immediate NS if any 3738 data packets are sent within this "expiration pending" 5 second 3739 window. If no additional data packets are sent within the 5 second 3740 window, delete the neighbor cache entry. 3742 The monitoring of the neighbor data packet traffic therefore becomes 3743 an asymmetric ongoing process during the neighbor cache entry 3744 lifetime. If the neighbor cache entry expires, future data packets 3745 will trigger a new NS/NA exchange while the packets themselves are 3746 delivered over a longer path until route optimization state is re- 3747 established. 3749 A.2. Implicit Mobility Management 3751 OMNI interface neighbors MAY provide a configuration option that 3752 allows them to perform implicit mobility management in which no ND 3753 messaging is used. In that case, the Client only transmits packets 3754 over a single interface at a time, and the neighbor always observes 3755 packets arriving from the Client from the same link-layer source 3756 address. 3758 If the Client's underlying interface address changes (either due to a 3759 readdressing of the original interface or switching to a new 3760 interface) the neighbor immediately updates the neighbor cache entry 3761 for the Client and begins accepting and sending packets according to 3762 the Client's new address. This implicit mobility method applies to 3763 use cases such as cellphones with both WiFi and Cellular interfaces 3764 where only one of the interfaces is active at a given time, and the 3765 Client automatically switches over to the backup interface if the 3766 primary interface fails. 3768 A.3. Direct Underlying Interfaces 3770 When a Client's OMNI interface is configured over a Direct interface, 3771 the neighbor at the other end of the Direct link can receive packets 3772 without any encapsulation. In that case, the Client sends packets 3773 over the Direct link according to QoS preferences. If the Direct 3774 interface has the highest QoS preference, then the Client's IP 3775 packets are transmitted directly to the peer without going through an 3776 ANET/INET. If other interfaces have higher QoS preferences, then the 3777 Client's IP packets are transmitted via a different interface, which 3778 may result in the inclusion of Proxys, Servers and Bridges in the 3779 communications path. Direct interfaces must be tested periodically 3780 for reachability, e.g., via NUD. 3782 A.4. AERO Critical Infrastructure Considerations 3784 AERO Bridges can be either Commercial off-the Shelf (COTS) standard 3785 IP routers or virtual machines in the cloud. Bridges must be 3786 provisioned, supported and managed by the INET administrative 3787 authority, and connected to the Bridges of other INETs via inter- 3788 domain peerings. Cost for purchasing, configuring and managing 3789 Bridges is nominal even for very large OMNI links. 3791 AERO Servers can be standard dedicated server platforms, but most 3792 often will be deployed as virtual machines in the cloud. The only 3793 requirements for Servers are that they can run the AERO user-level 3794 code and have at least one network interface connection to the INET. 3795 As with Bridges, Servers must be provisioned, supported and managed 3796 by the INET administrative authority. Cost for purchasing, 3797 configuring and managing Servers is nominal especially for virtual 3798 Servers hosted in the cloud. 3800 AERO Proxys are most often standard dedicated server platforms with 3801 one network interface connected to the ANET and a second interface 3802 connected to an INET. As with Servers, the only requirements are 3803 that they can run the AERO user-level code and have at least one 3804 interface connection to the INET. Proxys must be provisioned, 3805 supported and managed by the ANET administrative authority. Cost for 3806 purchasing, configuring and managing Proxys is nominal, and borne by 3807 the ANET administrative authority. 3809 AERO Relays can be any dedicated server or COTS router platform 3810 connected to INETs and/or EUNs. The Relay connects to the OMNI link 3811 and engages in eBGP peering with one or more Bridges as a stub AS. 3812 The Relay then injects its MNPs and/or non-MNP prefixes into the BGP 3813 routing system, and provisions the prefixes to its downstream- 3814 attached networks. The Relay can perform ROS/ROR services the same 3815 as for any Server, and can route between the MNP and non-MNP address 3816 spaces. 3818 A.5. AERO Server Failure Implications 3820 AERO Servers may appear as a single point of failure in the 3821 architecture, but such is not the case since all Servers on the link 3822 provide identical services and loss of a Server does not imply 3823 immediate and/or comprehensive communication failures. Although 3824 Clients typically associate with a single Server at a time, Server 3825 failure is quickly detected and conveyed by Bidirectional Forward 3826 Detection (BFD) and/or proactive NUD allowing Clients to migrate to 3827 new Servers. 3829 If a Server fails, ongoing packet forwarding to Clients will continue 3830 by virtue of the asymmetric neighbor cache entries that have already 3831 been established in route optimization sources (ROSs). If a Client 3832 also experiences mobility events at roughly the same time the Server 3833 fails, unsolicited NA messages may be lost but proxy neighbor cache 3834 entries in the DEPARTED state will ensure that packet forwarding to 3835 the Client's new locations will continue for up to DepartTime 3836 seconds. 3838 If a Client is left without a Server for an extended timeframe (e.g., 3839 greater than ReachableTime seconds) then existing asymmetric neighbor 3840 cache entries will eventually expire and both ongoing and new 3841 communications will fail. The original source will continue to 3842 retransmit until the Client has established a new Server 3843 relationship, after which time continuous communications will resume. 3845 Therefore, providing many Servers on the link with high availability 3846 profiles provides resilience against loss of individual Servers and 3847 assurance that Clients can establish new Server relationships quickly 3848 in event of a Server failure. 3850 A.6. AERO Client / Server Architecture 3852 The AERO architectural model is client / server in the control plane, 3853 with route optimization in the data plane. The same as for common 3854 Internet services, the AERO Client discovers the addresses of AERO 3855 Servers and selects one Server to connect to. The AERO service is 3856 analogous to common Internet services such as google.com, yahoo.com, 3857 cnn.com, etc. However, there is only one AERO service for the link 3858 and all Servers provide identical services. 3860 Common Internet services provide differing strategies for advertising 3861 server addresses to clients. The strategy is conveyed through the 3862 DNS resource records returned in response to name resolution queries. 3863 As of January 2020 Internet-based 'nslookup' services were used to 3864 determine the following: 3866 o When a client resolves the domainname "google.com", the DNS always 3867 returns one A record (i.e., an IPv4 address) and one AAAA record 3868 (i.e., an IPv6 address). The client receives the same addresses 3869 each time it resolves the domainname via the same DNS resolver, 3870 but may receive different addresses when it resolves the 3871 domainname via different DNS resolvers. But, in each case, 3872 exactly one A and one AAAA record are returned. 3874 o When a client resolves the domainname "ietf.org", the DNS always 3875 returns one A record and one AAAA record with the same addresses 3876 regardless of which DNS resolver is used. 3878 o When a client resolves the domainname "yahoo.com", the DNS always 3879 returns a list of 4 A records and 4 AAAA records. Each time the 3880 client resolves the domainname via the same DNS resolver, the same 3881 list of addresses are returned but in randomized order (i.e., 3882 consistent with a DNS round-robin strategy). But, interestingly, 3883 the same addresses are returned (albeit in randomized order) when 3884 the domainname is resolved via different DNS resolvers. 3886 o When a client resolves the domainname "amazon.com", the DNS always 3887 returns a list of 3 A records and no AAAA records. As with 3888 "yahoo.com", the same three A records are returned from any 3889 worldwide Internet connection point in randomized order. 3891 The above example strategies show differing approaches to Internet 3892 resilience and service distribution offered by major Internet 3893 services. The Google approach exposes only a single IPv4 and a 3894 single IPv6 address to clients. Clients can then select whichever IP 3895 protocol version offers the best response, but will always use the 3896 same IP address according to the current Internet connection point. 3897 This means that the IP address offered by the network must lead to a 3898 highly-available server and/or service distribution point. In other 3899 words, resilience is predicated on high availability within the 3900 network and with no client-initiated failovers expected (i.e., it is 3901 all-or-nothing from the client's perspective). However, Google does 3902 provide for worldwide distributed service distribution by virtue of 3903 the fact that each Internet connection point responds with a 3904 different IPv6 and IPv4 address. The IETF approach is like google 3905 (all-or-nothing from the client's perspective), but provides only a 3906 single IPv4 or IPv6 address on a worldwide basis. This means that 3907 the addresses must be made highly-available at the network level with 3908 no client failover possibility, and if there is any worldwide service 3909 distribution it would need to be conducted by a network element that 3910 is reached via the IP address acting as a service distribution point. 3912 In contrast to the Google and IETF philosophies, Yahoo and Amazon 3913 both provide clients with a (short) list of IP addresses with Yahoo 3914 providing both IP protocol versions and Amazon as IPv4-only. The 3915 order of the list is randomized with each name service query 3916 response, with the effect of round-robin load balancing for service 3917 distribution. With a short list of addresses, there is still 3918 expectation that the network will implement high availability for 3919 each address but in case any single address fails the client can 3920 switch over to using a different address. The balance then becomes 3921 one of function in the network vs function in the end system. 3923 The same implications observed for common highly-available services 3924 in the Internet apply also to the AERO client/server architecture. 3925 When an AERO Client connects to one or more ANETs, it discovers one 3926 or more AERO Server addresses through the mechanisms discussed in 3927 earlier sections. Each Server address presumably leads to a fault- 3928 tolerant clustering arrangement such as supported by Linux-HA, 3929 Extended Virtual Synchrony or Paxos. Such an arrangement has 3930 precedence in common Internet service deployments in lightweight 3931 virtual machines without requiring expensive hardware deployment. 3932 Similarly, common Internet service deployments set service IP 3933 addresses on service distribution points that may relay requests to 3934 many different servers. 3936 For AERO, the expectation is that a combination of the Google/IETF 3937 and Yahoo/Amazon philosophies would be employed. The AERO Client 3938 connects to different ANET access points and can receive 1-2 Server 3939 ADM-LLAs at each point. It then selects one AERO Server address, and 3940 engages in RS/RA exchanges with the same Server from all ANET 3941 connections. The Client remains with this Server unless or until the 3942 Server fails, in which case it can switch over to an alternate 3943 Server. The Client can likewise switch over to a different Server at 3944 any time if there is some reason for it to do so. So, the AERO 3945 expectation is for a balance of function in the network and end 3946 system, with fault tolerance and resilience at both levels. 3948 Appendix B. Change Log 3950 << RFC Editor - remove prior to publication >> 3952 Changes from draft-templin-intarea-6706bis-61 to draft-templin- 3953 intrea-6706bis-62: 3955 o New sub-section on OMNI Neighbor Interface Attributes 3957 Changes from draft-templin-intarea-6706bis-59 to draft-templin- 3958 intrea-6706bis-60: 3960 o Removed all references to S/TLLAO - all Interface Attributes are 3961 now maintained completely in the OMNI option. 3963 Changes from draft-templin-intarea-6706bis-58 to draft-templin- 3964 intrea-6706bis-59: 3966 o The term "Relay" used in older draft versions is now "Bridge". 3967 "Relay" now refers to what was formally called: "Gateway". 3969 o Fine-grained cleanup of Forwarding Algorithm; IPv6 ND message 3970 addressing; OMNI Prefix Lengths, etc. 3972 Changes from draft-templin-intarea-6706bis-54 to draft-templin- 3973 intrea-6706bis-55: 3975 o Updates on Segment Routing and S/TLLAO contents. 3977 o Various editorials and addressing cleanups. 3979 Changes from draft-templin-intarea-6706bis-52 to draft-templin- 3980 intrea-6706bis-53: 3982 o Normative reference to the OMNI spec, and remove portions that are 3983 already specified in OMNI. 3985 o Renamed "AERO interface/link" to "OMIN interface/link" throughout 3986 the document. 3988 o Truncated obsolete back section matter. 3990 Author's Address 3992 Fred L. Templin (editor) 3993 Boeing Research & Technology 3994 P.O. Box 3707 3995 Seattle, WA 98124 3996 USA 3998 Email: fltemplin@acm.org