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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, June 3, 2020 5 rfc6179, rfc6706 (if 6 approved) 7 Intended status: Standards Track 8 Expires: December 5, 2020 10 Asymmetric Extended Route Optimization (AERO) 11 draft-templin-intarea-6706bis-53 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 December 5, 2020. 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 . . . . . . . . . 20 78 3.3. OMNI Interface Characteristics . . . . . . . . . . . . . 21 79 3.4. OMNI Interface Initialization . . . . . . . . . . . . . . 26 80 3.4.1. AERO Server/Relay Behavior . . . . . . . . . . . . . 26 81 3.4.2. AERO Proxy Behavior . . . . . . . . . . . . . . . . . 26 82 3.4.3. AERO Client Behavior . . . . . . . . . . . . . . . . 26 83 3.4.4. AERO Bridge Behavior . . . . . . . . . . . . . . . . 27 84 3.5. OMNI Interface Neighbor Cache Maintenance . . . . . . . . 27 85 3.6. OMNI Interface Encapsulation and Re-encapsulation . . . . 29 86 3.7. OMNI Interface Decapsulation . . . . . . . . . . . . . . 30 87 3.8. OMNI Interface Data Origin Authentication . . . . . . . . 30 88 3.9. OMNI Interface MTU and Fragmentation . . . . . . . . . . 31 89 3.10. OMNI Interface Forwarding Algorithm . . . . . . . . . . . 31 90 3.10.1. Client Forwarding Algorithm . . . . . . . . . . . . 32 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 . . . . . . . . . . . . . . . . . . . . 38 97 3.12.1. AERO ND/PD Service Model . . . . . . . . . . . . . . 38 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. Detecting and Responding to Server Failures . . . . 45 102 3.13.2. Point-to-Multipoint Server Coordination . . . . . . 46 103 3.14. AERO Route Optimization / Address Resolution . . . . . . 46 104 3.14.1. Route Optimization Initiation . . . . . . . . . . . 47 105 3.14.2. Relaying the NS . . . . . . . . . . . . . . . . . . 47 106 3.14.3. Processing the NS and Sending the NA . . . . . . . . 48 107 3.14.4. Relaying the NA . . . . . . . . . . . . . . . . . . 49 108 3.14.5. Processing the NA . . . . . . . . . . . . . . . . . 49 109 3.14.6. Route Optimization Maintenance . . . . . . . . . . . 49 110 3.15. Neighbor Unreachability Detection (NUD) . . . . . . . . . 50 111 3.16. Mobility Management and Quality of Service (QoS) . . . . 52 112 3.16.1. Mobility Update Messaging . . . . . . . . . . . . . 52 113 3.16.2. Announcing Link-Layer Address and/or QoS Preference 114 Changes . . . . . . . . . . . . . . . . . . . . . . 53 115 3.16.3. Bringing New Links Into Service . . . . . . . . . . 53 116 3.16.4. Removing Existing Links from Service . . . . . . . . 54 117 3.16.5. Moving to a New Server . . . . . . . . . . . . . . . 54 118 3.17. Multicast . . . . . . . . . . . . . . . . . . . . . . . . 55 119 3.17.1. Source-Specific Multicast (SSM) . . . . . . . . . . 55 120 3.17.2. Any-Source Multicast (ASM) . . . . . . . . . . . . . 57 121 3.17.3. Bi-Directional PIM (BIDIR-PIM) . . . . . . . . . . . 57 122 3.18. Operation over Multiple OMNI Links . . . . . . . . . . . 58 123 3.19. DNS Considerations . . . . . . . . . . . . . . . . . . . 59 124 3.20. Transition Considerations . . . . . . . . . . . . . . . . 59 125 3.21. Detecting and Reacting to Server and Bridge Failures . . 60 126 3.22. AERO Clients on the Open Internet . . . . . . . . . . . . 60 127 3.22.1. Use of SEND and CGA . . . . . . . . . . . . . . . . 63 128 3.23. Time-Varying MNPs . . . . . . . . . . . . . . . . . . . . 64 129 4. Implementation Status . . . . . . . . . . . . . . . . . . . . 65 130 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 65 131 6. Security Considerations . . . . . . . . . . . . . . . . . . . 65 132 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 67 133 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 68 134 8.1. Normative References . . . . . . . . . . . . . . . . . . 69 135 8.2. Informative References . . . . . . . . . . . . . . . . . 70 136 Appendix A. Non-Normative Considerations . . . . . . . . . . . . 78 137 A.1. Implementation Strategies for Route Optimization . . . . 78 138 A.2. Implicit Mobility Management . . . . . . . . . . . . . . 79 139 A.3. Direct Underlying Interfaces . . . . . . . . . . . . . . 79 140 A.4. AERO Critical Infrastructure Considerations . . . . . . . 79 141 A.5. AERO Server Failure Implications . . . . . . . . . . . . 80 142 A.6. AERO Client / Server Architecture . . . . . . . . . . . . 81 144 Appendix B. Change Log . . . . . . . . . . . . . . . . . . . . . 83 145 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 83 147 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 scope 237 [I-D.templin-v6ops-pdhost][I-D.templin-6man-dhcpv6-ndopt]. Most 238 notably, a minimal form of PD known as "prefix registration" can 239 be used if the Client knows its prefix in advance and can 240 represent it in the IPv6 source address of an ND 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 Bridges provide hybrid routing/bridging services (as well as a 457 security trust anchor) for nodes on an OMNI link. Bridges use 458 standard IPv6 routing to forward packets both within the same INET 459 partitions and between disjoint INET partitions based on a mid-layer 460 IPv6 encapsulation per [RFC2473]. The inner IP layer experiences a 461 virtual bridging service since the inner IP TTL/Hop Limit is not 462 decremented during forwarding. Each Bridge also peers with Servers 463 and other Bridges in a dynamic routing protocol instance to provide a 464 Distributed Mobility Management (DMM) service for the list of active 465 MNPs (see Section 3.2.3). Bridges present the OMNI link as a set of 466 one or more Mobility Service Prefixes (MSPs) but as link-layer 467 devices need not connect directly to the OMNI link themselves unless 468 an administrative interface is desired. Bridges configure secured 469 tunnels with Servers, Relays, Proxys and other Bridges; they further 470 maintain IP forwarding table entries for each Mobile Network Prefix 471 (MNP) and any other reachable non-MNP prefixes. 473 AERO Servers provide default forwarding and mobility/multilink 474 services for AERO Client Mobile Nodes (MNs). Each Server also peers 475 with Bridges in a dynamic routing protocol instance to advertise its 476 list of associated MNPs (see Section 3.2.3). Servers facilitate PD 477 exchanges with Clients, where each delegated prefix becomes an MNP 478 taken from an MSP. Servers forward packets between OMNI interface 479 neighbors and track each Client's mobility profiles. 481 AERO Clients register their MNPs through PD exchanges with AERO 482 Servers over the OMNI link, and distribute the MNPs to nodes on EUNs. 483 A Client may also be co-resident on the same physical or virtual 484 platform as a Server; in that case, the Client and Server behave as a 485 single functional unit. 487 AERO Proxys provide a conduit for ANET Clients to associate with 488 Servers in external INETs. Client and Servers exchange control plane 489 messages via the Proxy acting as a bridge between the ANET/INET 490 boundary. The Proxy forwards data packets between Clients and the 491 OMNI link according to forwarding information in the neighbor cache. 492 The Proxy function is specified in Section 3.13. 494 AERO Relays are Servers that provide forwarding services between the 495 OMNI interface and INET/EUN interfaces. Relays are provisioned with 496 MNPs the same as for an AERO Client, and also run a dynamic routing 497 protocol to discover any non-MNP IP routes. The Relay advertises the 498 MSP(s) to its connected networks, and distributes all of its 499 associated MNPs and non-MNP IP routes via BGP peerings with Bridges. 501 AERO Bridges, Servers, Proxys and Relays are critical infrastructure 502 elements in fixed (i.e., non-mobile) INET deployments and hence have 503 permanent and unchanging INET addresses. AERO Clients are MNs that 504 connect via underlying interfaces with addresses that may change when 505 the Client moves to a new network connection point. 507 3.2. The AERO Service over OMNI Links 509 3.2.1. AERO/OMNI Reference Model 511 Figure 1 presents the basic OMNI link reference model: 513 +----------------+ 514 | AERO Bridge B1 | 515 | Nbr: S1, S2, P1| 516 |(X1->S1; X2->S2)| 517 | MSP M1 | 518 +-+---------+--+-+ 519 +--------------+ | Secured | | +--------------+ 520 |AERO Server S1| | tunnels | | |AERO Server S2| 521 | Nbr: C1, B1 +-----+ | +-----+ Nbr: C2, B1 | 522 | default->B1 | | | default->B1 | 523 | X1->C1 | | | X2->C2 | 524 +-------+------+ | +------+-------+ 525 | OMNI link | | 526 X===+===+===================+==)===============+===+===X 527 | | | | 528 +-----+--------+ +--------+--+-----+ +--------+-----+ 529 |AERO Client C1| | AERO Proxy P1 | |AERO Client C2| 530 | Nbr: S1 | |(Proxy Nbr Cache)| | Nbr: S2 | 531 | default->S1 | +--------+--------+ | default->S2 | 532 | MNP X1 | | | MNP X2 | 533 +------+-------+ .--------+------. +-----+--------+ 534 | (- Proxyed Clients -) | 535 .-. `---------------' .-. 536 ,-( _)-. ,-( _)-. 537 .-(_ IP )-. +-------+ +-------+ .-(_ IP )-. 538 (__ EUN )--|Host H1| |Host H2|--(__ EUN ) 539 `-(______)-' +-------+ +-------+ `-(______)-' 541 Figure 1: AERO/OMNI Reference Model 543 In this model: 545 o the OMNI link is an overlay network service configured over one or 546 more underlying INET partitions which may be managed by different 547 administrative authorities and have incompatible protocols and/or 548 addressing plans. 550 o AERO Bridge B1 aggregates Mobility Service Prefix (MSP) M1, 551 discovers Mobile Network Prefixes (MNPs) X* and advertises the MSP 552 via BGP peerings over secured tunnels to Servers (S1, S2). 553 Bridges connect the disjoint segments of a partitioned OMNI link. 555 o AERO Servers/Relays S1 and S2 configure secured tunnels with 556 Bridge B1 and also provide mobility, multilink and default router 557 services for their associated Clients C1 and C2. 559 o AERO Clients C1 and C2 associate with Servers S1 and S2, 560 respectively. They receive Mobile Network Prefix (MNP) 561 delegations X1 and X2, and also act as default routers for their 562 associated physical or internal virtual EUNs. Simple hosts H1 and 563 H2 attach to the EUNs served by Clients C1 and C2, respectively. 565 o AERO Proxy P1 configures a secured tunnel with Bridge B1 and 566 provides proxy services for AERO Clients in secured enclaves that 567 cannot associate directly with other OMNI link neighbors. 569 An OMNI link configured over a single INET appears as a single 570 unified link with a consistent underlying network addressing plan. 571 In that case, all nodes on the link can exchange packets via simple 572 INET encapsulation, since the underlying INET is connected. In 573 common practice, however, an OMNI link may be partitioned into 574 multiple "segments", where each segment is a distinct INET 575 potentially managed under a different administrative authority (e.g., 576 as for worldwide aviation service providers such as ARINC, SITA, 577 Inmarsat, etc.). Individual INETs may also themselves be partitioned 578 internally, in which case each internal partition is seen as a 579 separate segment. 581 The addressing plan of each segment is consistent internally but will 582 often bear no relation to the addressing plans of other segments. 583 Each segment is also likely to be separated from others by network 584 security devices (e.g., firewalls, proxies, packet filtering 585 gateways, etc.), and in many cases disjoint segments may not even 586 have any common physical link connections. Therefore, nodes can only 587 be assured of exchanging packets directly with correspondents in the 588 same segment, and not with those in other segments. The only means 589 for joining the segments therefore is through inter-domain peerings 590 between AERO Bridges. 592 The same as for traditional campus LANs, multiple OMNI link segments 593 can be joined into a single unified link via a virtual bridging 594 service using a mid-layer IPv6 encpasulation per [RFC2473] known as 595 the "SPAN header" that supports inter-segment forwarding (i.e., 596 bridging) without decrementing the network-layer TTL/Hop Limit. This 597 bridging of OMNI link segments is shown in Figure 2: 599 . . . . . . . . . . . . . . . . . . . . . . . 600 . . 601 . .-(::::::::) . 602 . .-(::::::::::::)-. +-+ . 603 . (:::: Segment A :::)--|B|---+ . 604 . `-(::::::::::::)-' +-+ | . 605 . `-(::::::)-' | . 606 . | . 607 . .-(::::::::) | . 608 . .-(::::::::::::)-. +-+ | . 609 . (:::: Segment B :::)--|B|---+ . 610 . `-(::::::::::::)-' +-+ | . 611 . `-(::::::)-' | . 612 . | . 613 . .-(::::::::) | . 614 . .-(::::::::::::)-. +-+ | . 615 . (:::: Segment C :::)--|B|---+ . 616 . `-(::::::::::::)-' +-+ | . 617 . `-(::::::)-' | . 618 . | . 619 . ..(etc).. x . 620 . . 621 . . 622 . <- OMNI link Bridged by encapsulation -> . 623 . . . . . . . . . . . . . .. . . . . . . . . 625 Figure 2: Bridging OMNI Link Segments 627 Bridges, Servers, Relays and Proxys connect via secured INET tunnels 628 over their respecitve segments in a spanning tree topology rooted at 629 the Bridges. The secured spanning tree supports strong 630 authentication for IPv6 ND control messages and may also be used to 631 convey the initial data packets in a flow. Route optimization can 632 then be employed to cause data packets to take more direct paths 633 between OMNI link neighbors without having to strictly follow the 634 spanning tree. 636 3.2.2. Link-Local Addresses (LLAs) and Unique Local Addresses (ULAs) 638 AERO nodes on OMNI links use the Link-Local Address (LLA) prefix 639 fe80::/10 [RFC4193] to assign LLAs used for network-layer addresses 640 in IPv6 ND and data messages. They also use the Unique Local Address 641 (ULA) prefix fc80::/10 [RFC4193] to form ULAs used for SPAN header 642 source and desitnation addresses. See 643 [I-D.templin-6man-omni-interface] for a full specification of the 644 LLAs and ULAs used by AERO nodes on OMNI links. 646 For routing system organization (see Section 3.2.3), ULAs are 647 organized in partition prefixes, e.g., fc80::1000/116. For each such 648 partition prefix, the Bridge(s) that connect that segment assign the 649 :: address of the prefix as a Subnet Router Anycast address. For 650 example, the Subnet Router Anycast address for fc80::1000/116 is 651 simply fc80::1000. 653 3.2.3. AERO Routing System 655 The AERO routing system comprises a private instance of the Border 656 Gateway Protocol (BGP) [RFC4271] that is coordinated between Bridges 657 and Servers and does not interact with either the public Internet BGP 658 routing system or any underlying INET routing systems. 660 In a reference deployment, each Server is configured as an Autonomous 661 System Border Router (ASBR) for a stub Autonomous System (AS) using 662 an AS Number (ASN) that is unique within the BGP instance, and each 663 Server further uses eBGP to peer with one or more Bridges but does 664 not peer with other Servers. Each INET of a multi-segment OMNI link 665 must include one or more Bridges, which peer with the Servers and 666 Proxys within that INET. All Bridges within the same INET are 667 members of the same hub AS using a common ASN, and use iBGP to 668 maintain a consistent view of all active MNPs currently in service. 669 The Bridges of different INETs peer with one another using eBGP. 671 Bridges advertise the OMNI link's MSPs and any non-MNP routes to each 672 of their Servers. This means that any aggregated non-MNPs (including 673 "default") are advertised to all Servers. Each Bridge configures a 674 black-hole route for each of its MSPs. By black-holing the MSPs, the 675 Bridge will maintain forwarding table entries only for the MNPs that 676 are currently active, and packets destined to all other MNPs will 677 correctly incur Destination Unreachable messages due to the black- 678 hole route. In this way, Servers have only partial topology 679 knowledge (i.e., they know only about the MNPs of their directly 680 associated Clients) and they forward all other packets to Bridges 681 which have full topology knowledge. 683 Each OMNI link segment assigns a unique sub-prefix of fc80::/96 known 684 as the ULA partition prefix. For example, a first segment could 685 assign fc80::1000/116, a second could assign fc80::2000/116, a third 686 could assign fc80::3000/116, etc. The administrative authorities for 687 each segment must therefore coordinate to assure mutually-exclusive 688 partiton prefix assignments, but internal provisioning of each prefix 689 is an independent local consideration for each administrative 690 authority. 692 ULA partition prefixes are statitcally represented in Bridge 693 forwarding tables. Bridges join multiple segments into a unified 694 OMNI link over multiple diverse administrative domains. They support 695 a bridging function by first establishing forwarding table entries 696 for their partiion prefixes either via standard BGP routing or static 697 routes. For example, if three Bridges ('A', 'B' and 'C') from 698 different segments serviced fc80::1000/116, fc80::2000/116 and 699 fc80::3000/116 respectively, then the forwarding tables in each 700 Bridge are as follows: 702 A: fc80::1000/116->local, fc80::2000/116->B, fc80::3000/116->C 704 B: fc80::1000/116->A, fc80::2000/116->local, fc80::3000/116->C 706 C: fc80::1000/116->A, fc80::2000/116->B, fc80::3000/116->local 708 These forwarding table entries are permanent and never change, since 709 they correspond to fixed infrastructure elements in their respective 710 segments. 712 ULA Client prefixes are instead dynamically advertised in the AERO 713 routing system by Servers and Relays that provide service for their 714 corresponding MNPs. For example, if three Servers ('D', 'E' and 'F') 715 service the MNPs 2001:db8:1000:2000::/56, 2001:db8:3000:4000::/56 and 716 2001:db8:5000:6000::/56 then the routing system would include: 718 D: fc80:2001:db8:1000:2000::/72 720 E: fc80:2001:db8:3000:4000::/72 722 F: fc80:2001:db8:5000:6000::/72 724 A full discussion of the BGP-based routing system used by AERO is 725 found in [I-D.ietf-rtgwg-atn-bgp]. The system provides for 726 Distributed Mobility Management (DMM) per the distributed mobility 727 anchoring architecture [I-D.ietf-dmm-distributed-mobility-anchoring]. 729 3.2.4. AERO Encapsulation 731 With the Client and partition prefixes in place in each Bridge's 732 forwarding table, control and data packets sent between AERO nodes in 733 different segments can therefore be carried over the via mid-layer 734 encapsulation using the SPAN header. For example, when a source AERO 735 node forwards a packet with IPv6 address 2001:db8:1:2::1 to a target 736 AERO node with IPv6 address 2001:db8:1000:2000::1, it first 737 encapsulates the packet in a SPAN header with source address set to 738 fc80:2001:db8:1:2:: and destination address set to 739 fc80:2001:db8:1000:2000::. Next, it encapsulates the resulting SPAN 740 packet in an INET header with source address set to its own INET 741 address (e.g., 192.0.2.100) and destination set to the INET address 742 of a Bridge (e.g., 192.0.2.1). 744 SPAN encapsulation is based on Generic Packet Tunneling in IPv6 745 [RFC2473]; the encapsulation format in the above example is shown in 746 Figure 3: 748 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 749 | INET Header | 750 | src = 192.0.2.100 | 751 | dst = 192.0.2.1 | 752 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 753 | SPAN Header | 754 | src = fc80:2001:db8:1:2:: | 755 | dst=fc80:2001:db8:1000:2000:: | 756 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 757 | Inner IP Header | 758 | src = 2001:db8:1:2::1 | 759 | dst = 2001:db8:1000:2000::1 | 760 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 761 | | 762 ~ ~ 763 ~ Inner Packet Body ~ 764 ~ ~ 765 | | 766 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 768 Figure 3: SPAN Encapsulation 770 In this format, the inner IP header and packet body are the original 771 IP packet, the SPAN header is an IPv6 header prepared according to 772 [RFC2473], and the INET header is prepared as discussed in 773 Section 3.6. 775 This gives rise to a routing system that contains both Client prefix 776 routes that may change dynamically due to regional node mobility and 777 partion prefix routes that never change. The Bridges can therefore 778 provide link-layer bridging by sending packets over the SRT instead 779 of network-layer routing according to MNP routes. As a result, 780 opportunities for packet loss due to node mobility between different 781 segments are mitigated. 783 In normal operations, IPv6 ND messages are conveyed over secured 784 paths between OMNI link neighbors so that specific Proxys, Servers or 785 Relays can be addressed without being subject to mobility events. 786 Conversely, only the first few packets destined to Clients need to 787 traverse secured paths until route optimization can determine a more 788 direct path. 790 3.2.5. Segment Routing Topologies (SRTs) 792 The 16-bit sub-prefixes of fc80::/10 (e.g., fc80::/16, fc81::/16, 793 fc82::/16, etc.) identify distinct Segment Routing Topologies (SRTs) 794 (see: Section 3.2.5). Each SRT is a mutually-exclusive OMNI link 795 overlay instance using a mutually-exclusive set of ULAs, and emulates 796 a Virtual LAN (VLAN) service for the OMNI link. In some cases (e.g., 797 when redundant topologies are needed for fault tolerance and 798 reliability) it may be beneficial to deploy multiple SRTs that act as 799 independent overlay instances. A communication failure in one 800 instance therefore will not affect communications in other instances. 802 Each SRT is identified by a distinct value in bits 10-15 of he SSP 803 fc80::10, i.e., as fc80::/16, fc81::/16, fc82::/16, etc. This 804 document asserts that up to four SRTs provide a level of safety 805 sufficient for critical communications such as civil aviation. Each 806 SRT is designated with a color that identifies a different OMNI link 807 instance as follows: 809 o Red - corresponds to the SSP fc80::/16 811 o Green - corresponds to the SSP fc81::/16 813 o Blue-1 - corresponds to the SSP fc82::/16 815 o Blue-2 - corresponds to SSP fc83::/16 817 o SSPs fc84::/16 through fcbf::/16 are reserved for future use. 819 Each OMNI interface assigns an anycast ULA corresponding to its SRT 820 prefix. For example, the anycast ULA for the Green SRT is simply 821 fc81::. The anycast ULA is used for OMNI interface determination in 822 Safety-Based Multilink (SBM) as discussed in 823 [I-D.templin-6man-omni-interface]. Each OMNI interface further 824 applies Performance-Based Multilink (PBM) internally. 826 3.2.6. Segment Routing To the OMNI Link 828 An original IPv6 source can direct a packet to a specific SRT ingress 829 router for the OMNI link by including a Segment Routing Header (SRH) 830 with the anycast ULA for the selected SRT as either the IPv6 831 destination or as an intermediate segment ID within the SRH. This 832 allows the original source to determine the specific topology a 833 packet will traverse when there may be multiple alternatives to 834 choose from. This form of Segment Routing supports Safety-Based 835 Multilink (SBM), and can be exercised through general-purpose SRH 836 types such as [RFC8754]. 838 3.2.7. Segment Routing Within the OMNI Link 840 AERO nodes that insert a SPAN header can use Segment Routing within 841 the OMNI link when necessary to influence the path of packets 842 destined to INET Clients without causing all packets to traverse the 843 Server. 845 When a Client, Proxy or Server has a packet to send to a target 846 discovered through route optimization located in the same OMNI link 847 segment, it encapsulates the packet in a SPAN header with the ULA of 848 the target as the destination address if fragmentation is necessary, 849 then uses the target's Link Layer Address information for INET 850 encapsulation without including an SRH. 852 When a Client, Proxy or Server has a packet to send to a route 853 optimization target located in a different OMNI link segment, it 854 encapsulates the packet in a SPAN header with its own ULA as the 855 source address and with destination set according to the target. If 856 the route optimization target is located behind a Proxy or Server, 857 the node sets the SPAN destination address to the ULA of the Proxy/ 858 Server and forwards the packet to a Bridge without including an SRH. 860 If the route optimization target in a foreign segment is an INET 861 Client, the node instead sets the SPAN destination address to the ULA 862 Subnet Router Anycast address of the foreign segment. The node also 863 includes a SRH [RFC8754] with the ULA of the target's Server as the 864 ultimate Segment ID (SID) and with an AERO Route Optimization 865 specification in the SRH TLV section as shown in Figure 4: 867 0 1 2 3 868 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 1 869 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 870 | Type=TBD | Length |FMT|V| Preflen | MNP[1] | 871 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 872 | MNP[2] | MNP[3] | ... | MNP[i] | 873 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 874 ~ Link Layer Address ~ 875 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 876 | Port Number | 877 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 879 Figure 4: AERO Route Optimization SRH TLV 881 In this format: 883 o Type is TBD to be assigned according to the Segment Routing Header 884 TLV registry [RFC8754]. 886 o Length is the length of the body of the TLV in bytes, excluding 887 the Type and Length fields. 889 o FMT is a two bit code that determines the format of the Link Layer 890 Address exactly as specified in Figure 5. 892 o V indicates the IP protocol version of the MNP that follows. V is 893 set to 0 for IPv4 or 1 for IPv6. 895 o Preflen encodes the value 'i' (between 0 and 16) that indicates 896 the number of bytes of the IPv4/IPv6 MNP prefix that follows. 898 o MNP{1], MNP[2], etc. up to MNP[i] encode the leading 'i' octets of 899 the MNP, beginning with the most significant octet followed by the 900 next most significant octet, etc. The number of MNP octets to be 901 included is determined by the number of trailing zero octets in 902 the prefix. For example, for the MNP 2001:db8:1:2::, 'i' is set 903 to 8 and only the leftmost 8 octets of the MNP are included. 905 o Link Layer Address and Port Number are encoded according to FMT 906 exactly as specified in Figure 5. 908 The node then forwards the packet via a local Bridge, which will 909 eventually direct it to a Bridge on the same segment as the target's 910 Server. 912 When a Bridge on the same segment as the target's Server receives a 913 SPAN-encapsulated packet, it examines the SRH. If Segments Left is 1 914 and the ultimate SID is a Server on the local segment, it checks to 915 see if there is an AERO Route Optimization TLV. If so, the Bridge 916 places the MNP into the IPv6 destination address (i.e., as a Subnet 917 Router Anycast address) and encapsulates the SPAN packet in an INET 918 header based on the target's Link Layer Address, then forwards the 919 packet to the target directly while bypassing the target's Server. 921 In this way, the Bridge participates in route optimization to greatly 922 reduce traffic load and suboptimal routing through the target's 923 Server. Note that if the Bridge does not recognize the AERO Route 924 Optimization TLV, it instead places the Server's address in the IPv6 925 destination address and forwards to the Server. This is the same 926 behavior that would occur if the AERO Route Optimization TLV were not 927 present. 929 3.2.8. Segment Routing Header Compression 931 In the Segment Routing use cases discussed above, the segment routing 932 headers must be kept to a minimum size since source and target 933 Clients may be located behind low-end wireless links (e.g., 1Mbps or 934 less). The Compressed Routing Header (CRH) 935 [I-D.bonica-6man-comp-rtg-hdr] provides a compact form that reduces 936 the header size by omitting information that can already be derived 937 by intermediate Bridges. The CRH Helper 938 option[I-D.bonica-6man-crh-helper-opt] can be used to encode the AERO 939 Route Optimization TLV, and the final hop Bridge that performs route 940 optimization may remove the CRH and its helper before encapsulating 941 and forwarding to the target Client. 943 The CRH and its companion helper option are therefore seen as 944 critical architectural elements that should be quickly progressed 945 through the standards process. Implementations SHOULD use the CRH 946 and its companion helper option instead of other Routing Header types 947 whenever possible to conserve bandwidth. 949 3.3. OMNI Interface Characteristics 951 OMNI interfaces are virtual interfaces configured over one or more 952 underlying interfaces classified as follows: 954 o INET interfaces connect to an INET either natively or through one 955 or several IPv4 Network Address Translators (NATs). Native INET 956 interfaces have global IP addresses that are reachable from any 957 INET correspondent. All Server, Relay and Bridge interfaces are 958 native interfaces, as are INET-facing interfaces of Proxys. NATed 959 INET interfaces connect to a private network behind one or more 960 NATs that provide INET access. Clients that are behind a NAT are 961 required to send periodic keepalive messages to keep NAT state 962 alive when there are no data packets flowing. 964 o Proxyed interfaces connect to an ANET that is separated from the 965 open INET by an AERO Proxy. Proxys can actively issue control 966 messages over the INET on behalf of the Client to reduce ANET 967 congestion. Clients connected to Proxyed interfaces receive RAs 968 with the P flag set to 1. 970 o VPNed interfaces use security encapsulation over the INET to a 971 Virtual Private Network (VPN) server that also acts as an AERO 972 Server. Other than the link-layer encapsulation format, VPNed 973 interfaces behave the same as Direct interfaces. 975 o Direct interfaces connect a Client directly to a Server without 976 crossing any ANET/INET paths. An example is a line-of-sight link 977 between a remote pilot and an unmanned aircraft. The same Client 978 considerations apply as for VPNed interfaces. 980 OMNI interfaces use SPAN encapsulation as necessary as discussed in 981 Section 3.2.4. OMNI interfaces use link-layer encapsulation (see: 983 Section 3.6) to exchange packets with OMNI link neighbors over INET 984 or VPNed interfaces. OMNI interfaces do not use link-layer 985 encapsulation over Proxyed and Direct underlying interfaces. 987 OMNI interfaces maintain a neighbor cache for tracking per-neighbor 988 state the same as for any interface. OMNI interfaces use ND messages 989 including Router Solicitation (RS), Router Advertisement (RA), 990 Neighbor Solicitation (NS) and Neighbor Advertisement (NA) for 991 neighbor cache management. 993 OMNI interfaces send ND messages with an OMNI option formatted as 994 specified in [I-D.templin-6man-omni-interface]. The OMNI option 995 includes prefix registration information and "ifIndex-tuples" 996 containing link information parameters for the OMNI interface's 997 underlying interfaces. 999 When SPAN encapsulation is used, OMNI interface ND messages MAY also 1000 include a Source/Target Link-Layer Address Option (S/TLLAO) formatted 1001 as shown in Figure 5: 1003 0 1 2 3 1004 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 1005 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1006 | Type | Length | ifIndex[1] | SRT | LHS |FMT| 1007 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1008 ~ Segment Routing List [1] ~ 1009 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1010 ~ Link Layer Address [1] ~ 1011 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1012 | Port Number [1] | ifIndex[2] | SRT | LHS |FMT| 1013 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1014 ~ Segment Routing List [2] ~ 1015 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1016 ~ Link Layer Address [2] ~ 1017 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1018 | Port Number [2] | .... ~ 1019 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ 1020 ~ ... ~ 1021 ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1022 ~ | ifIndex[N] | SRT | LHS |FMT| 1023 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1024 ~ Segment Routing List [N] ~ 1025 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1026 ~ Link Layer Address [N] ~ 1027 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1028 | Port Number [N] | Zero Padding (if necessary) ... 1029 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1031 Figure 5: OMNI Source/Target Link-Layer Address Option (S/TLLAO) 1032 Format 1034 In this format, Type and Length are set the same as specified for S/ 1035 TLLAOs in [RFC4861], with trailing zero padding octets added as 1036 necessary to produce an integral number of 8 octet blocks. The S/ 1037 TLLAO includes N ifIndex-tuples in correspondence to ifIndex-tuples 1038 that appear in the OMNI option. Each ifIndex-tuple includes the 1039 following information: 1041 o ifIndex[i] - the same value as in the corresponding ifIndex-tuple 1042 included in the OMNI option. 1044 o SRT[i] - a 3-bit "Segment Routing Topology" value (see: 1045 Section 3.2.5) coded as follows: 1047 * 000 - Red 1049 * 001 - Green 1050 * 010 - Blue-1 1052 * 011 - Blue-2 1054 * 100 - 111 - Reserved 1056 o LHS[i] - a 3-bit "LookaHead Segments" value that encodes the 1057 number (from 0 to 7) of entries in Segment Routing List [i]. 1059 o FMT[i] - a 2-bit "Format" code. Determines the format of the Link 1060 Layer Address [i] field as follows: 1062 * 00 - Link Layer Address [i] encodes an IPv4 address for a node 1063 behind a NAT. 1065 * 01 - Link Layer Address [i] encodes an IPv4 address for a node 1066 on the open INET. 1068 * 10 - Link Layer Address [i] encodes an IPv6 address for a node 1069 behind a NAT.. 1071 * 11 - Link Layer Address [i] encodes an IPv6 address for a node 1072 on the open INET. 1074 o Segment Routing List [i] - Includes LHS[i]-many 4 byte ULA 1075 suffixes from the SRT corresponding to the Segment IDs (SIDs) that 1076 must be visited prior to forwarding to Link Layer Address [i]. 1077 The ultimate SID appears first, followed by the penultimate SID 1078 second, etc. 1080 o Link Layer Address [i] - Included according to FMT[i], and 1081 identifies the link-layer address of the source/target. The IP 1082 address is recorded in ones-compliment "obfuscated" form per 1083 [RFC4380]. 1085 o Port Number [i] - The field is 2 bytes in length and immediately 1086 follows Link Layer Address [i]. Also recorded in ones-compliment 1087 "obfuscated" form. 1089 If an S/TLLAO is included, any ifIndex-tuples correspond to a proper 1090 subset of the OMNI option ifIndex-tuples. Any S/TLLAO ifIndex-tuple 1091 having an ifIndex value that does not appear in an OMNI option 1092 ifindex-tuple is ignored. If the same ifIndex value appears in 1093 multiple ifIndex-tuples, the first tuple is processed and the 1094 remaining tuples are ignored. Any S/TLLAO ifIndex-tuples can 1095 therefore be viewed as extensions of their corresponding OMNI option 1096 ifIndex-tuples, i.e., the OMNI option and S/TLLAO are companions that 1097 are interpreted in conjunction with each other. 1099 A Client's OMNI interface may be configured over multiple underlying 1100 interface connections. For example, common mobile handheld devices 1101 have both wireless local area network ("WLAN") and cellular wireless 1102 links. These links are often used "one at a time" with low-cost WLAN 1103 preferred and highly-available cellular wireless as a standby, but a 1104 simultaneous-use capability could provide benefits. In a more 1105 complex example, aircraft frequently have many wireless data link 1106 types (e.g. satellite-based, cellular, terrestrial, air-to-air 1107 directional, etc.) with diverse performance and cost properties. 1109 If a Client's multiple underlying interfaces are used "one at a time" 1110 (i.e., all other interfaces are in standby mode while one interface 1111 is active), then ND message OMNI options include only a single 1112 ifIndex-tuple set to constant values. In that case, the Client would 1113 appear to have a single interface but with a dynamically changing 1114 link-layer address. 1116 If the Client has multiple active underlying interfaces, then from 1117 the perspective of ND it would appear to have multiple link-layer 1118 addresses. In that case, ND message OMNI options MAY include 1119 multiple ifIndex-tuples - each with values that correspond to a 1120 specific interface. Every ND message need not include all OMNI and/ 1121 or S/TLLAO ifIndex-tuples; for any ifIndex-tuple not included, the 1122 neighbor considers the status as unchanged. 1124 Bridge, Server and Proxy OMNI interfaces may be configured over one 1125 or more secured tunnel interfaces. The OMNI interface configures 1126 both an LLA and its corresponding ULA, while the underlying secured 1127 tunnel interfaces are either unnumbered or configure the same ULA. 1128 The OMNI interface encapsulates each IP packet in a SPAN header and 1129 presents the packet to the underlying secured tunnel interface. For 1130 Bridges that do not configure an OMNI interface, the secured tunnel 1131 interfaces themselves are exposed to the IP layer with each interface 1132 configuring the Bridge's ULA. Routing protocols such as BGP 1133 therefore run directly over the Bridge's secured tunnel interfaces. 1134 For nodes that configure an OMNI interface, routing protocols such as 1135 BGP run over the OMNI interface but do not employ SPAN encapsulation. 1136 Instead, the OMNI interface presents the routing protocol messages 1137 directly to the underlying secured tunnels without applying 1138 encapsulation and while using the ULA as the source address. This 1139 distinction must be honored consistently according to each node's 1140 configuration so that the IP forwarding table will associate 1141 discovered IP routes with the correct interface. 1143 3.4. OMNI Interface Initialization 1145 AERO Servers, Proxys and Clients configure OMNI interfaces as their 1146 point of attachment to the OMNI link. AERO nodes assign the MSPs for 1147 the link to their OMNI interfaces (i.e., as a "route-to-interface") 1148 to ensure that packets with destination addresses covered by an MNP 1149 not explicitly assigned to a non-OMNI interface are directed to the 1150 OMNI interface. 1152 OMNI interface initialization procedures for Servers, Proxys, Clients 1153 and Bridges are discussed in the following sections. 1155 3.4.1. AERO Server/Relay Behavior 1157 When a Server enables an OMNI interface, it assigns an LLA/ULA 1158 appropriate for the given OMNI link segment. The Server also 1159 configures secured tunnels with one or more neighboring Bridges and 1160 engages in a BGP routing protocol session with each Bridge. 1162 The OMNI interface provides a single interface abstraction to the IP 1163 layer, but internally comprises multiple secured tunnels as well as 1164 an NBMA nexus for sending encapsulated data packets to OMNI interface 1165 neighbors. The Server further configures a service to facilitate ND/ 1166 PD exchanges with AERO Clients and manages per-Client neighbor cache 1167 entries and IP forwarding table entries based on control message 1168 exchanges. 1170 Relays are simply Servers that run a dynamic routing protocol to 1171 redistribute routes between the OMNI interface and INET/EUN 1172 interfaces (see: Section 3.2.3). The Relay provisions MNPs to 1173 networks on the INET/EUN interfaces (i.e., the same as a Client would 1174 do) and advertises the MSP(s) for the OMNI link over the INET/EUN 1175 interfaces. The Relay further provides an attachment point of the 1176 OMNI link to a non-MNP-based global topology. 1178 3.4.2. AERO Proxy Behavior 1180 When a Proxy enables an OMNI interface, it assigns an LLA/ULA and 1181 configures permanent neighbor cache entries the same as for Servers. 1182 The Proxy also configures secured tunnels with one or more 1183 neighboring Bridges and maintains per-Client neighbor cache entries 1184 based on control message exchanges. 1186 3.4.3. AERO Client Behavior 1188 When a Client enables an OMNI interface, it sends RS messages with 1189 ND/PD parameters over its underlying interfaces to a Server in the 1190 MAP list, which returns an RA message with corresponding parameters. 1192 (The RS/RA messages may pass through a Proxy in the case of a 1193 Client's Proxyed interface, or through one or more NATs in the case 1194 of a Client's INET interface.) 1196 3.4.4. AERO Bridge Behavior 1198 AERO Bridges configure an OMNI interface and assign the ULA Subnet 1199 Router Anycast address for each OMNI link segment they connect to. 1200 Bridges configure secured tunnels with Servers, Proxys and other 1201 Bridges; they also configure LLAs/ULAs and permanent neighbor cache 1202 entries the same as Servers. Bridges engage in a BGP routing 1203 protocol session with a subset of the Servers and other Bridges on 1204 the spanning tree (see: Section 3.2.3). 1206 3.5. OMNI Interface Neighbor Cache Maintenance 1208 Each OMNI interface maintains a conceptual neighbor cache that 1209 includes an entry for each neighbor it communicates with on the OMNI 1210 link per [RFC4861]. OMNI interface neighbor cache entries are said 1211 to be one of "permanent", "symmetric", "asymmetric" or "proxy". 1213 Permanent neighbor cache entries are created through explicit 1214 administrative action; they have no timeout values and remain in 1215 place until explicitly deleted. AERO Bridges maintain permanent 1216 neighbor cache entries for their associated Proxys and Servers (and 1217 vice-versa). Each entry maintains the mapping between the neighbor's 1218 network-layer LLA and corresponding INET address. 1220 Symmetric neighbor cache entries are created and maintained through 1221 RS/RA exchanges as specified in Section 3.12, and remain in place for 1222 durations bounded by ND/PD lifetimes. AERO Servers maintain 1223 symmetric neighbor cache entries for each of their associated 1224 Clients, and AERO Clients maintain symmetric neighbor cache entries 1225 for each of their associated Servers. The list of all Servers on the 1226 OMNI link is maintained in the link's MAP list. 1228 Asymmetric neighbor cache entries are created or updated based on 1229 route optimization messaging as specified in Section 3.14, and are 1230 garbage-collected when keepalive timers expire. AERO ROSs maintain 1231 asymmetric neighbor cache entries for active targets with lifetimes 1232 based on ND messaging constants. Asymmetric neighbor cache entries 1233 are unidirectional since only the ROS (and not the ROR) creates an 1234 entry. 1236 Proxy neighbor cache entries are created and maintained by AERO 1237 Proxys when they process Client/Server ND/PD exchanges, and remain in 1238 place for durations bounded by ND/PD lifetimes. AERO Proxys maintain 1239 proxy neighbor cache entries for each of their associated Clients. 1241 Proxy neighbor cache entries track the Client state and the address 1242 of the Client's associated Server(s). 1244 To the list of neighbor cache entry states in Section 7.3.2 of 1245 [RFC4861], Proxy and Server OMNI interfaces add an additional state 1246 DEPARTED that applies to symmetric and proxy neighbor cache entries 1247 for Clients that have recently departed. The interface sets a 1248 "DepartTime" variable for the neighbor cache entry to "DEPART_TIME" 1249 seconds. DepartTime is decremented unless a new ND message causes 1250 the state to return to REACHABLE. While a neighbor cache entry is in 1251 the DEPARTED state, packets destined to the target Client are 1252 forwarded to the Client's new location instead of being dropped. 1253 When DepartTime decrements to 0, the neighbor cache entry is deleted. 1254 It is RECOMMENDED that DEPART_TIME be set to the default constant 1255 value REACHABLE_TIME plus 10 seconds (40 seconds by default) to allow 1256 a window for packets in flight to be delivered while stale route 1257 optimization state may be present. 1259 When an ROR receives an authentic NS message used for route 1260 optimization, it searches for a symmetric neighbor cache entry for 1261 the target Client. The ROR then returns a solicited NA message 1262 without creating a neighbor cache entry for the ROS, but creates or 1263 updates a target Client "Report List" entry for the ROS and sets a 1264 "ReportTime" variable for the entry to REPORT_TIME seconds. The ROR 1265 resets ReportTime when it receives a new authentic NS message, and 1266 otherwise decrements ReportTime while no authentic NS messages have 1267 been received. It is RECOMMENDED that REPORT_TIME be set to the 1268 default constant value REACHABLE_TIME plus 10 seconds (40 seconds by 1269 default) to allow a window for route optimization to converge before 1270 ReportTime decrements below REACHABLE_TIME. 1272 When the ROS receives a solicited NA message response to its NS 1273 message used for route optimization, it creates or updates an 1274 asymmetric neighbor cache entry for the target network-layer and 1275 link-layer addresses. The ROS then (re)sets ReachableTime for the 1276 neighbor cache entry to REACHABLE_TIME seconds and uses this value to 1277 determine whether packets can be forwarded directly to the target, 1278 i.e., instead of via a default route. The ROS otherwise decrements 1279 ReachableTime while no further solicited NA messages arrive. It is 1280 RECOMMENDED that REACHABLE_TIME be set to the default constant value 1281 30 seconds as specified in [RFC4861]. 1283 AERO nodes also use the value MAX_UNICAST_SOLICIT to limit the number 1284 of NS keepalives sent when a correspondent may have gone unreachable, 1285 the value MAX_RTR_SOLICITATIONS to limit the number of RS messages 1286 sent without receiving an RA and the value MAX_NEIGHBOR_ADVERTISEMENT 1287 to limit the number of unsolicited NAs that can be sent based on a 1288 single event. It is RECOMMENDED that MAX_UNICAST_SOLICIT, 1289 MAX_RTR_SOLICITATIONS and MAX_NEIGHBOR_ADVERTISEMENT be set to 3 the 1290 same as specified in [RFC4861]. 1292 Different values for DEPART_TIME, REPORT_TIME, REACHABLE_TIME, 1293 MAX_UNICAST_SOLICIT, MAX_RTR_SOLCITATIONS and 1294 MAX_NEIGHBOR_ADVERTISEMENT MAY be administratively set; however, if 1295 different values are chosen, all nodes on the link MUST consistently 1296 configure the same values. Most importantly, DEPART_TIME and 1297 REPORT_TIME SHOULD be set to a value that is sufficiently longer than 1298 REACHABLE_TIME to avoid packet loss due to stale route optimization 1299 state. 1301 3.6. OMNI Interface Encapsulation and Re-encapsulation 1303 OMNI interfaces insert a mid-layer IPv6 header known as the SPAN 1304 header when necessary as discussed in the following sections. After 1305 either inserting or omitting the SPAN header, the OMNI interface also 1306 inserts or omits an outer encapsulation header as discussed below. 1308 OMNI interfaces avoid outer encapsulation over Direct underlying 1309 interfaces and Proxyed underlying interfaces for which the first-hop 1310 access router is AERO-aware. Other OMNI interfaces encapsulate 1311 packets according to whether they are entering the OMNI interface 1312 from the network layer or if they are being re-admitted into the same 1313 OMNI link they arrived on. This latter form of encapsulation is 1314 known as "re-encapsulation". 1316 For packets entering the OMNI interface from the network layer, the 1317 OMNI interface copies the "TTL/Hop Limit", "Type of Service/Traffic 1318 Class" [RFC2983], "Flow Label"[RFC6438] (for IPv6) and "Congestion 1319 Experienced" [RFC3168] values in the inner packet's IP header into 1320 the corresponding fields in the SPAN and outer encapsulation 1321 header(s). 1323 For packets undergoing re-encapsulation, the OMNI interface instead 1324 copies these values from the original encapsulation header into the 1325 new encapsulation header, i.e., the values are transferred between 1326 encapsulation headers and *not* copied from the encapsulated packet's 1327 network-layer header. (Note especially that by copying the TTL/Hop 1328 Limit between encapsulation headers the value will eventually 1329 decrement to 0 if there is a (temporary) routing loop.) 1331 OMNI interfaces configured over INET underlying interfaces 1332 encapsulate packets in INET headers according to the next hop 1333 determined in the forwarding algorithm in Section 3.10. If the next 1334 hop is reached via a secured tunnel, the OMNI interface uses an 1335 encapsulation format specific to the secured tunnel type (see: 1336 Section 6). If the next hop is reached via an unsecured INET 1337 interface, the OMNI interface instead uses UDP/IP encapsulation per 1338 [RFC4380] and as extended in [RFC6081]. 1340 When UDP/IP encapsulation is used, the OMNI interface next sets the 1341 UDP source port to a constant value that it will use in each 1342 successive packet it sends, and sets the UDP length field to the 1343 length of the encapsulated packet plus 8 bytes for the UDP header 1344 itself plus the length of any included extension headers or trailers. 1345 The encapsulated packet may be either IPv6 or IPv4, as distinguished 1346 by the version number found in the first four bits. 1348 For UDP/IP-encapsulated packets sent to a Server, Relay or Bridge, 1349 the OMNI interface sets the UDP destination port to 8060, i.e., the 1350 IANA-registered port number for AERO. For packets sent to a Client, 1351 the OMNI interface sets the UDP destination port to the port value 1352 stored in the neighbor cache entry for this Client. The OMNI 1353 interface finally includes/omits the UDP checksum according to 1354 [RFC6935][RFC6936]. 1356 3.7. OMNI Interface Decapsulation 1358 OMNI interfaces decapsulate packets destined either to the AERO node 1359 itself or to a destination reached via an interface other than the 1360 OMNI interface the packet was received on. When the encapsulated 1361 packet arrives in multiple SPAN fragments, the OMNI interface 1362 reassembles as discussed in Section 3.9. Further decapsulation steps 1363 are performed according to the appropriate encapsulation format 1364 specification. 1366 3.8. OMNI Interface Data Origin Authentication 1368 AERO nodes employ simple data origin authentication procedures. In 1369 particular: 1371 o AERO Bridges, Servers and Proxys accept encapsulated data packets 1372 and control messages received from the spanning tree. 1374 o AERO Proxys and Clients accept packets that originate from within 1375 the same secured ANET. 1377 o AERO Clients and Relays accept packets from downstream network 1378 correspondents based on ingress filtering. 1380 o AERO Clients, Relays and Servers verify the outer UDP/IP 1381 encapsulation addresses according to [RFC4380]. 1383 AERO nodes silently drop any packets that do not satisfy the above 1384 data origin authentication procedures. Further security 1385 considerations are discussed in Section 6. 1387 3.9. OMNI Interface MTU and Fragmentation 1389 The OMNI interface observes the link nature of tunnels, including the 1390 Maximum Transmission Unit (MTU) and the role of fragmentation and 1391 reassembly[I-D.ietf-intarea-tunnels]. OMNI interface MTU and 1392 fragmentation/reassembly procedures are specified in 1393 [I-D.templin-6man-omni-interface]. 1395 3.10. OMNI Interface Forwarding Algorithm 1397 IP packets enter a node's OMNI interface either from the network 1398 layer (i.e., from a local application or the IP forwarding system) or 1399 from the link layer (i.e., from an OMNI interface neighbor). All 1400 packets entering a node's OMNI interface first undergo data origin 1401 authentication as discussed in Section 3.8. Packets that satisfy 1402 data origin authentication are processed further, while all others 1403 are dropped silently. 1405 Packets that enter the OMNI interface from the network layer are 1406 forwarded to an OMNI interface neighbor. Packets that enter the OMNI 1407 interface from the link layer are either re-admitted into the OMNI 1408 link or forwarded to the network layer where they are subject to 1409 either local delivery or IP forwarding. In all cases, the OMNI 1410 interface itself MUST NOT decrement the network layer TTL/Hop-count 1411 since its forwarding actions occur below the network layer. 1413 OMNI interfaces may have multiple underlying interfaces and/or 1414 neighbor cache entries for neighbors with multiple ifIndex-tuple 1415 registrations (see Section 3.3). The OMNI interface uses traffic 1416 classifiers (e.g., DSCP value, port number, etc.) to select an 1417 outgoing underlying interface for each packet based on the node's own 1418 QoS preferences, and also to select a destination link-layer address 1419 based on the neighbor's underlying interface with the highest 1420 preference. AERO implementations SHOULD allow for QoS preference 1421 values to be modified at runtime through network management. 1423 If multiple outgoing interfaces and/or neighbor interfaces have a 1424 preference of "high", the AERO node replicates the packet and sends 1425 one copy via each of the (outgoing / neighbor) interface pairs; 1426 otherwise, the node sends a single copy of the packet via an 1427 interface with the highest preference. AERO nodes keep track of 1428 which underlying interfaces are currently "reachable" or 1429 "unreachable", and only use "reachable" interfaces for forwarding 1430 purposes. 1432 The following sections discuss the OMNI interface forwarding 1433 algorithms for Clients, Proxys, Servers and Bridges. In the 1434 following discussion, a packet's destination address is said to 1435 "match" if it is the same as a cached address, or if it is covered by 1436 a cached prefix (which may be encoded in an LLA). 1438 3.10.1. Client Forwarding Algorithm 1440 When an IP packet enters a Client's OMNI interface from the network 1441 layer the Client searches for an asymmetric neighbor cache entry that 1442 matches the destination. If there is a match, the Client uses one or 1443 more "reachable" neighbor interfaces in the entry for packet 1444 forwarding. If there is no asymmetric neighbor cache entry, the 1445 Client instead forwards the packet toward a Server (the packet is 1446 intercepted by a Proxy if there is a Proxy on the path). The Client 1447 encapsulates the packet in a SPAN header and fragments if necessary 1448 according to MTU requirements (see: Section 3.9). 1450 When an IP packet enters a Client's OMNI interface from the link- 1451 layer, if the destination matches one of the Client's MNPs or link- 1452 local addresses the Client reassembles and decapsulates as necessary 1453 and delivers the inner packet to the network layer. Otherwise, the 1454 Client drops the packet and MAY return a network-layer ICMP 1455 Destination Unreachable message subject to rate limiting (see: 1456 Section 3.11). 1458 3.10.2. Proxy Forwarding Algorithm 1460 For control messages originating from or destined to a Client, the 1461 Proxy intercepts the message and updates its proxy neighbor cache 1462 entry for the Client. The Proxy then forwards a (proxyed) copy of 1463 the control message. (For example, the Proxy forwards a proxied 1464 version of a Client's NS/RS message to the target neighbor, and 1465 forwards a proxied version of the NA/RA reply to the Client.) 1467 When the Proxy receives a data packet from a Client within the ANET, 1468 the Proxy reassembles and re-fragments if necessary then searches for 1469 an asymmetric neighbor cache entry that matches the destination and 1470 forwards as follows: 1472 o if the destination matches an asymmetric neighbor cache entry, the 1473 Proxy uses one or more "reachable" neighbor interfaces in the 1474 entry for packet forwarding using SPAN encapsulation and including 1475 a SRH if necessary according to the cached TLLAO information. If 1476 the neighbor interface is in the same SPAN segment, the Proxy 1477 forwards the packet directly to the neighbor; otherwise, it 1478 forwards the packet to a Bridge. 1480 o else, the Proxy uses SPAN encapsulation and forwards the packet to 1481 a Bridge while using the ULA corresponding to the packet's 1482 destination as the SPAN destination address. 1484 When the Proxy receives an encapsulated data packet from an INET 1485 neighbor or from a secured tunnel from a Bridge, it accepts the 1486 packet only if data origin authentication succeeds and if there is a 1487 proxy neighbor cache entry that matches the inner destination. Next, 1488 the Proxy reassembles the packet (if necessary) and continues 1489 processing. 1491 Next if reassembly is complete and the neighbor cache state is 1492 REACHABLE, the Proxy returns a PTB if necessary (see: Section 3.9) 1493 then either drops or forwards the packet to the Client while 1494 performing SPAN encapsulation and re-fragmentation to the ANET MTU 1495 size if necessary. If the neighbor cache entry state is DEPARTED, 1496 the Proxy instead changes the SPAN destination address to the address 1497 of the new Server and forwards it to a Bridge while performing re- 1498 fragmentation to 1280 bytes if necessary. 1500 3.10.3. Server/Relay Forwarding Algorithm 1502 For control messages destined to a target Client's LLA that are 1503 received from a secured tunnel, the Server intercepts the message and 1504 sends an appropriate response on behalf of the Client. (For example, 1505 the Server sends an NA message reply in response to an NS message 1506 directed to one of its associated Clients.) If the Client's neighbor 1507 cache entry is in the DEPARTED state, however, the Server instead 1508 forwards the packet to the Client's new Server as discussed in 1509 Section 3.16. 1511 When the Server receives an encapsulated data packet from an INET 1512 neighbor or from a secured tunnel, it accepts the packet only if data 1513 origin authentication succeeds. If the SPAN destination address is 1514 its own address, the Server continues processing as follows: 1516 o if the destination matches a symmetric neighbor cache entry in the 1517 REACHABLE state the Server prepares the packet for forwarding to 1518 the destination Client. The Server first reassembles (if 1519 necessary) and forwards the packet (while re-fragmenting if 1520 necessary) as specified in Section 3.9. 1522 o else, if the destination matches a symmetric neighbor cache entry 1523 in the DEPARETED state the Server re-encapsulates the packet and 1524 forwards it using the ULA of the Client's new Server as the 1525 destination. 1527 o else, if the destination matches an asymmetric neighbor cache 1528 entry, the Server uses one or more "reachable" neighbor interfaces 1529 in the entry for packet forwarding via the local INET if the 1530 neighbor is in the same OMNI link segment or using SPAN 1531 encapsulation and Segment Routing if necessary with the final 1532 destination set to the neighbor's ULA otherwise. 1534 o else, if the destination is an LLA that is not assigned on the 1535 OMNI interface the Server drops the packet. 1537 o else, the Server (acting as a Relay) reassembles if necessary, 1538 decapsulates the packet and releases it to the network layer for 1539 local delivery or IP forwarding. Based on the information in the 1540 forwarding table, the network layer may return the packet to the 1541 same OMNI interface in which case further processing occurs as 1542 below. (Note that this arrangement accommodates common 1543 implementations in which the IP forwarding table is not accessible 1544 from within the OMNI interface. If the OMNI interface can 1545 directly access the IP forwarding table (such as for in-kernel 1546 implementations) the forwarding table lookup can instead be 1547 performed internally from within the OMNI interface itself.) 1549 When the Server's OMNI interface receives a data packet from the 1550 network layer or from a VPNed or Direct Client, it performs SPAN 1551 encapsulation and fragmentation if necessary, then processes the 1552 packet according to the network-layer destination address as follows: 1554 o if the destination matches a symmetric or asymmetric neighbor 1555 cache entry the Server processes the packet as above. 1557 o else, the Server encapsulates the packet and forwards it to a 1558 Bridge using its own ULA as the source and the ULA corresponding 1559 to the destination as the destination. 1561 3.10.4. Bridge Forwarding Algorithm 1563 Bridges forward SPAN-encapsulated packets over secured tunnels the 1564 same as any IP router. When the Bridge receives a SPAN-encapsulated 1565 packet via a secured tunnel, it removes the outer INET header and 1566 searches for a forwarding table entry that matches the SPAN 1567 destination address. The Bridge then processes the packet as 1568 follows: 1570 o if the destination matches its ULA Subnet Router Anycast address, 1571 the Bridge checks for a SRH. If there is a SRH with Segments 1572 Left=1, with the ULA of a Server on the local segment as the 1573 ultimate segment ID, and with an AERO Route Optimization TLV, the 1574 Bridge examines the FMT to determine if the target is behind a 1575 NAT. If no NAT is indicated, the Bridge copies the MNP Subnet 1576 Router Anycast address into the destination address then forwards 1577 the packet directly to the Link Layer Address using link-layer 1578 (UDP/IP) encapsulation. If a NAT is indicated, the Bridge MAY 1579 perform NAT traversal procedures by sending bubbles per [RFC4380]. 1580 The Bridge then either applies AERO route optimization if NAT 1581 traversal procedures have been successfully applied, or forwards 1582 the packet directly to the Server. 1584 o if the destination matches one of the Bridge's own addresses, the 1585 Bridge submits the packet for local delivery. 1587 o else, if the destination matches a forwarding table entry the 1588 Bridge forwards the packet via a secured tunnel to the next hop. 1589 If the destination matches an MSP without matching an MNP, 1590 however, the Bridge instead drops the packet and returns an ICMP 1591 Destination Unreachable message subject to rate limiting (see: 1592 Section 3.11). 1594 o else, the Bridge drops the packet and returns an ICMP Destination 1595 Unreachable as above. 1597 As for any IP router, the Bridge decrements the TTL/Hop Limit when it 1598 forwards the packet. Therefore, only the Hop Limit in the SPAN 1599 header is decremented, and not the TTL/Hop Limit in the inner packet 1600 header. 1602 3.11. OMNI Interface Error Handling 1604 When an AERO node admits a packet into the OMNI interface, it may 1605 receive link-layer or network-layer error indications. 1607 A link-layer error indication is an ICMP error message generated by a 1608 router in the INET on the path to the neighbor or by the neighbor 1609 itself. The message includes an IP header with the address of the 1610 node that generated the error as the source address and with the 1611 link-layer address of the AERO node as the destination address. 1613 The IP header is followed by an ICMP header that includes an error 1614 Type, Code and Checksum. Valid type values include "Destination 1615 Unreachable", "Time Exceeded" and "Parameter Problem" 1616 [RFC0792][RFC4443]. (OMNI interfaces ignore all link-layer IPv4 1617 "Fragmentation Needed" and IPv6 "Packet Too Big" messages since they 1618 only emit packets that are guaranteed to be no larger than the IP 1619 minimum link MTU as discussed in Section 3.9.) 1621 The ICMP header is followed by the leading portion of the packet that 1622 generated the error, also known as the "packet-in-error". For 1623 ICMPv6, [RFC4443] specifies that the packet-in-error includes: "As 1624 much of invoking packet as possible without the ICMPv6 packet 1625 exceeding the minimum IPv6 MTU" (i.e., no more than 1280 bytes). For 1626 ICMPv4, [RFC0792] specifies that the packet-in-error includes: 1627 "Internet Header + 64 bits of Original Data Datagram", however 1628 [RFC1812] Section 4.3.2.3 updates this specification by stating: "the 1629 ICMP datagram SHOULD contain as much of the original datagram as 1630 possible without the length of the ICMP datagram exceeding 576 1631 bytes". 1633 The link-layer error message format is shown in Figure 6 (where, "L2" 1634 and "L3" refer to link-layer and network-layer, respectively): 1636 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1637 ~ ~ 1638 | L2 IP Header of | 1639 | error message | 1640 ~ ~ 1641 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1642 | L2 ICMP Header | 1643 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 1644 ~ ~ P 1645 | IP and other encapsulation | a 1646 | headers of original L3 packet | c 1647 ~ ~ k 1648 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ e 1649 ~ ~ t 1650 | IP header of | 1651 | original L3 packet | i 1652 ~ ~ n 1653 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1654 ~ ~ e 1655 | Upper layer headers and | r 1656 | leading portion of body | r 1657 | of the original L3 packet | o 1658 ~ ~ r 1659 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 1661 Figure 6: OMNI Interface Link-Layer Error Message Format 1663 The AERO node rules for processing these link-layer error messages 1664 are as follows: 1666 o When an AERO node receives a link-layer Parameter Problem message, 1667 it processes the message the same as described as for ordinary 1668 ICMP errors in the normative references [RFC0792][RFC4443]. 1670 o When an AERO node receives persistent link-layer Time Exceeded 1671 messages, the IP ID field may be wrapping before earlier fragments 1672 awaiting reassembly have been processed. In that case, the node 1673 should begin including integrity checks and/or institute rate 1674 limits for subsequent packets. 1676 o When an AERO node receives persistent link-layer Destination 1677 Unreachable messages in response to encapsulated packets that it 1678 sends to one of its asymmetric neighbor correspondents, the node 1679 should process the message as an indication that a path may be 1680 failing, and optionally initiate NUD over that path. If it 1681 receives Destination Unreachable messages over multiple paths, the 1682 node should allow future packets destined to the correspondent to 1683 flow through a default route and re-initiate route optimization. 1685 o When an AERO Client receives persistent link-layer Destination 1686 Unreachable messages in response to encapsulated packets that it 1687 sends to one of its symmetric neighbor Servers, the Client should 1688 mark the path as unusable and use another path. If it receives 1689 Destination Unreachable messages on many or all paths, the Client 1690 should associate with a new Server and release its association 1691 with the old Server as specified in Section 3.16.5. 1693 o When an AERO Server receives persistent link-layer Destination 1694 Unreachable messages in response to encapsulated packets that it 1695 sends to one of its symmetric neighbor Clients, the Server should 1696 mark the underlying path as unusable and use another underlying 1697 path. 1699 o When an AERO Server or Proxy receives link-layer Destination 1700 Unreachable messages in response to an encapsulated packet that it 1701 sends to one of its permanent neighbors, it treats the messages as 1702 an indication that the path to the neighbor may be failing. 1703 However, the dynamic routing protocol should soon reconverge and 1704 correct the temporary outage. 1706 When an AERO Bridge receives a packet for which the network-layer 1707 destination address is covered by an MSP, if there is no more- 1708 specific routing information for the destination the Bridge drops the 1709 packet and returns a network-layer Destination Unreachable message 1710 subject to rate limiting. The Bridge writes the network-layer source 1711 address of the original packet as the destination address and uses 1712 one of its non link-local addresses as the source address of the 1713 message. 1715 When an AERO node receives an encapsulated packet for which the 1716 reassembly buffer it too small, it drops the packet and returns a 1717 network-layer Packet Too Big (PTB) message. The node first writes 1718 the MRU value into the PTB message MTU field, writes the network- 1719 layer source address of the original packet as the destination 1720 address and writes one of its non link-local addresses as the source 1721 address. 1723 3.12. AERO Router Discovery, Prefix Delegation and Autoconfiguration 1725 AERO Router Discovery, Prefix Delegation and Autoconfiguration are 1726 coordinated as discussed in the following Sections. 1728 3.12.1. AERO ND/PD Service Model 1730 Each AERO Server on the OMNI link configures a PD service to 1731 facilitate Client requests. Each Server is provisioned with a 1732 database of MNP-to-Client ID mappings for all Clients enrolled in the 1733 AERO service, as well as any information necessary to authenticate 1734 each Client. The Client database is maintained by a central 1735 administrative authority for the OMNI link and securely distributed 1736 to all Servers, e.g., via the Lightweight Directory Access Protocol 1737 (LDAP) [RFC4511], via static configuration, etc. Clients receive the 1738 same service regardless of the Servers they select. 1740 AERO Clients and Servers use ND messages to maintain neighbor cache 1741 entries. AERO Servers configure their OMNI interfaces as advertising 1742 NBMA interfaces, and therefore send unicast RA messages with a short 1743 Router Lifetime value (e.g., ReachableTime seconds) in response to a 1744 Client's RS message. Thereafter, Clients send additional RS messages 1745 to keep Server state alive. 1747 AERO Clients and Servers include PD parameters in RS/RA messages (see 1748 [I-D.templin-6man-dhcpv6-ndopt] for ND/PD alternatives). The unified 1749 ND/PD messages are exchanged between Client and Server according to 1750 the prefix management schedule required by the PD service. If the 1751 Client knows its MNP in advance, it can instead employ prefix 1752 registration by including its LLA as the source address of an RS 1753 message and with an OMNI option with valid prefix registration 1754 information for the MNP. If the Server (and Proxy) accept the 1755 Client's MNP assertion, they inject the prefix into the routing 1756 system and establish the necessary neighbor cache state. 1758 The following sections specify the Client and Server behavior. 1760 3.12.2. AERO Client Behavior 1762 AERO Clients discover the addresses of Servers in a similar manner as 1763 described in [RFC5214]. Discovery methods include static 1764 configuration (e.g., from a flat-file map of Server addresses and 1765 locations), or through an automated means such as Domain Name System 1766 (DNS) name resolution [RFC1035]. Alternatively, the Client can 1767 discover Server addresses through a layer 2 data link login exchange, 1768 or through a unicast RA response to a multicast/anycast RS as 1769 described below. In the absence of other information, the Client can 1770 resolve the DNS Fully-Qualified Domain Name (FQDN) 1771 "linkupnetworks.[domainname]" where "linkupnetworks" is a constant 1772 text string and "[domainname]" is a DNS suffix for the OMNI link 1773 (e.g., "example.com"). 1775 To associate with a Server, the Client acts as a requesting router to 1776 request MNPs. The Client prepares an RS message with PD parameters 1777 and includes a Nonce and Timestamp option if the Client needs to 1778 correlate RA replies. If the Client already knows the Server's LLA, 1779 it includes the LLA as the network-layer destination address; 1780 otherwise, it includes the link-scoped All-Routers multicast 1781 (ff02::2) or Subnet-Router anycast (fe80::) address as the network- 1782 layer destination. If the Client already knows its own LLA, it uses 1783 the LLA as the network-layer source address; otherwise, it uses the 1784 unspecified IPv6 address (::/128) as the network-layer source 1785 address. 1787 The Client next includes an OMNI option in the RS message to register 1788 its link-layer information with the Server. The Client sets the OMNI 1789 option prefix registration information according to the MNP, and 1790 includes an ifIndex-tuple with S set to '1' corresponding to the 1791 underlying interface over which the Client will send the RS message. 1792 The Client MAY include additional ifIndex-tuples specific to other 1793 underlying interfaces. The Client MAY also include an SLLAO 1794 corresponding to the OMNI option ifIndex-tuple with S set to '1'. 1796 The Client then sends the RS message (either directly via Direct 1797 interfaces, via a VPN for VPNed interfaces, via a Proxy for proxyed 1798 interfaces or via INET encapsulation for INET interfaces) and waits 1799 for an RA message reply (see Section 3.12.3). The Client retries up 1800 to MAX_RTR_SOLICITATIONS times until an RA is received. If the 1801 Client receives no RAs, or if it receives an RA with Router Lifetime 1802 set to 0, the Client SHOULD abandon this Server and try another 1803 Server. Otherwise, the Client processes the PD information found in 1804 the RA message. 1806 Next, the Client creates a symmetric neighbor cache entry with the 1807 Server's LLA as the network-layer address and the Server's 1808 encapsulation and/or link-layer addresses as the link-layer address. 1809 The Client records the RA Router Lifetime field value in the neighbor 1810 cache entry as the time for which the Server has committed to 1811 maintaining the MNP in the routing system via this underlying 1812 interface, and caches the other RA configuration information 1813 including Cur Hop Limit, M and O flags, Reachable Time and Retrans 1814 Timer. The Client then autoconfigures LLAs for each of the delegated 1815 MNPs and assigns them to the OMNI interface. The Client also caches 1816 any MSPs included in Route Information Options (RIOs) [RFC4191] as 1817 MSPs to associate with the OMNI link, and assigns the MTU value in 1818 the MTU option to the underlying interface. 1820 The Client then registers additional underlying interfaces with the 1821 Server by sending RS messages via each additional interface. The RS 1822 messages include the same parameters as for the initial RS/RA 1823 exchange, but with destination address set to the Server's LLA. 1825 Following autoconfiguration, the Client sub-delegates the MNPs to its 1826 attached EUNs and/or the Client's own internal virtual interfaces as 1827 described in [I-D.templin-v6ops-pdhost] to support the Client's 1828 downstream attached "Internet of Things (IoT)". The Client 1829 subsequently sends additional RS messages over each underlying 1830 interface before the Router Lifetime received for that interface 1831 expires. 1833 After the Client registers its underlying interfaces, it may wish to 1834 change one or more registrations, e.g., if an interface changes 1835 address or becomes unavailable, if QoS preferences change, etc. To 1836 do so, the Client prepares an RS message to send over any available 1837 underlying interface. The RS includes an OMNI option with prefix 1838 registration information specific to its MNP, with an ifIndex-tuple 1839 specific to the selected underlying interface with S set to '1', and 1840 with any additional ifIndex-tuples specific to other underlying 1841 interfaces. The Client includes fresh ifIndex-tuple values to update 1842 the Server's neighbor cache entry. When the Client receives the 1843 Server's RA response, it has assurance that the Server has been 1844 updated with the new information. 1846 If the Client wishes to discontinue use of a Server it issues an RS 1847 message over any underlying interface with an OMNI option with a 1848 prefix release indication. When the Server processes the message, it 1849 releases the MNP, sets the symmetric neighbor cache entry state for 1850 the Client to DEPARTED and returns an RA reply with Router Lifetime 1851 set to 0. After a short delay (e.g., 2 seconds), the Server 1852 withdraws the MNP from the routing system. 1854 3.12.3. AERO Server Behavior 1856 AERO Servers act as IP routers and support a PD service for Clients. 1857 Servers arrange to add their LLAs to a static map of Server addresses 1858 for the link and/or the DNS resource records for the FQDN 1859 "linkupnetworks.[domainname]" before entering service. Server 1860 addresses should be geographically and/or topologically referenced, 1861 and made available for discovery by Clients on the OMNI link. 1863 When a Server receives a prospective Client's RS message on its OMNI 1864 interface, it SHOULD return an immediate RA reply with Router 1865 Lifetime set to 0 if it is currently too busy or otherwise unable to 1866 service the Client. Otherwise, the Server authenticates the RS 1867 message and processes the PD parameters. The Server first determines 1868 the correct MNPs to delegate to the Client by searching the Client 1869 database. When the Server delegates the MNPs, it also creates a 1870 forwarding table entry for each MNP so that the MNPs are propagated 1871 into the routing system (see: Section 3.2.3). For IPv6, the Server 1872 creates an IPv6 forwarding table entry for each MNP. For IPv4, the 1873 Server creates an IPv6 forwarding table entry with the SPAN 1874 Compatibility Prefix (SCP) corresponding to the IPv4 address. 1876 The Server next creates a symmetric neighbor cache entry for the 1877 Client using the base LLA as the network-layer address and with 1878 lifetime set to no more than the smallest PD lifetime. Next, the 1879 Server updates the neighbor cache entry by recording the information 1880 in each ifIndex-tuple in the RS OMNI option. The Server also records 1881 the actual SPAN/INET addresses in the neighbor cache entry. 1883 Next, the Server prepares an RA message using its LLA as the network- 1884 layer source address and the network-layer source address of the RS 1885 message as the network-layer destination address. The Server sets 1886 the Router Lifetime to the time for which it will maintain both this 1887 underlying interface individually and the symmetric neighbor cache 1888 entry as a whole. The Server also sets Cur Hop Limit, M and O flags, 1889 Reachable Time and Retrans Timer to values appropriate for the OMNI 1890 link. The Server includes the delegated MNPs, any other PD 1891 parameters and an OMNI option with no ifIndex-tuples. The Server 1892 then includes one or more RIOs that encode the MSPs for the OMNI 1893 link, plus an MTU option (see Section 3.9). The Server finally 1894 forwards the message to the Client using SPAN/INET, INET, or NULL 1895 encapsulation as necessary. 1897 After the initial RS/RA exchange, the Server maintains a 1898 ReachableTime timer for each of the Client's underlying interfaces 1899 individually (and for the Client's symmetric neighbor cache entry 1900 collectively) set to expire after ReachableTime seconds. If the 1901 Client (or Proxy) issues additional RS messages, the Server sends an 1902 RA response and resets ReachableTime. If the Server receives an ND 1903 message with PD release indication it sets the Client's symmetric 1904 neighbor cache entry to the DEPARTED state and withdraws the MNP from 1905 the routing system after a short delay (e.g., 2 seconds). If 1906 ReachableTime expires before a new RS is received on an individual 1907 underlying interface, the Server marks the interface as DOWN. If 1908 ReachableTime expires before any new RS is received on any individual 1909 underlying interface, the Server sets the symmetric neighbor cache 1910 entry state to STALE and sets a 10 second timer. If the Server has 1911 not received a new RS or ND message with PD release indication before 1912 the 10 second timer expires, it deletes the neighbor cache entry and 1913 withdraws the MNP from the routing system. 1915 The Server processes any ND/PD messages pertaining to the Client and 1916 returns an NA/RA reply in response to solicitations. The Server may 1917 also issue unsolicited RA messages, e.g., with PD reconfigure 1918 parameters to cause the Client to renegotiate its PDs, with Router 1919 Lifetime set to 0 if it can no longer service this Client, etc. 1920 Finally, If the symmetric neighbor cache entry is in the DEPARTED 1921 state, the Server deletes the entry after DepartTime expires. 1923 Note: Clients SHOULD notify former Servers of their departures, but 1924 Servers are responsible for expiring neighbor cache entries and 1925 withdrawing routes even if no departure notification is received 1926 (e.g., if the Client leaves the network unexpectedly). Servers 1927 SHOULD therefore set Router Lifetime to ReachableTime seconds in 1928 solicited RA messages to minimize persistent stale cache information 1929 in the absence of Client departure notifications. A short Router 1930 Lifetime also ensures that proactive Client/Server RS/RA messaging 1931 will keep any NAT state alive (see above). 1933 Note: All Servers on an OMNI link MUST advertise consistent values in 1934 the RA Cur Hop Limit, M and O flags, Reachable Time and Retrans Timer 1935 fields the same as for any link, since unpredictable behavior could 1936 result if different Servers on the same link advertised different 1937 values. 1939 3.12.3.1. Lightweight DHCPv6 Relay Agent (LDRA) 1941 When DHCPv6 is used as the ND/PD service back end, AERO Clients and 1942 Servers are always on the same link (i.e., the OMNI link) from the 1943 perspective of DHCPv6. However, in some implementations the DHCPv6 1944 server and ND function may be located in separate modules. In that 1945 case, the Server's OMNI interface module can act as a Lightweight 1946 DHCPv6 Relay Agent (LDRA)[RFC6221] to relay PD messages to and from 1947 the DHCPv6 server module. 1949 When the LDRA receives an authentic RS message, it extracts the PD 1950 message parameters and uses them to construct an IPv6/UDP/DHCPv6 1951 message. It sets the IPv6 source address to the source address of 1952 the RS message, sets the IPv6 destination address to 1953 'All_DHCP_Relay_Agents_and_Servers' and sets the UDP fields to values 1954 that will be understood by the DHCPv6 server. 1956 The LDRA then wraps the message in a DHCPv6 'Relay-Forward' message 1957 header and includes an 'Interface-Id' option that includes enough 1958 information to allow the LDRA to forward the resulting Reply message 1959 back to the Client (e.g., the Client's link-layer addresses, a 1960 security association identifier, etc.). The LDRA also wraps the OMNI 1961 option and SLLAO into the Interface-Id option, then forwards the 1962 message to the DHCPv6 server. 1964 When the DHCPv6 server prepares a Reply message, it wraps the message 1965 in a 'Relay-Reply' message and echoes the Interface-Id option. The 1966 DHCPv6 server then delivers the Relay-Reply message to the LDRA, 1967 which discards the Relay-Reply wrapper and IPv6/UDP headers, then 1968 uses the DHCPv6 message to construct an RA response to the Client. 1969 The Server uses the information in the Interface-Id option to prepare 1970 the RA message and to cache the link-layer addresses taken from the 1971 OMNI option and SLLAO echoed in the Interface-Id option. 1973 3.13. The AERO Proxy 1975 Clients may connect to protected-spectrum ANETs that deploy physical 1976 and/or link-layer security services to facilitate communications to 1977 Servers in outside INETs. In that case, the ANET can employ an AERO 1978 Proxy. The Proxy is located at the ANET/INET border and listens for 1979 RS messages originating from or RA messages destined to ANET Clients. 1980 The Proxy acts on these control messages as follows: 1982 o when the Proxy receives an RS message from a new ANET Client, it 1983 first authenticates the message then examines the network-layer 1984 destination address. If the destination address is a Server's 1985 LLA, the Proxy proceeds to the next step. Otherwise, if the 1986 destination is All-Routers multicast or Subnet-Router anycast, the 1987 Proxy selects a "nearby" Server that is likely to be a good 1988 candidate to serve the Client and replaces the destination address 1989 with the Server's LLA. Next, the Proxy creates a proxy neighbor 1990 cache entry and caches the Client and Server link-layer addresses 1991 along with the OMNI option information and any other identifying 1992 information including Transaction IDs, Client Identifiers, Nonce 1993 values, etc. The Proxy finally encapsulates the (proxyed) RS 1994 message in a SPAN header with source set to the Proxy's ULA and 1995 destination set to the Server's ULA then forwards the message into 1996 the SPAN. 1998 o when the Server receives the RS, it authenticates the message then 1999 creates or updates a symmetric neighbor cache entry for the Client 2000 with the Proxy's ULA as the link-layer address. The Server then 2001 sends an RA message back to the Proxy via the spanning tree. 2003 o when the Proxy receives the RA, it authenticates the message and 2004 matches it with the proxy neighbor cache entry created by the RS. 2005 The Proxy then caches the PD route information as a mapping from 2006 the Client's MNPs to the Client's link-layer address, caches the 2007 Server's advertised Router Lifetime and sets the neighbor cache 2008 entry state to REACHABLE. The Proxy then sets the P bit in the RA 2009 flags field, optionally rewrites the Router Lifetime and forwards 2010 the (proxyed) message to the Client. The Proxy finally includes 2011 an MTU option (if necessary) with an MTU to use for the underlying 2012 ANET interface. 2014 After the initial RS/RA exchange, the Proxy forwards any Client data 2015 packets for which there is no matching asymmetric neighbor cache 2016 entry to a Bridge using SPAN encapsulation with its own ULA as the 2017 source and the ULA corresponding to the Client as the destination. 2018 The Proxy instead forwards any Client data destined to an asymmetric 2019 neighbor cache target directly to the target according to the SPAN/ 2020 link-layer information - the process of establishing asymmetric 2021 neighbor cache entries is specified in Section 3.14. 2023 While the Client is still attached to the ANET, the Proxy sends NS, 2024 RS and/or unsolicited NA messages to update the Server's symmetric 2025 neighbor cache entries on behalf of the Client and/or to convey QoS 2026 updates. This allows for higher-frequency Proxy-initiated RS/RA 2027 messaging over well-connected INET infrastructure supplemented by 2028 lower-frequency Client-initiated RS/RA messaging over constrained 2029 ANET data links. 2031 If the Server ceases to send solicited advertisements, the Proxy 2032 sends unsolicited RAs on the ANET interface with destination set to 2033 link-scoped All-Nodes multicast (ff02::1) and with Router Lifetime 2034 set to zero to inform Clients that the Server has failed. Although 2035 the Proxy engages in ND exchanges on behalf of the Client, the Client 2036 can also send ND messages on its own behalf, e.g., if it is in a 2037 better position than the Proxy to convey QoS changes, etc. For this 2038 reason, the Proxy marks any Client-originated solicitation messages 2039 (e.g. by inserting a Nonce option) so that it can return the 2040 solicited advertisement to the Client instead of processing it 2041 locally. 2043 If the Client becomes unreachable, the Proxy sets the neighbor cache 2044 entry state to DEPARTED and retains the entry for DepartTime seconds. 2045 While the state is DEPARTED, the Proxy forwards any packets destined 2046 to the Client to a Bridge via SPAN encapsulation with the Client's 2047 current Server as the destination. The Bridge in turn forwards the 2048 packets to the Client's current Server. When DepartTime expires, the 2049 Proxy deletes the neighbor cache entry and discards any further 2050 packets destined to this (now forgotten) Client. 2052 In some ANETs that employ a Proxy, the Client's MNP can be injected 2053 into the ANET routing system. In that case, the Client can send data 2054 messages without encapsulation so that the ANET routing system 2055 transports the unencapsulated packets to the Proxy. This can be very 2056 beneficial, e.g., if the Client connects to the ANET via low-end data 2057 links such as some aviation wireless links. 2059 If the first-hop ANET access router is AERO-aware, the Client can 2060 avoid encapsulation for both its control and data messages. When the 2061 Client connects to the link, it can send an unencapsulated RS message 2062 with source address set to its LLA and with destination address set 2063 to the LLA of the Client's selected Server or to All-Routers 2064 multicast or Subnet-Router anycast. The Client includes an OMNI 2065 option formatted as specified in [I-D.templin-6man-omni-interface]. 2067 The Client then sends the unencapsulated RS message, which will be 2068 intercepted by the AERO-Aware access router. The access router then 2069 encapsulates the RS message in an ANET header with its own address as 2070 the source address and the address of a Proxy as the destination 2071 address. The access router further remembers the address of the 2072 Proxy so that it can encapsulate future data packets from the Client 2073 via the same Proxy. If the access router needs to change to a new 2074 Proxy, it simply sends another RS message toward the Server via the 2075 new Proxy on behalf of the Client. 2077 In some cases, the access router and Proxy may be one and the same 2078 node. In that case, the node would be located on the same physical 2079 link as the Client, but its message exchanges with the Server would 2080 need to pass through a security gateway at the ANET/INET border. The 2081 method for deploying access routers and Proxys (i.e. as a single node 2082 or multiple nodes) is an ANET-local administrative consideration. 2084 3.13.1. Detecting and Responding to Server Failures 2086 In environments where fast recovery from Server failure is required, 2087 Proxys SHOULD use proactive Neighbor Unreachability Detection (NUD) 2088 to track Server reachability in a similar fashion as for 2089 Bidirectional Forwarding Detection (BFD) [RFC5880]. Proxys can then 2090 quickly detect and react to failures so that cached information is 2091 re-established through alternate paths. The NUD control messaging is 2092 carried only over well-connected ground domain networks (i.e., and 2093 not low-end aeronautical radio links) and can therefore be tuned for 2094 rapid response. 2096 Proxys perform proactive NUD with Servers for which there are 2097 currently active ANET Clients by sending continuous NS messages in 2098 rapid succession, e.g., one message per second. The Proxy sends the 2099 NS message via the spanning tree with the Proxy's LLA as the source 2100 and the LLA of the Server as the destination. When the Proxy is also 2101 sending RS messages to the Server on behalf of ANET Clients, the 2102 resulting RA responses can be considered as equivalent hints of 2103 forward progress. This means that the Proxy need not also send a 2104 periodic NS if it has already sent an RS within the same period. If 2105 the Server fails (i.e., if the Proxy ceases to receive 2106 advertisements), the Proxy can quickly inform Clients by sending 2107 multicast RA messages on the ANET interface. 2109 The Proxy sends RA messages on the ANET interface with source address 2110 set to the Server's address, destination address set to All-Nodes 2111 multicast, and Router Lifetime set to 0. The Proxy SHOULD send 2112 MAX_FINAL_RTR_ADVERTISEMENTS RA messages separated by small delays 2113 [RFC4861]. Any Clients on the ANET that had been using the failed 2114 Server will receive the RA messages and associate with a new Server. 2116 3.13.2. Point-to-Multipoint Server Coordination 2118 In environments where Client messaging over ANETs is bandwidth- 2119 limited and/or expensive, Clients can enlist the services of the 2120 Proxy to coordinate with multiple Servers in a single RS/RA message 2121 exchange. The Client can send a single RS message to All-Routers 2122 multicast that includes the ID's of multiple Servers in MS-Register 2123 sub-options of the OMNI option. 2125 When the Proxy receives the RS and processes the OMNI option, it 2126 performs a separate RS/RA exchange with each MS-Register Server. 2127 When it has received the RA messages, it creates an "aggregate" RA 2128 message to return to the Client with an OMNI option with each 2129 responding Server's ID recorded in an MS-Register sub-option. 2131 Clients can thereafter employ efficient point-to-multipoint Server 2132 coordination under the assistance of the Proxy to dramatically reduce 2133 the number of messages sent over the ANET while enlisting the support 2134 of multiple Servers for fault tolerance. Clients can further include 2135 MS-Release suboptions in RS messages to request the Proxy to release 2136 from former Servers via the procedures discussed in Section 3.16.5. 2138 The OMNI interface specification [I-D.templin-6man-omni-interface] 2139 provides further discussion of the Client/Proxy RS/RA messaging 2140 involved in point-to-multipoint coordination. 2142 3.14. AERO Route Optimization / Address Resolution 2144 While data packets are flowing between a source and target node, 2145 route optimization SHOULD be used. Route optimization is initiated 2146 by the first eligible Route Optimization Source (ROS) closest to the 2147 source as follows: 2149 o For Clients on VPNed and Direct interfaces, the Server is the ROS. 2151 o For Clients on Proxyed interfaces, the Proxy is the ROS. 2153 o For Clients on INET interfaces, the Client itself is the ROS. 2155 o For correspondent nodes on INET/EUN interfaces serviced by a 2156 Relay, the Relay is the ROS. 2158 The route optimization procedure is conducted between the ROS and the 2159 target Server/Relay acting as a Route Optimization Responder (ROR) in 2160 the same manner as for IPv6 ND Address Resolution and using the same 2161 NS/NA messaging. The target may either be a MNP Client serviced by a 2162 Server, or a non-MNP correspondent reachable via a Relay. 2164 The procedures are specified in the following sections. 2166 3.14.1. Route Optimization Initiation 2168 While data packets are flowing from the source node toward a target 2169 node, the ROS performs address resolution by sending an NS message 2170 for Address Resolution (NS(AR)) to receive a solicited NA message 2171 from the ROR. When the ROS sends an NS(AR), it includes: 2173 o the LLA of the ROS as the source address. 2175 o the data packet's destination as the Target Address. 2177 o the Solicited-Node multicast address [RFC4291] formed from the 2178 lower 24 bits of the data packet's destination as the destination 2179 address, e.g., for 2001:db8:1:2::10:2000 the NS destination 2180 address is ff02:0:0:0:0:1:ff10:2000. 2182 The NS(AR) message includes an OMNI option with no ifIndex-tuples and 2183 no SLLAO, such that the target will not create a neighbor cache 2184 entry. 2186 The ROS then encapsulates the NS(AR) message in a SPAN header with 2187 source set to its own ULA and destination set to the ULA 2188 corresponding to the packet's final destination, then sends the 2189 message into the spanning tree without decrementing the network-layer 2190 TTL/Hop Limit field. 2192 3.14.2. Relaying the NS 2194 When the Bridge receives the NS(AR) message from the ROS, it discards 2195 the INET header and determines that the ROR is the next hop by 2196 consulting its standard IPv6 forwarding table for the SPAN header 2197 destination address. The Bridge then forwards the message toward the 2198 ROR via the spanning tree the same as for any IPv6 router. The 2199 final-hop Bridge in the spanning tree will deliver the message via a 2200 secured tunnel to the ROR. 2202 3.14.3. Processing the NS and Sending the NA 2204 When the ROR receives the NS(AR) message, it examines the Target 2205 Address to determine whether it has a neighbor cache entry and/or 2206 route that matches the target. If there is no match, the ROR drops 2207 the message. Otherwise, the ROR continues processing as follows: 2209 o if the target belongs to an MNP Client neighbor in the DEPARTED 2210 state the ROR changes the NS(AR) message SPAN destination address 2211 to the ULA of the Client's new Server, forwards the message into 2212 the spanning tree and returns from processing. 2214 o If the target belongs to an MNP Client neighbor in the REACHABLE 2215 state, the ROR instead adds the AERO source address to the target 2216 Client's Report List with time set to ReportTime. 2218 o If the target belongs to a non-MNP route, the ROR continues 2219 processing without adding an entry to the Report List. 2221 The ROR then prepares a solicited NA message to send back to the ROS 2222 but does not create a neighbor cache entry. The ROR sets the NA 2223 source address to the LLA corresponding to the target, sets the 2224 Target Address to the target of the solicitation, and sets the 2225 destination address to the source of the solicitation. 2227 The ROR then includes an OMNI option with prefix registration length 2228 set to the length of the MNP if the target is an MNP Client; 2229 otherwise, set to the maximum of the non-MNP prefix length and 64. 2230 (Note that a /64 limit is imposed to avoid causing the ROS to set 2231 short prefixes (e.g., "default") that would match destinations for 2232 which the routing system includes more-specific prefixes.) 2234 If the target is an MNP Client, the ROR next includes ifIndex-tuples 2235 in the OMNI option for each of the target Client's underlying 2236 interfaces with current information for each interface and with the S 2237 flag set to 0. The ROR then includes a TLLAO with ifIndex-tuples in 2238 one-to-one correspondence with the tuples that appear in the OMNI 2239 option. 2241 The ROR sets the Link Layer Address and Port Number to its own INET 2242 address for VPNed and Direct interfaces or to the INET address of the 2243 Proxy for Proxyed interface. The ROR then includes its own ULA or 2244 the ULA of the Proxy as the ultimate Segment Routing List entry, and 2245 includes the ultimate segment Subnet Router Anycast address in the 2246 penultimate entry. For INET interfaces, the ROR instead sets the 2247 Link Layer Address and Port Number to the Client's INET address then 2248 sets the ultimate Segment Routing List entry to 0, sets its own ULA 2249 in the penultimate entry and sets the ultimate segment Subnet Router 2250 Anycast in the tertiary entry. (Note that the value 0 in the 2251 ultimate entry signifies that the ultimate hop ULA imust be derived 2252 from the target address of the NA message in conjunction with the 2253 OMNI option prefix length and the LLAO SRT value. Note also that the 2254 ROR may include additional Subnet Router Anycast addresses for any 2255 earlier segments to be visited.) 2257 The ROR then sets the NA message R flag to 1 (as a router), S flag to 2258 1 (as a response to a solicitation), and O flag to 0 (as a proxy). 2259 The ROR finally encapsulates the NA message in a SPAN header with 2260 source set to its own ULA and destination set to the source ULA of 2261 the NS(AR) message, then forwards the message into the spanning tree 2262 without decrementing the network-layer TTL/Hop Limit field. 2264 3.14.4. Relaying the NA 2266 When the Bridge receives the NA message from the ROR, it discards the 2267 INET header and determines that the ROS is the next hop by consulting 2268 its standard IPv6 forwarding table for the SPAN header destination 2269 address. The Bridge then forwards the SPAN-encapsulated NA message 2270 toward the ROS the same as for any IPv6 router. The final-hop Bridge 2271 in the spanning tree will deliver the message via a secured tunnel to 2272 the ROS. 2274 3.14.5. Processing the NA 2276 When the ROS receives the solicited NA message, it processes the 2277 message the same as for standard IPv6 Address Resolution [RFC4861]. 2278 In the process, it caches the source ULA then creates an asymmetric 2279 neighbor cache entry for the ROR and caches all information found in 2280 the OMNI and TLLAO options. The ROS finally sets the asymmetric 2281 neighbor cache entry lifetime to ReachableTime seconds. 2283 3.14.6. Route Optimization Maintenance 2285 Following route optimization, the ROS forwards future data packets 2286 destined to the target via the addresses found in the cached link- 2287 layer information. The route optimization is shared by all sources 2288 that send packets to the target via the ROS, i.e., and not just the 2289 source on behalf of which the route optimization was initiated. 2291 While new data packets destined to the target are flowing through the 2292 ROS, it sends additional NS(AR) messages to the ROR before 2293 ReachableTime expires to receive a fresh solicited NA message the 2294 same as described in the previous sections (route optimization 2295 refreshment strategies are an implementation matter, with a non- 2296 normative example given in Appendix A.1). The ROS uses the cached 2297 ULA of the ROR as the NS(AR) SPAN destination address, and sends up 2298 to MAX_MULTICAST_SOLICIT NS(AR) messages separated by 1 second until 2299 an NA is received. If no NA is received, the ROS assumes that the 2300 current ROR has become unreachable and deletes the neighbor cache 2301 entry. Subsequent data packets will trigger a new route optimization 2302 per Section 3.14.1 to discover a new ROR while initial data packets 2303 travel over a suboptimal route. 2305 If an NA is received, the ROS then updates the asymmetric neighbor 2306 cache entry to refresh ReachableTime, while (for MNP destinations) 2307 the ROR adds or updates the ROS address to the target Client's Report 2308 List and with time set to ReportTime. While no data packets are 2309 flowing, the ROS instead allows ReachableTime for the asymmetric 2310 neighbor cache entry to expire. When ReachableTime expires, the ROS 2311 deletes the asymmetric neighbor cache entry. Any future data packets 2312 flowing through the ROS will again trigger a new route optimization. 2314 The ROS may also receive unsolicited NA messages from the ROR at any 2315 time (see: Section 3.16). If there is an asymmetric neighbor cache 2316 entry for the target, the ROS updates the link-layer information but 2317 does not update ReachableTime since the receipt of an unsolicited NA 2318 does not confirm that any forward paths are working. If there is no 2319 asymmetric neighbor cache entry, the ROS simply discards the 2320 unsolicited NA. 2322 In this arrangement, the ROS holds an asymmetric neighbor cache entry 2323 for the ROR, but the ROR does not hold an asymmetric neighbor cache 2324 entry for the ROS. The route optimization neighbor relationship is 2325 therefore asymmetric and unidirectional. If the target node also has 2326 packets to send back to the source node, then a separate route 2327 optimization procedure is performed in the reverse direction. But, 2328 there is no requirement that the forward and reverse paths be 2329 symmetric. 2331 3.15. Neighbor Unreachability Detection (NUD) 2333 AERO nodes perform Neighbor Unreachability Detection (NUD) per 2334 [RFC4861] either reactively in response to persistent link-layer 2335 errors (see Section 3.11) or proactively to confirm reachability. 2336 The NUD algorithm is based on periodic control message exchanges. 2337 The algorithm may further be seeded by ND hints of forward progress, 2338 but care must be taken to avoid inferring reachability based on 2339 spoofed information. For example, authentic IPv6 ND message 2340 exchanges may be considered as acceptable hints of forward progress, 2341 while spurious data packets should not be. 2343 AERO Servers, Proxys and Relays can use standard NS/NA NUD exchanges 2344 sent over the spanning tree to securely test reachability without 2345 risk of DoS attacks from nodes pretending to be a neighbor; Proxys 2346 can further perform NUD to securely verify Server reachability on 2347 behalf of their proxyed Clients. However, a means for a ROS to test 2348 the unsecured forward directions of target route optimized paths is 2349 also necessary. 2351 When an ROR directs an ROS to a neighbor with one or more target 2352 link-layer addresses, the ROS can proactively test each such 2353 unsecured route optimized path by sending "loopback" NS(NUD) 2354 messages. While testing the paths, the ROS can optionally continue 2355 to send packets via the spanning tree, maintain a small queue of 2356 packets until target reachability is confirmed, or (optimistically) 2357 allow packets to flow via the route optimized paths. 2359 When the ROS sends a loopback NS(NUD) message, it uses its LLA as 2360 both the IPv6 source and destination address, and the MNP Subnet- 2361 Router anycast address as the Target Address. The ROS includes a 2362 Nonce and Timestamp option, then encapsulates the message in SPAN/ 2363 INET headers with its own ULA as the source and the ULA of the route 2364 optimization target as the destination. The ROS then forwards the 2365 message to the target (either directly to the link layer address of 2366 the target if the target is in the same OMNI link segment, or via a 2367 Bridge if the target is in a different OMNI link segment). 2369 When the route optimization target receives the NS(NUD) message, it 2370 notices that the IPv6 destination address is the same as the source 2371 address. It then reverses the SPAN source and destination addresses 2372 and returns the message to the ROS (either directly or via the 2373 spanning tree). The route optimization target does not decrement the 2374 NS(NUD) message IPv6 Hop-Limit in the process, since the message has 2375 not exited the OMNI link. 2377 When the ROS receives the NS(NUD) message, it can determine from the 2378 Nonce, Timestamp and Target Address that the message originated from 2379 itself and that it transited the forward path. The ROS need not 2380 prepare an NA response, since the destination of the response would 2381 be itself and testing the route optimization path again would be 2382 redundant. 2384 The ROS marks route optimization target paths that pass these NUD 2385 tests as "reachable", and those that do not as "unreachable". These 2386 markings inform the OMNI interface forwarding algorithm specified in 2387 Section 3.10. 2389 Note that to avoid a DoS vector nodes MUST NOT return loopback 2390 NS(NUD) messages received from an unsecured link-layer source via the 2391 spanning tree. 2393 3.16. Mobility Management and Quality of Service (QoS) 2395 AERO is a Distributed Mobility Management (DMM) service. Each Server 2396 is responsible for only a subset of the Clients on the OMNI link, as 2397 opposed to a Centralized Mobility Management (CMM) service where 2398 there is a single network mobility collective entity for all Clients. 2399 Clients coordinate with their associated Servers via RS/RA exchanges 2400 to maintain the DMM profile, and the AERO routing system tracks all 2401 current Client/Server peering relationships. 2403 Servers provide default routing and mobility/multilink services for 2404 their dependent Clients. Clients are responsible for maintaining 2405 neighbor relationships with their Servers through periodic RS/RA 2406 exchanges, which also serves to confirm neighbor reachability. When 2407 a Client's underlying interface address and/or QoS information 2408 changes, the Client is responsible for updating the Server with this 2409 new information. Note that for Proxyed interfaces, however, the 2410 Proxy can also perform some RS/RA exchanges on the Client's behalf. 2412 Mobility management considerations are specified in the following 2413 sections. 2415 3.16.1. Mobility Update Messaging 2417 Servers accommodate Client mobility/multilink and/or QoS change 2418 events by sending unsolicited NA (uNA) messages to each ROS in the 2419 target Client's Report List. When a Server sends a uNA message, it 2420 sets the IPv6 source address to the Client's LLA, sets the 2421 destination address to All-Nodes multicast and sets the Target 2422 Address to the Client's Subnet-Router anycast address. The Server 2423 also includes an OMNI option with prefix registration information and 2424 with ifIndex-tuples for the target Client's remaining interfaces with 2425 S set to 0. The Server then includes a TLLAO with corresponding 2426 ifIndex-tuples prepared the same as for the initial route 2427 optimization event. The Server sets the NA R flag to 1, the S flag 2428 to 0 and the O flag to 0, then encapsulates the message in a SPAN 2429 header with source set to its own ULA and destination set to the ULA 2430 of the ROS and sends the message into the spanning tree. 2432 As discussed in Section 7.2.6 of [RFC4861], the transmission and 2433 reception of uNA messages is unreliable but provides a useful 2434 optimization. In well-connected Internetworks with robust data links 2435 uNA messages will be delivered with high probability, but in any case 2436 the Server can optionally send up to MAX_NEIGHBOR_ADVERTISEMENT uNAs 2437 to each ROS to increase the likelihood that at least one will be 2438 received. 2440 When the ROS receives a uNA message, it ignores the message if there 2441 is no existing neighbor cache entry for the Client. Otherwise, it 2442 uses the included OMNI option and TLLAO information to update the 2443 neighbor cache entry, but does not reset ReachableTime since the 2444 receipt of an unsolicited NA message from the target Server does not 2445 provide confirmation that any forward paths to the target Client are 2446 working. 2448 If uNA messages are lost, the ROS may be left with stale address and/ 2449 or QoS information for the Client for up to ReachableTime seconds. 2450 During this time, the ROS can continue sending packets according to 2451 its stale neighbor cache information. When ReachableTime is close to 2452 expiring, the ROS will re-initiate route optimization and receive 2453 fresh link-layer address information. 2455 In addition to sending uNA messages to the current set of ROSs for 2456 the Client, the Server also sends uNAs to the former link-layer 2457 address for any ifIndex-tuple for which the link-layer address has 2458 changed. The uNA messages update Proxys that cannot easily detect 2459 (e.g., without active probing) when a formerly-active Client has 2460 departed. 2462 3.16.2. Announcing Link-Layer Address and/or QoS Preference Changes 2464 When a Client needs to change its underlying interface addresses and/ 2465 or QoS preferences (e.g., due to a mobility event), either the Client 2466 or its Proxys send RS messages to the Server via the spanning tree 2467 with an OMNI option that includes an ifIndex-tuple with S set to 1 2468 and with the new link quality and address information. 2470 Up to MAX_RTR_SOLICITATIONS RS messages MAY be sent in parallel with 2471 sending actual data packets in case one or more RAs are lost. If all 2472 RAs are lost, the Client SHOULD re-associate with a new Server. 2474 When the Server receives the Client's changes, it sends uNA messages 2475 to all nodes in the Report List the same as described in the previous 2476 section. 2478 3.16.3. Bringing New Links Into Service 2480 When a Client needs to bring new underlying interfaces into service 2481 (e.g., when it activates a new data link), it sends an RS message to 2482 the Server via the underlying interface with an OMNI option that 2483 includes an ifIndex-tuple with S set to 1 and appropriate link 2484 quality values and with link-layer address information for the new 2485 link. 2487 3.16.4. Removing Existing Links from Service 2489 When a Client needs to remove existing underlying interfaces from 2490 service (e.g., when it de-activates an existing data link), it sends 2491 an RS or uNA message to its Server with an OMNI option with 2492 appropriate link quality values. 2494 If the Client needs to send RS/uNA messages over an underlying 2495 interface other than the one being removed from service, it MUST 2496 include ifIndex-tuples with appropriate link quality values for any 2497 underlying interfaces being removed from service. 2499 3.16.5. Moving to a New Server 2501 When a Client associates with a new Server, it performs the Client 2502 procedures specified in Section 3.12.2. The Client also includes MS- 2503 Release identifiers in the RS message OMNI option per 2504 [I-D.templin-6man-omni-interface] if it wants the new Server to 2505 notify any old Servers from which the Client is departing. 2507 When the new Server receives the Client's RS message, it returns an 2508 RA as specified in Section 3.12.3 and sends up to 2509 MAX_NEIGHBOR_ADVERTIISEMENT uNA messages to any old Servers listed in 2510 OMNI option MS-Release identifiers. Each uNA message includes the 2511 Client's LLA as the source address, the old Server's LLA as the 2512 destination address, and an OMNI option with the Register/Release bit 2513 set to 0. The new Server wraps the uNA in a SPAN header with its own 2514 ULA as the source and the old Server's ULA as the destination, then 2515 sends the message into the spanning tree. 2517 When an old Server receives the uNA, it changes the Client's neighbor 2518 cache entry state to DEPARTED, sets the link-layer address of the 2519 Client to the new Server's ULA, and resets DepartTime. After a short 2520 delay (e.g., 2 seconds) the old Server withdraws the Client's MNP 2521 from the routing system. After DepartTime expires, the old Server 2522 deletes the Client's neighbor cache entry. 2524 The old Server also sends unsolicited NA messages to all ROSs in the 2525 Client's Report List with an OMNI option with a single ifIndex-tuple 2526 with ifIndex set to 0 and S set to '1', and with the ULA of the new 2527 Server in a companion TLLAO. When the ROS receives the NA, it caches 2528 the address of the new Server in the existing asymmetric neighbor 2529 cache entry and marks the entry as STALE for a period of 10 seconds 2530 after which the cache entry is deleted. While in the STALE state, 2531 subsequent data packets flow according to any existing cached link- 2532 layer information and trigger a new NS(AR)/NA exchange via the new 2533 Server. 2535 Clients SHOULD NOT move rapidly between Servers in order to avoid 2536 causing excessive oscillations in the AERO routing system. Examples 2537 of when a Client might wish to change to a different Server include a 2538 Server that has gone unreachable, topological movements of 2539 significant distance, movement to a new geographic region, movement 2540 to a new OMNI link segment, etc. 2542 When a Client moves to a new Server, some of the fragments of a 2543 multiple fragment packet may have already arrived at the old Server 2544 while others are en route to the new Server, however no special 2545 attention in the reassembly algorithm is necessary when re-routed 2546 fragments are simply treated as loss. 2548 3.17. Multicast 2550 The AERO Client provides an IGMP (IPv4) [RFC2236] or MLD (IPv6) 2551 [RFC3810] proxy service for its EUNs and/or hosted applications 2552 [RFC4605]. The Client forwards IGMP/MLD messages over any of its 2553 underlying interfaces for which group membership is required. The 2554 IGMP/MLD messages may be further forwarded by a first-hop ANET access 2555 router acting as an IGMP/MLD-snooping switch [RFC4541], then 2556 ultimately delivered to an AERO Proxy/Server acting as a Protocol 2557 Independent Multicast - Sparse-Mode (PIM-SM, or simply "PIM") 2558 Designated Router (DR) [RFC7761]. AERO Relays also act as PIM 2559 routers (i.e., the same as AERO Proxys/Servers) on behalf of nodes on 2560 INET/EUN networks. The behaviors identified in the following 2561 sections correspond to Source-Specific Multicast (SSM) and Any-Source 2562 Multicast (ASM) operational modes. 2564 3.17.1. Source-Specific Multicast (SSM) 2566 When an ROS (i.e., an AERO Proxy/Server/Relay) "X" acting as PIM 2567 router receives a Join/Prune message from a node on its downstream 2568 interfaces containing one or more ((S)ource, (G)roup) pairs, it 2569 updates its Multicast Routing Information Base (MRIB) accordingly. 2570 For each S belonging to a prefix reachable via X's non-OMNI 2571 interfaces, X then forwards the (S, G) Join/Prune to any PIM routers 2572 on those interfaces per [RFC7761]. 2574 For each S belonging to a prefix reachable via X's OMNI interface, X 2575 originates a separate copy of the Join/Prune for each (S,G) in the 2576 message using its own LLA as the source address and ALL-PIM-ROUTERS 2577 as the destination address. X then encapsulates each message in a 2578 SPAN header with source address set to the ULA of X and destination 2579 address set to S then forwards the message into the spanning tree, 2580 which delivers it to AERO Server/Relay "Y" that services S. At the 2581 same time, if the message was a Join, X sends a route-optimization NS 2582 message toward each S the same as discussed in Section 3.14. The 2583 resulting NAs will return the LLA for the prefix that matches S as 2584 the network-layer source address and TLLAOs with the ULA 2585 corresponding to any ifIndex-tuples that are currently servicing S. 2587 When Y processes the Join/Prune message, if S located behind any 2588 INET, Direct, or VPNed interfaces Y acts as a PIM router and updates 2589 its MRIB to list X as the next hop in the reverse path. If S is 2590 located behind any Proxys "Z"*, Y also forwards the message to each 2591 Z* over the spanning tree while continuing to use the LLA of X as the 2592 source address. Each Z* then updates its MRIB accordingly and 2593 maintains the LLA of X as the next hop in the reverse path. Since 2594 the Bridges do not examine network layer control messages, this means 2595 that the (reverse) multicast tree path is simply from each Z* (and/or 2596 Y) to X with no other multicast-aware routers in the path. If any Z* 2597 (and/or Y) is located on the same OMNI link segment as X, the 2598 multicast data traffic sent to X directly using SPAN/INET 2599 encapsulation instead of via a Bridge. 2601 Following the initial Join/Prune and NS/NA messaging, X maintains an 2602 asymmetric neighbor cache entry for each S the same as if X was 2603 sending unicast data traffic to S. In particular, X performs 2604 additional NS/NA exchanges to keep the neighbor cache entry alive for 2605 up to t_periodic seconds [RFC7761]. If no new Joins are received 2606 within t_periodic seconds, X allows the neighbor cache entry to 2607 expire. Finally, if X receives any additional Join/Prune messages 2608 for (S,G) it forwards the messages to each Y and Z* in the neighbor 2609 cache entry over the spanning tree. 2611 At some later time, Client C that holds an MNP for source S may 2612 depart from a first Proxy Z1 and/or connect via a new Proxy Z2. In 2613 that case, Y sends an unsolicited NA message to X the same as 2614 specified for unicast mobility in Section 3.16. When X receives the 2615 unsolicited NA message, it updates its asymmetric neighbor cache 2616 entry for the LLA for source S and sends new Join messages to any new 2617 Proxys Z2. There is no requirement to send any Prune messages to old 2618 Proxys Z1 since source S will no longer source any multicast data 2619 traffic via Z1. Instead, the multicast state for (S,G) in Proxy Z1 2620 will soon time out since no new Joins will arrive. 2622 After some later time, C may move to a new Server Y2 and depart from 2623 old Sever Y1. In that case, Y1 sends Join messages for any of C's 2624 active (S,G) groups to Y2 while including its own LLA as the source 2625 address. This causes Y2 to include Y1 in the multicast forwarding 2626 tree during the interim time that Y1's symmetric neighbor cache entry 2627 for C is in the DEPARTED state. At the same time, Y1 sends an 2628 unsolicited NA message to X with an OMNI option and TLLAO with 2629 ifIndex-tuple set to 0 and a release indication to cause X to release 2630 its asymmetric neighbor cache entry. X then sends a new Join message 2631 to S via the spanning tree and re-initiates route optimization the 2632 same as if it were receiving a fresh Join message from a node on a 2633 downstream link. 2635 3.17.2. Any-Source Multicast (ASM) 2637 When an ROS X acting as a PIM router receives a Join/Prune from a 2638 node on its downstream interfaces containing one or more (*,G) pairs, 2639 it updates its Multicast Routing Information Base (MRIB) accordingly. 2640 X then forwards a copy of the message to the Rendezvous Point (RP) R 2641 for each G over the spanning tree. X uses its own LLA as the source 2642 address and ALL-PIM-ROUTERS as the destination address, then 2643 encapsulates each message in a SPAN header with source address set to 2644 the ULA of X and destination address set to R, then sends the message 2645 into the spanning tree. At the same time, if the message was a Join 2646 X initiates NS/NA route optimization the same as for the SSM case 2647 discussed in Section 3.17.1. 2649 For each source S that sends multicast traffic to group G via R, the 2650 Proxy/Server Z* for the Client that aggregates S encapsulates the 2651 packets in PIM Register messages and forwards them to R via the 2652 spanning tree, which may then elect to send a PIM Join to Z*. This 2653 will result in an (S,G) tree rooted at Z* with R as the next hop so 2654 that R will begin to receive two copies of the packet; one native 2655 copy from the (S, G) tree and a second copy from the pre-existing (*, 2656 G) tree that still uses PIM Register encapsulation. R can then issue 2657 a PIM Register-stop message to suppress the Register-encapsulated 2658 stream. At some later time, if C moves to a new Proxy/Server Z*, it 2659 resumes sending packets via PIM Register encapsulation via the new 2660 Z*. 2662 At the same time, as multicast listeners discover individual S's for 2663 a given G, they can initiate an (S,G) Join for each S under the same 2664 procedures discussed in Section 3.17.1. Once the (S,G) tree is 2665 established, the listeners can send (S, G) Prune messages to R so 2666 that multicast packets for group G sourced by S will only be 2667 delivered via the (S, G) tree and not from the (*, G) tree rooted at 2668 R. All mobility considerations discussed for SSM apply. 2670 3.17.3. Bi-Directional PIM (BIDIR-PIM) 2672 Bi-Directional PIM (BIDIR-PIM) [RFC5015] provides an alternate 2673 approach to ASM that treats the Rendezvous Point (RP) as a Designated 2674 Forwarder (DF). Further considerations for BIDIR-PIM are out of 2675 scope. 2677 3.18. Operation over Multiple OMNI Links 2679 An AERO Client can connect to multiple OMNI links the same as for any 2680 data link service. In that case, the Client maintains a distinct 2681 OMNI interface for each link, e.g., 'omni0' for the first link, 2682 'omni1' for the second, 'omni2' for the third, etc. Each OMNI link 2683 would include its own distinct set of Bridges, Servers and Proxys, 2684 thereby providing redundancy in case of failures. 2686 The Bridges, Servers and Proxys on each OMNI link can assign AERO and 2687 ULAs that use the same or different numberings from those on other 2688 links. Since the links are mutually independent there is no 2689 requirement for avoiding inter-link address duplication, e.g., the 2690 same LLA such as fe80::1000 could be used to number distinct nodes 2691 that connect to different OMNI links. 2693 Each OMNI link could utilize the same or different ANET connections. 2694 The links can be distinguished at the link-layer via the SSP in a 2695 similar fashion as for Virtual Local Area Network (VLAN) tagging 2696 (e.g., IEEE 802.1Q) and/or through assignment of distinct sets of 2697 MSPs on each link. This gives rise to the opportunity for supporting 2698 multiple redundant networked paths, where each VLAN is distinguished 2699 by a different SRT color (see: Section 3.2.5). In particular, the 2700 Client can tag its RS messages with the appropriate label to cause 2701 the network to select the desired VLAN. 2703 The Client's IP layer can select the outgoing OMNI interface 2704 appropriate for a given traffic profile while (in the reverse 2705 direction) correspondent nodes must have some way of steering their 2706 packets destined to a target via the correct OMNI link. 2708 In a first alternative, if each OMNI link services different MSPs, 2709 then the Client can receive a distinct MNP from each of the links. 2710 IP routing will therefore assure that the correct Red/Green/Blue/etc. 2711 network is used for both outbound and inbound traffic. This can be 2712 accomplished using existing technologies and approaches, and without 2713 requiring any special supporting code in correspondent nodes or 2714 Bridges. 2716 In a second alternative, if each OMNI link services the same MSP(s) 2717 then each link could assign a distinct "OMNI link Anycast" address 2718 that is configured by all Bridges on the link. Correspondent nodes 2719 can then perform Segment Routing to select the correct SRT, which 2720 will then direct the packet over multiple hops to the target. 2722 3.19. DNS Considerations 2724 AERO Client MNs and INET correspondent nodes consult the Domain Name 2725 System (DNS) the same as for any Internetworking node. When 2726 correspondent nodes and Client MNs use different IP protocol versions 2727 (e.g., IPv4 correspondents and IPv6 MNs), the INET DNS must maintain 2728 A records for IPv4 address mappings to MNs which must then be 2729 populated in Relay NAT64 mapping caches. In that way, an IPv4 2730 correspondent node can send packets to the IPv4 address mapping of 2731 the target MN, and the Relay will translate the IPv4 header and 2732 destination address into an IPv6 header and IPv6 destination address 2733 of the MN. 2735 When an AERO Client registers with an AERO Server, the Server can 2736 return the address(es) of DNS servers in RDNSS options [RFC6106]. 2737 The DNS server provides the IP addresses of other MNs and 2738 correspondent nodes in AAAA records for IPv6 or A records for IPv4. 2740 3.20. Transition Considerations 2742 SPAN encapsulation ensures that dissimilar INET partitions can be 2743 joined into a single unified OMNI link, even though the partitions 2744 themselves may have differing protocol versions and/or incompatible 2745 addressing plans. However, a commonality can be achieved by 2746 incrementally distributing globally routable (i.e., native) IP 2747 prefixes to eventually reach all nodes (both mobile and fixed) in all 2748 OMNI link segments. This can be accomplished by incrementally 2749 deploying AERO Relays on each INET partition, with each Relay 2750 distributing its MNPs and/or discovering non-MNP prefixes on its INET 2751 links. 2753 This gives rise to the opportunity to eventually distribute native IP 2754 addresses to all nodes, and to present a unified OMNI link view even 2755 if the INET partitions remain in their current protocol and 2756 addressing plans. In that way, the OMNI link can serve the dual 2757 purpose of providing a mobility/multilink service and a transition 2758 service. Or, if an INET partition is transitioned to a native IP 2759 protocol version and addressing scheme that is compatible with the 2760 OMNI link MNP-based addressing scheme, the partition and OMNI link 2761 can be joined by Relays. 2763 Relays that connect INETs/EUNs with dissimilar IP protocol versions 2764 may need to employ a network address and protocol translation 2765 function such as NAT64[RFC6146]. 2767 3.21. Detecting and Reacting to Server and Bridge Failures 2769 In environments where rapid failure recovery is required, Servers and 2770 Bridges SHOULD use Bidirectional Forwarding Detection (BFD) 2771 [RFC5880]. Nodes that use BFD can quickly detect and react to 2772 failures so that cached information is re-established through 2773 alternate nodes. BFD control messaging is carried only over well- 2774 connected ground domain networks (i.e., and not low-end radio links) 2775 and can therefore be tuned for rapid response. 2777 Servers and Bridges maintain BFD sessions in parallel with their BGP 2778 peerings. If a Server or Bridge fails, BGP peers will quickly re- 2779 establish routes through alternate paths the same as for common BGP 2780 deployments. Similarly, Proxys maintain BFD sessions with their 2781 associated Bridges even though they do not establish BGP peerings 2782 with them. 2784 Proxys SHOULD use proactive NUD for Servers for which there are 2785 currently active ANET Clients in a manner that parallels BFD, i.e., 2786 by sending unicast NS messages in rapid succession to receive 2787 solicited NA messages. When the Proxy is also sending RS messages on 2788 behalf of ANET Clients, the RS/RA messaging can be considered as 2789 equivalent hints of forward progress. This means that the Proxy need 2790 not also send a periodic NS if it has already sent an RS within the 2791 same period. If a Server fails, the Proxy will cease to receive 2792 advertisements and can quickly inform Clients of the outage by 2793 sending multicast RA messages on the ANET interface. 2795 The Proxy sends multicast RA messages with source address set to the 2796 Server's address, destination address set to All-Nodes multicast, and 2797 Router Lifetime set to 0. The Proxy SHOULD send 2798 MAX_FINAL_RTR_ADVERTISEMENTS RA messages separated by small delays 2799 [RFC4861]. Any Clients on the ANET interface that have been using 2800 the (now defunct) Server will receive the RA messages and associate 2801 with a new Server. 2803 3.22. AERO Clients on the Open Internet 2805 AERO Clients that connect to the open Internet via INET interfaces 2806 can establish a VPN or direct link to securely connect to a Server in 2807 a "tethered" arrangement with all of the Client's traffic transiting 2808 the Server. Alternatively, the Client can associate with an INET 2809 Server using UDP/IP encapsulation and asymmetric securing services as 2810 discussed in the following sections. 2812 When a Client's OMNI interface enables an INET underlying interface, 2813 it first determines whether the interface is likely to be behind a 2814 NAT. For IPv4, the Client might assume it is on the open Internet if 2815 the INET address is not a special-use IPv4 address per [RFC3330]. 2816 Similarly for IPv6, the Client might assume it is on the open 2817 Internet if the INET address is not a link-local [RFC4291] or unique- 2818 local [RFC4193] IPv6 address. 2820 The Client then prepares a UDP/IP-encapsulated RS message with IPv6 2821 source address set to its LLA, with IPv6 destination set to All- 2822 Routers multicast and with an OMNI option with underlying interface 2823 parameters. If the Client believes that it is on the open Internet, 2824 it SHOULD also include an SLLAO set according to the address used for 2825 INET encapsulation (otherwise, it MAY omit the SLLAO). If the 2826 underlying address is IPv4, the Client includes the IPv4 address and 2827 Port Number written in obfuscated form [RFC4380] and with FMT set to 2828 '01' (INET) as discussed in Section 3.3. If the underlying interface 2829 address is IPv6, the Client instead includes the IPv6 address and 2830 Port number in obfuscated form and sets FMT to '11' (INET). The 2831 Client finally includes an Authentication option per [RFC4380] to 2832 provide message authentication, sets the UDP/IP source to its INET 2833 address and UDP port, sets the UDP/IP destination to the Server's 2834 INET address and the AERO service port number (8060), then sends the 2835 message to the Server. 2837 When the Server receives the RS, it authenticates the message and 2838 registers the Client's MNP and INET interface information according 2839 to the OMNI option parameters. If the RS message includes an SLLAO, 2840 the Server compares the encapsulation IP address and UDP port number 2841 with the (unobfuscated) SLLAO values. If the values are the same, 2842 the Server caches the Client's information as "INET" addresses 2843 meaning that the Client is likely to accept direct messages without 2844 requiring NAT traversal exchanges. If the values are different (or, 2845 if there was no SLLAO) the Server instead caches the Client's 2846 information as "NAT" addresses meaning that NAT traversal exchanges 2847 may be necessary. 2849 The Server then returns an RA message with IPv6 source and 2850 destination set corresponding to the addresses in the RS, and with an 2851 Authentication option per [RFC4380]. For IPv4, the Server also 2852 includes an Origin option per [RFC4380] with the mapped and 2853 obfuscated IPv4 address and port number observed in the encapsulation 2854 headers. For IPv6, the Server instead includes an IPv6 Origin option 2855 per Figure 7 with the mapped and obfuscated observed IPv6 address and 2856 port number (note that the value 0x02 in the second octet 2857 differentiates from other [RFC4380] option types). 2859 +--------+--------+-----------------+ 2860 | 0x00 | 0x02 | Origin port # | 2861 +--------+--------+-----------------+ 2862 ~ Origin IPv6 address ~ 2863 +-----------------------------------+ 2865 Figure 7: IPv6 Origin Option 2867 When the Client receives the RA message, it compares the mapped IP 2868 address and port from the Origin option with its own address. If the 2869 addresses are the same, the Client assumes the open Internet / Cone 2870 NAT principle; if the addresses are different, the Client instead 2871 assumes that further qualification procedures are necessary to detect 2872 the type of NAT and proceeds according to standard [RFC4380] 2873 procedures. 2875 After the Client has registered its INET interfaces in such RS/RA 2876 exchanges it sends periodic RS messages to receive fresh RA messages 2877 before the Router Lifetime received on each INET interface expires. 2878 The Client also maintains default routes via its Servers, i.e., the 2879 same as described in earlier sections. 2881 When the Client sends messages to target IP addresses, it also 2882 invokes route optimization per Section 3.14 using IPv6 ND address 2883 resolution messaging. The Client sends the NS(AR) message to the 2884 Server wrapped in a UDP/IP header with an Authentication option with 2885 the NS source address set to the Client's LLA and destination address 2886 set to the target solicited node multicast address. The Server 2887 authenticates the message and sends a corresponding NS(AR) message 2888 over the spanning tree the same as if it were the ROS, but with the 2889 SPAN source address set to the Server's ULA and destination set to 2890 the ULA of the target. When the ROR receives the NS(AR), it adds the 2891 Server's ULA and Client's LLA to the target's Report List, and 2892 returns an NA with OMNI and TLLAO information for the target. The 2893 Server then returns a UDP/IP encapsulated NA message with an 2894 Authentication option to the Client. 2896 Following route optimization, for targets in the same OMNI link 2897 segment if the target's TLLAO addresss is on the open INET, the 2898 Client forwards data packets directly to the target INET address. If 2899 the target's TLLAO address is behind a NAT, the Client first 2900 establishes NAT state for the Link Layer Address using the "bubble" 2901 mechanisms specified in [RFC6081][RFC4380]. The Client continues to 2902 send data packets via its Server until NAT state is populated, then 2903 begins forwarding packets via the direct path through the NAT to the 2904 target. For targets in different OMNI link segments, the Client 2905 inserts a Segment Routing header and forwards data packets to the 2906 Bridge that returned the NA message. 2908 The ROR may return uNAs via the Server if the target moves, and the 2909 Server will send corresponding Authentication-protected uNAs to the 2910 Client. The Client can also send "loopback" NS(NUD) messages to test 2911 forward path reachability even though there is no security 2912 association between the Client and the target. 2914 The Client sends UDP/IP encapsulated IPv6 packets no larger than 1280 2915 bytes in one piece. In order to accommodate larger IPv6 packets (up 2916 to the OMNI interface MTU), the Client inserts a SPAN header with 2917 source set to its own ULA and destination set to the ULA of the 2918 target and uses IPv6 fragmentation according to Section 3.9. The 2919 Client then encapsulates each fragment in a UDP/IP header and sends 2920 the fragments to the next hop. 2922 3.22.1. Use of SEND and CGA 2924 In some environments, use of the [RFC4380] Authentication option 2925 alone may be sufficient for assuring IPv6 ND message authentication 2926 between Clients and Servers. When additional protection is 2927 necessary, nodes should employ SEcure Neighbor Discovery (SEND) 2928 [RFC3971] with Cryptographically-Generated Addresses (CGA) [RFC3972]. 2930 When SEND/CGA are used, the Client prepares RS messages with its 2931 link-local CGA as the IPv6 source and All-Routers as the IPv6 2932 Destination, includes any SEND options and wraps the message in a 2933 SPAN header. The Client sets the SPAN source address to its own ULA 2934 and sets the SPAN destination address to the "All-Routers" ULA. The 2935 Client then wraps the RS message in UDP/IP headers according to 2936 [RFC4380] and sends the message to the Server. 2938 When the Server receives the message, it first verifies the 2939 Authentication option (if present) then uses the SPAN source address 2940 to determine the MNP of the Client. The Server then processes the 2941 SEND options to authenticate the RS message and prepares an RA 2942 message response. The Server prepares the RA with its own link-local 2943 CGA and the CGA of the Client as the IPv6 source and destination, 2944 includes any SEND options and wraps the message in a SPAN header. 2945 The Server sets the SPAN source address to its own ULA and sets the 2946 SPAN destination address to the Client's ULA. The Server then wraps 2947 the RA message in UDP/IP headers according to [RFC4380] and sends the 2948 message to the Client. Thereafter, the Client/Server send additional 2949 RS/RA messages to maintain their association and any NAT state. 2951 The Client and Server also may exchange NS/NA messages using their 2952 own CGA as the source and with SPAN encapsulation as above. When a 2953 Client sends an NS(AR), it sets the IPv6 source to its CGA and sets 2954 the IPv6 destination to the Solicited-Node Multicast address of the 2955 target. The Client then wraps the message in a SPAN header with its 2956 own ULA as the source and the ULA of the target as the destination 2957 and sends it to the Server. The Server authenticates the message, 2958 then changes the IPv6 source address to the Client's LLA, removes the 2959 SEND options, and sends a corresponding NS(AR) into the spanning 2960 tree. When the Server receives the corresponding SPAN-encapsulated 2961 NA, it changes the IPv6 destination address to the Client's CGA, 2962 inserts SEND options, then wraps the message in UDP/IP headers and 2963 sends it to the Client. 2965 When a Client sends a uNA, it sets the IPv6 source address to its own 2966 CGA and sets the IPv6 destination address to All-Nodes multicast, 2967 includes SEND options, wraps the message in SPAN and UDP/IP headers 2968 and sends the message to the Server. The Server authenticates the 2969 message, then changes the IPv6 address to the Client's LLA, removes 2970 the SEND options and forwards the message the same as discussed in 2971 Section 3.16.1. In the reverse direction, when the Server forwards a 2972 uNA to the Client, it changes the IPv6 address to its own CGA and 2973 inserts SEND options then forwards the message to the Client. 2975 When a Client sends an NS(NUD), it sets both the IPv6 source and 2976 destination address to its own LLA, wraps the message in a SPAN 2977 header and UDP/IP headers, then sends the message directly to the 2978 peer which will loop the message back. In this case alone, the 2979 Client does not use the Server as a trust broker for forwarding the 2980 ND message. 2982 3.23. Time-Varying MNPs 2984 In some use cases, it is desirable, beneficial and efficient for the 2985 Client to receive a constant MNP that travels with the Client 2986 wherever it moves. For example, this would allow air traffic 2987 controllers to easily track aircraft, etc. In other cases, however 2988 (e.g., intelligent transportation systems), the MN may be willing to 2989 sacrifice a modicum of efficiency in order to have time-varying MNPs 2990 that can be changed every so often to defeat adversarial tracking. 2992 The DHCPv6-PD service offers a way for Clients that desire time- 2993 varying MNPs to obtain short-lived prefixes (e.g., on the order of a 2994 small number of minutes). In that case, the identity of the Client 2995 would not be bound to the MNP but rather the Client's identity would 2996 be bound to the DHCPv6 Device Unique Identifier (DUID) and used as 2997 the seed for Prefix Delegation. The Client would then be obligated 2998 to renumber its internal networks whenever its MNP (and therefore 2999 also its LLA) changes. This should not present a challenge for 3000 Clients with automated network renumbering services, however presents 3001 limits for the durations of ongoing sessions that would prefer to use 3002 a constant address. 3004 4. Implementation Status 3006 An AERO implementation based on OpenVPN (https://openvpn.net/) was 3007 announced on the v6ops mailing list on January 10, 2018 and an 3008 initial public release of the AERO proof-of-concept source code was 3009 announced on the intarea mailing list on August 21, 2015. 3011 As of 4/1/2020, more recent updated implementations are under 3012 internal development and testing with plans to release in the near 3013 future. 3015 5. IANA Considerations 3017 The IANA has assigned a 4-octet Private Enterprise Number "45282" for 3018 AERO in the "enterprise-numbers" registry. 3020 The IANA has assigned the UDP port number "8060" for an earlier 3021 experimental version of AERO [RFC6706]. This document obsoletes 3022 [RFC6706] and claims the UDP port number "8060" for all future use. 3024 The IANA is instructed to assign a new type value TBD in the Segment 3025 Routing Header TLV registry [RFC8754]. 3027 No further IANA actions are required. 3029 6. Security Considerations 3031 AERO Bridges configure secured tunnels with AERO Servers, Realys and 3032 Proxys within their local OMNI link segments. Applicable secured 3033 tunnel alternatives include IPsec [RFC4301], TLS/SSL [RFC8446], DTLS 3034 [RFC6347], WireGuard, etc. The AERO Bridges of all OMNI link 3035 segments in turn configure secured tunnels for their neighboring AERO 3036 Bridges in a spanning tree topology. Therefore, control messages 3037 exchanged between any pair of OMNI link neighbors on the spanning 3038 tree are already secured. 3040 AERO Servers, Relays and Proxys targeted by a route optimization may 3041 also receive data packets directly from arbitrary nodes in INET 3042 partitions instead of via the spanning tree. For INET partitions 3043 that apply effective ingress filtering to defeat source address 3044 spoofing, the simple data origin authentication procedures in 3045 Section 3.8 can be applied. 3047 For INET partitions that require strong security in the data plane, 3048 two options for securing communications include 1) disable route 3049 optimization so that all traffic is conveyed over secured tunnels, or 3050 2) enable on-demand secure tunnel creation between INET partition 3051 neighbors. Option 1) would result in longer routes than necessary 3052 and traffic concentration on critical infrastructure elements. 3053 Option 2) could be coordinated by establishing a secured tunnel on- 3054 demand instead of performing an NS/NA exchange in the route 3055 optimization procedures. Procedures for establishing on-demand 3056 secured tunnels are out of scope. 3058 AERO Clients that connect to secured ANETs need not apply security to 3059 their ND messages, since the messages will be intercepted by a 3060 perimeter Proxy that applies security on its INET-facing interface as 3061 part of the spanning tree (see above). AERO Clients connected to the 3062 open INET can use symmetric network and/or transport layer security 3063 services such as VPNs or can by some other means establish a direct 3064 link. When a VPN or direct link may be impractical, however, an 3065 asymmetric security service such as SEcure Neighbor Discovery (SEND) 3066 [RFC3971] with Cryptographically Generated Addresses (CGAs) [RFC3972] 3067 and/or the Authentication option [RFC4380] can be applied. 3069 Application endpoints SHOULD use application-layer security services 3070 such as TLS/SSL, DTLS or SSH [RFC4251] to assure the same level of 3071 protection as for critical secured Internet services. AERO Clients 3072 that require host-based VPN services SHOULD use symmetric network 3073 and/or transport layer security services such as IPsec, TLS/SSL, 3074 DTLS, etc. AERO Proxys and Servers can also provide a network-based 3075 VPN service on behalf of the Client, e.g., if the Client is located 3076 within a secured enclave and cannot establish a VPN on its own 3077 behalf. 3079 AERO Servers and Bridges present targets for traffic amplification 3080 Denial of Service (DoS) attacks. This concern is no different than 3081 for widely-deployed VPN security gateways in the Internet, where 3082 attackers could send spoofed packets to the gateways at high data 3083 rates. This can be mitigated by connecting Servers and Bridges over 3084 dedicated links with no connections to the Internet and/or when 3085 connections to the Internet are only permitted through well-managed 3086 firewalls. Traffic amplification DoS attacks can also target an AERO 3087 Client's low data rate links. This is a concern not only for Clients 3088 located on the open Internet but also for Clients in secured 3089 enclaves. AERO Servers and Proxys can institute rate limits that 3090 protect Clients from receiving packet floods that could DoS low data 3091 rate links. 3093 AERO Relays must implement ingress filtering to avoid a spoofing 3094 attack in which spurious messages with ULA addresses are injected 3095 into an OMNI link from an outside attacker. AERO Clients MUST ensure 3096 that their connectivity is not used by unauthorized nodes on their 3097 EUNs to gain access to a protected network, i.e., AERO Clients that 3098 act as routers MUST NOT provide routing services for unauthorized 3099 nodes. (This concern is no different than for ordinary hosts that 3100 receive an IP address delegation but then "share" the address with 3101 other nodes via some form of Internet connection sharing such as 3102 tethering.) 3104 The MAP list MUST be well-managed and secured from unauthorized 3105 tampering, even though the list contains only public information. 3106 The MAP list can be conveyed to the Client in a similar fashion as in 3107 [RFC5214] (e.g., through layer 2 data link login messaging, secure 3108 upload of a static file, DNS lookups, etc.). 3110 Although public domain and commercial SEND implementations exist, 3111 concerns regarding the strength of the cryptographic hash algorithm 3112 have been documented [RFC6273] [RFC4982]. 3114 SRH authentication facilities are specified in [RFC8754]. 3116 Security considerations for accepting link-layer ICMP messages and 3117 reflected packets are discussed throughout the document. 3119 Security considerations for IPv6 fragmentation and reassembly are 3120 discussed in [I-D.templin-6man-omni-interface]. 3122 7. Acknowledgements 3124 Discussions in the IETF, aviation standards communities and private 3125 exchanges helped shape some of the concepts in this work. 3126 Individuals who contributed insights include Mikael Abrahamsson, Mark 3127 Andrews, Fred Baker, Bob Braden, Stewart Bryant, Brian Carpenter, 3128 Wojciech Dec, Pavel Drasil, Ralph Droms, Adrian Farrel, Nick Green, 3129 Sri Gundavelli, Brian Haberman, Bernhard Haindl, Joel Halpern, Tom 3130 Herbert, Sascha Hlusiak, Lee Howard, Zdenek Jaron, Andre Kostur, 3131 Hubert Kuenig, Ted Lemon, Andy Malis, Satoru Matsushima, Tomek 3132 Mrugalski, Madhu Niraula, Alexandru Petrescu, Behcet Saikaya, Michal 3133 Skorepa, Joe Touch, Bernie Volz, Ryuji Wakikawa, Tony Whyman, Lloyd 3134 Wood and James Woodyatt. Members of the IESG also provided valuable 3135 input during their review process that greatly improved the document. 3136 Special thanks go to Stewart Bryant, Joel Halpern and Brian Haberman 3137 for their shepherding guidance during the publication of the AERO 3138 first edition. 3140 This work has further been encouraged and supported by Boeing 3141 colleagues including Kyle Bae, M. Wayne Benson, Dave Bernhardt, Cam 3142 Brodie, John Bush, Balaguruna Chidambaram, Irene Chin, Bruce Cornish, 3143 Claudiu Danilov, Don Dillenburg, Joe Dudkowski, Wen Fang, Samad 3144 Farooqui, Anthony Gregory, Jeff Holland, Seth Jahne, Brian Jaury, 3145 Greg Kimberly, Ed King, Madhuri Madhava Badgandi, Laurel Matthew, 3146 Gene MacLean III, Rob Muszkiewicz, Sean O'Sullivan, Vijay 3147 Rajagopalan, Greg Saccone, Rod Santiago, Kent Shuey, Brian Skeen, 3148 Mike Slane, Carrie Spiker, Katie Tran, Brendan Williams, Amelia 3149 Wilson, Julie Wulff, Yueli Yang, Eric Yeh and other members of the 3150 Boeing mobility, networking and autonomy teams. Kyle Bae, Wayne 3151 Benson, Katie Tran and Eric Yeh are especially acknowledged for 3152 implementing the AERO functions as extensions to the public domain 3153 OpenVPN distribution. 3155 Earlier works on NBMA tunneling approaches are found in 3156 [RFC2529][RFC5214][RFC5569]. 3158 Many of the constructs presented in this second edition of AERO are 3159 based on the author's earlier works, including: 3161 o The Internet Routing Overlay Network (IRON) 3162 [RFC6179][I-D.templin-ironbis] 3164 o Virtual Enterprise Traversal (VET) 3165 [RFC5558][I-D.templin-intarea-vet] 3167 o The Subnetwork Encapsulation and Adaptation Layer (SEAL) 3168 [RFC5320][I-D.templin-intarea-seal] 3170 o AERO, First Edition [RFC6706] 3172 Note that these works cite numerous earlier efforts that are not also 3173 cited here due to space limitations. The authors of those earlier 3174 works are acknowledged for their insights. 3176 This work is aligned with the NASA Safe Autonomous Systems Operation 3177 (SASO) program under NASA contract number NNA16BD84C. 3179 This work is aligned with the FAA as per the SE2025 contract number 3180 DTFAWA-15-D-00030. 3182 This work is aligned with the Boeing Commercial Airplanes (BCA) 3183 Internet of Things (IoT) and autonomy programs. 3185 This work is aligned with the Boeing Information Technology (BIT) 3186 MobileNet program. 3188 8. References 3189 8.1. Normative References 3191 [I-D.templin-6man-omni-interface] 3192 Templin, F. and T. Whyman, "Transmission of IPv6 Packets 3193 over Overlay Multilink Network (OMNI) Interfaces", draft- 3194 templin-6man-omni-interface-24 (work in progress), June 3195 2020. 3197 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, 3198 DOI 10.17487/RFC0791, September 1981, 3199 . 3201 [RFC0792] Postel, J., "Internet Control Message Protocol", STD 5, 3202 RFC 792, DOI 10.17487/RFC0792, September 1981, 3203 . 3205 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 3206 Requirement Levels", BCP 14, RFC 2119, 3207 DOI 10.17487/RFC2119, March 1997, 3208 . 3210 [RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in 3211 IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473, 3212 December 1998, . 3214 [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black, 3215 "Definition of the Differentiated Services Field (DS 3216 Field) in the IPv4 and IPv6 Headers", RFC 2474, 3217 DOI 10.17487/RFC2474, December 1998, 3218 . 3220 [RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander, 3221 "SEcure Neighbor Discovery (SEND)", RFC 3971, 3222 DOI 10.17487/RFC3971, March 2005, 3223 . 3225 [RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)", 3226 RFC 3972, DOI 10.17487/RFC3972, March 2005, 3227 . 3229 [RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and 3230 More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191, 3231 November 2005, . 3233 [RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast 3234 Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005, 3235 . 3237 [RFC4380] Huitema, C., "Teredo: Tunneling IPv6 over UDP through 3238 Network Address Translations (NATs)", RFC 4380, 3239 DOI 10.17487/RFC4380, February 2006, 3240 . 3242 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 3243 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 3244 DOI 10.17487/RFC4861, September 2007, 3245 . 3247 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 3248 Address Autoconfiguration", RFC 4862, 3249 DOI 10.17487/RFC4862, September 2007, 3250 . 3252 [RFC5175] Haberman, B., Ed. and R. Hinden, "IPv6 Router 3253 Advertisement Flags Option", RFC 5175, 3254 DOI 10.17487/RFC5175, March 2008, 3255 . 3257 [RFC6081] Thaler, D., "Teredo Extensions", RFC 6081, 3258 DOI 10.17487/RFC6081, January 2011, 3259 . 3261 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 3262 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 3263 May 2017, . 3265 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 3266 (IPv6) Specification", STD 86, RFC 8200, 3267 DOI 10.17487/RFC8200, July 2017, 3268 . 3270 [RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A., 3271 Richardson, M., Jiang, S., Lemon, T., and T. Winters, 3272 "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", 3273 RFC 8415, DOI 10.17487/RFC8415, November 2018, 3274 . 3276 8.2. Informative References 3278 [BGP] Huston, G., "BGP in 2015, http://potaroo.net", January 3279 2016. 3281 [I-D.bonica-6man-comp-rtg-hdr] 3282 Bonica, R., Kamite, Y., Niwa, T., Alston, A., and L. 3283 Jalil, "The IPv6 Compact Routing Header (CRH)", draft- 3284 bonica-6man-comp-rtg-hdr-22 (work in progress), May 2020. 3286 [I-D.bonica-6man-crh-helper-opt] 3287 Li, X., Bao, C., Ruan, E., and R. Bonica, "Compressed 3288 Routing Header (CRH) Helper Option", draft-bonica-6man- 3289 crh-helper-opt-01 (work in progress), May 2020. 3291 [I-D.ietf-dmm-distributed-mobility-anchoring] 3292 Chan, A., Wei, X., Lee, J., Jeon, S., and C. Bernardos, 3293 "Distributed Mobility Anchoring", draft-ietf-dmm- 3294 distributed-mobility-anchoring-15 (work in progress), 3295 March 2020. 3297 [I-D.ietf-intarea-frag-fragile] 3298 Bonica, R., Baker, F., Huston, G., Hinden, R., Troan, O., 3299 and F. Gont, "IP Fragmentation Considered Fragile", draft- 3300 ietf-intarea-frag-fragile-17 (work in progress), September 3301 2019. 3303 [I-D.ietf-intarea-gue] 3304 Herbert, T., Yong, L., and O. Zia, "Generic UDP 3305 Encapsulation", draft-ietf-intarea-gue-09 (work in 3306 progress), October 2019. 3308 [I-D.ietf-intarea-gue-extensions] 3309 Herbert, T., Yong, L., and F. Templin, "Extensions for 3310 Generic UDP Encapsulation", draft-ietf-intarea-gue- 3311 extensions-06 (work in progress), March 2019. 3313 [I-D.ietf-intarea-tunnels] 3314 Touch, J. and M. Townsley, "IP Tunnels in the Internet 3315 Architecture", draft-ietf-intarea-tunnels-10 (work in 3316 progress), September 2019. 3318 [I-D.ietf-rtgwg-atn-bgp] 3319 Templin, F., Saccone, G., Dawra, G., Lindem, A., and V. 3320 Moreno, "A Simple BGP-based Mobile Routing System for the 3321 Aeronautical Telecommunications Network", draft-ietf- 3322 rtgwg-atn-bgp-05 (work in progress), January 2020. 3324 [I-D.templin-6man-dhcpv6-ndopt] 3325 Templin, F., "A Unified Stateful/Stateless Configuration 3326 Service for IPv6", draft-templin-6man-dhcpv6-ndopt-09 3327 (work in progress), January 2020. 3329 [I-D.templin-intarea-grefrag] 3330 Templin, F., "GRE Tunnel Level Fragmentation", draft- 3331 templin-intarea-grefrag-04 (work in progress), July 2016. 3333 [I-D.templin-intarea-seal] 3334 Templin, F., "The Subnetwork Encapsulation and Adaptation 3335 Layer (SEAL)", draft-templin-intarea-seal-68 (work in 3336 progress), January 2014. 3338 [I-D.templin-intarea-vet] 3339 Templin, F., "Virtual Enterprise Traversal (VET)", draft- 3340 templin-intarea-vet-40 (work in progress), May 2013. 3342 [I-D.templin-ironbis] 3343 Templin, F., "The Interior Routing Overlay Network 3344 (IRON)", draft-templin-ironbis-16 (work in progress), 3345 March 2014. 3347 [I-D.templin-v6ops-pdhost] 3348 Templin, F., "IPv6 Prefix Delegation and Multi-Addressing 3349 Models", draft-templin-v6ops-pdhost-25 (work in progress), 3350 January 2020. 3352 [OVPN] OpenVPN, O., "http://openvpn.net", October 2016. 3354 [RFC1035] Mockapetris, P., "Domain names - implementation and 3355 specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, 3356 November 1987, . 3358 [RFC1122] Braden, R., Ed., "Requirements for Internet Hosts - 3359 Communication Layers", STD 3, RFC 1122, 3360 DOI 10.17487/RFC1122, October 1989, 3361 . 3363 [RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191, 3364 DOI 10.17487/RFC1191, November 1990, 3365 . 3367 [RFC1812] Baker, F., Ed., "Requirements for IP Version 4 Routers", 3368 RFC 1812, DOI 10.17487/RFC1812, June 1995, 3369 . 3371 [RFC2003] Perkins, C., "IP Encapsulation within IP", RFC 2003, 3372 DOI 10.17487/RFC2003, October 1996, 3373 . 3375 [RFC2236] Fenner, W., "Internet Group Management Protocol, Version 3376 2", RFC 2236, DOI 10.17487/RFC2236, November 1997, 3377 . 3379 [RFC2492] Armitage, G., Schulter, P., and M. Jork, "IPv6 over ATM 3380 Networks", RFC 2492, DOI 10.17487/RFC2492, January 1999, 3381 . 3383 [RFC2529] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4 3384 Domains without Explicit Tunnels", RFC 2529, 3385 DOI 10.17487/RFC2529, March 1999, 3386 . 3388 [RFC2764] Gleeson, B., Lin, A., Heinanen, J., Armitage, G., and A. 3389 Malis, "A Framework for IP Based Virtual Private 3390 Networks", RFC 2764, DOI 10.17487/RFC2764, February 2000, 3391 . 3393 [RFC2784] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P. 3394 Traina, "Generic Routing Encapsulation (GRE)", RFC 2784, 3395 DOI 10.17487/RFC2784, March 2000, 3396 . 3398 [RFC2890] Dommety, G., "Key and Sequence Number Extensions to GRE", 3399 RFC 2890, DOI 10.17487/RFC2890, September 2000, 3400 . 3402 [RFC2923] Lahey, K., "TCP Problems with Path MTU Discovery", 3403 RFC 2923, DOI 10.17487/RFC2923, September 2000, 3404 . 3406 [RFC2983] Black, D., "Differentiated Services and Tunnels", 3407 RFC 2983, DOI 10.17487/RFC2983, October 2000, 3408 . 3410 [RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition 3411 of Explicit Congestion Notification (ECN) to IP", 3412 RFC 3168, DOI 10.17487/RFC3168, September 2001, 3413 . 3415 [RFC3330] IANA, "Special-Use IPv4 Addresses", RFC 3330, 3416 DOI 10.17487/RFC3330, September 2002, 3417 . 3419 [RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener 3420 Discovery Version 2 (MLDv2) for IPv6", RFC 3810, 3421 DOI 10.17487/RFC3810, June 2004, 3422 . 3424 [RFC3819] Karn, P., Ed., Bormann, C., Fairhurst, G., Grossman, D., 3425 Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J., and L. 3426 Wood, "Advice for Internet Subnetwork Designers", BCP 89, 3427 RFC 3819, DOI 10.17487/RFC3819, July 2004, 3428 . 3430 [RFC4213] Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms 3431 for IPv6 Hosts and Routers", RFC 4213, 3432 DOI 10.17487/RFC4213, October 2005, 3433 . 3435 [RFC4251] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH) 3436 Protocol Architecture", RFC 4251, DOI 10.17487/RFC4251, 3437 January 2006, . 3439 [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A 3440 Border Gateway Protocol 4 (BGP-4)", RFC 4271, 3441 DOI 10.17487/RFC4271, January 2006, 3442 . 3444 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 3445 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 3446 2006, . 3448 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 3449 Internet Protocol", RFC 4301, DOI 10.17487/RFC4301, 3450 December 2005, . 3452 [RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery 3453 Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April 3454 2006, . 3456 [RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet 3457 Control Message Protocol (ICMPv6) for the Internet 3458 Protocol Version 6 (IPv6) Specification", STD 89, 3459 RFC 4443, DOI 10.17487/RFC4443, March 2006, 3460 . 3462 [RFC4511] Sermersheim, J., Ed., "Lightweight Directory Access 3463 Protocol (LDAP): The Protocol", RFC 4511, 3464 DOI 10.17487/RFC4511, June 2006, 3465 . 3467 [RFC4541] Christensen, M., Kimball, K., and F. Solensky, 3468 "Considerations for Internet Group Management Protocol 3469 (IGMP) and Multicast Listener Discovery (MLD) Snooping 3470 Switches", RFC 4541, DOI 10.17487/RFC4541, May 2006, 3471 . 3473 [RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick, 3474 "Internet Group Management Protocol (IGMP) / Multicast 3475 Listener Discovery (MLD)-Based Multicast Forwarding 3476 ("IGMP/MLD Proxying")", RFC 4605, DOI 10.17487/RFC4605, 3477 August 2006, . 3479 [RFC4607] Holbrook, H. and B. Cain, "Source-Specific Multicast for 3480 IP", RFC 4607, DOI 10.17487/RFC4607, August 2006, 3481 . 3483 [RFC4963] Heffner, J., Mathis, M., and B. Chandler, "IPv4 Reassembly 3484 Errors at High Data Rates", RFC 4963, 3485 DOI 10.17487/RFC4963, July 2007, 3486 . 3488 [RFC4982] Bagnulo, M. and J. Arkko, "Support for Multiple Hash 3489 Algorithms in Cryptographically Generated Addresses 3490 (CGAs)", RFC 4982, DOI 10.17487/RFC4982, July 2007, 3491 . 3493 [RFC5015] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano, 3494 "Bidirectional Protocol Independent Multicast (BIDIR- 3495 PIM)", RFC 5015, DOI 10.17487/RFC5015, October 2007, 3496 . 3498 [RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site 3499 Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214, 3500 DOI 10.17487/RFC5214, March 2008, 3501 . 3503 [RFC5320] Templin, F., Ed., "The Subnetwork Encapsulation and 3504 Adaptation Layer (SEAL)", RFC 5320, DOI 10.17487/RFC5320, 3505 February 2010, . 3507 [RFC5522] Eddy, W., Ivancic, W., and T. Davis, "Network Mobility 3508 Route Optimization Requirements for Operational Use in 3509 Aeronautics and Space Exploration Mobile Networks", 3510 RFC 5522, DOI 10.17487/RFC5522, October 2009, 3511 . 3513 [RFC5558] Templin, F., Ed., "Virtual Enterprise Traversal (VET)", 3514 RFC 5558, DOI 10.17487/RFC5558, February 2010, 3515 . 3517 [RFC5569] Despres, R., "IPv6 Rapid Deployment on IPv4 3518 Infrastructures (6rd)", RFC 5569, DOI 10.17487/RFC5569, 3519 January 2010, . 3521 [RFC5871] Arkko, J. and S. Bradner, "IANA Allocation Guidelines for 3522 the IPv6 Routing Header", RFC 5871, DOI 10.17487/RFC5871, 3523 May 2010, . 3525 [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 3526 (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, 3527 . 3529 [RFC5991] Thaler, D., Krishnan, S., and J. Hoagland, "Teredo 3530 Security Updates", RFC 5991, DOI 10.17487/RFC5991, 3531 September 2010, . 3533 [RFC6106] Jeong, J., Park, S., Beloeil, L., and S. Madanapalli, 3534 "IPv6 Router Advertisement Options for DNS Configuration", 3535 RFC 6106, DOI 10.17487/RFC6106, November 2010, 3536 . 3538 [RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful 3539 NAT64: Network Address and Protocol Translation from IPv6 3540 Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146, 3541 April 2011, . 3543 [RFC6179] Templin, F., Ed., "The Internet Routing Overlay Network 3544 (IRON)", RFC 6179, DOI 10.17487/RFC6179, March 2011, 3545 . 3547 [RFC6221] Miles, D., Ed., Ooghe, S., Dec, W., Krishnan, S., and A. 3548 Kavanagh, "Lightweight DHCPv6 Relay Agent", RFC 6221, 3549 DOI 10.17487/RFC6221, May 2011, 3550 . 3552 [RFC6273] Kukec, A., Krishnan, S., and S. Jiang, "The Secure 3553 Neighbor Discovery (SEND) Hash Threat Analysis", RFC 6273, 3554 DOI 10.17487/RFC6273, June 2011, 3555 . 3557 [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer 3558 Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, 3559 January 2012, . 3561 [RFC6438] Carpenter, B. and S. Amante, "Using the IPv6 Flow Label 3562 for Equal Cost Multipath Routing and Link Aggregation in 3563 Tunnels", RFC 6438, DOI 10.17487/RFC6438, November 2011, 3564 . 3566 [RFC6706] Templin, F., Ed., "Asymmetric Extended Route Optimization 3567 (AERO)", RFC 6706, DOI 10.17487/RFC6706, August 2012, 3568 . 3570 [RFC6864] Touch, J., "Updated Specification of the IPv4 ID Field", 3571 RFC 6864, DOI 10.17487/RFC6864, February 2013, 3572 . 3574 [RFC6935] Eubanks, M., Chimento, P., and M. Westerlund, "IPv6 and 3575 UDP Checksums for Tunneled Packets", RFC 6935, 3576 DOI 10.17487/RFC6935, April 2013, 3577 . 3579 [RFC6936] Fairhurst, G. and M. Westerlund, "Applicability Statement 3580 for the Use of IPv6 UDP Datagrams with Zero Checksums", 3581 RFC 6936, DOI 10.17487/RFC6936, April 2013, 3582 . 3584 [RFC7269] Chen, G., Cao, Z., Xie, C., and D. Binet, "NAT64 3585 Deployment Options and Experience", RFC 7269, 3586 DOI 10.17487/RFC7269, June 2014, 3587 . 3589 [RFC7333] Chan, H., Ed., Liu, D., Seite, P., Yokota, H., and J. 3590 Korhonen, "Requirements for Distributed Mobility 3591 Management", RFC 7333, DOI 10.17487/RFC7333, August 2014, 3592 . 3594 [RFC7421] Carpenter, B., Ed., Chown, T., Gont, F., Jiang, S., 3595 Petrescu, A., and A. Yourtchenko, "Analysis of the 64-bit 3596 Boundary in IPv6 Addressing", RFC 7421, 3597 DOI 10.17487/RFC7421, January 2015, 3598 . 3600 [RFC7739] Gont, F., "Security Implications of Predictable Fragment 3601 Identification Values", RFC 7739, DOI 10.17487/RFC7739, 3602 February 2016, . 3604 [RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I., 3605 Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent 3606 Multicast - Sparse Mode (PIM-SM): Protocol Specification 3607 (Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March 3608 2016, . 3610 [RFC8086] Yong, L., Ed., Crabbe, E., Xu, X., and T. Herbert, "GRE- 3611 in-UDP Encapsulation", RFC 8086, DOI 10.17487/RFC8086, 3612 March 2017, . 3614 [RFC8138] Thubert, P., Ed., Bormann, C., Toutain, L., and R. Cragie, 3615 "IPv6 over Low-Power Wireless Personal Area Network 3616 (6LoWPAN) Routing Header", RFC 8138, DOI 10.17487/RFC8138, 3617 April 2017, . 3619 [RFC8201] McCann, J., Deering, S., Mogul, J., and R. Hinden, Ed., 3620 "Path MTU Discovery for IP version 6", STD 87, RFC 8201, 3621 DOI 10.17487/RFC8201, July 2017, 3622 . 3624 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 3625 Decraene, B., Litkowski, S., and R. Shakir, "Segment 3626 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 3627 July 2018, . 3629 [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol 3630 Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, 3631 . 3633 [RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J., 3634 Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header 3635 (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020, 3636 . 3638 Appendix A. Non-Normative Considerations 3640 AERO can be applied to a multitude of Internetworking scenarios, with 3641 each having its own adaptations. The following considerations are 3642 provided as non-normative guidance: 3644 A.1. Implementation Strategies for Route Optimization 3646 Route optimization as discussed in Section 3.14 results in the route 3647 optimization source (ROS) creating an asymmetric neighbor cache entry 3648 for the target neighbor. The neighbor cache entry is maintained for 3649 at most ReachableTime seconds and then deleted unless updated. In 3650 order to refresh the neighbor cache entry lifetime before the 3651 ReachableTime timer expires, the specification requires 3652 implementations to issue a new NS/NA exchange to reset ReachableTime 3653 while data packets are still flowing. However, the decision of when 3654 to initiate a new NS/NA exchange and to perpetuate the process is 3655 left as an implementation detail. 3657 One possible strategy may be to monitor the neighbor cache entry 3658 watching for data packets for (ReachableTime - 5) seconds. If any 3659 data packets have been sent to the neighbor within this timeframe, 3660 then send an NS to receive a new NA. If no data packets have been 3661 sent, wait for 5 additional seconds and send an immediate NS if any 3662 data packets are sent within this "expiration pending" 5 second 3663 window. If no additional data packets are sent within the 5 second 3664 window, delete the neighbor cache entry. 3666 The monitoring of the neighbor data packet traffic therefore becomes 3667 an asymmetric ongoing process during the neighbor cache entry 3668 lifetime. If the neighbor cache entry expires, future data packets 3669 will trigger a new NS/NA exchange while the packets themselves are 3670 delivered over a longer path until route optimization state is re- 3671 established. 3673 A.2. Implicit Mobility Management 3675 OMNI interface neighbors MAY provide a configuration option that 3676 allows them to perform implicit mobility management in which no ND 3677 messaging is used. In that case, the Client only transmits packets 3678 over a single interface at a time, and the neighbor always observes 3679 packets arriving from the Client from the same link-layer source 3680 address. 3682 If the Client's underlying interface address changes (either due to a 3683 readdressing of the original interface or switching to a new 3684 interface) the neighbor immediately updates the neighbor cache entry 3685 for the Client and begins accepting and sending packets according to 3686 the Client's new address. This implicit mobility method applies to 3687 use cases such as cellphones with both WiFi and Cellular interfaces 3688 where only one of the interfaces is active at a given time, and the 3689 Client automatically switches over to the backup interface if the 3690 primary interface fails. 3692 A.3. Direct Underlying Interfaces 3694 When a Client's OMNI interface is configured over a Direct interface, 3695 the neighbor at the other end of the Direct link can receive packets 3696 without any encapsulation. In that case, the Client sends packets 3697 over the Direct link according to QoS preferences. If the Direct 3698 interface has the highest QoS preference, then the Client's IP 3699 packets are transmitted directly to the peer without going through an 3700 ANET/INET. If other interfaces have higher QoS preferences, then the 3701 Client's IP packets are transmitted via a different interface, which 3702 may result in the inclusion of Proxys, Servers and Bridges in the 3703 communications path. Direct interfaces must be tested periodically 3704 for reachability, e.g., via NUD. 3706 A.4. AERO Critical Infrastructure Considerations 3708 AERO Bridges can be either Commercial off-the Shelf (COTS) standard 3709 IP routers or virtual machines in the cloud. Bridges must be 3710 provisioned, supported and managed by the INET administrative 3711 authority, and connected to the Bridges of other INETs via inter- 3712 domain peerings. Cost for purchasing, configuring and managing 3713 Bridges is nominal even for very large OMNI links. 3715 AERO Servers can be standard dedicated server platforms, but most 3716 often will be deployed as virtual machines in the cloud. The only 3717 requirements for Servers are that they can run the AERO user-level 3718 code and have at least one network interface connection to the INET. 3719 As with Bridges, Servers must be provisioned, supported and managed 3720 by the INET administrative authority. Cost for purchasing, 3721 configuring and managing Servers is nominal especially for virtual 3722 Servers hosted in the cloud. 3724 AERO Proxys are most often standard dedicated server platforms with 3725 one network interface connected to the ANET and a second interface 3726 connected to an INET. As with Servers, the only requirements are 3727 that they can run the AERO user-level code and have at least one 3728 interface connection to the INET. Proxys must be provisioned, 3729 supported and managed by the ANET administrative authority. Cost for 3730 purchasing, configuring and managing Proxys is nominal, and borne by 3731 the ANET administrative authority. 3733 AERO Relays can be any dedicated server or COTS router platform 3734 connected to INETs and/or EUNs. The Relay connects to the OMNI link 3735 and engages in eBGP peering with one or more Bridges as a stub AS. 3736 The Relay then injects its MNPs and/or non-MNP prefixes into the BGP 3737 routing system, and provisions the prefixes to its downstream- 3738 attached networks. The Relay can perform ROS/ROR services the same 3739 as for any Server, and can route between the MNP and non-MNP address 3740 spaces. 3742 A.5. AERO Server Failure Implications 3744 AERO Servers may appear as a single point of failure in the 3745 architecture, but such is not the case since all Servers on the link 3746 provide identical services and loss of a Server does not imply 3747 immediate and/or comprehensive communication failures. Although 3748 Clients typically associate with a single Server at a time, Server 3749 failure is quickly detected and conveyed by Bidirectional Forward 3750 Detection (BFD) and/or proactive NUD allowing Clients to migrate to 3751 new Servers. 3753 If a Server fails, ongoing packet forwarding to Clients will continue 3754 by virtue of the asymmetric neighbor cache entries that have already 3755 been established in route optimization sources (ROSs). If a Client 3756 also experiences mobility events at roughly the same time the Server 3757 fails, unsolicited NA messages may be lost but proxy neighbor cache 3758 entries in the DEPARTED state will ensure that packet forwarding to 3759 the Client's new locations will continue for up to DepartTime 3760 seconds. 3762 If a Client is left without a Server for an extended timeframe (e.g., 3763 greater than ReachableTime seconds) then existing asymmetric neighbor 3764 cache entries will eventually expire and both ongoing and new 3765 communications will fail. The original source will continue to 3766 retransmit until the Client has established a new Server 3767 relationship, after which time continuous communications will resume. 3769 Therefore, providing many Servers on the link with high availability 3770 profiles provides resilience against loss of individual Servers and 3771 assurance that Clients can establish new Server relationships quickly 3772 in event of a Server failure. 3774 A.6. AERO Client / Server Architecture 3776 The AERO architectural model is client / server in the control plane, 3777 with route optimization in the data plane. The same as for common 3778 Internet services, the AERO Client discovers the addresses of AERO 3779 Servers and selects one Server to connect to. The AERO service is 3780 analogous to common Internet services such as google.com, yahoo.com, 3781 cnn.com, etc. However, there is only one AERO service for the link 3782 and all Servers provide identical services. 3784 Common Internet services provide differing strategies for advertising 3785 server addresses to clients. The strategy is conveyed through the 3786 DNS resource records returned in response to name resolution queries. 3787 As of January 2020 Internet-based 'nslookup' services were used to 3788 determine the following: 3790 o When a client resolves the domainname "google.com", the DNS always 3791 returns one A record (i.e., an IPv4 address) and one AAAA record 3792 (i.e., an IPv6 address). The client receives the same addresses 3793 each time it resolves the domainname via the same DNS resolver, 3794 but may receive different addresses when it resolves the 3795 domainname via different DNS resolvers. But, in each case, 3796 exactly one A and one AAAA record are returned. 3798 o When a client resolves the domainname "ietf.org", the DNS always 3799 returns one A record and one AAAA record with the same addresses 3800 regardless of which DNS resolver is used. 3802 o When a client resolves the domainname "yahoo.com", the DNS always 3803 returns a list of 4 A records and 4 AAAA records. Each time the 3804 client resolves the domainname via the same DNS resolver, the same 3805 list of addresses are returned but in randomized order (i.e., 3806 consistent with a DNS round-robin strategy). But, interestingly, 3807 the same addresses are returned (albeit in randomized order) when 3808 the domainname is resolved via different DNS resolvers. 3810 o When a client resolves the domainname "amazon.com", the DNS always 3811 returns a list of 3 A records and no AAAA records. As with 3812 "yahoo.com", the same three A records are returned from any 3813 worldwide Internet connection point in randomized order. 3815 The above example strategies show differing approaches to Internet 3816 resilience and service distribution offered by major Internet 3817 services. The Google approach exposes only a single IPv4 and a 3818 single IPv6 address to clients. Clients can then select whichever IP 3819 protocol version offers the best response, but will always use the 3820 same IP address according to the current Internet connection point. 3821 This means that the IP address offered by the network must lead to a 3822 highly-available server and/or service distribution point. In other 3823 words, resilience is predicated on high availability within the 3824 network and with no client-initiated failovers expected (i.e., it is 3825 all-or-nothing from the client's perspective). However, Google does 3826 provide for worldwide distributed service distribution by virtue of 3827 the fact that each Internet connection point responds with a 3828 different IPv6 and IPv4 address. The IETF approach is like google 3829 (all-or-nothing from the client's perspective), but provides only a 3830 single IPv4 or IPv6 address on a worldwide basis. This means that 3831 the addresses must be made highly-available at the network level with 3832 no client failover possibility, and if there is any worldwide service 3833 distribution it would need to be conducted by a network element that 3834 is reached via the IP address acting as a service distribution point. 3836 In contrast to the Google and IETF philosophies, Yahoo and Amazon 3837 both provide clients with a (short) list of IP addresses with Yahoo 3838 providing both IP protocol versions and Amazon as IPv4-only. The 3839 order of the list is randomized with each name service query 3840 response, with the effect of round-robin load balancing for service 3841 distribution. With a short list of addresses, there is still 3842 expectation that the network will implement high availability for 3843 each address but in case any single address fails the client can 3844 switch over to using a different address. The balance then becomes 3845 one of function in the network vs function in the end system. 3847 The same implications observed for common highly-available services 3848 in the Internet apply also to the AERO client/server architecture. 3849 When an AERO Client connects to one or more ANETs, it discovers one 3850 or more AERO Server addresses through the mechanisms discussed in 3851 earlier sections. Each Server address presumably leads to a fault- 3852 tolerant clustering arrangement such as supported by Linux-HA, 3853 Extended Virtual Synchrony or Paxos. Such an arrangement has 3854 precedence in common Internet service deployments in lightweight 3855 virtual machines without requiring expensive hardware deployment. 3856 Similarly, common Internet service deployments set service IP 3857 addresses on service distribution points that may relay requests to 3858 many different servers. 3860 For AERO, the expectation is that a combination of the Google/IETF 3861 and Yahoo/Amazon philosophies would be employed. The AERO Client 3862 connects to different ANET access points and can receive 1-2 Server 3863 LLAs at each point. It then selects one AERO Server address, and 3864 engages in RS/RA exchanges with the same Server from all ANET 3865 connections. The Client remains with this Server unless or until the 3866 Server fails, in which case it can switch over to an alternate 3867 Server. The Client can likewise switch over to a different Server at 3868 any time if there is some reason for it to do so. So, the AERO 3869 expectation is for a balance of function in the network and end 3870 system, with fault tolerance and resilience at both levels. 3872 Appendix B. Change Log 3874 << RFC Editor - remove prior to publication >> 3876 Changes from draft-templin-intarea-6706bis-52 to draft-templin- 3877 intrea-6706bis-53: 3879 o Normative reference to the OMNI spec, and remove portions that are 3880 already specified in OMNI. 3882 o Renamed "AERO interface/link" to "OMIN interface/link" throughout 3883 the document. 3885 o Truncated obsolete back section matter. 3887 Author's Address 3889 Fred L. Templin (editor) 3890 Boeing Research & Technology 3891 P.O. Box 3707 3892 Seattle, WA 98124 3893 USA 3895 Email: fltemplin@acm.org