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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, January 2, 2020 5 rfc6179, rfc6706 (if 6 approved) 7 Intended status: Standards Track 8 Expires: July 5, 2020 10 Asymmetric Extended Route Optimization (AERO) 11 draft-templin-intarea-6706bis-19 13 Abstract 15 This document specifies the operation of IP over tunnel virtual links 16 using Asymmetric Extended Route Optimization (AERO). AERO interfaces 17 use an IPv6 link-local address format that supports operation of the 18 IPv6 Neighbor Discovery (ND) protocol and links ND to IP forwarding. 19 Prefix delegation/registration services are employed for network 20 admission and to manage the routing system. Multilink operation, 21 mobility management, quality of service (QoS) signaling and route 22 optimization are naturally supported through dynamic neighbor cache 23 updates. Standard IP multicasting services are also supported. AERO 24 is a widely-applicable mobile internetworking service especially 25 well-suited to aviation services, mobile Virtual Private Networks 26 (VPNs) and many other applications. 28 Status of This Memo 30 This Internet-Draft is submitted in full conformance with the 31 provisions of BCP 78 and BCP 79. 33 Internet-Drafts are working documents of the Internet Engineering 34 Task Force (IETF). Note that other groups may also distribute 35 working documents as Internet-Drafts. The list of current Internet- 36 Drafts is at https://datatracker.ietf.org/drafts/current/. 38 Internet-Drafts are draft documents valid for a maximum of six months 39 and may be updated, replaced, or obsoleted by other documents at any 40 time. It is inappropriate to use Internet-Drafts as reference 41 material or to cite them other than as "work in progress." 43 This Internet-Draft will expire on July 5, 2020. 45 Copyright Notice 47 Copyright (c) 2020 IETF Trust and the persons identified as the 48 document authors. All rights reserved. 50 This document is subject to BCP 78 and the IETF Trust's Legal 51 Provisions Relating to IETF Documents 52 (https://trustee.ietf.org/license-info) in effect on the date of 53 publication of this document. Please review these documents 54 carefully, as they describe your rights and restrictions with respect 55 to this document. Code Components extracted from this document must 56 include Simplified BSD License text as described in Section 4.e of 57 the Trust Legal Provisions and are provided without warranty as 58 described in the Simplified BSD License. 60 Table of Contents 62 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 63 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 64 3. Asymmetric Extended Route Optimization (AERO) . . . . . . . . 10 65 3.1. AERO Link Reference Model . . . . . . . . . . . . . . . . 10 66 3.2. AERO Node Types . . . . . . . . . . . . . . . . . . . . . 12 67 3.3. AERO Routing System . . . . . . . . . . . . . . . . . . . 13 68 3.3.1. IPv4 Compatibility Routing . . . . . . . . . . . . . 15 69 3.4. AERO Addresses . . . . . . . . . . . . . . . . . . . . . 15 70 3.5. Spanning Partitioned AERO Networks (SPAN) . . . . . . . . 17 71 3.5.1. SPAN Compatibility Addressing . . . . . . . . . . . . 21 72 3.6. AERO Interface Characteristics . . . . . . . . . . . . . 21 73 3.7. AERO Interface Initialization . . . . . . . . . . . . . . 24 74 3.7.1. AERO Server/Gateway Behavior . . . . . . . . . . . . 25 75 3.7.2. AERO Proxy Behavior . . . . . . . . . . . . . . . . . 25 76 3.7.3. AERO Client Behavior . . . . . . . . . . . . . . . . 25 77 3.7.4. AERO Relay Behavior . . . . . . . . . . . . . . . . . 26 78 3.8. AERO Interface Neighbor Cache Maintenance . . . . . . . . 26 79 3.9. AERO Interface Encapsulation and Re-encapsulation . . . . 28 80 3.10. AERO Interface Decapsulation . . . . . . . . . . . . . . 29 81 3.11. AERO Interface Data Origin Authentication . . . . . . . . 29 82 3.12. AERO Interface Forwarding Algorithm . . . . . . . . . . . 30 83 3.12.1. Client Forwarding Algorithm . . . . . . . . . . . . 30 84 3.12.2. Proxy Forwarding Algorithm . . . . . . . . . . . . . 31 85 3.12.3. Server/Gateway Forwarding Algorithm . . . . . . . . 32 86 3.12.4. Relay Forwarding Algorithm . . . . . . . . . . . . . 33 87 3.13. AERO Interface MTU and Fragmentation . . . . . . . . . . 34 88 3.13.1. AERO MTU Requirements . . . . . . . . . . . . . . . 36 89 3.14. AERO Interface Error Handling . . . . . . . . . . . . . . 37 90 3.15. AERO Router Discovery, Prefix Delegation and 91 Autoconfiguration . . . . . . . . . . . . . . . . . . . . 40 92 3.15.1. AERO ND/PD Service Model . . . . . . . . . . . . . . 40 93 3.15.2. AERO Client Behavior . . . . . . . . . . . . . . . . 40 94 3.15.3. AERO Server Behavior . . . . . . . . . . . . . . . . 43 95 3.16. The AERO Proxy . . . . . . . . . . . . . . . . . . . . . 45 96 3.16.1. Detecting and Responding to Server Failures . . . . 47 97 3.17. AERO Route Optimization . . . . . . . . . . . . . . . . . 48 98 3.17.1. Route Optimization Initiation . . . . . . . . . . . 48 99 3.17.2. Relaying the NS . . . . . . . . . . . . . . . . . . 49 100 3.17.3. Processing the NS and Sending the NA . . . . . . . . 49 101 3.17.4. Relaying the NA . . . . . . . . . . . . . . . . . . 50 102 3.17.5. Processing the NA . . . . . . . . . . . . . . . . . 50 103 3.17.6. Route Optimization Maintenance . . . . . . . . . . . 50 104 3.18. Neighbor Unreachability Detection (NUD) . . . . . . . . . 51 105 3.19. Mobility Management and Quality of Service (QoS) . . . . 52 106 3.19.1. Mobility Update Messaging . . . . . . . . . . . . . 52 107 3.19.2. Announcing Link-Layer Address and/or QoS Preference 108 Changes . . . . . . . . . . . . . . . . . . . . . . 53 109 3.19.3. Bringing New Links Into Service . . . . . . . . . . 54 110 3.19.4. Removing Existing Links from Service . . . . . . . . 54 111 3.19.5. Moving to a New Server . . . . . . . . . . . . . . . 54 112 3.20. Multicast . . . . . . . . . . . . . . . . . . . . . . . . 55 113 3.20.1. Source-Specific Multicast (SSM) . . . . . . . . . . 55 114 3.20.2. Any-Source Multicast (ASM) . . . . . . . . . . . . . 57 115 3.20.3. Bi-Directional PIM (BIDIR-PIM) . . . . . . . . . . . 57 116 3.21. Operation over Multiple AERO Links (VLANs) . . . . . . . 58 117 3.22. DNS Considerations . . . . . . . . . . . . . . . . . . . 59 118 3.23. Transition Considerations . . . . . . . . . . . . . . . . 59 119 3.24. Detecting and Reacting to Server and Relay Failures . . . 60 120 4. Implementation Status . . . . . . . . . . . . . . . . . . . . 60 121 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 60 122 6. Security Considerations . . . . . . . . . . . . . . . . . . . 61 123 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 62 124 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 64 125 8.1. Normative References . . . . . . . . . . . . . . . . . . 64 126 8.2. Informative References . . . . . . . . . . . . . . . . . 65 127 Appendix A. P[i] Preference Value Extensions in S/TLLAOs . . . . 72 128 Appendix B. AERO Alternate Encapsulations . . . . . . . . . . . 73 129 Appendix C. Non-Normative Considerations . . . . . . . . . . . . 75 130 C.1. Implementation Strategies for Route Optimization . . . . 75 131 C.2. Implicit Mobility Management . . . . . . . . . . . . . . 76 132 C.3. Direct Underlying Interfaces . . . . . . . . . . . . . . 76 133 C.4. AERO Clients on the Open Internetwork . . . . . . . . . . 76 134 C.5. Operation on AERO Links with /64 ASPs . . . . . . . . . . 77 135 C.6. AERO Adaptations for SEcure Neighbor Discovery (SEND) . . 77 136 C.7. AERO Critical Infrastructure Considerations . . . . . . . 78 137 C.8. AERO Server Failure Implications . . . . . . . . . . . . 79 138 Appendix D. Change Log . . . . . . . . . . . . . . . . . . . . . 79 139 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 85 141 1. Introduction 143 Asymmetric Extended Route Optimization (AERO) fulfills the 144 requirements of Distributed Mobility Management (DMM) [RFC7333] and 145 route optimization [RFC5522] for aeronautical networking and other 146 network mobility use cases. AERO is based on a Non-Broadcast, 147 Multiple Access (NBMA) virtual link model known as the AERO link. 148 The AERO link is a virtual overlay configured over one or more 149 underlying Internetworks, and nodes on the link can exchange IP 150 packets via tunneling. Multilink operation allows for increased 151 reliability, bandwidth optimization and traffic path diversity. 153 The AERO service comprises Clients, Proxys, Servers, and Gateways 154 that are seen as AERO link neighbors. Each node's AERO interface 155 uses an IPv6 link-local address format (known as the AERO address) 156 that supports operation of the IPv6 Neighbor Discovery (ND) protocol 157 [RFC4861] and links ND to IP forwarding. A node's AERO interface can 158 be configured over multiple underlying interfaces, and may therefore 159 may appear as a single interface with multiple link-layer addresses. 160 Each link-layer address is subject to change due to mobility and/or 161 QoS fluctuations, and link-layer address changes are signaled by ND 162 messaging the same as for any IPv6 link. 164 AERO links provide a cloud-based service where mobile nodes may use 165 any Server acting as a Mobility Anchor Point (MAP) and fixed nodes 166 may use any Gateway on the link for efficient communications. Fixed 167 nodes forward packets destined to other AERO nodes to the nearest 168 Gateway, which forwards them through the cloud. A mobile node's 169 initial packets are forwarded through the MAP, while direct routing 170 is supported through asymmetric extended route optimization while 171 data packets are flowing. Both unicast and multicast communications 172 are supported, and mobile nodes may efficiently move between 173 locations while maintaining continuous communications with 174 correspondents and without changing their IP Address. 176 AERO Relays are interconnected in a secured private BGP overlay 177 routing instance known as the "SPAN". The SPAN provides a hybrid 178 routing/bridging service to join the underlying Internetworks of 179 multiple disjoint administrative domains into a single unified AERO 180 link. Each AERO link instance is characterized by the set of 181 Mobility Service Prefixes (MSPs) common to all mobile nodes. The 182 link should extend to the point where a Gateway/MAP is on the optimal 183 route from any correspondent node on the link, and provides a gateway 184 between the underlying Internetwork and the SPAN. To the underlying 185 Internetwork, the Gateway/MAP is the source of a route to its MSP, 186 and hence uplink traffic to the mobile node is naturally routed to 187 the nearest Gateway/MAP. 189 AERO assumes the use of PIM Sparse Mode in support of multicast 190 communication. In support of Source Specific Multicast (SSM) when a 191 Mobile Node is the source, AERO route optimization ensures that a 192 shortest-path multicast tree is established with provisions for 193 mobility and multilink operation. In all other multicast scenarios 194 there are no AERO dependencies. 196 AERO was designed for aeronautical networking for both manned and 197 unmanned aircraft, where the aircraft is treated as a mobile node 198 that can connect an Internet of Things (IoT). AERO is also 199 applicable to a wide variety of other use cases. For example, it can 200 be used to coordinate the Virtual Private Network (VPN) links of 201 mobile nodes (e.g., cellphones, tablets, laptop computers, etc.) that 202 connect into a home enterprise network via public access networks 203 using services such as OpenVPN [OVPN]. Other applicable use cases 204 are also in scope. 206 The following numbered sections present the AERO specification. The 207 appendices at the end of the document are non-normative. 209 2. Terminology 211 The terminology in the normative references applies; the following 212 terms are defined within the scope of this document: 214 IPv6 Neighbor Discovery (ND) 215 an IPv6 control message service for coordinating neighbor 216 relationships between nodes connected to a common link. AERO 217 interfaces use the ND service specified in [RFC4861]. 219 IPv6 Prefix Delegation (PD) 220 a networking service for delegating IPv6 prefixes to nodes on the 221 link. The nominal PD service is DHCPv6 [RFC8415], however 222 alternate services (e.g., based on ND messaging) are also in scope 223 [I-D.templin-v6ops-pdhost][I-D.templin-6man-dhcpv6-ndopt]. Most 224 notably, a form of PD known as "prefix registration" can be used 225 if the Client knows its prefix in advance and can represent it in 226 the IPv6 source address of an ND message. 228 Access Network (ANET) 229 a node's first-hop data link service network, e.g., a radio access 230 network, cellular service provider network, corporate enterprise 231 network, or the public Internet itself. For secured ANETs, link- 232 layer security services such as IEEE 802.1X and physical-layer 233 security prevent unauthorized access internally while border 234 network-layer security services such as firewalls and proxies 235 prevent unauthorized outside access. 237 ANET interface 238 a node's attachment to a link in an ANET. 240 ANET address 241 an IP address assigned to a node's interface connection to an 242 ANET. 244 Internetwork (INET) 245 a connected IP network topology with a coherent routing and 246 addressing plan and that provides a transit backbone service for 247 ANET end systems. INETs also provide an underlay service over 248 which the AERO virtual link is configured. Example INETs include 249 corporate enterprise networks, aviation networks, and the public 250 Internet itself. When there is no administrative boundary between 251 an ANET and the INET, the ANET and INET are one and the same. 253 INET Partition 254 frequently, INETs such as large corporate enterprise networks are 255 sub-divided internally into separate isolated partitions. Each 256 partition is fully connected internally but disconnected from 257 other partitions, and there is no requirement that separate 258 partitions maintain consistent Internet Protocol and/or addressing 259 plans. (An INET partition is the same as a SPAN segment discussed 260 below.) 262 INET interface 263 a node's attachment to a link in an INET. 265 INET address 266 an IP address assigned to a node's interface connection to an 267 INET. 269 AERO link 270 a Non-Broadcast, Multiple Access (NBMA) tunnel virtual overlay 271 configured over one or more underlying INETs. Nodes on the AERO 272 link appear as single-hop neighbors from the perspective of the 273 virtual overlay even though they may be separated by many 274 underlying INET hops. AERO links may be configured over multiple 275 underlying SPAN segments (see below). 277 AERO interface 278 a node's attachment to an AERO link. Since the addresses assigned 279 to an AERO interface are managed for uniqueness, AERO interfaces 280 do not require Duplicate Address Detection (DAD) and therefore set 281 the administrative variable 'DupAddrDetectTransmits' to zero 282 [RFC4862]. 284 underlying interface 285 an ANET or INET interface over which an AERO interface is 286 configured. 288 AERO address 289 an IPv6 link-local address assigned to an AERO interface and 290 constructed as specified in Section 3.4. 292 base AERO address 293 the lowest-numbered AERO address aggregated by the MNP (see 294 Section 3.4). 296 Mobility Service Prefix (MSP) 297 an IP prefix assigned to the AERO link and from which more- 298 specific Mobile Network Prefixes (MNPs) are derived. 300 Mobile Network Prefix (MNP) 301 an IP prefix allocated from an MSP and delegated to an AERO Client 302 or Gateway. 304 AERO node 305 a node that is connected to an AERO link, or that provides 306 services to other nodes on an AERO link. 308 AERO Client ("Client") 309 an AERO node that connects to one or more ANETs and requests MNP 310 PDs from AERO Servers. The Client assigns a Client AERO address 311 to the AERO interface for use in ND exchanges with other AERO 312 nodes and forwards packets to correspondents according to AERO 313 interface neighbor cache state. 315 AERO Server ("Server") 316 an INET node that configures an AERO interface to provide default 317 forwarding services and a Mobility Anchor Point (MAP) for AERO 318 Clients. The Server assigns an administratively-provisioned AERO 319 address to its AERO interface to support the operation of the ND/ 320 PD services, and advertises all of its associated MNPs via BGP 321 peerings with Relays. 323 AERO Gateway ("Gateway") 324 an AERO Server that also provides forwarding services between 325 nodes reached via the AERO link and correspondents on other links. 326 AERO Gateways are provisioned with MNPs (i.e., the same as for an 327 AERO Client) and run a dynamic routing protocol to discover any 328 non-MNP IP routes. In both cases, the Gateway advertises the 329 MSP(s) over INET interfaces, and distributes all of its associated 330 MNPs and non-MNP IP routes via BGP peerings with Relays (i.e., the 331 same as for an AERO Server). 333 AERO Relay ("Relay") 334 a node that provides hybrid routing/bridging services (as well as 335 a security trust anchor) for nodes on an AERO link. As a router, 336 the Relay forwards packets using standard IP forwarding. As a 337 bridge, the Relay forwards packets over the AERO link without 338 decrementing the IPv6 Hop Limit. AERO Relays peer with Servers 339 and other Relays to discover the full set of MNPs for the link as 340 well as any non-MNPs that are reachable via Gateways. 342 AERO Proxy ("Proxy") 343 a node that provides proxying services between Clients in an ANET 344 and Servers in external INETs. The AERO Proxy is a conduit 345 between the ANET and external INETs in the same manner as for 346 common web proxies, and behaves in a similar fashion as for ND 347 proxies [RFC4389]. 349 Spanning Partitioned AERO Networks (SPAN) 350 a means for bridging disjoint INET partitions as segments of a 351 unified AERO link the same as for a bridged campus LAN. The SPAN 352 is a mid-layer IPv6 encapsulation service in the AERO routing 353 system that supports a unified AERO link view for all segments. 354 Each segment in the SPAN is a distinct INET partition. 356 SPAN Service Prefix (SSP) 357 a global or unique local /96 IPv6 prefix assigned to the AERO link 358 to support SPAN services. 360 SPAN Partition Prefix (SPP) 361 a sub-prefix of the SPAN Service Prefix uniquely assigned to a 362 single SPAN segment. 364 SPAN Address 365 a global or unique local IPv6 address taken from a SPAN Partition 366 Prefix and constructed as specified in Section 3.5. SPAN 367 addresses are statelessly derived from AERO addresses, and vice- 368 versa. 370 ingress tunnel endpoint (ITE) 371 an AERO interface endpoint that injects encapsulated packets into 372 an AERO link. 374 egress tunnel endpoint (ETE) 375 an AERO interface endpoint that receives encapsulated packets from 376 an AERO link. 378 link-layer address 379 an IP address used as an encapsulation header source or 380 destination address from the perspective of the AERO interface. 382 When UDP encapsulation is used, the UDP port number is also 383 considered as part of the link-layer address. From the 384 perspective of the AERO interface, the link-layer address is 385 either an INET address for intra-segment encapsulation or a SPAN 386 address for inter-segment encapsulation. 388 network layer address 389 the source or destination address of an encapsulated IP packet 390 presented to the AERO interface. 392 end user network (EUN) 393 an internal virtual or external edge IP network that an AERO 394 Client or Gateway connects to the rest of the network via the AERO 395 interface. The Client/Gateway sees each EUN as a "downstream" 396 network, and sees the AERO interface as the point of attachment to 397 the "upstream" network. 399 Mobile Node (MN) 400 an AERO Client and all of its downstream-attached networks that 401 move together as a single unit, i.e., an end system that connects 402 an Internet of Things. 404 Mobile Router (MR) 405 a MN's on-board router that forwards packets between any 406 downstream-attached networks and the AERO link. 408 Mobility Anchor Point (MAP) 409 an AERO Server that is currently tracking and reporting the 410 mobility events of its associated Mobile Node Clients. 412 Route Optimization Source (ROS) 413 the AERO node nearest the source that initiates route 414 optimization. The ROS may be a Server or Proxy acting on behalf 415 of the source Client. 417 Route Optimization responder (ROR) 418 the AERO node nearest the target destination that responds to 419 route optimization requests. The ROR may be a Server acting as a 420 MAP on behalf of a target MNP Client, or a Gateway for a non-MNP 421 destination. 423 MAP List 424 a geographically and/or topologically referenced list of AERO 425 addresses of all MAPs within the same AERO link. There is a 426 single MAP list for the entire AERO link. 428 ROS List 429 a list of AERO/SPAN-to-INET address mappings of all ROSes within 430 the same SPAN segment. There is a distinct ROS list for each 431 segment. 433 Distributed Mobility Management (DMM) 434 a BGP-based overlay routing service coordinated by Servers and 435 Relays that tracks all MAP-to-Client associations. 437 Throughout the document, the simple terms "Client", "Server", 438 "Relay", "Proxy" and "Gateway" refer to "AERO Client", "AERO Server", 439 "AERO Relay", "AERO Proxy" and "AERO Gateway", respectively. 440 Capitalization is used to distinguish these terms from other common 441 Internetworking uses in which they appear without capitalization. 443 The terminology of DHCPv6 [RFC8415] and IPv6 ND [RFC4861] (including 444 the names of node variables, messages and protocol constants) is used 445 throughout this document. Also, the term "IP" is used to generically 446 refer to either Internet Protocol version, i.e., IPv4 [RFC0791] or 447 IPv6 [RFC8200]. 449 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 450 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 451 document are to be interpreted as described in [RFC2119]. Lower case 452 uses of these words are not to be interpreted as carrying RFC2119 453 significance. 455 3. Asymmetric Extended Route Optimization (AERO) 457 The following sections specify the operation of IP over Asymmetric 458 Extended Route Optimization (AERO) links: 460 3.1. AERO Link Reference Model 461 +----------------+ 462 | AERO Relay R1 | 463 | Nbr: S1, S2, P1| 464 |(X1->S1; X2->S2)| 465 | MSP M1 | 466 +-+---------+--+-+ 467 +--------------+ | Secured | | +--------------+ 468 |AERO Server S1| | tunnels | | |AERO Server S2| 469 | Nbr: C1, R1 +-----+ | +-----+ Nbr: C2, R1 | 470 | default->R1 | | | default->R1 | 471 | X1->C1 | | | X2->C2 | 472 +-------+------+ | +------+-------+ 473 | AERO Link | | 474 X===+===+===================+==)===============+===+===X 475 | | | | 476 +-----+--------+ +--------+--+-----+ +--------+-----+ 477 |AERO Client C1| | AERO Proxy P1 | |AERO Client C2| 478 | Nbr: S1 | |(Proxy Nbr Cache)| | Nbr: S2 | 479 | default->S1 | +--------+--------+ | default->S2 | 480 | MNP X1 | | | MNP X2 | 481 +------+-------+ .--------+------. +-----+--------+ 482 | (- Proxyed Clients -) | 483 .-. `---------------' .-. 484 ,-( _)-. ,-( _)-. 485 .-(_ IP )-. +-------+ +-------+ .-(_ IP )-. 486 (__ EUN )--|Host H1| |Host H2|--(__ EUN ) 487 `-(______)-' +-------+ +-------+ `-(______)-' 489 Figure 1: AERO Link Reference Model 491 Figure 1 presents the AERO link reference model. In this model: 493 o the AERO link is an overlay network service configured over one or 494 more underlying INET partitions which may be managed by different 495 administrative authorities and have incompatible protocols and/or 496 addressing plans. 498 o AERO Relay R1 aggregates Mobility Service Prefix (MSP) M1, 499 discovers Mobile Network Prefixes (MNPs) X* and advertises the MSP 500 via BGP peerings over secured tunnels to Servers (S1, S2). Relays 501 use the SPAN service to bridge disjoint segments of a partitioned 502 AERO link. 504 o AERO Servers S1 and S2 configure secured tunnels with Relay R1 and 505 also act as Mobility Anchor Points (MAPs) and default routers for 506 their associated Clients C1 and C2. 508 o AERO Clients C1 and C2 associate with Servers S1 and S2, 509 respectively. They receive Mobile Network Prefix (MNP) 510 delegations X1 and X2, and also act as default routers for their 511 associated physical or internal virtual EUNs. Simple hosts H1 and 512 H2 attach to the EUNs served by Clients C1 and C2, respectively. 514 o AERO Proxy P1 configures a secured tunnel with Relay R1 and 515 provides proxy services for AERO Clients in secured enclaves that 516 cannot associate directly with other AERO link neighbors. 518 Each node on the AERO link maintains an AERO interface neighbor cache 519 and an IP forwarding table the same as for any link. Although the 520 figure shows a limited deployment, in common operational practice 521 there will normally be many additional Relays, Servers, Clients and 522 Proxys. 524 3.2. AERO Node Types 526 AERO Relays provide hybrid routing/bridging services (as well as a 527 security trust anchor) for nodes on an AERO link. Relays use 528 standard IPv6 routing to forward packets both within the same INET 529 partitions and between disjoint INET partitions based on a mid-layer 530 IPv6 encapsulation known as the SPAN header. The inner IP layer 531 experiences a virtual bridging service since the inner IP TTL/Hop 532 Limit is not decremented during forwarding. Each Relay also peers 533 with Servers and other Relays in a dynamic routing protocol instance 534 to provide a Distributed Mobility Management (DMM) service for the 535 list of active MNPs (see Section 3.3). Relays present the AERO link 536 as a set of one or more Mobility Service Prefixes (MSPs) but as link- 537 layer devices need not connect directly to the AERO link themselves 538 unless an administrative interface is desired. Relays configure 539 secured tunnels with Servers, Proxys and other Relays; they further 540 maintain IP forwarding table entries for each Mobile Network Prefix 541 (MNP) and any other reachable non-MNP prefixes. 543 AERO Servers provide default forwarding services and a Mobility 544 Anchor Point (MAP) for AERO Client Mobile Nodes (MNs). Each Server 545 also peers with Relays in a dynamic routing protocol instance to 546 advertise its list of associated MNPs (see Section 3.3). Servers 547 facilitate PD exchanges with Clients, where each delegated prefix 548 becomes an MNP taken from an MSP. Servers forward packets between 549 AERO interface neighbors and track each Client's mobility profiles. 551 AERO Clients register their MNPs through PD exchanges with AERO 552 Servers over the AERO link, and distribute the MNPs to nodes on EUNs. 553 A Client may also be co-resident on the same physical or virtual 554 platform as a Server; in that case, the Client and Server behave as a 555 single functional unit and without the need for any Client/Server 556 control messaging. 558 AERO Proxys provide a conduit for ANET AERO Clients to associate with 559 AERO Servers in external INETs. Client and Servers exchange control 560 plane messages via the Proxy acting as a bridge between the ANET/INET 561 boundary. The Proxy forwards data packets to and from Clients 562 according to forwarding information in the neighbor cache. The Proxy 563 function is specified in Section 3.16. 565 AERO Gateways are Servers that provide forwarding services between 566 the AERO interface and INET/EUN interfaces. Gateways are provisioned 567 with MNPs the same as for an AERO Client, and also run a dynamic 568 routing protocol to discover any non-MNP IP routes. The Gateway 569 advertises the MSP(s) to INETs, and distributes all of its associated 570 MNPs and non-MNP IP routes via BGP peerings with Relays. 572 AERO Relays, Servers, Proxys and Gateways are critical infrastructure 573 elements in fixed (i.e., non-mobile) INET deployments and hence have 574 permanent and unchanging INET addresses. AERO Clients are MNs that 575 connect via ANET interfaces, i.e., their ANET addresses may change 576 when the Client moves to a new ANET connection. 578 3.3. AERO Routing System 580 The AERO routing system comprises a private instance of the Border 581 Gateway Protocol (BGP) [RFC4271] that is coordinated between Relays 582 and Servers and does not interact with either the public Internet BGP 583 routing system or any underlying INET routing systems. 585 In a reference deployment, each Server is configured as an Autonomous 586 System Border Router (ASBR) for a stub Autonomous System (AS) using 587 an AS Number (ASN) that is unique within the BGP instance, and each 588 Server further uses eBGP to peer with one or more Relays but does not 589 peer with other Servers. Each INET of a multi-segment AERO link must 590 include one or more Relays, which peer with the Servers and Proxys 591 within that INET. All Relays within the same INET are members of the 592 same hub AS using a common ASN, and use iBGP to maintain a consistent 593 view of all active MNPs currently in service. The Relays of 594 different INETs peer with one another using eBGP. 596 Relays advertise the AERO link's MSPs and any non-MNP routes to each 597 of their Servers. This means that any aggregated non-MNPs (including 598 "default") are advertised to all Servers. Each Relay configures a 599 black-hole route for each of its MSPs. By black-holing the MSPs, the 600 Relay will maintain forwarding table entries only for the MNPs that 601 are currently active, and packets destined to all other MNPs will 602 correctly incur Destination Unreachable messages due to the black- 603 hole route. In this way, Servers have only partial topology 604 knowledge (i.e., they know only about the MNPs of their directly 605 associated Clients) and they forward all other packets to Relays 606 which have full topology knowledge. 608 Servers maintain a working set of associated MNPs, and dynamically 609 announce new MNPs and withdraw departed MNPs in eBGP updates to 610 Relays. Servers that are configured as Gateways also redistribute 611 non-MNP routes learned from non-AERO interfaces via their eBGP Relay 612 peerings. 614 Clients are expected to remain associated with their current Servers 615 for extended timeframes, however Servers SHOULD selectively suppress 616 updates for impatient Clients that repeatedly associate and 617 disassociate with them in order to dampen routing churn. Servers 618 that are configured as Gateways advertise the MSPs via INET/EUN 619 interfaces, and forward packets between INET/EUN interfaces and the 620 AERO interface using standard IP forwarding. 622 Scaling properties of the AERO routing system are limited by the 623 number of BGP routes that can be carried by Relays. As of 2015, the 624 global public Internet BGP routing system manages more than 500K 625 routes with linear growth and no signs of router resource exhaustion 626 [BGP]. More recent network emulation studies have also shown that a 627 single Relay can accommodate at least 1M dynamically changing BGP 628 routes even on a lightweight virtual machine, i.e., and without 629 requiring high-end dedicated router hardware. 631 Therefore, assuming each Relay can carry 1M or more routes, this 632 means that at least 1M Clients can be serviced by a single set of 633 Relays. A means of increasing scaling would be to assign a different 634 set of Relays for each set of MSPs. In that case, each Server still 635 peers with one or more Relays, but institutes route filters so that 636 BGP updates are only sent to the specific set of Relays that 637 aggregate the MSP. For example, if the MSP for the AERO link is 638 2001:db8::/32, a first set of Relays could service the MSP 639 2001:db8::/40, a second set of Relays could service 640 2001:db8:0100::/40, a third set could service 2001:db8:0200::/40, 641 etc. 643 Assuming up to 1K sets of Relays, the AERO routing system can then 644 accommodate 1B or more MNPs with no additional overhead (for example, 645 it should be possible to service 1B /64 MNPs taken from a /34 MSP and 646 even more for shorter prefixes). In this way, each set of Relays 647 services a specific set of MSPs that they advertise to the native 648 Internetwork routing system, and each Server configures MSP-specific 649 routes that list the correct set of Relays as next hops. This 650 arrangement also allows for natural incremental deployment, and can 651 support small scale initial deployments followed by dynamic 652 deployment of additional Clients, Servers and Relays without 653 disturbing the already-deployed base. 655 Server and Relays can use the Bidirectional Forwarding Detection 656 (BFD) protocol [RFC5880] to quickly detect link failures that don't 657 result in interface state changes, BGP peer failures, and 658 administrative state changes. BFD is important in environments where 659 rapid response to failures is required for routing reconvergence and, 660 hence, communications continuity. 662 A full discussion of the BGP-based routing system used by AERO is 663 found in [I-D.ietf-rtgwg-atn-bgp]. The system provides for 664 Distributed Mobility Management (DMM) per the distributed mobility 665 anchoring architecture [I-D.ietf-dmm-distributed-mobility-anchoring]. 667 3.3.1. IPv4 Compatibility Routing 669 For IPv6 MNPs, the AERO routing system includes ordinary IPv6 routes. 670 For IPv4 MNPs, the AERO routing system includes IPv6 routes based on 671 an IPv4-embedded IPv6 address format discussed in Section 3.5.1. 673 3.4. AERO Addresses 675 A Client's AERO address is an IPv6 link-local address with an 676 interface identifier based on the Client's delegated MNP. Relay, 677 Server and Proxy AERO addresses are assigned from the range fe80::/96 678 and include an administratively-provisioned value in the lower 32 679 bits. 681 For IPv6, Client AERO addresses begin with the prefix fe80::/64 and 682 include in the interface identifier (i.e., the lower 64 bits) a 683 64-bit prefix taken from one of the Client's IPv6 MNPs. For example, 684 if the AERO Client receives the IPv6 MNP: 686 2001:db8:1000:2000::/56 688 it constructs its corresponding AERO addresses as: 690 fe80::2001:db8:1000:2000 692 fe80::2001:db8:1000:2001 694 fe80::2001:db8:1000:2002 696 ... etc. ... 698 fe80::2001:db8:1000:20ff 700 For IPv4, Client AERO addresses are based on an IPv4-mapped IPv6 701 address [RFC4291] formed from an IPv4 MNP and with a Prefix Length of 702 96 plus the MNP prefix length. For example, for the IPv4 MNP 703 192.0.2.32/28 the IPv4-mapped IPv6 MNP is: 705 0:0:0:0:0:FFFF:192.0.2.16/124 (also written as 706 0:0:0:0:0:FFFF:c000:0210/124) 708 The Client then constructs its AERO addresses with the prefix 709 fe80::/64 and with the lower 64 bits of the IPv4-mapped IPv6 address 710 in the interface identifier as: 712 fe80::FFFF:192.0.2.16 714 fe80::FFFF:192.0.2.17 716 fe80::FFFF:192.0.2.18 718 ... etc. ... 720 fe80:FFFF:192.0.2.31 722 Relay, Server and Proxy AERO addresses are allocated from the range 723 fe80::/96, and MUST be managed for uniqueness. The lower 32 bits of 724 the AERO address includes a unique integer value between 1 and 0xfffe 725 (e.g., fe80::1, fe80::2, fe80::3, etc.) as assigned by the 726 administrative authority for the link. If the link spans multiple 727 SPAN segments, the AERO addresses are assigned to each segment in 1x1 728 correspondence with SPAN addresses (see: Section 3.5). The address 729 fe80:: is the IPv6 link-local Subnet Router Anycast address, and the 730 address fe80::ffff:ffff is reserved as the unspecified AERO address. 732 The lowest-numbered AERO address from a Client's MNP delegation 733 serves as the "base" AERO address (for example, for the MNP 734 2001:db8:1000:2000::/56 the base AERO address is 735 fe80::2001:db8:1000:2000). The Client then assigns the base AERO 736 address to the AERO interface and uses it for the purpose of 737 maintaining the neighbor cache entry. The Server likewise uses the 738 AERO address as its index into the neighbor cache for this Client. 740 If the Client has multiple AERO addresses (i.e., when there are 741 multiple MNPs and/or MNPs with prefix lengths shorter than /64), the 742 Client originates ND messages using the base AERO address as the 743 source address and accepts and responds to ND messages destined to 744 any of its AERO addresses as equivalent to the base AERO address. In 745 this way, the Client maintains a single neighbor cache entry that may 746 be indexed by multiple AERO addresses. 748 The Client's Subnet Router Anycast address can be statelessly 749 determined from its AERO address by simply transposing the AERO 750 address into the upper N bits of the Anycast address followed by 751 128-N bits of zeroes. For example, for the AERO address 752 fe80::2001:db8:1:2 the subnet router anycast address is 753 2001:db8:1:2::. 755 AERO addresses for mobile node Clients embed a MNP as discussed 756 above, while AERO addresses for non-MNP destinations are constructed 757 in exactly the same way. A Client AERO address therefore encodes 758 either an MNP if the prefix is reached via the SPAN or a non-MNP if 759 the prefix is reached via a Gateway. 761 3.5. Spanning Partitioned AERO Networks (SPAN) 763 An AERO link configured over a single INET appears as a single 764 unified link with a consistent underlying network addressing plan. 765 In that case, all nodes on the link can exchange packets via 766 encapsulation with INET addresses, since the underlying INET is 767 connected. In common practice, however, an AERO link may be 768 partitioned into multiple "segments", where each segment is a 769 distinct INET potentially managed under a different administrative 770 authority (e.g., as for worldwide aviation service providers such as 771 ARINC, SITA, Inmarsat, etc.). Individual INETs may themselves be 772 partitioned internally, in which case each internal partition is seen 773 as a separate segment. 775 The addressing plan of each segment is consistent internally but will 776 often bear no relation to the addressing plans of other segments. 777 Each segment is also likely to be separated from others by network 778 security devices (e.g., firewalls, proxies, packet filtering 779 gateways, etc.), and in many cases disjoint segments may not even 780 have any common physical link connections at all. Therefore, nodes 781 can only be assured of exchanging packets directly with 782 correspondents in the same segment, and not with those in other 783 segments. The only means for joining the segments therefore is 784 through inter-domain peerings between AERO Relays. 786 The same as for traditional campus LANs, multiple AERO link segments 787 can be joined into a single unified link via a virtual bridging 788 service termed the "SPAN". The SPAN performs link-layer packet 789 forwarding between segments (i.e., bridging) without decrementing the 790 network-layer TTL/Hop Limit. The SPAN model is depicted in Figure 2: 792 . . . . . . . . . . . . . . . . . . . . . . . 793 . . 794 . .-(::::::::) . 795 . .-(::::::::::::)-. +-+ . 796 . (:::: Segment A :::)--|R|---+ . 797 . `-(::::::::::::)-' +-+ | . 798 . `-(::::::)-' | . 799 . | . 800 . .-(::::::::) | . 801 . .-(::::::::::::)-. +-+ | . 802 . (:::: Segment B :::)--|R|---+ . 803 . `-(::::::::::::)-' +-+ | . 804 . `-(::::::)-' | . 805 . | . 806 . .-(::::::::) | . 807 . .-(::::::::::::)-. +-+ | . 808 . (:::: Segment C :::)--|R|---+ . 809 . `-(::::::::::::)-' +-+ | . 810 . `-(::::::)-' | . 811 . | . 812 . ..(etc).. x . 813 . . 814 . . 815 . <- AERO Link Bridged by the SPAN -> . 816 . . . . . . . . . . . . . .. . . . . . . . . 818 Figure 2: The SPAN 820 To support the SPAN, AERO links require a reserved /64 IPv6 "SPAN 821 Service Prefix (SSP)". Although any routable IPv6 prefix can be 822 used, a Unique Local Address (ULA) prefix (e.g., fd00::/64) [RFC4389] 823 is recommended since border routers are commonly configured to 824 prevent packets with ULAs from being injected into the AERO link by 825 an external IPv6 node and from leaking out of the AERO link to the 826 outside world. 828 Each segment in the SPAN assigns a unique sub-prefix of SSP::/96 829 termed a "SPAN Partition Prefix (SPP)". For example, a first segment 830 could assign fd00::1000/116, a second could assign fd00::2000/116, a 831 third could assign fd00::3000/116, etc. The administrative 832 authorities for each segment must therefore coordinate to assure 833 mutually-exclusive SPP assignments, but internal provisioning of the 834 SPP is an independent local consideration for each administrative 835 authority. 837 A "SPAN address" is an address taken from a SPP and assigned to a 838 Relay, Server or Proxy interface. SPAN addresses are formed by 839 simply replacing the upper portion of an administratively-assigned 840 AERO address with the SPP. For example, if the SPP is 841 fd00::1000/116, the SPAN address formed from the AERO address 842 fe80::1001 is simply fd00::1001. 844 An "INET address" is an address of a node's interface connection to 845 an INET. AERO/SPAN/INET address mappings are maintained as permanent 846 neighbor cache entires as discussed in Section 3.8. 848 AERO Relays serve as bridges to join multiple segments into a unified 849 AERO link over multiple diverse administrative domains. They support 850 the bridging function by first establishing forwarding table entries 851 for their SPPs either via standard BGP routing or static routes. For 852 example, if three Relays ('A', 'B' and 'C') from different segments 853 serviced the SPPs fd00::1000/116, fd00::2000/116 and fd00::3000/116 854 respectively, then the forwarding tables in each Relay are as 855 follows: 857 A: fd00::1000/116->local, fd00::2000/116->B, fd00::3000/116->C 859 B: fd00::1000/116->A, fd00::2000/116->local, fd00::3000/116->C 861 C: fd00::1000/116->A, fd00::2000/116->B, fd00::3000/116->local 863 These forwarding table entries are permanent and never change, since 864 they correspond to fixed infrastructure elements in their respective 865 segments. This provides the basis for a link-layer forwarding 866 service that cannot be disrupted by routing updates due to node 867 mobility. 869 With the SPPs in place in each Relay's forwarding table, control and 870 data packets sent between AERO nodes in different segments can 871 therefore be carried over the SPAN via encapsulation. For example, 872 when a source node in segment A forwards a packet with IPv6 address 873 2001:db8:1:2::1 to a destination node in segment C with IPv6 address 874 2001:db8:1000:2000::1, it first encapsulates the packet in a SPAN 875 header with source SPAN address taken from fd00::1000/116 (e.g., 876 fd00::1001) and destination SPAN address taken from fd00::3000/116 877 (e.g., fd00::3001). Next, it encapsulates the SPAN message in an 878 INET header with source address set to its own INET address (e.g., 879 192.0.2.100) and destination set to the INET address of a Relay 880 (e.g., 192.0.2.1). 882 SPAN encapsulation is based on Generic Packet Tunneling in IPv6 883 [RFC2473]; the encapsulation format in the above example is shown in 884 Figure 3: 886 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 887 | INET Header | 888 | src = 192.0.2.100 | 889 | dst = 192.0.2.1 | 890 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 891 | SPAN Header | 892 | src = fd00::1001 | 893 | dst = fd00::3001 | 894 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 895 | Inner IP Header | 896 | src = 2001:db8:1:2::1 | 897 | dst = 2001:db8:1000:2000::1 | 898 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 899 | | 900 ~ ~ 901 ~ Inner Packet Body ~ 902 ~ ~ 903 | | 904 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 906 Figure 3: SPAN Encapsulation 908 In this format, the inner IP header and packet body are the original 909 IP packet, the SPAN header is an IPv6 header prepared according to 910 [RFC2473], and the INET header is prepared according to Section 3.9. 911 A packet is said to be "forwarded/sent into the SPAN" when it is 912 encapsulated as described above then forwarded via a secured tunnel 913 to a neighboring Relay. 915 This gives rise to a routing system that contains both MNP routes 916 that may change dynamically due to regional node mobility and SPAN 917 routes that never change. The Relays can therefore provide link- 918 layer bridging by sending packets into the SPAN instead of network- 919 layer routing according to MNP routes. As a result, opportunities 920 for packet loss due to node mobility between different segments are 921 mitigated. 923 With reference to Figure 3, for a Client's AERO address the SPAN 924 address is simply set to the Subnet Router Anycast address. For non- 925 link-local addresses, the destination SPAN address may not be known 926 in advance for the first few packets of a flow sent via the SPAN. In 927 that case, the SPAN destination address is set to the original 928 packet's destination, and the SPAN routing system will direct the 929 packet to the correct SPAN egress node. (In the above example, the 930 SPAN destination address is simply 2001:db8:1000:2000::1.) 932 3.5.1. SPAN Compatibility Addressing 934 For IPv4 MNPs, Servers injects a "SPAN Compatibility Prefix (SCP)" 935 that embeds the MNP into the BGP routing system. The SCP begins with 936 the upper 64 bits of the SSP, followed by the constant string 937 "0000:FFFF" followed by the IPv4 MNP. For example, if the SSP is 938 fd00::/64 and the MNP is 192.0.2.0/24 then the SCP is 939 fd00::FFFF:192.0.2.0/120. 941 This allows for encapsulation of IPv4 packets in IPv6 headers with 942 "SPAN Compatibility Addresses (SCAs)". In this example, the SCA 943 corresponding to the SCP is simply fd00::FFFF:192.0.2.0, and can be 944 used as the SPAN destination address for packets forwarded via the 945 SPAN. This allows for forwarding of initial IPv4 packets over IPv6 946 SPAN routes, followed by route optimization for direct 947 communications. 949 3.6. AERO Interface Characteristics 951 AERO interfaces are virtual interfaces configured over one or more 952 underlying interfaces classified as follows: 954 o Native interfaces have global IP addresses that are reachable from 955 any INET correspondent. All Server and Relay interfaces are 956 native interfaces, as are INET-facing interfaces of Proxys. 958 o NATed interfaces connect to a private network behind a Network 959 Address Translator (NAT). The NAT does not participate in any 960 AERO control message signaling, but the Server can issue control 961 messages on behalf of the Client. Clients that are behind a NAT 962 are required to send periodic keepalive messages to keep NAT state 963 alive when there are no data packets flowing. If no other 964 periodic messaging service is available, the Client can send RS 965 messages to receive RA replies from its Server(s). 967 o VPNed interfaces use security encapsulation to a Virtual Private 968 Network (VPN) server that also acts as an AERO Server. As with 969 NATed links, the Server can issue control messages on behalf of 970 the Client, but the Client need not send periodic keepalives in 971 addition to those already used to maintain the VPN connection. 973 o Proxyed interfaces connect to an ANET that is separated from the 974 open INET by an AERO Proxy. Unlike NATed and VPNed interfaces, 975 the Proxy can actively issue control messages on behalf of the 976 Client. 978 o Direct interfaces connect a Client directly to a neighbor without 979 crossing any ANET/INET paths. An example is a line-of-sight link 980 between a remote pilot and an unmanned aircraft. 982 AERO interfaces use encapsulation (see: Section 3.9) to exchange 983 packets with AERO link neighbors over Native, NATed or VPNed 984 interfaces. AERO interfaces avoid encapsulation on Proxyed and 985 Direct underlying interfaces. 987 AERO interfaces maintain a neighbor cache for tracking per-neighbor 988 state the same as for any interface. AERO interfaces use ND messages 989 including Router Solicitation (RS), Router Advertisement (RA), 990 Neighbor Solicitation (NS) and Neighbor Advertisement (NA) for 991 neighbor cache management. 993 AERO interfaces send ND messages over Proxyed and Direct interfaces 994 with an AERO option formatted as specified in 995 [I-D.templin-atn-aero-interface]. For native, NATed and VPNed 996 interfaces (i.e., for those that use encapsulation), the AERO 997 interface omits the AERO option and instead includes a Source/Target 998 Link-Layer Address Options (S/TLLAO) formatted as shown in Figure 4: 1000 0 1 2 3 1001 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 1002 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1003 | Type | Length | Prefix Length |R|X|N| Reserved| 1004 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1005 | ifIndex[1] | ifType[1] | Flags [1] |Link[1]|QoS[1] | 1006 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1007 |P00|P01|P02|P03|P04|P05|P06|P07|P08|P09|P10|P11|P12|P13|P14|P15| 1008 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1009 |P16|P17|P18|P19|P20|P21|P22|P23|P24|P25|P26|P27|P28|P29|P30|P31| 1010 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1011 |P32|P33|P34|P35|P36|P37|P38|P39|P40|P41|P42|P43|P44|P45|P46|P47| 1012 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1013 |P48|P49|P50|P51|P52|P53|P54|P55|P56|P57|P58|P59|P60|P61|P62|P63| 1014 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1015 | | 1016 + + 1017 | | 1018 + Link Layer Address [1] + 1019 | | 1020 + + 1021 | | 1022 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1023 | Port Number [1] | ifIndex[2] | ifType[2] | 1024 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1025 | Flags [2] |Link[2]|QoS[2] | ~ 1026 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ 1027 ~ ~ 1028 ~ P00 - P63, Link Layer Address, Port Number for ifIndex[2] ~ 1029 ~ ~ 1030 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1031 | ifIndex[3] | ifType[3] | Flags [3] |Link[3]|QoS[3] | 1032 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1033 ~ ~ 1034 ~ P00 - P63, Link Layer Address, Port Number for ifIndex[3] ~ 1035 ~ ~ 1036 ... ... 1037 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1038 | ifIndex[N] | ifType[N] | Flags [N] |Link[N]|QoS[N] | 1039 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1040 ~ ~ 1041 ~ P00 - P63, Link Layer Address, Port Number for ifIndex[N] ~ 1042 ~ ~ 1043 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1044 | Trailing zero padding | 1045 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1047 Figure 4: AERO Source/Target Link-Layer Address Option (S/TLLAO) 1048 Format 1050 In this format, the ifIndex-tuple field values have the same format 1051 and meaning as for the AERO option specified in 1052 [I-D.templin-atn-aero-interface] except that a 16-byte Link Layer 1053 address and 2-bye Port Number follows immediately after the P[i] 1054 fields. These values represent the link-layer addresses for this 1055 ifIndex-tuple. 1057 A Client's AERO interface may be configured over multiple underlying 1058 interface connections. For example, common mobile handheld devices 1059 have both wireless local area network ("WLAN") and cellular wireless 1060 links. These links are typically used "one at a time" with low-cost 1061 WLAN preferred and highly-available cellular wireless as a standby. 1062 In a more complex example, aircraft frequently have many wireless 1063 data link types (e.g. satellite-based, cellular, terrestrial, air-to- 1064 air directional, etc.) with diverse performance and cost properties. 1066 If a Client's multiple underlying interfaces are used "one at a time" 1067 (i.e., all other interfaces are in standby mode while one interface 1068 is active), then ND messages include only a single ifIndex-tuple in 1069 the option and set to a constant value. In that case, the Client 1070 would appear to have a single interface but with a dynamically 1071 changing Link Layer address. 1073 If the Client has multiple active underlying interfaces, then from 1074 the perspective of ND it would appear to have multiple link-layer 1075 addresses. In that case, ND messages options MAY include multiple 1076 ifIndex-tuples - each with a value that corresponds to a specific 1077 interface. The first ifIndex in the option MUST correspond to the 1078 interface over which the ND message is sent. Every ND message need 1079 not include all ifIndexes; for any ifIndex not included, the neighbor 1080 considers the status of that ifIndex as unchanged. 1082 When the Client includes an option for an underlying interface for 1083 which it is aware that there is a NAT on the path to the Server, or 1084 when a node includes an option solely for the purpose of announcing 1085 new QoS preferences, the node sets both Port Number and Link-Layer 1086 Address to 0 to indicate that the addresses are unspecified at the 1087 network layer and must instead be derived from the link-layer 1088 encapsulation headers. 1090 Relay, Server and Proxy AERO interfaces may be configured over one or 1091 more secured tunnel interfaces. The AERO interface configures both 1092 an AERO address and its corresponding SPAN address, while the 1093 underlying secured tunnel interfaces are either unnumbered or 1094 configure the same SPAN address. The AERO interface encapsulates 1095 each IP packet in a SPAN header and presents the packet to the 1096 underlying secured tunnel interface. For Relays that do not 1097 configure an AERO interface, the secured tunnel interfaces themselves 1098 are exposed to the IP layer with each interface configuring the 1099 Relay's SPAN address. Routing protocols such as BGP therefore run 1100 directly over the Relay's secured tunnel interfaces. For nodes that 1101 configure an AERO interface, routing protocols such as BGP run over 1102 the AERO interface but do not employ SPAN encapsulation. Instead, 1103 the AERO interface presents the routing protocol messages directly to 1104 the underlying secured tunnels without applying encapsulation and 1105 while using the SPAN address as the source address. This distinction 1106 must be honored consistently according to each node's configuration 1107 so that the IP forwarding table will associate discovered IP routes 1108 with the correct interface. 1110 3.7. AERO Interface Initialization 1112 AERO Servers, Proxys and Clients configure AERO interfaces as their 1113 point of attachment to the AERO link. AERO nodes assign the MSPs for 1114 the link to their AERO interfaces (i.e., as a "route-to-interface") 1115 to ensure that packets with destination addresses covered by an MNP 1116 not explicitly assigned to a non-AERO interface are directed to the 1117 AERO interface. 1119 AERO interface initialization procedures for Servers, Proxys, Clients 1120 and Relays are discussed in the following sections. 1122 3.7.1. AERO Server/Gateway Behavior 1124 When a Server enables an AERO interface, it assigns AERO/SPAN 1125 addresses and configures permanent neighbor cache entries for 1126 neighbors in the same SPAN segment by consulting the ROS list for the 1127 segment. The Server also configures secured tunnels with one or more 1128 neighboring Relays and engages in a BGP routing protocol session with 1129 each Relay. 1131 The AERO interface provides a single interface abstraction to the IP 1132 layer, but internally comprises multiple secured tunnels as well as 1133 an NBMA nexus for sending encapsulated data packets to AERO interface 1134 neighbors. The Server further configures a service to facilitate ND/ 1135 PD exchanges with AERO Clients and manages per-Client neighbor cache 1136 entries and IP forwarding table entries based on control message 1137 exchanges. 1139 Gateways are simply Servers that run a dynamic routing protocol 1140 between the AERO interface and INET/EUN interfaces (see: 1141 Section 3.3). The Gateway provisions MNPs to networks on the INET/ 1142 EUN interfaces (i.e., the same as a Client would do) and advertises 1143 the MSP(s) for the AERO link over the INET/EUN interfaces. The 1144 Gateway further provides an attachment point of the AERO link to the 1145 non-MNP-based global topology. 1147 3.7.2. AERO Proxy Behavior 1149 When a Proxy enables an AERO interface, it assigns AERO/SPAN 1150 addresses and configures permanent neighbor cache entries the same as 1151 for Servers. The Proxy also configures secured tunnels with one or 1152 more neighboring Relays and maintains per-Client neighbor cache 1153 entries based on control message exchanges. 1155 3.7.3. AERO Client Behavior 1157 When a Client enables an AERO interface, it sends RS messages with 1158 ND/PD parameters over an ANET interface to one or more Servers in the 1159 MAP list, which return RA messages with corresponding PD parameters. 1160 (The RS/RA messages may pass through a Proxy in the case of a 1161 Client's Proxyed interface.) 1163 After the initial ND/PD message exchange, the Client assigns AERO 1164 addresses to the AERO interface based on the delegated prefix(es). 1165 The Client can then register additional ANET interfaces with the 1166 Server by sending an RS message over each ANET interface. 1168 3.7.4. AERO Relay Behavior 1170 AERO Relays need not connect directly to the AERO link, since they 1171 operate as link-layer forwarding devices instead of network layer 1172 routers. Configuration of AERO interfaces on Relays is therefore 1173 OPTIONAL, e.g., if an administrative interface is needed. Relays 1174 configure secured tunnels with Servers, Proxys and other Relays; they 1175 also configure AERO/SPAN addresses and permanent neighbor cache 1176 entries the same as Servers. Relays engage in a BGP routing protocol 1177 session with a subset of the Servers on the local SPAN segment, and 1178 with other Relays on the SPAN (see: Section 3.3). 1180 3.8. AERO Interface Neighbor Cache Maintenance 1182 Each AERO interface maintains a conceptual neighbor cache that 1183 includes an entry for each neighbor it communicates with on the AERO 1184 link per [RFC4861]. AERO interface neighbor cache entries are said 1185 to be one of "permanent", "symmetric", "asymmetric" or "proxy". 1187 Permanent neighbor cache entries are created through explicit 1188 administrative action; they have no timeout values and remain in 1189 place until explicitly deleted. AERO Servers and Proxys maintain 1190 permanent neighbor cache entries for all other Servers and Proxys 1191 within the same SPAN segment. Each entry maintains the mapping 1192 between the neighbor's network-layer AERO address and corresponding 1193 INET address. The list of all permanent neighbor cache entries for 1194 the SPAN segment is maintained in the segment's ROS list. 1196 Symmetric neighbor cache entries are created and maintained through 1197 RS/RA exchanges as specified in Section 3.15, and remain in place for 1198 durations bounded by ND/PD lifetimes. AERO Servers maintain 1199 symmetric neighbor cache entries for each of their associated 1200 Clients, and AERO Clients maintain symmetric neighbor cache entries 1201 for each of their associated Servers. The list of all Servers on the 1202 AERO link is maintained in the link's MAP list. 1204 Asymmetric neighbor cache entries are created or updated based on 1205 route optimization messaging as specified in Section 3.17, and are 1206 garbage-collected when keepalive timers expire. AERO route 1207 optimization sources (ROSs) maintain asymmetric neighbor cache 1208 entries for active targets with lifetimes based on ND messaging 1209 constants. Asymmetric neighbor cache entries are unidirectional 1210 since only the ROS and not the target (e.g., a Client's MAP) creates 1211 an entry. 1213 Proxy neighbor cache entries are created and maintained by AERO 1214 Proxys when they process Client/Server ND/PD exchanges, and remain in 1215 place for durations bounded by ND/PD lifetimes. AERO Proxys maintain 1216 proxy neighbor cache entries for each of their associated Clients. 1217 Proxy neighbor cache entries track the Client state and the address 1218 of the Client's associated Server. 1220 To the list of neighbor cache entry states in Section 7.3.2 of 1221 [RFC4861], AERO interfaces add an additional state DEPARTED that 1222 applies to symmetric and proxy neighbor cache entries for Clients 1223 that have recently departed. The interface sets a "DepartTime" 1224 variable for the neighbor cache entry to "DEPARTTIME" seconds. 1225 DepartTime is decremented unless a new ND message causes the state to 1226 return to REACHABLE. While a neighbor cache entry is in the DEPARTED 1227 state, packets destined to the target Client are forwarded to the 1228 Client's new location instead of being dropped. When DepartTime 1229 decrements to 0, the neighbor cache entry is deleted. It is 1230 RECOMMENDED that DEPARTTIME be set to the default constant value 40 1231 seconds to allow for packets in flight to be delivered while stale 1232 route optimization state may be present. 1234 When a target Server (acting as a Mobility Anchor Point (MAP)) 1235 receives a valid NS message used for route optimization, it searches 1236 for a symmetric neighbor cache entry for the target Client. The MAP 1237 then returns a solicited NA message without creating a neighbor cache 1238 entry for the ROS, but creates a target Client "Report List" entry 1239 for the ROS and sets a "ReportTime" variable for the entry to 1240 REPORTTIME seconds. The MAP resets ReportTime when it receives a new 1241 authentic NS message, and otherwise decrements ReportTime while no NS 1242 messages have been received. It is RECOMMENDED that REPORTTIME be 1243 set to the default constant value 40 seconds to allow a 10 second 1244 window so that route optimization can converge before ReportTime 1245 decrements below REACHABLETIME. 1247 When the ROS receives a solicited NA message response to its NS 1248 message, it creates or updates an asymmetric neighbor cache entry for 1249 the target network-layer and link-layer addresses. The ROS then 1250 (re)sets ReachableTime for the neighbor cache entry to REACHABLETIME 1251 seconds and uses this value to determine whether packets can be 1252 forwarded directly to the target, i.e., instead of via a default 1253 route. The ROS otherwise decrements ReachableTime while no further 1254 solicited NA messages arrive. It is RECOMMENDED that REACHABLETIME 1255 be set to the default constant value 30 seconds as specified in 1256 [RFC4861]. 1258 The ROS also uses the value MAX_UNICAST_SOLICIT to limit the number 1259 of NS keepalives sent when a correspondent may have gone unreachable, 1260 the value MAX_RTR_SOLICITATIONS to limit the number of RS messages 1261 sent without receiving an RA and the value MAX_NEIGHBOR_ADVERTISEMENT 1262 to limit the number of unsolicited NAs that can be sent based on a 1263 single event. It is RECOMMENDED that MAX_UNICAST_SOLICIT, 1264 MAX_RTR_SOLICITATIONS and MAX_NEIGHBOR_ADVERTISEMENT be set to 3 the 1265 same as specified in [RFC4861]. 1267 Different values for DEPARTTIME, REPORTTIME, REACHABLETIME, 1268 MAX_UNICAST_SOLICIT, MAX_RTR_SOLCITATIONS and 1269 MAX_NEIGHBOR_ADVERTISEMENT MAY be administratively set; however, if 1270 different values are chosen, all nodes on the link MUST consistently 1271 configure the same values. Most importantly, DEPARTTIME and 1272 REPORTTIME SHOULD be set to a value that is sufficiently longer than 1273 REACHABLETIME to avoid packet loss due to stale route optimization 1274 state. 1276 3.9. AERO Interface Encapsulation and Re-encapsulation 1278 AERO interfaces encapsulate packets according to whether they are 1279 entering the AERO interface from the network layer or if they are 1280 being re-admitted into the same AERO link they arrived on. This 1281 latter form of encapsulation is known as "re-encapsulation". 1283 For packets entering the AERO interface from the network layer, the 1284 AERO interface copies the "TTL/Hop Limit", "Type of Service/Traffic 1285 Class" [RFC2983], "Flow Label"[RFC6438] (for IPv6) and "Congestion 1286 Experienced" [RFC3168] values in the packet's IP header into the 1287 corresponding fields in the encapsulation header(s). 1289 For packets undergoing re-encapsulation, the AERO interface instead 1290 copies these values from the original encapsulation header into the 1291 new encapsulation header, i.e., the values are transferred between 1292 encapsulation headers and *not* copied from the encapsulated packet's 1293 network-layer header. (Note especially that by copying the TTL/Hop 1294 Limit between encapsulation headers the value will eventually 1295 decrement to 0 if there is a (temporary) routing loop.) For IPv4 1296 encapsulation/re-encapsulation, the AERO interface sets the DF bit as 1297 discussed in Section 3.13. 1299 AERO interfaces configured over INET underlying interfaces 1300 encapsulate each packet in a SPAN header, then encapsulate the 1301 resulting SPAN packet in an INET header according to the next hop 1302 determined in the forwarding algorithm in Section 3.12. If the next 1303 hop is reached via a secured tunnel, the AERO interface uses an INET 1304 encapsulation format specific to the secured tunnel type (see: 1305 Section 6). If the next hop is reached via an unsecured underlying 1306 interface, the AERO interface instead uses Generic UDP Encapsulation 1307 (GUE) [I-D.ietf-intarea-gue] or an alternate minimal encapsulation 1308 format Appendix B. 1310 When GUE encapsulation is used, the AERO interface next sets the UDP 1311 source port to a constant value that it will use in each successive 1312 packet it sends, and sets the UDP length field to the length of the 1313 SPAN packet plus 8 bytes for the UDP header itself plus the length of 1314 the GUE header (or 0 if GUE direct IP encapsulation is used). For 1315 packets sent to a Server or Relay, the AERO interface sets the UDP 1316 destination port to 8060, i.e., the IANA-registered port number for 1317 AERO. For packets sent to a Client, the AERO interface sets the UDP 1318 destination port to the port value stored in the neighbor cache entry 1319 for this Client. The AERO interface then either includes or omits 1320 the UDP checksum according to the GUE specification. 1322 Client AERO interfaces can avoid encapsulation over Direct underlying 1323 interface and Proxyed underlying interfaces for which the first-hop 1324 access router is AERO-aware. 1326 AERO interfaces observes the packet sizing and fragmentation 1327 considerations found in Section 3.13. 1329 3.10. AERO Interface Decapsulation 1331 AERO interfaces decapsulate packets destined either to the AERO node 1332 itself or to a destination reached via an interface other than the 1333 AERO interface the packet was received on. When the encapsulated 1334 packet arrives in multiple fragments, the AERO interface reassembles 1335 as discussed in Section 3.13. Further decapsulation steps are 1336 performed according to the appropriate encapsulation format 1337 specification. 1339 3.11. AERO Interface Data Origin Authentication 1341 AERO nodes employ simple data origin authentication procedures. In 1342 particular: 1344 o AERO Relays, Servers and Proxys accept encapsulated data packets 1345 and control messages received from secured tunnels. 1347 o AERO Servers and Proxys accept encapsulated data packets and NS 1348 messages used for Neighbor Unreachability Detection (NUD) received 1349 from a source found in the ROS list. 1351 o AERO Proxys and Clients accept packets that originate from within 1352 the same secured ANET. 1354 o AERO Clients and Gateways accept packets from downstream network 1355 correspondents based on ingress filtering. 1357 AERO nodes silently drop any packets that do not satisfy the above 1358 data origin authentication procedures. Further security 1359 considerations are discussed Section 6. 1361 3.12. AERO Interface Forwarding Algorithm 1363 IP packets enter a node's AERO interface either from the network 1364 layer (i.e., from a local application or the IP forwarding system) or 1365 from the link layer (i.e., from an AERO interface neighbor). All 1366 packets entering a node's AERO interface first undergo data origin 1367 authentication as discussed in Section 3.11. Packets that satisfy 1368 data origin authentication are processed further, while all others 1369 are dropped silently. 1371 Packets that enter the AERO interface from the network layer are 1372 forwarded to an AERO interface neighbor. Packets that enter the AERO 1373 interface from the link layer are either re-admitted into the AERO 1374 link or forwarded to the network layer where they are subject to 1375 either local delivery or IP forwarding. In all cases, the AERO 1376 interface itself MUST NOT decrement the network layer TTL/Hop-count 1377 since its forwarding actions occur below the network layer. 1379 AERO interfaces may have multiple underlying interfaces and/or 1380 neighbor cache entries for neighbors with multiple ifIndex 1381 registrations (see Section 3.6). The AERO interface uses each 1382 packet's DSCP value (and/or port number) to select an outgoing 1383 underlying interface based on the node's own QoS preferences, and 1384 also to select a destination link-layer address based on the 1385 neighbor's underlying interface with the highest preference. AERO 1386 implementations SHOULD allow for QoS preference values to be modified 1387 at runtime through network management. 1389 If multiple outgoing interfaces and/or neighbor interfaces have a 1390 preference of "high", the AERO node replicates the packet and sends 1391 one copy via each of the (outgoing / neighbor) interface pairs; 1392 otherwise, the node sends a single copy of the packet via the 1393 interface with the highest preference. AERO nodes keep track of 1394 which underlying interfaces are currently "reachable" or 1395 "unreachable", and only use "reachable" interfaces for forwarding 1396 purposes. 1398 The following sections discuss the AERO interface forwarding 1399 algorithms for Clients, Proxys, Servers and Relays. In the following 1400 discussion, a packet's destination address is said to "match" if it 1401 is the same as a cached address, or if it is covered by a cached 1402 prefix (which may be encoded in an AERO address). 1404 3.12.1. Client Forwarding Algorithm 1406 When an IP packet enters a Client's AERO interface from the network 1407 layer the Client searches for an asymmetric neighbor cache entry that 1408 matches the destination. If there is a match, the Client uses one or 1409 more "reachable" neighbor interfaces in the entry for packet 1410 forwarding. If there is no asymmetric neighbor cache entry, the 1411 Client instead forwards the packet toward a Server (the packet is 1412 intercepted by a Proxy if there is a Proxy on the path). 1414 When an IP packet enters a Client's AERO interface from the link- 1415 layer, if the destination matches one of the Client's MNPs or link- 1416 local addresses the Client decapsulates the packet (if necessary) and 1417 delivers it to the network layer. Otherwise, the Client drops the 1418 packet and MAY return a network-layer ICMP Destination Unreachable 1419 message subject to rate limiting (see: Section 3.14). 1421 3.12.2. Proxy Forwarding Algorithm 1423 For control messages originating from or destined to a Client, the 1424 Proxy intercepts the message and updates its proxy neighbor cache 1425 entry for the Client. The Proxy then forwards a (proxyed) copy of 1426 the control message. (For example, the Proxy forwards a proxied 1427 version of a Client's NS/RS message to the target neighbor, and 1428 forwards a proxied version of the NA/RA reply to the Client.) 1430 When the Proxy receives a data packet from a Client within the ANET, 1431 the Proxy searches for an asymmetric neighbor cache entry that 1432 matches the destination and forwards the packet as follows: 1434 o if the destination matches an asymmetric neighbor cache entry, the 1435 Proxy uses one or more "reachable" neighbor interfaces in the 1436 entry for packet forwarding via encapsulation. If the neighbor 1437 interface is in the same SPAN segment, the Proxy forwards the 1438 packet directly to the neighbor; otherwise, it forwards the packet 1439 to a Relay. 1441 o else, the Proxy encapsulates and forwards the packet to a Relay 1442 while using the packet's destination address as the SPAN 1443 destination address. (If the destination is an AERO address, the 1444 Proxy instead uses the corresponding Subnet Router Anycast address 1445 for Client AERO addresses and the SPAN address for 1446 administratively-provisioned AERO addresses.). 1448 When the Proxy receives an encapsulated data packet from an INET 1449 neighbor or from a secured tunnel, it accepts the packet only if data 1450 origin authentication succeeds and the SPAN destination address is 1451 its own address. If the packet is a SPAN fragment, the Proxy then 1452 adds the fragment to the reassembly buffer and returns if the 1453 reassembly is still incomplete. Otherwise, the Proxy reassembles the 1454 packet (if necessary) and continues processing. 1456 Next, the Proxy searches for a proxy neighbor cache entry that 1457 matches the destination. If there is a proxy neighbor cache entry in 1458 the REACHABLE state, the Proxy decapsulates and forwards the packet 1459 to the Client. If the neighbor cache entry is in the DEPARTED state, 1460 the Proxy instead re-encapsulates the message and forwards it to a 1461 Relay. If there is no neighbor cache entry, the Proxy instead 1462 discards the packet. 1464 3.12.3. Server/Gateway Forwarding Algorithm 1466 For control messages destined to a target Client's AERO address that 1467 are received from a secured tunnel, the Server (acting as a MAP) 1468 intercepts the message and sends an appropriate response on behalf of 1469 the Client. (For example, the Server sends an NA message reply in 1470 response to an NS message directed to one of its associated Clients.) 1471 If the Client's neighbor cache entry is in the DEPARTED state, 1472 however, the Server instead forwards the packet to the Client's new 1473 Server as discussed in Section 3.19. 1475 When the Server receives an encapsulated data packet from an INET 1476 neighbor or from a secured tunnel, it accepts the packet only if data 1477 origin authentication succeeds. If the SPAN destination address is 1478 its own address, the Server reassembles if necessary and discards the 1479 SPAN header (if the reassembly is incomplete, the Server instead adds 1480 the fragment to the reassembly buffer and returns). The Server then 1481 continues processing as follows: 1483 o if the destination matches a symmetric neighbor cache entry in the 1484 REACHABLE state the Server prepares the packet for forwarding to 1485 the destination Client. If the current header is a SPAN header, 1486 the Server reassembles if necessary and discards the SPAN header 1487 (if the reassembly is incomplete, the Server instead adds the 1488 fragment to the reassembly buffer and returns). The Server then 1489 forwards the packet according to the cached link-layer 1490 information, while using SPAN encapsulation for the Client's 1491 Proxyed/Native interfaces, simple INET encapsulation for NATed/ 1492 VPNed interfaces, or no encapsulation for Direct interfaces. If 1493 the packet is destined to the same Client from which it arrived 1494 (i.e., if the packet was forwarded by one of the Client's Proxys), 1495 the Server forwards the packet via a different "reachable" 1496 neighbor interface than the one the packet arrived on. If there 1497 are no "reachable" neighbor interfaces, the Server drops the 1498 packet. 1500 o else, if the destination matches a symmetric neighbor cache entry 1501 in the DEPARETED state the Server encapsulates the packet in a new 1502 SPAN header and forwards it to the Client's new Server (noting 1503 that the encapsulation may result in the addition of a second SPAN 1504 header). The Server uses its own SPAN address as the source and 1505 the SPAN address of the new Server as the destination. 1507 o else, if the destination matches an asymmetric neighbor cache 1508 entry, the Server uses one or more "reachable" neighbor interfaces 1509 in the entry for packet forwarding via the local INET if the 1510 neighbor is in the same SPAN segment or via a Relay otherwise. 1512 o else, if the destination is an AERO address that is not assigned 1513 on the AERO interface the Server drops the packet. 1515 o else, the Server (acting as a Gateway) releases the packet to the 1516 network layer for local delivery or IP forwarding. Based on the 1517 information in the forwarding table, the network layer may return 1518 the packet to the same AERO interface in which case further 1519 processing occurs as below. (Note that this arrangement 1520 accommodates common implementations in which the IP forwarding 1521 table is not accessible from within the AERO interface. If the 1522 AERO interface can directly access the IP forwarding table, the 1523 forwarding table lookup can instead be performed internally from 1524 within the AERO interface itself.) 1526 When the Server's AERO interface receives a data packet from the 1527 network layer or from a NATed/VPNed/Direct Client, it processes the 1528 packet according to the network-layer destination address as follows: 1530 o if the destination matches a symmetric or asymmetric neighbor 1531 cache entry the Server processes the packet as above. 1533 o else, the Server encapsulates the packet and forwards it to a 1534 Relay. For administratively-assigned AERO address destinations, 1535 the Server uses the SPAN address corresponding to the destination 1536 as the SPAN destination address. For Client AERO address 1537 destinations, the Server uses the Subnet Router Anycast address 1538 corresponding to the destination as the SPAN destination address. 1539 For all others, the Server uses the packet's destination IP 1540 address as the SPAN destination address. 1542 3.12.4. Relay Forwarding Algorithm 1544 Relays forward packets over secured tunnels the same as any IP 1545 router. When the Relay receives an encapsulated packet via a secured 1546 tunnel, it removes the INET header and searches for a forwarding 1547 table entry that matches the destination address in the next header. 1548 The Relay then processes the packet as follows: 1550 o if the destination matches one of the Relay's own addresses, the 1551 Relay submits the packet for local delivery. 1553 o else, if the destination matches a forwarding table entry the 1554 Relay forwards the packet via a secured tunnel to the next hop. 1555 If the destination matches an MSP without matching an MNP, 1556 however, the Relay instead drops the packet and returns an ICMP 1557 Destination Unreachable message subject to rate limiting (see: 1558 Section 3.14). 1560 o else, the Relay drops the packet and returns an ICMP Destination 1561 Unreachable as above. 1563 As for any IP router, the Relay decrements the TTL/Hop Limit when it 1564 forwards the packet. If the packet is encapsulated in a SPAN header, 1565 only the Hop Limit in the SPAN header is decremented, and not the 1566 TTL/Hop Limit in the inner packet header. 1568 3.13. AERO Interface MTU and Fragmentation 1570 The AERO interface is the node's attachment to the AERO link. For 1571 AERO link neighbor underlying interface paths that do not require 1572 encapsulation, the AERO interface sends unencapsulated IP packets. 1573 For other paths, the AERO interface acts as a tunnel ingress when it 1574 sends packets to the neighbor and as a tunnel egress when it receives 1575 packets from the neighbor. 1577 AERO interfaces configure an MTU the same as for any IP interface, 1578 however the MTU does not reflect the physical size of any links in 1579 the path but rather determines the maximum size for reassembly. AERO 1580 interfaces observe the packet sizing considerations for tunnels 1581 discussed in [I-D.ietf-intarea-tunnels] and as specified below. 1583 The Internet Protocol expects that IP packets will either be 1584 delivered to the destination or a suitable Packet Too Big (PTB) 1585 message returned to support the process known as IP Path MTU 1586 Discovery (PMTUD) [RFC1191][RFC8201]. However, PTB messages may be 1587 crafted for malicious purposes or lost in the network [RFC2923]. 1588 This can be especially problematic for tunnels, where a condition 1589 known as a PMTUD "black hole" can result. For these reasons, AERO 1590 interfaces employ operational procedures that avoid interactions with 1591 PMTUD, including the use of fragmentation when necessary. 1593 AERO interfaces observe three different types of fragmentation. 1594 Source fragmentation occurs when the AERO interface (acting as a 1595 tunnel ingress) fragments the encapsulated packet into multiple 1596 fragments before admitting each fragment into the tunnel. Network 1597 fragmentation occurs when an encapsulated packet admitted into the 1598 tunnel by the ingress is fragmented by an IPv4 router on the path to 1599 the egress. Finally, link-layer fragmentation (aka link adaptation) 1600 occurs at a layer below IP and is coordinated between underlying data 1601 link endpoints. 1603 IPv6 specifies a minimum link Maximum Transmission Unit (MTU) of 1280 1604 bytes [RFC8200]. Although IPv4 specifies a smaller minimum link MTU 1605 of 68 bytes [RFC0791], AERO interfaces also observe the IPv6 minimum 1606 for IPv4 even if encapsulated packets may incur network 1607 fragmentation. 1609 IPv6 specifies a minimum Maximum Reassembly Unit (MRU) of 1500 bytes 1610 [RFC8200], while the minimum MRU for IPv4 is only 576 bytes [RFC1122] 1611 (but, note that many standard IPv6 over IPv4 tunnel types already 1612 assume a larger MRU than the IPv4 minimum). 1614 AERO interfaces therefore configure an MTU that MUST NOT be smaller 1615 than 1280 bytes, MUST NOT be larger than the minimum MRU among all 1616 nodes on the AERO link minus the encapsulation overhead ("ENCAPS"), 1617 and SHOULD NOT be smaller than 1500 bytes. AERO interfaces also 1618 configure a Maximum Segment Unit (MSU) as the maximum-sized 1619 encapsulated packet that the ingress can inject into the tunnel 1620 without source fragmentation. The MSU value MUST NOT be larger than 1621 1280 bytes unless there is operational assurance that a larger size 1622 can traverse the link along all paths. 1624 All AERO interfaces on the link MUST configure the same MTU value for 1625 reasons cited in [RFC3819][RFC4861]; in particular, multicast support 1626 requires a common MTU value among all nodes on the link. All AERO 1627 interfaces MUST configure an MRU large enough to reassemble packets 1628 up to (MTU+ENCAPS) bytes in length; nodes that cannot configure a 1629 large-enough MRU MUST NOT enable an AERO interface. For example, for 1630 an MTU of 1500 bytes an appropriate MRU might be 2KB. 1632 The network layer proceeds as follows when it forwards an IP packet 1633 to the AERO interface. For each IPv4 packet that is larger than the 1634 AERO interface MTU and with DF set to 0, the network layer uses IPv4 1635 fragmentation to break the packet into a minimum number of non- 1636 overlapping fragments where the first fragment is no larger than the 1637 MTU and the remaining fragments are no larger than the first. For 1638 all other IP packets, if the packet is larger than the AERO interface 1639 MTU, the network layer drops the packet and returns a PTB message to 1640 the original source. Otherwise, the network layer admits each IP 1641 packet or fragment into the AERO interface. 1643 For each IP packet admitted into AERO interface, if the neighbor is 1644 reached via an underlying interface that does not require 1645 encapsulation the AERO interface proceeds according to the underlying 1646 interface MTU. If the packet is no larger than the underlying 1647 interface MTU, the AERO interface presents the packet to the 1648 underlying interface. Otherwise, for IPv4 packets with DF set to 0 1649 the AERO interface uses IPv4 fragmentation to break the packet into 1650 fragments no larger than the underlying interface MTU. For other 1651 packets, the AERO interface either performs link adaptation or drops 1652 the packet and returns a PTB message to the original source. (If the 1653 original source corresponds to a local application, the PTB would 1654 appear to have originated from a router on the path when in fact it 1655 was locally generated from within the AERO interface.) In the same 1656 way, when a packet that has been admitted into the AERO link reaches 1657 a target neighbor but is too large to be delivered over the final-hop 1658 underlying interface, the target either performs link adaptation or 1659 drops the packet and returns a PTB. Link adaptation is preferred in 1660 both cases when possible to avoid packet loss. 1662 For underlying interfaces that require encapsulation, the AERO 1663 interface (acting as a tunnel ingress) instead encapsulates the 1664 packet and performs path MTU procedures according to the specific 1665 encapsulation format. For INET interfaces, the ingress encapsulates 1666 the packet in a SPAN header. If the SPAN packet is larger than the 1667 MSU, the ingress source fragments the SPAN packet into a minimum 1668 number of non-overlapping fragments where the first fragment is no 1669 larger than the MSU and the remaining fragments are no larger than 1670 the first. The ingress then encapsulates each SPAN packet/fragment 1671 in an INET header and admits them into the tunnel. For IPv4, the 1672 ingress sets the DF bit to 0 in the INET header in case any network 1673 fragmentation is necessary. The encapsulated packets will be 1674 delivered to the egress, which reassembles them into a whole packet 1675 if necessary. 1677 By fragmenting at the SPAN layer instead of lower layers, standard 1678 IPv6 fragmentation and reassembly [RFC8200] ensures that IPv4 issues 1679 such as data corruption due to reassembly misassociations will not 1680 occur [RFC6864][RFC4963]. The ingress sends each fragment with 1681 minimal delay so that individual fragments are unlikely to be 1682 diverted to different destinations due to routing fluctuations. 1684 Since the SPAN header and IPv6 fragment extension header reduces the 1685 room available for packet data, but the original source has no way to 1686 control its insertion, the ingress MUST include their lengths in 1687 ENCAPS even for packets in which the header is absent. 1689 3.13.1. AERO MTU Requirements 1691 In light of the above considerations, AERO interfaces configure an 1692 MTU of 9180 bytes. This means that the AERO interface MUST be 1693 capable of reassembling original IP packets up to 9180 bytes in 1694 length. When an IP packet is admitted into an AERO interface, the 1695 interface encapsulates the packet using SPAN encapsulation and 1696 fragments the encapsulated packet into fragments that are no larger 1697 than 1280 bytes. The fragments will be reassembled by the tunnel 1698 egress that services the final destination. 1700 AERO Clients behind Proxys MAY configure an MTU smaller than 9180 1701 (but no smaller than IP minimum link MTU). If Clients configure a 1702 diversity of MTUs (e.g., 1280, 1500, 4KB, 8KB, etc.) then neighbors 1703 on the link would appear to have multiple MTUs. IPv6 Path MTU 1704 Discovery [RFC8201] accounts for this possibility since MTU discovery 1705 must be performed even between nodes that appear to be connected to 1706 the same link. 1708 Applications that cannot tolerate loss in the network due to MTU 1709 restrictions should restrict themselves to sending packets no larger 1710 than the IP minimum link MTU, i.e., even if the current path MTU 1711 would appear to support a larger size. This is due to the fact that 1712 routing changes could cause the path to traverse links with smaller 1713 MTUs at any given point in time. 1715 3.14. AERO Interface Error Handling 1717 When an AERO node admits encapsulated packets into the AERO 1718 interface, it may receive link-layer or network-layer error 1719 indications. 1721 A link-layer error indication is an ICMP error message generated by a 1722 router in the INET on the path to the neighbor or by the neighbor 1723 itself. The message includes an IP header with the address of the 1724 node that generated the error as the source address and with the 1725 link-layer address of the AERO node as the destination address. 1727 The IP header is followed by an ICMP header that includes an error 1728 Type, Code and Checksum. Valid type values include "Destination 1729 Unreachable", "Time Exceeded" and "Parameter Problem" 1730 [RFC0792][RFC4443]. (AERO interfaces ignore all link-layer IPv4 1731 "Fragmentation Needed" and IPv6 "Packet Too Big" messages since they 1732 only emit packets that are guaranteed to be no larger than the IP 1733 minimum link MTU as discussed in Section 3.13.) 1735 The ICMP header is followed by the leading portion of the packet that 1736 generated the error, also known as the "packet-in-error". For 1737 ICMPv6, [RFC4443] specifies that the packet-in-error includes: "As 1738 much of invoking packet as possible without the ICMPv6 packet 1739 exceeding the minimum IPv6 MTU" (i.e., no more than 1280 bytes). For 1740 ICMPv4, [RFC0792] specifies that the packet-in-error includes: 1741 "Internet Header + 64 bits of Original Data Datagram", however 1742 [RFC1812] Section 4.3.2.3 updates this specification by stating: "the 1743 ICMP datagram SHOULD contain as much of the original datagram as 1744 possible without the length of the ICMP datagram exceeding 576 1745 bytes". 1747 The link-layer error message format is shown in Figure 5 (where, "L2" 1748 and "L3" refer to link-layer and network-layer, respectively): 1750 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1751 ~ ~ 1752 | L2 IP Header of | 1753 | error message | 1754 ~ ~ 1755 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1756 | L2 ICMP Header | 1757 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 1758 ~ ~ P 1759 | IP and other encapsulation | a 1760 | headers of original L3 packet | c 1761 ~ ~ k 1762 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ e 1763 ~ ~ t 1764 | IP header of | 1765 | original L3 packet | i 1766 ~ ~ n 1767 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1768 ~ ~ e 1769 | Upper layer headers and | r 1770 | leading portion of body | r 1771 | of the original L3 packet | o 1772 ~ ~ r 1773 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 1775 Figure 5: AERO Interface Link-Layer Error Message Format 1777 The AERO node rules for processing these link-layer error messages 1778 are as follows: 1780 o When an AERO node receives a link-layer Parameter Problem message, 1781 it processes the message the same as described as for ordinary 1782 ICMP errors in the normative references [RFC0792][RFC4443]. 1784 o When an AERO node receives persistent link-layer Time Exceeded 1785 messages, the IP ID field may be wrapping before earlier fragments 1786 awaiting reassembly have been processed. In that case, the node 1787 SHOULD begin including integrity checks and/or institute rate 1788 limits for subsequent packets. 1790 o When an AERO node receives persistent link-layer Destination 1791 Unreachable messages in response to encapsulated packets that it 1792 sends to one of its asymmetric neighbor correspondents, the node 1793 SHOULD process the message as an indication that a path may be 1794 failing, and MAY initiate NUD over that path. If it receives 1795 Destination Unreachable messages on many or all paths, the node 1796 SHOULD set ReachableTime for the corresponding asymmetric neighbor 1797 cache entry to 0 and allow future packets destined to the 1798 correspondent to flow through a default route. 1800 o When an AERO Client receives persistent link-layer Destination 1801 Unreachable messages in response to encapsulated packets that it 1802 sends to one of its symmetric neighbor Servers, the Client SHOULD 1803 mark the path as unusable and use another path. If it receives 1804 Destination Unreachable messages on many or all paths, the Client 1805 SHOULD associate with a new Server and release its association 1806 with the old Server as specified in Section 3.19.5. 1808 o When an AERO Server receives persistent link-layer Destination 1809 Unreachable messages in response to encapsulated packets that it 1810 sends to one of its symmetric neighbor Clients, the Server SHOULD 1811 mark the underlying path as unusable and use another underlying 1812 path. If it receives Destination Unreachable messages on multiple 1813 paths, the Server should take no further actions unless it 1814 receives an explicit ND/PD release message or if the PD lifetime 1815 expires. In that case, the Server MUST release the Client's 1816 delegated MNP, withdraw the MNP from the AERO routing system and 1817 delete the neighbor cache entry. 1819 o When an AERO Server or Proxy receives link-layer Destination 1820 Unreachable messages in response to an encapsulated packet that it 1821 sends to one of its permanent neighbors, it treats the messages as 1822 an indication that the path to the neighbor may be failing. 1823 However, the dynamic routing protocol should soon reconverge and 1824 correct the temporary outage. 1826 When an AERO Relay receives a packet for which the network-layer 1827 destination address is covered by an MSP, if there is no more- 1828 specific routing information for the destination the Relay drops the 1829 packet and returns a network-layer Destination Unreachable message 1830 subject to rate limiting. The Relay writes the network-layer source 1831 address of the original packet as the destination address and uses 1832 one of its non link-local addresses as the source address of the 1833 message. 1835 When an AERO node receives an encapsulated packet for which the 1836 reassembly buffer it too small, it drops the packet and returns a 1837 network-layer Packet Too Big (PTB) message. The node first writes 1838 the MRU value into the PTB message MTU field, writes the network- 1839 layer source address of the original packet as the destination 1840 address and writes one of its non link-local addresses as the source 1841 address. 1843 3.15. AERO Router Discovery, Prefix Delegation and Autoconfiguration 1845 AERO Router Discovery, Prefix Delegation and Autoconfiguration are 1846 coordinated as discussed in the following Sections. 1848 3.15.1. AERO ND/PD Service Model 1850 Each AERO Server on the link configures a PD service to facilitate 1851 Client requests. Each Server is provisioned with a database of MNP- 1852 to-Client ID mappings for all Clients enrolled in the AERO service, 1853 as well as any information necessary to authenticate each Client. 1854 The Client database is maintained by a central administrative 1855 authority for the AERO link and securely distributed to all Servers, 1856 e.g., via the Lightweight Directory Access Protocol (LDAP) [RFC4511], 1857 via static configuration, etc. Clients can receive new PDs from new 1858 Servers before releasing PDs received from existing Servers for 1859 service continuity. Clients receive the same service regardless of 1860 the Servers they select. 1862 AERO Clients and Servers use ND messages to maintain neighbor cache 1863 entries. AERO Servers configure their AERO interfaces as advertising 1864 interfaces, and therefore send unicast RA messages with configuration 1865 information in response to a Client's RS message. Thereafter, 1866 Clients send additional RS messages to refresh prefix and/or router 1867 lifetimes. 1869 AERO Clients and Servers include PD parameters in RS/RA messages (see 1870 [I-D.templin-6man-dhcpv6-ndopt] for ND/PD alternatives). The unified 1871 ND/PD messages are exchanged between Client and Server according to 1872 the prefix management schedule required by the PD service. If the 1873 Client knows its MNP in advance, it can include its AERO address as 1874 the source address of an RS message and with an SLLAO with a valid 1875 Prefix Length for the MNP. If the Server (and Proxy) accept the 1876 Client's MNP assertion, they inject the prefix into the routing 1877 system and establish the necessary neighbor cache state. 1879 The following sections specify the Client and Server behavior. 1881 3.15.2. AERO Client Behavior 1883 AERO Clients can discover the addresses of Servers in the same manner 1884 described in [RFC5214]. Discovery methods include static 1885 configuration (e.g., from a flat-file map of Server addresses and 1886 locations), or through an automated means such as Domain Name System 1887 (DNS) name resolution [RFC1035]. In the absence of other 1888 information, the Client can resolve the DNS Fully-Qualified Domain 1889 Name (FQDN) "linkupnetworks.[domainname]" where "linkupnetworks" is a 1890 constant text string and "[domainname]" is a DNS suffix for the AERO 1891 link (e.g., "example.com"). Alternatively, the Client can discover 1892 Server addresses through a layer 2 data link login exchange, or 1893 through a multicast or anycast RS as described below. 1895 To associate with a Server, the Client acts as a requesting router to 1896 request MNPs. The Client prepares an RS message with PD parameters 1897 and includes a Nonce and Timestamp option if the Client needs to 1898 correlate RA replies. If the Client already knows the Server's AERO 1899 address, it includes the AERO address as the network-layer 1900 destination address; otherwise, it includes all-routers multicast 1901 (ff02::2) or subnet routers anycast (fe80::) as the network-layer 1902 destination address. If the Client already knows its own AERO 1903 address, it uses the AERO address as the network-layer source 1904 address; otherwise, it uses the unspecified AERO address 1905 (fe80::ffff:ffff) as the network-layer source address. 1907 The Client next includes an SLLAO in the RS message formatted as 1908 described in Section 3.6 to register its link-layer information with 1909 the Server. The first ifIndex in the SLLAO MUST correspond to the 1910 underlying interface over which the Client will send the RS message. 1911 The Client MAY include additional ifIndexes specific to other 1912 underlying interfaces, but if so it MUST set their Port Number and 1913 Link Layer Address fields to 0. If the Client is connected to an 1914 ANET for which encapsulation is required, the Client finally 1915 encapsulates the RS message in an ANET header with its own ANET 1916 address as the source address and the INET address of the Server as 1917 the destination. 1919 The Client then sends the RS message (either directly via Direct 1920 interfaces, via INET encapsulation for NATed interfaces, via a VPN 1921 for VPNed interfaces, via a Proxy for proxyed interfaces or via a 1922 Relay for native interfaces) and waits for an RA message reply (see 1923 Section 3.15.3). The Client retries up to MAX_RTR_SOLICITATIONS 1924 times until an RA is received. If the Client receives no RAs, or if 1925 it receives an RA with Router Lifetime set to 0, the Client SHOULD 1926 abandon this Server and try another Server. Otherwise, the Client 1927 processes the PD information found in the RA message. 1929 Next, the Client creates a symmetric neighbor cache entry with the 1930 Server's AERO address as the network-layer address and the address in 1931 the SLLAO for ifIndex 0 as the Server's INET address. The Client 1932 records the RA Router Lifetime field value in the neighbor cache 1933 entry as the time for which the Server has committed to maintaining 1934 the MNP in the routing system. The Client then autoconfigures AERO 1935 addresses for each of the delegated MNPs and assigns them to the AERO 1936 interface. The Client also caches any MSPs included in Route 1937 Information Options (RIOs) [RFC4191] as MSPs to associate with the 1938 AERO link, and assigns the MTU value in the MTU option to its AERO 1939 interface while configuring an appropriate MRU. 1941 The Client then registers additional underlying interfaces with the 1942 Server by sending RS messages via each additional interface. The RS 1943 messages include the same parameters as for the initial RS/RA 1944 exchange, but with destination address set to the Server's AERO 1945 address and with an ifIndex in the SLLAO specific to the underlying 1946 interface. 1948 The Client examines the X and N bits in the SLLAO with S set to 1 in 1949 each RA message it receives. If X is 1 the Client infers that there 1950 is a Proxy on the path, and if N is 1 the Client infers that there is 1951 a NAT on the path. If N is 1, the Client SHOULD set Port Number and 1952 Link-Layer Address to 0 of any subsequent ND messages it sends to the 1953 Server over that link. 1955 Following autoconfiguration, the Client sub-delegates the MNPs to its 1956 attached EUNs and/or the Client's own internal virtual interfaces as 1957 described in [I-D.templin-v6ops-pdhost] to support the Client's 1958 downstream attached "Internet of Things (IoT)". The Client 1959 subsequently maintains its MNP delegations through each of its 1960 Servers by sending additional RS messages before Router Lifetime 1961 expires. 1963 After the Client registers its underlying interfaces, it may wish to 1964 change one or more registrations, e.g., if an interface changes 1965 address or becomes unavailable, if QoS preferences change, etc. To 1966 do so, the Client prepares an RS message to send over any available 1967 underlying interface. The RS MUST include an ifIndex for the 1968 selected interface as the first ifIndex in the SLLAO and MAY include 1969 any additional ifIndexes specific to other underlying interfaces. 1970 The Client includes fresh P(i) values for each ifIndex to update the 1971 Server's neighbor cache entry. If the Client wishes to update only 1972 the P(i) values, it sets the Port Number and Link-Layer Address 1973 fields to 0. If the Client wishes to disable the underlying 1974 interface, it sets all P(i) values to 0. When the Client receives 1975 the Server's RA response, it has assurance that the Server has been 1976 updated with the new information. 1978 If the Client wishes to discontinue use of a Server it issues an RS 1979 message over any underlying interface with an SLLAO with R set to 0. 1980 When the Server processes the message, it releases the MNP, sets the 1981 symmetric neighbor cache entry state for the Client to DEPARTED, 1982 withdraws the IP route from the routing system and returns an RA 1983 reply with Router Lifetime set to 0. 1985 3.15.3. AERO Server Behavior 1987 AERO Servers act as IP routers and support a PD service for Clients. 1988 Servers arrange to add their AERO and INET addresses to a static map 1989 of Server addresses for the link and/or the DNS resource records for 1990 the FQDN "linkupnetworks.[domainname]" before entering service. 1991 Server addresses should be geographically and/or topologically 1992 referenced, and made available for discovery by Clients on AERO link. 1994 When a Server receives a prospective Client's RS message on its AERO 1995 interface, it SHOULD return an immediate RA reply with Router 1996 Lifetime set to 0 if it is currently too busy or otherwise unable to 1997 service the Client. Otherwise, the Server authenticates the RS 1998 message and processes the PD parameters. The Server first determines 1999 the correct MNPs to delegate to the Client by searching the Client 2000 database. When the Server delegates the MNPs, it also creates an IP 2001 forwarding table entry for each MNP so that the MNPs are propagated 2002 into the routing system (see: Section 3.3). For IPv6, the Server 2003 creates a single IPv6 forwarding table entry for each MNP. For IPv4, 2004 the Server creates an IPv6 forwarding table entry with the 2005 IPv4-mapped IPv6 address corresponding to the IPv4 address. 2007 The Server next creates a symmetric neighbor cache entry for the 2008 Client using the base AERO address as the network-layer address and 2009 with lifetime set to no more than the smallest PD lifetime. Next, 2010 the Server updates the neighbor cache entry by recording the 2011 information in each ifIndex in the RS SLLAO including the Port 2012 Number, Link Layer Address and P(i) values. For the first ifIndex, 2013 however, the Server records the actual INET header source addresses 2014 instead of those that appear in the SLLAO in case there was a NAT in 2015 the path. The Server also records the value of the X bit to indicate 2016 whether there is a Proxy on the path. 2018 Next, the Server prepares an RA message using its AERO address as the 2019 network-layer source address and the network-layer source address of 2020 the RS message as the network-layer destination address. The Server 2021 includes the delegated MNPs, any other PD parameters and an SLLAO 2022 with the Link Layer Address set to the Server's SPAN address and with 2023 ifIndex set to 0. The Server then includes one or more RIOs that 2024 encode the MSPs for the AERO link, plus an MTU option for the link 2025 MTU (see Section 3.13). The Server finally forwards the message to 2026 the Client using SPAN, INET or NULL encapsulation according to the 2027 Client interface type. (For Proxy/Native interfaces, the Server 2028 encapsulates the message in a SPAN header with source address set to 2029 its own SPAN address and destination address set to the Proxy's (or 2030 Client's) SPAN address, then forwards the message into the SPAN.) 2031 After the initial RS/RA exchange, the Server maintains the symmetric 2032 neighbor cache entry for the Client. If the Client (or Proxy) issues 2033 additional NS/RS messages, the Server resets ReachableTime. If the 2034 Client (or Proxy) issues an RS with PD release parameters (e.g., by 2035 including an SLLAO with R set to 0), or if the Client becomes 2036 unreachable, the Server sets the Client's symmetric neighbor cache 2037 entry to the DEPARTED state and withdraws the IP routes from the AERO 2038 routing system. 2040 The Server processes these and any other Client ND/PD messages, and 2041 returns an NA/RA reply. The Server may also issue unsolicited RA 2042 messages, e.g., with PD reconfigure parameters to cause the Client to 2043 renegotiate its PDs, with Router Lifetime set to 0 if it can no 2044 longer service this Client, etc. Finally, If the symmetric neighbor 2045 cache entry is in the DEPARTED state, the Server deletes the entry 2046 after DepartTime expires. 2048 3.15.3.1. Lightweight DHCPv6 Relay Agent (LDRA) 2050 When DHCPv6 is used as the ND/PD service back end, AERO Clients and 2051 Servers are always on the same link (i.e., the AERO link) from the 2052 perspective of DHCPv6. However, in some implementations the DHCPv6 2053 server and ND function may be located in separate modules. In that 2054 case, the Server's AERO interface module can act as a Lightweight 2055 DHCPv6 Relay Agent (LDRA)[RFC6221] to relay PD messages to and from 2056 the DHCPv6 server module. 2058 When the LDRA receives an authentic RS message, it extracts the PD 2059 message parameters and uses them to construct an IPv6/UDP/DHCPv6 2060 message. It sets the IPv6 source address to the source address of 2061 the RS message, sets the IPv6 destination address to 2062 'All_DHCP_Relay_Agents_and_Servers' and sets the UDP fields to values 2063 that will be understood by the DHCPv6 server. 2065 The LDRA then wraps the message in a DHCPv6 'Relay-Forward' message 2066 header and includes an 'Interface-Id' option that includes enough 2067 information to allow the LDRA to forward the resulting Reply message 2068 back to the Client (e.g., the Client's link-layer addresses, a 2069 security association identifier, etc.). The LDRA also wraps the 2070 SLLAO into the Interface-Id option, then forwards the message to the 2071 DHCPv6 server. 2073 When the DHCPv6 server prepares a Reply message, it wraps the message 2074 in a 'Relay-Reply' message and echoes the Interface-Id option. The 2075 DHCPv6 server then delivers the Relay-Reply message to the LDRA, 2076 which discards the Relay-Reply wrapper and IPv6/UDP headers, then 2077 uses the DHCPv6 message to construct an RA response to the Client. 2078 The Server uses the information in the Interface-Id option to prepare 2079 the RA message and to cache the link-layer addresses taken from the 2080 SLLAOs echoed in the Interface-Id option. 2082 3.16. The AERO Proxy 2084 Clients may connect to ANETs that require a perimeter security 2085 gateway to enable communications to Servers in outside INETs. In 2086 that case, the ANET can employ an AERO Proxy. The Proxy is located 2087 at the ANET/INET border and listens for RS messages originating from 2088 or RA messages destined to ANET Clients. The Proxy acts on these 2089 control messages as follows: 2091 o when the Proxy receives an RS message from a new ANET Client, it 2092 first authenticates the message then examines the network-layer 2093 destination address. If the destination address is a Server's 2094 AERO address, the Proxy proceeds to the next step. Otherwise, if 2095 the destination is all-routers multicast or subnet routers 2096 anycast, the Proxy selects a "nearby" Server that is likely to be 2097 a good candidate to serve the Client and replaces the destination 2098 address with the Server's AERO address. Next, the Proxy creates a 2099 proxy neighbor cache entry and caches the Client and Server 2100 addresses along with any identifying information including 2101 Transaction IDs, Client Identifiers, Nonce values, etc. The Proxy 2102 then examines the address in the first ifIndex in the RS message 2103 AERO option. The Proxy then converts the AERO option into an 2104 SLLAO, sets X to 1 and changes the Link Layer Address to its own 2105 SPAN address. The Proxy finally encapsulates the (proxyed) RS 2106 message in a SPAN header with destination set to the Server's SPAN 2107 address then forwards the message into the SPAN. 2109 o when the Server receives the RS message, it authenticates the 2110 message then creates or updates a symmetric neighbor cache entry 2111 for the Client with the Proxy's SPAN address as the link-layer 2112 address. The Server then sends an RA message back to the Proxy 2113 via the SPAN. 2115 o when the Proxy receives the RA message, it matches the message 2116 with the RS that created the proxy neighbor cache entry. The 2117 Proxy then caches the PD route information as a mapping from the 2118 Client's MNPs to the Client's ANET address, and sets the neighbor 2119 cache entry state to REACHABLE. The Proxy then converts the SLLAO 2120 in the RA message to an AERO option and forwards the (proxyed) 2121 message to the Client. 2123 After the initial RS/RA exchange, the Proxy forwards any Client data 2124 packets for which there is no matching asymmetric neighbor cache 2125 entry to a Relay via the SPAN. Finally, the Proxy forwards any 2126 Client data destined to an asymmetric neighbor cache target directly 2127 to the target according to the link-layer information - the process 2128 of establishing asymmetric neighbor cache entries is specified in 2129 Section 3.17. 2131 While the Client is still attached to the ANET, the Proxy send RS or 2132 unsolicited NA messages to update the Server's symmetric neighbor 2133 cache entries on behalf of the Client and/or to convey QoS updates. 2134 If the Server ceases to send solicited RA responses, the Proxy marks 2135 the Server as unreachable and sends an unsolicited RA with Router 2136 Lifetime set to zero to inform Clients that this Server is no longer 2137 able to provide service. Although the Proxy engages in ND exchanges 2138 on behalf of the Client, the Client can also send ND messages on its 2139 own behalf, e.g., if it is in a better position than the Proxy to 2140 convey QoS changes, etc. 2142 If the Client becomes unreachable, the Proxy sets the neighbor cache 2143 entry state to DEPARTED and retains the entry for DEPARTTIME seconds. 2144 While the state is DEPARTED, the Proxy forwards any packets destined 2145 to the Client to a Relay. The Relay in turn forwards the packets to 2146 the Client's current Server. When DepartTime expires, the Proxy 2147 deletes the neighbor cache entry and discards any further packets 2148 destined to this (now forgotten) Client. 2150 When a neighbor cache entry transitions to DEPARTED, some of the 2151 fragments of a multiple fragment packet may have already arrived at 2152 the Proxy while others are en route to the Client's new location. 2153 However, no special attention in the reassembly algorithm is 2154 necessary when re-routed packets are simply treated as loss. Since 2155 the fragments of a multiple-fragment packet are sent with minimal 2156 inter-packet delay, such occasions will be rare. 2158 In some ANETs that employ a Proxy, the Client's MNP can be injected 2159 into the ANET routing system. In that case, the Client can send data 2160 messages without encapsulation so that the ANET native routing system 2161 transports the unencapsulated packets to the Proxy. This can be very 2162 beneficial, e.g., if the Client connects to the ANET via low-end data 2163 links such as some aviation wireless links. 2165 If the first-hop ANET access router is AERO-aware, the Client can 2166 avoid encapsulation for both its control and data messages. When the 2167 Client connects to the link, it can send an unencapsulated RS message 2168 with source address set to its AERO address and with destination 2169 address set to the AERO address of the Client's selected Server or to 2170 all-routers multicast or subnet router anycast. The Client includes 2171 an AERO option formatted as specified in 2172 [I-D.templin-atn-aero-interface]. 2174 The Client then sends the unencapsulated RS message, which will be 2175 intercepted by the AERO-Aware access router. The access router then 2176 encapsulates the RS message in an ANET header with its own address as 2177 the source address and the address of a Proxy as the destination 2178 address. The access router further remembers the address of the 2179 Proxy so that it can encapsulate future data packets from the Client 2180 via the same Proxy. If the access router needs to change to a new 2181 Proxy, it simply sends another RS message toward the Server via the 2182 new Proxy on behalf of the Client. 2184 In some cases, the access router and Proxy may be one and the same 2185 node. In that case, the node would be located on the same physical 2186 link as the Client, but its message exchanges with the Server would 2187 need to pass through a security gateway at the ANET/INET border. The 2188 method for deploying access routers and Proxys (i.e. as a single node 2189 or multiple nodes) is an ANET-local administrative consideration. 2191 3.16.1. Detecting and Responding to Server Failures 2193 In environments where fast recovery from Server failure is required, 2194 Proxys SHOULD use proactive Neighbor Unreachability Detection (NUD) 2195 to track Server reachability in a manner that parallels Bidirectional 2196 Forwarding Detection (BFD) [RFC5880]. Proxys can then quickly detect 2197 and react to failures so that cached information is re-established 2198 through alternate paths. The NUD control messaging is carried only 2199 over well-connected ground domain networks (i.e., and not low-end 2200 aeronautical radio links) and can therefore be tuned for rapid 2201 response. 2203 Proxys perform proactive NUD with Servers for which there are 2204 currently active ANET Clients by sending continuous NS messages in 2205 rapid succession, e.g., one message per second. The Proxy sends the 2206 NS message via the SPAN with the Proxy's AERO address as the source 2207 and the AERO address of the Server as the destination. If the Server 2208 fails (i.e., if the Proxy ceases to receive solicited NA messages), 2209 the Proxy can quickly inform Clients by sending RA messages on the 2210 ANET interface. The Proxy sends RA messages with source address set 2211 to the Server's address, destination address set to all-nodes 2212 multicast, and Router Lifetime set to 0. 2214 The Proxy SHOULD send MAX_FINAL_RTR_ADVERTISEMENTS RA messages 2215 separated by small delays [RFC4861]. Any Clients on the ANET that 2216 have been using the (now defunct) Server will receive the RA messages 2217 and associate with a new Server. 2219 3.17. AERO Route Optimization 2221 While data packets are flowing between a source and target node, 2222 route optimization SHOULD be used. Route optimization is initiated 2223 by the first eligible Route Optimization Source (ROS) closest to the 2224 source as follows: 2226 o For Clients on VPNed, NATed and Direct interfaces, the Server is 2227 the ROS. 2229 o For Clients on Proxyed interfaces, the Proxy is the ROS. 2231 o For Clients on native interfaces, the Client itself is the ROS. 2233 o For correspondent nodes on INET/EUN interfaces serviced by a 2234 Gateway, the Gateway is the ROS. 2236 The route optimization procedure is conducted between the ROS and the 2237 target Server/Gateway acting as a Route Optimization Responder (ROR) 2238 in the same manner as for IPv6 ND Address Resolution and using the 2239 same NS/NA messaging. The target may either be a MNP Client serviced 2240 by a Server, or a non-MNP correspondent reachable via a Gateway. 2242 The procedures are specified in the following sections. 2244 3.17.1. Route Optimization Initiation 2246 While data packets are flowing from the source node toward a target 2247 node, the ROS performs address resolution by sending an NS message to 2248 receive a solicited NA message from the ROR. 2250 When the ROS sends an NS, it includes the AERO address of the ROS as 2251 the source address (e.g., fe80::1) and the AERO address corresponding 2252 to the data packet's destination address as the destination address 2253 (e.g., if the destination address is 2001:db8:1:2::1 then the 2254 corresponding AERO address is fe80::2001:db8:1:2). The NS message 2255 includes an SLLAO with Link Layer Address set to the SPAN address of 2256 the ROS and with all other fields set to 0. The message includes a 2257 Nonce and Timestamp option if the ROS needs to correlate NA replies. 2259 The ROS then encapsulates the NS message in a SPAN header with source 2260 set to its own SPAN address and destination set to the data packet's 2261 destination address, then sends it into the SPAN without decrementing 2262 the network-layer TTL/Hop Limit field. 2264 3.17.2. Relaying the NS 2266 When the Relay receives the NS message from the ROS, it discards the 2267 INET header and determines that the ROR is the next hop by consulting 2268 its standard IPv6 forwarding table for the SPAN header destination 2269 address. The Relay then forwards the SPAN message toward the ROR the 2270 same as for any IPv6 router. The final-hop Relay in the SPAN will 2271 deliver the message via a secured tunnel to the ROR. 2273 3.17.3. Processing the NS and Sending the NA 2275 When the ROR receives the NS message, it examines the AERO 2276 destination address to determine whether it has a neighbor cache 2277 entry and/or route that matches the target; if not, it drops the NS 2278 message and returns from processing. Next, if the target belongs to 2279 an MNP Client neighbor in the DEPARTED state the ROR changes the NS 2280 message SPAN destination address to the address of the Client's new 2281 Server, forwards the message into the SPAN and returns from 2282 processing. If the target belongs to an MNP Client neighbor in the 2283 REACHABLE state, the ROR instead adds the AERO source address to the 2284 target Client's Report List with time set to ReportTime. If the 2285 target belongs to a non-MNP route, the ROR continues processing 2286 without adding an entry to the Report List. 2288 The ROR then prepares a solicited NA message to send back to the ROS 2289 but does not create a neighbor cache entry. The ROR sets the NA 2290 source address to the destination AERO address of the NS, and 2291 includes the Nonce value received in the NS plus the current 2292 Timestamp. The ROR next includes a TLLAO with ifIndex set to 0, with 2293 all P(i) values set to "low", and with Link Layer Address set to the 2294 ROR's SPAN address. If the target belongs to an MNP Client, the ROR 2295 sets the Prefix Length to the MNP prefix length; otherwise, it sets 2296 Prefix Length to the maximum of the non-MNP prefix length and 64. 2297 (Note that a /64 limit is imposed to avoid causing the ROS to set 2298 short prefixes (e.g., "default") that would match destinations for 2299 which the routing system includes more-specific prefixes. Note also 2300 that prefix lengths longer than /64 are out of scope for this 2301 specification.) 2303 If the target belongs to an MNP Client, the ROR next includes 2304 additional ifIndexes for all of the target Client's underlying 2305 interfaces. For NATed, VPNed and Direct interfaces, the Link Layer 2306 Addresses are the SPAN address of the ROR. For Proxyed and native 2307 interfaces, the Link Layer Addresses are the SPAN addresses of the 2308 Proxys and the Client's native interfaces. The ROR finally 2309 encapsulates the NA message in a SPAN header with source set to its 2310 own SPAN address and destination set to the source SPAN address of 2311 the NS message, then forwards the message into the SPAN without 2312 decrementing the network-layer TTL/Hop Limit field. 2314 3.17.4. Relaying the NA 2316 When the Relay receives the NA message from the ROR, it discards the 2317 INET header and determines that the ROS is the next hop by consulting 2318 its standard IPv6 forwarding table for the SPAN header destination 2319 address. The Relay then forwards the SPAN-encapsulated NA message 2320 toward the ROS the same as for any IPv6 router. The final-hop Relay 2321 in the SPAN will deliver the message via a secured tunnel to the ROS. 2323 3.17.5. Processing the NA 2325 When the ROS receives the solicited NA message, it discards the INET 2326 and SPAN headers. The ROS next verifies the Nonce and Timestamp 2327 values, then creates an asymmetric neighbor cache entry for the ROR 2328 and caches all information found in the solicited NA TLLAOs. The ROS 2329 finally sets the asymmetric neighbor cache entry lifetime to 2330 ReachableTime seconds. 2332 3.17.6. Route Optimization Maintenance 2334 Following route optimization, the ROS forwards future data packets 2335 destined to the target via the addresses found in the cached link- 2336 layer information. The route optimization is shared by all sources 2337 that send packets to the target via the ROS, i.e., and not just the 2338 source on behalf of which the route optimization was initiated. 2340 While new data packets destined to the target are flowing through the 2341 ROS, it sends additional NS messages to the ROR before ReachableTime 2342 expires to receive a fresh solicited NA message the same as described 2343 in the previous sections. (Route optimization refreshment strategies 2344 are an implementation matter, with a non-normative example given in 2345 Appendix C.1). 2347 The ROS then updates the asymmetric neighbor cache entry to refresh 2348 ReachableTime, while (for MNP destinations) the ROR adds or updates 2349 the ROS address to the target Client's Report List and with time set 2350 to ReportTime. While no data packets are flowing, the ROS instead 2351 allows ReachableTime for the asymmetric neighbor cache entry to 2352 expire. When ReachableTime expires, the ROS deletes the asymmetric 2353 neighbor cache entry. Future data packets flowing through the ROS 2354 will again trigger a new route optimization exchange while initial 2355 data packets travel over a suboptimal route. 2357 The ROS may also receive unsolicited NA messages from the ROR at any 2358 time. If there is an asymmetric neighbor cache entry for the target, 2359 the ROS updates the link-layer information but does not update 2360 ReachableTime since the receipt of an unsolicited NA does not confirm 2361 that the forward path is still working. If there is no asymmetric 2362 neighbor cache entry, the ROS simply discards the unsolicited NA. 2363 Cases in which unsolicited NA messages are generated are specified in 2364 Section 3.19. 2366 In this arrangement, the ROS holds an asymmetric neighbor cache entry 2367 for the ROR, but the ROR does not hold an asymmetric neighbor cache 2368 entry for the ROS. The route optimization neighbor relationship is 2369 therefore asymmetric and unidirectional. If the target node also has 2370 packets to send back to the source node, then a separate route 2371 optimization procedure is performed in the reverse direction. But, 2372 there is no requirement that the forward and reverse paths be 2373 symmetric. 2375 3.18. Neighbor Unreachability Detection (NUD) 2377 AERO nodes perform Neighbor Unreachability Detection (NUD) per 2378 [RFC4861]. NUD is performed either reactively in response to 2379 persistent link-layer errors (see Section 3.14) or proactively to 2380 confirm reachability. The NUD algorithm may further be seeded by ND 2381 hints of forward progress, but care must be taken to avoid inferring 2382 reachability based on spoofed information. 2384 When an ROR directs an ROS to a neighbor with one or more target 2385 link-layer addresses, the ROS can proactively test each direct path 2386 by sending an initial NS message to elicit a solicited NA response. 2387 While testing the paths, the ROS can optionally continue sending 2388 packets via the SPAN, maintain a small queue of packets until target 2389 reachability is confirmed, or (optimistically) allow packets to flow 2390 via the direct paths. In any case, the ROS should only consider the 2391 neighbor unreachable if NUD fails over multiple target link-layer 2392 address paths. 2394 When a ROS sends an NS message used for NUD, it uses its AERO 2395 addresses as the IPv6 source address and the AERO address 2396 corresponding to a target link-layer address as the destination. For 2397 each target link-layer address, the source node encapsulates the NS 2398 message in SPAN/INET headers with its own SPAN address as the source 2399 and the SPAN address of the target as the destination, If the target 2400 is located within the same SPAN segment, the source sets the INET 2401 address of the target as the destination; otherwise, it sets the INET 2402 address of a Relay as the destination. The source then forwards the 2403 message into the SPAN. 2405 Paths that pass NUD tests are marked as "reachable", while those that 2406 do not are marked as "unreachable". These markings inform the AERO 2407 interface forwarding algorithm specified in Section 3.12. 2409 Proxys can perform NUD to verify Server reachability on behalf of 2410 their proxyed Clients so that the Clients need not engage in NUD 2411 messaging themselves. 2413 3.19. Mobility Management and Quality of Service (QoS) 2415 AERO is a Distributed Mobility Management (DMM) service. Each Server 2416 is responsible for only a subset of the Clients on the AERO link, as 2417 opposed to a Centralized Mobility Management (CMM) service where 2418 there is a single network mobility service for all Clients. Clients 2419 coordinate with their associated Servers via RS/RA exchanges to 2420 maintain the DMM profile, and the AERO routing system tracks all 2421 current Client/Server peering relationships. 2423 Servers provide a Mobility Anchor Point (MAP) for their dependent 2424 Clients. Clients are responsible for maintaining neighbor 2425 relationships with their Servers through periodic RS/RA exchanges, 2426 which also serves to confirm neighbor reachability. When a Client's 2427 underlying interface address and/or QoS information changes, the 2428 Client is responsible for updating the Server with this new 2429 information. Note that for Proxyed interfaces, however, the Proxy 2430 can perform the RS/RA exchanges on the Client's behalf. 2432 Mobility management considerations are specified in the following 2433 sections. 2435 3.19.1. Mobility Update Messaging 2437 Servers acting as MAPs accommodate Client mobility and/or QoS change 2438 events by sending unsolicited NA messages to each ROS in the target 2439 Client's Report List. When a MAP sends an unsolicited NA message, it 2440 sets the IPv6 source address to the Client's AERO address and sets 2441 the IPv6 destination address to all-nodes multicast (ff02::1). The 2442 MAP also includes a TLLAO with a first ifIndex set to 0 and Link 2443 Layer address set to the MAP's SPAN address, and includes additional 2444 ifIndexes for all of the target Client's interfaces with Link Layer 2445 Addresses set to the corresponding SPAN addresses. The MAP finally 2446 encapsulates the message in a SPAN header with source set to its own 2447 SPAN address and destination set to the SPAN address of the ROS, then 2448 sends the message to a Relay in the SPAN. 2450 As for the hot-swap of interface cards discussed in Section 7.2.6 of 2451 [RFC4861], the transmission and reception of unsolicited NA messages 2452 is unreliable but provides a useful optimization. In well-connected 2453 Internetworks with robust data links unsolicited NA messages will be 2454 delivered with high probability, but in any case the MAP can 2455 optionally send up to MAX_NEIGHBOR_ADVERTISEMENT unsolicited NAs to 2456 each ROS to increase the likelihood that at least one will be 2457 received. 2459 When an ROS receives an unsolicited NA message, it ignores the 2460 message if there is no existing neighbor cache entry for the Client. 2461 Otherwise, it uses the included TLLAO to update the Link Layer 2462 Address and QoS information in the neighbor cache entry, but does not 2463 reset ReachableTime since the receipt of an unsolicited NA message 2464 from the target Server does not provide confirmation that any forward 2465 paths to the target Client are working. 2467 If unsolicited NA messages are lost, the ROS may be left with stale 2468 address and/or QoS information for the Client for up to ReachableTime 2469 seconds. During this time, the ROS can continue sending packets 2470 according to its stale neighbor cache information. When 2471 ReachableTime is close to expiring, the ROS will re-initiate route 2472 optimization and receive fresh state information. 2474 In addition to sending unsolicited NA messages to the current set of 2475 ROSs for the Client, the MAP also sends unsolicited NAs to the former 2476 Link-Layer address for any ifIndex for which the Link-Layer address 2477 has changed. The NA messages update Proxys or Servers that cannot 2478 easily detect (e.g., without active probing) when a formerly-active 2479 Client has departed. 2481 3.19.2. Announcing Link-Layer Address and/or QoS Preference Changes 2483 When a Client needs to change its ANET addresses and/or QoS 2484 preferences (e.g., due to a mobility event), either the Client or its 2485 Proxys send RS messages to the Server via the SPAN with SLLAOs that 2486 include the new Client Port Number, Link Layer Address and P(i) 2487 values. If the RS messages are sent solely for the purpose of 2488 updating QoS preferences, Port Number and Link-Layer Address are set 2489 to 0. 2491 Up to MAX_RTR_SOLICITATION RS messages MAY be sent in parallel with 2492 sending actual data packets in case one or more RAs are lost. If all 2493 RAs are lost, the Client SHOULD re-associate with a new Server. 2495 When the Server receives the Client's changes, it sends unsolicited 2496 NA messages to all nodes in the Report List the same as described in 2497 the previous section. 2499 3.19.3. Bringing New Links Into Service 2501 When a Client needs to bring new underlying interfaces into service 2502 (e.g., when it activates a new data link), it sends an RS message to 2503 its Server via the underlying interface with SLLAOs that include the 2504 new Client Link Layer Address information. 2506 3.19.4. Removing Existing Links from Service 2508 When a Client needs to remove existing underlying interfaces from 2509 service (e.g., when it de-activates an existing data link), it sends 2510 an RS message to its Server with SLLAO ifIndexes with Link values set 2511 to 0. 2513 If the Client needs to send RS messages over an underlying interface 2514 other than the one being removed from service, it MUST include an 2515 SLLAO ifIndex for the sending interface as the first ifIndex and 2516 include additional ifIndexes with Link values set to 0 for any 2517 underlying interfaces being removed from service. 2519 3.19.5. Moving to a New Server 2521 When a Client associates with a new Server, it performs the Client 2522 procedures specified in Section 3.15.2. The Client then sends an RS 2523 message over any working underlying interface with destination set to 2524 the old Server's AERO address and with an SLLAO with R set to 0 to 2525 fully release itself from the old Server. The SLLAO also includes 2526 the SPAN address of the new Server in the Link Layer Address. If the 2527 Client does not receive an RA reply after MAX_RTR_SOLICITATIONS 2528 attempts over multiple underlying interfaces, the old Server may have 2529 failed and the Client should discontinue its release attempts. 2531 When the old Server processes the RS, it sends unsolicited NA 2532 messages with a TLLAO with ifIndex set to 0 and with R set to 0 to 2533 all ROSs in the Client's Report List. The Server also changes the 2534 symmetric neighbor cache entry state to DEPARTED, sets the link-layer 2535 address of the Client to the address found in the RS SLLAO (i.e., the 2536 SPAN address of the new Server), and sets a timer to DEPARTTIME 2537 seconds. The old Server then returns an immediate RA message to the 2538 Client with Router Lifetime set to 0 and withdraws the Client's MNP 2539 from the routing system. After DepartTime expires, the old Server 2540 deletes the symmetric neighbor cache entry. 2542 Clients SHOULD NOT move rapidly between Servers in order to avoid 2543 causing excessive oscillations in the AERO routing system. Examples 2544 of when a Client might wish to change to a different Server include a 2545 Server that has gone unreachable, topological movements of 2546 significant distance, movement to a new geographic region, movement 2547 to a new SPAN segment, etc. 2549 When a Client moves to a new Server, some of the fragments of a 2550 multiple fragment packet may have already arrived at the old Server 2551 while others are en route to the new Server. However, no special 2552 attention in the reassembly algorithm is necessary when re-routed 2553 packets are simply treated as loss. Since the fragments of a 2554 multiple-fragment packet are sent with minimal inter-packet delay, 2555 such occasions will be rare. 2557 3.20. Multicast 2559 The AERO Client provides an IGMP (IPv4) [RFC2236] or MLD (IPv6) 2560 [RFC3810] proxy service for its EUNs and/or hosted applications 2561 [RFC4605]. The Client forwards IGMP/MLD messages over any of its 2562 underlying interfaces for which group membership is required. The 2563 IGMP/MLD messages may be further forwarded by a first-hop ANET access 2564 router acting as an IGMP/MLD-snooping switch [RFC4541], then 2565 ultimately delivered to an AERO Proxy/Server acting as a Protocol 2566 Independent Multicast - Sparse-Mode (PIM-SM, or simply "PIM") 2567 Designated Router (DR) [RFC7761]. AERO Gateways also act as PIM 2568 routers (i.e., the same as AERO Proxys/Servers) on behalf of nodes on 2569 INET/EUN networks. The behaviors identified in the following 2570 sections correspond to Source-Specific Multicast (SSM) and Any-Source 2571 Multicast (ASM) operational modes. 2573 3.20.1. Source-Specific Multicast (SSM) 2575 When an ROS (i.e., an AERO Proxy/Server/Gateway) "X" acting as PIM 2576 router receives a Join/Prune message from a node on its downstream 2577 interfaces containing one or more ((S)ource, (G)roup) pairs, it 2578 updates its Multicast Routing Information Base (MRIB) accordingly. 2579 For each S belonging to a prefix reachable via X's non-AERO 2580 interfaces, X then forwards the (S, G) Join/Prune to any PIM routers 2581 on those interfaces per [RFC7761]. 2583 For each S belonging to a prefix reachable via X's AERO interface, X 2584 originates a separate copy of the Join/Prune for each (S,G) in the 2585 message using its own AERO address as the source address and ALL-PIM- 2586 ROUTERS as the destination address. X then encapsulates each message 2587 in a SPAN header with source address set to the SPAN address of X and 2588 destination address set to S then forwards the message into the SPAN. 2589 The SPAN in turn forwards the message to AERO Server/Gateway "Y" that 2590 services S. At the same time, if the message was a Join, X sends a 2591 route-optimization NS message toward each S the same as discussed in 2592 Section 3.17. The resulting NAs will return the AERO address for the 2593 prefix that matches S as the network-layer source address and TLLAOs 2594 with the SPAN addresses corresponding to any ifIndexes that are 2595 currently servicing S. 2597 When Y processes the Join/Prune message, if S located behind any 2598 Native, Direct, VPNed or NATed interfaces Y acts as a PIM router and 2599 updates its MRIB to list X as the next hop in the reverse path. If S 2600 is located behind any Proxys "Z"*, Y also forwards the message to 2601 each Z* over the SPAN while continuing to use the AERO address of X 2602 as the source address. Each Z* then updates its MRIB accordingly and 2603 maintains the AERO address of X as the next hop in the reverse path. 2604 Since the Relays in the SPAN do not examine network layer control 2605 messages, this means that the (reverse) multicast tree path is simply 2606 from each Z* (and/or Y) to X with no other multicast-aware routers in 2607 the path. If any Z* (and/or Y) is located on the same SPAN segment 2608 as X, the multicast data traffic sent to X directly using SPAN/INET 2609 encapsulation instead of via a Relay. 2611 Following the initial Join/Prune and NS/NA messaging, X maintains an 2612 asymmetric neighbor cache entry for each S the same as if X was 2613 sending unicast data traffic to S. In particular, X performs 2614 additional NS/NA exchanges to keep the neighbor cache entry alive for 2615 up to t_periodic seconds [RFC7761]. If no new Joins are received 2616 within t_periodic seconds, X allows the neighbor cache entry to 2617 expire. Finally, if X receives any additional Join/Prune messages 2618 for (S,G) it forwards the messages to each Y and Z* in the neighbor 2619 cache entry over the SPAN. 2621 At some later time, Client C that holds an MNP for source S may 2622 depart from a first Proxy Z1 and/or connect via a new Proxy Z2. In 2623 that case, Y sends an unsolicited NA message to X the same as 2624 specified for unicast mobility in Section 3.19. When X receives the 2625 unsolicited NA message, it updates its asymmetric neighbor cache 2626 entry for the AERO address for source S and sends new Join messages 2627 to any new Proxys Z2. There is no requirement to send any Prune 2628 messages to old Proxys Z1 since source S will no longer source any 2629 multicast data traffic via Z1. Instead, the multicast state for 2630 (S,G) in Proxy Z1 will soon time out since no new Joins will arrive. 2632 After some later time, C may move to a new Server Y2 and depart from 2633 old Sever Y1. In that case, Y1 sends Join messages for any of C's 2634 active (S,G) groups to Y2 while including its own AERO address as the 2635 source address. This causes Y2 to include Y1 in the multicast 2636 forwarding tree during the interim time that Y1's symmetric neighbor 2637 cache entry for C is in the DEPARTED state. At the same time, Y1 2638 sends an unsolicited NA message to X with a TLLAO with ifIndex set to 2639 0 and R set to 1 to cause X to release its asymmetric neighbor cache 2640 entry. X then sends a new Join message to S via the SPAN and re- 2641 initiates route optimization the same as if it were receiving a fresh 2642 Join message from a node on a downstream link. 2644 3.20.2. Any-Source Multicast (ASM) 2646 When an ROS X acting as a PIM router receives a Join/Prune from a 2647 node on its downstream interfaces containing one or more (*,G) pairs, 2648 it updates its Multicast Routing Information Base (MRIB) accordingly. 2649 X then forwards a copy of the message to the Rendezvous Point (RP) R 2650 for each G over the SPAN. X uses its own AERO address as the source 2651 address and ALL-PIM-ROUTERS as the destination address, then 2652 encapsulates each message in a SPAN header with source address set to 2653 the SPAN address of X and destination address set to R, then sends 2654 the message into the SPAN. At the same time, if the message was a 2655 Join X initiates NS/NA route optimization the same as for the SSM 2656 case discussed in Section 3.20.1. 2658 For each source S that sends multicast traffic to group G via R, the 2659 Proxy/Server Z* for the Client that aggregates S encapsulates the 2660 packets in PIM Register messages and forwards them to R via the SPAN. 2661 R may then elect to send a PIM Join to Z* over the SPAN. This will 2662 result in an (S,G) tree rooted at Z* with R as the next hop so that R 2663 will begin to receive two copies of the packet; one native copy from 2664 the (S, G) tree and a second copy from the pre-existing (*, G) tree 2665 that still uses PIM Register encapsulation. R can then issue a PIM 2666 Register-stop message to suppress the Register-encapsulated stream. 2667 At some later time, if C moves to a new Proxy/Server Z*, it resumes 2668 sending packets via PIM Register encapsulation via the new Z*. 2670 At the same time, as multicast listeners discover individual S's for 2671 a given G, they can initiate an (S,G) Join for each S under the same 2672 procedures discussed in Section 3.20.1. Once the (S,G) tree is 2673 established, the listeners can send (S, G) Prune messages to R so 2674 that multicast packets for group G sourced by S will only be 2675 delivered via the (S, G) tree and not from the (*, G) tree rooted at 2676 R. All mobility considerations discussed for SSM apply. 2678 3.20.3. Bi-Directional PIM (BIDIR-PIM) 2680 Bi-Directional PIM (BIDIR-PIM) [RFC5015] provides an alternate 2681 approach to ASM that treats the Rendezvous Point (RP) as a Designated 2682 Forwarder (DF). Further considerations for BIDIR-PIM are out of 2683 scope. 2685 3.21. Operation over Multiple AERO Links (VLANs) 2687 An AERO Client can connect to multiple AERO links the same as for any 2688 data link service. In that case, the Client maintains a distinct 2689 AERO interface for each link, e.g., 'aero0' for the first link, 2690 'aero1' for the second, 'aero2' for the third, etc. Each AERO link 2691 would include its own distinct set of Relays, Servers and Proxys, 2692 thereby providing redundancy in case of failures. 2694 The Relays, Servers and Proxys on each AERO link can assign AERO and 2695 SPAN addresses that use the same or different numberings from those 2696 on other links. Since the links are mutually independent there is no 2697 requirement for avoiding inter-link address duplication, e.g., the 2698 same AERO address such as fe80::1000 could be used to number distinct 2699 nodes that connect to different links. 2701 Each AERO link could utilize the same or different ANET connections. 2702 The links can be distinguished at the link-layer via Virtual Local 2703 Area Network (VLAN) tagging (e.g., IEEE 802.1Q) and/or through 2704 assignment of distinct sets of MSPs on each link. This gives rise to 2705 the opportunity for supporting multiple redundant networked paths, 2706 where each VLAN is distinguished by a different label (e.g., colors 2707 such as Red, Green, Blue, etc.). In particular, the Client can tag 2708 its RS messages with the appropriate label to cause the network to 2709 select the desired VLAN. 2711 Clients that connect to multiple AERO interfaces can select the 2712 outgoing interface appropriate for a given Red/Blue/Green/etc. 2713 traffic profile while (in the reverse direction) correspondent nodes 2714 must have some way of steering their packets destined to a target via 2715 the correct AERO link. 2717 In a first alternative, if each AERO link services different MSPs, 2718 then the Client can receive a distinct MNP from each of the links. 2719 IP routing will therefore assure that the correct Red/Green/Blue/etc. 2720 network is used for both outbound and inbound traffic. This can be 2721 accomplished using existing technologies and approaches, and without 2722 requiring any special supporting code in correspondent nodes or 2723 Relays. 2725 In a second alternative, if each AERO link services the same MSP(s) 2726 then each link could assign a distinct "AERO Link Anycast" address 2727 that is configured by all Relays on the link. Correspondent nodes 2728 then include a "type 4" routing header with the Anycast address for 2729 the AERO link as the IPv6 destination and with the address of the 2730 target encoded as the "next segment" in the routing header 2731 [RFC8402][I-D.ietf-6man-segment-routing-header]. Standard IP routing 2732 will then direct the packet to the nearest Relay for the correct AERO 2733 link, which will replace the destination address with the target 2734 address then forward the packet to the target. 2736 3.22. DNS Considerations 2738 AERO Client MNs and INET correspondent nodes consult the Domain Name 2739 System (DNS) the same as for any Internetworking node. When 2740 correspondent nodes and Client MNs use different IP protocol versions 2741 (e.g., IPv4 correspondents and IPv6 MNs), the INET DNS must maintain 2742 A records for IPv4 address mappings to MNs which must then be 2743 populated in Gateway NAT64 mapping caches. In that way, an IPv4 2744 correspondent node can send packets to the IPv4 address mapping of 2745 the target MN, and the Gateway will translate the IPv4 header and 2746 destination address into an IPv6 header and IPv6 destination address 2747 of the MN. 2749 When an AERO Client registers with an AERO Server, the Server returns 2750 the address(es) of DNS servers in RDNSS options [RFC6106]. The DNS 2751 server provides the IP addresses of other MNs and correspondent nodes 2752 in AAAA records for IPv6 or A records for IPv4. 2754 3.23. Transition Considerations 2756 The SPAN ensures that dissimilar INET partitions can be joined into a 2757 single unified AERO link, even though the partitions themselves may 2758 have differing protocol versions and/or incompatible addressing 2759 plans. However, a commonality can be achieved by incrementally 2760 distributing globally routable (i.e., native) IP prefixes to 2761 eventually reach all nodes (both mobile and fixed) in all SPAN 2762 segments. This can be accomplished by incrementally deploying AERO 2763 Gateways on each INET partition, with each Gateway distributing its 2764 MNPs and/or discovering non-MNP prefixes on its INET links. 2766 This gives rise to the opportunity to eventually distribute native IP 2767 addresses to all nodes, and to present a unified AERO link view 2768 (bridged by the SPAN) even if the INET partitions remain in their 2769 current protocol and addressing plans. In that way, the AERO link 2770 can serve the dual purpose of providing a mobility service and a 2771 transition service. Or, if an INET partition is transitioned to a 2772 native IP protocol version and addressing scheme that is compatible 2773 with the AERO link MNP-based addressing scheme, the partition and 2774 AERO link can be joined by Gateways. 2776 Gateways that connect INETs/EUNs with dissimilar IP protocol versions 2777 must employ a network address and protocol translation function such 2778 as NAT64[RFC6146]. 2780 3.24. Detecting and Reacting to Server and Relay Failures 2782 In environments where rapid failure recovery is required, Servers and 2783 Relays SHOULD use Bidirectional Forwarding Detection (BFD) [RFC5880]. 2784 Nodes that use BFD can quickly detect and react to failures so that 2785 cached information is re-established through alternate nodes. BFD 2786 control messaging is carried only over well-connected ground domain 2787 networks (i.e., and not low-end radio links) and can therefore be 2788 tuned for rapid response. 2790 Servers and Relays maintain BFD sessions in parallel with their BGP 2791 peerings. If a Server or Relay fails, BGP peers will quickly re- 2792 establish routes through alternate paths the same as for common BGP 2793 deployments. 2795 Proxys use proactive NUD for Servers for which there are currently 2796 active ANET Clients in a manner that parallels BFD. If a Server 2797 fails, Proxys quickly inform Clients of the outage by sending RA 2798 messages on the ANET interface. 2800 The Proxy sends RA messages with source address set to the Server's 2801 address, destination address set to all-nodes multicast, and Router 2802 Lifetime set to 0. The Proxy SHOULD send 2803 MAX_FINAL_RTR_ADVERTISEMENTS RA messages separated by small delays 2804 [RFC4861]. Any Clients on the ANET interface that have been using 2805 the (now defunct) Server will receive the RA messages and associate 2806 with a new Server. 2808 4. Implementation Status 2810 An AERO implementation based on OpenVPN (https://openvpn.net/) was 2811 announced on the v6ops mailing list on January 10, 2018 and an 2812 initial public release of the AERO proof-of-concept source code was 2813 announced on the intarea mailing list on August 21, 2015. The latest 2814 versions are available at: http://linkupnetworks.net/aero. 2816 5. IANA Considerations 2818 The IANA has assigned a 4-octet Private Enterprise Number "45282" for 2819 AERO in the "enterprise-numbers" registry. 2821 The IANA has assigned the UDP port number "8060" for an earlier 2822 experimental version of AERO [RFC6706]. This document obsoletes 2823 [RFC6706] and claims the UDP port number "8060" for all future use. 2825 No further IANA actions are required. 2827 6. Security Considerations 2829 AERO Relays configure secured tunnels with AERO Servers and Proxys 2830 within their local SPAN segments. Applicable secured tunnel 2831 alternatives include IPsec [RFC4301], TLS/SSL [RFC8446], DTLS 2832 [RFC6347], etc. The AERO Relays of all SPAN segments in turn 2833 configure secured tunnels for their neighboring AERO Relays across 2834 the SPAN. Therefore, packets that traverse the SPAN between any pair 2835 of AERO link neighbors are already secured. 2837 AERO Servers, Gateways and Proxys targeted by a route optimization 2838 may also receive packets directly from the INET partitions instead of 2839 via the SPAN. For INET partitions that apply effective ingress 2840 filtering to defeat source address spoofing, the simple data origin 2841 authentication procedures in Section 3.11 can be applied. This 2842 implies that the ROS list must be maintained consistently by all 2843 route optimization targets within the same INET partition, and that 2844 the ROS list must be securely managed by the partition's 2845 administrative authority. 2847 For INET partitions that cannot apply effective ingress filtering, 2848 the two options for securing communications include 1) disable route 2849 optimization so that all traffic is conveyed over secured tunnels via 2850 the SPAN, or 2) enable on-demand secure tunnel creation between INET 2851 partition neighbors. Option 1) would result in longer routes than 2852 necessary and traffic concentration on critical infrastructure 2853 elements. Option 2) could be coordinated by establishing a secured 2854 tunnel on-demand instead of performing an NS/NA exchange in the route 2855 optimization procedures. Procedures for establishing on-demand 2856 secured tunnels are out of scope. 2858 AERO Clients that connect to secured enclaves need not apply security 2859 to their ND messages, since the messages will be intercepted by a 2860 perimeter Proxy that applies security on its outward-facing 2861 interface. AERO Clients located outside of secured enclaves SHOULD 2862 use symmetric network and/or transport layer security services, but 2863 when there are many prospective neighbors with dynamically changing 2864 connectivity an asymmetric security service such as SEND may be 2865 needed (see: Appendix C.6). 2867 Application endpoints SHOULD use application-layer security services 2868 such as TLS/SSL, DTLS or SSH [RFC4251] to assure the same level of 2869 protection as for critical secured Internet services. AERO Clients 2870 that require host-based VPN services SHOULD use symmetric network 2871 and/or transport layer security services such as IPsec, TLS/SSL, 2872 DTLS, etc. AERO Proxys and Servers can also provide a network-based 2873 VPN service on behalf of the Client, e.g., if the Client is located 2874 within a secured enclave and cannot establish a VPN on its own 2875 behalf. 2877 AERO Servers and Relays present targets for traffic amplification 2878 Denial of Service (DoS) attacks. This concern is no different than 2879 for widely-deployed VPN security gateways in the Internet, where 2880 attackers could send spoofed packets to the gateways at high data 2881 rates. This can be mitigated by connecting Servers and Relays over 2882 dedicated links with no connections to the Internet and/or when 2883 connections to the Internet are only permitted through well-managed 2884 firewalls. Traffic amplification DoS attacks can also target an AERO 2885 Client's low data rate links. This is a concern not only for Clients 2886 located on the open Internet but also for Clients in secured 2887 enclaves. AERO Servers and Proxys can institute rate limits that 2888 protect Clients from receiving packet floods that could DoS low data 2889 rate links. 2891 AERO Gateways must implement ingress filtering to avoid a spoofing 2892 attack in which spurious SPAN messages are injected into an AERO link 2893 from an outside attacker. AERO Clients MUST ensure that their 2894 connectivity is not used by unauthorized nodes on their EUNs to gain 2895 access to a protected network, i.e., AERO Clients that act as routers 2896 MUST NOT provide routing services for unauthorized nodes. (This 2897 concern is no different than for ordinary hosts that receive an IP 2898 address delegation but then "share" the address with other nodes via 2899 some form of Internet connection sharing such as tethering.) 2901 The MAP list and ROS lists MUST be well-managed and secured from 2902 unauthorized tampering, even though the list contains only public 2903 information. The MAP list can be conveyed to the Client in a similar 2904 fashion as in [RFC5214] (e.g., through layer 2 data link login 2905 messaging, secure upload of a static file, DNS lookups, etc.). The 2906 ROS list can be conveyed to Servers and Proxys through administrative 2907 action, secured file distribution, etc. 2909 Although public domain and commercial SEND implementations exist, 2910 concerns regarding the strength of the cryptographic hash algorithm 2911 have been documented [RFC6273] [RFC4982]. 2913 Security considerations for accepting link-layer ICMP messages and 2914 reflected packets are discussed throughout the document. 2916 7. Acknowledgements 2918 Discussions in the IETF, aviation standards communities and private 2919 exchanges helped shape some of the concepts in this work. 2920 Individuals who contributed insights include Mikael Abrahamsson, Mark 2921 Andrews, Fred Baker, Bob Braden, Stewart Bryant, Brian Carpenter, 2922 Wojciech Dec, Ralph Droms, Adrian Farrel, Nick Green, Sri Gundavelli, 2923 Brian Haberman, Bernhard Haindl, Joel Halpern, Tom Herbert, Sascha 2924 Hlusiak, Lee Howard, Andre Kostur, Hubert Kuenig, Ted Lemon, Andy 2925 Malis, Satoru Matsushima, Tomek Mrugalski, Madhu Niraula, Alexandru 2926 Petrescu, Behcet Saikaya, Michal Skorepa, Joe Touch, Bernie Volz, 2927 Ryuji Wakikawa, Tony Whyman, Lloyd Wood and James Woodyatt. Members 2928 of the IESG also provided valuable input during their review process 2929 that greatly improved the document. Special thanks go to Stewart 2930 Bryant, Joel Halpern and Brian Haberman for their shepherding 2931 guidance during the publication of the AERO first edition. 2933 This work has further been encouraged and supported by Boeing 2934 colleagues including Kyle Bae, M. Wayne Benson, Dave Bernhardt, Cam 2935 Brodie, Balaguruna Chidambaram, Irene Chin, Bruce Cornish, Claudiu 2936 Danilov, Don Dillenburg, Joe Dudkowski, Wen Fang, Anthony Gregory, 2937 Jeff Holland, Seth Jahne, Ed King, Laurel Matthew, Gene MacLean III, 2938 Rob Muszkiewicz, Sean O'Sullivan, Greg Saccone, Kent Shuey, Brian 2939 Skeen, Mike Slane, Carrie Spiker, Katie Tran, Brendan Williams, Julie 2940 Wulff, Yueli Yang, Eric Yeh and other members of the BR&T and BIT 2941 mobile networking teams. Kyle Bae, Wayne Benson, Katie Tran and Eric 2942 Yeh are especially acknowledged for implementing the AERO functions 2943 as extensions to the public domain OpenVPN distribution. 2945 Earlier works on NBMA tunneling approaches are found in 2946 [RFC2529][RFC5214][RFC5569]. 2948 Many of the constructs presented in this second edition of AERO are 2949 based on the author's earlier works, including: 2951 o The Internet Routing Overlay Network (IRON) 2952 [RFC6179][I-D.templin-ironbis] 2954 o Virtual Enterprise Traversal (VET) 2955 [RFC5558][I-D.templin-intarea-vet] 2957 o The Subnetwork Encapsulation and Adaptation Layer (SEAL) 2958 [RFC5320][I-D.templin-intarea-seal] 2960 o AERO, First Edition [RFC6706] 2962 Note that these works cite numerous earlier efforts that are not also 2963 cited here due to space limitations. The authors of those earlier 2964 works are acknowledged for their insights. 2966 This work is aligned with the NASA Safe Autonomous Systems Operation 2967 (SASO) program under NASA contract number NNA16BD84C. 2969 This work is aligned with the FAA as per the SE2025 contract number 2970 DTFAWA-15-D-00030. 2972 This work is aligned with the Boeing Commercial Airplanes (BCA) 2973 Internet of Things (IoT) and autonomy programs. 2975 This work is aligned with the Boeing Information Technology (BIT) 2976 MobileNet program. 2978 8. References 2980 8.1. Normative References 2982 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, 2983 DOI 10.17487/RFC0791, September 1981, 2984 . 2986 [RFC0792] Postel, J., "Internet Control Message Protocol", STD 5, 2987 RFC 792, DOI 10.17487/RFC0792, September 1981, 2988 . 2990 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 2991 Requirement Levels", BCP 14, RFC 2119, 2992 DOI 10.17487/RFC2119, March 1997, 2993 . 2995 [RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in 2996 IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473, 2997 December 1998, . 2999 [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black, 3000 "Definition of the Differentiated Services Field (DS 3001 Field) in the IPv4 and IPv6 Headers", RFC 2474, 3002 DOI 10.17487/RFC2474, December 1998, 3003 . 3005 [RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander, 3006 "SEcure Neighbor Discovery (SEND)", RFC 3971, 3007 DOI 10.17487/RFC3971, March 2005, 3008 . 3010 [RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)", 3011 RFC 3972, DOI 10.17487/RFC3972, March 2005, 3012 . 3014 [RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and 3015 More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191, 3016 November 2005, . 3018 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 3019 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 3020 DOI 10.17487/RFC4861, September 2007, 3021 . 3023 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 3024 Address Autoconfiguration", RFC 4862, 3025 DOI 10.17487/RFC4862, September 2007, 3026 . 3028 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 3029 (IPv6) Specification", STD 86, RFC 8200, 3030 DOI 10.17487/RFC8200, July 2017, 3031 . 3033 [RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A., 3034 Richardson, M., Jiang, S., Lemon, T., and T. Winters, 3035 "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", 3036 RFC 8415, DOI 10.17487/RFC8415, November 2018, 3037 . 3039 8.2. Informative References 3041 [BGP] Huston, G., "BGP in 2015, http://potaroo.net", January 3042 2016. 3044 [I-D.ietf-6man-segment-routing-header] 3045 Filsfils, C., Dukes, D., Previdi, S., Leddy, J., 3046 Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header 3047 (SRH)", draft-ietf-6man-segment-routing-header-26 (work in 3048 progress), October 2019. 3050 [I-D.ietf-dmm-distributed-mobility-anchoring] 3051 Chan, A., Wei, X., Lee, J., Jeon, S., and C. Bernardos, 3052 "Distributed Mobility Anchoring", draft-ietf-dmm- 3053 distributed-mobility-anchoring-14 (work in progress), 3054 November 2019. 3056 [I-D.ietf-intarea-gue] 3057 Herbert, T., Yong, L., and O. Zia, "Generic UDP 3058 Encapsulation", draft-ietf-intarea-gue-09 (work in 3059 progress), October 2019. 3061 [I-D.ietf-intarea-gue-extensions] 3062 Herbert, T., Yong, L., and F. Templin, "Extensions for 3063 Generic UDP Encapsulation", draft-ietf-intarea-gue- 3064 extensions-06 (work in progress), March 2019. 3066 [I-D.ietf-intarea-tunnels] 3067 Touch, J. and M. Townsley, "IP Tunnels in the Internet 3068 Architecture", draft-ietf-intarea-tunnels-10 (work in 3069 progress), September 2019. 3071 [I-D.ietf-rtgwg-atn-bgp] 3072 Templin, F., Saccone, G., Dawra, G., Lindem, A., and V. 3073 Moreno, "A Simple BGP-based Mobile Routing System for the 3074 Aeronautical Telecommunications Network", draft-ietf- 3075 rtgwg-atn-bgp-05 (work in progress), January 2020. 3077 [I-D.templin-6man-dhcpv6-ndopt] 3078 Templin, F., "A Unified Stateful/Stateless Configuration 3079 Service for IPv6", draft-templin-6man-dhcpv6-ndopt-09 3080 (work in progress), January 2020. 3082 [I-D.templin-atn-aero-interface] 3083 Templin, F. and T. Whyman, "Transmission of IPv6 Packets 3084 over Aeronautical ("aero") Interfaces", draft-templin-atn- 3085 aero-interface-09 (work in progress), January 2020. 3087 [I-D.templin-intarea-grefrag] 3088 Templin, F., "GRE Tunnel Level Fragmentation", draft- 3089 templin-intarea-grefrag-04 (work in progress), July 2016. 3091 [I-D.templin-intarea-seal] 3092 Templin, F., "The Subnetwork Encapsulation and Adaptation 3093 Layer (SEAL)", draft-templin-intarea-seal-68 (work in 3094 progress), January 2014. 3096 [I-D.templin-intarea-vet] 3097 Templin, F., "Virtual Enterprise Traversal (VET)", draft- 3098 templin-intarea-vet-40 (work in progress), May 2013. 3100 [I-D.templin-ironbis] 3101 Templin, F., "The Interior Routing Overlay Network 3102 (IRON)", draft-templin-ironbis-16 (work in progress), 3103 March 2014. 3105 [I-D.templin-v6ops-pdhost] 3106 Templin, F., "IPv6 Prefix Delegation and Multi-Addressing 3107 Models", draft-templin-v6ops-pdhost-25 (work in progress), 3108 January 2020. 3110 [OVPN] OpenVPN, O., "http://openvpn.net", October 2016. 3112 [RFC1035] Mockapetris, P., "Domain names - implementation and 3113 specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, 3114 November 1987, . 3116 [RFC1122] Braden, R., Ed., "Requirements for Internet Hosts - 3117 Communication Layers", STD 3, RFC 1122, 3118 DOI 10.17487/RFC1122, October 1989, 3119 . 3121 [RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191, 3122 DOI 10.17487/RFC1191, November 1990, 3123 . 3125 [RFC1812] Baker, F., Ed., "Requirements for IP Version 4 Routers", 3126 RFC 1812, DOI 10.17487/RFC1812, June 1995, 3127 . 3129 [RFC2003] Perkins, C., "IP Encapsulation within IP", RFC 2003, 3130 DOI 10.17487/RFC2003, October 1996, 3131 . 3133 [RFC2236] Fenner, W., "Internet Group Management Protocol, Version 3134 2", RFC 2236, DOI 10.17487/RFC2236, November 1997, 3135 . 3137 [RFC2529] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4 3138 Domains without Explicit Tunnels", RFC 2529, 3139 DOI 10.17487/RFC2529, March 1999, 3140 . 3142 [RFC2764] Gleeson, B., Lin, A., Heinanen, J., Armitage, G., and A. 3143 Malis, "A Framework for IP Based Virtual Private 3144 Networks", RFC 2764, DOI 10.17487/RFC2764, February 2000, 3145 . 3147 [RFC2784] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P. 3148 Traina, "Generic Routing Encapsulation (GRE)", RFC 2784, 3149 DOI 10.17487/RFC2784, March 2000, 3150 . 3152 [RFC2890] Dommety, G., "Key and Sequence Number Extensions to GRE", 3153 RFC 2890, DOI 10.17487/RFC2890, September 2000, 3154 . 3156 [RFC2923] Lahey, K., "TCP Problems with Path MTU Discovery", 3157 RFC 2923, DOI 10.17487/RFC2923, September 2000, 3158 . 3160 [RFC2983] Black, D., "Differentiated Services and Tunnels", 3161 RFC 2983, DOI 10.17487/RFC2983, October 2000, 3162 . 3164 [RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition 3165 of Explicit Congestion Notification (ECN) to IP", 3166 RFC 3168, DOI 10.17487/RFC3168, September 2001, 3167 . 3169 [RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener 3170 Discovery Version 2 (MLDv2) for IPv6", RFC 3810, 3171 DOI 10.17487/RFC3810, June 2004, 3172 . 3174 [RFC3819] Karn, P., Ed., Bormann, C., Fairhurst, G., Grossman, D., 3175 Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J., and L. 3176 Wood, "Advice for Internet Subnetwork Designers", BCP 89, 3177 RFC 3819, DOI 10.17487/RFC3819, July 2004, 3178 . 3180 [RFC4213] Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms 3181 for IPv6 Hosts and Routers", RFC 4213, 3182 DOI 10.17487/RFC4213, October 2005, 3183 . 3185 [RFC4251] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH) 3186 Protocol Architecture", RFC 4251, DOI 10.17487/RFC4251, 3187 January 2006, . 3189 [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A 3190 Border Gateway Protocol 4 (BGP-4)", RFC 4271, 3191 DOI 10.17487/RFC4271, January 2006, 3192 . 3194 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 3195 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 3196 2006, . 3198 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 3199 Internet Protocol", RFC 4301, DOI 10.17487/RFC4301, 3200 December 2005, . 3202 [RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery 3203 Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April 3204 2006, . 3206 [RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet 3207 Control Message Protocol (ICMPv6) for the Internet 3208 Protocol Version 6 (IPv6) Specification", STD 89, 3209 RFC 4443, DOI 10.17487/RFC4443, March 2006, 3210 . 3212 [RFC4511] Sermersheim, J., Ed., "Lightweight Directory Access 3213 Protocol (LDAP): The Protocol", RFC 4511, 3214 DOI 10.17487/RFC4511, June 2006, 3215 . 3217 [RFC4541] Christensen, M., Kimball, K., and F. Solensky, 3218 "Considerations for Internet Group Management Protocol 3219 (IGMP) and Multicast Listener Discovery (MLD) Snooping 3220 Switches", RFC 4541, DOI 10.17487/RFC4541, May 2006, 3221 . 3223 [RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick, 3224 "Internet Group Management Protocol (IGMP) / Multicast 3225 Listener Discovery (MLD)-Based Multicast Forwarding 3226 ("IGMP/MLD Proxying")", RFC 4605, DOI 10.17487/RFC4605, 3227 August 2006, . 3229 [RFC4607] Holbrook, H. and B. Cain, "Source-Specific Multicast for 3230 IP", RFC 4607, DOI 10.17487/RFC4607, August 2006, 3231 . 3233 [RFC4963] Heffner, J., Mathis, M., and B. Chandler, "IPv4 Reassembly 3234 Errors at High Data Rates", RFC 4963, 3235 DOI 10.17487/RFC4963, July 2007, 3236 . 3238 [RFC4982] Bagnulo, M. and J. Arkko, "Support for Multiple Hash 3239 Algorithms in Cryptographically Generated Addresses 3240 (CGAs)", RFC 4982, DOI 10.17487/RFC4982, July 2007, 3241 . 3243 [RFC5015] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano, 3244 "Bidirectional Protocol Independent Multicast (BIDIR- 3245 PIM)", RFC 5015, DOI 10.17487/RFC5015, October 2007, 3246 . 3248 [RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site 3249 Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214, 3250 DOI 10.17487/RFC5214, March 2008, 3251 . 3253 [RFC5320] Templin, F., Ed., "The Subnetwork Encapsulation and 3254 Adaptation Layer (SEAL)", RFC 5320, DOI 10.17487/RFC5320, 3255 February 2010, . 3257 [RFC5522] Eddy, W., Ivancic, W., and T. Davis, "Network Mobility 3258 Route Optimization Requirements for Operational Use in 3259 Aeronautics and Space Exploration Mobile Networks", 3260 RFC 5522, DOI 10.17487/RFC5522, October 2009, 3261 . 3263 [RFC5558] Templin, F., Ed., "Virtual Enterprise Traversal (VET)", 3264 RFC 5558, DOI 10.17487/RFC5558, February 2010, 3265 . 3267 [RFC5569] Despres, R., "IPv6 Rapid Deployment on IPv4 3268 Infrastructures (6rd)", RFC 5569, DOI 10.17487/RFC5569, 3269 January 2010, . 3271 [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 3272 (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, 3273 . 3275 [RFC6106] Jeong, J., Park, S., Beloeil, L., and S. Madanapalli, 3276 "IPv6 Router Advertisement Options for DNS Configuration", 3277 RFC 6106, DOI 10.17487/RFC6106, November 2010, 3278 . 3280 [RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful 3281 NAT64: Network Address and Protocol Translation from IPv6 3282 Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146, 3283 April 2011, . 3285 [RFC6179] Templin, F., Ed., "The Internet Routing Overlay Network 3286 (IRON)", RFC 6179, DOI 10.17487/RFC6179, March 2011, 3287 . 3289 [RFC6221] Miles, D., Ed., Ooghe, S., Dec, W., Krishnan, S., and A. 3290 Kavanagh, "Lightweight DHCPv6 Relay Agent", RFC 6221, 3291 DOI 10.17487/RFC6221, May 2011, 3292 . 3294 [RFC6273] Kukec, A., Krishnan, S., and S. Jiang, "The Secure 3295 Neighbor Discovery (SEND) Hash Threat Analysis", RFC 6273, 3296 DOI 10.17487/RFC6273, June 2011, 3297 . 3299 [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer 3300 Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, 3301 January 2012, . 3303 [RFC6438] Carpenter, B. and S. Amante, "Using the IPv6 Flow Label 3304 for Equal Cost Multipath Routing and Link Aggregation in 3305 Tunnels", RFC 6438, DOI 10.17487/RFC6438, November 2011, 3306 . 3308 [RFC6706] Templin, F., Ed., "Asymmetric Extended Route Optimization 3309 (AERO)", RFC 6706, DOI 10.17487/RFC6706, August 2012, 3310 . 3312 [RFC6864] Touch, J., "Updated Specification of the IPv4 ID Field", 3313 RFC 6864, DOI 10.17487/RFC6864, February 2013, 3314 . 3316 [RFC7269] Chen, G., Cao, Z., Xie, C., and D. Binet, "NAT64 3317 Deployment Options and Experience", RFC 7269, 3318 DOI 10.17487/RFC7269, June 2014, 3319 . 3321 [RFC7333] Chan, H., Ed., Liu, D., Seite, P., Yokota, H., and J. 3322 Korhonen, "Requirements for Distributed Mobility 3323 Management", RFC 7333, DOI 10.17487/RFC7333, August 2014, 3324 . 3326 [RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I., 3327 Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent 3328 Multicast - Sparse Mode (PIM-SM): Protocol Specification 3329 (Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March 3330 2016, . 3332 [RFC8086] Yong, L., Ed., Crabbe, E., Xu, X., and T. Herbert, "GRE- 3333 in-UDP Encapsulation", RFC 8086, DOI 10.17487/RFC8086, 3334 March 2017, . 3336 [RFC8201] McCann, J., Deering, S., Mogul, J., and R. Hinden, Ed., 3337 "Path MTU Discovery for IP version 6", STD 87, RFC 8201, 3338 DOI 10.17487/RFC8201, July 2017, 3339 . 3341 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 3342 Decraene, B., Litkowski, S., and R. Shakir, "Segment 3343 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 3344 July 2018, . 3346 [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol 3347 Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, 3348 . 3350 Appendix A. P[i] Preference Value Extensions in S/TLLAOs 3352 The AERO S/TLLAO format specified in Section 3.6 includes up to 64 3353 P[i] values which represent preferences for the 64 DSCP values. 3354 However, some AERO link types may require additional preference 3355 fields for "pseudo-DSCP" values P4, P65, P66, etc. 3357 For example, adaptation of AERO to the Aeronautical 3358 Telecommunications Network with Internet Protocol Services (ATN/IPS) 3359 includes link selection preferences based on transport port numbers 3360 in addition to the existing DSCP-based preferences. ATN/IPS nodes 3361 maintain a map of transport port numbers to additional P[i] 3362 preference fields, e.g., TCP port 22 maps to preference field P68, 3363 TCP port 443 maps to preference field P73, UDP port 8060 maps to 3364 preference field P89, etc. 3366 Figure 6 shows a format where two additional 4-byte blocks of P[i] 3367 preferences (i.e., P64 - P95) are included by setting the QoS field 3368 value to 6. 3370 0 1 2 3 3371 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 3372 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3373 | Type | Length | Prefix Length |R|X|N| Reserved| 3374 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3375 | ifIndex | ifType | Flags | Link | QoS=6 | 3376 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3377 |P00|P01|P02|P03|P04|P05|P06|P07|P08|P09|P10|P11|P12|P13|P14|P15| 3378 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3379 |P16|P17|P18|P19|P20|P21|P22|P23|P24|P25|P26|P27|P28|P29|P30|P31| 3380 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3381 |P32|P33|P34|P35|P36|P37|P38|P39|P40|P41|P42|P43|P44|P45|P46|P47| 3382 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3383 |P48|P49|P50|P51|P52|P53|P54|P55|P56|P57|P58|P59|P60|P61|P62|P63| 3384 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3385 |P64|P65|P66|P67|P68|P69|P70|P71|P72|P73|P74|P75|P76|P77|P78|P79| 3386 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3387 |P80|P81|P82|P83|P84|P85|P86|P87|P88|P89|P90|P91|P92|P93|P94|P95| 3388 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3389 | | 3390 + + 3391 | | 3392 + Link-Layer Address + 3393 | | 3394 + + 3395 | | 3396 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3397 | Port Number | ... 3398 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3400 Figure 6: P[i]-Extended S/TLLAO Format 3402 Appendix B. AERO Alternate Encapsulations 3404 When GUE encapsulation is not needed, AERO can use common 3405 encapsulations such as IP-in-IP [RFC2003][RFC2473][RFC4213], Generic 3406 Routing Encapsulation (GRE) [RFC2784][RFC2890] and others. The 3407 encapsulation is therefore only differentiated from non-AERO tunnels 3408 through the application of AERO control messaging and not through, 3409 e.g., a well-known UDP port number. 3411 As for GUE encapsulation, alternate AERO encapsulation formats may 3412 require encapsulation layer fragmentation. For simple IP-in-IP 3413 encapsulation, an IPv6 fragment header is inserted directly between 3414 the inner and outer IP headers when needed, i.e., even if the outer 3415 header is IPv4. The IPv6 Fragment Header is identified to the outer 3416 IP layer by its IP protocol number, and the Next Header field in the 3417 IPv6 Fragment Header identifies the inner IP header version. For GRE 3418 encapsulation, a GRE fragment header is inserted within the GRE 3419 header [I-D.templin-intarea-grefrag]. 3421 Figure 7 shows the AERO IP-in-IP encapsulation format before any 3422 fragmentation is applied: 3424 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3425 | Outer IPv4 Header | | Outer IPv6 Header | 3426 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3427 |IPv6 Frag Header (optional)| |IPv6 Frag Header (optional)| 3428 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3429 | Inner IP Header | | Inner IP Header | 3430 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3431 | | | | 3432 ~ ~ ~ ~ 3433 ~ Inner Packet Body ~ ~ Inner Packet Body ~ 3434 ~ ~ ~ ~ 3435 | | | | 3436 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3438 Minimal Encapsulation in IPv4 Minimal Encapsulation in IPv6 3440 Figure 7: Minimal Encapsulation Format using IP-in-IP 3442 Figure 8 shows the AERO GRE encapsulation format before any 3443 fragmentation is applied: 3445 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3446 | Outer IP Header | 3447 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3448 | GRE Header | 3449 | (with checksum, key, etc..) | 3450 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3451 | GRE Fragment Header (optional)| 3452 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3453 | Inner IP Header | 3454 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3455 | | 3456 ~ ~ 3457 ~ Inner Packet Body ~ 3458 ~ ~ 3459 | | 3460 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3462 Figure 8: Minimal Encapsulation Using GRE 3464 Alternate encapsulation may be preferred in environments where GUE 3465 encapsulation would add unnecessary overhead. For example, certain 3466 low-bandwidth wireless data links may benefit from a reduced 3467 encapsulation overhead. 3469 GUE encapsulation can traverse network paths that are inaccessible to 3470 non-UDP encapsulations, e.g., for crossing Network Address 3471 Translators (NATs). More and more, network middleboxes are also 3472 being configured to discard packets that include anything other than 3473 a well-known IP protocol such as UDP and TCP. It may therefore be 3474 necessary to determine the potential for middlebox filtering before 3475 enabling alternate encapsulation in a given environment. 3477 In addition to IP-in-IP, GRE and GUE, AERO can also use security 3478 encapsulations such as IPsec, TLS/SSL, DTLS, etc. In that case, AERO 3479 control messaging and route determination occur before security 3480 encapsulation is applied for outgoing packets and after security 3481 decapsulation is applied for incoming packets. 3483 AERO is especially well suited for use with VPN system encapsulations 3484 such as OpenVPN [OVPN]. 3486 Appendix C. Non-Normative Considerations 3488 AERO can be applied to a multitude of Internetworking scenarios, with 3489 each having its own adaptations. The following considerations are 3490 provided as non-normative guidance: 3492 C.1. Implementation Strategies for Route Optimization 3494 Route optimization as discussed in Section 3.17 results in the route 3495 optimization source (ROS) creating an asymmetric neighbor cache entry 3496 for the target neighbor. The neighbor cache entry is maintained for 3497 at most REACHABLETIME seconds and then deleted unless updated. In 3498 order to refresh the neighbor cache entry lifetime before the 3499 ReachableTime timer expires, the specification requires 3500 implementations to issue a new NS/NA exchange to reset ReachableTime 3501 to REACHABLETIME seconds while data packets are still flowing. 3502 However, the decision of when to initiate a new NS/NA exchange and to 3503 perpetuate the process is left as an implementation detail. 3505 One possible strategy may be to monitor the neighbor cache entry 3506 watching for data packets for (REACHABLETIME - 5) seconds. If any 3507 data packets have been sent to the neighbor within this timeframe, 3508 then send an NS to receive a new NA. If no data packets have been 3509 sent, wait for 5 additional seconds and send an immediate NS if any 3510 data packets are sent within this "expiration pending" 5 second 3511 window. If no additional data packets are sent within the 5 second 3512 window, delete the neighbor cache entry. 3514 The monitoring of the neighbor data packet traffic therefore becomes 3515 an asymmetric ongoing process during the neighbor cache entry 3516 lifetime. If the neighbor cache entry expires, future data packets 3517 will trigger a new NS/NA exchange while the packets themselves are 3518 delivered over a longer path until route optimization state is re- 3519 established. 3521 C.2. Implicit Mobility Management 3523 AERO interface neighbors MAY provide a configuration option that 3524 allows them to perform implicit mobility management in which no ND 3525 messaging is used. In that case, the Client only transmits packets 3526 over a single interface at a time, and the neighbor always observes 3527 packets arriving from the Client from the same link-layer source 3528 address. 3530 If the Client's underlying interface address changes (either due to a 3531 readdressing of the original interface or switching to a new 3532 interface) the neighbor immediately updates the neighbor cache entry 3533 for the Client and begins accepting and sending packets according to 3534 the Client's new address. This implicit mobility method applies to 3535 use cases such as cellphones with both WiFi and Cellular interfaces 3536 where only one of the interfaces is active at a given time, and the 3537 Client automatically switches over to the backup interface if the 3538 primary interface fails. 3540 C.3. Direct Underlying Interfaces 3542 When a Client's AERO interface is configured over a Direct interface, 3543 the neighbor at the other end of the Direct link can receive packets 3544 without any encapsulation. In that case, the Client sends packets 3545 over the Direct link according to QoS preferences. If the Direct 3546 interface has the highest QoS preference, then the Client's IP 3547 packets are transmitted directly to the peer without going through an 3548 ANET/INET. If other interfaces have higher QoS preferences, then the 3549 Client's IP packets are transmitted via a different interface, which 3550 may result in the inclusion of Proxys, Servers and Relays in the 3551 communications path. Direct interfaces must be tested periodically 3552 for reachability, e.g., via NUD. 3554 C.4. AERO Clients on the Open Internetwork 3556 AERO Clients that connect to the open Internetwork via either a 3557 native or NATed interface can establish a VPN to securely connect to 3558 a Server. Alternatively, the Client can exchange ND messages 3559 directly with other AERO nodes on the same SPAN segment using INET 3560 encapsulation only and without joining the SPAN. In that case, 3561 however, the Client must apply asymmetric security for ND messages to 3562 ensure routing and neighbor cache integrity (see: Section 6). 3564 C.5. Operation on AERO Links with /64 ASPs 3566 IPv6 AERO links typically have MSPs that aggregate many candidate 3567 MNPs of length /64 or shorter. However, in some cases it may be 3568 desirable to use AERO over links that have only a /64 MSP. This can 3569 be accommodated by treating all Clients on the AERO link as simple 3570 hosts that receive /128 prefix delegations. 3572 In that case, the Client sends an RS message to the Server the same 3573 as for ordinary AERO links. The Server responds with an RA message 3574 that includes one or more /128 prefixes (i.e., singleton addresses) 3575 that include the /64 MSP prefix along with an interface identifier 3576 portion to be assigned to the Client. The Client and Server then 3577 configure their AERO addresses based on the interface identifier 3578 portions of the /128s (i.e., the lower 64 bits) and not based on the 3579 /64 prefix (i.e., the upper 64 bits). 3581 For example, if the MSP for the host-only IPv6 AERO link is 3582 2001:db8:1000:2000::/64, each Client will receive one or more /128 3583 IPv6 prefix delegations such as 2001:db8:1000:2000::1/128, 3584 2001:db8:1000:2000::2/128, etc. When the Client receives the prefix 3585 delegations, it assigns the AERO addresses fe80::1, fe80::2, etc. to 3586 the AERO interface, and assigns the global IPv6 addresses (i.e., the 3587 /128s) to either the AERO interface or an internal virtual interface 3588 such as a loopback. In this arrangement, the Client conducts route 3589 optimization in the same sense as discussed in Section 3.17. 3591 This specification has applicability for nodes that act as a Client 3592 on an "upstream" AERO link, but also act as a Server on "downstream" 3593 AERO links. More specifically, if the node acts as a Client to 3594 receive a /64 prefix from the upstream AERO link it can then act as a 3595 Server to provision /128s to Clients on downstream AERO links. 3597 C.6. AERO Adaptations for SEcure Neighbor Discovery (SEND) 3599 SEcure Neighbor Discovery (SEND) [RFC3971] and Cryptographically 3600 Generated Addresses (CGAs) [RFC3972] were designed to secure IPv6 ND 3601 messaging in environments where symmetric network and/or transport- 3602 layer security services are impractical (see: Section 6). AERO nodes 3603 that use SEND/CGA employ the following adaptations. 3605 When a source AERO node prepares a SEND-protected ND message, it uses 3606 a link-local CGA as the IPv6 source address and writes the prefix 3607 embedded in its AERO address (i.e., instead of fe80::/64) in the CGA 3608 parameters Subnet Prefix field. When the neighbor receives the ND 3609 message, it first verifies the message checksum and SEND/CGA 3610 parameters while using the link-local prefix fe80::/64 (i.e., instead 3611 of the value in the Subnet Prefix field) to match against the IPv6 3612 source address of the ND message. 3614 The neighbor then derives the AERO address of the source by using the 3615 value in the Subnet Prefix field as the interface identifier of an 3616 AERO address. For example, if the Subnet Prefix field contains 3617 2001:db8:1:2, the neighbor constructs the AERO address as 3618 fe80::2001:db8:1:2. The neighbor then caches the AERO address in the 3619 neighbor cache entry it creates for the source, and uses the AERO 3620 address as the IPv6 destination address of any ND message replies. 3622 C.7. AERO Critical Infrastructure Considerations 3624 AERO Relays can be either Commercial off-the Shelf (COTS) standard IP 3625 routers or virtual machines in the cloud. Relays must be 3626 provisioned, supported and managed by the INET administrative 3627 authority, and connected to the Relays of other INETs via inter- 3628 domain peerings. Cost for purchasing, configuring and managing 3629 Relays is nominal even for very large AERO links. 3631 AERO Servers can be standard dedicated server platforms, but most 3632 often will be deployed as virtual machines in the cloud. The only 3633 requirements for Servers are that they can run the AERO user-level 3634 code and have at least one network interface connection to the INET. 3635 As with Relays, Servers must be provisioned, supported and managed by 3636 the INET administrative authority. Cost for purchasing, configuring 3637 and managing Servers is nominal especially for virtual Servers hosted 3638 in the cloud. 3640 AERO Proxys are most often standard dedicated server platforms with 3641 one network interface connected to the ANET and a second interface 3642 connected to an INET. As with Servers, the only requirements are 3643 that they can run the AERO user-level code and have at least one 3644 interface connection to the INET. Proxys must be provisioned, 3645 supported and managed by the ANET administrative authority. Cost for 3646 purchasing, configuring and managing Proxys is nominal, and borne by 3647 the ANET administrative authority. 3649 AERO Gateways can be any dedicated server or COTS router platform 3650 connected to INETs and/or EUNs. The Gateway joins the SPAN and 3651 engages in eBGP peering with one or more Relays as a stub AS. The 3652 Gateway then injects its MNPs and/or non-MNP prefixes into the BGP 3653 routing system, and provisions the prefixes to its downstream- 3654 attached networks. The Gateway can perform ROS and MAP services the 3655 same as for any Server, and can route between the MNP and non-MNP 3656 address spaces. 3658 C.8. AERO Server Failure Implications 3660 AERO Servers may appear as a single point of failure in the 3661 architecture, but such is not the case since all Servers on the link 3662 provide identical services and loss of a Server does not imply 3663 immediate and/or comprehensive communication failures. Although 3664 Clients typically associate with a single Server at a time, Server 3665 failure is quickly detected and conveyed by Bidirectional Forward 3666 Detection (BFD) and/or proactive NUD allowing Clients to migrate to 3667 new Servers. 3669 If a Server fails, ongoing packet forwarding to Clients will continue 3670 by virtue of the asymmetric neighbor cache entries that have already 3671 been established in route optimization sources (ROSs). If a Client 3672 also experiences mobility events at roughly the same time the Server 3673 fails, unsolicited NA messages may be lost but proxy neighbor cache 3674 entries in the DEPARTED state will ensure that packet forwarding to 3675 the Client's new locations will continue for up to DEPARTTIME 3676 seconds. 3678 If a Client is left without a Server for an extended timeframe (e.g., 3679 greater than REACHABLETIIME seconds) then existing asymmetric 3680 neighbor cache entries will eventually expire and both ongoing and 3681 new communications will fail. The original source will continue to 3682 retransmit until the Client has established a new Server 3683 relationship, after which time continuous communications will resume. 3685 Therefore, providing many Servers on the link with high availability 3686 profiles provides resilience against loss of individual Servers and 3687 assurance that Clients can establish new Server relationships quickly 3688 in event of a Server failure. 3690 Appendix D. Change Log 3692 << RFC Editor - remove prior to publication >> 3694 Changes from draft-templin-intarea-6706bis-18 to draft-templin- 3695 intrea-6706bis-19: 3697 o Changed Proxy/Server keepalives to use "proactive NUD" in a manner 3698 tha paralles BFD 3700 Changes from draft-templin-intarea-6706bis-17 to draft-templin- 3701 intrea-6706bis-18: 3703 o Discuss how AERO option is used in relation to S/TLLAOs 3705 o New text on Bidirectional Forwarding Detection (BFD) 3707 o Cleaned up usage (and non-usage) of unsolicited NAs 3709 o New appendix on Server failures 3711 Changes from draft-templin-intarea-6706bis-15 to draft-templin- 3712 intrea-6706bis-17: 3714 o S/TLLAO now includes multiple link-layer addresses within a single 3715 option instead of requiring multiple options 3717 o New unsolicited NA message to inform the old link that a Client 3718 has moved to a new link 3720 Changes from draft-templin-intarea-6706bis-14 to draft-templin- 3721 intrea-6706bis-15: 3723 o MTU and fragmentation 3725 o New details in movement to new Server 3727 Changes from draft-templin-intarea-6706bis-13 to draft-templin- 3728 intrea-6706bis-14: 3730 o Security based on secured tunnels, ingress filtering, MAP list and 3731 ROS list 3733 Changes from draft-templin-intarea-6706bis-12 to draft-templin- 3734 intrea-6706bis-13: 3736 o New paragraph in Section 3.6 on AERO interface layering over 3737 secured tunnels 3739 o Removed extraneous text in Section 3.7 3741 o Added new detail to the forwarding algorithm in Section 3.9 3743 o Clarified use of fragmentation 3745 o Route optimization now supported for both MNP and non-MNP-based 3746 prefixes 3748 o Relays are now seen as link-layer elements in the architecture. 3750 o Built out multicast section in detail. 3752 o New Appendix on implementation considerations for route 3753 optimization. 3755 Changes from draft-templin-intarea-6706bis-11 to draft-templin- 3756 intrea-6706bis-12: 3758 o Introduced Gateways as a new AERO element for connecting 3759 Correspondent Nodes on INET links 3761 o Introduced terms "Access Network (ANET)" and "Internetwork (INET)" 3763 o Changed "ASP" to "MSP", and "ACP" to "MNP" 3765 o New figure on the relation of Segments to the SPAN and AERO link 3767 o New "S" bit in S/TLLAO to indicate the "Source" S/TLLAO as opposed 3768 to additional S/TLLAOs 3770 o Changed Interface ID for Servers from 255 to 0xffff 3772 o Significant updates to Route Optimization, NUD, and Mobility 3773 Management 3775 o New Section on Multicast 3777 o New Section on AERO Clients in the open Internetwork 3779 o New Section on Operation over multiple AERO links (VLANs over the 3780 SPAN) 3782 o New Sections on DNS considerations and Transition considerations 3784 o 3786 Changes from draft-templin-intarea-6706bis-10 to draft-templin- 3787 intrea-6706bis-11: 3789 o Added The SPAN 3791 Changes from draft-templin-intarea-6706bis-09 to draft-templin- 3792 intrea-6706bis-10: 3794 o Orphaned packets in flight (e.g., when a neighbor cache entry is 3795 in the DEPARTED state) are now forwarded at the link layer instead 3796 of at the network layer. Forwarding at the network layer can 3797 result in routing loops and/or excessive delays of forwarded 3798 packets while the routing system is still reconverging. 3800 o Update route optimization to clarify the unsecured nature of the 3801 first NS used for route discovery 3803 o Many cleanups and clarifications on ND messaging parameters 3805 Changes from draft-templin-intarea-6706bis-08 to draft-templin- 3806 intrea-6706bis-09: 3808 o Changed PRL to "MAP list" 3810 o For neighbor cache entries, changed "static" to "symmetric", and 3811 "dynamic" to "asymmetric" 3813 o Specified Proxy RS/RA exchanges with Servers on behalf of Clients 3815 o Added discussion of unsolicited NAs in Section 3.16, and included 3816 forward reference to Section 3.18 3818 o Added discussion of AERO Clients used as critical infrastructure 3819 elements to connect fixed networks. 3821 o Added network-based VPN under security considerations 3823 Changes from draft-templin-intarea-6706bis-07 to draft-templin- 3824 intrea-6706bis-08: 3826 o New section on AERO-Aware Access Router 3828 Changes from draft-templin-intarea-6706bis-06 to draft-templin- 3829 intrea-6706bis-07: 3831 o Added "R" bit for release of PDs. Now have a full RS/RA service 3832 that can do PD without requiring DHCPv6 messaging over-the-air 3834 o Clarifications on solicited vs unsolicited NAs 3836 o Clarified use of MAX_NEIGHBOR_ADVERTISEMENTS for the purpose of 3837 increase reliability 3839 Changes from draft-templin-intarea-6706bis-05 to draft-templin- 3840 intrea-6706bis-06: 3842 o Major re-work and simplification of Route Optimization function 3844 o Added Distributed Mobility Management (DMM) and Mobility Anchor 3845 Point (MAP) terminology 3847 o New section on "AERO Critical Infrastructure Element 3848 Considerations" demonstrating low overall cost for the service 3850 o minor text revisions and deletions 3852 o removed extraneous appendices 3854 Changes from draft-templin-intarea-6706bis-04 to draft-templin- 3855 intrea-6706bis-05: 3857 o New Appendix E on S/TLLAO Extensions for special-purpose links. 3858 Discussed ATN/IPS as example. 3860 o New sentence in introduction to declare appendices as non- 3861 normative. 3863 Changes from draft-templin-intarea-6706bis-03 to draft-templin- 3864 intrea-6706bis-04: 3866 o Added definitions for Potential Router List (PRL) and secure 3867 enclave 3869 o Included text on mapping transport layer port numbers to network 3870 layer DSCP values 3872 o Added reference to DTLS and DMM Distributed Mobility Anchoring 3873 working group document 3875 o Reworked Security Considerations 3877 o Updated references. 3879 Changes from draft-templin-intarea-6706bis-02 to draft-templin- 3880 intrea-6706bis-03: 3882 o Added new section on SEND. 3884 o Clarifications on "AERO Address" section. 3886 o Updated references and added new reference for RFC8086. 3888 o Security considerations updates. 3890 o General text clarifications and cleanup. 3892 Changes from draft-templin-intarea-6706bis-01 to draft-templin- 3893 intrea-6706bis-02: 3895 o Note on encapsulation avoidance in Section 4. 3897 Changes from draft-templin-intarea-6706bis-00 to draft-templin- 3898 intrea-6706bis-01: 3900 o Remove DHCPv6 Server Release procedures that leveraged the old way 3901 Relays used to "route" between Server link-local addresses 3903 o Remove all text relating to Relays needing to do any AERO-specific 3904 operations 3906 o Proxy sends RS and receives RA from Server using SEND. Use CGAs 3907 as source addresses, and destination address of RA reply is to the 3908 AERO address corresponding to the Client's ACP. 3910 o Proxy uses SEND to protect RS and authenticate RA (Client does not 3911 use SEND, but rather relies on subnetwork security. When the 3912 Proxy receives an RS from the Client, it creates a new RS using 3913 its own addresses as the source and uses SEND with CGAs to send a 3914 new RS to the Server. 3916 o Emphasize distributed mobility management 3918 o AERO address-based RS injection of ACP into underlying routing 3919 system. 3921 Changes from draft-templin-aerolink-82 to draft-templin-intarea- 3922 6706bis-00: 3924 o Document use of NUD (NS/NA) for reliable link-layer address 3925 updates as an alternative to unreliable unsolicited NA. 3926 Consistent with Section 7.2.6 of RFC4861. 3928 o Server adds additional layer of encapsulation between outer and 3929 inner headers of NS/NA messages for transmission through Relays 3930 that act as vanilla IPv6 routers. The messages include the AERO 3931 Server Subnet Router Anycast address as the source and the Subnet 3932 Router Anycast address corresponding to the Client's ACP as the 3933 destination. 3935 o Clients use Subnet Router Anycast address as the encapsulation 3936 source address when the access network does not provide a 3937 topologically-fixed address. 3939 Author's Address 3941 Fred L. Templin (editor) 3942 Boeing Research & Technology 3943 P.O. Box 3707 3944 Seattle, WA 98124 3945 USA 3947 Email: fltemplin@acm.org