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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, August 4, 2020 5 rfc6179, rfc6706 (if 6 approved) 7 Intended status: Standards Track 8 Expires: February 5, 2021 10 Asymmetric Extended Route Optimization (AERO) 11 draft-templin-intarea-6706bis-59 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 uses an IPv6 link-local address format that supports operation 19 of the IPv6 Neighbor Discovery (ND) protocol and links ND to IP 20 forwarding. Prefix delegation/registration services are employed for 21 network admission and to manage the routing system. Multilink 22 operation, mobility management, quality of service (QoS) signaling 23 and route optimization are naturally supported through dynamic 24 neighbor cache updates. Standard IP multicasting services are also 25 supported. AERO is a widely-applicable mobile internetworking 26 service especially well-suited to aviation services, intelligent 27 transportation systems, mobile Virtual Private Networks (VPNs) and 28 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 February 5, 2021. 47 Copyright Notice 49 Copyright (c) 2020 IETF Trust and the persons identified as the 50 document authors. All rights reserved. 52 This document is subject to BCP 78 and the IETF Trust's Legal 53 Provisions Relating to IETF Documents 54 (https://trustee.ietf.org/license-info) in effect on the date of 55 publication of this document. Please review these documents 56 carefully, as they describe your rights and restrictions with respect 57 to this document. Code Components extracted from this document must 58 include Simplified BSD License text as described in Section 4.e of 59 the Trust Legal Provisions and are provided without warranty as 60 described in the Simplified BSD License. 62 Table of Contents 64 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 65 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 66 3. Asymmetric Extended Route Optimization (AERO) . . . . . . . . 10 67 3.1. AERO Node Types . . . . . . . . . . . . . . . . . . . . . 10 68 3.2. The AERO Service over OMNI Links . . . . . . . . . . . . 11 69 3.2.1. AERO/OMNI Reference Model . . . . . . . . . . . . . . 11 70 3.2.2. Link-Local Addresses (LLAs) and Unique Local 71 Addresses (ULAs) . . . . . . . . . . . . . . . . . . 14 72 3.2.3. AERO Routing System . . . . . . . . . . . . . . . . . 15 73 3.2.4. AERO Encapsulation . . . . . . . . . . . . . . . . . 16 74 3.2.5. Segment Routing Topologies (SRTs) . . . . . . . . . . 18 75 3.2.6. Segment Routing To the OMNI Link . . . . . . . . . . 18 76 3.2.7. Segment Routing Within the OMNI Link . . . . . . . . 19 77 3.2.8. Segment Routing Header Compression . . . . . . . . . 21 78 3.3. OMNI Interface Characteristics . . . . . . . . . . . . . 21 79 3.4. OMNI Interface Initialization . . . . . . . . . . . . . . 25 80 3.4.1. AERO Server/Relay Behavior . . . . . . . . . . . . . 25 81 3.4.2. AERO Proxy Behavior . . . . . . . . . . . . . . . . . 26 82 3.4.3. AERO Client Behavior . . . . . . . . . . . . . . . . 26 83 3.4.4. AERO Bridge Behavior . . . . . . . . . . . . . . . . 26 84 3.5. OMNI Interface Neighbor Cache Maintenance . . . . . . . . 26 85 3.6. OMNI Interface Encapsulation and Re-encapsulation . . . . 28 86 3.7. OMNI Interface Decapsulation . . . . . . . . . . . . . . 30 87 3.8. OMNI Interface Data Origin Authentication . . . . . . . . 30 88 3.9. OMNI Interface MTU and Fragmentation . . . . . . . . . . 30 89 3.10. OMNI Interface Forwarding Algorithm . . . . . . . . . . . 30 90 3.10.1. Client Forwarding Algorithm . . . . . . . . . . . . 31 91 3.10.2. Proxy Forwarding Algorithm . . . . . . . . . . . . . 32 92 3.10.3. Server/Relay Forwarding Algorithm . . . . . . . . . 33 93 3.10.4. Bridge Forwarding Algorithm . . . . . . . . . . . . 34 94 3.11. OMNI Interface Error Handling . . . . . . . . . . . . . . 35 95 3.12. AERO Router Discovery, Prefix Delegation and 96 Autoconfiguration . . . . . . . . . . . . . . . . . . . . 37 97 3.12.1. AERO ND/PD Service Model . . . . . . . . . . . . . . 37 98 3.12.2. AERO Client Behavior . . . . . . . . . . . . . . . . 38 99 3.12.3. AERO Server Behavior . . . . . . . . . . . . . . . . 40 100 3.13. The AERO Proxy . . . . . . . . . . . . . . . . . . . . . 43 101 3.13.1. Servers Acting as Proxies . . . . . . . . . . . . . 45 102 3.13.2. Detecting and Responding to Server Failures . . . . 45 103 3.13.3. Point-to-Multipoint Server Coordination . . . . . . 46 104 3.14. AERO Route Optimization / Address Resolution . . . . . . 47 105 3.14.1. Route Optimization Initiation . . . . . . . . . . . 47 106 3.14.2. Relaying the NS . . . . . . . . . . . . . . . . . . 48 107 3.14.3. Processing the NS and Sending the NA . . . . . . . . 48 108 3.14.4. Relaying the NA . . . . . . . . . . . . . . . . . . 49 109 3.14.5. Processing the NA . . . . . . . . . . . . . . . . . 49 110 3.14.6. Route Optimization Maintenance . . . . . . . . . . . 49 111 3.15. Neighbor Unreachability Detection (NUD) . . . . . . . . . 50 112 3.16. Mobility Management and Quality of Service (QoS) . . . . 52 113 3.16.1. Mobility Update Messaging . . . . . . . . . . . . . 52 114 3.16.2. Announcing Link-Layer Address and/or QoS Preference 115 Changes . . . . . . . . . . . . . . . . . . . . . . 53 116 3.16.3. Bringing New Links Into Service . . . . . . . . . . 53 117 3.16.4. Removing Existing Links from Service . . . . . . . . 54 118 3.16.5. Moving to a New Server . . . . . . . . . . . . . . . 54 119 3.17. Multicast . . . . . . . . . . . . . . . . . . . . . . . . 55 120 3.17.1. Source-Specific Multicast (SSM) . . . . . . . . . . 55 121 3.17.2. Any-Source Multicast (ASM) . . . . . . . . . . . . . 57 122 3.17.3. Bi-Directional PIM (BIDIR-PIM) . . . . . . . . . . . 57 123 3.18. Operation over Multiple OMNI Links . . . . . . . . . . . 58 124 3.19. DNS Considerations . . . . . . . . . . . . . . . . . . . 58 125 3.20. Transition Considerations . . . . . . . . . . . . . . . . 59 126 3.21. Detecting and Reacting to Server and Bridge Failures . . 59 127 3.22. AERO Clients on the Open Internet . . . . . . . . . . . . 60 128 3.22.1. Use of SEND and CGA . . . . . . . . . . . . . . . . 62 129 3.23. Time-Varying MNPs . . . . . . . . . . . . . . . . . . . . 64 130 4. Implementation Status . . . . . . . . . . . . . . . . . . . . 64 131 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 64 132 6. Security Considerations . . . . . . . . . . . . . . . . . . . 65 133 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 67 134 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 68 135 8.1. Normative References . . . . . . . . . . . . . . . . . . 68 136 8.2. Informative References . . . . . . . . . . . . . . . . . 70 137 Appendix A. Non-Normative Considerations . . . . . . . . . . . . 75 138 A.1. Implementation Strategies for Route Optimization . . . . 75 139 A.2. Implicit Mobility Management . . . . . . . . . . . . . . 76 140 A.3. Direct Underlying Interfaces . . . . . . . . . . . . . . 76 141 A.4. AERO Critical Infrastructure Considerations . . . . . . . 76 142 A.5. AERO Server Failure Implications . . . . . . . . . . . . 77 143 A.6. AERO Client / Server Architecture . . . . . . . . . . . . 78 144 Appendix B. Change Log . . . . . . . . . . . . . . . . . . . . . 80 145 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 80 147 1. Introduction 149 Asymmetric Extended Route Optimization (AERO) fulfills the 150 requirements of Distributed Mobility Management (DMM) [RFC7333] and 151 route optimization [RFC5522] for aeronautical networking and other 152 network mobility use cases such as intelligent transportation 153 systems. AERO is an internetworking and mobility management service 154 based on the Overlay Multilink Network Interface (OMNI) 155 [I-D.templin-6man-omni-interface] Non-Broadcast, Multiple Access 156 (NBMA) virtual link model. The OMNI link is a virtual overlay 157 configured over one or more underlying Internetworks, and nodes on 158 the link can exchange IP packets via tunneling. Multilink operation 159 allows for increased reliability, bandwidth optimization and traffic 160 path diversity. 162 The AERO service comprises Clients, Proxys, Servers and Relays that 163 are seen as OMNI link neighbors as well as Bridges that interconnect 164 OMNI link segments. Each node's OMNI interface uses an IPv6 link- 165 local address format that supports operation of the IPv6 Neighbor 166 Discovery (ND) protocol [RFC4861] and links ND to IP forwarding. A 167 node's OMNI interface can be configured over multiple underlying 168 interfaces, and may therefore appear as a single interface with 169 multiple link-layer addresses. Each link-layer address is subject to 170 change due to mobility and/or QoS fluctuations, and link-layer 171 address changes are signaled by ND messaging the same as for any IPv6 172 link. 174 AERO provides a cloud-based service where mobile nodes may use any 175 Server acting as a Mobility Anchor Point (MAP) and fixed nodes may 176 use any Relay on the link for efficient communications. Fixed nodes 177 forward packets destined to other AERO nodes to the nearest Relay, 178 which forwards them through the cloud. A mobile node's initial 179 packets are forwarded through the Server, while direct routing is 180 supported through asymmetric extended route optimization while data 181 packets are flowing. Both unicast and multicast communications are 182 supported, and mobile nodes may efficiently move between locations 183 while maintaining continuous communications with correspondents and 184 without changing their IP Address. 186 AERO Bridges are interconnected in a secured private BGP overlay 187 routing instance using encapsulation to provide a hybrid routing/ 188 bridging service that joins the underlying Internetworks of multiple 189 disjoint administrative domains into a single unified OMNI link. 190 Each OMNI link instance is characterized by the set of Mobility 191 Service Prefixes (MSPs) common to all mobile nodes. The link extends 192 to the point where a Relay/Server is on the optimal route from any 193 correspondent node on the link, and provides a conduit between the 194 underlying Internetwork and the OMNI link. To the underlying 195 Internetwork, the Relay/Server is the source of a route to the MSP, 196 and hence uplink traffic to the mobile node is naturally routed to 197 the nearest Relay/Server. 199 AERO assumes the use of PIM Sparse Mode in support of multicast 200 communication. In support of Source Specific Multicast (SSM) when a 201 Mobile Node is the source, AERO route optimization ensures that a 202 shortest-path multicast tree is established with provisions for 203 mobility and multilink operation. In all other multicast scenarios 204 there are no AERO dependencies. 206 AERO was designed for aeronautical networking for both manned and 207 unmanned aircraft, where the aircraft is treated as a mobile node 208 that can connect an Internet of Things (IoT). AERO is also 209 applicable to a wide variety of other use cases. For example, it can 210 be used to coordinate the Virtual Private Network (VPN) links of 211 mobile nodes (e.g., cellphones, tablets, laptop computers, etc.) that 212 connect into a home enterprise network via public access networks 213 using services such as OpenVPN [OVPN]. It can also be used to 214 facilitate vehicular and pedestrian communications services for 215 intelligent transportation systems. Other applicable use cases are 216 also in scope. 218 The following numbered sections present the AERO specification. The 219 appendices at the end of the document are non-normative. 221 2. Terminology 223 The terminology in the normative references applies; especially, the 224 terminology in the OMNI specification 225 [I-D.templin-6man-omni-interface] is used extensively throughout. 226 The following terms are defined within the scope of this document: 228 IPv6 Neighbor Discovery (ND) 229 an IPv6 control message service for coordinating neighbor 230 relationships between nodes connected to a common link. AERO uses 231 the ND service specified in [RFC4861]. 233 IPv6 Prefix Delegation (PD) 234 a networking service for delegating IPv6 prefixes to nodes on the 235 link. The nominal PD service is DHCPv6 [RFC8415], however 236 alternate services (e.g., based on ND messaging) are also in 237 scope. Most notably, a minimal form of PD known as "prefix 238 registration" can be used if the Client knows its prefix in 239 advance and can represent it in the IPv6 source address of an ND 240 message. 242 Access Network (ANET) 243 a node's first-hop data link service network (e.g., a radio access 244 network, cellular service provider network, corporate enterprise 245 network, etc.) that often provides link-layer security services 246 such as IEEE 802.1X and physical-layer security prevent 247 unauthorized access internally and with border network-layer 248 security services such as firewalls and proxies that prevent 249 unauthorized outside access. 251 ANET interface 252 a node's attachment to a link in an ANET. 254 Internetwork (INET) 255 a connected IP network topology with a coherent routing and 256 addressing plan and that provides a transit backbone service for 257 ANET end systems. INETs also provide an underlay service over 258 which the AERO virtual link is configured. Example INETs include 259 corporate enterprise networks, aviation networks, and the public 260 Internet itself. When there is no administrative boundary between 261 an ANET and the INET, the ANET and INET are one and the same. 263 INET Partition 264 frequently, INETs such as large corporate enterprise networks are 265 sub-divided internally into separate isolated partitions. Each 266 partition is fully connected internally but disconnected from 267 other partitions, and there is no requirement that separate 268 partitions maintain consistent Internet Protocol and/or addressing 269 plans. (Each INET partition is seen as a separate OMNI link 270 segment as discussed below.) 272 INET interface 273 a node's attachment to a link in an INET. 275 INET address 276 an IP address assigned to a node's interface connection to an 277 INET. 279 INET encapsulation 280 the encapsulation of a packet in an outer header or headers that 281 can be routed within the scope of the local INET partition. 283 OMNI link 284 the same as defined in [I-D.templin-6man-omni-interface], and 285 manifested by IPv6 encapsulation [RFC2473]. The OMNI link spans 286 underlying INET segments joined by virtual bridges in a spanning 287 tree the same as a bridged campus LAN. AERO nodes on the OMNI 288 link appear as single-hop neighbors even though they may be 289 separated by multiple underlying INET hops, and can use Segment 290 Routing [RFC8402] to cause packets to visit selected waypoints on 291 the link. 293 OMNI Interface 294 a node's attachment to an OMNI link. Since the addresses assigned 295 to an OMNI interface are managed for uniqueness, OMNI interfaces 296 do not require Duplicate Address Detection (DAD) and therefore set 297 the administrative variable 'DupAddrDetectTransmits' to zero 298 [RFC4862]. 300 OMNI Link-Local Address (LLA) 301 a link local IPv6 address per [RFC4291] constructed as specified 302 in Section 3.2.2. 304 OMNI Unique-Local Address (ULA) 305 a unique local IPv6 address per [RFC4193] constructed as specified 306 in Section 3.2.2. OMNI ULAs are statelessly derived from OMNI 307 LLAs, and vice-versa. 309 underlying interface 310 an ANET or INET interface over which an OMNI interface is 311 configured. 313 Mobility Service Prefix (MSP) 314 an IP prefix assigned to the OMNI link and from which more- 315 specific Mobile Network Prefixes (MNPs) are derived. 317 Mobile Network Prefix (MNP) 318 an IP prefix allocated from an MSP and delegated to an AERO Client 319 or Relay. 321 AERO node 322 a node that is connected to an OMNI link and participates in the 323 AERO internetworking and mobility service. 325 AERO Client ("Client") 326 an AERO node that connects over one or more underlying interfaces 327 and requests MNP PDs from AERO Servers. The Client assigns a 328 Client LLA to the OMNI interface for use in ND exchanges with 329 other AERO nodes and forwards packets to correspondents according 330 to OMNI interface neighbor cache state. 332 AERO Server ("Server") 333 an INET node that configures an OMNI interface to provide default 334 forwarding and mobility/multilink services for AERO Clients. The 335 Server assigns an administratively-provisioned LLA to its OMNI 336 interface to support the operation of the ND/PD services, and 337 advertises all of its associated MNPs via BGP peerings with 338 Bridges. 340 AERO Relay ("Relay") 341 an AERO Server that also provides forwarding services between 342 nodes reached via the OMNI link and correspondents on other links. 343 AERO Relays are provisioned with MNPs (i.e., the same as for an 344 AERO Client) and run a dynamic routing protocol to discover any 345 non-MNP IP routes. In both cases, the Relay advertises the MSP(s) 346 to its downstream networks, and distributes all of its associated 347 MNPs and non-MNP IP routes via BGP peerings with Bridges (i.e., 348 the same as for an AERO Server). 350 AERO Bridge ("Bridge") 351 a node that provides hybrid routing/bridging services (as well as 352 a security trust anchor) for nodes on an OMNI link. As a router, 353 the Bridge forwards packets using standard IP forwarding. As a 354 bridge, the Bridge forwards packets over the OMNI link without 355 decrementing the IPv6 Hop Limit. AERO Bridges peer with Servers 356 and other Bridges to discover the full set of MNPs for the link as 357 well as any non-MNPs that are reachable via Relays. 359 AERO Proxy ("Proxy") 360 a node that provides proxying services between Clients in an ANET 361 and Servers in external INETs. The AERO Proxy is a conduit 362 between the ANET and external INETs in the same manner as for 363 common web proxies, and behaves in a similar fashion as for ND 364 proxies [RFC4389]. 366 ingress tunnel endpoint (ITE) 367 an OMNI interface endpoint that injects encapsulated packets into 368 an OMNI link. 370 egress tunnel endpoint (ETE) 371 an OMNI interface endpoint that receives encapsulated packets from 372 an OMNI link. 374 link-layer address 375 an IP address used as an encapsulation header source or 376 destination address from the perspective of the OMNI interface. 377 When an upper layer protocol (e.g., UDP) is used as part of the 378 encapsulation, the port number is also considered as part of the 379 link-layer address. 381 network layer address 382 the source or destination address of an encapsulated IP packet 383 presented to the OMNI interface. 385 end user network (EUN) 386 an internal virtual or external edge IP network that an AERO 387 Client or Relay connects to the rest of the network via the OMNI 388 interface. The Client/Relay sees each EUN as a "downstream" 389 network, and sees the OMNI interface as the point of attachment to 390 the "upstream" network. 392 Mobile Node (MN) 393 an AERO Client and all of its downstream-attached networks that 394 move together as a single unit, i.e., an end system that connects 395 an Internet of Things. 397 Mobile Router (MR) 398 a MN's on-board router that forwards packets between any 399 downstream-attached networks and the OMNI link. 401 Route Optimization Source (ROS) 402 the AERO node nearest the source that initiates route 403 optimization. The ROS may be a Server or Proxy acting on behalf 404 of the source Client. 406 Route Optimization responder (ROR) 407 the AERO node nearest the target destination that responds to 408 route optimization requests. The ROR may be a Server acting on 409 behalf of a target MNP Client, or a Relay for a non-MNP 410 destination. 412 MAP List 413 a geographically and/or topologically referenced list of addresses 414 of all Servers within the same OMNI link. There is a single MAP 415 list for the entire OMNI link. 417 Distributed Mobility Management (DMM) 418 a BGP-based overlay routing service coordinated by Servers and 419 Bridges that tracks all Server-to-Client associations. 421 Mobility Service (MS) 422 the collective set of all Servers, Proxys, Bridges and Relays that 423 provide the AERO Service to Clients. 425 Mobility Service Endpoint MSE) 426 an individual Server, Proxy, Bridge or Relay in the Mobility 427 Service. 429 Throughout the document, the simple terms "Client", "Server", 430 "Bridge", "Proxy" and "Relay" refer to "AERO Client", "AERO Server", 431 "AERO Bridge", "AERO Proxy" and "AERO Relay", respectively. 432 Capitalization is used to distinguish these terms from other common 433 Internetworking uses in which they appear without capitalization. 435 The terminology of DHCPv6 [RFC8415] and IPv6 ND [RFC4861] (including 436 the names of node variables, messages and protocol constants) is used 437 throughout this document. The terms "All-Routers multicast", "All- 438 Nodes multicast", "Solicited-Node multicast" and "Subnet-Router 439 anycast" are defined in [RFC4291]. Also, the term "IP" is used to 440 generically refer to either Internet Protocol version, i.e., IPv4 441 [RFC0791] or IPv6 [RFC8200]. 443 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 444 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 445 "OPTIONAL" in this document are to be interpreted as described in BCP 446 14 [RFC2119][RFC8174] when, and only when, they appear in all 447 capitals, as shown here. 449 3. Asymmetric Extended Route Optimization (AERO) 451 The following sections specify the operation of IP over OMNI links 452 using the AERO service: 454 3.1. AERO Node Types 456 AERO Clients are Mobile Nodes (MNs) that connect via underlying 457 interfaces with addresses that may change when the Client moves to a 458 new network connection point. AERO Clients register their Mobile 459 Network Prefixes (MNPs) with the AERO service, and distribute the 460 MNPs to nodes on EUNs. AERO Bridges, Servers, Proxys and Relays are 461 critical infrastructure elements in fixed (i.e., non-mobile) INET 462 deployments and hence have permanent and unchanging INET addresses. 463 Together, they constitute the AERO service which provides an OMNI 464 link virtual overlay for connecting AERO Clients. 466 AERO Bridges provide hybrid routing/bridging services (as well as a 467 security trust anchor) for nodes on an OMNI link. Bridges use 468 standard IPv6 routing to forward packets both within the same INET 469 partitions and between disjoint INET partitions based on a mid-layer 470 IPv6 encapsulation per [RFC2473]. The inner IP layer experiences a 471 virtual bridging service since the inner IP TTL/Hop Limit is not 472 decremented during forwarding. Each Bridge also peers with Servers 473 and other Bridges in a dynamic routing protocol instance to provide a 474 Distributed Mobility Management (DMM) service for the list of active 475 MNPs (see Section 3.2.3). Bridges present the OMNI link as a set of 476 one or more Mobility Service Prefixes (MSPs) and configure secured 477 tunnels with Servers, Relays, Proxys and other Bridges; they further 478 maintain IP forwarding table entries for each MNP and any other 479 reachable non-MNP prefixes. 481 AERO Servers provide default forwarding and mobility/multilink 482 services for AERO Client Mobile Nodes (MNs). Each Server also peers 483 with Bridges in a dynamic routing protocol instance to advertise its 484 list of associated MNPs (see Section 3.2.3). Servers facilitate PD 485 exchanges with Clients, where each delegated prefix becomes an MNP 486 taken from an MSP. Servers forward packets between OMNI interface 487 neighbors and track each Client's mobility profiles. Servers may 488 further act as Servers for some sets of Clients and as Proxies for 489 others. 491 AERO Proxys provide a conduit for ANET Clients to associate with 492 Servers in external INETs. Client and Servers exchange control plane 493 messages via the Proxy acting as a bridge between the ANET/INET 494 boundary. The Proxy forwards data packets between Clients and the 495 OMNI link according to forwarding information in the neighbor cache. 496 The Proxy function is specified in Section 3.13. Proxys may further 497 act as Proxys for some sets of Clients and as Servers for others. 499 AERO Relays are Servers that provide forwarding services between the 500 OMNI interface and INET/EUN interfaces. Relays are provisioned with 501 MNPs the same as for an AERO Client, and also run a dynamic routing 502 protocol to discover any non-MNP IP routes. The Relay advertises the 503 MSP(s) to its connected networks, and distributes all of its 504 associated MNPs and non-MNP IP routes via BGP peerings with Bridges 506 3.2. The AERO Service over OMNI Links 508 3.2.1. AERO/OMNI Reference Model 510 Figure 1 presents the basic OMNI link reference model: 512 +----------------+ 513 | AERO Bridge B1 | 514 | Nbr: S1, S2, P1| 515 |(X1->S1; X2->S2)| 516 | MSP M1 | 517 +-+---------+--+-+ 518 +--------------+ | Secured | | +--------------+ 519 |AERO Server S1| | tunnels | | |AERO Server S2| 520 | Nbr: C1, B1 +-----+ | +-----+ Nbr: C2, B1 | 521 | default->B1 | | | default->B1 | 522 | X1->C1 | | | X2->C2 | 523 +-------+------+ | +------+-------+ 524 | OMNI link | | 525 X===+===+===================+==)===============+===+===X 526 | | | | 527 +-----+--------+ +--------+--+-----+ +--------+-----+ 528 |AERO Client C1| | AERO Proxy P1 | |AERO Client C2| 529 | Nbr: S1 | |(Proxy Nbr Cache)| | Nbr: S2 | 530 | default->S1 | +--------+--------+ | default->S2 | 531 | MNP X1 | | | MNP X2 | 532 +------+-------+ .--------+------. +-----+--------+ 533 | (- Proxyed Clients -) | 534 .-. `---------------' .-. 535 ,-( _)-. ,-( _)-. 536 .-(_ IP )-. +-------+ +-------+ .-(_ IP )-. 537 (__ EUN )--|Host H1| |Host H2|--(__ EUN ) 538 `-(______)-' +-------+ +-------+ `-(______)-' 540 Figure 1: AERO/OMNI Reference Model 542 In this model: 544 o the OMNI link is an overlay network service configured over one or 545 more underlying INET partitions which may be managed by different 546 administrative authorities and have incompatible protocols and/or 547 addressing plans. 549 o AERO Bridge B1 aggregates Mobility Service Prefix (MSP) M1, 550 discovers Mobile Network Prefixes (MNPs) X* and advertises the MSP 551 via BGP peerings over secured tunnels to Servers (S1, S2). 552 Bridges connect the disjoint segments of a partitioned OMNI link. 554 o AERO Servers/Relays S1 and S2 configure secured tunnels with 555 Bridge B1 and also provide mobility, multilink and default router 556 services for their associated Clients C1 and C2. 558 o AERO Clients C1 and C2 associate with Servers S1 and S2, 559 respectively. They receive Mobile Network Prefix (MNP) 560 delegations X1 and X2, and also act as default routers for their 561 associated physical or internal virtual EUNs. Simple hosts H1 and 562 H2 attach to the EUNs served by Clients C1 and C2, respectively. 564 o AERO Proxy P1 configures a secured tunnel with Bridge B1 and 565 provides proxy services for AERO Clients in secured enclaves that 566 cannot associate directly with other OMNI link neighbors. 568 An OMNI link configured over a single INET appears as a single 569 unified link with a consistent underlying network addressing plan. 570 In that case, all nodes on the link can exchange packets via simple 571 INET encapsulation, since the underlying INET is connected. In 572 common practice, however, an OMNI link may be partitioned into 573 multiple "segments", where each segment is a distinct INET 574 potentially managed under a different administrative authority (e.g., 575 as for worldwide aviation service providers such as ARINC, SITA, 576 Inmarsat, etc.). Individual INETs may also themselves be partitioned 577 internally, in which case each internal partition is seen as a 578 separate segment. 580 The addressing plan of each segment is consistent internally but will 581 often bear no relation to the addressing plans of other segments. 582 Each segment is also likely to be separated from others by network 583 security devices (e.g., firewalls, proxies, packet filtering 584 gateways, etc.), and in many cases disjoint segments may not even 585 have any common physical link connections. Therefore, nodes can only 586 be assured of exchanging packets directly with correspondents in the 587 same segment, and not with those in other segments. The only means 588 for joining the segments therefore is through inter-domain peerings 589 between AERO Bridges. 591 The same as for traditional campus LANs, multiple OMNI link segments 592 can be joined into a single unified link via a virtual bridging 593 service using a mid-layer IPv6 encpasulation per [RFC2473] known as 594 the "SPAN header" that supports inter-segment forwarding (i.e., 595 bridging) without decrementing the network-layer TTL/Hop Limit. This 596 bridging of OMNI link segments is shown in Figure 2: 598 . . . . . . . . . . . . . . . . . . . . . . . 599 . . 600 . .-(::::::::) . 601 . .-(::::::::::::)-. +-+ . 602 . (:::: Segment A :::)--|B|---+ . 603 . `-(::::::::::::)-' +-+ | . 604 . `-(::::::)-' | . 605 . | . 606 . .-(::::::::) | . 607 . .-(::::::::::::)-. +-+ | . 608 . (:::: Segment B :::)--|B|---+ . 609 . `-(::::::::::::)-' +-+ | . 610 . `-(::::::)-' | . 611 . | . 612 . .-(::::::::) | . 613 . .-(::::::::::::)-. +-+ | . 614 . (:::: Segment C :::)--|B|---+ . 615 . `-(::::::::::::)-' +-+ | . 616 . `-(::::::)-' | . 617 . | . 618 . ..(etc).. x . 619 . . 620 . . 621 . <- OMNI link Bridged by encapsulation -> . 622 . . . . . . . . . . . . . .. . . . . . . . . 624 Figure 2: Bridging OMNI Link Segments 626 Bridges, Servers, Relays and Proxys connect via secured INET tunnels 627 over their respecitve segments in a spanning tree topology rooted at 628 the Bridges. The secured spanning tree supports strong 629 authentication for IPv6 ND control messages and may also be used to 630 convey the initial data packets in a flow. Route optimization can 631 then be employed to cause data packets to take more direct paths 632 between OMNI link neighbors without having to strictly follow the 633 spanning tree. 635 3.2.2. Link-Local Addresses (LLAs) and Unique Local Addresses (ULAs) 637 AERO nodes on OMNI links use the Link-Local Address (LLA) prefix 638 fe80::/10 [RFC4193] to assign LLAs used for network-layer addresses 639 in IPv6 ND and data messages. They also use the Unique Local Address 640 (ULA) prefix fc80::/10 [RFC4193] to form ULAs used for SPAN header 641 source and desitnation addresses. See 642 [I-D.templin-6man-omni-interface] for a full specification of the 643 LLAs and ULAs used by AERO nodes on OMNI links. 645 For routing system organization (see Section 3.2.3), ULAs are 646 organized in partition prefixes, e.g., fc80::1000/116. For each such 647 partition prefix, the Bridge(s) that connect that segment assign the 648 all-zero's address of the prefix as a Subnet Router Anycast address. 649 For example, the Subnet Router Anycast address for fc80::1000/116 is 650 simply fc80::1000. 652 3.2.3. AERO Routing System 654 The AERO routing system comprises a private instance of the Border 655 Gateway Protocol (BGP) [RFC4271] that is coordinated between Bridges 656 and Servers and does not interact with either the public Internet BGP 657 routing system or any underlying INET routing systems. 659 In a reference deployment, each Server is configured as an Autonomous 660 System Border Router (ASBR) for a stub Autonomous System (AS) using 661 an AS Number (ASN) that is unique within the BGP instance, and each 662 Server further uses eBGP to peer with one or more Bridges but does 663 not peer with other Servers. Each INET of a multi-segment OMNI link 664 must include one or more Bridges, which peer with the Servers and 665 Proxys within that INET. All Bridges within the same INET are 666 members of the same hub AS using a common ASN, and use iBGP to 667 maintain a consistent view of all active MNPs currently in service. 668 The Bridges of different INETs peer with one another using eBGP. 670 Bridges advertise the OMNI link's MSPs and any non-MNP routes to each 671 of their Servers. This means that any aggregated non-MNPs (including 672 "default") are advertised to all Servers. Each Bridge configures a 673 black-hole route for each of its MSPs. By black-holing the MSPs, the 674 Bridge will maintain forwarding table entries only for the MNPs that 675 are currently active, and packets destined to all other MNPs will 676 correctly incur Destination Unreachable messages due to the black- 677 hole route. In this way, Servers have only partial topology 678 knowledge (i.e., they know only about the MNPs of their directly 679 associated Clients) and they forward all other packets to Bridges 680 which have full topology knowledge. 682 Each OMNI link segment assigns a unique sub-prefix of fc80::/96 known 683 as the ULA partition prefix. For example, a first segment could 684 assign fc80::1000/116, a second could assign fc80::2000/116, a third 685 could assign fc80::3000/116, etc. The administrative authorities for 686 each segment must therefore coordinate to assure mutually-exclusive 687 partiton prefix assignments, but internal provisioning of each prefix 688 is an independent local consideration for each administrative 689 authority. 691 ULA partition prefixes are statitcally represented in Bridge 692 forwarding tables. Bridges join multiple segments into a unified 693 OMNI link over multiple diverse administrative domains. They support 694 a bridging function by first establishing forwarding table entries 695 for their partiion prefixes either via standard BGP routing or static 696 routes. For example, if three Bridges ('A', 'B' and 'C') from 697 different segments serviced fc80::1000/116, fc80::2000/116 and 698 fc80::3000/116 respectively, then the forwarding tables in each 699 Bridge are as follows: 701 A: fc80::1000/116->local, fc80::2000/116->B, fc80::3000/116->C 703 B: fc80::1000/116->A, fc80::2000/116->local, fc80::3000/116->C 705 C: fc80::1000/116->A, fc80::2000/116->B, fc80::3000/116->local 707 These forwarding table entries are permanent and never change, since 708 they correspond to fixed infrastructure elements in their respective 709 segments. 711 ULA Client prefixes are instead dynamically advertised in the AERO 712 routing system by Servers and Relays that provide service for their 713 corresponding MNPs. For example, if three Servers ('D', 'E' and 'F') 714 service the MNPs 2001:db8:1000:2000::/56, 2001:db8:3000:4000::/56 and 715 2001:db8:5000:6000::/56 then the routing system would include: 717 D: fc80:2001:db8:1000:2000::/72 719 E: fc80:2001:db8:3000:4000::/72 721 F: fc80:2001:db8:5000:6000::/72 723 A full discussion of the BGP-based routing system used by AERO is 724 found in [I-D.ietf-rtgwg-atn-bgp]. 726 3.2.4. AERO Encapsulation 728 With the Client and partition prefixes in place in each Bridge's 729 forwarding table, control and data packets sent between AERO nodes in 730 different segments can therefore be carried over the spanning treee 731 via mid-layer encapsulation using the SPAN header. For example, when 732 an AERO service node forwards a packet with IPv6 address 733 2001:db8:1:2::1 to a target AERO node with IPv6 address 734 2001:db8:1000:2000::1, it first encapsulates the packet in a SPAN 735 header with source address set to its own SPAN address (e.g., 736 fc80::1000:2000) and destination address set to 737 fc80:2001:db8:1000:2000::. Next, it encapsulates the resulting SPAN 738 packet in an INET header with source address set to its own INET 739 address (e.g., 192.0.2.100) and destination set to the INET address 740 of a Bridge (e.g., 192.0.2.1). 742 SPAN encapsulation is based on Generic Packet Tunneling in IPv6 743 [RFC2473]; the encapsulation format in the above example is shown in 744 Figure 3: 746 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 747 | INET Header | 748 | src = 192.0.2.100 | 749 | dst = 192.0.2.1 | 750 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 751 | SPAN Header | 752 | src = fc80::1000:2000 | 753 | dst=fc80:2001:db8:1000:2000:: | 754 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 755 | Inner IP Header | 756 | src = 2001:db8:1:2::1 | 757 | dst = 2001:db8:1000:2000::1 | 758 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 759 | | 760 ~ ~ 761 ~ Inner Packet Body ~ 762 ~ ~ 763 | | 764 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 766 Figure 3: SPAN Encapsulation 768 In this format, the inner IP header and packet body are the original 769 IP packet, the SPAN header is an IPv6 header prepared according to 770 [RFC2473], and the INET header is prepared as discussed in 771 Section 3.6. 773 This gives rise to a routing system that contains both Client prefix 774 routes that may change dynamically due to regional node mobility and 775 partion prefix routes that never change. The Bridges can therefore 776 provide link-layer bridging by sending packets over the spanning tree 777 instead of network-layer routing according to MNP routes. As a 778 result, opportunities for packet loss due to node mobility between 779 different segments are mitigated. 781 In normal operations, IPv6 ND messages are conveyed over secured 782 paths between OMNI link neighbors so that specific Proxys, Servers or 783 Relays can be addressed without being subject to mobility events. 784 Conversely, only the first few packets destined to Clients need to 785 traverse secured paths until route optimization can determine a more 786 direct path. 788 3.2.5. Segment Routing Topologies (SRTs) 790 The 16-bit sub-prefixes of fc80::/10 identify up to 64 distinct 791 Segment Routing Topologies (SRTs). Each SRT is a mutually-exclusive 792 OMNI link overlay instance using a mutually-exclusive set of ULAs, 793 and emulates a Virtual LAN (VLAN) service for the OMNI link. In some 794 cases (e.g., when redundant topologies are needed for fault tolerance 795 and reliability) it may be beneficial to deploy multiple SRTs that 796 act as independent overlay instances. A communication failure in one 797 instance therefore will not affect communications in other instances. 799 Each SRT is identified by a distinct value in bits 10-15 of fc80::10, 800 i.e., as fc80::/16, fc81::/16, fc82::/16, etc. This document asserts 801 that up to four SRTs provide a level of safety sufficient for 802 critical communications such as civil aviation. Each SRT is 803 designated with a color that identifies a different OMNI link 804 instance as follows: 806 o Red - corresponds to fc80::/16 808 o Green - corresponds to fc81::/16 810 o Blue-1 - corresponds to fc82::/16 812 o Blue-2 - corresponds to fc83::/16 814 o fc84::/16 through fcbf::/16 are available for additional SRTs. 816 Each OMNI interface assigns an anycast ULA corresponding to its SRT 817 prefix. For example, the anycast ULA for the Green SRT is simply 818 fc81::. The anycast ULA is used for OMNI interface determination in 819 Safety-Based Multilink (SBM) as discussed in 820 [I-D.templin-6man-omni-interface]. Each OMNI interface further 821 applies Performance-Based Multilink (PBM) internally. 823 3.2.6. Segment Routing To the OMNI Link 825 An original IPv6 source can direct a packet to an OMNI link Client by 826 including a Segment Routing Header (SRH) with the anycast ULA for the 827 selected SRT as either the IPv6 destination or as an intermediate hop 828 within the SRH. This allows the original source to determine the 829 specific topology a packet will traverse when there may be multiple 830 alternatives to choose from. Since the SRH contains no useful 831 information for the destination, the Client may elect to delete the 832 SRH before forwarding in order to reduce overhead. This form of 833 Segment Routing supports Safety-Based Multilink (SBM), and can be 834 exercised through general-purpose SRH types such as [RFC8754]. 836 3.2.7. Segment Routing Within the OMNI Link 838 AERO nodes that insert a SPAN header can use Segment Routing within 839 the OMNI link when necessary to influence the path of packets 840 destined to targets in remote segments without requiring all packets 841 to traverse strict spanning tree paths. 843 When a Client, Proxy or Server has a packet to send to a target 844 discovered through route optimization located in the same OMNI link 845 segment, it encapsulates the packet in a SPAN header with the ULA of 846 the target as the destination address if fragmentation is necessary; 847 otherwise, it may omit the SPAN header. The node then uses the 848 target's Link Layer Address (L2ADDR) information for INET 849 encapsulation without including an SRH. 851 When a Client, Proxy or Server has a packet to send to a route 852 optimization target located in a remote OMNI link segment, it 853 encapsulates the packet in a SPAN header with its own ULA as the 854 source address. The node then SHOULD include an SRH [RFC8754] while 855 forwarding the packet to a Bridge. 857 When the SRH is omitted, the node sets the destination address to the 858 ULA of the target Client/Proxy/Server and packet forwarding is via 859 spanning tree paths. When the SRH is included, the node first sets 860 the destination address to the ULA Subnet Router Anycast address of 861 the remote segment and sets the lower 32 bits of the ULA of the 862 target's Proxy/Server as the Last Hop Segment (LHS). The node also 863 includes an AERO Route Optimization specification in the SRH TLV 864 section as shown in Figure 4: 866 0 1 2 3 867 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 1 868 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 869 | Type=TBD | Length | MNPlen|V| FMT | MNP[1] | 870 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 871 | MNP[2] | MNP[3] | ... | MNP[i] | 872 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 873 ~ Link Layer Address (L2ADDR) ~ 874 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 876 Figure 4: AERO Route Optimization SRH TLV 878 In this format: 880 o Type is TBD to be assigned according to the Segment Routing Header 881 TLV registry [RFC8754]. 883 o Length is the length of the body of the TLV in bytes, excluding 884 the Type and Length fields. 886 o MNPlen encodes a value 'i' (between 0 and 15) that indicates the 887 number of octets of the IPv4/IPv6 MNP prefix that follows. 889 o V indicates the IP protocol version of the MNP that follows. V is 890 set to 0 for IPv4 or 1 for IPv6. 892 o FMT is a three bit code that determines the context and format of 893 the L2ADDR exactly as specified in Figure 5. 895 o MNP{1], MNP[2], etc. up to MNP[i] encode the leading 'i' octets of 896 the MNP, beginning with the most significant octet followed by the 897 next most significant octet, etc. The number of MNP octets to be 898 included is determined by the number of trailing zero octets in 899 the prefix. For example, for the IPv6 MNP 2001:db8:1:2::/64, 'i' 900 is set to 8 and only the leftmost 8 octets of the MNP are 901 included. In the same way, for the IPv4 MNP 192.0.2/24, 'i' is 902 set to 3 and only the leftmost 3 octets of the MNP are included. 904 o Link Layer Address (L2ADDR) is a UDP Port Number and IP address 905 encoded according to FMT exactly as specified in Figure 5. 907 The node then forwards the packet via a local Bridge, which will 908 eventually direct it to a Bridge on the same segment as the target. 910 When a Bridge receives a packet with Segments Left=1 and with LHS on 911 a local segment, it checks to see if there is an AERO Route 912 Optimization TLV. If so, the Bridge creates a ULA destination 913 according to FMT. If FMT indicates that L2ADDR corresponds to a 914 target Proxy/Server, the Bridge concatenates the SRT fc*::/96 prefix 915 with the 32 bit LHS value to form the ULA destination. Otherwise, 916 the Bridge concatenates the SRT fc*::/16 prefix with the leading 917 MNPlen octets of the MNP and sets the remaining rightmost bits to 0 918 to form a Subnet Router Anycast ULA destination. The Bridge then 919 writes the ULA into the SPAN header destination address and 920 encapsulates the packet in an INET header with the target's L2ADDR as 921 the destination then forwards the packet. Since the SRH contains no 922 useful information for the destination, the Bridge may elect to 923 delete the SRH before forwarding in order to reduce overhead. 925 In this way, the Bridge participates in route optimization to reduce 926 traffic load and suboptimal routing through strict spanning tree 927 paths. Note that if the Bridge does not recognize the AERO Route 928 Optimization TLV, it instead places the SRT fc*::/96 prefix 929 concatenated with the 32 bit LHS in the IPv6 destination address and 930 forwards according to the spanning tree. (Note that this is the same 931 behavior that would occur if the AERO Route Optimization TLV were not 932 present). 934 3.2.8. Segment Routing Header Compression 936 In the Segment Routing use cases discussed above, the segment routing 937 headers must be kept to a minimum size since source and target 938 Clients may be located behind low-end wireless links (e.g., 1Mbps or 939 less). The Compressed Routing Header (CRH) 940 [I-D.bonica-6man-comp-rtg-hdr] provides a compact form that reduces 941 the header size by omitting invariant information. The CRH Helper 942 option [I-D.bonica-6man-crh-helper-opt] can be used to encode the 943 AERO Route Optimization TLV, and the final hop Bridge that performs 944 route optimization may remove the CRH and its helper before 945 encapsulating and forwarding to the target. 947 The CRH and its companion helper option are therefore seen as 948 critical architectural elements that should be quickly progressed 949 through the standards process. Implementations SHOULD use the CRH 950 and its companion helper option instead of other Routing Header types 951 whenever possible to conserve bandwidth. 953 3.3. OMNI Interface Characteristics 955 OMNI interfaces are virtual interfaces configured over one or more 956 underlying interfaces classified as follows: 958 o INET interfaces connect to an INET either natively or through one 959 or several IPv4 Network Address Translators (NATs). Native INET 960 interfaces have global IP addresses that are reachable from any 961 INET correspondent. All Server, Relay and Bridge interfaces are 962 native interfaces, as are INET-facing interfaces of Proxys. NATed 963 INET interfaces connect to a private network behind one or more 964 NATs that provide INET access. Clients that are behind a NAT are 965 required to send periodic keepalive messages to keep NAT state 966 alive when there are no data packets flowing. 968 o Proxyed interfaces connect to an ANET that is separated from the 969 open INET by a Proxy. Proxys can actively issue control messages 970 over the INET on behalf of the Client to reduce ANET congestion. 972 o VPNed interfaces use security encapsulation over the INET to a 973 Virtual Private Network (VPN) server that also acts as a Server or 974 Proxy. Other than the link-layer encapsulation format, VPNed 975 interfaces behave the same as Direct interfaces. 977 o Direct interfaces connect a Client directly to a Server or Proxy 978 without crossing any ANET/INET paths. An example is a line-of- 979 sight link between a remote pilot and an unmanned aircraft. The 980 same Client considerations apply as for VPNed interfaces. 982 OMNI interfaces use SPAN encapsulation as necessary as discussed in 983 Section 3.2.4. OMNI interfaces use link-layer encapsulation (see: 984 Section 3.6) to exchange packets with OMNI link neighbors over INET 985 or VPNed interfaces. OMNI interfaces do not use link-layer 986 encapsulation over Proxyed and Direct underlying interfaces. 988 OMNI interfaces maintain a neighbor cache for tracking per-neighbor 989 state the same as for any interface. OMNI interfaces use ND messages 990 including Router Solicitation (RS), Router Advertisement (RA), 991 Neighbor Solicitation (NS) and Neighbor Advertisement (NA) for 992 neighbor cache management. 994 OMNI interfaces send ND messages with an OMNI option formatted as 995 specified in [I-D.templin-6man-omni-interface]. The OMNI option 996 includes prefix registration information and "ifIndex-tuples" 997 containing link information parameters for the OMNI interface's 998 underlying interfaces. 1000 SPAN-encapsulated OMNI interface ND messages also include a Source/ 1001 Target Link-Layer Address Option (S/TLLAO) formatted as shown in 1002 Figure 5: 1004 0 1 2 3 1005 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 1006 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1007 | Type | Length | ifIndex[1] | SRT | FMT | 1008 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1009 | Last Hop Segment (LHS) [1] | 1010 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1011 ~ Link Layer Address (L2ADDR) [1] ~ 1012 ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1013 ~ | ifIndex[2] | SRT | FMT | 1014 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1015 | Last Hop Segment (LHS) [2] | 1016 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1017 ~ Link Layer Address (L2ADDR) [2] ~ 1018 ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1019 ~ | .... ~ 1020 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ 1021 ~ ... ~ 1022 ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1023 ~ | ifIndex[N] | SRT | FMT | 1024 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1025 | Last Hop Segment (LHS) [N] | 1026 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1027 ~ Link Layer Address (L2ADDR) [N] ~ 1028 ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1029 ~ | Zero Padding (if necessary) ... 1030 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1032 Figure 5: OMNI Source/Target Link-Layer Address Option (S/TLLAO) 1033 Format 1035 In this format, Type and Length are set the same as specified for S/ 1036 TLLAOs in [RFC4861], with trailing zero padding octets added as 1037 necessary to produce an integral number of 8 octet blocks. The S/ 1038 TLLAO includes N ifIndex-tuples corresponding to a proper subset of 1039 the ifIndex-tuples that appear in the OMNI option. Each ifIndex- 1040 tuple includes the following information: 1042 o ifIndex - the same value as in the corresponding ifIndex-tuple 1043 included in the OMNI option. 1045 o SRT - a 5-bit value that (when added to 96) determines the prefix 1046 length to apply to the ULA formed from concatenating the SRT 1047 fc*::/96 prefix with 32 bit Last Hop Segment (LHS) value. For 1048 example, the prefix length for the value 16 is 112. 1050 o FMT - a 3-bit "Framework/Mode/Type" code corresponding to the 1051 included Link Layer Address (L2ADDR) as follows: 1053 o 1055 * When the most significant bit (i.e., "Framework") is set to 0, 1056 L2ADDR is the INET encapsulation address of a Proxy/Server; 1057 otherwise, it is the addresss for the Source/Target itself 1059 * When the next most significant bit (i.e., "Mode") is set to 0, 1060 the Source/Target L2ADDR is on the open INET; otherwise, it is 1061 (likely) located behind a NAT. 1063 * When the least significant bit (i.e., "Type") is set to 0, 1064 L2ADDR is an IPv4 address; else, it is an IPv6 address. 1066 o Last Hop Segment (LHS) - Includes the least significant 32 bits of 1067 the last hop Proxy/Server ULA prior to encapsulation according to 1068 L2ADDR. When SRT and LHS are both set to 0, the last hop Proxy/ 1069 Server ULA is considered unspecified in this IPv6 ND message. 1071 o Link Layer Address (L2ADDR) - Included according to FMT, and 1072 identifies the link-layer address (i.e., the encapsulation 1073 address) of the source/target. The Port Number and IP address are 1074 recorded in ones-compliment "obfuscated" form per [RFC4380]. 1076 If an S/TLLAO is included, any ifIndex-tuples correspond to a proper 1077 subset of the OMNI option ifIndex-tuples. Any S/TLLAO ifIndex-tuple 1078 with an ifIndex value that does not appear in an OMNI option ifindex- 1079 tuple is ignored. If the same ifIndex value appears in multiple 1080 ifIndex-tuples, the first tuple is processed and the remaining tuples 1081 are ignored. Any S/TLLAO ifIndex-tuples can therefore be viewed as 1082 extensions of their corresponding OMNI option ifIndex-tuples, i.e., 1083 the OMNI option and S/TLLAO are companions that are interpreted in 1084 conjunction with each other. 1086 A Client's OMNI interface may be configured over multiple underlying 1087 interface connections. For example, common mobile handheld devices 1088 have both wireless local area network ("WLAN") and cellular wireless 1089 links. These links are often used "one at a time" with low-cost WLAN 1090 preferred and highly-available cellular wireless as a standby, but a 1091 simultaneous-use capability could provide benefits. In a more 1092 complex example, aircraft frequently have many wireless data link 1093 types (e.g. satellite-based, cellular, terrestrial, air-to-air 1094 directional, etc.) with diverse performance and cost properties. 1096 If a Client's multiple underlying interfaces are used "one at a time" 1097 (i.e., all other interfaces are in standby mode while one interface 1098 is active), then ND message OMNI options include only a single 1099 ifIndex-tuple set to constant values. In that case, the Client would 1100 appear to have a single interface but with a dynamically changing 1101 link-layer address. 1103 If the Client has multiple active underlying interfaces, then from 1104 the perspective of ND it would appear to have multiple link-layer 1105 addresses. In that case, ND message OMNI options MAY include 1106 multiple ifIndex-tuples - each with values that correspond to a 1107 specific interface. Every ND message need not include all OMNI and/ 1108 or S/TLLAO ifIndex-tuples; for any ifIndex-tuple not included, the 1109 neighbor considers the status as unchanged. 1111 Bridge, Server and Proxy OMNI interfaces may be configured over one 1112 or more secured tunnel interfaces. The OMNI interface configures 1113 both an LLA and its corresponding ULA, while the underlying secured 1114 tunnel interfaces are either unnumbered or configure the same ULA. 1115 The OMNI interface encapsulates each IP packet in a SPAN header and 1116 presents the packet to the underlying secured tunnel interface. 1117 Routing protocols such as BGP that run over the OMNI interface do not 1118 employ SPAN encapsulation, but rather present the routing protocol 1119 messages directly to the underlying secured tunnels while using the 1120 ULA as the source address. This distinction must be honored 1121 consistently according to each node's configuration so that the IP 1122 forwarding table will associate discovered IP routes with the correct 1123 interface. 1125 3.4. OMNI Interface Initialization 1127 AERO Servers, Proxys and Clients configure OMNI interfaces as their 1128 point of attachment to the OMNI link. AERO nodes assign the MSPs for 1129 the link to their OMNI interfaces (i.e., as a "route-to-interface") 1130 to ensure that packets with destination addresses covered by an MNP 1131 not explicitly assigned to a non-OMNI interface are directed to the 1132 OMNI interface. 1134 OMNI interface initialization procedures for Servers, Proxys, Clients 1135 and Bridges are discussed in the following sections. 1137 3.4.1. AERO Server/Relay Behavior 1139 When a Server enables an OMNI interface, it assigns an LLA/ULA 1140 appropriate for the given OMNI link segment. The Server also 1141 configures secured tunnels with one or more neighboring Bridges and 1142 engages in a BGP routing protocol session with each Bridge. 1144 The OMNI interface provides a single interface abstraction to the IP 1145 layer, but internally comprises multiple secured tunnels as well as 1146 an NBMA nexus for sending encapsulated data packets to OMNI interface 1147 neighbors. The Server further configures a service to facilitate ND/ 1148 PD exchanges with AERO Clients and manages per-Client neighbor cache 1149 entries and IP forwarding table entries based on control message 1150 exchanges. 1152 Relays are simply Servers that run a dynamic routing protocol to 1153 redistribute routes between the OMNI interface and INET/EUN 1154 interfaces (see: Section 3.2.3). The Relay provisions MNPs to 1155 networks on the INET/EUN interfaces (i.e., the same as a Client would 1156 do) and advertises the MSP(s) for the OMNI link over the INET/EUN 1157 interfaces. The Relay further provides an attachment point of the 1158 OMNI link to a non-MNP-based global topology. 1160 3.4.2. AERO Proxy Behavior 1162 When a Proxy enables an OMNI interface, it assigns an LLA/ULA and 1163 configures permanent neighbor cache entries the same as for Servers. 1164 The Proxy also configures secured tunnels with one or more 1165 neighboring Bridges and maintains per-Client neighbor cache entries 1166 based on control message exchanges. 1168 3.4.3. AERO Client Behavior 1170 When a Client enables an OMNI interface, it sends RS messages with 1171 ND/PD parameters over its underlying interfaces to a Server in the 1172 MAP list, which returns an RA message with corresponding parameters. 1173 (The RS/RA messages may pass through a Proxy in the case of a 1174 Client's Proxyed interface, or through one or more NATs in the case 1175 of a Client's INET interface.) 1177 3.4.4. AERO Bridge Behavior 1179 AERO Bridges configure an OMNI interface and assign the ULA Subnet 1180 Router Anycast address for each OMNI link segment they connect to. 1181 Bridges configure secured tunnels with Servers, Proxys and other 1182 Bridges; they also configure LLAs/ULAs and permanent neighbor cache 1183 entries the same as Servers. Bridges engage in a BGP routing 1184 protocol session with a subset of the Servers and other Bridges on 1185 the spanning tree (see: Section 3.2.3). 1187 3.5. OMNI Interface Neighbor Cache Maintenance 1189 Each OMNI interface maintains a conceptual neighbor cache that 1190 includes an entry for each neighbor it communicates with on the OMNI 1191 link per [RFC4861]. OMNI interface neighbor cache entries are said 1192 to be one of "permanent", "symmetric", "asymmetric" or "proxy". 1194 Permanent neighbor cache entries are created through explicit 1195 administrative action; they have no timeout values and remain in 1196 place until explicitly deleted. AERO Bridges maintain permanent 1197 neighbor cache entries for their associated Proxys and Servers (and 1198 vice-versa). Each entry maintains the mapping between the neighbor's 1199 network-layer LLA and corresponding INET address. 1201 Symmetric neighbor cache entries are created and maintained through 1202 RS/RA exchanges as specified in Section 3.12, and remain in place for 1203 durations bounded by ND/PD lifetimes. AERO Servers maintain 1204 symmetric neighbor cache entries for each of their associated 1205 Clients, and AERO Clients maintain symmetric neighbor cache entries 1206 for each of their associated Servers. The list of all Servers on the 1207 OMNI link is maintained in the link's MAP list. 1209 Asymmetric neighbor cache entries are created or updated based on 1210 route optimization messaging as specified in Section 3.14, and are 1211 garbage-collected when keepalive timers expire. AERO ROSs maintain 1212 asymmetric neighbor cache entries for active targets with lifetimes 1213 based on ND messaging constants. Asymmetric neighbor cache entries 1214 are unidirectional since only the ROS (and not the ROR) creates an 1215 entry. 1217 Proxy neighbor cache entries are created and maintained by AERO 1218 Proxys when they process Client/Server ND/PD exchanges, and remain in 1219 place for durations bounded by ND/PD lifetimes. AERO Proxys maintain 1220 proxy neighbor cache entries for each of their associated Clients. 1221 Proxy neighbor cache entries track the Client state and the address 1222 of the Client's associated Server(s). 1224 To the list of neighbor cache entry states in Section 7.3.2 of 1225 [RFC4861], Proxy and Server OMNI interfaces add an additional state 1226 DEPARTED that applies to symmetric and proxy neighbor cache entries 1227 for Clients that have recently departed. The interface sets a 1228 "DepartTime" variable for the neighbor cache entry to "DEPART_TIME" 1229 seconds. DepartTime is decremented unless a new ND message causes 1230 the state to return to REACHABLE. While a neighbor cache entry is in 1231 the DEPARTED state, packets destined to the target Client are 1232 forwarded to the Client's new location instead of being dropped. 1233 When DepartTime decrements to 0, the neighbor cache entry is deleted. 1234 It is RECOMMENDED that DEPART_TIME be set to the default constant 1235 value REACHABLE_TIME plus 10 seconds (40 seconds by default) to allow 1236 a window for packets in flight to be delivered while stale route 1237 optimization state may be present. 1239 When an ROR receives an authentic NS message used for route 1240 optimization, it searches for a symmetric neighbor cache entry for 1241 the target Client. The ROR then returns a solicited NA message 1242 without creating a neighbor cache entry for the ROS, but creates or 1243 updates a target Client "Report List" entry for the ROS and sets a 1244 "ReportTime" variable for the entry to REPORT_TIME seconds. The ROR 1245 resets ReportTime when it receives a new authentic NS message, and 1246 otherwise decrements ReportTime while no authentic NS messages have 1247 been received. It is RECOMMENDED that REPORT_TIME be set to the 1248 default constant value REACHABLE_TIME plus 10 seconds (40 seconds by 1249 default) to allow a window for route optimization to converge before 1250 ReportTime decrements below REACHABLE_TIME. 1252 When the ROS receives a solicited NA message response to its NS 1253 message used for route optimization, it creates or updates an 1254 asymmetric neighbor cache entry for the target network-layer and 1255 link-layer addresses. The ROS then (re)sets ReachableTime for the 1256 neighbor cache entry to REACHABLE_TIME seconds and uses this value to 1257 determine whether packets can be forwarded directly to the target, 1258 i.e., instead of via a default route. The ROS otherwise decrements 1259 ReachableTime while no further solicited NA messages arrive. It is 1260 RECOMMENDED that REACHABLE_TIME be set to the default constant value 1261 30 seconds as specified in [RFC4861]. 1263 AERO nodes also use the value MAX_UNICAST_SOLICIT to limit the number 1264 of NS keepalives sent when a correspondent may have gone unreachable, 1265 the value MAX_RTR_SOLICITATIONS to limit the number of RS messages 1266 sent without receiving an RA and the value MAX_NEIGHBOR_ADVERTISEMENT 1267 to limit the number of unsolicited NAs that can be sent based on a 1268 single event. It is RECOMMENDED that MAX_UNICAST_SOLICIT, 1269 MAX_RTR_SOLICITATIONS and MAX_NEIGHBOR_ADVERTISEMENT be set to 3 the 1270 same as specified in [RFC4861]. 1272 Different values for DEPART_TIME, REPORT_TIME, REACHABLE_TIME, 1273 MAX_UNICAST_SOLICIT, MAX_RTR_SOLCITATIONS and 1274 MAX_NEIGHBOR_ADVERTISEMENT MAY be administratively set; however, if 1275 different values are chosen, all nodes on the link MUST consistently 1276 configure the same values. Most importantly, DEPART_TIME and 1277 REPORT_TIME SHOULD be set to a value that is sufficiently longer than 1278 REACHABLE_TIME to avoid packet loss due to stale route optimization 1279 state. 1281 3.6. OMNI Interface Encapsulation and Re-encapsulation 1283 OMNI interfaces insert a mid-layer IPv6 header known as the SPAN 1284 header when necessary as discussed in the following sections. After 1285 either inserting or omitting the SPAN header, the OMNI interface also 1286 inserts or omits an outer encapsulation header as discussed below. 1288 OMNI interfaces avoid outer encapsulation over Direct underlying 1289 interfaces and Proxyed underlying interfaces for which the first-hop 1290 access router is AERO-aware. Other OMNI interfaces encapsulate 1291 packets according to whether they are entering the OMNI interface 1292 from the network layer or if they are being re-admitted into the same 1293 OMNI link they arrived on. This latter form of encapsulation is 1294 known as "re-encapsulation". 1296 For packets entering the OMNI interface from the network layer, the 1297 OMNI interface copies the "TTL/Hop Limit", "Type of Service/Traffic 1298 Class" [RFC2983], "Flow Label"[RFC6438] (for IPv6) and "Congestion 1299 Experienced" [RFC3168] values in the inner packet's IP header into 1300 the corresponding fields in the SPAN and outer encapsulation 1301 header(s). 1303 For packets undergoing re-encapsulation, the OMNI interface instead 1304 copies these values from the original encapsulation header into the 1305 new encapsulation header, i.e., the values are transferred between 1306 encapsulation headers and *not* copied from the encapsulated packet's 1307 network-layer header. (Note especially that by copying the TTL/Hop 1308 Limit between encapsulation headers the value will eventually 1309 decrement to 0 if there is a (temporary) routing loop.) 1311 OMNI interfaces configured over INET underlying interfaces 1312 encapsulate packets in INET headers according to the next hop 1313 determined in the forwarding algorithm in Section 3.10. If the next 1314 hop is reached via a secured tunnel, the OMNI interface uses an 1315 encapsulation format specific to the secured tunnel type (see: 1316 Section 6). If the next hop is reached via an unsecured INET 1317 interface, the OMNI interface instead uses UDP/IP encapsulation per 1318 [RFC4380] and as extended in [RFC6081]. 1320 When UDP/IP encapsulation is used, the OMNI interface next sets the 1321 UDP source port to a constant value that it will use in each 1322 successive packet it sends, and sets the UDP length field to the 1323 length of the encapsulated packet plus 8 bytes for the UDP header 1324 itself plus the length of any included extension headers or trailers. 1325 The encapsulated packet may be either IPv6 or IPv4, as distinguished 1326 by the version number found in the first four bits. 1328 For UDP/IP-encapsulated packets sent to a Server, Relay or Bridge, 1329 the OMNI interface sets the UDP destination port to 8060, i.e., the 1330 IANA-registered port number for AERO. For packets sent to a Client, 1331 the OMNI interface sets the UDP destination port to the port value 1332 stored in the neighbor cache entry for this Client. The OMNI 1333 interface finally includes/omits the UDP checksum according to 1334 [RFC6935][RFC6936]. 1336 3.7. OMNI Interface Decapsulation 1338 OMNI interfaces decapsulate packets destined either to the AERO node 1339 itself or to a destination reached via an interface other than the 1340 OMNI interface the packet was received on. When the encapsulated 1341 packet arrives in multiple SPAN fragments, the OMNI interface 1342 reassembles as discussed in Section 3.9. Further decapsulation steps 1343 are performed according to the appropriate encapsulation format 1344 specification. 1346 3.8. OMNI Interface Data Origin Authentication 1348 AERO nodes employ simple data origin authentication procedures. In 1349 particular: 1351 o AERO Bridges, Servers and Proxys accept encapsulated data packets 1352 and control messages received from the (secured) spanning tree. 1354 o AERO Proxys and Clients accept packets that originate from within 1355 the same secured ANET. 1357 o AERO Clients and Relays accept packets from downstream network 1358 correspondents based on ingress filtering. 1360 o AERO Clients, Relays and Servers verify the outer UDP/IP 1361 encapsulation addresses according to [RFC4380]. 1363 AERO nodes silently drop any packets that do not satisfy the above 1364 data origin authentication procedures. Further security 1365 considerations are discussed in Section 6. 1367 3.9. OMNI Interface MTU and Fragmentation 1369 The OMNI interface observes the link nature of tunnels, including the 1370 Maximum Transmission Unit (MTU) and the role of fragmentation and 1371 reassembly[I-D.ietf-intarea-tunnels]. OMNI interface MTU and 1372 fragmentation/reassembly procedures are specified in 1373 [I-D.templin-6man-omni-interface]. 1375 3.10. OMNI Interface Forwarding Algorithm 1377 IP packets enter a node's OMNI interface either from the network 1378 layer (i.e., from a local application or the IP forwarding system) or 1379 from the link layer (i.e., from an OMNI interface neighbor). All 1380 packets entering a node's OMNI interface first undergo data origin 1381 authentication as discussed in Section 3.8. Packets that satisfy 1382 data origin authentication are processed further, while all others 1383 are dropped silently. OMNI interfaces wrap accepted packets in a 1384 SPAN header and SRH if necessary as discussed above. 1386 Packets that enter the OMNI interface from the network layer are 1387 forwarded to an OMNI interface neighbor. Packets that enter the OMNI 1388 interface from the link layer are either re-admitted into the OMNI 1389 link or forwarded to the network layer where they are subject to 1390 either local delivery or IP forwarding. In all cases, the OMNI 1391 interface itself MUST NOT decrement the network layer TTL/Hop-count 1392 since its forwarding actions occur below the network layer. 1394 OMNI interfaces may have multiple underlying interfaces and/or 1395 neighbor cache entries for neighbors with multiple ifIndex-tuple 1396 registrations (see Section 3.3). The OMNI interface uses traffic 1397 classifiers (e.g., DSCP value, port number, etc.) to select an 1398 outgoing underlying interface for each packet based on the node's own 1399 QoS preferences, and also to select a destination link-layer address 1400 based on the neighbor's underlying interface with the highest 1401 preference. AERO implementations SHOULD allow for QoS preference 1402 values to be modified at runtime through network management. 1404 If multiple outgoing interfaces and/or neighbor interfaces have a 1405 preference of "high", the AERO node replicates the packet and sends 1406 one copy via each of the (outgoing / neighbor) interface pairs; 1407 otherwise, the node sends a single copy of the packet via an 1408 interface with the highest preference. AERO nodes keep track of 1409 which underlying interfaces are currently "reachable" or 1410 "unreachable", and only use "reachable" interfaces for forwarding 1411 purposes. 1413 The following sections discuss the OMNI interface forwarding 1414 algorithms for Clients, Proxys, Servers and Bridges. In the 1415 following discussion, a packet's destination address is said to 1416 "match" if it is the same as a cached address, or if it is covered by 1417 a cached prefix (which may be encoded in an LLA). 1419 3.10.1. Client Forwarding Algorithm 1421 When an IP packet enters a Client's OMNI interface from the network 1422 layer the Client searches for an asymmetric neighbor cache entry that 1423 matches the destination. If there is a match, the Client uses one or 1424 more "reachable" neighbor interfaces in the entry for packet 1425 forwarding. If there is no asymmetric neighbor cache entry, the 1426 Client instead forwards the packet toward a Server (the packet is 1427 intercepted by a Proxy if there is a Proxy on the path). The Client 1428 encapsulates the packet in a SPAN header and SRH if necessary and 1429 fragments according to MTU requirements (see: Section 3.9). 1431 When an IP packet enters a Client's OMNI interface from the link- 1432 layer, if the destination matches one of the Client's MNPs or link- 1433 local addresses the Client reassembles and decapsulates as necessary 1434 and delivers the inner packet to the network layer. Otherwise, the 1435 Client drops the packet and MAY return a network-layer ICMP 1436 Destination Unreachable message subject to rate limiting (see: 1437 Section 3.11). 1439 3.10.2. Proxy Forwarding Algorithm 1441 For control messages originating from or destined to a Client, the 1442 Proxy intercepts the message and updates its proxy neighbor cache 1443 entry for the Client. The Proxy then forwards a (proxyed) copy of 1444 the control message. (For example, the Proxy forwards a proxied 1445 version of a Client's NS/RS message to the target neighbor, and 1446 forwards a proxied version of the NA/RA reply to the Client.) 1448 When the Proxy receives a data packet from a Client within the ANET, 1449 the Proxy reassembles and re-fragments if necessary then searches for 1450 an asymmetric neighbor cache entry that matches the destination and 1451 forwards as follows: 1453 o if the destination matches an asymmetric neighbor cache entry, the 1454 Proxy uses one or more "reachable" neighbor interfaces in the 1455 entry for packet forwarding using SPAN encapsulation and including 1456 a SRH if necessary according to the cached link-layer address 1457 information. If the neighbor interface is in the same SPAN 1458 segment, the Proxy forwards the packet directly to the neighbor; 1459 otherwise, it forwards the packet to a Bridge. 1461 o else, the Proxy uses SPAN encapsulation and forwards the packet to 1462 a Bridge while using the ULA corresponding to the packet's 1463 destination as the SPAN destination address. 1465 When the Proxy receives an encapsulated data packet from an INET 1466 neighbor or from a secured tunnel from a Bridge, it accepts the 1467 packet only if data origin authentication succeeds and if there is a 1468 proxy neighbor cache entry that matches the inner destination. Next, 1469 the Proxy reassembles the packet (if necessary) and continues 1470 processing. If the reassembly is complete and the neighbor cache 1471 state is REACHABLE, the Proxy then returns a PTB if necessary (see: 1472 Section 3.9) then either drops or forwards the packet to the Client 1473 while performing SPAN encapsulation and re-fragmentation to the ANET 1474 MTU size if necessary. If the neighbor cache entry state is 1475 DEPARTED, the Proxy instead changes the SPAN destination address to 1476 the address of the new Server and forwards it to a Bridge while 1477 performing re-fragmentation to 1280 bytes if necessary. 1479 3.10.3. Server/Relay Forwarding Algorithm 1481 For control messages destined to a target Client's LLA that are 1482 received from a secured tunnel, the Server intercepts the message and 1483 sends a Proxyed response on behalf of the Client. (For example, the 1484 Server sends a Proxyed NA message reply in response to an NS message 1485 directed to one of its associated Clients.) If the Client's neighbor 1486 cache entry is in the DEPARTED state, however, the Server instead 1487 forwards the packet to the Client's new Server as discussed in 1488 Section 3.16. 1490 When the Server receives an encapsulated data packet from an INET 1491 neighbor or from a secured tunnel, it accepts the packet only if data 1492 origin authentication succeeds. The Server then continues processing 1493 as follows: 1495 o if the network layer destination matches a symmetric neighbor 1496 cache entry in the REACHABLE state the Server prepares the packet 1497 for forwarding to the destination Client. The Server first 1498 reassembles (if necessary) and forwards the packet (while re- 1499 fragmenting if necessary) as specified in Section 3.9. 1501 o else, if the destination matches a symmetric neighbor cache entry 1502 in the DEPARETED state the Server re-encapsulates the packet and 1503 forwards it using the ULA of the Client's new Server as the SPAN 1504 destination. 1506 o else, if the destination matches an asymmetric neighbor cache 1507 entry, the Server uses one or more "reachable" neighbor interfaces 1508 in the entry for packet forwarding via the local INET if the 1509 neighbor is in the same OMNI link segment or using SPAN 1510 encapsulation and Segment Routing if necessary with the final 1511 destination set to the neighbor's ULA otherwise. 1513 o else, if the destination matches a non-MNP route in the IP 1514 forwarding table or an LLA assigned to the Server's OMNI 1515 interface, the Server reassembles if necessary, decapsulates the 1516 packet and releases it to the network layer for local delivery or 1517 IP forwarding. 1519 o else, the Server drops the packet. 1521 When the Server's OMNI interface receives a data packet from the 1522 network layer or from a VPNed or Direct Client, it performs SPAN 1523 encapsulation and fragmentation if necessary, then processes the 1524 packet according to the network-layer destination address as follows: 1526 o if the destination matches a symmetric or asymmetric neighbor 1527 cache entry the Server processes the packet as above. 1529 o else, the Server encapsulates the packet and forwards it to a 1530 Bridge using its own ULA as the source and the ULA corresponding 1531 to the destination as the destination. 1533 3.10.4. Bridge Forwarding Algorithm 1535 Bridges forward SPAN-encapsulated packets over secured tunnels the 1536 same as any IP router. When the Bridge receives a SPAN-encapsulated 1537 packet via a secured tunnel, it removes the outer INET header and 1538 searches for a forwarding table entry that matches the SPAN 1539 destination address. The Bridge then processes the packet as 1540 follows: 1542 o if the destination matches its ULA Subnet Router Anycast address, 1543 the Bridge checks for a SRH. If there is a SRH with Segments 1544 Left=1, with the ULA of a Proxy/Server on the local segment as the 1545 LHS, and with an AERO Route Optimization TLV, the Bridge examines 1546 the FMT to determine if the target is behind a NAT. If no NAT is 1547 indicated, the Bridge copies the MNP Subnet Router Anycast address 1548 if an MNP is included (otherwise copies the Proxy/Server ULA) into 1549 the destination address then forwards the packet directly to the 1550 L2ADDR using link-layer (UDP/IP) encapsulation. If a NAT is 1551 indicated, the Bridge MAY perform NAT traversal procedures by 1552 sending bubbles per [RFC4380]. The Bridge then either applies 1553 AERO route optimization if NAT traversal procedures have been 1554 successfully applied, or forwards the packet directly to the 1555 Server. 1557 o if the destination matches one of the Bridge's own addresses, the 1558 Bridge submits the packet for local delivery. 1560 o else, if the destination matches a forwarding table entry the 1561 Bridge forwards the packet via a secured tunnel to the next hop. 1562 If the destination matches an MSP without matching an MNP, 1563 however, the Bridge instead drops the packet and returns an ICMP 1564 Destination Unreachable message subject to rate limiting (see: 1565 Section 3.11). 1567 o else, the Bridge drops the packet and returns an ICMP Destination 1568 Unreachable as above. 1570 As for any IP router, the Bridge decrements the TTL/Hop Limit when it 1571 forwards the packet. Therefore, only the Hop Limit in the SPAN 1572 header is decremented, and not the TTL/Hop Limit in the inner packet 1573 header. 1575 3.11. OMNI Interface Error Handling 1577 When an AERO node admits a packet into the OMNI interface, it may 1578 receive link-layer or network-layer error indications. 1580 A link-layer error indication is an ICMP error message generated by a 1581 router in the INET on the path to the neighbor or by the neighbor 1582 itself. The message includes an IP header with the address of the 1583 node that generated the error as the source address and with the 1584 link-layer address of the AERO node as the destination address. 1586 The IP header is followed by an ICMP header that includes an error 1587 Type, Code and Checksum. Valid type values include "Destination 1588 Unreachable", "Time Exceeded" and "Parameter Problem" 1589 [RFC0792][RFC4443]. (OMNI interfaces ignore all link-layer IPv4 1590 "Fragmentation Needed" and IPv6 "Packet Too Big" messages since they 1591 only emit packets that are guaranteed to be no larger than the IP 1592 minimum link MTU as discussed in Section 3.9.) 1594 The ICMP header is followed by the leading portion of the packet that 1595 generated the error, also known as the "packet-in-error". For 1596 ICMPv6, [RFC4443] specifies that the packet-in-error includes: "As 1597 much of invoking packet as possible without the ICMPv6 packet 1598 exceeding the minimum IPv6 MTU" (i.e., no more than 1280 bytes). For 1599 ICMPv4, [RFC0792] specifies that the packet-in-error includes: 1600 "Internet Header + 64 bits of Original Data Datagram", however 1601 [RFC1812] Section 4.3.2.3 updates this specification by stating: "the 1602 ICMP datagram SHOULD contain as much of the original datagram as 1603 possible without the length of the ICMP datagram exceeding 576 1604 bytes". 1606 The link-layer error message format is shown in Figure 6 (where, "L2" 1607 and "L3" refer to link-layer and network-layer, respectively): 1609 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1610 ~ ~ 1611 | L2 IP Header of | 1612 | error message | 1613 ~ ~ 1614 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1615 | L2 ICMP Header | 1616 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 1617 ~ ~ P 1618 | IP and other encapsulation | a 1619 | headers of original L3 packet | c 1620 ~ ~ k 1621 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ e 1622 ~ ~ t 1623 | IP header of | 1624 | original L3 packet | i 1625 ~ ~ n 1626 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1627 ~ ~ e 1628 | Upper layer headers and | r 1629 | leading portion of body | r 1630 | of the original L3 packet | o 1631 ~ ~ r 1632 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 1634 Figure 6: OMNI Interface Link-Layer Error Message Format 1636 The AERO node rules for processing these link-layer error messages 1637 are as follows: 1639 o When an AERO node receives a link-layer Parameter Problem message, 1640 it processes the message the same as described as for ordinary 1641 ICMP errors in the normative references [RFC0792][RFC4443]. 1643 o When an AERO node receives persistent link-layer Time Exceeded 1644 messages, the IP ID field may be wrapping before earlier fragments 1645 awaiting reassembly have been processed. In that case, the node 1646 should begin including integrity checks and/or institute rate 1647 limits for subsequent packets. 1649 o When an AERO node receives persistent link-layer Destination 1650 Unreachable messages in response to encapsulated packets that it 1651 sends to one of its asymmetric neighbor correspondents, the node 1652 should process the message as an indication that a path may be 1653 failing, and optionally initiate NUD over that path. If it 1654 receives Destination Unreachable messages over multiple paths, the 1655 node should allow future packets destined to the correspondent to 1656 flow through a default route and re-initiate route optimization. 1658 o When an AERO Client receives persistent link-layer Destination 1659 Unreachable messages in response to encapsulated packets that it 1660 sends to one of its symmetric neighbor Servers, the Client should 1661 mark the path as unusable and use another path. If it receives 1662 Destination Unreachable messages on many or all paths, the Client 1663 should associate with a new Server and release its association 1664 with the old Server as specified in Section 3.16.5. 1666 o When an AERO Server receives persistent link-layer Destination 1667 Unreachable messages in response to encapsulated packets that it 1668 sends to one of its symmetric neighbor Clients, the Server should 1669 mark the underlying path as unusable and use another underlying 1670 path. 1672 o When an AERO Server or Proxy receives link-layer Destination 1673 Unreachable messages in response to an encapsulated packet that it 1674 sends to one of its permanent neighbors, it treats the messages as 1675 an indication that the path to the neighbor may be failing. 1676 However, the dynamic routing protocol should soon reconverge and 1677 correct the temporary outage. 1679 When an AERO Bridge receives a packet for which the network-layer 1680 destination address is covered by an MSP, if there is no more- 1681 specific routing information for the destination the Bridge drops the 1682 packet and returns a network-layer Destination Unreachable message 1683 subject to rate limiting. The Bridge writes the network-layer source 1684 address of the original packet as the destination address and uses 1685 one of its non link-local addresses as the source address of the 1686 message. 1688 When an AERO node receives an encapsulated packet for which the 1689 reassembly buffer it too small, it drops the packet and returns a 1690 network-layer Packet Too Big (PTB) message. The node first writes 1691 the MRU value into the PTB message MTU field, writes the network- 1692 layer source address of the original packet as the destination 1693 address and writes one of its non link-local addresses as the source 1694 address. 1696 3.12. AERO Router Discovery, Prefix Delegation and Autoconfiguration 1698 AERO Router Discovery, Prefix Delegation and Autoconfiguration are 1699 coordinated as discussed in the following Sections. 1701 3.12.1. AERO ND/PD Service Model 1703 Each AERO Server on the OMNI link configures a PD service to 1704 facilitate Client requests. Each Server is provisioned with a 1705 database of MNP-to-Client ID mappings for all Clients enrolled in the 1706 AERO service, as well as any information necessary to authenticate 1707 each Client. The Client database is maintained by a central 1708 administrative authority for the OMNI link and securely distributed 1709 to all Servers, e.g., via the Lightweight Directory Access Protocol 1710 (LDAP) [RFC4511], via static configuration, etc. Clients receive the 1711 same service regardless of the Servers they select. 1713 AERO Clients and Servers use ND messages to maintain neighbor cache 1714 entries. AERO Servers configure their OMNI interfaces as advertising 1715 NBMA interfaces, and therefore send unicast RA messages with a short 1716 Router Lifetime value (e.g., ReachableTime seconds) in response to a 1717 Client's RS message. Thereafter, Clients send additional RS messages 1718 to keep Server state alive. 1720 AERO Clients and Servers include PD parameters in RS/RA messages (see 1721 [I-D.templin-6man-dhcpv6-ndopt] for ND/PD alternatives). The unified 1722 ND/PD messages are exchanged between Client and Server according to 1723 the prefix management schedule required by the PD service. If the 1724 Client knows its MNP in advance, it can instead employ prefix 1725 registration by including its LLA as the source address of an RS 1726 message and with an OMNI option with valid prefix registration 1727 information for the MNP. If the Server (and Proxy) accept the 1728 Client's MNP assertion, they inject the prefix into the routing 1729 system and establish the necessary neighbor cache state. 1731 The following sections specify the Client and Server behavior. 1733 3.12.2. AERO Client Behavior 1735 AERO Clients discover the addresses of Servers in a similar manner as 1736 described in [RFC5214]. Discovery methods include static 1737 configuration (e.g., from a flat-file map of Server addresses and 1738 locations), or through an automated means such as Domain Name System 1739 (DNS) name resolution [RFC1035]. Alternatively, the Client can 1740 discover Server addresses through a layer 2 data link login exchange, 1741 or through a unicast RA response to a multicast/anycast RS as 1742 described below. In the absence of other information, the Client can 1743 resolve the DNS Fully-Qualified Domain Name (FQDN) 1744 "linkupnetworks.[domainname]" where "linkupnetworks" is a constant 1745 text string and "[domainname]" is a DNS suffix for the OMNI link 1746 (e.g., "example.com"). 1748 To associate with a Server, the Client acts as a requesting router to 1749 request MNPs. The Client prepares an RS message with PD parameters 1750 and includes a Nonce and Timestamp option if the Client needs to 1751 correlate RA replies. If the Client already knows the Server's LLA, 1752 it includes the LLA as the network-layer destination address; 1753 otherwise, it includes (link-local) All-Routers multicast as the 1754 network-layer destination. If the Client already knows its own LLA, 1755 it uses the LLA as the network-layer source address; otherwise, it 1756 uses the unspecified IPv6 address (::/128) as the network-layer 1757 source address. 1759 The Client next includes an OMNI option in the RS message to register 1760 its link-layer information with the Server. The Client sets the OMNI 1761 option prefix registration information according to the MNP, and 1762 includes an ifIndex-tuple with S set to '1' corresponding to the 1763 underlying interface over which the Client will send the RS message. 1764 The Client MAY include additional ifIndex-tuples specific to other 1765 underlying interfaces. The Client MAY also include an SLLAO 1766 corresponding to the OMNI option ifIndex-tuple with S set to '1'. 1768 The Client then sends the RS message (either directly via Direct 1769 interfaces, via a VPN for VPNed interfaces, via a Proxy for proxyed 1770 interfaces or via INET encapsulation for INET interfaces) and waits 1771 for an RA message reply (see Section 3.12.3). The Client retries up 1772 to MAX_RTR_SOLICITATIONS times until an RA is received. If the 1773 Client receives no RAs, or if it receives an RA with Router Lifetime 1774 set to 0, the Client SHOULD abandon this Server and try another 1775 Server. Otherwise, the Client processes the PD information found in 1776 the RA message. 1778 Next, the Client creates a symmetric neighbor cache entry with the 1779 Server's LLA as the network-layer address and the Server's 1780 encapsulation and/or link-layer addresses as the link-layer address. 1781 The Client records the RA Router Lifetime field value in the neighbor 1782 cache entry as the time for which the Server has committed to 1783 maintaining the MNP in the routing system via this underlying 1784 interface, and caches the other RA configuration information 1785 including Cur Hop Limit, M and O flags, Reachable Time and Retrans 1786 Timer. The Client then autoconfigures LLAs for each of the delegated 1787 MNPs and assigns them to the OMNI interface. The Client also caches 1788 any MSPs included in Route Information Options (RIOs) [RFC4191] as 1789 MSPs to associate with the OMNI link, and assigns the MTU value in 1790 the MTU option to the underlying interface. 1792 The Client then registers additional underlying interfaces with the 1793 Server by sending RS messages via each additional interface. The RS 1794 messages include the same parameters as for the initial RS/RA 1795 exchange, but with destination address set to the Server's LLA. 1797 Following autoconfiguration, the Client sub-delegates the MNPs to its 1798 attached EUNs and/or the Client's own internal virtual interfaces as 1799 described in [I-D.templin-v6ops-pdhost] to support the Client's 1800 downstream attached "Internet of Things (IoT)". The Client 1801 subsequently sends additional RS messages over each underlying 1802 interface before the Router Lifetime received for that interface 1803 expires. 1805 After the Client registers its underlying interfaces, it may wish to 1806 change one or more registrations, e.g., if an interface changes 1807 address or becomes unavailable, if QoS preferences change, etc. To 1808 do so, the Client prepares an RS message to send over any available 1809 underlying interface. The RS includes an OMNI option with prefix 1810 registration information specific to its MNP, with an ifIndex-tuple 1811 specific to the selected underlying interface with S set to '1', and 1812 with any additional ifIndex-tuples specific to other underlying 1813 interfaces. The Client includes fresh ifIndex-tuple values to update 1814 the Server's neighbor cache entry. When the Client receives the 1815 Server's RA response, it has assurance that the Server has been 1816 updated with the new information. 1818 If the Client wishes to discontinue use of a Server it issues an RS 1819 message over any underlying interface with an OMNI option with a 1820 prefix release indication. When the Server processes the message, it 1821 releases the MNP, sets the symmetric neighbor cache entry state for 1822 the Client to DEPARTED and returns an RA reply with Router Lifetime 1823 set to 0. After a short delay (e.g., 2 seconds), the Server 1824 withdraws the MNP from the routing system. 1826 3.12.3. AERO Server Behavior 1828 AERO Servers act as IP routers and support a PD service for Clients. 1829 Servers arrange to add their LLAs to a static map of Server addresses 1830 for the link and/or the DNS resource records for the FQDN 1831 "linkupnetworks.[domainname]" before entering service. Server 1832 addresses should be geographically and/or topologically referenced, 1833 and made available for discovery by Clients on the OMNI link. 1835 When a Server receives a prospective Client's RS message on its OMNI 1836 interface, it SHOULD return an immediate RA reply with Router 1837 Lifetime set to 0 if it is currently too busy or otherwise unable to 1838 service the Client. Otherwise, the Server authenticates the RS 1839 message and processes the PD parameters. The Server first determines 1840 the correct MNPs to delegate to the Client by searching the Client 1841 database. When the Server delegates the MNPs, it also creates a 1842 forwarding table entry for each MNP so that the MNPs are propagated 1843 into the routing system (see: Section 3.2.3). For IPv6, the Server 1844 creates an IPv6 forwarding table entry for each MNP. For IPv4, the 1845 Server creates an IPv6 forwarding table entry with the SPAN 1846 Compatibility Prefix (SCP) corresponding to the IPv4 address. 1848 The Server next creates a symmetric neighbor cache entry for the 1849 Client using the base LLA as the network-layer address and with 1850 lifetime set to no more than the smallest PD lifetime. Next, the 1851 Server updates the neighbor cache entry by recording the information 1852 in each ifIndex-tuple in the RS OMNI option. The Server also records 1853 the actual SPAN/INET addresses in the neighbor cache entry. 1855 Next, the Server prepares an RA message using its LLA as the network- 1856 layer source address and the network-layer source address of the RS 1857 message as the network-layer destination address. The Server sets 1858 the Router Lifetime to the time for which it will maintain both this 1859 underlying interface individually and the symmetric neighbor cache 1860 entry as a whole. The Server also sets Cur Hop Limit, M and O flags, 1861 Reachable Time and Retrans Timer to values appropriate for the OMNI 1862 link. The Server includes the delegated MNPs, any other PD 1863 parameters and an OMNI option with no ifIndex-tuples. The Server 1864 then includes one or more RIOs that encode the MSPs for the OMNI 1865 link, plus an MTU option (see Section 3.9). The Server finally 1866 forwards the message to the Client using SPAN/INET, INET, or NULL 1867 encapsulation as necessary. 1869 After the initial RS/RA exchange, the Server maintains a 1870 ReachableTime timer for each of the Client's underlying interfaces 1871 individually (and for the Client's symmetric neighbor cache entry 1872 collectively) set to expire after ReachableTime seconds. If the 1873 Client (or Proxy) issues additional RS messages, the Server sends an 1874 RA response and resets ReachableTime. If the Server receives an ND 1875 message with PD release indication it sets the Client's symmetric 1876 neighbor cache entry to the DEPARTED state and withdraws the MNP from 1877 the routing system after a short delay (e.g., 2 seconds). If 1878 ReachableTime expires before a new RS is received on an individual 1879 underlying interface, the Server marks the interface as DOWN. If 1880 ReachableTime expires before any new RS is received on any individual 1881 underlying interface, the Server sets the symmetric neighbor cache 1882 entry state to STALE and sets a 10 second timer. If the Server has 1883 not received a new RS or ND message with PD release indication before 1884 the 10 second timer expires, it deletes the neighbor cache entry and 1885 withdraws the MNP from the routing system. 1887 The Server processes any ND/PD messages pertaining to the Client and 1888 returns an NA/RA reply in response to solicitations. The Server may 1889 also issue unsolicited RA messages, e.g., with PD reconfigure 1890 parameters to cause the Client to renegotiate its PDs, with Router 1891 Lifetime set to 0 if it can no longer service this Client, etc. 1892 Finally, If the symmetric neighbor cache entry is in the DEPARTED 1893 state, the Server deletes the entry after DepartTime expires. 1895 Note: Clients SHOULD notify former Servers of their departures, but 1896 Servers are responsible for expiring neighbor cache entries and 1897 withdrawing routes even if no departure notification is received 1898 (e.g., if the Client leaves the network unexpectedly). Servers 1899 SHOULD therefore set Router Lifetime to ReachableTime seconds in 1900 solicited RA messages to minimize persistent stale cache information 1901 in the absence of Client departure notifications. A short Router 1902 Lifetime also ensures that proactive Client/Server RS/RA messaging 1903 will keep any NAT state alive (see above). 1905 Note: All Servers on an OMNI link MUST advertise consistent values in 1906 the RA Cur Hop Limit, M and O flags, Reachable Time and Retrans Timer 1907 fields the same as for any link, since unpredictable behavior could 1908 result if different Servers on the same link advertised different 1909 values. 1911 3.12.3.1. Lightweight DHCPv6 Relay Agent (LDRA) 1913 When DHCPv6 is used as the ND/PD service back end, AERO Clients and 1914 Servers are always on the same link (i.e., the OMNI link) from the 1915 perspective of DHCPv6. However, in some implementations the DHCPv6 1916 server and ND function may be located in separate modules. In that 1917 case, the Server's OMNI interface module can act as a Lightweight 1918 DHCPv6 Relay Agent (LDRA)[RFC6221] to relay PD messages to and from 1919 the DHCPv6 server module. 1921 When the LDRA receives an authentic RS message, it extracts the PD 1922 message parameters and uses them to construct an IPv6/UDP/DHCPv6 1923 message. It sets the IPv6 source address to the source address of 1924 the RS message, sets the IPv6 destination address to 1925 'All_DHCP_Relay_Agents_and_Servers' and sets the UDP fields to values 1926 that will be understood by the DHCPv6 server. 1928 The LDRA then wraps the message in a DHCPv6 'Relay-Forward' message 1929 header and includes an 'Interface-Id' option that includes enough 1930 information to allow the LDRA to forward the resulting Reply message 1931 back to the Client (e.g., the Client's link-layer addresses, a 1932 security association identifier, etc.). The LDRA also wraps the OMNI 1933 option and SLLAO into the Interface-Id option, then forwards the 1934 message to the DHCPv6 server. 1936 When the DHCPv6 server prepares a Reply message, it wraps the message 1937 in a 'Relay-Reply' message and echoes the Interface-Id option. The 1938 DHCPv6 server then delivers the Relay-Reply message to the LDRA, 1939 which discards the Relay-Reply wrapper and IPv6/UDP headers, then 1940 uses the DHCPv6 message to construct an RA response to the Client. 1941 The Server uses the information in the Interface-Id option to prepare 1942 the RA message and to cache the link-layer addresses taken from the 1943 OMNI option and SLLAO echoed in the Interface-Id option. 1945 3.13. The AERO Proxy 1947 Clients may connect to protected-spectrum ANETs that employ physical 1948 and/or link-layer security services to facilitate communications to 1949 Servers in outside INETs. In that case, the ANET can employ an AERO 1950 Proxy. The Proxy is located at the ANET/INET border and listens for 1951 RS messages originating from or RA messages destined to ANET Clients. 1952 The Proxy acts on these control messages as follows: 1954 o when the Proxy receives an RS message from a new ANET Client, it 1955 first authenticates the message then examines the network-layer 1956 destination address. If the destination address is a Server's 1957 LLA, the Proxy proceeds to the next step. Otherwise, if the 1958 destination is (link-local) All-Routers multicast, the Proxy 1959 selects a "nearby" Server that is likely to be a good candidate to 1960 serve the Client and replaces the destination address with the 1961 Server's LLA. Next, the Proxy creates a proxy neighbor cache 1962 entry and caches the Client and Server link-layer addresses along 1963 with the OMNI option information and any other identifying 1964 information including Transaction IDs, Client Identifiers, Nonce 1965 values, etc. The Proxy finally encapsulates the (proxyed) RS 1966 message in a SPAN header with source set to the Proxy's ULA and 1967 destination set to the Server's ULA then forwards the message into 1968 the SPAN. 1970 o when the Server receives the RS, it authenticates the message then 1971 creates or updates a symmetric neighbor cache entry for the Client 1972 with the Proxy's ULA as the link-layer address. The Server then 1973 sends an RA message back to the Proxy via the spanning tree. 1975 o when the Proxy receives the RA, it authenticates the message and 1976 matches it with the proxy neighbor cache entry created by the RS. 1977 The Proxy then caches the PD route information as a mapping from 1978 the Client's MNPs to the Client's link-layer address, caches the 1979 Server's advertised Router Lifetime and sets the neighbor cache 1980 entry state to REACHABLE. The Proxy then sets the P bit in the 1981 OMNI option header, optionally rewrites the Router Lifetime and 1982 forwards the (proxyed) message to the Client. The Proxy finally 1983 includes an MTU option (if necessary) with an MTU to use for the 1984 underlying ANET interface. 1986 After the initial RS/RA exchange, the Proxy forwards any Client data 1987 packets for which there is no matching asymmetric neighbor cache 1988 entry to a Bridge using SPAN encapsulation with its own ULA as the 1989 source and the ULA corresponding to the Client as the destination. 1990 The Proxy instead forwards any Client data destined to an asymmetric 1991 neighbor cache target directly to the target according to the SPAN/ 1992 link-layer information - the process of establishing asymmetric 1993 neighbor cache entries is specified in Section 3.14. 1995 While the Client is still attached to the ANET, the Proxy sends NS, 1996 RS and/or unsolicited NA messages to update the Server's symmetric 1997 neighbor cache entries on behalf of the Client and/or to convey QoS 1998 updates. This allows for higher-frequency Proxy-initiated RS/RA 1999 messaging over well-connected INET infrastructure supplemented by 2000 lower-frequency Client-initiated RS/RA messaging over constrained 2001 ANET data links. 2003 If the Server ceases to send solicited advertisements, the Proxy 2004 sends unsolicited RAs on the ANET interface with destination set to 2005 (link-local) All-Nodes multicast and with Router Lifetime set to zero 2006 to inform Clients that the Server has failed. Although the Proxy 2007 engages in ND exchanges on behalf of the Client, the Client can also 2008 send ND messages on its own behalf, e.g., if it is in a better 2009 position than the Proxy to convey QoS changes, etc. For this reason, 2010 the Proxy marks any Client-originated solicitation messages (e.g. by 2011 inserting a Nonce option) so that it can return the solicited 2012 advertisement to the Client instead of processing it locally. 2014 If the Client becomes unreachable, the Proxy sets the neighbor cache 2015 entry state to DEPARTED and retains the entry for DepartTime seconds. 2016 While the state is DEPARTED, the Proxy forwards any packets destined 2017 to the Client to a Bridge via SPAN encapsulation with the Client's 2018 current Server as the destination. The Bridge in turn forwards the 2019 packets to the Client's current Server. When DepartTime expires, the 2020 Proxy deletes the neighbor cache entry and discards any further 2021 packets destined to this (now forgotten) Client. 2023 In some ANETs that employ a Proxy, the Client's MNP can be injected 2024 into the ANET routing system. In that case, the Client can send data 2025 messages without encapsulation so that the ANET routing system 2026 transports the unencapsulated packets to the Proxy. This can be very 2027 beneficial, e.g., if the Client connects to the ANET via low-end data 2028 links such as some aviation wireless links. 2030 If the first-hop ANET access router is AERO-aware, the Client can 2031 avoid encapsulation for both its control and data messages. When the 2032 Client connects to the link, it can send an unencapsulated RS message 2033 with source address set to its LLA and with destination address set 2034 to the LLA of the Client's selected Server or to (link-local) All- 2035 Routers multicast. The Client includes an OMNI option formatted as 2036 specified in [I-D.templin-6man-omni-interface]. 2038 The Client then sends the unencapsulated RS message, which will be 2039 intercepted by the AERO-Aware access router. The access router then 2040 encapsulates the RS message in an ANET header with its own address as 2041 the source address and the address of a Proxy as the destination 2042 address. The access router further remembers the address of the 2043 Proxy so that it can encapsulate future data packets from the Client 2044 via the same Proxy. If the access router needs to change to a new 2045 Proxy, it simply sends another RS message toward the Server via the 2046 new Proxy on behalf of the Client. 2048 In some cases, the access router and Proxy may be one and the same 2049 node. In that case, the node would be located on the same physical 2050 link as the Client, but its message exchanges with the Server would 2051 need to pass through a security gateway at the ANET/INET border. The 2052 method for deploying access routers and Proxys (i.e. as a single node 2053 or multiple nodes) is an ANET-local administrative consideration. 2055 3.13.1. Servers Acting as Proxies 2057 Clients may need to connect directly to Servers via INET, Direct and 2058 VPNed interfaces (i.e., non-ANET interfaces). If the Client's 2059 underlying interfaces all connect via the same INET partition, then 2060 it can connect to a single controlling Server via all interfaces. 2062 If some Client interfaces connect via different INET partitions, 2063 however, the Client still selects a single controlling Server and 2064 sends RS messages over interfaces that connect via ancillary Servers 2065 while using the LLA of the controlling Server as the destination. 2067 When an ancillary Server receives an RS with destination set to the 2068 LLA of the controlling Server, it acts as a Proxy to forward the 2069 message to the controlling Server while forwarding the corresponding 2070 RA reply to the Client. When the ancillary Server forwards the RA 2071 reply, it sets the P bit in the OMNI option header to indicate that 2072 it is acting in Proxy mode on behalf of this Client. 2074 3.13.2. Detecting and Responding to Server Failures 2076 In environments where fast recovery from Server failure is required, 2077 Proxys SHOULD use proactive Neighbor Unreachability Detection (NUD) 2078 to track Server reachability in a similar fashion as for 2079 Bidirectional Forwarding Detection (BFD) [RFC5880]. Proxys can then 2080 quickly detect and react to failures so that cached information is 2081 re-established through alternate paths. The NUD control messaging is 2082 carried only over well-connected ground domain networks (i.e., and 2083 not low-end aeronautical radio links) and can therefore be tuned for 2084 rapid response. 2086 Proxys perform proactive NUD with Servers for which there are 2087 currently active ANET Clients by sending continuous NS messages in 2088 rapid succession, e.g., one message per second. The Proxy sends the 2089 NS message via the spanning tree with the Proxy's LLA as the source 2090 and the LLA of the Server as the destination. When the Proxy is also 2091 sending RS messages to the Server on behalf of ANET Clients, the 2092 resulting RA responses can be considered as equivalent hints of 2093 forward progress. This means that the Proxy need not also send a 2094 periodic NS if it has already sent an RS within the same period. If 2095 the Server fails (i.e., if the Proxy ceases to receive 2096 advertisements), the Proxy can quickly inform Clients by sending 2097 multicast RA messages on the ANET interface. 2099 The Proxy sends RA messages on the ANET interface with source address 2100 set to the Server's address, destination address set to (link-local) 2101 All-Nodes multicast, and Router Lifetime set to 0. The Proxy SHOULD 2102 send MAX_FINAL_RTR_ADVERTISEMENTS RA messages separated by small 2103 delays [RFC4861]. Any Clients on the ANET that had been using the 2104 failed Server will receive the RA messages and associate with a new 2105 Server. 2107 3.13.3. Point-to-Multipoint Server Coordination 2109 In environments where Client messaging over ANETs is bandwidth- 2110 limited and/or expensive, Clients can enlist the services of the 2111 Proxy to coordinate with multiple Servers in a single RS/RA message 2112 exchange. The Client can send a single RS message to (link-local) 2113 All-Routers multicast that includes the ID's of multiple Servers in 2114 MS-Register sub-options of the OMNI option. 2116 When the Proxy receives the RS and processes the OMNI option, it 2117 sends a separate RS to each MS-Register Server ID. When the Proxy 2118 receives an RA, it can optionally return an immediate "singleton" RA 2119 to the Client or record the Server's ID for inclusion in a pending 2120 "aggregate" RA message. The Proxy can then return aggregate RA 2121 messages to the Client including multiple Server IDs in order to 2122 conserve bandwidth. Each RA includes a proper subset of the Server 2123 IDs from the original RS message, and the Proxy must ensure that the 2124 message contents of each RA are consistent with the information 2125 received from the (aggregated) Servers. 2127 Clients can thereafter employ efficient point-to-multipoint Server 2128 coordination under the assistance of the Proxy to reduce the number 2129 of messages sent over the ANET while enlisting the support of 2130 multiple Servers for fault tolerance. Clients can further include 2131 MS-Release suboptions in IPv6 ND messages to request the Proxy to 2132 release from former Servers via the procedures discussed in 2133 Section 3.16.5. 2135 The OMNI interface specification [I-D.templin-6man-omni-interface] 2136 provides further discussion of the Client/Proxy RS/RA messaging 2137 involved in point-to-multipoint coordination. 2139 3.14. AERO Route Optimization / Address Resolution 2141 While data packets are flowing between a source and target node, 2142 route optimization SHOULD be used. Route optimization is initiated 2143 by the first eligible Route Optimization Source (ROS) closest to the 2144 source as follows: 2146 o For Clients on VPNed and Direct interfaces, the Server is the ROS. 2148 o For Clients on Proxyed interfaces, the Proxy is the ROS. 2150 o For Clients on INET interfaces, the Client itself is the ROS. 2152 o For correspondent nodes on INET/EUN interfaces serviced by a 2153 Relay, the Relay is the ROS. 2155 The route optimization procedure is conducted between the ROS and the 2156 target Server/Relay acting as a Route Optimization Responder (ROR) in 2157 the same manner as for IPv6 ND Address Resolution and using the same 2158 NS/NA messaging. The target may either be a MNP Client serviced by a 2159 Server, or a non-MNP correspondent reachable via a Relay. 2161 The procedures are specified in the following sections. 2163 3.14.1. Route Optimization Initiation 2165 While data packets are flowing from the source node toward a target 2166 node, the ROS performs address resolution by sending an NS message 2167 for Address Resolution (NS(AR)) to receive a solicited NA message 2168 from the ROR. When the ROS sends an NS(AR), it includes: 2170 o the LLA of the ROS as the source address. 2172 o the data packet's destination as the Target Address. 2174 o the Solicited-Node multicast address [RFC4291] formed from the 2175 lower 24 bits of the data packet's destination as the destination 2176 address, e.g., for 2001:db8:1:2::10:2000 the NS destination 2177 address is ff02:0:0:0:0:1:ff10:2000. 2179 The NS(AR) message includes an OMNI option with no ifIndex-tuples and 2180 no SLLAO, such that the target will not create a neighbor cache 2181 entry. The Prefix Length in the OMNI option is set to the Prefix 2182 Length associated with the ROS's LLA. 2184 The ROS then encapsulates the NS(AR) message in a SPAN header with 2185 source set to its own ULA and destination set to the ULA 2186 corresponding to the packet's final destination, then sends the 2187 message into the spanning tree without decrementing the network-layer 2188 TTL/Hop Limit field. 2190 3.14.2. Relaying the NS 2192 When the Bridge receives the NS(AR) message from the ROS, it discards 2193 the INET header and determines that the ROR is the next hop by 2194 consulting its standard IPv6 forwarding table for the SPAN header 2195 destination address. The Bridge then forwards the message toward the 2196 ROR via the spanning tree the same as for any IPv6 router. The 2197 final-hop Bridge in the spanning tree will deliver the message via a 2198 secured tunnel to the ROR. 2200 3.14.3. Processing the NS and Sending the NA 2202 When the ROR receives the NS(AR) message, it examines the Target 2203 Address to determine whether it has a neighbor cache entry and/or 2204 route that matches the target. If there is no match, the ROR drops 2205 the message. Otherwise, the ROR continues processing as follows: 2207 o if the target belongs to an MNP Client neighbor in the DEPARTED 2208 state the ROR changes the NS(AR) message SPAN destination address 2209 to the ULA of the Client's new Server, forwards the message into 2210 the spanning tree and returns from processing. 2212 o If the target belongs to an MNP Client neighbor in the REACHABLE 2213 state, the ROR instead adds the AERO source address to the target 2214 Client's Report List with time set to ReportTime. 2216 o If the target belongs to a non-MNP route, the ROR continues 2217 processing without adding an entry to the Report List. 2219 The ROR then prepares a solicited NA message to send back to the ROS 2220 but does not create a neighbor cache entry. The ROR sets the NA 2221 source address to the LLA corresponding to the target, sets the 2222 Target Address to the target of the solicitation, and sets the 2223 destination address to the source of the solicitation. The ROR then 2224 includes an OMNI option with Prefix Length set to the length 2225 associated with the LLA. 2227 If the target is an MNP Client, the ROR next includes ifIndex-tuples 2228 in the OMNI option for each of the target Client's underlying 2229 interfaces with current information for each interface and with the S 2230 flag set to 0 and inlcludes an ifIndex-tuple with index set to 0 and 2231 with the S flag set to 1 for its own underlying interface. The ROR 2232 then includes a TLLAO with ifIndex-tuples in one-to-one 2233 correspondence with the tuples that appear in the OMNI option. 2235 For each ifIndex in the TLLAO, the ROR sets the Link-Layer address 2236 according to its own INET address for VPNed or Direct interfaces, to 2237 the INET address of the Proxy for Proxyed interfaces or to the 2238 Client's INET address for INET interfaces. The ROR then includes the 2239 lower 32 bits of its own ULA (or the ULA of the Proxy, for Proxyed 2240 interfaces) as the LHS, encodes the ULA prefix length code in the SRT 2241 field and sets the FMT code accordingly as specified in Section 3.3. 2243 The ROR then sets the NA message R flag to 1 (as a router), S flag to 2244 1 (as a response to a solicitation), and O flag to 0 (as a proxy). 2245 The ROR finally encapsulates the NA message in a SPAN header with 2246 source set to its own ULA and destination set to the source ULA of 2247 the NS(AR) message, then forwards the message into the spanning tree 2248 without decrementing the network-layer TTL/Hop Limit field. 2250 3.14.4. Relaying the NA 2252 When the Bridge receives the NA message from the ROR, it discards the 2253 INET header and determines that the ROS is the next hop by consulting 2254 its standard IPv6 forwarding table for the SPAN header destination 2255 address. The Bridge then forwards the SPAN-encapsulated NA message 2256 toward the ROS the same as for any IPv6 router. The final-hop Bridge 2257 in the spanning tree will deliver the message via a secured tunnel to 2258 the ROS. 2260 3.14.5. Processing the NA 2262 When the ROS receives the solicited NA message, it processes the 2263 message the same as for standard IPv6 Address Resolution [RFC4861]. 2264 In the process, it caches the source ULA then creates an asymmetric 2265 neighbor cache entry for the target and caches all information found 2266 in the OMNI and TLLAO options. The ROS finally sets the asymmetric 2267 neighbor cache entry lifetime to ReachableTime seconds. 2269 3.14.6. Route Optimization Maintenance 2271 Following route optimization, the ROS forwards future data packets 2272 destined to the target via the addresses found in the cached link- 2273 layer information. The route optimization is shared by all sources 2274 that send packets to the target via the ROS, i.e., and not just the 2275 source on behalf of which the route optimization was initiated. 2277 While new data packets destined to the target are flowing through the 2278 ROS, it sends additional NS(AR) messages to the ROR before 2279 ReachableTime expires to receive a fresh solicited NA message the 2280 same as described in the previous sections (route optimization 2281 refreshment strategies are an implementation matter, with a non- 2282 normative example given in Appendix A.1). The ROS uses the cached 2283 ULA of the ROR as the NS(AR) SPAN destination address, and sends up 2284 to MAX_MULTICAST_SOLICIT NS(AR) messages separated by 1 second until 2285 an NA is received. If no NA is received, the ROS assumes that the 2286 current ROR has become unreachable and deletes the target neighbor 2287 cache entry. Subsequent data packets will trigger a new route 2288 optimization per Section 3.14.1 to discover a new ROR while initial 2289 data packets travel over a suboptimal route. 2291 If an NA is received, the ROS then updates the asymmetric neighbor 2292 cache entry to refresh ReachableTime, while (for MNP destinations) 2293 the ROR adds or updates the ROS address to the target's Report List 2294 and with time set to ReportTime. While no data packets are flowing, 2295 the ROS instead allows ReachableTime for the asymmetric neighbor 2296 cache entry to expire. When ReachableTime expires, the ROS deletes 2297 the asymmetric neighbor cache entry. Any future data packets flowing 2298 through the ROS will again trigger a new route optimization. 2300 The ROS may also receive unsolicited NA messages from the ROR at any 2301 time (see: Section 3.16). If there is an asymmetric neighbor cache 2302 entry for the target, the ROS updates the link-layer information but 2303 does not update ReachableTime since the receipt of an unsolicited NA 2304 does not confirm that any forward paths are working. If there is no 2305 asymmetric neighbor cache entry, the ROS simply discards the 2306 unsolicited NA. 2308 In this arrangement, the ROS holds an asymmetric neighbor cache entry 2309 for the target via the ROR, but the ROR does not hold an asymmetric 2310 neighbor cache entry for the ROS. The route optimization neighbor 2311 relationship is therefore asymmetric and unidirectional. If the 2312 target node also has packets to send back to the source node, then a 2313 separate route optimization procedure is performed in the reverse 2314 direction. But, there is no requirement that the forward and reverse 2315 paths be symmetric. 2317 3.15. Neighbor Unreachability Detection (NUD) 2319 AERO nodes perform Neighbor Unreachability Detection (NUD) per 2320 [RFC4861] either reactively in response to persistent link-layer 2321 errors (see Section 3.11) or proactively to confirm reachability. 2322 The NUD algorithm is based on periodic control message exchanges. 2323 The algorithm may further be seeded by ND hints of forward progress, 2324 but care must be taken to avoid inferring reachability based on 2325 spoofed information. For example, authentic IPv6 ND message 2326 exchanges may be considered as acceptable hints of forward progress, 2327 while spurious data packets should not be. 2329 AERO Servers, Proxys and Relays can use (SPAN-encapsulated) standard 2330 NS/NA NUD exchanges sent over the spanning tree to securely test 2331 reachability without risk of DoS attacks from nodes pretending to be 2332 a neighbor; Proxys can further perform NUD to securely verify Server 2333 reachability on behalf of their proxyed Clients. However, a means 2334 for an ROS to test the unsecured forward directions of target route 2335 optimized paths is also necessary. 2337 When an ROR directs an ROS to a neighbor with one or more target 2338 link-layer addresses, the ROS can proactively test each such 2339 unsecured route optimized path by sending "loopback" NS(NUD) 2340 messages. While testing the paths, the ROS can optionally continue 2341 to send packets via the spanning tree, maintain a small queue of 2342 packets until target reachability is confirmed, or (optimistically) 2343 allow packets to flow via the route optimized paths. 2345 When the ROS sends a loopback NS(NUD) message, it uses its LLA as 2346 both the IPv6 source and destination address, and the MNP Subnet- 2347 Router anycast address as the Target Address. The ROS includes a 2348 Nonce and Timestamp option, then encapsulates the message in SPAN/ 2349 INET headers with its own ULA as the source and the ULA of the route 2350 optimization target as the destination. The ROS then forwards the 2351 message to the target (either directly to the L2ADDR of the target if 2352 the target is in the same OMNI link segment, or via a Bridge if the 2353 target is in a different OMNI link segment). 2355 When the route optimization target receives the NS(NUD) message, it 2356 notices that the IPv6 destination address is the same as the source 2357 address. It then reverses the SPAN source and destination addresses 2358 and returns the message to the ROS (either directly or via the 2359 spanning tree). The route optimization target does not decrement the 2360 NS(NUD) message IPv6 Hop-Limit in the process, since the message has 2361 not exited the OMNI link. 2363 When the ROS receives the NS(NUD) message, it can determine from the 2364 Nonce, Timestamp and Target Address that the message originated from 2365 itself and that it transited the forward path. The ROS need not 2366 prepare an NA response, since the destination of the response would 2367 be itself and testing the route optimization path again would be 2368 redundant. 2370 The ROS marks route optimization target paths that pass these NUD 2371 tests as "reachable", and those that do not as "unreachable". These 2372 markings inform the OMNI interface forwarding algorithm specified in 2373 Section 3.10. 2375 Note that to avoid a DoS vector nodes MUST NOT return loopback 2376 NS(NUD) messages received from an unsecured link-layer source via the 2377 spanning tree. 2379 3.16. Mobility Management and Quality of Service (QoS) 2381 AERO is a Distributed Mobility Management (DMM) service. Each Server 2382 is responsible for only a subset of the Clients on the OMNI link, as 2383 opposed to a Centralized Mobility Management (CMM) service where 2384 there is a single network mobility collective entity for all Clients. 2385 Clients coordinate with their associated Servers via RS/RA exchanges 2386 to maintain the DMM profile, and the AERO routing system tracks all 2387 current Client/Server peering relationships. 2389 Servers provide default routing and mobility/multilink services for 2390 their dependent Clients. Clients are responsible for maintaining 2391 neighbor relationships with their Servers through periodic RS/RA 2392 exchanges, which also serves to confirm neighbor reachability. When 2393 a Client's underlying interface address and/or QoS information 2394 changes, the Client is responsible for updating the Server with this 2395 new information. Note that for Proxyed interfaces, however, the 2396 Proxy can also perform some RS/RA exchanges on the Client's behalf. 2398 Mobility management considerations are specified in the following 2399 sections. 2401 3.16.1. Mobility Update Messaging 2403 Servers accommodate Client mobility/multilink and/or QoS change 2404 events by sending unsolicited NA (uNA) messages to each ROS in the 2405 target Client's Report List. When a Server sends a uNA message, it 2406 sets the IPv6 source address to the Client's LLA, sets the 2407 destination address to (link-local) All-Nodes multicast and sets the 2408 Target Address to the Client's Subnet-Router anycast address. The 2409 Server also includes an OMNI option with Prefix Length set to the 2410 length associated with the Client's LLA, with ifIndex-tuples for the 2411 target Client's underlying interfaces and with an ifIndex-tuple with 2412 index 0 for its own interface. The Server then includes a TLLAO with 2413 corresponding ifIndex-tuples prepared the same as for the initial 2414 route optimization event. The Server sets the NA R flag to 1, the S 2415 flag to 0 and the O flag to 0, then encapsulates the message in a 2416 SPAN header with source set to its own ULA and destination set to the 2417 ULA of the ROS and sends the message into the spanning tree. 2419 As discussed in Section 7.2.6 of [RFC4861], the transmission and 2420 reception of uNA messages is unreliable but provides a useful 2421 optimization. In well-connected Internetworks with robust data links 2422 uNA messages will be delivered with high probability, but in any case 2423 the Server can optionally send up to MAX_NEIGHBOR_ADVERTISEMENT uNAs 2424 to each ROS to increase the likelihood that at least one will be 2425 received. 2427 When the ROS receives a uNA message, it ignores the message if there 2428 is no existing neighbor cache entry for the Client. Otherwise, it 2429 uses the included OMNI option and TLLAO information to update the 2430 neighbor cache entry, but does not reset ReachableTime since the 2431 receipt of an unsolicited NA message from the target Server does not 2432 provide confirmation that any forward paths to the target Client are 2433 working. 2435 If uNA messages are lost, the ROS may be left with stale address and/ 2436 or QoS information for the Client for up to ReachableTime seconds. 2437 During this time, the ROS can continue sending packets according to 2438 its stale neighbor cache information. When ReachableTime is close to 2439 expiring, the ROS will re-initiate route optimization and receive 2440 fresh link-layer address information. 2442 In addition to sending uNA messages to the current set of ROSs for 2443 the Client, the Server also sends uNAs to the former link-layer 2444 address for any ifIndex-tuple for which the link-layer address has 2445 changed. The uNA messages update Proxys that cannot easily detect 2446 (e.g., without active probing) when a formerly-active Client has 2447 departed. 2449 3.16.2. Announcing Link-Layer Address and/or QoS Preference Changes 2451 When a Client needs to change its underlying interface addresses and/ 2452 or QoS preferences (e.g., due to a mobility event), either the Client 2453 or its Proxys send RS messages to the Server via the spanning tree 2454 with an OMNI option that includes an ifIndex-tuple with the new link 2455 quality and address information. 2457 Up to MAX_RTR_SOLICITATIONS RS messages MAY be sent in parallel with 2458 sending actual data packets in case one or more RAs are lost. If all 2459 RAs are lost, the Client SHOULD re-associate with a new Server. 2461 When the Server receives the Client's changes, it sends uNA messages 2462 to all nodes in the Report List the same as described in the previous 2463 section. 2465 3.16.3. Bringing New Links Into Service 2467 When a Client needs to bring new underlying interfaces into service 2468 (e.g., when it activates a new data link), it sends an RS message to 2469 the Server via the underlying interface with an OMNI option that 2470 includes an ifIndex-tuple with appropriate link quality values and 2471 with link-layer address information for the new link. 2473 3.16.4. Removing Existing Links from Service 2475 When a Client needs to remove existing underlying interfaces from 2476 service (e.g., when it de-activates an existing data link), it sends 2477 an RS or uNA message to its Server with an OMNI option with 2478 appropriate link quality values. 2480 If the Client needs to send RS/uNA messages over an underlying 2481 interface other than the one being removed from service, it MUST 2482 include ifIndex-tuples with appropriate link quality values for any 2483 underlying interfaces being removed from service. 2485 3.16.5. Moving to a New Server 2487 When a Client associates with a new Server, it performs the Client 2488 procedures specified in Section 3.12.2. The Client also includes MS- 2489 Release identifiers in the RS message OMNI option per 2490 [I-D.templin-6man-omni-interface] if it wants the new Server to 2491 notify any old Servers from which the Client is departing. 2493 When the new Server receives the Client's RS message, it returns an 2494 RA as specified in Section 3.12.3 and sends up to 2495 MAX_NEIGHBOR_ADVERTIISEMENT uNA messages to any old Servers listed in 2496 OMNI option MS-Release identifiers. Each uNA message includes the 2497 Client's LLA as the source address, the old Server's LLA as the 2498 destination address, and an OMNI option with the Register/Release bit 2499 set to 0. The new Server wraps the uNA in a SPAN header with its own 2500 ULA as the source and the old Server's ULA as the destination, then 2501 sends the message into the spanning tree. 2503 When an old Server receives the uNA, it changes the Client's neighbor 2504 cache entry state to DEPARTED, sets the link-layer address of the 2505 Client to the new Server's ULA, and resets DepartTime. After a short 2506 delay (e.g., 2 seconds) the old Server withdraws the Client's MNP 2507 from the routing system. After DepartTime expires, the old Server 2508 deletes the Client's neighbor cache entry. 2510 The old Server also sends unsolicited NA messages to all ROSs in the 2511 Client's Report List with an OMNI option with a single ifIndex-tuple 2512 with ifIndex set to 0, and with the ULA of the new Server in a 2513 companion TLLAO. When the ROS receives the NA, it caches the address 2514 of the new Server in the existing asymmetric neighbor cache entry and 2515 marks the entry as STALE for a period of 10 seconds after which the 2516 cache entry is deleted. While in the STALE state, subsequent data 2517 packets flow according to any existing cached link-layer information 2518 and trigger a new NS(AR)/NA exchange via the new Server. 2520 Clients SHOULD NOT move rapidly between Servers in order to avoid 2521 causing excessive oscillations in the AERO routing system. Examples 2522 of when a Client might wish to change to a different Server include a 2523 Server that has gone unreachable, topological movements of 2524 significant distance, movement to a new geographic region, movement 2525 to a new OMNI link segment, etc. 2527 When a Client moves to a new Server, some of the fragments of a 2528 multiple fragment packet may have already arrived at the old Server 2529 while others are en route to the new Server, however no special 2530 attention in the reassembly algorithm is necessary when re-routed 2531 fragments are simply treated as loss. 2533 3.17. Multicast 2535 The AERO Client provides an IGMP (IPv4) [RFC2236] or MLD (IPv6) 2536 [RFC3810] proxy service for its EUNs and/or hosted applications 2537 [RFC4605]. The Client forwards IGMP/MLD messages over any of its 2538 underlying interfaces for which group membership is required. The 2539 IGMP/MLD messages may be further forwarded by a first-hop ANET access 2540 router acting as an IGMP/MLD-snooping switch [RFC4541], then 2541 ultimately delivered to an AERO Proxy/Server acting as a Protocol 2542 Independent Multicast - Sparse-Mode (PIM-SM, or simply "PIM") 2543 Designated Router (DR) [RFC7761]. AERO Relays also act as PIM 2544 routers (i.e., the same as AERO Proxys/Servers) on behalf of nodes on 2545 INET/EUN networks. The behaviors identified in the following 2546 sections correspond to Source-Specific Multicast (SSM) and Any-Source 2547 Multicast (ASM) operational modes. 2549 3.17.1. Source-Specific Multicast (SSM) 2551 When an ROS (i.e., an AERO Proxy/Server/Relay) "X" acting as PIM 2552 router receives a Join/Prune message from a node on its downstream 2553 interfaces containing one or more ((S)ource, (G)roup) pairs, it 2554 updates its Multicast Routing Information Base (MRIB) accordingly. 2555 For each S belonging to a prefix reachable via X's non-OMNI 2556 interfaces, X then forwards the (S, G) Join/Prune to any PIM routers 2557 on those interfaces per [RFC7761]. 2559 For each S belonging to a prefix reachable via X's OMNI interface, X 2560 originates a separate copy of the Join/Prune for each (S,G) in the 2561 message using its own LLA as the source address and ALL-PIM-ROUTERS 2562 as the destination address. X then encapsulates each message in a 2563 SPAN header with source address set to the ULA of X and destination 2564 address set to S then forwards the message into the spanning tree, 2565 which delivers it to AERO Server/Relay "Y" that services S. At the 2566 same time, if the message was a Join, X sends a route-optimization NS 2567 message toward each S the same as discussed in Section 3.14. The 2568 resulting NAs will return the LLA for the prefix that matches S as 2569 the network-layer source address and TLLAOs with the ULA 2570 corresponding to any ifIndex-tuples that are currently servicing S. 2572 When Y processes the Join/Prune message, if S located behind any 2573 INET, Direct, or VPNed interfaces Y acts as a PIM router and updates 2574 its MRIB to list X as the next hop in the reverse path. If S is 2575 located behind any Proxys "Z"*, Y also forwards the message to each 2576 Z* over the spanning tree while continuing to use the LLA of X as the 2577 source address. Each Z* then updates its MRIB accordingly and 2578 maintains the LLA of X as the next hop in the reverse path. Since 2579 the Bridges do not examine network layer control messages, this means 2580 that the (reverse) multicast tree path is simply from each Z* (and/or 2581 Y) to X with no other multicast-aware routers in the path. If any Z* 2582 (and/or Y) is located on the same OMNI link segment as X, the 2583 multicast data traffic sent to X directly using SPAN/INET 2584 encapsulation instead of via a Bridge. 2586 Following the initial Join/Prune and NS/NA messaging, X maintains an 2587 asymmetric neighbor cache entry for each S the same as if X was 2588 sending unicast data traffic to S. In particular, X performs 2589 additional NS/NA exchanges to keep the neighbor cache entry alive for 2590 up to t_periodic seconds [RFC7761]. If no new Joins are received 2591 within t_periodic seconds, X allows the neighbor cache entry to 2592 expire. Finally, if X receives any additional Join/Prune messages 2593 for (S,G) it forwards the messages to each Y and Z* in the neighbor 2594 cache entry over the spanning tree. 2596 At some later time, Client C that holds an MNP for source S may 2597 depart from a first Proxy Z1 and/or connect via a new Proxy Z2. In 2598 that case, Y sends an unsolicited NA message to X the same as 2599 specified for unicast mobility in Section 3.16. When X receives the 2600 unsolicited NA message, it updates its asymmetric neighbor cache 2601 entry for the LLA for source S and sends new Join messages to any new 2602 Proxys Z2. There is no requirement to send any Prune messages to old 2603 Proxys Z1 since source S will no longer source any multicast data 2604 traffic via Z1. Instead, the multicast state for (S,G) in Proxy Z1 2605 will soon time out since no new Joins will arrive. 2607 After some later time, C may move to a new Server Y2 and depart from 2608 old Sever Y1. In that case, Y1 sends Join messages for any of C's 2609 active (S,G) groups to Y2 while including its own LLA as the source 2610 address. This causes Y2 to include Y1 in the multicast forwarding 2611 tree during the interim time that Y1's symmetric neighbor cache entry 2612 for C is in the DEPARTED state. At the same time, Y1 sends an 2613 unsolicited NA message to X with an OMNI option and TLLAO with 2614 ifIndex-tuple set to 0 and a release indication to cause X to release 2615 its asymmetric neighbor cache entry. X then sends a new Join message 2616 to S via the spanning tree and re-initiates route optimization the 2617 same as if it were receiving a fresh Join message from a node on a 2618 downstream link. 2620 3.17.2. Any-Source Multicast (ASM) 2622 When an ROS X acting as a PIM router receives a Join/Prune from a 2623 node on its downstream interfaces containing one or more (*,G) pairs, 2624 it updates its Multicast Routing Information Base (MRIB) accordingly. 2625 X then forwards a copy of the message to the Rendezvous Point (RP) R 2626 for each G over the spanning tree. X uses its own LLA as the source 2627 address and ALL-PIM-ROUTERS as the destination address, then 2628 encapsulates each message in a SPAN header with source address set to 2629 the ULA of X and destination address set to R, then sends the message 2630 into the spanning tree. At the same time, if the message was a Join 2631 X initiates NS/NA route optimization the same as for the SSM case 2632 discussed in Section 3.17.1. 2634 For each source S that sends multicast traffic to group G via R, the 2635 Proxy/Server Z* for the Client that aggregates S encapsulates the 2636 packets in PIM Register messages and forwards them to R via the 2637 spanning tree, which may then elect to send a PIM Join to Z*. This 2638 will result in an (S,G) tree rooted at Z* with R as the next hop so 2639 that R will begin to receive two copies of the packet; one native 2640 copy from the (S, G) tree and a second copy from the pre-existing (*, 2641 G) tree that still uses PIM Register encapsulation. R can then issue 2642 a PIM Register-stop message to suppress the Register-encapsulated 2643 stream. At some later time, if C moves to a new Proxy/Server Z*, it 2644 resumes sending packets via PIM Register encapsulation via the new 2645 Z*. 2647 At the same time, as multicast listeners discover individual S's for 2648 a given G, they can initiate an (S,G) Join for each S under the same 2649 procedures discussed in Section 3.17.1. Once the (S,G) tree is 2650 established, the listeners can send (S, G) Prune messages to R so 2651 that multicast packets for group G sourced by S will only be 2652 delivered via the (S, G) tree and not from the (*, G) tree rooted at 2653 R. All mobility considerations discussed for SSM apply. 2655 3.17.3. Bi-Directional PIM (BIDIR-PIM) 2657 Bi-Directional PIM (BIDIR-PIM) [RFC5015] provides an alternate 2658 approach to ASM that treats the Rendezvous Point (RP) as a Designated 2659 Forwarder (DF). Further considerations for BIDIR-PIM are out of 2660 scope. 2662 3.18. Operation over Multiple OMNI Links 2664 An AERO Client can connect to multiple OMNI links the same as for any 2665 data link service. In that case, the Client maintains a distinct 2666 OMNI interface for each link, e.g., 'omni0' for the first link, 2667 'omni1' for the second, 'omni2' for the third, etc. Each OMNI link 2668 would include its own distinct set of Bridges, Servers and Proxys, 2669 thereby providing redundancy in case of failures. 2671 Each OMNI link could utilize the same or different ANET connections. 2672 The links can be distinguished at the link-layer via the SRT prefix 2673 in a similar fashion as for Virtual Local Area Network (VLAN) tagging 2674 (e.g., IEEE 802.1Q) and/or through assignment of distinct sets of 2675 MSPs on each link. This gives rise to the opportunity for supporting 2676 multiple redundant networked paths, with each VLAN distinguished by a 2677 different SRT "color" (see: Section 3.2.5). 2679 The Client's IP layer can select the outgoing OMNI interface 2680 appropriate for a given traffic profile while (in the reverse 2681 direction) correspondent nodes must have some way of steering their 2682 packets destined to a target via the correct OMNI link. 2684 In a first alternative, if each OMNI link services different MSPs, 2685 then the Client can receive a distinct MNP from each of the links. 2686 IP routing will therefore assure that the correct Red/Green/Blue/etc. 2687 network is used for both outbound and inbound traffic. This can be 2688 accomplished using existing technologies and approaches, and without 2689 requiring any special supporting code in correspondent nodes or 2690 Bridges. 2692 In a second alternative, if each OMNI link services the same MSP(s) 2693 then each link could assign a distinct "OMNI link Anycast" address 2694 that is configured by all Bridges on the link. Correspondent nodes 2695 can then perform Segment Routing to select the correct SRT, which 2696 will then direct the packet over multiple hops to the target. 2698 3.19. DNS Considerations 2700 AERO Client MNs and INET correspondent nodes consult the Domain Name 2701 System (DNS) the same as for any Internetworking node. When 2702 correspondent nodes and Client MNs use different IP protocol versions 2703 (e.g., IPv4 correspondents and IPv6 MNs), the INET DNS must maintain 2704 A records for IPv4 address mappings to MNs which must then be 2705 populated in Relay NAT64 mapping caches. In that way, an IPv4 2706 correspondent node can send packets to the IPv4 address mapping of 2707 the target MN, and the Relay will translate the IPv4 header and 2708 destination address into an IPv6 header and IPv6 destination address 2709 of the MN. 2711 When an AERO Client registers with an AERO Server, the Server can 2712 return the address(es) of DNS servers in RDNSS options [RFC6106]. 2713 The DNS server provides the IP addresses of other MNs and 2714 correspondent nodes in AAAA records for IPv6 or A records for IPv4. 2716 3.20. Transition Considerations 2718 SPAN encapsulation ensures that dissimilar INET partitions can be 2719 joined into a single unified OMNI link, even though the partitions 2720 themselves may have differing protocol versions and/or incompatible 2721 addressing plans. However, a commonality can be achieved by 2722 incrementally distributing globally routable (i.e., native) IP 2723 prefixes to eventually reach all nodes (both mobile and fixed) in all 2724 OMNI link segments. This can be accomplished by incrementally 2725 deploying AERO Relays on each INET partition, with each Relay 2726 distributing its MNPs and/or discovering non-MNP prefixes on its INET 2727 links. 2729 This gives rise to the opportunity to eventually distribute native IP 2730 addresses to all nodes, and to present a unified OMNI link view even 2731 if the INET partitions remain in their current protocol and 2732 addressing plans. In that way, the OMNI link can serve the dual 2733 purpose of providing a mobility/multilink service and a transition 2734 service. Or, if an INET partition is transitioned to a native IP 2735 protocol version and addressing scheme that is compatible with the 2736 OMNI link MNP-based addressing scheme, the partition and OMNI link 2737 can be joined by Relays. 2739 Relays that connect INETs/EUNs with dissimilar IP protocol versions 2740 may need to employ a network address and protocol translation 2741 function such as NAT64[RFC6146]. 2743 3.21. Detecting and Reacting to Server and Bridge Failures 2745 In environments where rapid failure recovery is required, Servers and 2746 Bridges SHOULD use Bidirectional Forwarding Detection (BFD) 2747 [RFC5880]. Nodes that use BFD can quickly detect and react to 2748 failures so that cached information is re-established through 2749 alternate nodes. BFD control messaging is carried only over well- 2750 connected ground domain networks (i.e., and not low-end radio links) 2751 and can therefore be tuned for rapid response. 2753 Servers and Bridges maintain BFD sessions in parallel with their BGP 2754 peerings. If a Server or Bridge fails, BGP peers will quickly re- 2755 establish routes through alternate paths the same as for common BGP 2756 deployments. Similarly, Proxys maintain BFD sessions with their 2757 associated Bridges even though they do not establish BGP peerings 2758 with them. 2760 Proxys SHOULD use proactive NUD for Servers for which there are 2761 currently active ANET Clients in a manner that parallels BFD, i.e., 2762 by sending unicast NS messages in rapid succession to receive 2763 solicited NA messages. When the Proxy is also sending RS messages on 2764 behalf of ANET Clients, the RS/RA messaging can be considered as 2765 equivalent hints of forward progress. This means that the Proxy need 2766 not also send a periodic NS if it has already sent an RS within the 2767 same period. If a Server fails, the Proxy will cease to receive 2768 advertisements and can quickly inform Clients of the outage by 2769 sending multicast RA messages on the ANET interface. 2771 The Proxy sends multicast RA messages with source address set to the 2772 Server's address, destination address set to (link-local) All-Nodes 2773 multicast, and Router Lifetime set to 0. The Proxy SHOULD send 2774 MAX_FINAL_RTR_ADVERTISEMENTS RA messages separated by small delays 2775 [RFC4861]. Any Clients on the ANET interface that have been using 2776 the (now defunct) Server will receive the RA messages and associate 2777 with a new Server. 2779 3.22. AERO Clients on the Open Internet 2781 AERO Clients that connect to the open Internet via INET interfaces 2782 can establish a VPN or direct link to securely connect to a Server in 2783 a "tethered" arrangement with all of the Client's traffic transiting 2784 the Server. Alternatively, the Client can associate with an INET 2785 Server using UDP/IP encapsulation and asymmetric securing services as 2786 discussed in the following sections. 2788 When a Client's OMNI interface enables an INET underlying interface, 2789 it first determines whether the interface is likely to be behind a 2790 NAT. For IPv4, the Client assumes it is on the open Internet if the 2791 INET address is not a special-use IPv4 address per [RFC3330]. 2792 Similarly for IPv6, the Client assumes it is on the open Internet if 2793 the INET address is not a link-local [RFC4291] or unique-local 2794 [RFC4193] IPv6 address. 2796 The Client then prepares a UDP/IP-encapsulated RS message with IPv6 2797 source address set to its LLA, with IPv6 destination set to (link- 2798 local) All-Routers multicast and with an OMNI option with underlying 2799 interface parameters. If the Client believes that it is on the open 2800 Internet, it SHOULD also include an SLLAO set according to the 2801 address used for INET encapsulation (otherwise, it MAY omit the 2802 SLLAO). If the underlying address is IPv4, the Client includes the 2803 Port Number and IPv4 address written in obfuscated form [RFC4380] as 2804 discussed in Section 3.3. If the underlying interface address is 2805 IPv6, the Client instead includes the Port Number and IPv6 address in 2806 obfuscated form. The Client finally includes an Authentication 2807 option per [RFC4380] to provide message authentication, sets the UDP/ 2808 IP source to its INET address and UDP port, sets the UDP/IP 2809 destination to the Server's INET address and the AERO service port 2810 number (8060), then sends the message to the Server. 2812 When the Server receives the RS, it authenticates the message and 2813 registers the Client's MNP and INET interface information according 2814 to the OMNI option parameters. If the RS message includes an SLLAO, 2815 the Server compares the encapsulation IP address and UDP port number 2816 with the (unobfuscated) SLLAO values. If the values are the same, 2817 the Server caches the Client's information as "INET" addresses 2818 meaning that the Client is likely to accept direct messages without 2819 requiring NAT traversal exchanges. If the values are different (or, 2820 if there was no SLLAO) the Server instead caches the Client's 2821 information as "NAT" addresses meaning that NAT traversal exchanges 2822 may be necessary. 2824 The Server then returns an RA message with IPv6 source and 2825 destination set corresponding to the addresses in the RS, and with an 2826 Authentication option per [RFC4380]. For IPv4, the Server also 2827 includes an Origin option per [RFC4380] with the mapped and 2828 obfuscated Port Number and IPv4 address observed in the encapsulation 2829 headers. For IPv6, the Server instead includes an IPv6 Origin option 2830 per Figure 7 with the mapped and obfuscated observed Port Number and 2831 IPv6 address (note that the value 0x02 in the second octet 2832 differentiates from other [RFC4380] option types). 2834 +--------+--------+-----------------+ 2835 | 0x00 | 0x02 | Origin port # | 2836 +--------+--------+-----------------+ 2837 ~ Origin IPv6 address ~ 2838 +-----------------------------------+ 2840 Figure 7: IPv6 Origin Option 2842 When the Client receives the RA message, it compares the mapped Port 2843 Number and IP address from the Origin option with its own address. 2844 If the addresses are the same, the Client assumes the open Internet / 2845 Cone NAT principle; if the addresses are different, the Client 2846 instead assumes that further qualification procedures are necessary 2847 to detect the type of NAT and proceeds according to standard 2848 [RFC4380] procedures. 2850 After the Client has registered its INET interfaces in such RS/RA 2851 exchanges it sends periodic RS messages to receive fresh RA messages 2852 before the Router Lifetime received on each INET interface expires. 2853 The Client also maintains default routes via its Servers, i.e., the 2854 same as described in earlier sections. 2856 When the Client sends messages to target IP addresses, it also 2857 invokes route optimization per Section 3.14 using IPv6 ND address 2858 resolution messaging. The Client sends the NS(AR) message to the 2859 Server wrapped in a UDP/IP header with an Authentication option with 2860 the NS source address set to the Client's LLA and destination address 2861 set to the target solicited node multicast address. The Server 2862 authenticates the message and sends a corresponding NS(AR) message 2863 over the spanning tree the same as if it were the ROS, but with the 2864 SPAN source address set to the Server's ULA and destination set to 2865 the ULA of the target. When the ROR receives the NS(AR), it adds the 2866 Server's ULA and Client's LLA to the target's Report List, and 2867 returns an NA with OMNI and TLLAO information for the target. The 2868 Server then returns a UDP/IP encapsulated NA message with an 2869 Authentication option to the Client. 2871 Following route optimization, for targets in the same OMNI link 2872 segment if the target's TLLAO addresss is on the open INET, the 2873 Client forwards data packets directly to the target INET address. If 2874 the target's TLLAO address is behind a NAT, the Client first 2875 establishes NAT state for the L2ADDR using the "bubble" mechanisms 2876 specified in [RFC6081][RFC4380]. The Client continues to send data 2877 packets via its Server until NAT state is populated, then begins 2878 forwarding packets via the direct path through the NAT to the target. 2879 For targets in different OMNI link segments, the Client inserts an 2880 SRH and forwards data packets to the Bridge that returned the NA 2881 message. 2883 The ROR may return uNAs via the Server if the target moves, and the 2884 Server will send corresponding Authentication-protected uNAs to the 2885 Client. The Client can also send "loopback" NS(NUD) messages to test 2886 forward path reachability even though there is no security 2887 association between the Client and the target. 2889 The Client sends UDP/IP encapsulated IPv6 packets no larger than 1280 2890 bytes in one piece. In order to accommodate larger IPv6 packets (up 2891 to the OMNI interface MTU), the Client inserts a SPAN header with 2892 source set to its own ULA and destination set to the ULA of the 2893 target and uses IPv6 fragmentation according to Section 3.9. The 2894 Client then encapsulates each fragment in a UDP/IP header and sends 2895 the fragments to the next hop. 2897 3.22.1. Use of SEND and CGA 2899 In some environments, use of the [RFC4380] Authentication option 2900 alone may be sufficient for assuring IPv6 ND message authentication 2901 between Clients and Servers. When additional protection is 2902 necessary, nodes should employ SEcure Neighbor Discovery (SEND) 2903 [RFC3971] with Cryptographically-Generated Addresses (CGA) [RFC3972]. 2905 When SEND/CGA are used, the Client prepares RS messages with its 2906 link-local CGA as the IPv6 source and (link-local) All-Routers 2907 multicast as the IPv6 Destination, includes any SEND options and 2908 wraps the message in a SPAN header. The Client sets the SPAN source 2909 address to its own ULA and sets the SPAN destination address to 2910 (site-local) All-Routers multicast. The Client then wraps the RS 2911 message in UDP/IP headers according to [RFC4380] and sends the 2912 message to the Server. 2914 When the Server receives the message, it first verifies the 2915 Authentication option (if present) then uses the SPAN source address 2916 to determine the MNP of the Client. The Server then processes the 2917 SEND options to authenticate the RS message and prepares an RA 2918 message response. The Server prepares the RA with its own link-local 2919 CGA as the IPv6 source and the CGA of the Client as the IPv6 2920 destination, includes any SEND options and wraps the message in a 2921 SPAN header. The Server sets the SPAN source address to its own ULA 2922 and sets the SPAN destination address to the Client's ULA. The 2923 Server then wraps the RA message in UDP/IP headers according to 2924 [RFC4380] and sends the message to the Client. Thereafter, the 2925 Client/Server send additional RS/RA messages to maintain their 2926 association and any NAT state. 2928 The Client and Server also may exchange NS/NA messages using their 2929 own CGA as the source and with SPAN encapsulation as above. When a 2930 Client sends an NS(AR), it sets the IPv6 source to its CGA and sets 2931 the IPv6 destination to the Solicited-Node Multicast address of the 2932 target. The Client then wraps the message in a SPAN header with its 2933 own ULA as the source and the ULA of the target as the destination 2934 and sends it to the Server. The Server authenticates the message, 2935 then changes the IPv6 source address to the Client's LLA, removes the 2936 SEND options, and sends a corresponding NS(AR) into the spanning 2937 tree. When the Server receives the corresponding SPAN-encapsulated 2938 NA, it changes the IPv6 destination address to the Client's CGA, 2939 inserts SEND options, then wraps the message in UDP/IP headers and 2940 sends it to the Client. 2942 When a Client sends a uNA, it sets the IPv6 source address to its own 2943 CGA and sets the IPv6 destination address to (link-local) All-Nodes 2944 multicast, includes SEND options, wraps the message in SPAN and UDP/ 2945 IP headers and sends the message to the Server. The Server 2946 authenticates the message, then changes the IPv6 address to the 2947 Client's LLA, removes the SEND options and forwards the message the 2948 same as discussed in Section 3.16.1. In the reverse direction, when 2949 the Server forwards a uNA to the Client, it changes the IPv6 address 2950 to its own CGA and inserts SEND options then forwards the message to 2951 the Client. 2953 When a Client sends an NS(NUD), it sets both the IPv6 source and 2954 destination address to its own LLA, wraps the message in a SPAN 2955 header and UDP/IP headers, then sends the message directly to the 2956 peer which will loop the message back. In this case alone, the 2957 Client does not use the Server as a trust broker for forwarding the 2958 ND message. 2960 3.23. Time-Varying MNPs 2962 In some use cases, it is desirable, beneficial and efficient for the 2963 Client to receive a constant MNP that travels with the Client 2964 wherever it moves. For example, this would allow air traffic 2965 controllers to easily track aircraft, etc. In other cases, however 2966 (e.g., intelligent transportation systems), the MN may be willing to 2967 sacrifice a modicum of efficiency in order to have time-varying MNPs 2968 that can be changed every so often to defeat adversarial tracking. 2970 The DHCPv6-PD service offers a way for Clients that desire time- 2971 varying MNPs to obtain short-lived prefixes (e.g., on the order of a 2972 small number of minutes). In that case, the identity of the Client 2973 would not be bound to the MNP but rather the Client's identity would 2974 be bound to the DHCPv6 Device Unique Identifier (DUID) and used as 2975 the seed for Prefix Delegation. The Client would then be obligated 2976 to renumber its internal networks whenever its MNP (and therefore 2977 also its LLA) changes. This should not present a challenge for 2978 Clients with automated network renumbering services, however presents 2979 limits for the durations of ongoing sessions that would prefer to use 2980 a constant address. 2982 4. Implementation Status 2984 An AERO implementation based on OpenVPN (https://openvpn.net/) was 2985 announced on the v6ops mailing list on January 10, 2018 and an 2986 initial public release of the AERO proof-of-concept source code was 2987 announced on the intarea mailing list on August 21, 2015. 2989 As of 4/1/2020, more recent updated implementations are under 2990 internal development and testing with plans to release in Q42020. 2992 5. IANA Considerations 2994 The IANA has assigned a 4-octet Private Enterprise Number "45282" for 2995 AERO in the "enterprise-numbers" registry. 2997 The IANA has assigned the UDP port number "8060" for an earlier 2998 experimental version of AERO [RFC6706]. This document obsoletes 2999 [RFC6706] and claims the UDP port number "8060" for all future use. 3001 The IANA is instructed to assign a new type value TBD in the Segment 3002 Routing Header TLV registry [RFC8754]. 3004 No further IANA actions are required. 3006 6. Security Considerations 3008 AERO Bridges configure secured tunnels with AERO Servers, Realys and 3009 Proxys within their local OMNI link segments. Applicable secured 3010 tunnel alternatives include IPsec [RFC4301], TLS/SSL [RFC8446], DTLS 3011 [RFC6347], WireGuard [WG], etc. The AERO Bridges of all OMNI link 3012 segments in turn configure secured tunnels for their neighboring AERO 3013 Bridges in a spanning tree topology. Therefore, control messages 3014 exchanged between any pair of OMNI link neighbors on the spanning 3015 tree are already secured. 3017 AERO Servers, Relays and Proxys targeted by a route optimization may 3018 also receive data packets directly from arbitrary nodes in INET 3019 partitions instead of via the spanning tree. For INET partitions 3020 that apply effective ingress filtering to defeat source address 3021 spoofing, the simple data origin authentication procedures in 3022 Section 3.8 can be applied. 3024 For INET partitions that require strong security in the data plane, 3025 two options for securing communications include 1) disable route 3026 optimization so that all traffic is conveyed over secured tunnels, or 3027 2) enable on-demand secure tunnel creation between INET partition 3028 neighbors. Option 1) would result in longer routes than necessary 3029 and traffic concentration on critical infrastructure elements. 3030 Option 2) could be coordinated by establishing a secured tunnel on- 3031 demand instead of performing an NS/NA exchange in the route 3032 optimization procedures. Procedures for establishing on-demand 3033 secured tunnels are out of scope. 3035 AERO Clients that connect to secured ANETs need not apply security to 3036 their ND messages, since the messages will be intercepted by a 3037 perimeter Proxy that applies security on its INET-facing interface as 3038 part of the spanning tree (see above). AERO Clients connected to the 3039 open INET can use symmetric network and/or transport layer security 3040 services such as VPNs or can by some other means establish a direct 3041 link. When a VPN or direct link may be impractical, however, an 3042 asymmetric security service such as SEcure Neighbor Discovery (SEND) 3043 [RFC3971] with Cryptographically Generated Addresses (CGAs) [RFC3972] 3044 and/or the Authentication option [RFC4380] can be applied. 3046 Application endpoints SHOULD use application-layer security services 3047 such as TLS/SSL, DTLS or SSH [RFC4251] to assure the same level of 3048 protection as for critical secured Internet services. AERO Clients 3049 that require host-based VPN services SHOULD use symmetric network 3050 and/or transport layer security services such as IPsec, TLS/SSL, 3051 DTLS, etc. AERO Proxys and Servers can also provide a network-based 3052 VPN service on behalf of the Client, e.g., if the Client is located 3053 within a secured enclave and cannot establish a VPN on its own 3054 behalf. 3056 AERO Servers and Bridges present targets for traffic amplification 3057 Denial of Service (DoS) attacks. This concern is no different than 3058 for widely-deployed VPN security gateways in the Internet, where 3059 attackers could send spoofed packets to the gateways at high data 3060 rates. This can be mitigated by connecting Servers and Bridges over 3061 dedicated links with no connections to the Internet and/or when 3062 connections to the Internet are only permitted through well-managed 3063 firewalls. Traffic amplification DoS attacks can also target an AERO 3064 Client's low data rate links. This is a concern not only for Clients 3065 located on the open Internet but also for Clients in secured 3066 enclaves. AERO Servers and Proxys can institute rate limits that 3067 protect Clients from receiving packet floods that could DoS low data 3068 rate links. 3070 AERO Relays must implement ingress filtering to avoid a spoofing 3071 attack in which spurious messages with ULA addresses are injected 3072 into an OMNI link from an outside attacker. AERO Clients MUST ensure 3073 that their connectivity is not used by unauthorized nodes on their 3074 EUNs to gain access to a protected network, i.e., AERO Clients that 3075 act as routers MUST NOT provide routing services for unauthorized 3076 nodes. (This concern is no different than for ordinary hosts that 3077 receive an IP address delegation but then "share" the address with 3078 other nodes via some form of Internet connection sharing such as 3079 tethering.) 3081 The MAP list MUST be well-managed and secured from unauthorized 3082 tampering, even though the list contains only public information. 3083 The MAP list can be conveyed to the Client in a similar fashion as in 3084 [RFC5214] (e.g., through layer 2 data link login messaging, secure 3085 upload of a static file, DNS lookups, etc.). 3087 Although public domain and commercial SEND implementations exist, 3088 concerns regarding the strength of the cryptographic hash algorithm 3089 have been documented [RFC6273] [RFC4982]. 3091 SRH authentication facilities are specified in [RFC8754]. 3093 Security considerations for accepting link-layer ICMP messages and 3094 reflected packets are discussed throughout the document. 3096 Security considerations for IPv6 fragmentation and reassembly are 3097 discussed in [I-D.templin-6man-omni-interface]. 3099 7. Acknowledgements 3101 Discussions in the IETF, aviation standards communities and private 3102 exchanges helped shape some of the concepts in this work. 3103 Individuals who contributed insights include Mikael Abrahamsson, Mark 3104 Andrews, Fred Baker, Bob Braden, Stewart Bryant, Brian Carpenter, 3105 Wojciech Dec, Pavel Drasil, Ralph Droms, Adrian Farrel, Nick Green, 3106 Sri Gundavelli, Brian Haberman, Bernhard Haindl, Joel Halpern, Tom 3107 Herbert, Sascha Hlusiak, Lee Howard, Zdenek Jaron, Andre Kostur, 3108 Hubert Kuenig, Ted Lemon, Andy Malis, Satoru Matsushima, Tomek 3109 Mrugalski, Madhu Niraula, Alexandru Petrescu, Behcet Saikaya, Michal 3110 Skorepa, Joe Touch, Bernie Volz, Ryuji Wakikawa, Tony Whyman, Lloyd 3111 Wood and James Woodyatt. Members of the IESG also provided valuable 3112 input during their review process that greatly improved the document. 3113 Special thanks go to Stewart Bryant, Joel Halpern and Brian Haberman 3114 for their shepherding guidance during the publication of the AERO 3115 first edition. 3117 This work has further been encouraged and supported by Boeing 3118 colleagues including Kyle Bae, M. Wayne Benson, Dave Bernhardt, Cam 3119 Brodie, John Bush, Balaguruna Chidambaram, Irene Chin, Bruce Cornish, 3120 Claudiu Danilov, Don Dillenburg, Joe Dudkowski, Wen Fang, Samad 3121 Farooqui, Anthony Gregory, Jeff Holland, Seth Jahne, Brian Jaury, 3122 Greg Kimberly, Ed King, Madhuri Madhava Badgandi, Laurel Matthew, 3123 Gene MacLean III, Rob Muszkiewicz, Sean O'Sullivan, Vijay 3124 Rajagopalan, Greg Saccone, Rod Santiago, Kent Shuey, Brian Skeen, 3125 Mike Slane, Carrie Spiker, Katie Tran, Brendan Williams, Amelia 3126 Wilson, Julie Wulff, Yueli Yang, Eric Yeh and other members of the 3127 Boeing mobility, networking and autonomy teams. Kyle Bae, Wayne 3128 Benson, Katie Tran and Eric Yeh are especially acknowledged for 3129 implementing the AERO functions as extensions to the public domain 3130 OpenVPN distribution. 3132 Earlier works on NBMA tunneling approaches are found in 3133 [RFC2529][RFC5214][RFC5569]. 3135 Many of the constructs presented in this second edition of AERO are 3136 based on the author's earlier works, including: 3138 o The Internet Routing Overlay Network (IRON) 3139 [RFC6179][I-D.templin-ironbis] 3141 o Virtual Enterprise Traversal (VET) 3142 [RFC5558][I-D.templin-intarea-vet] 3144 o The Subnetwork Encapsulation and Adaptation Layer (SEAL) 3145 [RFC5320][I-D.templin-intarea-seal] 3147 o AERO, First Edition [RFC6706] 3149 Note that these works cite numerous earlier efforts that are not also 3150 cited here due to space limitations. The authors of those earlier 3151 works are acknowledged for their insights. 3153 This work is aligned with the NASA Safe Autonomous Systems Operation 3154 (SASO) program under NASA contract number NNA16BD84C. 3156 This work is aligned with the FAA as per the SE2025 contract number 3157 DTFAWA-15-D-00030. 3159 This work is aligned with the Boeing Commercial Airplanes (BCA) 3160 Internet of Things (IoT) and autonomy programs. 3162 This work is aligned with the Boeing Information Technology (BIT) 3163 MobileNet program. 3165 8. References 3167 8.1. Normative References 3169 [I-D.templin-6man-omni-interface] 3170 Templin, F. and T. Whyman, "Transmission of IPv6 Packets 3171 over Overlay Multilink Network (OMNI) Interfaces", draft- 3172 templin-6man-omni-interface-27 (work in progress), July 3173 2020. 3175 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, 3176 DOI 10.17487/RFC0791, September 1981, 3177 . 3179 [RFC0792] Postel, J., "Internet Control Message Protocol", STD 5, 3180 RFC 792, DOI 10.17487/RFC0792, September 1981, 3181 . 3183 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 3184 Requirement Levels", BCP 14, RFC 2119, 3185 DOI 10.17487/RFC2119, March 1997, 3186 . 3188 [RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in 3189 IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473, 3190 December 1998, . 3192 [RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander, 3193 "SEcure Neighbor Discovery (SEND)", RFC 3971, 3194 DOI 10.17487/RFC3971, March 2005, 3195 . 3197 [RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)", 3198 RFC 3972, DOI 10.17487/RFC3972, March 2005, 3199 . 3201 [RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and 3202 More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191, 3203 November 2005, . 3205 [RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast 3206 Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005, 3207 . 3209 [RFC4380] Huitema, C., "Teredo: Tunneling IPv6 over UDP through 3210 Network Address Translations (NATs)", RFC 4380, 3211 DOI 10.17487/RFC4380, February 2006, 3212 . 3214 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 3215 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 3216 DOI 10.17487/RFC4861, September 2007, 3217 . 3219 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 3220 Address Autoconfiguration", RFC 4862, 3221 DOI 10.17487/RFC4862, September 2007, 3222 . 3224 [RFC6081] Thaler, D., "Teredo Extensions", RFC 6081, 3225 DOI 10.17487/RFC6081, January 2011, 3226 . 3228 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 3229 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 3230 May 2017, . 3232 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 3233 (IPv6) Specification", STD 86, RFC 8200, 3234 DOI 10.17487/RFC8200, July 2017, 3235 . 3237 [RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A., 3238 Richardson, M., Jiang, S., Lemon, T., and T. Winters, 3239 "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", 3240 RFC 8415, DOI 10.17487/RFC8415, November 2018, 3241 . 3243 8.2. Informative References 3245 [BGP] Huston, G., "BGP in 2015, http://potaroo.net", January 3246 2016. 3248 [I-D.bonica-6man-comp-rtg-hdr] 3249 Bonica, R., Kamite, Y., Niwa, T., Alston, A., and L. 3250 Jalil, "The IPv6 Compact Routing Header (CRH)", draft- 3251 bonica-6man-comp-rtg-hdr-22 (work in progress), May 2020. 3253 [I-D.bonica-6man-crh-helper-opt] 3254 Li, X., Bao, C., Ruan, E., and R. Bonica, "Compressed 3255 Routing Header (CRH) Helper Option", draft-bonica-6man- 3256 crh-helper-opt-01 (work in progress), May 2020. 3258 [I-D.ietf-intarea-frag-fragile] 3259 Bonica, R., Baker, F., Huston, G., Hinden, R., Troan, O., 3260 and F. Gont, "IP Fragmentation Considered Fragile", draft- 3261 ietf-intarea-frag-fragile-17 (work in progress), September 3262 2019. 3264 [I-D.ietf-intarea-tunnels] 3265 Touch, J. and M. Townsley, "IP Tunnels in the Internet 3266 Architecture", draft-ietf-intarea-tunnels-10 (work in 3267 progress), September 2019. 3269 [I-D.ietf-rtgwg-atn-bgp] 3270 Templin, F., Saccone, G., Dawra, G., Lindem, A., and V. 3271 Moreno, "A Simple BGP-based Mobile Routing System for the 3272 Aeronautical Telecommunications Network", draft-ietf- 3273 rtgwg-atn-bgp-06 (work in progress), June 2020. 3275 [I-D.templin-6man-dhcpv6-ndopt] 3276 Templin, F., "A Unified Stateful/Stateless Configuration 3277 Service for IPv6", draft-templin-6man-dhcpv6-ndopt-10 3278 (work in progress), June 2020. 3280 [I-D.templin-intarea-seal] 3281 Templin, F., "The Subnetwork Encapsulation and Adaptation 3282 Layer (SEAL)", draft-templin-intarea-seal-68 (work in 3283 progress), January 2014. 3285 [I-D.templin-intarea-vet] 3286 Templin, F., "Virtual Enterprise Traversal (VET)", draft- 3287 templin-intarea-vet-40 (work in progress), May 2013. 3289 [I-D.templin-ironbis] 3290 Templin, F., "The Interior Routing Overlay Network 3291 (IRON)", draft-templin-ironbis-16 (work in progress), 3292 March 2014. 3294 [I-D.templin-v6ops-pdhost] 3295 Templin, F., "IPv6 Prefix Delegation and Multi-Addressing 3296 Models", draft-templin-v6ops-pdhost-26 (work in progress), 3297 June 2020. 3299 [OVPN] OpenVPN, O., "http://openvpn.net", October 2016. 3301 [RFC1035] Mockapetris, P., "Domain names - implementation and 3302 specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, 3303 November 1987, . 3305 [RFC1812] Baker, F., Ed., "Requirements for IP Version 4 Routers", 3306 RFC 1812, DOI 10.17487/RFC1812, June 1995, 3307 . 3309 [RFC2236] Fenner, W., "Internet Group Management Protocol, Version 3310 2", RFC 2236, DOI 10.17487/RFC2236, November 1997, 3311 . 3313 [RFC2529] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4 3314 Domains without Explicit Tunnels", RFC 2529, 3315 DOI 10.17487/RFC2529, March 1999, 3316 . 3318 [RFC2983] Black, D., "Differentiated Services and Tunnels", 3319 RFC 2983, DOI 10.17487/RFC2983, October 2000, 3320 . 3322 [RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition 3323 of Explicit Congestion Notification (ECN) to IP", 3324 RFC 3168, DOI 10.17487/RFC3168, September 2001, 3325 . 3327 [RFC3330] IANA, "Special-Use IPv4 Addresses", RFC 3330, 3328 DOI 10.17487/RFC3330, September 2002, 3329 . 3331 [RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener 3332 Discovery Version 2 (MLDv2) for IPv6", RFC 3810, 3333 DOI 10.17487/RFC3810, June 2004, 3334 . 3336 [RFC4251] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH) 3337 Protocol Architecture", RFC 4251, DOI 10.17487/RFC4251, 3338 January 2006, . 3340 [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A 3341 Border Gateway Protocol 4 (BGP-4)", RFC 4271, 3342 DOI 10.17487/RFC4271, January 2006, 3343 . 3345 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 3346 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 3347 2006, . 3349 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 3350 Internet Protocol", RFC 4301, DOI 10.17487/RFC4301, 3351 December 2005, . 3353 [RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery 3354 Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April 3355 2006, . 3357 [RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet 3358 Control Message Protocol (ICMPv6) for the Internet 3359 Protocol Version 6 (IPv6) Specification", STD 89, 3360 RFC 4443, DOI 10.17487/RFC4443, March 2006, 3361 . 3363 [RFC4511] Sermersheim, J., Ed., "Lightweight Directory Access 3364 Protocol (LDAP): The Protocol", RFC 4511, 3365 DOI 10.17487/RFC4511, June 2006, 3366 . 3368 [RFC4541] Christensen, M., Kimball, K., and F. Solensky, 3369 "Considerations for Internet Group Management Protocol 3370 (IGMP) and Multicast Listener Discovery (MLD) Snooping 3371 Switches", RFC 4541, DOI 10.17487/RFC4541, May 2006, 3372 . 3374 [RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick, 3375 "Internet Group Management Protocol (IGMP) / Multicast 3376 Listener Discovery (MLD)-Based Multicast Forwarding 3377 ("IGMP/MLD Proxying")", RFC 4605, DOI 10.17487/RFC4605, 3378 August 2006, . 3380 [RFC4982] Bagnulo, M. and J. Arkko, "Support for Multiple Hash 3381 Algorithms in Cryptographically Generated Addresses 3382 (CGAs)", RFC 4982, DOI 10.17487/RFC4982, July 2007, 3383 . 3385 [RFC5015] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano, 3386 "Bidirectional Protocol Independent Multicast (BIDIR- 3387 PIM)", RFC 5015, DOI 10.17487/RFC5015, October 2007, 3388 . 3390 [RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site 3391 Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214, 3392 DOI 10.17487/RFC5214, March 2008, 3393 . 3395 [RFC5320] Templin, F., Ed., "The Subnetwork Encapsulation and 3396 Adaptation Layer (SEAL)", RFC 5320, DOI 10.17487/RFC5320, 3397 February 2010, . 3399 [RFC5522] Eddy, W., Ivancic, W., and T. Davis, "Network Mobility 3400 Route Optimization Requirements for Operational Use in 3401 Aeronautics and Space Exploration Mobile Networks", 3402 RFC 5522, DOI 10.17487/RFC5522, October 2009, 3403 . 3405 [RFC5558] Templin, F., Ed., "Virtual Enterprise Traversal (VET)", 3406 RFC 5558, DOI 10.17487/RFC5558, February 2010, 3407 . 3409 [RFC5569] Despres, R., "IPv6 Rapid Deployment on IPv4 3410 Infrastructures (6rd)", RFC 5569, DOI 10.17487/RFC5569, 3411 January 2010, . 3413 [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 3414 (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, 3415 . 3417 [RFC6106] Jeong, J., Park, S., Beloeil, L., and S. Madanapalli, 3418 "IPv6 Router Advertisement Options for DNS Configuration", 3419 RFC 6106, DOI 10.17487/RFC6106, November 2010, 3420 . 3422 [RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful 3423 NAT64: Network Address and Protocol Translation from IPv6 3424 Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146, 3425 April 2011, . 3427 [RFC6179] Templin, F., Ed., "The Internet Routing Overlay Network 3428 (IRON)", RFC 6179, DOI 10.17487/RFC6179, March 2011, 3429 . 3431 [RFC6221] Miles, D., Ed., Ooghe, S., Dec, W., Krishnan, S., and A. 3432 Kavanagh, "Lightweight DHCPv6 Relay Agent", RFC 6221, 3433 DOI 10.17487/RFC6221, May 2011, 3434 . 3436 [RFC6273] Kukec, A., Krishnan, S., and S. Jiang, "The Secure 3437 Neighbor Discovery (SEND) Hash Threat Analysis", RFC 6273, 3438 DOI 10.17487/RFC6273, June 2011, 3439 . 3441 [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer 3442 Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, 3443 January 2012, . 3445 [RFC6438] Carpenter, B. and S. Amante, "Using the IPv6 Flow Label 3446 for Equal Cost Multipath Routing and Link Aggregation in 3447 Tunnels", RFC 6438, DOI 10.17487/RFC6438, November 2011, 3448 . 3450 [RFC6706] Templin, F., Ed., "Asymmetric Extended Route Optimization 3451 (AERO)", RFC 6706, DOI 10.17487/RFC6706, August 2012, 3452 . 3454 [RFC6935] Eubanks, M., Chimento, P., and M. Westerlund, "IPv6 and 3455 UDP Checksums for Tunneled Packets", RFC 6935, 3456 DOI 10.17487/RFC6935, April 2013, 3457 . 3459 [RFC6936] Fairhurst, G. and M. Westerlund, "Applicability Statement 3460 for the Use of IPv6 UDP Datagrams with Zero Checksums", 3461 RFC 6936, DOI 10.17487/RFC6936, April 2013, 3462 . 3464 [RFC7333] Chan, H., Ed., Liu, D., Seite, P., Yokota, H., and J. 3465 Korhonen, "Requirements for Distributed Mobility 3466 Management", RFC 7333, DOI 10.17487/RFC7333, August 2014, 3467 . 3469 [RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I., 3470 Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent 3471 Multicast - Sparse Mode (PIM-SM): Protocol Specification 3472 (Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March 3473 2016, . 3475 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 3476 Decraene, B., Litkowski, S., and R. Shakir, "Segment 3477 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 3478 July 2018, . 3480 [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol 3481 Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, 3482 . 3484 [RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J., 3485 Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header 3486 (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020, 3487 . 3489 [WG] Wireguard, "Wireguard, https://www.wireguard.com", August 3490 2020. 3492 Appendix A. Non-Normative Considerations 3494 AERO can be applied to a multitude of Internetworking scenarios, with 3495 each having its own adaptations. The following considerations are 3496 provided as non-normative guidance: 3498 A.1. Implementation Strategies for Route Optimization 3500 Route optimization as discussed in Section 3.14 results in the route 3501 optimization source (ROS) creating an asymmetric neighbor cache entry 3502 for the target neighbor. The neighbor cache entry is maintained for 3503 at most ReachableTime seconds and then deleted unless updated. In 3504 order to refresh the neighbor cache entry lifetime before the 3505 ReachableTime timer expires, the specification requires 3506 implementations to issue a new NS/NA exchange to reset ReachableTime 3507 while data packets are still flowing. However, the decision of when 3508 to initiate a new NS/NA exchange and to perpetuate the process is 3509 left as an implementation detail. 3511 One possible strategy may be to monitor the neighbor cache entry 3512 watching for data packets for (ReachableTime - 5) seconds. If any 3513 data packets have been sent to the neighbor within this timeframe, 3514 then send an NS to receive a new NA. If no data packets have been 3515 sent, wait for 5 additional seconds and send an immediate NS if any 3516 data packets are sent within this "expiration pending" 5 second 3517 window. If no additional data packets are sent within the 5 second 3518 window, delete the neighbor cache entry. 3520 The monitoring of the neighbor data packet traffic therefore becomes 3521 an asymmetric ongoing process during the neighbor cache entry 3522 lifetime. If the neighbor cache entry expires, future data packets 3523 will trigger a new NS/NA exchange while the packets themselves are 3524 delivered over a longer path until route optimization state is re- 3525 established. 3527 A.2. Implicit Mobility Management 3529 OMNI interface neighbors MAY provide a configuration option that 3530 allows them to perform implicit mobility management in which no ND 3531 messaging is used. In that case, the Client only transmits packets 3532 over a single interface at a time, and the neighbor always observes 3533 packets arriving from the Client from the same link-layer source 3534 address. 3536 If the Client's underlying interface address changes (either due to a 3537 readdressing of the original interface or switching to a new 3538 interface) the neighbor immediately updates the neighbor cache entry 3539 for the Client and begins accepting and sending packets according to 3540 the Client's new address. This implicit mobility method applies to 3541 use cases such as cellphones with both WiFi and Cellular interfaces 3542 where only one of the interfaces is active at a given time, and the 3543 Client automatically switches over to the backup interface if the 3544 primary interface fails. 3546 A.3. Direct Underlying Interfaces 3548 When a Client's OMNI interface is configured over a Direct interface, 3549 the neighbor at the other end of the Direct link can receive packets 3550 without any encapsulation. In that case, the Client sends packets 3551 over the Direct link according to QoS preferences. If the Direct 3552 interface has the highest QoS preference, then the Client's IP 3553 packets are transmitted directly to the peer without going through an 3554 ANET/INET. If other interfaces have higher QoS preferences, then the 3555 Client's IP packets are transmitted via a different interface, which 3556 may result in the inclusion of Proxys, Servers and Bridges in the 3557 communications path. Direct interfaces must be tested periodically 3558 for reachability, e.g., via NUD. 3560 A.4. AERO Critical Infrastructure Considerations 3562 AERO Bridges can be either Commercial off-the Shelf (COTS) standard 3563 IP routers or virtual machines in the cloud. Bridges must be 3564 provisioned, supported and managed by the INET administrative 3565 authority, and connected to the Bridges of other INETs via inter- 3566 domain peerings. Cost for purchasing, configuring and managing 3567 Bridges is nominal even for very large OMNI links. 3569 AERO Servers can be standard dedicated server platforms, but most 3570 often will be deployed as virtual machines in the cloud. The only 3571 requirements for Servers are that they can run the AERO user-level 3572 code and have at least one network interface connection to the INET. 3573 As with Bridges, Servers must be provisioned, supported and managed 3574 by the INET administrative authority. Cost for purchasing, 3575 configuring and managing Servers is nominal especially for virtual 3576 Servers hosted in the cloud. 3578 AERO Proxys are most often standard dedicated server platforms with 3579 one network interface connected to the ANET and a second interface 3580 connected to an INET. As with Servers, the only requirements are 3581 that they can run the AERO user-level code and have at least one 3582 interface connection to the INET. Proxys must be provisioned, 3583 supported and managed by the ANET administrative authority. Cost for 3584 purchasing, configuring and managing Proxys is nominal, and borne by 3585 the ANET administrative authority. 3587 AERO Relays can be any dedicated server or COTS router platform 3588 connected to INETs and/or EUNs. The Relay connects to the OMNI link 3589 and engages in eBGP peering with one or more Bridges as a stub AS. 3590 The Relay then injects its MNPs and/or non-MNP prefixes into the BGP 3591 routing system, and provisions the prefixes to its downstream- 3592 attached networks. The Relay can perform ROS/ROR services the same 3593 as for any Server, and can route between the MNP and non-MNP address 3594 spaces. 3596 A.5. AERO Server Failure Implications 3598 AERO Servers may appear as a single point of failure in the 3599 architecture, but such is not the case since all Servers on the link 3600 provide identical services and loss of a Server does not imply 3601 immediate and/or comprehensive communication failures. Although 3602 Clients typically associate with a single Server at a time, Server 3603 failure is quickly detected and conveyed by Bidirectional Forward 3604 Detection (BFD) and/or proactive NUD allowing Clients to migrate to 3605 new Servers. 3607 If a Server fails, ongoing packet forwarding to Clients will continue 3608 by virtue of the asymmetric neighbor cache entries that have already 3609 been established in route optimization sources (ROSs). If a Client 3610 also experiences mobility events at roughly the same time the Server 3611 fails, unsolicited NA messages may be lost but proxy neighbor cache 3612 entries in the DEPARTED state will ensure that packet forwarding to 3613 the Client's new locations will continue for up to DepartTime 3614 seconds. 3616 If a Client is left without a Server for an extended timeframe (e.g., 3617 greater than ReachableTime seconds) then existing asymmetric neighbor 3618 cache entries will eventually expire and both ongoing and new 3619 communications will fail. The original source will continue to 3620 retransmit until the Client has established a new Server 3621 relationship, after which time continuous communications will resume. 3623 Therefore, providing many Servers on the link with high availability 3624 profiles provides resilience against loss of individual Servers and 3625 assurance that Clients can establish new Server relationships quickly 3626 in event of a Server failure. 3628 A.6. AERO Client / Server Architecture 3630 The AERO architectural model is client / server in the control plane, 3631 with route optimization in the data plane. The same as for common 3632 Internet services, the AERO Client discovers the addresses of AERO 3633 Servers and selects one Server to connect to. The AERO service is 3634 analogous to common Internet services such as google.com, yahoo.com, 3635 cnn.com, etc. However, there is only one AERO service for the link 3636 and all Servers provide identical services. 3638 Common Internet services provide differing strategies for advertising 3639 server addresses to clients. The strategy is conveyed through the 3640 DNS resource records returned in response to name resolution queries. 3641 As of January 2020 Internet-based 'nslookup' services were used to 3642 determine the following: 3644 o When a client resolves the domainname "google.com", the DNS always 3645 returns one A record (i.e., an IPv4 address) and one AAAA record 3646 (i.e., an IPv6 address). The client receives the same addresses 3647 each time it resolves the domainname via the same DNS resolver, 3648 but may receive different addresses when it resolves the 3649 domainname via different DNS resolvers. But, in each case, 3650 exactly one A and one AAAA record are returned. 3652 o When a client resolves the domainname "ietf.org", the DNS always 3653 returns one A record and one AAAA record with the same addresses 3654 regardless of which DNS resolver is used. 3656 o When a client resolves the domainname "yahoo.com", the DNS always 3657 returns a list of 4 A records and 4 AAAA records. Each time the 3658 client resolves the domainname via the same DNS resolver, the same 3659 list of addresses are returned but in randomized order (i.e., 3660 consistent with a DNS round-robin strategy). But, interestingly, 3661 the same addresses are returned (albeit in randomized order) when 3662 the domainname is resolved via different DNS resolvers. 3664 o When a client resolves the domainname "amazon.com", the DNS always 3665 returns a list of 3 A records and no AAAA records. As with 3666 "yahoo.com", the same three A records are returned from any 3667 worldwide Internet connection point in randomized order. 3669 The above example strategies show differing approaches to Internet 3670 resilience and service distribution offered by major Internet 3671 services. The Google approach exposes only a single IPv4 and a 3672 single IPv6 address to clients. Clients can then select whichever IP 3673 protocol version offers the best response, but will always use the 3674 same IP address according to the current Internet connection point. 3675 This means that the IP address offered by the network must lead to a 3676 highly-available server and/or service distribution point. In other 3677 words, resilience is predicated on high availability within the 3678 network and with no client-initiated failovers expected (i.e., it is 3679 all-or-nothing from the client's perspective). However, Google does 3680 provide for worldwide distributed service distribution by virtue of 3681 the fact that each Internet connection point responds with a 3682 different IPv6 and IPv4 address. The IETF approach is like google 3683 (all-or-nothing from the client's perspective), but provides only a 3684 single IPv4 or IPv6 address on a worldwide basis. This means that 3685 the addresses must be made highly-available at the network level with 3686 no client failover possibility, and if there is any worldwide service 3687 distribution it would need to be conducted by a network element that 3688 is reached via the IP address acting as a service distribution point. 3690 In contrast to the Google and IETF philosophies, Yahoo and Amazon 3691 both provide clients with a (short) list of IP addresses with Yahoo 3692 providing both IP protocol versions and Amazon as IPv4-only. The 3693 order of the list is randomized with each name service query 3694 response, with the effect of round-robin load balancing for service 3695 distribution. With a short list of addresses, there is still 3696 expectation that the network will implement high availability for 3697 each address but in case any single address fails the client can 3698 switch over to using a different address. The balance then becomes 3699 one of function in the network vs function in the end system. 3701 The same implications observed for common highly-available services 3702 in the Internet apply also to the AERO client/server architecture. 3703 When an AERO Client connects to one or more ANETs, it discovers one 3704 or more AERO Server addresses through the mechanisms discussed in 3705 earlier sections. Each Server address presumably leads to a fault- 3706 tolerant clustering arrangement such as supported by Linux-HA, 3707 Extended Virtual Synchrony or Paxos. Such an arrangement has 3708 precedence in common Internet service deployments in lightweight 3709 virtual machines without requiring expensive hardware deployment. 3710 Similarly, common Internet service deployments set service IP 3711 addresses on service distribution points that may relay requests to 3712 many different servers. 3714 For AERO, the expectation is that a combination of the Google/IETF 3715 and Yahoo/Amazon philosophies would be employed. The AERO Client 3716 connects to different ANET access points and can receive 1-2 Server 3717 LLAs at each point. It then selects one AERO Server address, and 3718 engages in RS/RA exchanges with the same Server from all ANET 3719 connections. The Client remains with this Server unless or until the 3720 Server fails, in which case it can switch over to an alternate 3721 Server. The Client can likewise switch over to a different Server at 3722 any time if there is some reason for it to do so. So, the AERO 3723 expectation is for a balance of function in the network and end 3724 system, with fault tolerance and resilience at both levels. 3726 Appendix B. Change Log 3728 << RFC Editor - remove prior to publication >> 3730 Changes from draft-templin-intarea-6706bis-58 to draft-templin- 3731 intrea-6706bis-59: 3733 o The term "Relay"used in older draft versions is now "Bridge". 3734 "Relay" now refers to what was formally called: "Gateway". 3736 o Fine-grained cleanup of Forwarding Algorithm; IPv6 ND message 3737 addressing; OMNI Prefix Lengths, etc. 3739 Changes from draft-templin-intarea-6706bis-54 to draft-templin- 3740 intrea-6706bis-55: 3742 o Updates on Segment Routing and S/TLLAO contents. 3744 o Various editorials and addressing cleanups. 3746 Changes from draft-templin-intarea-6706bis-52 to draft-templin- 3747 intrea-6706bis-53: 3749 o Normative reference to the OMNI spec, and remove portions that are 3750 already specified in OMNI. 3752 o Renamed "AERO interface/link" to "OMIN interface/link" throughout 3753 the document. 3755 o Truncated obsolete back section matter. 3757 Author's Address 3758 Fred L. Templin (editor) 3759 Boeing Research & Technology 3760 P.O. Box 3707 3761 Seattle, WA 98124 3762 USA 3764 Email: fltemplin@acm.org