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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, April 8, 2020 5 rfc6179, rfc6706 (if 6 approved) 7 Intended status: Standards Track 8 Expires: October 10, 2020 10 Asymmetric Extended Route Optimization (AERO) 11 draft-templin-intarea-6706bis-39 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, mobile Virtual Private Networks 26 (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 October 10, 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) . . . . . . . . 10 65 3.1. AERO Link Reference Model . . . . . . . . . . . . . . . . 10 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 3.6. AERO Interface Characteristics . . . . . . . . . . . . . 20 71 3.7. AERO Interface Initialization . . . . . . . . . . . . . . 24 72 3.7.1. AERO Server/Gateway Behavior . . . . . . . . . . . . 24 73 3.7.2. AERO Proxy Behavior . . . . . . . . . . . . . . . . . 25 74 3.7.3. AERO Client Behavior . . . . . . . . . . . . . . . . 25 75 3.7.4. AERO Relay Behavior . . . . . . . . . . . . . . . . . 25 76 3.8. AERO Interface Neighbor Cache Maintenance . . . . . . . . 26 77 3.9. AERO Interface Encapsulation and Re-encapsulation . . . . 28 78 3.10. AERO Interface Decapsulation . . . . . . . . . . . . . . 29 79 3.11. AERO Interface Data Origin Authentication . . . . . . . . 29 80 3.12. AERO Interface MTU and Fragmentation . . . . . . . . . . 29 81 3.13. AERO Interface Forwarding Algorithm . . . . . . . . . . . 31 82 3.13.1. Client Forwarding Algorithm . . . . . . . . . . . . 32 83 3.13.2. Proxy Forwarding Algorithm . . . . . . . . . . . . . 32 84 3.13.3. Server/Gateway Forwarding Algorithm . . . . . . . . 33 85 3.13.4. Relay Forwarding Algorithm . . . . . . . . . . . . . 35 86 3.14. AERO Interface Error Handling . . . . . . . . . . . . . . 35 87 3.15. AERO Router Discovery, Prefix Delegation and 88 Autoconfiguration . . . . . . . . . . . . . . . . . . . . 38 89 3.15.1. AERO ND/PD Service Model . . . . . . . . . . . . . . 38 90 3.15.2. AERO Client Behavior . . . . . . . . . . . . . . . . 38 91 3.15.3. AERO Server Behavior . . . . . . . . . . . . . . . . 40 92 3.16. The AERO Proxy . . . . . . . . . . . . . . . . . . . . . 43 93 3.16.1. Detecting and Responding to Server Failures . . . . 45 94 3.16.2. Point-to-Multipoint Server Coordindation . . . . . . 46 95 3.17. AERO Route Optimization . . . . . . . . . . . . . . . . . 46 96 3.17.1. Route Optimization Initiation . . . . . . . . . . . 47 97 3.17.2. Relaying the NS . . . . . . . . . . . . . . . . . . 47 98 3.17.3. Processing the NS and Sending the NA . . . . . . . . 48 99 3.17.4. Relaying the NA . . . . . . . . . . . . . . . . . . 49 100 3.17.5. Processing the NA . . . . . . . . . . . . . . . . . 49 101 3.17.6. Route Optimization Maintenance . . . . . . . . . . . 49 102 3.18. Neighbor Unreachability Detection (NUD) . . . . . . . . . 50 103 3.19. Mobility Management and Quality of Service (QoS) . . . . 52 104 3.19.1. Mobility Update Messaging . . . . . . . . . . . . . 52 105 3.19.2. Announcing Link-Layer Address and/or QoS Preference 106 Changes . . . . . . . . . . . . . . . . . . . . . . 53 107 3.19.3. Bringing New Links Into Service . . . . . . . . . . 53 108 3.19.4. Removing Existing Links from Service . . . . . . . . 54 109 3.19.5. Moving to a New Server . . . . . . . . . . . . . . . 54 110 3.20. Multicast . . . . . . . . . . . . . . . . . . . . . . . . 55 111 3.20.1. Source-Specific Multicast (SSM) . . . . . . . . . . 55 112 3.20.2. Any-Source Multicast (ASM) . . . . . . . . . . . . . 57 113 3.20.3. Bi-Directional PIM (BIDIR-PIM) . . . . . . . . . . . 57 114 3.21. Operation over Multiple AERO Links (VLANs) . . . . . . . 58 115 3.22. DNS Considerations . . . . . . . . . . . . . . . . . . . 59 116 3.23. Transition Considerations . . . . . . . . . . . . . . . . 59 117 3.24. Detecting and Reacting to Server and Relay Failures . . . 60 118 3.25. AERO Clients on the Open Internet . . . . . . . . . . . . 60 119 4. Implementation Status . . . . . . . . . . . . . . . . . . . . 62 120 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 62 121 6. Security Considerations . . . . . . . . . . . . . . . . . . . 62 122 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 64 123 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 66 124 8.1. Normative References . . . . . . . . . . . . . . . . . . 66 125 8.2. Informative References . . . . . . . . . . . . . . . . . 67 126 Appendix A. AERO Alternate Encapsulations . . . . . . . . . . . 74 127 Appendix B. Non-Normative Considerations . . . . . . . . . . . . 76 128 B.1. Implementation Strategies for Route Optimization . . . . 76 129 B.2. Implicit Mobility Management . . . . . . . . . . . . . . 77 130 B.3. Direct Underlying Interfaces . . . . . . . . . . . . . . 77 131 B.4. Operation on AERO Links with /64 ASPs . . . . . . . . . . 77 132 B.5. AERO Critical Infrastructure Considerations . . . . . . . 78 133 B.6. AERO Server Failure Implications . . . . . . . . . . . . 79 134 B.7. AERO Client / Server Architecture . . . . . . . . . . . . 80 135 Appendix C. Change Log . . . . . . . . . . . . . . . . . . . . . 82 136 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 90 138 1. Introduction 140 Asymmetric Extended Route Optimization (AERO) fulfills the 141 requirements of Distributed Mobility Management (DMM) [RFC7333] and 142 route optimization [RFC5522] for aeronautical networking and other 143 network mobility use cases. AERO is based on a Non-Broadcast, 144 Multiple Access (NBMA) virtual link model known as the AERO link. 145 The AERO link is a virtual overlay configured over one or more 146 underlying Internetworks, and nodes on the link can exchange IP 147 packets via tunneling. Multilink operation allows for increased 148 reliability, bandwidth optimization and traffic path diversity. 150 The AERO service comprises Clients, Proxys, Servers and Gateways that 151 are seen as AERO link neighbors as well as Relays that bridge AERO 152 link partitions. Each node's AERO interface uses an IPv6 link-local 153 address format (known as the AERO address) that supports operation of 154 the IPv6 Neighbor Discovery (ND) protocol [RFC4861] and links ND to 155 IP forwarding. A node's AERO interface can be configured over 156 multiple underlying interfaces, and may therefore appear as a single 157 interface with multiple link-layer addresses. Each link-layer 158 address is subject to change due to mobility and/or QoS fluctuations, 159 and link-layer address changes are signaled by ND messaging the same 160 as for any IPv6 link. 162 AERO links provide a cloud-based service where mobile nodes may use 163 any Server acting as a Mobility Anchor Point (MAP) and fixed nodes 164 may use any Gateway on the link for efficient communications. Fixed 165 nodes forward packets destined to other AERO nodes to the nearest 166 Gateway, which forwards them through the cloud. A mobile node's 167 initial packets are forwarded through the Server, while direct 168 routing is supported through asymmetric extended route optimization 169 while data packets are flowing. Both unicast and multicast 170 communications are supported, and mobile nodes may efficiently move 171 between locations while maintaining continuous communications with 172 correspondents and without changing their IP Address. 174 AERO Relays are interconnected in a secured private BGP overlay 175 routing instance known as "The SPAN". The SPAN provides a hybrid 176 routing/bridging service to join the underlying Internetworks of 177 multiple disjoint administrative domains into a single unified AERO 178 link. Each AERO link instance is characterized by the set of 179 Mobility Service Prefixes (MSPs) common to all mobile nodes. The 180 link extends to the point where a Gateway/Server is on the optimal 181 route from any correspondent node on the link, and provides a gateway 182 between the underlying Internetwork and the SPAN. To the underlying 183 Internetwork, the Gateway/Server is the source of a route to the MSP, 184 and hence uplink traffic to the mobile node is naturally routed to 185 the nearest Gateway/Server. 187 AERO assumes the use of PIM Sparse Mode in support of multicast 188 communication. In support of Source Specific Multicast (SSM) when a 189 Mobile Node is the source, AERO route optimization ensures that a 190 shortest-path multicast tree is established with provisions for 191 mobility and multilink operation. In all other multicast scenarios 192 there are no AERO dependencies. 194 AERO was designed for aeronautical networking for both manned and 195 unmanned aircraft, where the aircraft is treated as a mobile node 196 that can connect an Internet of Things (IoT). AERO is also 197 applicable to a wide variety of other use cases. For example, it can 198 be used to coordinate the Virtual Private Network (VPN) links of 199 mobile nodes (e.g., cellphones, tablets, laptop computers, etc.) that 200 connect into a home enterprise network via public access networks 201 using services such as OpenVPN [OVPN]. Other applicable use cases 202 are also in scope. 204 The following numbered sections present the AERO specification. The 205 appendices at the end of the document are non-normative. 207 2. Terminology 209 The terminology in the normative references applies; the following 210 terms are defined within the scope of this document: 212 IPv6 Neighbor Discovery (ND) 213 an IPv6 control message service for coordinating neighbor 214 relationships between nodes connected to a common link. AERO 215 interfaces use the ND service specified in [RFC4861]. 217 IPv6 Prefix Delegation (PD) 218 a networking service for delegating IPv6 prefixes to nodes on the 219 link. The nominal PD service is DHCPv6 [RFC8415], however 220 alternate services (e.g., based on ND messaging) are also in scope 221 [I-D.templin-v6ops-pdhost][I-D.templin-6man-dhcpv6-ndopt]. Most 222 notably, a minimal form of PD known as "prefix registration" can 223 be used if the Client knows its prefix in advance and can 224 represent it in the IPv6 source address of an ND message. 226 Access Network (ANET) 227 a node's first-hop data link service network, e.g., a radio access 228 network, cellular service provider network, corporate enterprise 229 network, or the public Internet itself. For secured ANETs, link- 230 layer security services such as IEEE 802.1X and physical-layer 231 security prevent unauthorized access internally while border 232 network-layer security services such as firewalls and proxies 233 prevent unauthorized outside access. 235 ANET interface 236 a node's attachment to a link in an ANET. 238 ANET address 239 an IP address assigned to a node's interface connection to an 240 ANET. 242 Internetwork (INET) 243 a connected IP network topology with a coherent routing and 244 addressing plan and that provides a transit backbone service for 245 ANET end systems. INETs also provide an underlay service over 246 which the AERO virtual link is configured. Example INETs include 247 corporate enterprise networks, aviation networks, and the public 248 Internet itself. When there is no administrative boundary between 249 an ANET and the INET, the ANET and INET are one and the same. 251 INET Partition 252 frequently, INETs such as large corporate enterprise networks are 253 sub-divided internally into separate isolated partitions. Each 254 partition is fully connected internally but disconnected from 255 other partitions, and there is no requirement that separate 256 partitions maintain consistent Internet Protocol and/or addressing 257 plans. (An INET partition is the same as a SPAN segment discussed 258 below.) 260 INET interface 261 a node's attachment to a link in an INET. 263 INET address 264 an IP address assigned to a node's interface connection to an 265 INET. 267 AERO link 268 a Non-Broadcast, Multiple Access (NBMA) tunnel virtual overlay 269 configured over one or more underlying INETs. Nodes on the AERO 270 link appear as single-hop neighbors from the perspective of the 271 virtual overlay even though they may be separated by many 272 underlying INET hops. AERO links may be configured over multiple 273 underlying SPAN segments (see below). 275 AERO interface 276 a node's attachment to an AERO link. Since the addresses assigned 277 to an AERO interface are managed for uniqueness, AERO interfaces 278 do not require Duplicate Address Detection (DAD) and therefore set 279 the administrative variable 'DupAddrDetectTransmits' to zero 280 [RFC4862]. 282 underlying interface 283 an ANET or INET interface over which an AERO interface is 284 configured. 286 AERO address 287 an IPv6 link-local address assigned to an AERO interface and 288 constructed as specified in Section 3.4. 290 base AERO address 291 the lowest-numbered AERO address aggregated by the MNP (see 292 Section 3.4). 294 Mobility Service Prefix (MSP) 295 an IP prefix assigned to the AERO link and from which more- 296 specific Mobile Network Prefixes (MNPs) are derived. 298 Mobile Network Prefix (MNP) 299 an IP prefix allocated from an MSP and delegated to an AERO Client 300 or Gateway. 302 AERO node 303 a node that is connected to an AERO link, or that provides 304 services to other nodes on an AERO link. 306 AERO Client ("Client") 307 an AERO node that connects to one or more ANETs and requests MNP 308 PDs from AERO Servers. The Client assigns a Client AERO address 309 to the AERO interface for use in ND exchanges with other AERO 310 nodes and forwards packets to correspondents according to AERO 311 interface neighbor cache state. 313 AERO Server ("Server") 314 an INET node that configures an AERO interface to provide default 315 forwarding and mobility/multilink services for AERO Clients. The 316 Server assigns an administratively-provisioned AERO address to its 317 AERO interface to support the operation of the ND/PD services, and 318 advertises all of its associated MNPs via BGP peerings with 319 Relays. 321 AERO Gateway ("Gateway") 322 an AERO Server that also provides forwarding services between 323 nodes reached via the AERO link and correspondents on other links. 324 AERO Gateways are provisioned with MNPs (i.e., the same as for an 325 AERO Client) and run a dynamic routing protocol to discover any 326 non-MNP IP routes. In both cases, the Gateway advertises the 327 MSP(s) over INET interfaces, and distributes all of its associated 328 MNPs and non-MNP IP routes via BGP peerings with Relays (i.e., the 329 same as for an AERO Server). 331 AERO Relay ("Relay") 332 a node that provides hybrid routing/bridging services (as well as 333 a security trust anchor) for nodes on an AERO link. As a router, 334 the Relay forwards packets using standard IP forwarding. As a 335 bridge, the Relay forwards packets over the AERO link without 336 decrementing the IPv6 Hop Limit. AERO Relays peer with Servers 337 and other Relays to discover the full set of MNPs for the link as 338 well as any non-MNPs that are reachable via Gateways. 340 AERO Proxy ("Proxy") 341 a node that provides proxying services between Clients in an ANET 342 and Servers in external INETs. The AERO Proxy is a conduit 343 between the ANET and external INETs in the same manner as for 344 common web proxies, and behaves in a similar fashion as for ND 345 proxies [RFC4389]. 347 Spanning Partitioned AERO Networks (SPAN) 348 a means for bridging disjoint INET partitions as segments of a 349 unified AERO link the same as for a bridged campus LAN. The SPAN 350 is a mid-layer IPv6 encapsulation service in the AERO routing 351 system that supports a unified AERO link view for all segments. 352 Each segment in the SPAN is a distinct INET partition. 354 SPAN Service Prefix (SSP) 355 a global or unique local /96 IPv6 prefix assigned to the AERO link 356 to support SPAN services. 358 SPAN Partition Prefix (SPP) 359 a sub-prefix of the SPAN Service Prefix uniquely assigned to a 360 single SPAN segment. 362 SPAN Client Prefix (SCP) 363 a SPAN prefix formed from an AERO Client address. 365 SPAN Address 366 a unique local IPv6 address taken from a SPAN Client/Partition 367 Prefix and constructed as specified in Section 3.5. SPAN 368 addresses are statelessly derived from AERO addresses, and vice- 369 versa. 371 ingress tunnel endpoint (ITE) 372 an AERO interface endpoint that injects encapsulated packets into 373 an AERO link. 375 egress tunnel endpoint (ETE) 376 an AERO interface endpoint that receives encapsulated packets from 377 an AERO link. 379 link-layer address 380 an IP address used as an encapsulation header source or 381 destination address from the perspective of the AERO interface. 382 When an upper layer protocol (e.g., UDP) is used as part of the 383 encapsulation, the port number is also considered as part of the 384 link-layer address. From the perspective of the AERO interface, 385 the link-layer address is either an INET address for intra-segment 386 encapsulation or a SPAN address for inter-segment encapsulation. 388 network layer address 389 the source or destination address of an encapsulated IP packet 390 presented to the AERO interface. 392 end user network (EUN) 393 an internal virtual or external edge IP network that an AERO 394 Client or Gateway connects to the rest of the network via the AERO 395 interface. The Client/Gateway sees each EUN as a "downstream" 396 network, and sees the AERO interface as the point of attachment to 397 the "upstream" network. 399 Mobile Node (MN) 400 an AERO Client and all of its downstream-attached networks that 401 move together as a single unit, i.e., an end system that connects 402 an Internet of Things. 404 Mobile Router (MR) 405 a MN's on-board router that forwards packets between any 406 downstream-attached networks and the AERO link. 408 Route Optimization Source (ROS) 409 the AERO node nearest the source that initiates route 410 optimization. The ROS may be a Server or Proxy acting on behalf 411 of the source Client. 413 Route Optimization responder (ROR) 414 the AERO node nearest the target destination that responds to 415 route optimization requests. The ROR may be a Server acting on 416 behalf of a target MNP Client, or a Gateway for a non-MNP 417 destination. 419 MAP List 420 a geographically and/or topologically referenced list of AERO 421 addresses of all Servers within the same AERO link. There is a 422 single MAP list for the entire AERO link. 424 ROS List 425 a list of AERO/SPAN-to-INET address mappings of all ROSes within 426 the same SPAN segment. There is a distinct ROS list for each 427 segment. 429 Distributed Mobility Management (DMM) 430 a BGP-based overlay routing service coordinated by Servers and 431 Relays that tracks all Server-to-Client associations. 433 Mobility Service (MS) 434 the collective set of all Servers, Proxys, Relays and Gateways 435 that provide the AERO Service to Clients. 437 Mobility Service Endpoint MSE) 438 an individual Server, Proxy, Relay or Gateway in the Mobility 439 Service. 441 Throughout the document, the simple terms "Client", "Server", 442 "Relay", "Proxy" and "Gateway" refer to "AERO Client", "AERO Server", 443 "AERO Relay", "AERO Proxy" and "AERO Gateway", respectively. 444 Capitalization is used to distinguish these terms from other common 445 Internetworking uses in which they appear without capitalization. 447 The terminology of DHCPv6 [RFC8415] and IPv6 ND [RFC4861] (including 448 the names of node variables, messages and protocol constants) is used 449 throughout this document. The terms "All-Routers multicast", "All- 450 Nodes multicast", "Solicited-Node multicast" and "Subnet-Router 451 anycast" are defined in [RFC4291] (with Link-Local scope assumed). 452 Also, the term "IP" is used to generically refer to either Internet 453 Protocol version, i.e., IPv4 [RFC0791] or IPv6 [RFC8200]. 455 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 456 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 457 "OPTIONAL" in this document are to be interpreted as described in BCP 458 14 [RFC2119][RFC8174] when, and only when, they appear in all 459 capitals, as shown here. 461 3. Asymmetric Extended Route Optimization (AERO) 463 The following sections specify the operation of IP over Asymmetric 464 Extended Route Optimization (AERO) links: 466 3.1. AERO Link Reference Model 467 +----------------+ 468 | AERO Relay R1 | 469 | Nbr: S1, S2, P1| 470 |(X1->S1; X2->S2)| 471 | MSP M1 | 472 +-+---------+--+-+ 473 +--------------+ | Secured | | +--------------+ 474 |AERO Server S1| | tunnels | | |AERO Server S2| 475 | Nbr: C1, R1 +-----+ | +-----+ Nbr: C2, R1 | 476 | default->R1 | | | default->R1 | 477 | X1->C1 | | | X2->C2 | 478 +-------+------+ | +------+-------+ 479 | AERO Link | | 480 X===+===+===================+==)===============+===+===X 481 | | | | 482 +-----+--------+ +--------+--+-----+ +--------+-----+ 483 |AERO Client C1| | AERO Proxy P1 | |AERO Client C2| 484 | Nbr: S1 | |(Proxy Nbr Cache)| | Nbr: S2 | 485 | default->S1 | +--------+--------+ | default->S2 | 486 | MNP X1 | | | MNP X2 | 487 +------+-------+ .--------+------. +-----+--------+ 488 | (- Proxyed Clients -) | 489 .-. `---------------' .-. 490 ,-( _)-. ,-( _)-. 491 .-(_ IP )-. +-------+ +-------+ .-(_ IP )-. 492 (__ EUN )--|Host H1| |Host H2|--(__ EUN ) 493 `-(______)-' +-------+ +-------+ `-(______)-' 495 Figure 1: AERO Link Reference Model 497 Figure 1 presents the AERO link reference model. In this model: 499 o the AERO link is an overlay network service configured over one or 500 more underlying INET partitions which may be managed by different 501 administrative authorities and have incompatible protocols and/or 502 addressing plans. 504 o AERO Relay R1 aggregates Mobility Service Prefix (MSP) M1, 505 discovers Mobile Network Prefixes (MNPs) X* and advertises the MSP 506 via BGP peerings over secured tunnels to Servers (S1, S2). Relays 507 use the SPAN service to bridge disjoint segments of a partitioned 508 AERO link. 510 o AERO Servers S1 and S2 configure secured tunnels with Relay R1 and 511 also provide mobility, multilink and default router services for 512 their associated Clients C1 and C2. 514 o AERO Clients C1 and C2 associate with Servers S1 and S2, 515 respectively. They receive Mobile Network Prefix (MNP) 516 delegations X1 and X2, and also act as default routers for their 517 associated physical or internal virtual EUNs. Simple hosts H1 and 518 H2 attach to the EUNs served by Clients C1 and C2, respectively. 520 o AERO Proxy P1 configures a secured tunnel with Relay R1 and 521 provides proxy services for AERO Clients in secured enclaves that 522 cannot associate directly with other AERO link neighbors. 524 Each node on the AERO link maintains an AERO interface neighbor cache 525 and an IP forwarding table the same as for any link. Although the 526 figure shows a limited deployment, in common operational practice 527 there will normally be many additional Relays, Servers, Clients and 528 Proxys. 530 3.2. AERO Node Types 532 AERO Relays provide hybrid routing/bridging services (as well as a 533 security trust anchor) for nodes on an AERO link. Relays use 534 standard IPv6 routing to forward packets both within the same INET 535 partitions and between disjoint INET partitions based on a mid-layer 536 IPv6 encapsulation known as the SPAN header. The inner IP layer 537 experiences a virtual bridging service since the inner IP TTL/Hop 538 Limit is not decremented during forwarding. Each Relay also peers 539 with Servers and other Relays in a dynamic routing protocol instance 540 to provide a Distributed Mobility Management (DMM) service for the 541 list of active MNPs (see Section 3.3). Relays present the AERO link 542 as a set of one or more Mobility Service Prefixes (MSPs) but as link- 543 layer devices need not connect directly to the AERO link themselves 544 unless an administrative interface is desired. Relays configure 545 secured tunnels with Servers, Proxys and other Relays; they further 546 maintain IP forwarding table entries for each Mobile Network Prefix 547 (MNP) and any other reachable non-MNP prefixes. 549 AERO Servers provide default forwarding and mobility/multilink 550 services for AERO Client Mobile Nodes (MNs). Each Server also peers 551 with Relays in a dynamic routing protocol instance to advertise its 552 list of associated MNPs (see Section 3.3). Servers facilitate PD 553 exchanges with Clients, where each delegated prefix becomes an MNP 554 taken from an MSP. Servers forward packets between AERO interface 555 neighbors and track each Client's mobility profiles. 557 AERO Clients register their MNPs through PD exchanges with AERO 558 Servers over the AERO link, and distribute the MNPs to nodes on EUNs. 559 A Client may also be co-resident on the same physical or virtual 560 platform as a Server; in that case, the Client and Server behave as a 561 single functional unit. 563 AERO Proxys provide a conduit for ANET AERO Clients to associate with 564 AERO Servers in external INETs. Client and Servers exchange control 565 plane messages via the Proxy acting as a bridge between the ANET/INET 566 boundary. The Proxy forwards data packets between Clients and the 567 AERO link according to forwarding information in the neighbor cache. 568 The Proxy function is specified in Section 3.16. 570 AERO Gateways are Servers that provide forwarding services between 571 the AERO interface and INET/EUN interfaces. Gateways are provisioned 572 with MNPs the same as for an AERO Client, and also run a dynamic 573 routing protocol to discover any non-MNP IP routes. The Gateway 574 advertises the MSP(s) to INETs, and distributes all of its associated 575 MNPs and non-MNP IP routes via BGP peerings with Relays. 577 AERO Relays, Servers, Proxys and Gateways are critical infrastructure 578 elements in fixed (i.e., non-mobile) INET deployments and hence have 579 permanent and unchanging INET addresses. AERO Clients are MNs that 580 connect via ANET interfaces, i.e., their ANET addresses may change 581 when the Client moves to a new ANET connection. 583 3.3. AERO Routing System 585 The AERO routing system comprises a private instance of the Border 586 Gateway Protocol (BGP) [RFC4271] that is coordinated between Relays 587 and Servers and does not interact with either the public Internet BGP 588 routing system or any underlying INET routing systems. 590 In a reference deployment, each Server is configured as an Autonomous 591 System Border Router (ASBR) for a stub Autonomous System (AS) using 592 an AS Number (ASN) that is unique within the BGP instance, and each 593 Server further uses eBGP to peer with one or more Relays but does not 594 peer with other Servers. Each INET of a multi-segment AERO link must 595 include one or more Relays, which peer with the Servers and Proxys 596 within that INET. All Relays within the same INET are members of the 597 same hub AS using a common ASN, and use iBGP to maintain a consistent 598 view of all active MNPs currently in service. The Relays of 599 different INETs peer with one another using eBGP. 601 Relays advertise the AERO link's MSPs and any non-MNP routes to each 602 of their Servers. This means that any aggregated non-MNPs (including 603 "default") are advertised to all Servers. Each Relay configures a 604 black-hole route for each of its MSPs. By black-holing the MSPs, the 605 Relay will maintain forwarding table entries only for the MNPs that 606 are currently active, and packets destined to all other MNPs will 607 correctly incur Destination Unreachable messages due to the black- 608 hole route. In this way, Servers have only partial topology 609 knowledge (i.e., they know only about the MNPs of their directly 610 associated Clients) and they forward all other packets to Relays 611 which have full topology knowledge. 613 Servers maintain a working set of associated MNPs, and dynamically 614 announce new MNPs and withdraw departed MNPs in eBGP updates to 615 Relays. Servers that are configured as Gateways also redistribute 616 non-MNP routes learned from non-AERO interfaces via their eBGP Relay 617 peerings. 619 Clients are expected to remain associated with their current Servers 620 for extended timeframes, however Servers SHOULD selectively suppress 621 updates for impatient Clients that repeatedly associate and 622 disassociate with them in order to dampen routing churn. Servers 623 that are configured as Gateways advertise the MSPs via INET/EUN 624 interfaces, and forward packets between INET/EUN interfaces and the 625 AERO interface using standard IP forwarding. 627 Scaling properties of the AERO routing system are limited by the 628 number of BGP routes that can be carried by Relays. As of 2015, the 629 global public Internet BGP routing system manages more than 500K 630 routes with linear growth and no signs of router resource exhaustion 631 [BGP]. More recent network emulation studies have also shown that a 632 single Relay can accommodate at least 1M dynamically changing BGP 633 routes even on a lightweight virtual machine, i.e., and without 634 requiring high-end dedicated router hardware. 636 Therefore, assuming each Relay can carry 1M or more routes, this 637 means that at least 1M Clients can be serviced by a single set of 638 Relays. A means of increasing scaling would be to assign a different 639 set of Relays for each set of MSPs. In that case, each Server still 640 peers with one or more Relays, but institutes route filters so that 641 BGP updates are only sent to the specific set of Relays that 642 aggregate the MSP. For example, if the MSP for the AERO link is 643 2001:db8::/32, a first set of Relays could service the MSP 644 2001:db8::/40, a second set of Relays could service 645 2001:db8:0100::/40, a third set could service 2001:db8:0200::/40, 646 etc. 648 Assuming up to 1K sets of Relays, the AERO routing system can then 649 accommodate 1B or more MNPs with no additional overhead (for example, 650 it should be possible to service 1B /64 MNPs taken from a /34 MSP and 651 even more for shorter prefixes). In this way, each set of Relays 652 services a specific set of MSPs that they advertise to the native 653 Internetwork routing system, and each Server configures MSP-specific 654 routes that list the correct set of Relays as next hops. This 655 arrangement also allows for natural incremental deployment, and can 656 support small scale initial deployments followed by dynamic 657 deployment of additional Clients, Servers and Relays without 658 disturbing the already-deployed base. 660 Server and Relays can use the Bidirectional Forwarding Detection 661 (BFD) protocol [RFC5880] to quickly detect link failures that don't 662 result in interface state changes, BGP peer failures, and 663 administrative state changes. BFD is important in environments where 664 rapid response to failures is required for routing reconvergence and, 665 hence, communications continuity. 667 A full discussion of the BGP-based routing system used by AERO is 668 found in [I-D.ietf-rtgwg-atn-bgp]. The system provides for 669 Distributed Mobility Management (DMM) per the distributed mobility 670 anchoring architecture [I-D.ietf-dmm-distributed-mobility-anchoring]. 672 3.4. AERO Addresses 674 A Client's AERO address is an IPv6 link-local address formed from the 675 Client's delegated MNP. Relay, Server and Proxy AERO addresses are 676 assigned from the range fe80::/96 and include an administratively- 677 provisioned value in the lower 32 bits. 679 IPv6 Client AERO addresses encode the Subnet-Router anycast address 680 of a MNP within the least-significant 112 bits of the the IPv6 link- 681 local prefix fe80::/16. For example, for the MNP 682 2001:db8:1000:2000::/56 the corresponding AERO address is 683 fe80:2001:db8:1000:2000::/72. 685 IPv4-compatible Client AERO addresses are based on an IPv4-mapped 686 IPv6 address [RFC4291] formed from an IPv4 MNP and with a prefix 687 length of 96 plus the MNP prefix length. For example, for the IPv4 688 MNP 192.0.2.16/28 the IPv4-mapped IPv6 MNP is: 690 0:0:0:0:0:ffff:192.0.2.16/124 (also written as 691 0:0:0:0:0:ffff:c000:0210/124) 693 The Client then constructs its AERO address with the prefix fe80::/64 694 and with the lower 64 bits of the IPv4-mapped IPv6 address in the 695 interface identifier as: fe80::ffff:192.0.2.16. 697 Mobility Service (MS) AERO addresses (used by Relays, Servers, 698 Gateways and Proxys) are allocated from the range fe80::/96, and MUST 699 be managed for uniqueness. The lower 32 bits of the AERO address 700 includes a unique integer value between 1 and 0xfeffffff (e.g., 701 fe80::1, fe80::2, fe80::3, etc., fe80::feff:ffff) as assigned by the 702 administrative authority for the link. The address fe80:: is the 703 IPv6 link-local Subnet-Router anycast address, and the address range 704 fe80::ff00:0000/104 is reserved for future use. 706 AERO addresses for mobile node Clients embed an MNP as discussed 707 above, while AERO addresses for non-MNP destinations are constructed 708 in exactly the same way. A Client AERO address therefore encodes 709 either an MNP if the prefix is reached via the SPAN or a non-MNP if 710 the prefix is reached via a Gateway. 712 For a full discussion of the above address format and implications 713 for the /64 boundary, see: [I-D.templin-6man-omni-interface]. 715 3.5. Spanning Partitioned AERO Networks (SPAN) 717 An AERO link configured over a single INET appears as a single 718 unified link with a consistent underlying network addressing plan. 719 In that case, all nodes on the link can exchange packets via simple 720 INET encapsulation, since the underlying INET is connected. In 721 common practice, however, an AERO link may be partitioned into 722 multiple "segments", where each segment is a distinct INET 723 potentially managed under a different administrative authority (e.g., 724 as for worldwide aviation service providers such as ARINC, SITA, 725 Inmarsat, etc.). Individual INETs may also themselves be partitioned 726 internally, in which case each internal partition is seen as a 727 separate segment. 729 The addressing plan of each segment is consistent internally but will 730 often bear no relation to the addressing plans of other segments. 731 Each segment is also likely to be separated from others by network 732 security devices (e.g., firewalls, proxies, packet filtering 733 gateways, etc.), and in many cases disjoint segments may not even 734 have any common physical link connections. Therefore, nodes can only 735 be assured of exchanging packets directly with correspondents in the 736 same segment, and not with those in other segments. The only means 737 for joining the segments therefore is through inter-domain peerings 738 between AERO Relays. 740 The same as for traditional campus LANs, multiple AERO link segments 741 can be joined into a single unified link via a virtual bridging 742 service termed "The SPAN". The SPAN performs link-layer packet 743 forwarding between segments (i.e., bridging) without decrementing the 744 network-layer TTL/Hop Limit. The SPAN model is depicted in Figure 2: 746 . . . . . . . . . . . . . . . . . . . . . . . 747 . . 748 . .-(::::::::) . 749 . .-(::::::::::::)-. +-+ . 750 . (:::: Segment A :::)--|R|---+ . 751 . `-(::::::::::::)-' +-+ | . 752 . `-(::::::)-' | . 753 . | . 754 . .-(::::::::) | . 755 . .-(::::::::::::)-. +-+ | . 756 . (:::: Segment B :::)--|R|---+ . 757 . `-(::::::::::::)-' +-+ | . 758 . `-(::::::)-' | . 759 . | . 760 . .-(::::::::) | . 761 . .-(::::::::::::)-. +-+ | . 762 . (:::: Segment C :::)--|R|---+ . 763 . `-(::::::::::::)-' +-+ | . 764 . `-(::::::)-' | . 765 . | . 766 . ..(etc).. x . 767 . . 768 . . 769 . <- AERO Link Bridged by the SPAN -> . 770 . . . . . . . . . . . . . .. . . . . . . . . 772 Figure 2: The SPAN 774 To support the SPAN, AERO links use the Unique Local Address (ULA) 775 prefix fd80::/16 [RFC4193] as the SPAN Service Prefix (SSP). The 776 prefix length intentionally matches the IPv6 link-local prefix 777 (fe80::/16), and enables a simple 1-bit stateless translation between 778 AERO and SPAN addresses (i.e., bit 7 is '1' for AERO addresses or '0' 779 for SPAN addresses). 781 Each segment in the SPAN assigns a unique sub-prefix of fd80::/96 782 termed the "SPAN Partition Prefix (SPP)". For example, a first 783 segment could assign fd80::1000/116, a second could assign 784 fd80::2000/116, a third could assign fd80::3000/116, etc. The 785 administrative authorities for each segment must therefore coordinate 786 to assure mutually-exclusive SPP assignments, but internal 787 provisioning of the SPP is an independent local consideration for 788 each administrative authority. 790 SPAN addresses are formed by simply clearing bit 7 of the 791 corresponding AERO address. For example: 793 o the SPAN address formed from the IPv6 Client AERO address 794 fe80:2001:db8:1000:2000:: is simply fd80:2001:db8:1000:2000:: 796 o the SPAN address formed from the IPv4-compatible Client AERO 797 address fe80::ffff:192.0.2.1 is simply fd80::ffff:192.0.2.1 799 o the SPAN address formed from the administrative AERO address 800 fe80::1001 is simply fd80::1001. 802 AERO Relays serve as bridges to join multiple segments into a unified 803 AERO link over multiple diverse administrative domains. They support 804 the bridging function by first establishing forwarding table entries 805 for their SPPs either via standard BGP routing or static routes. For 806 example, if three Relays ('A', 'B' and 'C') from different segments 807 serviced the SPPs fd80::1000/116, fd80::2000/116 and fd80::3000/116 808 respectively, then the forwarding tables in each Relay are as 809 follows: 811 A: fd80::1000/116->local, fd80::2000/116->B, fd80::3000/116->C 813 B: fd80::1000/116->A, fd80::2000/116->local, fd80::3000/116->C 815 C: fd80::1000/116->A, fd80::2000/116->B, fd80::3000/116->local 817 These forwarding table entries are permanent and never change, since 818 they correspond to fixed infrastructure elements in their respective 819 segments. 821 SPAN Client Prefixes (SCPs) are instead dynamically advertised in the 822 AERO link routing system by Servers and Gateways that aggregate their 823 correspnding MNPs. For example, if three Servers ('D', 'E' and 'F') 824 aggregated the MNPs 2001:db8:1000:2000::/56, 2001:db8:3000:4000::/56 825 and 2001:db8:5000:6000::/56 then the routing system would include: 827 D: fd80:2001:db8:1000:2000::/72 829 E: fd80:2001:db8:3000:4000::/72 831 F: fd80:2001:db8:5000:6000::/72 833 With the SCPs and SPPs in place in each Relay's forwarding table, 834 control and data packets sent between AERO nodes in different 835 segments can therefore be carried over the via encapsulation in a 836 mid-layer IPv6 header known as the "SPAN header". For example, when 837 a source AERO node forwards a packet with IPv6 address 838 2001:db8:1:2::1 to a target AERO node with IPv6 address 839 2001:db8:1000:2000::1, it first encapsulates the packet in a SPAN 840 header with source address set to fd80:2001:db8:1:2:: and destination 841 address set to fd80:2001:db8:1000:2000::. Next, it encapsulates the 842 resulting SPAN packet in an INET header with source address set to 843 its own INET address (e.g., 192.0.2.100) and destination set to the 844 INET address of a Relay (e.g., 192.0.2.1). 846 SPAN encapsulation is based on Generic Packet Tunneling in IPv6 847 [RFC2473]; the encapsulation format in the above example is shown in 848 Figure 3: 850 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 851 | INET Header | 852 | src = 192.0.2.100 | 853 | dst = 192.0.2.1 | 854 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 855 | SPAN Header | 856 | src = fd80:2001:db8:1:2:: | 857 | dst=fd80:2001:db8:1000:2000:: | 858 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 859 | Inner IP Header | 860 | src = 2001:db8:1:2::1 | 861 | dst = 2001:db8:1000:2000::1 | 862 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 863 | | 864 ~ ~ 865 ~ Inner Packet Body ~ 866 ~ ~ 867 | | 868 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 870 Figure 3: SPAN Encapsulation 872 In this format, the inner IP header and packet body are the original 873 IP packet, the SPAN header is an IPv6 header prepared according to 874 [RFC2473], and the INET header is prepared as discussed in 875 Section 3.9. A packet is said to be "forwarded/sent into the SPAN" 876 when it is encapsulated as described above then forwarded via a 877 secured tunnel to a neighboring Relay. 879 This gives rise to a routing system that contains both SCP routes 880 that may change dynamically due to regional node mobility and SPP 881 routes that never change. The Relays can therefore provide link- 882 layer bridging by sending packets into the SPAN instead of network- 883 layer routing according to MNP routes. As a result, opportunities 884 for packet loss due to node mobility between different segments are 885 mitigated. 887 In normal operations, IPv6 ND messages are conveyed to SPP addresses 888 over the SPAN so that specific Proxys, Servers or Gateways can be 889 addressed without being subject to mobility events. Conversely, only 890 the first few packets destined to SCP addresses traverse the SPAN 891 until route optimization can determine a more direct path. 893 3.6. AERO Interface Characteristics 895 AERO interfaces are virtual interfaces configured over one or more 896 underlying interfaces classified as follows: 898 o Native interfaces have global IP addresses that are reachable from 899 any INET correspondent. All Server, Gateway and Relay interfaces 900 are native interfaces, as are INET-facing interfaces of Proxys. 901 Clients connected to native interfaces receive Router 902 Advertisemenets (RAs) with both the P and N flags set to 0, as 903 discussed in the following sections. 905 o NATed interfaces connect to a private network behind a Network 906 Address Translator (NAT). The NAT does not participate in any 907 AERO control message signaling, but the Server can issue control 908 messages on behalf of the Client. Clients that are behind a NAT 909 are required to send periodic keepalive messages to keep NAT state 910 alive when there are no data packets flowing. If no other 911 periodic messaging service is available, the Client can send 912 Router Solicitation (RS) messages to receive RA replies from its 913 Server(s). Clients connected to NATed interfaces receive RAs with 914 the N flag set to 1. 916 o Proxyed interfaces connect to an ANET that is separated from the 917 open INET by an AERO Proxy. Unlike NATed and VPNed interfaces, 918 the Proxy can actively issue control messages on behalf of the 919 Client. Clients connected to Proxyed interfaces receive RAs with 920 the P flag set to 1. 922 o VPNed interfaces use security encapsulation to a Virtual Private 923 Network (VPN) server that also acts as an AERO Server. As with 924 NATed links, the Server can issue control messages on behalf of 925 the Client, and the Client can send periodic messages such as RS/ 926 RA to keep the VPN state alive. Clients connected to VPNed 927 interfaces receive RAs with the P flag set to 1 the same as for 928 Proxyed interfaces. 930 o Direct interfaces connect a Client directly to a Server without 931 crossing any ANET/INET paths. An example is a line-of-sight link 932 between a remote pilot and an unmanned aircraft. The same Client 933 considerations apply as for VPNed interfaces above, and the Client 934 receives RA messages with the P flag set to 1. 936 AERO interfaces use SPAN-layer encapsualtion as necessary as 937 discussed in Section 3.5. AERO interfaces use link-layer 938 encapsulation (see: Section 3.9) to exchange packets with AERO link 939 neighbors over Native, NATed or VPNed interfaces. AERO interfaces do 940 not use encapsulation over Proxyed and Direct underlying interfaces. 942 AERO interfaces maintain a neighbor cache for tracking per-neighbor 943 state the same as for any interface. AERO interfaces use ND messages 944 including Router Solicitation (RS), Router Advertisement (RA), 945 Neighbor Solicitation (NS) and Neighbor Advertisement (NA) for 946 neighbor cache management. 948 AERO interfaces send ND messages with an Overlay Multilink Network 949 Interface (OMNI) option formatted as specified in 950 [I-D.templin-6man-omni-interface]. The OMNI option includes prefix 951 registration information and "ifIndex-tuples" containing link 952 information parameters for the AERO interface's underlying 953 interfaces. 955 When encapsulation is used, AERO interface ND messages MAY also 956 include an AERO Source/Target Link-Layer Address Option (S/TLLAO) 957 formatted as shown in Figure 4: 959 0 1 2 3 960 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 1 961 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 962 | Type | Length | ifIndex[1] |S|V|P}O|Rsvd[1]| 963 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 964 ~ Link Layer Address [1] ~ 965 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 966 | Port Number [1] | ifIndex[2] |S|V|P|O|Rsvd[2]| 967 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 968 ~ Link Layer Address [2] ~ 969 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 970 | Port Number [2] | ~ 971 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ 972 ~ ~ 973 ~ ... ~ 974 ~ ~ 975 ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 976 ~ | ifIndex[N] |S|V|P|O|Rsvd[N]| 977 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 978 ~ Link Layer Address [N] ~ 979 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 980 | Port Number [N] | Zero Padding (if necessary) ... 981 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- 983 Figure 4: AERO Source/Target Link-Layer Address Option (S/TLLAO) 984 Format 986 In this format, Type and Length are set the same as specified for S/ 987 TLLAOs in [RFC4861], with trailing zero padding octets added as 988 necessary to produce an integral number of 8 octet blocks. The S/ 989 TLLAO includes N ifIndex-tuples in correspondence to ifIndex-tuples 990 that appear in the OMNI option. Each ifIndex-tuple includes the 991 folllowing information: 993 o ifIndex[i] - the same value as in the corresponding ifIndex-tuple 994 included in the OMNI option. 996 o S[i] - the "SPAN" bit. If set to 1, the Link Layer Address [i] 997 field encodes the lower 32 bits of an administrative SPAN address. 998 Otherwise, the Link Layer Address [i] field encodes an INET 999 address. 1001 o V[i] - a bit that identifies the IP protocol version of the 1002 address found in the Link Layer Address [i] field. The bit is set 1003 to 0 for IPv4 or 1 for IPv6, and consulted only if S[i] is 0. 1005 o P[i] - the "Port" bit. If set to 1, the Port Number [i] field is 1006 included; otherwise, the Port Number [i] field is omitted. 1008 o O[i] - the "Obfuscated" bit. If set to 0, the Link Layer Address 1009 [i] and Port Number [i] (If present) values are included in their 1010 unmodified form. If set to 1, the fields are "Obfuscated" by 1011 applying an exclusive-or of all bits in the field with "all-ones" 1012 as discussed in [RFC4380] - see also Section 3.25. 1014 o Rsvd[i] - encodes the value 0 on transmission, and ignored on 1015 reception. 1017 o Link Layer Address [i] - when S[i] is 1, encodes the lower 32 bits 1018 of he administrative SPAN address of the target. Otherwise, 1019 encodes the IPv4 or IPv6 address used as the encapsulation source 1020 address. The field is 4 bytes in length for SPAN and IPv4, or 16 1021 bytes in length for IPv6. 1023 o Port Number [i] - included only when P[i] is 1. When present, 1024 encodes the upper layer protocol port number used as the 1025 encapsulation source port. The field is 2 bytes in length. 1027 If an S/TLLAO is included, any ifIndex-tuples correspond to a proper 1028 subset of the OMNI option ifIndex-tuples. Any S/TLLAO ifIndex-tuple 1029 having an ifIndex value that does not appear in an OMNI option 1030 ifindex-tuple is ignored. If the same ifIndex value appears in 1031 multiple ifIndex-tuples, the first tuple is processed and the 1032 remaining tuples are ignored. Any S/TLLAO ifIndex-tuples can 1033 therefore be viewed as inter-dependent extensions of their 1034 corresponidng OMNI option ifIndex-tuples, i.e., the OMNI option and 1035 S/TLLAO are companions that are interpreted in conjunction with each 1036 other. 1038 A Client's AERO interface may be configured over multiple underlying 1039 interface connections. For example, common mobile handheld devices 1040 have both wireless local area network ("WLAN") and cellular wireless 1041 links. These links are often used "one at a time" with low-cost WLAN 1042 preferred and highly-available cellular wireless as a standby, but a 1043 simultaneous-use capability could provide benefits. In a more 1044 complex example, aircraft frequently have many wireless data link 1045 types (e.g. satellite-based, cellular, terrestrial, air-to-air 1046 directional, etc.) with diverse performance and cost properties. 1048 If a Client's multiple underlying interfaces are used "one at a time" 1049 (i.e., all other interfaces are in standby mode while one interface 1050 is active), then ND message OMNI options include only a single 1051 ifIndex-tuple set to constant values. In that case, the Client would 1052 appear to have a single interface but with a dynamically changing 1053 link-layer address. 1055 If the Client has multiple active underlying interfaces, then from 1056 the perspective of ND it would appear to have multiple link-layer 1057 addresses. In that case, ND message OMNI options MAY include 1058 multiple ifIndex-tuples - each with values that correspond to a 1059 specific interface. Every ND message need not include all OMNI and/ 1060 or S/TLLAO ifIndex-tuples; for any ifIndex-tuple not included, the 1061 neighbor considers the status as unchanged. 1063 Relay, Server and Proxy AERO interfaces may be configured over one or 1064 more secured tunnel interfaces. The AERO interface configures both 1065 an AERO address and its corresponding SPAN address, while the 1066 underlying secured tunnel interfaces are either unnumbered or 1067 configure the same SPAN address. The AERO interface encapsulates 1068 each IP packet in a SPAN header and presents the packet to the 1069 underlying secured tunnel interface. For Relays that do not 1070 configure an AERO interface, the secured tunnel interfaces themselves 1071 are exposed to the IP layer with each interface configuring the 1072 Relay's SPAN address. Routing protocols such as BGP therefore run 1073 directly over the Relay's secured tunnel interfaces. For nodes that 1074 configure an AERO interface, routing protocols such as BGP run over 1075 the AERO interface but do not employ SPAN encapsulation. Instead, 1076 the AERO interface presents the routing protocol messages directly to 1077 the underlying secured tunnels without applying encapsulation and 1078 while using the SPAN address as the source address. This distinction 1079 must be honored consistently according to each node's configuration 1080 so that the IP forwarding table will associate discovered IP routes 1081 with the correct interface. 1083 3.7. AERO Interface Initialization 1085 AERO Servers, Proxys and Clients configure AERO interfaces as their 1086 point of attachment to the AERO link. AERO nodes assign the MSPs for 1087 the link to their AERO interfaces (i.e., as a "route-to-interface") 1088 to ensure that packets with destination addresses covered by an MNP 1089 not explicitly assigned to a non-AERO interface are directed to the 1090 AERO interface. 1092 AERO interface initialization procedures for Servers, Proxys, Clients 1093 and Relays are discussed in the following sections. 1095 3.7.1. AERO Server/Gateway Behavior 1097 When a Server enables an AERO interface, it assigns AERO/SPAN 1098 addresses and configures permanent neighbor cache entries for 1099 neighbors in the same SPAN segment by consulting the ROS list for the 1100 segment. The Server also configures secured tunnels with one or more 1101 neighboring Relays and engages in a BGP routing protocol session with 1102 each Relay. 1104 The AERO interface provides a single interface abstraction to the IP 1105 layer, but internally comprises multiple secured tunnels as well as 1106 an NBMA nexus for sending encapsulated data packets to AERO interface 1107 neighbors. The Server further configures a service to facilitate ND/ 1108 PD exchanges with AERO Clients and manages per-Client neighbor cache 1109 entries and IP forwarding table entries based on control message 1110 exchanges. 1112 Gateways are simply Servers that run a dynamic routing protocol to 1113 redistribute routes between the AERO interface and INET/EUN 1114 interfaces (see: Section 3.3). The Gateway provisions MNPs to 1115 networks on the INET/EUN interfaces (i.e., the same as a Client would 1116 do) and advertises the MSP(s) for the AERO link over the INET/EUN 1117 interfaces. The Gateway further provides an attachment point of the 1118 AERO link to the non-MNP-based global topology. 1120 3.7.2. AERO Proxy Behavior 1122 When a Proxy enables an AERO interface, it assigns AERO/SPAN 1123 addresses and configures permanent neighbor cache entries the same as 1124 for Servers. The Proxy also configures secured tunnels with one or 1125 more neighboring Relays and maintains per-Client neighbor cache 1126 entries based on control message exchanges. 1128 3.7.3. AERO Client Behavior 1130 When a Client enables an AERO interface, it sends RS messages with 1131 ND/PD parameters over its underlying interfaces to a Server in the 1132 MAP list, which returns an RA message with corresponding parameters. 1133 (The RS/RA messages may pass through a Proxy in the case of a 1134 Client's Proxyed interface.) 1136 3.7.4. AERO Relay Behavior 1138 AERO Relays need not connect directly to the AERO link, since they 1139 operate as link-layer forwarding devices instead of network layer 1140 routers. Configuration of AERO interfaces on Relays is therefore 1141 OPTIONAL, e.g., if an administrative interface is needed. Relays 1142 configure secured tunnels with Servers, Proxys and other Relays; they 1143 also configure AERO/SPAN addresses and permanent neighbor cache 1144 entries the same as Servers. Relays engage in a BGP routing protocol 1145 session with a subset of the Servers on the local SPAN segment, and 1146 with other Relays on the SPAN (see: Section 3.3). 1148 3.8. AERO Interface Neighbor Cache Maintenance 1150 Each AERO interface maintains a conceptual neighbor cache that 1151 includes an entry for each neighbor it communicates with on the AERO 1152 link per [RFC4861]. AERO interface neighbor cache entries are said 1153 to be one of "permanent", "symmetric", "asymmetric" or "proxy". 1155 Permanent neighbor cache entries are created through explicit 1156 administrative action; they have no timeout values and remain in 1157 place until explicitly deleted. AERO Servers and Proxys maintain 1158 permanent neighbor cache entries for all other Servers and Proxys 1159 within the same SPAN segment. Each entry maintains the mapping 1160 between the neighbor's network-layer AERO address and corresponding 1161 INET address. The list of all permanent neighbor cache entries for 1162 the SPAN segment is maintained in the segment's ROS list. 1164 Symmetric neighbor cache entries are created and maintained through 1165 RS/RA exchanges as specified in Section 3.15, and remain in place for 1166 durations bounded by ND/PD lifetimes. AERO Servers maintain 1167 symmetric neighbor cache entries for each of their associated 1168 Clients, and AERO Clients maintain symmetric neighbor cache entries 1169 for each of their associated Servers. The list of all Servers on the 1170 AERO link is maintained in the link's MAP list. 1172 Asymmetric neighbor cache entries are created or updated based on 1173 route optimization messaging as specified in Section 3.17, and are 1174 garbage-collected when keepalive timers expire. AERO ROSs maintain 1175 asymmetric neighbor cache entries for active targets with lifetimes 1176 based on ND messaging constants. Asymmetric neighbor cache entries 1177 are unidirectional since only the ROS (and not the ROR) creates an 1178 entry. 1180 Proxy neighbor cache entries are created and maintained by AERO 1181 Proxys when they process Client/Server ND/PD exchanges, and remain in 1182 place for durations bounded by ND/PD lifetimes. AERO Proxys maintain 1183 proxy neighbor cache entries for each of their associated Clients. 1184 Proxy neighbor cache entries track the Client state and the address 1185 of the Client's associated Server(s). 1187 To the list of neighbor cache entry states in Section 7.3.2 of 1188 [RFC4861], Proxy and Server AERO interfaces add an additional state 1189 DEPARTED that applies to symmetric and proxy neighbor cache entries 1190 for Clients that have recently departed. The interface sets a 1191 "DepartTime" variable for the neighbor cache entry to "DEPART_TIME" 1192 seconds. DepartTime is decremented unless a new ND message causes 1193 the state to return to REACHABLE. While a neighbor cache entry is in 1194 the DEPARTED state, packets destined to the target Client are 1195 forwarded to the Client's new location instead of being dropped. 1197 When DepartTime decrements to 0, the neighbor cache entry is deleted. 1198 It is RECOMMENDED that DEPART_TIME be set to the default constant 1199 value REACHABLE_TIME plus 10 seconds (40 seconds by default) to allow 1200 a window for packets in flight to be delivered while stale route 1201 optimization state may be present. 1203 When an ROR receives an authentic NS message used for route 1204 optimization, it searches for a symmetric neighbor cache entry for 1205 the target Client. The ROR then returns a solicited NA message 1206 without creating a neighbor cache entry for the ROS, but creates or 1207 updates a target Client "Report List" entry for the ROS and sets a 1208 "ReportTime" variable for the entry to REPORT_TIME seconds. The ROR 1209 resets ReportTime when it receives a new authentic NS message, and 1210 otherwise decrements ReportTime while no authentic NS messages have 1211 been received. It is RECOMMENDED that REPORT_TIME be set to the 1212 default constant value REACHABLE_TIME plus 10 seconds (40 seconds by 1213 default) to allow a window for route optimization to converge before 1214 ReportTime decrements below REACHABLE_TIME. 1216 When the ROS receives a solicited NA message response to its NS 1217 message used for route optimization, it creates or updates an 1218 asymmetric neighbor cache entry for the target network-layer and 1219 link-layer addresses. The ROS then (re)sets ReachableTime for the 1220 neighbor cache entry to REACHABLE_TIME seconds and uses this value to 1221 determine whether packets can be forwarded directly to the target, 1222 i.e., instead of via a default route. The ROS otherwise decrements 1223 ReachableTime while no further solicited NA messages arrive. It is 1224 RECOMMENDED that REACHABLE_TIME be set to the default constant value 1225 30 seconds as specified in [RFC4861]. 1227 AERO nodes also use the value MAX_UNICAST_SOLICIT to limit the number 1228 of NS keepalives sent when a correspondent may have gone unreachable, 1229 the value MAX_RTR_SOLICITATIONS to limit the number of RS messages 1230 sent without receiving an RA and the value MAX_NEIGHBOR_ADVERTISEMENT 1231 to limit the number of unsolicited NAs that can be sent based on a 1232 single event. It is RECOMMENDED that MAX_UNICAST_SOLICIT, 1233 MAX_RTR_SOLICITATIONS and MAX_NEIGHBOR_ADVERTISEMENT be set to 3 the 1234 same as specified in [RFC4861]. 1236 Different values for DEPART_TIME, REPORT_TIME, REACHABLE_TIME, 1237 MAX_UNICAST_SOLICIT, MAX_RTR_SOLCITATIONS and 1238 MAX_NEIGHBOR_ADVERTISEMENT MAY be administratively set; however, if 1239 different values are chosen, all nodes on the link MUST consistently 1240 configure the same values. Most importantly, DEPART_TIME and 1241 REPORT_TIME SHOULD be set to a value that is sufficiently longer than 1242 REACHABLE_TIME to avoid packet loss due to stale route optimization 1243 state. 1245 3.9. AERO Interface Encapsulation and Re-encapsulation 1247 In some instances, AERO interfaces insert a mid-layer IPv6 header 1248 known as the SPAN header as discussed in the following sections. 1249 After either inserting or omitting the SPAN header, the AERO 1250 interface inserts an outer encapsulation header as discussed below. 1252 AERO interfaces avoid outer encapsulation over Direct underlying 1253 interfaces and Proxyed underlying interfaces for which the first-hop 1254 access router is AERO-aware. Other AERO interfaces encapsulate 1255 packets according to whether they are entering the AERO interface 1256 from the network layer or if they are being re-admitted into the same 1257 AERO link they arrived on. This latter form of encapsulation is 1258 known as "re-encapsulation". 1260 For packets entering the AERO interface from the network layer, the 1261 AERO interface copies the "TTL/Hop Limit", "Type of Service/Traffic 1262 Class" [RFC2983], "Flow Label"[RFC6438] (for IPv6) and "Congestion 1263 Experienced" [RFC3168] values in the inner packet's IP header into 1264 the corresponding fields in the SPAN and outer encapsulation 1265 header(s). 1267 For packets undergoing re-encapsulation, the AERO interface instead 1268 copies these values from the original encapsulation header into the 1269 new encapsulation header, i.e., the values are transferred between 1270 encapsulation headers and *not* copied from the encapsulated packet's 1271 network-layer header. (Note especially that by copying the TTL/Hop 1272 Limit between encapsulation headers the value will eventually 1273 decrement to 0 if there is a (temporary) routing loop.) For IPv4 1274 encapsulation/re-encapsulation, the AERO interface sets the DF bit as 1275 discussed in Section 3.12. 1277 AERO interfaces configured over native and NATed underlying 1278 interfaces encapsulate packets in INET headers according to the next 1279 hop determined in the forwarding algorithm in Section 3.13. If the 1280 next hop is reached via a secured tunnel, the AERO interface uses an 1281 encapsulation format specific to the secured tunnel type (see: 1282 Section 6). If the next hop is reached via an unsecured underlying 1283 interface, the AERO interface instead uses Generic UDP Encapsulation 1284 (GUE) [I-D.ietf-intarea-gue] or an alternate minimal encapsulation 1285 format Appendix A. 1287 When GUE encapsulation is used, the AERO interface next sets the UDP 1288 source port to a constant value that it will use in each successive 1289 packet it sends, and sets the UDP length field to the length of the 1290 SPAN packet plus 8 bytes for the UDP header itself plus the length of 1291 the GUE header (or 0 if GUE direct IP encapsulation is used). For 1292 packets sent to a Server or Relay, the AERO interface sets the UDP 1293 destination port to 8060, i.e., the IANA-registered port number for 1294 AERO. For packets sent to a Client, the AERO interface sets the UDP 1295 destination port to the port value stored in the neighbor cache entry 1296 for this Client. The AERO interface then either includes or omits 1297 the UDP checksum according to the GUE specification. 1299 AERO interfaces observes the packet sizing and fragmentation 1300 considerations found in Section 3.12. 1302 3.10. AERO Interface Decapsulation 1304 AERO interfaces decapsulate packets destined either to the AERO node 1305 itself or to a destination reached via an interface other than the 1306 AERO interface the packet was received on. When the encapsulated 1307 packet arrives in multiple SPAN fragments, the AERO interface 1308 reassembles as discussed in Section 3.12. Further decapsulation 1309 steps are performed according to the appropriate encapsulation format 1310 specification. 1312 3.11. AERO Interface Data Origin Authentication 1314 AERO nodes employ simple data origin authentication procedures. In 1315 particular: 1317 o AERO Relays, Servers and Proxys accept encapsulated data packets 1318 and control messages received from secured tunnels via the SPAN. 1320 o AERO Servers and Proxys accept encapsulated data packets and NS 1321 messages used for Neighbor Unreachability Detection (NUD) received 1322 from a member of the ROS list. 1324 o AERO Proxys and Clients accept packets that originate from within 1325 the same secured ANET. 1327 o AERO Clients and Gateways accept packets from downstream network 1328 correspondents based on ingress filtering. 1330 AERO nodes silently drop any packets that do not satisfy the above 1331 data origin authentication procedures. Further security 1332 considerations are discussed inSection 6. 1334 3.12. AERO Interface MTU and Fragmentation 1336 IPv6 underlying interfaces are REQUIRED to configure a minimum 1337 Maximum Transmission Unit (MTU) of 1280 bytes [RFC8200]. The minimum 1338 MTU for IPv4 underlying interfaces is only 68 bytes [RFC1122], 1339 meaning that a packet smaller than the IPv6 MTU may require 1340 fragmentation when IPv4 encapsulation is used. Therefore, the Don't 1341 Fragment (DF) bit in the IPv4 encapsulation header MUST be set to 0. 1343 The AERO interface configures an MTU of 9180 bytes [RFC2492]; the 1344 size is therefore not a reflection of the underlying interface MTUs, 1345 but rather determines the largest packet the AERO interface can 1346 forward or reassemble. The AERO interface therefore accommodates IP 1347 packets up to 9180 bytes while generating IPv6 Path MTU Discovery 1348 (PMTUD) Packet Too Big (PTB) messages [RFC8201] as necessary (see 1349 below). 1351 AERO interfaces employ mid-layer IPv6 encapsulation and 1352 fragmentation/reassembly per [RFC2473] (aka "SPAN encapsulation") to 1353 accommodate the 9180 byte MTU. The AERO interface returns 1354 internally-generated PTB messages for packets admitted into the 1355 interface that it deems too large (e.g., according to link 1356 performance characteristics, reassembly cost, etc.) while either 1357 dropping or forwarding the packet as necessary. The AERO interface 1358 performs PMTUD even if the destination appears to be on the same link 1359 since intermediate AERO link nodes may return a PTB. This ensures 1360 that the path MTU is adaptive and reflects the current path used for 1361 a given data flow. 1363 AERO nodes perform SPAN encapsulation and fragmentation/reassembly as 1364 follows: 1366 o When a node's AERO interface sends a packet over a Proxyed, VPNed 1367 or Direct underlying interface, it sends without SPAN 1368 encapsulation if the packet is no larger than the underlying 1369 interface MTU. Otherwise, it encapsulates the packet in a SPAN 1370 header with source address set to the node's own SPAN address and 1371 destination set to the SPAN address of the link-layer peer Proxy, 1372 Server or Client on the underlying interface. The AERO interface 1373 then uses IPv6 fragmentation to break the encapsulated packet into 1374 a minimum number of non-overlapping fragments, where the largest 1375 fragment size is determined by the underlying interface MTU and 1376 the smallest fragment is no smaller than 640 bytes. The AERO 1377 interface then sends the fragments to the link-layer peer, which 1378 reassembles before forwarding toward the final destination. 1380 o When a node's AERO interface sends a packet over a Native or 1381 NATted underlying interface, it sends packets no larger than 1280 1382 bytes without SPAN encapsulation if the destination is reached via 1383 an INET address within the same SPAN segment. Otherwise, it 1384 encapsulates the packet in a SPAN header with source address set 1385 to the node's SPAN address and destination set to the SPAN address 1386 of the next hop AERO node toward the final destination. The AERO 1387 interface then uses IPv6 fragmentation to break the encapsulated 1388 packet into a minimum number of non-overlapping fragments, where 1389 the largest fragment size is 1280 bytes and the smallest fragment 1390 is no smaller than 640 bytes. The AERO interface then sends the 1391 fragments to the SPAN destination, which reassembles before 1392 forwarding toward the final destination. 1394 In order to avoid a "tiny fragment" attack, AERO interfaces 1395 unconditionally drop all SPAN fragments smaller than 640 bytes. In 1396 order to set the correct context for reassembly, the AERO interface 1397 that inserts a SPAN header MUST also be the one that inserts the IPv6 1398 Fragment Header Identification value. Although all fragmnets of the 1399 same fragmented SPAN packet are typically sent via the same 1400 underlying interface, this is not strictly required since all 1401 fragments will arrive at the AERO interface that performs reassembly 1402 even if they travel over different paths. 1404 Note that the AERO interface can forward large packets via 1405 encapsulation and fragmentation while at the same time returning 1406 advisory PTB messages, e.g., subject to rate limiting. The receiving 1407 node that performs reassembly can also send advisory PTB messages if 1408 reassembly conditions become unfavorable. The AERO interface can 1409 therefore continuously forward large packets without loss while 1410 returning advisory messages recommending a smaller size. Advisory 1411 PTB messages are differentiated from PTB messages that report loss by 1412 setting the Code field in the ICMPv6 message header to the value 1. 1413 This document therefore updates [RFC4443] and [RFC8201]. 1415 3.13. AERO Interface Forwarding Algorithm 1417 IP packets enter a node's AERO interface either from the network 1418 layer (i.e., from a local application or the IP forwarding system) or 1419 from the link layer (i.e., from an AERO interface neighbor). All 1420 packets entering a node's AERO interface first undergo data origin 1421 authentication as discussed in Section 3.11. Packets that satisfy 1422 data origin authentication are processed further, while all others 1423 are dropped silently. 1425 Packets that enter the AERO interface from the network layer are 1426 forwarded to an AERO interface neighbor. Packets that enter the AERO 1427 interface from the link layer are either re-admitted into the AERO 1428 link or forwarded to the network layer where they are subject to 1429 either local delivery or IP forwarding. In all cases, the AERO 1430 interface itself MUST NOT decrement the network layer TTL/Hop-count 1431 since its forwarding actions occur below the network layer. 1433 AERO interfaces may have multiple underlying interfaces and/or 1434 neighbor cache entries for neighbors with multiple ifIndex-tuple 1435 registrations (see Section 3.6). The AERO interface uses traffic 1436 classifiers (e.g., DSCP value, port number, etc.) to select an 1437 outgoing underlying interface for each packet based on the node's own 1438 QoS preferences, and also to select a destination link-layer address 1439 based on the neighbor's underlying interface with the highest 1440 preference. AERO implementations SHOULD allow for QoS preference 1441 values to be modified at runtime through network management. 1443 If multiple outgoing interfaces and/or neighbor interfaces have a 1444 preference of "high", the AERO node replicates the packet and sends 1445 one copy via each of the (outgoing / neighbor) interface pairs; 1446 otherwise, the node sends a single copy of the packet via an 1447 interface with the highest preference. AERO nodes keep track of 1448 which underlying interfaces are currently "reachable" or 1449 "unreachable", and only use "reachable" interfaces for forwarding 1450 purposes. 1452 The following sections discuss the AERO interface forwarding 1453 algorithms for Clients, Proxys, Servers and Relays. In the following 1454 discussion, a packet's destination address is said to "match" if it 1455 is the same as a cached address, or if it is covered by a cached 1456 prefix (which may be encoded in an AERO address). 1458 3.13.1. Client Forwarding Algorithm 1460 When an IP packet enters a Client's AERO interface from the network 1461 layer the Client searches for an asymmetric neighbor cache entry that 1462 matches the destination. If there is a match, the Client uses one or 1463 more "reachable" neighbor interfaces in the entry for packet 1464 forwarding. If there is no asymmetric neighbor cache entry, the 1465 Client instead forwards the packet toward a Server (the packet is 1466 intercepted by a Proxy if there is a Proxy on the path). The Client 1467 encapuslates the packet in an IPv6 header and fragments if necessary 1468 according to MTU requirements (see: Section 3.12). 1470 When an IP packet enters a Client's AERO interface from the link- 1471 layer, if the destination matches one of the Client's MNPs or link- 1472 local addresses the Client reassembles and decapsulates as necessary 1473 and delivers the inner packet to the network layer. Otherwise, the 1474 Client drops the packet and MAY return a network-layer ICMP 1475 Destination Unreachable message subject to rate limiting (see: 1476 Section 3.14). 1478 3.13.2. Proxy Forwarding Algorithm 1480 For control messages originating from or destined to a Client, the 1481 Proxy intercepts the message and updates its proxy neighbor cache 1482 entry for the Client. The Proxy then forwards a (proxyed) copy of 1483 the control message. (For example, the Proxy forwards a proxied 1484 version of a Client's NS/RS message to the target neighbor, and 1485 forwards a proxied version of the NA/RA reply to the Client.) 1487 When the Proxy receives a data packet from a Client within the ANET, 1488 ithe Proxy reassembles and re-fragments if necessary then searches 1489 for an asymmetric neighbor cache entry that matches the destination 1490 and forwards as follows: 1492 o if the destination matches an asymmetric neighbor cache entry, the 1493 Proxy uses one or more "reachable" neighbor interfaces in the 1494 entry for packet forwarding using SPAN encapsualtion if necessary 1495 with destination set to the neighbor's SPAN address. If the 1496 neighbor interface is in the same SPAN segment, the Proxy forwards 1497 the packet directly to the neighbor; otherwise, it forwards the 1498 packet to a Relay. 1500 o else, the Proxy encapsulates and forwards the packet to a Relay 1501 while using the SPAN address corresponding to the packet's 1502 destination as the SPAN destination address. 1504 When the Proxy receives an encapsulated data packet from an INET 1505 neighbor or from a secured tunnel from a Relay, it accepts the packet 1506 only if data origin authentication succeeds and if there is a proxy 1507 neighbor cache entry that matches the inner destination. Next, the 1508 Proxy reassembles the packet (if necessary) and continues processing. 1510 Next if reassembly is complete and the neighbor cache state is 1511 REACHABLE, the Proxy either drops and returns a PTB (see: 1512 Section 3.12) or forwards the packet to the Client while performing 1513 SPAN encapsulation and re-fragmentation to the ANET MTU size if 1514 necessary. If the neighbor cache entry state is DEPARTED, the Proxy 1515 instead changes the SPAN destination address to the address of the 1516 new Server and forwards it to a Relay while performing re- 1517 fragmentation to 1280 bytes if necessary. 1519 3.13.3. Server/Gateway Forwarding Algorithm 1521 For control messages destined to a target Client's AERO address that 1522 are received from a secured tunnel, the Server intercepts the message 1523 and sends an appropriate response on behalf of the Client. (For 1524 example, the Server sends an NA message reply in response to an NS 1525 message directed to one of its associated Clients.) If the Client's 1526 neighbor cache entry is in the DEPARTED state, however, the Server 1527 instead forwards the packet to the Client's new Server as discussed 1528 in Section 3.19. 1530 When the Server receives an encapsulated data packet from an INET 1531 neighbor or from a secured tunnel, it accepts the packet only if data 1532 origin authentication succeeds. If the SPAN destination address is 1533 its own address, the Server continues processing as follows: 1535 o if the destination matches a symmetric neighbor cache entry in the 1536 REACHABLE state the Server prepares the packet for forwarding to 1537 the destination Client. The Server first reassembles (if 1538 necessary) and forwards the packet (while re-fragmenting if 1539 necessary) as specified inSection 3.12. 1541 o else, if the destination matches a symmetric neighbor cache entry 1542 in the DEPARETED state the Server re-encapsulates the packet and 1543 forwards it using the SPAN address of the Client's new Server as 1544 the destination. 1546 o else, if the destination matches an asymmetric neighbor cache 1547 entry, the Server uses one or more "reachable" neighbor interfaces 1548 in the entry for packet forwarding via the local INET if the 1549 neighbor is in the same SPAN segment or via a Relay otherwise. 1551 o else, if the destination is an AERO address that is not assigned 1552 on the AERO interface the Server drops the packet. 1554 o else, the Server (acting as a Gateway) reassembles if necessary, 1555 decapsulates the packet and releases it to the network layer for 1556 local delivery or IP forwarding. Based on the information in the 1557 forwarding table, the network layer may return the packet to the 1558 same AERO interface in which case further processing occurs as 1559 below. (Note that this arrangement accommodates common 1560 implementations in which the IP forwarding table is not accessible 1561 from within the AERO interface. If the AERO interface can 1562 directly access the IP forwarding table (such as for in-kernel 1563 implementations) the forwarding table lookup can instead be 1564 performed internally from within the AERO interface itself.) 1566 When the Server's AERO interface receives a data packet from the 1567 network layer or from a VPNed or Direct Client, it performs SPAN 1568 encapsualtion and fragmentation if necessary, then processes the 1569 packet according to the network-layer destination address as follows: 1571 o if the destination matches a symmetric or asymmetric neighbor 1572 cache entry the Server processes the packet as above. 1574 o else, the Server encapsulates the packet and forwards it to a 1575 Relay using its own SPAN address as the source and the SPAN 1576 address corresponding to the destination as the destination. 1578 3.13.4. Relay Forwarding Algorithm 1580 Relays forward packets over secured tunnels the same as any IP 1581 router. When the Relay receives an encapsulated packet via a secured 1582 tunnel, it removes the INET header and searches for a forwarding 1583 table entry that matches the destination address in the next header. 1584 The Relay then processes the packet as follows: 1586 o if the destination matches one of the Relay's own addresses, the 1587 Relay submits the packet for local delivery. 1589 o else, if the destination matches a forwarding table entry the 1590 Relay forwards the packet via a secured tunnel to the next hop. 1591 If the destination matches an MSP without matching an MNP, 1592 however, the Relay instead drops the packet and returns an ICMP 1593 Destination Unreachable message subject to rate limiting (see: 1594 Section 3.14). 1596 o else, the Relay drops the packet and returns an ICMP Destination 1597 Unreachable as above. 1599 As for any IP router, the Relay decrements the TTL/Hop Limit when it 1600 forwards the packet. Therefore, only the Hop Limit in the SPAN 1601 header is decremented, and not the TTL/Hop Limit in the inner packet 1602 header. 1604 3.14. AERO Interface Error Handling 1606 When an AERO node admits a packet into the AERO interface, it may 1607 receive link-layer or network-layer error indications. 1609 A link-layer error indication is an ICMP error message generated by a 1610 router in the INET on the path to the neighbor or by the neighbor 1611 itself. The message includes an IP header with the address of the 1612 node that generated the error as the source address and with the 1613 link-layer address of the AERO node as the destination address. 1615 The IP header is followed by an ICMP header that includes an error 1616 Type, Code and Checksum. Valid type values include "Destination 1617 Unreachable", "Time Exceeded" and "Parameter Problem" 1618 [RFC0792][RFC4443]. (AERO interfaces ignore all link-layer IPv4 1619 "Fragmentation Needed" and IPv6 "Packet Too Big" messages since they 1620 only emit packets that are guaranteed to be no larger than the IP 1621 minimum link MTU as discussed in Section 3.12.) 1623 The ICMP header is followed by the leading portion of the packet that 1624 generated the error, also known as the "packet-in-error". For 1625 ICMPv6, [RFC4443] specifies that the packet-in-error includes: "As 1626 much of invoking packet as possible without the ICMPv6 packet 1627 exceeding the minimum IPv6 MTU" (i.e., no more than 1280 bytes). For 1628 ICMPv4, [RFC0792] specifies that the packet-in-error includes: 1629 "Internet Header + 64 bits of Original Data Datagram", however 1630 [RFC1812] Section 4.3.2.3 updates this specification by stating: "the 1631 ICMP datagram SHOULD contain as much of the original datagram as 1632 possible without the length of the ICMP datagram exceeding 576 1633 bytes". 1635 The link-layer error message format is shown in Figure 5 (where, "L2" 1636 and "L3" refer to link-layer and network-layer, respectively): 1638 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1639 ~ ~ 1640 | L2 IP Header of | 1641 | error message | 1642 ~ ~ 1643 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1644 | L2 ICMP Header | 1645 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 1646 ~ ~ P 1647 | IP and other encapsulation | a 1648 | headers of original L3 packet | c 1649 ~ ~ k 1650 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ e 1651 ~ ~ t 1652 | IP header of | 1653 | original L3 packet | i 1654 ~ ~ n 1655 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1656 ~ ~ e 1657 | Upper layer headers and | r 1658 | leading portion of body | r 1659 | of the original L3 packet | o 1660 ~ ~ r 1661 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 1663 Figure 5: AERO Interface Link-Layer Error Message Format 1665 The AERO node rules for processing these link-layer error messages 1666 are as follows: 1668 o When an AERO node receives a link-layer Parameter Problem message, 1669 it processes the message the same as described as for ordinary 1670 ICMP errors in the normative references [RFC0792][RFC4443]. 1672 o When an AERO node receives persistent link-layer Time Exceeded 1673 messages, the IP ID field may be wrapping before earlier fragments 1674 awaiting reassembly have been processed. In that case, the node 1675 should begin including integrity checks and/or institute rate 1676 limits for subsequent packets. 1678 o When an AERO node receives persistent link-layer Destination 1679 Unreachable messages in response to encapsulated packets that it 1680 sends to one of its asymmetric neighbor correspondents, the node 1681 should process the message as an indication that a path may be 1682 failing, and optionally initiate NUD over that path. If it 1683 receives Destination Unreachable messages over multiple paths, the 1684 node should allow future packets destined to the correspondent to 1685 flow through a default route and re-initiate route optimization. 1687 o When an AERO Client receives persistent link-layer Destination 1688 Unreachable messages in response to encapsulated packets that it 1689 sends to one of its symmetric neighbor Servers, the Client should 1690 mark the path as unusable and use another path. If it receives 1691 Destination Unreachable messages on many or all paths, the Client 1692 should associate with a new Server and release its association 1693 with the old Server as specified in Section 3.19.5. 1695 o When an AERO Server receives persistent link-layer Destination 1696 Unreachable messages in response to encapsulated packets that it 1697 sends to one of its symmetric neighbor Clients, the Server should 1698 mark the underlying path as unusable and use another underlying 1699 path. 1701 o When an AERO Server or Proxy receives link-layer Destination 1702 Unreachable messages in response to an encapsulated packet that it 1703 sends to one of its permanent neighbors, it treats the messages as 1704 an indication that the path to the neighbor may be failing. 1705 However, the dynamic routing protocol should soon reconverge and 1706 correct the temporary outage. 1708 When an AERO Relay receives a packet for which the network-layer 1709 destination address is covered by an MSP, if there is no more- 1710 specific routing information for the destination the Relay drops the 1711 packet and returns a network-layer Destination Unreachable message 1712 subject to rate limiting. The Relay writes the network-layer source 1713 address of the original packet as the destination address and uses 1714 one of its non link-local addresses as the source address of the 1715 message. 1717 When an AERO node receives an encapsulated packet for which the 1718 reassembly buffer it too small, it drops the packet and returns a 1719 network-layer Packet Too Big (PTB) message. The node first writes 1720 the MRU value into the PTB message MTU field, writes the network- 1721 layer source address of the original packet as the destination 1722 address and writes one of its non link-local addresses as the source 1723 address. 1725 3.15. AERO Router Discovery, Prefix Delegation and Autoconfiguration 1727 AERO Router Discovery, Prefix Delegation and Autoconfiguration are 1728 coordinated as discussed in the following Sections. 1730 3.15.1. AERO ND/PD Service Model 1732 Each AERO Server on the link configures a PD service to facilitate 1733 Client requests. Each Server is provisioned with a database of MNP- 1734 to-Client ID mappings for all Clients enrolled in the AERO service, 1735 as well as any information necessary to authenticate each Client. 1736 The Client database is maintained by a central administrative 1737 authority for the AERO link and securely distributed to all Servers, 1738 e.g., via the Lightweight Directory Access Protocol (LDAP) [RFC4511], 1739 via static configuration, etc. Clients receive the same service 1740 regardless of the Servers they select. 1742 AERO Clients and Servers use ND messages to maintain neighbor cache 1743 entries. AERO Servers configure their AERO interfaces as advertising 1744 NBMA interfaces, and therefore send unicast RA messages with a short 1745 Router Lifetime value (e.g., REACHABLE_TIME seconds) in response to a 1746 Client's RS message. Thereafter, Clients send additional RS messages 1747 to keep Server state alive. 1749 AERO Clients and Servers include PD parameters in RS/RA messages (see 1750 [I-D.templin-6man-dhcpv6-ndopt] for ND/PD alternatives). The unified 1751 ND/PD messages are exchanged between Client and Server according to 1752 the prefix management schedule required by the PD service. If the 1753 Client knows its MNP in advance, it can instead employ prefix 1754 registration by including its AERO address as the source address of 1755 an RS message and with an OMNI option with valid prefix registration 1756 information for the MNP. If the Server (and Proxy) accept the 1757 Client's MNP assertion, they inject the prefix into the routing 1758 system and establish the necessary neighbor cache state. 1760 The following sections specify the Client and Server behavior. 1762 3.15.2. AERO Client Behavior 1764 AERO Clients discover the addresses of Servers in a similar manner as 1765 described in [RFC5214]. Discovery methods include static 1766 configuration (e.g., from a flat-file map of Server addresses and 1767 locations), or through an automated means such as Domain Name System 1768 (DNS) name resolution [RFC1035]. Alternatively, the Client can 1769 discover Server addresses through a layer 2 data link login exchange, 1770 or through a unicast RA response to a multicast/anycast RS as 1771 described below. In the absence of other information, the Client can 1772 resolve the DNS Fully-Qualified Domain Name (FQDN) 1773 "linkupnetworks.[domainname]" where "linkupnetworks" is a constant 1774 text string and "[domainname]" is a DNS suffix for the AERO link 1775 (e.g., "example.com"). 1777 To associate with a Server, the Client acts as a requesting router to 1778 request MNPs. The Client prepares an RS message with PD parameters 1779 and includes a Nonce and Timestamp option if the Client needs to 1780 correlate RA replies. If the Client already knows the Server's AERO 1781 address, it includes the AERO address as the network-layer 1782 destination address; otherwise, it includes the link-scoped All- 1783 Routers multicast (ff02::2) or Subnet-Router anycast (fe80::) address 1784 as the network-layer destination. If the Client already knows its 1785 own AERO address, it uses the AERO address as the network-layer 1786 source address; otherwise, it uses the unspecified IPv6 address 1787 (::/128) as the network-layer source address. 1789 The Client next includes an OMNI option in the RS message to register 1790 its link-layer information with the Server. The Client sets the OMNI 1791 option prefix registration information according to the MNP, and 1792 includes an ifIndex-tuple with S set to '1' corresponding to the 1793 underlying interface over which the Client will send the RS message. 1794 The Client MAY include additional ifIndex-tuples specific to other 1795 underlying interfaces. The Client MAY also include an SLLAO with a 1796 link-layer address corresponding to the OMNI option ifIndex-tuple 1797 with S set to '1'. 1799 The Client then sends the RS message (either directly via Direct 1800 interfaces, via INET encapsulation for NATed interfaces, via a VPN 1801 for VPNed interfaces, via a Proxy for proxyed interfaces or via a 1802 Relay for native interfaces) and waits for an RA message reply (see 1803 Section 3.15.3). The Client retries up to MAX_RTR_SOLICITATIONS 1804 times until an RA is received. If the Client receives no RAs, or if 1805 it receives an RA with Router Lifetime set to 0, the Client SHOULD 1806 abandon this Server and try another Server. Otherwise, the Client 1807 processes the PD information found in the RA message. 1809 Next, the Client creates a symmetric neighbor cache entry with the 1810 Server's AERO address as the network-layer address and the Server's 1811 encapsulation and/or link-layer addresses as the link-layer address. 1812 The Client records the RA Router Lifetime field value in the neighbor 1813 cache entry as the time for which the Server has committed to 1814 maintaining the MNP in the routing system via this underlying 1815 interface, and caches the other RA configuration information 1816 including Cur Hop Limit, M and O flags, Reachable Time and Retrans 1817 Timer. The Client then autoconfigures AERO addresses for each of the 1818 delegated MNPs and assigns them to the AERO interface. The Client 1819 also caches any MSPs included in Route Information Options (RIOs) 1820 [RFC4191] as MSPs to associate with the AERO link, and assigns the 1821 MTU value in the MTU option to the underlying interface. 1823 The Client then registers additional underlying interfaces with the 1824 Server by sending RS messages via each additional interface. The RS 1825 messages include the same parameters as for the initial RS/RA 1826 exchange, but with destination address set to the Server's AERO 1827 address. 1829 Following autoconfiguration, the Client sub-delegates the MNPs to its 1830 attached EUNs and/or the Client's own internal virtual interfaces as 1831 described in [I-D.templin-v6ops-pdhost] to support the Client's 1832 downstream attached "Internet of Things (IoT)". The Client 1833 subsequently sends additional RS messages over each underlying 1834 interface before the Router Lifetime received for that interface 1835 expires. 1837 After the Client registers its underlying interfaces, it may wish to 1838 change one or more registrations, e.g., if an interface changes 1839 address or becomes unavailable, if QoS preferences change, etc. To 1840 do so, the Client prepares an RS message to send over any available 1841 underlying interface. The RS includes an OMNI option with prefix 1842 registration information specific to its MNP, with an ifIndex-tuple 1843 specific to the selected underlying interface with S set to '1', and 1844 with any additional ifIndex-tuples specific to other underlying 1845 interfaces. The Client includes fresh ifIndex-tuple values to update 1846 the Server's neighbor cache entry. When the Client receives the 1847 Server's RA response, it has assurance that the Server has been 1848 updated with the new information. 1850 If the Client wishes to discontinue use of a Server it issues an RS 1851 message over any underlying interface with an OMNI option with a 1852 prefix release indication. When the Server processes the message, it 1853 releases the MNP, sets the symmetric neighbor cache entry state for 1854 the Client to DEPARTED and returns an RA reply with Router Lifetime 1855 set to 0. After a short delay (e.g., 2 seconds), the Server 1856 withdraws the MNP from the routing system. 1858 3.15.3. AERO Server Behavior 1860 AERO Servers act as IP routers and support a PD service for Clients. 1861 Servers arrange to add their AERO addresses to a static map of Server 1862 addresses for the link and/or the DNS resource records for the FQDN 1863 "linkupnetworks.[domainname]" before entering service. Server 1864 addresses should be geographically and/or topologically referenced, 1865 and made available for discovery by Clients on the AERO link. 1867 When a Server receives a prospective Client's RS message on its AERO 1868 interface, it SHOULD return an immediate RA reply with Router 1869 Lifetime set to 0 if it is currently too busy or otherwise unable to 1870 service the Client. Otherwise, the Server authenticates the RS 1871 message and processes the PD parameters. The Server first determines 1872 the correct MNPs to delegate to the Client by searching the Client 1873 database. When the Server delegates the MNPs, it also creates a 1874 forwarding table entry for each MNP so that the MNPs are propagated 1875 into the routing system (see: Section 3.3). For IPv6, the Server 1876 creates an IPv6 forwarding table entry for each MNP. For IPv4, the 1877 Server creates an IPv6 forwarding table entry with the SPAN 1878 Compatibility Prefix (SCP) corresponding to the IPv4 address. 1880 The Server next creates a symmetric neighbor cache entry for the 1881 Client using the base AERO address as the network-layer address and 1882 with lifetime set to no more than the smallest PD lifetime. Next, 1883 the Server updates the neighbor cache entry by recording the 1884 information in each ifIndex-tuple in the RS OMNI option. The Server 1885 also records the actual SPAN/INET addresses in the neighbor cache 1886 entry. 1888 Next, the Server prepares an RA message using its AERO address as the 1889 network-layer source address and the network-layer source address of 1890 the RS message as the network-layer destination address. The Server 1891 sets the Router Lifetime to the time for which it will maintain both 1892 this underlying interface individually and the symmetric neighbor 1893 cache entry as a whole. The Server also sets Cur Hop Limit, M and O 1894 flags, Reachable Time and Retrans Timer to values appropriate for the 1895 AERO link. The Server includes the delegated MNPs, any other PD 1896 parameters and an OMNI option with no ifIndex-tuples. The Server 1897 then includes one or more RIOs that encode the MSPs for the AERO 1898 link, plus an MTU option (see Section 3.12). The Server finally 1899 forwards the message to the Client using SPAN/INET, INET, or NULL 1900 encapsulation as necessary. 1902 After the initial RS/RA exchange, the Server maintains a 1903 ReachableTime timer for each of the Client's underlying interfaces 1904 individually (and for the Client's symmetric neighbor cache entry 1905 collectively) set to expire after Router Lifetime seconds. If the 1906 Client (or Proxy) issues additional RS messages, the Server sends an 1907 RA response and resets ReachableTime. If the Server receives an ND 1908 message with PD release indication it sets the Client's symmetric 1909 neighbor cache entry to the DEPARTED state and withdraws the MNP from 1910 the routing system after a short delay (e.g., 2 seconds). If 1911 ReachableTime expires before a new RS is received on an individual 1912 underlying interface, the Server marks the interface as DOWN. If 1913 ReachableTime expires before any new RS is received on any individual 1914 underlying interface, the Server deletes the neighbor cache entry and 1915 withdraws the MNP without delay. 1917 The Server processes any ND/PD messages pertaining to the Client and 1918 returns an NA/RA reply in response to solicitations. The Server may 1919 also issue unsolicited RA messages, e.g., with PD reconfigure 1920 parameters to cause the Client to renegotiate its PDs, with Router 1921 Lifetime set to 0 if it can no longer service this Client, etc. 1922 Finally, If the symmetric neighbor cache entry is in the DEPARTED 1923 state, the Server deletes the entry after DepartTime expires. 1925 Note: Clients SHOULD notify former Servers of their departures, but 1926 Servers are responsible for expiring neighbor cache entries and 1927 withdrawing routes even if no departure notification is received 1928 (e.g., if the Client leaves the network unexpectedly). Servers 1929 SHOULD therefore set Router Lifetime to REACHABLE_TIME seconds in 1930 solicited RA messages to minimize persistent stale cache information 1931 in the absence of Client departure notifications. A short Router 1932 Lifetime also ensures that proactive Client/Server RS/RA messaging 1933 will keep any NAT state alive (see above). 1935 Note: All Servers on an AERO link MUST advertise consistent values in 1936 the RA Cur Hop Limit, M and O flags, Reachable Time and Retrans Timer 1937 fields the same as for any link, since unpredictable behavior could 1938 result if different Servers on the same link advertised different 1939 values. 1941 3.15.3.1. Lightweight DHCPv6 Relay Agent (LDRA) 1943 When DHCPv6 is used as the ND/PD service back end, AERO Clients and 1944 Servers are always on the same link (i.e., the AERO link) from the 1945 perspective of DHCPv6. However, in some implementations the DHCPv6 1946 server and ND function may be located in separate modules. In that 1947 case, the Server's AERO interface module can act as a Lightweight 1948 DHCPv6 Relay Agent (LDRA)[RFC6221] to relay PD messages to and from 1949 the DHCPv6 server module. 1951 When the LDRA receives an authentic RS message, it extracts the PD 1952 message parameters and uses them to construct an IPv6/UDP/DHCPv6 1953 message. It sets the IPv6 source address to the source address of 1954 the RS message, sets the IPv6 destination address to 1955 'All_DHCP_Relay_Agents_and_Servers' and sets the UDP fields to values 1956 that will be understood by the DHCPv6 server. 1958 The LDRA then wraps the message in a DHCPv6 'Relay-Forward' message 1959 header and includes an 'Interface-Id' option that includes enough 1960 information to allow the LDRA to forward the resulting Reply message 1961 back to the Client (e.g., the Client's link-layer addresses, a 1962 security association identifier, etc.). The LDRA also wraps the OMNI 1963 option and SLLAO into the Interface-Id option, then forwards the 1964 message to the DHCPv6 server. 1966 When the DHCPv6 server prepares a Reply message, it wraps the message 1967 in a 'Relay-Reply' message and echoes the Interface-Id option. The 1968 DHCPv6 server then delivers the Relay-Reply message to the LDRA, 1969 which discards the Relay-Reply wrapper and IPv6/UDP headers, then 1970 uses the DHCPv6 message to construct an RA response to the Client. 1971 The Server uses the information in the Interface-Id option to prepare 1972 the RA message and to cache the link-layer addresses taken from the 1973 OMNI option and SLLAO echoed in the Interface-Id option. 1975 3.16. The AERO Proxy 1977 Clients may connect to ANETs that deploy perimeter security services 1978 to facilitate communications to Servers in outside INETs. In that 1979 case, the ANET can employ an AERO Proxy. The Proxy is located at the 1980 ANET/INET border and listens for RS messages originating from or RA 1981 messages destined to ANET Clients. The Proxy acts on these control 1982 messages as follows: 1984 o when the Proxy receives an RS message from a new ANET Client, it 1985 first authenticates the message then examines the network-layer 1986 destination address. If the destination address is a Server's 1987 AERO address, the Proxy proceeds to the next step. Otherwise, if 1988 the destination is All-Routers multicast or Subnet-Router anycast, 1989 the Proxy selects a "nearby" Server that is likely to be a good 1990 candidate to serve the Client and replaces the destination address 1991 with the Server's AERO address. Next, the Proxy creates a proxy 1992 neighbor cache entry and caches the Client and Server link-layer 1993 addresses along with the OMNI option information and any other 1994 identifying information including Transaction IDs, Client 1995 Identifiers, Nonce values, etc. The Proxy finally encapsulates 1996 the (proxyed) RS message in a SPAN header with source set to the 1997 Proxy's SPAN address and destination set to the Server's SPAN 1998 address then forwards the message into the SPAN. 2000 o when the Server receives the RS, it authenticates the message then 2001 creates or updates a symmetric neighbor cache entry for the Client 2002 with the Proxy's SPAN address as the link-layer address. The 2003 Server then sends an RA message back to the Proxy via the SPAN. 2005 o when the Proxy receives the RA, it authenticates the message and 2006 matches it with the proxy neighbor cache entry created by the RS. 2007 The Proxy then caches the PD route information as a mapping from 2008 the Client's MNPs to the Client's ANET address, caches the 2009 Server's advertised Router Lifetime and sets the neighbor cache 2010 entry state to REACHABLE. The Proxy then sets the P bit in the RA 2011 flags field, optionally rewrites the Router Lifetime and forwards 2012 the (proxyed) message to the Client. The Proxy finally includes 2013 an MTU option (if necessary) with an MTU to use for the underlying 2014 ANET interface. 2016 After the initial RS/RA exchange, the Proxy forwards any Client data 2017 packets for which there is no matching asymmetric neighbor cache 2018 entry to a Relay using SPAN encapsulation with its own SPAN address 2019 as the source and the SPAN address corresponding to the Client as the 2020 destination. The Proxy instead forwards any Client data destined to 2021 an asymmetric neighbor cache target directly to the target according 2022 to the SPAN/link-layer information - the process of establishing 2023 asymmetric neighbor cache entries is specified in Section 3.17. 2025 While the Client is still attached to the ANET, the Proxy sends NS, 2026 RS and/or unsolicited NA messages to update the Server's symmetric 2027 neighbor cache entries on behalf of the Client and/or to convey QoS 2028 updates. This allows for higher-frequency Proxy-initiated RS/RA 2029 messaging over well-connected INET infrastructure supplemented by 2030 lower-frequency Client-initiated RS/RA messaging over constrained 2031 ANET data links. 2033 If the Server ceases to send solicited advertisements, the Proxy 2034 sends unsolicited RAs on the ANET interface with destination set to 2035 All-Nodes multicast (ff02::1) and with Router Lifetime set to zero to 2036 inform Clients that the Server has failed. Although the Proxy 2037 engages in ND exchanges on behalf of the Client, the Client can also 2038 send ND messages on its own behalf, e.g., if it is in a better 2039 position than the Proxy to convey QoS changes, etc. For this reason, 2040 the Proxy marks any Client-originated solicitation messages (e.g. by 2041 inserting a Nonce option) so that it can return the solicited 2042 advertisement to the Client instead of processsing it locally. 2044 If the Client becomes unreachable, the Proxy sets the neighbor cache 2045 entry state to DEPARTED and retains the entry for DEPART_TIME 2046 seconds. While the state is DEPARTED, the Proxy forwards any packets 2047 destined to the Client to a Relay via SPAN encapsulation with the 2048 Client's current Server as the destination. The Relay in turn 2049 forwards the packets to the Client's current Server. When DepartTime 2050 expires, the Proxy deletes the neighbor cache entry and discards any 2051 further packets destined to this (now forgotten) Client. 2053 In some ANETs that employ a Proxy, the Client's MNP can be injected 2054 into the ANET routing system. In that case, the Client can send data 2055 messages without encapsulation so that the ANET native routing system 2056 transports the unencapsulated packets to the Proxy. This can be very 2057 beneficial, e.g., if the Client connects to the ANET via low-end data 2058 links such as some aviation wireless links. 2060 If the first-hop ANET access router is AERO-aware, the Client can 2061 avoid encapsulation for both its control and data messages. When the 2062 Client connects to the link, it can send an unencapsulated RS message 2063 with source address set to its AERO address and with destination 2064 address set to the AERO address of the Client's selected Server or to 2065 All-Routers multicast or Subnet-Router anycast. The Client includes 2066 an OMNI option formatted as specified in 2067 [I-D.templin-6man-omni-interface]. 2069 The Client then sends the unencapsulated RS message, which will be 2070 intercepted by the AERO-Aware access router. The access router then 2071 encapsulates the RS message in an ANET header with its own address as 2072 the source address and the address of a Proxy as the destination 2073 address. The access router further remembers the address of the 2074 Proxy so that it can encapsulate future data packets from the Client 2075 via the same Proxy. If the access router needs to change to a new 2076 Proxy, it simply sends another RS message toward the Server via the 2077 new Proxy on behalf of the Client. 2079 In some cases, the access router and Proxy may be one and the same 2080 node. In that case, the node would be located on the same physical 2081 link as the Client, but its message exchanges with the Server would 2082 need to pass through a security gateway at the ANET/INET border. The 2083 method for deploying access routers and Proxys (i.e. as a single node 2084 or multiple nodes) is an ANET-local administrative consideration. 2086 3.16.1. Detecting and Responding to Server Failures 2088 In environments where fast recovery from Server failure is required, 2089 Proxys SHOULD use proactive Neighbor Unreachability Detection (NUD) 2090 to track Server reachability in a similar fashion as for 2091 Bidirectional Forwarding Detection (BFD) [RFC5880]. Proxys can then 2092 quickly detect and react to failures so that cached information is 2093 re-established through alternate paths. The NUD control messaging is 2094 carried only over well-connected ground domain networks (i.e., and 2095 not low-end aeronautical radio links) and can therefore be tuned for 2096 rapid response. 2098 Proxys perform proactive NUD with Servers for which there are 2099 currently active ANET Clients by sending continuous NS messages in 2100 rapid succession, e.g., one message per second. The Proxy sends the 2101 NS message via the SPAN with the Proxy's AERO address as the source 2102 and the AERO address of the Server as the destination. When the 2103 Proxy is also sending RS messages to the Server on behalf of ANET 2104 Clients, the resulting RA responses can be considered as equivalent 2105 hints of forward progress. This means that the Proxy need not also 2106 send a periodic NS if it has already sent an RS within the same 2107 period. If the Server fails (i.e., if the Proxy ceases to receive 2108 advertisements), the Proxy can quickly inform Clients by sending 2109 multicast RA messages on the ANET interface. 2111 The Proxy sends RA messages on the ANET interface with source address 2112 set to the Server's address, destination address set to All-Nodes 2113 multicast, and Router Lifetime set to 0. The Proxy SHOULD send 2114 MAX_FINAL_RTR_ADVERTISEMENTS RA messages separated by small delays 2115 [RFC4861]. Any Clients on the ANET that had been using the failed 2116 Server will receive the RA messages and associate with a new Server. 2118 3.16.2. Point-to-Multipoint Server Coordindation 2120 In environments where Client messaging over ANETs is bandwidth- 2121 limited and/or expensive, Clients can enlist the services of the 2122 Proxy to coordinate with multiple Servers in a single RS/RA message 2123 exchange. The Client can send a single RS message to All-Routers 2124 multicast that includes the ID's of multiple Servers in MS-Register 2125 sub-options of the OMNI option,. 2127 When the Proxy receives the RS and processes the OMNI option, it 2128 performs a separate RS/RA exchange with each MS-Register Server. 2129 When it has received the RA messages, it creates an "aggregate" RA 2130 message to return to the Client with an OMNI option with each 2131 responding Server's ID recorded in an MS-Register sub-option. 2133 Client's can thereafter employ efficient point-to-multipoint Server 2134 coordination under the assistance of the Proxy to dramatically reduce 2135 the number of messages sent over the ANET while enlisting the support 2136 of multiple Servers for fault tolerance. Clients can further include 2137 MS-Release suboptions in RS messages to request the Proxy to release 2138 from former Servers via the procedures discussed in Section 3.19.5. 2140 The OMNI interface specification [I-D.templin-6man-omni-interface] 2141 provides further discussion of the Client/Proxy RS/RA messaging 2142 involved in point-to-multipoint coordination. 2144 3.17. AERO Route Optimization 2146 While data packets are flowing between a source and target node, 2147 route optimization SHOULD be used. Route optimization is initiated 2148 by the first eligible Route Optimization Source (ROS) closest to the 2149 source as follows: 2151 o For Clients on VPNed and Direct interfaces, the Server is the ROS. 2153 o For Clients on Proxyed interfaces, the Proxy is the ROS. 2155 o For Clients on native and NATed interfaces, the Client itself is 2156 the ROS. 2158 o For correspondent nodes on INET/EUN interfaces serviced by a 2159 Gateway, the Gateway is the ROS. 2161 The route optimization procedure is conducted between the ROS and the 2162 target Server/Gateway acting as a Route Optimization Responder (ROR) 2163 in the same manner as for IPv6 ND Address Resolution and using the 2164 same NS/NA messaging. The target may either be a MNP Client serviced 2165 by a Server, or a non-MNP correspondent reachable via a Gateway. 2167 The procedures are specified in the following sections. 2169 3.17.1. Route Optimization Initiation 2171 While data packets are flowing from the source node toward a target 2172 node, the ROS performs address resolution by sending an NS message 2173 for Address Resolution (NS(AR)) to receive a solicited NA message 2174 from the ROR. When the ROS sends an NS(AR), it includes: 2176 o the AERO address of the ROS as the source address. 2178 o the data packet's destination as the Target Address. 2180 o the Solicited-Node multicast address [RFC4291] formed from the 2181 lower 24 bits of the data packet's destination as the destination 2182 address, e.g., for 2001:db8:1:2::10:2000 the NS destination 2183 address is ff02:0:0:0:0:1:ff10:2000. 2185 The NS(AR) message includes an OMNI option with no ifIndex-tuples and 2186 no SLLAO, such that the target will not create a neighbor cache 2187 entry. 2189 The ROS then encapsulates the NS(AR) message in a SPAN header with 2190 source set to its own SPAN address and destination set to the SPAN 2191 address corresponding to the packet's final destination, then sends 2192 the message into the SPAN without decrementing the network-layer TTL/ 2193 Hop Limit field. 2195 3.17.2. Relaying the NS 2197 When the Relay receives the NS(AR) message from the ROS, it discards 2198 the INET header and determines that the ROR is the next hop by 2199 consulting its standard IPv6 forwarding table for the SPAN header 2200 destination address. The Relay then forwards the message toward the 2201 ROR via the SPAN the same as for any IPv6 router. The final-hop 2202 Relay in the SPAN will deliver the message via a secured tunnel to 2203 the ROR. 2205 3.17.3. Processing the NS and Sending the NA 2207 When the ROR receives the NS(AR) message, it examines the Target 2208 Address to determine whether it has a neighbor cache entry and/or 2209 route that matches the target. If there is no match, the ROR drops 2210 the NS(AR) message. Otherwise, the ROR continues processing as 2211 follows: 2213 o if the target belongs to an MNP Client neighbor in the DEPARTED 2214 state the ROR changes the NS(AR) message SPAN destination address 2215 to the SPAN address of the Client's new Server, forwards the 2216 message into the SPAN and returns from processing. 2218 o If the target belongs to an MNP Client neighbor in the REACHABLE 2219 state, the ROR instead adds the AERO source address to the target 2220 Client's Report List with time set to ReportTime. 2222 o If the target belongs to a non-MNP route, the ROR continues 2223 processing without adding an entry to the Report List. 2225 The ROR then prepares a solicited NA message to send back to the ROS 2226 but does not create a neighbor cache entry. The ROR sets the NA 2227 source address to the AERO address corresponding to the target, sets 2228 the Target Addresss to the target of the solicitation, and sets the 2229 destination address to the source of the solicitation. 2231 The ROR then includes an OMNI option with prefix registration length 2232 set to the length of the MNP if the target is an MNP Client; 2233 otherwise, set to the maximum of the non-MNP prefix length and 64. 2234 (Note that a /64 limit is imposed to avoid causing the ROS to set 2235 short prefixes (e.g., "default") that would match destinations for 2236 which the routing system includes more-specific prefixes.) 2238 If the target is an MNP Client, the ROR next includes ifIndex-tuples 2239 in the OMNI option for each of the target Client's underlying 2240 interfaces with current information for each interface and with the S 2241 flag set to 0. The ROR then includes a TLLAO with ifIndex-tuples in 2242 one-to-one correspondence with the tuples that appear in the OMNI 2243 option while setting the Link Layer Address field as follows: 2245 o For each NATed, VPNed and Direct interface, the ROR sets the Link 2246 Layer Address to its own SPAN address. 2248 o For each Proxyed interface, the ROR sets the Link Layer Address to 2249 the Proxy's SPAN address. 2251 o For each native interface, if the ROS and ROR are located in the 2252 same SPAN partition the ROR sets the Link Layer Address to the 2253 INET addesses of the Client's native interface. Otherwise, the 2254 ROR sets the Link Layer Address to its own SPAN address. 2256 The ROR then sets the NA message R flag to 1 (as a router), S flag to 2257 1 (as a response to a solicitation), and O flag to 0 (as a proxy). 2258 The ROR finally encapsulates the NA message in a SPAN header with 2259 source set to its own SPAN address and destination set to the source 2260 SPAN address of the NS(AR) message, then forwards the message into 2261 the SPAN without decrementing the network-layer TTL/Hop Limit field. 2263 3.17.4. Relaying the NA 2265 When the Relay receives the NA message from the ROR, it discards the 2266 INET header and determines that the ROS is the next hop by consulting 2267 its standard IPv6 forwarding table for the SPAN header destination 2268 address. The Relay then forwards the SPAN-encapsulated NA message 2269 toward the ROS the same as for any IPv6 router. The final-hop Relay 2270 in the SPAN will deliver the message via a secured tunnel to the ROS. 2272 3.17.5. Processing the NA 2274 When the ROS receives the solicited NA message, it processes the 2275 message the same as for standard IPv6 Address Resolution [RFC4861]. 2276 In the process, it caches the source SPAN address then creates an 2277 asymmetric neighbor cache entry for the ROR and caches all 2278 information found in the OMNI and TLLAO options. The ROS finally 2279 sets the asymmetric neighbor cache entry lifetime to REACHABLE_TIME 2280 seconds. 2282 3.17.6. Route Optimization Maintenance 2284 Following route optimization, the ROS forwards future data packets 2285 destined to the target via the addresses found in the cached link- 2286 layer information. The route optimization is shared by all sources 2287 that send packets to the target via the ROS, i.e., and not just the 2288 source on behalf of which the route optimization was initiated. 2290 While new data packets destined to the target are flowing through the 2291 ROS, it sends additional NS(AR) messages to the ROR before 2292 ReachableTime expires to receive a fresh solicited NA message the 2293 same as described in the previous sections (route optimization 2294 refreshment strategies are an implementation matter, with a non- 2295 normative example given in Appendix B.1). The ROS uses the cached 2296 SPAN address of the ROR as the NS(AR) SPAN destination address, and 2297 sends up to MAX_MULTICAST_SOLICIT NS(AR) messages separated by 1 2298 second until an NA is received. If no NA is received, the ROS 2299 assumes that the current ROR has become unreachable and deletes the 2300 neighbor cache entry. Subsequent data packets will trigger a new 2301 route optimization per Section 3.17.1 to discover a new ROR while 2302 initial data packets travel over a suboptimal route. 2304 If an NA is received, the ROS then updates the asymmetric neighbor 2305 cache entry to refresh ReachableTime, while (for MNP destinations) 2306 the ROR adds or updates the ROS address to the target Client's Report 2307 List and with time set to ReportTime. While no data packets are 2308 flowing, the ROS instead allows ReachableTime for the asymmetric 2309 neighbor cache entry to expire. When ReachableTime expires, the ROS 2310 deletes the asymmetric neighbor cache entry. Any future data packets 2311 flowing through the ROS will again trigger a new route optimization. 2313 The ROS may also receive unsolicited NA messages from the ROR at any 2314 time (see: Section 3.19). If there is an asymmetric neighbor cache 2315 entry for the target, the ROS updates the link-layer information but 2316 does not update ReachableTime since the receipt of an unsolicited NA 2317 does not confirm that any forward paths are working. If there is no 2318 asymmetric neighbor cache entry, the ROS simply discards the 2319 unsolicited NA. 2321 In this arrangement, the ROS holds an asymmetric neighbor cache entry 2322 for the ROR, but the ROR does not hold an asymmetric neighbor cache 2323 entry for the ROS. The route optimization neighbor relationship is 2324 therefore asymmetric and unidirectional. If the target node also has 2325 packets to send back to the source node, then a separate route 2326 optimization procedure is performed in the reverse direction. But, 2327 there is no requirement that the forward and reverse paths be 2328 symmetric. 2330 3.18. Neighbor Unreachability Detection (NUD) 2332 AERO nodes perform Neighbor Unreachability Detection (NUD) per 2333 [RFC4861] either reactively in response to persistent link-layer 2334 errors (see Section 3.14) or proactively to confirm reachability. 2335 The NUD algorithm is based on periodic control message exchanges. 2336 The algorithm may further be seeded by ND hints of forward progress, 2337 but care must be taken to avoid inferring reachability based on 2338 spoofed information. For example, authentic IPv6 ND message 2339 exchanges may be considered as acceptable hints of forward progress, 2340 while spurious data packets should not be. 2342 AERO Servers, Proxys and Gateways can use standard NS/NA NUD 2343 exchanges sent over the SPAN to securely test reachability without 2344 risk of DoS attacks from nodes pretending to be a neighbor; Proxys 2345 can further perform NUD to securely verify Server reachability on 2346 behalf of their proxyed Clients. However, a means for a ROS to test 2347 the unsecured forward directions of target route optimized paths is 2348 also necessary. 2350 When an ROR directs an ROS to a neighbor with one or more target 2351 link-layer addresses, the ROS can proactively test each such 2352 unsecured route optimized path by sending "loopback" NS(NUD) 2353 messages. While testing the paths, the ROS can optionally continue 2354 to send packets via the SPAN, maintain a small queue of packets until 2355 target reachability is confirmed, or (optimistically) allow packets 2356 to flow via the route optimized paths. 2358 When the ROS sends a loopback NS(NUD) message, it uses its AERO 2359 address as both the IPv6 source and destination address, and the MNP 2360 Subnet-Router anycast address as the Target Address. The ROS 2361 includes a Nonce and Timestamp option, then encapsulates the message 2362 in SPAN/INET headers with its own SPAN address as the source and the 2363 SPAN address of the route optimization target as the destination. 2364 The ROS then forwards the message to the target (either directly to 2365 the link layer address of the target if the target is in the same 2366 SPAN segment, or via a Relay if the target is in a different SPAN 2367 segment). 2369 When the route optimization target receives the NS(NUD) message, it 2370 notices that the IPv6 destination address is the same as the source 2371 address. It then reverses the SPAN source and destination addresses 2372 and returns the message to the ROS (either directly or via the SPAN). 2373 The route optimization target does not decrement the NS(NUD) message 2374 IPv6 Hop-Limit in the process, since the message has not exited the 2375 SPAN. 2377 When the ROS receives the NS(NUD) message, it can determine from the 2378 Nonce, Timestamp and Target Address that the message originated from 2379 itself and that it transited the forward path. The ROS need not 2380 prepare an NA response, since the destination of the response would 2381 be itself and testing the route optimization path again would be 2382 redundant. 2384 The ROS marks route optimization target paths that pass these NUD 2385 tests as "reachable", and those that do not as "unreachable". These 2386 markings inform the AERO interface forwarding algorithm specified in 2387 Section 3.13. 2389 Note that to avoid a DoS vector nodes MUST NOT return loopback 2390 NS(NUD) messages received from an unsecured link-layer source via a 2391 secured SPAN path. 2393 3.19. Mobility Management and Quality of Service (QoS) 2395 AERO is a Distributed Mobility Management (DMM) service. Each Server 2396 is responsible for only a subset of the Clients on the AERO link, as 2397 opposed to a Centralized Mobility Management (CMM) service where 2398 there is a single network mobility collective entity for all Clients. 2399 Clients coordinate with their associated Servers via RS/RA exchanges 2400 to maintain the DMM profile, and the AERO routing system tracks all 2401 current Client/Server peering relationships. 2403 Servers provide default routing and mobility/multilink services for 2404 their dependent Clients. Clients are responsible for maintaining 2405 neighbor relationships with their Servers through periodic RS/RA 2406 exchanges, which also serves to confirm neighbor reachability. When 2407 a Client's underlying interface address and/or QoS information 2408 changes, the Client is responsible for updating the Server with this 2409 new information. Note that for Proxyed interfaces, however, the 2410 Proxy can also perform some RS/RA exchanges on the Client's behalf. 2412 Mobility management considerations are specified in the following 2413 sections. 2415 3.19.1. Mobility Update Messaging 2417 Servers accommodate Client mobility/multilink and/or QoS change 2418 events by sending unsolicited NA (uNA) messages to each ROS in the 2419 target Client's Report List. When a Server sends a uNA message, it 2420 sets the IPv6 source address to the Client's AERO address, sets the 2421 destination address to All-Nodes multicast and sets the Target 2422 Address to the Client's Subnet-Router anycast address. The Server 2423 also includes an OMNI option with prefix registration information and 2424 with ifIndex-tuples for the target Client's remaining interfaces with 2425 S set to 0. The Server then includes a TLLAO with corresponding 2426 ifIndex-tuples with link layer addresses set to the corresponding 2427 target SPAN addresses. The Server sets the NA R flag to 1, the S 2428 flag to 0 and the O flag to 0, then encapsulates the message in a 2429 SPAN header with source set to its own SPAN address and destination 2430 set to the SPAN address of the ROS and sends the message into the 2431 SPAN. 2433 As discussed in Section 7.2.6 of [RFC4861], the transmission and 2434 reception of uNA messages is unreliable but provides a useful 2435 optimization. In well-connected Internetworks with robust data links 2436 uNA messages will be delivered with high probability, but in any case 2437 the Server can optionally send up to MAX_NEIGHBOR_ADVERTISEMENT uNAs 2438 to each ROS to increase the likelihood that at least one will be 2439 received. 2441 When the ROS receives an uNA message, it ignores the message if there 2442 is no existing neighbor cache entry for the Client. Otherwise, it 2443 uses the included OMNI option and TLLAO information to update the 2444 neighbor cache entry, but does not reset ReachableTime since the 2445 receipt of an unsolicited NA message from the target Server does not 2446 provide confirmation that any forward paths to the target Client are 2447 working. 2449 If uNA messages are lost, the ROS may be left with stale address and/ 2450 or QoS information for the Client for up to REACHABLE_TIME seconds. 2451 During this time, the ROS can continue sending packets according to 2452 its stale neighbor cache information. When ReachableTime is close to 2453 expiring, the ROS will re-initiate route optimization and receive 2454 fresh link-layer address information. 2456 In addition to sending uNA messages to the current set of ROSs for 2457 the Client, the Server also sends uNAs to the former link-layer 2458 address for any ifIndex-tuple for which the link-layer address has 2459 changed. The uNA messages update Proxys that cannot easily detect 2460 (e.g., without active probing) when a formerly-active Client has 2461 departed. 2463 3.19.2. Announcing Link-Layer Address and/or QoS Preference Changes 2465 When a Client needs to change its ANET addresses and/or QoS 2466 preferences (e.g., due to a mobility event), either the Client or its 2467 Proxys send RS messages to the Server via the SPAN with an OMNI 2468 option that includes an ifIndex-tuple with S set to 1 and with the 2469 new link quality and address information. 2471 Up to MAX_RTR_SOLICITATIONS RS messages MAY be sent in parallel with 2472 sending actual data packets in case one or more RAs are lost. If all 2473 RAs are lost, the Client SHOULD re-associate with a new Server. 2475 When the Server receives the Client's changes, it sends uNA messages 2476 to all nodes in the Report List the same as described in the previous 2477 section. 2479 3.19.3. Bringing New Links Into Service 2481 When a Client needs to bring new underlying interfaces into service 2482 (e.g., when it activates a new data link), it sends an RS message to 2483 the Server via the underlying interface with an OMNI option that 2484 includes an ifIndex-tuple with S set to 1 and appropriate link 2485 quality values and with link-layer address information for the new 2486 link. 2488 3.19.4. Removing Existing Links from Service 2490 When a Client needs to remove existing underlying interfaces from 2491 service (e.g., when it de-activates an existing data link), it sends 2492 an RS or uNA message to its Server with an OMNI option with 2493 appropriate link quality values. 2495 If the Client needs to send RS/uNA messages over an underlying 2496 interface other than the one being removed from service, it MUST 2497 include ifIndex-tuples with appropriate link quality values for any 2498 underlying interfaces being removed from service. 2500 3.19.5. Moving to a New Server 2502 When a Client associates with a new Server, it performs the Client 2503 procedures specified in Section 3.15.2. The Client also includes MS- 2504 Release identifiers in the RS message OMNI option per 2505 [I-D.templin-6man-omni-interface] if it wants the new Server to 2506 notify any old Servers from which the Client is departing. 2508 When the new Server receives the Client's RS message, it returns an 2509 RA as specified in Section 3.15.3 and sends up to 2510 MAX_NEIGHBOR_ADVERTIISEMENT uNA messages to any old Servers listed in 2511 OMNI option MS-Release identifiers. Each uNA message includes the 2512 Client's AERO address as the source address, the old Server's AERO 2513 address as the destination address, and an OMNI option with the 2514 Register/Release bit set to 0. The new Server wraps the uNA in a 2515 SPAN header with its own SPAN address as the source and the old 2516 Server's SPAN address as the destination, then sends the message into 2517 the SPAN. 2519 When an old Server receives the uNA, it changes the Client's neighbor 2520 cache entry state to DEPARTED, sets the link-layer address of the 2521 Client to the new Server's SPAN address, and sets DepartTime to 2522 DEPART_TIME seconds. After a short delay (e.g., 2 seconds) the old 2523 Server withdraws the Client's MNP from the routing system. After 2524 DepartTime expires, the old Server deletes the Client's neighbor 2525 cache entry. 2527 The old Server also sends unsolicited NA messages to all ROSs in the 2528 Client's Report List with an OMNI option with a single ifIndex-tuple 2529 with ifIndex set to 0 and S set to '1', and with the SPAN address of 2530 the new Server in a companion TLLAO. When the ROS receives the NA, 2531 it caches the address of the new Server in the existing asymmetric 2532 neighbor cache entry and marks the entry as STALE. Subsequent data 2533 packets will then flow according to any existing cached link-layer 2534 information and trigger a new NS(AR)/NA exchange via the new Server. 2536 Clients SHOULD NOT move rapidly between Servers in order to avoid 2537 causing excessive oscillations in the AERO routing system. Examples 2538 of when a Client might wish to change to a different Server include a 2539 Server that has gone unreachable, topological movements of 2540 significant distance, movement to a new geographic region, movement 2541 to a new SPAN segment, etc. 2543 When a Client moves to a new Server, some of the fragments of a 2544 multiple fragment packet may have already arrived at the old Server 2545 while others are en route to the new Server, however no special 2546 attention in the reassembly algorithm is necessary when re-routed 2547 fragments are simply treated as loss. 2549 3.20. Multicast 2551 The AERO Client provides an IGMP (IPv4) [RFC2236] or MLD (IPv6) 2552 [RFC3810] proxy service for its EUNs and/or hosted applications 2553 [RFC4605]. The Client forwards IGMP/MLD messages over any of its 2554 underlying interfaces for which group membership is required. The 2555 IGMP/MLD messages may be further forwarded by a first-hop ANET access 2556 router acting as an IGMP/MLD-snooping switch [RFC4541], then 2557 ultimately delivered to an AERO Proxy/Server acting as a Protocol 2558 Independent Multicast - Sparse-Mode (PIM-SM, or simply "PIM") 2559 Designated Router (DR) [RFC7761]. AERO Gateways also act as PIM 2560 routers (i.e., the same as AERO Proxys/Servers) on behalf of nodes on 2561 INET/EUN networks. The behaviors identified in the following 2562 sections correspond to Source-Specific Multicast (SSM) and Any-Source 2563 Multicast (ASM) operational modes. 2565 3.20.1. Source-Specific Multicast (SSM) 2567 When an ROS (i.e., an AERO Proxy/Server/Gateway) "X" acting as PIM 2568 router receives a Join/Prune message from a node on its downstream 2569 interfaces containing one or more ((S)ource, (G)roup) pairs, it 2570 updates its Multicast Routing Information Base (MRIB) accordingly. 2571 For each S belonging to a prefix reachable via X's non-AERO 2572 interfaces, X then forwards the (S, G) Join/Prune to any PIM routers 2573 on those interfaces per [RFC7761]. 2575 For each S belonging to a prefix reachable via X's AERO interface, X 2576 originates a separate copy of the Join/Prune for each (S,G) in the 2577 message using its own AERO address as the source address and ALL-PIM- 2578 ROUTERS as the destination address. X then encapsulates each message 2579 in a SPAN header with source address set to the SPAN address of X and 2580 destination address set to S then forwards the message into the SPAN. 2581 The SPAN in turn forwards the message to AERO Server/Gateway "Y" that 2582 services S. At the same time, if the message was a Join, X sends a 2583 route-optimization NS message toward each S the same as discussed in 2584 Section 3.17. The resulting NAs will return the AERO address for the 2585 prefix that matches S as the network-layer source address and TLLAOs 2586 with the SPAN addresses corresponding to any ifIndex-tuples that are 2587 currently servicing S. 2589 When Y processes the Join/Prune message, if S located behind any 2590 Native, Direct, VPNed or NATed interfaces Y acts as a PIM router and 2591 updates its MRIB to list X as the next hop in the reverse path. If S 2592 is located behind any Proxys "Z"*, Y also forwards the message to 2593 each Z* over the SPAN while continuing to use the AERO address of X 2594 as the source address. Each Z* then updates its MRIB accordingly and 2595 maintains the AERO address of X as the next hop in the reverse path. 2596 Since the Relays in the SPAN do not examine network layer control 2597 messages, this means that the (reverse) multicast tree path is simply 2598 from each Z* (and/or Y) to X with no other multicast-aware routers in 2599 the path. If any Z* (and/or Y) is located on the same SPAN segment 2600 as X, the multicast data traffic sent to X directly using SPAN/INET 2601 encapsulation instead of via a Relay. 2603 Following the initial Join/Prune and NS/NA messaging, X maintains an 2604 asymmetric neighbor cache entry for each S the same as if X was 2605 sending unicast data traffic to S. In particular, X performs 2606 additional NS/NA exchanges to keep the neighbor cache entry alive for 2607 up to t_periodic seconds [RFC7761]. If no new Joins are received 2608 within t_periodic seconds, X allows the neighbor cache entry to 2609 expire. Finally, if X receives any additional Join/Prune messages 2610 for (S,G) it forwards the messages to each Y and Z* in the neighbor 2611 cache entry over the SPAN. 2613 At some later time, Client C that holds an MNP for source S may 2614 depart from a first Proxy Z1 and/or connect via a new Proxy Z2. In 2615 that case, Y sends an unsolicited NA message to X the same as 2616 specified for unicast mobility in Section 3.19. When X receives the 2617 unsolicited NA message, it updates its asymmetric neighbor cache 2618 entry for the AERO address for source S and sends new Join messages 2619 to any new Proxys Z2. There is no requirement to send any Prune 2620 messages to old Proxys Z1 since source S will no longer source any 2621 multicast data traffic via Z1. Instead, the multicast state for 2622 (S,G) in Proxy Z1 will soon time out since no new Joins will arrive. 2624 After some later time, C may move to a new Server Y2 and depart from 2625 old Sever Y1. In that case, Y1 sends Join messages for any of C's 2626 active (S,G) groups to Y2 while including its own AERO address as the 2627 source address. This causes Y2 to include Y1 in the multicast 2628 forwarding tree during the interim time that Y1's symmetric neighbor 2629 cache entry for C is in the DEPARTED state. At the same time, Y1 2630 sends an unsolicited NA message to X with an OMNI option and TLLAO 2631 with ifIndex-tuple set to 0 and a release indication to cause X to 2632 release its asymmetric neighbor cache entry. X then sends a new Join 2633 message to S via the SPAN and re-initiates route optimization the 2634 same as if it were receiving a fresh Join message from a node on a 2635 downstream link. 2637 3.20.2. Any-Source Multicast (ASM) 2639 When an ROS X acting as a PIM router receives a Join/Prune from a 2640 node on its downstream interfaces containing one or more (*,G) pairs, 2641 it updates its Multicast Routing Information Base (MRIB) accordingly. 2642 X then forwards a copy of the message to the Rendezvous Point (RP) R 2643 for each G over the SPAN. X uses its own AERO address as the source 2644 address and ALL-PIM-ROUTERS as the destination address, then 2645 encapsulates each message in a SPAN header with source address set to 2646 the SPAN address of X and destination address set to R, then sends 2647 the message into the SPAN. At the same time, if the message was a 2648 Join X initiates NS/NA route optimization the same as for the SSM 2649 case discussed in Section 3.20.1. 2651 For each source S that sends multicast traffic to group G via R, the 2652 Proxy/Server Z* for the Client that aggregates S encapsulates the 2653 packets in PIM Register messages and forwards them to R via the SPAN. 2654 R may then elect to send a PIM Join to Z* over the SPAN. This will 2655 result in an (S,G) tree rooted at Z* with R as the next hop so that R 2656 will begin to receive two copies of the packet; one native copy from 2657 the (S, G) tree and a second copy from the pre-existing (*, G) tree 2658 that still uses PIM Register encapsulation. R can then issue a PIM 2659 Register-stop message to suppress the Register-encapsulated stream. 2660 At some later time, if C moves to a new Proxy/Server Z*, it resumes 2661 sending packets via PIM Register encapsulation via the new Z*. 2663 At the same time, as multicast listeners discover individual S's for 2664 a given G, they can initiate an (S,G) Join for each S under the same 2665 procedures discussed in Section 3.20.1. Once the (S,G) tree is 2666 established, the listeners can send (S, G) Prune messages to R so 2667 that multicast packets for group G sourced by S will only be 2668 delivered via the (S, G) tree and not from the (*, G) tree rooted at 2669 R. All mobility considerations discussed for SSM apply. 2671 3.20.3. Bi-Directional PIM (BIDIR-PIM) 2673 Bi-Directional PIM (BIDIR-PIM) [RFC5015] provides an alternate 2674 approach to ASM that treats the Rendezvous Point (RP) as a Designated 2675 Forwarder (DF). Further considerations for BIDIR-PIM are out of 2676 scope. 2678 3.21. Operation over Multiple AERO Links (VLANs) 2680 An AERO Client can connect to multiple AERO links the same as for any 2681 data link service. In that case, the Client maintains a distinct 2682 AERO interface for each link, e.g., 'aero0' for the first link, 2683 'aero1' for the second, 'aero2' for the third, etc. Each AERO link 2684 would include its own distinct set of Relays, Servers and Proxys, 2685 thereby providing redundancy in case of failures. 2687 The Relays, Servers and Proxys on each AERO link can assign AERO and 2688 SPAN addresses that use the same or different numberings from those 2689 on other links. Since the links are mutually independent there is no 2690 requirement for avoiding inter-link address duplication, e.g., the 2691 same AERO address such as fe80::1000 could be used to number distinct 2692 nodes that connect to different AERO links. 2694 Each AERO link could utilize the same or different ANET connections. 2695 The links can be distinguished at the link-layer via Virtual Local 2696 Area Network (VLAN) tagging (e.g., IEEE 802.1Q) and/or through 2697 assignment of distinct sets of MSPs on each link. This gives rise to 2698 the opportunity for supporting multiple redundant networked paths, 2699 where each VLAN is distinguished by a different label (e.g., colors 2700 such as Red, Green, Blue, etc.). In particular, the Client can tag 2701 its RS messages with the appropriate label to cause the network to 2702 select the desired VLAN. 2704 Clients that connect to multiple AERO interfaces can select the 2705 outgoing interface appropriate for a given Red/Blue/Green/etc. 2706 traffic profile while (in the reverse direction) correspondent nodes 2707 must have some way of steering their packets destined to a target via 2708 the correct AERO link. 2710 In a first alternative, if each AERO link services different MSPs, 2711 then the Client can receive a distinct MNP from each of the links. 2712 IP routing will therefore assure that the correct Red/Green/Blue/etc. 2713 network is used for both outbound and inbound traffic. This can be 2714 accomplished using existing technologies and approaches, and without 2715 requiring any special supporting code in correspondent nodes or 2716 Relays. 2718 In a second alternative, if each AERO link services the same MSP(s) 2719 then each link could assign a distinct "AERO Link Anycast" address 2720 that is configured by all Relays on the link. Correspondent nodes 2721 then include a "type 4" routing header with the Anycast address for 2722 the AERO link as the IPv6 destination and with the address of the 2723 target encoded as the "next segment" in the routing header 2724 [RFC8402][I-D.ietf-6man-segment-routing-header]. Standard IP routing 2725 will then direct the packet to the nearest Relay for the correct AERO 2726 link, which will replace the destination address with the target 2727 address then forward the packet to the target. 2729 3.22. DNS Considerations 2731 AERO Client MNs and INET correspondent nodes consult the Domain Name 2732 System (DNS) the same as for any Internetworking node. When 2733 correspondent nodes and Client MNs use different IP protocol versions 2734 (e.g., IPv4 correspondents and IPv6 MNs), the INET DNS must maintain 2735 A records for IPv4 address mappings to MNs which must then be 2736 populated in Gateway NAT64 mapping caches. In that way, an IPv4 2737 correspondent node can send packets to the IPv4 address mapping of 2738 the target MN, and the Gateway will translate the IPv4 header and 2739 destination address into an IPv6 header and IPv6 destination address 2740 of the MN. 2742 When an AERO Client registers with an AERO Server, the Server can 2743 return the address(es) of DNS servers in RDNSS options [RFC6106]. 2744 The DNS server provides the IP addresses of other MNs and 2745 correspondent nodes in AAAA records for IPv6 or A records for IPv4. 2747 3.23. Transition Considerations 2749 The SPAN ensures that dissimilar INET partitions can be joined into a 2750 single unified AERO link, even though the partitions themselves may 2751 have differing protocol versions and/or incompatible addressing 2752 plans. However, a commonality can be achieved by incrementally 2753 distributing globally routable (i.e., native) IP prefixes to 2754 eventually reach all nodes (both mobile and fixed) in all SPAN 2755 segments. This can be accomplished by incrementally deploying AERO 2756 Gateways on each INET partition, with each Gateway distributing its 2757 MNPs and/or discovering non-MNP prefixes on its INET links. 2759 This gives rise to the opportunity to eventually distribute native IP 2760 addresses to all nodes, and to present a unified AERO link view 2761 (bridged by the SPAN) even if the INET partitions remain in their 2762 current protocol and addressing plans. In that way, the AERO link 2763 can serve the dual purpose of providing a mobility/multilink service 2764 and a transition service. Or, if an INET partition is transitioned 2765 to a native IP protocol version and addressing scheme that is 2766 compatible with the AERO link MNP-based addressing scheme, the 2767 partition and AERO link can be joined by Gateways. 2769 Gateways that connect INETs/EUNs with dissimilar IP protocol versions 2770 must employ a network address and protocol translation function such 2771 as NAT64[RFC6146]. 2773 3.24. Detecting and Reacting to Server and Relay Failures 2775 In environments where rapid failure recovery is required, Servers and 2776 Relays SHOULD use Bidirectional Forwarding Detection (BFD) [RFC5880]. 2777 Nodes that use BFD can quickly detect and react to failures so that 2778 cached information is re-established through alternate nodes. BFD 2779 control messaging is carried only over well-connected ground domain 2780 networks (i.e., and not low-end radio links) and can therefore be 2781 tuned for rapid response. 2783 Servers and Relays maintain BFD sessions in parallel with their BGP 2784 peerings. If a Server or Relay fails, BGP peers will quickly re- 2785 establish routes through alternate paths the same as for common BGP 2786 deployments. Similarly, Proxys maintain BFD sessions with their 2787 associated Relays even though they do not establish BGP peerings with 2788 them. 2790 Proxys SHOULD use proactive NUD for Servers for which there are 2791 currently active ANET Clients in a manner that parallels BFD, i.e., 2792 by sending unicast NS messages in rapid succession to receive 2793 solicited NA messages. When the Proxy is also sending RS messages on 2794 behalf of ANET Clients, the RS/RA messaging can be considered as 2795 equivalent hints of forward progress. This means that the Proxy need 2796 not also send a periodic NS if it has already sent an RS within the 2797 same period. If a Server fails, the Proxy will cease to receive 2798 advertisements and can quickly inform Clients of the outage by 2799 sending multicast RA messages on the ANET interface. 2801 The Proxy sends multicast RA messages with source address set to the 2802 Server's address, destination address set to All-Nodes multicast, and 2803 Router Lifetime set to 0. The Proxy SHOULD send 2804 MAX_FINAL_RTR_ADVERTISEMENTS RA messages separated by small delays 2805 [RFC4861]. Any Clients on the ANET interface that have been using 2806 the (now defunct) Server will receive the RA messages and associate 2807 with a new Server. 2809 3.25. AERO Clients on the Open Internet 2811 AERO Clients that connect to the open Internet via native and/or 2812 NATed interfaces can establish a VPN to securely connect to a Server 2813 in a "tethered" arrangement with all of the Client's traffic 2814 transiting the Server. Alternatively, the Client can exchange ND 2815 messages directly with other AERO nodes using SPAN/INET 2816 encapsulation. In that case, the Client must apply asymmetric 2817 security for IPv6 ND messages to ensure routing and neighbor cache 2818 integrity using SEcure Neighbor Discovery (SEND) [RFC3971] and 2819 Cryptographically Generated Addresses (CGAs) [RFC3972]. 2821 When a Client enables native and/or NATed interfaces underneath its 2822 AERO interface, it sends an RS message with IPv6 source address set 2823 to a link-local CGA, with IPv6 destination set to All-Routers 2824 multicast, with an OMNI opton and with SEND/CGA options to provide 2825 message authentication. The Client also includes an SLLAO with the 2826 IP address and Port Number used for INET enacpsulation written in 2827 obfuscated form as discussed in Section 3.6. The Client wraps the 2828 message in a SPAN header with source address set to the Client's SPAN 2829 address and with destination address set to the SPAN address of a 2830 Server. The Client then further wraps the SPAN message in an INET 2831 header with source set to the Client's INET address and destination 2832 set to the Server's INET address, then sends the message to the 2833 Server. 2835 When the Server receives the RS message, it authenticates the message 2836 and registers the Client's MNP and INET interface information 2837 according to the OMNI option parameters. The Server then returns an 2838 RA message with IPv6 source set to its CGA, with IPv6 destination set 2839 to the Client's CGA, with an OMNI option and with SEND/CGA options to 2840 provide message authentication. If the Client is located behind a 2841 NAT, the Server further sets the N bit in the RA flags field to 1 2842 (see: Section 5). The Server then wraps the message in a SPAN header 2843 with source address set to the Server's SPAN address and destination 2844 set to the Client's SPAN address, and further wraps the SPAN message 2845 in an INET header with source set to the Server's INET address and 2846 destination set to the Client's INET address. 2848 After the Client has registered its INET interfaces in such RS/RA 2849 exchanges it sends periodic RS messages to receive fresh RA messages 2850 before the Router Lifetime received on each INET interface expires 2851 (again, using SEND/CGA). The Client also maintains default routes 2852 via its Servers, i.e., the same as described in earlier sections. 2854 When the Client sends messages to target IP addresses, it also 2855 invokes route optimization per Section 3.17 using IPv6 ND address 2856 resolution messaging. The Client sends the (SEND/CGA-protected) 2857 NS(AR) message wrapped in a SPAN header with source set to the 2858 Client's SPAN address and destination set to the target IP address, 2859 and with INET destination address set to the address of the Server. 2860 The Server authenticates the message and sends a corresponding NS(AR) 2861 message over the SPAN. When the ROR receives the NS(AR), it adds the 2862 Client's SPAN address and Server's INET address to the target's 2863 Report List, and returns an NA with OMNI and TLLAO information for 2864 the target. (For any of the target's interfaces that are located 2865 behind a NAT, the ROR includes its own address and port in the TLLAO 2866 for that interface; otherwise, it includes the target's native 2867 address and port.) The Server then returns a (SEND/CGA-protected) NA 2868 message to the Client. 2870 Following route optimization, the Client forwards data packets 2871 directly to the INET addresses of the target according to the OMNI/ 2872 TLLAO information. The ROR may reutrn uNAs via the Server if the 2873 target moves, and the Server will send corresponding (SEND/CGA- 2874 protected) uNAs to the Client. The Client can also send "loopback" 2875 NS(NUD) messages as discussed in Section 3.18 to test forward path 2876 reachability even though there is no security association between the 2877 Client and the target. 2879 Note: when the target is an AERO Client interface located behind a 2880 NAT, the Client's Server is included in the forwarding path for 2881 delivery of packets to the Client via that interface. Future updates 2882 to this specification MAY include provisions for allowing direct 2883 packet forwarding to the Client via the NAT without transiting the 2884 Server. [RFC4380] provides example procedures for supporting such 2885 inbound NAT traversal. 2887 4. Implementation Status 2889 An AERO implementation based on OpenVPN (https://openvpn.net/) was 2890 announced on the v6ops mailing list on January 10, 2018 and an 2891 initial public release of the AERO proof-of-concept source code was 2892 announced on the intarea mailing list on August 21, 2015. 2894 As of 4/1/2020, more recent updated implementations are under 2895 internal development and testing with plans to release in the near 2896 future. 2898 5. IANA Considerations 2900 The IANA has assigned a 4-octet Private Enterprise Number "45282" for 2901 AERO in the "enterprise-numbers" registry. 2903 The IANA has assigned the UDP port number "8060" for an earlier 2904 experimental version of AERO [RFC6706]. This document obsoletes 2905 [RFC6706] and claims the UDP port number "8060" for all future use. 2907 The IANA is requested to assign a new IPv6 ND Router Advertiisement 2908 (RA) flag (value TBD per [RFC5175]), to be known as the "NAT 2909 Traversal (N)" flag. 2911 No further IANA actions are required. 2913 6. Security Considerations 2915 AERO Relays configure secured tunnels with AERO Servers and Proxys 2916 within their local SPAN segments. Applicable secured tunnel 2917 alternatives include IPsec [RFC4301], TLS/SSL [RFC8446], DTLS 2919 [RFC6347], WireGuard, etc. The AERO Relays of all SPAN segments in 2920 turn configure secured tunnels for their neighboring AERO Relays 2921 across the SPAN. Therefore, control messages that traverse the SPAN 2922 between any pair of AERO link neighbors are already secured. 2924 AERO Servers, Gateways and Proxys targeted by a route optimization 2925 may also receive packets directly from the INET partitions instead of 2926 via the SPAN. For INET partitions that apply effective ingress 2927 filtering to defeat source address spoofing, the simple data origin 2928 authentication procedures in Section 3.11 can be applied. 2930 For INET partitions that cannot apply effective ingress filtering, 2931 the two options for securing communications include 1) disable route 2932 optimization so that all traffic is conveyed over secured tunnels via 2933 the SPAN, or 2) enable on-demand secure tunnel creation between INET 2934 partition neighbors. Option 1) would result in longer routes than 2935 necessary and traffic concentration on critical infrastructure 2936 elements. Option 2) could be coordinated by establishing a secured 2937 tunnel on-demand instead of performing an NS/NA exchange in the route 2938 optimization procedures. Procedures for establishing on-demand 2939 secured tunnels are out of scope. 2941 AERO Clients that connect to secured enclaves need not apply security 2942 to their ND messages, since the messages will be intercepted by a 2943 perimeter Proxy that applies security on its outward-facing 2944 interface. AERO Clients located outside of secured enclaves can use 2945 symmetric network and/or transport layer security services such as 2946 VPNs, but when there are many prospective neighbors with dynamically 2947 changing connectivity an asymmetric security service such as SEcure 2948 Neighbor Discovery (SEND) [RFC3971] and Cryptographically Generated 2949 Addresses (CGAs) [RFC3972] may be more appropriate. 2951 Application endpoints SHOULD use application-layer security services 2952 such as TLS/SSL, DTLS or SSH [RFC4251] to assure the same level of 2953 protection as for critical secured Internet services. AERO Clients 2954 that require host-based VPN services SHOULD use symmetric network 2955 and/or transport layer security services such as IPsec, TLS/SSL, 2956 DTLS, etc. AERO Proxys and Servers can also provide a network-based 2957 VPN service on behalf of the Client, e.g., if the Client is located 2958 within a secured enclave and cannot establish a VPN on its own 2959 behalf. 2961 AERO Servers and Relays present targets for traffic amplification 2962 Denial of Service (DoS) attacks. This concern is no different than 2963 for widely-deployed VPN security gateways in the Internet, where 2964 attackers could send spoofed packets to the gateways at high data 2965 rates. This can be mitigated by connecting Servers and Relays over 2966 dedicated links with no connections to the Internet and/or when 2967 connections to the Internet are only permitted through well-managed 2968 firewalls. Traffic amplification DoS attacks can also target an AERO 2969 Client's low data rate links. This is a concern not only for Clients 2970 located on the open Internet but also for Clients in secured 2971 enclaves. AERO Servers and Proxys can institute rate limits that 2972 protect Clients from receiving packet floods that could DoS low data 2973 rate links. 2975 AERO Gateways must implement ingress filtering to avoid a spoofing 2976 attack in which spurious SPAN messages are injected into an AERO link 2977 from an outside attacker. AERO Clients MUST ensure that their 2978 connectivity is not used by unauthorized nodes on their EUNs to gain 2979 access to a protected network, i.e., AERO Clients that act as routers 2980 MUST NOT provide routing services for unauthorized nodes. (This 2981 concern is no different than for ordinary hosts that receive an IP 2982 address delegation but then "share" the address with other nodes via 2983 some form of Internet connection sharing such as tethering.) 2985 The MAP list MUST be well-managed and secured from unauthorized 2986 tampering, even though the list contains only public information. 2987 The MAP list can be conveyed to the Client in a similar fashion as in 2988 [RFC5214] (e.g., through layer 2 data link login messaging, secure 2989 upload of a static file, DNS lookups, etc.). 2991 Although public domain and commercial SEND implementations exist, 2992 concerns regarding the strength of the cryptographic hash algorithm 2993 have been documented [RFC6273] [RFC4982]. 2995 Security considerations for accepting link-layer ICMP messages and 2996 reflected packets are discussed throughout the document. 2998 7. Acknowledgements 3000 Discussions in the IETF, aviation standards communities and private 3001 exchanges helped shape some of the concepts in this work. 3002 Individuals who contributed insights include Mikael Abrahamsson, Mark 3003 Andrews, Fred Baker, Bob Braden, Stewart Bryant, Brian Carpenter, 3004 Wojciech Dec, Pavel Drasil, Ralph Droms, Adrian Farrel, Nick Green, 3005 Sri Gundavelli, Brian Haberman, Bernhard Haindl, Joel Halpern, Tom 3006 Herbert, Sascha Hlusiak, Lee Howard, Zdenek Jaron, Andre Kostur, 3007 Hubert Kuenig, Ted Lemon, Andy Malis, Satoru Matsushima, Tomek 3008 Mrugalski, Madhu Niraula, Alexandru Petrescu, Behcet Saikaya, Michal 3009 Skorepa, Joe Touch, Bernie Volz, Ryuji Wakikawa, Tony Whyman, Lloyd 3010 Wood and James Woodyatt. Members of the IESG also provided valuable 3011 input during their review process that greatly improved the document. 3012 Special thanks go to Stewart Bryant, Joel Halpern and Brian Haberman 3013 for their shepherding guidance during the publication of the AERO 3014 first edition. 3016 This work has further been encouraged and supported by Boeing 3017 colleagues including Kyle Bae, M. Wayne Benson, Dave Bernhardt, Cam 3018 Brodie, John Bush, Balaguruna Chidambaram, Irene Chin, Bruce Cornish, 3019 Claudiu Danilov, Don Dillenburg, Joe Dudkowski, Wen Fang, Samad 3020 Farooqui, Anthony Gregory, Jeff Holland, Seth Jahne, Brian Jaury, 3021 Greg Kimberly, Ed King, Madhuri Madhava Badgandi, Laurel Matthew, 3022 Gene MacLean III, Rob Muszkiewicz, Sean O'Sullivan, Vijay 3023 Rajagopalan, Greg Saccone, Rod Santiago, Kent Shuey, Brian Skeen, 3024 Mike Slane, Carrie Spiker, Katie Tran, Brendan Williams, Amelia 3025 Wilson, Julie Wulff, Yueli Yang, Eric Yeh and other members of the 3026 Boeing mobility, networking and autonomy teams. Kyle Bae, Wayne 3027 Benson, Katie Tran and Eric Yeh are especially acknowledged for 3028 implementing the AERO functions as extensions to the public domain 3029 OpenVPN distribution. 3031 Earlier works on NBMA tunneling approaches are found in 3032 [RFC2529][RFC5214][RFC5569]. 3034 Many of the constructs presented in this second edition of AERO are 3035 based on the author's earlier works, including: 3037 o The Internet Routing Overlay Network (IRON) 3038 [RFC6179][I-D.templin-ironbis] 3040 o Virtual Enterprise Traversal (VET) 3041 [RFC5558][I-D.templin-intarea-vet] 3043 o The Subnetwork Encapsulation and Adaptation Layer (SEAL) 3044 [RFC5320][I-D.templin-intarea-seal] 3046 o AERO, First Edition [RFC6706] 3048 Note that these works cite numerous earlier efforts that are not also 3049 cited here due to space limitations. The authors of those earlier 3050 works are acknowledged for their insights. 3052 This work is aligned with the NASA Safe Autonomous Systems Operation 3053 (SASO) program under NASA contract number NNA16BD84C. 3055 This work is aligned with the FAA as per the SE2025 contract number 3056 DTFAWA-15-D-00030. 3058 This work is aligned with the Boeing Commercial Airplanes (BCA) 3059 Internet of Things (IoT) and autonomy programs. 3061 This work is aligned with the Boeing Information Technology (BIT) 3062 MobileNet program. 3064 8. References 3066 8.1. Normative References 3068 [I-D.templin-6man-omni-interface] 3069 Templin, F. and T. Whyman, "Transmission of IPv6 Packets 3070 over Overlay Multilink Network (OMNI) Interfaces", draft- 3071 templin-6man-omni-interface-11 (work in progress), April 3072 2020. 3074 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, 3075 DOI 10.17487/RFC0791, September 1981, 3076 . 3078 [RFC0792] Postel, J., "Internet Control Message Protocol", STD 5, 3079 RFC 792, DOI 10.17487/RFC0792, September 1981, 3080 . 3082 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 3083 Requirement Levels", BCP 14, RFC 2119, 3084 DOI 10.17487/RFC2119, March 1997, 3085 . 3087 [RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in 3088 IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473, 3089 December 1998, . 3091 [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black, 3092 "Definition of the Differentiated Services Field (DS 3093 Field) in the IPv4 and IPv6 Headers", RFC 2474, 3094 DOI 10.17487/RFC2474, December 1998, 3095 . 3097 [RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander, 3098 "SEcure Neighbor Discovery (SEND)", RFC 3971, 3099 DOI 10.17487/RFC3971, March 2005, 3100 . 3102 [RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)", 3103 RFC 3972, DOI 10.17487/RFC3972, March 2005, 3104 . 3106 [RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and 3107 More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191, 3108 November 2005, . 3110 [RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast 3111 Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005, 3112 . 3114 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 3115 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 3116 DOI 10.17487/RFC4861, September 2007, 3117 . 3119 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 3120 Address Autoconfiguration", RFC 4862, 3121 DOI 10.17487/RFC4862, September 2007, 3122 . 3124 [RFC5175] Haberman, B., Ed. and R. Hinden, "IPv6 Router 3125 Advertisement Flags Option", RFC 5175, 3126 DOI 10.17487/RFC5175, March 2008, 3127 . 3129 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 3130 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 3131 May 2017, . 3133 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 3134 (IPv6) Specification", STD 86, RFC 8200, 3135 DOI 10.17487/RFC8200, July 2017, 3136 . 3138 [RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A., 3139 Richardson, M., Jiang, S., Lemon, T., and T. Winters, 3140 "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", 3141 RFC 8415, DOI 10.17487/RFC8415, November 2018, 3142 . 3144 8.2. Informative References 3146 [BGP] Huston, G., "BGP in 2015, http://potaroo.net", January 3147 2016. 3149 [I-D.ietf-6man-segment-routing-header] 3150 Filsfils, C., Dukes, D., Previdi, S., Leddy, J., 3151 Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header 3152 (SRH)", draft-ietf-6man-segment-routing-header-26 (work in 3153 progress), October 2019. 3155 [I-D.ietf-dmm-distributed-mobility-anchoring] 3156 Chan, A., Wei, X., Lee, J., Jeon, S., and C. Bernardos, 3157 "Distributed Mobility Anchoring", draft-ietf-dmm- 3158 distributed-mobility-anchoring-15 (work in progress), 3159 March 2020. 3161 [I-D.ietf-intarea-gue] 3162 Herbert, T., Yong, L., and O. Zia, "Generic UDP 3163 Encapsulation", draft-ietf-intarea-gue-09 (work in 3164 progress), October 2019. 3166 [I-D.ietf-intarea-gue-extensions] 3167 Herbert, T., Yong, L., and F. Templin, "Extensions for 3168 Generic UDP Encapsulation", draft-ietf-intarea-gue- 3169 extensions-06 (work in progress), March 2019. 3171 [I-D.ietf-intarea-tunnels] 3172 Touch, J. and M. Townsley, "IP Tunnels in the Internet 3173 Architecture", draft-ietf-intarea-tunnels-10 (work in 3174 progress), September 2019. 3176 [I-D.ietf-rtgwg-atn-bgp] 3177 Templin, F., Saccone, G., Dawra, G., Lindem, A., and V. 3178 Moreno, "A Simple BGP-based Mobile Routing System for the 3179 Aeronautical Telecommunications Network", draft-ietf- 3180 rtgwg-atn-bgp-05 (work in progress), January 2020. 3182 [I-D.templin-6man-dhcpv6-ndopt] 3183 Templin, F., "A Unified Stateful/Stateless Configuration 3184 Service for IPv6", draft-templin-6man-dhcpv6-ndopt-09 3185 (work in progress), January 2020. 3187 [I-D.templin-intarea-grefrag] 3188 Templin, F., "GRE Tunnel Level Fragmentation", draft- 3189 templin-intarea-grefrag-04 (work in progress), July 2016. 3191 [I-D.templin-intarea-seal] 3192 Templin, F., "The Subnetwork Encapsulation and Adaptation 3193 Layer (SEAL)", draft-templin-intarea-seal-68 (work in 3194 progress), January 2014. 3196 [I-D.templin-intarea-vet] 3197 Templin, F., "Virtual Enterprise Traversal (VET)", draft- 3198 templin-intarea-vet-40 (work in progress), May 2013. 3200 [I-D.templin-ironbis] 3201 Templin, F., "The Interior Routing Overlay Network 3202 (IRON)", draft-templin-ironbis-16 (work in progress), 3203 March 2014. 3205 [I-D.templin-v6ops-pdhost] 3206 Templin, F., "IPv6 Prefix Delegation and Multi-Addressing 3207 Models", draft-templin-v6ops-pdhost-25 (work in progress), 3208 January 2020. 3210 [OVPN] OpenVPN, O., "http://openvpn.net", October 2016. 3212 [RFC1035] Mockapetris, P., "Domain names - implementation and 3213 specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, 3214 November 1987, . 3216 [RFC1122] Braden, R., Ed., "Requirements for Internet Hosts - 3217 Communication Layers", STD 3, RFC 1122, 3218 DOI 10.17487/RFC1122, October 1989, 3219 . 3221 [RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191, 3222 DOI 10.17487/RFC1191, November 1990, 3223 . 3225 [RFC1812] Baker, F., Ed., "Requirements for IP Version 4 Routers", 3226 RFC 1812, DOI 10.17487/RFC1812, June 1995, 3227 . 3229 [RFC2003] Perkins, C., "IP Encapsulation within IP", RFC 2003, 3230 DOI 10.17487/RFC2003, October 1996, 3231 . 3233 [RFC2236] Fenner, W., "Internet Group Management Protocol, Version 3234 2", RFC 2236, DOI 10.17487/RFC2236, November 1997, 3235 . 3237 [RFC2492] Armitage, G., Schulter, P., and M. Jork, "IPv6 over ATM 3238 Networks", RFC 2492, DOI 10.17487/RFC2492, January 1999, 3239 . 3241 [RFC2529] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4 3242 Domains without Explicit Tunnels", RFC 2529, 3243 DOI 10.17487/RFC2529, March 1999, 3244 . 3246 [RFC2764] Gleeson, B., Lin, A., Heinanen, J., Armitage, G., and A. 3247 Malis, "A Framework for IP Based Virtual Private 3248 Networks", RFC 2764, DOI 10.17487/RFC2764, February 2000, 3249 . 3251 [RFC2784] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P. 3252 Traina, "Generic Routing Encapsulation (GRE)", RFC 2784, 3253 DOI 10.17487/RFC2784, March 2000, 3254 . 3256 [RFC2890] Dommety, G., "Key and Sequence Number Extensions to GRE", 3257 RFC 2890, DOI 10.17487/RFC2890, September 2000, 3258 . 3260 [RFC2923] Lahey, K., "TCP Problems with Path MTU Discovery", 3261 RFC 2923, DOI 10.17487/RFC2923, September 2000, 3262 . 3264 [RFC2983] Black, D., "Differentiated Services and Tunnels", 3265 RFC 2983, DOI 10.17487/RFC2983, October 2000, 3266 . 3268 [RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition 3269 of Explicit Congestion Notification (ECN) to IP", 3270 RFC 3168, DOI 10.17487/RFC3168, September 2001, 3271 . 3273 [RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener 3274 Discovery Version 2 (MLDv2) for IPv6", RFC 3810, 3275 DOI 10.17487/RFC3810, June 2004, 3276 . 3278 [RFC3819] Karn, P., Ed., Bormann, C., Fairhurst, G., Grossman, D., 3279 Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J., and L. 3280 Wood, "Advice for Internet Subnetwork Designers", BCP 89, 3281 RFC 3819, DOI 10.17487/RFC3819, July 2004, 3282 . 3284 [RFC4213] Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms 3285 for IPv6 Hosts and Routers", RFC 4213, 3286 DOI 10.17487/RFC4213, October 2005, 3287 . 3289 [RFC4251] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH) 3290 Protocol Architecture", RFC 4251, DOI 10.17487/RFC4251, 3291 January 2006, . 3293 [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A 3294 Border Gateway Protocol 4 (BGP-4)", RFC 4271, 3295 DOI 10.17487/RFC4271, January 2006, 3296 . 3298 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 3299 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 3300 2006, . 3302 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 3303 Internet Protocol", RFC 4301, DOI 10.17487/RFC4301, 3304 December 2005, . 3306 [RFC4380] Huitema, C., "Teredo: Tunneling IPv6 over UDP through 3307 Network Address Translations (NATs)", RFC 4380, 3308 DOI 10.17487/RFC4380, February 2006, 3309 . 3311 [RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery 3312 Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April 3313 2006, . 3315 [RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet 3316 Control Message Protocol (ICMPv6) for the Internet 3317 Protocol Version 6 (IPv6) Specification", STD 89, 3318 RFC 4443, DOI 10.17487/RFC4443, March 2006, 3319 . 3321 [RFC4511] Sermersheim, J., Ed., "Lightweight Directory Access 3322 Protocol (LDAP): The Protocol", RFC 4511, 3323 DOI 10.17487/RFC4511, June 2006, 3324 . 3326 [RFC4541] Christensen, M., Kimball, K., and F. Solensky, 3327 "Considerations for Internet Group Management Protocol 3328 (IGMP) and Multicast Listener Discovery (MLD) Snooping 3329 Switches", RFC 4541, DOI 10.17487/RFC4541, May 2006, 3330 . 3332 [RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick, 3333 "Internet Group Management Protocol (IGMP) / Multicast 3334 Listener Discovery (MLD)-Based Multicast Forwarding 3335 ("IGMP/MLD Proxying")", RFC 4605, DOI 10.17487/RFC4605, 3336 August 2006, . 3338 [RFC4607] Holbrook, H. and B. Cain, "Source-Specific Multicast for 3339 IP", RFC 4607, DOI 10.17487/RFC4607, August 2006, 3340 . 3342 [RFC4963] Heffner, J., Mathis, M., and B. Chandler, "IPv4 Reassembly 3343 Errors at High Data Rates", RFC 4963, 3344 DOI 10.17487/RFC4963, July 2007, 3345 . 3347 [RFC4982] Bagnulo, M. and J. Arkko, "Support for Multiple Hash 3348 Algorithms in Cryptographically Generated Addresses 3349 (CGAs)", RFC 4982, DOI 10.17487/RFC4982, July 2007, 3350 . 3352 [RFC5015] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano, 3353 "Bidirectional Protocol Independent Multicast (BIDIR- 3354 PIM)", RFC 5015, DOI 10.17487/RFC5015, October 2007, 3355 . 3357 [RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site 3358 Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214, 3359 DOI 10.17487/RFC5214, March 2008, 3360 . 3362 [RFC5320] Templin, F., Ed., "The Subnetwork Encapsulation and 3363 Adaptation Layer (SEAL)", RFC 5320, DOI 10.17487/RFC5320, 3364 February 2010, . 3366 [RFC5522] Eddy, W., Ivancic, W., and T. Davis, "Network Mobility 3367 Route Optimization Requirements for Operational Use in 3368 Aeronautics and Space Exploration Mobile Networks", 3369 RFC 5522, DOI 10.17487/RFC5522, October 2009, 3370 . 3372 [RFC5558] Templin, F., Ed., "Virtual Enterprise Traversal (VET)", 3373 RFC 5558, DOI 10.17487/RFC5558, February 2010, 3374 . 3376 [RFC5569] Despres, R., "IPv6 Rapid Deployment on IPv4 3377 Infrastructures (6rd)", RFC 5569, DOI 10.17487/RFC5569, 3378 January 2010, . 3380 [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 3381 (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, 3382 . 3384 [RFC6106] Jeong, J., Park, S., Beloeil, L., and S. Madanapalli, 3385 "IPv6 Router Advertisement Options for DNS Configuration", 3386 RFC 6106, DOI 10.17487/RFC6106, November 2010, 3387 . 3389 [RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful 3390 NAT64: Network Address and Protocol Translation from IPv6 3391 Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146, 3392 April 2011, . 3394 [RFC6179] Templin, F., Ed., "The Internet Routing Overlay Network 3395 (IRON)", RFC 6179, DOI 10.17487/RFC6179, March 2011, 3396 . 3398 [RFC6221] Miles, D., Ed., Ooghe, S., Dec, W., Krishnan, S., and A. 3399 Kavanagh, "Lightweight DHCPv6 Relay Agent", RFC 6221, 3400 DOI 10.17487/RFC6221, May 2011, 3401 . 3403 [RFC6273] Kukec, A., Krishnan, S., and S. Jiang, "The Secure 3404 Neighbor Discovery (SEND) Hash Threat Analysis", RFC 6273, 3405 DOI 10.17487/RFC6273, June 2011, 3406 . 3408 [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer 3409 Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, 3410 January 2012, . 3412 [RFC6438] Carpenter, B. and S. Amante, "Using the IPv6 Flow Label 3413 for Equal Cost Multipath Routing and Link Aggregation in 3414 Tunnels", RFC 6438, DOI 10.17487/RFC6438, November 2011, 3415 . 3417 [RFC6706] Templin, F., Ed., "Asymmetric Extended Route Optimization 3418 (AERO)", RFC 6706, DOI 10.17487/RFC6706, August 2012, 3419 . 3421 [RFC6864] Touch, J., "Updated Specification of the IPv4 ID Field", 3422 RFC 6864, DOI 10.17487/RFC6864, February 2013, 3423 . 3425 [RFC7269] Chen, G., Cao, Z., Xie, C., and D. Binet, "NAT64 3426 Deployment Options and Experience", RFC 7269, 3427 DOI 10.17487/RFC7269, June 2014, 3428 . 3430 [RFC7333] Chan, H., Ed., Liu, D., Seite, P., Yokota, H., and J. 3431 Korhonen, "Requirements for Distributed Mobility 3432 Management", RFC 7333, DOI 10.17487/RFC7333, August 2014, 3433 . 3435 [RFC7421] Carpenter, B., Ed., Chown, T., Gont, F., Jiang, S., 3436 Petrescu, A., and A. Yourtchenko, "Analysis of the 64-bit 3437 Boundary in IPv6 Addressing", RFC 7421, 3438 DOI 10.17487/RFC7421, January 2015, 3439 . 3441 [RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I., 3442 Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent 3443 Multicast - Sparse Mode (PIM-SM): Protocol Specification 3444 (Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March 3445 2016, . 3447 [RFC8086] Yong, L., Ed., Crabbe, E., Xu, X., and T. Herbert, "GRE- 3448 in-UDP Encapsulation", RFC 8086, DOI 10.17487/RFC8086, 3449 March 2017, . 3451 [RFC8201] McCann, J., Deering, S., Mogul, J., and R. Hinden, Ed., 3452 "Path MTU Discovery for IP version 6", STD 87, RFC 8201, 3453 DOI 10.17487/RFC8201, July 2017, 3454 . 3456 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 3457 Decraene, B., Litkowski, S., and R. Shakir, "Segment 3458 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 3459 July 2018, . 3461 [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol 3462 Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, 3463 . 3465 Appendix A. AERO Alternate Encapsulations 3467 When GUE encapsulation is not needed, AERO can use common 3468 encapsulations such as IP-in-IP [RFC2003][RFC2473][RFC4213], Generic 3469 Routing Encapsulation (GRE) [RFC2784][RFC2890] and others. The 3470 encapsulation is therefore only differentiated from non-AERO tunnels 3471 through the application of AERO control messaging and not through, 3472 e.g., a well-known UDP port number. 3474 As for GUE encapsulation, alternate AERO encapsulation formats may 3475 require encapsulation layer fragmentation. For simple IP-in-IP 3476 encapsulation, an IPv6 fragment header is inserted directly between 3477 the inner and outer IP headers when needed, i.e., even if the outer 3478 header is IPv4. The IPv6 Fragment Header is identified to the outer 3479 IP layer by its IP protocol number, and the Next Header field in the 3480 IPv6 Fragment Header identifies the inner IP header version. For GRE 3481 encapsulation, a GRE fragment header is inserted within the GRE 3482 header [I-D.templin-intarea-grefrag]. 3484 Figure 6 shows the AERO IP-in-IP encapsulation format before any 3485 fragmentation is applied: 3487 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3488 | Outer IPv4 Header | | Outer IPv6 Header | 3489 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3490 |IPv6 Frag Header (optional)| |IPv6 Frag Header (optional)| 3491 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3492 | Inner IP Header | | Inner IP Header | 3493 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3494 | | | | 3495 ~ ~ ~ ~ 3496 ~ Inner Packet Body ~ ~ Inner Packet Body ~ 3497 ~ ~ ~ ~ 3498 | | | | 3499 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3501 Minimal Encapsulation in IPv4 Minimal Encapsulation in IPv6 3503 Figure 6: Minimal Encapsulation Format using IP-in-IP 3505 Figure 7 shows the AERO GRE encapsulation format before any 3506 fragmentation is applied: 3508 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3509 | Outer IP Header | 3510 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3511 | GRE Header | 3512 | (with checksum, key, etc..) | 3513 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3514 | GRE Fragment Header (optional)| 3515 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3516 | Inner IP Header | 3517 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3518 | | 3519 ~ ~ 3520 ~ Inner Packet Body ~ 3521 ~ ~ 3522 | | 3523 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3525 Figure 7: Minimal Encapsulation Using GRE 3527 Alternate encapsulation may be preferred in environments where GUE 3528 encapsulation would add unnecessary overhead. For example, certain 3529 low-bandwidth wireless data links may benefit from a reduced 3530 encapsulation overhead. 3532 GUE encapsulation can traverse network paths that are inaccessible to 3533 non-UDP encapsulations, e.g., for crossing Network Address 3534 Translators (NATs). More and more, network middleboxes are also 3535 being configured to discard packets that include anything other than 3536 a well-known IP protocol such as UDP and TCP. It may therefore be 3537 necessary to determine the potential for middlebox filtering before 3538 enabling alternate encapsulation in a given environment. 3540 In addition to IP-in-IP, GRE and GUE, AERO can also use security 3541 encapsulations such as IPsec, TLS/SSL, DTLS, etc. In that case, AERO 3542 control messaging and route determination occur before security 3543 encapsulation is applied for outgoing packets and after security 3544 decapsulation is applied for incoming packets. 3546 AERO is especially well suited for use with VPN system encapsulations 3547 such as OpenVPN [OVPN]. 3549 Appendix B. Non-Normative Considerations 3551 AERO can be applied to a multitude of Internetworking scenarios, with 3552 each having its own adaptations. The following considerations are 3553 provided as non-normative guidance: 3555 B.1. Implementation Strategies for Route Optimization 3557 Route optimization as discussed in Section 3.17 results in the route 3558 optimization source (ROS) creating an asymmetric neighbor cache entry 3559 for the target neighbor. The neighbor cache entry is maintained for 3560 at most REACHABLE_TIME seconds and then deleted unless updated. In 3561 order to refresh the neighbor cache entry lifetime before the 3562 ReachableTime timer expires, the specification requires 3563 implementations to issue a new NS/NA exchange to reset ReachableTime 3564 to REACHABLE_TIME seconds while data packets are still flowing. 3565 However, the decision of when to initiate a new NS/NA exchange and to 3566 perpetuate the process is left as an implementation detail. 3568 One possible strategy may be to monitor the neighbor cache entry 3569 watching for data packets for (REACHABLE_TIME - 5) seconds. If any 3570 data packets have been sent to the neighbor within this timeframe, 3571 then send an NS to receive a new NA. If no data packets have been 3572 sent, wait for 5 additional seconds and send an immediate NS if any 3573 data packets are sent within this "expiration pending" 5 second 3574 window. If no additional data packets are sent within the 5 second 3575 window, delete the neighbor cache entry. 3577 The monitoring of the neighbor data packet traffic therefore becomes 3578 an asymmetric ongoing process during the neighbor cache entry 3579 lifetime. If the neighbor cache entry expires, future data packets 3580 will trigger a new NS/NA exchange while the packets themselves are 3581 delivered over a longer path until route optimization state is re- 3582 established. 3584 B.2. Implicit Mobility Management 3586 AERO interface neighbors MAY provide a configuration option that 3587 allows them to perform implicit mobility management in which no ND 3588 messaging is used. In that case, the Client only transmits packets 3589 over a single interface at a time, and the neighbor always observes 3590 packets arriving from the Client from the same link-layer source 3591 address. 3593 If the Client's underlying interface address changes (either due to a 3594 readdressing of the original interface or switching to a new 3595 interface) the neighbor immediately updates the neighbor cache entry 3596 for the Client and begins accepting and sending packets according to 3597 the Client's new address. This implicit mobility method applies to 3598 use cases such as cellphones with both WiFi and Cellular interfaces 3599 where only one of the interfaces is active at a given time, and the 3600 Client automatically switches over to the backup interface if the 3601 primary interface fails. 3603 B.3. Direct Underlying Interfaces 3605 When a Client's AERO interface is configured over a Direct interface, 3606 the neighbor at the other end of the Direct link can receive packets 3607 without any encapsulation. In that case, the Client sends packets 3608 over the Direct link according to QoS preferences. If the Direct 3609 interface has the highest QoS preference, then the Client's IP 3610 packets are transmitted directly to the peer without going through an 3611 ANET/INET. If other interfaces have higher QoS preferences, then the 3612 Client's IP packets are transmitted via a different interface, which 3613 may result in the inclusion of Proxys, Servers and Relays in the 3614 communications path. Direct interfaces must be tested periodically 3615 for reachability, e.g., via NUD. 3617 B.4. Operation on AERO Links with /64 ASPs 3619 IPv6 AERO links typically have MSPs that aggregate many candidate 3620 MNPs of length /64 or shorter. However, in some cases it may be 3621 desirable to use AERO over links that have only a /64 MSP. This can 3622 be accommodated by treating all Clients on the AERO link as simple 3623 hosts that receive /128 prefix delegations. 3625 In that case, the Client sends an RS message to the Server the same 3626 as for ordinary AERO links. The Server responds with an RA message 3627 that includes one or more /128 prefixes (i.e., singleton addresses) 3628 that include the /64 MSP prefix along with an interface identifier 3629 portion to be assigned to the Client. The Client and Server then 3630 configure their AERO addresses based on the interface identifier 3631 portions of the /128s (i.e., the lower 64 bits) and not based on the 3632 /64 prefix (i.e., the upper 64 bits). 3634 For example, if the MSP for the host-only IPv6 AERO link is 3635 2001:db8:1000:2000::/64, each Client will receive one or more /128 3636 IPv6 prefix delegations such as 2001:db8:1000:2000::1/128, 3637 2001:db8:1000:2000::2/128, etc. When the Client receives the prefix 3638 delegations, it assigns the AERO addresses fe80::1, fe80::2, etc. to 3639 the AERO interface, and assigns the global IPv6 addresses (i.e., the 3640 /128s) to either the AERO interface or an internal virtual interface 3641 such as a loopback. In this arrangement, the Client conducts route 3642 optimization in the same sense as discussed in Section 3.17. 3644 This specification has applicability for nodes that act as a Client 3645 on an "upstream" AERO link, but also act as a Server on "downstream" 3646 AERO links. More specifically, if the node acts as a Client to 3647 receive a /64 prefix from the upstream AERO link it can then act as a 3648 Server to provision /128s to Clients on downstream AERO links. 3650 B.5. AERO Critical Infrastructure Considerations 3652 AERO Relays can be either Commercial off-the Shelf (COTS) standard IP 3653 routers or virtual machines in the cloud. Relays must be 3654 provisioned, supported and managed by the INET administrative 3655 authority, and connected to the Relays of other INETs via inter- 3656 domain peerings. Cost for purchasing, configuring and managing 3657 Relays is nominal even for very large AERO links. 3659 AERO Servers can be standard dedicated server platforms, but most 3660 often will be deployed as virtual machines in the cloud. The only 3661 requirements for Servers are that they can run the AERO user-level 3662 code and have at least one network interface connection to the INET. 3663 As with Relays, Servers must be provisioned, supported and managed by 3664 the INET administrative authority. Cost for purchasing, configuring 3665 and managing Servers is nominal especially for virtual Servers hosted 3666 in the cloud. 3668 AERO Proxys are most often standard dedicated server platforms with 3669 one network interface connected to the ANET and a second interface 3670 connected to an INET. As with Servers, the only requirements are 3671 that they can run the AERO user-level code and have at least one 3672 interface connection to the INET. Proxys must be provisioned, 3673 supported and managed by the ANET administrative authority. Cost for 3674 purchasing, configuring and managing Proxys is nominal, and borne by 3675 the ANET administrative authority. 3677 AERO Gateways can be any dedicated server or COTS router platform 3678 connected to INETs and/or EUNs. The Gateway joins the SPAN and 3679 engages in eBGP peering with one or more Relays as a stub AS. The 3680 Gateway then injects its MNPs and/or non-MNP prefixes into the BGP 3681 routing system, and provisions the prefixes to its downstream- 3682 attached networks. The Gateway can perform ROS/ROR services the same 3683 as for any Server, and can route between the MNP and non-MNP address 3684 spaces. 3686 B.6. AERO Server Failure Implications 3688 AERO Servers may appear as a single point of failure in the 3689 architecture, but such is not the case since all Servers on the link 3690 provide identical services and loss of a Server does not imply 3691 immediate and/or comprehensive communication failures. Although 3692 Clients typically associate with a single Server at a time, Server 3693 failure is quickly detected and conveyed by Bidirectional Forward 3694 Detection (BFD) and/or proactive NUD allowing Clients to migrate to 3695 new Servers. 3697 If a Server fails, ongoing packet forwarding to Clients will continue 3698 by virtue of the asymmetric neighbor cache entries that have already 3699 been established in route optimization sources (ROSs). If a Client 3700 also experiences mobility events at roughly the same time the Server 3701 fails, unsolicited NA messages may be lost but proxy neighbor cache 3702 entries in the DEPARTED state will ensure that packet forwarding to 3703 the Client's new locations will continue for up to DEPART_TIME 3704 seconds. 3706 If a Client is left without a Server for an extended timeframe (e.g., 3707 greater than REACHABLETIIME seconds) then existing asymmetric 3708 neighbor cache entries will eventually expire and both ongoing and 3709 new communications will fail. The original source will continue to 3710 retransmit until the Client has established a new Server 3711 relationship, after which time continuous communications will resume. 3713 Therefore, providing many Servers on the link with high availability 3714 profiles provides resilience against loss of individual Servers and 3715 assurance that Clients can establish new Server relationships quickly 3716 in event of a Server failure. 3718 B.7. AERO Client / Server Architecture 3720 The AERO architectural model is client / server in the control plane, 3721 with route optimization in the data plane. The same as for common 3722 Internet services, the AERO Client discovers the addresses of AERO 3723 Servers and selects one Server to connect to. The AERO service is 3724 analogous to common Internet services such as google.com, yahoo.com, 3725 cnn.com, etc. However, there is only one AERO service for the link 3726 and all Servers provide identical services. 3728 Common Internet services provide differing strategies for advertising 3729 server addresses to clients. The strategy is conveyed through the 3730 DNS resource records returned in response to name resolution queries. 3731 As of January 2020 Internet-based 'nslookup' services were used to 3732 determine the following: 3734 o When a client resolves the domainname "google.com", the DNS always 3735 returns one A record (i.e., an IPv4 address) and one AAAA record 3736 (i.e., an IPv6 address). The client receives the same addresses 3737 each time it resolves the domainname via the same DNS resolver, 3738 but may receive different addresses when it resolves the 3739 domainname via different DNS resolvers. But, in each case, 3740 exactly one A and one AAAA record are returned. 3742 o When a client resolves the domainname "ietf.org", the DNS always 3743 returns one A record and one AAAA record with the same addresses 3744 regardless of which DNS resolver is used. 3746 o When a client resolves the domainname "yahoo.com", the DNS always 3747 returns a list of 4 A records and 4 AAAA records. Each time the 3748 client resolves the domainname via the same DNS resolver, the same 3749 list of addresses are returned but in randomized order (i.e., 3750 consistent with a DNS round-robin strategy). But, interestingly, 3751 the same addresses are returned (albeit in randomized order) when 3752 the domainname is resolved via different DNS resolvers. 3754 o When a client resolves the domainname "amazon.com", the DNS always 3755 returns a list of 3 A records and no AAAA records. As with 3756 "yahoo.com", the same three A records are returned from any 3757 worldwide Internet connection point in randomized order. 3759 The above example strategies show differing approaches to Internet 3760 resilience and service distribution offered by major Internet 3761 services. The Google approach exposes only a single IPv4 and a 3762 single IPv6 address to clients. Clients can then select whichever IP 3763 protocol version offers the best response, but will always use the 3764 same IP address according to the current Internet connection point. 3765 This means that the IP address offered by the network must lead to a 3766 highly-available server and/or service distribution point. In other 3767 words, resilience is predicated on high availability within the 3768 network and with no client-initiated failovers expected (i.e., it is 3769 all-or-nothing from the client's perspective). However, Google does 3770 provide for worldwide distributed service distribution by virtue of 3771 the fact that each Internet connection point responds with a 3772 different IPv6 and IPv4 address. The IETF approach is like google 3773 (all-or-nothing from the client's perspective), but provides only a 3774 single IPv4 or IPv6 address on a worldwide basis. This means that 3775 the addresses must be made highly-available at the network level with 3776 no client failover possibility, and if there is any worldwide service 3777 distribution it would need to be conducted by a network element that 3778 is reached via the IP address acting as a service distribution point. 3780 In contrast to the Google and IETF philosophies, Yahoo and Amazon 3781 both provide clients with a (short) list of IP addresses with Yahoo 3782 providing both IP protocol versions and Amazon as IPv4-only. The 3783 order of the list is randomized with each name service query 3784 response, with the effect of round-robin load balancing for service 3785 distribution. With a short list of addresses, there is still 3786 expectation that the network will implement high availability for 3787 each address but in case any single address fails the client can 3788 switch over to using a different address. The balance then becomes 3789 one of function in the network vs function in the end system. 3791 The same implications observed for common highly-available services 3792 in the Internet apply also to the AERO client/server architecture. 3793 When an AERO Client connects to one or more ANETs, it discovers one 3794 or more AERO Server addresses through the mechanisms discussed in 3795 earlier sections. Each Server address presumably leads to a fault- 3796 tolerant clustering arrangement such as supported by Linux-HA, 3797 Extended Virtual Synchrony or Paxos. Such an arrangement has 3798 precedence in common Internet service deployments in lightweight 3799 virtual machines without requiring expensive hardware deployment. 3800 Similarly, common Internet service deployments set service IP 3801 addresses on service distribution points that may relay requests to 3802 many different servers. 3804 For AERO, the expectation is that a combination of the Google/IETF 3805 and Yahoo/Amazon philosophies would be employed. The AERO Client 3806 connects to different ANET access points and can receive 1-2 Server 3807 AERO addresses at each point. It then selects one AERO Server 3808 address, and engages in RS/RA exchanges with the same Server from all 3809 ANET connections. The Client remains with this Server unless or 3810 until the Server fails, in which case it can switch over to an 3811 alternate Server. The Client can likewise switch over to a different 3812 Server at any time if there is some reason for it to do so. So, the 3813 AERO expectation is for a balance of function in the network and end 3814 system, with fault tolerance and resilience at both levels. 3816 Appendix C. Change Log 3818 << RFC Editor - remove prior to publication >> 3820 Changes from draft-templin-intarea-6706bis-38 to draft-templin- 3821 intrea-6706bis-39: 3823 o Major clrifications and simplifications of SPAN fragmentation/ 3824 reassembly. 3826 o Revised AERO address format to support prefix lengths up to 112. 3828 o New method for forming SPAN Client Prefixes and population in the 3829 routing system. 3831 o Updates RFC4443 to set a new value in the ICMP PTB Code field. 3833 Changes from draft-templin-intarea-6706bis-35 to draft-templin- 3834 intrea-6706bis-36: 3836 o Clients in the open Internet secured using SEND/CGA. 3838 Changes from draft-templin-intarea-6706bis-32 to draft-templin- 3839 intrea-6706bis-33: 3841 o Updated Proxy discussion with "point-to-multipoint" server 3842 coordination 3844 o Significant updates to Address Resolution and NUD to include 3845 correct addresses in messages 3847 o Differentiate between NS(AR) and NS(NUD) as their addresses and 3848 use cases differ. 3850 Changes from draft-templin-intarea-6706bis-30 to draft-templin- 3851 intrea-6706bis-31: 3853 o Added "advisory PTB messages" under FAA SE2025 contract number 3854 DTFAWA-15-D-00030. 3856 Changes from draft-templin-intarea-6706bis-29 to draft-templin- 3857 intrea-6706bis-30: 3859 o Deprecate "primary" concept. Now, RS/RA keepalives are 3860 mainatained over *all* underlying interfaces (i.e., and not just 3861 one primary). 3863 Changes from draft-templin-intarea-6706bis-28 to draft-templin- 3864 intrea-6706bis-29: 3866 o Changed OMNI interface citation to "draft-templin-6man-omni- 3867 interface" 3869 o Changed SPAN Service Prefix to fd80::/10. 3871 o Changed S/TLLAO format to include 'S' bit for ifIndex 3872 corresponding to the underlying interface that is Source of ND 3873 message. 3875 o Updated Path MTU 3877 Changes from draft-templin-intarea-6706bis-27 to draft-templin- 3878 intrea-6706bis-28: 3880 o MTU and fragmentation. 3882 Changes from draft-templin-intarea-6706bis-26 to draft-templin- 3883 intrea-6706bis-27: 3885 o MTU and fragmentation. 3887 o SPAN Service Prefix set to fd00::/10 3889 o Client SPAN addresses defined. 3891 Changes from draft-templin-intarea-6706bis-25 to draft-templin- 3892 intrea-6706bis-26: 3894 o MTU and RA configuration information updated. 3896 Changes from draft-templin-intarea-6706bis-24 to draft-templin- 3897 intrea-6706bis-25: 3899 o Added concept of "primary" to allow for proxyed RS/RA over only 3900 selected underlying interfaces. 3902 o General Cleanup. 3904 Changes from draft-templin-intarea-6706bis-23 to draft-templin- 3905 intrea-6706bis-24: 3907 o OMNI interface spec now a normative reference. 3909 o Use REACHABLE_TIME as the nominal Router Lifetime to return in 3910 RAs. 3912 o General cleanup. 3914 Changes from draft-templin-intarea-6706bis-22 to draft-templin- 3915 intrea-6706bis-23: 3917 o Choice of using either RS/RA or unsolicited NA for old Server 3918 notification. 3920 o General cleanup. 3922 Changes from draft-templin-intarea-6706bis-21 to draft-templin- 3923 intrea-6706bis-22: 3925 o Tightened up text on Proxy. 3927 o Removed unnecessarily restrictive texts. 3929 o General cleanup. 3931 Changes from draft-templin-intarea-6706bis-20 to draft-templin- 3932 intrea-6706bis-21: 3934 o Clarified relationship between OMNI and S/TLLAO ifIndex-tuples. 3936 o Important text in Section 13.15.3 on Servers timing out Clients 3937 that have gone silent without sending a departure notification. 3939 o New text on RS/RA as "hints of forward progress" for proactive 3940 NUD. 3942 Changes from draft-templin-intarea-6706bis-19 to draft-templin- 3943 intrea-6706bis-20: 3945 o Included new route optimization source and destination addressing 3946 strategy. Now, route optimization maintenance uses the address of 3947 the existing Server instead of the data packet destination address 3948 so that less pressure is placed on the BGP routing system 3949 convergence time and Server constancy is supported. 3951 o Included new method for releasing from old MSE without requiring 3952 Client messaging. 3954 o Included references to new OMNI interface spec (including the OMNI 3955 option). 3957 o New appendix on AERO Client/Server architecture. 3959 Changes from draft-templin-intarea-6706bis-18 to draft-templin- 3960 intrea-6706bis-19: 3962 o Changed Proxy/Server keepalives to use "proactive NUD" in a manner 3963 tha paralles BFD 3965 Changes from draft-templin-intarea-6706bis-17 to draft-templin- 3966 intrea-6706bis-18: 3968 o Discuss how AERO option is used in relation to S/TLLAOs 3970 o New text on Bidirectional Forwarding Detection (BFD) 3972 o Cleaned up usage (and non-usage) of unsolicited NAs 3974 o New appendix on Server failures 3976 Changes from draft-templin-intarea-6706bis-15 to draft-templin- 3977 intrea-6706bis-17: 3979 o S/TLLAO now includes multiple link-layer addresses within a single 3980 option instead of requiring multiple options 3982 o New unsolicited NA message to inform the old link that a Client 3983 has moved to a new link 3985 Changes from draft-templin-intarea-6706bis-14 to draft-templin- 3986 intrea-6706bis-15: 3988 o MTU and fragmentation 3990 o New details in movement to new Server 3992 Changes from draft-templin-intarea-6706bis-13 to draft-templin- 3993 intrea-6706bis-14: 3995 o Security based on secured tunnels, ingress filtering, MAP list and 3996 ROS list 3998 Changes from draft-templin-intarea-6706bis-12 to draft-templin- 3999 intrea-6706bis-13: 4001 o New paragraph in Section 3.6 on AERO interface layering over 4002 secured tunnels 4004 o Removed extraneous text in Section 3.7 4006 o Added new detail to the forwarding algorithm in Section 3.9 4008 o Clarified use of fragmentation 4010 o Route optimization now supported for both MNP and non-MNP-based 4011 prefixes 4013 o Relays are now seen as link-layer elements in the architecture. 4015 o Built out multicast section in detail. 4017 o New Appendix on implementation considerations for route 4018 optimization. 4020 Changes from draft-templin-intarea-6706bis-11 to draft-templin- 4021 intrea-6706bis-12: 4023 o Introduced Gateways as a new AERO element for connecting 4024 Correspondent Nodes on INET links 4026 o Introduced terms "Access Network (ANET)" and "Internetwork (INET)" 4028 o Changed "ASP" to "MSP", and "ACP" to "MNP" 4030 o New figure on the relation of Segments to the SPAN and AERO link 4032 o New "S" bit in S/TLLAO to indicate the "Source" S/TLLAO as opposed 4033 to additional S/TLLAOs 4035 o Changed Interface ID for Servers from 255 to 0xffff 4037 o Significant updates to Route Optimization, NUD, and Mobility 4038 Management 4040 o New Section on Multicast 4042 o New Section on AERO Clients in the open Internetwork 4044 o New Section on Operation over multiple AERO links (VLANs over the 4045 SPAN) 4047 o New Sections on DNS considerations and Transition considerations 4048 o 4050 Changes from draft-templin-intarea-6706bis-10 to draft-templin- 4051 intrea-6706bis-11: 4053 o Added The SPAN 4055 Changes from draft-templin-intarea-6706bis-09 to draft-templin- 4056 intrea-6706bis-10: 4058 o Orphaned packets in flight (e.g., when a neighbor cache entry is 4059 in the DEPARTED state) are now forwarded at the link layer instead 4060 of at the network layer. Forwarding at the network layer can 4061 result in routing loops and/or excessive delays of forwarded 4062 packets while the routing system is still reconverging. 4064 o Update route optimization to clarify the unsecured nature of the 4065 first NS used for route discovery 4067 o Many cleanups and clarifications on ND messaging parameters 4069 Changes from draft-templin-intarea-6706bis-08 to draft-templin- 4070 intrea-6706bis-09: 4072 o Changed PRL to "MAP list" 4074 o For neighbor cache entries, changed "static" to "symmetric", and 4075 "dynamic" to "asymmetric" 4077 o Specified Proxy RS/RA exchanges with Servers on behalf of Clients 4079 o Added discussion of unsolicited NAs in Section 3.16, and included 4080 forward reference to Section 3.18 4082 o Added discussion of AERO Clients used as critical infrastructure 4083 elements to connect fixed networks. 4085 o Added network-based VPN under security considerations 4087 Changes from draft-templin-intarea-6706bis-07 to draft-templin- 4088 intrea-6706bis-08: 4090 o New section on AERO-Aware Access Router 4092 Changes from draft-templin-intarea-6706bis-06 to draft-templin- 4093 intrea-6706bis-07: 4095 o Added "R" bit for release of PDs. Now have a full RS/RA service 4096 that can do PD without requiring DHCPv6 messaging over-the-air 4098 o Clarifications on solicited vs unsolicited NAs 4100 o Clarified use of MAX_NEIGHBOR_ADVERTISEMENT for the purpose of 4101 increase reliability 4103 Changes from draft-templin-intarea-6706bis-05 to draft-templin- 4104 intrea-6706bis-06: 4106 o Major re-work and simplification of Route Optimization function 4108 o Added Distributed Mobility Management (DMM) and Mobility Anchor 4109 Point (MAP) terminology 4111 o New section on "AERO Critical Infrastructure Element 4112 Considerations" demonstrating low overall cost for the service 4114 o minor text revisions and deletions 4116 o removed extraneous appendices 4118 Changes from draft-templin-intarea-6706bis-04 to draft-templin- 4119 intrea-6706bis-05: 4121 o New Appendix E on S/TLLAO Extensions for special-purpose links. 4122 Discussed ATN/IPS as example. 4124 o New sentence in introduction to declare appendices as non- 4125 normative. 4127 Changes from draft-templin-intarea-6706bis-03 to draft-templin- 4128 intrea-6706bis-04: 4130 o Added definitions for Potential Router List (PRL) and secure 4131 enclave 4133 o Included text on mapping transport layer port numbers to network 4134 layer DSCP values 4136 o Added reference to DTLS and DMM Distributed Mobility Anchoring 4137 working group document 4139 o Reworked Security Considerations 4141 o Updated references. 4143 Changes from draft-templin-intarea-6706bis-02 to draft-templin- 4144 intrea-6706bis-03: 4146 o Added new section on SEND. 4148 o Clarifications on "AERO Address" section. 4150 o Updated references and added new reference for RFC8086. 4152 o Security considerations updates. 4154 o General text clarifications and cleanup. 4156 Changes from draft-templin-intarea-6706bis-01 to draft-templin- 4157 intrea-6706bis-02: 4159 o Note on encapsulation avoidance in Section 4. 4161 Changes from draft-templin-intarea-6706bis-00 to draft-templin- 4162 intrea-6706bis-01: 4164 o Remove DHCPv6 Server Release procedures that leveraged the old way 4165 Relays used to "route" between Server link-local addresses 4167 o Remove all text relating to Relays needing to do any AERO-specific 4168 operations 4170 o Proxy sends RS and receives RA from Server using SEND. Use CGAs 4171 as source addresses, and destination address of RA reply is to the 4172 AERO address corresponding to the Client's ACP. 4174 o Proxy uses SEND to protect RS and authenticate RA (Client does not 4175 use SEND, but rather relies on subnetwork security. When the 4176 Proxy receives an RS from the Client, it creates a new RS using 4177 its own addresses as the source and uses SEND with CGAs to send a 4178 new RS to the Server. 4180 o Emphasize distributed mobility management 4182 o AERO address-based RS injection of ACP into underlying routing 4183 system. 4185 Changes from draft-templin-aerolink-82 to draft-templin-intarea- 4186 6706bis-00: 4188 o Document use of NUD (NS/NA) for reliable link-layer address 4189 updates as an alternative to unreliable unsolicited NA. 4190 Consistent with Section 7.2.6 of RFC4861. 4192 o Server adds additional layer of encapsulation between outer and 4193 inner headers of NS/NA messages for transmission through Relays 4194 that act as vanilla IPv6 routers. The messages include the AERO 4195 Server Subnet Router Anycast address as the source and the Subnet 4196 Router Anycast address corresponding to the Client's ACP as the 4197 destination. 4199 o Clients use Subnet Router Anycast address as the encapsulation 4200 source address when the access network does not provide a 4201 topologically-fixed address. 4203 Author's Address 4205 Fred L. Templin (editor) 4206 Boeing Research & Technology 4207 P.O. Box 3707 4208 Seattle, WA 98124 4209 USA 4211 Email: fltemplin@acm.org