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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 Intended status: Informational June 7, 2021 5 Expires: December 9, 2021 7 Asymmetric Extended Route Optimization (AERO) 8 draft-templin-6man-aero-12 10 Abstract 12 This document specifies an Asymmetric Extended Route Optimization 13 (AERO) service for IP internetworking over Overlay Multilink Network 14 (OMNI) interfaces. AERO/OMNI use an IPv6 link-local address format 15 that supports operation of the IPv6 Neighbor Discovery (ND) protocol 16 and links ND to IP forwarding. Prefix delegation/registration 17 services are employed for network admission and to manage the routing 18 system. Secure multilink operation, mobility management, multicast, 19 traffic selector signaling and route optimization are naturally 20 supported through dynamic neighbor cache updates. AERO is a widely- 21 applicable mobile internetworking service especially well-suited to 22 aviation services, intelligent transportation systems, mobile Virtual 23 Private Networks (VPNs) and many other applications. 25 Status of This Memo 27 This Internet-Draft is submitted in full conformance with the 28 provisions of BCP 78 and BCP 79. 30 Internet-Drafts are working documents of the Internet Engineering 31 Task Force (IETF). Note that other groups may also distribute 32 working documents as Internet-Drafts. The list of current Internet- 33 Drafts is at https://datatracker.ietf.org/drafts/current/. 35 Internet-Drafts are draft documents valid for a maximum of six months 36 and may be updated, replaced, or obsoleted by other documents at any 37 time. It is inappropriate to use Internet-Drafts as reference 38 material or to cite them other than as "work in progress." 40 This Internet-Draft will expire on December 9, 2021. 42 Copyright Notice 44 Copyright (c) 2021 IETF Trust and the persons identified as the 45 document authors. All rights reserved. 47 This document is subject to BCP 78 and the IETF Trust's Legal 48 Provisions Relating to IETF Documents 49 (https://trustee.ietf.org/license-info) in effect on the date of 50 publication of this document. Please review these documents 51 carefully, as they describe your rights and restrictions with respect 52 to this document. Code Components extracted from this document must 53 include Simplified BSD License text as described in Section 4.e of 54 the Trust Legal Provisions and are provided without warranty as 55 described in the Simplified BSD License. 57 Table of Contents 59 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 60 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6 61 3. Asymmetric Extended Route Optimization (AERO) . . . . . . . . 13 62 3.1. AERO Node Types . . . . . . . . . . . . . . . . . . . . . 13 63 3.2. The AERO Service over OMNI Links . . . . . . . . . . . . 14 64 3.2.1. AERO/OMNI Reference Model . . . . . . . . . . . . . . 14 65 3.2.2. Addressing and Node Identification . . . . . . . . . 17 66 3.2.3. AERO Routing System . . . . . . . . . . . . . . . . . 18 67 3.2.4. OMNI Link Segment Routing . . . . . . . . . . . . . . 20 68 3.2.5. Segment Routing Topologies (SRTs) . . . . . . . . . . 26 69 3.2.6. Segment Routing For OMNI Link Selection . . . . . . . 26 70 3.2.7. Segment Routing Within the OMNI Link . . . . . . . . 27 71 3.3. OMNI Interface Characteristics . . . . . . . . . . . . . 29 72 3.4. OMNI Interface Initialization . . . . . . . . . . . . . . 31 73 3.4.1. AERO Proxy/Server and Relay Behavior . . . . . . . . 31 74 3.4.2. AERO Client Behavior . . . . . . . . . . . . . . . . 32 75 3.4.3. AERO Bridge Behavior . . . . . . . . . . . . . . . . 32 76 3.5. OMNI Interface Neighbor Cache Maintenance . . . . . . . . 32 77 3.5.1. OMNI ND Messages . . . . . . . . . . . . . . . . . . 34 78 3.5.2. OMNI Neighbor Advertisement Message Flags . . . . . . 35 79 3.5.3. OMNI Neighbor Window Synchronization . . . . . . . . 36 80 3.6. OMNI Interface Encapsulation and Re-encapsulation . . . . 36 81 3.7. OMNI Interface Decapsulation . . . . . . . . . . . . . . 37 82 3.8. OMNI Interface Data Origin Authentication . . . . . . . . 37 83 3.9. OMNI Interface MTU . . . . . . . . . . . . . . . . . . . 38 84 3.10. OMNI Interface Forwarding Algorithm . . . . . . . . . . . 38 85 3.10.1. Client Forwarding Algorithm . . . . . . . . . . . . 40 86 3.10.2. Proxy/Server and Relay Forwarding Algorithm . . . . 41 87 3.10.3. Bridge Forwarding Algorithm . . . . . . . . . . . . 44 88 3.11. OMNI Interface Error Handling . . . . . . . . . . . . . . 45 89 3.12. AERO Router Discovery, Prefix Delegation and 90 Autoconfiguration . . . . . . . . . . . . . . . . . . . . 48 91 3.12.1. AERO Service Model . . . . . . . . . . . . . . . . . 49 92 3.12.2. AERO Client Behavior . . . . . . . . . . . . . . . . 49 93 3.12.3. AERO Proxy/Server Behavior . . . . . . . . . . . . . 51 94 3.13. The AERO Proxy Function . . . . . . . . . . . . . . . . . 54 95 3.13.1. Detecting and Responding to Proxy/Server Failures . 57 96 3.13.2. Point-to-Multipoint Proxy/Server Coordination . . . 58 98 3.14. AERO Route Optimization . . . . . . . . . . . . . . . . . 59 99 3.14.1. Route Optimization Initiation . . . . . . . . . . . 59 100 3.14.2. Relaying the NS(AR) *NET Packet(s) . . . . . . . . . 60 101 3.14.3. Processing the NS(AR) and Sending the NA(AR) . . . . 61 102 3.14.4. Relaying the NA(AR) . . . . . . . . . . . . . . . . 62 103 3.14.5. Processing the NA(AR) . . . . . . . . . . . . . . . 62 104 3.14.6. Forwarding Packets to Route Optimized Targets . . . 63 105 3.15. Neighbor Unreachability Detection (NUD) . . . . . . . . . 65 106 3.16. Mobility Management and Quality of Service (QoS) . . . . 67 107 3.16.1. Mobility Update Messaging . . . . . . . . . . . . . 68 108 3.16.2. Announcing Link-Layer Address and/or QoS Preference 109 Changes . . . . . . . . . . . . . . . . . . . . . . 69 110 3.16.3. Bringing New Links Into Service . . . . . . . . . . 69 111 3.16.4. Deactivating Existing Links . . . . . . . . . . . . 69 112 3.16.5. Moving Between Proxy/Servers . . . . . . . . . . . . 70 113 3.17. Multicast . . . . . . . . . . . . . . . . . . . . . . . . 71 114 3.17.1. Source-Specific Multicast (SSM) . . . . . . . . . . 72 115 3.17.2. Any-Source Multicast (ASM) . . . . . . . . . . . . . 73 116 3.17.3. Bi-Directional PIM (BIDIR-PIM) . . . . . . . . . . . 74 117 3.18. Operation over Multiple OMNI Links . . . . . . . . . . . 74 118 3.19. DNS Considerations . . . . . . . . . . . . . . . . . . . 75 119 3.20. Transition/Coexistence Considerations . . . . . . . . . . 75 120 3.21. Detecting and Reacting to Proxy/Server and Bridge 121 Failures . . . . . . . . . . . . . . . . . . . . . . . . 76 122 3.22. AERO Clients on the Open Internet . . . . . . . . . . . . 76 123 3.23. Time-Varying MNPs . . . . . . . . . . . . . . . . . . . . 78 124 4. Implementation Status . . . . . . . . . . . . . . . . . . . . 79 125 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 79 126 6. Security Considerations . . . . . . . . . . . . . . . . . . . 79 127 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 82 128 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 83 129 8.1. Normative References . . . . . . . . . . . . . . . . . . 83 130 8.2. Informative References . . . . . . . . . . . . . . . . . 85 131 Appendix A. Non-Normative Considerations . . . . . . . . . . . . 91 132 A.1. Implementation Strategies for Route Optimization . . . . 91 133 A.2. Implicit Mobility Management . . . . . . . . . . . . . . 92 134 A.3. Direct Underlying Interfaces . . . . . . . . . . . . . . 92 135 A.4. AERO Critical Infrastructure Considerations . . . . . . . 92 136 A.5. AERO Server Failure Implications . . . . . . . . . . . . 93 137 A.6. AERO Client / Server Architecture . . . . . . . . . . . . 94 138 Appendix B. Change Log . . . . . . . . . . . . . . . . . . . . . 96 139 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 98 141 1. Introduction 143 Asymmetric Extended Route Optimization (AERO) fulfills the 144 requirements of Distributed Mobility Management (DMM) [RFC7333] and 145 route optimization [RFC5522] for aeronautical networking and other 146 network mobility use cases including intelligent transportation 147 systems and enterprise mobile device users. AERO is a secure 148 internetworking and mobility management service that employs the 149 Overlay Multilink Network Interface (OMNI) [I-D.templin-6man-omni] 150 Non-Broadcast, Multiple Access (NBMA) virtual link model. The OMNI 151 link is a virtual overlay configured over one or more underlying 152 Internetworks, and nodes on the link can exchange original IP packets 153 as single-hop neighbors. The OMNI Adaptation Layer (OAL) supports 154 end system multilink operation for increased reliability, bandwidth 155 optimization and traffic path selection while performing 156 fragmentation and reassembly to support Internetwork segment routing 157 and Maximum Transmission Unit (MTU) diversity. In terms of 158 precedence, readers may appreciate reading the AERO specification 159 first to gain an understanding of the overall architecture and 160 mobility services then return to the OMNI specification for a deeper 161 analysis of the NBMA link model. 163 The AERO service comprises Clients, Proxy/Servers and Relays that are 164 seen as OMNI link neighbors as well as Bridges that interconnect 165 diverse Internetworks as OMNI link segments through OAL forwarding at 166 a layer below IP. Each node's OMNI interface uses an IPv6 link-local 167 address format that supports operation of the IPv6 Neighbor Discovery 168 (ND) protocol [RFC4861] and links ND to IP forwarding. A node's OMNI 169 interface can be configured over multiple underlying interfaces, and 170 therefore appears as a single interface with multiple link-layer 171 addresses. Each link-layer address is subject to change due to 172 mobility and/or multilink fluctuations, and link-layer address 173 changes are signaled by ND messaging the same as for any IPv6 link. 175 AERO provides a secure cloud-based service where mobile node Clients 176 may use any Proxy/Server acting as a Mobility Anchor Point (MAP) and 177 fixed nodes may use any Relay on the link for efficient 178 communications. Fixed nodes forward original IP packets destined to 179 other AERO nodes via the nearest Relay, which forwards them through 180 the cloud. A mobile node's initial packets are forwarded through the 181 Proxy/Server, and direct routing is supported through route 182 optimization while packets are flowing. Both unicast and multicast 183 communications are supported, and mobile nodes may efficiently move 184 between locations while maintaining continuous communications with 185 correspondents and without changing their IP Address. 187 AERO Bridges peer with Proxy/Servers in a secured private BGP overlay 188 routing instance to provide a Segment Routing Topology (SRT) that 189 allows the OAL to span the underlying Internetworks of multiple 190 disjoint administrative domains as a single unified OMNI link at a 191 layer below IP. Each OMNI link instance is characterized by the set 192 of Mobility Service Prefixes (MSPs) common to all mobile nodes. 193 Relays provide an optimal route from correspondent nodes on the 194 underlying Internetwork to nodes on the OMNI link. To the underlying 195 Internetwork, the Relay is the source of a route to the MSP, and 196 hence uplink traffic to the mobile node is naturally routed to the 197 nearest Relay. A Relay can be considered as a simple case of a 198 Proxy/Server that provides only forwarding and not proxying services. 200 AERO can be used with OMNI links that span private-use Internetworks 201 and/or public Internetworks such as the global Internet. In the 202 latter case, some end systems may be located behind global Internet 203 Network Address Translators (NATs). A means for robust traversal of 204 NATs while avoiding "triangle routing" is therefore provided. 206 AERO assumes the use of PIM Sparse Mode in support of multicast 207 communication. In support of Source Specific Multicast (SSM) when a 208 Mobile Node is the source, AERO route optimization ensures that a 209 shortest-path multicast tree is established with provisions for 210 mobility and multilink operation. In all other multicast scenarios 211 there are no AERO dependencies. 213 AERO was designed as a secure aeronautical internetworking service 214 for both manned and unmanned aircraft, where the aircraft is treated 215 as a mobile node that can connect an Internet of Things (IoT). AERO 216 is also applicable to a wide variety of other use cases. For 217 example, it can be used to coordinate the links of mobile nodes 218 (e.g., cellphones, tablets, laptop computers, etc.) that connect into 219 a home enterprise network via public access networks with VPN or non- 220 VPN services enabled according to the appropriate security model. 221 AERO can also be used to facilitate terrestrial vehicular and urban 222 air mobility (as well as pedestrian communication services) for 223 future intelligent transportation systems 224 [I-D.ietf-ipwave-vehicular-networking][I-D.templin-ipwave-uam-its]. 225 Other applicable use cases are also in scope. 227 Along with OMNI, AERO provides secured optimal routing support for 228 the "6M's" of modern Internetworking, including: 230 1. Multilink - a mobile node's ability to coordinate multiple 231 diverse underlying data links as a single logical unit (i.e., the 232 OMNI interface) to achieve the required communications 233 performance and reliability objectives. 235 2. Multinet - the ability to span the OMNI link over a segment 236 routing topology with multiple diverse network administrative 237 domains while maintaining seamless end-to-end communications 238 between mobile Clients and correspondents such as air traffic 239 controllers, fleet administrators, etc. 241 3. Mobility - a mobile node's ability to change network points of 242 attachment (e.g., moving between wireless base stations) which 243 may result in an underlying interface address change, but without 244 disruptions to ongoing communication sessions with peers over the 245 OMNI link. 247 4. Multicast - the ability to send a single network transmission 248 that reaches multiple nodes belonging to the same interest group, 249 but without disturbing other nodes not subscribed to the interest 250 group. 252 5. Multihop - a mobile node vehicle-to-vehicle relaying capability 253 useful when multiple forwarding hops between vehicles may be 254 necessary to "reach back" to an infrastructure access point 255 connection to the OMNI link. 257 6. MTU assurance - the ability to deliver packets of various robust 258 sizes between peers without loss due to a link size restriction, 259 and to dynamically adjust packets sizes to achieve the optimal 260 performance for each independent traffic flow. 262 The following numbered sections present the AERO specification. The 263 appendices at the end of the document are non-normative. 265 2. Terminology 267 The terminology in the normative references applies; especially, the 268 terminology in the OMNI specification [I-D.templin-6man-omni] is used 269 extensively throughout. The following terms are defined within the 270 scope of this document: 272 IPv6 Neighbor Discovery (ND) 273 a control message service for coordinating neighbor relationships 274 between nodes connected to a common link. AERO uses the IPv6 ND 275 messaging service specified in [RFC4861]. 277 IPv6 Prefix Delegation 278 a networking service for delegating IPv6 prefixes to nodes on the 279 link. The nominal service is DHCPv6 [RFC8415], however alternate 280 services (e.g., based on ND messaging) are also in scope. A 281 minimal form of prefix delegation known as "prefix registration" 282 can be used if the Client knows its prefix in advance and can 283 represent it in the IPv6 source address of an ND message. 285 Access Network (ANET) 286 a node's first-hop data link service network (e.g., a radio access 287 network, cellular service provider network, corporate enterprise 288 network, etc.) that often provides link-layer security services 289 such as IEEE 802.1X and physical-layer security (e.g., "protected 290 spectrum") to prevent unauthorized access internally and with 291 border network-layer security services such as firewalls and 292 proxys that prevent unauthorized outside access. 294 ANET interface 295 a node's attachment to a link in an ANET. 297 Internetwork (INET) 298 a connected IP network topology with a coherent routing and 299 addressing plan and that provides a transit backbone service for 300 ANET end systems. INETs also provide an underlay service over 301 which the AERO virtual link is configured. Example INETs include 302 corporate enterprise networks, aviation networks, and the public 303 Internet itself. When there is no administrative boundary between 304 an ANET and the INET, the ANET and INET are one and the same. 306 INET interface 307 a node's attachment to a link in an INET. 309 *NET 310 a "wildcard" term referring to either ANET or INET when it is not 311 necessary to draw a distinction between the two. 313 *NET interface 314 a node's attachment to a link in a *NET. 316 *NET Partition 317 frequently, *NETs such as large corporate enterprise networks are 318 sub-divided internally into separate isolated partitions (a 319 technique also known as "network segmentation"). Each partition 320 is fully connected internally but disconnected from other 321 partitions, and there is no requirement that separate partitions 322 maintain consistent Internet Protocol and/or addressing plans. 323 (Each *NET partition is seen as a separate OMNI link segment as 324 discussed below.) 326 *NET address 327 an IP address assigned to a node's interface connection to a *NET. 329 *NET encapsulation 330 the encapsulation of a packet in an outer header or headers that 331 can be routed within the scope of the local *NET partition. 333 OMNI link 334 the same as defined in [I-D.templin-6man-omni], and manifested by 335 IPv6 encapsulation [RFC2473]. The OMNI link spans underlying *NET 336 segments joined by virtual bridges in a spanning tree the same as 337 a bridged campus LAN. AERO nodes on the OMNI link appear as 338 single-hop neighbors at the network layer even though they may be 339 separated by multiple underlying *NET hops, and can use Segment 340 Routing [RFC8402] to cause packets to visit selected waypoints on 341 the link. 343 OMNI Interface 344 a node's attachment to an OMNI link. Since OMNI interface 345 addresses are managed for uniqueness, OMNI interfaces do not 346 require Duplicate Address Detection (DAD) and therefore set the 347 administrative variable 'DupAddrDetectTransmits' to zero 348 [RFC4862]. 350 OMNI Adaptation Layer (OAL) 351 an OMNI interface process whereby original IP packets admitted 352 into the interface are wrapped in a mid-layer IPv6 header and 353 subject to fragmentation and reassembly. The OAL is also 354 responsible for generating MTU-related control messages as 355 necessary, and for providing addressing context for spanning 356 multiple segments of a bridged OMNI link. 358 original IP packet 359 a whole IP packet or fragment admitted into the OMNI interface by 360 the network layer prior to OAL encapsulation and fragmentation, or 361 an IP packet delivered to the network layer by the OMNI interface 362 following OAL decapsulation and reassembly. 364 OAL packet 365 an original IP packet encapsulated in OAL headers and trailers 366 before OAL fragmentation, or following OAL reassembly. 368 OAL fragment 369 a portion of an OAL packet following fragmentation but prior to 370 *NET encapsulation, or following *NET encapsulation but prior to 371 OAL reassembly. 373 (OAL) atomic fragment 374 an OAL packet that does not require fragmentation is always 375 encapsulated as an "atomic fragment" and includes a Fragment 376 Header with Fragment Offset and More Fragments both set to 0, but 377 with a valid Identification value. 379 (OAL) carrier packet 380 an encapsulated OAL fragment following *NET encapsulation or prior 381 to *NET decapsulation. OAL sources and destinations exchange 382 carrier packets over underlying interfaces, and may be separated 383 by one or more OAL intermediate nodes. OAL intermediate nodes re- 384 encapsulate carrier packets during forwarding by removing the *NET 385 headers of the previous hop underlying network and replacing them 386 with new *NET headers for the next hop underlying network. 388 OAL source 389 an OMNI interface acts as an OAL source when it encapsulates 390 original IP packets to form OAL packets, then performs OAL 391 fragmentation and *NET encapsulation to create carrier packets. 393 OAL destination 394 an OMNI interface acts as an OAL destination when it decapsulates 395 carrier packets, then performs OAL reassembly and decapsulation to 396 derive the original IP packet. 398 OAL intermediate node 399 an OMNI interface acts as an OAL intermediate node when it removes 400 the *NET headers of carrier packets received on a first segment, 401 then re-encapsulates the carrier packets in new *NET headers and 402 forwards them into the next segment. OAL intermediate nodes 403 decrement the Hop Limit of the OAL IPv6 header during re- 404 encapsulation, and discard the packet if the Hop Limit reaches 0. 405 OAL intermediate nodes do not decrement the Hop Limit/TTL of the 406 original IP packet. 408 underlying interface 409 a *NET interface over which an OMNI interface is configured. 411 Mobility Service Prefix (MSP) 412 an aggregated IP Global Unicast Address (GUA) prefix (e.g., 413 2001:db8::/32, 192.0.2.0/24, etc.) assigned to the OMNI link and 414 from which more-specific Mobile Network Prefixes (MNPs) are 415 delegated. OMNI link administrators typically obtain MSPs from an 416 Internet address registry, however private-use prefixes can 417 alternatively be used subject to certain limitations (see: 418 [I-D.templin-6man-omni]). OMNI links that connect to the global 419 Internet advertise their MSPs to their interdomain routing peers. 421 Mobile Network Prefix (MNP) 422 a longer IP prefix delegated from an MSP (e.g., 423 2001:db8:1000:2000::/56, 192.0.2.8/30, etc.) and delegated to an 424 AERO Client or Relay. 426 Mobile Network Prefix Link Local Address (MNP-LLA) 427 an IPv6 Link Local Address that embeds the most significant 64 428 bits of an MNP in the lower 64 bits of fe80::/64, as specified in 429 [I-D.templin-6man-omni]. 431 Mobile Network Prefix Unique Local Address (MNP-ULA) 432 an IPv6 Unique-Local Address derived from an MNP-LLA. 434 Administrative Link Local Address (ADM-LLA) 435 an IPv6 Link Local Address that embeds a 32-bit administratively- 436 assigned identification value in the lower 32 bits of fe80::/96, 437 as specified in [I-D.templin-6man-omni]. 439 Administrative Unique Local Address (ADM-ULA) 440 an IPv6 Unique-Local Address derived from an ADM-LLA. 442 AERO node 443 a node that is connected to an OMNI link and participates in the 444 AERO internetworking and mobility service. 446 AERO Client ("Client") 447 an AERO node that connects over one or more underlying interfaces 448 and requests MNP delegation/registration service from AERO Proxy/ 449 Servers. The Client assigns an MNP-LLA to the OMNI interface for 450 use in ND exchanges with other AERO nodes and forwards original IP 451 packets to correspondents according to OMNI interface neighbor 452 cache state. 454 AERO Proxy/Server ("Proxy/Server") 455 a dual-function node that provides a proxying service between AERO 456 Clients and external peers on its Client-facing ANET interfaces 457 (i.e., in the same fashion as for an enterprise network proxy) as 458 well as default forwarding and Mobility Anchor Point (MAP) 459 services for coordination with correspondents on its INET-facing 460 interfaces. (Proxy/Servers in the open INET instead configure 461 only an INET interface and no ANET interfaces.) The Proxy/Server 462 configures an OMNI interface and assigns an ADM-LLA to support the 463 operation of IPv6 ND services, while advertising all of its 464 associated MNPs via BGP peerings with Bridges. Note that the 465 Proxy and Server functions can be considered logically separable, 466 but since each Proxy/Server must be informed of all of the 467 Client's other multilink Proxy/Server affiliations the AERO 468 service is best supported when the two functions are coresident on 469 the same physical or logical platform. 471 AERO Relay ("Relay") 472 a Proxy/Server that provides forwarding services between nodes 473 reached via the OMNI link and correspondents on connected 474 downstream links. AERO Relays configure an OMNI interface and 475 assign an ADM-LLA the same as Proxy/Servers. AERO Relays also run 476 a dynamic routing protocol to discover any non-MNP IP GUA routes 477 in service on its connected downstream network links. In both 478 cases, the Relay advertises the MSP(s) to its downstream networks, 479 and distributes all of its associated non-MNP IP GUA routes via 480 BGP peerings with Bridges (i.e., the same as for Proxy/Servers). 482 AERO Bridge ("Bridge") 483 a node that provides hybrid routing/bridging services (as well as 484 a security trust anchor) for nodes on an OMNI link. The Bridge 485 forwards carrier packets between OMNI link segments as OAL 486 intermediate nodes while decrementing the OAL IPv6 header Hop 487 Limit but without decrementing the network layer IP TTL/Hop Limit. 488 AERO Bridges peer with Proxy/Servers and other Bridges over 489 secured tunnels to discover the full set of MNPs for the link as 490 well as any non-MNP IP GUA routes that are reachable via Relays. 492 First-Hop Segment (FHS) Proxy/Server 493 a Proxy/Server for an underlying interface of the source Client 494 that forwards packets sent by the source Client over that 495 interface into the segment routing topology. 497 Last-Hop Segment (LHS) Proxy/Server 498 a Proxy/Server for an underlying interface of the target Client 499 that forwards packets received from the segment routing topology 500 to the target Client over that interface. 502 Segment Routing Topology (SRT) 503 a multinet forwarding region between the FHS Proxy/Server and LHS 504 Proxy/Server. FHS/LHS Proxy/Servers and SRT Bridges span the OMNI 505 link on behalf of source/target Client pairs as discussed in this 506 document. 508 link-layer address 509 an IP address used as an encapsulation header source or 510 destination address from the perspective of the OMNI interface. 511 When an upper layer protocol (e.g., UDP) is used as part of the 512 encapsulation, the port number is also considered as part of the 513 link-layer address. 515 network layer address 516 the source or destination address of an original IP packet 517 presented to the OMNI interface. 519 end user network (EUN) 520 an internal virtual or external edge IP network that an AERO 521 Client or Relay connects to the rest of the network via the OMNI 522 interface. The Client/Relay sees each EUN as a "downstream" 523 network, and sees the OMNI interface as the point of attachment to 524 the "upstream" network. 526 Mobile Node (MN) 527 an AERO Client and all of its downstream-attached networks that 528 move together as a single unit, i.e., an end system that connects 529 an Internet of Things. 531 Mobile Router (MR) 532 a MN's on-board router that forwards original IP packets between 533 any downstream-attached networks and the OMNI link. The MR is the 534 MN entity that hosts the AERO Client. 536 Route Optimization Source (ROS) 537 the AERO node nearest the source that initiates route 538 optimization. The ROS may be a FHS Proxy/Server or Relay for the 539 source, or may be the source Client itself. 541 Route Optimization responder (ROR) 542 the AERO node that responds to route optimization requests on 543 behalf of the target. The ROR may be an LHS Proxy/Server for a 544 target MNP Client or an LHS Relay for a non-MNP target. 546 MAP List 547 a geographically and/or topologically referenced list of addresses 548 of all Proxy/Servers within the same OMNI link. Each OMNI link 549 has its own MAP list. 551 Distributed Mobility Management (DMM) 552 a BGP-based overlay routing service coordinated by Proxy/Servers 553 and Bridges that tracks all Proxy/Server-to-Client associations. 555 Mobility Service (MS) 556 the collective set of all Proxy/Servers, Bridges and Relays that 557 provide the AERO Service to Clients. 559 Mobility Service Endpoint MSE) 560 an individual Proxy/Server, Bridge or Relay in the Mobility 561 Service. 563 Throughout the document, the simple terms "Client", "Proxy/Server", 564 "Bridge" and "Relay" refer to "AERO Client", "AERO Proxy/Server", 565 "AERO Bridge" and "AERO Relay", respectively. Capitalization is used 566 to distinguish these terms from other common Internetworking uses in 567 which they appear without capitalization. 569 The terminology of IPv6 ND [RFC4861] and DHCPv6 [RFC8415] (including 570 the names of node variables, messages and protocol constants) is used 571 throughout this document. The terms "All-Routers multicast", "All- 572 Nodes multicast", "Solicited-Node multicast" and "Subnet-Router 573 anycast" are defined in [RFC4291]. Also, the term "IP" is used to 574 generically refer to either Internet Protocol version, i.e., IPv4 575 [RFC0791] or IPv6 [RFC8200]. 577 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 578 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 579 "OPTIONAL" in this document are to be interpreted as described in BCP 580 14 [RFC2119][RFC8174] when, and only when, they appear in all 581 capitals, as shown here. 583 3. Asymmetric Extended Route Optimization (AERO) 585 The following sections specify the operation of IP over OMNI links 586 using the AERO service: 588 3.1. AERO Node Types 590 AERO Clients are Mobile Nodes (MNs) that configure OMNI interfaces 591 over underlying interfaces with addresses that may change when the 592 Client moves to a new network connection point. AERO Clients 593 register their Mobile Network Prefixes (MNPs) with the AERO service, 594 and distribute the MNPs to nodes on EUNs. AERO Bridges, Proxy/ 595 Servers and Relays are critical infrastructure elements in fixed 596 (i.e., non-mobile) INET deployments and hence have permanent and 597 unchanging INET addresses. Together, they constitute the AERO 598 service which provides an OMNI link virtual overlay for connecting 599 AERO Clients. 601 AERO Bridges (together with Proxy/Servers) provide the secured 602 backbone supporting infrastucture for a Segment Routing Topology 603 (SRT) that spans the OMNI link. Bridges forward carrier packets both 604 within the same SRT partition and between disjoint SRT partitions 605 based on an IPv6 encapsulation mid-layer known as the OMNI Adaptation 606 Layer (OAL) [I-D.templin-6man-omni]. During forwarding, the inner IP 607 layer experiences a virtual bridging service since the inner IP TTL/ 608 Hop Limit is not decremented. Each Bridge also peers with Proxy/ 609 Servers and other Bridges in a dynamic routing protocol instance to 610 provide a Distributed Mobility Management (DMM) service for the list 611 of active MNPs (see Section 3.2.3). Bridges present the OMNI link as 612 a set of one or more Mobility Service Prefixes (MSPs) and configure 613 secured tunnels with Proxy/Servers, Relays and other Bridges; they 614 further maintain IP forwarding table entries for each MNP and any 615 other reachable non-MNP prefixes. 617 AERO Proxy/Servers in distributed SRT segments provide default 618 forwarding and mobility/multilink services for AERO Client Mobile 619 Nodes (MNs). Each Proxy/Server also peers with Bridges in a dynamic 620 routing protocol instance to advertise its list of associated MNPs 621 (see Section 3.2.3). Proxy/Servers facilitate prefix delegation/ 622 registration exchanges with Clients, where each delegated prefix 623 becomes an MNP taken from an MSP. Proxy/Servers forward carrier 624 packets between OMNI interface neighbors and track each Client's 625 mobility profiles. Proxy/Servers at ANET/INET boundaries provide a 626 conduit for ANET Clients to associate with peers reached through 627 external INETs. Proxy/Servers in the open INET support INET Clients 628 through authenticated IPv6 ND message exchanges. Source Clients 629 employ First-Hop Segment (FHS) Proxy/Servers to forward packets over 630 the SRT to Last-Hop Segment (LHS) Proxy/Servers which finally forward 631 to target Clients. 633 AERO Relays are Proxy/Servers that provide forwarding services to 634 exchange original IP packets between the OMNI interface and INET/EUN 635 interfaces. Relays are provisioned with MNPs the same as for an AERO 636 Client, and also run a dynamic routing protocol to discover any non- 637 MNP IP routes. The Relay advertises the MSP(s) to its connected 638 networks, and distributes all of its associated MNP and non-MNP 639 routes via BGP peerings with Bridges 641 3.2. The AERO Service over OMNI Links 643 3.2.1. AERO/OMNI Reference Model 645 Figure 1 presents the basic OMNI link reference model: 647 +----------------+ 648 | AERO Bridge B1 | 649 | Nbr: S1, S2, P1| 650 |(X1->S1; X2->S2)| 651 | MSP M1 | 652 +-+------------+-+ 653 +--------------+ | Secured | +--------------+ 654 | AERO P/S S1 | | tunnels | | AERO P/S S2 | 655 | Nbr: C1, B1 +-----+ +-----+ Nbr: C2, B1 | 656 | default->B1 | | default->B1 | 657 | X1->C1 | | X2->C2 | 658 +-------+------+ +------+-------+ 659 | OMNI link | 660 X===+===+======================================+===+===X 661 | | 662 +-----+--------+ +--------+-----+ 663 |AERO Client C1| |AERO Client C2| 664 | Nbr: S1 | | Nbr: S2 | 665 | default->S1 | | default->S2 | 666 | MNP X1 | | MNP X2 | 667 +------+-------+ +-----+--------+ 668 | | 669 .-. .-. 670 ,-( _)-. ,-( _)-. 671 .-(_ IP )-. +-------+ +-------+ .-(_ IP )-. 672 (__ EUN )--|Host H1| |Host H2|--(__ EUN ) 673 `-(______)-' +-------+ +-------+ `-(______)-' 675 Figure 1: AERO/OMNI Reference Model 677 In this model: 679 o the OMNI link is an overlay network service configured over one or 680 more underlying SRT partitions which may be managed by different 681 administrative authorities and have incompatible protocols and/or 682 addressing plans. 684 o AERO Bridge B1 aggregates Mobility Service Prefix (MSP) M1, 685 discovers Mobile Network Prefixes (MNPs) X* and advertises the MSP 686 via BGP peerings over secured tunnels to Proxy/Servers (S1, S2). 687 Bridges provide the backbone for an SRT that spans the OMNI link. 689 o AERO Proxy/Servers S1 and S2 configure secured tunnels with Bridge 690 B1 and also provide mobility, multilink, multicast and default 691 router services for the MNPs of their associated Clients C1 and 692 C2. (Proxy/Servers that act as Relays can also advertise non-MNP 693 routes for non-mobile correspondent nodes the same as for MNP 694 Clients.) 696 o AERO Clients C1 and C2 associate with Proxy/Servers S1 and S2, 697 respectively. They receive MNP delegations X1 and X2, and also 698 act as default routers for their associated physical or internal 699 virtual EUNs. Simple hosts H1 and H2 attach to the EUNs served by 700 Clients C1 and C2, respectively. 702 An OMNI link configured over a single *NET appears as a single 703 unified link with a consistent underlying network addressing plan. 704 In that case, all nodes on the link can exchange carrier packets via 705 simple *NET encapsulation (i.e., following any necessary NAT 706 traversal), since the underlying *NET is connected. In common 707 practice, however, OMNI links are traversed by a Segment Routing 708 Topology (SRT) spanning tree, where each segment is a distinct *NET 709 potentially managed under a different administrative authority (e.g., 710 as for worldwide aviation service providers such as ARINC, SITA, 711 Inmarsat, etc.). Individual *NETs may also themselves be partitioned 712 internally, in which case each internal partition is seen as a 713 separate segment. 715 The addressing plan of each SRT segment is consistent internally but 716 will often bear no relation to the addressing plans of other 717 segments. Each segment is also likely to be separated from others by 718 network security devices (e.g., firewalls, proxys, packet filtering 719 gateways, etc.), and in many cases disjoint segments may not even 720 have any common physical link connections. Therefore, nodes can only 721 be assured of exchanging carrier packets directly with correspondents 722 in the same segment, and not with those in other segments. The only 723 means for joining the segments therefore is through inter-domain 724 peerings between AERO Bridges. 726 The same as for traditional campus LANs, the OMNI link SRT spans 727 multiple segments that can be joined into a single unified link using 728 the OMNI Adaptation Layer (OAL) [I-D.templin-6man-omni] which inserts 729 a mid-layer IPv6 encapsulation header that supports inter-segment 730 forwarding (i.e., bridging) without decrementing the network-layer 731 TTL/Hop Limit of the original IP packet. An example OMNI link SRT is 732 shown in Figure 2: 734 . . . . . . . . . . . . . . . . . . . . . . . 735 . . 736 . .-(::::::::) . 737 . .-(::::::::::::)-. +-+ . 738 . (:::: Segment A :::)--|B|---+ . 739 . `-(::::::::::::)-' +-+ | . 740 . `-(::::::)-' | . 741 . | . 742 . .-(::::::::) | . 743 . .-(::::::::::::)-. +-+ | . 744 . (:::: Segment B :::)--|B|---+ . 745 . `-(::::::::::::)-' +-+ | . 746 . `-(::::::)-' | . 747 . | . 748 . .-(::::::::) | . 749 . .-(::::::::::::)-. +-+ | . 750 . (:::: Segment C :::)--|B|---+ . 751 . `-(::::::::::::)-' +-+ | . 752 . `-(::::::)-' | . 753 . | . 754 . ..(etc).. x . 755 . . 756 . . 757 . <- Segment Routing Topology (SRT) -> . 758 . . . . . . . . . . . . . .. . . . . . . . . 760 Figure 2: OMNI Link Segment Routing Topology (SRT) 762 Bridges, Proxy/Servers and Relay OMNI interfaces are configured over 763 both secured tunnels and open INET underlying interfaces over their 764 respective segments in an SRT spanning tree topology rooted at the 765 Bridges. The "secured" spanning tree supports strong authentication 766 for control plane messages and may also be used to convey the initial 767 carrier packets in a flow. The "unsecured" spanning tree conveys 768 ordinary carrier packets without security codes and that must be 769 treated by destinations according to data origin authentication 770 procedures. Route optimization can be employed to cause carrier 771 packets to take more direct paths between OMNI link neighbors without 772 having to follow strict SRT spanning tree paths. 774 3.2.2. Addressing and Node Identification 776 AERO nodes on OMNI links use the Link-Local Address (LLA) prefix 777 fe80::/64 [RFC4291] to assign LLAs used for network-layer addresses 778 in link-scoped IPv6 ND and data messages. AERO Clients use LLAs 779 constructed from MNPs (i.e., "MNP-LLAs") while other AERO nodes use 780 LLAs constructed from administrative identification values ("ADM- 781 LLAs") as specified in [I-D.templin-6man-omni]. Non-MNP routes are 782 also represented the same as for MNP-LLAs, but may include a prefix 783 that is not properly covered by the MSP. 785 AERO nodes also use the Unique Local Address (ULA) prefix fd00::/8 786 followed by a pseudo-random 40-bit OMNI domain identifier to form the 787 prefix [ULA]::/48, then include a 16-bit OMNI link identifier '*' to 788 form the prefix [ULA*]::/64 [RFC4291]. The AERO node then uses the 789 prefix [ULA*]::/64 to form "MNP-ULAs" or "ADM-ULA"s as specified in 790 [I-D.templin-6man-omni] to support OAL addressing. (The prefix 791 [ULA*]::/64 appearing alone and with no suffix represents "default".) 792 AERO Clients also use Temporary ULAs constructed per 793 [I-D.templin-6man-omni], where the addresses are typically used only 794 in initial control message exchanges until a stable MNP-LLA/ULA is 795 assigned. 797 AERO MSPs, MNPs and non-MNP routes are typically based on Global 798 Unicast Addresses (GUAs), but in some cases may be based on private- 799 use addresses. See [I-D.templin-6man-omni] for a full specification 800 of LLAs, ULAs and GUAs used by AERO nodes on OMNI links. 802 Finally, AERO Clients and Proxy/Servers configure node identification 803 values as specified in [I-D.templin-6man-omni]. 805 3.2.3. AERO Routing System 807 The AERO routing system comprises a private instance of the Border 808 Gateway Protocol (BGP) [RFC4271] that is coordinated between Bridges 809 and Proxy/Servers and does not interact with either the public 810 Internet BGP routing system or any underlying INET routing systems. 812 In a reference deployment, each Proxy/Server is configured as an 813 Autonomous System Border Router (ASBR) for a stub Autonomous System 814 (AS) using a 32-bit AS Number (ASN) [RFC4271] that is unique within 815 the BGP instance, and each Proxy/Server further uses eBGP to peer 816 with one or more Bridges but does not peer with other Proxy/Servers. 817 Each SRT segment in the OMNI link must include one or more Bridges, 818 which peer with the Proxy/Servers within that segment. All Bridges 819 within the same segment are members of the same hub AS, and use iBGP 820 to maintain a consistent view of all active routes currently in 821 service. The Bridges of different segments peer with one another 822 using eBGP. 824 Bridges maintain forwarding table entries only for the MNP-ULAs 825 corresponding to MNP and non-MNP routes that are currently active, 826 and carrier packets destined to all other MNP-ULAs will correctly 827 incur Destination Unreachable messages due to the black-hole route. 828 In this way, Proxy/Servers and Relays have only partial topology 829 knowledge (i.e., they only maintain routing information for their 830 directly associated Clients and non-AERO links) and they forward all 831 other carrier packets to Bridges which have full topology knowledge. 833 Each OMNI link SRT segment assigns a unique ADM-ULA sub-prefix of 834 [ULA*]::/96. For example, a first segment could assign 835 [ULA*]::1000/116, a second could assign [ULA*]::2000/116, a third 836 could assign [ULA*]::3000/116, etc. Within each segment, each Proxy/ 837 Server configures an ADM-ULA within the segment's prefix, e.g., the 838 Proxy/Servers within [ULA*]::2000/116 could assign the ADM-ULAs 839 [ULA*]::2011/116, [ULA*]::2026/116, [ULA*]::2003/116, etc. 841 The administrative authorities for each segment must therefore 842 coordinate to assure mutually-exclusive ADM-ULA prefix assignments, 843 but internal provisioning of ADM-ULAs an independent local 844 consideration for each administrative authority. For each ADM-ULA 845 prefix, the Bridge(s) that connect that segment assign the all-zero's 846 address of the prefix as a Subnet Router Anycast address. For 847 example, the Subnet Router Anycast address for [ULA*]::1023/116 is 848 simply [ULA*]::1000. 850 ADM-ULA prefixes are statically represented in Bridge forwarding 851 tables. Bridges join multiple SRT segments into a unified OMNI link 852 over multiple diverse network administrative domains. They support a 853 bridging function by first establishing forwarding table entries for 854 their ADM-ULA prefixes either via standard BGP routing or static 855 routes. For example, if three Bridges ('A', 'B' and 'C') from 856 different segments serviced [ULA*]::1000/116, [ULA*]::2000/116 and 857 [ULA*]::3000/116 respectively, then the forwarding tables in each 858 Bridge are as follows: 860 A: [ULA*]::1000/116->local, [ULA*]::2000/116->B, [ULA*]::3000/116->C 862 B: [ULA*]::1000/116->A, [ULA*]::2000/116->local, [ULA*]::3000/116->C 864 C: [ULA*]::1000/116->A, [ULA*]::2000/116->B, [ULA*]::3000/116->local 866 These forwarding table entries are permanent and never change, since 867 they correspond to fixed infrastructure elements in their respective 868 segments. 870 MNP ULAs are instead dynamically advertised in the AERO routing 871 system by Proxy/Servers and Relays that provide service for their 872 corresponding MNPs. For example, if three Proxy/Servers ('D', 'E' 873 and 'F') service the MNPs 2001:db8:1000:2000::/56, 874 2001:db8:3000:4000::/56 and 2001:db8:5000:6000::/56 then the routing 875 system would include: 877 D: [ULA*]:2001:db8:1000:2000/120 878 E: [ULA*]:2001:db8:3000:4000/120 880 F: [ULA*]:2001:db8:5000:6000/120 882 A full discussion of the BGP-based routing system used by AERO is 883 found in [I-D.ietf-rtgwg-atn-bgp]. 885 3.2.4. OMNI Link Segment Routing 887 With the Client and partition prefixes in place in Bridge forwarding 888 tables, the OMNI interface sends control and data carrier packets 889 toward AERO destination nodes located in different OMNI link segments 890 over the SRT spanning tree. The OMNI interface uses the OMNI 891 Adaptation Layer (OAL) encapsulation service [I-D.templin-6man-omni], 892 and includes an OMNI Routing Header (ORH) as an extension to the OAL 893 header. Each carrier packet includes at most one ORH in compressed 894 or uncompressed form, with the uncompressed form shown in Figure 3: 896 0 1 2 3 897 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 1 898 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 899 | Next Header | Hdr Ext Len | Routing Type | Segments Left | 900 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 901 | omIndex | FMT | SRT | LHS (bits 0 -15) | 902 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 903 | LHS (bits 0 -15) | ~ 904 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ 905 ~ Link Layer Address (L2ADDR) ~ 906 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 907 | Null Padding (if necessary) | 908 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 909 ~ Destination Suffix ~ 910 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 912 Figure 3: OMNI Routing Header (ORH) Format 914 The ORH includes the following fields, in consecutive order: 916 o Next Header identifies the type of header immediately following 917 the ORH. 919 o Hdr Ext Len is the length of the Routing header in 8-octet units 920 (not including the first 8 octets). The field must encode a value 921 between 0 and 4 (all other values indicate a parameter problem). 923 o Routing Type is set to TBD1 (see IANA Considerations). 925 o Segments Left encodes the value 0 or 1 (all other values indicate 926 a parameter problem). 928 o omIndex - a 1-octet field consulted only when Segments Left is 0; 929 identifies a specific target Client underlying interface serviced 930 by the LHS Proxy-Server when there are multiple alternatives. 931 When FMT-Forward is clear, omIndex determines the interface for 932 forwarding the ORH packet following reassembly; when FMT-Forward 933 is set, omIndex determines the interface for forwarding the raw 934 carrier packets without first reassembling. When omIndex is set 935 to 0 (or when no ORH is present), the LHS Proxy/Server selects 936 among any of the Client's available underlying interfaces that it 937 services locally (i.e., and not those serviced by another Proxy/ 938 Server). 940 o FMT - a 3-bit "Forward/Mode/Trailer" code corresponding to the 941 included Link Layer Address as follows: 943 * When the most significant bit (i.e., "FMT-Forward") is clear, 944 the LHS Proxy/Server must reassemble. When FMT-Forward is set, 945 the LHS Proxy/Server must forward the fragments to the Client 946 (while changing the OAL destination address to the MNP-ULA of 947 the Client if necessary) without reassembling. 949 * When the next most significant bit (i.e., "FMT-Mode") is clear, 950 L2ADDR is the INET address of the LHS Proxy/Server and the 951 Client must be reached through the LHS Proxy/Server. When FMT- 952 Mode is set, the Client is eligible for route optimization over 953 the open INET where it may be located behind one or more NATs, 954 and L2ADDR is either the INET address of the LHS Proxy/Server 955 (when FMT-Forward is set) or the native INET address of the 956 Client itself (when FMT-Forward is clear). 958 * The least significant bit (i.e., "FMT-Type") is consulted only 959 when Hdr Ext Len is 1 and ignored otherwise. If FMT-Type is 960 clear, the remaining 10 ORH octets contain an LHS followed by 961 an IPv4 L2ADDR. If FMT-Type is set, the remainder instead 962 contains 2 null padding octets followed by an 8-octet (IPv6) 963 Destination Suffix. 965 o SRT - a 5-bit Segment Routing Topology prefix length consulted 966 only when Segments Left is 1, and encodes a value that (when added 967 to 96) determines the prefix length to apply to the ADM-ULA formed 968 from concatenating [ULA*]::/96 with the 32 bit LHS value (for 969 example, the value 16 corresponds to the prefix length 112). 971 o LHS - a 4-octet field present only when indicated by the ORH 972 length (see below) and consulted only when Segments Left is 1. 974 The field encodes the 32-bit ADM-ULA suffix of an LHS Proxy/Server 975 for the target. When SRT and LHS are both set to 0, the LHS 976 Proxy/Server must be reached directly via INET encapsulation 977 instead of over the spanning tree. When SRT is set to 0 and LHS 978 is non-zero, the prefix length is set to 128. SRT and LHS 979 determine the ADM-ULA of the LHS Proxy/Server over the spanning 980 tree. 982 o Link Layer Address (L2ADDR) - an IP encapsulation address present 983 only when indicated by the ORH length (see below) and consulted 984 only when Segments Left is 1. The ORH length also determines the 985 L2ADDR IP version since the field will always contain exactly 6 986 octets for UDP/IPv4 or 18 octets for UDP/IPv6. When present, 987 provides the link-layer address (i.e., the encapsulation address) 988 of the LHS Proxy/Server or the target Client itself. The UDP Port 989 Number appears in the first two octets and the IP address appears 990 in the remaining octets. The Port Number and IP address are 991 recorded in network byte order, and in ones-compliment 992 "obfuscated" form per [RFC4380]. The OMNI interface forwarding 993 algorithm uses L2ADDR as the INET encapsulation address for 994 forwarding when SRT/LHS is located in the same OMNI link segment. 995 If direct INET encapsulation is not permitted, L2ADDR is instead 996 set to all-zeros and the packet must be forwarded to the LHS 997 Proxy-Server via the spanning tree. 999 o Null Padding - zero-valued octets added as necessary to pad the 1000 portion of the ORH included up to this point to an even 8-octet 1001 boundary. 1003 o Destination Suffix - a trailing 8-octet field present only when 1004 indicated by the ORH length (see below). When ORH length is 1, 1005 FMT-Type determines whether the option includes a Destination 1006 Suffix or an LHS/L2ADDR for IPv4 since there is only enough space 1007 available for one. When present, encodes the 64-bit MNP-ULA 1008 suffix for the target Client. 1010 The ORH Hdr Ext Len field value also serves as an implicit ORH 1011 "Type", with 5 distinct Types specified (i.e., ORH-0 through ORH-4). 1012 All ORH-* Types include the same 6-octet preamble beginning with Next 1013 Header up to and including omIndex, followed by a Type-specific 1014 remainder as follows: 1016 o ORH-0 - The preamble Hdr Ext Len and Segments Left must both be 0. 1017 Two null padding octets follow the preamble, and all other fields 1018 are omitted. 1020 o ORH-1 - The preamble Hdr Ext Len is set to 1. When FMT-Type is 1021 clear, the LHS and L2ADDR for IPv4 fields are included and the 1022 Destination Suffix is omitted. When FMT-Type is set, the LHS and 1023 L2ADDR fields are omitted, the Destination Suffix field is 1024 included and Segments Left must be 0. 1026 o ORH-2 - The preamble Hdr Ext Len is set to 2. The LHS, L2ADDR for 1027 IPv4 and Destination Suffix fields are all included. 1029 o ORH-3 - The preamble Hdr Ext Len is set to 3. The LHS and L2ADDR 1030 for IPv6 fields are included and the Destination Suffix field is 1031 omitted. 1033 o ORH-4 - The preamble Hdr Ext Len is set to 4. The LHS, L2ADDR for 1034 IPv6 and Destination Suffix fields are all included. 1036 AERO neighbors use OAL encapsulation and fragmentation to exchange 1037 OAL packets as specified in [I-D.templin-6man-omni]. When an AERO 1038 node's OMNI interface (acting as an OAL source) uses OAL 1039 encapsulation for an original IP packet with source address 1040 2001:db8:1:2::1 and destination address 2001:db8:1234:5678::1, it 1041 sets the OAL header source address to its own ULA (e.g., 1042 [ULA*]::2001:db8:1:2), sets the destination address to the MNP-ULA 1043 corresponding to the IP destination address (e.g., 1044 [ULA*]::2001:db8:1234:5678), sets the Traffic Class, Flow Label, Hop 1045 Limit and Payload Length as discussed in [I-D.templin-6man-omni], 1046 then finally selects an Identification and appends an OAL checksum. 1048 If the neighbor cache information indicates that the target is in a 1049 different segment, the OAL source next inserts an ORH immediately 1050 following the OAL header while including Destination Suffix for non- 1051 first-fragments only when necessary (in this case, the Destination 1052 Suffix is 2001:db8:1234:5678). Next, to direct the packet to a 1053 first-hop Proxy/Server or a Bridge, the source prepares an ORH with 1054 Segments Left set to 1 and with SRT/LHS/L2ADDR included, then 1055 overwrites the OAL header destination address with the LHS Subnet 1056 Router Anycast address (for example, for LHS 3000:4567 with SRT 16, 1057 the Subnet Router Anycast address is [ULA*]::3000:0000). To send the 1058 packet to the LHS Proxy/Server either directly or via the spanning 1059 tree, the OAL source instead includes an ORH (Type 0 or 1) with 1060 Segments Left set to 0 and LHS/L2ADDR omitted, and overwrites the OAL 1061 header destination address with either the LHS Proxy/Server ADM-ULA 1062 or the MNP-ULA of the Client itself. 1064 The OAL source then fragments the OAL packet, with each resulting OAL 1065 fragment including the OAL/ORH headers while only the first fragment 1066 includes the original IPv6 header. If FMT-Forward is set, the 1067 Identification used for fragmentation must be within the window for 1068 the Client and a Destination Suffix must be included with each non- 1069 first-fragment when necessary; otherwise the Identification must be 1070 within the window for the Client's Proxy/Server and no Destination 1071 Suffix is needed. (Note that if no actual fragmentation is required 1072 the OAL source still prepares the packet as an "atomic" fragment that 1073 includes a Fragment Header with Offset and More Fragments both set to 1074 0.) The OAL source finally encapsulates each resulting OAL fragment 1075 in an *NET header to form an OAL carrier packet, with source address 1076 set to its own *NET address (e.g., 192.0.2.100) and destination set 1077 to the *NET address of the last hop itself or the next hop in the 1078 spanning tree (e.g., 192.0.2.1). 1080 The carrier packet encapsulation format in the above example is shown 1081 in Figure 4: 1083 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1084 | *NET Header | 1085 | src = 192.0.2.100 | 1086 | dst = 192.0.2.1 | 1087 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1088 | OAL IPv6 Header | 1089 | src = [ULA*]::2001:db8:1:2 | 1090 | dst= [ULA*]::3000:0000 | 1091 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1092 | ORH (if necessary) | 1093 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1094 | OAL Fragment Header | 1095 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1096 | Original IP Header | 1097 | (first-fragment only) | 1098 | src = 2001:db8:1:2::1 | 1099 | dst = 2001:db8:1234:5678::1 | 1100 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1101 | | 1102 ~ ~ 1103 ~ Original Packet Body/Fragment ~ 1104 ~ ~ 1105 | | 1106 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1108 Figure 4: Carrier Packet Format 1110 In this format, the original IP header and packet body/fragment are 1111 from the original IP packet, the OAL header is an IPv6 header 1112 prepared according to [RFC2473], the ORH is a Routing Header 1113 extension of the OAL header, the Fragment Header identifies each 1114 fragment, and the INET header is prepared as discussed in 1115 Section 3.6. When the OAL source transmits the resulting carrier 1116 packets, they are forwarded over possibly multiple OAL intermediate 1117 nodes in the OMNI link spanning tree until they arrive at the OAL 1118 destination. 1120 This gives rise to an SRT routing system that contains both Client 1121 MNP-ULA routes that may change dynamically due to regional node 1122 mobility and per-partition ADM-ULA routes that rarely if ever change. 1123 The spanning tree can therefore provide link-layer bridging by 1124 sending carrier packets over the spanning tree instead of network- 1125 layer routing according to MNP routes. As a result, opportunities 1126 for loss due to node mobility between different segments are 1127 mitigated. 1129 Note: The document recommends that AERO nodes transform ORHs with 1130 Segments Left set to 1 into ORH-0 or ORH-1 during forwarding. While 1131 this may yield encapsulation overhead savings in some cases, the AERO 1132 node may instead simply set Segments Left to 0 and leave the original 1133 ORH in place. The LHS Proxy/Server or target Client that processes 1134 the ORH will receive the same information in both cases. 1136 Note: When the OAL source sets a carrier packet OAL destination 1137 address to a target's MNP-ULA but does not assert a specific target 1138 underlying interface, it may omit the ORH whether forwarding to the 1139 LHS Proxy/Server or directly to the target itself. When the LHS 1140 Proxy/Server receives a carrier packet with OAL destination set to 1141 the target MNP-ULA but with no ORH, it forwards over any available 1142 underlying interface for the target that it services locally. 1144 Note: When the OAL source and destination are on the same INET 1145 segment, OAL header compression can be used to significantly reduce 1146 encapsulation overhead as discussed in [I-D.templin-6man-omni]. 1148 Note: Use of an IPv6 "minimal encapsulation" format (i.e., an IPv6 1149 variant of [RFC2004]) based on extensions to the ORH was considered 1150 and abandoned. In the approach, the ORH would be inserted as an 1151 extension header to the original IPv6 packet header. The IPv6 1152 destination address would then be written into the ORH, and the ULA 1153 corresponding to the destination would be overwritten in the IPv6 1154 destination address. This would seemingly convey enough forwarding 1155 information so that OAL encapsulation could be avoided. However, 1156 this "minimal encapsulation" IPv6 packet would then have a non-ULA 1157 source address and ULA destination address, an incorrect value in 1158 upper layer protocol checksums, and a Hop Limit that is decremented 1159 within the spanning tree when it should not be. The insertion and 1160 removal of the ORH would also entail rewriting the Payload Length and 1161 Next Header fields - again, invalidating upper layer checksums. 1162 These irregularities would result in implementation challenges and 1163 the potential for operational issues, e.g., since actionable ICMPv6 1164 error reports could not be delivered to the original source. In 1165 order to address the issues, still more information such as the 1166 original IPv6 source address could be written into the ORH. However, 1167 with the additional information the benefit of the "minimal 1168 encapsulation" savings quickly diminishes, and becomes overshadowed 1169 by the implementation and operational irregularities. 1171 3.2.5. Segment Routing Topologies (SRTs) 1173 The 64-bit sub-prefixes of [ULA]::/48 identify up to 2^16 distinct 1174 Segment Routing Topologies (SRTs). Each SRT is a mutually-exclusive 1175 OMNI link overlay instance using a distinct set of ULAs, and emulates 1176 a Virtual LAN (VLAN) service for the OMNI link. In some cases (e.g., 1177 when redundant topologies are needed for fault tolerance and 1178 reliability) it may be beneficial to deploy multiple SRTs that act as 1179 independent overlay instances. A communication failure in one 1180 instance therefore will not affect communications in other instances. 1182 Each SRT is identified by a distinct value in bits 48-63 of 1183 [ULA]::/48, i.e., as [ULA0]::/64, [ULA1]::/64, [ULA2]::/64, etc. 1184 Each OMNI interface is identified by a unique interface name (e.g., 1185 omni0, omni1, omni2, etc.) and assigns an anycast ADM-ULA 1186 corresponding to its SRT prefix length. The anycast ADM-ULA is used 1187 for OMNI interface determination in Safety-Based Multilink (SBM) as 1188 discussed in [I-D.templin-6man-omni]. Each OMNI interface further 1189 applies Performance-Based Multilink (PBM) internally. 1191 The Bridges and Proxy/Servers of each independent SRT engage in BGP 1192 peerings to form a spanning tree with the Bridges in non-leaf nodes 1193 and the Proxy/Servers in leaf nodes. The spanning tree is configured 1194 over both secured and unsecured underlying network paths. The 1195 secured spanning tree is used to convey secured control messages 1196 between FHS and LHS Proxy/Servers, while the unsecured spanning tree 1197 forwards data messages and/or unsecured control messages. 1199 3.2.6. Segment Routing For OMNI Link Selection 1201 Original IPv6 sourcse can direct IPv6 packets to an AERO node by 1202 including a standard IPv6 Segment Routing Header (SRH) [RFC8754] with 1203 the anycast ADM-ULA for the selected OMNI link as either the IPv6 1204 destination or as an intermediate hop within the SRH. This allows 1205 the original source to determine the specific OMNI link SRT an 1206 original IPv6 packet will traverse when there may be multiple 1207 alternatives. 1209 When an AERO node processes the SRH and forwards the original IPv6 1210 packet to the correct OMNI interface, the OMNI interface writes the 1211 next IPv6 address from the SRH into the IPv6 destination address and 1212 decrements Segments Left. If decrementing would cause Segments Left 1213 to become 0, the OMNI interface deletes the SRH before forwarding. 1214 This form of Segment Routing supports Safety-Based Multilink (SBM). 1216 3.2.7. Segment Routing Within the OMNI Link 1218 OAL sources can insert an ORH for Segment Routing within the same 1219 OMNI link to influence the paths of carrier packets sent to OAL 1220 destinations in remote SRT segments without requiring all carrier 1221 packets to traverse strict SRT spanning tree paths. (OAL sources can 1222 also insert an ORH in carrier packets sent to OAL destinations in the 1223 local segment if additional last-hop forwarding information is 1224 required.) 1226 When an AERO node's OMNI interface has an original IP packet to send 1227 to a target discovered through route optimization located in the same 1228 SRT segment, it acts as an OAL source to perform OAL encapsulation 1229 and fragmentation. The node then uses L2ADDR for INET encapsulation 1230 while including an ORH-0 when sending the resulting carrier packets 1231 to the ADM-ULA of the LHS Proxy/Server, or optionally omitting the 1232 ORH-0 when sending to the MNP-ULA of the target Client itself. When 1233 the node sends carrier packets with an ORH-0 to the LHS Proxy/Server, 1234 it sets the OAL destination to the ADM-ULA of the Proxy/Server if the 1235 Proxy/Server is responsible for reassembly; otherwise, it sets the 1236 OAL destination to the MNP-ULA of the target Client to cause the 1237 Proxy/Server to forward without reassembling. The node also sets 1238 omIndex to select a specific target Client underlying interface, or 1239 sets omIndex to 0 when no preference is selected. 1241 When an AERO node's OMNI interface has an original IP packet to send 1242 to a route optimization target located in a remote OMNI link segment, 1243 it acts as an OAL source the same as above but also includes an 1244 appropriate ORH type with Segments Left set to 1 and with SRT/LHS/ 1245 L2ADDR information while setting the OAL destination to the Subnet 1246 Router Anycast address for the LHS OMNI link segment. (The OAL 1247 source can alternatively include an ORH with Segments Left set to 0 1248 while setting the OAL destination to the ADM-ULA of the LHS Proxy/ 1249 Server, but this would cause the carrier packets to follow strict 1250 spanning tree paths.) The OMNI interface then forwards the resulting 1251 carrier packets into the spanning tree. 1253 When a Bridge receives a carrier packet destined to its Subnet Router 1254 Anycast address with any ORH type with Segments Left set to 1 and 1255 with SRT/LHS/L2ADDR values corresponding to the local segment, it 1256 examines FMT-Mode to determine whether the target Client can accept 1257 packets directly (i.e., following any NAT traversal procedures 1258 necessary) while bypassing the LHS Proxy/Server. If the Client can 1259 be reached directly and NAT traversal has converged, the Bridge then 1260 writes the MNP-ULA (found in the inner IPv6 header for first 1261 fragments or the ORH Destination Suffix for non-first fragments) into 1262 the OAL destination address, decrements the OAL IPv6 header Hop Limit 1263 (and discards the packet if Hop Limit reaches 0), removes the ORH, 1264 re-encapsulates the carrier packet according to L2ADDR then forwards 1265 the carrier packet directly to the target Client. If the Client 1266 cannot be reached directly (or if NAT traversal has not yet 1267 converged), the Bridge instead transforms the ORH into an ORH-0, re- 1268 encapsulates the packet according to L2ADDR, changes the OAL 1269 destination to the ADM-ULA of the LHS Proxy/Server if FMT-Forward is 1270 clear or the MNP-ULA of the Client if FMT-Forward is set and forwards 1271 the carrier packet to the LHS Proxy/Server. 1273 When a Bridge receives a carrier packet destined to its Subnet Router 1274 Anycast address with any ORH type with Segments Left set to 1 and 1275 L2ADDR set to 0, the Bridge instead forwards the packet toward the 1276 LHS Proxy/Server via the spanning tree. The Bridge changes the OAL 1277 destination to the ADM-ULA of the LHS Proxy/Server, transforms the 1278 ORH into an ORH-0 (or an ORH-1 with FMT-Type set and Segments Left 1279 0), then forwards the packet to the next hop in the spanning tree. 1280 The Bridge may also elect to forward via the spanning tree as above 1281 even when it receives a carrier packet with an ORH that includes a 1282 valid L2ADDR Port Number and IP address, however this may result in a 1283 longer path than necessary. If the carrier packet arrived via the 1284 secured spanning tree, the Bridge forwards to the next hop also via 1285 the secured spanning tree. If the carrier packet arrived via the 1286 unsecured spanning tree, the Bridge forwards to the next hop also via 1287 the unsecured spanning tree. 1289 When an LHS Proxy/Server receives carrier packets with any ORH type 1290 with Segments Left set to 0 and with OAL destination set to its own 1291 ADM-ULA, it proceeds according to FMT-Forward and omIndex. If FMT- 1292 Forward is set, the LHS Proxy/Server changes the OAL destination to 1293 the MNP-ULA of the target Client found in the IPv6 header for first 1294 fragments or in the ORH Destination Suffix for non-first-fragments, 1295 removes the ORH and forwards to the target Client interface 1296 identified by omIndex. If FMT-Forward is clear, the LHS Proxy/Server 1297 instead reassembles then re-encapsulates while refragmenting if 1298 necessary, removes the ORH and forwards to the target Client 1299 according to omIndex. 1301 When an LHS Proxy/Server receives carrier packets with any ORH type 1302 with Segments Left set to 0 and with OAL destination set to the MNP- 1303 ULA of the target Client, it removes the ORH and forwards to the 1304 target Client according to omIndex. During forwarding, the LHS 1305 Proxy/Server must first verify that the omIndex corresponds to a 1306 target underlying interface that it services locally and must not 1307 forward to other target underlying interfaces. If omIndex is 0 (or 1308 if no ORH is included) the LHS Proxy/Server instead selects among any 1309 of the target underlying interfaces it services. 1311 When a target Client receives carrier packets with OAL destination 1312 set to is MNP-ULA, it reassembles to obtain the OAL packet then 1313 decapsulates and delivers the original IP packet to upper layers. 1315 Note: Special handling procedures are employed for the exchange of 1316 IPv6 ND messages used to establish neighbor cache state as discussed 1317 in Section 3.14. The procedures call for hop-by-hop authentication 1318 and neighbor cache state establishment based on the encapsulation 1319 ULA, with next-hop determination based on the IPv6 ND message LLA. 1321 3.3. OMNI Interface Characteristics 1323 OMNI interfaces are virtual interfaces configured over one or more 1324 underlying interfaces classified as follows: 1326 o INET interfaces connect to an INET either natively or through one 1327 or more NATs. Native INET interfaces have global IP addresses 1328 that are reachable from any INET correspondent. The INET-facing 1329 interfaces of Proxy/Servers are native interfaces, as are Relay 1330 and Bridge interfaces. NATed INET interfaces connect to a private 1331 network behind one or more NATs that provide INET access. Clients 1332 that are behind a NAT are required to send periodic keepalive 1333 messages to keep NAT state alive when there are no carrier packets 1334 flowing. 1336 o ANET interfaces connect to an ANET that is separated from the open 1337 INET by an FHS Proxy/Server. Clients can issue control messages 1338 over the ANET without including an authentication signature since 1339 the ANET is secured at the network layer or below. Proxy/Servers 1340 can actively issue control messages over the INET on behalf of 1341 ANET Clients to reduce ANET congestion. 1343 o VPNed interfaces use security encapsulation over the INET to a 1344 Virtual Private Network (VPN) server that also acts as an FHS 1345 Proxy/Server. Other than the link-layer encapsulation format, 1346 VPNed interfaces behave the same as Direct interfaces. 1348 o Direct (i.e., single-hop point-to-point) interfaces connect a 1349 Client directly to an FHS Proxy/Server without crossing any ANET/ 1350 INET paths. An example is a line-of-sight link between a remote 1351 pilot and an unmanned aircraft. The same Client considerations 1352 apply as for VPNed interfaces. 1354 OMNI interfaces use OAL encapsulation and fragmentation as discussed 1355 in Section 3.2.4. OMNI interfaces use *NET encapsulation (see: 1357 Section 3.6) to exchange carrier packets with OMNI link neighbors 1358 over INET or VPNed interfaces as well as over ANET interfaces for 1359 which the Client and FHS Proxy/Server may be multiple IP hops away. 1360 OMNI interfaces do not use link-layer encapsulation over Direct 1361 underlying interfaces or ANET interfaces when the Client and FHS 1362 Proxy/Server are known to be on the same underlying link. 1364 OMNI interfaces maintain a neighbor cache for tracking per-neighbor 1365 state the same as for any interface. OMNI interfaces use ND messages 1366 including Router Solicitation (RS), Router Advertisement (RA), 1367 Neighbor Solicitation (NS) and Neighbor Advertisement (NA) for 1368 neighbor cache management. In environments where spoofing may be a 1369 threat, OMNI neighbors should employ OAL Identification window 1370 synchronization in their ND message exchanges. 1372 OMNI interfaces send ND messages with an OMNI option formatted as 1373 specified in [I-D.templin-6man-omni]. The OMNI option includes 1374 prefix registration information, Interface Attributes containing link 1375 information parameters for the OMNI interface's underlying interfaces 1376 and any other per-neighbor information. Each OMNI option may include 1377 multiple Interface Attributes sub-options identified by non-zero 1378 omIndex values. 1380 A Client's OMNI interface may be configured over multiple underlying 1381 interface connections. For example, common mobile handheld devices 1382 have both wireless local area network ("WLAN") and cellular wireless 1383 links. These links are often used "one at a time" with low-cost WLAN 1384 preferred and highly-available cellular wireless as a standby, but a 1385 simultaneous-use capability could provide benefits. In a more 1386 complex example, aircraft frequently have many wireless data link 1387 types (e.g. satellite-based, cellular, terrestrial, air-to-air 1388 directional, etc.) with diverse performance and cost properties. 1390 If a Client's multiple underlying interfaces are used "one at a time" 1391 (i.e., all other interfaces are in standby mode while one interface 1392 is active), then successive ND messages all include OMNI option 1393 Interface Attributes sub-options with the same underlying interface 1394 index. In that case, the Client would appear to have a single 1395 underlying interface but with a dynamically changing link-layer 1396 address. 1398 If the Client has multiple active underlying interfaces, then from 1399 the perspective of ND it would appear to have multiple link-layer 1400 addresses. In that case, ND message OMNI options MAY include 1401 Interface Attributes sub-options with different underlying interface 1402 indexes. Every ND message need not include Interface Attributes for 1403 all underlying interfaces; for any attributes not included, the 1404 neighbor considers the status as unchanged. 1406 Bridge and Proxy/Server OMNI interfaces are configured over secured 1407 tunnel underlying interfaces for carrying IPv6 ND and BGP protocol 1408 control plane messages, plus open INET underlying interfaces for 1409 carrying unsecured messages. The OMNI interface configures both an 1410 ADM-LLA and its corresponding ADM-ULA, and acts as an OAL source to 1411 encapsulate and fragment original IP packets while presenting the 1412 resulting carrier packets to a secured or unsecured underlying 1413 interface. Note that Bridge and Proxy/Server BGP protocol TCP 1414 sessions are run directly over the OMNI interface using ADM-ULA 1415 source and destination addresses. The OMNI interface encapsulates 1416 the original IP packets for these sessions as carrier packets (i.e., 1417 even though the OAL header may use the same ADM-ULAs as the original 1418 IP header) and forwards them over a secured underlying interface. 1420 3.4. OMNI Interface Initialization 1422 AERO Proxy/Servers and Clients configure OMNI interfaces as their 1423 point of attachment to the OMNI link. AERO nodes assign the MSPs for 1424 the link to their OMNI interfaces (i.e., as a "route-to-interface") 1425 to ensure that original IP packets with destination addresses covered 1426 by an MNP not explicitly assigned to a non-OMNI interface are 1427 directed to the OMNI interface. 1429 OMNI interface initialization procedures for Proxy/Servers, Clients 1430 and Bridges are discussed in the following sections. 1432 3.4.1. AERO Proxy/Server and Relay Behavior 1434 When a Proxy/Server enables an OMNI interface, it assigns an 1435 ADM-{LLA,ULA} appropriate for the given OMNI link segment. The 1436 Proxy/Server also configures secured tunnels with one or more 1437 neighboring Bridges and engages in a BGP routing protocol session 1438 with each Bridge. 1440 The OMNI interface provides a single interface abstraction to the IP 1441 layer, but internally includes an NBMA nexus for sending carrier 1442 packets to OMNI interface neighbors over underlying INET interfaces 1443 and secured tunnels. The Proxy/Server further configures a service 1444 to facilitate ND exchanges with AERO Clients and manages per-Client 1445 neighbor cache entries and IP forwarding table entries based on 1446 control message exchanges. 1448 Relays are simply Proxy/Servers that run a dynamic routing protocol 1449 to redistribute routes between the OMNI interface and INET/EUN 1450 interfaces (see: Section 3.2.3). The Relay provisions MNPs to 1451 networks on the INET/EUN interfaces (i.e., the same as a Client would 1452 do) and advertises the MSP(s) for the OMNI link over the INET/EUN 1453 interfaces. The Relay further provides an attachment point of the 1454 OMNI link to a non-MNP-based global topology. 1456 3.4.2. AERO Client Behavior 1458 When a Client enables an OMNI interface, it assigns either an 1459 MNP-{LLA, ULA} or a Temporary ULA and sends RS messages with ND 1460 parameters over its underlying interfaces to an FHS Proxy/Server, 1461 which returns an RA message with corresponding parameters. The RS/RA 1462 messages may pass through one or more NATs in the case of a Client's 1463 INET interface. (Note: if the Client used a Temporary ULA in its 1464 initial RS message, it will discover an MNP-{LLA, ULA} in the 1465 corresponding RA that it receives from the FHS Proxy/Server and begin 1466 using these new addresses. If the Client is operating outside the 1467 context of AERO infrastructure such as in a Mobile Ad-hoc Network 1468 (MANET), however, it may continue using Temporary ULAs for Client-to- 1469 Client communications until it encounters an infrastructure element 1470 that can provide an MNP.) 1472 3.4.3. AERO Bridge Behavior 1474 AERO Bridges configure an OMNI interface and assign the ADM-ULA 1475 Subnet Router Anycast address for each OMNI link segment they connect 1476 to. Bridges configure secured tunnels with Proxy/Servers and other 1477 Bridges, and engage in a BGP routing protocol session with neighbors 1478 on the spanning tree (see: Section 3.2.3). 1480 3.5. OMNI Interface Neighbor Cache Maintenance 1482 Each OMNI interface maintains a conceptual neighbor cache that 1483 includes a Neighbor Cache Entry (NCE) for each of its active 1484 neighbors on the OMNI link per [RFC4861]. Each route optimization 1485 source NCE is indexed by the LLA of the neighbor, while the OAL 1486 encapsulation ULA determines the context for Identification 1487 verification. In addition to ordinary neighbor cache entries, proxy 1488 neighbor cache entries are created and maintained by AERO Proxy/ 1489 Servers when they proxy Client ND message exchanges [RFC4389]. AERO 1490 Proxy/Servers maintain proxy neighbor cache entries for each of their 1491 associated Clients. 1493 To the list of NCE states in Section 7.3.2 of [RFC4861], Proxy/Server 1494 OMNI interfaces add an additional state DEPARTED that applies to 1495 Clients that have recently departed. The interface sets a 1496 "DepartTime" variable for the NCE to "DEPART_TIME" seconds. 1497 DepartTime is decremented unless a new ND message causes the state to 1498 return to REACHABLE. While a NCE is in the DEPARTED state, the 1499 Proxy/Server forwards carrier packets destined to the target Client 1500 to the Client's new location instead. When DepartTime decrements to 1501 0, the NCE is deleted. It is RECOMMENDED that DEPART_TIME be set to 1502 the default constant value REACHABLE_TIME plus 10 seconds (40 seconds 1503 by default) to allow a window for carrier packets in flight to be 1504 delivered while stale route optimization state may be present. 1506 Proxy/Servers can act as RORs on behalf of dependent Clients 1507 according to the Proxy Neighbor Advertisement specification in 1508 Section 7.2.8 of [RFC4861]. When a Proxy/Server ROR receives an 1509 authentic NS message used for route optimization, it first searches 1510 for a NCE for the target Client and accepts the message only if there 1511 is an entry. The Proxy/Server then returns a solicited NA message 1512 while creating or updating a "Report List" entry in the target 1513 Client's NCE that caches both the LLA and ULA of ROS with a 1514 "ReportTime" variable set to REPORT_TIME seconds. The ROR resets 1515 ReportTime when it receives a new authentic NS message, and otherwise 1516 decrements ReportTime while no authentic NS messages have been 1517 received. It is RECOMMENDED that REPORT_TIME be set to the default 1518 constant value REACHABLE_TIME plus 10 seconds (40 seconds by default) 1519 to allow a window for route optimization to converge before 1520 ReportTime decrements below REACHABLE_TIME. 1522 When the ROS receives a solicited NA message response to its NS 1523 message used for route optimization, it creates or updates a NCE for 1524 the target network-layer and link-layer addresses. The ROS then 1525 (re)sets ReachableTime for the NCE to REACHABLE_TIME seconds and uses 1526 this value to determine whether carrier packets can be forwarded 1527 directly to the target, i.e., instead of via a default route. The 1528 ROS otherwise decrements ReachableTime while no further solicited NA 1529 messages arrive. It is RECOMMENDED that REACHABLE_TIME be set to the 1530 default constant value 30 seconds as specified in [RFC4861]. 1532 AERO nodes also use the value MAX_UNICAST_SOLICIT to limit the number 1533 of NS messages sent when a correspondent may have gone unreachable, 1534 the value MAX_RTR_SOLICITATIONS to limit the number of RS messages 1535 sent without receiving an RA and the value MAX_NEIGHBOR_ADVERTISEMENT 1536 to limit the number of unsolicited NAs that can be sent based on a 1537 single event. It is RECOMMENDED that MAX_UNICAST_SOLICIT, 1538 MAX_RTR_SOLICITATIONS and MAX_NEIGHBOR_ADVERTISEMENT be set to 3 the 1539 same as specified in [RFC4861]. 1541 Different values for DEPART_TIME, REPORT_TIME, REACHABLE_TIME, 1542 MAX_UNICAST_SOLICIT, MAX_RTR_SOLCITATIONS and 1543 MAX_NEIGHBOR_ADVERTISEMENT MAY be administratively set; however, if 1544 different values are chosen, all nodes on the link MUST consistently 1545 configure the same values. Most importantly, DEPART_TIME and 1546 REPORT_TIME SHOULD be set to a value that is sufficiently longer than 1547 REACHABLE_TIME to avoid packet loss due to stale route optimization 1548 state. 1550 3.5.1. OMNI ND Messages 1552 OMNI interface IPv6 ND messages include OMNI options 1553 [I-D.templin-6man-omni] with per-neighbor information including 1554 Interface Attributes that provide Link-Layer Address and traffic 1555 selector information for the neighbor's underlying interfaces. This 1556 information is stored in the neighbor cache and provides the basis 1557 for the forwarding algorithm specified in Section 3.10. The 1558 information is cumulative and reflects the union of the OMNI 1559 information from the most recent ND messages received from the 1560 neighbor; it is therefore not required that each ND message contain 1561 all neighbor information. 1563 The OMNI option Interface Attributes for each underlying interface 1564 includes a two-part "Link-Layer Address" consisting of an INET 1565 encapsulation address determined by the FMT and L2ADDR fields and an 1566 ADM-ULA determined by the SRT and LHS fields. Underlying interfaces 1567 are further selected based on their associated traffic selectors. 1569 The OMNI option is distinct from any Source/Target Link-Layer Address 1570 Options (S/TLLAOs) that may appear in an ND message according to the 1571 appropriate IPv6 over specific link layer specification (e.g., 1572 [RFC2464]). If both an OMNI option and S/TLLAO appear, the former 1573 pertains to encapsulation addresses while the latter pertains to the 1574 native L2 address format of the underlying media 1576 OMNI interface IPv6 ND messages may also include other IPv6 ND 1577 options. In particular, solicitation messages may include Nonce and/ 1578 or Timestamp options if required for verification of advertisement 1579 replies. If an OMNI ND solicitation message includes a Nonce option, 1580 the advertisement reply must echo the same Nonce. If an OMNI ND 1581 solicitation message includes a Timestamp option, the advertisement 1582 reply should also include a Timestamp option. 1584 AERO Clients send RS messages to the All-Routers multicast address 1585 while using unicast link-layer addresses. AERO Proxy/Servers respond 1586 by returning unicast RA messages. During the RS/RA exchange, AERO 1587 Clients and Servers include state synchronization parameters to 1588 establish Identification windows and other state. 1590 AERO nodes use NS/NA messages for the following purposes: 1592 o NS/NA(AR) messages are used for address resolution only. The ROS 1593 sends an NS(AR) to the solicited-node multicast address of the 1594 target, and an ROR in the network with addressing information for 1595 the target returns a unicast NA(AR). The NA(AR) contains 1596 authentic and current target address resolution information, but 1597 only an implicit third-party assertion of target reachability. 1598 NS/NA(AR) messages must be secured. 1600 o NS/NA(WIN) messages are used for establishing and maintaining 1601 window synchronization (and any other) state. The source sends an 1602 NS(WIN) to the unicast address of the target, and the target 1603 returns a unicast NA(WIN). The NS/NA(WIN) exchange synchronizes 1604 sequence numbers the neighbors will include in subsequent packets, 1605 and asserts reachability for the target without necessarily 1606 testing a specific underlying interface pair. NS/NA(WIN) messages 1607 must be secured. 1609 o NS/NA(NUD) messages are used for determining target reachability. 1610 The source sends an NS(NUD) to the unicast address of the target 1611 while naming a specific underlying interface pair, and the target 1612 returns a unicast NA(NUD). NS/NA(NUD) messages that use an in- 1613 window sequence number and do not update any other state need not 1614 be secured. NS/NA(NUD) messages may also be used in combination 1615 with window synchronization (i.e., NUD+WIN), in which case the 1616 messages must be secured. 1618 o Unsolicited NA (uNA) messages are used to signal addressing and/or 1619 other neighbor state changes (e.g., due to mobility, signal 1620 degradation, traffic selector updates, etc.). uNA messages that 1621 include state update information must be secured. 1623 o NS/NA(DAD) messages are not used in AERO, since Duplicate Address 1624 Detection is not required. 1626 Additionally, nodes may send NA/RA messages with the OMNI option PNG 1627 flag set to receive a solicited NA response from the neighbor. The 1628 solicited NA response MUST set the ACK flag (without also setting the 1629 SYN or PNG flags) and include the Identification used in the PNG 1630 message in the Acknowledgement. 1632 3.5.2. OMNI Neighbor Advertisement Message Flags 1634 As discussed in Section 4.4 of [RFC4861] NA messages include three 1635 flag bits R, S and O. OMNI interface NA messages treat the flags as 1636 follows: 1638 o R: The R ("Router") flag is set to 1 in the NA messages sent by 1639 all AERO/OMNI node types. Simple hosts that would set R to 0 do 1640 not occur on the OMNI link itself, but may occur on the downstream 1641 links of Clients and Relays. 1643 o S: The S ("Solicited") flag is set exactly as specified in 1644 Section 4.4. of [RFC4861], i.e., it is set to 1 for Solicited NAs 1645 and set to 0 for uNAs (both unicast and multicast). 1647 o O: The O ("Override") flag is set to 0 for solicited NAs returned 1648 by a Proxy/Server ROR and set to 1 for all other solicited and 1649 unsolicited NAs. For further study is whether solicited NAs for 1650 anycast targets apply for OMNI links. Since MNP-LLAs must be 1651 uniquely assigned to Clients to support correct ND protocol 1652 operation, however, no role is currently seen for assigning the 1653 same MNP-LLA to multiple Clients. 1655 3.5.3. OMNI Neighbor Window Synchronization 1657 In secured environments (e.g., such as between nodes on the same 1658 secured ANET), OMNI interface neighbors can exchange OAL packets 1659 using randomly-initialized and monotonically-increasing 1660 Identification values (modulo 2*32) without window synchronization. 1661 In environments where spoofing is considered a threat, OMNI interface 1662 neighbors instead invoke window synchronization in ND message 1663 exchanges to maintain send/receive window state in their respective 1664 neighbor cache entries as specified in [I-D.templin-6man-omni]. 1666 In the asymmetric window synchronization case, the initial ND message 1667 exchange establishes only the initiator's send window and the 1668 responder's receive window such that a corresponding exchange would 1669 be needed to establish the reverse direction. In the symmetric case, 1670 the initiator and responder engage in a three-way handshake to 1671 symmetrically establish the send/receive windows of both parties. 1673 3.6. OMNI Interface Encapsulation and Re-encapsulation 1675 The OMNI interface admits original IP packets then (acting as an OAL 1676 source) performs OAL encapsulation and fragmentation as specified in 1677 [I-D.templin-6man-omni] while including an ORH if necessary as 1678 specified in Section 3.2.4. OAL encapsulation produces OAL packets 1679 subject to fragmentation, with the resulting fragments encapsulated 1680 in *NET headers as carrier packets. 1682 For carrier packets undergoing re-encapsulation at an OAL 1683 intermediate node, the OMNI interface decrements the OAL IPv6 header 1684 Hop Limit and discards the carrier packet if the Hop Limit reaches 0. 1685 The intermediate node next removes the *NET encapsulation headers 1686 from the first segment and re-encapsulates the packet in new *NET 1687 encapsulation headers for the next segment. 1689 When an FHS Proxy/Server re-encapsulates a carrier packet received 1690 from a Client that includes an OAL but no ORH, it inserts an ORH 1691 immediately following the OAL header and adjusts the OAL payload 1692 length and destination address field. The ORH will be removed by an 1693 LHS Bridge or Proxy/Server, but its insertion and removal will not 1694 interfere with reassembly at the final destination. For this reason, 1695 Clients must reserve 40 bytes for a maximum-length ORH when they 1696 perform OAL encapsulation (see: Section 3.9). 1698 3.7. OMNI Interface Decapsulation 1700 OMNI interfaces (acting as OAL destinations) decapsulate and 1701 reassemble OAL packets into original IP packets destined either to 1702 the AERO node itself or to a destination reached via an interface 1703 other than the OMNI interface the original IP packet was received on. 1704 When carrier packets containing OAL fragments addressed to itself 1705 arrive, the OMNI interface discards the NET encapsulation headers and 1706 reassembles as discussed in Section 3.9. 1708 3.8. OMNI Interface Data Origin Authentication 1710 AERO nodes employ simple data origin authentication procedures. In 1711 particular: 1713 o AERO Bridges and Proxy/Servers accept carrier packets received 1714 from secured underlying interfaces. 1716 o AERO Proxy/Servers and Clients accept carrier packets and original 1717 IP packets that originate from within the same secured ANET. 1719 o AERO Clients and Relays accept original IP packets from downstream 1720 network correspondents based on ingress filtering. 1722 o AERO Clients, Relays and Proxy/Servers verify carrier packet UDP/ 1723 IP encapsulation addresses according to [I-D.templin-6man-omni]. 1725 o AERO nodes accept carrier packets addressed to themselves with 1726 Identification values within the current window for the OAL source 1727 neighbor (when window synchronization is used) and drop any 1728 carrier packets with out-of-window Identification values. (AERO 1729 nodes may forward carrier packets not addressed to themselves 1730 without verifying the Identification value.) 1732 AERO nodes silently drop any packets that do not satisfy the above 1733 data origin authentication procedures. Further security 1734 considerations are discussed in Section 6. 1736 3.9. OMNI Interface MTU 1738 The OMNI interface observes the link nature of tunnels, including the 1739 Maximum Transmission Unit (MTU), Maximum Reassembly Unit (MRU) and 1740 the role of fragmentation and reassembly [I-D.ietf-intarea-tunnels]. 1741 The OMNI interface employs an OMNI Adaptation Layer (OAL) that 1742 accommodates multiple underlying links with diverse MTUs while 1743 observing both a minimum and per-path Maximum Payload Size (MPS). 1744 The functions of the OAL and the OMNI interface MTU/MRU/MPS are 1745 specified in [I-D.templin-6man-omni] with MTU/MRU both set to the 1746 constant value 9180 bytes, with minimum MPS set to 400 bytes, and 1747 with per-path MPS set to potentially larger values depending on the 1748 underlying path. 1750 When the network layer presents an original IP packet to the OMNI 1751 interface, the OAL source encapsulates and fragments the original IP 1752 packet if necessary. When the network layer presents the OMNI 1753 interface with multiple original IP packets bound to the same OAL 1754 destination, the OAL source can concatenate them together into a 1755 single OAL super-packet as discussed in [I-D.templin-6man-omni]. The 1756 OAL source then fragments the OAL packet if necessary according to 1757 the minimum/path MPS such that the OAL headers appear in each 1758 fragment while the original IP packet header appears only in the 1759 first fragment. The OAL source then encapsulates each OAL fragment 1760 in *NET headers for transmission as carrier packets over an 1761 underlying interface connected to either a physical link such as 1762 Ethernet, WiFi and the like or a virtual link such as an Internet or 1763 higher-layer tunnel (see the definition of link in [RFC8200]). 1765 Note: A Client that does not (yet) have neighbor cache state for a 1766 target may omit the ORH in carrier packets with the understanding 1767 that a Proxy/Server may insert an ORH on its behalf. For this 1768 reason, Clients reserve 40 bytes for the largest possible ORH in 1769 their OAL fragment size calculations. 1771 Note: Although the ORH may be removed or replaced by a Bridge or 1772 Proxy/Server on the path (see: Section 3.10.3), this does not 1773 interfere with the destination's ability to reassemble since the ORH 1774 is not included in the fragmentable part and its removal/ 1775 transformation does not invalidate fragment header information. 1777 3.10. OMNI Interface Forwarding Algorithm 1779 Original IP packets enter a node's OMNI interface either from the 1780 network layer (i.e., from a local application or the IP forwarding 1781 system) while carrier packets enter from the link layer (i.e., from 1782 an OMNI interface neighbor). All original IP packets and carrier 1783 packets entering a node's OMNI interface first undergo data origin 1784 authentication as discussed in Section 3.8. Those that satisfy data 1785 origin authentication are processed further, while all others are 1786 dropped silently. 1788 Original IP packets that enter the OMNI interface from the network 1789 layer are forwarded to an OMNI interface neighbor using OAL 1790 encapsulation and fragmentation to produce carrier packets for 1791 transmission over underlying interfaces. (If routing indicates that 1792 the original IP packet should instead be forwarded back to the 1793 network layer, the packet is dropped to avoid looping). Carrier 1794 packets that enter the OMNI interface from the link layer are either 1795 re-encapsulated and re-admitted into the OMNI link, or reassembled 1796 and forwarded to the network layer where they are subject to either 1797 local delivery or IP forwarding. In all cases, the OAL MUST NOT 1798 decrement the network layer TTL/Hop-count since its forwarding 1799 actions occur below the network layer. 1801 OMNI interfaces may have multiple underlying interfaces and/or 1802 neighbor cache entries for neighbors with multiple underlying 1803 interfaces (see Section 3.3). The OAL uses Interface Attribute 1804 traffic selectors (e.g., port number, flow specification, etc.) to 1805 select an outbound underlying interface for each OAL packet based on 1806 the node's own interface attributes, and also to select a destination 1807 link-layer address based on the neighbor's underlying interface 1808 attributes. AERO implementations SHOULD permit network management to 1809 dynamically adjust traffic selector values at runtime. 1811 If an OAL packet matches the traffic selectors of multiple outgoing 1812 interfaces and/or neighbor interfaces, the OMNI interface replicates 1813 the packet and sends one copy via each of the (outgoing / neighbor) 1814 interface pairs; otherwise, it sends a single copy of the OAL packet 1815 via an interface with the best matching traffic selector. (While not 1816 strictly required, the likelihood of successful reassembly may 1817 improve when the OMNI interface sends all fragments of the same 1818 fragmented OAL packet consecutively over the same underlying 1819 interface pair instead of spread across multiple underlying interface 1820 pairs.) AERO nodes keep track of which underlying interfaces are 1821 currently "reachable" or "unreachable", and only use "reachable" 1822 interfaces for forwarding purposes. 1824 The following sections discuss the OMNI interface forwarding 1825 algorithms for Clients, Proxy/Servers and Bridges. In the following 1826 discussion, an original IP packet's destination address is said to 1827 "match" if it is the same as a cached address, or if it is covered by 1828 a cached prefix (which may be encoded in an MNP-LLA). 1830 3.10.1. Client Forwarding Algorithm 1832 When an original IP packet enters a Client's OMNI interface from the 1833 network layer the Client searches for a NCE that matches the 1834 destination. If there is a match, the Client selects one or more 1835 "reachable" neighbor interfaces in the entry for forwarding purposes. 1836 If there is no NCE, the Client instead either enqueues the original 1837 IP packet and invokes route optimization or forwards the original IP 1838 packet toward a Proxy/Server. The Client (acting as an OAL source) 1839 performs OAL encapsulation and sets the OAL destination address to 1840 the MNP-ULA of the target if there is a matching NCE; otherwise, it 1841 sets the OAL destination to the ADM-ULA of the Proxy/Server. If the 1842 Client has multiple original IP packets to send to the same neighbor, 1843 it can concatenate them in a single super-packet 1844 [I-D.templin-6man-omni]. The OAL source then performs fragmentation 1845 to create OAL fragments (see: Section 3.9), appends any *NET 1846 encapsulation, and sends the resulting carrier packets over 1847 underlying interfaces to the neighbor acting as an OAL destination. 1849 If the neighbor interface selected for forwarding is located on the 1850 same OMNI link segment and not behind a NAT, the Client forwards the 1851 carrier packets directly according to the L2ADDR information for the 1852 neighbor. If the neighbor interface is behind a NAT on the same OMNI 1853 link segment, the Client instead forwards the initial carrier packets 1854 to the LHS Proxy/Server (while inserting an ORH-0 if necessary) and 1855 initiates NAT traversal procedures. If the Client's intended source 1856 underlying interface is also behind a NAT and located on the same 1857 OMNI link segment, it sends a "direct bubble" over the interface per 1858 [RFC6081][RFC4380] to the L2ADDR found in the neighbor cache in order 1859 to establish state in its own NAT by generating traffic toward the 1860 neighbor (note that no response to the bubble is expected). 1862 The Client next sends an NS(NUD) message toward the MNP-ULA of the 1863 neighbor via the LHS Proxy/Server as discussed in Section 3.15. If 1864 the Client receives an NA(NUD) from the neighbor over the underlying 1865 interface, it marks the neighbor interface as "trusted" and sends 1866 future carrier packets directly to the L2ADDR information for the 1867 neighbor instead of indirectly via the LHS Proxy/Server. The Client 1868 must honor the neighbor cache maintenance procedure by sending 1869 additional direct bubbles and/or NS/NA(NUD) messages as discussed in 1870 [RFC6081][RFC4380] in order to keep NAT state alive as long as 1871 carrier packets are still flowing. 1873 When a carrier packet enters a Client's OMNI interface from the link- 1874 layer, if the OAL destination matches one of the Client's ULAs the 1875 Client (acting as an OAL destination) verifies that the 1876 Identification is in-window for this OAL source, then reassembles and 1877 decapsulates as necessary and delivers the original IP packet to the 1878 network layer. Otherwise, the Client drops the original IP packet 1879 and MAY return a network-layer ICMP Destination Unreachable message 1880 subject to rate limiting (see: Section 3.11). 1882 Note: Clients and their FHS Proxy/Server (and other Client) peers can 1883 exchange original IP packets over ANET underlying interfaces without 1884 invoking the OAL, since the ANET is secured at the link and physical 1885 layers. By forwarding original IP packets without invoking the OAL, 1886 however, the ANET peers can engage only in classical path MTU 1887 discovery since the packets are subject to loss and/or corruption due 1888 to the various per-link MTU limitations that may occur within the 1889 ANET. Moreover, the original IP packets do not include either the 1890 OAL integrity check or per-packet Identification values that can be 1891 used for data origin authentication and link-layer retransmissions. 1892 The tradeoff therefore involves an assessment of the per-packet 1893 encapsulation overhead saved by bypassing the OAL vs. inheritance of 1894 classical network "brittleness". (Note however that ANET peers can 1895 send small original IP packets without invoking the OAL, while 1896 invoking the OAL for larger packets. This presents the beneficial 1897 aspects of both small packet efficiency and large packet robustness.) 1899 3.10.2. Proxy/Server and Relay Forwarding Algorithm 1901 When the Proxy/Server receives an original IP packet from the network 1902 layer, it drops the packet if routing indicates that it should be 1903 forwarded back to the network layer to avoid looping. Otherwise, the 1904 Proxy/Server regards the original IP packet the same as if it had 1905 arrived as carrier packets with OAL destination set to its own ADM- 1906 ULA. When the Proxy/Server receives carrier packets on underlying 1907 interfaces with OAL destination set to its own ADM-ULA, it performs 1908 OAL reassembly if necessary to obtain the original IP packet. 1910 The Proxy/Server next searches for a NCE that matches the original IP 1911 destination and proceeds as follows: 1913 o if the original IP packet destination matches a NCE, the Proxy/ 1914 Sever uses one or more "reachable" neighbor interfaces in the 1915 entry for packet forwarding using OAL encapsulation and 1916 fragmentation according to the cached link-layer address 1917 information. If the neighbor interface is in a different OMNI 1918 link segment, the Proxy/Server performs OAL encapsulation and 1919 fragmentation, inserts an ORH and forwards the resulting carrier 1920 packets via the spanning tree to a Bridge; otherwise, it forwards 1921 the carrier packets directly to the neighbor. If the neighbor is 1922 behind a NAT, the Proxy/Server instead forwards initial carrier 1923 packets via a Bridge while sending an NS(NUD) to the neighbor. 1924 When the Proxy/Server receives the NA(NUD), it can begin 1925 forwarding carrier packets directly to the neighbor the same as 1926 discussed in Section 3.10.1 while sending additional NS(NUD) 1927 messages as necessary to maintain NAT state. Note that no direct 1928 bubbles are necessary since the Proxy/Server is by definition not 1929 located behind a NAT. 1931 o else, if the original IP destination matches a non-MNP route in 1932 the IP forwarding table or an ADM-LLA assigned to the Proxy/ 1933 Server's OMNI interface, the Proxy/Server acting as a Relay 1934 presents the original IP packet to the network layer for local 1935 delivery or IP forwarding. 1937 o else, the Proxy/Server initiates address resolution as discussed 1938 in Section 3.14, while retaining initial original IP packets in a 1939 small queue awaiting address resolution completion. 1941 When the Proxy/Server receives a carrier packet with OAL destination 1942 set to an MNP-ULA that does not match the MSP, it accepts the carrier 1943 packet only if data origin authentication succeeds and if there is a 1944 network layer routing table entry for a GUA route that matches the 1945 MNP-ULA. If there is no route, the Proxy/Server drops the carrier 1946 packet; otherwise, it reassembles and decapsulates to obtain the 1947 original IP packet and acts as a Relay to present it to the network 1948 layer where it will be delivered according to standard IP forwarding. 1950 When a Proxy/Server receives a carrier packet from one of its Client 1951 neighbors with OAL destination set to another node, it forwards the 1952 packets via a matching NCE or via the spanning tree if there is no 1953 matching entry. When the Proxy/Server receives a carrier packet with 1954 OAL destination set to the MNP-ULA of one of its Client neighbors 1955 established through RS/RA exchanges, it accepts the carrier packet 1956 only if data origin authentication succeeds. If the NCE state is 1957 DEPARTED, the Proxy/Server inserts an ORH that encodes the MNP-ULA 1958 destination suffix and changes the OAL destination address to the 1959 ADM-ULA of the new Proxy/Server, then re-encapsulates the carrier 1960 packet and forwards it to a Bridge which will eventually deliver it 1961 to the new Proxy/Server. 1963 If the neighbor cache state for the MNP-ULA is REACHABLE, the Proxy/ 1964 Server forwards the carrier packets to the Client which then must 1965 reassemble. (Note that the Proxy/Server does not reassemble carrier 1966 packets not explicitly addressed to its own ADM-ULA, since routing 1967 could direct some of the carrier packet of the same original IP 1968 packet through a different Proxy/Server.) In that case, the Client 1969 may receive fragments that are smaller than its link MTU but can 1970 still be reassembled. 1972 Note: Proxy/Servers may receive carrier packets with ORHs that 1973 include additional forwarding information. Proxy/Servers use the 1974 forwarding information to determine the correct interface for 1975 forwarding to the target destination Client, then remove the ORH and 1976 forward the carrier packet. If the ORH information instead indicates 1977 that the Proxy/Server is responsible for reassembly, the Proxy/Server 1978 reassembles first before re-encapsulating (and possibly also re- 1979 fragmenting) then forwards to the target Client. For a full 1980 discussion of cases when the Proxy/Server may receive carrier packets 1981 with ORHs, see: Section 3.14.6. 1983 Note: Clients and their FHS Proxy/Server peers can exchange original 1984 IP packets over ANET underlying interfaces without invoking the OAL, 1985 since the ANET is secured at the link and physical layers. By 1986 forwarding original IP packets without invoking the OAL, however, the 1987 Client and Proxy/Server can engage only in classical path MTU 1988 discovery since the packets are subject to loss and/or corruption due 1989 to the various per-link MTU limitations that may occur within the 1990 ANET. Moreover, the original IP packets do not include either the 1991 OAL integrity check or per-packet Identification values that can be 1992 used for data origin authentication and link-layer retransmissions. 1993 The tradeoff therefore involves an assessment of the per-packet 1994 encapsulation overhead saved by bypassing the OAL vs. inheritance of 1995 classical network "brittleness". (Note however that ANET peers can 1996 send small original IP packets without invoking the OAL, while 1997 invoking the OAL for larger packets. This presents the beneficial 1998 aspects of both small packet efficiency and large packet robustness.) 2000 Note: When a Proxy/Server receives a (non-OAL) original IP packet 2001 from an ANET Client, or a carrier packet with OAL destination set to 2002 its own ADM-ULA from any Client, the Proxy/Server reassembles if 2003 necessary then performs ROS functions on behalf of the Client. The 2004 Client may at some later time begin sending carrier packets to the 2005 OAL address of the actual target instead of the Proxy/Server, at 2006 which point it may begin functioning as an ROS on its own behalf and 2007 thereby "override" the Proxy/Server's ROS role. 2009 Note; Proxy/Servers drop any original IP packets (received either 2010 directly from an ANET Client or following ANET/INET Client carrier 2011 packet reassembly) with a destination that corresponds to the 2012 Client's delegated MNP. Similiarly, Proxy/Servers drop any carrier 2013 packet received with both a source and destination that correspond to 2014 the Client's delegated MNP. These checks are necessary to prevent 2015 Clients from either accidentally or intentionally establishing an 2016 endless loop that could congest Proxy/Servers and/or ANET/INET links. 2018 Note: Proxy/Servers forward secure control plane carrier packets via 2019 the SRT secured spanning tree and forwards other carrier packets via 2020 the unsecured spanning tree. When a Proxy/Server receives a carrier 2021 packet from the secured spanning tree, it considers the message as 2022 authentic without having to verify upper layer authentication 2023 signatures. When a Proxy/Server receives a carrier packet from the 2024 unsecured spanning tree, it verifies any upper layer authentication 2025 signatures and/or forwards the unsecured message toward the 2026 destination which must apply data origin authentication. 2028 Note: If the Proxy/Server has multiple original IP packets to send to 2029 the same neighbor, it can concatenate them in a single OAL super- 2030 packet [I-D.templin-6man-omni]. 2032 3.10.3. Bridge Forwarding Algorithm 2034 Bridges forward carrier packets while decrementing the OAL header Hop 2035 Count but not the original IP header Hop Count/TTL. Bridges convey 2036 carrier packets that encapsulate IPv6 ND control messages or routing 2037 protocol control messages via the secured spanning tree, and may 2038 convey carrier packets that encapsulate ordinary data via the 2039 unsecured spanning tree. When the Bridge receives a carrier packet, 2040 it removes the outer *NET header and searches for a forwarding table 2041 entry that matches the OAL destination address. The Bridge then 2042 processes the packet as follows: 2044 o if the carrier packet destination matches its ADM-ULA or the 2045 corresponding ADM-ULA Subnet Router Anycast address and the OAL 2046 header is followed by an ORH, the Bridge reassembles if necessary 2047 then sets aside the ORH and processes the carrier packet locally 2048 before forwarding. If the OAL packet contains an NA(NUD) message, 2049 the Bridge replaces the OMNI option Interface Attributes sub- 2050 option with information for its own interface while retaining the 2051 omIndex value supplied by the NA(NUD) message source. The Bridge 2052 next examines the ORH, and if FMT-Mode indicates the destination 2053 is a Client on the open *NET (or, a Client behind a NAT for which 2054 NAT traversal procedures have already converged) the Bridge writes 2055 the MNP-ULA formed from the ORH Destination Suffix into the OAL 2056 destination. The Bridge then removes the ORH and forwards the 2057 packet using encapsulation based on L2ADDR. If the LHS Proxy/ 2058 Server will forward to the Client without reassembly, the Bridge 2059 writes the MNP-ULA into the OAL destination then replaces the ORH 2060 with an ORH-0 and forwards the carrier packet to the LHS Proxy/ 2061 Server while also invoking NAT traversal procedures if necessary 2062 (noting that no direct bubbles are necessary since only the target 2063 Client and not the Bridge is behind a NAT). If the LHS Proxy/ 2064 Server must perform reassembly before forwarding to the Client, 2065 the Bridge instead writes the ADM-ULA formed from the ORH SRT/LHS 2066 into the OAL destination address, replaces the ORH with an ORH-0 2067 and forwards the carrier packet to the LHS Proxy/Server. 2069 o else, if the carrier packet destination matches its ADM-ULA or the 2070 corresponding ADM-ULA Subnet Router Anycast address and the OAL 2071 header is not followed by an ORH with Segments Left set to 1, the 2072 Bridge submits the packet for reassembly. When reassembly is 2073 complete, the Bridge submits the original packet to the IP layer 2074 to support local applications such as BGP routing protocol 2075 sessions. 2077 o else, if the carrier packet destination matches a forwarding table 2078 entry the Bridge forwards the carrier packet to the next hop. (If 2079 the destination matches an MSP without matching an MNP, however, 2080 the Bridge instead drops the packet and returns an ICMP 2081 Destination Unreachable message subject to rate limiting - see: 2082 Section 3.11). 2084 o else, the Bridge drops the packet and returns an ICMP Destination 2085 Unreachable as above. 2087 The Bridge decrements the OAL IPv6 header Hop Limit when it forwards 2088 the carrier packet (i.e., the same as for any IPv6 router) and drops 2089 the packet if the Hop Limit reaches 0. Therefore, only the Hop Limit 2090 in the OAL header is decremented and not the TTL/Hop Limit in the 2091 original IP packet header. Bridges do not insert OAL/ORH headers 2092 themselves; instead, they act as IPv6 routers and forward carrier 2093 packets based on their destination addresses while also possibly 2094 transforming larger ORHs into an ORH-0 (or removing the ORH 2095 altogether). 2097 Bridges forward carrier packets received from a first segment via the 2098 SRT secured spanning tree to the next segment also via the secured 2099 spanning tree. Bridges forward carrier packets received from a first 2100 segment via the unsecured spanning tree to the next segment also via 2101 the unsecured spanning tree. Bridges use a single IPv6 routing table 2102 that always determines the same next hop for a given OAL destination, 2103 where the secured/unsecured spanning tree is determined through the 2104 selection of the underlying interface to be used for transmission 2105 (i.e., a secured tunnel or an open INET interface). 2107 3.11. OMNI Interface Error Handling 2109 When an AERO node admits an original IP packet into the OMNI 2110 interface, it may receive link-layer or network-layer error 2111 indications. The AERO node may also receive OMNI link error 2112 indications in OAL-encapsulated uNA messages that include 2113 authentication signatures. 2115 A link-layer error indication is an ICMP error message generated by a 2116 router in the INET on the path to the neighbor or by the neighbor 2117 itself. The message includes an IP header with the address of the 2118 node that generated the error as the source address and with the 2119 link-layer address of the AERO node as the destination address. 2121 The IP header is followed by an ICMP header that includes an error 2122 Type, Code and Checksum. Valid type values include "Destination 2123 Unreachable", "Time Exceeded" and "Parameter Problem" 2124 [RFC0792][RFC4443]. (OMNI interfaces ignore link-layer IPv4 2125 "Fragmentation Needed" and IPv6 "Packet Too Big" messages for carrier 2126 packets that are no larger than the minimum/path MPS as discussed in 2127 Section 3.9, however these messages may provide useful hints of probe 2128 failures during path MPS probing.) 2130 The ICMP header is followed by the leading portion of the carrier 2131 packet that generated the error, also known as the "packet-in-error". 2132 For ICMPv6, [RFC4443] specifies that the packet-in-error includes: 2133 "As much of invoking packet as possible without the ICMPv6 packet 2134 exceeding the minimum IPv6 MTU" (i.e., no more than 1280 bytes). For 2135 ICMPv4, [RFC0792] specifies that the packet-in-error includes: 2136 "Internet Header + 64 bits of Original Data Datagram", however 2137 [RFC1812] Section 4.3.2.3 updates this specification by stating: "the 2138 ICMP datagram SHOULD contain as much of the original datagram as 2139 possible without the length of the ICMP datagram exceeding 576 2140 bytes". 2142 The link-layer error message format is shown in Figure 5 (where, "L2" 2143 and "L3" refer to link-layer and network-layer, respectively): 2145 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2146 ~ ~ 2147 | L2 IP Header of | 2148 | error message | 2149 ~ ~ 2150 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2151 | L2 ICMP Header | 2152 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 2153 ~ ~ P 2154 | carrier packet *NET and OAL | a 2155 | encapsulation headers | c 2156 ~ ~ k 2157 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ e 2158 ~ ~ t 2159 | original IP packet headers | 2160 | (first-fragment only) | i 2161 ~ ~ n 2162 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2163 ~ ~ e 2164 | Portion of the body of | r 2165 | the original IP packet | r 2166 | (all fragments) | o 2167 ~ ~ r 2168 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 2170 Figure 5: OMNI Interface Link-Layer Error Message Format 2172 The AERO node rules for processing these link-layer error messages 2173 are as follows: 2175 o When an AERO node receives a link-layer Parameter Problem message, 2176 it processes the message the same as described as for ordinary 2177 ICMP errors in the normative references [RFC0792][RFC4443]. 2179 o When an AERO node receives persistent link-layer Time Exceeded 2180 messages, the IP ID field may be wrapping before earlier fragments 2181 awaiting reassembly have been processed. In that case, the node 2182 should begin including integrity checks and/or institute rate 2183 limits for subsequent packets. 2185 o When an AERO node receives persistent link-layer Destination 2186 Unreachable messages in response to carrier packets that it sends 2187 to one of its neighbor correspondents, the node should process the 2188 message as an indication that a path may be failing, and 2189 optionally initiate NUD over that path. If it receives 2190 Destination Unreachable messages over multiple paths, the node 2191 should allow future carrier packets destined to the correspondent 2192 to flow through a default route and re-initiate route 2193 optimization. 2195 o When an AERO Client receives persistent link-layer Destination 2196 Unreachable messages in response to carrier packets that it sends 2197 to one of its neighbor Proxy/Servers, the Client should mark the 2198 path as unusable and use another path. If it receives Destination 2199 Unreachable messages on many or all paths, the Client should 2200 associate with a new Proxy/Server and release its association with 2201 the old Proxy/Server as specified in Section 3.16.5. 2203 o When an AERO Proxy/Server receives persistent link-layer 2204 Destination Unreachable messages in response to carrier packets 2205 that it sends to one of its neighbor Clients, the Proxy/Server 2206 should mark the underlying path as unusable and use another 2207 underlying path. 2209 o When an AERO Proxy/Server receives link-layer Destination 2210 Unreachable messages in response to a carrier packet that it sends 2211 to one of its permanent neighbors, it treats the messages as an 2212 indication that the path to the neighbor may be failing. However, 2213 the dynamic routing protocol should soon reconverge and correct 2214 the temporary outage. 2216 When an AERO Bridge receives a carrier packet for which the network- 2217 layer destination address is covered by an MSP, the Bridge drops the 2218 packet if there is no more-specific routing information for the 2219 destination and returns an OMNI interface Destination Unreachable 2220 message subject to rate limiting. 2222 When an AERO node receives a carrier packet for which reassembly is 2223 currently congested, it returns an OMNI interface Packet Too Big 2224 (PTB) message as discussed in [I-D.templin-6man-omni] (note that the 2225 PTB messages could indicate either "hard" or "soft" errors). 2227 AERO nodes include ICMPv6 error messages intended for the OAL source 2228 as sub-options in the OMNI option of secured uNA messages. When the 2229 OAL source receives the uNA message, it can extract the ICMPv6 error 2230 message enclosed in the OMNI option and either process it locally or 2231 translate it into a network-layer error to return to the original 2232 source. 2234 3.12. AERO Router Discovery, Prefix Delegation and Autoconfiguration 2236 AERO Router Discovery, Prefix Delegation and Autoconfiguration are 2237 coordinated as discussed in the following Sections. 2239 3.12.1. AERO Service Model 2241 Each AERO Proxy/Server on the OMNI link is configured to facilitate 2242 Client prefix delegation/registration requests. Each Proxy/Server is 2243 provisioned with a database of MNP-to-Client ID mappings for all 2244 Clients enrolled in the AERO service, as well as any information 2245 necessary to authenticate each Client. The Client database is 2246 maintained by a central administrative authority for the OMNI link 2247 and securely distributed to all Proxy/Servers, e.g., via the 2248 Lightweight Directory Access Protocol (LDAP) [RFC4511], via static 2249 configuration, etc. Clients receive the same service regardless of 2250 the Proxy/Servers they select. 2252 AERO Clients and Proxy/Servers use ND messages to maintain neighbor 2253 cache entries. AERO Proxy/Servers configure their OMNI interfaces as 2254 advertising NBMA interfaces, and therefore send unicast RA messages 2255 with a short Router Lifetime value (e.g., ReachableTime seconds) in 2256 response to a Client's RS message. Thereafter, Clients send 2257 additional RS messages to keep Proxy/Server state alive. 2259 AERO Clients and Proxy/Servers include prefix delegation and/or 2260 registration parameters in RS/RA messages (see 2261 [I-D.templin-6man-omni]). The ND messages are exchanged between 2262 Client and FHS Proxy/Servers according to the prefix management 2263 schedule required by the service. If the Client knows its MNP in 2264 advance, it can employ prefix registration by including its MNP-LLA 2265 as the source address of an RS message and with an OMNI option with 2266 valid prefix registration information for the MNP. If the Proxy/ 2267 Server accepts the Client's MNP assertion, it injects the MNP into 2268 the routing system and establishes the necessary neighbor cache 2269 state. If the Client does not have a pre-assigned MNP, it can 2270 instead employ prefix delegation by including the unspecified address 2271 (::) as the source address of an RS message and with an OMNI option 2272 with prefix delegation parameters to request an MNP. 2274 The following sections specify the Client and Proxy/Server behavior. 2276 3.12.2. AERO Client Behavior 2278 AERO Clients discover the addresses of candidate FHS Proxy/Servers in 2279 a similar manner as described in [RFC5214]. Discovery methods 2280 include static configuration (e.g., from a flat-file map of Proxy/ 2281 Server addresses and locations), or through an automated means such 2282 as Domain Name System (DNS) name resolution [RFC1035]. 2283 Alternatively, the Client can discover Proxy/Server addresses through 2284 a layer 2 data link login exchange, or through a unicast RA response 2285 to a multicast/anycast RS as described below. In the absence of 2286 other information, the Client can resolve the DNS Fully-Qualified 2287 Domain Name (FQDN) "linkupnetworks.[domainname]" where 2288 "linkupnetworks" is a constant text string and "[domainname]" is a 2289 DNS suffix for the OMNI link (e.g., "example.com"). 2291 To associate with a FHS Proxy/Server over an underlying interface, 2292 the Client acts as a requesting router to request MNPs by preparing 2293 an RS message with prefix management parameters. If the Client 2294 already knows the Proxy/Server's ADM-LLA, it includes the LLA as the 2295 network-layer destination address; otherwise, the Client includes the 2296 (link-local) All-Routers multicast as the network-layer destination. 2297 If the Client already knows its own MNP-LLA, it can use the MNP-LLA 2298 as the network-layer source address and include an OMNI option with 2299 prefix registration information. Otherwise, the Client uses the 2300 unspecified address (::) as the network-layer source address and 2301 includes prefix delegation parameters in the OMNI option (see: 2302 [I-D.templin-6man-omni]). 2304 The Client next includes Interface Attributes corresponding to the 2305 underlying interface over which it will send the RS message, and MAY 2306 include additional Interface Attributes specific to other underlying 2307 interfaces. Next, the Client submits the RS for OAL encapsulation 2308 and fragmentation if necessary with its own MNP-ULA and the Proxy/ 2309 Server's ADM-ULA or (site-scoped) All-Routers multicast as the OAL 2310 addresses while selecting an Identification value and invoking window 2311 synchronization as specified in [I-D.templin-6man-omni]. 2313 The Client then sends the RS (either directly via Direct interfaces, 2314 via a VPN for VPNed interfaces, via an access router for ANET 2315 interfaces or via INET encapsulation for INET interfaces) then waits 2316 up to RetransTimer milliseconds for an RA message reply (see 2317 Section 3.12.3) (retrying up to MAX_RTR_SOLICITATIONS). If the 2318 Client receives no RAs, or if it receives an RA with Router Lifetime 2319 set to 0, the Client SHOULD abandon attempts through the first 2320 candidate FHS Proxy/Server and try another Proxy/Server. Otherwise, 2321 the Client processes the prefix information found in the RA message. 2323 When the Client processes an RA, it first performs OAL reassembly and 2324 decapsulation if necessary then creates a NCE with the Proxy/Server's 2325 ADM-LLA as the network-layer address and the Proxy/Server's 2326 encapsulation and/or link-layer addresses as the link-layer address. 2327 The Client next records the RA Router Lifetime field value in the NCE 2328 as the time for which the Proxy/Server has committed to maintaining 2329 the MNP in the routing system via this underlying interface, and 2330 caches the other RA configuration information including Cur Hop 2331 Limit, M and O flags, Reachable Time and Retrans Timer. The Client 2332 then autoconfigures MNP-LLAs for any delegated MNPs and assigns them 2333 to the OMNI interface. The Client also caches any MSPs included in 2334 Route Information Options (RIOs) [RFC4191] as MSPs to associate with 2335 the OMNI link, and assigns the MTU value in the MTU option to the 2336 underlying interface. 2338 The Client then registers its additional underlying interfaces with 2339 FHS Proxy/Servers for those interfaces discovered by sending RS 2340 messages via each additional interface as described above. The RS 2341 messages include the same parameters as for the initial RS/RA 2342 exchange, but with destination address set to the Proxy/Server's ADM- 2343 LLA. The Client finally sub-delegates the MNPs to its attached EUNs 2344 and/or the Client's own internal virtual interfaces as described in 2345 [I-D.templin-v6ops-pdhost] to support the Client's downstream 2346 attached "Internet of Things (IoT)". The Client then sends 2347 additional RS messages over each underlying interface before the 2348 Router Lifetime received for that interface expires. 2350 After the Client registers its underlying interfaces, it may wish to 2351 change one or more registrations, e.g., if an interface changes 2352 address or becomes unavailable, if traffic selectors change, etc. To 2353 do so, the Client prepares an RS message to send over any available 2354 underlying interface as above. The RS includes an OMNI option with 2355 prefix registration/delegation information, with Interface Attributes 2356 specific to the selected underlying interface, and with any 2357 additional Interface Attributes specific to other underlying 2358 interfaces. When the Client receives the Proxy/Server's RA response, 2359 it has assurance that the Proxy/Server has been updated with the new 2360 information. 2362 If the Client wishes to discontinue use of a Proxy/Server it issues 2363 an RS message over any underlying interface with an OMNI option with 2364 a prefix release indication. When the Proxy/Server processes the 2365 message, it releases the MNP, sets the NCE state for the Client to 2366 DEPARTED and returns an RA reply with Router Lifetime set to 0. 2367 After a short delay (e.g., 2 seconds), the Proxy/Server withdraws the 2368 MNP from the routing system. 2370 3.12.3. AERO Proxy/Server Behavior 2372 AERO Proxy/Servers act as both IP routers and ND proxies, and support 2373 a prefix delegation/registration service for Clients. Proxy/Servers 2374 arrange to add their ADM-LLAs to a static map of Proxy/Server 2375 addresses for the link and/or the DNS resource records for the FQDN 2376 "linkupnetworks.[domainname]" before entering service. Proxy/Server 2377 addresses should be geographically and/or topologically referenced, 2378 and made available for discovery by Clients on the OMNI link. 2380 When an FHS Proxy/Server receives a prospective Client's RS message 2381 on its OMNI interface, it SHOULD return an immediate RA reply with 2382 Router Lifetime set to 0 if it is currently too busy or otherwise 2383 unable to service the Client. Otherwise, the Proxy/Server performs 2384 OAL reassembly and decapsulation if necessary, then authenticates the 2385 RS message and processes the prefix delegation/registration 2386 parameters. The Proxy/Server first determines the correct MNPs to 2387 provide to the Client by processing the MNP-LLA prefix parameters 2388 and/or the DHCPv6 OMNI sub-option. When the Proxy/Server returns the 2389 MNPs, it also creates a forwarding table entry for the MNP-ULA 2390 corresponding to each MNP so that the MNPs are propagated into the 2391 routing system (see: Section 3.2.3). For IPv6, the Proxy/Server 2392 creates an IPv6 forwarding table entry for each MNP. For IPv4, the 2393 Proxy/Server creates an IPv6 forwarding table entry with the 2394 IPv4-compatibility MNP-ULA prefix corresponding to the IPv4 address. 2396 The Proxy/Server next creates a NCE for the Client using the base 2397 MNP-LLA as the network-layer address. Next, the Proxy/Server updates 2398 the NCE by recording the information in each Interface Attributes 2399 sub-option in the RS OMNI option. The Proxy/Server also records the 2400 actual OAL/*NET addresses and RS message window synchronization 2401 parameters (if any) in the NCE. 2403 Next, the Proxy/Server prepares an RA message using its ADM-LLA as 2404 the network-layer source address and the network-layer source address 2405 of the RS message as the network-layer destination address. The 2406 Proxy/Server sets the Router Lifetime to the time for which it will 2407 maintain both this underlying interface individually and the NCE as a 2408 whole. The Proxy/Server also sets Cur Hop Limit, M and O flags, 2409 Reachable Time and Retrans Timer to values appropriate for the OMNI 2410 link. The Proxy/Server includes the MNPs, any other prefix 2411 management parameters and an OMNI option with no Interface Attributes 2412 but with an Origin Indication sub-option per [I-D.templin-6man-omni] 2413 with the mapped and obfuscated Port Number and IP address 2414 corresponding to the Client's own INET address in the case of INET 2415 Clients or to the Proxy/Server's INET-facing address for all other 2416 Clients. The Proxy/Server should also include an Interface 2417 Attributes sub-option in the OMNI option with FMT/SRT/LHS information 2418 for its INET interface. The Proxy/Server then includes one or more 2419 RIOs that encode the MSPs for the OMNI link, plus an MTU option (see 2420 Section 3.9). The Proxy/Server finally forwards the message to the 2421 Client using OAL encapsulation/fragmentation if necessary while 2422 including an acknowledgement if the RS invoked window 2423 synchronization. 2425 After the initial RS/RA exchange, the Proxy/Server maintains a 2426 ReachableTime timer for each of the Client's underlying interfaces 2427 individually (and for the Client's NCE collectively) set to expire 2428 after ReachableTime seconds. If the Client (or Proxy) issues 2429 additional RS messages, the Proxy/Server sends an RA response and 2430 resets ReachableTime. If the Proxy/Server receives an ND message 2431 with a prefix release indication it sets the Client's NCE to the 2432 DEPARTED state and withdraws the MNP from the routing system after a 2433 short delay (e.g., 2 seconds). If ReachableTime expires before a new 2434 RS is received on an individual underlying interface, the Proxy/ 2435 Server marks the interface as DOWN. If ReachableTime expires before 2436 any new RS is received on any individual underlying interface, the 2437 Proxy/Server sets the NCE state to STALE and sets a 10 second timer. 2438 If the Proxy/Server has not received a new RS or ND message with a 2439 prefix release indication before the 10 second timer expires, it 2440 deletes the NCE and withdraws the MNP from the routing system. 2442 The Proxy/Server processes any ND messages pertaining to the Client 2443 and returns an NA/RA reply in response to solicitations. The Proxy/ 2444 Server may also issue unsolicited RA messages, e.g., with reconfigure 2445 parameters to cause the Client to renegotiate its prefix delegation/ 2446 registrations, with Router Lifetime set to 0 if it can no longer 2447 service this Client, etc. Finally, If the NCE is in the DEPARTED 2448 state, the Proxy/Server deletes the entry after DepartTime expires. 2450 Note: Clients SHOULD notify former Proxy/Servers of their departures, 2451 but Proxy/Servers are responsible for expiring neighbor cache entries 2452 and withdrawing routes even if no departure notification is received 2453 (e.g., if the Client leaves the network unexpectedly). Proxy/Servers 2454 SHOULD therefore set Router Lifetime to ReachableTime seconds in 2455 solicited RA messages to minimize persistent stale cache information 2456 in the absence of Client departure notifications. A short Router 2457 Lifetime also ensures that proactive RS/RA messaging between Clients 2458 and Proxy/Servers will keep any NAT state alive (see above). 2460 Note: All Proxy/Servers on an OMNI link MUST advertise consistent 2461 values in the RA Cur Hop Limit, M and O flags, Reachable Time and 2462 Retrans Timer fields the same as for any link, since unpredictable 2463 behavior could result if different Proxy/Servers on the same link 2464 advertised different values. 2466 3.12.3.1. DHCPv6-Based Prefix Registration 2468 When a Client is not pre-provisioned with an MNP-LLA, it will need 2469 for the FHS Proxy/Server to select one or more MNPs on its behalf and 2470 set up the correct state in the AERO routing service. (A Client with 2471 a pre-provisioned MNP may also request the Proxy/Server to select 2472 additional MNPs.) The DHCPv6 service [RFC8415] is used to support 2473 this requirement. 2475 When a Client needs to have the FHS Proxy/Server select MNPs, it 2476 sends an RS message with source address set to the unspecified 2477 address (::) and with an OMNI option that includes a DHCPv6 message 2478 sub-option with DHCPv6 Prefix Delegation (DHCPv6-PD) parameters. 2480 When the Proxy/Server receives the RS message, it extracts the 2481 DHCPv6-PD message from the OMNI option. 2483 The Proxy/Server then acts as a "Proxy DHCPv6 Client" in a message 2484 exchange with the locally-resident DHCPv6 server, which delegates 2485 MNPs and returns a DHCPv6-PD Reply message. (If the Proxy/Server 2486 wishes to defer creation of MN state until the DHCPv6-PD Reply is 2487 received, it can instead act as a Lightweight DHCPv6 Relay Agent per 2488 [RFC6221] by encapsulating the DHCPv6-PD message in a Relay-forward/ 2489 reply exchange with Relay Message and Interface ID options.) 2491 When the Proxy/Server receives the DHCPv6-PD Reply, it adds a route 2492 to the routing system and creates an MNP-LLA based on the delegated 2493 MNP. The Proxy/Server then sends an RA back to the Client with the 2494 (newly-created) MNP-LLA as the destination address and with the 2495 DHCPv6-PD Reply message coded in the OMNI option. When the Client 2496 receives the RA, it creates a default route, assigns the Subnet 2497 Router Anycast address and sets its MNP-LLA based on the delegated 2498 MNP. 2500 Note: See [I-D.templin-6man-omni] for an MNP delegation alternative 2501 that avoids including a DHCPv6 message sub-option in the RS. Namely, 2502 when the Client requests a single MNP it can set the RS source to the 2503 unspecified address (::) and include a Node Identification sub-option 2504 and Preflen in the OMNI option (but with no DHCPv6 message sub- 2505 option). When the Proxy/Server receives the RS message, it forwards 2506 a self-generated DHCPv6 Solicit message to the DHCPv6 server on 2507 behalf of the Client. When the Proxy/Server receives the DHCPv6 2508 Reply, it prepares an RA message with an OMNI option with Preflen 2509 information (but with no DHCPv6 message sub-option), then places the 2510 (newly-created) MNP-LLA in the RA destination address and returns the 2511 message to the Client. 2513 3.13. The AERO Proxy Function 2515 Clients connect to the OMNI link via FHS Proxy/Servers, with one or 2516 more FHS Proxy/Servers for each underlying interface. Each of the 2517 Client's FHS Proxy/Servers must be informed of all of the Client's 2518 additional underlying interfaces. For Clients on Direct and VPNed 2519 underlying interfaces the Proxy/Server "A" for that interface is 2520 directly connected, for Clients on ANET underlying interfaces Proxy/ 2521 Server "A" is located on the ANET/INET boundary, and for Clients on 2522 INET underlying interfaces Proxy/Server "A" is located somewhere in 2523 the connected Internetwork. When the Client registers with Proxy/ 2524 Server "A", it must also report the registration to any other Proxy/ 2525 Servers for other underlying interfaces "B", "C", "D", etc. for which 2526 an underlying interface relationship has already been established. 2527 The Proxy/Server satisfies these requirements as follows: 2529 o when FHS Proxy/Server "A" receives a Client RS message, it first 2530 verifies that the OAL Identification is within the window for the 2531 NCE that matches the MNP-ULA for this Client neighbor and 2532 authenticates the message. (If no NCE was found, Proxy/Server "A 2533 instead creates one in the STALE state and returns an RA message 2534 with an authentication signature and any window synchronization 2535 parameters.) Proxy/Server "A" then examines the network-layer 2536 destination address. If the destination address is the ADM-LLA of 2537 a different Proxy/Server "B" (or, if the OMNI option included an 2538 MS-Register sub-option with the ADM-LLAs of one or more different 2539 "LHS" Proxy/Servers "B", "C", "D", etc.), Proxy/Server "A" 2540 prepares a separate proxyed version of the RS message with an OAL 2541 header with source set to its own ADM-ULA and destination set to 2542 the LHS Proxy/Server's ADM-ULA. Proxy/Server "A" also includes an 2543 OMNI header with an Interface Attributes option that includes its 2544 own INET address, a unique UDP Port Number for this Client, and 2545 FMT/SRT/LHS information. Proxy/Server "A" then sets the S/ 2546 T-omIndex to the value for this Client underlying interface, then 2547 forwards the message into the OMNI link secured spanning tree. 2548 (Note: including a unique Port Number allows LHS Proxy/Server "B" 2549 to distinguish different Clients located behind the same FHS 2550 Proxy/Server "A" at the link-layer, whereas the link-layer 2551 addresses would otherwise be indistinguishable.) 2553 o when LHS Proxy/Server "B" receives the RS, it authenticates the 2554 message then creates or updates a NCE for the Client with FHS 2555 Proxy/Server "A"'s Interface Attributes as the link-layer address 2556 information for this S/T-omIndex and caches any window 2557 synchronization parameters supplied by the Client. LHS Proxy/ 2558 Server "B" then prepares an RA message with source set to its own 2559 LLA and destination set to the Client's MNP-LLA, and with any 2560 window synchronization acknowledgements (i.e., only if the RS 2561 destination was its own ADM-LLA). Proxy/Server "B" then 2562 encapsulates the RA in an OAL header with source set to its own 2563 ADM-ULA and destination set to the ADM-ULA of Proxy/Server "A, 2564 performs fragmentation if necessary, then sends the resulting 2565 carrier packets into the secured spanning tree. 2567 o when Proxy/Server "A" reassembles the RA, it locates the Client 2568 NCE based on the RA destination LLA. Proxy/Server "A" then re- 2569 encapsulates the RA message with OAL source set to its own ADM-ULA 2570 and OAL destination set to the MNP-ULA of the Client, includes an 2571 authentication signature if necessary, fragments if necessary and 2572 returns the fragments to the Client. 2574 o The Client repeats this process over each of its additional 2575 underlying interfaces while treating each Proxy/Server "B", "C", 2576 "D" as an FHS while providing MS-Register information for other 2577 Proxy/Servers as an LHS. 2579 After the initial RS/RA exchanges each Proxy/Server forwards any of 2580 the Client's carrier packets with OAL destinations for which there is 2581 no matching NCE to a Bridge using OAL encapsulation with its own ADM- 2582 ULA as the source and the destination determined by the ORH supplied 2583 by the Client. The Proxy/Server instead forwards any carrier packets 2584 destined to a neighbor cache target directly to the target according 2585 to the OAL/link-layer information - the process of establishing 2586 neighbor cache entries is specified in Section 3.14. 2588 While the Client is still associated with each Proxy/Server "A", "A" 2589 can send NS, RS and/or unsolicited NA messages to update the neighbor 2590 cache entries of other AERO nodes on behalf of the Client and/or to 2591 convey Interface Attribute updates. This allows for higher-frequency 2592 Proxy-initiated RS/RA messaging over well-connected INET 2593 infrastructure supplemented by lower-frequency Client-initiated RS/RA 2594 messaging over constrained ANET data links. 2596 If any Proxy/Server "B", "C", "D" ceases to send solicited 2597 advertisements, Proxy/Server "A" sends unsolicited RAs to the Client 2598 with destination set to (link-local) All-Nodes multicast and with 2599 Router Lifetime set to zero to inform Clients that a Proxy/Server has 2600 failed. Although Proxy/Server "A" can engage in ND exchanges on 2601 behalf of the Client, the Client can also send ND messages on its own 2602 behalf, e.g., if it is in a better position than "A" to convey 2603 Interface Attribute changes, etc. The ND messages sent by the Client 2604 include the Client's MNP-LLA as the source in order to differentiate 2605 them from the ND messages sent by Proxy/Server "A". 2607 If the Client becomes unreachable over an underlying interface, 2608 Proxy/Server "A" sets the NCE state to DEPARTED and retains the entry 2609 for DepartTime seconds. While the state is DEPARTED, Proxy/Server 2610 "A" forwards any carrier packets destined to the Client to a Bridge 2611 via OAL/ORH encapsulation. When DepartTime expires, Proxy/Server "A" 2612 deletes the NCE and discards any further carrier packets destined to 2613 the former Client. 2615 In some ANETs that employ a Proxy/Server, the Client's MNP can be 2616 injected into the ANET routing system. In that case, the Client can 2617 send original IP packets without invoking the OAL so that the ANET 2618 routing system transports the original IP packets to the Proxy. This 2619 can be very beneficial, e.g., if the Client connects to the ANET via 2620 low-end data links such as some aviation wireless links. 2622 If the ANET first-hop access router is on the same underlying link as 2623 the Client and recognizes the AERO/OMNI protocol, the Client can 2624 avoid OAL encapsulation for both its control and data messages. When 2625 the Client connects to the link, it can send an unencapsulated RS 2626 message with source address set to its own MNP-LLA (or to a Temporary 2627 LLA), and with destination address set to the ADM-LLA of the Client's 2628 selected Proxy/Server or to (link-local) All-Routers multicast. The 2629 Client includes an OMNI option formatted as specified in 2630 [I-D.templin-6man-omni]. The Client then sends the unencapsulated RS 2631 message, which will be intercepted by the AERO-Aware access router. 2633 The ANET access router then performs OAL encapsulation on the RS 2634 message and forwards it to a Proxy/Server at the ANET/INET boundary. 2635 When the access router and Proxy/Server are one and the same node, 2636 the Proxy/Server would share and underlying link with the Client but 2637 its message exchanges with outside correspondents would need to pass 2638 through a security gateway at the ANET/INET border. The method for 2639 deploying access routers and Proxys (i.e. as a single node or 2640 multiple nodes) is an ANET-local administrative consideration. 2642 Note: The Proxy/Server can apply packing as discussed in 2643 [I-D.templin-6man-omni] if an opportunity arises to concatenate 2644 multiple original IP packets destined to the same neighbor. 2646 3.13.1. Detecting and Responding to Proxy/Server Failures 2648 In environments where fast recovery from Proxy/Server failure is 2649 required, Proxy/Server "A" SHOULD use proactive Neighbor 2650 Unreachability Detection (NUD) to track each peer Proxy/Server "B" 2651 reachability in a similar fashion as for Bidirectional Forwarding 2652 Detection (BFD) [RFC5880]. Proxy/Server "A" can then quickly detect 2653 and react to failures so that cached information is re-established 2654 through alternate paths. The NUD control messaging is carried only 2655 over well-connected ground domain networks (i.e., and not low-end 2656 aeronautical radio links) and can therefore be tuned for rapid 2657 response. 2659 Proxy/Server "A" performs proactive NUD with peer Proxy/Server "B" 2660 for which there are currently active Clients by sending continuous NS 2661 messages in rapid succession, e.g., one message per second. Proxy/ 2662 Server "A" sends the NS message via the spanning tree with its own 2663 ADM-LLA as the source and the ADM-LLA of the peer Proxy/Server "B" as 2664 the destination. When Proxy/Server "A" is also sending RS messages 2665 to the peer Proxy/Server "B" on behalf of ANET Clients, the resulting 2666 RA responses can be considered as equivalent hints of forward 2667 progress. This means that Proxy/Server "B" need not also send a 2668 periodic NS if it has already sent an RS within the same period. If 2669 the peer Proxy/Server "B" fails (i.e., if "A" ceases to receive 2670 advertisements), Proxy/Server "A" can quickly inform Clients by 2671 sending multicast RA messages on the ANET interface. 2673 Proxy/Server "A" sends RA messages on the ANET interface with source 2674 address set to Proxy/Server "B"'s address, destination address set to 2675 (link-local) All-Nodes multicast, and Router Lifetime set to 0. 2676 Proxy/Server "A" SHOULD send MAX_FINAL_RTR_ADVERTISEMENTS RA messages 2677 separated by small delays [RFC4861]. Any Clients on the ANET that 2678 had been using the failed Proxy/Server "B" will receive the RA 2679 messages and associate with a new Proxy/Server. 2681 3.13.2. Point-to-Multipoint Proxy/Server Coordination 2683 In environments where Client messaging over ANETs is bandwidth- 2684 limited and/or expensive, Clients can enlist the services of Proxy/ 2685 Server "A" to coordinate with multiple Proxy/Servers "B", "C", "D" 2686 etc. in a single RS/RA message exchange. The Client can send a 2687 single RS message to (link-local) All-Routers multicast that includes 2688 the ID's of multiple Proxy/Servers in MS-Register sub-options of the 2689 OMNI option. 2691 When Proxy/Server "A" receives the RS and processes the OMNI option, 2692 it sends a separate RS to each MS-Register Proxy/Server ID. When 2693 Proxy/Server "A" receives an RA, it can optionally return an 2694 immediate "singleton" RA to the Client or record the Proxy/Server's 2695 ID for inclusion in a pending "aggregate" RA message. Proxy/Server 2696 "A" can then return aggregate RA messages to the Client including 2697 multiple Proxy/Server IDs in order to conserve bandwidth. Each RA 2698 includes a proper subset of the Proxy/Server IDs from the original RS 2699 message, and Proxy/Server "A" must ensure that the message contents 2700 of each RA are consistent with the information received from the 2701 (aggregated) additional Proxy/Servers. 2703 Clients can thereafter employ efficient point-to-multipoint Proxy/ 2704 Server coordination under the assistance of Proxy/Server "A" to 2705 reduce the number of messages sent over the ANET while enlisting the 2706 support of multiple Proxy/Servers for fault tolerance. Clients can 2707 further include MS-Release sub-options in IPv6 ND messages to request 2708 Proxy/Server "A" to release from former Proxy/Servers via the 2709 procedures discussed in Section 3.16.5. 2711 When the Client sends an RS with window synchronization parameters 2712 and with multiple MS-Register Proxy/Server IDs, Proxy/Server "A" may 2713 receive multiple RAs - each with their own window synchronization 2714 parameters. Proxy/Server "A" must then immediately forward these RAs 2715 to the Client as singletons instead of including them in an 2716 aggregate, and the Client will use each RA to establish a separate 2717 NCE and window for each individual Proxy/Server. 2719 The OMNI interface specification [I-D.templin-6man-omni] provides 2720 further discussion of the RS/RA messaging involved in point-to- 2721 multipoint coordination. 2723 3.14. AERO Route Optimization 2725 AERO nodes invoke route optimization when they need to forward 2726 packets to new target destinations. Route optimization is based on 2727 IPv6 ND Address Resolution messaging between a Route Optimization 2728 Source (ROS) and Route Optimization Responder (ROR). Route 2729 optimization is initiated by the first eligible ROS closest to the 2730 source as follows: 2732 o For Clients on VPNed and Direct interfaces, the Client's FHS 2733 Proxy/Server is the ROS. 2735 o For Clients on ANET interfaces, either the Client or the FHS 2736 Proxy/Server may be the ROS. 2738 o For Clients on INET interfaces, the Client itself is the ROS. 2740 o For correspondent nodes on INET/EUN interfaces serviced by a 2741 Relay, the Relay is the ROS. 2743 The route optimization procedure is conducted between the ROS and an 2744 LHS Proxy/Server/Relay for the target selected by routing as the ROR. 2745 In this arrangement, the ROS is always the Client or Proxy/Server/ 2746 Relay nearest the source over the selected source underlying 2747 interface, while the ROR is always an LHS Proxy/Server/Relay for the 2748 target regardless of the target underlying interface. 2750 The AERO routing system directs a route optimization solicitation 2751 sent by the ROS to the nearest available ROR, which returns a route 2752 optimization reply. The exact ROR selected is unimportant; all that 2753 matters is that the route optimization information returned must be 2754 current and authentic. The ROS is responsible for periodically 2755 refreshing the route optimization, and the ROR is responsible for 2756 quickly informing the ROS of any changes. 2758 The procedures are specified in the following sections. 2760 3.14.1. Route Optimization Initiation 2762 When an original IP packet from a source node destined to a target 2763 node arrives, the ROS checks for a NCE with an MNP-LLA that matches 2764 the target destination. If there is a NCE in the REACHABLE state, 2765 the ROS invokes the OAL and forwards the resulting carrier packets 2766 according to the cached state then returns from processing. 2768 Otherwise, if there is no NCE the ROS creates one in the INCOMPLETE 2769 state. 2771 The ROS next places the original IP packet on a short queue then 2772 sends an NS message for Address Resolution (NS(AR)) to receive a 2773 solicited NA(AR) message from an ROR. The NS(AR) message must be 2774 sent securely, and includes: 2776 o the LLA of the ROS as the source address. 2778 o the MNP-LLA corresponding to the original IP packet's destination 2779 as the Target Address, e.g., for 2001:db8:1:2::10:2000 the Target 2780 Address is fe80::2001:db8:1:2. 2782 o the Solicited-Node multicast address [RFC4291] formed from the 2783 lower 24 bits of the original IP packet's destination as the 2784 destination address, e.g., for 2001:db8:1:2::10:2000 the NS(AR) 2785 destination address is ff02:0:0:0:0:1:ff10:2000. 2787 The NS(AR) message also includes an OMNI option with an Interface 2788 Attributes entry for the underlying interface, with S/T-omIndex set 2789 to the underlying interface index and with Preflen set to the prefix 2790 length associated with the NS(AR) source. The ROS then selects an 2791 Identification value submits the NS(AR) message for OAL encapsulation 2792 with OAL source set to its own ULA and OAL destination set to the ULA 2793 corresponding to the target. (The ROS does not include any window 2794 synchronization parameters, since it will never exchange other 2795 carrier packet types directly with the ROR). 2797 The ROS then sends the resulting carrier packet(s) into the SRT 2798 secured spanning tree without decrementing the network-layer TTL/Hop 2799 Limit field. (When the ROS is an INET Client, it instead sends the 2800 resulting carrier packets to the ADM-ULA of one of its current Proxy/ 2801 Servers. The Proxy/Server then reassembles if necessary, verifies 2802 the NS(AR) signature, then re-encapsulates with the OAL source set to 2803 its own ADM-ULA and OAL destination set to the ULA corresponding to 2804 the target. The Proxy/Server then fragments if necessary and sends 2805 the resulting carrier packets into the secured spanning tree on 2806 behalf of the Client.) 2808 3.14.2. Relaying the NS(AR) *NET Packet(s) 2810 When the Bridge receives the carrier packet(s) containing the RS from 2811 the ROS, it discards the *NET headers and determines the next hop by 2812 consulting its standard IPv6 forwarding table for the OAL header 2813 destination address. The Bridge then decrements the OAL header Hop- 2814 Limit, then re-encapsulates and forwards the carrier packet(s) via 2815 the secured spanning tree the same as for any IPv6 router, where it 2816 may traverse multiple OMNI link segments. The final-hop Bridge will 2817 deliver the carrier packet(s) via the secured spanning tree to a 2818 Proxy/Server or Relay that services the target. 2820 3.14.3. Processing the NS(AR) and Sending the NA(AR) 2822 When an LHS Proxy/Server (or Relay) for the target receives the 2823 secured carrier packet(s), it reassembles if necessary then examines 2824 the NS(AR) target to determine whether it has a matching NCE and/or 2825 non-MNP route. If there is no match, the Proxy/Server drops the 2826 message. Otherwise, the LHS Proxy/Server/Relay continues processing 2827 as follows: 2829 o if the NS(AR) target matches a Client NCE in the DEPARTED state, 2830 the Proxy/Server re-encapsulates while setting the OAL source to 2831 the ULA of the ROS and OAL destination address to the ADM-ULA of 2832 the Client's new Proxy/Server. The (old) Proxy/Server then 2833 fragments if necessary and forwards the resulting carrier 2834 packet(s) over the secured spanning tree then returns from 2835 processing. 2837 o If the NS(AR) target matches the MNP-LLA of a Client NCE in the 2838 REACHABLE state, the Proxy/Server makes note of whether the NS 2839 (AR) arrived from the secured or unsecured spanning tree then acts 2840 as an ROR to provide route optimization information on behalf of 2841 the Client. (Note that if the message arrived via the secured 2842 spanning tree the ROR need not perform further authentication, but 2843 if it arrived over an open INET underlying interface it must 2844 verify the message authentication signature before accepting.) 2846 o If the NS(AR) target matches one of its non-MNP routes, the Relay 2847 acts as both an ROR and a route optimization target, since the 2848 Relay forwards IP packets toward the (fixed network) target at the 2849 network layer. 2851 The ROR next checks the target NCE for a Report List entry that 2852 matches the NS(AR) source LLA/ULA of the ROS. If there is a Report 2853 List entry, the ROR refreshes ReportTime for this ROR; otherwise, the 2854 ROR creates a new entry for the ROS and records both the LLA and ULA. 2856 The ROR then prepares a (solicited) NA(AR) message to return to the 2857 ROS with the source address set to the target's MNP-LLA, the 2858 destination address set to the NS(AR) LLA source address and the 2859 Target Address set to the same value that appeared in the NS(AR). 2860 The ROR then includes an OMNI option with Preflen set to the prefix 2861 length associated with the NA(AR) source address. The ROR next 2862 includes Interface Attributes in the OMNI option for all of the 2863 target's underlying interfaces with current information for each 2864 interface. 2866 For each Interface Attributes sub-option, the ROR sets the L2ADDR 2867 according to its own INET address for VPNed, Direct or ANET 2868 interfaces, to its own INET address for NATed Client interfaces, or 2869 to the Client's INET address for native Client interfaces. The ROR 2870 then includes the lower 32 bits of the Proxy/Server's ADM-ULA as the 2871 LHS, encodes the ADM-ULA prefix length code in the SRT field and sets 2872 FMT as specified in Section 3.3. 2874 The ROR then sets the NA(AR) message R flag to 1 (as a router) and S 2875 flag to 1 (as a response to a solicitation) and sets the O flag to 0 2876 (as a proxy) and sets the OMNI header S/T-omIndex to 0. The ROR 2877 finally submits the NA(AR) for OAL encapsulation with source set to 2878 its own ULA and destination set to the same ULA that appeared in the 2879 NS(AR) OAL source, then performs OAL encapsulation and fragmentation 2880 using the same Identification value that appeared in the NS(AR) and 2881 finally forwards the resulting (*NET-encapsulated) carrier packets 2882 via the secured spanning tree without decrementing the network-layer 2883 TTL/Hop Limit field. 2885 3.14.4. Relaying the NA(AR) 2887 When the Bridge receives NA(AR) carrier packets from the ROR, it 2888 discards the *NET header and determines the next hop by consulting 2889 its standard IPv6 forwarding table for the OAL header destination 2890 address. The Bridge then decrements the OAL header Hop-Limit, re- 2891 encapsulates the carrier packet and forwards it via the SRT secured 2892 spanning tree the same as for any IPv6 router, where it may traverse 2893 multiple OMNI link segments. The final-hop Bridge will deliver the 2894 carrier packet via the secured spanning tree to a Proxy/Server for 2895 the ROS. 2897 3.14.5. Processing the NA(AR) 2899 When the ROS receives the NA(AR) message from the ROR, it first 2900 searches for a NCE that matches the NA(AR) LLA source address. The 2901 ROS then processes the message the same as for standard IPv6 Address 2902 Resolution [RFC4861]. In the process, it caches all OMNI option 2903 information in the target NCE (including all Interface Attributes). 2905 When the ROS is a Client, the solicited NA(AR) message will first be 2906 delivered via the SRT secured spanning tree to the Proxy/Server that 2907 forwarded the NS(AR), which reassembles if necessary. The Proxy/ 2908 Server then forwards the message to the Client while re-encapsulating 2909 and re-fragmenting if necessary. If the Client is on an ANET, ANET 2910 physical security and protected spectrum ensures security for the 2911 unmodified NA(AR); if the Client is on the open INET the Proxy/Server 2912 must instead insert an authentication signature. The Proxy/Server 2913 uses its own ADM-ULA as the OAL source and the MNP-ULA of the Client 2914 as the OAL destination. 2916 3.14.6. Forwarding Packets to Route Optimized Targets 2918 After the ROS receives the route optimization NA(AR) and updates the 2919 target NCE, it can begin forwarding packets along the best paths 2920 based on the target's Interface Attributes. The ROS selects target 2921 underlying interfaces according to traffic selectors and/or any other 2922 traffic discriminators, however each underlying interface selected 2923 must first establish window synchronization state if necessary. 2925 To establish window synchronization state, the ROS performs a secured 2926 unicast NS/NA(WIN) exchange with window synchronization parameters 2927 according to the Interface Attribute FMT. If FMT-Forward is set, the 2928 ROS prepares an NS(WIN) with its own LLA as the source and the MNP- 2929 LLA of the target Client as the destination; otherwise, it sets the 2930 ADM-LLA of the LHS Proxy/Server as the destination. The ROS then 2931 encapsulates the NS(WIN) in an OAL header with its own ULA as the 2932 source. If the ROS is the Client, it sets the OAL destination to the 2933 ADM-ULA of its FHS Proxy/Server, includes an authentication signature 2934 if necessary, and includes an ORH-1 with FMT-Type clear for the first 2935 fragment. The Client sets the ORH Segments Left to 1 and includes 2936 valid SRT/LHS information for the LHS Proxy/Server with L2ADDR set to 2937 0, then forwards the NS(WIN) to its FHS Proxy/Server which must 2938 reassemble and verify the authentication signature if necessary. The 2939 FHS Proxy/Server then re-encapsulates, re-fragments and forwards the 2940 NS(WIN) carrier packets into the secured spanning tree with its own 2941 ADM-ULA as the OAL source and the ADM-ULA of the LHS Proxy/Server as 2942 the OAL destination while replacing the ORH-1 with an ORH-0. (If the 2943 ROS was the FHS Proxy/Server itself, it instead includes an ORH-0, 2944 and forwards the carrier packets into the secured spanning tree.) 2946 When an LHS Proxy/Server receives the NS(WIN) it first reassembles if 2947 necessary. If the NS(WIN) destination is its own ADM-LLA, the LHS 2948 Proxy/Server creates an NCE based on the NS(WIN) source LLA, caches 2949 the window synchronization information, and prepares an NA(WIN) while 2950 using its own ADM-LLA as the source and the ROS LLA as the 2951 destination. The LHS Proxy/Server then encapsulates the NA(WIN) in 2952 an OAL header with source set to its own ADM-ULA and destination set 2953 to the NS(WIN) OAL source. The LHS Proxy/Server then fragments if 2954 necessary includes an ORH-0 with omIndex set to the S/T-omIndex value 2955 found in the NS(WIN) OMNI option, then forwards the resulting carrier 2956 packets into the secured spanning tree which will deliver them to the 2957 ROS Proxy/Server. 2959 If the NS(WIN) destination is the MNP-LLA of the target Client, the 2960 LHS Proxy/Server instead re-encapsulates using the same OAL source 2961 and the MNP-ULA of the target as the OAL destination and includes an 2962 authentication signature if necessary while removing the ORH-0. The 2963 LHS Proxy/Server then forwards the NS(WIN) to the target over the 2964 underlying interface identified by the ORH-0 omIndex (or, over any 2965 underlying interface if omIndex is 0). When the target receives the 2966 NS(WIN), it verifies the authentication signature if necessary then 2967 creates an NCE for the ROS LLA, caches the window synchronization 2968 information and prepares an NA(WIN) to return to the ROS with its 2969 MNP-LLA as the source and the LLA of the ROS as the destination, and 2970 with an authentication signature if necessary. The target Client 2971 then encapsulates the NA(WIN) in an OAL header with its own MNP-ULA 2972 as the source, the ADM-ULA of the LHS Proxy/Server as the 2973 destination, and with an ORH-1 with SRT/LHS information copied from 2974 the ADM-ULA of the FHS Proxy/Server found in the NS(WIN) OAL source 2975 address. The target Client then sets the ORH-1 omIndex to the S/ 2976 T-omIndex value found in the NS(WIN) OMNI option, then forward the 2977 message to the LHS Proxy/Server. 2979 When the LHS Proxy/Server receives the message, it reassembles if 2980 necessary, verifies the authentication signature if necessary then 2981 re-encapsulates using its own ADM-ULA as the source and the ADM-ULA 2982 of the FHS Proxy/Server as the destination The LHS Proxy/Server then 2983 re-fragments and forwards the NS(WIN) carrier packets into the 2984 spanning tree while replacing the ORH-1 with an ORH-0. When the FHS 2985 Proxy/Server receives the NA(WIN), it reassembles if necessary then 2986 updates the target NCE based on the message contents if the Proxy/ 2987 Server itself is the ROS. If the NS(WIN) source was the ADM-LLA of 2988 the LHS Proxy/Server, the ROS must create and maintain a NCE for the 2989 LHS Proxy/Server which it must regard as a companion to the existing 2990 MNP-LLA NCE for the target Client. (The NCE for the LHS Proxy/Server 2991 can also be shared by multiple target Client NCEs if the ROS 2992 communicates with multiple active targets located behind the same LHS 2993 Proxy/Server.) If the Client is the ROS, the FHS Proxy/Server 2994 instead inserts an authentication signature if necessary, removes the 2995 ORH-0 then re-encapsulates and re-fragments if necessary while 2996 changing the OAL destination to the MNP-ULA of the Client. The FHS 2997 Proxy/Server then forwards the NA(WIN) to the Client over the 2998 underlying interface identified by the ORH-0 omIndex which then 2999 updates its own NCE based on the target Client MNP-LLA or LHS Proxy/ 3000 Server ADM-LLA. The ROS (whether the Proxy/Server or the Client 3001 itself) finally arranges to return an acknowledgement if requested by 3002 the NA(WIN). 3004 After window synchronization state has been established, the ROS can 3005 begin forwarding carrier packets as specified in Section 3.2.7 while 3006 performing additional NS/NA(WIN) exchanges as above to update window 3007 state and/or test reachability. These forwarding procedures apply to 3008 the case where the selected target interface SRT/LHS codes indicate 3009 that the interface is located in a foreign OMNI link segment. In 3010 that case, the ROS must include ORHs and send the resulting carrier 3011 packets into the spanning tree. 3013 If the SRT/LHS codes indicate that the interface is in the local OMNI 3014 link segment, the ROS can instead forward carrier packets directly to 3015 the LHS Proxy/Server using the L2ADDR for encapsulation, or even to 3016 the target Client itself while invoking NAT traversal if necessary. 3017 When the ROS sends packets directly to the LHS Proxy/Server, it 3018 includes an ORH-0 if necessary to inform the Proxy/Server as to 3019 whether it must reassemble and/or the correct target Client interface 3020 for (re)forwarding. If the LHS Proxy/Server is required to 3021 reassemble, the ROS sets the OAL destination to the ADM-ULA of the 3022 LHS Proxy/Server; otherwise, it sets the OAL destination to the MNP- 3023 ULA of the target Client itself. When the ROS sends packets directly 3024 to the target Client, it need not include an ORH. The LHS Proxy/ 3025 Server (or target Client) then saves the L2ADDR and full OAL 3026 addresses in the ROS NCE, and the ROS can begin applying OAL header 3027 compression in subsequent carrier packets as specified in 3028 [I-D.templin-6man-omni] since the OAL header is not examined by any 3029 forwarding nodes in the path. 3031 While the ROS continues to actively forward packets to the target 3032 Client, it is responsible for updating window synchronization state 3033 and per-interface reachability before expiration. Window 3034 synchronization state is shared by all underlying interfaces in the 3035 ROS' NCE that use the same destination LLA so that a single NS/ 3036 NA(NUD) exchange applies for all interfaces regardless of the 3037 (single) interface used to conduct the exchange. However, the window 3038 synchronization exchange only confirms target Client reachability 3039 over the specific interface used to conduct the exchange. 3040 Reachability for other underlying interfaces that share the same 3041 window synchronization state must be determined individually using 3042 NS/NA(NUD) messages which need not be secured as long as they use in- 3043 window Identifications and do not update other state information. 3045 3.15. Neighbor Unreachability Detection (NUD) 3047 AERO nodes perform Neighbor Unreachability Detection (NUD) per 3048 [RFC4861] either reactively in response to persistent link-layer 3049 errors (see Section 3.11) or proactively to confirm reachability. 3050 The NUD algorithm is based on periodic control message exchanges and 3051 may further be seeded by ND hints of forward progress, but care must 3052 be taken to avoid inferring reachability based on spoofed 3053 information. For example, IPv6 ND message exchanges that include 3054 authentication codes and/or in-window Identifications may be 3055 considered as acceptable hints of forward progress, while spurious 3056 random carrier packets should be ignored. 3058 AERO nodes can use standard NS/NA(NUD) exchanges sent over the OMNI 3059 link secured spanning tree (i.e. the same as described above for NS/ 3060 NA(WIN)) to test reachability without risk of DoS attacks from nodes 3061 pretending to be a neighbor. These NS/NA(NUD) messages use the 3062 unicast LLAs and ULAs of the parties involved in the NUD test the 3063 same as for standard IPv6 ND over the secured spanning tree. When 3064 only reachability information is required without updating any other 3065 NCE state, unsecured NS/NA(NUD) messages may instead be exchanged 3066 directly between neighbors as long as they include in-window 3067 Identifications. 3069 When an ROR directs an ROS to a target neighbor with one or more 3070 link-layer addresses, the ROS probes each unsecured target underlying 3071 interface either proactively or on-demand of carrier packets directed 3072 to the path by multilink forwarding to maintain the interface's state 3073 as reachable. Probing is performed through NS(NUD) messages over the 3074 SRT secured or unsecured spanning tree, or through NS(NUD) messages 3075 sent directly to an underlying interface of the target itself. While 3076 testing a target underlying interface, the ROS can optionally 3077 continue to forward carrier packets via alternate interfaces and/or 3078 maintain a small queue of carrier packets until target reachability 3079 is confirmed. 3081 NS(NUD) messages are encapsulated, fragmented and transmitted as 3082 carrier packets the same as for ordinary original IP data packets, 3083 however the encapsulated destinations are the LLA of the ROS and 3084 either the ADM-LLA of the LHS Proxy/Server or the MNP-LLA of the 3085 target itself. The ROS encapsulates the NS(NUD) message the same as 3086 described in Section 3.2.7, however Destination Suffixes (if present) 3087 are set according to the LLA destination (i.e., and not a ULA/GUA 3088 destination). The ROS sets the NS(NUD) OMNI header S/T-omIndex to 3089 identify the underlying interface used for forwarding (or to 0 if any 3090 underlying interface can be used). The ROS also includes an ORH with 3091 SRT/LHS/LLADDR information the same as for ordinary data packets, but 3092 no authentication signatures are included. The ROS then fragments 3093 the OAL packet and forwards the resulting carrier packets into the 3094 unsecured spanning tree or directly to the target (or LHS Proxy/ 3095 Server) if it is in the local segment. 3097 When the target (or LHS Proxy/Server) receives the NS(NUD) carrier 3098 packets, it verifies that it has a NCE for this ROS and that the 3099 Identification is in-window, then submits the carrier packets for 3100 reassembly. The node then searches for Interface Attributes in its 3101 NCE for the ROS that match the NS(NUD) S/T-omIndex and uses the 3102 SRT/LHS/L2ADDR and FMT information to prepare an ORH for the NA(NUD) 3103 reply. The node then prepares the NA(NUD) with the source and 3104 destination LLAs reversed, encapsulates and sets the OAL source and 3105 destination, sets the NA(NUD) S/T-omIndex to the index of the 3106 underlying interface the NS(NUD) arrived on and sets the Target 3107 Address to the same value included in the NS(NUD). The target next 3108 sets the R flag to 1, the S flag to 1 and the O flag to 1, then 3109 selects an in-window Identification for the ROS and performs 3110 fragmentation. The node then forwards the carrier packets into the 3111 unsecured spanning tree, directly to the ROS if it is in the local 3112 segment or directly to a Bridge in the local segment. 3114 When the ROS receives the NA(NUD), it marks the target underlying 3115 interface tested as "reachable". Note that underlying interface 3116 states are maintained independently of the overall NCE REACHABLE 3117 state, and that a single NCE may have multiple target underlying 3118 interfaces in various states "reachable" and otherwise while the NCE 3119 state as a whole remains REACHABLE. 3121 Note also that the exchange of NS/NA(NUD) messages has the useful 3122 side-benefit of opening holes in NATs that may be useful for NAT 3123 traversal. 3125 3.16. Mobility Management and Quality of Service (QoS) 3127 AERO is a Distributed Mobility Management (DMM) service. Each Proxy/ 3128 Server is responsible for only a subset of the Clients on the OMNI 3129 link, as opposed to a Centralized Mobility Management (CMM) service 3130 where there is a single network mobility collective entity for all 3131 Clients. Clients coordinate with their associated Proxy/Servers via 3132 RS/RA exchanges to maintain the DMM profile, and the AERO routing 3133 system tracks all current Client/Proxy/Server peering relationships. 3135 Proxy/Servers provide default routing and mobility/multilink services 3136 for their dependent Clients. Clients are responsible for maintaining 3137 neighbor relationships with their Proxy/Servers through periodic RS/ 3138 RA exchanges, which also serves to confirm neighbor reachability. 3139 When a Client's underlying Interface Attributes change, the Client is 3140 responsible for updating the Proxy/Server with this new information. 3141 Note that when there is a Proxy/Server in the path, the Proxy 3142 function can also perform some RS/RA exchanges on the Client's 3143 behalf. 3145 Mobility management messaging is based on the transmission and 3146 reception of unsolicited Neighbor Advertisement (uNA) messages. Each 3147 uNA message sets the IPv6 source address to the LLA of the ROR and 3148 the destination address to the unicast LLA of the ROS. 3150 Mobility management considerations are specified in the following 3151 sections. 3153 3.16.1. Mobility Update Messaging 3155 RORs accommodate Client mobility and/or multilink change events by 3156 sending secured uNA messages to each ROS in the target Client's 3157 Report List. When an ROR sends a uNA message, it sets the IPv6 3158 source address to the its own LLA, sets the destination address to 3159 the ROS LLA (i.e., an MNP-LLA if the ROS is a Client and an ADM-LLA 3160 if the ROS is a Proxy/Server) and sets the Target Address to the 3161 Client's MNP-LLA. The ROR also includes an OMNI option with Preflen 3162 set to the prefix length associated with the Client's MNP-LLA, with 3163 Interface Attributes for the target Client's underlying interfaces 3164 and with the OMNI header S/T-omIndex set to 0. The ROR then sets the 3165 uNA R flag to 1, S flag to 0 and O flag to 1, then encapsulates the 3166 message in an OAL header with source set to its own ADM-ULA and 3167 destination set to the ROS ULA (i.e., the ADM-ULA of the ROS Proxy/ 3168 Server) and sends the message into the secured spanning tree. 3170 As discussed in Section 7.2.6 of [RFC4861], the transmission and 3171 reception of uNA messages is unreliable but provides a useful 3172 optimization. In well-connected Internetworks with robust data links 3173 uNA messages will be delivered with high probability, but in any case 3174 the Proxy/Server can optionally send up to MAX_NEIGHBOR_ADVERTISEMENT 3175 uNAs to each ROS to increase the likelihood that at least one will be 3176 received. Alternatively, the Proxy/Server can set the PNG flag in 3177 the uNA OMNI option header to request a solicited NA acknowledgement 3178 as specified in [I-D.templin-6man-omni]. 3180 When the ROS Proxy/Server receives a uNA message prepared as above, 3181 it ignores the message if the destination is not its own ADM-ULA or 3182 the MNP-ULA of the ROS Client. In the former case, it uses the 3183 included OMNI option information to update its NCE for the target, 3184 but does not reset ReachableTime since the receipt of an unsolicited 3185 NA message from the ROR does not provide confirmation that any 3186 forward paths to the target Client are working. If the destination 3187 was the MNP-ULA of the ROS Client, the ROS Proxy/Server instead re- 3188 encapsulates with the OAL source set to its own ADM-ULA, OAL 3189 destination set to the MNP-ULA of the ROS Client with an 3190 authentication signature if necessary, and with an in-window 3191 Identification for this Client. Finally, if the uNA message PNG flag 3192 was set, the ROS returns a solicited NA acknowledgement as specified 3193 in [I-D.templin-6man-omni]. 3195 In addition to sending uNA messages to the current set of ROSs for 3196 the target Client, the ROR also sends uNAs to the MNP-ULA associated 3197 with the link-layer address for any underlying interface for which 3198 the link-layer address has changed. These uNA messages update an old 3199 Proxy/Server that cannot easily detect (e.g., without active probing) 3200 when a formerly-active Client has departed. When the ROR sends the 3201 uNA, it sets the IPv6 source address to its LLA, sets the destination 3202 address to the old Proxy/Server's ADM-LLA, and sets the Target 3203 Address to the Client's MNP-LLA. The ROR also includes an OMNI 3204 option with Preflen set to the prefix length associated with the 3205 Client's MNP-LLA, with Interface Attributes for the changed 3206 underlying interface, and with the OMNI header S/T-omIndex set to 0. 3207 The ROR then sets the uNA R flag to 1, S flag to 0 and O flag to 1, 3208 then encapsulates the message in an OAL header with source set to its 3209 own ULA and destination set to the ADM-ULA of the old Proxy/Server 3210 and sends the message into the secured spanning tree. 3212 3.16.2. Announcing Link-Layer Address and/or QoS Preference Changes 3214 When a Client needs to change its underlying Interface Attributes 3215 (e.g., due to a mobility event), the Client requests one of its 3216 Proxy/Servers to send uNA or RS messages to all of its other Proxy/ 3217 Servers via the secured spanning tree with an OMNI option that 3218 includes Interface attributes with the new link quality and address 3219 information. 3221 Up to MAX_RTR_SOLICITATIONS RS messages MAY be sent in parallel with 3222 sending carrier packets containing user data in case one or more RAs 3223 are lost. If all RAs are lost, the Client SHOULD re-associate with a 3224 new Proxy/Server. 3226 When the Proxy/Server receives the Client's changes, it sends uNA 3227 messages to all nodes in the Report List the same as described in the 3228 previous section. 3230 3.16.3. Bringing New Links Into Service 3232 When a Client needs to bring new underlying interfaces into service 3233 (e.g., when it activates a new data link), it sends an RS message to 3234 the Proxy/Server via the underlying interface with an OMNI option 3235 that includes Interface Attributes with appropriate link quality 3236 values and with link-layer address information for the new link. 3238 3.16.4. Deactivating Existing Links 3240 When a Client needs to deactivate an existing underlying interface, 3241 it sends an RS or uNA message to its Proxy/Server with an OMNI option 3242 with appropriate Interface Attribute values - in particular, the link 3243 quality value 0 assures that neighbors will cease to use the link. 3245 If the Client needs to send RS/uNA messages over an underlying 3246 interface other than the one being deactivated, it MUST include 3247 Interface Attributes with appropriate link quality values for any 3248 underlying interfaces being deactivated. 3250 Note that when a Client deactivates an underlying interface, 3251 neighbors that have received the RS/uNA messages need not purge all 3252 references for the underlying interface from their neighbor cache 3253 entries. The Client may reactivate or reuse the underlying interface 3254 and/or its omIndex at a later point in time, when it will send RS/uNA 3255 messages with fresh Interface Attributes to update any neighbors. 3257 3.16.5. Moving Between Proxy/Servers 3259 The Client performs the procedures specified in Section 3.12.2 when 3260 it first associates with a new FHS Proxy/Server or renews its 3261 association with an existing Proxy/Server. The Client also includes 3262 MS-Release identifiers in the RS message OMNI option per 3263 [I-D.templin-6man-omni] if it wants the new Proxy/Server to notify 3264 any old Proxy/Servers from which the Client is departing. 3266 When the new FHS Proxy/Server receives the Client's RS message, it 3267 returns an RA as specified in Section 3.12.3 and sends uNA messages 3268 to any old Proxy/Servers listed in OMNI option MS-Release 3269 identifiers. When the new Proxy/Server sends a uNA message, it sets 3270 the IPv6 source address to the Client's MNP-LLA, sets the destination 3271 address to the old Proxy/Server's ADM-LLA, and sets the Target 3272 Address to 0. The new Proxy/Server also includes an OMNI option with 3273 Preflen set to the prefix length associated with the Client's MNP- 3274 LLA, with Interface Attributes for its own underlying interface, and 3275 with the OMNI header S/T-omIndex set to 0. The new Proxy/Server then 3276 sets the uNA R flag to 1, S flag to 0 and O flag to 1, then 3277 encapsulates the message in an OAL header with source set to its own 3278 ADM-ULA and destination set to the ADM-ULA of the old Proxy/Server 3279 and sends the message into the secured spanning tree. 3281 When an old Proxy/Server receives the uNA, it notices that the 3282 message appears to have originated from the Client's MNP-LLA but that 3283 the Target Address is 0. The old Proxy/Server then changes the 3284 Client's NCE state to DEPARTED, sets the link-layer address of the 3285 Client to the new Proxy/Server's ADM-ULA, and resets DepartTime. 3286 After a short delay (e.g., 2 seconds) the old Proxy/Server withdraws 3287 the Client's MNP from the routing system. After DepartTime expires, 3288 the old Proxy/Server deletes the Client's NCE. 3290 The old Proxy/Server also iteratively forwards a copy of the uNA 3291 message to each ROS in the Client's Report List by changing the OAL 3292 destination address to the ULA of the ROS while leaving all other 3293 fields of the message unmodified. When the ROS receives the uNA, it 3294 examines the source address to determine the target Client NCE and 3295 verifies that the destination address matches the old Proxy/Server. 3296 The ROS then caches the ULA source address as the new Proxy/Server 3297 for the existing NCE and marks the entry as STALE. While in the 3298 STALE state, the ROS allows new carrier packets to flow according to 3299 any alternate reachable underlying interfaces and sends new NS(AR) 3300 messages using its own ULA as the OAL source and the ADM-ULA of the 3301 new Proxy/Server as the OAL destination address to elicit NA(AR) 3302 messages that reset the NCE state to REACHABLE. 3304 Clients SHOULD NOT move rapidly between Proxy/Servers in order to 3305 avoid causing excessive oscillations in the AERO routing system. 3306 Examples of when a Client might wish to change to a different Proxy/ 3307 Server include a Proxy/Server that has gone unreachable, topological 3308 movements of significant distance, movement to a new geographic 3309 region, movement to a new OMNI link segment, etc. 3311 When a Client moves to a new Proxy/Server, some of the carrier 3312 packets of a multiple fragment OAL packet may have already arrived at 3313 the old Proxy/Server while others are en route to the new Proxy/ 3314 Server, however no special attention in the reassembly algorithm is 3315 necessary since all carrier packets will eventually arrive at the 3316 Client which can then reassemble. However, any carrier packets that 3317 are somehow lost can often be recovered through retransmissions. 3319 3.17. Multicast 3321 The AERO Client provides an IGMP (IPv4) [RFC2236] or MLD (IPv6) 3322 [RFC3810] proxy service for its EUNs and/or hosted applications 3323 [RFC4605]. Proxy/Servers act as a Protocol Independent Multicast - 3324 Sparse-Mode (PIM-SM, or simply "PIM") Designated Router (DR) 3325 [RFC7761]. AERO Relays also act as PIM routers (i.e., the same as 3326 AERO Proxys/Servers) on behalf of nodes on INET/EUN networks. 3328 Clients on ANET underlying interfaces for which the ANET has deployed 3329 native multicast services forward IGMP/MLD messages into the ANET. 3330 The IGMP/MLD messages may be further forwarded by a first-hop ANET 3331 access router acting as an IGMP/MLD-snooping switch [RFC4541], then 3332 ultimately delivered to an ANET FHS Proxy/Server. 3334 Clients on ANET underlying interfaces without native multicast 3335 services instead send NS(AR) messages to cause their FHS Proxy/Server 3336 to act as an ROS and forward the message to an LHS Proxy/Server ROR. 3337 Clients on INET interfaces act as an ROS on their own behalf and 3338 forward NS(AR) messages directly to the LHS Proxy/Server ROR (i.e., 3339 via the FHS Proxy/Server as a proxy). When the Client receives an 3340 NA(AR) response, it initiates PIM protocol messaging according to the 3341 Source-Specific Multicast (SSM) and Any-Source Multicast (ASM) 3342 operational modes as discussed in the following sections. 3344 3.17.1. Source-Specific Multicast (SSM) 3346 When an ROS "X" (i.e., either a ROS Client or its FHS Proxy Server) 3347 acting as PIM router receives a Join/Prune message from a node on its 3348 downstream interfaces containing one or more ((S)ource, (G)roup) 3349 pairs, it updates its Multicast Routing Information Base (MRIB) 3350 accordingly. For each S belonging to a prefix reachable via X's non- 3351 OMNI interfaces, X then forwards the (S, G) Join/Prune to any PIM 3352 routers on those interfaces per [RFC7761]. 3354 For each S belonging to a prefix reachable via X's OMNI interface, X 3355 sends an NS(AR) message (see: Section 3.14) using its own LLA as the 3356 source address and the LLA of S as the destination address. X then 3357 encapsulates the NS(AR) in an OAL header with source address set to 3358 the ULA of X and destination address set to the solicited node 3359 multicast address for S, then forwards the message into the secured 3360 spanning tree, which delivers it to ROR "Y" that services S. The 3361 resulting NA(AR) will return the LLA for the prefix that matches S as 3362 the network-layer source address and with an OMNI option with 3363 interface attributes for any underlying interfaces that are currently 3364 servicing S. 3366 When X processes the NA(AR) it selects one or more underlying 3367 interfaces for S and performs an NS/NA(WIN) exchange while including 3368 a PIM Join/Prune message for each multicast group of interest in the 3369 OMNI option. If S is located behind any Proxys "Z"*, each Z* then 3370 updates its MRIB accordingly and maintains the LLA of X as the next 3371 hop in the reverse path. Since the Bridges do not examine network 3372 layer control messages, this means that the (reverse) multicast tree 3373 path is simply from each Z* (and/or S) to X with no other multicast- 3374 aware routers in the path. 3376 Following the initial combined Join/Prune and NS/NA messaging, X 3377 maintains a NCE for each S the same as if X was sending unicast data 3378 traffic to S. In particular, X performs additional NS/NA exchanges 3379 to keep the NCE alive for up to t_periodic seconds [RFC7761]. If no 3380 new Joins are received within t_periodic seconds, X allows the NCE to 3381 expire. Finally, if X receives any additional Join/Prune messages 3382 for (S,G) it forwards the messages over the secured spanning tree. 3384 At some later time, Client C that holds an MNP for source S may 3385 depart from a first Proxy/Server Z1 and/or connect via a new Proxy/ 3386 Server Z2. In that case, Y sends a uNA message to X the same as 3387 specified for unicast mobility in Section 3.16. When X receives the 3388 uNA message, it updates its NCE for the LLA for source S and sends 3389 new Join messages to any new Proxys Z2. There is no requirement to 3390 send any Prune messages to old Proxy/Server Z1 since source S will no 3391 longer source any multicast data traffic via Z1. Instead, the 3392 multicast state for (S,G) in Proxy/Server Z1 will soon time out since 3393 no new Joins will arrive. 3395 After some later time, C may move to a new Proxy/Server Y2 and depart 3396 from old Sever Y1. In that case, Y1 sends Join messages for any of 3397 C's active (S,G) groups to Y2 while including its own LLA as the 3398 source address. This causes Y2 to include Y1 in the multicast 3399 forwarding tree during the interim time that Y1's NCE for C is in the 3400 DEPARTED state. At the same time, Y1 sends a uNA message to X with 3401 an OMNI option with S/T-omIndex set to 0 and a release indication to 3402 cause X to release its NCE for S. X then sends a new Join message to 3403 S via the secured spanning tree and re-initiates route optimization 3404 the same as if it were receiving a fresh Join message from a node on 3405 a downstream link. 3407 3.17.2. Any-Source Multicast (ASM) 3409 When an ROS X acting as a PIM router receives a Join/Prune from a 3410 node on its downstream interfaces containing one or more (*,G) pairs, 3411 it updates its Multicast Routing Information Base (MRIB) accordingly. 3412 X then forwards a copy of the message within the OMNI option of an 3413 NS(WIN) message to the Rendezvous Point (RP) R for each G over the 3414 secured spanning tree. X uses its own LLA as the source address and 3415 the LLA for R as the destination address, then encapsulates the 3416 NS(WIN) message in an OAL header with source address set to the ULA 3417 of X and destination address set to the ULA of R's Proxy/Server then 3418 sends the message into the secured spanning tree. 3420 For each source S that sends multicast traffic to group G via R, the 3421 Proxy/Server Z* for the Client that aggregates S encapsulates the 3422 original IP packets in PIM Register messages and forwards them to R 3423 via the secured spanning tree, which may then elect to send a PIM 3424 Join to Z*. This will result in an (S,G) tree rooted at Z* with R as 3425 the next hop so that R will begin to receive two copies of the 3426 original IP packet; one native copy from the (S, G) tree and a second 3427 copy from the pre-existing (*, G) tree that still uses PIM Register 3428 encapsulation. R can then issue a PIM Register-stop message to 3429 suppress the Register-encapsulated stream. At some later time, if C 3430 moves to a new Proxy/Server Z*, it resumes sending original IP 3431 packets via PIM Register encapsulation via the new Z*. 3433 At the same time, as multicast listeners discover individual S's for 3434 a given G, they can initiate an (S,G) Join for each S under the same 3435 procedures discussed in Section 3.17.1. Once the (S,G) tree is 3436 established, the listeners can send (S, G) Prune messages to R so 3437 that multicast original IP packets for group G sourced by S will only 3438 be delivered via the (S, G) tree and not from the (*, G) tree rooted 3439 at R. All mobility considerations discussed for SSM apply. 3441 3.17.3. Bi-Directional PIM (BIDIR-PIM) 3443 Bi-Directional PIM (BIDIR-PIM) [RFC5015] provides an alternate 3444 approach to ASM that treats the Rendezvous Point (RP) as a Designated 3445 Forwarder (DF). Further considerations for BIDIR-PIM are out of 3446 scope. 3448 3.18. Operation over Multiple OMNI Links 3450 An AERO Client can connect to multiple OMNI links the same as for any 3451 data link service. In that case, the Client maintains a distinct 3452 OMNI interface for each link, e.g., 'omni0' for the first link, 3453 'omni1' for the second, 'omni2' for the third, etc. Each OMNI link 3454 would include its own distinct set of Bridges and Proxy/Servers, 3455 thereby providing redundancy in case of failures. 3457 Each OMNI link could utilize the same or different ANET connections. 3458 The links can be distinguished at the link-layer via the SRT prefix 3459 in a similar fashion as for Virtual Local Area Network (VLAN) tagging 3460 (e.g., IEEE 802.1Q) and/or through assignment of distinct sets of 3461 MSPs on each link. This gives rise to the opportunity for supporting 3462 multiple redundant networked paths, with each VLAN distinguished by a 3463 different SRT "color" (see: Section 3.2.5). 3465 The Client's IP layer can select the outgoing OMNI interface 3466 appropriate for a given traffic profile while (in the reverse 3467 direction) correspondent nodes must have some way of steering their 3468 original IP packets destined to a target via the correct OMNI link. 3470 In a first alternative, if each OMNI link services different MSPs, 3471 then the Client can receive a distinct MNP from each of the links. 3472 IP routing will therefore assure that the correct OMNI link is used 3473 for both outbound and inbound traffic. This can be accomplished 3474 using existing technologies and approaches, and without requiring any 3475 special supporting code in correspondent nodes or Bridges. 3477 In a second alternative, if each OMNI link services the same MSP(s) 3478 then each link could assign a distinct "OMNI link Anycast" address 3479 that is configured by all Bridges on the link. Correspondent nodes 3480 can then perform Segment Routing to select the correct SRT, which 3481 will then direct the original IP packet over multiple hops to the 3482 target. 3484 3.19. DNS Considerations 3486 AERO Client MNs and INET correspondent nodes consult the Domain Name 3487 System (DNS) the same as for any Internetworking node. When 3488 correspondent nodes and Client MNs use different IP protocol versions 3489 (e.g., IPv4 correspondents and IPv6 MNs), the INET DNS must maintain 3490 A records for IPv4 address mappings to MNs which must then be 3491 populated in Relay NAT64 mapping caches. In that way, an IPv4 3492 correspondent node can send original IPv4 packets to the IPv4 address 3493 mapping of the target MN, and the Relay will translate the IPv4 3494 header and destination address into an IPv6 header and IPv6 3495 destination address of the MN. 3497 When an AERO Client registers with an AERO Proxy/Server, the Proxy/ 3498 Server can return the address(es) of DNS servers in RDNSS options 3499 [RFC6106]. The DNS server provides the IP addresses of other MNs and 3500 correspondent nodes in AAAA records for IPv6 or A records for IPv4. 3502 3.20. Transition/Coexistence Considerations 3504 OAL encapsulation ensures that dissimilar INET partitions can be 3505 joined into a single unified OMNI link, even though the partitions 3506 themselves may have differing protocol versions and/or incompatible 3507 addressing plans. However, a commonality can be achieved by 3508 incrementally distributing globally routable (i.e., native) IP 3509 prefixes to eventually reach all nodes (both mobile and fixed) in all 3510 OMNI link segments. This can be accomplished by incrementally 3511 deploying AERO Bridges on each INET partition, with each Bridge 3512 distributing its MNPs and/or discovering non-MNP IP GUA prefixes on 3513 its INET links. 3515 This gives rise to the opportunity to eventually distribute native IP 3516 addresses to all nodes, and to present a unified OMNI link view even 3517 if the INET partitions remain in their current protocol and 3518 addressing plans. In that way, the OMNI link can serve the dual 3519 purpose of providing a mobility/multilink service and a transition/ 3520 coexistence service. Or, if an INET partition is transitioned to a 3521 native IP protocol version and addressing scheme that is compatible 3522 with the OMNI link MNP-based addressing scheme, the partition and 3523 OMNI link can be joined by Bridges. 3525 Relays that connect INETs/EUNs with dissimilar IP protocol versions 3526 may need to employ a network address and protocol translation 3527 function such as NAT64 [RFC6146]. 3529 3.21. Detecting and Reacting to Proxy/Server and Bridge Failures 3531 In environments where rapid failure recovery is required, Proxy/ 3532 Servers and Bridges SHOULD use Bidirectional Forwarding Detection 3533 (BFD) [RFC5880]. Nodes that use BFD can quickly detect and react to 3534 failures so that cached information is re-established through 3535 alternate nodes. BFD control messaging is carried only over well- 3536 connected ground domain networks (i.e., and not low-end radio links) 3537 and can therefore be tuned for rapid response. 3539 Proxy/Servers and Bridges maintain BFD sessions in parallel with 3540 their BGP peerings. If a Proxy/Server or Bridge fails, BGP peers 3541 will quickly re-establish routes through alternate paths the same as 3542 for common BGP deployments. Similarly, Proxys maintain BFD sessions 3543 with their associated Bridges even though they do not establish BGP 3544 peerings with them. 3546 3.22. AERO Clients on the Open Internet 3548 AERO Clients that connect to the open Internet via INET interfaces 3549 can establish a VPN or direct link to securely connect to a FHS 3550 Proxy/Server in a "tethered" arrangement with all of the Client's 3551 traffic transiting the Proxy/Server which acts as a router. 3552 Alternatively, the Client can associate with an INET FHS Proxy/Server 3553 using UDP/IP encapsulation and control message securing services as 3554 discussed in the following sections. 3556 When a Client's OMNI interface enables an INET underlying interface, 3557 it first examines the INET address. For IPv4, the Client assumes it 3558 is on the open Internet if the INET address is not a special-use IPv4 3559 address per [RFC3330]. Similarly for IPv6, the Client assumes it is 3560 on the open Internet if the INET address is a Global Unicast Address 3561 (GUA) [RFC4291]. Otherwise, the Client should assume it is behind 3562 one or several NATs. 3564 The Client then prepares an RS message with IPv6 source address set 3565 to its MNP-LLA, with IPv6 destination set to (link-local) All-Routers 3566 multicast and with an OMNI option with underlying interface 3567 attributes. If the Client believes that it is on the open Internet, 3568 it SHOULD include an L2ADDR in the Interface Attributes sub-option 3569 corresponding to the underlying interface; otherwise, it MAY set 3570 L2ADDR to 0. If the underlying address is IPv4, the Client includes 3571 the Port Number and IPv4 address written in obfuscated form [RFC4380] 3572 as discussed in Section 3.3. If the underlying interface address is 3573 IPv6, the Client instead includes the Port Number and IPv6 address in 3574 obfuscated form. The Client finally includes an authentication 3575 signature sub-option in the OMNI option [I-D.templin-6man-omni] to 3576 provide message authentication, selects an Identification value and 3577 window synchronization parameters, and submits the RS for OAL 3578 encapsulation. The Client then encapsulates the OAL fragment in UDP/ 3579 IP headers to form a carrier packet, sets the UDP/IP source to its 3580 INET address and UDP port, sets the UDP/IP destination to the FHS 3581 Proxy/Server's INET address and the AERO service port number (8060), 3582 then sends the carrier packet to the Proxy/Server. 3584 When the FHS Proxy/Server receives the RS, it discards the OAL 3585 encapsulation, authenticates the RS message, creates a NCE and 3586 registers the Client's MNP, window synchronization state and INET 3587 interface information according to the OMNI option parameters. If 3588 the RS message OMNI option includes Interface Attributes with an 3589 L2ADDR, the Proxy/Server compares the encapsulation IP address and 3590 UDP port number with the (unobfuscated) values. If the values are 3591 the same, the Proxy/Server caches the Client's information as "INET" 3592 addresses meaning that the Client is likely to accept direct messages 3593 without requiring NAT traversal exchanges. If the values are 3594 different (or, if the OMNI option did not include an L2ADDR) the 3595 Proxy/Server instead caches the Client's information as "mapped" 3596 addresses meaning that NAT traversal exchanges may be necessary. 3598 The FHS Proxy/Server then prepares an RA message with IPv6 source and 3599 destination set corresponding to the addresses in the RS, and with an 3600 OMNI option with an Origin Indication sub-option per 3601 [I-D.templin-6man-omni] with the mapped and obfuscated Port Number 3602 and IP address observed in the encapsulation headers. The Proxy/ 3603 Server also includes an Interface Attributes sub-option for its 3604 underlying interface with FMT/SRT/LHS information appropriate for its 3605 INET interface, and with an authentication signature sub-option per 3606 [I-D.templin-6man-omni] and/or a symmetric window synchronization/ 3607 acknowledgement if necessary. The Proxy/Server then performs OAL 3608 encapsulation and fragmentation if necessary and encapsulates each 3609 fragment in UDP/IP headers with addresses set per the L2ADDR 3610 information in the NCE for the Client. 3612 When the Client receives the RA, it authenticates the message then 3613 process the window synchronization/acknowledgement and compares the 3614 mapped Port Number and IP address from the Origin Indication sub- 3615 option with its own address. If the addresses are the same, the 3616 Client assumes the open Internet / Cone NAT principle; if the 3617 addresses are different, the Client instead assumes that further 3618 qualification procedures are necessary to detect the type of NAT and 3619 proceeds according to standard procedures [RFC6081][RFC4380]. The 3620 Client also caches the RA Interface Attributes FMT/SRT/LHS 3621 information to discover the Proxy/Server's spanning tree orientation. 3622 The Client finally arranges to return an explicit/implicit 3623 acknowledgement, and sends periodic RS messages to receive fresh RA 3624 messages before the Router Lifetime received on each INET interface 3625 expires. 3627 When the Client sends messages to target IP addresses, it also 3628 invokes route optimization per Section 3.14. For route optimized 3629 targets in the same OMNI link segment, if the target's L2ADDR is on 3630 the open INET, the Client forwards carrier packets directly to the 3631 target INET address. If the target is behind a NAT, the Client first 3632 establishes NAT state for the L2ADDR using the "direct bubble" and 3633 NUD mechanisms discussed in Section 3.10.1. The Client continues to 3634 send carrier packets via its Proxy/Server until NAT state is 3635 populated, then begins forwarding carrier packets via the direct path 3636 through the NAT to the target. For targets in different OMNI link 3637 segments, the Client uses OAL/ORH encapsulation and forwards carrier 3638 packets to the Bridge that returned the NA(AR) message. 3640 The Client can send original IP packets to route-optimized neighbors 3641 in the same OMNI link segment no larger than the minimum/path MPS in 3642 one piece and with OAL encapsulation as atomic fragments. For larger 3643 original IP packets, the Client applies OAL encapsulation and 3644 fragmentation if necessary according to Section 3.9, with OAL header 3645 with source set to its own MNP-ULA and destination set to the MNP-ULA 3646 of the target, and with an in-window Identification value. The 3647 Client then encapsulates each resulting carrier packet in UDP/IP *NET 3648 headers and sends them to the next hop. 3650 Note: The NAT traversal procedures specified in this document are 3651 applicable for Cone, Address-Restricted and Port-Restricted NATs 3652 only. While future updates to this document may specify procedures 3653 for other NAT variations (e.g., hairpinning and various forms of 3654 Symmetric NATs), it should be noted that continuous communications 3655 are always possible through forwarding via a Proxy/Server even if NAT 3656 traversal is not employed. 3658 3.23. Time-Varying MNPs 3660 In some use cases, it is desirable, beneficial and efficient for the 3661 Client to receive a constant MNP that travels with the Client 3662 wherever it moves. For example, this would allow air traffic 3663 controllers to easily track aircraft, etc. In other cases, however 3664 (e.g., intelligent transportation systems), the MN may be willing to 3665 sacrifice a modicum of efficiency in order to have time-varying MNPs 3666 that can be changed every so often to defeat adversarial tracking. 3668 The DHCPv6 service offers a way for Clients that desire time-varying 3669 MNPs to obtain short-lived prefixes (e.g., on the order of a small 3670 number of minutes). In that case, the identity of the Client would 3671 not be bound to the MNP but rather to a Node Identification value 3672 (see: [I-D.templin-6man-omni]) to be used as the Client ID seed for 3673 MNP prefix delegation. The Client would then be obligated to 3674 renumber its internal networks whenever its MNP (and therefore also 3675 its MNP-LLA) changes. This should not present a challenge for 3676 Clients with automated network renumbering services, however presents 3677 limits for the durations of ongoing sessions that would prefer to use 3678 a constant address. 3680 4. Implementation Status 3682 An early AERO implementation based on OpenVPN (https://openvpn.net/) 3683 was announced on the v6ops mailing list on January 10, 2018 and an 3684 initial public release of the AERO proof-of-concept source code was 3685 announced on the intarea mailing list on August 21, 2015. 3687 AERO Release-3.2 was tagged on March 30, 2021, and is undergoing 3688 internal testing. Additional internal releases expected within the 3689 coming months, with first public release expected end of 1H2021. 3691 Many AERO/OMNI functions are implemented and undergoing final 3692 integration. OAL fragmentation/reassembly buffer management code has 3693 been cleared for public release and will be presented at the June 3694 2021 ICAO mobility subgroup meeting. 3696 5. IANA Considerations 3698 The IANA is instructed to assign a new type value TBD1 in the IPv6 3699 Routing Types registry (IANA registration procedure is IETF Review or 3700 IESG Approval). 3702 The IANA has assigned the UDP port number "8060" for an earlier 3703 experimental first version of AERO [RFC6706]. This document 3704 obsoletes [RFC6706], and together with [I-D.templin-6man-omni] 3705 reclaims the UDP port number "8060" for 'aero' as the service port 3706 for UDP/IP encapsulation. (Note that, although [RFC6706] was not 3707 widely implemented or deployed, any messages coded to that 3708 specification can be easily distinguished and ignored since they use 3709 the invalid ICMPv6 message type number '0'.) This document makes no 3710 request of IANA, since [I-D.templin-6man-omni] already provides 3711 instructions. 3713 No further IANA actions are required. 3715 6. Security Considerations 3717 AERO Bridges configure secured tunnels with AERO Proxy/Servers and 3718 Relays within their local OMNI link segments. Applicable secured 3719 tunnel alternatives include IPsec [RFC4301], TLS/SSL [RFC8446], DTLS 3721 [RFC6347], WireGuard [WG], etc. The AERO Bridges of all OMNI link 3722 segments in turn configure secured tunnels for their neighboring AERO 3723 Bridges in a secured spanning tree topology. Therefore, control 3724 messages exchanged between any pair of OMNI link neighbors over the 3725 secured spanning tree are already protected. 3727 To prevent spoofing vectors, Proxy/Servers MUST discard without 3728 responding to any unsecured NS(AR) messages. Also, Proxy/Servers 3729 MUST discard without forwarding any original IP packets received from 3730 one of their own Clients (whether directly or following OAL 3731 reassembly) with a source address that does not match the Client's 3732 MNP and/or a destination address that does match the Client's MNP. 3733 Finally, Proxy/Servers MUST discard without forwarding any carrier 3734 packets with an OAL source and destination that both match the same 3735 MNP (i.e., after consulting the ORH if present). 3737 For INET partitions that require strong security in the data plane, 3738 two options for securing communications include 1) disable route 3739 optimization so that all traffic is conveyed over secured tunnels, or 3740 2) enable on-demand secure tunnel creation between Client neighbors. 3741 Option 1) would result in longer routes than necessary and impose 3742 traffic concentration on critical infrastructure elements. Option 2) 3743 could be coordinated between Clients using NS/NA messages with OMNI 3744 Host Identity Protocol (HIP) "Initiator/Responder" message sub- 3745 options [RFC7401][I-D.templin-6man-omni] to create a secured tunnel 3746 on-demand. 3748 AERO Clients that connect to secured ANETs need not apply security to 3749 their ND messages, since the messages will be authenticated and 3750 forwarded by a perimeter Proxy/Server that applies security on its 3751 INET-facing interface as part of the spanning tree (see above). AERO 3752 Clients connected to the open INET can use network and/or transport 3753 layer security services such as VPNs or can by some other means 3754 establish a direct link to a Proxy/Server. When a VPN or direct link 3755 may be impractical, however, INET Clients and Proxy/Servers SHOULD 3756 include and verify authentication signatures for their IPv6 ND 3757 messages as specified in [I-D.templin-6man-omni]. 3759 Application endpoints SHOULD use transport-layer (or higher-layer) 3760 security services such as TLS/SSL, DTLS or SSH [RFC4251] to assure 3761 the same level of protection as for critical secured Internet 3762 services. AERO Clients that require host-based VPN services SHOULD 3763 use network and/or transport layer security services such as IPsec, 3764 TLS/SSL, DTLS, etc. AERO Proxys and Proxy/Servers can also provide a 3765 network-based VPN service on behalf of the Client, e.g., if the 3766 Client is located within a secured enclave and cannot establish a VPN 3767 on its own behalf. 3769 AERO Proxy/Servers and Bridges present targets for traffic 3770 amplification Denial of Service (DoS) attacks. This concern is no 3771 different than for widely-deployed VPN security gateways in the 3772 Internet, where attackers could send spoofed packets to the gateways 3773 at high data rates. This can be mitigated through the AERO/OMNI data 3774 origin authentication procedures, as well as connecting Proxy/Servers 3775 and Bridges over dedicated links with no connections to the Internet 3776 and/or when connections to the Internet are only permitted through 3777 well-managed firewalls. Traffic amplification DoS attacks can also 3778 target an AERO Client's low data rate links. This is a concern not 3779 only for Clients located on the open Internet but also for Clients in 3780 secured enclaves. AERO Proxy/Servers and Proxys can institute rate 3781 limits that protect Clients from receiving packet floods that could 3782 DoS low data rate links. 3784 AERO Relays must implement ingress filtering to avoid a spoofing 3785 attack in which spurious messages with ULA addresses are injected 3786 into an OMNI link from an outside attacker. AERO Clients MUST ensure 3787 that their connectivity is not used by unauthorized nodes on their 3788 EUNs to gain access to a protected network, i.e., AERO Clients that 3789 act as routers MUST NOT provide routing services for unauthorized 3790 nodes. (This concern is no different than for ordinary hosts that 3791 receive an IP address delegation but then "share" the address with 3792 other nodes via some form of Internet connection sharing such as 3793 tethering.) 3795 The MAP list MUST be well-managed and secured from unauthorized 3796 tampering, even though the list contains only public information. 3797 The MAP list can be conveyed to the Client in a similar fashion as in 3798 [RFC5214] (e.g., through layer 2 data link login messaging, secure 3799 upload of a static file, DNS lookups, etc.). 3801 The AERO service for open INET Clients depends on a public key 3802 distribution service in which Client public keys and identities are 3803 maintained in a shared database accessible to all open INET Proxy/ 3804 Servers. Similarly, each Client must be able to determine the public 3805 key of each Proxy/Server, e.g. by consulting an online database. 3806 When AERO nodes register their public keys indexed by a unique Host 3807 Identity Tag (HIT) [RFC7401] in a distributed database such as the 3808 DNS, and use the HIT as an identity for applying IPv6 ND message 3809 authentication signatures, a means for determining public key 3810 attestation is available. 3812 Security considerations for IPv6 fragmentation and reassembly are 3813 discussed in [I-D.templin-6man-omni]. In environments where spoofing 3814 is considered a threat, OMNI nodes SHOULD employ Identification 3815 window synchronization and OAL destinations SHOULD configure an (end- 3816 system-based) firewall. 3818 SRH authentication facilities are specified in [RFC8754]. Security 3819 considerations for accepting link-layer ICMP messages and reflected 3820 packets are discussed throughout the document. 3822 7. Acknowledgements 3824 Discussions in the IETF, aviation standards communities and private 3825 exchanges helped shape some of the concepts in this work. 3826 Individuals who contributed insights include Mikael Abrahamsson, Mark 3827 Andrews, Fred Baker, Bob Braden, Stewart Bryant, Brian Carpenter, 3828 Wojciech Dec, Pavel Drasil, Ralph Droms, Adrian Farrel, Nick Green, 3829 Sri Gundavelli, Brian Haberman, Bernhard Haindl, Joel Halpern, Tom 3830 Herbert, Sascha Hlusiak, Lee Howard, Zdenek Jaron, Andre Kostur, 3831 Hubert Kuenig, Ted Lemon, Andy Malis, Satoru Matsushima, Tomek 3832 Mrugalski, Madhu Niraula, Alexandru Petrescu, Behcet Saikaya, Michal 3833 Skorepa, Joe Touch, Bernie Volz, Ryuji Wakikawa, Tony Whyman, Lloyd 3834 Wood and James Woodyatt. Members of the IESG also provided valuable 3835 input during their review process that greatly improved the document. 3836 Special thanks go to Stewart Bryant, Joel Halpern and Brian Haberman 3837 for their shepherding guidance during the publication of the AERO 3838 first edition. 3840 This work has further been encouraged and supported by Boeing 3841 colleagues including Kyle Bae, M. Wayne Benson, Dave Bernhardt, Cam 3842 Brodie, John Bush, Balaguruna Chidambaram, Irene Chin, Bruce Cornish, 3843 Claudiu Danilov, Don Dillenburg, Joe Dudkowski, Wen Fang, Samad 3844 Farooqui, Anthony Gregory, Jeff Holland, Seth Jahne, Brian Jaury, 3845 Greg Kimberly, Ed King, Madhuri Madhava Badgandi, Laurel Matthew, 3846 Gene MacLean III, Kyle Mikos, Rob Muszkiewicz, Sean O'Sullivan, Vijay 3847 Rajagopalan, Greg Saccone, Rod Santiago, Kent Shuey, Brian Skeen, 3848 Mike Slane, Carrie Spiker, Katie Tran, Brendan Williams, Amelia 3849 Wilson, Julie Wulff, Yueli Yang, Eric Yeh and other members of the 3850 Boeing mobility, networking and autonomy teams. Kyle Bae, Wayne 3851 Benson, Madhuri Madhava Badgandi, Vijayasarathy Rajagopalan, Katie 3852 Tran and Eric Yeh are especially acknowledged for implementing the 3853 AERO functions as extensions to the public domain OpenVPN 3854 distribution. Chuck Klabunde is honored and remembered for his early 3855 leadership, and we mourn his untimely loss. 3857 Earlier works on NBMA tunneling approaches are found in 3858 [RFC2529][RFC5214][RFC5569]. 3860 Many of the constructs presented in this second edition of AERO are 3861 based on the author's earlier works, including: 3863 o The Internet Routing Overlay Network (IRON) 3864 [RFC6179][I-D.templin-ironbis] 3866 o Virtual Enterprise Traversal (VET) 3867 [RFC5558][I-D.templin-intarea-vet] 3869 o The Subnetwork Encapsulation and Adaptation Layer (SEAL) 3870 [RFC5320][I-D.templin-intarea-seal] 3872 o AERO, First Edition [RFC6706] 3874 Note that these works cite numerous earlier efforts that are not also 3875 cited here due to space limitations. The authors of those earlier 3876 works are acknowledged for their insights. 3878 This work is aligned with the NASA Safe Autonomous Systems Operation 3879 (SASO) program under NASA contract number NNA16BD84C. 3881 This work is aligned with the FAA as per the SE2025 contract number 3882 DTFAWA-15-D-00030. 3884 This work is aligned with the Boeing Commercial Airplanes (BCA) 3885 Internet of Things (IoT) and autonomy programs. 3887 This work is aligned with the Boeing Information Technology (BIT) 3888 MobileNet program. 3890 8. References 3892 8.1. Normative References 3894 [I-D.templin-6man-omni] 3895 Templin, F. L. and T. Whyman, "Transmission of IP Packets 3896 over Overlay Multilink Network (OMNI) Interfaces", draft- 3897 templin-6man-omni-03 (work in progress), April 2021. 3899 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, 3900 DOI 10.17487/RFC0791, September 1981, 3901 . 3903 [RFC0792] Postel, J., "Internet Control Message Protocol", STD 5, 3904 RFC 792, DOI 10.17487/RFC0792, September 1981, 3905 . 3907 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 3908 Requirement Levels", BCP 14, RFC 2119, 3909 DOI 10.17487/RFC2119, March 1997, 3910 . 3912 [RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in 3913 IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473, 3914 December 1998, . 3916 [RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander, 3917 "SEcure Neighbor Discovery (SEND)", RFC 3971, 3918 DOI 10.17487/RFC3971, March 2005, 3919 . 3921 [RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)", 3922 RFC 3972, DOI 10.17487/RFC3972, March 2005, 3923 . 3925 [RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and 3926 More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191, 3927 November 2005, . 3929 [RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast 3930 Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005, 3931 . 3933 [RFC4380] Huitema, C., "Teredo: Tunneling IPv6 over UDP through 3934 Network Address Translations (NATs)", RFC 4380, 3935 DOI 10.17487/RFC4380, February 2006, 3936 . 3938 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 3939 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 3940 DOI 10.17487/RFC4861, September 2007, 3941 . 3943 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 3944 Address Autoconfiguration", RFC 4862, 3945 DOI 10.17487/RFC4862, September 2007, 3946 . 3948 [RFC6081] Thaler, D., "Teredo Extensions", RFC 6081, 3949 DOI 10.17487/RFC6081, January 2011, 3950 . 3952 [RFC7401] Moskowitz, R., Ed., Heer, T., Jokela, P., and T. 3953 Henderson, "Host Identity Protocol Version 2 (HIPv2)", 3954 RFC 7401, DOI 10.17487/RFC7401, April 2015, 3955 . 3957 [RFC7739] Gont, F., "Security Implications of Predictable Fragment 3958 Identification Values", RFC 7739, DOI 10.17487/RFC7739, 3959 February 2016, . 3961 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 3962 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 3963 May 2017, . 3965 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 3966 (IPv6) Specification", STD 86, RFC 8200, 3967 DOI 10.17487/RFC8200, July 2017, 3968 . 3970 [RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A., 3971 Richardson, M., Jiang, S., Lemon, T., and T. Winters, 3972 "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", 3973 RFC 8415, DOI 10.17487/RFC8415, November 2018, 3974 . 3976 8.2. Informative References 3978 [BGP] Huston, G., "BGP in 2015, http://potaroo.net", January 3979 2016. 3981 [I-D.bonica-6man-comp-rtg-hdr] 3982 Bonica, R., Kamite, Y., Alston, A., Henriques, D., and L. 3983 Jalil, "The IPv6 Compact Routing Header (CRH)", draft- 3984 bonica-6man-comp-rtg-hdr-24 (work in progress), January 3985 2021. 3987 [I-D.bonica-6man-crh-helper-opt] 3988 Li, X., Bao, C., Ruan, E., and R. Bonica, "Compressed 3989 Routing Header (CRH) Helper Option", draft-bonica-6man- 3990 crh-helper-opt-03 (work in progress), April 2021. 3992 [I-D.ietf-intarea-frag-fragile] 3993 Bonica, R., Baker, F., Huston, G., Hinden, R. M., Troan, 3994 O., and F. Gont, "IP Fragmentation Considered Fragile", 3995 draft-ietf-intarea-frag-fragile-17 (work in progress), 3996 September 2019. 3998 [I-D.ietf-intarea-tunnels] 3999 Touch, J. and M. Townsley, "IP Tunnels in the Internet 4000 Architecture", draft-ietf-intarea-tunnels-10 (work in 4001 progress), September 2019. 4003 [I-D.ietf-ipwave-vehicular-networking] 4004 (editor), J. (. J., "IPv6 Wireless Access in Vehicular 4005 Environments (IPWAVE): Problem Statement and Use Cases", 4006 draft-ietf-ipwave-vehicular-networking-20 (work in 4007 progress), March 2021. 4009 [I-D.ietf-rtgwg-atn-bgp] 4010 Templin, F. L., Saccone, G., Dawra, G., Lindem, A., and V. 4011 Moreno, "A Simple BGP-based Mobile Routing System for the 4012 Aeronautical Telecommunications Network", draft-ietf- 4013 rtgwg-atn-bgp-10 (work in progress), January 2021. 4015 [I-D.templin-6man-dhcpv6-ndopt] 4016 Templin, F. L., "A Unified Stateful/Stateless 4017 Configuration Service for IPv6", draft-templin-6man- 4018 dhcpv6-ndopt-11 (work in progress), January 2021. 4020 [I-D.templin-intarea-seal] 4021 Templin, F. L., "The Subnetwork Encapsulation and 4022 Adaptation Layer (SEAL)", draft-templin-intarea-seal-68 4023 (work in progress), January 2014. 4025 [I-D.templin-intarea-vet] 4026 Templin, F. L., "Virtual Enterprise Traversal (VET)", 4027 draft-templin-intarea-vet-40 (work in progress), May 2013. 4029 [I-D.templin-ipwave-uam-its] 4030 Templin, F. L., "Urban Air Mobility Implications for 4031 Intelligent Transportation Systems", draft-templin-ipwave- 4032 uam-its-04 (work in progress), January 2021. 4034 [I-D.templin-ironbis] 4035 Templin, F. L., "The Interior Routing Overlay Network 4036 (IRON)", draft-templin-ironbis-16 (work in progress), 4037 March 2014. 4039 [I-D.templin-v6ops-pdhost] 4040 Templin, F. L., "IPv6 Prefix Delegation and Multi- 4041 Addressing Models", draft-templin-v6ops-pdhost-27 (work in 4042 progress), January 2021. 4044 [OVPN] OpenVPN, O., "http://openvpn.net", October 2016. 4046 [RFC1035] Mockapetris, P., "Domain names - implementation and 4047 specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, 4048 November 1987, . 4050 [RFC1812] Baker, F., Ed., "Requirements for IP Version 4 Routers", 4051 RFC 1812, DOI 10.17487/RFC1812, June 1995, 4052 . 4054 [RFC2003] Perkins, C., "IP Encapsulation within IP", RFC 2003, 4055 DOI 10.17487/RFC2003, October 1996, 4056 . 4058 [RFC2004] Perkins, C., "Minimal Encapsulation within IP", RFC 2004, 4059 DOI 10.17487/RFC2004, October 1996, 4060 . 4062 [RFC2236] Fenner, W., "Internet Group Management Protocol, Version 4063 2", RFC 2236, DOI 10.17487/RFC2236, November 1997, 4064 . 4066 [RFC2464] Crawford, M., "Transmission of IPv6 Packets over Ethernet 4067 Networks", RFC 2464, DOI 10.17487/RFC2464, December 1998, 4068 . 4070 [RFC2529] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4 4071 Domains without Explicit Tunnels", RFC 2529, 4072 DOI 10.17487/RFC2529, March 1999, 4073 . 4075 [RFC2983] Black, D., "Differentiated Services and Tunnels", 4076 RFC 2983, DOI 10.17487/RFC2983, October 2000, 4077 . 4079 [RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition 4080 of Explicit Congestion Notification (ECN) to IP", 4081 RFC 3168, DOI 10.17487/RFC3168, September 2001, 4082 . 4084 [RFC3330] IANA, "Special-Use IPv4 Addresses", RFC 3330, 4085 DOI 10.17487/RFC3330, September 2002, 4086 . 4088 [RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener 4089 Discovery Version 2 (MLDv2) for IPv6", RFC 3810, 4090 DOI 10.17487/RFC3810, June 2004, 4091 . 4093 [RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally 4094 Unique IDentifier (UUID) URN Namespace", RFC 4122, 4095 DOI 10.17487/RFC4122, July 2005, 4096 . 4098 [RFC4251] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH) 4099 Protocol Architecture", RFC 4251, DOI 10.17487/RFC4251, 4100 January 2006, . 4102 [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A 4103 Border Gateway Protocol 4 (BGP-4)", RFC 4271, 4104 DOI 10.17487/RFC4271, January 2006, 4105 . 4107 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 4108 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 4109 2006, . 4111 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 4112 Internet Protocol", RFC 4301, DOI 10.17487/RFC4301, 4113 December 2005, . 4115 [RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery 4116 Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April 4117 2006, . 4119 [RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet 4120 Control Message Protocol (ICMPv6) for the Internet 4121 Protocol Version 6 (IPv6) Specification", STD 89, 4122 RFC 4443, DOI 10.17487/RFC4443, March 2006, 4123 . 4125 [RFC4511] Sermersheim, J., Ed., "Lightweight Directory Access 4126 Protocol (LDAP): The Protocol", RFC 4511, 4127 DOI 10.17487/RFC4511, June 2006, 4128 . 4130 [RFC4541] Christensen, M., Kimball, K., and F. Solensky, 4131 "Considerations for Internet Group Management Protocol 4132 (IGMP) and Multicast Listener Discovery (MLD) Snooping 4133 Switches", RFC 4541, DOI 10.17487/RFC4541, May 2006, 4134 . 4136 [RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick, 4137 "Internet Group Management Protocol (IGMP) / Multicast 4138 Listener Discovery (MLD)-Based Multicast Forwarding 4139 ("IGMP/MLD Proxying")", RFC 4605, DOI 10.17487/RFC4605, 4140 August 2006, . 4142 [RFC4982] Bagnulo, M. and J. Arkko, "Support for Multiple Hash 4143 Algorithms in Cryptographically Generated Addresses 4144 (CGAs)", RFC 4982, DOI 10.17487/RFC4982, July 2007, 4145 . 4147 [RFC5015] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano, 4148 "Bidirectional Protocol Independent Multicast (BIDIR- 4149 PIM)", RFC 5015, DOI 10.17487/RFC5015, October 2007, 4150 . 4152 [RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site 4153 Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214, 4154 DOI 10.17487/RFC5214, March 2008, 4155 . 4157 [RFC5320] Templin, F., Ed., "The Subnetwork Encapsulation and 4158 Adaptation Layer (SEAL)", RFC 5320, DOI 10.17487/RFC5320, 4159 February 2010, . 4161 [RFC5522] Eddy, W., Ivancic, W., and T. Davis, "Network Mobility 4162 Route Optimization Requirements for Operational Use in 4163 Aeronautics and Space Exploration Mobile Networks", 4164 RFC 5522, DOI 10.17487/RFC5522, October 2009, 4165 . 4167 [RFC5558] Templin, F., Ed., "Virtual Enterprise Traversal (VET)", 4168 RFC 5558, DOI 10.17487/RFC5558, February 2010, 4169 . 4171 [RFC5569] Despres, R., "IPv6 Rapid Deployment on IPv4 4172 Infrastructures (6rd)", RFC 5569, DOI 10.17487/RFC5569, 4173 January 2010, . 4175 [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 4176 (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, 4177 . 4179 [RFC6106] Jeong, J., Park, S., Beloeil, L., and S. Madanapalli, 4180 "IPv6 Router Advertisement Options for DNS Configuration", 4181 RFC 6106, DOI 10.17487/RFC6106, November 2010, 4182 . 4184 [RFC6139] Russert, S., Ed., Fleischman, E., Ed., and F. Templin, 4185 Ed., "Routing and Addressing in Networks with Global 4186 Enterprise Recursion (RANGER) Scenarios", RFC 6139, 4187 DOI 10.17487/RFC6139, February 2011, 4188 . 4190 [RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful 4191 NAT64: Network Address and Protocol Translation from IPv6 4192 Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146, 4193 April 2011, . 4195 [RFC6179] Templin, F., Ed., "The Internet Routing Overlay Network 4196 (IRON)", RFC 6179, DOI 10.17487/RFC6179, March 2011, 4197 . 4199 [RFC6221] Miles, D., Ed., Ooghe, S., Dec, W., Krishnan, S., and A. 4200 Kavanagh, "Lightweight DHCPv6 Relay Agent", RFC 6221, 4201 DOI 10.17487/RFC6221, May 2011, 4202 . 4204 [RFC6273] Kukec, A., Krishnan, S., and S. Jiang, "The Secure 4205 Neighbor Discovery (SEND) Hash Threat Analysis", RFC 6273, 4206 DOI 10.17487/RFC6273, June 2011, 4207 . 4209 [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer 4210 Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, 4211 January 2012, . 4213 [RFC6355] Narten, T. and J. Johnson, "Definition of the UUID-Based 4214 DHCPv6 Unique Identifier (DUID-UUID)", RFC 6355, 4215 DOI 10.17487/RFC6355, August 2011, 4216 . 4218 [RFC6438] Carpenter, B. and S. Amante, "Using the IPv6 Flow Label 4219 for Equal Cost Multipath Routing and Link Aggregation in 4220 Tunnels", RFC 6438, DOI 10.17487/RFC6438, November 2011, 4221 . 4223 [RFC6706] Templin, F., Ed., "Asymmetric Extended Route Optimization 4224 (AERO)", RFC 6706, DOI 10.17487/RFC6706, August 2012, 4225 . 4227 [RFC6935] Eubanks, M., Chimento, P., and M. Westerlund, "IPv6 and 4228 UDP Checksums for Tunneled Packets", RFC 6935, 4229 DOI 10.17487/RFC6935, April 2013, 4230 . 4232 [RFC6936] Fairhurst, G. and M. Westerlund, "Applicability Statement 4233 for the Use of IPv6 UDP Datagrams with Zero Checksums", 4234 RFC 6936, DOI 10.17487/RFC6936, April 2013, 4235 . 4237 [RFC7333] Chan, H., Ed., Liu, D., Seite, P., Yokota, H., and J. 4238 Korhonen, "Requirements for Distributed Mobility 4239 Management", RFC 7333, DOI 10.17487/RFC7333, August 2014, 4240 . 4242 [RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I., 4243 Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent 4244 Multicast - Sparse Mode (PIM-SM): Protocol Specification 4245 (Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March 4246 2016, . 4248 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 4249 Decraene, B., Litkowski, S., and R. Shakir, "Segment 4250 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 4251 July 2018, . 4253 [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol 4254 Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, 4255 . 4257 [RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J., 4258 Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header 4259 (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020, 4260 . 4262 [WG] Wireguard, "WireGuard, https://www.wireguard.com", August 4263 2020. 4265 Appendix A. Non-Normative Considerations 4267 AERO can be applied to a multitude of Internetworking scenarios, with 4268 each having its own adaptations. The following considerations are 4269 provided as non-normative guidance: 4271 A.1. Implementation Strategies for Route Optimization 4273 Route optimization as discussed in Section 3.14 results in the route 4274 optimization source (ROS) creating a NCE for the target neighbor. 4275 The NCE state is set to REACHABLE for at most ReachableTime seconds. 4276 In order to refresh the NCE lifetime before the ReachableTime timer 4277 expires, the specification requires implementations to issue a new 4278 NS/NA exchange to reset ReachableTime while data packets are still 4279 flowing. However, the decision of when to initiate a new NS/NA 4280 exchange and to perpetuate the process is left as an implementation 4281 detail. 4283 One possible strategy may be to monitor the NCE watching for data 4284 packets for (ReachableTime - 5) seconds. If any data packets have 4285 been sent to the neighbor within this timeframe, then send an NS to 4286 receive a new NA. If no data packets have been sent, wait for 5 4287 additional seconds and send an immediate NS if any data packets are 4288 sent within this "expiration pending" 5 second window. If no 4289 additional data packets are sent within the 5 second window, reset 4290 the NCE state to STALE. 4292 The monitoring of the neighbor data packet traffic therefore becomes 4293 an ongoing process during the NCE lifetime. If the NCE expires, 4294 future data packets will trigger a new NS/NA exchange while the 4295 packets themselves are delivered over a longer path until route 4296 optimization state is re-established. 4298 A.2. Implicit Mobility Management 4300 OMNI interface neighbors MAY provide a configuration option that 4301 allows them to perform implicit mobility management in which no ND 4302 messaging is used. In that case, the Client only transmits packets 4303 over a single interface at a time, and the neighbor always observes 4304 packets arriving from the Client from the same link-layer source 4305 address. 4307 If the Client's underlying interface address changes (either due to a 4308 readdressing of the original interface or switching to a new 4309 interface) the neighbor immediately updates the NCE for the Client 4310 and begins accepting and sending packets according to the Client's 4311 new address. This implicit mobility method applies to use cases such 4312 as cellphones with both WiFi and Cellular interfaces where only one 4313 of the interfaces is active at a given time, and the Client 4314 automatically switches over to the backup interface if the primary 4315 interface fails. 4317 A.3. Direct Underlying Interfaces 4319 When a Client's OMNI interface is configured over a Direct interface, 4320 the neighbor at the other end of the Direct link can receive packets 4321 without any encapsulation. In that case, the Client sends packets 4322 over the Direct link according to traffic selectors. If the Direct 4323 interface is selected, then the Client's IP packets are transmitted 4324 directly to the peer without going through an ANET/INET. If other 4325 interfaces are selected, then the Client's IP packets are transmitted 4326 via a different interface, which may result in the inclusion of 4327 Proxy/Servers and Bridges in the communications path. Direct 4328 interfaces must be tested periodically for reachability, e.g., via 4329 NUD. 4331 A.4. AERO Critical Infrastructure Considerations 4333 AERO Bridges can be either Commercial off-the Shelf (COTS) standard 4334 IP routers or virtual machines in the cloud. Bridges must be 4335 provisioned, supported and managed by the INET administrative 4336 authority, and connected to the Bridges of other INETs via inter- 4337 domain peerings. Cost for purchasing, configuring and managing 4338 Bridges is nominal even for very large OMNI links. 4340 AERO cloud Proxy/Servers can be standard dedicated server platforms, 4341 but most often will be deployed as virtual machines in the cloud. 4342 The only requirements for cloud Proxy/Servers are that they can run 4343 the AERO user-level code and have at least one network interface 4344 connection to the INET. Cloud Proxy/Servers must be provisioned, 4345 supported and managed by the INET administrative authority. Cost for 4346 purchasing, configuring and managing cloud Proxy/Servers is nominal 4347 especially for virtual machines. 4349 AERO ANET Proxy/Servers are most often standard dedicated server 4350 platforms with one underlying interface connected to the ANET and a 4351 second interface connected to an INET. As with cloud Proxy/Servers, 4352 the only requirements are that they can run the AERO user-level code 4353 and have at least one interface connection to the INET. ANET Proxy/ 4354 Servers must be provisioned, supported and managed by the ANET 4355 administrative authority. Cost for purchasing, configuring and 4356 managing Proxys is nominal, and borne by the ANET administrative 4357 authority. 4359 AERO Relays are simply Proxy/Servers connected to INETs and/or EUNs 4360 that provide forwarding services for non-MNP destinations. The Relay 4361 connects to the OMNI link and engages in eBGP peering with one or 4362 more Bridges as a stub AS. The Relay then injects its MNPs and/or 4363 non-MNP prefixes into the BGP routing system, and provisions the 4364 prefixes to its downstream-attached networks. The Relay can perform 4365 ROS/ROR services the same as for any Proxy/Server, and can route 4366 between the MNP and non-MNP address spaces. 4368 A.5. AERO Server Failure Implications 4370 AERO Proxy/Servers may appear as a single point of failure in the 4371 architecture, but such is not the case since all Proxy/Servers on the 4372 link provide identical services and loss of a Proxy/Server does not 4373 imply immediate and/or comprehensive communication failures. Proxy/ 4374 Server failure is quickly detected and conveyed by Bidirectional 4375 Forward Detection (BFD) and/or proactive NUD allowing Clients to 4376 migrate to new Proxy/Servers. 4378 If a Proxy/Server fails, ongoing packet forwarding to Clients will 4379 continue by virtue of the neighbor cache entries that have already 4380 been established in route optimization sources (ROSs). If a Client 4381 also experiences mobility events at roughly the same time the Proxy/ 4382 Server fails, unsolicited NA messages may be lost but neighbor cache 4383 entries in the DEPARTED state will ensure that packet forwarding to 4384 the Client's new locations will continue for up to DepartTime 4385 seconds. 4387 If a Client is left without a Proxy/Server for a considerable length 4388 of time (e.g., greater than ReachableTime seconds) then existing 4389 neighbor cache entries will eventually expire and both ongoing and 4390 new communications will fail. The original source will continue to 4391 retransmit until the Client has established a new Proxy/Server 4392 relationship, after which time continuous communications will resume. 4394 Therefore, providing many Proxy/Servers on the link with high 4395 availability profiles provides resilience against loss of individual 4396 Proxy/Servers and assurance that Clients can establish new Proxy/ 4397 Server relationships quickly in event of a Proxy/Server failure. 4399 A.6. AERO Client / Server Architecture 4401 The AERO architectural model is client / server in the control plane, 4402 with route optimization in the data plane. The same as for common 4403 Internet services, the AERO Client discovers the addresses of AERO 4404 Proxy/Servers and connects to one or more of them. The AERO service 4405 is analogous to common Internet services such as google.com, 4406 yahoo.com, cnn.com, etc. However, there is only one AERO service for 4407 the link and all Proxy/Servers provide identical services. 4409 Common Internet services provide differing strategies for advertising 4410 server addresses to clients. The strategy is conveyed through the 4411 DNS resource records returned in response to name resolution queries. 4412 As of January 2020 Internet-based 'nslookup' services were used to 4413 determine the following: 4415 o When a client resolves the domainname "google.com", the DNS always 4416 returns one A record (i.e., an IPv4 address) and one AAAA record 4417 (i.e., an IPv6 address). The client receives the same addresses 4418 each time it resolves the domainname via the same DNS resolver, 4419 but may receive different addresses when it resolves the 4420 domainname via different DNS resolvers. But, in each case, 4421 exactly one A and one AAAA record are returned. 4423 o When a client resolves the domainname "ietf.org", the DNS always 4424 returns one A record and one AAAA record with the same addresses 4425 regardless of which DNS resolver is used. 4427 o When a client resolves the domainname "yahoo.com", the DNS always 4428 returns a list of 4 A records and 4 AAAA records. Each time the 4429 client resolves the domainname via the same DNS resolver, the same 4430 list of addresses are returned but in randomized order (i.e., 4431 consistent with a DNS round-robin strategy). But, interestingly, 4432 the same addresses are returned (albeit in randomized order) when 4433 the domainname is resolved via different DNS resolvers. 4435 o When a client resolves the domainname "amazon.com", the DNS always 4436 returns a list of 3 A records and no AAAA records. As with 4437 "yahoo.com", the same three A records are returned from any 4438 worldwide Internet connection point in randomized order. 4440 The above example strategies show differing approaches to Internet 4441 resilience and service distribution offered by major Internet 4442 services. The Google approach exposes only a single IPv4 and a 4443 single IPv6 address to clients. Clients can then select whichever IP 4444 protocol version offers the best response, but will always use the 4445 same IP address according to the current Internet connection point. 4446 This means that the IP address offered by the network must lead to a 4447 highly-available server and/or service distribution point. In other 4448 words, resilience is predicated on high availability within the 4449 network and with no client-initiated failovers expected (i.e., it is 4450 all-or-nothing from the client's perspective). However, Google does 4451 provide for worldwide distributed service distribution by virtue of 4452 the fact that each Internet connection point responds with a 4453 different IPv6 and IPv4 address. The IETF approach is like google 4454 (all-or-nothing from the client's perspective), but provides only a 4455 single IPv4 or IPv6 address on a worldwide basis. This means that 4456 the addresses must be made highly-available at the network level with 4457 no client failover possibility, and if there is any worldwide service 4458 distribution it would need to be conducted by a network element that 4459 is reached via the IP address acting as a service distribution point. 4461 In contrast to the Google and IETF philosophies, Yahoo and Amazon 4462 both provide clients with a (short) list of IP addresses with Yahoo 4463 providing both IP protocol versions and Amazon as IPv4-only. The 4464 order of the list is randomized with each name service query 4465 response, with the effect of round-robin load balancing for service 4466 distribution. With a short list of addresses, there is still 4467 expectation that the network will implement high availability for 4468 each address but in case any single address fails the client can 4469 switch over to using a different address. The balance then becomes 4470 one of function in the network vs function in the end system. 4472 The same implications observed for common highly-available services 4473 in the Internet apply also to the AERO client/server architecture. 4474 When an AERO Client connects to one or more ANETs, it discovers one 4475 or more AERO Proxy/Server addresses through the mechanisms discussed 4476 in earlier sections. Each Proxy/Server address presumably leads to a 4477 fault-tolerant clustering arrangement such as supported by Linux-HA, 4478 Extended Virtual Synchrony or Paxos. Such an arrangement has 4479 precedence in common Internet service deployments in lightweight 4480 virtual machines without requiring expensive hardware deployment. 4481 Similarly, common Internet service deployments set service IP 4482 addresses on service distribution points that may relay requests to 4483 many different servers. 4485 For AERO, the expectation is that a combination of the Google/IETF 4486 and Yahoo/Amazon philosophies would be employed. The AERO Client 4487 connects to different ANET access points and can receive 1-2 Proxy/ 4488 Server ADM-LLAs at each point. It then selects one AERO Proxy/Server 4489 address, and engages in RS/RA exchanges with the same Proxy/Server 4490 from all ANET connections. The Client remains with this Proxy/Server 4491 unless or until the Proxy/Server fails, in which case it can switch 4492 over to an alternate Proxy/Server. The Client can likewise switch 4493 over to a different Proxy/Server at any time if there is some reason 4494 for it to do so. So, the AERO expectation is for a balance of 4495 function in the network and end system, with fault tolerance and 4496 resilience at both levels. 4498 Appendix B. Change Log 4500 << RFC Editor - remove prior to publication >> 4502 Changes from draft-templin-6man-aero-11 to draft-templin-6man-aero- 4503 12: 4505 o Final editorial review pass resulting in multiple changes. 4506 Document now submit for final approval (with reference to rfcdiff 4507 from previous version). 4509 Changes from draft-templin-6man-aero-10 to draft-templin-6man-aero- 4510 11: 4512 o Final editorial review pass resulting in multiple changes. 4513 Document now submit for final approval (with reference to rfcdiff 4514 from previous version). 4516 Changes from draft-templin-6man-aero-09 to draft-templin-6man-aero- 4517 10: 4519 o Final editorial review pass resulting in multiple changes. 4520 Document now submit for final approval (with reference to rfcdiff 4521 from previous version). 4523 Changes from draft-templin-6man-aero-08 to draft-templin-6man-aero- 4524 09: 4526 o Final editorial review pass resulting in multiple changes. 4527 Document now submit for final approval (with reference to rfcdiff 4528 from previous version). 4530 Changes from draft-templin-6man-aero-07 to draft-templin-6man-aero- 4531 08: 4533 o Final editorial review pass resulting in multiple changes. 4534 Document now submit for final approval (with reference to rfcdiff 4535 from previous version). 4537 Changes from draft-templin-6man-aero-06 to draft-templin-6man-aero- 4538 07: 4540 o Final editorial review pass resulting in multiple changes. 4541 Document now submit for final approval (with reference to rfcdiff 4542 from previous version). 4544 Changes from draft-templin-6man-aero-05 to draft-templin-6man-aero- 4545 06: 4547 o Final editorial review pass resulting in multiple changes. 4548 Document now submit for final approval. 4550 Changes from draft-templin-6man-aero-04 to draft-templin-6man-aero- 4551 05: 4553 o Changed to use traffic selectors instead of the former multilink 4554 selection strategy. 4556 Changes from draft-templin-6man-aero-03 to draft-templin-6man-aero- 4557 04: 4559 o Removed documents from "Obsoletes" list. 4561 o Introduced the concept of "secured" and "unsecured" spanning tree. 4563 o Additional security considerations. 4565 o Additional route optimization considerations. 4567 Changes from draft-templin-6man-aero-02 to draft-templin-6man-aero- 4568 03: 4570 o Support for extended route optimization from ROR to target over 4571 target's underlying interfaces. 4573 Changes from draft-templin-6man-aero-01 to draft-templin-6man-aero- 4574 02: 4576 o Changed reference citations to "draft-templin-6man-omni". 4578 o Several important updates to IPv6 ND cache states and route 4579 optimization message addressing. 4581 o Included introductory description of the "6M's". 4583 o Updated Multicast specification. 4585 Changes from draft-templin-6man-aero-00 to draft-templin-6man-aero- 4586 01: 4588 o Changed category to "Informational". 4590 o Updated implementation status. 4592 Changes from earlier versions to draft-templin-6man-aero-00: 4594 o Established working baseline reference. 4596 Author's Address 4598 Fred L. Templin (editor) 4599 Boeing Research & Technology 4600 P.O. Box 3707 4601 Seattle, WA 98124 4602 USA 4604 Email: fltemplin@acm.org