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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 11, 2021 5 Expires: December 13, 2021 7 Asymmetric Extended Route Optimization (AERO) 8 draft-templin-6man-aero-16 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 end 23 user devices 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 13, 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 . . . . . . . 27 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 . . . . . . 36 79 3.5.3. OMNI Neighbor Window Synchronization . . . . . . . . 37 80 3.6. OMNI Interface Encapsulation and Re-encapsulation . . . . 37 81 3.7. OMNI Interface Decapsulation . . . . . . . . . . . . . . 37 82 3.8. OMNI Interface Data Origin Authentication . . . . . . . . 38 83 3.9. OMNI Interface MTU . . . . . . . . . . . . . . . . . . . 38 84 3.10. OMNI Interface Forwarding Algorithm . . . . . . . . . . . 39 85 3.10.1. Client Forwarding Algorithm . . . . . . . . . . . . 40 86 3.10.2. Proxy/Server and Relay Forwarding Algorithm . . . . 42 87 3.10.3. Bridge Forwarding Algorithm . . . . . . . . . . . . 45 88 3.11. OMNI Interface Error Handling . . . . . . . . . . . . . . 46 89 3.12. AERO Router Discovery, Prefix Delegation and 90 Autoconfiguration . . . . . . . . . . . . . . . . . . . . 49 91 3.12.1. AERO Service Model . . . . . . . . . . . . . . . . . 49 92 3.12.2. AERO Client Behavior . . . . . . . . . . . . . . . . 50 93 3.12.3. AERO Proxy/Server Behavior . . . . . . . . . . . . . 52 94 3.13. The AERO Proxy Function . . . . . . . . . . . . . . . . . 55 95 3.13.1. Detecting and Responding to Proxy/Server Failures . 58 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 . . . . . . . . . . . 60 100 3.14.2. Relaying the NS(AR) *NET Packet(s) . . . . . . . . . 61 101 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) . . . . . . . . . . . . . . . 63 104 3.14.6. Forwarding Packets to Route Optimized Targets . . . 63 105 3.15. Neighbor Unreachability Detection (NUD) . . . . . . . . . 66 106 3.16. Mobility Management and Quality of Service (QoS) . . . . 68 107 3.16.1. Mobility Update Messaging . . . . . . . . . . . . . 68 108 3.16.2. Announcing Link-Layer Address and/or QoS Preference 109 Changes . . . . . . . . . . . . . . . . . . . . . . 70 110 3.16.3. Bringing New Links Into Service . . . . . . . . . . 70 111 3.16.4. Deactivating Existing Links . . . . . . . . . . . . 70 112 3.16.5. Moving Between Proxy/Servers . . . . . . . . . . . . 71 113 3.17. Multicast . . . . . . . . . . . . . . . . . . . . . . . . 72 114 3.17.1. Source-Specific Multicast (SSM) . . . . . . . . . . 72 115 3.17.2. Any-Source Multicast (ASM) . . . . . . . . . . . . . 74 116 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 . . . . . . . . . . 76 120 3.21. Detecting and Reacting to Proxy/Server and Bridge 121 Failures . . . . . . . . . . . . . . . . . . . . . . . . 76 122 3.22. AERO Clients on the Open Internet . . . . . . . . . . . . 77 123 3.23. Time-Varying MNPs . . . . . . . . . . . . . . . . . . . . 79 124 4. Implementation Status . . . . . . . . . . . . . . . . . . . . 79 125 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 80 126 6. Security Considerations . . . . . . . . . . . . . . . . . . . 80 127 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 82 128 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 84 129 8.1. Normative References . . . . . . . . . . . . . . . . . . 84 130 8.2. Informative References . . . . . . . . . . . . . . . . . 86 131 Appendix A. Non-Normative Considerations . . . . . . . . . . . . 92 132 A.1. Implementation Strategies for Route Optimization . . . . 92 133 A.2. Implicit Mobility Management . . . . . . . . . . . . . . 93 134 A.3. Direct Underlying Interfaces . . . . . . . . . . . . . . 93 135 A.4. AERO Critical Infrastructure Considerations . . . . . . . 94 136 A.5. AERO Server Failure Implications . . . . . . . . . . . . 94 137 A.6. AERO Client / Server Architecture . . . . . . . . . . . . 95 138 Appendix B. Change Log . . . . . . . . . . . . . . . . . . . . . 97 139 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 100 141 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 multilink operation for increased reliability and path optimization 155 while providing fragmentation and reassembly services to support 156 Maximum Transmission Unit (MTU) diversity. In terms of precedence, 157 readers may appreciate reading this specification first to gain an 158 understanding of the overall architecture and mobility services then 159 return to the OMNI specification for a deeper analysis of the NBMA 160 link model. 162 The AERO service comprises Clients, Proxy/Servers and Relays that are 163 seen as OMNI link neighbors as well as Bridges that interconnect 164 diverse Internetworks as OMNI link segments through OAL forwarding at 165 a layer below IP. Each node's OMNI interface uses an IPv6 link-local 166 address format that supports operation of the IPv6 Neighbor Discovery 167 (ND) protocol [RFC4861] and links ND to IP forwarding. A node's OMNI 168 interface can be configured over multiple underlying interfaces, and 169 therefore appears as a single interface with multiple link-layer 170 addresses. Each link-layer address is subject to change due to 171 mobility and/or multilink fluctuations, and link-layer address 172 changes are signaled by ND messaging the same as for any IPv6 link. 174 AERO provides a secure cloud-based service where mobile node Clients 175 may use any Proxy/Server acting as a Mobility Anchor Point (MAP) and 176 fixed nodes may use any Relay on the link for efficient 177 communications. Fixed nodes forward original IP packets destined to 178 other AERO nodes via the nearest Relay, which forwards them through 179 the cloud. Mobile node Clients discover shortest paths to OMNI link 180 neighbors through AERO route optimization. Both unicast and 181 multicast communications are supported, and Clients may efficiently 182 move between locations while maintaining continuous communications 183 with correspondents and without changing their IP Address. 185 AERO Bridges peer with Proxy/Servers in a secured private BGP overlay 186 routing instance to provide a Segment Routing Topology (SRT) that 187 allows the OAL to span the underlying Internetworks of multiple 188 disjoint administrative domains as a single unified OMNI link at a 189 layer below IP. Each OMNI link instance is characterized by the set 190 of Mobility Service Prefixes (MSPs) common to all mobile nodes. 191 Relays provide an optimal route from (fixed) correspondent nodes on 192 the underlying Internetwork to (mobile or fixed) nodes on the OMNI 193 link. To the underlying Internetwork, the Relay is the source of a 194 route to the MSP; hence uplink traffic to the mobile node is 195 naturally routed to the nearest Relay. A Relay can be considered as 196 a simple case of a Proxy/Server that provides only forwarding and not 197 proxying services. 199 AERO can be used with OMNI links that span private-use Internetworks 200 and/or public Internetworks such as the global Internet. In the 201 latter case, some end systems may be located behind global Internet 202 Network Address Translators (NATs). A means for robust traversal of 203 NATs while avoiding "triangle routing" and Proxy/Server traffic 204 concentration 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 provides a secure aeronautical internetworking service for both 214 manned and unmanned aircraft, where the aircraft is treated as a 215 mobile node that can connect an Internet of Things (IoT). AERO is 216 also applicable to a wide variety of other use cases. For example, 217 it can be used to coordinate the links of mobile nodes (e.g., 218 cellphones, tablets, laptop computers, etc.) that connect into a home 219 enterprise network via public access networks with VPN or non-VPN 220 services enabled according to the appropriate security model. AERO 221 can also be used to facilitate terrestrial vehicular and urban air 222 mobility (as well as pedestrian communication services) for future 223 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 network topology with a coherent IP routing and addressing plan 299 and that provides a transit backbone service for its connected end 300 systems. INETs also provide an underlay service over which the 301 AERO virtual link is configured. Example INETs include corporate 302 enterprise networks, aviation networks, and the public Internet 303 itself. When there is no administrative boundary between an ANET 304 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 intermediate nodes in a spanning tree the same 337 as 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; AERO nodes can use 340 Segment Routing [RFC8402] to cause packets to visit selected 341 waypoints on 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 service that subjects original IP packets 352 admitted into the interface to mid-layer IPv6 header encapsulation 353 followed by 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 node that provides a proxying service between AERO Clients and 456 external peers on its Client-facing ANET interfaces (i.e., in the 457 same fashion as for an enterprise network proxy) as well as 458 default forwarding and Mobility Anchor Point (MAP) services for 459 coordination with correspondents on its INET-facing interfaces. 460 (Proxy/Servers in the open INET instead configure only an INET 461 interface and no ANET interfaces.) The Proxy/Server configures an 462 OMNI interface and assigns an ADM-LLA to support the operation of 463 IPv6 ND services, while advertising all of its associated MNPs via 464 BGP peerings with Bridges. Note that the Proxy and Server 465 functions can be considered logically separable, but since each 466 Proxy/Server must be informed of all of the Client's other 467 multilink Proxy/Server affiliations the AERO service is best 468 supported when the two functions are coresident on the same 469 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 networks and links. AERO Relays configure an OMNI 475 interface and assign an ADM-LLA the same as Proxy/Servers, and 476 also run a dynamic routing protocol to discover any non-MNP IP GUA 477 routes in service on its connected downstream network links. The 478 Relay advertises the MSP(s) to its downstream networks, and 479 redistributes downstream network routes into the OMNI link routing 480 system the same as for Proxy/Servers. 482 AERO Bridge ("Bridge") 483 a BGP hub autonomous system node that also provides OAL forwarding 484 services (as well as a security trust anchor) for nodes on an OMNI 485 link. The Bridge forwards carrier packets between OMNI link 486 segments as an OAL intermediate node while decrementing the OAL 487 IPv6 header Hop Limit but without decrementing the network layer 488 IP TTL/Hop Limit. Bridges peer with Proxy/Servers and other 489 Bridges over an OMNI link secured spanning tree to discover the 490 full set of MNPs for the link as well as any non-MNP IP GUA routes 491 reached via Relays. 493 First-Hop Segment (FHS) Proxy/Server 494 a Proxy/Server for an underlying interface of the source Client 495 that forwards packets sent by the source Client over that 496 interface into the segment routing topology. 498 Last-Hop Segment (LHS) Proxy/Server 499 a Proxy/Server for an underlying interface of the target Client 500 that forwards packets received from the segment routing topology 501 to the target Client over that interface. 503 Segment Routing Topology (SRT) 504 a multinet forwarding region between the FHS Proxy/Server and LHS 505 Proxy/Server. FHS/LHS Proxy/Servers and SRT Bridges span the OMNI 506 link on behalf of source/target Client pairs. The SRT maintains a 507 spanning tree established through BGP peerings between Bridges and 508 Proxy/Servers. Each SRT segment includes Bridges in a "hub" and 509 Proxy/Servers in "spokes", while adjacent segments are 510 interconnected by Bridge-Bridge peerings. The BGP peerings are 511 configured over both secured and unsecured underlying network 512 paths such that a secured spanning tree is available for critical 513 control messages while other messages can use the unsecured 514 spanning tree. 516 link-layer address 517 an IP address used as an encapsulation header source or 518 destination address from the perspective of the OMNI interface. 519 When an upper layer protocol (e.g., UDP) is used as part of the 520 encapsulation, the port number is also considered as part of the 521 link-layer address. 523 network layer address 524 the source or destination address of an original IP packet 525 presented to the OMNI interface. 527 end user network (EUN) 528 an internal virtual or external edge IP network that an AERO 529 Client or Relay connects to the rest of the network via the OMNI 530 interface. The Client/Relay sees each EUN as a "downstream" 531 network, and sees the OMNI interface as the point of attachment to 532 the "upstream" network. 534 Mobile Node (MN) 535 an AERO Client and all of its downstream-attached networks that 536 move together as a single unit, i.e., an end system that connects 537 an Internet of Things. 539 Mobile Router (MR) 540 a MN's on-board router that forwards original IP packets between 541 any downstream-attached networks and the OMNI link. The MR is the 542 MN entity that hosts the AERO Client. 544 Route Optimization Source (ROS) 545 the AERO node nearest the source that initiates route 546 optimization. The ROS may be a FHS Proxy/Server or Relay for the 547 source, or may be the source Client itself. 549 Route Optimization responder (ROR) 550 the AERO node that responds to route optimization requests on 551 behalf of the target. The ROR may be an LHS Proxy/Server for a 552 target MNP Client or an LHS Relay for a non-MNP target. 554 MAP List 555 a geographically and/or topologically referenced list of addresses 556 of all Proxy/Servers within the same OMNI link. Each OMNI link 557 has its own MAP list. 559 Distributed Mobility Management (DMM) 560 a BGP-based overlay routing service coordinated by Proxy/Servers 561 and Bridges that tracks all Proxy/Server-to-Client associations. 563 Mobility Service (MS) 564 the collective set of all Proxy/Servers, Bridges and Relays that 565 provide the AERO Service to Clients. 567 Mobility Service Endpoint MSE) 568 an individual Proxy/Server, Bridge or Relay in the Mobility 569 Service. 571 Throughout the document, the simple terms "Client", "Proxy/Server", 572 "Bridge" and "Relay" refer to "AERO Client", "AERO Proxy/Server", 573 "AERO Bridge" and "AERO Relay", respectively. Capitalization is used 574 to distinguish these terms from other common Internetworking uses in 575 which they appear without capitalization. 577 The terminology of IPv6 ND [RFC4861] and DHCPv6 [RFC8415] (including 578 the names of node variables, messages and protocol constants) is used 579 throughout this document. The terms "All-Routers multicast", "All- 580 Nodes multicast", "Solicited-Node multicast" and "Subnet-Router 581 anycast" are defined in [RFC4291]. Also, the term "IP" is used to 582 generically refer to either Internet Protocol version, i.e., IPv4 583 [RFC0791] or IPv6 [RFC8200]. 585 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 586 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 587 "OPTIONAL" in this document are to be interpreted as described in BCP 588 14 [RFC2119][RFC8174] when, and only when, they appear in all 589 capitals, as shown here. 591 3. Asymmetric Extended Route Optimization (AERO) 593 The following sections specify the operation of IP over OMNI links 594 using the AERO service: 596 3.1. AERO Node Types 598 AERO Clients are Mobile Nodes (MNs) that configure OMNI interfaces 599 over underlying interfaces with addresses that may change when the 600 Client moves to a new network connection point. AERO Clients 601 register their Mobile Network Prefixes (MNPs) with the AERO service, 602 and distribute the MNPs to nodes on EUNs. AERO Bridges, Proxy/ 603 Servers and Relays are critical infrastructure elements in fixed 604 (i.e., non-mobile) INET deployments and hence have permanent and 605 unchanging INET addresses. Together, they constitute the AERO 606 service which provides an OMNI link virtual overlay for connecting 607 AERO Clients. 609 AERO Bridges (together with Proxy/Servers) provide the secured 610 backbone supporting infrastructure for a Segment Routing Topology 611 (SRT) that spans the OMNI link. Bridges forward carrier packets both 612 within the same SRT segment and between disjoint SRT segments based 613 on an IPv6 encapsulation mid-layer known as the OMNI Adaptation Layer 614 (OAL) [I-D.templin-6man-omni]. The OMNI interface and OAL provide a 615 virtual bridging service, since the inner IP TTL/Hop Limit is not 616 decremented. Each Bridge also peers with Proxy/Servers and other 617 Bridges in a dynamic routing protocol instance to provide a 618 Distributed Mobility Management (DMM) service for the list of active 619 MNPs (see Section 3.2.3). Bridges present the OMNI link as a set of 620 one or more Mobility Service Prefixes (MSPs) and configure secured 621 tunnels with Proxy/Servers, Relays and other Bridges; they further 622 maintain IP forwarding table entries for each MNP and any other 623 reachable non-MNP prefixes. 625 AERO Proxy/Servers in distributed SRT segments provide default 626 forwarding and mobility/multilink services for AERO Client mobile 627 nodes. Each Proxy/Server also peers with Bridges in a dynamic 628 routing protocol instance to advertise its list of associated MNPs 629 (see Section 3.2.3). Proxy/Servers facilitate prefix delegation/ 630 registration exchanges with Clients, where each delegated prefix 631 becomes an MNP taken from an MSP. Proxy/Servers forward carrier 632 packets between OMNI interface neighbors and track each Client's 633 mobility profiles. Proxy/Servers at ANET/INET boundaries provide a 634 conduit for ANET Clients to associate with peers reached through 635 external INETs. Proxy/Servers in the open INET support INET Clients 636 through authenticated IPv6 ND message exchanges. Source Clients 637 employ First-Hop Segment (FHS) Proxy/Servers to forward packets over 638 the SRT to Last-Hop Segment (LHS) Proxy/Servers which finally forward 639 to target Clients. 641 AERO Relays are Proxy/Servers that provide forwarding services to 642 exchange original IP packets between the OMNI interface and INET/EUN 643 interfaces. Relays are provisioned with MNPs the same as for an AERO 644 Client, and also run a dynamic routing protocol to discover any non- 645 MNP IP routes. The Relay advertises the MSP(s) to its connected 646 networks, and distributes all of its associated MNP and non-MNP 647 routes via BGP peerings with Bridges 649 3.2. The AERO Service over OMNI Links 651 3.2.1. AERO/OMNI Reference Model 653 Figure 1 presents the basic OMNI link reference model: 655 +----------------+ 656 | AERO Bridge B1 | 657 | Nbr: S1, S2, P1| 658 |(X1->S1; X2->S2)| 659 | MSP M1 | 660 +-------+--------+ 661 +--------------+ | +--------------+ 662 | AERO P/S S1 | | | AERO P/S S2 | 663 | Nbr: C1, B1 | | | Nbr: C2, B1 | 664 | default->B1 | | | default->B1 | 665 | X1->C1 | | | X2->C2 | 666 +-------+------+ | +------+-------+ 667 | OMNI link | | 668 X===+===+==================+===================+===+===X 669 | | 670 +-----+--------+ +--------+-----+ 671 |AERO Client C1| |AERO Client C2| 672 | Nbr: S1 | | Nbr: S2 | 673 | default->S1 | | default->S2 | 674 | MNP X1 | | MNP X2 | 675 +------+-------+ +-----+--------+ 676 | | 677 .-. .-. 678 ,-( _)-. ,-( _)-. 679 .-(_ IP )-. +-------+ +-------+ .-(_ IP )-. 680 (__ EUN )--|Host H1| |Host H2|--(__ EUN ) 681 `-(______)-' +-------+ +-------+ `-(______)-' 683 Figure 1: AERO/OMNI Reference Model 685 In this model: 687 o the OMNI link is an overlay network service configured over one or 688 more underlying SRT segments which may be managed by different 689 administrative authorities and have incompatible protocols and/or 690 addressing plans. 692 o AERO Bridge B1 aggregates Mobility Service Prefix (MSP) M1, 693 discovers Mobile Network Prefixes (MNPs) X* and advertises the MSP 694 via BGP peerings over secured tunnels to Proxy/Servers (S1, S2). 695 Bridges provide the backbone for an SRT that spans the OMNI link. 697 o AERO Proxy/Servers S1 and S2 configure secured tunnels with Bridge 698 B1 and also provide mobility, multilink, multicast and default 699 router services for the MNPs of their associated Clients C1 and 700 C2. (Proxy/Servers that act as Relays can also advertise non-MNP 701 routes for non-mobile correspondent nodes the same as for MNP 702 Clients.) 704 o AERO Clients C1 and C2 associate with Proxy/Servers S1 and S2, 705 respectively. They receive MNP delegations X1 and X2, and also 706 act as default routers for their associated physical or internal 707 virtual EUNs. Simple hosts H1 and H2 attach to the EUNs served by 708 Clients C1 and C2, respectively. 710 An OMNI link configured over a single *NET appears as a single 711 unified link with a consistent underlying network addressing plan; 712 all nodes on the link can exchange carrier packets via simple *NET 713 encapsulation (i.e., following any necessary NAT traversal) since the 714 underlying *NET is connected. In common practice, however, OMNI 715 links often traverse an SRT spanning tree that connects multiple 716 distinct *NET segments that may be managed under different 717 administrative authorities (e.g., as for worldwide aviation service 718 providers such as ARINC, SITA, Inmarsat, etc.). Individual *NETs may 719 also be partitioned internally, in which case each internal partition 720 is seen as a separate segment. 722 The addressing plan of each SRT segment is consistent internally but 723 will often bear no relation to the addressing plans of other 724 segments. Each segment is also likely to be separated from others by 725 network security devices (e.g., firewalls, proxys, packet filtering 726 gateways, etc.), and disjoint segments often have no common physical 727 link connections. Therefore, nodes can only be assured of exchanging 728 carrier packets directly with correspondents in the same segment, and 729 not with those in other segments. The only means for joining the 730 segments therefore is through inter-domain peerings between AERO 731 Bridges. 733 The same as for traditional campus LANs, the OMNI link spans multiple 734 SRT segments that can be joined into a single unified link using the 735 OMNI Adaptation Layer (OAL) [I-D.templin-6man-omni]. The OAL is an 736 OMNI interface sublayer that inserts a mid-layer IPv6 encapsulation 737 header for inter-segment forwarding (i.e., bridging) without 738 decrementing the network-layer TTL/Hop Limit of the original IP 739 packet. An example OMNI link SRT is shown in Figure 2: 741 . . . . . . . . . . . . . . . . . . . . . . . 742 . . 743 . .-(::::::::) . 744 . .-(::::::::::::)-. +-+ . 745 . (:::: Segment A :::)--|B|---+ . 746 . `-(::::::::::::)-' +-+ | . 747 . `-(::::::)-' | . 748 . | . 749 . .-(::::::::) | . 750 . .-(::::::::::::)-. +-+ | . 751 . (:::: Segment B :::)--|B|---+ . 752 . `-(::::::::::::)-' +-+ | . 753 . `-(::::::)-' | . 754 . | . 755 . .-(::::::::) | . 756 . .-(::::::::::::)-. +-+ | . 757 . (:::: Segment C :::)--|B|---+ . 758 . `-(::::::::::::)-' +-+ | . 759 . `-(::::::)-' | . 760 . | . 761 . ..(etc).. x . 762 . . 763 . . 764 . <- Segment Routing Topology (SRT) -> . 765 . . . . . . . . . . . . . .. . . . . . . . . 767 Figure 2: OMNI Link Segment Routing Topology (SRT) 769 Bridge, Proxy/Server and Relay OMNI interfaces are configured over 770 both secured tunnels and open INET underlying interfaces within their 771 respective SRT segments. Within each segment, Bridges configure 772 "hub-and-spokes" BGP peerings with Proxy/Server/Relays as "spokes". 773 Adjacent SRT segments are joined by Bridge-to-Bridge peerings to 774 collectively form a spanning tree over the entire SRT. The "secured" 775 spanning tree supports authentication and integrity for critical 776 control plane messages. The "unsecured" spanning tree conveys 777 ordinary carrier packets without security codes and that must be 778 treated by destinations according to data origin authentication 779 procedures. AERO nodes can employ route optimization to cause 780 carrier packets to take more direct paths between OMNI link neighbors 781 without having to follow strict SRT spanning tree paths. 783 3.2.2. Addressing and Node Identification 785 AERO nodes on OMNI links use the Link-Local Address (LLA) prefix 786 fe80::/64 [RFC4291] to assign LLAs used for network-layer addresses 787 in link-scoped IPv6 ND and data messages. AERO Clients use LLAs 788 constructed from MNPs (i.e., "MNP-LLAs") while other AERO nodes use 789 LLAs constructed from administrative identification values ("ADM- 790 LLAs") as specified in [I-D.templin-6man-omni]. Non-MNP routes are 791 also represented the same as for MNP-LLAs, but may include a prefix 792 that is not properly covered by the MSP. 794 AERO nodes also use the Unique Local Address (ULA) prefix fd00::/8 795 followed by a pseudo-random 40-bit OMNI domain identifier to form the 796 prefix [ULA]::/48, then include a 16-bit OMNI link identifier '*' to 797 form the prefix [ULA*]::/64 [RFC4291]. The AERO node then uses the 798 prefix [ULA*]::/64 to form "MNP-ULAs" or "ADM-ULA"s as specified in 799 [I-D.templin-6man-omni] to support OAL addressing. (The prefix 800 [ULA*]::/64 appearing alone and with no suffix represents "default".) 801 AERO Clients also use Temporary ULAs constructed per 802 [I-D.templin-6man-omni], where the addresses are typically used only 803 in initial control message exchanges until a stable MNP-LLA/ULA is 804 assigned. 806 AERO MSPs, MNPs and non-MNP routes are typically based on Global 807 Unicast Addresses (GUAs), but in some cases may be based on private- 808 use addresses. See [I-D.templin-6man-omni] for a full specification 809 of LLAs, ULAs and GUAs used by AERO nodes on OMNI links. 811 Finally, AERO Clients and Proxy/Servers configure node identification 812 values as specified in [I-D.templin-6man-omni]. 814 3.2.3. AERO Routing System 816 The AERO routing system comprises a private Border Gateway Protocol 817 (BGP) [RFC4271] service coordinated between Bridges and Proxy/ 818 Servers. The service supports carrier packet forwarding at a layer 819 below IP, and does not interact with either the public Internet BGP 820 routing system or any underlying INET routing systems. 822 In a reference deployment, each Proxy/Server is configured as an 823 Autonomous System Border Router (ASBR) for a stub Autonomous System 824 (AS) using a 32-bit AS Number (ASN) [RFC4271] that is unique within 825 the BGP instance, and each Proxy/Server further uses eBGP to peer 826 with one or more Bridges but does not peer with other Proxy/Servers. 827 Each SRT segment in the OMNI link must include one or more Bridges in 828 a "hub" AS, which peer with the Proxy/Servers within that segment as 829 "spoke" ASes. All Bridges within the same segment are members of the 830 same hub AS, and use iBGP to maintain a consistent view of all active 831 routes currently in service. The Bridges of different segments peer 832 with one another using eBGP. 834 Bridges maintain forwarding table entries only for the MNP-ULAs 835 corresponding to MNP and non-MNP routes that are currently active, 836 while carrier packets destined to all other MNP-ULAs are dropped with 837 a Destination Unreachable message returned due to the black-hole 838 route. In this way, Proxy/Servers and Relays have only partial 839 topology knowledge (i.e., they only maintain routing information for 840 their directly associated Clients and non-AERO links) and they 841 forward all other carrier packets to Bridges which have full topology 842 knowledge. 844 Each OMNI link SRT segment assigns a unique ADM-ULA sub-prefix of 845 [ULA*]::/96 known as the "SRT prefix". For example, a first segment 846 could assign [ULA*]::1000/116, a second could assign 847 [ULA*]::2000/116, a third could assign [ULA*]::3000/116, etc. Within 848 each segment, each Proxy/Server configures an ADM-ULA within the 849 segment's SRT prefix, e.g., the Proxy/Servers within [ULA*]::2000/116 850 could assign the ADM-ULAs [ULA*]::2011/116, [ULA*]::2026/116, 851 [ULA*]::2003/116, etc. 853 The administrative authorities for each segment must therefore 854 coordinate to assure mutually-exclusive ADM-ULA prefix assignments, 855 but internal provisioning of ADM-ULAs an independent local 856 consideration for each administrative authority. For each ADM-ULA 857 prefix, the Bridge(s) that connect that segment assign the all-zero's 858 address of the prefix as a Subnet Router Anycast address. For 859 example, the Subnet Router Anycast address for [ULA*]::1023/116 is 860 simply [ULA*]::1000. 862 ADM-ULA prefixes are statically represented in Bridge forwarding 863 tables. Bridges join multiple SRT segments into a unified OMNI link 864 over multiple diverse network administrative domains. They support a 865 bridging function by first establishing forwarding table entries for 866 their ADM-ULA prefixes either via standard BGP routing or static 867 routes. For example, if three Bridges ('A', 'B' and 'C') from 868 different segments serviced [ULA*]::1000/116, [ULA*]::2000/116 and 869 [ULA*]::3000/116 respectively, then the forwarding tables in each 870 Bridge are as follows: 872 A: [ULA*]::1000/116->local, [ULA*]::2000/116->B, [ULA*]::3000/116->C 874 B: [ULA*]::1000/116->A, [ULA*]::2000/116->local, [ULA*]::3000/116->C 876 C: [ULA*]::1000/116->A, [ULA*]::2000/116->B, [ULA*]::3000/116->local 878 These forwarding table entries are permanent and never change, since 879 they correspond to fixed infrastructure elements in their respective 880 segments. 882 MNP ULAs are instead dynamically advertised in the AERO routing 883 system by Proxy/Servers and Relays that provide service for their 884 corresponding MNPs. For example, if three Proxy/Servers ('D', 'E' 885 and 'F') service the MNPs 2001:db8:1000:2000::/56, 886 2001:db8:3000:4000::/56 and 2001:db8:5000:6000::/56 then the routing 887 system would include: 889 D: [ULA*]:2001:db8:1000:2000/120 891 E: [ULA*]:2001:db8:3000:4000/120 893 F: [ULA*]:2001:db8:5000:6000/120 895 A full discussion of the BGP-based routing system used by AERO is 896 found in [I-D.ietf-rtgwg-atn-bgp]. 898 3.2.4. OMNI Link Segment Routing 900 With the Client and SRT segment prefixes in place in Bridge 901 forwarding tables, the OMNI interface sends control and data carrier 902 packets toward AERO destination nodes located in different OMNI link 903 segments over the SRT spanning tree. The OMNI interface uses the 904 OMNI Adaptation Layer (OAL) encapsulation service 905 [I-D.templin-6man-omni], and includes an OMNI Routing Header (ORH) as 906 an OAL header extension. Each carrier packet includes at most one 907 ORH in compressed or uncompressed form (with the uncompressed form 908 shown in Figure 3): 910 0 1 2 3 911 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 1 912 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 913 | Next Header | Hdr Ext Len | Routing Type | Segments Left | 914 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 915 | omIndex | FMT | SRT | LHS (bits 0 -15) | 916 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 917 | LHS (bits 0 -15) | ~ 918 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ 919 ~ Link Layer Address (L2ADDR) ~ 920 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 921 | Null Padding (if necessary) | 922 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 923 ~ Destination Suffix ~ 924 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 926 Figure 3: OMNI Routing Header (ORH) Format 928 The ORH includes the following fields, in consecutive order: 930 o Next Header identifies the type of header immediately following 931 the ORH. 933 o Hdr Ext Len is the length of the Routing header in 8-octet units 934 (not including the first 8 octets). The field must encode a value 935 between 0 and 4 (all other values indicate a parameter problem). 937 o Routing Type is set to TBD1 (see IANA Considerations). 939 o Segments Left encodes the value 0 or 1 (all other values indicate 940 a parameter problem). 942 o omIndex - a 1-octet field consulted only when Segments Left is 0; 943 identifies a specific target Client underlying interface serviced 944 by the LHS Proxy-Server when there are multiple alternatives. 945 When FMT-Forward is clear, omIndex determines the interface for 946 forwarding the ORH packet following reassembly; when FMT-Forward 947 is set, omIndex determines the interface for forwarding the raw 948 carrier packets without first reassembling. When omIndex is set 949 to 0 (or when no ORH is present), the LHS Proxy/Server selects 950 among any of the Client's available underlying interfaces that it 951 services locally (i.e., and not those serviced by another Proxy/ 952 Server). 954 o FMT - a 3-bit "Forward/Mode/Trailer" code corresponding to the 955 included Link Layer Address as follows: 957 * When the most significant bit (i.e., "FMT-Forward") is clear, 958 the LHS Proxy/Server must reassemble. When FMT-Forward is set, 959 the LHS Proxy/Server must forward the fragments to the Client 960 (while changing the OAL destination address to the MNP-ULA of 961 the Client if necessary) without reassembling. 963 * When the next most significant bit (i.e., "FMT-Mode") is clear, 964 L2ADDR is the INET address of the LHS Proxy/Server and the 965 Client must be reached through the LHS Proxy/Server. When FMT- 966 Mode is set, the Client is eligible for route optimization over 967 the open INET where it may be located behind one or more NATs, 968 and L2ADDR is either the INET address of the LHS Proxy/Server 969 (when FMT-Forward is set) or the native INET address of the 970 Client itself (when FMT-Forward is clear). 972 * The least significant bit (i.e., "FMT-Type") is consulted only 973 when Hdr Ext Len is 1 and ignored otherwise. If FMT-Type is 974 clear, the remaining 10 ORH octets contain an LHS followed by 975 an IPv4 L2ADDR. If FMT-Type is set, the remainder instead 976 contains 2 null padding octets followed by an 8-octet (IPv6) 977 Destination Suffix. 979 o SRT - a 5-bit Segment Routing Topology prefix length consulted 980 only when Segments Left is 1, and encodes a value that (when added 981 to 96) determines the prefix length to apply to the ADM-ULA formed 982 from concatenating [ULA*]::/96 with the 32 bit LHS value (for 983 example, the value 16 corresponds to the prefix length 112). 985 o LHS - a 4-octet field present only when indicated by the ORH 986 length (see below) and consulted only when Segments Left is 1. 987 The field encodes the 32-bit ADM-ULA suffix of an LHS Proxy/Server 988 for the target. When SRT and LHS are both set to 0, the LHS 989 Proxy/Server must be reached directly via INET encapsulation 990 instead of over the spanning tree. When SRT is set to 0 and LHS 991 is non-zero, the prefix length is set to 128. SRT and LHS 992 determine the ADM-ULA of the LHS Proxy/Server over the spanning 993 tree. 995 o Link Layer Address (L2ADDR) - an IP encapsulation address present 996 only when indicated by the ORH length (see below) and consulted 997 only when Segments Left is 1. The ORH length also determines the 998 L2ADDR IP version since the field will always contain exactly 6 999 octets for UDP/IPv4 or 18 octets for UDP/IPv6. When present, 1000 provides the link-layer address (i.e., the encapsulation address) 1001 of the LHS Proxy/Server or the target Client itself. The UDP Port 1002 Number appears in the first two octets and the IP address appears 1003 in the remaining octets. The Port Number and IP address are 1004 recorded in network byte order, and in ones-compliment 1005 "obfuscated" form per [RFC4380]. The OMNI interface forwarding 1006 algorithm uses L2ADDR as the INET encapsulation address for 1007 forwarding when SRT/LHS is located in the same OMNI link segment. 1008 If direct INET encapsulation is not permitted, L2ADDR is instead 1009 set to all-zeros and the packet must be forwarded to the LHS 1010 Proxy-Server via the spanning tree. 1012 o Null Padding - zero-valued octets added as necessary to pad the 1013 portion of the ORH included up to this point to an even 8-octet 1014 boundary. 1016 o Destination Suffix - a trailing 8-octet field present only when 1017 indicated by the ORH length (see below). When ORH length is 1, 1018 FMT-Type determines whether the option includes a Destination 1019 Suffix or an LHS/L2ADDR for IPv4 since there is only enough space 1020 available for one. When present, encodes the 64-bit MNP-ULA 1021 suffix for the target Client. 1023 The ORH Hdr Ext Len field value also serves as an implicit ORH 1024 "Type", with 5 distinct Types possible (i.e., ORH-0 through ORH-4). 1025 All ORH-* Types include the same 6-octet preamble beginning with Next 1026 Header up to and including omIndex, followed by a Type-specific 1027 remainder as follows: 1029 o ORH-0 - The preamble Hdr Ext Len and Segments Left must both be 0. 1030 Two null padding octets follow the preamble, and all other fields 1031 are omitted. 1033 o ORH-1 - The preamble Hdr Ext Len is set to 1. When FMT-Type is 1034 clear, the LHS and L2ADDR for IPv4 fields are included and the 1035 Destination Suffix is omitted. When FMT-Type is set, the LHS and 1036 L2ADDR fields are omitted, the Destination Suffix field is 1037 included and Segments Left must be 0. 1039 o ORH-2 - The preamble Hdr Ext Len is set to 2. The LHS, L2ADDR for 1040 IPv4 and Destination Suffix fields are all included. 1042 o ORH-3 - The preamble Hdr Ext Len is set to 3. The LHS and L2ADDR 1043 for IPv6 fields are included and the Destination Suffix field is 1044 omitted. 1046 o ORH-4 - The preamble Hdr Ext Len is set to 4. The LHS, L2ADDR for 1047 IPv6 and Destination Suffix fields are all included. 1049 AERO neighbors use OAL encapsulation and fragmentation to exchange 1050 OAL packets as specified in [I-D.templin-6man-omni]. When an AERO 1051 node's OMNI interface (acting as an OAL source) uses OAL 1052 encapsulation for an original IP packet with source address 1053 2001:db8:1:2::1 and destination address 2001:db8:1234:5678::1, it 1054 sets the OAL header source address to its own ULA (e.g., 1055 [ULA*]::2001:db8:1:2), sets the destination address to the MNP-ULA 1056 corresponding to the IP destination address (e.g., 1057 [ULA*]::2001:db8:1234:5678), sets the Traffic Class, Flow Label, Hop 1058 Limit and Payload Length as discussed in [I-D.templin-6man-omni], 1059 then finally selects an Identification and appends an OAL checksum. 1061 If the neighbor cache information indicates that the target is in a 1062 different segment, the OAL source next inserts an ORH immediately 1063 following the OAL header while including Destination Suffix for non- 1064 first-fragments only when necessary (in this case, the Destination 1065 Suffix is 2001:db8:1234:5678). Next, to direct the packet to a 1066 first-hop Proxy/Server or a Bridge, the source prepares an ORH with 1067 Segments Left set to 1 and with FMT/SRT/LHS/L2ADDR included, then 1068 overwrites the OAL header destination address with the LHS Subnet 1069 Router Anycast address (for example, for LHS 3000:4567 with SRT 16, 1070 the Subnet Router Anycast address is [ULA*]::3000:0000). To send the 1071 packet to the LHS Proxy/Server either directly or via the spanning 1072 tree, the OAL source instead includes an ORH (Type 0 or 1) with 1073 Segments Left set to 0 and FMT/SRT/LHS/L2ADDR omitted, and overwrites 1074 the OAL header destination address with either the LHS Proxy/Server 1075 ADM-ULA or the MNP-ULA of the Client itself. 1077 The OAL source then fragments the OAL packet, with each resulting OAL 1078 fragment including the OAL/ORH headers while only the first fragment 1079 includes the original IPv6 header. If FMT-Forward is set, the 1080 Identification used for fragmentation must be within the window for 1081 the Client and a Destination Suffix must be included with each non- 1082 first-fragment when necessary; otherwise the Identification must be 1083 within the window for the Client's Proxy/Server and no Destination 1084 Suffix is needed. (Note that if no actual fragmentation is required 1085 the OAL source still prepares the packet as an "atomic" fragment that 1086 includes a Fragment Header with Offset and More Fragments both set to 1087 0.) The OAL source finally encapsulates each resulting OAL fragment 1088 in an *NET header to form an OAL carrier packet, with source address 1089 set to its own *NET address (e.g., 192.0.2.100) and destination set 1090 to the *NET address of the last hop itself or the next hop in the 1091 spanning tree (e.g., 192.0.2.1). 1093 The carrier packet encapsulation format in the above example is shown 1094 in Figure 4: 1096 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1097 | *NET Header | 1098 | src = 192.0.2.100 | 1099 | dst = 192.0.2.1 | 1100 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1101 | OAL IPv6 Header | 1102 | src = [ULA*]::2001:db8:1:2 | 1103 | dst= [ULA*]::3000:0000 | 1104 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1105 | ORH (if necessary) | 1106 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1107 | OAL Fragment Header | 1108 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1109 | Original IP Header | 1110 | (first-fragment only) | 1111 | src = 2001:db8:1:2::1 | 1112 | dst = 2001:db8:1234:5678::1 | 1113 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1114 | | 1115 ~ ~ 1116 ~ Original Packet Body/Fragment ~ 1117 ~ ~ 1118 | | 1119 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1121 Figure 4: Carrier Packet Format 1123 In this format, the original IP header and packet body/fragment are 1124 encapsulated in an OAL IPv6 header prepared according to [RFC2473], 1125 the ORH is a Routing Header extension of the OAL header, the Fragment 1126 Header identifies each fragment, and the *NET header is prepared as 1127 discussed in Section 3.6. The OAL source transmits each such carrier 1128 packet into the SRT spanning tree, where they are forwarded over 1129 possibly multiple OAL intermediate nodes until they arrive at the OAL 1130 destination. 1132 This gives rise to an SRT forwarding system that contains both Client 1133 MNP-ULA prefix information that may change dynamically due to 1134 regional node mobility and per-segment ADM-ULA prefix information 1135 that rarely if ever change. The spanning tree can therefore provide 1136 link-layer bridging by sending carrier packets over the spanning tree 1137 instead of network-layer routing according to MNP routes. As a 1138 result, opportunities for loss due to node mobility between different 1139 segments are mitigated. 1141 Note: The document recommends that AERO nodes transform ORHs with 1142 Segments Left set to 1 into ORH-0 or ORH-1 during forwarding. While 1143 this may yield encapsulation overhead savings in some cases, the AERO 1144 node can instead simply decrement Segments Left and leave the 1145 original ORH in place. The LHS Proxy/Server or target Client that 1146 processes the ORH will receive the same information in both cases. 1148 Note: When the OAL source sets a carrier packet OAL destination 1149 address to a target's MNP-ULA but does not assert a specific target 1150 underlying interface, it may omit the ORH whether forwarding to the 1151 LHS Proxy/Server or directly to the target itself. When the LHS 1152 Proxy/Server receives a carrier packet with OAL destination set to 1153 the target MNP-ULA but with no ORH, it forwards over any available 1154 underlying interface for the target that it services locally. 1156 Note: When the OAL source and destination are on the same INET 1157 segment, OAL header compression can be used to significantly reduce 1158 encapsulation overhead as discussed in [I-D.templin-6man-omni]. 1160 Note: Use of an IPv6 "minimal encapsulation" format (i.e., an IPv6 1161 variant of [RFC2004]) based on extensions to the ORH was considered 1162 and abandoned. In the approach, the ORH would be inserted as an 1163 extension header to the original IPv6 packet header. The IPv6 1164 destination address would then be written into the ORH, and the ULA 1165 corresponding to the destination would be overwritten in the IPv6 1166 destination address. This would seemingly convey enough forwarding 1167 information so that OAL encapsulation could be avoided. However, 1168 this "minimal encapsulation" IPv6 packet would then have a non-ULA 1169 source address and ULA destination address, an incorrect value in 1170 upper layer protocol checksums, and a Hop Limit that is decremented 1171 within the spanning tree when it should not be. The insertion and 1172 removal of the ORH would also entail rewriting the Payload Length and 1173 Next Header fields - again, invalidating upper layer checksums. 1174 These irregularities would result in implementation challenges and 1175 the potential for operational issues, e.g., since actionable ICMPv6 1176 error reports could not be delivered to the original source. In 1177 order to address the issues, still more information such as the 1178 original IPv6 source address could be written into the ORH. However, 1179 with the additional information the benefit of the "minimal 1180 encapsulation" savings quickly diminishes, and becomes overshadowed 1181 by the implementation and operational irregularities. 1183 3.2.5. Segment Routing Topologies (SRTs) 1185 The 64-bit sub-prefixes of [ULA]::/48 identify up to 2^16 distinct 1186 Segment Routing Topologies (SRTs). Each SRT is a mutually-exclusive 1187 OMNI link overlay instance using a distinct set of ULAs, and emulates 1188 a Virtual LAN (VLAN) service for the OMNI link. In some cases (e.g., 1189 when redundant topologies are needed for fault tolerance and 1190 reliability) it may be beneficial to deploy multiple SRTs that act as 1191 independent overlay instances. A communication failure in one 1192 instance therefore will not affect communications in other instances. 1194 Each SRT is identified by a distinct value in bits 48-63 of 1195 [ULA]::/48, i.e., as [ULA0]::/64, [ULA1]::/64, [ULA2]::/64, etc. 1196 Each OMNI interface is identified by a unique interface name (e.g., 1197 omni0, omni1, omni2, etc.) and assigns an anycast ADM-ULA 1198 corresponding to its SRT prefix length. The anycast ADM-ULA is used 1199 for OMNI interface determination in Safety-Based Multilink (SBM) as 1200 discussed in [I-D.templin-6man-omni]. Each OMNI interface further 1201 applies Performance-Based Multilink (PBM) internally. 1203 The Bridges and Proxy/Servers of each independent SRT engage in BGP 1204 peerings to form a spanning tree with the Bridges in non-leaf nodes 1205 and the Proxy/Servers in leaf nodes. The spanning tree is configured 1206 over both secured and unsecured underlying network paths. The 1207 secured spanning tree is used to convey secured control messages 1208 between FHS and LHS Proxy/Servers, while the unsecured spanning tree 1209 forwards data messages and/or unsecured control messages. 1211 Each SRT segment is identified by a unique ADM-ULA prefix used by all 1212 Proxy/Servers and Bridges in the segment. Each AERO node must 1213 therefore discover an SRT prefix that correspondents can use to 1214 determine the correct segment, and must publish the SRT prefix in 1215 IPv6 ND messages and carrier packet ORHs. 1217 3.2.6. Segment Routing For OMNI Link Selection 1219 Original IPv6 source can direct IPv6 packets to an AERO node by 1220 including a standard IPv6 Segment Routing Header (SRH) [RFC8754] with 1221 the anycast ADM-ULA for the selected OMNI link as either the IPv6 1222 destination or as an intermediate hop within the SRH. This allows 1223 the original source to determine the specific OMNI link SRT an 1224 original IPv6 packet will traverse when there may be multiple 1225 alternatives. 1227 When an AERO node processes the SRH and forwards the original IPv6 1228 packet to the correct OMNI interface, the OMNI interface writes the 1229 next IPv6 address from the SRH into the IPv6 destination address and 1230 decrements Segments Left. If decrementing would cause Segments Left 1231 to become 0, the OMNI interface deletes the SRH before forwarding. 1232 This form of Segment Routing supports Safety-Based Multilink (SBM). 1234 3.2.7. Segment Routing Within the OMNI Link 1236 OAL sources can insert an ORH for Segment Routing within the same 1237 OMNI link to influence the paths of carrier packets sent to OAL 1238 destinations in remote SRT segments without requiring all carrier 1239 packets to traverse strict SRT spanning tree paths. (OAL sources can 1240 also insert an ORH in carrier packets sent to OAL destinations in the 1241 local segment if additional last-hop forwarding information is 1242 required.) 1244 When an AERO node's OMNI interface has an original IP packet to send 1245 to a target discovered through route optimization located in the same 1246 SRT segment, it acts as an OAL source to perform OAL encapsulation 1247 and fragmentation. The node then uses L2ADDR for INET encapsulation 1248 while including an ORH-0 when sending the resulting carrier packets 1249 to the ADM-ULA of the LHS Proxy/Server, or optionally omitting the 1250 ORH-0 when sending to the MNP-ULA of the target Client itself. When 1251 the node sends carrier packets with an ORH-0 to the LHS Proxy/Server, 1252 it sets the OAL destination to the ADM-ULA of the Proxy/Server if the 1253 Proxy/Server is responsible for reassembly; otherwise, it sets the 1254 OAL destination to the MNP-ULA of the target Client to cause the 1255 Proxy/Server to forward without reassembling. The node also sets 1256 omIndex to select a specific target Client underlying interface, or 1257 sets omIndex to 0 when no preference is selected. 1259 When an AERO node's OMNI interface has an original IP packet to send 1260 to a route optimization target located in a remote OMNI link segment, 1261 it acts as an OAL source the same as above but also includes an 1262 appropriate ORH type with Segments Left set to 1 and with 1263 FMT/SRT/LHS/L2ADDR information while setting the OAL destination to 1264 the Subnet Router Anycast address for the LHS OMNI link segment. 1266 (The OAL source can alternatively include an ORH with Segments Left 1267 set to 0 while setting the OAL destination to the ADM-ULA of the LHS 1268 Proxy/Server, but this would cause the carrier packets to follow 1269 strict spanning tree paths.) The OMNI interface then forwards the 1270 resulting carrier packets into the spanning tree. 1272 When a Bridge receives a carrier packet destined to its Subnet Router 1273 Anycast address with any ORH type with Segments Left set to 1 and 1274 with FMT/SRT/LHS/L2ADDR values corresponding to the local segment, it 1275 examines FMT-Mode to determine whether the target Client can accept 1276 packets directly (i.e., following any NAT traversal procedures 1277 necessary) while bypassing the LHS Proxy/Server. If the Client can 1278 be reached directly and NAT traversal has converged, the Bridge then 1279 writes the MNP-ULA (found in the inner IPv6 header for first 1280 fragments or the ORH Destination Suffix for non-first fragments) into 1281 the OAL destination address, decrements the OAL IPv6 header Hop Limit 1282 (and discards the packet if Hop Limit reaches 0), removes the ORH, 1283 re-encapsulates the carrier packet according to L2ADDR then forwards 1284 the carrier packet directly to the target Client. If the Client 1285 cannot be reached directly (or if NAT traversal has not yet 1286 converged), the Bridge instead transforms the ORH into an ORH-0, re- 1287 encapsulates the packet according to L2ADDR, changes the OAL 1288 destination to the ADM-ULA of the LHS Proxy/Server if FMT-Forward is 1289 clear or the MNP-ULA of the Client if FMT-Forward is set and forwards 1290 the carrier packet to the LHS Proxy/Server. 1292 When a Bridge receives a carrier packet destined to its Subnet Router 1293 Anycast address with any ORH type with Segments Left set to 1 and 1294 L2ADDR set to 0, the Bridge instead forwards the packet toward the 1295 LHS Proxy/Server via the spanning tree. The Bridge changes the OAL 1296 destination to the ADM-ULA of the LHS Proxy/Server, transforms the 1297 ORH into an ORH-0 (or an ORH-1 with FMT-Type set and Segments Left 1298 0), then forwards the packet to the next hop in the spanning tree. 1299 The Bridge may also elect to forward via the spanning tree as above 1300 even when it receives a carrier packet with an ORH that includes a 1301 valid L2ADDR Port Number and IP address, however this may result in a 1302 longer path than necessary. If the carrier packet arrived via the 1303 secured spanning tree, the Bridge forwards to the next hop also via 1304 the secured spanning tree. If the carrier packet arrived via the 1305 unsecured spanning tree, the Bridge forwards to the next hop also via 1306 the unsecured spanning tree. 1308 When an LHS Proxy/Server receives carrier packets with any ORH type 1309 with Segments Left set to 0 and with OAL destination set to its own 1310 ADM-ULA, it proceeds according to FMT-Forward and omIndex. If FMT- 1311 Forward is set, the LHS Proxy/Server changes the OAL destination to 1312 the MNP-ULA of the target Client found in the IPv6 header for first 1313 fragments or in the ORH Destination Suffix for non-first-fragments, 1314 removes the ORH and forwards to the target Client interface 1315 identified by omIndex. If FMT-Forward is clear, the LHS Proxy/Server 1316 instead reassembles then re-encapsulates while refragmenting if 1317 necessary, removes the ORH and forwards to the target Client 1318 according to omIndex. 1320 When an LHS Proxy/Server receives carrier packets with any ORH type 1321 with Segments Left set to 0 and with OAL destination set to the MNP- 1322 ULA of the target Client, it removes the ORH and forwards to the 1323 target Client according to omIndex. During forwarding, the LHS 1324 Proxy/Server must first verify that the omIndex corresponds to a 1325 target underlying interface that it services locally and must not 1326 forward to other target underlying interfaces. If omIndex is 0 (or 1327 if no ORH is included) the LHS Proxy/Server instead selects among any 1328 of the target underlying interfaces it services. 1330 When a target Client receives carrier packets with OAL destination 1331 set to is MNP-ULA, it reassembles to obtain the OAL packet then 1332 decapsulates and delivers the original IP packet to upper layers. 1334 Note: Special handling procedures are employed for the exchange of 1335 IPv6 ND messages used to establish neighbor cache state as discussed 1336 in Section 3.14. The procedures call for hop-by-hop authentication 1337 and neighbor cache state establishment based on the encapsulation 1338 ULA, with next-hop determination based on the IPv6 ND message LLA. 1340 3.3. OMNI Interface Characteristics 1342 OMNI interfaces are virtual interfaces configured over one or more 1343 underlying interfaces classified as follows: 1345 o INET interfaces connect to an INET either natively or through one 1346 or more NATs. Native INET interfaces have global IP addresses 1347 that are reachable from any INET correspondent. The INET-facing 1348 interfaces of Proxy/Servers are native interfaces, as are Relay 1349 and Bridge interfaces. NATed INET interfaces connect to a private 1350 network behind one or more NATs that provide INET access. Clients 1351 that are behind a NAT are required to send periodic keepalive 1352 messages to keep NAT state alive when there are no carrier packets 1353 flowing. 1355 o ANET interfaces connect to an ANET that is separated from the open 1356 INET by an FHS Proxy/Server. Clients can issue control messages 1357 over the ANET without including an authentication signature since 1358 the ANET is secured at the network layer or below. Proxy/Servers 1359 can actively issue control messages over the INET on behalf of 1360 ANET Clients to reduce ANET congestion. 1362 o VPNed interfaces use security encapsulation over the INET to a 1363 Virtual Private Network (VPN) server that also acts as an FHS 1364 Proxy/Server. Other than the link-layer encapsulation format, 1365 VPNed interfaces behave the same as Direct interfaces. 1367 o Direct (i.e., single-hop point-to-point) interfaces connect a 1368 Client directly to an FHS Proxy/Server without crossing any ANET/ 1369 INET paths. An example is a line-of-sight link between a remote 1370 pilot and an unmanned aircraft. The same Client considerations 1371 apply as for VPNed interfaces. 1373 OMNI interfaces use OAL encapsulation and fragmentation as discussed 1374 in Section 3.2.4. OMNI interfaces use *NET encapsulation (see: 1375 Section 3.6) to exchange carrier packets with OMNI link neighbors 1376 over INET or VPNed interfaces as well as over ANET interfaces for 1377 which the Client and FHS Proxy/Server may be multiple IP hops away. 1378 OMNI interfaces do not use link-layer encapsulation over Direct 1379 underlying interfaces or ANET interfaces when the Client and FHS 1380 Proxy/Server are known to be on the same underlying link. 1382 OMNI interfaces maintain a neighbor cache for tracking per-neighbor 1383 state the same as for any interface. OMNI interfaces use ND messages 1384 including Router Solicitation (RS), Router Advertisement (RA), 1385 Neighbor Solicitation (NS) and Neighbor Advertisement (NA) for 1386 neighbor cache management. In environments where spoofing may be a 1387 threat, OMNI neighbors should employ OAL Identification window 1388 synchronization in their ND message exchanges. 1390 OMNI interfaces send ND messages with an OMNI option formatted as 1391 specified in [I-D.templin-6man-omni]. The OMNI option includes 1392 prefix registration information, Interface Attributes containing link 1393 information parameters for the OMNI interface's underlying interfaces 1394 and any other per-neighbor information. Each OMNI option may include 1395 multiple Interface Attributes sub-options identified by omIndex 1396 values. 1398 A Client's OMNI interface may be configured over multiple underlying 1399 interfaces. For example, common mobile handheld devices have both 1400 wireless local area network ("WLAN") and cellular wireless links. 1401 These links are often used "one at a time" with low-cost WLAN 1402 preferred and highly-available cellular wireless as a standby, but a 1403 simultaneous-use capability could provide benefits. In a more 1404 complex example, aircraft frequently have many wireless data link 1405 types (e.g. satellite-based, cellular, terrestrial, air-to-air 1406 directional, etc.) with diverse performance and cost properties. 1408 If a Client's multiple underlying interfaces are used "one at a time" 1409 (i.e., all other interfaces are in standby mode while one interface 1410 is active), then successive ND messages all include OMNI option 1411 Interface Attributes sub-options with the same underlying interface 1412 index. In that case, the Client would appear to have a single 1413 underlying interface but with a dynamically changing link-layer 1414 address. 1416 If the Client has multiple active underlying interfaces, then from 1417 the perspective of ND it would appear to have multiple link-layer 1418 addresses. In that case, ND message OMNI options MAY include 1419 Interface Attributes sub-options with different underlying interface 1420 indexes. Every ND message need not include Interface Attributes for 1421 all underlying interfaces; for any attributes not included, the 1422 neighbor considers the status as unchanged. 1424 Bridge and Proxy/Server OMNI interfaces are configured over 1425 underlying interfaces that provide both secured tunnels for carrying 1426 IPv6 ND and BGP protocol control plane messages and open INET access 1427 for carrying unsecured messages. The OMNI interface configures both 1428 an ADM-LLA and its corresponding ADM-ULA, and acts as an OAL source 1429 to encapsulate and fragment original IP packets while presenting the 1430 resulting carrier packets over the secured or unsecured underlying 1431 paths. Note that Bridge and Proxy/Server BGP protocol TCP sessions 1432 are run directly over the OMNI interface and use ADM-ULA source and 1433 destination addresses. The OMNI interface employs the OAL to 1434 encapsulate the original IP packets for these sessions as carrier 1435 packets (i.e., even though the OAL header may use the same ADM-ULAs 1436 as the original IP header) and forwards them over the secured 1437 underlying path. 1439 3.4. OMNI Interface Initialization 1441 AERO Proxy/Servers and Clients configure OMNI interfaces as their 1442 point of attachment to the OMNI link. AERO nodes assign the MSPs for 1443 the link to their OMNI interfaces (i.e., as a "route-to-interface") 1444 to ensure that original IP packets with destination addresses covered 1445 by an MNP not explicitly associated with another interface are 1446 directed to an OMNI interface. 1448 OMNI interface initialization procedures for Proxy/Servers, Clients 1449 and Bridges are discussed in the following sections. 1451 3.4.1. AERO Proxy/Server and Relay Behavior 1453 When a Proxy/Server enables an OMNI interface, it assigns an 1454 ADM-{LLA,ULA} appropriate for the given OMNI link SRT segment. The 1455 Proxy/Server also configures secured tunnels with one or more 1456 neighboring Bridges and engages in a BGP routing protocol session 1457 with each Bridge. 1459 The OMNI interface provides a single interface abstraction to the IP 1460 layer, but internally includes an NBMA nexus for sending carrier 1461 packets to OMNI interface neighbors over underlying INET interfaces 1462 and secured tunnels. The Proxy/Server further configures a service 1463 to facilitate ND exchanges with AERO Clients and manages per-Client 1464 neighbor cache entries and IP forwarding table entries based on 1465 control message exchanges. 1467 Relays are simply Proxy/Servers that run a dynamic routing protocol 1468 to redistribute routes between the OMNI interface and INET/EUN 1469 interfaces (see: Section 3.2.3). The Relay provisions MNPs to 1470 networks on the INET/EUN interfaces (i.e., the same as a Client would 1471 do) and advertises the MSP(s) for the OMNI link over the INET/EUN 1472 interfaces. The Relay further provides an attachment point of the 1473 OMNI link to a non-MNP-based global topology. 1475 3.4.2. AERO Client Behavior 1477 When a Client enables an OMNI interface, it assigns either an 1478 MNP-{LLA, ULA} or a Temporary ULA and sends RS messages with ND 1479 parameters over its underlying interfaces to an FHS Proxy/Server, 1480 which returns an RA message with corresponding parameters. The RS/RA 1481 messages may pass through one or more NATs in the case of a Client's 1482 INET interface. (Note: if the Client used a Temporary ULA in its 1483 initial RS message, it will discover an MNP-{LLA, ULA} in the 1484 corresponding RA that it receives from the FHS Proxy/Server and begin 1485 using these new addresses. If the Client is operating outside the 1486 context of AERO infrastructure such as in a Mobile Ad-hoc Network 1487 (MANET), however, it may continue using Temporary ULAs for Client-to- 1488 Client communications until it encounters an infrastructure element 1489 that can provide an MNP.) 1491 3.4.3. AERO Bridge Behavior 1493 AERO Bridges configure an OMNI interface and assign the ADM-ULA 1494 Subnet Router Anycast address for each OMNI link SRT segment they 1495 connect to. Bridges configure secured tunnels with Proxy/Servers in 1496 the same SRT segment and other Bridges in the same (or an adjacent) 1497 SRT segment. Bridges then engage in a BGP routing protocol session 1498 with neighbors over the secured spanning tree (see: Section 3.2.3). 1500 3.5. OMNI Interface Neighbor Cache Maintenance 1502 Each OMNI interface maintains a conceptual neighbor cache that 1503 includes a Neighbor Cache Entry (NCE) for each of its active 1504 neighbors on the OMNI link per [RFC4861]. Each route optimization 1505 source NCE is indexed by the LLA of the neighbor, while the OAL 1506 encapsulation ULA determines the context for Identification 1507 verification. In addition to ordinary neighbor cache entries, proxy 1508 neighbor cache entries are created and maintained by AERO Proxy/ 1509 Servers when they proxy Client ND message exchanges [RFC4389]. AERO 1510 Proxy/Servers maintain proxy neighbor cache entries for each of their 1511 associated Clients. 1513 To the list of NCE states in Section 7.3.2 of [RFC4861], Proxy/Server 1514 OMNI interfaces add an additional state DEPARTED that applies to 1515 Clients that have recently departed. The interface sets a 1516 "DepartTime" variable for the NCE to "DEPART_TIME" seconds. 1517 DepartTime is decremented unless a new ND message causes the state to 1518 return to REACHABLE. While a NCE is in the DEPARTED state, the 1519 Proxy/Server forwards carrier packets destined to the target Client 1520 to the Client's new location instead. When DepartTime decrements to 1521 0, the NCE is deleted. It is RECOMMENDED that DEPART_TIME be set to 1522 the default constant value REACHABLE_TIME plus 10 seconds (40 seconds 1523 by default) to allow a window for carrier packets in flight to be 1524 delivered while stale route optimization state may be present. 1526 Proxy/Servers can act as RORs on behalf of their associated Clients 1527 according to the Proxy Neighbor Advertisement specification in 1528 Section 7.2.8 of [RFC4861]. When a Proxy/Server ROR receives an 1529 authentic NS message used for route optimization, it first searches 1530 for a NCE for the target Client and accepts the message only if there 1531 is an entry. The Proxy/Server then returns a solicited NA message 1532 while creating or updating a "Report List" entry in the target 1533 Client's NCE that caches both the LLA and ULA of ROS with a 1534 "ReportTime" variable set to REPORT_TIME seconds. The ROR resets 1535 ReportTime when it receives a new authentic NS message, and otherwise 1536 decrements ReportTime while no authentic NS messages have been 1537 received. It is RECOMMENDED that REPORT_TIME be set to the default 1538 constant value REACHABLE_TIME plus 10 seconds (40 seconds by default) 1539 to allow a window for route optimization to converge before 1540 ReportTime decrements below REACHABLE_TIME. 1542 When the ROS receives a solicited NA message response to its NS 1543 message used for route optimization, it creates or updates a NCE for 1544 the target network-layer and link-layer addresses. The ROS then 1545 (re)sets ReachableTime for the NCE to REACHABLE_TIME seconds and 1546 performs reachability tests over specific underlying interface pairs 1547 to determine paths for forwarding carrier packets directly to the 1548 target. The ROS otherwise decrements ReachableTime while no further 1549 solicited NA messages arrive. It is RECOMMENDED that REACHABLE_TIME 1550 be set to the default constant value 30 seconds as specified in 1551 [RFC4861]. 1553 AERO nodes also use the value MAX_UNICAST_SOLICIT to limit the number 1554 of NS messages sent when a correspondent may have gone unreachable, 1555 the value MAX_RTR_SOLICITATIONS to limit the number of RS messages 1556 sent without receiving an RA and the value MAX_NEIGHBOR_ADVERTISEMENT 1557 to limit the number of unsolicited NAs that can be sent based on a 1558 single event. It is RECOMMENDED that MAX_UNICAST_SOLICIT, 1559 MAX_RTR_SOLICITATIONS and MAX_NEIGHBOR_ADVERTISEMENT be set to 3 the 1560 same as specified in [RFC4861]. 1562 Different values for DEPART_TIME, REPORT_TIME, REACHABLE_TIME, 1563 MAX_UNICAST_SOLICIT, MAX_RTR_SOLCITATIONS and 1564 MAX_NEIGHBOR_ADVERTISEMENT MAY be administratively set; however, if 1565 different values are chosen, all nodes on the link MUST consistently 1566 configure the same values. Most importantly, DEPART_TIME and 1567 REPORT_TIME SHOULD be set to a value that is sufficiently longer than 1568 REACHABLE_TIME to avoid packet loss due to stale route optimization 1569 state. 1571 3.5.1. OMNI ND Messages 1573 OMNI interfaces prepare IPv6 ND messages the same as for standard 1574 IPv6 ND, but also include a new option type termed the OMNI option 1575 [I-D.templin-6man-omni]. OMNI interfaces prepare IPv6 ND messages 1576 the same as for standard IPv6 ND, and include one or more OMNI 1577 options and any other options then completely populate all option 1578 information. If the OMNI interface includes an authentication 1579 signature, it sets the IPv6 ND message Checksum field to 0 and 1580 calculates the authentication signature over the entire length of the 1581 message (beginning with a pseudo-header of the IPv6 header) but does 1582 not then proceed to calculate the IPv6 ND message checksum itself. 1583 If the OMNI interface forwards the message to a next hop over the 1584 secured spanning tree path, it omits both the authentication 1585 signature or checksum since lower layers already ensure 1586 authentication and integrity. In all other cases, the OMNI interface 1587 calculates the standard IPv6 ND message checksum and writes the value 1588 in the Checksum field. OMNI interfaces verify authentication and 1589 integrity of each IPv6 ND message received according to the specific 1590 check(s) included, and process the message further only following 1591 verification. 1593 OMNI options include per-neighbor information such as Interface 1594 Attributes that provide link-layer address and traffic selector 1595 information for the neighbor's underlying interfaces. This 1596 information is stored in the neighbor cache and provides the basis 1597 for the forwarding algorithm specified in Section 3.10. The 1598 information is cumulative and reflects the union of the OMNI 1599 information from the most recent ND messages received from the 1600 neighbor; it is therefore not required that each ND message contain 1601 all neighbor information. 1603 The OMNI option Interface Attributes for each underlying interface 1604 includes a two-part "Link-Layer Address" consisting of an INET 1605 encapsulation address determined by the FMT and L2ADDR fields and an 1606 ADM-ULA determined by the SRT and LHS fields. Underlying interfaces 1607 are further selected based on their associated traffic selectors. 1609 The OMNI option is distinct from any Source/Target Link-Layer Address 1610 Options (S/TLLAOs) that may appear in an ND message according to the 1611 appropriate IPv6 over specific link layer specification (e.g., 1612 [RFC2464]). If both an OMNI option and S/TLLAO appear, the former 1613 pertains to encapsulation addresses while the latter pertains to the 1614 native L2 address format of the underlying media 1616 OMNI interface IPv6 ND messages may also include other IPv6 ND 1617 options. In particular, solicitation messages may include Nonce and/ 1618 or Timestamp options if required for verification of advertisement 1619 replies. If an OMNI ND solicitation message includes a Nonce option, 1620 the advertisement reply must echo the same Nonce. If an OMNI ND 1621 solicitation message includes a Timestamp option, the advertisement 1622 reply should also include a Timestamp option. 1624 AERO Clients send RS messages to the All-Routers multicast address 1625 while using unicast link-layer addresses. AERO Proxy/Servers respond 1626 by returning unicast RA messages. During the RS/RA exchange, AERO 1627 Clients and Servers include state synchronization parameters to 1628 establish Identification windows and other state. 1630 AERO nodes use NS/NA messages for the following purposes: 1632 o NS/NA(AR) messages are used for address resolution only. The ROS 1633 sends an NS(AR) to the solicited-node multicast address of the 1634 target, and an ROR in the network with addressing information for 1635 the target returns a unicast NA(AR). The NA(AR) contains 1636 authentic and current target address resolution information, but 1637 only an implicit third-party assertion of target reachability. 1638 NS/NA(AR) messages must be secured. 1640 o NS/NA(WIN) messages are used for establishing and maintaining 1641 window synchronization state (and/or any other state such as 1642 Interface Attributes). The source sends an NS(WIN) to the unicast 1643 address of the target, and the target returns a unicast NA(WIN). 1644 The NS/NA(WIN) exchange synchronizes the sequence number windows 1645 for Identification values the neighbors will include in subsequent 1646 carrier packets, and asserts reachability for the target without 1647 necessarily testing a specific underlying interface pair. NS/ 1648 NA(WIN) messages must be secured. 1650 o NS/NA(NUD) messages are used for determining target reachability. 1651 The source sends an NS(NUD) to the unicast address of the target 1652 while naming a specific underlying interface pair, and the target 1653 returns a unicast NA(NUD). NS/NA(NUD) messages that use an in- 1654 window sequence number and do not update any other state need not 1655 be secured but should include an IPv6 ND message checksum. NS/ 1656 NA(NUD) messages may also be used in combination with window 1657 synchronization (i.e., NUD+WIN), in which case the messages must 1658 be secured. 1660 o Unsolicited NA (uNA) messages are used to signal addressing and/or 1661 other neighbor state changes (e.g., address changes due to 1662 mobility, signal degradation, traffic selector updates, etc.). uNA 1663 messages that include state update information must be secured. 1665 o NS/NA(DAD) messages are not used in AERO, since Duplicate Address 1666 Detection is not required. 1668 Additionally, nodes may send NA/RA messages with the OMNI option PNG 1669 flag set to receive a solicited NA response from the neighbor. The 1670 solicited NA response MUST set the ACK flag (without also setting the 1671 SYN or PNG flags) and include the Identification used in the PNG 1672 message in the Acknowledgement. 1674 3.5.2. OMNI Neighbor Advertisement Message Flags 1676 As discussed in Section 4.4 of [RFC4861] NA messages include three 1677 flag bits R, S and O. OMNI interface NA messages treat the flags as 1678 follows: 1680 o R: The R ("Router") flag is set to 1 in the NA messages sent by 1681 all AERO/OMNI node types. Simple hosts that would set R to 0 do 1682 not occur on the OMNI link itself, but may occur on the downstream 1683 links of Clients and Relays. 1685 o S: The S ("Solicited") flag is set exactly as specified in 1686 Section 4.4. of [RFC4861], i.e., it is set to 1 for Solicited NAs 1687 and set to 0 for uNAs (both unicast and multicast). 1689 o O: The O ("Override") flag is set to 0 for solicited NAs returned 1690 by a Proxy/Server ROR and set to 1 for all other solicited and 1691 unsolicited NAs. For further study is whether solicited NAs for 1692 anycast targets apply for OMNI links. Since MNP-LLAs must be 1693 uniquely assigned to Clients to support correct ND protocol 1694 operation, however, no role is currently seen for assigning the 1695 same MNP-LLA to multiple Clients. 1697 3.5.3. OMNI Neighbor Window Synchronization 1699 In secured environments (e.g., such as between nodes on the same 1700 secured ANET), OMNI interface neighbors can exchange OAL packets 1701 using randomly-initialized and monotonically-increasing 1702 Identification values (modulo 2*32) without window synchronization. 1703 In environments where spoofing is considered a threat, OMNI interface 1704 neighbors instead invoke window synchronization in ND message 1705 exchanges to maintain send/receive window state in their respective 1706 neighbor cache entries as specified in [I-D.templin-6man-omni]. 1708 In the asymmetric window synchronization case, the initial ND message 1709 exchange establishes only the initiator's send window and the 1710 responder's receive window such that a corresponding exchange would 1711 be needed to establish the reverse direction. In the symmetric case, 1712 the initiator and responder engage in a three-way handshake to 1713 symmetrically establish the send/receive windows of both parties. 1715 3.6. OMNI Interface Encapsulation and Re-encapsulation 1717 The OMNI interface admits original IP packets then acts as an OAL 1718 source to perform OAL encapsulation and fragmentation as specified in 1719 [I-D.templin-6man-omni] while including an ORH if necessary as 1720 specified in Section 3.2.4. The OAL encapsulates original IP packets 1721 to form OAL packets subject to fragmentation, then encapsulates the 1722 resulting OAL fragments in *NET headers as carrier packets. 1724 For carrier packets undergoing re-encapsulation at an OAL 1725 intermediate node, the OMNI interface decrements the OAL IPv6 header 1726 Hop Limit and discards the carrier packet if the Hop Limit reaches 0. 1727 The intermediate node next removes the *NET encapsulation headers 1728 from the first segment and re-encapsulates the packet in new *NET 1729 encapsulation headers for the next segment. 1731 When an FHS Proxy/Server re-encapsulates a carrier packet received 1732 from a Client that includes an OAL but no ORH, it inserts an ORH 1733 immediately following the OAL header and adjusts the OAL payload 1734 length and destination address field. The ORH may be removed by an 1735 LHS Bridge or Proxy/Server, but its insertion and removal will not 1736 interfere with reassembly at the final destination. For this reason, 1737 Clients must reserve 40 bytes for a maximum-length ORH when they 1738 perform OAL encapsulation (see: Section 3.9). 1740 3.7. OMNI Interface Decapsulation 1742 OMNI interfaces (acting as OAL destinations) decapsulate and 1743 reassemble OAL packets into original IP packets destined either to 1744 the AERO node itself or to a destination reached via an interface 1745 other than the OMNI interface the original IP packet was received on. 1746 When carrier packets containing OAL fragments addressed to itself 1747 arrive, the OMNI interface discards the NET encapsulation headers and 1748 reassembles as discussed in Section 3.9. 1750 3.8. OMNI Interface Data Origin Authentication 1752 AERO nodes employ simple data origin authentication procedures. In 1753 particular: 1755 o AERO Bridges and Proxy/Servers accept carrier packets received 1756 from secured underlying interfaces. 1758 o AERO Proxy/Servers and Clients accept carrier packets and original 1759 IP packets that originate from within the same secured ANET. 1761 o AERO Clients and Relays accept original IP packets from downstream 1762 network correspondents based on ingress filtering. 1764 o AERO Clients, Relays and Proxy/Servers verify carrier packet UDP/ 1765 IP encapsulation addresses according to [I-D.templin-6man-omni]. 1767 o AERO nodes accept carrier packets addressed to themselves with 1768 Identification values within the current window for the OAL source 1769 neighbor (when window synchronization is used) and drop any 1770 carrier packets with out-of-window Identification values. (AERO 1771 nodes may forward carrier packets not addressed to themselves 1772 without verifying the Identification value.) 1774 AERO nodes silently drop any packets that do not satisfy the above 1775 data origin authentication procedures. Further security 1776 considerations are discussed in Section 6. 1778 3.9. OMNI Interface MTU 1780 The OMNI interface observes the link nature of tunnels, including the 1781 Maximum Transmission Unit (MTU), Maximum Reassembly Unit (MRU) and 1782 the role of fragmentation and reassembly [I-D.ietf-intarea-tunnels]. 1783 The OMNI interface employs an OMNI Adaptation Layer (OAL) that 1784 accommodates multiple underlying links with diverse MTUs while 1785 observing both a minimum and per-path Maximum Payload Size (MPS). 1786 The functions of the OAL and the OMNI interface MTU/MRU/MPS are 1787 specified in [I-D.templin-6man-omni] with MTU/MRU both set to the 1788 constant value 9180 bytes, with minimum MPS set to 400 bytes, and 1789 with potentially larger per-path MPS values depending on the 1790 underlying path. 1792 When the network layer presents an original IP packet to the OMNI 1793 interface, the OAL source encapsulates and fragments the original IP 1794 packet if necessary. When the network layer presents the OMNI 1795 interface with multiple original IP packets bound to the same OAL 1796 destination, the OAL source can concatenate them together into a 1797 single OAL super-packet as discussed in [I-D.templin-6man-omni]. The 1798 OAL source then fragments the OAL packet if necessary according to 1799 the minimum/path MPS such that the OAL headers appear in each 1800 fragment while the original IP packet header appears only in the 1801 first fragment. The OAL source then encapsulates each OAL fragment 1802 in *NET headers for transmission as carrier packets over an 1803 underlying interface connected to either a physical link (such as 1804 Ethernet, WiFi and the like) or a virtual link such as an Internet or 1805 higher-layer tunnel (see the definition of link in [RFC8200]). 1807 Note: A Client that does not (yet) have neighbor cache state for a 1808 target may omit the ORH in carrier packets with the understanding 1809 that a Proxy/Server may insert an ORH on its behalf. For this 1810 reason, Clients reserve 40 bytes for the largest possible ORH in 1811 their OAL fragment size calculations. 1813 Note: Although the ORH may be removed or replaced by a Bridge or 1814 Proxy/Server on the path (see: Section 3.10.3), this does not 1815 interfere with the destination's ability to reassemble since the ORH 1816 is not included in the fragmentable part and its removal/ 1817 transformation does not invalidate fragment header information. 1819 3.10. OMNI Interface Forwarding Algorithm 1821 Original IP packets enter a node's OMNI interface either from the 1822 network layer (i.e., from a local application or the IP forwarding 1823 system) while carrier packets enter from the link layer (i.e., from 1824 an OMNI interface neighbor). All original IP packets and carrier 1825 packets entering a node's OMNI interface first undergo data origin 1826 authentication as discussed in Section 3.8. Those that satisfy data 1827 origin authentication are processed further, while all others are 1828 dropped silently. 1830 Original IP packets that enter the OMNI interface from the network 1831 layer are forwarded to an OMNI interface neighbor using OAL 1832 encapsulation and fragmentation to produce carrier packets for 1833 transmission over underlying interfaces. (If routing indicates that 1834 the original IP packet should instead be forwarded back to the 1835 network layer, the packet is dropped to avoid looping). Carrier 1836 packets that enter the OMNI interface from the link layer are either 1837 re-encapsulated and re-admitted into the OMNI link, or reassembled 1838 and forwarded to the network layer where they are subject to either 1839 local delivery or IP forwarding. In all cases, the OAL MUST NOT 1840 decrement the network layer TTL/Hop-count since its forwarding 1841 actions occur below the network layer. 1843 OMNI interfaces may have multiple underlying interfaces and/or 1844 neighbor cache entries for neighbors with multiple underlying 1845 interfaces (see Section 3.3). The OAL uses Interface Attributes 1846 traffic selectors (e.g., port number, flow specification, etc.) to 1847 select an outbound underlying interface for each OAL packet based on 1848 the node's own interface attributes, and also to select a destination 1849 link-layer address based on the neighbor's underlying interface 1850 attributes. AERO implementations SHOULD permit network management to 1851 dynamically adjust traffic selector values at runtime. 1853 If an OAL packet matches the traffic selectors of multiple outgoing 1854 interfaces and/or neighbor interfaces, the OMNI interface replicates 1855 the packet and sends one copy via each of the (outgoing / neighbor) 1856 interface pairs; otherwise, it sends a single copy of the OAL packet 1857 via an interface with the best matching traffic selector. (While not 1858 strictly required, the likelihood of successful reassembly may 1859 improve when the OMNI interface sends all fragments of the same 1860 fragmented OAL packet consecutively over the same underlying 1861 interface pair to avoid complicating factors such as delay variance 1862 and reordering.) AERO nodes keep track of which underlying 1863 interfaces are currently "reachable" or "unreachable", and only use 1864 "reachable" interfaces for forwarding purposes. 1866 The following sections discuss the OMNI interface forwarding 1867 algorithms for Clients, Proxy/Servers and Bridges. In the following 1868 discussion, an original IP packet's destination address is said to 1869 "match" if it is the same as a cached address, or if it is covered by 1870 a cached prefix (which may be encoded in an MNP-LLA). 1872 3.10.1. Client Forwarding Algorithm 1874 When an original IP packet enters a Client's OMNI interface from the 1875 network layer the Client searches for a NCE that matches the 1876 destination. If there is a match, the Client selects one or more 1877 "reachable" neighbor interfaces in the entry for forwarding purposes. 1878 If there is no NCE, the Client instead either enqueues the original 1879 IP packet and invokes route optimization or forwards the original IP 1880 packet toward a Proxy/Server. The Client (acting as an OAL source) 1881 performs OAL encapsulation and sets the OAL destination address to 1882 the MNP-ULA of the target if there is a matching NCE; otherwise, it 1883 sets the OAL destination to the ADM-ULA of the Proxy/Server. If the 1884 Client has multiple original IP packets to send to the same neighbor, 1885 it can concatenate them in a single super-packet 1886 [I-D.templin-6man-omni]. The OAL source then performs fragmentation 1887 to create OAL fragments (see: Section 3.9), appends any *NET 1888 encapsulation, and sends the resulting carrier packets over 1889 underlying interfaces to the neighbor acting as an OAL destination. 1891 If the neighbor interface selected for forwarding is located on the 1892 same OMNI link segment and not behind a NAT, the Client forwards the 1893 carrier packets directly according to the L2ADDR information for the 1894 neighbor. If the neighbor interface is behind a NAT on the same OMNI 1895 link segment, the Client instead forwards the initial carrier packets 1896 to the LHS Proxy/Server (while inserting an ORH-0 if necessary) and 1897 initiates NAT traversal procedures. If the Client's intended source 1898 underlying interface is also behind a NAT and located on the same 1899 OMNI link segment, it sends a "direct bubble" over the interface per 1900 [RFC6081][RFC4380] to the L2ADDR found in the neighbor cache in order 1901 to establish state in its own NAT by generating traffic toward the 1902 neighbor (note that no response to the bubble is expected). 1904 The Client next sends an NS(NUD) message toward the MNP-ULA of the 1905 neighbor via the LHS Proxy/Server as discussed in Section 3.15. If 1906 the Client receives an NA(NUD) from the neighbor over the underlying 1907 interface, it marks the neighbor interface as "trusted" and sends 1908 future carrier packets directly to the L2ADDR information for the 1909 neighbor instead of indirectly via the LHS Proxy/Server. The Client 1910 must honor the neighbor cache maintenance procedure by sending 1911 additional direct bubbles and/or NS/NA(NUD) messages as discussed in 1912 [RFC6081][RFC4380] in order to keep NAT state alive as long as 1913 carrier packets are still flowing. 1915 When a carrier packet enters a Client's OMNI interface from the link- 1916 layer, if the OAL destination matches one of the Client's ULAs the 1917 Client (acting as an OAL destination) verifies that the 1918 Identification is in-window for this OAL source, then reassembles and 1919 decapsulates as necessary and delivers the original IP packet to the 1920 network layer. Otherwise, the Client drops the original IP packet 1921 and MAY return a network-layer ICMP Destination Unreachable message 1922 subject to rate limiting (see: Section 3.11). 1924 Note: Clients and their FHS Proxy/Server (and other Client) peers can 1925 exchange original IP packets over ANET underlying interfaces without 1926 invoking the OAL, since the ANET is secured at the link and physical 1927 layers. By forwarding original IP packets without invoking the OAL, 1928 however, the ANET peers can engage only in classical path MTU 1929 discovery since the packets are subject to loss and/or corruption due 1930 to the various per-link MTU limitations that may occur within the 1931 ANET. Moreover, the original IP packets do not include either the 1932 OAL integrity check or per-packet Identification values that can be 1933 used for data origin authentication and link-layer retransmissions. 1934 The tradeoff therefore involves an assessment of the per-packet 1935 encapsulation overhead saved by bypassing the OAL vs. inheritance of 1936 classical network "brittleness". (Note however that ANET peers can 1937 send small original IP packets without invoking the OAL, while 1938 invoking the OAL for larger packets. This presents the beneficial 1939 aspects of both small packet efficiency and large packet robustness, 1940 with delay variance and reordering as possible side effects.) 1942 3.10.2. Proxy/Server and Relay Forwarding Algorithm 1944 When the Proxy/Server receives an original IP packet from the network 1945 layer, it drops the packet if routing indicates that it should be 1946 forwarded back to the network layer to avoid looping. Otherwise, the 1947 Proxy/Server regards the original IP packet the same as if it had 1948 arrived as carrier packets with OAL destination set to its own ADM- 1949 ULA. When the Proxy/Server receives carrier packets on underlying 1950 interfaces with OAL destination set to its own ADM-ULA, it performs 1951 OAL reassembly if necessary to obtain the original IP packet. 1953 The Proxy/Server next searches for a NCE that matches the original IP 1954 destination and proceeds as follows: 1956 o if the original IP packet destination matches a NCE, the Proxy/ 1957 Sever uses one or more "reachable" neighbor interfaces in the 1958 entry for packet forwarding using OAL encapsulation and 1959 fragmentation according to the cached link-layer address 1960 information. If the neighbor interface is in a different OMNI 1961 link segment, the Proxy/Server performs OAL encapsulation and 1962 fragmentation, inserts an ORH and forwards the resulting carrier 1963 packets via the spanning tree to a Bridge; otherwise, it forwards 1964 the carrier packets directly to the neighbor. If the neighbor is 1965 behind a NAT, the Proxy/Server instead forwards initial carrier 1966 packets via a Bridge while sending an NS(NUD) to the neighbor. 1967 When the Proxy/Server receives the NA(NUD), it can begin 1968 forwarding carrier packets directly to the neighbor the same as 1969 discussed in Section 3.10.1 while sending additional NS(NUD) 1970 messages as necessary to maintain NAT state. Note that no direct 1971 bubbles are necessary since the Proxy/Server is by definition not 1972 located behind a NAT. 1974 o else, if the original IP destination matches a non-MNP route in 1975 the IP forwarding table or an ADM-LLA assigned to the Proxy/ 1976 Server's OMNI interface, the Proxy/Server acting as a Relay 1977 presents the original IP packet to the network layer for local 1978 delivery or IP forwarding. 1980 o else, the Proxy/Server initiates address resolution as discussed 1981 in Section 3.14, while retaining initial original IP packets in a 1982 small queue awaiting address resolution completion. 1984 When the Proxy/Server receives a carrier packet with OAL destination 1985 set to an MNP-ULA that does not match the MSP, it accepts the carrier 1986 packet only if data origin authentication succeeds and if there is a 1987 network layer routing table entry for a GUA route that matches the 1988 MNP-ULA. If there is no route, the Proxy/Server drops the carrier 1989 packet; otherwise, it reassembles and decapsulates to obtain the 1990 original IP packet then acts as a Relay to present it to the network 1991 layer where it will be delivered according to standard IP forwarding. 1993 When a Proxy/Server receives a carrier packet from one of its Client 1994 neighbors with OAL destination set to another node, it forwards the 1995 packets via a matching NCE or via the spanning tree if there is no 1996 matching entry. When the Proxy/Server receives a carrier packet with 1997 OAL destination set to the MNP-ULA of one of its Client neighbors 1998 established through RS/RA exchanges, it accepts the carrier packet 1999 only if data origin authentication succeeds. If the NCE state is 2000 DEPARTED, the Proxy/Server inserts an ORH that encodes the MNP-ULA 2001 destination suffix and changes the OAL destination address to the 2002 ADM-ULA of the new Proxy/Server, then re-encapsulates the carrier 2003 packet and forwards it to a Bridge which will eventually deliver it 2004 to the new Proxy/Server. 2006 If the neighbor cache state for the MNP-ULA is REACHABLE, the Proxy/ 2007 Server forwards the carrier packets to the Client which then must 2008 reassemble. (Note that the Proxy/Server does not reassemble carrier 2009 packets not explicitly addressed to its own ADM-ULA, since some of 2010 the carrier packets of the same original IP packet could be forwarded 2011 through a different Proxy/Server.) In that case, the Client may 2012 receive fragments that are smaller than its link MTU but that can 2013 still be reassembled. 2015 Note: Proxy/Servers may receive carrier packets with ORHs that 2016 include additional forwarding information. Proxy/Servers use the 2017 forwarding information to determine the correct interface for 2018 forwarding to the target Client, then remove the ORH and forward the 2019 carrier packet. If the ORH information instead indicates that the 2020 Proxy/Server is responsible for reassembly, the Proxy/Server 2021 reassembles first before re-encapsulating (and possibly also re- 2022 fragmenting) then forwards to the target Client. For a full 2023 discussion of cases when the Proxy/Server may receive carrier packets 2024 with ORHs, see: Section 3.14.6. 2026 Note: Clients and their FHS Proxy/Server peers can exchange original 2027 IP packets over ANET underlying interfaces without invoking the OAL, 2028 since the ANET is secured at the link and physical layers. By 2029 forwarding original IP packets without invoking the OAL, however, the 2030 Client and Proxy/Server can engage only in classical path MTU 2031 discovery since the packets are subject to loss and/or corruption due 2032 to the various per-link MTU limitations that may occur within the 2033 ANET. Moreover, the original IP packets do not include either the 2034 OAL integrity check or per-packet Identification values that can be 2035 used for data origin authentication and link-layer retransmissions. 2036 The tradeoff therefore involves an assessment of the per-packet 2037 encapsulation overhead saved by bypassing the OAL vs. inheritance of 2038 classical network "brittleness". (Note however that ANET peers can 2039 send small original IP packets without invoking the OAL, while 2040 invoking the OAL for larger packets. This presents the beneficial 2041 aspects of both small packet efficiency and large packet robustness.) 2043 Note: When a Proxy/Server receives a (non-OAL) original IP packet 2044 from an ANET Client, or a carrier packet with OAL destination set to 2045 its own ADM-ULA from any Client, the Proxy/Server reassembles if 2046 necessary then performs ROS functions on behalf of the Client. The 2047 Client may at some later time begin sending carrier packets to the 2048 OAL address of the actual target instead of the Proxy/Server, at 2049 which point it may begin functioning as an ROS on its own behalf and 2050 thereby "override" the Proxy/Server's ROS role. 2052 Note; Proxy/Servers drop any original IP packets (received either 2053 directly from an ANET Client or following reassembly of carrier 2054 packets received from an ANET/INET Client) with a destination that 2055 corresponds to the Client's delegated MNP. Similarly, Proxy/Servers 2056 drop any carrier packet received with both a source and destination 2057 that correspond to the Client's delegated MNP regardless of their 2058 OMNI link point of origin. These checks are necessary to prevent 2059 Clients from either accidentally or intentionally establishing 2060 endless loops that could congest Proxy/Servers and/or ANET/INET 2061 links. 2063 Note: Proxy/Servers forward secure control plane carrier packets via 2064 the SRT secured spanning tree and forwards other carrier packets via 2065 the unsecured spanning tree. When a Proxy/Server receives a carrier 2066 packet from the secured spanning tree, it considers the message as 2067 authentic without having to verify upper layer authentication 2068 signatures. When a Proxy/Server receives a carrier packet from the 2069 unsecured spanning tree, it verifies any upper layer authentication 2070 signatures and/or forwards the unsecured message toward the 2071 destination which must apply data origin authentication. 2073 Note: If the Proxy/Server has multiple original IP packets to send to 2074 the same neighbor, it can concatenate them in a single OAL super- 2075 packet [I-D.templin-6man-omni]. 2077 3.10.3. Bridge Forwarding Algorithm 2079 Bridges forward carrier packets while decrementing the OAL header Hop 2080 Count but not the original IP header Hop Count/TTL. Bridges convey 2081 carrier packets that encapsulate IPv6 ND control messages or routing 2082 protocol control messages via the secured spanning tree, and may 2083 convey carrier packets that encapsulate ordinary data via the 2084 unsecured spanning tree. When the Bridge receives a carrier packet, 2085 it removes the outer *NET header and searches for a forwarding table 2086 entry that matches the OAL destination address. The Bridge then 2087 processes the packet as follows: 2089 o if the carrier packet destination matches its ADM-ULA or the 2090 corresponding ADM-ULA Subnet Router Anycast address and the OAL 2091 header is followed by an ORH, the Bridge reassembles if necessary 2092 then sets aside the ORH and processes the carrier packet locally 2093 before forwarding. If the OAL packet contains an NA(NUD) message, 2094 the Bridge writes its own INET FMT/SRT/LHS/L2ADDR information over 2095 the OMNI option Interface Attributes sub-option supplied by the 2096 NA(NUD) message source. The Bridge next examines the ORH, and if 2097 FMT-Mode indicates the destination is a Client on the open *NET 2098 (or, a Client behind a NAT for which NAT traversal procedures have 2099 already converged) the Bridge writes the MNP-ULA formed from the 2100 ORH Destination Suffix into the OAL destination. The Bridge then 2101 removes the ORH and forwards the packet using encapsulation based 2102 on L2ADDR. If the LHS Proxy/Server will forward to the Client 2103 without reassembly, the Bridge writes the MNP-ULA into the OAL 2104 destination then replaces the ORH with an ORH-0 and forwards the 2105 carrier packet to the LHS Proxy/Server while also invoking NAT 2106 traversal procedures if necessary (noting that no direct bubbles 2107 are necessary since only the target Client and not the Bridge is 2108 behind a NAT). If the LHS Proxy/Server must perform reassembly 2109 before forwarding to the Client, the Bridge instead writes the 2110 ADM-ULA formed from the ORH SRT/LHS into the OAL destination 2111 address, replaces the ORH with an ORH-0 and forwards the carrier 2112 packet to the LHS Proxy/Server. 2114 o else, if the carrier packet destination matches its ADM-ULA or the 2115 corresponding ADM-ULA Subnet Router Anycast address and the OAL 2116 header is not followed by an ORH with Segments Left set to 1, the 2117 Bridge submits the packet for reassembly. When reassembly is 2118 complete, the Bridge submits the original IP packet to the network 2119 layer to support local applications such as BGP routing protocol 2120 sessions. 2122 o else, if the carrier packet destination matches a forwarding table 2123 entry the Bridge forwards the carrier packet to the next hop. (If 2124 the destination matches an MSP without matching an MNP, however, 2125 the Bridge instead drops the packet and returns a Destination 2126 Unreachable message subject to rate limiting - see: Section 3.11). 2128 o else, the Bridge drops the packet and returns an Destination 2129 Unreachable as above. 2131 The Bridge decrements the OAL IPv6 header Hop Limit when it forwards 2132 the carrier packet and drops the packet if the Hop Limit reaches 0. 2133 Therefore, only the Hop Limit in the OAL header is decremented and 2134 not the TTL/Hop Limit in the original IP packet header. Bridges do 2135 not insert OAL/ORH headers themselves; instead, they simply forward 2136 carrier packets based on their destination addresses while also 2137 possibly transforming larger ORHs into an ORH-0 (or removing the ORH 2138 altogether). 2140 Bridges forward carrier packets received from a first segment via the 2141 SRT secured spanning tree to the next segment also via the secured 2142 spanning tree. Bridges forward carrier packets received from a first 2143 segment via the unsecured spanning tree to the next segment also via 2144 the unsecured spanning tree. Bridges use a single IPv6 routing table 2145 that always determines the same next hop for a given OAL destination, 2146 where the secured/unsecured spanning tree is determined through the 2147 selection of the underlying interface to be used for transmission 2148 (i.e., a secured tunnel or an open INET interface). 2150 3.11. OMNI Interface Error Handling 2152 When an AERO node admits an original IP packet into the OMNI 2153 interface, it may receive link-layer or network-layer error 2154 indications. The AERO node may also receive OMNI link error 2155 indications in OAL-encapsulated uNA messages that include 2156 authentication signatures. 2158 A link-layer error indication is an ICMP error message generated by a 2159 router in the INET on the path to the neighbor or by the neighbor 2160 itself. The message includes an IP header with the address of the 2161 node that generated the error as the source address and with the 2162 link-layer address of the AERO node as the destination address. 2164 The IP header is followed by an ICMP header that includes an error 2165 Type, Code and Checksum. Valid type values include "Destination 2166 Unreachable", "Time Exceeded" and "Parameter Problem" 2167 [RFC0792][RFC4443]. (OMNI interfaces ignore link-layer IPv4 2168 "Fragmentation Needed" and IPv6 "Packet Too Big" messages for carrier 2169 packets that are no larger than the minimum/path MPS as discussed in 2170 Section 3.9, however these messages may provide useful hints of probe 2171 failures during path MPS probing.) 2172 The ICMP header is followed by the leading portion of the carrier 2173 packet that generated the error, also known as the "packet-in-error". 2174 For ICMPv6, [RFC4443] specifies that the packet-in-error includes: 2175 "As much of invoking packet as possible without the ICMPv6 packet 2176 exceeding the minimum IPv6 MTU" (i.e., no more than 1280 bytes). For 2177 ICMPv4, [RFC0792] specifies that the packet-in-error includes: 2178 "Internet Header + 64 bits of Original Data Datagram", however 2179 [RFC1812] Section 4.3.2.3 updates this specification by stating: "the 2180 ICMP datagram SHOULD contain as much of the original datagram as 2181 possible without the length of the ICMP datagram exceeding 576 2182 bytes". 2184 The link-layer error message format is shown in Figure 5: 2186 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2187 ~ ~ 2188 | IP Header of link layer | 2189 | error message | 2190 ~ ~ 2191 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2192 | ICMP Header | 2193 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 2194 ~ ~ P 2195 | carrier packet *NET and OAL | a 2196 | encapsulation headers | c 2197 ~ ~ k 2198 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ e 2199 ~ ~ t 2200 | original IP packet headers | 2201 | (first-fragment only) | i 2202 ~ ~ n 2203 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2204 ~ ~ e 2205 | Portion of the body of | r 2206 | the original IP packet | r 2207 | (all fragments) | o 2208 ~ ~ r 2209 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 2211 Figure 5: OMNI Interface Link-Layer Error Message Format 2213 The AERO node rules for processing these link-layer error messages 2214 are as follows: 2216 o When an AERO node receives a link-layer Parameter Problem message, 2217 it processes the message the same as described as for ordinary 2218 ICMP errors in the normative references [RFC0792][RFC4443]. 2220 o When an AERO node receives persistent link-layer Time Exceeded 2221 messages, the IP ID field may be wrapping before earlier fragments 2222 awaiting reassembly have been processed. In that case, the node 2223 should begin including integrity checks and/or institute rate 2224 limits for subsequent packets. 2226 o When an AERO node receives persistent link-layer Destination 2227 Unreachable messages in response to carrier packets that it sends 2228 to one of its neighbor correspondents, the node should process the 2229 message as an indication that a path may be failing, and 2230 optionally initiate NUD over that path. If it receives 2231 Destination Unreachable messages over multiple paths, the node 2232 should allow future carrier packets destined to the correspondent 2233 to flow through a default route and re-initiate route 2234 optimization. 2236 o When an AERO Client receives persistent link-layer Destination 2237 Unreachable messages in response to carrier packets that it sends 2238 to one of its neighbor Proxy/Servers, the Client should mark the 2239 path as unusable and use another path. If it receives Destination 2240 Unreachable messages on many or all paths, the Client should 2241 associate with a new Proxy/Server and release its association with 2242 the old Proxy/Server as specified in Section 3.16.5. 2244 o When an AERO Proxy/Server receives persistent link-layer 2245 Destination Unreachable messages in response to carrier packets 2246 that it sends to one of its neighbor Clients, the Proxy/Server 2247 should mark the underlying path as unusable and use another 2248 underlying path. 2250 o When an AERO Proxy/Server receives link-layer Destination 2251 Unreachable messages in response to a carrier packet that it sends 2252 to one of its permanent neighbors, it treats the messages as an 2253 indication that the path to the neighbor may be failing. However, 2254 the dynamic routing protocol should soon reconverge and correct 2255 the temporary outage. 2257 When an AERO Bridge receives a carrier packet for which the network- 2258 layer destination address is covered by an MSP, the Bridge drops the 2259 packet if there is no more-specific routing information for the 2260 destination and returns an OMNI interface Destination Unreachable 2261 message subject to rate limiting. 2263 When an AERO node receives a carrier packet for which reassembly is 2264 currently congested, it returns an OMNI interface Packet Too Big 2265 (PTB) message as discussed in [I-D.templin-6man-omni] (note that the 2266 PTB messages could indicate either "hard" or "soft" errors). 2268 AERO nodes include ICMPv6 error messages intended for the OAL source 2269 as sub-options in the OMNI option of secured uNA messages. When the 2270 OAL source receives the uNA message, it can extract the ICMPv6 error 2271 message enclosed in the OMNI option and either process it locally or 2272 translate it into a network-layer error to return to the original 2273 source. 2275 3.12. AERO Router Discovery, Prefix Delegation and Autoconfiguration 2277 AERO Router Discovery, Prefix Delegation and Autoconfiguration are 2278 coordinated as discussed in the following Sections. 2280 3.12.1. AERO Service Model 2282 Each AERO Proxy/Server on the OMNI link is configured to facilitate 2283 Client prefix delegation/registration requests. Each Proxy/Server is 2284 provisioned with a database of MNP-to-Client ID mappings for all 2285 Clients enrolled in the AERO service, as well as any information 2286 necessary to authenticate each Client. The Client database is 2287 maintained by a central administrative authority for the OMNI link 2288 and securely distributed to all Proxy/Servers, e.g., via the 2289 Lightweight Directory Access Protocol (LDAP) [RFC4511], via static 2290 configuration, etc. Clients receive the same service regardless of 2291 the Proxy/Servers they select. 2293 AERO Clients and Proxy/Servers use ND messages to maintain neighbor 2294 cache entries. AERO Proxy/Servers configure their OMNI interfaces as 2295 advertising NBMA interfaces, and therefore send unicast RA messages 2296 with a short Router Lifetime value (e.g., ReachableTime seconds) in 2297 response to a Client's RS message. Thereafter, Clients send 2298 additional RS messages to keep Proxy/Server state alive. 2300 AERO Clients and Proxy/Servers include prefix delegation and/or 2301 registration parameters in RS/RA messages (see 2302 [I-D.templin-6man-omni]). The ND messages are exchanged between 2303 Client and FHS Proxy/Servers according to the prefix management 2304 schedule required by the service. If the Client knows its MNP in 2305 advance, it can employ prefix registration by including its MNP-LLA 2306 as the source address of an RS message and with an OMNI option with 2307 valid prefix registration information for the MNP. If the Proxy/ 2308 Server accepts the Client's MNP assertion, it injects the MNP into 2309 the routing system and establishes the necessary neighbor cache 2310 state. If the Client does not have a pre-assigned MNP, it can 2311 instead employ prefix delegation by including the unspecified address 2312 (::) as the source address of an RS message and with an OMNI option 2313 with prefix delegation parameters to request an MNP. 2315 The following sections specify the Client and Proxy/Server behavior. 2317 3.12.2. AERO Client Behavior 2319 AERO Clients discover the addresses of candidate FHS Proxy/Servers in 2320 a similar manner as described in [RFC5214]. Discovery methods 2321 include static configuration (e.g., from a flat-file map of Proxy/ 2322 Server addresses and locations), or through an automated means such 2323 as Domain Name System (DNS) name resolution [RFC1035]. 2324 Alternatively, the Client can discover Proxy/Server addresses through 2325 a layer 2 data link login exchange, or through a unicast RA response 2326 to a multicast/anycast RS as described below. In the absence of 2327 other information, the Client can resolve the DNS Fully-Qualified 2328 Domain Name (FQDN) "linkupnetworks.[domainname]" where 2329 "linkupnetworks" is a constant text string and "[domainname]" is a 2330 DNS suffix for the OMNI link (e.g., "example.com"). 2332 To associate with a FHS Proxy/Server over an underlying interface, 2333 the Client acts as a requesting router to request MNPs by preparing 2334 an RS message with prefix management parameters. If the Client 2335 already knows the Proxy/Server's ADM-LLA, it includes the LLA as the 2336 network-layer destination address; otherwise, the Client includes the 2337 (link-local) All-Routers multicast as the network-layer destination. 2338 The Client can use its MNP-LLA as the network-layer source address 2339 and include an OMNI option with prefix registration information. If 2340 the Client does not yet have an MNP-LLA, it instead sets the network- 2341 layer source address to unspecified (::) and includes prefix 2342 delegation parameters in the OMNI option (see: 2343 [I-D.templin-6man-omni]). 2345 The Client next includes an authentication sub-option if necessary, 2346 Interface Attributes corresponding to the underlying interface over 2347 which it will send the RS message, and optionally any additional 2348 Interface Attributes corresponding to other underlying interfaces. 2349 Next, the Client submits the RS for OAL encapsulation and 2350 fragmentation if necessary with its own MNP-ULA and the Proxy/ 2351 Server's ADM-ULA or (site-scoped) All-Routers multicast as the OAL 2352 addresses while selecting an Identification value and invoking window 2353 synchronization as specified in [I-D.templin-6man-omni]. 2355 The Client then sends the RS (either directly via Direct interfaces, 2356 via a VPN for VPNed interfaces, via an access router for ANET 2357 interfaces or via INET encapsulation for INET interfaces) then waits 2358 up to RetransTimer milliseconds for an RA message reply (see 2359 Section 3.12.3) (retrying up to MAX_RTR_SOLICITATIONS). If the 2360 Client receives no RAs, or if it receives an RA with Router Lifetime 2361 set to 0, the Client SHOULD abandon attempts through the first 2362 candidate FHS Proxy/Server and try another Proxy/Server. Otherwise, 2363 the Client processes the prefix information found in the RA message. 2365 When the Client processes an RA, it first performs OAL reassembly and 2366 decapsulation if necessary then creates a NCE with the Proxy/Server's 2367 ADM-LLA as the network-layer address and the Proxy/Server's 2368 encapsulation and/or link-layer addresses as the link-layer address. 2369 The Client then caches the FMT/SRT/LHS/L2ADDR information from the 2370 Interface Attributes for omIndex 0 included in the RA as an SRT 2371 point-of-reference for this Proxy/Server. The Client next records 2372 the RA Router Lifetime field value in the NCE as the time for which 2373 the Proxy/Server has committed to maintaining the MNP in the routing 2374 system via this underlying interface, and caches the other RA 2375 configuration information including Cur Hop Limit, M and O flags, 2376 Reachable Time and Retrans Timer. The Client then autoconfigures 2377 MNP-LLAs for any delegated MNPs and assigns them to the OMNI 2378 interface. The Client also caches any MSPs included in Route 2379 Information Options (RIOs) [RFC4191] as MSPs to associate with the 2380 OMNI link, and assigns the MTU value in the MTU option to the 2381 underlying interface. 2383 The Client then registers its additional underlying interfaces with 2384 FHS Proxy/Servers for those interfaces discovered by sending RS 2385 messages via each additional interface as described above. The RS 2386 messages include the same parameters as for the initial RS/RA 2387 exchange, but with destination address set to the Proxy/Server's ADM- 2388 LLA. The Client finally sub-delegates the MNPs to its attached EUNs 2389 and/or the Client's own internal virtual interfaces as described in 2390 [I-D.templin-v6ops-pdhost] to support the Client's downstream 2391 attached "Internet of Things (IoT)". The Client then sends 2392 additional RS messages over each underlying interface before the 2393 Router Lifetime received for that interface expires. 2395 After the Client registers its underlying interfaces, it may wish to 2396 change one or more registrations, e.g., if an interface changes 2397 address or becomes unavailable, if traffic selectors change, etc. To 2398 do so, the Client prepares an RS message to send over any available 2399 underlying interface as above. The RS includes an OMNI option with 2400 prefix registration/delegation information, with Interface Attributes 2401 specific to the selected underlying interface, and with any 2402 additional Interface Attributes specific to other underlying 2403 interfaces. When the Client receives the Proxy/Server's RA response, 2404 it has assurance that the Proxy/Server has been updated with the new 2405 information. 2407 If the Client wishes to discontinue use of a Proxy/Server it issues 2408 an RS message over any underlying interface with an OMNI option with 2409 a prefix release indication. When the Proxy/Server processes the 2410 message, it releases the MNP, sets the NCE state for the Client to 2411 DEPARTED and returns an RA reply with Router Lifetime set to 0. 2413 After a short delay (e.g., 2 seconds), the Proxy/Server withdraws the 2414 MNP from the routing system. 2416 3.12.3. AERO Proxy/Server Behavior 2418 AERO Proxy/Servers act as both IP routers and ND proxies, and support 2419 a prefix delegation/registration service for Clients. Proxy/Servers 2420 arrange to add their ADM-LLAs to a static map of Proxy/Server 2421 addresses for the link and/or the DNS resource records for the FQDN 2422 "linkupnetworks.[domainname]" before entering service. The static 2423 map and/or DNS resource records should be arranged such that Clients 2424 can discover the addresses of Proxy/Servers that are geographically 2425 and/or topologically "close" to their underlying network connections. 2427 When an FHS Proxy/Server receives a prospective Client's RS message, 2428 it SHOULD return an immediate RA reply with Router Lifetime set to 0 2429 if it is currently too busy or otherwise unable to service the 2430 Client. Otherwise, the Proxy/Server performs OAL reassembly if 2431 necessary, then decapsulates and authenticates the RS message before 2432 processing the prefix delegation/registration parameters. The Proxy/ 2433 Server then determines the correct MNPs to provide to the Client by 2434 processing the MNP-LLA prefix parameters and/or the DHCPv6 OMNI sub- 2435 option. When the Proxy/Server returns the MNPs, it also creates a 2436 forwarding table entry for the MNP-ULA corresponding to each MNP 2437 resulting in a BGP update (see: Section 3.2.3). For IPv6, the Proxy/ 2438 Server creates an IPv6 forwarding table entry for each MNP. For 2439 IPv4, the Proxy/Server creates an IPv6 forwarding table entry with 2440 the IPv4-compatibility MNP-ULA prefix corresponding to the IPv4 2441 address. 2443 The Proxy/Server next creates a NCE for the Client using the base 2444 MNP-LLA as the network-layer address. Next, the Proxy/Server updates 2445 the NCE by recording the information in each Interface Attributes 2446 sub-option in the RS OMNI option. The Proxy/Server also records the 2447 actual OAL/*NET addresses and RS message window synchronization 2448 parameters (if any) in the NCE. 2450 Next, the Proxy/Server prepares an RA message using its ADM-LLA as 2451 the network-layer source address and the network-layer source address 2452 of the RS message as the network-layer destination address. The 2453 Proxy/Server sets the Router Lifetime to the time for which it will 2454 maintain both this underlying interface individually and the NCE as a 2455 whole. The Proxy/Server also sets Cur Hop Limit, M and O flags, 2456 Reachable Time and Retrans Timer to values appropriate for the OMNI 2457 link. The Proxy/Server includes the MNPs, any other prefix 2458 management parameters and an OMNI option with an Interface Attributes 2459 sub-option with omIndex 0 and FMT/SRT/LHS/L2ADDR information for its 2460 INET interface and an Origin Indication sub-option with the mapped 2461 and obfuscated Port Number and IP address corresponding to the 2462 Client's RS encapsulation addresses. The Proxy/Server then includes 2463 one or more RIOs that encode the MSPs for the OMNI link, plus an MTU 2464 option (see Section 3.9). The Proxy/Server finally forwards the 2465 message to the Client using OAL encapsulation/fragmentation if 2466 necessary while including an acknowledgement if the RS invoked window 2467 synchronization. 2469 After the initial RS/RA exchange, the Proxy/Server maintains a 2470 ReachableTime timer for each of the Client's underlying interfaces 2471 individually (and for the Client's NCE collectively) set to expire 2472 after ReachableTime seconds. If the Client (or Proxy) issues 2473 additional RS messages, the Proxy/Server sends an RA response and 2474 resets ReachableTime. If the Proxy/Server receives an ND message 2475 with a prefix release indication it sets the Client's NCE to the 2476 DEPARTED state and withdraws the MNP from the routing system after a 2477 short delay (e.g., 2 seconds). If ReachableTime expires before a new 2478 RS is received on an individual underlying interface, the Proxy/ 2479 Server marks the interface as DOWN. If ReachableTime expires before 2480 any new RS is received on any individual underlying interface, the 2481 Proxy/Server sets the NCE state to STALE and sets a 10 second timer. 2482 If the Proxy/Server has not received a new RS or ND message with a 2483 prefix release indication before the 10 second timer expires, it 2484 deletes the NCE and withdraws the MNP from the routing system. 2486 The Proxy/Server processes any ND messages pertaining to the Client 2487 and returns an NA/RA reply in response to solicitations. The Proxy/ 2488 Server may also issue unsolicited RA messages, e.g., with reconfigure 2489 parameters to cause the Client to renegotiate its prefix delegation/ 2490 registrations, with Router Lifetime set to 0 if it can no longer 2491 service this Client, etc. Finally, If the NCE is in the DEPARTED 2492 state, the Proxy/Server deletes the entry after DepartTime expires. 2494 Note: Clients SHOULD notify former Proxy/Servers of their departures, 2495 but Proxy/Servers are responsible for expiring neighbor cache entries 2496 and withdrawing routes even if no departure notification is received 2497 (e.g., if the Client leaves the network unexpectedly). Proxy/Servers 2498 SHOULD therefore set Router Lifetime to ReachableTime seconds in 2499 solicited RA messages to minimize persistent stale cache information 2500 in the absence of Client departure notifications. A short Router 2501 Lifetime also ensures that proactive RS/RA messaging between Clients 2502 and Proxy/Servers will keep any NAT state alive (see above). 2504 Note: All Proxy/Servers on an OMNI link MUST advertise consistent 2505 values in the RA Cur Hop Limit, M and O flags, Reachable Time and 2506 Retrans Timer fields the same as for any link, since unpredictable 2507 behavior could result if different Proxy/Servers on the same link 2508 advertised different values. 2510 3.12.3.1. DHCPv6-Based Prefix Registration 2512 When a Client is not pre-provisioned with an MNP-LLA, it will need 2513 for the FHS Proxy/Server to select one or more MNPs on its behalf and 2514 set up the correct state in the AERO routing service. (A Client with 2515 a pre-provisioned MNP may also request the Proxy/Server to select 2516 additional MNPs.) The DHCPv6 service [RFC8415] is used to support 2517 this requirement. 2519 When a Client needs to have the FHS Proxy/Server select MNPs, it 2520 sends an RS message with source address set to the unspecified 2521 address (::) and with an OMNI option that includes a DHCPv6 message 2522 sub-option with DHCPv6 Prefix Delegation (DHCPv6-PD) parameters. 2523 When the Proxy/Server receives the RS message, it extracts the 2524 DHCPv6-PD message from the OMNI option. 2526 The Proxy/Server then acts as a "Proxy DHCPv6 Client" in a message 2527 exchange with the locally-resident DHCPv6 server, which delegates 2528 MNPs and returns a DHCPv6-PD Reply message. (If the Proxy/Server 2529 wishes to defer creation of MN state until the DHCPv6-PD Reply is 2530 received, it can instead act as a Lightweight DHCPv6 Relay Agent per 2531 [RFC6221] by encapsulating the DHCPv6-PD message in a Relay-forward/ 2532 reply exchange with Relay Message and Interface ID options.) 2534 When the Proxy/Server receives the DHCPv6-PD Reply, it adds a route 2535 to the routing system and creates an MNP-LLA based on the delegated 2536 MNP. The Proxy/Server then sends an RA back to the Client with the 2537 (newly-created) MNP-LLA as the destination address and with the 2538 DHCPv6-PD Reply message coded in the OMNI option. When the Client 2539 receives the RA, it creates a default route, assigns the Subnet 2540 Router Anycast address and sets its MNP-LLA based on the delegated 2541 MNP. 2543 Note: See [I-D.templin-6man-omni] for an MNP delegation alternative 2544 that avoids including a DHCPv6 message sub-option in the RS. Namely, 2545 when the Client requests a single MNP it can set the RS source to the 2546 unspecified address (::) and include a Node Identification sub-option 2547 and Preflen in the OMNI option (but with no DHCPv6 message sub- 2548 option). When the Proxy/Server receives the RS message, it forwards 2549 a self-generated DHCPv6 Solicit message to the DHCPv6 server on 2550 behalf of the Client. When the Proxy/Server receives the DHCPv6 2551 Reply, it prepares an RA message with an OMNI option with Preflen 2552 information (but with no DHCPv6 message sub-option), then places the 2553 (newly-created) MNP-LLA in the RA destination address and returns the 2554 message to the Client. 2556 3.13. The AERO Proxy Function 2558 OMNI link Clients register with one or more FHS Proxy/Servers for 2559 each underlying interface. Each of the Client's FHS Proxy/Servers 2560 must be informed of all of the Client's additional underlying 2561 interfaces. For Clients on Direct and VPNed underlying interfaces, 2562 the FHS Proxy/Server for each interface is directly connected, for 2563 Clients on ANET underlying interfaces the Proxy/Server is located on 2564 the ANET/INET boundary, and for Clients on INET underlying interfaces 2565 the FHS Proxy/Server is located somewhere in the connected 2566 Internetwork. When FHS Proxy/Server "A" processes a Client 2567 registration, it must also forward a proxyed registration to any 2568 Proxy/Servers "B", "C", "D", etc. for the Client's other underlying 2569 interfaces, which it perceives as LHS Proxy/Servers (i.e., and not 2570 FHS) from its own reference point. Proxy/Servers satisfies these 2571 requirements as follows: 2573 o when FHS Proxy/Server "A" receives a Client RS message, it first 2574 verifies that the OAL Identification is within the window for the 2575 NCE that matches the MNP-ULA for this Client neighbor and 2576 authenticates the message. (If no NCE was found, Proxy/Server "A 2577 instead creates one in the STALE state and returns an RA message 2578 with an authentication signature if necessary and any window 2579 synchronization parameters.) Proxy/Server "A" then examines the 2580 network-layer destination address. If the destination address is 2581 the ADM-LLA of a different Proxy/Server "B" (or, if the OMNI 2582 option included MS-Register/Release sub-options with the ADM-LLAs 2583 of one or more different LHS Proxy/Servers "B", "C", "D", etc.), 2584 Proxy/Server "A" prepares a separate proxyed version of the RS 2585 message with an OAL header with source set to its own ADM-ULA and 2586 destination set to the LHS Proxy/Server's ADM-ULA. Proxy/Server 2587 "A" also writes its own FMT/SRT/LHS/L2ADDR information over the 2588 first Interface Attributes supplied by the Client (i.e., by 2589 inserting the FMT/SRT/LHS/L2ADDR fields if not already present, or 2590 increasing/decreasing the L2ADDR field size if the IP version of 2591 the Client underlying interface differs from its own INET 2592 interface). Proxy/Server "A" then sets the S/T-omIndex to the 2593 value for this Client underlying interface, then forwards the 2594 message into the OMNI link secured spanning tree. 2596 o when LHS Proxy/Server "B" receives the RS, it authenticates the 2597 message then creates or updates a NCE for the Client with FHS 2598 Proxy/Server "A"'s Interface Attributes as the link-layer address 2599 information for this S/T-omIndex and caches any window 2600 synchronization parameters supplied by the Client. LHS Proxy/ 2601 Server "B" then prepares an RA message with source set to its own 2602 LLA and destination set to the Client's MNP-LLA, and with any 2603 window synchronization acknowledgements. Proxy/Server "B" then 2604 encapsulates the RA in an OAL header with source set to its own 2605 ADM-ULA and destination set to the ADM-ULA of Proxy/Server "A, 2606 performs fragmentation if necessary, then sends the resulting 2607 carrier packets into the secured spanning tree. 2609 o when Proxy/Server "A" reassembles the RA, it locates the Client 2610 NCE based on the RA destination LLA. Proxy/Server "A" then re- 2611 encapsulates the RA message with OAL source set to its own ADM-ULA 2612 and OAL destination set to the MNP-ULA of the Client, includes an 2613 authentication signature if necessary, and includes an Interface 2614 Attributes sub-option with omIndex 0 and with FMT/SRT/LHS/L2ADDR 2615 information for its INET interface. Proxy/Server "A" then 2616 fragments if necessary and returns the fragments to the Client. 2618 o The Client repeats this process over each of its additional 2619 underlying interfaces while treating each "B", "C", "D" as a FHS 2620 Proxy/Server while providing MS-Register//Release information for 2621 the others as LHS Proxy/Servers. 2623 After the initial RS/RA exchanges each Proxy/Server forwards any of 2624 the Client's carrier packets with OAL destinations for which there is 2625 no matching NCE to a Bridge using OAL encapsulation with its own ADM- 2626 ULA as the source and the destination determined by the ORH supplied 2627 by the Client. The Proxy/Server instead forwards any carrier packets 2628 destined to a neighbor cache target directly to the target according 2629 to the OAL/link-layer information - the process of establishing 2630 neighbor cache entries is specified in Section 3.14. 2632 While the Client is still associated with each Proxy/Server "A", "A" 2633 can send NS, RS and/or unsolicited NA messages to update the neighbor 2634 cache entries of other AERO nodes on behalf of the Client and/or to 2635 convey Interface Attributes updates. This allows for higher- 2636 frequency Proxy-initiated RS/RA messaging over well-connected INET 2637 infrastructure supplemented by lower-frequency Client-initiated RS/RA 2638 messaging over constrained ANET data links. 2640 If any Proxy/Server "B", "C", "D" ceases to send solicited RAs, 2641 Proxy/Server "A" sends unsolicited RAs over the Client's underlying 2642 interface with destination set to (link-local) All-Nodes multicast 2643 and with Router Lifetime set to zero to inform Clients that another 2644 Proxy/Server has failed. Although Proxy/Server "A" can engage in ND 2645 exchanges on behalf of the Client, the Client can also send ND 2646 messages on its own behalf, e.g., if it is in a better position than 2647 "A" to convey Interface Attribute changes, etc. The ND messages sent 2648 by the Client include the Client's MNP-LLA as the source in order to 2649 differentiate them from the ND messages sent by Proxy/Server "A". 2651 If the Client becomes unreachable over all underlying interface it 2652 serves, Proxy/Server "A" sets the NCE state to DEPARTED and retains 2653 the entry for DepartTime seconds. While the state is DEPARTED, 2654 Proxy/Server "A" forwards any carrier packets destined to the Client 2655 to a Bridge via OAL/ORH encapsulation. When DepartTime expires, 2656 Proxy/Server "A" deletes the NCE and discards any further carrier 2657 packets destined to the former Client. 2659 In some ANETs that employ a Proxy/Server, the Client's MNP can be 2660 injected into the ANET routing system. In that case, the Client can 2661 send original IP packets without invoking the OAL so that the ANET 2662 routing system transports the original IP packets to the Proxy. This 2663 can be very beneficial, e.g., if the Client connects to the ANET via 2664 low-end data links such as some aviation wireless links. 2666 If the ANET first-hop access router is on the same underlying link as 2667 the Client and recognizes the AERO/OMNI protocol, the Client can 2668 avoid OAL encapsulation for both its control and data messages. When 2669 the Client connects to the link, it can send an unencapsulated RS 2670 message with source address set to its own MNP-LLA (or to a Temporary 2671 LLA), and with destination address set to the ADM-LLA of the Client's 2672 selected Proxy/Server or to (link-local) All-Routers multicast. The 2673 Client includes an OMNI option formatted as specified in 2674 [I-D.templin-6man-omni]. The Client then sends the unencapsulated RS 2675 message, which will be intercepted by the AERO-Aware access router. 2677 The ANET access router then performs OAL encapsulation on the RS 2678 message and forwards it to a Proxy/Server at the ANET/INET boundary. 2679 When the access router and Proxy/Server are one and the same node, 2680 the Proxy/Server would share and underlying link with the Client but 2681 its message exchanges with outside correspondents would need to pass 2682 through a security gateway at the ANET/INET border. The method for 2683 deploying access routers and Proxys (i.e. as a single node or 2684 multiple nodes) is an ANET-local administrative consideration. 2686 Note: When a Proxy/Server alters the IPv6 ND message contents before 2687 forwarding (e.g., such as altering the OMNI option contents), the 2688 IPv6 ND message checksum and/or authentication signature are 2689 invalidated. If the Proxy/Server forwards the message over the 2690 secured spanning tree, however, it need not re-calculate the 2691 checksum/signature since they will not be examined by the next hop. 2693 Note: When a Proxy/Server receives a secured Client NS message, it 2694 performs the same proxying procedures as for described for RS 2695 messages above. The proxying procedures for NS/NA message exchanges 2696 is specified in Section 3.14. 2698 3.13.1. Detecting and Responding to Proxy/Server Failures 2700 In environments where fast recovery from Proxy/Server failure is 2701 required, Proxy/Server "A" SHOULD use proactive Neighbor 2702 Unreachability Detection (NUD) to track each peer Proxy/Server "B" 2703 reachability in a similar fashion as for Bidirectional Forwarding 2704 Detection (BFD) [RFC5880]. Proxy/Server "A" can then quickly detect 2705 and react to failures so that cached information is re-established 2706 through alternate paths. The NS/NA(NUD) control messaging is carried 2707 only over well-connected ground domain networks (i.e., and not low- 2708 end aeronautical radio links) and can therefore be tuned for rapid 2709 response. 2711 Proxy/Server "A" performs continuous NS/NA(NUD) exchanges with peer 2712 Proxy/Server "B" for which there are currently active Clients in 2713 rapid succession, e.g., one exchange per second. Proxy/Server "A" 2714 sends the NS(NUD) message via the spanning tree with its own ADM-LLA 2715 as the source and the ADM-LLA of the peer Proxy/Server "B" as the 2716 destination, and Proxy/Server "B" responds with an NA(NUD). When 2717 Proxy/Server "A" is also sending RS messages to the peer Proxy/Server 2718 "B" on behalf of Clients, the resulting RA responses can be 2719 considered as equivalent hints of forward progress. This means that 2720 Proxy/Server "B" need not also send a periodic NS(NUD) if it has 2721 already sent an RS within the same period. If the peer Proxy/Server 2722 "B" fails (i.e., if "A" ceases to receive advertisements), Proxy/ 2723 Server "A" can quickly inform Clients by sending unsolicited RA 2724 messages 2726 Proxy/Server "A" sends unsolicited RA messages with source address 2727 set to Proxy/Server "B"'s address, destination address set to (link- 2728 local) All-Nodes multicast, and Router Lifetime set to 0. Proxy/ 2729 Server "A" SHOULD send MAX_FINAL_RTR_ADVERTISEMENTS RA messages 2730 separated by small delays [RFC4861]. Any Clients that had been using 2731 the failed Proxy/Server "B" will receive the RA messages and 2732 associate with a new Proxy/Server. 2734 3.13.2. Point-to-Multipoint Proxy/Server Coordination 2736 In environments where Client messaging over ANETs is bandwidth- 2737 limited and/or expensive, Clients can enlist the services of FHS 2738 Proxy/Server "A" to coordinate with multiple LHS Proxy/Servers "B", 2739 "C", "D" etc. in a single RS/RA message exchange. The Client can 2740 send a single RS message to (link-local) All-Routers multicast that 2741 includes the ID's of multiple Proxy/Servers in MS-Register/MS-Release 2742 OMNI sub-options. 2744 When FHS Proxy/Server "A" receives the RS and processes the OMNI 2745 option, it sends a separate RS to each MS-Register/MS-Release LHS 2746 Proxy/Server "B", "C", "D", etc. When FHS Proxy/Server "A" receives 2747 an LHS Proxy/Server RA, it can optionally return an immediate 2748 "singleton" RA to the Client or record the LHS Proxy/Server's MSID 2749 for inclusion in a pending "aggregate" RA message. FHS Proxy/Server 2750 "A" can then return aggregate RA messages to the Client including 2751 multiple LHS Proxy/Server MSIDs in order to conserve bandwidth. Each 2752 RA includes a proper subset of the LHS Proxy/Server MSIDs from the 2753 original RS message, and FHS Proxy/Server "A" must ensure that the 2754 message contents of each RA are consistent with the information 2755 received from the (aggregated) LHS Proxy/Servers. 2757 Clients can thereafter employ efficient point-to-multipoint LHS 2758 Proxy/Server coordination under the assistance of FHS Proxy/Server 2759 "A" to reduce the number of messages sent over the *NET. Clients can 2760 further include MS-Release sub-options in IPv6 ND messages to request 2761 FHS Proxy/Server "A" to release from former LHS Proxy/Servers via the 2762 procedures discussed in Section 3.16.5. 2764 The OMNI interface specification [I-D.templin-6man-omni] provides 2765 further discussion of the RS/RA messaging involved in point-to- 2766 multipoint coordination. 2768 3.14. AERO Route Optimization 2770 AERO nodes invoke route optimization when they need to forward 2771 packets to new target destinations. Route optimization is based on 2772 IPv6 ND Address Resolution messaging between a Route Optimization 2773 Source (ROS) and Route Optimization Responder (ROR). Route 2774 optimization is initiated by the first eligible ROS closest to the 2775 source as follows: 2777 o For Clients on VPNed and Direct interfaces, the Client's FHS 2778 Proxy/Server is the ROS. 2780 o For Clients on ANET interfaces, either the Client or the FHS 2781 Proxy/Server may be the ROS. 2783 o For Clients on INET interfaces, the Client itself is the ROS. 2785 o For correspondent nodes on INET/EUN interfaces serviced by a 2786 Relay, the Relay is the ROS. 2788 The route optimization procedure is conducted between the ROS and an 2789 LHS Proxy/Server/Relay for the target selected by routing as the ROR. 2790 In this arrangement, the ROS is always the Client or Proxy/Server/ 2791 Relay nearest the source over the selected source underlying 2792 interface, while the ROR is always an LHS Proxy/Server/Relay for the 2793 target regardless of the target underlying interface. 2795 The AERO routing system directs a route optimization request sent by 2796 the ROS to the nearest available ROR, which returns a route 2797 optimization reply. The exact ROR selected is unimportant as long as 2798 the information returned is current, consistent and authentic. The 2799 ROS is responsible for periodically refreshing the route 2800 optimization, and the ROR is responsible for quickly informing the 2801 ROS of any changes. 2803 The procedures are specified in the following sections. 2805 3.14.1. Route Optimization Initiation 2807 When an original IP packet from a source node destined to a target 2808 node arrives, the ROS checks for a NCE with an MNP-LLA that matches 2809 the target destination. If there is a NCE in the REACHABLE state, 2810 the ROS invokes the OAL and forwards the resulting carrier packets 2811 according to the cached state then returns from processing. 2812 Otherwise, if there is no NCE the ROS creates one in the INCOMPLETE 2813 state. 2815 The ROS next places the original IP packet on a short queue then 2816 sends an NS message for Address Resolution (NS(AR)) to receive a 2817 solicited NA(AR) message from an ROR. The NS(AR) message must be 2818 sent securely, and includes: 2820 o the LLA of the ROS as the source address. 2822 o the MNP-LLA corresponding to the original IP packet's destination 2823 as the Target Address, e.g., for 2001:db8:1:2::10:2000 the Target 2824 Address is fe80::2001:db8:1:2. 2826 o the Solicited-Node multicast address [RFC4291] formed from the 2827 lower 24 bits of the original IP packet's destination as the 2828 destination address, e.g., for 2001:db8:1:2::10:2000 the NS(AR) 2829 destination address is ff02:0:0:0:0:1:ff10:2000. 2831 The NS(AR) message also includes an OMNI option with an 2832 authentication sub-option if necessary, an Interface Attributes sub- 2833 option for the underlying interface, with S/T-omIndex set to the 2834 underlying interface index and with Preflen set to the prefix length 2835 associated with the NS(AR) source. The ROS then selects an 2836 Identification value submits the NS(AR) message for OAL encapsulation 2837 with OAL source set to its own ULA and OAL destination set to the ULA 2838 corresponding to the target. (The ROS does not include any window 2839 synchronization parameters, since it will not exchange other packet 2840 types with the ROR.) The ROS then sends the resulting carrier 2841 packet(s) into the SRT secured spanning tree without decrementing the 2842 network-layer TTL/Hop Limit field. 2844 When the ROS is an INET Client, it must instead forward the resulting 2845 carrier packets to the ADM-ULA of one of its current Proxy/Servers. 2846 The Proxy/Server reassembles if necessary, then verifies the NS(AR) 2847 authentication signature and writes its FMT/SRT/LHS/L2ADDR 2848 information into the Interface Attributes sub-option the same as 2849 described for RS messages in Section 3.13. The Proxy/Server then re- 2850 encapsulates the NS(AR) with the OAL source set to its own ADM-ULA 2851 and OAL destination set to the ULA corresponding to the target, 2852 fragments if necessary and forwards the resulting carrier packets 2853 into the secured spanning tree on behalf of the Client. 2855 3.14.2. Relaying the NS(AR) *NET Packet(s) 2857 When the Bridge receives the carrier packet(s) containing the RS from 2858 the ROS, it discards the *NET headers and determines the next hop by 2859 consulting its standard IPv6 forwarding table for the OAL header 2860 destination address. The Bridge then decrements the OAL header Hop- 2861 Limit, then re-encapsulates and forwards the carrier packet(s) via 2862 the secured spanning tree the same as for any IPv6 router, where it 2863 may traverse multiple OMNI link segments. The final-hop Bridge will 2864 deliver the carrier packet(s) via the secured spanning tree to a 2865 Proxy/Server or Relay that services the target. 2867 3.14.3. Processing the NS(AR) and Sending the NA(AR) 2869 When an LHS Proxy/Server (or Relay) for the target receives the 2870 secured carrier packet(s), it reassembles if necessary then examines 2871 the NS(AR) target to determine whether it has a matching NCE and/or 2872 non-MNP route. If there is no match, the Proxy/Server drops the 2873 message. Otherwise, the LHS Proxy/Server/Relay continues processing 2874 as follows: 2876 o if the NS(AR) target matches a Client NCE in the DEPARTED state, 2877 the Proxy/Server re-encapsulates while setting the OAL source to 2878 the ULA of the ROS and OAL destination address to the ADM-ULA of 2879 the Client's new Proxy/Server. The (old) Proxy/Server then 2880 fragments if necessary and forwards the resulting carrier 2881 packet(s) over the secured spanning tree then returns from 2882 processing. 2884 o If the NS(AR) target matches the MNP-LLA of a Client NCE in the 2885 REACHABLE state, the Proxy/Server notes whether the NS (AR) 2886 arrived from the secured or unsecured spanning tree then acts as 2887 an ROR to provide route optimization information on behalf of the 2888 Client. If the message arrived via the secured spanning tree the 2889 ROR need not perform further authentication; otherwise, it must 2890 verify the message authentication signature before accepting. 2892 o If the NS(AR) target matches one of its non-MNP routes, the Relay 2893 acts as both an ROR and a route optimization target, since the 2894 Relay forwards IP packets toward the (fixed network) target at the 2895 network layer. 2897 The ROR next checks the target NCE for a Report List entry that 2898 matches the NS(AR) source LLA/ULA of the ROS. If there is a Report 2899 List entry, the ROR refreshes ReportTime for this ROR; otherwise, the 2900 ROR creates a new entry for the ROS and records both the LLA and ULA. 2902 The ROR then prepares a (solicited) NA(AR) message to return to the 2903 ROS with the source address set to its own ADM-LLA, the destination 2904 address set to the NS(AR) LLA source address and the Target Address 2905 set to the target Client's MNP-LLA. The ROR includes an OMNI option 2906 with Preflen set to the prefix length associated with the NA(AR) 2907 source address as well as Interface Attributes sub-options for all of 2908 the target's underlying interfaces with current information for each 2909 interface. 2911 For each Interface Attributes sub-option, the ROR sets the L2ADDR 2912 according to its own INET address for VPNed, Direct, ANET and NATed 2913 Client interfaces, or to the Client's INET address for native Client 2914 interfaces. The ROR then includes the lower 32 bits of the Proxy/ 2915 Server's ADM-ULA as the LHS, encodes the ADM-ULA SRT prefix length in 2916 the SRT field and sets FMT as specified in Section 3.3. 2918 The ROR then sets the NA(AR) message R flag to 1 (as a router) and S 2919 flag to 1 (as a response to a solicitation) and sets the O flag to 0 2920 (as a proxy) and sets the OMNI header S/T-omIndex to 0. The ROR 2921 finally submits the NA(AR) for OAL encapsulation with source set to 2922 its own ULA and destination set to the same ULA that appeared in the 2923 NS(AR) OAL source, then performs OAL encapsulation and fragmentation 2924 using the same Identification value that appeared in the NS(AR) and 2925 finally forwards the resulting (*NET-encapsulated) carrier packets 2926 via the secured spanning tree without decrementing the network-layer 2927 TTL/Hop Limit field. 2929 3.14.4. Relaying the NA(AR) 2931 When the Bridge receives NA(AR) carrier packets from the ROR, it 2932 discards the *NET header and determines the next hop by consulting 2933 its standard IPv6 forwarding table for the OAL header destination 2934 address. The Bridge then decrements the OAL header Hop-Limit, re- 2935 encapsulates the carrier packet and forwards it via the SRT secured 2936 spanning tree the same as for any IPv6 router, where it may traverse 2937 multiple OMNI link segments. The final-hop Bridge will deliver the 2938 carrier packet via the secured spanning tree to a Proxy/Server for 2939 the ROS. 2941 3.14.5. Processing the NA(AR) 2943 When the ROS receives the NA(AR) message from the ROR, it first 2944 searches for a NCE that matches the NA(AR) target address. The ROS 2945 then processes the message the same as for standard IPv6 Address 2946 Resolution [RFC4861]. In the process, it caches all OMNI option 2947 information in the target NCE (including all Interface Attributes), 2948 and caches the NA(AR) ADM-{LLA,ULA} source addresses as the addresses 2949 of the ROR. If the ROS receives additional NA(AR) or uNA messages 2950 for this target Client with the same ADM-LLA source address but a 2951 different ADM-ULA source address, it caches the new MSID as the new 2952 ADM-{LLA,ULA} and deprecates the former ADM-{LLA,ULA}. 2954 When the ROS is a Client, the solicited NA(AR) message will first be 2955 delivered via the SRT secured spanning tree to the Proxy/Server that 2956 forwarded the NS(AR), which reassembles if necessary. The Proxy/ 2957 Server then forwards the message to the Client while re-encapsulating 2958 and re-fragmenting if necessary. If the Client is on a well-managed 2959 ANET, physical security and protected spectrum ensures security for 2960 the unmodified NA(AR); if the Client is on the open INET the Proxy/ 2961 Server must instead include an authentication signature (while 2962 adjusting the OMNI option size, if necessary). The Proxy/Server uses 2963 its own ADM-ULA as the OAL source and the MNP-ULA of the Client as 2964 the OAL destination. 2966 3.14.6. Forwarding Packets to Route Optimized Targets 2968 After the ROS receives the route optimization NA(AR) and updates the 2969 target NCE, it sends additional NS(AR) messages to the ADM-ULA of the 2970 ROR to refresh the NCE ReachableTime before expiration while it still 2971 has sustained interest in this target. While the NCE remains 2972 REACHABLE, the ROS can forward packets along the best underlying 2973 interface paths based on the target's Interface Attributes. The ROS 2974 selects target underlying interfaces according to traffic selectors 2975 and/or any other traffic discriminators, however each underlying 2976 interface selected must first establish window synchronization state 2977 if necessary. 2979 To establish window synchronization state, the ROS performs a secured 2980 unicast NS/NA(WIN) exchange with window synchronization parameters 2981 according to the Interface Attributes FMT code. If FMT-Forward is 2982 set, the ROS prepares an NS(WIN) with its own LLA as the source and 2983 the MNP-LLA of the target Client as the destination; otherwise, it 2984 sets the ADM-LLA of the LHS Proxy/Server as the destination. The ROS 2985 then encapsulates the NS(WIN) in an OAL header with its own ULA as 2986 the source. If the ROS is the Client, it sets the OAL destination to 2987 the ADM-ULA of its FHS Proxy/Server, includes an authentication 2988 signature if necessary, includes an Interface Attributes sub-option 2989 for its underlying interface and includes an ORH-1 with FMT-Type set 2990 for fragments that require a Destination Suffix (otherwise clear). 2991 The Client sets the ORH Segments Left to 1 and includes valid SRT/LHS 2992 information for the LHS Proxy/Server with L2ADDR set to 0, then 2993 forwards the NS(WIN) to its FHS Proxy/Server which must reassemble, 2994 verify the authentication signature and rewrite the Interface 2995 Attributes FMT/SRT/LHS/L2ADDR information if necessary. The FHS 2996 Proxy/Server then re-encapsulates, re-fragments and forwards the 2997 NS(WIN) carrier packets into the secured spanning tree with its own 2998 ADM-ULA as the OAL source and the ADM-ULA of the LHS Proxy/Server as 2999 the OAL destination while replacing the ORH-1 with an ORH-0. (If the 3000 ROS was the FHS Proxy/Server itself, it instead includes an ORH-0, 3001 and forwards the carrier packets into the secured spanning tree.) 3003 When an LHS Proxy/Server receives the NS(WIN) it first reassembles if 3004 necessary. If the NS(WIN) destination is its own ADM-LLA, the LHS 3005 Proxy/Server creates an NCE based on the NS(WIN) source LLA, caches 3006 the window synchronization information, and prepares an NA(WIN) while 3007 using its own ADM-LLA as the source and the ROS LLA as the 3008 destination. The LHS Proxy/Server then encapsulates the NA(WIN) in 3009 an OAL header with source set to its own ADM-ULA and destination set 3010 to the NS(WIN) OAL source. The LHS Proxy/Server then fragments if 3011 necessary, includes an ORH-0 with omIndex set to the S/T-omIndex 3012 value found in the NS(WIN) OMNI option, then forwards the resulting 3013 carrier packets into the secured spanning tree which will deliver 3014 them to the ROS Proxy/Server. 3016 If the NS(WIN) destination is the MNP-LLA of the target Client, the 3017 LHS Proxy/Server instead removes the ORH-0, re-encapsulates using the 3018 same OAL source and the MNP-ULA of the target as the OAL destination 3019 and includes an authentication signature (while adjusting the OMNI 3020 option size) if necessary. The LHS Proxy/Server then forwards the 3021 NS(WIN) to the target over the underlying interface identified by the 3022 ORH-0 omIndex (or, over any underlying interface if omIndex is 0). 3023 When the target receives the NS(WIN), it verifies the authentication 3024 signature if necessary then creates an NCE for the ROS LLA, caches 3025 the window synchronization information and prepares an NA(WIN) to 3026 return to the ROS with its MNP-LLA as the source and the LLA of the 3027 ROS as the destination, and with an authentication signature and 3028 Interface Attributes sub-option if necessary. The target Client then 3029 encapsulates the NA(WIN) in an OAL header with its own MNP-ULA as the 3030 source, the ADM-ULA of the LHS Proxy/Server as the destination, and 3031 with an ORH-1 with SRT/LHS information copied from the ADM-ULA of the 3032 FHS Proxy/Server found in the NS(WIN) OAL source address. The target 3033 Client then sets the ORH-1 omIndex to the S/T-omIndex value found in 3034 the NS(WIN) OMNI option, then forwards the message to the LHS Proxy/ 3035 Server. 3037 When the LHS Proxy/Server receives the message, it reassembles if 3038 necessary, verifies the authentication signature and rewrites the 3039 Interface Attributes FMT/SRT/LHS/L2ADDR information if necessary, 3040 then re-encapsulates using its own ADM-ULA as the source and the ADM- 3041 ULA of the FHS Proxy/Server as the destination. The LHS Proxy/Server 3042 then re-fragments and forwards the NS(WIN) carrier packets into the 3043 spanning tree while replacing the ORH-1 with an ORH-0. 3045 When the FHS Proxy/Server receives the NA(WIN), it reassembles if 3046 necessary then updates the target NCE based on the message contents 3047 if the Proxy/Server itself is the ROS. If the NS(WIN) source was the 3048 ADM-LLA of the LHS Proxy/Server, the ROS must create and maintain a 3049 NCE for the LHS Proxy/Server which it must regard as a companion to 3050 the existing MNP-LLA NCE for the target Client. (The NCE for the LHS 3051 Proxy/Server can also be shared by multiple target Client NCEs if the 3052 ROS communicates with multiple active targets located behind the same 3053 LHS Proxy/Server.) 3055 If the Client is the ROS, the FHS Proxy/Server instead inserts an 3056 authentication signature (while adjusting the OMNI option size) if 3057 necessary, removes the ORH-0 then re-encapsulates and re-fragments if 3058 necessary while changing the OAL destination to the MNP-ULA of the 3059 Client. The FHS Proxy/Server then forwards the NA(WIN) to the Client 3060 over the underlying interface identified by the ORH-0 omIndex which 3061 then updates its own NCE based on the target Client MNP-LLA or LHS 3062 Proxy/Server ADM-LLA. The ROS (whether the Proxy/Server or the 3063 Client itself) finally arranges to return an acknowledgement if 3064 requested by the NA(WIN). 3066 After window synchronization state has been established, the ROS can 3067 begin forwarding carrier packets as specified in Section 3.2.7 while 3068 performing additional NS/NA(WIN) exchanges as above to update window 3069 state and/or test reachability. These forwarding procedures apply to 3070 the case where the selected target interface SRT/LHS codes indicate 3071 that the interface is located in a foreign OMNI link segment. In 3072 that case, the ROS must include ORHs and send the resulting carrier 3073 packets into the spanning tree. 3075 If the SRT/LHS codes indicate that the interface is in the local OMNI 3076 link segment, the ROS can instead forward carrier packets directly to 3077 the LHS Proxy/Server using the L2ADDR for encapsulation, or even 3078 directly to the target Client itself while invoking NAT traversal if 3079 necessary. When the ROS sends packets directly to the LHS Proxy/ 3080 Server, it includes an ORH-0 if necessary to inform the Proxy/Server 3081 as to whether it must reassemble and/or the correct target Client 3082 interface for (re)forwarding. If the LHS Proxy/Server is required to 3083 reassemble, the ROS sets the OAL destination to the ADM-ULA of the 3084 LHS Proxy/Server; otherwise, it sets the OAL destination to the MNP- 3085 ULA of the target Client itself. When the ROS sends packets directly 3086 to the target Client, it need not include an ORH. The LHS Proxy/ 3087 Server (or target Client) then saves the L2ADDR and full OAL 3088 addresses in the ROS NCE, and the ROS can begin applying OAL header 3089 compression in subsequent carrier packets as specified in 3090 [I-D.templin-6man-omni] since the OAL header is not examined by any 3091 forwarding nodes in the path. 3093 While the ROS continues to actively forward packets to the target 3094 Client, it is responsible for updating window synchronization state 3095 and per-interface reachability before expiration. Window 3096 synchronization state is shared by all underlying interfaces in the 3097 ROS' NCE that use the same destination LLA so that a single NS/ 3098 NA(NUD) exchange applies for all interfaces regardless of the 3099 (single) interface used to conduct the exchange. However, the window 3100 synchronization exchange only confirms target Client reachability 3101 over the specific interface used to conduct the exchange. 3102 Reachability for other underlying interfaces that share the same 3103 window synchronization state must be determined individually using 3104 NS/NA(NUD) messages which need not be secured as long as they use in- 3105 window Identifications and do not update other state information. 3107 3.15. Neighbor Unreachability Detection (NUD) 3109 AERO nodes perform Neighbor Unreachability Detection (NUD) per 3110 [RFC4861] either reactively in response to persistent link-layer 3111 errors (see Section 3.11) or proactively to confirm reachability. 3112 The NUD algorithm is based on periodic control message exchanges and 3113 may further be seeded by ND hints of forward progress, but care must 3114 be taken to avoid inferring reachability based on spoofed 3115 information. For example, IPv6 ND message exchanges that include 3116 authentication codes and/or in-window Identifications may be 3117 considered as acceptable hints of forward progress, while spurious 3118 random carrier packets should be ignored. 3120 AERO nodes can perform NS/NA(NUD) exchanges over the OMNI link 3121 secured spanning tree (i.e. the same as described above for NS/ 3122 NA(WIN)) to test reachability without risk of DoS attacks from nodes 3123 pretending to be a neighbor. These NS/NA(NUD) messages use the 3124 unicast LLAs and ULAs of the parties involved in the NUD test the 3125 same as for standard IPv6 ND over the secured spanning tree. When 3126 only reachability information is required without updating any other 3127 NCE state, AERO nodes can instead perform NS/NA(NUD) exchanges 3128 directly between neighbors without employing the secured spanning 3129 tree as long as they include in-window Identifications and either an 3130 authentication signature or checksum. 3132 When an ROR directs an ROS to a target neighbor with one or more 3133 link-layer addresses, the ROS probes each unsecured target underlying 3134 interface either proactively or on-demand of carrier packets directed 3135 to the path by multilink forwarding to maintain the interface's state 3136 as reachable. Probing is performed through NS(NUD) messages over the 3137 SRT secured or unsecured spanning tree, or through NS(NUD) messages 3138 sent directly to an underlying interface of the target itself. While 3139 testing a target underlying interface, the ROS can optionally 3140 continue to forward carrier packets via alternate interfaces and/or 3141 maintain a small queue of carrier packets until target reachability 3142 is confirmed. 3144 NS(NUD) messages are encapsulated, fragmented and transmitted as 3145 carrier packets the same as for ordinary original IP data packets, 3146 however the encapsulated destinations are the LLA of the ROS and 3147 either the ADM-LLA of the LHS Proxy/Server or the MNP-LLA of the 3148 target itself. The ROS encapsulates the NS(NUD) message the same as 3149 described in Section 3.2.7, however Destination Suffixes (if present) 3150 are set according to the LLA destination (i.e., and not the ULA/GUA 3151 destination). The ROS sets the NS(NUD) OMNI header S/T-omIndex to 3152 identify the underlying interface used for forwarding (or to 0 if any 3153 underlying interface can be used). The ROS also includes an ORH with 3154 FMT/SRT/LHS/L2ADDR information the same as for ordinary data packets, 3155 but does not include an authentication signature. The ROS then 3156 fragments the OAL packet and forwards the resulting carrier packets 3157 into the unsecured spanning tree or directly to the target (or LHS 3158 Proxy/Server) if it is in the local segment. 3160 When the target (or LHS Proxy/Server) receives the NS(NUD) carrier 3161 packets, it verifies that it has a NCE for this ROS and that the 3162 Identification is in-window, then submits the carrier packets for 3163 reassembly. The node then verifies the authentication signature or 3164 checksum, then searches for Interface Attributes in its NCE for the 3165 ROS that match the NS(NUD) S/T-omIndex and uses the FMT/SRT/LHS/ 3166 L2ADDR information to prepare an ORH for the NA(NUD) reply. The node 3167 then prepares the NA(NUD) with the source and destination LLAs 3168 reversed, encapsulates and sets the OAL source and destination, sets 3169 the NA(NUD) S/T-omIndex to the index of the underlying interface the 3170 NS(NUD) arrived on and sets the Target Address to the same value 3171 included in the NS(NUD). The target next sets the R flag to 1, the S 3172 flag to 1 and the O flag to 1, then selects an in-window 3173 Identification for the ROS and performs fragmentation. The node then 3174 forwards the carrier packets into the unsecured spanning tree, 3175 directly to the ROS if it is in the local segment or directly to a 3176 Bridge in the local segment. 3178 When the ROS receives the NA(NUD), it marks the target underlying 3179 interface tested as "reachable". Note that underlying interface 3180 states are maintained independently of the overall NCE REACHABLE 3181 state, and that a single NCE may have multiple target underlying 3182 interfaces in various states "reachable" and otherwise while the NCE 3183 state as a whole remains REACHABLE. 3185 Note also that the exchange of NS/NA(NUD) messages has the useful 3186 side-benefit of opening holes in NATs that may be useful for NAT 3187 traversal. 3189 3.16. Mobility Management and Quality of Service (QoS) 3191 AERO is a Distributed Mobility Management (DMM) service. Each Proxy/ 3192 Server is responsible for only a subset of the Clients on the OMNI 3193 link, as opposed to a Centralized Mobility Management (CMM) service 3194 where there is a single network mobility collective entity for all 3195 Clients. Clients coordinate with their associated Proxy/Servers via 3196 RS/RA exchanges to maintain the DMM profile, and the AERO routing 3197 system tracks all current Client/Proxy/Server peering relationships. 3199 Proxy/Servers provide default routing and mobility/multilink services 3200 for their dependent Clients. Clients are responsible for maintaining 3201 neighbor relationships with their Proxy/Servers through periodic RS/ 3202 RA exchanges, which also serves to confirm neighbor reachability. 3203 When a Client's underlying Interface Attributes change, the Client is 3204 responsible for updating the Proxy/Server with this new information. 3205 Note that when there is a Proxy/Server in the path, the Proxy 3206 function can also perform some RS/RA exchanges on the Client's 3207 behalf. 3209 Mobility management messaging is based on the transmission and 3210 reception of unsolicited Neighbor Advertisement (uNA) messages. Each 3211 uNA message sets the IPv6 source address to the LLA of the ROR and 3212 the destination address to the unicast LLA of the ROS. 3214 Mobility management considerations are specified in the following 3215 sections. 3217 3.16.1. Mobility Update Messaging 3219 RORs accommodate Client mobility and/or multilink change events by 3220 sending secured uNA messages to each ROS in the target Client's 3221 Report List. When an ROR sends a uNA message, it sets the IPv6 3222 source address to the its own LLA, sets the destination address to 3223 the ROS LLA (i.e., an MNP-LLA if the ROS is a Client and an ADM-LLA 3224 if the ROS is a Proxy/Server) and sets the Target Address to the 3225 Client's MNP-LLA. The ROR also includes an OMNI option with Preflen 3226 set to the prefix length associated with the Client's MNP-LLA, with 3227 Interface Attributes for the target Client's underlying interfaces 3228 and with the OMNI header S/T-omIndex set to 0. The ROR then sets the 3229 uNA R flag to 1, S flag to 0 and O flag to 1, then encapsulates the 3230 message in an OAL header with source set to its own ADM-ULA and 3231 destination set to the ROS ULA (i.e., the ADM-ULA of the ROS Proxy/ 3232 Server) and sends the message into the secured spanning tree. 3234 As discussed in Section 7.2.6 of [RFC4861], the transmission and 3235 reception of uNA messages is unreliable but provides a useful 3236 optimization. In well-connected Internetworks with robust data links 3237 uNA messages will be delivered with high probability, but in any case 3238 the Proxy/Server can optionally send up to MAX_NEIGHBOR_ADVERTISEMENT 3239 uNAs to each ROS to increase the likelihood that at least one will be 3240 received. Alternatively, the Proxy/Server can set the PNG flag in 3241 the uNA OMNI option header to request a solicited NA acknowledgement 3242 as specified in [I-D.templin-6man-omni]. 3244 When the ROS Proxy/Server receives a uNA message prepared as above, 3245 it ignores the message if the destination is not its own ADM-ULA or 3246 the MNP-ULA of the ROS Client. If the destination was its own ADM- 3247 ULA, the ROS Proxy/Server uses the included OMNI option information 3248 to update its NCE for the target but does not reset ReachableTime 3249 since the receipt of an unsolicited NA message from the ROR does not 3250 provide confirmation that any forward paths to the target Client are 3251 working. If the destination was the MNP-ULA of the ROS Client, the 3252 Proxy/Server instead re-encapsulates with the OAL source set to its 3253 own ADM-ULA, OAL destination set to the MNP-ULA of the ROS Client 3254 with an authentication signature if necessary, and with an in-window 3255 Identification for this Client. Finally, if the uNA message PNG flag 3256 was set, the ROS returns a solicited NA acknowledgement as specified 3257 in [I-D.templin-6man-omni]. 3259 In addition to sending uNA messages to the current set of ROSs for 3260 the target Client, the ROR also sends uNAs to the former Proxy/Server 3261 associated with the underlying interface for which the link-layer 3262 address has changed. These uNA messages update former Proxy/Servers 3263 that cannot easily detect (e.g., without active probing) when a 3264 formerly-active Client has departed. When the ROR sends the uNA, it 3265 sets the IPv6 source address to its LLA, sets the destination address 3266 to the former Proxy/Server's ADM-LLA, and sets the Target Address to 3267 the Client's MNP-LLA. The ROR also includes an OMNI option with 3268 Preflen set to the prefix length associated with the Client's MNP- 3269 LLA, with Interface Attributes for the changed underlying interface, 3270 and with the OMNI header S/T-omIndex set to 0. The ROR then sets the 3271 uNA R flag to 1, S flag to 0 and O flag to 1, then encapsulates the 3272 message in an OAL header with source set to its own ULA and 3273 destination set to the ADM-ULA of the former Proxy/Server and sends 3274 the message into the secured spanning tree. 3276 3.16.2. Announcing Link-Layer Address and/or QoS Preference Changes 3278 When a Client needs to change its underlying Interface Attributes 3279 (e.g., due to a mobility event), the Client requests one of its 3280 Proxy/Servers to send RS messages to all of its other Proxy/Servers 3281 via the secured spanning tree with an OMNI option that includes 3282 Interface Attributes with the new link quality and address 3283 information. 3285 Up to MAX_RTR_SOLICITATIONS RS messages MAY be sent in parallel with 3286 sending carrier packets containing user data in case one or more RAs 3287 are lost. If all RAs are lost, the Client SHOULD re-associate with a 3288 new Proxy/Server. 3290 When the Proxy/Server receives the Client's changes, it sends uNA 3291 messages to all nodes in the Report List the same as described in the 3292 previous section. 3294 3.16.3. Bringing New Links Into Service 3296 When a Client needs to bring new underlying interfaces into service 3297 (e.g., when it activates a new data link), it sends an RS message to 3298 the Proxy/Server via the underlying interface with an OMNI option 3299 that includes Interface Attributes with appropriate link quality 3300 values and with link-layer address information for the new link. 3302 3.16.4. Deactivating Existing Links 3304 When a Client needs to deactivate an existing underlying interface, 3305 it sends an RS message to an FHS Proxy/Server with an OMNI option 3306 with appropriate Interface Attribute values for the deactivated link 3307 - in particular, the link quality value 0 assures that neighbors will 3308 cease to use the link. 3310 If the Client needs to send RS messages over an underlying interface 3311 other than the one being deactivated, it MUST include Interface 3312 Attributes with appropriate link quality values for any underlying 3313 interfaces being deactivated. 3315 Note that when a Client deactivates an underlying interface, 3316 neighbors that have received the RS/uNA messages need not purge all 3317 references for the underlying interface from their neighbor cache 3318 entries. The Client may reactivate or reuse the underlying interface 3319 and/or its omIndex at a later point in time, when it will send new RS 3320 messages to an FHS Proxy/Server with fresh Interface Attributes to 3321 update any neighbors. 3323 3.16.5. Moving Between Proxy/Servers 3325 The Client performs the procedures specified in Section 3.12.2 when 3326 it first associates with a new FHS Proxy/Server or renews its 3327 association with an existing Proxy/Server. The Client also includes 3328 MS-Release identifiers in the RS message OMNI option per 3329 [I-D.templin-6man-omni] if it wants the new Proxy/Server to notify 3330 any old Proxy/Servers from which the Client is departing. 3332 When the new FHS Proxy/Server receives the Client's RS message, it 3333 returns an RA as specified in Section 3.12.3 and sends RS messages to 3334 any old Proxy/Servers listed in OMNI option MS-Release identifiers. 3335 When the new Proxy/Server sends an RS message, it sets the source to 3336 the MNP-LLA of the Client and sets the destination to the ADM-LLA of 3337 the old Proxy/Server. The new Proxy/Server also includes an OMNI 3338 option with Preflen set to the prefix length associated with the 3339 Client's MNP-LLA, with Interface Attributes for its INET underlying 3340 interface, and with the OMNI header S/T-omIndex set to 0. The new 3341 Proxy/Server then encapsulates the message in an OAL header with 3342 source set to its own ADM-ULA and destination set to the ADM-ULA of 3343 the old Proxy/Server and sends the message into the secured spanning 3344 tree. 3346 When an old Proxy/Server receives the RS, it notices that the message 3347 appears to have originated from the Client's MNP-LLA but that it 3348 includes an Interface Attributes sub-option for the new Proxy/Server 3349 and with S/T-omIndex set to 0. The old Proxy/Server then changes the 3350 Client's NCE state to DEPARTED, sets the FMT/SRT/LHS/L2ADDR 3351 information for the Client to point to the new Proxy/Server, and 3352 resets DepartTime. The old Proxy/Server then returns an RA message 3353 with zero Router Lifetime via the secured spanning tree by reversing 3354 the LLA and ULA addresses found in the RS message. After a short 3355 delay (e.g., 2 seconds) the old Proxy/Server withdraws the Client's 3356 MNP from the routing system. After DepartTime expires, the old 3357 Proxy/Server deletes the Client's NCE. 3359 The old Proxy/Server also iteratively sends uNA messages to each ROS 3360 in the Client's Report List with OAL source address set to the ADM- 3361 ULA of the new Proxy/Server and OAL destination address set to the 3362 ULA of the ROS. When the ROS receives the uNA, it examines the uNA 3363 Target Address to locate the target Client's NCE and the LLA source 3364 address to identify the old Proxy/Server. The ROS then caches the 3365 ULA source address as the ADM-{LLA/ULA} for the new Proxy/Server for 3366 this target NCE and marks the entry as STALE. While in the STALE 3367 state, the ROS sends new NS(AR) messages using its own ULA as the OAL 3368 source and the ADM-ULA of the new Proxy/Server as the OAL destination 3369 address. The new Proxy/Server will then process the NS(AR) and 3370 return an NA(AR) response. 3372 Clients SHOULD NOT move rapidly between Proxy/Servers in order to 3373 avoid causing excessive oscillations in the AERO routing system. 3374 Examples of when a Client might wish to change to a different Proxy/ 3375 Server include a Proxy/Server that has gone unreachable, topological 3376 movements of significant distance, movement to a new geographic 3377 region, movement to a new OMNI link segment, etc. 3379 3.17. Multicast 3381 The AERO Client provides an IGMP (IPv4) [RFC2236] or MLD (IPv6) 3382 [RFC3810] proxy service for its EUNs and/or hosted applications 3383 [RFC4605]. Proxy/Servers act as a Protocol Independent Multicast - 3384 Sparse-Mode (PIM-SM, or simply "PIM") Designated Router (DR) 3385 [RFC7761]. AERO Relays also act as PIM routers (i.e., the same as 3386 AERO Proxys/Servers) on behalf of nodes on INET/EUN networks. 3388 Clients on ANET underlying interfaces for which the ANET has deployed 3389 native multicast services forward IGMP/MLD messages into the ANET. 3390 The IGMP/MLD messages may be further forwarded by a first-hop ANET 3391 access router acting as an IGMP/MLD-snooping switch [RFC4541], then 3392 ultimately delivered to an ANET FHS Proxy/Server. 3394 Clients on ANET underlying interfaces without native multicast 3395 services instead send NS(AR) messages to cause their FHS Proxy/Server 3396 to act as an ROS and forward the message to an LHS Proxy/Server ROR. 3397 Clients on INET interfaces act as an ROS on their own behalf and 3398 forward NS(AR) messages directly to the LHS Proxy/Server ROR (i.e., 3399 via the FHS Proxy/Server as a proxy). When the Client receives an 3400 NA(AR) response, it initiates PIM protocol messaging according to the 3401 Source-Specific Multicast (SSM) and Any-Source Multicast (ASM) 3402 operational modes as discussed in the following sections. 3404 3.17.1. Source-Specific Multicast (SSM) 3406 When an ROS "X" (i.e., either a ROS Client or its FHS Proxy Server) 3407 acting as PIM router receives a Join/Prune message from a node on its 3408 downstream interfaces containing one or more ((S)ource, (G)roup) 3409 pairs, it updates its Multicast Routing Information Base (MRIB) 3410 accordingly. For each S belonging to a prefix reachable via X's non- 3411 OMNI interfaces, X then forwards the (S, G) Join/Prune to any PIM 3412 routers on those interfaces per [RFC7761]. 3414 For each S belonging to a prefix reachable via X's OMNI interface, X 3415 sends an NS(AR) message (see: Section 3.14) using its own LLA as the 3416 source address and the LLA of S as the destination address. X then 3417 encapsulates the NS(AR) in an OAL header with source address set to 3418 the ULA of X and destination address set to the solicited node 3419 multicast address for S, then forwards the message into the secured 3420 spanning tree, which delivers it to ROR "Y" that services S. The 3421 resulting NA(AR) will return the LLA for the prefix that matches S as 3422 the network-layer source address and with an OMNI option with 3423 interface attributes for any underlying interfaces that are currently 3424 servicing S. 3426 When X processes the NA(AR) it selects one or more underlying 3427 interfaces for S and performs an NS/NA(WIN) exchange while including 3428 a PIM Join/Prune message for each multicast group of interest in the 3429 OMNI option. If S is located behind any Proxys "Z"*, each Z* then 3430 updates its MRIB accordingly and maintains the LLA of X as the next 3431 hop in the reverse path. Since the Bridges do not examine network 3432 layer control messages, this means that the (reverse) multicast tree 3433 path is simply from each Z* (and/or S) to X with no other multicast- 3434 aware routers in the path. 3436 Following the initial combined Join/Prune and NS/NA messaging, X 3437 maintains a NCE for each S the same as if X was sending unicast data 3438 traffic to S. In particular, X performs additional NS/NA exchanges 3439 to keep the NCE alive for up to t_periodic seconds [RFC7761]. If no 3440 new Joins are received within t_periodic seconds, X allows the NCE to 3441 expire. Finally, if X receives any additional Join/Prune messages 3442 for (S,G) it forwards the messages over the secured spanning tree. 3444 At some later time, Client C that holds an MNP for source S may 3445 depart from a first Proxy/Server Z1 and/or connect via a new Proxy/ 3446 Server Z2. In that case, Y sends a uNA message to X the same as 3447 specified for unicast mobility in Section 3.16. When X receives the 3448 uNA message, it updates its NCE for the LLA for source S and sends 3449 new Join messages to any new Proxys Z2. There is no requirement to 3450 send any Prune messages to old Proxy/Server Z1 since source S will no 3451 longer source any multicast data traffic via Z1. Instead, the 3452 multicast state for (S,G) in Proxy/Server Z1 will soon time out since 3453 no new Joins will arrive. 3455 After some later time, C may move to a new Proxy/Server Y2 and depart 3456 from old Sever Y1. In that case, Y1 sends Join messages for any of 3457 C's active (S,G) groups to Y2 while including its own LLA as the 3458 source address. This causes Y2 to include Y1 in the multicast 3459 forwarding tree during the interim time that Y1's NCE for C is in the 3460 DEPARTED state. At the same time, Y1 sends a uNA message to X with 3461 an OMNI option with S/T-omIndex set to 0 and a release indication to 3462 cause X to release its NCE for S. X then sends a new Join message to 3463 S via the secured spanning tree and re-initiates route optimization 3464 the same as if it were receiving a fresh Join message from a node on 3465 a downstream link. 3467 3.17.2. Any-Source Multicast (ASM) 3469 When an ROS X acting as a PIM router receives a Join/Prune from a 3470 node on its downstream interfaces containing one or more (*,G) pairs, 3471 it updates its Multicast Routing Information Base (MRIB) accordingly. 3472 X then forwards a copy of the message within the OMNI option of an 3473 NS(WIN) message to the Rendezvous Point (RP) R for each G over the 3474 secured spanning tree. X uses its own LLA as the source address and 3475 the LLA for R as the destination address, then encapsulates the 3476 NS(WIN) message in an OAL header with source address set to the ULA 3477 of X and destination address set to the ULA of R's Proxy/Server then 3478 sends the message into the secured spanning tree. 3480 For each source S that sends multicast traffic to group G via R, the 3481 Proxy/Server Z* for the Client that aggregates S encapsulates the 3482 original IP packets in PIM Register messages and forwards them to R 3483 via the secured spanning tree, which may then elect to send a PIM 3484 Join to Z*. This will result in an (S,G) tree rooted at Z* with R as 3485 the next hop so that R will begin to receive two copies of the 3486 original IP packet; one native copy from the (S, G) tree and a second 3487 copy from the pre-existing (*, G) tree that still uses PIM Register 3488 encapsulation. R can then issue a PIM Register-stop message to 3489 suppress the Register-encapsulated stream. At some later time, if C 3490 moves to a new Proxy/Server Z*, it resumes sending original IP 3491 packets via PIM Register encapsulation via the new Z*. 3493 At the same time, as multicast listeners discover individual S's for 3494 a given G, they can initiate an (S,G) Join for each S under the same 3495 procedures discussed in Section 3.17.1. Once the (S,G) tree is 3496 established, the listeners can send (S, G) Prune messages to R so 3497 that multicast original IP packets for group G sourced by S will only 3498 be delivered via the (S, G) tree and not from the (*, G) tree rooted 3499 at R. All mobility considerations discussed for SSM apply. 3501 3.17.3. Bi-Directional PIM (BIDIR-PIM) 3503 Bi-Directional PIM (BIDIR-PIM) [RFC5015] provides an alternate 3504 approach to ASM that treats the Rendezvous Point (RP) as a Designated 3505 Forwarder (DF). Further considerations for BIDIR-PIM are out of 3506 scope. 3508 3.18. Operation over Multiple OMNI Links 3510 An AERO Client can connect to multiple OMNI links the same as for any 3511 data link service. In that case, the Client maintains a distinct 3512 OMNI interface for each link, e.g., 'omni0' for the first link, 3513 'omni1' for the second, 'omni2' for the third, etc. Each OMNI link 3514 would include its own distinct set of Bridges and Proxy/Servers, 3515 thereby providing redundancy in case of failures. 3517 Each OMNI link could utilize the same or different ANET connections. 3518 The links can be distinguished at the link-layer via the SRT prefix 3519 in a similar fashion as for Virtual Local Area Network (VLAN) tagging 3520 (e.g., IEEE 802.1Q) and/or through assignment of distinct sets of 3521 MSPs on each link. This gives rise to the opportunity for supporting 3522 multiple redundant networked paths (see: Section 3.2.5). 3524 The Client's IP layer can select the outgoing OMNI interface 3525 appropriate for a given traffic profile while (in the reverse 3526 direction) correspondent nodes must have some way of steering their 3527 original IP packets destined to a target via the correct OMNI link. 3529 In a first alternative, if each OMNI link services different MSPs the 3530 Client can receive a distinct MNP from each of the links. IP routing 3531 will therefore assure that the correct OMNI link is used for both 3532 outbound and inbound traffic. This can be accomplished using 3533 existing technologies and approaches, and without requiring any 3534 special supporting code in correspondent nodes or Bridges. 3536 In a second alternative, if each OMNI link services the same MSP(s) 3537 then each link could assign a distinct "OMNI link Anycast" address 3538 that is configured by all Bridges on the link. Correspondent nodes 3539 can then perform Segment Routing to select the correct SRT, which 3540 will then direct the original IP packet over multiple hops to the 3541 target. 3543 3.19. DNS Considerations 3545 AERO Client MNs and INET correspondent nodes consult the Domain Name 3546 System (DNS) the same as for any Internetworking node. When 3547 correspondent nodes and Client MNs use different IP protocol versions 3548 (e.g., IPv4 correspondents and IPv6 MNs), the INET DNS must maintain 3549 A records for IPv4 address mappings to MNs which must then be 3550 populated in Relay NAT64 mapping caches. In that way, an IPv4 3551 correspondent node can send original IPv4 packets to the IPv4 address 3552 mapping of the target MN, and the Relay will translate the IPv4 3553 header and destination address into an IPv6 header and IPv6 3554 destination address of the MN. 3556 When an AERO Client registers with an AERO Proxy/Server, the Proxy/ 3557 Server can return the address(es) of DNS servers in RDNSS options 3558 [RFC6106]. The DNS server provides the IP addresses of other MNs and 3559 correspondent nodes in AAAA records for IPv6 or A records for IPv4. 3561 3.20. Transition/Coexistence Considerations 3563 OAL encapsulation ensures that dissimilar INET partitions can be 3564 joined into a single unified OMNI link, even though the partitions 3565 themselves may have differing protocol versions and/or incompatible 3566 addressing plans. However, a commonality can be achieved by 3567 incrementally distributing globally routable (i.e., native) IP 3568 prefixes to eventually reach all nodes (both mobile and fixed) in all 3569 OMNI link segments. This can be accomplished by incrementally 3570 deploying AERO Bridges on each INET partition, with each Bridge 3571 distributing its MNPs and/or discovering non-MNP IP GUA prefixes on 3572 its INET links. 3574 This gives rise to the opportunity to eventually distribute native IP 3575 addresses to all nodes, and to present a unified OMNI link view even 3576 if the INET partitions remain in their current protocol and 3577 addressing plans. In that way, the OMNI link can serve the dual 3578 purpose of providing a mobility/multilink service and a transition/ 3579 coexistence service. Or, if an INET partition is transitioned to a 3580 native IP protocol version and addressing scheme that is compatible 3581 with the OMNI link MNP-based addressing scheme, the partition and 3582 OMNI link can be joined by Bridges. 3584 Relays that connect INETs/EUNs with dissimilar IP protocol versions 3585 may need to employ a network address and protocol translation 3586 function such as NAT64 [RFC6146]. 3588 3.21. Detecting and Reacting to Proxy/Server and Bridge Failures 3590 In environments where rapid failure recovery is required, Proxy/ 3591 Servers and Bridges SHOULD use Bidirectional Forwarding Detection 3592 (BFD) [RFC5880]. Nodes that use BFD can quickly detect and react to 3593 failures so that cached information is re-established through 3594 alternate nodes. BFD control messaging is carried only over well- 3595 connected ground domain networks (i.e., and not low-end radio links) 3596 and can therefore be tuned for rapid response. 3598 Proxy/Servers and Bridges maintain BFD sessions in parallel with 3599 their BGP peerings. If a Proxy/Server or Bridge fails, BGP peers 3600 will quickly re-establish routes through alternate paths the same as 3601 for common BGP deployments. Similarly, Proxys maintain BFD sessions 3602 with their associated Bridges even though they do not establish BGP 3603 peerings with them. 3605 3.22. AERO Clients on the Open Internet 3607 AERO Clients that connect to the open Internet via INET interfaces 3608 can establish a VPN or direct link to securely connect to a FHS 3609 Proxy/Server in a "tethered" arrangement with all of the Client's 3610 traffic transiting the Proxy/Server which acts as a router. 3611 Alternatively, the Client can associate with an INET FHS Proxy/Server 3612 using UDP/IP encapsulation and control message securing services as 3613 discussed in the following sections. 3615 When a Client's OMNI interface enables an INET underlying interface, 3616 it first examines the INET address. For IPv4, the Client assumes it 3617 is on the open Internet if the INET address is not a special-use IPv4 3618 address per [RFC3330]. Similarly for IPv6, the Client assumes it is 3619 on the open Internet if the INET address is a Global Unicast Address 3620 (GUA) [RFC4291]. Otherwise, the Client should assume it is behind 3621 one or several NATs. 3623 The Client then prepares an RS message with IPv6 source address set 3624 to its MNP-LLA, with IPv6 destination set to (link-local) All-Routers 3625 multicast and with an OMNI option with underlying interface 3626 attributes. If the Client believes that it is on the open Internet, 3627 it SHOULD include its IP address and UDP port number in the Interface 3628 Attributes sub-option corresponding to the underlying interface 3629 (otherwise it may omit the FMT/SRT/LHS/L2ADDR fields). If the 3630 underlying address is IPv4, the Client includes the Port Number and 3631 IPv4 address written in obfuscated form [RFC4380] as discussed in 3632 Section 3.3. If the underlying interface address is IPv6, the Client 3633 instead includes the Port Number and IPv6 address in obfuscated form. 3634 The Client finally includes an authentication signature per 3635 [I-D.templin-6man-omni] to provide message authentication, selects an 3636 Identification value and window synchronization parameters, and 3637 submits the RS for OAL encapsulation. The Client then encapsulates 3638 the OAL fragment in UDP/IP headers to form a carrier packet, sets the 3639 UDP/IP source to its INET address and UDP port, sets the UDP/IP 3640 destination to the FHS Proxy/Server's INET address and the AERO 3641 service port number (8060), then sends the carrier packet to the 3642 Proxy/Server. 3644 When the FHS Proxy/Server receives the RS, it discards the OAL 3645 encapsulation, authenticates the RS message, creates a NCE and 3646 registers the Client's MNP, window synchronization state and INET 3647 interface information according to the OMNI option parameters. If 3648 the Interface Attributes sub-option includes an L2ADDR, the Proxy/ 3649 Server compares the encapsulation IP address and UDP port number with 3650 the (unobfuscated) values. If the values are the same, the Proxy/ 3651 Server caches the Client's information as an "INET" address meaning 3652 that the Client is likely to accept direct messages without requiring 3653 NAT traversal exchanges. If the values are different (or, if the 3654 OMNI option did not include an L2ADDR) the Proxy/Server instead 3655 caches the Client's information as a "mapped" address meaning that 3656 NAT traversal exchanges may be necessary. 3658 The FHS Proxy/Server then prepares an RA message with IPv6 source and 3659 destination set corresponding to the addresses in the RS, and with an 3660 OMNI option with an Origin Indication sub-option per 3661 [I-D.templin-6man-omni] with the mapped and obfuscated Port Number 3662 and IP address observed in the encapsulation headers. The Proxy/ 3663 Server also includes an Interface Attributes sub-option with omIndex 3664 0 and FMT/SRT/LHS/L2ADDR information appropriate for its INET 3665 interface, an authentication signature sub-option per 3666 [I-D.templin-6man-omni] and/or a symmetric window synchronization/ 3667 acknowledgement if necessary. The Proxy/Server then performs OAL 3668 encapsulation and fragmentation if necessary and encapsulates each 3669 fragment in UDP/IP headers with addresses set per the L2ADDR 3670 information in the NCE for the Client. 3672 When the Client receives the RA, it authenticates the message then 3673 process the window synchronization/acknowledgement and compares the 3674 mapped Port Number and IP address from the Origin Indication sub- 3675 option with its own address. If the addresses are the same, the 3676 Client assumes the open Internet / Cone NAT principle; if the 3677 addresses are different, the Client instead assumes that further 3678 qualification procedures are necessary to detect the type of NAT and 3679 proceeds according to standard procedures [RFC6081][RFC4380]. The 3680 Client also caches the RA Interface Attributes FMT/SRT/LHS/L2ADDR 3681 information to discover the Proxy/Server's spanning tree orientation. 3682 The Client finally arranges to return an explicit/implicit 3683 acknowledgement, and sends periodic RS messages to receive fresh RA 3684 messages before the Router Lifetime received on each INET interface 3685 expires. 3687 When the Client sends messages to target IP addresses, it also 3688 invokes route optimization per Section 3.14. For route optimized 3689 targets in the same OMNI link segment, if the target's L2ADDR is on 3690 the open INET, the Client forwards carrier packets directly to the 3691 target INET address. If the target is behind a NAT, the Client first 3692 establishes NAT state for the L2ADDR using the "direct bubble" and 3693 NUD mechanisms discussed in Section 3.10.1. The Client continues to 3694 send carrier packets via its Proxy/Server until NAT state is 3695 populated, then begins forwarding carrier packets via the direct path 3696 through the NAT to the target. For targets in different OMNI link 3697 segments, the Client uses OAL/ORH encapsulation and forwards carrier 3698 packets to the Bridge that returned the NA(AR) message. 3700 The Client can send original IP packets to route-optimized neighbors 3701 in the same OMNI link segment no larger than the minimum/path MPS in 3702 one piece and with OAL encapsulation as atomic fragments. For larger 3703 original IP packets, the Client applies OAL encapsulation then 3704 fragments if necessary according to Section 3.9, with OAL header with 3705 source set to its own MNP-ULA and destination set to the MNP-ULA of 3706 the target, and with an in-window Identification value. The Client 3707 then encapsulates each resulting carrier packet in UDP/IP *NET 3708 headers and sends them to the next hop. 3710 Note: The NAT traversal procedures specified in this document are 3711 applicable for Cone, Address-Restricted and Port-Restricted NATs 3712 only. While future updates to this document may specify procedures 3713 for other NAT variations (e.g., hairpinning and various forms of 3714 Symmetric NATs), it should be noted that continuous communications 3715 are always possible through Proxy/Server forwarding even for these 3716 other NAT variations. 3718 3.23. Time-Varying MNPs 3720 In some use cases, it is desirable, beneficial and efficient for the 3721 Client to receive a constant MNP that travels with the Client 3722 wherever it moves. For example, this would allow air traffic 3723 controllers to easily track aircraft, etc. In other cases, however 3724 (e.g., intelligent transportation systems), the MN may be willing to 3725 sacrifice a modicum of efficiency in order to have time-varying MNPs 3726 that can be changed every so often to defeat adversarial tracking. 3728 The DHCPv6 service offers a way for Clients that desire time-varying 3729 MNPs to obtain short-lived prefixes (e.g., on the order of a small 3730 number of minutes). In that case, the identity of the Client would 3731 not be bound to the MNP but rather to a Node Identification value 3732 (see: [I-D.templin-6man-omni]) to be used as the Client ID seed for 3733 MNP prefix delegation. The Client would then be obligated to 3734 renumber its internal networks whenever its MNP (and therefore also 3735 its MNP-LLA) changes. This should not present a challenge for 3736 Clients with automated network renumbering services, however presents 3737 limits for the durations of ongoing sessions that would prefer to use 3738 a constant address. 3740 4. Implementation Status 3742 An early AERO implementation based on OpenVPN (https://openvpn.net/) 3743 was announced on the v6ops mailing list on January 10, 2018 and an 3744 initial public release of the AERO proof-of-concept source code was 3745 announced on the intarea mailing list on August 21, 2015. 3747 AERO Release-3.2 was tagged on March 30, 2021, and is undergoing 3748 internal testing. Additional internal releases expected within the 3749 coming months, with first public release expected end of 1H2021. 3751 Many AERO/OMNI functions are implemented and undergoing final 3752 integration. OAL fragmentation/reassembly buffer management code has 3753 been cleared for public release and will be presented at the June 3754 2021 ICAO mobility subgroup meeting. 3756 5. IANA Considerations 3758 The IANA is instructed to assign a new type value TBD1 in the IPv6 3759 Routing Types registry (IANA registration procedure is IETF Review or 3760 IESG Approval). 3762 The IANA has assigned the UDP port number "8060" for an earlier 3763 experimental first version of AERO [RFC6706]. This document together 3764 with [I-D.templin-6man-omni] reclaims UDP port number "8060" for 3765 'aero' as the service port for UDP/IP encapsulation. This document 3766 makes no request of IANA, since [I-D.templin-6man-omni] already 3767 provides instructions. (Note: although [RFC6706] was not widely 3768 implemented or deployed, it need not be obsoleted since its messages 3769 use the invalid ICMPv6 message type number '0' which implementations 3770 of this specification can easily distinguish and ignore.) 3772 No further IANA actions are required. 3774 6. Security Considerations 3776 AERO Bridges configure secured tunnels with AERO Proxy/Servers and 3777 Relays within their local OMNI link segments. Applicable secured 3778 tunnel alternatives include IPsec [RFC4301], TLS/SSL [RFC8446], DTLS 3779 [RFC6347], WireGuard [WG], etc. The AERO Bridges of all OMNI link 3780 segments in turn configure secured tunnels for their neighboring AERO 3781 Bridges in a secured spanning tree topology. Therefore, control 3782 messages exchanged between any pair of OMNI link neighbors over the 3783 secured spanning tree are already protected. 3785 To prevent spoofing vectors, Proxy/Servers MUST discard without 3786 responding to any unsecured NS(AR) messages. Also, Proxy/Servers 3787 MUST discard without forwarding any original IP packets received from 3788 one of their own Clients (whether directly or following OAL 3789 reassembly) with a source address that does not match the Client's 3790 MNP and/or a destination address that does match the Client's MNP. 3791 Finally, Proxy/Servers MUST discard without forwarding any carrier 3792 packets with an OAL source and destination that both match the same 3793 MNP (i.e., after consulting the ORH if present). 3795 For INET partitions that require strong security in the data plane, 3796 two options for securing communications include 1) disable route 3797 optimization so that all traffic is conveyed over secured tunnels, or 3798 2) enable on-demand secure tunnel creation between Client neighbors. 3799 Option 1) would result in longer routes than necessary and impose 3800 traffic concentration on critical infrastructure elements. Option 2) 3801 could be coordinated between Clients using NS/NA messages with OMNI 3802 Host Identity Protocol (HIP) "Initiator/Responder" message sub- 3803 options [RFC7401][I-D.templin-6man-omni] to create a secured tunnel 3804 on-demand. 3806 AERO Clients that connect to secured ANETs need not apply security to 3807 their ND messages, since the messages will be authenticated and 3808 forwarded by a perimeter Proxy/Server that applies security on its 3809 INET-facing interface as part of the spanning tree (see above). AERO 3810 Clients connected to the open INET can use network and/or transport 3811 layer security services such as VPNs or can by some other means 3812 establish a direct link to a Proxy/Server. When a VPN or direct link 3813 may be impractical, however, INET Clients and Proxy/Servers SHOULD 3814 include and verify authentication signatures for their IPv6 ND 3815 messages as specified in [I-D.templin-6man-omni]. 3817 Application endpoints SHOULD use transport-layer (or higher-layer) 3818 security services such as TLS/SSL, DTLS or SSH [RFC4251] to assure 3819 the same level of protection as for critical secured Internet 3820 services. AERO Clients that require host-based VPN services SHOULD 3821 use network and/or transport layer security services such as IPsec, 3822 TLS/SSL, DTLS, etc. AERO Proxys and Proxy/Servers can also provide a 3823 network-based VPN service on behalf of the Client, e.g., if the 3824 Client is located within a secured enclave and cannot establish a VPN 3825 on its own behalf. 3827 AERO Proxy/Servers and Bridges present targets for traffic 3828 amplification Denial of Service (DoS) attacks. This concern is no 3829 different than for widely-deployed VPN security gateways in the 3830 Internet, where attackers could send spoofed packets to the gateways 3831 at high data rates. This can be mitigated through the AERO/OMNI data 3832 origin authentication procedures, as well as connecting Proxy/Servers 3833 and Bridges over dedicated links with no connections to the Internet 3834 and/or when connections to the Internet are only permitted through 3835 well-managed firewalls. Traffic amplification DoS attacks can also 3836 target an AERO Client's low data rate links. This is a concern not 3837 only for Clients located on the open Internet but also for Clients in 3838 secured enclaves. AERO Proxy/Servers and Proxys can institute rate 3839 limits that protect Clients from receiving packet floods that could 3840 DoS low data rate links. 3842 AERO Relays must implement ingress filtering to avoid a spoofing 3843 attack in which spurious messages with ULA addresses are injected 3844 into an OMNI link from an outside attacker. AERO Clients MUST ensure 3845 that their connectivity is not used by unauthorized nodes on their 3846 EUNs to gain access to a protected network, i.e., AERO Clients that 3847 act as routers MUST NOT provide routing services for unauthorized 3848 nodes. (This concern is no different than for ordinary hosts that 3849 receive an IP address delegation but then "share" the address with 3850 other nodes via some form of Internet connection sharing such as 3851 tethering.) 3853 The MAP list MUST be well-managed and secured from unauthorized 3854 tampering, even though the list contains only public information. 3855 The MAP list can be conveyed to the Client in a similar fashion as in 3856 [RFC5214] (e.g., through layer 2 data link login messaging, secure 3857 upload of a static file, DNS lookups, etc.). 3859 The AERO service for open INET Clients depends on a public key 3860 distribution service in which Client public keys and identities are 3861 maintained in a shared database accessible to all open INET Proxy/ 3862 Servers. Similarly, each Client must be able to determine the public 3863 key of each Proxy/Server, e.g. by consulting an online database. 3864 When AERO nodes register their public keys indexed by a unique Host 3865 Identity Tag (HIT) [RFC7401] in a distributed database such as the 3866 DNS, and use the HIT as an identity for applying IPv6 ND message 3867 authentication signatures, a means for determining public key 3868 attestation is available. 3870 Security considerations for IPv6 fragmentation and reassembly are 3871 discussed in [I-D.templin-6man-omni]. In environments where spoofing 3872 is considered a threat, OMNI nodes SHOULD employ Identification 3873 window synchronization and OAL destinations SHOULD configure an (end- 3874 system-based) firewall. 3876 SRH authentication facilities are specified in [RFC8754]. Security 3877 considerations for accepting link-layer ICMP messages and reflected 3878 packets are discussed throughout the document. 3880 7. Acknowledgements 3882 Discussions in the IETF, aviation standards communities and private 3883 exchanges helped shape some of the concepts in this work. 3884 Individuals who contributed insights include Mikael Abrahamsson, Mark 3885 Andrews, Fred Baker, Bob Braden, Stewart Bryant, Scott Burleigh, 3886 Brian Carpenter, Wojciech Dec, Pavel Drasil, Ralph Droms, Adrian 3887 Farrel, Nick Green, Sri Gundavelli, Brian Haberman, Bernhard Haindl, 3888 Joel Halpern, Tom Herbert, Bob Hinden, Sascha Hlusiak, Lee Howard, 3889 Christian Huitema, Zdenek Jaron, Andre Kostur, Hubert Kuenig, Ted 3890 Lemon, Andy Malis, Satoru Matsushima, Tomek Mrugalski, Thomas Narten, 3891 Madhu Niraula, Alexandru Petrescu, Behcet Saikaya, Michal Skorepa, 3892 Dave Thaler, Joe Touch, Bernie Volz, Ryuji Wakikawa, Tony Whyman, 3893 Lloyd Wood and James Woodyatt. Members of the IESG also provided 3894 valuable input during their review process that greatly improved the 3895 document. Special thanks go to Stewart Bryant, Joel Halpern and 3896 Brian Haberman for their shepherding guidance during the publication 3897 of the AERO first edition. 3899 This work has further been encouraged and supported by Boeing 3900 colleagues including Kyle Bae, M. Wayne Benson, Dave Bernhardt, Cam 3901 Brodie, John Bush, Balaguruna Chidambaram, Irene Chin, Bruce Cornish, 3902 Claudiu Danilov, Don Dillenburg, Joe Dudkowski, Wen Fang, Samad 3903 Farooqui, Anthony Gregory, Jeff Holland, Seth Jahne, Brian Jaury, 3904 Greg Kimberly, Ed King, Madhuri Madhava Badgandi, Laurel Matthew, 3905 Gene MacLean III, Kyle Mikos, Rob Muszkiewicz, Sean O'Sullivan, Vijay 3906 Rajagopalan, Greg Saccone, Rod Santiago, Kent Shuey, Brian Skeen, 3907 Mike Slane, Carrie Spiker, Katie Tran, Brendan Williams, Amelia 3908 Wilson, Julie Wulff, Yueli Yang, Eric Yeh and other members of the 3909 Boeing mobility, networking and autonomy teams. Kyle Bae, Wayne 3910 Benson, Madhuri Madhava Badgandi, Vijayasarathy Rajagopalan, Katie 3911 Tran and Eric Yeh are especially acknowledged for their work on the 3912 AERO implementation. Chuck Klabunde is honored and remembered for 3913 his early leadership, and we mourn his untimely loss. 3915 This work was inspired by the support and encouragement of countless 3916 outstanding colleagues, managers and program directors over the span 3917 of many decades. Beginning in the late 1980s,' the Digital Equipment 3918 Corporation (DEC) Ultrix Engineering and DECnet Architects groups 3919 identified early issues with fragmentation and bridging links with 3920 diverse MTUs. In the early 1990s, engagements at DEC Project Sequoia 3921 at UC Berkeley and the DEC Western Research Lab in Palo Alto included 3922 investigations into large-scale networked filesystems, ATM vs 3923 Internet and network security proxies. In the mid-1990s to early 3924 2000s employment at the NASA Ames Research Center (Sterling Software) 3925 and SRI International supported early investigations of IPv6, ONR UAV 3926 Communications and the IETF. An employment at Nokia where important 3927 IETF documents were published gave way to a present-day engagement 3928 with The Boeing Company. The work matured at Boeing through major 3929 programs including Future Combat Systems, Advanced Airplane Program, 3930 DTN for the International Space Station, Mobility Vision Lab, CAST, 3931 Caravan, the NASA UAS/CNS program, the FAA/ICAO ATN/IPS program and 3932 many others. An attempt to name all who gave support and 3933 encouragement would double the current document size and result in 3934 many unintentional omissions - but to all a humble thanks. 3936 Earlier works on NBMA tunneling approaches are found in 3937 [RFC2529][RFC5214][RFC5569]. 3939 Many of the constructs presented in this second edition of AERO are 3940 based on the author's earlier works, including: 3942 o The Internet Routing Overlay Network (IRON) 3943 [RFC6179][I-D.templin-ironbis] 3945 o Virtual Enterprise Traversal (VET) 3946 [RFC5558][I-D.templin-intarea-vet] 3948 o The Subnetwork Encapsulation and Adaptation Layer (SEAL) 3949 [RFC5320][I-D.templin-intarea-seal] 3951 o AERO, First Edition [RFC6706] 3953 Note that these works cite numerous earlier efforts that are not also 3954 cited here due to space limitations. The authors of those earlier 3955 works are acknowledged for their insights. 3957 This work is aligned with the NASA Safe Autonomous Systems Operation 3958 (SASO) program under NASA contract number NNA16BD84C. 3960 This work is aligned with the FAA as per the SE2025 contract number 3961 DTFAWA-15-D-00030. 3963 This work is aligned with the Boeing Commercial Airplanes (BCA) 3964 Internet of Things (IoT) and autonomy programs. 3966 This work is aligned with the Boeing Information Technology (BIT) 3967 MobileNet program. 3969 8. References 3971 8.1. Normative References 3973 [I-D.templin-6man-omni] 3974 Templin, F. L. and T. Whyman, "Transmission of IP Packets 3975 over Overlay Multilink Network (OMNI) Interfaces", draft- 3976 templin-6man-omni-03 (work in progress), April 2021. 3978 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, 3979 DOI 10.17487/RFC0791, September 1981, 3980 . 3982 [RFC0792] Postel, J., "Internet Control Message Protocol", STD 5, 3983 RFC 792, DOI 10.17487/RFC0792, September 1981, 3984 . 3986 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 3987 Requirement Levels", BCP 14, RFC 2119, 3988 DOI 10.17487/RFC2119, March 1997, 3989 . 3991 [RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in 3992 IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473, 3993 December 1998, . 3995 [RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander, 3996 "SEcure Neighbor Discovery (SEND)", RFC 3971, 3997 DOI 10.17487/RFC3971, March 2005, 3998 . 4000 [RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)", 4001 RFC 3972, DOI 10.17487/RFC3972, March 2005, 4002 . 4004 [RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and 4005 More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191, 4006 November 2005, . 4008 [RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast 4009 Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005, 4010 . 4012 [RFC4380] Huitema, C., "Teredo: Tunneling IPv6 over UDP through 4013 Network Address Translations (NATs)", RFC 4380, 4014 DOI 10.17487/RFC4380, February 2006, 4015 . 4017 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 4018 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 4019 DOI 10.17487/RFC4861, September 2007, 4020 . 4022 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 4023 Address Autoconfiguration", RFC 4862, 4024 DOI 10.17487/RFC4862, September 2007, 4025 . 4027 [RFC6081] Thaler, D., "Teredo Extensions", RFC 6081, 4028 DOI 10.17487/RFC6081, January 2011, 4029 . 4031 [RFC7401] Moskowitz, R., Ed., Heer, T., Jokela, P., and T. 4032 Henderson, "Host Identity Protocol Version 2 (HIPv2)", 4033 RFC 7401, DOI 10.17487/RFC7401, April 2015, 4034 . 4036 [RFC7739] Gont, F., "Security Implications of Predictable Fragment 4037 Identification Values", RFC 7739, DOI 10.17487/RFC7739, 4038 February 2016, . 4040 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 4041 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 4042 May 2017, . 4044 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 4045 (IPv6) Specification", STD 86, RFC 8200, 4046 DOI 10.17487/RFC8200, July 2017, 4047 . 4049 [RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A., 4050 Richardson, M., Jiang, S., Lemon, T., and T. Winters, 4051 "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", 4052 RFC 8415, DOI 10.17487/RFC8415, November 2018, 4053 . 4055 8.2. Informative References 4057 [BGP] Huston, G., "BGP in 2015, http://potaroo.net", January 4058 2016. 4060 [I-D.bonica-6man-comp-rtg-hdr] 4061 Bonica, R., Kamite, Y., Alston, A., Henriques, D., and L. 4062 Jalil, "The IPv6 Compact Routing Header (CRH)", draft- 4063 bonica-6man-comp-rtg-hdr-24 (work in progress), January 4064 2021. 4066 [I-D.bonica-6man-crh-helper-opt] 4067 Li, X., Bao, C., Ruan, E., and R. Bonica, "Compressed 4068 Routing Header (CRH) Helper Option", draft-bonica-6man- 4069 crh-helper-opt-03 (work in progress), April 2021. 4071 [I-D.ietf-intarea-frag-fragile] 4072 Bonica, R., Baker, F., Huston, G., Hinden, R. M., Troan, 4073 O., and F. Gont, "IP Fragmentation Considered Fragile", 4074 draft-ietf-intarea-frag-fragile-17 (work in progress), 4075 September 2019. 4077 [I-D.ietf-intarea-tunnels] 4078 Touch, J. and M. Townsley, "IP Tunnels in the Internet 4079 Architecture", draft-ietf-intarea-tunnels-10 (work in 4080 progress), September 2019. 4082 [I-D.ietf-ipwave-vehicular-networking] 4083 (editor), J. (. J., "IPv6 Wireless Access in Vehicular 4084 Environments (IPWAVE): Problem Statement and Use Cases", 4085 draft-ietf-ipwave-vehicular-networking-20 (work in 4086 progress), March 2021. 4088 [I-D.ietf-rtgwg-atn-bgp] 4089 Templin, F. L., Saccone, G., Dawra, G., Lindem, A., and V. 4090 Moreno, "A Simple BGP-based Mobile Routing System for the 4091 Aeronautical Telecommunications Network", draft-ietf- 4092 rtgwg-atn-bgp-10 (work in progress), January 2021. 4094 [I-D.templin-6man-dhcpv6-ndopt] 4095 Templin, F. L., "A Unified Stateful/Stateless 4096 Configuration Service for IPv6", draft-templin-6man- 4097 dhcpv6-ndopt-11 (work in progress), January 2021. 4099 [I-D.templin-intarea-seal] 4100 Templin, F. L., "The Subnetwork Encapsulation and 4101 Adaptation Layer (SEAL)", draft-templin-intarea-seal-68 4102 (work in progress), January 2014. 4104 [I-D.templin-intarea-vet] 4105 Templin, F. L., "Virtual Enterprise Traversal (VET)", 4106 draft-templin-intarea-vet-40 (work in progress), May 2013. 4108 [I-D.templin-ipwave-uam-its] 4109 Templin, F. L., "Urban Air Mobility Implications for 4110 Intelligent Transportation Systems", draft-templin-ipwave- 4111 uam-its-04 (work in progress), January 2021. 4113 [I-D.templin-ironbis] 4114 Templin, F. L., "The Interior Routing Overlay Network 4115 (IRON)", draft-templin-ironbis-16 (work in progress), 4116 March 2014. 4118 [I-D.templin-v6ops-pdhost] 4119 Templin, F. L., "IPv6 Prefix Delegation and Multi- 4120 Addressing Models", draft-templin-v6ops-pdhost-27 (work in 4121 progress), January 2021. 4123 [OVPN] OpenVPN, O., "http://openvpn.net", October 2016. 4125 [RFC1035] Mockapetris, P., "Domain names - implementation and 4126 specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, 4127 November 1987, . 4129 [RFC1812] Baker, F., Ed., "Requirements for IP Version 4 Routers", 4130 RFC 1812, DOI 10.17487/RFC1812, June 1995, 4131 . 4133 [RFC2003] Perkins, C., "IP Encapsulation within IP", RFC 2003, 4134 DOI 10.17487/RFC2003, October 1996, 4135 . 4137 [RFC2004] Perkins, C., "Minimal Encapsulation within IP", RFC 2004, 4138 DOI 10.17487/RFC2004, October 1996, 4139 . 4141 [RFC2236] Fenner, W., "Internet Group Management Protocol, Version 4142 2", RFC 2236, DOI 10.17487/RFC2236, November 1997, 4143 . 4145 [RFC2464] Crawford, M., "Transmission of IPv6 Packets over Ethernet 4146 Networks", RFC 2464, DOI 10.17487/RFC2464, December 1998, 4147 . 4149 [RFC2529] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4 4150 Domains without Explicit Tunnels", RFC 2529, 4151 DOI 10.17487/RFC2529, March 1999, 4152 . 4154 [RFC2983] Black, D., "Differentiated Services and Tunnels", 4155 RFC 2983, DOI 10.17487/RFC2983, October 2000, 4156 . 4158 [RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition 4159 of Explicit Congestion Notification (ECN) to IP", 4160 RFC 3168, DOI 10.17487/RFC3168, September 2001, 4161 . 4163 [RFC3330] IANA, "Special-Use IPv4 Addresses", RFC 3330, 4164 DOI 10.17487/RFC3330, September 2002, 4165 . 4167 [RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener 4168 Discovery Version 2 (MLDv2) for IPv6", RFC 3810, 4169 DOI 10.17487/RFC3810, June 2004, 4170 . 4172 [RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally 4173 Unique IDentifier (UUID) URN Namespace", RFC 4122, 4174 DOI 10.17487/RFC4122, July 2005, 4175 . 4177 [RFC4251] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH) 4178 Protocol Architecture", RFC 4251, DOI 10.17487/RFC4251, 4179 January 2006, . 4181 [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A 4182 Border Gateway Protocol 4 (BGP-4)", RFC 4271, 4183 DOI 10.17487/RFC4271, January 2006, 4184 . 4186 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 4187 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 4188 2006, . 4190 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 4191 Internet Protocol", RFC 4301, DOI 10.17487/RFC4301, 4192 December 2005, . 4194 [RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery 4195 Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April 4196 2006, . 4198 [RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet 4199 Control Message Protocol (ICMPv6) for the Internet 4200 Protocol Version 6 (IPv6) Specification", STD 89, 4201 RFC 4443, DOI 10.17487/RFC4443, March 2006, 4202 . 4204 [RFC4511] Sermersheim, J., Ed., "Lightweight Directory Access 4205 Protocol (LDAP): The Protocol", RFC 4511, 4206 DOI 10.17487/RFC4511, June 2006, 4207 . 4209 [RFC4541] Christensen, M., Kimball, K., and F. Solensky, 4210 "Considerations for Internet Group Management Protocol 4211 (IGMP) and Multicast Listener Discovery (MLD) Snooping 4212 Switches", RFC 4541, DOI 10.17487/RFC4541, May 2006, 4213 . 4215 [RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick, 4216 "Internet Group Management Protocol (IGMP) / Multicast 4217 Listener Discovery (MLD)-Based Multicast Forwarding 4218 ("IGMP/MLD Proxying")", RFC 4605, DOI 10.17487/RFC4605, 4219 August 2006, . 4221 [RFC4982] Bagnulo, M. and J. Arkko, "Support for Multiple Hash 4222 Algorithms in Cryptographically Generated Addresses 4223 (CGAs)", RFC 4982, DOI 10.17487/RFC4982, July 2007, 4224 . 4226 [RFC5015] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano, 4227 "Bidirectional Protocol Independent Multicast (BIDIR- 4228 PIM)", RFC 5015, DOI 10.17487/RFC5015, October 2007, 4229 . 4231 [RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site 4232 Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214, 4233 DOI 10.17487/RFC5214, March 2008, 4234 . 4236 [RFC5320] Templin, F., Ed., "The Subnetwork Encapsulation and 4237 Adaptation Layer (SEAL)", RFC 5320, DOI 10.17487/RFC5320, 4238 February 2010, . 4240 [RFC5522] Eddy, W., Ivancic, W., and T. Davis, "Network Mobility 4241 Route Optimization Requirements for Operational Use in 4242 Aeronautics and Space Exploration Mobile Networks", 4243 RFC 5522, DOI 10.17487/RFC5522, October 2009, 4244 . 4246 [RFC5558] Templin, F., Ed., "Virtual Enterprise Traversal (VET)", 4247 RFC 5558, DOI 10.17487/RFC5558, February 2010, 4248 . 4250 [RFC5569] Despres, R., "IPv6 Rapid Deployment on IPv4 4251 Infrastructures (6rd)", RFC 5569, DOI 10.17487/RFC5569, 4252 January 2010, . 4254 [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 4255 (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, 4256 . 4258 [RFC6106] Jeong, J., Park, S., Beloeil, L., and S. Madanapalli, 4259 "IPv6 Router Advertisement Options for DNS Configuration", 4260 RFC 6106, DOI 10.17487/RFC6106, November 2010, 4261 . 4263 [RFC6139] Russert, S., Ed., Fleischman, E., Ed., and F. Templin, 4264 Ed., "Routing and Addressing in Networks with Global 4265 Enterprise Recursion (RANGER) Scenarios", RFC 6139, 4266 DOI 10.17487/RFC6139, February 2011, 4267 . 4269 [RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful 4270 NAT64: Network Address and Protocol Translation from IPv6 4271 Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146, 4272 April 2011, . 4274 [RFC6179] Templin, F., Ed., "The Internet Routing Overlay Network 4275 (IRON)", RFC 6179, DOI 10.17487/RFC6179, March 2011, 4276 . 4278 [RFC6221] Miles, D., Ed., Ooghe, S., Dec, W., Krishnan, S., and A. 4279 Kavanagh, "Lightweight DHCPv6 Relay Agent", RFC 6221, 4280 DOI 10.17487/RFC6221, May 2011, 4281 . 4283 [RFC6273] Kukec, A., Krishnan, S., and S. Jiang, "The Secure 4284 Neighbor Discovery (SEND) Hash Threat Analysis", RFC 6273, 4285 DOI 10.17487/RFC6273, June 2011, 4286 . 4288 [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer 4289 Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, 4290 January 2012, . 4292 [RFC6355] Narten, T. and J. Johnson, "Definition of the UUID-Based 4293 DHCPv6 Unique Identifier (DUID-UUID)", RFC 6355, 4294 DOI 10.17487/RFC6355, August 2011, 4295 . 4297 [RFC6438] Carpenter, B. and S. Amante, "Using the IPv6 Flow Label 4298 for Equal Cost Multipath Routing and Link Aggregation in 4299 Tunnels", RFC 6438, DOI 10.17487/RFC6438, November 2011, 4300 . 4302 [RFC6706] Templin, F., Ed., "Asymmetric Extended Route Optimization 4303 (AERO)", RFC 6706, DOI 10.17487/RFC6706, August 2012, 4304 . 4306 [RFC6935] Eubanks, M., Chimento, P., and M. Westerlund, "IPv6 and 4307 UDP Checksums for Tunneled Packets", RFC 6935, 4308 DOI 10.17487/RFC6935, April 2013, 4309 . 4311 [RFC6936] Fairhurst, G. and M. Westerlund, "Applicability Statement 4312 for the Use of IPv6 UDP Datagrams with Zero Checksums", 4313 RFC 6936, DOI 10.17487/RFC6936, April 2013, 4314 . 4316 [RFC7333] Chan, H., Ed., Liu, D., Seite, P., Yokota, H., and J. 4317 Korhonen, "Requirements for Distributed Mobility 4318 Management", RFC 7333, DOI 10.17487/RFC7333, August 2014, 4319 . 4321 [RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I., 4322 Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent 4323 Multicast - Sparse Mode (PIM-SM): Protocol Specification 4324 (Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March 4325 2016, . 4327 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 4328 Decraene, B., Litkowski, S., and R. Shakir, "Segment 4329 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 4330 July 2018, . 4332 [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol 4333 Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, 4334 . 4336 [RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J., 4337 Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header 4338 (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020, 4339 . 4341 [WG] Wireguard, "WireGuard, https://www.wireguard.com", August 4342 2020. 4344 Appendix A. Non-Normative Considerations 4346 AERO can be applied to a multitude of Internetworking scenarios, with 4347 each having its own adaptations. The following considerations are 4348 provided as non-normative guidance: 4350 A.1. Implementation Strategies for Route Optimization 4352 Route optimization as discussed in Section 3.14 results in the route 4353 optimization source (ROS) creating a NCE for the target neighbor. 4354 The NCE state is set to REACHABLE for at most ReachableTime seconds. 4355 In order to refresh the NCE lifetime before the ReachableTime timer 4356 expires, the specification requires implementations to issue a new 4357 NS/NA(AR) exchange to reset ReachableTime while data packets are 4358 still flowing. However, the decision of when to initiate a new NS/ 4359 NA(AR) exchange and to perpetuate the process is left as an 4360 implementation detail. 4362 One possible strategy may be to monitor the NCE watching for data 4363 packets for (ReachableTime - 5) seconds. If any data packets have 4364 been sent to the neighbor within this timeframe, then send an NS(AR) 4365 to receive a new NA(AR). If no data packets have been sent, wait for 4366 5 additional seconds and send an immediate NS(AR) if any data packets 4367 are sent within this "expiration pending" 5 second window. If no 4368 additional data packets are sent within the 5 second window, reset 4369 the NCE state to STALE. 4371 The monitoring of the neighbor data packet traffic therefore becomes 4372 an ongoing process during the NCE lifetime. If the NCE expires, 4373 future data packets will trigger a new NS/NA(AR) exchange while the 4374 packets themselves are delivered over a longer path until route 4375 optimization state is re-established. 4377 A.2. Implicit Mobility Management 4379 OMNI interface neighbors MAY provide a configuration option that 4380 allows them to perform implicit mobility management in which no ND 4381 messaging is used. In that case, the Client only transmits packets 4382 over a single interface at a time, and the neighbor always observes 4383 packets arriving from the Client from the same link-layer source 4384 address. 4386 If the Client's underlying interface address changes (either due to a 4387 readdressing of the original interface or switching to a new 4388 interface) the neighbor immediately updates the NCE for the Client 4389 and begins accepting and sending packets according to the Client's 4390 new address. This implicit mobility method applies to use cases such 4391 as cellphones with both WiFi and Cellular interfaces where only one 4392 of the interfaces is active at a given time, and the Client 4393 automatically switches over to the backup interface if the primary 4394 interface fails. 4396 A.3. Direct Underlying Interfaces 4398 When a Client's OMNI interface is configured over a Direct interface, 4399 the neighbor at the other end of the Direct link can receive packets 4400 without any encapsulation. In that case, the Client sends packets 4401 over the Direct link according to traffic selectors. If the Direct 4402 interface is selected, then the Client's IP packets are transmitted 4403 directly to the peer without going through an ANET/INET. If other 4404 interfaces are selected, then the Client's IP packets are transmitted 4405 via a different interface, which may result in the inclusion of 4406 Proxy/Servers and Bridges in the communications path. Direct 4407 interfaces must be tested periodically for reachability, e.g., via 4408 NUD. 4410 A.4. AERO Critical Infrastructure Considerations 4412 AERO Bridges can be either Commercial off-the Shelf (COTS) standard 4413 IP routers or virtual machines in the cloud. Bridges must be 4414 provisioned, supported and managed by the INET administrative 4415 authority, and connected to the Bridges of other INETs via inter- 4416 domain peerings. Cost for purchasing, configuring and managing 4417 Bridges is nominal even for very large OMNI links. 4419 AERO INET Proxy/Servers can be standard dedicated server platforms, 4420 but most often will be deployed as virtual machines in the cloud. 4421 The only requirements for INET Proxy/Servers are that they can run 4422 the AERO/OMNI code and have at least one network interface connection 4423 to the INET. INET Proxy/Servers must be provisioned, supported and 4424 managed by the INET administrative authority. Cost for purchasing, 4425 configuring and managing cloud Proxy/Servers is nominal especially 4426 for virtual machines. 4428 AERO ANET Proxy/Servers are most often standard dedicated server 4429 platforms with one underlying interface connected to the ANET and a 4430 second interface connected to an INET. As with INET Proxy/Servers, 4431 the only requirements are that they can run the AERO/OMNI code and 4432 have at least one interface connection to the INET. ANET Proxy/ 4433 Servers must be provisioned, supported and managed by the ANET 4434 administrative authority. Cost for purchasing, configuring and 4435 managing Proxys is nominal, and borne by the ANET administrative 4436 authority. 4438 AERO Relays are simply Proxy/Servers connected to INETs and/or EUNs 4439 that provide forwarding services for non-MNP destinations. The Relay 4440 connects to the OMNI link and engages in eBGP peering with one or 4441 more Bridges as a stub AS. The Relay then injects its MNPs and/or 4442 non-MNP prefixes into the BGP routing system, and provisions the 4443 prefixes to its downstream-attached networks. The Relay can perform 4444 ROS/ROR services the same as for any Proxy/Server, and can route 4445 between the MNP and non-MNP address spaces. 4447 A.5. AERO Server Failure Implications 4449 AERO Proxy/Servers may appear as a single point of failure in the 4450 architecture, but such is not the case since all Proxy/Servers on the 4451 link provide identical services and loss of a Proxy/Server does not 4452 imply immediate and/or comprehensive communication failures. Proxy/ 4453 Server failure is quickly detected and conveyed by Bidirectional 4454 Forward Detection (BFD) and/or proactive NUD allowing Clients to 4455 migrate to new Proxy/Servers. 4457 If a Proxy/Server fails, ongoing packet forwarding to Clients will 4458 continue by virtue of the neighbor cache entries that have already 4459 been established in route optimization sources (ROSs). If a Client 4460 also experiences mobility events at roughly the same time the Proxy/ 4461 Server fails, uNA messages may be lost but neighbor cache entries in 4462 the DEPARTED state will ensure that packet forwarding to the Client's 4463 new locations will continue for up to DepartTime seconds. 4465 If a Client is left without a Proxy/Server for a considerable length 4466 of time (e.g., greater than ReachableTime seconds) then existing 4467 neighbor cache entries will eventually expire and both ongoing and 4468 new communications will fail. The original source will continue to 4469 retransmit until the Client has established a new Proxy/Server 4470 relationship, after which time continuous communications will resume. 4472 Therefore, providing many Proxy/Servers on the link with high 4473 availability profiles provides resilience against loss of individual 4474 Proxy/Servers and assurance that Clients can establish new Proxy/ 4475 Server relationships quickly in event of a Proxy/Server failure. 4477 A.6. AERO Client / Server Architecture 4479 The AERO architectural model is client / server in the control plane, 4480 with route optimization in the data plane. The same as for common 4481 Internet services, the AERO Client discovers the addresses of AERO 4482 Proxy/Servers and connects to one or more of them. The AERO service 4483 is analogous to common Internet services such as google.com, 4484 yahoo.com, cnn.com, etc. However, there is only one AERO service for 4485 the link and all Proxy/Servers provide identical services. 4487 Common Internet services provide differing strategies for advertising 4488 server addresses to clients. The strategy is conveyed through the 4489 DNS resource records returned in response to name resolution queries. 4490 As of January 2020 Internet-based 'nslookup' services were used to 4491 determine the following: 4493 o When a client resolves the domainname "google.com", the DNS always 4494 returns one A record (i.e., an IPv4 address) and one AAAA record 4495 (i.e., an IPv6 address). The client receives the same addresses 4496 each time it resolves the domainname via the same DNS resolver, 4497 but may receive different addresses when it resolves the 4498 domainname via different DNS resolvers. But, in each case, 4499 exactly one A and one AAAA record are returned. 4501 o When a client resolves the domainname "ietf.org", the DNS always 4502 returns one A record and one AAAA record with the same addresses 4503 regardless of which DNS resolver is used. 4505 o When a client resolves the domainname "yahoo.com", the DNS always 4506 returns a list of 4 A records and 4 AAAA records. Each time the 4507 client resolves the domainname via the same DNS resolver, the same 4508 list of addresses are returned but in randomized order (i.e., 4509 consistent with a DNS round-robin strategy). But, interestingly, 4510 the same addresses are returned (albeit in randomized order) when 4511 the domainname is resolved via different DNS resolvers. 4513 o When a client resolves the domainname "amazon.com", the DNS always 4514 returns a list of 3 A records and no AAAA records. As with 4515 "yahoo.com", the same three A records are returned from any 4516 worldwide Internet connection point in randomized order. 4518 The above example strategies show differing approaches to Internet 4519 resilience and service distribution offered by major Internet 4520 services. The Google approach exposes only a single IPv4 and a 4521 single IPv6 address to clients. Clients can then select whichever IP 4522 protocol version offers the best response, but will always use the 4523 same IP address according to the current Internet connection point. 4524 This means that the IP address offered by the network must lead to a 4525 highly-available server and/or service distribution point. In other 4526 words, resilience is predicated on high availability within the 4527 network and with no client-initiated failovers expected (i.e., it is 4528 all-or-nothing from the client's perspective). However, Google does 4529 provide for worldwide distributed service distribution by virtue of 4530 the fact that each Internet connection point responds with a 4531 different IPv6 and IPv4 address. The IETF approach is like google 4532 (all-or-nothing from the client's perspective), but provides only a 4533 single IPv4 or IPv6 address on a worldwide basis. This means that 4534 the addresses must be made highly-available at the network level with 4535 no client failover possibility, and if there is any worldwide service 4536 distribution it would need to be conducted by a network element that 4537 is reached via the IP address acting as a service distribution point. 4539 In contrast to the Google and IETF philosophies, Yahoo and Amazon 4540 both provide clients with a (short) list of IP addresses with Yahoo 4541 providing both IP protocol versions and Amazon as IPv4-only. The 4542 order of the list is randomized with each name service query 4543 response, with the effect of round-robin load balancing for service 4544 distribution. With a short list of addresses, there is still 4545 expectation that the network will implement high availability for 4546 each address but in case any single address fails the client can 4547 switch over to using a different address. The balance then becomes 4548 one of function in the network vs function in the end system. 4550 The same implications observed for common highly-available services 4551 in the Internet apply also to the AERO client/server architecture. 4552 When an AERO Client connects to one or more ANETs, it discovers one 4553 or more AERO Proxy/Server addresses through the mechanisms discussed 4554 in earlier sections. Each Proxy/Server address presumably leads to a 4555 fault-tolerant clustering arrangement such as supported by Linux-HA, 4556 Extended Virtual Synchrony or Paxos. Such an arrangement has 4557 precedence in common Internet service deployments in lightweight 4558 virtual machines without requiring expensive hardware deployment. 4559 Similarly, common Internet service deployments set service IP 4560 addresses on service distribution points that may relay requests to 4561 many different servers. 4563 For AERO, the expectation is that a combination of the Google/IETF 4564 and Yahoo/Amazon philosophies would be employed. The AERO Client 4565 connects to different ANET access points and can receive 1-2 Proxy/ 4566 Server ADM-LLAs at each point. It then selects one AERO Proxy/Server 4567 address, and engages in RS/RA exchanges with the same Proxy/Server 4568 from all ANET connections. The Client remains with this Proxy/Server 4569 unless or until the Proxy/Server fails, in which case it can switch 4570 over to an alternate Proxy/Server. The Client can likewise switch 4571 over to a different Proxy/Server at any time if there is some reason 4572 for it to do so. So, the AERO expectation is for a balance of 4573 function in the network and end system, with fault tolerance and 4574 resilience at both levels. 4576 Appendix B. Change Log 4578 << RFC Editor - remove prior to publication >> 4580 Changes from draft-templin-6man-aero-15 to draft-templin-6man-aero- 4581 16: 4583 o Final editorial review pass resulting in multiple changes. 4584 Document now submit for final approval (with reference to rfcdiff 4585 from previous version). 4587 Changes from draft-templin-6man-aero-14 to draft-templin-6man-aero- 4588 15: 4590 o Final editorial review pass resulting in multiple changes. 4591 Document now submit for final approval (with reference to rfcdiff 4592 from previous version). 4594 Changes from draft-templin-6man-aero-13 to draft-templin-6man-aero- 4595 14: 4597 o Final editorial review pass resulting in multiple changes. 4598 Document now submit for final approval (with reference to rfcdiff 4599 from previous version). 4601 Changes from draft-templin-6man-aero-12 to draft-templin-6man-aero- 4602 13: 4604 o Final editorial review pass resulting in multiple changes. 4605 Document now submit for final approval (with reference to rfcdiff 4606 from previous version). 4608 Changes from draft-templin-6man-aero-11 to draft-templin-6man-aero- 4609 12: 4611 o Final editorial review pass resulting in multiple changes. 4612 Document now submit for final approval (with reference to rfcdiff 4613 from previous version). 4615 Changes from draft-templin-6man-aero-10 to draft-templin-6man-aero- 4616 11: 4618 o Final editorial review pass resulting in multiple changes. 4619 Document now submit for final approval (with reference to rfcdiff 4620 from previous version). 4622 Changes from draft-templin-6man-aero-09 to draft-templin-6man-aero- 4623 10: 4625 o Final editorial review pass resulting in multiple changes. 4626 Document now submit for final approval (with reference to rfcdiff 4627 from previous version). 4629 Changes from draft-templin-6man-aero-08 to draft-templin-6man-aero- 4630 09: 4632 o Final editorial review pass resulting in multiple changes. 4633 Document now submit for final approval (with reference to rfcdiff 4634 from previous version). 4636 Changes from draft-templin-6man-aero-07 to draft-templin-6man-aero- 4637 08: 4639 o Final editorial review pass resulting in multiple changes. 4640 Document now submit for final approval (with reference to rfcdiff 4641 from previous version). 4643 Changes from draft-templin-6man-aero-06 to draft-templin-6man-aero- 4644 07: 4646 o Final editorial review pass resulting in multiple changes. 4647 Document now submit for final approval (with reference to rfcdiff 4648 from previous version). 4650 Changes from draft-templin-6man-aero-05 to draft-templin-6man-aero- 4651 06: 4653 o Final editorial review pass resulting in multiple changes. 4654 Document now submit for final approval. 4656 Changes from draft-templin-6man-aero-04 to draft-templin-6man-aero- 4657 05: 4659 o Changed to use traffic selectors instead of the former multilink 4660 selection strategy. 4662 Changes from draft-templin-6man-aero-03 to draft-templin-6man-aero- 4663 04: 4665 o Removed documents from "Obsoletes" list. 4667 o Introduced the concept of "secured" and "unsecured" spanning tree. 4669 o Additional security considerations. 4671 o Additional route optimization considerations. 4673 Changes from draft-templin-6man-aero-02 to draft-templin-6man-aero- 4674 03: 4676 o Support for extended route optimization from ROR to target over 4677 target's underlying interfaces. 4679 Changes from draft-templin-6man-aero-01 to draft-templin-6man-aero- 4680 02: 4682 o Changed reference citations to "draft-templin-6man-omni". 4684 o Several important updates to IPv6 ND cache states and route 4685 optimization message addressing. 4687 o Included introductory description of the "6M's". 4689 o Updated Multicast specification. 4691 Changes from draft-templin-6man-aero-00 to draft-templin-6man-aero- 4692 01: 4694 o Changed category to "Informational". 4696 o Updated implementation status. 4698 Changes from earlier versions to draft-templin-6man-aero-00: 4700 o Established working baseline reference. 4702 Author's Address 4704 Fred L. Templin (editor) 4705 Boeing Research & Technology 4706 P.O. Box 3707 4707 Seattle, WA 98124 4708 USA 4710 Email: fltemplin@acm.org