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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 6, 2020 5 rfc6179, rfc6706 (if 6 approved) 7 Intended status: Standards Track 8 Expires: September 7, 2020 10 Asymmetric Extended Route Optimization (AERO) 11 draft-templin-intarea-6706bis-31 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 7, 2020. 45 Copyright Notice 47 Copyright (c) 2020 IETF Trust and the persons identified as the 48 document authors. All rights reserved. 50 This document is subject to BCP 78 and the IETF Trust's Legal 51 Provisions Relating to IETF Documents 52 (https://trustee.ietf.org/license-info) in effect on the date of 53 publication of this document. Please review these documents 54 carefully, as they describe your rights and restrictions with respect 55 to this document. Code Components extracted from this document must 56 include Simplified BSD License text as described in Section 4.e of 57 the Trust Legal Provisions and are provided without warranty as 58 described in the Simplified BSD License. 60 Table of Contents 62 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 63 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 64 3. Asymmetric Extended Route Optimization (AERO) . . . . . . . . 10 65 3.1. AERO Link Reference Model . . . . . . . . . . . . . . . . 10 66 3.2. AERO Node Types . . . . . . . . . . . . . . . . . . . . . 12 67 3.3. AERO Routing System . . . . . . . . . . . . . . . . . . . 13 68 3.3.1. IPv4 Compatibility Routing . . . . . . . . . . . . . 15 69 3.4. AERO Addresses . . . . . . . . . . . . . . . . . . . . . 15 70 3.5. Spanning Partitioned AERO Networks (SPAN) . . . . . . . . 17 71 3.5.1. SPAN Compatibility Addressing . . . . . . . . . . . . 21 72 3.5.2. Client SPAN Addresses . . . . . . . . . . . . . . . . 21 73 3.6. AERO Interface Characteristics . . . . . . . . . . . . . 21 74 3.7. AERO Interface Initialization . . . . . . . . . . . . . . 25 75 3.7.1. AERO Server/Gateway Behavior . . . . . . . . . . . . 25 76 3.7.2. AERO Proxy Behavior . . . . . . . . . . . . . . . . . 26 77 3.7.3. AERO Client Behavior . . . . . . . . . . . . . . . . 26 78 3.7.4. AERO Relay Behavior . . . . . . . . . . . . . . . . . 26 79 3.8. AERO Interface Neighbor Cache Maintenance . . . . . . . . 26 80 3.9. AERO Interface Encapsulation and Re-encapsulation . . . . 28 81 3.10. AERO Interface Decapsulation . . . . . . . . . . . . . . 29 82 3.11. AERO Interface Data Origin Authentication . . . . . . . . 30 83 3.12. AERO Interface MTU and Fragmentation . . . . . . . . . . 30 84 3.13. AERO Interface Forwarding Algorithm . . . . . . . . . . . 32 85 3.13.1. Client Forwarding Algorithm . . . . . . . . . . . . 33 86 3.13.2. Proxy Forwarding Algorithm . . . . . . . . . . . . . 33 87 3.13.3. Server/Gateway Forwarding Algorithm . . . . . . . . 35 88 3.13.4. Relay Forwarding Algorithm . . . . . . . . . . . . . 36 89 3.14. AERO Interface Error Handling . . . . . . . . . . . . . . 37 90 3.15. AERO Router Discovery, Prefix Delegation and 91 Autoconfiguration . . . . . . . . . . . . . . . . . . . . 39 92 3.15.1. AERO ND/PD Service Model . . . . . . . . . . . . . . 39 93 3.15.2. AERO Client Behavior . . . . . . . . . . . . . . . . 40 94 3.15.3. AERO Server Behavior . . . . . . . . . . . . . . . . 42 95 3.16. The AERO Proxy . . . . . . . . . . . . . . . . . . . . . 45 96 3.16.1. Detecting and Responding to Server Failures . . . . 47 97 3.17. AERO Route Optimization . . . . . . . . . . . . . . . . . 48 98 3.17.1. Route Optimization Initiation . . . . . . . . . . . 48 99 3.17.2. Relaying the NS . . . . . . . . . . . . . . . . . . 49 100 3.17.3. Processing the NS and Sending the NA . . . . . . . . 49 101 3.17.4. Relaying the NA . . . . . . . . . . . . . . . . . . 50 102 3.17.5. Processing the NA . . . . . . . . . . . . . . . . . 50 103 3.17.6. Route Optimization Maintenance . . . . . . . . . . . 50 104 3.18. Neighbor Unreachability Detection (NUD) . . . . . . . . . 51 105 3.19. Mobility Management and Quality of Service (QoS) . . . . 52 106 3.19.1. Mobility Update Messaging . . . . . . . . . . . . . 53 107 3.19.2. Announcing Link-Layer Address and/or QoS Preference 108 Changes . . . . . . . . . . . . . . . . . . . . . . 54 109 3.19.3. Bringing New Links Into Service . . . . . . . . . . 54 110 3.19.4. Removing Existing Links from Service . . . . . . . . 54 111 3.19.5. Moving to a New Server . . . . . . . . . . . . . . . 54 112 3.20. Multicast . . . . . . . . . . . . . . . . . . . . . . . . 56 113 3.20.1. Source-Specific Multicast (SSM) . . . . . . . . . . 56 114 3.20.2. Any-Source Multicast (ASM) . . . . . . . . . . . . . 58 115 3.20.3. Bi-Directional PIM (BIDIR-PIM) . . . . . . . . . . . 58 116 3.21. Operation over Multiple AERO Links (VLANs) . . . . . . . 58 117 3.22. DNS Considerations . . . . . . . . . . . . . . . . . . . 60 118 3.23. Transition Considerations . . . . . . . . . . . . . . . . 60 119 3.24. Detecting and Reacting to Server and Relay Failures . . . 61 120 4. Implementation Status . . . . . . . . . . . . . . . . . . . . 61 121 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 61 122 6. Security Considerations . . . . . . . . . . . . . . . . . . . 62 123 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 64 124 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 65 125 8.1. Normative References . . . . . . . . . . . . . . . . . . 65 126 8.2. Informative References . . . . . . . . . . . . . . . . . 67 127 Appendix A. AERO Alternate Encapsulations . . . . . . . . . . . 73 128 Appendix B. Non-Normative Considerations . . . . . . . . . . . . 75 129 B.1. Implementation Strategies for Route Optimization . . . . 76 130 B.2. Implicit Mobility Management . . . . . . . . . . . . . . 76 131 B.3. Direct Underlying Interfaces . . . . . . . . . . . . . . 77 132 B.4. AERO Clients on the Open Internetwork . . . . . . . . . . 77 133 B.5. Operation on AERO Links with /64 ASPs . . . . . . . . . . 77 134 B.6. AERO Adaptations for SEcure Neighbor Discovery (SEND) . . 78 135 B.7. AERO Critical Infrastructure Considerations . . . . . . . 78 136 B.8. AERO Server Failure Implications . . . . . . . . . . . . 79 137 B.9. AERO Client / Server Architecture . . . . . . . . . . . . 80 138 Appendix C. Change Log . . . . . . . . . . . . . . . . . . . . . 82 139 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 89 141 1. Introduction 143 Asymmetric Extended Route Optimization (AERO) fulfills the 144 requirements of Distributed Mobility Management (DMM) [RFC7333] and 145 route optimization [RFC5522] for aeronautical networking and other 146 network mobility use cases. AERO is based on a Non-Broadcast, 147 Multiple Access (NBMA) virtual link model known as the AERO link. 148 The AERO link is a virtual overlay configured over one or more 149 underlying Internetworks, and nodes on the link can exchange IP 150 packets via tunneling. Multilink operation allows for increased 151 reliability, bandwidth optimization and traffic path diversity. 153 The AERO service comprises Clients, Proxys, Servers and Gateways that 154 are seen as AERO link neighbors. Each node's AERO interface uses an 155 IPv6 link-local address format (known as the AERO address) that 156 supports operation of the IPv6 Neighbor Discovery (ND) protocol 157 [RFC4861] and links ND to IP forwarding. A node's AERO interface can 158 be configured over multiple underlying interfaces, and may therefore 159 may appear as a single interface with multiple link-layer addresses. 160 Each link-layer address is subject to change due to mobility and/or 161 QoS fluctuations, and link-layer address changes are signaled by ND 162 messaging the same as for any IPv6 link. 164 AERO links provide a cloud-based service where mobile nodes may use 165 any Server acting as a Mobility Anchor Point (MAP) and fixed nodes 166 may use any Gateway on the link for efficient communications. Fixed 167 nodes forward packets destined to other AERO nodes to the nearest 168 Gateway, which forwards them through the cloud. A mobile node's 169 initial packets are forwarded through the MAP, while direct routing 170 is supported through asymmetric extended route optimization while 171 data packets are flowing. Both unicast and multicast communications 172 are supported, and mobile nodes may efficiently move between 173 locations while maintaining continuous communications with 174 correspondents and without changing their IP Address. 176 AERO Relays are interconnected in a secured private BGP overlay 177 routing instance known as the "SPAN". The SPAN provides a hybrid 178 routing/bridging service to join the underlying Internetworks of 179 multiple disjoint administrative domains into a single unified AERO 180 link. Each AERO link instance is characterized by the set of 181 Mobility Service Prefixes (MSPs) common to all mobile nodes. The 182 link extends to the point where a Gateway/MAP is on the optimal route 183 from any correspondent node on the link, and provides a gateway 184 between the underlying Internetwork and the SPAN. To the underlying 185 Internetwork, the Gateway/MAP is the source of a route to its MSP, 186 and hence uplink traffic to the mobile node is naturally routed to 187 the nearest Gateway/MAP. 189 AERO assumes the use of PIM Sparse Mode in support of multicast 190 communication. In support of Source Specific Multicast (SSM) when a 191 Mobile Node is the source, AERO route optimization ensures that a 192 shortest-path multicast tree is established with provisions for 193 mobility and multilink operation. In all other multicast scenarios 194 there are no AERO dependencies. 196 AERO was designed for aeronautical networking for both manned and 197 unmanned aircraft, where the aircraft is treated as a mobile node 198 that can connect an Internet of Things (IoT). AERO is also 199 applicable to a wide variety of other use cases. For example, it can 200 be used to coordinate the Virtual Private Network (VPN) links of 201 mobile nodes (e.g., cellphones, tablets, laptop computers, etc.) that 202 connect into a home enterprise network via public access networks 203 using services such as OpenVPN [OVPN]. Other applicable use cases 204 are also in scope. 206 The following numbered sections present the AERO specification. The 207 appendices at the end of the document are non-normative. 209 2. Terminology 211 The terminology in the normative references applies; the following 212 terms are defined within the scope of this document: 214 IPv6 Neighbor Discovery (ND) 215 an IPv6 control message service for coordinating neighbor 216 relationships between nodes connected to a common link. AERO 217 interfaces use the ND service specified in [RFC4861]. 219 IPv6 Prefix Delegation (PD) 220 a networking service for delegating IPv6 prefixes to nodes on the 221 link. The nominal PD service is DHCPv6 [RFC8415], however 222 alternate services (e.g., based on ND messaging) are also in scope 223 [I-D.templin-v6ops-pdhost][I-D.templin-6man-dhcpv6-ndopt]. Most 224 notably, a minimal form of PD known as "prefix registration" can 225 be used if the Client knows its prefix in advance and can 226 represent it in the IPv6 source address of an ND message. 228 Access Network (ANET) 229 a node's first-hop data link service network, e.g., a radio access 230 network, cellular service provider network, corporate enterprise 231 network, or the public Internet itself. For secured ANETs, link- 232 layer security services such as IEEE 802.1X and physical-layer 233 security prevent unauthorized access internally while border 234 network-layer security services such as firewalls and proxies 235 prevent unauthorized outside access. 237 ANET interface 238 a node's attachment to a link in an ANET. 240 ANET address 241 an IP address assigned to a node's interface connection to an 242 ANET. 244 Internetwork (INET) 245 a connected IP network topology with a coherent routing and 246 addressing plan and that provides a transit backbone service for 247 ANET end systems. INETs also provide an underlay service over 248 which the AERO virtual link is configured. Example INETs include 249 corporate enterprise networks, aviation networks, and the public 250 Internet itself. When there is no administrative boundary between 251 an ANET and the INET, the ANET and INET are one and the same. 253 INET Partition 254 frequently, INETs such as large corporate enterprise networks are 255 sub-divided internally into separate isolated partitions. Each 256 partition is fully connected internally but disconnected from 257 other partitions, and there is no requirement that separate 258 partitions maintain consistent Internet Protocol and/or addressing 259 plans. (An INET partition is the same as a SPAN segment discussed 260 below.) 262 INET interface 263 a node's attachment to a link in an INET. 265 INET address 266 an IP address assigned to a node's interface connection to an 267 INET. 269 AERO link 270 a Non-Broadcast, Multiple Access (NBMA) tunnel virtual overlay 271 configured over one or more underlying INETs. Nodes on the AERO 272 link appear as single-hop neighbors from the perspective of the 273 virtual overlay even though they may be separated by many 274 underlying INET hops. AERO links may be configured over multiple 275 underlying SPAN segments (see below). 277 AERO interface 278 a node's attachment to an AERO link. Since the addresses assigned 279 to an AERO interface are managed for uniqueness, AERO interfaces 280 do not require Duplicate Address Detection (DAD) and therefore set 281 the administrative variable 'DupAddrDetectTransmits' to zero 282 [RFC4862]. 284 underlying interface 285 an ANET or INET interface over which an AERO interface is 286 configured. 288 AERO address 289 an IPv6 link-local address assigned to an AERO interface and 290 constructed as specified in Section 3.4. 292 base AERO address 293 the lowest-numbered AERO address aggregated by the MNP (see 294 Section 3.4). 296 Mobility Service Prefix (MSP) 297 an IP prefix assigned to the AERO link and from which more- 298 specific Mobile Network Prefixes (MNPs) are derived. 300 Mobile Network Prefix (MNP) 301 an IP prefix allocated from an MSP and delegated to an AERO Client 302 or Gateway. 304 AERO node 305 a node that is connected to an AERO link, or that provides 306 services to other nodes on an AERO link. 308 AERO Client ("Client") 309 an AERO node that connects to one or more ANETs and requests MNP 310 PDs from AERO Servers. The Client assigns a Client AERO address 311 to the AERO interface for use in ND exchanges with other AERO 312 nodes and forwards packets to correspondents according to AERO 313 interface neighbor cache state. 315 AERO Server ("Server") 316 an INET node that configures an AERO interface to provide default 317 forwarding services and a Mobility Anchor Point (MAP) for AERO 318 Clients. The Server assigns an administratively-provisioned AERO 319 address to its AERO interface to support the operation of the ND/ 320 PD services, and advertises all of its associated MNPs via BGP 321 peerings with Relays. 323 AERO Gateway ("Gateway") 324 an AERO Server that also provides forwarding services between 325 nodes reached via the AERO link and correspondents on other links. 326 AERO Gateways are provisioned with MNPs (i.e., the same as for an 327 AERO Client) and run a dynamic routing protocol to discover any 328 non-MNP IP routes. In both cases, the Gateway advertises the 329 MSP(s) over INET interfaces, and distributes all of its associated 330 MNPs and non-MNP IP routes via BGP peerings with Relays (i.e., the 331 same as for an AERO Server). 333 AERO Relay ("Relay") 334 a node that provides hybrid routing/bridging services (as well as 335 a security trust anchor) for nodes on an AERO link. As a router, 336 the Relay forwards packets using standard IP forwarding. As a 337 bridge, the Relay forwards packets over the AERO link without 338 decrementing the IPv6 Hop Limit. AERO Relays peer with Servers 339 and other Relays to discover the full set of MNPs for the link as 340 well as any non-MNPs that are reachable via Gateways. 342 AERO Proxy ("Proxy") 343 a node that provides proxying services between Clients in an ANET 344 and Servers in external INETs. The AERO Proxy is a conduit 345 between the ANET and external INETs in the same manner as for 346 common web proxies, and behaves in a similar fashion as for ND 347 proxies [RFC4389]. 349 Spanning Partitioned AERO Networks (SPAN) 350 a means for bridging disjoint INET partitions as segments of a 351 unified AERO link the same as for a bridged campus LAN. The SPAN 352 is a mid-layer IPv6 encapsulation service in the AERO routing 353 system that supports a unified AERO link view for all segments. 354 Each segment in the SPAN is a distinct INET partition. 356 SPAN Service Prefix (SSP) 357 a global or unique local /96 IPv6 prefix assigned to the AERO link 358 to support SPAN services. 360 SPAN Partition Prefix (SPP) 361 a sub-prefix of the SPAN Service Prefix uniquely assigned to a 362 single SPAN segment. 364 SPAN Address 365 a global or unique local IPv6 address taken from a SPAN Partition 366 Prefix and constructed as specified in Section 3.5. SPAN 367 addresses are statelessly derived from AERO addresses, and vice- 368 versa. 370 ingress tunnel endpoint (ITE) 371 an AERO interface endpoint that injects encapsulated packets into 372 an AERO link. 374 egress tunnel endpoint (ETE) 375 an AERO interface endpoint that receives encapsulated packets from 376 an AERO link. 378 link-layer address 379 an IP address used as an encapsulation header source or 380 destination address from the perspective of the AERO interface. 382 When an upper layer protocol (e.g., UDP) is used as part of the 383 encapsulation, the port number is also considered as part of the 384 link-layer address. From the perspective of the AERO interface, 385 the link-layer address is either an INET address for intra-segment 386 encapsulation or a SPAN address for inter-segment encapsulation. 388 network layer address 389 the source or destination address of an encapsulated IP packet 390 presented to the AERO interface. 392 end user network (EUN) 393 an internal virtual or external edge IP network that an AERO 394 Client or Gateway connects to the rest of the network via the AERO 395 interface. The Client/Gateway sees each EUN as a "downstream" 396 network, and sees the AERO interface as the point of attachment to 397 the "upstream" network. 399 Mobile Node (MN) 400 an AERO Client and all of its downstream-attached networks that 401 move together as a single unit, i.e., an end system that connects 402 an Internet of Things. 404 Mobile Router (MR) 405 a MN's on-board router that forwards packets between any 406 downstream-attached networks and the AERO link. 408 Mobility Anchor Point (MAP) 409 an AERO Server that is currently tracking and reporting the 410 mobility events of its associated Mobile Node Clients. 412 Route Optimization Source (ROS) 413 the AERO node nearest the source that initiates route 414 optimization. The ROS may be a Server or Proxy acting on behalf 415 of the source Client. 417 Route Optimization responder (ROR) 418 the AERO node nearest the target destination that responds to 419 route optimization requests. The ROR may be a Server acting as a 420 MAP on behalf of a target MNP Client, or a Gateway for a non-MNP 421 destination. 423 MAP List 424 a geographically and/or topologically referenced list of AERO 425 addresses of all MAPs within the same AERO link. There is a 426 single MAP list for the entire AERO link. 428 ROS List 429 a list of AERO/SPAN-to-INET address mappings of all ROSes within 430 the same SPAN segment. There is a distinct ROS list for each 431 segment. 433 Distributed Mobility Management (DMM) 434 a BGP-based overlay routing service coordinated by Servers and 435 Relays that tracks all MAP-to-Client associations. 437 Throughout the document, the simple terms "Client", "Server", 438 "Relay", "Proxy" and "Gateway" refer to "AERO Client", "AERO Server", 439 "AERO Relay", "AERO Proxy" and "AERO Gateway", respectively. 440 Capitalization is used to distinguish these terms from other common 441 Internetworking uses in which they appear without capitalization. 443 The terminology of DHCPv6 [RFC8415] and IPv6 ND [RFC4861] (including 444 the names of node variables, messages and protocol constants) is used 445 throughout this document. The terms "All-Routers multicast", "All- 446 Nodes multicast" and "Subnet-Router anycast" are defined in [RFC4291] 447 (with Link-Local scope assumed). Also, the term "IP" is used to 448 generically refer to either Internet Protocol version, i.e., IPv4 449 [RFC0791] or IPv6 [RFC8200]. 451 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 452 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 453 "OPTIONAL" in this document are to be interpreted as described in BCP 454 14 [RFC2119][RFC8174] when, and only when, they appear in all 455 capitals, as shown here. 457 3. Asymmetric Extended Route Optimization (AERO) 459 The following sections specify the operation of IP over Asymmetric 460 Extended Route Optimization (AERO) links: 462 3.1. AERO Link Reference Model 463 +----------------+ 464 | AERO Relay R1 | 465 | Nbr: S1, S2, P1| 466 |(X1->S1; X2->S2)| 467 | MSP M1 | 468 +-+---------+--+-+ 469 +--------------+ | Secured | | +--------------+ 470 |AERO Server S1| | tunnels | | |AERO Server S2| 471 | Nbr: C1, R1 +-----+ | +-----+ Nbr: C2, R1 | 472 | default->R1 | | | default->R1 | 473 | X1->C1 | | | X2->C2 | 474 +-------+------+ | +------+-------+ 475 | AERO Link | | 476 X===+===+===================+==)===============+===+===X 477 | | | | 478 +-----+--------+ +--------+--+-----+ +--------+-----+ 479 |AERO Client C1| | AERO Proxy P1 | |AERO Client C2| 480 | Nbr: S1 | |(Proxy Nbr Cache)| | Nbr: S2 | 481 | default->S1 | +--------+--------+ | default->S2 | 482 | MNP X1 | | | MNP X2 | 483 +------+-------+ .--------+------. +-----+--------+ 484 | (- Proxyed Clients -) | 485 .-. `---------------' .-. 486 ,-( _)-. ,-( _)-. 487 .-(_ IP )-. +-------+ +-------+ .-(_ IP )-. 488 (__ EUN )--|Host H1| |Host H2|--(__ EUN ) 489 `-(______)-' +-------+ +-------+ `-(______)-' 491 Figure 1: AERO Link Reference Model 493 Figure 1 presents the AERO link reference model. In this model: 495 o the AERO link is an overlay network service configured over one or 496 more underlying INET partitions which may be managed by different 497 administrative authorities and have incompatible protocols and/or 498 addressing plans. 500 o AERO Relay R1 aggregates Mobility Service Prefix (MSP) M1, 501 discovers Mobile Network Prefixes (MNPs) X* and advertises the MSP 502 via BGP peerings over secured tunnels to Servers (S1, S2). Relays 503 use the SPAN service to bridge disjoint segments of a partitioned 504 AERO link. 506 o AERO Servers S1 and S2 configure secured tunnels with Relay R1 and 507 also act as Mobility Anchor Points (MAPs) and default routers for 508 their associated Clients C1 and C2. 510 o AERO Clients C1 and C2 associate with Servers S1 and S2, 511 respectively. They receive Mobile Network Prefix (MNP) 512 delegations X1 and X2, and also act as default routers for their 513 associated physical or internal virtual EUNs. Simple hosts H1 and 514 H2 attach to the EUNs served by Clients C1 and C2, respectively. 516 o AERO Proxy P1 configures a secured tunnel with Relay R1 and 517 provides proxy services for AERO Clients in secured enclaves that 518 cannot associate directly with other AERO link neighbors. 520 Each node on the AERO link maintains an AERO interface neighbor cache 521 and an IP forwarding table the same as for any link. Although the 522 figure shows a limited deployment, in common operational practice 523 there will normally be many additional Relays, Servers, Clients and 524 Proxys. 526 3.2. AERO Node Types 528 AERO Relays provide hybrid routing/bridging services (as well as a 529 security trust anchor) for nodes on an AERO link. Relays use 530 standard IPv6 routing to forward packets both within the same INET 531 partitions and between disjoint INET partitions based on a mid-layer 532 IPv6 encapsulation known as the SPAN header. The inner IP layer 533 experiences a virtual bridging service since the inner IP TTL/Hop 534 Limit is not decremented during forwarding. Each Relay also peers 535 with Servers and other Relays in a dynamic routing protocol instance 536 to provide a Distributed Mobility Management (DMM) service for the 537 list of active MNPs (see Section 3.3). Relays present the AERO link 538 as a set of one or more Mobility Service Prefixes (MSPs) but as link- 539 layer devices need not connect directly to the AERO link themselves 540 unless an administrative interface is desired. Relays configure 541 secured tunnels with Servers, Proxys and other Relays; they further 542 maintain IP forwarding table entries for each Mobile Network Prefix 543 (MNP) and any other reachable non-MNP prefixes. 545 AERO Servers provide default forwarding services and a Mobility 546 Anchor Point (MAP) for AERO Client Mobile Nodes (MNs). Each Server 547 also peers with Relays in a dynamic routing protocol instance to 548 advertise its list of associated MNPs (see Section 3.3). Servers 549 facilitate PD exchanges with Clients, where each delegated prefix 550 becomes an MNP taken from an MSP. Servers forward packets between 551 AERO interface neighbors and track each Client's mobility profiles. 553 AERO Clients register their MNPs through PD exchanges with AERO 554 Servers over the AERO link, and distribute the MNPs to nodes on EUNs. 555 A Client may also be co-resident on the same physical or virtual 556 platform as a Server; in that case, the Client and Server behave as a 557 single functional unit. 559 AERO Proxys provide a conduit for ANET AERO Clients to associate with 560 AERO Servers in external INETs. Client and Servers exchange control 561 plane messages via the Proxy acting as a bridge between the ANET/INET 562 boundary. The Proxy forwards data packets between Clients and the 563 AERO link according to forwarding information in the neighbor cache. 564 The Proxy function is specified in Section 3.16. 566 AERO Gateways are Servers that provide forwarding services between 567 the AERO interface and INET/EUN interfaces. Gateways are provisioned 568 with MNPs the same as for an AERO Client, and also run a dynamic 569 routing protocol to discover any non-MNP IP routes. The Gateway 570 advertises the MSP(s) to INETs, and distributes all of its associated 571 MNPs and non-MNP IP routes via BGP peerings with Relays. 573 AERO Relays, Servers, Proxys and Gateways are critical infrastructure 574 elements in fixed (i.e., non-mobile) INET deployments and hence have 575 permanent and unchanging INET addresses. AERO Clients are MNs that 576 connect via ANET interfaces, i.e., their ANET addresses may change 577 when the Client moves to a new ANET connection. 579 3.3. AERO Routing System 581 The AERO routing system comprises a private instance of the Border 582 Gateway Protocol (BGP) [RFC4271] that is coordinated between Relays 583 and Servers and does not interact with either the public Internet BGP 584 routing system or any underlying INET routing systems. 586 In a reference deployment, each Server is configured as an Autonomous 587 System Border Router (ASBR) for a stub Autonomous System (AS) using 588 an AS Number (ASN) that is unique within the BGP instance, and each 589 Server further uses eBGP to peer with one or more Relays but does not 590 peer with other Servers. Each INET of a multi-segment AERO link must 591 include one or more Relays, which peer with the Servers and Proxys 592 within that INET. All Relays within the same INET are members of the 593 same hub AS using a common ASN, and use iBGP to maintain a consistent 594 view of all active MNPs currently in service. The Relays of 595 different INETs peer with one another using eBGP. 597 Relays advertise the AERO link's MSPs and any non-MNP routes to each 598 of their Servers. This means that any aggregated non-MNPs (including 599 "default") are advertised to all Servers. Each Relay configures a 600 black-hole route for each of its MSPs. By black-holing the MSPs, the 601 Relay will maintain forwarding table entries only for the MNPs that 602 are currently active, and packets destined to all other MNPs will 603 correctly incur Destination Unreachable messages due to the black- 604 hole route. In this way, Servers have only partial topology 605 knowledge (i.e., they know only about the MNPs of their directly 606 associated Clients) and they forward all other packets to Relays 607 which have full topology knowledge. 609 Servers maintain a working set of associated MNPs, and dynamically 610 announce new MNPs and withdraw departed MNPs in eBGP updates to 611 Relays. Servers that are configured as Gateways also redistribute 612 non-MNP routes learned from non-AERO interfaces via their eBGP Relay 613 peerings. 615 Clients are expected to remain associated with their current Servers 616 for extended timeframes, however Servers SHOULD selectively suppress 617 updates for impatient Clients that repeatedly associate and 618 disassociate with them in order to dampen routing churn. Servers 619 that are configured as Gateways advertise the MSPs via INET/EUN 620 interfaces, and forward packets between INET/EUN interfaces and the 621 AERO interface using standard IP forwarding. 623 Scaling properties of the AERO routing system are limited by the 624 number of BGP routes that can be carried by Relays. As of 2015, the 625 global public Internet BGP routing system manages more than 500K 626 routes with linear growth and no signs of router resource exhaustion 627 [BGP]. More recent network emulation studies have also shown that a 628 single Relay can accommodate at least 1M dynamically changing BGP 629 routes even on a lightweight virtual machine, i.e., and without 630 requiring high-end dedicated router hardware. 632 Therefore, assuming each Relay can carry 1M or more routes, this 633 means that at least 1M Clients can be serviced by a single set of 634 Relays. A means of increasing scaling would be to assign a different 635 set of Relays for each set of MSPs. In that case, each Server still 636 peers with one or more Relays, but institutes route filters so that 637 BGP updates are only sent to the specific set of Relays that 638 aggregate the MSP. For example, if the MSP for the AERO link is 639 2001:db8::/32, a first set of Relays could service the MSP 640 2001:db8::/40, a second set of Relays could service 641 2001:db8:0100::/40, a third set could service 2001:db8:0200::/40, 642 etc. 644 Assuming up to 1K sets of Relays, the AERO routing system can then 645 accommodate 1B or more MNPs with no additional overhead (for example, 646 it should be possible to service 1B /64 MNPs taken from a /34 MSP and 647 even more for shorter prefixes). In this way, each set of Relays 648 services a specific set of MSPs that they advertise to the native 649 Internetwork routing system, and each Server configures MSP-specific 650 routes that list the correct set of Relays as next hops. This 651 arrangement also allows for natural incremental deployment, and can 652 support small scale initial deployments followed by dynamic 653 deployment of additional Clients, Servers and Relays without 654 disturbing the already-deployed base. 656 Server and Relays can use the Bidirectional Forwarding Detection 657 (BFD) protocol [RFC5880] to quickly detect link failures that don't 658 result in interface state changes, BGP peer failures, and 659 administrative state changes. BFD is important in environments where 660 rapid response to failures is required for routing reconvergence and, 661 hence, communications continuity. 663 A full discussion of the BGP-based routing system used by AERO is 664 found in [I-D.ietf-rtgwg-atn-bgp]. The system provides for 665 Distributed Mobility Management (DMM) per the distributed mobility 666 anchoring architecture [I-D.ietf-dmm-distributed-mobility-anchoring]. 668 3.3.1. IPv4 Compatibility Routing 670 For IPv6 MNPs, the AERO routing system includes ordinary IPv6 routes. 671 For IPv4 MNPs, the AERO routing system includes IPv6 routes based on 672 an IPv4-embedded IPv6 address format discussed in Section 3.5.1. 674 3.4. AERO Addresses 676 A Client's AERO address is an IPv6 link-local address with an 677 interface identifier based on the Client's delegated MNP. Relay, 678 Server and Proxy AERO addresses are assigned from the range fe80::/96 679 and include an administratively-provisioned value in the lower 32 680 bits. 682 For IPv6, Client AERO addresses begin with the prefix fe80::/64 and 683 include in the interface identifier (i.e., the lower 64 bits) a 684 64-bit prefix taken from one of the Client's IPv6 MNPs. For example, 685 if the AERO Client receives the IPv6 MNP: 687 2001:db8:1000:2000::/56 689 it constructs its corresponding AERO addresses as: 691 fe80::2001:db8:1000:2000 693 fe80::2001:db8:1000:2001 695 fe80::2001:db8:1000:2002 697 ... etc. ... 699 fe80::2001:db8:1000:20ff 701 For IPv4, Client AERO addresses are based on an IPv4-mapped IPv6 702 address [RFC4291] formed from an IPv4 MNP and with a prefix length of 703 96 plus the MNP prefix length. For example, for the IPv4 MNP 704 192.0.2.32/28 the IPv4-mapped IPv6 MNP is: 706 0:0:0:0:0:FFFF:192.0.2.16/124 (also written as 707 0:0:0:0:0:FFFF:c000:0210/124) 709 The Client then constructs its AERO addresses with the prefix 710 fe80::/64 and with the lower 64 bits of the IPv4-mapped IPv6 address 711 in the interface identifier as: 713 fe80::FFFF:192.0.2.16 715 fe80::FFFF:192.0.2.17 717 fe80::FFFF:192.0.2.18 719 ... etc. ... 721 fe80:FFFF:192.0.2.31 723 Relay, Server and Proxy AERO addresses are allocated from the range 724 fe80::/96, and MUST be managed for uniqueness. The lower 32 bits of 725 the AERO address includes a unique integer value between 1 and 726 0xfeffffff (e.g., fe80::1, fe80::2, fe80::3, etc., fe80::feff:ffff) 727 as assigned by the administrative authority for the link. If the 728 link spans multiple SPAN segments, the AERO addresses are assigned to 729 each segment in 1x1 correspondence with SPAN addresses (see: 730 Section 3.5). The address fe80:: is the IPv6 link-local Subnet- 731 Router anycast address, and the address fe80::ffff:ffff is the "All- 732 AERO-Servers" address. The address range fe80::ff00:0000/104 is 733 reserved for future use. 735 The lowest-numbered AERO address from a Client's MNP delegation 736 serves as the "base" AERO address (for example, for the MNP 737 2001:db8:1000:2000::/56 the base AERO address is 738 fe80::2001:db8:1000:2000). The Client then assigns the base AERO 739 address to the AERO interface and uses it for the purpose of 740 maintaining the neighbor cache entry. The Server likewise uses the 741 AERO address as its index into the neighbor cache for this Client. 743 If the Client has multiple AERO addresses (i.e., when there are 744 multiple MNPs and/or MNPs with prefix lengths shorter than /64), the 745 Client originates ND messages using the base AERO address as the 746 source address and accepts and responds to ND messages destined to 747 any of its AERO addresses as equivalent to the base AERO address. In 748 this way, the Client maintains a single neighbor cache entry that may 749 be indexed by multiple AERO addresses. 751 The Client's Subnet-Router anycast address can be statelessly 752 determined from its AERO address by simply transposing the AERO 753 address into the upper N bits of the Anycast address followed by 754 128-N bits of zeroes. For example, for the AERO address 755 fe80::2001:db8:1:2 the Subnet-Router anycast address is 756 2001:db8:1:2::. 758 AERO addresses for mobile node Clients embed a MNP as discussed 759 above, while AERO addresses for non-MNP destinations are constructed 760 in exactly the same way. A Client AERO address therefore encodes 761 either an MNP if the prefix is reached via the SPAN or a non-MNP if 762 the prefix is reached via a Gateway. 764 3.5. Spanning Partitioned AERO Networks (SPAN) 766 An AERO link configured over a single INET appears as a single 767 unified link with a consistent underlying network addressing plan. 768 In that case, all nodes on the link can exchange packets via simple 769 INET encapsulation, since the underlying INET is connected. In 770 common practice, however, an AERO link may be partitioned into 771 multiple "segments", where each segment is a distinct INET 772 potentially managed under a different administrative authority (e.g., 773 as for worldwide aviation service providers such as ARINC, SITA, 774 Inmarsat, etc.). Individual INETs may also themselves be partitioned 775 internally, in which case each internal partition is seen as a 776 separate segment. 778 The addressing plan of each segment is consistent internally but will 779 often bear no relation to the addressing plans of other segments. 780 Each segment is also likely to be separated from others by network 781 security devices (e.g., firewalls, proxies, packet filtering 782 gateways, etc.), and in many cases disjoint segments may not even 783 have any common physical link connections at all. Therefore, nodes 784 can only be assured of exchanging packets directly with 785 correspondents in the same segment, and not with those in other 786 segments. The only means for joining the segments therefore is 787 through inter-domain peerings between AERO Relays. 789 The same as for traditional campus LANs, multiple AERO link segments 790 can be joined into a single unified link via a virtual bridging 791 service termed the "SPAN". The SPAN performs link-layer packet 792 forwarding between segments (i.e., bridging) without decrementing the 793 network-layer TTL/Hop Limit. The SPAN model is depicted in Figure 2: 795 . . . . . . . . . . . . . . . . . . . . . . . 796 . . 797 . .-(::::::::) . 798 . .-(::::::::::::)-. +-+ . 799 . (:::: Segment A :::)--|R|---+ . 800 . `-(::::::::::::)-' +-+ | . 801 . `-(::::::)-' | . 802 . | . 803 . .-(::::::::) | . 804 . .-(::::::::::::)-. +-+ | . 805 . (:::: Segment B :::)--|R|---+ . 806 . `-(::::::::::::)-' +-+ | . 807 . `-(::::::)-' | . 808 . | . 809 . .-(::::::::) | . 810 . .-(::::::::::::)-. +-+ | . 811 . (:::: Segment C :::)--|R|---+ . 812 . `-(::::::::::::)-' +-+ | . 813 . `-(::::::)-' | . 814 . | . 815 . ..(etc).. x . 816 . . 817 . . 818 . <- AERO Link Bridged by the SPAN -> . 819 . . . . . . . . . . . . . .. . . . . . . . . 821 Figure 2: The SPAN 823 To support the SPAN, AERO links use the Unique Local Address (ULA) 824 prefix fd80::/10 [RFC4193] as the SPAN Service Prefix (SSP). The 825 prefix length intentionally matches the IPv6 link-local prefix 826 (fe80::/10), and enables a simple 1-bit stateless translation between 827 link-local and SPAN prefixes (i.e., bit 7 is '1' for link-local or 828 '0' for SPAN). 830 Each segment in the SPAN assigns a unique sub-prefix of SSP::/96 831 termed a "SPAN Partition Prefix (SPP)". For example, a first segment 832 could assign fd80::1000/116, a second could assign fd80::2000/116, a 833 third could assign fd80::3000/116, etc. The administrative 834 authorities for each segment must therefore coordinate to assure 835 mutually-exclusive SPP assignments, but internal provisioning of the 836 SPP is an independent local consideration for each administrative 837 authority. 839 An administratively-assigned "SPAN address" is an address taken from 840 a SPP and assigned to a Relay, Server, Gateway or Proxy interface. 841 SPAN addresses are formed by simply clearing bit 7 of an 842 administratively-assigned AERO address. For example, if the SPP is 843 fd80::1000/116, the SPAN address formed from the AERO address 844 fe80::1001 is simply fd80::1001. 846 An "INET address" is an address of a node's interface connection to 847 an INET. AERO/SPAN/INET address mappings are maintained as permanent 848 neighbor cache entires as discussed in Section 3.8. 850 AERO Relays serve as bridges to join multiple segments into a unified 851 AERO link over multiple diverse administrative domains. They support 852 the bridging function by first establishing forwarding table entries 853 for their SPPs either via standard BGP routing or static routes. For 854 example, if three Relays ('A', 'B' and 'C') from different segments 855 serviced the SPPs fd80::1000/116, fd80::2000/116 and fd80::3000/116 856 respectively, then the forwarding tables in each Relay are as 857 follows: 859 A: fd80::1000/116->local, fd80::2000/116->B, fd80::3000/116->C 861 B: fd80::1000/116->A, fd80::2000/116->local, fd80::3000/116->C 863 C: fd80::1000/116->A, fd80::2000/116->B, fd80::3000/116->local 865 These forwarding table entries are permanent and never change, since 866 they correspond to fixed infrastructure elements in their respective 867 segments. This provides the basis for a link-layer forwarding 868 service that cannot be disrupted by routing updates due to node 869 mobility. 871 With the SPPs in place in each Relay's forwarding table, control and 872 data packets sent between AERO nodes in different segments can 873 therefore be carried over the SPAN via encapsulation. For example, 874 when a source AERO node in segment A forwards a packet with IPv6 875 address 2001:db8:1:2::1 to a target AERO node in segment C with IPv6 876 address 2001:db8:1000:2000::1, it first encapsulates the packet in a 877 SPAN header with source SPAN address taken from fd80::1000/116 (e.g., 878 fd80::1001) and destination SPAN address taken from fd80::3000/116 879 (e.g., fd80::3001). Next, it encapsulates the SPAN message in an 880 INET header with source address set to its own INET address (e.g., 881 192.0.2.100) and destination set to the INET address of a Relay 882 (e.g., 192.0.2.1). 884 SPAN encapsulation is based on Generic Packet Tunneling in IPv6 885 [RFC2473]; the encapsulation format in the above example is shown in 886 Figure 3: 888 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 889 | INET Header | 890 | src = 192.0.2.100 | 891 | dst = 192.0.2.1 | 892 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 893 | SPAN Header | 894 | src = fd80::1001 | 895 | dst = fd80::3001 | 896 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 897 | Inner IP Header | 898 | src = 2001:db8:1:2::1 | 899 | dst = 2001:db8:1000:2000::1 | 900 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 901 | | 902 ~ ~ 903 ~ Inner Packet Body ~ 904 ~ ~ 905 | | 906 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 908 Figure 3: SPAN Encapsulation 910 In this format, the inner IP header and packet body are the original 911 IP packet, the SPAN header is an IPv6 header prepared according to 912 [RFC2473], and the INET header is prepared according to Section 3.9. 913 A packet is said to be "forwarded/sent into the SPAN" when it is 914 encapsulated as described above then forwarded via a secured tunnel 915 to a neighboring Relay. 917 This gives rise to a routing system that contains both MNP routes 918 that may change dynamically due to regional node mobility and SPAN 919 routes that never change. The Relays can therefore provide link- 920 layer bridging by sending packets into the SPAN instead of network- 921 layer routing according to MNP routes. As a result, opportunities 922 for packet loss due to node mobility between different segments are 923 mitigated. 925 With reference to Figure 3, for a Client's AERO address the SPAN 926 destination address is simply set to the Subnet-Router anycast 927 address. For non-link-local addresses, the destination SPAN address 928 may not be known in advance for the first few packets of a flow sent 929 via the SPAN. In that case, the SPAN destination address is set to 930 the original packet's destination, and the SPAN routing system will 931 direct the packet to the correct SPAN egress node. (In the above 932 example, the SPAN destination address is simply 933 2001:db8:1000:2000::1.) 935 3.5.1. SPAN Compatibility Addressing 937 For IPv4 MNPs, Servers inject a "SPAN Compatibility Prefix (SCP)" 938 that embeds the MNP into the BGP routing system. The SCP begins with 939 the upper 64 bits of the SSP, followed by the constant string 940 "0000:FFFF" followed by the IPv4 MNP. For example, if the MNP is 941 192.0.2.0/24 then the SCP is fd80::FFFF:192.0.2.0/120. 943 This allows for encapsulation of IPv4 packets in IPv6 headers with 944 "SPAN Compatibility Addresses (SCAs)". In this example, the SCA 945 corresponding to the SCP is simply fd80::FFFF:192.0.2.0, and can be 946 used as the SPAN destination address for packets forwarded via the 947 SPAN. This allows for forwarding of initial IPv4 packets over IPv6 948 SPAN routes, followed by route optimization for direct 949 communications. 951 3.5.2. Client SPAN Addresses 953 When an AERO Client or Proxy encapsulates and fragments a packet 954 (see: Section 3.12), it inserts its "Client SPAN Address" as the IPv6 955 source address of the encapsulation header. This is necessary to 956 provide reassemblers with a source address corresponding to the node 957 that actually inserted the fragment header so that the correct 958 Identification value context is provided. 960 The Client SPAN address is formed by simply clearing bit 7 of the 961 Client's AERO address. For example, for the Client AERO address 962 fe80::2001:db8:1:2 the corresponding Client SPAN address is 963 fd80::2001:db8:1:2. 965 Note that the Client's MNP itself (and not the Client SPAN address) 966 is injected into the routing system due to the /64 assumption in the 967 AERO address construction [RFC7421]. Because of the /64 assumption, 968 the most-significant 64 bits of the Client's MNP are written into the 969 least-significant 64 bits of the AERO address. If MNPs longer than 970 /64 are used in the future (i.e., /65 up to /118) the least- 971 significant bits of the MNP would need to be written into bits 10 972 through 63 of the SPAN address, which would render the address format 973 useless for longest-prefix-match. For more details, see Appendix B 974 of [I-D.templin-6man-omni-interface]. 976 3.6. AERO Interface Characteristics 978 AERO interfaces are virtual interfaces configured over one or more 979 underlying interfaces classified as follows: 981 o Native interfaces have global IP addresses that are reachable from 982 any INET correspondent. All Server, Gateway and Relay interfaces 983 are native interfaces, as are INET-facing interfaces of Proxys. 985 o NATed interfaces connect to a private network behind a Network 986 Address Translator (NAT). The NAT does not participate in any 987 AERO control message signaling, but the Server can issue control 988 messages on behalf of the Client. Clients that are behind a NAT 989 are required to send periodic keepalive messages to keep NAT state 990 alive when there are no data packets flowing. If no other 991 periodic messaging service is available, the Client can send RS 992 messages to receive RA replies from its Server(s). 994 o VPNed interfaces use security encapsulation to a Virtual Private 995 Network (VPN) server that also acts as an AERO Server. As with 996 NATed links, the Server can issue control messages on behalf of 997 the Client, but the Client need not send periodic keepalives in 998 addition to those already used to maintain the VPN connection. 1000 o Proxyed interfaces connect to an ANET that is separated from the 1001 open INET by an AERO Proxy. Unlike NATed and VPNed interfaces, 1002 the Proxy can actively issue control messages on behalf of the 1003 Client. 1005 o Direct interfaces connect a Client directly to a neighbor without 1006 crossing any ANET/INET paths. An example is a line-of-sight link 1007 between a remote pilot and an unmanned aircraft. 1009 AERO interfaces use encapsulation (see: Section 3.9) to exchange 1010 packets with AERO link neighbors over Native, NATed or VPNed 1011 interfaces. AERO interfaces do not use encapsulation over Proxyed 1012 and Direct underlying interfaces. 1014 AERO interfaces maintain a neighbor cache for tracking per-neighbor 1015 state the same as for any interface. AERO interfaces use ND messages 1016 including Router Solicitation (RS), Router Advertisement (RA), 1017 Neighbor Solicitation (NS) and Neighbor Advertisement (NA) for 1018 neighbor cache management. 1020 AERO interfaces send ND messages with an Overlay Multilink Network 1021 Interface (OMNI) option formatted as specified in 1022 [I-D.templin-6man-omni-interface]. The OMNI option includes prefix 1023 registration information and "ifIndex-tuples" containing link quality 1024 information for the AERO interface's underlying interfaces. 1026 When encapsulation is used, AERO interface ND messages MAY also 1027 include an AERO Source/Target Link-Layer Address Option (S/TLLAO) 1028 formatted as shown in Figure 4: 1030 0 1 2 3 1031 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 1032 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1033 | Type | Length | ifIndex[1] |V|S|Reserved[1]| 1034 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1035 ~ Link Layer Address [1] ~ 1036 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1037 | Port Number [1] | ifIndex[2] |V|S|Reserved[2]| 1038 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1039 ~ Link Layer Address [2] ~ 1040 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1041 | Port Number [2] | ~ 1042 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ 1043 ~ ~ 1044 ~ ... ~ 1045 ~ ~ 1046 ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1047 ~ | ifIndex[N] |V|S|Reserved[N]| 1048 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1049 ~ Link Layer Address [N] ~ 1050 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1051 | Port Number [N] | Trailing zero padding | 1052 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1053 | Trailing zero padding (if necessary) | 1054 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1056 Figure 4: AERO Source/Target Link-Layer Address Option (S/TLLAO) 1057 Format 1059 In this format, Type and Length are set the same as specified for S/ 1060 TLLAOs in [RFC4861], with trailing zero padding octets added as 1061 necessary to produce an integral number of 8 octet blocks. The S/ 1062 TLLAO includes N ifIndex-tuples in correspondence to ifIndex-tuples 1063 that appear in the OMNI option. Each ifIndex-tuple includes the 1064 folllowing information: 1066 o ifIndex[i] - the same value as in the corresponding ifIndex-tuple 1067 included in the OMNI option. 1069 o V[i] - a bit that identifies the IP protocol version of the 1070 address found in the Link Layer Address [i] field. The bit is set 1071 to 0 for IPv4 or 1 for IPv6. 1073 o S[i] - a bit that indicates whether this ifIndex[i] corresponds to 1074 the underlying interface that is the source of the ND message 1076 o Reserved[i] - MUST encode the value 0 on transmission, and ignored 1077 on reception. 1079 o Link Layer Address [i] - the IPv4 or IPv6 address used as the 1080 encapsulation source address. The field is 4 bytes in length for 1081 IPv4 or 16 bytes in length for IPv6. 1083 o Port Number [i] - the upper layer protocol port number used as the 1084 encapsulation source port, or 0 when no upper layer protocol 1085 encapsulation is used. The field is 2 bytes in length. 1087 If an S/TLLAO is included, any ifIndex-tuples correspond to a proper 1088 subset of the OMNI option ifIndex-tuples. Any S/TLLAO ifIndex-tuple 1089 having an ifIndex value that does not appear in an OMNI option 1090 ifindex-tuple is ignored. If the same ifIndex value appears in 1091 multiple ifIndex-tuples, the first tuple is processed and the 1092 remaining tuples are ignored. Any S/TLLAO ifIndex-tuples can 1093 therefore be viewed as inter-dependent extensions of their 1094 corresponidng OMNI option ifIndex-tuples, i.e., the OMNI option and 1095 S/TLLAO are companions that are interpreted in conjunction with each 1096 other. 1098 A Client's AERO interface may be configured over multiple underlying 1099 interface connections. For example, common mobile handheld devices 1100 have both wireless local area network ("WLAN") and cellular wireless 1101 links. These links are typically used "one at a time" with low-cost 1102 WLAN preferred and highly-available cellular wireless as a standby. 1103 In a more complex example, aircraft frequently have many wireless 1104 data link types (e.g. satellite-based, cellular, terrestrial, air-to- 1105 air directional, etc.) with diverse performance and cost properties. 1107 If a Client's multiple underlying interfaces are used "one at a time" 1108 (i.e., all other interfaces are in standby mode while one interface 1109 is active), then ND message OMNI options include only a single 1110 ifIndex-tuple and set to a constant value. In that case, the Client 1111 would appear to have a single interface but with a dynamically 1112 changing link-layer address. 1114 If the Client has multiple active underlying interfaces, then from 1115 the perspective of ND it would appear to have multiple link-layer 1116 addresses. In that case, ND message OMNI options MAY include 1117 multiple ifIndex-tuples - each with a value that corresponds to a 1118 specific interface. Every ND message need not include all OMNI and/ 1119 or S/TLLAO ifIndex-tuples; for any ifIndex-tuple not included, the 1120 neighbor considers the status as unchanged. 1122 Relay, Server and Proxy AERO interfaces may be configured over one or 1123 more secured tunnel interfaces. The AERO interface configures both 1124 an AERO address and its corresponding SPAN address, while the 1125 underlying secured tunnel interfaces are either unnumbered or 1126 configure the same SPAN address. The AERO interface encapsulates 1127 each IP packet in a SPAN header and presents the packet to the 1128 underlying secured tunnel interface. For Relays that do not 1129 configure an AERO interface, the secured tunnel interfaces themselves 1130 are exposed to the IP layer with each interface configuring the 1131 Relay's SPAN address. Routing protocols such as BGP therefore run 1132 directly over the Relay's secured tunnel interfaces. For nodes that 1133 configure an AERO interface, routing protocols such as BGP run over 1134 the AERO interface but do not employ SPAN encapsulation. Instead, 1135 the AERO interface presents the routing protocol messages directly to 1136 the underlying secured tunnels without applying encapsulation and 1137 while using the SPAN address as the source address. This distinction 1138 must be honored consistently according to each node's configuration 1139 so that the IP forwarding table will associate discovered IP routes 1140 with the correct interface. 1142 3.7. AERO Interface Initialization 1144 AERO Servers, Proxys and Clients configure AERO interfaces as their 1145 point of attachment to the AERO link. AERO nodes assign the MSPs for 1146 the link to their AERO interfaces (i.e., as a "route-to-interface") 1147 to ensure that packets with destination addresses covered by an MNP 1148 not explicitly assigned to a non-AERO interface are directed to the 1149 AERO interface. 1151 AERO interface initialization procedures for Servers, Proxys, Clients 1152 and Relays are discussed in the following sections. 1154 3.7.1. AERO Server/Gateway Behavior 1156 When a Server enables an AERO interface, it assigns AERO/SPAN 1157 addresses and configures permanent neighbor cache entries for 1158 neighbors in the same SPAN segment by consulting the ROS list for the 1159 segment. The Server also configures secured tunnels with one or more 1160 neighboring Relays and engages in a BGP routing protocol session with 1161 each Relay. 1163 The AERO interface provides a single interface abstraction to the IP 1164 layer, but internally comprises multiple secured tunnels as well as 1165 an NBMA nexus for sending encapsulated data packets to AERO interface 1166 neighbors. The Server further configures a service to facilitate ND/ 1167 PD exchanges with AERO Clients and manages per-Client neighbor cache 1168 entries and IP forwarding table entries based on control message 1169 exchanges. 1171 Gateways are simply Servers that run a dynamic routing protocol 1172 between the AERO interface and INET/EUN interfaces (see: 1173 Section 3.3). The Gateway provisions MNPs to networks on the INET/ 1174 EUN interfaces (i.e., the same as a Client would do) and advertises 1175 the MSP(s) for the AERO link over the INET/EUN interfaces. The 1176 Gateway further provides an attachment point of the AERO link to the 1177 non-MNP-based global topology. 1179 3.7.2. AERO Proxy Behavior 1181 When a Proxy enables an AERO interface, it assigns AERO/SPAN 1182 addresses and configures permanent neighbor cache entries the same as 1183 for Servers. The Proxy also configures secured tunnels with one or 1184 more neighboring Relays and maintains per-Client neighbor cache 1185 entries based on control message exchanges. 1187 3.7.3. AERO Client Behavior 1189 When a Client enables an AERO interface, it sends an RS message with 1190 ND/PD parameters over an ANET interface to a Server in the MAP list, 1191 which returns an RA message with corresponding parameters. (The RS/ 1192 RA messages may pass through a Proxy in the case of a Client's 1193 Proxyed interface.) 1195 After the initial ND/PD message exchange, the Client assigns AERO 1196 addresses to the AERO interface based on the delegated prefix(es). 1197 The Client can then register additional ANET interfaces with the 1198 Server by sending an RS message over each ANET interface. 1200 3.7.4. AERO Relay Behavior 1202 AERO Relays need not connect directly to the AERO link, since they 1203 operate as link-layer forwarding devices instead of network layer 1204 routers. Configuration of AERO interfaces on Relays is therefore 1205 OPTIONAL, e.g., if an administrative interface is needed. Relays 1206 configure secured tunnels with Servers, Proxys and other Relays; they 1207 also configure AERO/SPAN addresses and permanent neighbor cache 1208 entries the same as Servers. Relays engage in a BGP routing protocol 1209 session with a subset of the Servers on the local SPAN segment, and 1210 with other Relays on the SPAN (see: Section 3.3). 1212 3.8. AERO Interface Neighbor Cache Maintenance 1214 Each AERO interface maintains a conceptual neighbor cache that 1215 includes an entry for each neighbor it communicates with on the AERO 1216 link per [RFC4861]. AERO interface neighbor cache entries are said 1217 to be one of "permanent", "symmetric", "asymmetric" or "proxy". 1219 Permanent neighbor cache entries are created through explicit 1220 administrative action; they have no timeout values and remain in 1221 place until explicitly deleted. AERO Servers and Proxys maintain 1222 permanent neighbor cache entries for all other Servers and Proxys 1223 within the same SPAN segment. Each entry maintains the mapping 1224 between the neighbor's network-layer AERO address and corresponding 1225 INET address. The list of all permanent neighbor cache entries for 1226 the SPAN segment is maintained in the segment's ROS list. 1228 Symmetric neighbor cache entries are created and maintained through 1229 RS/RA exchanges as specified in Section 3.15, and remain in place for 1230 durations bounded by ND/PD lifetimes. AERO Servers maintain 1231 symmetric neighbor cache entries for each of their associated 1232 Clients, and AERO Clients maintain symmetric neighbor cache entries 1233 for each of their associated Servers. The list of all Servers on the 1234 AERO link is maintained in the link's MAP list. 1236 Asymmetric neighbor cache entries are created or updated based on 1237 route optimization messaging as specified in Section 3.17, and are 1238 garbage-collected when keepalive timers expire. AERO route 1239 optimization sources (ROSs) maintain asymmetric neighbor cache 1240 entries for active targets with lifetimes based on ND messaging 1241 constants. Asymmetric neighbor cache entries are unidirectional 1242 since only the ROS and not the target (e.g., a Client's MAP) creates 1243 an entry. 1245 Proxy neighbor cache entries are created and maintained by AERO 1246 Proxys when they process Client/Server ND/PD exchanges, and remain in 1247 place for durations bounded by ND/PD lifetimes. AERO Proxys maintain 1248 proxy neighbor cache entries for each of their associated Clients. 1249 Proxy neighbor cache entries track the Client state and the address 1250 of the Client's associated Server. 1252 To the list of neighbor cache entry states in Section 7.3.2 of 1253 [RFC4861], Proxy and Server AERO interfaces add an additional state 1254 DEPARTED that applies to symmetric and proxy neighbor cache entries 1255 for Clients that have recently departed. The interface sets a 1256 "DepartTime" variable for the neighbor cache entry to "DEPARTTIME" 1257 seconds. DepartTime is decremented unless a new ND message causes 1258 the state to return to REACHABLE. While a neighbor cache entry is in 1259 the DEPARTED state, packets destined to the target Client are 1260 forwarded to the Client's new location instead of being dropped. 1261 When DepartTime decrements to 0, the neighbor cache entry is deleted. 1262 It is RECOMMENDED that DEPARTTIME be set to the default constant 1263 value REACHABLETIME plus 10 seconds (40 seconds by default) to allow 1264 a window for packets in flight to be delivered while stale route 1265 optimization state may be present. 1267 When a target Server (acting as a MAP) receives a valid NS message 1268 used for route optimization, it searches for a symmetric neighbor 1269 cache entry for the target Client. The MAP then returns a solicited 1270 NA message without creating a neighbor cache entry for the ROS, but 1271 creates or updates a target Client "Report List" entry for the ROS 1272 and sets a "ReportTime" variable for the entry to REPORTTIME seconds. 1273 The MAP resets ReportTime when it receives a new authentic NS 1274 message, and otherwise decrements ReportTime while no NS messages 1275 have been received. It is RECOMMENDED that REPORTTIME be set to the 1276 default constant value REACHABLETIME plus 10 seconds (40 seconds by 1277 default) to allow a window for route optimization to converge before 1278 ReportTime decrements below REACHABLETIME. 1280 When the ROS receives a solicited NA message response to its NS 1281 message, it creates or updates an asymmetric neighbor cache entry for 1282 the target network-layer and link-layer addresses. The ROS then 1283 (re)sets ReachableTime for the neighbor cache entry to REACHABLETIME 1284 seconds and uses this value to determine whether packets can be 1285 forwarded directly to the target, i.e., instead of via a default 1286 route. The ROS otherwise decrements ReachableTime while no further 1287 solicited NA messages arrive. It is RECOMMENDED that REACHABLETIME 1288 be set to the default constant value 30 seconds as specified in 1289 [RFC4861]. 1291 The ROS also uses the value MAX_UNICAST_SOLICIT to limit the number 1292 of NS keepalives sent when a correspondent may have gone unreachable, 1293 the value MAX_RTR_SOLICITATIONS to limit the number of RS messages 1294 sent without receiving an RA and the value MAX_NEIGHBOR_ADVERTISEMENT 1295 to limit the number of unsolicited NAs that can be sent based on a 1296 single event. It is RECOMMENDED that MAX_UNICAST_SOLICIT, 1297 MAX_RTR_SOLICITATIONS and MAX_NEIGHBOR_ADVERTISEMENT be set to 3 the 1298 same as specified in [RFC4861]. 1300 Different values for DEPARTTIME, REPORTTIME, REACHABLETIME, 1301 MAX_UNICAST_SOLICIT, MAX_RTR_SOLCITATIONS and 1302 MAX_NEIGHBOR_ADVERTISEMENT MAY be administratively set; however, if 1303 different values are chosen, all nodes on the link MUST consistently 1304 configure the same values. Most importantly, DEPARTTIME and 1305 REPORTTIME SHOULD be set to a value that is sufficiently longer than 1306 REACHABLETIME to avoid packet loss due to stale route optimization 1307 state. 1309 3.9. AERO Interface Encapsulation and Re-encapsulation 1311 Client AERO interfaces avoid encapsulation over Direct underlying 1312 interfaces and Proxyed underlying interfaces for which the first-hop 1313 access router is AERO-aware. Other AERO interfaces encapsulate 1314 packets according to whether they are entering the AERO interface 1315 from the network layer or if they are being re-admitted into the same 1316 AERO link they arrived on. This latter form of encapsulation is 1317 known as "re-encapsulation". 1319 For packets entering the AERO interface from the network layer, the 1320 AERO interface copies the "TTL/Hop Limit", "Type of Service/Traffic 1321 Class" [RFC2983], "Flow Label"[RFC6438] (for IPv6) and "Congestion 1322 Experienced" [RFC3168] values in the packet's IP header into the 1323 corresponding fields in the encapsulation header(s). 1325 For packets undergoing re-encapsulation, the AERO interface instead 1326 copies these values from the original encapsulation header into the 1327 new encapsulation header, i.e., the values are transferred between 1328 encapsulation headers and *not* copied from the encapsulated packet's 1329 network-layer header. (Note especially that by copying the TTL/Hop 1330 Limit between encapsulation headers the value will eventually 1331 decrement to 0 if there is a (temporary) routing loop.) For IPv4 1332 encapsulation/re-encapsulation, the AERO interface sets the DF bit as 1333 discussed in Section 3.12. 1335 AERO interfaces configured over INET underlying interfaces 1336 encapsulate each packet in a SPAN header, then encapsulate the 1337 resulting SPAN packet in an INET header according to the next hop 1338 determined in the forwarding algorithm in Section 3.13. If the next 1339 hop is reached via a secured tunnel, the AERO interface uses an INET 1340 encapsulation format specific to the secured tunnel type (see: 1341 Section 6). If the next hop is reached via an unsecured underlying 1342 interface, the AERO interface instead uses Generic UDP Encapsulation 1343 (GUE) [I-D.ietf-intarea-gue] or an alternate minimal encapsulation 1344 format Appendix A. 1346 When GUE encapsulation is used, the AERO interface next sets the UDP 1347 source port to a constant value that it will use in each successive 1348 packet it sends, and sets the UDP length field to the length of the 1349 SPAN packet plus 8 bytes for the UDP header itself plus the length of 1350 the GUE header (or 0 if GUE direct IP encapsulation is used). For 1351 packets sent to a Server or Relay, the AERO interface sets the UDP 1352 destination port to 8060, i.e., the IANA-registered port number for 1353 AERO. For packets sent to a Client, the AERO interface sets the UDP 1354 destination port to the port value stored in the neighbor cache entry 1355 for this Client. The AERO interface then either includes or omits 1356 the UDP checksum according to the GUE specification. 1358 AERO interfaces observes the packet sizing and fragmentation 1359 considerations found in Section 3.12. 1361 3.10. AERO Interface Decapsulation 1363 AERO interfaces decapsulate packets destined either to the AERO node 1364 itself or to a destination reached via an interface other than the 1365 AERO interface the packet was received on. When the encapsulated 1366 packet arrives in multiple fragments, the AERO interface reassembles 1367 as discussed in Section 3.12. Further decapsulation steps are 1368 performed according to the appropriate encapsulation format 1369 specification. 1371 3.11. AERO Interface Data Origin Authentication 1373 AERO nodes employ simple data origin authentication procedures. In 1374 particular: 1376 o AERO Relays, Servers and Proxys accept encapsulated data packets 1377 and control messages received from secured tunnels. 1379 o AERO Servers and Proxys accept encapsulated data packets and NS 1380 messages used for Neighbor Unreachability Detection (NUD) received 1381 from a source found in the ROS list. 1383 o AERO Proxys and Clients accept packets that originate from within 1384 the same secured ANET. 1386 o AERO Clients and Gateways accept packets from downstream network 1387 correspondents based on ingress filtering. 1389 AERO nodes silently drop any packets that do not satisfy the above 1390 data origin authentication procedures. Further security 1391 considerations are discussed Section 6. 1393 3.12. AERO Interface MTU and Fragmentation 1395 All IPv6 interfaces are REQUIRED to configure a minimum Maximum 1396 Transmission Unit (MTU) of 1280 bytes [RFC8200]. (IPv4 interfaces 1397 have a smaller minimum MTU [RFC1122], but SHOULD also observe the 1398 IPv6 minimum MTU if possible.) The AERO link therefore MUST forward 1399 IPv6 packets of at least 1280 bytes without generating an IPv6 Path 1400 MTU Discovery (PMTUD) Packet Too Big (PTB) message [RFC8201]. 1402 The AERO interface configures an MTU of 9180 bytes [RFC2492]; the 1403 size is therefore not a reflection of the underlying interface MTUs, 1404 but rather determines the largest packet the AERO interface can 1405 forward or reassemble. 1407 The AERO interface can employ link-layer IPv6 encapsulation and 1408 fragmentation/reassembly per [RFC2473], but its use is OPTIONAL since 1409 correct operation will result in either case. Implementations that 1410 omit link-layer IPv6 fragmentation/reassembly may be more prone to 1411 dropping large packets and returning a PTB, while those that include 1412 it may see improved performance at the expense of including 1413 additional code. In both cases, AERO interface neighbors are 1414 responsible for advertising their willingness to reassemble. 1416 The AERO interface returns internally-generated PTB messages for 1417 packets admitted into the interface that it deems too large for the 1418 outbound underlying interface (e.g., according to underlying 1419 interface performance characteristics, MTU, etc). For all other 1420 packets, the AERO interface performs PMTUD even if the destination 1421 appears to be on the same link since a proxy on the path could return 1422 a PTB message. This ensures that the path MTU is adaptive and 1423 reflects the current path used for a given data flow. 1425 When a Client's AERO interface sends a packet that is no larger than 1426 the MTU of the selected underlying interface, it sends according to 1427 the underlying interface L2 frame format. When the AERO interface 1428 sends a packet that is larger than the underlying interface MTU, it 1429 drops the packet and returns a PTB if the neighbor is not willing to 1430 reassemble. 1432 Otherwise, the AERO interface encapsulates the packet in an IPv6 1433 header per [RFC2473] with source address set to the Client's link- 1434 local address and destination address set to the link-local address 1435 of the next hop. The AERO interface then uses IPv6 fragmentation to 1436 break the encapsulated packet into fragments that are no larger than 1437 the underlying interface MTU and sends the fragments over the 1438 underlying interface. The next hop then reassembles, then conveys 1439 the packets toward the final destination. 1441 When a Proxy or Server receives a fragmented or whole packet from the 1442 INET destined to a Client, it must determine whether to forward or 1443 drop and return a PTB (e.g., according to the underlying interface 1444 performance characteristics, MTU, etc). If the Proxy/Server deems 1445 the packet to be of acceptable size, it first reassembles locally (if 1446 necessary) then forwards the packet to the Client. If the 1447 (reassembled) packet is no larger than the underlying interface MTU, 1448 the Proxy/Server forwards according to the underlying interface L2 1449 frame format. If the packet is larger than the MTU, the Proxy/Server 1450 instead uses link-layer encapsulation and IPv6 fragmentation as above 1451 if the Client accepts fragments or drops and returns a PTB otherwise. 1452 The Client then reassembles and discards the encapsulation header, 1453 then forwards the whole packet to the final destination. 1455 When a Proxy, Server or Gateway forwards a Client's packet over the 1456 SPAN, it uses IPv6 encapsulation with the Client's SPAN address as 1457 the source address and the SPAN address of the next hop as the 1458 destination, then uses fragmentation to break the SPAN-encapsulated 1459 packet into pieces no larger than 1280 bytes. When a Server or 1460 Gateway forwards a Client's SPAN-encapsulated packet to a destination 1461 outside of the AERO link, it first reassembles if necessary. This 1462 implies that Proxys, Servers and Gateways MUST support fragmentation 1463 and reassembly for packet exchanges over the SPAN even though 1464 fragmentation and reassembly is OPTIONAL for Clients. 1466 Applications that cannot tolerate loss due to MTU restrictions SHOULD 1467 avoid sending packets larger than 1280 bytes, since dynamic path 1468 changes can reduce the path MTU at any time. Applications that may 1469 benefit from sending larger packets even though the path MTU may 1470 change dynamically MAY use larger sizes (i.e., up to the AERO 1471 interface MTU). 1473 Note that when a Proxy/Server forwards a fragmented packet received 1474 from the INET to a Client, it reassembles locally first instead of 1475 blindly forwarding fragments directly to the Client to avoid attacks 1476 such as tiny fragments, overlapping fragments, etc. 1478 Note also that the AERO interface can forward large packets via 1479 encapsulation and fragmentation while at the same time returning 1480 advisory PTB messages, e.g., subject to rate limiting. The interface 1481 can therefore continuously forward large packets without loss while 1482 sending advisory messages recommending a smaller size. 1484 3.13. AERO Interface Forwarding Algorithm 1486 IP packets enter a node's AERO interface either from the network 1487 layer (i.e., from a local application or the IP forwarding system) or 1488 from the link layer (i.e., from an AERO interface neighbor). All 1489 packets entering a node's AERO interface first undergo data origin 1490 authentication as discussed in Section 3.11. Packets that satisfy 1491 data origin authentication are processed further, while all others 1492 are dropped silently. 1494 Packets that enter the AERO interface from the network layer are 1495 forwarded to an AERO interface neighbor. Packets that enter the AERO 1496 interface from the link layer are either re-admitted into the AERO 1497 link or forwarded to the network layer where they are subject to 1498 either local delivery or IP forwarding. In all cases, the AERO 1499 interface itself MUST NOT decrement the network layer TTL/Hop-count 1500 since its forwarding actions occur below the network layer. 1502 AERO interfaces may have multiple underlying interfaces and/or 1503 neighbor cache entries for neighbors with multiple ifIndex-tuple 1504 registrations (see Section 3.6). The AERO interface uses each 1505 packet's DSCP value (and/or other traffic discriminators such as port 1506 number) to select an outgoing underlying interface based on the 1507 node's own QoS preferences, and also to select a destination link- 1508 layer address based on the neighbor's underlying interface with the 1509 highest preference. AERO implementations SHOULD allow for QoS 1510 preference values to be modified at runtime through network 1511 management. 1513 If multiple outgoing interfaces and/or neighbor interfaces have a 1514 preference of "high", the AERO node replicates the packet and sends 1515 one copy via each of the (outgoing / neighbor) interface pairs; 1516 otherwise, the node sends a single copy of the packet via an 1517 interface with the highest preference. AERO nodes keep track of 1518 which underlying interfaces are currently "reachable" or 1519 "unreachable", and only use "reachable" interfaces for forwarding 1520 purposes. 1522 The following sections discuss the AERO interface forwarding 1523 algorithms for Clients, Proxys, Servers and Relays. In the following 1524 discussion, a packet's destination address is said to "match" if it 1525 is the same as a cached address, or if it is covered by a cached 1526 prefix (which may be encoded in an AERO address). 1528 3.13.1. Client Forwarding Algorithm 1530 When an IP packet enters a Client's AERO interface from the network 1531 layer the Client searches for an asymmetric neighbor cache entry that 1532 matches the destination. If there is a match, the Client uses one or 1533 more "reachable" neighbor interfaces in the entry for packet 1534 forwarding. If there is no asymmetric neighbor cache entry, the 1535 Client instead forwards the packet toward a Server (the packet is 1536 intercepted by a Proxy if there is a Proxy on the path). The Client 1537 inserts a SPAN header and fragments if necessary according to MTU 1538 requirements (see: Section 3.12). 1540 When an IP packet enters a Client's AERO interface from the link- 1541 layer, if the destination matches one of the Client's MNPs or link- 1542 local addresses the Client reassembles and decapsulates the packet as 1543 necessary and delivers it to the network layer. Otherwise, the 1544 Client drops the packet and MAY return a network-layer ICMP 1545 Destination Unreachable message subject to rate limiting (see: 1546 Section 3.14). 1548 3.13.2. Proxy Forwarding Algorithm 1550 For control messages originating from or destined to a Client, the 1551 Proxy intercepts the message and updates its proxy neighbor cache 1552 entry for the Client. The Proxy then forwards a (proxyed) copy of 1553 the control message. (For example, the Proxy forwards a proxied 1554 version of a Client's NS/RS message to the target neighbor, and 1555 forwards a proxied version of the NA/RA reply to the Client.) 1556 When the Proxy receives a data packet from a Client within the ANET, 1557 it first inserts a SPAN header if the packet does not already contain 1558 a SPAN header. The Proxy then sets/changes the SPAN header source 1559 address to the Client's SPAN address and changes the destination 1560 address to the SPAN address of the next hop. The Proxy then 1561 fragments the SPAN packet into fragments no larger than 1280 bytes, 1562 then searches for an asymmetric neighbor cache entry that matches the 1563 destination and forwards the fragments as follows: 1565 o if the destination matches an asymmetric neighbor cache entry, the 1566 Proxy uses one or more "reachable" neighbor interfaces in the 1567 entry for packet forwarding via encapsulation. If the neighbor 1568 interface is in the same SPAN segment, the Proxy forwards the 1569 packet directly to the neighbor; otherwise, it forwards the packet 1570 to a Relay. 1572 o else, the Proxy encapsulates and forwards the packet to a Relay 1573 while using the packet's destination address as the SPAN 1574 destination address. (If the destination is an AERO address, the 1575 Proxy instead uses the corresponding Subnet-Router anycast address 1576 for Client AERO addresses and the SPAN address for 1577 administratively-provisioned AERO addresses.). 1579 When the Proxy receives an encapsulated data packet from an INET 1580 neighbor or from a secured tunnel from a Relay, it accepts the packet 1581 only if data origin authentication succeeds and if there is a proxy 1582 neighbor cache entry that matches the inner destination. Next, if 1583 the packet is a SPAN fragment the Proxy adds the fragment to the 1584 reassembly buffer. The Proxy then reassembles the packet (if 1585 necessary) and continues processing. 1587 Next if reassembly is complete and the neighbor cache state is 1588 REACHABLE, the Proxy either drops and returns a PTB (see: 1589 Section 3.12) or forwards the packet to the Client while performing 1590 SPAN encapsulation and re-fragmentation to the ANET MTU size if 1591 necessary. If the neighbor cache entry state is DEPARTED, the Proxy 1592 instead changes the SPAN destination address to the address of the 1593 new Server and forwards it to a Relay while performing re- 1594 fragmentation to 1280 bytes if necessary. 1596 When the Proxy forwards a SPAN packet to a REACHABLE Client for which 1597 the packet is no larger than the ANET MTU, it decapsulates the SPAN 1598 header first and forwards the (unencapsulated) packet to the Client 1599 to avoid the unnecessary overhead for carrying the SPAN header. Note 1600 also that the Proxy can alternatively hold SPAN fragments for a 1601 DEPARTED Client in its local reassembly buffer, or forward the 1602 fragments to the Client's new Server if it does not already have a 1603 partial reassembly already in progress. 1605 3.13.3. Server/Gateway Forwarding Algorithm 1607 For control messages destined to a target Client's AERO address that 1608 are received from a secured tunnel, the Server (acting as a MAP) 1609 intercepts the message and sends an appropriate response on behalf of 1610 the Client. (For example, the Server sends an NA message reply in 1611 response to an NS message directed to one of its associated Clients.) 1612 If the Client's neighbor cache entry is in the DEPARTED state, 1613 however, the Server instead forwards the packet to the Client's new 1614 Server as discussed in Section 3.19. 1616 When the Server receives an encapsulated data packet from an INET 1617 neighbor or from a secured tunnel, it accepts the packet only if data 1618 origin authentication succeeds. If the SPAN destination address is 1619 its own address, the Server continues processing as follows: 1621 o if the destination matches a symmetric neighbor cache entry in the 1622 REACHABLE state the Server prepares the packet for forwarding to 1623 the destination Client. For the Client's Proxyed interfaces, the 1624 Server changes the SPAN destination address to the address of the 1625 Proxy and forwards the packet to the Proxy. For the Client's 1626 other interfaces, the Server reassembles then either drops and 1627 returns a PTB (see: Section 3.12) or forwards the packet (while 1628 re-fragmenting if necessary) using SPAN encapsulation for the 1629 Client's Native, NATed or VPNed interfaces, or no encapsulation 1630 for Direct interfaces. 1632 o else, if the destination matches a symmetric neighbor cache entry 1633 in the DEPARETED state the Server re-encapsulates the packet and 1634 forwards it using the SPAN address of the Client's new Server as 1635 the destination. 1637 o else, if the destination matches an asymmetric neighbor cache 1638 entry, the Server uses one or more "reachable" neighbor interfaces 1639 in the entry for packet forwarding via the local INET if the 1640 neighbor is in the same SPAN segment or via a Relay otherwise. 1642 o else, if the destination is an AERO address that is not assigned 1643 on the AERO interface the Server drops the packet. 1645 o else, the Server (acting as a Gateway) reassembles if necessary, 1646 decapsulates the packet and releases it to the network layer for 1647 local delivery or IP forwarding. Based on the information in the 1648 forwarding table, the network layer may return the packet to the 1649 same AERO interface in which case further processing occurs as 1650 below. (Note that this arrangement accommodates common 1651 implementations in which the IP forwarding table is not accessible 1652 from within the AERO interface. If the AERO interface can 1653 directly access the IP forwarding table (such as for in-kernel 1654 implementations) the forwarding table lookup can instead be 1655 performed internally from within the AERO interface itself.) 1657 When the Server's AERO interface receives a data packet from the 1658 network layer or from a NATed/VPNed/Direct Client, it performs SPAN 1659 encapsualtion and fragmentation if necessary, then processes the 1660 packet according to the network-layer destination address as follows: 1662 o if the destination matches a symmetric or asymmetric neighbor 1663 cache entry the Server processes the packet as above. 1665 o else, the Server encapsulates the packet and forwards it to a 1666 Relay. For administratively-assigned AERO address destinations, 1667 the Server uses the SPAN address corresponding to the destination 1668 as the SPAN destination address. For Client AERO address 1669 destinations, the Server uses the Subnet-Router anycast address 1670 corresponding to the destination as the SPAN destination address. 1671 For all others, the Server uses the packet's destination IP 1672 address as the SPAN destination address. 1674 3.13.4. Relay Forwarding Algorithm 1676 Relays forward packets over secured tunnels the same as any IP 1677 router. When the Relay receives an encapsulated packet via a secured 1678 tunnel, it removes the INET header and searches for a forwarding 1679 table entry that matches the destination address in the next header. 1680 The Relay then processes the packet as follows: 1682 o if the destination matches one of the Relay's own addresses, the 1683 Relay submits the packet for local delivery. 1685 o else, if the destination matches a forwarding table entry the 1686 Relay forwards the packet via a secured tunnel to the next hop. 1687 If the destination matches an MSP without matching an MNP, 1688 however, the Relay instead drops the packet and returns an ICMP 1689 Destination Unreachable message subject to rate limiting (see: 1690 Section 3.14). 1692 o else, the Relay drops the packet and returns an ICMP Destination 1693 Unreachable as above. 1695 As for any IP router, the Relay decrements the TTL/Hop Limit when it 1696 forwards the packet. If the packet is encapsulated in a SPAN header, 1697 only the Hop Limit in the SPAN header is decremented, and not the 1698 TTL/Hop Limit in the inner packet header. 1700 3.14. AERO Interface Error Handling 1702 When an AERO node admits a packet into the AERO interface, it may 1703 receive link-layer or network-layer error indications. 1705 A link-layer error indication is an ICMP error message generated by a 1706 router in the INET on the path to the neighbor or by the neighbor 1707 itself. The message includes an IP header with the address of the 1708 node that generated the error as the source address and with the 1709 link-layer address of the AERO node as the destination address. 1711 The IP header is followed by an ICMP header that includes an error 1712 Type, Code and Checksum. Valid type values include "Destination 1713 Unreachable", "Time Exceeded" and "Parameter Problem" 1714 [RFC0792][RFC4443]. (AERO interfaces ignore all link-layer IPv4 1715 "Fragmentation Needed" and IPv6 "Packet Too Big" messages since they 1716 only emit packets that are guaranteed to be no larger than the IP 1717 minimum link MTU as discussed in Section 3.12.) 1719 The ICMP header is followed by the leading portion of the packet that 1720 generated the error, also known as the "packet-in-error". For 1721 ICMPv6, [RFC4443] specifies that the packet-in-error includes: "As 1722 much of invoking packet as possible without the ICMPv6 packet 1723 exceeding the minimum IPv6 MTU" (i.e., no more than 1280 bytes). For 1724 ICMPv4, [RFC0792] specifies that the packet-in-error includes: 1725 "Internet Header + 64 bits of Original Data Datagram", however 1726 [RFC1812] Section 4.3.2.3 updates this specification by stating: "the 1727 ICMP datagram SHOULD contain as much of the original datagram as 1728 possible without the length of the ICMP datagram exceeding 576 1729 bytes". 1731 The link-layer error message format is shown in Figure 5 (where, "L2" 1732 and "L3" refer to link-layer and network-layer, respectively): 1734 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1735 ~ ~ 1736 | L2 IP Header of | 1737 | error message | 1738 ~ ~ 1739 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1740 | L2 ICMP Header | 1741 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 1742 ~ ~ P 1743 | IP and other encapsulation | a 1744 | headers of original L3 packet | c 1745 ~ ~ k 1746 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ e 1747 ~ ~ t 1748 | IP header of | 1749 | original L3 packet | i 1750 ~ ~ n 1751 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1752 ~ ~ e 1753 | Upper layer headers and | r 1754 | leading portion of body | r 1755 | of the original L3 packet | o 1756 ~ ~ r 1757 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 1759 Figure 5: AERO Interface Link-Layer Error Message Format 1761 The AERO node rules for processing these link-layer error messages 1762 are as follows: 1764 o When an AERO node receives a link-layer Parameter Problem message, 1765 it processes the message the same as described as for ordinary 1766 ICMP errors in the normative references [RFC0792][RFC4443]. 1768 o When an AERO node receives persistent link-layer Time Exceeded 1769 messages, the IP ID field may be wrapping before earlier fragments 1770 awaiting reassembly have been processed. In that case, the node 1771 should begin including integrity checks and/or institute rate 1772 limits for subsequent packets. 1774 o When an AERO node receives persistent link-layer Destination 1775 Unreachable messages in response to encapsulated packets that it 1776 sends to one of its asymmetric neighbor correspondents, the node 1777 should process the message as an indication that a path may be 1778 failing, and optionally initiate NUD over that path. If it 1779 receives Destination Unreachable messages over multiple paths, the 1780 node should allow future packets destined to the correspondent to 1781 flow through a default route and re-initiate route optimization. 1783 o When an AERO Client receives persistent link-layer Destination 1784 Unreachable messages in response to encapsulated packets that it 1785 sends to one of its symmetric neighbor Servers, the Client should 1786 mark the path as unusable and use another path. If it receives 1787 Destination Unreachable messages on many or all paths, the Client 1788 should associate with a new Server and release its association 1789 with the old Server as specified in Section 3.19.5. 1791 o When an AERO Server receives persistent link-layer Destination 1792 Unreachable messages in response to encapsulated packets that it 1793 sends to one of its symmetric neighbor Clients, the Server should 1794 mark the underlying path as unusable and use another underlying 1795 path. 1797 o When an AERO Server or Proxy receives link-layer Destination 1798 Unreachable messages in response to an encapsulated packet that it 1799 sends to one of its permanent neighbors, it treats the messages as 1800 an indication that the path to the neighbor may be failing. 1801 However, the dynamic routing protocol should soon reconverge and 1802 correct the temporary outage. 1804 When an AERO Relay receives a packet for which the network-layer 1805 destination address is covered by an MSP, if there is no more- 1806 specific routing information for the destination the Relay drops the 1807 packet and returns a network-layer Destination Unreachable message 1808 subject to rate limiting. The Relay writes the network-layer source 1809 address of the original packet as the destination address and uses 1810 one of its non link-local addresses as the source address of the 1811 message. 1813 When an AERO node receives an encapsulated packet for which the 1814 reassembly buffer it too small, it drops the packet and returns a 1815 network-layer Packet Too Big (PTB) message. The node first writes 1816 the MRU value into the PTB message MTU field, writes the network- 1817 layer source address of the original packet as the destination 1818 address and writes one of its non link-local addresses as the source 1819 address. 1821 3.15. AERO Router Discovery, Prefix Delegation and Autoconfiguration 1823 AERO Router Discovery, Prefix Delegation and Autoconfiguration are 1824 coordinated as discussed in the following Sections. 1826 3.15.1. AERO ND/PD Service Model 1828 Each AERO Server on the link configures a PD service to facilitate 1829 Client requests. Each Server is provisioned with a database of MNP- 1830 to-Client ID mappings for all Clients enrolled in the AERO service, 1831 as well as any information necessary to authenticate each Client. 1832 The Client database is maintained by a central administrative 1833 authority for the AERO link and securely distributed to all Servers, 1834 e.g., via the Lightweight Directory Access Protocol (LDAP) [RFC4511], 1835 via static configuration, etc. Clients receive the same service 1836 regardless of the Servers they select. 1838 AERO Clients and Servers use ND messages to maintain neighbor cache 1839 entries. AERO Servers configure their AERO interfaces as advertising 1840 NBMA interfaces, and therefore send unicast RA messages with a short 1841 Router Lifetime value (e.g., REACHABLETIME seconds) in response to a 1842 Client's RS message. Thereafter, Clients send additional RS messages 1843 to keep Server state alive. 1845 AERO Clients and Servers include PD parameters in RS/RA messages (see 1846 [I-D.templin-6man-dhcpv6-ndopt] for ND/PD alternatives). The unified 1847 ND/PD messages are exchanged between Client and Server according to 1848 the prefix management schedule required by the PD service. If the 1849 Client knows its MNP in advance, it can instead employ prefix 1850 registration by including its AERO address as the source address of 1851 an RS message and with an OMNI option with valid prefix registration 1852 information for the MNP. If the Server (and Proxy) accept the 1853 Client's MNP assertion, they inject the prefix into the routing 1854 system and establish the necessary neighbor cache state. 1856 The following sections specify the Client and Server behavior. 1858 3.15.2. AERO Client Behavior 1860 AERO Clients discover the addresses of Servers in a similar manner as 1861 described in [RFC5214]. Discovery methods include static 1862 configuration (e.g., from a flat-file map of Server addresses and 1863 locations), or through an automated means such as Domain Name System 1864 (DNS) name resolution [RFC1035]. Alternatively, the Client can 1865 discover Server addresses through a layer 2 data link login exchange, 1866 or through a unicast RA response to a multicast/anycast RS as 1867 described below. In the absence of other information, the Client can 1868 resolve the DNS Fully-Qualified Domain Name (FQDN) 1869 "linkupnetworks.[domainname]" where "linkupnetworks" is a constant 1870 text string and "[domainname]" is a DNS suffix for the AERO link 1871 (e.g., "example.com"). 1873 To associate with a Server, the Client acts as a requesting router to 1874 request MNPs. The Client prepares an RS message with PD parameters 1875 and includes a Nonce and Timestamp option if the Client needs to 1876 correlate RA replies. If the Client already knows the Server's AERO 1877 address, it includes the AERO address as the network-layer 1878 destination address; otherwise, it includes the link-scoped All- 1879 Routers multicast (ff02::2) or Subnet-Router anycast (fe80::) address 1880 as the network-layer destination. If the Client already knows its 1881 own AERO address, it uses the AERO address as the network-layer 1882 source address; otherwise, it uses the unspecified IPv6 address 1883 (::/128) as the network-layer source address. 1885 The Client next includes an OMNI option in the RS message to register 1886 its link-layer information with the Server. The Client sets the OMNI 1887 option prefix registration information according to the MNP, and 1888 includes an ifIndex-tuple with S set to '1' corresponding to the 1889 underlying interface over which the Client will send the RS message. 1890 The Client MAY include additional ifIndex-tuples specific to other 1891 underlying interfaces. The Client MAY also include an SLLAO with a 1892 link-layer address corresponding to the OMNI option ifIndex-tuple 1893 with S set to '1'. 1895 The Client then sends the RS message (either directly via Direct 1896 interfaces, via INET encapsulation for NATed interfaces, via a VPN 1897 for VPNed interfaces, via a Proxy for proxyed interfaces or via a 1898 Relay for native interfaces) and waits for an RA message reply (see 1899 Section 3.15.3). The Client retries up to MAX_RTR_SOLICITATIONS 1900 times until an RA is received. If the Client receives no RAs, or if 1901 it receives an RA with Router Lifetime set to 0, the Client SHOULD 1902 abandon this Server and try another Server. Otherwise, the Client 1903 processes the PD information found in the RA message. 1905 Next, the Client creates a symmetric neighbor cache entry with the 1906 Server's AERO address as the network-layer address and the Server's 1907 encapsulation and/or link-layer addresses as the link-layer address. 1908 The Client records the RA Router Lifetime field value in the neighbor 1909 cache entry as the time for which the Server has committed to 1910 maintaining the MNP in the routing system via this underlying 1911 interface, and caches the other RA configuration information 1912 including Cur Hop Limit, M and O flags, Reachable Time and Retrans 1913 Timer. The Client then autoconfigures AERO addresses for each of the 1914 delegated MNPs and assigns them to the AERO interface. The Client 1915 also caches any MSPs included in Route Information Options (RIOs) 1916 [RFC4191] as MSPs to associate with the AERO link, and assigns the 1917 MTU value in the MTU option to the underlying interface. 1919 The Client then registers additional underlying interfaces with the 1920 Server by sending RS messages via each additional interface. The RS 1921 messages include the same parameters as for the initial RS/RA 1922 exchange, but with destination address set to the Server's AERO 1923 address. 1925 Following autoconfiguration, the Client sub-delegates the MNPs to its 1926 attached EUNs and/or the Client's own internal virtual interfaces as 1927 described in [I-D.templin-v6ops-pdhost] to support the Client's 1928 downstream attached "Internet of Things (IoT)". The Client 1929 subsequently sends additional RS messages over each underlying 1930 interface before the Router Lifetime received for that interface 1931 expires. 1933 After the Client registers its underlying interfaces, it may wish to 1934 change one or more registrations, e.g., if an interface changes 1935 address or becomes unavailable, if QoS preferences change, etc. To 1936 do so, the Client prepares an RS message to send over any available 1937 underlying interface. The RS includes an OMNI option with prefix 1938 registration information specific to its MNP, with an ifIndex-tuple 1939 specific to the selected underlying interface with S set to '1', and 1940 with any additional ifIndex-tuples specific to other underlying 1941 interfaces. The Client includes fresh ifIndex-tuple values to update 1942 the Server's neighbor cache entry. When the Client receives the 1943 Server's RA response, it has assurance that the Server has been 1944 updated with the new information. 1946 If the Client wishes to discontinue use of a Server it issues an RS 1947 message over any underlying interface with an OMNI option with a 1948 prefix release indication. When the Server processes the message, it 1949 releases the MNP, sets the symmetric neighbor cache entry state for 1950 the Client to DEPARTED and returns an RA reply with Router Lifetime 1951 set to 0. After a short delay (e.g., 2 seconds), the Server 1952 withdraws the MNP from the routing system. 1954 3.15.3. AERO Server Behavior 1956 AERO Servers act as IP routers and support a PD service for Clients. 1957 Servers arrange to add their AERO addresses to a static map of Server 1958 addresses for the link and/or the DNS resource records for the FQDN 1959 "linkupnetworks.[domainname]" before entering service. Server 1960 addresses should be geographically and/or topologically referenced, 1961 and made available for discovery by Clients on the AERO link. 1963 When a Server receives a prospective Client's RS message on its AERO 1964 interface, it SHOULD return an immediate RA reply with Router 1965 Lifetime set to 0 if it is currently too busy or otherwise unable to 1966 service the Client. Otherwise, the Server authenticates the RS 1967 message and processes the PD parameters. The Server first determines 1968 the correct MNPs to delegate to the Client by searching the Client 1969 database. When the Server delegates the MNPs, it also creates a 1970 forwarding table entry for each MNP so that the MNPs are propagated 1971 into the routing system (see: Section 3.3). For IPv6, the Server 1972 creates an IPv6 forwarding table entry for each MNP. For IPv4, the 1973 Server creates an IPv6 forwarding table entry with the SPAN 1974 Compatibility Prefix (SCP) corresponding to the IPv4 address. 1976 The Server next creates a symmetric neighbor cache entry for the 1977 Client using the base AERO address as the network-layer address and 1978 with lifetime set to no more than the smallest PD lifetime. Next, 1979 the Server updates the neighbor cache entry by recording the 1980 information in each ifIndex-tuple in the RS OMNI option. The Server 1981 also records the actual SPAN/INET addresses in the neighbor cache 1982 entry. If an SLLAO was present, the Server also compares the SLLAO 1983 address information for the first ifIndex-tuple with the SPAN/INET 1984 information to determine if there is a NAT on the path. 1986 Next, the Server prepares an RA message using its AERO address as the 1987 network-layer source address and the network-layer source address of 1988 the RS message as the network-layer destination address. The Server 1989 sets the Router Lifetime to the time for which it will maintain both 1990 this underlying interface individually and the symmetric neighbor 1991 cache entry as a whole. The Server also sets Cur Hop Limit, M and O 1992 flags, Reachable Time and Retrans Timer to values appropriate for the 1993 AERO link. The Server includes the delegated MNPs, any other PD 1994 parameters and an OMNI option with no ifIndex-tuples, or with an 1995 ifIndex-tuple with ifIndex set to 0 and S set to '1'. The Server 1996 then includes one or more RIOs that encode the MSPs for the AERO 1997 link, plus an MTU option (see Section 3.12). The Server finally 1998 forwards the message to the Client using SPAN/INET, INET, or NULL 1999 encapsulation as necessary. 2001 After the initial RS/RA exchange, the Server maintains a 2002 ReachableTime timer for each of the Client's underlying interfaces 2003 individually (and for the Client's symmetric neighbor cache entry 2004 collectively) set to expire after Router Lifetime seconds. If the 2005 Client (or Proxy) issues additional RS messages, the Server sends an 2006 RA response and resets ReachableTime. If the Server receives an ND 2007 message with PD release indication it sets the Client's symmetric 2008 neighbor cache entry to the DEPARTED state and withdraws the MNP from 2009 the routing system after a short delay (e.g., 2 seconds). If 2010 ReachableTime expires before a new RS is received on an individual 2011 underlying interface, the Server marks the interface as DOWN. If 2012 ReachableTime expires before any new RS is received on any individual 2013 underlying interface, the Server deletes the neighbor cache entry and 2014 withdraws the MNP without delay. 2016 The Server processes any ND/PD messages pertaining to the Client and 2017 returns an NA/RA reply in response to solicitations. The Server may 2018 also issue unsolicited RA messages, e.g., with PD reconfigure 2019 parameters to cause the Client to renegotiate its PDs, with Router 2020 Lifetime set to 0 if it can no longer service this Client, etc. 2021 Finally, If the symmetric neighbor cache entry is in the DEPARTED 2022 state, the Server deletes the entry after DepartTime expires. 2024 Note: Clients SHOULD notify former Servers of their departures, but 2025 Servers are responsible for expiring neighbor cache entries and 2026 withdrawing routes even if no departure notification is received 2027 (e.g., if the Client leaves the network unexpectedly). Servers 2028 SHOULD therefore set Router Lifetime to REACHABLETIME seconds in 2029 solicited RA messages to minimize persistent stale cache information 2030 in the absence of Client departure notifications. A short Router 2031 Lifetime also ensures that proactive Client/Server RS/RA messaging 2032 will keep any NAT state alive (see above). 2034 Note: All Servers on an AERO link MUST advertise consistent values in 2035 the RA Cur Hop Limit, M and O flags, Reachable Time and Retrans Timer 2036 fields the same as for any link, since unpredictable behavior could 2037 result if different Servers on the same link advertised different 2038 values. 2040 3.15.3.1. Lightweight DHCPv6 Relay Agent (LDRA) 2042 When DHCPv6 is used as the ND/PD service back end, AERO Clients and 2043 Servers are always on the same link (i.e., the AERO link) from the 2044 perspective of DHCPv6. However, in some implementations the DHCPv6 2045 server and ND function may be located in separate modules. In that 2046 case, the Server's AERO interface module can act as a Lightweight 2047 DHCPv6 Relay Agent (LDRA)[RFC6221] to relay PD messages to and from 2048 the DHCPv6 server module. 2050 When the LDRA receives an authentic RS message, it extracts the PD 2051 message parameters and uses them to construct an IPv6/UDP/DHCPv6 2052 message. It sets the IPv6 source address to the source address of 2053 the RS message, sets the IPv6 destination address to 2054 'All_DHCP_Relay_Agents_and_Servers' and sets the UDP fields to values 2055 that will be understood by the DHCPv6 server. 2057 The LDRA then wraps the message in a DHCPv6 'Relay-Forward' message 2058 header and includes an 'Interface-Id' option that includes enough 2059 information to allow the LDRA to forward the resulting Reply message 2060 back to the Client (e.g., the Client's link-layer addresses, a 2061 security association identifier, etc.). The LDRA also wraps the OMNI 2062 option and SLLAO into the Interface-Id option, then forwards the 2063 message to the DHCPv6 server. 2065 When the DHCPv6 server prepares a Reply message, it wraps the message 2066 in a 'Relay-Reply' message and echoes the Interface-Id option. The 2067 DHCPv6 server then delivers the Relay-Reply message to the LDRA, 2068 which discards the Relay-Reply wrapper and IPv6/UDP headers, then 2069 uses the DHCPv6 message to construct an RA response to the Client. 2070 The Server uses the information in the Interface-Id option to prepare 2071 the RA message and to cache the link-layer addresses taken from the 2072 OMNI option and SLLAO echoed in the Interface-Id option. 2074 3.16. The AERO Proxy 2076 Clients may connect to ANETs that deploy perimeter security services 2077 to facilitate communications to Servers in outside INETs. In that 2078 case, the ANET can employ an AERO Proxy. The Proxy is located at the 2079 ANET/INET border and listens for RS messages originating from or RA 2080 messages destined to ANET Clients. The Proxy acts on these control 2081 messages as follows: 2083 o when the Proxy receives an RS message from a new ANET Client, it 2084 first authenticates the message then examines the network-layer 2085 destination address. If the destination address is a Server's 2086 AERO address, the Proxy proceeds to the next step. Otherwise, if 2087 the destination is All-Routers multicast or Subnet-Router anycast, 2088 the Proxy selects a "nearby" Server that is likely to be a good 2089 candidate to serve the Client and replaces the destination address 2090 with the Server's AERO address. Next, the Proxy creates a proxy 2091 neighbor cache entry and caches the Client and Server link-layer 2092 addresses along with the OMNI option information and any other 2093 identifying information including Transaction IDs, Client 2094 Identifiers, Nonce values, etc. The Proxy then replaces the SLLAO 2095 in the RS message (if present) with a new SLLAO with an ifIndex- 2096 tuple matching the ifIndex-tuple in the OMNI option with S stet to 2097 '1' and with the Link Layer Address and Port Number fields set to 2098 the Proxy's SPAN address. The Proxy finally encapsulates the 2099 (proxyed) RS message in a SPAN header with destination set to the 2100 Server's SPAN address then forwards the message into the SPAN. 2102 o when the Server receives the RS, it authenticates the message then 2103 creates or updates a symmetric neighbor cache entry for the Client 2104 with the Proxy's SPAN address as the link-layer address. The 2105 Server then sends an RA message back to the Proxy via the SPAN. 2107 o when the Proxy receives the RA, it authenticates the message and 2108 matches it with the proxy neighbor cache entry created by the RS. 2109 The Proxy then caches the PD route information as a mapping from 2110 the Client's MNPs to the Client's ANET address, caches the 2111 Server's advertised Router Lifetime and sets the neighbor cache 2112 entry state to REACHABLE. The Proxy then replaces the RA SLLAO 2113 with an SLLAO with its own ANET address, sets the P bit in the RA 2114 flags field, optionally rewrites the Router Lifetime and forwards 2115 the (proxyed) message to the Client. The Proxy finally includes 2116 an MTU option (if necessary) with an MTU to use for the underlying 2117 ANET interface. 2119 After the initial RS/RA exchange, the Proxy forwards any Client data 2120 packets for which there is no matching asymmetric neighbor cache 2121 entry to a Relay via the SPAN. The Proxy instead forwards any Client 2122 data destined to an asymmetric neighbor cache target directly to the 2123 target according to the link-layer information - the process of 2124 establishing asymmetric neighbor cache entries is specified in 2125 Section 3.17. 2127 While the Client is still attached to the ANET, the Proxy sends NS, 2128 RS and/or unsolicited NA messages to update the Server's symmetric 2129 neighbor cache entries on behalf of the Client and/or to convey QoS 2130 updates. This allows for higher-frequency Proxy-initiated RS/RA 2131 messaging over well-connected INET infrastructure supplemented by 2132 lower-frequency Client-initiated RS/RA messaging over constrained 2133 ANET data links. 2135 If the Server ceases to send solicited advertisements, the Proxy 2136 sends unsolicited RAs on the ANET interface with destination set to 2137 All-Nodes multicast (ff02::1) and with Router Lifetime set to zero to 2138 inform Clients that the Server has failed. Although the Proxy 2139 engages in ND exchanges on behalf of the Client, the Client can also 2140 send ND messages on its own behalf, e.g., if it is in a better 2141 position than the Proxy to convey QoS changes, etc. For this reason, 2142 the Proxy marks any Client-originated solicitation messages (e.g. by 2143 inserting a Nonce option) so that it can return the solicited 2144 advertisement to the Client instead of processsing it locally. 2146 If the Client becomes unreachable, the Proxy sets the neighbor cache 2147 entry state to DEPARTED and retains the entry for DEPARTTIME seconds. 2148 While the state is DEPARTED, the Proxy forwards any packets destined 2149 to the Client to a Relay. The Relay in turn forwards the packets to 2150 the Client's current Server. When DepartTime expires, the Proxy 2151 deletes the neighbor cache entry and discards any further packets 2152 destined to this (now forgotten) Client. 2154 When a neighbor cache entry transitions to DEPARTED, some of the 2155 fragments of a multiple fragment packet may have already arrived at 2156 the Proxy while others are en route to the Client's new location, 2157 however no special attention in the reassembly algorithm is necessary 2158 when re-routed packets are simply treated as loss. 2160 In some ANETs that employ a Proxy, the Client's MNP can be injected 2161 into the ANET routing system. In that case, the Client can send data 2162 messages without encapsulation so that the ANET native routing system 2163 transports the unencapsulated packets to the Proxy. This can be very 2164 beneficial, e.g., if the Client connects to the ANET via low-end data 2165 links such as some aviation wireless links. 2167 If the first-hop ANET access router is AERO-aware, the Client can 2168 avoid encapsulation for both its control and data messages. When the 2169 Client connects to the link, it can send an unencapsulated RS message 2170 with source address set to its AERO address and with destination 2171 address set to the AERO address of the Client's selected Server or to 2172 All-Routers multicast or Subnet-Router anycast. The Client includes 2173 an OMNI option formatted as specified in 2174 [I-D.templin-6man-omni-interface]. 2176 The Client then sends the unencapsulated RS message, which will be 2177 intercepted by the AERO-Aware access router. The access router then 2178 encapsulates the RS message in an ANET header with its own address as 2179 the source address and the address of a Proxy as the destination 2180 address. The access router further remembers the address of the 2181 Proxy so that it can encapsulate future data packets from the Client 2182 via the same Proxy. If the access router needs to change to a new 2183 Proxy, it simply sends another RS message toward the Server via the 2184 new Proxy on behalf of the Client. 2186 In some cases, the access router and Proxy may be one and the same 2187 node. In that case, the node would be located on the same physical 2188 link as the Client, but its message exchanges with the Server would 2189 need to pass through a security gateway at the ANET/INET border. The 2190 method for deploying access routers and Proxys (i.e. as a single node 2191 or multiple nodes) is an ANET-local administrative consideration. 2193 3.16.1. Detecting and Responding to Server Failures 2195 In environments where fast recovery from Server failure is required, 2196 Proxys SHOULD use proactive Neighbor Unreachability Detection (NUD) 2197 to track Server reachability in a similar fashion as for 2198 Bidirectional Forwarding Detection (BFD) [RFC5880]. Proxys can then 2199 quickly detect and react to failures so that cached information is 2200 re-established through alternate paths. The NUD control messaging is 2201 carried only over well-connected ground domain networks (i.e., and 2202 not low-end aeronautical radio links) and can therefore be tuned for 2203 rapid response. 2205 Proxys perform proactive NUD with Servers for which there are 2206 currently active ANET Clients by sending continuous NS messages in 2207 rapid succession, e.g., one message per second. The Proxy sends the 2208 NS message via the SPAN with the Proxy's AERO address as the source 2209 and the AERO address of the Server as the destination. When the 2210 Proxy is also sending RS messages to the Server on behalf of ANET 2211 Clients, the resulting RA responses can be considered as equivalent 2212 hints of forward progress. This means that the Proxy need not also 2213 send a periodic NS if it has already sent an RS within the same 2214 period. If the Server fails (i.e., if the Proxy ceases to receive 2215 advertisements), the Proxy can quickly inform Clients by sending 2216 multicast RA messages on the ANET interface. 2218 The Proxy sends RA messages on the ANET interface with source address 2219 set to the Server's address, destination address set to All-Nodes 2220 multicast, and Router Lifetime set to 0. The Proxy SHOULD send 2221 MAX_FINAL_RTR_ADVERTISEMENTS RA messages separated by small delays 2222 [RFC4861]. Any Clients on the ANET that had been using the failed 2223 Server will receive the RA messages and associate with a new Server. 2225 3.17. AERO Route Optimization 2227 While data packets are flowing between a source and target node, 2228 route optimization SHOULD be used. Route optimization is initiated 2229 by the first eligible Route Optimization Source (ROS) closest to the 2230 source as follows: 2232 o For Clients on VPNed, NATed and Direct interfaces, the Server is 2233 the ROS. 2235 o For Clients on Proxyed interfaces, the Proxy is the ROS. 2237 o For Clients on native interfaces, the Client itself is the ROS. 2239 o For correspondent nodes on INET/EUN interfaces serviced by a 2240 Gateway, the Gateway is the ROS. 2242 The route optimization procedure is conducted between the ROS and the 2243 target Server/Gateway acting as a Route Optimization Responder (ROR) 2244 in the same manner as for IPv6 ND Address Resolution and using the 2245 same NS/NA messaging. The target may either be a MNP Client serviced 2246 by a Server, or a non-MNP correspondent reachable via a Gateway. 2248 The procedures are specified in the following sections. 2250 3.17.1. Route Optimization Initiation 2252 While data packets are flowing from the source node toward a target 2253 node, the ROS performs address resolution by sending an NS message to 2254 receive a solicited NA message from the ROR. 2256 When the ROS sends an NS, it includes the AERO address of the ROS as 2257 the source address (e.g., fe80::1) and the AERO address corresponding 2258 to the data packet's destination address as the destination address 2259 (e.g., if the destination address is 2001:db8:1:2::1 then the 2260 corresponding AERO address is fe80::2001:db8:1:2). The NS message 2261 includes an OMNI option with a single ifIndex-tuple with ifIndex set 2262 to 0, and an SLLAO with the SPAN address of the ROS. The message 2263 also includes a Nonce and Timestamp option if the ROS needs to 2264 correlate NA replies. 2266 The ROS then encapsulates the NS message in a SPAN header with source 2267 set to its own SPAN address and destination set to the data packet's 2268 destination address, then sends the message into the SPAN without 2269 decrementing the network-layer TTL/Hop Limit field. 2271 3.17.2. Relaying the NS 2273 When the Relay receives the NS message from the ROS, it discards the 2274 INET header and determines that the ROR is the next hop by consulting 2275 its standard IPv6 forwarding table for the SPAN header destination 2276 address. The Relay then forwards the SPAN message toward the ROR the 2277 same as for any IPv6 router. The final-hop Relay in the SPAN will 2278 deliver the message via a secured tunnel to the ROR. 2280 3.17.3. Processing the NS and Sending the NA 2282 When the ROR receives the NS message, it examines the AERO 2283 destination address to determine whether it has a neighbor cache 2284 entry and/or route that matches the target. If there is no match, 2285 the ROR drops the NS message. Otherwise, the ROR continues 2286 processing as follows: 2288 o if the target belongs to an MNP Client neighbor in the DEPARTED 2289 state the ROR changes the NS message SPAN destination address to 2290 the SPAN address of the Client's new Server, forwards the message 2291 into the SPAN and returns from processing. 2293 o If the target belongs to an MNP Client neighbor in the REACHABLE 2294 state, the ROR instead adds the AERO source address to the target 2295 Client's Report List with time set to ReportTime. 2297 o If the target belongs to a non-MNP route, the ROR continues 2298 processing without adding an entry to the Report List. 2300 The ROR then prepares a solicited NA message to send back to the ROS 2301 but does not create a neighbor cache entry. The ROR sets the NA 2302 source address to the destination AERO address of the NS, and 2303 includes the Nonce value received in the NS plus the current 2304 Timestamp. 2306 If the target belongs to an MNP Client, the ROR then includes an OMNI 2307 option with prefix registration length set to the length of the MNP; 2308 otherwise, set to the maximum of the non-MNP prefix length and 64. 2309 (Note that a /64 limit is imposed to avoid causing the ROS to set 2310 short prefixes (e.g., "default") that would match destinations for 2311 which the routing system includes more-specific prefixes.) 2313 The ROR next includes an ifIndex-tuple in the OMNI option with 2314 ifIndex set to 0 and S set to '1'. If the target belongs to an MNP 2315 Client, the ROR next includes additional ifIndex-tuples in the OMNI 2316 option for each of the target Client's underlying interfaces with 2317 current information for each interface 2319 The ROR then includes a TLLAO option with ifIndex-tuples in one-to- 2320 one correspondence with the tuples that appear in the OMNI option. 2321 For NATed, VPNed and Direct interfaces, the link layer addresses are 2322 the SPAN address of the ROR. For Proxyed interfaces, the link-layer 2323 addresses are the SPAN addresses of the Proxy's INET interfaces. For 2324 native interfaces, the link-layer addresses are the SPAN addesses of 2325 the Client's native interfaces. 2327 The ROR finally encapsulates the NA message in a SPAN header with 2328 source set to its own SPAN address and destination set to the source 2329 SPAN address of the NS message, then forwards the message into the 2330 SPAN without decrementing the network-layer TTL/Hop Limit field. 2332 3.17.4. Relaying the NA 2334 When the Relay receives the NA message from the ROR, it discards the 2335 INET header and determines that the ROS is the next hop by consulting 2336 its standard IPv6 forwarding table for the SPAN header destination 2337 address. The Relay then forwards the SPAN-encapsulated NA message 2338 toward the ROS the same as for any IPv6 router. The final-hop Relay 2339 in the SPAN will deliver the message via a secured tunnel to the ROS. 2341 3.17.5. Processing the NA 2343 When the ROS receives the solicited NA message, it caches the source 2344 SPAN address then discards the INET and SPAN headers. The ROS next 2345 verifies the Nonce and Timestamp values (if present), then creates an 2346 asymmetric neighbor cache entry for the ROR and caches all 2347 information found in the solicited NA OMNI and TLLAO options. The 2348 ROS finally sets the asymmetric neighbor cache entry lifetime to 2349 REACHABLETIME seconds. 2351 3.17.6. Route Optimization Maintenance 2353 Following route optimization, the ROS forwards future data packets 2354 destined to the target via the addresses found in the cached link- 2355 layer information. The route optimization is shared by all sources 2356 that send packets to the target via the ROS, i.e., and not just the 2357 source on behalf of which the route optimization was initiated. 2359 While new data packets destined to the target are flowing through the 2360 ROS, it sends additional NS messages to the ROR before ReachableTime 2361 expires to receive a fresh solicited NA message the same as described 2362 in the previous sections (route optimization refreshment strategies 2363 are an implementation matter, with a non-normative example given in 2364 Appendix B.1). The ROS uses the cached SPAN address of the ROR as 2365 the NS SPAN destination address, and sends up to MAX_UNICAST_SOLICIT 2366 NS messages separated by 1 second until an NA is received. If no NA 2367 is received, the ROS assumes that the current ROR has become 2368 unreachable and deletes the neighbor cache entry. Subsequent data 2369 packets will trigger a new route optimization per Section 3.17.1 to 2370 discover a new ROR while initial data packets travel over a 2371 suboptimal route. 2373 If an NA is received, the ROS then updates the asymmetric neighbor 2374 cache entry to refresh ReachableTime, while (for MNP destinations) 2375 the ROR adds or updates the ROS address to the target Client's Report 2376 List and with time set to ReportTime. While no data packets are 2377 flowing, the ROS instead allows ReachableTime for the asymmetric 2378 neighbor cache entry to expire. When ReachableTime expires, the ROS 2379 deletes the asymmetric neighbor cache entry. Any future data packets 2380 flowing through the ROS will again trigger a new route optimization. 2382 The ROS may also receive unsolicited NA messages from the ROR at any 2383 time (see: Section 3.19). If there is an asymmetric neighbor cache 2384 entry for the target, the ROS updates the link-layer information but 2385 does not update ReachableTime since the receipt of an unsolicited NA 2386 does not confirm that the forward path is still working. If there is 2387 no asymmetric neighbor cache entry, the ROS simply discards the 2388 unsolicited NA. 2390 In this arrangement, the ROS holds an asymmetric neighbor cache entry 2391 for the ROR, but the ROR does not hold an asymmetric neighbor cache 2392 entry for the ROS. The route optimization neighbor relationship is 2393 therefore asymmetric and unidirectional. If the target node also has 2394 packets to send back to the source node, then a separate route 2395 optimization procedure is performed in the reverse direction. But, 2396 there is no requirement that the forward and reverse paths be 2397 symmetric. 2399 3.18. Neighbor Unreachability Detection (NUD) 2401 AERO nodes perform Neighbor Unreachability Detection (NUD) per 2402 [RFC4861]. NUD is performed either reactively in response to 2403 persistent link-layer errors (see Section 3.14) or proactively to 2404 confirm reachability. The NUD algorithm is based on periodic 2405 authentic NS/NA message exchanges. The algorithm may further be 2406 seeded by ND hints of forward progress, but care must be taken to 2407 avoid inferring reachability based on spoofed information. For 2408 example, authentic RS/RA exchanges may be considered as acceptable 2409 hints of forward progress, while spurious data packets should not be. 2411 When an ROR directs an ROS to a neighbor with one or more target 2412 link-layer addresses, the ROS can proactively test each direct path 2413 by sending an initial NS message to elicit a solicited NA response. 2414 While testing the paths, the ROS can optionally continue sending 2415 packets via the SPAN, maintain a small queue of packets until target 2416 reachability is confirmed, or (optimistically) allow packets to flow 2417 via the direct paths. In any case, the ROS should only consider the 2418 neighbor unreachable if NUD fails over multiple target link-layer 2419 address paths. 2421 When a ROS sends an NS message used for NUD, it uses its AERO 2422 addresses as the IPv6 source address and the AERO address 2423 corresponding to a target link-layer address as the destination. For 2424 each target link-layer address, the source node encapsulates the NS 2425 message in SPAN/INET headers with its own SPAN address as the source 2426 and the SPAN address of the target as the destination, If the target 2427 is located within the same SPAN segment, the source sets the INET 2428 address of the target as the destination; otherwise, it sets the INET 2429 address of a Relay as the destination. The source then forwards the 2430 message into the SPAN. 2432 Paths that pass NUD tests are marked as "reachable", while those that 2433 do not are marked as "unreachable". These markings inform the AERO 2434 interface forwarding algorithm specified in Section 3.13. 2436 Proxys can perform NUD to verify Server reachability on behalf of 2437 their proxyed Clients to reduce Client-initated control messaging 2438 overhead. 2440 3.19. Mobility Management and Quality of Service (QoS) 2442 AERO is a Distributed Mobility Management (DMM) service. Each Server 2443 is responsible for only a subset of the Clients on the AERO link, as 2444 opposed to a Centralized Mobility Management (CMM) service where 2445 there is a single network mobility collective entity for all Clients. 2446 Clients coordinate with their associated Servers via RS/RA exchanges 2447 to maintain the DMM profile, and the AERO routing system tracks all 2448 current Client/Server peering relationships. 2450 Servers provide a Mobility Anchor Point (MAP) for their dependent 2451 Clients. Clients are responsible for maintaining neighbor 2452 relationships with their Servers through periodic RS/RA exchanges, 2453 which also serves to confirm neighbor reachability. When a Client's 2454 underlying interface address and/or QoS information changes, the 2455 Client is responsible for updating the Server with this new 2456 information. Note that for Proxyed interfaces, however, the Proxy 2457 can also perform some RS/RA exchanges on the Client's behalf. 2459 Mobility management considerations are specified in the following 2460 sections. 2462 3.19.1. Mobility Update Messaging 2464 Servers acting as MAPs accommodate Client mobility and/or QoS change 2465 events by sending unsolicited NA messages to each ROS in the target 2466 Client's Report List. When a MAP sends an unsolicited NA message, it 2467 sets the IPv6 source address to the Client's AERO address and sets 2468 the IPv6 destination address to All-Nodes multicast. The MAP also 2469 includes an OMNI option with prefix registration information, with an 2470 ifIndex-tuple with ifIndex set to 0 and S set to '1', and with 2471 additional ifIndex-tuples for the target Client's remaining 2472 interfaces. The MAP then includes a TLLAO with corresponding 2473 ifIndex-tuples, with the link layer address of ifIndex-tuple 0 set to 2474 the MAP's SPAN address and with link layer addresses of the remaining 2475 tuples set to the corresponding target SPAN addresses. The MAP 2476 finally encapsulates the message in a SPAN header with source set to 2477 its own SPAN address and destination set to the SPAN address of the 2478 ROS, then sends the message to a Relay which in turn forwards it to 2479 the ROS. 2481 As discussed in Section 7.2.6 of [RFC4861], the transmission and 2482 reception of unsolicited NA messages is unreliable but provides a 2483 useful optimization. In well-connected Internetworks with robust 2484 data links unsolicited NA messages will be delivered with high 2485 probability, but in any case the MAP can optionally send up to 2486 MAX_NEIGHBOR_ADVERTISEMENT unsolicited NAs to each ROS to increase 2487 the likelihood that at least one will be received. 2489 When the ROS receives an unsolicited NA message, it ignores the 2490 message if there is no existing neighbor cache entry for the Client. 2491 Otherwise, it uses the included OMNI option and TLLAO information to 2492 update the neighbor cache entry, but does not reset ReachableTime 2493 since the receipt of an unsolicited NA message from the target Server 2494 does not provide confirmation that any forward paths to the target 2495 Client are working. 2497 If unsolicited NA messages are lost, the ROS may be left with stale 2498 address and/or QoS information for the Client for up to REACHABLETIME 2499 seconds. During this time, the ROS can continue sending packets 2500 according to its stale neighbor cache information. When 2501 ReachableTime is close to expiring, the ROS will re-initiate route 2502 optimization and receive fresh link-layer address information. 2504 In addition to sending unsolicited NA messages to the current set of 2505 ROSs for the Client, the MAP also sends unsolicited NAs to the former 2506 link-layer address for any ifIndex-tuple for which the link-layer 2507 address has changed. The NA messages update Proxys or Servers that 2508 cannot easily detect (e.g., without active probing) when a formerly- 2509 active Client has departed. 2511 3.19.2. Announcing Link-Layer Address and/or QoS Preference Changes 2513 When a Client needs to change its ANET addresses and/or QoS 2514 preferences (e.g., due to a mobility event), either the Client or its 2515 Proxys send RS messages to the Server via the SPAN with an OMNI 2516 option and SLLAO that include an ifIndex-tuple with the new link 2517 quality and address information. 2519 Up to MAX_RTR_SOLICITATION RS messages MAY be sent in parallel with 2520 sending actual data packets in case one or more RAs are lost. If all 2521 RAs are lost, the Client SHOULD re-associate with a new Server. 2523 When the Server receives the Client's changes, it sends unsolicited 2524 NA messages to all nodes in the Report List the same as described in 2525 the previous section. 2527 3.19.3. Bringing New Links Into Service 2529 When a Client needs to bring new underlying interfaces into service 2530 (e.g., when it activates a new data link), it sends an RS message to 2531 the Server via the underlying interface with an OMNI option with 2532 appropriate link quality values and with an SLLAO (if necessary) with 2533 link-layer address information for the new link. 2535 3.19.4. Removing Existing Links from Service 2537 When a Client needs to remove existing underlying interfaces from 2538 service (e.g., when it de-activates an existing data link), it sends 2539 an RS message to its Server with an OMNI option with appropriate link 2540 quality values. 2542 If the Client needs to send RS messages over an underlying interface 2543 other than the one being removed from service, it MUST include 2544 ifIndex-tuples with appropriate link quality values for any 2545 underlying interfaces being removed from service. 2547 3.19.5. Moving to a New Server 2549 When a Client associates with a new Server, it performs the Client 2550 procedures specified in Section 3.15.2. The Client also includes 2551 notification identifiers in the RS message OMNI option per 2553 [I-D.templin-6man-omni-interface] if it wants the new Server to 2554 notify the old Server(s). 2556 When the new Server receives the Client's RS message, it responds by 2557 returning an RA as specified in Section 3.15.3. If the Client's RS 2558 includes a notification identifier, the new Server also prepares an 2559 RS or unsolicited NA message to send to the old Server. The RS/NA 2560 message includes the Client's AERO address as the source address, the 2561 old Server's AERO address as the destination address, and an OMNI 2562 option and S/TLLAO with an ifIndex-tuple with ifIndex set to 0. The 2563 OMNI option includes a prefix release indication, and the S/TLLAO 2564 includes the SPAN address of the new Server. For RS messages, the 2565 new Server retries up to MAX_RTR_SOLICITATIONS attempts until an RA 2566 is received. (Note that the Client can alternatively send RS/NA 2567 messages with a release indication to the old Server on its own 2568 behalf, however, this additional Client messaging may be undesirable 2569 in some environments. Note also that the choice of using RS or 2570 unsolicited NA is based on the need for a reliable acknowledgement; 2571 in environments where Router Lifetimes can be expected to be short, 2572 sending up to MAX_NEIGHBOR_ADVERTISEMENT unsolicited NAs may be 2573 sufficient.) 2575 When the old Server processes the RS/NA, it changes the symmetric 2576 neighbor cache entry state to DEPARTED, sets the link-layer address 2577 of the Client to the address found in the S/TLLAO, and sets 2578 DepartTime to DEPARTTIME seconds. For RS messages, the old Server 2579 then returns an immediate RA message with Router Lifetime set to 0. 2580 After a short delay (e.g., 2 seconds) the old Server withdraws the 2581 Client's MNP from the routing system. After DepartTime expires, the 2582 old Server deletes the symmetric neighbor cache entry. 2584 The old Server also sends unsolicited NA messages to all ROSs in the 2585 Client's Report List with an OMNI option with prefix release 2586 indication, with a single ifIndex-tuple with ifIndex set to 0 and S 2587 set to '1', and with the SPAN address of the new Server in a 2588 companion TLLAO. When the ROS receives the NA, it caches the address 2589 of the new Server in the existing asymmetric neighbor cache entry and 2590 marks the entry as STALE. Subsequent data packets will then flow 2591 according to any existing cached link-layer information and trigger a 2592 new NS/NA exchange via the new Server. 2594 Clients SHOULD NOT move rapidly between Servers in order to avoid 2595 causing excessive oscillations in the AERO routing system. Examples 2596 of when a Client might wish to change to a different Server include a 2597 Server that has gone unreachable, topological movements of 2598 significant distance, movement to a new geographic region, movement 2599 to a new SPAN segment, etc. 2601 When a Client moves to a new Server, some of the fragments of a 2602 multiple fragment packet may have already arrived at the old Server 2603 while others are en route to the new Server, however no special 2604 attention in the reassembly algorithm is necessary when re-routed 2605 fragments are simply treated as loss. 2607 3.20. Multicast 2609 The AERO Client provides an IGMP (IPv4) [RFC2236] or MLD (IPv6) 2610 [RFC3810] proxy service for its EUNs and/or hosted applications 2611 [RFC4605]. The Client forwards IGMP/MLD messages over any of its 2612 underlying interfaces for which group membership is required. The 2613 IGMP/MLD messages may be further forwarded by a first-hop ANET access 2614 router acting as an IGMP/MLD-snooping switch [RFC4541], then 2615 ultimately delivered to an AERO Proxy/Server acting as a Protocol 2616 Independent Multicast - Sparse-Mode (PIM-SM, or simply "PIM") 2617 Designated Router (DR) [RFC7761]. AERO Gateways also act as PIM 2618 routers (i.e., the same as AERO Proxys/Servers) on behalf of nodes on 2619 INET/EUN networks. The behaviors identified in the following 2620 sections correspond to Source-Specific Multicast (SSM) and Any-Source 2621 Multicast (ASM) operational modes. 2623 3.20.1. Source-Specific Multicast (SSM) 2625 When an ROS (i.e., an AERO Proxy/Server/Gateway) "X" acting as PIM 2626 router receives a Join/Prune message from a node on its downstream 2627 interfaces containing one or more ((S)ource, (G)roup) pairs, it 2628 updates its Multicast Routing Information Base (MRIB) accordingly. 2629 For each S belonging to a prefix reachable via X's non-AERO 2630 interfaces, X then forwards the (S, G) Join/Prune to any PIM routers 2631 on those interfaces per [RFC7761]. 2633 For each S belonging to a prefix reachable via X's AERO interface, X 2634 originates a separate copy of the Join/Prune for each (S,G) in the 2635 message using its own AERO address as the source address and ALL-PIM- 2636 ROUTERS as the destination address. X then encapsulates each message 2637 in a SPAN header with source address set to the SPAN address of X and 2638 destination address set to S then forwards the message into the SPAN. 2639 The SPAN in turn forwards the message to AERO Server/Gateway "Y" that 2640 services S. At the same time, if the message was a Join, X sends a 2641 route-optimization NS message toward each S the same as discussed in 2642 Section 3.17. The resulting NAs will return the AERO address for the 2643 prefix that matches S as the network-layer source address and TLLAOs 2644 with the SPAN addresses corresponding to any ifIndex-tuples that are 2645 currently servicing S. 2647 When Y processes the Join/Prune message, if S located behind any 2648 Native, Direct, VPNed or NATed interfaces Y acts as a PIM router and 2649 updates its MRIB to list X as the next hop in the reverse path. If S 2650 is located behind any Proxys "Z"*, Y also forwards the message to 2651 each Z* over the SPAN while continuing to use the AERO address of X 2652 as the source address. Each Z* then updates its MRIB accordingly and 2653 maintains the AERO address of X as the next hop in the reverse path. 2654 Since the Relays in the SPAN do not examine network layer control 2655 messages, this means that the (reverse) multicast tree path is simply 2656 from each Z* (and/or Y) to X with no other multicast-aware routers in 2657 the path. If any Z* (and/or Y) is located on the same SPAN segment 2658 as X, the multicast data traffic sent to X directly using SPAN/INET 2659 encapsulation instead of via a Relay. 2661 Following the initial Join/Prune and NS/NA messaging, X maintains an 2662 asymmetric neighbor cache entry for each S the same as if X was 2663 sending unicast data traffic to S. In particular, X performs 2664 additional NS/NA exchanges to keep the neighbor cache entry alive for 2665 up to t_periodic seconds [RFC7761]. If no new Joins are received 2666 within t_periodic seconds, X allows the neighbor cache entry to 2667 expire. Finally, if X receives any additional Join/Prune messages 2668 for (S,G) it forwards the messages to each Y and Z* in the neighbor 2669 cache entry over the SPAN. 2671 At some later time, Client C that holds an MNP for source S may 2672 depart from a first Proxy Z1 and/or connect via a new Proxy Z2. In 2673 that case, Y sends an unsolicited NA message to X the same as 2674 specified for unicast mobility in Section 3.19. When X receives the 2675 unsolicited NA message, it updates its asymmetric neighbor cache 2676 entry for the AERO address for source S and sends new Join messages 2677 to any new Proxys Z2. There is no requirement to send any Prune 2678 messages to old Proxys Z1 since source S will no longer source any 2679 multicast data traffic via Z1. Instead, the multicast state for 2680 (S,G) in Proxy Z1 will soon time out since no new Joins will arrive. 2682 After some later time, C may move to a new Server Y2 and depart from 2683 old Sever Y1. In that case, Y1 sends Join messages for any of C's 2684 active (S,G) groups to Y2 while including its own AERO address as the 2685 source address. This causes Y2 to include Y1 in the multicast 2686 forwarding tree during the interim time that Y1's symmetric neighbor 2687 cache entry for C is in the DEPARTED state. At the same time, Y1 2688 sends an unsolicited NA message to X with an OMNI option and TLLAO 2689 with ifIndex-tuple set to 0 and a release indication to cause X to 2690 release its asymmetric neighbor cache entry. X then sends a new Join 2691 message to S via the SPAN and re-initiates route optimization the 2692 same as if it were receiving a fresh Join message from a node on a 2693 downstream link. 2695 3.20.2. Any-Source Multicast (ASM) 2697 When an ROS X acting as a PIM router receives a Join/Prune from a 2698 node on its downstream interfaces containing one or more (*,G) pairs, 2699 it updates its Multicast Routing Information Base (MRIB) accordingly. 2700 X then forwards a copy of the message to the Rendezvous Point (RP) R 2701 for each G over the SPAN. X uses its own AERO address as the source 2702 address and ALL-PIM-ROUTERS as the destination address, then 2703 encapsulates each message in a SPAN header with source address set to 2704 the SPAN address of X and destination address set to R, then sends 2705 the message into the SPAN. At the same time, if the message was a 2706 Join X initiates NS/NA route optimization the same as for the SSM 2707 case discussed in Section 3.20.1. 2709 For each source S that sends multicast traffic to group G via R, the 2710 Proxy/Server Z* for the Client that aggregates S encapsulates the 2711 packets in PIM Register messages and forwards them to R via the SPAN. 2712 R may then elect to send a PIM Join to Z* over the SPAN. This will 2713 result in an (S,G) tree rooted at Z* with R as the next hop so that R 2714 will begin to receive two copies of the packet; one native copy from 2715 the (S, G) tree and a second copy from the pre-existing (*, G) tree 2716 that still uses PIM Register encapsulation. R can then issue a PIM 2717 Register-stop message to suppress the Register-encapsulated stream. 2718 At some later time, if C moves to a new Proxy/Server Z*, it resumes 2719 sending packets via PIM Register encapsulation via the new Z*. 2721 At the same time, as multicast listeners discover individual S's for 2722 a given G, they can initiate an (S,G) Join for each S under the same 2723 procedures discussed in Section 3.20.1. Once the (S,G) tree is 2724 established, the listeners can send (S, G) Prune messages to R so 2725 that multicast packets for group G sourced by S will only be 2726 delivered via the (S, G) tree and not from the (*, G) tree rooted at 2727 R. All mobility considerations discussed for SSM apply. 2729 3.20.3. Bi-Directional PIM (BIDIR-PIM) 2731 Bi-Directional PIM (BIDIR-PIM) [RFC5015] provides an alternate 2732 approach to ASM that treats the Rendezvous Point (RP) as a Designated 2733 Forwarder (DF). Further considerations for BIDIR-PIM are out of 2734 scope. 2736 3.21. Operation over Multiple AERO Links (VLANs) 2738 An AERO Client can connect to multiple AERO links the same as for any 2739 data link service. In that case, the Client maintains a distinct 2740 AERO interface for each link, e.g., 'aero0' for the first link, 2741 'aero1' for the second, 'aero2' for the third, etc. Each AERO link 2742 would include its own distinct set of Relays, Servers and Proxys, 2743 thereby providing redundancy in case of failures. 2745 The Relays, Servers and Proxys on each AERO link can assign AERO and 2746 SPAN addresses that use the same or different numberings from those 2747 on other links. Since the links are mutually independent there is no 2748 requirement for avoiding inter-link address duplication, e.g., the 2749 same AERO address such as fe80::1000 could be used to number distinct 2750 nodes that connect to different AERO links. 2752 Each AERO link could utilize the same or different ANET connections. 2753 The links can be distinguished at the link-layer via Virtual Local 2754 Area Network (VLAN) tagging (e.g., IEEE 802.1Q) and/or through 2755 assignment of distinct sets of MSPs on each link. This gives rise to 2756 the opportunity for supporting multiple redundant networked paths, 2757 where each VLAN is distinguished by a different label (e.g., colors 2758 such as Red, Green, Blue, etc.). In particular, the Client can tag 2759 its RS messages with the appropriate label to cause the network to 2760 select the desired VLAN. 2762 Clients that connect to multiple AERO interfaces can select the 2763 outgoing interface appropriate for a given Red/Blue/Green/etc. 2764 traffic profile while (in the reverse direction) correspondent nodes 2765 must have some way of steering their packets destined to a target via 2766 the correct AERO link. 2768 In a first alternative, if each AERO link services different MSPs, 2769 then the Client can receive a distinct MNP from each of the links. 2770 IP routing will therefore assure that the correct Red/Green/Blue/etc. 2771 network is used for both outbound and inbound traffic. This can be 2772 accomplished using existing technologies and approaches, and without 2773 requiring any special supporting code in correspondent nodes or 2774 Relays. 2776 In a second alternative, if each AERO link services the same MSP(s) 2777 then each link could assign a distinct "AERO Link Anycast" address 2778 that is configured by all Relays on the link. Correspondent nodes 2779 then include a "type 4" routing header with the Anycast address for 2780 the AERO link as the IPv6 destination and with the address of the 2781 target encoded as the "next segment" in the routing header 2782 [RFC8402][I-D.ietf-6man-segment-routing-header]. Standard IP routing 2783 will then direct the packet to the nearest Relay for the correct AERO 2784 link, which will replace the destination address with the target 2785 address then forward the packet to the target. 2787 3.22. DNS Considerations 2789 AERO Client MNs and INET correspondent nodes consult the Domain Name 2790 System (DNS) the same as for any Internetworking node. When 2791 correspondent nodes and Client MNs use different IP protocol versions 2792 (e.g., IPv4 correspondents and IPv6 MNs), the INET DNS must maintain 2793 A records for IPv4 address mappings to MNs which must then be 2794 populated in Gateway NAT64 mapping caches. In that way, an IPv4 2795 correspondent node can send packets to the IPv4 address mapping of 2796 the target MN, and the Gateway will translate the IPv4 header and 2797 destination address into an IPv6 header and IPv6 destination address 2798 of the MN. 2800 When an AERO Client registers with an AERO Server, the Server can 2801 return the address(es) of DNS servers in RDNSS options [RFC6106]. 2802 The DNS server provides the IP addresses of other MNs and 2803 correspondent nodes in AAAA records for IPv6 or A records for IPv4. 2805 3.23. Transition Considerations 2807 The SPAN ensures that dissimilar INET partitions can be joined into a 2808 single unified AERO link, even though the partitions themselves may 2809 have differing protocol versions and/or incompatible addressing 2810 plans. However, a commonality can be achieved by incrementally 2811 distributing globally routable (i.e., native) IP prefixes to 2812 eventually reach all nodes (both mobile and fixed) in all SPAN 2813 segments. This can be accomplished by incrementally deploying AERO 2814 Gateways on each INET partition, with each Gateway distributing its 2815 MNPs and/or discovering non-MNP prefixes on its INET links. 2817 This gives rise to the opportunity to eventually distribute native IP 2818 addresses to all nodes, and to present a unified AERO link view 2819 (bridged by the SPAN) even if the INET partitions remain in their 2820 current protocol and addressing plans. In that way, the AERO link 2821 can serve the dual purpose of providing a mobility service and a 2822 transition service. Or, if an INET partition is transitioned to a 2823 native IP protocol version and addressing scheme that is compatible 2824 with the AERO link MNP-based addressing scheme, the partition and 2825 AERO link can be joined by Gateways. 2827 Gateways that connect INETs/EUNs with dissimilar IP protocol versions 2828 must employ a network address and protocol translation function such 2829 as NAT64[RFC6146]. 2831 3.24. Detecting and Reacting to Server and Relay Failures 2833 In environments where rapid failure recovery is required, Servers and 2834 Relays SHOULD use Bidirectional Forwarding Detection (BFD) [RFC5880]. 2835 Nodes that use BFD can quickly detect and react to failures so that 2836 cached information is re-established through alternate nodes. BFD 2837 control messaging is carried only over well-connected ground domain 2838 networks (i.e., and not low-end radio links) and can therefore be 2839 tuned for rapid response. 2841 Servers and Relays maintain BFD sessions in parallel with their BGP 2842 peerings. If a Server or Relay fails, BGP peers will quickly re- 2843 establish routes through alternate paths the same as for common BGP 2844 deployments. Similarly, Proxys maintain BFD sessions with their 2845 associated Relays even though they do not establish BGP peerings with 2846 them. 2848 Proxys SHOULD use proactive NUD for Servers for which there are 2849 currently active ANET Clients in a manner that parallels BFD, i.e., 2850 by sending unicast NS messages in rapid succession to receive 2851 solicited NA messages. When the Proxy is also sending RS messages on 2852 behalf of ANET Clients, the RS/RA messaging can be considered as 2853 equivalent hints of forward progress. This means that the Proxy need 2854 not also send a periodic NS if it has already sent an RS within the 2855 same period. If a Server fails, the Proxy will cease to receive 2856 advertisements and can quickly inform Clients of the outage by 2857 sending multicast RA messages on the ANET interface. 2859 The Proxy sends multicast RA messages with source address set to the 2860 Server's address, destination address set to All-Nodes multicast, and 2861 Router Lifetime set to 0. The Proxy SHOULD send 2862 MAX_FINAL_RTR_ADVERTISEMENTS RA messages separated by small delays 2863 [RFC4861]. Any Clients on the ANET interface that have been using 2864 the (now defunct) Server will receive the RA messages and associate 2865 with a new Server. 2867 4. Implementation Status 2869 An AERO implementation based on OpenVPN (https://openvpn.net/) was 2870 announced on the v6ops mailing list on January 10, 2018 and an 2871 initial public release of the AERO proof-of-concept source code was 2872 announced on the intarea mailing list on August 21, 2015. 2874 5. IANA Considerations 2876 The IANA has assigned a 4-octet Private Enterprise Number "45282" for 2877 AERO in the "enterprise-numbers" registry. 2879 The IANA has assigned the UDP port number "8060" for an earlier 2880 experimental version of AERO [RFC6706]. This document obsoletes 2881 [RFC6706] and claims the UDP port number "8060" for all future use. 2883 No further IANA actions are required. 2885 6. Security Considerations 2887 AERO Relays configure secured tunnels with AERO Servers and Proxys 2888 within their local SPAN segments. Applicable secured tunnel 2889 alternatives include IPsec [RFC4301], TLS/SSL [RFC8446], DTLS 2890 [RFC6347], WireGuard, etc. The AERO Relays of all SPAN segments in 2891 turn configure secured tunnels for their neighboring AERO Relays 2892 across the SPAN. Therefore, packets that traverse the SPAN between 2893 any pair of AERO link neighbors are already secured. 2895 AERO Servers, Gateways and Proxys targeted by a route optimization 2896 may also receive packets directly from the INET partitions instead of 2897 via the SPAN. For INET partitions that apply effective ingress 2898 filtering to defeat source address spoofing, the simple data origin 2899 authentication procedures in Section 3.11 can be applied. This 2900 implies that the ROS list must be maintained consistently by all 2901 route optimization targets within the same INET partition, and that 2902 the ROS list must be securely managed by the partition administrative 2903 authority. 2905 For INET partitions that cannot apply effective ingress filtering, 2906 the two options for securing communications include 1) disable route 2907 optimization so that all traffic is conveyed over secured tunnels via 2908 the SPAN, or 2) enable on-demand secure tunnel creation between INET 2909 partition neighbors. Option 1) would result in longer routes than 2910 necessary and traffic concentration on critical infrastructure 2911 elements. Option 2) could be coordinated by establishing a secured 2912 tunnel on-demand instead of performing an NS/NA exchange in the route 2913 optimization procedures. Procedures for establishing on-demand 2914 secured tunnels are out of scope. 2916 AERO Clients that connect to secured enclaves need not apply security 2917 to their ND messages, since the messages will be intercepted by a 2918 perimeter Proxy that applies security on its outward-facing 2919 interface. AERO Clients located outside of secured enclaves SHOULD 2920 use symmetric network and/or transport layer security services, but 2921 when there are many prospective neighbors with dynamically changing 2922 connectivity an asymmetric security service such as SEND may be 2923 needed (see: Appendix B.6). 2925 Application endpoints SHOULD use application-layer security services 2926 such as TLS/SSL, DTLS or SSH [RFC4251] to assure the same level of 2927 protection as for critical secured Internet services. AERO Clients 2928 that require host-based VPN services SHOULD use symmetric network 2929 and/or transport layer security services such as IPsec, TLS/SSL, 2930 DTLS, etc. AERO Proxys and Servers can also provide a network-based 2931 VPN service on behalf of the Client, e.g., if the Client is located 2932 within a secured enclave and cannot establish a VPN on its own 2933 behalf. 2935 AERO Servers and Relays present targets for traffic amplification 2936 Denial of Service (DoS) attacks. This concern is no different than 2937 for widely-deployed VPN security gateways in the Internet, where 2938 attackers could send spoofed packets to the gateways at high data 2939 rates. This can be mitigated by connecting Servers and Relays over 2940 dedicated links with no connections to the Internet and/or when 2941 connections to the Internet are only permitted through well-managed 2942 firewalls. Traffic amplification DoS attacks can also target an AERO 2943 Client's low data rate links. This is a concern not only for Clients 2944 located on the open Internet but also for Clients in secured 2945 enclaves. AERO Servers and Proxys can institute rate limits that 2946 protect Clients from receiving packet floods that could DoS low data 2947 rate links. 2949 AERO Gateways must implement ingress filtering to avoid a spoofing 2950 attack in which spurious SPAN messages are injected into an AERO link 2951 from an outside attacker. AERO Clients MUST ensure that their 2952 connectivity is not used by unauthorized nodes on their EUNs to gain 2953 access to a protected network, i.e., AERO Clients that act as routers 2954 MUST NOT provide routing services for unauthorized nodes. (This 2955 concern is no different than for ordinary hosts that receive an IP 2956 address delegation but then "share" the address with other nodes via 2957 some form of Internet connection sharing such as tethering.) 2959 The MAP list and ROS lists MUST be well-managed and secured from 2960 unauthorized tampering, even though the list contains only public 2961 information. The MAP list can be conveyed to the Client in a similar 2962 fashion as in [RFC5214] (e.g., through layer 2 data link login 2963 messaging, secure upload of a static file, DNS lookups, etc.). The 2964 ROS list can be conveyed to Servers and Proxys through administrative 2965 action, secured file distribution, etc. 2967 Although public domain and commercial SEND implementations exist, 2968 concerns regarding the strength of the cryptographic hash algorithm 2969 have been documented [RFC6273] [RFC4982]. 2971 Security considerations for accepting link-layer ICMP messages and 2972 reflected packets are discussed throughout the document. 2974 7. Acknowledgements 2976 Discussions in the IETF, aviation standards communities and private 2977 exchanges helped shape some of the concepts in this work. 2978 Individuals who contributed insights include Mikael Abrahamsson, Mark 2979 Andrews, Fred Baker, Bob Braden, Stewart Bryant, Brian Carpenter, 2980 Wojciech Dec, Pavel Drasil, Ralph Droms, Adrian Farrel, Nick Green, 2981 Sri Gundavelli, Brian Haberman, Bernhard Haindl, Joel Halpern, Tom 2982 Herbert, Sascha Hlusiak, Lee Howard, Zdenek Jaron, Andre Kostur, 2983 Hubert Kuenig, Ted Lemon, Andy Malis, Satoru Matsushima, Tomek 2984 Mrugalski, Madhu Niraula, Alexandru Petrescu, Behcet Saikaya, Michal 2985 Skorepa, Joe Touch, Bernie Volz, Ryuji Wakikawa, Tony Whyman, Lloyd 2986 Wood and James Woodyatt. Members of the IESG also provided valuable 2987 input during their review process that greatly improved the document. 2988 Special thanks go to Stewart Bryant, Joel Halpern and Brian Haberman 2989 for their shepherding guidance during the publication of the AERO 2990 first edition. 2992 This work has further been encouraged and supported by Boeing 2993 colleagues including Kyle Bae, M. Wayne Benson, Dave Bernhardt, Cam 2994 Brodie, John Bush, Balaguruna Chidambaram, Irene Chin, Bruce Cornish, 2995 Claudiu Danilov, Don Dillenburg, Joe Dudkowski, Wen Fang, Samad 2996 Farooqui, Anthony Gregory, Jeff Holland, Seth Jahne, Brian Jaury, 2997 Greg Kimberly, Ed King, Madhuri Madhava Badgandi, Laurel Matthew, 2998 Gene MacLean III, Rob Muszkiewicz, Sean O'Sullivan, Vijay 2999 Rajagopalan, Greg Saccone, Rod Santiago, Kent Shuey, Brian Skeen, 3000 Mike Slane, Carrie Spiker, Katie Tran, Brendan Williams, Amelia 3001 Wilson, Julie Wulff, Yueli Yang, Eric Yeh and other members of the 3002 Boeing mobility, networking and autonomy teams. Kyle Bae, Wayne 3003 Benson, Katie Tran and Eric Yeh are especially acknowledged for 3004 implementing the AERO functions as extensions to the public domain 3005 OpenVPN distribution. 3007 Earlier works on NBMA tunneling approaches are found in 3008 [RFC2529][RFC5214][RFC5569]. 3010 Many of the constructs presented in this second edition of AERO are 3011 based on the author's earlier works, including: 3013 o The Internet Routing Overlay Network (IRON) 3014 [RFC6179][I-D.templin-ironbis] 3016 o Virtual Enterprise Traversal (VET) 3017 [RFC5558][I-D.templin-intarea-vet] 3019 o The Subnetwork Encapsulation and Adaptation Layer (SEAL) 3020 [RFC5320][I-D.templin-intarea-seal] 3022 o AERO, First Edition [RFC6706] 3024 Note that these works cite numerous earlier efforts that are not also 3025 cited here due to space limitations. The authors of those earlier 3026 works are acknowledged for their insights. 3028 This work is aligned with the NASA Safe Autonomous Systems Operation 3029 (SASO) program under NASA contract number NNA16BD84C. 3031 This work is aligned with the FAA as per the SE2025 contract number 3032 DTFAWA-15-D-00030. 3034 This work is aligned with the Boeing Commercial Airplanes (BCA) 3035 Internet of Things (IoT) and autonomy programs. 3037 This work is aligned with the Boeing Information Technology (BIT) 3038 MobileNet program. 3040 8. References 3042 8.1. Normative References 3044 [I-D.templin-6man-omni-interface] 3045 Templin, F. and T. Whyman, "Transmission of IPv6 Packets 3046 over Overlay Multilink Network (OMNI) Interfaces", draft- 3047 templin-6man-omni-interface-02 (work in progress), 3048 February 2020. 3050 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, 3051 DOI 10.17487/RFC0791, September 1981, 3052 . 3054 [RFC0792] Postel, J., "Internet Control Message Protocol", STD 5, 3055 RFC 792, DOI 10.17487/RFC0792, September 1981, 3056 . 3058 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 3059 Requirement Levels", BCP 14, RFC 2119, 3060 DOI 10.17487/RFC2119, March 1997, 3061 . 3063 [RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in 3064 IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473, 3065 December 1998, . 3067 [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black, 3068 "Definition of the Differentiated Services Field (DS 3069 Field) in the IPv4 and IPv6 Headers", RFC 2474, 3070 DOI 10.17487/RFC2474, December 1998, 3071 . 3073 [RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander, 3074 "SEcure Neighbor Discovery (SEND)", RFC 3971, 3075 DOI 10.17487/RFC3971, March 2005, 3076 . 3078 [RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)", 3079 RFC 3972, DOI 10.17487/RFC3972, March 2005, 3080 . 3082 [RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and 3083 More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191, 3084 November 2005, . 3086 [RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast 3087 Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005, 3088 . 3090 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 3091 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 3092 DOI 10.17487/RFC4861, September 2007, 3093 . 3095 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 3096 Address Autoconfiguration", RFC 4862, 3097 DOI 10.17487/RFC4862, September 2007, 3098 . 3100 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 3101 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 3102 May 2017, . 3104 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 3105 (IPv6) Specification", STD 86, RFC 8200, 3106 DOI 10.17487/RFC8200, July 2017, 3107 . 3109 [RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A., 3110 Richardson, M., Jiang, S., Lemon, T., and T. Winters, 3111 "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", 3112 RFC 8415, DOI 10.17487/RFC8415, November 2018, 3113 . 3115 8.2. Informative References 3117 [BGP] Huston, G., "BGP in 2015, http://potaroo.net", January 3118 2016. 3120 [I-D.ietf-6man-segment-routing-header] 3121 Filsfils, C., Dukes, D., Previdi, S., Leddy, J., 3122 Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header 3123 (SRH)", draft-ietf-6man-segment-routing-header-26 (work in 3124 progress), October 2019. 3126 [I-D.ietf-dmm-distributed-mobility-anchoring] 3127 Chan, A., Wei, X., Lee, J., Jeon, S., and C. Bernardos, 3128 "Distributed Mobility Anchoring", draft-ietf-dmm- 3129 distributed-mobility-anchoring-14 (work in progress), 3130 November 2019. 3132 [I-D.ietf-intarea-gue] 3133 Herbert, T., Yong, L., and O. Zia, "Generic UDP 3134 Encapsulation", draft-ietf-intarea-gue-09 (work in 3135 progress), October 2019. 3137 [I-D.ietf-intarea-gue-extensions] 3138 Herbert, T., Yong, L., and F. Templin, "Extensions for 3139 Generic UDP Encapsulation", draft-ietf-intarea-gue- 3140 extensions-06 (work in progress), March 2019. 3142 [I-D.ietf-intarea-tunnels] 3143 Touch, J. and M. Townsley, "IP Tunnels in the Internet 3144 Architecture", draft-ietf-intarea-tunnels-10 (work in 3145 progress), September 2019. 3147 [I-D.ietf-rtgwg-atn-bgp] 3148 Templin, F., Saccone, G., Dawra, G., Lindem, A., and V. 3149 Moreno, "A Simple BGP-based Mobile Routing System for the 3150 Aeronautical Telecommunications Network", draft-ietf- 3151 rtgwg-atn-bgp-05 (work in progress), January 2020. 3153 [I-D.templin-6man-dhcpv6-ndopt] 3154 Templin, F., "A Unified Stateful/Stateless Configuration 3155 Service for IPv6", draft-templin-6man-dhcpv6-ndopt-09 3156 (work in progress), January 2020. 3158 [I-D.templin-intarea-grefrag] 3159 Templin, F., "GRE Tunnel Level Fragmentation", draft- 3160 templin-intarea-grefrag-04 (work in progress), July 2016. 3162 [I-D.templin-intarea-seal] 3163 Templin, F., "The Subnetwork Encapsulation and Adaptation 3164 Layer (SEAL)", draft-templin-intarea-seal-68 (work in 3165 progress), January 2014. 3167 [I-D.templin-intarea-vet] 3168 Templin, F., "Virtual Enterprise Traversal (VET)", draft- 3169 templin-intarea-vet-40 (work in progress), May 2013. 3171 [I-D.templin-ironbis] 3172 Templin, F., "The Interior Routing Overlay Network 3173 (IRON)", draft-templin-ironbis-16 (work in progress), 3174 March 2014. 3176 [I-D.templin-v6ops-pdhost] 3177 Templin, F., "IPv6 Prefix Delegation and Multi-Addressing 3178 Models", draft-templin-v6ops-pdhost-25 (work in progress), 3179 January 2020. 3181 [OVPN] OpenVPN, O., "http://openvpn.net", October 2016. 3183 [RFC1035] Mockapetris, P., "Domain names - implementation and 3184 specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, 3185 November 1987, . 3187 [RFC1122] Braden, R., Ed., "Requirements for Internet Hosts - 3188 Communication Layers", STD 3, RFC 1122, 3189 DOI 10.17487/RFC1122, October 1989, 3190 . 3192 [RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191, 3193 DOI 10.17487/RFC1191, November 1990, 3194 . 3196 [RFC1812] Baker, F., Ed., "Requirements for IP Version 4 Routers", 3197 RFC 1812, DOI 10.17487/RFC1812, June 1995, 3198 . 3200 [RFC2003] Perkins, C., "IP Encapsulation within IP", RFC 2003, 3201 DOI 10.17487/RFC2003, October 1996, 3202 . 3204 [RFC2236] Fenner, W., "Internet Group Management Protocol, Version 3205 2", RFC 2236, DOI 10.17487/RFC2236, November 1997, 3206 . 3208 [RFC2492] Armitage, G., Schulter, P., and M. Jork, "IPv6 over ATM 3209 Networks", RFC 2492, DOI 10.17487/RFC2492, January 1999, 3210 . 3212 [RFC2529] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4 3213 Domains without Explicit Tunnels", RFC 2529, 3214 DOI 10.17487/RFC2529, March 1999, 3215 . 3217 [RFC2764] Gleeson, B., Lin, A., Heinanen, J., Armitage, G., and A. 3218 Malis, "A Framework for IP Based Virtual Private 3219 Networks", RFC 2764, DOI 10.17487/RFC2764, February 2000, 3220 . 3222 [RFC2784] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P. 3223 Traina, "Generic Routing Encapsulation (GRE)", RFC 2784, 3224 DOI 10.17487/RFC2784, March 2000, 3225 . 3227 [RFC2890] Dommety, G., "Key and Sequence Number Extensions to GRE", 3228 RFC 2890, DOI 10.17487/RFC2890, September 2000, 3229 . 3231 [RFC2923] Lahey, K., "TCP Problems with Path MTU Discovery", 3232 RFC 2923, DOI 10.17487/RFC2923, September 2000, 3233 . 3235 [RFC2983] Black, D., "Differentiated Services and Tunnels", 3236 RFC 2983, DOI 10.17487/RFC2983, October 2000, 3237 . 3239 [RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition 3240 of Explicit Congestion Notification (ECN) to IP", 3241 RFC 3168, DOI 10.17487/RFC3168, September 2001, 3242 . 3244 [RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener 3245 Discovery Version 2 (MLDv2) for IPv6", RFC 3810, 3246 DOI 10.17487/RFC3810, June 2004, 3247 . 3249 [RFC3819] Karn, P., Ed., Bormann, C., Fairhurst, G., Grossman, D., 3250 Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J., and L. 3251 Wood, "Advice for Internet Subnetwork Designers", BCP 89, 3252 RFC 3819, DOI 10.17487/RFC3819, July 2004, 3253 . 3255 [RFC4213] Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms 3256 for IPv6 Hosts and Routers", RFC 4213, 3257 DOI 10.17487/RFC4213, October 2005, 3258 . 3260 [RFC4251] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH) 3261 Protocol Architecture", RFC 4251, DOI 10.17487/RFC4251, 3262 January 2006, . 3264 [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A 3265 Border Gateway Protocol 4 (BGP-4)", RFC 4271, 3266 DOI 10.17487/RFC4271, January 2006, 3267 . 3269 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 3270 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 3271 2006, . 3273 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 3274 Internet Protocol", RFC 4301, DOI 10.17487/RFC4301, 3275 December 2005, . 3277 [RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery 3278 Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April 3279 2006, . 3281 [RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet 3282 Control Message Protocol (ICMPv6) for the Internet 3283 Protocol Version 6 (IPv6) Specification", STD 89, 3284 RFC 4443, DOI 10.17487/RFC4443, March 2006, 3285 . 3287 [RFC4511] Sermersheim, J., Ed., "Lightweight Directory Access 3288 Protocol (LDAP): The Protocol", RFC 4511, 3289 DOI 10.17487/RFC4511, June 2006, 3290 . 3292 [RFC4541] Christensen, M., Kimball, K., and F. Solensky, 3293 "Considerations for Internet Group Management Protocol 3294 (IGMP) and Multicast Listener Discovery (MLD) Snooping 3295 Switches", RFC 4541, DOI 10.17487/RFC4541, May 2006, 3296 . 3298 [RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick, 3299 "Internet Group Management Protocol (IGMP) / Multicast 3300 Listener Discovery (MLD)-Based Multicast Forwarding 3301 ("IGMP/MLD Proxying")", RFC 4605, DOI 10.17487/RFC4605, 3302 August 2006, . 3304 [RFC4607] Holbrook, H. and B. Cain, "Source-Specific Multicast for 3305 IP", RFC 4607, DOI 10.17487/RFC4607, August 2006, 3306 . 3308 [RFC4963] Heffner, J., Mathis, M., and B. Chandler, "IPv4 Reassembly 3309 Errors at High Data Rates", RFC 4963, 3310 DOI 10.17487/RFC4963, July 2007, 3311 . 3313 [RFC4982] Bagnulo, M. and J. Arkko, "Support for Multiple Hash 3314 Algorithms in Cryptographically Generated Addresses 3315 (CGAs)", RFC 4982, DOI 10.17487/RFC4982, July 2007, 3316 . 3318 [RFC5015] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano, 3319 "Bidirectional Protocol Independent Multicast (BIDIR- 3320 PIM)", RFC 5015, DOI 10.17487/RFC5015, October 2007, 3321 . 3323 [RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site 3324 Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214, 3325 DOI 10.17487/RFC5214, March 2008, 3326 . 3328 [RFC5320] Templin, F., Ed., "The Subnetwork Encapsulation and 3329 Adaptation Layer (SEAL)", RFC 5320, DOI 10.17487/RFC5320, 3330 February 2010, . 3332 [RFC5522] Eddy, W., Ivancic, W., and T. Davis, "Network Mobility 3333 Route Optimization Requirements for Operational Use in 3334 Aeronautics and Space Exploration Mobile Networks", 3335 RFC 5522, DOI 10.17487/RFC5522, October 2009, 3336 . 3338 [RFC5558] Templin, F., Ed., "Virtual Enterprise Traversal (VET)", 3339 RFC 5558, DOI 10.17487/RFC5558, February 2010, 3340 . 3342 [RFC5569] Despres, R., "IPv6 Rapid Deployment on IPv4 3343 Infrastructures (6rd)", RFC 5569, DOI 10.17487/RFC5569, 3344 January 2010, . 3346 [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 3347 (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, 3348 . 3350 [RFC6106] Jeong, J., Park, S., Beloeil, L., and S. Madanapalli, 3351 "IPv6 Router Advertisement Options for DNS Configuration", 3352 RFC 6106, DOI 10.17487/RFC6106, November 2010, 3353 . 3355 [RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful 3356 NAT64: Network Address and Protocol Translation from IPv6 3357 Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146, 3358 April 2011, . 3360 [RFC6179] Templin, F., Ed., "The Internet Routing Overlay Network 3361 (IRON)", RFC 6179, DOI 10.17487/RFC6179, March 2011, 3362 . 3364 [RFC6221] Miles, D., Ed., Ooghe, S., Dec, W., Krishnan, S., and A. 3365 Kavanagh, "Lightweight DHCPv6 Relay Agent", RFC 6221, 3366 DOI 10.17487/RFC6221, May 2011, 3367 . 3369 [RFC6273] Kukec, A., Krishnan, S., and S. Jiang, "The Secure 3370 Neighbor Discovery (SEND) Hash Threat Analysis", RFC 6273, 3371 DOI 10.17487/RFC6273, June 2011, 3372 . 3374 [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer 3375 Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, 3376 January 2012, . 3378 [RFC6438] Carpenter, B. and S. Amante, "Using the IPv6 Flow Label 3379 for Equal Cost Multipath Routing and Link Aggregation in 3380 Tunnels", RFC 6438, DOI 10.17487/RFC6438, November 2011, 3381 . 3383 [RFC6706] Templin, F., Ed., "Asymmetric Extended Route Optimization 3384 (AERO)", RFC 6706, DOI 10.17487/RFC6706, August 2012, 3385 . 3387 [RFC6864] Touch, J., "Updated Specification of the IPv4 ID Field", 3388 RFC 6864, DOI 10.17487/RFC6864, February 2013, 3389 . 3391 [RFC7269] Chen, G., Cao, Z., Xie, C., and D. Binet, "NAT64 3392 Deployment Options and Experience", RFC 7269, 3393 DOI 10.17487/RFC7269, June 2014, 3394 . 3396 [RFC7333] Chan, H., Ed., Liu, D., Seite, P., Yokota, H., and J. 3397 Korhonen, "Requirements for Distributed Mobility 3398 Management", RFC 7333, DOI 10.17487/RFC7333, August 2014, 3399 . 3401 [RFC7421] Carpenter, B., Ed., Chown, T., Gont, F., Jiang, S., 3402 Petrescu, A., and A. Yourtchenko, "Analysis of the 64-bit 3403 Boundary in IPv6 Addressing", RFC 7421, 3404 DOI 10.17487/RFC7421, January 2015, 3405 . 3407 [RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I., 3408 Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent 3409 Multicast - Sparse Mode (PIM-SM): Protocol Specification 3410 (Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March 3411 2016, . 3413 [RFC8086] Yong, L., Ed., Crabbe, E., Xu, X., and T. Herbert, "GRE- 3414 in-UDP Encapsulation", RFC 8086, DOI 10.17487/RFC8086, 3415 March 2017, . 3417 [RFC8201] McCann, J., Deering, S., Mogul, J., and R. Hinden, Ed., 3418 "Path MTU Discovery for IP version 6", STD 87, RFC 8201, 3419 DOI 10.17487/RFC8201, July 2017, 3420 . 3422 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 3423 Decraene, B., Litkowski, S., and R. Shakir, "Segment 3424 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 3425 July 2018, . 3427 [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol 3428 Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, 3429 . 3431 Appendix A. AERO Alternate Encapsulations 3433 When GUE encapsulation is not needed, AERO can use common 3434 encapsulations such as IP-in-IP [RFC2003][RFC2473][RFC4213], Generic 3435 Routing Encapsulation (GRE) [RFC2784][RFC2890] and others. The 3436 encapsulation is therefore only differentiated from non-AERO tunnels 3437 through the application of AERO control messaging and not through, 3438 e.g., a well-known UDP port number. 3440 As for GUE encapsulation, alternate AERO encapsulation formats may 3441 require encapsulation layer fragmentation. For simple IP-in-IP 3442 encapsulation, an IPv6 fragment header is inserted directly between 3443 the inner and outer IP headers when needed, i.e., even if the outer 3444 header is IPv4. The IPv6 Fragment Header is identified to the outer 3445 IP layer by its IP protocol number, and the Next Header field in the 3446 IPv6 Fragment Header identifies the inner IP header version. For GRE 3447 encapsulation, a GRE fragment header is inserted within the GRE 3448 header [I-D.templin-intarea-grefrag]. 3450 Figure 6 shows the AERO IP-in-IP encapsulation format before any 3451 fragmentation is applied: 3453 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3454 | Outer IPv4 Header | | Outer IPv6 Header | 3455 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3456 |IPv6 Frag Header (optional)| |IPv6 Frag Header (optional)| 3457 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3458 | Inner IP Header | | Inner IP Header | 3459 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3460 | | | | 3461 ~ ~ ~ ~ 3462 ~ Inner Packet Body ~ ~ Inner Packet Body ~ 3463 ~ ~ ~ ~ 3464 | | | | 3465 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3467 Minimal Encapsulation in IPv4 Minimal Encapsulation in IPv6 3469 Figure 6: Minimal Encapsulation Format using IP-in-IP 3471 Figure 7 shows the AERO GRE encapsulation format before any 3472 fragmentation is applied: 3474 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3475 | Outer IP Header | 3476 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3477 | GRE Header | 3478 | (with checksum, key, etc..) | 3479 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3480 | GRE Fragment Header (optional)| 3481 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3482 | Inner IP Header | 3483 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3484 | | 3485 ~ ~ 3486 ~ Inner Packet Body ~ 3487 ~ ~ 3488 | | 3489 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3491 Figure 7: Minimal Encapsulation Using GRE 3493 Alternate encapsulation may be preferred in environments where GUE 3494 encapsulation would add unnecessary overhead. For example, certain 3495 low-bandwidth wireless data links may benefit from a reduced 3496 encapsulation overhead. 3498 GUE encapsulation can traverse network paths that are inaccessible to 3499 non-UDP encapsulations, e.g., for crossing Network Address 3500 Translators (NATs). More and more, network middleboxes are also 3501 being configured to discard packets that include anything other than 3502 a well-known IP protocol such as UDP and TCP. It may therefore be 3503 necessary to determine the potential for middlebox filtering before 3504 enabling alternate encapsulation in a given environment. 3506 In addition to IP-in-IP, GRE and GUE, AERO can also use security 3507 encapsulations such as IPsec, TLS/SSL, DTLS, etc. In that case, AERO 3508 control messaging and route determination occur before security 3509 encapsulation is applied for outgoing packets and after security 3510 decapsulation is applied for incoming packets. 3512 AERO is especially well suited for use with VPN system encapsulations 3513 such as OpenVPN [OVPN]. 3515 Appendix B. Non-Normative Considerations 3517 AERO can be applied to a multitude of Internetworking scenarios, with 3518 each having its own adaptations. The following considerations are 3519 provided as non-normative guidance: 3521 B.1. Implementation Strategies for Route Optimization 3523 Route optimization as discussed in Section 3.17 results in the route 3524 optimization source (ROS) creating an asymmetric neighbor cache entry 3525 for the target neighbor. The neighbor cache entry is maintained for 3526 at most REACHABLETIME seconds and then deleted unless updated. In 3527 order to refresh the neighbor cache entry lifetime before the 3528 ReachableTime timer expires, the specification requires 3529 implementations to issue a new NS/NA exchange to reset ReachableTime 3530 to REACHABLETIME seconds while data packets are still flowing. 3531 However, the decision of when to initiate a new NS/NA exchange and to 3532 perpetuate the process is left as an implementation detail. 3534 One possible strategy may be to monitor the neighbor cache entry 3535 watching for data packets for (REACHABLETIME - 5) seconds. If any 3536 data packets have been sent to the neighbor within this timeframe, 3537 then send an NS to receive a new NA. If no data packets have been 3538 sent, wait for 5 additional seconds and send an immediate NS if any 3539 data packets are sent within this "expiration pending" 5 second 3540 window. If no additional data packets are sent within the 5 second 3541 window, delete the neighbor cache entry. 3543 The monitoring of the neighbor data packet traffic therefore becomes 3544 an asymmetric ongoing process during the neighbor cache entry 3545 lifetime. If the neighbor cache entry expires, future data packets 3546 will trigger a new NS/NA exchange while the packets themselves are 3547 delivered over a longer path until route optimization state is re- 3548 established. 3550 B.2. Implicit Mobility Management 3552 AERO interface neighbors MAY provide a configuration option that 3553 allows them to perform implicit mobility management in which no ND 3554 messaging is used. In that case, the Client only transmits packets 3555 over a single interface at a time, and the neighbor always observes 3556 packets arriving from the Client from the same link-layer source 3557 address. 3559 If the Client's underlying interface address changes (either due to a 3560 readdressing of the original interface or switching to a new 3561 interface) the neighbor immediately updates the neighbor cache entry 3562 for the Client and begins accepting and sending packets according to 3563 the Client's new address. This implicit mobility method applies to 3564 use cases such as cellphones with both WiFi and Cellular interfaces 3565 where only one of the interfaces is active at a given time, and the 3566 Client automatically switches over to the backup interface if the 3567 primary interface fails. 3569 B.3. Direct Underlying Interfaces 3571 When a Client's AERO interface is configured over a Direct interface, 3572 the neighbor at the other end of the Direct link can receive packets 3573 without any encapsulation. In that case, the Client sends packets 3574 over the Direct link according to QoS preferences. If the Direct 3575 interface has the highest QoS preference, then the Client's IP 3576 packets are transmitted directly to the peer without going through an 3577 ANET/INET. If other interfaces have higher QoS preferences, then the 3578 Client's IP packets are transmitted via a different interface, which 3579 may result in the inclusion of Proxys, Servers and Relays in the 3580 communications path. Direct interfaces must be tested periodically 3581 for reachability, e.g., via NUD. 3583 B.4. AERO Clients on the Open Internetwork 3585 AERO Clients that connect to the open Internetwork via either a 3586 native or NATed interface can establish a VPN to securely connect to 3587 a Server. Alternatively, the Client can exchange ND messages 3588 directly with other AERO nodes on the same SPAN segment using INET 3589 encapsulation only and without joining the SPAN. In that case, 3590 however, the Client must apply asymmetric security for ND messages to 3591 ensure routing and neighbor cache integrity (see: Section 6). 3593 B.5. Operation on AERO Links with /64 ASPs 3595 IPv6 AERO links typically have MSPs that aggregate many candidate 3596 MNPs of length /64 or shorter. However, in some cases it may be 3597 desirable to use AERO over links that have only a /64 MSP. This can 3598 be accommodated by treating all Clients on the AERO link as simple 3599 hosts that receive /128 prefix delegations. 3601 In that case, the Client sends an RS message to the Server the same 3602 as for ordinary AERO links. The Server responds with an RA message 3603 that includes one or more /128 prefixes (i.e., singleton addresses) 3604 that include the /64 MSP prefix along with an interface identifier 3605 portion to be assigned to the Client. The Client and Server then 3606 configure their AERO addresses based on the interface identifier 3607 portions of the /128s (i.e., the lower 64 bits) and not based on the 3608 /64 prefix (i.e., the upper 64 bits). 3610 For example, if the MSP for the host-only IPv6 AERO link is 3611 2001:db8:1000:2000::/64, each Client will receive one or more /128 3612 IPv6 prefix delegations such as 2001:db8:1000:2000::1/128, 3613 2001:db8:1000:2000::2/128, etc. When the Client receives the prefix 3614 delegations, it assigns the AERO addresses fe80::1, fe80::2, etc. to 3615 the AERO interface, and assigns the global IPv6 addresses (i.e., the 3616 /128s) to either the AERO interface or an internal virtual interface 3617 such as a loopback. In this arrangement, the Client conducts route 3618 optimization in the same sense as discussed in Section 3.17. 3620 This specification has applicability for nodes that act as a Client 3621 on an "upstream" AERO link, but also act as a Server on "downstream" 3622 AERO links. More specifically, if the node acts as a Client to 3623 receive a /64 prefix from the upstream AERO link it can then act as a 3624 Server to provision /128s to Clients on downstream AERO links. 3626 B.6. AERO Adaptations for SEcure Neighbor Discovery (SEND) 3628 SEcure Neighbor Discovery (SEND) [RFC3971] and Cryptographically 3629 Generated Addresses (CGAs) [RFC3972] were designed to secure IPv6 ND 3630 messaging in environments where symmetric network and/or transport- 3631 layer security services are impractical (see: Section 6). AERO nodes 3632 that use SEND/CGA employ the following adaptations. 3634 When a source AERO node prepares a SEND-protected ND message, it uses 3635 a link-local CGA as the IPv6 source address and writes the prefix 3636 embedded in its AERO address (i.e., instead of fe80::/64) in the CGA 3637 parameters Subnet Prefix field. When the neighbor receives the ND 3638 message, it first verifies the message checksum and SEND/CGA 3639 parameters while using the link-local prefix fe80::/64 (i.e., instead 3640 of the value in the Subnet Prefix field) to match against the IPv6 3641 source address of the ND message. 3643 The neighbor then derives the AERO address of the source by using the 3644 value in the Subnet Prefix field as the interface identifier of an 3645 AERO address. For example, if the Subnet Prefix field contains 3646 2001:db8:1:2, the neighbor constructs the AERO address as 3647 fe80::2001:db8:1:2. The neighbor then caches the AERO address in the 3648 neighbor cache entry it creates for the source, and uses the AERO 3649 address as the IPv6 destination address of any ND message replies. 3651 B.7. AERO Critical Infrastructure Considerations 3653 AERO Relays can be either Commercial off-the Shelf (COTS) standard IP 3654 routers or virtual machines in the cloud. Relays must be 3655 provisioned, supported and managed by the INET administrative 3656 authority, and connected to the Relays of other INETs via inter- 3657 domain peerings. Cost for purchasing, configuring and managing 3658 Relays is nominal even for very large AERO links. 3660 AERO Servers can be standard dedicated server platforms, but most 3661 often will be deployed as virtual machines in the cloud. The only 3662 requirements for Servers are that they can run the AERO user-level 3663 code and have at least one network interface connection to the INET. 3664 As with Relays, Servers must be provisioned, supported and managed by 3665 the INET administrative authority. Cost for purchasing, configuring 3666 and managing Servers is nominal especially for virtual Servers hosted 3667 in the cloud. 3669 AERO Proxys are most often standard dedicated server platforms with 3670 one network interface connected to the ANET and a second interface 3671 connected to an INET. As with Servers, the only requirements are 3672 that they can run the AERO user-level code and have at least one 3673 interface connection to the INET. Proxys must be provisioned, 3674 supported and managed by the ANET administrative authority. Cost for 3675 purchasing, configuring and managing Proxys is nominal, and borne by 3676 the ANET administrative authority. 3678 AERO Gateways can be any dedicated server or COTS router platform 3679 connected to INETs and/or EUNs. The Gateway joins the SPAN and 3680 engages in eBGP peering with one or more Relays as a stub AS. The 3681 Gateway then injects its MNPs and/or non-MNP prefixes into the BGP 3682 routing system, and provisions the prefixes to its downstream- 3683 attached networks. The Gateway can perform ROS and MAP services the 3684 same as for any Server, and can route between the MNP and non-MNP 3685 address spaces. 3687 B.8. AERO Server Failure Implications 3689 AERO Servers may appear as a single point of failure in the 3690 architecture, but such is not the case since all Servers on the link 3691 provide identical services and loss of a Server does not imply 3692 immediate and/or comprehensive communication failures. Although 3693 Clients typically associate with a single Server at a time, Server 3694 failure is quickly detected and conveyed by Bidirectional Forward 3695 Detection (BFD) and/or proactive NUD allowing Clients to migrate to 3696 new Servers. 3698 If a Server fails, ongoing packet forwarding to Clients will continue 3699 by virtue of the asymmetric neighbor cache entries that have already 3700 been established in route optimization sources (ROSs). If a Client 3701 also experiences mobility events at roughly the same time the Server 3702 fails, unsolicited NA messages may be lost but proxy neighbor cache 3703 entries in the DEPARTED state will ensure that packet forwarding to 3704 the Client's new locations will continue for up to DEPARTTIME 3705 seconds. 3707 If a Client is left without a Server for an extended timeframe (e.g., 3708 greater than REACHABLETIIME seconds) then existing asymmetric 3709 neighbor cache entries will eventually expire and both ongoing and 3710 new communications will fail. The original source will continue to 3711 retransmit until the Client has established a new Server 3712 relationship, after which time continuous communications will resume. 3714 Therefore, providing many Servers on the link with high availability 3715 profiles provides resilience against loss of individual Servers and 3716 assurance that Clients can establish new Server relationships quickly 3717 in event of a Server failure. 3719 B.9. AERO Client / Server Architecture 3721 The AERO architectural model is client / server in the control plane, 3722 with route optimization in the data plane. The same as for common 3723 Internet services, the AERO Client discovers the addresses of AERO 3724 Servers and selects one Server to connect to. The AERO service is 3725 analogous to common Internet services such as google.com, yahoo.com, 3726 cnn.com, etc. However, there is only one AERO service for the link 3727 and all Servers provide identical services. 3729 Common Internet services provide differing strategies for advertising 3730 server addresses to clients. The strategy is conveyed through the 3731 DNS resource records returned in response to name resolution queries. 3732 As of January 2020 Internet-based 'nslookup' services were used to 3733 determine the following: 3735 o When a client resolves the domainname "google.com", the DNS always 3736 returns one A record (i.e., an IPv4 address) and one AAAA record 3737 (i.e., an IPv6 address). The client receives the same addresses 3738 each time it resolves the domainname via the same DNS resolver, 3739 but may receive different addresses when it resolves the 3740 domainname via different DNS resolvers. But, in each case, 3741 exactly one A and one AAAA record are returned. 3743 o When a client resolves the domainname "ietf.org", the DNS always 3744 returns one A record and one AAAA record with the same addresses 3745 regardless of which DNS resolver is used. 3747 o When a client resolves the domainname "yahoo.com", the DNS always 3748 returns a list of 4 A records and 4 AAAA records. Each time the 3749 client resolves the domainname via the same DNS resolver, the same 3750 list of addresses are returned but in randomized order (i.e., 3751 consistent with a DNS round-robin strategy). But, interestingly, 3752 the same addresses are returned (albeit in randomized order) when 3753 the domainname is resolved via different DNS resolvers. 3755 o When a client resolves the domainname "amazon.com", the DNS always 3756 returns a list of 3 A records and no AAAA records. As with 3757 "yahoo.com", the same three A records are returned from any 3758 worldwide Internet connection point in randomized order. 3760 The above example strategies show differing approaches to Internet 3761 resilience and service distribution offered by major Internet 3762 services. The Google approach exposes only a single IPv4 and a 3763 single IPv6 address to clients. Clients can then select whichever IP 3764 protocol version offers the best response, but will always use the 3765 same IP address according to the current Internet connection point. 3766 This means that the IP address offered by the network must lead to a 3767 highly-available server and/or service distribution point. In other 3768 words, resilience is predicated on high availability within the 3769 network and with no client-initiated failovers expected (i.e., it is 3770 all-or-nothing from the client's perspective). However, Google does 3771 provide for worldwide distributed service distribution by virtue of 3772 the fact that each Internet connection point responds with a 3773 different IPv6 and IPv4 address. The IETF approach is like google 3774 (all-or-nothing from the client's perspective), but provides only a 3775 single IPv4 or IPv6 address on a worldwide basis. This means that 3776 the addresses must be made highly-available at the network level with 3777 no client failover possibility, and if there is any worldwide service 3778 distribution it would need to be conducted by a network element that 3779 is reached via the IP address acting as a service distribution point. 3781 In contrast to the Google and IETF philosophies, Yahoo and Amazon 3782 both provide clients with a (short) list of IP addresses with Yahoo 3783 providing both IP protocol versions and Amazon as IPv4-only. The 3784 order of the list is randomized with each name service query 3785 response, with the effect of round-robin load balancing for service 3786 distribution. With a short list of addresses, there is still 3787 expectation that the network will implement high availability for 3788 each address but in case any single address fails the client can 3789 switch over to using a different address. The balance then becomes 3790 one of function in the network vs function in the end system. 3792 The same implications observed for common highly-available services 3793 in the Internet apply also to the AERO client/server architecture. 3794 When an AERO Client connects to one or more ANETs, it discovers one 3795 or more AERO Server addresses through the mechanisms discussed in 3796 earlier sections. Each Server address presumably leads to a fault- 3797 tolerant clustering arrangement such as supported by Linux-HA, 3798 Extended Virtual Synchrony or Paxos. Such an arrangement has 3799 precedence in common Internet service deployments in lightweight 3800 virtual machines without requiring expensive hardware deployment. 3801 Similarly, common Internet service deployments set service IP 3802 addresses on service distribution points that may relay requests to 3803 many different servers. 3805 For AERO, the expectation is that a combination of the Google/IETF 3806 and Yahoo/Amazon philosophies would be employed. The AERO Client 3807 connects to different ANET access points and can receive 1-2 Server 3808 AERO addresses at each point. It then selects one AERO Server 3809 address, and engages in RS/RA exchanges with the same Server from all 3810 ANET connections. The Client remains with this Server unless or 3811 until the Server fails, in which case it can switch over to an 3812 alternate Server. The Client can likewise switch over to a different 3813 Server at any time if there is some reason for it to do so. So, the 3814 AERO expectation is for a balance of function in the network and end 3815 system, with fault tolerance and resilience at both levels. 3817 Appendix C. Change Log 3819 << RFC Editor - remove prior to publication >> 3821 Changes from draft-templin-intarea-6706bis-30 to draft-templin- 3822 intrea-6706bis-31: 3824 o Added "advisory PTB messages" under FAA SE2025 contract number 3825 DTFAWA-15-D-00030. 3827 Changes from draft-templin-intarea-6706bis-29 to draft-templin- 3828 intrea-6706bis-30: 3830 o Deprecate "primary" concept. Now, RS/RA keepalives are 3831 mainatained over *all* underlying interfaces (i.e., and not just 3832 one primary). 3834 Changes from draft-templin-intarea-6706bis-28 to draft-templin- 3835 intrea-6706bis-29: 3837 o Changed OMNI interface citation to "draft-templin-6man-omni- 3838 interface" 3840 o Changed SPAN Service Prefix to fd80::/10. 3842 o Changed S/TLLAO format to include 'S' bit for ifIndex 3843 corresponding to the underlying interface that is Source of ND 3844 message. 3846 o Updated Path MTU 3848 Changes from draft-templin-intarea-6706bis-27 to draft-templin- 3849 intrea-6706bis-28: 3851 o MTU and fragmentation. 3853 Changes from draft-templin-intarea-6706bis-26 to draft-templin- 3854 intrea-6706bis-27: 3856 o MTU and fragmentation. 3858 o SPAN Service Prefix set to fd00::/10 3860 o Client SPAN addresses defined. 3862 Changes from draft-templin-intarea-6706bis-25 to draft-templin- 3863 intrea-6706bis-26: 3865 o MTU and RA configuration information updated. 3867 Changes from draft-templin-intarea-6706bis-24 to draft-templin- 3868 intrea-6706bis-25: 3870 o Added concept of "primary" to allow for proxyed RS/RA over only 3871 selected underlying interfaces. 3873 o General Cleanup. 3875 Changes from draft-templin-intarea-6706bis-23 to draft-templin- 3876 intrea-6706bis-24: 3878 o OMNI interface spec now a normative reference. 3880 o Use REACHABLETIME as the nominal Router Lifetime to return in RAs. 3882 o General cleanup. 3884 Changes from draft-templin-intarea-6706bis-22 to draft-templin- 3885 intrea-6706bis-23: 3887 o Choice of using either RS/RA or unsolicited NA for old Server 3888 notification. 3890 o General cleanup. 3892 Changes from draft-templin-intarea-6706bis-21 to draft-templin- 3893 intrea-6706bis-22: 3895 o Tightened up text on Proxy. 3897 o Removed unnecessarily restrictive texts. 3899 o General cleanup. 3901 Changes from draft-templin-intarea-6706bis-20 to draft-templin- 3902 intrea-6706bis-21: 3904 o Clarified relationship between OMNI and S/TLLAO ifIndex-tuples. 3906 o Important text in Section 13.15.3 on Servers timing out Clients 3907 that have gone silent without sending a departure notification. 3909 o New text on RS/RA as "hints of forward progress" for proactive 3910 NUD. 3912 Changes from draft-templin-intarea-6706bis-19 to draft-templin- 3913 intrea-6706bis-20: 3915 o Included new route optimization source and destination addressing 3916 strategy. Now, route optimization maintenance uses the address of 3917 the existing Server instead of the data packet destination address 3918 so that less pressure is placed on the BGP routing system 3919 convergence time and Server constancy is supported. 3921 o Included new method for releasing from old MSE without requiring 3922 Client messaging. 3924 o Included references to new OMNI interface spec (including the OMNI 3925 option). 3927 o New appendix on AERO Client/Server architecture. 3929 Changes from draft-templin-intarea-6706bis-18 to draft-templin- 3930 intrea-6706bis-19: 3932 o Changed Proxy/Server keepalives to use "proactive NUD" in a manner 3933 tha paralles BFD 3935 Changes from draft-templin-intarea-6706bis-17 to draft-templin- 3936 intrea-6706bis-18: 3938 o Discuss how AERO option is used in relation to S/TLLAOs 3940 o New text on Bidirectional Forwarding Detection (BFD) 3942 o Cleaned up usage (and non-usage) of unsolicited NAs 3944 o New appendix on Server failures 3946 Changes from draft-templin-intarea-6706bis-15 to draft-templin- 3947 intrea-6706bis-17: 3949 o S/TLLAO now includes multiple link-layer addresses within a single 3950 option instead of requiring multiple options 3952 o New unsolicited NA message to inform the old link that a Client 3953 has moved to a new link 3955 Changes from draft-templin-intarea-6706bis-14 to draft-templin- 3956 intrea-6706bis-15: 3958 o MTU and fragmentation 3960 o New details in movement to new Server 3962 Changes from draft-templin-intarea-6706bis-13 to draft-templin- 3963 intrea-6706bis-14: 3965 o Security based on secured tunnels, ingress filtering, MAP list and 3966 ROS list 3968 Changes from draft-templin-intarea-6706bis-12 to draft-templin- 3969 intrea-6706bis-13: 3971 o New paragraph in Section 3.6 on AERO interface layering over 3972 secured tunnels 3974 o Removed extraneous text in Section 3.7 3976 o Added new detail to the forwarding algorithm in Section 3.9 3978 o Clarified use of fragmentation 3980 o Route optimization now supported for both MNP and non-MNP-based 3981 prefixes 3983 o Relays are now seen as link-layer elements in the architecture. 3985 o Built out multicast section in detail. 3987 o New Appendix on implementation considerations for route 3988 optimization. 3990 Changes from draft-templin-intarea-6706bis-11 to draft-templin- 3991 intrea-6706bis-12: 3993 o Introduced Gateways as a new AERO element for connecting 3994 Correspondent Nodes on INET links 3996 o Introduced terms "Access Network (ANET)" and "Internetwork (INET)" 3998 o Changed "ASP" to "MSP", and "ACP" to "MNP" 4000 o New figure on the relation of Segments to the SPAN and AERO link 4001 o New "S" bit in S/TLLAO to indicate the "Source" S/TLLAO as opposed 4002 to additional S/TLLAOs 4004 o Changed Interface ID for Servers from 255 to 0xffff 4006 o Significant updates to Route Optimization, NUD, and Mobility 4007 Management 4009 o New Section on Multicast 4011 o New Section on AERO Clients in the open Internetwork 4013 o New Section on Operation over multiple AERO links (VLANs over the 4014 SPAN) 4016 o New Sections on DNS considerations and Transition considerations 4018 o 4020 Changes from draft-templin-intarea-6706bis-10 to draft-templin- 4021 intrea-6706bis-11: 4023 o Added The SPAN 4025 Changes from draft-templin-intarea-6706bis-09 to draft-templin- 4026 intrea-6706bis-10: 4028 o Orphaned packets in flight (e.g., when a neighbor cache entry is 4029 in the DEPARTED state) are now forwarded at the link layer instead 4030 of at the network layer. Forwarding at the network layer can 4031 result in routing loops and/or excessive delays of forwarded 4032 packets while the routing system is still reconverging. 4034 o Update route optimization to clarify the unsecured nature of the 4035 first NS used for route discovery 4037 o Many cleanups and clarifications on ND messaging parameters 4039 Changes from draft-templin-intarea-6706bis-08 to draft-templin- 4040 intrea-6706bis-09: 4042 o Changed PRL to "MAP list" 4044 o For neighbor cache entries, changed "static" to "symmetric", and 4045 "dynamic" to "asymmetric" 4047 o Specified Proxy RS/RA exchanges with Servers on behalf of Clients 4048 o Added discussion of unsolicited NAs in Section 3.16, and included 4049 forward reference to Section 3.18 4051 o Added discussion of AERO Clients used as critical infrastructure 4052 elements to connect fixed networks. 4054 o Added network-based VPN under security considerations 4056 Changes from draft-templin-intarea-6706bis-07 to draft-templin- 4057 intrea-6706bis-08: 4059 o New section on AERO-Aware Access Router 4061 Changes from draft-templin-intarea-6706bis-06 to draft-templin- 4062 intrea-6706bis-07: 4064 o Added "R" bit for release of PDs. Now have a full RS/RA service 4065 that can do PD without requiring DHCPv6 messaging over-the-air 4067 o Clarifications on solicited vs unsolicited NAs 4069 o Clarified use of MAX_NEIGHBOR_ADVERTISEMENTS for the purpose of 4070 increase reliability 4072 Changes from draft-templin-intarea-6706bis-05 to draft-templin- 4073 intrea-6706bis-06: 4075 o Major re-work and simplification of Route Optimization function 4077 o Added Distributed Mobility Management (DMM) and Mobility Anchor 4078 Point (MAP) terminology 4080 o New section on "AERO Critical Infrastructure Element 4081 Considerations" demonstrating low overall cost for the service 4083 o minor text revisions and deletions 4085 o removed extraneous appendices 4087 Changes from draft-templin-intarea-6706bis-04 to draft-templin- 4088 intrea-6706bis-05: 4090 o New Appendix E on S/TLLAO Extensions for special-purpose links. 4091 Discussed ATN/IPS as example. 4093 o New sentence in introduction to declare appendices as non- 4094 normative. 4096 Changes from draft-templin-intarea-6706bis-03 to draft-templin- 4097 intrea-6706bis-04: 4099 o Added definitions for Potential Router List (PRL) and secure 4100 enclave 4102 o Included text on mapping transport layer port numbers to network 4103 layer DSCP values 4105 o Added reference to DTLS and DMM Distributed Mobility Anchoring 4106 working group document 4108 o Reworked Security Considerations 4110 o Updated references. 4112 Changes from draft-templin-intarea-6706bis-02 to draft-templin- 4113 intrea-6706bis-03: 4115 o Added new section on SEND. 4117 o Clarifications on "AERO Address" section. 4119 o Updated references and added new reference for RFC8086. 4121 o Security considerations updates. 4123 o General text clarifications and cleanup. 4125 Changes from draft-templin-intarea-6706bis-01 to draft-templin- 4126 intrea-6706bis-02: 4128 o Note on encapsulation avoidance in Section 4. 4130 Changes from draft-templin-intarea-6706bis-00 to draft-templin- 4131 intrea-6706bis-01: 4133 o Remove DHCPv6 Server Release procedures that leveraged the old way 4134 Relays used to "route" between Server link-local addresses 4136 o Remove all text relating to Relays needing to do any AERO-specific 4137 operations 4139 o Proxy sends RS and receives RA from Server using SEND. Use CGAs 4140 as source addresses, and destination address of RA reply is to the 4141 AERO address corresponding to the Client's ACP. 4143 o Proxy uses SEND to protect RS and authenticate RA (Client does not 4144 use SEND, but rather relies on subnetwork security. When the 4145 Proxy receives an RS from the Client, it creates a new RS using 4146 its own addresses as the source and uses SEND with CGAs to send a 4147 new RS to the Server. 4149 o Emphasize distributed mobility management 4151 o AERO address-based RS injection of ACP into underlying routing 4152 system. 4154 Changes from draft-templin-aerolink-82 to draft-templin-intarea- 4155 6706bis-00: 4157 o Document use of NUD (NS/NA) for reliable link-layer address 4158 updates as an alternative to unreliable unsolicited NA. 4159 Consistent with Section 7.2.6 of RFC4861. 4161 o Server adds additional layer of encapsulation between outer and 4162 inner headers of NS/NA messages for transmission through Relays 4163 that act as vanilla IPv6 routers. The messages include the AERO 4164 Server Subnet Router Anycast address as the source and the Subnet 4165 Router Anycast address corresponding to the Client's ACP as the 4166 destination. 4168 o Clients use Subnet Router Anycast address as the encapsulation 4169 source address when the access network does not provide a 4170 topologically-fixed address. 4172 Author's Address 4174 Fred L. Templin (editor) 4175 Boeing Research & Technology 4176 P.O. Box 3707 4177 Seattle, WA 98124 4178 USA 4180 Email: fltemplin@acm.org