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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, March 26, 2020 5 rfc6179, rfc6706 (if 6 approved) 7 Intended status: Standards Track 8 Expires: September 27, 2020 10 Asymmetric Extended Route Optimization (AERO) 11 draft-templin-intarea-6706bis-33 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 September 27, 2020. 45 Copyright Notice 47 Copyright (c) 2020 IETF Trust and the persons identified as the 48 document authors. All rights reserved. 50 This document is subject to BCP 78 and the IETF Trust's Legal 51 Provisions Relating to IETF Documents 52 (https://trustee.ietf.org/license-info) in effect on the date of 53 publication of this document. Please review these documents 54 carefully, as they describe your rights and restrictions with respect 55 to this document. Code Components extracted from this document must 56 include Simplified BSD License text as described in Section 4.e of 57 the Trust Legal Provisions and are provided without warranty as 58 described in the Simplified BSD License. 60 Table of Contents 62 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 63 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 64 3. Asymmetric Extended Route Optimization (AERO) . . . . . . . . 10 65 3.1. AERO Link Reference Model . . . . . . . . . . . . . . . . 10 66 3.2. AERO Node Types . . . . . . . . . . . . . . . . . . . . . 12 67 3.3. AERO Routing System . . . . . . . . . . . . . . . . . . . 13 68 3.3.1. IPv4 Compatibility Routing . . . . . . . . . . . . . 15 69 3.4. AERO Addresses . . . . . . . . . . . . . . . . . . . . . 15 70 3.5. Spanning Partitioned AERO Networks (SPAN) . . . . . . . . 16 71 3.5.1. SPAN Compatibility Addressing . . . . . . . . . . . . 20 72 3.5.2. Client SPAN Addresses . . . . . . . . . . . . . . . . 20 73 3.6. AERO Interface Characteristics . . . . . . . . . . . . . 21 74 3.7. AERO Interface Initialization . . . . . . . . . . . . . . 24 75 3.7.1. AERO Server/Gateway Behavior . . . . . . . . . . . . 24 76 3.7.2. AERO Proxy Behavior . . . . . . . . . . . . . . . . . 25 77 3.7.3. AERO Client Behavior . . . . . . . . . . . . . . . . 25 78 3.7.4. AERO Relay Behavior . . . . . . . . . . . . . . . . . 25 79 3.8. AERO Interface Neighbor Cache Maintenance . . . . . . . . 26 80 3.9. AERO Interface Encapsulation and Re-encapsulation . . . . 28 81 3.10. AERO Interface Decapsulation . . . . . . . . . . . . . . 29 82 3.11. AERO Interface Data Origin Authentication . . . . . . . . 29 83 3.12. AERO Interface MTU and Fragmentation . . . . . . . . . . 29 84 3.13. AERO Interface Forwarding Algorithm . . . . . . . . . . . 31 85 3.13.1. Client Forwarding Algorithm . . . . . . . . . . . . 32 86 3.13.2. Proxy Forwarding Algorithm . . . . . . . . . . . . . 33 87 3.13.3. Server/Gateway Forwarding Algorithm . . . . . . . . 34 88 3.13.4. Relay Forwarding Algorithm . . . . . . . . . . . . . 35 89 3.14. AERO Interface Error Handling . . . . . . . . . . . . . . 36 90 3.15. AERO Router Discovery, Prefix Delegation and 91 Autoconfiguration . . . . . . . . . . . . . . . . . . . . 38 92 3.15.1. AERO ND/PD Service Model . . . . . . . . . . . . . . 38 93 3.15.2. AERO Client Behavior . . . . . . . . . . . . . . . . 39 94 3.15.3. AERO Server Behavior . . . . . . . . . . . . . . . . 41 95 3.16. The AERO Proxy . . . . . . . . . . . . . . . . . . . . . 44 96 3.16.1. Detecting and Responding to Server Failures . . . . 46 97 3.16.2. Point-to-Multipoint Server Coordindation . . . . . . 47 98 3.17. AERO Route Optimization . . . . . . . . . . . . . . . . . 47 99 3.17.1. Route Optimization Initiation . . . . . . . . . . . 48 100 3.17.2. Relaying the NS . . . . . . . . . . . . . . . . . . 48 101 3.17.3. Processing the NS and Sending the NA . . . . . . . . 49 102 3.17.4. Relaying the NA . . . . . . . . . . . . . . . . . . 50 103 3.17.5. Processing the NA . . . . . . . . . . . . . . . . . 50 104 3.17.6. Route Optimization Maintenance . . . . . . . . . . . 50 105 3.18. Neighbor Unreachability Detection (NUD) . . . . . . . . . 51 106 3.19. Mobility Management and Quality of Service (QoS) . . . . 52 107 3.19.1. Mobility Update Messaging . . . . . . . . . . . . . 53 108 3.19.2. Announcing Link-Layer Address and/or QoS Preference 109 Changes . . . . . . . . . . . . . . . . . . . . . . 54 110 3.19.3. Bringing New Links Into Service . . . . . . . . . . 54 111 3.19.4. Removing Existing Links from Service . . . . . . . . 54 112 3.19.5. Moving to a New Server . . . . . . . . . . . . . . . 55 113 3.20. Multicast . . . . . . . . . . . . . . . . . . . . . . . . 56 114 3.20.1. Source-Specific Multicast (SSM) . . . . . . . . . . 56 115 3.20.2. Any-Source Multicast (ASM) . . . . . . . . . . . . . 57 116 3.20.3. Bi-Directional PIM (BIDIR-PIM) . . . . . . . . . . . 58 117 3.21. Operation over Multiple AERO Links (VLANs) . . . . . . . 58 118 3.22. DNS Considerations . . . . . . . . . . . . . . . . . . . 59 119 3.23. Transition Considerations . . . . . . . . . . . . . . . . 60 120 3.24. Detecting and Reacting to Server and Relay Failures . . . 60 121 4. Implementation Status . . . . . . . . . . . . . . . . . . . . 61 122 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 61 123 6. Security Considerations . . . . . . . . . . . . . . . . . . . 61 124 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 63 125 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 65 126 8.1. Normative References . . . . . . . . . . . . . . . . . . 65 127 8.2. Informative References . . . . . . . . . . . . . . . . . 66 128 Appendix A. AERO Alternate Encapsulations . . . . . . . . . . . 73 129 Appendix B. Non-Normative Considerations . . . . . . . . . . . . 75 130 B.1. Implementation Strategies for Route Optimization . . . . 75 131 B.2. Implicit Mobility Management . . . . . . . . . . . . . . 76 132 B.3. Direct Underlying Interfaces . . . . . . . . . . . . . . 76 133 B.4. AERO Clients on the Open Internetwork . . . . . . . . . . 76 134 B.5. Operation on AERO Links with /64 ASPs . . . . . . . . . . 77 135 B.6. AERO Adaptations for SEcure Neighbor Discovery (SEND) . . 77 136 B.7. AERO Critical Infrastructure Considerations . . . . . . . 78 137 B.8. AERO Server Failure Implications . . . . . . . . . . . . 79 138 B.9. AERO Client / Server Architecture . . . . . . . . . . . . 79 139 Appendix C. Change Log . . . . . . . . . . . . . . . . . . . . . 81 140 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 89 142 1. Introduction 144 Asymmetric Extended Route Optimization (AERO) fulfills the 145 requirements of Distributed Mobility Management (DMM) [RFC7333] and 146 route optimization [RFC5522] for aeronautical networking and other 147 network mobility use cases. AERO is based on a Non-Broadcast, 148 Multiple Access (NBMA) virtual link model known as the AERO link. 149 The AERO link is a virtual overlay configured over one or more 150 underlying Internetworks, and nodes on the link can exchange IP 151 packets via tunneling. Multilink operation allows for increased 152 reliability, bandwidth optimization and traffic path diversity. 154 The AERO service comprises Clients, Proxys, Servers and Gateways that 155 are seen as AERO link neighbors. Each node's AERO interface uses an 156 IPv6 link-local address format (known as the AERO address) that 157 supports operation of the IPv6 Neighbor Discovery (ND) protocol 158 [RFC4861] and links ND to IP forwarding. A node's AERO interface can 159 be configured over multiple underlying interfaces, and may therefore 160 appear as a single interface with multiple link-layer addresses. 161 Each link-layer address is subject to change due to mobility and/or 162 QoS fluctuations, and link-layer address changes are signaled by ND 163 messaging the same as for any IPv6 link. 165 AERO links provide a cloud-based service where mobile nodes may use 166 any Server acting as a Mobility Anchor Point (MAP) and fixed nodes 167 may use any Gateway on the link for efficient communications. Fixed 168 nodes forward packets destined to other AERO nodes to the nearest 169 Gateway, which forwards them through the cloud. A mobile node's 170 initial packets are forwarded through the Server, while direct 171 routing is supported through asymmetric extended route optimization 172 while data packets are flowing. Both unicast and multicast 173 communications are supported, and mobile nodes may efficiently move 174 between locations while maintaining continuous communications with 175 correspondents and without changing their IP Address. 177 AERO Relays are interconnected in a secured private BGP overlay 178 routing instance known as the "SPAN". The SPAN provides a hybrid 179 routing/bridging service to join the underlying Internetworks of 180 multiple disjoint administrative domains into a single unified AERO 181 link. Each AERO link instance is characterized by the set of 182 Mobility Service Prefixes (MSPs) common to all mobile nodes. The 183 link extends to the point where a Gateway/Server is on the optimal 184 route from any correspondent node on the link, and provides a gateway 185 between the underlying Internetwork and the SPAN. To the underlying 186 Internetwork, the Gateway/Server is the source of a route to its MSP, 187 and hence uplink traffic to the mobile node is naturally routed to 188 the nearest Gateway/Server. 190 AERO assumes the use of PIM Sparse Mode in support of multicast 191 communication. In support of Source Specific Multicast (SSM) when a 192 Mobile Node is the source, AERO route optimization ensures that a 193 shortest-path multicast tree is established with provisions for 194 mobility and multilink operation. In all other multicast scenarios 195 there are no AERO dependencies. 197 AERO was designed for aeronautical networking for both manned and 198 unmanned aircraft, where the aircraft is treated as a mobile node 199 that can connect an Internet of Things (IoT). AERO is also 200 applicable to a wide variety of other use cases. For example, it can 201 be used to coordinate the Virtual Private Network (VPN) links of 202 mobile nodes (e.g., cellphones, tablets, laptop computers, etc.) that 203 connect into a home enterprise network via public access networks 204 using services such as OpenVPN [OVPN]. Other applicable use cases 205 are also in scope. 207 The following numbered sections present the AERO specification. The 208 appendices at the end of the document are non-normative. 210 2. Terminology 212 The terminology in the normative references applies; the following 213 terms are defined within the scope of this document: 215 IPv6 Neighbor Discovery (ND) 216 an IPv6 control message service for coordinating neighbor 217 relationships between nodes connected to a common link. AERO 218 interfaces use the ND service specified in [RFC4861]. 220 IPv6 Prefix Delegation (PD) 221 a networking service for delegating IPv6 prefixes to nodes on the 222 link. The nominal PD service is DHCPv6 [RFC8415], however 223 alternate services (e.g., based on ND messaging) are also in scope 224 [I-D.templin-v6ops-pdhost][I-D.templin-6man-dhcpv6-ndopt]. Most 225 notably, a minimal form of PD known as "prefix registration" can 226 be used if the Client knows its prefix in advance and can 227 represent it in the IPv6 source address of an ND message. 229 Access Network (ANET) 230 a node's first-hop data link service network, e.g., a radio access 231 network, cellular service provider network, corporate enterprise 232 network, or the public Internet itself. For secured ANETs, link- 233 layer security services such as IEEE 802.1X and physical-layer 234 security prevent unauthorized access internally while border 235 network-layer security services such as firewalls and proxies 236 prevent unauthorized outside access. 238 ANET interface 239 a node's attachment to a link in an ANET. 241 ANET address 242 an IP address assigned to a node's interface connection to an 243 ANET. 245 Internetwork (INET) 246 a connected IP network topology with a coherent routing and 247 addressing plan and that provides a transit backbone service for 248 ANET end systems. INETs also provide an underlay service over 249 which the AERO virtual link is configured. Example INETs include 250 corporate enterprise networks, aviation networks, and the public 251 Internet itself. When there is no administrative boundary between 252 an ANET and the INET, the ANET and INET are one and the same. 254 INET Partition 255 frequently, INETs such as large corporate enterprise networks are 256 sub-divided internally into separate isolated partitions. Each 257 partition is fully connected internally but disconnected from 258 other partitions, and there is no requirement that separate 259 partitions maintain consistent Internet Protocol and/or addressing 260 plans. (An INET partition is the same as a SPAN segment discussed 261 below.) 263 INET interface 264 a node's attachment to a link in an INET. 266 INET address 267 an IP address assigned to a node's interface connection to an 268 INET. 270 AERO link 271 a Non-Broadcast, Multiple Access (NBMA) tunnel virtual overlay 272 configured over one or more underlying INETs. Nodes on the AERO 273 link appear as single-hop neighbors from the perspective of the 274 virtual overlay even though they may be separated by many 275 underlying INET hops. AERO links may be configured over multiple 276 underlying SPAN segments (see below). 278 AERO interface 279 a node's attachment to an AERO link. Since the addresses assigned 280 to an AERO interface are managed for uniqueness, AERO interfaces 281 do not require Duplicate Address Detection (DAD) and therefore set 282 the administrative variable 'DupAddrDetectTransmits' to zero 283 [RFC4862]. 285 underlying interface 286 an ANET or INET interface over which an AERO interface is 287 configured. 289 AERO address 290 an IPv6 link-local address assigned to an AERO interface and 291 constructed as specified in Section 3.4. 293 base AERO address 294 the lowest-numbered AERO address aggregated by the MNP (see 295 Section 3.4). 297 Mobility Service Prefix (MSP) 298 an IP prefix assigned to the AERO link and from which more- 299 specific Mobile Network Prefixes (MNPs) are derived. 301 Mobile Network Prefix (MNP) 302 an IP prefix allocated from an MSP and delegated to an AERO Client 303 or Gateway. 305 AERO node 306 a node that is connected to an AERO link, or that provides 307 services to other nodes on an AERO link. 309 AERO Client ("Client") 310 an AERO node that connects to one or more ANETs and requests MNP 311 PDs from AERO Servers. The Client assigns a Client AERO address 312 to the AERO interface for use in ND exchanges with other AERO 313 nodes and forwards packets to correspondents according to AERO 314 interface neighbor cache state. 316 AERO Server ("Server") 317 an INET node that configures an AERO interface to provide default 318 forwarding and mobility/multilink services for AERO Clients. The 319 Server assigns an administratively-provisioned AERO address to its 320 AERO interface to support the operation of the ND/PD services, and 321 advertises all of its associated MNPs via BGP peerings with 322 Relays. 324 AERO Gateway ("Gateway") 325 an AERO Server that also provides forwarding services between 326 nodes reached via the AERO link and correspondents on other links. 327 AERO Gateways are provisioned with MNPs (i.e., the same as for an 328 AERO Client) and run a dynamic routing protocol to discover any 329 non-MNP IP routes. In both cases, the Gateway advertises the 330 MSP(s) over INET interfaces, and distributes all of its associated 331 MNPs and non-MNP IP routes via BGP peerings with Relays (i.e., the 332 same as for an AERO Server). 334 AERO Relay ("Relay") 335 a node that provides hybrid routing/bridging services (as well as 336 a security trust anchor) for nodes on an AERO link. As a router, 337 the Relay forwards packets using standard IP forwarding. As a 338 bridge, the Relay forwards packets over the AERO link without 339 decrementing the IPv6 Hop Limit. AERO Relays peer with Servers 340 and other Relays to discover the full set of MNPs for the link as 341 well as any non-MNPs that are reachable via Gateways. 343 AERO Proxy ("Proxy") 344 a node that provides proxying services between Clients in an ANET 345 and Servers in external INETs. The AERO Proxy is a conduit 346 between the ANET and external INETs in the same manner as for 347 common web proxies, and behaves in a similar fashion as for ND 348 proxies [RFC4389]. 350 Spanning Partitioned AERO Networks (SPAN) 351 a means for bridging disjoint INET partitions as segments of a 352 unified AERO link the same as for a bridged campus LAN. The SPAN 353 is a mid-layer IPv6 encapsulation service in the AERO routing 354 system that supports a unified AERO link view for all segments. 355 Each segment in the SPAN is a distinct INET partition. 357 SPAN Service Prefix (SSP) 358 a global or unique local /96 IPv6 prefix assigned to the AERO link 359 to support SPAN services. 361 SPAN Partition Prefix (SPP) 362 a sub-prefix of the SPAN Service Prefix uniquely assigned to a 363 single SPAN segment. 365 SPAN Address 366 a global or unique local IPv6 address taken from a SPAN Partition 367 Prefix and constructed as specified in Section 3.5. SPAN 368 addresses are statelessly derived from AERO addresses, and vice- 369 versa. 371 ingress tunnel endpoint (ITE) 372 an AERO interface endpoint that injects encapsulated packets into 373 an AERO link. 375 egress tunnel endpoint (ETE) 376 an AERO interface endpoint that receives encapsulated packets from 377 an AERO link. 379 link-layer address 380 an IP address used as an encapsulation header source or 381 destination address from the perspective of the AERO interface. 383 When an upper layer protocol (e.g., UDP) is used as part of the 384 encapsulation, the port number is also considered as part of the 385 link-layer address. From the perspective of the AERO interface, 386 the link-layer address is either an INET address for intra-segment 387 encapsulation or a SPAN address for inter-segment encapsulation. 389 network layer address 390 the source or destination address of an encapsulated IP packet 391 presented to the AERO interface. 393 end user network (EUN) 394 an internal virtual or external edge IP network that an AERO 395 Client or Gateway connects to the rest of the network via the AERO 396 interface. The Client/Gateway sees each EUN as a "downstream" 397 network, and sees the AERO interface as the point of attachment to 398 the "upstream" network. 400 Mobile Node (MN) 401 an AERO Client and all of its downstream-attached networks that 402 move together as a single unit, i.e., an end system that connects 403 an Internet of Things. 405 Mobile Router (MR) 406 a MN's on-board router that forwards packets between any 407 downstream-attached networks and the AERO link. 409 Route Optimization Source (ROS) 410 the AERO node nearest the source that initiates route 411 optimization. The ROS may be a Server or Proxy acting on behalf 412 of the source Client. 414 Route Optimization responder (ROR) 415 the AERO node nearest the target destination that responds to 416 route optimization requests. The ROR may be a Server acting on 417 behalf of a target MNP Client, or a Gateway for a non-MNP 418 destination. 420 MAP List 421 a geographically and/or topologically referenced list of AERO 422 addresses of all Servers within the same AERO link. There is a 423 single MAP list for the entire AERO link. 425 ROS List 426 a list of AERO/SPAN-to-INET address mappings of all ROSes within 427 the same SPAN segment. There is a distinct ROS list for each 428 segment. 430 Distributed Mobility Management (DMM) 431 a BGP-based overlay routing service coordinated by Servers and 432 Relays that tracks all Server-to-Client associations. 434 Mobility Service (MS) 435 the collective set of all Servers, Proxys, Relays and Gateways 436 that provide the AERO Service to Clients. 438 Mobility Service Endpoint MSE) 439 an individual Server, Proxy, Relay or Gateway in the Mobility 440 Service. 442 Throughout the document, the simple terms "Client", "Server", 443 "Relay", "Proxy" and "Gateway" refer to "AERO Client", "AERO Server", 444 "AERO Relay", "AERO Proxy" and "AERO Gateway", respectively. 445 Capitalization is used to distinguish these terms from other common 446 Internetworking uses in which they appear without capitalization. 448 The terminology of DHCPv6 [RFC8415] and IPv6 ND [RFC4861] (including 449 the names of node variables, messages and protocol constants) is used 450 throughout this document. The terms "All-Routers multicast", "All- 451 Nodes multicast", "Solicited-Node multicast" and "Subnet-Router 452 anycast" are defined in [RFC4291] (with Link-Local scope assumed). 453 Also, the term "IP" is used to generically refer to either Internet 454 Protocol version, i.e., IPv4 [RFC0791] or IPv6 [RFC8200]. 456 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 457 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 458 "OPTIONAL" in this document are to be interpreted as described in BCP 459 14 [RFC2119][RFC8174] when, and only when, they appear in all 460 capitals, as shown here. 462 3. Asymmetric Extended Route Optimization (AERO) 464 The following sections specify the operation of IP over Asymmetric 465 Extended Route Optimization (AERO) links: 467 3.1. AERO Link Reference Model 468 +----------------+ 469 | AERO Relay R1 | 470 | Nbr: S1, S2, P1| 471 |(X1->S1; X2->S2)| 472 | MSP M1 | 473 +-+---------+--+-+ 474 +--------------+ | Secured | | +--------------+ 475 |AERO Server S1| | tunnels | | |AERO Server S2| 476 | Nbr: C1, R1 +-----+ | +-----+ Nbr: C2, R1 | 477 | default->R1 | | | default->R1 | 478 | X1->C1 | | | X2->C2 | 479 +-------+------+ | +------+-------+ 480 | AERO Link | | 481 X===+===+===================+==)===============+===+===X 482 | | | | 483 +-----+--------+ +--------+--+-----+ +--------+-----+ 484 |AERO Client C1| | AERO Proxy P1 | |AERO Client C2| 485 | Nbr: S1 | |(Proxy Nbr Cache)| | Nbr: S2 | 486 | default->S1 | +--------+--------+ | default->S2 | 487 | MNP X1 | | | MNP X2 | 488 +------+-------+ .--------+------. +-----+--------+ 489 | (- Proxyed Clients -) | 490 .-. `---------------' .-. 491 ,-( _)-. ,-( _)-. 492 .-(_ IP )-. +-------+ +-------+ .-(_ IP )-. 493 (__ EUN )--|Host H1| |Host H2|--(__ EUN ) 494 `-(______)-' +-------+ +-------+ `-(______)-' 496 Figure 1: AERO Link Reference Model 498 Figure 1 presents the AERO link reference model. In this model: 500 o the AERO link is an overlay network service configured over one or 501 more underlying INET partitions which may be managed by different 502 administrative authorities and have incompatible protocols and/or 503 addressing plans. 505 o AERO Relay R1 aggregates Mobility Service Prefix (MSP) M1, 506 discovers Mobile Network Prefixes (MNPs) X* and advertises the MSP 507 via BGP peerings over secured tunnels to Servers (S1, S2). Relays 508 use the SPAN service to bridge disjoint segments of a partitioned 509 AERO link. 511 o AERO Servers S1 and S2 configure secured tunnels with Relay R1 and 512 also provide mobility, multilink and default router services for 513 their associated Clients C1 and C2. 515 o AERO Clients C1 and C2 associate with Servers S1 and S2, 516 respectively. They receive Mobile Network Prefix (MNP) 517 delegations X1 and X2, and also act as default routers for their 518 associated physical or internal virtual EUNs. Simple hosts H1 and 519 H2 attach to the EUNs served by Clients C1 and C2, respectively. 521 o AERO Proxy P1 configures a secured tunnel with Relay R1 and 522 provides proxy services for AERO Clients in secured enclaves that 523 cannot associate directly with other AERO link neighbors. 525 Each node on the AERO link maintains an AERO interface neighbor cache 526 and an IP forwarding table the same as for any link. Although the 527 figure shows a limited deployment, in common operational practice 528 there will normally be many additional Relays, Servers, Clients and 529 Proxys. 531 3.2. AERO Node Types 533 AERO Relays provide hybrid routing/bridging services (as well as a 534 security trust anchor) for nodes on an AERO link. Relays use 535 standard IPv6 routing to forward packets both within the same INET 536 partitions and between disjoint INET partitions based on a mid-layer 537 IPv6 encapsulation known as the SPAN header. The inner IP layer 538 experiences a virtual bridging service since the inner IP TTL/Hop 539 Limit is not decremented during forwarding. Each Relay also peers 540 with Servers and other Relays in a dynamic routing protocol instance 541 to provide a Distributed Mobility Management (DMM) service for the 542 list of active MNPs (see Section 3.3). Relays present the AERO link 543 as a set of one or more Mobility Service Prefixes (MSPs) but as link- 544 layer devices need not connect directly to the AERO link themselves 545 unless an administrative interface is desired. Relays configure 546 secured tunnels with Servers, Proxys and other Relays; they further 547 maintain IP forwarding table entries for each Mobile Network Prefix 548 (MNP) and any other reachable non-MNP prefixes. 550 AERO Servers provide default forwarding and mobility/multilink 551 services for AERO Client Mobile Nodes (MNs). Each Server also peers 552 with Relays in a dynamic routing protocol instance to advertise its 553 list of associated MNPs (see Section 3.3). Servers facilitate PD 554 exchanges with Clients, where each delegated prefix becomes an MNP 555 taken from an MSP. Servers forward packets between AERO interface 556 neighbors and track each Client's mobility profiles. 558 AERO Clients register their MNPs through PD exchanges with AERO 559 Servers over the AERO link, and distribute the MNPs to nodes on EUNs. 560 A Client may also be co-resident on the same physical or virtual 561 platform as a Server; in that case, the Client and Server behave as a 562 single functional unit. 564 AERO Proxys provide a conduit for ANET AERO Clients to associate with 565 AERO Servers in external INETs. Client and Servers exchange control 566 plane messages via the Proxy acting as a bridge between the ANET/INET 567 boundary. The Proxy forwards data packets between Clients and the 568 AERO link according to forwarding information in the neighbor cache. 569 The Proxy function is specified in Section 3.16. 571 AERO Gateways are Servers that provide forwarding services between 572 the AERO interface and INET/EUN interfaces. Gateways are provisioned 573 with MNPs the same as for an AERO Client, and also run a dynamic 574 routing protocol to discover any non-MNP IP routes. The Gateway 575 advertises the MSP(s) to INETs, and distributes all of its associated 576 MNPs and non-MNP IP routes via BGP peerings with Relays. 578 AERO Relays, Servers, Proxys and Gateways are critical infrastructure 579 elements in fixed (i.e., non-mobile) INET deployments and hence have 580 permanent and unchanging INET addresses. AERO Clients are MNs that 581 connect via ANET interfaces, i.e., their ANET addresses may change 582 when the Client moves to a new ANET connection. 584 3.3. AERO Routing System 586 The AERO routing system comprises a private instance of the Border 587 Gateway Protocol (BGP) [RFC4271] that is coordinated between Relays 588 and Servers and does not interact with either the public Internet BGP 589 routing system or any underlying INET routing systems. 591 In a reference deployment, each Server is configured as an Autonomous 592 System Border Router (ASBR) for a stub Autonomous System (AS) using 593 an AS Number (ASN) that is unique within the BGP instance, and each 594 Server further uses eBGP to peer with one or more Relays but does not 595 peer with other Servers. Each INET of a multi-segment AERO link must 596 include one or more Relays, which peer with the Servers and Proxys 597 within that INET. All Relays within the same INET are members of the 598 same hub AS using a common ASN, and use iBGP to maintain a consistent 599 view of all active MNPs currently in service. The Relays of 600 different INETs peer with one another using eBGP. 602 Relays advertise the AERO link's MSPs and any non-MNP routes to each 603 of their Servers. This means that any aggregated non-MNPs (including 604 "default") are advertised to all Servers. Each Relay configures a 605 black-hole route for each of its MSPs. By black-holing the MSPs, the 606 Relay will maintain forwarding table entries only for the MNPs that 607 are currently active, and packets destined to all other MNPs will 608 correctly incur Destination Unreachable messages due to the black- 609 hole route. In this way, Servers have only partial topology 610 knowledge (i.e., they know only about the MNPs of their directly 611 associated Clients) and they forward all other packets to Relays 612 which have full topology knowledge. 614 Servers maintain a working set of associated MNPs, and dynamically 615 announce new MNPs and withdraw departed MNPs in eBGP updates to 616 Relays. Servers that are configured as Gateways also redistribute 617 non-MNP routes learned from non-AERO interfaces via their eBGP Relay 618 peerings. 620 Clients are expected to remain associated with their current Servers 621 for extended timeframes, however Servers SHOULD selectively suppress 622 updates for impatient Clients that repeatedly associate and 623 disassociate with them in order to dampen routing churn. Servers 624 that are configured as Gateways advertise the MSPs via INET/EUN 625 interfaces, and forward packets between INET/EUN interfaces and the 626 AERO interface using standard IP forwarding. 628 Scaling properties of the AERO routing system are limited by the 629 number of BGP routes that can be carried by Relays. As of 2015, the 630 global public Internet BGP routing system manages more than 500K 631 routes with linear growth and no signs of router resource exhaustion 632 [BGP]. More recent network emulation studies have also shown that a 633 single Relay can accommodate at least 1M dynamically changing BGP 634 routes even on a lightweight virtual machine, i.e., and without 635 requiring high-end dedicated router hardware. 637 Therefore, assuming each Relay can carry 1M or more routes, this 638 means that at least 1M Clients can be serviced by a single set of 639 Relays. A means of increasing scaling would be to assign a different 640 set of Relays for each set of MSPs. In that case, each Server still 641 peers with one or more Relays, but institutes route filters so that 642 BGP updates are only sent to the specific set of Relays that 643 aggregate the MSP. For example, if the MSP for the AERO link is 644 2001:db8::/32, a first set of Relays could service the MSP 645 2001:db8::/40, a second set of Relays could service 646 2001:db8:0100::/40, a third set could service 2001:db8:0200::/40, 647 etc. 649 Assuming up to 1K sets of Relays, the AERO routing system can then 650 accommodate 1B or more MNPs with no additional overhead (for example, 651 it should be possible to service 1B /64 MNPs taken from a /34 MSP and 652 even more for shorter prefixes). In this way, each set of Relays 653 services a specific set of MSPs that they advertise to the native 654 Internetwork routing system, and each Server configures MSP-specific 655 routes that list the correct set of Relays as next hops. This 656 arrangement also allows for natural incremental deployment, and can 657 support small scale initial deployments followed by dynamic 658 deployment of additional Clients, Servers and Relays without 659 disturbing the already-deployed base. 661 Server and Relays can use the Bidirectional Forwarding Detection 662 (BFD) protocol [RFC5880] to quickly detect link failures that don't 663 result in interface state changes, BGP peer failures, and 664 administrative state changes. BFD is important in environments where 665 rapid response to failures is required for routing reconvergence and, 666 hence, communications continuity. 668 A full discussion of the BGP-based routing system used by AERO is 669 found in [I-D.ietf-rtgwg-atn-bgp]. The system provides for 670 Distributed Mobility Management (DMM) per the distributed mobility 671 anchoring architecture [I-D.ietf-dmm-distributed-mobility-anchoring]. 673 3.3.1. IPv4 Compatibility Routing 675 For IPv6 MNPs, the AERO routing system includes ordinary IPv6 routes. 676 For IPv4 MNPs, the AERO routing system includes IPv6 routes based on 677 an IPv4-embedded IPv6 address format discussed in Section 3.5.1. 679 3.4. AERO Addresses 681 A Client's AERO address is an IPv6 link-local address with an 682 interface identifier based on the Client's delegated MNP. Relay, 683 Server and Proxy AERO addresses are assigned from the range fe80::/96 684 and include an administratively-provisioned value in the lower 32 685 bits. 687 For IPv6, Client AERO addresses begin with the prefix fe80::/64 and 688 include in the interface identifier (i.e., the lower 64 bits) the 689 most-significant 64 bits of the Client's IPv6 MNPs. For example, if 690 the AERO Client receives the IPv6 MNP: 2001:db8:1000:2000::/56 it 691 constructs its corresponding AERO address as: 692 fe80::2001:db8:1000:2000. 694 For IPv4, Client AERO addresses are based on an IPv4-mapped IPv6 695 address [RFC4291] formed from an IPv4 MNP and with a prefix length of 696 96 plus the MNP prefix length. For example, for the IPv4 MNP 697 192.0.2.32/28 the IPv4-mapped IPv6 MNP is: 699 0:0:0:0:0:FFFF:192.0.2.16/124 (also written as 700 0:0:0:0:0:FFFF:c000:0210/124) 702 The Client then constructs its AERO address with the prefix fe80::/64 703 and with the lower 64 bits of the IPv4-mapped IPv6 address in the 704 interface identifier as: fe80::FFFF:192.0.2.16. 706 Mobility Service (MS) AERO addresses (used by Relays, Servers, 707 Gateways and Proxys) are allocated from the range fe80::/96, and MUST 708 be managed for uniqueness. The lower 32 bits of the AERO address 709 includes a unique integer value between 1 and 0xfeffffff (e.g., 710 fe80::1, fe80::2, fe80::3, etc., fe80::feff:ffff) as assigned by the 711 administrative authority for the link. If the link spans multiple 712 SPAN segments, the AERO addresses are assigned to each segment in 1x1 713 correspondence with SPAN addresses (see: Section 3.5). The address 714 fe80:: is the IPv6 link-local Subnet-Router anycast address, and the 715 address fe80::ffff:ffff is the "All-AERO-Servers" address. The 716 address range fe80::ff00:0000/104 is reserved for future use. 718 The Client's Subnet-Router anycast address can be statelessly 719 determined from its AERO address by simply transposing the AERO 720 address into the upper N bits of the Anycast address followed by 721 128-N bits of zeroes. For example, for the AERO address 722 fe80::2001:db8:1:2 the Subnet-Router anycast address is 723 2001:db8:1:2::. 725 AERO addresses for mobile node Clients embed a MNP as discussed 726 above, while AERO addresses for non-MNP destinations are constructed 727 in exactly the same way. A Client AERO address therefore encodes 728 either an MNP if the prefix is reached via the SPAN or a non-MNP if 729 the prefix is reached via a Gateway. 731 3.5. Spanning Partitioned AERO Networks (SPAN) 733 An AERO link configured over a single INET appears as a single 734 unified link with a consistent underlying network addressing plan. 735 In that case, all nodes on the link can exchange packets via simple 736 INET encapsulation, since the underlying INET is connected. In 737 common practice, however, an AERO link may be partitioned into 738 multiple "segments", where each segment is a distinct INET 739 potentially managed under a different administrative authority (e.g., 740 as for worldwide aviation service providers such as ARINC, SITA, 741 Inmarsat, etc.). Individual INETs may also themselves be partitioned 742 internally, in which case each internal partition is seen as a 743 separate segment. 745 The addressing plan of each segment is consistent internally but will 746 often bear no relation to the addressing plans of other segments. 747 Each segment is also likely to be separated from others by network 748 security devices (e.g., firewalls, proxies, packet filtering 749 gateways, etc.), and in many cases disjoint segments may not even 750 have any common physical link connections. Therefore, nodes can only 751 be assured of exchanging packets directly with correspondents in the 752 same segment, and not with those in other segments. The only means 753 for joining the segments therefore is through inter-domain peerings 754 between AERO Relays. 756 The same as for traditional campus LANs, multiple AERO link segments 757 can be joined into a single unified link via a virtual bridging 758 service termed the "SPAN". The SPAN performs link-layer packet 759 forwarding between segments (i.e., bridging) without decrementing the 760 network-layer TTL/Hop Limit. The SPAN model is depicted in Figure 2: 762 . . . . . . . . . . . . . . . . . . . . . . . 763 . . 764 . .-(::::::::) . 765 . .-(::::::::::::)-. +-+ . 766 . (:::: Segment A :::)--|R|---+ . 767 . `-(::::::::::::)-' +-+ | . 768 . `-(::::::)-' | . 769 . | . 770 . .-(::::::::) | . 771 . .-(::::::::::::)-. +-+ | . 772 . (:::: Segment B :::)--|R|---+ . 773 . `-(::::::::::::)-' +-+ | . 774 . `-(::::::)-' | . 775 . | . 776 . .-(::::::::) | . 777 . .-(::::::::::::)-. +-+ | . 778 . (:::: Segment C :::)--|R|---+ . 779 . `-(::::::::::::)-' +-+ | . 780 . `-(::::::)-' | . 781 . | . 782 . ..(etc).. x . 783 . . 784 . . 785 . <- AERO Link Bridged by the SPAN -> . 786 . . . . . . . . . . . . . .. . . . . . . . . 788 Figure 2: The SPAN 790 To support the SPAN, AERO links use the Unique Local Address (ULA) 791 prefix fd80::/10 [RFC4193] as the SPAN Service Prefix (SSP). The 792 prefix length intentionally matches the IPv6 link-local prefix 793 (fe80::/10), and enables a simple 1-bit stateless translation between 794 link-local and SPAN prefixes (i.e., bit 7 is '1' for link-local or 795 '0' for SPAN). 797 Each segment in the SPAN assigns a unique sub-prefix of SSP::/96 798 termed a "SPAN Partition Prefix (SPP)". For example, a first segment 799 could assign fd80::1000/116, a second could assign fd80::2000/116, a 800 third could assign fd80::3000/116, etc. The administrative 801 authorities for each segment must therefore coordinate to assure 802 mutually-exclusive SPP assignments, but internal provisioning of the 803 SPP is an independent local consideration for each administrative 804 authority. 806 An administratively-assigned "SPAN address" is an address taken from 807 a SPP and assigned to a Relay, Server, Gateway or Proxy interface. 808 SPAN addresses are formed by simply clearing bit 7 of an 809 administratively-assigned AERO address. For example, if the SPP is 810 fd80::1000/116, the SPAN address formed from the AERO address 811 fe80::1001 is simply fd80::1001. 813 An "INET address" is an address of a node's interface connection to 814 an INET. AERO/SPAN/INET address mappings are maintained as permanent 815 neighbor cache entires as discussed in Section 3.8. 817 AERO Relays serve as bridges to join multiple segments into a unified 818 AERO link over multiple diverse administrative domains. They support 819 the bridging function by first establishing forwarding table entries 820 for their SPPs either via standard BGP routing or static routes. For 821 example, if three Relays ('A', 'B' and 'C') from different segments 822 serviced the SPPs fd80::1000/116, fd80::2000/116 and fd80::3000/116 823 respectively, then the forwarding tables in each Relay are as 824 follows: 826 A: fd80::1000/116->local, fd80::2000/116->B, fd80::3000/116->C 828 B: fd80::1000/116->A, fd80::2000/116->local, fd80::3000/116->C 830 C: fd80::1000/116->A, fd80::2000/116->B, fd80::3000/116->local 832 These forwarding table entries are permanent and never change, since 833 they correspond to fixed infrastructure elements in their respective 834 segments. This provides the basis for a link-layer forwarding 835 service that cannot be disrupted by routing updates due to node 836 mobility. 838 With the SPPs in place in each Relay's forwarding table, control and 839 data packets sent between AERO nodes in different segments can 840 therefore be carried over the SPAN via encapsulation. For example, 841 when a source AERO node in segment A forwards a packet with IPv6 842 address 2001:db8:1:2::1 to a target AERO node in segment C with IPv6 843 address 2001:db8:1000:2000::1, it first encapsulates the packet in a 844 SPAN header with source SPAN address taken from fd80::1000/116 (e.g., 845 fd80::1001) and destination SPAN address taken from fd80::3000/116 846 (e.g., fd80::3001). Next, it encapsulates the SPAN message in an 847 INET header with source address set to its own INET address (e.g., 848 192.0.2.100) and destination set to the INET address of a Relay 849 (e.g., 192.0.2.1). 851 SPAN encapsulation is based on Generic Packet Tunneling in IPv6 852 [RFC2473]; the encapsulation format in the above example is shown in 853 Figure 3: 855 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 856 | INET Header | 857 | src = 192.0.2.100 | 858 | dst = 192.0.2.1 | 859 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 860 | SPAN Header | 861 | src = fd80::1001 | 862 | dst = fd80::3001 | 863 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 864 | Inner IP Header | 865 | src = 2001:db8:1:2::1 | 866 | dst = 2001:db8:1000:2000::1 | 867 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 868 | | 869 ~ ~ 870 ~ Inner Packet Body ~ 871 ~ ~ 872 | | 873 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 875 Figure 3: SPAN Encapsulation 877 In this format, the inner IP header and packet body are the original 878 IP packet, the SPAN header is an IPv6 header prepared according to 879 [RFC2473], and the INET header is prepared according to Section 3.9. 880 A packet is said to be "forwarded/sent into the SPAN" when it is 881 encapsulated as described above then forwarded via a secured tunnel 882 to a neighboring Relay. 884 This gives rise to a routing system that contains both MNP routes 885 that may change dynamically due to regional node mobility and SPAN 886 routes that never change. The Relays can therefore provide link- 887 layer bridging by sending packets into the SPAN instead of network- 888 layer routing according to MNP routes. As a result, opportunities 889 for packet loss due to node mobility between different segments are 890 mitigated. 892 With reference to Figure 3, for a Client's AERO address the SPAN 893 destination address is simply set to the Subnet-Router anycast 894 address. For non-link-local addresses, the destination SPAN address 895 may not be known in advance for the first few packets of a flow sent 896 via the SPAN. In that case, the SPAN destination address is set to 897 the original packet's destination, and the SPAN routing system will 898 direct the packet to the correct SPAN egress node. (In the above 899 example, the SPAN destination address is simply 900 2001:db8:1000:2000::1.) 902 3.5.1. SPAN Compatibility Addressing 904 For IPv4 MNPs, Servers inject a "SPAN Compatibility Prefix (SCP)" 905 that embeds the MNP into the BGP routing system. The SCP begins with 906 the upper 64 bits of the SSP, followed by the constant string 907 "0000:FFFF" followed by the IPv4 MNP. For example, if the MNP is 908 192.0.2.0/24 then the SCP is fd80::FFFF:192.0.2.0/120. 910 This allows for encapsulation of IPv4 packets in IPv6 headers with 911 "SPAN Compatibility Addresses (SCAs)". In this example, the SCA 912 corresponding to the SCP is simply fd80::FFFF:192.0.2.0, and can be 913 used as the SPAN destination address for packets forwarded via the 914 SPAN. This allows for forwarding of initial IPv4 packets over IPv6 915 SPAN routes, followed by route optimization for direct 916 communications. 918 3.5.2. Client SPAN Addresses 920 When an AERO Client or Proxy encapsulates and fragments a packet 921 (see: Section 3.12), it inserts its "Client SPAN Address" as the IPv6 922 source address of the encapsulation header. This is necessary to 923 provide reassemblers with a source address corresponding to the node 924 that actually inserted the fragment header so that the correct 925 Identification value context is provided. 927 The Client SPAN address is formed by simply clearing bit 7 of the 928 Client's AERO address. For example, for the Client AERO address 929 fe80::2001:db8:1:2 the corresponding Client SPAN address is 930 fd80::2001:db8:1:2. 932 Note that the Client's MNP itself (and not the Client SPAN address) 933 is injected into the routing system due to the /64 assumption in the 934 AERO address construction [RFC7421]. Because of the /64 assumption, 935 the most-significant 64 bits of the Client's MNP are written into the 936 least-significant 64 bits of the AERO address. If MNPs longer than 937 /64 are used in the future (i.e., /65 up to /118) the least- 938 significant bits of the MNP would need to be written into bits 10 939 through 63 of the SPAN address, which would render the address format 940 useless for longest-prefix-match. For more details, see Appendix B 941 of [I-D.templin-6man-omni-interface]. 943 3.6. AERO Interface Characteristics 945 AERO interfaces are virtual interfaces configured over one or more 946 underlying interfaces classified as follows: 948 o Native interfaces have global IP addresses that are reachable from 949 any INET correspondent. All Server, Gateway and Relay interfaces 950 are native interfaces, as are INET-facing interfaces of Proxys. 952 o NATed interfaces connect to a private network behind a Network 953 Address Translator (NAT). The NAT does not participate in any 954 AERO control message signaling, but the Server can issue control 955 messages on behalf of the Client. Clients that are behind a NAT 956 are required to send periodic keepalive messages to keep NAT state 957 alive when there are no data packets flowing. If no other 958 periodic messaging service is available, the Client can send RS 959 messages to receive RA replies from its Server(s). 961 o VPNed interfaces use security encapsulation to a Virtual Private 962 Network (VPN) server that also acts as an AERO Server. As with 963 NATed links, the Server can issue control messages on behalf of 964 the Client, but the Client need not send periodic keepalives in 965 addition to those already used to maintain the VPN connection. 967 o Proxyed interfaces connect to an ANET that is separated from the 968 open INET by an AERO Proxy. Unlike NATed and VPNed interfaces, 969 the Proxy can actively issue control messages on behalf of the 970 Client. 972 o Direct interfaces connect a Client directly to a neighbor without 973 crossing any ANET/INET paths. An example is a line-of-sight link 974 between a remote pilot and an unmanned aircraft. 976 AERO interfaces use encapsulation (see: Section 3.9) to exchange 977 packets with AERO link neighbors over Native, NATed or VPNed 978 interfaces. AERO interfaces do not use encapsulation over Proxyed 979 and Direct underlying interfaces. 981 AERO interfaces maintain a neighbor cache for tracking per-neighbor 982 state the same as for any interface. AERO interfaces use ND messages 983 including Router Solicitation (RS), Router Advertisement (RA), 984 Neighbor Solicitation (NS) and Neighbor Advertisement (NA) for 985 neighbor cache management. 987 AERO interfaces send ND messages with an Overlay Multilink Network 988 Interface (OMNI) option formatted as specified in 989 [I-D.templin-6man-omni-interface]. The OMNI option includes prefix 990 registration information and "ifIndex-tuples" containing link quality 991 information for the AERO interface's underlying interfaces. 993 When encapsulation is used, AERO interface ND messages MAY also 994 include an AERO Source/Target Link-Layer Address Option (S/TLLAO) 995 formatted as shown in Figure 4: 997 0 1 2 3 998 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 1 999 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1000 | Type | Length | ifIndex[1] |V| Reserved[1] | 1001 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1002 ~ Link Layer Address [1] ~ 1003 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1004 | Port Number [1] | ifIndex[2] |V| Reserved[2] | 1005 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1006 ~ Link Layer Address [2] ~ 1007 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1008 | Port Number [2] | ~ 1009 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ 1010 ~ ~ 1011 ~ ... ~ 1012 ~ ~ 1013 ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1014 ~ | ifIndex[N] |V| Reserved[N] | 1015 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1016 ~ Link Layer Address [N] ~ 1017 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1018 | Port Number [N] | Trailing zero padding | 1019 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1020 | Trailing zero padding (if necessary) | 1021 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1023 Figure 4: AERO Source/Target Link-Layer Address Option (S/TLLAO) 1024 Format 1026 In this format, Type and Length are set the same as specified for S/ 1027 TLLAOs in [RFC4861], with trailing zero padding octets added as 1028 necessary to produce an integral number of 8 octet blocks. The S/ 1029 TLLAO includes N ifIndex-tuples in correspondence to ifIndex-tuples 1030 that appear in the OMNI option. Each ifIndex-tuple includes the 1031 folllowing information: 1033 o ifIndex[i] - the same value as in the corresponding ifIndex-tuple 1034 included in the OMNI option. 1036 o V[i] - a bit that identifies the IP protocol version of the 1037 address found in the Link Layer Address [i] field. The bit is set 1038 to 0 for IPv4 or 1 for IPv6. 1040 o Reserved[i] - MUST encode the value 0 on transmission, and ignored 1041 on reception. 1043 o Link Layer Address [i] - the IPv4 or IPv6 address used as the 1044 encapsulation source address. The field is 4 bytes in length for 1045 IPv4 or 16 bytes in length for IPv6. 1047 o Port Number [i] - the upper layer protocol port number used as the 1048 encapsulation source port, or 0 when no upper layer protocol 1049 encapsulation is used. The field is 2 bytes in length. 1051 If an S/TLLAO is included, any ifIndex-tuples correspond to a proper 1052 subset of the OMNI option ifIndex-tuples. Any S/TLLAO ifIndex-tuple 1053 having an ifIndex value that does not appear in an OMNI option 1054 ifindex-tuple is ignored. If the same ifIndex value appears in 1055 multiple ifIndex-tuples, the first tuple is processed and the 1056 remaining tuples are ignored. Any S/TLLAO ifIndex-tuples can 1057 therefore be viewed as inter-dependent extensions of their 1058 corresponidng OMNI option ifIndex-tuples, i.e., the OMNI option and 1059 S/TLLAO are companions that are interpreted in conjunction with each 1060 other. 1062 A Client's AERO interface may be configured over multiple underlying 1063 interface connections. For example, common mobile handheld devices 1064 have both wireless local area network ("WLAN") and cellular wireless 1065 links. These links are typically used "one at a time" with low-cost 1066 WLAN preferred and highly-available cellular wireless as a standby. 1067 In a more complex example, aircraft frequently have many wireless 1068 data link types (e.g. satellite-based, cellular, terrestrial, air-to- 1069 air directional, etc.) with diverse performance and cost properties. 1071 If a Client's multiple underlying interfaces are used "one at a time" 1072 (i.e., all other interfaces are in standby mode while one interface 1073 is active), then ND message OMNI options include only a single 1074 ifIndex-tuple and set to a constant value. In that case, the Client 1075 would appear to have a single interface but with a dynamically 1076 changing link-layer address. 1078 If the Client has multiple active underlying interfaces, then from 1079 the perspective of ND it would appear to have multiple link-layer 1080 addresses. In that case, ND message OMNI options MAY include 1081 multiple ifIndex-tuples - each with a value that corresponds to a 1082 specific interface. Every ND message need not include all OMNI and/ 1083 or S/TLLAO ifIndex-tuples; for any ifIndex-tuple not included, the 1084 neighbor considers the status as unchanged. 1086 Relay, Server and Proxy AERO interfaces may be configured over one or 1087 more secured tunnel interfaces. The AERO interface configures both 1088 an AERO address and its corresponding SPAN address, while the 1089 underlying secured tunnel interfaces are either unnumbered or 1090 configure the same SPAN address. The AERO interface encapsulates 1091 each IP packet in a SPAN header and presents the packet to the 1092 underlying secured tunnel interface. For Relays that do not 1093 configure an AERO interface, the secured tunnel interfaces themselves 1094 are exposed to the IP layer with each interface configuring the 1095 Relay's SPAN address. Routing protocols such as BGP therefore run 1096 directly over the Relay's secured tunnel interfaces. For nodes that 1097 configure an AERO interface, routing protocols such as BGP run over 1098 the AERO interface but do not employ SPAN encapsulation. Instead, 1099 the AERO interface presents the routing protocol messages directly to 1100 the underlying secured tunnels without applying encapsulation and 1101 while using the SPAN address as the source address. This distinction 1102 must be honored consistently according to each node's configuration 1103 so that the IP forwarding table will associate discovered IP routes 1104 with the correct interface. 1106 3.7. AERO Interface Initialization 1108 AERO Servers, Proxys and Clients configure AERO interfaces as their 1109 point of attachment to the AERO link. AERO nodes assign the MSPs for 1110 the link to their AERO interfaces (i.e., as a "route-to-interface") 1111 to ensure that packets with destination addresses covered by an MNP 1112 not explicitly assigned to a non-AERO interface are directed to the 1113 AERO interface. 1115 AERO interface initialization procedures for Servers, Proxys, Clients 1116 and Relays are discussed in the following sections. 1118 3.7.1. AERO Server/Gateway Behavior 1120 When a Server enables an AERO interface, it assigns AERO/SPAN 1121 addresses and configures permanent neighbor cache entries for 1122 neighbors in the same SPAN segment by consulting the ROS list for the 1123 segment. The Server also configures secured tunnels with one or more 1124 neighboring Relays and engages in a BGP routing protocol session with 1125 each Relay. 1127 The AERO interface provides a single interface abstraction to the IP 1128 layer, but internally comprises multiple secured tunnels as well as 1129 an NBMA nexus for sending encapsulated data packets to AERO interface 1130 neighbors. The Server further configures a service to facilitate ND/ 1131 PD exchanges with AERO Clients and manages per-Client neighbor cache 1132 entries and IP forwarding table entries based on control message 1133 exchanges. 1135 Gateways are simply Servers that run a dynamic routing protocol 1136 between the AERO interface and INET/EUN interfaces (see: 1137 Section 3.3). The Gateway provisions MNPs to networks on the INET/ 1138 EUN interfaces (i.e., the same as a Client would do) and advertises 1139 the MSP(s) for the AERO link over the INET/EUN interfaces. The 1140 Gateway further provides an attachment point of the AERO link to the 1141 non-MNP-based global topology. 1143 3.7.2. AERO Proxy Behavior 1145 When a Proxy enables an AERO interface, it assigns AERO/SPAN 1146 addresses and configures permanent neighbor cache entries the same as 1147 for Servers. The Proxy also configures secured tunnels with one or 1148 more neighboring Relays and maintains per-Client neighbor cache 1149 entries based on control message exchanges. 1151 3.7.3. AERO Client Behavior 1153 When a Client enables an AERO interface, it sends an RS message with 1154 ND/PD parameters over an ANET interface to a Server in the MAP list, 1155 which returns an RA message with corresponding parameters. (The RS/ 1156 RA messages may pass through a Proxy in the case of a Client's 1157 Proxyed interface.) 1159 After the initial ND/PD message exchange, the Client assigns AERO 1160 addresses to the AERO interface based on the delegated prefix(es). 1161 The Client can then register additional ANET interfaces with the 1162 Server by sending an RS message over each ANET interface. 1164 3.7.4. AERO Relay Behavior 1166 AERO Relays need not connect directly to the AERO link, since they 1167 operate as link-layer forwarding devices instead of network layer 1168 routers. Configuration of AERO interfaces on Relays is therefore 1169 OPTIONAL, e.g., if an administrative interface is needed. Relays 1170 configure secured tunnels with Servers, Proxys and other Relays; they 1171 also configure AERO/SPAN addresses and permanent neighbor cache 1172 entries the same as Servers. Relays engage in a BGP routing protocol 1173 session with a subset of the Servers on the local SPAN segment, and 1174 with other Relays on the SPAN (see: Section 3.3). 1176 3.8. AERO Interface Neighbor Cache Maintenance 1178 Each AERO interface maintains a conceptual neighbor cache that 1179 includes an entry for each neighbor it communicates with on the AERO 1180 link per [RFC4861]. AERO interface neighbor cache entries are said 1181 to be one of "permanent", "symmetric", "asymmetric" or "proxy". 1183 Permanent neighbor cache entries are created through explicit 1184 administrative action; they have no timeout values and remain in 1185 place until explicitly deleted. AERO Servers and Proxys maintain 1186 permanent neighbor cache entries for all other Servers and Proxys 1187 within the same SPAN segment. Each entry maintains the mapping 1188 between the neighbor's network-layer AERO address and corresponding 1189 INET address. The list of all permanent neighbor cache entries for 1190 the SPAN segment is maintained in the segment's ROS list. 1192 Symmetric neighbor cache entries are created and maintained through 1193 RS/RA exchanges as specified in Section 3.15, and remain in place for 1194 durations bounded by ND/PD lifetimes. AERO Servers maintain 1195 symmetric neighbor cache entries for each of their associated 1196 Clients, and AERO Clients maintain symmetric neighbor cache entries 1197 for each of their associated Servers. The list of all Servers on the 1198 AERO link is maintained in the link's MAP list. 1200 Asymmetric neighbor cache entries are created or updated based on 1201 route optimization messaging as specified in Section 3.17, and are 1202 garbage-collected when keepalive timers expire. AERO route 1203 optimization sources (ROSs) maintain asymmetric neighbor cache 1204 entries for active targets with lifetimes based on ND messaging 1205 constants. Asymmetric neighbor cache entries are unidirectional 1206 since only the ROS (and not the target) creates an entry. 1208 Proxy neighbor cache entries are created and maintained by AERO 1209 Proxys when they process Client/Server ND/PD exchanges, and remain in 1210 place for durations bounded by ND/PD lifetimes. AERO Proxys maintain 1211 proxy neighbor cache entries for each of their associated Clients. 1212 Proxy neighbor cache entries track the Client state and the address 1213 of the Client's associated Server. 1215 To the list of neighbor cache entry states in Section 7.3.2 of 1216 [RFC4861], Proxy and Server AERO interfaces add an additional state 1217 DEPARTED that applies to symmetric and proxy neighbor cache entries 1218 for Clients that have recently departed. The interface sets a 1219 "DepartTime" variable for the neighbor cache entry to "DEPARTTIME" 1220 seconds. DepartTime is decremented unless a new ND message causes 1221 the state to return to REACHABLE. While a neighbor cache entry is in 1222 the DEPARTED state, packets destined to the target Client are 1223 forwarded to the Client's new location instead of being dropped. 1225 When DepartTime decrements to 0, the neighbor cache entry is deleted. 1226 It is RECOMMENDED that DEPARTTIME be set to the default constant 1227 value REACHABLETIME plus 10 seconds (40 seconds by default) to allow 1228 a window for packets in flight to be delivered while stale route 1229 optimization state may be present. 1231 When a target Server receives an authentic NS message used for route 1232 optimization, it searches for a symmetric neighbor cache entry for 1233 the target Client. The Server then returns a solicited NA message 1234 without creating a neighbor cache entry for the ROS, but creates or 1235 updates a target Client "Report List" entry for the ROS and sets a 1236 "ReportTime" variable for the entry to REPORTTIME seconds. The 1237 Server resets ReportTime when it receives a new authentic NS message, 1238 and otherwise decrements ReportTime while no authentic NS messages 1239 have been received. It is RECOMMENDED that REPORTTIME be set to the 1240 default constant value REACHABLETIME plus 10 seconds (40 seconds by 1241 default) to allow a window for route optimization to converge before 1242 ReportTime decrements below REACHABLETIME. 1244 When the ROS receives a solicited NA message response to its NS 1245 message used for route optimization, it creates or updates an 1246 asymmetric neighbor cache entry for the target network-layer and 1247 link-layer addresses. The ROS then (re)sets ReachableTime for the 1248 neighbor cache entry to REACHABLETIME seconds and uses this value to 1249 determine whether packets can be forwarded directly to the target, 1250 i.e., instead of via a default route. The ROS otherwise decrements 1251 ReachableTime while no further solicited NA messages arrive. It is 1252 RECOMMENDED that REACHABLETIME be set to the default constant value 1253 30 seconds as specified in [RFC4861]. 1255 The ROS also uses the value MAX_UNICAST_SOLICIT to limit the number 1256 of NS keepalives sent when a correspondent may have gone unreachable, 1257 the value MAX_RTR_SOLICITATIONS to limit the number of RS messages 1258 sent without receiving an RA and the value MAX_NEIGHBOR_ADVERTISEMENT 1259 to limit the number of unsolicited NAs that can be sent based on a 1260 single event. It is RECOMMENDED that MAX_UNICAST_SOLICIT, 1261 MAX_RTR_SOLICITATIONS and MAX_NEIGHBOR_ADVERTISEMENT be set to 3 the 1262 same as specified in [RFC4861]. 1264 Different values for DEPARTTIME, REPORTTIME, REACHABLETIME, 1265 MAX_UNICAST_SOLICIT, MAX_RTR_SOLCITATIONS and 1266 MAX_NEIGHBOR_ADVERTISEMENT MAY be administratively set; however, if 1267 different values are chosen, all nodes on the link MUST consistently 1268 configure the same values. Most importantly, DEPARTTIME and 1269 REPORTTIME SHOULD be set to a value that is sufficiently longer than 1270 REACHABLETIME to avoid packet loss due to stale route optimization 1271 state. 1273 3.9. AERO Interface Encapsulation and Re-encapsulation 1275 Client AERO interfaces avoid encapsulation over Direct underlying 1276 interfaces and Proxyed underlying interfaces for which the first-hop 1277 access router is AERO-aware. Other AERO interfaces encapsulate 1278 packets according to whether they are entering the AERO interface 1279 from the network layer or if they are being re-admitted into the same 1280 AERO link they arrived on. This latter form of encapsulation is 1281 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 3.12. 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 3.13. 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 A. 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 AERO interfaces observes the packet sizing and fragmentation 1323 considerations found in Section 3.12. 1325 3.10. AERO Interface Decapsulation 1327 AERO interfaces decapsulate packets destined either to the AERO node 1328 itself or to a destination reached via an interface other than the 1329 AERO interface the packet was received on. When the encapsulated 1330 packet arrives in multiple fragments, the AERO interface reassembles 1331 as discussed in Section 3.12. Further decapsulation steps are 1332 performed according to the appropriate encapsulation format 1333 specification. 1335 3.11. AERO Interface Data Origin Authentication 1337 AERO nodes employ simple data origin authentication procedures. In 1338 particular: 1340 o AERO Relays, Servers and Proxys accept encapsulated data packets 1341 and control messages received from secured tunnels. 1343 o AERO Servers and Proxys accept encapsulated data packets and NS 1344 messages used for Neighbor Unreachability Detection (NUD) received 1345 from a member of the target's Report List. 1347 o AERO Proxys and Clients accept packets that originate from within 1348 the same secured ANET. 1350 o AERO Clients and Gateways accept packets from downstream network 1351 correspondents based on ingress filtering. 1353 AERO nodes silently drop any packets that do not satisfy the above 1354 data origin authentication procedures. Further security 1355 considerations are discussed Section 6. 1357 3.12. AERO Interface MTU and Fragmentation 1359 All IPv6 interfaces are REQUIRED to configure a minimum Maximum 1360 Transmission Unit (MTU) of 1280 bytes [RFC8200]. (IPv4 interfaces 1361 have a smaller minimum MTU [RFC1122], but SHOULD also observe the 1362 IPv6 minimum MTU if possible.) The AERO link therefore MUST forward 1363 IPv6 packets of at least 1280 bytes without generating an IPv6 Path 1364 MTU Discovery (PMTUD) Packet Too Big (PTB) message [RFC8201]. 1366 The AERO interface configures an MTU of 9180 bytes [RFC2492]; the 1367 size is therefore not a reflection of the underlying interface MTUs, 1368 but rather determines the largest packet the AERO interface can 1369 forward or reassemble. 1371 The AERO interface can employ link-layer IPv6 encapsulation and 1372 fragmentation/reassembly per [RFC2473], but its use is OPTIONAL since 1373 correct operation will result in either case. Implementations that 1374 omit link-layer IPv6 fragmentation/reassembly may be more prone to 1375 dropping large packets and returning a PTB, while those that include 1376 it may see improved performance at the expense of including 1377 additional code. In both cases, AERO interface neighbors are 1378 responsible for advertising their willingness to reassemble. 1380 The AERO interface returns internally-generated PTB messages for 1381 packets admitted into the interface that it deems too large for the 1382 outbound underlying interface (e.g., according to underlying 1383 interface performance characteristics, MTU, etc). For all other 1384 packets, the AERO interface performs PMTUD even if the destination 1385 appears to be on the same link since a proxy on the path could return 1386 a PTB message. This ensures that the path MTU is adaptive and 1387 reflects the current path used for a given data flow. 1389 When a Client's AERO interface sends a packet that is no larger than 1390 the MTU of the selected underlying interface, it sends according to 1391 the underlying interface L2 frame format. When the AERO interface 1392 sends a packet that is larger than the underlying interface MTU, it 1393 drops the packet and returns a PTB if the neighbor is not willing to 1394 reassemble. 1396 Otherwise, the AERO interface encapsulates the packet in an IPv6 1397 header per [RFC2473] with source address set to the Client's link- 1398 local address and destination address set to the link-local address 1399 of the next hop. The AERO interface then uses IPv6 fragmentation to 1400 break the encapsulated packet into fragments that are no larger than 1401 the underlying interface MTU and sends the fragments over the 1402 underlying interface. The next hop then reassembles, then conveys 1403 the packets toward the final destination. 1405 When a Proxy or Server receives a fragmented or whole packet from the 1406 INET destined to a Client, it must determine whether to forward or 1407 drop and return a PTB (e.g., according to the underlying interface 1408 performance characteristics, MTU, etc). If the Proxy/Server deems 1409 the packet to be of acceptable size, it first reassembles locally (if 1410 necessary) then forwards the packet to the Client. If the 1411 (reassembled) packet is no larger than the underlying interface MTU, 1412 the Proxy/Server forwards according to the underlying interface L2 1413 frame format. If the packet is larger than the MTU, the Proxy/Server 1414 instead uses link-layer encapsulation and IPv6 fragmentation as above 1415 if the Client accepts fragments or drops and returns a PTB otherwise. 1416 The Client then reassembles and discards the encapsulation header, 1417 then forwards the whole packet to the final destination. 1419 When a Proxy, Server or Gateway forwards a Client's packet over the 1420 SPAN, it uses IPv6 encapsulation with the Client's SPAN address as 1421 the source address and the SPAN address of the next hop as the 1422 destination, then uses fragmentation to break the SPAN-encapsulated 1423 packet into pieces no larger than 1280 bytes. When a Server or 1424 Gateway forwards a Client's SPAN-encapsulated packet to a destination 1425 outside of the AERO link, it first reassembles if necessary. This 1426 implies that Proxys, Servers and Gateways MUST support fragmentation 1427 and reassembly for packet exchanges over the SPAN even though 1428 fragmentation and reassembly is OPTIONAL for Clients. 1430 Applications that cannot tolerate loss due to MTU restrictions SHOULD 1431 avoid sending packets larger than 1280 bytes, since dynamic path 1432 changes can reduce the path MTU at any time. Applications that may 1433 benefit from sending larger packets even though the path MTU may 1434 change dynamically MAY use larger sizes (i.e., up to the AERO 1435 interface MTU). 1437 Note that when a Proxy/Server forwards a fragmented packet received 1438 from the INET to a Client, it reassembles locally first instead of 1439 blindly forwarding fragments directly to the Client to avoid attacks 1440 such as tiny fragments, overlapping fragments, etc. 1442 Note also that the AERO interface can forward large packets via 1443 encapsulation and fragmentation while at the same time returning 1444 advisory PTB messages, e.g., subject to rate limiting. The interface 1445 can therefore continuously forward large packets without loss while 1446 sending advisory messages recommending a smaller size. Even more 1447 appropriately, the receiving OMNI node that performs reassembly can 1448 send advisory PTB messages if reassembly conditions are currently 1449 unfavorable. 1451 3.13. AERO Interface Forwarding Algorithm 1453 IP packets enter a node's AERO interface either from the network 1454 layer (i.e., from a local application or the IP forwarding system) or 1455 from the link layer (i.e., from an AERO interface neighbor). All 1456 packets entering a node's AERO interface first undergo data origin 1457 authentication as discussed in Section 3.11. Packets that satisfy 1458 data origin authentication are processed further, while all others 1459 are dropped silently. 1461 Packets that enter the AERO interface from the network layer are 1462 forwarded to an AERO interface neighbor. Packets that enter the AERO 1463 interface from the link layer are either re-admitted into the AERO 1464 link or forwarded to the network layer where they are subject to 1465 either local delivery or IP forwarding. In all cases, the AERO 1466 interface itself MUST NOT decrement the network layer TTL/Hop-count 1467 since its forwarding actions occur below the network layer. 1469 AERO interfaces may have multiple underlying interfaces and/or 1470 neighbor cache entries for neighbors with multiple ifIndex-tuple 1471 registrations (see Section 3.6). The AERO interface uses each 1472 packet's DSCP value (and/or other traffic discriminators such as port 1473 number) to select an outgoing underlying interface based on the 1474 node's own QoS preferences, and also to select a destination link- 1475 layer address based on the neighbor's underlying interface with the 1476 highest preference. AERO implementations SHOULD allow for QoS 1477 preference values to be modified at runtime through network 1478 management. 1480 If multiple outgoing interfaces and/or neighbor interfaces have a 1481 preference of "high", the AERO node replicates the packet and sends 1482 one copy via each of the (outgoing / neighbor) interface pairs; 1483 otherwise, the node sends a single copy of the packet via an 1484 interface with the highest preference. AERO nodes keep track of 1485 which underlying interfaces are currently "reachable" or 1486 "unreachable", and only use "reachable" interfaces for forwarding 1487 purposes. 1489 The following sections discuss the AERO interface forwarding 1490 algorithms for Clients, Proxys, Servers and Relays. In the following 1491 discussion, a packet's destination address is said to "match" if it 1492 is the same as a cached address, or if it is covered by a cached 1493 prefix (which may be encoded in an AERO address). 1495 3.13.1. Client Forwarding Algorithm 1497 When an IP packet enters a Client's AERO interface from the network 1498 layer the Client searches for an asymmetric neighbor cache entry that 1499 matches the destination. If there is a match, the Client uses one or 1500 more "reachable" neighbor interfaces in the entry for packet 1501 forwarding. If there is no asymmetric neighbor cache entry, the 1502 Client instead forwards the packet toward a Server (the packet is 1503 intercepted by a Proxy if there is a Proxy on the path). The Client 1504 inserts a SPAN header and fragments if necessary according to MTU 1505 requirements (see: Section 3.12). 1507 When an IP packet enters a Client's AERO interface from the link- 1508 layer, if the destination matches one of the Client's MNPs or link- 1509 local addresses the Client reassembles and decapsulates the packet as 1510 necessary and delivers it to the network layer. Otherwise, the 1511 Client drops the packet and MAY return a network-layer ICMP 1512 Destination Unreachable message subject to rate limiting (see: 1513 Section 3.14). 1515 3.13.2. Proxy Forwarding Algorithm 1517 For control messages originating from or destined to a Client, the 1518 Proxy intercepts the message and updates its proxy neighbor cache 1519 entry for the Client. The Proxy then forwards a (proxyed) copy of 1520 the control message. (For example, the Proxy forwards a proxied 1521 version of a Client's NS/RS message to the target neighbor, and 1522 forwards a proxied version of the NA/RA reply to the Client.) 1524 When the Proxy receives a data packet from a Client within the ANET, 1525 it first inserts a SPAN header if the packet does not already contain 1526 a SPAN header. The Proxy then sets/changes the SPAN header source 1527 address to the Client's SPAN address and changes the destination 1528 address to the SPAN address of the next hop. The Proxy then 1529 fragments the SPAN packet into fragments no larger than 1280 bytes, 1530 then searches for an asymmetric neighbor cache entry that matches the 1531 destination and forwards the fragments as follows: 1533 o if the destination matches an asymmetric neighbor cache entry, the 1534 Proxy uses one or more "reachable" neighbor interfaces in the 1535 entry for packet forwarding via encapsulation. If the neighbor 1536 interface is in the same SPAN segment, the Proxy forwards the 1537 packet directly to the neighbor; otherwise, it forwards the packet 1538 to a Relay. 1540 o else, the Proxy encapsulates and forwards the packet to a Relay 1541 while using the packet's destination address as the SPAN 1542 destination address. (If the destination is an AERO address, the 1543 Proxy instead uses the corresponding Subnet-Router anycast address 1544 for Client AERO addresses and the SPAN address for 1545 administratively-provisioned AERO addresses.). 1547 When the Proxy receives an encapsulated data packet from an INET 1548 neighbor or from a secured tunnel from a Relay, it accepts the packet 1549 only if data origin authentication succeeds and if there is a proxy 1550 neighbor cache entry that matches the inner destination. Next, if 1551 the packet is a SPAN fragment the Proxy adds the fragment to the 1552 reassembly buffer. The Proxy then reassembles the packet (if 1553 necessary) and continues processing. 1555 Next if reassembly is complete and the neighbor cache state is 1556 REACHABLE, the Proxy either drops and returns a PTB (see: 1557 Section 3.12) or forwards the packet to the Client while performing 1558 SPAN encapsulation and re-fragmentation to the ANET MTU size if 1559 necessary. If the neighbor cache entry state is DEPARTED, the Proxy 1560 instead changes the SPAN destination address to the address of the 1561 new Server and forwards it to a Relay while performing re- 1562 fragmentation to 1280 bytes if necessary. 1564 When the Proxy forwards a SPAN packet to a REACHABLE Client for which 1565 the packet is no larger than the ANET MTU, it decapsulates the SPAN 1566 header first and forwards the (unencapsulated) packet to the Client 1567 to avoid the unnecessary overhead for carrying the SPAN header. Note 1568 also that the Proxy can alternatively hold SPAN fragments for a 1569 DEPARTED Client in its local reassembly buffer, or forward the 1570 fragments to the Client's new Server if it does not already have a 1571 partial reassembly already in progress. 1573 3.13.3. Server/Gateway Forwarding Algorithm 1575 For control messages destined to a target Client's AERO address that 1576 are received from a secured tunnel, the Server intercepts the message 1577 and sends an appropriate response on behalf of the Client. (For 1578 example, the Server sends an NA message reply in response to an NS 1579 message directed to one of its associated Clients.) If the Client's 1580 neighbor cache entry is in the DEPARTED state, however, the Server 1581 instead forwards the packet to the Client's new Server as discussed 1582 in Section 3.19. 1584 When the Server receives an encapsulated data packet from an INET 1585 neighbor or from a secured tunnel, it accepts the packet only if data 1586 origin authentication succeeds. If the SPAN destination address is 1587 its own address, the Server continues processing as follows: 1589 o if the destination matches a symmetric neighbor cache entry in the 1590 REACHABLE state the Server prepares the packet for forwarding to 1591 the destination Client. For the Client's Proxyed interfaces, the 1592 Server changes the SPAN destination address to the address of the 1593 Proxy and forwards the packet to the Proxy. For the Client's 1594 other interfaces, the Server reassembles then either drops and 1595 returns a PTB (see: Section 3.12) or forwards the packet (while 1596 re-fragmenting if necessary) using SPAN encapsulation for the 1597 Client's Native, NATed or VPNed interfaces, or no encapsulation 1598 for Direct interfaces. 1600 o else, if the destination matches a symmetric neighbor cache entry 1601 in the DEPARETED state the Server re-encapsulates the packet and 1602 forwards it using the SPAN address of the Client's new Server as 1603 the destination. 1605 o else, if the destination matches an asymmetric neighbor cache 1606 entry, the Server uses one or more "reachable" neighbor interfaces 1607 in the entry for packet forwarding via the local INET if the 1608 neighbor is in the same SPAN segment or via a Relay otherwise. 1610 o else, if the destination is an AERO address that is not assigned 1611 on the AERO interface the Server drops the packet. 1613 o else, the Server (acting as a Gateway) reassembles if necessary, 1614 decapsulates the packet and releases it to the network layer for 1615 local delivery or IP forwarding. Based on the information in the 1616 forwarding table, the network layer may return the packet to the 1617 same AERO interface in which case further processing occurs as 1618 below. (Note that this arrangement accommodates common 1619 implementations in which the IP forwarding table is not accessible 1620 from within the AERO interface. If the AERO interface can 1621 directly access the IP forwarding table (such as for in-kernel 1622 implementations) the forwarding table lookup can instead be 1623 performed internally from within the AERO interface itself.) 1625 When the Server's AERO interface receives a data packet from the 1626 network layer or from a NATed/VPNed/Direct Client, it performs SPAN 1627 encapsualtion and fragmentation if necessary, then processes the 1628 packet according to the network-layer destination address as follows: 1630 o if the destination matches a symmetric or asymmetric neighbor 1631 cache entry the Server processes the packet as above. 1633 o else, the Server encapsulates the packet and forwards it to a 1634 Relay. For administratively-assigned AERO address destinations, 1635 the Server uses the SPAN address corresponding to the destination 1636 as the SPAN destination address. For Client AERO address 1637 destinations, the Server uses the Subnet-Router anycast address 1638 corresponding to the destination as the SPAN destination address. 1639 For all others, the Server uses the packet's destination IP 1640 address as the SPAN destination address. 1642 3.13.4. Relay Forwarding Algorithm 1644 Relays forward packets over secured tunnels the same as any IP 1645 router. When the Relay receives an encapsulated packet via a secured 1646 tunnel, it removes the INET header and searches for a forwarding 1647 table entry that matches the destination address in the next header. 1648 The Relay then processes the packet as follows: 1650 o if the destination matches one of the Relay's own addresses, the 1651 Relay submits the packet for local delivery. 1653 o else, if the destination matches a forwarding table entry the 1654 Relay forwards the packet via a secured tunnel to the next hop. 1655 If the destination matches an MSP without matching an MNP, 1656 however, the Relay instead drops the packet and returns an ICMP 1657 Destination Unreachable message subject to rate limiting (see: 1658 Section 3.14). 1660 o else, the Relay drops the packet and returns an ICMP Destination 1661 Unreachable as above. 1663 As for any IP router, the Relay decrements the TTL/Hop Limit when it 1664 forwards the packet. If the packet is encapsulated in a SPAN header, 1665 only the Hop Limit in the SPAN header is decremented, and not the 1666 TTL/Hop Limit in the inner packet header. 1668 3.14. AERO Interface Error Handling 1670 When an AERO node admits a packet into the AERO interface, it may 1671 receive link-layer or network-layer error indications. 1673 A link-layer error indication is an ICMP error message generated by a 1674 router in the INET on the path to the neighbor or by the neighbor 1675 itself. The message includes an IP header with the address of the 1676 node that generated the error as the source address and with the 1677 link-layer address of the AERO node as the destination address. 1679 The IP header is followed by an ICMP header that includes an error 1680 Type, Code and Checksum. Valid type values include "Destination 1681 Unreachable", "Time Exceeded" and "Parameter Problem" 1682 [RFC0792][RFC4443]. (AERO interfaces ignore all link-layer IPv4 1683 "Fragmentation Needed" and IPv6 "Packet Too Big" messages since they 1684 only emit packets that are guaranteed to be no larger than the IP 1685 minimum link MTU as discussed in Section 3.12.) 1687 The ICMP header is followed by the leading portion of the packet that 1688 generated the error, also known as the "packet-in-error". For 1689 ICMPv6, [RFC4443] specifies that the packet-in-error includes: "As 1690 much of invoking packet as possible without the ICMPv6 packet 1691 exceeding the minimum IPv6 MTU" (i.e., no more than 1280 bytes). For 1692 ICMPv4, [RFC0792] specifies that the packet-in-error includes: 1693 "Internet Header + 64 bits of Original Data Datagram", however 1694 [RFC1812] Section 4.3.2.3 updates this specification by stating: "the 1695 ICMP datagram SHOULD contain as much of the original datagram as 1696 possible without the length of the ICMP datagram exceeding 576 1697 bytes". 1699 The link-layer error message format is shown in Figure 5 (where, "L2" 1700 and "L3" refer to link-layer and network-layer, respectively): 1702 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1703 ~ ~ 1704 | L2 IP Header of | 1705 | error message | 1706 ~ ~ 1707 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1708 | L2 ICMP Header | 1709 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 1710 ~ ~ P 1711 | IP and other encapsulation | a 1712 | headers of original L3 packet | c 1713 ~ ~ k 1714 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ e 1715 ~ ~ t 1716 | IP header of | 1717 | original L3 packet | i 1718 ~ ~ n 1719 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1720 ~ ~ e 1721 | Upper layer headers and | r 1722 | leading portion of body | r 1723 | of the original L3 packet | o 1724 ~ ~ r 1725 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 1727 Figure 5: AERO Interface Link-Layer Error Message Format 1729 The AERO node rules for processing these link-layer error messages 1730 are as follows: 1732 o When an AERO node receives a link-layer Parameter Problem message, 1733 it processes the message the same as described as for ordinary 1734 ICMP errors in the normative references [RFC0792][RFC4443]. 1736 o When an AERO node receives persistent link-layer Time Exceeded 1737 messages, the IP ID field may be wrapping before earlier fragments 1738 awaiting reassembly have been processed. In that case, the node 1739 should begin including integrity checks and/or institute rate 1740 limits for subsequent packets. 1742 o When an AERO node receives persistent link-layer Destination 1743 Unreachable messages in response to encapsulated packets that it 1744 sends to one of its asymmetric neighbor correspondents, the node 1745 should process the message as an indication that a path may be 1746 failing, and optionally initiate NUD over that path. If it 1747 receives Destination Unreachable messages over multiple paths, the 1748 node should allow future packets destined to the correspondent to 1749 flow through a default route and re-initiate route optimization. 1751 o When an AERO Client receives persistent link-layer Destination 1752 Unreachable messages in response to encapsulated packets that it 1753 sends to one of its symmetric neighbor Servers, the Client should 1754 mark the path as unusable and use another path. If it receives 1755 Destination Unreachable messages on many or all paths, the Client 1756 should associate with a new Server and release its association 1757 with the old Server as specified in Section 3.19.5. 1759 o When an AERO Server receives persistent link-layer Destination 1760 Unreachable messages in response to encapsulated packets that it 1761 sends to one of its symmetric neighbor Clients, the Server should 1762 mark the underlying path as unusable and use another underlying 1763 path. 1765 o When an AERO Server or Proxy receives link-layer Destination 1766 Unreachable messages in response to an encapsulated packet that it 1767 sends to one of its permanent neighbors, it treats the messages as 1768 an indication that the path to the neighbor may be failing. 1769 However, the dynamic routing protocol should soon reconverge and 1770 correct the temporary outage. 1772 When an AERO Relay receives a packet for which the network-layer 1773 destination address is covered by an MSP, if there is no more- 1774 specific routing information for the destination the Relay drops the 1775 packet and returns a network-layer Destination Unreachable message 1776 subject to rate limiting. The Relay writes the network-layer source 1777 address of the original packet as the destination address and uses 1778 one of its non link-local addresses as the source address of the 1779 message. 1781 When an AERO node receives an encapsulated packet for which the 1782 reassembly buffer it too small, it drops the packet and returns a 1783 network-layer Packet Too Big (PTB) message. The node first writes 1784 the MRU value into the PTB message MTU field, writes the network- 1785 layer source address of the original packet as the destination 1786 address and writes one of its non link-local addresses as the source 1787 address. 1789 3.15. AERO Router Discovery, Prefix Delegation and Autoconfiguration 1791 AERO Router Discovery, Prefix Delegation and Autoconfiguration are 1792 coordinated as discussed in the following Sections. 1794 3.15.1. AERO ND/PD Service Model 1796 Each AERO Server on the link configures a PD service to facilitate 1797 Client requests. Each Server is provisioned with a database of MNP- 1798 to-Client ID mappings for all Clients enrolled in the AERO service, 1799 as well as any information necessary to authenticate each Client. 1800 The Client database is maintained by a central administrative 1801 authority for the AERO link and securely distributed to all Servers, 1802 e.g., via the Lightweight Directory Access Protocol (LDAP) [RFC4511], 1803 via static configuration, etc. Clients receive the same service 1804 regardless of the Servers they select. 1806 AERO Clients and Servers use ND messages to maintain neighbor cache 1807 entries. AERO Servers configure their AERO interfaces as advertising 1808 NBMA interfaces, and therefore send unicast RA messages with a short 1809 Router Lifetime value (e.g., REACHABLETIME seconds) in response to a 1810 Client's RS message. Thereafter, Clients send additional RS messages 1811 to keep Server state alive. 1813 AERO Clients and Servers include PD parameters in RS/RA messages (see 1814 [I-D.templin-6man-dhcpv6-ndopt] for ND/PD alternatives). The unified 1815 ND/PD messages are exchanged between Client and Server according to 1816 the prefix management schedule required by the PD service. If the 1817 Client knows its MNP in advance, it can instead employ prefix 1818 registration by including its AERO address as the source address of 1819 an RS message and with an OMNI option with valid prefix registration 1820 information for the MNP. If the Server (and Proxy) accept the 1821 Client's MNP assertion, they inject the prefix into the routing 1822 system and establish the necessary neighbor cache state. 1824 The following sections specify the Client and Server behavior. 1826 3.15.2. AERO Client Behavior 1828 AERO Clients discover the addresses of Servers in a similar manner as 1829 described in [RFC5214]. Discovery methods include static 1830 configuration (e.g., from a flat-file map of Server addresses and 1831 locations), or through an automated means such as Domain Name System 1832 (DNS) name resolution [RFC1035]. Alternatively, the Client can 1833 discover Server addresses through a layer 2 data link login exchange, 1834 or through a unicast RA response to a multicast/anycast RS as 1835 described below. In the absence of other information, the Client can 1836 resolve the DNS Fully-Qualified Domain Name (FQDN) 1837 "linkupnetworks.[domainname]" where "linkupnetworks" is a constant 1838 text string and "[domainname]" is a DNS suffix for the AERO link 1839 (e.g., "example.com"). 1841 To associate with a Server, the Client acts as a requesting router to 1842 request MNPs. The Client prepares an RS message with PD parameters 1843 and includes a Nonce and Timestamp option if the Client needs to 1844 correlate RA replies. If the Client already knows the Server's AERO 1845 address, it includes the AERO address as the network-layer 1846 destination address; otherwise, it includes the link-scoped All- 1847 Routers multicast (ff02::2) or Subnet-Router anycast (fe80::) address 1848 as the network-layer destination. If the Client already knows its 1849 own AERO address, it uses the AERO address as the network-layer 1850 source address; otherwise, it uses the unspecified IPv6 address 1851 (::/128) as the network-layer source address. 1853 The Client next includes an OMNI option in the RS message to register 1854 its link-layer information with the Server. The Client sets the OMNI 1855 option prefix registration information according to the MNP, and 1856 includes an ifIndex-tuple with S set to '1' corresponding to the 1857 underlying interface over which the Client will send the RS message. 1858 The Client MAY include additional ifIndex-tuples specific to other 1859 underlying interfaces. The Client MAY also include an SLLAO with a 1860 link-layer address corresponding to the OMNI option ifIndex-tuple 1861 with S set to '1'. 1863 The Client then sends the RS message (either directly via Direct 1864 interfaces, via INET encapsulation for NATed interfaces, via a VPN 1865 for VPNed interfaces, via a Proxy for proxyed interfaces or via a 1866 Relay for native interfaces) and waits for an RA message reply (see 1867 Section 3.15.3). The Client retries up to MAX_RTR_SOLICITATIONS 1868 times until an RA is received. If the Client receives no RAs, or if 1869 it receives an RA with Router Lifetime set to 0, the Client SHOULD 1870 abandon this Server and try another Server. Otherwise, the Client 1871 processes the PD information found in the RA message. 1873 Next, the Client creates a symmetric neighbor cache entry with the 1874 Server's AERO address as the network-layer address and the Server's 1875 encapsulation and/or link-layer addresses as the link-layer address. 1876 The Client records the RA Router Lifetime field value in the neighbor 1877 cache entry as the time for which the Server has committed to 1878 maintaining the MNP in the routing system via this underlying 1879 interface, and caches the other RA configuration information 1880 including Cur Hop Limit, M and O flags, Reachable Time and Retrans 1881 Timer. The Client then autoconfigures AERO addresses for each of the 1882 delegated MNPs and assigns them to the AERO interface. The Client 1883 also caches any MSPs included in Route Information Options (RIOs) 1884 [RFC4191] as MSPs to associate with the AERO link, and assigns the 1885 MTU value in the MTU option to the underlying interface. 1887 The Client then registers additional underlying interfaces with the 1888 Server by sending RS messages via each additional interface. The RS 1889 messages include the same parameters as for the initial RS/RA 1890 exchange, but with destination address set to the Server's AERO 1891 address. 1893 Following autoconfiguration, the Client sub-delegates the MNPs to its 1894 attached EUNs and/or the Client's own internal virtual interfaces as 1895 described in [I-D.templin-v6ops-pdhost] to support the Client's 1896 downstream attached "Internet of Things (IoT)". The Client 1897 subsequently sends additional RS messages over each underlying 1898 interface before the Router Lifetime received for that interface 1899 expires. 1901 After the Client registers its underlying interfaces, it may wish to 1902 change one or more registrations, e.g., if an interface changes 1903 address or becomes unavailable, if QoS preferences change, etc. To 1904 do so, the Client prepares an RS message to send over any available 1905 underlying interface. The RS includes an OMNI option with prefix 1906 registration information specific to its MNP, with an ifIndex-tuple 1907 specific to the selected underlying interface with S set to '1', and 1908 with any additional ifIndex-tuples specific to other underlying 1909 interfaces. The Client includes fresh ifIndex-tuple values to update 1910 the Server's neighbor cache entry. When the Client receives the 1911 Server's RA response, it has assurance that the Server has been 1912 updated with the new information. 1914 If the Client wishes to discontinue use of a Server it issues an RS 1915 message over any underlying interface with an OMNI option with a 1916 prefix release indication. When the Server processes the message, it 1917 releases the MNP, sets the symmetric neighbor cache entry state for 1918 the Client to DEPARTED and returns an RA reply with Router Lifetime 1919 set to 0. After a short delay (e.g., 2 seconds), the Server 1920 withdraws the MNP from the routing system. 1922 3.15.3. AERO Server Behavior 1924 AERO Servers act as IP routers and support a PD service for Clients. 1925 Servers arrange to add their AERO addresses to a static map of Server 1926 addresses for the link and/or the DNS resource records for the FQDN 1927 "linkupnetworks.[domainname]" before entering service. Server 1928 addresses should be geographically and/or topologically referenced, 1929 and made available for discovery by Clients on the AERO link. 1931 When a Server receives a prospective Client's RS message on its AERO 1932 interface, it SHOULD return an immediate RA reply with Router 1933 Lifetime set to 0 if it is currently too busy or otherwise unable to 1934 service the Client. Otherwise, the Server authenticates the RS 1935 message and processes the PD parameters. The Server first determines 1936 the correct MNPs to delegate to the Client by searching the Client 1937 database. When the Server delegates the MNPs, it also creates a 1938 forwarding table entry for each MNP so that the MNPs are propagated 1939 into the routing system (see: Section 3.3). For IPv6, the Server 1940 creates an IPv6 forwarding table entry for each MNP. For IPv4, the 1941 Server creates an IPv6 forwarding table entry with the SPAN 1942 Compatibility Prefix (SCP) corresponding to the IPv4 address. 1944 The Server next creates a symmetric neighbor cache entry for the 1945 Client using the base AERO address as the network-layer address and 1946 with lifetime set to no more than the smallest PD lifetime. Next, 1947 the Server updates the neighbor cache entry by recording the 1948 information in each ifIndex-tuple in the RS OMNI option. The Server 1949 also records the actual SPAN/INET addresses in the neighbor cache 1950 entry. If an SLLAO was present, the Server also compares the SLLAO 1951 address information for the first ifIndex-tuple with the SPAN/INET 1952 information to determine if there is a NAT on the path. 1954 Next, the Server prepares an RA message using its AERO address as the 1955 network-layer source address and the network-layer source address of 1956 the RS message as the network-layer destination address. The Server 1957 sets the Router Lifetime to the time for which it will maintain both 1958 this underlying interface individually and the symmetric neighbor 1959 cache entry as a whole. The Server also sets Cur Hop Limit, M and O 1960 flags, Reachable Time and Retrans Timer to values appropriate for the 1961 AERO link. The Server includes the delegated MNPs, any other PD 1962 parameters and an OMNI option with no ifIndex-tuples. The Server 1963 then includes one or more RIOs that encode the MSPs for the AERO 1964 link, plus an MTU option (see Section 3.12). The Server finally 1965 forwards the message to the Client using SPAN/INET, INET, or NULL 1966 encapsulation as necessary. 1968 After the initial RS/RA exchange, the Server maintains a 1969 ReachableTime timer for each of the Client's underlying interfaces 1970 individually (and for the Client's symmetric neighbor cache entry 1971 collectively) set to expire after Router Lifetime seconds. If the 1972 Client (or Proxy) issues additional RS messages, the Server sends an 1973 RA response and resets ReachableTime. If the Server receives an ND 1974 message with PD release indication it sets the Client's symmetric 1975 neighbor cache entry to the DEPARTED state and withdraws the MNP from 1976 the routing system after a short delay (e.g., 2 seconds). If 1977 ReachableTime expires before a new RS is received on an individual 1978 underlying interface, the Server marks the interface as DOWN. If 1979 ReachableTime expires before any new RS is received on any individual 1980 underlying interface, the Server deletes the neighbor cache entry and 1981 withdraws the MNP without delay. 1983 The Server processes any ND/PD messages pertaining to the Client and 1984 returns an NA/RA reply in response to solicitations. The Server may 1985 also issue unsolicited RA messages, e.g., with PD reconfigure 1986 parameters to cause the Client to renegotiate its PDs, with Router 1987 Lifetime set to 0 if it can no longer service this Client, etc. 1988 Finally, If the symmetric neighbor cache entry is in the DEPARTED 1989 state, the Server deletes the entry after DepartTime expires. 1991 Note: Clients SHOULD notify former Servers of their departures, but 1992 Servers are responsible for expiring neighbor cache entries and 1993 withdrawing routes even if no departure notification is received 1994 (e.g., if the Client leaves the network unexpectedly). Servers 1995 SHOULD therefore set Router Lifetime to REACHABLETIME seconds in 1996 solicited RA messages to minimize persistent stale cache information 1997 in the absence of Client departure notifications. A short Router 1998 Lifetime also ensures that proactive Client/Server RS/RA messaging 1999 will keep any NAT state alive (see above). 2001 Note: All Servers on an AERO link MUST advertise consistent values in 2002 the RA Cur Hop Limit, M and O flags, Reachable Time and Retrans Timer 2003 fields the same as for any link, since unpredictable behavior could 2004 result if different Servers on the same link advertised different 2005 values. 2007 3.15.3.1. Lightweight DHCPv6 Relay Agent (LDRA) 2009 When DHCPv6 is used as the ND/PD service back end, AERO Clients and 2010 Servers are always on the same link (i.e., the AERO link) from the 2011 perspective of DHCPv6. However, in some implementations the DHCPv6 2012 server and ND function may be located in separate modules. In that 2013 case, the Server's AERO interface module can act as a Lightweight 2014 DHCPv6 Relay Agent (LDRA)[RFC6221] to relay PD messages to and from 2015 the DHCPv6 server module. 2017 When the LDRA receives an authentic RS message, it extracts the PD 2018 message parameters and uses them to construct an IPv6/UDP/DHCPv6 2019 message. It sets the IPv6 source address to the source address of 2020 the RS message, sets the IPv6 destination address to 2021 'All_DHCP_Relay_Agents_and_Servers' and sets the UDP fields to values 2022 that will be understood by the DHCPv6 server. 2024 The LDRA then wraps the message in a DHCPv6 'Relay-Forward' message 2025 header and includes an 'Interface-Id' option that includes enough 2026 information to allow the LDRA to forward the resulting Reply message 2027 back to the Client (e.g., the Client's link-layer addresses, a 2028 security association identifier, etc.). The LDRA also wraps the OMNI 2029 option and SLLAO into the Interface-Id option, then forwards the 2030 message to the DHCPv6 server. 2032 When the DHCPv6 server prepares a Reply message, it wraps the message 2033 in a 'Relay-Reply' message and echoes the Interface-Id option. The 2034 DHCPv6 server then delivers the Relay-Reply message to the LDRA, 2035 which discards the Relay-Reply wrapper and IPv6/UDP headers, then 2036 uses the DHCPv6 message to construct an RA response to the Client. 2037 The Server uses the information in the Interface-Id option to prepare 2038 the RA message and to cache the link-layer addresses taken from the 2039 OMNI option and SLLAO echoed in the Interface-Id option. 2041 3.16. The AERO Proxy 2043 Clients may connect to ANETs that deploy perimeter security services 2044 to facilitate communications to Servers in outside INETs. In that 2045 case, the ANET can employ an AERO Proxy. The Proxy is located at the 2046 ANET/INET border and listens for RS messages originating from or RA 2047 messages destined to ANET Clients. The Proxy acts on these control 2048 messages as follows: 2050 o when the Proxy receives an RS message from a new ANET Client, it 2051 first authenticates the message then examines the network-layer 2052 destination address. If the destination address is a Server's 2053 AERO address, the Proxy proceeds to the next step. Otherwise, if 2054 the destination is All-Routers multicast or Subnet-Router anycast, 2055 the Proxy selects a "nearby" Server that is likely to be a good 2056 candidate to serve the Client and replaces the destination address 2057 with the Server's AERO address. Next, the Proxy creates a proxy 2058 neighbor cache entry and caches the Client and Server link-layer 2059 addresses along with the OMNI option information and any other 2060 identifying information including Transaction IDs, Client 2061 Identifiers, Nonce values, etc. The Proxy finally encapsulates 2062 the (proxyed) RS message in a SPAN header with destination set to 2063 the Server's SPAN address then forwards the message into the SPAN. 2065 o when the Server receives the RS, it authenticates the message then 2066 creates or updates a symmetric neighbor cache entry for the Client 2067 with the Proxy's SPAN address as the link-layer address. The 2068 Server then sends an RA message back to the Proxy via the SPAN. 2070 o when the Proxy receives the RA, it authenticates the message and 2071 matches it with the proxy neighbor cache entry created by the RS. 2072 The Proxy then caches the PD route information as a mapping from 2073 the Client's MNPs to the Client's ANET address, caches the 2074 Server's advertised Router Lifetime and sets the neighbor cache 2075 entry state to REACHABLE. The Proxy then sets the P bit in the RA 2076 flags field, optionally rewrites the Router Lifetime and forwards 2077 the (proxyed) message to the Client. The Proxy finally includes 2078 an MTU option (if necessary) with an MTU to use for the underlying 2079 ANET interface. 2081 After the initial RS/RA exchange, the Proxy forwards any Client data 2082 packets for which there is no matching asymmetric neighbor cache 2083 entry to a Relay via the SPAN. The Proxy instead forwards any Client 2084 data destined to an asymmetric neighbor cache target directly to the 2085 target according to the link-layer information - the process of 2086 establishing asymmetric neighbor cache entries is specified in 2087 Section 3.17. 2089 While the Client is still attached to the ANET, the Proxy sends NS, 2090 RS and/or unsolicited NA messages to update the Server's symmetric 2091 neighbor cache entries on behalf of the Client and/or to convey QoS 2092 updates. This allows for higher-frequency Proxy-initiated RS/RA 2093 messaging over well-connected INET infrastructure supplemented by 2094 lower-frequency Client-initiated RS/RA messaging over constrained 2095 ANET data links. 2097 If the Server ceases to send solicited advertisements, the Proxy 2098 sends unsolicited RAs on the ANET interface with destination set to 2099 All-Nodes multicast (ff02::1) and with Router Lifetime set to zero to 2100 inform Clients that the Server has failed. Although the Proxy 2101 engages in ND exchanges on behalf of the Client, the Client can also 2102 send ND messages on its own behalf, e.g., if it is in a better 2103 position than the Proxy to convey QoS changes, etc. For this reason, 2104 the Proxy marks any Client-originated solicitation messages (e.g. by 2105 inserting a Nonce option) so that it can return the solicited 2106 advertisement to the Client instead of processsing it locally. 2108 If the Client becomes unreachable, the Proxy sets the neighbor cache 2109 entry state to DEPARTED and retains the entry for DEPARTTIME seconds. 2110 While the state is DEPARTED, the Proxy forwards any packets destined 2111 to the Client to a Relay. The Relay in turn forwards the packets to 2112 the Client's current Server. When DepartTime expires, the Proxy 2113 deletes the neighbor cache entry and discards any further packets 2114 destined to this (now forgotten) Client. 2116 When a neighbor cache entry transitions to DEPARTED, some of the 2117 fragments of a multiple fragment packet may have already arrived at 2118 the Proxy while others are en route to the Client's new location, 2119 however no special attention in the reassembly algorithm is necessary 2120 when re-routed packets are simply treated as loss. 2122 In some ANETs that employ a Proxy, the Client's MNP can be injected 2123 into the ANET routing system. In that case, the Client can send data 2124 messages without encapsulation so that the ANET native routing system 2125 transports the unencapsulated packets to the Proxy. This can be very 2126 beneficial, e.g., if the Client connects to the ANET via low-end data 2127 links such as some aviation wireless links. 2129 If the first-hop ANET access router is AERO-aware, the Client can 2130 avoid encapsulation for both its control and data messages. When the 2131 Client connects to the link, it can send an unencapsulated RS message 2132 with source address set to its AERO address and with destination 2133 address set to the AERO address of the Client's selected Server or to 2134 All-Routers multicast or Subnet-Router anycast. The Client includes 2135 an OMNI option formatted as specified in 2136 [I-D.templin-6man-omni-interface]. 2138 The Client then sends the unencapsulated RS message, which will be 2139 intercepted by the AERO-Aware access router. The access router then 2140 encapsulates the RS message in an ANET header with its own address as 2141 the source address and the address of a Proxy as the destination 2142 address. The access router further remembers the address of the 2143 Proxy so that it can encapsulate future data packets from the Client 2144 via the same Proxy. If the access router needs to change to a new 2145 Proxy, it simply sends another RS message toward the Server via the 2146 new Proxy on behalf of the Client. 2148 In some cases, the access router and Proxy may be one and the same 2149 node. In that case, the node would be located on the same physical 2150 link as the Client, but its message exchanges with the Server would 2151 need to pass through a security gateway at the ANET/INET border. The 2152 method for deploying access routers and Proxys (i.e. as a single node 2153 or multiple nodes) is an ANET-local administrative consideration. 2155 3.16.1. Detecting and Responding to Server Failures 2157 In environments where fast recovery from Server failure is required, 2158 Proxys SHOULD use proactive Neighbor Unreachability Detection (NUD) 2159 to track Server reachability in a similar fashion as for 2160 Bidirectional Forwarding Detection (BFD) [RFC5880]. Proxys can then 2161 quickly detect and react to failures so that cached information is 2162 re-established through alternate paths. The NUD control messaging is 2163 carried only over well-connected ground domain networks (i.e., and 2164 not low-end aeronautical radio links) and can therefore be tuned for 2165 rapid response. 2167 Proxys perform proactive NUD with Servers for which there are 2168 currently active ANET Clients by sending continuous NS messages in 2169 rapid succession, e.g., one message per second. The Proxy sends the 2170 NS message via the SPAN with the Proxy's AERO address as the source 2171 and the AERO address of the Server as the destination. When the 2172 Proxy is also sending RS messages to the Server on behalf of ANET 2173 Clients, the resulting RA responses can be considered as equivalent 2174 hints of forward progress. This means that the Proxy need not also 2175 send a periodic NS if it has already sent an RS within the same 2176 period. If the Server fails (i.e., if the Proxy ceases to receive 2177 advertisements), the Proxy can quickly inform Clients by sending 2178 multicast RA messages on the ANET interface. 2180 The Proxy sends RA messages on the ANET interface with source address 2181 set to the Server's address, destination address set to All-Nodes 2182 multicast, and Router Lifetime set to 0. The Proxy SHOULD send 2183 MAX_FINAL_RTR_ADVERTISEMENTS RA messages separated by small delays 2184 [RFC4861]. Any Clients on the ANET that had been using the failed 2185 Server will receive the RA messages and associate with a new Server. 2187 3.16.2. Point-to-Multipoint Server Coordindation 2189 In environments where Client messaging over ANETs is bandwidth- 2190 limited and/or expensive, Clients can enlist the services of the 2191 Proxy to coordinate with multiple Servers in a single RS/RA message 2192 exchange. The Client can send a single RS message to All-Routers 2193 multicast that includes the ID's of multiple Servers in MS-Register 2194 sub-options of the OMNI option,. 2196 When the Proxy receives the RS and processes the OMNI option, it 2197 performs a separate RS/RA exchange with each MS-Register Server. 2198 When it has received the RA messages, it creates an "aggregate" RA 2199 message to return to the Client with an OMNI option with each 2200 responding Server's ID recorded in an MS-Register sub-option. 2202 Client's can thereafter employ efficient point-to-multipoint Server 2203 coordination under the assistance of the Proxy to dramatically reduce 2204 the number of messages sent over the ANET while enlisting the support 2205 of multiple Servers for fault tolerance. Clients can further include 2206 MS-Release suboptions in RS messages to request the Proxy to release 2207 from former Servers via the procedures discussed in Section 3.19.5. 2209 The OMNI interface specification [I-D.templin-6man-omni-interface] 2210 provides further discussion of the Client/Proxy RS/RA messaging 2211 involved in point-to-multipoint coordination. 2213 3.17. AERO Route Optimization 2215 While data packets are flowing between a source and target node, 2216 route optimization SHOULD be used. Route optimization is initiated 2217 by the first eligible Route Optimization Source (ROS) closest to the 2218 source as follows: 2220 o For Clients on VPNed, NATed and Direct interfaces, the Server is 2221 the ROS. 2223 o For Clients on Proxyed interfaces, the Proxy is the ROS. 2225 o For Clients on native interfaces, the Client itself is the ROS. 2227 o For correspondent nodes on INET/EUN interfaces serviced by a 2228 Gateway, the Gateway is the ROS. 2230 The route optimization procedure is conducted between the ROS and the 2231 target Server/Gateway acting as a Route Optimization Responder (ROR) 2232 in the same manner as for IPv6 ND Address Resolution and using the 2233 same NS/NA messaging. The target may either be a MNP Client serviced 2234 by a Server, or a non-MNP correspondent reachable via a Gateway. 2236 The procedures are specified in the following sections. 2238 3.17.1. Route Optimization Initiation 2240 While data packets are flowing from the source node toward a target 2241 node, the ROS performs address resolution by sending an NS message 2242 for Address Resolution (NS(AR)) to receive a solicited NA message 2243 from the ROR. When the ROS sends an NS(AR), it includes: 2245 o the AERO address of the ROS as the source address. 2247 o the data packet's destination as the target address. 2249 o the Solicited-Node multicast address [RFC4291] formed from the 2250 lower 24 bits of the data packet's destination as the destination 2251 address, e.g., for 2001:db8:1:2::10:2000 the NS destination 2252 address is ff02:0:0:0:0:1:ff10:2000. 2254 The NS(AR) message includes an OMNI option with no ifIndex-tuples and 2255 no SLLAO, such that the target will not create a neighbor cache 2256 entry. The message also includes a Nonce and Timestamp option if the 2257 ROS needs to correlate NA replies. 2259 The ROS then encapsulates the NS(AR) message in a SPAN header with 2260 source set to its own SPAN address and destination set to the data 2261 packet's destination address, then sends the message into the SPAN 2262 without decrementing the network-layer TTL/Hop Limit field. 2264 3.17.2. Relaying the NS 2266 When the Relay receives the NS(AR) message from the ROS, it discards 2267 the INET header and determines that the ROR is the next hop by 2268 consulting its standard IPv6 forwarding table for the SPAN header 2269 destination address. The Relay then forwards the message toward the 2270 ROR via the SPAN the same as for any IPv6 router. The final-hop 2271 Relay in the SPAN will deliver the message via a secured tunnel to 2272 the ROR. 2274 3.17.3. Processing the NS and Sending the NA 2276 When the ROR receives the NS(AR) message, it examines the target 2277 address to determine whether it has a neighbor cache entry and/or 2278 route that matches the target. If there is no match, the ROR drops 2279 the NS(AR) message. Otherwise, the ROR continues processing as 2280 follows: 2282 o if the target belongs to an MNP Client neighbor in the DEPARTED 2283 state the ROR changes the NS(AR) message SPAN destination address 2284 to the SPAN address of the Client's new Server, forwards the 2285 message into the SPAN and returns from processing. 2287 o If the target belongs to an MNP Client neighbor in the REACHABLE 2288 state, the ROR instead adds the AERO source address to the target 2289 Client's Report List with time set to ReportTime. 2291 o If the target belongs to a non-MNP route, the ROR continues 2292 processing without adding an entry to the Report List. 2294 The ROR then prepares a solicited NA message to send back to the ROS 2295 but does not create a neighbor cache entry. The ROR sets the NA 2296 source address to the AERO address corresponding to the target, sets 2297 the target addresss to the target of the solicitation, and sets the 2298 destination address to the source of the solicitation. If the NS(AR) 2299 message included a Nonce and/or Timestamp option, the ROR also 2300 includes a Nonce and/or timestamp. 2302 The ROR then includes an OMNI option with prefix registration length 2303 set to the length of the MNP if the target is an MNP Client; 2304 otherwise, set to the maximum of the non-MNP prefix length and 64. 2305 (Note that a /64 limit is imposed to avoid causing the ROS to set 2306 short prefixes (e.g., "default") that would match destinations for 2307 which the routing system includes more-specific prefixes.) 2309 If the target is an MNP Client, the ROR next includes ifIndex-tuples 2310 in the OMNI option for each of the target Client's underlying 2311 interfaces with current information for each interface and with the S 2312 flag set to 0. The ROR then includes a TLLAO with ifIndex-tuples in 2313 one-to-one correspondence with the tuples that appear in the OMNI 2314 option. For NATed, VPNed and Direct interfaces, the link layer 2315 addresses are the SPAN address of the ROR. For Proxyed interfaces, 2316 the link-layer addresses are the SPAN addresses of the Proxy's INET 2317 interfaces. For native interfaces, the link-layer addresses are the 2318 SPAN addesses of the Client's native interfaces. 2320 The ROR then sets the NA message R flag to 1 (as a router), S flag to 2321 1 (as a response to a solicitation), and O flag to 0 (as a proxy). 2323 The ROR finally encapsulates the NA message in a SPAN header with 2324 source set to its own SPAN address and destination set to the source 2325 SPAN address of the NS(AR) message, then forwards the message into 2326 the SPAN without decrementing the network-layer TTL/Hop Limit field. 2328 3.17.4. Relaying the NA 2330 When the Relay receives the NA message from the ROR, it discards the 2331 INET header and determines that the ROS is the next hop by consulting 2332 its standard IPv6 forwarding table for the SPAN header destination 2333 address. The Relay then forwards the SPAN-encapsulated NA message 2334 toward the ROS the same as for any IPv6 router. The final-hop Relay 2335 in the SPAN will deliver the message via a secured tunnel to the ROS. 2337 3.17.5. Processing the NA 2339 When the ROS receives the solicited NA message, it processes the 2340 message the same as for standard IPv6 Address Resolution [RFC4861]. 2341 In the process, it caches the source SPAN address, verifies the Nonce 2342 and Timestamp values (if present), then creates an asymmetric 2343 neighbor cache entry for the ROR and caches all information found in 2344 the OMNI and TLLAO options. The ROS finally sets the asymmetric 2345 neighbor cache entry lifetime to REACHABLETIME seconds. 2347 3.17.6. Route Optimization Maintenance 2349 Following route optimization, the ROS forwards future data packets 2350 destined to the target via the addresses found in the cached link- 2351 layer information. The route optimization is shared by all sources 2352 that send packets to the target via the ROS, i.e., and not just the 2353 source on behalf of which the route optimization was initiated. 2355 While new data packets destined to the target are flowing through the 2356 ROS, it sends additional NS(AR) messages to the ROR before 2357 ReachableTime expires to receive a fresh solicited NA message the 2358 same as described in the previous sections (route optimization 2359 refreshment strategies are an implementation matter, with a non- 2360 normative example given in Appendix B.1). The ROS uses the cached 2361 SPAN address of the ROR as the NS(AR) SPAN destination address, and 2362 sends up to MAX_MULTICAST_SOLICIT NS(AR) messages separated by 1 2363 second until an NA is received. If no NA is received, the ROS 2364 assumes that the current ROR has become unreachable and deletes the 2365 neighbor cache entry. Subsequent data packets will trigger a new 2366 route optimization per Section 3.17.1 to discover a new ROR while 2367 initial data packets travel over a suboptimal route. 2369 If an NA is received, the ROS then updates the asymmetric neighbor 2370 cache entry to refresh ReachableTime, while (for MNP destinations) 2371 the ROR adds or updates the ROS address to the target Client's Report 2372 List and with time set to ReportTime. While no data packets are 2373 flowing, the ROS instead allows ReachableTime for the asymmetric 2374 neighbor cache entry to expire. When ReachableTime expires, the ROS 2375 deletes the asymmetric neighbor cache entry. Any future data packets 2376 flowing through the ROS will again trigger a new route optimization. 2378 The ROS may also receive unsolicited NA messages from the ROR at any 2379 time (see: Section 3.19). If there is an asymmetric neighbor cache 2380 entry for the target, the ROS updates the link-layer information but 2381 does not update ReachableTime since the receipt of an unsolicited NA 2382 does not confirm that the forward path is still working. If there is 2383 no asymmetric neighbor cache entry, the ROS simply discards the 2384 unsolicited NA. 2386 In this arrangement, the ROS holds an asymmetric neighbor cache entry 2387 for the ROR, but the ROR does not hold an asymmetric neighbor cache 2388 entry for the ROS. The route optimization neighbor relationship is 2389 therefore asymmetric and unidirectional. If the target node also has 2390 packets to send back to the source node, then a separate route 2391 optimization procedure is performed in the reverse direction. But, 2392 there is no requirement that the forward and reverse paths be 2393 symmetric. 2395 3.18. Neighbor Unreachability Detection (NUD) 2397 AERO nodes perform Neighbor Unreachability Detection (NUD) per 2398 [RFC4861]. NUD is performed either reactively in response to 2399 persistent link-layer errors (see Section 3.14) or proactively to 2400 confirm reachability. The NUD algorithm is based on periodic 2401 authentic NS/NA message exchanges. The algorithm may further be 2402 seeded by ND hints of forward progress, but care must be taken to 2403 avoid inferring reachability based on spoofed information. For 2404 example, authentic RS/RA exchanges may be considered as acceptable 2405 hints of forward progress, while spurious data packets should not be. 2407 When an ROR directs an ROS to a neighbor with one or more target 2408 link-layer addresses, the ROS can proactively test each direct path 2409 by sending an initial NS message to elicit a solicited NA response. 2410 While testing the paths, the ROS can optionally continue sending 2411 packets via the SPAN, maintain a small queue of packets until target 2412 reachability is confirmed, or (optimistically) allow packets to flow 2413 via the direct paths. In any case, the ROS should only consider the 2414 neighbor unreachable if NUD fails over multiple target link-layer 2415 address paths. 2417 When a ROS sends an NS(NUD) message, it uses its AERO addresses as 2418 the IPv6 source address, the AERO address in the neighbor cache entry 2419 as the destination and the Subnet-Router Anycast address 2420 corresponding to the destination as the target. For each target 2421 link-layer address, the source node encapsulates the NS(NUD) message 2422 in SPAN/INET headers with its own SPAN address as the source and the 2423 SPAN address of the target as the destination. If the target is 2424 located in the same SPAN segment, the source forwards the message 2425 directly to the target's link-layer address; otherwise, it forwards 2426 the message into the SPAN. 2428 When the target receives the NS(NUD) message, it first determines 2429 whether the source is in the Report List for this target. If so, it 2430 returns an NA with IPv6 source/destination address set to the 2431 destination/source of the NS(NUD) and with target set to the target 2432 of the NS(NUD). The target wraps the NA message in a SPAN header 2433 with source/destination set to the destination/source of the NS(NUD) 2434 SPAN header. The target finally sets the NA R bit to 1, S to 1 and O 2435 to 0, and forwards the NA into the SPAN. Targets that pass NUD tests 2436 are marked as "reachable", while those that do not are marked as 2437 "unreachable". These markings inform the AERO interface forwarding 2438 algorithm specified in Section 3.13. 2440 Note that NS(NUD) messages follow the actual path used for data 2441 messages even if the path is not protected by security associations. 2442 Conversely, any resulting NA messages are sent via the secured SPAN. 2443 This ensures that the forward path taken by data packets will be 2444 tested with a secured confirmation received in the reverse direction. 2445 Since NS(NUD) messages can be spoofed along unsecured paths, however, 2446 they should include Nonce options and corresponding NA responses 2447 should be rate limited. 2449 Note also that Proxys can perform NUD to verify Server reachability 2450 on behalf of their proxyed Clients to reduce Client-initated control 2451 messaging overhead. 2453 3.19. Mobility Management and Quality of Service (QoS) 2455 AERO is a Distributed Mobility Management (DMM) service. Each Server 2456 is responsible for only a subset of the Clients on the AERO link, as 2457 opposed to a Centralized Mobility Management (CMM) service where 2458 there is a single network mobility collective entity for all Clients. 2459 Clients coordinate with their associated Servers via RS/RA exchanges 2460 to maintain the DMM profile, and the AERO routing system tracks all 2461 current Client/Server peering relationships. 2463 Servers provide default routing and mobility/multilink services for 2464 their dependent Clients. Clients are responsible for maintaining 2465 neighbor relationships with their Servers through periodic RS/RA 2466 exchanges, which also serves to confirm neighbor reachability. When 2467 a Client's underlying interface address and/or QoS information 2468 changes, the Client is responsible for updating the Server with this 2469 new information. Note that for Proxyed interfaces, however, the 2470 Proxy can also perform some RS/RA exchanges on the Client's behalf. 2472 Mobility management considerations are specified in the following 2473 sections. 2475 3.19.1. Mobility Update Messaging 2477 Servers accommodate Client mobility/multilink and/or QoS change 2478 events by sending unsolicited NA (uNA) messages to each ROS in the 2479 target Client's Report List. When a Server sends a uNA message, it 2480 sets the IPv6 source address to the Client's AERO address, sets the 2481 destination address to All-Nodes multicast and sets the target 2482 address to the Client's Subnet-Router anycast address. The Server 2483 also includes an OMNI option with prefix registration information and 2484 with ifIndex-tuples for the target Client's remaining interfaces with 2485 S set to 0. The Server then includes a TLLAO with corresponding 2486 ifIndex-tuples with link layer addresses set to the corresponding 2487 target SPAN addresses. The Server sets the NA R flag to 1, the S 2488 flag to 0 and the O flag to 0, then encapsulates the message in a 2489 SPAN header with source set to its own SPAN address and destination 2490 set to the SPAN address of the ROS and sends the message into the 2491 SPAN. 2493 As discussed in Section 7.2.6 of [RFC4861], the transmission and 2494 reception of uNA messages is unreliable but provides a useful 2495 optimization. In well-connected Internetworks with robust data links 2496 uNA messages will be delivered with high probability, but in any case 2497 the Server can optionally send up to MAX_NEIGHBOR_ADVERTISEMENT uNAs 2498 to each ROS to increase the likelihood that at least one will be 2499 received. 2501 When the ROS receives an uNA message, it ignores the message if there 2502 is no existing neighbor cache entry for the Client. Otherwise, it 2503 uses the included OMNI option and TLLAO information to update the 2504 neighbor cache entry, but does not reset ReachableTime since the 2505 receipt of an unsolicited NA message from the target Server does not 2506 provide confirmation that any forward paths to the target Client are 2507 working. 2509 If uNA messages are lost, the ROS may be left with stale address and/ 2510 or QoS information for the Client for up to REACHABLETIME seconds. 2511 During this time, the ROS can continue sending packets according to 2512 its stale neighbor cache information. When ReachableTime is close to 2513 expiring, the ROS will re-initiate route optimization and receive 2514 fresh link-layer address information. 2516 In addition to sending uNA messages to the current set of ROSs for 2517 the Client, the Server also sends uNAs to the former link-layer 2518 address for any ifIndex-tuple for which the link-layer address has 2519 changed. The uNA messages update Proxys that cannot easily detect 2520 (e.g., without active probing) when a formerly-active Client has 2521 departed. 2523 3.19.2. Announcing Link-Layer Address and/or QoS Preference Changes 2525 When a Client needs to change its ANET addresses and/or QoS 2526 preferences (e.g., due to a mobility event), either the Client or its 2527 Proxys send RS messages to the Server via the SPAN with an OMNI 2528 option that includes an ifIndex-tuple with S set to 1 and with the 2529 new link quality and address information. 2531 Up to MAX_RTR_SOLICITATION RS messages MAY be sent in parallel with 2532 sending actual data packets in case one or more RAs are lost. If all 2533 RAs are lost, the Client SHOULD re-associate with a new Server. 2535 When the Server receives the Client's changes, it sends uNA messages 2536 to all nodes in the Report List the same as described in the previous 2537 section. 2539 3.19.3. Bringing New Links Into Service 2541 When a Client needs to bring new underlying interfaces into service 2542 (e.g., when it activates a new data link), it sends an RS message to 2543 the Server via the underlying interface with an OMNI option that 2544 includes an ifIndex-tuple with S set to 1 and appropriate link 2545 quality values and with link-layer address information for the new 2546 link. 2548 3.19.4. Removing Existing Links from Service 2550 When a Client needs to remove existing underlying interfaces from 2551 service (e.g., when it de-activates an existing data link), it sends 2552 an RS or uNA message to its Server with an OMNI option with 2553 appropriate link quality values. 2555 If the Client needs to send RS/uNA messages over an underlying 2556 interface other than the one being removed from service, it MUST 2557 include ifIndex-tuples with appropriate link quality values for any 2558 underlying interfaces being removed from service. 2560 3.19.5. Moving to a New Server 2562 When a Client associates with a new Server, it performs the Client 2563 procedures specified in Section 3.15.2. The Client also includes MS- 2564 Release identifiers in the RS message OMNI option per 2565 [I-D.templin-6man-omni-interface] if it wants the new Server to 2566 notify any old Servers from which the Client is departing. 2568 When the new Server receives the Client's RS message, it returns an 2569 RA as specified in Section 3.15.3 and sends up to 2570 MAX_NEIGHBOR_ADVERTIISEMENT uNA messages to any old Servers listed in 2571 OMNI option MS-Release identifiers. Each uNA message includes the 2572 Client's AERO address as the source address, the old Server's AERO 2573 address as the destination address, and an OMNI option with the 2574 Register/Release bit set to 0. The new Server wraps the uNA in a 2575 SPAN header with its own SPAN address as the source and the old 2576 Server's SPAN address as the destination, then sends the message into 2577 the SPAN. 2579 When an old Server receives the uNA, it changes the Client's neighbor 2580 cache entry state to DEPARTED, sets the link-layer address of the 2581 Client to the new Server's SPAN address, and sets DepartTime to 2582 DEPARTTIME seconds. After a short delay (e.g., 2 seconds) the old 2583 Server withdraws the Client's MNP from the routing system. After 2584 DepartTime expires, the old Server deletes the Client's neighbor 2585 cache entry. 2587 The old Server also sends unsolicited NA messages to all ROSs in the 2588 Client's Report List with an OMNI option with a single ifIndex-tuple 2589 with ifIndex set to 0 and S set to '1', and with the SPAN address of 2590 the new Server in a companion TLLAO. When the ROS receives the NA, 2591 it caches the address of the new Server in the existing asymmetric 2592 neighbor cache entry and marks the entry as STALE. Subsequent data 2593 packets will then flow according to any existing cached link-layer 2594 information and trigger a new NS(AR)/NA exchange via the new Server. 2596 Clients SHOULD NOT move rapidly between Servers in order to avoid 2597 causing excessive oscillations in the AERO routing system. Examples 2598 of when a Client might wish to change to a different Server include a 2599 Server that has gone unreachable, topological movements of 2600 significant distance, movement to a new geographic region, movement 2601 to a new SPAN segment, etc. 2603 When a Client moves to a new Server, some of the fragments of a 2604 multiple fragment packet may have already arrived at the old Server 2605 while others are en route to the new Server, however no special 2606 attention in the reassembly algorithm is necessary when re-routed 2607 fragments are simply treated as loss. 2609 3.20. Multicast 2611 The AERO Client provides an IGMP (IPv4) [RFC2236] or MLD (IPv6) 2612 [RFC3810] proxy service for its EUNs and/or hosted applications 2613 [RFC4605]. The Client forwards IGMP/MLD messages over any of its 2614 underlying interfaces for which group membership is required. The 2615 IGMP/MLD messages may be further forwarded by a first-hop ANET access 2616 router acting as an IGMP/MLD-snooping switch [RFC4541], then 2617 ultimately delivered to an AERO Proxy/Server acting as a Protocol 2618 Independent Multicast - Sparse-Mode (PIM-SM, or simply "PIM") 2619 Designated Router (DR) [RFC7761]. AERO Gateways also act as PIM 2620 routers (i.e., the same as AERO Proxys/Servers) on behalf of nodes on 2621 INET/EUN networks. The behaviors identified in the following 2622 sections correspond to Source-Specific Multicast (SSM) and Any-Source 2623 Multicast (ASM) operational modes. 2625 3.20.1. Source-Specific Multicast (SSM) 2627 When an ROS (i.e., an AERO Proxy/Server/Gateway) "X" acting as PIM 2628 router receives a Join/Prune message from a node on its downstream 2629 interfaces containing one or more ((S)ource, (G)roup) pairs, it 2630 updates its Multicast Routing Information Base (MRIB) accordingly. 2631 For each S belonging to a prefix reachable via X's non-AERO 2632 interfaces, X then forwards the (S, G) Join/Prune to any PIM routers 2633 on those interfaces per [RFC7761]. 2635 For each S belonging to a prefix reachable via X's AERO interface, X 2636 originates a separate copy of the Join/Prune for each (S,G) in the 2637 message using its own AERO address as the source address and ALL-PIM- 2638 ROUTERS as the destination address. X then encapsulates each message 2639 in a SPAN header with source address set to the SPAN address of X and 2640 destination address set to S then forwards the message into the SPAN. 2641 The SPAN in turn forwards the message to AERO Server/Gateway "Y" that 2642 services S. At the same time, if the message was a Join, X sends a 2643 route-optimization NS message toward each S the same as discussed in 2644 Section 3.17. The resulting NAs will return the AERO address for the 2645 prefix that matches S as the network-layer source address and TLLAOs 2646 with the SPAN addresses corresponding to any ifIndex-tuples that are 2647 currently servicing S. 2649 When Y processes the Join/Prune message, if S located behind any 2650 Native, Direct, VPNed or NATed interfaces Y acts as a PIM router and 2651 updates its MRIB to list X as the next hop in the reverse path. If S 2652 is located behind any Proxys "Z"*, Y also forwards the message to 2653 each Z* over the SPAN while continuing to use the AERO address of X 2654 as the source address. Each Z* then updates its MRIB accordingly and 2655 maintains the AERO address of X as the next hop in the reverse path. 2656 Since the Relays in the SPAN do not examine network layer control 2657 messages, this means that the (reverse) multicast tree path is simply 2658 from each Z* (and/or Y) to X with no other multicast-aware routers in 2659 the path. If any Z* (and/or Y) is located on the same SPAN segment 2660 as X, the multicast data traffic sent to X directly using SPAN/INET 2661 encapsulation instead of via a Relay. 2663 Following the initial Join/Prune and NS/NA messaging, X maintains an 2664 asymmetric neighbor cache entry for each S the same as if X was 2665 sending unicast data traffic to S. In particular, X performs 2666 additional NS/NA exchanges to keep the neighbor cache entry alive for 2667 up to t_periodic seconds [RFC7761]. If no new Joins are received 2668 within t_periodic seconds, X allows the neighbor cache entry to 2669 expire. Finally, if X receives any additional Join/Prune messages 2670 for (S,G) it forwards the messages to each Y and Z* in the neighbor 2671 cache entry over the SPAN. 2673 At some later time, Client C that holds an MNP for source S may 2674 depart from a first Proxy Z1 and/or connect via a new Proxy Z2. In 2675 that case, Y sends an unsolicited NA message to X the same as 2676 specified for unicast mobility in Section 3.19. When X receives the 2677 unsolicited NA message, it updates its asymmetric neighbor cache 2678 entry for the AERO address for source S and sends new Join messages 2679 to any new Proxys Z2. There is no requirement to send any Prune 2680 messages to old Proxys Z1 since source S will no longer source any 2681 multicast data traffic via Z1. Instead, the multicast state for 2682 (S,G) in Proxy Z1 will soon time out since no new Joins will arrive. 2684 After some later time, C may move to a new Server Y2 and depart from 2685 old Sever Y1. In that case, Y1 sends Join messages for any of C's 2686 active (S,G) groups to Y2 while including its own AERO address as the 2687 source address. This causes Y2 to include Y1 in the multicast 2688 forwarding tree during the interim time that Y1's symmetric neighbor 2689 cache entry for C is in the DEPARTED state. At the same time, Y1 2690 sends an unsolicited NA message to X with an OMNI option and TLLAO 2691 with ifIndex-tuple set to 0 and a release indication to cause X to 2692 release its asymmetric neighbor cache entry. X then sends a new Join 2693 message to S via the SPAN and re-initiates route optimization the 2694 same as if it were receiving a fresh Join message from a node on a 2695 downstream link. 2697 3.20.2. Any-Source Multicast (ASM) 2699 When an ROS X acting as a PIM router receives a Join/Prune from a 2700 node on its downstream interfaces containing one or more (*,G) pairs, 2701 it updates its Multicast Routing Information Base (MRIB) accordingly. 2702 X then forwards a copy of the message to the Rendezvous Point (RP) R 2703 for each G over the SPAN. X uses its own AERO address as the source 2704 address and ALL-PIM-ROUTERS as the destination address, then 2705 encapsulates each message in a SPAN header with source address set to 2706 the SPAN address of X and destination address set to R, then sends 2707 the message into the SPAN. At the same time, if the message was a 2708 Join X initiates NS/NA route optimization the same as for the SSM 2709 case discussed in Section 3.20.1. 2711 For each source S that sends multicast traffic to group G via R, the 2712 Proxy/Server Z* for the Client that aggregates S encapsulates the 2713 packets in PIM Register messages and forwards them to R via the SPAN. 2714 R may then elect to send a PIM Join to Z* over the SPAN. This will 2715 result in an (S,G) tree rooted at Z* with R as the next hop so that R 2716 will begin to receive two copies of the packet; one native copy from 2717 the (S, G) tree and a second copy from the pre-existing (*, G) tree 2718 that still uses PIM Register encapsulation. R can then issue a PIM 2719 Register-stop message to suppress the Register-encapsulated stream. 2720 At some later time, if C moves to a new Proxy/Server Z*, it resumes 2721 sending packets via PIM Register encapsulation via the new Z*. 2723 At the same time, as multicast listeners discover individual S's for 2724 a given G, they can initiate an (S,G) Join for each S under the same 2725 procedures discussed in Section 3.20.1. Once the (S,G) tree is 2726 established, the listeners can send (S, G) Prune messages to R so 2727 that multicast packets for group G sourced by S will only be 2728 delivered via the (S, G) tree and not from the (*, G) tree rooted at 2729 R. All mobility considerations discussed for SSM apply. 2731 3.20.3. Bi-Directional PIM (BIDIR-PIM) 2733 Bi-Directional PIM (BIDIR-PIM) [RFC5015] provides an alternate 2734 approach to ASM that treats the Rendezvous Point (RP) as a Designated 2735 Forwarder (DF). Further considerations for BIDIR-PIM are out of 2736 scope. 2738 3.21. Operation over Multiple AERO Links (VLANs) 2740 An AERO Client can connect to multiple AERO links the same as for any 2741 data link service. In that case, the Client maintains a distinct 2742 AERO interface for each link, e.g., 'aero0' for the first link, 2743 'aero1' for the second, 'aero2' for the third, etc. Each AERO link 2744 would include its own distinct set of Relays, Servers and Proxys, 2745 thereby providing redundancy in case of failures. 2747 The Relays, Servers and Proxys on each AERO link can assign AERO and 2748 SPAN addresses that use the same or different numberings from those 2749 on other links. Since the links are mutually independent there is no 2750 requirement for avoiding inter-link address duplication, e.g., the 2751 same AERO address such as fe80::1000 could be used to number distinct 2752 nodes that connect to different AERO links. 2754 Each AERO link could utilize the same or different ANET connections. 2755 The links can be distinguished at the link-layer via Virtual Local 2756 Area Network (VLAN) tagging (e.g., IEEE 802.1Q) and/or through 2757 assignment of distinct sets of MSPs on each link. This gives rise to 2758 the opportunity for supporting multiple redundant networked paths, 2759 where each VLAN is distinguished by a different label (e.g., colors 2760 such as Red, Green, Blue, etc.). In particular, the Client can tag 2761 its RS messages with the appropriate label to cause the network to 2762 select the desired VLAN. 2764 Clients that connect to multiple AERO interfaces can select the 2765 outgoing interface appropriate for a given Red/Blue/Green/etc. 2766 traffic profile while (in the reverse direction) correspondent nodes 2767 must have some way of steering their packets destined to a target via 2768 the correct AERO link. 2770 In a first alternative, if each AERO link services different MSPs, 2771 then the Client can receive a distinct MNP from each of the links. 2772 IP routing will therefore assure that the correct Red/Green/Blue/etc. 2773 network is used for both outbound and inbound traffic. This can be 2774 accomplished using existing technologies and approaches, and without 2775 requiring any special supporting code in correspondent nodes or 2776 Relays. 2778 In a second alternative, if each AERO link services the same MSP(s) 2779 then each link could assign a distinct "AERO Link Anycast" address 2780 that is configured by all Relays on the link. Correspondent nodes 2781 then include a "type 4" routing header with the Anycast address for 2782 the AERO link as the IPv6 destination and with the address of the 2783 target encoded as the "next segment" in the routing header 2784 [RFC8402][I-D.ietf-6man-segment-routing-header]. Standard IP routing 2785 will then direct the packet to the nearest Relay for the correct AERO 2786 link, which will replace the destination address with the target 2787 address then forward the packet to the target. 2789 3.22. DNS Considerations 2791 AERO Client MNs and INET correspondent nodes consult the Domain Name 2792 System (DNS) the same as for any Internetworking node. When 2793 correspondent nodes and Client MNs use different IP protocol versions 2794 (e.g., IPv4 correspondents and IPv6 MNs), the INET DNS must maintain 2795 A records for IPv4 address mappings to MNs which must then be 2796 populated in Gateway NAT64 mapping caches. In that way, an IPv4 2797 correspondent node can send packets to the IPv4 address mapping of 2798 the target MN, and the Gateway will translate the IPv4 header and 2799 destination address into an IPv6 header and IPv6 destination address 2800 of the MN. 2802 When an AERO Client registers with an AERO Server, the Server can 2803 return the address(es) of DNS servers in RDNSS options [RFC6106]. 2804 The DNS server provides the IP addresses of other MNs and 2805 correspondent nodes in AAAA records for IPv6 or A records for IPv4. 2807 3.23. Transition Considerations 2809 The SPAN ensures that dissimilar INET partitions can be joined into a 2810 single unified AERO link, even though the partitions themselves may 2811 have differing protocol versions and/or incompatible addressing 2812 plans. However, a commonality can be achieved by incrementally 2813 distributing globally routable (i.e., native) IP prefixes to 2814 eventually reach all nodes (both mobile and fixed) in all SPAN 2815 segments. This can be accomplished by incrementally deploying AERO 2816 Gateways on each INET partition, with each Gateway distributing its 2817 MNPs and/or discovering non-MNP prefixes on its INET links. 2819 This gives rise to the opportunity to eventually distribute native IP 2820 addresses to all nodes, and to present a unified AERO link view 2821 (bridged by the SPAN) even if the INET partitions remain in their 2822 current protocol and addressing plans. In that way, the AERO link 2823 can serve the dual purpose of providing a mobility/multilink service 2824 and a transition service. Or, if an INET partition is transitioned 2825 to a native IP protocol version and addressing scheme that is 2826 compatible with the AERO link MNP-based addressing scheme, the 2827 partition and AERO link can be joined by Gateways. 2829 Gateways that connect INETs/EUNs with dissimilar IP protocol versions 2830 must employ a network address and protocol translation function such 2831 as NAT64[RFC6146]. 2833 3.24. Detecting and Reacting to Server and Relay Failures 2835 In environments where rapid failure recovery is required, Servers and 2836 Relays SHOULD use Bidirectional Forwarding Detection (BFD) [RFC5880]. 2837 Nodes that use BFD can quickly detect and react to failures so that 2838 cached information is re-established through alternate nodes. BFD 2839 control messaging is carried only over well-connected ground domain 2840 networks (i.e., and not low-end radio links) and can therefore be 2841 tuned for rapid response. 2843 Servers and Relays maintain BFD sessions in parallel with their BGP 2844 peerings. If a Server or Relay fails, BGP peers will quickly re- 2845 establish routes through alternate paths the same as for common BGP 2846 deployments. Similarly, Proxys maintain BFD sessions with their 2847 associated Relays even though they do not establish BGP peerings with 2848 them. 2850 Proxys SHOULD use proactive NUD for Servers for which there are 2851 currently active ANET Clients in a manner that parallels BFD, i.e., 2852 by sending unicast NS messages in rapid succession to receive 2853 solicited NA messages. When the Proxy is also sending RS messages on 2854 behalf of ANET Clients, the RS/RA messaging can be considered as 2855 equivalent hints of forward progress. This means that the Proxy need 2856 not also send a periodic NS if it has already sent an RS within the 2857 same period. If a Server fails, the Proxy will cease to receive 2858 advertisements and can quickly inform Clients of the outage by 2859 sending multicast RA messages on the ANET interface. 2861 The Proxy sends multicast RA messages with source address set to the 2862 Server's address, destination address set to All-Nodes multicast, and 2863 Router Lifetime set to 0. The Proxy SHOULD send 2864 MAX_FINAL_RTR_ADVERTISEMENTS RA messages separated by small delays 2865 [RFC4861]. Any Clients on the ANET interface that have been using 2866 the (now defunct) Server will receive the RA messages and associate 2867 with a new Server. 2869 4. Implementation Status 2871 An AERO implementation based on OpenVPN (https://openvpn.net/) was 2872 announced on the v6ops mailing list on January 10, 2018 and an 2873 initial public release of the AERO proof-of-concept source code was 2874 announced on the intarea mailing list on August 21, 2015. 2876 5. IANA Considerations 2878 The IANA has assigned a 4-octet Private Enterprise Number "45282" for 2879 AERO in the "enterprise-numbers" registry. 2881 The IANA has assigned the UDP port number "8060" for an earlier 2882 experimental version of AERO [RFC6706]. This document obsoletes 2883 [RFC6706] and claims the UDP port number "8060" for all future use. 2885 No further IANA actions are required. 2887 6. Security Considerations 2889 AERO Relays configure secured tunnels with AERO Servers and Proxys 2890 within their local SPAN segments. Applicable secured tunnel 2891 alternatives include IPsec [RFC4301], TLS/SSL [RFC8446], DTLS 2892 [RFC6347], WireGuard, etc. The AERO Relays of all SPAN segments in 2893 turn configure secured tunnels for their neighboring AERO Relays 2894 across the SPAN. Therefore, control messages that traverse the SPAN 2895 between any pair of AERO link neighbors are already secured. 2897 AERO Servers, Gateways and Proxys targeted by a route optimization 2898 may also receive packets directly from the INET partitions instead of 2899 via the SPAN. For INET partitions that apply effective ingress 2900 filtering to defeat source address spoofing, the simple data origin 2901 authentication procedures in Section 3.11 can be applied. 2903 For INET partitions that cannot apply effective ingress filtering, 2904 the two options for securing communications include 1) disable route 2905 optimization so that all traffic is conveyed over secured tunnels via 2906 the SPAN, or 2) enable on-demand secure tunnel creation between INET 2907 partition neighbors. Option 1) would result in longer routes than 2908 necessary and traffic concentration on critical infrastructure 2909 elements. Option 2) could be coordinated by establishing a secured 2910 tunnel on-demand instead of performing an NS/NA exchange in the route 2911 optimization procedures. Procedures for establishing on-demand 2912 secured tunnels are out of scope. 2914 AERO Clients that connect to secured enclaves need not apply security 2915 to their ND messages, since the messages will be intercepted by a 2916 perimeter Proxy that applies security on its outward-facing 2917 interface. AERO Clients located outside of secured enclaves SHOULD 2918 use symmetric network and/or transport layer security services, but 2919 when there are many prospective neighbors with dynamically changing 2920 connectivity an asymmetric security service such as SEND may be 2921 needed (see: Appendix B.6). 2923 Application endpoints SHOULD use application-layer security services 2924 such as TLS/SSL, DTLS or SSH [RFC4251] to assure the same level of 2925 protection as for critical secured Internet services. AERO Clients 2926 that require host-based VPN services SHOULD use symmetric network 2927 and/or transport layer security services such as IPsec, TLS/SSL, 2928 DTLS, etc. AERO Proxys and Servers can also provide a network-based 2929 VPN service on behalf of the Client, e.g., if the Client is located 2930 within a secured enclave and cannot establish a VPN on its own 2931 behalf. 2933 AERO Servers and Relays present targets for traffic amplification 2934 Denial of Service (DoS) attacks. This concern is no different than 2935 for widely-deployed VPN security gateways in the Internet, where 2936 attackers could send spoofed packets to the gateways at high data 2937 rates. This can be mitigated by connecting Servers and Relays over 2938 dedicated links with no connections to the Internet and/or when 2939 connections to the Internet are only permitted through well-managed 2940 firewalls. Traffic amplification DoS attacks can also target an AERO 2941 Client's low data rate links. This is a concern not only for Clients 2942 located on the open Internet but also for Clients in secured 2943 enclaves. AERO Servers and Proxys can institute rate limits that 2944 protect Clients from receiving packet floods that could DoS low data 2945 rate links. 2947 AERO Gateways must implement ingress filtering to avoid a spoofing 2948 attack in which spurious SPAN messages are injected into an AERO link 2949 from an outside attacker. AERO Clients MUST ensure that their 2950 connectivity is not used by unauthorized nodes on their EUNs to gain 2951 access to a protected network, i.e., AERO Clients that act as routers 2952 MUST NOT provide routing services for unauthorized nodes. (This 2953 concern is no different than for ordinary hosts that receive an IP 2954 address delegation but then "share" the address with other nodes via 2955 some form of Internet connection sharing such as tethering.) 2957 The MAP list MUST be well-managed and secured from unauthorized 2958 tampering, even though the list contains only public information. 2959 The MAP list can be conveyed to the Client in a similar fashion as in 2960 [RFC5214] (e.g., through layer 2 data link login messaging, secure 2961 upload of a static file, DNS lookups, etc.). 2963 Although public domain and commercial SEND implementations exist, 2964 concerns regarding the strength of the cryptographic hash algorithm 2965 have been documented [RFC6273] [RFC4982]. 2967 Security considerations for accepting link-layer ICMP messages and 2968 reflected packets are discussed throughout the document. 2970 7. Acknowledgements 2972 Discussions in the IETF, aviation standards communities and private 2973 exchanges helped shape some of the concepts in this work. 2974 Individuals who contributed insights include Mikael Abrahamsson, Mark 2975 Andrews, Fred Baker, Bob Braden, Stewart Bryant, Brian Carpenter, 2976 Wojciech Dec, Pavel Drasil, Ralph Droms, Adrian Farrel, Nick Green, 2977 Sri Gundavelli, Brian Haberman, Bernhard Haindl, Joel Halpern, Tom 2978 Herbert, Sascha Hlusiak, Lee Howard, Zdenek Jaron, Andre Kostur, 2979 Hubert Kuenig, Ted Lemon, Andy Malis, Satoru Matsushima, Tomek 2980 Mrugalski, Madhu Niraula, Alexandru Petrescu, Behcet Saikaya, Michal 2981 Skorepa, Joe Touch, Bernie Volz, Ryuji Wakikawa, Tony Whyman, Lloyd 2982 Wood and James Woodyatt. Members of the IESG also provided valuable 2983 input during their review process that greatly improved the document. 2984 Special thanks go to Stewart Bryant, Joel Halpern and Brian Haberman 2985 for their shepherding guidance during the publication of the AERO 2986 first edition. 2988 This work has further been encouraged and supported by Boeing 2989 colleagues including Kyle Bae, M. Wayne Benson, Dave Bernhardt, Cam 2990 Brodie, John Bush, Balaguruna Chidambaram, Irene Chin, Bruce Cornish, 2991 Claudiu Danilov, Don Dillenburg, Joe Dudkowski, Wen Fang, Samad 2992 Farooqui, Anthony Gregory, Jeff Holland, Seth Jahne, Brian Jaury, 2993 Greg Kimberly, Ed King, Madhuri Madhava Badgandi, Laurel Matthew, 2994 Gene MacLean III, Rob Muszkiewicz, Sean O'Sullivan, Vijay 2995 Rajagopalan, Greg Saccone, Rod Santiago, Kent Shuey, Brian Skeen, 2996 Mike Slane, Carrie Spiker, Katie Tran, Brendan Williams, Amelia 2997 Wilson, Julie Wulff, Yueli Yang, Eric Yeh and other members of the 2998 Boeing mobility, networking and autonomy teams. Kyle Bae, Wayne 2999 Benson, Katie Tran and Eric Yeh are especially acknowledged for 3000 implementing the AERO functions as extensions to the public domain 3001 OpenVPN distribution. 3003 Earlier works on NBMA tunneling approaches are found in 3004 [RFC2529][RFC5214][RFC5569]. 3006 Many of the constructs presented in this second edition of AERO are 3007 based on the author's earlier works, including: 3009 o The Internet Routing Overlay Network (IRON) 3010 [RFC6179][I-D.templin-ironbis] 3012 o Virtual Enterprise Traversal (VET) 3013 [RFC5558][I-D.templin-intarea-vet] 3015 o The Subnetwork Encapsulation and Adaptation Layer (SEAL) 3016 [RFC5320][I-D.templin-intarea-seal] 3018 o AERO, First Edition [RFC6706] 3020 Note that these works cite numerous earlier efforts that are not also 3021 cited here due to space limitations. The authors of those earlier 3022 works are acknowledged for their insights. 3024 This work is aligned with the NASA Safe Autonomous Systems Operation 3025 (SASO) program under NASA contract number NNA16BD84C. 3027 This work is aligned with the FAA as per the SE2025 contract number 3028 DTFAWA-15-D-00030. 3030 This work is aligned with the Boeing Commercial Airplanes (BCA) 3031 Internet of Things (IoT) and autonomy programs. 3033 This work is aligned with the Boeing Information Technology (BIT) 3034 MobileNet program. 3036 8. References 3038 8.1. Normative References 3040 [I-D.templin-6man-omni-interface] 3041 Templin, F. and T. Whyman, "Transmission of IPv6 Packets 3042 over Overlay Multilink Network (OMNI) Interfaces", draft- 3043 templin-6man-omni-interface-07 (work in progress), March 3044 2020. 3046 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, 3047 DOI 10.17487/RFC0791, September 1981, 3048 . 3050 [RFC0792] Postel, J., "Internet Control Message Protocol", STD 5, 3051 RFC 792, DOI 10.17487/RFC0792, September 1981, 3052 . 3054 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 3055 Requirement Levels", BCP 14, RFC 2119, 3056 DOI 10.17487/RFC2119, March 1997, 3057 . 3059 [RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in 3060 IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473, 3061 December 1998, . 3063 [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black, 3064 "Definition of the Differentiated Services Field (DS 3065 Field) in the IPv4 and IPv6 Headers", RFC 2474, 3066 DOI 10.17487/RFC2474, December 1998, 3067 . 3069 [RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander, 3070 "SEcure Neighbor Discovery (SEND)", RFC 3971, 3071 DOI 10.17487/RFC3971, March 2005, 3072 . 3074 [RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)", 3075 RFC 3972, DOI 10.17487/RFC3972, March 2005, 3076 . 3078 [RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and 3079 More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191, 3080 November 2005, . 3082 [RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast 3083 Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005, 3084 . 3086 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 3087 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 3088 DOI 10.17487/RFC4861, September 2007, 3089 . 3091 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 3092 Address Autoconfiguration", RFC 4862, 3093 DOI 10.17487/RFC4862, September 2007, 3094 . 3096 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 3097 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 3098 May 2017, . 3100 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 3101 (IPv6) Specification", STD 86, RFC 8200, 3102 DOI 10.17487/RFC8200, July 2017, 3103 . 3105 [RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A., 3106 Richardson, M., Jiang, S., Lemon, T., and T. Winters, 3107 "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", 3108 RFC 8415, DOI 10.17487/RFC8415, November 2018, 3109 . 3111 8.2. Informative References 3113 [BGP] Huston, G., "BGP in 2015, http://potaroo.net", January 3114 2016. 3116 [I-D.ietf-6man-segment-routing-header] 3117 Filsfils, C., Dukes, D., Previdi, S., Leddy, J., 3118 Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header 3119 (SRH)", draft-ietf-6man-segment-routing-header-26 (work in 3120 progress), October 2019. 3122 [I-D.ietf-dmm-distributed-mobility-anchoring] 3123 Chan, A., Wei, X., Lee, J., Jeon, S., and C. Bernardos, 3124 "Distributed Mobility Anchoring", draft-ietf-dmm- 3125 distributed-mobility-anchoring-15 (work in progress), 3126 March 2020. 3128 [I-D.ietf-intarea-gue] 3129 Herbert, T., Yong, L., and O. Zia, "Generic UDP 3130 Encapsulation", draft-ietf-intarea-gue-09 (work in 3131 progress), October 2019. 3133 [I-D.ietf-intarea-gue-extensions] 3134 Herbert, T., Yong, L., and F. Templin, "Extensions for 3135 Generic UDP Encapsulation", draft-ietf-intarea-gue- 3136 extensions-06 (work in progress), March 2019. 3138 [I-D.ietf-intarea-tunnels] 3139 Touch, J. and M. Townsley, "IP Tunnels in the Internet 3140 Architecture", draft-ietf-intarea-tunnels-10 (work in 3141 progress), September 2019. 3143 [I-D.ietf-rtgwg-atn-bgp] 3144 Templin, F., Saccone, G., Dawra, G., Lindem, A., and V. 3145 Moreno, "A Simple BGP-based Mobile Routing System for the 3146 Aeronautical Telecommunications Network", draft-ietf- 3147 rtgwg-atn-bgp-05 (work in progress), January 2020. 3149 [I-D.templin-6man-dhcpv6-ndopt] 3150 Templin, F., "A Unified Stateful/Stateless Configuration 3151 Service for IPv6", draft-templin-6man-dhcpv6-ndopt-09 3152 (work in progress), January 2020. 3154 [I-D.templin-intarea-grefrag] 3155 Templin, F., "GRE Tunnel Level Fragmentation", draft- 3156 templin-intarea-grefrag-04 (work in progress), July 2016. 3158 [I-D.templin-intarea-seal] 3159 Templin, F., "The Subnetwork Encapsulation and Adaptation 3160 Layer (SEAL)", draft-templin-intarea-seal-68 (work in 3161 progress), January 2014. 3163 [I-D.templin-intarea-vet] 3164 Templin, F., "Virtual Enterprise Traversal (VET)", draft- 3165 templin-intarea-vet-40 (work in progress), May 2013. 3167 [I-D.templin-ironbis] 3168 Templin, F., "The Interior Routing Overlay Network 3169 (IRON)", draft-templin-ironbis-16 (work in progress), 3170 March 2014. 3172 [I-D.templin-v6ops-pdhost] 3173 Templin, F., "IPv6 Prefix Delegation and Multi-Addressing 3174 Models", draft-templin-v6ops-pdhost-25 (work in progress), 3175 January 2020. 3177 [OVPN] OpenVPN, O., "http://openvpn.net", October 2016. 3179 [RFC1035] Mockapetris, P., "Domain names - implementation and 3180 specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, 3181 November 1987, . 3183 [RFC1122] Braden, R., Ed., "Requirements for Internet Hosts - 3184 Communication Layers", STD 3, RFC 1122, 3185 DOI 10.17487/RFC1122, October 1989, 3186 . 3188 [RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191, 3189 DOI 10.17487/RFC1191, November 1990, 3190 . 3192 [RFC1812] Baker, F., Ed., "Requirements for IP Version 4 Routers", 3193 RFC 1812, DOI 10.17487/RFC1812, June 1995, 3194 . 3196 [RFC2003] Perkins, C., "IP Encapsulation within IP", RFC 2003, 3197 DOI 10.17487/RFC2003, October 1996, 3198 . 3200 [RFC2236] Fenner, W., "Internet Group Management Protocol, Version 3201 2", RFC 2236, DOI 10.17487/RFC2236, November 1997, 3202 . 3204 [RFC2492] Armitage, G., Schulter, P., and M. Jork, "IPv6 over ATM 3205 Networks", RFC 2492, DOI 10.17487/RFC2492, January 1999, 3206 . 3208 [RFC2529] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4 3209 Domains without Explicit Tunnels", RFC 2529, 3210 DOI 10.17487/RFC2529, March 1999, 3211 . 3213 [RFC2764] Gleeson, B., Lin, A., Heinanen, J., Armitage, G., and A. 3214 Malis, "A Framework for IP Based Virtual Private 3215 Networks", RFC 2764, DOI 10.17487/RFC2764, February 2000, 3216 . 3218 [RFC2784] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P. 3219 Traina, "Generic Routing Encapsulation (GRE)", RFC 2784, 3220 DOI 10.17487/RFC2784, March 2000, 3221 . 3223 [RFC2890] Dommety, G., "Key and Sequence Number Extensions to GRE", 3224 RFC 2890, DOI 10.17487/RFC2890, September 2000, 3225 . 3227 [RFC2923] Lahey, K., "TCP Problems with Path MTU Discovery", 3228 RFC 2923, DOI 10.17487/RFC2923, September 2000, 3229 . 3231 [RFC2983] Black, D., "Differentiated Services and Tunnels", 3232 RFC 2983, DOI 10.17487/RFC2983, October 2000, 3233 . 3235 [RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition 3236 of Explicit Congestion Notification (ECN) to IP", 3237 RFC 3168, DOI 10.17487/RFC3168, September 2001, 3238 . 3240 [RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener 3241 Discovery Version 2 (MLDv2) for IPv6", RFC 3810, 3242 DOI 10.17487/RFC3810, June 2004, 3243 . 3245 [RFC3819] Karn, P., Ed., Bormann, C., Fairhurst, G., Grossman, D., 3246 Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J., and L. 3247 Wood, "Advice for Internet Subnetwork Designers", BCP 89, 3248 RFC 3819, DOI 10.17487/RFC3819, July 2004, 3249 . 3251 [RFC4213] Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms 3252 for IPv6 Hosts and Routers", RFC 4213, 3253 DOI 10.17487/RFC4213, October 2005, 3254 . 3256 [RFC4251] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH) 3257 Protocol Architecture", RFC 4251, DOI 10.17487/RFC4251, 3258 January 2006, . 3260 [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A 3261 Border Gateway Protocol 4 (BGP-4)", RFC 4271, 3262 DOI 10.17487/RFC4271, January 2006, 3263 . 3265 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 3266 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 3267 2006, . 3269 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 3270 Internet Protocol", RFC 4301, DOI 10.17487/RFC4301, 3271 December 2005, . 3273 [RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery 3274 Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April 3275 2006, . 3277 [RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet 3278 Control Message Protocol (ICMPv6) for the Internet 3279 Protocol Version 6 (IPv6) Specification", STD 89, 3280 RFC 4443, DOI 10.17487/RFC4443, March 2006, 3281 . 3283 [RFC4511] Sermersheim, J., Ed., "Lightweight Directory Access 3284 Protocol (LDAP): The Protocol", RFC 4511, 3285 DOI 10.17487/RFC4511, June 2006, 3286 . 3288 [RFC4541] Christensen, M., Kimball, K., and F. Solensky, 3289 "Considerations for Internet Group Management Protocol 3290 (IGMP) and Multicast Listener Discovery (MLD) Snooping 3291 Switches", RFC 4541, DOI 10.17487/RFC4541, May 2006, 3292 . 3294 [RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick, 3295 "Internet Group Management Protocol (IGMP) / Multicast 3296 Listener Discovery (MLD)-Based Multicast Forwarding 3297 ("IGMP/MLD Proxying")", RFC 4605, DOI 10.17487/RFC4605, 3298 August 2006, . 3300 [RFC4607] Holbrook, H. and B. Cain, "Source-Specific Multicast for 3301 IP", RFC 4607, DOI 10.17487/RFC4607, August 2006, 3302 . 3304 [RFC4963] Heffner, J., Mathis, M., and B. Chandler, "IPv4 Reassembly 3305 Errors at High Data Rates", RFC 4963, 3306 DOI 10.17487/RFC4963, July 2007, 3307 . 3309 [RFC4982] Bagnulo, M. and J. Arkko, "Support for Multiple Hash 3310 Algorithms in Cryptographically Generated Addresses 3311 (CGAs)", RFC 4982, DOI 10.17487/RFC4982, July 2007, 3312 . 3314 [RFC5015] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano, 3315 "Bidirectional Protocol Independent Multicast (BIDIR- 3316 PIM)", RFC 5015, DOI 10.17487/RFC5015, October 2007, 3317 . 3319 [RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site 3320 Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214, 3321 DOI 10.17487/RFC5214, March 2008, 3322 . 3324 [RFC5320] Templin, F., Ed., "The Subnetwork Encapsulation and 3325 Adaptation Layer (SEAL)", RFC 5320, DOI 10.17487/RFC5320, 3326 February 2010, . 3328 [RFC5522] Eddy, W., Ivancic, W., and T. Davis, "Network Mobility 3329 Route Optimization Requirements for Operational Use in 3330 Aeronautics and Space Exploration Mobile Networks", 3331 RFC 5522, DOI 10.17487/RFC5522, October 2009, 3332 . 3334 [RFC5558] Templin, F., Ed., "Virtual Enterprise Traversal (VET)", 3335 RFC 5558, DOI 10.17487/RFC5558, February 2010, 3336 . 3338 [RFC5569] Despres, R., "IPv6 Rapid Deployment on IPv4 3339 Infrastructures (6rd)", RFC 5569, DOI 10.17487/RFC5569, 3340 January 2010, . 3342 [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 3343 (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, 3344 . 3346 [RFC6106] Jeong, J., Park, S., Beloeil, L., and S. Madanapalli, 3347 "IPv6 Router Advertisement Options for DNS Configuration", 3348 RFC 6106, DOI 10.17487/RFC6106, November 2010, 3349 . 3351 [RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful 3352 NAT64: Network Address and Protocol Translation from IPv6 3353 Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146, 3354 April 2011, . 3356 [RFC6179] Templin, F., Ed., "The Internet Routing Overlay Network 3357 (IRON)", RFC 6179, DOI 10.17487/RFC6179, March 2011, 3358 . 3360 [RFC6221] Miles, D., Ed., Ooghe, S., Dec, W., Krishnan, S., and A. 3361 Kavanagh, "Lightweight DHCPv6 Relay Agent", RFC 6221, 3362 DOI 10.17487/RFC6221, May 2011, 3363 . 3365 [RFC6273] Kukec, A., Krishnan, S., and S. Jiang, "The Secure 3366 Neighbor Discovery (SEND) Hash Threat Analysis", RFC 6273, 3367 DOI 10.17487/RFC6273, June 2011, 3368 . 3370 [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer 3371 Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, 3372 January 2012, . 3374 [RFC6438] Carpenter, B. and S. Amante, "Using the IPv6 Flow Label 3375 for Equal Cost Multipath Routing and Link Aggregation in 3376 Tunnels", RFC 6438, DOI 10.17487/RFC6438, November 2011, 3377 . 3379 [RFC6706] Templin, F., Ed., "Asymmetric Extended Route Optimization 3380 (AERO)", RFC 6706, DOI 10.17487/RFC6706, August 2012, 3381 . 3383 [RFC6864] Touch, J., "Updated Specification of the IPv4 ID Field", 3384 RFC 6864, DOI 10.17487/RFC6864, February 2013, 3385 . 3387 [RFC7269] Chen, G., Cao, Z., Xie, C., and D. Binet, "NAT64 3388 Deployment Options and Experience", RFC 7269, 3389 DOI 10.17487/RFC7269, June 2014, 3390 . 3392 [RFC7333] Chan, H., Ed., Liu, D., Seite, P., Yokota, H., and J. 3393 Korhonen, "Requirements for Distributed Mobility 3394 Management", RFC 7333, DOI 10.17487/RFC7333, August 2014, 3395 . 3397 [RFC7421] Carpenter, B., Ed., Chown, T., Gont, F., Jiang, S., 3398 Petrescu, A., and A. Yourtchenko, "Analysis of the 64-bit 3399 Boundary in IPv6 Addressing", RFC 7421, 3400 DOI 10.17487/RFC7421, January 2015, 3401 . 3403 [RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I., 3404 Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent 3405 Multicast - Sparse Mode (PIM-SM): Protocol Specification 3406 (Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March 3407 2016, . 3409 [RFC8086] Yong, L., Ed., Crabbe, E., Xu, X., and T. Herbert, "GRE- 3410 in-UDP Encapsulation", RFC 8086, DOI 10.17487/RFC8086, 3411 March 2017, . 3413 [RFC8201] McCann, J., Deering, S., Mogul, J., and R. Hinden, Ed., 3414 "Path MTU Discovery for IP version 6", STD 87, RFC 8201, 3415 DOI 10.17487/RFC8201, July 2017, 3416 . 3418 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 3419 Decraene, B., Litkowski, S., and R. Shakir, "Segment 3420 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 3421 July 2018, . 3423 [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol 3424 Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, 3425 . 3427 Appendix A. AERO Alternate Encapsulations 3429 When GUE encapsulation is not needed, AERO can use common 3430 encapsulations such as IP-in-IP [RFC2003][RFC2473][RFC4213], Generic 3431 Routing Encapsulation (GRE) [RFC2784][RFC2890] and others. The 3432 encapsulation is therefore only differentiated from non-AERO tunnels 3433 through the application of AERO control messaging and not through, 3434 e.g., a well-known UDP port number. 3436 As for GUE encapsulation, alternate AERO encapsulation formats may 3437 require encapsulation layer fragmentation. For simple IP-in-IP 3438 encapsulation, an IPv6 fragment header is inserted directly between 3439 the inner and outer IP headers when needed, i.e., even if the outer 3440 header is IPv4. The IPv6 Fragment Header is identified to the outer 3441 IP layer by its IP protocol number, and the Next Header field in the 3442 IPv6 Fragment Header identifies the inner IP header version. For GRE 3443 encapsulation, a GRE fragment header is inserted within the GRE 3444 header [I-D.templin-intarea-grefrag]. 3446 Figure 6 shows the AERO IP-in-IP encapsulation format before any 3447 fragmentation is applied: 3449 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3450 | Outer IPv4 Header | | Outer IPv6 Header | 3451 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3452 |IPv6 Frag Header (optional)| |IPv6 Frag Header (optional)| 3453 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3454 | Inner IP Header | | Inner IP Header | 3455 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3456 | | | | 3457 ~ ~ ~ ~ 3458 ~ Inner Packet Body ~ ~ Inner Packet Body ~ 3459 ~ ~ ~ ~ 3460 | | | | 3461 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3463 Minimal Encapsulation in IPv4 Minimal Encapsulation in IPv6 3465 Figure 6: Minimal Encapsulation Format using IP-in-IP 3467 Figure 7 shows the AERO GRE encapsulation format before any 3468 fragmentation is applied: 3470 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3471 | Outer IP Header | 3472 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3473 | GRE Header | 3474 | (with checksum, key, etc..) | 3475 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3476 | GRE Fragment Header (optional)| 3477 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3478 | Inner IP Header | 3479 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3480 | | 3481 ~ ~ 3482 ~ Inner Packet Body ~ 3483 ~ ~ 3484 | | 3485 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3487 Figure 7: Minimal Encapsulation Using GRE 3489 Alternate encapsulation may be preferred in environments where GUE 3490 encapsulation would add unnecessary overhead. For example, certain 3491 low-bandwidth wireless data links may benefit from a reduced 3492 encapsulation overhead. 3494 GUE encapsulation can traverse network paths that are inaccessible to 3495 non-UDP encapsulations, e.g., for crossing Network Address 3496 Translators (NATs). More and more, network middleboxes are also 3497 being configured to discard packets that include anything other than 3498 a well-known IP protocol such as UDP and TCP. It may therefore be 3499 necessary to determine the potential for middlebox filtering before 3500 enabling alternate encapsulation in a given environment. 3502 In addition to IP-in-IP, GRE and GUE, AERO can also use security 3503 encapsulations such as IPsec, TLS/SSL, DTLS, etc. In that case, AERO 3504 control messaging and route determination occur before security 3505 encapsulation is applied for outgoing packets and after security 3506 decapsulation is applied for incoming packets. 3508 AERO is especially well suited for use with VPN system encapsulations 3509 such as OpenVPN [OVPN]. 3511 Appendix B. Non-Normative Considerations 3513 AERO can be applied to a multitude of Internetworking scenarios, with 3514 each having its own adaptations. The following considerations are 3515 provided as non-normative guidance: 3517 B.1. Implementation Strategies for Route Optimization 3519 Route optimization as discussed in Section 3.17 results in the route 3520 optimization source (ROS) creating an asymmetric neighbor cache entry 3521 for the target neighbor. The neighbor cache entry is maintained for 3522 at most REACHABLETIME seconds and then deleted unless updated. In 3523 order to refresh the neighbor cache entry lifetime before the 3524 ReachableTime timer expires, the specification requires 3525 implementations to issue a new NS/NA exchange to reset ReachableTime 3526 to REACHABLETIME seconds while data packets are still flowing. 3527 However, the decision of when to initiate a new NS/NA exchange and to 3528 perpetuate the process is left as an implementation detail. 3530 One possible strategy may be to monitor the neighbor cache entry 3531 watching for data packets for (REACHABLETIME - 5) seconds. If any 3532 data packets have been sent to the neighbor within this timeframe, 3533 then send an NS to receive a new NA. If no data packets have been 3534 sent, wait for 5 additional seconds and send an immediate NS if any 3535 data packets are sent within this "expiration pending" 5 second 3536 window. If no additional data packets are sent within the 5 second 3537 window, delete the neighbor cache entry. 3539 The monitoring of the neighbor data packet traffic therefore becomes 3540 an asymmetric ongoing process during the neighbor cache entry 3541 lifetime. If the neighbor cache entry expires, future data packets 3542 will trigger a new NS/NA exchange while the packets themselves are 3543 delivered over a longer path until route optimization state is re- 3544 established. 3546 B.2. Implicit Mobility Management 3548 AERO interface neighbors MAY provide a configuration option that 3549 allows them to perform implicit mobility management in which no ND 3550 messaging is used. In that case, the Client only transmits packets 3551 over a single interface at a time, and the neighbor always observes 3552 packets arriving from the Client from the same link-layer source 3553 address. 3555 If the Client's underlying interface address changes (either due to a 3556 readdressing of the original interface or switching to a new 3557 interface) the neighbor immediately updates the neighbor cache entry 3558 for the Client and begins accepting and sending packets according to 3559 the Client's new address. This implicit mobility method applies to 3560 use cases such as cellphones with both WiFi and Cellular interfaces 3561 where only one of the interfaces is active at a given time, and the 3562 Client automatically switches over to the backup interface if the 3563 primary interface fails. 3565 B.3. Direct Underlying Interfaces 3567 When a Client's AERO interface is configured over a Direct interface, 3568 the neighbor at the other end of the Direct link can receive packets 3569 without any encapsulation. In that case, the Client sends packets 3570 over the Direct link according to QoS preferences. If the Direct 3571 interface has the highest QoS preference, then the Client's IP 3572 packets are transmitted directly to the peer without going through an 3573 ANET/INET. If other interfaces have higher QoS preferences, then the 3574 Client's IP packets are transmitted via a different interface, which 3575 may result in the inclusion of Proxys, Servers and Relays in the 3576 communications path. Direct interfaces must be tested periodically 3577 for reachability, e.g., via NUD. 3579 B.4. AERO Clients on the Open Internetwork 3581 AERO Clients that connect to the open Internetwork via either a 3582 native or NATed interface can establish a VPN to securely connect to 3583 a Server. Alternatively, the Client can exchange ND messages 3584 directly with other AERO nodes on the same SPAN segment using INET 3585 encapsulation only and without joining the SPAN. In that case, 3586 however, the Client must apply asymmetric security for ND messages to 3587 ensure routing and neighbor cache integrity (see: Section 6). 3589 B.5. Operation on AERO Links with /64 ASPs 3591 IPv6 AERO links typically have MSPs that aggregate many candidate 3592 MNPs of length /64 or shorter. However, in some cases it may be 3593 desirable to use AERO over links that have only a /64 MSP. This can 3594 be accommodated by treating all Clients on the AERO link as simple 3595 hosts that receive /128 prefix delegations. 3597 In that case, the Client sends an RS message to the Server the same 3598 as for ordinary AERO links. The Server responds with an RA message 3599 that includes one or more /128 prefixes (i.e., singleton addresses) 3600 that include the /64 MSP prefix along with an interface identifier 3601 portion to be assigned to the Client. The Client and Server then 3602 configure their AERO addresses based on the interface identifier 3603 portions of the /128s (i.e., the lower 64 bits) and not based on the 3604 /64 prefix (i.e., the upper 64 bits). 3606 For example, if the MSP for the host-only IPv6 AERO link is 3607 2001:db8:1000:2000::/64, each Client will receive one or more /128 3608 IPv6 prefix delegations such as 2001:db8:1000:2000::1/128, 3609 2001:db8:1000:2000::2/128, etc. When the Client receives the prefix 3610 delegations, it assigns the AERO addresses fe80::1, fe80::2, etc. to 3611 the AERO interface, and assigns the global IPv6 addresses (i.e., the 3612 /128s) to either the AERO interface or an internal virtual interface 3613 such as a loopback. In this arrangement, the Client conducts route 3614 optimization in the same sense as discussed in Section 3.17. 3616 This specification has applicability for nodes that act as a Client 3617 on an "upstream" AERO link, but also act as a Server on "downstream" 3618 AERO links. More specifically, if the node acts as a Client to 3619 receive a /64 prefix from the upstream AERO link it can then act as a 3620 Server to provision /128s to Clients on downstream AERO links. 3622 B.6. AERO Adaptations for SEcure Neighbor Discovery (SEND) 3624 SEcure Neighbor Discovery (SEND) [RFC3971] and Cryptographically 3625 Generated Addresses (CGAs) [RFC3972] were designed to secure IPv6 ND 3626 messaging in environments where symmetric network and/or transport- 3627 layer security services are impractical (see: Section 6). AERO nodes 3628 that use SEND/CGA employ the following adaptations. 3630 When a source AERO node prepares a SEND-protected ND message, it uses 3631 a link-local CGA as the IPv6 source address and writes the prefix 3632 embedded in its AERO address (i.e., instead of fe80::/64) in the CGA 3633 parameters Subnet Prefix field. When the neighbor receives the ND 3634 message, it first verifies the message checksum and SEND/CGA 3635 parameters while using the link-local prefix fe80::/64 (i.e., instead 3636 of the value in the Subnet Prefix field) to match against the IPv6 3637 source address of the ND message. 3639 The neighbor then derives the AERO address of the source by using the 3640 value in the Subnet Prefix field as the interface identifier of an 3641 AERO address. For example, if the Subnet Prefix field contains 3642 2001:db8:1:2, the neighbor constructs the AERO address as 3643 fe80::2001:db8:1:2. The neighbor then caches the AERO address in the 3644 neighbor cache entry it creates for the source, and uses the AERO 3645 address as the IPv6 destination address of any ND message replies. 3647 B.7. AERO Critical Infrastructure Considerations 3649 AERO Relays can be either Commercial off-the Shelf (COTS) standard IP 3650 routers or virtual machines in the cloud. Relays must be 3651 provisioned, supported and managed by the INET administrative 3652 authority, and connected to the Relays of other INETs via inter- 3653 domain peerings. Cost for purchasing, configuring and managing 3654 Relays is nominal even for very large AERO links. 3656 AERO Servers can be standard dedicated server platforms, but most 3657 often will be deployed as virtual machines in the cloud. The only 3658 requirements for Servers are that they can run the AERO user-level 3659 code and have at least one network interface connection to the INET. 3660 As with Relays, Servers must be provisioned, supported and managed by 3661 the INET administrative authority. Cost for purchasing, configuring 3662 and managing Servers is nominal especially for virtual Servers hosted 3663 in the cloud. 3665 AERO Proxys are most often standard dedicated server platforms with 3666 one network interface connected to the ANET and a second interface 3667 connected to an INET. As with Servers, the only requirements are 3668 that they can run the AERO user-level code and have at least one 3669 interface connection to the INET. Proxys must be provisioned, 3670 supported and managed by the ANET administrative authority. Cost for 3671 purchasing, configuring and managing Proxys is nominal, and borne by 3672 the ANET administrative authority. 3674 AERO Gateways can be any dedicated server or COTS router platform 3675 connected to INETs and/or EUNs. The Gateway joins the SPAN and 3676 engages in eBGP peering with one or more Relays as a stub AS. The 3677 Gateway then injects its MNPs and/or non-MNP prefixes into the BGP 3678 routing system, and provisions the prefixes to its downstream- 3679 attached networks. The Gateway can perform ROS/ROR services the same 3680 as for any Server, and can route between the MNP and non-MNP address 3681 spaces. 3683 B.8. AERO Server Failure Implications 3685 AERO Servers may appear as a single point of failure in the 3686 architecture, but such is not the case since all Servers on the link 3687 provide identical services and loss of a Server does not imply 3688 immediate and/or comprehensive communication failures. Although 3689 Clients typically associate with a single Server at a time, Server 3690 failure is quickly detected and conveyed by Bidirectional Forward 3691 Detection (BFD) and/or proactive NUD allowing Clients to migrate to 3692 new Servers. 3694 If a Server fails, ongoing packet forwarding to Clients will continue 3695 by virtue of the asymmetric neighbor cache entries that have already 3696 been established in route optimization sources (ROSs). If a Client 3697 also experiences mobility events at roughly the same time the Server 3698 fails, unsolicited NA messages may be lost but proxy neighbor cache 3699 entries in the DEPARTED state will ensure that packet forwarding to 3700 the Client's new locations will continue for up to DEPARTTIME 3701 seconds. 3703 If a Client is left without a Server for an extended timeframe (e.g., 3704 greater than REACHABLETIIME seconds) then existing asymmetric 3705 neighbor cache entries will eventually expire and both ongoing and 3706 new communications will fail. The original source will continue to 3707 retransmit until the Client has established a new Server 3708 relationship, after which time continuous communications will resume. 3710 Therefore, providing many Servers on the link with high availability 3711 profiles provides resilience against loss of individual Servers and 3712 assurance that Clients can establish new Server relationships quickly 3713 in event of a Server failure. 3715 B.9. AERO Client / Server Architecture 3717 The AERO architectural model is client / server in the control plane, 3718 with route optimization in the data plane. The same as for common 3719 Internet services, the AERO Client discovers the addresses of AERO 3720 Servers and selects one Server to connect to. The AERO service is 3721 analogous to common Internet services such as google.com, yahoo.com, 3722 cnn.com, etc. However, there is only one AERO service for the link 3723 and all Servers provide identical services. 3725 Common Internet services provide differing strategies for advertising 3726 server addresses to clients. The strategy is conveyed through the 3727 DNS resource records returned in response to name resolution queries. 3728 As of January 2020 Internet-based 'nslookup' services were used to 3729 determine the following: 3731 o When a client resolves the domainname "google.com", the DNS always 3732 returns one A record (i.e., an IPv4 address) and one AAAA record 3733 (i.e., an IPv6 address). The client receives the same addresses 3734 each time it resolves the domainname via the same DNS resolver, 3735 but may receive different addresses when it resolves the 3736 domainname via different DNS resolvers. But, in each case, 3737 exactly one A and one AAAA record are returned. 3739 o When a client resolves the domainname "ietf.org", the DNS always 3740 returns one A record and one AAAA record with the same addresses 3741 regardless of which DNS resolver is used. 3743 o When a client resolves the domainname "yahoo.com", the DNS always 3744 returns a list of 4 A records and 4 AAAA records. Each time the 3745 client resolves the domainname via the same DNS resolver, the same 3746 list of addresses are returned but in randomized order (i.e., 3747 consistent with a DNS round-robin strategy). But, interestingly, 3748 the same addresses are returned (albeit in randomized order) when 3749 the domainname is resolved via different DNS resolvers. 3751 o When a client resolves the domainname "amazon.com", the DNS always 3752 returns a list of 3 A records and no AAAA records. As with 3753 "yahoo.com", the same three A records are returned from any 3754 worldwide Internet connection point in randomized order. 3756 The above example strategies show differing approaches to Internet 3757 resilience and service distribution offered by major Internet 3758 services. The Google approach exposes only a single IPv4 and a 3759 single IPv6 address to clients. Clients can then select whichever IP 3760 protocol version offers the best response, but will always use the 3761 same IP address according to the current Internet connection point. 3762 This means that the IP address offered by the network must lead to a 3763 highly-available server and/or service distribution point. In other 3764 words, resilience is predicated on high availability within the 3765 network and with no client-initiated failovers expected (i.e., it is 3766 all-or-nothing from the client's perspective). However, Google does 3767 provide for worldwide distributed service distribution by virtue of 3768 the fact that each Internet connection point responds with a 3769 different IPv6 and IPv4 address. The IETF approach is like google 3770 (all-or-nothing from the client's perspective), but provides only a 3771 single IPv4 or IPv6 address on a worldwide basis. This means that 3772 the addresses must be made highly-available at the network level with 3773 no client failover possibility, and if there is any worldwide service 3774 distribution it would need to be conducted by a network element that 3775 is reached via the IP address acting as a service distribution point. 3777 In contrast to the Google and IETF philosophies, Yahoo and Amazon 3778 both provide clients with a (short) list of IP addresses with Yahoo 3779 providing both IP protocol versions and Amazon as IPv4-only. The 3780 order of the list is randomized with each name service query 3781 response, with the effect of round-robin load balancing for service 3782 distribution. With a short list of addresses, there is still 3783 expectation that the network will implement high availability for 3784 each address but in case any single address fails the client can 3785 switch over to using a different address. The balance then becomes 3786 one of function in the network vs function in the end system. 3788 The same implications observed for common highly-available services 3789 in the Internet apply also to the AERO client/server architecture. 3790 When an AERO Client connects to one or more ANETs, it discovers one 3791 or more AERO Server addresses through the mechanisms discussed in 3792 earlier sections. Each Server address presumably leads to a fault- 3793 tolerant clustering arrangement such as supported by Linux-HA, 3794 Extended Virtual Synchrony or Paxos. Such an arrangement has 3795 precedence in common Internet service deployments in lightweight 3796 virtual machines without requiring expensive hardware deployment. 3797 Similarly, common Internet service deployments set service IP 3798 addresses on service distribution points that may relay requests to 3799 many different servers. 3801 For AERO, the expectation is that a combination of the Google/IETF 3802 and Yahoo/Amazon philosophies would be employed. The AERO Client 3803 connects to different ANET access points and can receive 1-2 Server 3804 AERO addresses at each point. It then selects one AERO Server 3805 address, and engages in RS/RA exchanges with the same Server from all 3806 ANET connections. The Client remains with this Server unless or 3807 until the Server fails, in which case it can switch over to an 3808 alternate Server. The Client can likewise switch over to a different 3809 Server at any time if there is some reason for it to do so. So, the 3810 AERO expectation is for a balance of function in the network and end 3811 system, with fault tolerance and resilience at both levels. 3813 Appendix C. Change Log 3815 << RFC Editor - remove prior to publication >> 3817 Changes from draft-templin-intarea-6706bis-32 to draft-templin- 3818 intrea-6706bis-33: 3820 o Updated Proxy discussion with "point-to-multipoint" server 3821 coordination 3823 o Significant updates to Address Resolution and NUD to include 3824 correct addresses in messages 3826 o Differentiate between NS(AR) and NS(NUD) as their addresses and 3827 use cases differ. 3829 Changes from draft-templin-intarea-6706bis-30 to draft-templin- 3830 intrea-6706bis-31: 3832 o Added "advisory PTB messages" under FAA SE2025 contract number 3833 DTFAWA-15-D-00030. 3835 Changes from draft-templin-intarea-6706bis-29 to draft-templin- 3836 intrea-6706bis-30: 3838 o Deprecate "primary" concept. Now, RS/RA keepalives are 3839 mainatained over *all* underlying interfaces (i.e., and not just 3840 one primary). 3842 Changes from draft-templin-intarea-6706bis-28 to draft-templin- 3843 intrea-6706bis-29: 3845 o Changed OMNI interface citation to "draft-templin-6man-omni- 3846 interface" 3848 o Changed SPAN Service Prefix to fd80::/10. 3850 o Changed S/TLLAO format to include 'S' bit for ifIndex 3851 corresponding to the underlying interface that is Source of ND 3852 message. 3854 o Updated Path MTU 3856 Changes from draft-templin-intarea-6706bis-27 to draft-templin- 3857 intrea-6706bis-28: 3859 o MTU and fragmentation. 3861 Changes from draft-templin-intarea-6706bis-26 to draft-templin- 3862 intrea-6706bis-27: 3864 o MTU and fragmentation. 3866 o SPAN Service Prefix set to fd00::/10 3868 o Client SPAN addresses defined. 3870 Changes from draft-templin-intarea-6706bis-25 to draft-templin- 3871 intrea-6706bis-26: 3873 o MTU and RA configuration information updated. 3875 Changes from draft-templin-intarea-6706bis-24 to draft-templin- 3876 intrea-6706bis-25: 3878 o Added concept of "primary" to allow for proxyed RS/RA over only 3879 selected underlying interfaces. 3881 o General Cleanup. 3883 Changes from draft-templin-intarea-6706bis-23 to draft-templin- 3884 intrea-6706bis-24: 3886 o OMNI interface spec now a normative reference. 3888 o Use REACHABLETIME as the nominal Router Lifetime to return in RAs. 3890 o General cleanup. 3892 Changes from draft-templin-intarea-6706bis-22 to draft-templin- 3893 intrea-6706bis-23: 3895 o Choice of using either RS/RA or unsolicited NA for old Server 3896 notification. 3898 o General cleanup. 3900 Changes from draft-templin-intarea-6706bis-21 to draft-templin- 3901 intrea-6706bis-22: 3903 o Tightened up text on Proxy. 3905 o Removed unnecessarily restrictive texts. 3907 o General cleanup. 3909 Changes from draft-templin-intarea-6706bis-20 to draft-templin- 3910 intrea-6706bis-21: 3912 o Clarified relationship between OMNI and S/TLLAO ifIndex-tuples. 3914 o Important text in Section 13.15.3 on Servers timing out Clients 3915 that have gone silent without sending a departure notification. 3917 o New text on RS/RA as "hints of forward progress" for proactive 3918 NUD. 3920 Changes from draft-templin-intarea-6706bis-19 to draft-templin- 3921 intrea-6706bis-20: 3923 o Included new route optimization source and destination addressing 3924 strategy. Now, route optimization maintenance uses the address of 3925 the existing Server instead of the data packet destination address 3926 so that less pressure is placed on the BGP routing system 3927 convergence time and Server constancy is supported. 3929 o Included new method for releasing from old MSE without requiring 3930 Client messaging. 3932 o Included references to new OMNI interface spec (including the OMNI 3933 option). 3935 o New appendix on AERO Client/Server architecture. 3937 Changes from draft-templin-intarea-6706bis-18 to draft-templin- 3938 intrea-6706bis-19: 3940 o Changed Proxy/Server keepalives to use "proactive NUD" in a manner 3941 tha paralles BFD 3943 Changes from draft-templin-intarea-6706bis-17 to draft-templin- 3944 intrea-6706bis-18: 3946 o Discuss how AERO option is used in relation to S/TLLAOs 3948 o New text on Bidirectional Forwarding Detection (BFD) 3950 o Cleaned up usage (and non-usage) of unsolicited NAs 3952 o New appendix on Server failures 3954 Changes from draft-templin-intarea-6706bis-15 to draft-templin- 3955 intrea-6706bis-17: 3957 o S/TLLAO now includes multiple link-layer addresses within a single 3958 option instead of requiring multiple options 3960 o New unsolicited NA message to inform the old link that a Client 3961 has moved to a new link 3963 Changes from draft-templin-intarea-6706bis-14 to draft-templin- 3964 intrea-6706bis-15: 3966 o MTU and fragmentation 3968 o New details in movement to new Server 3969 Changes from draft-templin-intarea-6706bis-13 to draft-templin- 3970 intrea-6706bis-14: 3972 o Security based on secured tunnels, ingress filtering, MAP list and 3973 ROS list 3975 Changes from draft-templin-intarea-6706bis-12 to draft-templin- 3976 intrea-6706bis-13: 3978 o New paragraph in Section 3.6 on AERO interface layering over 3979 secured tunnels 3981 o Removed extraneous text in Section 3.7 3983 o Added new detail to the forwarding algorithm in Section 3.9 3985 o Clarified use of fragmentation 3987 o Route optimization now supported for both MNP and non-MNP-based 3988 prefixes 3990 o Relays are now seen as link-layer elements in the architecture. 3992 o Built out multicast section in detail. 3994 o New Appendix on implementation considerations for route 3995 optimization. 3997 Changes from draft-templin-intarea-6706bis-11 to draft-templin- 3998 intrea-6706bis-12: 4000 o Introduced Gateways as a new AERO element for connecting 4001 Correspondent Nodes on INET links 4003 o Introduced terms "Access Network (ANET)" and "Internetwork (INET)" 4005 o Changed "ASP" to "MSP", and "ACP" to "MNP" 4007 o New figure on the relation of Segments to the SPAN and AERO link 4009 o New "S" bit in S/TLLAO to indicate the "Source" S/TLLAO as opposed 4010 to additional S/TLLAOs 4012 o Changed Interface ID for Servers from 255 to 0xffff 4014 o Significant updates to Route Optimization, NUD, and Mobility 4015 Management 4017 o New Section on Multicast 4019 o New Section on AERO Clients in the open Internetwork 4021 o New Section on Operation over multiple AERO links (VLANs over the 4022 SPAN) 4024 o New Sections on DNS considerations and Transition considerations 4026 o 4028 Changes from draft-templin-intarea-6706bis-10 to draft-templin- 4029 intrea-6706bis-11: 4031 o Added The SPAN 4033 Changes from draft-templin-intarea-6706bis-09 to draft-templin- 4034 intrea-6706bis-10: 4036 o Orphaned packets in flight (e.g., when a neighbor cache entry is 4037 in the DEPARTED state) are now forwarded at the link layer instead 4038 of at the network layer. Forwarding at the network layer can 4039 result in routing loops and/or excessive delays of forwarded 4040 packets while the routing system is still reconverging. 4042 o Update route optimization to clarify the unsecured nature of the 4043 first NS used for route discovery 4045 o Many cleanups and clarifications on ND messaging parameters 4047 Changes from draft-templin-intarea-6706bis-08 to draft-templin- 4048 intrea-6706bis-09: 4050 o Changed PRL to "MAP list" 4052 o For neighbor cache entries, changed "static" to "symmetric", and 4053 "dynamic" to "asymmetric" 4055 o Specified Proxy RS/RA exchanges with Servers on behalf of Clients 4057 o Added discussion of unsolicited NAs in Section 3.16, and included 4058 forward reference to Section 3.18 4060 o Added discussion of AERO Clients used as critical infrastructure 4061 elements to connect fixed networks. 4063 o Added network-based VPN under security considerations 4064 Changes from draft-templin-intarea-6706bis-07 to draft-templin- 4065 intrea-6706bis-08: 4067 o New section on AERO-Aware Access Router 4069 Changes from draft-templin-intarea-6706bis-06 to draft-templin- 4070 intrea-6706bis-07: 4072 o Added "R" bit for release of PDs. Now have a full RS/RA service 4073 that can do PD without requiring DHCPv6 messaging over-the-air 4075 o Clarifications on solicited vs unsolicited NAs 4077 o Clarified use of MAX_NEIGHBOR_ADVERTISEMENTS for the purpose of 4078 increase reliability 4080 Changes from draft-templin-intarea-6706bis-05 to draft-templin- 4081 intrea-6706bis-06: 4083 o Major re-work and simplification of Route Optimization function 4085 o Added Distributed Mobility Management (DMM) and Mobility Anchor 4086 Point (MAP) terminology 4088 o New section on "AERO Critical Infrastructure Element 4089 Considerations" demonstrating low overall cost for the service 4091 o minor text revisions and deletions 4093 o removed extraneous appendices 4095 Changes from draft-templin-intarea-6706bis-04 to draft-templin- 4096 intrea-6706bis-05: 4098 o New Appendix E on S/TLLAO Extensions for special-purpose links. 4099 Discussed ATN/IPS as example. 4101 o New sentence in introduction to declare appendices as non- 4102 normative. 4104 Changes from draft-templin-intarea-6706bis-03 to draft-templin- 4105 intrea-6706bis-04: 4107 o Added definitions for Potential Router List (PRL) and secure 4108 enclave 4110 o Included text on mapping transport layer port numbers to network 4111 layer DSCP values 4113 o Added reference to DTLS and DMM Distributed Mobility Anchoring 4114 working group document 4116 o Reworked Security Considerations 4118 o Updated references. 4120 Changes from draft-templin-intarea-6706bis-02 to draft-templin- 4121 intrea-6706bis-03: 4123 o Added new section on SEND. 4125 o Clarifications on "AERO Address" section. 4127 o Updated references and added new reference for RFC8086. 4129 o Security considerations updates. 4131 o General text clarifications and cleanup. 4133 Changes from draft-templin-intarea-6706bis-01 to draft-templin- 4134 intrea-6706bis-02: 4136 o Note on encapsulation avoidance in Section 4. 4138 Changes from draft-templin-intarea-6706bis-00 to draft-templin- 4139 intrea-6706bis-01: 4141 o Remove DHCPv6 Server Release procedures that leveraged the old way 4142 Relays used to "route" between Server link-local addresses 4144 o Remove all text relating to Relays needing to do any AERO-specific 4145 operations 4147 o Proxy sends RS and receives RA from Server using SEND. Use CGAs 4148 as source addresses, and destination address of RA reply is to the 4149 AERO address corresponding to the Client's ACP. 4151 o Proxy uses SEND to protect RS and authenticate RA (Client does not 4152 use SEND, but rather relies on subnetwork security. When the 4153 Proxy receives an RS from the Client, it creates a new RS using 4154 its own addresses as the source and uses SEND with CGAs to send a 4155 new RS to the Server. 4157 o Emphasize distributed mobility management 4159 o AERO address-based RS injection of ACP into underlying routing 4160 system. 4162 Changes from draft-templin-aerolink-82 to draft-templin-intarea- 4163 6706bis-00: 4165 o Document use of NUD (NS/NA) for reliable link-layer address 4166 updates as an alternative to unreliable unsolicited NA. 4167 Consistent with Section 7.2.6 of RFC4861. 4169 o Server adds additional layer of encapsulation between outer and 4170 inner headers of NS/NA messages for transmission through Relays 4171 that act as vanilla IPv6 routers. The messages include the AERO 4172 Server Subnet Router Anycast address as the source and the Subnet 4173 Router Anycast address corresponding to the Client's ACP as the 4174 destination. 4176 o Clients use Subnet Router Anycast address as the encapsulation 4177 source address when the access network does not provide a 4178 topologically-fixed address. 4180 Author's Address 4182 Fred L. Templin (editor) 4183 Boeing Research & Technology 4184 P.O. Box 3707 4185 Seattle, WA 98124 4186 USA 4188 Email: fltemplin@acm.org