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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, May 1, 2020 5 rfc6179, rfc6706 (if 6 approved) 7 Intended status: Standards Track 8 Expires: November 2, 2020 10 Asymmetric Extended Route Optimization (AERO) 11 draft-templin-intarea-6706bis-48 13 Abstract 15 This document specifies the operation of IP over tunnel virtual links 16 using Asymmetric Extended Route Optimization (AERO). AERO interfaces 17 use an IPv6 link-local address format that supports operation of the 18 IPv6 Neighbor Discovery (ND) protocol and links ND to IP forwarding. 19 Prefix delegation/registration services are employed for network 20 admission and to manage the routing system. Multilink operation, 21 mobility management, quality of service (QoS) signaling and route 22 optimization are naturally supported through dynamic neighbor cache 23 updates. Standard IP multicasting services are also supported. AERO 24 is a widely-applicable mobile internetworking service especially 25 well-suited to aviation services, intelligent transportation systems, 26 mobile Virtual Private Networks (VPNs) and many other applications. 28 Status of This Memo 30 This Internet-Draft is submitted in full conformance with the 31 provisions of BCP 78 and BCP 79. 33 Internet-Drafts are working documents of the Internet Engineering 34 Task Force (IETF). Note that other groups may also distribute 35 working documents as Internet-Drafts. The list of current Internet- 36 Drafts is at https://datatracker.ietf.org/drafts/current/. 38 Internet-Drafts are draft documents valid for a maximum of six months 39 and may be updated, replaced, or obsoleted by other documents at any 40 time. It is inappropriate to use Internet-Drafts as reference 41 material or to cite them other than as "work in progress." 43 This Internet-Draft will expire on November 2, 2020. 45 Copyright Notice 47 Copyright (c) 2020 IETF Trust and the persons identified as the 48 document authors. All rights reserved. 50 This document is subject to BCP 78 and the IETF Trust's Legal 51 Provisions Relating to IETF Documents 52 (https://trustee.ietf.org/license-info) in effect on the date of 53 publication of this document. Please review these documents 54 carefully, as they describe your rights and restrictions with respect 55 to this document. Code Components extracted from this document must 56 include Simplified BSD License text as described in Section 4.e of 57 the Trust Legal Provisions and are provided without warranty as 58 described in the Simplified BSD License. 60 Table of Contents 62 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 63 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 64 3. Asymmetric Extended Route Optimization (AERO) . . . . . . . . 11 65 3.1. AERO Link Reference Model . . . . . . . . . . . . . . . . 11 66 3.2. AERO Node Types . . . . . . . . . . . . . . . . . . . . . 12 67 3.3. AERO Routing System . . . . . . . . . . . . . . . . . . . 13 68 3.4. AERO Addresses . . . . . . . . . . . . . . . . . . . . . 15 69 3.5. Spanning Partitioned AERO Networks (SPAN) . . . . . . . . 16 70 3.5.1. SPAN Routing Topologies . . . . . . . . . . . . . . . 20 71 3.5.2. Segment Routing Over the SPAN . . . . . . . . . . . . 20 72 3.6. AERO Interface Characteristics . . . . . . . . . . . . . 21 73 3.7. AERO Interface Initialization . . . . . . . . . . . . . . 26 74 3.7.1. AERO Server/Relay Behavior . . . . . . . . . . . . . 26 75 3.7.2. AERO Proxy Behavior . . . . . . . . . . . . . . . . . 26 76 3.7.3. AERO Client Behavior . . . . . . . . . . . . . . . . 26 77 3.7.4. AERO Bridge Behavior . . . . . . . . . . . . . . . . 27 78 3.8. AERO Interface Neighbor Cache Maintenance . . . . . . . . 27 79 3.9. AERO Interface Encapsulation and Re-encapsulation . . . . 29 80 3.10. AERO Interface Decapsulation . . . . . . . . . . . . . . 30 81 3.11. AERO Interface Data Origin Authentication . . . . . . . . 30 82 3.12. AERO Interface MTU and Fragmentation . . . . . . . . . . 31 83 3.13. AERO Interface Forwarding Algorithm . . . . . . . . . . . 33 84 3.13.1. Client Forwarding Algorithm . . . . . . . . . . . . 33 85 3.13.2. Proxy Forwarding Algorithm . . . . . . . . . . . . . 34 86 3.13.3. Server/Relay Forwarding Algorithm . . . . . . . . . 35 87 3.13.4. Bridge Forwarding Algorithm . . . . . . . . . . . . 36 88 3.14. AERO Interface Error Handling . . . . . . . . . . . . . . 37 89 3.15. AERO Router Discovery, Prefix Delegation and 90 Autoconfiguration . . . . . . . . . . . . . . . . . . . . 39 91 3.15.1. AERO ND/PD Service Model . . . . . . . . . . . . . . 39 92 3.15.2. AERO Client Behavior . . . . . . . . . . . . . . . . 40 93 3.15.3. AERO Server Behavior . . . . . . . . . . . . . . . . 42 94 3.16. The AERO Proxy . . . . . . . . . . . . . . . . . . . . . 45 95 3.16.1. Detecting and Responding to Server Failures . . . . 47 96 3.16.2. Point-to-Multipoint Server Coordination . . . . . . 48 97 3.17. AERO Route Optimization . . . . . . . . . . . . . . . . . 48 98 3.17.1. Route Optimization Initiation . . . . . . . . . . . 49 99 3.17.2. Relaying the NS . . . . . . . . . . . . . . . . . . 49 100 3.17.3. Processing the NS and Sending the NA . . . . . . . . 49 101 3.17.4. Relaying the NA . . . . . . . . . . . . . . . . . . 51 102 3.17.5. Processing the NA . . . . . . . . . . . . . . . . . 51 103 3.17.6. Route Optimization Maintenance . . . . . . . . . . . 51 104 3.18. Neighbor Unreachability Detection (NUD) . . . . . . . . . 52 105 3.19. Mobility Management and Quality of Service (QoS) . . . . 53 106 3.19.1. Mobility Update Messaging . . . . . . . . . . . . . 54 107 3.19.2. Announcing Link-Layer Address and/or QoS Preference 108 Changes . . . . . . . . . . . . . . . . . . . . . . 55 109 3.19.3. Bringing New Links Into Service . . . . . . . . . . 55 110 3.19.4. Removing Existing Links from Service . . . . . . . . 55 111 3.19.5. Moving to a New Server . . . . . . . . . . . . . . . 56 112 3.20. Multicast . . . . . . . . . . . . . . . . . . . . . . . . 57 113 3.20.1. Source-Specific Multicast (SSM) . . . . . . . . . . 57 114 3.20.2. Any-Source Multicast (ASM) . . . . . . . . . . . . . 58 115 3.20.3. Bi-Directional PIM (BIDIR-PIM) . . . . . . . . . . . 59 116 3.21. Operation over Multiple AERO Links (VLANs) . . . . . . . 59 117 3.22. DNS Considerations . . . . . . . . . . . . . . . . . . . 60 118 3.23. Transition Considerations . . . . . . . . . . . . . . . . 61 119 3.24. Detecting and Reacting to Server and Bridge Failures . . 61 120 3.25. AERO Clients on the Open Internet . . . . . . . . . . . . 62 121 3.25.1. Use of SEND and CGA . . . . . . . . . . . . . . . . 64 122 3.26. Time-Varying MNPs . . . . . . . . . . . . . . . . . . . . 65 123 4. Implementation Status . . . . . . . . . . . . . . . . . . . . 66 124 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 66 125 6. Security Considerations . . . . . . . . . . . . . . . . . . . 66 126 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 68 127 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 69 128 8.1. Normative References . . . . . . . . . . . . . . . . . . 70 129 8.2. Informative References . . . . . . . . . . . . . . . . . 71 130 Appendix A. AERO Alternate Encapsulations . . . . . . . . . . . 79 131 Appendix B. Non-Normative Considerations . . . . . . . . . . . . 80 132 B.1. Implementation Strategies for Route Optimization . . . . 81 133 B.2. Implicit Mobility Management . . . . . . . . . . . . . . 81 134 B.3. Direct Underlying Interfaces . . . . . . . . . . . . . . 82 135 B.4. Operation on AERO Links with /64 ASPs . . . . . . . . . . 82 136 B.5. AERO Critical Infrastructure Considerations . . . . . . . 83 137 B.6. AERO Server Failure Implications . . . . . . . . . . . . 83 138 B.7. AERO Client / Server Architecture . . . . . . . . . . . . 84 139 Appendix C. Change Log . . . . . . . . . . . . . . . . . . . . . 86 140 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 95 142 1. Introduction 144 Asymmetric Extended Route Optimization (AERO) fulfills the 145 requirements of Distributed Mobility Management (DMM) [RFC7333] and 146 route optimization [RFC5522] for aeronautical networking and other 147 network mobility use cases such as intelligent transportation 148 systems. AERO is based on a Non-Broadcast, Multiple Access (NBMA) 149 virtual link model known as the AERO link. The AERO link is a 150 virtual overlay configured over one or more underlying Internetworks, 151 and nodes on the link can exchange IP packets via tunneling. 152 Multilink operation allows for increased reliability, bandwidth 153 optimization and traffic path diversity. 155 The AERO service comprises Clients, Proxys, Servers and Relays that 156 are seen as AERO link neighbors as well as Bridges that interconnect 157 AERO link segments. Each node's AERO interface uses an IPv6 link- 158 local address format (known as the AERO address) that supports 159 operation of the IPv6 Neighbor Discovery (ND) protocol [RFC4861] and 160 links ND to IP forwarding. A node's AERO interface can be configured 161 over multiple underlying interfaces, and may therefore appear as a 162 single interface with multiple link-layer addresses. Each link-layer 163 address is subject to change due to mobility and/or QoS fluctuations, 164 and link-layer address changes are signaled by ND messaging the same 165 as for any IPv6 link. 167 AERO links provide a cloud-based service where mobile nodes may use 168 any Server acting as a Mobility Anchor Point (MAP) and fixed nodes 169 may use any Relay on the link for efficient communications. Fixed 170 nodes forward packets destined to other AERO nodes to the nearest 171 Relay, which forwards them through the cloud. A mobile node's 172 initial packets are forwarded through the Server, while direct 173 routing is supported through asymmetric extended route optimization 174 while data packets are flowing. Both unicast and multicast 175 communications are supported, and mobile nodes may efficiently move 176 between locations while maintaining continuous communications with 177 correspondents and without changing their IP Address. 179 AERO Bridges are interconnected in a secured private BGP overlay 180 routing instance known as "The SPAN". The SPAN provides a hybrid 181 routing/bridging service to join the underlying Internetworks of 182 multiple disjoint administrative domains into a single unified AERO 183 link. Each AERO link instance is characterized by the set of 184 Mobility Service Prefixes (MSPs) common to all mobile nodes. The 185 link extends to the point where a Relay/Server is on the optimal 186 route from any correspondent node on the link, and provides a conduit 187 between the underlying Internetwork and the SPAN. To the underlying 188 Internetwork, the Relay/Server is the source of a route to the MSP, 189 and hence uplink traffic to the mobile node is naturally routed to 190 the nearest Relay/Server. 192 AERO assumes the use of PIM Sparse Mode in support of multicast 193 communication. In support of Source Specific Multicast (SSM) when a 194 Mobile Node is the source, AERO route optimization ensures that a 195 shortest-path multicast tree is established with provisions for 196 mobility and multilink operation. In all other multicast scenarios 197 there are no AERO dependencies. 199 AERO was designed for aeronautical networking for both manned and 200 unmanned aircraft, where the aircraft is treated as a mobile node 201 that can connect an Internet of Things (IoT). AERO is also 202 applicable to a wide variety of other use cases. For example, it can 203 be used to coordinate the Virtual Private Network (VPN) links of 204 mobile nodes (e.g., cellphones, tablets, laptop computers, etc.) that 205 connect into a home enterprise network via public access networks 206 using services such as OpenVPN [OVPN]. It can also be used to 207 facilitate vehicular and pedestrian communications services for 208 intelligent transportation systems. Other applicable use cases are 209 also in scope. 211 The following numbered sections present the AERO specification. The 212 appendices at the end of the document are non-normative. 214 2. Terminology 216 The terminology in the normative references applies; the following 217 terms are defined within the scope of this document: 219 IPv6 Neighbor Discovery (ND) 220 an IPv6 control message service for coordinating neighbor 221 relationships between nodes connected to a common link. AERO 222 interfaces use the ND service specified in [RFC4861]. 224 IPv6 Prefix Delegation (PD) 225 a networking service for delegating IPv6 prefixes to nodes on the 226 link. The nominal PD service is DHCPv6 [RFC8415], however 227 alternate services (e.g., based on ND messaging) are also in scope 228 [I-D.templin-v6ops-pdhost][I-D.templin-6man-dhcpv6-ndopt]. Most 229 notably, a minimal form of PD known as "prefix registration" can 230 be used if the Client knows its prefix in advance and can 231 represent it in the IPv6 source address of an ND message. 233 Access Network (ANET) 234 a node's first-hop data link service network, e.g., a radio access 235 network, cellular service provider network, corporate enterprise 236 network, or the public Internet itself. For secured ANETs, link- 237 layer security services such as IEEE 802.1X and physical-layer 238 security prevent unauthorized access internally while border 239 network-layer security services such as firewalls and proxies 240 prevent unauthorized outside access. 242 ANET interface 243 a node's attachment to a link in an ANET. 245 ANET address 246 an IP address assigned to a node's interface connection to an 247 ANET. 249 Internetwork (INET) 250 a connected IP network topology with a coherent routing and 251 addressing plan and that provides a transit backbone service for 252 ANET end systems. INETs also provide an underlay service over 253 which the AERO virtual link is configured. Example INETs include 254 corporate enterprise networks, aviation networks, and the public 255 Internet itself. When there is no administrative boundary between 256 an ANET and the INET, the ANET and INET are one and the same. 258 INET Partition 259 frequently, INETs such as large corporate enterprise networks are 260 sub-divided internally into separate isolated partitions. Each 261 partition is fully connected internally but disconnected from 262 other partitions, and there is no requirement that separate 263 partitions maintain consistent Internet Protocol and/or addressing 264 plans. (Each INET partition is seen as a separate SPAN segment as 265 discussed below.) 267 INET interface 268 a node's attachment to a link in an INET. 270 INET address 271 an IP address assigned to a node's interface connection to an 272 INET. 274 INET encapsulation 275 the encapsulation of a packet in an outer header or headers that 276 can be routed within the scope of the local INET partition. 278 AERO link 279 a Non-Broadcast, Multiple Access (NBMA) tunnel virtual overlay 280 configured over one or more underlying INETs. Nodes on the AERO 281 link appear as single-hop neighbors from the perspective of the 282 virtual overlay even though they may be separated by many 283 underlying INET hops. AERO links may be configured over multiple 284 underlying SPAN segments (see below). 286 AERO interface 287 a node's attachment to an AERO link. Since the addresses assigned 288 to an AERO interface are managed for uniqueness, AERO interfaces 289 do not require Duplicate Address Detection (DAD) and therefore set 290 the administrative variable 'DupAddrDetectTransmits' to zero 291 [RFC4862]. 293 underlying interface 294 an ANET or INET interface over which an AERO interface is 295 configured. 297 AERO address 298 an IPv6 link-local address assigned to an AERO interface and 299 constructed as specified in Section 3.4. 301 base AERO address 302 the lowest-numbered AERO address aggregated by the MNP (see 303 Section 3.4). 305 Mobility Service Prefix (MSP) 306 an IP prefix assigned to the AERO link and from which more- 307 specific Mobile Network Prefixes (MNPs) are derived. 309 Mobile Network Prefix (MNP) 310 an IP prefix allocated from an MSP and delegated to an AERO Client 311 or Relay. 313 AERO node 314 a node that is connected to an AERO link, or that provides 315 services to other nodes on an AERO link. 317 AERO Client ("Client") 318 an AERO node that connects over one or more underlying interfaces 319 and requests MNP PDs from AERO Servers. The Client assigns a 320 Client AERO address to the AERO interface for use in ND exchanges 321 with other AERO nodes and forwards packets to correspondents 322 according to AERO interface neighbor cache state. 324 AERO Server ("Server") 325 an INET node that configures an AERO interface to provide default 326 forwarding and mobility/multilink services for AERO Clients. The 327 Server assigns an administratively-provisioned AERO address to its 328 AERO interface to support the operation of the ND/PD services, and 329 advertises all of its associated MNPs via BGP peerings with 330 Bridges. 332 AERO Relay ("Relay") 333 an AERO Server that also provides forwarding services between 334 nodes reached via the AERO link and correspondents on other links. 335 AERO Relays are provisioned with MNPs (i.e., the same as for an 336 AERO Client) and run a dynamic routing protocol to discover any 337 non-MNP IP routes. In both cases, the Relay advertises the MSP(s) 338 to its downstream networks, and distributes all of its associated 339 MNPs and non-MNP IP routes via BGP peerings with Bridges (i.e., 340 the same as for an AERO Server). 342 AERO Bridge ("Bridge") 343 a node that provides hybrid routing/bridging services (as well as 344 a security trust anchor) for nodes on an AERO link. As a router, 345 the Bridge forwards packets using standard IP forwarding. As a 346 bridge, the Bridge forwards packets over the AERO link without 347 decrementing the IPv6 Hop Limit. AERO Bridges peer with Servers 348 and other Bridges to discover the full set of MNPs for the link as 349 well as any non-MNPs that are reachable via Relays. 351 AERO Proxy ("Proxy") 352 a node that provides proxying services between Clients in an ANET 353 and Servers in external INETs. The AERO Proxy is a conduit 354 between the ANET and external INETs in the same manner as for 355 common web proxies, and behaves in a similar fashion as for ND 356 proxies [RFC4389]. 358 Spanning Partitioned AERO Networks (SPAN) 359 a means for bridging disjoint INET partitions as segments of a 360 unified AERO link the same as for a bridged campus LAN. The SPAN 361 is a mid-layer IPv6 encapsulation service in the AERO routing 362 system that supports a unified AERO link view for all segments. 363 Each segment in the SPAN is a distinct INET partition, and 364 individual segments are joined by AERO Bridges. Segment Routing 365 [RFC8402][RFC8754] can be used to cause packets to visit selected 366 hops on the SPAN. 368 SPAN Service Prefix (SSP) 369 a global or unique local /96 IPv6 prefix assigned to the AERO link 370 to support SPAN services. 372 SPAN Partition Prefix (SPP) 373 a sub-prefix of the SPAN Service Prefix uniquely assigned to a 374 single SPAN segment. 376 SPAN Client Prefix (SCP) 377 a SPAN prefix formed from an AERO Client address. 379 SPAN Address 380 a unique local IPv6 address taken from a SPAN Client/Partition 381 Prefix and constructed as specified in Section 3.5. SPAN 382 addresses are statelessly derived from AERO addresses, and vice- 383 versa. 385 SPAN encapsulation 386 the addition of an IPv6 header with SPAN source and destinations 387 per [RFC2473]. SPAN encapsulation is often used in conjunction 388 with INET encapsulation, or in raw form over ANET interfaces. 390 ingress tunnel endpoint (ITE) 391 an AERO interface endpoint that injects encapsulated packets into 392 an AERO link. 394 egress tunnel endpoint (ETE) 395 an AERO interface endpoint that receives encapsulated packets from 396 an AERO link. 398 link-layer address 399 an IP address used as an encapsulation header source or 400 destination address from the perspective of the AERO interface. 401 When an upper layer protocol (e.g., UDP) is used as part of the 402 encapsulation, the port number is also considered as part of the 403 link-layer address. From the perspective of the AERO interface, 404 the link-layer address is either an INET address for intra-segment 405 encapsulation or a SPAN address for inter-segment encapsulation. 407 network layer address 408 the source or destination address of an encapsulated IP packet 409 presented to the AERO interface. 411 end user network (EUN) 412 an internal virtual or external edge IP network that an AERO 413 Client or Relay connects to the rest of the network via the AERO 414 interface. The Client/Relay sees each EUN as a "downstream" 415 network, and sees the AERO interface as the point of attachment to 416 the "upstream" network. 418 Mobile Node (MN) 419 an AERO Client and all of its downstream-attached networks that 420 move together as a single unit, i.e., an end system that connects 421 an Internet of Things. 423 Mobile Router (MR) 424 a MN's on-board router that forwards packets between any 425 downstream-attached networks and the AERO link. 427 Route Optimization Source (ROS) 428 the AERO node nearest the source that initiates route 429 optimization. The ROS may be a Server or Proxy acting on behalf 430 of the source Client. 432 Route Optimization responder (ROR) 433 the AERO node nearest the target destination that responds to 434 route optimization requests. The ROR may be a Server acting on 435 behalf of a target MNP Client, or a Relay for a non-MNP 436 destination. 438 MAP List 439 a geographically and/or topologically referenced list of AERO 440 addresses of all Servers within the same AERO link. There is a 441 single MAP list for the entire AERO link. 443 Distributed Mobility Management (DMM) 444 a BGP-based overlay routing service coordinated by Servers and 445 Bridges that tracks all Server-to-Client associations. 447 Mobility Service (MS) 448 the collective set of all Servers, Proxys, Bridges and Relays that 449 provide the AERO Service to Clients. 451 Mobility Service Endpoint MSE) 452 an individual Server, Proxy, Bridge or Relay in the Mobility 453 Service. 455 Throughout the document, the simple terms "Client", "Server", 456 "Bridge", "Proxy" and "Relay" refer to "AERO Client", "AERO Server", 457 "AERO Bridge", "AERO Proxy" and "AERO Relay", respectively. 458 Capitalization is used to distinguish these terms from other common 459 Internetworking uses in which they appear without capitalization. 461 The terminology of DHCPv6 [RFC8415] and IPv6 ND [RFC4861] (including 462 the names of node variables, messages and protocol constants) is used 463 throughout this document. The terms "All-Routers multicast", "All- 464 Nodes multicast", "Solicited-Node multicast" and "Subnet-Router 465 anycast" are defined in [RFC4291] (with Link-Local scope assumed). 466 Also, the term "IP" is used to generically refer to either Internet 467 Protocol version, i.e., IPv4 [RFC0791] or IPv6 [RFC8200]. 469 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 470 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 471 "OPTIONAL" in this document are to be interpreted as described in BCP 472 14 [RFC2119][RFC8174] when, and only when, they appear in all 473 capitals, as shown here. 475 3. Asymmetric Extended Route Optimization (AERO) 477 The following sections specify the operation of IP over Asymmetric 478 Extended Route Optimization (AERO) links: 480 3.1. AERO Link Reference Model 482 +----------------+ 483 | AERO Bridge B1 | 484 | Nbr: S1, S2, P1| 485 |(X1->S1; X2->S2)| 486 | MSP M1 | 487 +-+---------+--+-+ 488 +--------------+ | Secured | | +--------------+ 489 |AERO Server S1| | tunnels | | |AERO Server S2| 490 | Nbr: C1, B1 +-----+ | +-----+ Nbr: C2, B1 | 491 | default->B1 | | | default->B1 | 492 | X1->C1 | | | X2->C2 | 493 +-------+------+ | +------+-------+ 494 | AERO Link | | 495 X===+===+===================+==)===============+===+===X 496 | | | | 497 +-----+--------+ +--------+--+-----+ +--------+-----+ 498 |AERO Client C1| | AERO Proxy P1 | |AERO Client C2| 499 | Nbr: S1 | |(Proxy Nbr Cache)| | Nbr: S2 | 500 | default->S1 | +--------+--------+ | default->S2 | 501 | MNP X1 | | | MNP X2 | 502 +------+-------+ .--------+------. +-----+--------+ 503 | (- Proxyed Clients -) | 504 .-. `---------------' .-. 505 ,-( _)-. ,-( _)-. 506 .-(_ IP )-. +-------+ +-------+ .-(_ IP )-. 507 (__ EUN )--|Host H1| |Host H2|--(__ EUN ) 508 `-(______)-' +-------+ +-------+ `-(______)-' 510 Figure 1: AERO Link Reference Model 512 Figure 1 presents the AERO link reference model. In this model: 514 o the AERO link is an overlay network service configured over one or 515 more underlying INET partitions which may be managed by different 516 administrative authorities and have incompatible protocols and/or 517 addressing plans. 519 o AERO Bridge B1 aggregates Mobility Service Prefix (MSP) M1, 520 discovers Mobile Network Prefixes (MNPs) X* and advertises the MSP 521 via BGP peerings over secured tunnels to Servers (S1, S2). 523 Bridges use the SPAN service to bridge disjoint segments of a 524 partitioned AERO link. 526 o AERO Servers S1 and S2 configure secured tunnels with Bridge B1 527 and also provide mobility, multilink and default router services 528 for their associated Clients C1 and C2. 530 o AERO Clients C1 and C2 associate with Servers S1 and S2, 531 respectively. They receive Mobile Network Prefix (MNP) 532 delegations X1 and X2, and also act as default routers for their 533 associated physical or internal virtual EUNs. Simple hosts H1 and 534 H2 attach to the EUNs served by Clients C1 and C2, respectively. 536 o AERO Proxy P1 configures a secured tunnel with Bridge B1 and 537 provides proxy services for AERO Clients in secured enclaves that 538 cannot associate directly with other AERO link neighbors. 540 Each node on the AERO link maintains an AERO interface neighbor cache 541 and an IP forwarding table the same as for any link. Although the 542 figure shows a limited deployment, in common operational practice 543 there will normally be many additional Bridges, Servers, Clients and 544 Proxys. 546 3.2. AERO Node Types 548 AERO Bridges provide hybrid routing/bridging services (as well as a 549 security trust anchor) for nodes on an AERO link. Bridges use 550 standard IPv6 routing to forward packets both within the same INET 551 partitions and between disjoint INET partitions based on a mid-layer 552 IPv6 encapsulation known as the SPAN header. The inner IP layer 553 experiences a virtual bridging service since the inner IP TTL/Hop 554 Limit is not decremented during forwarding. Each Bridge also peers 555 with Servers and other Bridges in a dynamic routing protocol instance 556 to provide a Distributed Mobility Management (DMM) service for the 557 list of active MNPs (see Section 3.3). Bridges present the AERO link 558 as a set of one or more Mobility Service Prefixes (MSPs) but as link- 559 layer devices need not connect directly to the AERO link themselves 560 unless an administrative interface is desired. Bridges configure 561 secured tunnels with Servers, Proxys and other Bridges; they further 562 maintain IP forwarding table entries for each Mobile Network Prefix 563 (MNP) and any other reachable non-MNP prefixes. 565 AERO Servers provide default forwarding and mobility/multilink 566 services for AERO Client Mobile Nodes (MNs). Each Server also peers 567 with Bridges in a dynamic routing protocol instance to advertise its 568 list of associated MNPs (see Section 3.3). Servers facilitate PD 569 exchanges with Clients, where each delegated prefix becomes an MNP 570 taken from an MSP. Servers forward packets between AERO interface 571 neighbors and track each Client's mobility profiles. 573 AERO Clients register their MNPs through PD exchanges with AERO 574 Servers over the AERO link, and distribute the MNPs to nodes on EUNs. 575 A Client may also be co-resident on the same physical or virtual 576 platform as a Server; in that case, the Client and Server behave as a 577 single functional unit. 579 AERO Proxys provide a conduit for ANET Clients to associate with 580 Servers in external INETs. Client and Servers exchange control plane 581 messages via the Proxy acting as a bridge between the ANET/INET 582 boundary. The Proxy forwards data packets between Clients and the 583 AERO link according to forwarding information in the neighbor cache. 584 The Proxy function is specified in Section 3.16. 586 AERO Relays are Servers that provide forwarding services between the 587 AERO interface and INET/EUN interfaces. Relays are provisioned with 588 MNPs the same as for an AERO Client, and also run a dynamic routing 589 protocol to discover any non-MNP IP routes. The Relay advertises the 590 MSP(s) to its connected networks, and distributes all of its 591 associated MNPs and non-MNP IP routes via BGP peerings with Bridges. 593 AERO Bridges, Servers, Proxys and Relays are critical infrastructure 594 elements in fixed (i.e., non-mobile) INET deployments and hence have 595 permanent and unchanging INET addresses. AERO Clients are MNs that 596 connect via underlying interfaces with addresses that may change when 597 the Client moves to a new network connection point. 599 3.3. AERO Routing System 601 The AERO routing system comprises a private instance of the Border 602 Gateway Protocol (BGP) [RFC4271] that is coordinated between Bridges 603 and Servers and does not interact with either the public Internet BGP 604 routing system or any underlying INET routing systems. 606 In a reference deployment, each Server is configured as an Autonomous 607 System Border Router (ASBR) for a stub Autonomous System (AS) using 608 an AS Number (ASN) that is unique within the BGP instance, and each 609 Server further uses eBGP to peer with one or more Bridges but does 610 not peer with other Servers. Each INET of a multi-segment AERO link 611 must include one or more Bridges, which peer with the Servers and 612 Proxys within that INET. All Bridges within the same INET are 613 members of the same hub AS using a common ASN, and use iBGP to 614 maintain a consistent view of all active MNPs currently in service. 615 The Bridges of different INETs peer with one another using eBGP. 617 Bridges advertise the AERO link's MSPs and any non-MNP routes to each 618 of their Servers. This means that any aggregated non-MNPs (including 619 "default") are advertised to all Servers. Each Bridge configures a 620 black-hole route for each of its MSPs. By black-holing the MSPs, the 621 Bridge will maintain forwarding table entries only for the MNPs that 622 are currently active, and packets destined to all other MNPs will 623 correctly incur Destination Unreachable messages due to the black- 624 hole route. In this way, Servers have only partial topology 625 knowledge (i.e., they know only about the MNPs of their directly 626 associated Clients) and they forward all other packets to Bridges 627 which have full topology knowledge. 629 Servers maintain a working set of associated MNPs, and dynamically 630 announce new MNPs and withdraw departed MNPs in eBGP updates to 631 Bridges. Servers that are configured as Relays also redistribute 632 non-MNP routes learned from non-AERO interfaces via their eBGP Bridge 633 peerings. 635 Clients are expected to remain associated with their current Servers 636 for extended timeframes, however Servers SHOULD selectively suppress 637 updates for impatient Clients that repeatedly associate and 638 disassociate with them in order to dampen routing churn. Servers 639 that are configured as Relays advertise the MSPs via INET/EUN 640 interfaces, and forward packets between INET/EUN interfaces and the 641 AERO interface using standard IP forwarding. 643 Scaling properties of the AERO routing system are limited by the 644 number of BGP routes that can be carried by Bridges. As of 2015, the 645 global public Internet BGP routing system manages more than 500K 646 routes with linear growth and no signs of router resource exhaustion 647 [BGP]. More recent network emulation studies have also shown that a 648 single Bridge can accommodate at least 1M dynamically changing BGP 649 routes even on a lightweight virtual machine, i.e., and without 650 requiring high-end dedicated router hardware. 652 Therefore, assuming each Bridge can carry 1M or more routes, this 653 means that at least 1M Clients can be serviced by a single set of 654 Bridges. A means of increasing scaling would be to assign a 655 different set of Bridges for each set of MSPs. In that case, each 656 Server still peers with one or more Bridges, but institutes route 657 filters so that BGP updates are only sent to the specific set of 658 Bridges that aggregate the MSP. For example, if the MSP for the AERO 659 link is 2001:db8::/32, a first set of Bridges could service the MSP 660 2001:db8::/40, a second set of Bridges could service 661 2001:db8:0100::/40, a third set could service 2001:db8:0200::/40, 662 etc. 664 Assuming up to 1K sets of Bridges, the AERO routing system can then 665 accommodate 1B or more MNPs with no additional overhead (for example, 666 it should be possible to service 1B /64 MNPs taken from a /34 MSP and 667 even more for shorter prefixes). In this way, each set of Bridges 668 services a specific set of MSPs that they advertise to the native 669 Internetwork routing system, and each Server configures MSP-specific 670 routes that list the correct set of Bridges as next hops. This 671 arrangement also allows for natural incremental deployment, and can 672 support small scale initial deployments followed by dynamic 673 deployment of additional Clients, Servers and Bridges without 674 disturbing the already-deployed base. 676 Server and Bridges can use the Bidirectional Forwarding Detection 677 (BFD) protocol [RFC5880] to quickly detect link failures that don't 678 result in interface state changes, BGP peer failures, and 679 administrative state changes. BFD is important in environments where 680 rapid response to failures is required for routing reconvergence and, 681 hence, communications continuity. 683 A full discussion of the BGP-based routing system used by AERO is 684 found in [I-D.ietf-rtgwg-atn-bgp]. The system provides for 685 Distributed Mobility Management (DMM) per the distributed mobility 686 anchoring architecture [I-D.ietf-dmm-distributed-mobility-anchoring]. 688 3.4. AERO Addresses 690 A Client's AERO address is an IPv6 link-local address formed from the 691 Client's delegated MNP. Bridge, Server, Relay and Proxy AERO 692 addresses are assigned from the range fe80::/96 and include an 693 administratively-provisioned value in the lower 32 bits. 695 IPv6 Client AERO addresses encode the Subnet-Router anycast address 696 of a MNP (or non-MNP globally routable prefix) within the least- 697 significant 112 bits of the IPv6 link-local prefix fe80::/16. For 698 example, for the MNP 2001:db8:1000:2000::/56 the corresponding AERO 699 address is fe80:2001:db8:1000:2000::/72. 701 IPv4-compatible Client AERO addresses are based on an IPv4-mapped 702 IPv6 address [RFC4291] formed from an IPv4 MNP and with a prefix 703 length of 96 plus the MNP prefix length. For example, for the IPv4 704 MNP 192.0.2.16/28 the IPv4-mapped IPv6 MNP is: 706 0:0:0:0:0:ffff:192.0.2.16/124 (also written as 707 0:0:0:0:0:ffff:c000:0210/124) 709 The Client then constructs its AERO address with the prefix fe80::/64 710 and with the lower 64 bits of the IPv4-mapped IPv6 address in the 711 interface identifier as: fe80::ffff:192.0.2.16. 713 Mobility Service (MS) AERO addresses (used by Bridges, Servers, 714 Relays and Proxys) are allocated from the range fe80::/96, and MUST 715 be managed for uniqueness. The lower 32 bits of the AERO address 716 includes a unique integer value between 1 and 0xfeffffff (e.g., 717 fe80::1, fe80::2, fe80::3, etc., fe80::feff:ffff) as assigned by the 718 administrative authority for the link. The address fe80:: is the 719 IPv6 link-local Subnet-Router anycast address, and the address range 720 fe80::ff00:0000/104 is reserved for future use. 722 Finally, the address range fe80::/32 is used as the Teredo service 723 prefix for AERO according to the format in Section 4 of [RFC4380] 724 (see Section 3.25 for further discussion). 726 For a full discussion of the above address format and implications 727 for the /64 boundary, see: [I-D.templin-6man-omni-interface]. 729 3.5. Spanning Partitioned AERO Networks (SPAN) 731 An AERO link configured over a single INET appears as a single 732 unified link with a consistent underlying network addressing plan. 733 In that case, all nodes on the link can exchange packets via simple 734 INET encapsulation, since the underlying INET is connected. In 735 common practice, however, an AERO link may be partitioned into 736 multiple "segments", where each segment is a distinct INET 737 potentially managed under a different administrative authority (e.g., 738 as for worldwide aviation service providers such as ARINC, SITA, 739 Inmarsat, etc.). Individual INETs may also themselves be partitioned 740 internally, in which case each internal partition is seen as a 741 separate segment. 743 The addressing plan of each segment is consistent internally but will 744 often bear no relation to the addressing plans of other segments. 745 Each segment is also likely to be separated from others by network 746 security devices (e.g., firewalls, proxies, packet filtering 747 gateways, etc.), and in many cases disjoint segments may not even 748 have any common physical link connections. Therefore, nodes can only 749 be assured of exchanging packets directly with correspondents in the 750 same segment, and not with those in other segments. The only means 751 for joining the segments therefore is through inter-domain peerings 752 between AERO Bridges. 754 The same as for traditional campus LANs, multiple AERO link segments 755 can be joined into a single unified link via a virtual bridging 756 service termed "The SPAN". The SPAN performs link-layer packet 757 forwarding between segments (i.e., bridging) without decrementing the 758 network-layer TTL/Hop Limit. The SPAN model is depicted in Figure 2: 760 . . . . . . . . . . . . . . . . . . . . . . . 761 . . 762 . .-(::::::::) . 763 . .-(::::::::::::)-. +-+ . 764 . (:::: Segment A :::)--|B|---+ . 765 . `-(::::::::::::)-' +-+ | . 766 . `-(::::::)-' | . 767 . | . 768 . .-(::::::::) | . 769 . .-(::::::::::::)-. +-+ | . 770 . (:::: Segment B :::)--|B|---+ . 771 . `-(::::::::::::)-' +-+ | . 772 . `-(::::::)-' | . 773 . | . 774 . .-(::::::::) | . 775 . .-(::::::::::::)-. +-+ | . 776 . (:::: Segment C :::)--|B|---+ . 777 . `-(::::::::::::)-' +-+ | . 778 . `-(::::::)-' | . 779 . | . 780 . ..(etc).. x . 781 . . 782 . . 783 . <- AERO Link Bridged by the SPAN -> . 784 . . . . . . . . . . . . . .. . . . . . . . . 786 Figure 2: The SPAN 788 To support the SPAN, AERO links use the Unique Local Address (ULA) 789 prefix fd80::/10 [RFC4193] as the SPAN Service Prefix (SSP). The 790 prefix length intentionally matches the IPv6 link-local prefix 791 (fe80::/10), and enables a simple stateless translation between AERO 792 and SPAN addresses. Additional SSPs can be employed to identify 793 distinct SPAN Routing Topologies (SRTs) (see: Section 3.5.1). 795 Each segment in the SPAN assigns a unique sub-prefix of SSP::/96 796 termed the "SPAN Partition Prefix (SPP)". For example, for fd80::/96 797 a first segment could assign fd80::1000/116, a second could assign 798 fd80::2000/116, a third could assign fd80::3000/116, etc. The 799 administrative authorities for each segment must therefore coordinate 800 to assure mutually-exclusive SPP assignments, but internal 801 provisioning of the SPP is an independent local consideration for 802 each administrative authority. 804 SPAN addresses are formed by simply rewriting the upper 16 bits of 805 the corresponding AERO address. For example: 807 o the SPAN address formed from the IPv6 Client AERO address 808 fe80:2001:db8:1000:2000:: is simply fd80:2001:db8:1000:2000:: 810 o the SPAN address formed from the IPv4-compatible Client AERO 811 address fe80::ffff:192.0.2.1 is simply fd80::ffff:192.0.2.1 813 o the SPAN address formed from the administrative AERO address 814 fe80::1001 is simply fd80::1001. 816 AERO Bridges join multiple segments into a unified AERO link over 817 multiple diverse administrative domains. They support a bridging 818 function by first establishing forwarding table entries for their 819 SPPs either via standard BGP routing or static routes. For example, 820 if three Bridges ('A', 'B' and 'C') from different segments serviced 821 the SPPs fd80::1000/116, fd80::2000/116 and fd80::3000/116 822 respectively, then the forwarding tables in each Bridge are as 823 follows: 825 A: fd80::1000/116->local, fd80::2000/116->B, fd80::3000/116->C 827 B: fd80::1000/116->A, fd80::2000/116->local, fd80::3000/116->C 829 C: fd80::1000/116->A, fd80::2000/116->B, fd80::3000/116->local 831 These forwarding table entries are permanent and never change, since 832 they correspond to fixed infrastructure elements in their respective 833 segments. 835 SPAN Client Prefixes (SCPs) are instead dynamically advertised in the 836 AERO link routing system by Servers and Relays that provide service 837 for their corresponding MNPs. For example, if three Servers ('D', 838 'E' and 'F') service the MNPs 2001:db8:1000:2000::/56, 839 2001:db8:3000:4000::/56 and 2001:db8:5000:6000::/56 then the routing 840 system would include: 842 D: fd80:2001:db8:1000:2000::/72 844 E: fd80:2001:db8:3000:4000::/72 846 F: fd80:2001:db8:5000:6000::/72 848 With the SCPs and SPPs in place in each Bridge's forwarding table, 849 control and data packets sent between AERO nodes in different 850 segments can therefore be carried over the via encapsulation in a 851 mid-layer IPv6 header known as the "SPAN header". For example, when 852 a source AERO node forwards a packet with IPv6 address 853 2001:db8:1:2::1 to a target AERO node with IPv6 address 854 2001:db8:1000:2000::1, it first encapsulates the packet in a SPAN 855 header with source address set to fd80:2001:db8:1:2:: and destination 856 address set to fd80:2001:db8:1000:2000::. Next, it encapsulates the 857 resulting SPAN packet in an INET header with source address set to 858 its own INET address (e.g., 192.0.2.100) and destination set to the 859 INET address of a Bridge (e.g., 192.0.2.1). 861 SPAN encapsulation is based on Generic Packet Tunneling in IPv6 862 [RFC2473]; the encapsulation format in the above example is shown in 863 Figure 3: 865 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 866 | INET Header | 867 | src = 192.0.2.100 | 868 | dst = 192.0.2.1 | 869 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 870 | SPAN Header | 871 | src = fd80:2001:db8:1:2:: | 872 | dst=fd80:2001:db8:1000:2000:: | 873 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 874 | Inner IP Header | 875 | src = 2001:db8:1:2::1 | 876 | dst = 2001:db8:1000:2000::1 | 877 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 878 | | 879 ~ ~ 880 ~ Inner Packet Body ~ 881 ~ ~ 882 | | 883 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 885 Figure 3: SPAN Encapsulation 887 In this format, the inner IP header and packet body are the original 888 IP packet, the SPAN header is an IPv6 header prepared according to 889 [RFC2473], and the INET header is prepared as discussed in 890 Section 3.9. A packet is said to be "forwarded/sent into the SPAN" 891 when it is encapsulated as described above then forwarded via a 892 secured tunnel to a neighboring Bridge. 894 This gives rise to a routing system that contains both SCP routes 895 that may change dynamically due to regional node mobility and SPP 896 routes that never change. The Bridges can therefore provide link- 897 layer bridging by sending packets into the SPAN instead of network- 898 layer routing according to MNP routes. As a result, opportunities 899 for packet loss due to node mobility between different segments are 900 mitigated. 902 In normal operations, IPv6 ND messages are conveyed to SPP addresses 903 over the SPAN so that specific Proxys, Servers or Relays can be 904 addressed without being subject to mobility events. Conversely, only 905 the first few packets destined to SCP addresses traverse the SPAN 906 until route optimization can determine a more direct path. 908 3.5.1. SPAN Routing Topologies 910 In some cases (e.g., when redundant topologies are needed for fault 911 tolerance and reliability) it may be beneficial to deploy multiple 912 SPAN Routing Topologies (SRTs) that act as independent overlay 913 instances. A communication failure in one instance therefore will 914 not affect communications in other instances. 916 This document asserts that up to four SRTs provide a level of safety 917 sufficient for critical communications such as civil aviation. Each 918 SRT is designated with a color that identifies a different SSP as 919 follows: 921 o Red (default) - corresponds to the SSP fd80::/16 923 o Green - corresponds to the SSP fd81::/16 925 o Blue-1 - corresponds to the SSP fd82::/16 927 o Blue-2 - corresponds to SSP fd83::/16 929 o SSPs fd84::/16 through fdbf::/16 are reserved for future use. 931 3.5.2. Segment Routing Over the SPAN 933 As discussed in the following sections, Segment Routing is used over 934 the SPAN to influence the path of packets destined to Clients on INET 935 interfaces without causing all packets to traverse the Client's 936 Server. When a Client, Proxy or Server has a packet to send to a 937 target discovered through route optimization located in the same SPAN 938 segment, it encapsulates the packet in a SPAN header with the SPAN 939 address of the target as the destination address, then uses the 940 target's Link Layer Address information for INET encapsulation. 942 When a Client, Proxy or Server has a packet to send to a route 943 optimization target located in a different SPAN segment, it 944 encapsulates the packet in a SPAN header with the SPAN address of the 945 target's Server as the destination. The node also includes a Segment 946 Routing Header (SRH) [RFC8754] with the SPAN address of the target as 947 the penultimate address and with the IP encapsulation address of the 948 target as the ultimate address. (When the encapsulation address is 949 an IPv6 address and a port number is included, the port number is 950 written into the SRH Tag field.) The node then forwards the packet 951 into the SPAN, which will eventually direct it to a Bridge on the 952 same segment as the target's Server. 954 When a Bridge on the same segment as the target's Server receives a 955 SPAN-encapsulated packet destined to the target Server, it looks 956 ahead into the Segment Routing List to determine that the penultimate 957 destination is set to the target's SPAN address and the ultimate 958 destination is set to the target's Link Layer Address. The Bridge 959 then advances the SPAN destination address to the target's SPAN 960 address and encapsulates the SPAN packet in an INET header based on 961 the target's Link Layer Address, then forwards the packet to the 962 target directly while bypassing the target's Server. In this way, 963 the Bridge participates in route optimization to greatly reduce 964 traffic load and suboptimal routing through the target's Server. 966 3.6. AERO Interface Characteristics 968 AERO interfaces are virtual interfaces configured over one or more 969 underlying interfaces classified as follows: 971 o INET interfaces connect to an INET either natively or through one 972 or several IPv4 Network Address Translators (NATs). Native INET 973 interfaces have global IP addresses that are reachable from any 974 INET correspondent. All Server, Relay and Bridge interfaces are 975 native interfaces, as are INET-facing interfaces of Proxys. NATed 976 INET interfaces connect to a private network behind one or more 977 NATs that provide INET access. Clients that are behind a NAT are 978 required to send periodic keepalive messages to keep NAT state 979 alive when there are no data packets flowing. 981 o Proxyed interfaces connect to an ANET that is separated from the 982 open INET by an AERO Proxy. Proxys can actively issue control 983 messages over the INET on behalf of the Client to reduce ANET 984 congestion. Clients connected to Proxyed interfaces receive RAs 985 with the P flag set to 1. 987 o VPNed interfaces use security encapsulation over the INET to a 988 Virtual Private Network (VPN) server that also acts as an AERO 989 Server. Clients connected to VPNed interfaces receive RAs with 990 the P flag set to 1 the same as for Proxyed interfaces. Other 991 than the link-layer encapsulation format, VPNed interfaces behave 992 the same as Direct interfaces. 994 o Direct interfaces connect a Client directly to a Server without 995 crossing any ANET/INET paths. An example is a line-of-sight link 996 between a remote pilot and an unmanned aircraft. The same Client 997 considerations apply as for VPNed interfaces above, and the Client 998 receives RA messages with the P flag set to 1. 1000 AERO interfaces use SPAN-layer encapsulation as necessary as 1001 discussed in Section 3.5. AERO interfaces use link-layer 1002 encapsulation (see: Section 3.9) to exchange packets with AERO link 1003 neighbors over INET or VPNed interfaces. AERO interfaces do not use 1004 encapsulation over Proxyed and Direct underlying interfaces. 1006 AERO interfaces maintain a neighbor cache for tracking per-neighbor 1007 state the same as for any interface. AERO interfaces use ND messages 1008 including Router Solicitation (RS), Router Advertisement (RA), 1009 Neighbor Solicitation (NS) and Neighbor Advertisement (NA) for 1010 neighbor cache management. 1012 AERO interfaces send ND messages with an Overlay Multilink Network 1013 Interface (OMNI) option formatted as specified in 1014 [I-D.templin-6man-omni-interface]. The OMNI option includes prefix 1015 registration information and "ifIndex-tuples" containing link 1016 information parameters for the AERO interface's underlying 1017 interfaces. 1019 When encapsulation is used, AERO interface ND messages MAY also 1020 include an AERO Source/Target Link-Layer Address Option (S/TLLAO) 1021 formatted as shown in Figure 4: 1023 0 1 2 3 1024 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 1025 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1026 | Type | Length | ifIndex[1] | SRT | LHS |FMT| 1027 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1028 ~ Segment Routing List [1] ~ 1029 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1030 ~ Link Layer Address [1] ~ 1031 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1032 | Port Number [1] | ifIndex[2] | SRT | LHS |FMT| 1033 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1034 ~ Segment Routing List [2] ~ 1035 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1036 ~ Link Layer Address [2] ~ 1037 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1038 | Port Number [2] | .... ~ 1039 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ 1040 ~ ... ~ 1041 ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1042 ~ | ifIndex[N] | SRT | LHS |FMT| 1043 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1044 ~ Segment Routing List [N] ~ 1045 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1046 ~ Link Layer Address [N] ~ 1047 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1048 | Port Number [N] | Zero Padding (if necessary) ... 1049 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1051 Figure 4: AERO Source/Target Link-Layer Address Option (S/TLLAO) 1052 Format 1054 In this format, Type and Length are set the same as specified for S/ 1055 TLLAOs in [RFC4861], with trailing zero padding octets added as 1056 necessary to produce an integral number of 8 octet blocks. The S/ 1057 TLLAO includes N ifIndex-tuples in correspondence to ifIndex-tuples 1058 that appear in the OMNI option. Each ifIndex-tuple includes the 1059 following information: 1061 o ifIndex[i] - the same value as in the corresponding ifIndex-tuple 1062 included in the OMNI option. 1064 o SRT[i] - a 2-bit "SPAN Routing Topology" value (see: 1065 Section 3.5.1) coded as follows: 1067 * 000 - Red 1069 * 001 - Green 1070 * 010 - Blue-1 1072 * 011 - Blue-2 1074 * 100 - 111 - Reserved 1076 o LHS[i] - a 3-bit "LookaHead Segments" value that encodes the 1077 number (from 0 to 7) of entries in Segment Routing List [i]. 1079 o FMT[i] - a 2-bit "Format" code. Determines the format of the Link 1080 Layer Address [i] field as follows: 1082 * 00 - Link Layer Address [i] encodes a Teredo-format AERO 1083 address for a node behind a NAT. 1085 * 01 - Link Layer Address [i] encodes a Teredo-format AERO 1086 address for a node on the open INET. 1088 * 10 - Link Layer Address [i] encodes a native IPv6 address. 1090 * 11 - Link Layer Address [i] encodes a native IPv6 address with 1091 Port Number [i] field included. 1093 o Segment Routing List [i] - Includes LHS[i]-many 16 byte SPAN 1094 addresses corresponding to the Segment IDs (SIDs) that must be 1095 visited prior to forwarding to Link Layer Address [i]. The 1096 ultimate SID appears first, followed by the penultimate SID 1097 second, etc. 1099 o Link Layer Address [i] - Included according to FMT[i], and 1100 identifies the link-layer address of the source/target. 1102 o Port Number [i] - Present only when FMT[i] is 11. When present, 1103 the field is 2 bytes in length and immediately follows Link Layer 1104 Address [i]. Encodes the upper layer protocol port number to be 1105 used as the encapsulation source port. 1107 If an S/TLLAO is included, any ifIndex-tuples correspond to a proper 1108 subset of the OMNI option ifIndex-tuples. Any S/TLLAO ifIndex-tuple 1109 having an ifIndex value that does not appear in an OMNI option 1110 ifindex-tuple is ignored. If the same ifIndex value appears in 1111 multiple ifIndex-tuples, the first tuple is processed and the 1112 remaining tuples are ignored. Any S/TLLAO ifIndex-tuples can 1113 therefore be viewed as inter-dependent extensions of their 1114 corresponding OMNI option ifIndex-tuples, i.e., the OMNI option and 1115 S/TLLAO are companions that are interpreted in conjunction with each 1116 other. 1118 A Client's AERO interface may be configured over multiple underlying 1119 interface connections. For example, common mobile handheld devices 1120 have both wireless local area network ("WLAN") and cellular wireless 1121 links. These links are often used "one at a time" with low-cost WLAN 1122 preferred and highly-available cellular wireless as a standby, but a 1123 simultaneous-use capability could provide benefits. In a more 1124 complex example, aircraft frequently have many wireless data link 1125 types (e.g. satellite-based, cellular, terrestrial, air-to-air 1126 directional, etc.) with diverse performance and cost properties. 1128 If a Client's multiple underlying interfaces are used "one at a time" 1129 (i.e., all other interfaces are in standby mode while one interface 1130 is active), then ND message OMNI options include only a single 1131 ifIndex-tuple set to constant values. In that case, the Client would 1132 appear to have a single interface but with a dynamically changing 1133 link-layer address. 1135 If the Client has multiple active underlying interfaces, then from 1136 the perspective of ND it would appear to have multiple link-layer 1137 addresses. In that case, ND message OMNI options MAY include 1138 multiple ifIndex-tuples - each with values that correspond to a 1139 specific interface. Every ND message need not include all OMNI and/ 1140 or S/TLLAO ifIndex-tuples; for any ifIndex-tuple not included, the 1141 neighbor considers the status as unchanged. 1143 Bridge, Server and Proxy AERO interfaces may be configured over one 1144 or more secured tunnel interfaces. The AERO interface configures 1145 both an AERO address and its corresponding SPAN address, while the 1146 underlying secured tunnel interfaces are either unnumbered or 1147 configure the same SPAN address. The AERO interface encapsulates 1148 each IP packet in a SPAN header and presents the packet to the 1149 underlying secured tunnel interface. For Bridges that do not 1150 configure an AERO interface, the secured tunnel interfaces themselves 1151 are exposed to the IP layer with each interface configuring the 1152 Bridge's SPAN address. Routing protocols such as BGP therefore run 1153 directly over the Bridge's secured tunnel interfaces. For nodes that 1154 configure an AERO interface, routing protocols such as BGP run over 1155 the AERO interface but do not employ SPAN encapsulation. Instead, 1156 the AERO interface presents the routing protocol messages directly to 1157 the underlying secured tunnels without applying encapsulation and 1158 while using the SPAN address as the source address. This distinction 1159 must be honored consistently according to each node's configuration 1160 so that the IP forwarding table will associate discovered IP routes 1161 with the correct interface. 1163 3.7. AERO Interface Initialization 1165 AERO Servers, Proxys and Clients configure AERO interfaces as their 1166 point of attachment to the AERO link. AERO nodes assign the MSPs for 1167 the link to their AERO interfaces (i.e., as a "route-to-interface") 1168 to ensure that packets with destination addresses covered by an MNP 1169 not explicitly assigned to a non-AERO interface are directed to the 1170 AERO interface. 1172 AERO interface initialization procedures for Servers, Proxys, Clients 1173 and Bridges are discussed in the following sections. 1175 3.7.1. AERO Server/Relay Behavior 1177 When a Server enables an AERO interface, it assigns AERO/SPAN 1178 addresses appropriate for the given SPAN segment. The Server also 1179 configures secured tunnels with one or more neighboring Bridges and 1180 engages in a BGP routing protocol session with each Bridge. 1182 The AERO interface provides a single interface abstraction to the IP 1183 layer, but internally comprises multiple secured tunnels as well as 1184 an NBMA nexus for sending encapsulated data packets to AERO interface 1185 neighbors. The Server further configures a service to facilitate ND/ 1186 PD exchanges with AERO Clients and manages per-Client neighbor cache 1187 entries and IP forwarding table entries based on control message 1188 exchanges. 1190 Relays are simply Servers that run a dynamic routing protocol to 1191 redistribute routes between the AERO interface and INET/EUN 1192 interfaces (see: Section 3.3). The Relay provisions MNPs to networks 1193 on the INET/EUN interfaces (i.e., the same as a Client would do) and 1194 advertises the MSP(s) for the AERO link over the INET/EUN interfaces. 1195 The Relay further provides an attachment point of the AERO link to a 1196 non-MNP-based global topology. 1198 3.7.2. AERO Proxy Behavior 1200 When a Proxy enables an AERO interface, it assigns AERO/SPAN 1201 addresses and configures permanent neighbor cache entries the same as 1202 for Servers. The Proxy also configures secured tunnels with one or 1203 more neighboring Bridges and maintains per-Client neighbor cache 1204 entries based on control message exchanges. 1206 3.7.3. AERO Client Behavior 1208 When a Client enables an AERO interface, it sends RS messages with 1209 ND/PD parameters over its underlying interfaces to a Server in the 1210 MAP list, which returns an RA message with corresponding parameters. 1212 (The RS/RA messages may pass through a Proxy in the case of a 1213 Client's Proxyed interface, or through one or more NATs in the case 1214 of a Client's INET interface.) 1216 3.7.4. AERO Bridge Behavior 1218 AERO Bridges need not connect directly to the AERO link, since they 1219 operate as link-layer forwarding devices instead of network layer 1220 routers. Configuration of AERO interfaces on Bridges is therefore 1221 OPTIONAL, e.g., if an administrative interface is needed. Bridges 1222 configure secured tunnels with Servers, Proxys and other Bridges; 1223 they also configure AERO/SPAN addresses and permanent neighbor cache 1224 entries the same as Servers. Bridges engage in a BGP routing 1225 protocol session with a subset of the Servers on the local SPAN 1226 segment, and with other Bridges on the SPAN (see: Section 3.3). 1228 3.8. AERO Interface Neighbor Cache Maintenance 1230 Each AERO interface maintains a conceptual neighbor cache that 1231 includes an entry for each neighbor it communicates with on the AERO 1232 link per [RFC4861]. AERO interface neighbor cache entries are said 1233 to be one of "permanent", "symmetric", "asymmetric" or "proxy". 1235 Permanent neighbor cache entries are created through explicit 1236 administrative action; they have no timeout values and remain in 1237 place until explicitly deleted. AERO Bridges maintain permanent 1238 neighbor cache entries for their associated Proxys and Servers (and 1239 vice-versa). Each entry maintains the mapping between the neighbor's 1240 network-layer AERO address and corresponding INET address. 1242 Symmetric neighbor cache entries are created and maintained through 1243 RS/RA exchanges as specified in Section 3.15, and remain in place for 1244 durations bounded by ND/PD lifetimes. AERO Servers maintain 1245 symmetric neighbor cache entries for each of their associated 1246 Clients, and AERO Clients maintain symmetric neighbor cache entries 1247 for each of their associated Servers. The list of all Servers on the 1248 AERO link is maintained in the link's MAP list. 1250 Asymmetric neighbor cache entries are created or updated based on 1251 route optimization messaging as specified in Section 3.17, and are 1252 garbage-collected when keepalive timers expire. AERO ROSs maintain 1253 asymmetric neighbor cache entries for active targets with lifetimes 1254 based on ND messaging constants. Asymmetric neighbor cache entries 1255 are unidirectional since only the ROS (and not the ROR) creates an 1256 entry. 1258 Proxy neighbor cache entries are created and maintained by AERO 1259 Proxys when they process Client/Server ND/PD exchanges, and remain in 1260 place for durations bounded by ND/PD lifetimes. AERO Proxys maintain 1261 proxy neighbor cache entries for each of their associated Clients. 1262 Proxy neighbor cache entries track the Client state and the address 1263 of the Client's associated Server(s). 1265 To the list of neighbor cache entry states in Section 7.3.2 of 1266 [RFC4861], Proxy and Server AERO interfaces add an additional state 1267 DEPARTED that applies to symmetric and proxy neighbor cache entries 1268 for Clients that have recently departed. The interface sets a 1269 "DepartTime" variable for the neighbor cache entry to "DEPART_TIME" 1270 seconds. DepartTime is decremented unless a new ND message causes 1271 the state to return to REACHABLE. While a neighbor cache entry is in 1272 the DEPARTED state, packets destined to the target Client are 1273 forwarded to the Client's new location instead of being dropped. 1274 When DepartTime decrements to 0, the neighbor cache entry is deleted. 1275 It is RECOMMENDED that DEPART_TIME be set to the default constant 1276 value REACHABLE_TIME plus 10 seconds (40 seconds by default) to allow 1277 a window for packets in flight to be delivered while stale route 1278 optimization state may be present. 1280 When an ROR receives an authentic NS message used for route 1281 optimization, it searches for a symmetric neighbor cache entry for 1282 the target Client. The ROR then returns a solicited NA message 1283 without creating a neighbor cache entry for the ROS, but creates or 1284 updates a target Client "Report List" entry for the ROS and sets a 1285 "ReportTime" variable for the entry to REPORT_TIME seconds. The ROR 1286 resets ReportTime when it receives a new authentic NS message, and 1287 otherwise decrements ReportTime while no authentic NS messages have 1288 been received. It is RECOMMENDED that REPORT_TIME be set to the 1289 default constant value REACHABLE_TIME plus 10 seconds (40 seconds by 1290 default) to allow a window for route optimization to converge before 1291 ReportTime decrements below REACHABLE_TIME. 1293 When the ROS receives a solicited NA message response to its NS 1294 message used for route optimization, it creates or updates an 1295 asymmetric neighbor cache entry for the target network-layer and 1296 link-layer addresses. The ROS then (re)sets ReachableTime for the 1297 neighbor cache entry to REACHABLE_TIME seconds and uses this value to 1298 determine whether packets can be forwarded directly to the target, 1299 i.e., instead of via a default route. The ROS otherwise decrements 1300 ReachableTime while no further solicited NA messages arrive. It is 1301 RECOMMENDED that REACHABLE_TIME be set to the default constant value 1302 30 seconds as specified in [RFC4861]. 1304 AERO nodes also use the value MAX_UNICAST_SOLICIT to limit the number 1305 of NS keepalives sent when a correspondent may have gone unreachable, 1306 the value MAX_RTR_SOLICITATIONS to limit the number of RS messages 1307 sent without receiving an RA and the value MAX_NEIGHBOR_ADVERTISEMENT 1308 to limit the number of unsolicited NAs that can be sent based on a 1309 single event. It is RECOMMENDED that MAX_UNICAST_SOLICIT, 1310 MAX_RTR_SOLICITATIONS and MAX_NEIGHBOR_ADVERTISEMENT be set to 3 the 1311 same as specified in [RFC4861]. 1313 Different values for DEPART_TIME, REPORT_TIME, REACHABLE_TIME, 1314 MAX_UNICAST_SOLICIT, MAX_RTR_SOLCITATIONS and 1315 MAX_NEIGHBOR_ADVERTISEMENT MAY be administratively set; however, if 1316 different values are chosen, all nodes on the link MUST consistently 1317 configure the same values. Most importantly, DEPART_TIME and 1318 REPORT_TIME SHOULD be set to a value that is sufficiently longer than 1319 REACHABLE_TIME to avoid packet loss due to stale route optimization 1320 state. 1322 3.9. AERO Interface Encapsulation and Re-encapsulation 1324 In some instances, AERO interfaces insert a mid-layer IPv6 header 1325 known as the SPAN header as discussed in the following sections. 1326 After either inserting or omitting the SPAN header, the AERO 1327 interface inserts an outer encapsulation header as discussed below. 1329 AERO interfaces avoid outer encapsulation over Direct underlying 1330 interfaces and Proxyed underlying interfaces for which the first-hop 1331 access router is AERO-aware. Other AERO interfaces encapsulate 1332 packets according to whether they are entering the AERO interface 1333 from the network layer or if they are being re-admitted into the same 1334 AERO link they arrived on. This latter form of encapsulation is 1335 known as "re-encapsulation". 1337 For packets entering the AERO interface from the network layer, the 1338 AERO interface copies the "TTL/Hop Limit", "Type of Service/Traffic 1339 Class" [RFC2983], "Flow Label"[RFC6438] (for IPv6) and "Congestion 1340 Experienced" [RFC3168] values in the inner packet's IP header into 1341 the corresponding fields in the SPAN and outer encapsulation 1342 header(s). 1344 For packets undergoing re-encapsulation, the AERO interface instead 1345 copies these values from the original encapsulation header into the 1346 new encapsulation header, i.e., the values are transferred between 1347 encapsulation headers and *not* copied from the encapsulated packet's 1348 network-layer header. (Note especially that by copying the TTL/Hop 1349 Limit between encapsulation headers the value will eventually 1350 decrement to 0 if there is a (temporary) routing loop.) For IPv4 1351 encapsulation/re-encapsulation, the AERO interface sets the DF bit as 1352 discussed in Section 3.12. 1354 AERO interfaces configured over INET underlying interfaces 1355 encapsulate packets in INET headers according to the next hop 1356 determined in the forwarding algorithm in Section 3.13. If the next 1357 hop is reached via a secured tunnel, the AERO interface uses an 1358 encapsulation format specific to the secured tunnel type (see: 1359 Section 6). If the next hop is reached via an unsecured INET 1360 interface, the AERO interface instead uses UDP/IP encapsulation 1361 according to the Teredo format specified in [RFC4380] and as extended 1362 in [RFC6081]. 1364 When Teredo encapsulation is used, the AERO interface next sets the 1365 UDP source port to a constant value that it will use in each 1366 successive packet it sends, and sets the UDP length field to the 1367 length of the encapsulated packet plus 8 bytes for the UDP header 1368 itself plus the length of any included Teredo extension headers or 1369 trailers. The encapsulated packet may be either IPv6 or IPv4, as 1370 distinguished by the version number found in the first four bits. 1372 For Teredo-encapsulated packets sent to a Server, Relay or Bridge, 1373 the AERO interface sets the UDP destination port to 8060, i.e., the 1374 IANA-registered port number for AERO. For packets sent to a Client, 1375 the AERO interface sets the UDP destination port to the port value 1376 stored in the neighbor cache entry for this Client. The AERO 1377 interface finally includes/omits the UDP checksum according to 1378 [RFC6935][RFC6936]. 1380 AERO interfaces observe the packet sizing and fragmentation 1381 considerations found in Section 3.12. 1383 3.10. AERO Interface Decapsulation 1385 AERO interfaces decapsulate packets destined either to the AERO node 1386 itself or to a destination reached via an interface other than the 1387 AERO interface the packet was received on. When the encapsulated 1388 packet arrives in multiple SPAN fragments, the AERO interface 1389 reassembles as discussed in Section 3.12. Further decapsulation 1390 steps are performed according to the appropriate encapsulation format 1391 specification. 1393 3.11. AERO Interface Data Origin Authentication 1395 AERO nodes employ simple data origin authentication procedures. In 1396 particular: 1398 o AERO Bridges, Servers and Proxys accept encapsulated data packets 1399 and control messages received from secured tunnels via the SPAN. 1401 o AERO Proxys and Clients accept packets that originate from within 1402 the same secured ANET. 1404 o AERO Clients and Relays accept packets from downstream network 1405 correspondents based on ingress filtering. 1407 o AERO Clients, Relays and Servers verify the outer UDP/IP 1408 encapsulation addresses according to the Teredo specification 1409 [RFC4380]. 1411 AERO nodes silently drop any packets that do not satisfy the above 1412 data origin authentication procedures. Further security 1413 considerations are discussed in Section 6. 1415 3.12. AERO Interface MTU and Fragmentation 1417 IPv6 underlying interfaces are REQUIRED to configure a minimum 1418 Maximum Transmission Unit (MTU) of 1280 bytes [RFC8200]. The minimum 1419 MTU for IPv4 underlying interfaces is only 68 bytes [RFC1122], 1420 meaning that a packet smaller than the IPv6 MTU may require 1421 fragmentation when IPv4 encapsulation is used. Therefore, the Don't 1422 Fragment (DF) bit in the IPv4 encapsulation header MUST be set to 0. 1424 The AERO interface configures an MTU of 9180 bytes [RFC2492]; the 1425 size is therefore not a reflection of the underlying interface MTUs, 1426 but rather determines the largest packet the AERO interface can 1427 forward or reassemble. The AERO interface therefore accommodates IP 1428 packets up to 9180 bytes while generating IPv6 Path MTU Discovery 1429 (PMTUD) Packet Too Big (PTB) messages [RFC8201] as necessary (see 1430 below). 1432 AERO interfaces employ mid-layer IPv6 encapsulation and 1433 fragmentation/reassembly per [RFC2473] (aka "SPAN encapsulation") to 1434 accommodate the 9180 byte MTU. The AERO interface returns 1435 internally-generated PTB messages for packets admitted into the 1436 interface that it deems too large (e.g., according to link 1437 performance characteristics, reassembly cost, etc.) while either 1438 dropping or forwarding the packet as necessary. The AERO interface 1439 performs PMTUD even if the destination appears to be on the same link 1440 since intermediate AERO link nodes may return a PTB. This ensures 1441 that the path MTU is adaptive and reflects the current path used for 1442 a given data flow. 1444 AERO nodes perform SPAN encapsulation and fragmentation/reassembly as 1445 follows: 1447 o When a node's AERO interface sends a packet over a Proxyed, VPNed 1448 or Direct underlying interface, it sends without SPAN 1449 encapsulation if the packet is no larger than the underlying 1450 interface MTU. Otherwise, it inserts a SPAN header with source 1451 address set to the node's own SPAN address and destination set to 1452 the SPAN address of the link-layer peer Proxy, Server or Client on 1453 the underlying interface. The AERO interface then uses IPv6 1454 fragmentation to break the packet into a minimum number of non- 1455 overlapping fragments, where the largest fragment size is 1456 determined by the underlying interface MTU and the smallest 1457 fragment is no smaller than 640 bytes. The AERO interface then 1458 sends the fragments to the link-layer peer, which reassembles 1459 before forwarding toward the final destination. 1461 o When a node's AERO interface sends a packet over an INET 1462 underlying interface, it sends encapsulated packets no larger than 1463 1280 bytes without a SPAN header if the destination is reached via 1464 an INET address within the same SPAN segment. Otherwise, it 1465 inserts a SPAN header with source address set to the node's SPAN 1466 address, destination set to the SPAN address of the next hop AERO 1467 node toward the final destination and (if necessary) with a SRH 1468 with the remaining Segment IDs on the path to the final 1469 destination. The AERO interface then uses IPv6 fragmentation to 1470 break the encapsulated packet into a minimum number of non- 1471 overlapping fragments, where the largest fragment size (including 1472 both SPAN and INET encapsulation) is 1280 bytes and the smallest 1473 fragment is no smaller than 640 bytes. The AERO interface then 1474 encapsulates the SPAN fragments in INET headers and sends them to 1475 the SPAN destination, which reassembles before forwarding toward 1476 the final destination. 1478 In order to avoid a "tiny fragment" attack, AERO interfaces 1479 unconditionally drop all SPAN fragments smaller than 640 bytes. In 1480 order to set the correct context for reassembly, the AERO interface 1481 that inserts a SPAN header MUST also be the one that inserts the IPv6 1482 Fragment Header Identification value. Although all fragments of the 1483 same fragmented SPAN packet are typically sent via the same 1484 underlying interface, this is not strictly required since all 1485 fragments will arrive at the AERO interface that performs reassembly 1486 even if they travel over different paths. 1488 Note that the AERO interface can forward large packets via 1489 encapsulation and fragmentation while at the same time returning 1490 advisory PTB messages, e.g., subject to rate limiting. The receiving 1491 node that performs reassembly can also send advisory PTB messages if 1492 reassembly conditions become unfavorable. The AERO interface can 1493 therefore continuously forward large packets without loss while 1494 returning advisory messages recommending a smaller size (but no 1495 smaller than 1280). Advisory PTB messages are differentiated from 1496 PTB messages that report loss by setting the Code field in the ICMPv6 1497 message header to the value 1. This document therefore updates 1498 [RFC4443] and [RFC8201]. 1500 3.13. AERO Interface Forwarding Algorithm 1502 IP packets enter a node's AERO interface either from the network 1503 layer (i.e., from a local application or the IP forwarding system) or 1504 from the link layer (i.e., from an AERO interface neighbor). All 1505 packets entering a node's AERO interface first undergo data origin 1506 authentication as discussed in Section 3.11. Packets that satisfy 1507 data origin authentication are processed further, while all others 1508 are dropped silently. 1510 Packets that enter the AERO interface from the network layer are 1511 forwarded to an AERO interface neighbor. Packets that enter the AERO 1512 interface from the link layer are either re-admitted into the AERO 1513 link or forwarded to the network layer where they are subject to 1514 either local delivery or IP forwarding. In all cases, the AERO 1515 interface itself MUST NOT decrement the network layer TTL/Hop-count 1516 since its forwarding actions occur below the network layer. 1518 AERO interfaces may have multiple underlying interfaces and/or 1519 neighbor cache entries for neighbors with multiple ifIndex-tuple 1520 registrations (see Section 3.6). The AERO interface uses traffic 1521 classifiers (e.g., DSCP value, port number, etc.) to select an 1522 outgoing underlying interface for each packet based on the node's own 1523 QoS preferences, and also to select a destination link-layer address 1524 based on the neighbor's underlying interface with the highest 1525 preference. AERO implementations SHOULD allow for QoS preference 1526 values to be modified at runtime through network management. 1528 If multiple outgoing interfaces and/or neighbor interfaces have a 1529 preference of "high", the AERO node replicates the packet and sends 1530 one copy via each of the (outgoing / neighbor) interface pairs; 1531 otherwise, the node sends a single copy of the packet via an 1532 interface with the highest preference. AERO nodes keep track of 1533 which underlying interfaces are currently "reachable" or 1534 "unreachable", and only use "reachable" interfaces for forwarding 1535 purposes. 1537 The following sections discuss the AERO interface forwarding 1538 algorithms for Clients, Proxys, Servers and Bridges. In the 1539 following discussion, a packet's destination address is said to 1540 "match" if it is the same as a cached address, or if it is covered by 1541 a cached prefix (which may be encoded in an AERO address). 1543 3.13.1. Client Forwarding Algorithm 1545 When an IP packet enters a Client's AERO interface from the network 1546 layer the Client searches for an asymmetric neighbor cache entry that 1547 matches the destination. If there is a match, the Client uses one or 1548 more "reachable" neighbor interfaces in the entry for packet 1549 forwarding. If there is no asymmetric neighbor cache entry, the 1550 Client instead forwards the packet toward a Server (the packet is 1551 intercepted by a Proxy if there is a Proxy on the path). The Client 1552 encapsulates the packet in a SPAN header and fragments if necessary 1553 according to MTU requirements (see: Section 3.12). 1555 When an IP packet enters a Client's AERO interface from the link- 1556 layer, if the destination matches one of the Client's MNPs or link- 1557 local addresses the Client reassembles and decapsulates as necessary 1558 and delivers the inner packet to the network layer. Otherwise, the 1559 Client drops the packet and MAY return a network-layer ICMP 1560 Destination Unreachable message subject to rate limiting (see: 1561 Section 3.14). 1563 3.13.2. Proxy Forwarding Algorithm 1565 For control messages originating from or destined to a Client, the 1566 Proxy intercepts the message and updates its proxy neighbor cache 1567 entry for the Client. The Proxy then forwards a (proxyed) copy of 1568 the control message. (For example, the Proxy forwards a proxied 1569 version of a Client's NS/RS message to the target neighbor, and 1570 forwards a proxied version of the NA/RA reply to the Client.) 1572 When the Proxy receives a data packet from a Client within the ANET, 1573 the Proxy reassembles and re-fragments if necessary then searches for 1574 an asymmetric neighbor cache entry that matches the destination and 1575 forwards as follows: 1577 o if the destination matches an asymmetric neighbor cache entry, the 1578 Proxy uses one or more "reachable" neighbor interfaces in the 1579 entry for packet forwarding using SPAN encapsulation and including 1580 a SRH if necessary according to the cached TLLAO information. If 1581 the neighbor interface is in the same SPAN segment, the Proxy 1582 forwards the packet directly to the neighbor; otherwise, it 1583 forwards the packet to a Bridge. 1585 o else, the Proxy uses SPAN encapsulation and forwards the packet to 1586 a Bridge while using the SPAN address corresponding to the 1587 packet's destination as the SPAN destination address. 1589 When the Proxy receives an encapsulated data packet from an INET 1590 neighbor or from a secured tunnel from a Bridge, it accepts the 1591 packet only if data origin authentication succeeds and if there is a 1592 proxy neighbor cache entry that matches the inner destination. Next, 1593 the Proxy reassembles the packet (if necessary) and continues 1594 processing. 1596 Next if reassembly is complete and the neighbor cache state is 1597 REACHABLE, the Proxy returns a PTB if necessary (see: Section 3.12) 1598 then either drops or forwards the packet to the Client while 1599 performing SPAN encapsulation and re-fragmentation to the ANET MTU 1600 size if necessary. If the neighbor cache entry state is DEPARTED, 1601 the Proxy instead changes the SPAN destination address to the address 1602 of the new Server and forwards it to a Bridge while performing re- 1603 fragmentation to 1280 bytes if necessary. 1605 3.13.3. Server/Relay Forwarding Algorithm 1607 For control messages destined to a target Client's AERO address that 1608 are received from a secured tunnel, the Server intercepts the message 1609 and sends an appropriate response on behalf of the Client. (For 1610 example, the Server sends an NA message reply in response to an NS 1611 message directed to one of its associated Clients.) If the Client's 1612 neighbor cache entry is in the DEPARTED state, however, the Server 1613 instead forwards the packet to the Client's new Server as discussed 1614 in Section 3.19. 1616 When the Server receives an encapsulated data packet from an INET 1617 neighbor or from a secured tunnel, it accepts the packet only if data 1618 origin authentication succeeds. If the SPAN destination address is 1619 its own address, the Server continues processing as follows: 1621 o if the destination matches a symmetric neighbor cache entry in the 1622 REACHABLE state the Server prepares the packet for forwarding to 1623 the destination Client. The Server first reassembles (if 1624 necessary) and forwards the packet (while re-fragmenting if 1625 necessary) as specified in Section 3.12. 1627 o else, if the destination matches a symmetric neighbor cache entry 1628 in the DEPARETED state the Server re-encapsulates the packet and 1629 forwards it using the SPAN address of the Client's new Server as 1630 the destination. 1632 o else, if the destination matches an asymmetric neighbor cache 1633 entry, the Server uses one or more "reachable" neighbor interfaces 1634 in the entry for packet forwarding via the local INET if the 1635 neighbor is in the same SPAN segment or using SPAN encapsulation 1636 and Segment Routing if necessary with the final destination set to 1637 the neighbor's SPAN address otherwise. 1639 o else, if the destination is an AERO address that is not assigned 1640 on the AERO interface the Server drops the packet. 1642 o else, the Server (acting as a Relay) reassembles if necessary, 1643 decapsulates the packet and releases it to the network layer for 1644 local delivery or IP forwarding. Based on the information in the 1645 forwarding table, the network layer may return the packet to the 1646 same AERO interface in which case further processing occurs as 1647 below. (Note that this arrangement accommodates common 1648 implementations in which the IP forwarding table is not accessible 1649 from within the AERO interface. If the AERO interface can 1650 directly access the IP forwarding table (such as for in-kernel 1651 implementations) the forwarding table lookup can instead be 1652 performed internally from within the AERO interface itself.) 1654 When the Server's AERO interface receives a data packet from the 1655 network layer or from a VPNed or Direct Client, it performs SPAN 1656 encapsulation and fragmentation if necessary, then processes the 1657 packet according to the network-layer destination address as follows: 1659 o if the destination matches a symmetric or asymmetric neighbor 1660 cache entry the Server processes the packet as above. 1662 o else, the Server encapsulates the packet and forwards it to a 1663 Bridge using its own SPAN address as the source and the SPAN 1664 address corresponding to the destination as the destination. 1666 3.13.4. Bridge Forwarding Algorithm 1668 Bridges forward SPAN-encapsulated packets over secured tunnels the 1669 same as any IP router. When the Bridge receives a SPAN-encapsulated 1670 packet via a secured tunnel, it removes the outer INET header and 1671 searches for a forwarding table entry that matches the SPAN 1672 destination address. The Bridge then processes the packet as 1673 follows: 1675 o if the destination is the SPAN address of a Server located in the 1676 local SPAN partition, the Bridge checks for a SRH. If there is a 1677 SRH with the SPAN address of the final destination as the 1678 penultimate ID and with a Link Layer Address of the final 1679 destination as the ultimate ID, the Bridge copies the SPAN address 1680 of the final destination into the destination address. If the 1681 Link Layer Address does not indicate the presence of a NAT, the 1682 Bridge then forwards the packet directly to the Link Layer Address 1683 using link-layer (UDP/IP) encapsulation. Otherwise, the Bridge 1684 forwards the packet directly to the Server. 1686 o if the destination matches one of the Bridge's own addresses, the 1687 Bridge submits the packet for local delivery. 1689 o else, if the destination matches a forwarding table entry the 1690 Bridge forwards the packet via a secured tunnel to the next hop. 1691 If the destination matches an MSP without matching an MNP, 1692 however, the Bridge instead drops the packet and returns an ICMP 1693 Destination Unreachable message subject to rate limiting (see: 1694 Section 3.14). 1696 o else, the Bridge drops the packet and returns an ICMP Destination 1697 Unreachable as above. 1699 As for any IP router, the Bridge decrements the TTL/Hop Limit when it 1700 forwards the packet. Therefore, only the Hop Limit in the SPAN 1701 header is decremented, and not the TTL/Hop Limit in the inner packet 1702 header. 1704 3.14. AERO Interface Error Handling 1706 When an AERO node admits a packet into the AERO interface, it may 1707 receive link-layer or network-layer error indications. 1709 A link-layer error indication is an ICMP error message generated by a 1710 router in the INET on the path to the neighbor or by the neighbor 1711 itself. The message includes an IP header with the address of the 1712 node that generated the error as the source address and with the 1713 link-layer address of the AERO node as the destination address. 1715 The IP header is followed by an ICMP header that includes an error 1716 Type, Code and Checksum. Valid type values include "Destination 1717 Unreachable", "Time Exceeded" and "Parameter Problem" 1718 [RFC0792][RFC4443]. (AERO interfaces ignore all link-layer IPv4 1719 "Fragmentation Needed" and IPv6 "Packet Too Big" messages since they 1720 only emit packets that are guaranteed to be no larger than the IP 1721 minimum link MTU as discussed in Section 3.12.) 1723 The ICMP header is followed by the leading portion of the packet that 1724 generated the error, also known as the "packet-in-error". For 1725 ICMPv6, [RFC4443] specifies that the packet-in-error includes: "As 1726 much of invoking packet as possible without the ICMPv6 packet 1727 exceeding the minimum IPv6 MTU" (i.e., no more than 1280 bytes). For 1728 ICMPv4, [RFC0792] specifies that the packet-in-error includes: 1729 "Internet Header + 64 bits of Original Data Datagram", however 1730 [RFC1812] Section 4.3.2.3 updates this specification by stating: "the 1731 ICMP datagram SHOULD contain as much of the original datagram as 1732 possible without the length of the ICMP datagram exceeding 576 1733 bytes". 1735 The link-layer error message format is shown in Figure 5 (where, "L2" 1736 and "L3" refer to link-layer and network-layer, respectively): 1738 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1739 ~ ~ 1740 | L2 IP Header of | 1741 | error message | 1742 ~ ~ 1743 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1744 | L2 ICMP Header | 1745 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 1746 ~ ~ P 1747 | IP and other encapsulation | a 1748 | headers of original L3 packet | c 1749 ~ ~ k 1750 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ e 1751 ~ ~ t 1752 | IP header of | 1753 | original L3 packet | i 1754 ~ ~ n 1755 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1756 ~ ~ e 1757 | Upper layer headers and | r 1758 | leading portion of body | r 1759 | of the original L3 packet | o 1760 ~ ~ r 1761 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 1763 Figure 5: AERO Interface Link-Layer Error Message Format 1765 The AERO node rules for processing these link-layer error messages 1766 are as follows: 1768 o When an AERO node receives a link-layer Parameter Problem message, 1769 it processes the message the same as described as for ordinary 1770 ICMP errors in the normative references [RFC0792][RFC4443]. 1772 o When an AERO node receives persistent link-layer Time Exceeded 1773 messages, the IP ID field may be wrapping before earlier fragments 1774 awaiting reassembly have been processed. In that case, the node 1775 should begin including integrity checks and/or institute rate 1776 limits for subsequent packets. 1778 o When an AERO node receives persistent link-layer Destination 1779 Unreachable messages in response to encapsulated packets that it 1780 sends to one of its asymmetric neighbor correspondents, the node 1781 should process the message as an indication that a path may be 1782 failing, and optionally initiate NUD over that path. If it 1783 receives Destination Unreachable messages over multiple paths, the 1784 node should allow future packets destined to the correspondent to 1785 flow through a default route and re-initiate route optimization. 1787 o When an AERO Client receives persistent link-layer Destination 1788 Unreachable messages in response to encapsulated packets that it 1789 sends to one of its symmetric neighbor Servers, the Client should 1790 mark the path as unusable and use another path. If it receives 1791 Destination Unreachable messages on many or all paths, the Client 1792 should associate with a new Server and release its association 1793 with the old Server as specified in Section 3.19.5. 1795 o When an AERO Server receives persistent link-layer Destination 1796 Unreachable messages in response to encapsulated packets that it 1797 sends to one of its symmetric neighbor Clients, the Server should 1798 mark the underlying path as unusable and use another underlying 1799 path. 1801 o When an AERO Server or Proxy receives link-layer Destination 1802 Unreachable messages in response to an encapsulated packet that it 1803 sends to one of its permanent neighbors, it treats the messages as 1804 an indication that the path to the neighbor may be failing. 1805 However, the dynamic routing protocol should soon reconverge and 1806 correct the temporary outage. 1808 When an AERO Bridge receives a packet for which the network-layer 1809 destination address is covered by an MSP, if there is no more- 1810 specific routing information for the destination the Bridge drops the 1811 packet and returns a network-layer Destination Unreachable message 1812 subject to rate limiting. The Bridge writes the network-layer source 1813 address of the original packet as the destination address and uses 1814 one of its non link-local addresses as the source address of the 1815 message. 1817 When an AERO node receives an encapsulated packet for which the 1818 reassembly buffer it too small, it drops the packet and returns a 1819 network-layer Packet Too Big (PTB) message. The node first writes 1820 the MRU value into the PTB message MTU field, writes the network- 1821 layer source address of the original packet as the destination 1822 address and writes one of its non link-local addresses as the source 1823 address. 1825 3.15. AERO Router Discovery, Prefix Delegation and Autoconfiguration 1827 AERO Router Discovery, Prefix Delegation and Autoconfiguration are 1828 coordinated as discussed in the following Sections. 1830 3.15.1. AERO ND/PD Service Model 1832 Each AERO Server on the link configures a PD service to facilitate 1833 Client requests. Each Server is provisioned with a database of MNP- 1834 to-Client ID mappings for all Clients enrolled in the AERO service, 1835 as well as any information necessary to authenticate each Client. 1836 The Client database is maintained by a central administrative 1837 authority for the AERO link and securely distributed to all Servers, 1838 e.g., via the Lightweight Directory Access Protocol (LDAP) [RFC4511], 1839 via static configuration, etc. Clients receive the same service 1840 regardless of the Servers they select. 1842 AERO Clients and Servers use ND messages to maintain neighbor cache 1843 entries. AERO Servers configure their AERO interfaces as advertising 1844 NBMA interfaces, and therefore send unicast RA messages with a short 1845 Router Lifetime value (e.g., REACHABLE_TIME seconds) in response to a 1846 Client's RS message. Thereafter, Clients send additional RS messages 1847 to keep Server state alive. 1849 AERO Clients and Servers include PD parameters in RS/RA messages (see 1850 [I-D.templin-6man-dhcpv6-ndopt] for ND/PD alternatives). The unified 1851 ND/PD messages are exchanged between Client and Server according to 1852 the prefix management schedule required by the PD service. If the 1853 Client knows its MNP in advance, it can instead employ prefix 1854 registration by including its AERO address as the source address of 1855 an RS message and with an OMNI option with valid prefix registration 1856 information for the MNP. If the Server (and Proxy) accept the 1857 Client's MNP assertion, they inject the prefix into the routing 1858 system and establish the necessary neighbor cache state. 1860 The following sections specify the Client and Server behavior. 1862 3.15.2. AERO Client Behavior 1864 AERO Clients discover the addresses of Servers in a similar manner as 1865 described in [RFC5214]. Discovery methods include static 1866 configuration (e.g., from a flat-file map of Server addresses and 1867 locations), or through an automated means such as Domain Name System 1868 (DNS) name resolution [RFC1035]. Alternatively, the Client can 1869 discover Server addresses through a layer 2 data link login exchange, 1870 or through a unicast RA response to a multicast/anycast RS as 1871 described below. In the absence of other information, the Client can 1872 resolve the DNS Fully-Qualified Domain Name (FQDN) 1873 "linkupnetworks.[domainname]" where "linkupnetworks" is a constant 1874 text string and "[domainname]" is a DNS suffix for the AERO link 1875 (e.g., "example.com"). 1877 To associate with a Server, the Client acts as a requesting router to 1878 request MNPs. The Client prepares an RS message with PD parameters 1879 and includes a Nonce and Timestamp option if the Client needs to 1880 correlate RA replies. If the Client already knows the Server's AERO 1881 address, it includes the AERO address as the network-layer 1882 destination address; otherwise, it includes the link-scoped All- 1883 Routers multicast (ff02::2) or Subnet-Router anycast (fe80::) address 1884 as the network-layer destination. If the Client already knows its 1885 own AERO address, it uses the AERO address as the network-layer 1886 source address; otherwise, it uses the unspecified IPv6 address 1887 (::/128) as the network-layer source address. 1889 The Client next includes an OMNI option in the RS message to register 1890 its link-layer information with the Server. The Client sets the OMNI 1891 option prefix registration information according to the MNP, and 1892 includes an ifIndex-tuple with S set to '1' corresponding to the 1893 underlying interface over which the Client will send the RS message. 1894 The Client MAY include additional ifIndex-tuples specific to other 1895 underlying interfaces. The Client MAY also include an SLLAO 1896 corresponding to the OMNI option ifIndex-tuple with S set to '1'. 1898 The Client then sends the RS message (either directly via Direct 1899 interfaces, via a VPN for VPNed interfaces, via a Proxy for proxyed 1900 interfaces or via INET encapsulation for INET interfaces) and waits 1901 for an RA message reply (see Section 3.15.3). The Client retries up 1902 to MAX_RTR_SOLICITATIONS times until an RA is received. If the 1903 Client receives no RAs, or if it receives an RA with Router Lifetime 1904 set to 0, the Client SHOULD abandon this Server and try another 1905 Server. Otherwise, the Client processes the PD information found in 1906 the RA message. 1908 Next, the Client creates a symmetric neighbor cache entry with the 1909 Server's AERO address as the network-layer address and the Server's 1910 encapsulation and/or link-layer addresses as the link-layer address. 1911 The Client records the RA Router Lifetime field value in the neighbor 1912 cache entry as the time for which the Server has committed to 1913 maintaining the MNP in the routing system via this underlying 1914 interface, and caches the other RA configuration information 1915 including Cur Hop Limit, M and O flags, Reachable Time and Retrans 1916 Timer. The Client then autoconfigures AERO addresses for each of the 1917 delegated MNPs and assigns them to the AERO interface. The Client 1918 also caches any MSPs included in Route Information Options (RIOs) 1919 [RFC4191] as MSPs to associate with the AERO link, and assigns the 1920 MTU value in the MTU option to the underlying interface. 1922 The Client then registers additional underlying interfaces with the 1923 Server by sending RS messages via each additional interface. The RS 1924 messages include the same parameters as for the initial RS/RA 1925 exchange, but with destination address set to the Server's AERO 1926 address. 1928 Following autoconfiguration, the Client sub-delegates the MNPs to its 1929 attached EUNs and/or the Client's own internal virtual interfaces as 1930 described in [I-D.templin-v6ops-pdhost] to support the Client's 1931 downstream attached "Internet of Things (IoT)". The Client 1932 subsequently sends additional RS messages over each underlying 1933 interface before the Router Lifetime received for that interface 1934 expires. 1936 After the Client registers its underlying interfaces, it may wish to 1937 change one or more registrations, e.g., if an interface changes 1938 address or becomes unavailable, if QoS preferences change, etc. To 1939 do so, the Client prepares an RS message to send over any available 1940 underlying interface. The RS includes an OMNI option with prefix 1941 registration information specific to its MNP, with an ifIndex-tuple 1942 specific to the selected underlying interface with S set to '1', and 1943 with any additional ifIndex-tuples specific to other underlying 1944 interfaces. The Client includes fresh ifIndex-tuple values to update 1945 the Server's neighbor cache entry. When the Client receives the 1946 Server's RA response, it has assurance that the Server has been 1947 updated with the new information. 1949 If the Client wishes to discontinue use of a Server it issues an RS 1950 message over any underlying interface with an OMNI option with a 1951 prefix release indication. When the Server processes the message, it 1952 releases the MNP, sets the symmetric neighbor cache entry state for 1953 the Client to DEPARTED and returns an RA reply with Router Lifetime 1954 set to 0. After a short delay (e.g., 2 seconds), the Server 1955 withdraws the MNP from the routing system. 1957 3.15.3. AERO Server Behavior 1959 AERO Servers act as IP routers and support a PD service for Clients. 1960 Servers arrange to add their AERO addresses to a static map of Server 1961 addresses for the link and/or the DNS resource records for the FQDN 1962 "linkupnetworks.[domainname]" before entering service. Server 1963 addresses should be geographically and/or topologically referenced, 1964 and made available for discovery by Clients on the AERO link. 1966 When a Server receives a prospective Client's RS message on its AERO 1967 interface, it SHOULD return an immediate RA reply with Router 1968 Lifetime set to 0 if it is currently too busy or otherwise unable to 1969 service the Client. Otherwise, the Server authenticates the RS 1970 message and processes the PD parameters. The Server first determines 1971 the correct MNPs to delegate to the Client by searching the Client 1972 database. When the Server delegates the MNPs, it also creates a 1973 forwarding table entry for each MNP so that the MNPs are propagated 1974 into the routing system (see: Section 3.3). For IPv6, the Server 1975 creates an IPv6 forwarding table entry for each MNP. For IPv4, the 1976 Server creates an IPv6 forwarding table entry with the SPAN 1977 Compatibility Prefix (SCP) corresponding to the IPv4 address. 1979 The Server next creates a symmetric neighbor cache entry for the 1980 Client using the base AERO address as the network-layer address and 1981 with lifetime set to no more than the smallest PD lifetime. Next, 1982 the Server updates the neighbor cache entry by recording the 1983 information in each ifIndex-tuple in the RS OMNI option. The Server 1984 also records the actual SPAN/INET addresses in the neighbor cache 1985 entry. 1987 Next, the Server prepares an RA message using its AERO address as the 1988 network-layer source address and the network-layer source address of 1989 the RS message as the network-layer destination address. The Server 1990 sets the Router Lifetime to the time for which it will maintain both 1991 this underlying interface individually and the symmetric neighbor 1992 cache entry as a whole. The Server also sets Cur Hop Limit, M and O 1993 flags, Reachable Time and Retrans Timer to values appropriate for the 1994 AERO link. The Server includes the delegated MNPs, any other PD 1995 parameters and an OMNI option with no ifIndex-tuples. The Server 1996 then includes one or more RIOs that encode the MSPs for the AERO 1997 link, plus an MTU option (see Section 3.12). The Server finally 1998 forwards the message to the Client using SPAN/INET, INET, or NULL 1999 encapsulation as necessary. 2001 After the initial RS/RA exchange, the Server maintains a 2002 ReachableTime timer for each of the Client's underlying interfaces 2003 individually (and for the Client's symmetric neighbor cache entry 2004 collectively) set to expire after Router Lifetime seconds. If the 2005 Client (or Proxy) issues additional RS messages, the Server sends an 2006 RA response and resets ReachableTime. If the Server receives an ND 2007 message with PD release indication it sets the Client's symmetric 2008 neighbor cache entry to the DEPARTED state and withdraws the MNP from 2009 the routing system after a short delay (e.g., 2 seconds). If 2010 ReachableTime expires before a new RS is received on an individual 2011 underlying interface, the Server marks the interface as DOWN. If 2012 ReachableTime expires before any new RS is received on any individual 2013 underlying interface, the Server deletes the neighbor cache entry and 2014 withdraws the MNP without delay. 2016 The Server processes any ND/PD messages pertaining to the Client and 2017 returns an NA/RA reply in response to solicitations. The Server may 2018 also issue unsolicited RA messages, e.g., with PD reconfigure 2019 parameters to cause the Client to renegotiate its PDs, with Router 2020 Lifetime set to 0 if it can no longer service this Client, etc. 2021 Finally, If the symmetric neighbor cache entry is in the DEPARTED 2022 state, the Server deletes the entry after DepartTime expires. 2024 Note: Clients SHOULD notify former Servers of their departures, but 2025 Servers are responsible for expiring neighbor cache entries and 2026 withdrawing routes even if no departure notification is received 2027 (e.g., if the Client leaves the network unexpectedly). Servers 2028 SHOULD therefore set Router Lifetime to REACHABLE_TIME seconds in 2029 solicited RA messages to minimize persistent stale cache information 2030 in the absence of Client departure notifications. A short Router 2031 Lifetime also ensures that proactive Client/Server RS/RA messaging 2032 will keep any NAT state alive (see above). 2034 Note: All Servers on an AERO link MUST advertise consistent values in 2035 the RA Cur Hop Limit, M and O flags, Reachable Time and Retrans Timer 2036 fields the same as for any link, since unpredictable behavior could 2037 result if different Servers on the same link advertised different 2038 values. 2040 3.15.3.1. Lightweight DHCPv6 Relay Agent (LDRA) 2042 When DHCPv6 is used as the ND/PD service back end, AERO Clients and 2043 Servers are always on the same link (i.e., the AERO link) from the 2044 perspective of DHCPv6. However, in some implementations the DHCPv6 2045 server and ND function may be located in separate modules. In that 2046 case, the Server's AERO interface module can act as a Lightweight 2047 DHCPv6 Relay Agent (LDRA)[RFC6221] to relay PD messages to and from 2048 the DHCPv6 server module. 2050 When the LDRA receives an authentic RS message, it extracts the PD 2051 message parameters and uses them to construct an IPv6/UDP/DHCPv6 2052 message. It sets the IPv6 source address to the source address of 2053 the RS message, sets the IPv6 destination address to 2054 'All_DHCP_Relay_Agents_and_Servers' and sets the UDP fields to values 2055 that will be understood by the DHCPv6 server. 2057 The LDRA then wraps the message in a DHCPv6 'Relay-Forward' message 2058 header and includes an 'Interface-Id' option that includes enough 2059 information to allow the LDRA to forward the resulting Reply message 2060 back to the Client (e.g., the Client's link-layer addresses, a 2061 security association identifier, etc.). The LDRA also wraps the OMNI 2062 option and SLLAO into the Interface-Id option, then forwards the 2063 message to the DHCPv6 server. 2065 When the DHCPv6 server prepares a Reply message, it wraps the message 2066 in a 'Relay-Reply' message and echoes the Interface-Id option. The 2067 DHCPv6 server then delivers the Relay-Reply message to the LDRA, 2068 which discards the Relay-Reply wrapper and IPv6/UDP headers, then 2069 uses the DHCPv6 message to construct an RA response to the Client. 2070 The Server uses the information in the Interface-Id option to prepare 2071 the RA message and to cache the link-layer addresses taken from the 2072 OMNI option and SLLAO echoed in the Interface-Id option. 2074 3.16. The AERO Proxy 2076 Clients may connect to ANETs that deploy perimeter security services 2077 to facilitate communications to Servers in outside INETs. In that 2078 case, the ANET can employ an AERO Proxy. The Proxy is located at the 2079 ANET/INET border and listens for RS messages originating from or RA 2080 messages destined to ANET Clients. The Proxy acts on these control 2081 messages as follows: 2083 o when the Proxy receives an RS message from a new ANET Client, it 2084 first authenticates the message then examines the network-layer 2085 destination address. If the destination address is a Server's 2086 AERO address, the Proxy proceeds to the next step. Otherwise, if 2087 the destination is All-Routers multicast or Subnet-Router anycast, 2088 the Proxy selects a "nearby" Server that is likely to be a good 2089 candidate to serve the Client and replaces the destination address 2090 with the Server's AERO address. Next, the Proxy creates a proxy 2091 neighbor cache entry and caches the Client and Server link-layer 2092 addresses along with the OMNI option information and any other 2093 identifying information including Transaction IDs, Client 2094 Identifiers, Nonce values, etc. The Proxy finally encapsulates 2095 the (proxyed) RS message in a SPAN header with source set to the 2096 Proxy's SPAN address and destination set to the Server's SPAN 2097 address then forwards the message into the SPAN. 2099 o when the Server receives the RS, it authenticates the message then 2100 creates or updates a symmetric neighbor cache entry for the Client 2101 with the Proxy's SPAN address as the link-layer address. The 2102 Server then sends an RA message back to the Proxy via the SPAN. 2104 o when the Proxy receives the RA, it authenticates the message and 2105 matches it with the proxy neighbor cache entry created by the RS. 2106 The Proxy then caches the PD route information as a mapping from 2107 the Client's MNPs to the Client's ANET address, caches the 2108 Server's advertised Router Lifetime and sets the neighbor cache 2109 entry state to REACHABLE. The Proxy then sets the P bit in the RA 2110 flags field, optionally rewrites the Router Lifetime and forwards 2111 the (proxyed) message to the Client. The Proxy finally includes 2112 an MTU option (if necessary) with an MTU to use for the underlying 2113 ANET interface. 2115 After the initial RS/RA exchange, the Proxy forwards any Client data 2116 packets for which there is no matching asymmetric neighbor cache 2117 entry to a Bridge using SPAN encapsulation with its own SPAN address 2118 as the source and the SPAN address corresponding to the Client as the 2119 destination. The Proxy instead forwards any Client data destined to 2120 an asymmetric neighbor cache target directly to the target according 2121 to the SPAN/link-layer information - the process of establishing 2122 asymmetric neighbor cache entries is specified in Section 3.17. 2124 While the Client is still attached to the ANET, the Proxy sends NS, 2125 RS and/or unsolicited NA messages to update the Server's symmetric 2126 neighbor cache entries on behalf of the Client and/or to convey QoS 2127 updates. This allows for higher-frequency Proxy-initiated RS/RA 2128 messaging over well-connected INET infrastructure supplemented by 2129 lower-frequency Client-initiated RS/RA messaging over constrained 2130 ANET data links. 2132 If the Server ceases to send solicited advertisements, the Proxy 2133 sends unsolicited RAs on the ANET interface with destination set to 2134 All-Nodes multicast (ff02::1) and with Router Lifetime set to zero to 2135 inform Clients that the Server has failed. Although the Proxy 2136 engages in ND exchanges on behalf of the Client, the Client can also 2137 send ND messages on its own behalf, e.g., if it is in a better 2138 position than the Proxy to convey QoS changes, etc. For this reason, 2139 the Proxy marks any Client-originated solicitation messages (e.g. by 2140 inserting a Nonce option) so that it can return the solicited 2141 advertisement to the Client instead of processing it locally. 2143 If the Client becomes unreachable, the Proxy sets the neighbor cache 2144 entry state to DEPARTED and retains the entry for DEPART_TIME 2145 seconds. While the state is DEPARTED, the Proxy forwards any packets 2146 destined to the Client to a Bridge via SPAN encapsulation with the 2147 Client's current Server as the destination. The Bridge in turn 2148 forwards the packets to the Client's current Server. When DepartTime 2149 expires, the Proxy deletes the neighbor cache entry and discards any 2150 further packets destined to this (now forgotten) Client. 2152 In some ANETs that employ a Proxy, the Client's MNP can be injected 2153 into the ANET routing system. In that case, the Client can send data 2154 messages without encapsulation so that the ANET routing system 2155 transports the unencapsulated packets to the Proxy. This can be very 2156 beneficial, e.g., if the Client connects to the ANET via low-end data 2157 links such as some aviation wireless links. 2159 If the first-hop ANET access router is AERO-aware, the Client can 2160 avoid encapsulation for both its control and data messages. When the 2161 Client connects to the link, it can send an unencapsulated RS message 2162 with source address set to its AERO address and with destination 2163 address set to the AERO address of the Client's selected Server or to 2164 All-Routers multicast or Subnet-Router anycast. The Client includes 2165 an OMNI option formatted as specified in 2166 [I-D.templin-6man-omni-interface]. 2168 The Client then sends the unencapsulated RS message, which will be 2169 intercepted by the AERO-Aware access router. The access router then 2170 encapsulates the RS message in an ANET header with its own address as 2171 the source address and the address of a Proxy as the destination 2172 address. The access router further remembers the address of the 2173 Proxy so that it can encapsulate future data packets from the Client 2174 via the same Proxy. If the access router needs to change to a new 2175 Proxy, it simply sends another RS message toward the Server via the 2176 new Proxy on behalf of the Client. 2178 In some cases, the access router and Proxy may be one and the same 2179 node. In that case, the node would be located on the same physical 2180 link as the Client, but its message exchanges with the Server would 2181 need to pass through a security gateway at the ANET/INET border. The 2182 method for deploying access routers and Proxys (i.e. as a single node 2183 or multiple nodes) is an ANET-local administrative consideration. 2185 3.16.1. Detecting and Responding to Server Failures 2187 In environments where fast recovery from Server failure is required, 2188 Proxys SHOULD use proactive Neighbor Unreachability Detection (NUD) 2189 to track Server reachability in a similar fashion as for 2190 Bidirectional Forwarding Detection (BFD) [RFC5880]. Proxys can then 2191 quickly detect and react to failures so that cached information is 2192 re-established through alternate paths. The NUD control messaging is 2193 carried only over well-connected ground domain networks (i.e., and 2194 not low-end aeronautical radio links) and can therefore be tuned for 2195 rapid response. 2197 Proxys perform proactive NUD with Servers for which there are 2198 currently active ANET Clients by sending continuous NS messages in 2199 rapid succession, e.g., one message per second. The Proxy sends the 2200 NS message via the SPAN with the Proxy's AERO address as the source 2201 and the AERO address of the Server as the destination. When the 2202 Proxy is also sending RS messages to the Server on behalf of ANET 2203 Clients, the resulting RA responses can be considered as equivalent 2204 hints of forward progress. This means that the Proxy need not also 2205 send a periodic NS if it has already sent an RS within the same 2206 period. If the Server fails (i.e., if the Proxy ceases to receive 2207 advertisements), the Proxy can quickly inform Clients by sending 2208 multicast RA messages on the ANET interface. 2210 The Proxy sends RA messages on the ANET interface with source address 2211 set to the Server's address, destination address set to All-Nodes 2212 multicast, and Router Lifetime set to 0. The Proxy SHOULD send 2213 MAX_FINAL_RTR_ADVERTISEMENTS RA messages separated by small delays 2214 [RFC4861]. Any Clients on the ANET that had been using the failed 2215 Server will receive the RA messages and associate with a new Server. 2217 3.16.2. Point-to-Multipoint Server Coordination 2219 In environments where Client messaging over ANETs is bandwidth- 2220 limited and/or expensive, Clients can enlist the services of the 2221 Proxy to coordinate with multiple Servers in a single RS/RA message 2222 exchange. The Client can send a single RS message to All-Routers 2223 multicast that includes the ID's of multiple Servers in MS-Register 2224 sub-options of the OMNI option. 2226 When the Proxy receives the RS and processes the OMNI option, it 2227 performs a separate RS/RA exchange with each MS-Register Server. 2228 When it has received the RA messages, it creates an "aggregate" RA 2229 message to return to the Client with an OMNI option with each 2230 responding Server's ID recorded in an MS-Register sub-option. 2232 Clients can thereafter employ efficient point-to-multipoint Server 2233 coordination under the assistance of the Proxy to dramatically reduce 2234 the number of messages sent over the ANET while enlisting the support 2235 of multiple Servers for fault tolerance. Clients can further include 2236 MS-Release suboptions in RS messages to request the Proxy to release 2237 from former Servers via the procedures discussed in Section 3.19.5. 2239 The OMNI interface specification [I-D.templin-6man-omni-interface] 2240 provides further discussion of the Client/Proxy RS/RA messaging 2241 involved in point-to-multipoint coordination. 2243 3.17. AERO Route Optimization 2245 While data packets are flowing between a source and target node, 2246 route optimization SHOULD be used. Route optimization is initiated 2247 by the first eligible Route Optimization Source (ROS) closest to the 2248 source as follows: 2250 o For Clients on VPNed and Direct interfaces, the Server is the ROS. 2252 o For Clients on Proxyed interfaces, the Proxy is the ROS. 2254 o For Clients on INET interfaces, the Client itself is the ROS. 2256 o For correspondent nodes on INET/EUN interfaces serviced by a 2257 Relay, the Relay is the ROS. 2259 The route optimization procedure is conducted between the ROS and the 2260 target Server/Relay acting as a Route Optimization Responder (ROR) in 2261 the same manner as for IPv6 ND Address Resolution and using the same 2262 NS/NA messaging. The target may either be a MNP Client serviced by a 2263 Server, or a non-MNP correspondent reachable via a Relay. 2265 The procedures are specified in the following sections. 2267 3.17.1. Route Optimization Initiation 2269 While data packets are flowing from the source node toward a target 2270 node, the ROS performs address resolution by sending an NS message 2271 for Address Resolution (NS(AR)) to receive a solicited NA message 2272 from the ROR. When the ROS sends an NS(AR), it includes: 2274 o the AERO address of the ROS as the source address. 2276 o the data packet's destination as the Target Address. 2278 o the Solicited-Node multicast address [RFC4291] formed from the 2279 lower 24 bits of the data packet's destination as the destination 2280 address, e.g., for 2001:db8:1:2::10:2000 the NS destination 2281 address is ff02:0:0:0:0:1:ff10:2000. 2283 The NS(AR) message includes an OMNI option with no ifIndex-tuples and 2284 no SLLAO, such that the target will not create a neighbor cache 2285 entry. 2287 The ROS then encapsulates the NS(AR) message in a SPAN header with 2288 source set to its own SPAN address and destination set to the SPAN 2289 address corresponding to the packet's final destination, then sends 2290 the message into the SPAN without decrementing the network-layer TTL/ 2291 Hop Limit field. 2293 3.17.2. Relaying the NS 2295 When the Bridge receives the NS(AR) message from the ROS, it discards 2296 the INET header and determines that the ROR is the next hop by 2297 consulting its standard IPv6 forwarding table for the SPAN header 2298 destination address. The Bridge then forwards the message toward the 2299 ROR via the SPAN the same as for any IPv6 router. The final-hop 2300 Bridge in the SPAN will deliver the message via a secured tunnel to 2301 the ROR. 2303 3.17.3. Processing the NS and Sending the NA 2305 When the ROR receives the NS(AR) message, it examines the Target 2306 Address to determine whether it has a neighbor cache entry and/or 2307 route that matches the target. If there is no match, the ROR drops 2308 the message. Otherwise, the ROR continues processing as follows: 2310 o if the target belongs to an MNP Client neighbor in the DEPARTED 2311 state the ROR changes the NS(AR) message SPAN destination address 2312 to the SPAN address of the Client's new Server, forwards the 2313 message into the SPAN and returns from processing. 2315 o If the target belongs to an MNP Client neighbor in the REACHABLE 2316 state, the ROR instead adds the AERO source address to the target 2317 Client's Report List with time set to ReportTime. 2319 o If the target belongs to a non-MNP route, the ROR continues 2320 processing without adding an entry to the Report List. 2322 The ROR then prepares a solicited NA message to send back to the ROS 2323 but does not create a neighbor cache entry. The ROR sets the NA 2324 source address to the AERO address corresponding to the target, sets 2325 the Target Address to the target of the solicitation, and sets the 2326 destination address to the source of the solicitation. 2328 The ROR then includes an OMNI option with prefix registration length 2329 set to the length of the MNP if the target is an MNP Client; 2330 otherwise, set to the maximum of the non-MNP prefix length and 64. 2331 (Note that a /64 limit is imposed to avoid causing the ROS to set 2332 short prefixes (e.g., "default") that would match destinations for 2333 which the routing system includes more-specific prefixes.) 2335 If the target is an MNP Client, the ROR next includes ifIndex-tuples 2336 in the OMNI option for each of the target Client's underlying 2337 interfaces with current information for each interface and with the S 2338 flag set to 0. The ROR then includes a TLLAO with ifIndex-tuples in 2339 one-to-one correspondence with the tuples that appear in the OMNI 2340 option. 2342 The ROR sets the Link Layer Address and Port Number (if necessary) to 2343 its own INET address for VPNed and Direct interfaces or to the INET 2344 address of the Proxy for Proxyed interface, then includes its own 2345 SPAN address or the SPAN address of the Proxy as the ultimate Segment 2346 Routing List entry. For INET interfaces, the ROR instead sets the 2347 Link Layer Address and Port Number (if necessary) to the Client's 2348 INET address then sets its own SPAN address in the penultimate 2349 Segment Routing List entry and sets the target's SPAN address in the 2350 ultimate Segment Routing List entry. 2352 The ROR then sets the NA message R flag to 1 (as a router), S flag to 2353 1 (as a response to a solicitation), and O flag to 0 (as a proxy). 2354 The ROR finally encapsulates the NA message in a SPAN header with 2355 source set to its own SPAN address and destination set to the source 2356 SPAN address of the NS(AR) message, then forwards the message into 2357 the SPAN without decrementing the network-layer TTL/Hop Limit field. 2359 3.17.4. Relaying the NA 2361 When the Bridge receives the NA message from the ROR, it discards the 2362 INET header and determines that the ROS is the next hop by consulting 2363 its standard IPv6 forwarding table for the SPAN header destination 2364 address. The Bridge then forwards the SPAN-encapsulated NA message 2365 toward the ROS the same as for any IPv6 router. The final-hop Bridge 2366 in the SPAN will deliver the message via a secured tunnel to the ROS. 2368 3.17.5. Processing the NA 2370 When the ROS receives the solicited NA message, it processes the 2371 message the same as for standard IPv6 Address Resolution [RFC4861]. 2372 In the process, it caches the source SPAN address then creates an 2373 asymmetric neighbor cache entry for the ROR and caches all 2374 information found in the OMNI and TLLAO options. The ROS finally 2375 sets the asymmetric neighbor cache entry lifetime to REACHABLE_TIME 2376 seconds. 2378 3.17.6. Route Optimization Maintenance 2380 Following route optimization, the ROS forwards future data packets 2381 destined to the target via the addresses found in the cached link- 2382 layer information. The route optimization is shared by all sources 2383 that send packets to the target via the ROS, i.e., and not just the 2384 source on behalf of which the route optimization was initiated. 2386 While new data packets destined to the target are flowing through the 2387 ROS, it sends additional NS(AR) messages to the ROR before 2388 ReachableTime expires to receive a fresh solicited NA message the 2389 same as described in the previous sections (route optimization 2390 refreshment strategies are an implementation matter, with a non- 2391 normative example given in Appendix B.1). The ROS uses the cached 2392 SPAN address of the ROR as the NS(AR) SPAN destination address, and 2393 sends up to MAX_MULTICAST_SOLICIT NS(AR) messages separated by 1 2394 second until an NA is received. If no NA is received, the ROS 2395 assumes that the current ROR has become unreachable and deletes the 2396 neighbor cache entry. Subsequent data packets will trigger a new 2397 route optimization per Section 3.17.1 to discover a new ROR while 2398 initial data packets travel over a suboptimal route. 2400 If an NA is received, the ROS then updates the asymmetric neighbor 2401 cache entry to refresh ReachableTime, while (for MNP destinations) 2402 the ROR adds or updates the ROS address to the target Client's Report 2403 List and with time set to ReportTime. While no data packets are 2404 flowing, the ROS instead allows ReachableTime for the asymmetric 2405 neighbor cache entry to expire. When ReachableTime expires, the ROS 2406 deletes the asymmetric neighbor cache entry. Any future data packets 2407 flowing through the ROS will again trigger a new route optimization. 2409 The ROS may also receive unsolicited NA messages from the ROR at any 2410 time (see: Section 3.19). If there is an asymmetric neighbor cache 2411 entry for the target, the ROS updates the link-layer information but 2412 does not update ReachableTime since the receipt of an unsolicited NA 2413 does not confirm that any forward paths are working. If there is no 2414 asymmetric neighbor cache entry, the ROS simply discards the 2415 unsolicited NA. 2417 In this arrangement, the ROS holds an asymmetric neighbor cache entry 2418 for the ROR, but the ROR does not hold an asymmetric neighbor cache 2419 entry for the ROS. The route optimization neighbor relationship is 2420 therefore asymmetric and unidirectional. If the target node also has 2421 packets to send back to the source node, then a separate route 2422 optimization procedure is performed in the reverse direction. But, 2423 there is no requirement that the forward and reverse paths be 2424 symmetric. 2426 3.18. Neighbor Unreachability Detection (NUD) 2428 AERO nodes perform Neighbor Unreachability Detection (NUD) per 2429 [RFC4861] either reactively in response to persistent link-layer 2430 errors (see Section 3.14) or proactively to confirm reachability. 2431 The NUD algorithm is based on periodic control message exchanges. 2432 The algorithm may further be seeded by ND hints of forward progress, 2433 but care must be taken to avoid inferring reachability based on 2434 spoofed information. For example, authentic IPv6 ND message 2435 exchanges may be considered as acceptable hints of forward progress, 2436 while spurious data packets should not be. 2438 AERO Servers, Proxys and Relays can use standard NS/NA NUD exchanges 2439 sent over the SPAN to securely test reachability without risk of DoS 2440 attacks from nodes pretending to be a neighbor; Proxys can further 2441 perform NUD to securely verify Server reachability on behalf of their 2442 proxyed Clients. However, a means for a ROS to test the unsecured 2443 forward directions of target route optimized paths is also necessary. 2445 When an ROR directs an ROS to a neighbor with one or more target 2446 link-layer addresses, the ROS can proactively test each such 2447 unsecured route optimized path by sending "loopback" NS(NUD) 2448 messages. While testing the paths, the ROS can optionally continue 2449 to send packets via the SPAN, maintain a small queue of packets until 2450 target reachability is confirmed, or (optimistically) allow packets 2451 to flow via the route optimized paths. 2453 When the ROS sends a loopback NS(NUD) message, it uses its AERO 2454 address as both the IPv6 source and destination address, and the MNP 2455 Subnet-Router anycast address as the Target Address. The ROS 2456 includes a Nonce and Timestamp option, then encapsulates the message 2457 in SPAN/INET headers with its own SPAN address as the source and the 2458 SPAN address of the route optimization target as the destination. 2459 The ROS then forwards the message to the target (either directly to 2460 the link layer address of the target if the target is in the same 2461 SPAN segment, or via a Bridge if the target is in a different SPAN 2462 segment). 2464 When the route optimization target receives the NS(NUD) message, it 2465 notices that the IPv6 destination address is the same as the source 2466 address. It then reverses the SPAN source and destination addresses 2467 and returns the message to the ROS (either directly or via the SPAN). 2468 The route optimization target does not decrement the NS(NUD) message 2469 IPv6 Hop-Limit in the process, since the message has not exited the 2470 SPAN. 2472 When the ROS receives the NS(NUD) message, it can determine from the 2473 Nonce, Timestamp and Target Address that the message originated from 2474 itself and that it transited the forward path. The ROS need not 2475 prepare an NA response, since the destination of the response would 2476 be itself and testing the route optimization path again would be 2477 redundant. 2479 The ROS marks route optimization target paths that pass these NUD 2480 tests as "reachable", and those that do not as "unreachable". These 2481 markings inform the AERO interface forwarding algorithm specified in 2482 Section 3.13. 2484 Note that to avoid a DoS vector nodes MUST NOT return loopback 2485 NS(NUD) messages received from an unsecured link-layer source via a 2486 secured SPAN path. 2488 3.19. Mobility Management and Quality of Service (QoS) 2490 AERO is a Distributed Mobility Management (DMM) service. Each Server 2491 is responsible for only a subset of the Clients on the AERO link, as 2492 opposed to a Centralized Mobility Management (CMM) service where 2493 there is a single network mobility collective entity for all Clients. 2494 Clients coordinate with their associated Servers via RS/RA exchanges 2495 to maintain the DMM profile, and the AERO routing system tracks all 2496 current Client/Server peering relationships. 2498 Servers provide default routing and mobility/multilink services for 2499 their dependent Clients. Clients are responsible for maintaining 2500 neighbor relationships with their Servers through periodic RS/RA 2501 exchanges, which also serves to confirm neighbor reachability. When 2502 a Client's underlying interface address and/or QoS information 2503 changes, the Client is responsible for updating the Server with this 2504 new information. Note that for Proxyed interfaces, however, the 2505 Proxy can also perform some RS/RA exchanges on the Client's behalf. 2507 Mobility management considerations are specified in the following 2508 sections. 2510 3.19.1. Mobility Update Messaging 2512 Servers accommodate Client mobility/multilink and/or QoS change 2513 events by sending unsolicited NA (uNA) messages to each ROS in the 2514 target Client's Report List. When a Server sends a uNA message, it 2515 sets the IPv6 source address to the Client's AERO address, sets the 2516 destination address to All-Nodes multicast and sets the Target 2517 Address to the Client's Subnet-Router anycast address. The Server 2518 also includes an OMNI option with prefix registration information and 2519 with ifIndex-tuples for the target Client's remaining interfaces with 2520 S set to 0. The Server then includes a TLLAO with corresponding 2521 ifIndex-tuples prepared the same as for the initial route 2522 optimization event. The Server sets the NA R flag to 1, the S flag 2523 to 0 and the O flag to 0, then encapsulates the message in a SPAN 2524 header with source set to its own SPAN address and destination set to 2525 the SPAN address of the ROS and sends the message into the SPAN. 2527 As discussed in Section 7.2.6 of [RFC4861], the transmission and 2528 reception of uNA messages is unreliable but provides a useful 2529 optimization. In well-connected Internetworks with robust data links 2530 uNA messages will be delivered with high probability, but in any case 2531 the Server can optionally send up to MAX_NEIGHBOR_ADVERTISEMENT uNAs 2532 to each ROS to increase the likelihood that at least one will be 2533 received. 2535 When the ROS receives a uNA message, it ignores the message if there 2536 is no existing neighbor cache entry for the Client. Otherwise, it 2537 uses the included OMNI option and TLLAO information to update the 2538 neighbor cache entry, but does not reset ReachableTime since the 2539 receipt of an unsolicited NA message from the target Server does not 2540 provide confirmation that any forward paths to the target Client are 2541 working. 2543 If uNA messages are lost, the ROS may be left with stale address and/ 2544 or QoS information for the Client for up to REACHABLE_TIME seconds. 2545 During this time, the ROS can continue sending packets according to 2546 its stale neighbor cache information. When ReachableTime is close to 2547 expiring, the ROS will re-initiate route optimization and receive 2548 fresh link-layer address information. 2550 In addition to sending uNA messages to the current set of ROSs for 2551 the Client, the Server also sends uNAs to the former link-layer 2552 address for any ifIndex-tuple for which the link-layer address has 2553 changed. The uNA messages update Proxys that cannot easily detect 2554 (e.g., without active probing) when a formerly-active Client has 2555 departed. 2557 3.19.2. Announcing Link-Layer Address and/or QoS Preference Changes 2559 When a Client needs to change its underlying interface addresses and/ 2560 or QoS preferences (e.g., due to a mobility event), either the Client 2561 or its Proxys send RS messages to the Server via the SPAN with an 2562 OMNI option that includes an ifIndex-tuple with S set to 1 and with 2563 the new link quality and address information. 2565 Up to MAX_RTR_SOLICITATIONS RS messages MAY be sent in parallel with 2566 sending actual data packets in case one or more RAs are lost. If all 2567 RAs are lost, the Client SHOULD re-associate with a new Server. 2569 When the Server receives the Client's changes, it sends uNA messages 2570 to all nodes in the Report List the same as described in the previous 2571 section. 2573 3.19.3. Bringing New Links Into Service 2575 When a Client needs to bring new underlying interfaces into service 2576 (e.g., when it activates a new data link), it sends an RS message to 2577 the Server via the underlying interface with an OMNI option that 2578 includes an ifIndex-tuple with S set to 1 and appropriate link 2579 quality values and with link-layer address information for the new 2580 link. 2582 3.19.4. Removing Existing Links from Service 2584 When a Client needs to remove existing underlying interfaces from 2585 service (e.g., when it de-activates an existing data link), it sends 2586 an RS or uNA message to its Server with an OMNI option with 2587 appropriate link quality values. 2589 If the Client needs to send RS/uNA messages over an underlying 2590 interface other than the one being removed from service, it MUST 2591 include ifIndex-tuples with appropriate link quality values for any 2592 underlying interfaces being removed from service. 2594 3.19.5. Moving to a New Server 2596 When a Client associates with a new Server, it performs the Client 2597 procedures specified in Section 3.15.2. The Client also includes MS- 2598 Release identifiers in the RS message OMNI option per 2599 [I-D.templin-6man-omni-interface] if it wants the new Server to 2600 notify any old Servers from which the Client is departing. 2602 When the new Server receives the Client's RS message, it returns an 2603 RA as specified in Section 3.15.3 and sends up to 2604 MAX_NEIGHBOR_ADVERTIISEMENT uNA messages to any old Servers listed in 2605 OMNI option MS-Release identifiers. Each uNA message includes the 2606 Client's AERO address as the source address, the old Server's AERO 2607 address as the destination address, and an OMNI option with the 2608 Register/Release bit set to 0. The new Server wraps the uNA in a 2609 SPAN header with its own SPAN address as the source and the old 2610 Server's SPAN address as the destination, then sends the message into 2611 the SPAN. 2613 When an old Server receives the uNA, it changes the Client's neighbor 2614 cache entry state to DEPARTED, sets the link-layer address of the 2615 Client to the new Server's SPAN address, and sets DepartTime to 2616 DEPART_TIME seconds. After a short delay (e.g., 2 seconds) the old 2617 Server withdraws the Client's MNP from the routing system. After 2618 DepartTime expires, the old Server deletes the Client's neighbor 2619 cache entry. 2621 The old Server also sends unsolicited NA messages to all ROSs in the 2622 Client's Report List with an OMNI option with a single ifIndex-tuple 2623 with ifIndex set to 0 and S set to '1', and with the SPAN address of 2624 the new Server in a companion TLLAO. When the ROS receives the NA, 2625 it caches the address of the new Server in the existing asymmetric 2626 neighbor cache entry and marks the entry as STALE. Subsequent data 2627 packets will then flow according to any existing cached link-layer 2628 information and trigger a new NS(AR)/NA exchange via the new Server. 2630 Clients SHOULD NOT move rapidly between Servers in order to avoid 2631 causing excessive oscillations in the AERO routing system. Examples 2632 of when a Client might wish to change to a different Server include a 2633 Server that has gone unreachable, topological movements of 2634 significant distance, movement to a new geographic region, movement 2635 to a new SPAN segment, etc. 2637 When a Client moves to a new Server, some of the fragments of a 2638 multiple fragment packet may have already arrived at the old Server 2639 while others are en route to the new Server, however no special 2640 attention in the reassembly algorithm is necessary when re-routed 2641 fragments are simply treated as loss. 2643 3.20. Multicast 2645 The AERO Client provides an IGMP (IPv4) [RFC2236] or MLD (IPv6) 2646 [RFC3810] proxy service for its EUNs and/or hosted applications 2647 [RFC4605]. The Client forwards IGMP/MLD messages over any of its 2648 underlying interfaces for which group membership is required. The 2649 IGMP/MLD messages may be further forwarded by a first-hop ANET access 2650 router acting as an IGMP/MLD-snooping switch [RFC4541], then 2651 ultimately delivered to an AERO Proxy/Server acting as a Protocol 2652 Independent Multicast - Sparse-Mode (PIM-SM, or simply "PIM") 2653 Designated Router (DR) [RFC7761]. AERO Relays also act as PIM 2654 routers (i.e., the same as AERO Proxys/Servers) on behalf of nodes on 2655 INET/EUN networks. The behaviors identified in the following 2656 sections correspond to Source-Specific Multicast (SSM) and Any-Source 2657 Multicast (ASM) operational modes. 2659 3.20.1. Source-Specific Multicast (SSM) 2661 When an ROS (i.e., an AERO Proxy/Server/Relay) "X" acting as PIM 2662 router receives a Join/Prune message from a node on its downstream 2663 interfaces containing one or more ((S)ource, (G)roup) pairs, it 2664 updates its Multicast Routing Information Base (MRIB) accordingly. 2665 For each S belonging to a prefix reachable via X's non-AERO 2666 interfaces, X then forwards the (S, G) Join/Prune to any PIM routers 2667 on those interfaces per [RFC7761]. 2669 For each S belonging to a prefix reachable via X's AERO interface, X 2670 originates a separate copy of the Join/Prune for each (S,G) in the 2671 message using its own AERO address as the source address and ALL-PIM- 2672 ROUTERS as the destination address. X then encapsulates each message 2673 in a SPAN header with source address set to the SPAN address of X and 2674 destination address set to S then forwards the message into the SPAN. 2675 The SPAN in turn forwards the message to AERO Server/Relay "Y" that 2676 services S. At the same time, if the message was a Join, X sends a 2677 route-optimization NS message toward each S the same as discussed in 2678 Section 3.17. The resulting NAs will return the AERO address for the 2679 prefix that matches S as the network-layer source address and TLLAOs 2680 with the SPAN addresses corresponding to any ifIndex-tuples that are 2681 currently servicing S. 2683 When Y processes the Join/Prune message, if S located behind any 2684 INET, Direct, or VPNed interfaces Y acts as a PIM router and updates 2685 its MRIB to list X as the next hop in the reverse path. If S is 2686 located behind any Proxys "Z"*, Y also forwards the message to each 2687 Z* over the SPAN while continuing to use the AERO address of X as the 2688 source address. Each Z* then updates its MRIB accordingly and 2689 maintains the AERO address of X as the next hop in the reverse path. 2690 Since the Bridges in the SPAN do not examine network layer control 2691 messages, this means that the (reverse) multicast tree path is simply 2692 from each Z* (and/or Y) to X with no other multicast-aware routers in 2693 the path. If any Z* (and/or Y) is located on the same SPAN segment 2694 as X, the multicast data traffic sent to X directly using SPAN/INET 2695 encapsulation instead of via a Bridge. 2697 Following the initial Join/Prune and NS/NA messaging, X maintains an 2698 asymmetric neighbor cache entry for each S the same as if X was 2699 sending unicast data traffic to S. In particular, X performs 2700 additional NS/NA exchanges to keep the neighbor cache entry alive for 2701 up to t_periodic seconds [RFC7761]. If no new Joins are received 2702 within t_periodic seconds, X allows the neighbor cache entry to 2703 expire. Finally, if X receives any additional Join/Prune messages 2704 for (S,G) it forwards the messages to each Y and Z* in the neighbor 2705 cache entry over the SPAN. 2707 At some later time, Client C that holds an MNP for source S may 2708 depart from a first Proxy Z1 and/or connect via a new Proxy Z2. In 2709 that case, Y sends an unsolicited NA message to X the same as 2710 specified for unicast mobility in Section 3.19. When X receives the 2711 unsolicited NA message, it updates its asymmetric neighbor cache 2712 entry for the AERO address for source S and sends new Join messages 2713 to any new Proxys Z2. There is no requirement to send any Prune 2714 messages to old Proxys Z1 since source S will no longer source any 2715 multicast data traffic via Z1. Instead, the multicast state for 2716 (S,G) in Proxy Z1 will soon time out since no new Joins will arrive. 2718 After some later time, C may move to a new Server Y2 and depart from 2719 old Sever Y1. In that case, Y1 sends Join messages for any of C's 2720 active (S,G) groups to Y2 while including its own AERO address as the 2721 source address. This causes Y2 to include Y1 in the multicast 2722 forwarding tree during the interim time that Y1's symmetric neighbor 2723 cache entry for C is in the DEPARTED state. At the same time, Y1 2724 sends an unsolicited NA message to X with an OMNI option and TLLAO 2725 with ifIndex-tuple set to 0 and a release indication to cause X to 2726 release its asymmetric neighbor cache entry. X then sends a new Join 2727 message to S via the SPAN and re-initiates route optimization the 2728 same as if it were receiving a fresh Join message from a node on a 2729 downstream link. 2731 3.20.2. Any-Source Multicast (ASM) 2733 When an ROS X acting as a PIM router receives a Join/Prune from a 2734 node on its downstream interfaces containing one or more (*,G) pairs, 2735 it updates its Multicast Routing Information Base (MRIB) accordingly. 2736 X then forwards a copy of the message to the Rendezvous Point (RP) R 2737 for each G over the SPAN. X uses its own AERO address as the source 2738 address and ALL-PIM-ROUTERS as the destination address, then 2739 encapsulates each message in a SPAN header with source address set to 2740 the SPAN address of X and destination address set to R, then sends 2741 the message into the SPAN. At the same time, if the message was a 2742 Join X initiates NS/NA route optimization the same as for the SSM 2743 case discussed in Section 3.20.1. 2745 For each source S that sends multicast traffic to group G via R, the 2746 Proxy/Server Z* for the Client that aggregates S encapsulates the 2747 packets in PIM Register messages and forwards them to R via the SPAN. 2748 R may then elect to send a PIM Join to Z* over the SPAN. This will 2749 result in an (S,G) tree rooted at Z* with R as the next hop so that R 2750 will begin to receive two copies of the packet; one native copy from 2751 the (S, G) tree and a second copy from the pre-existing (*, G) tree 2752 that still uses PIM Register encapsulation. R can then issue a PIM 2753 Register-stop message to suppress the Register-encapsulated stream. 2754 At some later time, if C moves to a new Proxy/Server Z*, it resumes 2755 sending packets via PIM Register encapsulation via the new Z*. 2757 At the same time, as multicast listeners discover individual S's for 2758 a given G, they can initiate an (S,G) Join for each S under the same 2759 procedures discussed in Section 3.20.1. Once the (S,G) tree is 2760 established, the listeners can send (S, G) Prune messages to R so 2761 that multicast packets for group G sourced by S will only be 2762 delivered via the (S, G) tree and not from the (*, G) tree rooted at 2763 R. All mobility considerations discussed for SSM apply. 2765 3.20.3. Bi-Directional PIM (BIDIR-PIM) 2767 Bi-Directional PIM (BIDIR-PIM) [RFC5015] provides an alternate 2768 approach to ASM that treats the Rendezvous Point (RP) as a Designated 2769 Forwarder (DF). Further considerations for BIDIR-PIM are out of 2770 scope. 2772 3.21. Operation over Multiple AERO Links (VLANs) 2774 An AERO Client can connect to multiple AERO links the same as for any 2775 data link service. In that case, the Client maintains a distinct 2776 AERO interface for each link, e.g., 'aero0' for the first link, 2777 'aero1' for the second, 'aero2' for the third, etc. Each AERO link 2778 would include its own distinct set of Bridges, Servers and Proxys, 2779 thereby providing redundancy in case of failures. 2781 The Bridges, Servers and Proxys on each AERO link can assign AERO and 2782 SPAN addresses that use the same or different numberings from those 2783 on other links. Since the links are mutually independent there is no 2784 requirement for avoiding inter-link address duplication, e.g., the 2785 same AERO address such as fe80::1000 could be used to number distinct 2786 nodes that connect to different AERO links. 2788 Each AERO link could utilize the same or different ANET connections. 2789 The links can be distinguished at the link-layer via the SSP in a 2790 similar fashion as for Virtual Local Area Network (VLAN) tagging 2791 (e.g., IEEE 802.1Q) and/or through assignment of distinct sets of 2792 MSPs on each link. This gives rise to the opportunity for supporting 2793 multiple redundant networked paths, where each VLAN is distinguished 2794 by a different SRT color (see: Section 3.5.1). In particular, the 2795 Client can tag its RS messages with the appropriate label to cause 2796 the network to select the desired VLAN. 2798 The Client's IP layer can select the outgoing AERO interface 2799 appropriate for a given traffic profile while (in the reverse 2800 direction) correspondent nodes must have some way of steering their 2801 packets destined to a target via the correct AERO link. 2803 In a first alternative, if each AERO link services different MSPs, 2804 then the Client can receive a distinct MNP from each of the links. 2805 IP routing will therefore assure that the correct Red/Green/Blue/etc. 2806 network is used for both outbound and inbound traffic. This can be 2807 accomplished using existing technologies and approaches, and without 2808 requiring any special supporting code in correspondent nodes or 2809 Bridges. 2811 In a second alternative, if each AERO link services the same MSP(s) 2812 then each link could assign a distinct "AERO Link Anycast" address 2813 that is configured by all Bridges on the link. Correspondent nodes 2814 can then perform segment routing at the SPAN layer 2815 [RFC8402][RFC8754]. Segment Routing in the correct SRT will then 2816 direct the packet over multiple hops to the target. 2818 3.22. DNS Considerations 2820 AERO Client MNs and INET correspondent nodes consult the Domain Name 2821 System (DNS) the same as for any Internetworking node. When 2822 correspondent nodes and Client MNs use different IP protocol versions 2823 (e.g., IPv4 correspondents and IPv6 MNs), the INET DNS must maintain 2824 A records for IPv4 address mappings to MNs which must then be 2825 populated in Relay NAT64 mapping caches. In that way, an IPv4 2826 correspondent node can send packets to the IPv4 address mapping of 2827 the target MN, and the Relay will translate the IPv4 header and 2828 destination address into an IPv6 header and IPv6 destination address 2829 of the MN. 2831 When an AERO Client registers with an AERO Server, the Server can 2832 return the address(es) of DNS servers in RDNSS options [RFC6106]. 2833 The DNS server provides the IP addresses of other MNs and 2834 correspondent nodes in AAAA records for IPv6 or A records for IPv4. 2836 3.23. Transition Considerations 2838 The SPAN ensures that dissimilar INET partitions can be joined into a 2839 single unified AERO link, even though the partitions themselves may 2840 have differing protocol versions and/or incompatible addressing 2841 plans. However, a commonality can be achieved by incrementally 2842 distributing globally routable (i.e., native) IP prefixes to 2843 eventually reach all nodes (both mobile and fixed) in all SPAN 2844 segments. This can be accomplished by incrementally deploying AERO 2845 Relays on each INET partition, with each Relay distributing its MNPs 2846 and/or discovering non-MNP prefixes on its INET links. 2848 This gives rise to the opportunity to eventually distribute native IP 2849 addresses to all nodes, and to present a unified AERO link view 2850 (bridged by the SPAN) even if the INET partitions remain in their 2851 current protocol and addressing plans. In that way, the AERO link 2852 can serve the dual purpose of providing a mobility/multilink service 2853 and a transition service. Or, if an INET partition is transitioned 2854 to a native IP protocol version and addressing scheme that is 2855 compatible with the AERO link MNP-based addressing scheme, the 2856 partition and AERO link can be joined by Relays. 2858 Relays that connect INETs/EUNs with dissimilar IP protocol versions 2859 may need to employ a network address and protocol translation 2860 function such as NAT64[RFC6146]. 2862 3.24. Detecting and Reacting to Server and Bridge Failures 2864 In environments where rapid failure recovery is required, Servers and 2865 Bridges SHOULD use Bidirectional Forwarding Detection (BFD) 2866 [RFC5880]. Nodes that use BFD can quickly detect and react to 2867 failures so that cached information is re-established through 2868 alternate nodes. BFD control messaging is carried only over well- 2869 connected ground domain networks (i.e., and not low-end radio links) 2870 and can therefore be tuned for rapid response. 2872 Servers and Bridges maintain BFD sessions in parallel with their BGP 2873 peerings. If a Server or Bridge fails, BGP peers will quickly re- 2874 establish routes through alternate paths the same as for common BGP 2875 deployments. Similarly, Proxys maintain BFD sessions with their 2876 associated Bridges even though they do not establish BGP peerings 2877 with them. 2879 Proxys SHOULD use proactive NUD for Servers for which there are 2880 currently active ANET Clients in a manner that parallels BFD, i.e., 2881 by sending unicast NS messages in rapid succession to receive 2882 solicited NA messages. When the Proxy is also sending RS messages on 2883 behalf of ANET Clients, the RS/RA messaging can be considered as 2884 equivalent hints of forward progress. This means that the Proxy need 2885 not also send a periodic NS if it has already sent an RS within the 2886 same period. If a Server fails, the Proxy will cease to receive 2887 advertisements and can quickly inform Clients of the outage by 2888 sending multicast RA messages on the ANET interface. 2890 The Proxy sends multicast RA messages with source address set to the 2891 Server's address, destination address set to All-Nodes multicast, and 2892 Router Lifetime set to 0. The Proxy SHOULD send 2893 MAX_FINAL_RTR_ADVERTISEMENTS RA messages separated by small delays 2894 [RFC4861]. Any Clients on the ANET interface that have been using 2895 the (now defunct) Server will receive the RA messages and associate 2896 with a new Server. 2898 3.25. AERO Clients on the Open Internet 2900 AERO Clients that connect to the open Internet via INET interfaces 2901 can establish a VPN or direct link to securely connect to a Server in 2902 a "tethered" arrangement with all of the Client's traffic transiting 2903 the Server. Alternatively, the Client can associate with an INET 2904 Server using UDP/IP encapsulation and asymmetric securing services as 2905 discussed in the following sections. 2907 When a Client's AERO interface enables INET underlying interfaces, it 2908 sends a UDP/IP-encapsulated RS message with IPv6 source address set 2909 to its AERO address, with IPv6 destination set to All-Routers 2910 multicast, with an OMNI option and with a Teredo Authentication 2911 option to provide message authentication. The Client also includes 2912 an SLLAO with Link Layer Address set according to the address of the 2913 underlying interface used for INET encapsulation. If the underlying 2914 interface address is IPv6, the Client sets the FMT according to 2915 whether the Port Number also must be included as discussed in 2916 Section 3.6. If the underlying address is IPv4, the Client includes 2917 a Teredo address [RFC4380] using the prefix fe80::/32 with the 2918 Server's IPv4 address, and with the IP address and Port Number used 2919 for INET encapsulation written in obfuscated form and sets FMT to 2920 NAT. The Client then sets the UDP/IP source to its INET address and 2921 UDP port, and sets the destination to the Server's INET address and 2922 the AERO service port number (8060), then sends the message to the 2923 Server. 2925 When the Server receives the RS message, it authenticates the message 2926 and registers the Client's MNP and INET interface information 2927 according to the OMNI option parameters. The Server then returns an 2928 RA message with IPv6 source and destination set corresponding to the 2929 addresses in the RS, and with a Teredo Authentication option. For 2930 IPv4 INET interfaces, the Server also includes a Teredo Origin option 2931 with the mapped and obfuscated Client observed IP address and port 2932 number for the Client, and with a Teredo Authentication option. The 2933 Server then sends the message to the Client and records the Client's 2934 IPv6 address (for IPv6 INET interfaces) or fe80:: Teredo address (for 2935 IPv4 INET interfaces) as the link layer address in the neighbor 2936 cache. For IPv4, if the Client's IPv4 address and port from the 2937 SLLAO match the UDP/IPv4 header information (and if the IPv4 address 2938 is global unicast) the Server notes the FMT for this Client as Teredo 2939 on the open INET. 2941 When the Client receives the RA message, for IPv6 INET interfaces the 2942 Client proceeds under the assumption that any NATs on the path to the 2943 Server will behave according to the Cone NAT principle. For IPv4 2944 INET interfaces, the Client instead compares the mapped IP address 2945 and port from the Teredo Origin option with its own address. If the 2946 addresses are the same, the Client assumes the Cone NAT principle; if 2947 the addresses are different, the Client instead assumes that further 2948 Server qualification procedures are necessary to detect the type of 2949 NAT and proceeds according to standard Teredo procedures. 2951 After the Client has registered its INET interfaces in such RS/RA 2952 exchanges it sends periodic RS messages to receive fresh RA messages 2953 before the Router Lifetime received on each INET interface expires. 2954 The Client also maintains default routes via its Servers, i.e., the 2955 same as described in earlier sections. 2957 When the Client sends messages to target IP addresses, it also 2958 invokes route optimization per Section 3.17 using IPv6 ND address 2959 resolution messaging. The Client sends the NS(AR) message to the 2960 Server wrapped in a UDP/IP header with a Teredo Authentication option 2961 with the NS source address set to the Client's AERO address and 2962 destination address set to the target solicited node multicast 2963 address. The Server authenticates the message and sends a 2964 corresponding NS(AR) message over the SPAN the same as if it were the 2965 ROS, but with the SPAN source address set to the Server's SPAN 2966 address and destination set to the SPAN address of the target. When 2967 the ROR receives the NS(AR), it adds the Server's SPAN address and 2968 Client's AERO address to the target's Report List, and returns an NA 2969 with OMNI and TLLAO information for the target. The Server then 2970 returns a UDP/IP encapsulated NA message with a Teredo Authentication 2971 option to the Client. 2973 Following route optimization, for targets in the same SPAN segment if 2974 the target's Link Layer Address is native IPv6 or a Teredo address on 2975 the open INET, the Client forwards data packets directly to the 2976 target INET address. If the Link Layer Address is a Teredo address 2977 for a peer behind a NAT, the Client first establishes NAT state for 2978 the Link Layer Address using the "bubble" mechanisms specified in 2979 [RFC6081][RFC4380]. The Client continues to send data packets via 2980 its Server until NAT state is populated, then begins forwarding 2981 packets via the direct path through the NAT to the target. For 2982 targets in different SPAN segments, the Client inserts a Segment 2983 Routing header and forwards data packets to the Bridge that returned 2984 the NA message. 2986 The ROR may return uNAs via the Server if the target moves, and the 2987 Server will send corresponding Teredo Authentication-protected uNAs 2988 to the Client. The Client can also send "loopback" NS(NUD) messages 2989 to test forward path reachability even though there is no security 2990 association between the Client and the target. 2992 The Client sends Teredo UDP/IP encapsulated IPv6 packets no larger 2993 than 1280 bytes in one piece. In order to accommodate larger IPv6 2994 packets (up to the AERO interface 9180 MTU), the Client inserts a 2995 SPAN header with source set to its own SPAN address and destination 2996 set to the SPAN address of the target and uses IPv6 fragmentation 2997 according to Section 3.12. The Client then encapsulates each 2998 fragment in a UDP/IP header and sends the fragments to the next hop. 3000 3.25.1. Use of SEND and CGA 3002 In some environments, use of the Teredo Authentication option alone 3003 may be sufficient for assuring IPv6 ND message authentication between 3004 Clients and Servers. When additional protection is necessary, nodes 3005 should employ SEcure Neighbor Discovery (SEND) [RFC3971] with 3006 Cryptographically-Generated Addresses (CGA) [RFC3972]. 3008 When SEND/CGA are used, the Client prepares RS messages with its 3009 link-local CGA as the IPv6 source and All-Routers as the IPv6 3010 Destination, includes any SEND options and wraps the message in a 3011 SPAN header. The Client sets the SPAN source address to its own SPAN 3012 address and sets the SPAN destination address to the "All-Routers" 3013 SPAN address. The Client then wraps the RS message in UDP/IP headers 3014 according to the Teredo format and sends the message to the Server. 3016 When the Server receives the message, it first verifies the Teredo 3017 Authentication option (if present) then uses the SPAN source address 3018 to determine the MNP of the Client. The Server then processes the 3019 SEND options to authenticate the RS message and prepares an RA 3020 message response. The Server prepares the RA with its own link-local 3021 CGA and the CGA of the Client as the IPv6 source and destination, 3022 includes any SEND options and wraps the message in a SPAN header. 3023 The Server sets the SPAN source address to its own SPAN address and 3024 sets the SPAN destination address to the Client's SPAN address. The 3025 Server then wraps the RA message in UDP/IP headers according to the 3026 Teredo format and sends the message to the Client. Thereafter, the 3027 Client/Server send additional RS/RA messages to maintain their 3028 association and any NAT state. 3030 The Client and Server also may exchange NS/NA messages using their 3031 own CGA as the source and with SPAN encapsulation as above. When a 3032 Client sends an NS(AR), it sets the IPv6 source to its CGA and sets 3033 the IPv6 destination to the Solicited-Node Multicast address of the 3034 target. The Client then wraps the message in a SPAN header with its 3035 own SPAN address as the source and the SPAN address of the target as 3036 the destination and sends it to the Server. The Server authenticates 3037 the message, then changes the IPv6 source address to the Client's 3038 AERO address, removes the SEND options, and sends a corresponding 3039 NS(AR) into the SPAN. When the Server receives the corresponding 3040 SPAN-encapsulated NA, it changes the IPv6 destination address to the 3041 Client's CGA, inserts SEND options, then wraps the message in UDP/IP 3042 headers and sends it to the Client. 3044 When a Client sends a uNA, it sets the IPv6 source address to its own 3045 CGA and sets the IPv6 destination address to All-Nodes multicast, 3046 includes SEND options, wraps the message in SPAN and UDP/IP headers 3047 and sends the message to the Server. The Server authenticates the 3048 message, then changes the IPv6 address to the Client's AERO address, 3049 removes the SEND options and forwards the message the same as 3050 discussed in Section 3.19.1. In the reverse direction, when the 3051 Server forwards a uNA to the Client, it changes the IPv6 address to 3052 its own CGA and inserts SEND options then forwards the message to the 3053 Client. 3055 When a Client sends an NS(NUD), it sets both the IPv6 source and 3056 destination address to its own AERO address, wraps the message in a 3057 SPAN header and UDP/IP headers, then sends the message directly to 3058 the peer which will loop the message back. In this case alone, the 3059 Client does not use the Server as a trust broker for forwarding the 3060 ND message. 3062 3.26. Time-Varying MNPs 3064 In some use cases, it is desirable, beneficial and efficient for the 3065 Client to receive a constant MNP that travels with the Client 3066 wherever it moves. For example, this would allow air traffic 3067 controllers to easily track aircraft, etc. In other cases, however 3068 (e.g., intelligent transportation systems), the MN may be willing to 3069 sacrifice a modicum of efficiency in order to have time-varying MNPs 3070 that can be changed every so often to defeat adversarial tracking. 3072 The DHCPv6-PD service offers a way for Clients that desire time- 3073 varying MNPs to obtain short-lived prefixes (e.g., on the order of a 3074 small number of minutes). In that case, the identity of the Client 3075 would not be bound to the MNP but rather the Client's identity would 3076 be bound to the DHCPv6 Device Unique Identifier (DUID) and used as 3077 the seed for Prefix Delegation. The Client would then be obligated 3078 to renumber its internal networks whenever its MNP (and therefore 3079 also its AERO address) changes. This should not present a challenge 3080 for Clients with automated network renumbering services, however 3081 presents limits for the durations of ongoing sessions that would 3082 prefer to use a constant address. 3084 4. Implementation Status 3086 An AERO implementation based on OpenVPN (https://openvpn.net/) was 3087 announced on the v6ops mailing list on January 10, 2018 and an 3088 initial public release of the AERO proof-of-concept source code was 3089 announced on the intarea mailing list on August 21, 2015. 3091 As of 4/1/2020, more recent updated implementations are under 3092 internal development and testing with plans to release in the near 3093 future. 3095 5. IANA Considerations 3097 The IANA has assigned a 4-octet Private Enterprise Number "45282" for 3098 AERO in the "enterprise-numbers" registry. 3100 The IANA has assigned the UDP port number "8060" for an earlier 3101 experimental version of AERO [RFC6706]. This document obsoletes 3102 [RFC6706] and claims the UDP port number "8060" for all future use. 3104 No further IANA actions are required. 3106 6. Security Considerations 3108 AERO Bridges configure secured tunnels with AERO Servers and Proxys 3109 within their local SPAN segments. Applicable secured tunnel 3110 alternatives include IPsec [RFC4301], TLS/SSL [RFC8446], DTLS 3111 [RFC6347], WireGuard, etc. The AERO Bridges of all SPAN segments in 3112 turn configure secured tunnels for their neighboring AERO Bridges 3113 across the SPAN. Therefore, control messages that traverse the SPAN 3114 between any pair of AERO link neighbors are already secured. 3116 AERO Servers, Relays and Proxys targeted by a route optimization may 3117 also receive packets directly from the INET partitions instead of via 3118 the SPAN. For INET partitions that apply effective ingress filtering 3119 to defeat source address spoofing, the simple data origin 3120 authentication procedures in Section 3.11 can be applied. 3122 For INET partitions that cannot apply effective ingress filtering, 3123 the two options for securing communications include 1) disable route 3124 optimization so that all traffic is conveyed over secured tunnels via 3125 the SPAN, or 2) enable on-demand secure tunnel creation between INET 3126 partition neighbors. Option 1) would result in longer routes than 3127 necessary and traffic concentration on critical infrastructure 3128 elements. Option 2) could be coordinated by establishing a secured 3129 tunnel on-demand instead of performing an NS/NA exchange in the route 3130 optimization procedures. Procedures for establishing on-demand 3131 secured tunnels are out of scope. 3133 AERO Clients that connect to secured ANETs need not apply security to 3134 their ND messages, since the messages will be intercepted by a 3135 perimeter Proxy that applies security on its INET-facing interface. 3136 AERO Clients connected to the open INET can use symmetric network 3137 and/or transport layer security services such as VPNs or can by some 3138 other means establish a direct link. When a VPN or direct link may 3139 be impractical, however, an asymmetric security service such as 3140 SEcure Neighbor Discovery (SEND) [RFC3971] with Cryptographically 3141 Generated Addresses (CGAs) [RFC3972] and/or the Teredo Authentication 3142 option [RFC4380] may be necessary. 3144 Application endpoints SHOULD use application-layer security services 3145 such as TLS/SSL, DTLS or SSH [RFC4251] to assure the same level of 3146 protection as for critical secured Internet services. AERO Clients 3147 that require host-based VPN services SHOULD use symmetric network 3148 and/or transport layer security services such as IPsec, TLS/SSL, 3149 DTLS, etc. AERO Proxys and Servers can also provide a network-based 3150 VPN service on behalf of the Client, e.g., if the Client is located 3151 within a secured enclave and cannot establish a VPN on its own 3152 behalf. 3154 AERO Servers and Bridges present targets for traffic amplification 3155 Denial of Service (DoS) attacks. This concern is no different than 3156 for widely-deployed VPN security gateways in the Internet, where 3157 attackers could send spoofed packets to the gateways at high data 3158 rates. This can be mitigated by connecting Servers and Bridges over 3159 dedicated links with no connections to the Internet and/or when 3160 connections to the Internet are only permitted through well-managed 3161 firewalls. Traffic amplification DoS attacks can also target an AERO 3162 Client's low data rate links. This is a concern not only for Clients 3163 located on the open Internet but also for Clients in secured 3164 enclaves. AERO Servers and Proxys can institute rate limits that 3165 protect Clients from receiving packet floods that could DoS low data 3166 rate links. 3168 AERO Relays must implement ingress filtering to avoid a spoofing 3169 attack in which spurious SPAN messages are injected into an AERO link 3170 from an outside attacker. AERO Clients MUST ensure that their 3171 connectivity is not used by unauthorized nodes on their EUNs to gain 3172 access to a protected network, i.e., AERO Clients that act as routers 3173 MUST NOT provide routing services for unauthorized nodes. (This 3174 concern is no different than for ordinary hosts that receive an IP 3175 address delegation but then "share" the address with other nodes via 3176 some form of Internet connection sharing such as tethering.) 3178 The MAP list MUST be well-managed and secured from unauthorized 3179 tampering, even though the list contains only public information. 3180 The MAP list can be conveyed to the Client in a similar fashion as in 3181 [RFC5214] (e.g., through layer 2 data link login messaging, secure 3182 upload of a static file, DNS lookups, etc.). 3184 Although public domain and commercial SEND implementations exist, 3185 concerns regarding the strength of the cryptographic hash algorithm 3186 have been documented [RFC6273] [RFC4982]. 3188 Segment routing provides authentication facilities that can be used 3189 to authenticate the information in the SRH [RFC8754]. 3191 Security considerations for accepting link-layer ICMP messages and 3192 reflected packets are discussed throughout the document. 3194 7. Acknowledgements 3196 Discussions in the IETF, aviation standards communities and private 3197 exchanges helped shape some of the concepts in this work. 3198 Individuals who contributed insights include Mikael Abrahamsson, Mark 3199 Andrews, Fred Baker, Bob Braden, Stewart Bryant, Brian Carpenter, 3200 Wojciech Dec, Pavel Drasil, Ralph Droms, Adrian Farrel, Nick Green, 3201 Sri Gundavelli, Brian Haberman, Bernhard Haindl, Joel Halpern, Tom 3202 Herbert, Sascha Hlusiak, Lee Howard, Zdenek Jaron, Andre Kostur, 3203 Hubert Kuenig, Ted Lemon, Andy Malis, Satoru Matsushima, Tomek 3204 Mrugalski, Madhu Niraula, Alexandru Petrescu, Behcet Saikaya, Michal 3205 Skorepa, Joe Touch, Bernie Volz, Ryuji Wakikawa, Tony Whyman, Lloyd 3206 Wood and James Woodyatt. Members of the IESG also provided valuable 3207 input during their review process that greatly improved the document. 3208 Special thanks go to Stewart Bryant, Joel Halpern and Brian Haberman 3209 for their shepherding guidance during the publication of the AERO 3210 first edition. 3212 This work has further been encouraged and supported by Boeing 3213 colleagues including Kyle Bae, M. Wayne Benson, Dave Bernhardt, Cam 3214 Brodie, John Bush, Balaguruna Chidambaram, Irene Chin, Bruce Cornish, 3215 Claudiu Danilov, Don Dillenburg, Joe Dudkowski, Wen Fang, Samad 3216 Farooqui, Anthony Gregory, Jeff Holland, Seth Jahne, Brian Jaury, 3217 Greg Kimberly, Ed King, Madhuri Madhava Badgandi, Laurel Matthew, 3218 Gene MacLean III, Rob Muszkiewicz, Sean O'Sullivan, Vijay 3219 Rajagopalan, Greg Saccone, Rod Santiago, Kent Shuey, Brian Skeen, 3220 Mike Slane, Carrie Spiker, Katie Tran, Brendan Williams, Amelia 3221 Wilson, Julie Wulff, Yueli Yang, Eric Yeh and other members of the 3222 Boeing mobility, networking and autonomy teams. Kyle Bae, Wayne 3223 Benson, Katie Tran and Eric Yeh are especially acknowledged for 3224 implementing the AERO functions as extensions to the public domain 3225 OpenVPN distribution. 3227 Earlier works on NBMA tunneling approaches are found in 3228 [RFC2529][RFC5214][RFC5569]. 3230 Many of the constructs presented in this second edition of AERO are 3231 based on the author's earlier works, including: 3233 o The Internet Routing Overlay Network (IRON) 3234 [RFC6179][I-D.templin-ironbis] 3236 o Virtual Enterprise Traversal (VET) 3237 [RFC5558][I-D.templin-intarea-vet] 3239 o The Subnetwork Encapsulation and Adaptation Layer (SEAL) 3240 [RFC5320][I-D.templin-intarea-seal] 3242 o AERO, First Edition [RFC6706] 3244 Note that these works cite numerous earlier efforts that are not also 3245 cited here due to space limitations. The authors of those earlier 3246 works are acknowledged for their insights. 3248 This work is aligned with the NASA Safe Autonomous Systems Operation 3249 (SASO) program under NASA contract number NNA16BD84C. 3251 This work is aligned with the FAA as per the SE2025 contract number 3252 DTFAWA-15-D-00030. 3254 This work is aligned with the Boeing Commercial Airplanes (BCA) 3255 Internet of Things (IoT) and autonomy programs. 3257 This work is aligned with the Boeing Information Technology (BIT) 3258 MobileNet program. 3260 8. References 3261 8.1. Normative References 3263 [I-D.templin-6man-omni-interface] 3264 Templin, F. and T. Whyman, "Transmission of IPv6 Packets 3265 over Overlay Multilink Network (OMNI) Interfaces", draft- 3266 templin-6man-omni-interface-18 (work in progress), April 3267 2020. 3269 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, 3270 DOI 10.17487/RFC0791, September 1981, 3271 . 3273 [RFC0792] Postel, J., "Internet Control Message Protocol", STD 5, 3274 RFC 792, DOI 10.17487/RFC0792, September 1981, 3275 . 3277 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 3278 Requirement Levels", BCP 14, RFC 2119, 3279 DOI 10.17487/RFC2119, March 1997, 3280 . 3282 [RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in 3283 IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473, 3284 December 1998, . 3286 [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black, 3287 "Definition of the Differentiated Services Field (DS 3288 Field) in the IPv4 and IPv6 Headers", RFC 2474, 3289 DOI 10.17487/RFC2474, December 1998, 3290 . 3292 [RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander, 3293 "SEcure Neighbor Discovery (SEND)", RFC 3971, 3294 DOI 10.17487/RFC3971, March 2005, 3295 . 3297 [RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)", 3298 RFC 3972, DOI 10.17487/RFC3972, March 2005, 3299 . 3301 [RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and 3302 More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191, 3303 November 2005, . 3305 [RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast 3306 Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005, 3307 . 3309 [RFC4380] Huitema, C., "Teredo: Tunneling IPv6 over UDP through 3310 Network Address Translations (NATs)", RFC 4380, 3311 DOI 10.17487/RFC4380, February 2006, 3312 . 3314 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 3315 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 3316 DOI 10.17487/RFC4861, September 2007, 3317 . 3319 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 3320 Address Autoconfiguration", RFC 4862, 3321 DOI 10.17487/RFC4862, September 2007, 3322 . 3324 [RFC5175] Haberman, B., Ed. and R. Hinden, "IPv6 Router 3325 Advertisement Flags Option", RFC 5175, 3326 DOI 10.17487/RFC5175, March 2008, 3327 . 3329 [RFC6081] Thaler, D., "Teredo Extensions", RFC 6081, 3330 DOI 10.17487/RFC6081, January 2011, 3331 . 3333 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 3334 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 3335 May 2017, . 3337 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 3338 (IPv6) Specification", STD 86, RFC 8200, 3339 DOI 10.17487/RFC8200, July 2017, 3340 . 3342 [RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A., 3343 Richardson, M., Jiang, S., Lemon, T., and T. Winters, 3344 "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", 3345 RFC 8415, DOI 10.17487/RFC8415, November 2018, 3346 . 3348 8.2. Informative References 3350 [BGP] Huston, G., "BGP in 2015, http://potaroo.net", January 3351 2016. 3353 [I-D.ietf-6man-segment-routing-header] 3354 Filsfils, C., Dukes, D., Previdi, S., Leddy, J., 3355 Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header 3356 (SRH)", draft-ietf-6man-segment-routing-header-26 (work in 3357 progress), October 2019. 3359 [I-D.ietf-dmm-distributed-mobility-anchoring] 3360 Chan, A., Wei, X., Lee, J., Jeon, S., and C. Bernardos, 3361 "Distributed Mobility Anchoring", draft-ietf-dmm- 3362 distributed-mobility-anchoring-15 (work in progress), 3363 March 2020. 3365 [I-D.ietf-intarea-gue] 3366 Herbert, T., Yong, L., and O. Zia, "Generic UDP 3367 Encapsulation", draft-ietf-intarea-gue-09 (work in 3368 progress), October 2019. 3370 [I-D.ietf-intarea-gue-extensions] 3371 Herbert, T., Yong, L., and F. Templin, "Extensions for 3372 Generic UDP Encapsulation", draft-ietf-intarea-gue- 3373 extensions-06 (work in progress), March 2019. 3375 [I-D.ietf-intarea-tunnels] 3376 Touch, J. and M. Townsley, "IP Tunnels in the Internet 3377 Architecture", draft-ietf-intarea-tunnels-10 (work in 3378 progress), September 2019. 3380 [I-D.ietf-rtgwg-atn-bgp] 3381 Templin, F., Saccone, G., Dawra, G., Lindem, A., and V. 3382 Moreno, "A Simple BGP-based Mobile Routing System for the 3383 Aeronautical Telecommunications Network", draft-ietf- 3384 rtgwg-atn-bgp-05 (work in progress), January 2020. 3386 [I-D.templin-6man-dhcpv6-ndopt] 3387 Templin, F., "A Unified Stateful/Stateless Configuration 3388 Service for IPv6", draft-templin-6man-dhcpv6-ndopt-09 3389 (work in progress), January 2020. 3391 [I-D.templin-intarea-grefrag] 3392 Templin, F., "GRE Tunnel Level Fragmentation", draft- 3393 templin-intarea-grefrag-04 (work in progress), July 2016. 3395 [I-D.templin-intarea-seal] 3396 Templin, F., "The Subnetwork Encapsulation and Adaptation 3397 Layer (SEAL)", draft-templin-intarea-seal-68 (work in 3398 progress), January 2014. 3400 [I-D.templin-intarea-vet] 3401 Templin, F., "Virtual Enterprise Traversal (VET)", draft- 3402 templin-intarea-vet-40 (work in progress), May 2013. 3404 [I-D.templin-ironbis] 3405 Templin, F., "The Interior Routing Overlay Network 3406 (IRON)", draft-templin-ironbis-16 (work in progress), 3407 March 2014. 3409 [I-D.templin-v6ops-pdhost] 3410 Templin, F., "IPv6 Prefix Delegation and Multi-Addressing 3411 Models", draft-templin-v6ops-pdhost-25 (work in progress), 3412 January 2020. 3414 [OVPN] OpenVPN, O., "http://openvpn.net", October 2016. 3416 [RFC1035] Mockapetris, P., "Domain names - implementation and 3417 specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, 3418 November 1987, . 3420 [RFC1122] Braden, R., Ed., "Requirements for Internet Hosts - 3421 Communication Layers", STD 3, RFC 1122, 3422 DOI 10.17487/RFC1122, October 1989, 3423 . 3425 [RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191, 3426 DOI 10.17487/RFC1191, November 1990, 3427 . 3429 [RFC1812] Baker, F., Ed., "Requirements for IP Version 4 Routers", 3430 RFC 1812, DOI 10.17487/RFC1812, June 1995, 3431 . 3433 [RFC2003] Perkins, C., "IP Encapsulation within IP", RFC 2003, 3434 DOI 10.17487/RFC2003, October 1996, 3435 . 3437 [RFC2236] Fenner, W., "Internet Group Management Protocol, Version 3438 2", RFC 2236, DOI 10.17487/RFC2236, November 1997, 3439 . 3441 [RFC2492] Armitage, G., Schulter, P., and M. Jork, "IPv6 over ATM 3442 Networks", RFC 2492, DOI 10.17487/RFC2492, January 1999, 3443 . 3445 [RFC2529] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4 3446 Domains without Explicit Tunnels", RFC 2529, 3447 DOI 10.17487/RFC2529, March 1999, 3448 . 3450 [RFC2764] Gleeson, B., Lin, A., Heinanen, J., Armitage, G., and A. 3451 Malis, "A Framework for IP Based Virtual Private 3452 Networks", RFC 2764, DOI 10.17487/RFC2764, February 2000, 3453 . 3455 [RFC2784] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P. 3456 Traina, "Generic Routing Encapsulation (GRE)", RFC 2784, 3457 DOI 10.17487/RFC2784, March 2000, 3458 . 3460 [RFC2890] Dommety, G., "Key and Sequence Number Extensions to GRE", 3461 RFC 2890, DOI 10.17487/RFC2890, September 2000, 3462 . 3464 [RFC2923] Lahey, K., "TCP Problems with Path MTU Discovery", 3465 RFC 2923, DOI 10.17487/RFC2923, September 2000, 3466 . 3468 [RFC2983] Black, D., "Differentiated Services and Tunnels", 3469 RFC 2983, DOI 10.17487/RFC2983, October 2000, 3470 . 3472 [RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition 3473 of Explicit Congestion Notification (ECN) to IP", 3474 RFC 3168, DOI 10.17487/RFC3168, September 2001, 3475 . 3477 [RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener 3478 Discovery Version 2 (MLDv2) for IPv6", RFC 3810, 3479 DOI 10.17487/RFC3810, June 2004, 3480 . 3482 [RFC3819] Karn, P., Ed., Bormann, C., Fairhurst, G., Grossman, D., 3483 Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J., and L. 3484 Wood, "Advice for Internet Subnetwork Designers", BCP 89, 3485 RFC 3819, DOI 10.17487/RFC3819, July 2004, 3486 . 3488 [RFC4213] Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms 3489 for IPv6 Hosts and Routers", RFC 4213, 3490 DOI 10.17487/RFC4213, October 2005, 3491 . 3493 [RFC4251] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH) 3494 Protocol Architecture", RFC 4251, DOI 10.17487/RFC4251, 3495 January 2006, . 3497 [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A 3498 Border Gateway Protocol 4 (BGP-4)", RFC 4271, 3499 DOI 10.17487/RFC4271, January 2006, 3500 . 3502 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 3503 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 3504 2006, . 3506 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 3507 Internet Protocol", RFC 4301, DOI 10.17487/RFC4301, 3508 December 2005, . 3510 [RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery 3511 Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April 3512 2006, . 3514 [RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet 3515 Control Message Protocol (ICMPv6) for the Internet 3516 Protocol Version 6 (IPv6) Specification", STD 89, 3517 RFC 4443, DOI 10.17487/RFC4443, March 2006, 3518 . 3520 [RFC4511] Sermersheim, J., Ed., "Lightweight Directory Access 3521 Protocol (LDAP): The Protocol", RFC 4511, 3522 DOI 10.17487/RFC4511, June 2006, 3523 . 3525 [RFC4541] Christensen, M., Kimball, K., and F. Solensky, 3526 "Considerations for Internet Group Management Protocol 3527 (IGMP) and Multicast Listener Discovery (MLD) Snooping 3528 Switches", RFC 4541, DOI 10.17487/RFC4541, May 2006, 3529 . 3531 [RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick, 3532 "Internet Group Management Protocol (IGMP) / Multicast 3533 Listener Discovery (MLD)-Based Multicast Forwarding 3534 ("IGMP/MLD Proxying")", RFC 4605, DOI 10.17487/RFC4605, 3535 August 2006, . 3537 [RFC4607] Holbrook, H. and B. Cain, "Source-Specific Multicast for 3538 IP", RFC 4607, DOI 10.17487/RFC4607, August 2006, 3539 . 3541 [RFC4963] Heffner, J., Mathis, M., and B. Chandler, "IPv4 Reassembly 3542 Errors at High Data Rates", RFC 4963, 3543 DOI 10.17487/RFC4963, July 2007, 3544 . 3546 [RFC4982] Bagnulo, M. and J. Arkko, "Support for Multiple Hash 3547 Algorithms in Cryptographically Generated Addresses 3548 (CGAs)", RFC 4982, DOI 10.17487/RFC4982, July 2007, 3549 . 3551 [RFC5015] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano, 3552 "Bidirectional Protocol Independent Multicast (BIDIR- 3553 PIM)", RFC 5015, DOI 10.17487/RFC5015, October 2007, 3554 . 3556 [RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site 3557 Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214, 3558 DOI 10.17487/RFC5214, March 2008, 3559 . 3561 [RFC5320] Templin, F., Ed., "The Subnetwork Encapsulation and 3562 Adaptation Layer (SEAL)", RFC 5320, DOI 10.17487/RFC5320, 3563 February 2010, . 3565 [RFC5522] Eddy, W., Ivancic, W., and T. Davis, "Network Mobility 3566 Route Optimization Requirements for Operational Use in 3567 Aeronautics and Space Exploration Mobile Networks", 3568 RFC 5522, DOI 10.17487/RFC5522, October 2009, 3569 . 3571 [RFC5558] Templin, F., Ed., "Virtual Enterprise Traversal (VET)", 3572 RFC 5558, DOI 10.17487/RFC5558, February 2010, 3573 . 3575 [RFC5569] Despres, R., "IPv6 Rapid Deployment on IPv4 3576 Infrastructures (6rd)", RFC 5569, DOI 10.17487/RFC5569, 3577 January 2010, . 3579 [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 3580 (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, 3581 . 3583 [RFC5991] Thaler, D., Krishnan, S., and J. Hoagland, "Teredo 3584 Security Updates", RFC 5991, DOI 10.17487/RFC5991, 3585 September 2010, . 3587 [RFC6106] Jeong, J., Park, S., Beloeil, L., and S. Madanapalli, 3588 "IPv6 Router Advertisement Options for DNS Configuration", 3589 RFC 6106, DOI 10.17487/RFC6106, November 2010, 3590 . 3592 [RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful 3593 NAT64: Network Address and Protocol Translation from IPv6 3594 Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146, 3595 April 2011, . 3597 [RFC6179] Templin, F., Ed., "The Internet Routing Overlay Network 3598 (IRON)", RFC 6179, DOI 10.17487/RFC6179, March 2011, 3599 . 3601 [RFC6221] Miles, D., Ed., Ooghe, S., Dec, W., Krishnan, S., and A. 3602 Kavanagh, "Lightweight DHCPv6 Relay Agent", RFC 6221, 3603 DOI 10.17487/RFC6221, May 2011, 3604 . 3606 [RFC6273] Kukec, A., Krishnan, S., and S. Jiang, "The Secure 3607 Neighbor Discovery (SEND) Hash Threat Analysis", RFC 6273, 3608 DOI 10.17487/RFC6273, June 2011, 3609 . 3611 [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer 3612 Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, 3613 January 2012, . 3615 [RFC6438] Carpenter, B. and S. Amante, "Using the IPv6 Flow Label 3616 for Equal Cost Multipath Routing and Link Aggregation in 3617 Tunnels", RFC 6438, DOI 10.17487/RFC6438, November 2011, 3618 . 3620 [RFC6706] Templin, F., Ed., "Asymmetric Extended Route Optimization 3621 (AERO)", RFC 6706, DOI 10.17487/RFC6706, August 2012, 3622 . 3624 [RFC6864] Touch, J., "Updated Specification of the IPv4 ID Field", 3625 RFC 6864, DOI 10.17487/RFC6864, February 2013, 3626 . 3628 [RFC6935] Eubanks, M., Chimento, P., and M. Westerlund, "IPv6 and 3629 UDP Checksums for Tunneled Packets", RFC 6935, 3630 DOI 10.17487/RFC6935, April 2013, 3631 . 3633 [RFC6936] Fairhurst, G. and M. Westerlund, "Applicability Statement 3634 for the Use of IPv6 UDP Datagrams with Zero Checksums", 3635 RFC 6936, DOI 10.17487/RFC6936, April 2013, 3636 . 3638 [RFC7269] Chen, G., Cao, Z., Xie, C., and D. Binet, "NAT64 3639 Deployment Options and Experience", RFC 7269, 3640 DOI 10.17487/RFC7269, June 2014, 3641 . 3643 [RFC7333] Chan, H., Ed., Liu, D., Seite, P., Yokota, H., and J. 3644 Korhonen, "Requirements for Distributed Mobility 3645 Management", RFC 7333, DOI 10.17487/RFC7333, August 2014, 3646 . 3648 [RFC7421] Carpenter, B., Ed., Chown, T., Gont, F., Jiang, S., 3649 Petrescu, A., and A. Yourtchenko, "Analysis of the 64-bit 3650 Boundary in IPv6 Addressing", RFC 7421, 3651 DOI 10.17487/RFC7421, January 2015, 3652 . 3654 [RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I., 3655 Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent 3656 Multicast - Sparse Mode (PIM-SM): Protocol Specification 3657 (Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March 3658 2016, . 3660 [RFC8086] Yong, L., Ed., Crabbe, E., Xu, X., and T. Herbert, "GRE- 3661 in-UDP Encapsulation", RFC 8086, DOI 10.17487/RFC8086, 3662 March 2017, . 3664 [RFC8201] McCann, J., Deering, S., Mogul, J., and R. Hinden, Ed., 3665 "Path MTU Discovery for IP version 6", STD 87, RFC 8201, 3666 DOI 10.17487/RFC8201, July 2017, 3667 . 3669 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 3670 Decraene, B., Litkowski, S., and R. Shakir, "Segment 3671 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 3672 July 2018, . 3674 [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol 3675 Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, 3676 . 3678 [RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J., 3679 Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header 3680 (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020, 3681 . 3683 Appendix A. AERO Alternate Encapsulations 3685 When GUE encapsulation is not needed, AERO can use common 3686 encapsulations such as IP-in-IP [RFC2003][RFC2473][RFC4213], Generic 3687 Routing Encapsulation (GRE) [RFC2784][RFC2890] and others. The 3688 encapsulation is therefore only differentiated from non-AERO tunnels 3689 through the application of AERO control messaging and not through, 3690 e.g., a well-known UDP port number. 3692 As for GUE encapsulation, alternate AERO encapsulation formats may 3693 require encapsulation layer fragmentation. For simple IP-in-IP 3694 encapsulation, an IPv6 fragment header is inserted directly between 3695 the inner and outer IP headers when needed, i.e., even if the outer 3696 header is IPv4. The IPv6 Fragment Header is identified to the outer 3697 IP layer by its IP protocol number, and the Next Header field in the 3698 IPv6 Fragment Header identifies the inner IP header version. For GRE 3699 encapsulation, a GRE fragment header is inserted within the GRE 3700 header [I-D.templin-intarea-grefrag]. 3702 Figure 6 shows the AERO IP-in-IP encapsulation format before any 3703 fragmentation is applied: 3705 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3706 | Outer IPv4 Header | | Outer IPv6 Header | 3707 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3708 |IPv6 Frag Header (optional)| |IPv6 Frag Header (optional)| 3709 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3710 | Inner IP Header | | Inner IP Header | 3711 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3712 | | | | 3713 ~ ~ ~ ~ 3714 ~ Inner Packet Body ~ ~ Inner Packet Body ~ 3715 ~ ~ ~ ~ 3716 | | | | 3717 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3719 Minimal Encapsulation in IPv4 Minimal Encapsulation in IPv6 3721 Figure 6: Minimal Encapsulation Format using IP-in-IP 3723 Figure 7 shows the AERO GRE encapsulation format before any 3724 fragmentation is applied: 3726 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3727 | Outer IP Header | 3728 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3729 | GRE Header | 3730 | (with checksum, key, etc..) | 3731 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3732 | GRE Fragment Header (optional)| 3733 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3734 | Inner IP Header | 3735 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3736 | | 3737 ~ ~ 3738 ~ Inner Packet Body ~ 3739 ~ ~ 3740 | | 3741 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3743 Figure 7: Minimal Encapsulation Using GRE 3745 Alternate encapsulation may be preferred in environments where GUE 3746 encapsulation would add unnecessary overhead. For example, certain 3747 low-bandwidth wireless data links may benefit from a reduced 3748 encapsulation overhead. 3750 GUE encapsulation can traverse network paths that are inaccessible to 3751 non-UDP encapsulations, e.g., for crossing Network Address 3752 Translators (NATs). More and more, network middleboxes are also 3753 being configured to discard packets that include anything other than 3754 a well-known IP protocol such as UDP and TCP. It may therefore be 3755 necessary to determine the potential for middlebox filtering before 3756 enabling alternate encapsulation in a given environment. 3758 In addition to IP-in-IP, GRE and GUE, AERO can also use security 3759 encapsulations such as IPsec, TLS/SSL, DTLS, etc. In that case, AERO 3760 control messaging and route determination occur before security 3761 encapsulation is applied for outgoing packets and after security 3762 decapsulation is applied for incoming packets. 3764 AERO is especially well suited for use with VPN system encapsulations 3765 such as OpenVPN [OVPN]. 3767 Appendix B. Non-Normative Considerations 3769 AERO can be applied to a multitude of Internetworking scenarios, with 3770 each having its own adaptations. The following considerations are 3771 provided as non-normative guidance: 3773 B.1. Implementation Strategies for Route Optimization 3775 Route optimization as discussed in Section 3.17 results in the route 3776 optimization source (ROS) creating an asymmetric neighbor cache entry 3777 for the target neighbor. The neighbor cache entry is maintained for 3778 at most REACHABLE_TIME seconds and then deleted unless updated. In 3779 order to refresh the neighbor cache entry lifetime before the 3780 ReachableTime timer expires, the specification requires 3781 implementations to issue a new NS/NA exchange to reset ReachableTime 3782 to REACHABLE_TIME seconds while data packets are still flowing. 3783 However, the decision of when to initiate a new NS/NA exchange and to 3784 perpetuate the process is left as an implementation detail. 3786 One possible strategy may be to monitor the neighbor cache entry 3787 watching for data packets for (REACHABLE_TIME - 5) seconds. If any 3788 data packets have been sent to the neighbor within this timeframe, 3789 then send an NS to receive a new NA. If no data packets have been 3790 sent, wait for 5 additional seconds and send an immediate NS if any 3791 data packets are sent within this "expiration pending" 5 second 3792 window. If no additional data packets are sent within the 5 second 3793 window, delete the neighbor cache entry. 3795 The monitoring of the neighbor data packet traffic therefore becomes 3796 an asymmetric ongoing process during the neighbor cache entry 3797 lifetime. If the neighbor cache entry expires, future data packets 3798 will trigger a new NS/NA exchange while the packets themselves are 3799 delivered over a longer path until route optimization state is re- 3800 established. 3802 B.2. Implicit Mobility Management 3804 AERO interface neighbors MAY provide a configuration option that 3805 allows them to perform implicit mobility management in which no ND 3806 messaging is used. In that case, the Client only transmits packets 3807 over a single interface at a time, and the neighbor always observes 3808 packets arriving from the Client from the same link-layer source 3809 address. 3811 If the Client's underlying interface address changes (either due to a 3812 readdressing of the original interface or switching to a new 3813 interface) the neighbor immediately updates the neighbor cache entry 3814 for the Client and begins accepting and sending packets according to 3815 the Client's new address. This implicit mobility method applies to 3816 use cases such as cellphones with both WiFi and Cellular interfaces 3817 where only one of the interfaces is active at a given time, and the 3818 Client automatically switches over to the backup interface if the 3819 primary interface fails. 3821 B.3. Direct Underlying Interfaces 3823 When a Client's AERO interface is configured over a Direct interface, 3824 the neighbor at the other end of the Direct link can receive packets 3825 without any encapsulation. In that case, the Client sends packets 3826 over the Direct link according to QoS preferences. If the Direct 3827 interface has the highest QoS preference, then the Client's IP 3828 packets are transmitted directly to the peer without going through an 3829 ANET/INET. If other interfaces have higher QoS preferences, then the 3830 Client's IP packets are transmitted via a different interface, which 3831 may result in the inclusion of Proxys, Servers and Bridges in the 3832 communications path. Direct interfaces must be tested periodically 3833 for reachability, e.g., via NUD. 3835 B.4. Operation on AERO Links with /64 ASPs 3837 IPv6 AERO links typically have MSPs that aggregate many candidate 3838 MNPs of length /64 or shorter. However, in some cases it may be 3839 desirable to use AERO over links that have only a /64 MSP. This can 3840 be accommodated by treating all Clients on the AERO link as simple 3841 hosts that receive /128 prefix delegations. 3843 In that case, the Client sends an RS message to the Server the same 3844 as for ordinary AERO links. The Server responds with an RA message 3845 that includes one or more /128 prefixes (i.e., singleton addresses) 3846 that include the /64 MSP prefix along with an interface identifier 3847 portion to be assigned to the Client. The Client and Server then 3848 configure their AERO addresses based on the interface identifier 3849 portions of the /128s (i.e., the lower 64 bits) and not based on the 3850 /64 prefix (i.e., the upper 64 bits). 3852 For example, if the MSP for the host-only IPv6 AERO link is 3853 2001:db8:1000:2000::/64, each Client will receive one or more /128 3854 IPv6 prefix delegations such as 2001:db8:1000:2000::1/128, 3855 2001:db8:1000:2000::2/128, etc. When the Client receives the prefix 3856 delegations, it assigns the AERO addresses fe80::1, fe80::2, etc. to 3857 the AERO interface, and assigns the global IPv6 addresses (i.e., the 3858 /128s) to either the AERO interface or an internal virtual interface 3859 such as a loopback. In this arrangement, the Client conducts route 3860 optimization in the same sense as discussed in Section 3.17. 3862 This specification has applicability for nodes that act as a Client 3863 on an "upstream" AERO link, but also act as a Server on "downstream" 3864 AERO links. More specifically, if the node acts as a Client to 3865 receive a /64 prefix from the upstream AERO link it can then act as a 3866 Server to provision /128s to Clients on downstream AERO links. 3868 B.5. AERO Critical Infrastructure Considerations 3870 AERO Bridges can be either Commercial off-the Shelf (COTS) standard 3871 IP routers or virtual machines in the cloud. Bridges must be 3872 provisioned, supported and managed by the INET administrative 3873 authority, and connected to the Bridges of other INETs via inter- 3874 domain peerings. Cost for purchasing, configuring and managing 3875 Bridges is nominal even for very large AERO links. 3877 AERO Servers can be standard dedicated server platforms, but most 3878 often will be deployed as virtual machines in the cloud. The only 3879 requirements for Servers are that they can run the AERO user-level 3880 code and have at least one network interface connection to the INET. 3881 As with Bridges, Servers must be provisioned, supported and managed 3882 by the INET administrative authority. Cost for purchasing, 3883 configuring and managing Servers is nominal especially for virtual 3884 Servers hosted in the cloud. 3886 AERO Proxys are most often standard dedicated server platforms with 3887 one network interface connected to the ANET and a second interface 3888 connected to an INET. As with Servers, the only requirements are 3889 that they can run the AERO user-level code and have at least one 3890 interface connection to the INET. Proxys must be provisioned, 3891 supported and managed by the ANET administrative authority. Cost for 3892 purchasing, configuring and managing Proxys is nominal, and borne by 3893 the ANET administrative authority. 3895 AERO Relays can be any dedicated server or COTS router platform 3896 connected to INETs and/or EUNs. The Relay joins the SPAN and engages 3897 in eBGP peering with one or more Bridges as a stub AS. The Relay 3898 then injects its MNPs and/or non-MNP prefixes into the BGP routing 3899 system, and provisions the prefixes to its downstream-attached 3900 networks. The Relay can perform ROS/ROR services the same as for any 3901 Server, and can route between the MNP and non-MNP address spaces. 3903 B.6. AERO Server Failure Implications 3905 AERO Servers may appear as a single point of failure in the 3906 architecture, but such is not the case since all Servers on the link 3907 provide identical services and loss of a Server does not imply 3908 immediate and/or comprehensive communication failures. Although 3909 Clients typically associate with a single Server at a time, Server 3910 failure is quickly detected and conveyed by Bidirectional Forward 3911 Detection (BFD) and/or proactive NUD allowing Clients to migrate to 3912 new Servers. 3914 If a Server fails, ongoing packet forwarding to Clients will continue 3915 by virtue of the asymmetric neighbor cache entries that have already 3916 been established in route optimization sources (ROSs). If a Client 3917 also experiences mobility events at roughly the same time the Server 3918 fails, unsolicited NA messages may be lost but proxy neighbor cache 3919 entries in the DEPARTED state will ensure that packet forwarding to 3920 the Client's new locations will continue for up to DEPART_TIME 3921 seconds. 3923 If a Client is left without a Server for an extended timeframe (e.g., 3924 greater than REACHABLETIIME seconds) then existing asymmetric 3925 neighbor cache entries will eventually expire and both ongoing and 3926 new communications will fail. The original source will continue to 3927 retransmit until the Client has established a new Server 3928 relationship, after which time continuous communications will resume. 3930 Therefore, providing many Servers on the link with high availability 3931 profiles provides resilience against loss of individual Servers and 3932 assurance that Clients can establish new Server relationships quickly 3933 in event of a Server failure. 3935 B.7. AERO Client / Server Architecture 3937 The AERO architectural model is client / server in the control plane, 3938 with route optimization in the data plane. The same as for common 3939 Internet services, the AERO Client discovers the addresses of AERO 3940 Servers and selects one Server to connect to. The AERO service is 3941 analogous to common Internet services such as google.com, yahoo.com, 3942 cnn.com, etc. However, there is only one AERO service for the link 3943 and all Servers provide identical services. 3945 Common Internet services provide differing strategies for advertising 3946 server addresses to clients. The strategy is conveyed through the 3947 DNS resource records returned in response to name resolution queries. 3948 As of January 2020 Internet-based 'nslookup' services were used to 3949 determine the following: 3951 o When a client resolves the domainname "google.com", the DNS always 3952 returns one A record (i.e., an IPv4 address) and one AAAA record 3953 (i.e., an IPv6 address). The client receives the same addresses 3954 each time it resolves the domainname via the same DNS resolver, 3955 but may receive different addresses when it resolves the 3956 domainname via different DNS resolvers. But, in each case, 3957 exactly one A and one AAAA record are returned. 3959 o When a client resolves the domainname "ietf.org", the DNS always 3960 returns one A record and one AAAA record with the same addresses 3961 regardless of which DNS resolver is used. 3963 o When a client resolves the domainname "yahoo.com", the DNS always 3964 returns a list of 4 A records and 4 AAAA records. Each time the 3965 client resolves the domainname via the same DNS resolver, the same 3966 list of addresses are returned but in randomized order (i.e., 3967 consistent with a DNS round-robin strategy). But, interestingly, 3968 the same addresses are returned (albeit in randomized order) when 3969 the domainname is resolved via different DNS resolvers. 3971 o When a client resolves the domainname "amazon.com", the DNS always 3972 returns a list of 3 A records and no AAAA records. As with 3973 "yahoo.com", the same three A records are returned from any 3974 worldwide Internet connection point in randomized order. 3976 The above example strategies show differing approaches to Internet 3977 resilience and service distribution offered by major Internet 3978 services. The Google approach exposes only a single IPv4 and a 3979 single IPv6 address to clients. Clients can then select whichever IP 3980 protocol version offers the best response, but will always use the 3981 same IP address according to the current Internet connection point. 3982 This means that the IP address offered by the network must lead to a 3983 highly-available server and/or service distribution point. In other 3984 words, resilience is predicated on high availability within the 3985 network and with no client-initiated failovers expected (i.e., it is 3986 all-or-nothing from the client's perspective). However, Google does 3987 provide for worldwide distributed service distribution by virtue of 3988 the fact that each Internet connection point responds with a 3989 different IPv6 and IPv4 address. The IETF approach is like google 3990 (all-or-nothing from the client's perspective), but provides only a 3991 single IPv4 or IPv6 address on a worldwide basis. This means that 3992 the addresses must be made highly-available at the network level with 3993 no client failover possibility, and if there is any worldwide service 3994 distribution it would need to be conducted by a network element that 3995 is reached via the IP address acting as a service distribution point. 3997 In contrast to the Google and IETF philosophies, Yahoo and Amazon 3998 both provide clients with a (short) list of IP addresses with Yahoo 3999 providing both IP protocol versions and Amazon as IPv4-only. The 4000 order of the list is randomized with each name service query 4001 response, with the effect of round-robin load balancing for service 4002 distribution. With a short list of addresses, there is still 4003 expectation that the network will implement high availability for 4004 each address but in case any single address fails the client can 4005 switch over to using a different address. The balance then becomes 4006 one of function in the network vs function in the end system. 4008 The same implications observed for common highly-available services 4009 in the Internet apply also to the AERO client/server architecture. 4010 When an AERO Client connects to one or more ANETs, it discovers one 4011 or more AERO Server addresses through the mechanisms discussed in 4012 earlier sections. Each Server address presumably leads to a fault- 4013 tolerant clustering arrangement such as supported by Linux-HA, 4014 Extended Virtual Synchrony or Paxos. Such an arrangement has 4015 precedence in common Internet service deployments in lightweight 4016 virtual machines without requiring expensive hardware deployment. 4017 Similarly, common Internet service deployments set service IP 4018 addresses on service distribution points that may relay requests to 4019 many different servers. 4021 For AERO, the expectation is that a combination of the Google/IETF 4022 and Yahoo/Amazon philosophies would be employed. The AERO Client 4023 connects to different ANET access points and can receive 1-2 Server 4024 AERO addresses at each point. It then selects one AERO Server 4025 address, and engages in RS/RA exchanges with the same Server from all 4026 ANET connections. The Client remains with this Server unless or 4027 until the Server fails, in which case it can switch over to an 4028 alternate Server. The Client can likewise switch over to a different 4029 Server at any time if there is some reason for it to do so. So, the 4030 AERO expectation is for a balance of function in the network and end 4031 system, with fault tolerance and resilience at both levels. 4033 Appendix C. Change Log 4035 << RFC Editor - remove prior to publication >> 4037 Changes from draft-templin-intarea-6706bis-47 to draft-templin- 4038 intrea-6706bis-48: 4040 o SEND/CGA. 4042 Changes from draft-templin-intarea-6706bis-46 to draft-templin- 4043 intrea-6706bis-47: 4045 o Major changes to align with Teredo, including changed AERO "Relay" 4046 to "Bridge", and changed AERO "Gateway" to "Relay". The term 4047 "[Rr]elay" now refers to exactly the same thing in both AERO and 4048 Teredo. 4050 o Changed to use Teredo message authentication instead of SEND. 4052 Changes from draft-templin-intarea-6706bis-42 to draft-templin- 4053 intrea-6706bis-43: 4055 o Segment Routing. 4057 Changes from draft-templin-intarea-6706bis-39 to draft-templin- 4058 intrea-6706bis-40: 4060 o Teredo. 4062 Changes from draft-templin-intarea-6706bis-38 to draft-templin- 4063 intrea-6706bis-39: 4065 o Major clarifications and simplifications of SPAN fragmentation/ 4066 reassembly. 4068 o Revised AERO address format to support prefix lengths up to 112. 4070 o New method for forming SPAN Client Prefixes and population in the 4071 routing system. 4073 o Updates RFC4443 to set a new value in the ICMP PTB Code field. 4075 Changes from draft-templin-intarea-6706bis-35 to draft-templin- 4076 intrea-6706bis-36: 4078 o Clients in the open Internet secured using SEND/CGA. 4080 Changes from draft-templin-intarea-6706bis-32 to draft-templin- 4081 intrea-6706bis-33: 4083 o Updated Proxy discussion with "point-to-multipoint" server 4084 coordination 4086 o Significant updates to Address Resolution and NUD to include 4087 correct addresses in messages 4089 o Differentiate between NS(AR) and NS(NUD) as their addresses and 4090 use cases differ. 4092 Changes from draft-templin-intarea-6706bis-30 to draft-templin- 4093 intrea-6706bis-31: 4095 o Added "advisory PTB messages" under FAA SE2025 contract number 4096 DTFAWA-15-D-00030. 4098 Changes from draft-templin-intarea-6706bis-29 to draft-templin- 4099 intrea-6706bis-30: 4101 o Deprecate "primary" concept. Now, RS/RA keepalives are maintained 4102 over *all* underlying interfaces (i.e., and not just one primary). 4104 Changes from draft-templin-intarea-6706bis-28 to draft-templin- 4105 intrea-6706bis-29: 4107 o Changed OMNI interface citation to "draft-templin-6man-omni- 4108 interface" 4110 o Changed SPAN Service Prefix to fd80::/10. 4112 o Changed S/TLLAO format to include 'S' bit for ifIndex 4113 corresponding to the underlying interface that is Source of ND 4114 message. 4116 o Updated Path MTU 4118 Changes from draft-templin-intarea-6706bis-27 to draft-templin- 4119 intrea-6706bis-28: 4121 o MTU and fragmentation. 4123 Changes from draft-templin-intarea-6706bis-26 to draft-templin- 4124 intrea-6706bis-27: 4126 o MTU and fragmentation. 4128 o SPAN Service Prefix set to fd00::/10 4130 o Client SPAN addresses defined. 4132 Changes from draft-templin-intarea-6706bis-25 to draft-templin- 4133 intrea-6706bis-26: 4135 o MTU and RA configuration information updated. 4137 Changes from draft-templin-intarea-6706bis-24 to draft-templin- 4138 intrea-6706bis-25: 4140 o Added concept of "primary" to allow for proxyed RS/RA over only 4141 selected underlying interfaces. 4143 o General Cleanup. 4145 Changes from draft-templin-intarea-6706bis-23 to draft-templin- 4146 intrea-6706bis-24: 4148 o OMNI interface spec now a normative reference. 4150 o Use REACHABLE_TIME as the nominal Router Lifetime to return in 4151 RAs. 4153 o General cleanup. 4155 Changes from draft-templin-intarea-6706bis-22 to draft-templin- 4156 intrea-6706bis-23: 4158 o Choice of using either RS/RA or unsolicited NA for old Server 4159 notification. 4161 o General cleanup. 4163 Changes from draft-templin-intarea-6706bis-21 to draft-templin- 4164 intrea-6706bis-22: 4166 o Tightened up text on Proxy. 4168 o Removed unnecessarily restrictive texts. 4170 o General cleanup. 4172 Changes from draft-templin-intarea-6706bis-20 to draft-templin- 4173 intrea-6706bis-21: 4175 o Clarified relationship between OMNI and S/TLLAO ifIndex-tuples. 4177 o Important text in Section 13.15.3 on Servers timing out Clients 4178 that have gone silent without sending a departure notification. 4180 o New text on RS/RA as "hints of forward progress" for proactive 4181 NUD. 4183 Changes from draft-templin-intarea-6706bis-19 to draft-templin- 4184 intrea-6706bis-20: 4186 o Included new route optimization source and destination addressing 4187 strategy. Now, route optimization maintenance uses the address of 4188 the existing Server instead of the data packet destination address 4189 so that less pressure is placed on the BGP routing system 4190 convergence time and Server constancy is supported. 4192 o Included new method for releasing from old MSE without requiring 4193 Client messaging. 4195 o Included references to new OMNI interface spec (including the OMNI 4196 option). 4198 o New appendix on AERO Client/Server architecture. 4200 Changes from draft-templin-intarea-6706bis-18 to draft-templin- 4201 intrea-6706bis-19: 4203 o Changed Proxy/Server keepalives to use "proactive NUD" in a manner 4204 that parallels BFD 4206 Changes from draft-templin-intarea-6706bis-17 to draft-templin- 4207 intrea-6706bis-18: 4209 o Discuss how AERO option is used in relation to S/TLLAOs 4211 o New text on Bidirectional Forwarding Detection (BFD) 4213 o Cleaned up usage (and non-usage) of unsolicited NAs 4215 o New appendix on Server failures 4217 Changes from draft-templin-intarea-6706bis-15 to draft-templin- 4218 intrea-6706bis-17: 4220 o S/TLLAO now includes multiple link-layer addresses within a single 4221 option instead of requiring multiple options 4223 o New unsolicited NA message to inform the old link that a Client 4224 has moved to a new link 4226 Changes from draft-templin-intarea-6706bis-14 to draft-templin- 4227 intrea-6706bis-15: 4229 o MTU and fragmentation 4231 o New details in movement to new Server 4233 Changes from draft-templin-intarea-6706bis-13 to draft-templin- 4234 intrea-6706bis-14: 4236 o Security based on secured tunnels, ingress filtering, MAP list and 4237 ROS list 4239 Changes from draft-templin-intarea-6706bis-12 to draft-templin- 4240 intrea-6706bis-13: 4242 o New paragraph in Section 3.6 on AERO interface layering over 4243 secured tunnels 4245 o Removed extraneous text in Section 3.7 4247 o Added new detail to the forwarding algorithm in Section 3.9 4249 o Clarified use of fragmentation 4250 o Route optimization now supported for both MNP and non-MNP-based 4251 prefixes 4253 o Relays are now seen as link-layer elements in the architecture. 4255 o Built out multicast section in detail. 4257 o New Appendix on implementation considerations for route 4258 optimization. 4260 Changes from draft-templin-intarea-6706bis-11 to draft-templin- 4261 intrea-6706bis-12: 4263 o Introduced Gateways as a new AERO element for connecting 4264 Correspondent Nodes on INET links 4266 o Introduced terms "Access Network (ANET)" and "Internetwork (INET)" 4268 o Changed "ASP" to "MSP", and "ACP" to "MNP" 4270 o New figure on the relation of Segments to the SPAN and AERO link 4272 o New "S" bit in S/TLLAO to indicate the "Source" S/TLLAO as opposed 4273 to additional S/TLLAOs 4275 o Changed Interface ID for Servers from 255 to 0xffff 4277 o Significant updates to Route Optimization, NUD, and Mobility 4278 Management 4280 o New Section on Multicast 4282 o New Section on AERO Clients in the open Internetwork 4284 o New Section on Operation over multiple AERO links (VLANs over the 4285 SPAN) 4287 o New Sections on DNS considerations and Transition considerations 4289 o 4291 Changes from draft-templin-intarea-6706bis-10 to draft-templin- 4292 intrea-6706bis-11: 4294 o Added The SPAN 4296 Changes from draft-templin-intarea-6706bis-09 to draft-templin- 4297 intrea-6706bis-10: 4299 o Orphaned packets in flight (e.g., when a neighbor cache entry is 4300 in the DEPARTED state) are now forwarded at the link layer instead 4301 of at the network layer. Forwarding at the network layer can 4302 result in routing loops and/or excessive delays of forwarded 4303 packets while the routing system is still reconverging. 4305 o Update route optimization to clarify the unsecured nature of the 4306 first NS used for route discovery 4308 o Many cleanups and clarifications on ND messaging parameters 4310 Changes from draft-templin-intarea-6706bis-08 to draft-templin- 4311 intrea-6706bis-09: 4313 o Changed PRL to "MAP list" 4315 o For neighbor cache entries, changed "static" to "symmetric", and 4316 "dynamic" to "asymmetric" 4318 o Specified Proxy RS/RA exchanges with Servers on behalf of Clients 4320 o Added discussion of unsolicited NAs in Section 3.16, and included 4321 forward reference to Section 3.18 4323 o Added discussion of AERO Clients used as critical infrastructure 4324 elements to connect fixed networks. 4326 o Added network-based VPN under security considerations 4328 Changes from draft-templin-intarea-6706bis-07 to draft-templin- 4329 intrea-6706bis-08: 4331 o New section on AERO-Aware Access Router 4333 Changes from draft-templin-intarea-6706bis-06 to draft-templin- 4334 intrea-6706bis-07: 4336 o Added "R" bit for release of PDs. Now have a full RS/RA service 4337 that can do PD without requiring DHCPv6 messaging over-the-air 4339 o Clarifications on solicited vs unsolicited NAs 4341 o Clarified use of MAX_NEIGHBOR_ADVERTISEMENT for the purpose of 4342 increase reliability 4344 Changes from draft-templin-intarea-6706bis-05 to draft-templin- 4345 intrea-6706bis-06: 4347 o Major re-work and simplification of Route Optimization function 4349 o Added Distributed Mobility Management (DMM) and Mobility Anchor 4350 Point (MAP) terminology 4352 o New section on "AERO Critical Infrastructure Element 4353 Considerations" demonstrating low overall cost for the service 4355 o minor text revisions and deletions 4357 o removed extraneous appendices 4359 Changes from draft-templin-intarea-6706bis-04 to draft-templin- 4360 intrea-6706bis-05: 4362 o New Appendix E on S/TLLAO Extensions for special-purpose links. 4363 Discussed ATN/IPS as example. 4365 o New sentence in introduction to declare appendices as non- 4366 normative. 4368 Changes from draft-templin-intarea-6706bis-03 to draft-templin- 4369 intrea-6706bis-04: 4371 o Added definitions for Potential Router List (PRL) and secure 4372 enclave 4374 o Included text on mapping transport layer port numbers to network 4375 layer DSCP values 4377 o Added reference to DTLS and DMM Distributed Mobility Anchoring 4378 working group document 4380 o Reworked Security Considerations 4382 o Updated references. 4384 Changes from draft-templin-intarea-6706bis-02 to draft-templin- 4385 intrea-6706bis-03: 4387 o Added new section on SEND. 4389 o Clarifications on "AERO Address" section. 4391 o Updated references and added new reference for RFC8086. 4393 o Security considerations updates. 4395 o General text clarifications and cleanup. 4397 Changes from draft-templin-intarea-6706bis-01 to draft-templin- 4398 intrea-6706bis-02: 4400 o Note on encapsulation avoidance in Section 4. 4402 Changes from draft-templin-intarea-6706bis-00 to draft-templin- 4403 intrea-6706bis-01: 4405 o Remove DHCPv6 Server Release procedures that leveraged the old way 4406 Relays used to "route" between Server link-local addresses 4408 o Remove all text relating to Relays needing to do any AERO-specific 4409 operations 4411 o Proxy sends RS and receives RA from Server using SEND. Use CGAs 4412 as source addresses, and destination address of RA reply is to the 4413 AERO address corresponding to the Client's ACP. 4415 o Proxy uses SEND to protect RS and authenticate RA (Client does not 4416 use SEND, but rather relies on subnetwork security. When the 4417 Proxy receives an RS from the Client, it creates a new RS using 4418 its own addresses as the source and uses SEND with CGAs to send a 4419 new RS to the Server. 4421 o Emphasize distributed mobility management 4423 o AERO address-based RS injection of ACP into underlying routing 4424 system. 4426 Changes from draft-templin-aerolink-82 to draft-templin-intarea- 4427 6706bis-00: 4429 o Document use of NUD (NS/NA) for reliable link-layer address 4430 updates as an alternative to unreliable unsolicited NA. 4431 Consistent with Section 7.2.6 of RFC4861. 4433 o Server adds additional layer of encapsulation between outer and 4434 inner headers of NS/NA messages for transmission through Relays 4435 that act as vanilla IPv6 routers. The messages include the AERO 4436 Server Subnet Router Anycast address as the source and the Subnet 4437 Router Anycast address corresponding to the Client's ACP as the 4438 destination. 4440 o Clients use Subnet Router Anycast address as the encapsulation 4441 source address when the access network does not provide a 4442 topologically-fixed address. 4444 Author's Address 4446 Fred L. Templin (editor) 4447 Boeing Research & Technology 4448 P.O. Box 3707 4449 Seattle, WA 98124 4450 USA 4452 Email: fltemplin@acm.org