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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 15, 2020 5 rfc6179, rfc6706 (if 6 approved) 7 Intended status: Standards Track 8 Expires: December 17, 2020 10 Asymmetric Extended Route Optimization (AERO) 11 draft-templin-intarea-6706bis-54 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 17, 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 . . . . . . . . . . . . . . 26 80 3.4.1. AERO Server/Relay Behavior . . . . . . . . . . . . . 26 81 3.4.2. AERO Proxy Behavior . . . . . . . . . . . . . . . . . 26 82 3.4.3. AERO Client Behavior . . . . . . . . . . . . . . . . 26 83 3.4.4. AERO Bridge Behavior . . . . . . . . . . . . . . . . 27 84 3.5. OMNI Interface Neighbor Cache Maintenance . . . . . . . . 27 85 3.6. OMNI Interface Encapsulation and Re-encapsulation . . . . 29 86 3.7. OMNI Interface Decapsulation . . . . . . . . . . . . . . 30 87 3.8. OMNI Interface Data Origin Authentication . . . . . . . . 30 88 3.9. OMNI Interface MTU and Fragmentation . . . . . . . . . . 31 89 3.10. OMNI Interface Forwarding Algorithm . . . . . . . . . . . 31 90 3.10.1. Client Forwarding Algorithm . . . . . . . . . . . . 32 91 3.10.2. Proxy Forwarding Algorithm . . . . . . . . . . . . . 32 92 3.10.3. Server/Relay Forwarding Algorithm . . . . . . . . . 33 93 3.10.4. Bridge Forwarding Algorithm . . . . . . . . . . . . 34 94 3.11. OMNI Interface Error Handling . . . . . . . . . . . . . . 35 95 3.12. AERO Router Discovery, Prefix Delegation and 96 Autoconfiguration . . . . . . . . . . . . . . . . . . . . 38 97 3.12.1. AERO ND/PD Service Model . . . . . . . . . . . . . . 38 98 3.12.2. AERO Client Behavior . . . . . . . . . . . . . . . . 38 99 3.12.3. AERO Server Behavior . . . . . . . . . . . . . . . . 40 100 3.13. The AERO Proxy . . . . . . . . . . . . . . . . . . . . . 43 101 3.13.1. Detecting and Responding to Server Failures . . . . 45 102 3.13.2. Point-to-Multipoint Server Coordination . . . . . . 46 103 3.14. AERO Route Optimization / Address Resolution . . . . . . 46 104 3.14.1. Route Optimization Initiation . . . . . . . . . . . 47 105 3.14.2. Relaying the NS . . . . . . . . . . . . . . . . . . 47 106 3.14.3. Processing the NS and Sending the NA . . . . . . . . 48 107 3.14.4. Relaying the NA . . . . . . . . . . . . . . . . . . 49 108 3.14.5. Processing the NA . . . . . . . . . . . . . . . . . 49 109 3.14.6. Route Optimization Maintenance . . . . . . . . . . . 49 110 3.15. Neighbor Unreachability Detection (NUD) . . . . . . . . . 50 111 3.16. Mobility Management and Quality of Service (QoS) . . . . 52 112 3.16.1. Mobility Update Messaging . . . . . . . . . . . . . 52 113 3.16.2. Announcing Link-Layer Address and/or QoS Preference 114 Changes . . . . . . . . . . . . . . . . . . . . . . 53 115 3.16.3. Bringing New Links Into Service . . . . . . . . . . 53 116 3.16.4. Removing Existing Links from Service . . . . . . . . 54 117 3.16.5. Moving to a New Server . . . . . . . . . . . . . . . 54 118 3.17. Multicast . . . . . . . . . . . . . . . . . . . . . . . . 55 119 3.17.1. Source-Specific Multicast (SSM) . . . . . . . . . . 55 120 3.17.2. Any-Source Multicast (ASM) . . . . . . . . . . . . . 57 121 3.17.3. Bi-Directional PIM (BIDIR-PIM) . . . . . . . . . . . 57 122 3.18. Operation over Multiple OMNI Links . . . . . . . . . . . 58 123 3.19. DNS Considerations . . . . . . . . . . . . . . . . . . . 59 124 3.20. Transition Considerations . . . . . . . . . . . . . . . . 59 125 3.21. Detecting and Reacting to Server and Bridge Failures . . 60 126 3.22. AERO Clients on the Open Internet . . . . . . . . . . . . 60 127 3.22.1. Use of SEND and CGA . . . . . . . . . . . . . . . . 63 128 3.23. Time-Varying MNPs . . . . . . . . . . . . . . . . . . . . 64 129 4. Implementation Status . . . . . . . . . . . . . . . . . . . . 65 130 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 65 131 6. Security Considerations . . . . . . . . . . . . . . . . . . . 65 132 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 67 133 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 68 134 8.1. Normative References . . . . . . . . . . . . . . . . . . 69 135 8.2. Informative References . . . . . . . . . . . . . . . . . 70 136 Appendix A. Non-Normative Considerations . . . . . . . . . . . . 78 137 A.1. Implementation Strategies for Route Optimization . . . . 78 138 A.2. Implicit Mobility Management . . . . . . . . . . . . . . 79 139 A.3. Direct Underlying Interfaces . . . . . . . . . . . . . . 79 140 A.4. AERO Critical Infrastructure Considerations . . . . . . . 79 141 A.5. AERO Server Failure Implications . . . . . . . . . . . . 80 142 A.6. AERO Client / Server Architecture . . . . . . . . . . . . 81 144 Appendix B. Change Log . . . . . . . . . . . . . . . . . . . . . 83 145 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 83 147 1. Introduction 149 Asymmetric Extended Route Optimization (AERO) fulfills the 150 requirements of Distributed Mobility Management (DMM) [RFC7333] and 151 route optimization [RFC5522] for aeronautical networking and other 152 network mobility use cases such as intelligent transportation 153 systems. AERO is an internetworking and mobility management service 154 based on the Overlay Multilink Network Interface (OMNI) 155 [I-D.templin-6man-omni-interface] Non-Broadcast, Multiple Access 156 (NBMA) virtual link model. The OMNI link is a virtual overlay 157 configured over one or more underlying Internetworks, and nodes on 158 the link can exchange IP packets via tunneling. Multilink operation 159 allows for increased reliability, bandwidth optimization and traffic 160 path diversity. 162 The AERO service comprises Clients, Proxys, Servers and Relays that 163 are seen as OMNI link neighbors as well as Bridges that interconnect 164 OMNI link segments. Each node's OMNI interface uses an IPv6 link- 165 local address format that supports operation of the IPv6 Neighbor 166 Discovery (ND) protocol [RFC4861] and links ND to IP forwarding. A 167 node's OMNI interface can be configured over multiple underlying 168 interfaces, and may therefore appear as a single interface with 169 multiple link-layer addresses. Each link-layer address is subject to 170 change due to mobility and/or QoS fluctuations, and link-layer 171 address changes are signaled by ND messaging the same as for any IPv6 172 link. 174 AERO provides a cloud-based service where mobile nodes may use any 175 Server acting as a Mobility Anchor Point (MAP) and fixed nodes may 176 use any Relay on the link for efficient communications. Fixed nodes 177 forward packets destined to other AERO nodes to the nearest Relay, 178 which forwards them through the cloud. A mobile node's initial 179 packets are forwarded through the Server, while direct routing is 180 supported through asymmetric extended route optimization while data 181 packets are flowing. Both unicast and multicast communications are 182 supported, and mobile nodes may efficiently move between locations 183 while maintaining continuous communications with correspondents and 184 without changing their IP Address. 186 AERO Bridges are interconnected in a secured private BGP overlay 187 routing instance using encapsulation to provide a hybrid routing/ 188 bridging service that joins the underlying Internetworks of multiple 189 disjoint administrative domains into a single unified OMNI link. 190 Each OMNI link instance is characterized by the set of Mobility 191 Service Prefixes (MSPs) common to all mobile nodes. The link extends 192 to the point where a Relay/Server is on the optimal route from any 193 correspondent node on the link, and provides a conduit between the 194 underlying Internetwork and the OMNI link. To the underlying 195 Internetwork, the Relay/Server is the source of a route to the MSP, 196 and hence uplink traffic to the mobile node is naturally routed to 197 the nearest Relay/Server. 199 AERO assumes the use of PIM Sparse Mode in support of multicast 200 communication. In support of Source Specific Multicast (SSM) when a 201 Mobile Node is the source, AERO route optimization ensures that a 202 shortest-path multicast tree is established with provisions for 203 mobility and multilink operation. In all other multicast scenarios 204 there are no AERO dependencies. 206 AERO was designed for aeronautical networking for both manned and 207 unmanned aircraft, where the aircraft is treated as a mobile node 208 that can connect an Internet of Things (IoT). AERO is also 209 applicable to a wide variety of other use cases. For example, it can 210 be used to coordinate the Virtual Private Network (VPN) links of 211 mobile nodes (e.g., cellphones, tablets, laptop computers, etc.) that 212 connect into a home enterprise network via public access networks 213 using services such as OpenVPN [OVPN]. It can also be used to 214 facilitate vehicular and pedestrian communications services for 215 intelligent transportation systems. Other applicable use cases are 216 also in scope. 218 The following numbered sections present the AERO specification. The 219 appendices at the end of the document are non-normative. 221 2. Terminology 223 The terminology in the normative references applies; especially, the 224 terminology in the OMNI specification 225 [I-D.templin-6man-omni-interface] is used extensively throughout. 226 The following terms are defined within the scope of this document: 228 IPv6 Neighbor Discovery (ND) 229 an IPv6 control message service for coordinating neighbor 230 relationships between nodes connected to a common link. AERO uses 231 the ND service specified in [RFC4861]. 233 IPv6 Prefix Delegation (PD) 234 a networking service for delegating IPv6 prefixes to nodes on the 235 link. The nominal PD service is DHCPv6 [RFC8415], however 236 alternate services (e.g., based on ND messaging) are also in scope 237 [I-D.templin-v6ops-pdhost][I-D.templin-6man-dhcpv6-ndopt]. Most 238 notably, a minimal form of PD known as "prefix registration" can 239 be used if the Client knows its prefix in advance and can 240 represent it in the IPv6 source address of an ND message. 242 Access Network (ANET) 243 a node's first-hop data link service network (e.g., a radio access 244 network, cellular service provider network, corporate enterprise 245 network, etc.) that often provides link-layer security services 246 such as IEEE 802.1X and physical-layer security prevent 247 unauthorized access internally and with border network-layer 248 security services such as firewalls and proxies that prevent 249 unauthorized outside access. 251 ANET interface 252 a node's attachment to a link in an ANET. 254 Internetwork (INET) 255 a connected IP network topology with a coherent routing and 256 addressing plan and that provides a transit backbone service for 257 ANET end systems. INETs also provide an underlay service over 258 which the AERO virtual link is configured. Example INETs include 259 corporate enterprise networks, aviation networks, and the public 260 Internet itself. When there is no administrative boundary between 261 an ANET and the INET, the ANET and INET are one and the same. 263 INET Partition 264 frequently, INETs such as large corporate enterprise networks are 265 sub-divided internally into separate isolated partitions. Each 266 partition is fully connected internally but disconnected from 267 other partitions, and there is no requirement that separate 268 partitions maintain consistent Internet Protocol and/or addressing 269 plans. (Each INET partition is seen as a separate OMNI link 270 segment as discussed below.) 272 INET interface 273 a node's attachment to a link in an INET. 275 INET address 276 an IP address assigned to a node's interface connection to an 277 INET. 279 INET encapsulation 280 the encapsulation of a packet in an outer header or headers that 281 can be routed within the scope of the local INET partition. 283 OMNI link 284 the same as defined in [I-D.templin-6man-omni-interface], and 285 manifested by IPv6 encapsulation [RFC2473]. The OMNI link spans 286 underlying INET segments joined by virtual bridges in a spanning 287 tree the same as a bridged campus LAN. AERO nodes on the OMNI 288 link appear as single-hop neighbors even though they may be 289 separated by multiple underlying INET hops, and can use Segment 290 Routing [RFC8402] to cause packets to visit selected waypoints on 291 the link. 293 OMNI Interface 294 a node's attachment to an OMNI link. Since the addresses assigned 295 to an OMNI interface are managed for uniqueness, OMNI interfaces 296 do not require Duplicate Address Detection (DAD) and therefore set 297 the administrative variable 'DupAddrDetectTransmits' to zero 298 [RFC4862]. 300 OMNI Link-Local Address (LLA) 301 a link local IPv6 address per [RFC4291] constructed as specified 302 in Section 3.2.2. 304 OMNI Unique-Local Address (ULA) 305 a unique local IPv6 address per [RFC4193] constructed as specified 306 in Section 3.2.2. OMNI ULAs are statelessly derived from OMNI 307 LLAs, and vice-versa. 309 underlying interface 310 an ANET or INET interface over which an OMNI interface is 311 configured. 313 Mobility Service Prefix (MSP) 314 an IP prefix assigned to the OMNI link and from which more- 315 specific Mobile Network Prefixes (MNPs) are derived. 317 Mobile Network Prefix (MNP) 318 an IP prefix allocated from an MSP and delegated to an AERO Client 319 or Relay. 321 AERO node 322 a node that is connected to an OMNI link and participates in the 323 AERO internetworking and mobility service. 325 AERO Client ("Client") 326 an AERO node that connects over one or more underlying interfaces 327 and requests MNP PDs from AERO Servers. The Client assigns a 328 Client LLA to the OMNI interface for use in ND exchanges with 329 other AERO nodes and forwards packets to correspondents according 330 to OMNI interface neighbor cache state. 332 AERO Server ("Server") 333 an INET node that configures an OMNI interface to provide default 334 forwarding and mobility/multilink services for AERO Clients. The 335 Server assigns an administratively-provisioned LLA to its OMNI 336 interface to support the operation of the ND/PD services, and 337 advertises all of its associated MNPs via BGP peerings with 338 Bridges. 340 AERO Relay ("Relay") 341 an AERO Server that also provides forwarding services between 342 nodes reached via the OMNI link and correspondents on other links. 343 AERO Relays are provisioned with MNPs (i.e., the same as for an 344 AERO Client) and run a dynamic routing protocol to discover any 345 non-MNP IP routes. In both cases, the Relay advertises the MSP(s) 346 to its downstream networks, and distributes all of its associated 347 MNPs and non-MNP IP routes via BGP peerings with Bridges (i.e., 348 the same as for an AERO Server). 350 AERO Bridge ("Bridge") 351 a node that provides hybrid routing/bridging services (as well as 352 a security trust anchor) for nodes on an OMNI link. As a router, 353 the Bridge forwards packets using standard IP forwarding. As a 354 bridge, the Bridge forwards packets over the OMNI link without 355 decrementing the IPv6 Hop Limit. AERO Bridges peer with Servers 356 and other Bridges to discover the full set of MNPs for the link as 357 well as any non-MNPs that are reachable via Relays. 359 AERO Proxy ("Proxy") 360 a node that provides proxying services between Clients in an ANET 361 and Servers in external INETs. The AERO Proxy is a conduit 362 between the ANET and external INETs in the same manner as for 363 common web proxies, and behaves in a similar fashion as for ND 364 proxies [RFC4389]. 366 ingress tunnel endpoint (ITE) 367 an OMNI interface endpoint that injects encapsulated packets into 368 an OMNI link. 370 egress tunnel endpoint (ETE) 371 an OMNI interface endpoint that receives encapsulated packets from 372 an OMNI link. 374 link-layer address 375 an IP address used as an encapsulation header source or 376 destination address from the perspective of the OMNI interface. 377 When an upper layer protocol (e.g., UDP) is used as part of the 378 encapsulation, the port number is also considered as part of the 379 link-layer address. 381 network layer address 382 the source or destination address of an encapsulated IP packet 383 presented to the OMNI interface. 385 end user network (EUN) 386 an internal virtual or external edge IP network that an AERO 387 Client or Relay connects to the rest of the network via the OMNI 388 interface. The Client/Relay sees each EUN as a "downstream" 389 network, and sees the OMNI interface as the point of attachment to 390 the "upstream" network. 392 Mobile Node (MN) 393 an AERO Client and all of its downstream-attached networks that 394 move together as a single unit, i.e., an end system that connects 395 an Internet of Things. 397 Mobile Router (MR) 398 a MN's on-board router that forwards packets between any 399 downstream-attached networks and the OMNI link. 401 Route Optimization Source (ROS) 402 the AERO node nearest the source that initiates route 403 optimization. The ROS may be a Server or Proxy acting on behalf 404 of the source Client. 406 Route Optimization responder (ROR) 407 the AERO node nearest the target destination that responds to 408 route optimization requests. The ROR may be a Server acting on 409 behalf of a target MNP Client, or a Relay for a non-MNP 410 destination. 412 MAP List 413 a geographically and/or topologically referenced list of addresses 414 of all Servers within the same OMNI link. There is a single MAP 415 list for the entire OMNI link. 417 Distributed Mobility Management (DMM) 418 a BGP-based overlay routing service coordinated by Servers and 419 Bridges that tracks all Server-to-Client associations. 421 Mobility Service (MS) 422 the collective set of all Servers, Proxys, Bridges and Relays that 423 provide the AERO Service to Clients. 425 Mobility Service Endpoint MSE) 426 an individual Server, Proxy, Bridge or Relay in the Mobility 427 Service. 429 Throughout the document, the simple terms "Client", "Server", 430 "Bridge", "Proxy" and "Relay" refer to "AERO Client", "AERO Server", 431 "AERO Bridge", "AERO Proxy" and "AERO Relay", respectively. 432 Capitalization is used to distinguish these terms from other common 433 Internetworking uses in which they appear without capitalization. 435 The terminology of DHCPv6 [RFC8415] and IPv6 ND [RFC4861] (including 436 the names of node variables, messages and protocol constants) is used 437 throughout this document. The terms "All-Routers multicast", "All- 438 Nodes multicast", "Solicited-Node multicast" and "Subnet-Router 439 anycast" are defined in [RFC4291]. Also, the term "IP" is used to 440 generically refer to either Internet Protocol version, i.e., IPv4 441 [RFC0791] or IPv6 [RFC8200]. 443 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 444 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 445 "OPTIONAL" in this document are to be interpreted as described in BCP 446 14 [RFC2119][RFC8174] when, and only when, they appear in all 447 capitals, as shown here. 449 3. Asymmetric Extended Route Optimization (AERO) 451 The following sections specify the operation of IP over OMNI links 452 using the AERO service: 454 3.1. AERO Node Types 456 AERO Bridges provide hybrid routing/bridging services (as well as a 457 security trust anchor) for nodes on an OMNI link. Bridges use 458 standard IPv6 routing to forward packets both within the same INET 459 partitions and between disjoint INET partitions based on a mid-layer 460 IPv6 encapsulation per [RFC2473]. The inner IP layer experiences a 461 virtual bridging service since the inner IP TTL/Hop Limit is not 462 decremented during forwarding. Each Bridge also peers with Servers 463 and other Bridges in a dynamic routing protocol instance to provide a 464 Distributed Mobility Management (DMM) service for the list of active 465 MNPs (see Section 3.2.3). Bridges present the OMNI link as a set of 466 one or more Mobility Service Prefixes (MSPs) but as link-layer 467 devices need not connect directly to the OMNI link themselves unless 468 an administrative interface is desired. Bridges configure secured 469 tunnels with Servers, Relays, Proxys and other Bridges; they further 470 maintain IP forwarding table entries for each Mobile Network Prefix 471 (MNP) and any other reachable non-MNP prefixes. 473 AERO Servers provide default forwarding and mobility/multilink 474 services for AERO Client Mobile Nodes (MNs). Each Server also peers 475 with Bridges in a dynamic routing protocol instance to advertise its 476 list of associated MNPs (see Section 3.2.3). Servers facilitate PD 477 exchanges with Clients, where each delegated prefix becomes an MNP 478 taken from an MSP. Servers forward packets between OMNI interface 479 neighbors and track each Client's mobility profiles. 481 AERO Clients register their MNPs through PD exchanges with AERO 482 Servers over the OMNI link, and distribute the MNPs to nodes on EUNs. 483 A Client may also be co-resident on the same physical or virtual 484 platform as a Server; in that case, the Client and Server behave as a 485 single functional unit. 487 AERO Proxys provide a conduit for ANET Clients to associate with 488 Servers in external INETs. Client and Servers exchange control plane 489 messages via the Proxy acting as a bridge between the ANET/INET 490 boundary. The Proxy forwards data packets between Clients and the 491 OMNI link according to forwarding information in the neighbor cache. 492 The Proxy function is specified in Section 3.13. 494 AERO Relays are Servers that provide forwarding services between the 495 OMNI interface and INET/EUN interfaces. Relays are provisioned with 496 MNPs the same as for an AERO Client, and also run a dynamic routing 497 protocol to discover any non-MNP IP routes. The Relay advertises the 498 MSP(s) to its connected networks, and distributes all of its 499 associated MNPs and non-MNP IP routes via BGP peerings with Bridges. 501 AERO Bridges, Servers, Proxys and Relays are critical infrastructure 502 elements in fixed (i.e., non-mobile) INET deployments and hence have 503 permanent and unchanging INET addresses. AERO Clients are MNs that 504 connect via underlying interfaces with addresses that may change when 505 the Client moves to a new network connection point. 507 3.2. The AERO Service over OMNI Links 509 3.2.1. AERO/OMNI Reference Model 511 Figure 1 presents the basic OMNI link reference model: 513 +----------------+ 514 | AERO Bridge B1 | 515 | Nbr: S1, S2, P1| 516 |(X1->S1; X2->S2)| 517 | MSP M1 | 518 +-+---------+--+-+ 519 +--------------+ | Secured | | +--------------+ 520 |AERO Server S1| | tunnels | | |AERO Server S2| 521 | Nbr: C1, B1 +-----+ | +-----+ Nbr: C2, B1 | 522 | default->B1 | | | default->B1 | 523 | X1->C1 | | | X2->C2 | 524 +-------+------+ | +------+-------+ 525 | OMNI link | | 526 X===+===+===================+==)===============+===+===X 527 | | | | 528 +-----+--------+ +--------+--+-----+ +--------+-----+ 529 |AERO Client C1| | AERO Proxy P1 | |AERO Client C2| 530 | Nbr: S1 | |(Proxy Nbr Cache)| | Nbr: S2 | 531 | default->S1 | +--------+--------+ | default->S2 | 532 | MNP X1 | | | MNP X2 | 533 +------+-------+ .--------+------. +-----+--------+ 534 | (- Proxyed Clients -) | 535 .-. `---------------' .-. 536 ,-( _)-. ,-( _)-. 537 .-(_ IP )-. +-------+ +-------+ .-(_ IP )-. 538 (__ EUN )--|Host H1| |Host H2|--(__ EUN ) 539 `-(______)-' +-------+ +-------+ `-(______)-' 541 Figure 1: AERO/OMNI Reference Model 543 In this model: 545 o the OMNI link is an overlay network service configured over one or 546 more underlying INET partitions which may be managed by different 547 administrative authorities and have incompatible protocols and/or 548 addressing plans. 550 o AERO Bridge B1 aggregates Mobility Service Prefix (MSP) M1, 551 discovers Mobile Network Prefixes (MNPs) X* and advertises the MSP 552 via BGP peerings over secured tunnels to Servers (S1, S2). 553 Bridges connect the disjoint segments of a partitioned OMNI link. 555 o AERO Servers/Relays S1 and S2 configure secured tunnels with 556 Bridge B1 and also provide mobility, multilink and default router 557 services for their associated Clients C1 and C2. 559 o AERO Clients C1 and C2 associate with Servers S1 and S2, 560 respectively. They receive Mobile Network Prefix (MNP) 561 delegations X1 and X2, and also act as default routers for their 562 associated physical or internal virtual EUNs. Simple hosts H1 and 563 H2 attach to the EUNs served by Clients C1 and C2, respectively. 565 o AERO Proxy P1 configures a secured tunnel with Bridge B1 and 566 provides proxy services for AERO Clients in secured enclaves that 567 cannot associate directly with other OMNI link neighbors. 569 An OMNI link configured over a single INET appears as a single 570 unified link with a consistent underlying network addressing plan. 571 In that case, all nodes on the link can exchange packets via simple 572 INET encapsulation, since the underlying INET is connected. In 573 common practice, however, an OMNI link may be partitioned into 574 multiple "segments", where each segment is a distinct INET 575 potentially managed under a different administrative authority (e.g., 576 as for worldwide aviation service providers such as ARINC, SITA, 577 Inmarsat, etc.). Individual INETs may also themselves be partitioned 578 internally, in which case each internal partition is seen as a 579 separate segment. 581 The addressing plan of each segment is consistent internally but will 582 often bear no relation to the addressing plans of other segments. 583 Each segment is also likely to be separated from others by network 584 security devices (e.g., firewalls, proxies, packet filtering 585 gateways, etc.), and in many cases disjoint segments may not even 586 have any common physical link connections. Therefore, nodes can only 587 be assured of exchanging packets directly with correspondents in the 588 same segment, and not with those in other segments. The only means 589 for joining the segments therefore is through inter-domain peerings 590 between AERO Bridges. 592 The same as for traditional campus LANs, multiple OMNI link segments 593 can be joined into a single unified link via a virtual bridging 594 service using a mid-layer IPv6 encpasulation per [RFC2473] known as 595 the "SPAN header" that supports inter-segment forwarding (i.e., 596 bridging) without decrementing the network-layer TTL/Hop Limit. This 597 bridging of OMNI link segments is shown in Figure 2: 599 . . . . . . . . . . . . . . . . . . . . . . . 600 . . 601 . .-(::::::::) . 602 . .-(::::::::::::)-. +-+ . 603 . (:::: Segment A :::)--|B|---+ . 604 . `-(::::::::::::)-' +-+ | . 605 . `-(::::::)-' | . 606 . | . 607 . .-(::::::::) | . 608 . .-(::::::::::::)-. +-+ | . 609 . (:::: Segment B :::)--|B|---+ . 610 . `-(::::::::::::)-' +-+ | . 611 . `-(::::::)-' | . 612 . | . 613 . .-(::::::::) | . 614 . .-(::::::::::::)-. +-+ | . 615 . (:::: Segment C :::)--|B|---+ . 616 . `-(::::::::::::)-' +-+ | . 617 . `-(::::::)-' | . 618 . | . 619 . ..(etc).. x . 620 . . 621 . . 622 . <- OMNI link Bridged by encapsulation -> . 623 . . . . . . . . . . . . . .. . . . . . . . . 625 Figure 2: Bridging OMNI Link Segments 627 Bridges, Servers, Relays and Proxys connect via secured INET tunnels 628 over their respecitve segments in a spanning tree topology rooted at 629 the Bridges. The secured spanning tree supports strong 630 authentication for IPv6 ND control messages and may also be used to 631 convey the initial data packets in a flow. Route optimization can 632 then be employed to cause data packets to take more direct paths 633 between OMNI link neighbors without having to strictly follow the 634 spanning tree. 636 3.2.2. Link-Local Addresses (LLAs) and Unique Local Addresses (ULAs) 638 AERO nodes on OMNI links use the Link-Local Address (LLA) prefix 639 fe80::/10 [RFC4193] to assign LLAs used for network-layer addresses 640 in IPv6 ND and data messages. They also use the Unique Local Address 641 (ULA) prefix fc80::/10 [RFC4193] to form ULAs used for SPAN header 642 source and desitnation addresses. See 643 [I-D.templin-6man-omni-interface] for a full specification of the 644 LLAs and ULAs used by AERO nodes on OMNI links. 646 For routing system organization (see Section 3.2.3), ULAs are 647 organized in partition prefixes, e.g., fc80::1000/116. For each such 648 partition prefix, the Bridge(s) that connect that segment assign the 649 :: address of the prefix as a Subnet Router Anycast address. For 650 example, the Subnet Router Anycast address for fc80::1000/116 is 651 simply fc80::1000. 653 3.2.3. AERO Routing System 655 The AERO routing system comprises a private instance of the Border 656 Gateway Protocol (BGP) [RFC4271] that is coordinated between Bridges 657 and Servers and does not interact with either the public Internet BGP 658 routing system or any underlying INET routing systems. 660 In a reference deployment, each Server is configured as an Autonomous 661 System Border Router (ASBR) for a stub Autonomous System (AS) using 662 an AS Number (ASN) that is unique within the BGP instance, and each 663 Server further uses eBGP to peer with one or more Bridges but does 664 not peer with other Servers. Each INET of a multi-segment OMNI link 665 must include one or more Bridges, which peer with the Servers and 666 Proxys within that INET. All Bridges within the same INET are 667 members of the same hub AS using a common ASN, and use iBGP to 668 maintain a consistent view of all active MNPs currently in service. 669 The Bridges of different INETs peer with one another using eBGP. 671 Bridges advertise the OMNI link's MSPs and any non-MNP routes to each 672 of their Servers. This means that any aggregated non-MNPs (including 673 "default") are advertised to all Servers. Each Bridge configures a 674 black-hole route for each of its MSPs. By black-holing the MSPs, the 675 Bridge will maintain forwarding table entries only for the MNPs that 676 are currently active, and packets destined to all other MNPs will 677 correctly incur Destination Unreachable messages due to the black- 678 hole route. In this way, Servers have only partial topology 679 knowledge (i.e., they know only about the MNPs of their directly 680 associated Clients) and they forward all other packets to Bridges 681 which have full topology knowledge. 683 Each OMNI link segment assigns a unique sub-prefix of fc80::/96 known 684 as the ULA partition prefix. For example, a first segment could 685 assign fc80::1000/116, a second could assign fc80::2000/116, a third 686 could assign fc80::3000/116, etc. The administrative authorities for 687 each segment must therefore coordinate to assure mutually-exclusive 688 partiton prefix assignments, but internal provisioning of each prefix 689 is an independent local consideration for each administrative 690 authority. 692 ULA partition prefixes are statitcally represented in Bridge 693 forwarding tables. Bridges join multiple segments into a unified 694 OMNI link over multiple diverse administrative domains. They support 695 a bridging function by first establishing forwarding table entries 696 for their partiion prefixes either via standard BGP routing or static 697 routes. For example, if three Bridges ('A', 'B' and 'C') from 698 different segments serviced fc80::1000/116, fc80::2000/116 and 699 fc80::3000/116 respectively, then the forwarding tables in each 700 Bridge are as follows: 702 A: fc80::1000/116->local, fc80::2000/116->B, fc80::3000/116->C 704 B: fc80::1000/116->A, fc80::2000/116->local, fc80::3000/116->C 706 C: fc80::1000/116->A, fc80::2000/116->B, fc80::3000/116->local 708 These forwarding table entries are permanent and never change, since 709 they correspond to fixed infrastructure elements in their respective 710 segments. 712 ULA Client prefixes are instead dynamically advertised in the AERO 713 routing system by Servers and Relays that provide service for their 714 corresponding MNPs. For example, if three Servers ('D', 'E' and 'F') 715 service the MNPs 2001:db8:1000:2000::/56, 2001:db8:3000:4000::/56 and 716 2001:db8:5000:6000::/56 then the routing system would include: 718 D: fc80:2001:db8:1000:2000::/72 720 E: fc80:2001:db8:3000:4000::/72 722 F: fc80:2001:db8:5000:6000::/72 724 A full discussion of the BGP-based routing system used by AERO is 725 found in [I-D.ietf-rtgwg-atn-bgp]. The system provides for 726 Distributed Mobility Management (DMM) per the distributed mobility 727 anchoring architecture [I-D.ietf-dmm-distributed-mobility-anchoring]. 729 3.2.4. AERO Encapsulation 731 With the Client and partition prefixes in place in each Bridge's 732 forwarding table, control and data packets sent between AERO nodes in 733 different segments can therefore be carried over the via mid-layer 734 encapsulation using the SPAN header. For example, when a source AERO 735 node forwards a packet with IPv6 address 2001:db8:1:2::1 to a target 736 AERO node with IPv6 address 2001:db8:1000:2000::1, it first 737 encapsulates the packet in a SPAN header with source address set to 738 fc80:2001:db8:1:2:: and destination address set to 739 fc80:2001:db8:1000:2000::. Next, it encapsulates the resulting SPAN 740 packet in an INET header with source address set to its own INET 741 address (e.g., 192.0.2.100) and destination set to the INET address 742 of a Bridge (e.g., 192.0.2.1). 744 SPAN encapsulation is based on Generic Packet Tunneling in IPv6 745 [RFC2473]; the encapsulation format in the above example is shown in 746 Figure 3: 748 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 749 | INET Header | 750 | src = 192.0.2.100 | 751 | dst = 192.0.2.1 | 752 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 753 | SPAN Header | 754 | src = fc80:2001:db8:1:2:: | 755 | dst=fc80:2001:db8:1000:2000:: | 756 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 757 | Inner IP Header | 758 | src = 2001:db8:1:2::1 | 759 | dst = 2001:db8:1000:2000::1 | 760 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 761 | | 762 ~ ~ 763 ~ Inner Packet Body ~ 764 ~ ~ 765 | | 766 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 768 Figure 3: SPAN Encapsulation 770 In this format, the inner IP header and packet body are the original 771 IP packet, the SPAN header is an IPv6 header prepared according to 772 [RFC2473], and the INET header is prepared as discussed in 773 Section 3.6. 775 This gives rise to a routing system that contains both Client prefix 776 routes that may change dynamically due to regional node mobility and 777 partion prefix routes that never change. The Bridges can therefore 778 provide link-layer bridging by sending packets over the SRT instead 779 of network-layer routing according to MNP routes. As a result, 780 opportunities for packet loss due to node mobility between different 781 segments are mitigated. 783 In normal operations, IPv6 ND messages are conveyed over secured 784 paths between OMNI link neighbors so that specific Proxys, Servers or 785 Relays can be addressed without being subject to mobility events. 786 Conversely, only the first few packets destined to Clients need to 787 traverse secured paths until route optimization can determine a more 788 direct path. 790 3.2.5. Segment Routing Topologies (SRTs) 792 The 16-bit sub-prefixes of fc80::/10 (e.g., fc80::/16, fc81::/16, 793 fc82::/16, etc.) identify distinct Segment Routing Topologies (SRTs) 794 (see: Section 3.2.5). Each SRT is a mutually-exclusive OMNI link 795 overlay instance using a mutually-exclusive set of ULAs, and emulates 796 a Virtual LAN (VLAN) service for the OMNI link. In some cases (e.g., 797 when redundant topologies are needed for fault tolerance and 798 reliability) it may be beneficial to deploy multiple SRTs that act as 799 independent overlay instances. A communication failure in one 800 instance therefore will not affect communications in other instances. 802 Each SRT is identified by a distinct value in bits 10-15 of he SSP 803 fc80::10, i.e., as fc80::/16, fc81::/16, fc82::/16, etc. This 804 document asserts that up to four SRTs provide a level of safety 805 sufficient for critical communications such as civil aviation. Each 806 SRT is designated with a color that identifies a different OMNI link 807 instance as follows: 809 o Red - corresponds to the SSP fc80::/16 811 o Green - corresponds to the SSP fc81::/16 813 o Blue-1 - corresponds to the SSP fc82::/16 815 o Blue-2 - corresponds to SSP fc83::/16 817 o SSPs fc84::/16 through fcbf::/16 are reserved for future use. 819 Each OMNI interface assigns an anycast ULA corresponding to its SRT 820 prefix. For example, the anycast ULA for the Green SRT is simply 821 fc81::. The anycast ULA is used for OMNI interface determination in 822 Safety-Based Multilink (SBM) as discussed in 823 [I-D.templin-6man-omni-interface]. Each OMNI interface further 824 applies Performance-Based Multilink (PBM) internally. 826 3.2.6. Segment Routing To the OMNI Link 828 An original IPv6 source can direct a packet to a specific SRT ingress 829 router for the OMNI link by including a Segment Routing Header (SRH) 830 with the anycast ULA for the selected SRT as either the IPv6 831 destination or as an intermediate segment ID within the SRH. This 832 allows the original source to determine the specific topology a 833 packet will traverse when there may be multiple alternatives to 834 choose from. This form of Segment Routing supports Safety-Based 835 Multilink (SBM), and can be exercised through general-purpose SRH 836 types such as [RFC8754]. 838 3.2.7. Segment Routing Within the OMNI Link 840 AERO nodes that insert a SPAN header can use Segment Routing within 841 the OMNI link when necessary to influence the path of packets 842 destined to targets in remote segments without causing all packets to 843 traverse strict spanning tree paths. 845 When a Client, Proxy or Server has a packet to send to a target 846 discovered through route optimization located in the same OMNI link 847 segment, it encapsulates the packet in a SPAN header with the ULA of 848 the target as the destination address if fragmentation is necessary; 849 otherwise, it may omit the SPAN header. The node then uses the 850 target's Link Layer Address information for INET encapsulation 851 without including an SRH. 853 When a Client, Proxy or Server has a packet to send to a route 854 optimization target located in a remote OMNI link segment, it 855 encapsulates the packet in a SPAN header with its own ULA as the 856 source address. If the route optimization target is located behind a 857 Proxy or Server, the node forwards the packet to a Bridge while 858 OPTIONALLY including an SRH [RFC8754]. If the route optimization 859 target is an INET Client associated with a Server in a remote 860 segment, the node SHOULD include an SRH. 862 When the SRH is omitted, the node sets the destination address to the 863 ULA of the target Proxy/Server. When the SRH is included, the node 864 first sets the destination address to the ULA Subnet Router Anycast 865 address of the remote segment and sets the ULA of the target's Proxy/ 866 Server as the ultimate Segment ID (SID). The node also includes an 867 AERO Route Optimization specification in the SRH TLV section as shown 868 in Figure 4: 870 0 1 2 3 871 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 1 872 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 873 | Type=TBD | Length |FMT|V|R|Preflen| MNP[1] | 874 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 875 | MNP[2] | MNP[3] | ... | MNP[i] | 876 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 877 ~ Link Layer Address ~ 878 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 879 | Port Number | 880 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 882 Figure 4: AERO Route Optimization SRH TLV 884 In this format: 886 o Type is TBD to be assigned according to the Segment Routing Header 887 TLV registry [RFC8754]. 889 o Length is the length of the body of the TLV in bytes, excluding 890 the Type and Length fields. 892 o FMT is a two bit code that determines the format of the Link Layer 893 Address exactly as specified in Figure 5. 895 o V indicates the IP protocol version of the MNP that follows. V is 896 set to 0 for IPv4 or 1 for IPv6. 898 o R is reserved. 900 o Preflen encodes a value 'i' (between 0 and 15) that indicates the 901 number of octets of the IPv4/IPv6 MNP prefix that follows. 903 o MNP{1], MNP[2], etc. up to MNP[i] encode the leading 'i' octets of 904 the MNP, beginning with the most significant octet followed by the 905 next most significant octet, etc. The number of MNP octets to be 906 included is determined by the number of trailing zero octets in 907 the prefix. For example, for the IPv6 MNP 2001:db8:1:2::/64, 'i' 908 is set to 8 and only the leftmost 8 octets of the MNP are 909 included. In the same way, for the IPv4 MNP 192.0.2/24, 'i' is 910 set to 3 and only the leftmost 3 octets of the MNP are included. 912 o Link Layer Address and Port Number are encoded according to FMT 913 exactly as specified in Figure 5. 915 The node then forwards the packet via a local Bridge, which will 916 eventually direct it to a Bridge on the same segment as the target. 918 When a Bridge receives a packet with Segments Left=1 and with 919 ultimate SID on a local segment, it checks to see if there is an AERO 920 Route Optimization TLV. If so, the Bridge creates a ULA destination 921 according to Preflen. If Preflen is 0, the Bridge concatenates the 922 SRT ::/16 prefix with the ultimate SID to form the ULA destination. 923 Otherwise, the Bridge concatenates the SRT ::/16 prefix with the MNP 924 and sets the remaining rightmost bits to 0 to form a Subnet Router 925 Anycast ULA destination. The Bridge then writes the ULA into the 926 SPAN header destination address and encapsulates the packet in an 927 INET header with the target's Link Layer Address as the destination 928 then forwards the packet. 930 In this way, the Bridge participates in route optimization to greatly 931 reduce traffic load and suboptimal routing through strict spanning 932 tree paths. Note that if the Bridge does not recognize the AERO 933 Route Optimization TLV, it instead places the ultimate SID 934 concatentaed with the SRT ::/16 prefix in the IPv6 destination 935 address and forwards according to the spanning tree. (Note that this 936 is the same behavior that would occur if the AERO Route Optimization 937 TLV were not present). 939 3.2.8. Segment Routing Header Compression 941 In the Segment Routing use cases discussed above, the segment routing 942 headers must be kept to a minimum size since source and target 943 Clients may be located behind low-end wireless links (e.g., 1Mbps or 944 less). The Compressed Routing Header (CRH) 945 [I-D.bonica-6man-comp-rtg-hdr] provides a compact form that reduces 946 the header size by omitting information that can already be derived 947 by intermediate Bridges. The CRH Helper 948 option[I-D.bonica-6man-crh-helper-opt] can be used to encode the AERO 949 Route Optimization TLV, and the final hop Bridge that performs route 950 optimization may remove the CRH and its helper before encapsulating 951 and forwarding to the target. 953 The CRH and its companion helper option are therefore seen as 954 critical architectural elements that should be quickly progressed 955 through the standards process. Implementations SHOULD use the CRH 956 and its companion helper option instead of other Routing Header types 957 whenever possible to conserve bandwidth. 959 3.3. OMNI Interface Characteristics 961 OMNI interfaces are virtual interfaces configured over one or more 962 underlying interfaces classified as follows: 964 o INET interfaces connect to an INET either natively or through one 965 or several IPv4 Network Address Translators (NATs). Native INET 966 interfaces have global IP addresses that are reachable from any 967 INET correspondent. All Server, Relay and Bridge interfaces are 968 native interfaces, as are INET-facing interfaces of Proxys. NATed 969 INET interfaces connect to a private network behind one or more 970 NATs that provide INET access. Clients that are behind a NAT are 971 required to send periodic keepalive messages to keep NAT state 972 alive when there are no data packets flowing. 974 o Proxyed interfaces connect to an ANET that is separated from the 975 open INET by an AERO Proxy. Proxys can actively issue control 976 messages over the INET on behalf of the Client to reduce ANET 977 congestion. Clients connected to Proxyed interfaces receive RAs 978 with the P flag set to 1. 980 o VPNed interfaces use security encapsulation over the INET to a 981 Virtual Private Network (VPN) server that also acts as an AERO 982 Server. Other than the link-layer encapsulation format, VPNed 983 interfaces behave the same as Direct interfaces. 985 o Direct interfaces connect a Client directly to a Server without 986 crossing any ANET/INET paths. An example is a line-of-sight link 987 between a remote pilot and an unmanned aircraft. The same Client 988 considerations apply as for VPNed interfaces. 990 OMNI interfaces use SPAN encapsulation as necessary as discussed in 991 Section 3.2.4. OMNI interfaces use link-layer encapsulation (see: 992 Section 3.6) to exchange packets with OMNI link neighbors over INET 993 or VPNed interfaces. OMNI interfaces do not use link-layer 994 encapsulation over Proxyed and Direct underlying interfaces. 996 OMNI interfaces maintain a neighbor cache for tracking per-neighbor 997 state the same as for any interface. OMNI interfaces use ND messages 998 including Router Solicitation (RS), Router Advertisement (RA), 999 Neighbor Solicitation (NS) and Neighbor Advertisement (NA) for 1000 neighbor cache management. 1002 OMNI interfaces send ND messages with an OMNI option formatted as 1003 specified in [I-D.templin-6man-omni-interface]. The OMNI option 1004 includes prefix registration information and "ifIndex-tuples" 1005 containing link information parameters for the OMNI interface's 1006 underlying interfaces. 1008 SPAN-encapsulated OMNI interface ND messages MAY also include a 1009 Source/Target Link-Layer Address Option (S/TLLAO) formatted as shown 1010 in Figure 5: 1012 0 1 2 3 1013 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 1014 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1015 | Type | Length | ifIndex[1] |I| SRT |LHS|FMT| 1016 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1017 ~ Segment ID (SID) List [1] ~ 1018 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1019 ~ Link Layer Address [1] ~ 1020 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1021 | Port Number [1] | ifIndex[2] |I| SRT |LHS|FMT| 1022 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1023 ~ Segment ID (SID) List [2] ~ 1024 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1025 ~ Link Layer Address [2] ~ 1026 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1027 | Port Number [2] | .... ~ 1028 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ 1029 ~ ... ~ 1030 ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1031 ~ | ifIndex[N] |I| SRT |LHS|FMT| 1032 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1033 ~ Segment ID (SID) List [N] ~ 1034 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1035 ~ Link Layer Address [N] ~ 1036 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1037 | Port Number [N] | Zero Padding (if necessary) ... 1038 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1040 Figure 5: OMNI Source/Target Link-Layer Address Option (S/TLLAO) 1041 Format 1043 In this format, Type and Length are set the same as specified for S/ 1044 TLLAOs in [RFC4861], with trailing zero padding octets added as 1045 necessary to produce an integral number of 8 octet blocks. The S/ 1046 TLLAO includes N ifIndex-tuples in correspondence to ifIndex-tuples 1047 that appear in the OMNI option. Each ifIndex-tuple includes the 1048 following information: 1050 o ifIndex[i] - the same value as in the corresponding ifIndex-tuple 1051 included in the OMNI option. 1053 o I[i] - set to 0 if the Link-Layer Addresss is the address of a 1054 Proxy/Server; set to 1 if the Link Layer Address is the INET 1055 encapsulation address for the Source/Target itself. 1057 o SRT[i] - a 3-bit "Segment Routing Topology" value (see: 1058 Section 3.2.5) coded as follows: 1060 * 000 - Red 1062 * 001 - Green 1064 * 010 - Blue-1 1066 * 011 - Blue-2 1068 * 100 - 111 - Reserved 1070 o LHS[i] - a 2-bit "Last Hop SIDs" value that encodes the number 1071 (from 0 to 3) of entries in SID List [i]. 1073 o FMT[i] - a 2-bit "Format" code. Determines the format of the Link 1074 Layer Address [i] field as follows: 1076 * 00 - Link Layer Address [i] encodes an IPv4 address for a node 1077 behind a NAT. 1079 * 01 - Link Layer Address [i] encodes an IPv4 address for a node 1080 on the open INET. 1082 * 10 - Link Layer Address [i] encodes an IPv6 address for a node 1083 behind a NAT.. 1085 * 11 - Link Layer Address [i] encodes an IPv6 address for a node 1086 on the open INET. 1088 o Segment ID (SID) List [i] - Includes LHS[i]-many 4 byte ULA 1089 suffixes from the SRT corresponding to the SIDs prior to final 1090 encapsulation according to Link Layer Address [i]. The ultimate 1091 SID appears first, followed by the penultimate SID second, etc. 1093 o Link Layer Address [i] - Included according to FMT[i], and 1094 identifies the link-layer address (i.e., the encapsulation 1095 address) of the source/target. The address is recorded in ones- 1096 compliment "obfuscated" form per [RFC4380]. 1098 o Port Number [i] - The field is 2 bytes in length and immediately 1099 follows Link Layer Address [i]. Also recorded in ones-compliment 1100 "obfuscated" form. 1102 If an S/TLLAO is included, any ifIndex-tuples correspond to a proper 1103 subset of the OMNI option ifIndex-tuples. Any S/TLLAO ifIndex-tuple 1104 having an ifIndex value that does not appear in an OMNI option 1105 ifindex-tuple is ignored. If the same ifIndex value appears in 1106 multiple ifIndex-tuples, the first tuple is processed and the 1107 remaining tuples are ignored. Any S/TLLAO ifIndex-tuples can 1108 therefore be viewed as extensions of their corresponding OMNI option 1109 ifIndex-tuples, i.e., the OMNI option and S/TLLAO are companions that 1110 are interpreted in conjunction with each other. 1112 A Client's OMNI interface may be configured over multiple underlying 1113 interface connections. For example, common mobile handheld devices 1114 have both wireless local area network ("WLAN") and cellular wireless 1115 links. These links are often used "one at a time" with low-cost WLAN 1116 preferred and highly-available cellular wireless as a standby, but a 1117 simultaneous-use capability could provide benefits. In a more 1118 complex example, aircraft frequently have many wireless data link 1119 types (e.g. satellite-based, cellular, terrestrial, air-to-air 1120 directional, etc.) with diverse performance and cost properties. 1122 If a Client's multiple underlying interfaces are used "one at a time" 1123 (i.e., all other interfaces are in standby mode while one interface 1124 is active), then ND message OMNI options include only a single 1125 ifIndex-tuple set to constant values. In that case, the Client would 1126 appear to have a single interface but with a dynamically changing 1127 link-layer address. 1129 If the Client has multiple active underlying interfaces, then from 1130 the perspective of ND it would appear to have multiple link-layer 1131 addresses. In that case, ND message OMNI options MAY include 1132 multiple ifIndex-tuples - each with values that correspond to a 1133 specific interface. Every ND message need not include all OMNI and/ 1134 or S/TLLAO ifIndex-tuples; for any ifIndex-tuple not included, the 1135 neighbor considers the status as unchanged. 1137 Bridge, Server and Proxy OMNI interfaces may be configured over one 1138 or more secured tunnel interfaces. The OMNI interface configures 1139 both an LLA and its corresponding ULA, while the underlying secured 1140 tunnel interfaces are either unnumbered or configure the same ULA. 1141 The OMNI interface encapsulates each IP packet in a SPAN header and 1142 presents the packet to the underlying secured tunnel interface. For 1143 Bridges that do not configure an OMNI interface, the secured tunnel 1144 interfaces themselves are exposed to the IP layer with each interface 1145 configuring the Bridge's ULA. Routing protocols such as BGP 1146 therefore run directly over the Bridge's secured tunnel interfaces. 1147 For nodes that configure an OMNI interface, routing protocols such as 1148 BGP run over the OMNI interface but do not employ SPAN encapsulation. 1149 Instead, the OMNI interface presents the routing protocol messages 1150 directly to the underlying secured tunnels without applying 1151 encapsulation and while using the ULA as the source address. This 1152 distinction must be honored consistently according to each node's 1153 configuration so that the IP forwarding table will associate 1154 discovered IP routes with the correct interface. 1156 3.4. OMNI Interface Initialization 1158 AERO Servers, Proxys and Clients configure OMNI interfaces as their 1159 point of attachment to the OMNI link. AERO nodes assign the MSPs for 1160 the link to their OMNI interfaces (i.e., as a "route-to-interface") 1161 to ensure that packets with destination addresses covered by an MNP 1162 not explicitly assigned to a non-OMNI interface are directed to the 1163 OMNI interface. 1165 OMNI interface initialization procedures for Servers, Proxys, Clients 1166 and Bridges are discussed in the following sections. 1168 3.4.1. AERO Server/Relay Behavior 1170 When a Server enables an OMNI interface, it assigns an LLA/ULA 1171 appropriate for the given OMNI link segment. The Server also 1172 configures secured tunnels with one or more neighboring Bridges and 1173 engages in a BGP routing protocol session with each Bridge. 1175 The OMNI interface provides a single interface abstraction to the IP 1176 layer, but internally comprises multiple secured tunnels as well as 1177 an NBMA nexus for sending encapsulated data packets to OMNI interface 1178 neighbors. The Server further configures a service to facilitate ND/ 1179 PD exchanges with AERO Clients and manages per-Client neighbor cache 1180 entries and IP forwarding table entries based on control message 1181 exchanges. 1183 Relays are simply Servers that run a dynamic routing protocol to 1184 redistribute routes between the OMNI interface and INET/EUN 1185 interfaces (see: Section 3.2.3). The Relay provisions MNPs to 1186 networks on the INET/EUN interfaces (i.e., the same as a Client would 1187 do) and advertises the MSP(s) for the OMNI link over the INET/EUN 1188 interfaces. The Relay further provides an attachment point of the 1189 OMNI link to a non-MNP-based global topology. 1191 3.4.2. AERO Proxy Behavior 1193 When a Proxy enables an OMNI interface, it assigns an LLA/ULA and 1194 configures permanent neighbor cache entries the same as for Servers. 1195 The Proxy also configures secured tunnels with one or more 1196 neighboring Bridges and maintains per-Client neighbor cache entries 1197 based on control message exchanges. 1199 3.4.3. AERO Client Behavior 1201 When a Client enables an OMNI interface, it sends RS messages with 1202 ND/PD parameters over its underlying interfaces to a Server in the 1203 MAP list, which returns an RA message with corresponding parameters. 1205 (The RS/RA messages may pass through a Proxy in the case of a 1206 Client's Proxyed interface, or through one or more NATs in the case 1207 of a Client's INET interface.) 1209 3.4.4. AERO Bridge Behavior 1211 AERO Bridges configure an OMNI interface and assign the ULA Subnet 1212 Router Anycast address for each OMNI link segment they connect to. 1213 Bridges configure secured tunnels with Servers, Proxys and other 1214 Bridges; they also configure LLAs/ULAs and permanent neighbor cache 1215 entries the same as Servers. Bridges engage in a BGP routing 1216 protocol session with a subset of the Servers and other Bridges on 1217 the spanning tree (see: Section 3.2.3). 1219 3.5. OMNI Interface Neighbor Cache Maintenance 1221 Each OMNI interface maintains a conceptual neighbor cache that 1222 includes an entry for each neighbor it communicates with on the OMNI 1223 link per [RFC4861]. OMNI interface neighbor cache entries are said 1224 to be one of "permanent", "symmetric", "asymmetric" or "proxy". 1226 Permanent neighbor cache entries are created through explicit 1227 administrative action; they have no timeout values and remain in 1228 place until explicitly deleted. AERO Bridges maintain permanent 1229 neighbor cache entries for their associated Proxys and Servers (and 1230 vice-versa). Each entry maintains the mapping between the neighbor's 1231 network-layer LLA and corresponding INET address. 1233 Symmetric neighbor cache entries are created and maintained through 1234 RS/RA exchanges as specified in Section 3.12, and remain in place for 1235 durations bounded by ND/PD lifetimes. AERO Servers maintain 1236 symmetric neighbor cache entries for each of their associated 1237 Clients, and AERO Clients maintain symmetric neighbor cache entries 1238 for each of their associated Servers. The list of all Servers on the 1239 OMNI link is maintained in the link's MAP list. 1241 Asymmetric neighbor cache entries are created or updated based on 1242 route optimization messaging as specified in Section 3.14, and are 1243 garbage-collected when keepalive timers expire. AERO ROSs maintain 1244 asymmetric neighbor cache entries for active targets with lifetimes 1245 based on ND messaging constants. Asymmetric neighbor cache entries 1246 are unidirectional since only the ROS (and not the ROR) creates an 1247 entry. 1249 Proxy neighbor cache entries are created and maintained by AERO 1250 Proxys when they process Client/Server ND/PD exchanges, and remain in 1251 place for durations bounded by ND/PD lifetimes. AERO Proxys maintain 1252 proxy neighbor cache entries for each of their associated Clients. 1254 Proxy neighbor cache entries track the Client state and the address 1255 of the Client's associated Server(s). 1257 To the list of neighbor cache entry states in Section 7.3.2 of 1258 [RFC4861], Proxy and Server OMNI interfaces add an additional state 1259 DEPARTED that applies to symmetric and proxy neighbor cache entries 1260 for Clients that have recently departed. The interface sets a 1261 "DepartTime" variable for the neighbor cache entry to "DEPART_TIME" 1262 seconds. DepartTime is decremented unless a new ND message causes 1263 the state to return to REACHABLE. While a neighbor cache entry is in 1264 the DEPARTED state, packets destined to the target Client are 1265 forwarded to the Client's new location instead of being dropped. 1266 When DepartTime decrements to 0, the neighbor cache entry is deleted. 1267 It is RECOMMENDED that DEPART_TIME be set to the default constant 1268 value REACHABLE_TIME plus 10 seconds (40 seconds by default) to allow 1269 a window for packets in flight to be delivered while stale route 1270 optimization state may be present. 1272 When an ROR receives an authentic NS message used for route 1273 optimization, it searches for a symmetric neighbor cache entry for 1274 the target Client. The ROR then returns a solicited NA message 1275 without creating a neighbor cache entry for the ROS, but creates or 1276 updates a target Client "Report List" entry for the ROS and sets a 1277 "ReportTime" variable for the entry to REPORT_TIME seconds. The ROR 1278 resets ReportTime when it receives a new authentic NS message, and 1279 otherwise decrements ReportTime while no authentic NS messages have 1280 been received. It is RECOMMENDED that REPORT_TIME be set to the 1281 default constant value REACHABLE_TIME plus 10 seconds (40 seconds by 1282 default) to allow a window for route optimization to converge before 1283 ReportTime decrements below REACHABLE_TIME. 1285 When the ROS receives a solicited NA message response to its NS 1286 message used for route optimization, it creates or updates an 1287 asymmetric neighbor cache entry for the target network-layer and 1288 link-layer addresses. The ROS then (re)sets ReachableTime for the 1289 neighbor cache entry to REACHABLE_TIME seconds and uses this value to 1290 determine whether packets can be forwarded directly to the target, 1291 i.e., instead of via a default route. The ROS otherwise decrements 1292 ReachableTime while no further solicited NA messages arrive. It is 1293 RECOMMENDED that REACHABLE_TIME be set to the default constant value 1294 30 seconds as specified in [RFC4861]. 1296 AERO nodes also use the value MAX_UNICAST_SOLICIT to limit the number 1297 of NS keepalives sent when a correspondent may have gone unreachable, 1298 the value MAX_RTR_SOLICITATIONS to limit the number of RS messages 1299 sent without receiving an RA and the value MAX_NEIGHBOR_ADVERTISEMENT 1300 to limit the number of unsolicited NAs that can be sent based on a 1301 single event. It is RECOMMENDED that MAX_UNICAST_SOLICIT, 1302 MAX_RTR_SOLICITATIONS and MAX_NEIGHBOR_ADVERTISEMENT be set to 3 the 1303 same as specified in [RFC4861]. 1305 Different values for DEPART_TIME, REPORT_TIME, REACHABLE_TIME, 1306 MAX_UNICAST_SOLICIT, MAX_RTR_SOLCITATIONS and 1307 MAX_NEIGHBOR_ADVERTISEMENT MAY be administratively set; however, if 1308 different values are chosen, all nodes on the link MUST consistently 1309 configure the same values. Most importantly, DEPART_TIME and 1310 REPORT_TIME SHOULD be set to a value that is sufficiently longer than 1311 REACHABLE_TIME to avoid packet loss due to stale route optimization 1312 state. 1314 3.6. OMNI Interface Encapsulation and Re-encapsulation 1316 OMNI interfaces insert a mid-layer IPv6 header known as the SPAN 1317 header when necessary as discussed in the following sections. After 1318 either inserting or omitting the SPAN header, the OMNI interface also 1319 inserts or omits an outer encapsulation header as discussed below. 1321 OMNI interfaces avoid outer encapsulation over Direct underlying 1322 interfaces and Proxyed underlying interfaces for which the first-hop 1323 access router is AERO-aware. Other OMNI interfaces encapsulate 1324 packets according to whether they are entering the OMNI interface 1325 from the network layer or if they are being re-admitted into the same 1326 OMNI link they arrived on. This latter form of encapsulation is 1327 known as "re-encapsulation". 1329 For packets entering the OMNI interface from the network layer, the 1330 OMNI interface copies the "TTL/Hop Limit", "Type of Service/Traffic 1331 Class" [RFC2983], "Flow Label"[RFC6438] (for IPv6) and "Congestion 1332 Experienced" [RFC3168] values in the inner packet's IP header into 1333 the corresponding fields in the SPAN and outer encapsulation 1334 header(s). 1336 For packets undergoing re-encapsulation, the OMNI interface instead 1337 copies these values from the original encapsulation header into the 1338 new encapsulation header, i.e., the values are transferred between 1339 encapsulation headers and *not* copied from the encapsulated packet's 1340 network-layer header. (Note especially that by copying the TTL/Hop 1341 Limit between encapsulation headers the value will eventually 1342 decrement to 0 if there is a (temporary) routing loop.) 1344 OMNI interfaces configured over INET underlying interfaces 1345 encapsulate packets in INET headers according to the next hop 1346 determined in the forwarding algorithm in Section 3.10. If the next 1347 hop is reached via a secured tunnel, the OMNI interface uses an 1348 encapsulation format specific to the secured tunnel type (see: 1349 Section 6). If the next hop is reached via an unsecured INET 1350 interface, the OMNI interface instead uses UDP/IP encapsulation per 1351 [RFC4380] and as extended in [RFC6081]. 1353 When UDP/IP encapsulation is used, the OMNI interface next sets the 1354 UDP source port to a constant value that it will use in each 1355 successive packet it sends, and sets the UDP length field to the 1356 length of the encapsulated packet plus 8 bytes for the UDP header 1357 itself plus the length of any included extension headers or trailers. 1358 The encapsulated packet may be either IPv6 or IPv4, as distinguished 1359 by the version number found in the first four bits. 1361 For UDP/IP-encapsulated packets sent to a Server, Relay or Bridge, 1362 the OMNI interface sets the UDP destination port to 8060, i.e., the 1363 IANA-registered port number for AERO. For packets sent to a Client, 1364 the OMNI interface sets the UDP destination port to the port value 1365 stored in the neighbor cache entry for this Client. The OMNI 1366 interface finally includes/omits the UDP checksum according to 1367 [RFC6935][RFC6936]. 1369 3.7. OMNI Interface Decapsulation 1371 OMNI interfaces decapsulate packets destined either to the AERO node 1372 itself or to a destination reached via an interface other than the 1373 OMNI interface the packet was received on. When the encapsulated 1374 packet arrives in multiple SPAN fragments, the OMNI interface 1375 reassembles as discussed in Section 3.9. Further decapsulation steps 1376 are performed according to the appropriate encapsulation format 1377 specification. 1379 3.8. OMNI Interface Data Origin Authentication 1381 AERO nodes employ simple data origin authentication procedures. In 1382 particular: 1384 o AERO Bridges, Servers and Proxys accept encapsulated data packets 1385 and control messages received from the spanning tree. 1387 o AERO Proxys and Clients accept packets that originate from within 1388 the same secured ANET. 1390 o AERO Clients and Relays accept packets from downstream network 1391 correspondents based on ingress filtering. 1393 o AERO Clients, Relays and Servers verify the outer UDP/IP 1394 encapsulation addresses according to [RFC4380]. 1396 AERO nodes silently drop any packets that do not satisfy the above 1397 data origin authentication procedures. Further security 1398 considerations are discussed in Section 6. 1400 3.9. OMNI Interface MTU and Fragmentation 1402 The OMNI interface observes the link nature of tunnels, including the 1403 Maximum Transmission Unit (MTU) and the role of fragmentation and 1404 reassembly[I-D.ietf-intarea-tunnels]. OMNI interface MTU and 1405 fragmentation/reassembly procedures are specified in 1406 [I-D.templin-6man-omni-interface]. 1408 3.10. OMNI Interface Forwarding Algorithm 1410 IP packets enter a node's OMNI interface either from the network 1411 layer (i.e., from a local application or the IP forwarding system) or 1412 from the link layer (i.e., from an OMNI interface neighbor). All 1413 packets entering a node's OMNI interface first undergo data origin 1414 authentication as discussed in Section 3.8. Packets that satisfy 1415 data origin authentication are processed further, while all others 1416 are dropped silently. 1418 Packets that enter the OMNI interface from the network layer are 1419 forwarded to an OMNI interface neighbor. Packets that enter the OMNI 1420 interface from the link layer are either re-admitted into the OMNI 1421 link or forwarded to the network layer where they are subject to 1422 either local delivery or IP forwarding. In all cases, the OMNI 1423 interface itself MUST NOT decrement the network layer TTL/Hop-count 1424 since its forwarding actions occur below the network layer. 1426 OMNI interfaces may have multiple underlying interfaces and/or 1427 neighbor cache entries for neighbors with multiple ifIndex-tuple 1428 registrations (see Section 3.3). The OMNI interface uses traffic 1429 classifiers (e.g., DSCP value, port number, etc.) to select an 1430 outgoing underlying interface for each packet based on the node's own 1431 QoS preferences, and also to select a destination link-layer address 1432 based on the neighbor's underlying interface with the highest 1433 preference. AERO implementations SHOULD allow for QoS preference 1434 values to be modified at runtime through network management. 1436 If multiple outgoing interfaces and/or neighbor interfaces have a 1437 preference of "high", the AERO node replicates the packet and sends 1438 one copy via each of the (outgoing / neighbor) interface pairs; 1439 otherwise, the node sends a single copy of the packet via an 1440 interface with the highest preference. AERO nodes keep track of 1441 which underlying interfaces are currently "reachable" or 1442 "unreachable", and only use "reachable" interfaces for forwarding 1443 purposes. 1445 The following sections discuss the OMNI interface forwarding 1446 algorithms for Clients, Proxys, Servers and Bridges. In the 1447 following discussion, a packet's destination address is said to 1448 "match" if it is the same as a cached address, or if it is covered by 1449 a cached prefix (which may be encoded in an LLA). 1451 3.10.1. Client Forwarding Algorithm 1453 When an IP packet enters a Client's OMNI interface from the network 1454 layer the Client searches for an asymmetric neighbor cache entry that 1455 matches the destination. If there is a match, the Client uses one or 1456 more "reachable" neighbor interfaces in the entry for packet 1457 forwarding. If there is no asymmetric neighbor cache entry, the 1458 Client instead forwards the packet toward a Server (the packet is 1459 intercepted by a Proxy if there is a Proxy on the path). The Client 1460 encapsulates the packet in a SPAN header and fragments if necessary 1461 according to MTU requirements (see: Section 3.9). 1463 When an IP packet enters a Client's OMNI interface from the link- 1464 layer, if the destination matches one of the Client's MNPs or link- 1465 local addresses the Client reassembles and decapsulates as necessary 1466 and delivers the inner packet to the network layer. Otherwise, the 1467 Client drops the packet and MAY return a network-layer ICMP 1468 Destination Unreachable message subject to rate limiting (see: 1469 Section 3.11). 1471 3.10.2. Proxy Forwarding Algorithm 1473 For control messages originating from or destined to a Client, the 1474 Proxy intercepts the message and updates its proxy neighbor cache 1475 entry for the Client. The Proxy then forwards a (proxyed) copy of 1476 the control message. (For example, the Proxy forwards a proxied 1477 version of a Client's NS/RS message to the target neighbor, and 1478 forwards a proxied version of the NA/RA reply to the Client.) 1480 When the Proxy receives a data packet from a Client within the ANET, 1481 the Proxy reassembles and re-fragments if necessary then searches for 1482 an asymmetric neighbor cache entry that matches the destination and 1483 forwards as follows: 1485 o if the destination matches an asymmetric neighbor cache entry, the 1486 Proxy uses one or more "reachable" neighbor interfaces in the 1487 entry for packet forwarding using SPAN encapsulation and including 1488 a SRH if necessary according to the cached TLLAO information. If 1489 the neighbor interface is in the same SPAN segment, the Proxy 1490 forwards the packet directly to the neighbor; otherwise, it 1491 forwards the packet to a Bridge. 1493 o else, the Proxy uses SPAN encapsulation and forwards the packet to 1494 a Bridge while using the ULA corresponding to the packet's 1495 destination as the SPAN destination address. 1497 When the Proxy receives an encapsulated data packet from an INET 1498 neighbor or from a secured tunnel from a Bridge, it accepts the 1499 packet only if data origin authentication succeeds and if there is a 1500 proxy neighbor cache entry that matches the inner destination. Next, 1501 the Proxy reassembles the packet (if necessary) and continues 1502 processing. 1504 Next if reassembly is complete and the neighbor cache state is 1505 REACHABLE, the Proxy returns a PTB if necessary (see: Section 3.9) 1506 then either drops or forwards the packet to the Client while 1507 performing SPAN encapsulation and re-fragmentation to the ANET MTU 1508 size if necessary. If the neighbor cache entry state is DEPARTED, 1509 the Proxy instead changes the SPAN destination address to the address 1510 of the new Server and forwards it to a Bridge while performing re- 1511 fragmentation to 1280 bytes if necessary. 1513 3.10.3. Server/Relay Forwarding Algorithm 1515 For control messages destined to a target Client's LLA that are 1516 received from a secured tunnel, the Server intercepts the message and 1517 sends an appropriate response on behalf of the Client. (For example, 1518 the Server sends an NA message reply in response to an NS message 1519 directed to one of its associated Clients.) If the Client's neighbor 1520 cache entry is in the DEPARTED state, however, the Server instead 1521 forwards the packet to the Client's new Server as discussed in 1522 Section 3.16. 1524 When the Server receives an encapsulated data packet from an INET 1525 neighbor or from a secured tunnel, it accepts the packet only if data 1526 origin authentication succeeds. If the SPAN destination address is 1527 its own address, the Server continues processing as follows: 1529 o if the destination matches a symmetric neighbor cache entry in the 1530 REACHABLE state the Server prepares the packet for forwarding to 1531 the destination Client. The Server first reassembles (if 1532 necessary) and forwards the packet (while re-fragmenting if 1533 necessary) as specified in Section 3.9. 1535 o else, if the destination matches a symmetric neighbor cache entry 1536 in the DEPARETED state the Server re-encapsulates the packet and 1537 forwards it using the ULA of the Client's new Server as the 1538 destination. 1540 o else, if the destination matches an asymmetric neighbor cache 1541 entry, the Server uses one or more "reachable" neighbor interfaces 1542 in the entry for packet forwarding via the local INET if the 1543 neighbor is in the same OMNI link segment or using SPAN 1544 encapsulation and Segment Routing if necessary with the final 1545 destination set to the neighbor's ULA otherwise. 1547 o else, if the destination is an LLA that is not assigned on the 1548 OMNI interface the Server drops the packet. 1550 o else, the Server (acting as a Relay) reassembles if necessary, 1551 decapsulates the packet and releases it to the network layer for 1552 local delivery or IP forwarding. Based on the information in the 1553 forwarding table, the network layer may return the packet to the 1554 same OMNI interface in which case further processing occurs as 1555 below. (Note that this arrangement accommodates common 1556 implementations in which the IP forwarding table is not accessible 1557 from within the OMNI interface. If the OMNI interface can 1558 directly access the IP forwarding table (such as for in-kernel 1559 implementations) the forwarding table lookup can instead be 1560 performed internally from within the OMNI interface itself.) 1562 When the Server's OMNI interface receives a data packet from the 1563 network layer or from a VPNed or Direct Client, it performs SPAN 1564 encapsulation and fragmentation if necessary, then processes the 1565 packet according to the network-layer destination address as follows: 1567 o if the destination matches a symmetric or asymmetric neighbor 1568 cache entry the Server processes the packet as above. 1570 o else, the Server encapsulates the packet and forwards it to a 1571 Bridge using its own ULA as the source and the ULA corresponding 1572 to the destination as the destination. 1574 3.10.4. Bridge Forwarding Algorithm 1576 Bridges forward SPAN-encapsulated packets over secured tunnels the 1577 same as any IP router. When the Bridge receives a SPAN-encapsulated 1578 packet via a secured tunnel, it removes the outer INET header and 1579 searches for a forwarding table entry that matches the SPAN 1580 destination address. The Bridge then processes the packet as 1581 follows: 1583 o if the destination matches its ULA Subnet Router Anycast address, 1584 the Bridge checks for a SRH. If there is a SRH with Segments 1585 Left=1, with the ULA of a Server on the local segment as the 1586 ultimate segment ID, and with an AERO Route Optimization TLV, the 1587 Bridge examines the FMT to determine if the target is behind a 1588 NAT. If no NAT is indicated, the Bridge copies the MNP Subnet 1589 Router Anycast address into the destination address then forwards 1590 the packet directly to the Link Layer Address using link-layer 1591 (UDP/IP) encapsulation. If a NAT is indicated, the Bridge MAY 1592 perform NAT traversal procedures by sending bubbles per [RFC4380]. 1593 The Bridge then either applies AERO route optimization if NAT 1594 traversal procedures have been successfully applied, or forwards 1595 the packet directly to the Server. 1597 o if the destination matches one of the Bridge's own addresses, the 1598 Bridge submits the packet for local delivery. 1600 o else, if the destination matches a forwarding table entry the 1601 Bridge forwards the packet via a secured tunnel to the next hop. 1602 If the destination matches an MSP without matching an MNP, 1603 however, the Bridge instead drops the packet and returns an ICMP 1604 Destination Unreachable message subject to rate limiting (see: 1605 Section 3.11). 1607 o else, the Bridge drops the packet and returns an ICMP Destination 1608 Unreachable as above. 1610 As for any IP router, the Bridge decrements the TTL/Hop Limit when it 1611 forwards the packet. Therefore, only the Hop Limit in the SPAN 1612 header is decremented, and not the TTL/Hop Limit in the inner packet 1613 header. 1615 3.11. OMNI Interface Error Handling 1617 When an AERO node admits a packet into the OMNI interface, it may 1618 receive link-layer or network-layer error indications. 1620 A link-layer error indication is an ICMP error message generated by a 1621 router in the INET on the path to the neighbor or by the neighbor 1622 itself. The message includes an IP header with the address of the 1623 node that generated the error as the source address and with the 1624 link-layer address of the AERO node as the destination address. 1626 The IP header is followed by an ICMP header that includes an error 1627 Type, Code and Checksum. Valid type values include "Destination 1628 Unreachable", "Time Exceeded" and "Parameter Problem" 1629 [RFC0792][RFC4443]. (OMNI interfaces ignore all link-layer IPv4 1630 "Fragmentation Needed" and IPv6 "Packet Too Big" messages since they 1631 only emit packets that are guaranteed to be no larger than the IP 1632 minimum link MTU as discussed in Section 3.9.) 1634 The ICMP header is followed by the leading portion of the packet that 1635 generated the error, also known as the "packet-in-error". For 1636 ICMPv6, [RFC4443] specifies that the packet-in-error includes: "As 1637 much of invoking packet as possible without the ICMPv6 packet 1638 exceeding the minimum IPv6 MTU" (i.e., no more than 1280 bytes). For 1639 ICMPv4, [RFC0792] specifies that the packet-in-error includes: 1640 "Internet Header + 64 bits of Original Data Datagram", however 1641 [RFC1812] Section 4.3.2.3 updates this specification by stating: "the 1642 ICMP datagram SHOULD contain as much of the original datagram as 1643 possible without the length of the ICMP datagram exceeding 576 1644 bytes". 1646 The link-layer error message format is shown in Figure 6 (where, "L2" 1647 and "L3" refer to link-layer and network-layer, respectively): 1649 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1650 ~ ~ 1651 | L2 IP Header of | 1652 | error message | 1653 ~ ~ 1654 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1655 | L2 ICMP Header | 1656 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 1657 ~ ~ P 1658 | IP and other encapsulation | a 1659 | headers of original L3 packet | c 1660 ~ ~ k 1661 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ e 1662 ~ ~ t 1663 | IP header of | 1664 | original L3 packet | i 1665 ~ ~ n 1666 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1667 ~ ~ e 1668 | Upper layer headers and | r 1669 | leading portion of body | r 1670 | of the original L3 packet | o 1671 ~ ~ r 1672 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 1674 Figure 6: OMNI Interface Link-Layer Error Message Format 1676 The AERO node rules for processing these link-layer error messages 1677 are as follows: 1679 o When an AERO node receives a link-layer Parameter Problem message, 1680 it processes the message the same as described as for ordinary 1681 ICMP errors in the normative references [RFC0792][RFC4443]. 1683 o When an AERO node receives persistent link-layer Time Exceeded 1684 messages, the IP ID field may be wrapping before earlier fragments 1685 awaiting reassembly have been processed. In that case, the node 1686 should begin including integrity checks and/or institute rate 1687 limits for subsequent packets. 1689 o When an AERO node receives persistent link-layer Destination 1690 Unreachable messages in response to encapsulated packets that it 1691 sends to one of its asymmetric neighbor correspondents, the node 1692 should process the message as an indication that a path may be 1693 failing, and optionally initiate NUD over that path. If it 1694 receives Destination Unreachable messages over multiple paths, the 1695 node should allow future packets destined to the correspondent to 1696 flow through a default route and re-initiate route optimization. 1698 o When an AERO Client receives persistent link-layer Destination 1699 Unreachable messages in response to encapsulated packets that it 1700 sends to one of its symmetric neighbor Servers, the Client should 1701 mark the path as unusable and use another path. If it receives 1702 Destination Unreachable messages on many or all paths, the Client 1703 should associate with a new Server and release its association 1704 with the old Server as specified in Section 3.16.5. 1706 o When an AERO Server receives persistent link-layer Destination 1707 Unreachable messages in response to encapsulated packets that it 1708 sends to one of its symmetric neighbor Clients, the Server should 1709 mark the underlying path as unusable and use another underlying 1710 path. 1712 o When an AERO Server or Proxy receives link-layer Destination 1713 Unreachable messages in response to an encapsulated packet that it 1714 sends to one of its permanent neighbors, it treats the messages as 1715 an indication that the path to the neighbor may be failing. 1716 However, the dynamic routing protocol should soon reconverge and 1717 correct the temporary outage. 1719 When an AERO Bridge receives a packet for which the network-layer 1720 destination address is covered by an MSP, if there is no more- 1721 specific routing information for the destination the Bridge drops the 1722 packet and returns a network-layer Destination Unreachable message 1723 subject to rate limiting. The Bridge writes the network-layer source 1724 address of the original packet as the destination address and uses 1725 one of its non link-local addresses as the source address of the 1726 message. 1728 When an AERO node receives an encapsulated packet for which the 1729 reassembly buffer it too small, it drops the packet and returns a 1730 network-layer Packet Too Big (PTB) message. The node first writes 1731 the MRU value into the PTB message MTU field, writes the network- 1732 layer source address of the original packet as the destination 1733 address and writes one of its non link-local addresses as the source 1734 address. 1736 3.12. AERO Router Discovery, Prefix Delegation and Autoconfiguration 1738 AERO Router Discovery, Prefix Delegation and Autoconfiguration are 1739 coordinated as discussed in the following Sections. 1741 3.12.1. AERO ND/PD Service Model 1743 Each AERO Server on the OMNI link configures a PD service to 1744 facilitate Client requests. Each Server is provisioned with a 1745 database of MNP-to-Client ID mappings for all Clients enrolled in the 1746 AERO service, as well as any information necessary to authenticate 1747 each Client. The Client database is maintained by a central 1748 administrative authority for the OMNI link and securely distributed 1749 to all Servers, e.g., via the Lightweight Directory Access Protocol 1750 (LDAP) [RFC4511], via static configuration, etc. Clients receive the 1751 same service regardless of the Servers they select. 1753 AERO Clients and Servers use ND messages to maintain neighbor cache 1754 entries. AERO Servers configure their OMNI interfaces as advertising 1755 NBMA interfaces, and therefore send unicast RA messages with a short 1756 Router Lifetime value (e.g., ReachableTime seconds) in response to a 1757 Client's RS message. Thereafter, Clients send additional RS messages 1758 to keep Server state alive. 1760 AERO Clients and Servers include PD parameters in RS/RA messages (see 1761 [I-D.templin-6man-dhcpv6-ndopt] for ND/PD alternatives). The unified 1762 ND/PD messages are exchanged between Client and Server according to 1763 the prefix management schedule required by the PD service. If the 1764 Client knows its MNP in advance, it can instead employ prefix 1765 registration by including its LLA as the source address of an RS 1766 message and with an OMNI option with valid prefix registration 1767 information for the MNP. If the Server (and Proxy) accept the 1768 Client's MNP assertion, they inject the prefix into the routing 1769 system and establish the necessary neighbor cache state. 1771 The following sections specify the Client and Server behavior. 1773 3.12.2. AERO Client Behavior 1775 AERO Clients discover the addresses of Servers in a similar manner as 1776 described in [RFC5214]. Discovery methods include static 1777 configuration (e.g., from a flat-file map of Server addresses and 1778 locations), or through an automated means such as Domain Name System 1779 (DNS) name resolution [RFC1035]. Alternatively, the Client can 1780 discover Server addresses through a layer 2 data link login exchange, 1781 or through a unicast RA response to a multicast/anycast RS as 1782 described below. In the absence of other information, the Client can 1783 resolve the DNS Fully-Qualified Domain Name (FQDN) 1784 "linkupnetworks.[domainname]" where "linkupnetworks" is a constant 1785 text string and "[domainname]" is a DNS suffix for the OMNI link 1786 (e.g., "example.com"). 1788 To associate with a Server, the Client acts as a requesting router to 1789 request MNPs. The Client prepares an RS message with PD parameters 1790 and includes a Nonce and Timestamp option if the Client needs to 1791 correlate RA replies. If the Client already knows the Server's LLA, 1792 it includes the LLA as the network-layer destination address; 1793 otherwise, it includes the link-scoped All-Routers multicast 1794 (ff02::2) or Subnet-Router anycast (fe80::) address as the network- 1795 layer destination. If the Client already knows its own LLA, it uses 1796 the LLA as the network-layer source address; otherwise, it uses the 1797 unspecified IPv6 address (::/128) as the network-layer source 1798 address. 1800 The Client next includes an OMNI option in the RS message to register 1801 its link-layer information with the Server. The Client sets the OMNI 1802 option prefix registration information according to the MNP, and 1803 includes an ifIndex-tuple with S set to '1' corresponding to the 1804 underlying interface over which the Client will send the RS message. 1805 The Client MAY include additional ifIndex-tuples specific to other 1806 underlying interfaces. The Client MAY also include an SLLAO 1807 corresponding to the OMNI option ifIndex-tuple with S set to '1'. 1809 The Client then sends the RS message (either directly via Direct 1810 interfaces, via a VPN for VPNed interfaces, via a Proxy for proxyed 1811 interfaces or via INET encapsulation for INET interfaces) and waits 1812 for an RA message reply (see Section 3.12.3). The Client retries up 1813 to MAX_RTR_SOLICITATIONS times until an RA is received. If the 1814 Client receives no RAs, or if it receives an RA with Router Lifetime 1815 set to 0, the Client SHOULD abandon this Server and try another 1816 Server. Otherwise, the Client processes the PD information found in 1817 the RA message. 1819 Next, the Client creates a symmetric neighbor cache entry with the 1820 Server's LLA as the network-layer address and the Server's 1821 encapsulation and/or link-layer addresses as the link-layer address. 1822 The Client records the RA Router Lifetime field value in the neighbor 1823 cache entry as the time for which the Server has committed to 1824 maintaining the MNP in the routing system via this underlying 1825 interface, and caches the other RA configuration information 1826 including Cur Hop Limit, M and O flags, Reachable Time and Retrans 1827 Timer. The Client then autoconfigures LLAs for each of the delegated 1828 MNPs and assigns them to the OMNI interface. The Client also caches 1829 any MSPs included in Route Information Options (RIOs) [RFC4191] as 1830 MSPs to associate with the OMNI link, and assigns the MTU value in 1831 the MTU option to the underlying interface. 1833 The Client then registers additional underlying interfaces with the 1834 Server by sending RS messages via each additional interface. The RS 1835 messages include the same parameters as for the initial RS/RA 1836 exchange, but with destination address set to the Server's LLA. 1838 Following autoconfiguration, the Client sub-delegates the MNPs to its 1839 attached EUNs and/or the Client's own internal virtual interfaces as 1840 described in [I-D.templin-v6ops-pdhost] to support the Client's 1841 downstream attached "Internet of Things (IoT)". The Client 1842 subsequently sends additional RS messages over each underlying 1843 interface before the Router Lifetime received for that interface 1844 expires. 1846 After the Client registers its underlying interfaces, it may wish to 1847 change one or more registrations, e.g., if an interface changes 1848 address or becomes unavailable, if QoS preferences change, etc. To 1849 do so, the Client prepares an RS message to send over any available 1850 underlying interface. The RS includes an OMNI option with prefix 1851 registration information specific to its MNP, with an ifIndex-tuple 1852 specific to the selected underlying interface with S set to '1', and 1853 with any additional ifIndex-tuples specific to other underlying 1854 interfaces. The Client includes fresh ifIndex-tuple values to update 1855 the Server's neighbor cache entry. When the Client receives the 1856 Server's RA response, it has assurance that the Server has been 1857 updated with the new information. 1859 If the Client wishes to discontinue use of a Server it issues an RS 1860 message over any underlying interface with an OMNI option with a 1861 prefix release indication. When the Server processes the message, it 1862 releases the MNP, sets the symmetric neighbor cache entry state for 1863 the Client to DEPARTED and returns an RA reply with Router Lifetime 1864 set to 0. After a short delay (e.g., 2 seconds), the Server 1865 withdraws the MNP from the routing system. 1867 3.12.3. AERO Server Behavior 1869 AERO Servers act as IP routers and support a PD service for Clients. 1870 Servers arrange to add their LLAs to a static map of Server addresses 1871 for the link and/or the DNS resource records for the FQDN 1872 "linkupnetworks.[domainname]" before entering service. Server 1873 addresses should be geographically and/or topologically referenced, 1874 and made available for discovery by Clients on the OMNI link. 1876 When a Server receives a prospective Client's RS message on its OMNI 1877 interface, it SHOULD return an immediate RA reply with Router 1878 Lifetime set to 0 if it is currently too busy or otherwise unable to 1879 service the Client. Otherwise, the Server authenticates the RS 1880 message and processes the PD parameters. The Server first determines 1881 the correct MNPs to delegate to the Client by searching the Client 1882 database. When the Server delegates the MNPs, it also creates a 1883 forwarding table entry for each MNP so that the MNPs are propagated 1884 into the routing system (see: Section 3.2.3). For IPv6, the Server 1885 creates an IPv6 forwarding table entry for each MNP. For IPv4, the 1886 Server creates an IPv6 forwarding table entry with the SPAN 1887 Compatibility Prefix (SCP) corresponding to the IPv4 address. 1889 The Server next creates a symmetric neighbor cache entry for the 1890 Client using the base LLA as the network-layer address and with 1891 lifetime set to no more than the smallest PD lifetime. Next, the 1892 Server updates the neighbor cache entry by recording the information 1893 in each ifIndex-tuple in the RS OMNI option. The Server also records 1894 the actual SPAN/INET addresses in the neighbor cache entry. 1896 Next, the Server prepares an RA message using its LLA as the network- 1897 layer source address and the network-layer source address of the RS 1898 message as the network-layer destination address. The Server sets 1899 the Router Lifetime to the time for which it will maintain both this 1900 underlying interface individually and the symmetric neighbor cache 1901 entry as a whole. The Server also sets Cur Hop Limit, M and O flags, 1902 Reachable Time and Retrans Timer to values appropriate for the OMNI 1903 link. The Server includes the delegated MNPs, any other PD 1904 parameters and an OMNI option with no ifIndex-tuples. The Server 1905 then includes one or more RIOs that encode the MSPs for the OMNI 1906 link, plus an MTU option (see Section 3.9). The Server finally 1907 forwards the message to the Client using SPAN/INET, INET, or NULL 1908 encapsulation as necessary. 1910 After the initial RS/RA exchange, the Server maintains a 1911 ReachableTime timer for each of the Client's underlying interfaces 1912 individually (and for the Client's symmetric neighbor cache entry 1913 collectively) set to expire after ReachableTime seconds. If the 1914 Client (or Proxy) issues additional RS messages, the Server sends an 1915 RA response and resets ReachableTime. If the Server receives an ND 1916 message with PD release indication it sets the Client's symmetric 1917 neighbor cache entry to the DEPARTED state and withdraws the MNP from 1918 the routing system after a short delay (e.g., 2 seconds). If 1919 ReachableTime expires before a new RS is received on an individual 1920 underlying interface, the Server marks the interface as DOWN. If 1921 ReachableTime expires before any new RS is received on any individual 1922 underlying interface, the Server sets the symmetric neighbor cache 1923 entry state to STALE and sets a 10 second timer. If the Server has 1924 not received a new RS or ND message with PD release indication before 1925 the 10 second timer expires, it deletes the neighbor cache entry and 1926 withdraws the MNP from the routing system. 1928 The Server processes any ND/PD messages pertaining to the Client and 1929 returns an NA/RA reply in response to solicitations. The Server may 1930 also issue unsolicited RA messages, e.g., with PD reconfigure 1931 parameters to cause the Client to renegotiate its PDs, with Router 1932 Lifetime set to 0 if it can no longer service this Client, etc. 1933 Finally, If the symmetric neighbor cache entry is in the DEPARTED 1934 state, the Server deletes the entry after DepartTime expires. 1936 Note: Clients SHOULD notify former Servers of their departures, but 1937 Servers are responsible for expiring neighbor cache entries and 1938 withdrawing routes even if no departure notification is received 1939 (e.g., if the Client leaves the network unexpectedly). Servers 1940 SHOULD therefore set Router Lifetime to ReachableTime seconds in 1941 solicited RA messages to minimize persistent stale cache information 1942 in the absence of Client departure notifications. A short Router 1943 Lifetime also ensures that proactive Client/Server RS/RA messaging 1944 will keep any NAT state alive (see above). 1946 Note: All Servers on an OMNI link MUST advertise consistent values in 1947 the RA Cur Hop Limit, M and O flags, Reachable Time and Retrans Timer 1948 fields the same as for any link, since unpredictable behavior could 1949 result if different Servers on the same link advertised different 1950 values. 1952 3.12.3.1. Lightweight DHCPv6 Relay Agent (LDRA) 1954 When DHCPv6 is used as the ND/PD service back end, AERO Clients and 1955 Servers are always on the same link (i.e., the OMNI link) from the 1956 perspective of DHCPv6. However, in some implementations the DHCPv6 1957 server and ND function may be located in separate modules. In that 1958 case, the Server's OMNI interface module can act as a Lightweight 1959 DHCPv6 Relay Agent (LDRA)[RFC6221] to relay PD messages to and from 1960 the DHCPv6 server module. 1962 When the LDRA receives an authentic RS message, it extracts the PD 1963 message parameters and uses them to construct an IPv6/UDP/DHCPv6 1964 message. It sets the IPv6 source address to the source address of 1965 the RS message, sets the IPv6 destination address to 1966 'All_DHCP_Relay_Agents_and_Servers' and sets the UDP fields to values 1967 that will be understood by the DHCPv6 server. 1969 The LDRA then wraps the message in a DHCPv6 'Relay-Forward' message 1970 header and includes an 'Interface-Id' option that includes enough 1971 information to allow the LDRA to forward the resulting Reply message 1972 back to the Client (e.g., the Client's link-layer addresses, a 1973 security association identifier, etc.). The LDRA also wraps the OMNI 1974 option and SLLAO into the Interface-Id option, then forwards the 1975 message to the DHCPv6 server. 1977 When the DHCPv6 server prepares a Reply message, it wraps the message 1978 in a 'Relay-Reply' message and echoes the Interface-Id option. The 1979 DHCPv6 server then delivers the Relay-Reply message to the LDRA, 1980 which discards the Relay-Reply wrapper and IPv6/UDP headers, then 1981 uses the DHCPv6 message to construct an RA response to the Client. 1982 The Server uses the information in the Interface-Id option to prepare 1983 the RA message and to cache the link-layer addresses taken from the 1984 OMNI option and SLLAO echoed in the Interface-Id option. 1986 3.13. The AERO Proxy 1988 Clients may connect to protected-spectrum ANETs that deploy physical 1989 and/or link-layer security services to facilitate communications to 1990 Servers in outside INETs. In that case, the ANET can employ an AERO 1991 Proxy. The Proxy is located at the ANET/INET border and listens for 1992 RS messages originating from or RA messages destined to ANET Clients. 1993 The Proxy acts on these control messages as follows: 1995 o when the Proxy receives an RS message from a new ANET Client, it 1996 first authenticates the message then examines the network-layer 1997 destination address. If the destination address is a Server's 1998 LLA, the Proxy proceeds to the next step. Otherwise, if the 1999 destination is All-Routers multicast or Subnet-Router anycast, the 2000 Proxy selects a "nearby" Server that is likely to be a good 2001 candidate to serve the Client and replaces the destination address 2002 with the Server's LLA. Next, the Proxy creates a proxy neighbor 2003 cache entry and caches the Client and Server link-layer addresses 2004 along with the OMNI option information and any other identifying 2005 information including Transaction IDs, Client Identifiers, Nonce 2006 values, etc. The Proxy finally encapsulates the (proxyed) RS 2007 message in a SPAN header with source set to the Proxy's ULA and 2008 destination set to the Server's ULA then forwards the message into 2009 the SPAN. 2011 o when the Server receives the RS, it authenticates the message then 2012 creates or updates a symmetric neighbor cache entry for the Client 2013 with the Proxy's ULA as the link-layer address. The Server then 2014 sends an RA message back to the Proxy via the spanning tree. 2016 o when the Proxy receives the RA, it authenticates the message and 2017 matches it with the proxy neighbor cache entry created by the RS. 2018 The Proxy then caches the PD route information as a mapping from 2019 the Client's MNPs to the Client's link-layer address, caches the 2020 Server's advertised Router Lifetime and sets the neighbor cache 2021 entry state to REACHABLE. The Proxy then sets the P bit in the RA 2022 flags field, optionally rewrites the Router Lifetime and forwards 2023 the (proxyed) message to the Client. The Proxy finally includes 2024 an MTU option (if necessary) with an MTU to use for the underlying 2025 ANET interface. 2027 After the initial RS/RA exchange, the Proxy forwards any Client data 2028 packets for which there is no matching asymmetric neighbor cache 2029 entry to a Bridge using SPAN encapsulation with its own ULA as the 2030 source and the ULA corresponding to the Client as the destination. 2031 The Proxy instead forwards any Client data destined to an asymmetric 2032 neighbor cache target directly to the target according to the SPAN/ 2033 link-layer information - the process of establishing asymmetric 2034 neighbor cache entries is specified in Section 3.14. 2036 While the Client is still attached to the ANET, the Proxy sends NS, 2037 RS and/or unsolicited NA messages to update the Server's symmetric 2038 neighbor cache entries on behalf of the Client and/or to convey QoS 2039 updates. This allows for higher-frequency Proxy-initiated RS/RA 2040 messaging over well-connected INET infrastructure supplemented by 2041 lower-frequency Client-initiated RS/RA messaging over constrained 2042 ANET data links. 2044 If the Server ceases to send solicited advertisements, the Proxy 2045 sends unsolicited RAs on the ANET interface with destination set to 2046 link-scoped All-Nodes multicast (ff02::1) and with Router Lifetime 2047 set to zero to inform Clients that the Server has failed. Although 2048 the Proxy engages in ND exchanges on behalf of the Client, the Client 2049 can also send ND messages on its own behalf, e.g., if it is in a 2050 better position than the Proxy to convey QoS changes, etc. For this 2051 reason, the Proxy marks any Client-originated solicitation messages 2052 (e.g. by inserting a Nonce option) so that it can return the 2053 solicited advertisement to the Client instead of processing it 2054 locally. 2056 If the Client becomes unreachable, the Proxy sets the neighbor cache 2057 entry state to DEPARTED and retains the entry for DepartTime seconds. 2058 While the state is DEPARTED, the Proxy forwards any packets destined 2059 to the Client to a Bridge via SPAN encapsulation with the Client's 2060 current Server as the destination. The Bridge in turn forwards the 2061 packets to the Client's current Server. When DepartTime expires, the 2062 Proxy deletes the neighbor cache entry and discards any further 2063 packets destined to this (now forgotten) Client. 2065 In some ANETs that employ a Proxy, the Client's MNP can be injected 2066 into the ANET routing system. In that case, the Client can send data 2067 messages without encapsulation so that the ANET routing system 2068 transports the unencapsulated packets to the Proxy. This can be very 2069 beneficial, e.g., if the Client connects to the ANET via low-end data 2070 links such as some aviation wireless links. 2072 If the first-hop ANET access router is AERO-aware, the Client can 2073 avoid encapsulation for both its control and data messages. When the 2074 Client connects to the link, it can send an unencapsulated RS message 2075 with source address set to its LLA and with destination address set 2076 to the LLA of the Client's selected Server or to All-Routers 2077 multicast or Subnet-Router anycast. The Client includes an OMNI 2078 option formatted as specified in [I-D.templin-6man-omni-interface]. 2080 The Client then sends the unencapsulated RS message, which will be 2081 intercepted by the AERO-Aware access router. The access router then 2082 encapsulates the RS message in an ANET header with its own address as 2083 the source address and the address of a Proxy as the destination 2084 address. The access router further remembers the address of the 2085 Proxy so that it can encapsulate future data packets from the Client 2086 via the same Proxy. If the access router needs to change to a new 2087 Proxy, it simply sends another RS message toward the Server via the 2088 new Proxy on behalf of the Client. 2090 In some cases, the access router and Proxy may be one and the same 2091 node. In that case, the node would be located on the same physical 2092 link as the Client, but its message exchanges with the Server would 2093 need to pass through a security gateway at the ANET/INET border. The 2094 method for deploying access routers and Proxys (i.e. as a single node 2095 or multiple nodes) is an ANET-local administrative consideration. 2097 3.13.1. Detecting and Responding to Server Failures 2099 In environments where fast recovery from Server failure is required, 2100 Proxys SHOULD use proactive Neighbor Unreachability Detection (NUD) 2101 to track Server reachability in a similar fashion as for 2102 Bidirectional Forwarding Detection (BFD) [RFC5880]. Proxys can then 2103 quickly detect and react to failures so that cached information is 2104 re-established through alternate paths. The NUD control messaging is 2105 carried only over well-connected ground domain networks (i.e., and 2106 not low-end aeronautical radio links) and can therefore be tuned for 2107 rapid response. 2109 Proxys perform proactive NUD with Servers for which there are 2110 currently active ANET Clients by sending continuous NS messages in 2111 rapid succession, e.g., one message per second. The Proxy sends the 2112 NS message via the spanning tree with the Proxy's LLA as the source 2113 and the LLA of the Server as the destination. When the Proxy is also 2114 sending RS messages to the Server on behalf of ANET Clients, the 2115 resulting RA responses can be considered as equivalent hints of 2116 forward progress. This means that the Proxy need not also send a 2117 periodic NS if it has already sent an RS within the same period. If 2118 the Server fails (i.e., if the Proxy ceases to receive 2119 advertisements), the Proxy can quickly inform Clients by sending 2120 multicast RA messages on the ANET interface. 2122 The Proxy sends RA messages on the ANET interface with source address 2123 set to the Server's address, destination address set to All-Nodes 2124 multicast, and Router Lifetime set to 0. The Proxy SHOULD send 2125 MAX_FINAL_RTR_ADVERTISEMENTS RA messages separated by small delays 2126 [RFC4861]. Any Clients on the ANET that had been using the failed 2127 Server will receive the RA messages and associate with a new Server. 2129 3.13.2. Point-to-Multipoint Server Coordination 2131 In environments where Client messaging over ANETs is bandwidth- 2132 limited and/or expensive, Clients can enlist the services of the 2133 Proxy to coordinate with multiple Servers in a single RS/RA message 2134 exchange. The Client can send a single RS message to All-Routers 2135 multicast that includes the ID's of multiple Servers in MS-Register 2136 sub-options of the OMNI option. 2138 When the Proxy receives the RS and processes the OMNI option, it 2139 performs a separate RS/RA exchange with each MS-Register Server. 2140 When it has received the RA messages, it creates an "aggregate" RA 2141 message to return to the Client with an OMNI option with each 2142 responding Server's ID recorded in an MS-Register sub-option. 2144 Clients can thereafter employ efficient point-to-multipoint Server 2145 coordination under the assistance of the Proxy to dramatically reduce 2146 the number of messages sent over the ANET while enlisting the support 2147 of multiple Servers for fault tolerance. Clients can further include 2148 MS-Release suboptions in RS messages to request the Proxy to release 2149 from former Servers via the procedures discussed in Section 3.16.5. 2151 The OMNI interface specification [I-D.templin-6man-omni-interface] 2152 provides further discussion of the Client/Proxy RS/RA messaging 2153 involved in point-to-multipoint coordination. 2155 3.14. AERO Route Optimization / Address Resolution 2157 While data packets are flowing between a source and target node, 2158 route optimization SHOULD be used. Route optimization is initiated 2159 by the first eligible Route Optimization Source (ROS) closest to the 2160 source as follows: 2162 o For Clients on VPNed and Direct interfaces, the Server is the ROS. 2164 o For Clients on Proxyed interfaces, the Proxy is the ROS. 2166 o For Clients on INET interfaces, the Client itself is the ROS. 2168 o For correspondent nodes on INET/EUN interfaces serviced by a 2169 Relay, the Relay is the ROS. 2171 The route optimization procedure is conducted between the ROS and the 2172 target Server/Relay acting as a Route Optimization Responder (ROR) in 2173 the same manner as for IPv6 ND Address Resolution and using the same 2174 NS/NA messaging. The target may either be a MNP Client serviced by a 2175 Server, or a non-MNP correspondent reachable via a Relay. 2177 The procedures are specified in the following sections. 2179 3.14.1. Route Optimization Initiation 2181 While data packets are flowing from the source node toward a target 2182 node, the ROS performs address resolution by sending an NS message 2183 for Address Resolution (NS(AR)) to receive a solicited NA message 2184 from the ROR. When the ROS sends an NS(AR), it includes: 2186 o the LLA of the ROS as the source address. 2188 o the data packet's destination as the Target Address. 2190 o the Solicited-Node multicast address [RFC4291] formed from the 2191 lower 24 bits of the data packet's destination as the destination 2192 address, e.g., for 2001:db8:1:2::10:2000 the NS destination 2193 address is ff02:0:0:0:0:1:ff10:2000. 2195 The NS(AR) message includes an OMNI option with no ifIndex-tuples and 2196 no SLLAO, such that the target will not create a neighbor cache 2197 entry. 2199 The ROS then encapsulates the NS(AR) message in a SPAN header with 2200 source set to its own ULA and destination set to the ULA 2201 corresponding to the packet's final destination, then sends the 2202 message into the spanning tree without decrementing the network-layer 2203 TTL/Hop Limit field. 2205 3.14.2. Relaying the NS 2207 When the Bridge receives the NS(AR) message from the ROS, it discards 2208 the INET header and determines that the ROR is the next hop by 2209 consulting its standard IPv6 forwarding table for the SPAN header 2210 destination address. The Bridge then forwards the message toward the 2211 ROR via the spanning tree the same as for any IPv6 router. The 2212 final-hop Bridge in the spanning tree will deliver the message via a 2213 secured tunnel to the ROR. 2215 3.14.3. Processing the NS and Sending the NA 2217 When the ROR receives the NS(AR) message, it examines the Target 2218 Address to determine whether it has a neighbor cache entry and/or 2219 route that matches the target. If there is no match, the ROR drops 2220 the message. Otherwise, the ROR continues processing as follows: 2222 o if the target belongs to an MNP Client neighbor in the DEPARTED 2223 state the ROR changes the NS(AR) message SPAN destination address 2224 to the ULA of the Client's new Server, forwards the message into 2225 the spanning tree and returns from processing. 2227 o If the target belongs to an MNP Client neighbor in the REACHABLE 2228 state, the ROR instead adds the AERO source address to the target 2229 Client's Report List with time set to ReportTime. 2231 o If the target belongs to a non-MNP route, the ROR continues 2232 processing without adding an entry to the Report List. 2234 The ROR then prepares a solicited NA message to send back to the ROS 2235 but does not create a neighbor cache entry. The ROR sets the NA 2236 source address to the LLA corresponding to the target, sets the 2237 Target Address to the target of the solicitation, and sets the 2238 destination address to the source of the solicitation. 2240 The ROR then includes an OMNI option with prefix registration length 2241 set to the length of the MNP if the target is an MNP Client; 2242 otherwise, set to the maximum of the non-MNP prefix length and 64. 2243 (Note that a /64 limit is imposed to avoid causing the ROS to set 2244 short prefixes (e.g., "default") that would match destinations for 2245 which the routing system includes more-specific prefixes.) 2247 If the target is an MNP Client, the ROR next includes ifIndex-tuples 2248 in the OMNI option for each of the target Client's underlying 2249 interfaces with current information for each interface and with the S 2250 flag set to 0. The ROR then includes a TLLAO with ifIndex-tuples in 2251 one-to-one correspondence with the tuples that appear in the OMNI 2252 option. 2254 The ROR sets the Link Layer Address and Port Number to its own INET 2255 address for VPNed or Direct interfaces, to the INET address of the 2256 Proxy for Proxyed interfaces or to the Client's INET address for INET 2257 interfaces. The ROR then includes the lower 32 bits of its own ULA 2258 (or the ULA of the Proxy, for Proxyed interfaces) as the ultimate SID 2259 List entry, and includes the ultimate segment Subnet Router Anycast 2260 address lower 32 bits as the penultimate entry. The ROR finally sets 2261 the ifIndex control fields in the TLLAO accordingly as specified in 2262 Section 3.3. (Note that the ROR may include additional SIDs for any 2263 earlier segments to be visited prior to the ultimate segment.) 2265 The ROR then sets the NA message R flag to 1 (as a router), S flag to 2266 1 (as a response to a solicitation), and O flag to 0 (as a proxy). 2267 The ROR finally encapsulates the NA message in a SPAN header with 2268 source set to its own ULA and destination set to the source ULA of 2269 the NS(AR) message, then forwards the message into the spanning tree 2270 without decrementing the network-layer TTL/Hop Limit field. 2272 3.14.4. Relaying the NA 2274 When the Bridge receives the NA message from the ROR, it discards the 2275 INET header and determines that the ROS is the next hop by consulting 2276 its standard IPv6 forwarding table for the SPAN header destination 2277 address. The Bridge then forwards the SPAN-encapsulated NA message 2278 toward the ROS the same as for any IPv6 router. The final-hop Bridge 2279 in the spanning tree will deliver the message via a secured tunnel to 2280 the ROS. 2282 3.14.5. Processing the NA 2284 When the ROS receives the solicited NA message, it processes the 2285 message the same as for standard IPv6 Address Resolution [RFC4861]. 2286 In the process, it caches the source ULA then creates an asymmetric 2287 neighbor cache entry for the ROR and caches all information found in 2288 the OMNI and TLLAO options. The ROS finally sets the asymmetric 2289 neighbor cache entry lifetime to ReachableTime seconds. 2291 3.14.6. Route Optimization Maintenance 2293 Following route optimization, the ROS forwards future data packets 2294 destined to the target via the addresses found in the cached link- 2295 layer information. The route optimization is shared by all sources 2296 that send packets to the target via the ROS, i.e., and not just the 2297 source on behalf of which the route optimization was initiated. 2299 While new data packets destined to the target are flowing through the 2300 ROS, it sends additional NS(AR) messages to the ROR before 2301 ReachableTime expires to receive a fresh solicited NA message the 2302 same as described in the previous sections (route optimization 2303 refreshment strategies are an implementation matter, with a non- 2304 normative example given in Appendix A.1). The ROS uses the cached 2305 ULA of the ROR as the NS(AR) SPAN destination address, and sends up 2306 to MAX_MULTICAST_SOLICIT NS(AR) messages separated by 1 second until 2307 an NA is received. If no NA is received, the ROS assumes that the 2308 current ROR has become unreachable and deletes the neighbor cache 2309 entry. Subsequent data packets will trigger a new route optimization 2310 per Section 3.14.1 to discover a new ROR while initial data packets 2311 travel over a suboptimal route. 2313 If an NA is received, the ROS then updates the asymmetric neighbor 2314 cache entry to refresh ReachableTime, while (for MNP destinations) 2315 the ROR adds or updates the ROS address to the target Client's Report 2316 List and with time set to ReportTime. While no data packets are 2317 flowing, the ROS instead allows ReachableTime for the asymmetric 2318 neighbor cache entry to expire. When ReachableTime expires, the ROS 2319 deletes the asymmetric neighbor cache entry. Any future data packets 2320 flowing through the ROS will again trigger a new route optimization. 2322 The ROS may also receive unsolicited NA messages from the ROR at any 2323 time (see: Section 3.16). If there is an asymmetric neighbor cache 2324 entry for the target, the ROS updates the link-layer information but 2325 does not update ReachableTime since the receipt of an unsolicited NA 2326 does not confirm that any forward paths are working. If there is no 2327 asymmetric neighbor cache entry, the ROS simply discards the 2328 unsolicited NA. 2330 In this arrangement, the ROS holds an asymmetric neighbor cache entry 2331 for the ROR, but the ROR does not hold an asymmetric neighbor cache 2332 entry for the ROS. The route optimization neighbor relationship is 2333 therefore asymmetric and unidirectional. If the target node also has 2334 packets to send back to the source node, then a separate route 2335 optimization procedure is performed in the reverse direction. But, 2336 there is no requirement that the forward and reverse paths be 2337 symmetric. 2339 3.15. Neighbor Unreachability Detection (NUD) 2341 AERO nodes perform Neighbor Unreachability Detection (NUD) per 2342 [RFC4861] either reactively in response to persistent link-layer 2343 errors (see Section 3.11) or proactively to confirm reachability. 2344 The NUD algorithm is based on periodic control message exchanges. 2345 The algorithm may further be seeded by ND hints of forward progress, 2346 but care must be taken to avoid inferring reachability based on 2347 spoofed information. For example, authentic IPv6 ND message 2348 exchanges may be considered as acceptable hints of forward progress, 2349 while spurious data packets should not be. 2351 AERO Servers, Proxys and Relays can use standard NS/NA NUD exchanges 2352 sent over the spanning tree to securely test reachability without 2353 risk of DoS attacks from nodes pretending to be a neighbor; Proxys 2354 can further perform NUD to securely verify Server reachability on 2355 behalf of their proxyed Clients. However, a means for a ROS to test 2356 the unsecured forward directions of target route optimized paths is 2357 also necessary. 2359 When an ROR directs an ROS to a neighbor with one or more target 2360 link-layer addresses, the ROS can proactively test each such 2361 unsecured route optimized path by sending "loopback" NS(NUD) 2362 messages. While testing the paths, the ROS can optionally continue 2363 to send packets via the spanning tree, maintain a small queue of 2364 packets until target reachability is confirmed, or (optimistically) 2365 allow packets to flow via the route optimized paths. 2367 When the ROS sends a loopback NS(NUD) message, it uses its LLA as 2368 both the IPv6 source and destination address, and the MNP Subnet- 2369 Router anycast address as the Target Address. The ROS includes a 2370 Nonce and Timestamp option, then encapsulates the message in SPAN/ 2371 INET headers with its own ULA as the source and the ULA of the route 2372 optimization target as the destination. The ROS then forwards the 2373 message to the target (either directly to the link layer address of 2374 the target if the target is in the same OMNI link segment, or via a 2375 Bridge if the target is in a different OMNI link segment). 2377 When the route optimization target receives the NS(NUD) message, it 2378 notices that the IPv6 destination address is the same as the source 2379 address. It then reverses the SPAN source and destination addresses 2380 and returns the message to the ROS (either directly or via the 2381 spanning tree). The route optimization target does not decrement the 2382 NS(NUD) message IPv6 Hop-Limit in the process, since the message has 2383 not exited the OMNI link. 2385 When the ROS receives the NS(NUD) message, it can determine from the 2386 Nonce, Timestamp and Target Address that the message originated from 2387 itself and that it transited the forward path. The ROS need not 2388 prepare an NA response, since the destination of the response would 2389 be itself and testing the route optimization path again would be 2390 redundant. 2392 The ROS marks route optimization target paths that pass these NUD 2393 tests as "reachable", and those that do not as "unreachable". These 2394 markings inform the OMNI interface forwarding algorithm specified in 2395 Section 3.10. 2397 Note that to avoid a DoS vector nodes MUST NOT return loopback 2398 NS(NUD) messages received from an unsecured link-layer source via the 2399 spanning tree. 2401 3.16. Mobility Management and Quality of Service (QoS) 2403 AERO is a Distributed Mobility Management (DMM) service. Each Server 2404 is responsible for only a subset of the Clients on the OMNI link, as 2405 opposed to a Centralized Mobility Management (CMM) service where 2406 there is a single network mobility collective entity for all Clients. 2407 Clients coordinate with their associated Servers via RS/RA exchanges 2408 to maintain the DMM profile, and the AERO routing system tracks all 2409 current Client/Server peering relationships. 2411 Servers provide default routing and mobility/multilink services for 2412 their dependent Clients. Clients are responsible for maintaining 2413 neighbor relationships with their Servers through periodic RS/RA 2414 exchanges, which also serves to confirm neighbor reachability. When 2415 a Client's underlying interface address and/or QoS information 2416 changes, the Client is responsible for updating the Server with this 2417 new information. Note that for Proxyed interfaces, however, the 2418 Proxy can also perform some RS/RA exchanges on the Client's behalf. 2420 Mobility management considerations are specified in the following 2421 sections. 2423 3.16.1. Mobility Update Messaging 2425 Servers accommodate Client mobility/multilink and/or QoS change 2426 events by sending unsolicited NA (uNA) messages to each ROS in the 2427 target Client's Report List. When a Server sends a uNA message, it 2428 sets the IPv6 source address to the Client's LLA, sets the 2429 destination address to All-Nodes multicast and sets the Target 2430 Address to the Client's Subnet-Router anycast address. The Server 2431 also includes an OMNI option with prefix registration information and 2432 with ifIndex-tuples for the target Client's remaining interfaces with 2433 S set to 0. The Server then includes a TLLAO with corresponding 2434 ifIndex-tuples prepared the same as for the initial route 2435 optimization event. The Server sets the NA R flag to 1, the S flag 2436 to 0 and the O flag to 0, then encapsulates the message in a SPAN 2437 header with source set to its own ULA and destination set to the ULA 2438 of the ROS and sends the message into the spanning tree. 2440 As discussed in Section 7.2.6 of [RFC4861], the transmission and 2441 reception of uNA messages is unreliable but provides a useful 2442 optimization. In well-connected Internetworks with robust data links 2443 uNA messages will be delivered with high probability, but in any case 2444 the Server can optionally send up to MAX_NEIGHBOR_ADVERTISEMENT uNAs 2445 to each ROS to increase the likelihood that at least one will be 2446 received. 2448 When the ROS receives a uNA message, it ignores the message if there 2449 is no existing neighbor cache entry for the Client. Otherwise, it 2450 uses the included OMNI option and TLLAO information to update the 2451 neighbor cache entry, but does not reset ReachableTime since the 2452 receipt of an unsolicited NA message from the target Server does not 2453 provide confirmation that any forward paths to the target Client are 2454 working. 2456 If uNA messages are lost, the ROS may be left with stale address and/ 2457 or QoS information for the Client for up to ReachableTime seconds. 2458 During this time, the ROS can continue sending packets according to 2459 its stale neighbor cache information. When ReachableTime is close to 2460 expiring, the ROS will re-initiate route optimization and receive 2461 fresh link-layer address information. 2463 In addition to sending uNA messages to the current set of ROSs for 2464 the Client, the Server also sends uNAs to the former link-layer 2465 address for any ifIndex-tuple for which the link-layer address has 2466 changed. The uNA messages update Proxys that cannot easily detect 2467 (e.g., without active probing) when a formerly-active Client has 2468 departed. 2470 3.16.2. Announcing Link-Layer Address and/or QoS Preference Changes 2472 When a Client needs to change its underlying interface addresses and/ 2473 or QoS preferences (e.g., due to a mobility event), either the Client 2474 or its Proxys send RS messages to the Server via the spanning tree 2475 with an OMNI option that includes an ifIndex-tuple with S set to 1 2476 and with the new link quality and address information. 2478 Up to MAX_RTR_SOLICITATIONS RS messages MAY be sent in parallel with 2479 sending actual data packets in case one or more RAs are lost. If all 2480 RAs are lost, the Client SHOULD re-associate with a new Server. 2482 When the Server receives the Client's changes, it sends uNA messages 2483 to all nodes in the Report List the same as described in the previous 2484 section. 2486 3.16.3. Bringing New Links Into Service 2488 When a Client needs to bring new underlying interfaces into service 2489 (e.g., when it activates a new data link), it sends an RS message to 2490 the Server via the underlying interface with an OMNI option that 2491 includes an ifIndex-tuple with S set to 1 and appropriate link 2492 quality values and with link-layer address information for the new 2493 link. 2495 3.16.4. Removing Existing Links from Service 2497 When a Client needs to remove existing underlying interfaces from 2498 service (e.g., when it de-activates an existing data link), it sends 2499 an RS or uNA message to its Server with an OMNI option with 2500 appropriate link quality values. 2502 If the Client needs to send RS/uNA messages over an underlying 2503 interface other than the one being removed from service, it MUST 2504 include ifIndex-tuples with appropriate link quality values for any 2505 underlying interfaces being removed from service. 2507 3.16.5. Moving to a New Server 2509 When a Client associates with a new Server, it performs the Client 2510 procedures specified in Section 3.12.2. The Client also includes MS- 2511 Release identifiers in the RS message OMNI option per 2512 [I-D.templin-6man-omni-interface] if it wants the new Server to 2513 notify any old Servers from which the Client is departing. 2515 When the new Server receives the Client's RS message, it returns an 2516 RA as specified in Section 3.12.3 and sends up to 2517 MAX_NEIGHBOR_ADVERTIISEMENT uNA messages to any old Servers listed in 2518 OMNI option MS-Release identifiers. Each uNA message includes the 2519 Client's LLA as the source address, the old Server's LLA as the 2520 destination address, and an OMNI option with the Register/Release bit 2521 set to 0. The new Server wraps the uNA in a SPAN header with its own 2522 ULA as the source and the old Server's ULA as the destination, then 2523 sends the message into the spanning tree. 2525 When an old Server receives the uNA, it changes the Client's neighbor 2526 cache entry state to DEPARTED, sets the link-layer address of the 2527 Client to the new Server's ULA, and resets DepartTime. After a short 2528 delay (e.g., 2 seconds) the old Server withdraws the Client's MNP 2529 from the routing system. After DepartTime expires, the old Server 2530 deletes the Client's neighbor cache entry. 2532 The old Server also sends unsolicited NA messages to all ROSs in the 2533 Client's Report List with an OMNI option with a single ifIndex-tuple 2534 with ifIndex set to 0 and S set to '1', and with the ULA of the new 2535 Server in a companion TLLAO. When the ROS receives the NA, it caches 2536 the address of the new Server in the existing asymmetric neighbor 2537 cache entry and marks the entry as STALE for a period of 10 seconds 2538 after which the cache entry is deleted. While in the STALE state, 2539 subsequent data packets flow according to any existing cached link- 2540 layer information and trigger a new NS(AR)/NA exchange via the new 2541 Server. 2543 Clients SHOULD NOT move rapidly between Servers in order to avoid 2544 causing excessive oscillations in the AERO routing system. Examples 2545 of when a Client might wish to change to a different Server include a 2546 Server that has gone unreachable, topological movements of 2547 significant distance, movement to a new geographic region, movement 2548 to a new OMNI link segment, etc. 2550 When a Client moves to a new Server, some of the fragments of a 2551 multiple fragment packet may have already arrived at the old Server 2552 while others are en route to the new Server, however no special 2553 attention in the reassembly algorithm is necessary when re-routed 2554 fragments are simply treated as loss. 2556 3.17. Multicast 2558 The AERO Client provides an IGMP (IPv4) [RFC2236] or MLD (IPv6) 2559 [RFC3810] proxy service for its EUNs and/or hosted applications 2560 [RFC4605]. The Client forwards IGMP/MLD messages over any of its 2561 underlying interfaces for which group membership is required. The 2562 IGMP/MLD messages may be further forwarded by a first-hop ANET access 2563 router acting as an IGMP/MLD-snooping switch [RFC4541], then 2564 ultimately delivered to an AERO Proxy/Server acting as a Protocol 2565 Independent Multicast - Sparse-Mode (PIM-SM, or simply "PIM") 2566 Designated Router (DR) [RFC7761]. AERO Relays also act as PIM 2567 routers (i.e., the same as AERO Proxys/Servers) on behalf of nodes on 2568 INET/EUN networks. The behaviors identified in the following 2569 sections correspond to Source-Specific Multicast (SSM) and Any-Source 2570 Multicast (ASM) operational modes. 2572 3.17.1. Source-Specific Multicast (SSM) 2574 When an ROS (i.e., an AERO Proxy/Server/Relay) "X" acting as PIM 2575 router receives a Join/Prune message from a node on its downstream 2576 interfaces containing one or more ((S)ource, (G)roup) pairs, it 2577 updates its Multicast Routing Information Base (MRIB) accordingly. 2578 For each S belonging to a prefix reachable via X's non-OMNI 2579 interfaces, X then forwards the (S, G) Join/Prune to any PIM routers 2580 on those interfaces per [RFC7761]. 2582 For each S belonging to a prefix reachable via X's OMNI interface, X 2583 originates a separate copy of the Join/Prune for each (S,G) in the 2584 message using its own LLA as the source address and ALL-PIM-ROUTERS 2585 as the destination address. X then encapsulates each message in a 2586 SPAN header with source address set to the ULA of X and destination 2587 address set to S then forwards the message into the spanning tree, 2588 which delivers it to AERO Server/Relay "Y" that services S. At the 2589 same time, if the message was a Join, X sends a route-optimization NS 2590 message toward each S the same as discussed in Section 3.14. The 2591 resulting NAs will return the LLA for the prefix that matches S as 2592 the network-layer source address and TLLAOs with the ULA 2593 corresponding to any ifIndex-tuples that are currently servicing S. 2595 When Y processes the Join/Prune message, if S located behind any 2596 INET, Direct, or VPNed interfaces Y acts as a PIM router and updates 2597 its MRIB to list X as the next hop in the reverse path. If S is 2598 located behind any Proxys "Z"*, Y also forwards the message to each 2599 Z* over the spanning tree while continuing to use the LLA of X as the 2600 source address. Each Z* then updates its MRIB accordingly and 2601 maintains the LLA of X as the next hop in the reverse path. Since 2602 the Bridges do not examine network layer control messages, this means 2603 that the (reverse) multicast tree path is simply from each Z* (and/or 2604 Y) to X with no other multicast-aware routers in the path. If any Z* 2605 (and/or Y) is located on the same OMNI link segment as X, the 2606 multicast data traffic sent to X directly using SPAN/INET 2607 encapsulation instead of via a Bridge. 2609 Following the initial Join/Prune and NS/NA messaging, X maintains an 2610 asymmetric neighbor cache entry for each S the same as if X was 2611 sending unicast data traffic to S. In particular, X performs 2612 additional NS/NA exchanges to keep the neighbor cache entry alive for 2613 up to t_periodic seconds [RFC7761]. If no new Joins are received 2614 within t_periodic seconds, X allows the neighbor cache entry to 2615 expire. Finally, if X receives any additional Join/Prune messages 2616 for (S,G) it forwards the messages to each Y and Z* in the neighbor 2617 cache entry over the spanning tree. 2619 At some later time, Client C that holds an MNP for source S may 2620 depart from a first Proxy Z1 and/or connect via a new Proxy Z2. In 2621 that case, Y sends an unsolicited NA message to X the same as 2622 specified for unicast mobility in Section 3.16. When X receives the 2623 unsolicited NA message, it updates its asymmetric neighbor cache 2624 entry for the LLA for source S and sends new Join messages to any new 2625 Proxys Z2. There is no requirement to send any Prune messages to old 2626 Proxys Z1 since source S will no longer source any multicast data 2627 traffic via Z1. Instead, the multicast state for (S,G) in Proxy Z1 2628 will soon time out since no new Joins will arrive. 2630 After some later time, C may move to a new Server Y2 and depart from 2631 old Sever Y1. In that case, Y1 sends Join messages for any of C's 2632 active (S,G) groups to Y2 while including its own LLA as the source 2633 address. This causes Y2 to include Y1 in the multicast forwarding 2634 tree during the interim time that Y1's symmetric neighbor cache entry 2635 for C is in the DEPARTED state. At the same time, Y1 sends an 2636 unsolicited NA message to X with an OMNI option and TLLAO with 2637 ifIndex-tuple set to 0 and a release indication to cause X to release 2638 its asymmetric neighbor cache entry. X then sends a new Join message 2639 to S via the spanning tree and re-initiates route optimization the 2640 same as if it were receiving a fresh Join message from a node on a 2641 downstream link. 2643 3.17.2. Any-Source Multicast (ASM) 2645 When an ROS X acting as a PIM router receives a Join/Prune from a 2646 node on its downstream interfaces containing one or more (*,G) pairs, 2647 it updates its Multicast Routing Information Base (MRIB) accordingly. 2648 X then forwards a copy of the message to the Rendezvous Point (RP) R 2649 for each G over the spanning tree. X uses its own LLA as the source 2650 address and ALL-PIM-ROUTERS as the destination address, then 2651 encapsulates each message in a SPAN header with source address set to 2652 the ULA of X and destination address set to R, then sends the message 2653 into the spanning tree. At the same time, if the message was a Join 2654 X initiates NS/NA route optimization the same as for the SSM case 2655 discussed in Section 3.17.1. 2657 For each source S that sends multicast traffic to group G via R, the 2658 Proxy/Server Z* for the Client that aggregates S encapsulates the 2659 packets in PIM Register messages and forwards them to R via the 2660 spanning tree, which may then elect to send a PIM Join to Z*. This 2661 will result in an (S,G) tree rooted at Z* with R as the next hop so 2662 that R will begin to receive two copies of the packet; one native 2663 copy from the (S, G) tree and a second copy from the pre-existing (*, 2664 G) tree that still uses PIM Register encapsulation. R can then issue 2665 a PIM Register-stop message to suppress the Register-encapsulated 2666 stream. At some later time, if C moves to a new Proxy/Server Z*, it 2667 resumes sending packets via PIM Register encapsulation via the new 2668 Z*. 2670 At the same time, as multicast listeners discover individual S's for 2671 a given G, they can initiate an (S,G) Join for each S under the same 2672 procedures discussed in Section 3.17.1. Once the (S,G) tree is 2673 established, the listeners can send (S, G) Prune messages to R so 2674 that multicast packets for group G sourced by S will only be 2675 delivered via the (S, G) tree and not from the (*, G) tree rooted at 2676 R. All mobility considerations discussed for SSM apply. 2678 3.17.3. Bi-Directional PIM (BIDIR-PIM) 2680 Bi-Directional PIM (BIDIR-PIM) [RFC5015] provides an alternate 2681 approach to ASM that treats the Rendezvous Point (RP) as a Designated 2682 Forwarder (DF). Further considerations for BIDIR-PIM are out of 2683 scope. 2685 3.18. Operation over Multiple OMNI Links 2687 An AERO Client can connect to multiple OMNI links the same as for any 2688 data link service. In that case, the Client maintains a distinct 2689 OMNI interface for each link, e.g., 'omni0' for the first link, 2690 'omni1' for the second, 'omni2' for the third, etc. Each OMNI link 2691 would include its own distinct set of Bridges, Servers and Proxys, 2692 thereby providing redundancy in case of failures. 2694 The Bridges, Servers and Proxys on each OMNI link can assign AERO and 2695 ULAs that use the same or different numberings from those on other 2696 links. Since the links are mutually independent there is no 2697 requirement for avoiding inter-link address duplication, e.g., the 2698 same LLA such as fe80::1000 could be used to number distinct nodes 2699 that connect to different OMNI links. 2701 Each OMNI link could utilize the same or different ANET connections. 2702 The links can be distinguished at the link-layer via the SSP in a 2703 similar fashion as for Virtual Local Area Network (VLAN) tagging 2704 (e.g., IEEE 802.1Q) and/or through assignment of distinct sets of 2705 MSPs on each link. This gives rise to the opportunity for supporting 2706 multiple redundant networked paths, where each VLAN is distinguished 2707 by a different SRT color (see: Section 3.2.5). In particular, the 2708 Client can tag its RS messages with the appropriate label to cause 2709 the network to select the desired VLAN. 2711 The Client's IP layer can select the outgoing OMNI interface 2712 appropriate for a given traffic profile while (in the reverse 2713 direction) correspondent nodes must have some way of steering their 2714 packets destined to a target via the correct OMNI link. 2716 In a first alternative, if each OMNI link services different MSPs, 2717 then the Client can receive a distinct MNP from each of the links. 2718 IP routing will therefore assure that the correct Red/Green/Blue/etc. 2719 network is used for both outbound and inbound traffic. This can be 2720 accomplished using existing technologies and approaches, and without 2721 requiring any special supporting code in correspondent nodes or 2722 Bridges. 2724 In a second alternative, if each OMNI link services the same MSP(s) 2725 then each link could assign a distinct "OMNI link Anycast" address 2726 that is configured by all Bridges on the link. Correspondent nodes 2727 can then perform Segment Routing to select the correct SRT, which 2728 will then direct the packet over multiple hops to the target. 2730 3.19. DNS Considerations 2732 AERO Client MNs and INET correspondent nodes consult the Domain Name 2733 System (DNS) the same as for any Internetworking node. When 2734 correspondent nodes and Client MNs use different IP protocol versions 2735 (e.g., IPv4 correspondents and IPv6 MNs), the INET DNS must maintain 2736 A records for IPv4 address mappings to MNs which must then be 2737 populated in Relay NAT64 mapping caches. In that way, an IPv4 2738 correspondent node can send packets to the IPv4 address mapping of 2739 the target MN, and the Relay will translate the IPv4 header and 2740 destination address into an IPv6 header and IPv6 destination address 2741 of the MN. 2743 When an AERO Client registers with an AERO Server, the Server can 2744 return the address(es) of DNS servers in RDNSS options [RFC6106]. 2745 The DNS server provides the IP addresses of other MNs and 2746 correspondent nodes in AAAA records for IPv6 or A records for IPv4. 2748 3.20. Transition Considerations 2750 SPAN encapsulation ensures that dissimilar INET partitions can be 2751 joined into a single unified OMNI link, even though the partitions 2752 themselves may have differing protocol versions and/or incompatible 2753 addressing plans. However, a commonality can be achieved by 2754 incrementally distributing globally routable (i.e., native) IP 2755 prefixes to eventually reach all nodes (both mobile and fixed) in all 2756 OMNI link segments. This can be accomplished by incrementally 2757 deploying AERO Relays on each INET partition, with each Relay 2758 distributing its MNPs and/or discovering non-MNP prefixes on its INET 2759 links. 2761 This gives rise to the opportunity to eventually distribute native IP 2762 addresses to all nodes, and to present a unified OMNI link view even 2763 if the INET partitions remain in their current protocol and 2764 addressing plans. In that way, the OMNI link can serve the dual 2765 purpose of providing a mobility/multilink service and a transition 2766 service. Or, if an INET partition is transitioned to a native IP 2767 protocol version and addressing scheme that is compatible with the 2768 OMNI link MNP-based addressing scheme, the partition and OMNI link 2769 can be joined by Relays. 2771 Relays that connect INETs/EUNs with dissimilar IP protocol versions 2772 may need to employ a network address and protocol translation 2773 function such as NAT64[RFC6146]. 2775 3.21. Detecting and Reacting to Server and Bridge Failures 2777 In environments where rapid failure recovery is required, Servers and 2778 Bridges SHOULD use Bidirectional Forwarding Detection (BFD) 2779 [RFC5880]. Nodes that use BFD can quickly detect and react to 2780 failures so that cached information is re-established through 2781 alternate nodes. BFD control messaging is carried only over well- 2782 connected ground domain networks (i.e., and not low-end radio links) 2783 and can therefore be tuned for rapid response. 2785 Servers and Bridges maintain BFD sessions in parallel with their BGP 2786 peerings. If a Server or Bridge fails, BGP peers will quickly re- 2787 establish routes through alternate paths the same as for common BGP 2788 deployments. Similarly, Proxys maintain BFD sessions with their 2789 associated Bridges even though they do not establish BGP peerings 2790 with them. 2792 Proxys SHOULD use proactive NUD for Servers for which there are 2793 currently active ANET Clients in a manner that parallels BFD, i.e., 2794 by sending unicast NS messages in rapid succession to receive 2795 solicited NA messages. When the Proxy is also sending RS messages on 2796 behalf of ANET Clients, the RS/RA messaging can be considered as 2797 equivalent hints of forward progress. This means that the Proxy need 2798 not also send a periodic NS if it has already sent an RS within the 2799 same period. If a Server fails, the Proxy will cease to receive 2800 advertisements and can quickly inform Clients of the outage by 2801 sending multicast RA messages on the ANET interface. 2803 The Proxy sends multicast RA messages with source address set to the 2804 Server's address, destination address set to All-Nodes multicast, and 2805 Router Lifetime set to 0. The Proxy SHOULD send 2806 MAX_FINAL_RTR_ADVERTISEMENTS RA messages separated by small delays 2807 [RFC4861]. Any Clients on the ANET interface that have been using 2808 the (now defunct) Server will receive the RA messages and associate 2809 with a new Server. 2811 3.22. AERO Clients on the Open Internet 2813 AERO Clients that connect to the open Internet via INET interfaces 2814 can establish a VPN or direct link to securely connect to a Server in 2815 a "tethered" arrangement with all of the Client's traffic transiting 2816 the Server. Alternatively, the Client can associate with an INET 2817 Server using UDP/IP encapsulation and asymmetric securing services as 2818 discussed in the following sections. 2820 When a Client's OMNI interface enables an INET underlying interface, 2821 it first determines whether the interface is likely to be behind a 2822 NAT. For IPv4, the Client might assume it is on the open Internet if 2823 the INET address is not a special-use IPv4 address per [RFC3330]. 2824 Similarly for IPv6, the Client might assume it is on the open 2825 Internet if the INET address is not a link-local [RFC4291] or unique- 2826 local [RFC4193] IPv6 address. 2828 The Client then prepares a UDP/IP-encapsulated RS message with IPv6 2829 source address set to its LLA, with IPv6 destination set to All- 2830 Routers multicast and with an OMNI option with underlying interface 2831 parameters. If the Client believes that it is on the open Internet, 2832 it SHOULD also include an SLLAO set according to the address used for 2833 INET encapsulation (otherwise, it MAY omit the SLLAO). If the 2834 underlying address is IPv4, the Client includes the IPv4 address and 2835 Port Number written in obfuscated form [RFC4380] and with FMT set to 2836 '01' (INET) as discussed in Section 3.3. If the underlying interface 2837 address is IPv6, the Client instead includes the IPv6 address and 2838 Port number in obfuscated form and sets FMT to '11' (INET). The 2839 Client finally includes an Authentication option per [RFC4380] to 2840 provide message authentication, sets the UDP/IP source to its INET 2841 address and UDP port, sets the UDP/IP destination to the Server's 2842 INET address and the AERO service port number (8060), then sends the 2843 message to the Server. 2845 When the Server receives the RS, it authenticates the message and 2846 registers the Client's MNP and INET interface information according 2847 to the OMNI option parameters. If the RS message includes an SLLAO, 2848 the Server compares the encapsulation IP address and UDP port number 2849 with the (unobfuscated) SLLAO values. If the values are the same, 2850 the Server caches the Client's information as "INET" addresses 2851 meaning that the Client is likely to accept direct messages without 2852 requiring NAT traversal exchanges. If the values are different (or, 2853 if there was no SLLAO) the Server instead caches the Client's 2854 information as "NAT" addresses meaning that NAT traversal exchanges 2855 may be necessary. 2857 The Server then returns an RA message with IPv6 source and 2858 destination set corresponding to the addresses in the RS, and with an 2859 Authentication option per [RFC4380]. For IPv4, the Server also 2860 includes an Origin option per [RFC4380] with the mapped and 2861 obfuscated IPv4 address and port number observed in the encapsulation 2862 headers. For IPv6, the Server instead includes an IPv6 Origin option 2863 per Figure 7 with the mapped and obfuscated observed IPv6 address and 2864 port number (note that the value 0x02 in the second octet 2865 differentiates from other [RFC4380] option types). 2867 +--------+--------+-----------------+ 2868 | 0x00 | 0x02 | Origin port # | 2869 +--------+--------+-----------------+ 2870 ~ Origin IPv6 address ~ 2871 +-----------------------------------+ 2873 Figure 7: IPv6 Origin Option 2875 When the Client receives the RA message, it compares the mapped IP 2876 address and port from the Origin option with its own address. If the 2877 addresses are the same, the Client assumes the open Internet / Cone 2878 NAT principle; if the addresses are different, the Client instead 2879 assumes that further qualification procedures are necessary to detect 2880 the type of NAT and proceeds according to standard [RFC4380] 2881 procedures. 2883 After the Client has registered its INET interfaces in such RS/RA 2884 exchanges it sends periodic RS messages to receive fresh RA messages 2885 before the Router Lifetime received on each INET interface expires. 2886 The Client also maintains default routes via its Servers, i.e., the 2887 same as described in earlier sections. 2889 When the Client sends messages to target IP addresses, it also 2890 invokes route optimization per Section 3.14 using IPv6 ND address 2891 resolution messaging. The Client sends the NS(AR) message to the 2892 Server wrapped in a UDP/IP header with an Authentication option with 2893 the NS source address set to the Client's LLA and destination address 2894 set to the target solicited node multicast address. The Server 2895 authenticates the message and sends a corresponding NS(AR) message 2896 over the spanning tree the same as if it were the ROS, but with the 2897 SPAN source address set to the Server's ULA and destination set to 2898 the ULA of the target. When the ROR receives the NS(AR), it adds the 2899 Server's ULA and Client's LLA to the target's Report List, and 2900 returns an NA with OMNI and TLLAO information for the target. The 2901 Server then returns a UDP/IP encapsulated NA message with an 2902 Authentication option to the Client. 2904 Following route optimization, for targets in the same OMNI link 2905 segment if the target's TLLAO addresss is on the open INET, the 2906 Client forwards data packets directly to the target INET address. If 2907 the target's TLLAO address is behind a NAT, the Client first 2908 establishes NAT state for the Link Layer Address using the "bubble" 2909 mechanisms specified in [RFC6081][RFC4380]. The Client continues to 2910 send data packets via its Server until NAT state is populated, then 2911 begins forwarding packets via the direct path through the NAT to the 2912 target. For targets in different OMNI link segments, the Client 2913 inserts a Segment Routing header and forwards data packets to the 2914 Bridge that returned the NA message. 2916 The ROR may return uNAs via the Server if the target moves, and the 2917 Server will send corresponding Authentication-protected uNAs to the 2918 Client. The Client can also send "loopback" NS(NUD) messages to test 2919 forward path reachability even though there is no security 2920 association between the Client and the target. 2922 The Client sends UDP/IP encapsulated IPv6 packets no larger than 1280 2923 bytes in one piece. In order to accommodate larger IPv6 packets (up 2924 to the OMNI interface MTU), the Client inserts a SPAN header with 2925 source set to its own ULA and destination set to the ULA of the 2926 target and uses IPv6 fragmentation according to Section 3.9. The 2927 Client then encapsulates each fragment in a UDP/IP header and sends 2928 the fragments to the next hop. 2930 3.22.1. Use of SEND and CGA 2932 In some environments, use of the [RFC4380] Authentication option 2933 alone may be sufficient for assuring IPv6 ND message authentication 2934 between Clients and Servers. When additional protection is 2935 necessary, nodes should employ SEcure Neighbor Discovery (SEND) 2936 [RFC3971] with Cryptographically-Generated Addresses (CGA) [RFC3972]. 2938 When SEND/CGA are used, the Client prepares RS messages with its 2939 link-local CGA as the IPv6 source and All-Routers as the IPv6 2940 Destination, includes any SEND options and wraps the message in a 2941 SPAN header. The Client sets the SPAN source address to its own ULA 2942 and sets the SPAN destination address to the "All-Routers" ULA. The 2943 Client then wraps the RS message in UDP/IP headers according to 2944 [RFC4380] and sends the message to the Server. 2946 When the Server receives the message, it first verifies the 2947 Authentication option (if present) then uses the SPAN source address 2948 to determine the MNP of the Client. The Server then processes the 2949 SEND options to authenticate the RS message and prepares an RA 2950 message response. The Server prepares the RA with its own link-local 2951 CGA and the CGA of the Client as the IPv6 source and destination, 2952 includes any SEND options and wraps the message in a SPAN header. 2953 The Server sets the SPAN source address to its own ULA and sets the 2954 SPAN destination address to the Client's ULA. The Server then wraps 2955 the RA message in UDP/IP headers according to [RFC4380] and sends the 2956 message to the Client. Thereafter, the Client/Server send additional 2957 RS/RA messages to maintain their association and any NAT state. 2959 The Client and Server also may exchange NS/NA messages using their 2960 own CGA as the source and with SPAN encapsulation as above. When a 2961 Client sends an NS(AR), it sets the IPv6 source to its CGA and sets 2962 the IPv6 destination to the Solicited-Node Multicast address of the 2963 target. The Client then wraps the message in a SPAN header with its 2964 own ULA as the source and the ULA of the target as the destination 2965 and sends it to the Server. The Server authenticates the message, 2966 then changes the IPv6 source address to the Client's LLA, removes the 2967 SEND options, and sends a corresponding NS(AR) into the spanning 2968 tree. When the Server receives the corresponding SPAN-encapsulated 2969 NA, it changes the IPv6 destination address to the Client's CGA, 2970 inserts SEND options, then wraps the message in UDP/IP headers and 2971 sends it to the Client. 2973 When a Client sends a uNA, it sets the IPv6 source address to its own 2974 CGA and sets the IPv6 destination address to All-Nodes multicast, 2975 includes SEND options, wraps the message in SPAN and UDP/IP headers 2976 and sends the message to the Server. The Server authenticates the 2977 message, then changes the IPv6 address to the Client's LLA, removes 2978 the SEND options and forwards the message the same as discussed in 2979 Section 3.16.1. In the reverse direction, when the Server forwards a 2980 uNA to the Client, it changes the IPv6 address to its own CGA and 2981 inserts SEND options then forwards the message to the Client. 2983 When a Client sends an NS(NUD), it sets both the IPv6 source and 2984 destination address to its own LLA, wraps the message in a SPAN 2985 header and UDP/IP headers, then sends the message directly to the 2986 peer which will loop the message back. In this case alone, the 2987 Client does not use the Server as a trust broker for forwarding the 2988 ND message. 2990 3.23. Time-Varying MNPs 2992 In some use cases, it is desirable, beneficial and efficient for the 2993 Client to receive a constant MNP that travels with the Client 2994 wherever it moves. For example, this would allow air traffic 2995 controllers to easily track aircraft, etc. In other cases, however 2996 (e.g., intelligent transportation systems), the MN may be willing to 2997 sacrifice a modicum of efficiency in order to have time-varying MNPs 2998 that can be changed every so often to defeat adversarial tracking. 3000 The DHCPv6-PD service offers a way for Clients that desire time- 3001 varying MNPs to obtain short-lived prefixes (e.g., on the order of a 3002 small number of minutes). In that case, the identity of the Client 3003 would not be bound to the MNP but rather the Client's identity would 3004 be bound to the DHCPv6 Device Unique Identifier (DUID) and used as 3005 the seed for Prefix Delegation. The Client would then be obligated 3006 to renumber its internal networks whenever its MNP (and therefore 3007 also its LLA) changes. This should not present a challenge for 3008 Clients with automated network renumbering services, however presents 3009 limits for the durations of ongoing sessions that would prefer to use 3010 a constant address. 3012 4. Implementation Status 3014 An AERO implementation based on OpenVPN (https://openvpn.net/) was 3015 announced on the v6ops mailing list on January 10, 2018 and an 3016 initial public release of the AERO proof-of-concept source code was 3017 announced on the intarea mailing list on August 21, 2015. 3019 As of 4/1/2020, more recent updated implementations are under 3020 internal development and testing with plans to release in the near 3021 future. 3023 5. IANA Considerations 3025 The IANA has assigned a 4-octet Private Enterprise Number "45282" for 3026 AERO in the "enterprise-numbers" registry. 3028 The IANA has assigned the UDP port number "8060" for an earlier 3029 experimental version of AERO [RFC6706]. This document obsoletes 3030 [RFC6706] and claims the UDP port number "8060" for all future use. 3032 The IANA is instructed to assign a new type value TBD in the Segment 3033 Routing Header TLV registry [RFC8754]. 3035 No further IANA actions are required. 3037 6. Security Considerations 3039 AERO Bridges configure secured tunnels with AERO Servers, Realys and 3040 Proxys within their local OMNI link segments. Applicable secured 3041 tunnel alternatives include IPsec [RFC4301], TLS/SSL [RFC8446], DTLS 3042 [RFC6347], WireGuard, etc. The AERO Bridges of all OMNI link 3043 segments in turn configure secured tunnels for their neighboring AERO 3044 Bridges in a spanning tree topology. Therefore, control messages 3045 exchanged between any pair of OMNI link neighbors on the spanning 3046 tree are already secured. 3048 AERO Servers, Relays and Proxys targeted by a route optimization may 3049 also receive data packets directly from arbitrary nodes in INET 3050 partitions instead of via the spanning tree. For INET partitions 3051 that apply effective ingress filtering to defeat source address 3052 spoofing, the simple data origin authentication procedures in 3053 Section 3.8 can be applied. 3055 For INET partitions that require strong security in the data plane, 3056 two options for securing communications include 1) disable route 3057 optimization so that all traffic is conveyed over secured tunnels, or 3058 2) enable on-demand secure tunnel creation between INET partition 3059 neighbors. Option 1) would result in longer routes than necessary 3060 and traffic concentration on critical infrastructure elements. 3061 Option 2) could be coordinated by establishing a secured tunnel on- 3062 demand instead of performing an NS/NA exchange in the route 3063 optimization procedures. Procedures for establishing on-demand 3064 secured tunnels are out of scope. 3066 AERO Clients that connect to secured ANETs need not apply security to 3067 their ND messages, since the messages will be intercepted by a 3068 perimeter Proxy that applies security on its INET-facing interface as 3069 part of the spanning tree (see above). AERO Clients connected to the 3070 open INET can use symmetric network and/or transport layer security 3071 services such as VPNs or can by some other means establish a direct 3072 link. When a VPN or direct link may be impractical, however, an 3073 asymmetric security service such as SEcure Neighbor Discovery (SEND) 3074 [RFC3971] with Cryptographically Generated Addresses (CGAs) [RFC3972] 3075 and/or the Authentication option [RFC4380] can be applied. 3077 Application endpoints SHOULD use application-layer security services 3078 such as TLS/SSL, DTLS or SSH [RFC4251] to assure the same level of 3079 protection as for critical secured Internet services. AERO Clients 3080 that require host-based VPN services SHOULD use symmetric network 3081 and/or transport layer security services such as IPsec, TLS/SSL, 3082 DTLS, etc. AERO Proxys and Servers can also provide a network-based 3083 VPN service on behalf of the Client, e.g., if the Client is located 3084 within a secured enclave and cannot establish a VPN on its own 3085 behalf. 3087 AERO Servers and Bridges present targets for traffic amplification 3088 Denial of Service (DoS) attacks. This concern is no different than 3089 for widely-deployed VPN security gateways in the Internet, where 3090 attackers could send spoofed packets to the gateways at high data 3091 rates. This can be mitigated by connecting Servers and Bridges over 3092 dedicated links with no connections to the Internet and/or when 3093 connections to the Internet are only permitted through well-managed 3094 firewalls. Traffic amplification DoS attacks can also target an AERO 3095 Client's low data rate links. This is a concern not only for Clients 3096 located on the open Internet but also for Clients in secured 3097 enclaves. AERO Servers and Proxys can institute rate limits that 3098 protect Clients from receiving packet floods that could DoS low data 3099 rate links. 3101 AERO Relays must implement ingress filtering to avoid a spoofing 3102 attack in which spurious messages with ULA addresses are injected 3103 into an OMNI link from an outside attacker. AERO Clients MUST ensure 3104 that their connectivity is not used by unauthorized nodes on their 3105 EUNs to gain access to a protected network, i.e., AERO Clients that 3106 act as routers MUST NOT provide routing services for unauthorized 3107 nodes. (This concern is no different than for ordinary hosts that 3108 receive an IP address delegation but then "share" the address with 3109 other nodes via some form of Internet connection sharing such as 3110 tethering.) 3112 The MAP list MUST be well-managed and secured from unauthorized 3113 tampering, even though the list contains only public information. 3114 The MAP list can be conveyed to the Client in a similar fashion as in 3115 [RFC5214] (e.g., through layer 2 data link login messaging, secure 3116 upload of a static file, DNS lookups, etc.). 3118 Although public domain and commercial SEND implementations exist, 3119 concerns regarding the strength of the cryptographic hash algorithm 3120 have been documented [RFC6273] [RFC4982]. 3122 SRH authentication facilities are specified in [RFC8754]. 3124 Security considerations for accepting link-layer ICMP messages and 3125 reflected packets are discussed throughout the document. 3127 Security considerations for IPv6 fragmentation and reassembly are 3128 discussed in [I-D.templin-6man-omni-interface]. 3130 7. Acknowledgements 3132 Discussions in the IETF, aviation standards communities and private 3133 exchanges helped shape some of the concepts in this work. 3134 Individuals who contributed insights include Mikael Abrahamsson, Mark 3135 Andrews, Fred Baker, Bob Braden, Stewart Bryant, Brian Carpenter, 3136 Wojciech Dec, Pavel Drasil, Ralph Droms, Adrian Farrel, Nick Green, 3137 Sri Gundavelli, Brian Haberman, Bernhard Haindl, Joel Halpern, Tom 3138 Herbert, Sascha Hlusiak, Lee Howard, Zdenek Jaron, Andre Kostur, 3139 Hubert Kuenig, Ted Lemon, Andy Malis, Satoru Matsushima, Tomek 3140 Mrugalski, Madhu Niraula, Alexandru Petrescu, Behcet Saikaya, Michal 3141 Skorepa, Joe Touch, Bernie Volz, Ryuji Wakikawa, Tony Whyman, Lloyd 3142 Wood and James Woodyatt. Members of the IESG also provided valuable 3143 input during their review process that greatly improved the document. 3144 Special thanks go to Stewart Bryant, Joel Halpern and Brian Haberman 3145 for their shepherding guidance during the publication of the AERO 3146 first edition. 3148 This work has further been encouraged and supported by Boeing 3149 colleagues including Kyle Bae, M. Wayne Benson, Dave Bernhardt, Cam 3150 Brodie, John Bush, Balaguruna Chidambaram, Irene Chin, Bruce Cornish, 3151 Claudiu Danilov, Don Dillenburg, Joe Dudkowski, Wen Fang, Samad 3152 Farooqui, Anthony Gregory, Jeff Holland, Seth Jahne, Brian Jaury, 3153 Greg Kimberly, Ed King, Madhuri Madhava Badgandi, Laurel Matthew, 3154 Gene MacLean III, Rob Muszkiewicz, Sean O'Sullivan, Vijay 3155 Rajagopalan, Greg Saccone, Rod Santiago, Kent Shuey, Brian Skeen, 3156 Mike Slane, Carrie Spiker, Katie Tran, Brendan Williams, Amelia 3157 Wilson, Julie Wulff, Yueli Yang, Eric Yeh and other members of the 3158 Boeing mobility, networking and autonomy teams. Kyle Bae, Wayne 3159 Benson, Katie Tran and Eric Yeh are especially acknowledged for 3160 implementing the AERO functions as extensions to the public domain 3161 OpenVPN distribution. 3163 Earlier works on NBMA tunneling approaches are found in 3164 [RFC2529][RFC5214][RFC5569]. 3166 Many of the constructs presented in this second edition of AERO are 3167 based on the author's earlier works, including: 3169 o The Internet Routing Overlay Network (IRON) 3170 [RFC6179][I-D.templin-ironbis] 3172 o Virtual Enterprise Traversal (VET) 3173 [RFC5558][I-D.templin-intarea-vet] 3175 o The Subnetwork Encapsulation and Adaptation Layer (SEAL) 3176 [RFC5320][I-D.templin-intarea-seal] 3178 o AERO, First Edition [RFC6706] 3180 Note that these works cite numerous earlier efforts that are not also 3181 cited here due to space limitations. The authors of those earlier 3182 works are acknowledged for their insights. 3184 This work is aligned with the NASA Safe Autonomous Systems Operation 3185 (SASO) program under NASA contract number NNA16BD84C. 3187 This work is aligned with the FAA as per the SE2025 contract number 3188 DTFAWA-15-D-00030. 3190 This work is aligned with the Boeing Commercial Airplanes (BCA) 3191 Internet of Things (IoT) and autonomy programs. 3193 This work is aligned with the Boeing Information Technology (BIT) 3194 MobileNet program. 3196 8. References 3197 8.1. Normative References 3199 [I-D.templin-6man-omni-interface] 3200 Templin, F. and T. Whyman, "Transmission of IPv6 Packets 3201 over Overlay Multilink Network (OMNI) Interfaces", draft- 3202 templin-6man-omni-interface-24 (work in progress), June 3203 2020. 3205 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, 3206 DOI 10.17487/RFC0791, September 1981, 3207 . 3209 [RFC0792] Postel, J., "Internet Control Message Protocol", STD 5, 3210 RFC 792, DOI 10.17487/RFC0792, September 1981, 3211 . 3213 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 3214 Requirement Levels", BCP 14, RFC 2119, 3215 DOI 10.17487/RFC2119, March 1997, 3216 . 3218 [RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in 3219 IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473, 3220 December 1998, . 3222 [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black, 3223 "Definition of the Differentiated Services Field (DS 3224 Field) in the IPv4 and IPv6 Headers", RFC 2474, 3225 DOI 10.17487/RFC2474, December 1998, 3226 . 3228 [RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander, 3229 "SEcure Neighbor Discovery (SEND)", RFC 3971, 3230 DOI 10.17487/RFC3971, March 2005, 3231 . 3233 [RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)", 3234 RFC 3972, DOI 10.17487/RFC3972, March 2005, 3235 . 3237 [RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and 3238 More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191, 3239 November 2005, . 3241 [RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast 3242 Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005, 3243 . 3245 [RFC4380] Huitema, C., "Teredo: Tunneling IPv6 over UDP through 3246 Network Address Translations (NATs)", RFC 4380, 3247 DOI 10.17487/RFC4380, February 2006, 3248 . 3250 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 3251 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 3252 DOI 10.17487/RFC4861, September 2007, 3253 . 3255 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 3256 Address Autoconfiguration", RFC 4862, 3257 DOI 10.17487/RFC4862, September 2007, 3258 . 3260 [RFC5175] Haberman, B., Ed. and R. Hinden, "IPv6 Router 3261 Advertisement Flags Option", RFC 5175, 3262 DOI 10.17487/RFC5175, March 2008, 3263 . 3265 [RFC6081] Thaler, D., "Teredo Extensions", RFC 6081, 3266 DOI 10.17487/RFC6081, January 2011, 3267 . 3269 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 3270 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 3271 May 2017, . 3273 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 3274 (IPv6) Specification", STD 86, RFC 8200, 3275 DOI 10.17487/RFC8200, July 2017, 3276 . 3278 [RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A., 3279 Richardson, M., Jiang, S., Lemon, T., and T. Winters, 3280 "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", 3281 RFC 8415, DOI 10.17487/RFC8415, November 2018, 3282 . 3284 8.2. Informative References 3286 [BGP] Huston, G., "BGP in 2015, http://potaroo.net", January 3287 2016. 3289 [I-D.bonica-6man-comp-rtg-hdr] 3290 Bonica, R., Kamite, Y., Niwa, T., Alston, A., and L. 3291 Jalil, "The IPv6 Compact Routing Header (CRH)", draft- 3292 bonica-6man-comp-rtg-hdr-22 (work in progress), May 2020. 3294 [I-D.bonica-6man-crh-helper-opt] 3295 Li, X., Bao, C., Ruan, E., and R. Bonica, "Compressed 3296 Routing Header (CRH) Helper Option", draft-bonica-6man- 3297 crh-helper-opt-01 (work in progress), May 2020. 3299 [I-D.ietf-dmm-distributed-mobility-anchoring] 3300 Chan, A., Wei, X., Lee, J., Jeon, S., and C. Bernardos, 3301 "Distributed Mobility Anchoring", draft-ietf-dmm- 3302 distributed-mobility-anchoring-15 (work in progress), 3303 March 2020. 3305 [I-D.ietf-intarea-frag-fragile] 3306 Bonica, R., Baker, F., Huston, G., Hinden, R., Troan, O., 3307 and F. Gont, "IP Fragmentation Considered Fragile", draft- 3308 ietf-intarea-frag-fragile-17 (work in progress), September 3309 2019. 3311 [I-D.ietf-intarea-gue] 3312 Herbert, T., Yong, L., and O. Zia, "Generic UDP 3313 Encapsulation", draft-ietf-intarea-gue-09 (work in 3314 progress), October 2019. 3316 [I-D.ietf-intarea-gue-extensions] 3317 Herbert, T., Yong, L., and F. Templin, "Extensions for 3318 Generic UDP Encapsulation", draft-ietf-intarea-gue- 3319 extensions-06 (work in progress), March 2019. 3321 [I-D.ietf-intarea-tunnels] 3322 Touch, J. and M. Townsley, "IP Tunnels in the Internet 3323 Architecture", draft-ietf-intarea-tunnels-10 (work in 3324 progress), September 2019. 3326 [I-D.ietf-rtgwg-atn-bgp] 3327 Templin, F., Saccone, G., Dawra, G., Lindem, A., and V. 3328 Moreno, "A Simple BGP-based Mobile Routing System for the 3329 Aeronautical Telecommunications Network", draft-ietf- 3330 rtgwg-atn-bgp-05 (work in progress), January 2020. 3332 [I-D.templin-6man-dhcpv6-ndopt] 3333 Templin, F., "A Unified Stateful/Stateless Configuration 3334 Service for IPv6", draft-templin-6man-dhcpv6-ndopt-09 3335 (work in progress), January 2020. 3337 [I-D.templin-intarea-grefrag] 3338 Templin, F., "GRE Tunnel Level Fragmentation", draft- 3339 templin-intarea-grefrag-04 (work in progress), July 2016. 3341 [I-D.templin-intarea-seal] 3342 Templin, F., "The Subnetwork Encapsulation and Adaptation 3343 Layer (SEAL)", draft-templin-intarea-seal-68 (work in 3344 progress), January 2014. 3346 [I-D.templin-intarea-vet] 3347 Templin, F., "Virtual Enterprise Traversal (VET)", draft- 3348 templin-intarea-vet-40 (work in progress), May 2013. 3350 [I-D.templin-ironbis] 3351 Templin, F., "The Interior Routing Overlay Network 3352 (IRON)", draft-templin-ironbis-16 (work in progress), 3353 March 2014. 3355 [I-D.templin-v6ops-pdhost] 3356 Templin, F., "IPv6 Prefix Delegation and Multi-Addressing 3357 Models", draft-templin-v6ops-pdhost-25 (work in progress), 3358 January 2020. 3360 [OVPN] OpenVPN, O., "http://openvpn.net", October 2016. 3362 [RFC1035] Mockapetris, P., "Domain names - implementation and 3363 specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, 3364 November 1987, . 3366 [RFC1122] Braden, R., Ed., "Requirements for Internet Hosts - 3367 Communication Layers", STD 3, RFC 1122, 3368 DOI 10.17487/RFC1122, October 1989, 3369 . 3371 [RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191, 3372 DOI 10.17487/RFC1191, November 1990, 3373 . 3375 [RFC1812] Baker, F., Ed., "Requirements for IP Version 4 Routers", 3376 RFC 1812, DOI 10.17487/RFC1812, June 1995, 3377 . 3379 [RFC2003] Perkins, C., "IP Encapsulation within IP", RFC 2003, 3380 DOI 10.17487/RFC2003, October 1996, 3381 . 3383 [RFC2236] Fenner, W., "Internet Group Management Protocol, Version 3384 2", RFC 2236, DOI 10.17487/RFC2236, November 1997, 3385 . 3387 [RFC2492] Armitage, G., Schulter, P., and M. Jork, "IPv6 over ATM 3388 Networks", RFC 2492, DOI 10.17487/RFC2492, January 1999, 3389 . 3391 [RFC2529] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4 3392 Domains without Explicit Tunnels", RFC 2529, 3393 DOI 10.17487/RFC2529, March 1999, 3394 . 3396 [RFC2764] Gleeson, B., Lin, A., Heinanen, J., Armitage, G., and A. 3397 Malis, "A Framework for IP Based Virtual Private 3398 Networks", RFC 2764, DOI 10.17487/RFC2764, February 2000, 3399 . 3401 [RFC2784] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P. 3402 Traina, "Generic Routing Encapsulation (GRE)", RFC 2784, 3403 DOI 10.17487/RFC2784, March 2000, 3404 . 3406 [RFC2890] Dommety, G., "Key and Sequence Number Extensions to GRE", 3407 RFC 2890, DOI 10.17487/RFC2890, September 2000, 3408 . 3410 [RFC2923] Lahey, K., "TCP Problems with Path MTU Discovery", 3411 RFC 2923, DOI 10.17487/RFC2923, September 2000, 3412 . 3414 [RFC2983] Black, D., "Differentiated Services and Tunnels", 3415 RFC 2983, DOI 10.17487/RFC2983, October 2000, 3416 . 3418 [RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition 3419 of Explicit Congestion Notification (ECN) to IP", 3420 RFC 3168, DOI 10.17487/RFC3168, September 2001, 3421 . 3423 [RFC3330] IANA, "Special-Use IPv4 Addresses", RFC 3330, 3424 DOI 10.17487/RFC3330, September 2002, 3425 . 3427 [RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener 3428 Discovery Version 2 (MLDv2) for IPv6", RFC 3810, 3429 DOI 10.17487/RFC3810, June 2004, 3430 . 3432 [RFC3819] Karn, P., Ed., Bormann, C., Fairhurst, G., Grossman, D., 3433 Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J., and L. 3434 Wood, "Advice for Internet Subnetwork Designers", BCP 89, 3435 RFC 3819, DOI 10.17487/RFC3819, July 2004, 3436 . 3438 [RFC4213] Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms 3439 for IPv6 Hosts and Routers", RFC 4213, 3440 DOI 10.17487/RFC4213, October 2005, 3441 . 3443 [RFC4251] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH) 3444 Protocol Architecture", RFC 4251, DOI 10.17487/RFC4251, 3445 January 2006, . 3447 [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A 3448 Border Gateway Protocol 4 (BGP-4)", RFC 4271, 3449 DOI 10.17487/RFC4271, January 2006, 3450 . 3452 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 3453 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 3454 2006, . 3456 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 3457 Internet Protocol", RFC 4301, DOI 10.17487/RFC4301, 3458 December 2005, . 3460 [RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery 3461 Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April 3462 2006, . 3464 [RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet 3465 Control Message Protocol (ICMPv6) for the Internet 3466 Protocol Version 6 (IPv6) Specification", STD 89, 3467 RFC 4443, DOI 10.17487/RFC4443, March 2006, 3468 . 3470 [RFC4511] Sermersheim, J., Ed., "Lightweight Directory Access 3471 Protocol (LDAP): The Protocol", RFC 4511, 3472 DOI 10.17487/RFC4511, June 2006, 3473 . 3475 [RFC4541] Christensen, M., Kimball, K., and F. Solensky, 3476 "Considerations for Internet Group Management Protocol 3477 (IGMP) and Multicast Listener Discovery (MLD) Snooping 3478 Switches", RFC 4541, DOI 10.17487/RFC4541, May 2006, 3479 . 3481 [RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick, 3482 "Internet Group Management Protocol (IGMP) / Multicast 3483 Listener Discovery (MLD)-Based Multicast Forwarding 3484 ("IGMP/MLD Proxying")", RFC 4605, DOI 10.17487/RFC4605, 3485 August 2006, . 3487 [RFC4607] Holbrook, H. and B. Cain, "Source-Specific Multicast for 3488 IP", RFC 4607, DOI 10.17487/RFC4607, August 2006, 3489 . 3491 [RFC4963] Heffner, J., Mathis, M., and B. Chandler, "IPv4 Reassembly 3492 Errors at High Data Rates", RFC 4963, 3493 DOI 10.17487/RFC4963, July 2007, 3494 . 3496 [RFC4982] Bagnulo, M. and J. Arkko, "Support for Multiple Hash 3497 Algorithms in Cryptographically Generated Addresses 3498 (CGAs)", RFC 4982, DOI 10.17487/RFC4982, July 2007, 3499 . 3501 [RFC5015] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano, 3502 "Bidirectional Protocol Independent Multicast (BIDIR- 3503 PIM)", RFC 5015, DOI 10.17487/RFC5015, October 2007, 3504 . 3506 [RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site 3507 Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214, 3508 DOI 10.17487/RFC5214, March 2008, 3509 . 3511 [RFC5320] Templin, F., Ed., "The Subnetwork Encapsulation and 3512 Adaptation Layer (SEAL)", RFC 5320, DOI 10.17487/RFC5320, 3513 February 2010, . 3515 [RFC5522] Eddy, W., Ivancic, W., and T. Davis, "Network Mobility 3516 Route Optimization Requirements for Operational Use in 3517 Aeronautics and Space Exploration Mobile Networks", 3518 RFC 5522, DOI 10.17487/RFC5522, October 2009, 3519 . 3521 [RFC5558] Templin, F., Ed., "Virtual Enterprise Traversal (VET)", 3522 RFC 5558, DOI 10.17487/RFC5558, February 2010, 3523 . 3525 [RFC5569] Despres, R., "IPv6 Rapid Deployment on IPv4 3526 Infrastructures (6rd)", RFC 5569, DOI 10.17487/RFC5569, 3527 January 2010, . 3529 [RFC5871] Arkko, J. and S. Bradner, "IANA Allocation Guidelines for 3530 the IPv6 Routing Header", RFC 5871, DOI 10.17487/RFC5871, 3531 May 2010, . 3533 [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 3534 (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, 3535 . 3537 [RFC5991] Thaler, D., Krishnan, S., and J. Hoagland, "Teredo 3538 Security Updates", RFC 5991, DOI 10.17487/RFC5991, 3539 September 2010, . 3541 [RFC6106] Jeong, J., Park, S., Beloeil, L., and S. Madanapalli, 3542 "IPv6 Router Advertisement Options for DNS Configuration", 3543 RFC 6106, DOI 10.17487/RFC6106, November 2010, 3544 . 3546 [RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful 3547 NAT64: Network Address and Protocol Translation from IPv6 3548 Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146, 3549 April 2011, . 3551 [RFC6179] Templin, F., Ed., "The Internet Routing Overlay Network 3552 (IRON)", RFC 6179, DOI 10.17487/RFC6179, March 2011, 3553 . 3555 [RFC6221] Miles, D., Ed., Ooghe, S., Dec, W., Krishnan, S., and A. 3556 Kavanagh, "Lightweight DHCPv6 Relay Agent", RFC 6221, 3557 DOI 10.17487/RFC6221, May 2011, 3558 . 3560 [RFC6273] Kukec, A., Krishnan, S., and S. Jiang, "The Secure 3561 Neighbor Discovery (SEND) Hash Threat Analysis", RFC 6273, 3562 DOI 10.17487/RFC6273, June 2011, 3563 . 3565 [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer 3566 Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, 3567 January 2012, . 3569 [RFC6438] Carpenter, B. and S. Amante, "Using the IPv6 Flow Label 3570 for Equal Cost Multipath Routing and Link Aggregation in 3571 Tunnels", RFC 6438, DOI 10.17487/RFC6438, November 2011, 3572 . 3574 [RFC6706] Templin, F., Ed., "Asymmetric Extended Route Optimization 3575 (AERO)", RFC 6706, DOI 10.17487/RFC6706, August 2012, 3576 . 3578 [RFC6864] Touch, J., "Updated Specification of the IPv4 ID Field", 3579 RFC 6864, DOI 10.17487/RFC6864, February 2013, 3580 . 3582 [RFC6935] Eubanks, M., Chimento, P., and M. Westerlund, "IPv6 and 3583 UDP Checksums for Tunneled Packets", RFC 6935, 3584 DOI 10.17487/RFC6935, April 2013, 3585 . 3587 [RFC6936] Fairhurst, G. and M. Westerlund, "Applicability Statement 3588 for the Use of IPv6 UDP Datagrams with Zero Checksums", 3589 RFC 6936, DOI 10.17487/RFC6936, April 2013, 3590 . 3592 [RFC7269] Chen, G., Cao, Z., Xie, C., and D. Binet, "NAT64 3593 Deployment Options and Experience", RFC 7269, 3594 DOI 10.17487/RFC7269, June 2014, 3595 . 3597 [RFC7333] Chan, H., Ed., Liu, D., Seite, P., Yokota, H., and J. 3598 Korhonen, "Requirements for Distributed Mobility 3599 Management", RFC 7333, DOI 10.17487/RFC7333, August 2014, 3600 . 3602 [RFC7421] Carpenter, B., Ed., Chown, T., Gont, F., Jiang, S., 3603 Petrescu, A., and A. Yourtchenko, "Analysis of the 64-bit 3604 Boundary in IPv6 Addressing", RFC 7421, 3605 DOI 10.17487/RFC7421, January 2015, 3606 . 3608 [RFC7739] Gont, F., "Security Implications of Predictable Fragment 3609 Identification Values", RFC 7739, DOI 10.17487/RFC7739, 3610 February 2016, . 3612 [RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I., 3613 Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent 3614 Multicast - Sparse Mode (PIM-SM): Protocol Specification 3615 (Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March 3616 2016, . 3618 [RFC8086] Yong, L., Ed., Crabbe, E., Xu, X., and T. Herbert, "GRE- 3619 in-UDP Encapsulation", RFC 8086, DOI 10.17487/RFC8086, 3620 March 2017, . 3622 [RFC8138] Thubert, P., Ed., Bormann, C., Toutain, L., and R. Cragie, 3623 "IPv6 over Low-Power Wireless Personal Area Network 3624 (6LoWPAN) Routing Header", RFC 8138, DOI 10.17487/RFC8138, 3625 April 2017, . 3627 [RFC8201] McCann, J., Deering, S., Mogul, J., and R. Hinden, Ed., 3628 "Path MTU Discovery for IP version 6", STD 87, RFC 8201, 3629 DOI 10.17487/RFC8201, July 2017, 3630 . 3632 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 3633 Decraene, B., Litkowski, S., and R. Shakir, "Segment 3634 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 3635 July 2018, . 3637 [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol 3638 Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, 3639 . 3641 [RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J., 3642 Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header 3643 (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020, 3644 . 3646 Appendix A. Non-Normative Considerations 3648 AERO can be applied to a multitude of Internetworking scenarios, with 3649 each having its own adaptations. The following considerations are 3650 provided as non-normative guidance: 3652 A.1. Implementation Strategies for Route Optimization 3654 Route optimization as discussed in Section 3.14 results in the route 3655 optimization source (ROS) creating an asymmetric neighbor cache entry 3656 for the target neighbor. The neighbor cache entry is maintained for 3657 at most ReachableTime seconds and then deleted unless updated. In 3658 order to refresh the neighbor cache entry lifetime before the 3659 ReachableTime timer expires, the specification requires 3660 implementations to issue a new NS/NA exchange to reset ReachableTime 3661 while data packets are still flowing. However, the decision of when 3662 to initiate a new NS/NA exchange and to perpetuate the process is 3663 left as an implementation detail. 3665 One possible strategy may be to monitor the neighbor cache entry 3666 watching for data packets for (ReachableTime - 5) seconds. If any 3667 data packets have been sent to the neighbor within this timeframe, 3668 then send an NS to receive a new NA. If no data packets have been 3669 sent, wait for 5 additional seconds and send an immediate NS if any 3670 data packets are sent within this "expiration pending" 5 second 3671 window. If no additional data packets are sent within the 5 second 3672 window, delete the neighbor cache entry. 3674 The monitoring of the neighbor data packet traffic therefore becomes 3675 an asymmetric ongoing process during the neighbor cache entry 3676 lifetime. If the neighbor cache entry expires, future data packets 3677 will trigger a new NS/NA exchange while the packets themselves are 3678 delivered over a longer path until route optimization state is re- 3679 established. 3681 A.2. Implicit Mobility Management 3683 OMNI interface neighbors MAY provide a configuration option that 3684 allows them to perform implicit mobility management in which no ND 3685 messaging is used. In that case, the Client only transmits packets 3686 over a single interface at a time, and the neighbor always observes 3687 packets arriving from the Client from the same link-layer source 3688 address. 3690 If the Client's underlying interface address changes (either due to a 3691 readdressing of the original interface or switching to a new 3692 interface) the neighbor immediately updates the neighbor cache entry 3693 for the Client and begins accepting and sending packets according to 3694 the Client's new address. This implicit mobility method applies to 3695 use cases such as cellphones with both WiFi and Cellular interfaces 3696 where only one of the interfaces is active at a given time, and the 3697 Client automatically switches over to the backup interface if the 3698 primary interface fails. 3700 A.3. Direct Underlying Interfaces 3702 When a Client's OMNI interface is configured over a Direct interface, 3703 the neighbor at the other end of the Direct link can receive packets 3704 without any encapsulation. In that case, the Client sends packets 3705 over the Direct link according to QoS preferences. If the Direct 3706 interface has the highest QoS preference, then the Client's IP 3707 packets are transmitted directly to the peer without going through an 3708 ANET/INET. If other interfaces have higher QoS preferences, then the 3709 Client's IP packets are transmitted via a different interface, which 3710 may result in the inclusion of Proxys, Servers and Bridges in the 3711 communications path. Direct interfaces must be tested periodically 3712 for reachability, e.g., via NUD. 3714 A.4. AERO Critical Infrastructure Considerations 3716 AERO Bridges can be either Commercial off-the Shelf (COTS) standard 3717 IP routers or virtual machines in the cloud. Bridges must be 3718 provisioned, supported and managed by the INET administrative 3719 authority, and connected to the Bridges of other INETs via inter- 3720 domain peerings. Cost for purchasing, configuring and managing 3721 Bridges is nominal even for very large OMNI links. 3723 AERO Servers can be standard dedicated server platforms, but most 3724 often will be deployed as virtual machines in the cloud. The only 3725 requirements for Servers are that they can run the AERO user-level 3726 code and have at least one network interface connection to the INET. 3727 As with Bridges, Servers must be provisioned, supported and managed 3728 by the INET administrative authority. Cost for purchasing, 3729 configuring and managing Servers is nominal especially for virtual 3730 Servers hosted in the cloud. 3732 AERO Proxys are most often standard dedicated server platforms with 3733 one network interface connected to the ANET and a second interface 3734 connected to an INET. As with Servers, the only requirements are 3735 that they can run the AERO user-level code and have at least one 3736 interface connection to the INET. Proxys must be provisioned, 3737 supported and managed by the ANET administrative authority. Cost for 3738 purchasing, configuring and managing Proxys is nominal, and borne by 3739 the ANET administrative authority. 3741 AERO Relays can be any dedicated server or COTS router platform 3742 connected to INETs and/or EUNs. The Relay connects to the OMNI link 3743 and engages in eBGP peering with one or more Bridges as a stub AS. 3744 The Relay then injects its MNPs and/or non-MNP prefixes into the BGP 3745 routing system, and provisions the prefixes to its downstream- 3746 attached networks. The Relay can perform ROS/ROR services the same 3747 as for any Server, and can route between the MNP and non-MNP address 3748 spaces. 3750 A.5. AERO Server Failure Implications 3752 AERO Servers may appear as a single point of failure in the 3753 architecture, but such is not the case since all Servers on the link 3754 provide identical services and loss of a Server does not imply 3755 immediate and/or comprehensive communication failures. Although 3756 Clients typically associate with a single Server at a time, Server 3757 failure is quickly detected and conveyed by Bidirectional Forward 3758 Detection (BFD) and/or proactive NUD allowing Clients to migrate to 3759 new Servers. 3761 If a Server fails, ongoing packet forwarding to Clients will continue 3762 by virtue of the asymmetric neighbor cache entries that have already 3763 been established in route optimization sources (ROSs). If a Client 3764 also experiences mobility events at roughly the same time the Server 3765 fails, unsolicited NA messages may be lost but proxy neighbor cache 3766 entries in the DEPARTED state will ensure that packet forwarding to 3767 the Client's new locations will continue for up to DepartTime 3768 seconds. 3770 If a Client is left without a Server for an extended timeframe (e.g., 3771 greater than ReachableTime seconds) then existing asymmetric neighbor 3772 cache entries will eventually expire and both ongoing and new 3773 communications will fail. The original source will continue to 3774 retransmit until the Client has established a new Server 3775 relationship, after which time continuous communications will resume. 3777 Therefore, providing many Servers on the link with high availability 3778 profiles provides resilience against loss of individual Servers and 3779 assurance that Clients can establish new Server relationships quickly 3780 in event of a Server failure. 3782 A.6. AERO Client / Server Architecture 3784 The AERO architectural model is client / server in the control plane, 3785 with route optimization in the data plane. The same as for common 3786 Internet services, the AERO Client discovers the addresses of AERO 3787 Servers and selects one Server to connect to. The AERO service is 3788 analogous to common Internet services such as google.com, yahoo.com, 3789 cnn.com, etc. However, there is only one AERO service for the link 3790 and all Servers provide identical services. 3792 Common Internet services provide differing strategies for advertising 3793 server addresses to clients. The strategy is conveyed through the 3794 DNS resource records returned in response to name resolution queries. 3795 As of January 2020 Internet-based 'nslookup' services were used to 3796 determine the following: 3798 o When a client resolves the domainname "google.com", the DNS always 3799 returns one A record (i.e., an IPv4 address) and one AAAA record 3800 (i.e., an IPv6 address). The client receives the same addresses 3801 each time it resolves the domainname via the same DNS resolver, 3802 but may receive different addresses when it resolves the 3803 domainname via different DNS resolvers. But, in each case, 3804 exactly one A and one AAAA record are returned. 3806 o When a client resolves the domainname "ietf.org", the DNS always 3807 returns one A record and one AAAA record with the same addresses 3808 regardless of which DNS resolver is used. 3810 o When a client resolves the domainname "yahoo.com", the DNS always 3811 returns a list of 4 A records and 4 AAAA records. Each time the 3812 client resolves the domainname via the same DNS resolver, the same 3813 list of addresses are returned but in randomized order (i.e., 3814 consistent with a DNS round-robin strategy). But, interestingly, 3815 the same addresses are returned (albeit in randomized order) when 3816 the domainname is resolved via different DNS resolvers. 3818 o When a client resolves the domainname "amazon.com", the DNS always 3819 returns a list of 3 A records and no AAAA records. As with 3820 "yahoo.com", the same three A records are returned from any 3821 worldwide Internet connection point in randomized order. 3823 The above example strategies show differing approaches to Internet 3824 resilience and service distribution offered by major Internet 3825 services. The Google approach exposes only a single IPv4 and a 3826 single IPv6 address to clients. Clients can then select whichever IP 3827 protocol version offers the best response, but will always use the 3828 same IP address according to the current Internet connection point. 3829 This means that the IP address offered by the network must lead to a 3830 highly-available server and/or service distribution point. In other 3831 words, resilience is predicated on high availability within the 3832 network and with no client-initiated failovers expected (i.e., it is 3833 all-or-nothing from the client's perspective). However, Google does 3834 provide for worldwide distributed service distribution by virtue of 3835 the fact that each Internet connection point responds with a 3836 different IPv6 and IPv4 address. The IETF approach is like google 3837 (all-or-nothing from the client's perspective), but provides only a 3838 single IPv4 or IPv6 address on a worldwide basis. This means that 3839 the addresses must be made highly-available at the network level with 3840 no client failover possibility, and if there is any worldwide service 3841 distribution it would need to be conducted by a network element that 3842 is reached via the IP address acting as a service distribution point. 3844 In contrast to the Google and IETF philosophies, Yahoo and Amazon 3845 both provide clients with a (short) list of IP addresses with Yahoo 3846 providing both IP protocol versions and Amazon as IPv4-only. The 3847 order of the list is randomized with each name service query 3848 response, with the effect of round-robin load balancing for service 3849 distribution. With a short list of addresses, there is still 3850 expectation that the network will implement high availability for 3851 each address but in case any single address fails the client can 3852 switch over to using a different address. The balance then becomes 3853 one of function in the network vs function in the end system. 3855 The same implications observed for common highly-available services 3856 in the Internet apply also to the AERO client/server architecture. 3857 When an AERO Client connects to one or more ANETs, it discovers one 3858 or more AERO Server addresses through the mechanisms discussed in 3859 earlier sections. Each Server address presumably leads to a fault- 3860 tolerant clustering arrangement such as supported by Linux-HA, 3861 Extended Virtual Synchrony or Paxos. Such an arrangement has 3862 precedence in common Internet service deployments in lightweight 3863 virtual machines without requiring expensive hardware deployment. 3864 Similarly, common Internet service deployments set service IP 3865 addresses on service distribution points that may relay requests to 3866 many different servers. 3868 For AERO, the expectation is that a combination of the Google/IETF 3869 and Yahoo/Amazon philosophies would be employed. The AERO Client 3870 connects to different ANET access points and can receive 1-2 Server 3871 LLAs at each point. It then selects one AERO Server address, and 3872 engages in RS/RA exchanges with the same Server from all ANET 3873 connections. The Client remains with this Server unless or until the 3874 Server fails, in which case it can switch over to an alternate 3875 Server. The Client can likewise switch over to a different Server at 3876 any time if there is some reason for it to do so. So, the AERO 3877 expectation is for a balance of function in the network and end 3878 system, with fault tolerance and resilience at both levels. 3880 Appendix B. Change Log 3882 << RFC Editor - remove prior to publication >> 3884 Changes from draft-templin-intarea-6706bis-52 to draft-templin- 3885 intrea-6706bis-53: 3887 o Normative reference to the OMNI spec, and remove portions that are 3888 already specified in OMNI. 3890 o Renamed "AERO interface/link" to "OMIN interface/link" throughout 3891 the document. 3893 o Truncated obsolete back section matter. 3895 Author's Address 3897 Fred L. Templin (editor) 3898 Boeing Research & Technology 3899 P.O. Box 3707 3900 Seattle, WA 98124 3901 USA 3903 Email: fltemplin@acm.org