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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 3, 2020 5 rfc6179, rfc6706 (if 6 approved) 7 Intended status: Standards Track 8 Expires: October 5, 2020 10 Asymmetric Extended Route Optimization (AERO) 11 draft-templin-intarea-6706bis-38 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 5, 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 3.3.1. IPv4 Compatibility Routing . . . . . . . . . . . . . 15 69 3.4. AERO Addresses . . . . . . . . . . . . . . . . . . . . . 15 70 3.5. Spanning Partitioned AERO Networks (SPAN) . . . . . . . . 16 71 3.5.1. SPAN Compatibility Addressing . . . . . . . . . . . . 20 72 3.5.2. Client SPAN Addresses . . . . . . . . . . . . . . . . 20 73 3.6. AERO Interface Characteristics . . . . . . . . . . . . . 21 74 3.7. AERO Interface Initialization . . . . . . . . . . . . . . 24 75 3.7.1. AERO Server/Gateway Behavior . . . . . . . . . . . . 25 76 3.7.2. AERO Proxy Behavior . . . . . . . . . . . . . . . . . 25 77 3.7.3. AERO Client Behavior . . . . . . . . . . . . . . . . 25 78 3.7.4. AERO Relay Behavior . . . . . . . . . . . . . . . . . 26 79 3.8. AERO Interface Neighbor Cache Maintenance . . . . . . . . 26 80 3.9. AERO Interface Encapsulation and Re-encapsulation . . . . 28 81 3.10. AERO Interface Decapsulation . . . . . . . . . . . . . . 29 82 3.11. AERO Interface Data Origin Authentication . . . . . . . . 29 83 3.12. AERO Interface MTU and Fragmentation . . . . . . . . . . 30 84 3.13. AERO Interface Forwarding Algorithm . . . . . . . . . . . 31 85 3.13.1. Client Forwarding Algorithm . . . . . . . . . . . . 32 86 3.13.2. Proxy Forwarding Algorithm . . . . . . . . . . . . . 33 87 3.13.3. Server/Gateway Forwarding Algorithm . . . . . . . . 34 88 3.13.4. Relay Forwarding Algorithm . . . . . . . . . . . . . 35 89 3.14. AERO Interface Error Handling . . . . . . . . . . . . . . 36 90 3.15. AERO Router Discovery, Prefix Delegation and 91 Autoconfiguration . . . . . . . . . . . . . . . . . . . . 38 92 3.15.1. AERO ND/PD Service Model . . . . . . . . . . . . . . 38 93 3.15.2. AERO Client Behavior . . . . . . . . . . . . . . . . 39 94 3.15.3. AERO Server Behavior . . . . . . . . . . . . . . . . 41 95 3.16. The AERO Proxy . . . . . . . . . . . . . . . . . . . . . 44 96 3.16.1. Detecting and Responding to Server Failures . . . . 46 97 3.16.2. Point-to-Multipoint Server Coordindation . . . . . . 47 98 3.17. AERO Route Optimization . . . . . . . . . . . . . . . . . 47 99 3.17.1. Route Optimization Initiation . . . . . . . . . . . 48 100 3.17.2. Relaying the NS . . . . . . . . . . . . . . . . . . 48 101 3.17.3. Processing the NS and Sending the NA . . . . . . . . 48 102 3.17.4. Relaying the NA . . . . . . . . . . . . . . . . . . 49 103 3.17.5. Processing the NA . . . . . . . . . . . . . . . . . 50 104 3.17.6. Route Optimization Maintenance . . . . . . . . . . . 50 105 3.18. Neighbor Unreachability Detection (NUD) . . . . . . . . . 51 106 3.19. Mobility Management and Quality of Service (QoS) . . . . 52 107 3.19.1. Mobility Update Messaging . . . . . . . . . . . . . 53 108 3.19.2. Announcing Link-Layer Address and/or QoS Preference 109 Changes . . . . . . . . . . . . . . . . . . . . . . 54 110 3.19.3. Bringing New Links Into Service . . . . . . . . . . 54 111 3.19.4. Removing Existing Links from Service . . . . . . . . 54 112 3.19.5. Moving to a New Server . . . . . . . . . . . . . . . 54 113 3.20. Multicast . . . . . . . . . . . . . . . . . . . . . . . . 55 114 3.20.1. Source-Specific Multicast (SSM) . . . . . . . . . . 56 115 3.20.2. Any-Source Multicast (ASM) . . . . . . . . . . . . . 57 116 3.20.3. Bi-Directional PIM (BIDIR-PIM) . . . . . . . . . . . 58 117 3.21. Operation over Multiple AERO Links (VLANs) . . . . . . . 58 118 3.22. DNS Considerations . . . . . . . . . . . . . . . . . . . 59 119 3.23. Transition Considerations . . . . . . . . . . . . . . . . 60 120 3.24. Detecting and Reacting to Server and Relay Failures . . . 60 121 3.25. AERO Clients on the Open Internet . . . . . . . . . . . . 61 122 4. Implementation Status . . . . . . . . . . . . . . . . . . . . 63 123 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 63 124 6. Security Considerations . . . . . . . . . . . . . . . . . . . 63 125 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 65 126 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 66 127 8.1. Normative References . . . . . . . . . . . . . . . . . . 66 128 8.2. Informative References . . . . . . . . . . . . . . . . . 68 129 Appendix A. AERO Alternate Encapsulations . . . . . . . . . . . 75 130 Appendix B. Non-Normative Considerations . . . . . . . . . . . . 76 131 B.1. Implementation Strategies for Route Optimization . . . . 77 132 B.2. Implicit Mobility Management . . . . . . . . . . . . . . 77 133 B.3. Direct Underlying Interfaces . . . . . . . . . . . . . . 78 134 B.4. Operation on AERO Links with /64 ASPs . . . . . . . . . . 78 135 B.5. AERO Critical Infrastructure Considerations . . . . . . . 79 136 B.6. AERO Server Failure Implications . . . . . . . . . . . . 79 137 B.7. AERO Client / Server Architecture . . . . . . . . . . . . 80 138 Appendix C. Change Log . . . . . . . . . . . . . . . . . . . . . 82 139 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 90 141 1. Introduction 143 Asymmetric Extended Route Optimization (AERO) fulfills the 144 requirements of Distributed Mobility Management (DMM) [RFC7333] and 145 route optimization [RFC5522] for aeronautical networking and other 146 network mobility use cases. AERO is based on a Non-Broadcast, 147 Multiple Access (NBMA) virtual link model known as the AERO link. 148 The AERO link is a virtual overlay configured over one or more 149 underlying Internetworks, and nodes on the link can exchange IP 150 packets via tunneling. Multilink operation allows for increased 151 reliability, bandwidth optimization and traffic path diversity. 153 The AERO service comprises Clients, Proxys, Servers and Gateways that 154 are seen as AERO link neighbors. Each node's AERO interface uses an 155 IPv6 link-local address format (known as the AERO address) that 156 supports operation of the IPv6 Neighbor Discovery (ND) protocol 157 [RFC4861] and links ND to IP forwarding. A node's AERO interface can 158 be configured over multiple underlying interfaces, and may therefore 159 appear as a single interface with multiple link-layer addresses. 160 Each link-layer address is subject to change due to mobility and/or 161 QoS fluctuations, and link-layer address changes are signaled by ND 162 messaging the same as for any IPv6 link. 164 AERO links provide a cloud-based service where mobile nodes may use 165 any Server acting as a Mobility Anchor Point (MAP) and fixed nodes 166 may use any Gateway on the link for efficient communications. Fixed 167 nodes forward packets destined to other AERO nodes to the nearest 168 Gateway, which forwards them through the cloud. A mobile node's 169 initial packets are forwarded through the Server, while direct 170 routing is supported through asymmetric extended route optimization 171 while data packets are flowing. Both unicast and multicast 172 communications are supported, and mobile nodes may efficiently move 173 between locations while maintaining continuous communications with 174 correspondents and without changing their IP Address. 176 AERO Relays are interconnected in a secured private BGP overlay 177 routing instance known as the "SPAN". The SPAN provides a hybrid 178 routing/bridging service to join the underlying Internetworks of 179 multiple disjoint administrative domains into a single unified AERO 180 link. Each AERO link instance is characterized by the set of 181 Mobility Service Prefixes (MSPs) common to all mobile nodes. The 182 link extends to the point where a Gateway/Server is on the optimal 183 route from any correspondent node on the link, and provides a gateway 184 between the underlying Internetwork and the SPAN. To the underlying 185 Internetwork, the Gateway/Server is the source of a route to its MSP, 186 and hence uplink traffic to the mobile node is naturally routed to 187 the nearest Gateway/Server. 189 AERO assumes the use of PIM Sparse Mode in support of multicast 190 communication. In support of Source Specific Multicast (SSM) when a 191 Mobile Node is the source, AERO route optimization ensures that a 192 shortest-path multicast tree is established with provisions for 193 mobility and multilink operation. In all other multicast scenarios 194 there are no AERO dependencies. 196 AERO was designed for aeronautical networking for both manned and 197 unmanned aircraft, where the aircraft is treated as a mobile node 198 that can connect an Internet of Things (IoT). AERO is also 199 applicable to a wide variety of other use cases. For example, it can 200 be used to coordinate the Virtual Private Network (VPN) links of 201 mobile nodes (e.g., cellphones, tablets, laptop computers, etc.) that 202 connect into a home enterprise network via public access networks 203 using services such as OpenVPN [OVPN]. Other applicable use cases 204 are also in scope. 206 The following numbered sections present the AERO specification. The 207 appendices at the end of the document are non-normative. 209 2. Terminology 211 The terminology in the normative references applies; the following 212 terms are defined within the scope of this document: 214 IPv6 Neighbor Discovery (ND) 215 an IPv6 control message service for coordinating neighbor 216 relationships between nodes connected to a common link. AERO 217 interfaces use the ND service specified in [RFC4861]. 219 IPv6 Prefix Delegation (PD) 220 a networking service for delegating IPv6 prefixes to nodes on the 221 link. The nominal PD service is DHCPv6 [RFC8415], however 222 alternate services (e.g., based on ND messaging) are also in scope 223 [I-D.templin-v6ops-pdhost][I-D.templin-6man-dhcpv6-ndopt]. Most 224 notably, a minimal form of PD known as "prefix registration" can 225 be used if the Client knows its prefix in advance and can 226 represent it in the IPv6 source address of an ND message. 228 Access Network (ANET) 229 a node's first-hop data link service network, e.g., a radio access 230 network, cellular service provider network, corporate enterprise 231 network, or the public Internet itself. For secured ANETs, link- 232 layer security services such as IEEE 802.1X and physical-layer 233 security prevent unauthorized access internally while border 234 network-layer security services such as firewalls and proxies 235 prevent unauthorized outside access. 237 ANET interface 238 a node's attachment to a link in an ANET. 240 ANET address 241 an IP address assigned to a node's interface connection to an 242 ANET. 244 Internetwork (INET) 245 a connected IP network topology with a coherent routing and 246 addressing plan and that provides a transit backbone service for 247 ANET end systems. INETs also provide an underlay service over 248 which the AERO virtual link is configured. Example INETs include 249 corporate enterprise networks, aviation networks, and the public 250 Internet itself. When there is no administrative boundary between 251 an ANET and the INET, the ANET and INET are one and the same. 253 INET Partition 254 frequently, INETs such as large corporate enterprise networks are 255 sub-divided internally into separate isolated partitions. Each 256 partition is fully connected internally but disconnected from 257 other partitions, and there is no requirement that separate 258 partitions maintain consistent Internet Protocol and/or addressing 259 plans. (An INET partition is the same as a SPAN segment discussed 260 below.) 262 INET interface 263 a node's attachment to a link in an INET. 265 INET address 266 an IP address assigned to a node's interface connection to an 267 INET. 269 AERO link 270 a Non-Broadcast, Multiple Access (NBMA) tunnel virtual overlay 271 configured over one or more underlying INETs. Nodes on the AERO 272 link appear as single-hop neighbors from the perspective of the 273 virtual overlay even though they may be separated by many 274 underlying INET hops. AERO links may be configured over multiple 275 underlying SPAN segments (see below). 277 AERO interface 278 a node's attachment to an AERO link. Since the addresses assigned 279 to an AERO interface are managed for uniqueness, AERO interfaces 280 do not require Duplicate Address Detection (DAD) and therefore set 281 the administrative variable 'DupAddrDetectTransmits' to zero 282 [RFC4862]. 284 underlying interface 285 an ANET or INET interface over which an AERO interface is 286 configured. 288 AERO address 289 an IPv6 link-local address assigned to an AERO interface and 290 constructed as specified in Section 3.4. 292 base AERO address 293 the lowest-numbered AERO address aggregated by the MNP (see 294 Section 3.4). 296 Mobility Service Prefix (MSP) 297 an IP prefix assigned to the AERO link and from which more- 298 specific Mobile Network Prefixes (MNPs) are derived. 300 Mobile Network Prefix (MNP) 301 an IP prefix allocated from an MSP and delegated to an AERO Client 302 or Gateway. 304 AERO node 305 a node that is connected to an AERO link, or that provides 306 services to other nodes on an AERO link. 308 AERO Client ("Client") 309 an AERO node that connects to one or more ANETs and requests MNP 310 PDs from AERO Servers. The Client assigns a Client AERO address 311 to the AERO interface for use in ND exchanges with other AERO 312 nodes and forwards packets to correspondents according to AERO 313 interface neighbor cache state. 315 AERO Server ("Server") 316 an INET node that configures an AERO interface to provide default 317 forwarding and mobility/multilink services for AERO Clients. The 318 Server assigns an administratively-provisioned AERO address to its 319 AERO interface to support the operation of the ND/PD services, and 320 advertises all of its associated MNPs via BGP peerings with 321 Relays. 323 AERO Gateway ("Gateway") 324 an AERO Server that also provides forwarding services between 325 nodes reached via the AERO link and correspondents on other links. 326 AERO Gateways are provisioned with MNPs (i.e., the same as for an 327 AERO Client) and run a dynamic routing protocol to discover any 328 non-MNP IP routes. In both cases, the Gateway advertises the 329 MSP(s) over INET interfaces, and distributes all of its associated 330 MNPs and non-MNP IP routes via BGP peerings with Relays (i.e., the 331 same as for an AERO Server). 333 AERO Relay ("Relay") 334 a node that provides hybrid routing/bridging services (as well as 335 a security trust anchor) for nodes on an AERO link. As a router, 336 the Relay forwards packets using standard IP forwarding. As a 337 bridge, the Relay forwards packets over the AERO link without 338 decrementing the IPv6 Hop Limit. AERO Relays peer with Servers 339 and other Relays to discover the full set of MNPs for the link as 340 well as any non-MNPs that are reachable via Gateways. 342 AERO Proxy ("Proxy") 343 a node that provides proxying services between Clients in an ANET 344 and Servers in external INETs. The AERO Proxy is a conduit 345 between the ANET and external INETs in the same manner as for 346 common web proxies, and behaves in a similar fashion as for ND 347 proxies [RFC4389]. 349 Spanning Partitioned AERO Networks (SPAN) 350 a means for bridging disjoint INET partitions as segments of a 351 unified AERO link the same as for a bridged campus LAN. The SPAN 352 is a mid-layer IPv6 encapsulation service in the AERO routing 353 system that supports a unified AERO link view for all segments. 354 Each segment in the SPAN is a distinct INET partition. 356 SPAN Service Prefix (SSP) 357 a global or unique local /96 IPv6 prefix assigned to the AERO link 358 to support SPAN services. 360 SPAN Partition Prefix (SPP) 361 a sub-prefix of the SPAN Service Prefix uniquely assigned to a 362 single SPAN segment. 364 SPAN Address 365 a global or unique local IPv6 address taken from a SPAN Partition 366 Prefix and constructed as specified in Section 3.5. SPAN 367 addresses are statelessly derived from AERO addresses, and vice- 368 versa. 370 ingress tunnel endpoint (ITE) 371 an AERO interface endpoint that injects encapsulated packets into 372 an AERO link. 374 egress tunnel endpoint (ETE) 375 an AERO interface endpoint that receives encapsulated packets from 376 an AERO link. 378 link-layer address 379 an IP address used as an encapsulation header source or 380 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 3.3.1. IPv4 Compatibility Routing 674 For IPv6 MNPs, the AERO routing system includes ordinary IPv6 routes. 675 For IPv4 MNPs, the AERO routing system includes IPv6 routes based on 676 an IPv4-embedded IPv6 address format discussed in Section 3.5.1. 678 3.4. AERO Addresses 680 A Client's AERO address is an IPv6 link-local address with an 681 interface identifier based on the Client's delegated MNP. Relay, 682 Server and Proxy AERO addresses are assigned from the range fe80::/96 683 and include an administratively-provisioned value in the lower 32 684 bits. 686 For IPv6, Client AERO addresses begin with the prefix fe80::/64 and 687 include in the interface identifier (i.e., the lower 64 bits) the 688 most-significant 64 bits of the Client's IPv6 MNPs. For example, if 689 the AERO Client receives the IPv6 MNP: 2001:db8:1000:2000::/56 it 690 constructs its corresponding AERO address as: 691 fe80::2001:db8:1000:2000. 693 For IPv4, Client AERO addresses are based on an IPv4-mapped IPv6 694 address [RFC4291] formed from an IPv4 MNP and with a prefix length of 695 96 plus the MNP prefix length. For example, for the IPv4 MNP 696 192.0.2.32/28 the IPv4-mapped IPv6 MNP is: 698 0:0:0:0:0:FFFF:192.0.2.16/124 (also written as 699 0:0:0:0:0:FFFF:c000:0210/124) 701 The Client then constructs its AERO address with the prefix fe80::/64 702 and with the lower 64 bits of the IPv4-mapped IPv6 address in the 703 interface identifier as: fe80::FFFF:192.0.2.16. 705 Mobility Service (MS) AERO addresses (used by Relays, Servers, 706 Gateways and Proxys) are allocated from the range fe80::/96, and MUST 707 be managed for uniqueness. The lower 32 bits of the AERO address 708 includes a unique integer value between 1 and 0xfeffffff (e.g., 709 fe80::1, fe80::2, fe80::3, etc., fe80::feff:ffff) as assigned by the 710 administrative authority for the link. If the link spans multiple 711 SPAN segments, the AERO addresses are assigned to each segment in 1x1 712 correspondence with SPAN addresses (see: Section 3.5). The address 713 fe80:: is the IPv6 link-local Subnet-Router anycast address, and the 714 address fe80::ffff:ffff is the "All-AERO-Servers" address. The 715 address range fe80::ff00:0000/104 is reserved for future use. 717 The Client's Subnet-Router anycast address can be statelessly 718 determined from its AERO address by simply transposing the AERO 719 address into the upper N bits of the Anycast address followed by 720 128-N bits of zeroes. For example, for the AERO address 721 fe80::2001:db8:1:2 the Subnet-Router anycast address is 722 2001:db8:1:2::. 724 AERO addresses for mobile node Clients embed a MNP as discussed 725 above, while AERO addresses for non-MNP destinations are constructed 726 in exactly the same way. A Client AERO address therefore encodes 727 either an MNP if the prefix is reached via the SPAN or a non-MNP if 728 the prefix is reached via a Gateway. 730 3.5. Spanning Partitioned AERO Networks (SPAN) 732 An AERO link configured over a single INET appears as a single 733 unified link with a consistent underlying network addressing plan. 734 In that case, all nodes on the link can exchange packets via simple 735 INET encapsulation, since the underlying INET is connected. In 736 common practice, however, an AERO link may be partitioned into 737 multiple "segments", where each segment is a distinct INET 738 potentially managed under a different administrative authority (e.g., 739 as for worldwide aviation service providers such as ARINC, SITA, 740 Inmarsat, etc.). Individual INETs may also themselves be partitioned 741 internally, in which case each internal partition is seen as a 742 separate segment. 744 The addressing plan of each segment is consistent internally but will 745 often bear no relation to the addressing plans of other segments. 746 Each segment is also likely to be separated from others by network 747 security devices (e.g., firewalls, proxies, packet filtering 748 gateways, etc.), and in many cases disjoint segments may not even 749 have any common physical link connections. Therefore, nodes can only 750 be assured of exchanging packets directly with correspondents in the 751 same segment, and not with those in other segments. The only means 752 for joining the segments therefore is through inter-domain peerings 753 between AERO Relays. 755 The same as for traditional campus LANs, multiple AERO link segments 756 can be joined into a single unified link via a virtual bridging 757 service termed the "SPAN". The SPAN performs link-layer packet 758 forwarding between segments (i.e., bridging) without decrementing the 759 network-layer TTL/Hop Limit. The SPAN model is depicted in Figure 2: 761 . . . . . . . . . . . . . . . . . . . . . . . 762 . . 763 . .-(::::::::) . 764 . .-(::::::::::::)-. +-+ . 765 . (:::: Segment A :::)--|R|---+ . 766 . `-(::::::::::::)-' +-+ | . 767 . `-(::::::)-' | . 768 . | . 769 . .-(::::::::) | . 770 . .-(::::::::::::)-. +-+ | . 771 . (:::: Segment B :::)--|R|---+ . 772 . `-(::::::::::::)-' +-+ | . 773 . `-(::::::)-' | . 774 . | . 775 . .-(::::::::) | . 776 . .-(::::::::::::)-. +-+ | . 777 . (:::: Segment C :::)--|R|---+ . 778 . `-(::::::::::::)-' +-+ | . 779 . `-(::::::)-' | . 780 . | . 781 . ..(etc).. x . 782 . . 783 . . 784 . <- AERO Link Bridged by the SPAN -> . 785 . . . . . . . . . . . . . .. . . . . . . . . 787 Figure 2: The SPAN 789 To support the SPAN, AERO links use the Unique Local Address (ULA) 790 prefix fd80::/10 [RFC4193] as the SPAN Service Prefix (SSP). The 791 prefix length intentionally matches the IPv6 link-local prefix 792 (fe80::/10), and enables a simple 1-bit stateless translation between 793 link-local and SPAN prefixes (i.e., bit 7 is '1' for link-local or 794 '0' for SPAN). 796 Each segment in the SPAN assigns a unique sub-prefix of SSP::/96 797 termed a "SPAN Partition Prefix (SPP)". For example, a first segment 798 could assign fd80::1000/116, a second could assign fd80::2000/116, a 799 third could assign fd80::3000/116, etc. The administrative 800 authorities for each segment must therefore coordinate to assure 801 mutually-exclusive SPP assignments, but internal provisioning of the 802 SPP is an independent local consideration for each administrative 803 authority. 805 An administratively-assigned "SPAN address" is an address taken from 806 a SPP and assigned to a Relay, Server, Gateway or Proxy interface. 807 SPAN addresses are formed by simply clearing bit 7 of an 808 administratively-assigned AERO address. For example, if the SPP is 809 fd80::1000/116, the SPAN address formed from the AERO address 810 fe80::1001 is simply fd80::1001. 812 An "INET address" is an address of a node's interface connection to 813 an INET. AERO/SPAN/INET address mappings are maintained as permanent 814 neighbor cache entires as discussed in Section 3.8. 816 AERO Relays serve as bridges to join multiple segments into a unified 817 AERO link over multiple diverse administrative domains. They support 818 the bridging function by first establishing forwarding table entries 819 for their SPPs either via standard BGP routing or static routes. For 820 example, if three Relays ('A', 'B' and 'C') from different segments 821 serviced the SPPs fd80::1000/116, fd80::2000/116 and fd80::3000/116 822 respectively, then the forwarding tables in each Relay are as 823 follows: 825 A: fd80::1000/116->local, fd80::2000/116->B, fd80::3000/116->C 827 B: fd80::1000/116->A, fd80::2000/116->local, fd80::3000/116->C 829 C: fd80::1000/116->A, fd80::2000/116->B, fd80::3000/116->local 831 These forwarding table entries are permanent and never change, since 832 they correspond to fixed infrastructure elements in their respective 833 segments. This provides the basis for a link-layer forwarding 834 service that cannot be disrupted by routing updates due to node 835 mobility. 837 With the SPPs in place in each Relay's forwarding table, control and 838 data packets sent between AERO nodes in different segments can 839 therefore be carried over the SPAN via encapsulation. For example, 840 when a source AERO node in segment A forwards a packet with IPv6 841 address 2001:db8:1:2::1 to a target AERO node in segment C with IPv6 842 address 2001:db8:1000:2000::1, it first encapsulates the packet in a 843 SPAN header with source SPAN address taken from fd80::1000/116 (e.g., 844 fd80::1001) and destination SPAN address taken from fd80::3000/116 845 (e.g., fd80::3001). Next, it encapsulates the SPAN message in an 846 INET header with source address set to its own INET address (e.g., 847 192.0.2.100) and destination set to the INET address of a Relay 848 (e.g., 192.0.2.1). 850 SPAN encapsulation is based on Generic Packet Tunneling in IPv6 851 [RFC2473]; the encapsulation format in the above example is shown in 852 Figure 3: 854 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 855 | INET Header | 856 | src = 192.0.2.100 | 857 | dst = 192.0.2.1 | 858 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 859 | SPAN Header | 860 | src = fd80::1001 | 861 | dst = fd80::3001 | 862 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 863 | Inner IP Header | 864 | src = 2001:db8:1:2::1 | 865 | dst = 2001:db8:1000:2000::1 | 866 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 867 | | 868 ~ ~ 869 ~ Inner Packet Body ~ 870 ~ ~ 871 | | 872 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 874 Figure 3: SPAN Encapsulation 876 In this format, the inner IP header and packet body are the original 877 IP packet, the SPAN header is an IPv6 header prepared according to 878 [RFC2473], and the INET header is prepared according to Section 3.9. 879 A packet is said to be "forwarded/sent into the SPAN" when it is 880 encapsulated as described above then forwarded via a secured tunnel 881 to a neighboring Relay. 883 This gives rise to a routing system that contains both MNP routes 884 that may change dynamically due to regional node mobility and SPAN 885 routes that never change. The Relays can therefore provide link- 886 layer bridging by sending packets into the SPAN instead of network- 887 layer routing according to MNP routes. As a result, opportunities 888 for packet loss due to node mobility between different segments are 889 mitigated. 891 With reference to Figure 3, for a Client's AERO address the SPAN 892 destination address is simply set to the Subnet-Router anycast 893 address. For non-link-local addresses, the destination SPAN address 894 may not be known in advance for the first few packets of a flow sent 895 via the SPAN. In that case, the SPAN destination address is set to 896 the original packet's destination, and the SPAN routing system will 897 direct the packet to the correct SPAN egress node. (In the above 898 example, the SPAN destination address is simply 899 2001:db8:1000:2000::1.) 901 3.5.1. SPAN Compatibility Addressing 903 For IPv4 MNPs, Servers inject a "SPAN Compatibility Prefix (SCP)" 904 that embeds the MNP into the BGP routing system. The SCP begins with 905 the upper 64 bits of the SSP, followed by the constant string 906 "0000:FFFF" followed by the IPv4 MNP. For example, if the MNP is 907 192.0.2.0/24 then the SCP is fd80::FFFF:192.0.2.0/120. 909 This allows for encapsulation of IPv4 packets in IPv6 headers with 910 "SPAN Compatibility Addresses (SCAs)". In this example, the SCA 911 corresponding to the SCP is simply fd80::FFFF:192.0.2.0, and can be 912 used as the SPAN destination address for packets forwarded via the 913 SPAN. This allows for forwarding of initial IPv4 packets over IPv6 914 SPAN routes, followed by route optimization for direct 915 communications. 917 3.5.2. Client SPAN Addresses 919 When an AERO Client or Proxy encapsulates and fragments a packet 920 (see: Section 3.12), it inserts its "Client SPAN Address" as the IPv6 921 source address of the encapsulation header. This is necessary to 922 provide reassemblers with a source address corresponding to the node 923 that actually inserted the fragment header so that the correct 924 Identification value context is provided. 926 The Client SPAN address is formed by simply clearing bit 7 of the 927 Client's AERO address. For example, for the Client AERO address 928 fe80::2001:db8:1:2 the corresponding Client SPAN address is 929 fd80::2001:db8:1:2. 931 Note that the Client's MNP itself (and not the Client SPAN address) 932 is injected into the routing system due to the /64 assumption in the 933 AERO address construction [RFC7421]. Because of the /64 assumption, 934 the most-significant 64 bits of the Client's MNP are written into the 935 least-significant 64 bits of the AERO address. If MNPs longer than 936 /64 are used in the future (i.e., /65 up to /118) the least- 937 significant bits of the MNP would need to be written into bits 10 938 through 63 of the SPAN address, which would render the address format 939 useless for longest-prefix-match. For more details, see Appendix B 940 of [I-D.templin-6man-omni-interface]. 942 3.6. AERO Interface Characteristics 944 AERO interfaces are virtual interfaces configured over one or more 945 underlying interfaces classified as follows: 947 o Native interfaces have global IP addresses that are reachable from 948 any INET correspondent. All Server, Gateway and Relay interfaces 949 are native interfaces, as are INET-facing interfaces of Proxys. 950 Clients connected to native interfaces receive Router 951 Advertisemenets (RAs) with both the P and N flags set to 0, as 952 discussed in the following sections. 954 o NATed interfaces connect to a private network behind a Network 955 Address Translator (NAT). The NAT does not participate in any 956 AERO control message signaling, but the Server can issue control 957 messages on behalf of the Client. Clients that are behind a NAT 958 are required to send periodic keepalive messages to keep NAT state 959 alive when there are no data packets flowing. If no other 960 periodic messaging service is available, the Client can send 961 Router Solicitation (RS) messages to receive RA replies from its 962 Server(s). Clients connected to NATed interfaces receive RAs with 963 the N flag set to 1. 965 o Proxyed interfaces connect to an ANET that is separated from the 966 open INET by an AERO Proxy. Unlike NATed and VPNed interfaces, 967 the Proxy can actively issue control messages on behalf of the 968 Client. Clients connected to Proxyed interfaces receive RAs with 969 the P flag set to 1. 971 o VPNed interfaces use security encapsulation to a Virtual Private 972 Network (VPN) server that also acts as an AERO Server. As with 973 NATed links, the Server can issue control messages on behalf of 974 the Client, and the Client can send periodic messages such as RS/ 975 RA to keep the VPN state alive. Clients connected to VPNed 976 interfaces receive RAs with the P flag set to 1 the same as for 977 Proxyed interfaces. 979 o Direct interfaces connect a Client directly to a Server without 980 crossing any ANET/INET paths. An example is a line-of-sight link 981 between a remote pilot and an unmanned aircraft. The same Client 982 considerations apply as for VPNed interfaces above, and the Client 983 receives RA messages with the P flag set to 1. 985 AERO interfaces use encapsulation (see: Section 3.9) to exchange 986 packets with AERO link neighbors over Native, NATed or VPNed 987 interfaces. AERO interfaces do not use encapsulation over Proxyed 988 and Direct underlying interfaces. 990 AERO interfaces maintain a neighbor cache for tracking per-neighbor 991 state the same as for any interface. AERO interfaces use ND messages 992 including Router Solicitation (RS), Router Advertisement (RA), 993 Neighbor Solicitation (NS) and Neighbor Advertisement (NA) for 994 neighbor cache management. 996 AERO interfaces send ND messages with an Overlay Multilink Network 997 Interface (OMNI) option formatted as specified in 998 [I-D.templin-6man-omni-interface]. The OMNI option includes prefix 999 registration information and "ifIndex-tuples" containing link quality 1000 information for the AERO interface's underlying interfaces. 1002 When encapsulation is used, AERO interface ND messages MAY also 1003 include an AERO Source/Target Link-Layer Address Option (S/TLLAO) 1004 formatted as shown in Figure 4: 1006 0 1 2 3 1007 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 1008 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1009 | Type | Length | ifIndex[1] |V|O|Reserved[1]| 1010 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1011 ~ Link Layer Address [1] ~ 1012 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1013 | Port Number [1] | ifIndex[2] |V|O|Reserved[2]| 1014 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1015 ~ Link Layer Address [2] ~ 1016 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1017 | Port Number [2] | ~ 1018 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ 1019 ~ ~ 1020 ~ ... ~ 1021 ~ ~ 1022 ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1023 ~ | ifIndex[N] |V|O|Reserved[N]| 1024 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1025 ~ Link Layer Address [N] ~ 1026 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1027 | Port Number [N] | Trailing zero padding | 1028 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1029 | Trailing zero padding (if necessary) | 1030 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1032 Figure 4: AERO Source/Target Link-Layer Address Option (S/TLLAO) 1033 Format 1035 In this format, Type and Length are set the same as specified for S/ 1036 TLLAOs in [RFC4861], with trailing zero padding octets added as 1037 necessary to produce an integral number of 8 octet blocks. The S/ 1038 TLLAO includes N ifIndex-tuples in correspondence to ifIndex-tuples 1039 that appear in the OMNI option. Each ifIndex-tuple includes the 1040 folllowing information: 1042 o ifIndex[i] - the same value as in the corresponding ifIndex-tuple 1043 included in the OMNI option. 1045 o V[i] - a bit that identifies the IP protocol version of the 1046 address found in the Link Layer Address [i] field. The bit is set 1047 to 0 for IPv4 or 1 for IPv6. 1049 o O[i] - the "Obfuscated" bit. If set to 0, the Link Layer Address 1050 [i] and Port Number [i] values are included in their unmodified 1051 form. If set to 1, the fields are "Obfuscated" by applying an 1052 exclusive-or of all bits in the field with "all-ones" as discussed 1053 in [RFC4380] - see also Section 3.25. 1055 o Reserved[i] - MUST encode the value 0 on transmission, and ignored 1056 on reception. 1058 o Link Layer Address [i] - the IPv4 or IPv6 address used as the 1059 encapsulation source address. The field is 4 bytes in length for 1060 IPv4 or 16 bytes in length for IPv6. 1062 o Port Number [i] - the upper layer protocol port number used as the 1063 encapsulation source port, or 0 when no upper layer protocol 1064 encapsulation is used. The field is 2 bytes in length. 1066 If an S/TLLAO is included, any ifIndex-tuples correspond to a proper 1067 subset of the OMNI option ifIndex-tuples. Any S/TLLAO ifIndex-tuple 1068 having an ifIndex value that does not appear in an OMNI option 1069 ifindex-tuple is ignored. If the same ifIndex value appears in 1070 multiple ifIndex-tuples, the first tuple is processed and the 1071 remaining tuples are ignored. Any S/TLLAO ifIndex-tuples can 1072 therefore be viewed as inter-dependent extensions of their 1073 corresponidng OMNI option ifIndex-tuples, i.e., the OMNI option and 1074 S/TLLAO are companions that are interpreted in conjunction with each 1075 other. 1077 A Client's AERO interface may be configured over multiple underlying 1078 interface connections. For example, common mobile handheld devices 1079 have both wireless local area network ("WLAN") and cellular wireless 1080 links. These links are typically used "one at a time" with low-cost 1081 WLAN preferred and highly-available cellular wireless as a standby. 1082 In a more complex example, aircraft frequently have many wireless 1083 data link types (e.g. satellite-based, cellular, terrestrial, air-to- 1084 air directional, etc.) with diverse performance and cost properties. 1086 If a Client's multiple underlying interfaces are used "one at a time" 1087 (i.e., all other interfaces are in standby mode while one interface 1088 is active), then ND message OMNI options include only a single 1089 ifIndex-tuple and set to a constant value. In that case, the Client 1090 would appear to have a single interface but with a dynamically 1091 changing link-layer address. 1093 If the Client has multiple active underlying interfaces, then from 1094 the perspective of ND it would appear to have multiple link-layer 1095 addresses. In that case, ND message OMNI options MAY include 1096 multiple ifIndex-tuples - each with a value that corresponds to a 1097 specific interface. Every ND message need not include all OMNI and/ 1098 or S/TLLAO ifIndex-tuples; for any ifIndex-tuple not included, the 1099 neighbor considers the status as unchanged. 1101 Relay, Server and Proxy AERO interfaces may be configured over one or 1102 more secured tunnel interfaces. The AERO interface configures both 1103 an AERO address and its corresponding SPAN address, while the 1104 underlying secured tunnel interfaces are either unnumbered or 1105 configure the same SPAN address. The AERO interface encapsulates 1106 each IP packet in a SPAN header and presents the packet to the 1107 underlying secured tunnel interface. For Relays that do not 1108 configure an AERO interface, the secured tunnel interfaces themselves 1109 are exposed to the IP layer with each interface configuring the 1110 Relay's SPAN address. Routing protocols such as BGP therefore run 1111 directly over the Relay's secured tunnel interfaces. For nodes that 1112 configure an AERO interface, routing protocols such as BGP run over 1113 the AERO interface but do not employ SPAN encapsulation. Instead, 1114 the AERO interface presents the routing protocol messages directly to 1115 the underlying secured tunnels without applying encapsulation and 1116 while using the SPAN address as the source address. This distinction 1117 must be honored consistently according to each node's configuration 1118 so that the IP forwarding table will associate discovered IP routes 1119 with the correct interface. 1121 3.7. AERO Interface Initialization 1123 AERO Servers, Proxys and Clients configure AERO interfaces as their 1124 point of attachment to the AERO link. AERO nodes assign the MSPs for 1125 the link to their AERO interfaces (i.e., as a "route-to-interface") 1126 to ensure that packets with destination addresses covered by an MNP 1127 not explicitly assigned to a non-AERO interface are directed to the 1128 AERO interface. 1130 AERO interface initialization procedures for Servers, Proxys, Clients 1131 and Relays are discussed in the following sections. 1133 3.7.1. AERO Server/Gateway Behavior 1135 When a Server enables an AERO interface, it assigns AERO/SPAN 1136 addresses and configures permanent neighbor cache entries for 1137 neighbors in the same SPAN segment by consulting the ROS list for the 1138 segment. The Server also configures secured tunnels with one or more 1139 neighboring Relays and engages in a BGP routing protocol session with 1140 each Relay. 1142 The AERO interface provides a single interface abstraction to the IP 1143 layer, but internally comprises multiple secured tunnels as well as 1144 an NBMA nexus for sending encapsulated data packets to AERO interface 1145 neighbors. The Server further configures a service to facilitate ND/ 1146 PD exchanges with AERO Clients and manages per-Client neighbor cache 1147 entries and IP forwarding table entries based on control message 1148 exchanges. 1150 Gateways are simply Servers that run a dynamic routing protocol 1151 between the AERO interface and INET/EUN interfaces (see: 1152 Section 3.3). The Gateway provisions MNPs to networks on the INET/ 1153 EUN interfaces (i.e., the same as a Client would do) and advertises 1154 the MSP(s) for the AERO link over the INET/EUN interfaces. The 1155 Gateway further provides an attachment point of the AERO link to the 1156 non-MNP-based global topology. 1158 3.7.2. AERO Proxy Behavior 1160 When a Proxy enables an AERO interface, it assigns AERO/SPAN 1161 addresses and configures permanent neighbor cache entries the same as 1162 for Servers. The Proxy also configures secured tunnels with one or 1163 more neighboring Relays and maintains per-Client neighbor cache 1164 entries based on control message exchanges. 1166 3.7.3. AERO Client Behavior 1168 When a Client enables an AERO interface, it sends an RS message with 1169 ND/PD parameters over an ANET interface to a Server in the MAP list, 1170 which returns an RA message with corresponding parameters. (The RS/ 1171 RA messages may pass through a Proxy in the case of a Client's 1172 Proxyed interface.) 1174 After the initial ND/PD message exchange, the Client assigns AERO 1175 addresses to the AERO interface based on the delegated prefix(es). 1176 The Client can then register additional ANET interfaces with the 1177 Server by sending an RS message over each ANET interface. 1179 3.7.4. AERO Relay Behavior 1181 AERO Relays need not connect directly to the AERO link, since they 1182 operate as link-layer forwarding devices instead of network layer 1183 routers. Configuration of AERO interfaces on Relays is therefore 1184 OPTIONAL, e.g., if an administrative interface is needed. Relays 1185 configure secured tunnels with Servers, Proxys and other Relays; they 1186 also configure AERO/SPAN addresses and permanent neighbor cache 1187 entries the same as Servers. Relays engage in a BGP routing protocol 1188 session with a subset of the Servers on the local SPAN segment, and 1189 with other Relays on the SPAN (see: Section 3.3). 1191 3.8. AERO Interface Neighbor Cache Maintenance 1193 Each AERO interface maintains a conceptual neighbor cache that 1194 includes an entry for each neighbor it communicates with on the AERO 1195 link per [RFC4861]. AERO interface neighbor cache entries are said 1196 to be one of "permanent", "symmetric", "asymmetric" or "proxy". 1198 Permanent neighbor cache entries are created through explicit 1199 administrative action; they have no timeout values and remain in 1200 place until explicitly deleted. AERO Servers and Proxys maintain 1201 permanent neighbor cache entries for all other Servers and Proxys 1202 within the same SPAN segment. Each entry maintains the mapping 1203 between the neighbor's network-layer AERO address and corresponding 1204 INET address. The list of all permanent neighbor cache entries for 1205 the SPAN segment is maintained in the segment's ROS list. 1207 Symmetric neighbor cache entries are created and maintained through 1208 RS/RA exchanges as specified in Section 3.15, and remain in place for 1209 durations bounded by ND/PD lifetimes. AERO Servers maintain 1210 symmetric neighbor cache entries for each of their associated 1211 Clients, and AERO Clients maintain symmetric neighbor cache entries 1212 for each of their associated Servers. The list of all Servers on the 1213 AERO link is maintained in the link's MAP list. 1215 Asymmetric neighbor cache entries are created or updated based on 1216 route optimization messaging as specified in Section 3.17, and are 1217 garbage-collected when keepalive timers expire. AERO route 1218 optimization sources (ROSs) maintain asymmetric neighbor cache 1219 entries for active targets with lifetimes based on ND messaging 1220 constants. Asymmetric neighbor cache entries are unidirectional 1221 since only the ROS (and not the target) creates an entry. 1223 Proxy neighbor cache entries are created and maintained by AERO 1224 Proxys when they process Client/Server ND/PD exchanges, and remain in 1225 place for durations bounded by ND/PD lifetimes. AERO Proxys maintain 1226 proxy neighbor cache entries for each of their associated Clients. 1228 Proxy neighbor cache entries track the Client state and the address 1229 of the Client's associated Server. 1231 To the list of neighbor cache entry states in Section 7.3.2 of 1232 [RFC4861], Proxy and Server AERO interfaces add an additional state 1233 DEPARTED that applies to symmetric and proxy neighbor cache entries 1234 for Clients that have recently departed. The interface sets a 1235 "DepartTime" variable for the neighbor cache entry to "DEPARTTIME" 1236 seconds. DepartTime is decremented unless a new ND message causes 1237 the state to return to REACHABLE. While a neighbor cache entry is in 1238 the DEPARTED state, packets destined to the target Client are 1239 forwarded to the Client's new location instead of being dropped. 1240 When DepartTime decrements to 0, the neighbor cache entry is deleted. 1241 It is RECOMMENDED that DEPARTTIME be set to the default constant 1242 value REACHABLETIME plus 10 seconds (40 seconds by default) to allow 1243 a window for packets in flight to be delivered while stale route 1244 optimization state may be present. 1246 When a target Server receives an authentic NS message used for route 1247 optimization, it searches for a symmetric neighbor cache entry for 1248 the target Client. The Server then returns a solicited NA message 1249 without creating a neighbor cache entry for the ROS, but creates or 1250 updates a target Client "Report List" entry for the ROS and sets a 1251 "ReportTime" variable for the entry to REPORTTIME seconds. The 1252 Server resets ReportTime when it receives a new authentic NS message, 1253 and otherwise decrements ReportTime while no authentic NS messages 1254 have been received. It is RECOMMENDED that REPORTTIME be set to the 1255 default constant value REACHABLETIME plus 10 seconds (40 seconds by 1256 default) to allow a window for route optimization to converge before 1257 ReportTime decrements below REACHABLETIME. 1259 When the ROS receives a solicited NA message response to its NS 1260 message used for route optimization, it creates or updates an 1261 asymmetric neighbor cache entry for the target network-layer and 1262 link-layer addresses. The ROS then (re)sets ReachableTime for the 1263 neighbor cache entry to REACHABLETIME seconds and uses this value to 1264 determine whether packets can be forwarded directly to the target, 1265 i.e., instead of via a default route. The ROS otherwise decrements 1266 ReachableTime while no further solicited NA messages arrive. It is 1267 RECOMMENDED that REACHABLETIME be set to the default constant value 1268 30 seconds as specified in [RFC4861]. 1270 The ROS also uses the value MAX_UNICAST_SOLICIT to limit the number 1271 of NS keepalives sent when a correspondent may have gone unreachable, 1272 the value MAX_RTR_SOLICITATIONS to limit the number of RS messages 1273 sent without receiving an RA and the value MAX_NEIGHBOR_ADVERTISEMENT 1274 to limit the number of unsolicited NAs that can be sent based on a 1275 single event. It is RECOMMENDED that MAX_UNICAST_SOLICIT, 1276 MAX_RTR_SOLICITATIONS and MAX_NEIGHBOR_ADVERTISEMENT be set to 3 the 1277 same as specified in [RFC4861]. 1279 Different values for DEPARTTIME, REPORTTIME, REACHABLETIME, 1280 MAX_UNICAST_SOLICIT, MAX_RTR_SOLCITATIONS and 1281 MAX_NEIGHBOR_ADVERTISEMENT MAY be administratively set; however, if 1282 different values are chosen, all nodes on the link MUST consistently 1283 configure the same values. Most importantly, DEPARTTIME and 1284 REPORTTIME SHOULD be set to a value that is sufficiently longer than 1285 REACHABLETIME to avoid packet loss due to stale route optimization 1286 state. 1288 3.9. AERO Interface Encapsulation and Re-encapsulation 1290 Client AERO interfaces avoid encapsulation over Direct underlying 1291 interfaces and Proxyed underlying interfaces for which the first-hop 1292 access router is AERO-aware. Other AERO interfaces encapsulate 1293 packets according to whether they are entering the AERO interface 1294 from the network layer or if they are being re-admitted into the same 1295 AERO link they arrived on. This latter form of encapsulation is 1296 known as "re-encapsulation". 1298 For packets entering the AERO interface from the network layer, the 1299 AERO interface copies the "TTL/Hop Limit", "Type of Service/Traffic 1300 Class" [RFC2983], "Flow Label"[RFC6438] (for IPv6) and "Congestion 1301 Experienced" [RFC3168] values in the packet's IP header into the 1302 corresponding fields in the encapsulation header(s). 1304 For packets undergoing re-encapsulation, the AERO interface instead 1305 copies these values from the original encapsulation header into the 1306 new encapsulation header, i.e., the values are transferred between 1307 encapsulation headers and *not* copied from the encapsulated packet's 1308 network-layer header. (Note especially that by copying the TTL/Hop 1309 Limit between encapsulation headers the value will eventually 1310 decrement to 0 if there is a (temporary) routing loop.) For IPv4 1311 encapsulation/re-encapsulation, the AERO interface sets the DF bit as 1312 discussed in Section 3.12. 1314 AERO interfaces configured over INET underlying interfaces 1315 encapsulate each packet in a SPAN header, then encapsulate the 1316 resulting SPAN packet in an INET header according to the next hop 1317 determined in the forwarding algorithm in Section 3.13. If the next 1318 hop is reached via a secured tunnel, the AERO interface uses an INET 1319 encapsulation format specific to the secured tunnel type (see: 1320 Section 6). If the next hop is reached via an unsecured underlying 1321 interface, the AERO interface instead uses Generic UDP Encapsulation 1322 (GUE) [I-D.ietf-intarea-gue] or an alternate minimal encapsulation 1323 format Appendix A. 1325 When GUE encapsulation is used, the AERO interface next sets the UDP 1326 source port to a constant value that it will use in each successive 1327 packet it sends, and sets the UDP length field to the length of the 1328 SPAN packet plus 8 bytes for the UDP header itself plus the length of 1329 the GUE header (or 0 if GUE direct IP encapsulation is used). For 1330 packets sent to a Server or Relay, the AERO interface sets the UDP 1331 destination port to 8060, i.e., the IANA-registered port number for 1332 AERO. For packets sent to a Client, the AERO interface sets the UDP 1333 destination port to the port value stored in the neighbor cache entry 1334 for this Client. The AERO interface then either includes or omits 1335 the UDP checksum according to the GUE specification. 1337 AERO interfaces observes the packet sizing and fragmentation 1338 considerations found in Section 3.12. 1340 3.10. AERO Interface Decapsulation 1342 AERO interfaces decapsulate packets destined either to the AERO node 1343 itself or to a destination reached via an interface other than the 1344 AERO interface the packet was received on. When the encapsulated 1345 packet arrives in multiple fragments, the AERO interface reassembles 1346 as discussed in Section 3.12. Further decapsulation steps are 1347 performed according to the appropriate encapsulation format 1348 specification. 1350 3.11. AERO Interface Data Origin Authentication 1352 AERO nodes employ simple data origin authentication procedures. In 1353 particular: 1355 o AERO Relays, Servers and Proxys accept encapsulated data packets 1356 and control messages received from secured tunnels via the SPAN. 1358 o AERO Servers and Proxys accept encapsulated data packets and NS 1359 messages used for Neighbor Unreachability Detection (NUD) received 1360 from a member of the ROS list. 1362 o AERO Proxys and Clients accept packets that originate from within 1363 the same secured ANET. 1365 o AERO Clients and Gateways accept packets from downstream network 1366 correspondents based on ingress filtering. 1368 AERO nodes silently drop any packets that do not satisfy the above 1369 data origin authentication procedures. Further security 1370 considerations are discussed Section 6. 1372 3.12. AERO Interface MTU and Fragmentation 1374 All IPv6 interfaces are REQUIRED to configure a minimum Maximum 1375 Transmission Unit (MTU) of 1280 bytes [RFC8200]. (IPv4 interfaces 1376 have a smaller minimum MTU [RFC1122], but SHOULD also observe the 1377 IPv6 minimum MTU if possible.) The AERO link therefore MUST forward 1378 IPv6 packets of at least 1280 bytes without generating an IPv6 Path 1379 MTU Discovery (PMTUD) Packet Too Big (PTB) message [RFC8201]. 1381 The AERO interface configures an MTU of 9180 bytes [RFC2492]; the 1382 size is therefore not a reflection of the underlying interface MTUs, 1383 but rather determines the largest packet the AERO interface can 1384 forward or reassemble. 1386 AERO interfaces employ mid-layer IPv6 encapsulation and 1387 fragmentation/reassembly per [RFC2473] for packets that are too large 1388 to traverse an underlying interface in one piece. The AERO interface 1389 returns internally-generated PTB messages for packets admitted into 1390 the interface that it deems too large for the outbound underlying 1391 interface (e.g., according to performance characteristics, cost, MTU, 1392 etc). For all other packets, the AERO interface performs PMTUD even 1393 if the destination appears to be on the same link since an AERO node 1394 on the path could return a PTB message. This ensures that the path 1395 MTU is adaptive and reflects the current path used for a given data 1396 flow. 1398 For underlying interfaces that have sufficiently large MTUs and that 1399 return RAs with the P bit set, the Client's AERO interface sends 1400 packets according to the underlying interface L2 frame format without 1401 fragmentation. For all other cases, the AERO interface encapsulates 1402 the packet in a mid-layer IPv6 header with source address set to the 1403 Client's SPAN address and destination set to the SPAN address 1404 corresponding to the packet's destination. The AERO interface then 1405 uses IPv6 fragmentation to break the encapsulated packet into a 1406 minimum number of non-overlapping fragments, where the smallest 1407 fragment generated MUST be no smaller than 640 bytes. For interfaces 1408 that return RAs with the P bit set, the largest fragment size is 1409 determined by the underlying interface MTU, while for other 1410 interfaces the largest fragment size MUST be 1280 bytes. The AERO 1411 interface then sends the fragments over the selected underlying 1412 interfaces. (Note that the outbound fragments can further be spread 1413 across multiple underlying interfaces, since they will be reassembled 1414 by the AERO interface closest to the final destination.) 1416 When a Proxy or Server receives a fragmented or whole packet from the 1417 INET destined to a Client, it must determine whether to forward or 1418 drop and return a PTB (e.g., according to the underlying interface 1419 performance characteristics, MTU, etc). If the packet is no larger 1420 than the underlying interface MTU, the Proxy/Server forwards 1421 according to the underlying interface L2 frame format. If the packet 1422 is larger than the MTU, the Proxy/Server instead uses SPAN 1423 encapsulation and IPv6 fragmentation as above. The Client then 1424 reassembles and discards the SPAN header, then forwards the whole 1425 packet to the final destination. 1427 When a Proxy, Server or Gateway forwards an original source's packet 1428 over the SPAN, it uses IPv6 encapsulation with its own SPAN address 1429 as the source address and with destination set to the SPAN address 1430 corresponding to the packet's destination if the packet is not 1431 already SPAN encapsulated. The node then uses fragmentation to break 1432 the SPAN-encapsulated packet into non-overlapping fragments that are 1433 no larger than 1280 bytes and no smaler than 640 bytes (i.e., even if 1434 the SPAN header was inserted by the original source). When a Server 1435 or Gateway forwards a SPAN-encapsulated packet to a destination 1436 outside of the AERO link, it first reassembles if necessary. 1438 In order to avoid a "tiny fragment" attack, AERO nodes 1439 unconditionally drop all fragments smaller than 640 bytes. In order 1440 to set the correct context for reassembly, the AERO node that inserts 1441 a SPAN header MUST also be the node that inserts the IPv6 Fragment 1442 Header Identification value. 1444 Note also that the AERO interface can forward large packets via 1445 encapsulation and fragmentation while at the same time returning 1446 advisory PTB messages, e.g., subject to rate limiting. The receiving 1447 node that performs reassembly can also send advisory PTB messages if 1448 reassembly conditions become unfavorable. The AERO interface can 1449 therefore continuously forward large packets without loss while 1450 returning advisory messages recommending a smaller size. 1452 3.13. AERO Interface Forwarding Algorithm 1454 IP packets enter a node's AERO interface either from the network 1455 layer (i.e., from a local application or the IP forwarding system) or 1456 from the link layer (i.e., from an AERO interface neighbor). All 1457 packets entering a node's AERO interface first undergo data origin 1458 authentication as discussed in Section 3.11. Packets that satisfy 1459 data origin authentication are processed further, while all others 1460 are dropped silently. 1462 Packets that enter the AERO interface from the network layer are 1463 forwarded to an AERO interface neighbor. Packets that enter the AERO 1464 interface from the link layer are either re-admitted into the AERO 1465 link or forwarded to the network layer where they are subject to 1466 either local delivery or IP forwarding. In all cases, the AERO 1467 interface itself MUST NOT decrement the network layer TTL/Hop-count 1468 since its forwarding actions occur below the network layer. 1470 AERO interfaces may have multiple underlying interfaces and/or 1471 neighbor cache entries for neighbors with multiple ifIndex-tuple 1472 registrations (see Section 3.6). The AERO interface uses each 1473 packet's DSCP value (and/or other traffic discriminators such as port 1474 number) to select an outgoing underlying interface based on the 1475 node's own QoS preferences, and also to select a destination link- 1476 layer address based on the neighbor's underlying interface with the 1477 highest preference. AERO implementations SHOULD allow for QoS 1478 preference values to be modified at runtime through network 1479 management. 1481 If multiple outgoing interfaces and/or neighbor interfaces have a 1482 preference of "high", the AERO node replicates the packet and sends 1483 one copy via each of the (outgoing / neighbor) interface pairs; 1484 otherwise, the node sends a single copy of the packet via an 1485 interface with the highest preference. AERO nodes keep track of 1486 which underlying interfaces are currently "reachable" or 1487 "unreachable", and only use "reachable" interfaces for forwarding 1488 purposes. 1490 The following sections discuss the AERO interface forwarding 1491 algorithms for Clients, Proxys, Servers and Relays. In the following 1492 discussion, a packet's destination address is said to "match" if it 1493 is the same as a cached address, or if it is covered by a cached 1494 prefix (which may be encoded in an AERO address). 1496 3.13.1. Client Forwarding Algorithm 1498 When an IP packet enters a Client's AERO interface from the network 1499 layer the Client searches for an asymmetric neighbor cache entry that 1500 matches the destination. If there is a match, the Client uses one or 1501 more "reachable" neighbor interfaces in the entry for packet 1502 forwarding. If there is no asymmetric neighbor cache entry, the 1503 Client instead forwards the packet toward a Server (the packet is 1504 intercepted by a Proxy if there is a Proxy on the path). The Client 1505 encapuslates the packet in an IPv6 header and fragments if necessary 1506 according to MTU requirements (see: Section 3.12). 1508 When an IP packet enters a Client's AERO interface from the link- 1509 layer, if the destination matches one of the Client's MNPs or link- 1510 local addresses the Client reassembles and decapsulates as necessary 1511 and delivers the (now-unencapsulated) packet to the network layer. 1512 Otherwise, the Client drops the packet and MAY return a network-layer 1513 ICMP Destination Unreachable message subject to rate limiting (see: 1514 Section 3.14). 1516 3.13.2. Proxy Forwarding Algorithm 1518 For control messages originating from or destined to a Client, the 1519 Proxy intercepts the message and updates its proxy neighbor cache 1520 entry for the Client. The Proxy then forwards a (proxyed) copy of 1521 the control message. (For example, the Proxy forwards a proxied 1522 version of a Client's NS/RS message to the target neighbor, and 1523 forwards a proxied version of the NA/RA reply to the Client.) 1525 When the Proxy receives a data packet from a Client within the ANET, 1526 it first reassembles and decapsulates if the packet was a link-local 1527 fragment. The Proxy next inserts a SPAN header with source address 1528 set to the Proxy's SPAN address and destination address set to the 1529 SPAN address of the next hop. The Proxy then fragments the SPAN 1530 packet if necessary into fragments no larger than 1280 bytes, then 1531 searches for an asymmetric neighbor cache entry that matches the 1532 destination and forwards the fragments as follows: 1534 o if the destination matches an asymmetric neighbor cache entry, the 1535 Proxy uses one or more "reachable" neighbor interfaces in the 1536 entry for packet forwarding via encapsulation. If the neighbor 1537 interface is in the same SPAN segment, the Proxy forwards the 1538 packet directly to the neighbor; otherwise, it forwards the packet 1539 to a Relay. 1541 o else, the Proxy encapsulates and forwards the packet to a Relay 1542 while using the packet's destination address as the SPAN 1543 destination address. (If the destination is an AERO address, the 1544 Proxy instead uses the corresponding Subnet-Router anycast address 1545 for Client AERO addresses and the SPAN address for 1546 administratively-provisioned AERO addresses.). 1548 When the Proxy receives an encapsulated data packet from an INET 1549 neighbor or from a secured tunnel from a Relay, it accepts the packet 1550 only if data origin authentication succeeds and if there is a proxy 1551 neighbor cache entry that matches the inner destination. Next, if 1552 the packet is a SPAN fragment the Proxy adds the fragment to the 1553 reassembly buffer. The Proxy then reassembles the packet (if 1554 necessary) and continues processing. 1556 Next if reassembly is complete and the neighbor cache state is 1557 REACHABLE, the Proxy either drops and returns a PTB (see: 1558 Section 3.12) or forwards the packet to the Client while performing 1559 link-local encapsulation and re-fragmentation to the ANET MTU size if 1560 necessary. If the neighbor cache entry state is DEPARTED, the Proxy 1561 instead changes the SPAN destination address to the address of the 1562 new Server and forwards it to a Relay while performing re- 1563 fragmentation to 1280 bytes if necessary. 1565 When the Proxy forwards a SPAN packet to a REACHABLE Client for which 1566 the packet is no larger than the ANET MTU, it decapsulates the SPAN 1567 header first and forwards the (unencapsulated) packet to the Client 1568 to avoid the unnecessary overhead for carrying the SPAN header. 1570 3.13.3. Server/Gateway Forwarding Algorithm 1572 For control messages destined to a target Client's AERO address that 1573 are received from a secured tunnel, the Server intercepts the message 1574 and sends an appropriate response on behalf of the Client. (For 1575 example, the Server sends an NA message reply in response to an NS 1576 message directed to one of its associated Clients.) If the Client's 1577 neighbor cache entry is in the DEPARTED state, however, the Server 1578 instead forwards the packet to the Client's new Server as discussed 1579 in Section 3.19. 1581 When the Server receives an encapsulated data packet from an INET 1582 neighbor or from a secured tunnel, it accepts the packet only if data 1583 origin authentication succeeds. If the SPAN destination address is 1584 its own address, the Server continues processing as follows: 1586 o if the destination matches a symmetric neighbor cache entry in the 1587 REACHABLE state the Server prepares the packet for forwarding to 1588 the destination Client. For the Client's Proxyed interfaces, the 1589 Server changes the SPAN destination address to the address of the 1590 Proxy and forwards the packet to the Proxy. For the Client's 1591 other interfaces, the Server reassembles then either drops and 1592 returns a PTB (see: Section 3.12) or forwards the packet (while 1593 re-fragmenting if necessary) using SPAN encapsulation for the 1594 Client's Native, NATed or VPNed interfaces, or no encapsulation 1595 for Direct interfaces. 1597 o else, if the destination matches a symmetric neighbor cache entry 1598 in the DEPARETED state the Server re-encapsulates the packet and 1599 forwards it using the SPAN address of the Client's new Server as 1600 the destination. 1602 o else, if the destination matches an asymmetric neighbor cache 1603 entry, the Server uses one or more "reachable" neighbor interfaces 1604 in the entry for packet forwarding via the local INET if the 1605 neighbor is in the same SPAN segment or via a Relay otherwise. 1607 o else, if the destination is an AERO address that is not assigned 1608 on the AERO interface the Server drops the packet. 1610 o else, the Server (acting as a Gateway) reassembles if necessary, 1611 decapsulates the packet and releases it to the network layer for 1612 local delivery or IP forwarding. Based on the information in the 1613 forwarding table, the network layer may return the packet to the 1614 same AERO interface in which case further processing occurs as 1615 below. (Note that this arrangement accommodates common 1616 implementations in which the IP forwarding table is not accessible 1617 from within the AERO interface. If the AERO interface can 1618 directly access the IP forwarding table (such as for in-kernel 1619 implementations) the forwarding table lookup can instead be 1620 performed internally from within the AERO interface itself.) 1622 When the Server's AERO interface receives a data packet from the 1623 network layer or from a NATed/VPNed/Direct Client, it performs SPAN 1624 encapsualtion and fragmentation if necessary, then processes the 1625 packet according to the network-layer destination address as follows: 1627 o if the destination matches a symmetric or asymmetric neighbor 1628 cache entry the Server processes the packet as above. 1630 o else, the Server encapsulates the packet and forwards it to a 1631 Relay. For administratively-assigned AERO address destinations, 1632 the Server uses the SPAN address corresponding to the destination 1633 as the SPAN destination address. For Client AERO address 1634 destinations, the Server uses the Subnet-Router anycast address 1635 corresponding to the destination as the SPAN destination address. 1636 For all others, the Server uses the packet's destination IP 1637 address as the SPAN destination address. 1639 3.13.4. Relay Forwarding Algorithm 1641 Relays forward packets over secured tunnels the same as any IP 1642 router. When the Relay receives an encapsulated packet via a secured 1643 tunnel, it removes the INET header and searches for a forwarding 1644 table entry that matches the destination address in the next header. 1645 The Relay then processes the packet as follows: 1647 o if the destination matches one of the Relay's own addresses, the 1648 Relay submits the packet for local delivery. 1650 o else, if the destination matches a forwarding table entry the 1651 Relay forwards the packet via a secured tunnel to the next hop. 1652 If the destination matches an MSP without matching an MNP, 1653 however, the Relay instead drops the packet and returns an ICMP 1654 Destination Unreachable message subject to rate limiting (see: 1655 Section 3.14). 1657 o else, the Relay drops the packet and returns an ICMP Destination 1658 Unreachable as above. 1660 As for any IP router, the Relay decrements the TTL/Hop Limit when it 1661 forwards the packet. Therefore, only the Hop Limit in the SPAN 1662 header is decremented, and not the TTL/Hop Limit in the inner packet 1663 header. 1665 3.14. AERO Interface Error Handling 1667 When an AERO node admits a packet into the AERO interface, it may 1668 receive link-layer or network-layer error indications. 1670 A link-layer error indication is an ICMP error message generated by a 1671 router in the INET on the path to the neighbor or by the neighbor 1672 itself. The message includes an IP header with the address of the 1673 node that generated the error as the source address and with the 1674 link-layer address of the AERO node as the destination address. 1676 The IP header is followed by an ICMP header that includes an error 1677 Type, Code and Checksum. Valid type values include "Destination 1678 Unreachable", "Time Exceeded" and "Parameter Problem" 1679 [RFC0792][RFC4443]. (AERO interfaces ignore all link-layer IPv4 1680 "Fragmentation Needed" and IPv6 "Packet Too Big" messages since they 1681 only emit packets that are guaranteed to be no larger than the IP 1682 minimum link MTU as discussed in Section 3.12.) 1684 The ICMP header is followed by the leading portion of the packet that 1685 generated the error, also known as the "packet-in-error". For 1686 ICMPv6, [RFC4443] specifies that the packet-in-error includes: "As 1687 much of invoking packet as possible without the ICMPv6 packet 1688 exceeding the minimum IPv6 MTU" (i.e., no more than 1280 bytes). For 1689 ICMPv4, [RFC0792] specifies that the packet-in-error includes: 1690 "Internet Header + 64 bits of Original Data Datagram", however 1691 [RFC1812] Section 4.3.2.3 updates this specification by stating: "the 1692 ICMP datagram SHOULD contain as much of the original datagram as 1693 possible without the length of the ICMP datagram exceeding 576 1694 bytes". 1696 The link-layer error message format is shown in Figure 5 (where, "L2" 1697 and "L3" refer to link-layer and network-layer, respectively): 1699 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1700 ~ ~ 1701 | L2 IP Header of | 1702 | error message | 1703 ~ ~ 1704 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1705 | L2 ICMP Header | 1706 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 1707 ~ ~ P 1708 | IP and other encapsulation | a 1709 | headers of original L3 packet | c 1710 ~ ~ k 1711 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ e 1712 ~ ~ t 1713 | IP header of | 1714 | original L3 packet | i 1715 ~ ~ n 1716 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1717 ~ ~ e 1718 | Upper layer headers and | r 1719 | leading portion of body | r 1720 | of the original L3 packet | o 1721 ~ ~ r 1722 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 1724 Figure 5: AERO Interface Link-Layer Error Message Format 1726 The AERO node rules for processing these link-layer error messages 1727 are as follows: 1729 o When an AERO node receives a link-layer Parameter Problem message, 1730 it processes the message the same as described as for ordinary 1731 ICMP errors in the normative references [RFC0792][RFC4443]. 1733 o When an AERO node receives persistent link-layer Time Exceeded 1734 messages, the IP ID field may be wrapping before earlier fragments 1735 awaiting reassembly have been processed. In that case, the node 1736 should begin including integrity checks and/or institute rate 1737 limits for subsequent packets. 1739 o When an AERO node receives persistent link-layer Destination 1740 Unreachable messages in response to encapsulated packets that it 1741 sends to one of its asymmetric neighbor correspondents, the node 1742 should process the message as an indication that a path may be 1743 failing, and optionally initiate NUD over that path. If it 1744 receives Destination Unreachable messages over multiple paths, the 1745 node should allow future packets destined to the correspondent to 1746 flow through a default route and re-initiate route optimization. 1748 o When an AERO Client receives persistent link-layer Destination 1749 Unreachable messages in response to encapsulated packets that it 1750 sends to one of its symmetric neighbor Servers, the Client should 1751 mark the path as unusable and use another path. If it receives 1752 Destination Unreachable messages on many or all paths, the Client 1753 should associate with a new Server and release its association 1754 with the old Server as specified in Section 3.19.5. 1756 o When an AERO Server receives persistent link-layer Destination 1757 Unreachable messages in response to encapsulated packets that it 1758 sends to one of its symmetric neighbor Clients, the Server should 1759 mark the underlying path as unusable and use another underlying 1760 path. 1762 o When an AERO Server or Proxy receives link-layer Destination 1763 Unreachable messages in response to an encapsulated packet that it 1764 sends to one of its permanent neighbors, it treats the messages as 1765 an indication that the path to the neighbor may be failing. 1766 However, the dynamic routing protocol should soon reconverge and 1767 correct the temporary outage. 1769 When an AERO Relay receives a packet for which the network-layer 1770 destination address is covered by an MSP, if there is no more- 1771 specific routing information for the destination the Relay drops the 1772 packet and returns a network-layer Destination Unreachable message 1773 subject to rate limiting. The Relay writes the network-layer source 1774 address of the original packet as the destination address and uses 1775 one of its non link-local addresses as the source address of the 1776 message. 1778 When an AERO node receives an encapsulated packet for which the 1779 reassembly buffer it too small, it drops the packet and returns a 1780 network-layer Packet Too Big (PTB) message. The node first writes 1781 the MRU value into the PTB message MTU field, writes the network- 1782 layer source address of the original packet as the destination 1783 address and writes one of its non link-local addresses as the source 1784 address. 1786 3.15. AERO Router Discovery, Prefix Delegation and Autoconfiguration 1788 AERO Router Discovery, Prefix Delegation and Autoconfiguration are 1789 coordinated as discussed in the following Sections. 1791 3.15.1. AERO ND/PD Service Model 1793 Each AERO Server on the link configures a PD service to facilitate 1794 Client requests. Each Server is provisioned with a database of MNP- 1795 to-Client ID mappings for all Clients enrolled in the AERO service, 1796 as well as any information necessary to authenticate each Client. 1797 The Client database is maintained by a central administrative 1798 authority for the AERO link and securely distributed to all Servers, 1799 e.g., via the Lightweight Directory Access Protocol (LDAP) [RFC4511], 1800 via static configuration, etc. Clients receive the same service 1801 regardless of the Servers they select. 1803 AERO Clients and Servers use ND messages to maintain neighbor cache 1804 entries. AERO Servers configure their AERO interfaces as advertising 1805 NBMA interfaces, and therefore send unicast RA messages with a short 1806 Router Lifetime value (e.g., REACHABLETIME seconds) in response to a 1807 Client's RS message. Thereafter, Clients send additional RS messages 1808 to keep Server state alive. 1810 AERO Clients and Servers include PD parameters in RS/RA messages (see 1811 [I-D.templin-6man-dhcpv6-ndopt] for ND/PD alternatives). The unified 1812 ND/PD messages are exchanged between Client and Server according to 1813 the prefix management schedule required by the PD service. If the 1814 Client knows its MNP in advance, it can instead employ prefix 1815 registration by including its AERO address as the source address of 1816 an RS message and with an OMNI option with valid prefix registration 1817 information for the MNP. If the Server (and Proxy) accept the 1818 Client's MNP assertion, they inject the prefix into the routing 1819 system and establish the necessary neighbor cache state. 1821 The following sections specify the Client and Server behavior. 1823 3.15.2. AERO Client Behavior 1825 AERO Clients discover the addresses of Servers in a similar manner as 1826 described in [RFC5214]. Discovery methods include static 1827 configuration (e.g., from a flat-file map of Server addresses and 1828 locations), or through an automated means such as Domain Name System 1829 (DNS) name resolution [RFC1035]. Alternatively, the Client can 1830 discover Server addresses through a layer 2 data link login exchange, 1831 or through a unicast RA response to a multicast/anycast RS as 1832 described below. In the absence of other information, the Client can 1833 resolve the DNS Fully-Qualified Domain Name (FQDN) 1834 "linkupnetworks.[domainname]" where "linkupnetworks" is a constant 1835 text string and "[domainname]" is a DNS suffix for the AERO link 1836 (e.g., "example.com"). 1838 To associate with a Server, the Client acts as a requesting router to 1839 request MNPs. The Client prepares an RS message with PD parameters 1840 and includes a Nonce and Timestamp option if the Client needs to 1841 correlate RA replies. If the Client already knows the Server's AERO 1842 address, it includes the AERO address as the network-layer 1843 destination address; otherwise, it includes the link-scoped All- 1844 Routers multicast (ff02::2) or Subnet-Router anycast (fe80::) address 1845 as the network-layer destination. If the Client already knows its 1846 own AERO address, it uses the AERO address as the network-layer 1847 source address; otherwise, it uses the unspecified IPv6 address 1848 (::/128) as the network-layer source address. 1850 The Client next includes an OMNI option in the RS message to register 1851 its link-layer information with the Server. The Client sets the OMNI 1852 option prefix registration information according to the MNP, and 1853 includes an ifIndex-tuple with S set to '1' corresponding to the 1854 underlying interface over which the Client will send the RS message. 1855 The Client MAY include additional ifIndex-tuples specific to other 1856 underlying interfaces. The Client MAY also include an SLLAO with a 1857 link-layer address corresponding to the OMNI option ifIndex-tuple 1858 with S set to '1'. 1860 The Client then sends the RS message (either directly via Direct 1861 interfaces, via INET encapsulation for NATed interfaces, via a VPN 1862 for VPNed interfaces, via a Proxy for proxyed interfaces or via a 1863 Relay for native interfaces) and waits for an RA message reply (see 1864 Section 3.15.3). The Client retries up to MAX_RTR_SOLICITATIONS 1865 times until an RA is received. If the Client receives no RAs, or if 1866 it receives an RA with Router Lifetime set to 0, the Client SHOULD 1867 abandon this Server and try another Server. Otherwise, the Client 1868 processes the PD information found in the RA message. 1870 Next, the Client creates a symmetric neighbor cache entry with the 1871 Server's AERO address as the network-layer address and the Server's 1872 encapsulation and/or link-layer addresses as the link-layer address. 1873 The Client records the RA Router Lifetime field value in the neighbor 1874 cache entry as the time for which the Server has committed to 1875 maintaining the MNP in the routing system via this underlying 1876 interface, and caches the other RA configuration information 1877 including Cur Hop Limit, M and O flags, Reachable Time and Retrans 1878 Timer. The Client then autoconfigures AERO addresses for each of the 1879 delegated MNPs and assigns them to the AERO interface. The Client 1880 also caches any MSPs included in Route Information Options (RIOs) 1881 [RFC4191] as MSPs to associate with the AERO link, and assigns the 1882 MTU value in the MTU option to the underlying interface. 1884 The Client then registers additional underlying interfaces with the 1885 Server by sending RS messages via each additional interface. The RS 1886 messages include the same parameters as for the initial RS/RA 1887 exchange, but with destination address set to the Server's AERO 1888 address. 1890 Following autoconfiguration, the Client sub-delegates the MNPs to its 1891 attached EUNs and/or the Client's own internal virtual interfaces as 1892 described in [I-D.templin-v6ops-pdhost] to support the Client's 1893 downstream attached "Internet of Things (IoT)". The Client 1894 subsequently sends additional RS messages over each underlying 1895 interface before the Router Lifetime received for that interface 1896 expires. 1898 After the Client registers its underlying interfaces, it may wish to 1899 change one or more registrations, e.g., if an interface changes 1900 address or becomes unavailable, if QoS preferences change, etc. To 1901 do so, the Client prepares an RS message to send over any available 1902 underlying interface. The RS includes an OMNI option with prefix 1903 registration information specific to its MNP, with an ifIndex-tuple 1904 specific to the selected underlying interface with S set to '1', and 1905 with any additional ifIndex-tuples specific to other underlying 1906 interfaces. The Client includes fresh ifIndex-tuple values to update 1907 the Server's neighbor cache entry. When the Client receives the 1908 Server's RA response, it has assurance that the Server has been 1909 updated with the new information. 1911 If the Client wishes to discontinue use of a Server it issues an RS 1912 message over any underlying interface with an OMNI option with a 1913 prefix release indication. When the Server processes the message, it 1914 releases the MNP, sets the symmetric neighbor cache entry state for 1915 the Client to DEPARTED and returns an RA reply with Router Lifetime 1916 set to 0. After a short delay (e.g., 2 seconds), the Server 1917 withdraws the MNP from the routing system. 1919 3.15.3. AERO Server Behavior 1921 AERO Servers act as IP routers and support a PD service for Clients. 1922 Servers arrange to add their AERO addresses to a static map of Server 1923 addresses for the link and/or the DNS resource records for the FQDN 1924 "linkupnetworks.[domainname]" before entering service. Server 1925 addresses should be geographically and/or topologically referenced, 1926 and made available for discovery by Clients on the AERO link. 1928 When a Server receives a prospective Client's RS message on its AERO 1929 interface, it SHOULD return an immediate RA reply with Router 1930 Lifetime set to 0 if it is currently too busy or otherwise unable to 1931 service the Client. Otherwise, the Server authenticates the RS 1932 message and processes the PD parameters. The Server first determines 1933 the correct MNPs to delegate to the Client by searching the Client 1934 database. When the Server delegates the MNPs, it also creates a 1935 forwarding table entry for each MNP so that the MNPs are propagated 1936 into the routing system (see: Section 3.3). For IPv6, the Server 1937 creates an IPv6 forwarding table entry for each MNP. For IPv4, the 1938 Server creates an IPv6 forwarding table entry with the SPAN 1939 Compatibility Prefix (SCP) corresponding to the IPv4 address. 1941 The Server next creates a symmetric neighbor cache entry for the 1942 Client using the base AERO address as the network-layer address and 1943 with lifetime set to no more than the smallest PD lifetime. Next, 1944 the Server updates the neighbor cache entry by recording the 1945 information in each ifIndex-tuple in the RS OMNI option. The Server 1946 also records the actual SPAN/INET addresses in the neighbor cache 1947 entry. 1949 Next, the Server prepares an RA message using its AERO address as the 1950 network-layer source address and the network-layer source address of 1951 the RS message as the network-layer destination address. The Server 1952 sets the Router Lifetime to the time for which it will maintain both 1953 this underlying interface individually and the symmetric neighbor 1954 cache entry as a whole. The Server also sets Cur Hop Limit, M and O 1955 flags, Reachable Time and Retrans Timer to values appropriate for the 1956 AERO link. The Server includes the delegated MNPs, any other PD 1957 parameters and an OMNI option with no ifIndex-tuples. The Server 1958 then includes one or more RIOs that encode the MSPs for the AERO 1959 link, plus an MTU option (see Section 3.12). The Server finally 1960 forwards the message to the Client using SPAN/INET, INET, or NULL 1961 encapsulation as necessary. 1963 After the initial RS/RA exchange, the Server maintains a 1964 ReachableTime timer for each of the Client's underlying interfaces 1965 individually (and for the Client's symmetric neighbor cache entry 1966 collectively) set to expire after Router Lifetime seconds. If the 1967 Client (or Proxy) issues additional RS messages, the Server sends an 1968 RA response and resets ReachableTime. If the Server receives an ND 1969 message with PD release indication it sets the Client's symmetric 1970 neighbor cache entry to the DEPARTED state and withdraws the MNP from 1971 the routing system after a short delay (e.g., 2 seconds). If 1972 ReachableTime expires before a new RS is received on an individual 1973 underlying interface, the Server marks the interface as DOWN. If 1974 ReachableTime expires before any new RS is received on any individual 1975 underlying interface, the Server deletes the neighbor cache entry and 1976 withdraws the MNP without delay. 1978 The Server processes any ND/PD messages pertaining to the Client and 1979 returns an NA/RA reply in response to solicitations. The Server may 1980 also issue unsolicited RA messages, e.g., with PD reconfigure 1981 parameters to cause the Client to renegotiate its PDs, with Router 1982 Lifetime set to 0 if it can no longer service this Client, etc. 1983 Finally, If the symmetric neighbor cache entry is in the DEPARTED 1984 state, the Server deletes the entry after DepartTime expires. 1986 Note: Clients SHOULD notify former Servers of their departures, but 1987 Servers are responsible for expiring neighbor cache entries and 1988 withdrawing routes even if no departure notification is received 1989 (e.g., if the Client leaves the network unexpectedly). Servers 1990 SHOULD therefore set Router Lifetime to REACHABLETIME seconds in 1991 solicited RA messages to minimize persistent stale cache information 1992 in the absence of Client departure notifications. A short Router 1993 Lifetime also ensures that proactive Client/Server RS/RA messaging 1994 will keep any NAT state alive (see above). 1996 Note: All Servers on an AERO link MUST advertise consistent values in 1997 the RA Cur Hop Limit, M and O flags, Reachable Time and Retrans Timer 1998 fields the same as for any link, since unpredictable behavior could 1999 result if different Servers on the same link advertised different 2000 values. 2002 3.15.3.1. Lightweight DHCPv6 Relay Agent (LDRA) 2004 When DHCPv6 is used as the ND/PD service back end, AERO Clients and 2005 Servers are always on the same link (i.e., the AERO link) from the 2006 perspective of DHCPv6. However, in some implementations the DHCPv6 2007 server and ND function may be located in separate modules. In that 2008 case, the Server's AERO interface module can act as a Lightweight 2009 DHCPv6 Relay Agent (LDRA)[RFC6221] to relay PD messages to and from 2010 the DHCPv6 server module. 2012 When the LDRA receives an authentic RS message, it extracts the PD 2013 message parameters and uses them to construct an IPv6/UDP/DHCPv6 2014 message. It sets the IPv6 source address to the source address of 2015 the RS message, sets the IPv6 destination address to 2016 'All_DHCP_Relay_Agents_and_Servers' and sets the UDP fields to values 2017 that will be understood by the DHCPv6 server. 2019 The LDRA then wraps the message in a DHCPv6 'Relay-Forward' message 2020 header and includes an 'Interface-Id' option that includes enough 2021 information to allow the LDRA to forward the resulting Reply message 2022 back to the Client (e.g., the Client's link-layer addresses, a 2023 security association identifier, etc.). The LDRA also wraps the OMNI 2024 option and SLLAO into the Interface-Id option, then forwards the 2025 message to the DHCPv6 server. 2027 When the DHCPv6 server prepares a Reply message, it wraps the message 2028 in a 'Relay-Reply' message and echoes the Interface-Id option. The 2029 DHCPv6 server then delivers the Relay-Reply message to the LDRA, 2030 which discards the Relay-Reply wrapper and IPv6/UDP headers, then 2031 uses the DHCPv6 message to construct an RA response to the Client. 2032 The Server uses the information in the Interface-Id option to prepare 2033 the RA message and to cache the link-layer addresses taken from the 2034 OMNI option and SLLAO echoed in the Interface-Id option. 2036 3.16. The AERO Proxy 2038 Clients may connect to ANETs that deploy perimeter security services 2039 to facilitate communications to Servers in outside INETs. In that 2040 case, the ANET can employ an AERO Proxy. The Proxy is located at the 2041 ANET/INET border and listens for RS messages originating from or RA 2042 messages destined to ANET Clients. The Proxy acts on these control 2043 messages as follows: 2045 o when the Proxy receives an RS message from a new ANET Client, it 2046 first authenticates the message then examines the network-layer 2047 destination address. If the destination address is a Server's 2048 AERO address, the Proxy proceeds to the next step. Otherwise, if 2049 the destination is All-Routers multicast or Subnet-Router anycast, 2050 the Proxy selects a "nearby" Server that is likely to be a good 2051 candidate to serve the Client and replaces the destination address 2052 with the Server's AERO address. Next, the Proxy creates a proxy 2053 neighbor cache entry and caches the Client and Server link-layer 2054 addresses along with the OMNI option information and any other 2055 identifying information including Transaction IDs, Client 2056 Identifiers, Nonce values, etc. The Proxy finally encapsulates 2057 the (proxyed) RS message in a SPAN header with source set to the 2058 Proxy's SPAN address and destination set to the Server's SPAN 2059 address then forwards the message into the SPAN. 2061 o when the Server receives the RS, it authenticates the message then 2062 creates or updates a symmetric neighbor cache entry for the Client 2063 with the Proxy's SPAN address as the link-layer address. The 2064 Server then sends an RA message back to the Proxy via the SPAN. 2066 o when the Proxy receives the RA, it authenticates the message and 2067 matches it with the proxy neighbor cache entry created by the RS. 2068 The Proxy then caches the PD route information as a mapping from 2069 the Client's MNPs to the Client's ANET address, caches the 2070 Server's advertised Router Lifetime and sets the neighbor cache 2071 entry state to REACHABLE. The Proxy then sets the P bit in the RA 2072 flags field, optionally rewrites the Router Lifetime and forwards 2073 the (proxyed) message to the Client. The Proxy finally includes 2074 an MTU option (if necessary) with an MTU to use for the underlying 2075 ANET interface. 2077 After the initial RS/RA exchange, the Proxy forwards any Client data 2078 packets for which there is no matching asymmetric neighbor cache 2079 entry to a Relay via the SPAN. The Proxy instead forwards any Client 2080 data destined to an asymmetric neighbor cache target directly to the 2081 target according to the link-layer information - the process of 2082 establishing asymmetric neighbor cache entries is specified in 2083 Section 3.17. 2085 While the Client is still attached to the ANET, the Proxy sends NS, 2086 RS and/or unsolicited NA messages to update the Server's symmetric 2087 neighbor cache entries on behalf of the Client and/or to convey QoS 2088 updates. This allows for higher-frequency Proxy-initiated RS/RA 2089 messaging over well-connected INET infrastructure supplemented by 2090 lower-frequency Client-initiated RS/RA messaging over constrained 2091 ANET data links. 2093 If the Server ceases to send solicited advertisements, the Proxy 2094 sends unsolicited RAs on the ANET interface with destination set to 2095 All-Nodes multicast (ff02::1) and with Router Lifetime set to zero to 2096 inform Clients that the Server has failed. Although the Proxy 2097 engages in ND exchanges on behalf of the Client, the Client can also 2098 send ND messages on its own behalf, e.g., if it is in a better 2099 position than the Proxy to convey QoS changes, etc. For this reason, 2100 the Proxy marks any Client-originated solicitation messages (e.g. by 2101 inserting a Nonce option) so that it can return the solicited 2102 advertisement to the Client instead of processsing it locally. 2104 If the Client becomes unreachable, the Proxy sets the neighbor cache 2105 entry state to DEPARTED and retains the entry for DEPARTTIME seconds. 2106 While the state is DEPARTED, the Proxy forwards any packets destined 2107 to the Client to a Relay. The Relay in turn forwards the packets to 2108 the Client's current Server. When DepartTime expires, the Proxy 2109 deletes the neighbor cache entry and discards any further packets 2110 destined to this (now forgotten) Client. 2112 In some ANETs that employ a Proxy, the Client's MNP can be injected 2113 into the ANET routing system. In that case, the Client can send data 2114 messages without encapsulation so that the ANET native routing system 2115 transports the unencapsulated packets to the Proxy. This can be very 2116 beneficial, e.g., if the Client connects to the ANET via low-end data 2117 links such as some aviation wireless links. 2119 If the first-hop ANET access router is AERO-aware, the Client can 2120 avoid encapsulation for both its control and data messages. When the 2121 Client connects to the link, it can send an unencapsulated RS message 2122 with source address set to its AERO address and with destination 2123 address set to the AERO address of the Client's selected Server or to 2124 All-Routers multicast or Subnet-Router anycast. The Client includes 2125 an OMNI option formatted as specified in 2126 [I-D.templin-6man-omni-interface]. 2128 The Client then sends the unencapsulated RS message, which will be 2129 intercepted by the AERO-Aware access router. The access router then 2130 encapsulates the RS message in an ANET header with its own address as 2131 the source address and the address of a Proxy as the destination 2132 address. The access router further remembers the address of the 2133 Proxy so that it can encapsulate future data packets from the Client 2134 via the same Proxy. If the access router needs to change to a new 2135 Proxy, it simply sends another RS message toward the Server via the 2136 new Proxy on behalf of the Client. 2138 In some cases, the access router and Proxy may be one and the same 2139 node. In that case, the node would be located on the same physical 2140 link as the Client, but its message exchanges with the Server would 2141 need to pass through a security gateway at the ANET/INET border. The 2142 method for deploying access routers and Proxys (i.e. as a single node 2143 or multiple nodes) is an ANET-local administrative consideration. 2145 3.16.1. Detecting and Responding to Server Failures 2147 In environments where fast recovery from Server failure is required, 2148 Proxys SHOULD use proactive Neighbor Unreachability Detection (NUD) 2149 to track Server reachability in a similar fashion as for 2150 Bidirectional Forwarding Detection (BFD) [RFC5880]. Proxys can then 2151 quickly detect and react to failures so that cached information is 2152 re-established through alternate paths. The NUD control messaging is 2153 carried only over well-connected ground domain networks (i.e., and 2154 not low-end aeronautical radio links) and can therefore be tuned for 2155 rapid response. 2157 Proxys perform proactive NUD with Servers for which there are 2158 currently active ANET Clients by sending continuous NS messages in 2159 rapid succession, e.g., one message per second. The Proxy sends the 2160 NS message via the SPAN with the Proxy's AERO address as the source 2161 and the AERO address of the Server as the destination. When the 2162 Proxy is also sending RS messages to the Server on behalf of ANET 2163 Clients, the resulting RA responses can be considered as equivalent 2164 hints of forward progress. This means that the Proxy need not also 2165 send a periodic NS if it has already sent an RS within the same 2166 period. If the Server fails (i.e., if the Proxy ceases to receive 2167 advertisements), the Proxy can quickly inform Clients by sending 2168 multicast RA messages on the ANET interface. 2170 The Proxy sends RA messages on the ANET interface with source address 2171 set to the Server's address, destination address set to All-Nodes 2172 multicast, and Router Lifetime set to 0. The Proxy SHOULD send 2173 MAX_FINAL_RTR_ADVERTISEMENTS RA messages separated by small delays 2174 [RFC4861]. Any Clients on the ANET that had been using the failed 2175 Server will receive the RA messages and associate with a new Server. 2177 3.16.2. Point-to-Multipoint Server Coordindation 2179 In environments where Client messaging over ANETs is bandwidth- 2180 limited and/or expensive, Clients can enlist the services of the 2181 Proxy to coordinate with multiple Servers in a single RS/RA message 2182 exchange. The Client can send a single RS message to All-Routers 2183 multicast that includes the ID's of multiple Servers in MS-Register 2184 sub-options of the OMNI option,. 2186 When the Proxy receives the RS and processes the OMNI option, it 2187 performs a separate RS/RA exchange with each MS-Register Server. 2188 When it has received the RA messages, it creates an "aggregate" RA 2189 message to return to the Client with an OMNI option with each 2190 responding Server's ID recorded in an MS-Register sub-option. 2192 Client's can thereafter employ efficient point-to-multipoint Server 2193 coordination under the assistance of the Proxy to dramatically reduce 2194 the number of messages sent over the ANET while enlisting the support 2195 of multiple Servers for fault tolerance. Clients can further include 2196 MS-Release suboptions in RS messages to request the Proxy to release 2197 from former Servers via the procedures discussed in Section 3.19.5. 2199 The OMNI interface specification [I-D.templin-6man-omni-interface] 2200 provides further discussion of the Client/Proxy RS/RA messaging 2201 involved in point-to-multipoint coordination. 2203 3.17. AERO Route Optimization 2205 While data packets are flowing between a source and target node, 2206 route optimization SHOULD be used. Route optimization is initiated 2207 by the first eligible Route Optimization Source (ROS) closest to the 2208 source as follows: 2210 o For Clients on VPNed, NATed and Direct interfaces, the Server is 2211 the ROS. 2213 o For Clients on Proxyed interfaces, the Proxy is the ROS. 2215 o For Clients on native interfaces, the Client itself is the ROS. 2217 o For correspondent nodes on INET/EUN interfaces serviced by a 2218 Gateway, the Gateway is the ROS. 2220 The route optimization procedure is conducted between the ROS and the 2221 target Server/Gateway acting as a Route Optimization Responder (ROR) 2222 in the same manner as for IPv6 ND Address Resolution and using the 2223 same NS/NA messaging. The target may either be a MNP Client serviced 2224 by a Server, or a non-MNP correspondent reachable via a Gateway. 2226 The procedures are specified in the following sections. 2228 3.17.1. Route Optimization Initiation 2230 While data packets are flowing from the source node toward a target 2231 node, the ROS performs address resolution by sending an NS message 2232 for Address Resolution (NS(AR)) to receive a solicited NA message 2233 from the ROR. When the ROS sends an NS(AR), it includes: 2235 o the AERO address of the ROS as the source address. 2237 o the data packet's destination as the Target Address. 2239 o the Solicited-Node multicast address [RFC4291] formed from the 2240 lower 24 bits of the data packet's destination as the destination 2241 address, e.g., for 2001:db8:1:2::10:2000 the NS destination 2242 address is ff02:0:0:0:0:1:ff10:2000. 2244 The NS(AR) message includes an OMNI option with no ifIndex-tuples and 2245 no SLLAO, such that the target will not create a neighbor cache 2246 entry. 2248 The ROS then encapsulates the NS(AR) message in a SPAN header with 2249 source set to its own SPAN address and destination set to the data 2250 packet's destination address, then sends the message into the SPAN 2251 without decrementing the network-layer TTL/Hop Limit field. 2253 3.17.2. Relaying the NS 2255 When the Relay receives the NS(AR) message from the ROS, it discards 2256 the INET header and determines that the ROR is the next hop by 2257 consulting its standard IPv6 forwarding table for the SPAN header 2258 destination address. The Relay then forwards the message toward the 2259 ROR via the SPAN the same as for any IPv6 router. The final-hop 2260 Relay in the SPAN will deliver the message via a secured tunnel to 2261 the ROR. 2263 3.17.3. Processing the NS and Sending the NA 2265 When the ROR receives the NS(AR) message, it examines the Target 2266 Address to determine whether it has a neighbor cache entry and/or 2267 route that matches the target. If there is no match, the ROR drops 2268 the NS(AR) message. Otherwise, the ROR continues processing as 2269 follows: 2271 o if the target belongs to an MNP Client neighbor in the DEPARTED 2272 state the ROR changes the NS(AR) message SPAN destination address 2273 to the SPAN address of the Client's new Server, forwards the 2274 message into the SPAN and returns from processing. 2276 o If the target belongs to an MNP Client neighbor in the REACHABLE 2277 state, the ROR instead adds the AERO source address to the target 2278 Client's Report List with time set to ReportTime. 2280 o If the target belongs to a non-MNP route, the ROR continues 2281 processing without adding an entry to the Report List. 2283 The ROR then prepares a solicited NA message to send back to the ROS 2284 but does not create a neighbor cache entry. The ROR sets the NA 2285 source address to the AERO address corresponding to the target, sets 2286 the Target Addresss to the target of the solicitation, and sets the 2287 destination address to the source of the solicitation. 2289 The ROR then includes an OMNI option with prefix registration length 2290 set to the length of the MNP if the target is an MNP Client; 2291 otherwise, set to the maximum of the non-MNP prefix length and 64. 2292 (Note that a /64 limit is imposed to avoid causing the ROS to set 2293 short prefixes (e.g., "default") that would match destinations for 2294 which the routing system includes more-specific prefixes.) 2296 If the target is an MNP Client, the ROR next includes ifIndex-tuples 2297 in the OMNI option for each of the target Client's underlying 2298 interfaces with current information for each interface and with the S 2299 flag set to 0. The ROR then includes a TLLAO with ifIndex-tuples in 2300 one-to-one correspondence with the tuples that appear in the OMNI 2301 option. For NATed, VPNed and Direct interfaces, the link layer 2302 addresses are the SPAN address of the ROR. For Proxyed interfaces, 2303 the link-layer addresses are the SPAN addresses of the Proxy's INET 2304 interfaces. For native interfaces, the link-layer addresses are the 2305 INET addesses of the Client's native interfaces. 2307 The ROR then sets the NA message R flag to 1 (as a router), S flag to 2308 1 (as a response to a solicitation), and O flag to 0 (as a proxy). 2309 The ROR finally encapsulates the NA message in a SPAN header with 2310 source set to its own SPAN address and destination set to the source 2311 SPAN address of the NS(AR) message, then forwards the message into 2312 the SPAN without decrementing the network-layer TTL/Hop Limit field. 2314 3.17.4. Relaying the NA 2316 When the Relay receives the NA message from the ROR, it discards the 2317 INET header and determines that the ROS is the next hop by consulting 2318 its standard IPv6 forwarding table for the SPAN header destination 2319 address. The Relay then forwards the SPAN-encapsulated NA message 2320 toward the ROS the same as for any IPv6 router. The final-hop Relay 2321 in the SPAN will deliver the message via a secured tunnel to the ROS. 2323 3.17.5. Processing the NA 2325 When the ROS receives the solicited NA message, it processes the 2326 message the same as for standard IPv6 Address Resolution [RFC4861]. 2327 In the process, it caches the source SPAN address then creates an 2328 asymmetric neighbor cache entry for the ROR and caches all 2329 information found in the OMNI and TLLAO options. The ROS finally 2330 sets the asymmetric neighbor cache entry lifetime to REACHABLETIME 2331 seconds. 2333 3.17.6. Route Optimization Maintenance 2335 Following route optimization, the ROS forwards future data packets 2336 destined to the target via the addresses found in the cached link- 2337 layer information. The route optimization is shared by all sources 2338 that send packets to the target via the ROS, i.e., and not just the 2339 source on behalf of which the route optimization was initiated. 2341 While new data packets destined to the target are flowing through the 2342 ROS, it sends additional NS(AR) messages to the ROR before 2343 ReachableTime expires to receive a fresh solicited NA message the 2344 same as described in the previous sections (route optimization 2345 refreshment strategies are an implementation matter, with a non- 2346 normative example given in Appendix B.1). The ROS uses the cached 2347 SPAN address of the ROR as the NS(AR) SPAN destination address, and 2348 sends up to MAX_MULTICAST_SOLICIT NS(AR) messages separated by 1 2349 second until an NA is received. If no NA is received, the ROS 2350 assumes that the current ROR has become unreachable and deletes the 2351 neighbor cache entry. Subsequent data packets will trigger a new 2352 route optimization per Section 3.17.1 to discover a new ROR while 2353 initial data packets travel over a suboptimal route. 2355 If an NA is received, the ROS then updates the asymmetric neighbor 2356 cache entry to refresh ReachableTime, while (for MNP destinations) 2357 the ROR adds or updates the ROS address to the target Client's Report 2358 List and with time set to ReportTime. While no data packets are 2359 flowing, the ROS instead allows ReachableTime for the asymmetric 2360 neighbor cache entry to expire. When ReachableTime expires, the ROS 2361 deletes the asymmetric neighbor cache entry. Any future data packets 2362 flowing through the ROS will again trigger a new route optimization. 2364 The ROS may also receive unsolicited NA messages from the ROR at any 2365 time (see: Section 3.19). If there is an asymmetric neighbor cache 2366 entry for the target, the ROS updates the link-layer information but 2367 does not update ReachableTime since the receipt of an unsolicited NA 2368 does not confirm that any forward paths are working. If there is no 2369 asymmetric neighbor cache entry, the ROS simply discards the 2370 unsolicited NA. 2372 In this arrangement, the ROS holds an asymmetric neighbor cache entry 2373 for the ROR, but the ROR does not hold an asymmetric neighbor cache 2374 entry for the ROS. The route optimization neighbor relationship is 2375 therefore asymmetric and unidirectional. If the target node also has 2376 packets to send back to the source node, then a separate route 2377 optimization procedure is performed in the reverse direction. But, 2378 there is no requirement that the forward and reverse paths be 2379 symmetric. 2381 3.18. Neighbor Unreachability Detection (NUD) 2383 AERO nodes perform Neighbor Unreachability Detection (NUD) per 2384 [RFC4861] either reactively in response to persistent link-layer 2385 errors (see Section 3.14) or proactively to confirm reachability. 2386 The NUD algorithm is based on periodic control message exchanges. 2387 The algorithm may further be seeded by ND hints of forward progress, 2388 but care must be taken to avoid inferring reachability based on 2389 spoofed information. For example, authentic IPv6 ND message 2390 exchanges may be considered as acceptable hints of forward progress, 2391 while spurious data packets should not be. 2393 AERO Servers, Proxys and Gateways can use standard NS/NA NUD 2394 exchanges sent over the SPAN to securely test reachability without 2395 risk of DoS attacks from nodes pretending to be a neighbor; Proxys 2396 can further perform NUD to securely verify Server reachability on 2397 behalf of their proxyed Clients. However, a means for a ROS to test 2398 the unsecured forward directions of target route optimized paths is 2399 also necessary. The following paragraphs present the suggested 2400 method. 2402 When an ROR directs an ROS to a neighbor with one or more target 2403 link-layer addresses, the ROS can proactively test each such 2404 unsecured route optimized path by sending "loopback" NS(NUD) 2405 messages. While testing the paths, the ROS can optionally continue 2406 to send packets via the SPAN, maintain a small queue of packets until 2407 target reachability is confirmed, or (optimistically) allow packets 2408 to flow via the route optimized paths. 2410 When the ROS sends a loopback NS(NUD) message, it uses its AERO 2411 address as both the IPv6 source and destination address, and any IPv6 2412 address as the Target Address. The ROS includes a Nonce and 2413 Timestamp option, then encapsulates the message in SPAN/INET headers 2414 with its own SPAN address as the source and the SPAN address of the 2415 route optimization target as the destination. The ROS then forwards 2416 the message to the target (either directly to the link layer address 2417 of the target if the target is in the same SPAN segment, or via a 2418 Relay if the target is in a different SPAN segment). 2420 When the route optimization target receives the NS(NUD) message, it 2421 notices that the IPv6 destination address is the same as the source 2422 address. It then reverses the SPAN source and destination addresses 2423 and returns the message to the ROS (either directly or via the SPAN). 2424 The route optimization target does not decrement the NS(NUD) message 2425 IPv6 Hop-Limit in the process, since the message has not exited the 2426 SPAN. 2428 When the ROS receives the NS(NUD) message, it can determine from the 2429 Nonce, Timestamp and Target Address that the message originated from 2430 itself and that it transited the forward path. The ROS need not 2431 prepare a NA response, since the destination of the response would be 2432 itself and testing the route optimization path again would be 2433 redundant. 2435 The ROS marks route optimization target paths that pass these NUD 2436 tests as "reachable", and those that do not as "unreachable". These 2437 markings inform the AERO interface forwarding algorithm specified in 2438 Section 3.13. 2440 Note that to avoid a DoS vector nodes MUST NOT return loopback 2441 NS(NUD) messages received from an unsecured link-layer source via a 2442 secured SPAN path. 2444 3.19. Mobility Management and Quality of Service (QoS) 2446 AERO is a Distributed Mobility Management (DMM) service. Each Server 2447 is responsible for only a subset of the Clients on the AERO link, as 2448 opposed to a Centralized Mobility Management (CMM) service where 2449 there is a single network mobility collective entity for all Clients. 2450 Clients coordinate with their associated Servers via RS/RA exchanges 2451 to maintain the DMM profile, and the AERO routing system tracks all 2452 current Client/Server peering relationships. 2454 Servers provide default routing and mobility/multilink services for 2455 their dependent Clients. Clients are responsible for maintaining 2456 neighbor relationships with their Servers through periodic RS/RA 2457 exchanges, which also serves to confirm neighbor reachability. When 2458 a Client's underlying interface address and/or QoS information 2459 changes, the Client is responsible for updating the Server with this 2460 new information. Note that for Proxyed interfaces, however, the 2461 Proxy can also perform some RS/RA exchanges on the Client's behalf. 2463 Mobility management considerations are specified in the following 2464 sections. 2466 3.19.1. Mobility Update Messaging 2468 Servers accommodate Client mobility/multilink and/or QoS change 2469 events by sending unsolicited NA (uNA) messages to each ROS in the 2470 target Client's Report List. When a Server sends a uNA message, it 2471 sets the IPv6 source address to the Client's AERO address, sets the 2472 destination address to All-Nodes multicast and sets the Target 2473 Address to the Client's Subnet-Router anycast address. The Server 2474 also includes an OMNI option with prefix registration information and 2475 with ifIndex-tuples for the target Client's remaining interfaces with 2476 S set to 0. The Server then includes a TLLAO with corresponding 2477 ifIndex-tuples with link layer addresses set to the corresponding 2478 target SPAN addresses. The Server sets the NA R flag to 1, the S 2479 flag to 0 and the O flag to 0, then encapsulates the message in a 2480 SPAN header with source set to its own SPAN address and destination 2481 set to the SPAN address of the ROS and sends the message into the 2482 SPAN. 2484 As discussed in Section 7.2.6 of [RFC4861], the transmission and 2485 reception of uNA messages is unreliable but provides a useful 2486 optimization. In well-connected Internetworks with robust data links 2487 uNA messages will be delivered with high probability, but in any case 2488 the Server can optionally send up to MAX_NEIGHBOR_ADVERTISEMENT uNAs 2489 to each ROS to increase the likelihood that at least one will be 2490 received. 2492 When the ROS receives an uNA message, it ignores the message if there 2493 is no existing neighbor cache entry for the Client. Otherwise, it 2494 uses the included OMNI option and TLLAO information to update the 2495 neighbor cache entry, but does not reset ReachableTime since the 2496 receipt of an unsolicited NA message from the target Server does not 2497 provide confirmation that any forward paths to the target Client are 2498 working. 2500 If uNA messages are lost, the ROS may be left with stale address and/ 2501 or QoS information for the Client for up to REACHABLETIME seconds. 2502 During this time, the ROS can continue sending packets according to 2503 its stale neighbor cache information. When ReachableTime is close to 2504 expiring, the ROS will re-initiate route optimization and receive 2505 fresh link-layer address information. 2507 In addition to sending uNA messages to the current set of ROSs for 2508 the Client, the Server also sends uNAs to the former link-layer 2509 address for any ifIndex-tuple for which the link-layer address has 2510 changed. The uNA messages update Proxys that cannot easily detect 2511 (e.g., without active probing) when a formerly-active Client has 2512 departed. 2514 3.19.2. Announcing Link-Layer Address and/or QoS Preference Changes 2516 When a Client needs to change its ANET addresses and/or QoS 2517 preferences (e.g., due to a mobility event), either the Client or its 2518 Proxys send RS messages to the Server via the SPAN with an OMNI 2519 option that includes an ifIndex-tuple with S set to 1 and with the 2520 new link quality and address information. 2522 Up to MAX_RTR_SOLICITATION RS messages MAY be sent in parallel with 2523 sending actual data packets in case one or more RAs are lost. If all 2524 RAs are lost, the Client SHOULD re-associate with a new Server. 2526 When the Server receives the Client's changes, it sends uNA messages 2527 to all nodes in the Report List the same as described in the previous 2528 section. 2530 3.19.3. Bringing New Links Into Service 2532 When a Client needs to bring new underlying interfaces into service 2533 (e.g., when it activates a new data link), it sends an RS message to 2534 the Server via the underlying interface with an OMNI option that 2535 includes an ifIndex-tuple with S set to 1 and appropriate link 2536 quality values and with link-layer address information for the new 2537 link. 2539 3.19.4. Removing Existing Links from Service 2541 When a Client needs to remove existing underlying interfaces from 2542 service (e.g., when it de-activates an existing data link), it sends 2543 an RS or uNA message to its Server with an OMNI option with 2544 appropriate link quality values. 2546 If the Client needs to send RS/uNA messages over an underlying 2547 interface other than the one being removed from service, it MUST 2548 include ifIndex-tuples with appropriate link quality values for any 2549 underlying interfaces being removed from service. 2551 3.19.5. Moving to a New Server 2553 When a Client associates with a new Server, it performs the Client 2554 procedures specified in Section 3.15.2. The Client also includes MS- 2555 Release identifiers in the RS message OMNI option per 2556 [I-D.templin-6man-omni-interface] if it wants the new Server to 2557 notify any old Servers from which the Client is departing. 2559 When the new Server receives the Client's RS message, it returns an 2560 RA as specified in Section 3.15.3 and sends up to 2561 MAX_NEIGHBOR_ADVERTIISEMENT uNA messages to any old Servers listed in 2562 OMNI option MS-Release identifiers. Each uNA message includes the 2563 Client's AERO address as the source address, the old Server's AERO 2564 address as the destination address, and an OMNI option with the 2565 Register/Release bit set to 0. The new Server wraps the uNA in a 2566 SPAN header with its own SPAN address as the source and the old 2567 Server's SPAN address as the destination, then sends the message into 2568 the SPAN. 2570 When an old Server receives the uNA, it changes the Client's neighbor 2571 cache entry state to DEPARTED, sets the link-layer address of the 2572 Client to the new Server's SPAN address, and sets DepartTime to 2573 DEPARTTIME seconds. After a short delay (e.g., 2 seconds) the old 2574 Server withdraws the Client's MNP from the routing system. After 2575 DepartTime expires, the old Server deletes the Client's neighbor 2576 cache entry. 2578 The old Server also sends unsolicited NA messages to all ROSs in the 2579 Client's Report List with an OMNI option with a single ifIndex-tuple 2580 with ifIndex set to 0 and S set to '1', and with the SPAN address of 2581 the new Server in a companion TLLAO. When the ROS receives the NA, 2582 it caches the address of the new Server in the existing asymmetric 2583 neighbor cache entry and marks the entry as STALE. Subsequent data 2584 packets will then flow according to any existing cached link-layer 2585 information and trigger a new NS(AR)/NA exchange via the new Server. 2587 Clients SHOULD NOT move rapidly between Servers in order to avoid 2588 causing excessive oscillations in the AERO routing system. Examples 2589 of when a Client might wish to change to a different Server include a 2590 Server that has gone unreachable, topological movements of 2591 significant distance, movement to a new geographic region, movement 2592 to a new SPAN segment, etc. 2594 When a Client moves to a new Server, some of the fragments of a 2595 multiple fragment packet may have already arrived at the old Server 2596 while others are en route to the new Server, however no special 2597 attention in the reassembly algorithm is necessary when re-routed 2598 fragments are simply treated as loss. 2600 3.20. Multicast 2602 The AERO Client provides an IGMP (IPv4) [RFC2236] or MLD (IPv6) 2603 [RFC3810] proxy service for its EUNs and/or hosted applications 2604 [RFC4605]. The Client forwards IGMP/MLD messages over any of its 2605 underlying interfaces for which group membership is required. The 2606 IGMP/MLD messages may be further forwarded by a first-hop ANET access 2607 router acting as an IGMP/MLD-snooping switch [RFC4541], then 2608 ultimately delivered to an AERO Proxy/Server acting as a Protocol 2609 Independent Multicast - Sparse-Mode (PIM-SM, or simply "PIM") 2610 Designated Router (DR) [RFC7761]. AERO Gateways also act as PIM 2611 routers (i.e., the same as AERO Proxys/Servers) on behalf of nodes on 2612 INET/EUN networks. The behaviors identified in the following 2613 sections correspond to Source-Specific Multicast (SSM) and Any-Source 2614 Multicast (ASM) operational modes. 2616 3.20.1. Source-Specific Multicast (SSM) 2618 When an ROS (i.e., an AERO Proxy/Server/Gateway) "X" acting as PIM 2619 router receives a Join/Prune message from a node on its downstream 2620 interfaces containing one or more ((S)ource, (G)roup) pairs, it 2621 updates its Multicast Routing Information Base (MRIB) accordingly. 2622 For each S belonging to a prefix reachable via X's non-AERO 2623 interfaces, X then forwards the (S, G) Join/Prune to any PIM routers 2624 on those interfaces per [RFC7761]. 2626 For each S belonging to a prefix reachable via X's AERO interface, X 2627 originates a separate copy of the Join/Prune for each (S,G) in the 2628 message using its own AERO address as the source address and ALL-PIM- 2629 ROUTERS as the destination address. X then encapsulates each message 2630 in a SPAN header with source address set to the SPAN address of X and 2631 destination address set to S then forwards the message into the SPAN. 2632 The SPAN in turn forwards the message to AERO Server/Gateway "Y" that 2633 services S. At the same time, if the message was a Join, X sends a 2634 route-optimization NS message toward each S the same as discussed in 2635 Section 3.17. The resulting NAs will return the AERO address for the 2636 prefix that matches S as the network-layer source address and TLLAOs 2637 with the SPAN addresses corresponding to any ifIndex-tuples that are 2638 currently servicing S. 2640 When Y processes the Join/Prune message, if S located behind any 2641 Native, Direct, VPNed or NATed interfaces Y acts as a PIM router and 2642 updates its MRIB to list X as the next hop in the reverse path. If S 2643 is located behind any Proxys "Z"*, Y also forwards the message to 2644 each Z* over the SPAN while continuing to use the AERO address of X 2645 as the source address. Each Z* then updates its MRIB accordingly and 2646 maintains the AERO address of X as the next hop in the reverse path. 2647 Since the Relays in the SPAN do not examine network layer control 2648 messages, this means that the (reverse) multicast tree path is simply 2649 from each Z* (and/or Y) to X with no other multicast-aware routers in 2650 the path. If any Z* (and/or Y) is located on the same SPAN segment 2651 as X, the multicast data traffic sent to X directly using SPAN/INET 2652 encapsulation instead of via a Relay. 2654 Following the initial Join/Prune and NS/NA messaging, X maintains an 2655 asymmetric neighbor cache entry for each S the same as if X was 2656 sending unicast data traffic to S. In particular, X performs 2657 additional NS/NA exchanges to keep the neighbor cache entry alive for 2658 up to t_periodic seconds [RFC7761]. If no new Joins are received 2659 within t_periodic seconds, X allows the neighbor cache entry to 2660 expire. Finally, if X receives any additional Join/Prune messages 2661 for (S,G) it forwards the messages to each Y and Z* in the neighbor 2662 cache entry over the SPAN. 2664 At some later time, Client C that holds an MNP for source S may 2665 depart from a first Proxy Z1 and/or connect via a new Proxy Z2. In 2666 that case, Y sends an unsolicited NA message to X the same as 2667 specified for unicast mobility in Section 3.19. When X receives the 2668 unsolicited NA message, it updates its asymmetric neighbor cache 2669 entry for the AERO address for source S and sends new Join messages 2670 to any new Proxys Z2. There is no requirement to send any Prune 2671 messages to old Proxys Z1 since source S will no longer source any 2672 multicast data traffic via Z1. Instead, the multicast state for 2673 (S,G) in Proxy Z1 will soon time out since no new Joins will arrive. 2675 After some later time, C may move to a new Server Y2 and depart from 2676 old Sever Y1. In that case, Y1 sends Join messages for any of C's 2677 active (S,G) groups to Y2 while including its own AERO address as the 2678 source address. This causes Y2 to include Y1 in the multicast 2679 forwarding tree during the interim time that Y1's symmetric neighbor 2680 cache entry for C is in the DEPARTED state. At the same time, Y1 2681 sends an unsolicited NA message to X with an OMNI option and TLLAO 2682 with ifIndex-tuple set to 0 and a release indication to cause X to 2683 release its asymmetric neighbor cache entry. X then sends a new Join 2684 message to S via the SPAN and re-initiates route optimization the 2685 same as if it were receiving a fresh Join message from a node on a 2686 downstream link. 2688 3.20.2. Any-Source Multicast (ASM) 2690 When an ROS X acting as a PIM router receives a Join/Prune from a 2691 node on its downstream interfaces containing one or more (*,G) pairs, 2692 it updates its Multicast Routing Information Base (MRIB) accordingly. 2693 X then forwards a copy of the message to the Rendezvous Point (RP) R 2694 for each G over the SPAN. X uses its own AERO address as the source 2695 address and ALL-PIM-ROUTERS as the destination address, then 2696 encapsulates each message in a SPAN header with source address set to 2697 the SPAN address of X and destination address set to R, then sends 2698 the message into the SPAN. At the same time, if the message was a 2699 Join X initiates NS/NA route optimization the same as for the SSM 2700 case discussed in Section 3.20.1. 2702 For each source S that sends multicast traffic to group G via R, the 2703 Proxy/Server Z* for the Client that aggregates S encapsulates the 2704 packets in PIM Register messages and forwards them to R via the SPAN. 2705 R may then elect to send a PIM Join to Z* over the SPAN. This will 2706 result in an (S,G) tree rooted at Z* with R as the next hop so that R 2707 will begin to receive two copies of the packet; one native copy from 2708 the (S, G) tree and a second copy from the pre-existing (*, G) tree 2709 that still uses PIM Register encapsulation. R can then issue a PIM 2710 Register-stop message to suppress the Register-encapsulated stream. 2711 At some later time, if C moves to a new Proxy/Server Z*, it resumes 2712 sending packets via PIM Register encapsulation via the new Z*. 2714 At the same time, as multicast listeners discover individual S's for 2715 a given G, they can initiate an (S,G) Join for each S under the same 2716 procedures discussed in Section 3.20.1. Once the (S,G) tree is 2717 established, the listeners can send (S, G) Prune messages to R so 2718 that multicast packets for group G sourced by S will only be 2719 delivered via the (S, G) tree and not from the (*, G) tree rooted at 2720 R. All mobility considerations discussed for SSM apply. 2722 3.20.3. Bi-Directional PIM (BIDIR-PIM) 2724 Bi-Directional PIM (BIDIR-PIM) [RFC5015] provides an alternate 2725 approach to ASM that treats the Rendezvous Point (RP) as a Designated 2726 Forwarder (DF). Further considerations for BIDIR-PIM are out of 2727 scope. 2729 3.21. Operation over Multiple AERO Links (VLANs) 2731 An AERO Client can connect to multiple AERO links the same as for any 2732 data link service. In that case, the Client maintains a distinct 2733 AERO interface for each link, e.g., 'aero0' for the first link, 2734 'aero1' for the second, 'aero2' for the third, etc. Each AERO link 2735 would include its own distinct set of Relays, Servers and Proxys, 2736 thereby providing redundancy in case of failures. 2738 The Relays, Servers and Proxys on each AERO link can assign AERO and 2739 SPAN addresses that use the same or different numberings from those 2740 on other links. Since the links are mutually independent there is no 2741 requirement for avoiding inter-link address duplication, e.g., the 2742 same AERO address such as fe80::1000 could be used to number distinct 2743 nodes that connect to different AERO links. 2745 Each AERO link could utilize the same or different ANET connections. 2746 The links can be distinguished at the link-layer via Virtual Local 2747 Area Network (VLAN) tagging (e.g., IEEE 802.1Q) and/or through 2748 assignment of distinct sets of MSPs on each link. This gives rise to 2749 the opportunity for supporting multiple redundant networked paths, 2750 where each VLAN is distinguished by a different label (e.g., colors 2751 such as Red, Green, Blue, etc.). In particular, the Client can tag 2752 its RS messages with the appropriate label to cause the network to 2753 select the desired VLAN. 2755 Clients that connect to multiple AERO interfaces can select the 2756 outgoing interface appropriate for a given Red/Blue/Green/etc. 2757 traffic profile while (in the reverse direction) correspondent nodes 2758 must have some way of steering their packets destined to a target via 2759 the correct AERO link. 2761 In a first alternative, if each AERO link services different MSPs, 2762 then the Client can receive a distinct MNP from each of the links. 2763 IP routing will therefore assure that the correct Red/Green/Blue/etc. 2764 network is used for both outbound and inbound traffic. This can be 2765 accomplished using existing technologies and approaches, and without 2766 requiring any special supporting code in correspondent nodes or 2767 Relays. 2769 In a second alternative, if each AERO link services the same MSP(s) 2770 then each link could assign a distinct "AERO Link Anycast" address 2771 that is configured by all Relays on the link. Correspondent nodes 2772 then include a "type 4" routing header with the Anycast address for 2773 the AERO link as the IPv6 destination and with the address of the 2774 target encoded as the "next segment" in the routing header 2775 [RFC8402][I-D.ietf-6man-segment-routing-header]. Standard IP routing 2776 will then direct the packet to the nearest Relay for the correct AERO 2777 link, which will replace the destination address with the target 2778 address then forward the packet to the target. 2780 3.22. DNS Considerations 2782 AERO Client MNs and INET correspondent nodes consult the Domain Name 2783 System (DNS) the same as for any Internetworking node. When 2784 correspondent nodes and Client MNs use different IP protocol versions 2785 (e.g., IPv4 correspondents and IPv6 MNs), the INET DNS must maintain 2786 A records for IPv4 address mappings to MNs which must then be 2787 populated in Gateway NAT64 mapping caches. In that way, an IPv4 2788 correspondent node can send packets to the IPv4 address mapping of 2789 the target MN, and the Gateway will translate the IPv4 header and 2790 destination address into an IPv6 header and IPv6 destination address 2791 of the MN. 2793 When an AERO Client registers with an AERO Server, the Server can 2794 return the address(es) of DNS servers in RDNSS options [RFC6106]. 2795 The DNS server provides the IP addresses of other MNs and 2796 correspondent nodes in AAAA records for IPv6 or A records for IPv4. 2798 3.23. Transition Considerations 2800 The SPAN ensures that dissimilar INET partitions can be joined into a 2801 single unified AERO link, even though the partitions themselves may 2802 have differing protocol versions and/or incompatible addressing 2803 plans. However, a commonality can be achieved by incrementally 2804 distributing globally routable (i.e., native) IP prefixes to 2805 eventually reach all nodes (both mobile and fixed) in all SPAN 2806 segments. This can be accomplished by incrementally deploying AERO 2807 Gateways on each INET partition, with each Gateway distributing its 2808 MNPs and/or discovering non-MNP prefixes on its INET links. 2810 This gives rise to the opportunity to eventually distribute native IP 2811 addresses to all nodes, and to present a unified AERO link view 2812 (bridged by the SPAN) even if the INET partitions remain in their 2813 current protocol and addressing plans. In that way, the AERO link 2814 can serve the dual purpose of providing a mobility/multilink service 2815 and a transition service. Or, if an INET partition is transitioned 2816 to a native IP protocol version and addressing scheme that is 2817 compatible with the AERO link MNP-based addressing scheme, the 2818 partition and AERO link can be joined by Gateways. 2820 Gateways that connect INETs/EUNs with dissimilar IP protocol versions 2821 must employ a network address and protocol translation function such 2822 as NAT64[RFC6146]. 2824 3.24. Detecting and Reacting to Server and Relay Failures 2826 In environments where rapid failure recovery is required, Servers and 2827 Relays SHOULD use Bidirectional Forwarding Detection (BFD) [RFC5880]. 2828 Nodes that use BFD can quickly detect and react to failures so that 2829 cached information is re-established through alternate nodes. BFD 2830 control messaging is carried only over well-connected ground domain 2831 networks (i.e., and not low-end radio links) and can therefore be 2832 tuned for rapid response. 2834 Servers and Relays maintain BFD sessions in parallel with their BGP 2835 peerings. If a Server or Relay fails, BGP peers will quickly re- 2836 establish routes through alternate paths the same as for common BGP 2837 deployments. Similarly, Proxys maintain BFD sessions with their 2838 associated Relays even though they do not establish BGP peerings with 2839 them. 2841 Proxys SHOULD use proactive NUD for Servers for which there are 2842 currently active ANET Clients in a manner that parallels BFD, i.e., 2843 by sending unicast NS messages in rapid succession to receive 2844 solicited NA messages. When the Proxy is also sending RS messages on 2845 behalf of ANET Clients, the RS/RA messaging can be considered as 2846 equivalent hints of forward progress. This means that the Proxy need 2847 not also send a periodic NS if it has already sent an RS within the 2848 same period. If a Server fails, the Proxy will cease to receive 2849 advertisements and can quickly inform Clients of the outage by 2850 sending multicast RA messages on the ANET interface. 2852 The Proxy sends multicast RA messages with source address set to the 2853 Server's address, destination address set to All-Nodes multicast, and 2854 Router Lifetime set to 0. The Proxy SHOULD send 2855 MAX_FINAL_RTR_ADVERTISEMENTS RA messages separated by small delays 2856 [RFC4861]. Any Clients on the ANET interface that have been using 2857 the (now defunct) Server will receive the RA messages and associate 2858 with a new Server. 2860 3.25. AERO Clients on the Open Internet 2862 AERO Clients that connect to the open Internet via native and/or 2863 NATed interfaces can establish a VPN to securely connect to a Server 2864 in a "tethered" arrangement with all of the Client's traffic 2865 transiting the Server. Alternatively, the Client can exchange ND 2866 messages directly with other AERO nodes using SPAN/INET 2867 encapsulation. In that case, the Client must apply asymmetric 2868 security for IPv6 ND messages to ensure routing and neighbor cache 2869 integrity using SEcure Neighbor Discovery (SEND) [RFC3971] and 2870 Cryptographically Generated Addresses (CGAs) [RFC3972]. 2872 When a Client enables native and/or NATed interfaces underneath its 2873 AERO interface, it sends an RS message with IPv6 source address set 2874 to a link-local CGA, with IPv6 destination set to All-Routers 2875 multicast, with an OMNI opton and with SEND/CGA options to provide 2876 message authentication. The Client also includes an SLLAO with the 2877 IP address and Port Number used for INET enacpsulation written in 2878 obfuscated form as discussed in Section 3.6. The Client wraps the 2879 message in a SPAN header with source address set to the Client's SPAN 2880 address and with destination address set to the SPAN address of a 2881 Server. The Client then further wraps the SPAN message in an INET 2882 header with source set to the Client's INET address and destination 2883 set to the Server's INET address, then sends the message to the 2884 Server. 2886 When the Server receives the RS message, it authenticates the message 2887 and registers the Client's MNP and INET interface information 2888 according to the OMNI option parameters. The Server then returns an 2889 RA message with IPv6 source set to its CGA, with IPv6 destination set 2890 to the Client's CGA, with an OMNI option and with SEND/CGA options to 2891 provide message authentication. If the Client is located behind a 2892 NAT, the Server further sets the N bit in the RA flags field to 1 2893 (see: Section 5). The Server then wraps the message in a SPAN header 2894 with source address set to the Server's SPAN address and destination 2895 set to the Client's SPAN address, and further wraps the SPAN message 2896 in an INET header with source set to the Server's INET address and 2897 destination set to the Client's INET address. 2899 After the Client has registered its INET interfaces in such RS/RA 2900 exchanges it sends periodic RS messages to receive fresh RA messages 2901 before the Router Lifetime received on each INET interface expires 2902 (again, using SEND/CGA). The Client also maintains default routes 2903 via its Servers, i.e., the same as described in earlier sections. 2905 When the Client sends messages to target IP addresses, it also 2906 invokes route optimization per Section 3.17 using IPv6 ND address 2907 resolution messaging. The Client sends the (SEND/CGA-protected) 2908 NS(AR) message wrapped in a SPAN header with source set to the 2909 Client's SPAN address and destination set to the target IP address, 2910 and with INET destination address set to the address of the Server. 2911 The Server authenticates the message and sends a corresponding NS(AR) 2912 message over the SPAN. When the ROR receives the NS(AR), it adds the 2913 Client's SPAN addressand Server's INET address to the target's Report 2914 List, and returns an NA with OMNI and TLLAO information for the 2915 target. (For any of the target's interfaces that are located behind 2916 a NAT, the ROR includes its own address and port in the TLLAO for 2917 that interface; otherwise, it includes the target's native address 2918 and port.) The Server then returns a (SEND/CGA-protected) NA message 2919 to the Client. 2921 Following route optimization, the Client forwards data packets 2922 directly to the INET addresses of the target according to the OMNI/ 2923 TLLAO information. The ROR may reutrn uNAs via the Server if the 2924 target moves, and the Server will send corresponding (SEND/CGA- 2925 protected) uNAs to the Client. The Client can also send "loopback" 2926 NS(NUD) messages as discussed in Section 3.18 to test forward path 2927 reachability even though there is no security association between the 2928 Client and the target. 2930 Note: when the target is an AERO Client interface located behind a 2931 NAT, the Client's Server is included in the forwarding path for 2932 delivery of packets to the Client via that interface. Future updates 2933 to this specification MAY include provisions for allowing direct 2934 packet forwarding to the Client via the NAT without transiting the 2935 Server. [RFC4380] provides example procedures for supporting such 2936 inbound NAT traversal. 2938 4. Implementation Status 2940 An AERO implementation based on OpenVPN (https://openvpn.net/) was 2941 announced on the v6ops mailing list on January 10, 2018 and an 2942 initial public release of the AERO proof-of-concept source code was 2943 announced on the intarea mailing list on August 21, 2015. 2945 As of 4/1/2020, more recent updated implementations are under 2946 internal development and testing with plans to release in the near 2947 future. 2949 5. IANA Considerations 2951 The IANA has assigned a 4-octet Private Enterprise Number "45282" for 2952 AERO in the "enterprise-numbers" registry. 2954 The IANA has assigned the UDP port number "8060" for an earlier 2955 experimental version of AERO [RFC6706]. This document obsoletes 2956 [RFC6706] and claims the UDP port number "8060" for all future use. 2958 The IANA is requested to assign a new IPv6 ND Router Advertiisement 2959 (RA) flag (value TBD per [RFC5175]), to be known as the "NAT 2960 Traversal (N)" flag. 2962 No further IANA actions are required. 2964 6. Security Considerations 2966 AERO Relays configure secured tunnels with AERO Servers and Proxys 2967 within their local SPAN segments. Applicable secured tunnel 2968 alternatives include IPsec [RFC4301], TLS/SSL [RFC8446], DTLS 2969 [RFC6347], WireGuard, etc. The AERO Relays of all SPAN segments in 2970 turn configure secured tunnels for their neighboring AERO Relays 2971 across the SPAN. Therefore, control messages that traverse the SPAN 2972 between any pair of AERO link neighbors are already secured. 2974 AERO Servers, Gateways and Proxys targeted by a route optimization 2975 may also receive packets directly from the INET partitions instead of 2976 via the SPAN. For INET partitions that apply effective ingress 2977 filtering to defeat source address spoofing, the simple data origin 2978 authentication procedures in Section 3.11 can be applied. 2980 For INET partitions that cannot apply effective ingress filtering, 2981 the two options for securing communications include 1) disable route 2982 optimization so that all traffic is conveyed over secured tunnels via 2983 the SPAN, or 2) enable on-demand secure tunnel creation between INET 2984 partition neighbors. Option 1) would result in longer routes than 2985 necessary and traffic concentration on critical infrastructure 2986 elements. Option 2) could be coordinated by establishing a secured 2987 tunnel on-demand instead of performing an NS/NA exchange in the route 2988 optimization procedures. Procedures for establishing on-demand 2989 secured tunnels are out of scope. 2991 AERO Clients that connect to secured enclaves need not apply security 2992 to their ND messages, since the messages will be intercepted by a 2993 perimeter Proxy that applies security on its outward-facing 2994 interface. AERO Clients located outside of secured enclaves can use 2995 symmetric network and/or transport layer security services such as 2996 VPNs, but when there are many prospective neighbors with dynamically 2997 changing connectivity an asymmetric security service such as SEcure 2998 Neighbor Discovery (SEND) [RFC3971] and Cryptographically Generated 2999 Addresses (CGAs) [RFC3972] may be more appropriate. 3001 Application endpoints SHOULD use application-layer security services 3002 such as TLS/SSL, DTLS or SSH [RFC4251] to assure the same level of 3003 protection as for critical secured Internet services. AERO Clients 3004 that require host-based VPN services SHOULD use symmetric network 3005 and/or transport layer security services such as IPsec, TLS/SSL, 3006 DTLS, etc. AERO Proxys and Servers can also provide a network-based 3007 VPN service on behalf of the Client, e.g., if the Client is located 3008 within a secured enclave and cannot establish a VPN on its own 3009 behalf. 3011 AERO Servers and Relays present targets for traffic amplification 3012 Denial of Service (DoS) attacks. This concern is no different than 3013 for widely-deployed VPN security gateways in the Internet, where 3014 attackers could send spoofed packets to the gateways at high data 3015 rates. This can be mitigated by connecting Servers and Relays over 3016 dedicated links with no connections to the Internet and/or when 3017 connections to the Internet are only permitted through well-managed 3018 firewalls. Traffic amplification DoS attacks can also target an AERO 3019 Client's low data rate links. This is a concern not only for Clients 3020 located on the open Internet but also for Clients in secured 3021 enclaves. AERO Servers and Proxys can institute rate limits that 3022 protect Clients from receiving packet floods that could DoS low data 3023 rate links. 3025 AERO Gateways must implement ingress filtering to avoid a spoofing 3026 attack in which spurious SPAN messages are injected into an AERO link 3027 from an outside attacker. AERO Clients MUST ensure that their 3028 connectivity is not used by unauthorized nodes on their EUNs to gain 3029 access to a protected network, i.e., AERO Clients that act as routers 3030 MUST NOT provide routing services for unauthorized nodes. (This 3031 concern is no different than for ordinary hosts that receive an IP 3032 address delegation but then "share" the address with other nodes via 3033 some form of Internet connection sharing such as tethering.) 3034 The MAP list MUST be well-managed and secured from unauthorized 3035 tampering, even though the list contains only public information. 3036 The MAP list can be conveyed to the Client in a similar fashion as in 3037 [RFC5214] (e.g., through layer 2 data link login messaging, secure 3038 upload of a static file, DNS lookups, etc.). 3040 Although public domain and commercial SEND implementations exist, 3041 concerns regarding the strength of the cryptographic hash algorithm 3042 have been documented [RFC6273] [RFC4982]. 3044 Security considerations for accepting link-layer ICMP messages and 3045 reflected packets are discussed throughout the document. 3047 7. Acknowledgements 3049 Discussions in the IETF, aviation standards communities and private 3050 exchanges helped shape some of the concepts in this work. 3051 Individuals who contributed insights include Mikael Abrahamsson, Mark 3052 Andrews, Fred Baker, Bob Braden, Stewart Bryant, Brian Carpenter, 3053 Wojciech Dec, Pavel Drasil, Ralph Droms, Adrian Farrel, Nick Green, 3054 Sri Gundavelli, Brian Haberman, Bernhard Haindl, Joel Halpern, Tom 3055 Herbert, Sascha Hlusiak, Lee Howard, Zdenek Jaron, Andre Kostur, 3056 Hubert Kuenig, Ted Lemon, Andy Malis, Satoru Matsushima, Tomek 3057 Mrugalski, Madhu Niraula, Alexandru Petrescu, Behcet Saikaya, Michal 3058 Skorepa, Joe Touch, Bernie Volz, Ryuji Wakikawa, Tony Whyman, Lloyd 3059 Wood and James Woodyatt. Members of the IESG also provided valuable 3060 input during their review process that greatly improved the document. 3061 Special thanks go to Stewart Bryant, Joel Halpern and Brian Haberman 3062 for their shepherding guidance during the publication of the AERO 3063 first edition. 3065 This work has further been encouraged and supported by Boeing 3066 colleagues including Kyle Bae, M. Wayne Benson, Dave Bernhardt, Cam 3067 Brodie, John Bush, Balaguruna Chidambaram, Irene Chin, Bruce Cornish, 3068 Claudiu Danilov, Don Dillenburg, Joe Dudkowski, Wen Fang, Samad 3069 Farooqui, Anthony Gregory, Jeff Holland, Seth Jahne, Brian Jaury, 3070 Greg Kimberly, Ed King, Madhuri Madhava Badgandi, Laurel Matthew, 3071 Gene MacLean III, Rob Muszkiewicz, Sean O'Sullivan, Vijay 3072 Rajagopalan, Greg Saccone, Rod Santiago, Kent Shuey, Brian Skeen, 3073 Mike Slane, Carrie Spiker, Katie Tran, Brendan Williams, Amelia 3074 Wilson, Julie Wulff, Yueli Yang, Eric Yeh and other members of the 3075 Boeing mobility, networking and autonomy teams. Kyle Bae, Wayne 3076 Benson, Katie Tran and Eric Yeh are especially acknowledged for 3077 implementing the AERO functions as extensions to the public domain 3078 OpenVPN distribution. 3080 Earlier works on NBMA tunneling approaches are found in 3081 [RFC2529][RFC5214][RFC5569]. 3083 Many of the constructs presented in this second edition of AERO are 3084 based on the author's earlier works, including: 3086 o The Internet Routing Overlay Network (IRON) 3087 [RFC6179][I-D.templin-ironbis] 3089 o Virtual Enterprise Traversal (VET) 3090 [RFC5558][I-D.templin-intarea-vet] 3092 o The Subnetwork Encapsulation and Adaptation Layer (SEAL) 3093 [RFC5320][I-D.templin-intarea-seal] 3095 o AERO, First Edition [RFC6706] 3097 Note that these works cite numerous earlier efforts that are not also 3098 cited here due to space limitations. The authors of those earlier 3099 works are acknowledged for their insights. 3101 This work is aligned with the NASA Safe Autonomous Systems Operation 3102 (SASO) program under NASA contract number NNA16BD84C. 3104 This work is aligned with the FAA as per the SE2025 contract number 3105 DTFAWA-15-D-00030. 3107 This work is aligned with the Boeing Commercial Airplanes (BCA) 3108 Internet of Things (IoT) and autonomy programs. 3110 This work is aligned with the Boeing Information Technology (BIT) 3111 MobileNet program. 3113 8. References 3115 8.1. Normative References 3117 [I-D.templin-6man-omni-interface] 3118 Templin, F. and T. Whyman, "Transmission of IPv6 Packets 3119 over Overlay Multilink Network (OMNI) Interfaces", draft- 3120 templin-6man-omni-interface-09 (work in progress), April 3121 2020. 3123 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, 3124 DOI 10.17487/RFC0791, September 1981, 3125 . 3127 [RFC0792] Postel, J., "Internet Control Message Protocol", STD 5, 3128 RFC 792, DOI 10.17487/RFC0792, September 1981, 3129 . 3131 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 3132 Requirement Levels", BCP 14, RFC 2119, 3133 DOI 10.17487/RFC2119, March 1997, 3134 . 3136 [RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in 3137 IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473, 3138 December 1998, . 3140 [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black, 3141 "Definition of the Differentiated Services Field (DS 3142 Field) in the IPv4 and IPv6 Headers", RFC 2474, 3143 DOI 10.17487/RFC2474, December 1998, 3144 . 3146 [RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander, 3147 "SEcure Neighbor Discovery (SEND)", RFC 3971, 3148 DOI 10.17487/RFC3971, March 2005, 3149 . 3151 [RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)", 3152 RFC 3972, DOI 10.17487/RFC3972, March 2005, 3153 . 3155 [RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and 3156 More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191, 3157 November 2005, . 3159 [RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast 3160 Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005, 3161 . 3163 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 3164 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 3165 DOI 10.17487/RFC4861, September 2007, 3166 . 3168 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 3169 Address Autoconfiguration", RFC 4862, 3170 DOI 10.17487/RFC4862, September 2007, 3171 . 3173 [RFC5175] Haberman, B., Ed. and R. Hinden, "IPv6 Router 3174 Advertisement Flags Option", RFC 5175, 3175 DOI 10.17487/RFC5175, March 2008, 3176 . 3178 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 3179 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 3180 May 2017, . 3182 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 3183 (IPv6) Specification", STD 86, RFC 8200, 3184 DOI 10.17487/RFC8200, July 2017, 3185 . 3187 [RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A., 3188 Richardson, M., Jiang, S., Lemon, T., and T. Winters, 3189 "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", 3190 RFC 8415, DOI 10.17487/RFC8415, November 2018, 3191 . 3193 8.2. Informative References 3195 [BGP] Huston, G., "BGP in 2015, http://potaroo.net", January 3196 2016. 3198 [I-D.ietf-6man-segment-routing-header] 3199 Filsfils, C., Dukes, D., Previdi, S., Leddy, J., 3200 Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header 3201 (SRH)", draft-ietf-6man-segment-routing-header-26 (work in 3202 progress), October 2019. 3204 [I-D.ietf-dmm-distributed-mobility-anchoring] 3205 Chan, A., Wei, X., Lee, J., Jeon, S., and C. Bernardos, 3206 "Distributed Mobility Anchoring", draft-ietf-dmm- 3207 distributed-mobility-anchoring-15 (work in progress), 3208 March 2020. 3210 [I-D.ietf-intarea-gue] 3211 Herbert, T., Yong, L., and O. Zia, "Generic UDP 3212 Encapsulation", draft-ietf-intarea-gue-09 (work in 3213 progress), October 2019. 3215 [I-D.ietf-intarea-gue-extensions] 3216 Herbert, T., Yong, L., and F. Templin, "Extensions for 3217 Generic UDP Encapsulation", draft-ietf-intarea-gue- 3218 extensions-06 (work in progress), March 2019. 3220 [I-D.ietf-intarea-tunnels] 3221 Touch, J. and M. Townsley, "IP Tunnels in the Internet 3222 Architecture", draft-ietf-intarea-tunnels-10 (work in 3223 progress), September 2019. 3225 [I-D.ietf-rtgwg-atn-bgp] 3226 Templin, F., Saccone, G., Dawra, G., Lindem, A., and V. 3227 Moreno, "A Simple BGP-based Mobile Routing System for the 3228 Aeronautical Telecommunications Network", draft-ietf- 3229 rtgwg-atn-bgp-05 (work in progress), January 2020. 3231 [I-D.templin-6man-dhcpv6-ndopt] 3232 Templin, F., "A Unified Stateful/Stateless Configuration 3233 Service for IPv6", draft-templin-6man-dhcpv6-ndopt-09 3234 (work in progress), January 2020. 3236 [I-D.templin-intarea-grefrag] 3237 Templin, F., "GRE Tunnel Level Fragmentation", draft- 3238 templin-intarea-grefrag-04 (work in progress), July 2016. 3240 [I-D.templin-intarea-seal] 3241 Templin, F., "The Subnetwork Encapsulation and Adaptation 3242 Layer (SEAL)", draft-templin-intarea-seal-68 (work in 3243 progress), January 2014. 3245 [I-D.templin-intarea-vet] 3246 Templin, F., "Virtual Enterprise Traversal (VET)", draft- 3247 templin-intarea-vet-40 (work in progress), May 2013. 3249 [I-D.templin-ironbis] 3250 Templin, F., "The Interior Routing Overlay Network 3251 (IRON)", draft-templin-ironbis-16 (work in progress), 3252 March 2014. 3254 [I-D.templin-v6ops-pdhost] 3255 Templin, F., "IPv6 Prefix Delegation and Multi-Addressing 3256 Models", draft-templin-v6ops-pdhost-25 (work in progress), 3257 January 2020. 3259 [OVPN] OpenVPN, O., "http://openvpn.net", October 2016. 3261 [RFC1035] Mockapetris, P., "Domain names - implementation and 3262 specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, 3263 November 1987, . 3265 [RFC1122] Braden, R., Ed., "Requirements for Internet Hosts - 3266 Communication Layers", STD 3, RFC 1122, 3267 DOI 10.17487/RFC1122, October 1989, 3268 . 3270 [RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191, 3271 DOI 10.17487/RFC1191, November 1990, 3272 . 3274 [RFC1812] Baker, F., Ed., "Requirements for IP Version 4 Routers", 3275 RFC 1812, DOI 10.17487/RFC1812, June 1995, 3276 . 3278 [RFC2003] Perkins, C., "IP Encapsulation within IP", RFC 2003, 3279 DOI 10.17487/RFC2003, October 1996, 3280 . 3282 [RFC2236] Fenner, W., "Internet Group Management Protocol, Version 3283 2", RFC 2236, DOI 10.17487/RFC2236, November 1997, 3284 . 3286 [RFC2492] Armitage, G., Schulter, P., and M. Jork, "IPv6 over ATM 3287 Networks", RFC 2492, DOI 10.17487/RFC2492, January 1999, 3288 . 3290 [RFC2529] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4 3291 Domains without Explicit Tunnels", RFC 2529, 3292 DOI 10.17487/RFC2529, March 1999, 3293 . 3295 [RFC2764] Gleeson, B., Lin, A., Heinanen, J., Armitage, G., and A. 3296 Malis, "A Framework for IP Based Virtual Private 3297 Networks", RFC 2764, DOI 10.17487/RFC2764, February 2000, 3298 . 3300 [RFC2784] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P. 3301 Traina, "Generic Routing Encapsulation (GRE)", RFC 2784, 3302 DOI 10.17487/RFC2784, March 2000, 3303 . 3305 [RFC2890] Dommety, G., "Key and Sequence Number Extensions to GRE", 3306 RFC 2890, DOI 10.17487/RFC2890, September 2000, 3307 . 3309 [RFC2923] Lahey, K., "TCP Problems with Path MTU Discovery", 3310 RFC 2923, DOI 10.17487/RFC2923, September 2000, 3311 . 3313 [RFC2983] Black, D., "Differentiated Services and Tunnels", 3314 RFC 2983, DOI 10.17487/RFC2983, October 2000, 3315 . 3317 [RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition 3318 of Explicit Congestion Notification (ECN) to IP", 3319 RFC 3168, DOI 10.17487/RFC3168, September 2001, 3320 . 3322 [RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener 3323 Discovery Version 2 (MLDv2) for IPv6", RFC 3810, 3324 DOI 10.17487/RFC3810, June 2004, 3325 . 3327 [RFC3819] Karn, P., Ed., Bormann, C., Fairhurst, G., Grossman, D., 3328 Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J., and L. 3329 Wood, "Advice for Internet Subnetwork Designers", BCP 89, 3330 RFC 3819, DOI 10.17487/RFC3819, July 2004, 3331 . 3333 [RFC4213] Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms 3334 for IPv6 Hosts and Routers", RFC 4213, 3335 DOI 10.17487/RFC4213, October 2005, 3336 . 3338 [RFC4251] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH) 3339 Protocol Architecture", RFC 4251, DOI 10.17487/RFC4251, 3340 January 2006, . 3342 [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A 3343 Border Gateway Protocol 4 (BGP-4)", RFC 4271, 3344 DOI 10.17487/RFC4271, January 2006, 3345 . 3347 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 3348 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 3349 2006, . 3351 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 3352 Internet Protocol", RFC 4301, DOI 10.17487/RFC4301, 3353 December 2005, . 3355 [RFC4380] Huitema, C., "Teredo: Tunneling IPv6 over UDP through 3356 Network Address Translations (NATs)", RFC 4380, 3357 DOI 10.17487/RFC4380, February 2006, 3358 . 3360 [RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery 3361 Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April 3362 2006, . 3364 [RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet 3365 Control Message Protocol (ICMPv6) for the Internet 3366 Protocol Version 6 (IPv6) Specification", STD 89, 3367 RFC 4443, DOI 10.17487/RFC4443, March 2006, 3368 . 3370 [RFC4511] Sermersheim, J., Ed., "Lightweight Directory Access 3371 Protocol (LDAP): The Protocol", RFC 4511, 3372 DOI 10.17487/RFC4511, June 2006, 3373 . 3375 [RFC4541] Christensen, M., Kimball, K., and F. Solensky, 3376 "Considerations for Internet Group Management Protocol 3377 (IGMP) and Multicast Listener Discovery (MLD) Snooping 3378 Switches", RFC 4541, DOI 10.17487/RFC4541, May 2006, 3379 . 3381 [RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick, 3382 "Internet Group Management Protocol (IGMP) / Multicast 3383 Listener Discovery (MLD)-Based Multicast Forwarding 3384 ("IGMP/MLD Proxying")", RFC 4605, DOI 10.17487/RFC4605, 3385 August 2006, . 3387 [RFC4607] Holbrook, H. and B. Cain, "Source-Specific Multicast for 3388 IP", RFC 4607, DOI 10.17487/RFC4607, August 2006, 3389 . 3391 [RFC4963] Heffner, J., Mathis, M., and B. Chandler, "IPv4 Reassembly 3392 Errors at High Data Rates", RFC 4963, 3393 DOI 10.17487/RFC4963, July 2007, 3394 . 3396 [RFC4982] Bagnulo, M. and J. Arkko, "Support for Multiple Hash 3397 Algorithms in Cryptographically Generated Addresses 3398 (CGAs)", RFC 4982, DOI 10.17487/RFC4982, July 2007, 3399 . 3401 [RFC5015] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano, 3402 "Bidirectional Protocol Independent Multicast (BIDIR- 3403 PIM)", RFC 5015, DOI 10.17487/RFC5015, October 2007, 3404 . 3406 [RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site 3407 Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214, 3408 DOI 10.17487/RFC5214, March 2008, 3409 . 3411 [RFC5320] Templin, F., Ed., "The Subnetwork Encapsulation and 3412 Adaptation Layer (SEAL)", RFC 5320, DOI 10.17487/RFC5320, 3413 February 2010, . 3415 [RFC5522] Eddy, W., Ivancic, W., and T. Davis, "Network Mobility 3416 Route Optimization Requirements for Operational Use in 3417 Aeronautics and Space Exploration Mobile Networks", 3418 RFC 5522, DOI 10.17487/RFC5522, October 2009, 3419 . 3421 [RFC5558] Templin, F., Ed., "Virtual Enterprise Traversal (VET)", 3422 RFC 5558, DOI 10.17487/RFC5558, February 2010, 3423 . 3425 [RFC5569] Despres, R., "IPv6 Rapid Deployment on IPv4 3426 Infrastructures (6rd)", RFC 5569, DOI 10.17487/RFC5569, 3427 January 2010, . 3429 [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 3430 (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, 3431 . 3433 [RFC6106] Jeong, J., Park, S., Beloeil, L., and S. Madanapalli, 3434 "IPv6 Router Advertisement Options for DNS Configuration", 3435 RFC 6106, DOI 10.17487/RFC6106, November 2010, 3436 . 3438 [RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful 3439 NAT64: Network Address and Protocol Translation from IPv6 3440 Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146, 3441 April 2011, . 3443 [RFC6179] Templin, F., Ed., "The Internet Routing Overlay Network 3444 (IRON)", RFC 6179, DOI 10.17487/RFC6179, March 2011, 3445 . 3447 [RFC6221] Miles, D., Ed., Ooghe, S., Dec, W., Krishnan, S., and A. 3448 Kavanagh, "Lightweight DHCPv6 Relay Agent", RFC 6221, 3449 DOI 10.17487/RFC6221, May 2011, 3450 . 3452 [RFC6273] Kukec, A., Krishnan, S., and S. Jiang, "The Secure 3453 Neighbor Discovery (SEND) Hash Threat Analysis", RFC 6273, 3454 DOI 10.17487/RFC6273, June 2011, 3455 . 3457 [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer 3458 Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, 3459 January 2012, . 3461 [RFC6438] Carpenter, B. and S. Amante, "Using the IPv6 Flow Label 3462 for Equal Cost Multipath Routing and Link Aggregation in 3463 Tunnels", RFC 6438, DOI 10.17487/RFC6438, November 2011, 3464 . 3466 [RFC6706] Templin, F., Ed., "Asymmetric Extended Route Optimization 3467 (AERO)", RFC 6706, DOI 10.17487/RFC6706, August 2012, 3468 . 3470 [RFC6864] Touch, J., "Updated Specification of the IPv4 ID Field", 3471 RFC 6864, DOI 10.17487/RFC6864, February 2013, 3472 . 3474 [RFC7269] Chen, G., Cao, Z., Xie, C., and D. Binet, "NAT64 3475 Deployment Options and Experience", RFC 7269, 3476 DOI 10.17487/RFC7269, June 2014, 3477 . 3479 [RFC7333] Chan, H., Ed., Liu, D., Seite, P., Yokota, H., and J. 3480 Korhonen, "Requirements for Distributed Mobility 3481 Management", RFC 7333, DOI 10.17487/RFC7333, August 2014, 3482 . 3484 [RFC7421] Carpenter, B., Ed., Chown, T., Gont, F., Jiang, S., 3485 Petrescu, A., and A. Yourtchenko, "Analysis of the 64-bit 3486 Boundary in IPv6 Addressing", RFC 7421, 3487 DOI 10.17487/RFC7421, January 2015, 3488 . 3490 [RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I., 3491 Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent 3492 Multicast - Sparse Mode (PIM-SM): Protocol Specification 3493 (Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March 3494 2016, . 3496 [RFC8086] Yong, L., Ed., Crabbe, E., Xu, X., and T. Herbert, "GRE- 3497 in-UDP Encapsulation", RFC 8086, DOI 10.17487/RFC8086, 3498 March 2017, . 3500 [RFC8201] McCann, J., Deering, S., Mogul, J., and R. Hinden, Ed., 3501 "Path MTU Discovery for IP version 6", STD 87, RFC 8201, 3502 DOI 10.17487/RFC8201, July 2017, 3503 . 3505 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 3506 Decraene, B., Litkowski, S., and R. Shakir, "Segment 3507 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 3508 July 2018, . 3510 [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol 3511 Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, 3512 . 3514 Appendix A. AERO Alternate Encapsulations 3516 When GUE encapsulation is not needed, AERO can use common 3517 encapsulations such as IP-in-IP [RFC2003][RFC2473][RFC4213], Generic 3518 Routing Encapsulation (GRE) [RFC2784][RFC2890] and others. The 3519 encapsulation is therefore only differentiated from non-AERO tunnels 3520 through the application of AERO control messaging and not through, 3521 e.g., a well-known UDP port number. 3523 As for GUE encapsulation, alternate AERO encapsulation formats may 3524 require encapsulation layer fragmentation. For simple IP-in-IP 3525 encapsulation, an IPv6 fragment header is inserted directly between 3526 the inner and outer IP headers when needed, i.e., even if the outer 3527 header is IPv4. The IPv6 Fragment Header is identified to the outer 3528 IP layer by its IP protocol number, and the Next Header field in the 3529 IPv6 Fragment Header identifies the inner IP header version. For GRE 3530 encapsulation, a GRE fragment header is inserted within the GRE 3531 header [I-D.templin-intarea-grefrag]. 3533 Figure 6 shows the AERO IP-in-IP encapsulation format before any 3534 fragmentation is applied: 3536 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3537 | Outer IPv4 Header | | Outer IPv6 Header | 3538 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3539 |IPv6 Frag Header (optional)| |IPv6 Frag Header (optional)| 3540 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3541 | Inner IP Header | | Inner IP Header | 3542 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3543 | | | | 3544 ~ ~ ~ ~ 3545 ~ Inner Packet Body ~ ~ Inner Packet Body ~ 3546 ~ ~ ~ ~ 3547 | | | | 3548 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3550 Minimal Encapsulation in IPv4 Minimal Encapsulation in IPv6 3552 Figure 6: Minimal Encapsulation Format using IP-in-IP 3554 Figure 7 shows the AERO GRE encapsulation format before any 3555 fragmentation is applied: 3557 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3558 | Outer IP Header | 3559 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3560 | GRE Header | 3561 | (with checksum, key, etc..) | 3562 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3563 | GRE Fragment Header (optional)| 3564 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3565 | Inner IP Header | 3566 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3567 | | 3568 ~ ~ 3569 ~ Inner Packet Body ~ 3570 ~ ~ 3571 | | 3572 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3574 Figure 7: Minimal Encapsulation Using GRE 3576 Alternate encapsulation may be preferred in environments where GUE 3577 encapsulation would add unnecessary overhead. For example, certain 3578 low-bandwidth wireless data links may benefit from a reduced 3579 encapsulation overhead. 3581 GUE encapsulation can traverse network paths that are inaccessible to 3582 non-UDP encapsulations, e.g., for crossing Network Address 3583 Translators (NATs). More and more, network middleboxes are also 3584 being configured to discard packets that include anything other than 3585 a well-known IP protocol such as UDP and TCP. It may therefore be 3586 necessary to determine the potential for middlebox filtering before 3587 enabling alternate encapsulation in a given environment. 3589 In addition to IP-in-IP, GRE and GUE, AERO can also use security 3590 encapsulations such as IPsec, TLS/SSL, DTLS, etc. In that case, AERO 3591 control messaging and route determination occur before security 3592 encapsulation is applied for outgoing packets and after security 3593 decapsulation is applied for incoming packets. 3595 AERO is especially well suited for use with VPN system encapsulations 3596 such as OpenVPN [OVPN]. 3598 Appendix B. Non-Normative Considerations 3600 AERO can be applied to a multitude of Internetworking scenarios, with 3601 each having its own adaptations. The following considerations are 3602 provided as non-normative guidance: 3604 B.1. Implementation Strategies for Route Optimization 3606 Route optimization as discussed in Section 3.17 results in the route 3607 optimization source (ROS) creating an asymmetric neighbor cache entry 3608 for the target neighbor. The neighbor cache entry is maintained for 3609 at most REACHABLETIME seconds and then deleted unless updated. In 3610 order to refresh the neighbor cache entry lifetime before the 3611 ReachableTime timer expires, the specification requires 3612 implementations to issue a new NS/NA exchange to reset ReachableTime 3613 to REACHABLETIME seconds while data packets are still flowing. 3614 However, the decision of when to initiate a new NS/NA exchange and to 3615 perpetuate the process is left as an implementation detail. 3617 One possible strategy may be to monitor the neighbor cache entry 3618 watching for data packets for (REACHABLETIME - 5) seconds. If any 3619 data packets have been sent to the neighbor within this timeframe, 3620 then send an NS to receive a new NA. If no data packets have been 3621 sent, wait for 5 additional seconds and send an immediate NS if any 3622 data packets are sent within this "expiration pending" 5 second 3623 window. If no additional data packets are sent within the 5 second 3624 window, delete the neighbor cache entry. 3626 The monitoring of the neighbor data packet traffic therefore becomes 3627 an asymmetric ongoing process during the neighbor cache entry 3628 lifetime. If the neighbor cache entry expires, future data packets 3629 will trigger a new NS/NA exchange while the packets themselves are 3630 delivered over a longer path until route optimization state is re- 3631 established. 3633 B.2. Implicit Mobility Management 3635 AERO interface neighbors MAY provide a configuration option that 3636 allows them to perform implicit mobility management in which no ND 3637 messaging is used. In that case, the Client only transmits packets 3638 over a single interface at a time, and the neighbor always observes 3639 packets arriving from the Client from the same link-layer source 3640 address. 3642 If the Client's underlying interface address changes (either due to a 3643 readdressing of the original interface or switching to a new 3644 interface) the neighbor immediately updates the neighbor cache entry 3645 for the Client and begins accepting and sending packets according to 3646 the Client's new address. This implicit mobility method applies to 3647 use cases such as cellphones with both WiFi and Cellular interfaces 3648 where only one of the interfaces is active at a given time, and the 3649 Client automatically switches over to the backup interface if the 3650 primary interface fails. 3652 B.3. Direct Underlying Interfaces 3654 When a Client's AERO interface is configured over a Direct interface, 3655 the neighbor at the other end of the Direct link can receive packets 3656 without any encapsulation. In that case, the Client sends packets 3657 over the Direct link according to QoS preferences. If the Direct 3658 interface has the highest QoS preference, then the Client's IP 3659 packets are transmitted directly to the peer without going through an 3660 ANET/INET. If other interfaces have higher QoS preferences, then the 3661 Client's IP packets are transmitted via a different interface, which 3662 may result in the inclusion of Proxys, Servers and Relays in the 3663 communications path. Direct interfaces must be tested periodically 3664 for reachability, e.g., via NUD. 3666 B.4. Operation on AERO Links with /64 ASPs 3668 IPv6 AERO links typically have MSPs that aggregate many candidate 3669 MNPs of length /64 or shorter. However, in some cases it may be 3670 desirable to use AERO over links that have only a /64 MSP. This can 3671 be accommodated by treating all Clients on the AERO link as simple 3672 hosts that receive /128 prefix delegations. 3674 In that case, the Client sends an RS message to the Server the same 3675 as for ordinary AERO links. The Server responds with an RA message 3676 that includes one or more /128 prefixes (i.e., singleton addresses) 3677 that include the /64 MSP prefix along with an interface identifier 3678 portion to be assigned to the Client. The Client and Server then 3679 configure their AERO addresses based on the interface identifier 3680 portions of the /128s (i.e., the lower 64 bits) and not based on the 3681 /64 prefix (i.e., the upper 64 bits). 3683 For example, if the MSP for the host-only IPv6 AERO link is 3684 2001:db8:1000:2000::/64, each Client will receive one or more /128 3685 IPv6 prefix delegations such as 2001:db8:1000:2000::1/128, 3686 2001:db8:1000:2000::2/128, etc. When the Client receives the prefix 3687 delegations, it assigns the AERO addresses fe80::1, fe80::2, etc. to 3688 the AERO interface, and assigns the global IPv6 addresses (i.e., the 3689 /128s) to either the AERO interface or an internal virtual interface 3690 such as a loopback. In this arrangement, the Client conducts route 3691 optimization in the same sense as discussed in Section 3.17. 3693 This specification has applicability for nodes that act as a Client 3694 on an "upstream" AERO link, but also act as a Server on "downstream" 3695 AERO links. More specifically, if the node acts as a Client to 3696 receive a /64 prefix from the upstream AERO link it can then act as a 3697 Server to provision /128s to Clients on downstream AERO links. 3699 B.5. AERO Critical Infrastructure Considerations 3701 AERO Relays can be either Commercial off-the Shelf (COTS) standard IP 3702 routers or virtual machines in the cloud. Relays must be 3703 provisioned, supported and managed by the INET administrative 3704 authority, and connected to the Relays of other INETs via inter- 3705 domain peerings. Cost for purchasing, configuring and managing 3706 Relays is nominal even for very large AERO links. 3708 AERO Servers can be standard dedicated server platforms, but most 3709 often will be deployed as virtual machines in the cloud. The only 3710 requirements for Servers are that they can run the AERO user-level 3711 code and have at least one network interface connection to the INET. 3712 As with Relays, Servers must be provisioned, supported and managed by 3713 the INET administrative authority. Cost for purchasing, configuring 3714 and managing Servers is nominal especially for virtual Servers hosted 3715 in the cloud. 3717 AERO Proxys are most often standard dedicated server platforms with 3718 one network interface connected to the ANET and a second interface 3719 connected to an INET. As with Servers, the only requirements are 3720 that they can run the AERO user-level code and have at least one 3721 interface connection to the INET. Proxys must be provisioned, 3722 supported and managed by the ANET administrative authority. Cost for 3723 purchasing, configuring and managing Proxys is nominal, and borne by 3724 the ANET administrative authority. 3726 AERO Gateways can be any dedicated server or COTS router platform 3727 connected to INETs and/or EUNs. The Gateway joins the SPAN and 3728 engages in eBGP peering with one or more Relays as a stub AS. The 3729 Gateway then injects its MNPs and/or non-MNP prefixes into the BGP 3730 routing system, and provisions the prefixes to its downstream- 3731 attached networks. The Gateway can perform ROS/ROR services the same 3732 as for any Server, and can route between the MNP and non-MNP address 3733 spaces. 3735 B.6. AERO Server Failure Implications 3737 AERO Servers may appear as a single point of failure in the 3738 architecture, but such is not the case since all Servers on the link 3739 provide identical services and loss of a Server does not imply 3740 immediate and/or comprehensive communication failures. Although 3741 Clients typically associate with a single Server at a time, Server 3742 failure is quickly detected and conveyed by Bidirectional Forward 3743 Detection (BFD) and/or proactive NUD allowing Clients to migrate to 3744 new Servers. 3746 If a Server fails, ongoing packet forwarding to Clients will continue 3747 by virtue of the asymmetric neighbor cache entries that have already 3748 been established in route optimization sources (ROSs). If a Client 3749 also experiences mobility events at roughly the same time the Server 3750 fails, unsolicited NA messages may be lost but proxy neighbor cache 3751 entries in the DEPARTED state will ensure that packet forwarding to 3752 the Client's new locations will continue for up to DEPARTTIME 3753 seconds. 3755 If a Client is left without a Server for an extended timeframe (e.g., 3756 greater than REACHABLETIIME seconds) then existing asymmetric 3757 neighbor cache entries will eventually expire and both ongoing and 3758 new communications will fail. The original source will continue to 3759 retransmit until the Client has established a new Server 3760 relationship, after which time continuous communications will resume. 3762 Therefore, providing many Servers on the link with high availability 3763 profiles provides resilience against loss of individual Servers and 3764 assurance that Clients can establish new Server relationships quickly 3765 in event of a Server failure. 3767 B.7. AERO Client / Server Architecture 3769 The AERO architectural model is client / server in the control plane, 3770 with route optimization in the data plane. The same as for common 3771 Internet services, the AERO Client discovers the addresses of AERO 3772 Servers and selects one Server to connect to. The AERO service is 3773 analogous to common Internet services such as google.com, yahoo.com, 3774 cnn.com, etc. However, there is only one AERO service for the link 3775 and all Servers provide identical services. 3777 Common Internet services provide differing strategies for advertising 3778 server addresses to clients. The strategy is conveyed through the 3779 DNS resource records returned in response to name resolution queries. 3780 As of January 2020 Internet-based 'nslookup' services were used to 3781 determine the following: 3783 o When a client resolves the domainname "google.com", the DNS always 3784 returns one A record (i.e., an IPv4 address) and one AAAA record 3785 (i.e., an IPv6 address). The client receives the same addresses 3786 each time it resolves the domainname via the same DNS resolver, 3787 but may receive different addresses when it resolves the 3788 domainname via different DNS resolvers. But, in each case, 3789 exactly one A and one AAAA record are returned. 3791 o When a client resolves the domainname "ietf.org", the DNS always 3792 returns one A record and one AAAA record with the same addresses 3793 regardless of which DNS resolver is used. 3795 o When a client resolves the domainname "yahoo.com", the DNS always 3796 returns a list of 4 A records and 4 AAAA records. Each time the 3797 client resolves the domainname via the same DNS resolver, the same 3798 list of addresses are returned but in randomized order (i.e., 3799 consistent with a DNS round-robin strategy). But, interestingly, 3800 the same addresses are returned (albeit in randomized order) when 3801 the domainname is resolved via different DNS resolvers. 3803 o When a client resolves the domainname "amazon.com", the DNS always 3804 returns a list of 3 A records and no AAAA records. As with 3805 "yahoo.com", the same three A records are returned from any 3806 worldwide Internet connection point in randomized order. 3808 The above example strategies show differing approaches to Internet 3809 resilience and service distribution offered by major Internet 3810 services. The Google approach exposes only a single IPv4 and a 3811 single IPv6 address to clients. Clients can then select whichever IP 3812 protocol version offers the best response, but will always use the 3813 same IP address according to the current Internet connection point. 3814 This means that the IP address offered by the network must lead to a 3815 highly-available server and/or service distribution point. In other 3816 words, resilience is predicated on high availability within the 3817 network and with no client-initiated failovers expected (i.e., it is 3818 all-or-nothing from the client's perspective). However, Google does 3819 provide for worldwide distributed service distribution by virtue of 3820 the fact that each Internet connection point responds with a 3821 different IPv6 and IPv4 address. The IETF approach is like google 3822 (all-or-nothing from the client's perspective), but provides only a 3823 single IPv4 or IPv6 address on a worldwide basis. This means that 3824 the addresses must be made highly-available at the network level with 3825 no client failover possibility, and if there is any worldwide service 3826 distribution it would need to be conducted by a network element that 3827 is reached via the IP address acting as a service distribution point. 3829 In contrast to the Google and IETF philosophies, Yahoo and Amazon 3830 both provide clients with a (short) list of IP addresses with Yahoo 3831 providing both IP protocol versions and Amazon as IPv4-only. The 3832 order of the list is randomized with each name service query 3833 response, with the effect of round-robin load balancing for service 3834 distribution. With a short list of addresses, there is still 3835 expectation that the network will implement high availability for 3836 each address but in case any single address fails the client can 3837 switch over to using a different address. The balance then becomes 3838 one of function in the network vs function in the end system. 3840 The same implications observed for common highly-available services 3841 in the Internet apply also to the AERO client/server architecture. 3842 When an AERO Client connects to one or more ANETs, it discovers one 3843 or more AERO Server addresses through the mechanisms discussed in 3844 earlier sections. Each Server address presumably leads to a fault- 3845 tolerant clustering arrangement such as supported by Linux-HA, 3846 Extended Virtual Synchrony or Paxos. Such an arrangement has 3847 precedence in common Internet service deployments in lightweight 3848 virtual machines without requiring expensive hardware deployment. 3849 Similarly, common Internet service deployments set service IP 3850 addresses on service distribution points that may relay requests to 3851 many different servers. 3853 For AERO, the expectation is that a combination of the Google/IETF 3854 and Yahoo/Amazon philosophies would be employed. The AERO Client 3855 connects to different ANET access points and can receive 1-2 Server 3856 AERO addresses at each point. It then selects one AERO Server 3857 address, and engages in RS/RA exchanges with the same Server from all 3858 ANET connections. The Client remains with this Server unless or 3859 until the Server fails, in which case it can switch over to an 3860 alternate Server. The Client can likewise switch over to a different 3861 Server at any time if there is some reason for it to do so. So, the 3862 AERO expectation is for a balance of function in the network and end 3863 system, with fault tolerance and resilience at both levels. 3865 Appendix C. Change Log 3867 << RFC Editor - remove prior to publication >> 3869 Changes from draft-templin-intarea-6706bis-35 to draft-templin- 3870 intrea-6706bis-36: 3872 o Clients in the open Internet secured using SEND/CGA. 3874 Changes from draft-templin-intarea-6706bis-32 to draft-templin- 3875 intrea-6706bis-33: 3877 o Updated Proxy discussion with "point-to-multipoint" server 3878 coordination 3880 o Significant updates to Address Resolution and NUD to include 3881 correct addresses in messages 3883 o Differentiate between NS(AR) and NS(NUD) as their addresses and 3884 use cases differ. 3886 Changes from draft-templin-intarea-6706bis-30 to draft-templin- 3887 intrea-6706bis-31: 3889 o Added "advisory PTB messages" under FAA SE2025 contract number 3890 DTFAWA-15-D-00030. 3892 Changes from draft-templin-intarea-6706bis-29 to draft-templin- 3893 intrea-6706bis-30: 3895 o Deprecate "primary" concept. Now, RS/RA keepalives are 3896 mainatained over *all* underlying interfaces (i.e., and not just 3897 one primary). 3899 Changes from draft-templin-intarea-6706bis-28 to draft-templin- 3900 intrea-6706bis-29: 3902 o Changed OMNI interface citation to "draft-templin-6man-omni- 3903 interface" 3905 o Changed SPAN Service Prefix to fd80::/10. 3907 o Changed S/TLLAO format to include 'S' bit for ifIndex 3908 corresponding to the underlying interface that is Source of ND 3909 message. 3911 o Updated Path MTU 3913 Changes from draft-templin-intarea-6706bis-27 to draft-templin- 3914 intrea-6706bis-28: 3916 o MTU and fragmentation. 3918 Changes from draft-templin-intarea-6706bis-26 to draft-templin- 3919 intrea-6706bis-27: 3921 o MTU and fragmentation. 3923 o SPAN Service Prefix set to fd00::/10 3925 o Client SPAN addresses defined. 3927 Changes from draft-templin-intarea-6706bis-25 to draft-templin- 3928 intrea-6706bis-26: 3930 o MTU and RA configuration information updated. 3932 Changes from draft-templin-intarea-6706bis-24 to draft-templin- 3933 intrea-6706bis-25: 3935 o Added concept of "primary" to allow for proxyed RS/RA over only 3936 selected underlying interfaces. 3938 o General Cleanup. 3940 Changes from draft-templin-intarea-6706bis-23 to draft-templin- 3941 intrea-6706bis-24: 3943 o OMNI interface spec now a normative reference. 3945 o Use REACHABLETIME as the nominal Router Lifetime to return in RAs. 3947 o General cleanup. 3949 Changes from draft-templin-intarea-6706bis-22 to draft-templin- 3950 intrea-6706bis-23: 3952 o Choice of using either RS/RA or unsolicited NA for old Server 3953 notification. 3955 o General cleanup. 3957 Changes from draft-templin-intarea-6706bis-21 to draft-templin- 3958 intrea-6706bis-22: 3960 o Tightened up text on Proxy. 3962 o Removed unnecessarily restrictive texts. 3964 o General cleanup. 3966 Changes from draft-templin-intarea-6706bis-20 to draft-templin- 3967 intrea-6706bis-21: 3969 o Clarified relationship between OMNI and S/TLLAO ifIndex-tuples. 3971 o Important text in Section 13.15.3 on Servers timing out Clients 3972 that have gone silent without sending a departure notification. 3974 o New text on RS/RA as "hints of forward progress" for proactive 3975 NUD. 3977 Changes from draft-templin-intarea-6706bis-19 to draft-templin- 3978 intrea-6706bis-20: 3980 o Included new route optimization source and destination addressing 3981 strategy. Now, route optimization maintenance uses the address of 3982 the existing Server instead of the data packet destination address 3983 so that less pressure is placed on the BGP routing system 3984 convergence time and Server constancy is supported. 3986 o Included new method for releasing from old MSE without requiring 3987 Client messaging. 3989 o Included references to new OMNI interface spec (including the OMNI 3990 option). 3992 o New appendix on AERO Client/Server architecture. 3994 Changes from draft-templin-intarea-6706bis-18 to draft-templin- 3995 intrea-6706bis-19: 3997 o Changed Proxy/Server keepalives to use "proactive NUD" in a manner 3998 tha paralles BFD 4000 Changes from draft-templin-intarea-6706bis-17 to draft-templin- 4001 intrea-6706bis-18: 4003 o Discuss how AERO option is used in relation to S/TLLAOs 4005 o New text on Bidirectional Forwarding Detection (BFD) 4007 o Cleaned up usage (and non-usage) of unsolicited NAs 4009 o New appendix on Server failures 4011 Changes from draft-templin-intarea-6706bis-15 to draft-templin- 4012 intrea-6706bis-17: 4014 o S/TLLAO now includes multiple link-layer addresses within a single 4015 option instead of requiring multiple options 4017 o New unsolicited NA message to inform the old link that a Client 4018 has moved to a new link 4020 Changes from draft-templin-intarea-6706bis-14 to draft-templin- 4021 intrea-6706bis-15: 4023 o MTU and fragmentation 4025 o New details in movement to new Server 4027 Changes from draft-templin-intarea-6706bis-13 to draft-templin- 4028 intrea-6706bis-14: 4030 o Security based on secured tunnels, ingress filtering, MAP list and 4031 ROS list 4033 Changes from draft-templin-intarea-6706bis-12 to draft-templin- 4034 intrea-6706bis-13: 4036 o New paragraph in Section 3.6 on AERO interface layering over 4037 secured tunnels 4039 o Removed extraneous text in Section 3.7 4041 o Added new detail to the forwarding algorithm in Section 3.9 4043 o Clarified use of fragmentation 4045 o Route optimization now supported for both MNP and non-MNP-based 4046 prefixes 4048 o Relays are now seen as link-layer elements in the architecture. 4050 o Built out multicast section in detail. 4052 o New Appendix on implementation considerations for route 4053 optimization. 4055 Changes from draft-templin-intarea-6706bis-11 to draft-templin- 4056 intrea-6706bis-12: 4058 o Introduced Gateways as a new AERO element for connecting 4059 Correspondent Nodes on INET links 4061 o Introduced terms "Access Network (ANET)" and "Internetwork (INET)" 4063 o Changed "ASP" to "MSP", and "ACP" to "MNP" 4065 o New figure on the relation of Segments to the SPAN and AERO link 4067 o New "S" bit in S/TLLAO to indicate the "Source" S/TLLAO as opposed 4068 to additional S/TLLAOs 4070 o Changed Interface ID for Servers from 255 to 0xffff 4072 o Significant updates to Route Optimization, NUD, and Mobility 4073 Management 4075 o New Section on Multicast 4077 o New Section on AERO Clients in the open Internetwork 4079 o New Section on Operation over multiple AERO links (VLANs over the 4080 SPAN) 4082 o New Sections on DNS considerations and Transition considerations 4083 o 4085 Changes from draft-templin-intarea-6706bis-10 to draft-templin- 4086 intrea-6706bis-11: 4088 o Added The SPAN 4090 Changes from draft-templin-intarea-6706bis-09 to draft-templin- 4091 intrea-6706bis-10: 4093 o Orphaned packets in flight (e.g., when a neighbor cache entry is 4094 in the DEPARTED state) are now forwarded at the link layer instead 4095 of at the network layer. Forwarding at the network layer can 4096 result in routing loops and/or excessive delays of forwarded 4097 packets while the routing system is still reconverging. 4099 o Update route optimization to clarify the unsecured nature of the 4100 first NS used for route discovery 4102 o Many cleanups and clarifications on ND messaging parameters 4104 Changes from draft-templin-intarea-6706bis-08 to draft-templin- 4105 intrea-6706bis-09: 4107 o Changed PRL to "MAP list" 4109 o For neighbor cache entries, changed "static" to "symmetric", and 4110 "dynamic" to "asymmetric" 4112 o Specified Proxy RS/RA exchanges with Servers on behalf of Clients 4114 o Added discussion of unsolicited NAs in Section 3.16, and included 4115 forward reference to Section 3.18 4117 o Added discussion of AERO Clients used as critical infrastructure 4118 elements to connect fixed networks. 4120 o Added network-based VPN under security considerations 4122 Changes from draft-templin-intarea-6706bis-07 to draft-templin- 4123 intrea-6706bis-08: 4125 o New section on AERO-Aware Access Router 4127 Changes from draft-templin-intarea-6706bis-06 to draft-templin- 4128 intrea-6706bis-07: 4130 o Added "R" bit for release of PDs. Now have a full RS/RA service 4131 that can do PD without requiring DHCPv6 messaging over-the-air 4133 o Clarifications on solicited vs unsolicited NAs 4135 o Clarified use of MAX_NEIGHBOR_ADVERTISEMENTS for the purpose of 4136 increase reliability 4138 Changes from draft-templin-intarea-6706bis-05 to draft-templin- 4139 intrea-6706bis-06: 4141 o Major re-work and simplification of Route Optimization function 4143 o Added Distributed Mobility Management (DMM) and Mobility Anchor 4144 Point (MAP) terminology 4146 o New section on "AERO Critical Infrastructure Element 4147 Considerations" demonstrating low overall cost for the service 4149 o minor text revisions and deletions 4151 o removed extraneous appendices 4153 Changes from draft-templin-intarea-6706bis-04 to draft-templin- 4154 intrea-6706bis-05: 4156 o New Appendix E on S/TLLAO Extensions for special-purpose links. 4157 Discussed ATN/IPS as example. 4159 o New sentence in introduction to declare appendices as non- 4160 normative. 4162 Changes from draft-templin-intarea-6706bis-03 to draft-templin- 4163 intrea-6706bis-04: 4165 o Added definitions for Potential Router List (PRL) and secure 4166 enclave 4168 o Included text on mapping transport layer port numbers to network 4169 layer DSCP values 4171 o Added reference to DTLS and DMM Distributed Mobility Anchoring 4172 working group document 4174 o Reworked Security Considerations 4176 o Updated references. 4178 Changes from draft-templin-intarea-6706bis-02 to draft-templin- 4179 intrea-6706bis-03: 4181 o Added new section on SEND. 4183 o Clarifications on "AERO Address" section. 4185 o Updated references and added new reference for RFC8086. 4187 o Security considerations updates. 4189 o General text clarifications and cleanup. 4191 Changes from draft-templin-intarea-6706bis-01 to draft-templin- 4192 intrea-6706bis-02: 4194 o Note on encapsulation avoidance in Section 4. 4196 Changes from draft-templin-intarea-6706bis-00 to draft-templin- 4197 intrea-6706bis-01: 4199 o Remove DHCPv6 Server Release procedures that leveraged the old way 4200 Relays used to "route" between Server link-local addresses 4202 o Remove all text relating to Relays needing to do any AERO-specific 4203 operations 4205 o Proxy sends RS and receives RA from Server using SEND. Use CGAs 4206 as source addresses, and destination address of RA reply is to the 4207 AERO address corresponding to the Client's ACP. 4209 o Proxy uses SEND to protect RS and authenticate RA (Client does not 4210 use SEND, but rather relies on subnetwork security. When the 4211 Proxy receives an RS from the Client, it creates a new RS using 4212 its own addresses as the source and uses SEND with CGAs to send a 4213 new RS to the Server. 4215 o Emphasize distributed mobility management 4217 o AERO address-based RS injection of ACP into underlying routing 4218 system. 4220 Changes from draft-templin-aerolink-82 to draft-templin-intarea- 4221 6706bis-00: 4223 o Document use of NUD (NS/NA) for reliable link-layer address 4224 updates as an alternative to unreliable unsolicited NA. 4225 Consistent with Section 7.2.6 of RFC4861. 4227 o Server adds additional layer of encapsulation between outer and 4228 inner headers of NS/NA messages for transmission through Relays 4229 that act as vanilla IPv6 routers. The messages include the AERO 4230 Server Subnet Router Anycast address as the source and the Subnet 4231 Router Anycast address corresponding to the Client's ACP as the 4232 destination. 4234 o Clients use Subnet Router Anycast address as the encapsulation 4235 source address when the access network does not provide a 4236 topologically-fixed address. 4238 Author's Address 4240 Fred L. Templin (editor) 4241 Boeing Research & Technology 4242 P.O. Box 3707 4243 Seattle, WA 98124 4244 USA 4246 Email: fltemplin@acm.org