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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 14, 2021 5 Expires: December 16, 2021 7 Asymmetric Extended Route Optimization (AERO) 8 draft-templin-6man-aero-17 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 16, 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 . . . . . . . . . . . . . 30 72 3.4. OMNI Interface Initialization . . . . . . . . . . . . . . 32 73 3.4.1. AERO Proxy/Server and Relay Behavior . . . . . . . . 32 74 3.4.2. AERO Client Behavior . . . . . . . . . . . . . . . . 33 75 3.4.3. AERO Bridge Behavior . . . . . . . . . . . . . . . . 33 76 3.5. OMNI Interface Neighbor Cache Maintenance . . . . . . . . 33 77 3.5.1. OMNI ND Messages . . . . . . . . . . . . . . . . . . 35 78 3.5.2. OMNI Neighbor Advertisement Message Flags . . . . . . 37 79 3.5.3. OMNI Neighbor Window Synchronization . . . . . . . . 38 80 3.6. OMNI Interface Encapsulation and Re-encapsulation . . . . 38 81 3.7. OMNI Interface Decapsulation . . . . . . . . . . . . . . 38 82 3.8. OMNI Interface Data Origin Authentication . . . . . . . . 39 83 3.9. OMNI Interface MTU . . . . . . . . . . . . . . . . . . . 39 84 3.10. OMNI Interface Forwarding Algorithm . . . . . . . . . . . 40 85 3.10.1. Client Forwarding Algorithm . . . . . . . . . . . . 41 86 3.10.2. Proxy/Server and Relay Forwarding Algorithm . . . . 43 87 3.10.3. Bridge Forwarding Algorithm . . . . . . . . . . . . 46 88 3.11. OMNI Interface Error Handling . . . . . . . . . . . . . . 47 89 3.12. AERO Router Discovery, Prefix Delegation and 90 Autoconfiguration . . . . . . . . . . . . . . . . . . . . 50 91 3.12.1. AERO Service Model . . . . . . . . . . . . . . . . . 50 92 3.12.2. AERO Client Behavior . . . . . . . . . . . . . . . . 51 93 3.12.3. AERO Proxy/Server Behavior . . . . . . . . . . . . . 53 94 3.13. The AERO Proxy Function . . . . . . . . . . . . . . . . . 56 95 3.13.1. Detecting and Responding to Proxy/Server Failures . 59 96 3.13.2. Point-to-Multipoint Proxy/Server Coordination . . . 59 98 3.14. AERO Route Optimization . . . . . . . . . . . . . . . . . 60 99 3.14.1. Route Optimization Initiation . . . . . . . . . . . 61 100 3.14.2. Relaying the NS(AR) *NET Packet(s) . . . . . . . . . 62 101 3.14.3. Processing the NS(AR) and Sending the NA(AR) . . . . 62 102 3.14.4. Relaying the NA(AR) . . . . . . . . . . . . . . . . 64 103 3.14.5. Processing the NA(AR) . . . . . . . . . . . . . . . 64 104 3.14.6. Forwarding Packets to Route Optimized Targets . . . 64 105 3.15. Neighbor Unreachability Detection (NUD) . . . . . . . . . 68 106 3.16. Mobility Management and Quality of Service (QoS) . . . . 69 107 3.16.1. Mobility Update Messaging . . . . . . . . . . . . . 70 108 3.16.2. Announcing Link-Layer Address and/or QoS Preference 109 Changes . . . . . . . . . . . . . . . . . . . . . . 71 110 3.16.3. Bringing New Links Into Service . . . . . . . . . . 72 111 3.16.4. Deactivating Existing Links . . . . . . . . . . . . 72 112 3.16.5. Moving Between Proxy/Servers . . . . . . . . . . . . 72 113 3.17. Multicast . . . . . . . . . . . . . . . . . . . . . . . . 73 114 3.17.1. Source-Specific Multicast (SSM) . . . . . . . . . . 74 115 3.17.2. Any-Source Multicast (ASM) . . . . . . . . . . . . . 75 116 3.17.3. Bi-Directional PIM (BIDIR-PIM) . . . . . . . . . . . 76 117 3.18. Operation over Multiple OMNI Links . . . . . . . . . . . 76 118 3.19. DNS Considerations . . . . . . . . . . . . . . . . . . . 77 119 3.20. Transition/Coexistence Considerations . . . . . . . . . . 77 120 3.21. Detecting and Reacting to Proxy/Server and Bridge 121 Failures . . . . . . . . . . . . . . . . . . . . . . . . 78 122 3.22. AERO Clients on the Open Internet . . . . . . . . . . . . 78 123 3.23. Time-Varying MNPs . . . . . . . . . . . . . . . . . . . . 81 124 4. Implementation Status . . . . . . . . . . . . . . . . . . . . 81 125 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 81 126 6. Security Considerations . . . . . . . . . . . . . . . . . . . 82 127 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 84 128 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 86 129 8.1. Normative References . . . . . . . . . . . . . . . . . . 86 130 8.2. Informative References . . . . . . . . . . . . . . . . . 88 131 Appendix A. Non-Normative Considerations . . . . . . . . . . . . 94 132 A.1. Implementation Strategies for Route Optimization . . . . 94 133 A.2. Implicit Mobility Management . . . . . . . . . . . . . . 95 134 A.3. Direct Underlying Interfaces . . . . . . . . . . . . . . 95 135 A.4. AERO Critical Infrastructure Considerations . . . . . . . 95 136 A.5. AERO Server Failure Implications . . . . . . . . . . . . 96 137 A.6. AERO Client / Server Architecture . . . . . . . . . . . . 97 138 Appendix B. Change Log . . . . . . . . . . . . . . . . . . . . . 99 139 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 102 141 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 | NIndex | omIndex | 916 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 917 | FMT | SRT | LHS (bits 0 - 23) | 918 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 919 | LHS (24-31) | ~ 920 +-+-+-+-+-+-+-+-+ ~ 921 ~ Link Layer Address (L2ADDR) ~ 922 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 923 | Null Padding (if necessary) | 924 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 925 ~ Destination Suffix ~ 926 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 928 Figure 3: OMNI Routing Header (ORH) Format 930 The ORH includes the following fields, in consecutive order: 932 o Next Header identifies the type of header immediately following 933 the ORH. 935 o Hdr Ext Len is the length of the Routing header in 8-octet units 936 (not including the first 8 octets). The field must encode a value 937 between 0 and 4 (all other values indicate a parameter problem). 939 o Routing Type is set to TBD1 (see IANA Considerations). 941 o Segments Left encodes the value 0 or 1 (all other values indicate 942 a parameter problem). 944 o NIndex - a 3-octet "Neighbor Index" value corresponding to a 945 Client NCE maintained by a Proxy/Server or Bridge. Values between 946 1 and 2**24 represent a specific NCE, while the value 0 represents 947 "unspecified". The Proxy/Server or Bridge assigns a unique NIndex 948 value when it creates a new Client NCE, and maintains the 949 assignment until the NCE is deleted. 951 o omIndex - a 1-octet field that identifies a specific Client 952 underlying interface when there are multiple alternatives. When 953 FMT-Forward is clear, omIndex determines the interface for 954 forwarding the ORH packet following reassembly; when FMT-Forward 955 is set, omIndex determines the interface for forwarding the raw 956 carrier packets without first reassembling. When omIndex is 0 (or 957 when no ORH is present), the LHS Proxy/Server selects among any of 958 the Client's available underlying interfaces that it services 959 locally (i.e., and not those serviced by another Proxy/Server). 961 o FMT - a 3-bit "Forward/Mode/Trailer" code corresponding to the 962 included Link Layer Address as follows: 964 * When the most significant bit (i.e., "FMT-Forward") is clear, 965 the LHS Proxy/Server must reassemble. When FMT-Forward is set, 966 the LHS Proxy/Server must forward the fragments to the Client 967 (while changing the OAL destination address to the MNP-ULA of 968 the Client if necessary) without reassembling. 970 * When the next most significant bit (i.e., "FMT-Mode") is clear, 971 L2ADDR is the INET address of the LHS Proxy/Server and the 972 Client must be reached through the LHS Proxy/Server. When FMT- 973 Mode is set, the Client is eligible for route optimization over 974 the open INET where it may be located behind one or more NATs, 975 and L2ADDR is either the INET address of the LHS Proxy/Server 976 (when FMT-Forward is set) or the native INET address of the 977 Client itself (when FMT-Forward is clear). 979 * The least significant bit (i.e., "FMT-Type") is consulted only 980 when Hdr Ext Len is 3 and ignored otherwise. If FMT-Type is 981 clear, the remainder includes an IPv4 L2ADDR followed by null 982 padding followed by an 8-octet (IPv6) Destination Suffix. If 983 FMT-Type is set, the remainder instead contains an IPv6 L2ADDR 984 followed by null padding and no Destination Suffix. 986 o SRT - a 5-bit Segment Routing Topology prefix length consulted 987 only when Segments Left is 1, and encodes a value that (when added 988 to 96) determines the prefix length to apply to the ADM-ULA formed 989 from concatenating [ULA*]::/96 with the 32 bit LHS value (for 990 example, the value 16 corresponds to the prefix length 112). 992 o LHS - a 4-octet field consulted only when Segments Left is 1. The 993 field encodes the 32-bit ADM-ULA suffix of an LHS Proxy/Server for 994 the target. When SRT is non-zero, SRT and LHS together determine 995 the ADM-ULA of the LHS Proxy/Server over the spanning tree. When 996 SRT is 0, LHS instead encodes an NIndex value and the LHS Proxy/ 997 Server or Client must be reached directly via INET encapsulation 998 instead of over the spanning tree. 1000 o Link Layer Address (L2ADDR) - an IP encapsulation address 1001 consulted only when Segments Left is 1. The ORH length also 1002 determines the L2ADDR IP version since the field will always 1003 contain exactly 6 octets for UDP/IPv4 or 18 octets for UDP/IPv6. 1004 When present, provides the link-layer address (i.e., the 1005 encapsulation address) of the LHS Proxy/Server or the target 1006 Client itself. The UDP Port Number appears in the first two 1007 octets and the IP address appears in the remaining octets. The 1008 Port Number and IP address are recorded in network byte order, and 1009 in ones-compliment "obfuscated" form per [RFC4380]. The OMNI 1010 interface forwarding algorithm uses L2ADDR as the INET 1011 encapsulation address for forwarding when SRT/LHS is located in 1012 the local OMNI link segment. If direct INET encapsulation is not 1013 permitted, L2ADDR is instead set to all-zeros and the packet must 1014 be forwarded to the LHS Proxy-Server via the spanning tree. 1016 o Null Padding - zero-valued octets added as necessary to pad the 1017 portion of the ORH included up to this point to an even 8-octet 1018 boundary. 1020 o Destination Suffix - a trailing 8-octet field present only when 1021 indicated by the ORH length and FMT-Type (see below). When 1022 present, encodes the 64-bit MNP-ULA suffix for the target Client. 1023 (For first-fragments, the MNP-LLA is already encoded in the 1024 original IP packet header and Destination Suffix may be omitted.) 1026 The ORH Hdr Ext Len field value also serves as an implicit ORH 1027 "Type", with 5 distinct Types possible (i.e., ORH-0 through ORH-4). 1028 All ORH-* Types include the same 8-octet preamble beginning with Next 1029 Header up to and including NIndex/omIndex, followed by a Type- 1030 specific remainder as follows: 1032 o ORH-0 - The preamble Hdr Ext Len and Segments Left must both be 0. 1033 All other fields are omitted. 1035 o ORH-1 - The preamble Hdr Ext Len is set to 1 and Segments Left 1036 must be 0. Destination Suffix is included and all other fields 1037 are omitted. 1039 o ORH-2 - The preamble Hdr Ext Len is set to 2. FMT/SRT/LHS and 1040 L2ADDR for IPv4 are included, and Destination Suffix is omitted. 1042 o ORH-3 - The preamble Hdr Ext Len is set to 3. FMT/SRT/LHS are 1043 included. If FMT-Type is clear, L2ADDR for IPv4 and Destination 1044 Suffix is included. If FMT-Type is set, L2ADDR for IPv6 is 1045 included and Destination Suffix is omitted. 1047 o ORH-4 - The preamble Hdr Ext Len is set to 4. FMT/SRT/LHS, L2ADDR 1048 for IPv6 and Destination Suffix are included. 1050 AERO neighbors use OAL encapsulation and fragmentation to exchange 1051 OAL packets as specified in [I-D.templin-6man-omni]. When an AERO 1052 node's OMNI interface (acting as an OAL source) uses OAL 1053 encapsulation for an original IP packet with source address 1054 2001:db8:1:2::1 and destination address 2001:db8:1234:5678::1, it 1055 sets the OAL header source address to its own ULA (e.g., 1056 [ULA*]::2001:db8:1:2), sets the destination address to the MNP-ULA 1057 corresponding to the IP destination address (e.g., 1058 [ULA*]::2001:db8:1234:5678), sets the Traffic Class, Flow Label, Hop 1059 Limit and Payload Length as discussed in [I-D.templin-6man-omni], 1060 then finally selects an Identification and appends an OAL checksum. 1062 If the neighbor cache information indicates that the target is in a 1063 different segment, the OAL source next inserts an ORH immediately 1064 following the OAL header while including Destination Suffix only when 1065 necessary (in this case, the Destination Suffix is 1066 2001:db8:1234:5678). Next, to direct the packet to an LHS Bridge, 1067 the source prepares an ORH with Segments Left set to 1 and with 1068 NIndex/omIndex and FMT/SRT/LHS/L2ADDR included, then overwrites the 1069 OAL header destination address with the LHS Subnet Router Anycast 1070 address (for example, for LHS 3000:4567 with SRT 16, the Subnet 1071 Router Anycast address is [ULA*]::3000:0000). To direct the packet 1072 to the LHS Proxy/Server (either directly in the local segment or in a 1073 remote segment via the spanning tree), the OAL source instead 1074 includes an ORH (Type 0 or 1) with Segments Left set to 0 and 1075 FMT/SRT/LHS/L2ADDR omitted, and overwrites the OAL header destination 1076 address with either the LHS Proxy/Server ADM-ULA or the MNP-ULA of 1077 the Client itself. 1079 The OAL source then fragments the OAL packet, with each resulting OAL 1080 fragment including the OAL/ORH headers while only the first fragment 1081 includes the original IPv6 header. If FMT-Forward is set, the 1082 Identification used for fragmentation must be within the window for 1083 the Client and a Destination Suffix must be included when necessary; 1084 otherwise the Identification must be within the window for the LHS 1085 Proxy/Server and no Destination Suffix is needed. (Note that if no 1086 actual fragmentation is required the OAL source still prepares the 1087 packet as an "atomic" fragment that includes a Fragment Header with 1088 Offset and More Fragments both set to 0.) The OAL source finally 1089 encapsulates each resulting OAL fragment in an *NET header to form an 1090 OAL carrier packet, with source address set to its own *NET address 1091 (e.g., 192.0.2.100) and destination set to the *NET address of the 1092 last hop itself or the next hop in the spanning tree (e.g., 1093 192.0.2.1). 1095 The carrier packet encapsulation format in the above example is shown 1096 in Figure 4: 1098 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1099 | *NET Header | 1100 | src = 192.0.2.100 | 1101 | dst = 192.0.2.1 | 1102 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1103 | OAL IPv6 Header | 1104 | src = [ULA*]::2001:db8:1:2 | 1105 | dst= [ULA*]::3000:0000 | 1106 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1107 | ORH (if necessary) | 1108 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1109 | OAL Fragment Header | 1110 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1111 | Original IP Header | 1112 | (first-fragment only) | 1113 | src = 2001:db8:1:2::1 | 1114 | dst = 2001:db8:1234:5678::1 | 1115 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1116 | | 1117 ~ ~ 1118 ~ Original Packet Body/Fragment ~ 1119 ~ ~ 1120 | | 1121 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1123 Figure 4: Carrier Packet Format 1125 In this format, the original IP header and packet body/fragment are 1126 encapsulated in an OAL IPv6 header prepared according to [RFC2473], 1127 the ORH is a Routing Header extension of the OAL header, the Fragment 1128 Header identifies each fragment, and the *NET header is prepared as 1129 discussed in Section 3.6. The OAL source transmits each such carrier 1130 packet into the SRT spanning tree, where they are forwarded over 1131 possibly multiple OAL intermediate nodes until they arrive at the OAL 1132 destination. 1134 The SRT forwarding system therefore contains both Client MNP-ULA 1135 prefix information that may change dynamically due to regional node 1136 mobility and per-segment ADM-ULA prefix information that rarely if 1137 ever changes. The spanning tree can therefore provide link-layer 1138 bridging by sending carrier packets over the spanning tree instead of 1139 network-layer routing according to MNP routes. As a result, 1140 opportunities for loss due to node mobility between different 1141 segments are mitigated. 1143 Note: The document recommends that AERO nodes transform ORHs with 1144 Segments Left set to 1 into ORH-0/1 during forwarding. While this 1145 may yield encapsulation overhead savings in some cases, the AERO node 1146 can instead simply decrement Segments Left and leave the original ORH 1147 in place. The LHS Proxy/Server or destination Client that processes 1148 the ORH will receive the same information in both cases. 1150 Note: When the OAL source sets a carrier packet destination address 1151 to a target's MNP-ULA but does not assert a specific target 1152 underlying interface, it may omit the ORH whether forwarding to the 1153 LHS Proxy/Server or directly to the target itself. When the LHS 1154 Proxy/Server receives a carrier packet with OAL destination set to 1155 the target MNP-ULA but with no ORH, it forwards over any available 1156 underlying interface for the target that it services locally. 1158 Note: When the OAL source and destination are on the same INET 1159 segment, OAL header compression can be used to significantly reduce 1160 encapsulation overhead as discussed in [I-D.templin-6man-omni]. 1162 Note: Use of an IPv6 "minimal encapsulation" format (i.e., an IPv6 1163 variant of [RFC2004]) based on extensions to the ORH was considered 1164 and abandoned. In the approach, the ORH would be inserted as an 1165 extension header to the original IPv6 packet header. The IPv6 1166 destination address would then be written into the ORH, and the ULA 1167 corresponding to the destination would be overwritten in the IPv6 1168 destination address. This would seemingly convey enough forwarding 1169 information so that OAL encapsulation could be avoided. However, 1170 this "minimal encapsulation" IPv6 packet would then have a non-ULA 1171 source address and ULA destination address, an incorrect value in 1172 upper layer protocol checksums, and a Hop Limit that is decremented 1173 within the spanning tree when it should not be. The insertion and 1174 removal of the ORH would also entail rewriting the Payload Length and 1175 Next Header fields - again, invalidating upper layer checksums. 1176 These irregularities would result in implementation challenges and 1177 the potential for operational issues, e.g., since actionable ICMPv6 1178 error reports could not be delivered to the original source. In 1179 order to address the issues, still more information such as the 1180 original IPv6 source address could be written into the ORH. However, 1181 with the additional information the benefit of the "minimal 1182 encapsulation" savings quickly diminishes, and becomes overshadowed 1183 by the implementation and operational irregularities. 1185 3.2.5. Segment Routing Topologies (SRTs) 1187 The 64-bit sub-prefixes of [ULA]::/48 identify up to 2^16 distinct 1188 Segment Routing Topologies (SRTs). Each SRT is a mutually-exclusive 1189 OMNI link overlay instance using a distinct set of ULAs, and emulates 1190 a Virtual LAN (VLAN) service for the OMNI link. In some cases (e.g., 1191 when redundant topologies are needed for fault tolerance and 1192 reliability) it may be beneficial to deploy multiple SRTs that act as 1193 independent overlay instances. A communication failure in one 1194 instance therefore will not affect communications in other instances. 1196 Each SRT is identified by a distinct value in bits 48-63 of 1197 [ULA]::/48, i.e., as [ULA0]::/64, [ULA1]::/64, [ULA2]::/64, etc. 1198 Each OMNI interface is identified by a unique interface name (e.g., 1199 omni0, omni1, omni2, etc.) and assigns an anycast ADM-ULA 1200 corresponding to its SRT prefix length. The anycast ADM-ULA is used 1201 for OMNI interface determination in Safety-Based Multilink (SBM) as 1202 discussed in [I-D.templin-6man-omni]. Each OMNI interface further 1203 applies Performance-Based Multilink (PBM) internally. 1205 The Bridges and Proxy/Servers of each independent SRT engage in BGP 1206 peerings to form a spanning tree with the Bridges in non-leaf nodes 1207 and the Proxy/Servers in leaf nodes. The spanning tree is configured 1208 over both secured and unsecured underlying network paths. The 1209 secured spanning tree is used to convey secured control messages 1210 between FHS and LHS Proxy/Servers, while the unsecured spanning tree 1211 forwards data messages and/or unsecured control messages. 1213 Each SRT segment is identified by a unique ADM-ULA prefix used by all 1214 Proxy/Servers and Bridges in the segment. Each AERO node must 1215 therefore discover an SRT prefix that correspondents can use to 1216 determine the correct segment, and must publish the SRT prefix in 1217 IPv6 ND messages and carrier packet ORHs. 1219 3.2.6. Segment Routing For OMNI Link Selection 1221 Original IPv6 source can direct IPv6 packets to an AERO node by 1222 including a standard IPv6 Segment Routing Header (SRH) [RFC8754] with 1223 the anycast ADM-ULA for the selected OMNI link as either the IPv6 1224 destination or as an intermediate hop within the SRH. This allows 1225 the original source to determine the specific OMNI link SRT an 1226 original IPv6 packet will traverse when there may be multiple 1227 alternatives. 1229 When an AERO node processes the SRH and forwards the original IPv6 1230 packet to the correct OMNI interface, the OMNI interface writes the 1231 next IPv6 address from the SRH into the IPv6 destination address and 1232 decrements Segments Left. If decrementing would cause Segments Left 1233 to become 0, the OMNI interface deletes the SRH before forwarding. 1234 This form of Segment Routing supports Safety-Based Multilink (SBM). 1236 3.2.7. Segment Routing Within the OMNI Link 1238 OAL sources can insert an ORH for Segment Routing within the same 1239 OMNI link to influence the paths of carrier packets sent to OAL 1240 destinations in remote SRT segments without requiring all carrier 1241 packets to traverse strict SRT spanning tree paths. (OAL sources can 1242 also insert an ORH in carrier packets sent to OAL destinations in the 1243 local segment if additional last-hop forwarding information is 1244 required.) 1246 When an AERO node's OMNI interface has an original IP packet to send 1247 to a target discovered through route optimization located in the same 1248 SRT segment, it acts as an OAL source to perform OAL encapsulation 1249 and fragmentation. The node then uses L2ADDR for INET encapsulation 1250 while including an ORH-0 when sending the resulting carrier packets 1251 to the ADM-ULA of the LHS Proxy/Server, or optionally omitting the 1252 ORH-0 when sending to the MNP-ULA of the target Client itself. When 1253 the node sends carrier packets with an ORH-0 to the LHS Proxy/Server, 1254 it sets the OAL destination to the ADM-ULA of the Proxy/Server if the 1255 Proxy/Server is responsible for reassembly; otherwise, it sets the 1256 OAL destination to the MNP-ULA of the target Client to cause the 1257 Proxy/Server to forward without reassembling. The node also sets 1258 omIndex to select a specific target Client underlying interface, or 1259 sets omIndex to 0 when no preference is selected. 1261 When an AERO node's OMNI interface has an original IP packet to send 1262 to a route optimization target located in a remote OMNI link segment, 1263 it acts as an OAL source the same as above but also includes an 1264 appropriate ORH type with Segments Left set to 1 and with (NIndex/ 1265 omIndex) and FMT/SRT/LHS/L2ADDR information while setting the OAL 1266 destination to the Subnet Router Anycast address for the LHS OMNI 1267 link segment. (The OAL source can alternatively include an ORH with 1268 Segments Left set to 0 while setting the OAL destination to the ADM- 1269 ULA of the LHS Proxy/Server, but this would cause the carrier packets 1270 to follow strict spanning tree paths.) The OMNI interface then 1271 forwards the resulting carrier packets into the spanning tree. 1273 When a Bridge receives carrier packest destined to its Subnet Router 1274 Anycast address with an ORH with Segments Left set to 1 and with 1275 FMT/SRT/LHS/L2ADDR values corresponding to the local segment, it 1276 first reassembles if necessary. If the reassembled packet arrived 1277 over the secured spanning tree and contains an NS(WIN) or NA(WIN) 1278 (see: Section 3.5.1 and Section 3.14.6), the Bridge creates or 1279 updates a NCE for the NS/NA target address and caches the ULA/LLA 1280 source/destination addresses and receive window information. For 1281 NS(WIN), the Bridge also caches the omIndex and FMT/SRT/LHS/L2ADDR 1282 information found in the ORH. For NA(WIN), the Bridge instead caches 1283 the omIndex and FMT/SRT/LHS/L2ADDR information found in the OMNI 1284 option Interface Attributes. The Bridge then selects a unique NIndex 1285 value for this NCE and, for NA(WIN), rewrites the Interface 1286 Attributes SRT to 0 and LHS to (NIndex/omIndex) and rewrites L2ADDR 1287 to its own INET address. The Bridge then forwards the NS/NA(WIN) to 1288 the LHS Proxy/Server over the secured spanning tree. 1290 For all other carrier packets addressed to the Subnet Router Anycast 1291 address, the Bridge next examines FMT-Mode to determine whether the 1292 target Client can accept packets directly (i.e., following any NAT 1293 traversal procedures necessary) while bypassing the LHS Proxy/Server. 1294 If the Client can be reached directly and NAT traversal has 1295 converged, the Bridge then writes the MNP-ULA (found in the inner 1296 IPv6 header for first fragments or the ORH Destination Suffix for 1297 non-first fragments) into the OAL destination address, decrements the 1298 OAL IPv6 header Hop Limit (and discards the packet if Hop Limit 1299 reaches 0), removes the ORH, re-encapsulates the carrier packet 1300 according to L2ADDR then forwards the carrier packets directly to the 1301 target Client. If the Client cannot be reached directly (or if NAT 1302 traversal has not yet converged), the Bridge instead transforms the 1303 ORH into an ORH-0, re-encapsulates the packet according to L2ADDR, 1304 changes the OAL destination to the ADM-ULA of the LHS Proxy/Server if 1305 FMT-Forward is clear or the MNP-ULA of the Client if FMT-Forward is 1306 set and forwards the carrier packet to the LHS Proxy/Server. 1308 When a Bridge receives a carrier packet destined to another ADM-ULA 1309 or MNP-ULA address (i.e., and not the Subnet Router Anycast address) 1310 the Bridge forwards the packet via spanning tree. If the carrier 1311 packet arrived via the secured spanning tree, the Bridge forwards to 1312 the next hop also via the secured spanning tree. If the carrier 1313 packet arrived via the unsecured spanning tree, the Bridge forwards 1314 to the next hop also via the unsecured spanning tree. 1316 When an LHS Proxy/Server receives carrier packets with any ORH type 1317 with Segments Left set to 0 and with OAL destination set to its own 1318 ADM-ULA, it first determines if the carrier packet contains an 1319 NA(WIN). If so, and if the OMNI option Interface Attributes SRT code 1320 is non-zero (i.e., meaning that it was not processed by a Bridge) the 1321 LHS Proxy/Server creates or updates a NCE for the NA target address 1322 while assigning a unique NIndex value and caches the ULA/LLA source/ 1323 destination addresses and receive window information. The LHS Proxy/ 1324 Server also caches the omIndex and FMT/SRT/LHS/L2ADDR information 1325 found in the OMNI option Interface Attributes, rewrites the Interface 1326 Attributes SRT to 0 and LHS to (NIndex/omIndex) and rewrites L2ADDR 1327 to its own INET address The LHS Proxy/Server then proceeds according 1328 to FMT-Forward and omIndex, while including an authentication 1329 signature in any IPv6 ND messages. If FMT-Forward is set, the LHS 1330 Proxy/Server changes the OAL destination to the MNP-ULA of the target 1331 Client found in the IPv6 header for first fragments or in the ORH 1332 Destination Suffix for non-first-fragments, removes the ORH and 1333 forwards to the target Client interface identified by omIndex. If 1334 FMT-Forward is clear, the LHS Proxy/Server instead reassembles then 1335 re-encapsulates while refragmenting if necessary, removes the ORH and 1336 forwards to the target Client according to omIndex. 1338 When an LHS Proxy/Server receives carrier packets with any ORH type 1339 with Segments Left set to 0 and with OAL destination set to the MNP- 1340 ULA of the target Client, it removes the ORH and forwards to the 1341 target Client according to omIndex. During forwarding, the LHS 1342 Proxy/Server must first verify that the omIndex corresponds to a 1343 target underlying interface that it services locally and must not 1344 forward to other target underlying interfaces. If omIndex is 0 (or 1345 if no ORH is included) the LHS Proxy/Server instead selects among any 1346 of the target underlying interfaces it services. 1348 When a target Client receives carrier packets with OAL destination 1349 set to is MNP-ULA, it reassembles to obtain the OAL packet then 1350 decapsulates and delivers the original IP packet to upper layers. 1352 Note: Special handling procedures are employed for the exchange of 1353 IPv6 ND messages used to establish neighbor cache state as discussed 1354 in Section 3.14. The procedures call for hop-by-hop authentication 1355 and neighbor cache state establishment based on the encapsulation 1356 ULA, with next-hop determination based on the IPv6 ND message LLA. 1358 3.3. OMNI Interface Characteristics 1360 OMNI interfaces are virtual interfaces configured over one or more 1361 underlying interfaces classified as follows: 1363 o INET interfaces connect to an INET either natively or through one 1364 or more NATs. Native INET interfaces have global IP addresses 1365 that are reachable from any INET correspondent. The INET-facing 1366 interfaces of Proxy/Servers are native interfaces, as are Relay 1367 and Bridge interfaces. NATed INET interfaces connect to a private 1368 network behind one or more NATs that provide INET access. Clients 1369 that are behind a NAT are required to send periodic keepalive 1370 messages to keep NAT state alive when there are no carrier packets 1371 flowing. 1373 o ANET interfaces connect to an ANET that is separated from the open 1374 INET by an FHS Proxy/Server. Clients can issue control messages 1375 over the ANET without including an authentication signature since 1376 the ANET is secured at the network layer or below. Proxy/Servers 1377 can actively issue control messages over the INET on behalf of 1378 ANET Clients to reduce ANET congestion. 1380 o VPNed interfaces use security encapsulation over the INET to a 1381 Virtual Private Network (VPN) server that also acts as an FHS 1382 Proxy/Server. Other than the link-layer encapsulation format, 1383 VPNed interfaces behave the same as Direct interfaces. 1385 o Direct (i.e., single-hop point-to-point) interfaces connect a 1386 Client directly to an FHS Proxy/Server without crossing any ANET/ 1387 INET paths. An example is a line-of-sight link between a remote 1388 pilot and an unmanned aircraft. The same Client considerations 1389 apply as for VPNed interfaces. 1391 OMNI interfaces use OAL encapsulation and fragmentation as discussed 1392 in Section 3.2.4. OMNI interfaces use *NET encapsulation (see: 1393 Section 3.6) to exchange carrier packets with OMNI link neighbors 1394 over INET or VPNed interfaces as well as over ANET interfaces for 1395 which the Client and FHS Proxy/Server may be multiple IP hops away. 1396 OMNI interfaces do not use link-layer encapsulation over Direct 1397 underlying interfaces or ANET interfaces when the Client and FHS 1398 Proxy/Server are known to be on the same underlying link. 1400 OMNI interfaces maintain a neighbor cache for tracking per-neighbor 1401 state the same as for any interface. OMNI interfaces use ND messages 1402 including Router Solicitation (RS), Router Advertisement (RA), 1403 Neighbor Solicitation (NS) and Neighbor Advertisement (NA) for 1404 neighbor cache management. In environments where spoofing may be a 1405 threat, OMNI neighbors should employ OAL Identification window 1406 synchronization in their ND message exchanges. 1408 OMNI interfaces send ND messages with an OMNI option formatted as 1409 specified in [I-D.templin-6man-omni]. The OMNI option includes 1410 prefix registration information, Interface Attributes containing link 1411 information parameters for the OMNI interface's underlying interfaces 1412 and any other per-neighbor information. Each OMNI option may include 1413 multiple Interface Attributes sub-options identified by omIndex 1414 values. 1416 A Client's OMNI interface may be configured over multiple underlying 1417 interfaces. For example, common mobile handheld devices have both 1418 wireless local area network ("WLAN") and cellular wireless links. 1419 These links are often used "one at a time" with low-cost WLAN 1420 preferred and highly-available cellular wireless as a standby, but a 1421 simultaneous-use capability could provide benefits. In a more 1422 complex example, aircraft frequently have many wireless data link 1423 types (e.g. satellite-based, cellular, terrestrial, air-to-air 1424 directional, etc.) with diverse performance and cost properties. 1426 If a Client's multiple underlying interfaces are used "one at a time" 1427 (i.e., all other interfaces are in standby mode while one interface 1428 is active), then successive ND messages all include OMNI option 1429 Interface Attributes sub-options with the same underlying interface 1430 index. In that case, the Client would appear to have a single 1431 underlying interface but with a dynamically changing link-layer 1432 address. 1434 If the Client has multiple active underlying interfaces, then from 1435 the perspective of ND it would appear to have multiple link-layer 1436 addresses. In that case, ND message OMNI options MAY include 1437 Interface Attributes sub-options with different underlying interface 1438 indexes. Every ND message need not include Interface Attributes for 1439 all underlying interfaces; for any attributes not included, the 1440 neighbor considers the status as unchanged. 1442 Bridge and Proxy/Server OMNI interfaces are configured over 1443 underlying interfaces that provide both secured tunnels for carrying 1444 IPv6 ND and BGP protocol control plane messages and open INET access 1445 for carrying unsecured messages. The OMNI interface configures both 1446 an ADM-LLA and its corresponding ADM-ULA, and acts as an OAL source 1447 to encapsulate and fragment original IP packets while presenting the 1448 resulting carrier packets over the secured or unsecured underlying 1449 paths. Note that Bridge and Proxy/Server BGP protocol TCP sessions 1450 are run directly over the OMNI interface and use ADM-ULA source and 1451 destination addresses. The OMNI interface employs the OAL to 1452 encapsulate the original IP packets for these sessions as carrier 1453 packets (i.e., even though the OAL header may use the same ADM-ULAs 1454 as the original IP header) and forwards them over the secured 1455 underlying path. 1457 3.4. OMNI Interface Initialization 1459 AERO Proxy/Servers and Clients configure OMNI interfaces as their 1460 point of attachment to the OMNI link. AERO nodes assign the MSPs for 1461 the link to their OMNI interfaces (i.e., as a "route-to-interface") 1462 to ensure that original IP packets with destination addresses covered 1463 by an MNP not explicitly associated with another interface are 1464 directed to an OMNI interface. 1466 OMNI interface initialization procedures for Proxy/Servers, Clients 1467 and Bridges are discussed in the following sections. 1469 3.4.1. AERO Proxy/Server and Relay Behavior 1471 When a Proxy/Server enables an OMNI interface, it assigns an 1472 ADM-{LLA,ULA} appropriate for the given OMNI link SRT segment. The 1473 Proxy/Server also configures secured tunnels with one or more 1474 neighboring Bridges and engages in a BGP routing protocol session 1475 with each Bridge. 1477 The OMNI interface provides a single interface abstraction to the IP 1478 layer, but internally includes an NBMA nexus for sending carrier 1479 packets to OMNI interface neighbors over underlying INET interfaces 1480 and secured tunnels. The Proxy/Server further configures a service 1481 to facilitate ND exchanges with AERO Clients and manages per-Client 1482 neighbor cache entries and IP forwarding table entries based on 1483 control message exchanges. 1485 Relays are simply Proxy/Servers that run a dynamic routing protocol 1486 to redistribute routes between the OMNI interface and INET/EUN 1487 interfaces (see: Section 3.2.3). The Relay provisions MNPs to 1488 networks on the INET/EUN interfaces (i.e., the same as a Client would 1489 do) and advertises the MSP(s) for the OMNI link over the INET/EUN 1490 interfaces. The Relay further provides an attachment point of the 1491 OMNI link to a non-MNP-based global topology. 1493 3.4.2. AERO Client Behavior 1495 When a Client enables an OMNI interface, it assigns either an 1496 MNP-{LLA, ULA} or a Temporary ULA and sends RS messages with ND 1497 parameters over its underlying interfaces to an FHS Proxy/Server, 1498 which returns an RA message with corresponding parameters. The RS/RA 1499 messages may pass through one or more NATs in the case of a Client's 1500 INET interface. (Note: if the Client used a Temporary ULA in its 1501 initial RS message, it will discover an MNP-{LLA, ULA} in the 1502 corresponding RA that it receives from the FHS Proxy/Server and begin 1503 using these new addresses. If the Client is operating outside the 1504 context of AERO infrastructure such as in a Mobile Ad-hoc Network 1505 (MANET), however, it may continue using Temporary ULAs for Client-to- 1506 Client communications until it encounters an infrastructure element 1507 that can provide an MNP.) 1509 3.4.3. AERO Bridge Behavior 1511 AERO Bridges configure an OMNI interface and assign the ADM-ULA 1512 Subnet Router Anycast address for each OMNI link SRT segment they 1513 connect to. Bridges configure secured tunnels with Proxy/Servers in 1514 the same SRT segment and other Bridges in the same (or an adjacent) 1515 SRT segment. Bridges then engage in a BGP routing protocol session 1516 with neighbors over the secured spanning tree (see: Section 3.2.3). 1518 3.5. OMNI Interface Neighbor Cache Maintenance 1520 Each OMNI interface maintains a conceptual neighbor cache that 1521 includes a Neighbor Cache Entry (NCE) for each of its active 1522 neighbors on the OMNI link per [RFC4861]. Each NCE is indexed by the 1523 LLA of the neighbor, while the OAL encapsulation ULA determines the 1524 context for Identification verification. 1526 Proxy/Servers maintain NCEs for each of their associated local 1527 Clients discovered through RS/RA exchanges. Proxy/Servers and 1528 Bridges also maintain NCEs for non-local target Clients associated 1529 with other Proxy/Servers through NS/NA(WIN) route optimization. When 1530 a Proxy/Server or Bridge creates a NCE for a local or target Client, 1531 it assigns a unique "Neighbor Index" value between (1 - 2**24) that 1532 remains associated with the NCE until the NCE is deleted. 1534 To the list of NCE states in Section 7.3.2 of [RFC4861], Proxy/Server 1535 OMNI interfaces add an additional state DEPARTED that applies to 1536 Clients that have recently departed. The interface sets a 1537 "DepartTime" variable for the NCE to "DEPART_TIME" seconds. 1538 DepartTime is decremented unless a new ND message causes the state to 1539 return to REACHABLE. While a NCE is in the DEPARTED state, the 1540 Proxy/Server forwards carrier packets destined to the target Client 1541 to the Client's new location instead. When DepartTime decrements to 1542 0, the NCE is deleted. It is RECOMMENDED that DEPART_TIME be set to 1543 the default constant value REACHABLE_TIME plus 10 seconds (40 seconds 1544 by default) to allow a window for carrier packets in flight to be 1545 delivered while stale route optimization state may be present. 1547 Proxy/Servers can act as RORs on behalf of their associated Clients 1548 according to the Proxy Neighbor Advertisement specification in 1549 Section 7.2.8 of [RFC4861]. When a Proxy/Server ROR receives an 1550 authentic NS message used for route optimization, it first searches 1551 for a NCE for the target Client and accepts the message only if there 1552 is an entry. The Proxy/Server then returns a solicited NA message 1553 while creating or updating a "Report List" entry in the target 1554 Client's NCE that caches both the LLA and ULA of ROS with a 1555 "ReportTime" variable set to REPORT_TIME seconds. The ROR resets 1556 ReportTime when it receives a new authentic NS message, and otherwise 1557 decrements ReportTime while no authentic NS messages have been 1558 received. It is RECOMMENDED that REPORT_TIME be set to the default 1559 constant value REACHABLE_TIME plus 10 seconds (40 seconds by default) 1560 to allow a window for route optimization to converge before 1561 ReportTime decrements below REACHABLE_TIME. 1563 When the ROS receives a solicited NA message response to its NS 1564 message used for route optimization, it creates or updates a NCE for 1565 the target network-layer and link-layer addresses. The ROS then 1566 (re)sets ReachableTime for the NCE to REACHABLE_TIME seconds and 1567 performs reachability tests over specific underlying interface pairs 1568 to determine paths for forwarding carrier packets directly to the 1569 target. The ROS otherwise decrements ReachableTime while no further 1570 solicited NA messages arrive. It is RECOMMENDED that REACHABLE_TIME 1571 be set to the default constant value 30 seconds as specified in 1572 [RFC4861]. 1574 AERO nodes also use the value MAX_UNICAST_SOLICIT to limit the number 1575 of NS messages sent when a correspondent may have gone unreachable, 1576 the value MAX_RTR_SOLICITATIONS to limit the number of RS messages 1577 sent without receiving an RA and the value MAX_NEIGHBOR_ADVERTISEMENT 1578 to limit the number of unsolicited NAs that can be sent based on a 1579 single event. It is RECOMMENDED that MAX_UNICAST_SOLICIT, 1580 MAX_RTR_SOLICITATIONS and MAX_NEIGHBOR_ADVERTISEMENT be set to 3 the 1581 same as specified in [RFC4861]. 1583 Different values for DEPART_TIME, REPORT_TIME, REACHABLE_TIME, 1584 MAX_UNICAST_SOLICIT, MAX_RTR_SOLCITATIONS and 1585 MAX_NEIGHBOR_ADVERTISEMENT MAY be administratively set; however, if 1586 different values are chosen, all nodes on the link MUST consistently 1587 configure the same values. Most importantly, DEPART_TIME and 1588 REPORT_TIME SHOULD be set to a value that is sufficiently longer than 1589 REACHABLE_TIME to avoid packet loss due to stale route optimization 1590 state. 1592 3.5.1. OMNI ND Messages 1594 OMNI interfaces prepare IPv6 ND messages the same as for standard 1595 IPv6 ND, but also include a new option type termed the OMNI option 1596 [I-D.templin-6man-omni]. OMNI interfaces prepare IPv6 ND messages 1597 the same as for standard IPv6 ND, and include one or more OMNI 1598 options and any other options then completely populate all option 1599 information. If the OMNI interface includes an authentication 1600 signature, it sets the IPv6 ND message Checksum field to 0 and 1601 calculates the authentication signature over the entire length of the 1602 message (beginning with a pseudo-header of the IPv6 header) but does 1603 not then proceed to calculate the IPv6 ND message checksum itself. 1604 If the OMNI interface forwards the message to a next hop over the 1605 secured spanning tree path, it omits both the authentication 1606 signature an checksum since lower layers already ensure 1607 authentication and integrity. In all other cases, the OMNI interface 1608 calculates the standard IPv6 ND message checksum and writes the value 1609 in the Checksum field. OMNI interfaces verify authentication and 1610 integrity of each IPv6 ND message received according to the specific 1611 check(s) included, and process the message further only following 1612 verification. 1614 OMNI options include per-neighbor information such as Interface 1615 Attributes that provide link-layer address and traffic selector 1616 information for the neighbor's underlying interfaces. This 1617 information is stored in the neighbor cache and provides the basis 1618 for the forwarding algorithm specified in Section 3.10. The 1619 information is cumulative and reflects the union of the OMNI 1620 information from the most recent ND messages received from the 1621 neighbor; it is therefore not required that each ND message contain 1622 all neighbor information. 1624 The OMNI option Interface Attributes for each underlying interface 1625 includes a two-part "Link-Layer Address" consisting of an INET 1626 encapsulation address determined by the FMT and L2ADDR fields and an 1627 ADM-ULA determined by the SRT and LHS fields. Underlying interfaces 1628 are further selected based on their associated traffic selectors. 1630 The OMNI option is distinct from any Source/Target Link-Layer Address 1631 Options (S/TLLAOs) that may appear in an ND message according to the 1632 appropriate IPv6 over specific link layer specification (e.g., 1633 [RFC2464]). If both an OMNI option and S/TLLAO appear, the former 1634 pertains to encapsulation addresses while the latter pertains to the 1635 native L2 address format of the underlying media 1637 OMNI interface IPv6 ND messages may also include other IPv6 ND 1638 options. In particular, solicitation messages may include Nonce and/ 1639 or Timestamp options if required for verification of advertisement 1640 replies. If an OMNI ND solicitation message includes a Nonce option, 1641 the advertisement reply must echo the same Nonce. If an OMNI ND 1642 solicitation message includes a Timestamp option, the advertisement 1643 reply should also include a Timestamp option. 1645 AERO Clients send RS messages to the All-Routers multicast address 1646 while using unicast link-layer addresses. AERO Proxy/Servers respond 1647 by returning unicast RA messages. During the RS/RA exchange, AERO 1648 Clients and Servers include state synchronization parameters to 1649 establish Identification windows and other state. 1651 AERO nodes use NS/NA messages for the following purposes: 1653 o NS/NA(AR) messages are used for address resolution only. The ROS 1654 sends an NS(AR) to the solicited-node multicast address of the 1655 target, and an ROR in the network with addressing information for 1656 the target returns a unicast NA(AR). The NA(AR) contains current, 1657 consistent and authentic target address resolution information, 1658 but only an implicit third-party assertion of target reachability. 1659 NS/NA(AR) messages must be secured. 1661 o NS/NA(WIN) messages are used for establishing and maintaining 1662 window synchronization state (and/or any other state such as 1663 Interface Attributes). The source sends an NS(WIN) to the unicast 1664 address of the target, and the target returns a unicast NA(WIN). 1665 The NS/NA(WIN) exchange synchronizes the sequence number windows 1666 for Identification values the neighbors will include in subsequent 1667 carrier packets, and asserts reachability for the target without 1668 necessarily testing a specific underlying interface pair. NS/ 1669 NA(WIN) messages must be secured. 1671 o NS/NA(NUD) messages are used for determining target reachability. 1672 The source sends an NS(NUD) to the unicast address of the target 1673 while naming a specific underlying interface pair, and the target 1674 returns a unicast NA(NUD). NS/NA(NUD) messages that use an in- 1675 window sequence number and do not update any other state need not 1676 be secured but should include an IPv6 ND message checksum. NS/ 1677 NA(NUD) messages may also be used in combination with window 1678 synchronization (i.e., NUD+WIN), in which case the messages must 1679 be secured. 1681 o Unsolicited NA (uNA) messages are used to signal addressing and/or 1682 other neighbor state changes (e.g., address changes due to 1683 mobility, signal degradation, traffic selector updates, etc.). uNA 1684 messages that include state update information must be secured. 1686 o NS/NA(DAD) messages are not used in AERO, since Duplicate Address 1687 Detection is not required. 1689 Additionally, nodes may send NA/RA messages with the OMNI option PNG 1690 flag set to receive a solicited NA response from the neighbor. The 1691 solicited NA response MUST set the ACK flag (without also setting the 1692 SYN or PNG flags) and include the Identification used in the PNG 1693 message in the Acknowledgement. 1695 3.5.2. OMNI Neighbor Advertisement Message Flags 1697 As discussed in Section 4.4 of [RFC4861] NA messages include three 1698 flag bits R, S and O. OMNI interface NA messages treat the flags as 1699 follows: 1701 o R: The R ("Router") flag is set to 1 in the NA messages sent by 1702 all AERO/OMNI node types. Simple hosts that would set R to 0 do 1703 not occur on the OMNI link itself, but may occur on the downstream 1704 links of Clients and Relays. 1706 o S: The S ("Solicited") flag is set exactly as specified in 1707 Section 4.4. of [RFC4861], i.e., it is set to 1 for Solicited NAs 1708 and set to 0 for uNAs (both unicast and multicast). 1710 o O: The O ("Override") flag is set to 0 for solicited NAs returned 1711 by a Proxy/Server ROR and set to 1 for all other solicited and 1712 unsolicited NAs. For further study is whether solicited NAs for 1713 anycast targets apply for OMNI links. Since MNP-LLAs must be 1714 uniquely assigned to Clients to support correct ND protocol 1715 operation, however, no role is currently seen for assigning the 1716 same MNP-LLA to multiple Clients. 1718 3.5.3. OMNI Neighbor Window Synchronization 1720 In secured environments (e.g., such as between nodes on the same 1721 secured ANET), OMNI interface neighbors can exchange OAL packets 1722 using randomly-initialized and monotonically-increasing 1723 Identification values (modulo 2*32) without window synchronization. 1724 In environments where spoofing is considered a threat, OMNI interface 1725 neighbors instead invoke window synchronization in ND message 1726 exchanges to maintain send/receive window state in their respective 1727 neighbor cache entries as specified in [I-D.templin-6man-omni]. 1729 In the asymmetric window synchronization case, the initial ND message 1730 exchange establishes only the initiator's send window and the 1731 responder's receive window such that a corresponding exchange would 1732 be needed to establish the reverse direction. In the symmetric case, 1733 the initiator and responder engage in a three-way handshake to 1734 symmetrically establish the send/receive windows of both parties. 1736 3.6. OMNI Interface Encapsulation and Re-encapsulation 1738 The OMNI interface admits original IP packets then acts as an OAL 1739 source to perform OAL encapsulation and fragmentation as specified in 1740 [I-D.templin-6man-omni] while including an ORH if necessary as 1741 specified in Section 3.2.4. The OAL encapsulates original IP packets 1742 to form OAL packets subject to fragmentation, then encapsulates the 1743 resulting OAL fragments in *NET headers as carrier packets. 1745 For carrier packets undergoing re-encapsulation at an OAL 1746 intermediate node, the OMNI interface decrements the OAL IPv6 header 1747 Hop Limit and discards the carrier packet if the Hop Limit reaches 0. 1748 The intermediate node next removes the *NET encapsulation headers 1749 from the first segment and re-encapsulates the packet in new *NET 1750 encapsulation headers for the next segment. 1752 When an FHS Proxy/Server re-encapsulates a carrier packet received 1753 from a Client that includes an OAL but no ORH, it inserts an ORH 1754 immediately following the OAL header and adjusts the OAL payload 1755 length and destination address field. The ORH may be removed by an 1756 LHS Bridge or Proxy/Server, but its insertion and removal will not 1757 interfere with reassembly at the final destination. For this reason, 1758 Clients must reserve 40 bytes for a maximum-length ORH when they 1759 perform OAL encapsulation (see: Section 3.9). 1761 3.7. OMNI Interface Decapsulation 1763 OMNI interfaces (acting as OAL destinations) decapsulate and 1764 reassemble OAL packets into original IP packets destined either to 1765 the AERO node itself or to a destination reached via an interface 1766 other than the OMNI interface the original IP packet was received on. 1767 When carrier packets containing OAL fragments addressed to itself 1768 arrive, the OMNI interface discards the NET encapsulation headers and 1769 reassembles as discussed in Section 3.9. 1771 3.8. OMNI Interface Data Origin Authentication 1773 AERO nodes employ simple data origin authentication procedures. In 1774 particular: 1776 o AERO Bridges and Proxy/Servers accept carrier packets received 1777 from secured underlying interfaces. 1779 o AERO Proxy/Servers and Clients accept carrier packets and original 1780 IP packets that originate from within the same secured ANET. 1782 o AERO Clients and Relays accept original IP packets from downstream 1783 network correspondents based on ingress filtering. 1785 o AERO Clients, Relays and Proxy/Servers verify carrier packet UDP/ 1786 IP encapsulation addresses according to [I-D.templin-6man-omni]. 1788 o AERO nodes accept carrier packets addressed to themselves with 1789 Identification values within the current window for the OAL source 1790 neighbor (when window synchronization is used) and drop any 1791 carrier packets with out-of-window Identification values. (AERO 1792 nodes may forward carrier packets not addressed to themselves 1793 without verifying the Identification value.) 1795 AERO nodes silently drop any packets that do not satisfy the above 1796 data origin authentication procedures. Further security 1797 considerations are discussed in Section 6. 1799 3.9. OMNI Interface MTU 1801 The OMNI interface observes the link nature of tunnels, including the 1802 Maximum Transmission Unit (MTU), Maximum Reassembly Unit (MRU) and 1803 the role of fragmentation and reassembly [I-D.ietf-intarea-tunnels]. 1804 The OMNI interface employs an OMNI Adaptation Layer (OAL) that 1805 accommodates multiple underlying links with diverse MTUs while 1806 observing both a minimum and per-path Maximum Payload Size (MPS). 1807 The functions of the OAL and the OMNI interface MTU/MRU/MPS are 1808 specified in [I-D.templin-6man-omni] with MTU/MRU both set to the 1809 constant value 9180 bytes, with minimum MPS set to 400 bytes, and 1810 with potentially larger per-path MPS values depending on the 1811 underlying path. 1813 When the network layer presents an original IP packet to the OMNI 1814 interface, the OAL source encapsulates and fragments the original IP 1815 packet if necessary. When the network layer presents the OMNI 1816 interface with multiple original IP packets bound to the same OAL 1817 destination, the OAL source can concatenate them together into a 1818 single OAL super-packet as discussed in [I-D.templin-6man-omni]. The 1819 OAL source then fragments the OAL packet if necessary according to 1820 the minimum/path MPS such that the OAL headers appear in each 1821 fragment while the original IP packet header appears only in the 1822 first fragment. The OAL source then encapsulates each OAL fragment 1823 in *NET headers for transmission as carrier packets over an 1824 underlying interface connected to either a physical link (such as 1825 Ethernet, WiFi and the like) or a virtual link such as an Internet or 1826 higher-layer tunnel (see the definition of link in [RFC8200]). 1828 Note: A Client that does not (yet) have neighbor cache state for a 1829 target may omit the ORH in carrier packets with the understanding 1830 that a Proxy/Server may insert an ORH on its behalf. For this 1831 reason, Clients reserve 40 bytes for the largest possible ORH in 1832 their OAL fragment size calculations. 1834 Note: Although the ORH may be removed or replaced by a Bridge or 1835 Proxy/Server on the path (see: Section 3.10.3), this does not 1836 interfere with the destination's ability to reassemble since the ORH 1837 is not included in the fragmentable part and its removal/ 1838 transformation does not invalidate fragment header information. 1840 3.10. OMNI Interface Forwarding Algorithm 1842 Original IP packets enter a node's OMNI interface either from the 1843 network layer (i.e., from a local application or the IP forwarding 1844 system) while carrier packets enter from the link layer (i.e., from 1845 an OMNI interface neighbor). All original IP packets and carrier 1846 packets entering a node's OMNI interface first undergo data origin 1847 authentication as discussed in Section 3.8. Those that satisfy data 1848 origin authentication are processed further, while all others are 1849 dropped silently. 1851 Original IP packets that enter the OMNI interface from the network 1852 layer are forwarded to an OMNI interface neighbor using OAL 1853 encapsulation and fragmentation to produce carrier packets for 1854 transmission over underlying interfaces. (If routing indicates that 1855 the original IP packet should instead be forwarded back to the 1856 network layer, the packet is dropped to avoid looping). Carrier 1857 packets that enter the OMNI interface from the link layer are either 1858 re-encapsulated and re-admitted into the OMNI link, or reassembled 1859 and forwarded to the network layer where they are subject to either 1860 local delivery or IP forwarding. In all cases, the OAL MUST NOT 1861 decrement the network layer TTL/Hop-count since its forwarding 1862 actions occur below the network layer. 1864 OMNI interfaces may have multiple underlying interfaces and/or 1865 neighbor cache entries for neighbors with multiple underlying 1866 interfaces (see Section 3.3). The OAL uses Interface Attributes 1867 traffic selectors (e.g., port number, flow specification, etc.) to 1868 select an outbound underlying interface for each OAL packet based on 1869 the node's own interface attributes, and also to select a destination 1870 link-layer address based on the neighbor's underlying interface 1871 attributes. AERO implementations SHOULD permit network management to 1872 dynamically adjust traffic selector values at runtime. 1874 If an OAL packet matches the traffic selectors of multiple outgoing 1875 interfaces and/or neighbor interfaces, the OMNI interface replicates 1876 the packet and sends one copy via each of the (outgoing / neighbor) 1877 interface pairs; otherwise, it sends a single copy of the OAL packet 1878 via an interface with the best matching traffic selector. (While not 1879 strictly required, the likelihood of successful reassembly may 1880 improve when the OMNI interface sends all fragments of the same 1881 fragmented OAL packet consecutively over the same underlying 1882 interface pair to avoid complicating factors such as delay variance 1883 and reordering.) AERO nodes keep track of which underlying 1884 interfaces are currently "reachable" or "unreachable", and only use 1885 "reachable" interfaces for forwarding purposes. 1887 The following sections discuss the OMNI interface forwarding 1888 algorithms for Clients, Proxy/Servers and Bridges. In the following 1889 discussion, an original IP packet's destination address is said to 1890 "match" if it is the same as a cached address, or if it is covered by 1891 a cached prefix (which may be encoded in an MNP-LLA). 1893 3.10.1. Client Forwarding Algorithm 1895 When an original IP packet enters a Client's OMNI interface from the 1896 network layer the Client searches for a NCE that matches the 1897 destination. If there is a match, the Client selects one or more 1898 "reachable" neighbor interfaces in the entry for forwarding purposes. 1899 If there is no NCE, the Client instead either enqueues the original 1900 IP packet and invokes route optimization or forwards the original IP 1901 packet toward a Proxy/Server. The Client (acting as an OAL source) 1902 performs OAL encapsulation and sets the OAL destination address to 1903 the MNP-ULA of the target if there is a matching NCE; otherwise, it 1904 sets the OAL destination to the ADM-ULA of the Proxy/Server. If the 1905 Client has multiple original IP packets to send to the same neighbor, 1906 it can concatenate them in a single super-packet 1907 [I-D.templin-6man-omni]. The OAL source then performs fragmentation 1908 to create OAL fragments (see: Section 3.9), appends any *NET 1909 encapsulation, and sends the resulting carrier packets over 1910 underlying interfaces to the neighbor acting as an OAL destination. 1912 If the neighbor interface selected for forwarding is located on the 1913 same OMNI link segment and not behind a NAT, the Client forwards the 1914 carrier packets directly according to the L2ADDR information for the 1915 neighbor. If the neighbor interface is behind a NAT on the same OMNI 1916 link segment, the Client instead forwards the initial carrier packets 1917 to the LHS Proxy/Server (while inserting an ORH-0 if necessary) and 1918 initiates NAT traversal procedures. If the Client's intended source 1919 underlying interface is also behind a NAT and located on the same 1920 OMNI link segment, it sends a "direct bubble" over the interface per 1921 [RFC6081][RFC4380] to the L2ADDR found in the neighbor cache in order 1922 to establish state in its own NAT by generating traffic toward the 1923 neighbor (note that no response to the bubble is expected). 1925 The Client next sends an NS(NUD) message toward the MNP-ULA of the 1926 neighbor via the LHS Proxy/Server as discussed in Section 3.15. If 1927 the Client receives an NA(NUD) from the neighbor over the underlying 1928 interface, it marks the neighbor interface as "trusted" and sends 1929 future carrier packets directly to the L2ADDR information for the 1930 neighbor instead of indirectly via the LHS Proxy/Server. The Client 1931 must honor the neighbor cache maintenance procedure by sending 1932 additional direct bubbles and/or NS/NA(NUD) messages as discussed in 1933 [RFC6081][RFC4380] in order to keep NAT state alive as long as 1934 carrier packets are still flowing. 1936 When a carrier packet enters a Client's OMNI interface from the link- 1937 layer, if the OAL destination matches one of the Client's ULAs the 1938 Client (acting as an OAL destination) verifies that the 1939 Identification is in-window for this OAL source, then reassembles and 1940 decapsulates as necessary and delivers the original IP packet to the 1941 network layer. Otherwise, the Client drops the original IP packet 1942 and MAY return a network-layer ICMP Destination Unreachable message 1943 subject to rate limiting (see: Section 3.11). 1945 Note: Clients and their FHS Proxy/Server (and other Client) peers can 1946 exchange original IP packets over ANET underlying interfaces without 1947 invoking the OAL, since the ANET is secured at the link and physical 1948 layers. By forwarding original IP packets without invoking the OAL, 1949 however, the ANET peers can engage only in classical path MTU 1950 discovery since the packets are subject to loss and/or corruption due 1951 to the various per-link MTU limitations that may occur within the 1952 ANET. Moreover, the original IP packets do not include either the 1953 OAL integrity check or per-packet Identification values that can be 1954 used for data origin authentication and link-layer retransmissions. 1955 The tradeoff therefore involves an assessment of the per-packet 1956 encapsulation overhead saved by bypassing the OAL vs. inheritance of 1957 classical network "brittleness". (Note however that ANET peers can 1958 send small original IP packets without invoking the OAL, while 1959 invoking the OAL for larger packets. This presents the beneficial 1960 aspects of both small packet efficiency and large packet robustness, 1961 with delay variance and reordering as possible side effects.) 1963 3.10.2. Proxy/Server and Relay Forwarding Algorithm 1965 When the Proxy/Server receives an original IP packet from the network 1966 layer, it drops the packet if routing indicates that it should be 1967 forwarded back to the network layer to avoid looping. Otherwise, the 1968 Proxy/Server regards the original IP packet the same as if it had 1969 arrived as carrier packets with OAL destination set to its own ADM- 1970 ULA. When the Proxy/Server receives carrier packets on underlying 1971 interfaces with OAL destination set to its own ADM-ULA, it performs 1972 OAL reassembly if necessary to obtain the original IP packet. 1974 The Proxy/Server next searches for a NCE that matches the original IP 1975 destination and proceeds as follows: 1977 o if the packet is an NA(WIN) message for a local Client NCE, the 1978 Proxy/Server examines the Interface Attributes information and 1979 rewrites the fields if the NA(WIN) was not already processed by a 1980 (local segment) Bridge as discussed in Section 3.2.7. 1982 o else, if the original IP packet destination matches a NCE, the 1983 Proxy/Sever uses one or more "reachable" neighbor interfaces in 1984 the entry for packet forwarding using OAL encapsulation and 1985 fragmentation according to the cached link-layer address 1986 information. If the neighbor interface is in a different OMNI 1987 link segment, the Proxy/Server performs OAL encapsulation and 1988 fragmentation, inserts an ORH and forwards the resulting carrier 1989 packets via the spanning tree to a Bridge; otherwise, it forwards 1990 the carrier packets directly to the neighbor. If the neighbor is 1991 behind a NAT, the Proxy/Server instead forwards initial carrier 1992 packets via a Bridge while sending an NS(NUD) to the neighbor. 1993 When the Proxy/Server receives the NA(NUD), it can begin 1994 forwarding carrier packets directly to the neighbor the same as 1995 discussed in Section 3.10.1 while sending additional NS(NUD) 1996 messages as necessary to maintain NAT state. Note that no direct 1997 bubbles are necessary since the Proxy/Server is by definition not 1998 located behind a NAT. 2000 o else, if the original IP destination matches a non-MNP route in 2001 the IP forwarding table or an ADM-LLA assigned to the Proxy/ 2002 Server's OMNI interface, the Proxy/Server acting as a Relay 2003 presents the original IP packet to the network layer for local 2004 delivery or IP forwarding. 2006 o 2008 o else, the Proxy/Server initiates address resolution as discussed 2009 in Section 3.14, while retaining initial original IP packets in a 2010 small queue awaiting address resolution completion. 2012 When the Proxy/Server receives a carrier packet with OAL destination 2013 set to an MNP-ULA that does not match the MSP, it accepts the carrier 2014 packet only if data origin authentication succeeds and if there is a 2015 network layer routing table entry for a GUA route that matches the 2016 MNP-ULA. If there is no route, the Proxy/Server drops the carrier 2017 packet; otherwise, it reassembles and decapsulates to obtain the 2018 original IP packet then acts as a Relay to present it to the network 2019 layer where it will be delivered according to standard IP forwarding. 2021 When a Proxy/Server receives a carrier packet from one of its Client 2022 neighbors with OAL destination set to another node, it forwards the 2023 packets via a matching NCE or via the spanning tree if there is no 2024 matching entry. When the Proxy/Server receives a carrier packet with 2025 OAL destination set to the MNP-ULA of one of its Client neighbors 2026 established through RS/RA exchanges, it accepts the carrier packet 2027 only if data origin authentication succeeds. If the NCE state is 2028 DEPARTED, the Proxy/Server inserts an ORH that encodes the MNP-ULA 2029 destination suffix and changes the OAL destination address to the 2030 ADM-ULA of the new Proxy/Server, then re-encapsulates the carrier 2031 packet and forwards it to a Bridge which will eventually deliver it 2032 to the new Proxy/Server. 2034 If the neighbor cache state for the MNP-ULA is REACHABLE, the Proxy/ 2035 Server forwards the carrier packets to the Client which then must 2036 reassemble. (Note that the Proxy/Server does not reassemble carrier 2037 packets not explicitly addressed to its own ADM-ULA, since some of 2038 the carrier packets of the same original IP packet could be forwarded 2039 through a different Proxy/Server.) In that case, the Client may 2040 receive fragments that are smaller than its link MTU but that can 2041 still be reassembled. 2043 Note: Proxy/Servers may receive carrier packets with ORHs that 2044 include additional forwarding information. Proxy/Servers use the 2045 forwarding information to determine the correct NCE and underlying 2046 interface for forwarding to the target Client, then remove the ORH 2047 and forward the carrier packet. If the ORH information instead 2048 indicates that the Proxy/Server is responsible for reassembly, the 2049 Proxy/Server reassembles first before re-encapsulating (and possibly 2050 also re-fragmenting) then forwards to the target Client. For a full 2051 discussion of cases when the Proxy/Server may receive carrier packets 2052 with ORHs, see: Section 3.14.6. 2054 Note: Clients and their FHS Proxy/Server peers can exchange original 2055 IP packets over ANET underlying interfaces without invoking the OAL, 2056 since the ANET is secured at the link and physical layers. By 2057 forwarding original IP packets without invoking the OAL, however, the 2058 Client and Proxy/Server can engage only in classical path MTU 2059 discovery since the packets are subject to loss and/or corruption due 2060 to the various per-link MTU limitations that may occur within the 2061 ANET. Moreover, the original IP packets do not include either the 2062 OAL integrity check or per-packet Identification values that can be 2063 used for data origin authentication and link-layer retransmissions. 2064 The tradeoff therefore involves an assessment of the per-packet 2065 encapsulation overhead saved by bypassing the OAL vs. inheritance of 2066 classical network "brittleness". (Note however that ANET peers can 2067 send small original IP packets without invoking the OAL, while 2068 invoking the OAL for larger packets. This presents the beneficial 2069 aspects of both small packet efficiency and large packet robustness.) 2071 Note: When a Proxy/Server receives a (non-OAL) original IP packet 2072 from an ANET Client, or a carrier packet with OAL destination set to 2073 its own ADM-ULA from any Client, the Proxy/Server reassembles if 2074 necessary then performs ROS functions on behalf of the Client. The 2075 Client may at some later time begin sending carrier packets to the 2076 OAL address of the actual target instead of the Proxy/Server, at 2077 which point it may begin functioning as an ROS on its own behalf and 2078 thereby "override" the Proxy/Server's ROS role. 2080 Note; Proxy/Servers drop any original IP packets (received either 2081 directly from an ANET Client or following reassembly of carrier 2082 packets received from an ANET/INET Client) with a destination that 2083 corresponds to the Client's delegated MNP. Similarly, Proxy/Servers 2084 drop any carrier packet received with both a source and destination 2085 that correspond to the Client's delegated MNP regardless of their 2086 OMNI link point of origin. These checks are necessary to prevent 2087 Clients from either accidentally or intentionally establishing 2088 endless loops that could congest Proxy/Servers and/or ANET/INET 2089 links. 2091 Note: Proxy/Servers forward secure control plane carrier packets via 2092 the SRT secured spanning tree and forwards other carrier packets via 2093 the unsecured spanning tree. When a Proxy/Server receives a carrier 2094 packet from the secured spanning tree, it considers the message as 2095 authentic without having to verify upper layer authentication 2096 signatures. When a Proxy/Server receives a carrier packet from the 2097 unsecured spanning tree, it verifies any upper layer authentication 2098 signatures and/or forwards the unsecured message toward the 2099 destination which must apply data origin authentication. 2101 Note: If the Proxy/Server has multiple original IP packets to send to 2102 the same neighbor, it can concatenate them in a single OAL super- 2103 packet [I-D.templin-6man-omni]. 2105 3.10.3. Bridge Forwarding Algorithm 2107 Bridges forward carrier packets while decrementing the OAL header Hop 2108 Count but not the original IP header Hop Count/TTL. Bridges convey 2109 carrier packets that encapsulate IPv6 ND control messages or routing 2110 protocol control messages via the secured spanning tree, and may 2111 convey carrier packets that encapsulate ordinary data via the 2112 unsecured spanning tree. When the Bridge receives a carrier packet, 2113 it removes the outer *NET header and searches for a forwarding table 2114 entry that matches the OAL destination address. The Bridge then 2115 processes the packet as follows: 2117 o if the carrier packet destination matches its ADM-ULA or the 2118 corresponding ADM-ULA Subnet Router Anycast address and the OAL 2119 header is followed by an ORH, the Bridge reassembles if necessary 2120 then sets aside the ORH and processes the carrier packet locally 2121 before forwarding. If the carrier packet contains an NS/NA(WIN) 2122 message, the Bridge creates/updates an NCE for the target and 2123 rewrites the Interface Attributes as discussed in Section 3.2.7. 2124 The Bridge next examines the ORH, and if FMT-Mode indicates the 2125 destination is a Client on the open *NET (or, a Client behind a 2126 NAT for which NAT traversal procedures have already converged) the 2127 Bridge writes the MNP-ULA formed from the ORH Destination Suffix 2128 into the OAL destination. The Bridge then removes the ORH and 2129 forwards the packet using encapsulation based on L2ADDR. If the 2130 LHS Proxy/Server will forward to the Client without reassembly, 2131 the Bridge writes the MNP-ULA into the OAL destination then 2132 replaces the ORH with an ORH-0 and forwards the carrier packet to 2133 the LHS Proxy/Server while also invoking NAT traversal procedures 2134 if necessary (noting that no direct bubbles are necessary since 2135 only the target Client and not the Bridge is behind a NAT). If 2136 the LHS Proxy/Server must perform reassembly before forwarding to 2137 the Client, the Bridge instead writes the ADM-ULA formed from the 2138 ORH SRT/LHS into the OAL destination address, replaces the ORH 2139 with an ORH-0 and forwards the carrier packet to the LHS Proxy/ 2140 Server. (Note: for NA/NA(WIN) messages, the Bridge must forward 2141 the message to the LHS Proxy/Server over the secured spanning tree 2142 instead of directly to the Client itself even if NAT traversal has 2143 converged.) 2145 o else, if the carrier packet destination matches its ADM-ULA or the 2146 corresponding ADM-ULA Subnet Router Anycast address and the OAL 2147 header is not followed by an ORH with Segments Left set to 1, the 2148 Bridge submits the packet for reassembly. When reassembly is 2149 complete, the Bridge submits the original IP packet to the network 2150 layer to support local applications such as BGP routing protocol 2151 sessions. 2153 o else, if the carrier packet destination matches a forwarding table 2154 entry the Bridge forwards the carrier packet to the next hop. (If 2155 the destination matches an MSP without matching an MNP, however, 2156 the Bridge instead drops the packet and returns a Destination 2157 Unreachable message subject to rate limiting - see: Section 3.11). 2159 o else, the Bridge drops the packet and returns an Destination 2160 Unreachable as above. 2162 The Bridge decrements the OAL IPv6 header Hop Limit when it forwards 2163 the carrier packet and drops the packet if the Hop Limit reaches 0. 2164 Therefore, only the Hop Limit in the OAL header is decremented and 2165 not the TTL/Hop Limit in the original IP packet header. Bridges do 2166 not insert OAL/ORH headers themselves; instead, they simply forward 2167 carrier packets based on their destination addresses while also 2168 possibly transforming larger ORHs into an ORH-0 (or removing the ORH 2169 altogether). 2171 Bridges forward carrier packets received from a first segment via the 2172 SRT secured spanning tree to the next segment also via the secured 2173 spanning tree. Bridges forward carrier packets received from a first 2174 segment via the unsecured spanning tree to the next segment also via 2175 the unsecured spanning tree. Bridges use a single IPv6 routing table 2176 that always determines the same next hop for a given OAL destination, 2177 where the secured/unsecured spanning tree is determined through the 2178 selection of the underlying interface to be used for transmission 2179 (i.e., a secured tunnel or an open INET interface). 2181 3.11. OMNI Interface Error Handling 2183 When an AERO node admits an original IP packet into the OMNI 2184 interface, it may receive link-layer or network-layer error 2185 indications. The AERO node may also receive OMNI link error 2186 indications in OAL-encapsulated uNA messages that include 2187 authentication signatures. 2189 A link-layer error indication is an ICMP error message generated by a 2190 router in the INET on the path to the neighbor or by the neighbor 2191 itself. The message includes an IP header with the address of the 2192 node that generated the error as the source address and with the 2193 link-layer address of the AERO node as the destination address. 2195 The IP header is followed by an ICMP header that includes an error 2196 Type, Code and Checksum. Valid type values include "Destination 2197 Unreachable", "Time Exceeded" and "Parameter Problem" 2198 [RFC0792][RFC4443]. (OMNI interfaces ignore link-layer IPv4 2199 "Fragmentation Needed" and IPv6 "Packet Too Big" messages for carrier 2200 packets that are no larger than the minimum/path MPS as discussed in 2201 Section 3.9, however these messages may provide useful hints of probe 2202 failures during path MPS probing.) 2204 The ICMP header is followed by the leading portion of the carrier 2205 packet that generated the error, also known as the "packet-in-error". 2206 For ICMPv6, [RFC4443] specifies that the packet-in-error includes: 2207 "As much of invoking packet as possible without the ICMPv6 packet 2208 exceeding the minimum IPv6 MTU" (i.e., no more than 1280 bytes). For 2209 ICMPv4, [RFC0792] specifies that the packet-in-error includes: 2210 "Internet Header + 64 bits of Original Data Datagram", however 2211 [RFC1812] Section 4.3.2.3 updates this specification by stating: "the 2212 ICMP datagram SHOULD contain as much of the original datagram as 2213 possible without the length of the ICMP datagram exceeding 576 2214 bytes". 2216 The link-layer error message format is shown in Figure 5: 2218 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2219 ~ ~ 2220 | IP Header of link layer | 2221 | error message | 2222 ~ ~ 2223 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2224 | ICMP Header | 2225 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 2226 ~ ~ P 2227 | carrier packet *NET and OAL | a 2228 | encapsulation headers | c 2229 ~ ~ k 2230 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ e 2231 ~ ~ t 2232 | original IP packet headers | 2233 | (first-fragment only) | i 2234 ~ ~ n 2235 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 2236 ~ ~ e 2237 | Portion of the body of | r 2238 | the original IP packet | r 2239 | (all fragments) | o 2240 ~ ~ r 2241 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 2243 Figure 5: OMNI Interface Link-Layer Error Message Format 2245 The AERO node rules for processing these link-layer error messages 2246 are as follows: 2248 o When an AERO node receives a link-layer Parameter Problem message, 2249 it processes the message the same as described as for ordinary 2250 ICMP errors in the normative references [RFC0792][RFC4443]. 2252 o When an AERO node receives persistent link-layer Time Exceeded 2253 messages, the IP ID field may be wrapping before earlier fragments 2254 awaiting reassembly have been processed. In that case, the node 2255 should begin including integrity checks and/or institute rate 2256 limits for subsequent packets. 2258 o When an AERO node receives persistent link-layer Destination 2259 Unreachable messages in response to carrier packets that it sends 2260 to one of its neighbor correspondents, the node should process the 2261 message as an indication that a path may be failing, and 2262 optionally initiate NUD over that path. If it receives 2263 Destination Unreachable messages over multiple paths, the node 2264 should allow future carrier packets destined to the correspondent 2265 to flow through a default route and re-initiate route 2266 optimization. 2268 o When an AERO Client receives persistent link-layer Destination 2269 Unreachable messages in response to carrier packets that it sends 2270 to one of its neighbor Proxy/Servers, the Client should mark the 2271 path as unusable and use another path. If it receives Destination 2272 Unreachable messages on many or all paths, the Client should 2273 associate with a new Proxy/Server and release its association with 2274 the old Proxy/Server as specified in Section 3.16.5. 2276 o When an AERO Proxy/Server receives persistent link-layer 2277 Destination Unreachable messages in response to carrier packets 2278 that it sends to one of its neighbor Clients, the Proxy/Server 2279 should mark the underlying path as unusable and use another 2280 underlying path. 2282 o When an AERO Proxy/Server receives link-layer Destination 2283 Unreachable messages in response to a carrier packet that it sends 2284 to one of its permanent neighbors, it treats the messages as an 2285 indication that the path to the neighbor may be failing. However, 2286 the dynamic routing protocol should soon reconverge and correct 2287 the temporary outage. 2289 When an AERO Bridge receives a carrier packet for which the network- 2290 layer destination address is covered by an MSP, the Bridge drops the 2291 packet if there is no more-specific routing information for the 2292 destination and returns an OMNI interface Destination Unreachable 2293 message subject to rate limiting. 2295 When an AERO node receives a carrier packet for which reassembly is 2296 currently congested, it returns an OMNI interface Packet Too Big 2297 (PTB) message as discussed in [I-D.templin-6man-omni] (note that the 2298 PTB messages could indicate either "hard" or "soft" errors). 2300 AERO nodes include ICMPv6 error messages intended for the OAL source 2301 as sub-options in the OMNI option of secured uNA messages. When the 2302 OAL source receives the uNA message, it can extract the ICMPv6 error 2303 message enclosed in the OMNI option and either process it locally or 2304 translate it into a network-layer error to return to the original 2305 source. 2307 3.12. AERO Router Discovery, Prefix Delegation and Autoconfiguration 2309 AERO Router Discovery, Prefix Delegation and Autoconfiguration are 2310 coordinated as discussed in the following Sections. 2312 3.12.1. AERO Service Model 2314 Each AERO Proxy/Server on the OMNI link is configured to facilitate 2315 Client prefix delegation/registration requests. Each Proxy/Server is 2316 provisioned with a database of MNP-to-Client ID mappings for all 2317 Clients enrolled in the AERO service, as well as any information 2318 necessary to authenticate each Client. The Client database is 2319 maintained by a central administrative authority for the OMNI link 2320 and securely distributed to all Proxy/Servers, e.g., via the 2321 Lightweight Directory Access Protocol (LDAP) [RFC4511], via static 2322 configuration, etc. Clients receive the same service regardless of 2323 the Proxy/Servers they select. 2325 AERO Clients and Proxy/Servers use ND messages to maintain neighbor 2326 cache entries. AERO Proxy/Servers configure their OMNI interfaces as 2327 advertising NBMA interfaces, and therefore send unicast RA messages 2328 with a short Router Lifetime value (e.g., ReachableTime seconds) in 2329 response to a Client's RS message. Thereafter, Clients send 2330 additional RS messages to keep Proxy/Server state alive. 2332 AERO Clients and Proxy/Servers include prefix delegation and/or 2333 registration parameters in RS/RA messages (see 2334 [I-D.templin-6man-omni]). The ND messages are exchanged between 2335 Client and FHS Proxy/Servers according to the prefix management 2336 schedule required by the service. If the Client knows its MNP in 2337 advance, it can employ prefix registration by including its MNP-LLA 2338 as the source address of an RS message and with an OMNI option with 2339 valid prefix registration information for the MNP. If the Proxy/ 2340 Server accepts the Client's MNP assertion, it injects the MNP into 2341 the routing system and establishes the necessary neighbor cache 2342 state. If the Client does not have a pre-assigned MNP, it can 2343 instead employ prefix delegation by including the unspecified address 2344 (::) as the source address of an RS message and with an OMNI option 2345 with prefix delegation parameters to request an MNP. 2347 The following sections specify the Client and Proxy/Server behavior. 2349 3.12.2. AERO Client Behavior 2351 AERO Clients discover the addresses of candidate FHS Proxy/Servers in 2352 a similar manner as described in [RFC5214]. Discovery methods 2353 include static configuration (e.g., from a flat-file map of Proxy/ 2354 Server addresses and locations), or through an automated means such 2355 as Domain Name System (DNS) name resolution [RFC1035]. 2356 Alternatively, the Client can discover Proxy/Server addresses through 2357 a layer 2 data link login exchange, or through a unicast RA response 2358 to a multicast/anycast RS as described below. In the absence of 2359 other information, the Client can resolve the DNS Fully-Qualified 2360 Domain Name (FQDN) "linkupnetworks.[domainname]" where 2361 "linkupnetworks" is a constant text string and "[domainname]" is a 2362 DNS suffix for the OMNI link (e.g., "example.com"). 2364 To associate with a FHS Proxy/Server over an underlying interface, 2365 the Client acts as a requesting router to request MNPs by preparing 2366 an RS message with prefix management parameters. If the Client 2367 already knows the Proxy/Server's ADM-LLA, it includes the LLA as the 2368 network-layer destination address; otherwise, the Client includes the 2369 (link-local) All-Routers multicast as the network-layer destination. 2370 The Client can use its MNP-LLA as the network-layer source address 2371 and include an OMNI option with prefix registration information. If 2372 the Client does not yet have an MNP-LLA, it instead sets the network- 2373 layer source address to unspecified (::) and includes prefix 2374 delegation parameters in the OMNI option (see: 2375 [I-D.templin-6man-omni]). 2377 The Client next includes an authentication sub-option if necessary, 2378 Interface Attributes corresponding to the underlying interface over 2379 which it will send the RS message, and optionally any additional 2380 Interface Attributes corresponding to other underlying interfaces. 2381 Next, the Client submits the RS for OAL encapsulation and 2382 fragmentation if necessary with its own MNP-ULA and the Proxy/ 2383 Server's ADM-ULA or (site-scoped) All-Routers multicast as the OAL 2384 addresses while selecting an Identification value and invoking window 2385 synchronization as specified in [I-D.templin-6man-omni]. 2387 The Client then sends the RS (either directly via Direct interfaces, 2388 via a VPN for VPNed interfaces, via an access router for ANET 2389 interfaces or via INET encapsulation for INET interfaces) then waits 2390 up to RetransTimer milliseconds for an RA message reply (see 2391 Section 3.12.3) (retrying up to MAX_RTR_SOLICITATIONS). If the 2392 Client receives no RAs, or if it receives an RA with Router Lifetime 2393 set to 0, the Client SHOULD abandon attempts through the first 2394 candidate FHS Proxy/Server and try another Proxy/Server. Otherwise, 2395 the Client processes the prefix information found in the RA message. 2397 When the Client processes an RA, it first performs OAL reassembly and 2398 decapsulation if necessary then creates a NCE with the Proxy/Server's 2399 ADM-LLA as the network-layer address and the Proxy/Server's 2400 encapsulation and/or link-layer addresses as the link-layer address. 2401 The Client then caches the FMT/SRT/LHS/L2ADDR information from the 2402 Interface Attributes for omIndex 0 included in the RA as an SRT 2403 point-of-reference for this Proxy/Server. The Client next records 2404 the RA Router Lifetime field value in the NCE as the time for which 2405 the Proxy/Server has committed to maintaining the MNP in the routing 2406 system via this underlying interface, and caches the other RA 2407 configuration information including Cur Hop Limit, M and O flags, 2408 Reachable Time and Retrans Timer. The Client then autoconfigures 2409 MNP-LLAs for any delegated MNPs and assigns them to the OMNI 2410 interface. The Client also caches any MSPs included in Route 2411 Information Options (RIOs) [RFC4191] as MSPs to associate with the 2412 OMNI link, and assigns the MTU value in the MTU option to the 2413 underlying interface. 2415 The Client then registers its additional underlying interfaces with 2416 FHS Proxy/Servers for those interfaces discovered by sending RS 2417 messages via each additional interface as described above. The RS 2418 messages include the same parameters as for the initial RS/RA 2419 exchange, but with destination address set to the Proxy/Server's ADM- 2420 LLA. The Client finally sub-delegates the MNPs to its attached EUNs 2421 and/or the Client's own internal virtual interfaces as described in 2422 [I-D.templin-v6ops-pdhost] to support the Client's downstream 2423 attached "Internet of Things (IoT)". The Client then sends 2424 additional RS messages over each underlying interface before the 2425 Router Lifetime received for that interface expires. 2427 After the Client registers its underlying interfaces, it may wish to 2428 change one or more registrations, e.g., if an interface changes 2429 address or becomes unavailable, if traffic selectors change, etc. To 2430 do so, the Client prepares an RS message to send over any available 2431 underlying interface as above. The RS includes an OMNI option with 2432 prefix registration/delegation information, with Interface Attributes 2433 specific to the selected underlying interface, and with any 2434 additional Interface Attributes specific to other underlying 2435 interfaces. When the Client receives the Proxy/Server's RA response, 2436 it has assurance that the Proxy/Server has been updated with the new 2437 information. 2439 If the Client wishes to discontinue use of a Proxy/Server it issues 2440 an RS message over any underlying interface with an OMNI option with 2441 a prefix release indication. When the Proxy/Server processes the 2442 message, it releases the MNP, sets the NCE state for the Client to 2443 DEPARTED and returns an RA reply with Router Lifetime set to 0. 2444 After a short delay (e.g., 2 seconds), the Proxy/Server withdraws the 2445 MNP from the routing system. 2447 3.12.3. AERO Proxy/Server Behavior 2449 AERO Proxy/Servers act as both IP routers and ND proxies, and support 2450 a prefix delegation/registration service for Clients. Proxy/Servers 2451 arrange to add their ADM-LLAs to a static map of Proxy/Server 2452 addresses for the link and/or the DNS resource records for the FQDN 2453 "linkupnetworks.[domainname]" before entering service. The static 2454 map and/or DNS resource records should be arranged such that Clients 2455 can discover the addresses of Proxy/Servers that are geographically 2456 and/or topologically "close" to their underlying network connections. 2458 When an FHS Proxy/Server receives a prospective Client's RS message, 2459 it SHOULD return an immediate RA reply with Router Lifetime set to 0 2460 if it is currently too busy or otherwise unable to service the 2461 Client. Otherwise, the Proxy/Server performs OAL reassembly if 2462 necessary, then decapsulates and authenticates the RS message before 2463 processing the prefix delegation/registration parameters. The Proxy/ 2464 Server then determines the correct MNPs to provide to the Client by 2465 processing the MNP-LLA prefix parameters and/or the DHCPv6 OMNI sub- 2466 option. When the Proxy/Server returns the MNPs, it also creates a 2467 forwarding table entry for the MNP-ULA corresponding to each MNP 2468 resulting in a BGP update (see: Section 3.2.3). For IPv6, the Proxy/ 2469 Server creates an IPv6 forwarding table entry for each MNP. For 2470 IPv4, the Proxy/Server creates an IPv6 forwarding table entry with 2471 the IPv4-compatibility MNP-ULA prefix corresponding to the IPv4 2472 address. 2474 The Proxy/Server next creates a NCE for the Client using the base 2475 MNP-LLA as the network-layer address. Next, the Proxy/Server updates 2476 the NCE by recording the information in each Interface Attributes 2477 sub-option in the RS OMNI option. The Proxy/Server also records the 2478 actual OAL/*NET addresses and RS message window synchronization 2479 parameters (if any) in the NCE. 2481 Next, the Proxy/Server prepares an RA message using its ADM-LLA as 2482 the network-layer source address and the network-layer source address 2483 of the RS message as the network-layer destination address. The 2484 Proxy/Server sets the Router Lifetime to the time for which it will 2485 maintain both this underlying interface individually and the NCE as a 2486 whole. The Proxy/Server also sets Cur Hop Limit, M and O flags, 2487 Reachable Time and Retrans Timer to values appropriate for the OMNI 2488 link. The Proxy/Server includes the MNPs, any other prefix 2489 management parameters and an OMNI option with an Interface Attributes 2490 sub-option with omIndex 0 and FMT/SRT/LHS/L2ADDR information for its 2491 INET interface and an Origin Indication sub-option with the mapped 2492 and obfuscated Port Number and IP address corresponding to the 2493 Client's RS encapsulation addresses. The Proxy/Server then includes 2494 one or more RIOs that encode the MSPs for the OMNI link, plus an MTU 2495 option (see Section 3.9). The Proxy/Server finally forwards the 2496 message to the Client using OAL encapsulation/fragmentation if 2497 necessary while including an acknowledgement if the RS invoked window 2498 synchronization. 2500 After the initial RS/RA exchange, the Proxy/Server maintains a 2501 ReachableTime timer for each of the Client's underlying interfaces 2502 individually (and for the Client's NCE collectively) set to expire 2503 after ReachableTime seconds. If the Client (or Proxy) issues 2504 additional RS messages, the Proxy/Server sends an RA response and 2505 resets ReachableTime. If the Proxy/Server receives an ND message 2506 with a prefix release indication it sets the Client's NCE to the 2507 DEPARTED state and withdraws the MNP from the routing system after a 2508 short delay (e.g., 2 seconds). If ReachableTime expires before a new 2509 RS is received on an individual underlying interface, the Proxy/ 2510 Server marks the interface as DOWN. If ReachableTime expires before 2511 any new RS is received on any individual underlying interface, the 2512 Proxy/Server sets the NCE state to STALE and sets a 10 second timer. 2513 If the Proxy/Server has not received a new RS or ND message with a 2514 prefix release indication before the 10 second timer expires, it 2515 deletes the NCE and withdraws the MNP from the routing system. 2517 The Proxy/Server processes any ND messages pertaining to the Client 2518 and returns an NA/RA reply in response to solicitations. The Proxy/ 2519 Server may also issue unsolicited RA messages, e.g., with reconfigure 2520 parameters to cause the Client to renegotiate its prefix delegation/ 2521 registrations, with Router Lifetime set to 0 if it can no longer 2522 service this Client, etc. Finally, If the NCE is in the DEPARTED 2523 state, the Proxy/Server deletes the entry after DepartTime expires. 2525 Note: Clients SHOULD notify former Proxy/Servers of their departures, 2526 but Proxy/Servers are responsible for expiring neighbor cache entries 2527 and withdrawing routes even if no departure notification is received 2528 (e.g., if the Client leaves the network unexpectedly). Proxy/Servers 2529 SHOULD therefore set Router Lifetime to ReachableTime seconds in 2530 solicited RA messages to minimize persistent stale cache information 2531 in the absence of Client departure notifications. A short Router 2532 Lifetime also ensures that proactive RS/RA messaging between Clients 2533 and Proxy/Servers will keep any NAT state alive (see above). 2535 Note: All Proxy/Servers on an OMNI link MUST advertise consistent 2536 values in the RA Cur Hop Limit, M and O flags, Reachable Time and 2537 Retrans Timer fields the same as for any link, since unpredictable 2538 behavior could result if different Proxy/Servers on the same link 2539 advertised different values. 2541 3.12.3.1. DHCPv6-Based Prefix Registration 2543 When a Client is not pre-provisioned with an MNP-LLA, it will need 2544 for the FHS Proxy/Server to select one or more MNPs on its behalf and 2545 set up the correct state in the AERO routing service. (A Client with 2546 a pre-provisioned MNP may also request the Proxy/Server to select 2547 additional MNPs.) The DHCPv6 service [RFC8415] is used to support 2548 this requirement. 2550 When a Client needs to have the FHS Proxy/Server select MNPs, it 2551 sends an RS message with source address set to the unspecified 2552 address (::) and with an OMNI option that includes a DHCPv6 message 2553 sub-option with DHCPv6 Prefix Delegation (DHCPv6-PD) parameters. 2554 When the Proxy/Server receives the RS message, it extracts the 2555 DHCPv6-PD message from the OMNI option. 2557 The Proxy/Server then acts as a "Proxy DHCPv6 Client" in a message 2558 exchange with the locally-resident DHCPv6 server, which delegates 2559 MNPs and returns a DHCPv6-PD Reply message. (If the Proxy/Server 2560 wishes to defer creation of MN state until the DHCPv6-PD Reply is 2561 received, it can instead act as a Lightweight DHCPv6 Relay Agent per 2562 [RFC6221] by encapsulating the DHCPv6-PD message in a Relay-forward/ 2563 reply exchange with Relay Message and Interface ID options.) 2565 When the Proxy/Server receives the DHCPv6-PD Reply, it adds a route 2566 to the routing system and creates an MNP-LLA based on the delegated 2567 MNP. The Proxy/Server then sends an RA back to the Client with the 2568 (newly-created) MNP-LLA as the destination address and with the 2569 DHCPv6-PD Reply message coded in the OMNI option. When the Client 2570 receives the RA, it creates a default route, assigns the Subnet 2571 Router Anycast address and sets its MNP-LLA based on the delegated 2572 MNP. 2574 Note: See [I-D.templin-6man-omni] for an MNP delegation alternative 2575 that avoids including a DHCPv6 message sub-option in the RS. Namely, 2576 when the Client requests a single MNP it can set the RS source to the 2577 unspecified address (::) and include a Node Identification sub-option 2578 and Preflen in the OMNI option (but with no DHCPv6 message sub- 2579 option). When the Proxy/Server receives the RS message, it forwards 2580 a self-generated DHCPv6 Solicit message to the DHCPv6 server on 2581 behalf of the Client. When the Proxy/Server receives the DHCPv6 2582 Reply, it prepares an RA message with an OMNI option with Preflen 2583 information (but with no DHCPv6 message sub-option), then places the 2584 (newly-created) MNP-LLA in the RA destination address and returns the 2585 message to the Client. 2587 3.13. The AERO Proxy Function 2589 OMNI link Clients register with one or more FHS Proxy/Servers for 2590 each underlying interface. Each of the Client's FHS Proxy/Servers 2591 must be informed of all of the Client's additional underlying 2592 interfaces. For Clients on Direct and VPNed underlying interfaces, 2593 the FHS Proxy/Server for each interface is directly connected, for 2594 Clients on ANET underlying interfaces the Proxy/Server is located on 2595 the ANET/INET boundary, and for Clients on INET underlying interfaces 2596 the FHS Proxy/Server is located somewhere in the connected 2597 Internetwork. When FHS Proxy/Server "A" processes a Client 2598 registration, it must also forward a proxyed registration to any 2599 Proxy/Servers "B", "C", "D", etc. for the Client's other underlying 2600 interfaces, which it perceives as LHS Proxy/Servers (i.e., and not 2601 FHS) from its own reference point. Proxy/Servers satisfies these 2602 requirements as follows: 2604 o when FHS Proxy/Server "A" receives a Client RS message, it first 2605 verifies that the OAL Identification is within the window for the 2606 NCE that matches the MNP-ULA for this Client neighbor and 2607 authenticates the message. (If no NCE was found, Proxy/Server "A 2608 instead creates one in the STALE state and returns an RA message 2609 with an authentication signature if necessary and any window 2610 synchronization parameters.) Proxy/Server "A" then examines the 2611 network-layer destination address. If the destination address is 2612 the ADM-LLA of a different Proxy/Server "B" (or, if the OMNI 2613 option included MS-Register/Release sub-options with the ADM-LLAs 2614 of one or more different LHS Proxy/Servers "B", "C", "D", etc.), 2615 Proxy/Server "A" prepares a separate proxyed version of the RS 2616 message with an OAL header with source set to its own ADM-ULA and 2617 destination set to the LHS Proxy/Server's ADM-ULA. Proxy/Server 2618 "A" also writes its own FMT/SRT/LHS/L2ADDR information over the 2619 first Interface Attributes supplied by the Client (i.e., by 2620 inserting the FMT/SRT/LHS/L2ADDR fields if not already present, or 2621 increasing/decreasing the L2ADDR field size if the IP version of 2622 the Client underlying interface differs from its own INET 2623 interface). Proxy/Server "A" then sets the S/T-omIndex to the 2624 value for this Client underlying interface, then forwards the 2625 message into the OMNI link secured spanning tree. 2627 o when LHS Proxy/Server "B" receives the RS, it authenticates the 2628 message then creates or updates a NCE for the Client with FHS 2629 Proxy/Server "A"'s Interface Attributes as the link-layer address 2630 information for this S/T-omIndex and caches any window 2631 synchronization parameters supplied by the Client. LHS Proxy/ 2632 Server "B" then prepares an RA message with source set to its own 2633 LLA and destination set to the Client's MNP-LLA, and with any 2634 window synchronization acknowledgements. Proxy/Server "B" then 2635 encapsulates the RA in an OAL header with source set to its own 2636 ADM-ULA and destination set to the ADM-ULA of Proxy/Server "A, 2637 performs fragmentation if necessary, then sends the resulting 2638 carrier packets into the secured spanning tree. 2640 o when Proxy/Server "A" reassembles the RA, it locates the Client 2641 NCE based on the RA destination LLA. Proxy/Server "A" then re- 2642 encapsulates the RA message with OAL source set to its own ADM-ULA 2643 and OAL destination set to the MNP-ULA of the Client, includes an 2644 authentication signature if necessary, and includes an Interface 2645 Attributes sub-option with omIndex 0 and with FMT/SRT/LHS/L2ADDR 2646 information for its INET interface. Proxy/Server "A" then 2647 fragments if necessary and returns the fragments to the Client. 2649 o The Client repeats this process over each of its additional 2650 underlying interfaces while treating each "B", "C", "D" as a FHS 2651 Proxy/Server while providing MS-Register//Release information for 2652 the others as LHS Proxy/Servers. 2654 After the initial RS/RA exchanges each Proxy/Server forwards any of 2655 the Client's carrier packets with OAL destinations for which there is 2656 no matching NCE to a Bridge using OAL encapsulation with its own ADM- 2657 ULA as the source and the destination determined by the ORH supplied 2658 by the Client. The Proxy/Server instead forwards any carrier packets 2659 destined to a neighbor cache target directly to the target according 2660 to the OAL/link-layer information - the process of establishing 2661 neighbor cache entries is specified in Section 3.14. 2663 While the Client is still associated with each Proxy/Server "A", "A" 2664 can send NS, RS and/or unsolicited NA messages to update the neighbor 2665 cache entries of other AERO nodes on behalf of the Client and/or to 2666 convey Interface Attributes updates. This allows for higher- 2667 frequency Proxy-initiated RS/RA messaging over well-connected INET 2668 infrastructure supplemented by lower-frequency Client-initiated RS/RA 2669 messaging over constrained ANET data links. 2671 If any Proxy/Server "B", "C", "D" ceases to send solicited RAs, 2672 Proxy/Server "A" sends unsolicited RAs over the Client's underlying 2673 interface with destination set to (link-local) All-Nodes multicast 2674 and with Router Lifetime set to zero to inform Clients that another 2675 Proxy/Server has failed. Although Proxy/Server "A" can engage in ND 2676 exchanges on behalf of the Client, the Client can also send ND 2677 messages on its own behalf, e.g., if it is in a better position than 2678 "A" to convey Interface Attribute changes, etc. The ND messages sent 2679 by the Client include the Client's MNP-LLA as the source in order to 2680 differentiate them from the ND messages sent by Proxy/Server "A". 2682 If the Client becomes unreachable over all underlying interface it 2683 serves, Proxy/Server "A" sets the NCE state to DEPARTED and retains 2684 the entry for DepartTime seconds. While the state is DEPARTED, 2685 Proxy/Server "A" forwards any carrier packets destined to the Client 2686 to a Bridge via OAL/ORH encapsulation. When DepartTime expires, 2687 Proxy/Server "A" deletes the NCE and discards any further carrier 2688 packets destined to the former Client. 2690 In some ANETs that employ a Proxy/Server, the Client's MNP can be 2691 injected into the ANET routing system. In that case, the Client can 2692 send original IP packets without invoking the OAL so that the ANET 2693 routing system transports the original IP packets to the Proxy. This 2694 can be very beneficial, e.g., if the Client connects to the ANET via 2695 low-end data links such as some aviation wireless links. 2697 If the ANET first-hop access router is on the same underlying link as 2698 the Client and recognizes the AERO/OMNI protocol, the Client can 2699 avoid OAL encapsulation for both its control and data messages. When 2700 the Client connects to the link, it can send an unencapsulated RS 2701 message with source address set to its own MNP-LLA (or to a Temporary 2702 LLA), and with destination address set to the ADM-LLA of the Client's 2703 selected Proxy/Server or to (link-local) All-Routers multicast. The 2704 Client includes an OMNI option formatted as specified in 2705 [I-D.templin-6man-omni]. The Client then sends the unencapsulated RS 2706 message, which will be intercepted by the AERO-Aware access router. 2708 The ANET access router then performs OAL encapsulation on the RS 2709 message and forwards it to a Proxy/Server at the ANET/INET boundary. 2710 When the access router and Proxy/Server are one and the same node, 2711 the Proxy/Server would share and underlying link with the Client but 2712 its message exchanges with outside correspondents would need to pass 2713 through a security gateway at the ANET/INET border. The method for 2714 deploying access routers and Proxys (i.e. as a single node or 2715 multiple nodes) is an ANET-local administrative consideration. 2717 Note: When a Proxy/Server alters the IPv6 ND message contents before 2718 forwarding (e.g., such as altering the OMNI option contents), the 2719 IPv6 ND message checksum and/or authentication signature are 2720 invalidated. If the Proxy/Server forwards the message over the 2721 secured spanning tree, however, it need not re-calculate the 2722 checksum/signature since they will not be examined by the next hop. 2724 Note: When a Proxy/Server receives a secured Client NS message, it 2725 performs the same proxying procedures as for described for RS 2726 messages above. The proxying procedures for NS/NA message exchanges 2727 is specified in Section 3.14. 2729 3.13.1. Detecting and Responding to Proxy/Server Failures 2731 In environments where fast recovery from Proxy/Server failure is 2732 required, Proxy/Server "A" SHOULD use proactive Neighbor 2733 Unreachability Detection (NUD) to track each peer Proxy/Server "B" 2734 reachability in a similar fashion as for Bidirectional Forwarding 2735 Detection (BFD) [RFC5880]. Proxy/Server "A" can then quickly detect 2736 and react to failures so that cached information is re-established 2737 through alternate paths. The NS/NA(NUD) control messaging is carried 2738 only over well-connected ground domain networks (i.e., and not low- 2739 end aeronautical radio links) and can therefore be tuned for rapid 2740 response. 2742 Proxy/Server "A" performs continuous NS/NA(NUD) exchanges with peer 2743 Proxy/Server "B" for which there are currently active Clients in 2744 rapid succession, e.g., one exchange per second. Proxy/Server "A" 2745 sends the NS(NUD) message via the spanning tree with its own ADM-LLA 2746 as the source and the ADM-LLA of the peer Proxy/Server "B" as the 2747 destination, and Proxy/Server "B" responds with an NA(NUD). When 2748 Proxy/Server "A" is also sending RS messages to the peer Proxy/Server 2749 "B" on behalf of Clients, the resulting RA responses can be 2750 considered as equivalent hints of forward progress. This means that 2751 Proxy/Server "B" need not also send a periodic NS(NUD) if it has 2752 already sent an RS within the same period. If the peer Proxy/Server 2753 "B" fails (i.e., if "A" ceases to receive advertisements), Proxy/ 2754 Server "A" can quickly inform Clients by sending unsolicited RA 2755 messages 2757 Proxy/Server "A" sends unsolicited RA messages with source address 2758 set to Proxy/Server "B"'s address, destination address set to (link- 2759 local) All-Nodes multicast, and Router Lifetime set to 0. Proxy/ 2760 Server "A" SHOULD send MAX_FINAL_RTR_ADVERTISEMENTS RA messages 2761 separated by small delays [RFC4861]. Any Clients that had been using 2762 the failed Proxy/Server "B" will receive the RA messages and 2763 associate with a new Proxy/Server. 2765 3.13.2. Point-to-Multipoint Proxy/Server Coordination 2767 In environments where Client messaging over ANETs is bandwidth- 2768 limited and/or expensive, Clients can enlist the services of FHS 2769 Proxy/Server "A" to coordinate with multiple LHS Proxy/Servers "B", 2770 "C", "D" etc. in a single RS/RA message exchange. The Client can 2771 send a single RS message to (link-local) All-Routers multicast that 2772 includes the ID's of multiple Proxy/Servers in MS-Register/MS-Release 2773 OMNI sub-options. 2775 When FHS Proxy/Server "A" receives the RS and processes the OMNI 2776 option, it sends a separate RS to each MS-Register/MS-Release LHS 2777 Proxy/Server "B", "C", "D", etc. When FHS Proxy/Server "A" receives 2778 an LHS Proxy/Server RA, it can optionally return an immediate 2779 "singleton" RA to the Client or record the LHS Proxy/Server's MSID 2780 for inclusion in a pending "aggregate" RA message. FHS Proxy/Server 2781 "A" can then return aggregate RA messages to the Client including 2782 multiple LHS Proxy/Server MSIDs in order to conserve bandwidth. Each 2783 RA includes a proper subset of the LHS Proxy/Server MSIDs from the 2784 original RS message, and FHS Proxy/Server "A" must ensure that the 2785 message contents of each RA are consistent with the information 2786 received from the (aggregated) LHS Proxy/Servers. 2788 Clients can thereafter employ efficient point-to-multipoint LHS 2789 Proxy/Server coordination under the assistance of FHS Proxy/Server 2790 "A" to reduce the number of messages sent over the *NET. Clients can 2791 further include MS-Release sub-options in IPv6 ND messages to request 2792 FHS Proxy/Server "A" to release from former LHS Proxy/Servers via the 2793 procedures discussed in Section 3.16.5. 2795 The OMNI interface specification [I-D.templin-6man-omni] provides 2796 further discussion of the RS/RA messaging involved in point-to- 2797 multipoint coordination. 2799 3.14. AERO Route Optimization 2801 AERO nodes invoke route optimization when they need to forward 2802 packets to new target destinations. Route optimization is based on 2803 IPv6 ND Address Resolution messaging between a Route Optimization 2804 Source (ROS) and Route Optimization Responder (ROR). Route 2805 optimization is initiated by the first eligible ROS closest to the 2806 source as follows: 2808 o For Clients on VPNed and Direct interfaces, the Client's FHS 2809 Proxy/Server is the ROS. 2811 o For Clients on ANET interfaces, either the Client or the FHS 2812 Proxy/Server may be the ROS. 2814 o For Clients on INET interfaces, the Client itself is the ROS. 2816 o For correspondent nodes on INET/EUN interfaces serviced by a 2817 Relay, the Relay is the ROS. 2819 The route optimization procedure is conducted between the ROS and an 2820 LHS Proxy/Server/Relay for the target selected by routing as the ROR. 2821 In this arrangement, the ROS is always the Client or Proxy/Server/ 2822 Relay nearest the source over the selected source underlying 2823 interface, while the ROR is always an LHS Proxy/Server/Relay for the 2824 target regardless of the target underlying interface. 2826 The AERO routing system directs a route optimization request sent by 2827 the ROS to the nearest available ROR, which returns a route 2828 optimization reply. The exact ROR selected is unimportant as long as 2829 the information returned is current, consistent and authentic. The 2830 ROS is responsible for periodically refreshing the route 2831 optimization, and the ROR is responsible for quickly informing the 2832 ROS of any changes. 2834 The procedures are specified in the following sections. 2836 3.14.1. Route Optimization Initiation 2838 When an original IP packet from a source node destined to a target 2839 node arrives, the ROS checks for a NCE with an MNP-LLA that matches 2840 the target destination. If there is a NCE in the REACHABLE state, 2841 the ROS invokes the OAL and forwards the resulting carrier packets 2842 according to the cached state then returns from processing. 2843 Otherwise, if there is no NCE the ROS creates one in the INCOMPLETE 2844 state. 2846 The ROS next places the original IP packet on a short queue then 2847 sends an NS message for Address Resolution (NS(AR)) to receive a 2848 solicited NA(AR) message from an ROR. The NS(AR) message must be 2849 sent securely, and includes: 2851 o the LLA of the ROS as the source address. 2853 o the MNP-LLA corresponding to the original IP packet's destination 2854 as the Target Address, e.g., for 2001:db8:1:2::10:2000 the Target 2855 Address is fe80::2001:db8:1:2. 2857 o the Solicited-Node multicast address [RFC4291] formed from the 2858 lower 24 bits of the original IP packet's destination as the 2859 destination address, e.g., for 2001:db8:1:2::10:2000 the NS(AR) 2860 destination address is ff02:0:0:0:0:1:ff10:2000. 2862 The NS(AR) message also includes an OMNI option with an 2863 authentication sub-option if necessary, an Interface Attributes sub- 2864 option for the underlying interface, with S/T-omIndex set to the 2865 underlying interface index and with Preflen set to the prefix length 2866 associated with the NS(AR) source. The ROS then selects an 2867 Identification value submits the NS(AR) message for OAL encapsulation 2868 with OAL source set to its own ULA and OAL destination set to the ULA 2869 corresponding to the target. (The ROS does not include any window 2870 synchronization parameters, since it will not exchange other packet 2871 types with the ROR.) The ROS then sends the resulting carrier 2872 packet(s) into the SRT secured spanning tree without decrementing the 2873 network-layer TTL/Hop Limit field. 2875 When the ROS is an INET Client, it must instead forward the resulting 2876 carrier packets to the ADM-ULA of one of its current Proxy/Servers. 2877 The Proxy/Server reassembles if necessary, then verifies the NS(AR) 2878 authentication signature and writes its FMT/SRT/LHS/L2ADDR 2879 information into the Interface Attributes sub-option the same as 2880 described for RS messages in Section 3.13. The Proxy/Server then re- 2881 encapsulates the NS(AR) with the OAL source set to its own ADM-ULA 2882 and OAL destination set to the ULA corresponding to the target, 2883 fragments if necessary and forwards the resulting carrier packets 2884 into the secured spanning tree on behalf of the Client. 2886 3.14.2. Relaying the NS(AR) *NET Packet(s) 2888 When the Bridge receives the carrier packet(s) containing the RS from 2889 the ROS, it discards the *NET headers and determines the next hop by 2890 consulting its standard IPv6 forwarding table for the OAL header 2891 destination address. The Bridge then decrements the OAL header Hop- 2892 Limit, then re-encapsulates and forwards the carrier packet(s) via 2893 the secured spanning tree the same as for any IPv6 router, where it 2894 may traverse multiple OMNI link segments. The final-hop Bridge will 2895 deliver the carrier packet(s) via the secured spanning tree to a 2896 Proxy/Server or Relay that services the target. 2898 3.14.3. Processing the NS(AR) and Sending the NA(AR) 2900 When an LHS Proxy/Server (or Relay) for the target receives the 2901 secured carrier packet(s), it reassembles if necessary then examines 2902 the NS(AR) target to determine whether it has a matching NCE and/or 2903 non-MNP route. If there is no match, the Proxy/Server drops the 2904 message. Otherwise, the LHS Proxy/Server/Relay continues processing 2905 as follows: 2907 o if the NS(AR) target matches a Client NCE in the DEPARTED state, 2908 the Proxy/Server re-encapsulates while setting the OAL source to 2909 the ULA of the ROS and OAL destination address to the ADM-ULA of 2910 the Client's new Proxy/Server. The (old) Proxy/Server then 2911 fragments if necessary and forwards the resulting carrier 2912 packet(s) over the secured spanning tree then returns from 2913 processing. 2915 o If the NS(AR) target matches the MNP-LLA of a Client NCE in the 2916 REACHABLE state, the Proxy/Server notes whether the NS (AR) 2917 arrived from the secured or unsecured spanning tree then acts as 2918 an ROR to provide route optimization information on behalf of the 2919 Client. If the message arrived via the secured spanning tree the 2920 ROR need not perform further authentication; otherwise, it must 2921 verify the message authentication signature before accepting. 2923 o If the NS(AR) target matches one of its non-MNP routes, the Relay 2924 acts as both an ROR and a route optimization target, since the 2925 Relay forwards IP packets toward the (fixed network) target at the 2926 network layer. 2928 The ROR next checks the target NCE for a Report List entry that 2929 matches the NS(AR) source LLA/ULA of the ROS. If there is a Report 2930 List entry, the ROR refreshes ReportTime for this ROR; otherwise, the 2931 ROR creates a new entry for the ROS and records both the LLA and ULA. 2933 The ROR then prepares a (solicited) NA(AR) message to return to the 2934 ROS with the source address set to its own ADM-LLA, the destination 2935 address set to the NS(AR) LLA source address and the Target Address 2936 set to the target Client's MNP-LLA. The ROR includes an OMNI option 2937 with Preflen set to the prefix length associated with the NA(AR) 2938 source address as well as Interface Attributes sub-options for all of 2939 the target's underlying interfaces with current information for each 2940 interface. 2942 For each Interface Attributes sub-option, the ROR sets the L2ADDR 2943 according to its own INET address for VPNed, Direct, ANET and NATed 2944 Client interfaces, or to the Client's INET address for native Client 2945 interfaces. The ROR then includes the lower 32 bits of the Proxy/ 2946 Server's ADM-ULA as the LHS, encodes the ADM-ULA SRT prefix length in 2947 the SRT field and sets FMT as specified in Section 3.3. 2949 The ROR then sets the NA(AR) message R flag to 1 (as a router) and S 2950 flag to 1 (as a response to a solicitation) and sets the O flag to 0 2951 (as a proxy) and sets the OMNI header S/T-omIndex to 0. The ROR 2952 finally submits the NA(AR) for OAL encapsulation with source set to 2953 its own ULA and destination set to the same ULA that appeared in the 2954 NS(AR) OAL source, then performs OAL encapsulation and fragmentation 2955 using the same Identification value that appeared in the NS(AR) and 2956 finally forwards the resulting (*NET-encapsulated) carrier packets 2957 via the secured spanning tree without decrementing the network-layer 2958 TTL/Hop Limit field. 2960 3.14.4. Relaying the NA(AR) 2962 When the Bridge receives NA(AR) carrier packets from the ROR, it 2963 discards the *NET header and determines the next hop by consulting 2964 its standard IPv6 forwarding table for the OAL header destination 2965 address. The Bridge then decrements the OAL header Hop-Limit, re- 2966 encapsulates the carrier packet and forwards it via the SRT secured 2967 spanning tree the same as for any IPv6 router, where it may traverse 2968 multiple OMNI link segments. The final-hop Bridge will deliver the 2969 carrier packet via the secured spanning tree to a Proxy/Server for 2970 the ROS. 2972 3.14.5. Processing the NA(AR) 2974 When the ROS receives the NA(AR) message from the ROR, it first 2975 searches for a NCE that matches the NA(AR) target address. The ROS 2976 then processes the message the same as for standard IPv6 Address 2977 Resolution [RFC4861]. In the process, it caches all OMNI option 2978 information in the target NCE (including all Interface Attributes), 2979 and caches the NA(AR) ADM-{LLA,ULA} source addresses as the addresses 2980 of the ROR. If the ROS receives additional NA(AR) or uNA messages 2981 for this target Client with the same ADM-LLA source address but a 2982 different ADM-ULA source address, it caches the new MSID as the new 2983 ADM-{LLA,ULA} and deprecates the former ADM-{LLA,ULA}. 2985 When the ROS is a Client, the solicited NA(AR) message will first be 2986 delivered via the SRT secured spanning tree to the Proxy/Server that 2987 forwarded the NS(AR), which reassembles if necessary. The Proxy/ 2988 Server then forwards the message to the Client while re-encapsulating 2989 and re-fragmenting if necessary. If the Client is on a well-managed 2990 ANET, physical security and protected spectrum ensures security for 2991 the unmodified NA(AR); if the Client is on the open INET the Proxy/ 2992 Server must instead include an authentication signature (while 2993 adjusting the OMNI option size, if necessary). The Proxy/Server uses 2994 its own ADM-ULA as the OAL source and the MNP-ULA of the Client as 2995 the OAL destination. 2997 3.14.6. Forwarding Packets to Route Optimized Targets 2999 After the ROS receives the route optimization NA(AR) and updates the 3000 target NCE, it sends additional NS(AR) messages to the ADM-ULA of the 3001 ROR to refresh the NCE ReachableTime before expiration while it still 3002 has sustained interest in this target. While the NCE remains 3003 REACHABLE, the ROS can forward packets along the best underlying 3004 interface paths based on the target's Interface Attributes. The ROS 3005 selects target underlying interfaces according to traffic selectors 3006 and/or any other traffic discriminators, however each underlying 3007 interface selected must first establish window synchronization state 3008 if necessary. 3010 To establish window synchronization state, the ROS performs a secured 3011 unicast NS/NA(WIN) exchange with window synchronization parameters 3012 according to the Interface Attributes FMT code. If FMT-Forward is 3013 set, the ROS prepares an NS(WIN) with its own LLA as the source and 3014 the MNP-LLA of the target Client as the destination; otherwise, it 3015 sets the ADM-LLA of the LHS Proxy/Server as the destination. The ROS 3016 then encapsulates the NS(WIN) in an OAL header with its own ULA as 3017 the source and includes an ORH with Segments Left set to 1 and with 3018 FMT/SRT/LHSL2ADDR addressing information for the LHS Proxy/Server. 3019 If the ROS is the Client, it sets the OAL destination to the ADM-ULA 3020 of its FHS Proxy/Server, includes an authentication signature if 3021 necessary, includes an Interface Attributes sub-option for its 3022 underlying interface and, then forwards the NS(WIN) to its FHS Proxy/ 3023 Server which must reassemble, verify the authentication signature and 3024 rewrite the Interface Attributes FMT/SRT/LHS/L2ADDR information if 3025 necessary. The FHS Proxy/Server then re-encapsulates, re-fragments 3026 and forwards the NS(WIN) carrier packets into the secured spanning 3027 tree with its own ADM-ULA as the OAL source and the Subnet Router 3028 Anycast address for the LHS as the OAL destination. 3030 When an LHS Bridge that configures the Subnet Router Anycast address 3031 receives the NS(WIN) carrier packets over the secured spanning tree, 3032 it reassembles if necessary then creates a NCE for the NS(WIN) target 3033 and assigns an NIndex value as discussed in Section 3.2.7. The 3034 Bridge then re-encapsulates, re-fragments and forwards the NS(WIN) 3035 carrier packets into the secured spanning tree with the ADM-ULA of 3036 the LHS Proxy/Server as the OAL destination. 3038 When the LHS Proxy/Server receives the NS(WIN) carrier packets it 3039 first reassembles if necessary. If the NS(WIN) destination is its 3040 own ADM-LLA, the LHS Proxy/Server creates an NCE based on the NS(WIN) 3041 source LLA, caches the window synchronization information, and 3042 prepares an NA(WIN) while using its own ADM-LLA as the source and the 3043 ROS LLA as the destination. The LHS Proxy/Server then encapsulates 3044 the NA(WIN) in an OAL header with source set to its own ADM-ULA and 3045 destination set to the Subnet Router Anycast address for the NS(WIN) 3046 OAL source. The LHS Proxy/Server then fragments if necessary, 3047 includes an ORH with FMT/SRT/LHS/L2ADDR found in the NS(WIN) OMNI 3048 option, then forwards the resulting carrier packets into the secured 3049 spanning tree which will deliver them to a FHS Bridge on the ROS 3050 Proxy/Server segment. 3052 If the NS(WIN) destination is the MNP-LLA of the target Client, the 3053 LHS Proxy/Server instead removes the ORH, re-encapsulates using the 3054 same OAL source and the MNP-ULA of the target as the OAL destination 3055 and includes an authentication signature (while adjusting the OMNI 3056 option size) if necessary. The LHS Proxy/Server then forwards the 3057 NS(WIN) to the target Client over the underlying interface identified 3058 by the ORH omIndex (or, over any underlying interface if omIndex is 3059 0). When the target Client receives the NS(WIN), it verifies the 3060 authentication signature if necessary then creates an NCE for the ROS 3061 LLA, caches the window synchronization information and prepares an 3062 NA(WIN) to return to the ROS with its MNP-LLA as the source and the 3063 LLA of the ROS as the destination, and with an Interface Attributes 3064 sub-option and an authentication signature if necessary. The target 3065 Client then encapsulates the NA(WIN) in an OAL header with its own 3066 MNP-ULA as the source, the ADM-ULA of the LHS Proxy/Server as the 3067 destination, and with an ORH with FMT/SRT/LHS/L2ADDR information 3068 copied from the NS(WIN) Interface Attributes. The target Client then 3069 sets the ORH omIndex to the S/T-omIndex value found in the NS(WIN) 3070 OMNI option, then forwards the NA(WIN) message to the LHS Proxy/ 3071 Server. 3073 When the LHS Proxy/Server receives the message, it reassembles if 3074 necessary, verifies the authentication signature and rewrites the 3075 Interface Attributes FMT/SRT/LHS/L2ADDR information if necessary, 3076 then re-encapsulates using its own ADM-ULA as the source and the 3077 Subnet Router Anycast address for the FHS Proxy/Server as the 3078 destination. The LHS Proxy/Server then re-fragments and forwards the 3079 NA(WIN) carrier packets into the secured spanning tree. 3081 When an FHS Bridge that configures the Subnet Router Anycast address 3082 receives the NA(WIN) carrier packets, it reassembles if necessary 3083 then creates a NCE for the NA(WIN) target, assigns an NIndex value 3084 and rewrites the Interface Attributes FMT/SRT/LHS/L2ADDR information 3085 as discussed in Section 3.2.7. The Bridge then re-encapsulates, re- 3086 fragments and forwards the NA(WIN) carrier packets into the secured 3087 spanning tree with the ADM-ULA of the FHS Proxy/Server as the OAL 3088 destination. 3090 When the FHS Proxy/Server receives the NA(WIN), it reassembles if 3091 necessary then updates the NCE for the NA(WIN) target based on the 3092 message contents if the Proxy/Server itself is the ROS. If the 3093 NA(WIN) source was the ADM-LLA of the LHS Proxy/Server, the ROS must 3094 also create and maintain a NCE for the LHS Proxy/Server which it must 3095 regard as a companion to the existing target Client NCE. (The NCE 3096 for the LHS Proxy/Server can also be shared by multiple target Client 3097 NCEs if the ROS communicates with multiple active targets located 3098 behind the same LHS Proxy/Server.) 3100 If the Client is the ROS, the FHS Proxy/Server instead inserts an 3101 authentication signature (while adjusting the OMNI option size) if 3102 necessary, removes the ORH then re-encapsulates and re-fragments if 3103 necessary while changing the OAL destination to the MNP-ULA of the 3104 ROS Client. The FHS Proxy/Server then forwards the NA(WIN) to the 3105 ROS Client over the underlying interface identified by the ORH 3106 omIndex which then updates its own NCE based on the target Client 3107 MNP-LLA or LHS Proxy/Server ADM-LLA. The ROS (whether the Proxy/ 3108 Server or the Client itself) finally arranges to return an 3109 acknowledgement if requested by the NA(WIN) by sending an NA(WIN) 3110 acknowledgement in the reverse path over the secured spanning tree, 3111 where it will first visit the LHS Bridge which updates the taregt 3112 Client NCE and securely forwards the NA(WIN) toward the target 3113 itself. 3115 After window synchronization state has been established, the ROS and 3116 taget Client can begin forwarding carrier packets as specified in 3117 Section 3.2.7 while performing additional NS/NA(WIN) exchanges as 3118 above to update window state and/or test reachability. The ROS sends 3119 carrier packets to the FHS Bridge discovered through the NS/NA(WIN) 3120 exhange which verifies the Identification is in window. The FHS 3121 Bridge then forwards the carrier packets over the unsecured spanning 3122 tree to the LHS Bridge, whch forwards them via LHS encapsulation to 3123 the LHS Proxy/Server or directly to the target Client itself. The 3124 target Client in turn sends packes to the ROS in the reverse 3125 direction while forwarding through the Bridges to minimize Proxy/ 3126 Server load whenever possible. 3128 The above forwarding procedures apply to the case where the selected 3129 target interface SRT/LHS codes indicate that the interface is located 3130 in a foreign OMNI link segment. If the SRT/LHS codes indicate that 3131 the interface is in the local OMNI link segment, the ROS can instead 3132 forward carrier packets directly to the LHS Proxy/Server using the 3133 L2ADDR for encapsulation following the initial secured NS/NA(WIN) 3134 exchange (or even directly to the target Client itself while invoking 3135 NAT traversal if necessary). When the ROS sends packets directly to 3136 the LHS Proxy/Server, it includes an ORH if necessary to inform the 3137 Proxy/Server as to whether it must reassemble and/or the correct 3138 target Client (NIndex/omIndex) for (re)forwarding. If the LHS Proxy/ 3139 Server is required to reassemble, the ROS sets the OAL destination to 3140 the ADM-ULA of the LHS Proxy/Server; otherwise, it sets the OAL 3141 destination to the MNP-ULA of the target Client itself. When the ROS 3142 sends packets directly to the target Client, it need not include an 3143 ORH. The LHS Proxy/Server (or target Client) then saves the L2ADDR 3144 and full OAL addresses in the ROS NCE. 3146 While the ROS continues to actively forward packets to the target 3147 Client, it is responsible for updating window synchronization state 3148 and per-interface reachability before expiration. Window 3149 synchronization state is shared by all underlying interfaces in the 3150 ROS' NCE that use the same destination LLA so that a single NS/ 3151 NA(NUD) exchange applies for all interfaces regardless of the 3152 (single) interface used to conduct the exchange. However, the window 3153 synchronization exchange only confirms target Client reachability 3154 over the specific interface used to conduct the exchange. 3155 Reachability for other underlying interfaces that share the same 3156 window synchronization state must be determined individually using 3157 NS/NA(NUD) messages which need not be secured as long as they use in- 3158 window Identifications and do not update other state information. 3160 3.15. Neighbor Unreachability Detection (NUD) 3162 AERO nodes perform Neighbor Unreachability Detection (NUD) per 3163 [RFC4861] either reactively in response to persistent link-layer 3164 errors (see Section 3.11) or proactively to confirm reachability. 3165 The NUD algorithm is based on periodic control message exchanges and 3166 may further be seeded by ND hints of forward progress, but care must 3167 be taken to avoid inferring reachability based on spoofed 3168 information. For example, IPv6 ND message exchanges that include 3169 authentication codes and/or in-window Identifications may be 3170 considered as acceptable hints of forward progress, while spurious 3171 random carrier packets should be ignored. 3173 AERO nodes can perform NS/NA(NUD) exchanges over the OMNI link 3174 secured spanning tree (i.e. the same as described above for NS/ 3175 NA(WIN)) to test reachability without risk of DoS attacks from nodes 3176 pretending to be a neighbor. These NS/NA(NUD) messages use the 3177 unicast LLAs and ULAs of the parties involved in the NUD test the 3178 same as for standard IPv6 ND over the secured spanning tree. When 3179 only reachability information is required without updating any other 3180 NCE state, AERO nodes can instead perform NS/NA(NUD) exchanges 3181 directly between neighbors without employing the secured spanning 3182 tree as long as they include in-window Identifications and either an 3183 authentication signature or checksum. 3185 When an ROR directs an ROS to a target neighbor with one or more 3186 link-layer addresses, the ROS probes each unsecured target underlying 3187 interface either proactively or on-demand of carrier packets directed 3188 to the path by multilink forwarding to maintain the interface's state 3189 as reachable. Probing is performed through NS(NUD) messages over the 3190 SRT secured or unsecured spanning tree, or through NS(NUD) messages 3191 sent directly to an underlying interface of the target itself. While 3192 testing a target underlying interface, the ROS can optionally 3193 continue to forward carrier packets via alternate interfaces and/or 3194 maintain a small queue of carrier packets until target reachability 3195 is confirmed. 3197 NS(NUD) messages are encapsulated, fragmented and transmitted as 3198 carrier packets the same as for ordinary original IP data packets, 3199 however the encapsulated destinations are the LLA of the ROS and 3200 either the ADM-LLA of the LHS Proxy/Server or the MNP-LLA of the 3201 target itself. The ROS encapsulates the NS(NUD) message the same as 3202 described in Section 3.2.7, however Destination Suffixes (if present) 3203 are set according to the LLA destination (i.e., and not the ULA/GUA 3204 destination). The ROS sets the NS(NUD) OMNI header S/T-omIndex to 3205 identify the underlying interface used for forwarding (or to 0 if any 3206 underlying interface can be used). The ROS also includes an ORH with 3207 FMT/SRT/LHS/L2ADDR information the same as for ordinary data packets, 3208 but does not include an authentication signature. The ROS then 3209 fragments the OAL packet and forwards the resulting carrier packets 3210 into the unsecured spanning tree or directly to the target (or LHS 3211 Proxy/Server) if it is in the local segment. 3213 When the target (or LHS Proxy/Server) receives the NS(NUD) carrier 3214 packets, it verifies that it has a NCE for this ROS and that the 3215 Identification is in-window, then submits the carrier packets for 3216 reassembly. The node then verifies the authentication signature or 3217 checksum, then searches for Interface Attributes in its NCE for the 3218 ROS that match the NS(NUD) S/T-omIndex and uses the FMT/SRT/LHS/ 3219 L2ADDR information to prepare an ORH for the NA(NUD) reply. The node 3220 then prepares the NA(NUD) with the source and destination LLAs 3221 reversed, encapsulates and sets the OAL source and destination, sets 3222 the NA(NUD) S/T-omIndex to the index of the underlying interface the 3223 NS(NUD) arrived on and sets the Target Address to the same value 3224 included in the NS(NUD). The target next sets the R flag to 1, the S 3225 flag to 1 and the O flag to 1, then selects an in-window 3226 Identification for the ROS and performs fragmentation. The node then 3227 forwards the carrier packets into the unsecured spanning tree, 3228 directly to the ROS if it is in the local segment or directly to a 3229 Bridge in the local segment. 3231 When the ROS receives the NA(NUD), it marks the target underlying 3232 interface tested as "reachable". Note that underlying interface 3233 states are maintained independently of the overall NCE REACHABLE 3234 state, and that a single NCE may have multiple target underlying 3235 interfaces in various states "reachable" and otherwise while the NCE 3236 state as a whole remains REACHABLE. 3238 Note also that the exchange of NS/NA(NUD) messages has the useful 3239 side-benefit of opening holes in NATs that may be useful for NAT 3240 traversal. 3242 3.16. Mobility Management and Quality of Service (QoS) 3244 AERO is a Distributed Mobility Management (DMM) service. Each Proxy/ 3245 Server is responsible for only a subset of the Clients on the OMNI 3246 link, as opposed to a Centralized Mobility Management (CMM) service 3247 where there is a single network mobility collective entity for all 3248 Clients. Clients coordinate with their associated Proxy/Servers via 3249 RS/RA exchanges to maintain the DMM profile, and the AERO routing 3250 system tracks all current Client/Proxy/Server peering relationships. 3252 Proxy/Servers provide default routing and mobility/multilink services 3253 for their dependent Clients. Clients are responsible for maintaining 3254 neighbor relationships with their Proxy/Servers through periodic RS/ 3255 RA exchanges, which also serves to confirm neighbor reachability. 3256 When a Client's underlying Interface Attributes change, the Client is 3257 responsible for updating the Proxy/Server with this new information. 3258 Note that when there is a Proxy/Server in the path, the Proxy 3259 function can also perform some RS/RA exchanges on the Client's 3260 behalf. 3262 Mobility management messaging is based on the transmission and 3263 reception of unsolicited Neighbor Advertisement (uNA) messages. Each 3264 uNA message sets the IPv6 source address to the LLA of the ROR and 3265 the destination address to the unicast LLA of the ROS. 3267 Mobility management considerations are specified in the following 3268 sections. 3270 3.16.1. Mobility Update Messaging 3272 RORs accommodate Client mobility and/or multilink change events by 3273 sending secured uNA messages to each ROS in the target Client's 3274 Report List. When an ROR sends a uNA message, it sets the IPv6 3275 source address to the its own LLA, sets the destination address to 3276 the ROS LLA (i.e., an MNP-LLA if the ROS is a Client and an ADM-LLA 3277 if the ROS is a Proxy/Server) and sets the Target Address to the 3278 Client's MNP-LLA. The ROR also includes an OMNI option with Preflen 3279 set to the prefix length associated with the Client's MNP-LLA, with 3280 Interface Attributes for the target Client's underlying interfaces 3281 and with the OMNI header S/T-omIndex set to 0. The ROR then sets the 3282 uNA R flag to 1, S flag to 0 and O flag to 1, then encapsulates the 3283 message in an OAL header with source set to its own ADM-ULA and 3284 destination set to the ROS ULA (i.e., the ADM-ULA of the ROS Proxy/ 3285 Server) and sends the message into the secured spanning tree. 3287 As discussed in Section 7.2.6 of [RFC4861], the transmission and 3288 reception of uNA messages is unreliable but provides a useful 3289 optimization. In well-connected Internetworks with robust data links 3290 uNA messages will be delivered with high probability, but in any case 3291 the Proxy/Server can optionally send up to MAX_NEIGHBOR_ADVERTISEMENT 3292 uNAs to each ROS to increase the likelihood that at least one will be 3293 received. Alternatively, the Proxy/Server can set the PNG flag in 3294 the uNA OMNI option header to request a solicited NA acknowledgement 3295 as specified in [I-D.templin-6man-omni]. 3297 When the ROS Proxy/Server receives a uNA message prepared as above, 3298 it ignores the message if the destination is not its own ADM-ULA or 3299 the MNP-ULA of the ROS Client. If the destination was its own ADM- 3300 ULA, the ROS Proxy/Server uses the included OMNI option information 3301 to update its NCE for the target but does not reset ReachableTime 3302 since the receipt of an unsolicited NA message from the ROR does not 3303 provide confirmation that any forward paths to the target Client are 3304 working. If the destination was the MNP-ULA of the ROS Client, the 3305 Proxy/Server instead re-encapsulates with the OAL source set to its 3306 own ADM-ULA, OAL destination set to the MNP-ULA of the ROS Client 3307 with an authentication signature if necessary, and with an in-window 3308 Identification for this Client. Finally, if the uNA message PNG flag 3309 was set, the ROS returns a solicited NA acknowledgement as specified 3310 in [I-D.templin-6man-omni]. 3312 In addition to sending uNA messages to the current set of ROSs for 3313 the target Client, the ROR also sends uNAs to the former Proxy/Server 3314 associated with the underlying interface for which the link-layer 3315 address has changed. These uNA messages update former Proxy/Servers 3316 that cannot easily detect (e.g., without active probing) when a 3317 formerly-active Client has departed. When the ROR sends the uNA, it 3318 sets the IPv6 source address to its LLA, sets the destination address 3319 to the former Proxy/Server's ADM-LLA, and sets the Target Address to 3320 the Client's MNP-LLA. The ROR also includes an OMNI option with 3321 Preflen set to the prefix length associated with the Client's MNP- 3322 LLA, with Interface Attributes for the changed underlying interface, 3323 and with the OMNI header S/T-omIndex set to 0. The ROR then sets the 3324 uNA R flag to 1, S flag to 0 and O flag to 1, then encapsulates the 3325 message in an OAL header with source set to its own ULA and 3326 destination set to the ADM-ULA of the former Proxy/Server and sends 3327 the message into the secured spanning tree. 3329 3.16.2. Announcing Link-Layer Address and/or QoS Preference Changes 3331 When a Client needs to change its underlying Interface Attributes 3332 (e.g., due to a mobility event), the Client requests one of its 3333 Proxy/Servers to send RS messages to all of its other Proxy/Servers 3334 via the secured spanning tree with an OMNI option that includes 3335 Interface Attributes with the new link quality and address 3336 information. 3338 Up to MAX_RTR_SOLICITATIONS RS messages MAY be sent in parallel with 3339 sending carrier packets containing user data in case one or more RAs 3340 are lost. If all RAs are lost, the Client SHOULD re-associate with a 3341 new Proxy/Server. 3343 When the Proxy/Server receives the Client's changes, it sends uNA 3344 messages to all nodes in the Report List the same as described in the 3345 previous section. 3347 3.16.3. Bringing New Links Into Service 3349 When a Client needs to bring new underlying interfaces into service 3350 (e.g., when it activates a new data link), it sends an RS message to 3351 the Proxy/Server via the underlying interface with an OMNI option 3352 that includes Interface Attributes with appropriate link quality 3353 values and with link-layer address information for the new link. 3355 3.16.4. Deactivating Existing Links 3357 When a Client needs to deactivate an existing underlying interface, 3358 it sends an RS message to an FHS Proxy/Server with an OMNI option 3359 with appropriate Interface Attribute values for the deactivated link 3360 - in particular, the link quality value 0 assures that neighbors will 3361 cease to use the link. 3363 If the Client needs to send RS messages over an underlying interface 3364 other than the one being deactivated, it MUST include Interface 3365 Attributes with appropriate link quality values for any underlying 3366 interfaces being deactivated. 3368 Note that when a Client deactivates an underlying interface, 3369 neighbors that have received the RS/uNA messages need not purge all 3370 references for the underlying interface from their neighbor cache 3371 entries. The Client may reactivate or reuse the underlying interface 3372 and/or its omIndex at a later point in time, when it will send new RS 3373 messages to an FHS Proxy/Server with fresh Interface Attributes to 3374 update any neighbors. 3376 3.16.5. Moving Between Proxy/Servers 3378 The Client performs the procedures specified in Section 3.12.2 when 3379 it first associates with a new FHS Proxy/Server or renews its 3380 association with an existing Proxy/Server. The Client also includes 3381 MS-Release identifiers in the RS message OMNI option per 3382 [I-D.templin-6man-omni] if it wants the new Proxy/Server to notify 3383 any old Proxy/Servers from which the Client is departing. 3385 When the new FHS Proxy/Server receives the Client's RS message, it 3386 returns an RA as specified in Section 3.12.3 and sends RS messages to 3387 any old Proxy/Servers listed in OMNI option MS-Release identifiers. 3388 When the new Proxy/Server sends an RS message, it sets the source to 3389 the MNP-LLA of the Client and sets the destination to the ADM-LLA of 3390 the old Proxy/Server. The new Proxy/Server also includes an OMNI 3391 option with Preflen set to the prefix length associated with the 3392 Client's MNP-LLA, with Interface Attributes for its INET underlying 3393 interface, and with the OMNI header S/T-omIndex set to 0. The new 3394 Proxy/Server then encapsulates the message in an OAL header with 3395 source set to its own ADM-ULA and destination set to the ADM-ULA of 3396 the old Proxy/Server and sends the message into the secured spanning 3397 tree. 3399 When an old Proxy/Server receives the RS, it notices that the message 3400 appears to have originated from the Client's MNP-LLA but that it 3401 includes an Interface Attributes sub-option for the new Proxy/Server 3402 and with S/T-omIndex set to 0. The old Proxy/Server then changes the 3403 Client's NCE state to DEPARTED, sets the FMT/SRT/LHS/L2ADDR 3404 information for the Client to point to the new Proxy/Server, and 3405 resets DepartTime. The old Proxy/Server then returns an RA message 3406 with zero Router Lifetime via the secured spanning tree by reversing 3407 the LLA and ULA addresses found in the RS message. After a short 3408 delay (e.g., 2 seconds) the old Proxy/Server withdraws the Client's 3409 MNP from the routing system. After DepartTime expires, the old 3410 Proxy/Server deletes the Client's NCE. 3412 The old Proxy/Server also iteratively sends uNA messages to each ROS 3413 in the Client's Report List with OAL source address set to the ADM- 3414 ULA of the new Proxy/Server and OAL destination address set to the 3415 ULA of the ROS. When the ROS receives the uNA, it examines the uNA 3416 Target Address to locate the target Client's NCE and the LLA source 3417 address to identify the old Proxy/Server. The ROS then caches the 3418 ULA source address as the ADM-{LLA/ULA} for the new Proxy/Server for 3419 this target NCE and marks the entry as STALE. While in the STALE 3420 state, the ROS sends new NS(AR) messages using its own ULA as the OAL 3421 source and the ADM-ULA of the new Proxy/Server as the OAL destination 3422 address. The new Proxy/Server will then process the NS(AR) and 3423 return an NA(AR) response. 3425 Clients SHOULD NOT move rapidly between Proxy/Servers in order to 3426 avoid causing excessive oscillations in the AERO routing system. 3427 Examples of when a Client might wish to change to a different Proxy/ 3428 Server include a Proxy/Server that has gone unreachable, topological 3429 movements of significant distance, movement to a new geographic 3430 region, movement to a new OMNI link segment, etc. 3432 3.17. Multicast 3434 The AERO Client provides an IGMP (IPv4) [RFC2236] or MLD (IPv6) 3435 [RFC3810] proxy service for its EUNs and/or hosted applications 3436 [RFC4605]. Proxy/Servers act as a Protocol Independent Multicast - 3437 Sparse-Mode (PIM-SM, or simply "PIM") Designated Router (DR) 3439 [RFC7761]. AERO Relays also act as PIM routers (i.e., the same as 3440 AERO Proxys/Servers) on behalf of nodes on INET/EUN networks. 3442 Clients on ANET underlying interfaces for which the ANET has deployed 3443 native multicast services forward IGMP/MLD messages into the ANET. 3444 The IGMP/MLD messages may be further forwarded by a first-hop ANET 3445 access router acting as an IGMP/MLD-snooping switch [RFC4541], then 3446 ultimately delivered to an ANET FHS Proxy/Server. 3448 Clients on ANET underlying interfaces without native multicast 3449 services instead send NS(AR) messages to cause their FHS Proxy/Server 3450 to act as an ROS and forward the message to an LHS Proxy/Server ROR. 3451 Clients on INET interfaces act as an ROS on their own behalf and 3452 forward NS(AR) messages directly to the LHS Proxy/Server ROR (i.e., 3453 via the FHS Proxy/Server as a proxy). When the Client receives an 3454 NA(AR) response, it initiates PIM protocol messaging according to the 3455 Source-Specific Multicast (SSM) and Any-Source Multicast (ASM) 3456 operational modes as discussed in the following sections. 3458 3.17.1. Source-Specific Multicast (SSM) 3460 When an ROS "X" (i.e., either a ROS Client or its FHS Proxy Server) 3461 acting as PIM router receives a Join/Prune message from a node on its 3462 downstream interfaces containing one or more ((S)ource, (G)roup) 3463 pairs, it updates its Multicast Routing Information Base (MRIB) 3464 accordingly. For each S belonging to a prefix reachable via X's non- 3465 OMNI interfaces, X then forwards the (S, G) Join/Prune to any PIM 3466 routers on those interfaces per [RFC7761]. 3468 For each S belonging to a prefix reachable via X's OMNI interface, X 3469 sends an NS(AR) message (see: Section 3.14) using its own LLA as the 3470 source address and the LLA of S as the destination address. X then 3471 encapsulates the NS(AR) in an OAL header with source address set to 3472 the ULA of X and destination address set to the solicited node 3473 multicast address for S, then forwards the message into the secured 3474 spanning tree, which delivers it to ROR "Y" that services S. The 3475 resulting NA(AR) will return the LLA for the prefix that matches S as 3476 the network-layer source address and with an OMNI option with 3477 interface attributes for any underlying interfaces that are currently 3478 servicing S. 3480 When X processes the NA(AR) it selects one or more underlying 3481 interfaces for S and performs an NS/NA(WIN) exchange while including 3482 a PIM Join/Prune message for each multicast group of interest in the 3483 OMNI option. If S is located behind any Proxys "Z"*, each Z* then 3484 updates its MRIB accordingly and maintains the LLA of X as the next 3485 hop in the reverse path. Since the Bridges do not examine network 3486 layer control messages, this means that the (reverse) multicast tree 3487 path is simply from each Z* (and/or S) to X with no other multicast- 3488 aware routers in the path. 3490 Following the initial combined Join/Prune and NS/NA messaging, X 3491 maintains a NCE for each S the same as if X was sending unicast data 3492 traffic to S. In particular, X performs additional NS/NA exchanges 3493 to keep the NCE alive for up to t_periodic seconds [RFC7761]. If no 3494 new Joins are received within t_periodic seconds, X allows the NCE to 3495 expire. Finally, if X receives any additional Join/Prune messages 3496 for (S,G) it forwards the messages over the secured spanning tree. 3498 At some later time, Client C that holds an MNP for source S may 3499 depart from a first Proxy/Server Z1 and/or connect via a new Proxy/ 3500 Server Z2. In that case, Y sends a uNA message to X the same as 3501 specified for unicast mobility in Section 3.16. When X receives the 3502 uNA message, it updates its NCE for the LLA for source S and sends 3503 new Join messages to any new Proxys Z2. There is no requirement to 3504 send any Prune messages to old Proxy/Server Z1 since source S will no 3505 longer source any multicast data traffic via Z1. Instead, the 3506 multicast state for (S,G) in Proxy/Server Z1 will soon time out since 3507 no new Joins will arrive. 3509 After some later time, C may move to a new Proxy/Server Y2 and depart 3510 from old Sever Y1. In that case, Y1 sends Join messages for any of 3511 C's active (S,G) groups to Y2 while including its own LLA as the 3512 source address. This causes Y2 to include Y1 in the multicast 3513 forwarding tree during the interim time that Y1's NCE for C is in the 3514 DEPARTED state. At the same time, Y1 sends a uNA message to X with 3515 an OMNI option with S/T-omIndex set to 0 and a release indication to 3516 cause X to release its NCE for S. X then sends a new Join message to 3517 S via the secured spanning tree and re-initiates route optimization 3518 the same as if it were receiving a fresh Join message from a node on 3519 a downstream link. 3521 3.17.2. Any-Source Multicast (ASM) 3523 When an ROS X acting as a PIM router receives a Join/Prune from a 3524 node on its downstream interfaces containing one or more (*,G) pairs, 3525 it updates its Multicast Routing Information Base (MRIB) accordingly. 3526 X then forwards a copy of the message within the OMNI option of an 3527 NS(WIN) message to the Rendezvous Point (RP) R for each G over the 3528 secured spanning tree. X uses its own LLA as the source address and 3529 the LLA for R as the destination address, then encapsulates the 3530 NS(WIN) message in an OAL header with source address set to the ULA 3531 of X and destination address set to the ULA of R's Proxy/Server then 3532 sends the message into the secured spanning tree. 3534 For each source S that sends multicast traffic to group G via R, the 3535 Proxy/Server Z* for the Client that aggregates S encapsulates the 3536 original IP packets in PIM Register messages and forwards them to R 3537 via the secured spanning tree, which may then elect to send a PIM 3538 Join to Z*. This will result in an (S,G) tree rooted at Z* with R as 3539 the next hop so that R will begin to receive two copies of the 3540 original IP packet; one native copy from the (S, G) tree and a second 3541 copy from the pre-existing (*, G) tree that still uses PIM Register 3542 encapsulation. R can then issue a PIM Register-stop message to 3543 suppress the Register-encapsulated stream. At some later time, if C 3544 moves to a new Proxy/Server Z*, it resumes sending original IP 3545 packets via PIM Register encapsulation via the new Z*. 3547 At the same time, as multicast listeners discover individual S's for 3548 a given G, they can initiate an (S,G) Join for each S under the same 3549 procedures discussed in Section 3.17.1. Once the (S,G) tree is 3550 established, the listeners can send (S, G) Prune messages to R so 3551 that multicast original IP packets for group G sourced by S will only 3552 be delivered via the (S, G) tree and not from the (*, G) tree rooted 3553 at R. All mobility considerations discussed for SSM apply. 3555 3.17.3. Bi-Directional PIM (BIDIR-PIM) 3557 Bi-Directional PIM (BIDIR-PIM) [RFC5015] provides an alternate 3558 approach to ASM that treats the Rendezvous Point (RP) as a Designated 3559 Forwarder (DF). Further considerations for BIDIR-PIM are out of 3560 scope. 3562 3.18. Operation over Multiple OMNI Links 3564 An AERO Client can connect to multiple OMNI links the same as for any 3565 data link service. In that case, the Client maintains a distinct 3566 OMNI interface for each link, e.g., 'omni0' for the first link, 3567 'omni1' for the second, 'omni2' for the third, etc. Each OMNI link 3568 would include its own distinct set of Bridges and Proxy/Servers, 3569 thereby providing redundancy in case of failures. 3571 Each OMNI link could utilize the same or different ANET connections. 3572 The links can be distinguished at the link-layer via the SRT prefix 3573 in a similar fashion as for Virtual Local Area Network (VLAN) tagging 3574 (e.g., IEEE 802.1Q) and/or through assignment of distinct sets of 3575 MSPs on each link. This gives rise to the opportunity for supporting 3576 multiple redundant networked paths (see: Section 3.2.5). 3578 The Client's IP layer can select the outgoing OMNI interface 3579 appropriate for a given traffic profile while (in the reverse 3580 direction) correspondent nodes must have some way of steering their 3581 original IP packets destined to a target via the correct OMNI link. 3583 In a first alternative, if each OMNI link services different MSPs the 3584 Client can receive a distinct MNP from each of the links. IP routing 3585 will therefore assure that the correct OMNI link is used for both 3586 outbound and inbound traffic. This can be accomplished using 3587 existing technologies and approaches, and without requiring any 3588 special supporting code in correspondent nodes or Bridges. 3590 In a second alternative, if each OMNI link services the same MSP(s) 3591 then each link could assign a distinct "OMNI link Anycast" address 3592 that is configured by all Bridges on the link. Correspondent nodes 3593 can then perform Segment Routing to select the correct SRT, which 3594 will then direct the original IP packet over multiple hops to the 3595 target. 3597 3.19. DNS Considerations 3599 AERO Client MNs and INET correspondent nodes consult the Domain Name 3600 System (DNS) the same as for any Internetworking node. When 3601 correspondent nodes and Client MNs use different IP protocol versions 3602 (e.g., IPv4 correspondents and IPv6 MNs), the INET DNS must maintain 3603 A records for IPv4 address mappings to MNs which must then be 3604 populated in Relay NAT64 mapping caches. In that way, an IPv4 3605 correspondent node can send original IPv4 packets to the IPv4 address 3606 mapping of the target MN, and the Relay will translate the IPv4 3607 header and destination address into an IPv6 header and IPv6 3608 destination address of the MN. 3610 When an AERO Client registers with an AERO Proxy/Server, the Proxy/ 3611 Server can return the address(es) of DNS servers in RDNSS options 3612 [RFC6106]. The DNS server provides the IP addresses of other MNs and 3613 correspondent nodes in AAAA records for IPv6 or A records for IPv4. 3615 3.20. Transition/Coexistence Considerations 3617 OAL encapsulation ensures that dissimilar INET partitions can be 3618 joined into a single unified OMNI link, even though the partitions 3619 themselves may have differing protocol versions and/or incompatible 3620 addressing plans. However, a commonality can be achieved by 3621 incrementally distributing globally routable (i.e., native) IP 3622 prefixes to eventually reach all nodes (both mobile and fixed) in all 3623 OMNI link segments. This can be accomplished by incrementally 3624 deploying AERO Bridges on each INET partition, with each Bridge 3625 distributing its MNPs and/or discovering non-MNP IP GUA prefixes on 3626 its INET links. 3628 This gives rise to the opportunity to eventually distribute native IP 3629 addresses to all nodes, and to present a unified OMNI link view even 3630 if the INET partitions remain in their current protocol and 3631 addressing plans. In that way, the OMNI link can serve the dual 3632 purpose of providing a mobility/multilink service and a transition/ 3633 coexistence service. Or, if an INET partition is transitioned to a 3634 native IP protocol version and addressing scheme that is compatible 3635 with the OMNI link MNP-based addressing scheme, the partition and 3636 OMNI link can be joined by Bridges. 3638 Relays that connect INETs/EUNs with dissimilar IP protocol versions 3639 may need to employ a network address and protocol translation 3640 function such as NAT64 [RFC6146]. 3642 3.21. Detecting and Reacting to Proxy/Server and Bridge Failures 3644 In environments where rapid failure recovery is required, Proxy/ 3645 Servers and Bridges SHOULD use Bidirectional Forwarding Detection 3646 (BFD) [RFC5880]. Nodes that use BFD can quickly detect and react to 3647 failures so that cached information is re-established through 3648 alternate nodes. BFD control messaging is carried only over well- 3649 connected ground domain networks (i.e., and not low-end radio links) 3650 and can therefore be tuned for rapid response. 3652 Proxy/Servers and Bridges maintain BFD sessions in parallel with 3653 their BGP peerings. If a Proxy/Server or Bridge fails, BGP peers 3654 will quickly re-establish routes through alternate paths the same as 3655 for common BGP deployments. Similarly, Proxys maintain BFD sessions 3656 with their associated Bridges even though they do not establish BGP 3657 peerings with them. 3659 3.22. AERO Clients on the Open Internet 3661 AERO Clients that connect to the open Internet via INET interfaces 3662 can establish a VPN or direct link to securely connect to a FHS 3663 Proxy/Server in a "tethered" arrangement with all of the Client's 3664 traffic transiting the Proxy/Server which acts as a router. 3665 Alternatively, the Client can associate with an INET FHS Proxy/Server 3666 using UDP/IP encapsulation and control message securing services as 3667 discussed in the following sections. 3669 When a Client's OMNI interface enables an INET underlying interface, 3670 it first examines the INET address. For IPv4, the Client assumes it 3671 is on the open Internet if the INET address is not a special-use IPv4 3672 address per [RFC3330]. Similarly for IPv6, the Client assumes it is 3673 on the open Internet if the INET address is a Global Unicast Address 3674 (GUA) [RFC4291]. Otherwise, the Client should assume it is behind 3675 one or several NATs. 3677 The Client then prepares an RS message with IPv6 source address set 3678 to its MNP-LLA, with IPv6 destination set to (link-local) All-Routers 3679 multicast and with an OMNI option with underlying interface 3680 attributes. If the Client believes that it is on the open Internet, 3681 it SHOULD include its IP address and UDP port number in the Interface 3682 Attributes sub-option corresponding to the underlying interface 3683 (otherwise it may omit the FMT/SRT/LHS/L2ADDR fields). If the 3684 underlying address is IPv4, the Client includes the Port Number and 3685 IPv4 address written in obfuscated form [RFC4380] as discussed in 3686 Section 3.3. If the underlying interface address is IPv6, the Client 3687 instead includes the Port Number and IPv6 address in obfuscated form. 3688 The Client finally includes an authentication signature per 3689 [I-D.templin-6man-omni] to provide message authentication, selects an 3690 Identification value and window synchronization parameters, and 3691 submits the RS for OAL encapsulation. The Client then encapsulates 3692 the OAL fragment in UDP/IP headers to form a carrier packet, sets the 3693 UDP/IP source to its INET address and UDP port, sets the UDP/IP 3694 destination to the FHS Proxy/Server's INET address and the AERO 3695 service port number (8060), then sends the carrier packet to the 3696 Proxy/Server. 3698 When the FHS Proxy/Server receives the RS, it discards the OAL 3699 encapsulation, authenticates the RS message, creates a NCE and 3700 registers the Client's MNP, window synchronization state and INET 3701 interface information according to the OMNI option parameters. If 3702 the Interface Attributes sub-option includes an L2ADDR, the Proxy/ 3703 Server compares the encapsulation IP address and UDP port number with 3704 the (unobfuscated) values. If the values are the same, the Proxy/ 3705 Server caches the Client's information as an "INET" address meaning 3706 that the Client is likely to accept direct messages without requiring 3707 NAT traversal exchanges. If the values are different (or, if the 3708 OMNI option did not include an L2ADDR) the Proxy/Server instead 3709 caches the Client's information as a "mapped" address meaning that 3710 NAT traversal exchanges may be necessary. 3712 The FHS Proxy/Server then prepares an RA message with IPv6 source and 3713 destination set corresponding to the addresses in the RS, and with an 3714 OMNI option with an Origin Indication sub-option per 3715 [I-D.templin-6man-omni] with the mapped and obfuscated Port Number 3716 and IP address observed in the encapsulation headers. The Proxy/ 3717 Server also includes an Interface Attributes sub-option with omIndex 3718 0 and FMT/SRT/LHS/L2ADDR information appropriate for its INET 3719 interface, an authentication signature sub-option per 3720 [I-D.templin-6man-omni] and/or a symmetric window synchronization/ 3721 acknowledgement if necessary. The Proxy/Server then performs OAL 3722 encapsulation and fragmentation if necessary and encapsulates each 3723 fragment in UDP/IP headers with addresses set per the L2ADDR 3724 information in the NCE for the Client. 3726 When the Client receives the RA, it authenticates the message then 3727 process the window synchronization/acknowledgement and compares the 3728 mapped Port Number and IP address from the Origin Indication sub- 3729 option with its own address. If the addresses are the same, the 3730 Client assumes the open Internet / Cone NAT principle; if the 3731 addresses are different, the Client instead assumes that further 3732 qualification procedures are necessary to detect the type of NAT and 3733 proceeds according to standard procedures [RFC6081][RFC4380]. The 3734 Client also caches the RA Interface Attributes FMT/SRT/LHS/L2ADDR 3735 information to discover the Proxy/Server's spanning tree orientation. 3736 The Client finally arranges to return an explicit/implicit 3737 acknowledgement, and sends periodic RS messages to receive fresh RA 3738 messages before the Router Lifetime received on each INET interface 3739 expires. 3741 When the Client sends messages to target IP addresses, it also 3742 invokes route optimization per Section 3.14. For route optimized 3743 targets in the same OMNI link segment, if the target's L2ADDR is on 3744 the open INET, the Client forwards carrier packets directly to the 3745 target INET address. If the target is behind a NAT, the Client first 3746 establishes NAT state for the L2ADDR using the "direct bubble" and 3747 NUD mechanisms discussed in Section 3.10.1. The Client continues to 3748 send carrier packets via its Proxy/Server until NAT state is 3749 populated, then begins forwarding carrier packets via the direct path 3750 through the NAT to the target. For targets in different OMNI link 3751 segments, the Client uses OAL/ORH encapsulation and forwards carrier 3752 packets to the Bridge that returned the NA(AR) message. 3754 The Client can send original IP packets to route-optimized neighbors 3755 in the same OMNI link segment no larger than the minimum/path MPS in 3756 one piece and with OAL encapsulation as atomic fragments. For larger 3757 original IP packets, the Client applies OAL encapsulation then 3758 fragments if necessary according to Section 3.9, with OAL header with 3759 source set to its own MNP-ULA and destination set to the MNP-ULA of 3760 the target, and with an in-window Identification value. The Client 3761 then encapsulates each resulting carrier packet in UDP/IP *NET 3762 headers and sends them to the next hop. 3764 Note: The NAT traversal procedures specified in this document are 3765 applicable for Cone, Address-Restricted and Port-Restricted NATs 3766 only. While future updates to this document may specify procedures 3767 for other NAT variations (e.g., hairpinning and various forms of 3768 Symmetric NATs), it should be noted that continuous communications 3769 are always possible through Proxy/Server forwarding even for these 3770 other NAT variations. 3772 3.23. Time-Varying MNPs 3774 In some use cases, it is desirable, beneficial and efficient for the 3775 Client to receive a constant MNP that travels with the Client 3776 wherever it moves. For example, this would allow air traffic 3777 controllers to easily track aircraft, etc. In other cases, however 3778 (e.g., intelligent transportation systems), the MN may be willing to 3779 sacrifice a modicum of efficiency in order to have time-varying MNPs 3780 that can be changed every so often to defeat adversarial tracking. 3782 The DHCPv6 service offers a way for Clients that desire time-varying 3783 MNPs to obtain short-lived prefixes (e.g., on the order of a small 3784 number of minutes). In that case, the identity of the Client would 3785 not be bound to the MNP but rather to a Node Identification value 3786 (see: [I-D.templin-6man-omni]) to be used as the Client ID seed for 3787 MNP prefix delegation. The Client would then be obligated to 3788 renumber its internal networks whenever its MNP (and therefore also 3789 its MNP-LLA) changes. This should not present a challenge for 3790 Clients with automated network renumbering services, however presents 3791 limits for the durations of ongoing sessions that would prefer to use 3792 a constant address. 3794 4. Implementation Status 3796 An early AERO implementation based on OpenVPN (https://openvpn.net/) 3797 was announced on the v6ops mailing list on January 10, 2018 and an 3798 initial public release of the AERO proof-of-concept source code was 3799 announced on the intarea mailing list on August 21, 2015. 3801 AERO Release-3.2 was tagged on March 30, 2021, and is undergoing 3802 internal testing. Additional internal releases expected within the 3803 coming months, with first public release expected end of 1H2021. 3805 Many AERO/OMNI functions are implemented and undergoing final 3806 integration. OAL fragmentation/reassembly buffer management code has 3807 been cleared for public release and will be presented at the June 3808 2021 ICAO mobility subgroup meeting. 3810 5. IANA Considerations 3812 The IANA is instructed to assign a new type value TBD1 in the IPv6 3813 Routing Types registry (IANA registration procedure is IETF Review or 3814 IESG Approval). 3816 The IANA has assigned the UDP port number "8060" for an earlier 3817 experimental first version of AERO [RFC6706]. This document together 3818 with [I-D.templin-6man-omni] reclaims UDP port number "8060" for 3819 'aero' as the service port for UDP/IP encapsulation. This document 3820 makes no request of IANA, since [I-D.templin-6man-omni] already 3821 provides instructions. (Note: although [RFC6706] was not widely 3822 implemented or deployed, it need not be obsoleted since its messages 3823 use the invalid ICMPv6 message type number '0' which implementations 3824 of this specification can easily distinguish and ignore.) 3826 No further IANA actions are required. 3828 6. Security Considerations 3830 AERO Bridges configure secured tunnels with AERO Proxy/Servers and 3831 Relays within their local OMNI link segments. Applicable secured 3832 tunnel alternatives include IPsec [RFC4301], TLS/SSL [RFC8446], DTLS 3833 [RFC6347], WireGuard [WG], etc. The AERO Bridges of all OMNI link 3834 segments in turn configure secured tunnels for their neighboring AERO 3835 Bridges in a secured spanning tree topology. Therefore, control 3836 messages exchanged between any pair of OMNI link neighbors over the 3837 secured spanning tree are already protected. 3839 To prevent spoofing vectors, Proxy/Servers MUST discard without 3840 responding to any unsecured NS(AR) messages. Also, Proxy/Servers 3841 MUST discard without forwarding any original IP packets received from 3842 one of their own Clients (whether directly or following OAL 3843 reassembly) with a source address that does not match the Client's 3844 MNP and/or a destination address that does match the Client's MNP. 3845 Finally, Proxy/Servers MUST discard without forwarding any carrier 3846 packets with an OAL source and destination that both match the same 3847 MNP (i.e., after consulting the ORH if present). 3849 For INET partitions that require strong security in the data plane, 3850 two options for securing communications include 1) disable route 3851 optimization so that all traffic is conveyed over secured tunnels, or 3852 2) enable on-demand secure tunnel creation between Client neighbors. 3853 Option 1) would result in longer routes than necessary and impose 3854 traffic concentration on critical infrastructure elements. Option 2) 3855 could be coordinated between Clients using NS/NA messages with OMNI 3856 Host Identity Protocol (HIP) "Initiator/Responder" message sub- 3857 options [RFC7401][I-D.templin-6man-omni] to create a secured tunnel 3858 on-demand. 3860 AERO Clients that connect to secured ANETs need not apply security to 3861 their ND messages, since the messages will be authenticated and 3862 forwarded by a perimeter Proxy/Server that applies security on its 3863 INET-facing interface as part of the spanning tree (see above). AERO 3864 Clients connected to the open INET can use network and/or transport 3865 layer security services such as VPNs or can by some other means 3866 establish a direct link to a Proxy/Server. When a VPN or direct link 3867 may be impractical, however, INET Clients and Proxy/Servers SHOULD 3868 include and verify authentication signatures for their IPv6 ND 3869 messages as specified in [I-D.templin-6man-omni]. 3871 Application endpoints SHOULD use transport-layer (or higher-layer) 3872 security services such as TLS/SSL, DTLS or SSH [RFC4251] to assure 3873 the same level of protection as for critical secured Internet 3874 services. AERO Clients that require host-based VPN services SHOULD 3875 use network and/or transport layer security services such as IPsec, 3876 TLS/SSL, DTLS, etc. AERO Proxys and Proxy/Servers can also provide a 3877 network-based VPN service on behalf of the Client, e.g., if the 3878 Client is located within a secured enclave and cannot establish a VPN 3879 on its own behalf. 3881 AERO Proxy/Servers and Bridges present targets for traffic 3882 amplification Denial of Service (DoS) attacks. This concern is no 3883 different than for widely-deployed VPN security gateways in the 3884 Internet, where attackers could send spoofed packets to the gateways 3885 at high data rates. This can be mitigated through the AERO/OMNI data 3886 origin authentication procedures, as well as connecting Proxy/Servers 3887 and Bridges over dedicated links with no connections to the Internet 3888 and/or when connections to the Internet are only permitted through 3889 well-managed firewalls. Traffic amplification DoS attacks can also 3890 target an AERO Client's low data rate links. This is a concern not 3891 only for Clients located on the open Internet but also for Clients in 3892 secured enclaves. AERO Proxy/Servers and Proxys can institute rate 3893 limits that protect Clients from receiving packet floods that could 3894 DoS low data rate links. 3896 AERO Relays must implement ingress filtering to avoid a spoofing 3897 attack in which spurious messages with ULA addresses are injected 3898 into an OMNI link from an outside attacker. AERO Clients MUST ensure 3899 that their connectivity is not used by unauthorized nodes on their 3900 EUNs to gain access to a protected network, i.e., AERO Clients that 3901 act as routers MUST NOT provide routing services for unauthorized 3902 nodes. (This concern is no different than for ordinary hosts that 3903 receive an IP address delegation but then "share" the address with 3904 other nodes via some form of Internet connection sharing such as 3905 tethering.) 3907 The MAP list MUST be well-managed and secured from unauthorized 3908 tampering, even though the list contains only public information. 3909 The MAP list can be conveyed to the Client in a similar fashion as in 3910 [RFC5214] (e.g., through layer 2 data link login messaging, secure 3911 upload of a static file, DNS lookups, etc.). 3913 The AERO service for open INET Clients depends on a public key 3914 distribution service in which Client public keys and identities are 3915 maintained in a shared database accessible to all open INET Proxy/ 3916 Servers. Similarly, each Client must be able to determine the public 3917 key of each Proxy/Server, e.g. by consulting an online database. 3918 When AERO nodes register their public keys indexed by a unique Host 3919 Identity Tag (HIT) [RFC7401] in a distributed database such as the 3920 DNS, and use the HIT as an identity for applying IPv6 ND message 3921 authentication signatures, a means for determining public key 3922 attestation is available. 3924 Security considerations for IPv6 fragmentation and reassembly are 3925 discussed in [I-D.templin-6man-omni]. In environments where spoofing 3926 is considered a threat, OMNI nodes SHOULD employ Identification 3927 window synchronization and OAL destinations SHOULD configure an (end- 3928 system-based) firewall. 3930 SRH authentication facilities are specified in [RFC8754]. Security 3931 considerations for accepting link-layer ICMP messages and reflected 3932 packets are discussed throughout the document. 3934 7. Acknowledgements 3936 Discussions in the IETF, aviation standards communities and private 3937 exchanges helped shape some of the concepts in this work. 3938 Individuals who contributed insights include Mikael Abrahamsson, Mark 3939 Andrews, Fred Baker, Bob Braden, Stewart Bryant, Scott Burleigh, 3940 Brian Carpenter, Wojciech Dec, Pavel Drasil, Ralph Droms, Adrian 3941 Farrel, Nick Green, Sri Gundavelli, Brian Haberman, Bernhard Haindl, 3942 Joel Halpern, Tom Herbert, Bob Hinden, Sascha Hlusiak, Lee Howard, 3943 Christian Huitema, Zdenek Jaron, Andre Kostur, Hubert Kuenig, Ted 3944 Lemon, Andy Malis, Satoru Matsushima, Tomek Mrugalski, Thomas Narten, 3945 Madhu Niraula, Alexandru Petrescu, Behcet Saikaya, Michal Skorepa, 3946 Dave Thaler, Joe Touch, Bernie Volz, Ryuji Wakikawa, Tony Whyman, 3947 Lloyd Wood and James Woodyatt. Members of the IESG also provided 3948 valuable input during their review process that greatly improved the 3949 document. Special thanks go to Stewart Bryant, Joel Halpern and 3950 Brian Haberman for their shepherding guidance during the publication 3951 of the AERO first edition. 3953 This work has further been encouraged and supported by Boeing 3954 colleagues including Kyle Bae, M. Wayne Benson, Dave Bernhardt, Cam 3955 Brodie, John Bush, Balaguruna Chidambaram, Irene Chin, Bruce Cornish, 3956 Claudiu Danilov, Don Dillenburg, Joe Dudkowski, Wen Fang, Samad 3957 Farooqui, Anthony Gregory, Jeff Holland, Seth Jahne, Brian Jaury, 3958 Greg Kimberly, Ed King, Madhuri Madhava Badgandi, Laurel Matthew, 3959 Gene MacLean III, Kyle Mikos, Rob Muszkiewicz, Sean O'Sullivan, Vijay 3960 Rajagopalan, Greg Saccone, Rod Santiago, Kent Shuey, Brian Skeen, 3961 Mike Slane, Carrie Spiker, Katie Tran, Brendan Williams, Amelia 3962 Wilson, Julie Wulff, Yueli Yang, Eric Yeh and other members of the 3963 Boeing mobility, networking and autonomy teams. Kyle Bae, Wayne 3964 Benson, Madhuri Madhava Badgandi, Vijayasarathy Rajagopalan, Katie 3965 Tran and Eric Yeh are especially acknowledged for their work on the 3966 AERO implementation. Chuck Klabunde is honored and remembered for 3967 his early leadership, and we mourn his untimely loss. 3969 This work was inspired by the support and encouragement of countless 3970 outstanding colleagues, managers and program directors over the span 3971 of many decades. Beginning in the late 1980s,' the Digital Equipment 3972 Corporation (DEC) Ultrix Engineering and DECnet Architects groups 3973 identified early issues with fragmentation and bridging links with 3974 diverse MTUs. In the early 1990s, engagements at DEC Project Sequoia 3975 at UC Berkeley and the DEC Western Research Lab in Palo Alto included 3976 investigations into large-scale networked filesystems, ATM vs 3977 Internet and network security proxies. In the mid-1990s to early 3978 2000s employment at the NASA Ames Research Center (Sterling Software) 3979 and SRI International supported early investigations of IPv6, ONR UAV 3980 Communications and the IETF. An employment at Nokia where important 3981 IETF documents were published gave way to a present-day engagement 3982 with The Boeing Company. The work matured at Boeing through major 3983 programs including Future Combat Systems, Advanced Airplane Program, 3984 DTN for the International Space Station, Mobility Vision Lab, CAST, 3985 Caravan, the NASA UAS/CNS program, the FAA/ICAO ATN/IPS program and 3986 many others. An attempt to name all who gave support and 3987 encouragement would double the current document size and result in 3988 many unintentional omissions - but to all a humble thanks. 3990 Earlier works on NBMA tunneling approaches are found in 3991 [RFC2529][RFC5214][RFC5569]. 3993 Many of the constructs presented in this second edition of AERO are 3994 based on the author's earlier works, including: 3996 o The Internet Routing Overlay Network (IRON) 3997 [RFC6179][I-D.templin-ironbis] 3999 o Virtual Enterprise Traversal (VET) 4000 [RFC5558][I-D.templin-intarea-vet] 4002 o The Subnetwork Encapsulation and Adaptation Layer (SEAL) 4003 [RFC5320][I-D.templin-intarea-seal] 4005 o AERO, First Edition [RFC6706] 4007 Note that these works cite numerous earlier efforts that are not also 4008 cited here due to space limitations. The authors of those earlier 4009 works are acknowledged for their insights. 4011 This work is aligned with the NASA Safe Autonomous Systems Operation 4012 (SASO) program under NASA contract number NNA16BD84C. 4014 This work is aligned with the FAA as per the SE2025 contract number 4015 DTFAWA-15-D-00030. 4017 This work is aligned with the Boeing Commercial Airplanes (BCA) 4018 Internet of Things (IoT) and autonomy programs. 4020 This work is aligned with the Boeing Information Technology (BIT) 4021 MobileNet program. 4023 8. References 4025 8.1. Normative References 4027 [I-D.templin-6man-omni] 4028 Templin, F. L. and T. Whyman, "Transmission of IP Packets 4029 over Overlay Multilink Network (OMNI) Interfaces", draft- 4030 templin-6man-omni-03 (work in progress), April 2021. 4032 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, 4033 DOI 10.17487/RFC0791, September 1981, 4034 . 4036 [RFC0792] Postel, J., "Internet Control Message Protocol", STD 5, 4037 RFC 792, DOI 10.17487/RFC0792, September 1981, 4038 . 4040 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 4041 Requirement Levels", BCP 14, RFC 2119, 4042 DOI 10.17487/RFC2119, March 1997, 4043 . 4045 [RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in 4046 IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473, 4047 December 1998, . 4049 [RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander, 4050 "SEcure Neighbor Discovery (SEND)", RFC 3971, 4051 DOI 10.17487/RFC3971, March 2005, 4052 . 4054 [RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)", 4055 RFC 3972, DOI 10.17487/RFC3972, March 2005, 4056 . 4058 [RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and 4059 More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191, 4060 November 2005, . 4062 [RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast 4063 Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005, 4064 . 4066 [RFC4380] Huitema, C., "Teredo: Tunneling IPv6 over UDP through 4067 Network Address Translations (NATs)", RFC 4380, 4068 DOI 10.17487/RFC4380, February 2006, 4069 . 4071 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 4072 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 4073 DOI 10.17487/RFC4861, September 2007, 4074 . 4076 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 4077 Address Autoconfiguration", RFC 4862, 4078 DOI 10.17487/RFC4862, September 2007, 4079 . 4081 [RFC6081] Thaler, D., "Teredo Extensions", RFC 6081, 4082 DOI 10.17487/RFC6081, January 2011, 4083 . 4085 [RFC7401] Moskowitz, R., Ed., Heer, T., Jokela, P., and T. 4086 Henderson, "Host Identity Protocol Version 2 (HIPv2)", 4087 RFC 7401, DOI 10.17487/RFC7401, April 2015, 4088 . 4090 [RFC7739] Gont, F., "Security Implications of Predictable Fragment 4091 Identification Values", RFC 7739, DOI 10.17487/RFC7739, 4092 February 2016, . 4094 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 4095 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 4096 May 2017, . 4098 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 4099 (IPv6) Specification", STD 86, RFC 8200, 4100 DOI 10.17487/RFC8200, July 2017, 4101 . 4103 [RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A., 4104 Richardson, M., Jiang, S., Lemon, T., and T. Winters, 4105 "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", 4106 RFC 8415, DOI 10.17487/RFC8415, November 2018, 4107 . 4109 8.2. Informative References 4111 [BGP] Huston, G., "BGP in 2015, http://potaroo.net", January 4112 2016. 4114 [I-D.bonica-6man-comp-rtg-hdr] 4115 Bonica, R., Kamite, Y., Alston, A., Henriques, D., and L. 4116 Jalil, "The IPv6 Compact Routing Header (CRH)", draft- 4117 bonica-6man-comp-rtg-hdr-24 (work in progress), January 4118 2021. 4120 [I-D.bonica-6man-crh-helper-opt] 4121 Li, X., Bao, C., Ruan, E., and R. Bonica, "Compressed 4122 Routing Header (CRH) Helper Option", draft-bonica-6man- 4123 crh-helper-opt-03 (work in progress), April 2021. 4125 [I-D.ietf-intarea-frag-fragile] 4126 Bonica, R., Baker, F., Huston, G., Hinden, R. M., Troan, 4127 O., and F. Gont, "IP Fragmentation Considered Fragile", 4128 draft-ietf-intarea-frag-fragile-17 (work in progress), 4129 September 2019. 4131 [I-D.ietf-intarea-tunnels] 4132 Touch, J. and M. Townsley, "IP Tunnels in the Internet 4133 Architecture", draft-ietf-intarea-tunnels-10 (work in 4134 progress), September 2019. 4136 [I-D.ietf-ipwave-vehicular-networking] 4137 (editor), J. (. J., "IPv6 Wireless Access in Vehicular 4138 Environments (IPWAVE): Problem Statement and Use Cases", 4139 draft-ietf-ipwave-vehicular-networking-20 (work in 4140 progress), March 2021. 4142 [I-D.ietf-rtgwg-atn-bgp] 4143 Templin, F. L., Saccone, G., Dawra, G., Lindem, A., and V. 4144 Moreno, "A Simple BGP-based Mobile Routing System for the 4145 Aeronautical Telecommunications Network", draft-ietf- 4146 rtgwg-atn-bgp-10 (work in progress), January 2021. 4148 [I-D.templin-6man-dhcpv6-ndopt] 4149 Templin, F. L., "A Unified Stateful/Stateless 4150 Configuration Service for IPv6", draft-templin-6man- 4151 dhcpv6-ndopt-11 (work in progress), January 2021. 4153 [I-D.templin-intarea-seal] 4154 Templin, F. L., "The Subnetwork Encapsulation and 4155 Adaptation Layer (SEAL)", draft-templin-intarea-seal-68 4156 (work in progress), January 2014. 4158 [I-D.templin-intarea-vet] 4159 Templin, F. L., "Virtual Enterprise Traversal (VET)", 4160 draft-templin-intarea-vet-40 (work in progress), May 2013. 4162 [I-D.templin-ipwave-uam-its] 4163 Templin, F. L., "Urban Air Mobility Implications for 4164 Intelligent Transportation Systems", draft-templin-ipwave- 4165 uam-its-04 (work in progress), January 2021. 4167 [I-D.templin-ironbis] 4168 Templin, F. L., "The Interior Routing Overlay Network 4169 (IRON)", draft-templin-ironbis-16 (work in progress), 4170 March 2014. 4172 [I-D.templin-v6ops-pdhost] 4173 Templin, F. L., "IPv6 Prefix Delegation and Multi- 4174 Addressing Models", draft-templin-v6ops-pdhost-27 (work in 4175 progress), January 2021. 4177 [OVPN] OpenVPN, O., "http://openvpn.net", October 2016. 4179 [RFC1035] Mockapetris, P., "Domain names - implementation and 4180 specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, 4181 November 1987, . 4183 [RFC1812] Baker, F., Ed., "Requirements for IP Version 4 Routers", 4184 RFC 1812, DOI 10.17487/RFC1812, June 1995, 4185 . 4187 [RFC2003] Perkins, C., "IP Encapsulation within IP", RFC 2003, 4188 DOI 10.17487/RFC2003, October 1996, 4189 . 4191 [RFC2004] Perkins, C., "Minimal Encapsulation within IP", RFC 2004, 4192 DOI 10.17487/RFC2004, October 1996, 4193 . 4195 [RFC2236] Fenner, W., "Internet Group Management Protocol, Version 4196 2", RFC 2236, DOI 10.17487/RFC2236, November 1997, 4197 . 4199 [RFC2464] Crawford, M., "Transmission of IPv6 Packets over Ethernet 4200 Networks", RFC 2464, DOI 10.17487/RFC2464, December 1998, 4201 . 4203 [RFC2529] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4 4204 Domains without Explicit Tunnels", RFC 2529, 4205 DOI 10.17487/RFC2529, March 1999, 4206 . 4208 [RFC2983] Black, D., "Differentiated Services and Tunnels", 4209 RFC 2983, DOI 10.17487/RFC2983, October 2000, 4210 . 4212 [RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition 4213 of Explicit Congestion Notification (ECN) to IP", 4214 RFC 3168, DOI 10.17487/RFC3168, September 2001, 4215 . 4217 [RFC3330] IANA, "Special-Use IPv4 Addresses", RFC 3330, 4218 DOI 10.17487/RFC3330, September 2002, 4219 . 4221 [RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener 4222 Discovery Version 2 (MLDv2) for IPv6", RFC 3810, 4223 DOI 10.17487/RFC3810, June 2004, 4224 . 4226 [RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally 4227 Unique IDentifier (UUID) URN Namespace", RFC 4122, 4228 DOI 10.17487/RFC4122, July 2005, 4229 . 4231 [RFC4251] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH) 4232 Protocol Architecture", RFC 4251, DOI 10.17487/RFC4251, 4233 January 2006, . 4235 [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A 4236 Border Gateway Protocol 4 (BGP-4)", RFC 4271, 4237 DOI 10.17487/RFC4271, January 2006, 4238 . 4240 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 4241 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 4242 2006, . 4244 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 4245 Internet Protocol", RFC 4301, DOI 10.17487/RFC4301, 4246 December 2005, . 4248 [RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery 4249 Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April 4250 2006, . 4252 [RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet 4253 Control Message Protocol (ICMPv6) for the Internet 4254 Protocol Version 6 (IPv6) Specification", STD 89, 4255 RFC 4443, DOI 10.17487/RFC4443, March 2006, 4256 . 4258 [RFC4511] Sermersheim, J., Ed., "Lightweight Directory Access 4259 Protocol (LDAP): The Protocol", RFC 4511, 4260 DOI 10.17487/RFC4511, June 2006, 4261 . 4263 [RFC4541] Christensen, M., Kimball, K., and F. Solensky, 4264 "Considerations for Internet Group Management Protocol 4265 (IGMP) and Multicast Listener Discovery (MLD) Snooping 4266 Switches", RFC 4541, DOI 10.17487/RFC4541, May 2006, 4267 . 4269 [RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick, 4270 "Internet Group Management Protocol (IGMP) / Multicast 4271 Listener Discovery (MLD)-Based Multicast Forwarding 4272 ("IGMP/MLD Proxying")", RFC 4605, DOI 10.17487/RFC4605, 4273 August 2006, . 4275 [RFC4982] Bagnulo, M. and J. Arkko, "Support for Multiple Hash 4276 Algorithms in Cryptographically Generated Addresses 4277 (CGAs)", RFC 4982, DOI 10.17487/RFC4982, July 2007, 4278 . 4280 [RFC5015] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano, 4281 "Bidirectional Protocol Independent Multicast (BIDIR- 4282 PIM)", RFC 5015, DOI 10.17487/RFC5015, October 2007, 4283 . 4285 [RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site 4286 Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214, 4287 DOI 10.17487/RFC5214, March 2008, 4288 . 4290 [RFC5320] Templin, F., Ed., "The Subnetwork Encapsulation and 4291 Adaptation Layer (SEAL)", RFC 5320, DOI 10.17487/RFC5320, 4292 February 2010, . 4294 [RFC5522] Eddy, W., Ivancic, W., and T. Davis, "Network Mobility 4295 Route Optimization Requirements for Operational Use in 4296 Aeronautics and Space Exploration Mobile Networks", 4297 RFC 5522, DOI 10.17487/RFC5522, October 2009, 4298 . 4300 [RFC5558] Templin, F., Ed., "Virtual Enterprise Traversal (VET)", 4301 RFC 5558, DOI 10.17487/RFC5558, February 2010, 4302 . 4304 [RFC5569] Despres, R., "IPv6 Rapid Deployment on IPv4 4305 Infrastructures (6rd)", RFC 5569, DOI 10.17487/RFC5569, 4306 January 2010, . 4308 [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 4309 (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, 4310 . 4312 [RFC6106] Jeong, J., Park, S., Beloeil, L., and S. Madanapalli, 4313 "IPv6 Router Advertisement Options for DNS Configuration", 4314 RFC 6106, DOI 10.17487/RFC6106, November 2010, 4315 . 4317 [RFC6139] Russert, S., Ed., Fleischman, E., Ed., and F. Templin, 4318 Ed., "Routing and Addressing in Networks with Global 4319 Enterprise Recursion (RANGER) Scenarios", RFC 6139, 4320 DOI 10.17487/RFC6139, February 2011, 4321 . 4323 [RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful 4324 NAT64: Network Address and Protocol Translation from IPv6 4325 Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146, 4326 April 2011, . 4328 [RFC6179] Templin, F., Ed., "The Internet Routing Overlay Network 4329 (IRON)", RFC 6179, DOI 10.17487/RFC6179, March 2011, 4330 . 4332 [RFC6221] Miles, D., Ed., Ooghe, S., Dec, W., Krishnan, S., and A. 4333 Kavanagh, "Lightweight DHCPv6 Relay Agent", RFC 6221, 4334 DOI 10.17487/RFC6221, May 2011, 4335 . 4337 [RFC6273] Kukec, A., Krishnan, S., and S. Jiang, "The Secure 4338 Neighbor Discovery (SEND) Hash Threat Analysis", RFC 6273, 4339 DOI 10.17487/RFC6273, June 2011, 4340 . 4342 [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer 4343 Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, 4344 January 2012, . 4346 [RFC6355] Narten, T. and J. Johnson, "Definition of the UUID-Based 4347 DHCPv6 Unique Identifier (DUID-UUID)", RFC 6355, 4348 DOI 10.17487/RFC6355, August 2011, 4349 . 4351 [RFC6438] Carpenter, B. and S. Amante, "Using the IPv6 Flow Label 4352 for Equal Cost Multipath Routing and Link Aggregation in 4353 Tunnels", RFC 6438, DOI 10.17487/RFC6438, November 2011, 4354 . 4356 [RFC6706] Templin, F., Ed., "Asymmetric Extended Route Optimization 4357 (AERO)", RFC 6706, DOI 10.17487/RFC6706, August 2012, 4358 . 4360 [RFC6935] Eubanks, M., Chimento, P., and M. Westerlund, "IPv6 and 4361 UDP Checksums for Tunneled Packets", RFC 6935, 4362 DOI 10.17487/RFC6935, April 2013, 4363 . 4365 [RFC6936] Fairhurst, G. and M. Westerlund, "Applicability Statement 4366 for the Use of IPv6 UDP Datagrams with Zero Checksums", 4367 RFC 6936, DOI 10.17487/RFC6936, April 2013, 4368 . 4370 [RFC7333] Chan, H., Ed., Liu, D., Seite, P., Yokota, H., and J. 4371 Korhonen, "Requirements for Distributed Mobility 4372 Management", RFC 7333, DOI 10.17487/RFC7333, August 2014, 4373 . 4375 [RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I., 4376 Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent 4377 Multicast - Sparse Mode (PIM-SM): Protocol Specification 4378 (Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March 4379 2016, . 4381 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 4382 Decraene, B., Litkowski, S., and R. Shakir, "Segment 4383 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 4384 July 2018, . 4386 [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol 4387 Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, 4388 . 4390 [RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J., 4391 Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header 4392 (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020, 4393 . 4395 [WG] Wireguard, "WireGuard, https://www.wireguard.com", August 4396 2020. 4398 Appendix A. Non-Normative Considerations 4400 AERO can be applied to a multitude of Internetworking scenarios, with 4401 each having its own adaptations. The following considerations are 4402 provided as non-normative guidance: 4404 A.1. Implementation Strategies for Route Optimization 4406 Route optimization as discussed in Section 3.14 results in the route 4407 optimization source (ROS) creating a NCE for the target neighbor. 4408 The NCE state is set to REACHABLE for at most ReachableTime seconds. 4409 In order to refresh the NCE lifetime before the ReachableTime timer 4410 expires, the specification requires implementations to issue a new 4411 NS/NA(AR) exchange to reset ReachableTime while data packets are 4412 still flowing. However, the decision of when to initiate a new NS/ 4413 NA(AR) exchange and to perpetuate the process is left as an 4414 implementation detail. 4416 One possible strategy may be to monitor the NCE watching for data 4417 packets for (ReachableTime - 5) seconds. If any data packets have 4418 been sent to the neighbor within this timeframe, then send an NS(AR) 4419 to receive a new NA(AR). If no data packets have been sent, wait for 4420 5 additional seconds and send an immediate NS(AR) if any data packets 4421 are sent within this "expiration pending" 5 second window. If no 4422 additional data packets are sent within the 5 second window, reset 4423 the NCE state to STALE. 4425 The monitoring of the neighbor data packet traffic therefore becomes 4426 an ongoing process during the NCE lifetime. If the NCE expires, 4427 future data packets will trigger a new NS/NA(AR) exchange while the 4428 packets themselves are delivered over a longer path until route 4429 optimization state is re-established. 4431 A.2. Implicit Mobility Management 4433 OMNI interface neighbors MAY provide a configuration option that 4434 allows them to perform implicit mobility management in which no ND 4435 messaging is used. In that case, the Client only transmits packets 4436 over a single interface at a time, and the neighbor always observes 4437 packets arriving from the Client from the same link-layer source 4438 address. 4440 If the Client's underlying interface address changes (either due to a 4441 readdressing of the original interface or switching to a new 4442 interface) the neighbor immediately updates the NCE for the Client 4443 and begins accepting and sending packets according to the Client's 4444 new address. This implicit mobility method applies to use cases such 4445 as cellphones with both WiFi and Cellular interfaces where only one 4446 of the interfaces is active at a given time, and the Client 4447 automatically switches over to the backup interface if the primary 4448 interface fails. 4450 A.3. Direct Underlying Interfaces 4452 When a Client's OMNI interface is configured over a Direct interface, 4453 the neighbor at the other end of the Direct link can receive packets 4454 without any encapsulation. In that case, the Client sends packets 4455 over the Direct link according to traffic selectors. If the Direct 4456 interface is selected, then the Client's IP packets are transmitted 4457 directly to the peer without going through an ANET/INET. If other 4458 interfaces are selected, then the Client's IP packets are transmitted 4459 via a different interface, which may result in the inclusion of 4460 Proxy/Servers and Bridges in the communications path. Direct 4461 interfaces must be tested periodically for reachability, e.g., via 4462 NUD. 4464 A.4. AERO Critical Infrastructure Considerations 4466 AERO Bridges can be either Commercial off-the Shelf (COTS) standard 4467 IP routers or virtual machines in the cloud. Bridges must be 4468 provisioned, supported and managed by the INET administrative 4469 authority, and connected to the Bridges of other INETs via inter- 4470 domain peerings. Cost for purchasing, configuring and managing 4471 Bridges is nominal even for very large OMNI links. 4473 AERO INET Proxy/Servers can be standard dedicated server platforms, 4474 but most often will be deployed as virtual machines in the cloud. 4475 The only requirements for INET Proxy/Servers are that they can run 4476 the AERO/OMNI code and have at least one network interface connection 4477 to the INET. INET Proxy/Servers must be provisioned, supported and 4478 managed by the INET administrative authority. Cost for purchasing, 4479 configuring and managing cloud Proxy/Servers is nominal especially 4480 for virtual machines. 4482 AERO ANET Proxy/Servers are most often standard dedicated server 4483 platforms with one underlying interface connected to the ANET and a 4484 second interface connected to an INET. As with INET Proxy/Servers, 4485 the only requirements are that they can run the AERO/OMNI code and 4486 have at least one interface connection to the INET. ANET Proxy/ 4487 Servers must be provisioned, supported and managed by the ANET 4488 administrative authority. Cost for purchasing, configuring and 4489 managing Proxys is nominal, and borne by the ANET administrative 4490 authority. 4492 AERO Relays are simply Proxy/Servers connected to INETs and/or EUNs 4493 that provide forwarding services for non-MNP destinations. The Relay 4494 connects to the OMNI link and engages in eBGP peering with one or 4495 more Bridges as a stub AS. The Relay then injects its MNPs and/or 4496 non-MNP prefixes into the BGP routing system, and provisions the 4497 prefixes to its downstream-attached networks. The Relay can perform 4498 ROS/ROR services the same as for any Proxy/Server, and can route 4499 between the MNP and non-MNP address spaces. 4501 A.5. AERO Server Failure Implications 4503 AERO Proxy/Servers may appear as a single point of failure in the 4504 architecture, but such is not the case since all Proxy/Servers on the 4505 link provide identical services and loss of a Proxy/Server does not 4506 imply immediate and/or comprehensive communication failures. Proxy/ 4507 Server failure is quickly detected and conveyed by Bidirectional 4508 Forward Detection (BFD) and/or proactive NUD allowing Clients to 4509 migrate to new Proxy/Servers. 4511 If a Proxy/Server fails, ongoing packet forwarding to Clients will 4512 continue by virtue of the neighbor cache entries that have already 4513 been established in route optimization sources (ROSs). If a Client 4514 also experiences mobility events at roughly the same time the Proxy/ 4515 Server fails, uNA messages may be lost but neighbor cache entries in 4516 the DEPARTED state will ensure that packet forwarding to the Client's 4517 new locations will continue for up to DepartTime seconds. 4519 If a Client is left without a Proxy/Server for a considerable length 4520 of time (e.g., greater than ReachableTime seconds) then existing 4521 neighbor cache entries will eventually expire and both ongoing and 4522 new communications will fail. The original source will continue to 4523 retransmit until the Client has established a new Proxy/Server 4524 relationship, after which time continuous communications will resume. 4526 Therefore, providing many Proxy/Servers on the link with high 4527 availability profiles provides resilience against loss of individual 4528 Proxy/Servers and assurance that Clients can establish new Proxy/ 4529 Server relationships quickly in event of a Proxy/Server failure. 4531 A.6. AERO Client / Server Architecture 4533 The AERO architectural model is client / server in the control plane, 4534 with route optimization in the data plane. The same as for common 4535 Internet services, the AERO Client discovers the addresses of AERO 4536 Proxy/Servers and connects to one or more of them. The AERO service 4537 is analogous to common Internet services such as google.com, 4538 yahoo.com, cnn.com, etc. However, there is only one AERO service for 4539 the link and all Proxy/Servers provide identical services. 4541 Common Internet services provide differing strategies for advertising 4542 server addresses to clients. The strategy is conveyed through the 4543 DNS resource records returned in response to name resolution queries. 4544 As of January 2020 Internet-based 'nslookup' services were used to 4545 determine the following: 4547 o When a client resolves the domainname "google.com", the DNS always 4548 returns one A record (i.e., an IPv4 address) and one AAAA record 4549 (i.e., an IPv6 address). The client receives the same addresses 4550 each time it resolves the domainname via the same DNS resolver, 4551 but may receive different addresses when it resolves the 4552 domainname via different DNS resolvers. But, in each case, 4553 exactly one A and one AAAA record are returned. 4555 o When a client resolves the domainname "ietf.org", the DNS always 4556 returns one A record and one AAAA record with the same addresses 4557 regardless of which DNS resolver is used. 4559 o When a client resolves the domainname "yahoo.com", the DNS always 4560 returns a list of 4 A records and 4 AAAA records. Each time the 4561 client resolves the domainname via the same DNS resolver, the same 4562 list of addresses are returned but in randomized order (i.e., 4563 consistent with a DNS round-robin strategy). But, interestingly, 4564 the same addresses are returned (albeit in randomized order) when 4565 the domainname is resolved via different DNS resolvers. 4567 o When a client resolves the domainname "amazon.com", the DNS always 4568 returns a list of 3 A records and no AAAA records. As with 4569 "yahoo.com", the same three A records are returned from any 4570 worldwide Internet connection point in randomized order. 4572 The above example strategies show differing approaches to Internet 4573 resilience and service distribution offered by major Internet 4574 services. The Google approach exposes only a single IPv4 and a 4575 single IPv6 address to clients. Clients can then select whichever IP 4576 protocol version offers the best response, but will always use the 4577 same IP address according to the current Internet connection point. 4578 This means that the IP address offered by the network must lead to a 4579 highly-available server and/or service distribution point. In other 4580 words, resilience is predicated on high availability within the 4581 network and with no client-initiated failovers expected (i.e., it is 4582 all-or-nothing from the client's perspective). However, Google does 4583 provide for worldwide distributed service distribution by virtue of 4584 the fact that each Internet connection point responds with a 4585 different IPv6 and IPv4 address. The IETF approach is like google 4586 (all-or-nothing from the client's perspective), but provides only a 4587 single IPv4 or IPv6 address on a worldwide basis. This means that 4588 the addresses must be made highly-available at the network level with 4589 no client failover possibility, and if there is any worldwide service 4590 distribution it would need to be conducted by a network element that 4591 is reached via the IP address acting as a service distribution point. 4593 In contrast to the Google and IETF philosophies, Yahoo and Amazon 4594 both provide clients with a (short) list of IP addresses with Yahoo 4595 providing both IP protocol versions and Amazon as IPv4-only. The 4596 order of the list is randomized with each name service query 4597 response, with the effect of round-robin load balancing for service 4598 distribution. With a short list of addresses, there is still 4599 expectation that the network will implement high availability for 4600 each address but in case any single address fails the client can 4601 switch over to using a different address. The balance then becomes 4602 one of function in the network vs function in the end system. 4604 The same implications observed for common highly-available services 4605 in the Internet apply also to the AERO client/server architecture. 4606 When an AERO Client connects to one or more ANETs, it discovers one 4607 or more AERO Proxy/Server addresses through the mechanisms discussed 4608 in earlier sections. Each Proxy/Server address presumably leads to a 4609 fault-tolerant clustering arrangement such as supported by Linux-HA, 4610 Extended Virtual Synchrony or Paxos. Such an arrangement has 4611 precedence in common Internet service deployments in lightweight 4612 virtual machines without requiring expensive hardware deployment. 4613 Similarly, common Internet service deployments set service IP 4614 addresses on service distribution points that may relay requests to 4615 many different servers. 4617 For AERO, the expectation is that a combination of the Google/IETF 4618 and Yahoo/Amazon philosophies would be employed. The AERO Client 4619 connects to different ANET access points and can receive 1-2 Proxy/ 4620 Server ADM-LLAs at each point. It then selects one AERO Proxy/Server 4621 address, and engages in RS/RA exchanges with the same Proxy/Server 4622 from all ANET connections. The Client remains with this Proxy/Server 4623 unless or until the Proxy/Server fails, in which case it can switch 4624 over to an alternate Proxy/Server. The Client can likewise switch 4625 over to a different Proxy/Server at any time if there is some reason 4626 for it to do so. So, the AERO expectation is for a balance of 4627 function in the network and end system, with fault tolerance and 4628 resilience at both levels. 4630 Appendix B. Change Log 4632 << RFC Editor - remove prior to publication >> 4634 Changes from draft-templin-6man-aero-16 to draft-templin-6man-aero- 4635 17: 4637 o Final editorial review pass resulting in multiple changes. 4638 Document now submit for final approval (with reference to rfcdiff 4639 from previous version). 4641 Changes from draft-templin-6man-aero-15 to draft-templin-6man-aero- 4642 16: 4644 o Final editorial review pass resulting in multiple changes. 4645 Document now submit for final approval (with reference to rfcdiff 4646 from previous version). 4648 Changes from draft-templin-6man-aero-14 to draft-templin-6man-aero- 4649 15: 4651 o Final editorial review pass resulting in multiple changes. 4652 Document now submit for final approval (with reference to rfcdiff 4653 from previous version). 4655 Changes from draft-templin-6man-aero-13 to draft-templin-6man-aero- 4656 14: 4658 o Final editorial review pass resulting in multiple changes. 4659 Document now submit for final approval (with reference to rfcdiff 4660 from previous version). 4662 Changes from draft-templin-6man-aero-12 to draft-templin-6man-aero- 4663 13: 4665 o Final editorial review pass resulting in multiple changes. 4666 Document now submit for final approval (with reference to rfcdiff 4667 from previous version). 4669 Changes from draft-templin-6man-aero-11 to draft-templin-6man-aero- 4670 12: 4672 o Final editorial review pass resulting in multiple changes. 4673 Document now submit for final approval (with reference to rfcdiff 4674 from previous version). 4676 Changes from draft-templin-6man-aero-10 to draft-templin-6man-aero- 4677 11: 4679 o Final editorial review pass resulting in multiple changes. 4680 Document now submit for final approval (with reference to rfcdiff 4681 from previous version). 4683 Changes from draft-templin-6man-aero-09 to draft-templin-6man-aero- 4684 10: 4686 o Final editorial review pass resulting in multiple changes. 4687 Document now submit for final approval (with reference to rfcdiff 4688 from previous version). 4690 Changes from draft-templin-6man-aero-08 to draft-templin-6man-aero- 4691 09: 4693 o Final editorial review pass resulting in multiple changes. 4694 Document now submit for final approval (with reference to rfcdiff 4695 from previous version). 4697 Changes from draft-templin-6man-aero-07 to draft-templin-6man-aero- 4698 08: 4700 o Final editorial review pass resulting in multiple changes. 4701 Document now submit for final approval (with reference to rfcdiff 4702 from previous version). 4704 Changes from draft-templin-6man-aero-06 to draft-templin-6man-aero- 4705 07: 4707 o Final editorial review pass resulting in multiple changes. 4708 Document now submit for final approval (with reference to rfcdiff 4709 from previous version). 4711 Changes from draft-templin-6man-aero-05 to draft-templin-6man-aero- 4712 06: 4714 o Final editorial review pass resulting in multiple changes. 4715 Document now submit for final approval. 4717 Changes from draft-templin-6man-aero-04 to draft-templin-6man-aero- 4718 05: 4720 o Changed to use traffic selectors instead of the former multilink 4721 selection strategy. 4723 Changes from draft-templin-6man-aero-03 to draft-templin-6man-aero- 4724 04: 4726 o Removed documents from "Obsoletes" list. 4728 o Introduced the concept of "secured" and "unsecured" spanning tree. 4730 o Additional security considerations. 4732 o Additional route optimization considerations. 4734 Changes from draft-templin-6man-aero-02 to draft-templin-6man-aero- 4735 03: 4737 o Support for extended route optimization from ROR to target over 4738 target's underlying interfaces. 4740 Changes from draft-templin-6man-aero-01 to draft-templin-6man-aero- 4741 02: 4743 o Changed reference citations to "draft-templin-6man-omni". 4745 o Several important updates to IPv6 ND cache states and route 4746 optimization message addressing. 4748 o Included introductory description of the "6M's". 4750 o Updated Multicast specification. 4752 Changes from draft-templin-6man-aero-00 to draft-templin-6man-aero- 4753 01: 4755 o Changed category to "Informational". 4757 o Updated implementation status. 4759 Changes from earlier versions to draft-templin-6man-aero-00: 4761 o Established working baseline reference. 4763 Author's Address 4765 Fred L. Templin (editor) 4766 Boeing Research & Technology 4767 P.O. Box 3707 4768 Seattle, WA 98124 4769 USA 4771 Email: fltemplin@acm.org