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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, February 4, 2020 5 rfc6179, rfc6706 (if 6 approved) 7 Intended status: Standards Track 8 Expires: August 7, 2020 10 Asymmetric Extended Route Optimization (AERO) 11 draft-templin-intarea-6706bis-25 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 August 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 3.6. AERO Interface Characteristics . . . . . . . . . . . . . 21 73 3.7. AERO Interface Initialization . . . . . . . . . . . . . . 25 74 3.7.1. AERO Server/Gateway Behavior . . . . . . . . . . . . 25 75 3.7.2. AERO Proxy Behavior . . . . . . . . . . . . . . . . . 26 76 3.7.3. AERO Client Behavior . . . . . . . . . . . . . . . . 26 77 3.7.4. AERO Relay Behavior . . . . . . . . . . . . . . . . . 26 78 3.8. AERO Interface Neighbor Cache Maintenance . . . . . . . . 26 79 3.9. AERO Interface Encapsulation and Re-encapsulation . . . . 28 80 3.10. AERO Interface Decapsulation . . . . . . . . . . . . . . 30 81 3.11. AERO Interface Data Origin Authentication . . . . . . . . 30 82 3.12. AERO Interface Forwarding Algorithm . . . . . . . . . . . 30 83 3.12.1. Client Forwarding Algorithm . . . . . . . . . . . . 31 84 3.12.2. Proxy Forwarding Algorithm . . . . . . . . . . . . . 32 85 3.12.3. Server/Gateway Forwarding Algorithm . . . . . . . . 32 86 3.12.4. Relay Forwarding Algorithm . . . . . . . . . . . . . 34 87 3.13. AERO Interface MTU and Fragmentation . . . . . . . . . . 34 88 3.13.1. AERO MTU Requirements . . . . . . . . . . . . . . . 37 89 3.14. AERO Interface Error Handling . . . . . . . . . . . . . . 37 90 3.15. AERO Router Discovery, Prefix Delegation and 91 Autoconfiguration . . . . . . . . . . . . . . . . . . . . 40 92 3.15.1. AERO ND/PD Service Model . . . . . . . . . . . . . . 40 93 3.15.2. AERO Client Behavior . . . . . . . . . . . . . . . . 41 94 3.15.3. AERO Server Behavior . . . . . . . . . . . . . . . . 43 95 3.16. The AERO Proxy . . . . . . . . . . . . . . . . . . . . . 45 96 3.16.1. Detecting and Responding to Server Failures . . . . 48 97 3.17. AERO Route Optimization . . . . . . . . . . . . . . . . . 49 98 3.17.1. Route Optimization Initiation . . . . . . . . . . . 49 99 3.17.2. Relaying the NS . . . . . . . . . . . . . . . . . . 50 100 3.17.3. Processing the NS and Sending the NA . . . . . . . . 50 101 3.17.4. Relaying the NA . . . . . . . . . . . . . . . . . . 51 102 3.17.5. Processing the NA . . . . . . . . . . . . . . . . . 51 103 3.17.6. Route Optimization Maintenance . . . . . . . . . . . 51 104 3.18. Neighbor Unreachability Detection (NUD) . . . . . . . . . 52 105 3.19. Mobility Management and Quality of Service (QoS) . . . . 53 106 3.19.1. Mobility Update Messaging . . . . . . . . . . . . . 54 107 3.19.2. Announcing Link-Layer Address and/or QoS Preference 108 Changes . . . . . . . . . . . . . . . . . . . . . . 55 109 3.19.3. Bringing New Links Into Service . . . . . . . . . . 55 110 3.19.4. Removing Existing Links from Service . . . . . . . . 55 111 3.19.5. Moving to a New Server . . . . . . . . . . . . . . . 55 112 3.20. Multicast . . . . . . . . . . . . . . . . . . . . . . . . 57 113 3.20.1. Source-Specific Multicast (SSM) . . . . . . . . . . 57 114 3.20.2. Any-Source Multicast (ASM) . . . . . . . . . . . . . 58 115 3.20.3. Bi-Directional PIM (BIDIR-PIM) . . . . . . . . . . . 59 116 3.21. Operation over Multiple AERO Links (VLANs) . . . . . . . 59 117 3.22. DNS Considerations . . . . . . . . . . . . . . . . . . . 60 118 3.23. Transition Considerations . . . . . . . . . . . . . . . . 61 119 3.24. Detecting and Reacting to Server and Relay Failures . . . 61 120 4. Implementation Status . . . . . . . . . . . . . . . . . . . . 62 121 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 62 122 6. Security Considerations . . . . . . . . . . . . . . . . . . . 62 123 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 64 124 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 66 125 8.1. Normative References . . . . . . . . . . . . . . . . . . 66 126 8.2. Informative References . . . . . . . . . . . . . . . . . 67 127 Appendix A. AERO Alternate Encapsulations . . . . . . . . . . . 74 128 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 . . . . . . . . . . . . . . . . . . . . . . . . 88 141 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 0xfffffffe (e.g., fe80::1, fe80::2, fe80::3, etc., fe80::ffff:fffe) 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 reserved 732 as the unspecified AERO address. 734 The lowest-numbered AERO address from a Client's MNP delegation 735 serves as the "base" AERO address (for example, for the MNP 736 2001:db8:1000:2000::/56 the base AERO address is 737 fe80::2001:db8:1000:2000). The Client then assigns the base AERO 738 address to the AERO interface and uses it for the purpose of 739 maintaining the neighbor cache entry. The Server likewise uses the 740 AERO address as its index into the neighbor cache for this Client. 742 If the Client has multiple AERO addresses (i.e., when there are 743 multiple MNPs and/or MNPs with prefix lengths shorter than /64), the 744 Client originates ND messages using the base AERO address as the 745 source address and accepts and responds to ND messages destined to 746 any of its AERO addresses as equivalent to the base AERO address. In 747 this way, the Client maintains a single neighbor cache entry that may 748 be indexed by multiple AERO addresses. 750 The Client's Subnet-Router anycast address can be statelessly 751 determined from its AERO address by simply transposing the AERO 752 address into the upper N bits of the Anycast address followed by 753 128-N bits of zeroes. For example, for the AERO address 754 fe80::2001:db8:1:2 the Subnet-Router anycast address is 755 2001:db8:1:2::. 757 AERO addresses for mobile node Clients embed a MNP as discussed 758 above, while AERO addresses for non-MNP destinations are constructed 759 in exactly the same way. A Client AERO address therefore encodes 760 either an MNP if the prefix is reached via the SPAN or a non-MNP if 761 the prefix is reached via a Gateway. 763 3.5. Spanning Partitioned AERO Networks (SPAN) 765 An AERO link configured over a single INET appears as a single 766 unified link with a consistent underlying network addressing plan. 767 In that case, all nodes on the link can exchange packets via simple 768 INET encapsulation, since the underlying INET is connected. In 769 common practice, however, an AERO link may be partitioned into 770 multiple "segments", where each segment is a distinct INET 771 potentially managed under a different administrative authority (e.g., 772 as for worldwide aviation service providers such as ARINC, SITA, 773 Inmarsat, etc.). Individual INETs may also themselves be partitioned 774 internally, in which case each internal partition is seen as a 775 separate segment. 777 The addressing plan of each segment is consistent internally but will 778 often bear no relation to the addressing plans of other segments. 779 Each segment is also likely to be separated from others by network 780 security devices (e.g., firewalls, proxies, packet filtering 781 gateways, etc.), and in many cases disjoint segments may not even 782 have any common physical link connections at all. Therefore, nodes 783 can only be assured of exchanging packets directly with 784 correspondents in the same segment, and not with those in other 785 segments. The only means for joining the segments therefore is 786 through inter-domain peerings between AERO Relays. 788 The same as for traditional campus LANs, multiple AERO link segments 789 can be joined into a single unified link via a virtual bridging 790 service termed the "SPAN". The SPAN performs link-layer packet 791 forwarding between segments (i.e., bridging) without decrementing the 792 network-layer TTL/Hop Limit. The SPAN model is depicted in Figure 2: 794 . . . . . . . . . . . . . . . . . . . . . . . 795 . . 796 . .-(::::::::) . 797 . .-(::::::::::::)-. +-+ . 798 . (:::: Segment A :::)--|R|---+ . 799 . `-(::::::::::::)-' +-+ | . 800 . `-(::::::)-' | . 801 . | . 802 . .-(::::::::) | . 803 . .-(::::::::::::)-. +-+ | . 804 . (:::: Segment B :::)--|R|---+ . 805 . `-(::::::::::::)-' +-+ | . 806 . `-(::::::)-' | . 807 . | . 808 . .-(::::::::) | . 809 . .-(::::::::::::)-. +-+ | . 810 . (:::: Segment C :::)--|R|---+ . 811 . `-(::::::::::::)-' +-+ | . 812 . `-(::::::)-' | . 813 . | . 814 . ..(etc).. x . 815 . . 816 . . 817 . <- AERO Link Bridged by the SPAN -> . 818 . . . . . . . . . . . . . .. . . . . . . . . 820 Figure 2: The SPAN 822 To support the SPAN, AERO links require a reserved /64 IPv6 "SPAN 823 Service Prefix (SSP)". Although any routable IPv6 prefix can be 824 used, a Unique Local Address (ULA) prefix (e.g., fd00::/64) [RFC4389] 825 is recommended since border routers are commonly configured to 826 prevent packets with ULAs from being injected into the AERO link by 827 an external IPv6 node and from leaking out of the AERO link to the 828 outside world. 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 fd00::1000/116, a second could assign fd00::2000/116, a 833 third could assign fd00::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 A "SPAN address" is an address taken from a SPP and assigned to a 840 Relay, Server, Gateway or Proxy interface. SPAN addresses are formed 841 by simply replacing the upper portion of an administratively-assigned 842 AERO address with the SPP. For example, if the SPP is 843 fd00::1000/116, the SPAN address formed from the AERO address 844 fe80::1001 is simply fd00::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 fd00::1000/116, fd00::2000/116 and fd00::3000/116 856 respectively, then the forwarding tables in each Relay are as 857 follows: 859 A: fd00::1000/116->local, fd00::2000/116->B, fd00::3000/116->C 861 B: fd00::1000/116->A, fd00::2000/116->local, fd00::3000/116->C 863 C: fd00::1000/116->A, fd00::2000/116->B, fd00::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 fd00::1000/116 (e.g., 878 fd00::1001) and destination SPAN address taken from fd00::3000/116 879 (e.g., fd00::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 = fd00::1001 | 895 | dst = fd00::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 address is simply set to the Subnet-Router anycast address. For non- 927 link-local addresses, the destination SPAN address may not be known 928 in advance for the first few packets of a flow sent via the SPAN. In 929 that case, the SPAN destination address is set to the original 930 packet's destination, and the SPAN routing system will direct the 931 packet to the correct SPAN egress node. (In the above example, the 932 SPAN destination address is simply 2001:db8:1000:2000::1.) 934 3.5.1. SPAN Compatibility Addressing 936 For IPv4 MNPs, Servers inject a "SPAN Compatibility Prefix (SCP)" 937 that embeds the MNP into the BGP routing system. The SCP begins with 938 the upper 64 bits of the SSP, followed by the constant string 939 "0000:FFFF" followed by the IPv4 MNP. For example, if the SSP is 940 fd00::/64 and the MNP is 192.0.2.0/24 then the SCP is 941 fd00::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 fd00::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 3.6. AERO Interface Characteristics 953 AERO interfaces are virtual interfaces configured over one or more 954 underlying interfaces classified as follows: 956 o Native interfaces have global IP addresses that are reachable from 957 any INET correspondent. All Server, Gateway and Relay interfaces 958 are native interfaces, as are INET-facing interfaces of Proxys. 960 o NATed interfaces connect to a private network behind a Network 961 Address Translator (NAT). The NAT does not participate in any 962 AERO control message signaling, but the Server can issue control 963 messages on behalf of the Client. Clients that are behind a NAT 964 are required to send periodic keepalive messages to keep NAT state 965 alive when there are no data packets flowing. If no other 966 periodic messaging service is available, the Client can send RS 967 messages to receive RA replies from its Server(s). 969 o VPNed interfaces use security encapsulation to a Virtual Private 970 Network (VPN) server that also acts as an AERO Server. As with 971 NATed links, the Server can issue control messages on behalf of 972 the Client, but the Client need not send periodic keepalives in 973 addition to those already used to maintain the VPN connection. 975 o Proxyed interfaces connect to an ANET that is separated from the 976 open INET by an AERO Proxy. Unlike NATed and VPNed interfaces, 977 the Proxy can actively issue control messages on behalf of the 978 Client. 980 o Direct interfaces connect a Client directly to a neighbor without 981 crossing any ANET/INET paths. An example is a line-of-sight link 982 between a remote pilot and an unmanned aircraft. 984 AERO interfaces use encapsulation (see: Section 3.9) to exchange 985 packets with AERO link neighbors over Native, NATed or VPNed 986 interfaces. AERO interfaces do not use encapsulation over Proxyed 987 and Direct underlying interfaces. 989 AERO interfaces maintain a neighbor cache for tracking per-neighbor 990 state the same as for any interface. AERO interfaces use ND messages 991 including Router Solicitation (RS), Router Advertisement (RA), 992 Neighbor Solicitation (NS) and Neighbor Advertisement (NA) for 993 neighbor cache management. 995 AERO interfaces send ND messages with an Overlay Multilink Network 996 Interface (OMNI) option formatted as specified in 997 [I-D.templin-atn-aero-interface]. The OMNI option includes prefix 998 registration information and "ifIndex-tuples" containing link quality 999 information for the AERO interface's underlying interfaces. 1001 When encapsulation is used, AERO interface ND messages MAY also 1002 include an AERO Source/Target Link-Layer Address Option (S/TLLAO) 1003 formatted as shown in Figure 4: 1005 0 1 2 3 1006 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 1007 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1008 | Type | Length | ifIndex[1] |V| Reserved[1] | 1009 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1010 ~ Link Layer Address [1] ~ 1011 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1012 | Port Number [1] | ifIndex[2] |V| Reserved[2] | 1013 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1014 ~ Link Layer Address [2] ~ 1015 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1016 | Port Number [2] | ~ 1017 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ 1018 ~ ~ 1019 ~ ... ~ 1020 ~ ~ 1021 ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1022 ~ | ifIndex[N] |V| Reserved[N] | 1023 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1024 ~ Link Layer Address [N] ~ 1025 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1026 | Port Number [N] | Trailing zero padding | 1027 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1028 | Trailing zero padding (if necessary) | 1029 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1031 Figure 4: AERO Source/Target Link-Layer Address Option (S/TLLAO) 1032 Format 1034 In this format, Type and Length are set the same as specified for S/ 1035 TLLAOs in [RFC4861], with trailing zero padding octets added as 1036 necessary to produce an integral number of 8 octet blocks. The S/ 1037 TLLAO includes N ifIndex-tuples in correspondence to ifIndex-tuples 1038 that appear in the OMNI option. Each ifIndex-tuple includes the 1039 folllowing information: 1041 o ifIndex[i] - the same value as in the corresponding ifIndex-tuple 1042 included in the OMNI option. 1044 o V[i] - a bit that identifies the IP protocol version of the 1045 address found in the Link Layer Address [i] field. The bit is set 1046 to 0 for IPv4 or 1 for IPv6. 1048 o Reserved[i] - MUST encode the value 0 on transmission, and ignored 1049 on reception. 1051 o Link Layer Address [i] - the IPv4 or IPv6 address used as the 1052 encapsulation source address. The field is 4 bytes in length for 1053 IPv4 or 16 bytes in length for IPv6. 1055 o Port Number [i] - the upper layer protocol port number used as the 1056 encapsulation source port, or 0 when no upper layer protocol 1057 encapsulation is used. The field is 2 bytes in length. 1059 If an S/TLLAO is included, the first S/TLLAO ifIndex-tuple MUST 1060 correspond to the first OMNI option ifIndex-tuple, and any additional 1061 S/TLLAO ifIndex-tuples MUST correspond to a proper subset of the 1062 remaining OMNI option ifIndex-tuples. Any S/TLLAO ifIndex-tuple 1063 having an ifIndex value that does not appear in an OMNI option 1064 ifindex-tuple is ignored. If the same ifIndex value appears in 1065 multiple ifIndex-tuples, the first tuple is processed and the 1066 remaining tuples are ignored. Any S/TLLAO ifIndex-tuples can 1067 therefore be viewed as inter-dependent extensions of their 1068 corresponidng OMNI option ifIndex-tuples, i.e., the OMNI option and 1069 S/TLLAO are companion options that are interpreted in conjunction 1070 with each other. 1072 A Client's AERO interface may be configured over multiple underlying 1073 interface connections. For example, common mobile handheld devices 1074 have both wireless local area network ("WLAN") and cellular wireless 1075 links. These links are typically used "one at a time" with low-cost 1076 WLAN preferred and highly-available cellular wireless as a standby. 1077 In a more complex example, aircraft frequently have many wireless 1078 data link types (e.g. satellite-based, cellular, terrestrial, air-to- 1079 air directional, etc.) with diverse performance and cost properties. 1081 If a Client's multiple underlying interfaces are used "one at a time" 1082 (i.e., all other interfaces are in standby mode while one interface 1083 is active), then ND message OMNI options include only a single 1084 ifIndex-tuple and set to a constant value. In that case, the Client 1085 would appear to have a single interface but with a dynamically 1086 changing link-layer address. 1088 If the Client has multiple active underlying interfaces, then from 1089 the perspective of ND it would appear to have multiple link-layer 1090 addresses. In that case, ND message OMNI options MAY include 1091 multiple ifIndex-tuples - each with a value that corresponds to a 1092 specific interface. The OMNI option MUST include a first ifIndex- 1093 tuple that corresponds to the interface over which the ND message is 1094 sent. Every ND message need not include all OMNI and/or S/TLLAO 1095 ifIndex-tuples; for any ifIndex-tuple not included, the neighbor 1096 considers the status as unchanged. 1098 Relay, Server and Proxy AERO interfaces may be configured over one or 1099 more secured tunnel interfaces. The AERO interface configures both 1100 an AERO address and its corresponding SPAN address, while the 1101 underlying secured tunnel interfaces are either unnumbered or 1102 configure the same SPAN address. The AERO interface encapsulates 1103 each IP packet in a SPAN header and presents the packet to the 1104 underlying secured tunnel interface. For Relays that do not 1105 configure an AERO interface, the secured tunnel interfaces themselves 1106 are exposed to the IP layer with each interface configuring the 1107 Relay's SPAN address. Routing protocols such as BGP therefore run 1108 directly over the Relay's secured tunnel interfaces. For nodes that 1109 configure an AERO interface, routing protocols such as BGP run over 1110 the AERO interface but do not employ SPAN encapsulation. Instead, 1111 the AERO interface presents the routing protocol messages directly to 1112 the underlying secured tunnels without applying encapsulation and 1113 while using the SPAN address as the source address. This distinction 1114 must be honored consistently according to each node's configuration 1115 so that the IP forwarding table will associate discovered IP routes 1116 with the correct interface. 1118 3.7. AERO Interface Initialization 1120 AERO Servers, Proxys and Clients configure AERO interfaces as their 1121 point of attachment to the AERO link. AERO nodes assign the MSPs for 1122 the link to their AERO interfaces (i.e., as a "route-to-interface") 1123 to ensure that packets with destination addresses covered by an MNP 1124 not explicitly assigned to a non-AERO interface are directed to the 1125 AERO interface. 1127 AERO interface initialization procedures for Servers, Proxys, Clients 1128 and Relays are discussed in the following sections. 1130 3.7.1. AERO Server/Gateway Behavior 1132 When a Server enables an AERO interface, it assigns AERO/SPAN 1133 addresses and configures permanent neighbor cache entries for 1134 neighbors in the same SPAN segment by consulting the ROS list for the 1135 segment. The Server also configures secured tunnels with one or more 1136 neighboring Relays and engages in a BGP routing protocol session with 1137 each Relay. 1139 The AERO interface provides a single interface abstraction to the IP 1140 layer, but internally comprises multiple secured tunnels as well as 1141 an NBMA nexus for sending encapsulated data packets to AERO interface 1142 neighbors. The Server further configures a service to facilitate ND/ 1143 PD exchanges with AERO Clients and manages per-Client neighbor cache 1144 entries and IP forwarding table entries based on control message 1145 exchanges. 1147 Gateways are simply Servers that run a dynamic routing protocol 1148 between the AERO interface and INET/EUN interfaces (see: 1149 Section 3.3). The Gateway provisions MNPs to networks on the INET/ 1150 EUN interfaces (i.e., the same as a Client would do) and advertises 1151 the MSP(s) for the AERO link over the INET/EUN interfaces. The 1152 Gateway further provides an attachment point of the AERO link to the 1153 non-MNP-based global topology. 1155 3.7.2. AERO Proxy Behavior 1157 When a Proxy enables an AERO interface, it assigns AERO/SPAN 1158 addresses and configures permanent neighbor cache entries the same as 1159 for Servers. The Proxy also configures secured tunnels with one or 1160 more neighboring Relays and maintains per-Client neighbor cache 1161 entries based on control message exchanges. 1163 3.7.3. AERO Client Behavior 1165 When a Client enables an AERO interface, it sends an RS message with 1166 ND/PD parameters over an ANET interface to a Server in the MAP list, 1167 which returns an RA message with corresponding parameters. (The RS/ 1168 RA messages may pass through a Proxy in the case of a Client's 1169 Proxyed interface.) 1171 After the initial ND/PD message exchange, the Client assigns AERO 1172 addresses to the AERO interface based on the delegated prefix(es). 1173 The Client can then register additional ANET interfaces with the 1174 Server by sending an RS message over each ANET interface. 1176 3.7.4. AERO Relay Behavior 1178 AERO Relays need not connect directly to the AERO link, since they 1179 operate as link-layer forwarding devices instead of network layer 1180 routers. Configuration of AERO interfaces on Relays is therefore 1181 OPTIONAL, e.g., if an administrative interface is needed. Relays 1182 configure secured tunnels with Servers, Proxys and other Relays; they 1183 also configure AERO/SPAN addresses and permanent neighbor cache 1184 entries the same as Servers. Relays engage in a BGP routing protocol 1185 session with a subset of the Servers on the local SPAN segment, and 1186 with other Relays on the SPAN (see: Section 3.3). 1188 3.8. AERO Interface Neighbor Cache Maintenance 1190 Each AERO interface maintains a conceptual neighbor cache that 1191 includes an entry for each neighbor it communicates with on the AERO 1192 link per [RFC4861]. AERO interface neighbor cache entries are said 1193 to be one of "permanent", "symmetric", "asymmetric" or "proxy". 1195 Permanent neighbor cache entries are created through explicit 1196 administrative action; they have no timeout values and remain in 1197 place until explicitly deleted. AERO Servers and Proxys maintain 1198 permanent neighbor cache entries for all other Servers and Proxys 1199 within the same SPAN segment. Each entry maintains the mapping 1200 between the neighbor's network-layer AERO address and corresponding 1201 INET address. The list of all permanent neighbor cache entries for 1202 the SPAN segment is maintained in the segment's ROS list. 1204 Symmetric neighbor cache entries are created and maintained through 1205 RS/RA exchanges as specified in Section 3.15, and remain in place for 1206 durations bounded by ND/PD lifetimes. AERO Servers maintain 1207 symmetric neighbor cache entries for each of their associated 1208 Clients, and AERO Clients maintain symmetric neighbor cache entries 1209 for each of their associated Servers. The list of all Servers on the 1210 AERO link is maintained in the link's MAP list. 1212 Asymmetric neighbor cache entries are created or updated based on 1213 route optimization messaging as specified in Section 3.17, and are 1214 garbage-collected when keepalive timers expire. AERO route 1215 optimization sources (ROSs) maintain asymmetric neighbor cache 1216 entries for active targets with lifetimes based on ND messaging 1217 constants. Asymmetric neighbor cache entries are unidirectional 1218 since only the ROS and not the target (e.g., a Client's MAP) creates 1219 an entry. 1221 Proxy neighbor cache entries are created and maintained by AERO 1222 Proxys when they process Client/Server ND/PD exchanges, and remain in 1223 place for durations bounded by ND/PD lifetimes. AERO Proxys maintain 1224 proxy neighbor cache entries for each of their associated Clients. 1225 Proxy neighbor cache entries track the Client state and the address 1226 of the Client's associated Server. 1228 To the list of neighbor cache entry states in Section 7.3.2 of 1229 [RFC4861], Proxy and Server AERO interfaces add an additional state 1230 DEPARTED that applies to symmetric and proxy neighbor cache entries 1231 for Clients that have recently departed. The interface sets a 1232 "DepartTime" variable for the neighbor cache entry to "DEPARTTIME" 1233 seconds. DepartTime is decremented unless a new ND message causes 1234 the state to return to REACHABLE. While a neighbor cache entry is in 1235 the DEPARTED state, packets destined to the target Client are 1236 forwarded to the Client's new location instead of being dropped. 1237 When DepartTime decrements to 0, the neighbor cache entry is deleted. 1238 It is RECOMMENDED that DEPARTTIME be set to the default constant 1239 value 40 seconds to allow for packets in flight to be delivered while 1240 stale route optimization state may be present. 1242 When a target Server (acting as a MAP) receives a valid NS message 1243 used for route optimization, it searches for a symmetric neighbor 1244 cache entry for the target Client. The MAP then returns a solicited 1245 NA message without creating a neighbor cache entry for the ROS, but 1246 creates or updates a target Client "Report List" entry for the ROS 1247 and sets a "ReportTime" variable for the entry to REPORTTIME seconds. 1248 The MAP resets ReportTime when it receives a new authentic NS 1249 message, and otherwise decrements ReportTime while no NS messages 1250 have been received. It is RECOMMENDED that REPORTTIME be set to the 1251 default constant value 40 seconds to allow a 10 second window so that 1252 route optimization can converge before ReportTime decrements below 1253 REACHABLETIME. 1255 When the ROS receives a solicited NA message response to its NS 1256 message, it creates or updates an asymmetric neighbor cache entry for 1257 the target network-layer and link-layer addresses. The ROS then 1258 (re)sets ReachableTime for the neighbor cache entry to REACHABLETIME 1259 seconds and uses this value to determine whether packets can be 1260 forwarded directly to the target, i.e., instead of via a default 1261 route. The ROS otherwise decrements ReachableTime while no further 1262 solicited NA messages arrive. It is RECOMMENDED that REACHABLETIME 1263 be set to the default constant value 30 seconds as specified in 1264 [RFC4861]. 1266 The ROS also uses the value MAX_UNICAST_SOLICIT to limit the number 1267 of NS keepalives sent when a correspondent may have gone unreachable, 1268 the value MAX_RTR_SOLICITATIONS to limit the number of RS messages 1269 sent without receiving an RA and the value MAX_NEIGHBOR_ADVERTISEMENT 1270 to limit the number of unsolicited NAs that can be sent based on a 1271 single event. It is RECOMMENDED that MAX_UNICAST_SOLICIT, 1272 MAX_RTR_SOLICITATIONS and MAX_NEIGHBOR_ADVERTISEMENT be set to 3 the 1273 same as specified in [RFC4861]. 1275 Different values for DEPARTTIME, REPORTTIME, REACHABLETIME, 1276 MAX_UNICAST_SOLICIT, MAX_RTR_SOLCITATIONS and 1277 MAX_NEIGHBOR_ADVERTISEMENT MAY be administratively set; however, if 1278 different values are chosen, all nodes on the link MUST consistently 1279 configure the same values. Most importantly, DEPARTTIME and 1280 REPORTTIME SHOULD be set to a value that is sufficiently longer than 1281 REACHABLETIME to avoid packet loss due to stale route optimization 1282 state. 1284 3.9. AERO Interface Encapsulation and Re-encapsulation 1286 Client AERO interfaces avoid encapsulation over Direct underlying 1287 interfaces and Proxyed underlying interfaces for which the first-hop 1288 access router is AERO-aware. Other AERO interfaces encapsulate 1289 packets according to whether they are entering the AERO interface 1290 from the network layer or if they are being re-admitted into the same 1291 AERO link they arrived on. This latter form of encapsulation is 1292 known as "re-encapsulation". 1294 For packets entering the AERO interface from the network layer, the 1295 AERO interface copies the "TTL/Hop Limit", "Type of Service/Traffic 1296 Class" [RFC2983], "Flow Label"[RFC6438] (for IPv6) and "Congestion 1297 Experienced" [RFC3168] values in the packet's IP header into the 1298 corresponding fields in the encapsulation header(s). 1300 For packets undergoing re-encapsulation, the AERO interface instead 1301 copies these values from the original encapsulation header into the 1302 new encapsulation header, i.e., the values are transferred between 1303 encapsulation headers and *not* copied from the encapsulated packet's 1304 network-layer header. (Note especially that by copying the TTL/Hop 1305 Limit between encapsulation headers the value will eventually 1306 decrement to 0 if there is a (temporary) routing loop.) For IPv4 1307 encapsulation/re-encapsulation, the AERO interface sets the DF bit as 1308 discussed in Section 3.13. 1310 AERO interfaces configured over INET underlying interfaces 1311 encapsulate each packet in a SPAN header, then encapsulate the 1312 resulting SPAN packet in an INET header according to the next hop 1313 determined in the forwarding algorithm in Section 3.12. If the next 1314 hop is reached via a secured tunnel, the AERO interface uses an INET 1315 encapsulation format specific to the secured tunnel type (see: 1316 Section 6). If the next hop is reached via an unsecured underlying 1317 interface, the AERO interface instead uses Generic UDP Encapsulation 1318 (GUE) [I-D.ietf-intarea-gue] or an alternate minimal encapsulation 1319 format Appendix A. 1321 When GUE encapsulation is used, the AERO interface next sets the UDP 1322 source port to a constant value that it will use in each successive 1323 packet it sends, and sets the UDP length field to the length of the 1324 SPAN packet plus 8 bytes for the UDP header itself plus the length of 1325 the GUE header (or 0 if GUE direct IP encapsulation is used). For 1326 packets sent to a Server or Relay, the AERO interface sets the UDP 1327 destination port to 8060, i.e., the IANA-registered port number for 1328 AERO. For packets sent to a Client, the AERO interface sets the UDP 1329 destination port to the port value stored in the neighbor cache entry 1330 for this Client. The AERO interface then either includes or omits 1331 the UDP checksum according to the GUE specification. 1333 AERO interfaces observes the packet sizing and fragmentation 1334 considerations found in Section 3.13. 1336 3.10. AERO Interface Decapsulation 1338 AERO interfaces decapsulate packets destined either to the AERO node 1339 itself or to a destination reached via an interface other than the 1340 AERO interface the packet was received on. When the encapsulated 1341 packet arrives in multiple fragments, the AERO interface reassembles 1342 as discussed in Section 3.13. Further decapsulation steps are 1343 performed according to the appropriate encapsulation format 1344 specification. 1346 3.11. AERO Interface Data Origin Authentication 1348 AERO nodes employ simple data origin authentication procedures. In 1349 particular: 1351 o AERO Relays, Servers and Proxys accept encapsulated data packets 1352 and control messages received from secured tunnels. 1354 o AERO Servers and Proxys accept encapsulated data packets and NS 1355 messages used for Neighbor Unreachability Detection (NUD) received 1356 from a source found in the ROS list. 1358 o AERO Proxys and Clients accept packets that originate from within 1359 the same secured ANET. 1361 o AERO Clients and Gateways accept packets from downstream network 1362 correspondents based on ingress filtering. 1364 AERO nodes silently drop any packets that do not satisfy the above 1365 data origin authentication procedures. Further security 1366 considerations are discussed Section 6. 1368 3.12. AERO Interface Forwarding Algorithm 1370 IP packets enter a node's AERO interface either from the network 1371 layer (i.e., from a local application or the IP forwarding system) or 1372 from the link layer (i.e., from an AERO interface neighbor). All 1373 packets entering a node's AERO interface first undergo data origin 1374 authentication as discussed in Section 3.11. Packets that satisfy 1375 data origin authentication are processed further, while all others 1376 are dropped silently. 1378 Packets that enter the AERO interface from the network layer are 1379 forwarded to an AERO interface neighbor. Packets that enter the AERO 1380 interface from the link layer are either re-admitted into the AERO 1381 link or forwarded to the network layer where they are subject to 1382 either local delivery or IP forwarding. In all cases, the AERO 1383 interface itself MUST NOT decrement the network layer TTL/Hop-count 1384 since its forwarding actions occur below the network layer. 1386 AERO interfaces may have multiple underlying interfaces and/or 1387 neighbor cache entries for neighbors with multiple ifIndex-tuple 1388 registrations (see Section 3.6). The AERO interface uses each 1389 packet's DSCP value (and/or other traffic discriminators such as port 1390 number) to select an outgoing underlying interface based on the 1391 node's own QoS preferences, and also to select a destination link- 1392 layer address based on the neighbor's underlying interface with the 1393 highest preference. AERO implementations SHOULD allow for QoS 1394 preference values to be modified at runtime through network 1395 management. 1397 If multiple outgoing interfaces and/or neighbor interfaces have a 1398 preference of "high", the AERO node replicates the packet and sends 1399 one copy via each of the (outgoing / neighbor) interface pairs; 1400 otherwise, the node sends a single copy of the packet via an 1401 interface with the highest preference. AERO nodes keep track of 1402 which underlying interfaces are currently "reachable" or 1403 "unreachable", and only use "reachable" interfaces for forwarding 1404 purposes. 1406 The following sections discuss the AERO interface forwarding 1407 algorithms for Clients, Proxys, Servers and Relays. In the following 1408 discussion, a packet's destination address is said to "match" if it 1409 is the same as a cached address, or if it is covered by a cached 1410 prefix (which may be encoded in an AERO address). 1412 3.12.1. Client Forwarding Algorithm 1414 When an IP packet enters a Client's AERO interface from the network 1415 layer the Client searches for an asymmetric neighbor cache entry that 1416 matches the destination. If there is a match, the Client uses one or 1417 more "reachable" neighbor interfaces in the entry for packet 1418 forwarding. If there is no asymmetric neighbor cache entry, the 1419 Client instead forwards the packet toward a Server (the packet is 1420 intercepted by a Proxy if there is a Proxy on the path). 1422 When an IP packet enters a Client's AERO interface from the link- 1423 layer, if the destination matches one of the Client's MNPs or link- 1424 local addresses the Client decapsulates the packet (if necessary) and 1425 delivers it to the network layer. Otherwise, the Client drops the 1426 packet and MAY return a network-layer ICMP Destination Unreachable 1427 message subject to rate limiting (see: Section 3.14). 1429 3.12.2. Proxy Forwarding Algorithm 1431 For control messages originating from or destined to a Client, the 1432 Proxy intercepts the message and updates its proxy neighbor cache 1433 entry for the Client. The Proxy then forwards a (proxyed) copy of 1434 the control message. (For example, the Proxy forwards a proxied 1435 version of a Client's NS/RS message to the target neighbor, and 1436 forwards a proxied version of the NA/RA reply to the Client.) 1438 When the Proxy receives a data packet from a Client within the ANET, 1439 the Proxy searches for an asymmetric neighbor cache entry that 1440 matches the destination and forwards the packet as follows: 1442 o if the destination matches an asymmetric neighbor cache entry, the 1443 Proxy uses one or more "reachable" neighbor interfaces in the 1444 entry for packet forwarding via encapsulation. If the neighbor 1445 interface is in the same SPAN segment, the Proxy forwards the 1446 packet directly to the neighbor; otherwise, it forwards the packet 1447 to a Relay. 1449 o else, the Proxy encapsulates and forwards the packet to a Relay 1450 while using the packet's destination address as the SPAN 1451 destination address. (If the destination is an AERO address, the 1452 Proxy instead uses the corresponding Subnet-Router anycast address 1453 for Client AERO addresses and the SPAN address for 1454 administratively-provisioned AERO addresses.). 1456 When the Proxy receives an encapsulated data packet from an INET 1457 neighbor or from a secured tunnel, it accepts the packet only if data 1458 origin authentication succeeds and the SPAN destination address is 1459 its own address. If the packet is a SPAN fragment, the Proxy then 1460 adds the fragment to the reassembly buffer and returns if the 1461 reassembly is still incomplete. Otherwise, the Proxy reassembles the 1462 packet (if necessary) and continues processing. 1464 Next, the Proxy searches for a proxy neighbor cache entry that 1465 matches the destination. If there is a proxy neighbor cache entry in 1466 the REACHABLE state, the Proxy decapsulates and forwards the packet 1467 to the Client. If the neighbor cache entry is in the DEPARTED state, 1468 the Proxy instead re-encapsulates the packet and forwards it to a 1469 Relay. If there is no neighbor cache entry, the Proxy instead 1470 discards the packet. 1472 3.12.3. Server/Gateway Forwarding Algorithm 1474 For control messages destined to a target Client's AERO address that 1475 are received from a secured tunnel, the Server (acting as a MAP) 1476 intercepts the message and sends an appropriate response on behalf of 1477 the Client. (For example, the Server sends an NA message reply in 1478 response to an NS message directed to one of its associated Clients.) 1479 If the Client's neighbor cache entry is in the DEPARTED state, 1480 however, the Server instead forwards the packet to the Client's new 1481 Server as discussed in Section 3.19. 1483 When the Server receives an encapsulated data packet from an INET 1484 neighbor or from a secured tunnel, it accepts the packet only if data 1485 origin authentication succeeds. If the SPAN destination address is 1486 its own address, the Server reassembles if necessary and discards the 1487 SPAN header (if the reassembly is incomplete, the Server instead adds 1488 the fragment to the reassembly buffer and returns). The Server then 1489 continues processing as follows: 1491 o if the destination matches a symmetric neighbor cache entry in the 1492 REACHABLE state the Server prepares the packet for forwarding to 1493 the destination Client. If the current header is a SPAN header, 1494 the Server reassembles if necessary and discards the SPAN header. 1495 The Server then forwards the packet according to the cached link- 1496 layer information, while using SPAN encapsulation for the Client's 1497 Proxyed/Native interfaces, simple INET encapsulation for NATed/ 1498 VPNed interfaces, or no encapsulation for Direct interfaces. 1500 o else, if the destination matches a symmetric neighbor cache entry 1501 in the DEPARETED state the Server re-encapsulates the packet and 1502 forwards it using the SPAN address of the Client's new Server as 1503 the destination. 1505 o else, if the destination matches an asymmetric neighbor cache 1506 entry, the Server uses one or more "reachable" neighbor interfaces 1507 in the entry for packet forwarding via the local INET if the 1508 neighbor is in the same SPAN segment or via a Relay otherwise. 1510 o else, if the destination is an AERO address that is not assigned 1511 on the AERO interface the Server drops the packet. 1513 o else, the Server (acting as a Gateway) releases the packet to the 1514 network layer for local delivery or IP forwarding. Based on the 1515 information in the forwarding table, the network layer may return 1516 the packet to the same AERO interface in which case further 1517 processing occurs as below. (Note that this arrangement 1518 accommodates common implementations in which the IP forwarding 1519 table is not accessible from within the AERO interface. If the 1520 AERO interface can directly access the IP forwarding table, the 1521 forwarding table lookup can instead be performed internally from 1522 within the AERO interface itself.) 1524 When the Server's AERO interface receives a data packet from the 1525 network layer or from a NATed/VPNed/Direct Client, it processes the 1526 packet according to the network-layer destination address as follows: 1528 o if the destination matches a symmetric or asymmetric neighbor 1529 cache entry the Server processes the packet as above. 1531 o else, the Server encapsulates the packet and forwards it to a 1532 Relay. For administratively-assigned AERO address destinations, 1533 the Server uses the SPAN address corresponding to the destination 1534 as the SPAN destination address. For Client AERO address 1535 destinations, the Server uses the Subnet-Router anycast address 1536 corresponding to the destination as the SPAN destination address. 1537 For all others, the Server uses the packet's destination IP 1538 address as the SPAN destination address. 1540 3.12.4. Relay Forwarding Algorithm 1542 Relays forward packets over secured tunnels the same as any IP 1543 router. When the Relay receives an encapsulated packet via a secured 1544 tunnel, it removes the INET header and searches for a forwarding 1545 table entry that matches the destination address in the next header. 1546 The Relay then processes the packet as follows: 1548 o if the destination matches one of the Relay's own addresses, the 1549 Relay submits the packet for local delivery. 1551 o else, if the destination matches a forwarding table entry the 1552 Relay forwards the packet via a secured tunnel to the next hop. 1553 If the destination matches an MSP without matching an MNP, 1554 however, the Relay instead drops the packet and returns an ICMP 1555 Destination Unreachable message subject to rate limiting (see: 1556 Section 3.14). 1558 o else, the Relay drops the packet and returns an ICMP Destination 1559 Unreachable as above. 1561 As for any IP router, the Relay decrements the TTL/Hop Limit when it 1562 forwards the packet. If the packet is encapsulated in a SPAN header, 1563 only the Hop Limit in the SPAN header is decremented, and not the 1564 TTL/Hop Limit in the inner packet header. 1566 3.13. AERO Interface MTU and Fragmentation 1568 The AERO interface is the node's attachment to the AERO link. For 1569 AERO link neighbor underlying interface paths that do not require 1570 encapsulation, the AERO interface sends unencapsulated IP packets. 1571 For other paths, the AERO interface acts as a tunnel ingress when it 1572 sends packets to the neighbor and as a tunnel egress when it receives 1573 packets from the neighbor. 1575 AERO interfaces configure an MTU the same as for any IP interface, 1576 however the MTU does not reflect the physical size of any links in 1577 the path but rather determines the maximum size for reassembly. AERO 1578 interfaces observe the packet sizing considerations for tunnels 1579 discussed in [I-D.ietf-intarea-tunnels] and as specified below. 1581 The Internet Protocol expects that IP packets will either be 1582 delivered to the destination or a suitable Packet Too Big (PTB) 1583 message returned to support the process known as IP Path MTU 1584 Discovery (PMTUD) [RFC1191][RFC8201]. However, PTB messages may be 1585 crafted for malicious purposes or lost in the network [RFC2923]. 1586 This can be especially problematic for tunnels, where a condition 1587 known as a PMTUD "black hole" can result. For these reasons, AERO 1588 interfaces employ operational procedures that avoid interactions with 1589 PMTUD, including the use of fragmentation when necessary. 1591 AERO interfaces observe three different types of fragmentation. 1592 Source fragmentation occurs when the AERO interface (acting as a 1593 tunnel ingress) fragments the encapsulated packet into multiple 1594 fragments before admitting each fragment into the tunnel. Network 1595 fragmentation occurs when an encapsulated packet admitted into the 1596 tunnel by the ingress is fragmented by an IPv4 router on the path to 1597 the egress. Finally, link-layer fragmentation (aka link adaptation) 1598 occurs at a layer below IP and is coordinated between underlying data 1599 link endpoints. 1601 IPv6 specifies a minimum link Maximum Transmission Unit (MTU) of 1280 1602 bytes [RFC8200]. Although IPv4 specifies a smaller minimum link MTU 1603 of 68 bytes [RFC0791], AERO interfaces also observe the IPv6 minimum 1604 for IPv4 even if encapsulated packets may incur network 1605 fragmentation. 1607 IPv6 specifies a minimum Maximum Reassembly Unit (MRU) of 1500 bytes 1608 [RFC8200], while the minimum MRU for IPv4 is only 576 bytes [RFC1122] 1609 (but, note that many standard IPv6 over IPv4 tunnel types already 1610 assume a larger MRU than the IPv4 minimum). 1612 AERO interfaces therefore configure an MTU that MUST NOT be smaller 1613 than 1280 bytes, MUST NOT be larger than the minimum MRU among all 1614 nodes on the AERO link minus the encapsulation overhead ("ENCAPS"), 1615 and SHOULD NOT be smaller than 1500 bytes. AERO interfaces also 1616 configure a Maximum Segment Unit (MSU) as the maximum-sized 1617 encapsulated packet that the ingress can inject into the tunnel 1618 without source fragmentation. The MSU value SHOULD NOT be larger 1619 than 1280 bytes if there is no operational assurance that a larger 1620 size can traverse the link along all paths. 1622 The network layer proceeds as follows when it forwards an IP packet 1623 to the AERO interface. For each IPv4 packet that is larger than the 1624 AERO interface MTU and with DF set to 0, the network layer uses IPv4 1625 fragmentation to break the packet into a minimum number of non- 1626 overlapping fragments where the first fragment is no larger than the 1627 MTU and the remaining fragments are no larger than the first. For 1628 all other IP packets, if the packet is larger than the AERO interface 1629 MTU, the network layer drops the packet and returns a PTB message to 1630 the original source. Otherwise, the network layer admits each IP 1631 packet or fragment into the AERO interface. 1633 For each IP packet admitted into AERO interface, if the neighbor is 1634 reached via an underlying interface that does not require 1635 encapsulation the AERO interface proceeds according to the underlying 1636 interface MTU. If the packet is no larger than the underlying 1637 interface MTU, the AERO interface presents the packet to the 1638 underlying interface. Otherwise, for IPv4 packets with DF set to 0 1639 the AERO interface uses IPv4 fragmentation to break the packet into 1640 fragments no larger than the underlying interface MTU. For other 1641 packets, the AERO interface either performs link adaptation or drops 1642 the packet and returns a PTB message to the original source. (If the 1643 original source corresponds to a local application, the PTB would 1644 appear to have originated from a router on the path when in fact it 1645 was locally generated from within the AERO interface.) In the same 1646 way, when a packet that has been admitted into the AERO link reaches 1647 a target neighbor but is too large to be delivered over the final-hop 1648 underlying interface, the target either performs link adaptation or 1649 drops the packet and returns a PTB. Link adaptation is preferred in 1650 both cases when possible to avoid packet loss. 1652 For underlying interfaces that require encapsulation, the AERO 1653 interface (acting as a tunnel ingress) instead encapsulates the 1654 packet and performs path MTU procedures according to the specific 1655 encapsulation format. For INET interfaces, the ingress encapsulates 1656 the packet in a SPAN header. If the SPAN packet is larger than the 1657 MSU, the ingress source fragments the SPAN packet into a minimum 1658 number of non-overlapping fragments where the first fragment is no 1659 larger than the MSU and the remaining fragments are no larger than 1660 the first. The ingress then encapsulates each SPAN packet/fragment 1661 in an INET header and admits them into the tunnel. For IPv4, the 1662 ingress sets the DF bit to 0 in the INET header in case any network 1663 fragmentation is necessary. The encapsulated packets will be 1664 delivered to the egress, which reassembles them into a whole packet 1665 if necessary. 1667 By fragmenting at the SPAN layer instead of lower layers, standard 1668 IPv6 fragmentation and reassembly [RFC8200] ensures that IPv4 issues 1669 such as data corruption due to reassembly misassociations will not 1670 occur [RFC6864][RFC4963]. The ingress sends each fragment with 1671 minimal delay (i.e., in a multi-fragment burst) so that individual 1672 fragments are unlikely to be diverted to different destinations due 1673 to routing fluctuations. 1675 Since the SPAN header and IPv6 fragment extension header reduces the 1676 room available for packet data, but the original source has no way to 1677 control its insertion, the ingress MUST include their lengths in 1678 ENCAPS even for packets in which the header is absent. 1680 3.13.1. AERO MTU Requirements 1682 In light of the above considerations, AERO interfaces SHOULD 1683 configure an MTU of 9180 bytes. This means that the AERO interface 1684 MUST be capable of reassembling original IP packets up to 9180 bytes 1685 in length. When an IP packet is admitted into an AERO interface, the 1686 interface encapsulates the packet using SPAN encapsulation and 1687 fragments the encapsulated packet into fragments that are no larger 1688 than 1280 bytes. The fragments will be reassembled by the tunnel 1689 egress that services the final destination. 1691 AERO Clients behind Proxys MAY configure an MTU smaller than 9180 1692 (but no smaller than IP minimum link MTU). If Clients configure a 1693 diversity of MTUs (e.g., 1280, 1500, 4KB, 8KB, etc.) then neighbors 1694 on the link would appear to have multiple MTUs. IPv6 Path MTU 1695 Discovery [RFC8201] accounts for this possibility since MTU discovery 1696 must be performed even between nodes that appear to be connected to 1697 the same link. 1699 Applications that cannot tolerate loss in the network due to MTU 1700 restrictions should restrict themselves to sending packets no larger 1701 than the IP minimum link MTU, i.e., even if the current path MTU 1702 would appear to support a larger size. This is due to the fact that 1703 routing changes could cause the path to traverse links with smaller 1704 MTUs at any given point in time. 1706 3.14. AERO Interface Error Handling 1708 When an AERO node admits a packet into the AERO interface, it may 1709 receive link-layer or network-layer error indications. 1711 A link-layer error indication is an ICMP error message generated by a 1712 router in the INET on the path to the neighbor or by the neighbor 1713 itself. The message includes an IP header with the address of the 1714 node that generated the error as the source address and with the 1715 link-layer address of the AERO node as the destination address. 1717 The IP header is followed by an ICMP header that includes an error 1718 Type, Code and Checksum. Valid type values include "Destination 1719 Unreachable", "Time Exceeded" and "Parameter Problem" 1720 [RFC0792][RFC4443]. (AERO interfaces ignore all link-layer IPv4 1721 "Fragmentation Needed" and IPv6 "Packet Too Big" messages since they 1722 only emit packets that are guaranteed to be no larger than the IP 1723 minimum link MTU as discussed in Section 3.13.) 1725 The ICMP header is followed by the leading portion of the packet that 1726 generated the error, also known as the "packet-in-error". For 1727 ICMPv6, [RFC4443] specifies that the packet-in-error includes: "As 1728 much of invoking packet as possible without the ICMPv6 packet 1729 exceeding the minimum IPv6 MTU" (i.e., no more than 1280 bytes). For 1730 ICMPv4, [RFC0792] specifies that the packet-in-error includes: 1731 "Internet Header + 64 bits of Original Data Datagram", however 1732 [RFC1812] Section 4.3.2.3 updates this specification by stating: "the 1733 ICMP datagram SHOULD contain as much of the original datagram as 1734 possible without the length of the ICMP datagram exceeding 576 1735 bytes". 1737 The link-layer error message format is shown in Figure 5 (where, "L2" 1738 and "L3" refer to link-layer and network-layer, respectively): 1740 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1741 ~ ~ 1742 | L2 IP Header of | 1743 | error message | 1744 ~ ~ 1745 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1746 | L2 ICMP Header | 1747 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 1748 ~ ~ P 1749 | IP and other encapsulation | a 1750 | headers of original L3 packet | c 1751 ~ ~ k 1752 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ e 1753 ~ ~ t 1754 | IP header of | 1755 | original L3 packet | i 1756 ~ ~ n 1757 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1758 ~ ~ e 1759 | Upper layer headers and | r 1760 | leading portion of body | r 1761 | of the original L3 packet | o 1762 ~ ~ r 1763 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 1765 Figure 5: AERO Interface Link-Layer Error Message Format 1767 The AERO node rules for processing these link-layer error messages 1768 are as follows: 1770 o When an AERO node receives a link-layer Parameter Problem message, 1771 it processes the message the same as described as for ordinary 1772 ICMP errors in the normative references [RFC0792][RFC4443]. 1774 o When an AERO node receives persistent link-layer Time Exceeded 1775 messages, the IP ID field may be wrapping before earlier fragments 1776 awaiting reassembly have been processed. In that case, the node 1777 should begin including integrity checks and/or institute rate 1778 limits for subsequent packets. 1780 o When an AERO node receives persistent link-layer Destination 1781 Unreachable messages in response to encapsulated packets that it 1782 sends to one of its asymmetric neighbor correspondents, the node 1783 should process the message as an indication that a path may be 1784 failing, and optionally initiate NUD over that path. If it 1785 receives Destination Unreachable messages over multiple paths, the 1786 node should allow future packets destined to the correspondent to 1787 flow through a default route and re-initiate route optimization. 1789 o When an AERO Client receives persistent link-layer Destination 1790 Unreachable messages in response to encapsulated packets that it 1791 sends to one of its symmetric neighbor Servers, the Client should 1792 mark the path as unusable and use another path. If it receives 1793 Destination Unreachable messages on many or all paths, the Client 1794 should associate with a new Server and release its association 1795 with the old Server as specified in Section 3.19.5. 1797 o When an AERO Server receives persistent link-layer Destination 1798 Unreachable messages in response to encapsulated packets that it 1799 sends to one of its symmetric neighbor Clients, the Server should 1800 mark the underlying path as unusable and use another underlying 1801 path. 1803 o When an AERO Server or Proxy receives link-layer Destination 1804 Unreachable messages in response to an encapsulated packet that it 1805 sends to one of its permanent neighbors, it treats the messages as 1806 an indication that the path to the neighbor may be failing. 1807 However, the dynamic routing protocol should soon reconverge and 1808 correct the temporary outage. 1810 When an AERO Relay receives a packet for which the network-layer 1811 destination address is covered by an MSP, if there is no more- 1812 specific routing information for the destination the Relay drops the 1813 packet and returns a network-layer Destination Unreachable message 1814 subject to rate limiting. The Relay writes the network-layer source 1815 address of the original packet as the destination address and uses 1816 one of its non link-local addresses as the source address of the 1817 message. 1819 When an AERO node receives an encapsulated packet for which the 1820 reassembly buffer it too small, it drops the packet and returns a 1821 network-layer Packet Too Big (PTB) message. The node first writes 1822 the MRU value into the PTB message MTU field, writes the network- 1823 layer source address of the original packet as the destination 1824 address and writes one of its non link-local addresses as the source 1825 address. 1827 3.15. AERO Router Discovery, Prefix Delegation and Autoconfiguration 1829 AERO Router Discovery, Prefix Delegation and Autoconfiguration are 1830 coordinated as discussed in the following Sections. 1832 3.15.1. AERO ND/PD Service Model 1834 Each AERO Server on the link configures a PD service to facilitate 1835 Client requests. Each Server is provisioned with a database of MNP- 1836 to-Client ID mappings for all Clients enrolled in the AERO service, 1837 as well as any information necessary to authenticate each Client. 1838 The Client database is maintained by a central administrative 1839 authority for the AERO link and securely distributed to all Servers, 1840 e.g., via the Lightweight Directory Access Protocol (LDAP) [RFC4511], 1841 via static configuration, etc. Clients receive the same service 1842 regardless of the Servers they select. 1844 AERO Clients and Servers use ND messages to maintain neighbor cache 1845 entries. AERO Servers configure their AERO interfaces as advertising 1846 interfaces, and therefore send unicast RA messages with a short 1847 Router Lifetime value (e.g., REACHABLETIME seconds) in response to a 1848 Client's RS message. Thereafter, Clients send additional RS messages 1849 to keep Server state alive. 1851 AERO Clients and Servers include PD parameters in RS/RA messages (see 1852 [I-D.templin-6man-dhcpv6-ndopt] for ND/PD alternatives). The unified 1853 ND/PD messages are exchanged between Client and Server according to 1854 the prefix management schedule required by the PD service. If the 1855 Client knows its MNP in advance, it can instead employ prefix 1856 registration by including its AERO address as the source address of 1857 an RS message and with an OMNI option with valid prefix registration 1858 information for the MNP. If the Server (and Proxy) accept the 1859 Client's MNP assertion, they inject the prefix into the routing 1860 system and establish the necessary neighbor cache state. 1862 The following sections specify the Client and Server behavior. 1864 3.15.2. AERO Client Behavior 1866 AERO Clients discover the addresses of Servers in a similar manner as 1867 described in [RFC5214]. Discovery methods include static 1868 configuration (e.g., from a flat-file map of Server addresses and 1869 locations), or through an automated means such as Domain Name System 1870 (DNS) name resolution [RFC1035]. Alternatively, the Client can 1871 discover Server addresses through a layer 2 data link login exchange, 1872 or through a unicast RA response to a multicast/anycast RS as 1873 described below. In the absence of other information, the Client can 1874 resolve the DNS Fully-Qualified Domain Name (FQDN) 1875 "linkupnetworks.[domainname]" where "linkupnetworks" is a constant 1876 text string and "[domainname]" is a DNS suffix for the AERO link 1877 (e.g., "example.com"). 1879 To associate with a Server, the Client acts as a requesting router to 1880 request MNPs. The Client prepares an RS message with PD parameters 1881 and includes a Nonce and Timestamp option if the Client needs to 1882 correlate RA replies. If the Client already knows the Server's AERO 1883 address, it includes the AERO address as the network-layer 1884 destination address; otherwise, it includes the link-scoped All- 1885 Routers multicast (ff02::2) or Subnet-Router anycast (fe80::) address 1886 as the network-layer destination. If the Client already knows its 1887 own AERO address, it uses the AERO address as the network-layer 1888 source address; otherwise, it uses the unspecified AERO address 1889 (fe80::ffff:ffff) as the network-layer source address. 1891 The Client next includes an OMNI option in the RS message to register 1892 its link-layer information with the Server. The Client sets the OMNI 1893 option prefix registration information according to the MNP, and 1894 includes a first ifIndex-tuple corresponding to the underlying 1895 interface over which the Client will send the RS message. The Client 1896 MAY include additional ifIndex-tuples specific to other underlying 1897 interfaces. The Client MAY also include an SLLAO with a single link- 1898 layer address corresponding to the first OMNI option ifIndex-tuple. 1899 The Client sets a "primary" flag in the OMNI option if it wishes to 1900 enable proxy keepalives on this underlying interface. 1902 The Client then sends the RS message (either directly via Direct 1903 interfaces, via INET encapsulation for NATed interfaces, via a VPN 1904 for VPNed interfaces, via a Proxy for proxyed interfaces or via a 1905 Relay for native interfaces) and waits for an RA message reply (see 1906 Section 3.15.3). The Client retries up to MAX_RTR_SOLICITATIONS 1907 times until an RA is received. If the Client receives no RAs, or if 1908 it receives an RA with Router Lifetime set to 0, the Client SHOULD 1909 abandon this Server and try another Server. Otherwise, the Client 1910 processes the PD information found in the RA message. 1912 Next, the Client creates a symmetric neighbor cache entry with the 1913 Server's AERO address as the network-layer address and the Server's 1914 encapsulation and/or link-layer addresses as the link-layer address. 1915 The Client records the RA Router Lifetime field value in the neighbor 1916 cache entry as the time for which the Server has committed to 1917 maintaining the MNP in the routing system. The Client then 1918 autoconfigures AERO addresses for each of the delegated MNPs and 1919 assigns them to the AERO interface. The Client also caches any MSPs 1920 included in Route Information Options (RIOs) [RFC4191] as MSPs to 1921 associate with the AERO link, and assigns the MTU value in the MTU 1922 option to its AERO interface while configuring an appropriate MRU. 1924 The Client then registers additional underlying interfaces with the 1925 Server by sending RS messages via each additional interface. The RS 1926 messages include the same parameters as for the initial RS/RA 1927 exchange, but with destination address set to the Server's AERO 1928 address and with the initial OMNI option ifIndex-tuple corresponding 1929 to the underlying interface. The Client sets a "primary" flag in the 1930 OMNI option if it wishes to enable proxy keepalives on this 1931 underlying interface. 1933 Following autoconfiguration, the Client sub-delegates the MNPs to its 1934 attached EUNs and/or the Client's own internal virtual interfaces as 1935 described in [I-D.templin-v6ops-pdhost] to support the Client's 1936 downstream attached "Internet of Things (IoT)". The Client 1937 subsequently sends additional RS messages over each underlying 1938 interface before the Router Lifetime received for that interface 1939 expires. 1941 After the Client registers its underlying interfaces, it may wish to 1942 change one or more registrations, e.g., if an interface changes 1943 address or becomes unavailable, if QoS preferences change, etc. To 1944 do so, the Client prepares an RS message to send over any available 1945 underlying interface. The RS includes an OMNI option with prefix 1946 registration information specific to its MNP, with a first ifIndex- 1947 tuple specific to the selected underlying interface, and with any 1948 additional ifIndex-tuples specific to other underlying interfaces. 1949 The Client includes fresh ifIndex-tuple values to update the Server's 1950 neighbor cache entry. When the Client receives the Server's RA 1951 response, it has assurance that the Server has been updated with the 1952 new information. 1954 If the Client wishes to discontinue use of a Server it issues an RS 1955 message over any underlying interface with an OMNI option with a 1956 prefix release indication. When the Server processes the message, it 1957 releases the MNP, sets the symmetric neighbor cache entry state for 1958 the Client to DEPARTED and returns an RA reply with Router Lifetime 1959 set to 0. After a short delay (e.g., 2 seconds), the Server 1960 withdraws the MNP from the routing system. 1962 3.15.3. AERO Server Behavior 1964 AERO Servers act as IP routers and support a PD service for Clients. 1965 Servers arrange to add their AERO addresses to a static map of Server 1966 addresses for the link and/or the DNS resource records for the FQDN 1967 "linkupnetworks.[domainname]" before entering service. Server 1968 addresses should be geographically and/or topologically referenced, 1969 and made available for discovery by Clients on the AERO link. 1971 When a Server receives a prospective Client's RS message on its AERO 1972 interface, it SHOULD return an immediate RA reply with Router 1973 Lifetime set to 0 if it is currently too busy or otherwise unable to 1974 service the Client. Otherwise, the Server authenticates the RS 1975 message and processes the PD parameters. The Server first determines 1976 the correct MNPs to delegate to the Client by searching the Client 1977 database. When the Server delegates the MNPs, it also creates a 1978 forwarding table entry for each MNP so that the MNPs are propagated 1979 into the routing system (see: Section 3.3). For IPv6, the Server 1980 creates an IPv6 forwarding table entry for each MNP. For IPv4, the 1981 Server creates an IPv6 forwarding table entry with the SPAN 1982 Compatibility Prefix (SCP) corresponding to the IPv4 address. 1984 The Server next creates a symmetric neighbor cache entry for the 1985 Client using the base AERO address as the network-layer address and 1986 with lifetime set to no more than the smallest PD lifetime. Next, 1987 the Server updates the neighbor cache entry by recording the 1988 information in each ifIndex-tuple in the RS OMNI option. The Server 1989 also records the actual SPAN/INET addresses in the neighbor cache 1990 entry. If an SLLAO was present, the Server also compares the SLLAO 1991 address information for the first ifIndex-tuple with the SPAN/INET 1992 information to determine if there is a NAT on the path. 1994 Next, the Server prepares an RA message using its AERO address as the 1995 network-layer source address and the network-layer source address of 1996 the RS message as the network-layer destination address. The Server 1997 includes the delegated MNPs, any other PD parameters and an OMNI 1998 option with an ifIndex-tuple with ifIndex set to 0. The Server then 1999 includes one or more RIOs that encode the MSPs for the AERO link, 2000 plus an MTU option for the link MTU (see Section 3.13). The Server 2001 finally forwards the message to the Client using SPAN/INET, INET, or 2002 NULL encapsulation as necessary. 2004 After the initial RS/RA exchange, the Server maintains a 2005 ReachableTime timer for the Client's symmetric neighbor cache entry 2006 set to expire after Router Lifetime seconds. If the Client (or 2007 Proxy) issues additional RS messages, the Server sends an RA response 2008 and resets ReachableTime. If the Server receives an ND message with 2009 PD release indication it sets the Client's symmetric neighbor cache 2010 entry to the DEPARTED state and withdraws the MNP from the routing 2011 system after a short delay (e.g., 2 seconds). If ReachableTime 2012 expires before a new RS is received, the Server deletes the neighbor 2013 cache entry and withdraws the MNP without delay. 2015 The Server processes any ND/PD messages pertaining to the Client and 2016 returns an NA/RA reply in response to solicitations. The Server may 2017 also issue unsolicited RA messages, e.g., with PD reconfigure 2018 parameters to cause the Client to renegotiate its PDs, with Router 2019 Lifetime set to 0 if it can no longer service this Client, etc. 2020 Finally, If the symmetric neighbor cache entry is in the DEPARTED 2021 state, the Server deletes the entry after DepartTime expires. 2023 Note: Clients SHOULD notify former Servers of their departures, but 2024 Servers are responsible for expiring neighbor cache entries and 2025 withdrawing routes even if no departure notification is received 2026 (e.g., if the Client leaves the network unexpectedly). Servers 2027 SHOULD therefore set Router Lifetime to REACHABLETIME seconds in 2028 solicited RA messages to minimize persistent stale cache information 2029 in the absence of Client departure notifications. A short Router 2030 Lifetime also ensures that proactive Client/Server RS/RA messaging 2031 will keep any NAT state alive (see above). 2033 3.15.3.1. Lightweight DHCPv6 Relay Agent (LDRA) 2035 When DHCPv6 is used as the ND/PD service back end, AERO Clients and 2036 Servers are always on the same link (i.e., the AERO link) from the 2037 perspective of DHCPv6. However, in some implementations the DHCPv6 2038 server and ND function may be located in separate modules. In that 2039 case, the Server's AERO interface module can act as a Lightweight 2040 DHCPv6 Relay Agent (LDRA)[RFC6221] to relay PD messages to and from 2041 the DHCPv6 server module. 2043 When the LDRA receives an authentic RS message, it extracts the PD 2044 message parameters and uses them to construct an IPv6/UDP/DHCPv6 2045 message. It sets the IPv6 source address to the source address of 2046 the RS message, sets the IPv6 destination address to 2047 'All_DHCP_Relay_Agents_and_Servers' and sets the UDP fields to values 2048 that will be understood by the DHCPv6 server. 2050 The LDRA then wraps the message in a DHCPv6 'Relay-Forward' message 2051 header and includes an 'Interface-Id' option that includes enough 2052 information to allow the LDRA to forward the resulting Reply message 2053 back to the Client (e.g., the Client's link-layer addresses, a 2054 security association identifier, etc.). The LDRA also wraps the OMNI 2055 option and SLLAO into the Interface-Id option, then forwards the 2056 message to the DHCPv6 server. 2058 When the DHCPv6 server prepares a Reply message, it wraps the message 2059 in a 'Relay-Reply' message and echoes the Interface-Id option. The 2060 DHCPv6 server then delivers the Relay-Reply message to the LDRA, 2061 which discards the Relay-Reply wrapper and IPv6/UDP headers, then 2062 uses the DHCPv6 message to construct an RA response to the Client. 2063 The Server uses the information in the Interface-Id option to prepare 2064 the RA message and to cache the link-layer addresses taken from the 2065 OMNI option and SLLAO echoed in the Interface-Id option. 2067 3.16. The AERO Proxy 2069 Clients may connect to ANETs that require a perimeter security 2070 gateway to enable communications to Servers in outside INETs. In 2071 that case, the ANET can employ an AERO Proxy. The Proxy is located 2072 at the ANET/INET border and listens for RS messages originating from 2073 or RA messages destined to ANET Clients. The Proxy acts on these 2074 control messages as follows: 2076 o when the Proxy receives an RS message from a new ANET Client, it 2077 first authenticates the message then examines the network-layer 2078 destination address. If the destination address is a Server's 2079 AERO address, the Proxy proceeds to the next step. Otherwise, if 2080 the destination is All-Routers multicast or Subnet-Router anycast, 2081 the Proxy selects a "nearby" Server that is likely to be a good 2082 candidate to serve the Client and replaces the destination address 2083 with the Server's AERO address. Next, the Proxy creates a proxy 2084 neighbor cache entry and caches the Client and Server link-layer 2085 addresses along with the OMNI option information and any other 2086 identifying information including Transaction IDs, Client 2087 Identifiers, Nonce values, etc. The Proxy then replaces the SLLAO 2088 in the RS message (if present) with a new SLLAO with a single 2089 ifIndex-tuple matching the first ifIndex-tuple in the OMNI option 2090 and with the Link Layer Address and Port Number fields set to the 2091 Proxy's SPAN address. The Proxy finally encapsulates the 2092 (proxyed) RS message in a SPAN header with destination set to the 2093 Server's SPAN address then forwards the message into the SPAN. 2095 o when the Server receives the RS, it authenticates the message then 2096 creates or updates a symmetric neighbor cache entry for the Client 2097 with the Proxy's SPAN address as the link-layer address. The 2098 Server then sends an RA message back to the Proxy via the SPAN. 2100 o when the Proxy receives the RA, it authenticates the message and 2101 matches it with the proxy neighbor cache entry created by the RS. 2102 The Proxy then caches the PD route information as a mapping from 2103 the Client's MNPs to the Client's ANET address, caches the 2104 Server's advertised Router Lifetime and sets the neighbor cache 2105 entry state to REACHABLE. The Proxy then replaces the RA SLLAO 2106 with an SLLAO with its own ANET address, sets the P bit in the RA 2107 flags field, sets the OMNI option "primary" flag according to the 2108 cached value from the RS, optionally rewrites the Router Lifetime 2109 and forwards the (proxyed) message to the Client. 2111 After the initial RS/RA exchange, the Proxy forwards any Client data 2112 packets for which there is no matching asymmetric neighbor cache 2113 entry to a Relay via the SPAN. The Proxy instead forwards any Client 2114 data destined to an asymmetric neighbor cache target directly to the 2115 target according to the link-layer information - the process of 2116 establishing asymmetric neighbor cache entries is specified in 2117 Section 3.17. 2119 While the Client is still attached to the ANET, the Proxy sends NS, 2120 RS and/or unsolicited NA messages to update the Server's symmetric 2121 neighbor cache entries on behalf of the Client and/or to convey QoS 2122 updates. If the "primary" flag was set, the Proxy performs periodic 2123 RS/RA exchanges on the Client's behalf according to the cached Server 2124 lifetime. This allows for higher-frequency Proxy-initiated RS/RA 2125 messaging over well-connected INET infrastructure supplemented by 2126 lower-frequency Client-initiated RS/RA messaging over constrained 2127 ANET data links. 2129 If the Server ceases to send solicited advertisements, the Proxy 2130 deletes the neighbor cache entry and sends unsolicited RAs on the 2131 ANET interface with destination set to All-Nodes multicast (ff02::1) 2132 and with Router Lifetime set to zero to inform Clients that the 2133 Server has failed. Although the Proxy engages in ND exchanges on 2134 behalf of the Client, the Client can also send ND messages on its own 2135 behalf, e.g., if it is in a better position than the Proxy to convey 2136 QoS changes, etc. For this reason, the Proxy marks any Client- 2137 originated solicitation messages (e.g. by inserting a Nonce option) 2138 so that it can return the solicited advertisement to the Client 2139 instead of processsing it locally. 2141 If the Client becomes unreachable, the Proxy sets the neighbor cache 2142 entry state to DEPARTED and retains the entry for DEPARTTIME seconds. 2143 While the state is DEPARTED, the Proxy forwards any packets destined 2144 to the Client to a Relay. The Relay in turn forwards the packets to 2145 the Client's current Server. When DepartTime expires, the Proxy 2146 deletes the neighbor cache entry and discards any further packets 2147 destined to this (now forgotten) Client. 2149 When a neighbor cache entry transitions to DEPARTED, some of the 2150 fragments of a multiple fragment packet may have already arrived at 2151 the Proxy while others are en route to the Client's new location, 2152 however no special attention in the reassembly algorithm is necessary 2153 when re-routed packets are simply treated as loss. Since the 2154 fragments of a multiple-fragment packet are sent in minimal inter- 2155 packet delay bursts, such occasions will be rare. 2157 In some ANETs that employ a Proxy, the Client's MNP can be injected 2158 into the ANET routing system. In that case, the Client can send data 2159 messages without encapsulation so that the ANET native routing system 2160 transports the unencapsulated packets to the Proxy. This can be very 2161 beneficial, e.g., if the Client connects to the ANET via low-end data 2162 links such as some aviation wireless links. 2164 If the first-hop ANET access router is AERO-aware, the Client can 2165 avoid encapsulation for both its control and data messages. When the 2166 Client connects to the link, it can send an unencapsulated RS message 2167 with source address set to its AERO address and with destination 2168 address set to the AERO address of the Client's selected Server or to 2169 All-Routers multicast or Subnet-Router anycast. The Client includes 2170 an OMNI option formatted as specified in 2171 [I-D.templin-atn-aero-interface]. 2173 The Client then sends the unencapsulated RS message, which will be 2174 intercepted by the AERO-Aware access router. The access router then 2175 encapsulates the RS message in an ANET header with its own address as 2176 the source address and the address of a Proxy as the destination 2177 address. The access router further remembers the address of the 2178 Proxy so that it can encapsulate future data packets from the Client 2179 via the same Proxy. If the access router needs to change to a new 2180 Proxy, it simply sends another RS message toward the Server via the 2181 new Proxy on behalf of the Client. 2183 In some cases, the access router and Proxy may be one and the same 2184 node. In that case, the node would be located on the same physical 2185 link as the Client, but its message exchanges with the Server would 2186 need to pass through a security gateway at the ANET/INET border. The 2187 method for deploying access routers and Proxys (i.e. as a single node 2188 or multiple nodes) is an ANET-local administrative consideration. 2190 3.16.1. Detecting and Responding to Server Failures 2192 In environments where fast recovery from Server failure is required, 2193 Proxys SHOULD use proactive Neighbor Unreachability Detection (NUD) 2194 to track Server reachability in a similar fashion as for 2195 Bidirectional Forwarding Detection (BFD) [RFC5880]. Proxys can then 2196 quickly detect and react to failures so that cached information is 2197 re-established through alternate paths. The NUD control messaging is 2198 carried only over well-connected ground domain networks (i.e., and 2199 not low-end aeronautical radio links) and can therefore be tuned for 2200 rapid response. 2202 Proxys perform proactive NUD with Servers for which there are 2203 currently active ANET Clients by sending continuous NS messages in 2204 rapid succession, e.g., one message per second. The Proxy sends the 2205 NS message via the SPAN with the Proxy's AERO address as the source 2206 and the AERO address of the Server as the destination. When the 2207 Proxy is also sending RS messages to the Server on behalf of ANET 2208 Clients, the resulting RA responses can be considered as equivalent 2209 hints of forward progress. This means that the Proxy need not also 2210 send a periodic NS if it has already sent an RS within the same 2211 period. If the Server fails (i.e., if the Proxy ceases to receive 2212 advertisements), the Proxy can quickly inform Clients by sending 2213 multicast RA messages on the ANET interface. 2215 The Proxy sends RA messages on the ANET interface with source address 2216 set to the Server's address, destination address set to All-Nodes 2217 multicast, and Router Lifetime set to 0. The Proxy SHOULD send 2218 MAX_FINAL_RTR_ADVERTISEMENTS RA messages separated by small delays 2219 [RFC4861]. Any Clients on the ANET that had been using the failed 2220 Server will receive the RA messages and associate with a new Server. 2222 3.17. AERO Route Optimization 2224 While data packets are flowing between a source and target node, 2225 route optimization SHOULD be used. Route optimization is initiated 2226 by the first eligible Route Optimization Source (ROS) closest to the 2227 source as follows: 2229 o For Clients on VPNed, NATed and Direct interfaces, the Server is 2230 the ROS. 2232 o For Clients on Proxyed interfaces, the Proxy is the ROS. 2234 o For Clients on native interfaces, the Client itself is the ROS. 2236 o For correspondent nodes on INET/EUN interfaces serviced by a 2237 Gateway, the Gateway is the ROS. 2239 The route optimization procedure is conducted between the ROS and the 2240 target Server/Gateway acting as a Route Optimization Responder (ROR) 2241 in the same manner as for IPv6 ND Address Resolution and using the 2242 same NS/NA messaging. The target may either be a MNP Client serviced 2243 by a Server, or a non-MNP correspondent reachable via a Gateway. 2245 The procedures are specified in the following sections. 2247 3.17.1. Route Optimization Initiation 2249 While data packets are flowing from the source node toward a target 2250 node, the ROS performs address resolution by sending an NS message to 2251 receive a solicited NA message from the ROR. 2253 When the ROS sends an NS, it includes the AERO address of the ROS as 2254 the source address (e.g., fe80::1) and the AERO address corresponding 2255 to the data packet's destination address as the destination address 2256 (e.g., if the destination address is 2001:db8:1:2::1 then the 2257 corresponding AERO address is fe80::2001:db8:1:2). The NS message 2258 includes an OMNI option with a single ifIndex-tuple with ifIndex set 2259 to 0, and an SLLAO with the SPAN address of the ROS. The message 2260 also includes a Nonce and Timestamp option if the ROS needs to 2261 correlate NA replies. 2263 The ROS then encapsulates the NS message in a SPAN header with source 2264 set to its own SPAN address and destination set to the data packet's 2265 destination address, then sends the message into the SPAN without 2266 decrementing the network-layer TTL/Hop Limit field. 2268 3.17.2. Relaying the NS 2270 When the Relay receives the NS message from the ROS, it discards the 2271 INET header and determines that the ROR is the next hop by consulting 2272 its standard IPv6 forwarding table for the SPAN header destination 2273 address. The Relay then forwards the SPAN message toward the ROR the 2274 same as for any IPv6 router. The final-hop Relay in the SPAN will 2275 deliver the message via a secured tunnel to the ROR. 2277 3.17.3. Processing the NS and Sending the NA 2279 When the ROR receives the NS message, it examines the AERO 2280 destination address to determine whether it has a neighbor cache 2281 entry and/or route that matches the target. If there is no match, 2282 the ROR drops the NS message. Otherwise, the ROR continues 2283 processing as follows: 2285 o if the target belongs to an MNP Client neighbor in the DEPARTED 2286 state the ROR changes the NS message SPAN destination address to 2287 the SPAN address of the Client's new Server, forwards the message 2288 into the SPAN and returns from processing. 2290 o If the target belongs to an MNP Client neighbor in the REACHABLE 2291 state, the ROR instead adds the AERO source address to the target 2292 Client's Report List with time set to ReportTime. 2294 o If the target belongs to a non-MNP route, the ROR continues 2295 processing without adding an entry to the Report List. 2297 The ROR then prepares a solicited NA message to send back to the ROS 2298 but does not create a neighbor cache entry. The ROR sets the NA 2299 source address to the destination AERO address of the NS, and 2300 includes the Nonce value received in the NS plus the current 2301 Timestamp. 2303 If the target belongs to an MNP Client, the ROR then includes an OMNI 2304 option with prefix registration length set to the length of the MNP; 2305 otherwise, set to the maximum of the non-MNP prefix length and 64. 2306 (Note that a /64 limit is imposed to avoid causing the ROS to set 2307 short prefixes (e.g., "default") that would match destinations for 2308 which the routing system includes more-specific prefixes.) 2310 The ROR next includes a first ifIndex-tuple in the OMNI option with 2311 ifIndex set to 0. If the target belongs to an MNP Client, the ROR 2312 next includes additional ifIndex-tuples in the OMNI option for each 2313 of the target Client's underlying interfaces with current information 2314 for each interface 2315 The ROR then includes a TLLAO option with ifIndex-tuples in one-to- 2316 one correspondence with the tuples that appear in the OMNI option. 2317 For NATed, VPNed and Direct interfaces, the link layer addresses are 2318 the SPAN address of the ROR. For Proxyed interfaces, the link-layer 2319 addresses are the SPAN addresses of the Proxy's INET interfaces. For 2320 native interfaces, the link-layer addresses are the SPAN addesses of 2321 the Client's native interfaces. 2323 The ROR finally encapsulates the NA message in a SPAN header with 2324 source set to its own SPAN address and destination set to the source 2325 SPAN address of the NS message, then forwards the message into the 2326 SPAN without decrementing the network-layer TTL/Hop Limit field. 2328 3.17.4. Relaying the NA 2330 When the Relay receives the NA message from the ROR, it discards the 2331 INET header and determines that the ROS is the next hop by consulting 2332 its standard IPv6 forwarding table for the SPAN header destination 2333 address. The Relay then forwards the SPAN-encapsulated NA message 2334 toward the ROS the same as for any IPv6 router. The final-hop Relay 2335 in the SPAN will deliver the message via a secured tunnel to the ROS. 2337 3.17.5. Processing the NA 2339 When the ROS receives the solicited NA message, it caches the source 2340 SPAN address then discards the INET and SPAN headers. The ROS next 2341 verifies the Nonce and Timestamp values (if present), then creates an 2342 asymmetric neighbor cache entry for the ROR and caches all 2343 information found in the solicited NA OMNI and TLLAO options. The 2344 ROS finally sets the asymmetric neighbor cache entry lifetime to 2345 REACHABLETIME seconds. 2347 3.17.6. Route Optimization Maintenance 2349 Following route optimization, the ROS forwards future data packets 2350 destined to the target via the addresses found in the cached link- 2351 layer information. The route optimization is shared by all sources 2352 that send packets to the target via the ROS, i.e., and not just the 2353 source on behalf of which the route optimization was initiated. 2355 While new data packets destined to the target are flowing through the 2356 ROS, it sends additional NS messages to the ROR before ReachableTime 2357 expires to receive a fresh solicited NA message the same as described 2358 in the previous sections (route optimization refreshment strategies 2359 are an implementation matter, with a non-normative example given in 2360 Appendix B.1). The ROS uses the cached SPAN address of the ROR as 2361 the NS SPAN destination address, and sends up to MAX_UNICAST_SOLICIT 2362 NS messages separated by 1 second until an NA is received. If no NA 2363 is received, the ROS assumes that the current ROR has become 2364 unreachable and deletes the neighbor cache entry. Subsequent data 2365 packets will trigger a new route optimization per Section 3.17.1 to 2366 discover a new ROR while initial data packets travel over a 2367 suboptimal route. 2369 If an NA is received, the ROS then updates the asymmetric neighbor 2370 cache entry to refresh ReachableTime, while (for MNP destinations) 2371 the ROR adds or updates the ROS address to the target Client's Report 2372 List and with time set to ReportTime. While no data packets are 2373 flowing, the ROS instead allows ReachableTime for the asymmetric 2374 neighbor cache entry to expire. When ReachableTime expires, the ROS 2375 deletes the asymmetric neighbor cache entry. Any future data packets 2376 flowing through the ROS will again trigger a new route optimization. 2378 The ROS may also receive unsolicited NA messages from the ROR at any 2379 time (see: Section 3.19). If there is an asymmetric neighbor cache 2380 entry for the target, the ROS updates the link-layer information but 2381 does not update ReachableTime since the receipt of an unsolicited NA 2382 does not confirm that the forward path is still working. If there is 2383 no asymmetric neighbor cache entry, the ROS simply discards the 2384 unsolicited NA. 2386 In this arrangement, the ROS holds an asymmetric neighbor cache entry 2387 for the ROR, but the ROR does not hold an asymmetric neighbor cache 2388 entry for the ROS. The route optimization neighbor relationship is 2389 therefore asymmetric and unidirectional. If the target node also has 2390 packets to send back to the source node, then a separate route 2391 optimization procedure is performed in the reverse direction. But, 2392 there is no requirement that the forward and reverse paths be 2393 symmetric. 2395 3.18. Neighbor Unreachability Detection (NUD) 2397 AERO nodes perform Neighbor Unreachability Detection (NUD) per 2398 [RFC4861]. NUD is performed either reactively in response to 2399 persistent link-layer errors (see Section 3.14) or proactively to 2400 confirm reachability. The NUD algorithm is based on periodic 2401 authentic NS/NA message exchanges. The algorithm may further be 2402 seeded by ND hints of forward progress, but care must be taken to 2403 avoid inferring reachability based on spoofed information. For 2404 example, authentic RS/RA exchanges may be considered as acceptable 2405 hints of forward progress, while spurious data packets should not be. 2407 When an ROR directs an ROS to a neighbor with one or more target 2408 link-layer addresses, the ROS can proactively test each direct path 2409 by sending an initial NS message to elicit a solicited NA response. 2410 While testing the paths, the ROS can optionally continue sending 2411 packets via the SPAN, maintain a small queue of packets until target 2412 reachability is confirmed, or (optimistically) allow packets to flow 2413 via the direct paths. In any case, the ROS should only consider the 2414 neighbor unreachable if NUD fails over multiple target link-layer 2415 address paths. 2417 When a ROS sends an NS message used for NUD, it uses its AERO 2418 addresses as the IPv6 source address and the AERO address 2419 corresponding to a target link-layer address as the destination. For 2420 each target link-layer address, the source node encapsulates the NS 2421 message in SPAN/INET headers with its own SPAN address as the source 2422 and the SPAN address of the target as the destination, If the target 2423 is located within the same SPAN segment, the source sets the INET 2424 address of the target as the destination; otherwise, it sets the INET 2425 address of a Relay as the destination. The source then forwards the 2426 message into the SPAN. 2428 Paths that pass NUD tests are marked as "reachable", while those that 2429 do not are marked as "unreachable". These markings inform the AERO 2430 interface forwarding algorithm specified in Section 3.12. 2432 Proxys can perform NUD to verify Server reachability on behalf of 2433 their proxyed Clients to reduce Client-initated control messaging 2434 overhead. 2436 3.19. Mobility Management and Quality of Service (QoS) 2438 AERO is a Distributed Mobility Management (DMM) service. Each Server 2439 is responsible for only a subset of the Clients on the AERO link, as 2440 opposed to a Centralized Mobility Management (CMM) service where 2441 there is a single network mobility collective entity for all Clients. 2442 Clients coordinate with their associated Servers via RS/RA exchanges 2443 to maintain the DMM profile, and the AERO routing system tracks all 2444 current Client/Server peering relationships. 2446 Servers provide a Mobility Anchor Point (MAP) for their dependent 2447 Clients. Clients are responsible for maintaining neighbor 2448 relationships with their Servers through periodic RS/RA exchanges, 2449 which also serves to confirm neighbor reachability. When a Client's 2450 underlying interface address and/or QoS information changes, the 2451 Client is responsible for updating the Server with this new 2452 information. Note that for Proxyed interfaces, however, the Proxy 2453 can perform the RS/RA exchanges on the Client's behalf. 2455 Mobility management considerations are specified in the following 2456 sections. 2458 3.19.1. Mobility Update Messaging 2460 Servers acting as MAPs accommodate Client mobility and/or QoS change 2461 events by sending unsolicited NA messages to each ROS in the target 2462 Client's Report List. When a MAP sends an unsolicited NA message, it 2463 sets the IPv6 source address to the Client's AERO address and sets 2464 the IPv6 destination address to All-Nodes multicast. The MAP also 2465 includes an OMNI option with prefix registration information, with a 2466 first ifIndex-tuple with ifIndex set to 0, and with additional 2467 ifIndex-tuples for the target Client's remaining interfaces. The MAP 2468 then includes a TLLAO with corresponding ifIndex-tuples, with the 2469 link layer address of the first tuple set to the MAP's SPAN address 2470 and with link layer addresses of the remaining tuples set to the 2471 corresponding target SPAN addresses. The MAP finally encapsulates 2472 the message in a SPAN header with source set to its own SPAN address 2473 and destination set to the SPAN address of the ROS, then sends the 2474 message to a Relay which in turn forwards it to the ROS. 2476 As discussed in Section 7.2.6 of [RFC4861], the transmission and 2477 reception of unsolicited NA messages is unreliable but provides a 2478 useful optimization. In well-connected Internetworks with robust 2479 data links unsolicited NA messages will be delivered with high 2480 probability, but in any case the MAP can optionally send up to 2481 MAX_NEIGHBOR_ADVERTISEMENT unsolicited NAs to each ROS to increase 2482 the likelihood that at least one will be received. 2484 When the ROS receives an unsolicited NA message, it ignores the 2485 message if there is no existing neighbor cache entry for the Client. 2486 Otherwise, it uses the included OMNI option and TLLAO information to 2487 update the neighbor cache entry, but does not reset ReachableTime 2488 since the receipt of an unsolicited NA message from the target Server 2489 does not provide confirmation that any forward paths to the target 2490 Client are working. 2492 If unsolicited NA messages are lost, the ROS may be left with stale 2493 address and/or QoS information for the Client for up to REACHABLETIME 2494 seconds. During this time, the ROS can continue sending packets 2495 according to its stale neighbor cache information. When 2496 ReachableTime is close to expiring, the ROS will re-initiate route 2497 optimization and receive fresh state information. 2499 In addition to sending unsolicited NA messages to the current set of 2500 ROSs for the Client, the MAP also sends unsolicited NAs to the former 2501 link-layer address for any ifIndex-tuple for which the link-layer 2502 address has changed. The NA messages update Proxys or Servers that 2503 cannot easily detect (e.g., without active probing) when a formerly- 2504 active Client has departed. 2506 3.19.2. Announcing Link-Layer Address and/or QoS Preference Changes 2508 When a Client needs to change its ANET addresses and/or QoS 2509 preferences (e.g., due to a mobility event), either the Client or its 2510 Proxys send RS messages to the Server via the SPAN with an OMNI 2511 option and SLLAO that include an ifIndex-tuple with the new link 2512 quality and address information. 2514 Up to MAX_RTR_SOLICITATION RS messages MAY be sent in parallel with 2515 sending actual data packets in case one or more RAs are lost. If all 2516 RAs are lost, the Client SHOULD re-associate with a new Server. 2518 When the Server receives the Client's changes, it sends unsolicited 2519 NA messages to all nodes in the Report List the same as described in 2520 the previous section. 2522 3.19.3. Bringing New Links Into Service 2524 When a Client needs to bring new underlying interfaces into service 2525 (e.g., when it activates a new data link), it sends an RS message to 2526 the Server via the underlying interface with an OMNI option with 2527 appropriate link quality values and with an SLLAO (if necessary) with 2528 link-layer address information for the new link.. 2530 3.19.4. Removing Existing Links from Service 2532 When a Client needs to remove existing underlying interfaces from 2533 service (e.g., when it de-activates an existing data link), it sends 2534 an RS message to its Server with an OMNI option with appropriate link 2535 quality values. 2537 If the Client needs to send RS messages over an underlying interface 2538 other than the one being removed from service, it MUST include an 2539 ifIndex-tuple for the sending interface as the first tuple and 2540 include additional ifIndex-tuples with appropriate link quality 2541 values for any underlying interfaces being removed from service. 2543 3.19.5. Moving to a New Server 2545 When a Client associates with a new Server, it performs the Client 2546 procedures specified in Section 3.15.2. The Client also includes a 2547 notification identifier in the RS message OMNI option per 2548 [I-D.templin-atn-aero-interface] if it wants the new Server to notify 2549 the old Server. 2551 When the new Server receives the Client's RS message, it responds by 2552 returning an RA as specified in Section 3.15.3. If the Client's RS 2553 includes a notification identifier, the new Server also prepares an 2554 RS or unsolicited NA message to send to the old Server. The RS/NA 2555 message includes the Client's AERO address as the source address, the 2556 old Server's AERO address as the destination address, and an OMNI 2557 option and S/TLLAO with an ifIndex-tuple with ifIndex set to 0. The 2558 OMNI option includes a prefix release indication, and the S/TLLAO 2559 includes the SPAN address of the new Server. For RS messages, the 2560 new Server retries up to MAX_RTR_SOLICITATIONS attempts until an RA 2561 is received. (Note that the Client can alternatively send RS/NA 2562 messages with a release indication to the old Server on its own 2563 behalf, however, this additional Client messaging may be undesirable 2564 in some environments. Note also that the choice of using RS or 2565 unsolicited NA is based on the need for a reliable acknowledgement; 2566 in environments where Router Lifetimes can be expected to be short, 2567 sending up to MAX_NEIGHBOR_ADVERTISEMENT unsolicited NAs may be 2568 sufficient.) 2570 When the old Server processes the RS/NA, it changes the symmetric 2571 neighbor cache entry state to DEPARTED, sets the link-layer address 2572 of the Client to the address found in the S/TLLAO, and sets 2573 DepartTime to DEPARTTIME seconds. For RS messages, the old Server 2574 then returns an immediate RA message with Router Lifetime set to 0. 2575 After a short delay (e.g., 2 seconds) the old Server withdraws the 2576 Client's MNP from the routing system. After DepartTime expires, the 2577 old Server deletes the symmetric neighbor cache entry. 2579 The old Server also sends unsolicited NA messages to all ROSs in the 2580 Client's Report List with an OMNI option with prefix release 2581 indication, with a single ifIndex-tuple with ifIndex set to 0 and 2582 with the SPAN address of the new Server in a companion TLLAO. When 2583 the ROS receives the NA, it caches the address of the new Server in 2584 the existing asymmetric neighbor cache entry and marks the entry as 2585 STALE. Subsequent data packets will then flow according to any 2586 existing cached link-layer information and trigger a new NS/NA 2587 exchange via the new Server. 2589 Clients SHOULD NOT move rapidly between Servers in order to avoid 2590 causing excessive oscillations in the AERO routing system. Examples 2591 of when a Client might wish to change to a different Server include a 2592 Server that has gone unreachable, topological movements of 2593 significant distance, movement to a new geographic region, movement 2594 to a new SPAN segment, etc. 2596 When a Client moves to a new Server, some of the fragments of a 2597 multiple fragment packet may have already arrived at the old Server 2598 while others are en route to the new Server, however no special 2599 attention in the reassembly algorithm is necessary when re-routed 2600 fragments are simply treated as loss. Since the fragments of a 2601 multiple-fragment packet are sent in a minimal inter-packet delay 2602 burst, such occasions will be rare. 2604 3.20. Multicast 2606 The AERO Client provides an IGMP (IPv4) [RFC2236] or MLD (IPv6) 2607 [RFC3810] proxy service for its EUNs and/or hosted applications 2608 [RFC4605]. The Client forwards IGMP/MLD messages over any of its 2609 underlying interfaces for which group membership is required. The 2610 IGMP/MLD messages may be further forwarded by a first-hop ANET access 2611 router acting as an IGMP/MLD-snooping switch [RFC4541], then 2612 ultimately delivered to an AERO Proxy/Server acting as a Protocol 2613 Independent Multicast - Sparse-Mode (PIM-SM, or simply "PIM") 2614 Designated Router (DR) [RFC7761]. AERO Gateways also act as PIM 2615 routers (i.e., the same as AERO Proxys/Servers) on behalf of nodes on 2616 INET/EUN networks. The behaviors identified in the following 2617 sections correspond to Source-Specific Multicast (SSM) and Any-Source 2618 Multicast (ASM) operational modes. 2620 3.20.1. Source-Specific Multicast (SSM) 2622 When an ROS (i.e., an AERO Proxy/Server/Gateway) "X" acting as PIM 2623 router receives a Join/Prune message from a node on its downstream 2624 interfaces containing one or more ((S)ource, (G)roup) pairs, it 2625 updates its Multicast Routing Information Base (MRIB) accordingly. 2626 For each S belonging to a prefix reachable via X's non-AERO 2627 interfaces, X then forwards the (S, G) Join/Prune to any PIM routers 2628 on those interfaces per [RFC7761]. 2630 For each S belonging to a prefix reachable via X's AERO interface, X 2631 originates a separate copy of the Join/Prune for each (S,G) in the 2632 message using its own AERO address as the source address and ALL-PIM- 2633 ROUTERS as the destination address. X then encapsulates each message 2634 in a SPAN header with source address set to the SPAN address of X and 2635 destination address set to S then forwards the message into the SPAN. 2636 The SPAN in turn forwards the message to AERO Server/Gateway "Y" that 2637 services S. At the same time, if the message was a Join, X sends a 2638 route-optimization NS message toward each S the same as discussed in 2639 Section 3.17. The resulting NAs will return the AERO address for the 2640 prefix that matches S as the network-layer source address and TLLAOs 2641 with the SPAN addresses corresponding to any ifIndex-tuples that are 2642 currently servicing S. 2644 When Y processes the Join/Prune message, if S located behind any 2645 Native, Direct, VPNed or NATed interfaces Y acts as a PIM router and 2646 updates its MRIB to list X as the next hop in the reverse path. If S 2647 is located behind any Proxys "Z"*, Y also forwards the message to 2648 each Z* over the SPAN while continuing to use the AERO address of X 2649 as the source address. Each Z* then updates its MRIB accordingly and 2650 maintains the AERO address of X as the next hop in the reverse path. 2651 Since the Relays in the SPAN do not examine network layer control 2652 messages, this means that the (reverse) multicast tree path is simply 2653 from each Z* (and/or Y) to X with no other multicast-aware routers in 2654 the path. If any Z* (and/or Y) is located on the same SPAN segment 2655 as X, the multicast data traffic sent to X directly using SPAN/INET 2656 encapsulation instead of via a Relay. 2658 Following the initial Join/Prune and NS/NA messaging, X maintains an 2659 asymmetric neighbor cache entry for each S the same as if X was 2660 sending unicast data traffic to S. In particular, X performs 2661 additional NS/NA exchanges to keep the neighbor cache entry alive for 2662 up to t_periodic seconds [RFC7761]. If no new Joins are received 2663 within t_periodic seconds, X allows the neighbor cache entry to 2664 expire. Finally, if X receives any additional Join/Prune messages 2665 for (S,G) it forwards the messages to each Y and Z* in the neighbor 2666 cache entry over the SPAN. 2668 At some later time, Client C that holds an MNP for source S may 2669 depart from a first Proxy Z1 and/or connect via a new Proxy Z2. In 2670 that case, Y sends an unsolicited NA message to X the same as 2671 specified for unicast mobility in Section 3.19. When X receives the 2672 unsolicited NA message, it updates its asymmetric neighbor cache 2673 entry for the AERO address for source S and sends new Join messages 2674 to any new Proxys Z2. There is no requirement to send any Prune 2675 messages to old Proxys Z1 since source S will no longer source any 2676 multicast data traffic via Z1. Instead, the multicast state for 2677 (S,G) in Proxy Z1 will soon time out since no new Joins will arrive. 2679 After some later time, C may move to a new Server Y2 and depart from 2680 old Sever Y1. In that case, Y1 sends Join messages for any of C's 2681 active (S,G) groups to Y2 while including its own AERO address as the 2682 source address. This causes Y2 to include Y1 in the multicast 2683 forwarding tree during the interim time that Y1's symmetric neighbor 2684 cache entry for C is in the DEPARTED state. At the same time, Y1 2685 sends an unsolicited NA message to X with an OMNI option and TLLAO 2686 with ifIndex-tuple set to 0 and a release indication to cause X to 2687 release its asymmetric neighbor cache entry. X then sends a new Join 2688 message to S via the SPAN and re-initiates route optimization the 2689 same as if it were receiving a fresh Join message from a node on a 2690 downstream link. 2692 3.20.2. Any-Source Multicast (ASM) 2694 When an ROS X acting as a PIM router receives a Join/Prune from a 2695 node on its downstream interfaces containing one or more (*,G) pairs, 2696 it updates its Multicast Routing Information Base (MRIB) accordingly. 2698 X then forwards a copy of the message to the Rendezvous Point (RP) R 2699 for each G over the SPAN. X uses its own AERO address as the source 2700 address and ALL-PIM-ROUTERS as the destination address, then 2701 encapsulates each message in a SPAN header with source address set to 2702 the SPAN address of X and destination address set to R, then sends 2703 the message into the SPAN. At the same time, if the message was a 2704 Join X initiates NS/NA route optimization the same as for the SSM 2705 case discussed in Section 3.20.1. 2707 For each source S that sends multicast traffic to group G via R, the 2708 Proxy/Server Z* for the Client that aggregates S encapsulates the 2709 packets in PIM Register messages and forwards them to R via the SPAN. 2710 R may then elect to send a PIM Join to Z* over the SPAN. This will 2711 result in an (S,G) tree rooted at Z* with R as the next hop so that R 2712 will begin to receive two copies of the packet; one native copy from 2713 the (S, G) tree and a second copy from the pre-existing (*, G) tree 2714 that still uses PIM Register encapsulation. R can then issue a PIM 2715 Register-stop message to suppress the Register-encapsulated stream. 2716 At some later time, if C moves to a new Proxy/Server Z*, it resumes 2717 sending packets via PIM Register encapsulation via the new Z*. 2719 At the same time, as multicast listeners discover individual S's for 2720 a given G, they can initiate an (S,G) Join for each S under the same 2721 procedures discussed in Section 3.20.1. Once the (S,G) tree is 2722 established, the listeners can send (S, G) Prune messages to R so 2723 that multicast packets for group G sourced by S will only be 2724 delivered via the (S, G) tree and not from the (*, G) tree rooted at 2725 R. All mobility considerations discussed for SSM apply. 2727 3.20.3. Bi-Directional PIM (BIDIR-PIM) 2729 Bi-Directional PIM (BIDIR-PIM) [RFC5015] provides an alternate 2730 approach to ASM that treats the Rendezvous Point (RP) as a Designated 2731 Forwarder (DF). Further considerations for BIDIR-PIM are out of 2732 scope. 2734 3.21. Operation over Multiple AERO Links (VLANs) 2736 An AERO Client can connect to multiple AERO links the same as for any 2737 data link service. In that case, the Client maintains a distinct 2738 AERO interface for each link, e.g., 'aero0' for the first link, 2739 'aero1' for the second, 'aero2' for the third, etc. Each AERO link 2740 would include its own distinct set of Relays, Servers and Proxys, 2741 thereby providing redundancy in case of failures. 2743 The Relays, Servers and Proxys on each AERO link can assign AERO and 2744 SPAN addresses that use the same or different numberings from those 2745 on other links. Since the links are mutually independent there is no 2746 requirement for avoiding inter-link address duplication, e.g., the 2747 same AERO address such as fe80::1000 could be used to number distinct 2748 nodes that connect to different AERO links. 2750 Each AERO link could utilize the same or different ANET connections. 2751 The links can be distinguished at the link-layer via Virtual Local 2752 Area Network (VLAN) tagging (e.g., IEEE 802.1Q) and/or through 2753 assignment of distinct sets of MSPs on each link. This gives rise to 2754 the opportunity for supporting multiple redundant networked paths, 2755 where each VLAN is distinguished by a different label (e.g., colors 2756 such as Red, Green, Blue, etc.). In particular, the Client can tag 2757 its RS messages with the appropriate label to cause the network to 2758 select the desired VLAN. 2760 Clients that connect to multiple AERO interfaces can select the 2761 outgoing interface appropriate for a given Red/Blue/Green/etc. 2762 traffic profile while (in the reverse direction) correspondent nodes 2763 must have some way of steering their packets destined to a target via 2764 the correct AERO link. 2766 In a first alternative, if each AERO link services different MSPs, 2767 then the Client can receive a distinct MNP from each of the links. 2768 IP routing will therefore assure that the correct Red/Green/Blue/etc. 2769 network is used for both outbound and inbound traffic. This can be 2770 accomplished using existing technologies and approaches, and without 2771 requiring any special supporting code in correspondent nodes or 2772 Relays. 2774 In a second alternative, if each AERO link services the same MSP(s) 2775 then each link could assign a distinct "AERO Link Anycast" address 2776 that is configured by all Relays on the link. Correspondent nodes 2777 then include a "type 4" routing header with the Anycast address for 2778 the AERO link as the IPv6 destination and with the address of the 2779 target encoded as the "next segment" in the routing header 2780 [RFC8402][I-D.ietf-6man-segment-routing-header]. Standard IP routing 2781 will then direct the packet to the nearest Relay for the correct AERO 2782 link, which will replace the destination address with the target 2783 address then forward the packet to the target. 2785 3.22. DNS Considerations 2787 AERO Client MNs and INET correspondent nodes consult the Domain Name 2788 System (DNS) the same as for any Internetworking node. When 2789 correspondent nodes and Client MNs use different IP protocol versions 2790 (e.g., IPv4 correspondents and IPv6 MNs), the INET DNS must maintain 2791 A records for IPv4 address mappings to MNs which must then be 2792 populated in Gateway NAT64 mapping caches. In that way, an IPv4 2793 correspondent node can send packets to the IPv4 address mapping of 2794 the target MN, and the Gateway will translate the IPv4 header and 2795 destination address into an IPv6 header and IPv6 destination address 2796 of the MN. 2798 When an AERO Client registers with an AERO Server, the Server can 2799 return the address(es) of DNS servers in RDNSS options [RFC6106]. 2800 The DNS server provides the IP addresses of other MNs and 2801 correspondent nodes in AAAA records for IPv6 or A records for IPv4. 2803 3.23. Transition Considerations 2805 The SPAN ensures that dissimilar INET partitions can be joined into a 2806 single unified AERO link, even though the partitions themselves may 2807 have differing protocol versions and/or incompatible addressing 2808 plans. However, a commonality can be achieved by incrementally 2809 distributing globally routable (i.e., native) IP prefixes to 2810 eventually reach all nodes (both mobile and fixed) in all SPAN 2811 segments. This can be accomplished by incrementally deploying AERO 2812 Gateways on each INET partition, with each Gateway distributing its 2813 MNPs and/or discovering non-MNP prefixes on its INET links. 2815 This gives rise to the opportunity to eventually distribute native IP 2816 addresses to all nodes, and to present a unified AERO link view 2817 (bridged by the SPAN) even if the INET partitions remain in their 2818 current protocol and addressing plans. In that way, the AERO link 2819 can serve the dual purpose of providing a mobility service and a 2820 transition service. Or, if an INET partition is transitioned to a 2821 native IP protocol version and addressing scheme that is compatible 2822 with the AERO link MNP-based addressing scheme, the partition and 2823 AERO link can be joined by Gateways. 2825 Gateways that connect INETs/EUNs with dissimilar IP protocol versions 2826 must employ a network address and protocol translation function such 2827 as NAT64[RFC6146]. 2829 3.24. Detecting and Reacting to Server and Relay Failures 2831 In environments where rapid failure recovery is required, Servers and 2832 Relays SHOULD use Bidirectional Forwarding Detection (BFD) [RFC5880]. 2833 Nodes that use BFD can quickly detect and react to failures so that 2834 cached information is re-established through alternate nodes. BFD 2835 control messaging is carried only over well-connected ground domain 2836 networks (i.e., and not low-end radio links) and can therefore be 2837 tuned for rapid response. 2839 Servers and Relays maintain BFD sessions in parallel with their BGP 2840 peerings. If a Server or Relay fails, BGP peers will quickly re- 2841 establish routes through alternate paths the same as for common BGP 2842 deployments. Similarly, Proxys maintain BFD sessions with their 2843 associated Relays even though they do not establish BGP peerings with 2844 them. 2846 Proxys SHOULD use proactive NUD for Servers for which there are 2847 currently active ANET Clients in a manner that parallels BFD, i.e., 2848 by sending unicast NS messages in rapid succession to receive 2849 solicited NA messages. When the Proxy is also sending RS messages on 2850 behalf of ANET Clients, the RS/RA messaging can be considered as 2851 equivalent hints of forward progress. This means that the Proxy need 2852 not also send a periodic NS if it has already sent an RS within the 2853 same period. If a Server fails, the Proxy will cease to receive 2854 advertisements and can quickly inform Clients of the outage by 2855 sending multicast RA messages on the ANET interface. 2857 The Proxy sends multicast RA messages with source address set to the 2858 Server's address, destination address set to All-Nodes multicast, and 2859 Router Lifetime set to 0. The Proxy SHOULD send 2860 MAX_FINAL_RTR_ADVERTISEMENTS RA messages separated by small delays 2861 [RFC4861]. Any Clients on the ANET interface that have been using 2862 the (now defunct) Server will receive the RA messages and associate 2863 with a new Server. 2865 4. Implementation Status 2867 An AERO implementation based on OpenVPN (https://openvpn.net/) was 2868 announced on the v6ops mailing list on January 10, 2018 and an 2869 initial public release of the AERO proof-of-concept source code was 2870 announced on the intarea mailing list on August 21, 2015. 2872 5. IANA Considerations 2874 The IANA has assigned a 4-octet Private Enterprise Number "45282" for 2875 AERO in the "enterprise-numbers" registry. 2877 The IANA has assigned the UDP port number "8060" for an earlier 2878 experimental version of AERO [RFC6706]. This document obsoletes 2879 [RFC6706] and claims the UDP port number "8060" for all future use. 2881 No further IANA actions are required. 2883 6. Security Considerations 2885 AERO Relays configure secured tunnels with AERO Servers and Proxys 2886 within their local SPAN segments. Applicable secured tunnel 2887 alternatives include IPsec [RFC4301], TLS/SSL [RFC8446], DTLS 2888 [RFC6347], etc. The AERO Relays of all SPAN segments in turn 2889 configure secured tunnels for their neighboring AERO Relays across 2890 the SPAN. Therefore, packets that traverse the SPAN between any pair 2891 of AERO link neighbors are already secured. 2893 AERO Servers, Gateways and Proxys targeted by a route optimization 2894 may also receive packets directly from the INET partitions instead of 2895 via the SPAN. For INET partitions that apply effective ingress 2896 filtering to defeat source address spoofing, the simple data origin 2897 authentication procedures in Section 3.11 can be applied. This 2898 implies that the ROS list must be maintained consistently by all 2899 route optimization targets within the same INET partition, and that 2900 the ROS list must be securely managed by the partition administrative 2901 authority. 2903 For INET partitions that cannot apply effective ingress filtering, 2904 the two options for securing communications include 1) disable route 2905 optimization so that all traffic is conveyed over secured tunnels via 2906 the SPAN, or 2) enable on-demand secure tunnel creation between INET 2907 partition neighbors. Option 1) would result in longer routes than 2908 necessary and traffic concentration on critical infrastructure 2909 elements. Option 2) could be coordinated by establishing a secured 2910 tunnel on-demand instead of performing an NS/NA exchange in the route 2911 optimization procedures. Procedures for establishing on-demand 2912 secured tunnels are out of scope. 2914 AERO Clients that connect to secured enclaves need not apply security 2915 to their ND messages, since the messages will be intercepted by a 2916 perimeter Proxy that applies security on its outward-facing 2917 interface. AERO Clients located outside of secured enclaves SHOULD 2918 use symmetric network and/or transport layer security services, but 2919 when there are many prospective neighbors with dynamically changing 2920 connectivity an asymmetric security service such as SEND may be 2921 needed (see: Appendix B.6). 2923 Application endpoints SHOULD use application-layer security services 2924 such as TLS/SSL, DTLS or SSH [RFC4251] to assure the same level of 2925 protection as for critical secured Internet services. AERO Clients 2926 that require host-based VPN services SHOULD use symmetric network 2927 and/or transport layer security services such as IPsec, TLS/SSL, 2928 DTLS, etc. AERO Proxys and Servers can also provide a network-based 2929 VPN service on behalf of the Client, e.g., if the Client is located 2930 within a secured enclave and cannot establish a VPN on its own 2931 behalf. 2933 AERO Servers and Relays present targets for traffic amplification 2934 Denial of Service (DoS) attacks. This concern is no different than 2935 for widely-deployed VPN security gateways in the Internet, where 2936 attackers could send spoofed packets to the gateways at high data 2937 rates. This can be mitigated by connecting Servers and Relays over 2938 dedicated links with no connections to the Internet and/or when 2939 connections to the Internet are only permitted through well-managed 2940 firewalls. Traffic amplification DoS attacks can also target an AERO 2941 Client's low data rate links. This is a concern not only for Clients 2942 located on the open Internet but also for Clients in secured 2943 enclaves. AERO Servers and Proxys can institute rate limits that 2944 protect Clients from receiving packet floods that could DoS low data 2945 rate links. 2947 AERO Gateways must implement ingress filtering to avoid a spoofing 2948 attack in which spurious SPAN messages are injected into an AERO link 2949 from an outside attacker. AERO Clients MUST ensure that their 2950 connectivity is not used by unauthorized nodes on their EUNs to gain 2951 access to a protected network, i.e., AERO Clients that act as routers 2952 MUST NOT provide routing services for unauthorized nodes. (This 2953 concern is no different than for ordinary hosts that receive an IP 2954 address delegation but then "share" the address with other nodes via 2955 some form of Internet connection sharing such as tethering.) 2957 The MAP list and ROS lists MUST be well-managed and secured from 2958 unauthorized tampering, even though the list contains only public 2959 information. The MAP list can be conveyed to the Client in a similar 2960 fashion as in [RFC5214] (e.g., through layer 2 data link login 2961 messaging, secure upload of a static file, DNS lookups, etc.). The 2962 ROS list can be conveyed to Servers and Proxys through administrative 2963 action, secured file distribution, etc. 2965 Although public domain and commercial SEND implementations exist, 2966 concerns regarding the strength of the cryptographic hash algorithm 2967 have been documented [RFC6273] [RFC4982]. 2969 Security considerations for accepting link-layer ICMP messages and 2970 reflected packets are discussed throughout the document. 2972 7. Acknowledgements 2974 Discussions in the IETF, aviation standards communities and private 2975 exchanges helped shape some of the concepts in this work. 2976 Individuals who contributed insights include Mikael Abrahamsson, Mark 2977 Andrews, Fred Baker, Bob Braden, Stewart Bryant, Brian Carpenter, 2978 Wojciech Dec, Ralph Droms, Adrian Farrel, Nick Green, Sri Gundavelli, 2979 Brian Haberman, Bernhard Haindl, Joel Halpern, Tom Herbert, Sascha 2980 Hlusiak, Lee Howard, Andre Kostur, Hubert Kuenig, Ted Lemon, Andy 2981 Malis, Satoru Matsushima, Tomek Mrugalski, Madhu Niraula, Alexandru 2982 Petrescu, Behcet Saikaya, Michal Skorepa, Joe Touch, Bernie Volz, 2983 Ryuji Wakikawa, Tony Whyman, Lloyd Wood and James Woodyatt. Members 2984 of the IESG also provided valuable input during their review process 2985 that greatly improved the document. Special thanks go to Stewart 2986 Bryant, Joel Halpern and Brian Haberman for their shepherding 2987 guidance during the publication of the AERO first edition. 2989 This work has further been encouraged and supported by Boeing 2990 colleagues including Kyle Bae, M. Wayne Benson, Dave Bernhardt, Cam 2991 Brodie, John Bush, Balaguruna Chidambaram, Irene Chin, Bruce Cornish, 2992 Claudiu Danilov, Don Dillenburg, Joe Dudkowski, Wen Fang, Samad 2993 Farooqui, Anthony Gregory, Jeff Holland, Seth Jahne, Brian Jaury, 2994 Greg Kimberly, Ed King, Madhuri Madhava Badgandi, Laurel Matthew, 2995 Gene MacLean III, Rob Muszkiewicz, Sean O'Sullivan, Vijay 2996 Rajagopalan, Greg Saccone, Rod Santiago, Kent Shuey, Brian Skeen, 2997 Mike Slane, Carrie Spiker, Katie Tran, Brendan Williams, Amelia 2998 Wilson, Julie Wulff, Yueli Yang, Eric Yeh and other members of the 2999 Boeing mobility, networking and autonomy teams. Kyle Bae, Wayne 3000 Benson, Katie Tran and Eric Yeh are especially acknowledged for 3001 implementing the AERO functions as extensions to the public domain 3002 OpenVPN distribution. 3004 Earlier works on NBMA tunneling approaches are found in 3005 [RFC2529][RFC5214][RFC5569]. 3007 Many of the constructs presented in this second edition of AERO are 3008 based on the author's earlier works, including: 3010 o The Internet Routing Overlay Network (IRON) 3011 [RFC6179][I-D.templin-ironbis] 3013 o Virtual Enterprise Traversal (VET) 3014 [RFC5558][I-D.templin-intarea-vet] 3016 o The Subnetwork Encapsulation and Adaptation Layer (SEAL) 3017 [RFC5320][I-D.templin-intarea-seal] 3019 o AERO, First Edition [RFC6706] 3021 Note that these works cite numerous earlier efforts that are not also 3022 cited here due to space limitations. The authors of those earlier 3023 works are acknowledged for their insights. 3025 This work is aligned with the NASA Safe Autonomous Systems Operation 3026 (SASO) program under NASA contract number NNA16BD84C. 3028 This work is aligned with the FAA as per the SE2025 contract number 3029 DTFAWA-15-D-00030. 3031 This work is aligned with the Boeing Commercial Airplanes (BCA) 3032 Internet of Things (IoT) and autonomy programs. 3034 This work is aligned with the Boeing Information Technology (BIT) 3035 MobileNet program. 3037 8. References 3039 8.1. Normative References 3041 [I-D.templin-atn-aero-interface] 3042 Templin, F. and T. Whyman, "Transmission of IPv6 Packets 3043 over Overlay Multilink Network (OMNI) Interfaces", draft- 3044 templin-atn-aero-interface-17 (work in progress), February 3045 2020. 3047 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, 3048 DOI 10.17487/RFC0791, September 1981, 3049 . 3051 [RFC0792] Postel, J., "Internet Control Message Protocol", STD 5, 3052 RFC 792, DOI 10.17487/RFC0792, September 1981, 3053 . 3055 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 3056 Requirement Levels", BCP 14, RFC 2119, 3057 DOI 10.17487/RFC2119, March 1997, 3058 . 3060 [RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in 3061 IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473, 3062 December 1998, . 3064 [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black, 3065 "Definition of the Differentiated Services Field (DS 3066 Field) in the IPv4 and IPv6 Headers", RFC 2474, 3067 DOI 10.17487/RFC2474, December 1998, 3068 . 3070 [RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander, 3071 "SEcure Neighbor Discovery (SEND)", RFC 3971, 3072 DOI 10.17487/RFC3971, March 2005, 3073 . 3075 [RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)", 3076 RFC 3972, DOI 10.17487/RFC3972, March 2005, 3077 . 3079 [RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and 3080 More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191, 3081 November 2005, . 3083 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 3084 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 3085 DOI 10.17487/RFC4861, September 2007, 3086 . 3088 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 3089 Address Autoconfiguration", RFC 4862, 3090 DOI 10.17487/RFC4862, September 2007, 3091 . 3093 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 3094 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 3095 May 2017, . 3097 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 3098 (IPv6) Specification", STD 86, RFC 8200, 3099 DOI 10.17487/RFC8200, July 2017, 3100 . 3102 [RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A., 3103 Richardson, M., Jiang, S., Lemon, T., and T. Winters, 3104 "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", 3105 RFC 8415, DOI 10.17487/RFC8415, November 2018, 3106 . 3108 8.2. Informative References 3110 [BGP] Huston, G., "BGP in 2015, http://potaroo.net", January 3111 2016. 3113 [I-D.ietf-6man-segment-routing-header] 3114 Filsfils, C., Dukes, D., Previdi, S., Leddy, J., 3115 Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header 3116 (SRH)", draft-ietf-6man-segment-routing-header-26 (work in 3117 progress), October 2019. 3119 [I-D.ietf-dmm-distributed-mobility-anchoring] 3120 Chan, A., Wei, X., Lee, J., Jeon, S., and C. Bernardos, 3121 "Distributed Mobility Anchoring", draft-ietf-dmm- 3122 distributed-mobility-anchoring-14 (work in progress), 3123 November 2019. 3125 [I-D.ietf-intarea-gue] 3126 Herbert, T., Yong, L., and O. Zia, "Generic UDP 3127 Encapsulation", draft-ietf-intarea-gue-09 (work in 3128 progress), October 2019. 3130 [I-D.ietf-intarea-gue-extensions] 3131 Herbert, T., Yong, L., and F. Templin, "Extensions for 3132 Generic UDP Encapsulation", draft-ietf-intarea-gue- 3133 extensions-06 (work in progress), March 2019. 3135 [I-D.ietf-intarea-tunnels] 3136 Touch, J. and M. Townsley, "IP Tunnels in the Internet 3137 Architecture", draft-ietf-intarea-tunnels-10 (work in 3138 progress), September 2019. 3140 [I-D.ietf-rtgwg-atn-bgp] 3141 Templin, F., Saccone, G., Dawra, G., Lindem, A., and V. 3142 Moreno, "A Simple BGP-based Mobile Routing System for the 3143 Aeronautical Telecommunications Network", draft-ietf- 3144 rtgwg-atn-bgp-05 (work in progress), January 2020. 3146 [I-D.templin-6man-dhcpv6-ndopt] 3147 Templin, F., "A Unified Stateful/Stateless Configuration 3148 Service for IPv6", draft-templin-6man-dhcpv6-ndopt-09 3149 (work in progress), January 2020. 3151 [I-D.templin-intarea-grefrag] 3152 Templin, F., "GRE Tunnel Level Fragmentation", draft- 3153 templin-intarea-grefrag-04 (work in progress), July 2016. 3155 [I-D.templin-intarea-seal] 3156 Templin, F., "The Subnetwork Encapsulation and Adaptation 3157 Layer (SEAL)", draft-templin-intarea-seal-68 (work in 3158 progress), January 2014. 3160 [I-D.templin-intarea-vet] 3161 Templin, F., "Virtual Enterprise Traversal (VET)", draft- 3162 templin-intarea-vet-40 (work in progress), May 2013. 3164 [I-D.templin-ironbis] 3165 Templin, F., "The Interior Routing Overlay Network 3166 (IRON)", draft-templin-ironbis-16 (work in progress), 3167 March 2014. 3169 [I-D.templin-v6ops-pdhost] 3170 Templin, F., "IPv6 Prefix Delegation and Multi-Addressing 3171 Models", draft-templin-v6ops-pdhost-25 (work in progress), 3172 January 2020. 3174 [OVPN] OpenVPN, O., "http://openvpn.net", October 2016. 3176 [RFC1035] Mockapetris, P., "Domain names - implementation and 3177 specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, 3178 November 1987, . 3180 [RFC1122] Braden, R., Ed., "Requirements for Internet Hosts - 3181 Communication Layers", STD 3, RFC 1122, 3182 DOI 10.17487/RFC1122, October 1989, 3183 . 3185 [RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191, 3186 DOI 10.17487/RFC1191, November 1990, 3187 . 3189 [RFC1812] Baker, F., Ed., "Requirements for IP Version 4 Routers", 3190 RFC 1812, DOI 10.17487/RFC1812, June 1995, 3191 . 3193 [RFC2003] Perkins, C., "IP Encapsulation within IP", RFC 2003, 3194 DOI 10.17487/RFC2003, October 1996, 3195 . 3197 [RFC2236] Fenner, W., "Internet Group Management Protocol, Version 3198 2", RFC 2236, DOI 10.17487/RFC2236, November 1997, 3199 . 3201 [RFC2529] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4 3202 Domains without Explicit Tunnels", RFC 2529, 3203 DOI 10.17487/RFC2529, March 1999, 3204 . 3206 [RFC2764] Gleeson, B., Lin, A., Heinanen, J., Armitage, G., and A. 3207 Malis, "A Framework for IP Based Virtual Private 3208 Networks", RFC 2764, DOI 10.17487/RFC2764, February 2000, 3209 . 3211 [RFC2784] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P. 3212 Traina, "Generic Routing Encapsulation (GRE)", RFC 2784, 3213 DOI 10.17487/RFC2784, March 2000, 3214 . 3216 [RFC2890] Dommety, G., "Key and Sequence Number Extensions to GRE", 3217 RFC 2890, DOI 10.17487/RFC2890, September 2000, 3218 . 3220 [RFC2923] Lahey, K., "TCP Problems with Path MTU Discovery", 3221 RFC 2923, DOI 10.17487/RFC2923, September 2000, 3222 . 3224 [RFC2983] Black, D., "Differentiated Services and Tunnels", 3225 RFC 2983, DOI 10.17487/RFC2983, October 2000, 3226 . 3228 [RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition 3229 of Explicit Congestion Notification (ECN) to IP", 3230 RFC 3168, DOI 10.17487/RFC3168, September 2001, 3231 . 3233 [RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener 3234 Discovery Version 2 (MLDv2) for IPv6", RFC 3810, 3235 DOI 10.17487/RFC3810, June 2004, 3236 . 3238 [RFC3819] Karn, P., Ed., Bormann, C., Fairhurst, G., Grossman, D., 3239 Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J., and L. 3240 Wood, "Advice for Internet Subnetwork Designers", BCP 89, 3241 RFC 3819, DOI 10.17487/RFC3819, July 2004, 3242 . 3244 [RFC4213] Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms 3245 for IPv6 Hosts and Routers", RFC 4213, 3246 DOI 10.17487/RFC4213, October 2005, 3247 . 3249 [RFC4251] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH) 3250 Protocol Architecture", RFC 4251, DOI 10.17487/RFC4251, 3251 January 2006, . 3253 [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A 3254 Border Gateway Protocol 4 (BGP-4)", RFC 4271, 3255 DOI 10.17487/RFC4271, January 2006, 3256 . 3258 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 3259 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 3260 2006, . 3262 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 3263 Internet Protocol", RFC 4301, DOI 10.17487/RFC4301, 3264 December 2005, . 3266 [RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery 3267 Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April 3268 2006, . 3270 [RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet 3271 Control Message Protocol (ICMPv6) for the Internet 3272 Protocol Version 6 (IPv6) Specification", STD 89, 3273 RFC 4443, DOI 10.17487/RFC4443, March 2006, 3274 . 3276 [RFC4511] Sermersheim, J., Ed., "Lightweight Directory Access 3277 Protocol (LDAP): The Protocol", RFC 4511, 3278 DOI 10.17487/RFC4511, June 2006, 3279 . 3281 [RFC4541] Christensen, M., Kimball, K., and F. Solensky, 3282 "Considerations for Internet Group Management Protocol 3283 (IGMP) and Multicast Listener Discovery (MLD) Snooping 3284 Switches", RFC 4541, DOI 10.17487/RFC4541, May 2006, 3285 . 3287 [RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick, 3288 "Internet Group Management Protocol (IGMP) / Multicast 3289 Listener Discovery (MLD)-Based Multicast Forwarding 3290 ("IGMP/MLD Proxying")", RFC 4605, DOI 10.17487/RFC4605, 3291 August 2006, . 3293 [RFC4607] Holbrook, H. and B. Cain, "Source-Specific Multicast for 3294 IP", RFC 4607, DOI 10.17487/RFC4607, August 2006, 3295 . 3297 [RFC4963] Heffner, J., Mathis, M., and B. Chandler, "IPv4 Reassembly 3298 Errors at High Data Rates", RFC 4963, 3299 DOI 10.17487/RFC4963, July 2007, 3300 . 3302 [RFC4982] Bagnulo, M. and J. Arkko, "Support for Multiple Hash 3303 Algorithms in Cryptographically Generated Addresses 3304 (CGAs)", RFC 4982, DOI 10.17487/RFC4982, July 2007, 3305 . 3307 [RFC5015] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano, 3308 "Bidirectional Protocol Independent Multicast (BIDIR- 3309 PIM)", RFC 5015, DOI 10.17487/RFC5015, October 2007, 3310 . 3312 [RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site 3313 Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214, 3314 DOI 10.17487/RFC5214, March 2008, 3315 . 3317 [RFC5320] Templin, F., Ed., "The Subnetwork Encapsulation and 3318 Adaptation Layer (SEAL)", RFC 5320, DOI 10.17487/RFC5320, 3319 February 2010, . 3321 [RFC5522] Eddy, W., Ivancic, W., and T. Davis, "Network Mobility 3322 Route Optimization Requirements for Operational Use in 3323 Aeronautics and Space Exploration Mobile Networks", 3324 RFC 5522, DOI 10.17487/RFC5522, October 2009, 3325 . 3327 [RFC5558] Templin, F., Ed., "Virtual Enterprise Traversal (VET)", 3328 RFC 5558, DOI 10.17487/RFC5558, February 2010, 3329 . 3331 [RFC5569] Despres, R., "IPv6 Rapid Deployment on IPv4 3332 Infrastructures (6rd)", RFC 5569, DOI 10.17487/RFC5569, 3333 January 2010, . 3335 [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 3336 (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, 3337 . 3339 [RFC6106] Jeong, J., Park, S., Beloeil, L., and S. Madanapalli, 3340 "IPv6 Router Advertisement Options for DNS Configuration", 3341 RFC 6106, DOI 10.17487/RFC6106, November 2010, 3342 . 3344 [RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful 3345 NAT64: Network Address and Protocol Translation from IPv6 3346 Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146, 3347 April 2011, . 3349 [RFC6179] Templin, F., Ed., "The Internet Routing Overlay Network 3350 (IRON)", RFC 6179, DOI 10.17487/RFC6179, March 2011, 3351 . 3353 [RFC6221] Miles, D., Ed., Ooghe, S., Dec, W., Krishnan, S., and A. 3354 Kavanagh, "Lightweight DHCPv6 Relay Agent", RFC 6221, 3355 DOI 10.17487/RFC6221, May 2011, 3356 . 3358 [RFC6273] Kukec, A., Krishnan, S., and S. Jiang, "The Secure 3359 Neighbor Discovery (SEND) Hash Threat Analysis", RFC 6273, 3360 DOI 10.17487/RFC6273, June 2011, 3361 . 3363 [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer 3364 Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, 3365 January 2012, . 3367 [RFC6438] Carpenter, B. and S. Amante, "Using the IPv6 Flow Label 3368 for Equal Cost Multipath Routing and Link Aggregation in 3369 Tunnels", RFC 6438, DOI 10.17487/RFC6438, November 2011, 3370 . 3372 [RFC6706] Templin, F., Ed., "Asymmetric Extended Route Optimization 3373 (AERO)", RFC 6706, DOI 10.17487/RFC6706, August 2012, 3374 . 3376 [RFC6864] Touch, J., "Updated Specification of the IPv4 ID Field", 3377 RFC 6864, DOI 10.17487/RFC6864, February 2013, 3378 . 3380 [RFC7269] Chen, G., Cao, Z., Xie, C., and D. Binet, "NAT64 3381 Deployment Options and Experience", RFC 7269, 3382 DOI 10.17487/RFC7269, June 2014, 3383 . 3385 [RFC7333] Chan, H., Ed., Liu, D., Seite, P., Yokota, H., and J. 3386 Korhonen, "Requirements for Distributed Mobility 3387 Management", RFC 7333, DOI 10.17487/RFC7333, August 2014, 3388 . 3390 [RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I., 3391 Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent 3392 Multicast - Sparse Mode (PIM-SM): Protocol Specification 3393 (Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March 3394 2016, . 3396 [RFC8086] Yong, L., Ed., Crabbe, E., Xu, X., and T. Herbert, "GRE- 3397 in-UDP Encapsulation", RFC 8086, DOI 10.17487/RFC8086, 3398 March 2017, . 3400 [RFC8201] McCann, J., Deering, S., Mogul, J., and R. Hinden, Ed., 3401 "Path MTU Discovery for IP version 6", STD 87, RFC 8201, 3402 DOI 10.17487/RFC8201, July 2017, 3403 . 3405 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 3406 Decraene, B., Litkowski, S., and R. Shakir, "Segment 3407 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 3408 July 2018, . 3410 [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol 3411 Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, 3412 . 3414 Appendix A. AERO Alternate Encapsulations 3416 When GUE encapsulation is not needed, AERO can use common 3417 encapsulations such as IP-in-IP [RFC2003][RFC2473][RFC4213], Generic 3418 Routing Encapsulation (GRE) [RFC2784][RFC2890] and others. The 3419 encapsulation is therefore only differentiated from non-AERO tunnels 3420 through the application of AERO control messaging and not through, 3421 e.g., a well-known UDP port number. 3423 As for GUE encapsulation, alternate AERO encapsulation formats may 3424 require encapsulation layer fragmentation. For simple IP-in-IP 3425 encapsulation, an IPv6 fragment header is inserted directly between 3426 the inner and outer IP headers when needed, i.e., even if the outer 3427 header is IPv4. The IPv6 Fragment Header is identified to the outer 3428 IP layer by its IP protocol number, and the Next Header field in the 3429 IPv6 Fragment Header identifies the inner IP header version. For GRE 3430 encapsulation, a GRE fragment header is inserted within the GRE 3431 header [I-D.templin-intarea-grefrag]. 3433 Figure 6 shows the AERO IP-in-IP encapsulation format before any 3434 fragmentation is applied: 3436 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3437 | Outer IPv4 Header | | Outer IPv6 Header | 3438 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3439 |IPv6 Frag Header (optional)| |IPv6 Frag Header (optional)| 3440 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3441 | Inner IP Header | | Inner IP Header | 3442 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3443 | | | | 3444 ~ ~ ~ ~ 3445 ~ Inner Packet Body ~ ~ Inner Packet Body ~ 3446 ~ ~ ~ ~ 3447 | | | | 3448 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3450 Minimal Encapsulation in IPv4 Minimal Encapsulation in IPv6 3452 Figure 6: Minimal Encapsulation Format using IP-in-IP 3454 Figure 7 shows the AERO GRE encapsulation format before any 3455 fragmentation is applied: 3457 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3458 | Outer IP Header | 3459 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3460 | GRE Header | 3461 | (with checksum, key, etc..) | 3462 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3463 | GRE Fragment Header (optional)| 3464 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3465 | Inner IP Header | 3466 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3467 | | 3468 ~ ~ 3469 ~ Inner Packet Body ~ 3470 ~ ~ 3471 | | 3472 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3474 Figure 7: Minimal Encapsulation Using GRE 3476 Alternate encapsulation may be preferred in environments where GUE 3477 encapsulation would add unnecessary overhead. For example, certain 3478 low-bandwidth wireless data links may benefit from a reduced 3479 encapsulation overhead. 3481 GUE encapsulation can traverse network paths that are inaccessible to 3482 non-UDP encapsulations, e.g., for crossing Network Address 3483 Translators (NATs). More and more, network middleboxes are also 3484 being configured to discard packets that include anything other than 3485 a well-known IP protocol such as UDP and TCP. It may therefore be 3486 necessary to determine the potential for middlebox filtering before 3487 enabling alternate encapsulation in a given environment. 3489 In addition to IP-in-IP, GRE and GUE, AERO can also use security 3490 encapsulations such as IPsec, TLS/SSL, DTLS, etc. In that case, AERO 3491 control messaging and route determination occur before security 3492 encapsulation is applied for outgoing packets and after security 3493 decapsulation is applied for incoming packets. 3495 AERO is especially well suited for use with VPN system encapsulations 3496 such as OpenVPN [OVPN]. 3498 Appendix B. Non-Normative Considerations 3500 AERO can be applied to a multitude of Internetworking scenarios, with 3501 each having its own adaptations. The following considerations are 3502 provided as non-normative guidance: 3504 B.1. Implementation Strategies for Route Optimization 3506 Route optimization as discussed in Section 3.17 results in the route 3507 optimization source (ROS) creating an asymmetric neighbor cache entry 3508 for the target neighbor. The neighbor cache entry is maintained for 3509 at most REACHABLETIME seconds and then deleted unless updated. In 3510 order to refresh the neighbor cache entry lifetime before the 3511 ReachableTime timer expires, the specification requires 3512 implementations to issue a new NS/NA exchange to reset ReachableTime 3513 to REACHABLETIME seconds while data packets are still flowing. 3514 However, the decision of when to initiate a new NS/NA exchange and to 3515 perpetuate the process is left as an implementation detail. 3517 One possible strategy may be to monitor the neighbor cache entry 3518 watching for data packets for (REACHABLETIME - 5) seconds. If any 3519 data packets have been sent to the neighbor within this timeframe, 3520 then send an NS to receive a new NA. If no data packets have been 3521 sent, wait for 5 additional seconds and send an immediate NS if any 3522 data packets are sent within this "expiration pending" 5 second 3523 window. If no additional data packets are sent within the 5 second 3524 window, delete the neighbor cache entry. 3526 The monitoring of the neighbor data packet traffic therefore becomes 3527 an asymmetric ongoing process during the neighbor cache entry 3528 lifetime. If the neighbor cache entry expires, future data packets 3529 will trigger a new NS/NA exchange while the packets themselves are 3530 delivered over a longer path until route optimization state is re- 3531 established. 3533 B.2. Implicit Mobility Management 3535 AERO interface neighbors MAY provide a configuration option that 3536 allows them to perform implicit mobility management in which no ND 3537 messaging is used. In that case, the Client only transmits packets 3538 over a single interface at a time, and the neighbor always observes 3539 packets arriving from the Client from the same link-layer source 3540 address. 3542 If the Client's underlying interface address changes (either due to a 3543 readdressing of the original interface or switching to a new 3544 interface) the neighbor immediately updates the neighbor cache entry 3545 for the Client and begins accepting and sending packets according to 3546 the Client's new address. This implicit mobility method applies to 3547 use cases such as cellphones with both WiFi and Cellular interfaces 3548 where only one of the interfaces is active at a given time, and the 3549 Client automatically switches over to the backup interface if the 3550 primary interface fails. 3552 B.3. Direct Underlying Interfaces 3554 When a Client's AERO interface is configured over a Direct interface, 3555 the neighbor at the other end of the Direct link can receive packets 3556 without any encapsulation. In that case, the Client sends packets 3557 over the Direct link according to QoS preferences. If the Direct 3558 interface has the highest QoS preference, then the Client's IP 3559 packets are transmitted directly to the peer without going through an 3560 ANET/INET. If other interfaces have higher QoS preferences, then the 3561 Client's IP packets are transmitted via a different interface, which 3562 may result in the inclusion of Proxys, Servers and Relays in the 3563 communications path. Direct interfaces must be tested periodically 3564 for reachability, e.g., via NUD. 3566 B.4. AERO Clients on the Open Internetwork 3568 AERO Clients that connect to the open Internetwork via either a 3569 native or NATed interface can establish a VPN to securely connect to 3570 a Server. Alternatively, the Client can exchange ND messages 3571 directly with other AERO nodes on the same SPAN segment using INET 3572 encapsulation only and without joining the SPAN. In that case, 3573 however, the Client must apply asymmetric security for ND messages to 3574 ensure routing and neighbor cache integrity (see: Section 6). 3576 B.5. Operation on AERO Links with /64 ASPs 3578 IPv6 AERO links typically have MSPs that aggregate many candidate 3579 MNPs of length /64 or shorter. However, in some cases it may be 3580 desirable to use AERO over links that have only a /64 MSP. This can 3581 be accommodated by treating all Clients on the AERO link as simple 3582 hosts that receive /128 prefix delegations. 3584 In that case, the Client sends an RS message to the Server the same 3585 as for ordinary AERO links. The Server responds with an RA message 3586 that includes one or more /128 prefixes (i.e., singleton addresses) 3587 that include the /64 MSP prefix along with an interface identifier 3588 portion to be assigned to the Client. The Client and Server then 3589 configure their AERO addresses based on the interface identifier 3590 portions of the /128s (i.e., the lower 64 bits) and not based on the 3591 /64 prefix (i.e., the upper 64 bits). 3593 For example, if the MSP for the host-only IPv6 AERO link is 3594 2001:db8:1000:2000::/64, each Client will receive one or more /128 3595 IPv6 prefix delegations such as 2001:db8:1000:2000::1/128, 3596 2001:db8:1000:2000::2/128, etc. When the Client receives the prefix 3597 delegations, it assigns the AERO addresses fe80::1, fe80::2, etc. to 3598 the AERO interface, and assigns the global IPv6 addresses (i.e., the 3599 /128s) to either the AERO interface or an internal virtual interface 3600 such as a loopback. In this arrangement, the Client conducts route 3601 optimization in the same sense as discussed in Section 3.17. 3603 This specification has applicability for nodes that act as a Client 3604 on an "upstream" AERO link, but also act as a Server on "downstream" 3605 AERO links. More specifically, if the node acts as a Client to 3606 receive a /64 prefix from the upstream AERO link it can then act as a 3607 Server to provision /128s to Clients on downstream AERO links. 3609 B.6. AERO Adaptations for SEcure Neighbor Discovery (SEND) 3611 SEcure Neighbor Discovery (SEND) [RFC3971] and Cryptographically 3612 Generated Addresses (CGAs) [RFC3972] were designed to secure IPv6 ND 3613 messaging in environments where symmetric network and/or transport- 3614 layer security services are impractical (see: Section 6). AERO nodes 3615 that use SEND/CGA employ the following adaptations. 3617 When a source AERO node prepares a SEND-protected ND message, it uses 3618 a link-local CGA as the IPv6 source address and writes the prefix 3619 embedded in its AERO address (i.e., instead of fe80::/64) in the CGA 3620 parameters Subnet Prefix field. When the neighbor receives the ND 3621 message, it first verifies the message checksum and SEND/CGA 3622 parameters while using the link-local prefix fe80::/64 (i.e., instead 3623 of the value in the Subnet Prefix field) to match against the IPv6 3624 source address of the ND message. 3626 The neighbor then derives the AERO address of the source by using the 3627 value in the Subnet Prefix field as the interface identifier of an 3628 AERO address. For example, if the Subnet Prefix field contains 3629 2001:db8:1:2, the neighbor constructs the AERO address as 3630 fe80::2001:db8:1:2. The neighbor then caches the AERO address in the 3631 neighbor cache entry it creates for the source, and uses the AERO 3632 address as the IPv6 destination address of any ND message replies. 3634 B.7. AERO Critical Infrastructure Considerations 3636 AERO Relays can be either Commercial off-the Shelf (COTS) standard IP 3637 routers or virtual machines in the cloud. Relays must be 3638 provisioned, supported and managed by the INET administrative 3639 authority, and connected to the Relays of other INETs via inter- 3640 domain peerings. Cost for purchasing, configuring and managing 3641 Relays is nominal even for very large AERO links. 3643 AERO Servers can be standard dedicated server platforms, but most 3644 often will be deployed as virtual machines in the cloud. The only 3645 requirements for Servers are that they can run the AERO user-level 3646 code and have at least one network interface connection to the INET. 3647 As with Relays, Servers must be provisioned, supported and managed by 3648 the INET administrative authority. Cost for purchasing, configuring 3649 and managing Servers is nominal especially for virtual Servers hosted 3650 in the cloud. 3652 AERO Proxys are most often standard dedicated server platforms with 3653 one network interface connected to the ANET and a second interface 3654 connected to an INET. As with Servers, the only requirements are 3655 that they can run the AERO user-level code and have at least one 3656 interface connection to the INET. Proxys must be provisioned, 3657 supported and managed by the ANET administrative authority. Cost for 3658 purchasing, configuring and managing Proxys is nominal, and borne by 3659 the ANET administrative authority. 3661 AERO Gateways can be any dedicated server or COTS router platform 3662 connected to INETs and/or EUNs. The Gateway joins the SPAN and 3663 engages in eBGP peering with one or more Relays as a stub AS. The 3664 Gateway then injects its MNPs and/or non-MNP prefixes into the BGP 3665 routing system, and provisions the prefixes to its downstream- 3666 attached networks. The Gateway can perform ROS and MAP services the 3667 same as for any Server, and can route between the MNP and non-MNP 3668 address spaces. 3670 B.8. AERO Server Failure Implications 3672 AERO Servers may appear as a single point of failure in the 3673 architecture, but such is not the case since all Servers on the link 3674 provide identical services and loss of a Server does not imply 3675 immediate and/or comprehensive communication failures. Although 3676 Clients typically associate with a single Server at a time, Server 3677 failure is quickly detected and conveyed by Bidirectional Forward 3678 Detection (BFD) and/or proactive NUD allowing Clients to migrate to 3679 new Servers. 3681 If a Server fails, ongoing packet forwarding to Clients will continue 3682 by virtue of the asymmetric neighbor cache entries that have already 3683 been established in route optimization sources (ROSs). If a Client 3684 also experiences mobility events at roughly the same time the Server 3685 fails, unsolicited NA messages may be lost but proxy neighbor cache 3686 entries in the DEPARTED state will ensure that packet forwarding to 3687 the Client's new locations will continue for up to DEPARTTIME 3688 seconds. 3690 If a Client is left without a Server for an extended timeframe (e.g., 3691 greater than REACHABLETIIME seconds) then existing asymmetric 3692 neighbor cache entries will eventually expire and both ongoing and 3693 new communications will fail. The original source will continue to 3694 retransmit until the Client has established a new Server 3695 relationship, after which time continuous communications will resume. 3697 Therefore, providing many Servers on the link with high availability 3698 profiles provides resilience against loss of individual Servers and 3699 assurance that Clients can establish new Server relationships quickly 3700 in event of a Server failure. 3702 B.9. AERO Client / Server Architecture 3704 The AERO architectural model is client / server in the control plane, 3705 with route optimization in the data plane. The same as for common 3706 Internet services, the AERO Client discovers the addresses of AERO 3707 Servers and selects one Server to connect to. The AERO service is 3708 analogous to common Internet services such as google.com, yahoo.com, 3709 cnn.com, etc. However, there is only one AERO service for the link 3710 and all Servers provide identical services. 3712 Common Internet services provide differing strategies for advertising 3713 server addresses to clients. The strategy is conveyed through the 3714 DNS resource records returned in response to name resolution queries. 3715 As of January 2020 Internet-based 'nslookup' services were used to 3716 determine the following: 3718 o When a client resolves the domainname "google.com", the DNS always 3719 returns one A record (i.e., an IPv4 address) and one AAAA record 3720 (i.e., an IPv6 address). The client receives the same addresses 3721 each time it resolves the domainname via the same DNS resolver, 3722 but may receive different addresses when it resolves the 3723 domainname via different DNS resolvers. But, in each case, 3724 exactly one A and one AAAA record are returned. 3726 o When a client resolves the domainname "ietf.org", the DNS always 3727 returns one A record and one AAAA record with the same addresses 3728 regardless of which DNS resolver is used. 3730 o When a client resolves the domainname "yahoo.com", the DNS always 3731 returns a list of 4 A records and 4 AAAA records. Each time the 3732 client resolves the domainname via the same DNS resolver, the same 3733 list of addresses are returned but in randomized order (i.e., 3734 consistent with a DNS round-robin strategy). But, interestingly, 3735 the same addresses are returned (albeit in randomized order) when 3736 the domainname is resolved via different DNS resolvers. 3738 o When a client resolves the domainname "amazon.com", the DNS always 3739 returns a list of 3 A records and no AAAA records. As with 3740 "yahoo.com", the same three A records are returned from any 3741 worldwide Internet connection point in randomized order. 3743 The above example strategies show differing approaches to Internet 3744 resilience and service distribution offered by major Internet 3745 services. The Google approach exposes only a single IPv4 and a 3746 single IPv6 address to clients. Clients can then select whichever IP 3747 protocol version offers the best response, but will always use the 3748 same IP address according to the current Internet connection point. 3749 This means that the IP address offered by the network must lead to a 3750 highly-available server and/or service distribution point. In other 3751 words, resilience is predicated on high availability within the 3752 network and with no client-initiated failovers expected (i.e., it is 3753 all-or-nothing from the client's perspective). However, Google does 3754 provide for worldwide distributed service distribution by virtue of 3755 the fact that each Internet connection point responds with a 3756 different IPv6 and IPv4 address. The IETF approach is like google 3757 (all-or-nothing from the client's perspective), but provides only a 3758 single IPv4 or IPv6 address on a worldwide basis. This means that 3759 the addresses must be made highly-available at the network level with 3760 no client failover possibility, and if there is any worldwide service 3761 distribution it would need to be conducted by a network element that 3762 is reached via the IP address acting as a service distribution point. 3764 In contrast to the Google and IETF philosophies, Yahoo and Amazon 3765 both provide clients with a (short) list of IP addresses with Yahoo 3766 providing both IP protocol versions and Amazon as IPv4-only. The 3767 order of the list is randomized with each name service query 3768 response, with the effect of round-robin load balancing for service 3769 distribution. With a short list of addresses, there is still 3770 expectation that the network will implement high availability for 3771 each address but in case any single address fails the client can 3772 switch over to using a different address. The balance then becomes 3773 one of function in the network vs function in the end system. 3775 The same implications observed for common highly-available services 3776 in the Internet apply also to the AERO client/server architecture. 3777 When an AERO Client connects to one or more ANETs, it discovers one 3778 or more AERO Server addresses through the mechanisms discussed in 3779 earlier sections. Each Server address presumably leads to a fault- 3780 tolerant clustering arrangement such as supported by Linux-HA, 3781 Extended Virtual Synchrony or Paxos. Such an arrangement has 3782 precedence in common Internet service deployments in lightweight 3783 virtual machines without requiring expensive hardware deployment. 3784 Similarly, common Internet service deployments set service IP 3785 addresses on service distribution points that may relay requests to 3786 many different servers. 3788 For AERO, the expectation is that a combination of the Google/IETF 3789 and Yahoo/Amazon philosophies would be employed. The AERO Client 3790 connects to different ANET access points and can receive 1-2 Server 3791 AERO addresses at each point. It then selects one AERO Server 3792 address, and engages in RS/RA exchanges with the same Server from all 3793 ANET connections. The Client remains with this Server unless or 3794 until the Server fails, in which case it can switch over to an 3795 alternate Server. The Client can likewise switch over to a different 3796 Server at any time if there is some reason for it to do so. So, the 3797 AERO expectation is for a balance of function in the network and end 3798 system, with fault tolerance and resilience at both levels. 3800 Appendix C. Change Log 3802 << RFC Editor - remove prior to publication >> 3804 Changes from draft-templin-intarea-6706bis-24 to draft-templin- 3805 intrea-6706bis-25: 3807 o Added concept of "primary" to allow for proxyed RS/RA over only 3808 selected underlying interfaces. 3810 o General Cleanup. 3812 Changes from draft-templin-intarea-6706bis-23 to draft-templin- 3813 intrea-6706bis-24: 3815 o OMNI interface spec now a normative reference. 3817 o Use REACHABLETIME as the nominal Router Lifetime to return in RAs. 3819 o General cleanup. 3821 Changes from draft-templin-intarea-6706bis-22 to draft-templin- 3822 intrea-6706bis-23: 3824 o Choice of using either RS/RA or unsolicited NA for old Server 3825 notification. 3827 o General cleanup. 3829 Changes from draft-templin-intarea-6706bis-21 to draft-templin- 3830 intrea-6706bis-22: 3832 o Tightened up text on Proxy. 3834 o Removed unnecessarily restrictive texts. 3836 o General cleanup. 3838 Changes from draft-templin-intarea-6706bis-20 to draft-templin- 3839 intrea-6706bis-21: 3841 o Clarified relationship between OMNI and S/TLLAO ifIndex-tuples. 3843 o Important text in Section 13.15.3 on Servers timing out Clients 3844 that have gone silent without sending a departure notification. 3846 o New text on RS/RA as "hints of forward progress" for proactive 3847 NUD. 3849 Changes from draft-templin-intarea-6706bis-19 to draft-templin- 3850 intrea-6706bis-20: 3852 o Included new route optimization source and destination addressing 3853 strategy. Now, route optimization maintenance uses the address of 3854 the existing Server instead of the data packet destination address 3855 so that less pressure is placed on the BGP routing system 3856 convergence time and Server constancy is supported. 3858 o Included new method for releasing from old MSE without requiring 3859 Client messaging. 3861 o Included references to new OMNI interface spec (including the OMNI 3862 option). 3864 o New appendix on AERO Client/Server architecture. 3866 Changes from draft-templin-intarea-6706bis-18 to draft-templin- 3867 intrea-6706bis-19: 3869 o Changed Proxy/Server keepalives to use "proactive NUD" in a manner 3870 tha paralles BFD 3872 Changes from draft-templin-intarea-6706bis-17 to draft-templin- 3873 intrea-6706bis-18: 3875 o Discuss how AERO option is used in relation to S/TLLAOs 3877 o New text on Bidirectional Forwarding Detection (BFD) 3879 o Cleaned up usage (and non-usage) of unsolicited NAs 3881 o New appendix on Server failures 3883 Changes from draft-templin-intarea-6706bis-15 to draft-templin- 3884 intrea-6706bis-17: 3886 o S/TLLAO now includes multiple link-layer addresses within a single 3887 option instead of requiring multiple options 3889 o New unsolicited NA message to inform the old link that a Client 3890 has moved to a new link 3892 Changes from draft-templin-intarea-6706bis-14 to draft-templin- 3893 intrea-6706bis-15: 3895 o MTU and fragmentation 3897 o New details in movement to new Server 3899 Changes from draft-templin-intarea-6706bis-13 to draft-templin- 3900 intrea-6706bis-14: 3902 o Security based on secured tunnels, ingress filtering, MAP list and 3903 ROS list 3905 Changes from draft-templin-intarea-6706bis-12 to draft-templin- 3906 intrea-6706bis-13: 3908 o New paragraph in Section 3.6 on AERO interface layering over 3909 secured tunnels 3911 o Removed extraneous text in Section 3.7 3913 o Added new detail to the forwarding algorithm in Section 3.9 3915 o Clarified use of fragmentation 3917 o Route optimization now supported for both MNP and non-MNP-based 3918 prefixes 3920 o Relays are now seen as link-layer elements in the architecture. 3922 o Built out multicast section in detail. 3924 o New Appendix on implementation considerations for route 3925 optimization. 3927 Changes from draft-templin-intarea-6706bis-11 to draft-templin- 3928 intrea-6706bis-12: 3930 o Introduced Gateways as a new AERO element for connecting 3931 Correspondent Nodes on INET links 3933 o Introduced terms "Access Network (ANET)" and "Internetwork (INET)" 3935 o Changed "ASP" to "MSP", and "ACP" to "MNP" 3936 o New figure on the relation of Segments to the SPAN and AERO link 3938 o New "S" bit in S/TLLAO to indicate the "Source" S/TLLAO as opposed 3939 to additional S/TLLAOs 3941 o Changed Interface ID for Servers from 255 to 0xffff 3943 o Significant updates to Route Optimization, NUD, and Mobility 3944 Management 3946 o New Section on Multicast 3948 o New Section on AERO Clients in the open Internetwork 3950 o New Section on Operation over multiple AERO links (VLANs over the 3951 SPAN) 3953 o New Sections on DNS considerations and Transition considerations 3955 o 3957 Changes from draft-templin-intarea-6706bis-10 to draft-templin- 3958 intrea-6706bis-11: 3960 o Added The SPAN 3962 Changes from draft-templin-intarea-6706bis-09 to draft-templin- 3963 intrea-6706bis-10: 3965 o Orphaned packets in flight (e.g., when a neighbor cache entry is 3966 in the DEPARTED state) are now forwarded at the link layer instead 3967 of at the network layer. Forwarding at the network layer can 3968 result in routing loops and/or excessive delays of forwarded 3969 packets while the routing system is still reconverging. 3971 o Update route optimization to clarify the unsecured nature of the 3972 first NS used for route discovery 3974 o Many cleanups and clarifications on ND messaging parameters 3976 Changes from draft-templin-intarea-6706bis-08 to draft-templin- 3977 intrea-6706bis-09: 3979 o Changed PRL to "MAP list" 3981 o For neighbor cache entries, changed "static" to "symmetric", and 3982 "dynamic" to "asymmetric" 3984 o Specified Proxy RS/RA exchanges with Servers on behalf of Clients 3986 o Added discussion of unsolicited NAs in Section 3.16, and included 3987 forward reference to Section 3.18 3989 o Added discussion of AERO Clients used as critical infrastructure 3990 elements to connect fixed networks. 3992 o Added network-based VPN under security considerations 3994 Changes from draft-templin-intarea-6706bis-07 to draft-templin- 3995 intrea-6706bis-08: 3997 o New section on AERO-Aware Access Router 3999 Changes from draft-templin-intarea-6706bis-06 to draft-templin- 4000 intrea-6706bis-07: 4002 o Added "R" bit for release of PDs. Now have a full RS/RA service 4003 that can do PD without requiring DHCPv6 messaging over-the-air 4005 o Clarifications on solicited vs unsolicited NAs 4007 o Clarified use of MAX_NEIGHBOR_ADVERTISEMENTS for the purpose of 4008 increase reliability 4010 Changes from draft-templin-intarea-6706bis-05 to draft-templin- 4011 intrea-6706bis-06: 4013 o Major re-work and simplification of Route Optimization function 4015 o Added Distributed Mobility Management (DMM) and Mobility Anchor 4016 Point (MAP) terminology 4018 o New section on "AERO Critical Infrastructure Element 4019 Considerations" demonstrating low overall cost for the service 4021 o minor text revisions and deletions 4023 o removed extraneous appendices 4025 Changes from draft-templin-intarea-6706bis-04 to draft-templin- 4026 intrea-6706bis-05: 4028 o New Appendix E on S/TLLAO Extensions for special-purpose links. 4029 Discussed ATN/IPS as example. 4031 o New sentence in introduction to declare appendices as non- 4032 normative. 4034 Changes from draft-templin-intarea-6706bis-03 to draft-templin- 4035 intrea-6706bis-04: 4037 o Added definitions for Potential Router List (PRL) and secure 4038 enclave 4040 o Included text on mapping transport layer port numbers to network 4041 layer DSCP values 4043 o Added reference to DTLS and DMM Distributed Mobility Anchoring 4044 working group document 4046 o Reworked Security Considerations 4048 o Updated references. 4050 Changes from draft-templin-intarea-6706bis-02 to draft-templin- 4051 intrea-6706bis-03: 4053 o Added new section on SEND. 4055 o Clarifications on "AERO Address" section. 4057 o Updated references and added new reference for RFC8086. 4059 o Security considerations updates. 4061 o General text clarifications and cleanup. 4063 Changes from draft-templin-intarea-6706bis-01 to draft-templin- 4064 intrea-6706bis-02: 4066 o Note on encapsulation avoidance in Section 4. 4068 Changes from draft-templin-intarea-6706bis-00 to draft-templin- 4069 intrea-6706bis-01: 4071 o Remove DHCPv6 Server Release procedures that leveraged the old way 4072 Relays used to "route" between Server link-local addresses 4074 o Remove all text relating to Relays needing to do any AERO-specific 4075 operations 4077 o Proxy sends RS and receives RA from Server using SEND. Use CGAs 4078 as source addresses, and destination address of RA reply is to the 4079 AERO address corresponding to the Client's ACP. 4081 o Proxy uses SEND to protect RS and authenticate RA (Client does not 4082 use SEND, but rather relies on subnetwork security. When the 4083 Proxy receives an RS from the Client, it creates a new RS using 4084 its own addresses as the source and uses SEND with CGAs to send a 4085 new RS to the Server. 4087 o Emphasize distributed mobility management 4089 o AERO address-based RS injection of ACP into underlying routing 4090 system. 4092 Changes from draft-templin-aerolink-82 to draft-templin-intarea- 4093 6706bis-00: 4095 o Document use of NUD (NS/NA) for reliable link-layer address 4096 updates as an alternative to unreliable unsolicited NA. 4097 Consistent with Section 7.2.6 of RFC4861. 4099 o Server adds additional layer of encapsulation between outer and 4100 inner headers of NS/NA messages for transmission through Relays 4101 that act as vanilla IPv6 routers. The messages include the AERO 4102 Server Subnet Router Anycast address as the source and the Subnet 4103 Router Anycast address corresponding to the Client's ACP as the 4104 destination. 4106 o Clients use Subnet Router Anycast address as the encapsulation 4107 source address when the access network does not provide a 4108 topologically-fixed address. 4110 Author's Address 4112 Fred L. Templin (editor) 4113 Boeing Research & Technology 4114 P.O. Box 3707 4115 Seattle, WA 98124 4116 USA 4118 Email: fltemplin@acm.org