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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 23, 2020 5 rfc6179, rfc6706 (if 6 approved) 7 Intended status: Standards Track 8 Expires: December 25, 2020 10 Asymmetric Extended Route Optimization (AERO) 11 draft-templin-intarea-6706bis-55 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 25, 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 . . . . . . . . . 21 78 3.3. OMNI Interface Characteristics . . . . . . . . . . . . . 21 79 3.4. OMNI Interface Initialization . . . . . . . . . . . . . . 25 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 . . . . . . . . . . . . . . . . 26 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 . . . . . . . . . . 30 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) . . . . 51 112 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 . . . . . . . . 53 117 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) . . . . . . . . . . . . . 56 121 3.17.3. Bi-Directional PIM (BIDIR-PIM) . . . . . . . . . . . 57 122 3.18. Operation over Multiple OMNI Links . . . . . . . . . . . 57 123 3.19. DNS Considerations . . . . . . . . . . . . . . . . . . . 58 124 3.20. Transition Considerations . . . . . . . . . . . . . . . . 59 125 3.21. Detecting and Reacting to Server and Bridge Failures . . 59 126 3.22. AERO Clients on the Open Internet . . . . . . . . . . . . 60 127 3.22.1. Use of SEND and CGA . . . . . . . . . . . . . . . . 62 128 3.23. Time-Varying MNPs . . . . . . . . . . . . . . . . . . . . 64 129 4. Implementation Status . . . . . . . . . . . . . . . . . . . . 64 130 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 64 131 6. Security Considerations . . . . . . . . . . . . . . . . . . . 65 132 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 67 133 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 68 134 8.1. Normative References . . . . . . . . . . . . . . . . . . 68 135 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 . . . . . . . . . . . . . . 78 139 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) and configure secured 467 tunnels with Servers, Relays, Proxys and other Bridges; they further 468 maintain IP forwarding table entries for each Mobile Network Prefix 469 (MNP) and any other reachable non-MNP prefixes. 471 AERO Servers provide default forwarding and mobility/multilink 472 services for AERO Client Mobile Nodes (MNs). Each Server also peers 473 with Bridges in a dynamic routing protocol instance to advertise its 474 list of associated MNPs (see Section 3.2.3). Servers facilitate PD 475 exchanges with Clients, where each delegated prefix becomes an MNP 476 taken from an MSP. Servers forward packets between OMNI interface 477 neighbors and track each Client's mobility profiles. 479 AERO Clients register their MNPs through PD exchanges with AERO 480 Servers over the OMNI link, and distribute the MNPs to nodes on EUNs. 481 A Client may also be co-resident on the same physical or virtual 482 platform as a Server; in that case, the Client and Server behave as a 483 single functional unit. 485 AERO Proxys provide a conduit for ANET Clients to associate with 486 Servers in external INETs. Client and Servers exchange control plane 487 messages via the Proxy acting as a bridge between the ANET/INET 488 boundary. The Proxy forwards data packets between Clients and the 489 OMNI link according to forwarding information in the neighbor cache. 490 The Proxy function is specified in Section 3.13. 492 AERO Relays are Servers that provide forwarding services between the 493 OMNI interface and INET/EUN interfaces. Relays are provisioned with 494 MNPs the same as for an AERO Client, and also run a dynamic routing 495 protocol to discover any non-MNP IP routes. The Relay advertises the 496 MSP(s) to its connected networks, and distributes all of its 497 associated MNPs and non-MNP IP routes via BGP peerings with Bridges. 499 AERO Bridges, Servers, Proxys and Relays are critical infrastructure 500 elements in fixed (i.e., non-mobile) INET deployments and hence have 501 permanent and unchanging INET addresses. AERO Clients are MNs that 502 connect via underlying interfaces with addresses that may change when 503 the Client moves to a new network connection point. 505 3.2. The AERO Service over OMNI Links 507 3.2.1. AERO/OMNI Reference Model 509 Figure 1 presents the basic OMNI link reference model: 511 +----------------+ 512 | AERO Bridge B1 | 513 | Nbr: S1, S2, P1| 514 |(X1->S1; X2->S2)| 515 | MSP M1 | 516 +-+---------+--+-+ 517 +--------------+ | Secured | | +--------------+ 518 |AERO Server S1| | tunnels | | |AERO Server S2| 519 | Nbr: C1, B1 +-----+ | +-----+ Nbr: C2, B1 | 520 | default->B1 | | | default->B1 | 521 | X1->C1 | | | X2->C2 | 522 +-------+------+ | +------+-------+ 523 | OMNI link | | 524 X===+===+===================+==)===============+===+===X 525 | | | | 526 +-----+--------+ +--------+--+-----+ +--------+-----+ 527 |AERO Client C1| | AERO Proxy P1 | |AERO Client C2| 528 | Nbr: S1 | |(Proxy Nbr Cache)| | Nbr: S2 | 529 | default->S1 | +--------+--------+ | default->S2 | 530 | MNP X1 | | | MNP X2 | 531 +------+-------+ .--------+------. +-----+--------+ 532 | (- Proxyed Clients -) | 533 .-. `---------------' .-. 534 ,-( _)-. ,-( _)-. 535 .-(_ IP )-. +-------+ +-------+ .-(_ IP )-. 536 (__ EUN )--|Host H1| |Host H2|--(__ EUN ) 537 `-(______)-' +-------+ +-------+ `-(______)-' 539 Figure 1: AERO/OMNI Reference Model 541 In this model: 543 o the OMNI link is an overlay network service configured over one or 544 more underlying INET partitions which may be managed by different 545 administrative authorities and have incompatible protocols and/or 546 addressing plans. 548 o AERO Bridge B1 aggregates Mobility Service Prefix (MSP) M1, 549 discovers Mobile Network Prefixes (MNPs) X* and advertises the MSP 550 via BGP peerings over secured tunnels to Servers (S1, S2). 551 Bridges connect the disjoint segments of a partitioned OMNI link. 553 o AERO Servers/Relays S1 and S2 configure secured tunnels with 554 Bridge B1 and also provide mobility, multilink and default router 555 services for their associated Clients C1 and C2. 557 o AERO Clients C1 and C2 associate with Servers S1 and S2, 558 respectively. They receive Mobile Network Prefix (MNP) 559 delegations X1 and X2, and also act as default routers for their 560 associated physical or internal virtual EUNs. Simple hosts H1 and 561 H2 attach to the EUNs served by Clients C1 and C2, respectively. 563 o AERO Proxy P1 configures a secured tunnel with Bridge B1 and 564 provides proxy services for AERO Clients in secured enclaves that 565 cannot associate directly with other OMNI link neighbors. 567 An OMNI link configured over a single INET appears as a single 568 unified link with a consistent underlying network addressing plan. 569 In that case, all nodes on the link can exchange packets via simple 570 INET encapsulation, since the underlying INET is connected. In 571 common practice, however, an OMNI link may be partitioned into 572 multiple "segments", where each segment is a distinct INET 573 potentially managed under a different administrative authority (e.g., 574 as for worldwide aviation service providers such as ARINC, SITA, 575 Inmarsat, etc.). Individual INETs may also themselves be partitioned 576 internally, in which case each internal partition is seen as a 577 separate segment. 579 The addressing plan of each segment is consistent internally but will 580 often bear no relation to the addressing plans of other segments. 581 Each segment is also likely to be separated from others by network 582 security devices (e.g., firewalls, proxies, packet filtering 583 gateways, etc.), and in many cases disjoint segments may not even 584 have any common physical link connections. Therefore, nodes can only 585 be assured of exchanging packets directly with correspondents in the 586 same segment, and not with those in other segments. The only means 587 for joining the segments therefore is through inter-domain peerings 588 between AERO Bridges. 590 The same as for traditional campus LANs, multiple OMNI link segments 591 can be joined into a single unified link via a virtual bridging 592 service using a mid-layer IPv6 encpasulation per [RFC2473] known as 593 the "SPAN header" that supports inter-segment forwarding (i.e., 594 bridging) without decrementing the network-layer TTL/Hop Limit. This 595 bridging of OMNI link segments is shown in Figure 2: 597 . . . . . . . . . . . . . . . . . . . . . . . 598 . . 599 . .-(::::::::) . 600 . .-(::::::::::::)-. +-+ . 601 . (:::: Segment A :::)--|B|---+ . 602 . `-(::::::::::::)-' +-+ | . 603 . `-(::::::)-' | . 604 . | . 605 . .-(::::::::) | . 606 . .-(::::::::::::)-. +-+ | . 607 . (:::: Segment B :::)--|B|---+ . 608 . `-(::::::::::::)-' +-+ | . 609 . `-(::::::)-' | . 610 . | . 611 . .-(::::::::) | . 612 . .-(::::::::::::)-. +-+ | . 613 . (:::: Segment C :::)--|B|---+ . 614 . `-(::::::::::::)-' +-+ | . 615 . `-(::::::)-' | . 616 . | . 617 . ..(etc).. x . 618 . . 619 . . 620 . <- OMNI link Bridged by encapsulation -> . 621 . . . . . . . . . . . . . .. . . . . . . . . 623 Figure 2: Bridging OMNI Link Segments 625 Bridges, Servers, Relays and Proxys connect via secured INET tunnels 626 over their respecitve segments in a spanning tree topology rooted at 627 the Bridges. The secured spanning tree supports strong 628 authentication for IPv6 ND control messages and may also be used to 629 convey the initial data packets in a flow. Route optimization can 630 then be employed to cause data packets to take more direct paths 631 between OMNI link neighbors without having to strictly follow the 632 spanning tree. 634 3.2.2. Link-Local Addresses (LLAs) and Unique Local Addresses (ULAs) 636 AERO nodes on OMNI links use the Link-Local Address (LLA) prefix 637 fe80::/10 [RFC4193] to assign LLAs used for network-layer addresses 638 in IPv6 ND and data messages. They also use the Unique Local Address 639 (ULA) prefix fc80::/10 [RFC4193] to form ULAs used for SPAN header 640 source and desitnation addresses. See 641 [I-D.templin-6man-omni-interface] for a full specification of the 642 LLAs and ULAs used by AERO nodes on OMNI links. 644 For routing system organization (see Section 3.2.3), ULAs are 645 organized in partition prefixes, e.g., fc80::1000/116. For each such 646 partition prefix, the Bridge(s) that connect that segment assign the 647 all-zero's address of the prefix as a Subnet Router Anycast address. 648 For example, the Subnet Router Anycast address for fc80::1000/116 is 649 simply fc80::1000. 651 3.2.3. AERO Routing System 653 The AERO routing system comprises a private instance of the Border 654 Gateway Protocol (BGP) [RFC4271] that is coordinated between Bridges 655 and Servers and does not interact with either the public Internet BGP 656 routing system or any underlying INET routing systems. 658 In a reference deployment, each Server is configured as an Autonomous 659 System Border Router (ASBR) for a stub Autonomous System (AS) using 660 an AS Number (ASN) that is unique within the BGP instance, and each 661 Server further uses eBGP to peer with one or more Bridges but does 662 not peer with other Servers. Each INET of a multi-segment OMNI link 663 must include one or more Bridges, which peer with the Servers and 664 Proxys within that INET. All Bridges within the same INET are 665 members of the same hub AS using a common ASN, and use iBGP to 666 maintain a consistent view of all active MNPs currently in service. 667 The Bridges of different INETs peer with one another using eBGP. 669 Bridges advertise the OMNI link's MSPs and any non-MNP routes to each 670 of their Servers. This means that any aggregated non-MNPs (including 671 "default") are advertised to all Servers. Each Bridge configures a 672 black-hole route for each of its MSPs. By black-holing the MSPs, the 673 Bridge will maintain forwarding table entries only for the MNPs that 674 are currently active, and packets destined to all other MNPs will 675 correctly incur Destination Unreachable messages due to the black- 676 hole route. In this way, Servers have only partial topology 677 knowledge (i.e., they know only about the MNPs of their directly 678 associated Clients) and they forward all other packets to Bridges 679 which have full topology knowledge. 681 Each OMNI link segment assigns a unique sub-prefix of fc80::/96 known 682 as the ULA partition prefix. For example, a first segment could 683 assign fc80::1000/116, a second could assign fc80::2000/116, a third 684 could assign fc80::3000/116, etc. The administrative authorities for 685 each segment must therefore coordinate to assure mutually-exclusive 686 partiton prefix assignments, but internal provisioning of each prefix 687 is an independent local consideration for each administrative 688 authority. 690 ULA partition prefixes are statitcally represented in Bridge 691 forwarding tables. Bridges join multiple segments into a unified 692 OMNI link over multiple diverse administrative domains. They support 693 a bridging function by first establishing forwarding table entries 694 for their partiion prefixes either via standard BGP routing or static 695 routes. For example, if three Bridges ('A', 'B' and 'C') from 696 different segments serviced fc80::1000/116, fc80::2000/116 and 697 fc80::3000/116 respectively, then the forwarding tables in each 698 Bridge are as follows: 700 A: fc80::1000/116->local, fc80::2000/116->B, fc80::3000/116->C 702 B: fc80::1000/116->A, fc80::2000/116->local, fc80::3000/116->C 704 C: fc80::1000/116->A, fc80::2000/116->B, fc80::3000/116->local 706 These forwarding table entries are permanent and never change, since 707 they correspond to fixed infrastructure elements in their respective 708 segments. 710 ULA Client prefixes are instead dynamically advertised in the AERO 711 routing system by Servers and Relays that provide service for their 712 corresponding MNPs. For example, if three Servers ('D', 'E' and 'F') 713 service the MNPs 2001:db8:1000:2000::/56, 2001:db8:3000:4000::/56 and 714 2001:db8:5000:6000::/56 then the routing system would include: 716 D: fc80:2001:db8:1000:2000::/72 718 E: fc80:2001:db8:3000:4000::/72 720 F: fc80:2001:db8:5000:6000::/72 722 A full discussion of the BGP-based routing system used by AERO is 723 found in [I-D.ietf-rtgwg-atn-bgp]. The system provides for 724 Distributed Mobility Management (DMM) per the distributed mobility 725 anchoring architecture [I-D.ietf-dmm-distributed-mobility-anchoring]. 727 3.2.4. AERO Encapsulation 729 With the Client and partition prefixes in place in each Bridge's 730 forwarding table, control and data packets sent between AERO nodes in 731 different segments can therefore be carried over the via mid-layer 732 encapsulation using the SPAN header. For example, when a source AERO 733 node forwards a packet with IPv6 address 2001:db8:1:2::1 to a target 734 AERO node with IPv6 address 2001:db8:1000:2000::1, it first 735 encapsulates the packet in a SPAN header with source address set to 736 fc80:2001:db8:1:2:: and destination address set to 737 fc80:2001:db8:1000:2000::. Next, it encapsulates the resulting SPAN 738 packet in an INET header with source address set to its own INET 739 address (e.g., 192.0.2.100) and destination set to the INET address 740 of a Bridge (e.g., 192.0.2.1). 742 SPAN encapsulation is based on Generic Packet Tunneling in IPv6 743 [RFC2473]; the encapsulation format in the above example is shown in 744 Figure 3: 746 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 747 | INET Header | 748 | src = 192.0.2.100 | 749 | dst = 192.0.2.1 | 750 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 751 | SPAN Header | 752 | src = fc80:2001:db8:1:2:: | 753 | dst=fc80:2001:db8:1000:2000:: | 754 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 755 | Inner IP Header | 756 | src = 2001:db8:1:2::1 | 757 | dst = 2001:db8:1000:2000::1 | 758 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 759 | | 760 ~ ~ 761 ~ Inner Packet Body ~ 762 ~ ~ 763 | | 764 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 766 Figure 3: SPAN Encapsulation 768 In this format, the inner IP header and packet body are the original 769 IP packet, the SPAN header is an IPv6 header prepared according to 770 [RFC2473], and the INET header is prepared as discussed in 771 Section 3.6. 773 This gives rise to a routing system that contains both Client prefix 774 routes that may change dynamically due to regional node mobility and 775 partion prefix routes that never change. The Bridges can therefore 776 provide link-layer bridging by sending packets over the spanning tree 777 instead of network-layer routing according to MNP routes. As a 778 result, opportunities for packet loss due to node mobility between 779 different segments are mitigated. 781 In normal operations, IPv6 ND messages are conveyed over secured 782 paths between OMNI link neighbors so that specific Proxys, Servers or 783 Relays can be addressed without being subject to mobility events. 784 Conversely, only the first few packets destined to Clients need to 785 traverse secured paths until route optimization can determine a more 786 direct path. 788 3.2.5. Segment Routing Topologies (SRTs) 790 The 16-bit sub-prefixes of fc80::/10 identify up to 64 distinct 791 Segment Routing Topologies (SRTs). Each SRT is a mutually-exclusive 792 OMNI link overlay instance using a mutually-exclusive set of ULAs, 793 and emulates a Virtual LAN (VLAN) service for the OMNI link. In some 794 cases (e.g., when redundant topologies are needed for fault tolerance 795 and reliability) it may be beneficial to deploy multiple SRTs that 796 act as independent overlay instances. A communication failure in one 797 instance therefore will not affect communications in other instances. 799 Each SRT is identified by a distinct value in bits 10-15 of fc80::10, 800 i.e., as fc80::/16, fc81::/16, fc82::/16, etc. This document asserts 801 that up to four SRTs provide a level of safety sufficient for 802 critical communications such as civil aviation. Each SRT is 803 designated with a color that identifies a different OMNI link 804 instance as follows: 806 o Red - corresponds to fc80::/16 808 o Green - corresponds to fc81::/16 810 o Blue-1 - corresponds to fc82::/16 812 o Blue-2 - corresponds to fc83::/16 814 o fc84::/16 through fcbf::/16 are available for additional SRTs. 816 Each OMNI interface assigns an anycast ULA corresponding to its SRT 817 prefix. For example, the anycast ULA for the Green SRT is simply 818 fc81::. The anycast ULA is used for OMNI interface determination in 819 Safety-Based Multilink (SBM) as discussed in 820 [I-D.templin-6man-omni-interface]. Each OMNI interface further 821 applies Performance-Based Multilink (PBM) internally. 823 3.2.6. Segment Routing To the OMNI Link 825 An original IPv6 source can direct a packet to an OMNI link Client by 826 including a Segment Routing Header (SRH) with the anycast ULA for the 827 selected SRT as either the IPv6 destination or as an intermediate hop 828 within the SRH. This allows the original source to determine the 829 specific topology a packet will traverse when there may be multiple 830 alternatives to choose from. Since the SRH contains no useful 831 information for the destination, the Client may elect to delete the 832 SRH before forwarding in order to reduce overhead. This form of 833 Segment Routing supports Safety-Based Multilink (SBM), and can be 834 exercised through general-purpose SRH types such as [RFC8754]. 836 3.2.7. Segment Routing Within the OMNI Link 838 AERO nodes that insert a SPAN header can use Segment Routing within 839 the OMNI link when necessary to influence the path of packets 840 destined to targets in remote segments without requiring all packets 841 to traverse strict spanning tree paths. 843 When a Client, Proxy or Server has a packet to send to a target 844 discovered through route optimization located in the same OMNI link 845 segment, it encapsulates the packet in a SPAN header with the ULA of 846 the target as the destination address if fragmentation is necessary; 847 otherwise, it may omit the SPAN header. The node then uses the 848 target's Link Layer Address information for INET encapsulation 849 without including an SRH. 851 When a Client, Proxy or Server has a packet to send to a route 852 optimization target located in a remote OMNI link segment, it 853 encapsulates the packet in a SPAN header with its own ULA as the 854 source address. The node then SHOULD include an SRH [RFC8754] while 855 forwarding the packet to a Bridge. 857 When the SRH is omitted, the node sets the destination address to the 858 ULA of the target Client/Proxy/Server and packet forwarding is via 859 spanning tree paths. When the SRH is included, the node first sets 860 the destination address to the ULA Subnet Router Anycast address of 861 the remote segment and sets the ULA of the target's Proxy/Server as 862 the Last Hop Segment (LHS) ID. The node also includes an AERO Route 863 Optimization specification in the SRH TLV section as shown in 864 Figure 4: 866 0 1 2 3 867 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 868 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 869 | Type=TBD | Length | Plen |V| FMT | MNP[1] | 870 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 871 | MNP[2] | MNP[3] | ... | MNP[i] | 872 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 873 ~ Link Layer Address ~ 874 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 876 Figure 4: AERO Route Optimization SRH TLV 878 In this format: 880 o Type is TBD to be assigned according to the Segment Routing Header 881 TLV registry [RFC8754]. 883 o Length is the length of the body of the TLV in bytes, excluding 884 the Type and Length fields. 886 o Plen encodes a value 'i' (between 0 and 15) that indicates the 887 number of octets of the IPv4/IPv6 MNP prefix that follows. 889 o V indicates the IP protocol version of the MNP that follows. V is 890 set to 0 for IPv4 or 1 for IPv6. 892 o FMT is a three bit code that determines the context and format of 893 the Link Layer Address exactly as specified in Figure 5. 895 o MNP{1], MNP[2], etc. up to MNP[i] encode the leading 'i' octets of 896 the MNP, beginning with the most significant octet followed by the 897 next most significant octet, etc. The number of MNP octets to be 898 included is determined by the number of trailing zero octets in 899 the prefix. For example, for the IPv6 MNP 2001:db8:1:2::/64, 'i' 900 is set to 8 and only the leftmost 8 octets of the MNP are 901 included. In the same way, for the IPv4 MNP 192.0.2/24, 'i' is 902 set to 3 and only the leftmost 3 octets of the MNP are included. 904 o Link Layer Address is encoded according to FMT exactly as 905 specified in Figure 5. 907 The node then forwards the packet via a local Bridge, which will 908 eventually direct it to a Bridge on the same segment as the target. 910 When a Bridge receives a packet with Segments Left=1 and with LHS ID 911 on a local segment, it checks to see if there is an AERO Route 912 Optimization TLV. If so, the Bridge creates a ULA destination 913 according to FMT. If FMT indicates that Link Layer Address 914 corresponds to a target Proxy/Server, the Bridge concatenates the SRT 915 ::/16 prefix with the LHS ID to form the ULA destination. Otherwise, 916 the Bridge concatenates the SRT ::/16 prefix with the leading Plen 917 octets of the MNP and sets the remaining rightmost bits to 0 to form 918 a Subnet Router Anycast ULA destination. The Bridge then writes the 919 ULA into the SPAN header destination address and encapsulates the 920 packet in an INET header with the target's Link Layer Address as the 921 destination then forwards the packet. Since the SRH contains no 922 useful information for the destination, the Bridge may elect to 923 delete the SRH before forwarding in order to reduce overhead. 925 In this way, the Bridge participates in route optimization to reduce 926 traffic load and suboptimal routing through strict spanning tree 927 paths. Note that if the Bridge does not recognize the AERO Route 928 Optimization TLV, it instead places the LHS ID concatentaed with the 929 SRT ::/16 prefix in the IPv6 destination address and forwards 930 according to the spanning tree. (Note that this is the same behavior 931 that would occur if the AERO Route Optimization TLV were not 932 present). 934 3.2.8. Segment Routing Header Compression 936 In the Segment Routing use cases discussed above, the segment routing 937 headers must be kept to a minimum size since source and target 938 Clients may be located behind low-end wireless links (e.g., 1Mbps or 939 less). The Compressed Routing Header (CRH) 940 [I-D.bonica-6man-comp-rtg-hdr] provides a compact form that reduces 941 the header size by omitting invariant information. The CRH Helper 942 option [I-D.bonica-6man-crh-helper-opt] can be used to encode the 943 AERO Route Optimization TLV, and the final hop Bridge that performs 944 route optimization may remove the CRH and its helper before 945 encapsulating and forwarding to the target. 947 The CRH and its companion helper option are therefore seen as 948 critical architectural elements that should be quickly progressed 949 through the standards process. Implementations SHOULD use the CRH 950 and its companion helper option instead of other Routing Header types 951 whenever possible to conserve bandwidth. 953 3.3. OMNI Interface Characteristics 955 OMNI interfaces are virtual interfaces configured over one or more 956 underlying interfaces classified as follows: 958 o INET interfaces connect to an INET either natively or through one 959 or several IPv4 Network Address Translators (NATs). Native INET 960 interfaces have global IP addresses that are reachable from any 961 INET correspondent. All Server, Relay and Bridge interfaces are 962 native interfaces, as are INET-facing interfaces of Proxys. NATed 963 INET interfaces connect to a private network behind one or more 964 NATs that provide INET access. Clients that are behind a NAT are 965 required to send periodic keepalive messages to keep NAT state 966 alive when there are no data packets flowing. 968 o Proxyed interfaces connect to an ANET that is separated from the 969 open INET by an AERO Proxy. Proxys can actively issue control 970 messages over the INET on behalf of the Client to reduce ANET 971 congestion. Clients connected to Proxyed interfaces receive RAs 972 with the P flag set to 1. 974 o VPNed interfaces use security encapsulation over the INET to a 975 Virtual Private Network (VPN) server that also acts as an AERO 976 Server. Other than the link-layer encapsulation format, VPNed 977 interfaces behave the same as Direct interfaces. 979 o Direct interfaces connect a Client directly to a Server without 980 crossing any ANET/INET paths. An example is a line-of-sight link 981 between a remote pilot and an unmanned aircraft. The same Client 982 considerations apply as for VPNed interfaces. 984 OMNI interfaces use SPAN encapsulation as necessary as discussed in 985 Section 3.2.4. OMNI interfaces use link-layer encapsulation (see: 986 Section 3.6) to exchange packets with OMNI link neighbors over INET 987 or VPNed interfaces. OMNI interfaces do not use link-layer 988 encapsulation over Proxyed and Direct underlying interfaces. 990 OMNI interfaces maintain a neighbor cache for tracking per-neighbor 991 state the same as for any interface. OMNI interfaces use ND messages 992 including Router Solicitation (RS), Router Advertisement (RA), 993 Neighbor Solicitation (NS) and Neighbor Advertisement (NA) for 994 neighbor cache management. 996 OMNI interfaces send ND messages with an OMNI option formatted as 997 specified in [I-D.templin-6man-omni-interface]. The OMNI option 998 includes prefix registration information and "ifIndex-tuples" 999 containing link information parameters for the OMNI interface's 1000 underlying interfaces. 1002 SPAN-encapsulated OMNI interface ND messages also include a Source/ 1003 Target Link-Layer Address Option (S/TLLAO) formatted as shown in 1004 Figure 5: 1006 0 1 2 3 1007 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 1008 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1009 | Type | Length | ifIndex[1] | SRT | FMT | 1010 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1011 ~ Last Hop Segment (LHS) ID [1] ~ 1012 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1013 ~ Link Layer Address [1] ~ 1014 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1015 ~ | ifIndex[2] | SRT | FMT | 1016 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1017 ~ Last Hop Segment (LHS) ID [2] ~ 1018 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1019 ~ Link Layer Address [2] ~ 1020 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1021 ~ | .... ~ 1022 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ 1023 ~ ... ~ 1024 ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1025 ~ | ifIndex[N] | SRT | FMT | 1026 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1027 ~ Last Hop Segment (LHS) ID [N] ~ 1028 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1029 ~ Link Layer Address [N] ~ 1030 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1031 ~ | Zero Padding (if necessary) ... 1032 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1034 Figure 5: OMNI Source/Target Link-Layer Address Option (S/TLLAO) 1035 Format 1037 In this format, Type and Length are set the same as specified for S/ 1038 TLLAOs in [RFC4861], with trailing zero padding octets added as 1039 necessary to produce an integral number of 8 octet blocks. The S/ 1040 TLLAO includes N ifIndex-tuples corresponding to a proper subset of 1041 the ifIndex-tuples that appear in the OMNI option. Each ifIndex- 1042 tuple includes the following information: 1044 o ifIndex[i] - the same value as in the corresponding ifIndex-tuple 1045 included in the OMNI option. 1047 o SRT[i] - a 5-bit value (between 0 and 31) that when added to 96 1048 determines the SRT prefix length to apply to the Last Hop Segment 1049 (LHS) ULA. For example, the SRT prefix length for the value 16 is 1050 112. 1052 o FMT[i] - a 3-bit "Format" code, with the most significant bit set 1053 to 0 if the Link-Layer Addresss is the address of a Proxy/Server 1054 or set to 1 if the Link Layer Address is the INET encapsulation 1055 address for the Source/Target itself. The least significant two 1056 bits determine the format of the Link Layer Address [i] field as 1057 follows: 1059 * 00 - Link Layer Address [i] encodes a 2 byte Port Number 1060 followed by a 4 byte IPv4 address for a node behind a NAT. 1062 * 01 - Link Layer Address [i] encodes a 2 byte Port Number 1063 followed by a 4 byte IPv4 address for a node on the open INET. 1065 * 10 - Link Layer Address [i] encodes a 2 byte Port Number 1066 followed by a 16 byte IPv6 address for a node behind a NAT. 1068 * 11 - Link Layer Address [i] encodes a 2 byte Port Number 1069 followed by a 16 byte IPv6 address for a node on the open INET. 1071 o Last Hop Segment (LHS) ID [i] - Includes the least significant 32 1072 ULA bits of the last hop Proxy/Server prior to final encapsulation 1073 according to Link Layer Address [i]. 1075 o Link Layer Address [i] - Included according to FMT[i], and 1076 identifies the link-layer address (i.e., the encapsulation 1077 address) of the source/target. The Port Number and IP address are 1078 recorded in ones-compliment "obfuscated" form per [RFC4380]. 1080 If an S/TLLAO is included, any ifIndex-tuples correspond to a proper 1081 subset of the OMNI option ifIndex-tuples. Any S/TLLAO ifIndex-tuple 1082 with an ifIndex value that does not appear in an OMNI option ifindex- 1083 tuple is ignored. If the same ifIndex value appears in multiple 1084 ifIndex-tuples, the first tuple is processed and the remaining tuples 1085 are ignored. Any S/TLLAO ifIndex-tuples can therefore be viewed as 1086 extensions of their corresponding OMNI option ifIndex-tuples, i.e., 1087 the OMNI option and S/TLLAO are companions that are interpreted in 1088 conjunction with each other. 1090 A Client's OMNI interface may be configured over multiple underlying 1091 interface connections. For example, common mobile handheld devices 1092 have both wireless local area network ("WLAN") and cellular wireless 1093 links. These links are often used "one at a time" with low-cost WLAN 1094 preferred and highly-available cellular wireless as a standby, but a 1095 simultaneous-use capability could provide benefits. In a more 1096 complex example, aircraft frequently have many wireless data link 1097 types (e.g. satellite-based, cellular, terrestrial, air-to-air 1098 directional, etc.) with diverse performance and cost properties. 1100 If a Client's multiple underlying interfaces are used "one at a time" 1101 (i.e., all other interfaces are in standby mode while one interface 1102 is active), then ND message OMNI options include only a single 1103 ifIndex-tuple set to constant values. In that case, the Client would 1104 appear to have a single interface but with a dynamically changing 1105 link-layer address. 1107 If the Client has multiple active underlying interfaces, then from 1108 the perspective of ND it would appear to have multiple link-layer 1109 addresses. In that case, ND message OMNI options MAY include 1110 multiple ifIndex-tuples - each with values that correspond to a 1111 specific interface. Every ND message need not include all OMNI and/ 1112 or S/TLLAO ifIndex-tuples; for any ifIndex-tuple not included, the 1113 neighbor considers the status as unchanged. 1115 Bridge, Server and Proxy OMNI interfaces may be configured over one 1116 or more secured tunnel interfaces. The OMNI interface configures 1117 both an LLA and its corresponding ULA, while the underlying secured 1118 tunnel interfaces are either unnumbered or configure the same ULA. 1119 The OMNI interface encapsulates each IP packet in a SPAN header and 1120 presents the packet to the underlying secured tunnel interface. For 1121 Bridges that do not configure an OMNI interface, the secured tunnel 1122 interfaces themselves are exposed to the IP layer with each interface 1123 configuring the Bridge's ULA. Routing protocols such as BGP 1124 therefore run directly over the Bridge's secured tunnel interfaces. 1125 For nodes that configure an OMNI interface, routing protocols such as 1126 BGP run over the OMNI interface but do not employ SPAN encapsulation. 1127 Instead, the OMNI interface presents the routing protocol messages 1128 directly to the underlying secured tunnels without applying 1129 encapsulation and while using the ULA as the source address. This 1130 distinction must be honored consistently according to each node's 1131 configuration so that the IP forwarding table will associate 1132 discovered IP routes with the correct interface. 1134 3.4. OMNI Interface Initialization 1136 AERO Servers, Proxys and Clients configure OMNI interfaces as their 1137 point of attachment to the OMNI link. AERO nodes assign the MSPs for 1138 the link to their OMNI interfaces (i.e., as a "route-to-interface") 1139 to ensure that packets with destination addresses covered by an MNP 1140 not explicitly assigned to a non-OMNI interface are directed to the 1141 OMNI interface. 1143 OMNI interface initialization procedures for Servers, Proxys, Clients 1144 and Bridges are discussed in the following sections. 1146 3.4.1. AERO Server/Relay Behavior 1148 When a Server enables an OMNI interface, it assigns an LLA/ULA 1149 appropriate for the given OMNI link segment. The Server also 1150 configures secured tunnels with one or more neighboring Bridges and 1151 engages in a BGP routing protocol session with each Bridge. 1153 The OMNI interface provides a single interface abstraction to the IP 1154 layer, but internally comprises multiple secured tunnels as well as 1155 an NBMA nexus for sending encapsulated data packets to OMNI interface 1156 neighbors. The Server further configures a service to facilitate ND/ 1157 PD exchanges with AERO Clients and manages per-Client neighbor cache 1158 entries and IP forwarding table entries based on control message 1159 exchanges. 1161 Relays are simply Servers that run a dynamic routing protocol to 1162 redistribute routes between the OMNI interface and INET/EUN 1163 interfaces (see: Section 3.2.3). The Relay provisions MNPs to 1164 networks on the INET/EUN interfaces (i.e., the same as a Client would 1165 do) and advertises the MSP(s) for the OMNI link over the INET/EUN 1166 interfaces. The Relay further provides an attachment point of the 1167 OMNI link to a non-MNP-based global topology. 1169 3.4.2. AERO Proxy Behavior 1171 When a Proxy enables an OMNI interface, it assigns an LLA/ULA and 1172 configures permanent neighbor cache entries the same as for Servers. 1173 The Proxy also configures secured tunnels with one or more 1174 neighboring Bridges and maintains per-Client neighbor cache entries 1175 based on control message exchanges. 1177 3.4.3. AERO Client Behavior 1179 When a Client enables an OMNI interface, it sends RS messages with 1180 ND/PD parameters over its underlying interfaces to a Server in the 1181 MAP list, which returns an RA message with corresponding parameters. 1182 (The RS/RA messages may pass through a Proxy in the case of a 1183 Client's Proxyed interface, or through one or more NATs in the case 1184 of a Client's INET interface.) 1186 3.4.4. AERO Bridge Behavior 1188 AERO Bridges configure an OMNI interface and assign the ULA Subnet 1189 Router Anycast address for each OMNI link segment they connect to. 1190 Bridges configure secured tunnels with Servers, Proxys and other 1191 Bridges; they also configure LLAs/ULAs and permanent neighbor cache 1192 entries the same as Servers. Bridges engage in a BGP routing 1193 protocol session with a subset of the Servers and other Bridges on 1194 the spanning tree (see: Section 3.2.3). 1196 3.5. OMNI Interface Neighbor Cache Maintenance 1198 Each OMNI interface maintains a conceptual neighbor cache that 1199 includes an entry for each neighbor it communicates with on the OMNI 1200 link per [RFC4861]. OMNI interface neighbor cache entries are said 1201 to be one of "permanent", "symmetric", "asymmetric" or "proxy". 1203 Permanent neighbor cache entries are created through explicit 1204 administrative action; they have no timeout values and remain in 1205 place until explicitly deleted. AERO Bridges maintain permanent 1206 neighbor cache entries for their associated Proxys and Servers (and 1207 vice-versa). Each entry maintains the mapping between the neighbor's 1208 network-layer LLA and corresponding INET address. 1210 Symmetric neighbor cache entries are created and maintained through 1211 RS/RA exchanges as specified in Section 3.12, and remain in place for 1212 durations bounded by ND/PD lifetimes. AERO Servers maintain 1213 symmetric neighbor cache entries for each of their associated 1214 Clients, and AERO Clients maintain symmetric neighbor cache entries 1215 for each of their associated Servers. The list of all Servers on the 1216 OMNI link is maintained in the link's MAP list. 1218 Asymmetric neighbor cache entries are created or updated based on 1219 route optimization messaging as specified in Section 3.14, and are 1220 garbage-collected when keepalive timers expire. AERO ROSs maintain 1221 asymmetric neighbor cache entries for active targets with lifetimes 1222 based on ND messaging constants. Asymmetric neighbor cache entries 1223 are unidirectional since only the ROS (and not the ROR) creates an 1224 entry. 1226 Proxy neighbor cache entries are created and maintained by AERO 1227 Proxys when they process Client/Server ND/PD exchanges, and remain in 1228 place for durations bounded by ND/PD lifetimes. AERO Proxys maintain 1229 proxy neighbor cache entries for each of their associated Clients. 1230 Proxy neighbor cache entries track the Client state and the address 1231 of the Client's associated Server(s). 1233 To the list of neighbor cache entry states in Section 7.3.2 of 1234 [RFC4861], Proxy and Server OMNI interfaces add an additional state 1235 DEPARTED that applies to symmetric and proxy neighbor cache entries 1236 for Clients that have recently departed. The interface sets a 1237 "DepartTime" variable for the neighbor cache entry to "DEPART_TIME" 1238 seconds. DepartTime is decremented unless a new ND message causes 1239 the state to return to REACHABLE. While a neighbor cache entry is in 1240 the DEPARTED state, packets destined to the target Client are 1241 forwarded to the Client's new location instead of being dropped. 1242 When DepartTime decrements to 0, the neighbor cache entry is deleted. 1243 It is RECOMMENDED that DEPART_TIME be set to the default constant 1244 value REACHABLE_TIME plus 10 seconds (40 seconds by default) to allow 1245 a window for packets in flight to be delivered while stale route 1246 optimization state may be present. 1248 When an ROR receives an authentic NS message used for route 1249 optimization, it searches for a symmetric neighbor cache entry for 1250 the target Client. The ROR then returns a solicited NA message 1251 without creating a neighbor cache entry for the ROS, but creates or 1252 updates a target Client "Report List" entry for the ROS and sets a 1253 "ReportTime" variable for the entry to REPORT_TIME seconds. The ROR 1254 resets ReportTime when it receives a new authentic NS message, and 1255 otherwise decrements ReportTime while no authentic NS messages have 1256 been received. It is RECOMMENDED that REPORT_TIME be set to the 1257 default constant value REACHABLE_TIME plus 10 seconds (40 seconds by 1258 default) to allow a window for route optimization to converge before 1259 ReportTime decrements below REACHABLE_TIME. 1261 When the ROS receives a solicited NA message response to its NS 1262 message used for route optimization, it creates or updates an 1263 asymmetric neighbor cache entry for the target network-layer and 1264 link-layer addresses. The ROS then (re)sets ReachableTime for the 1265 neighbor cache entry to REACHABLE_TIME seconds and uses this value to 1266 determine whether packets can be forwarded directly to the target, 1267 i.e., instead of via a default route. The ROS otherwise decrements 1268 ReachableTime while no further solicited NA messages arrive. It is 1269 RECOMMENDED that REACHABLE_TIME be set to the default constant value 1270 30 seconds as specified in [RFC4861]. 1272 AERO nodes also use the value MAX_UNICAST_SOLICIT to limit the number 1273 of NS keepalives sent when a correspondent may have gone unreachable, 1274 the value MAX_RTR_SOLICITATIONS to limit the number of RS messages 1275 sent without receiving an RA and the value MAX_NEIGHBOR_ADVERTISEMENT 1276 to limit the number of unsolicited NAs that can be sent based on a 1277 single event. It is RECOMMENDED that MAX_UNICAST_SOLICIT, 1278 MAX_RTR_SOLICITATIONS and MAX_NEIGHBOR_ADVERTISEMENT be set to 3 the 1279 same as specified in [RFC4861]. 1281 Different values for DEPART_TIME, REPORT_TIME, REACHABLE_TIME, 1282 MAX_UNICAST_SOLICIT, MAX_RTR_SOLCITATIONS and 1283 MAX_NEIGHBOR_ADVERTISEMENT MAY be administratively set; however, if 1284 different values are chosen, all nodes on the link MUST consistently 1285 configure the same values. Most importantly, DEPART_TIME and 1286 REPORT_TIME SHOULD be set to a value that is sufficiently longer than 1287 REACHABLE_TIME to avoid packet loss due to stale route optimization 1288 state. 1290 3.6. OMNI Interface Encapsulation and Re-encapsulation 1292 OMNI interfaces insert a mid-layer IPv6 header known as the SPAN 1293 header when necessary as discussed in the following sections. After 1294 either inserting or omitting the SPAN header, the OMNI interface also 1295 inserts or omits an outer encapsulation header as discussed below. 1297 OMNI interfaces avoid outer encapsulation over Direct underlying 1298 interfaces and Proxyed underlying interfaces for which the first-hop 1299 access router is AERO-aware. Other OMNI interfaces encapsulate 1300 packets according to whether they are entering the OMNI interface 1301 from the network layer or if they are being re-admitted into the same 1302 OMNI link they arrived on. This latter form of encapsulation is 1303 known as "re-encapsulation". 1305 For packets entering the OMNI interface from the network layer, the 1306 OMNI interface copies the "TTL/Hop Limit", "Type of Service/Traffic 1307 Class" [RFC2983], "Flow Label"[RFC6438] (for IPv6) and "Congestion 1308 Experienced" [RFC3168] values in the inner packet's IP header into 1309 the corresponding fields in the SPAN and outer encapsulation 1310 header(s). 1312 For packets undergoing re-encapsulation, the OMNI interface instead 1313 copies these values from the original encapsulation header into the 1314 new encapsulation header, i.e., the values are transferred between 1315 encapsulation headers and *not* copied from the encapsulated packet's 1316 network-layer header. (Note especially that by copying the TTL/Hop 1317 Limit between encapsulation headers the value will eventually 1318 decrement to 0 if there is a (temporary) routing loop.) 1320 OMNI interfaces configured over INET underlying interfaces 1321 encapsulate packets in INET headers according to the next hop 1322 determined in the forwarding algorithm in Section 3.10. If the next 1323 hop is reached via a secured tunnel, the OMNI interface uses an 1324 encapsulation format specific to the secured tunnel type (see: 1325 Section 6). If the next hop is reached via an unsecured INET 1326 interface, the OMNI interface instead uses UDP/IP encapsulation per 1327 [RFC4380] and as extended in [RFC6081]. 1329 When UDP/IP encapsulation is used, the OMNI interface next sets the 1330 UDP source port to a constant value that it will use in each 1331 successive packet it sends, and sets the UDP length field to the 1332 length of the encapsulated packet plus 8 bytes for the UDP header 1333 itself plus the length of any included extension headers or trailers. 1334 The encapsulated packet may be either IPv6 or IPv4, as distinguished 1335 by the version number found in the first four bits. 1337 For UDP/IP-encapsulated packets sent to a Server, Relay or Bridge, 1338 the OMNI interface sets the UDP destination port to 8060, i.e., the 1339 IANA-registered port number for AERO. For packets sent to a Client, 1340 the OMNI interface sets the UDP destination port to the port value 1341 stored in the neighbor cache entry for this Client. The OMNI 1342 interface finally includes/omits the UDP checksum according to 1343 [RFC6935][RFC6936]. 1345 3.7. OMNI Interface Decapsulation 1347 OMNI interfaces decapsulate packets destined either to the AERO node 1348 itself or to a destination reached via an interface other than the 1349 OMNI interface the packet was received on. When the encapsulated 1350 packet arrives in multiple SPAN fragments, the OMNI interface 1351 reassembles as discussed in Section 3.9. Further decapsulation steps 1352 are performed according to the appropriate encapsulation format 1353 specification. 1355 3.8. OMNI Interface Data Origin Authentication 1357 AERO nodes employ simple data origin authentication procedures. In 1358 particular: 1360 o AERO Bridges, Servers and Proxys accept encapsulated data packets 1361 and control messages received from the (secured) spanning tree. 1363 o AERO Proxys and Clients accept packets that originate from within 1364 the same secured ANET. 1366 o AERO Clients and Relays accept packets from downstream network 1367 correspondents based on ingress filtering. 1369 o AERO Clients, Relays and Servers verify the outer UDP/IP 1370 encapsulation addresses according to [RFC4380]. 1372 AERO nodes silently drop any packets that do not satisfy the above 1373 data origin authentication procedures. Further security 1374 considerations are discussed in Section 6. 1376 3.9. OMNI Interface MTU and Fragmentation 1378 The OMNI interface observes the link nature of tunnels, including the 1379 Maximum Transmission Unit (MTU) and the role of fragmentation and 1380 reassembly[I-D.ietf-intarea-tunnels]. OMNI interface MTU and 1381 fragmentation/reassembly procedures are specified in 1382 [I-D.templin-6man-omni-interface]. 1384 3.10. OMNI Interface Forwarding Algorithm 1386 IP packets enter a node's OMNI interface either from the network 1387 layer (i.e., from a local application or the IP forwarding system) or 1388 from the link layer (i.e., from an OMNI interface neighbor). All 1389 packets entering a node's OMNI interface first undergo data origin 1390 authentication as discussed in Section 3.8. Packets that satisfy 1391 data origin authentication are processed further, while all others 1392 are dropped silently. OMNI interfaces wrap accepted packets in a 1393 SPAN header and SRH if necessary as discussed above. 1395 Packets that enter the OMNI interface from the network layer are 1396 forwarded to an OMNI interface neighbor. Packets that enter the OMNI 1397 interface from the link layer are either re-admitted into the OMNI 1398 link or forwarded to the network layer where they are subject to 1399 either local delivery or IP forwarding. In all cases, the OMNI 1400 interface itself MUST NOT decrement the network layer TTL/Hop-count 1401 since its forwarding actions occur below the network layer. 1403 OMNI interfaces may have multiple underlying interfaces and/or 1404 neighbor cache entries for neighbors with multiple ifIndex-tuple 1405 registrations (see Section 3.3). The OMNI interface uses traffic 1406 classifiers (e.g., DSCP value, port number, etc.) to select an 1407 outgoing underlying interface for each packet based on the node's own 1408 QoS preferences, and also to select a destination link-layer address 1409 based on the neighbor's underlying interface with the highest 1410 preference. AERO implementations SHOULD allow for QoS preference 1411 values to be modified at runtime through network management. 1413 If multiple outgoing interfaces and/or neighbor interfaces have a 1414 preference of "high", the AERO node replicates the packet and sends 1415 one copy via each of the (outgoing / neighbor) interface pairs; 1416 otherwise, the node sends a single copy of the packet via an 1417 interface with the highest preference. AERO nodes keep track of 1418 which underlying interfaces are currently "reachable" or 1419 "unreachable", and only use "reachable" interfaces for forwarding 1420 purposes. 1422 The following sections discuss the OMNI interface forwarding 1423 algorithms for Clients, Proxys, Servers and Bridges. In the 1424 following discussion, a packet's destination address is said to 1425 "match" if it is the same as a cached address, or if it is covered by 1426 a cached prefix (which may be encoded in an LLA). 1428 3.10.1. Client Forwarding Algorithm 1430 When an IP packet enters a Client's OMNI interface from the network 1431 layer the Client searches for an asymmetric neighbor cache entry that 1432 matches the destination. If there is a match, the Client uses one or 1433 more "reachable" neighbor interfaces in the entry for packet 1434 forwarding. If there is no asymmetric neighbor cache entry, the 1435 Client instead forwards the packet toward a Server (the packet is 1436 intercepted by a Proxy if there is a Proxy on the path). The Client 1437 encapsulates the packet in a SPAN header and SRH if necessary and 1438 fragments according to MTU requirements (see: Section 3.9). 1440 When an IP packet enters a Client's OMNI interface from the link- 1441 layer, if the destination matches one of the Client's MNPs or link- 1442 local addresses the Client reassembles and decapsulates as necessary 1443 and delivers the inner packet to the network layer. Otherwise, the 1444 Client drops the packet and MAY return a network-layer ICMP 1445 Destination Unreachable message subject to rate limiting (see: 1446 Section 3.11). 1448 3.10.2. Proxy Forwarding Algorithm 1450 For control messages originating from or destined to a Client, the 1451 Proxy intercepts the message and updates its proxy neighbor cache 1452 entry for the Client. The Proxy then forwards a (proxyed) copy of 1453 the control message. (For example, the Proxy forwards a proxied 1454 version of a Client's NS/RS message to the target neighbor, and 1455 forwards a proxied version of the NA/RA reply to the Client.) 1457 When the Proxy receives a data packet from a Client within the ANET, 1458 the Proxy reassembles and re-fragments if necessary then searches for 1459 an asymmetric neighbor cache entry that matches the destination and 1460 forwards as follows: 1462 o if the destination matches an asymmetric neighbor cache entry, the 1463 Proxy uses one or more "reachable" neighbor interfaces in the 1464 entry for packet forwarding using SPAN encapsulation and including 1465 a SRH if necessary according to the cached TLLAO information. If 1466 the neighbor interface is in the same SPAN segment, the Proxy 1467 forwards the packet directly to the neighbor; otherwise, it 1468 forwards the packet to a Bridge. 1470 o else, the Proxy uses SPAN encapsulation and forwards the packet to 1471 a Bridge while using the ULA corresponding to the packet's 1472 destination as the SPAN destination address. 1474 When the Proxy receives an encapsulated data packet from an INET 1475 neighbor or from a secured tunnel from a Bridge, it accepts the 1476 packet only if data origin authentication succeeds and if there is a 1477 proxy neighbor cache entry that matches the inner destination. Next, 1478 the Proxy reassembles the packet (if necessary) and continues 1479 processing. 1481 Next if reassembly is complete and the neighbor cache state is 1482 REACHABLE, the Proxy returns a PTB if necessary (see: Section 3.9) 1483 then either drops or forwards the packet to the Client while 1484 performing SPAN encapsulation and re-fragmentation to the ANET MTU 1485 size if necessary. If the neighbor cache entry state is DEPARTED, 1486 the Proxy instead changes the SPAN destination address to the address 1487 of the new Server and forwards it to a Bridge while performing re- 1488 fragmentation to 1280 bytes if necessary. 1490 3.10.3. Server/Relay Forwarding Algorithm 1492 For control messages destined to a target Client's LLA that are 1493 received from a secured tunnel, the Server intercepts the message and 1494 sends an appropriate response on behalf of the Client. (For example, 1495 the Server sends an NA message reply in response to an NS message 1496 directed to one of its associated Clients.) If the Client's neighbor 1497 cache entry is in the DEPARTED state, however, the Server instead 1498 forwards the packet to the Client's new Server as discussed in 1499 Section 3.16. 1501 When the Server receives an encapsulated data packet from an INET 1502 neighbor or from a secured tunnel, it accepts the packet only if data 1503 origin authentication succeeds. If the SPAN destination address is 1504 its own address, the Server continues processing as follows: 1506 o if the destination matches a symmetric neighbor cache entry in the 1507 REACHABLE state the Server prepares the packet for forwarding to 1508 the destination Client. The Server first reassembles (if 1509 necessary) and forwards the packet (while re-fragmenting if 1510 necessary) as specified in Section 3.9. 1512 o else, if the destination matches a symmetric neighbor cache entry 1513 in the DEPARETED state the Server re-encapsulates the packet and 1514 forwards it using the ULA of the Client's new Server as the 1515 destination. 1517 o else, if the destination matches an asymmetric neighbor cache 1518 entry, the Server uses one or more "reachable" neighbor interfaces 1519 in the entry for packet forwarding via the local INET if the 1520 neighbor is in the same OMNI link segment or using SPAN 1521 encapsulation and Segment Routing if necessary with the final 1522 destination set to the neighbor's ULA otherwise. 1524 o else, if the destination is an LLA that is not assigned on the 1525 OMNI interface the Server drops the packet. 1527 o else, the Server (acting as a Relay) reassembles if necessary, 1528 decapsulates the packet and releases it to the network layer for 1529 local delivery or IP forwarding. Based on the information in the 1530 forwarding table, the network layer may return the packet to the 1531 same OMNI interface in which case further processing occurs as 1532 below. (Note that this arrangement accommodates common 1533 implementations in which the IP forwarding table is not accessible 1534 from within the OMNI interface. If the OMNI interface can 1535 directly access the IP forwarding table (such as for in-kernel 1536 implementations) the forwarding table lookup can instead be 1537 performed internally from within the OMNI interface itself.) 1539 When the Server's OMNI interface receives a data packet from the 1540 network layer or from a VPNed or Direct Client, it performs SPAN 1541 encapsulation and fragmentation if necessary, then processes the 1542 packet according to the network-layer destination address as follows: 1544 o if the destination matches a symmetric or asymmetric neighbor 1545 cache entry the Server processes the packet as above. 1547 o else, the Server encapsulates the packet and forwards it to a 1548 Bridge using its own ULA as the source and the ULA corresponding 1549 to the destination as the destination. 1551 3.10.4. Bridge Forwarding Algorithm 1553 Bridges forward SPAN-encapsulated packets over secured tunnels the 1554 same as any IP router. When the Bridge receives a SPAN-encapsulated 1555 packet via a secured tunnel, it removes the outer INET header and 1556 searches for a forwarding table entry that matches the SPAN 1557 destination address. The Bridge then processes the packet as 1558 follows: 1560 o if the destination matches its ULA Subnet Router Anycast address, 1561 the Bridge checks for a SRH. If there is a SRH with Segments 1562 Left=1, with the ULA of a Proxy/Server on the local segment as the 1563 LHS ID, and with an AERO Route Optimization TLV, the Bridge 1564 examines the FMT to determine if the target is behind a NAT. If 1565 no NAT is indicated, the Bridge copies the MNP Subnet Router 1566 Anycast address if an MNP is included (otherwise copies the Proxy/ 1567 Server ULA) into the destination address then forwards the packet 1568 directly to the Link Layer Address using link-layer (UDP/IP) 1569 encapsulation. If a NAT is indicated, the Bridge MAY perform NAT 1570 traversal procedures by sending bubbles per [RFC4380]. The Bridge 1571 then either applies AERO route optimization if NAT traversal 1572 procedures have been successfully applied, or forwards the packet 1573 directly to the Server. 1575 o if the destination matches one of the Bridge's own addresses, the 1576 Bridge submits the packet for local delivery. 1578 o else, if the destination matches a forwarding table entry the 1579 Bridge forwards the packet via a secured tunnel to the next hop. 1580 If the destination matches an MSP without matching an MNP, 1581 however, the Bridge instead drops the packet and returns an ICMP 1582 Destination Unreachable message subject to rate limiting (see: 1583 Section 3.11). 1585 o else, the Bridge drops the packet and returns an ICMP Destination 1586 Unreachable as above. 1588 As for any IP router, the Bridge decrements the TTL/Hop Limit when it 1589 forwards the packet. Therefore, only the Hop Limit in the SPAN 1590 header is decremented, and not the TTL/Hop Limit in the inner packet 1591 header. 1593 3.11. OMNI Interface Error Handling 1595 When an AERO node admits a packet into the OMNI interface, it may 1596 receive link-layer or network-layer error indications. 1598 A link-layer error indication is an ICMP error message generated by a 1599 router in the INET on the path to the neighbor or by the neighbor 1600 itself. The message includes an IP header with the address of the 1601 node that generated the error as the source address and with the 1602 link-layer address of the AERO node as the destination address. 1604 The IP header is followed by an ICMP header that includes an error 1605 Type, Code and Checksum. Valid type values include "Destination 1606 Unreachable", "Time Exceeded" and "Parameter Problem" 1607 [RFC0792][RFC4443]. (OMNI interfaces ignore all link-layer IPv4 1608 "Fragmentation Needed" and IPv6 "Packet Too Big" messages since they 1609 only emit packets that are guaranteed to be no larger than the IP 1610 minimum link MTU as discussed in Section 3.9.) 1612 The ICMP header is followed by the leading portion of the packet that 1613 generated the error, also known as the "packet-in-error". For 1614 ICMPv6, [RFC4443] specifies that the packet-in-error includes: "As 1615 much of invoking packet as possible without the ICMPv6 packet 1616 exceeding the minimum IPv6 MTU" (i.e., no more than 1280 bytes). For 1617 ICMPv4, [RFC0792] specifies that the packet-in-error includes: 1618 "Internet Header + 64 bits of Original Data Datagram", however 1619 [RFC1812] Section 4.3.2.3 updates this specification by stating: "the 1620 ICMP datagram SHOULD contain as much of the original datagram as 1621 possible without the length of the ICMP datagram exceeding 576 1622 bytes". 1624 The link-layer error message format is shown in Figure 6 (where, "L2" 1625 and "L3" refer to link-layer and network-layer, respectively): 1627 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1628 ~ ~ 1629 | L2 IP Header of | 1630 | error message | 1631 ~ ~ 1632 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1633 | L2 ICMP Header | 1634 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 1635 ~ ~ P 1636 | IP and other encapsulation | a 1637 | headers of original L3 packet | c 1638 ~ ~ k 1639 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ e 1640 ~ ~ t 1641 | IP header of | 1642 | original L3 packet | i 1643 ~ ~ n 1644 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1645 ~ ~ e 1646 | Upper layer headers and | r 1647 | leading portion of body | r 1648 | of the original L3 packet | o 1649 ~ ~ r 1650 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 1652 Figure 6: OMNI Interface Link-Layer Error Message Format 1654 The AERO node rules for processing these link-layer error messages 1655 are as follows: 1657 o When an AERO node receives a link-layer Parameter Problem message, 1658 it processes the message the same as described as for ordinary 1659 ICMP errors in the normative references [RFC0792][RFC4443]. 1661 o When an AERO node receives persistent link-layer Time Exceeded 1662 messages, the IP ID field may be wrapping before earlier fragments 1663 awaiting reassembly have been processed. In that case, the node 1664 should begin including integrity checks and/or institute rate 1665 limits for subsequent packets. 1667 o When an AERO node receives persistent link-layer Destination 1668 Unreachable messages in response to encapsulated packets that it 1669 sends to one of its asymmetric neighbor correspondents, the node 1670 should process the message as an indication that a path may be 1671 failing, and optionally initiate NUD over that path. If it 1672 receives Destination Unreachable messages over multiple paths, the 1673 node should allow future packets destined to the correspondent to 1674 flow through a default route and re-initiate route optimization. 1676 o When an AERO Client receives persistent link-layer Destination 1677 Unreachable messages in response to encapsulated packets that it 1678 sends to one of its symmetric neighbor Servers, the Client should 1679 mark the path as unusable and use another path. If it receives 1680 Destination Unreachable messages on many or all paths, the Client 1681 should associate with a new Server and release its association 1682 with the old Server as specified in Section 3.16.5. 1684 o When an AERO Server receives persistent link-layer Destination 1685 Unreachable messages in response to encapsulated packets that it 1686 sends to one of its symmetric neighbor Clients, the Server should 1687 mark the underlying path as unusable and use another underlying 1688 path. 1690 o When an AERO Server or Proxy receives link-layer Destination 1691 Unreachable messages in response to an encapsulated packet that it 1692 sends to one of its permanent neighbors, it treats the messages as 1693 an indication that the path to the neighbor may be failing. 1694 However, the dynamic routing protocol should soon reconverge and 1695 correct the temporary outage. 1697 When an AERO Bridge receives a packet for which the network-layer 1698 destination address is covered by an MSP, if there is no more- 1699 specific routing information for the destination the Bridge drops the 1700 packet and returns a network-layer Destination Unreachable message 1701 subject to rate limiting. The Bridge writes the network-layer source 1702 address of the original packet as the destination address and uses 1703 one of its non link-local addresses as the source address of the 1704 message. 1706 When an AERO node receives an encapsulated packet for which the 1707 reassembly buffer it too small, it drops the packet and returns a 1708 network-layer Packet Too Big (PTB) message. The node first writes 1709 the MRU value into the PTB message MTU field, writes the network- 1710 layer source address of the original packet as the destination 1711 address and writes one of its non link-local addresses as the source 1712 address. 1714 3.12. AERO Router Discovery, Prefix Delegation and Autoconfiguration 1716 AERO Router Discovery, Prefix Delegation and Autoconfiguration are 1717 coordinated as discussed in the following Sections. 1719 3.12.1. AERO ND/PD Service Model 1721 Each AERO Server on the OMNI link configures a PD service to 1722 facilitate Client requests. Each Server is provisioned with a 1723 database of MNP-to-Client ID mappings for all Clients enrolled in the 1724 AERO service, as well as any information necessary to authenticate 1725 each Client. The Client database is maintained by a central 1726 administrative authority for the OMNI link and securely distributed 1727 to all Servers, e.g., via the Lightweight Directory Access Protocol 1728 (LDAP) [RFC4511], via static configuration, etc. Clients receive the 1729 same service regardless of the Servers they select. 1731 AERO Clients and Servers use ND messages to maintain neighbor cache 1732 entries. AERO Servers configure their OMNI interfaces as advertising 1733 NBMA interfaces, and therefore send unicast RA messages with a short 1734 Router Lifetime value (e.g., ReachableTime seconds) in response to a 1735 Client's RS message. Thereafter, Clients send additional RS messages 1736 to keep Server state alive. 1738 AERO Clients and Servers include PD parameters in RS/RA messages (see 1739 [I-D.templin-6man-dhcpv6-ndopt] for ND/PD alternatives). The unified 1740 ND/PD messages are exchanged between Client and Server according to 1741 the prefix management schedule required by the PD service. If the 1742 Client knows its MNP in advance, it can instead employ prefix 1743 registration by including its LLA as the source address of an RS 1744 message and with an OMNI option with valid prefix registration 1745 information for the MNP. If the Server (and Proxy) accept the 1746 Client's MNP assertion, they inject the prefix into the routing 1747 system and establish the necessary neighbor cache state. 1749 The following sections specify the Client and Server behavior. 1751 3.12.2. AERO Client Behavior 1753 AERO Clients discover the addresses of Servers in a similar manner as 1754 described in [RFC5214]. Discovery methods include static 1755 configuration (e.g., from a flat-file map of Server addresses and 1756 locations), or through an automated means such as Domain Name System 1757 (DNS) name resolution [RFC1035]. Alternatively, the Client can 1758 discover Server addresses through a layer 2 data link login exchange, 1759 or through a unicast RA response to a multicast/anycast RS as 1760 described below. In the absence of other information, the Client can 1761 resolve the DNS Fully-Qualified Domain Name (FQDN) 1762 "linkupnetworks.[domainname]" where "linkupnetworks" is a constant 1763 text string and "[domainname]" is a DNS suffix for the OMNI link 1764 (e.g., "example.com"). 1766 To associate with a Server, the Client acts as a requesting router to 1767 request MNPs. The Client prepares an RS message with PD parameters 1768 and includes a Nonce and Timestamp option if the Client needs to 1769 correlate RA replies. If the Client already knows the Server's LLA, 1770 it includes the LLA as the network-layer destination address; 1771 otherwise, it includes (link-local) All-Routers multicast as the 1772 network-layer destination. If the Client already knows its own LLA, 1773 it uses the LLA as the network-layer source address; otherwise, it 1774 uses the unspecified IPv6 address (::/128) as the network-layer 1775 source address. 1777 The Client next includes an OMNI option in the RS message to register 1778 its link-layer information with the Server. The Client sets the OMNI 1779 option prefix registration information according to the MNP, and 1780 includes an ifIndex-tuple with S set to '1' corresponding to the 1781 underlying interface over which the Client will send the RS message. 1782 The Client MAY include additional ifIndex-tuples specific to other 1783 underlying interfaces. The Client MAY also include an SLLAO 1784 corresponding to the OMNI option ifIndex-tuple with S set to '1'. 1786 The Client then sends the RS message (either directly via Direct 1787 interfaces, via a VPN for VPNed interfaces, via a Proxy for proxyed 1788 interfaces or via INET encapsulation for INET interfaces) and waits 1789 for an RA message reply (see Section 3.12.3). The Client retries up 1790 to MAX_RTR_SOLICITATIONS times until an RA is received. If the 1791 Client receives no RAs, or if it receives an RA with Router Lifetime 1792 set to 0, the Client SHOULD abandon this Server and try another 1793 Server. Otherwise, the Client processes the PD information found in 1794 the RA message. 1796 Next, the Client creates a symmetric neighbor cache entry with the 1797 Server's LLA as the network-layer address and the Server's 1798 encapsulation and/or link-layer addresses as the link-layer address. 1799 The Client records the RA Router Lifetime field value in the neighbor 1800 cache entry as the time for which the Server has committed to 1801 maintaining the MNP in the routing system via this underlying 1802 interface, and caches the other RA configuration information 1803 including Cur Hop Limit, M and O flags, Reachable Time and Retrans 1804 Timer. The Client then autoconfigures LLAs for each of the delegated 1805 MNPs and assigns them to the OMNI interface. The Client also caches 1806 any MSPs included in Route Information Options (RIOs) [RFC4191] as 1807 MSPs to associate with the OMNI link, and assigns the MTU value in 1808 the MTU option to the underlying interface. 1810 The Client then registers additional underlying interfaces with the 1811 Server by sending RS messages via each additional interface. The RS 1812 messages include the same parameters as for the initial RS/RA 1813 exchange, but with destination address set to the Server's LLA. 1815 Following autoconfiguration, the Client sub-delegates the MNPs to its 1816 attached EUNs and/or the Client's own internal virtual interfaces as 1817 described in [I-D.templin-v6ops-pdhost] to support the Client's 1818 downstream attached "Internet of Things (IoT)". The Client 1819 subsequently sends additional RS messages over each underlying 1820 interface before the Router Lifetime received for that interface 1821 expires. 1823 After the Client registers its underlying interfaces, it may wish to 1824 change one or more registrations, e.g., if an interface changes 1825 address or becomes unavailable, if QoS preferences change, etc. To 1826 do so, the Client prepares an RS message to send over any available 1827 underlying interface. The RS includes an OMNI option with prefix 1828 registration information specific to its MNP, with an ifIndex-tuple 1829 specific to the selected underlying interface with S set to '1', and 1830 with any additional ifIndex-tuples specific to other underlying 1831 interfaces. The Client includes fresh ifIndex-tuple values to update 1832 the Server's neighbor cache entry. When the Client receives the 1833 Server's RA response, it has assurance that the Server has been 1834 updated with the new information. 1836 If the Client wishes to discontinue use of a Server it issues an RS 1837 message over any underlying interface with an OMNI option with a 1838 prefix release indication. When the Server processes the message, it 1839 releases the MNP, sets the symmetric neighbor cache entry state for 1840 the Client to DEPARTED and returns an RA reply with Router Lifetime 1841 set to 0. After a short delay (e.g., 2 seconds), the Server 1842 withdraws the MNP from the routing system. 1844 3.12.3. AERO Server Behavior 1846 AERO Servers act as IP routers and support a PD service for Clients. 1847 Servers arrange to add their LLAs to a static map of Server addresses 1848 for the link and/or the DNS resource records for the FQDN 1849 "linkupnetworks.[domainname]" before entering service. Server 1850 addresses should be geographically and/or topologically referenced, 1851 and made available for discovery by Clients on the OMNI link. 1853 When a Server receives a prospective Client's RS message on its OMNI 1854 interface, it SHOULD return an immediate RA reply with Router 1855 Lifetime set to 0 if it is currently too busy or otherwise unable to 1856 service the Client. Otherwise, the Server authenticates the RS 1857 message and processes the PD parameters. The Server first determines 1858 the correct MNPs to delegate to the Client by searching the Client 1859 database. When the Server delegates the MNPs, it also creates a 1860 forwarding table entry for each MNP so that the MNPs are propagated 1861 into the routing system (see: Section 3.2.3). For IPv6, the Server 1862 creates an IPv6 forwarding table entry for each MNP. For IPv4, the 1863 Server creates an IPv6 forwarding table entry with the SPAN 1864 Compatibility Prefix (SCP) corresponding to the IPv4 address. 1866 The Server next creates a symmetric neighbor cache entry for the 1867 Client using the base LLA as the network-layer address and with 1868 lifetime set to no more than the smallest PD lifetime. Next, the 1869 Server updates the neighbor cache entry by recording the information 1870 in each ifIndex-tuple in the RS OMNI option. The Server also records 1871 the actual SPAN/INET addresses in the neighbor cache entry. 1873 Next, the Server prepares an RA message using its LLA as the network- 1874 layer source address and the network-layer source address of the RS 1875 message as the network-layer destination address. The Server sets 1876 the Router Lifetime to the time for which it will maintain both this 1877 underlying interface individually and the symmetric neighbor cache 1878 entry as a whole. The Server also sets Cur Hop Limit, M and O flags, 1879 Reachable Time and Retrans Timer to values appropriate for the OMNI 1880 link. The Server includes the delegated MNPs, any other PD 1881 parameters and an OMNI option with no ifIndex-tuples. The Server 1882 then includes one or more RIOs that encode the MSPs for the OMNI 1883 link, plus an MTU option (see Section 3.9). The Server finally 1884 forwards the message to the Client using SPAN/INET, INET, or NULL 1885 encapsulation as necessary. 1887 After the initial RS/RA exchange, the Server maintains a 1888 ReachableTime timer for each of the Client's underlying interfaces 1889 individually (and for the Client's symmetric neighbor cache entry 1890 collectively) set to expire after ReachableTime seconds. If the 1891 Client (or Proxy) issues additional RS messages, the Server sends an 1892 RA response and resets ReachableTime. If the Server receives an ND 1893 message with PD release indication it sets the Client's symmetric 1894 neighbor cache entry to the DEPARTED state and withdraws the MNP from 1895 the routing system after a short delay (e.g., 2 seconds). If 1896 ReachableTime expires before a new RS is received on an individual 1897 underlying interface, the Server marks the interface as DOWN. If 1898 ReachableTime expires before any new RS is received on any individual 1899 underlying interface, the Server sets the symmetric neighbor cache 1900 entry state to STALE and sets a 10 second timer. If the Server has 1901 not received a new RS or ND message with PD release indication before 1902 the 10 second timer expires, it deletes the neighbor cache entry and 1903 withdraws the MNP from the routing system. 1905 The Server processes any ND/PD messages pertaining to the Client and 1906 returns an NA/RA reply in response to solicitations. The Server may 1907 also issue unsolicited RA messages, e.g., with PD reconfigure 1908 parameters to cause the Client to renegotiate its PDs, with Router 1909 Lifetime set to 0 if it can no longer service this Client, etc. 1910 Finally, If the symmetric neighbor cache entry is in the DEPARTED 1911 state, the Server deletes the entry after DepartTime expires. 1913 Note: Clients SHOULD notify former Servers of their departures, but 1914 Servers are responsible for expiring neighbor cache entries and 1915 withdrawing routes even if no departure notification is received 1916 (e.g., if the Client leaves the network unexpectedly). Servers 1917 SHOULD therefore set Router Lifetime to ReachableTime seconds in 1918 solicited RA messages to minimize persistent stale cache information 1919 in the absence of Client departure notifications. A short Router 1920 Lifetime also ensures that proactive Client/Server RS/RA messaging 1921 will keep any NAT state alive (see above). 1923 Note: All Servers on an OMNI link MUST advertise consistent values in 1924 the RA Cur Hop Limit, M and O flags, Reachable Time and Retrans Timer 1925 fields the same as for any link, since unpredictable behavior could 1926 result if different Servers on the same link advertised different 1927 values. 1929 3.12.3.1. Lightweight DHCPv6 Relay Agent (LDRA) 1931 When DHCPv6 is used as the ND/PD service back end, AERO Clients and 1932 Servers are always on the same link (i.e., the OMNI link) from the 1933 perspective of DHCPv6. However, in some implementations the DHCPv6 1934 server and ND function may be located in separate modules. In that 1935 case, the Server's OMNI interface module can act as a Lightweight 1936 DHCPv6 Relay Agent (LDRA)[RFC6221] to relay PD messages to and from 1937 the DHCPv6 server module. 1939 When the LDRA receives an authentic RS message, it extracts the PD 1940 message parameters and uses them to construct an IPv6/UDP/DHCPv6 1941 message. It sets the IPv6 source address to the source address of 1942 the RS message, sets the IPv6 destination address to 1943 'All_DHCP_Relay_Agents_and_Servers' and sets the UDP fields to values 1944 that will be understood by the DHCPv6 server. 1946 The LDRA then wraps the message in a DHCPv6 'Relay-Forward' message 1947 header and includes an 'Interface-Id' option that includes enough 1948 information to allow the LDRA to forward the resulting Reply message 1949 back to the Client (e.g., the Client's link-layer addresses, a 1950 security association identifier, etc.). The LDRA also wraps the OMNI 1951 option and SLLAO into the Interface-Id option, then forwards the 1952 message to the DHCPv6 server. 1954 When the DHCPv6 server prepares a Reply message, it wraps the message 1955 in a 'Relay-Reply' message and echoes the Interface-Id option. The 1956 DHCPv6 server then delivers the Relay-Reply message to the LDRA, 1957 which discards the Relay-Reply wrapper and IPv6/UDP headers, then 1958 uses the DHCPv6 message to construct an RA response to the Client. 1959 The Server uses the information in the Interface-Id option to prepare 1960 the RA message and to cache the link-layer addresses taken from the 1961 OMNI option and SLLAO echoed in the Interface-Id option. 1963 3.13. The AERO Proxy 1965 Clients may connect to protected-spectrum ANETs that deploy physical 1966 and/or link-layer security services to facilitate communications to 1967 Servers in outside INETs. In that case, the ANET can employ an AERO 1968 Proxy. The Proxy is located at the ANET/INET border and listens for 1969 RS messages originating from or RA messages destined to ANET Clients. 1970 The Proxy acts on these control messages as follows: 1972 o when the Proxy receives an RS message from a new ANET Client, it 1973 first authenticates the message then examines the network-layer 1974 destination address. If the destination address is a Server's 1975 LLA, the Proxy proceeds to the next step. Otherwise, if the 1976 destination is (link-local) All-Routers multicast, the Proxy 1977 selects a "nearby" Server that is likely to be a good candidate to 1978 serve the Client and replaces the destination address with the 1979 Server's LLA. Next, the Proxy creates a proxy neighbor cache 1980 entry and caches the Client and Server link-layer addresses along 1981 with the OMNI option information and any other identifying 1982 information including Transaction IDs, Client Identifiers, Nonce 1983 values, etc. The Proxy finally encapsulates the (proxyed) RS 1984 message in a SPAN header with source set to the Proxy's ULA and 1985 destination set to the Server's ULA then forwards the message into 1986 the SPAN. 1988 o when the Server receives the RS, it authenticates the message then 1989 creates or updates a symmetric neighbor cache entry for the Client 1990 with the Proxy's ULA as the link-layer address. The Server then 1991 sends an RA message back to the Proxy via the spanning tree. 1993 o when the Proxy receives the RA, it authenticates the message and 1994 matches it with the proxy neighbor cache entry created by the RS. 1995 The Proxy then caches the PD route information as a mapping from 1996 the Client's MNPs to the Client's link-layer address, caches the 1997 Server's advertised Router Lifetime and sets the neighbor cache 1998 entry state to REACHABLE. The Proxy then sets the P bit in the RA 1999 flags field, optionally rewrites the Router Lifetime and forwards 2000 the (proxyed) message to the Client. The Proxy finally includes 2001 an MTU option (if necessary) with an MTU to use for the underlying 2002 ANET interface. 2004 After the initial RS/RA exchange, the Proxy forwards any Client data 2005 packets for which there is no matching asymmetric neighbor cache 2006 entry to a Bridge using SPAN encapsulation with its own ULA as the 2007 source and the ULA corresponding to the Client as the destination. 2008 The Proxy instead forwards any Client data destined to an asymmetric 2009 neighbor cache target directly to the target according to the SPAN/ 2010 link-layer information - the process of establishing asymmetric 2011 neighbor cache entries is specified in Section 3.14. 2013 While the Client is still attached to the ANET, the Proxy sends NS, 2014 RS and/or unsolicited NA messages to update the Server's symmetric 2015 neighbor cache entries on behalf of the Client and/or to convey QoS 2016 updates. This allows for higher-frequency Proxy-initiated RS/RA 2017 messaging over well-connected INET infrastructure supplemented by 2018 lower-frequency Client-initiated RS/RA messaging over constrained 2019 ANET data links. 2021 If the Server ceases to send solicited advertisements, the Proxy 2022 sends unsolicited RAs on the ANET interface with destination set to 2023 (link-local) All-Nodes multicast and with Router Lifetime set to zero 2024 to inform Clients that the Server has failed. Although the Proxy 2025 engages in ND exchanges on behalf of the Client, the Client can also 2026 send ND messages on its own behalf, e.g., if it is in a better 2027 position than the Proxy to convey QoS changes, etc. For this reason, 2028 the Proxy marks any Client-originated solicitation messages (e.g. by 2029 inserting a Nonce option) so that it can return the solicited 2030 advertisement to the Client instead of processing it locally. 2032 If the Client becomes unreachable, the Proxy sets the neighbor cache 2033 entry state to DEPARTED and retains the entry for DepartTime seconds. 2034 While the state is DEPARTED, the Proxy forwards any packets destined 2035 to the Client to a Bridge via SPAN encapsulation with the Client's 2036 current Server as the destination. The Bridge in turn forwards the 2037 packets to the Client's current Server. When DepartTime expires, the 2038 Proxy deletes the neighbor cache entry and discards any further 2039 packets destined to this (now forgotten) Client. 2041 In some ANETs that employ a Proxy, the Client's MNP can be injected 2042 into the ANET routing system. In that case, the Client can send data 2043 messages without encapsulation so that the ANET routing system 2044 transports the unencapsulated packets to the Proxy. This can be very 2045 beneficial, e.g., if the Client connects to the ANET via low-end data 2046 links such as some aviation wireless links. 2048 If the first-hop ANET access router is AERO-aware, the Client can 2049 avoid encapsulation for both its control and data messages. When the 2050 Client connects to the link, it can send an unencapsulated RS message 2051 with source address set to its LLA and with destination address set 2052 to the LLA of the Client's selected Server or to (link-local) All- 2053 Routers multicast. The Client includes an OMNI option formatted as 2054 specified in [I-D.templin-6man-omni-interface]. 2056 The Client then sends the unencapsulated RS message, which will be 2057 intercepted by the AERO-Aware access router. The access router then 2058 encapsulates the RS message in an ANET header with its own address as 2059 the source address and the address of a Proxy as the destination 2060 address. The access router further remembers the address of the 2061 Proxy so that it can encapsulate future data packets from the Client 2062 via the same Proxy. If the access router needs to change to a new 2063 Proxy, it simply sends another RS message toward the Server via the 2064 new Proxy on behalf of the Client. 2066 In some cases, the access router and Proxy may be one and the same 2067 node. In that case, the node would be located on the same physical 2068 link as the Client, but its message exchanges with the Server would 2069 need to pass through a security gateway at the ANET/INET border. The 2070 method for deploying access routers and Proxys (i.e. as a single node 2071 or multiple nodes) is an ANET-local administrative consideration. 2073 3.13.1. Detecting and Responding to Server Failures 2075 In environments where fast recovery from Server failure is required, 2076 Proxys SHOULD use proactive Neighbor Unreachability Detection (NUD) 2077 to track Server reachability in a similar fashion as for 2078 Bidirectional Forwarding Detection (BFD) [RFC5880]. Proxys can then 2079 quickly detect and react to failures so that cached information is 2080 re-established through alternate paths. The NUD control messaging is 2081 carried only over well-connected ground domain networks (i.e., and 2082 not low-end aeronautical radio links) and can therefore be tuned for 2083 rapid response. 2085 Proxys perform proactive NUD with Servers for which there are 2086 currently active ANET Clients by sending continuous NS messages in 2087 rapid succession, e.g., one message per second. The Proxy sends the 2088 NS message via the spanning tree with the Proxy's LLA as the source 2089 and the LLA of the Server as the destination. When the Proxy is also 2090 sending RS messages to the Server on behalf of ANET Clients, the 2091 resulting RA responses can be considered as equivalent hints of 2092 forward progress. This means that the Proxy need not also send a 2093 periodic NS if it has already sent an RS within the same period. If 2094 the Server fails (i.e., if the Proxy ceases to receive 2095 advertisements), the Proxy can quickly inform Clients by sending 2096 multicast RA messages on the ANET interface. 2098 The Proxy sends RA messages on the ANET interface with source address 2099 set to the Server's address, destination address set to (link-local) 2100 All-Nodes multicast, and Router Lifetime set to 0. The Proxy SHOULD 2101 send MAX_FINAL_RTR_ADVERTISEMENTS RA messages separated by small 2102 delays [RFC4861]. Any Clients on the ANET that had been using the 2103 failed Server will receive the RA messages and associate with a new 2104 Server. 2106 3.13.2. Point-to-Multipoint Server Coordination 2108 In environments where Client messaging over ANETs is bandwidth- 2109 limited and/or expensive, Clients can enlist the services of the 2110 Proxy to coordinate with multiple Servers in a single RS/RA message 2111 exchange. The Client can send a single RS message to (link-local) 2112 All-Routers multicast that includes the ID's of multiple Servers in 2113 MS-Register sub-options of the OMNI option. 2115 When the Proxy receives the RS and processes the OMNI option, it 2116 performs a separate RS/RA exchange with each MS-Register Server. 2117 When it has received the RA messages, it creates an "aggregate" RA 2118 message to return to the Client with an OMNI option with each 2119 responding Server's ID recorded in an MS-Register sub-option. 2121 Clients can thereafter employ efficient point-to-multipoint Server 2122 coordination under the assistance of the Proxy to dramatically reduce 2123 the number of messages sent over the ANET while enlisting the support 2124 of multiple Servers for fault tolerance. Clients can further include 2125 MS-Release suboptions in RS messages to request the Proxy to release 2126 from former Servers via the procedures discussed in Section 3.16.5. 2128 The OMNI interface specification [I-D.templin-6man-omni-interface] 2129 provides further discussion of the Client/Proxy RS/RA messaging 2130 involved in point-to-multipoint coordination. 2132 3.14. AERO Route Optimization / Address Resolution 2134 While data packets are flowing between a source and target node, 2135 route optimization SHOULD be used. Route optimization is initiated 2136 by the first eligible Route Optimization Source (ROS) closest to the 2137 source as follows: 2139 o For Clients on VPNed and Direct interfaces, the Server is the ROS. 2141 o For Clients on Proxyed interfaces, the Proxy is the ROS. 2143 o For Clients on INET interfaces, the Client itself is the ROS. 2145 o For correspondent nodes on INET/EUN interfaces serviced by a 2146 Relay, the Relay is the ROS. 2148 The route optimization procedure is conducted between the ROS and the 2149 target Server/Relay acting as a Route Optimization Responder (ROR) in 2150 the same manner as for IPv6 ND Address Resolution and using the same 2151 NS/NA messaging. The target may either be a MNP Client serviced by a 2152 Server, or a non-MNP correspondent reachable via a Relay. 2154 The procedures are specified in the following sections. 2156 3.14.1. Route Optimization Initiation 2158 While data packets are flowing from the source node toward a target 2159 node, the ROS performs address resolution by sending an NS message 2160 for Address Resolution (NS(AR)) to receive a solicited NA message 2161 from the ROR. When the ROS sends an NS(AR), it includes: 2163 o the LLA of the ROS as the source address. 2165 o the data packet's destination as the Target Address. 2167 o the Solicited-Node multicast address [RFC4291] formed from the 2168 lower 24 bits of the data packet's destination as the destination 2169 address, e.g., for 2001:db8:1:2::10:2000 the NS destination 2170 address is ff02:0:0:0:0:1:ff10:2000. 2172 The NS(AR) message includes an OMNI option with no ifIndex-tuples and 2173 no SLLAO, such that the target will not create a neighbor cache 2174 entry. 2176 The ROS then encapsulates the NS(AR) message in a SPAN header with 2177 source set to its own ULA and destination set to the ULA 2178 corresponding to the packet's final destination, then sends the 2179 message into the spanning tree without decrementing the network-layer 2180 TTL/Hop Limit field. 2182 3.14.2. Relaying the NS 2184 When the Bridge receives the NS(AR) message from the ROS, it discards 2185 the INET header and determines that the ROR is the next hop by 2186 consulting its standard IPv6 forwarding table for the SPAN header 2187 destination address. The Bridge then forwards the message toward the 2188 ROR via the spanning tree the same as for any IPv6 router. The 2189 final-hop Bridge in the spanning tree will deliver the message via a 2190 secured tunnel to the ROR. 2192 3.14.3. Processing the NS and Sending the NA 2194 When the ROR receives the NS(AR) message, it examines the Target 2195 Address to determine whether it has a neighbor cache entry and/or 2196 route that matches the target. If there is no match, the ROR drops 2197 the message. Otherwise, the ROR continues processing as follows: 2199 o if the target belongs to an MNP Client neighbor in the DEPARTED 2200 state the ROR changes the NS(AR) message SPAN destination address 2201 to the ULA of the Client's new Server, forwards the message into 2202 the spanning tree and returns from processing. 2204 o If the target belongs to an MNP Client neighbor in the REACHABLE 2205 state, the ROR instead adds the AERO source address to the target 2206 Client's Report List with time set to ReportTime. 2208 o If the target belongs to a non-MNP route, the ROR continues 2209 processing without adding an entry to the Report List. 2211 The ROR then prepares a solicited NA message to send back to the ROS 2212 but does not create a neighbor cache entry. The ROR sets the NA 2213 source address to the LLA corresponding to the target, sets the 2214 Target Address to the target of the solicitation, and sets the 2215 destination address to the source of the solicitation. 2217 The ROR then includes an OMNI option with prefix registration length 2218 set to the length of the MNP if the target is an MNP Client; 2219 otherwise, set to the maximum of the non-MNP prefix length and 64. 2220 (Note that a /64 limit is imposed to avoid causing the ROS to set 2221 short prefixes (e.g., "default") that would match destinations for 2222 which the routing system includes more-specific prefixes.) 2224 If the target is an MNP Client, the ROR next includes ifIndex-tuples 2225 in the OMNI option for each of the target Client's underlying 2226 interfaces with current information for each interface and with the S 2227 flag set to 0. The ROR then includes a TLLAO with ifIndex-tuples in 2228 one-to-one correspondence with the tuples that appear in the OMNI 2229 option. 2231 The ROR sets the Link Layer Address and Port Number to its own INET 2232 address for VPNed or Direct interfaces, to the INET address of the 2233 Proxy for Proxyed interfaces or to the Client's INET address for INET 2234 interfaces. The ROR then includes the lower 32 bits of its own ULA 2235 (or the ULA of the Proxy, for Proxyed interfaces) as the LHS ID, 2236 encodes the ULA prefix length code in the SRT field and sets the FMT 2237 code accordingly as specified in Section 3.3. 2239 The ROR then sets the NA message R flag to 1 (as a router), S flag to 2240 1 (as a response to a solicitation), and O flag to 0 (as a proxy). 2241 The ROR finally encapsulates the NA message in a SPAN header with 2242 source set to its own ULA and destination set to the source ULA of 2243 the NS(AR) message, then forwards the message into the spanning tree 2244 without decrementing the network-layer TTL/Hop Limit field. 2246 3.14.4. Relaying the NA 2248 When the Bridge receives the NA message from the ROR, it discards the 2249 INET header and determines that the ROS is the next hop by consulting 2250 its standard IPv6 forwarding table for the SPAN header destination 2251 address. The Bridge then forwards the SPAN-encapsulated NA message 2252 toward the ROS the same as for any IPv6 router. The final-hop Bridge 2253 in the spanning tree will deliver the message via a secured tunnel to 2254 the ROS. 2256 3.14.5. Processing the NA 2258 When the ROS receives the solicited NA message, it processes the 2259 message the same as for standard IPv6 Address Resolution [RFC4861]. 2260 In the process, it caches the source ULA then creates an asymmetric 2261 neighbor cache entry for the ROR and caches all information found in 2262 the OMNI and TLLAO options. The ROS finally sets the asymmetric 2263 neighbor cache entry lifetime to ReachableTime seconds. 2265 3.14.6. Route Optimization Maintenance 2267 Following route optimization, the ROS forwards future data packets 2268 destined to the target via the addresses found in the cached link- 2269 layer information. The route optimization is shared by all sources 2270 that send packets to the target via the ROS, i.e., and not just the 2271 source on behalf of which the route optimization was initiated. 2273 While new data packets destined to the target are flowing through the 2274 ROS, it sends additional NS(AR) messages to the ROR before 2275 ReachableTime expires to receive a fresh solicited NA message the 2276 same as described in the previous sections (route optimization 2277 refreshment strategies are an implementation matter, with a non- 2278 normative example given in Appendix A.1). The ROS uses the cached 2279 ULA of the ROR as the NS(AR) SPAN destination address, and sends up 2280 to MAX_MULTICAST_SOLICIT NS(AR) messages separated by 1 second until 2281 an NA is received. If no NA is received, the ROS assumes that the 2282 current ROR has become unreachable and deletes the neighbor cache 2283 entry. Subsequent data packets will trigger a new route optimization 2284 per Section 3.14.1 to discover a new ROR while initial data packets 2285 travel over a suboptimal route. 2287 If an NA is received, the ROS then updates the asymmetric neighbor 2288 cache entry to refresh ReachableTime, while (for MNP destinations) 2289 the ROR adds or updates the ROS address to the target Client's Report 2290 List and with time set to ReportTime. While no data packets are 2291 flowing, the ROS instead allows ReachableTime for the asymmetric 2292 neighbor cache entry to expire. When ReachableTime expires, the ROS 2293 deletes the asymmetric neighbor cache entry. Any future data packets 2294 flowing through the ROS will again trigger a new route optimization. 2296 The ROS may also receive unsolicited NA messages from the ROR at any 2297 time (see: Section 3.16). If there is an asymmetric neighbor cache 2298 entry for the target, the ROS updates the link-layer information but 2299 does not update ReachableTime since the receipt of an unsolicited NA 2300 does not confirm that any forward paths are working. If there is no 2301 asymmetric neighbor cache entry, the ROS simply discards the 2302 unsolicited NA. 2304 In this arrangement, the ROS holds an asymmetric neighbor cache entry 2305 for the ROR, but the ROR does not hold an asymmetric neighbor cache 2306 entry for the ROS. The route optimization neighbor relationship is 2307 therefore asymmetric and unidirectional. If the target node also has 2308 packets to send back to the source node, then a separate route 2309 optimization procedure is performed in the reverse direction. But, 2310 there is no requirement that the forward and reverse paths be 2311 symmetric. 2313 3.15. Neighbor Unreachability Detection (NUD) 2315 AERO nodes perform Neighbor Unreachability Detection (NUD) per 2316 [RFC4861] either reactively in response to persistent link-layer 2317 errors (see Section 3.11) or proactively to confirm reachability. 2318 The NUD algorithm is based on periodic control message exchanges. 2319 The algorithm may further be seeded by ND hints of forward progress, 2320 but care must be taken to avoid inferring reachability based on 2321 spoofed information. For example, authentic IPv6 ND message 2322 exchanges may be considered as acceptable hints of forward progress, 2323 while spurious data packets should not be. 2325 AERO Servers, Proxys and Relays can use standard NS/NA NUD exchanges 2326 sent over the spanning tree to securely test reachability without 2327 risk of DoS attacks from nodes pretending to be a neighbor; Proxys 2328 can further perform NUD to securely verify Server reachability on 2329 behalf of their proxyed Clients. However, a means for a ROS to test 2330 the unsecured forward directions of target route optimized paths is 2331 also necessary. 2333 When an ROR directs an ROS to a neighbor with one or more target 2334 link-layer addresses, the ROS can proactively test each such 2335 unsecured route optimized path by sending "loopback" NS(NUD) 2336 messages. While testing the paths, the ROS can optionally continue 2337 to send packets via the spanning tree, maintain a small queue of 2338 packets until target reachability is confirmed, or (optimistically) 2339 allow packets to flow via the route optimized paths. 2341 When the ROS sends a loopback NS(NUD) message, it uses its LLA as 2342 both the IPv6 source and destination address, and the MNP Subnet- 2343 Router anycast address as the Target Address. The ROS includes a 2344 Nonce and Timestamp option, then encapsulates the message in SPAN/ 2345 INET headers with its own ULA as the source and the ULA of the route 2346 optimization target as the destination. The ROS then forwards the 2347 message to the target (either directly to the link layer address of 2348 the target if the target is in the same OMNI link segment, or via a 2349 Bridge if the target is in a different OMNI link segment). 2351 When the route optimization target receives the NS(NUD) message, it 2352 notices that the IPv6 destination address is the same as the source 2353 address. It then reverses the SPAN source and destination addresses 2354 and returns the message to the ROS (either directly or via the 2355 spanning tree). The route optimization target does not decrement the 2356 NS(NUD) message IPv6 Hop-Limit in the process, since the message has 2357 not exited the OMNI link. 2359 When the ROS receives the NS(NUD) message, it can determine from the 2360 Nonce, Timestamp and Target Address that the message originated from 2361 itself and that it transited the forward path. The ROS need not 2362 prepare an NA response, since the destination of the response would 2363 be itself and testing the route optimization path again would be 2364 redundant. 2366 The ROS marks route optimization target paths that pass these NUD 2367 tests as "reachable", and those that do not as "unreachable". These 2368 markings inform the OMNI interface forwarding algorithm specified in 2369 Section 3.10. 2371 Note that to avoid a DoS vector nodes MUST NOT return loopback 2372 NS(NUD) messages received from an unsecured link-layer source via the 2373 spanning tree. 2375 3.16. Mobility Management and Quality of Service (QoS) 2377 AERO is a Distributed Mobility Management (DMM) service. Each Server 2378 is responsible for only a subset of the Clients on the OMNI link, as 2379 opposed to a Centralized Mobility Management (CMM) service where 2380 there is a single network mobility collective entity for all Clients. 2381 Clients coordinate with their associated Servers via RS/RA exchanges 2382 to maintain the DMM profile, and the AERO routing system tracks all 2383 current Client/Server peering relationships. 2385 Servers provide default routing and mobility/multilink services for 2386 their dependent Clients. Clients are responsible for maintaining 2387 neighbor relationships with their Servers through periodic RS/RA 2388 exchanges, which also serves to confirm neighbor reachability. When 2389 a Client's underlying interface address and/or QoS information 2390 changes, the Client is responsible for updating the Server with this 2391 new information. Note that for Proxyed interfaces, however, the 2392 Proxy can also perform some RS/RA exchanges on the Client's behalf. 2394 Mobility management considerations are specified in the following 2395 sections. 2397 3.16.1. Mobility Update Messaging 2399 Servers accommodate Client mobility/multilink and/or QoS change 2400 events by sending unsolicited NA (uNA) messages to each ROS in the 2401 target Client's Report List. When a Server sends a uNA message, it 2402 sets the IPv6 source address to the Client's LLA, sets the 2403 destination address to (link-local) All-Nodes multicast and sets the 2404 Target Address to the Client's Subnet-Router anycast address. The 2405 Server also includes an OMNI option with prefix registration 2406 information and with ifIndex-tuples for the target Client's remaining 2407 interfaces. The Server then includes a TLLAO with corresponding 2408 ifIndex-tuples prepared the same as for the initial route 2409 optimization event. The Server sets the NA R flag to 1, the S flag 2410 to 0 and the O flag to 0, then encapsulates the message in a SPAN 2411 header with source set to its own ULA and destination set to the ULA 2412 of the ROS and sends the message into the spanning tree. 2414 As discussed in Section 7.2.6 of [RFC4861], the transmission and 2415 reception of uNA messages is unreliable but provides a useful 2416 optimization. In well-connected Internetworks with robust data links 2417 uNA messages will be delivered with high probability, but in any case 2418 the Server can optionally send up to MAX_NEIGHBOR_ADVERTISEMENT uNAs 2419 to each ROS to increase the likelihood that at least one will be 2420 received. 2422 When the ROS receives a uNA message, it ignores the message if there 2423 is no existing neighbor cache entry for the Client. Otherwise, it 2424 uses the included OMNI option and TLLAO information to update the 2425 neighbor cache entry, but does not reset ReachableTime since the 2426 receipt of an unsolicited NA message from the target Server does not 2427 provide confirmation that any forward paths to the target Client are 2428 working. 2430 If uNA messages are lost, the ROS may be left with stale address and/ 2431 or QoS information for the Client for up to ReachableTime seconds. 2432 During this time, the ROS can continue sending packets according to 2433 its stale neighbor cache information. When ReachableTime is close to 2434 expiring, the ROS will re-initiate route optimization and receive 2435 fresh link-layer address information. 2437 In addition to sending uNA messages to the current set of ROSs for 2438 the Client, the Server also sends uNAs to the former link-layer 2439 address for any ifIndex-tuple for which the link-layer address has 2440 changed. The uNA messages update Proxys that cannot easily detect 2441 (e.g., without active probing) when a formerly-active Client has 2442 departed. 2444 3.16.2. Announcing Link-Layer Address and/or QoS Preference Changes 2446 When a Client needs to change its underlying interface addresses and/ 2447 or QoS preferences (e.g., due to a mobility event), either the Client 2448 or its Proxys send RS messages to the Server via the spanning tree 2449 with an OMNI option that includes an ifIndex-tuple with the new link 2450 quality and address information. 2452 Up to MAX_RTR_SOLICITATIONS RS messages MAY be sent in parallel with 2453 sending actual data packets in case one or more RAs are lost. If all 2454 RAs are lost, the Client SHOULD re-associate with a new Server. 2456 When the Server receives the Client's changes, it sends uNA messages 2457 to all nodes in the Report List the same as described in the previous 2458 section. 2460 3.16.3. Bringing New Links Into Service 2462 When a Client needs to bring new underlying interfaces into service 2463 (e.g., when it activates a new data link), it sends an RS message to 2464 the Server via the underlying interface with an OMNI option that 2465 includes an ifIndex-tuple with appropriate link quality values and 2466 with link-layer address information for the new link. 2468 3.16.4. Removing Existing Links from Service 2470 When a Client needs to remove existing underlying interfaces from 2471 service (e.g., when it de-activates an existing data link), it sends 2472 an RS or uNA message to its Server with an OMNI option with 2473 appropriate link quality values. 2475 If the Client needs to send RS/uNA messages over an underlying 2476 interface other than the one being removed from service, it MUST 2477 include ifIndex-tuples with appropriate link quality values for any 2478 underlying interfaces being removed from service. 2480 3.16.5. Moving to a New Server 2482 When a Client associates with a new Server, it performs the Client 2483 procedures specified in Section 3.12.2. The Client also includes MS- 2484 Release identifiers in the RS message OMNI option per 2485 [I-D.templin-6man-omni-interface] if it wants the new Server to 2486 notify any old Servers from which the Client is departing. 2488 When the new Server receives the Client's RS message, it returns an 2489 RA as specified in Section 3.12.3 and sends up to 2490 MAX_NEIGHBOR_ADVERTIISEMENT uNA messages to any old Servers listed in 2491 OMNI option MS-Release identifiers. Each uNA message includes the 2492 Client's LLA as the source address, the old Server's LLA as the 2493 destination address, and an OMNI option with the Register/Release bit 2494 set to 0. The new Server wraps the uNA in a SPAN header with its own 2495 ULA as the source and the old Server's ULA as the destination, then 2496 sends the message into the spanning tree. 2498 When an old Server receives the uNA, it changes the Client's neighbor 2499 cache entry state to DEPARTED, sets the link-layer address of the 2500 Client to the new Server's ULA, and resets DepartTime. After a short 2501 delay (e.g., 2 seconds) the old Server withdraws the Client's MNP 2502 from the routing system. After DepartTime expires, the old Server 2503 deletes the Client's neighbor cache entry. 2505 The old Server also sends unsolicited NA messages to all ROSs in the 2506 Client's Report List with an OMNI option with a single ifIndex-tuple 2507 with ifIndex set to 0, and with the ULA of the new Server in a 2508 companion TLLAO. When the ROS receives the NA, it caches the address 2509 of the new Server in the existing asymmetric neighbor cache entry and 2510 marks the entry as STALE for a period of 10 seconds after which the 2511 cache entry is deleted. While in the STALE state, subsequent data 2512 packets flow according to any existing cached link-layer information 2513 and trigger a new NS(AR)/NA exchange via the new Server. 2515 Clients SHOULD NOT move rapidly between Servers in order to avoid 2516 causing excessive oscillations in the AERO routing system. Examples 2517 of when a Client might wish to change to a different Server include a 2518 Server that has gone unreachable, topological movements of 2519 significant distance, movement to a new geographic region, movement 2520 to a new OMNI link segment, etc. 2522 When a Client moves to a new Server, some of the fragments of a 2523 multiple fragment packet may have already arrived at the old Server 2524 while others are en route to the new Server, however no special 2525 attention in the reassembly algorithm is necessary when re-routed 2526 fragments are simply treated as loss. 2528 3.17. Multicast 2530 The AERO Client provides an IGMP (IPv4) [RFC2236] or MLD (IPv6) 2531 [RFC3810] proxy service for its EUNs and/or hosted applications 2532 [RFC4605]. The Client forwards IGMP/MLD messages over any of its 2533 underlying interfaces for which group membership is required. The 2534 IGMP/MLD messages may be further forwarded by a first-hop ANET access 2535 router acting as an IGMP/MLD-snooping switch [RFC4541], then 2536 ultimately delivered to an AERO Proxy/Server acting as a Protocol 2537 Independent Multicast - Sparse-Mode (PIM-SM, or simply "PIM") 2538 Designated Router (DR) [RFC7761]. AERO Relays also act as PIM 2539 routers (i.e., the same as AERO Proxys/Servers) on behalf of nodes on 2540 INET/EUN networks. The behaviors identified in the following 2541 sections correspond to Source-Specific Multicast (SSM) and Any-Source 2542 Multicast (ASM) operational modes. 2544 3.17.1. Source-Specific Multicast (SSM) 2546 When an ROS (i.e., an AERO Proxy/Server/Relay) "X" acting as PIM 2547 router receives a Join/Prune message from a node on its downstream 2548 interfaces containing one or more ((S)ource, (G)roup) pairs, it 2549 updates its Multicast Routing Information Base (MRIB) accordingly. 2550 For each S belonging to a prefix reachable via X's non-OMNI 2551 interfaces, X then forwards the (S, G) Join/Prune to any PIM routers 2552 on those interfaces per [RFC7761]. 2554 For each S belonging to a prefix reachable via X's OMNI interface, X 2555 originates a separate copy of the Join/Prune for each (S,G) in the 2556 message using its own LLA as the source address and ALL-PIM-ROUTERS 2557 as the destination address. X then encapsulates each message in a 2558 SPAN header with source address set to the ULA of X and destination 2559 address set to S then forwards the message into the spanning tree, 2560 which delivers it to AERO Server/Relay "Y" that services S. At the 2561 same time, if the message was a Join, X sends a route-optimization NS 2562 message toward each S the same as discussed in Section 3.14. The 2563 resulting NAs will return the LLA for the prefix that matches S as 2564 the network-layer source address and TLLAOs with the ULA 2565 corresponding to any ifIndex-tuples that are currently servicing S. 2567 When Y processes the Join/Prune message, if S located behind any 2568 INET, Direct, or VPNed interfaces Y acts as a PIM router and updates 2569 its MRIB to list X as the next hop in the reverse path. If S is 2570 located behind any Proxys "Z"*, Y also forwards the message to each 2571 Z* over the spanning tree while continuing to use the LLA of X as the 2572 source address. Each Z* then updates its MRIB accordingly and 2573 maintains the LLA of X as the next hop in the reverse path. Since 2574 the Bridges do not examine network layer control messages, this means 2575 that the (reverse) multicast tree path is simply from each Z* (and/or 2576 Y) to X with no other multicast-aware routers in the path. If any Z* 2577 (and/or Y) is located on the same OMNI link segment as X, the 2578 multicast data traffic sent to X directly using SPAN/INET 2579 encapsulation instead of via a Bridge. 2581 Following the initial Join/Prune and NS/NA messaging, X maintains an 2582 asymmetric neighbor cache entry for each S the same as if X was 2583 sending unicast data traffic to S. In particular, X performs 2584 additional NS/NA exchanges to keep the neighbor cache entry alive for 2585 up to t_periodic seconds [RFC7761]. If no new Joins are received 2586 within t_periodic seconds, X allows the neighbor cache entry to 2587 expire. Finally, if X receives any additional Join/Prune messages 2588 for (S,G) it forwards the messages to each Y and Z* in the neighbor 2589 cache entry over the spanning tree. 2591 At some later time, Client C that holds an MNP for source S may 2592 depart from a first Proxy Z1 and/or connect via a new Proxy Z2. In 2593 that case, Y sends an unsolicited NA message to X the same as 2594 specified for unicast mobility in Section 3.16. When X receives the 2595 unsolicited NA message, it updates its asymmetric neighbor cache 2596 entry for the LLA for source S and sends new Join messages to any new 2597 Proxys Z2. There is no requirement to send any Prune messages to old 2598 Proxys Z1 since source S will no longer source any multicast data 2599 traffic via Z1. Instead, the multicast state for (S,G) in Proxy Z1 2600 will soon time out since no new Joins will arrive. 2602 After some later time, C may move to a new Server Y2 and depart from 2603 old Sever Y1. In that case, Y1 sends Join messages for any of C's 2604 active (S,G) groups to Y2 while including its own LLA as the source 2605 address. This causes Y2 to include Y1 in the multicast forwarding 2606 tree during the interim time that Y1's symmetric neighbor cache entry 2607 for C is in the DEPARTED state. At the same time, Y1 sends an 2608 unsolicited NA message to X with an OMNI option and TLLAO with 2609 ifIndex-tuple set to 0 and a release indication to cause X to release 2610 its asymmetric neighbor cache entry. X then sends a new Join message 2611 to S via the spanning tree and re-initiates route optimization the 2612 same as if it were receiving a fresh Join message from a node on a 2613 downstream link. 2615 3.17.2. Any-Source Multicast (ASM) 2617 When an ROS X acting as a PIM router receives a Join/Prune from a 2618 node on its downstream interfaces containing one or more (*,G) pairs, 2619 it updates its Multicast Routing Information Base (MRIB) accordingly. 2620 X then forwards a copy of the message to the Rendezvous Point (RP) R 2621 for each G over the spanning tree. X uses its own LLA as the source 2622 address and ALL-PIM-ROUTERS as the destination address, then 2623 encapsulates each message in a SPAN header with source address set to 2624 the ULA of X and destination address set to R, then sends the message 2625 into the spanning tree. At the same time, if the message was a Join 2626 X initiates NS/NA route optimization the same as for the SSM case 2627 discussed in Section 3.17.1. 2629 For each source S that sends multicast traffic to group G via R, the 2630 Proxy/Server Z* for the Client that aggregates S encapsulates the 2631 packets in PIM Register messages and forwards them to R via the 2632 spanning tree, which may then elect to send a PIM Join to Z*. This 2633 will result in an (S,G) tree rooted at Z* with R as the next hop so 2634 that R will begin to receive two copies of the packet; one native 2635 copy from the (S, G) tree and a second copy from the pre-existing (*, 2636 G) tree that still uses PIM Register encapsulation. R can then issue 2637 a PIM Register-stop message to suppress the Register-encapsulated 2638 stream. At some later time, if C moves to a new Proxy/Server Z*, it 2639 resumes sending packets via PIM Register encapsulation via the new 2640 Z*. 2642 At the same time, as multicast listeners discover individual S's for 2643 a given G, they can initiate an (S,G) Join for each S under the same 2644 procedures discussed in Section 3.17.1. Once the (S,G) tree is 2645 established, the listeners can send (S, G) Prune messages to R so 2646 that multicast packets for group G sourced by S will only be 2647 delivered via the (S, G) tree and not from the (*, G) tree rooted at 2648 R. All mobility considerations discussed for SSM apply. 2650 3.17.3. Bi-Directional PIM (BIDIR-PIM) 2652 Bi-Directional PIM (BIDIR-PIM) [RFC5015] provides an alternate 2653 approach to ASM that treats the Rendezvous Point (RP) as a Designated 2654 Forwarder (DF). Further considerations for BIDIR-PIM are out of 2655 scope. 2657 3.18. Operation over Multiple OMNI Links 2659 An AERO Client can connect to multiple OMNI links the same as for any 2660 data link service. In that case, the Client maintains a distinct 2661 OMNI interface for each link, e.g., 'omni0' for the first link, 2662 'omni1' for the second, 'omni2' for the third, etc. Each OMNI link 2663 would include its own distinct set of Bridges, Servers and Proxys, 2664 thereby providing redundancy in case of failures. 2666 The Bridges, Servers and Proxys on each OMNI link can assign AERO and 2667 ULAs that use the same or different numberings from those on other 2668 links. Since the links are mutually independent there is no 2669 requirement for avoiding inter-link address duplication, e.g., the 2670 same LLA such as fe80::1000 could be used to number distinct nodes 2671 that connect to different OMNI links. 2673 Each OMNI link could utilize the same or different ANET connections. 2674 The links can be distinguished at the link-layer via the SRT prefix 2675 in a similar fashion as for Virtual Local Area Network (VLAN) tagging 2676 (e.g., IEEE 802.1Q) and/or through assignment of distinct sets of 2677 MSPs on each link. This gives rise to the opportunity for supporting 2678 multiple redundant networked paths, where each VLAN is distinguished 2679 by a different SRT color (see: Section 3.2.5). In particular, the 2680 Client can tag its RS messages with the appropriate label to cause 2681 the network to select the desired VLAN. 2683 The Client's IP layer can select the outgoing OMNI interface 2684 appropriate for a given traffic profile while (in the reverse 2685 direction) correspondent nodes must have some way of steering their 2686 packets destined to a target via the correct OMNI link. 2688 In a first alternative, if each OMNI link services different MSPs, 2689 then the Client can receive a distinct MNP from each of the links. 2690 IP routing will therefore assure that the correct Red/Green/Blue/etc. 2691 network is used for both outbound and inbound traffic. This can be 2692 accomplished using existing technologies and approaches, and without 2693 requiring any special supporting code in correspondent nodes or 2694 Bridges. 2696 In a second alternative, if each OMNI link services the same MSP(s) 2697 then each link could assign a distinct "OMNI link Anycast" address 2698 that is configured by all Bridges on the link. Correspondent nodes 2699 can then perform Segment Routing to select the correct SRT, which 2700 will then direct the packet over multiple hops to the target. 2702 3.19. DNS Considerations 2704 AERO Client MNs and INET correspondent nodes consult the Domain Name 2705 System (DNS) the same as for any Internetworking node. When 2706 correspondent nodes and Client MNs use different IP protocol versions 2707 (e.g., IPv4 correspondents and IPv6 MNs), the INET DNS must maintain 2708 A records for IPv4 address mappings to MNs which must then be 2709 populated in Relay NAT64 mapping caches. In that way, an IPv4 2710 correspondent node can send packets to the IPv4 address mapping of 2711 the target MN, and the Relay will translate the IPv4 header and 2712 destination address into an IPv6 header and IPv6 destination address 2713 of the MN. 2715 When an AERO Client registers with an AERO Server, the Server can 2716 return the address(es) of DNS servers in RDNSS options [RFC6106]. 2718 The DNS server provides the IP addresses of other MNs and 2719 correspondent nodes in AAAA records for IPv6 or A records for IPv4. 2721 3.20. Transition Considerations 2723 SPAN encapsulation ensures that dissimilar INET partitions can be 2724 joined into a single unified OMNI link, even though the partitions 2725 themselves may have differing protocol versions and/or incompatible 2726 addressing plans. However, a commonality can be achieved by 2727 incrementally distributing globally routable (i.e., native) IP 2728 prefixes to eventually reach all nodes (both mobile and fixed) in all 2729 OMNI link segments. This can be accomplished by incrementally 2730 deploying AERO Relays on each INET partition, with each Relay 2731 distributing its MNPs and/or discovering non-MNP prefixes on its INET 2732 links. 2734 This gives rise to the opportunity to eventually distribute native IP 2735 addresses to all nodes, and to present a unified OMNI link view even 2736 if the INET partitions remain in their current protocol and 2737 addressing plans. In that way, the OMNI link can serve the dual 2738 purpose of providing a mobility/multilink service and a transition 2739 service. Or, if an INET partition is transitioned to a native IP 2740 protocol version and addressing scheme that is compatible with the 2741 OMNI link MNP-based addressing scheme, the partition and OMNI link 2742 can be joined by Relays. 2744 Relays that connect INETs/EUNs with dissimilar IP protocol versions 2745 may need to employ a network address and protocol translation 2746 function such as NAT64[RFC6146]. 2748 3.21. Detecting and Reacting to Server and Bridge Failures 2750 In environments where rapid failure recovery is required, Servers and 2751 Bridges SHOULD use Bidirectional Forwarding Detection (BFD) 2752 [RFC5880]. Nodes that use BFD can quickly detect and react to 2753 failures so that cached information is re-established through 2754 alternate nodes. BFD control messaging is carried only over well- 2755 connected ground domain networks (i.e., and not low-end radio links) 2756 and can therefore be tuned for rapid response. 2758 Servers and Bridges maintain BFD sessions in parallel with their BGP 2759 peerings. If a Server or Bridge fails, BGP peers will quickly re- 2760 establish routes through alternate paths the same as for common BGP 2761 deployments. Similarly, Proxys maintain BFD sessions with their 2762 associated Bridges even though they do not establish BGP peerings 2763 with them. 2765 Proxys SHOULD use proactive NUD for Servers for which there are 2766 currently active ANET Clients in a manner that parallels BFD, i.e., 2767 by sending unicast NS messages in rapid succession to receive 2768 solicited NA messages. When the Proxy is also sending RS messages on 2769 behalf of ANET Clients, the RS/RA messaging can be considered as 2770 equivalent hints of forward progress. This means that the Proxy need 2771 not also send a periodic NS if it has already sent an RS within the 2772 same period. If a Server fails, the Proxy will cease to receive 2773 advertisements and can quickly inform Clients of the outage by 2774 sending multicast RA messages on the ANET interface. 2776 The Proxy sends multicast RA messages with source address set to the 2777 Server's address, destination address set to (link-local) All-Nodes 2778 multicast, and Router Lifetime set to 0. The Proxy SHOULD send 2779 MAX_FINAL_RTR_ADVERTISEMENTS RA messages separated by small delays 2780 [RFC4861]. Any Clients on the ANET interface that have been using 2781 the (now defunct) Server will receive the RA messages and associate 2782 with a new Server. 2784 3.22. AERO Clients on the Open Internet 2786 AERO Clients that connect to the open Internet via INET interfaces 2787 can establish a VPN or direct link to securely connect to a Server in 2788 a "tethered" arrangement with all of the Client's traffic transiting 2789 the Server. Alternatively, the Client can associate with an INET 2790 Server using UDP/IP encapsulation and asymmetric securing services as 2791 discussed in the following sections. 2793 When a Client's OMNI interface enables an INET underlying interface, 2794 it first determines whether the interface is likely to be behind a 2795 NAT. For IPv4, the Client assumes it is on the open Internet if the 2796 INET address is not a special-use IPv4 address per [RFC3330]. 2797 Similarly for IPv6, the Client assumes it is on the open Internet if 2798 the INET address is not a link-local [RFC4291] or unique-local 2799 [RFC4193] IPv6 address. 2801 The Client then prepares a UDP/IP-encapsulated RS message with IPv6 2802 source address set to its LLA, with IPv6 destination set to (link- 2803 local) All-Routers multicast and with an OMNI option with underlying 2804 interface parameters. If the Client believes that it is on the open 2805 Internet, it SHOULD also include an SLLAO set according to the 2806 address used for INET encapsulation (otherwise, it MAY omit the 2807 SLLAO). If the underlying address is IPv4, the Client includes the 2808 Port Number and IPv4 address written in obfuscated form [RFC4380] as 2809 discussed in Section 3.3. If the underlying interface address is 2810 IPv6, the Client instead includes the Port Number and IPv6 address in 2811 obfuscated form. The Client finally includes an Authentication 2812 option per [RFC4380] to provide message authentication, sets the UDP/ 2813 IP source to its INET address and UDP port, sets the UDP/IP 2814 destination to the Server's INET address and the AERO service port 2815 number (8060), then sends the message to the Server. 2817 When the Server receives the RS, it authenticates the message and 2818 registers the Client's MNP and INET interface information according 2819 to the OMNI option parameters. If the RS message includes an SLLAO, 2820 the Server compares the encapsulation IP address and UDP port number 2821 with the (unobfuscated) SLLAO values. If the values are the same, 2822 the Server caches the Client's information as "INET" addresses 2823 meaning that the Client is likely to accept direct messages without 2824 requiring NAT traversal exchanges. If the values are different (or, 2825 if there was no SLLAO) the Server instead caches the Client's 2826 information as "NAT" addresses meaning that NAT traversal exchanges 2827 may be necessary. 2829 The Server then returns an RA message with IPv6 source and 2830 destination set corresponding to the addresses in the RS, and with an 2831 Authentication option per [RFC4380]. For IPv4, the Server also 2832 includes an Origin option per [RFC4380] with the mapped and 2833 obfuscated Port Number and IPv4 address observed in the encapsulation 2834 headers. For IPv6, the Server instead includes an IPv6 Origin option 2835 per Figure 7 with the mapped and obfuscated observed Port Number and 2836 IPv6 address (note that the value 0x02 in the second octet 2837 differentiates from other [RFC4380] option types). 2839 +--------+--------+-----------------+ 2840 | 0x00 | 0x02 | Origin port # | 2841 +--------+--------+-----------------+ 2842 ~ Origin IPv6 address ~ 2843 +-----------------------------------+ 2845 Figure 7: IPv6 Origin Option 2847 When the Client receives the RA message, it compares the mapped Port 2848 Number and IP address from the Origin option with its own address. 2849 If the addresses are the same, the Client assumes the open Internet / 2850 Cone NAT principle; if the addresses are different, the Client 2851 instead assumes that further qualification procedures are necessary 2852 to detect the type of NAT and proceeds according to standard 2853 [RFC4380] procedures. 2855 After the Client has registered its INET interfaces in such RS/RA 2856 exchanges it sends periodic RS messages to receive fresh RA messages 2857 before the Router Lifetime received on each INET interface expires. 2858 The Client also maintains default routes via its Servers, i.e., the 2859 same as described in earlier sections. 2861 When the Client sends messages to target IP addresses, it also 2862 invokes route optimization per Section 3.14 using IPv6 ND address 2863 resolution messaging. The Client sends the NS(AR) message to the 2864 Server wrapped in a UDP/IP header with an Authentication option with 2865 the NS source address set to the Client's LLA and destination address 2866 set to the target solicited node multicast address. The Server 2867 authenticates the message and sends a corresponding NS(AR) message 2868 over the spanning tree the same as if it were the ROS, but with the 2869 SPAN source address set to the Server's ULA and destination set to 2870 the ULA of the target. When the ROR receives the NS(AR), it adds the 2871 Server's ULA and Client's LLA to the target's Report List, and 2872 returns an NA with OMNI and TLLAO information for the target. The 2873 Server then returns a UDP/IP encapsulated NA message with an 2874 Authentication option to the Client. 2876 Following route optimization, for targets in the same OMNI link 2877 segment if the target's TLLAO addresss is on the open INET, the 2878 Client forwards data packets directly to the target INET address. If 2879 the target's TLLAO address is behind a NAT, the Client first 2880 establishes NAT state for the Link Layer Address using the "bubble" 2881 mechanisms specified in [RFC6081][RFC4380]. The Client continues to 2882 send data packets via its Server until NAT state is populated, then 2883 begins forwarding packets via the direct path through the NAT to the 2884 target. For targets in different OMNI link segments, the Client 2885 inserts an SRH and forwards data packets to the Bridge that returned 2886 the NA message. 2888 The ROR may return uNAs via the Server if the target moves, and the 2889 Server will send corresponding Authentication-protected uNAs to the 2890 Client. The Client can also send "loopback" NS(NUD) messages to test 2891 forward path reachability even though there is no security 2892 association between the Client and the target. 2894 The Client sends UDP/IP encapsulated IPv6 packets no larger than 1280 2895 bytes in one piece. In order to accommodate larger IPv6 packets (up 2896 to the OMNI interface MTU), the Client inserts a SPAN header with 2897 source set to its own ULA and destination set to the ULA of the 2898 target and uses IPv6 fragmentation according to Section 3.9. The 2899 Client then encapsulates each fragment in a UDP/IP header and sends 2900 the fragments to the next hop. 2902 3.22.1. Use of SEND and CGA 2904 In some environments, use of the [RFC4380] Authentication option 2905 alone may be sufficient for assuring IPv6 ND message authentication 2906 between Clients and Servers. When additional protection is 2907 necessary, nodes should employ SEcure Neighbor Discovery (SEND) 2908 [RFC3971] with Cryptographically-Generated Addresses (CGA) [RFC3972]. 2910 When SEND/CGA are used, the Client prepares RS messages with its 2911 link-local CGA as the IPv6 source and (link-local) All-Routers 2912 multicast as the IPv6 Destination, includes any SEND options and 2913 wraps the message in a SPAN header. The Client sets the SPAN source 2914 address to its own ULA and sets the SPAN destination address to 2915 (site-local) All-Routers multicast. The Client then wraps the RS 2916 message in UDP/IP headers according to [RFC4380] and sends the 2917 message to the Server. 2919 When the Server receives the message, it first verifies the 2920 Authentication option (if present) then uses the SPAN source address 2921 to determine the MNP of the Client. The Server then processes the 2922 SEND options to authenticate the RS message and prepares an RA 2923 message response. The Server prepares the RA with its own link-local 2924 CGA as the IPv6 source and the CGA of the Client as the IPv6 2925 destination, includes any SEND options and wraps the message in a 2926 SPAN header. The Server sets the SPAN source address to its own ULA 2927 and sets the SPAN destination address to the Client's ULA. The 2928 Server then wraps the RA message in UDP/IP headers according to 2929 [RFC4380] and sends the message to the Client. Thereafter, the 2930 Client/Server send additional RS/RA messages to maintain their 2931 association and any NAT state. 2933 The Client and Server also may exchange NS/NA messages using their 2934 own CGA as the source and with SPAN encapsulation as above. When a 2935 Client sends an NS(AR), it sets the IPv6 source to its CGA and sets 2936 the IPv6 destination to the Solicited-Node Multicast address of the 2937 target. The Client then wraps the message in a SPAN header with its 2938 own ULA as the source and the ULA of the target as the destination 2939 and sends it to the Server. The Server authenticates the message, 2940 then changes the IPv6 source address to the Client's LLA, removes the 2941 SEND options, and sends a corresponding NS(AR) into the spanning 2942 tree. When the Server receives the corresponding SPAN-encapsulated 2943 NA, it changes the IPv6 destination address to the Client's CGA, 2944 inserts SEND options, then wraps the message in UDP/IP headers and 2945 sends it to the Client. 2947 When a Client sends a uNA, it sets the IPv6 source address to its own 2948 CGA and sets the IPv6 destination address to (link-local) All-Nodes 2949 multicast, includes SEND options, wraps the message in SPAN and UDP/ 2950 IP headers and sends the message to the Server. The Server 2951 authenticates the message, then changes the IPv6 address to the 2952 Client's LLA, removes the SEND options and forwards the message the 2953 same as discussed in Section 3.16.1. In the reverse direction, when 2954 the Server forwards a uNA to the Client, it changes the IPv6 address 2955 to its own CGA and inserts SEND options then forwards the message to 2956 the Client. 2958 When a Client sends an NS(NUD), it sets both the IPv6 source and 2959 destination address to its own LLA, wraps the message in a SPAN 2960 header and UDP/IP headers, then sends the message directly to the 2961 peer which will loop the message back. In this case alone, the 2962 Client does not use the Server as a trust broker for forwarding the 2963 ND message. 2965 3.23. Time-Varying MNPs 2967 In some use cases, it is desirable, beneficial and efficient for the 2968 Client to receive a constant MNP that travels with the Client 2969 wherever it moves. For example, this would allow air traffic 2970 controllers to easily track aircraft, etc. In other cases, however 2971 (e.g., intelligent transportation systems), the MN may be willing to 2972 sacrifice a modicum of efficiency in order to have time-varying MNPs 2973 that can be changed every so often to defeat adversarial tracking. 2975 The DHCPv6-PD service offers a way for Clients that desire time- 2976 varying MNPs to obtain short-lived prefixes (e.g., on the order of a 2977 small number of minutes). In that case, the identity of the Client 2978 would not be bound to the MNP but rather the Client's identity would 2979 be bound to the DHCPv6 Device Unique Identifier (DUID) and used as 2980 the seed for Prefix Delegation. The Client would then be obligated 2981 to renumber its internal networks whenever its MNP (and therefore 2982 also its LLA) changes. This should not present a challenge for 2983 Clients with automated network renumbering services, however presents 2984 limits for the durations of ongoing sessions that would prefer to use 2985 a constant address. 2987 4. Implementation Status 2989 An AERO implementation based on OpenVPN (https://openvpn.net/) was 2990 announced on the v6ops mailing list on January 10, 2018 and an 2991 initial public release of the AERO proof-of-concept source code was 2992 announced on the intarea mailing list on August 21, 2015. 2994 As of 4/1/2020, more recent updated implementations are under 2995 internal development and testing with plans to release in the near 2996 future. 2998 5. IANA Considerations 3000 The IANA has assigned a 4-octet Private Enterprise Number "45282" for 3001 AERO in the "enterprise-numbers" registry. 3003 The IANA has assigned the UDP port number "8060" for an earlier 3004 experimental version of AERO [RFC6706]. This document obsoletes 3005 [RFC6706] and claims the UDP port number "8060" for all future use. 3007 The IANA is instructed to assign a new type value TBD in the Segment 3008 Routing Header TLV registry [RFC8754]. 3010 No further IANA actions are required. 3012 6. Security Considerations 3014 AERO Bridges configure secured tunnels with AERO Servers, Realys and 3015 Proxys within their local OMNI link segments. Applicable secured 3016 tunnel alternatives include IPsec [RFC4301], TLS/SSL [RFC8446], DTLS 3017 [RFC6347], WireGuard, etc. The AERO Bridges of all OMNI link 3018 segments in turn configure secured tunnels for their neighboring AERO 3019 Bridges in a spanning tree topology. Therefore, control messages 3020 exchanged between any pair of OMNI link neighbors on the spanning 3021 tree are already secured. 3023 AERO Servers, Relays and Proxys targeted by a route optimization may 3024 also receive data packets directly from arbitrary nodes in INET 3025 partitions instead of via the spanning tree. For INET partitions 3026 that apply effective ingress filtering to defeat source address 3027 spoofing, the simple data origin authentication procedures in 3028 Section 3.8 can be applied. 3030 For INET partitions that require strong security in the data plane, 3031 two options for securing communications include 1) disable route 3032 optimization so that all traffic is conveyed over secured tunnels, or 3033 2) enable on-demand secure tunnel creation between INET partition 3034 neighbors. Option 1) would result in longer routes than necessary 3035 and traffic concentration on critical infrastructure elements. 3036 Option 2) could be coordinated by establishing a secured tunnel on- 3037 demand instead of performing an NS/NA exchange in the route 3038 optimization procedures. Procedures for establishing on-demand 3039 secured tunnels are out of scope. 3041 AERO Clients that connect to secured ANETs need not apply security to 3042 their ND messages, since the messages will be intercepted by a 3043 perimeter Proxy that applies security on its INET-facing interface as 3044 part of the spanning tree (see above). AERO Clients connected to the 3045 open INET can use symmetric network and/or transport layer security 3046 services such as VPNs or can by some other means establish a direct 3047 link. When a VPN or direct link may be impractical, however, an 3048 asymmetric security service such as SEcure Neighbor Discovery (SEND) 3049 [RFC3971] with Cryptographically Generated Addresses (CGAs) [RFC3972] 3050 and/or the Authentication option [RFC4380] can be applied. 3052 Application endpoints SHOULD use application-layer security services 3053 such as TLS/SSL, DTLS or SSH [RFC4251] to assure the same level of 3054 protection as for critical secured Internet services. AERO Clients 3055 that require host-based VPN services SHOULD use symmetric network 3056 and/or transport layer security services such as IPsec, TLS/SSL, 3057 DTLS, etc. AERO Proxys and Servers can also provide a network-based 3058 VPN service on behalf of the Client, e.g., if the Client is located 3059 within a secured enclave and cannot establish a VPN on its own 3060 behalf. 3062 AERO Servers and Bridges present targets for traffic amplification 3063 Denial of Service (DoS) attacks. This concern is no different than 3064 for widely-deployed VPN security gateways in the Internet, where 3065 attackers could send spoofed packets to the gateways at high data 3066 rates. This can be mitigated by connecting Servers and Bridges over 3067 dedicated links with no connections to the Internet and/or when 3068 connections to the Internet are only permitted through well-managed 3069 firewalls. Traffic amplification DoS attacks can also target an AERO 3070 Client's low data rate links. This is a concern not only for Clients 3071 located on the open Internet but also for Clients in secured 3072 enclaves. AERO Servers and Proxys can institute rate limits that 3073 protect Clients from receiving packet floods that could DoS low data 3074 rate links. 3076 AERO Relays must implement ingress filtering to avoid a spoofing 3077 attack in which spurious messages with ULA addresses are injected 3078 into an OMNI link from an outside attacker. AERO Clients MUST ensure 3079 that their connectivity is not used by unauthorized nodes on their 3080 EUNs to gain access to a protected network, i.e., AERO Clients that 3081 act as routers MUST NOT provide routing services for unauthorized 3082 nodes. (This concern is no different than for ordinary hosts that 3083 receive an IP address delegation but then "share" the address with 3084 other nodes via some form of Internet connection sharing such as 3085 tethering.) 3087 The MAP list MUST be well-managed and secured from unauthorized 3088 tampering, even though the list contains only public information. 3089 The MAP list can be conveyed to the Client in a similar fashion as in 3090 [RFC5214] (e.g., through layer 2 data link login messaging, secure 3091 upload of a static file, DNS lookups, etc.). 3093 Although public domain and commercial SEND implementations exist, 3094 concerns regarding the strength of the cryptographic hash algorithm 3095 have been documented [RFC6273] [RFC4982]. 3097 SRH authentication facilities are specified in [RFC8754]. 3099 Security considerations for accepting link-layer ICMP messages and 3100 reflected packets are discussed throughout the document. 3102 Security considerations for IPv6 fragmentation and reassembly are 3103 discussed in [I-D.templin-6man-omni-interface]. 3105 7. Acknowledgements 3107 Discussions in the IETF, aviation standards communities and private 3108 exchanges helped shape some of the concepts in this work. 3109 Individuals who contributed insights include Mikael Abrahamsson, Mark 3110 Andrews, Fred Baker, Bob Braden, Stewart Bryant, Brian Carpenter, 3111 Wojciech Dec, Pavel Drasil, Ralph Droms, Adrian Farrel, Nick Green, 3112 Sri Gundavelli, Brian Haberman, Bernhard Haindl, Joel Halpern, Tom 3113 Herbert, Sascha Hlusiak, Lee Howard, Zdenek Jaron, Andre Kostur, 3114 Hubert Kuenig, Ted Lemon, Andy Malis, Satoru Matsushima, Tomek 3115 Mrugalski, Madhu Niraula, Alexandru Petrescu, Behcet Saikaya, Michal 3116 Skorepa, Joe Touch, Bernie Volz, Ryuji Wakikawa, Tony Whyman, Lloyd 3117 Wood and James Woodyatt. Members of the IESG also provided valuable 3118 input during their review process that greatly improved the document. 3119 Special thanks go to Stewart Bryant, Joel Halpern and Brian Haberman 3120 for their shepherding guidance during the publication of the AERO 3121 first edition. 3123 This work has further been encouraged and supported by Boeing 3124 colleagues including Kyle Bae, M. Wayne Benson, Dave Bernhardt, Cam 3125 Brodie, John Bush, Balaguruna Chidambaram, Irene Chin, Bruce Cornish, 3126 Claudiu Danilov, Don Dillenburg, Joe Dudkowski, Wen Fang, Samad 3127 Farooqui, Anthony Gregory, Jeff Holland, Seth Jahne, Brian Jaury, 3128 Greg Kimberly, Ed King, Madhuri Madhava Badgandi, Laurel Matthew, 3129 Gene MacLean III, Rob Muszkiewicz, Sean O'Sullivan, Vijay 3130 Rajagopalan, Greg Saccone, Rod Santiago, Kent Shuey, Brian Skeen, 3131 Mike Slane, Carrie Spiker, Katie Tran, Brendan Williams, Amelia 3132 Wilson, Julie Wulff, Yueli Yang, Eric Yeh and other members of the 3133 Boeing mobility, networking and autonomy teams. Kyle Bae, Wayne 3134 Benson, Katie Tran and Eric Yeh are especially acknowledged for 3135 implementing the AERO functions as extensions to the public domain 3136 OpenVPN distribution. 3138 Earlier works on NBMA tunneling approaches are found in 3139 [RFC2529][RFC5214][RFC5569]. 3141 Many of the constructs presented in this second edition of AERO are 3142 based on the author's earlier works, including: 3144 o The Internet Routing Overlay Network (IRON) 3145 [RFC6179][I-D.templin-ironbis] 3147 o Virtual Enterprise Traversal (VET) 3148 [RFC5558][I-D.templin-intarea-vet] 3150 o The Subnetwork Encapsulation and Adaptation Layer (SEAL) 3151 [RFC5320][I-D.templin-intarea-seal] 3153 o AERO, First Edition [RFC6706] 3155 Note that these works cite numerous earlier efforts that are not also 3156 cited here due to space limitations. The authors of those earlier 3157 works are acknowledged for their insights. 3159 This work is aligned with the NASA Safe Autonomous Systems Operation 3160 (SASO) program under NASA contract number NNA16BD84C. 3162 This work is aligned with the FAA as per the SE2025 contract number 3163 DTFAWA-15-D-00030. 3165 This work is aligned with the Boeing Commercial Airplanes (BCA) 3166 Internet of Things (IoT) and autonomy programs. 3168 This work is aligned with the Boeing Information Technology (BIT) 3169 MobileNet program. 3171 8. References 3173 8.1. Normative References 3175 [I-D.templin-6man-omni-interface] 3176 Templin, F. and T. Whyman, "Transmission of IPv6 Packets 3177 over Overlay Multilink Network (OMNI) Interfaces", draft- 3178 templin-6man-omni-interface-24 (work in progress), June 3179 2020. 3181 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, 3182 DOI 10.17487/RFC0791, September 1981, 3183 . 3185 [RFC0792] Postel, J., "Internet Control Message Protocol", STD 5, 3186 RFC 792, DOI 10.17487/RFC0792, September 1981, 3187 . 3189 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 3190 Requirement Levels", BCP 14, RFC 2119, 3191 DOI 10.17487/RFC2119, March 1997, 3192 . 3194 [RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in 3195 IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473, 3196 December 1998, . 3198 [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black, 3199 "Definition of the Differentiated Services Field (DS 3200 Field) in the IPv4 and IPv6 Headers", RFC 2474, 3201 DOI 10.17487/RFC2474, December 1998, 3202 . 3204 [RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander, 3205 "SEcure Neighbor Discovery (SEND)", RFC 3971, 3206 DOI 10.17487/RFC3971, March 2005, 3207 . 3209 [RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)", 3210 RFC 3972, DOI 10.17487/RFC3972, March 2005, 3211 . 3213 [RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and 3214 More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191, 3215 November 2005, . 3217 [RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast 3218 Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005, 3219 . 3221 [RFC4380] Huitema, C., "Teredo: Tunneling IPv6 over UDP through 3222 Network Address Translations (NATs)", RFC 4380, 3223 DOI 10.17487/RFC4380, February 2006, 3224 . 3226 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 3227 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 3228 DOI 10.17487/RFC4861, September 2007, 3229 . 3231 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 3232 Address Autoconfiguration", RFC 4862, 3233 DOI 10.17487/RFC4862, September 2007, 3234 . 3236 [RFC5175] Haberman, B., Ed. and R. Hinden, "IPv6 Router 3237 Advertisement Flags Option", RFC 5175, 3238 DOI 10.17487/RFC5175, March 2008, 3239 . 3241 [RFC6081] Thaler, D., "Teredo Extensions", RFC 6081, 3242 DOI 10.17487/RFC6081, January 2011, 3243 . 3245 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 3246 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 3247 May 2017, . 3249 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 3250 (IPv6) Specification", STD 86, RFC 8200, 3251 DOI 10.17487/RFC8200, July 2017, 3252 . 3254 [RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A., 3255 Richardson, M., Jiang, S., Lemon, T., and T. Winters, 3256 "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", 3257 RFC 8415, DOI 10.17487/RFC8415, November 2018, 3258 . 3260 8.2. Informative References 3262 [BGP] Huston, G., "BGP in 2015, http://potaroo.net", January 3263 2016. 3265 [I-D.bonica-6man-comp-rtg-hdr] 3266 Bonica, R., Kamite, Y., Niwa, T., Alston, A., and L. 3267 Jalil, "The IPv6 Compact Routing Header (CRH)", draft- 3268 bonica-6man-comp-rtg-hdr-22 (work in progress), May 2020. 3270 [I-D.bonica-6man-crh-helper-opt] 3271 Li, X., Bao, C., Ruan, E., and R. Bonica, "Compressed 3272 Routing Header (CRH) Helper Option", draft-bonica-6man- 3273 crh-helper-opt-01 (work in progress), May 2020. 3275 [I-D.ietf-dmm-distributed-mobility-anchoring] 3276 Chan, A., Wei, X., Lee, J., Jeon, S., and C. Bernardos, 3277 "Distributed Mobility Anchoring", draft-ietf-dmm- 3278 distributed-mobility-anchoring-15 (work in progress), 3279 March 2020. 3281 [I-D.ietf-intarea-frag-fragile] 3282 Bonica, R., Baker, F., Huston, G., Hinden, R., Troan, O., 3283 and F. Gont, "IP Fragmentation Considered Fragile", draft- 3284 ietf-intarea-frag-fragile-17 (work in progress), September 3285 2019. 3287 [I-D.ietf-intarea-gue] 3288 Herbert, T., Yong, L., and O. Zia, "Generic UDP 3289 Encapsulation", draft-ietf-intarea-gue-09 (work in 3290 progress), October 2019. 3292 [I-D.ietf-intarea-gue-extensions] 3293 Herbert, T., Yong, L., and F. Templin, "Extensions for 3294 Generic UDP Encapsulation", draft-ietf-intarea-gue- 3295 extensions-06 (work in progress), March 2019. 3297 [I-D.ietf-intarea-tunnels] 3298 Touch, J. and M. Townsley, "IP Tunnels in the Internet 3299 Architecture", draft-ietf-intarea-tunnels-10 (work in 3300 progress), September 2019. 3302 [I-D.ietf-rtgwg-atn-bgp] 3303 Templin, F., Saccone, G., Dawra, G., Lindem, A., and V. 3304 Moreno, "A Simple BGP-based Mobile Routing System for the 3305 Aeronautical Telecommunications Network", draft-ietf- 3306 rtgwg-atn-bgp-05 (work in progress), January 2020. 3308 [I-D.templin-6man-dhcpv6-ndopt] 3309 Templin, F., "A Unified Stateful/Stateless Configuration 3310 Service for IPv6", draft-templin-6man-dhcpv6-ndopt-09 3311 (work in progress), January 2020. 3313 [I-D.templin-intarea-grefrag] 3314 Templin, F., "GRE Tunnel Level Fragmentation", draft- 3315 templin-intarea-grefrag-04 (work in progress), July 2016. 3317 [I-D.templin-intarea-seal] 3318 Templin, F., "The Subnetwork Encapsulation and Adaptation 3319 Layer (SEAL)", draft-templin-intarea-seal-68 (work in 3320 progress), January 2014. 3322 [I-D.templin-intarea-vet] 3323 Templin, F., "Virtual Enterprise Traversal (VET)", draft- 3324 templin-intarea-vet-40 (work in progress), May 2013. 3326 [I-D.templin-ironbis] 3327 Templin, F., "The Interior Routing Overlay Network 3328 (IRON)", draft-templin-ironbis-16 (work in progress), 3329 March 2014. 3331 [I-D.templin-v6ops-pdhost] 3332 Templin, F., "IPv6 Prefix Delegation and Multi-Addressing 3333 Models", draft-templin-v6ops-pdhost-25 (work in progress), 3334 January 2020. 3336 [OVPN] OpenVPN, O., "http://openvpn.net", October 2016. 3338 [RFC1035] Mockapetris, P., "Domain names - implementation and 3339 specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, 3340 November 1987, . 3342 [RFC1122] Braden, R., Ed., "Requirements for Internet Hosts - 3343 Communication Layers", STD 3, RFC 1122, 3344 DOI 10.17487/RFC1122, October 1989, 3345 . 3347 [RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191, 3348 DOI 10.17487/RFC1191, November 1990, 3349 . 3351 [RFC1812] Baker, F., Ed., "Requirements for IP Version 4 Routers", 3352 RFC 1812, DOI 10.17487/RFC1812, June 1995, 3353 . 3355 [RFC2003] Perkins, C., "IP Encapsulation within IP", RFC 2003, 3356 DOI 10.17487/RFC2003, October 1996, 3357 . 3359 [RFC2236] Fenner, W., "Internet Group Management Protocol, Version 3360 2", RFC 2236, DOI 10.17487/RFC2236, November 1997, 3361 . 3363 [RFC2492] Armitage, G., Schulter, P., and M. Jork, "IPv6 over ATM 3364 Networks", RFC 2492, DOI 10.17487/RFC2492, January 1999, 3365 . 3367 [RFC2529] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4 3368 Domains without Explicit Tunnels", RFC 2529, 3369 DOI 10.17487/RFC2529, March 1999, 3370 . 3372 [RFC2764] Gleeson, B., Lin, A., Heinanen, J., Armitage, G., and A. 3373 Malis, "A Framework for IP Based Virtual Private 3374 Networks", RFC 2764, DOI 10.17487/RFC2764, February 2000, 3375 . 3377 [RFC2784] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P. 3378 Traina, "Generic Routing Encapsulation (GRE)", RFC 2784, 3379 DOI 10.17487/RFC2784, March 2000, 3380 . 3382 [RFC2890] Dommety, G., "Key and Sequence Number Extensions to GRE", 3383 RFC 2890, DOI 10.17487/RFC2890, September 2000, 3384 . 3386 [RFC2923] Lahey, K., "TCP Problems with Path MTU Discovery", 3387 RFC 2923, DOI 10.17487/RFC2923, September 2000, 3388 . 3390 [RFC2983] Black, D., "Differentiated Services and Tunnels", 3391 RFC 2983, DOI 10.17487/RFC2983, October 2000, 3392 . 3394 [RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition 3395 of Explicit Congestion Notification (ECN) to IP", 3396 RFC 3168, DOI 10.17487/RFC3168, September 2001, 3397 . 3399 [RFC3330] IANA, "Special-Use IPv4 Addresses", RFC 3330, 3400 DOI 10.17487/RFC3330, September 2002, 3401 . 3403 [RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener 3404 Discovery Version 2 (MLDv2) for IPv6", RFC 3810, 3405 DOI 10.17487/RFC3810, June 2004, 3406 . 3408 [RFC3819] Karn, P., Ed., Bormann, C., Fairhurst, G., Grossman, D., 3409 Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J., and L. 3410 Wood, "Advice for Internet Subnetwork Designers", BCP 89, 3411 RFC 3819, DOI 10.17487/RFC3819, July 2004, 3412 . 3414 [RFC4213] Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms 3415 for IPv6 Hosts and Routers", RFC 4213, 3416 DOI 10.17487/RFC4213, October 2005, 3417 . 3419 [RFC4251] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH) 3420 Protocol Architecture", RFC 4251, DOI 10.17487/RFC4251, 3421 January 2006, . 3423 [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A 3424 Border Gateway Protocol 4 (BGP-4)", RFC 4271, 3425 DOI 10.17487/RFC4271, January 2006, 3426 . 3428 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 3429 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 3430 2006, . 3432 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 3433 Internet Protocol", RFC 4301, DOI 10.17487/RFC4301, 3434 December 2005, . 3436 [RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery 3437 Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April 3438 2006, . 3440 [RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet 3441 Control Message Protocol (ICMPv6) for the Internet 3442 Protocol Version 6 (IPv6) Specification", STD 89, 3443 RFC 4443, DOI 10.17487/RFC4443, March 2006, 3444 . 3446 [RFC4511] Sermersheim, J., Ed., "Lightweight Directory Access 3447 Protocol (LDAP): The Protocol", RFC 4511, 3448 DOI 10.17487/RFC4511, June 2006, 3449 . 3451 [RFC4541] Christensen, M., Kimball, K., and F. Solensky, 3452 "Considerations for Internet Group Management Protocol 3453 (IGMP) and Multicast Listener Discovery (MLD) Snooping 3454 Switches", RFC 4541, DOI 10.17487/RFC4541, May 2006, 3455 . 3457 [RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick, 3458 "Internet Group Management Protocol (IGMP) / Multicast 3459 Listener Discovery (MLD)-Based Multicast Forwarding 3460 ("IGMP/MLD Proxying")", RFC 4605, DOI 10.17487/RFC4605, 3461 August 2006, . 3463 [RFC4607] Holbrook, H. and B. Cain, "Source-Specific Multicast for 3464 IP", RFC 4607, DOI 10.17487/RFC4607, August 2006, 3465 . 3467 [RFC4963] Heffner, J., Mathis, M., and B. Chandler, "IPv4 Reassembly 3468 Errors at High Data Rates", RFC 4963, 3469 DOI 10.17487/RFC4963, July 2007, 3470 . 3472 [RFC4982] Bagnulo, M. and J. Arkko, "Support for Multiple Hash 3473 Algorithms in Cryptographically Generated Addresses 3474 (CGAs)", RFC 4982, DOI 10.17487/RFC4982, July 2007, 3475 . 3477 [RFC5015] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano, 3478 "Bidirectional Protocol Independent Multicast (BIDIR- 3479 PIM)", RFC 5015, DOI 10.17487/RFC5015, October 2007, 3480 . 3482 [RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site 3483 Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214, 3484 DOI 10.17487/RFC5214, March 2008, 3485 . 3487 [RFC5320] Templin, F., Ed., "The Subnetwork Encapsulation and 3488 Adaptation Layer (SEAL)", RFC 5320, DOI 10.17487/RFC5320, 3489 February 2010, . 3491 [RFC5522] Eddy, W., Ivancic, W., and T. Davis, "Network Mobility 3492 Route Optimization Requirements for Operational Use in 3493 Aeronautics and Space Exploration Mobile Networks", 3494 RFC 5522, DOI 10.17487/RFC5522, October 2009, 3495 . 3497 [RFC5558] Templin, F., Ed., "Virtual Enterprise Traversal (VET)", 3498 RFC 5558, DOI 10.17487/RFC5558, February 2010, 3499 . 3501 [RFC5569] Despres, R., "IPv6 Rapid Deployment on IPv4 3502 Infrastructures (6rd)", RFC 5569, DOI 10.17487/RFC5569, 3503 January 2010, . 3505 [RFC5871] Arkko, J. and S. Bradner, "IANA Allocation Guidelines for 3506 the IPv6 Routing Header", RFC 5871, DOI 10.17487/RFC5871, 3507 May 2010, . 3509 [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 3510 (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, 3511 . 3513 [RFC5991] Thaler, D., Krishnan, S., and J. Hoagland, "Teredo 3514 Security Updates", RFC 5991, DOI 10.17487/RFC5991, 3515 September 2010, . 3517 [RFC6106] Jeong, J., Park, S., Beloeil, L., and S. Madanapalli, 3518 "IPv6 Router Advertisement Options for DNS Configuration", 3519 RFC 6106, DOI 10.17487/RFC6106, November 2010, 3520 . 3522 [RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful 3523 NAT64: Network Address and Protocol Translation from IPv6 3524 Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146, 3525 April 2011, . 3527 [RFC6179] Templin, F., Ed., "The Internet Routing Overlay Network 3528 (IRON)", RFC 6179, DOI 10.17487/RFC6179, March 2011, 3529 . 3531 [RFC6221] Miles, D., Ed., Ooghe, S., Dec, W., Krishnan, S., and A. 3532 Kavanagh, "Lightweight DHCPv6 Relay Agent", RFC 6221, 3533 DOI 10.17487/RFC6221, May 2011, 3534 . 3536 [RFC6273] Kukec, A., Krishnan, S., and S. Jiang, "The Secure 3537 Neighbor Discovery (SEND) Hash Threat Analysis", RFC 6273, 3538 DOI 10.17487/RFC6273, June 2011, 3539 . 3541 [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer 3542 Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, 3543 January 2012, . 3545 [RFC6438] Carpenter, B. and S. Amante, "Using the IPv6 Flow Label 3546 for Equal Cost Multipath Routing and Link Aggregation in 3547 Tunnels", RFC 6438, DOI 10.17487/RFC6438, November 2011, 3548 . 3550 [RFC6706] Templin, F., Ed., "Asymmetric Extended Route Optimization 3551 (AERO)", RFC 6706, DOI 10.17487/RFC6706, August 2012, 3552 . 3554 [RFC6864] Touch, J., "Updated Specification of the IPv4 ID Field", 3555 RFC 6864, DOI 10.17487/RFC6864, February 2013, 3556 . 3558 [RFC6935] Eubanks, M., Chimento, P., and M. Westerlund, "IPv6 and 3559 UDP Checksums for Tunneled Packets", RFC 6935, 3560 DOI 10.17487/RFC6935, April 2013, 3561 . 3563 [RFC6936] Fairhurst, G. and M. Westerlund, "Applicability Statement 3564 for the Use of IPv6 UDP Datagrams with Zero Checksums", 3565 RFC 6936, DOI 10.17487/RFC6936, April 2013, 3566 . 3568 [RFC7269] Chen, G., Cao, Z., Xie, C., and D. Binet, "NAT64 3569 Deployment Options and Experience", RFC 7269, 3570 DOI 10.17487/RFC7269, June 2014, 3571 . 3573 [RFC7333] Chan, H., Ed., Liu, D., Seite, P., Yokota, H., and J. 3574 Korhonen, "Requirements for Distributed Mobility 3575 Management", RFC 7333, DOI 10.17487/RFC7333, August 2014, 3576 . 3578 [RFC7421] Carpenter, B., Ed., Chown, T., Gont, F., Jiang, S., 3579 Petrescu, A., and A. Yourtchenko, "Analysis of the 64-bit 3580 Boundary in IPv6 Addressing", RFC 7421, 3581 DOI 10.17487/RFC7421, January 2015, 3582 . 3584 [RFC7739] Gont, F., "Security Implications of Predictable Fragment 3585 Identification Values", RFC 7739, DOI 10.17487/RFC7739, 3586 February 2016, . 3588 [RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I., 3589 Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent 3590 Multicast - Sparse Mode (PIM-SM): Protocol Specification 3591 (Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March 3592 2016, . 3594 [RFC8086] Yong, L., Ed., Crabbe, E., Xu, X., and T. Herbert, "GRE- 3595 in-UDP Encapsulation", RFC 8086, DOI 10.17487/RFC8086, 3596 March 2017, . 3598 [RFC8138] Thubert, P., Ed., Bormann, C., Toutain, L., and R. Cragie, 3599 "IPv6 over Low-Power Wireless Personal Area Network 3600 (6LoWPAN) Routing Header", RFC 8138, DOI 10.17487/RFC8138, 3601 April 2017, . 3603 [RFC8201] McCann, J., Deering, S., Mogul, J., and R. Hinden, Ed., 3604 "Path MTU Discovery for IP version 6", STD 87, RFC 8201, 3605 DOI 10.17487/RFC8201, July 2017, 3606 . 3608 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 3609 Decraene, B., Litkowski, S., and R. Shakir, "Segment 3610 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 3611 July 2018, . 3613 [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol 3614 Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, 3615 . 3617 [RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J., 3618 Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header 3619 (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020, 3620 . 3622 Appendix A. Non-Normative Considerations 3624 AERO can be applied to a multitude of Internetworking scenarios, with 3625 each having its own adaptations. The following considerations are 3626 provided as non-normative guidance: 3628 A.1. Implementation Strategies for Route Optimization 3630 Route optimization as discussed in Section 3.14 results in the route 3631 optimization source (ROS) creating an asymmetric neighbor cache entry 3632 for the target neighbor. The neighbor cache entry is maintained for 3633 at most ReachableTime seconds and then deleted unless updated. In 3634 order to refresh the neighbor cache entry lifetime before the 3635 ReachableTime timer expires, the specification requires 3636 implementations to issue a new NS/NA exchange to reset ReachableTime 3637 while data packets are still flowing. However, the decision of when 3638 to initiate a new NS/NA exchange and to perpetuate the process is 3639 left as an implementation detail. 3641 One possible strategy may be to monitor the neighbor cache entry 3642 watching for data packets for (ReachableTime - 5) seconds. If any 3643 data packets have been sent to the neighbor within this timeframe, 3644 then send an NS to receive a new NA. If no data packets have been 3645 sent, wait for 5 additional seconds and send an immediate NS if any 3646 data packets are sent within this "expiration pending" 5 second 3647 window. If no additional data packets are sent within the 5 second 3648 window, delete the neighbor cache entry. 3650 The monitoring of the neighbor data packet traffic therefore becomes 3651 an asymmetric ongoing process during the neighbor cache entry 3652 lifetime. If the neighbor cache entry expires, future data packets 3653 will trigger a new NS/NA exchange while the packets themselves are 3654 delivered over a longer path until route optimization state is re- 3655 established. 3657 A.2. Implicit Mobility Management 3659 OMNI interface neighbors MAY provide a configuration option that 3660 allows them to perform implicit mobility management in which no ND 3661 messaging is used. In that case, the Client only transmits packets 3662 over a single interface at a time, and the neighbor always observes 3663 packets arriving from the Client from the same link-layer source 3664 address. 3666 If the Client's underlying interface address changes (either due to a 3667 readdressing of the original interface or switching to a new 3668 interface) the neighbor immediately updates the neighbor cache entry 3669 for the Client and begins accepting and sending packets according to 3670 the Client's new address. This implicit mobility method applies to 3671 use cases such as cellphones with both WiFi and Cellular interfaces 3672 where only one of the interfaces is active at a given time, and the 3673 Client automatically switches over to the backup interface if the 3674 primary interface fails. 3676 A.3. Direct Underlying Interfaces 3678 When a Client's OMNI interface is configured over a Direct interface, 3679 the neighbor at the other end of the Direct link can receive packets 3680 without any encapsulation. In that case, the Client sends packets 3681 over the Direct link according to QoS preferences. If the Direct 3682 interface has the highest QoS preference, then the Client's IP 3683 packets are transmitted directly to the peer without going through an 3684 ANET/INET. If other interfaces have higher QoS preferences, then the 3685 Client's IP packets are transmitted via a different interface, which 3686 may result in the inclusion of Proxys, Servers and Bridges in the 3687 communications path. Direct interfaces must be tested periodically 3688 for reachability, e.g., via NUD. 3690 A.4. AERO Critical Infrastructure Considerations 3692 AERO Bridges can be either Commercial off-the Shelf (COTS) standard 3693 IP routers or virtual machines in the cloud. Bridges must be 3694 provisioned, supported and managed by the INET administrative 3695 authority, and connected to the Bridges of other INETs via inter- 3696 domain peerings. Cost for purchasing, configuring and managing 3697 Bridges is nominal even for very large OMNI links. 3699 AERO Servers can be standard dedicated server platforms, but most 3700 often will be deployed as virtual machines in the cloud. The only 3701 requirements for Servers are that they can run the AERO user-level 3702 code and have at least one network interface connection to the INET. 3703 As with Bridges, Servers must be provisioned, supported and managed 3704 by the INET administrative authority. Cost for purchasing, 3705 configuring and managing Servers is nominal especially for virtual 3706 Servers hosted in the cloud. 3708 AERO Proxys are most often standard dedicated server platforms with 3709 one network interface connected to the ANET and a second interface 3710 connected to an INET. As with Servers, the only requirements are 3711 that they can run the AERO user-level code and have at least one 3712 interface connection to the INET. Proxys must be provisioned, 3713 supported and managed by the ANET administrative authority. Cost for 3714 purchasing, configuring and managing Proxys is nominal, and borne by 3715 the ANET administrative authority. 3717 AERO Relays can be any dedicated server or COTS router platform 3718 connected to INETs and/or EUNs. The Relay connects to the OMNI link 3719 and engages in eBGP peering with one or more Bridges as a stub AS. 3720 The Relay then injects its MNPs and/or non-MNP prefixes into the BGP 3721 routing system, and provisions the prefixes to its downstream- 3722 attached networks. The Relay can perform ROS/ROR services the same 3723 as for any Server, and can route between the MNP and non-MNP address 3724 spaces. 3726 A.5. AERO Server Failure Implications 3728 AERO Servers may appear as a single point of failure in the 3729 architecture, but such is not the case since all Servers on the link 3730 provide identical services and loss of a Server does not imply 3731 immediate and/or comprehensive communication failures. Although 3732 Clients typically associate with a single Server at a time, Server 3733 failure is quickly detected and conveyed by Bidirectional Forward 3734 Detection (BFD) and/or proactive NUD allowing Clients to migrate to 3735 new Servers. 3737 If a Server fails, ongoing packet forwarding to Clients will continue 3738 by virtue of the asymmetric neighbor cache entries that have already 3739 been established in route optimization sources (ROSs). If a Client 3740 also experiences mobility events at roughly the same time the Server 3741 fails, unsolicited NA messages may be lost but proxy neighbor cache 3742 entries in the DEPARTED state will ensure that packet forwarding to 3743 the Client's new locations will continue for up to DepartTime 3744 seconds. 3746 If a Client is left without a Server for an extended timeframe (e.g., 3747 greater than ReachableTime seconds) then existing asymmetric neighbor 3748 cache entries will eventually expire and both ongoing and new 3749 communications will fail. The original source will continue to 3750 retransmit until the Client has established a new Server 3751 relationship, after which time continuous communications will resume. 3753 Therefore, providing many Servers on the link with high availability 3754 profiles provides resilience against loss of individual Servers and 3755 assurance that Clients can establish new Server relationships quickly 3756 in event of a Server failure. 3758 A.6. AERO Client / Server Architecture 3760 The AERO architectural model is client / server in the control plane, 3761 with route optimization in the data plane. The same as for common 3762 Internet services, the AERO Client discovers the addresses of AERO 3763 Servers and selects one Server to connect to. The AERO service is 3764 analogous to common Internet services such as google.com, yahoo.com, 3765 cnn.com, etc. However, there is only one AERO service for the link 3766 and all Servers provide identical services. 3768 Common Internet services provide differing strategies for advertising 3769 server addresses to clients. The strategy is conveyed through the 3770 DNS resource records returned in response to name resolution queries. 3771 As of January 2020 Internet-based 'nslookup' services were used to 3772 determine the following: 3774 o When a client resolves the domainname "google.com", the DNS always 3775 returns one A record (i.e., an IPv4 address) and one AAAA record 3776 (i.e., an IPv6 address). The client receives the same addresses 3777 each time it resolves the domainname via the same DNS resolver, 3778 but may receive different addresses when it resolves the 3779 domainname via different DNS resolvers. But, in each case, 3780 exactly one A and one AAAA record are returned. 3782 o When a client resolves the domainname "ietf.org", the DNS always 3783 returns one A record and one AAAA record with the same addresses 3784 regardless of which DNS resolver is used. 3786 o When a client resolves the domainname "yahoo.com", the DNS always 3787 returns a list of 4 A records and 4 AAAA records. Each time the 3788 client resolves the domainname via the same DNS resolver, the same 3789 list of addresses are returned but in randomized order (i.e., 3790 consistent with a DNS round-robin strategy). But, interestingly, 3791 the same addresses are returned (albeit in randomized order) when 3792 the domainname is resolved via different DNS resolvers. 3794 o When a client resolves the domainname "amazon.com", the DNS always 3795 returns a list of 3 A records and no AAAA records. As with 3796 "yahoo.com", the same three A records are returned from any 3797 worldwide Internet connection point in randomized order. 3799 The above example strategies show differing approaches to Internet 3800 resilience and service distribution offered by major Internet 3801 services. The Google approach exposes only a single IPv4 and a 3802 single IPv6 address to clients. Clients can then select whichever IP 3803 protocol version offers the best response, but will always use the 3804 same IP address according to the current Internet connection point. 3805 This means that the IP address offered by the network must lead to a 3806 highly-available server and/or service distribution point. In other 3807 words, resilience is predicated on high availability within the 3808 network and with no client-initiated failovers expected (i.e., it is 3809 all-or-nothing from the client's perspective). However, Google does 3810 provide for worldwide distributed service distribution by virtue of 3811 the fact that each Internet connection point responds with a 3812 different IPv6 and IPv4 address. The IETF approach is like google 3813 (all-or-nothing from the client's perspective), but provides only a 3814 single IPv4 or IPv6 address on a worldwide basis. This means that 3815 the addresses must be made highly-available at the network level with 3816 no client failover possibility, and if there is any worldwide service 3817 distribution it would need to be conducted by a network element that 3818 is reached via the IP address acting as a service distribution point. 3820 In contrast to the Google and IETF philosophies, Yahoo and Amazon 3821 both provide clients with a (short) list of IP addresses with Yahoo 3822 providing both IP protocol versions and Amazon as IPv4-only. The 3823 order of the list is randomized with each name service query 3824 response, with the effect of round-robin load balancing for service 3825 distribution. With a short list of addresses, there is still 3826 expectation that the network will implement high availability for 3827 each address but in case any single address fails the client can 3828 switch over to using a different address. The balance then becomes 3829 one of function in the network vs function in the end system. 3831 The same implications observed for common highly-available services 3832 in the Internet apply also to the AERO client/server architecture. 3833 When an AERO Client connects to one or more ANETs, it discovers one 3834 or more AERO Server addresses through the mechanisms discussed in 3835 earlier sections. Each Server address presumably leads to a fault- 3836 tolerant clustering arrangement such as supported by Linux-HA, 3837 Extended Virtual Synchrony or Paxos. Such an arrangement has 3838 precedence in common Internet service deployments in lightweight 3839 virtual machines without requiring expensive hardware deployment. 3840 Similarly, common Internet service deployments set service IP 3841 addresses on service distribution points that may relay requests to 3842 many different servers. 3844 For AERO, the expectation is that a combination of the Google/IETF 3845 and Yahoo/Amazon philosophies would be employed. The AERO Client 3846 connects to different ANET access points and can receive 1-2 Server 3847 LLAs at each point. It then selects one AERO Server address, and 3848 engages in RS/RA exchanges with the same Server from all ANET 3849 connections. The Client remains with this Server unless or until the 3850 Server fails, in which case it can switch over to an alternate 3851 Server. The Client can likewise switch over to a different Server at 3852 any time if there is some reason for it to do so. So, the AERO 3853 expectation is for a balance of function in the network and end 3854 system, with fault tolerance and resilience at both levels. 3856 Appendix B. Change Log 3858 << RFC Editor - remove prior to publication >> 3860 Changes from draft-templin-intarea-6706bis-54 to draft-templin- 3861 intrea-6706bis-55: 3863 o Updates on Segment Routing and S/TLLAO contents. 3865 o Various editorials and addressing cleanups. 3867 Changes from draft-templin-intarea-6706bis-52 to draft-templin- 3868 intrea-6706bis-53: 3870 o Normative reference to the OMNI spec, and remove portions that are 3871 already specified in OMNI. 3873 o Renamed "AERO interface/link" to "OMIN interface/link" throughout 3874 the document. 3876 o Truncated obsolete back section matter. 3878 Author's Address 3880 Fred L. Templin (editor) 3881 Boeing Research & Technology 3882 P.O. Box 3707 3883 Seattle, WA 98124 3884 USA 3886 Email: fltemplin@acm.org