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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, April 16, 2020 5 rfc6179, rfc6706 (if 6 approved) 7 Intended status: Standards Track 8 Expires: October 18, 2020 10 Asymmetric Extended Route Optimization (AERO) 11 draft-templin-intarea-6706bis-44 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 October 18, 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 3.4. AERO Addresses . . . . . . . . . . . . . . . . . . . . . 15 69 3.5. Spanning Partitioned AERO Networks (SPAN) . . . . . . . . 16 70 3.5.1. SPAN Routing Transports . . . . . . . . . . . . . . . 20 71 3.6. AERO Interface Characteristics . . . . . . . . . . . . . 20 72 3.7. AERO Interface Initialization . . . . . . . . . . . . . . 25 73 3.7.1. AERO Server/Gateway Behavior . . . . . . . . . . . . 25 74 3.7.2. AERO Proxy Behavior . . . . . . . . . . . . . . . . . 25 75 3.7.3. AERO Client Behavior . . . . . . . . . . . . . . . . 26 76 3.7.4. AERO Relay Behavior . . . . . . . . . . . . . . . . . 26 77 3.8. AERO Interface Neighbor Cache Maintenance . . . . . . . . 26 78 3.9. AERO Interface Encapsulation and Re-encapsulation . . . . 28 79 3.10. AERO Interface Decapsulation . . . . . . . . . . . . . . 29 80 3.11. AERO Interface Data Origin Authentication . . . . . . . . 29 81 3.12. AERO Interface MTU and Fragmentation . . . . . . . . . . 30 82 3.13. AERO Interface Forwarding Algorithm . . . . . . . . . . . 32 83 3.13.1. Client Forwarding Algorithm . . . . . . . . . . . . 32 84 3.13.2. Proxy Forwarding Algorithm . . . . . . . . . . . . . 33 85 3.13.3. Server/Gateway Forwarding Algorithm . . . . . . . . 34 86 3.13.4. Relay Forwarding Algorithm . . . . . . . . . . . . . 35 87 3.14. AERO Interface Error Handling . . . . . . . . . . . . . . 36 88 3.15. AERO Router Discovery, Prefix Delegation and 89 Autoconfiguration . . . . . . . . . . . . . . . . . . . . 38 90 3.15.1. AERO ND/PD Service Model . . . . . . . . . . . . . . 38 91 3.15.2. AERO Client Behavior . . . . . . . . . . . . . . . . 39 92 3.15.3. AERO Server Behavior . . . . . . . . . . . . . . . . 41 94 3.16. The AERO Proxy . . . . . . . . . . . . . . . . . . . . . 44 95 3.16.1. Detecting and Responding to Server Failures . . . . 46 96 3.16.2. Point-to-Multipoint Server Coordindation . . . . . . 47 97 3.17. AERO Route Optimization . . . . . . . . . . . . . . . . . 47 98 3.17.1. Route Optimization Initiation . . . . . . . . . . . 48 99 3.17.2. Relaying the NS . . . . . . . . . . . . . . . . . . 48 100 3.17.3. Processing the NS and Sending the NA . . . . . . . . 48 101 3.17.4. Relaying the NA . . . . . . . . . . . . . . . . . . 50 102 3.17.5. Processing the NA . . . . . . . . . . . . . . . . . 50 103 3.17.6. Route Optimization Maintenance . . . . . . . . . . . 50 104 3.18. Neighbor Unreachability Detection (NUD) . . . . . . . . . 51 105 3.19. Mobility Management and Quality of Service (QoS) . . . . 52 106 3.19.1. Mobility Update Messaging . . . . . . . . . . . . . 53 107 3.19.2. Announcing Link-Layer Address and/or QoS Preference 108 Changes . . . . . . . . . . . . . . . . . . . . . . 54 109 3.19.3. Bringing New Links Into Service . . . . . . . . . . 54 110 3.19.4. Removing Existing Links from Service . . . . . . . . 54 111 3.19.5. Moving to a New Server . . . . . . . . . . . . . . . 55 112 3.20. Multicast . . . . . . . . . . . . . . . . . . . . . . . . 56 113 3.20.1. Source-Specific Multicast (SSM) . . . . . . . . . . 56 114 3.20.2. Any-Source Multicast (ASM) . . . . . . . . . . . . . 57 115 3.20.3. Bi-Directional PIM (BIDIR-PIM) . . . . . . . . . . . 58 116 3.21. Operation over Multiple AERO Links (VLANs) . . . . . . . 58 117 3.22. DNS Considerations . . . . . . . . . . . . . . . . . . . 59 118 3.23. Transition Considerations . . . . . . . . . . . . . . . . 60 119 3.24. Detecting and Reacting to Server and Relay Failures . . . 60 120 3.25. AERO Clients on the Open Internet . . . . . . . . . . . . 61 121 4. Implementation Status . . . . . . . . . . . . . . . . . . . . 62 122 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 63 123 6. Security Considerations . . . . . . . . . . . . . . . . . . . 63 124 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 65 125 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 66 126 8.1. Normative References . . . . . . . . . . . . . . . . . . 66 127 8.2. Informative References . . . . . . . . . . . . . . . . . 68 128 Appendix A. AERO Alternate Encapsulations . . . . . . . . . . . 75 129 Appendix B. Non-Normative Considerations . . . . . . . . . . . . 76 130 B.1. Implementation Strategies for Route Optimization . . . . 77 131 B.2. Implicit Mobility Management . . . . . . . . . . . . . . 77 132 B.3. Direct Underlying Interfaces . . . . . . . . . . . . . . 78 133 B.4. Operation on AERO Links with /64 ASPs . . . . . . . . . . 78 134 B.5. AERO Critical Infrastructure Considerations . . . . . . . 79 135 B.6. AERO Server Failure Implications . . . . . . . . . . . . 79 136 B.7. AERO Client / Server Architecture . . . . . . . . . . . . 80 137 Appendix C. Change Log . . . . . . . . . . . . . . . . . . . . . 82 138 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 90 140 1. Introduction 142 Asymmetric Extended Route Optimization (AERO) fulfills the 143 requirements of Distributed Mobility Management (DMM) [RFC7333] and 144 route optimization [RFC5522] for aeronautical networking and other 145 network mobility use cases. AERO is based on a Non-Broadcast, 146 Multiple Access (NBMA) virtual link model known as the AERO link. 147 The AERO link is a virtual overlay configured over one or more 148 underlying Internetworks, and nodes on the link can exchange IP 149 packets via tunneling. Multilink operation allows for increased 150 reliability, bandwidth optimization and traffic path diversity. 152 The AERO service comprises Clients, Proxys, Servers and Gateways that 153 are seen as AERO link neighbors as well as Relays that bridge AERO 154 link partitions. Each node's AERO interface uses an IPv6 link-local 155 address format (known as the AERO address) that supports operation of 156 the IPv6 Neighbor Discovery (ND) protocol [RFC4861] and links ND to 157 IP forwarding. A node's AERO interface can be configured over 158 multiple underlying interfaces, and may therefore appear as a single 159 interface with multiple link-layer addresses. Each link-layer 160 address is subject to change due to mobility and/or QoS fluctuations, 161 and link-layer address changes are signaled by ND messaging the same 162 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 Server, while direct 170 routing is supported through asymmetric extended route optimization 171 while data packets are flowing. Both unicast and multicast 172 communications are supported, and mobile nodes may efficiently move 173 between 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/Server is on the optimal 183 route from any correspondent node on the link, and provides a gateway 184 between the underlying Internetwork and the SPAN. To the underlying 185 Internetwork, the Gateway/Server is the source of a route to the MSP, 186 and hence uplink traffic to the mobile node is naturally routed to 187 the nearest Gateway/Server. 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 and mobility/multilink services for AERO Clients. The 318 Server assigns an administratively-provisioned AERO address to its 319 AERO interface to support the operation of the ND/PD services, and 320 advertises all of its associated MNPs via BGP peerings with 321 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. Segment 355 Routing [RFC8754] can be used to cause packets to visit selected 356 hops on the SPAN. 358 SPAN Service Prefix (SSP) 359 a global or unique local /96 IPv6 prefix assigned to the AERO link 360 to support SPAN services. 362 SPAN Partition Prefix (SPP) 363 a sub-prefix of the SPAN Service Prefix uniquely assigned to a 364 single SPAN segment. 366 SPAN Client Prefix (SCP) 367 a SPAN prefix formed from an AERO Client address. 369 SPAN Address 370 a unique local IPv6 address taken from a SPAN Client/Partition 371 Prefix and constructed as specified in Section 3.5. SPAN 372 addresses are statelessly derived from AERO addresses, and vice- 373 versa. 375 ingress tunnel endpoint (ITE) 376 an AERO interface endpoint that injects encapsulated packets into 377 an AERO link. 379 egress tunnel endpoint (ETE) 380 an AERO interface endpoint that receives encapsulated packets from 381 an AERO link. 383 link-layer address 384 an IP address used as an encapsulation header source or 385 destination address from the perspective of the AERO interface. 386 When an upper layer protocol (e.g., UDP) is used as part of the 387 encapsulation, the port number is also considered as part of the 388 link-layer address. From the perspective of the AERO interface, 389 the link-layer address is either an INET address for intra-segment 390 encapsulation or a SPAN address for inter-segment encapsulation. 392 network layer address 393 the source or destination address of an encapsulated IP packet 394 presented to the AERO interface. 396 end user network (EUN) 397 an internal virtual or external edge IP network that an AERO 398 Client or Gateway connects to the rest of the network via the AERO 399 interface. The Client/Gateway sees each EUN as a "downstream" 400 network, and sees the AERO interface as the point of attachment to 401 the "upstream" network. 403 Mobile Node (MN) 404 an AERO Client and all of its downstream-attached networks that 405 move together as a single unit, i.e., an end system that connects 406 an Internet of Things. 408 Mobile Router (MR) 409 a MN's on-board router that forwards packets between any 410 downstream-attached networks and the AERO link. 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 on 420 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 Servers 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 Server-to-Client associations. 437 Mobility Service (MS) 438 the collective set of all Servers, Proxys, Relays and Gateways 439 that provide the AERO Service to Clients. 441 Mobility Service Endpoint MSE) 442 an individual Server, Proxy, Relay or Gateway in the Mobility 443 Service. 445 Throughout the document, the simple terms "Client", "Server", 446 "Relay", "Proxy" and "Gateway" refer to "AERO Client", "AERO Server", 447 "AERO Relay", "AERO Proxy" and "AERO Gateway", respectively. 448 Capitalization is used to distinguish these terms from other common 449 Internetworking uses in which they appear without capitalization. 451 The terminology of DHCPv6 [RFC8415] and IPv6 ND [RFC4861] (including 452 the names of node variables, messages and protocol constants) is used 453 throughout this document. The terms "All-Routers multicast", "All- 454 Nodes multicast", "Solicited-Node multicast" and "Subnet-Router 455 anycast" are defined in [RFC4291] (with Link-Local scope assumed). 456 Also, the term "IP" is used to generically refer to either Internet 457 Protocol version, i.e., IPv4 [RFC0791] or IPv6 [RFC8200]. 459 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 460 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 461 "OPTIONAL" in this document are to be interpreted as described in BCP 462 14 [RFC2119][RFC8174] when, and only when, they appear in all 463 capitals, as shown here. 465 3. Asymmetric Extended Route Optimization (AERO) 467 The following sections specify the operation of IP over Asymmetric 468 Extended Route Optimization (AERO) links: 470 3.1. AERO Link Reference Model 471 +----------------+ 472 | AERO Relay R1 | 473 | Nbr: S1, S2, P1| 474 |(X1->S1; X2->S2)| 475 | MSP M1 | 476 +-+---------+--+-+ 477 +--------------+ | Secured | | +--------------+ 478 |AERO Server S1| | tunnels | | |AERO Server S2| 479 | Nbr: C1, R1 +-----+ | +-----+ Nbr: C2, R1 | 480 | default->R1 | | | default->R1 | 481 | X1->C1 | | | X2->C2 | 482 +-------+------+ | +------+-------+ 483 | AERO Link | | 484 X===+===+===================+==)===============+===+===X 485 | | | | 486 +-----+--------+ +--------+--+-----+ +--------+-----+ 487 |AERO Client C1| | AERO Proxy P1 | |AERO Client C2| 488 | Nbr: S1 | |(Proxy Nbr Cache)| | Nbr: S2 | 489 | default->S1 | +--------+--------+ | default->S2 | 490 | MNP X1 | | | MNP X2 | 491 +------+-------+ .--------+------. +-----+--------+ 492 | (- Proxyed Clients -) | 493 .-. `---------------' .-. 494 ,-( _)-. ,-( _)-. 495 .-(_ IP )-. +-------+ +-------+ .-(_ IP )-. 496 (__ EUN )--|Host H1| |Host H2|--(__ EUN ) 497 `-(______)-' +-------+ +-------+ `-(______)-' 499 Figure 1: AERO Link Reference Model 501 Figure 1 presents the AERO link reference model. In this model: 503 o the AERO link is an overlay network service configured over one or 504 more underlying INET partitions which may be managed by different 505 administrative authorities and have incompatible protocols and/or 506 addressing plans. 508 o AERO Relay R1 aggregates Mobility Service Prefix (MSP) M1, 509 discovers Mobile Network Prefixes (MNPs) X* and advertises the MSP 510 via BGP peerings over secured tunnels to Servers (S1, S2). Relays 511 use the SPAN service to bridge disjoint segments of a partitioned 512 AERO link. 514 o AERO Servers S1 and S2 configure secured tunnels with Relay R1 and 515 also provide mobility, multilink and default router services for 516 their associated Clients C1 and C2. 518 o AERO Clients C1 and C2 associate with Servers S1 and S2, 519 respectively. They receive Mobile Network Prefix (MNP) 520 delegations X1 and X2, and also act as default routers for their 521 associated physical or internal virtual EUNs. Simple hosts H1 and 522 H2 attach to the EUNs served by Clients C1 and C2, respectively. 524 o AERO Proxy P1 configures a secured tunnel with Relay R1 and 525 provides proxy services for AERO Clients in secured enclaves that 526 cannot associate directly with other AERO link neighbors. 528 Each node on the AERO link maintains an AERO interface neighbor cache 529 and an IP forwarding table the same as for any link. Although the 530 figure shows a limited deployment, in common operational practice 531 there will normally be many additional Relays, Servers, Clients and 532 Proxys. 534 3.2. AERO Node Types 536 AERO Relays provide hybrid routing/bridging services (as well as a 537 security trust anchor) for nodes on an AERO link. Relays use 538 standard IPv6 routing to forward packets both within the same INET 539 partitions and between disjoint INET partitions based on a mid-layer 540 IPv6 encapsulation known as the SPAN header. The inner IP layer 541 experiences a virtual bridging service since the inner IP TTL/Hop 542 Limit is not decremented during forwarding. Each Relay also peers 543 with Servers and other Relays in a dynamic routing protocol instance 544 to provide a Distributed Mobility Management (DMM) service for the 545 list of active MNPs (see Section 3.3). Relays present the AERO link 546 as a set of one or more Mobility Service Prefixes (MSPs) but as link- 547 layer devices need not connect directly to the AERO link themselves 548 unless an administrative interface is desired. Relays configure 549 secured tunnels with Servers, Proxys and other Relays; they further 550 maintain IP forwarding table entries for each Mobile Network Prefix 551 (MNP) and any other reachable non-MNP prefixes. 553 AERO Servers provide default forwarding and mobility/multilink 554 services for AERO Client Mobile Nodes (MNs). Each Server also peers 555 with Relays in a dynamic routing protocol instance to advertise its 556 list of associated MNPs (see Section 3.3). Servers facilitate PD 557 exchanges with Clients, where each delegated prefix becomes an MNP 558 taken from an MSP. Servers forward packets between AERO interface 559 neighbors and track each Client's mobility profiles. 561 AERO Clients register their MNPs through PD exchanges with AERO 562 Servers over the AERO link, and distribute the MNPs to nodes on EUNs. 563 A Client may also be co-resident on the same physical or virtual 564 platform as a Server; in that case, the Client and Server behave as a 565 single functional unit. 567 AERO Proxys provide a conduit for ANET AERO Clients to associate with 568 AERO Servers in external INETs. Client and Servers exchange control 569 plane messages via the Proxy acting as a bridge between the ANET/INET 570 boundary. The Proxy forwards data packets between Clients and the 571 AERO link according to forwarding information in the neighbor cache. 572 The Proxy function is specified in Section 3.16. 574 AERO Gateways are Servers that provide forwarding services between 575 the AERO interface and INET/EUN interfaces. Gateways are provisioned 576 with MNPs the same as for an AERO Client, and also run a dynamic 577 routing protocol to discover any non-MNP IP routes. The Gateway 578 advertises the MSP(s) to INETs, and distributes all of its associated 579 MNPs and non-MNP IP routes via BGP peerings with Relays. 581 AERO Relays, Servers, Proxys and Gateways are critical infrastructure 582 elements in fixed (i.e., non-mobile) INET deployments and hence have 583 permanent and unchanging INET addresses. AERO Clients are MNs that 584 connect via ANET interfaces, i.e., their ANET addresses may change 585 when the Client moves to a new ANET connection. 587 3.3. AERO Routing System 589 The AERO routing system comprises a private instance of the Border 590 Gateway Protocol (BGP) [RFC4271] that is coordinated between Relays 591 and Servers and does not interact with either the public Internet BGP 592 routing system or any underlying INET routing systems. 594 In a reference deployment, each Server is configured as an Autonomous 595 System Border Router (ASBR) for a stub Autonomous System (AS) using 596 an AS Number (ASN) that is unique within the BGP instance, and each 597 Server further uses eBGP to peer with one or more Relays but does not 598 peer with other Servers. Each INET of a multi-segment AERO link must 599 include one or more Relays, which peer with the Servers and Proxys 600 within that INET. All Relays within the same INET are members of the 601 same hub AS using a common ASN, and use iBGP to maintain a consistent 602 view of all active MNPs currently in service. The Relays of 603 different INETs peer with one another using eBGP. 605 Relays advertise the AERO link's MSPs and any non-MNP routes to each 606 of their Servers. This means that any aggregated non-MNPs (including 607 "default") are advertised to all Servers. Each Relay configures a 608 black-hole route for each of its MSPs. By black-holing the MSPs, the 609 Relay will maintain forwarding table entries only for the MNPs that 610 are currently active, and packets destined to all other MNPs will 611 correctly incur Destination Unreachable messages due to the black- 612 hole route. In this way, Servers have only partial topology 613 knowledge (i.e., they know only about the MNPs of their directly 614 associated Clients) and they forward all other packets to Relays 615 which have full topology knowledge. 617 Servers maintain a working set of associated MNPs, and dynamically 618 announce new MNPs and withdraw departed MNPs in eBGP updates to 619 Relays. Servers that are configured as Gateways also redistribute 620 non-MNP routes learned from non-AERO interfaces via their eBGP Relay 621 peerings. 623 Clients are expected to remain associated with their current Servers 624 for extended timeframes, however Servers SHOULD selectively suppress 625 updates for impatient Clients that repeatedly associate and 626 disassociate with them in order to dampen routing churn. Servers 627 that are configured as Gateways advertise the MSPs via INET/EUN 628 interfaces, and forward packets between INET/EUN interfaces and the 629 AERO interface using standard IP forwarding. 631 Scaling properties of the AERO routing system are limited by the 632 number of BGP routes that can be carried by Relays. As of 2015, the 633 global public Internet BGP routing system manages more than 500K 634 routes with linear growth and no signs of router resource exhaustion 635 [BGP]. More recent network emulation studies have also shown that a 636 single Relay can accommodate at least 1M dynamically changing BGP 637 routes even on a lightweight virtual machine, i.e., and without 638 requiring high-end dedicated router hardware. 640 Therefore, assuming each Relay can carry 1M or more routes, this 641 means that at least 1M Clients can be serviced by a single set of 642 Relays. A means of increasing scaling would be to assign a different 643 set of Relays for each set of MSPs. In that case, each Server still 644 peers with one or more Relays, but institutes route filters so that 645 BGP updates are only sent to the specific set of Relays that 646 aggregate the MSP. For example, if the MSP for the AERO link is 647 2001:db8::/32, a first set of Relays could service the MSP 648 2001:db8::/40, a second set of Relays could service 649 2001:db8:0100::/40, a third set could service 2001:db8:0200::/40, 650 etc. 652 Assuming up to 1K sets of Relays, the AERO routing system can then 653 accommodate 1B or more MNPs with no additional overhead (for example, 654 it should be possible to service 1B /64 MNPs taken from a /34 MSP and 655 even more for shorter prefixes). In this way, each set of Relays 656 services a specific set of MSPs that they advertise to the native 657 Internetwork routing system, and each Server configures MSP-specific 658 routes that list the correct set of Relays as next hops. This 659 arrangement also allows for natural incremental deployment, and can 660 support small scale initial deployments followed by dynamic 661 deployment of additional Clients, Servers and Relays without 662 disturbing the already-deployed base. 664 Server and Relays can use the Bidirectional Forwarding Detection 665 (BFD) protocol [RFC5880] to quickly detect link failures that don't 666 result in interface state changes, BGP peer failures, and 667 administrative state changes. BFD is important in environments where 668 rapid response to failures is required for routing reconvergence and, 669 hence, communications continuity. 671 A full discussion of the BGP-based routing system used by AERO is 672 found in [I-D.ietf-rtgwg-atn-bgp]. The system provides for 673 Distributed Mobility Management (DMM) per the distributed mobility 674 anchoring architecture [I-D.ietf-dmm-distributed-mobility-anchoring]. 676 3.4. AERO Addresses 678 A Client's AERO address is an IPv6 link-local address formed from the 679 Client's delegated MNP. Relay, Server and Proxy AERO addresses are 680 assigned from the range fe80::/96 and include an administratively- 681 provisioned value in the lower 32 bits. 683 IPv6 Client AERO addresses encode the Subnet-Router anycast address 684 of a MNP (or non-MNP globally routable prefix) within the least- 685 significant 112 bits of the IPv6 link-local prefix fe80::/16. For 686 example, for the MNP 2001:db8:1000:2000::/56 the corresponding AERO 687 address is fe80:2001:db8:1000:2000::/72. 689 IPv4-compatible Client AERO addresses are based on an IPv4-mapped 690 IPv6 address [RFC4291] formed from an IPv4 MNP and with a prefix 691 length of 96 plus the MNP prefix length. For example, for the IPv4 692 MNP 192.0.2.16/28 the IPv4-mapped IPv6 MNP is: 694 0:0:0:0:0:ffff:192.0.2.16/124 (also written as 695 0:0:0:0:0:ffff:c000:0210/124) 697 The Client then constructs its AERO address with the prefix fe80::/64 698 and with the lower 64 bits of the IPv4-mapped IPv6 address in the 699 interface identifier as: fe80::ffff:192.0.2.16. 701 Mobility Service (MS) AERO addresses (used by Relays, Servers, 702 Gateways and Proxys) are allocated from the range fe80::/96, and MUST 703 be managed for uniqueness. The lower 32 bits of the AERO address 704 includes a unique integer value between 1 and 0xfeffffff (e.g., 705 fe80::1, fe80::2, fe80::3, etc., fe80::feff:ffff) as assigned by the 706 administrative authority for the link. The address fe80:: is the 707 IPv6 link-local Subnet-Router anycast address, and the address range 708 fe80::ff00:0000/104 is reserved for future use. 710 Finally, the address range fe80::/32 is used as the Teredo service 711 prefix for AERO according to the format in Section 4 of [RFC4380] 712 (see Section 3.25 for further discussion). 714 For a full discussion of the above address format and implications 715 for the /64 boundary, see: [I-D.templin-6man-omni-interface]. 717 3.5. Spanning Partitioned AERO Networks (SPAN) 719 An AERO link configured over a single INET appears as a single 720 unified link with a consistent underlying network addressing plan. 721 In that case, all nodes on the link can exchange packets via simple 722 INET encapsulation, since the underlying INET is connected. In 723 common practice, however, an AERO link may be partitioned into 724 multiple "segments", where each segment is a distinct INET 725 potentially managed under a different administrative authority (e.g., 726 as for worldwide aviation service providers such as ARINC, SITA, 727 Inmarsat, etc.). Individual INETs may also themselves be partitioned 728 internally, in which case each internal partition is seen as a 729 separate segment. 731 The addressing plan of each segment is consistent internally but will 732 often bear no relation to the addressing plans of other segments. 733 Each segment is also likely to be separated from others by network 734 security devices (e.g., firewalls, proxies, packet filtering 735 gateways, etc.), and in many cases disjoint segments may not even 736 have any common physical link connections. Therefore, nodes can only 737 be assured of exchanging packets directly with correspondents in the 738 same segment, and not with those in other segments. The only means 739 for joining the segments therefore is through inter-domain peerings 740 between AERO Relays. 742 The same as for traditional campus LANs, multiple AERO link segments 743 can be joined into a single unified link via a virtual bridging 744 service termed "The SPAN". The SPAN performs link-layer packet 745 forwarding between segments (i.e., bridging) without decrementing the 746 network-layer TTL/Hop Limit. The SPAN model is depicted in Figure 2: 748 . . . . . . . . . . . . . . . . . . . . . . . 749 . . 750 . .-(::::::::) . 751 . .-(::::::::::::)-. +-+ . 752 . (:::: Segment A :::)--|R|---+ . 753 . `-(::::::::::::)-' +-+ | . 754 . `-(::::::)-' | . 755 . | . 756 . .-(::::::::) | . 757 . .-(::::::::::::)-. +-+ | . 758 . (:::: Segment B :::)--|R|---+ . 759 . `-(::::::::::::)-' +-+ | . 760 . `-(::::::)-' | . 761 . | . 762 . .-(::::::::) | . 763 . .-(::::::::::::)-. +-+ | . 764 . (:::: Segment C :::)--|R|---+ . 765 . `-(::::::::::::)-' +-+ | . 766 . `-(::::::)-' | . 767 . | . 768 . ..(etc).. x . 769 . . 770 . . 771 . <- AERO Link Bridged by the SPAN -> . 772 . . . . . . . . . . . . . .. . . . . . . . . 774 Figure 2: The SPAN 776 To support the SPAN, AERO links use the Unique Local Address (ULA) 777 prefix fd80::/10 [RFC4193] as the SPAN Service Prefix (SSP). The 778 prefix length intentionally matches the IPv6 link-local prefix 779 (fe80::/10), and enables a simple stateless translation between AERO 780 and SPAN addresses. Additional SSPs can be employed to identify 781 distinct SPAN Routing Transports (SRTs) (see: Section 3.5.1). 783 Each segment in the SPAN assigns a unique sub-prefix of SSP::/96 784 termed the "SPAN Partition Prefix (SPP)". For example, for fd80::/96 785 a first segment could assign fd80::1000/116, a second could assign 786 fd80::2000/116, a third could assign fd80::3000/116, etc. The 787 administrative authorities for each segment must therefore coordinate 788 to assure mutually-exclusive SPP assignments, but internal 789 provisioning of the SPP is an independent local consideration for 790 each administrative authority. 792 SPAN addresses are formed by simply rewriting the upper 16 bits of 793 the corresponding AERO address. For example: 795 o the SPAN address formed from the IPv6 Client AERO address 796 fe80:2001:db8:1000:2000:: is simply fd80:2001:db8:1000:2000:: 798 o the SPAN address formed from the IPv4-compatible Client AERO 799 address fe80::ffff:192.0.2.1 is simply fd80::ffff:192.0.2.1 801 o the SPAN address formed from the administrative AERO address 802 fe80::1001 is simply fd80::1001. 804 AERO Relays serve as bridges to join multiple segments into a unified 805 AERO link over multiple diverse administrative domains. They support 806 the bridging function by first establishing forwarding table entries 807 for their SPPs either via standard BGP routing or static routes. For 808 example, if three Relays ('A', 'B' and 'C') from different segments 809 serviced the SPPs fd80::1000/116, fd80::2000/116 and fd80::3000/116 810 respectively, then the forwarding tables in each Relay are as 811 follows: 813 A: fd80::1000/116->local, fd80::2000/116->B, fd80::3000/116->C 815 B: fd80::1000/116->A, fd80::2000/116->local, fd80::3000/116->C 817 C: fd80::1000/116->A, fd80::2000/116->B, fd80::3000/116->local 819 These forwarding table entries are permanent and never change, since 820 they correspond to fixed infrastructure elements in their respective 821 segments. 823 SPAN Client Prefixes (SCPs) are instead dynamically advertised in the 824 AERO link routing system by Servers and Gateways that provide service 825 for their correspnding MNPs. For example, if three Servers ('D', 'E' 826 and 'F') service the MNPs 2001:db8:1000:2000::/56, 827 2001:db8:3000:4000::/56 and 2001:db8:5000:6000::/56 then the routing 828 system would include: 830 D: fd80:2001:db8:1000:2000::/72 832 E: fd80:2001:db8:3000:4000::/72 834 F: fd80:2001:db8:5000:6000::/72 836 With the SCPs and SPPs in place in each Relay's forwarding table, 837 control and data packets sent between AERO nodes in different 838 segments can therefore be carried over the via encapsulation in a 839 mid-layer IPv6 header known as the "SPAN header". For example, when 840 a source AERO node forwards a packet with IPv6 address 841 2001:db8:1:2::1 to a target AERO node with IPv6 address 842 2001:db8:1000:2000::1, it first encapsulates the packet in a SPAN 843 header with source address set to fd80:2001:db8:1:2:: and destination 844 address set to fd80:2001:db8:1000:2000::. Next, it encapsulates the 845 resulting SPAN packet in an INET header with source address set to 846 its own INET address (e.g., 192.0.2.100) and destination set to the 847 INET address of a Relay (e.g., 192.0.2.1). 849 SPAN encapsulation is based on Generic Packet Tunneling in IPv6 850 [RFC2473]; the encapsulation format in the above example is shown in 851 Figure 3: 853 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 854 | INET Header | 855 | src = 192.0.2.100 | 856 | dst = 192.0.2.1 | 857 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 858 | SPAN Header | 859 | src = fd80:2001:db8:1:2:: | 860 | dst=fd80:2001:db8:1000:2000:: | 861 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 862 | Inner IP Header | 863 | src = 2001:db8:1:2::1 | 864 | dst = 2001:db8:1000:2000::1 | 865 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 866 | | 867 ~ ~ 868 ~ Inner Packet Body ~ 869 ~ ~ 870 | | 871 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 873 Figure 3: SPAN Encapsulation 875 In this format, the inner IP header and packet body are the original 876 IP packet, the SPAN header is an IPv6 header prepared according to 877 [RFC2473], and the INET header is prepared as discussed in 878 Section 3.9. A packet is said to be "forwarded/sent into the SPAN" 879 when it is encapsulated as described above then forwarded via a 880 secured tunnel to a neighboring Relay. 882 This gives rise to a routing system that contains both SCP routes 883 that may change dynamically due to regional node mobility and SPP 884 routes that never change. The Relays can therefore provide link- 885 layer bridging by sending packets into the SPAN instead of network- 886 layer routing according to MNP routes. As a result, opportunities 887 for packet loss due to node mobility between different segments are 888 mitigated. 890 In normal operations, IPv6 ND messages are conveyed to SPP addresses 891 over the SPAN so that specific Proxys, Servers or Gateways can be 892 addressed without being subject to mobility events. Conversely, only 893 the first few packets destined to SCP addresses traverse the SPAN 894 until route optimization can determine a more direct path. 896 3.5.1. SPAN Routing Transports 898 In some cases (e.g., when redundant topologies are needed for fault 899 tolerance and reliability) it may be beneficial to deploy multiple 900 SPAN Routing Transports (SRTs) that act as independent overlay 901 instances. A communication failure in one instance therefore will 902 not affect communications in other instances. 904 This document asserts that up to four SRTs provide a level of safety 905 satisfactory for critical communications such as civil aviation. 906 Each SRT is designated with a color that identifies a different SSP 907 as follows: 909 o Red (default) - corresponds to the SSP fd80::/16 911 o Green - corresponds to the SSP fd81::/16 913 o Blue-1 - corresponds to the SSP fd82::/16 915 o Blue-2 - corresponds to SSP fd83::/16 917 o SSPs fd84::/16 through fdbf::/16 are reserved for future use. 919 3.6. AERO Interface Characteristics 921 AERO interfaces are virtual interfaces configured over one or more 922 underlying interfaces classified as follows: 924 o Native interfaces have global IP addresses that are reachable from 925 any INET correspondent. All Server, Gateway and Relay interfaces 926 are native interfaces, as are INET-facing interfaces of Proxys. 927 Clients connected to native interfaces receive Router 928 Advertisemenets (RAs) with a Client AERO destination address and 929 the P flag set to 0, as discussed in the following sections. 931 o NATed interfaces connect to a private network behind a Network 932 Address Translator (NAT). The NAT does not participate in any 933 AERO control message signaling, but the Server can issue control 934 messages on behalf of the Client. Clients that are behind a NAT 935 are required to send periodic keepalive messages to keep NAT state 936 alive when there are no data packets flowing. If no other 937 periodic messaging service is available, the Client can send 938 Router Solicitation (RS) messages to receive RA replies from its 939 Server(s). Clients connected to NATed interfaces receive RAs with 940 a Teredo-formatted AERO destination address. 942 o Proxyed interfaces connect to an ANET that is separated from the 943 open INET by an AERO Proxy. Unlike NATed and VPNed interfaces, 944 the Proxy can actively issue control messages on behalf of the 945 Client. Clients connected to Proxyed interfaces receive RAs with 946 the P flag set to 1. 948 o VPNed interfaces use security encapsulation to a Virtual Private 949 Network (VPN) server that also acts as an AERO Server. As with 950 NATed links, the Server can issue control messages on behalf of 951 the Client, and the Client can send periodic messages such as RS/ 952 RA to keep the VPN state alive. Clients connected to VPNed 953 interfaces receive RAs with the P flag set to 1 the same as for 954 Proxyed interfaces. 956 o Direct interfaces connect a Client directly to a Server without 957 crossing any ANET/INET paths. An example is a line-of-sight link 958 between a remote pilot and an unmanned aircraft. The same Client 959 considerations apply as for VPNed interfaces above, and the Client 960 receives RA messages with the P flag set to 1. 962 AERO interfaces use SPAN-layer encapsualtion as necessary as 963 discussed in Section 3.5. AERO interfaces use link-layer 964 encapsulation (see: Section 3.9) to exchange packets with AERO link 965 neighbors over Native, NATed or VPNed interfaces. AERO interfaces do 966 not use encapsulation over Proxyed and Direct underlying interfaces. 968 AERO interfaces maintain a neighbor cache for tracking per-neighbor 969 state the same as for any interface. AERO interfaces use ND messages 970 including Router Solicitation (RS), Router Advertisement (RA), 971 Neighbor Solicitation (NS) and Neighbor Advertisement (NA) for 972 neighbor cache management. 974 AERO interfaces send ND messages with an Overlay Multilink Network 975 Interface (OMNI) option formatted as specified in 976 [I-D.templin-6man-omni-interface]. The OMNI option includes prefix 977 registration information and "ifIndex-tuples" containing link 978 information parameters for the AERO interface's underlying 979 interfaces. 981 When encapsulation is used, AERO interface ND messages MAY also 982 include an AERO Source/Target Link-Layer Address Option (S/TLLAO) 983 formatted as shown in Figure 4: 985 0 1 2 3 986 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 1 987 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 988 | Type | Length | ifIndex[1] |SRT| LHS |FMT|P| 989 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 990 ~ Segment Routing List [1] ~ 991 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 992 ~ Link Layer Address [1] ~ 993 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 994 | Port Number [1] | ifIndex[2] |SRT| LHS |FMT|P| 995 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 996 ~ Segment Routing List [2] ~ 997 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 998 ~ Link Layer Address [2] ~ 999 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1000 | Port Number [2] | .... ~ 1001 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ 1002 ~ ... ~ 1003 ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1004 ~ | ifIndex[N] |SRT| LHS |FMT|P| 1005 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1006 ~ Segment Routing List [N] ~ 1007 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1008 ~ Link Layer Address [N] ~ 1009 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1010 | Port Number [N] | Zero Padding (if necessary) ... 1011 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--+-+-+-+-+-+-+-+-+-+-+-+-+-+- 1013 Figure 4: AERO Source/Target Link-Layer Address Option (S/TLLAO) 1014 Format 1016 In this format, Type and Length are set the same as specified for S/ 1017 TLLAOs in [RFC4861], with trailing zero padding octets added as 1018 necessary to produce an integral number of 8 octet blocks. The S/ 1019 TLLAO includes N ifIndex-tuples in correspondence to ifIndex-tuples 1020 that appear in the OMNI option. Each ifIndex-tuple includes the 1021 folllowing information: 1023 o ifIndex[i] - the same value as in the corresponding ifIndex-tuple 1024 included in the OMNI option. 1026 o SRT[i] - a 2-bit "SPAN Routing Transport" value (see: 1027 Section 3.5.1) coded as follows: 1029 * 00 - Red 1031 * 01 - Green 1032 * 10 - Blue-1 1034 * 11 - Blue-2 1036 o LHS[i] - a 3-bit "LookaHead Segments" value that encodes the 1037 number (from 0 to 7) of entries in Segment Routing List [i]. 1039 o FMT[i] - a 2-bit "Format" code. Determines the format of the Link 1040 Layer Address [i] field as follows: 1042 * 00 - Link Layer Address [i] is the lower 32 bits of an 1043 administrative SPAN address (I.e., the SPAN ID). 1045 * 01 - Link Layer Address [i] encodes a native IPv4 address. 1047 * 10 - Link Layer Address [i] encodes a NATed IPv4 address. 1049 * 11 - Link Layer Address [i] encodes an IPv6 address. 1051 o P[i] - the "Port" bit. If set to 0 the Port Number [i] field is 1052 omitted; otherwise, the Port Number [i] field is included. 1054 o Segment Routing List [i] - Includes LHS[i]-many 4 byte 1055 administrative SPAN IDs for Segment routing, in the order to be 1056 visited on the path to the source/target (i.e., ID 1 first, then 1057 ID 2, then ID 3, etc). If LHS[i] is 0, no SPAN IDs are present 1058 and the FMT[i] and Link Layer Address [i] fields are consulted. 1060 o Link Layer Address [i] - Included according to FMT[i], and is 4 1061 bytes in length for SPAN IDs or IPv4 addresses, or 16 bytes in 1062 length for IPv6 addresses. For IP addresses, the value is written 1063 in "obfuscated" form by applying an exclusive-or of all bits of 1064 the address with "all-ones" as discussed in [RFC4380] - see also 1065 Section 3.25. 1067 o Port Number [i] - When present, the field is 2 bytes in length and 1068 immediately follows Link Layer Address [i]. Encodes the upper 1069 layer protocol port number used as the encapsulation source port. 1070 As with the Link-Layer Address, the value is written in 1071 "obfuscated" form. 1073 If an S/TLLAO is included, any ifIndex-tuples correspond to a proper 1074 subset of the OMNI option ifIndex-tuples. Any S/TLLAO ifIndex-tuple 1075 having an ifIndex value that does not appear in an OMNI option 1076 ifindex-tuple is ignored. If the same ifIndex value appears in 1077 multiple ifIndex-tuples, the first tuple is processed and the 1078 remaining tuples are ignored. Any S/TLLAO ifIndex-tuples can 1079 therefore be viewed as inter-dependent extensions of their 1080 corresponidng OMNI option ifIndex-tuples, i.e., the OMNI option and 1081 S/TLLAO are companions that are interpreted in conjunction with each 1082 other. 1084 A Client's AERO interface may be configured over multiple underlying 1085 interface connections. For example, common mobile handheld devices 1086 have both wireless local area network ("WLAN") and cellular wireless 1087 links. These links are often used "one at a time" with low-cost WLAN 1088 preferred and highly-available cellular wireless as a standby, but a 1089 simultaneous-use capability could provide benefits. In a more 1090 complex example, aircraft frequently have many wireless data link 1091 types (e.g. satellite-based, cellular, terrestrial, air-to-air 1092 directional, etc.) with diverse performance and cost properties. 1094 If a Client's multiple underlying interfaces are used "one at a time" 1095 (i.e., all other interfaces are in standby mode while one interface 1096 is active), then ND message OMNI options include only a single 1097 ifIndex-tuple set to constant values. In that case, the Client would 1098 appear to have a single interface but with a dynamically changing 1099 link-layer address. 1101 If the Client has multiple active underlying interfaces, then from 1102 the perspective of ND it would appear to have multiple link-layer 1103 addresses. In that case, ND message OMNI options MAY include 1104 multiple ifIndex-tuples - each with values that correspond to a 1105 specific interface. Every ND message need not include all OMNI and/ 1106 or S/TLLAO ifIndex-tuples; for any ifIndex-tuple not included, the 1107 neighbor considers the status as unchanged. 1109 Relay, Server and Proxy AERO interfaces may be configured over one or 1110 more secured tunnel interfaces. The AERO interface configures both 1111 an AERO address and its corresponding SPAN address, while the 1112 underlying secured tunnel interfaces are either unnumbered or 1113 configure the same SPAN address. The AERO interface encapsulates 1114 each IP packet in a SPAN header and presents the packet to the 1115 underlying secured tunnel interface. For Relays that do not 1116 configure an AERO interface, the secured tunnel interfaces themselves 1117 are exposed to the IP layer with each interface configuring the 1118 Relay's SPAN address. Routing protocols such as BGP therefore run 1119 directly over the Relay's secured tunnel interfaces. For nodes that 1120 configure an AERO interface, routing protocols such as BGP run over 1121 the AERO interface but do not employ SPAN encapsulation. Instead, 1122 the AERO interface presents the routing protocol messages directly to 1123 the underlying secured tunnels without applying encapsulation and 1124 while using the SPAN address as the source address. This distinction 1125 must be honored consistently according to each node's configuration 1126 so that the IP forwarding table will associate discovered IP routes 1127 with the correct interface. 1129 3.7. AERO Interface Initialization 1131 AERO Servers, Proxys and Clients configure AERO interfaces as their 1132 point of attachment to the AERO link. AERO nodes assign the MSPs for 1133 the link to their AERO interfaces (i.e., as a "route-to-interface") 1134 to ensure that packets with destination addresses covered by an MNP 1135 not explicitly assigned to a non-AERO interface are directed to the 1136 AERO interface. 1138 AERO interface initialization procedures for Servers, Proxys, Clients 1139 and Relays are discussed in the following sections. 1141 3.7.1. AERO Server/Gateway Behavior 1143 When a Server enables an AERO interface, it assigns AERO/SPAN 1144 addresses and configures permanent neighbor cache entries for 1145 neighbors in the same SPAN segment by consulting the ROS list for the 1146 segment. The Server also configures secured tunnels with one or more 1147 neighboring Relays and engages in a BGP routing protocol session with 1148 each Relay. 1150 The AERO interface provides a single interface abstraction to the IP 1151 layer, but internally comprises multiple secured tunnels as well as 1152 an NBMA nexus for sending encapsulated data packets to AERO interface 1153 neighbors. The Server further configures a service to facilitate ND/ 1154 PD exchanges with AERO Clients and manages per-Client neighbor cache 1155 entries and IP forwarding table entries based on control message 1156 exchanges. 1158 Gateways are simply Servers that run a dynamic routing protocol to 1159 redistribute routes between the AERO interface and INET/EUN 1160 interfaces (see: Section 3.3). The Gateway provisions MNPs to 1161 networks on the INET/EUN interfaces (i.e., the same as a Client would 1162 do) and advertises the MSP(s) for the AERO link over the INET/EUN 1163 interfaces. The Gateway further provides an attachment point of the 1164 AERO link to the non-MNP-based global topology. 1166 3.7.2. AERO Proxy Behavior 1168 When a Proxy enables an AERO interface, it assigns AERO/SPAN 1169 addresses and configures permanent neighbor cache entries the same as 1170 for Servers. The Proxy also configures secured tunnels with one or 1171 more neighboring Relays and maintains per-Client neighbor cache 1172 entries based on control message exchanges. 1174 3.7.3. AERO Client Behavior 1176 When a Client enables an AERO interface, it sends RS messages with 1177 ND/PD parameters over its underlying interfaces to a Server in the 1178 MAP list, which returns an RA message with corresponding parameters. 1179 (The RS/RA messages may pass through a Proxy in the case of a 1180 Client's Proxyed interface.) 1182 3.7.4. AERO Relay Behavior 1184 AERO Relays need not connect directly to the AERO link, since they 1185 operate as link-layer forwarding devices instead of network layer 1186 routers. Configuration of AERO interfaces on Relays is therefore 1187 OPTIONAL, e.g., if an administrative interface is needed. Relays 1188 configure secured tunnels with Servers, Proxys and other Relays; they 1189 also configure AERO/SPAN addresses and permanent neighbor cache 1190 entries the same as Servers. Relays engage in a BGP routing protocol 1191 session with a subset of the Servers on the local SPAN segment, and 1192 with other Relays on the SPAN (see: Section 3.3). 1194 3.8. AERO Interface Neighbor Cache Maintenance 1196 Each AERO interface maintains a conceptual neighbor cache that 1197 includes an entry for each neighbor it communicates with on the AERO 1198 link per [RFC4861]. AERO interface neighbor cache entries are said 1199 to be one of "permanent", "symmetric", "asymmetric" or "proxy". 1201 Permanent neighbor cache entries are created through explicit 1202 administrative action; they have no timeout values and remain in 1203 place until explicitly deleted. AERO Servers and Proxys maintain 1204 permanent neighbor cache entries for all other Servers and Proxys 1205 within the same SPAN segment. Each entry maintains the mapping 1206 between the neighbor's network-layer AERO address and corresponding 1207 INET address. The list of all permanent neighbor cache entries for 1208 the SPAN segment is maintained in the segment's ROS list. 1210 Symmetric neighbor cache entries are created and maintained through 1211 RS/RA exchanges as specified in Section 3.15, and remain in place for 1212 durations bounded by ND/PD lifetimes. AERO Servers maintain 1213 symmetric neighbor cache entries for each of their associated 1214 Clients, and AERO Clients maintain symmetric neighbor cache entries 1215 for each of their associated Servers. The list of all Servers on the 1216 AERO link is maintained in the link's MAP list. 1218 Asymmetric neighbor cache entries are created or updated based on 1219 route optimization messaging as specified in Section 3.17, and are 1220 garbage-collected when keepalive timers expire. AERO ROSs maintain 1221 asymmetric neighbor cache entries for active targets with lifetimes 1222 based on ND messaging constants. Asymmetric neighbor cache entries 1223 are unidirectional since only the ROS (and not the ROR) creates an 1224 entry. 1226 Proxy neighbor cache entries are created and maintained by AERO 1227 Proxys when they process Client/Server ND/PD exchanges, and remain in 1228 place for durations bounded by ND/PD lifetimes. AERO Proxys maintain 1229 proxy neighbor cache entries for each of their associated Clients. 1230 Proxy neighbor cache entries track the Client state and the address 1231 of the Client's associated Server(s). 1233 To the list of neighbor cache entry states in Section 7.3.2 of 1234 [RFC4861], Proxy and Server AERO interfaces add an additional state 1235 DEPARTED that applies to symmetric and proxy neighbor cache entries 1236 for Clients that have recently departed. The interface sets a 1237 "DepartTime" variable for the neighbor cache entry to "DEPART_TIME" 1238 seconds. DepartTime is decremented unless a new ND message causes 1239 the state to return to REACHABLE. While a neighbor cache entry is in 1240 the DEPARTED state, packets destined to the target Client are 1241 forwarded to the Client's new location instead of being dropped. 1242 When DepartTime decrements to 0, the neighbor cache entry is deleted. 1243 It is RECOMMENDED that DEPART_TIME be set to the default constant 1244 value REACHABLE_TIME plus 10 seconds (40 seconds by default) to allow 1245 a window for packets in flight to be delivered while stale route 1246 optimization state may be present. 1248 When an ROR receives an authentic NS message used for route 1249 optimization, it searches for a symmetric neighbor cache entry for 1250 the target Client. The ROR then returns a solicited NA message 1251 without creating a neighbor cache entry for the ROS, but creates or 1252 updates a target Client "Report List" entry for the ROS and sets a 1253 "ReportTime" variable for the entry to REPORT_TIME seconds. The ROR 1254 resets ReportTime when it receives a new authentic NS message, and 1255 otherwise decrements ReportTime while no authentic NS messages have 1256 been received. It is RECOMMENDED that REPORT_TIME be set to the 1257 default constant value REACHABLE_TIME plus 10 seconds (40 seconds by 1258 default) to allow a window for route optimization to converge before 1259 ReportTime decrements below REACHABLE_TIME. 1261 When the ROS receives a solicited NA message response to its NS 1262 message used for route optimization, it creates or updates an 1263 asymmetric neighbor cache entry for the target network-layer and 1264 link-layer addresses. The ROS then (re)sets ReachableTime for the 1265 neighbor cache entry to REACHABLE_TIME seconds and uses this value to 1266 determine whether packets can be forwarded directly to the target, 1267 i.e., instead of via a default route. The ROS otherwise decrements 1268 ReachableTime while no further solicited NA messages arrive. It is 1269 RECOMMENDED that REACHABLE_TIME be set to the default constant value 1270 30 seconds as specified in [RFC4861]. 1272 AERO nodes also use the value MAX_UNICAST_SOLICIT to limit the number 1273 of NS keepalives sent when a correspondent may have gone unreachable, 1274 the value MAX_RTR_SOLICITATIONS to limit the number of RS messages 1275 sent without receiving an RA and the value MAX_NEIGHBOR_ADVERTISEMENT 1276 to limit the number of unsolicited NAs that can be sent based on a 1277 single event. It is RECOMMENDED that MAX_UNICAST_SOLICIT, 1278 MAX_RTR_SOLICITATIONS and MAX_NEIGHBOR_ADVERTISEMENT be set to 3 the 1279 same as specified in [RFC4861]. 1281 Different values for DEPART_TIME, REPORT_TIME, REACHABLE_TIME, 1282 MAX_UNICAST_SOLICIT, MAX_RTR_SOLCITATIONS and 1283 MAX_NEIGHBOR_ADVERTISEMENT MAY be administratively set; however, if 1284 different values are chosen, all nodes on the link MUST consistently 1285 configure the same values. Most importantly, DEPART_TIME and 1286 REPORT_TIME SHOULD be set to a value that is sufficiently longer than 1287 REACHABLE_TIME to avoid packet loss due to stale route optimization 1288 state. 1290 3.9. AERO Interface Encapsulation and Re-encapsulation 1292 In some instances, AERO interfaces insert a mid-layer IPv6 header 1293 known as the SPAN header as discussed in the following sections. 1294 After either inserting or omitting the SPAN header, the AERO 1295 interface inserts an outer encapsulation header as discussed below. 1297 AERO interfaces avoid outer encapsulation over Direct underlying 1298 interfaces and Proxyed underlying interfaces for which the first-hop 1299 access router is AERO-aware. Other AERO interfaces encapsulate 1300 packets according to whether they are entering the AERO interface 1301 from the network layer or if they are being re-admitted into the same 1302 AERO link they arrived on. This latter form of encapsulation is 1303 known as "re-encapsulation". 1305 For packets entering the AERO interface from the network layer, the 1306 AERO interface copies the "TTL/Hop Limit", "Type of Service/Traffic 1307 Class" [RFC2983], "Flow Label"[RFC6438] (for IPv6) and "Congestion 1308 Experienced" [RFC3168] values in the inner packet's IP header into 1309 the corresponding fields in the SPAN and outer encapsulation 1310 header(s). 1312 For packets undergoing re-encapsulation, the AERO interface instead 1313 copies these values from the original encapsulation header into the 1314 new encapsulation header, i.e., the values are transferred between 1315 encapsulation headers and *not* copied from the encapsulated packet's 1316 network-layer header. (Note especially that by copying the TTL/Hop 1317 Limit between encapsulation headers the value will eventually 1318 decrement to 0 if there is a (temporary) routing loop.) For IPv4 1319 encapsulation/re-encapsulation, the AERO interface sets the DF bit as 1320 discussed in Section 3.12. 1322 AERO interfaces configured over native and NATed underlying 1323 interfaces encapsulate packets in INET headers according to the next 1324 hop determined in the forwarding algorithm in Section 3.13. If the 1325 next hop is reached via a secured tunnel, the AERO interface uses an 1326 encapsulation format specific to the secured tunnel type (see: 1327 Section 6). If the next hop is reached via an unsecured underlying 1328 interface, the AERO interface instead uses Generic UDP Encapsulation 1329 (GUE) [I-D.ietf-intarea-gue] or an alternate minimal encapsulation 1330 format Appendix A. 1332 When GUE encapsulation is used, the AERO interface next sets the UDP 1333 source port to a constant value that it will use in each successive 1334 packet it sends, and sets the UDP length field to the length of the 1335 SPAN packet plus 8 bytes for the UDP header itself plus the length of 1336 the GUE header (or 0 if GUE direct IP encapsulation is used). For 1337 packets sent to a Server or Relay, the AERO interface sets the UDP 1338 destination port to 8060, i.e., the IANA-registered port number for 1339 AERO. For packets sent to a Client, the AERO interface sets the UDP 1340 destination port to the port value stored in the neighbor cache entry 1341 for this Client. The AERO interface then either includes or omits 1342 the UDP checksum according to the GUE specification. 1344 AERO interfaces observes the packet sizing and fragmentation 1345 considerations found in Section 3.12. 1347 3.10. AERO Interface Decapsulation 1349 AERO interfaces decapsulate packets destined either to the AERO node 1350 itself or to a destination reached via an interface other than the 1351 AERO interface the packet was received on. When the encapsulated 1352 packet arrives in multiple SPAN fragments, the AERO interface 1353 reassembles as discussed in Section 3.12. Further decapsulation 1354 steps are performed according to the appropriate encapsulation format 1355 specification. 1357 3.11. AERO Interface Data Origin Authentication 1359 AERO nodes employ simple data origin authentication procedures. In 1360 particular: 1362 o AERO Relays, Servers and Proxys accept encapsulated data packets 1363 and control messages received from secured tunnels via the SPAN. 1365 o AERO Servers and Proxys accept encapsulated data packets and NS 1366 messages used for Neighbor Unreachability Detection (NUD) received 1367 from a member of the ROS list. 1369 o AERO Proxys and Clients accept packets that originate from within 1370 the same secured ANET. 1372 o AERO Clients and Gateways accept packets from downstream network 1373 correspondents based on ingress filtering. 1375 AERO nodes silently drop any packets that do not satisfy the above 1376 data origin authentication procedures. Further security 1377 considerations are discussed inSection 6. 1379 3.12. AERO Interface MTU and Fragmentation 1381 IPv6 underlying interfaces are REQUIRED to configure a minimum 1382 Maximum Transmission Unit (MTU) of 1280 bytes [RFC8200]. The minimum 1383 MTU for IPv4 underlying interfaces is only 68 bytes [RFC1122], 1384 meaning that a packet smaller than the IPv6 MTU may require 1385 fragmentation when IPv4 encapsulation is used. Therefore, the Don't 1386 Fragment (DF) bit in the IPv4 encapsulation header MUST be set to 0. 1388 The AERO interface configures an MTU of 9180 bytes [RFC2492]; the 1389 size is therefore not a reflection of the underlying interface MTUs, 1390 but rather determines the largest packet the AERO interface can 1391 forward or reassemble. The AERO interface therefore accommodates IP 1392 packets up to 9180 bytes while generating IPv6 Path MTU Discovery 1393 (PMTUD) Packet Too Big (PTB) messages [RFC8201] as necessary (see 1394 below). 1396 AERO interfaces employ mid-layer IPv6 encapsulation and 1397 fragmentation/reassembly per [RFC2473] (aka "SPAN encapsulation") to 1398 accommodate the 9180 byte MTU. The AERO interface returns 1399 internally-generated PTB messages for packets admitted into the 1400 interface that it deems too large (e.g., according to link 1401 performance characteristics, reassembly cost, etc.) while either 1402 dropping or forwarding the packet as necessary. The AERO interface 1403 performs PMTUD even if the destination appears to be on the same link 1404 since intermediate AERO link nodes may return a PTB. This ensures 1405 that the path MTU is adaptive and reflects the current path used for 1406 a given data flow. 1408 AERO nodes perform SPAN encapsulation and fragmentation/reassembly as 1409 follows: 1411 o When a node's AERO interface sends a packet over a Proxyed, VPNed 1412 or Direct underlying interface, it sends without SPAN 1413 encapsulation if the packet is no larger than the underlying 1414 interface MTU. Otherwise, it encapsulates the packet in a SPAN 1415 header with source address set to the node's own SPAN address and 1416 destination set to the SPAN address of the link-layer peer Proxy, 1417 Server or Client on the underlying interface. The AERO interface 1418 then uses IPv6 fragmentation to break the encapsulated packet into 1419 a minimum number of non-overlapping fragments, where the largest 1420 fragment size is determined by the underlying interface MTU and 1421 the smallest fragment is no smaller than 640 bytes. The AERO 1422 interface then sends the fragments to the link-layer peer, which 1423 reassembles before forwarding toward the final destination. 1425 o When a node's AERO interface sends a packet over a Native or 1426 NATted underlying interface, it sends packets no larger than 1280 1427 bytes without SPAN encapsulation if the destination is reached via 1428 an INET address within the same SPAN segment. Otherwise, it 1429 encapsulates the packet in a SPAN header with source address set 1430 to the node's SPAN address and destination set to the SPAN address 1431 of the next hop AERO node toward the final destination. The AERO 1432 interface then uses IPv6 fragmentation to break the encapsulated 1433 packet into a minimum number of non-overlapping fragments, where 1434 the largest fragment size is 1280 bytes and the smallest fragment 1435 is no smaller than 640 bytes. The AERO interface then sends the 1436 fragments to the SPAN destination, which reassembles before 1437 forwarding toward the final destination. 1439 In order to avoid a "tiny fragment" attack, AERO interfaces 1440 unconditionally drop all SPAN fragments smaller than 640 bytes. In 1441 order to set the correct context for reassembly, the AERO interface 1442 that inserts a SPAN header MUST also be the one that inserts the IPv6 1443 Fragment Header Identification value. Although all fragmnets of the 1444 same fragmented SPAN packet are typically sent via the same 1445 underlying interface, this is not strictly required since all 1446 fragments will arrive at the AERO interface that performs reassembly 1447 even if they travel over different paths. 1449 Note that the AERO interface can forward large packets via 1450 encapsulation and fragmentation while at the same time returning 1451 advisory PTB messages, e.g., subject to rate limiting. The receiving 1452 node that performs reassembly can also send advisory PTB messages if 1453 reassembly conditions become unfavorable. The AERO interface can 1454 therefore continuously forward large packets without loss while 1455 returning advisory messages recommending a smaller size. Advisory 1456 PTB messages are differentiated from PTB messages that report loss by 1457 setting the Code field in the ICMPv6 message header to the value 1. 1458 This document therefore updates [RFC4443] and [RFC8201]. 1460 3.13. AERO Interface Forwarding Algorithm 1462 IP packets enter a node's AERO interface either from the network 1463 layer (i.e., from a local application or the IP forwarding system) or 1464 from the link layer (i.e., from an AERO interface neighbor). All 1465 packets entering a node's AERO interface first undergo data origin 1466 authentication as discussed in Section 3.11. Packets that satisfy 1467 data origin authentication are processed further, while all others 1468 are dropped silently. 1470 Packets that enter the AERO interface from the network layer are 1471 forwarded to an AERO interface neighbor. Packets that enter the AERO 1472 interface from the link layer are either re-admitted into the AERO 1473 link or forwarded to the network layer where they are subject to 1474 either local delivery or IP forwarding. In all cases, the AERO 1475 interface itself MUST NOT decrement the network layer TTL/Hop-count 1476 since its forwarding actions occur below the network layer. 1478 AERO interfaces may have multiple underlying interfaces and/or 1479 neighbor cache entries for neighbors with multiple ifIndex-tuple 1480 registrations (see Section 3.6). The AERO interface uses traffic 1481 classifiers (e.g., DSCP value, port number, etc.) to select an 1482 outgoing underlying interface for each packet based on the node's own 1483 QoS preferences, and also to select a destination link-layer address 1484 based on the neighbor's underlying interface with the highest 1485 preference. AERO implementations SHOULD allow for QoS preference 1486 values to be modified at runtime through network management. 1488 If multiple outgoing interfaces and/or neighbor interfaces have a 1489 preference of "high", the AERO node replicates the packet and sends 1490 one copy via each of the (outgoing / neighbor) interface pairs; 1491 otherwise, the node sends a single copy of the packet via an 1492 interface with the highest preference. AERO nodes keep track of 1493 which underlying interfaces are currently "reachable" or 1494 "unreachable", and only use "reachable" interfaces for forwarding 1495 purposes. 1497 The following sections discuss the AERO interface forwarding 1498 algorithms for Clients, Proxys, Servers and Relays. In the following 1499 discussion, a packet's destination address is said to "match" if it 1500 is the same as a cached address, or if it is covered by a cached 1501 prefix (which may be encoded in an AERO address). 1503 3.13.1. Client Forwarding Algorithm 1505 When an IP packet enters a Client's AERO interface from the network 1506 layer the Client searches for an asymmetric neighbor cache entry that 1507 matches the destination. If there is a match, the Client uses one or 1508 more "reachable" neighbor interfaces in the entry for packet 1509 forwarding. If there is no asymmetric neighbor cache entry, the 1510 Client instead forwards the packet toward a Server (the packet is 1511 intercepted by a Proxy if there is a Proxy on the path). The Client 1512 encapuslates the packet in an IPv6 header and fragments if necessary 1513 according to MTU requirements (see: Section 3.12). 1515 When an IP packet enters a Client's AERO interface from the link- 1516 layer, if the destination matches one of the Client's MNPs or link- 1517 local addresses the Client reassembles and decapsulates as necessary 1518 and delivers the inner packet to the network layer. Otherwise, the 1519 Client drops the packet and MAY return a network-layer ICMP 1520 Destination Unreachable message subject to rate limiting (see: 1521 Section 3.14). 1523 3.13.2. Proxy Forwarding Algorithm 1525 For control messages originating from or destined to a Client, the 1526 Proxy intercepts the message and updates its proxy neighbor cache 1527 entry for the Client. The Proxy then forwards a (proxyed) copy of 1528 the control message. (For example, the Proxy forwards a proxied 1529 version of a Client's NS/RS message to the target neighbor, and 1530 forwards a proxied version of the NA/RA reply to the Client.) 1532 When the Proxy receives a data packet from a Client within the ANET, 1533 ithe Proxy reassembles and re-fragments if necessary then searches 1534 for an asymmetric neighbor cache entry that matches the destination 1535 and forwards as follows: 1537 o if the destination matches an asymmetric neighbor cache entry, the 1538 Proxy uses one or more "reachable" neighbor interfaces in the 1539 entry for packet forwarding using SPAN encapsualtion and Segment 1540 Routing if necessary with the final destination set to the 1541 neighbor's SPAN address. If the neighbor interface is in the same 1542 SPAN segment, the Proxy forwards the packet directly to the 1543 neighbor; otherwise, it forwards the packet to a Relay. 1545 o else, the Proxy encapsulates and forwards the packet to a Relay 1546 while using the SPAN address corresponding to the packet's 1547 destination as the SPAN destination address. 1549 When the Proxy receives an encapsulated data packet from an INET 1550 neighbor or from a secured tunnel from a Relay, it accepts the packet 1551 only if data origin authentication succeeds and if there is a proxy 1552 neighbor cache entry that matches the inner destination. Next, the 1553 Proxy reassembles the packet (if necessary) and continues processing. 1555 Next if reassembly is complete and the neighbor cache state is 1556 REACHABLE, the Proxy either drops and returns a PTB (see: 1557 Section 3.12) or forwards the packet to the Client while performing 1558 SPAN encapsulation and re-fragmentation to the ANET MTU size if 1559 necessary. If the neighbor cache entry state is DEPARTED, the Proxy 1560 instead changes the SPAN destination address to the address of the 1561 new Server and forwards it to a Relay while performing re- 1562 fragmentation to 1280 bytes if necessary. 1564 3.13.3. Server/Gateway Forwarding Algorithm 1566 For control messages destined to a target Client's AERO address that 1567 are received from a secured tunnel, the Server intercepts the message 1568 and sends an appropriate response on behalf of the Client. (For 1569 example, the Server sends an NA message reply in response to an NS 1570 message directed to one of its associated Clients.) If the Client's 1571 neighbor cache entry is in the DEPARTED state, however, the Server 1572 instead forwards the packet to the Client's new Server as discussed 1573 in Section 3.19. 1575 When the Server receives an encapsulated data packet from an INET 1576 neighbor or from a secured tunnel, it accepts the packet only if data 1577 origin authentication succeeds. If the SPAN destination address is 1578 its own address, the Server continues processing as follows: 1580 o if the destination matches a symmetric neighbor cache entry in the 1581 REACHABLE state the Server prepares the packet for forwarding to 1582 the destination Client. The Server first reassembles (if 1583 necessary) and forwards the packet (while re-fragmenting if 1584 necessary) as specified inSection 3.12. 1586 o else, if the destination matches a symmetric neighbor cache entry 1587 in the DEPARETED state the Server re-encapsulates the packet and 1588 forwards it using the SPAN address of the Client's new Server as 1589 the destination. 1591 o else, if the destination matches an asymmetric neighbor cache 1592 entry, the Server uses one or more "reachable" neighbor interfaces 1593 in the entry for packet forwarding via the local INET if the 1594 neighbor is in the same SPAN segment or using SPAN encapsualtion 1595 and Segment Routing if necessary with the final destination set to 1596 the neighbor's SPAN address otherwise. 1598 o else, if the destination is an AERO address that is not assigned 1599 on the AERO interface the Server drops the packet. 1601 o else, the Server (acting as a Gateway) reassembles if necessary, 1602 decapsulates the packet and releases it to the network layer for 1603 local delivery or IP forwarding. Based on the information in the 1604 forwarding table, the network layer may return the packet to the 1605 same AERO interface in which case further processing occurs as 1606 below. (Note that this arrangement accommodates common 1607 implementations in which the IP forwarding table is not accessible 1608 from within the AERO interface. If the AERO interface can 1609 directly access the IP forwarding table (such as for in-kernel 1610 implementations) the forwarding table lookup can instead be 1611 performed internally from within the AERO interface itself.) 1613 When the Server's AERO interface receives a data packet from the 1614 network layer or from a VPNed or Direct Client, it performs SPAN 1615 encapsualtion and fragmentation if necessary, then processes the 1616 packet according to the network-layer destination address as follows: 1618 o if the destination matches a symmetric or asymmetric neighbor 1619 cache entry the Server processes the packet as above. 1621 o else, the Server encapsulates the packet and forwards it to a 1622 Relay using its own SPAN address as the source and the SPAN 1623 address corresponding to the destination as the destination. 1625 3.13.4. Relay Forwarding Algorithm 1627 Relays forward packets over secured tunnels the same as any IP 1628 router. When the Relay receives an encapsulated packet via a secured 1629 tunnel, it removes the INET header and searches for a forwarding 1630 table entry that matches the destination address in the next header. 1631 The Relay then processes the packet as follows: 1633 o if the destination matches one of the Relay's own addresses, the 1634 Relay submits the packet for local delivery. 1636 o else, if the destination matches a forwarding table entry the 1637 Relay forwards the packet via a secured tunnel to the next hop. 1638 If the destination matches an MSP without matching an MNP, 1639 however, the Relay instead drops the packet and returns an ICMP 1640 Destination Unreachable message subject to rate limiting (see: 1641 Section 3.14). 1643 o else, the Relay drops the packet and returns an ICMP Destination 1644 Unreachable as above. 1646 As for any IP router, the Relay decrements the TTL/Hop Limit when it 1647 forwards the packet. Therefore, only the Hop Limit in the SPAN 1648 header is decremented, and not the TTL/Hop Limit in the inner packet 1649 header. 1651 3.14. AERO Interface Error Handling 1653 When an AERO node admits a packet into the AERO interface, it may 1654 receive link-layer or network-layer error indications. 1656 A link-layer error indication is an ICMP error message generated by a 1657 router in the INET on the path to the neighbor or by the neighbor 1658 itself. The message includes an IP header with the address of the 1659 node that generated the error as the source address and with the 1660 link-layer address of the AERO node as the destination address. 1662 The IP header is followed by an ICMP header that includes an error 1663 Type, Code and Checksum. Valid type values include "Destination 1664 Unreachable", "Time Exceeded" and "Parameter Problem" 1665 [RFC0792][RFC4443]. (AERO interfaces ignore all link-layer IPv4 1666 "Fragmentation Needed" and IPv6 "Packet Too Big" messages since they 1667 only emit packets that are guaranteed to be no larger than the IP 1668 minimum link MTU as discussed in Section 3.12.) 1670 The ICMP header is followed by the leading portion of the packet that 1671 generated the error, also known as the "packet-in-error". For 1672 ICMPv6, [RFC4443] specifies that the packet-in-error includes: "As 1673 much of invoking packet as possible without the ICMPv6 packet 1674 exceeding the minimum IPv6 MTU" (i.e., no more than 1280 bytes). For 1675 ICMPv4, [RFC0792] specifies that the packet-in-error includes: 1676 "Internet Header + 64 bits of Original Data Datagram", however 1677 [RFC1812] Section 4.3.2.3 updates this specification by stating: "the 1678 ICMP datagram SHOULD contain as much of the original datagram as 1679 possible without the length of the ICMP datagram exceeding 576 1680 bytes". 1682 The link-layer error message format is shown in Figure 5 (where, "L2" 1683 and "L3" refer to link-layer and network-layer, respectively): 1685 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1686 ~ ~ 1687 | L2 IP Header of | 1688 | error message | 1689 ~ ~ 1690 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1691 | L2 ICMP Header | 1692 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 1693 ~ ~ P 1694 | IP and other encapsulation | a 1695 | headers of original L3 packet | c 1696 ~ ~ k 1697 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ e 1698 ~ ~ t 1699 | IP header of | 1700 | original L3 packet | i 1701 ~ ~ n 1702 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1703 ~ ~ e 1704 | Upper layer headers and | r 1705 | leading portion of body | r 1706 | of the original L3 packet | o 1707 ~ ~ r 1708 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 1710 Figure 5: AERO Interface Link-Layer Error Message Format 1712 The AERO node rules for processing these link-layer error messages 1713 are as follows: 1715 o When an AERO node receives a link-layer Parameter Problem message, 1716 it processes the message the same as described as for ordinary 1717 ICMP errors in the normative references [RFC0792][RFC4443]. 1719 o When an AERO node receives persistent link-layer Time Exceeded 1720 messages, the IP ID field may be wrapping before earlier fragments 1721 awaiting reassembly have been processed. In that case, the node 1722 should begin including integrity checks and/or institute rate 1723 limits for subsequent packets. 1725 o When an AERO node receives persistent link-layer Destination 1726 Unreachable messages in response to encapsulated packets that it 1727 sends to one of its asymmetric neighbor correspondents, the node 1728 should process the message as an indication that a path may be 1729 failing, and optionally initiate NUD over that path. If it 1730 receives Destination Unreachable messages over multiple paths, the 1731 node should allow future packets destined to the correspondent to 1732 flow through a default route and re-initiate route optimization. 1734 o When an AERO Client receives persistent link-layer Destination 1735 Unreachable messages in response to encapsulated packets that it 1736 sends to one of its symmetric neighbor Servers, the Client should 1737 mark the path as unusable and use another path. If it receives 1738 Destination Unreachable messages on many or all paths, the Client 1739 should associate with a new Server and release its association 1740 with the old Server as specified in Section 3.19.5. 1742 o When an AERO Server receives persistent link-layer Destination 1743 Unreachable messages in response to encapsulated packets that it 1744 sends to one of its symmetric neighbor Clients, the Server should 1745 mark the underlying path as unusable and use another underlying 1746 path. 1748 o When an AERO Server or Proxy receives link-layer Destination 1749 Unreachable messages in response to an encapsulated packet that it 1750 sends to one of its permanent neighbors, it treats the messages as 1751 an indication that the path to the neighbor may be failing. 1752 However, the dynamic routing protocol should soon reconverge and 1753 correct the temporary outage. 1755 When an AERO Relay receives a packet for which the network-layer 1756 destination address is covered by an MSP, if there is no more- 1757 specific routing information for the destination the Relay drops the 1758 packet and returns a network-layer Destination Unreachable message 1759 subject to rate limiting. The Relay writes the network-layer source 1760 address of the original packet as the destination address and uses 1761 one of its non link-local addresses as the source address of the 1762 message. 1764 When an AERO node receives an encapsulated packet for which the 1765 reassembly buffer it too small, it drops the packet and returns a 1766 network-layer Packet Too Big (PTB) message. The node first writes 1767 the MRU value into the PTB message MTU field, writes the network- 1768 layer source address of the original packet as the destination 1769 address and writes one of its non link-local addresses as the source 1770 address. 1772 3.15. AERO Router Discovery, Prefix Delegation and Autoconfiguration 1774 AERO Router Discovery, Prefix Delegation and Autoconfiguration are 1775 coordinated as discussed in the following Sections. 1777 3.15.1. AERO ND/PD Service Model 1779 Each AERO Server on the link configures a PD service to facilitate 1780 Client requests. Each Server is provisioned with a database of MNP- 1781 to-Client ID mappings for all Clients enrolled in the AERO service, 1782 as well as any information necessary to authenticate each Client. 1783 The Client database is maintained by a central administrative 1784 authority for the AERO link and securely distributed to all Servers, 1785 e.g., via the Lightweight Directory Access Protocol (LDAP) [RFC4511], 1786 via static configuration, etc. Clients receive the same service 1787 regardless of the Servers they select. 1789 AERO Clients and Servers use ND messages to maintain neighbor cache 1790 entries. AERO Servers configure their AERO interfaces as advertising 1791 NBMA interfaces, and therefore send unicast RA messages with a short 1792 Router Lifetime value (e.g., REACHABLE_TIME seconds) in response to a 1793 Client's RS message. Thereafter, Clients send additional RS messages 1794 to keep Server state alive. 1796 AERO Clients and Servers include PD parameters in RS/RA messages (see 1797 [I-D.templin-6man-dhcpv6-ndopt] for ND/PD alternatives). The unified 1798 ND/PD messages are exchanged between Client and Server according to 1799 the prefix management schedule required by the PD service. If the 1800 Client knows its MNP in advance, it can instead employ prefix 1801 registration by including its AERO address as the source address of 1802 an RS message and with an OMNI option with valid prefix registration 1803 information for the MNP. If the Server (and Proxy) accept the 1804 Client's MNP assertion, they inject the prefix into the routing 1805 system and establish the necessary neighbor cache state. 1807 The following sections specify the Client and Server behavior. 1809 3.15.2. AERO Client Behavior 1811 AERO Clients discover the addresses of Servers in a similar manner as 1812 described in [RFC5214]. Discovery methods include static 1813 configuration (e.g., from a flat-file map of Server addresses and 1814 locations), or through an automated means such as Domain Name System 1815 (DNS) name resolution [RFC1035]. Alternatively, the Client can 1816 discover Server addresses through a layer 2 data link login exchange, 1817 or through a unicast RA response to a multicast/anycast RS as 1818 described below. In the absence of other information, the Client can 1819 resolve the DNS Fully-Qualified Domain Name (FQDN) 1820 "linkupnetworks.[domainname]" where "linkupnetworks" is a constant 1821 text string and "[domainname]" is a DNS suffix for the AERO link 1822 (e.g., "example.com"). 1824 To associate with a Server, the Client acts as a requesting router to 1825 request MNPs. The Client prepares an RS message with PD parameters 1826 and includes a Nonce and Timestamp option if the Client needs to 1827 correlate RA replies. If the Client already knows the Server's AERO 1828 address, it includes the AERO address as the network-layer 1829 destination address; otherwise, it includes the link-scoped All- 1830 Routers multicast (ff02::2) or Subnet-Router anycast (fe80::) address 1831 as the network-layer destination. If the Client already knows its 1832 own AERO address, it uses the AERO address as the network-layer 1833 source address; otherwise, it uses the unspecified IPv6 address 1834 (::/128) as the network-layer source address. 1836 The Client next includes an OMNI option in the RS message to register 1837 its link-layer information with the Server. The Client sets the OMNI 1838 option prefix registration information according to the MNP, and 1839 includes an ifIndex-tuple with S set to '1' corresponding to the 1840 underlying interface over which the Client will send the RS message. 1841 The Client MAY include additional ifIndex-tuples specific to other 1842 underlying interfaces. The Client MAY also include an SLLAO 1843 corresponding to the OMNI option ifIndex-tuple with S set to '1'. 1845 The Client then sends the RS message (either directly via Direct 1846 interfaces, via INET encapsulation for NATed interfaces, via a VPN 1847 for VPNed interfaces, via a Proxy for proxyed interfaces or via a 1848 Relay for native interfaces) and waits for an RA message reply (see 1849 Section 3.15.3). The Client retries up to MAX_RTR_SOLICITATIONS 1850 times until an RA is received. If the Client receives no RAs, or if 1851 it receives an RA with Router Lifetime set to 0, the Client SHOULD 1852 abandon this Server and try another Server. Otherwise, the Client 1853 processes the PD information found in the RA message. 1855 Next, the Client creates a symmetric neighbor cache entry with the 1856 Server's AERO address as the network-layer address and the Server's 1857 encapsulation and/or link-layer addresses as the link-layer address. 1858 The Client records the RA Router Lifetime field value in the neighbor 1859 cache entry as the time for which the Server has committed to 1860 maintaining the MNP in the routing system via this underlying 1861 interface, and caches the other RA configuration information 1862 including Cur Hop Limit, M and O flags, Reachable Time and Retrans 1863 Timer. The Client then autoconfigures AERO addresses for each of the 1864 delegated MNPs and assigns them to the AERO interface. The Client 1865 also caches any MSPs included in Route Information Options (RIOs) 1866 [RFC4191] as MSPs to associate with the AERO link, and assigns the 1867 MTU value in the MTU option to the underlying interface. 1869 The Client then registers additional underlying interfaces with the 1870 Server by sending RS messages via each additional interface. The RS 1871 messages include the same parameters as for the initial RS/RA 1872 exchange, but with destination address set to the Server's AERO 1873 address. 1875 Following autoconfiguration, the Client sub-delegates the MNPs to its 1876 attached EUNs and/or the Client's own internal virtual interfaces as 1877 described in [I-D.templin-v6ops-pdhost] to support the Client's 1878 downstream attached "Internet of Things (IoT)". The Client 1879 subsequently sends additional RS messages over each underlying 1880 interface before the Router Lifetime received for that interface 1881 expires. 1883 After the Client registers its underlying interfaces, it may wish to 1884 change one or more registrations, e.g., if an interface changes 1885 address or becomes unavailable, if QoS preferences change, etc. To 1886 do so, the Client prepares an RS message to send over any available 1887 underlying interface. The RS includes an OMNI option with prefix 1888 registration information specific to its MNP, with an ifIndex-tuple 1889 specific to the selected underlying interface with S set to '1', and 1890 with any additional ifIndex-tuples specific to other underlying 1891 interfaces. The Client includes fresh ifIndex-tuple values to update 1892 the Server's neighbor cache entry. When the Client receives the 1893 Server's RA response, it has assurance that the Server has been 1894 updated with the new information. 1896 If the Client wishes to discontinue use of a Server it issues an RS 1897 message over any underlying interface with an OMNI option with a 1898 prefix release indication. When the Server processes the message, it 1899 releases the MNP, sets the symmetric neighbor cache entry state for 1900 the Client to DEPARTED and returns an RA reply with Router Lifetime 1901 set to 0. After a short delay (e.g., 2 seconds), the Server 1902 withdraws the MNP from the routing system. 1904 3.15.3. AERO Server Behavior 1906 AERO Servers act as IP routers and support a PD service for Clients. 1907 Servers arrange to add their AERO addresses to a static map of Server 1908 addresses for the link and/or the DNS resource records for the FQDN 1909 "linkupnetworks.[domainname]" before entering service. Server 1910 addresses should be geographically and/or topologically referenced, 1911 and made available for discovery by Clients on the AERO link. 1913 When a Server receives a prospective Client's RS message on its AERO 1914 interface, it SHOULD return an immediate RA reply with Router 1915 Lifetime set to 0 if it is currently too busy or otherwise unable to 1916 service the Client. Otherwise, the Server authenticates the RS 1917 message and processes the PD parameters. The Server first determines 1918 the correct MNPs to delegate to the Client by searching the Client 1919 database. When the Server delegates the MNPs, it also creates a 1920 forwarding table entry for each MNP so that the MNPs are propagated 1921 into the routing system (see: Section 3.3). For IPv6, the Server 1922 creates an IPv6 forwarding table entry for each MNP. For IPv4, the 1923 Server creates an IPv6 forwarding table entry with the SPAN 1924 Compatibility Prefix (SCP) corresponding to the IPv4 address. 1926 The Server next creates a symmetric neighbor cache entry for the 1927 Client using the base AERO address as the network-layer address and 1928 with lifetime set to no more than the smallest PD lifetime. Next, 1929 the Server updates the neighbor cache entry by recording the 1930 information in each ifIndex-tuple in the RS OMNI option. The Server 1931 also records the actual SPAN/INET addresses in the neighbor cache 1932 entry. 1934 Next, the Server prepares an RA message using its AERO address as the 1935 network-layer source address and the network-layer source address of 1936 the RS message as the network-layer destination address. The Server 1937 sets the Router Lifetime to the time for which it will maintain both 1938 this underlying interface individually and the symmetric neighbor 1939 cache entry as a whole. The Server also sets Cur Hop Limit, M and O 1940 flags, Reachable Time and Retrans Timer to values appropriate for the 1941 AERO link. The Server includes the delegated MNPs, any other PD 1942 parameters and an OMNI option with no ifIndex-tuples. The Server 1943 then includes one or more RIOs that encode the MSPs for the AERO 1944 link, plus an MTU option (see Section 3.12). The Server finally 1945 forwards the message to the Client using SPAN/INET, INET, or NULL 1946 encapsulation as necessary. 1948 After the initial RS/RA exchange, the Server maintains a 1949 ReachableTime timer for each of the Client's underlying interfaces 1950 individually (and for the Client's symmetric neighbor cache entry 1951 collectively) set to expire after Router Lifetime seconds. If the 1952 Client (or Proxy) issues additional RS messages, the Server sends an 1953 RA response and resets ReachableTime. If the Server receives an ND 1954 message with PD release indication it sets the Client's symmetric 1955 neighbor cache entry to the DEPARTED state and withdraws the MNP from 1956 the routing system after a short delay (e.g., 2 seconds). If 1957 ReachableTime expires before a new RS is received on an individual 1958 underlying interface, the Server marks the interface as DOWN. If 1959 ReachableTime expires before any new RS is received on any individual 1960 underlying interface, the Server deletes the neighbor cache entry and 1961 withdraws the MNP without delay. 1963 The Server processes any ND/PD messages pertaining to the Client and 1964 returns an NA/RA reply in response to solicitations. The Server may 1965 also issue unsolicited RA messages, e.g., with PD reconfigure 1966 parameters to cause the Client to renegotiate its PDs, with Router 1967 Lifetime set to 0 if it can no longer service this Client, etc. 1968 Finally, If the symmetric neighbor cache entry is in the DEPARTED 1969 state, the Server deletes the entry after DepartTime expires. 1971 Note: Clients SHOULD notify former Servers of their departures, but 1972 Servers are responsible for expiring neighbor cache entries and 1973 withdrawing routes even if no departure notification is received 1974 (e.g., if the Client leaves the network unexpectedly). Servers 1975 SHOULD therefore set Router Lifetime to REACHABLE_TIME seconds in 1976 solicited RA messages to minimize persistent stale cache information 1977 in the absence of Client departure notifications. A short Router 1978 Lifetime also ensures that proactive Client/Server RS/RA messaging 1979 will keep any NAT state alive (see above). 1981 Note: All Servers on an AERO link MUST advertise consistent values in 1982 the RA Cur Hop Limit, M and O flags, Reachable Time and Retrans Timer 1983 fields the same as for any link, since unpredictable behavior could 1984 result if different Servers on the same link advertised different 1985 values. 1987 3.15.3.1. Lightweight DHCPv6 Relay Agent (LDRA) 1989 When DHCPv6 is used as the ND/PD service back end, AERO Clients and 1990 Servers are always on the same link (i.e., the AERO link) from the 1991 perspective of DHCPv6. However, in some implementations the DHCPv6 1992 server and ND function may be located in separate modules. In that 1993 case, the Server's AERO interface module can act as a Lightweight 1994 DHCPv6 Relay Agent (LDRA)[RFC6221] to relay PD messages to and from 1995 the DHCPv6 server module. 1997 When the LDRA receives an authentic RS message, it extracts the PD 1998 message parameters and uses them to construct an IPv6/UDP/DHCPv6 1999 message. It sets the IPv6 source address to the source address of 2000 the RS message, sets the IPv6 destination address to 2001 'All_DHCP_Relay_Agents_and_Servers' and sets the UDP fields to values 2002 that will be understood by the DHCPv6 server. 2004 The LDRA then wraps the message in a DHCPv6 'Relay-Forward' message 2005 header and includes an 'Interface-Id' option that includes enough 2006 information to allow the LDRA to forward the resulting Reply message 2007 back to the Client (e.g., the Client's link-layer addresses, a 2008 security association identifier, etc.). The LDRA also wraps the OMNI 2009 option and SLLAO into the Interface-Id option, then forwards the 2010 message to the DHCPv6 server. 2012 When the DHCPv6 server prepares a Reply message, it wraps the message 2013 in a 'Relay-Reply' message and echoes the Interface-Id option. The 2014 DHCPv6 server then delivers the Relay-Reply message to the LDRA, 2015 which discards the Relay-Reply wrapper and IPv6/UDP headers, then 2016 uses the DHCPv6 message to construct an RA response to the Client. 2017 The Server uses the information in the Interface-Id option to prepare 2018 the RA message and to cache the link-layer addresses taken from the 2019 OMNI option and SLLAO echoed in the Interface-Id option. 2021 3.16. The AERO Proxy 2023 Clients may connect to ANETs that deploy perimeter security services 2024 to facilitate communications to Servers in outside INETs. In that 2025 case, the ANET can employ an AERO Proxy. The Proxy is located at the 2026 ANET/INET border and listens for RS messages originating from or RA 2027 messages destined to ANET Clients. The Proxy acts on these control 2028 messages as follows: 2030 o when the Proxy receives an RS message from a new ANET Client, it 2031 first authenticates the message then examines the network-layer 2032 destination address. If the destination address is a Server's 2033 AERO address, the Proxy proceeds to the next step. Otherwise, if 2034 the destination is All-Routers multicast or Subnet-Router anycast, 2035 the Proxy selects a "nearby" Server that is likely to be a good 2036 candidate to serve the Client and replaces the destination address 2037 with the Server's AERO address. Next, the Proxy creates a proxy 2038 neighbor cache entry and caches the Client and Server link-layer 2039 addresses along with the OMNI option information and any other 2040 identifying information including Transaction IDs, Client 2041 Identifiers, Nonce values, etc. The Proxy finally encapsulates 2042 the (proxyed) RS message in a SPAN header with source set to the 2043 Proxy's SPAN address and destination set to the Server's SPAN 2044 address then forwards the message into the SPAN. 2046 o when the Server receives the RS, it authenticates the message then 2047 creates or updates a symmetric neighbor cache entry for the Client 2048 with the Proxy's SPAN address as the link-layer address. The 2049 Server then sends an RA message back to the Proxy via the SPAN. 2051 o when the Proxy receives the RA, it authenticates the message and 2052 matches it with the proxy neighbor cache entry created by the RS. 2053 The Proxy then caches the PD route information as a mapping from 2054 the Client's MNPs to the Client's ANET address, caches the 2055 Server's advertised Router Lifetime and sets the neighbor cache 2056 entry state to REACHABLE. The Proxy then sets the P bit in the RA 2057 flags field, optionally rewrites the Router Lifetime and forwards 2058 the (proxyed) message to the Client. The Proxy finally includes 2059 an MTU option (if necessary) with an MTU to use for the underlying 2060 ANET interface. 2062 After the initial RS/RA exchange, the Proxy forwards any Client data 2063 packets for which there is no matching asymmetric neighbor cache 2064 entry to a Relay using SPAN encapsulation with its own SPAN address 2065 as the source and the SPAN address corresponding to the Client as the 2066 destination. The Proxy instead forwards any Client data destined to 2067 an asymmetric neighbor cache target directly to the target according 2068 to the SPAN/link-layer information - the process of establishing 2069 asymmetric neighbor cache entries is specified in Section 3.17. 2071 While the Client is still attached to the ANET, the Proxy sends NS, 2072 RS and/or unsolicited NA messages to update the Server's symmetric 2073 neighbor cache entries on behalf of the Client and/or to convey QoS 2074 updates. This allows for higher-frequency Proxy-initiated RS/RA 2075 messaging over well-connected INET infrastructure supplemented by 2076 lower-frequency Client-initiated RS/RA messaging over constrained 2077 ANET data links. 2079 If the Server ceases to send solicited advertisements, the Proxy 2080 sends unsolicited RAs on the ANET interface with destination set to 2081 All-Nodes multicast (ff02::1) and with Router Lifetime set to zero to 2082 inform Clients that the Server has failed. Although the Proxy 2083 engages in ND exchanges on behalf of the Client, the Client can also 2084 send ND messages on its own behalf, e.g., if it is in a better 2085 position than the Proxy to convey QoS changes, etc. For this reason, 2086 the Proxy marks any Client-originated solicitation messages (e.g. by 2087 inserting a Nonce option) so that it can return the solicited 2088 advertisement to the Client instead of processsing it locally. 2090 If the Client becomes unreachable, the Proxy sets the neighbor cache 2091 entry state to DEPARTED and retains the entry for DEPART_TIME 2092 seconds. While the state is DEPARTED, the Proxy forwards any packets 2093 destined to the Client to a Relay via SPAN encapsulation with the 2094 Client's current Server as the destination. The Relay in turn 2095 forwards the packets to the Client's current Server. When DepartTime 2096 expires, the Proxy deletes the neighbor cache entry and discards any 2097 further packets destined to this (now forgotten) Client. 2099 In some ANETs that employ a Proxy, the Client's MNP can be injected 2100 into the ANET routing system. In that case, the Client can send data 2101 messages without encapsulation so that the ANET native routing system 2102 transports the unencapsulated packets to the Proxy. This can be very 2103 beneficial, e.g., if the Client connects to the ANET via low-end data 2104 links such as some aviation wireless links. 2106 If the first-hop ANET access router is AERO-aware, the Client can 2107 avoid encapsulation for both its control and data messages. When the 2108 Client connects to the link, it can send an unencapsulated RS message 2109 with source address set to its AERO address and with destination 2110 address set to the AERO address of the Client's selected Server or to 2111 All-Routers multicast or Subnet-Router anycast. The Client includes 2112 an OMNI option formatted as specified in 2113 [I-D.templin-6man-omni-interface]. 2115 The Client then sends the unencapsulated RS message, which will be 2116 intercepted by the AERO-Aware access router. The access router then 2117 encapsulates the RS message in an ANET header with its own address as 2118 the source address and the address of a Proxy as the destination 2119 address. The access router further remembers the address of the 2120 Proxy so that it can encapsulate future data packets from the Client 2121 via the same Proxy. If the access router needs to change to a new 2122 Proxy, it simply sends another RS message toward the Server via the 2123 new Proxy on behalf of the Client. 2125 In some cases, the access router and Proxy may be one and the same 2126 node. In that case, the node would be located on the same physical 2127 link as the Client, but its message exchanges with the Server would 2128 need to pass through a security gateway at the ANET/INET border. The 2129 method for deploying access routers and Proxys (i.e. as a single node 2130 or multiple nodes) is an ANET-local administrative consideration. 2132 3.16.1. Detecting and Responding to Server Failures 2134 In environments where fast recovery from Server failure is required, 2135 Proxys SHOULD use proactive Neighbor Unreachability Detection (NUD) 2136 to track Server reachability in a similar fashion as for 2137 Bidirectional Forwarding Detection (BFD) [RFC5880]. Proxys can then 2138 quickly detect and react to failures so that cached information is 2139 re-established through alternate paths. The NUD control messaging is 2140 carried only over well-connected ground domain networks (i.e., and 2141 not low-end aeronautical radio links) and can therefore be tuned for 2142 rapid response. 2144 Proxys perform proactive NUD with Servers for which there are 2145 currently active ANET Clients by sending continuous NS messages in 2146 rapid succession, e.g., one message per second. The Proxy sends the 2147 NS message via the SPAN with the Proxy's AERO address as the source 2148 and the AERO address of the Server as the destination. When the 2149 Proxy is also sending RS messages to the Server on behalf of ANET 2150 Clients, the resulting RA responses can be considered as equivalent 2151 hints of forward progress. This means that the Proxy need not also 2152 send a periodic NS if it has already sent an RS within the same 2153 period. If the Server fails (i.e., if the Proxy ceases to receive 2154 advertisements), the Proxy can quickly inform Clients by sending 2155 multicast RA messages on the ANET interface. 2157 The Proxy sends RA messages on the ANET interface with source address 2158 set to the Server's address, destination address set to All-Nodes 2159 multicast, and Router Lifetime set to 0. The Proxy SHOULD send 2160 MAX_FINAL_RTR_ADVERTISEMENTS RA messages separated by small delays 2161 [RFC4861]. Any Clients on the ANET that had been using the failed 2162 Server will receive the RA messages and associate with a new Server. 2164 3.16.2. Point-to-Multipoint Server Coordindation 2166 In environments where Client messaging over ANETs is bandwidth- 2167 limited and/or expensive, Clients can enlist the services of the 2168 Proxy to coordinate with multiple Servers in a single RS/RA message 2169 exchange. The Client can send a single RS message to All-Routers 2170 multicast that includes the ID's of multiple Servers in MS-Register 2171 sub-options of the OMNI option,. 2173 When the Proxy receives the RS and processes the OMNI option, it 2174 performs a separate RS/RA exchange with each MS-Register Server. 2175 When it has received the RA messages, it creates an "aggregate" RA 2176 message to return to the Client with an OMNI option with each 2177 responding Server's ID recorded in an MS-Register sub-option. 2179 Client's can thereafter employ efficient point-to-multipoint Server 2180 coordination under the assistance of the Proxy to dramatically reduce 2181 the number of messages sent over the ANET while enlisting the support 2182 of multiple Servers for fault tolerance. Clients can further include 2183 MS-Release suboptions in RS messages to request the Proxy to release 2184 from former Servers via the procedures discussed in Section 3.19.5. 2186 The OMNI interface specification [I-D.templin-6man-omni-interface] 2187 provides further discussion of the Client/Proxy RS/RA messaging 2188 involved in point-to-multipoint coordination. 2190 3.17. AERO Route Optimization 2192 While data packets are flowing between a source and target node, 2193 route optimization SHOULD be used. Route optimization is initiated 2194 by the first eligible Route Optimization Source (ROS) closest to the 2195 source as follows: 2197 o For Clients on VPNed and Direct interfaces, the Server is the ROS. 2199 o For Clients on Proxyed interfaces, the Proxy is the ROS. 2201 o For Clients on native and NATed interfaces, the Client itself is 2202 the ROS. 2204 o For correspondent nodes on INET/EUN interfaces serviced by a 2205 Gateway, the Gateway is the ROS. 2207 The route optimization procedure is conducted between the ROS and the 2208 target Server/Gateway acting as a Route Optimization Responder (ROR) 2209 in the same manner as for IPv6 ND Address Resolution and using the 2210 same NS/NA messaging. The target may either be a MNP Client serviced 2211 by a Server, or a non-MNP correspondent reachable via a Gateway. 2213 The procedures are specified in the following sections. 2215 3.17.1. Route Optimization Initiation 2217 While data packets are flowing from the source node toward a target 2218 node, the ROS performs address resolution by sending an NS message 2219 for Address Resolution (NS(AR)) to receive a solicited NA message 2220 from the ROR. When the ROS sends an NS(AR), it includes: 2222 o the AERO address of the ROS as the source address. 2224 o the data packet's destination as the Target Address. 2226 o the Solicited-Node multicast address [RFC4291] formed from the 2227 lower 24 bits of the data packet's destination as the destination 2228 address, e.g., for 2001:db8:1:2::10:2000 the NS destination 2229 address is ff02:0:0:0:0:1:ff10:2000. 2231 The NS(AR) message includes an OMNI option with no ifIndex-tuples and 2232 no SLLAO, such that the target will not create a neighbor cache 2233 entry. 2235 The ROS then encapsulates the NS(AR) message in a SPAN header with 2236 source set to its own SPAN address and destination set to the SPAN 2237 address corresponding to the packet's final destination, then sends 2238 the message into the SPAN without decrementing the network-layer TTL/ 2239 Hop Limit field. 2241 3.17.2. Relaying the NS 2243 When the Relay receives the NS(AR) message from the ROS, it discards 2244 the INET header and determines that the ROR is the next hop by 2245 consulting its standard IPv6 forwarding table for the SPAN header 2246 destination address. The Relay then forwards the message toward the 2247 ROR via the SPAN the same as for any IPv6 router. The final-hop 2248 Relay in the SPAN will deliver the message via a secured tunnel to 2249 the ROR. 2251 3.17.3. Processing the NS and Sending the NA 2253 When the ROR receives the NS(AR) message, it examines the Target 2254 Address to determine whether it has a neighbor cache entry and/or 2255 route that matches the target. If there is no match, the ROR drops 2256 the NS(AR) message. Otherwise, the ROR continues processing as 2257 follows: 2259 o if the target belongs to an MNP Client neighbor in the DEPARTED 2260 state the ROR changes the NS(AR) message SPAN destination address 2261 to the SPAN address of the Client's new Server, forwards the 2262 message into the SPAN and returns from processing. 2264 o If the target belongs to an MNP Client neighbor in the REACHABLE 2265 state, the ROR instead adds the AERO source address to the target 2266 Client's Report List with time set to ReportTime. 2268 o If the target belongs to a non-MNP route, the ROR continues 2269 processing without adding an entry to the Report List. 2271 The ROR then prepares a solicited NA message to send back to the ROS 2272 but does not create a neighbor cache entry. The ROR sets the NA 2273 source address to the AERO address corresponding to the target, sets 2274 the Target Address to the target of the solicitation, and sets the 2275 destination address to the source of the solicitation. 2277 The ROR then includes an OMNI option with prefix registration length 2278 set to the length of the MNP if the target is an MNP Client; 2279 otherwise, set to the maximum of the non-MNP prefix length and 64. 2280 (Note that a /64 limit is imposed to avoid causing the ROS to set 2281 short prefixes (e.g., "default") that would match destinations for 2282 which the routing system includes more-specific prefixes.) 2284 If the target is an MNP Client, the ROR next includes ifIndex-tuples 2285 in the OMNI option for each of the target Client's underlying 2286 interfaces with current information for each interface and with the S 2287 flag set to 0. The ROR then includes a TLLAO with ifIndex-tuples in 2288 one-to-one correspondence with the tuples that appear in the OMNI 2289 option. 2291 The ROR includes the IDs of all intermediate SPAN endpoints to be 2292 visited in the Segment Routing List, while setting the Link Layer 2293 Address to its own SPAN ID for VPNed and Direct interfaces or to the 2294 SPAN ID of the Proxy for Proxyed interfaces. For NATed and Native 2295 interfaces, if the ROS and ROR are located in the same SPAN partition 2296 the ROR sets the Link Layer Address and Port Number (if necessary) to 2297 the Client's INET address. Otherwise, the ROR sets the Link Layer 2298 Address to its SPAN ID. 2300 The ROR then sets the NA message R flag to 1 (as a router), S flag to 2301 1 (as a response to a solicitation), and O flag to 0 (as a proxy). 2302 The ROR finally encapsulates the NA message in a SPAN header with 2303 source set to its own SPAN address and destination set to the source 2304 SPAN address of the NS(AR) message, then forwards the message into 2305 the SPAN without decrementing the network-layer TTL/Hop Limit field. 2307 3.17.4. Relaying the NA 2309 When the Relay receives the NA message from the ROR, it discards the 2310 INET header and determines that the ROS is the next hop by consulting 2311 its standard IPv6 forwarding table for the SPAN header destination 2312 address. The Relay then forwards the SPAN-encapsulated NA message 2313 toward the ROS the same as for any IPv6 router. The final-hop Relay 2314 in the SPAN will deliver the message via a secured tunnel to the ROS. 2316 3.17.5. Processing the NA 2318 When the ROS receives the solicited NA message, it processes the 2319 message the same as for standard IPv6 Address Resolution [RFC4861]. 2320 In the process, it caches the source SPAN address then creates an 2321 asymmetric neighbor cache entry for the ROR and caches all 2322 information found in the OMNI and TLLAO options. The ROS finally 2323 sets the asymmetric neighbor cache entry lifetime to REACHABLE_TIME 2324 seconds. 2326 3.17.6. Route Optimization Maintenance 2328 Following route optimization, the ROS forwards future data packets 2329 destined to the target via the addresses found in the cached link- 2330 layer information. The route optimization is shared by all sources 2331 that send packets to the target via the ROS, i.e., and not just the 2332 source on behalf of which the route optimization was initiated. 2334 While new data packets destined to the target are flowing through the 2335 ROS, it sends additional NS(AR) messages to the ROR before 2336 ReachableTime expires to receive a fresh solicited NA message the 2337 same as described in the previous sections (route optimization 2338 refreshment strategies are an implementation matter, with a non- 2339 normative example given in Appendix B.1). The ROS uses the cached 2340 SPAN address of the ROR as the NS(AR) SPAN destination address, and 2341 sends up to MAX_MULTICAST_SOLICIT NS(AR) messages separated by 1 2342 second until an NA is received. If no NA is received, the ROS 2343 assumes that the current ROR has become unreachable and deletes the 2344 neighbor cache entry. Subsequent data packets will trigger a new 2345 route optimization per Section 3.17.1 to discover a new ROR while 2346 initial data packets travel over a suboptimal route. 2348 If an NA is received, the ROS then updates the asymmetric neighbor 2349 cache entry to refresh ReachableTime, while (for MNP destinations) 2350 the ROR adds or updates the ROS address to the target Client's Report 2351 List and with time set to ReportTime. While no data packets are 2352 flowing, the ROS instead allows ReachableTime for the asymmetric 2353 neighbor cache entry to expire. When ReachableTime expires, the ROS 2354 deletes the asymmetric neighbor cache entry. Any future data packets 2355 flowing through the ROS will again trigger a new route optimization. 2357 The ROS may also receive unsolicited NA messages from the ROR at any 2358 time (see: Section 3.19). If there is an asymmetric neighbor cache 2359 entry for the target, the ROS updates the link-layer information but 2360 does not update ReachableTime since the receipt of an unsolicited NA 2361 does not confirm that any forward paths are working. If there is no 2362 asymmetric neighbor cache entry, the ROS simply discards the 2363 unsolicited NA. 2365 In this arrangement, the ROS holds an asymmetric neighbor cache entry 2366 for the ROR, but the ROR does not hold an asymmetric neighbor cache 2367 entry for the ROS. The route optimization neighbor relationship is 2368 therefore asymmetric and unidirectional. If the target node also has 2369 packets to send back to the source node, then a separate route 2370 optimization procedure is performed in the reverse direction. But, 2371 there is no requirement that the forward and reverse paths be 2372 symmetric. 2374 3.18. Neighbor Unreachability Detection (NUD) 2376 AERO nodes perform Neighbor Unreachability Detection (NUD) per 2377 [RFC4861] either reactively in response to persistent link-layer 2378 errors (see Section 3.14) or proactively to confirm reachability. 2379 The NUD algorithm is based on periodic control message exchanges. 2380 The algorithm may further be seeded by ND hints of forward progress, 2381 but care must be taken to avoid inferring reachability based on 2382 spoofed information. For example, authentic IPv6 ND message 2383 exchanges may be considered as acceptable hints of forward progress, 2384 while spurious data packets should not be. 2386 AERO Servers, Proxys and Gateways can use standard NS/NA NUD 2387 exchanges sent over the SPAN to securely test reachability without 2388 risk of DoS attacks from nodes pretending to be a neighbor; Proxys 2389 can further perform NUD to securely verify Server reachability on 2390 behalf of their proxyed Clients. However, a means for a ROS to test 2391 the unsecured forward directions of target route optimized paths is 2392 also necessary. 2394 When an ROR directs an ROS to a neighbor with one or more target 2395 link-layer addresses, the ROS can proactively test each such 2396 unsecured route optimized path by sending "loopback" NS(NUD) 2397 messages. While testing the paths, the ROS can optionally continue 2398 to send packets via the SPAN, maintain a small queue of packets until 2399 target reachability is confirmed, or (optimistically) allow packets 2400 to flow via the route optimized paths. 2402 When the ROS sends a loopback NS(NUD) message, it uses its AERO 2403 address as both the IPv6 source and destination address, and the MNP 2404 Subnet-Router anycast address as the Target Address. The ROS 2405 includes a Nonce and Timestamp option, then encapsulates the message 2406 in SPAN/INET headers with its own SPAN address as the source and the 2407 SPAN address of the route optimization target as the destination. 2408 The ROS then forwards the message to the target (either directly to 2409 the link layer address of the target if the target is in the same 2410 SPAN segment, or via a Relay if the target is in a different SPAN 2411 segment). 2413 When the route optimization target receives the NS(NUD) message, it 2414 notices that the IPv6 destination address is the same as the source 2415 address. It then reverses the SPAN source and destination addresses 2416 and returns the message to the ROS (either directly or via the SPAN). 2417 The route optimization target does not decrement the NS(NUD) message 2418 IPv6 Hop-Limit in the process, since the message has not exited the 2419 SPAN. 2421 When the ROS receives the NS(NUD) message, it can determine from the 2422 Nonce, Timestamp and Target Address that the message originated from 2423 itself and that it transited the forward path. The ROS need not 2424 prepare an NA response, since the destination of the response would 2425 be itself and testing the route optimization path again would be 2426 redundant. 2428 The ROS marks route optimization target paths that pass these NUD 2429 tests as "reachable", and those that do not as "unreachable". These 2430 markings inform the AERO interface forwarding algorithm specified in 2431 Section 3.13. 2433 Note that to avoid a DoS vector nodes MUST NOT return loopback 2434 NS(NUD) messages received from an unsecured link-layer source via a 2435 secured SPAN path. 2437 3.19. Mobility Management and Quality of Service (QoS) 2439 AERO is a Distributed Mobility Management (DMM) service. Each Server 2440 is responsible for only a subset of the Clients on the AERO link, as 2441 opposed to a Centralized Mobility Management (CMM) service where 2442 there is a single network mobility collective entity for all Clients. 2443 Clients coordinate with their associated Servers via RS/RA exchanges 2444 to maintain the DMM profile, and the AERO routing system tracks all 2445 current Client/Server peering relationships. 2447 Servers provide default routing and mobility/multilink services for 2448 their dependent Clients. Clients are responsible for maintaining 2449 neighbor relationships with their Servers through periodic RS/RA 2450 exchanges, which also serves to confirm neighbor reachability. When 2451 a Client's underlying interface address and/or QoS information 2452 changes, the Client is responsible for updating the Server with this 2453 new information. Note that for Proxyed interfaces, however, the 2454 Proxy can also perform some RS/RA exchanges on the Client's behalf. 2456 Mobility management considerations are specified in the following 2457 sections. 2459 3.19.1. Mobility Update Messaging 2461 Servers accommodate Client mobility/multilink and/or QoS change 2462 events by sending unsolicited NA (uNA) messages to each ROS in the 2463 target Client's Report List. When a Server sends a uNA message, it 2464 sets the IPv6 source address to the Client's AERO address, sets the 2465 destination address to All-Nodes multicast and sets the Target 2466 Address to the Client's Subnet-Router anycast address. The Server 2467 also includes an OMNI option with prefix registration information and 2468 with ifIndex-tuples for the target Client's remaining interfaces with 2469 S set to 0. The Server then includes a TLLAO with corresponding 2470 ifIndex-tuples prepared the same as for the initial route 2471 optimization event. The Server sets the NA R flag to 1, the S flag 2472 to 0 and the O flag to 0, then encapsulates the message in a SPAN 2473 header with source set to its own SPAN address and destination set to 2474 the SPAN address of the ROS and sends the message into the SPAN. 2476 As discussed in Section 7.2.6 of [RFC4861], the transmission and 2477 reception of uNA messages is unreliable but provides a useful 2478 optimization. In well-connected Internetworks with robust data links 2479 uNA messages will be delivered with high probability, but in any case 2480 the Server can optionally send up to MAX_NEIGHBOR_ADVERTISEMENT uNAs 2481 to each ROS to increase the likelihood that at least one will be 2482 received. 2484 When the ROS receives an uNA message, it ignores the message if there 2485 is no existing neighbor cache entry for the Client. Otherwise, it 2486 uses the included OMNI option and TLLAO information to update the 2487 neighbor cache entry, but does not reset ReachableTime since the 2488 receipt of an unsolicited NA message from the target Server does not 2489 provide confirmation that any forward paths to the target Client are 2490 working. 2492 If uNA messages are lost, the ROS may be left with stale address and/ 2493 or QoS information for the Client for up to REACHABLE_TIME seconds. 2494 During this time, the ROS can continue sending packets according to 2495 its stale neighbor cache information. When ReachableTime is close to 2496 expiring, the ROS will re-initiate route optimization and receive 2497 fresh link-layer address information. 2499 In addition to sending uNA messages to the current set of ROSs for 2500 the Client, the Server also sends uNAs to the former link-layer 2501 address for any ifIndex-tuple for which the link-layer address has 2502 changed. The uNA messages update Proxys that cannot easily detect 2503 (e.g., without active probing) when a formerly-active Client has 2504 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 that includes an ifIndex-tuple with S set to 1 and with the 2512 new link quality and address information. 2514 Up to MAX_RTR_SOLICITATIONS 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 uNA messages 2519 to all nodes in the Report List the same as described in the previous 2520 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 that 2527 includes an ifIndex-tuple with S set to 1 and appropriate link 2528 quality values and with link-layer address information for the new 2529 link. 2531 3.19.4. Removing Existing Links from Service 2533 When a Client needs to remove existing underlying interfaces from 2534 service (e.g., when it de-activates an existing data link), it sends 2535 an RS or uNA message to its Server with an OMNI option with 2536 appropriate link quality values. 2538 If the Client needs to send RS/uNA messages over an underlying 2539 interface other than the one being removed from service, it MUST 2540 include ifIndex-tuples with appropriate link quality values for any 2541 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 MS- 2547 Release identifiers in the RS message OMNI option per 2548 [I-D.templin-6man-omni-interface] if it wants the new Server to 2549 notify any old Servers from which the Client is departing. 2551 When the new Server receives the Client's RS message, it returns an 2552 RA as specified in Section 3.15.3 and sends up to 2553 MAX_NEIGHBOR_ADVERTIISEMENT uNA messages to any old Servers listed in 2554 OMNI option MS-Release identifiers. Each uNA message includes the 2555 Client's AERO address as the source address, the old Server's AERO 2556 address as the destination address, and an OMNI option with the 2557 Register/Release bit set to 0. The new Server wraps the uNA in a 2558 SPAN header with its own SPAN address as the source and the old 2559 Server's SPAN address as the destination, then sends the message into 2560 the SPAN. 2562 When an old Server receives the uNA, it changes the Client's neighbor 2563 cache entry state to DEPARTED, sets the link-layer address of the 2564 Client to the new Server's SPAN address, and sets DepartTime to 2565 DEPART_TIME seconds. After a short delay (e.g., 2 seconds) the old 2566 Server withdraws the Client's MNP from the routing system. After 2567 DepartTime expires, the old Server deletes the Client's neighbor 2568 cache entry. 2570 The old Server also sends unsolicited NA messages to all ROSs in the 2571 Client's Report List with an OMNI option with a single ifIndex-tuple 2572 with ifIndex set to 0 and S set to '1', and with the SPAN address of 2573 the new Server in a companion TLLAO. When the ROS receives the NA, 2574 it caches the address of the new Server in the existing asymmetric 2575 neighbor cache entry and marks the entry as STALE. Subsequent data 2576 packets will then flow according to any existing cached link-layer 2577 information and trigger a new NS(AR)/NA exchange via the new Server. 2579 Clients SHOULD NOT move rapidly between Servers in order to avoid 2580 causing excessive oscillations in the AERO routing system. Examples 2581 of when a Client might wish to change to a different Server include a 2582 Server that has gone unreachable, topological movements of 2583 significant distance, movement to a new geographic region, movement 2584 to a new SPAN segment, etc. 2586 When a Client moves to a new Server, some of the fragments of a 2587 multiple fragment packet may have already arrived at the old Server 2588 while others are en route to the new Server, however no special 2589 attention in the reassembly algorithm is necessary when re-routed 2590 fragments are simply treated as loss. 2592 3.20. Multicast 2594 The AERO Client provides an IGMP (IPv4) [RFC2236] or MLD (IPv6) 2595 [RFC3810] proxy service for its EUNs and/or hosted applications 2596 [RFC4605]. The Client forwards IGMP/MLD messages over any of its 2597 underlying interfaces for which group membership is required. The 2598 IGMP/MLD messages may be further forwarded by a first-hop ANET access 2599 router acting as an IGMP/MLD-snooping switch [RFC4541], then 2600 ultimately delivered to an AERO Proxy/Server acting as a Protocol 2601 Independent Multicast - Sparse-Mode (PIM-SM, or simply "PIM") 2602 Designated Router (DR) [RFC7761]. AERO Gateways also act as PIM 2603 routers (i.e., the same as AERO Proxys/Servers) on behalf of nodes on 2604 INET/EUN networks. The behaviors identified in the following 2605 sections correspond to Source-Specific Multicast (SSM) and Any-Source 2606 Multicast (ASM) operational modes. 2608 3.20.1. Source-Specific Multicast (SSM) 2610 When an ROS (i.e., an AERO Proxy/Server/Gateway) "X" acting as PIM 2611 router receives a Join/Prune message from a node on its downstream 2612 interfaces containing one or more ((S)ource, (G)roup) pairs, it 2613 updates its Multicast Routing Information Base (MRIB) accordingly. 2614 For each S belonging to a prefix reachable via X's non-AERO 2615 interfaces, X then forwards the (S, G) Join/Prune to any PIM routers 2616 on those interfaces per [RFC7761]. 2618 For each S belonging to a prefix reachable via X's AERO interface, X 2619 originates a separate copy of the Join/Prune for each (S,G) in the 2620 message using its own AERO address as the source address and ALL-PIM- 2621 ROUTERS as the destination address. X then encapsulates each message 2622 in a SPAN header with source address set to the SPAN address of X and 2623 destination address set to S then forwards the message into the SPAN. 2624 The SPAN in turn forwards the message to AERO Server/Gateway "Y" that 2625 services S. At the same time, if the message was a Join, X sends a 2626 route-optimization NS message toward each S the same as discussed in 2627 Section 3.17. The resulting NAs will return the AERO address for the 2628 prefix that matches S as the network-layer source address and TLLAOs 2629 with the SPAN addresses corresponding to any ifIndex-tuples that are 2630 currently servicing S. 2632 When Y processes the Join/Prune message, if S located behind any 2633 Native, Direct, VPNed or NATed interfaces Y acts as a PIM router and 2634 updates its MRIB to list X as the next hop in the reverse path. If S 2635 is located behind any Proxys "Z"*, Y also forwards the message to 2636 each Z* over the SPAN while continuing to use the AERO address of X 2637 as the source address. Each Z* then updates its MRIB accordingly and 2638 maintains the AERO address of X as the next hop in the reverse path. 2639 Since the Relays in the SPAN do not examine network layer control 2640 messages, this means that the (reverse) multicast tree path is simply 2641 from each Z* (and/or Y) to X with no other multicast-aware routers in 2642 the path. If any Z* (and/or Y) is located on the same SPAN segment 2643 as X, the multicast data traffic sent to X directly using SPAN/INET 2644 encapsulation instead of via a Relay. 2646 Following the initial Join/Prune and NS/NA messaging, X maintains an 2647 asymmetric neighbor cache entry for each S the same as if X was 2648 sending unicast data traffic to S. In particular, X performs 2649 additional NS/NA exchanges to keep the neighbor cache entry alive for 2650 up to t_periodic seconds [RFC7761]. If no new Joins are received 2651 within t_periodic seconds, X allows the neighbor cache entry to 2652 expire. Finally, if X receives any additional Join/Prune messages 2653 for (S,G) it forwards the messages to each Y and Z* in the neighbor 2654 cache entry over the SPAN. 2656 At some later time, Client C that holds an MNP for source S may 2657 depart from a first Proxy Z1 and/or connect via a new Proxy Z2. In 2658 that case, Y sends an unsolicited NA message to X the same as 2659 specified for unicast mobility in Section 3.19. When X receives the 2660 unsolicited NA message, it updates its asymmetric neighbor cache 2661 entry for the AERO address for source S and sends new Join messages 2662 to any new Proxys Z2. There is no requirement to send any Prune 2663 messages to old Proxys Z1 since source S will no longer source any 2664 multicast data traffic via Z1. Instead, the multicast state for 2665 (S,G) in Proxy Z1 will soon time out since no new Joins will arrive. 2667 After some later time, C may move to a new Server Y2 and depart from 2668 old Sever Y1. In that case, Y1 sends Join messages for any of C's 2669 active (S,G) groups to Y2 while including its own AERO address as the 2670 source address. This causes Y2 to include Y1 in the multicast 2671 forwarding tree during the interim time that Y1's symmetric neighbor 2672 cache entry for C is in the DEPARTED state. At the same time, Y1 2673 sends an unsolicited NA message to X with an OMNI option and TLLAO 2674 with ifIndex-tuple set to 0 and a release indication to cause X to 2675 release its asymmetric neighbor cache entry. X then sends a new Join 2676 message to S via the SPAN and re-initiates route optimization the 2677 same as if it were receiving a fresh Join message from a node on a 2678 downstream link. 2680 3.20.2. Any-Source Multicast (ASM) 2682 When an ROS X acting as a PIM router receives a Join/Prune from a 2683 node on its downstream interfaces containing one or more (*,G) pairs, 2684 it updates its Multicast Routing Information Base (MRIB) accordingly. 2685 X then forwards a copy of the message to the Rendezvous Point (RP) R 2686 for each G over the SPAN. X uses its own AERO address as the source 2687 address and ALL-PIM-ROUTERS as the destination address, then 2688 encapsulates each message in a SPAN header with source address set to 2689 the SPAN address of X and destination address set to R, then sends 2690 the message into the SPAN. At the same time, if the message was a 2691 Join X initiates NS/NA route optimization the same as for the SSM 2692 case discussed in Section 3.20.1. 2694 For each source S that sends multicast traffic to group G via R, the 2695 Proxy/Server Z* for the Client that aggregates S encapsulates the 2696 packets in PIM Register messages and forwards them to R via the SPAN. 2697 R may then elect to send a PIM Join to Z* over the SPAN. This will 2698 result in an (S,G) tree rooted at Z* with R as the next hop so that R 2699 will begin to receive two copies of the packet; one native copy from 2700 the (S, G) tree and a second copy from the pre-existing (*, G) tree 2701 that still uses PIM Register encapsulation. R can then issue a PIM 2702 Register-stop message to suppress the Register-encapsulated stream. 2703 At some later time, if C moves to a new Proxy/Server Z*, it resumes 2704 sending packets via PIM Register encapsulation via the new Z*. 2706 At the same time, as multicast listeners discover individual S's for 2707 a given G, they can initiate an (S,G) Join for each S under the same 2708 procedures discussed in Section 3.20.1. Once the (S,G) tree is 2709 established, the listeners can send (S, G) Prune messages to R so 2710 that multicast packets for group G sourced by S will only be 2711 delivered via the (S, G) tree and not from the (*, G) tree rooted at 2712 R. All mobility considerations discussed for SSM apply. 2714 3.20.3. Bi-Directional PIM (BIDIR-PIM) 2716 Bi-Directional PIM (BIDIR-PIM) [RFC5015] provides an alternate 2717 approach to ASM that treats the Rendezvous Point (RP) as a Designated 2718 Forwarder (DF). Further considerations for BIDIR-PIM are out of 2719 scope. 2721 3.21. Operation over Multiple AERO Links (VLANs) 2723 An AERO Client can connect to multiple AERO links the same as for any 2724 data link service. In that case, the Client maintains a distinct 2725 AERO interface for each link, e.g., 'aero0' for the first link, 2726 'aero1' for the second, 'aero2' for the third, etc. Each AERO link 2727 would include its own distinct set of Relays, Servers and Proxys, 2728 thereby providing redundancy in case of failures. 2730 The Relays, Servers and Proxys on each AERO link can assign AERO and 2731 SPAN addresses that use the same or different numberings from those 2732 on other links. Since the links are mutually independent there is no 2733 requirement for avoiding inter-link address duplication, e.g., the 2734 same AERO address such as fe80::1000 could be used to number distinct 2735 nodes that connect to different AERO links. 2737 Each AERO link could utilize the same or different ANET connections. 2738 The links can be distinguished at the link-layer via the SSP in a 2739 similar fashion as for Virtual Local Area Network (VLAN) tagging 2740 (e.g., IEEE 802.1Q) and/or through assignment of distinct sets of 2741 MSPs on each link. This gives rise to the opportunity for supporting 2742 multiple redundant networked paths, where each VLAN is distinguished 2743 by a different SRT color (see: Section 3.5.1). In particular, the 2744 Client can tag its RS messages with the appropriate label to cause 2745 the network to select the desired VLAN. 2747 The Client's IP layer can select the outgoing AERO interface 2748 appropriate for a given traffic profile while (in the reverse 2749 direction) correspondent nodes must have some way of steering their 2750 packets destined to a target via the correct AERO link. 2752 In a first alternative, if each AERO link services different MSPs, 2753 then the Client can receive a distinct MNP from each of the links. 2754 IP routing will therefore assure that the correct Red/Green/Blue/etc. 2755 network is used for both outbound and inbound traffic. This can be 2756 accomplished using existing technologies and approaches, and without 2757 requiring any special supporting code in correspondent nodes or 2758 Relays. 2760 In a second alternative, if each AERO link services the same MSP(s) 2761 then each link could assign a distinct "AERO Link Anycast" address 2762 that is configured by all Relays on the link. Correspondent nodes 2763 can then perform segment routing at the SPAN layer 2764 [RFC8402][RFC8754]. Segment Routing in the correct SRT will then 2765 direct the packet over multiple hops to the target. 2767 3.22. DNS Considerations 2769 AERO Client MNs and INET correspondent nodes consult the Domain Name 2770 System (DNS) the same as for any Internetworking node. When 2771 correspondent nodes and Client MNs use different IP protocol versions 2772 (e.g., IPv4 correspondents and IPv6 MNs), the INET DNS must maintain 2773 A records for IPv4 address mappings to MNs which must then be 2774 populated in Gateway NAT64 mapping caches. In that way, an IPv4 2775 correspondent node can send packets to the IPv4 address mapping of 2776 the target MN, and the Gateway will translate the IPv4 header and 2777 destination address into an IPv6 header and IPv6 destination address 2778 of the MN. 2780 When an AERO Client registers with an AERO Server, the Server can 2781 return the address(es) of DNS servers in RDNSS options [RFC6106]. 2782 The DNS server provides the IP addresses of other MNs and 2783 correspondent nodes in AAAA records for IPv6 or A records for IPv4. 2785 3.23. Transition Considerations 2787 The SPAN ensures that dissimilar INET partitions can be joined into a 2788 single unified AERO link, even though the partitions themselves may 2789 have differing protocol versions and/or incompatible addressing 2790 plans. However, a commonality can be achieved by incrementally 2791 distributing globally routable (i.e., native) IP prefixes to 2792 eventually reach all nodes (both mobile and fixed) in all SPAN 2793 segments. This can be accomplished by incrementally deploying AERO 2794 Gateways on each INET partition, with each Gateway distributing its 2795 MNPs and/or discovering non-MNP prefixes on its INET links. 2797 This gives rise to the opportunity to eventually distribute native IP 2798 addresses to all nodes, and to present a unified AERO link view 2799 (bridged by the SPAN) even if the INET partitions remain in their 2800 current protocol and addressing plans. In that way, the AERO link 2801 can serve the dual purpose of providing a mobility/multilink service 2802 and a transition service. Or, if an INET partition is transitioned 2803 to a native IP protocol version and addressing scheme that is 2804 compatible with the AERO link MNP-based addressing scheme, the 2805 partition and AERO link can be joined by Gateways. 2807 Gateways that connect INETs/EUNs with dissimilar IP protocol versions 2808 must employ a network address and protocol translation function such 2809 as NAT64[RFC6146]. 2811 3.24. Detecting and Reacting to Server and Relay Failures 2813 In environments where rapid failure recovery is required, Servers and 2814 Relays SHOULD use Bidirectional Forwarding Detection (BFD) [RFC5880]. 2815 Nodes that use BFD can quickly detect and react to failures so that 2816 cached information is re-established through alternate nodes. BFD 2817 control messaging is carried only over well-connected ground domain 2818 networks (i.e., and not low-end radio links) and can therefore be 2819 tuned for rapid response. 2821 Servers and Relays maintain BFD sessions in parallel with their BGP 2822 peerings. If a Server or Relay fails, BGP peers will quickly re- 2823 establish routes through alternate paths the same as for common BGP 2824 deployments. Similarly, Proxys maintain BFD sessions with their 2825 associated Relays even though they do not establish BGP peerings with 2826 them. 2828 Proxys SHOULD use proactive NUD for Servers for which there are 2829 currently active ANET Clients in a manner that parallels BFD, i.e., 2830 by sending unicast NS messages in rapid succession to receive 2831 solicited NA messages. When the Proxy is also sending RS messages on 2832 behalf of ANET Clients, the RS/RA messaging can be considered as 2833 equivalent hints of forward progress. This means that the Proxy need 2834 not also send a periodic NS if it has already sent an RS within the 2835 same period. If a Server fails, the Proxy will cease to receive 2836 advertisements and can quickly inform Clients of the outage by 2837 sending multicast RA messages on the ANET interface. 2839 The Proxy sends multicast RA messages with source address set to the 2840 Server's address, destination address set to All-Nodes multicast, and 2841 Router Lifetime set to 0. The Proxy SHOULD send 2842 MAX_FINAL_RTR_ADVERTISEMENTS RA messages separated by small delays 2843 [RFC4861]. Any Clients on the ANET interface that have been using 2844 the (now defunct) Server will receive the RA messages and associate 2845 with a new Server. 2847 3.25. AERO Clients on the Open Internet 2849 AERO Clients that connect to the open Internet via native and/or 2850 NATed interfaces can establish a VPN to securely connect to a Server 2851 in a "tethered" arrangement with all of the Client's traffic 2852 transiting the Server. Alternatively, the Client can exchange ND 2853 messages directly with other AERO nodes using SPAN/INET 2854 encapsulation. In that case, the Client must apply asymmetric 2855 security for IPv6 ND messages to ensure routing and neighbor cache 2856 integrity using SEcure Neighbor Discovery (SEND) [RFC3971] and 2857 Cryptographically Generated Addresses (CGAs) [RFC3972]. 2859 When a Client enables native and/or NATed underlying interfaces, the 2860 AERO interface sends an RS message with IPv6 source address set to a 2861 link-local CGA, with IPv6 destination set to All-Routers multicast, 2862 with an OMNI opton and with SEND/CGA options to provide message 2863 authentication. The Client also includes an SLLAO with the IP 2864 address and Port Number used for INET enacpsulation written in 2865 obfuscated form as discussed in Section 3.6. The Client wraps the 2866 message in a SPAN header with source address set to the Client's SPAN 2867 address and with destination address set to the SPAN address of a 2868 Server. The Client then further wraps the SPAN message in an INET 2869 header with source set to the Client's INET address and destination 2870 set to the Server's INET address, then sends the message to the 2871 Server. 2873 When the Server receives the RS message, it authenticates the message 2874 and registers the Client's MNP and INET interface information 2875 according to the OMNI option parameters. The Server then returns an 2876 RA message with IPv6 source set to its CGA, with IPv6 destination set 2877 to the Client's CGA, with an OMNI option and with SEND/CGA options to 2878 provide message authentication. If the Client is located behind a 2879 NAT, the Server instead sets the IPv6 destination to the Teredo IPv6 2880 address formed using the service prefix fe80::/32 (see Section 4 of 2882 [RFC4380]). The Server then wraps the message in a SPAN header with 2883 source address set to the Server's SPAN address and destination set 2884 to the Client's SPAN address, and further wraps the SPAN message in 2885 an INET header with source set to the Server's INET address and 2886 destination set to the Client's INET address. 2888 After the Client has registered its INET interfaces in such RS/RA 2889 exchanges it sends periodic RS messages to receive fresh RA messages 2890 before the Router Lifetime received on each INET interface expires 2891 (again, using SEND/CGA). The Client also maintains default routes 2892 via its Servers, i.e., the same as described in earlier sections. 2894 When the Client sends messages to target IP addresses, it also 2895 invokes route optimization per Section 3.17 using IPv6 ND address 2896 resolution messaging. The Client sends the (SEND/CGA-protected) 2897 NS(AR) message wrapped in a SPAN header with source set to the 2898 Client's SPAN address and destination set to the SPAN address 2899 corresponding to the target, and with INET destination address set to 2900 the address of the Server. The Server authenticates the message and 2901 sends a corresponding NS(AR) message over the SPAN. When the ROR 2902 receives the NS(AR), it adds the Client's SPAN address and Server's 2903 INET address to the target's Report List, and returns an NA with OMNI 2904 and TLLAO information for the target. The Server then returns a 2905 (SEND/CGA-protected) NA message to the Client. 2907 Following route optimization, for any of the target's Native 2908 addresses the Client forwards data packets directly to the target 2909 INET addresses according to the OMNI/TLLAO information. For any 2910 NATed addresses, the Client first establishes NAT state as specified 2911 in [RFC6081][RFC4380] while using "loopback" NS(NUD) messages as 2912 discussed in Section 3.18 as "bubbles". The Client continues to send 2913 data packets via the SPAN until NAT state is populated, then begins 2914 forwarding packets via the direct path through the NAT to the target. 2916 The ROR may return uNAs via the Server if the target moves, and the 2917 Server will send corresponding (SEND/CGA-protected) uNAs to the 2918 Client. The Client can also send "loopback" NS(NUD) messages to test 2919 forward path reachability even though there is no security 2920 association between the Client and the target. 2922 4. Implementation Status 2924 An AERO implementation based on OpenVPN (https://openvpn.net/) was 2925 announced on the v6ops mailing list on January 10, 2018 and an 2926 initial public release of the AERO proof-of-concept source code was 2927 announced on the intarea mailing list on August 21, 2015. 2929 As of 4/1/2020, more recent updated implementations are under 2930 internal development and testing with plans to release in the near 2931 future. 2933 5. IANA Considerations 2935 The IANA has assigned a 4-octet Private Enterprise Number "45282" for 2936 AERO in the "enterprise-numbers" registry. 2938 The IANA has assigned the UDP port number "8060" for an earlier 2939 experimental version of AERO [RFC6706]. This document obsoletes 2940 [RFC6706] and claims the UDP port number "8060" for all future use. 2942 No further IANA actions are required. 2944 6. Security Considerations 2946 AERO Relays configure secured tunnels with AERO Servers and Proxys 2947 within their local SPAN segments. Applicable secured tunnel 2948 alternatives include IPsec [RFC4301], TLS/SSL [RFC8446], DTLS 2949 [RFC6347], WireGuard, etc. The AERO Relays of all SPAN segments in 2950 turn configure secured tunnels for their neighboring AERO Relays 2951 across the SPAN. Therefore, control messages that traverse the SPAN 2952 between any pair of AERO link neighbors are already secured. 2954 AERO Servers, Gateways and Proxys targeted by a route optimization 2955 may also receive packets directly from the INET partitions instead of 2956 via the SPAN. For INET partitions that apply effective ingress 2957 filtering to defeat source address spoofing, the simple data origin 2958 authentication procedures in Section 3.11 can be applied. 2960 For INET partitions that cannot apply effective ingress filtering, 2961 the two options for securing communications include 1) disable route 2962 optimization so that all traffic is conveyed over secured tunnels via 2963 the SPAN, or 2) enable on-demand secure tunnel creation between INET 2964 partition neighbors. Option 1) would result in longer routes than 2965 necessary and traffic concentration on critical infrastructure 2966 elements. Option 2) could be coordinated by establishing a secured 2967 tunnel on-demand instead of performing an NS/NA exchange in the route 2968 optimization procedures. Procedures for establishing on-demand 2969 secured tunnels are out of scope. 2971 AERO Clients that connect to secured enclaves need not apply security 2972 to their ND messages, since the messages will be intercepted by a 2973 perimeter Proxy that applies security on its outward-facing 2974 interface. AERO Clients located outside of secured enclaves can use 2975 symmetric network and/or transport layer security services such as 2976 VPNs, but when there are many prospective neighbors with dynamically 2977 changing connectivity an asymmetric security service such as SEcure 2978 Neighbor Discovery (SEND) [RFC3971] and Cryptographically Generated 2979 Addresses (CGAs) [RFC3972] may be more appropriate. 2981 Application endpoints SHOULD use application-layer security services 2982 such as TLS/SSL, DTLS or SSH [RFC4251] to assure the same level of 2983 protection as for critical secured Internet services. AERO Clients 2984 that require host-based VPN services SHOULD use symmetric network 2985 and/or transport layer security services such as IPsec, TLS/SSL, 2986 DTLS, etc. AERO Proxys and Servers can also provide a network-based 2987 VPN service on behalf of the Client, e.g., if the Client is located 2988 within a secured enclave and cannot establish a VPN on its own 2989 behalf. 2991 AERO Servers and Relays present targets for traffic amplification 2992 Denial of Service (DoS) attacks. This concern is no different than 2993 for widely-deployed VPN security gateways in the Internet, where 2994 attackers could send spoofed packets to the gateways at high data 2995 rates. This can be mitigated by connecting Servers and Relays over 2996 dedicated links with no connections to the Internet and/or when 2997 connections to the Internet are only permitted through well-managed 2998 firewalls. Traffic amplification DoS attacks can also target an AERO 2999 Client's low data rate links. This is a concern not only for Clients 3000 located on the open Internet but also for Clients in secured 3001 enclaves. AERO Servers and Proxys can institute rate limits that 3002 protect Clients from receiving packet floods that could DoS low data 3003 rate links. 3005 AERO Gateways must implement ingress filtering to avoid a spoofing 3006 attack in which spurious SPAN messages are injected into an AERO link 3007 from an outside attacker. AERO Clients MUST ensure that their 3008 connectivity is not used by unauthorized nodes on their EUNs to gain 3009 access to a protected network, i.e., AERO Clients that act as routers 3010 MUST NOT provide routing services for unauthorized nodes. (This 3011 concern is no different than for ordinary hosts that receive an IP 3012 address delegation but then "share" the address with other nodes via 3013 some form of Internet connection sharing such as tethering.) 3015 The MAP list MUST be well-managed and secured from unauthorized 3016 tampering, even though the list contains only public information. 3017 The MAP list can be conveyed to the Client in a similar fashion as in 3018 [RFC5214] (e.g., through layer 2 data link login messaging, secure 3019 upload of a static file, DNS lookups, etc.). 3021 Although public domain and commercial SEND implementations exist, 3022 concerns regarding the strength of the cryptographic hash algorithm 3023 have been documented [RFC6273] [RFC4982]. 3025 Security considerations for accepting link-layer ICMP messages and 3026 reflected packets are discussed throughout the document. 3028 7. Acknowledgements 3030 Discussions in the IETF, aviation standards communities and private 3031 exchanges helped shape some of the concepts in this work. 3032 Individuals who contributed insights include Mikael Abrahamsson, Mark 3033 Andrews, Fred Baker, Bob Braden, Stewart Bryant, Brian Carpenter, 3034 Wojciech Dec, Pavel Drasil, Ralph Droms, Adrian Farrel, Nick Green, 3035 Sri Gundavelli, Brian Haberman, Bernhard Haindl, Joel Halpern, Tom 3036 Herbert, Sascha Hlusiak, Lee Howard, Zdenek Jaron, Andre Kostur, 3037 Hubert Kuenig, Ted Lemon, Andy Malis, Satoru Matsushima, Tomek 3038 Mrugalski, Madhu Niraula, Alexandru Petrescu, Behcet Saikaya, Michal 3039 Skorepa, Joe Touch, Bernie Volz, Ryuji Wakikawa, Tony Whyman, Lloyd 3040 Wood and James Woodyatt. Members of the IESG also provided valuable 3041 input during their review process that greatly improved the document. 3042 Special thanks go to Stewart Bryant, Joel Halpern and Brian Haberman 3043 for their shepherding guidance during the publication of the AERO 3044 first edition. 3046 This work has further been encouraged and supported by Boeing 3047 colleagues including Kyle Bae, M. Wayne Benson, Dave Bernhardt, Cam 3048 Brodie, John Bush, Balaguruna Chidambaram, Irene Chin, Bruce Cornish, 3049 Claudiu Danilov, Don Dillenburg, Joe Dudkowski, Wen Fang, Samad 3050 Farooqui, Anthony Gregory, Jeff Holland, Seth Jahne, Brian Jaury, 3051 Greg Kimberly, Ed King, Madhuri Madhava Badgandi, Laurel Matthew, 3052 Gene MacLean III, Rob Muszkiewicz, Sean O'Sullivan, Vijay 3053 Rajagopalan, Greg Saccone, Rod Santiago, Kent Shuey, Brian Skeen, 3054 Mike Slane, Carrie Spiker, Katie Tran, Brendan Williams, Amelia 3055 Wilson, Julie Wulff, Yueli Yang, Eric Yeh and other members of the 3056 Boeing mobility, networking and autonomy teams. Kyle Bae, Wayne 3057 Benson, Katie Tran and Eric Yeh are especially acknowledged for 3058 implementing the AERO functions as extensions to the public domain 3059 OpenVPN distribution. 3061 Earlier works on NBMA tunneling approaches are found in 3062 [RFC2529][RFC5214][RFC5569]. 3064 Many of the constructs presented in this second edition of AERO are 3065 based on the author's earlier works, including: 3067 o The Internet Routing Overlay Network (IRON) 3068 [RFC6179][I-D.templin-ironbis] 3070 o Virtual Enterprise Traversal (VET) 3071 [RFC5558][I-D.templin-intarea-vet] 3073 o The Subnetwork Encapsulation and Adaptation Layer (SEAL) 3074 [RFC5320][I-D.templin-intarea-seal] 3076 o AERO, First Edition [RFC6706] 3078 Note that these works cite numerous earlier efforts that are not also 3079 cited here due to space limitations. The authors of those earlier 3080 works are acknowledged for their insights. 3082 This work is aligned with the NASA Safe Autonomous Systems Operation 3083 (SASO) program under NASA contract number NNA16BD84C. 3085 This work is aligned with the FAA as per the SE2025 contract number 3086 DTFAWA-15-D-00030. 3088 This work is aligned with the Boeing Commercial Airplanes (BCA) 3089 Internet of Things (IoT) and autonomy programs. 3091 This work is aligned with the Boeing Information Technology (BIT) 3092 MobileNet program. 3094 8. References 3096 8.1. Normative References 3098 [I-D.templin-6man-omni-interface] 3099 Templin, F. and T. Whyman, "Transmission of IPv6 Packets 3100 over Overlay Multilink Network (OMNI) Interfaces", draft- 3101 templin-6man-omni-interface-15 (work in progress), April 3102 2020. 3104 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, 3105 DOI 10.17487/RFC0791, September 1981, 3106 . 3108 [RFC0792] Postel, J., "Internet Control Message Protocol", STD 5, 3109 RFC 792, DOI 10.17487/RFC0792, September 1981, 3110 . 3112 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 3113 Requirement Levels", BCP 14, RFC 2119, 3114 DOI 10.17487/RFC2119, March 1997, 3115 . 3117 [RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in 3118 IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473, 3119 December 1998, . 3121 [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black, 3122 "Definition of the Differentiated Services Field (DS 3123 Field) in the IPv4 and IPv6 Headers", RFC 2474, 3124 DOI 10.17487/RFC2474, December 1998, 3125 . 3127 [RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander, 3128 "SEcure Neighbor Discovery (SEND)", RFC 3971, 3129 DOI 10.17487/RFC3971, March 2005, 3130 . 3132 [RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)", 3133 RFC 3972, DOI 10.17487/RFC3972, March 2005, 3134 . 3136 [RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and 3137 More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191, 3138 November 2005, . 3140 [RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast 3141 Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005, 3142 . 3144 [RFC4380] Huitema, C., "Teredo: Tunneling IPv6 over UDP through 3145 Network Address Translations (NATs)", RFC 4380, 3146 DOI 10.17487/RFC4380, February 2006, 3147 . 3149 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 3150 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 3151 DOI 10.17487/RFC4861, September 2007, 3152 . 3154 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 3155 Address Autoconfiguration", RFC 4862, 3156 DOI 10.17487/RFC4862, September 2007, 3157 . 3159 [RFC5175] Haberman, B., Ed. and R. Hinden, "IPv6 Router 3160 Advertisement Flags Option", RFC 5175, 3161 DOI 10.17487/RFC5175, March 2008, 3162 . 3164 [RFC6081] Thaler, D., "Teredo Extensions", RFC 6081, 3165 DOI 10.17487/RFC6081, January 2011, 3166 . 3168 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 3169 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 3170 May 2017, . 3172 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 3173 (IPv6) Specification", STD 86, RFC 8200, 3174 DOI 10.17487/RFC8200, July 2017, 3175 . 3177 [RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A., 3178 Richardson, M., Jiang, S., Lemon, T., and T. Winters, 3179 "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", 3180 RFC 8415, DOI 10.17487/RFC8415, November 2018, 3181 . 3183 8.2. Informative References 3185 [BGP] Huston, G., "BGP in 2015, http://potaroo.net", January 3186 2016. 3188 [I-D.ietf-6man-segment-routing-header] 3189 Filsfils, C., Dukes, D., Previdi, S., Leddy, J., 3190 Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header 3191 (SRH)", draft-ietf-6man-segment-routing-header-26 (work in 3192 progress), October 2019. 3194 [I-D.ietf-dmm-distributed-mobility-anchoring] 3195 Chan, A., Wei, X., Lee, J., Jeon, S., and C. Bernardos, 3196 "Distributed Mobility Anchoring", draft-ietf-dmm- 3197 distributed-mobility-anchoring-15 (work in progress), 3198 March 2020. 3200 [I-D.ietf-intarea-gue] 3201 Herbert, T., Yong, L., and O. Zia, "Generic UDP 3202 Encapsulation", draft-ietf-intarea-gue-09 (work in 3203 progress), October 2019. 3205 [I-D.ietf-intarea-gue-extensions] 3206 Herbert, T., Yong, L., and F. Templin, "Extensions for 3207 Generic UDP Encapsulation", draft-ietf-intarea-gue- 3208 extensions-06 (work in progress), March 2019. 3210 [I-D.ietf-intarea-tunnels] 3211 Touch, J. and M. Townsley, "IP Tunnels in the Internet 3212 Architecture", draft-ietf-intarea-tunnels-10 (work in 3213 progress), September 2019. 3215 [I-D.ietf-rtgwg-atn-bgp] 3216 Templin, F., Saccone, G., Dawra, G., Lindem, A., and V. 3217 Moreno, "A Simple BGP-based Mobile Routing System for the 3218 Aeronautical Telecommunications Network", draft-ietf- 3219 rtgwg-atn-bgp-05 (work in progress), January 2020. 3221 [I-D.templin-6man-dhcpv6-ndopt] 3222 Templin, F., "A Unified Stateful/Stateless Configuration 3223 Service for IPv6", draft-templin-6man-dhcpv6-ndopt-09 3224 (work in progress), January 2020. 3226 [I-D.templin-intarea-grefrag] 3227 Templin, F., "GRE Tunnel Level Fragmentation", draft- 3228 templin-intarea-grefrag-04 (work in progress), July 2016. 3230 [I-D.templin-intarea-seal] 3231 Templin, F., "The Subnetwork Encapsulation and Adaptation 3232 Layer (SEAL)", draft-templin-intarea-seal-68 (work in 3233 progress), January 2014. 3235 [I-D.templin-intarea-vet] 3236 Templin, F., "Virtual Enterprise Traversal (VET)", draft- 3237 templin-intarea-vet-40 (work in progress), May 2013. 3239 [I-D.templin-ironbis] 3240 Templin, F., "The Interior Routing Overlay Network 3241 (IRON)", draft-templin-ironbis-16 (work in progress), 3242 March 2014. 3244 [I-D.templin-v6ops-pdhost] 3245 Templin, F., "IPv6 Prefix Delegation and Multi-Addressing 3246 Models", draft-templin-v6ops-pdhost-25 (work in progress), 3247 January 2020. 3249 [OVPN] OpenVPN, O., "http://openvpn.net", October 2016. 3251 [RFC1035] Mockapetris, P., "Domain names - implementation and 3252 specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, 3253 November 1987, . 3255 [RFC1122] Braden, R., Ed., "Requirements for Internet Hosts - 3256 Communication Layers", STD 3, RFC 1122, 3257 DOI 10.17487/RFC1122, October 1989, 3258 . 3260 [RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191, 3261 DOI 10.17487/RFC1191, November 1990, 3262 . 3264 [RFC1812] Baker, F., Ed., "Requirements for IP Version 4 Routers", 3265 RFC 1812, DOI 10.17487/RFC1812, June 1995, 3266 . 3268 [RFC2003] Perkins, C., "IP Encapsulation within IP", RFC 2003, 3269 DOI 10.17487/RFC2003, October 1996, 3270 . 3272 [RFC2236] Fenner, W., "Internet Group Management Protocol, Version 3273 2", RFC 2236, DOI 10.17487/RFC2236, November 1997, 3274 . 3276 [RFC2492] Armitage, G., Schulter, P., and M. Jork, "IPv6 over ATM 3277 Networks", RFC 2492, DOI 10.17487/RFC2492, January 1999, 3278 . 3280 [RFC2529] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4 3281 Domains without Explicit Tunnels", RFC 2529, 3282 DOI 10.17487/RFC2529, March 1999, 3283 . 3285 [RFC2764] Gleeson, B., Lin, A., Heinanen, J., Armitage, G., and A. 3286 Malis, "A Framework for IP Based Virtual Private 3287 Networks", RFC 2764, DOI 10.17487/RFC2764, February 2000, 3288 . 3290 [RFC2784] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P. 3291 Traina, "Generic Routing Encapsulation (GRE)", RFC 2784, 3292 DOI 10.17487/RFC2784, March 2000, 3293 . 3295 [RFC2890] Dommety, G., "Key and Sequence Number Extensions to GRE", 3296 RFC 2890, DOI 10.17487/RFC2890, September 2000, 3297 . 3299 [RFC2923] Lahey, K., "TCP Problems with Path MTU Discovery", 3300 RFC 2923, DOI 10.17487/RFC2923, September 2000, 3301 . 3303 [RFC2983] Black, D., "Differentiated Services and Tunnels", 3304 RFC 2983, DOI 10.17487/RFC2983, October 2000, 3305 . 3307 [RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition 3308 of Explicit Congestion Notification (ECN) to IP", 3309 RFC 3168, DOI 10.17487/RFC3168, September 2001, 3310 . 3312 [RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener 3313 Discovery Version 2 (MLDv2) for IPv6", RFC 3810, 3314 DOI 10.17487/RFC3810, June 2004, 3315 . 3317 [RFC3819] Karn, P., Ed., Bormann, C., Fairhurst, G., Grossman, D., 3318 Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J., and L. 3319 Wood, "Advice for Internet Subnetwork Designers", BCP 89, 3320 RFC 3819, DOI 10.17487/RFC3819, July 2004, 3321 . 3323 [RFC4213] Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms 3324 for IPv6 Hosts and Routers", RFC 4213, 3325 DOI 10.17487/RFC4213, October 2005, 3326 . 3328 [RFC4251] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH) 3329 Protocol Architecture", RFC 4251, DOI 10.17487/RFC4251, 3330 January 2006, . 3332 [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A 3333 Border Gateway Protocol 4 (BGP-4)", RFC 4271, 3334 DOI 10.17487/RFC4271, January 2006, 3335 . 3337 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 3338 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 3339 2006, . 3341 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 3342 Internet Protocol", RFC 4301, DOI 10.17487/RFC4301, 3343 December 2005, . 3345 [RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery 3346 Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April 3347 2006, . 3349 [RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet 3350 Control Message Protocol (ICMPv6) for the Internet 3351 Protocol Version 6 (IPv6) Specification", STD 89, 3352 RFC 4443, DOI 10.17487/RFC4443, March 2006, 3353 . 3355 [RFC4511] Sermersheim, J., Ed., "Lightweight Directory Access 3356 Protocol (LDAP): The Protocol", RFC 4511, 3357 DOI 10.17487/RFC4511, June 2006, 3358 . 3360 [RFC4541] Christensen, M., Kimball, K., and F. Solensky, 3361 "Considerations for Internet Group Management Protocol 3362 (IGMP) and Multicast Listener Discovery (MLD) Snooping 3363 Switches", RFC 4541, DOI 10.17487/RFC4541, May 2006, 3364 . 3366 [RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick, 3367 "Internet Group Management Protocol (IGMP) / Multicast 3368 Listener Discovery (MLD)-Based Multicast Forwarding 3369 ("IGMP/MLD Proxying")", RFC 4605, DOI 10.17487/RFC4605, 3370 August 2006, . 3372 [RFC4607] Holbrook, H. and B. Cain, "Source-Specific Multicast for 3373 IP", RFC 4607, DOI 10.17487/RFC4607, August 2006, 3374 . 3376 [RFC4963] Heffner, J., Mathis, M., and B. Chandler, "IPv4 Reassembly 3377 Errors at High Data Rates", RFC 4963, 3378 DOI 10.17487/RFC4963, July 2007, 3379 . 3381 [RFC4982] Bagnulo, M. and J. Arkko, "Support for Multiple Hash 3382 Algorithms in Cryptographically Generated Addresses 3383 (CGAs)", RFC 4982, DOI 10.17487/RFC4982, July 2007, 3384 . 3386 [RFC5015] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano, 3387 "Bidirectional Protocol Independent Multicast (BIDIR- 3388 PIM)", RFC 5015, DOI 10.17487/RFC5015, October 2007, 3389 . 3391 [RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site 3392 Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214, 3393 DOI 10.17487/RFC5214, March 2008, 3394 . 3396 [RFC5320] Templin, F., Ed., "The Subnetwork Encapsulation and 3397 Adaptation Layer (SEAL)", RFC 5320, DOI 10.17487/RFC5320, 3398 February 2010, . 3400 [RFC5522] Eddy, W., Ivancic, W., and T. Davis, "Network Mobility 3401 Route Optimization Requirements for Operational Use in 3402 Aeronautics and Space Exploration Mobile Networks", 3403 RFC 5522, DOI 10.17487/RFC5522, October 2009, 3404 . 3406 [RFC5558] Templin, F., Ed., "Virtual Enterprise Traversal (VET)", 3407 RFC 5558, DOI 10.17487/RFC5558, February 2010, 3408 . 3410 [RFC5569] Despres, R., "IPv6 Rapid Deployment on IPv4 3411 Infrastructures (6rd)", RFC 5569, DOI 10.17487/RFC5569, 3412 January 2010, . 3414 [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 3415 (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, 3416 . 3418 [RFC6106] Jeong, J., Park, S., Beloeil, L., and S. Madanapalli, 3419 "IPv6 Router Advertisement Options for DNS Configuration", 3420 RFC 6106, DOI 10.17487/RFC6106, November 2010, 3421 . 3423 [RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful 3424 NAT64: Network Address and Protocol Translation from IPv6 3425 Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146, 3426 April 2011, . 3428 [RFC6179] Templin, F., Ed., "The Internet Routing Overlay Network 3429 (IRON)", RFC 6179, DOI 10.17487/RFC6179, March 2011, 3430 . 3432 [RFC6221] Miles, D., Ed., Ooghe, S., Dec, W., Krishnan, S., and A. 3433 Kavanagh, "Lightweight DHCPv6 Relay Agent", RFC 6221, 3434 DOI 10.17487/RFC6221, May 2011, 3435 . 3437 [RFC6273] Kukec, A., Krishnan, S., and S. Jiang, "The Secure 3438 Neighbor Discovery (SEND) Hash Threat Analysis", RFC 6273, 3439 DOI 10.17487/RFC6273, June 2011, 3440 . 3442 [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer 3443 Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, 3444 January 2012, . 3446 [RFC6438] Carpenter, B. and S. Amante, "Using the IPv6 Flow Label 3447 for Equal Cost Multipath Routing and Link Aggregation in 3448 Tunnels", RFC 6438, DOI 10.17487/RFC6438, November 2011, 3449 . 3451 [RFC6706] Templin, F., Ed., "Asymmetric Extended Route Optimization 3452 (AERO)", RFC 6706, DOI 10.17487/RFC6706, August 2012, 3453 . 3455 [RFC6864] Touch, J., "Updated Specification of the IPv4 ID Field", 3456 RFC 6864, DOI 10.17487/RFC6864, February 2013, 3457 . 3459 [RFC7269] Chen, G., Cao, Z., Xie, C., and D. Binet, "NAT64 3460 Deployment Options and Experience", RFC 7269, 3461 DOI 10.17487/RFC7269, June 2014, 3462 . 3464 [RFC7333] Chan, H., Ed., Liu, D., Seite, P., Yokota, H., and J. 3465 Korhonen, "Requirements for Distributed Mobility 3466 Management", RFC 7333, DOI 10.17487/RFC7333, August 2014, 3467 . 3469 [RFC7421] Carpenter, B., Ed., Chown, T., Gont, F., Jiang, S., 3470 Petrescu, A., and A. Yourtchenko, "Analysis of the 64-bit 3471 Boundary in IPv6 Addressing", RFC 7421, 3472 DOI 10.17487/RFC7421, January 2015, 3473 . 3475 [RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I., 3476 Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent 3477 Multicast - Sparse Mode (PIM-SM): Protocol Specification 3478 (Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March 3479 2016, . 3481 [RFC8086] Yong, L., Ed., Crabbe, E., Xu, X., and T. Herbert, "GRE- 3482 in-UDP Encapsulation", RFC 8086, DOI 10.17487/RFC8086, 3483 March 2017, . 3485 [RFC8201] McCann, J., Deering, S., Mogul, J., and R. Hinden, Ed., 3486 "Path MTU Discovery for IP version 6", STD 87, RFC 8201, 3487 DOI 10.17487/RFC8201, July 2017, 3488 . 3490 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 3491 Decraene, B., Litkowski, S., and R. Shakir, "Segment 3492 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 3493 July 2018, . 3495 [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol 3496 Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, 3497 . 3499 [RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J., 3500 Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header 3501 (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020, 3502 . 3504 Appendix A. AERO Alternate Encapsulations 3506 When GUE encapsulation is not needed, AERO can use common 3507 encapsulations such as IP-in-IP [RFC2003][RFC2473][RFC4213], Generic 3508 Routing Encapsulation (GRE) [RFC2784][RFC2890] and others. The 3509 encapsulation is therefore only differentiated from non-AERO tunnels 3510 through the application of AERO control messaging and not through, 3511 e.g., a well-known UDP port number. 3513 As for GUE encapsulation, alternate AERO encapsulation formats may 3514 require encapsulation layer fragmentation. For simple IP-in-IP 3515 encapsulation, an IPv6 fragment header is inserted directly between 3516 the inner and outer IP headers when needed, i.e., even if the outer 3517 header is IPv4. The IPv6 Fragment Header is identified to the outer 3518 IP layer by its IP protocol number, and the Next Header field in the 3519 IPv6 Fragment Header identifies the inner IP header version. For GRE 3520 encapsulation, a GRE fragment header is inserted within the GRE 3521 header [I-D.templin-intarea-grefrag]. 3523 Figure 6 shows the AERO IP-in-IP encapsulation format before any 3524 fragmentation is applied: 3526 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3527 | Outer IPv4 Header | | Outer IPv6 Header | 3528 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3529 |IPv6 Frag Header (optional)| |IPv6 Frag Header (optional)| 3530 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3531 | Inner IP Header | | Inner IP Header | 3532 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3533 | | | | 3534 ~ ~ ~ ~ 3535 ~ Inner Packet Body ~ ~ Inner Packet Body ~ 3536 ~ ~ ~ ~ 3537 | | | | 3538 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3540 Minimal Encapsulation in IPv4 Minimal Encapsulation in IPv6 3542 Figure 6: Minimal Encapsulation Format using IP-in-IP 3544 Figure 7 shows the AERO GRE encapsulation format before any 3545 fragmentation is applied: 3547 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3548 | Outer IP Header | 3549 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3550 | GRE Header | 3551 | (with checksum, key, etc..) | 3552 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3553 | GRE Fragment Header (optional)| 3554 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3555 | Inner IP Header | 3556 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3557 | | 3558 ~ ~ 3559 ~ Inner Packet Body ~ 3560 ~ ~ 3561 | | 3562 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3564 Figure 7: Minimal Encapsulation Using GRE 3566 Alternate encapsulation may be preferred in environments where GUE 3567 encapsulation would add unnecessary overhead. For example, certain 3568 low-bandwidth wireless data links may benefit from a reduced 3569 encapsulation overhead. 3571 GUE encapsulation can traverse network paths that are inaccessible to 3572 non-UDP encapsulations, e.g., for crossing Network Address 3573 Translators (NATs). More and more, network middleboxes are also 3574 being configured to discard packets that include anything other than 3575 a well-known IP protocol such as UDP and TCP. It may therefore be 3576 necessary to determine the potential for middlebox filtering before 3577 enabling alternate encapsulation in a given environment. 3579 In addition to IP-in-IP, GRE and GUE, AERO can also use security 3580 encapsulations such as IPsec, TLS/SSL, DTLS, etc. In that case, AERO 3581 control messaging and route determination occur before security 3582 encapsulation is applied for outgoing packets and after security 3583 decapsulation is applied for incoming packets. 3585 AERO is especially well suited for use with VPN system encapsulations 3586 such as OpenVPN [OVPN]. 3588 Appendix B. Non-Normative Considerations 3590 AERO can be applied to a multitude of Internetworking scenarios, with 3591 each having its own adaptations. The following considerations are 3592 provided as non-normative guidance: 3594 B.1. Implementation Strategies for Route Optimization 3596 Route optimization as discussed in Section 3.17 results in the route 3597 optimization source (ROS) creating an asymmetric neighbor cache entry 3598 for the target neighbor. The neighbor cache entry is maintained for 3599 at most REACHABLE_TIME seconds and then deleted unless updated. In 3600 order to refresh the neighbor cache entry lifetime before the 3601 ReachableTime timer expires, the specification requires 3602 implementations to issue a new NS/NA exchange to reset ReachableTime 3603 to REACHABLE_TIME seconds while data packets are still flowing. 3604 However, the decision of when to initiate a new NS/NA exchange and to 3605 perpetuate the process is left as an implementation detail. 3607 One possible strategy may be to monitor the neighbor cache entry 3608 watching for data packets for (REACHABLE_TIME - 5) seconds. If any 3609 data packets have been sent to the neighbor within this timeframe, 3610 then send an NS to receive a new NA. If no data packets have been 3611 sent, wait for 5 additional seconds and send an immediate NS if any 3612 data packets are sent within this "expiration pending" 5 second 3613 window. If no additional data packets are sent within the 5 second 3614 window, delete the neighbor cache entry. 3616 The monitoring of the neighbor data packet traffic therefore becomes 3617 an asymmetric ongoing process during the neighbor cache entry 3618 lifetime. If the neighbor cache entry expires, future data packets 3619 will trigger a new NS/NA exchange while the packets themselves are 3620 delivered over a longer path until route optimization state is re- 3621 established. 3623 B.2. Implicit Mobility Management 3625 AERO interface neighbors MAY provide a configuration option that 3626 allows them to perform implicit mobility management in which no ND 3627 messaging is used. In that case, the Client only transmits packets 3628 over a single interface at a time, and the neighbor always observes 3629 packets arriving from the Client from the same link-layer source 3630 address. 3632 If the Client's underlying interface address changes (either due to a 3633 readdressing of the original interface or switching to a new 3634 interface) the neighbor immediately updates the neighbor cache entry 3635 for the Client and begins accepting and sending packets according to 3636 the Client's new address. This implicit mobility method applies to 3637 use cases such as cellphones with both WiFi and Cellular interfaces 3638 where only one of the interfaces is active at a given time, and the 3639 Client automatically switches over to the backup interface if the 3640 primary interface fails. 3642 B.3. Direct Underlying Interfaces 3644 When a Client's AERO interface is configured over a Direct interface, 3645 the neighbor at the other end of the Direct link can receive packets 3646 without any encapsulation. In that case, the Client sends packets 3647 over the Direct link according to QoS preferences. If the Direct 3648 interface has the highest QoS preference, then the Client's IP 3649 packets are transmitted directly to the peer without going through an 3650 ANET/INET. If other interfaces have higher QoS preferences, then the 3651 Client's IP packets are transmitted via a different interface, which 3652 may result in the inclusion of Proxys, Servers and Relays in the 3653 communications path. Direct interfaces must be tested periodically 3654 for reachability, e.g., via NUD. 3656 B.4. Operation on AERO Links with /64 ASPs 3658 IPv6 AERO links typically have MSPs that aggregate many candidate 3659 MNPs of length /64 or shorter. However, in some cases it may be 3660 desirable to use AERO over links that have only a /64 MSP. This can 3661 be accommodated by treating all Clients on the AERO link as simple 3662 hosts that receive /128 prefix delegations. 3664 In that case, the Client sends an RS message to the Server the same 3665 as for ordinary AERO links. The Server responds with an RA message 3666 that includes one or more /128 prefixes (i.e., singleton addresses) 3667 that include the /64 MSP prefix along with an interface identifier 3668 portion to be assigned to the Client. The Client and Server then 3669 configure their AERO addresses based on the interface identifier 3670 portions of the /128s (i.e., the lower 64 bits) and not based on the 3671 /64 prefix (i.e., the upper 64 bits). 3673 For example, if the MSP for the host-only IPv6 AERO link is 3674 2001:db8:1000:2000::/64, each Client will receive one or more /128 3675 IPv6 prefix delegations such as 2001:db8:1000:2000::1/128, 3676 2001:db8:1000:2000::2/128, etc. When the Client receives the prefix 3677 delegations, it assigns the AERO addresses fe80::1, fe80::2, etc. to 3678 the AERO interface, and assigns the global IPv6 addresses (i.e., the 3679 /128s) to either the AERO interface or an internal virtual interface 3680 such as a loopback. In this arrangement, the Client conducts route 3681 optimization in the same sense as discussed in Section 3.17. 3683 This specification has applicability for nodes that act as a Client 3684 on an "upstream" AERO link, but also act as a Server on "downstream" 3685 AERO links. More specifically, if the node acts as a Client to 3686 receive a /64 prefix from the upstream AERO link it can then act as a 3687 Server to provision /128s to Clients on downstream AERO links. 3689 B.5. AERO Critical Infrastructure Considerations 3691 AERO Relays can be either Commercial off-the Shelf (COTS) standard IP 3692 routers or virtual machines in the cloud. Relays must be 3693 provisioned, supported and managed by the INET administrative 3694 authority, and connected to the Relays of other INETs via inter- 3695 domain peerings. Cost for purchasing, configuring and managing 3696 Relays is nominal even for very large AERO links. 3698 AERO Servers can be standard dedicated server platforms, but most 3699 often will be deployed as virtual machines in the cloud. The only 3700 requirements for Servers are that they can run the AERO user-level 3701 code and have at least one network interface connection to the INET. 3702 As with Relays, Servers must be provisioned, supported and managed by 3703 the INET administrative authority. Cost for purchasing, configuring 3704 and managing Servers is nominal especially for virtual Servers hosted 3705 in the cloud. 3707 AERO Proxys are most often standard dedicated server platforms with 3708 one network interface connected to the ANET and a second interface 3709 connected to an INET. As with Servers, the only requirements are 3710 that they can run the AERO user-level code and have at least one 3711 interface connection to the INET. Proxys must be provisioned, 3712 supported and managed by the ANET administrative authority. Cost for 3713 purchasing, configuring and managing Proxys is nominal, and borne by 3714 the ANET administrative authority. 3716 AERO Gateways can be any dedicated server or COTS router platform 3717 connected to INETs and/or EUNs. The Gateway joins the SPAN and 3718 engages in eBGP peering with one or more Relays as a stub AS. The 3719 Gateway then injects its MNPs and/or non-MNP prefixes into the BGP 3720 routing system, and provisions the prefixes to its downstream- 3721 attached networks. The Gateway can perform ROS/ROR services the same 3722 as for any Server, and can route between the MNP and non-MNP address 3723 spaces. 3725 B.6. AERO Server Failure Implications 3727 AERO Servers may appear as a single point of failure in the 3728 architecture, but such is not the case since all Servers on the link 3729 provide identical services and loss of a Server does not imply 3730 immediate and/or comprehensive communication failures. Although 3731 Clients typically associate with a single Server at a time, Server 3732 failure is quickly detected and conveyed by Bidirectional Forward 3733 Detection (BFD) and/or proactive NUD allowing Clients to migrate to 3734 new Servers. 3736 If a Server fails, ongoing packet forwarding to Clients will continue 3737 by virtue of the asymmetric neighbor cache entries that have already 3738 been established in route optimization sources (ROSs). If a Client 3739 also experiences mobility events at roughly the same time the Server 3740 fails, unsolicited NA messages may be lost but proxy neighbor cache 3741 entries in the DEPARTED state will ensure that packet forwarding to 3742 the Client's new locations will continue for up to DEPART_TIME 3743 seconds. 3745 If a Client is left without a Server for an extended timeframe (e.g., 3746 greater than REACHABLETIIME seconds) then existing asymmetric 3747 neighbor cache entries will eventually expire and both ongoing and 3748 new communications will fail. The original source will continue to 3749 retransmit until the Client has established a new Server 3750 relationship, after which time continuous communications will resume. 3752 Therefore, providing many Servers on the link with high availability 3753 profiles provides resilience against loss of individual Servers and 3754 assurance that Clients can establish new Server relationships quickly 3755 in event of a Server failure. 3757 B.7. AERO Client / Server Architecture 3759 The AERO architectural model is client / server in the control plane, 3760 with route optimization in the data plane. The same as for common 3761 Internet services, the AERO Client discovers the addresses of AERO 3762 Servers and selects one Server to connect to. The AERO service is 3763 analogous to common Internet services such as google.com, yahoo.com, 3764 cnn.com, etc. However, there is only one AERO service for the link 3765 and all Servers provide identical services. 3767 Common Internet services provide differing strategies for advertising 3768 server addresses to clients. The strategy is conveyed through the 3769 DNS resource records returned in response to name resolution queries. 3770 As of January 2020 Internet-based 'nslookup' services were used to 3771 determine the following: 3773 o When a client resolves the domainname "google.com", the DNS always 3774 returns one A record (i.e., an IPv4 address) and one AAAA record 3775 (i.e., an IPv6 address). The client receives the same addresses 3776 each time it resolves the domainname via the same DNS resolver, 3777 but may receive different addresses when it resolves the 3778 domainname via different DNS resolvers. But, in each case, 3779 exactly one A and one AAAA record are returned. 3781 o When a client resolves the domainname "ietf.org", the DNS always 3782 returns one A record and one AAAA record with the same addresses 3783 regardless of which DNS resolver is used. 3785 o When a client resolves the domainname "yahoo.com", the DNS always 3786 returns a list of 4 A records and 4 AAAA records. Each time the 3787 client resolves the domainname via the same DNS resolver, the same 3788 list of addresses are returned but in randomized order (i.e., 3789 consistent with a DNS round-robin strategy). But, interestingly, 3790 the same addresses are returned (albeit in randomized order) when 3791 the domainname is resolved via different DNS resolvers. 3793 o When a client resolves the domainname "amazon.com", the DNS always 3794 returns a list of 3 A records and no AAAA records. As with 3795 "yahoo.com", the same three A records are returned from any 3796 worldwide Internet connection point in randomized order. 3798 The above example strategies show differing approaches to Internet 3799 resilience and service distribution offered by major Internet 3800 services. The Google approach exposes only a single IPv4 and a 3801 single IPv6 address to clients. Clients can then select whichever IP 3802 protocol version offers the best response, but will always use the 3803 same IP address according to the current Internet connection point. 3804 This means that the IP address offered by the network must lead to a 3805 highly-available server and/or service distribution point. In other 3806 words, resilience is predicated on high availability within the 3807 network and with no client-initiated failovers expected (i.e., it is 3808 all-or-nothing from the client's perspective). However, Google does 3809 provide for worldwide distributed service distribution by virtue of 3810 the fact that each Internet connection point responds with a 3811 different IPv6 and IPv4 address. The IETF approach is like google 3812 (all-or-nothing from the client's perspective), but provides only a 3813 single IPv4 or IPv6 address on a worldwide basis. This means that 3814 the addresses must be made highly-available at the network level with 3815 no client failover possibility, and if there is any worldwide service 3816 distribution it would need to be conducted by a network element that 3817 is reached via the IP address acting as a service distribution point. 3819 In contrast to the Google and IETF philosophies, Yahoo and Amazon 3820 both provide clients with a (short) list of IP addresses with Yahoo 3821 providing both IP protocol versions and Amazon as IPv4-only. The 3822 order of the list is randomized with each name service query 3823 response, with the effect of round-robin load balancing for service 3824 distribution. With a short list of addresses, there is still 3825 expectation that the network will implement high availability for 3826 each address but in case any single address fails the client can 3827 switch over to using a different address. The balance then becomes 3828 one of function in the network vs function in the end system. 3830 The same implications observed for common highly-available services 3831 in the Internet apply also to the AERO client/server architecture. 3832 When an AERO Client connects to one or more ANETs, it discovers one 3833 or more AERO Server addresses through the mechanisms discussed in 3834 earlier sections. Each Server address presumably leads to a fault- 3835 tolerant clustering arrangement such as supported by Linux-HA, 3836 Extended Virtual Synchrony or Paxos. Such an arrangement has 3837 precedence in common Internet service deployments in lightweight 3838 virtual machines without requiring expensive hardware deployment. 3839 Similarly, common Internet service deployments set service IP 3840 addresses on service distribution points that may relay requests to 3841 many different servers. 3843 For AERO, the expectation is that a combination of the Google/IETF 3844 and Yahoo/Amazon philosophies would be employed. The AERO Client 3845 connects to different ANET access points and can receive 1-2 Server 3846 AERO addresses at each point. It then selects one AERO Server 3847 address, and engages in RS/RA exchanges with the same Server from all 3848 ANET connections. The Client remains with this Server unless or 3849 until the Server fails, in which case it can switch over to an 3850 alternate Server. The Client can likewise switch over to a different 3851 Server at any time if there is some reason for it to do so. So, the 3852 AERO expectation is for a balance of function in the network and end 3853 system, with fault tolerance and resilience at both levels. 3855 Appendix C. Change Log 3857 << RFC Editor - remove prior to publication >> 3859 Changes from draft-templin-intarea-6706bis-42 to draft-templin- 3860 intrea-6706bis-43: 3862 o Segment Routing. 3864 Changes from draft-templin-intarea-6706bis-39 to draft-templin- 3865 intrea-6706bis-40: 3867 o Teredo. 3869 Changes from draft-templin-intarea-6706bis-38 to draft-templin- 3870 intrea-6706bis-39: 3872 o Major clrifications and simplifications of SPAN fragmentation/ 3873 reassembly. 3875 o Revised AERO address format to support prefix lengths up to 112. 3877 o New method for forming SPAN Client Prefixes and population in the 3878 routing system. 3880 o Updates RFC4443 to set a new value in the ICMP PTB Code field. 3882 Changes from draft-templin-intarea-6706bis-35 to draft-templin- 3883 intrea-6706bis-36: 3885 o Clients in the open Internet secured using SEND/CGA. 3887 Changes from draft-templin-intarea-6706bis-32 to draft-templin- 3888 intrea-6706bis-33: 3890 o Updated Proxy discussion with "point-to-multipoint" server 3891 coordination 3893 o Significant updates to Address Resolution and NUD to include 3894 correct addresses in messages 3896 o Differentiate between NS(AR) and NS(NUD) as their addresses and 3897 use cases differ. 3899 Changes from draft-templin-intarea-6706bis-30 to draft-templin- 3900 intrea-6706bis-31: 3902 o Added "advisory PTB messages" under FAA SE2025 contract number 3903 DTFAWA-15-D-00030. 3905 Changes from draft-templin-intarea-6706bis-29 to draft-templin- 3906 intrea-6706bis-30: 3908 o Deprecate "primary" concept. Now, RS/RA keepalives are 3909 mainatained over *all* underlying interfaces (i.e., and not just 3910 one primary). 3912 Changes from draft-templin-intarea-6706bis-28 to draft-templin- 3913 intrea-6706bis-29: 3915 o Changed OMNI interface citation to "draft-templin-6man-omni- 3916 interface" 3918 o Changed SPAN Service Prefix to fd80::/10. 3920 o Changed S/TLLAO format to include 'S' bit for ifIndex 3921 corresponding to the underlying interface that is Source of ND 3922 message. 3924 o Updated Path MTU 3926 Changes from draft-templin-intarea-6706bis-27 to draft-templin- 3927 intrea-6706bis-28: 3929 o MTU and fragmentation. 3931 Changes from draft-templin-intarea-6706bis-26 to draft-templin- 3932 intrea-6706bis-27: 3934 o MTU and fragmentation. 3936 o SPAN Service Prefix set to fd00::/10 3938 o Client SPAN addresses defined. 3940 Changes from draft-templin-intarea-6706bis-25 to draft-templin- 3941 intrea-6706bis-26: 3943 o MTU and RA configuration information updated. 3945 Changes from draft-templin-intarea-6706bis-24 to draft-templin- 3946 intrea-6706bis-25: 3948 o Added concept of "primary" to allow for proxyed RS/RA over only 3949 selected underlying interfaces. 3951 o General Cleanup. 3953 Changes from draft-templin-intarea-6706bis-23 to draft-templin- 3954 intrea-6706bis-24: 3956 o OMNI interface spec now a normative reference. 3958 o Use REACHABLE_TIME as the nominal Router Lifetime to return in 3959 RAs. 3961 o General cleanup. 3963 Changes from draft-templin-intarea-6706bis-22 to draft-templin- 3964 intrea-6706bis-23: 3966 o Choice of using either RS/RA or unsolicited NA for old Server 3967 notification. 3969 o General cleanup. 3971 Changes from draft-templin-intarea-6706bis-21 to draft-templin- 3972 intrea-6706bis-22: 3974 o Tightened up text on Proxy. 3976 o Removed unnecessarily restrictive texts. 3978 o General cleanup. 3980 Changes from draft-templin-intarea-6706bis-20 to draft-templin- 3981 intrea-6706bis-21: 3983 o Clarified relationship between OMNI and S/TLLAO ifIndex-tuples. 3985 o Important text in Section 13.15.3 on Servers timing out Clients 3986 that have gone silent without sending a departure notification. 3988 o New text on RS/RA as "hints of forward progress" for proactive 3989 NUD. 3991 Changes from draft-templin-intarea-6706bis-19 to draft-templin- 3992 intrea-6706bis-20: 3994 o Included new route optimization source and destination addressing 3995 strategy. Now, route optimization maintenance uses the address of 3996 the existing Server instead of the data packet destination address 3997 so that less pressure is placed on the BGP routing system 3998 convergence time and Server constancy is supported. 4000 o Included new method for releasing from old MSE without requiring 4001 Client messaging. 4003 o Included references to new OMNI interface spec (including the OMNI 4004 option). 4006 o New appendix on AERO Client/Server architecture. 4008 Changes from draft-templin-intarea-6706bis-18 to draft-templin- 4009 intrea-6706bis-19: 4011 o Changed Proxy/Server keepalives to use "proactive NUD" in a manner 4012 tha paralles BFD 4014 Changes from draft-templin-intarea-6706bis-17 to draft-templin- 4015 intrea-6706bis-18: 4017 o Discuss how AERO option is used in relation to S/TLLAOs 4019 o New text on Bidirectional Forwarding Detection (BFD) 4021 o Cleaned up usage (and non-usage) of unsolicited NAs 4023 o New appendix on Server failures 4025 Changes from draft-templin-intarea-6706bis-15 to draft-templin- 4026 intrea-6706bis-17: 4028 o S/TLLAO now includes multiple link-layer addresses within a single 4029 option instead of requiring multiple options 4031 o New unsolicited NA message to inform the old link that a Client 4032 has moved to a new link 4034 Changes from draft-templin-intarea-6706bis-14 to draft-templin- 4035 intrea-6706bis-15: 4037 o MTU and fragmentation 4039 o New details in movement to new Server 4041 Changes from draft-templin-intarea-6706bis-13 to draft-templin- 4042 intrea-6706bis-14: 4044 o Security based on secured tunnels, ingress filtering, MAP list and 4045 ROS list 4047 Changes from draft-templin-intarea-6706bis-12 to draft-templin- 4048 intrea-6706bis-13: 4050 o New paragraph in Section 3.6 on AERO interface layering over 4051 secured tunnels 4053 o Removed extraneous text in Section 3.7 4055 o Added new detail to the forwarding algorithm in Section 3.9 4057 o Clarified use of fragmentation 4059 o Route optimization now supported for both MNP and non-MNP-based 4060 prefixes 4062 o Relays are now seen as link-layer elements in the architecture. 4064 o Built out multicast section in detail. 4066 o New Appendix on implementation considerations for route 4067 optimization. 4069 Changes from draft-templin-intarea-6706bis-11 to draft-templin- 4070 intrea-6706bis-12: 4072 o Introduced Gateways as a new AERO element for connecting 4073 Correspondent Nodes on INET links 4075 o Introduced terms "Access Network (ANET)" and "Internetwork (INET)" 4076 o Changed "ASP" to "MSP", and "ACP" to "MNP" 4078 o New figure on the relation of Segments to the SPAN and AERO link 4080 o New "S" bit in S/TLLAO to indicate the "Source" S/TLLAO as opposed 4081 to additional S/TLLAOs 4083 o Changed Interface ID for Servers from 255 to 0xffff 4085 o Significant updates to Route Optimization, NUD, and Mobility 4086 Management 4088 o New Section on Multicast 4090 o New Section on AERO Clients in the open Internetwork 4092 o New Section on Operation over multiple AERO links (VLANs over the 4093 SPAN) 4095 o New Sections on DNS considerations and Transition considerations 4097 o 4099 Changes from draft-templin-intarea-6706bis-10 to draft-templin- 4100 intrea-6706bis-11: 4102 o Added The SPAN 4104 Changes from draft-templin-intarea-6706bis-09 to draft-templin- 4105 intrea-6706bis-10: 4107 o Orphaned packets in flight (e.g., when a neighbor cache entry is 4108 in the DEPARTED state) are now forwarded at the link layer instead 4109 of at the network layer. Forwarding at the network layer can 4110 result in routing loops and/or excessive delays of forwarded 4111 packets while the routing system is still reconverging. 4113 o Update route optimization to clarify the unsecured nature of the 4114 first NS used for route discovery 4116 o Many cleanups and clarifications on ND messaging parameters 4118 Changes from draft-templin-intarea-6706bis-08 to draft-templin- 4119 intrea-6706bis-09: 4121 o Changed PRL to "MAP list" 4122 o For neighbor cache entries, changed "static" to "symmetric", and 4123 "dynamic" to "asymmetric" 4125 o Specified Proxy RS/RA exchanges with Servers on behalf of Clients 4127 o Added discussion of unsolicited NAs in Section 3.16, and included 4128 forward reference to Section 3.18 4130 o Added discussion of AERO Clients used as critical infrastructure 4131 elements to connect fixed networks. 4133 o Added network-based VPN under security considerations 4135 Changes from draft-templin-intarea-6706bis-07 to draft-templin- 4136 intrea-6706bis-08: 4138 o New section on AERO-Aware Access Router 4140 Changes from draft-templin-intarea-6706bis-06 to draft-templin- 4141 intrea-6706bis-07: 4143 o Added "R" bit for release of PDs. Now have a full RS/RA service 4144 that can do PD without requiring DHCPv6 messaging over-the-air 4146 o Clarifications on solicited vs unsolicited NAs 4148 o Clarified use of MAX_NEIGHBOR_ADVERTISEMENT for the purpose of 4149 increase reliability 4151 Changes from draft-templin-intarea-6706bis-05 to draft-templin- 4152 intrea-6706bis-06: 4154 o Major re-work and simplification of Route Optimization function 4156 o Added Distributed Mobility Management (DMM) and Mobility Anchor 4157 Point (MAP) terminology 4159 o New section on "AERO Critical Infrastructure Element 4160 Considerations" demonstrating low overall cost for the service 4162 o minor text revisions and deletions 4164 o removed extraneous appendices 4166 Changes from draft-templin-intarea-6706bis-04 to draft-templin- 4167 intrea-6706bis-05: 4169 o New Appendix E on S/TLLAO Extensions for special-purpose links. 4170 Discussed ATN/IPS as example. 4172 o New sentence in introduction to declare appendices as non- 4173 normative. 4175 Changes from draft-templin-intarea-6706bis-03 to draft-templin- 4176 intrea-6706bis-04: 4178 o Added definitions for Potential Router List (PRL) and secure 4179 enclave 4181 o Included text on mapping transport layer port numbers to network 4182 layer DSCP values 4184 o Added reference to DTLS and DMM Distributed Mobility Anchoring 4185 working group document 4187 o Reworked Security Considerations 4189 o Updated references. 4191 Changes from draft-templin-intarea-6706bis-02 to draft-templin- 4192 intrea-6706bis-03: 4194 o Added new section on SEND. 4196 o Clarifications on "AERO Address" section. 4198 o Updated references and added new reference for RFC8086. 4200 o Security considerations updates. 4202 o General text clarifications and cleanup. 4204 Changes from draft-templin-intarea-6706bis-01 to draft-templin- 4205 intrea-6706bis-02: 4207 o Note on encapsulation avoidance in Section 4. 4209 Changes from draft-templin-intarea-6706bis-00 to draft-templin- 4210 intrea-6706bis-01: 4212 o Remove DHCPv6 Server Release procedures that leveraged the old way 4213 Relays used to "route" between Server link-local addresses 4215 o Remove all text relating to Relays needing to do any AERO-specific 4216 operations 4218 o Proxy sends RS and receives RA from Server using SEND. Use CGAs 4219 as source addresses, and destination address of RA reply is to the 4220 AERO address corresponding to the Client's ACP. 4222 o Proxy uses SEND to protect RS and authenticate RA (Client does not 4223 use SEND, but rather relies on subnetwork security. When the 4224 Proxy receives an RS from the Client, it creates a new RS using 4225 its own addresses as the source and uses SEND with CGAs to send a 4226 new RS to the Server. 4228 o Emphasize distributed mobility management 4230 o AERO address-based RS injection of ACP into underlying routing 4231 system. 4233 Changes from draft-templin-aerolink-82 to draft-templin-intarea- 4234 6706bis-00: 4236 o Document use of NUD (NS/NA) for reliable link-layer address 4237 updates as an alternative to unreliable unsolicited NA. 4238 Consistent with Section 7.2.6 of RFC4861. 4240 o Server adds additional layer of encapsulation between outer and 4241 inner headers of NS/NA messages for transmission through Relays 4242 that act as vanilla IPv6 routers. The messages include the AERO 4243 Server Subnet Router Anycast address as the source and the Subnet 4244 Router Anycast address corresponding to the Client's ACP as the 4245 destination. 4247 o Clients use Subnet Router Anycast address as the encapsulation 4248 source address when the access network does not provide a 4249 topologically-fixed address. 4251 Author's Address 4253 Fred L. Templin (editor) 4254 Boeing Research & Technology 4255 P.O. Box 3707 4256 Seattle, WA 98124 4257 USA 4259 Email: fltemplin@acm.org