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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group F. Templin, Ed. 3 Internet-Draft Boeing Research & Technology 4 Obsoletes: rfc5320, rfc5558, rfc5720, June 6, 2019 5 rfc6179, rfc6706 (if 6 approved) 7 Intended status: Standards Track 8 Expires: December 8, 2019 10 Asymmetric Extended Route Optimization (AERO) 11 draft-templin-intarea-6706bis-15.txt 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 services are employed for network admission and to 20 manage the routing system. Multilink operation, mobility management, 21 quality of service (QoS) signaling and route optimization are 22 naturally supported through dynamic neighbor cache updates. Standard 23 IP multicasting services are also supported. AERO is a widely- 24 applicable tunneling solution especially well-suited to aviation 25 services, mobile Virtual Private Networks (VPNs) and many other 26 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 December 8, 2019. 45 Copyright Notice 47 Copyright (c) 2019 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 . . . . . . . . . . . . . . . . . . . . . . . . 3 63 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 64 3. Asymmetric Extended Route Optimization (AERO) . . . . . . . . 10 65 3.1. AERO Link Reference Model . . . . . . . . . . . . . . . . 10 66 3.2. AERO Node Types . . . . . . . . . . . . . . . . . . . . . 12 67 3.3. AERO Routing System . . . . . . . . . . . . . . . . . . . 13 68 3.4. AERO Addresses . . . . . . . . . . . . . . . . . . . . . 15 69 3.5. Spanning Partitioned AERO Networks (SPAN) . . . . . . . . 17 70 3.6. AERO Interface Characteristics . . . . . . . . . . . . . 21 71 3.7. AERO Interface Initialization . . . . . . . . . . . . . . 24 72 3.7.1. AERO Server/Gateway Behavior . . . . . . . . . . . . 25 73 3.7.2. AERO Proxy Behavior . . . . . . . . . . . . . . . . . 25 74 3.7.3. AERO Client Behavior . . . . . . . . . . . . . . . . 25 75 3.7.4. AERO Relay Behavior . . . . . . . . . . . . . . . . . 26 76 3.8. AERO Interface Neighbor Cache Maintenance . . . . . . . . 26 77 3.9. AERO Interface Encapsulation and Re-encapsulation . . . . 28 78 3.10. AERO Interface Decapsulation . . . . . . . . . . . . . . 29 79 3.11. AERO Interface Data Origin Authentication . . . . . . . . 29 80 3.12. AERO Interface Forwarding Algorithm . . . . . . . . . . . 30 81 3.12.1. Client Forwarding Algorithm . . . . . . . . . . . . 31 82 3.12.2. Proxy Forwarding Algorithm . . . . . . . . . . . . . 31 83 3.12.3. Server/Gateway Forwarding Algorithm . . . . . . . . 32 84 3.12.4. Relay Forwarding Algorithm . . . . . . . . . . . . . 34 85 3.13. AERO Interface MTU and Fragmentation . . . . . . . . . . 34 86 3.14. AERO Interface Error Handling . . . . . . . . . . . . . . 36 87 3.15. AERO Router Discovery, Prefix Delegation and 88 Autoconfiguration . . . . . . . . . . . . . . . . . . . . 40 89 3.15.1. AERO ND/PD Service Model . . . . . . . . . . . . . . 40 90 3.15.2. AERO Client Behavior . . . . . . . . . . . . . . . . 40 91 3.15.3. AERO Server Behavior . . . . . . . . . . . . . . . . 43 92 3.16. The AERO Proxy . . . . . . . . . . . . . . . . . . . . . 45 93 3.17. AERO Route Optimization . . . . . . . . . . . . . . . . . 47 94 3.17.1. Route Optimization Initiation . . . . . . . . . . . 47 95 3.17.2. Relaying the NS . . . . . . . . . . . . . . . . . . 48 96 3.17.3. Processing the NS and Sending the NA . . . . . . . . 48 97 3.17.4. Relaying the NA . . . . . . . . . . . . . . . . . . 49 98 3.17.5. Processing the NA . . . . . . . . . . . . . . . . . 49 99 3.17.6. Route Optimization Maintenance . . . . . . . . . . . 49 100 3.18. Neighbor Unreachability Detection (NUD) . . . . . . . . . 50 101 3.19. Mobility Management and Quality of Service (QoS) . . . . 51 102 3.19.1. Mobility Update Messaging . . . . . . . . . . . . . 51 103 3.19.2. Announcing Link-Layer Address and/or QoS Preference 104 Changes . . . . . . . . . . . . . . . . . . . . . . 52 105 3.19.3. Bringing New Links Into Service . . . . . . . . . . 52 106 3.19.4. Removing Existing Links from Service . . . . . . . . 53 107 3.19.5. Moving to a New Server . . . . . . . . . . . . . . . 53 108 3.20. Multicast . . . . . . . . . . . . . . . . . . . . . . . . 54 109 3.20.1. Source-Specific Multicast (SSM) . . . . . . . . . . 54 110 3.20.2. Any-Source Multicast (ASM) . . . . . . . . . . . . . 56 111 3.20.3. Bi-Directional PIM (BIDIR-PIM) . . . . . . . . . . . 57 112 3.21. Operation over Multiple AERO Links (VLANs) . . . . . . . 57 113 3.22. DNS Considerations . . . . . . . . . . . . . . . . . . . 58 114 3.23. Transition Considerations . . . . . . . . . . . . . . . . 58 115 4. Implementation Status . . . . . . . . . . . . . . . . . . . . 59 116 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 59 117 6. Security Considerations . . . . . . . . . . . . . . . . . . . 59 118 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 61 119 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 62 120 8.1. Normative References . . . . . . . . . . . . . . . . . . 62 121 8.2. Informative References . . . . . . . . . . . . . . . . . 64 122 Appendix A. AERO Alternate Encapsulations . . . . . . . . . . . 70 123 Appendix B. S/TLLAO Extensions for Special-Purpose Links . . . . 72 124 Appendix C. Non-Normative Considerations . . . . . . . . . . . . 73 125 C.1. Implementation Strategies for Route Optimization . . . . 73 126 C.2. Implicit Mobility Management . . . . . . . . . . . . . . 74 127 C.3. Direct Underlying Interfaces . . . . . . . . . . . . . . 74 128 C.4. AERO Clients on the Open Internetwork . . . . . . . . . . 75 129 C.5. Operation on AERO Links with /64 ASPs . . . . . . . . . . 75 130 C.6. AERO Adaptations for SEcure Neighbor Discovery (SEND) . . 76 131 C.7. AERO Critical Infrastructure Considerations . . . . . . . 76 132 Appendix D. Change Log . . . . . . . . . . . . . . . . . . . . . 77 133 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 82 135 1. Introduction 137 Asymmetric Extended Route Optimization (AERO) fulfills the 138 requirements of Distributed Mobility Management (DMM) [RFC7333] and 139 route optimization [RFC5522] for aeronautical networking and other 140 network mobility use cases. AERO is based on a Non-Broadcast, 141 Multiple Access (NBMA) virtual link model known as the AERO link. 142 The AERO link is configured over one or more underlying 143 Internetworks, and nodes on the link can exchange IP packets via 144 tunneling. Multilink operation allows for increased reliability, 145 bandwidth optimization and traffic path diversity. 147 The AERO service comprises Clients, Proxys, Servers, and Gateways 148 that are seen as AERO link neighbors. Each node's AERO interface 149 uses an IPv6 link-local address format (known as the AERO address) 150 that supports operation of the IPv6 Neighbor Discovery (ND) protocol 151 [RFC4861] and links ND to IP forwarding. A node's AERO interface can 152 be configured over multiple underlying interfaces, and may therefore 153 may appear as a single interface with multiple link-layer addresses. 154 Each link-layer address is subject to change due to mobility and/or 155 QoS fluctuations, and link-layer address changes are signaled by ND 156 messaging the same as for any IPv6 link. 158 AERO links provide a cloud-based service where mobile nodes may use 159 any Server acting as a Mobility Anchor Point (MAP) and fixed nodes 160 may use any Gateway on the link for efficient communications. Fixed 161 nodes forward packets destined to other AERO nodes to the nearest 162 Gateway, which forwards them through the cloud. A mobile node's 163 initial packets are forwarded through the MAP, while direct routing 164 is supported through asymmetric route optimization while data packets 165 are flowing. Both unicast and multicast communications are 166 supported, and mobile nodes may efficiently move between locations 167 while maintaining continuous communications with correspondents and 168 without changing their IP Address. 170 AERO Relays are interconnected in a secured private BGP overlay 171 routing instance known as the "SPAN". The SPAN provides a hybrid 172 routing/bridging service to join the underlying Internetworks of 173 multiple disjoint administrative domains into a single unified AERO 174 link. Each AERO link instance is characterized by the set of 175 Mobility Service Prefixes (MSPs) common to all mobile nodes. The 176 link should extend to the point where a Gateway/MAP is on the optimal 177 route from any correspondent node on the link, and provides a gateway 178 between the underlying Internetwork and the SPAN. To the underlying 179 Internetwork, the Gateway/MAP is the source of a route to its MSP, 180 and hence uplink traffic to the mobile node is naturally routed to 181 the nearest Gateway/MAP. 183 AERO assumes the use of PIM Sparse Mode in support of multicast 184 communication. In support of Source Specific Multicast (SSM) when a 185 Mobile Node is the source, AERO route optimization ensures that a 186 shortest-path multicast tree is established with provisions for 187 mobility and multilink operation. In all other multicast scenarios 188 there are no AERO dependencies. 190 AERO was designed for aeronautical networking for both manned and 191 unmanned aircraft, where the aircraft is treated as a mobile node 192 that can connect an Internet of Things (IoT). AERO is also 193 applicable to a wide variety of other use cases. For example, it can 194 be used to coordinate the Virtual Private Network (VPN) links of 195 mobile nodes (e.g., cellphones, tablets, laptop computers, etc.) that 196 connect into a home enterprise network via public access networks 197 using services such as OpenVPN [OVPN]. Other applicable use cases 198 are also in scope. 200 The following numbered sections present the AERO specification. The 201 appendices at the end of the document are non-normative. 203 2. Terminology 205 The terminology in the normative references applies; the following 206 terms are defined within the scope of this document: 208 IPv6 Neighbor Discovery (ND) 209 an IPv6 control message service for coordinating neighbor 210 relationships between nodes connected to a common link. AERO 211 interfaces use the ND service specified in [RFC4861]. 213 IPv6 Prefix Delegation (PD) 214 a networking service for delegating IPv6 prefixes to nodes on the 215 link. The nominal PD service is DHCPv6 [RFC8415], however 216 alternate services (e.g., based on ND messaging) are also in scope 217 [I-D.templin-v6ops-pdhost][I-D.templin-6man-dhcpv6-ndopt]. Most 218 notably, a form of PD known as "Prefix Assertion" can be used if 219 the prefix can be represented in the IPv6 source address of an ND 220 message. 222 Access Network (ANET) 223 a node's first-hop data link service network, e.g., a radio access 224 network, cellular service provider network, corporate enterprise 225 network, or the public Internet itself. For secured ANETs, link- 226 layer security services such as IEEE 802.1X and physical-layer 227 security prevent unauthorized access internally while border 228 network-layer security services such as firewalls and proxies 229 prevent unauthorized outside access. 231 ANET interface 232 a node's attachment to a link in an ANET. 234 ANET address 235 an IP address assigned to a node's interface connection to an 236 ANET. 238 Internetwork (INET) 239 a connected IP network topology with a coherent routing and 240 addressing plan and that provides an Internetworking backbone 241 service. INETs also provide an underlay service over which the 242 AERO virtual link is configured. Example INETs include corporate 243 enterprise networks, aviation networks, and the public Internet 244 itself. When there is no administrative boundary between an ANET 245 and the INET, the ANET and INET are one and the same. 247 INET Partition 248 frequently, INETs such as large corporate enterprise networks are 249 sub-divided internally into separate isolated partitions. Each 250 partition is fully connected internally but disconnected form 251 other partitions, and there is no requirement that separate 252 partitions maintain consistent Internet Protocol and/or addressing 253 plans. (An INET partition is the same as a SPAN segment discussed 254 below.) 256 INET interface 257 a node's attachment to a link in an INET. 259 INET address 260 an IP address assigned to a node's interface connection to an 261 INET. 263 AERO link 264 a Non-Broadcast, Multiple Access (NBMA) tunnel virtual overlay 265 configured over one or more underlying INETs. Nodes on the AERO 266 link appear as single-hop neighbors from the perspective of the 267 virtual overlay even though they may be separated by many 268 underlying INET hops. AERO links may be configured over multiple 269 underlying SPAN segments (see below). 271 AERO interface 272 a node's attachment to an AERO link. Since the addresses assigned 273 to an AERO interface are managed for uniqueness, AERO interfaces 274 do not require Duplicate Address Detection (DAD) and therefore set 275 the administrative variable 'DupAddrDetectTransmits' to zero 276 [RFC4862]. 278 AERO address 279 an IPv6 link-local address assigned to an AERO interface and 280 constructed as specified in Section 3.4. 282 base AERO address 283 the lowest-numbered AERO address aggregated by the MNP (see 284 Section 3.4). 286 Mobility Service Prefix (MSP) 287 an IP prefix assigned to the AERO link and from which more- 288 specific Mobile Network Prefixes (MNPs) are derived. 290 Mobile Network Prefix (MNP) 291 an IP prefix allocated from an MSP and delegated to an AERO Client 292 or Gateway. 294 AERO node 295 a node that is connected to an AERO link, or that provides 296 services to other nodes on an AERO link. 298 AERO Client ("Client") 299 an AERO node that connects to one or more ANETs and requests MNP 300 PDs from AERO Servers. Following PD, the Client assigns a Client 301 AERO address to the AERO interface for use in ND exchanges with 302 other AERO nodes and forwards packets to correspondents according 303 to AERO interface neighbor cache state. 305 AERO Server ("Server") 306 an INET node that configures an AERO interface to provide default 307 forwarding services and a Mobility Anchor Point (MAP) for AERO 308 Clients. The Server assigns an administratively-provisioned AERO 309 address to the AERO interface to support the operation of the ND/ 310 PD services, and advertises all of its associated MNPs via BGP 311 peerings with Relays. 313 AERO Gateway ("Gateway") 314 an AERO Server that also provides forwarding services between 315 nodes reached via the AERO link and correspondents on other links. 316 AERO Gateways are provisioned with MNPs (i.e., the same as for an 317 AERO Client) and run a dynamic routing protocol to discover any 318 non-MNP IP routes. In both cases, the Gateway advertises the 319 MSP(s) over INET interfaces, and distributes all of its associated 320 MNPs and non-MNP IP routes via BGP peerings with Relays (i.e., the 321 same as for an AERO Server). 323 AERO Relay ("Relay") 324 a node that provides hybrid routing/bridging services (as well as 325 a security trust anchor) for nodes on an AERO link. As a router, 326 the Relay forwards packets using standard IP forwarding. As a 327 bridge, the Relay forwards packets over the AERO link without 328 decrementing the IPv6 Hop Limit. AERO Relays peer with Servers 329 and other Relays to discover the full set of MNPs for the link as 330 well as any non-MNPs that are reachable via Gateways. 332 AERO Proxy ("Proxy") 333 a node that provides proxying services between Clients in an ANET 334 and Servers in external INETs. The AERO Proxy is a conduit 335 between the ANET and external INETs in the same manner as for 336 common web proxies, and behaves in a similar fashion as for ND 337 proxies [RFC4389]. 339 Spanning Partitioned AERO Networks (SPAN) 340 a means for bridging disjoint INET partitions as segments of a 341 unified AERO link the same as for a bridged campus LAN. The SPAN 342 is a mid-layer IPv6 encapsulation service in the AERO routing 343 system that supports a unified AERO link view for all segments. 344 Each segment in the SPAN is a distinct INET partition. 346 SPAN Service Prefix (SSP) 347 a global or unique local /96 IPv6 prefix assigned to the AERO link 348 to support SPAN services. 350 SPAN Partition Prefix (SPP) 351 a sub-prefix of the SPAN Service Prefix uniquely assigned to a 352 single SPAN segment. 354 SPAN Address 355 a global or unique local IPv6 address taken from a SPAN Partition 356 Prefix and constructed as specified in Section 3.5. SPAN 357 addresses are statelessly derived from AERO addresses, and vice- 358 versa. 360 ingress tunnel endpoint (ITE) 361 an AERO interface endpoint that injects encapsulated packets into 362 an AERO link. 364 egress tunnel endpoint (ETE) 365 an AERO interface endpoint that receives encapsulated packets from 366 an AERO link. 368 link-layer address 369 an IP address used as an encapsulation header source or 370 destination address from the perspective of the AERO interface. 371 When UDP encapsulation is used, the UDP port number is also 372 considered as part of the link-layer address. From the 373 perspective of the AERO interface, the link-layer address is 374 either an INET address for intra-segment encapsulation or a SPAN 375 address for inter-segment encapsulation. 377 network layer address 378 the source or destination address of an encapsulated IP packet 379 presented to the AERO interface. 381 end user network (EUN) 382 an internal virtual or external edge IP network that an AERO 383 Client or Gateway connects to the rest of the network via the AERO 384 interface. The Client/Gateway sees each EUN as a "downstream" 385 network, and sees the AERO interface as the point of attachment to 386 the "upstream" network. 388 Mobile Node (MN) 389 an AERO Client and all of its downstream-attached networks that 390 move together as a single unit, i.e., an end system that connects 391 an Internet of Things. 393 Mobile Router (MR) 394 a MN's on-board router that forwards packets between any 395 downstream-attached networks and the AERO link. 397 Mobility Anchor Point (MAP) 398 an AERO Server that is currently tracking and reporting the 399 mobility events of its associated Mobile Node Clients. 401 Route Optimization Source (ROS) 402 the AERO node nearest the source that initiates route 403 optimization. The ROS may be a Server or Proxy acting on behalf 404 of the source Client. 406 Route Optimization responder (ROR) 407 the AERO node nearest the target destination that responds to 408 route optimization requests. The ROR may be a Server acting as a 409 MAP on behalf of a target MNP Client, or a Gateway for a non-MNP 410 destination. 412 MAP List 413 a geographically and/or topologically referenced list of AERO 414 addresses of all MAPs within the same AERO link. There is a 415 single MAP list for the entire AERO link. 417 ROS List 418 a list of AERO/SPAN-to-INET address mappings of all ROSes within 419 the same SPAN segment. There is a distinct ROS list for each 420 segment. 422 Distributed Mobility Management (DMM) 423 a BGP-based overlay routing service coordinated by Servers and 424 Relays that tracks all MAP-to-Client associations. 426 Throughout the document, the simple terms "Client", "Server", 427 "Relay", "Proxy" and "Gateway" refer to "AERO Client", "AERO Server", 428 "AERO Relay", "AERO Proxy" and "AERO Gateway", respectively. 430 Capitalization is used to distinguish these terms from other common 431 Internetworking uses in which they appear without capitalization. 433 The terminology of DHCPv6 [RFC8415] and IPv6 ND [RFC4861] (including 434 the names of node variables, messages and protocol constants) is used 435 throughout this document. Also, the term "IP" is used to generically 436 refer to either Internet Protocol version, i.e., IPv4 [RFC0791] or 437 IPv6 [RFC8200]. 439 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 440 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 441 document are to be interpreted as described in [RFC2119]. Lower case 442 uses of these words are not to be interpreted as carrying RFC2119 443 significance. 445 3. Asymmetric Extended Route Optimization (AERO) 447 The following sections specify the operation of IP over Asymmetric 448 Extended Route Optimization (AERO) links: 450 3.1. AERO Link Reference Model 451 +----------------+ 452 | AERO Relay R1 | 453 | Nbr: S1, S2, P1| 454 |(X1->S1; X2->S2)| 455 | MSP M1 | 456 +-+---------+--+-+ 457 +--------------+ | Secured | | +--------------+ 458 |AERO Server S1| | tunnels | | |AERO Server S2| 459 | Nbr: C1, R1 +-----+ | +-----+ Nbr: C2, R1 | 460 | default->R1 | | | default->R1 | 461 | X1->C1 | | | X2->C2 | 462 +-------+------+ | +------+-------+ 463 | AERO Link | | 464 X---+---+-------------------+--)---------------+---+---X 465 | | | | 466 +-----+--------+ +--------+--+-----+ +--------+-----+ 467 |AERO Client C1| | AERO Proxy P1 | |AERO Client C2| 468 | Nbr: S1 | |(Proxy Nbr Cache)| | Nbr: S2 | 469 | default->S1 | +--------+--------+ | default->S2 | 470 | MNP X1 | | | MNP X2 | 471 +------+-------+ .--------+------. +-----+--------+ 472 | (- Proxyed Clients -) | 473 .-. `---------------' .-. 474 ,-( _)-. ,-( _)-. 475 .-(_ IP )-. +-------+ +-------+ .-(_ IP )-. 476 (__ EUN )--|Host H1| |Host H2|--(__ EUN ) 477 `-(______)-' +-------+ +-------+ `-(______)-' 479 Figure 1: AERO Link Reference Model 481 Figure 1 presents the AERO link reference model. In this model: 483 o the AERO link is an overlay network service configured over one or 484 more underlying INET partitions which may be managed by different 485 administrative authorities and have incompatible protocols and/or 486 addressing plans. 488 o AERO Relay R1 aggregates Mobility Service Prefix (MSP) M1, 489 discovers Mobile Network Prefixes (MNPs) X* and advertises the MSP 490 via BGP peerings over secured tunnels to Servers (S1, S2). Relays 491 use the SPAN service to bridge disjoint segments of a partitioned 492 AERO link. 494 o AERO Servers S1 and S2 configure secured tunnels with Relay R1 and 495 also act as Mobility Anchor Points (MAPs) and default routers for 496 their associated Clients C1 and C2. 498 o AERO Clients C1 and C2 associate with Servers S1 and S2, 499 respectively. They receive Mobile Network Prefix (MNP) 500 delegations X1 and X2, and also act as default routers for their 501 associated physical or internal virtual EUNs. Simple hosts H1 and 502 H2 attach to the EUNs served by Clients C1 and C2, respectively. 504 o AERO Proxy P1 configures a secured tunnel with Relay R1 and 505 provides proxy services for AERO Clients in secured enclaves that 506 cannot associate directly with other AERO link neighbors. 508 Each node on the AERO link maintains an AERO interface neighbor cache 509 and an IP forwarding table the same as for any link. Although the 510 figure shows a limited deployment, in common operational practice 511 there will normally be many additional Relays, Servers, Clients and 512 Proxys. 514 3.2. AERO Node Types 516 AERO Relays provide hybrid routing/bridging services (as well as a 517 security trust anchor) for nodes on an AERO link. Relays use 518 standard IPv6 routing to forward packets both within the same INET 519 partitions and between disjoint INET partitions based on a mid-layer 520 IPv6 encapsulation known as the SPAN header. The inner IP layer 521 experiences a virtual bridging service since the inner IP TTL/Hop 522 Limit is not decremented during forwarding. Each Relay also peers 523 with Servers and other Relays in a dynamic routing protocol instance 524 to provide a Distributed Mobility Management (DMM) service for the 525 list of active MNPs (see Section 3.3). Relays present the AERO link 526 as a set of one or more Mobility Service Prefixes (MSPs) but as link- 527 layer devices need not connect directly to the AERO link themselves 528 unless an administrative interface is desired. Relays configure 529 secured tunnels with Servers, Proxys and other Relays; they further 530 maintain IP forwarding table entries for each Mobile Network Prefix 531 (MNP) and any other reachable non-MNP prefixes. 533 AERO Servers provide default forwarding services and a Mobility 534 Anchor Point (MAP) for AERO Client Mobile Nodes (MNs). Each Server 535 also peers with Relays in a dynamic routing protocol instance to 536 advertise its list of associated MNPs (see Section 3.3). Servers 537 facilitate PD exchanges with Clients, where each delegated prefix 538 becomes an MNP taken from an MSP. Servers forward packets between 539 AERO interface neighbors and track each Client's mobility profiles. 541 AERO Clients receive MNPs through PD exchanges with AERO Servers over 542 the AERO link, and distribute the MNPs to nodes on EUNs. Each Client 543 can associate with a single Server or with multiple Servers (e.g., 544 for fault tolerance, load balancing, etc). A Client may also be co- 545 resident on the same physical or virtual platform as a Server; in 546 that case, the Client and Server behave as a single functional unit 547 and without the need for any Client/Server control messaging. 549 AERO Proxys provide a conduit for AERO Clients in ANETs to associate 550 with AERO Servers in external INETs. Client and Servers exchange 551 control plane messages via the Proxy, which intercepts them at the 552 ANET/INET boundary. The Proxy forwards data packets to and from 553 Clients according to forwarding information in the neighbor cache. 554 The Proxy function is specified in Section 3.16. 556 AERO Gateways are Servers that provide forwarding services between 557 the AERO interface and INET/EUN interfaces. Gateways are provisioned 558 with MNPs the same as for an AERO Client, and also run a dynamic 559 routing protocol to discover any non-MNP IP routes. The Gateway 560 advertises the MSP(s) to INETs, and distributes all of its associated 561 MNPs and non-MNP IP routes via BGP peerings with Relays. 563 AERO Relays, Servers, Proxys and Gateways are critical infrastructure 564 elements in fixed (i.e., non-mobile) INET deployments and hence have 565 permanent and unchanging INET addresses. AERO Clients are MNs that 566 connect via ANET interfaces, i.e., their ANET addresses may change 567 when the Client moves to a new ANET connection. 569 3.3. AERO Routing System 571 The AERO routing system comprises a private instance of the Border 572 Gateway Protocol (BGP) [RFC4271] that is coordinated between Relays 573 and Servers and does not interact with either the public Internet BGP 574 routing system or any underlying INET routing systems. 576 In a reference deployment, each Server is configured as an Autonomous 577 System Border Router (ASBR) for a stub Autonomous System (AS) using 578 an AS Number (ASN) that is unique within the BGP instance, and each 579 Server further uses eBGP to peer with one or more Relays but does not 580 peer with other Servers. Each INET of a multi-segment AERO link must 581 include one or more Relays, which peer with the Servers and Proxys 582 within that INET. All Relays within the same INET are members of the 583 same hub AS using a common ASN, and use iBGP to maintain a consistent 584 view of all active MNPs currently in service. The Relays of 585 different INETs peer with one another using eBGP. 587 Relays advertise the AERO link's MSPs and any non-MNP routes to each 588 of their Servers. This means that any aggregated non-MNPs (including 589 "default") are advertised to all Servers. Each Relay configures a 590 black-hole route for each of its MSPs. By black-holing the MSPs, the 591 Relay will maintain forwarding table entries only for the MNPs that 592 are currently active, and packets destined to all other MNPs will 593 correctly incur Destination Unreachable messages due to the black- 594 hole route. In this way, Servers have only partial topology 595 knowledge (i.e., they know only about the MNPs of their directly 596 associated Clients) and they forward all other packets to Relays 597 which have full topology knowledge. 599 Servers maintain a working set of associated MNPs, and dynamically 600 announce new MNPs and withdraw departed MNPs in eBGP updates to 601 Relays. Servers that are configured as Gateways also redistribute 602 non-MNP routes learned from non-AERO interfaces via their eBGP Relay 603 peerings. 605 Clients are expected to remain associated with their current Servers 606 for extended timeframes, however Servers SHOULD selectively suppress 607 updates for impatient Clients that repeatedly associate and 608 disassociate with them in order to dampen routing churn. Servers 609 that are configured as Gateways advertise the MSPs via INET/EUN 610 interfaces, and forward packets between INET/EUN interfaces and the 611 AERO interface using standard IP forwarding. 613 For IPv6 MNPs, the AERO routing system includes only IPv6 routes. 614 For IPv4 MNPs, the AERO routing system includes both IPv4 routes and 615 also IPv6 routes based on the IPv4-mapped IPv6 address corresponding 616 to the MNP and with prefix length set to 96 plus the length of the 617 IPv4 prefix. (For example, if the IPv4 MNP is 192.0.2.0/24 then the 618 IPv4-mapped prefix is 0:0:0:0:0:FFFF:192.0.2.0/120.) 620 Scaling properties of the AERO routing system are limited by the 621 number of BGP routes that can be carried by Relays. As of 2015, the 622 global public Internet BGP routing system manages more than 500K 623 routes with linear growth and no signs of router resource exhaustion 624 [BGP]. More recent network emulation studies have also shown that a 625 single Relay can accommodate at least 1M dynamically changing BGP 626 routes even on a lightweight virtual machine, i.e., and without 627 requiring high-end dedicated router hardware. 629 Therefore, assuming each Relay can carry 1M or more routes, this 630 means that at least 1M Clients can be serviced by a single set of 631 Relays. A means of increasing scaling would be to assign a different 632 set of Relays for each set of MSPs. In that case, each Server still 633 peers with one or more Relays, but institutes route filters so that 634 BGP updates are only sent to the specific set of Relays that 635 aggregate the MSP. For example, if the MSP for the AERO link is 636 2001:db8::/32, a first set of Relays could service the MSP 637 2001:db8::/40, a second set of Relays could service 638 2001:db8:0100::/40, a third set could service 2001:db8:0200::/40, 639 etc. 641 Assuming up to 1K sets of Relays, the AERO routing system can then 642 accommodate 1B or more MNPs with no additional overhead (for example, 643 it should be possible to service 1B /64 MNPs taken from a /34 MSP and 644 even more for shorter prefixes). In this way, each set of Relays 645 services a specific set of MSPs that they advertise to the native 646 Internetwork routing system, and each Server configures MSP-specific 647 routes that list the correct set of Relays as next hops. This 648 arrangement also allows for natural incremental deployment, and can 649 support small scale initial deployments followed by dynamic 650 deployment of additional Clients, Servers and Relays without 651 disturbing the already-deployed base. 653 A full discussion of the BGP-based routing system used by AERO is 654 found in [I-D.ietf-rtgwg-atn-bgp]. The system provides for 655 Distributed Mobility Management (DMM) per the distributed mobility 656 anchoring architecture [I-D.ietf-dmm-distributed-mobility-anchoring]. 658 3.4. AERO Addresses 660 A Client's AERO address is an IPv6 link-local address with an 661 interface identifier based on the Client's delegated MNP. Relay, 662 Server and Proxy AERO addresses are assigned from the range fe80::/96 663 and include an administratively-provisioned value in the lower 32 664 bits. 666 For IPv6, Client AERO addresses begin with the prefix fe80::/64 and 667 include in the interface identifier (i.e., the lower 64 bits) a 668 64-bit prefix taken from one of the Client's IPv6 MNPs. For example, 669 if the AERO Client receives the IPv6 MNP: 671 2001:db8:1000:2000::/56 673 it constructs its corresponding AERO addresses as: 675 fe80::2001:db8:1000:2000 677 fe80::2001:db8:1000:2001 679 fe80::2001:db8:1000:2002 681 ... etc. ... 683 fe80::2001:db8:1000:20ff 685 For IPv4, Client AERO addresses are based on an IPv4-mapped IPv6 686 address formed from an IPv4 MNP and with a Prefix Length of 96 plus 687 the MNP prefix length. For example, for the IPv4 MNP 192.0.2.32/28 688 the IPv4-mapped IPv6 MNP is: 690 0:0:0:0:0:FFFF:192.0.2.16/124 692 The Client then constructs its AERO addresses with the prefix 693 fe80::/64 and with the lower 64 bits of the IPv4-mapped IPv6 address 694 in the interface identifier as: 696 fe80::FFFF:192.0.2.16 698 fe80::FFFF:192.0.2.17 700 fe80::FFFF:192.0.2.18 702 ... etc. ... 704 fe80:FFFF:192.0.2.31 706 Relay, Server and Proxy AERO addresses are allocated from the range 707 fe80::/96, and MUST be managed for uniqueness. The lower 32 bits of 708 the AERO address includes a unique integer value (e.g., fe80::1, 709 fe80::2, fe80::3, etc.) as assigned by the administrative authority 710 for the link. If the link spans multiple SPAN segments, the AERO 711 addresses are assigned to each segment in 1x1 correspondence with 712 SPAN addresses (see: Section 3.5). The address fe80:: is reserved as 713 the IPv6 link-local Subnet Router Anycast address [RFC4291], and the 714 address fe80::ffff:ffff is reserved as the unspecified AERO address; 715 hence, these values are not available general assignment. 717 The lowest-numbered AERO address from a Client's MNP delegation 718 serves as the "base" AERO address (for example, for the MNP 719 2001:db8:1000:2000::/56 the base AERO address is 720 fe80::2001:db8:1000:2000). The Client then assigns the base AERO 721 address to the AERO interface and uses it for the purpose of 722 maintaining the neighbor cache entry. The Server likewise uses the 723 AERO address as its index into the neighbor cache for this Client. 725 If the Client has multiple AERO addresses (i.e., when there are 726 multiple MNPs and/or MNPs with prefix lengths shorter than /64), the 727 Client originates ND messages using the base AERO address as the 728 source address and accepts and responds to ND messages destined to 729 any of its AERO addresses as equivalent to the base AERO address. In 730 this way, the Client maintains a single neighbor cache entry that may 731 be indexed by multiple AERO addresses. 733 The Client's Subnet Router Anycast address can be statelessly 734 determined from its AERO address by simply transposing the AERO 735 address into the upper N bits of the Anycast address followed by 736 128-N bits of zeros. For example, for the AERO address 737 fe80::2001:db8:1:2 the subnet router anycast address is 738 2001:db8:1:2::/64. 740 AERO addresses for mobile node Clients embed a MNP as discussed 741 above, while AERO addresses for non-MNP destinations are constructed 742 in exactly the same way. A Client AERO address therefore encodes 743 either an MNP if the prefix is reached via the SPAN or a non-MNP if 744 the prefix is reached via a Gateway. 746 3.5. Spanning Partitioned AERO Networks (SPAN) 748 In the simplest case, an AERO link configured over a single INET 749 appears as a single unified link with a consistent underlying network 750 addressing plan. In that case, all nodes on the link can exchange 751 packets via encapsulation with INET addresses, since the underlying 752 INET is connected. In common practice, however, an AERO link may be 753 partitioned into multiple "segments", where each segment is a 754 distinct INET potentially managed under a different administrative 755 authority (e.g., as for worldwide aviation service providers such as 756 ARINC, SITA, Inmarsat, etc.). Individual INETs may themselves be 757 partitioned internally, in which case each internal partition is seen 758 as a separate segment. 760 The addressing plan of each segment is consistent internally but will 761 often bear no relation to the addressing plans of other segments. 762 Each segment is also likely to be separated from others by network 763 security devices (e.g., firewalls, proxies, packet filtering 764 gateways, etc.), and in many cases disjoint segments may not even 765 have any common physical link connections at all. Therefore, nodes 766 can only be assured of exchanging packets directly with 767 correspondents in the same segment, and not with those in other 768 segments. The only means for joining the segments therefore is 769 through inter-domain peerings between AERO Relays. 771 The same as for traditional campus LANs, multiple AERO link segments 772 can be joined into a single unified link via a virtual bridging 773 service termed the "SPAN". The SPAN performs link-layer packet 774 forwarding between segments (i.e., bridging) without decrementing the 775 network-layer TTL/Hop Limit. The SPAN model is depicted in Figure 2: 777 . . . . . . . . . . . . . . . . . . . . . . . 778 . . 779 . .-(::::::::) . 780 . .-(::::::::::::)-. +-+ . 781 . (:::: Segment A :::)--|R|---+ . 782 . `-(::::::::::::)-' +-+ | . 783 . `-(::::::)-' | . 784 . | . 785 . .-(::::::::) | . 786 . .-(::::::::::::)-. +-+ | . 787 . (:::: Segment B :::)--|R|---+ . 788 . `-(::::::::::::)-' +-+ | . 789 . `-(::::::)-' | . 790 . | . 791 . .-(::::::::) | . 792 . .-(::::::::::::)-. +-+ | . 793 . (:::: Segment C :::)--|R|---+ . 794 . `-(::::::::::::)-' +-+ | . 795 . `-(::::::)-' | . 796 . | . 797 . ..(etc).. x . 798 . . 799 . . 800 . <- AERO Link Bridged by the SPAN -> . 801 . . . . . . . . . . . . . .. . . . . . . . . 803 Figure 2: The SPAN 805 To support the SPAN, AERO links require a reserved /96 IPv6 "SPAN 806 Service Prefix (SSP)". Although any routable IPv6 prefix can be 807 used, a Unique Local Address (ULA) prefix (e.g., fd00::/96) [RFC4389] 808 is recommended since border routers are commonly configured to 809 prevent packets with ULAs from being injected into the AERO link by 810 an external IPv6 node and from leaking out of the AERO link to the 811 outside world. 813 Each segment in the SPAN assigns a unique sub-prefix of the SSP 814 termed a "SPAN Partition Prefix (SPP)". For example, a first segment 815 could assign fd00::1000/116, a second could assign fd00::2000/116, a 816 third could assign fd00::3000/116, etc. The administrative 817 authorities for each segment must therefore coordinate to assure 818 mutually-exclusive SPP assignments, but internal provisioning of the 819 SPP is a local consideration for each administrative authority. 821 A "SPAN address" is an address taken from a SPP and assigned to a 822 Relay, Server or Proxy interface. SPAN addresses are formed by 823 simply replacing the upper portion of an administratively-assigned 824 AERO address with the SPP. For example, if the SPP is 825 fd00::1000/116, the SPAN address formed from the AERO address 826 fe80::1001 is simply fd00::1001. 828 An "INET address" is an address of a node's interface connection to 829 an INET. AERO/SPAN/INET address mappings are maintained as permanent 830 neighbor cache entires as discussed in Section 3.8. 832 AERO Relays serve as bridges to join multiple segments into a unified 833 AERO link over multiple diverse administrative domains. They support 834 the bridging function by first establishing forwarding table entries 835 for their SPPs either via standard BGP routing or static routes. For 836 example, if three Relays ('A', 'B' and 'C') from different segments 837 serviced the SPPs fd00::1000/116, fd00::2000/116 and fd00::3000/116 838 respectively, then the forwarding tables in each Relay are as 839 follows: 841 A: fd00::1000/116->local, fd00::2000/116->B, fd00::3000/116->C 843 B: fd00::1000/116->A, fd00::2000/116->local, fd00::3000/116->C 845 C: fd00::1000/116->A, fd00::2000/116->B, fd00::3000/116->local 847 These forwarding table entries are permanent and never change, since 848 they correspond to fixed infrastructure elements in their respective 849 segments. This provides the basis for a link-layer forwarding 850 service that cannot be disrupted by routing updates due to node 851 mobility. 853 With the SPPs in place in each Relay's forwarding table, control and 854 data packets sent between AERO nodes in different segments can 855 therefore be carried over the SPAN via encapsulation. For example, 856 when a source node in segment A forwards a packet with IPv6 address 857 2001:db8:1:2::1 to a destination node in segment C with IPv6 address 858 2001:db8:1000:2000::1, it first encapsulates the packet in a SPAN 859 header with source SPAN address taken from fd00::1000/116 (e.g., 860 fd00::1001) and destination SPAN address taken from fd00::3000/116 861 (e.g., fd00::3001). Next, it encapsulates the SPAN message in an 862 INET header with source address set to its own INET address (e.g., 863 192.0.2.100) and destination set to the INET address of a Relay 864 (e.g., 192.0.2.1). 866 SPAN encapsulation is based on Generic Packet Tunneling in IPv6 867 [RFC2473]; the encapsulation format in the above example is shown 868 inFigure 3: 870 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 871 | INET Header | 872 | src = 192.0.2.100 | 873 | dst = 192.0.2.1 | 874 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 875 | SPAN Header | 876 | src = fd00::1001 | 877 | dst = fd00::3001 | 878 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 879 | Inner IP Header | 880 | src = 2001:db8:1:2::1 | 881 | dst = 2001:db8:1000:2000::1 | 882 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 883 | | 884 ~ ~ 885 ~ Inner Packet Body ~ 886 ~ ~ 887 | | 888 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 890 Figure 3: SPAN Encapsulation 892 In this format, the inner IP header and packet body are the original 893 IP packet, the SPAN header is an IPv6 header prepared according to 894 [RFC2473], and the INET header is prepared according to Section 3.9. 895 A packet is said to be "forwarded/sent into the SPAN" when it is 896 encapsulated as described above then forwarded via a secured tunnel 897 to a neighboring Relay. 899 This gives rise to a routing system that contains both MNP routes 900 that may change dynamically due to regional node mobility and SPAN 901 routes that never change. The Relays can therefore provide link- 902 layer bridging by sending packets into the SPAN instead of network- 903 layer routing according to MNP routes. As a result, opportunities 904 for packet loss due to node mobility between different segments are 905 mitigated. 907 With reference to Figure 3, for a Client's AERO address the SPAN 908 address is simply set to the Subnet Router Anycast address. For non- 909 link-local addresses, the destination SPAN address may not be known 910 in advance for the first few packets of a flow sent via the SPAN. In 911 that case, the SPAN destination address is set to the original 912 packet's destination, and the SPAN routing system will direct the 913 packet to the correct SPAN egress node. (In the above example, the 914 SPAN destination address is simply 2001:db8:1000:2000::1.) 916 3.6. AERO Interface Characteristics 918 AERO interfaces use encapsulation (see: Section 3.9) to exchange 919 packets with neighbors attached to the AERO link. 921 AERO interfaces maintain a neighbor cache for tracking per-neighbor 922 state the same as for any interface. AERO interfaces use ND messages 923 including Router Solicitation (RS), Router Advertisement (RA), 924 Neighbor Solicitation (NS) and Neighbor Advertisement (NA) for 925 neighbor cache management. 927 AERO interface ND messages include one or more Source/Target Link- 928 Layer Address Options (S/TLLAOs) formatted as shown in Figure 4: 930 0 1 2 3 931 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 1 932 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 933 | Type | Length = 5 | Prefix Length |S|R|D|X|N|Resvd| 934 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 935 | Interface ID | Port Number | 936 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 937 | | 938 + + 939 | | 940 + Link Layer Address + 941 | | 942 + + 943 | | 944 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 945 |P00|P01|P02|P03|P04|P05|P06|P07|P08|P09|P10|P11|P12|P13|P14|P15| 946 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 947 |P16|P17|P18|P19|P20|P21|P22|P23|P24|P25|P26|P27|P28|P29|P30|P31| 948 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 949 |P32|P33|P34|P35|P36|P37|P38|P39|P40|P41|P42|P43|P44|P45|P46|P47| 950 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 951 |P48|P49|P50|P51|P52|P53|P54|P55|P56|P57|P58|P59|P60|P61|P62|P63| 952 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 954 Figure 4: AERO Source/Target Link-Layer Address Option (S/TLLAO) 955 Format 957 In this format: 959 o Type is set to '1' for SLLAO or '2' for TLLAO. 961 o Length is set to the constant value '5' (i.e., 5 units of 8 962 octets). 964 o Prefix Length is set to the MNP prefix length in an ND message for 965 the Client AERO address found in the source (RS), destination (RA) 966 or target (NA) address; otherwise set to 0. If the message 967 contains multiple SLLAOs, only the Prefix Length value in the 968 SLLAO with S set to 1 is consulted and the values in other SLLAOs 969 are ignored. 971 o S (the 'Source' bit) is set to '1' in the S/TLLAO of an ND message 972 that corresponds to the ANET/INET interface over which the ND 973 message is sent, and set to 0 in all other S/TLLAOs. 975 o R (the "Release" bit) is set to '1' in an S/TLLAO in an RS/NA sent 976 for the purpose of departing from a Server; otherwise, set to '0'. 977 The recipient places the corresponding neighbor cache entry in the 978 DEPARTED state. For RS message, the recipient then releases the 979 corresponding PD and returns an RA with Router Lifetime set to '0' 981 o D (the "Disable" bit) is set to '1' in the S/TLLAOs of an RS/NA 982 message for each Interface ID that is to be disabled in the 983 neighbor cache entry; otherwise, set to '0'. 985 o X (the "proXy" bit) is set to '1' in the SLLAO of an RS/RA message 986 by the Proxy when there is a Proxy in the path; otherwise, set to 987 '0'. If the message contains multiple SLLAOs, only the X value in 988 the SLLAO with S set to 1 is consulted and the values in other 989 SLLAOs are ignored. 991 o N (the "(Network Address) Translator (NAT)" bit) is set to '1' in 992 the SLLAO of an RA message by the Server if there is a translator 993 in the path; otherwise, set to '0'. If the message contains 994 multiple SLLAOs, only the N value in the SLLAO with S set to 1 is 995 consulted and the values in other SLLAOs are ignored. 997 o Resvd is set to the value '0' on transmission and ignored on 998 receipt. 1000 o Interface ID is set to a 16-bit integer value corresponding to an 1001 AERO node's ANET/INET interface. Once the node has assigned an 1002 Interface ID to an ANET interface, the assignment must remain 1003 unchanged until the node fully detaches from the AERO link. The 1004 value 0xffff is reserved as the Server's INET Interface ID, i.e., 1005 Servers MUST use Interface ID 0xffff, and Clients MUST number 1006 their ANET Interface IDs with values in the range of 0-0xfffe. 1008 o Port Number and Link Layer Address are set to the encapsulation 1009 addresses required to send packets via the target node (or to '0' 1010 when the addresses are left unspecified). When UDP is not used as 1011 part of the encapsulation, Port Number is set to '0'. When the 1012 encapsulation IP address family is IPv4, IP Address is formed as 1013 an IPv4-mapped IPv6 address as specified in Section 3.4. 1015 o P(i) is a set of Preferences that correspond to the 64 1016 Differentiated Service Code Point (DSCP) values [RFC2474]. Each 1017 P(i) is set to the value '0' ("disabled"), '1' ("low"), '2' 1018 ("medium") or '3' ("high") to indicate a QoS preference level for 1019 packet forwarding purposes. 1021 A Client's AERO interface may be configured over multiple ANET 1022 interface connections. For example, common mobile handheld devices 1023 have both wireless local area network ("WLAN") and cellular wireless 1024 links. These links are typically used "one at a time" with low-cost 1025 WLAN preferred and highly-available cellular wireless as a standby. 1026 In a more complex example, aircraft frequently have many wireless 1027 data link types (e.g. satellite-based, cellular, terrestrial, air-to- 1028 air directional, etc.) with diverse performance and cost properties. 1030 A Client's ANET interfaces are classified as follows: 1032 o Native interfaces connect to the open INET, and have a global IP 1033 address that is reachable from any INET correspondent. 1035 o NATed interfaces connect to an ANET behind a Network Address 1036 Translator (NAT). The NAT does not participate in any AERO 1037 control message signaling, but the Server can issue control 1038 messages on behalf of the Client. Clients that are behind a NAT 1039 are required to send periodic keepalive messages to keep NAT state 1040 alive when there are no data packets flowing. If no other 1041 periodic messaging service is available, the Client can send RS 1042 messages to receive RA replies from its Server(s). 1044 o VPNed interfaces use security encapsulation over the ANET to a 1045 Virtual Private Network (VPN) server that also acts as an AERO 1046 Server. As with NATed links, the Server can issue control 1047 messages on behalf of the Client, but the Client need not send 1048 periodic keepalives in addition to those already used to maintain 1049 the VPN connection. 1051 o Proxyed interfaces connect to an ANET that is separated from the 1052 open INET by an AERO Proxy. Unlike NATed and VPNed interfaces, 1053 the Proxy can actively issue control messages on behalf of the 1054 Client. 1056 o Direct interfaces connect the Client directly to a neighbor 1057 without crossing any ANET/INET paths. An example is a line-of- 1058 sight link between a remote pilot and an unmanned aircraft. 1060 If a Client's multiple ANET interfaces are used "one at a time" 1061 (i.e., all other interfaces are in standby mode while one interface 1062 is active), then ND messages include only a single S/TLLAO with 1063 Interface ID set to a constant value. In that case, the Client would 1064 appear to have a single ANET interface but with a dynamically 1065 changing ANET address. 1067 If the Client has multiple active ANET interfaces, then from the 1068 perspective of ND it would appear to have multiple link-layer 1069 addresses. In that case, ND messages MAY include multiple S/TLLAOs 1070 -- each with an Interface ID that corresponds to a specific ANET 1071 interface. S must be set to 1 in the S/TLLAO corresponding to the 1072 AERO node's ANET interface used to transmit the message and set to 0 1073 in all other S/TLLAOs. 1075 When the Client includes an S/TLLAO for an ANET interface for which 1076 it is aware that there is a NAT on the path to the Server, or when a 1077 node includes an S/TLLAO solely for the purpose of announcing new QoS 1078 preferences, the node MAY set both Port Number and Link-Layer Address 1079 to 0 to indicate that the addresses are unspecified at the network 1080 layer and must instead be derived from the link-layer encapsulation 1081 headers. 1083 Relay, Server and Proxy AERO interfaces may be configured over one or 1084 more secured tunnel interfaces. The AERO interface configures both 1085 an AERO address and its corresponding SPAN address, while the 1086 underlying secured tunnel interfaces are either unnumbered or 1087 configure the same SPAN address. The AERO interface encapsulates 1088 each IP packet in a SPAN header and presents the packet to the 1089 underlying secured tunnel interface. For Relays that do not 1090 configure an AERO interface, the secured tunnel interfaces themselves 1091 are exposed to the IP layer with each interface configuring the 1092 Relay's SPAN address. Routing protocols such as BGP therefore run 1093 directly over the Relay's secured tunnel interfaces. For nodes that 1094 configure an AERO interface, routing protocols such as BGP run over 1095 the AERO interface but do not employ SPAN encapsulation. Instead, 1096 the AERO interface presents the routing protocol messages directly to 1097 the underlying secured tunnels without applying encapsulation and 1098 while using the SPAN address as the source address. This distinction 1099 must be honored consistently according to each node's configuration 1100 so that the IP forwarding table will associate discovered IP routes 1101 with the correct interface. 1103 3.7. AERO Interface Initialization 1105 AERO Servers, Proxys and Clients configure AERO interfaces as their 1106 point of attachment to the AERO link. AERO nodes assign the MSPs for 1107 the link to their AERO interfaces (i.e., as a "route-to-interface") 1108 to ensure that packets with destination addresses covered by an MNP 1109 not explicitly assigned to a non-AERO interface are directed to the 1110 AERO interface. 1112 AERO interface initialization procedures for Servers, Proxys, Clients 1113 and Relays are discussed in the following sections. 1115 3.7.1. AERO Server/Gateway Behavior 1117 When a Server enables an AERO interface, it assigns AERO/SPAN 1118 addresses and configures permanent neighbor cache entries for 1119 neighbors in the same SPAN segment by consulting the ROS list for the 1120 segment. The Server also configures secured tunnels with one or more 1121 neighboring Relays and engages in a BGP routing protocol session with 1122 each Relay. 1124 The AERO interface provides a single interface abstraction to the IP 1125 layer, but internally comprises multiple secured tunnels as well as 1126 an NBMA nexus for sending encapsulated data packets to AERO interface 1127 neighbors. The Server further configures a service to facilitate ND/ 1128 PD exchanges with AERO Clients and manages per-Client neighbor cache 1129 entries and IP forwarding table entries based on control message 1130 exchanges. 1132 Gateways are simply Servers that run a dynamic routing protocol 1133 between the AERO interface and INET/EUN interfaces (see: 1134 Section 3.3). The Gateway provisions MNPs to networks on the INET/ 1135 EUN interfaces (i.e., the same as a Client would do) and advertises 1136 the MSP(s) for the AERO link over the INET/EUN interfaces. The 1137 Gateway further provides an attachment point of the AERO link to the 1138 non-MNP-based global topology. 1140 3.7.2. AERO Proxy Behavior 1142 When a Proxy enables an AERO interface, it assigns AERO/SPAN 1143 addresses and configures permanent neighbor cache entries the same as 1144 for Servers. The Proxy also configues secured tunnels with one or 1145 more neighboring Relays and maintains per-Client neighbor cache 1146 entries based on control message exchanges. 1148 3.7.3. AERO Client Behavior 1150 When a Client enables an AERO interface, it sends RS messages with 1151 ND/PD parameters over an ANET interface to one or more Servers in the 1152 MAP list, which return RA messages with corresponding PD parameters. 1153 (The RS/RA messages may pass through a Proxy in the case of a 1154 Client's Proxyed interface.) 1155 After the initial ND/PD message exchange, the Client assigns AERO 1156 addresses to the AERO interface based on the delegated prefix(es). 1157 The Client can then register additional ANET interfaces with the 1158 Server by sending an RS message over each ANET interface. 1160 3.7.4. AERO Relay Behavior 1162 AERO Relays need not connect directly to the AERO link, since they 1163 operate as link-layer forwarding devices instead of network layer 1164 routers. Configuration of AERO interfaces on Relays is therefore 1165 OPTIONAL, e.g., if an administrative interface is needed. Relays 1166 configure secured tunnels with Servers, Proxys and other Relays; they 1167 also configure AERO/SPAN addresses and permanent neighbor cache 1168 entries the same as Servers. Relays engage in a BGP routing protocol 1169 session with a subset of the Servers on the local SPAN segment, and 1170 with other Relays on the SPAN (see: Section 3.3). 1172 3.8. AERO Interface Neighbor Cache Maintenance 1174 Each AERO interface maintains a conceptual neighbor cache that 1175 includes an entry for each neighbor it communicates with on the AERO 1176 link per [RFC4861]. AERO interface neighbor cache entries are said 1177 to be one of "permanent", "symmetric", "asymmetric" or "proxy". 1179 Permanent neighbor cache entries are created through explicit 1180 administrative action; they have no timeout values and remain in 1181 place until explicitly deleted. AERO Servers and Proxys maintain 1182 permanent neighbor cache entries for all other Servers and Proxys 1183 within the same SPAN segment. Each entry maintains the mapping 1184 between the neighbor's network-layer AERO address and corresponding 1185 INET address. The list of all permanent neighbor cache entries for 1186 the SPAN segment is maintained in the segment's ROS list. 1188 Symmetric neighbor cache entries are created and maintained through 1189 RS/RA exchanges as specified in Section 3.15, and remain in place for 1190 durations bounded by ND/PD lifetimes. AERO Servers maintain 1191 symmetric neighbor cache entries for each of their associated 1192 Clients, and AERO Clients maintain symmetric neighbor cache entries 1193 for each of their associated Servers. The list of all Servers on the 1194 AERO link is maintained in the link's MAP list. 1196 Asymmetric neighbor cache entries are created or updated based on 1197 route optimization messaging as specified in Section 3.17, and are 1198 garbage-collected when keepalive timers expire. AERO route 1199 optimization sources (ROSs) maintain asymmetric neighbor cache 1200 entries for active targets with lifetimes based on ND messaging 1201 constants. Asymmetric neighbor cache entries are unidirectional 1202 since only the ROS and not the target (e.g., a Client's MAP) creates 1203 an entry. 1205 Proxy neighbor cache entries are created and maintained by AERO 1206 Proxys when they process Client/Server ND/PD exchanges, and remain in 1207 place for durations bounded by ND/PD lifetimes. AERO Proxys maintain 1208 proxy neighbor cache entries for each of their associated Clients. 1209 Proxy neighbor cache entries track the Client state and the address 1210 of the Client's associated Server. 1212 To the list of neighbor cache entry states in Section 7.3.2 of 1213 [RFC4861], AERO interfaces add an additional state DEPARTED that 1214 applies to symmetric and proxy neighbor cache entries for Clients 1215 that have recently departed. The interface sets a "DepartTime" 1216 variable for the neighbor cache entry to "DEPARTTIME" seconds. 1217 DepartTime is decremented unless a new ND message causes the state to 1218 return to REACHABLE. While a neighbor cache entry is in the DEPARTED 1219 state, packets destined to the target Client are forwarded to the 1220 Client's new location instead of being dropped. When DepartTime 1221 decrements to 0, the neighbor cache entry is deleted. It is 1222 RECOMMENDED that DEPARTTIME be set to the default constant value 40 1223 seconds to allow for packets in flight to be delivered while stale 1224 route optimization state may be present. 1226 When a target Server (acting as a Mobility Anchor Point (MAP)) 1227 receives a valid NS message used for route optimization, it searches 1228 for a symmetric neighbor cache entry for the target Client. The MAP 1229 then returns a solicited NA message without creating a neighbor cache 1230 entry for the ROS, but creates a target Client "Report List" entry 1231 for the ROS and sets a "ReportTime" variable for the entry to 1232 REPORTTIME seconds. The MAP resets ReportTime when it receives a new 1233 authentic NS message, and otherwise decrements ReportTime while no NS 1234 messages have been received. It is RECOMMENDED that REPORTTIME be 1235 set to the default constant value 40 seconds to allow a 10 second 1236 window so that route optimization can converge before ReportTime 1237 decrements below REACHABLETIME. 1239 When the ROS receives a solicited NA message response to its NS 1240 message, it creates or updates an asymmetric neighbor cache entry for 1241 the target network-layer and link-layer addresses. The ROS then 1242 (re)sets ReachableTime for the neighbor cache entry to REACHABLETIME 1243 seconds and uses this value to determine whether packets can be 1244 forwarded directly to the target, i.e., instead of via a default 1245 route. The ROS otherwise decrements ReachableTime while no further 1246 solicited NA messages arrive. It is RECOMMENDED that REACHABLETIME 1247 be set to the default constant value 30 seconds as specified in 1248 [RFC4861]. 1250 The ROS also uses the value MAX_UNICAST_SOLICIT to limit the number 1251 of NS keepalives sent when a correspondent may have gone unreachable, 1252 the value MAX_RTR_SOLICITATIONS to limit the number of RS messages 1253 sent without receiving an RA and the value MAX_NEIGHBOR_ADVERTISEMENT 1254 to limit the number of unsolicited NAs that can be sent based on a 1255 single event. It is RECOMMENDED that MAX_UNICAST_SOLICIT, 1256 MAX_RTR_SOLICITATIONS and MAX_NEIGHBOR_ADVERTISEMENT be set to 3 the 1257 same as specified in [RFC4861]. 1259 Different values for DEPARTTIME, REPORTTIME, REACHABLETIME, 1260 MAX_UNICAST_SOLICIT, MAX_RTR_SOLCITATIONS and 1261 MAX_NEIGHBOR_ADVERTISEMENT MAY be administratively set; however, if 1262 different values are chosen, all nodes on the link MUST consistently 1263 configure the same values. Most importantly, DEPARTTIME and 1264 REPORTTIME SHOULD be set to a value that is sufficiently longer than 1265 REACHABLETIME to avoid packet loss due to stale route optimization 1266 state. 1268 3.9. AERO Interface Encapsulation and Re-encapsulation 1270 AERO interfaces encapsulate packets according to whether they are 1271 entering the AERO interface from the network layer or if they are 1272 being re-admitted into the same AERO link they arrived on. This 1273 latter form of encapsulation is known as "re-encapsulation". 1275 For packets entering the AERO interface from the network layer, the 1276 AERO interface copies the "TTL/Hop Limit", "Type of Service/Traffic 1277 Class" [RFC2983], "Flow Label"[RFC6438] (for IPv6) and "Congestion 1278 Experienced" [RFC3168] values in the packet's IP header into the 1279 corresponding fields in the encapsulation header(s). 1281 For packets undergoing re-encapsulation, the AERO interface instead 1282 copies these values from the original encapsulation header into the 1283 new encapsulation header, i.e., the values are transferred between 1284 encapsulation headers and *not* copied from the encapsulated packet's 1285 network-layer header. (Note especially that by copying the TTL/Hop 1286 Limit between encapsulation headers the value will eventually 1287 decrement to 0 if there is a (temporary) routing loop.) For IPv4 1288 encapsulation/re-encapsulation, the AERO interface sets the DF bit as 1289 discussed in Section 3.13. 1291 Proxy and Relay AERO interfaces encapsulate each packet in a SPAN 1292 header, then encapsulate the resulting SPAN packet in an INET header 1293 according to the next hop determined in the forwarding algorithm in 1294 Section 3.12. If the next hop is reached via a secured tunnel, the 1295 AERO interface uses an INET encapsulation format specific to the 1296 secured tunnel type (see: Section 6). If the next hop is reached via 1297 an unsecured underlying interface, the AERO interface instead uses 1298 Generic UDP Encapsulation (GUE) [I-D.ietf-intarea-gue] or an 1299 alternate minimal encapsulation format Appendix A. 1301 Client AERO interfaces can avoid encapsulation over underlying 1302 interfaces for which the first-hop access router is AERO-aware. For 1303 other underlying interfaces, Client interfaces use INET encapsulation 1304 the same as for Relays/Proxys but do not use SPAN encapsulation 1305 unless the underlying interface itself connects to the SPAN. 1307 When GUE encapsulation is used, the AERO interface next sets the UDP 1308 source port to a constant value that it will use in each successive 1309 packet it sends, and sets the UDP length field to the length of the 1310 SPAN packet plus 8 bytes for the UDP header itself plus the length of 1311 the GUE header (or 0 if GUE direct IP encapsulation is used). For 1312 packets sent to a Server or Relay, the AERO interface sets the UDP 1313 destination port to 8060, i.e., the IANA-registered port number for 1314 AERO. For packets sent to a Client, the AERO interface sets the UDP 1315 destination port to the port value stored in the neighbor cache entry 1316 for this Client. The AERO interface then either includes or omits 1317 the UDP checksum according to the GUE specification. 1319 AERO interfaces observes the packet sizing and fragmentation 1320 considerations found in Section 3.13. 1322 3.10. AERO Interface Decapsulation 1324 AERO interfaces decapsulate packets destined either to the AERO node 1325 itself or to a destination reached via an interface other than the 1326 AERO interface the packet was received on. When the encapsulated 1327 packet arrives in multiple fragments, the AERO interface reassembles 1328 as discussed in Section 3.13. Further decapsulation steps are 1329 performed according to the appropriate encapsulation format 1330 specification. 1332 3.11. AERO Interface Data Origin Authentication 1334 AERO nodes employ simple data origin authentication procedures. In 1335 particular: 1337 o AERO Relays, Servers and Proxys accept encapsulated data packets 1338 and control messages received from secured tunnels. 1340 o AERO Servers and Proxys accept encapsulated data packets and NS 1341 messages used for Neighbor Unreachability Detection (NUD) received 1342 from a source found in the ROS list. 1344 o AERO Proxys and Clients accept packets that originate from within 1345 the same secured ANET. 1347 o AERO Clients and Gateways accept packets from downstream network 1348 correspondents based on ingress filtering. 1350 AERO nodes silently drop any packets that do not satisfy the above 1351 data origin authentication procedures. Further security 1352 considerations are discussed Section 6. 1354 3.12. AERO Interface Forwarding Algorithm 1356 IP packets enter a node's AERO interface either from the network 1357 layer (i.e., from a local application or the IP forwarding system) or 1358 from the link layer (i.e., from an AERO interface neighbor). All 1359 packets entering a node's AERO interface first undergo data origin 1360 authentication as discussed in Section 3.11. Packets that satisfy 1361 data origin authentication are processed further, while all others 1362 are dropped silently. 1364 Packets that enter the AERO interface from the network layer are 1365 forwarded to an AERO interface neighbor. Packets that enter the AERO 1366 interface from the link layer are either re-admitted into the AERO 1367 link or forwarded to the network layer where they are subject to 1368 either local delivery or IP forwarding. In all cases, the AERO 1369 interface itself MUST NOT decrement the network layer TTL/Hop-count 1370 since its forwarding actions occur below the network layer. 1372 AERO interfaces may have multiple underlying ANET/INET interfaces 1373 and/or neighbor cache entries for neighbors with multiple Interface 1374 ID registrations (see Section 3.6). The AERO interface uses each 1375 packet's DSCP value (and/or port number) to select an outgoing ANET/ 1376 INET interface based on the node's own QoS preferences, and also to 1377 select a destination link-layer address based on the neighbor's ANET/ 1378 INET interface with the highest preference. AERO implementations 1379 SHOULD allow for QoS preference values to be modified at runtime 1380 through network management. 1382 If multiple outgoing interfaces and/or neighbor interfaces have a 1383 preference of "high", the AERO node replicates the packet and sends 1384 one copy via each of the (outgoing / neighbor) interface pairs; 1385 otherwise, the node sends a single copy of the packet via the 1386 interface with the highest preference. AERO nodes keep track of 1387 which ANET/INET interfaces are currently "reachable" or 1388 "unreachable", and only use "reachable" interfaces for forwarding 1389 purposes. 1391 The following sections discuss the AERO interface forwarding 1392 algorithms for Clients, Proxys, Servers and Relays. In the following 1393 discussion, a packet's destination address is said to "match" if it 1394 is the same as a cached address, or if it is covered by a cached 1395 prefix (which may be encoded in an AERO address). 1397 3.12.1. Client Forwarding Algorithm 1399 When an IP packet enters a Client's AERO interface from the network 1400 layer the Client searches for an asymmetric neighbor cache entry that 1401 matches the destination. If there is a match, the Client uses one or 1402 more "reachable" neighbor interfaces in the entry for packet 1403 forwarding. If there is no asymmetric neighbor cache entry, the 1404 Client instead forwards the packet toward a Server (the packet is 1405 intercepted by a Proxy if there is a Proxy on the path). 1407 When an IP packet enters a Client's AERO interface from the link- 1408 layer, if the destination matches one of the Client's MNPs or link- 1409 local addresses the Client decapsulates the packet (if necessary) and 1410 delivers it to the network layer. Otherwise, the Client drops the 1411 packet and MAY return a network-layer ICMP Destination Unreachable 1412 message subject to rate limiting (see: Section 3.14). 1414 3.12.2. Proxy Forwarding Algorithm 1416 For control messages originating from or destined to a Client, the 1417 Proxy intercepts the message and updates its proxy neighbor cache 1418 entry for the Client. The Proxy then forwards a (proxyed) copy of 1419 the control message. (For example, the Proxy forwards a proxied 1420 version of a Client's NS/RS message to the target neighbor, and 1421 forwards a proxied version of the NA/RA reply to the Client.) 1423 When the Proxy receives a data packet from a Client within the ANET, 1424 the Proxy searches for an asymmetric neighbor cache entry that 1425 matches the destination and forwards the packet as follows: 1427 o if the destination matches an asymmetric neighbor cache entry, the 1428 Proxy uses one or more "reachable" neighbor interfaces in the 1429 entry for packet forwarding via encapsulation. If the neighbor 1430 interface is in the same SPAN segment, the Proxy forwards the 1431 packet directly to the neighbor; otherwise, it forwards the packet 1432 to a Relay. 1434 o else, the Proxy encapsulates and forwards the packet to a Relay 1435 while using the packet's destination address as the SPAN 1436 destination address. (If the destination is an AERO address, the 1437 Proxy instead uses the corresponding Subnet Router Anycast address 1438 for Client AERO addresses and the SPAN address for 1439 administratively-provisioned AERO addresses.). 1441 When the Proxy receives an encapsulated data packet from an INET 1442 neighbor or from a secured tunnel, it accepts the packet only if data 1443 origin authentication succeeds and the SPAN destination address is 1444 its own adddress. If the packet is a SPAN fragment, the Proxy then 1445 adds the fragment to the reassembly buffer and returns if the 1446 reassembly is still incomplete. Otherwise, the Proxy reassembles the 1447 packet (if necessary) and continues processing. 1449 Next, the Proxy searches for a proxy neighbor cache entry that 1450 matches the destination. If there is a proxy neighbor cache entry in 1451 the REACHABLE state, the Proxy decapsulates and forwards the packet 1452 to the Client. If the neighbor cache entry is in the DEPARTED state, 1453 the Proxy instead re-encpasulates the message with the address of the 1454 Client's Server as the SPAN destination address and forwards the 1455 packet to a Relay. The Proxy then returns an unsolicited NA message 1456 as discussed in Section 3.19. If there is no neighbor cache entry, 1457 the Proxy instead discards the packet. 1459 3.12.3. Server/Gateway Forwarding Algorithm 1461 For control messages destined to a target Client's AERO address that 1462 are received from a secured tunnel, the Server (acting as a MAP) 1463 intercepts the message and sends an appropriate response on behalf of 1464 the Client. (For example, the Server sends an NA message reply in 1465 response to an NS message directed to one of its associated Clients.) 1466 If the Client's neighbor cache entry is in the DEPARTED state, 1467 however, the Server instead forwards the packet to the Client's new 1468 Server as discussed in Section 3.19. 1470 When the Server receives an encapsulated data packet from an INET 1471 neighbor or from a secured tunnel, it accepts the packet only if data 1472 origin authentication succeeds. If the SPAN destination address is 1473 its own adddress, the Server reassembles if necessary and discards 1474 the SPAN header (if the reassembly is incomplete, the Server instead 1475 adds the fragment to the reassembly buffer and returns). The Server 1476 then continues processing as follows: 1478 o if the destination matches a symmetric neighbor cache entry in the 1479 REACHABLE state the Server prepares the packet for forwarding to 1480 the destination Client. If the current header is a SPAN header, 1481 the Server reassembles if necessary and discards the SPAN header 1482 (if the reassembly is incomplete, the Server instead adds the 1483 fragment to the reassembly buffer and returns). The Server then 1484 forwards the packet according to the cached link-layer 1485 information, while using SPAN encapsulation for the Client's 1486 Proxyed/Native interfaces, simple INET encapsulation for NATed/ 1487 VPNed interfaces, or no encapsulation for Direct interfaces. If 1488 the packet is destined to the same Client from which it arrived 1489 (i.e., if the packet was forwarded by one of the Client's Proxys), 1490 the Server forwards the packet via a different "reachable" 1491 neighbor interface than the one the packet arrived on. If there 1492 are no "reachable" neighbor interfaces, the Server drops the 1493 packet. 1495 o else, if the destination matches a symmetric neighbor cache entry 1496 in the DEPARETED state the Server encapsulates the packet in a new 1497 SPAN header and forwards it to the Client's new Server (noting 1498 that the encapsulation may result in the addition of a second SPAN 1499 header). The Server uses its own SPAN address as the source and 1500 the SPAN address of the new Server as the destination. 1502 o else, if the destination matches an asymmetric neighbor cache 1503 entry, the Server uses one or more "reachable" neighbor interfaces 1504 in the entry for packet forwarding via the local INET if the 1505 neighbor is in the same SPAN segment or via a Relay otherwise. 1507 o else, if the destination is an AERO address that is not assigned 1508 on the AERO interface the Server drops the packet. 1510 o else, the Server (acting as a Gateway) releases the packet to the 1511 network layer for local delivery or IP forwarding. Based on the 1512 information in the forwarding table, the network layer may return 1513 the packet to the same AERO interface in which case further 1514 processing occurs as below. (Note that this arrangement 1515 accommodates common implementations in which the IP forwarding 1516 table is not accessible from within the AERO interface. If the 1517 AERO interface can directly access the IP forwarding table, the 1518 forwarding table lookup can instead be performed internally from 1519 within the AERO interface itself.) 1521 When the Server's AERO interface receives a data packet from the 1522 network layer or from a NATed/VPNed/Direct Client, it processes the 1523 packet according to the network-layer destination address as follows: 1525 o if the destination matches a symmetric or asymmetric neighbor 1526 cache entry the Server processes the packet as above. 1528 o else, the Server encapsulates the packet and forwards it to a 1529 Relay. For administratively-assigned AERO address destinations, 1530 the Server uses the SPAN address corresponding to the destination 1531 as the SPAN destination address. For Client AERO address 1532 destinations, the Server uses the Subnet Router Anycast address 1533 corresponding to the destination as the SPAN destination address. 1534 For all others, the Server uses the packet's destination IP 1535 address as the SPAN destination address. 1537 3.12.4. Relay Forwarding Algorithm 1539 Relays forward packets over secured tunnels the same as any IP 1540 router. When the Relay receives an encapsulated packet via a secured 1541 tunnel, it removes the INET header and searches for a forwarding 1542 table entry that matches the destination address in the next header. 1543 The Relay then processes the packet as follows: 1545 o if the destination matches one of the Relay's own addresses, the 1546 Relay submits the packet for local delivery. 1548 o else, if the destination matches a forwarding table entry the 1549 Relay forwards the packet via a secured tunnel to the next hop. 1550 If the destination matches an MSP without matching an MNP, 1551 however, the Relay instead drops the packet and returns an ICMP 1552 Destination Unreachable message subject to rate limiting (see: 1553 Section 3.14). 1555 o else, the Relay drops the packet and returns an ICMP Destination 1556 Unreachable as above. 1558 As for any IP router, the Relay decrements the TTL/Hop Limit when it 1559 forwards the packet. If the packet is encapsulated in a SPAN header, 1560 only the Hop Limit in the SPAN header is decremented, and not the 1561 TTL/Hop Limit in the inner packet header. 1563 3.13. AERO Interface MTU and Fragmentation 1565 The AERO interface is the node's attachment to the AERO link. For 1566 AERO link neighbor underlying interface paths that do not require 1567 encapsulation, the AERO interface sends unencapsulated IP packets. 1568 For other paths, the AERO interface acts as a tunnel ingress when it 1569 sends packets to the neighbor and as a tunnel egress when it receives 1570 packets from the neighbor. AERO interfaces observe the packet sizing 1571 considerations for tunnels discussed in [I-D.ietf-intarea-tunnels] 1572 and as specified below. 1574 The Internet Protocol expects that IP packets will either be 1575 delivered to the destination or a suitable Packet Too Big (PTB) 1576 message returned to support the process known as IP Path MTU 1577 Discovery (PMTUD) [RFC1191][RFC8201]. However, PTB messages may be 1578 crafted for malicious purposes or lost in the network [RFC2923]. 1579 This can be especially problematic for tunnels, where a condition 1580 known as a PMTUD "black hole" can result. For these reasons, AERO 1581 interfaces employ operational procedures that avoid interactions with 1582 PMTUD, including the use of fragmentation when necessary. 1584 AERO interfaces observe two different types of fragmentation. Source 1585 fragmentation occurs when the AERO interface (acting as a tunnel 1586 ingress) fragments the encapsulated packet into multiple fragments 1587 before admitting each fragment into the tunnel. Network 1588 fragmentation occurs when an encapsulated packet admitted into the 1589 tunnel by the ingress is fragmented by an IPv4 router on the path to 1590 the egress. Note that an IPv4 packet that incurs source 1591 fragmentation may also incur network fragmentation. 1593 IPv6 specifies a minimum link Maximum Transmission Unit (MTU) of 1280 1594 bytes [RFC8200]. Although IPv4 specifies a smaller minimum link MTU 1595 of 68 bytes [RFC0791], AERO interfaces also observe the IPv6 minimum 1596 for IPv4 even if encapsulated packets may incur network 1597 fragmentation. 1599 IPv6 specifies a minimum Maximum Reassembly Unit (MRU) of 1500 bytes 1600 [RFC8200], while the minimum MRU for IPv4 is only 576 bytes [RFC1122] 1601 (but, note that many standard IPv6 over IPv4 tunnel types already 1602 assume a larger MRU than the IPv4 minimum). 1604 AERO interfaces therefore configure an MTU that MUST NOT be smaller 1605 than 1280 bytes, MUST NOT be larger than the minimum MRU among all 1606 nodes on the AERO link minus the encapsulation overhead ("ENCAPS"), 1607 and SHOULD NOT be smaller than 1500 bytes. AERO interfaces also 1608 configure a Maximum Segment Unit (MSU) as the maximum-sized 1609 encapsulated packet that the ingress can inject into the tunnel 1610 without source fragmentation. The MSU value MUST NOT be larger than 1611 (MTU+ENCAPS) and MUST NOT be larger than 1280 bytes unless there is 1612 operational assurance that a larger size can traverse the link along 1613 all paths. The MSU value SHOULD also be reduced by 40 bytes to 1614 accommodate the possibility that an additional encapsulation is added 1615 (e.g., see: Section 3.12.3). 1617 All AERO nodes MUST configure the same MTU value for reasons cited in 1618 [RFC3819][RFC4861]; in particular, multicast support requires a 1619 common MTU value among all nodes on the link. All AERO nodes MUST 1620 configure an MRU large enough to reassemble packets up to 1621 (MTU+ENCAPS) bytes in length; nodes that cannot configure a large- 1622 enough MRU MUST NOT enable an AERO interface. For example, for an 1623 MTU of 1500 bytes (or slightly larger) an appropriate MRU might be 1624 2KB. 1626 The network layer proceeds as follows when it forwards an IP packet 1627 to the AERO interface. For each IPv4 packet that is larger than the 1628 AERO interface MTU and with DF set to 0, the network layer uses IPv4 1629 fragmentation to break the packet into a minimum number of non- 1630 overlapping fragments where the first fragment is no larger than the 1631 MTU and the remaining fragments are no larger than the first. For 1632 all other IP packets, if the packet is larger than the AERO interface 1633 MTU, the network layer drops the packet and returns a PTB message to 1634 the original source. Otherwise, the network layer admits each IP 1635 packet or fragment into the AERO interface. 1637 For each IP packet admitted into the AERO interface, if the neighbor 1638 is reached via an underlying interface that does not require 1639 encapsulation the AERO interface proceeds according to the underlying 1640 interface MTU. If the packet is no larger than the underlying 1641 interface MTU, the AERO interface presents the packet to the 1642 underlying interface. Otherwise, for IPv4 packets with DF set to 0 1643 the AERO interface uses IPv4 fragmentation to break the packet into 1644 fragments no larger than the underlying interface MTU. For other 1645 packets, the AERO interface drops the packet and returns a PTB 1646 message to the original source. (If the original source corresponds 1647 to a local application, the PTB would appear to have originated from 1648 a router on the path when in fact it was locally generated from 1649 within the AERO interface.) 1651 For underlying interfaces that require encapsulation, the AERO 1652 interface (acting as a tunnel ingress) instead encapsulates the 1653 packet in a SPAN heaedr. If the SPAN packet is larger than the MSU, 1654 the ingress source fragments the SPAN packet into a minimum number of 1655 non-overlapping and (roughly) equal-length fragments where the first 1656 fragment is no larger than the MSU and the remaining fragments are no 1657 larger than the first. The ingress then encapsulates each SPAN 1658 packet/fragment in an INET header and admits them into the tunnel. 1659 For IPv4, the ingress sets the DF bit to 0 in the INET header in case 1660 any network fragmentation is necessary. The encapsulated packets 1661 will be delivered to the egress, which reassembles them into a whole 1662 packet if necessary. 1664 By fragmenting at the SPAN layer instead of lower layers, standard 1665 IPv6 fragmentation and reassembly [RFC8200] ensures that IPv4 issues 1666 such as data corruption due to reassembly misassociations will not 1667 occur [RFC6864][RFC4963]. Incomplete reassemblies are discarded when 1668 the corresponding neighbor cache entry is deleted. 1670 3.14. AERO Interface Error Handling 1672 When an AERO node admits encapsulated packets into the AERO 1673 interface, it may receive link-layer or network-layer error 1674 indications. 1676 A link-layer error indication is an ICMP error message generated by a 1677 router in the INET on the path to the neighbor or by the neighbor 1678 itself. The message includes an IP header with the address of the 1679 node that generated the error as the source address and with the 1680 link-layer address of the AERO node as the destination address. 1682 The IP header is followed by an ICMP header that includes an error 1683 Type, Code and Checksum. Valid type values include "Destination 1684 Unreachable", "Time Exceeded" and "Parameter Problem" 1685 [RFC0792][RFC4443]. (AERO interfaces ignore all link-layer IPv4 1686 "Fragmentation Needed" and IPv6 "Packet Too Big" messages since they 1687 only emit packets that are guaranteed to be no larger than the IP 1688 minimum link MTU as discussed in Section 3.13.) 1690 The ICMP header is followed by the leading portion of the packet that 1691 generated the error, also known as the "packet-in-error". For 1692 ICMPv6, [RFC4443] specifies that the packet-in-error includes: "As 1693 much of invoking packet as possible without the ICMPv6 packet 1694 exceeding the minimum IPv6 MTU" (i.e., no more than 1280 bytes). For 1695 ICMPv4, [RFC0792] specifies that the packet-in-error includes: 1696 "Internet Header + 64 bits of Original Data Datagram", however 1697 [RFC1812] Section 4.3.2.3 updates this specification by stating: "the 1698 ICMP datagram SHOULD contain as much of the original datagram as 1699 possible without the length of the ICMP datagram exceeding 576 1700 bytes". 1702 The link-layer error message format is shown in Figure 5 (where, "L2" 1703 and "L3" refer to link-layer and network-layer, respectively): 1705 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1706 ~ ~ 1707 | L2 IP Header of | 1708 | error message | 1709 ~ ~ 1710 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1711 | L2 ICMP Header | 1712 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 1713 ~ ~ P 1714 | IP and other encapsulation | a 1715 | headers of original L3 packet | c 1716 ~ ~ k 1717 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ e 1718 ~ ~ t 1719 | IP header of | 1720 | original L3 packet | i 1721 ~ ~ n 1722 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1723 ~ ~ e 1724 | Upper layer headers and | r 1725 | leading portion of body | r 1726 | of the original L3 packet | o 1727 ~ ~ r 1728 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 1730 Figure 5: AERO Interface Link-Layer Error Message Format 1732 The AERO node rules for processing these link-layer error messages 1733 are as follows: 1735 o When an AERO node receives a link-layer Parameter Problem message, 1736 it processes the message the same as described as for ordinary 1737 ICMP errors in the normative references [RFC0792][RFC4443]. 1739 o When an AERO node receives persistent link-layer Time Exceeded 1740 messages, the IP ID field may be wrapping before earlier fragments 1741 awaiting reassembly have been processed. In that case, the node 1742 SHOULD begin including integrity checks and/or institute rate 1743 limits for subsequent packets. 1745 o When an AERO node receives persistent link-layer Destination 1746 Unreachable messages in response to encapsulated packets that it 1747 sends to one of its asymmetric neighbor correspondents, the node 1748 SHOULD process the message as an indication that a path may be 1749 failing, and MAY initiate NUD over that path. If it receives 1750 Destination Unreachable messages on many or all paths, the node 1751 SHOULD set ReachableTime for the corresponding asymmetric neighbor 1752 cache entry to 0 and allow future packets destined to the 1753 correspondent to flow through a default route. 1755 o When an AERO Client receives persistent link-layer Destination 1756 Unreachable messages in response to encapsulated packets that it 1757 sends to one of its symmetric neighbor Servers, the Client SHOULD 1758 mark the path as unusable and use another path. If it receives 1759 Destination Unreachable messages on many or all paths, the Client 1760 SHOULD associate with a new Server and release its association 1761 with the old Server as specified in Section 3.19.5. 1763 o When an AERO Server receives persistent link-layer Destination 1764 Unreachable messages in response to encapsulated packets that it 1765 sends to one of its symmetric neighbor Clients, the Server SHOULD 1766 mark the underlying path as unusable and use another underlying 1767 path. If it receives Destination Unreachable messages on multiple 1768 paths, the Server should take no further actions unless it 1769 receives an explicit ND/PD release message or if the PD lifetime 1770 expires. In that case, the Server MUST release the Client's 1771 delegated MNP, withdraw the MNP from the AERO routing system and 1772 delete the neighbor cache entry. 1774 o When an AERO Server or Proxy receives link-layer Destination 1775 Unreachable messages in response to an encapsulated packet that it 1776 sends to one of its permanent neighbors, it treats the messages as 1777 an indication that the path to the neighbor may be failing. 1778 However, the dynamic routing protocol should soon reconverge and 1779 correct the temporary outage. 1781 When an AERO Relay receives a packet for which the network-layer 1782 destination address is covered by an MSP, if there is no more- 1783 specific routing information for the destination the Relay drops the 1784 packet and returns a network-layer Destination Unreachable message 1785 subject to rate limiting. The Relay writes the network-layer source 1786 address of the original packet as the destination address and uses 1787 one of its non link-local addresses as the source address of the 1788 message. 1790 When an AERO node receives an encapsulated packet for which the 1791 reassembly buffer it too small, it drops the packet and returns a 1792 network-layer Packet Too Big (PTB) message. The node first writes 1793 the MRU value into the PTB message MTU field, writes the network- 1794 layer source address of the original packet as the destination 1795 address and writes one of its non link-local addresses as the source 1796 address. 1798 3.15. AERO Router Discovery, Prefix Delegation and Autoconfiguration 1800 AERO Router Discovery, Prefix Delegation and Autoconfiguration are 1801 coordinated as discussed in the following Sections. 1803 3.15.1. AERO ND/PD Service Model 1805 Each AERO Server on the link configures a PD service to facilitate 1806 Client requests. Each Server is provisioned with a database of MNP- 1807 to-Client ID mappings for all Clients enrolled in the AERO service, 1808 as well as any information necessary to authenticate each Client. 1809 The Client database is maintained by a central administrative 1810 authority for the AERO link and securely distributed to all Servers, 1811 e.g., via the Lightweight Directory Access Protocol (LDAP) [RFC4511], 1812 via static configuration, etc. Clients can receive new PDs from new 1813 Servers before releasing PDs received from existing Servers for 1814 service continuity. Clients receive the same service regardless of 1815 the Servers they select, although selecting Servers that are 1816 topologically nearby may provide better routing. 1818 AERO Clients and Servers use ND messages to maintain neighbor cache 1819 entries. AERO Servers configure their AERO interfaces as advertising 1820 interfaces, and therefore send unicast RA messages with configuration 1821 information in response to a Client's RS message. Thereafter, 1822 Clients send additional RS messages to refresh prefix and/or router 1823 lifetimes. 1825 AERO Clients and Servers include PD parameters in RS/RA messages (see 1826 [I-D.templin-6man-dhcpv6-ndopt] for ND/PD alternatives). The unified 1827 ND/PD messages are exchanged between Client and Server according to 1828 the prefix management schedule required by the PD service. If the 1829 Client knows its MNP in advance, it can include its AERO address as 1830 the source address of an RS message and with an SLLAO with a valid 1831 Prefix Length for the MNP. If the Server (and Proxy) accept the 1832 Client's MNP assertion, they inject the prefix into the routing 1833 system and establish the necessary neighbor cache state. 1835 The following sections specify the Client and Server behavior. 1837 3.15.2. AERO Client Behavior 1839 AERO Clients can discover the addresses of Servers in the MAP list 1840 via static configuration (e.g., from a flat-file map of Server 1841 addresses and locations), or through an automated means such as 1842 Domain Name System (DNS) name resolution [RFC1035]. In the absence 1843 of other information, the Client can resolve the DNS Fully-Qualified 1844 Domain Name (FQDN) "linkupnetworks.[domainname]" where 1845 "linkupnetworks" is a constant text string and "[domainname]" is a 1846 DNS suffix for the AERO link (e.g., "example.com"). Alternatively, 1847 the Client can discover the Server's address through a multicast RS 1848 as described below. 1850 To associate with a Server, the Client acts as a requesting router to 1851 request MNPs. The Client prepares an RS message with PD parameters 1852 (e.g., with an SLLAO with non-zero Prefix Length) and SHOULD include 1853 a Nonce and Timestamp option if the Client needs to correlate RA 1854 replies. If the Client already knows the Server's AERO address, it 1855 includes the AERO address as the network-layer destination address; 1856 otherwise, it includes all-routers multicast (ff02::2) as the 1857 network-layer destination address. If the Client already knows its 1858 own AERO address, it uses the AERO address as the network-layer 1859 source address; otherwise, it uses the unspecified AERO address 1860 (fe80::ffff:ffff) as the network-layer source address. 1862 The Client next includes an SLLAO in the RS message formatted as 1863 described in Section 3.6 to register its link-layer information with 1864 the Server. The SLLAO corresponding to the ANET interface over which 1865 the Client will send the RS message MUST set S to 1. The Client MAY 1866 include additional SLLAOs specific to other underlying interfaces, 1867 but if so it MUST set their S, Port Number and Link Layer Address 1868 fields to 0. If the Client is connected to an ANET for which 1869 encapsulation is required, the Client finally encapsulates the RS 1870 message in an ANET header with its own ANET address as the source 1871 address and the INET address of the Server as the destination. 1873 The Client then sends the RS message (either directly via Direct 1874 interfaces, via INET encapsulation for NATed interfaces, via a VPN 1875 for VPNed interfaces, via a Proxy for proxyed interfaces or via a 1876 Relay for native interfaces) and waits for an RA message reply (see 1877 Section 3.15.3). The Client retries up to MAX_RTR_SOLICITATIONS 1878 times until an RA is received. If the Client receives no RAs, or if 1879 it receives an RA with Router Lifetime set to 0, the Client SHOULD 1880 abandon this Server and try another Server. Otherwise, the Client 1881 processes the PD information found in the RA message. 1883 Next, the Client creates a symmetric neighbor cache entry with the 1884 Server's AERO address as the network-layer address and the address in 1885 the first SLLAO as the Server's INET address. The Client records the 1886 RA Router Lifetime field value in the neighbor cache entry as the 1887 time for which the Server has committed to maintaining the MNP in the 1888 routing system. The Client then autoconfigures AERO addresses for 1889 each of the delegated MNPs and assigns them to the AERO interface. 1890 The Client also caches any MSPs included in Route Information Options 1891 (RIOs) [RFC4191] as MSPs to associate with the AERO link, and assigns 1892 the MTU value in the MTU option to its AERO interface while 1893 configuring an appropriate MRU. 1895 The Client then registers additional ANET interfaces with the Server 1896 by sending RS messages via each additional ANET interface. The RS 1897 messages include the same parameters as for the initial RS/RA 1898 exchange, but with destination address set to the Server's AERO 1899 address and with an SLLAO specific to the ANET interface. 1901 The Client examines the X and N bits in the SLLAO with S set to 1 in 1902 each RA message it receives. If X is 1 the Client infers that there 1903 is a Proxy on the path, and if N is 1 the Client infers that there is 1904 a NAT on the path. If N is 1, the Client SHOULD set Port Number and 1905 Link-Layer Address to 0 in the first S/TLLAO of any subsequent ND 1906 messages it sends to the Server over that link. 1908 Following autoconfiguration, the Client sub-delegates the MNPs to its 1909 attached EUNs and/or the Client's own internal virtual interfaces as 1910 described in [I-D.templin-v6ops-pdhost] to support the Client's 1911 downstream attached "Internet of Things (IoT)". The Client 1912 subsequently maintains its MNP delegations through each of its 1913 Servers by sending additional RS messages before Router Lifetime 1914 expires. 1916 After the Client registers its ANET interfaces, it may wish to change 1917 one or more registrations, e.g., if an ANET interface changes address 1918 or becomes unavailable, if QoS preferences change, etc. To do so, 1919 the Client prepares an RS message to send over any available ANET 1920 interface. The RS MUST include an SLLAO with S set to 1 for the 1921 selected ANET interface and MAY include any additional SLLAOs 1922 specific to other ANET interfaces. The Client includes fresh P(i) 1923 values in each SLLAO to update the Server's neighbor cache entry. If 1924 the Client wishes to update only the P(i) values, it sets the Port 1925 Number and Link-Layer Address fields to 0. If the Client wishes to 1926 disable the underlying interface, it sets D to 1. When the Client 1927 receives the Server's RA response, it has assurance that the Server 1928 has been updated with the new information. 1930 If the Client wishes to discontinue use of a Server it issues an RS 1931 message over any underlying interface with an SLLAO with R set to 1 . 1932 When the Server processes the message, it releases the MNP, sets the 1933 symmetric neighbor cache entry state for the Client to DEPARTED, 1934 withdraws the IP route from the routing system and returns an RA 1935 reply with Router Lifetime set to 0. 1937 Clients SHOULD NOT remain associated with multiple Servers for long 1938 durations, since routing inconsistencies could cause some fragments 1939 of a fragmented packet to be delivered to Server A and others to 1940 Server B. Clients SHOULD therefore associate with a single primary 1941 Server, and send a departure message to the former Server soon after 1942 moving to a new Server. 1944 3.15.3. AERO Server Behavior 1946 AERO Servers act as IP routers and support a PD service for Clients. 1947 Servers arrange to add their AERO and INET addresses to a static map 1948 of Server addresses for the link and/or the DNS resource records for 1949 the FQDN "linkupnetworks.[domainname]" before entering service. The 1950 list of Server addresses should be geographically and/or 1951 topologically referenced, and forms the MAP list for the AERO link. 1953 When a Server receives a prospective Client's RS message on its AERO 1954 interface, it SHOULD return an immediate RA reply with Router 1955 Lifetime set to 0 if it is currently too busy or otherwise unable to 1956 service the Client. Otherwise, the Server authenticates the RS 1957 message and processes the PD parameters. The Server first determines 1958 the correct MNPs to delegate to the Client by searching the Client 1959 database. When the Server delegates the MNPs, it also creates an IP 1960 forwarding table entry for each MNP so that the MNPs are propagated 1961 into the routing system (see: Section 3.3). For IPv6, the Server 1962 creates a single IPv6 forwarding table entry for each MNP. For IPv4, 1963 the Server creates both an IPv4 forwarding table entry and an IPv6 1964 forwarding table entry with the IPv4-mapped IPv6 address 1965 corresponding to the IPv4 address. 1967 The Server next creates a symmetric neighbor cache entry for the 1968 Client using the base AERO address as the network-layer address and 1969 with lifetime set to no more than the smallest PD lifetime. Next, 1970 the Server updates the neighbor cache entry by recording the 1971 information in each SLLAO in the RS indexed by the Interface ID and 1972 including the Port Number, Link Layer Address and P(i) values. For 1973 the SLLAO with S set to 1, however, the Server records the actual 1974 INET header source addresses instead of those that appear in the 1975 SLLAO in case there was a NAT in the path. The Server also records 1976 the value of the X bit to indicate whether there is a Proxy on the 1977 path. 1979 Next, the Server prepares an RA message using its AERO address as the 1980 network-layer source address and the network-layer source address of 1981 the RS message as the network-layer destination address. The Server 1982 includes the delegated MNPs, any other PD parameters and an SLLAO 1983 with the Link Layer Address set to the Server's SPAN address and with 1984 Interface ID set to 0xffff. The Server then includes one or more 1985 RIOs that encode the MSPs for the AERO link, plus an MTU option for 1986 the link MTU (see Section 3.13). The Server finally forwards the 1987 message to the Client using SPAN, INET or NULL encapsulation 1988 according to the Client interface type. (For Proxy/Native 1989 interfaces, the Server encapsulates the message in a SPAN header with 1990 source address set to its own SPAN address and destination address 1991 set to the Proxy's (or Client's) SPAN address, then forwards the 1992 message into the SPAN.) 1994 After the initial RS/RA exchange, the Server maintains the symmetric 1995 neighbor cache entry for the Client. If the Client (or Proxy) issues 1996 additional NS/RS messages, the Server resets ReachableTime. If the 1997 Client (or Proxy) issues an RS with PD release parameters (e.g., by 1998 including an SLLAO with R set to 1), or if the Client becomes 1999 unreachable, the Server sets the Client's symmetric neighbor cache 2000 entry to the DEPARTED state and withdraws the IP routes from the AERO 2001 routing system. 2003 The Server processes these and any other Client ND/PD messages, and 2004 returns an NA/RA reply. The Server may also issue unsolicited RA 2005 messages, e.g., with PD reconfigure parameters to cause the Client to 2006 renegotiate its PDs, with Router Lifetime set to 0 if it can no 2007 longer service this Client, etc. Finally, If the symmetric neighbor 2008 cache entry is in the DEPARTED state, the Server deletes the entry 2009 after DepartTime expires. 2011 3.15.3.1. Lightweight DHCPv6 Relay Agent (LDRA) 2013 When DHCPv6 is used as the ND/PD service back end, AERO Clients and 2014 Servers are always on the same link (i.e., the AERO link) from the 2015 perspective of DHCPv6. However, in some implementations the DHCPv6 2016 server and ND function may be located in separate modules. In that 2017 case, the Server's AERO interface module can act as a Lightweight 2018 DHCPv6 Relay Agent (LDRA)[RFC6221] to relay PD messages to and from 2019 the DHCPv6 server module. 2021 When the LDRA receives an authentic RS message, it extracts the PD 2022 message parameters and uses them to construct an IPv6/UDP/DHCPv6 2023 message. It sets the IPv6 source address to the source address of 2024 the RS message, sets the IPv6 destination address to 2025 'All_DHCP_Relay_Agents_and_Servers' and sets the UDP fields to values 2026 that will be understood by the DHCPv6 server. 2028 The LDRA then wraps the message in a DHCPv6 'Relay-Forward' message 2029 header and includes an 'Interface-Id' option that includes enough 2030 information to allow the LDRA to forward the resulting Reply message 2031 back to the Client (e.g., the Client's link-layer addresses, a 2032 security association identifier, etc.). The LDRA also wraps the 2033 information in all of the SLLAOs from the RS message into the 2034 Interface-Id option, then forwards the message to the DHCPv6 server. 2036 When the DHCPv6 server prepares a Reply message, it wraps the message 2037 in a 'Relay-Reply' message and echoes the Interface-Id option. The 2038 DHCPv6 server then delivers the Relay-Reply message to the LDRA, 2039 which discards the Relay-Reply wrapper and IPv6/UDP headers, then 2040 uses the DHCPv6 message to construct an RA response to the Client. 2041 The Server uses the information in the Interface-Id option to prepare 2042 the RA message and to cache the link-layer addresses taken from the 2043 SLLAOs echoed in the Interface-Id option. 2045 3.16. The AERO Proxy 2047 Clients may connect to ANETs that require a perimeter security 2048 gateway to enable communications to Servers in outside INETs. In 2049 that case, the ANET can employ an AERO Proxy. The Proxy is located 2050 at the ANET/INET border and listens for RS messages originating from 2051 or RA messages destined to ANET Clients. The Proxy acts on these 2052 control messages as follows: 2054 o when the Proxy receives an RS message from a new ANET Client, it 2055 first authenticates the message then examines the network-layer 2056 destination address. If the destination address is a Server's 2057 AERO address, the Proxy proceeds to the next step. Otherwise, if 2058 the destination is all-routers multicast the Proxy selects a 2059 "nearby" Server that is likely to be a good candidate to serve the 2060 Client and replaces the destination address with the Server's AERO 2061 address. Next, the Proxy creates a proxy neighbor cache entry and 2062 caches the Client and Server addresses along with any identifying 2063 information including Transaction IDs, Client Identifiers, Nonce 2064 values, etc. The Proxy then examines the address in the RS 2065 message SLLAO with S set to 1. If the address is different than 2066 the Client's ANET address, the Proxy notes that the Client is 2067 behind a NAT. The Proxy then sets X to 1 and changes the Link 2068 Layer Address to its own SPAN address. The Proxy finally 2069 encapsulates the RS message in a SPAN header with destination set 2070 to the Server's SPAN address then forwards the message into the 2071 SPAN. 2073 o when the Server receives the RS message, it authenticates the 2074 message then creates or updates a symmetric neighbor cache entry 2075 for the Client with the Proxy's SPAN address as the link-layer 2076 address. The Server then sends an RA message with a single SLLAO 2077 back to the Proxy via the SPAN. 2079 o when the Proxy receives the RA message, it matches the message 2080 with the RS that created the proxy neighbor cache entry. The 2081 Proxy then caches the PD route information as a mapping from the 2082 Client's MNPs to the Client's ANET address, and sets the neighbor 2083 cache entry state to REACHABLE. The Proxy then changes the SLLAO 2084 Link Layer Address to its own ANET address, sets X to 1, sets N to 2085 1 if the Client is behind a NAT, then re-encapsulates the RA 2086 message in an ANET header and forwards it to the Client. 2088 After the initial RS/RA exchange, the Proxy forwards any Client data 2089 packets for which there is no matching asymmetric neighbor cache 2090 entry to the Server via the SPAN. Finally, the Proxy forwards any 2091 Client data destined to an asymmetric neighbor cache target directly 2092 to the target according to the link-layer information - the process 2093 of establishing asymmetric neighbor cache entries is specified in 2094 Section 3.17. 2096 While the Client is still attached to the ANET, the Proxy 2097 periodically sends NS/RS messages to update the Server's symmetric 2098 neighbor cache entries on behalf of the Client and/or to convey QoS 2099 updates. If the Server ceases to send solicited NA/RA responses, the 2100 Proxy marks the Server as unreachable and sends an unsolicited RA 2101 with Router Lifetime set to zero to inform the Client that this 2102 Server is no longer able to provide Service. If the Client becomes 2103 unreachable, the Proxy sets the neighbor cache entry state to 2104 DEPARTED and sends an RS message to the Server with an SLLAO with D 2105 set to 1 and with Interface ID set to the Client's interface ID so 2106 that the Server will de-register this Interface ID. Although the 2107 Proxy engages in these ND exchanges on behalf of the Client, the 2108 Client can also send ND messages on its own behalf, e.g., if it is in 2109 a better position than the Proxy to convey QoS changes, etc. 2111 In some ANETs that employ a Proxy, the Client's MNP can be injected 2112 into the ANET routing system. In that case, the Client can send data 2113 messages without encapsulation so that the ANET native routing system 2114 transports the unencapsulated packets to the Proxy. This can be very 2115 beneficial, e.g., if the Client connects to the ANET via low-end data 2116 links such as some aviation wireless links. 2118 If the first-hop ANET access router is AERO-aware, the Client can 2119 avoid encapsulation for both its control and data messages. When the 2120 Client connects to the link, it can send an unencapsulated RS message 2121 with source address set to its AERO address and with destination 2122 address set to the AERO address of the Client's selected Server or to 2123 all-routers multicast. The Client includes an SLLAO with Interface 2124 ID, Prefix Length and P(i) information but with Port Number and Link- 2125 Layer Address set to 0. 2127 The Client then sends the unencapsulated RS message, which will be 2128 intercepted by the AERO-Aware access router. The access router then 2129 encapsulates the RS message in an ANET header with its own address as 2130 the source address and the address of a Proxy as the destination 2131 address. The access router further remembers the address of the 2132 Proxy so that it can encapsulate future data packets from the Client 2133 via the same Proxy. If the access router needs to change to a new 2134 Proxy, it simply sends another RS message toward the Server via the 2135 new Proxy on behalf of the Client. 2137 In some cases, the access router and Proxy may be one and the same 2138 node. In that case, the node would be located on the same physical 2139 link as the Client, but its message exchanges with the Server would 2140 need to pass through a security gateway at the ANET/INET border. The 2141 method for deploying access routers and Proxys (i.e. as a single node 2142 or multiple nodes) is an ANET-local administrative consideration. 2144 3.17. AERO Route Optimization 2146 While data packets are flowing between a source and target node, 2147 route optimization SHOULD be used. Route optimization is initiated 2148 by the first eligible Route Optimization Source (ROS) closest to the 2149 source as follows: 2151 o For Clients on VPNed, NATed and Direct interfaces, the Server is 2152 the ROS. 2154 o For Clients on Proxyed interfaces, the Proxy is the ROS. 2156 o For Clients on native interfaces, the Client itself is the ROS. 2158 o For correspondent nodes on INET/EUN interfaces serviced by a 2159 Gateway, the Gateway is the ROS. 2161 The route optimization procedure is conducted between the ROS and the 2162 target Server/Gateway acting as a Route Optimization Responder (ROR) 2163 in the same manner as for IPv6 ND Address Resolution and using the 2164 same NS/NA messaging. The target may either be a MNP Client serviced 2165 by a Server, or a non-MNP correspondent reachable via a Gateway. 2167 The procedures are specified in the following sections. 2169 3.17.1. Route Optimization Initiation 2171 While data packets are flowing from the source node toward a target 2172 node, the ROS performs address resolution by sending an NS message to 2173 receive a solicited NA message from the ROR. 2175 When the ROS sends an NS, it includes the AERO address of the ROS as 2176 the source address (e.g., fe80::1) and the AERO address corresponding 2177 to the data packet's destination address as the destination address 2178 (e.g., if the destination address is 2001:db8:1:2::1 then the 2179 corresponding AERO address is fe80::2001:db8:1:2). The NS message 2180 includes an SLLAO with Link Layer Address set to the SPAN address of 2181 the ROS and with all other fields set to 0. The message SHOULD also 2182 include a Nonce and Timestamp option if the ROS needs to correlate NA 2183 replies. 2185 The ROS then encapsulates the NS message in a SPAN header with source 2186 set to its own SPAN address and destination set to the data packet's 2187 destination address, then sends it into the SPAN without decrementing 2188 the network-layer TTL/Hop Limit field. 2190 3.17.2. Relaying the NS 2192 When the Relay receives the NS message from the ROS, it discards the 2193 INET header and determines that the ROR is the next hop by consulting 2194 its standard IPv6 forwarding table for the SPAN header destination 2195 address. The Relay then forwards the SPAN message toward the ROR the 2196 same as for any IPv6 router. The final-hop Relay in the SPAN will 2197 deliver the message via a secured tunnel to the ROR. 2199 3.17.3. Processing the NS and Sending the NA 2201 When the ROR receives the NS message, it examines the AERO 2202 destination address to determine whether it has a neighbor cache 2203 entry and/or route that matches the target; if not, it drops the NS 2204 message and returns from processing. Next, if the target belongs to 2205 an MNP Client neighbor in the DEPARTED state the ROR changes the NS 2206 message SPAN destination address to the address of the Client's new 2207 Server, forwards the message into the SPAN and returns from 2208 processing. If the target belongs to an MNP Client neighbor in the 2209 REACHABLE state, the ROR instead adds the AERO source address to the 2210 target Client's Report List with time set to ReportTime. If the 2211 target belongs to a non-MNP route, the ROR continues processing 2212 without adding an entry to the Report List. 2214 The ROR then prepares a solicited NA message to send back to the ROS 2215 but does not create a neighbor cache entry. The ROR sets the NA 2216 source address to the destination AERO address of the NS, and 2217 includes the Nonce value received in the NS plus the current 2218 Timestamp. The ROR next includes a TLLAO with Interface ID set to 2219 0xffff, with S set to 1, with all P(i) values set to "low", and with 2220 Link Layer Address set to the ROR's SPAN address. If the target 2221 belongs to an MNP Client, the ROR sets the Prefix Length to the MNP 2222 prefix length; otherwise, it sets Prefix Length to the maximum of the 2223 non-MNP prefix length and 64. (Note that a /64 limit is imposed to 2224 avoid causing the ROS to set short prefixes (e.g., "default") that 2225 would match destinations for which the routing system includes more- 2226 specific prefixes. Note also that prefix lengths longer than /64 are 2227 out of scope for this specification.) 2229 If the target belongs to an MNP Client, the ROR next includes 2230 additional TLLAOs for all of the target Client's Interface IDs. For 2231 NATed, VPNed and Direct interfaces, the TLLAO Link Layer Addresses 2232 are the SPAN address of the ROR. For Proxyed and native interfaces, 2233 the TLLAO Link Layer Addresses are the SPAN addresses of the Proxys 2234 and the Client's native interfaces. The ROR finally encapsulates the 2235 NA message in a SPAN header with source set to its own SPAN address 2236 and destination set to the source SPAN address of the NS message, 2237 then forwards the message into the SPAN without decrementing the 2238 network-layer TTL/Hop Limit field. 2240 3.17.4. Relaying the NA 2242 When the Relay receives the NA message from the ROR, it discards the 2243 INET header and determines that the ROS is the next hop by consulting 2244 its standard IPv6 forwarding table for the SPAN header destination 2245 address. The Relay then forwards the SPAN-encapsulated NA message 2246 toward the ROS the same as for any IPv6 router. The final-hop Relay 2247 in the SPAN will deliver the message via a secured tunnel to the ROS. 2249 3.17.5. Processing the NA 2251 When the ROS receives the solicited NA message, it discards the INET 2252 and SPAN headers. The ROS next verifies the Nonce and Timestamp 2253 values, then creates an asymmetric neighbor cache entry for the ROR 2254 and caches all information found in the solicited NA TLLAOs. The ROS 2255 finally sets the asymmetric neighbor cache entry lifetime to 2256 ReachableTime seconds. 2258 3.17.6. Route Optimization Maintenance 2260 Following route optimization, the ROS forwards future data packets 2261 destined to the target via the addresses found in the cached link- 2262 layer information. The route optimization is shared by all sources 2263 that send packets to the target via the ROS, i.e., and not just the 2264 source on behalf of which the route optimization was initiated. 2266 While new data packets destined to the target are flowing through the 2267 ROS, it sends additional NS messages to the ROR before ReachableTime 2268 expires to receive a fresh solicited NA message the same as described 2269 in the previous sections. (Route optimization refreshment strategies 2270 are an implementation matter, with a non-normative example given in 2271 Appendix C.1). 2273 The ROS then updates the asymmetric neighbor cache entry to refresh 2274 ReachableTime, while (for MNP destinations) the ROR adds or updates 2275 the ROS address to the target Client's Report List and with time set 2276 to ReportTime. While no data packets are flowing, the ROS instead 2277 allows ReachableTime for the asymmetric neighbor cache entry to 2278 expire. When ReachableTime expires, the ROS deletes the asymmetric 2279 neighbor cache entry. Future data packets flowing through the ROS 2280 will again trigger a new route optimization exchange while initial 2281 data packets travel over a suboptimal route. 2283 The ROS may also receive unsolicited NA messages from the ROR at any 2284 time. If there is an asymmetric neighbor cache entry for the target, 2285 the ROS updates the link-layer information but does not update 2286 ReachableTime since the receipt of an unsolicited NA does not confirm 2287 that the forward path is still working. If there is no asymmetric 2288 neighbor cache entry, the route optimization source simply discards 2289 the unsolicited NA. Cases in which unsolicited NA messages are 2290 generated are specified in Section 3.19. 2292 In this arrangement, the ROS holds an asymmetric neighbor cache entry 2293 for the ROR, but the ROR does not hold an asymmetric neighbor cache 2294 entry for the ROS. The route optimization neighbor relationship is 2295 therefore asymmetric and unidirectional. If the target node also has 2296 packets to send back to the source node, then a separate route 2297 optimization procedure is performed in the reverse direction. But, 2298 there is no requirement that the forward and reverse paths be 2299 symmetric. 2301 3.18. Neighbor Unreachability Detection (NUD) 2303 AERO nodes perform Neighbor Unreachability Detection (NUD) per 2304 [RFC4861]. NUD is performed either reactively in response to 2305 persistent link-layer errors (see Section 3.14) or proactively to 2306 confirm reachability. The NUD algorithm may further be seeded by ND 2307 hints of forward progress, but care must be taken to avoid inferring 2308 reachability based on spoofed information. 2310 When an ROR directs an ROS to a neighbor with one or more target 2311 link-layer addresses, the ROS can proactively test each direct path 2312 by sending an initial NS message to elicit a solicited NA response. 2313 While testing the paths, the ROS can optionally continue sending 2314 packets via the SPAN, maintain a small queue of packets until target 2315 reachability is confirmed, or (optimistically) allow packets to flow 2316 via the direct paths. In any case, the ROS should only consider the 2317 neighbor unreachable if NUD fails over multiple target link-layer 2318 address paths. 2320 When a ROS sends an NS message used for NUD, it uses its AERO 2321 addresses as the IPv6 source address and the AERO address 2322 corresponding to a target link-layer address as the destination. For 2323 each target link-layer address, the source node encapsulates the NS 2324 message in SPAN/INET headers with its own SPAN address as the source 2325 and the SPAN address of the target as the destination, If the target 2326 is located within the same SPAN segment, the source sets the INET 2327 address of the target as the destination; otherwise, it sets the INET 2328 address of a Relay as the destination. The source then forwards the 2329 message into the SPAN. 2331 Paths that pass NUD tests are marked as "reachable", while those that 2332 do not are marked as "unreachable". These markings inform the AERO 2333 interface forwarding algorithm specified in Section 3.12. 2335 Proxys can perform NUD to verify Server reachability on behalf of 2336 their proxyed Clients so that the Clients need not engage in NUD 2337 messaging themselves. 2339 3.19. Mobility Management and Quality of Service (QoS) 2341 AERO is a Distributed Mobility Management (DMM) service. Each Server 2342 is responsible for only a subset of the Clients on the AERO link, as 2343 opposed to a Centralized Mobility Management (CMM) service where 2344 there is a single network mobility service for all Clients. Clients 2345 coordinate with their associated Servers via RS/RA exchanges to 2346 maintain the DMM profile, and the AERO routing system tracks all 2347 current Client/Server peering relationships. 2349 Servers provide a Mobility Anchor Point (MAP) for their dependent 2350 Clients. Clients are responsible for maintaining neighbor 2351 relationships with their Servers through periodic RS/RA exchanges, 2352 which also serves to confirm neighbor reachability. When a Client's 2353 underlying interface address and/or QoS information changes, the 2354 Client is responsible for updating the Server with this new 2355 information. Note that for Proxyed interfaces, however, the Proxy 2356 can perform the RS/RA exchanges on the Client's behalf. 2358 Mobility management considerations are specified in the following 2359 sections. 2361 3.19.1. Mobility Update Messaging 2363 Servers acting as MAPs accommodate mobility and/or QoS change events 2364 by sending an unsolicited NA message to each ROS in the target 2365 Client's Report List. When a MAP sends an unsolicited NA message, it 2366 sets the IPv6 source address to the Client's AERO address and sets 2367 the IPv6 destination address to all-nodes multicast (ff02::1). The 2368 MAP also includes a TLLAO with Interface ID 0xffff, S set to 1 and 2369 Link Layer address set to the MAP's SPAN address, and includes 2370 additional TLLAOs for all of the target Client's Interface IDs with 2371 Link Layer Addresses set to the corresponding SPAN addresses. The 2372 MAP finally encapsulates the message in a SPAN header with source set 2373 to its own SPAN address and destination set to the SPAN address of 2374 the ROS, then sends the message to a Relay in the SPAN. 2376 As for the hot-swap of interface cards discussed in Section 7.2.6 of 2377 [RFC4861], the transmission and reception of unsolicited NA messages 2378 is unreliable but provides a useful optimization. In well-connected 2379 Internetworks with robust data links unsolicited NA messages will be 2380 delivered with high probability, but in any case the MAP can 2381 optionally send up to MAX_NEIGHBOR_ADVERTISEMENT unsolicited NAs to 2382 each ROS to increase the likelihood that at least one will be 2383 received. 2385 When an ROS receives an unsolicited NA message, it ignores the 2386 message if there is no existing neighbor cache entry for the Client. 2387 Otherwise, it uses the included TLLAOs to update the Link Layer 2388 Address and QoS information in the neighbor cache entry, but does not 2389 reset ReachableTime since the receipt of an unsolicited NA message 2390 from the target Server does not provide confirmation that any forward 2391 paths to the target Client are working. 2393 If unsolicited NA messages are lost, the ROS may be left with stale 2394 address and/or QoS information for the Client for up to ReachableTime 2395 seconds. During this time, the ROS can continue sending packets to 2396 the target Client according to its current neighbor cache information 2397 but may receive persistent unsolicited NA messages as discussed in 2398 Section 3.19.5.1. 2400 3.19.2. Announcing Link-Layer Address and/or QoS Preference Changes 2402 When a Client needs to change its ANET addresses and/or QoS 2403 preferences (e.g., due to a mobility event), either the Client or its 2404 Proxys send RS messages to the Server via the SPAN with SLLAOs that 2405 include the new Client Port Number, Link Layer Address and P(i) 2406 values. If the RS messages are sent solely for the purpose of 2407 updating QoS preferences, Port Number and Link-Layer Address are set 2408 to 0. 2410 Up to MAX_RTR_SOLICITATION RS messages MAY be sent in parallel with 2411 sending actual data packets in case one or more RAs are lost. If all 2412 RAs are lost, the Client SHOULD re-associate with a new Server. 2414 When the Server receives the Client's changes, it sends unsolicited 2415 NA messages to all nodes in the Report List the same as described in 2416 the previous section. 2418 3.19.3. Bringing New Links Into Service 2420 When a Client needs to bring new ANET interfaces into service (e.g., 2421 when it activates a new data link), it sends an RS message to its 2422 Server via the ANET interface with SLLAOs that include the new Client 2423 Link Layer Address information. 2425 3.19.4. Removing Existing Links from Service 2427 When a Client needs to remove existing ANET interfaces from service 2428 (e.g., when it de-activates an existing data link), it sends an RS 2429 message to its Server with SLLAOs with D set to 1. 2431 If the Client needs to send RS messages over an ANET interface other 2432 than the one being removed from service, it MUST include a current 2433 SLLAO with S set to 1 for the sending interface and include 2434 additional SLLAOs with S set to 0 for any ANET interfaces being 2435 removed from service. 2437 3.19.5. Moving to a New Server 2439 When a Client associates with a new Server, it performs the Client 2440 procedures specified in Section 3.15.2. The Client then sends an RS 2441 message over any working ANET interface with destination set to the 2442 old Server's AERO address and with an SLLAO with R set to 1 to fully 2443 release itself from the old Server. The SLLAO also includes the SPAN 2444 address of the new Server in the Link Layer Address. If the Client 2445 does not receive an RA reply after MAX_RTR_SOLICITATIONS attempts 2446 over multiple ANET interfaces, the old Server may have failed and the 2447 Client should discontinue its release attempts. 2449 When the old Server processes the RS, it sends unsolicited NA 2450 messages with a single TLLAO with Interface ID set to 0xffff and with 2451 R and S set to 1 to all ROSs in the Client's Report List. The Server 2452 also changes the symmetric neighbor cache entry state to DEPARTED, 2453 sets the link-layer address of the Client to the address found in the 2454 RS SLLAO (i.e., the SPAN address of the new Server), and sets a timer 2455 to DepartTime seconds. The old Server then returns an immediate RA 2456 message to the Client with Router Lifetime set to 0. After a short 2457 delay (e.g., 2 seconds), the old Server withdraws the Client's MNP 2458 from the routing system. After DepartTime expires, the old Server 2459 deletes the symmetric neighbor cache entry. 2461 Clients SHOULD NOT move rapidly between Servers in order to avoid 2462 causing excessive oscillations in the AERO routing system. Examples 2463 of when a Client might wish to change to a different Server include a 2464 Server that has gone unreachable, topological movements of 2465 significant distance, movement to a new geographic region, movement 2466 to a new SPAN segment, etc. 2468 3.19.5.1. Accommodating Orphaned Fragments 2470 When a Client moves to a new Server, there is a chance that some of 2471 the fragments of a multiple fragment SPAN packet have already arrived 2472 at the old Server, while others are en route to the new Server. The 2473 old Server forwards these orphaned fragments to the new Server over 2474 the SPAN by encapsulating them in a second SPAN header with the old 2475 Server's SPAN address as the source and the SPAN address of the new 2476 Server as the destination. 2478 The new Server will then receive a packet that has an outer SPAN 2479 header inserted by the old Server and an inner SPAN header inserted 2480 by the original ROS. It then discards the outer SPAN header and adds 2481 the enclosed fragment to the reassembly buffer for this SPAN packet. 2482 If the Client has already departed from this new Server, the new 2483 Server instead re-encapsulates the fragment by replacing the outer 2484 SPAN header and forwarding the packet to the next Server the same as 2485 described above. In this way, wayward fragments will follow the 2486 trail of departed Servers until they eventually reach the current 2487 Server. 2489 Note that in some cases reassemblies may be left incomplete after the 2490 Client has departed. Proxys and Servers discard any incomplete 2491 reassemblies when the DEPARTED neighbor cache entry is deleted. 2493 3.20. Multicast 2495 The AERO Client provides an IGMP (IPv4) [RFC2236] or MLD (IPv6) 2496 [RFC3810] proxy service for its EUNs and/or hosted applications 2497 [RFC4605]. The Client forwards IGMP/MLD messages over any of its 2498 ANET interfaces for which group membership is required. The IGMP/MLD 2499 messages may be further forwarded by a first-hop ANET access router 2500 acting as an IGMP/MLD-snooping switch [RFC4541], then ultimately 2501 delivered to an AERO Proxy/Server acting as a Protocol Independent 2502 Multicast - Sparse-Mode (PIM-SM, or simply "PIM") Designated Router 2503 (DR) [RFC7761]. AERO Gateways also act as PIM routers (i.e., the 2504 same as AERO Proxys/Servers) on behalf of nodes on INET/EUN networks. 2505 The behaviors identified in the following sections correspond to 2506 Source-Specific Multicast (SSM) and Any-Source Multicast (ASM) 2507 operational modes. 2509 3.20.1. Source-Specific Multicast (SSM) 2511 When an ROS (i.e., an AERO Proxy/Server/Gateway) "X" acting as PIM 2512 router receives a Join/Prune message from a node on its downstream 2513 interfaces containing one or more ((S)ource, (G)roup) pairs, it 2514 updates its Multicast Routing Information Base (MRIB) accordingly. 2515 For each S belonging to a prefix reachable via X's non-AERO 2516 interfaces, X then forwards the (S, G) Join/Prune to any PIM routers 2517 on those interfaces per [RFC7761]. 2519 For each S belonging to a prefix reachable via X's AERO interface, X 2520 originates a separate copy of the Join/Prune for each (S,G) in the 2521 message using its own AERO address as the source address and ALL-PIM- 2522 ROUTERS as the destination address. X then encapsulates each message 2523 in a SPAN header with source address set to the SPAN address of X and 2524 destination address set to S then forwards the message into the SPAN. 2525 The SPAN in turn forwards the message to AERO Server/Gateway "Y" that 2526 services S. At the same time, if the message was a Join, X sends a 2527 route-optimization NS message toward each S the same as discussed in 2528 Section 3.17. The resulting NAs will return the AERO address for the 2529 prefix that matches S as the network-layer source address and TLLAOs 2530 with the SPAN addresses corresponding to any Interface IDs that are 2531 currently servicing S. 2533 When Y processes the Join/Prune message, if S located behind any 2534 Native, Direct, VPNed or NATed interfaces Y acts as a PIM router and 2535 updates its MRIB to list X as the next hop in the reverse path. If S 2536 is located behind any Proxys "Z"*, Y also forwards the message to 2537 each Z* over the SPAN while continuing to use the AERO address of X 2538 as the source address. Each Z* then updates its MRIB accordingly and 2539 maintains the AERO address of X as the next hop in the reverse path. 2540 Since the Relays in the SPAN do not examine network layer control 2541 messages, this means that the (reverse) multicast tree path is simply 2542 from each Z* (and/or Y) to X with no other multicast-aware routers in 2543 the path. If any Z* (and/or Y) is located on the same SPAN segment 2544 as X, the multicast data traffic sent to X directly using SPAN/INET 2545 encapsulation instead of via a Relay. 2547 Following the initial Join/Prune and NS/NA messaging, X maintains an 2548 asymmetric neighbor cache entry for each S the same as if X was 2549 sending unicast data traffic to S. In particular, X performs 2550 additional NS/NA exchanges to keep the neighbor cache entry alive for 2551 up to t_periodic seconds [RFC7761]. If no new Joins are received 2552 within t_periodic seconds, X allows the neighbor cache entry to 2553 expire. Finally, if X receives any additional Join/Prune messages 2554 for (S,G) it forwards the messages to each Y and Z* in the neighbor 2555 cache entry over the SPAN. 2557 At some later time, Client C that holds an MNP for source S may 2558 depart from a first Proxy Z1 and/or connect via a new Proxy Z2. In 2559 that case, Y sends an unsolicited NA message to X the same as 2560 specified for unicast mobility in Section 3.19. When X receives the 2561 unsolicited NA message, it updates its asymmetric neighbor cache 2562 entry for the AERO address for source S and sends new Join messages 2563 to any new Proxys Z2. There is no requirement to send any Prune 2564 messages to old Proxys Z1 since source S will no longer source any 2565 multicast data traffic via Z1. Instead, the multicast state for 2566 (S,G) in Proxy Z1 will soon time out since no new Joins will arrive. 2568 After some later time, C may move to a new Server Y2 and depart from 2569 old Sever Y1. In that case, Y1 sends Join messages for any of C's 2570 active (S,G) groups to Y2 while including its own AERO address as the 2571 source address. This causes Y2 to include Y1 in the multicast 2572 forwarding tree during the interim time that Y1's symmetric neighbor 2573 cache entry for C is in the DEPARTED state. At the same time, Y1 2574 sends an unsolicited NA message to X with an Interface ID 0xffff and 2575 R set to 1 to cause X to release its asymmetric neighbor cache entry. 2576 X then sends a new Join message to S via the SPAN and re-initiates 2577 route optimization the same as if it were receiving a fresh Join 2578 message from a node on a downstream link. 2580 3.20.2. Any-Source Multicast (ASM) 2582 When an ROS X acting as a PIM router receives a Join/Prune from a 2583 node on its downstream interfaces containing one or more (*,G) pairs, 2584 it updates its Multicast Routing Information Base (MRIB) accordingly. 2585 X then forwards a copy of the message to the Rendezvous Point (RP) R 2586 for each G over the SPAN. X uses its own AERO address as the source 2587 address and ALL-PIM-ROUTERS as the destination address, then 2588 encapsulates each message in a SPAN header with source address set to 2589 the SPAN address of X and destination address set to R, then sends 2590 the message into the SPAN. At the same time, if the message was a 2591 Join X initiates NS/NA route optimization the same as for the SSM 2592 case discussed in Section 3.20.1. 2594 For each source S that sends multicast traffic to group G via R, the 2595 Proxy/Server Z* for the Client that aggregates S encapsulates the 2596 packets in PIM Register messages and forwards them to R via the SPAN. 2597 R may then elect to send a PIM Join to Z* over the SPAN. This will 2598 result in an (S,G) tree rooted at Z* with R as the next hop so that R 2599 will begin to receive two copies of the packet; one native copy from 2600 the (S, G) tree and a second copy from the pre-existing (*, G) tree 2601 that still uses PIM Register encapsulation. R can then issue a PIM 2602 Register-stop message to suppress the Register-encapsulated stream. 2603 At some later time, if C moves to a new Proxy/Server Z*, it resumes 2604 sending packets via PIM Register encapsulation via the new Z*. 2606 At the same time, as multicast listeners discover individual S's for 2607 a given G, they can initiate an (S,G) Join for each S under the same 2608 procedures discussed in Section 3.20.1. Once the (S,G) tree is 2609 established, the listeners can send (S, G) Prune messages to R so 2610 that multicast packets for group G sourced by S will only be 2611 delivered via the (S, G) tree and not from the (*, G) tree rooted at 2612 R. All mobility considerations discussed for SSM apply. 2614 3.20.3. Bi-Directional PIM (BIDIR-PIM) 2616 Bi-Directional PIM (BIDIR-PIM) [RFC5015] provides an alternate 2617 approach to ASM that treats the Rendezvous Point (RP) as a Designated 2618 Forwarder (DF). Further considerations for BIDIR-PIM are out of 2619 scope. 2621 3.21. Operation over Multiple AERO Links (VLANs) 2623 An AERO Client can connect to multiple AERO links the same as for any 2624 data link service. In that case, the Client maintains a distinct 2625 AERO interface for each link, e.g., 'aero0' for the first link, 2626 'aero1' for the second, 'aero2' for the third, etc. Each AERO link 2627 would include its own distinct set of Relays, Servers and Proxys, 2628 thereby providing redundancy in case of failures. 2630 The Relays, Servers and Proxys on each AERO link can assign AERO and 2631 SPAN addresses that use the same or different numberings from those 2632 on other links. Since the links are mutually independent there is no 2633 requirement for avoiding inter-link address duplication, e.g., the 2634 same AERO address such as fe80::1000 could be used to number distinct 2635 nodes that connect to different links. 2637 Each AERO link could utilize the same or different ANET connections. 2638 The links can be distinguished at the link-layer via Virtual Local 2639 Area Network (VLAN) tagging (e.g., IEEE 802.1Q) and/or through 2640 assignment of distinct sets of MSPs on each link. This gives rise to 2641 the opportunity for supporting multiple redundant networked paths, 2642 where each VLAN is distinguished by a different label (e.g., colors 2643 such as Red, Green, Blue, etc.). In particular, the Client can tag 2644 its RS messages with the appropriate label to cause the network to 2645 select the desired VLAN. 2647 Clients that connect to multiple AERO interfaces can select the 2648 outgoing interface appropriate for a given Red/Blue/Green/etc. 2649 traffic profile while (in the reverse direction) correspondent nodes 2650 must have some way of steering their packets destined to a target via 2651 the correct AERO link. 2653 In a first alternative, if each AERO link services different MSPs, 2654 then the Client can receive a distinct MNP from each of the links. 2655 IP routing will therefore assure that the correct Red/Green/Blue/etc. 2656 network is used for both outbound and inbound traffic. This can be 2657 accomplished using existing technologies and approaches, and without 2658 requiring any special supporting code in correspondent nodes or 2659 Relays. 2661 In a second alternative, if each AERO link services the same MSP(s) 2662 then each link could assign a distinct "AERO Link Anycast" address 2663 that is configured by all Relays on the link. Correspondent nodes 2664 then include a "type 4" routing header with the Anycast address for 2665 the AERO link as the IPv6 destination and with the address of the 2666 target encoded as the "next segment" in the routing header 2667 [RFC8402][I-D.ietf-6man-segment-routing-header]. Standard IP routing 2668 will then direct the packet to the nearest Relay for the correct AERO 2669 link, which will replace the destination address with the target 2670 address then forward the packet to the target. 2672 3.22. DNS Considerations 2674 AERO Client MNs and INET correspondent nodes consult the Domain Name 2675 System (DNS) the same as for any Internetworking node. When 2676 correspondent nodes and Client MNs use different IP protocol versions 2677 (e.g., IPv4 correspondents and IPv6 MNs), the INET DNS must maintain 2678 A records for IPv4 address mappings to MNs which must then be 2679 populated in Gateway NAT64 mapping caches. In that way, an IPv4 2680 correspondent node can send packets to the IPv4 address mapping of 2681 the target MN, and the Gateway will translate the IPv4 header and 2682 destination address into an IPv6 header and IPv6 destination address 2683 of the MN. 2685 When an AERO Client registers with an AERO Server, the Server returns 2686 the address(es) of DNS servers in RDNSS options [RFC6106]. The DNS 2687 server provides the IP addresses of other MNs and correspondent nodes 2688 in AAAA records for IPv6 or A records for IPv4. 2690 3.23. Transition Considerations 2692 The SPAN ensures that dissimilar INET partitions can be joined into a 2693 single unified AERO link, even though the partitions themselves may 2694 have differing protocol versions and/or incompatible addressing 2695 plans. However, a commonality can be achieved by incrementally 2696 distributing globally routable (i.e., native) IP prefixes to 2697 eventually reach all nodes (both mobile and fixed) in all SPAN 2698 segments. This can be accomplished by incrementally deploying AERO 2699 Gateways on each INET partition, with each Gateway distributing its 2700 MNPs and/or discovering non-MNP prefixes on its INET links. 2702 This gives rise to the opportunity to eventually distribute native IP 2703 addresses to all nodes, and to present a unified AERO link view 2704 (bridged by the SPAN) even if the INET partitions remain in their 2705 current protocol and addressing plans. In that way, the AERO link 2706 can serve the dual purpose of providing a mobility service and a 2707 transition service. Or, if an INET partition is transitioned to a 2708 native IP protocol version and addressing scheme that is compatible 2709 with the AERO link MNP-based addressing scheme, the partition and 2710 AERO link can be joined by Gateways. 2712 Gateways that connect INETs/EUNs with dissimilar IP protocol versions 2713 must employ a network address and protocol translation function such 2714 as NAT64[RFC6146]. 2716 4. Implementation Status 2718 An AERO implementation based on OpenVPN (https://openvpn.net/) was 2719 announced on the v6ops mailing list on January 10, 2018 and an 2720 initial public release of the AERO proof-of-concept source code was 2721 announced on the intarea mailing list on August 21, 2015. The latest 2722 versions are available at: http://linkupnetworks.net/aero. 2724 5. IANA Considerations 2726 The IANA has assigned a 4-octet Private Enterprise Number "45282" for 2727 AERO in the "enterprise-numbers" registry. 2729 The IANA has assigned the UDP port number "8060" for an earlier 2730 experimental version of AERO [RFC6706]. This document obsoletes 2731 [RFC6706] and claims the UDP port number "8060" for all future use. 2733 No further IANA actions are required. 2735 6. Security Considerations 2737 AERO Relays configure secured tunnels with AERO Servers and Proxys 2738 within their local SPAN segments. Applicable secured tunnel 2739 alternatives include IPsec [RFC4301], TLS/SSL [RFC8446], DTLS 2740 [RFC6347], etc. The AERO Relays of all SPAN segments in turn 2741 configure secured tunnels for their neighboring AERO Relays across 2742 the SPAN. Therefore, packets that traverse the SPAN between any pair 2743 of AERO link neighbors are already secured. 2745 AERO Servers, Gateways and Proxys targeted by a route optimization 2746 may also receive packets directly from the INET partitions instead of 2747 via the SPAN. For INET partitions that apply effective ingress 2748 filtering to defeat source address spoofing, the simple data origin 2749 authentication procedures in Section 3.11 can be applied. This 2750 implies that the ROS list must be maintained consistently by all 2751 route optimization targets within the same INET partition, and that 2752 the ROS list must be securely managed by the partition's 2753 administrative authority. 2755 For INET partitions that cannot apply effective ingress filtering, 2756 the two options for securing communications include 1) disable route 2757 optimization so that all traffic is conveyed over secured tunnels via 2758 the SPAN, or 2) enable on-demand secure tunnel creation between INET 2759 partition neighbors. Option 1) would result in longer routes than 2760 necessary and traffic concentration on overburdened critical 2761 infrastructure elements. Option 2) could be coordinated by 2762 establishing a secured tunnel on-demand instead of performing an NS/ 2763 NA exchange in the route optimization procedures. Procedures for 2764 establishing on-demand secured tunnels are out of scope. 2766 AERO Clients that connect to secured enclaves need not apply security 2767 to their ND messages, since the messages will be intercepted by a 2768 perimeter Proxy that applies security on its outward-facing 2769 interface. AERO Clients located outside of secured enclaves SHOULD 2770 use symmetric network and/or transport layer security services, but 2771 when there are many prospective neighbors with dynamically changing 2772 connectivity an asymmetric security service such as SEND may be 2773 needed (see: Appendix C.6). 2775 Application endpoints SHOULD use application-layer security services 2776 such as TLS/SSL, DTLS or SSH [RFC4251] to assure the same level of 2777 protection as for critical secured Internet services. AERO Clients 2778 that require host-based VPN services SHOULD use symmetric network 2779 and/or transport layer security services such as IPsec, TLS/SSL, 2780 DTLS, etc. AERO Proxys and Servers can also provide a network-based 2781 VPN service on behalf of the Client, e.g., if the Client is located 2782 within a secured enclave and cannot establish a VPN on its own 2783 behalf. 2785 AERO Servers and Relays present targets for traffic amplification 2786 Denial of Service (DoS) attacks. This concern is no different than 2787 for widely-deployed VPN security gateways in the Internet, where 2788 attackers could send spoofed packets to the gateways at high data 2789 rates. This can be mitigated by connecting Servers and Relays over 2790 dedicated links with no connections to the Internet and/or when 2791 connections to the Internet are only permitted through well-managed 2792 firewalls. Traffic amplification DoS attacks can also target an AERO 2793 Client's low data rate links. This is a concern not only for Clients 2794 located on the open Internet but also for Clients in secured 2795 enclaves. AERO Servers and Proxys can institute rate limits that 2796 protect Clients from receiving packet floods that could DoS low data 2797 rate links. 2799 AERO Gateways must implement ingress filtering to avoid a spoofing 2800 attack in which spurious SPAN messages are injected into an AERO link 2801 from an outside attacker. AERO Clients MUST ensure that their 2802 connectivity is not used by unauthorized nodes on their EUNs to gain 2803 access to a protected network, i.e., AERO Clients that act as routers 2804 MUST NOT provide routing services for unauthorized nodes. (This 2805 concern is no different than for ordinary hosts that receive an IP 2806 address delegation but then "share" the address with other nodes via 2807 some form of Internet connection sharing such as tethering.) 2809 The MAP list and ROS lists MUST be well-managed and secured from 2810 unauthorized tampering, even though the list contains only public 2811 information. The MAP list can be conveyed to the Client, e.g., 2812 through secure upload of a static file, through DNS lookups, etc. 2813 The ROS list can be conveyed to Servers and Proxys through 2814 administrative action, secured file distribution, etc. 2816 Although public domain and commercial SEND implementations exist, 2817 concerns regarding the strength of the cryptographic hash algorithm 2818 have been documented [RFC6273] [RFC4982]. 2820 Security considerations for accepting link-layer ICMP messages and 2821 reflected packets are discussed throughout the document. 2823 7. Acknowledgements 2825 Discussions in the IETF, aviation standards communities and private 2826 exchanges helped shape some of the concepts in this work. 2827 Individuals who contributed insights include Mikael Abrahamsson, Mark 2828 Andrews, Fred Baker, Bob Braden, Stewart Bryant, Brian Carpenter, 2829 Wojciech Dec, Ralph Droms, Adrian Farrel, Nick Green, Sri Gundavelli, 2830 Brian Haberman, Bernhard Haindl, Joel Halpern, Tom Herbert, Sascha 2831 Hlusiak, Lee Howard, Andre Kostur, Hubert Kuenig, Ted Lemon, Andy 2832 Malis, Satoru Matsushima, Tomek Mrugalski, Madhu Niraula, Alexandru 2833 Petrescu, Behcet Saikaya, Michal Skorepa, Joe Touch, Bernie Volz, 2834 Ryuji Wakikawa, Tony Whyman, Lloyd Wood and James Woodyatt. Members 2835 of the IESG also provided valuable input during their review process 2836 that greatly improved the document. Special thanks go to Stewart 2837 Bryant, Joel Halpern and Brian Haberman for their shepherding 2838 guidance during the publication of the AERO first edition. 2840 This work has further been encouraged and supported by Boeing 2841 colleagues including Kyle Bae, M. Wayne Benson, Dave Bernhardt, Cam 2842 Brodie, Balaguruna Chidambaram, Irene Chin, Bruce Cornish, Claudiu 2843 Danilov, Wen Fang, Anthony Gregory, Jeff Holland, Seth Jahne, Ed 2844 King, Gene MacLean III, Rob Muszkiewicz, Sean O'Sullivan, Greg 2845 Saccone, Kent Shuey, Brian Skeen, Mike Slane, Carrie Spiker, Brendan 2846 Williams, Julie Wulff, Yueli Yang, Eric Yeh and other members of the 2847 BR&T and BIT mobile networking teams. Kyle Bae, Wayne Benson and 2848 Eric Yeh are especially acknowledged for implementing the AERO 2849 functions as extensions to the public domain OpenVPN distribution. 2851 Earlier works on NBMA tunneling approaches are found in 2852 [RFC2529][RFC5214][RFC5569]. 2854 Many of the constructs presented in this second edition of AERO are 2855 based on the author's earlier works, including: 2857 o The Internet Routing Overlay Network (IRON) 2858 [RFC6179][I-D.templin-ironbis] 2860 o Virtual Enterprise Traversal (VET) 2861 [RFC5558][I-D.templin-intarea-vet] 2863 o The Subnetwork Encapsulation and Adaptation Layer (SEAL) 2864 [RFC5320][I-D.templin-intarea-seal] 2866 o AERO, First Edition [RFC6706] 2868 Note that these works cite numerous earlier efforts that are not also 2869 cited here due to space limitations. The authors of those earlier 2870 works are acknowledged for their insights. 2872 This work is aligned with the NASA Safe Autonomous Systems Operation 2873 (SASO) program under NASA contract number NNA16BD84C. 2875 This work is aligned with the FAA as per the SE2025 contract number 2876 DTFAWA-15-D-00030. 2878 This work is aligned with the Boeing Information Technology (BIT) 2879 MobileNet program. 2881 This work is aligned with the Boeing autonomy program. 2883 8. References 2885 8.1. Normative References 2887 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, 2888 DOI 10.17487/RFC0791, September 1981, 2889 . 2891 [RFC0792] Postel, J., "Internet Control Message Protocol", STD 5, 2892 RFC 792, DOI 10.17487/RFC0792, September 1981, 2893 . 2895 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 2896 Requirement Levels", BCP 14, RFC 2119, 2897 DOI 10.17487/RFC2119, March 1997, 2898 . 2900 [RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in 2901 IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473, 2902 December 1998, . 2904 [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black, 2905 "Definition of the Differentiated Services Field (DS 2906 Field) in the IPv4 and IPv6 Headers", RFC 2474, 2907 DOI 10.17487/RFC2474, December 1998, 2908 . 2910 [RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander, 2911 "SEcure Neighbor Discovery (SEND)", RFC 3971, 2912 DOI 10.17487/RFC3971, March 2005, 2913 . 2915 [RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)", 2916 RFC 3972, DOI 10.17487/RFC3972, March 2005, 2917 . 2919 [RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and 2920 More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191, 2921 November 2005, . 2923 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 2924 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 2925 DOI 10.17487/RFC4861, September 2007, 2926 . 2928 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 2929 Address Autoconfiguration", RFC 4862, 2930 DOI 10.17487/RFC4862, September 2007, 2931 . 2933 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 2934 (IPv6) Specification", STD 86, RFC 8200, 2935 DOI 10.17487/RFC8200, July 2017, 2936 . 2938 [RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A., 2939 Richardson, M., Jiang, S., Lemon, T., and T. Winters, 2940 "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", 2941 RFC 8415, DOI 10.17487/RFC8415, November 2018, 2942 . 2944 8.2. Informative References 2946 [BGP] Huston, G., "BGP in 2015, http://potaroo.net", January 2947 2016. 2949 [I-D.ietf-6man-segment-routing-header] 2950 Filsfils, C., Dukes, D., Previdi, S., Leddy, J., 2951 Matsushima, S., and d. daniel.voyer@bell.ca, "IPv6 Segment 2952 Routing Header (SRH)", draft-ietf-6man-segment-routing- 2953 header-19 (work in progress), May 2019. 2955 [I-D.ietf-dmm-distributed-mobility-anchoring] 2956 Chan, A., Wei, X., Lee, J., Jeon, S., and C. Bernardos, 2957 "Distributed Mobility Anchoring", draft-ietf-dmm- 2958 distributed-mobility-anchoring-13 (work in progress), 2959 March 2019. 2961 [I-D.ietf-intarea-gue] 2962 Herbert, T., Yong, L., and O. Zia, "Generic UDP 2963 Encapsulation", draft-ietf-intarea-gue-07 (work in 2964 progress), March 2019. 2966 [I-D.ietf-intarea-gue-extensions] 2967 Herbert, T., Yong, L., and F. Templin, "Extensions for 2968 Generic UDP Encapsulation", draft-ietf-intarea-gue- 2969 extensions-06 (work in progress), March 2019. 2971 [I-D.ietf-intarea-tunnels] 2972 Touch, J. and M. Townsley, "IP Tunnels in the Internet 2973 Architecture", draft-ietf-intarea-tunnels-09 (work in 2974 progress), July 2018. 2976 [I-D.ietf-rtgwg-atn-bgp] 2977 Templin, F., Saccone, G., Dawra, G., Lindem, A., and V. 2978 Moreno, "A Simple BGP-based Mobile Routing System for the 2979 Aeronautical Telecommunications Network", draft-ietf- 2980 rtgwg-atn-bgp-02 (work in progress), May 2019. 2982 [I-D.templin-6man-dhcpv6-ndopt] 2983 Templin, F., "A Unified Stateful/Stateless Configuration 2984 Service for IPv6", draft-templin-6man-dhcpv6-ndopt-07 2985 (work in progress), December 2018. 2987 [I-D.templin-intarea-grefrag] 2988 Templin, F., "GRE Tunnel Level Fragmentation", draft- 2989 templin-intarea-grefrag-04 (work in progress), July 2016. 2991 [I-D.templin-intarea-seal] 2992 Templin, F., "The Subnetwork Encapsulation and Adaptation 2993 Layer (SEAL)", draft-templin-intarea-seal-68 (work in 2994 progress), January 2014. 2996 [I-D.templin-intarea-vet] 2997 Templin, F., "Virtual Enterprise Traversal (VET)", draft- 2998 templin-intarea-vet-40 (work in progress), May 2013. 3000 [I-D.templin-ironbis] 3001 Templin, F., "The Interior Routing Overlay Network 3002 (IRON)", draft-templin-ironbis-16 (work in progress), 3003 March 2014. 3005 [I-D.templin-v6ops-pdhost] 3006 Templin, F., "IPv6 Prefix Delegation and Multi-Addressing 3007 Models", draft-templin-v6ops-pdhost-23 (work in progress), 3008 December 2018. 3010 [OVPN] OpenVPN, O., "http://openvpn.net", October 2016. 3012 [RFC1035] Mockapetris, P., "Domain names - implementation and 3013 specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, 3014 November 1987, . 3016 [RFC1122] Braden, R., Ed., "Requirements for Internet Hosts - 3017 Communication Layers", STD 3, RFC 1122, 3018 DOI 10.17487/RFC1122, October 1989, 3019 . 3021 [RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191, 3022 DOI 10.17487/RFC1191, November 1990, 3023 . 3025 [RFC1812] Baker, F., Ed., "Requirements for IP Version 4 Routers", 3026 RFC 1812, DOI 10.17487/RFC1812, June 1995, 3027 . 3029 [RFC2003] Perkins, C., "IP Encapsulation within IP", RFC 2003, 3030 DOI 10.17487/RFC2003, October 1996, 3031 . 3033 [RFC2236] Fenner, W., "Internet Group Management Protocol, Version 3034 2", RFC 2236, DOI 10.17487/RFC2236, November 1997, 3035 . 3037 [RFC2529] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4 3038 Domains without Explicit Tunnels", RFC 2529, 3039 DOI 10.17487/RFC2529, March 1999, 3040 . 3042 [RFC2764] Gleeson, B., Lin, A., Heinanen, J., Armitage, G., and A. 3043 Malis, "A Framework for IP Based Virtual Private 3044 Networks", RFC 2764, DOI 10.17487/RFC2764, February 2000, 3045 . 3047 [RFC2784] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P. 3048 Traina, "Generic Routing Encapsulation (GRE)", RFC 2784, 3049 DOI 10.17487/RFC2784, March 2000, 3050 . 3052 [RFC2890] Dommety, G., "Key and Sequence Number Extensions to GRE", 3053 RFC 2890, DOI 10.17487/RFC2890, September 2000, 3054 . 3056 [RFC2923] Lahey, K., "TCP Problems with Path MTU Discovery", 3057 RFC 2923, DOI 10.17487/RFC2923, September 2000, 3058 . 3060 [RFC2983] Black, D., "Differentiated Services and Tunnels", 3061 RFC 2983, DOI 10.17487/RFC2983, October 2000, 3062 . 3064 [RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition 3065 of Explicit Congestion Notification (ECN) to IP", 3066 RFC 3168, DOI 10.17487/RFC3168, September 2001, 3067 . 3069 [RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener 3070 Discovery Version 2 (MLDv2) for IPv6", RFC 3810, 3071 DOI 10.17487/RFC3810, June 2004, 3072 . 3074 [RFC3819] Karn, P., Ed., Bormann, C., Fairhurst, G., Grossman, D., 3075 Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J., and L. 3076 Wood, "Advice for Internet Subnetwork Designers", BCP 89, 3077 RFC 3819, DOI 10.17487/RFC3819, July 2004, 3078 . 3080 [RFC4213] Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms 3081 for IPv6 Hosts and Routers", RFC 4213, 3082 DOI 10.17487/RFC4213, October 2005, 3083 . 3085 [RFC4251] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH) 3086 Protocol Architecture", RFC 4251, DOI 10.17487/RFC4251, 3087 January 2006, . 3089 [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A 3090 Border Gateway Protocol 4 (BGP-4)", RFC 4271, 3091 DOI 10.17487/RFC4271, January 2006, 3092 . 3094 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 3095 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 3096 2006, . 3098 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 3099 Internet Protocol", RFC 4301, DOI 10.17487/RFC4301, 3100 December 2005, . 3102 [RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery 3103 Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April 3104 2006, . 3106 [RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet 3107 Control Message Protocol (ICMPv6) for the Internet 3108 Protocol Version 6 (IPv6) Specification", STD 89, 3109 RFC 4443, DOI 10.17487/RFC4443, March 2006, 3110 . 3112 [RFC4511] Sermersheim, J., Ed., "Lightweight Directory Access 3113 Protocol (LDAP): The Protocol", RFC 4511, 3114 DOI 10.17487/RFC4511, June 2006, 3115 . 3117 [RFC4541] Christensen, M., Kimball, K., and F. Solensky, 3118 "Considerations for Internet Group Management Protocol 3119 (IGMP) and Multicast Listener Discovery (MLD) Snooping 3120 Switches", RFC 4541, DOI 10.17487/RFC4541, May 2006, 3121 . 3123 [RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick, 3124 "Internet Group Management Protocol (IGMP) / Multicast 3125 Listener Discovery (MLD)-Based Multicast Forwarding 3126 ("IGMP/MLD Proxying")", RFC 4605, DOI 10.17487/RFC4605, 3127 August 2006, . 3129 [RFC4607] Holbrook, H. and B. Cain, "Source-Specific Multicast for 3130 IP", RFC 4607, DOI 10.17487/RFC4607, August 2006, 3131 . 3133 [RFC4963] Heffner, J., Mathis, M., and B. Chandler, "IPv4 Reassembly 3134 Errors at High Data Rates", RFC 4963, 3135 DOI 10.17487/RFC4963, July 2007, 3136 . 3138 [RFC4982] Bagnulo, M. and J. Arkko, "Support for Multiple Hash 3139 Algorithms in Cryptographically Generated Addresses 3140 (CGAs)", RFC 4982, DOI 10.17487/RFC4982, July 2007, 3141 . 3143 [RFC5015] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano, 3144 "Bidirectional Protocol Independent Multicast (BIDIR- 3145 PIM)", RFC 5015, DOI 10.17487/RFC5015, October 2007, 3146 . 3148 [RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site 3149 Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214, 3150 DOI 10.17487/RFC5214, March 2008, 3151 . 3153 [RFC5320] Templin, F., Ed., "The Subnetwork Encapsulation and 3154 Adaptation Layer (SEAL)", RFC 5320, DOI 10.17487/RFC5320, 3155 February 2010, . 3157 [RFC5522] Eddy, W., Ivancic, W., and T. Davis, "Network Mobility 3158 Route Optimization Requirements for Operational Use in 3159 Aeronautics and Space Exploration Mobile Networks", 3160 RFC 5522, DOI 10.17487/RFC5522, October 2009, 3161 . 3163 [RFC5558] Templin, F., Ed., "Virtual Enterprise Traversal (VET)", 3164 RFC 5558, DOI 10.17487/RFC5558, February 2010, 3165 . 3167 [RFC5569] Despres, R., "IPv6 Rapid Deployment on IPv4 3168 Infrastructures (6rd)", RFC 5569, DOI 10.17487/RFC5569, 3169 January 2010, . 3171 [RFC6106] Jeong, J., Park, S., Beloeil, L., and S. Madanapalli, 3172 "IPv6 Router Advertisement Options for DNS Configuration", 3173 RFC 6106, DOI 10.17487/RFC6106, November 2010, 3174 . 3176 [RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful 3177 NAT64: Network Address and Protocol Translation from IPv6 3178 Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146, 3179 April 2011, . 3181 [RFC6179] Templin, F., Ed., "The Internet Routing Overlay Network 3182 (IRON)", RFC 6179, DOI 10.17487/RFC6179, March 2011, 3183 . 3185 [RFC6221] Miles, D., Ed., Ooghe, S., Dec, W., Krishnan, S., and A. 3186 Kavanagh, "Lightweight DHCPv6 Relay Agent", RFC 6221, 3187 DOI 10.17487/RFC6221, May 2011, 3188 . 3190 [RFC6273] Kukec, A., Krishnan, S., and S. Jiang, "The Secure 3191 Neighbor Discovery (SEND) Hash Threat Analysis", RFC 6273, 3192 DOI 10.17487/RFC6273, June 2011, 3193 . 3195 [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer 3196 Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, 3197 January 2012, . 3199 [RFC6438] Carpenter, B. and S. Amante, "Using the IPv6 Flow Label 3200 for Equal Cost Multipath Routing and Link Aggregation in 3201 Tunnels", RFC 6438, DOI 10.17487/RFC6438, November 2011, 3202 . 3204 [RFC6706] Templin, F., Ed., "Asymmetric Extended Route Optimization 3205 (AERO)", RFC 6706, DOI 10.17487/RFC6706, August 2012, 3206 . 3208 [RFC6864] Touch, J., "Updated Specification of the IPv4 ID Field", 3209 RFC 6864, DOI 10.17487/RFC6864, February 2013, 3210 . 3212 [RFC7269] Chen, G., Cao, Z., Xie, C., and D. Binet, "NAT64 3213 Deployment Options and Experience", RFC 7269, 3214 DOI 10.17487/RFC7269, June 2014, 3215 . 3217 [RFC7333] Chan, H., Ed., Liu, D., Seite, P., Yokota, H., and J. 3218 Korhonen, "Requirements for Distributed Mobility 3219 Management", RFC 7333, DOI 10.17487/RFC7333, August 2014, 3220 . 3222 [RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I., 3223 Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent 3224 Multicast - Sparse Mode (PIM-SM): Protocol Specification 3225 (Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March 3226 2016, . 3228 [RFC8086] Yong, L., Ed., Crabbe, E., Xu, X., and T. Herbert, "GRE- 3229 in-UDP Encapsulation", RFC 8086, DOI 10.17487/RFC8086, 3230 March 2017, . 3232 [RFC8201] McCann, J., Deering, S., Mogul, J., and R. Hinden, Ed., 3233 "Path MTU Discovery for IP version 6", STD 87, RFC 8201, 3234 DOI 10.17487/RFC8201, July 2017, 3235 . 3237 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 3238 Decraene, B., Litkowski, S., and R. Shakir, "Segment 3239 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 3240 July 2018, . 3242 [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol 3243 Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, 3244 . 3246 Appendix A. AERO Alternate Encapsulations 3248 When GUE encapsulation is not needed, AERO can use common 3249 encapsulations such as IP-in-IP [RFC2003][RFC2473][RFC4213], Generic 3250 Routing Encapsulation (GRE) [RFC2784][RFC2890] and others. The 3251 encapsulation is therefore only differentiated from non-AERO tunnels 3252 through the application of AERO control messaging and not through, 3253 e.g., a well-known UDP port number. 3255 As for GUE encapsulation, alternate AERO encapsulation formats may 3256 require encapsulation layer fragmentation. For simple IP-in-IP 3257 encapsulation, an IPv6 fragment header is inserted directly between 3258 the inner and outer IP headers when needed, i.e., even if the outer 3259 header is IPv4. The IPv6 Fragment Header is identified to the outer 3260 IP layer by its IP protocol number, and the Next Header field in the 3261 IPv6 Fragment Header identifies the inner IP header version. For GRE 3262 encapsulation, a GRE fragment header is inserted within the GRE 3263 header [I-D.templin-intarea-grefrag]. 3265 Figure 6 shows the AERO IP-in-IP encapsulation format before any 3266 fragmentation is applied: 3268 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3269 | Outer IPv4 Header | | Outer IPv6 Header | 3270 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3271 |IPv6 Frag Header (optional)| |IPv6 Frag Header (optional)| 3272 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3273 | Inner IP Header | | Inner IP Header | 3274 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3275 | | | | 3276 ~ ~ ~ ~ 3277 ~ Inner Packet Body ~ ~ Inner Packet Body ~ 3278 ~ ~ ~ ~ 3279 | | | | 3280 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3282 Minimal Encapsulation in IPv4 Minimal Encapsulation in IPv6 3284 Figure 6: Minimal Encapsulation Format using IP-in-IP 3286 Figure 7 shows the AERO GRE encapsulation format before any 3287 fragmentation is applied: 3289 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3290 | Outer IP Header | 3291 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3292 | GRE Header | 3293 | (with checksum, key, etc..) | 3294 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3295 | GRE Fragment Header (optional)| 3296 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3297 | Inner IP Header | 3298 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3299 | | 3300 ~ ~ 3301 ~ Inner Packet Body ~ 3302 ~ ~ 3303 | | 3304 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3306 Figure 7: Minimal Encapsulation Using GRE 3308 Alternate encapsulation may be preferred in environments where GUE 3309 encapsulation would add unnecessary overhead. For example, certain 3310 low-bandwidth wireless data links may benefit from a reduced 3311 encapsulation overhead. 3313 GUE encapsulation can traverse network paths that are inaccessible to 3314 non-UDP encapsulations, e.g., for crossing Network Address 3315 Translators (NATs). More and more, network middleboxes are also 3316 being configured to discard packets that include anything other than 3317 a well-known IP protocol such as UDP and TCP. It may therefore be 3318 necessary to determine the potential for middlebox filtering before 3319 enabling alternate encapsulation in a given environment. 3321 In addition to IP-in-IP, GRE and GUE, AERO can also use security 3322 encapsulations such as IPsec, TLS/SSL, DTLS, etc. In that case, AERO 3323 control messaging and route determination occur before security 3324 encapsulation is applied for outgoing packets and after security 3325 decapsulation is applied for incoming packets. 3327 AERO is especially well suited for use with VPN system encapsulations 3328 such as OpenVPN [OVPN]. 3330 Appendix B. S/TLLAO Extensions for Special-Purpose Links 3332 The AERO S/TLLAO format specified in Section 3.6 includes a Length 3333 value of 5 (i.e., 5 units of 8 octets). However, special-purpose 3334 links may extend the basic format to include additional fields and a 3335 Length value larger than 5. 3337 For example, adaptation of AERO to the Aeronautical 3338 Telecommunications Network with Internet Protocol Services (ATN/IPS) 3339 includes link selection preferences based on transport port numbers 3340 in addition to the existing DSCP-based preferences. ATN/IPS nodes 3341 maintain a map of transport port numbers to 64 possible preference 3342 fields, e.g., TCP port 22 maps to preference field 8, TCP port 443 3343 maps to preference field 20, UDP port 8060 maps to preference field 3344 34, etc. The extended S/TLLAO format for ATN/IPS is shown in 3345 Figure 8, where the Length value is 7 and the 'Q(i)' fields provide 3346 link preferences for the corresponding transport port number. 3348 0 1 2 3 3349 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 3350 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3351 | Type | Length = 7 | Prefix Length | Reserved | 3352 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3353 | Interface ID | Port Number | 3354 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3355 | | 3356 + + 3357 | | 3358 + Link-Layer Address + 3359 | | 3360 + + 3361 | | 3362 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3363 |P00|P01|P02|P03|P04|P05|P06|P07|P08|P09|P10|P11|P12|P13|P14|P15| 3364 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3365 |P16|P17|P18|P19|P20|P21|P22|P23|P24|P25|P26|P27|P28|P29|P30|P31| 3366 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3367 |P32|P33|P34|P35|P36|P37|P38|P39|P40|P41|P42|P43|P44|P45|P46|P47| 3368 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3369 |P48|P49|P50|P51|P52|P53|P54|P55|P56|P57|P58|P59|P60|P61|P62|P63| 3370 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3371 |Q00|Q01|Q02|Q03|Q04|Q05|Q06|Q07|Q08|Q09|Q10|Q11|Q12|Q13|Q14|Q15| 3372 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3373 |Q16|Q17|Q18|Q19|Q20|Q21|Q22|Q23|Q24|Q25|Q26|Q27|Q28|Q29|Q30|Q31| 3374 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3375 |Q32|Q33|Q34|Q35|Q36|Q37|Q38|Q39|Q40|Q41|Q42|Q43|Q44|Q45|Q46|Q47| 3376 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3377 |Q48|Q49|Q50|Q51|Q52|Q53|Q54|Q55|Q56|Q57|Q58|Q59|Q60|Q61|Q62|Q63| 3378 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3380 Figure 8: ATN/IPS Extended S/TLLAO Format 3382 Appendix C. Non-Normative Considerations 3384 AERO can be applied to a multitude of Internetworking scenarios, with 3385 each having its own adapations. The following considerations are 3386 provided as non-normative guidance: 3388 C.1. Implementation Strategies for Route Optimization 3390 Route optimization as discussed in Section 3.17 results in the route 3391 optimization source (ROS) creating an asymmetric neighbor cache entry 3392 for the target neighbor. The neighbor cache entry is maintained for 3393 at most REACHABLE_TIME seconds and then deleted unless updated. In 3394 order to refresh the neighbor cache entry lifetime before the 3395 ReachableTime timer expires, the specification requires 3396 implementations to issue a new NS/NA exchange to reset ReachableTime 3397 to REACHABLE_TIME seconds while data packets are still flowing. 3398 However, the decision of when to initiate a new NS/NA exchange and to 3399 perpetuate the process is left as an implementation detail. 3401 One possible strategy may be to monitor the neighbor cache entry 3402 watching for data packets for (REACHABLE_TIME - 5) seconds. If any 3403 data packets have been sent to the neighbor within this timeframe, 3404 then send an NS to receive a new NA. If no data packets have been 3405 sent, wait for 5 additional seconds and send an immediate NS if any 3406 data packets are sent within this "expiration pending" 5 second 3407 window. If no additional data packets are sent within the 5 second 3408 window, delete the neighbor cache entry. 3410 The monitoring of the neighbor data packet traffic therefore becomes 3411 an asymmetric ongoing process during the neighbor cache entry 3412 lifetime. If the neighbor cache entry expires, future data packets 3413 will trigger a new NS/NA exchange while the packets themselves are 3414 delivered over a longer path until route optimization state is re- 3415 established. 3417 C.2. Implicit Mobility Management 3419 AERO interface neighbors MAY provide a configuration option that 3420 allows them to perform implicit mobility management in which no ND 3421 messaging is used. In that case, the Client only transmits packets 3422 over a single interface at a time, and the neighbor always observes 3423 packets arriving from the Client from the same link-layer source 3424 address. 3426 If the Client's ANET interface address changes (either due to a 3427 readdressing of the original interface or switching to a new 3428 interface) the neighbor immediately updates the neighbor cache entry 3429 for the Client and begins accepting and sending packets according to 3430 the Client's new ANET address. This implicit mobility method applies 3431 to use cases such as cellphones with both WiFi and Cellular 3432 interfaces where only one of the interfaces is active at a given 3433 time, and the Client automatically switches over to the backup 3434 interface if the primary interface fails. 3436 C.3. Direct Underlying Interfaces 3438 When a Client's AERO interface is configured over a Direct interface, 3439 the neighbor at the other end of the Direct link can receive packets 3440 without any encapsulation. In that case, the Client sends packets 3441 over the Direct link according to QoS preferences. If the Direct 3442 interface has the highest QoS preference, then the Client's IP 3443 packets are transmitted directly to the peer without going through an 3444 ANET/INET. If other interfaces have higher QoS preferences, then the 3445 Client's IP packets are transmitted via a different interface, which 3446 may result in the inclusion of Proxys, Servers and Relays in the 3447 communications path. Direct interfaces must be tested periodically 3448 for reachability, e.g., via NUD. 3450 C.4. AERO Clients on the Open Internetwork 3452 AERO Clients that connect to the open Internetwork via either a 3453 native or NATed interface can establish a VPN to securely connect to 3454 a Server. Alternatively, the Client can exchange ND messages 3455 directly with other AERO nodes on the same SPAN segment using INET 3456 encapsulation only and without joining the SPAN. In that case, 3457 however, the Client must apply asymmetric security for ND messages to 3458 ensure routing and neighbor cache integrity (see: Section 6). 3460 C.5. Operation on AERO Links with /64 ASPs 3462 IPv6 AERO links typically have MSPs that aggregate many candidate 3463 MNPs of length /64 or shorter. However, in some cases it may be 3464 desirable to use AERO over links that have only a /64 MSP. This can 3465 be accommodated by treating all Clients on the AERO link as simple 3466 hosts that receive /128 prefix delegations. 3468 In that case, the Client sends an RS message to the Server the same 3469 as for ordinary AERO links. The Server responds with an RA message 3470 that includes one or more /128 prefixes (i.e., singleton addresses) 3471 that include the /64 MSP prefix along with an interface identifier 3472 portion to be assigned to the Client. The Client and Server then 3473 configure their AERO addresses based on the interface identifier 3474 portions of the /128s (i.e., the lower 64 bits) and not based on the 3475 /64 prefix (i.e., the upper 64 bits). 3477 For example, if the MSP for the host-only IPv6 AERO link is 3478 2001:db8:1000:2000::/64, each Client will receive one or more /128 3479 IPv6 prefix delegations such as 2001:db8:1000:2000::1/128, 3480 2001:db8:1000:2000::2/128, etc. When the Client receives the prefix 3481 delegations, it assigns the AERO addresses fe80::1, fe80::2, etc. to 3482 the AERO interface, and assigns the global IPv6 addresses (i.e., the 3483 /128s) to either the AERO interface or an internal virtual interface 3484 such as a loopback. In this arrangement, the Client conducts route 3485 optimization in the same sense as discussed in Section 3.17. 3487 This specification has applicability for nodes that act as a Client 3488 on an "upstream" AERO link, but also act as a Server on "downstream" 3489 AERO links. More specifically, if the node acts as a Client to 3490 receive a /64 prefix from the upstream AERO link it can then act as a 3491 Server to provision /128s to Clients on downstream AERO links. 3493 C.6. AERO Adaptations for SEcure Neighbor Discovery (SEND) 3495 SEcure Neighbor Discovery (SEND) [RFC3971] and Cryptographically 3496 Generated Addresses (CGAs) [RFC3972] were designed to secure IPv6 ND 3497 messaging in environments where symmetric network and/or transport- 3498 layer security services are impractical (see: Section 6). AERO nodes 3499 that use SEND/CGA employ the following adaptations. 3501 When a source AERO node prepares a SEND-protected ND message, it uses 3502 a link-local CGA as the IPv6 source address and writes the prefix 3503 embedded in its AERO address (i.e., instead of fe80::/64) in the CGA 3504 parameters Subnet Prefix field. When the neighbor receives the ND 3505 message, it first verifies the message checksum and SEND/CGA 3506 parameters while using the link-local prefix fe80::/64 (i.e., instead 3507 of the value in the Subnet Prefix field) to match against the IPv6 3508 source address of the ND message. 3510 The neighbor then derives the AERO address of the source by using the 3511 value in the Subnet Prefix field as the interface identifier of an 3512 AERO address. For example, if the Subnet Prefix field contains 3513 2001:db8:1:2, the neighbor constructs the AERO address as 3514 fe80::2001:db8:1:2. The neighbor then caches the AERO address in the 3515 neighbor cache entry it creates for the source, and uses the AERO 3516 address as the IPv6 destination address of any ND message replies. 3518 C.7. AERO Critical Infrastructure Considerations 3520 AERO Relays can be either Commercial off-the Shelf (COTS) standard IP 3521 routers or virtual machines in the cloud. Relays must be 3522 provisioned, supported and managed by the INET administrative 3523 authority, and connected to the Relays of other INETs via inter- 3524 domain peerings. Cost for purchasing, configuring and managing 3525 Relays is nominal even for very large AERO links. 3527 AERO Servers can be standard dedicated server platforms, but most 3528 often will be deployed as virtual machines in the cloud. The only 3529 requirements for Servers are that they can run the AERO user-level 3530 code and have at least one network interface connection to the INET. 3531 As with Relays, Servers must be provisioned, supported and managed by 3532 the INET administrative authority. Cost for purchasing, configuring 3533 and managing Servers is nominal especially for virtual Servers hosted 3534 in the cloud. 3536 AERO Proxys are most often standard dedicated server platforms with 3537 one network interface connected to the ANET and a second interface 3538 connected to an INET. As with Servers, the only requirements are 3539 that they can run the AERO user-level code and have at least one 3540 interface connection to the INET. Proxys must be provisioned, 3541 supported and managed by the ANET administrative authority. Cost for 3542 purchasing, configuring and managing Proxys is nominal, and borne by 3543 the ANET administrative authority. 3545 AERO Gateways can be any dedicated server or COTS router platform 3546 connected to INETs and/or EUNs. The Gateway joins the SPAN and 3547 engages in eBGP peering with one or more Relays as a stub AS. The 3548 Gateway then injects its MNPs and/or non-MNP prefixes into the BGP 3549 routing system, and provisions the prefixes to its downstream- 3550 attached networks. The Gateway can perform ROS and MAP services the 3551 same as for any Server, and can route between the MNP and non-MNP 3552 address spaces. 3554 Appendix D. Change Log 3556 << RFC Editor - remove prior to publication >> 3558 Changes from draft-templin-intarea-6706bis-14 to draft-templin- 3559 intrea-6706bis-15: 3561 o MTU and fragmentation 3563 o New details in movement to new Server 3565 Changes from draft-templin-intarea-6706bis-13 to draft-templin- 3566 intrea-6706bis-14: 3568 o Security based on secured tunnels, ingress filtering, MAP list and 3569 ROS list 3571 Changes from draft-templin-intarea-6706bis-12 to draft-templin- 3572 intrea-6706bis-13: 3574 o New paragraph in Section 3.6 on AERO interface layering over 3575 secured tunnels 3577 o Removed extraneous text in Section 3.7 3579 o Added new detail to the forwarding algorithm in Section 3.9 3581 o Clarified use of fragmentation 3583 o Route optimization now supported for both MNP and non-MNP-based 3584 prefixes 3586 o Relays are now seen as link-layer elements in the architecture. 3588 o Built out multicast section in detail. 3590 o New Appendix on implementation considerations for route 3591 optimization. 3593 Changes from draft-templin-intarea-6706bis-11 to draft-templin- 3594 intrea-6706bis-12: 3596 o Introduced Gateways as a new AERO element for connecting 3597 Correspondent Nodes on INET links 3599 o Introduced terms "Access Network (ANET)" and "Internetwork (INET)" 3601 o Changed "ASP" to "MSP", and "ACP" to "MNP" 3603 o New figure on the relation of Segments to the SPAN and AERO link 3605 o New "S" bit in S/TLLAO to indicate the "Source" S/TLLAO as opposed 3606 to additional S/TLLAOs 3608 o Changed Interface ID for Servers from 255 to 0xffff 3610 o Significant updates to Route Optimization, NUD, and Mobility 3611 Management 3613 o New Section on Multicast 3615 o New Section on AERO Clients in the open Internetwork 3617 o New Section on Operation over multiple AERO links (VLANs over the 3618 SPAN) 3620 o New Sections on DNS considerations and Transition considerations 3622 o 3624 Changes from draft-templin-intarea-6706bis-10 to draft-templin- 3625 intrea-6706bis-11: 3627 o Added The SPAN 3629 Changes from draft-templin-intarea-6706bis-09 to draft-templin- 3630 intrea-6706bis-10: 3632 o Orphaned packets in flight (e.g., when a neighbor cache entry is 3633 in the DEPARTED state) are now forwarded at the link layer instead 3634 of at the network layer. Forwarding at the network layer can 3635 result in routing loops and/or excessive delays of forwarded 3636 packets while the routing system is still reconverging. 3638 o Update route optimization to clarify the unsecured nature of the 3639 first NS used for route discovery 3641 o Many cleanups and clarifications on ND messaging parameters 3643 Changes from draft-templin-intarea-6706bis-08 to draft-templin- 3644 intrea-6706bis-09: 3646 o Changed PRL to "MAP list" 3648 o For neighbor cache entries, changed "static" to "symmetric", and 3649 "dynamic" to "asymmetric" 3651 o Specified Proxy RS/RA exchanges with Servers on behalf of Clients 3653 o Added discussion of unsolicited NAs in Section 3.16, and included 3654 forward reference to Section 3.18 3656 o Added discussion of AERO Clients used as critical infrastructure 3657 elements to connect fixed networks. 3659 o Added network-based VPN under security considerations 3661 Changes from draft-templin-intarea-6706bis-07 to draft-templin- 3662 intrea-6706bis-08: 3664 o New section on AERO-Aware Access Router 3666 Changes from draft-templin-intarea-6706bis-06 to draft-templin- 3667 intrea-6706bis-07: 3669 o Added "R" bit for release of PDs. Now have a full RS/RA service 3670 that can do PD without requiring DHCPv6 messaging over-the-air 3672 o Clarifications on solicited vs unsolicited NAs 3674 o Clarified use of MAX_NEIGHBOR_ADVERTISEMENTS for the purpose of 3675 increase reliability 3677 Changes from draft-templin-intarea-6706bis-05 to draft-templin- 3678 intrea-6706bis-06: 3680 o Major re-work and simplification of Route Optimization function 3682 o Added Distributed Mobility Management (DMM) and Mobility Anchor 3683 Point (MAP) terminology 3685 o New section on "AERO Critical Infrastructure Element 3686 Considerations" demonstrating low overall cost for the service 3688 o minor text revisions and deletions 3690 o removed extraneous appendices 3692 Changes from draft-templin-intarea-6706bis-04 to draft-templin- 3693 intrea-6706bis-05: 3695 o New Appendix E on S/TLLAO Extensions for special-purpose links. 3696 Discussed ATN/IPS as example. 3698 o New sentence in introduction to declare appendices as non- 3699 normative. 3701 Changes from draft-templin-intarea-6706bis-03 to draft-templin- 3702 intrea-6706bis-04: 3704 o Added definitions for Potential Router List (PRL) and secure 3705 enclave 3707 o Included text on mapping transport layer port numbers to network 3708 layer DSCP values 3710 o Added reference to DTLS and DMM Distributed Mobility Anchoring 3711 working group document 3713 o Reworked Security Considerations 3715 o Updated references. 3717 Changes from draft-templin-intarea-6706bis-02 to draft-templin- 3718 intrea-6706bis-03: 3720 o Added new section on SEND. 3722 o Clarifications on "AERO Address" section. 3724 o Updated references and added new reference for RFC8086. 3726 o Security considerations updates. 3728 o General text clarifications and cleanup. 3730 Changes from draft-templin-intarea-6706bis-01 to draft-templin- 3731 intrea-6706bis-02: 3733 o Note on encapsulation avoidance in Section 4. 3735 Changes from draft-templin-intarea-6706bis-00 to draft-templin- 3736 intrea-6706bis-01: 3738 o Remove DHCPv6 Server Release procedures that leveraged the old way 3739 Relays used to "route" between Server link-local addresses 3741 o Remove all text relating to Relays needing to do any AERO-specific 3742 operations 3744 o Proxy sends RS and receives RA from Server using SEND. Use CGAs 3745 as source addresses, and destination address of RA reply is to the 3746 AERO address corresponding to the Client's ACP. 3748 o Proxy uses SEND to protect RS and authenticate RA (Client does not 3749 use SEND, but rather relies on subnetwork security. When the 3750 Proxy receives an RS from the Client, it creates a new RS using 3751 its own addresses as the source and uses SEND with CGAs to send a 3752 new RS to the Server. 3754 o Emphasize distributed mobility management 3756 o AERO address-based RS injection of ACP into underlying routing 3757 system. 3759 Changes from draft-templin-aerolink-82 to draft-templin-intarea- 3760 6706bis-00: 3762 o Document use of NUD (NS/NA) for reliable link-layer address 3763 updates as an alternative to unreliable unsolicited NA. 3764 Consistent with Section 7.2.6 of RFC4861. 3766 o Server adds additional layer of encapsulation between outer and 3767 inner headers of NS/NA messages for transmission through Relays 3768 that act as vanilla IPv6 routers. The messages include the AERO 3769 Server Subnet Router Anycast address as the source and the Subnet 3770 Router Anycast address corresponding to the Client's ACP as the 3771 destination. 3773 o Clients use Subnet Router Anycast address as the encapsulation 3774 source address when the access network does not provide a 3775 topologically-fixed address. 3777 Author's Address 3779 Fred L. Templin (editor) 3780 Boeing Research & Technology 3781 P.O. Box 3707 3782 Seattle, WA 98124 3783 USA 3785 Email: fltemplin@acm.org