idnits 2.17.1 draft-templin-intarea-6706bis-27.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- == The 'Obsoletes: ' line in the draft header should list only the _numbers_ of the RFCs which will be obsoleted by this document (if approved); it should not include the word 'RFC' in the list. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (February 6, 2020) is 1541 days in the past. Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) -- Looks like a reference, but probably isn't: '1' on line 1036 -- Looks like a reference, but probably isn't: '2' on line 1040 == Missing Reference: 'N' is mentioned on line 1050, but not defined == Unused Reference: 'RFC2474' is defined on line 2994, but no explicit reference was found in the text == Unused Reference: 'I-D.ietf-intarea-gue-extensions' is defined on line 3064, but no explicit reference was found in the text == Unused Reference: 'I-D.ietf-intarea-tunnels' is defined on line 3069, but no explicit reference was found in the text == Unused Reference: 'RFC1191' is defined on line 3119, but no explicit reference was found in the text == Unused Reference: 'RFC2764' is defined on line 3144, but no explicit reference was found in the text == Unused Reference: 'RFC2923' is defined on line 3158, but no explicit reference was found in the text == Unused Reference: 'RFC3819' is defined on line 3176, but no explicit reference was found in the text == Unused Reference: 'RFC4607' is defined on line 3231, but no explicit reference was found in the text == Unused Reference: 'RFC4963' is defined on line 3235, but no explicit reference was found in the text == Unused Reference: 'RFC6864' is defined on line 3314, but no explicit reference was found in the text == Unused Reference: 'RFC7269' is defined on line 3318, but no explicit reference was found in the text == Unused Reference: 'RFC8086' is defined on line 3334, but no explicit reference was found in the text == Unused Reference: 'RFC8201' is defined on line 3338, but no explicit reference was found in the text == Outdated reference: A later version (-21) exists of draft-templin-atn-aero-interface-18 == Outdated reference: A later version (-15) exists of draft-ietf-dmm-distributed-mobility-anchoring-14 == Outdated reference: A later version (-13) exists of draft-ietf-intarea-tunnels-10 == Outdated reference: A later version (-26) exists of draft-ietf-rtgwg-atn-bgp-05 == Outdated reference: A later version (-11) exists of draft-templin-6man-dhcpv6-ndopt-09 == Outdated reference: A later version (-27) exists of draft-templin-v6ops-pdhost-25 -- Obsolete informational reference (is this intentional?): RFC 6106 (Obsoleted by RFC 8106) -- Obsolete informational reference (is this intentional?): RFC 6347 (Obsoleted by RFC 9147) Summary: 0 errors (**), 0 flaws (~~), 22 warnings (==), 5 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group F. Templin, Ed. 3 Internet-Draft Boeing Research & Technology 4 Obsoletes: rfc5320, rfc5558, rfc5720, February 6, 2020 5 rfc6179, rfc6706 (if 6 approved) 7 Intended status: Standards Track 8 Expires: August 9, 2020 10 Asymmetric Extended Route Optimization (AERO) 11 draft-templin-intarea-6706bis-27 13 Abstract 15 This document specifies the operation of IP over tunnel virtual links 16 using Asymmetric Extended Route Optimization (AERO). AERO interfaces 17 use an IPv6 link-local address format that supports operation of the 18 IPv6 Neighbor Discovery (ND) protocol and links ND to IP forwarding. 19 Prefix delegation/registration services are employed for network 20 admission and to manage the routing system. Multilink operation, 21 mobility management, quality of service (QoS) signaling and route 22 optimization are naturally supported through dynamic neighbor cache 23 updates. Standard IP multicasting services are also supported. AERO 24 is a widely-applicable mobile internetworking service especially 25 well-suited to aviation services, mobile Virtual Private Networks 26 (VPNs) and many other applications. 28 Status of This Memo 30 This Internet-Draft is submitted in full conformance with the 31 provisions of BCP 78 and BCP 79. 33 Internet-Drafts are working documents of the Internet Engineering 34 Task Force (IETF). Note that other groups may also distribute 35 working documents as Internet-Drafts. The list of current Internet- 36 Drafts is at https://datatracker.ietf.org/drafts/current/. 38 Internet-Drafts are draft documents valid for a maximum of six months 39 and may be updated, replaced, or obsoleted by other documents at any 40 time. It is inappropriate to use Internet-Drafts as reference 41 material or to cite them other than as "work in progress." 43 This Internet-Draft will expire on August 9, 2020. 45 Copyright Notice 47 Copyright (c) 2020 IETF Trust and the persons identified as the 48 document authors. All rights reserved. 50 This document is subject to BCP 78 and the IETF Trust's Legal 51 Provisions Relating to IETF Documents 52 (https://trustee.ietf.org/license-info) in effect on the date of 53 publication of this document. Please review these documents 54 carefully, as they describe your rights and restrictions with respect 55 to this document. Code Components extracted from this document must 56 include Simplified BSD License text as described in Section 4.e of 57 the Trust Legal Provisions and are provided without warranty as 58 described in the Simplified BSD License. 60 Table of Contents 62 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 63 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 64 3. Asymmetric Extended Route Optimization (AERO) . . . . . . . . 10 65 3.1. AERO Link Reference Model . . . . . . . . . . . . . . . . 10 66 3.2. AERO Node Types . . . . . . . . . . . . . . . . . . . . . 12 67 3.3. AERO Routing System . . . . . . . . . . . . . . . . . . . 13 68 3.3.1. IPv4 Compatibility Routing . . . . . . . . . . . . . 15 69 3.4. AERO Addresses . . . . . . . . . . . . . . . . . . . . . 15 70 3.5. Spanning Partitioned AERO Networks (SPAN) . . . . . . . . 17 71 3.5.1. SPAN Compatibility Addressing . . . . . . . . . . . . 21 72 3.5.2. Client SPAN Addresses . . . . . . . . . . . . . . . . 21 73 3.6. AERO Interface Characteristics . . . . . . . . . . . . . 21 74 3.7. AERO Interface Initialization . . . . . . . . . . . . . . 25 75 3.7.1. AERO Server/Gateway Behavior . . . . . . . . . . . . 25 76 3.7.2. AERO Proxy Behavior . . . . . . . . . . . . . . . . . 26 77 3.7.3. AERO Client Behavior . . . . . . . . . . . . . . . . 26 78 3.7.4. AERO Relay Behavior . . . . . . . . . . . . . . . . . 26 79 3.8. AERO Interface Neighbor Cache Maintenance . . . . . . . . 26 80 3.9. AERO Interface Encapsulation and Re-encapsulation . . . . 28 81 3.10. AERO Interface Decapsulation . . . . . . . . . . . . . . 30 82 3.11. AERO Interface Data Origin Authentication . . . . . . . . 30 83 3.12. AERO Interface MTU and Fragmentation . . . . . . . . . . 30 84 3.13. AERO Interface Forwarding Algorithm . . . . . . . . . . . 31 85 3.13.1. Client Forwarding Algorithm . . . . . . . . . . . . 32 86 3.13.2. Proxy Forwarding Algorithm . . . . . . . . . . . . . 32 87 3.13.3. Server/Gateway Forwarding Algorithm . . . . . . . . 33 88 3.13.4. Relay Forwarding Algorithm . . . . . . . . . . . . . 35 89 3.14. AERO Interface Error Handling . . . . . . . . . . . . . . 35 90 3.15. AERO Router Discovery, Prefix Delegation and 91 Autoconfiguration . . . . . . . . . . . . . . . . . . . . 38 92 3.15.1. AERO ND/PD Service Model . . . . . . . . . . . . . . 38 93 3.15.2. AERO Client Behavior . . . . . . . . . . . . . . . . 39 94 3.15.3. AERO Server Behavior . . . . . . . . . . . . . . . . 41 95 3.16. The AERO Proxy . . . . . . . . . . . . . . . . . . . . . 44 96 3.16.1. Detecting and Responding to Server Failures . . . . 46 97 3.17. AERO Route Optimization . . . . . . . . . . . . . . . . . 47 98 3.17.1. Route Optimization Initiation . . . . . . . . . . . 47 99 3.17.2. Relaying the NS . . . . . . . . . . . . . . . . . . 48 100 3.17.3. Processing the NS and Sending the NA . . . . . . . . 48 101 3.17.4. Relaying the NA . . . . . . . . . . . . . . . . . . 49 102 3.17.5. Processing the NA . . . . . . . . . . . . . . . . . 49 103 3.17.6. Route Optimization Maintenance . . . . . . . . . . . 49 104 3.18. Neighbor Unreachability Detection (NUD) . . . . . . . . . 50 105 3.19. Mobility Management and Quality of Service (QoS) . . . . 51 106 3.19.1. Mobility Update Messaging . . . . . . . . . . . . . 52 107 3.19.2. Announcing Link-Layer Address and/or QoS Preference 108 Changes . . . . . . . . . . . . . . . . . . . . . . 53 109 3.19.3. Bringing New Links Into Service . . . . . . . . . . 53 110 3.19.4. Removing Existing Links from Service . . . . . . . . 53 111 3.19.5. Moving to a New Server . . . . . . . . . . . . . . . 54 112 3.20. Multicast . . . . . . . . . . . . . . . . . . . . . . . . 55 113 3.20.1. Source-Specific Multicast (SSM) . . . . . . . . . . 55 114 3.20.2. Any-Source Multicast (ASM) . . . . . . . . . . . . . 57 115 3.20.3. Bi-Directional PIM (BIDIR-PIM) . . . . . . . . . . . 57 116 3.21. Operation over Multiple AERO Links (VLANs) . . . . . . . 57 117 3.22. DNS Considerations . . . . . . . . . . . . . . . . . . . 59 118 3.23. Transition Considerations . . . . . . . . . . . . . . . . 59 119 3.24. Detecting and Reacting to Server and Relay Failures . . . 60 120 4. Implementation Status . . . . . . . . . . . . . . . . . . . . 60 121 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 60 122 6. Security Considerations . . . . . . . . . . . . . . . . . . . 61 123 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 63 124 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 64 125 8.1. Normative References . . . . . . . . . . . . . . . . . . 64 126 8.2. Informative References . . . . . . . . . . . . . . . . . 65 127 Appendix A. AERO Alternate Encapsulations . . . . . . . . . . . 72 128 Appendix B. Non-Normative Considerations . . . . . . . . . . . . 74 129 B.1. Implementation Strategies for Route Optimization . . . . 74 130 B.2. Implicit Mobility Management . . . . . . . . . . . . . . 75 131 B.3. Direct Underlying Interfaces . . . . . . . . . . . . . . 75 132 B.4. AERO Clients on the Open Internetwork . . . . . . . . . . 75 133 B.5. Operation on AERO Links with /64 ASPs . . . . . . . . . . 76 134 B.6. AERO Adaptations for SEcure Neighbor Discovery (SEND) . . 76 135 B.7. AERO Critical Infrastructure Considerations . . . . . . . 77 136 B.8. AERO Server Failure Implications . . . . . . . . . . . . 78 137 B.9. AERO Client / Server Architecture . . . . . . . . . . . . 78 138 Appendix C. Change Log . . . . . . . . . . . . . . . . . . . . . 80 139 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 87 141 1. Introduction 143 Asymmetric Extended Route Optimization (AERO) fulfills the 144 requirements of Distributed Mobility Management (DMM) [RFC7333] and 145 route optimization [RFC5522] for aeronautical networking and other 146 network mobility use cases. AERO is based on a Non-Broadcast, 147 Multiple Access (NBMA) virtual link model known as the AERO link. 148 The AERO link is a virtual overlay configured over one or more 149 underlying Internetworks, and nodes on the link can exchange IP 150 packets via tunneling. Multilink operation allows for increased 151 reliability, bandwidth optimization and traffic path diversity. 153 The AERO service comprises Clients, Proxys, Servers and Gateways that 154 are seen as AERO link neighbors. Each node's AERO interface uses an 155 IPv6 link-local address format (known as the AERO address) that 156 supports operation of the IPv6 Neighbor Discovery (ND) protocol 157 [RFC4861] and links ND to IP forwarding. A node's AERO interface can 158 be configured over multiple underlying interfaces, and may therefore 159 may appear as a single interface with multiple link-layer addresses. 160 Each link-layer address is subject to change due to mobility and/or 161 QoS fluctuations, and link-layer address changes are signaled by ND 162 messaging the same as for any IPv6 link. 164 AERO links provide a cloud-based service where mobile nodes may use 165 any Server acting as a Mobility Anchor Point (MAP) and fixed nodes 166 may use any Gateway on the link for efficient communications. Fixed 167 nodes forward packets destined to other AERO nodes to the nearest 168 Gateway, which forwards them through the cloud. A mobile node's 169 initial packets are forwarded through the MAP, while direct routing 170 is supported through asymmetric extended route optimization while 171 data packets are flowing. Both unicast and multicast communications 172 are supported, and mobile nodes may efficiently move between 173 locations while maintaining continuous communications with 174 correspondents and without changing their IP Address. 176 AERO Relays are interconnected in a secured private BGP overlay 177 routing instance known as the "SPAN". The SPAN provides a hybrid 178 routing/bridging service to join the underlying Internetworks of 179 multiple disjoint administrative domains into a single unified AERO 180 link. Each AERO link instance is characterized by the set of 181 Mobility Service Prefixes (MSPs) common to all mobile nodes. The 182 link extends to the point where a Gateway/MAP is on the optimal route 183 from any correspondent node on the link, and provides a gateway 184 between the underlying Internetwork and the SPAN. To the underlying 185 Internetwork, the Gateway/MAP is the source of a route to its MSP, 186 and hence uplink traffic to the mobile node is naturally routed to 187 the nearest Gateway/MAP. 189 AERO assumes the use of PIM Sparse Mode in support of multicast 190 communication. In support of Source Specific Multicast (SSM) when a 191 Mobile Node is the source, AERO route optimization ensures that a 192 shortest-path multicast tree is established with provisions for 193 mobility and multilink operation. In all other multicast scenarios 194 there are no AERO dependencies. 196 AERO was designed for aeronautical networking for both manned and 197 unmanned aircraft, where the aircraft is treated as a mobile node 198 that can connect an Internet of Things (IoT). AERO is also 199 applicable to a wide variety of other use cases. For example, it can 200 be used to coordinate the Virtual Private Network (VPN) links of 201 mobile nodes (e.g., cellphones, tablets, laptop computers, etc.) that 202 connect into a home enterprise network via public access networks 203 using services such as OpenVPN [OVPN]. Other applicable use cases 204 are also in scope. 206 The following numbered sections present the AERO specification. The 207 appendices at the end of the document are non-normative. 209 2. Terminology 211 The terminology in the normative references applies; the following 212 terms are defined within the scope of this document: 214 IPv6 Neighbor Discovery (ND) 215 an IPv6 control message service for coordinating neighbor 216 relationships between nodes connected to a common link. AERO 217 interfaces use the ND service specified in [RFC4861]. 219 IPv6 Prefix Delegation (PD) 220 a networking service for delegating IPv6 prefixes to nodes on the 221 link. The nominal PD service is DHCPv6 [RFC8415], however 222 alternate services (e.g., based on ND messaging) are also in scope 223 [I-D.templin-v6ops-pdhost][I-D.templin-6man-dhcpv6-ndopt]. Most 224 notably, a minimal form of PD known as "prefix registration" can 225 be used if the Client knows its prefix in advance and can 226 represent it in the IPv6 source address of an ND message. 228 Access Network (ANET) 229 a node's first-hop data link service network, e.g., a radio access 230 network, cellular service provider network, corporate enterprise 231 network, or the public Internet itself. For secured ANETs, link- 232 layer security services such as IEEE 802.1X and physical-layer 233 security prevent unauthorized access internally while border 234 network-layer security services such as firewalls and proxies 235 prevent unauthorized outside access. 237 ANET interface 238 a node's attachment to a link in an ANET. 240 ANET address 241 an IP address assigned to a node's interface connection to an 242 ANET. 244 Internetwork (INET) 245 a connected IP network topology with a coherent routing and 246 addressing plan and that provides a transit backbone service for 247 ANET end systems. INETs also provide an underlay service over 248 which the AERO virtual link is configured. Example INETs include 249 corporate enterprise networks, aviation networks, and the public 250 Internet itself. When there is no administrative boundary between 251 an ANET and the INET, the ANET and INET are one and the same. 253 INET Partition 254 frequently, INETs such as large corporate enterprise networks are 255 sub-divided internally into separate isolated partitions. Each 256 partition is fully connected internally but disconnected from 257 other partitions, and there is no requirement that separate 258 partitions maintain consistent Internet Protocol and/or addressing 259 plans. (An INET partition is the same as a SPAN segment discussed 260 below.) 262 INET interface 263 a node's attachment to a link in an INET. 265 INET address 266 an IP address assigned to a node's interface connection to an 267 INET. 269 AERO link 270 a Non-Broadcast, Multiple Access (NBMA) tunnel virtual overlay 271 configured over one or more underlying INETs. Nodes on the AERO 272 link appear as single-hop neighbors from the perspective of the 273 virtual overlay even though they may be separated by many 274 underlying INET hops. AERO links may be configured over multiple 275 underlying SPAN segments (see below). 277 AERO interface 278 a node's attachment to an AERO link. Since the addresses assigned 279 to an AERO interface are managed for uniqueness, AERO interfaces 280 do not require Duplicate Address Detection (DAD) and therefore set 281 the administrative variable 'DupAddrDetectTransmits' to zero 282 [RFC4862]. 284 underlying interface 285 an ANET or INET interface over which an AERO interface is 286 configured. 288 AERO address 289 an IPv6 link-local address assigned to an AERO interface and 290 constructed as specified in Section 3.4. 292 base AERO address 293 the lowest-numbered AERO address aggregated by the MNP (see 294 Section 3.4). 296 Mobility Service Prefix (MSP) 297 an IP prefix assigned to the AERO link and from which more- 298 specific Mobile Network Prefixes (MNPs) are derived. 300 Mobile Network Prefix (MNP) 301 an IP prefix allocated from an MSP and delegated to an AERO Client 302 or Gateway. 304 AERO node 305 a node that is connected to an AERO link, or that provides 306 services to other nodes on an AERO link. 308 AERO Client ("Client") 309 an AERO node that connects to one or more ANETs and requests MNP 310 PDs from AERO Servers. The Client assigns a Client AERO address 311 to the AERO interface for use in ND exchanges with other AERO 312 nodes and forwards packets to correspondents according to AERO 313 interface neighbor cache state. 315 AERO Server ("Server") 316 an INET node that configures an AERO interface to provide default 317 forwarding services and a Mobility Anchor Point (MAP) for AERO 318 Clients. The Server assigns an administratively-provisioned AERO 319 address to its AERO interface to support the operation of the ND/ 320 PD services, and advertises all of its associated MNPs via BGP 321 peerings with Relays. 323 AERO Gateway ("Gateway") 324 an AERO Server that also provides forwarding services between 325 nodes reached via the AERO link and correspondents on other links. 326 AERO Gateways are provisioned with MNPs (i.e., the same as for an 327 AERO Client) and run a dynamic routing protocol to discover any 328 non-MNP IP routes. In both cases, the Gateway advertises the 329 MSP(s) over INET interfaces, and distributes all of its associated 330 MNPs and non-MNP IP routes via BGP peerings with Relays (i.e., the 331 same as for an AERO Server). 333 AERO Relay ("Relay") 334 a node that provides hybrid routing/bridging services (as well as 335 a security trust anchor) for nodes on an AERO link. As a router, 336 the Relay forwards packets using standard IP forwarding. As a 337 bridge, the Relay forwards packets over the AERO link without 338 decrementing the IPv6 Hop Limit. AERO Relays peer with Servers 339 and other Relays to discover the full set of MNPs for the link as 340 well as any non-MNPs that are reachable via Gateways. 342 AERO Proxy ("Proxy") 343 a node that provides proxying services between Clients in an ANET 344 and Servers in external INETs. The AERO Proxy is a conduit 345 between the ANET and external INETs in the same manner as for 346 common web proxies, and behaves in a similar fashion as for ND 347 proxies [RFC4389]. 349 Spanning Partitioned AERO Networks (SPAN) 350 a means for bridging disjoint INET partitions as segments of a 351 unified AERO link the same as for a bridged campus LAN. The SPAN 352 is a mid-layer IPv6 encapsulation service in the AERO routing 353 system that supports a unified AERO link view for all segments. 354 Each segment in the SPAN is a distinct INET partition. 356 SPAN Service Prefix (SSP) 357 a global or unique local /96 IPv6 prefix assigned to the AERO link 358 to support SPAN services. 360 SPAN Partition Prefix (SPP) 361 a sub-prefix of the SPAN Service Prefix uniquely assigned to a 362 single SPAN segment. 364 SPAN Address 365 a global or unique local IPv6 address taken from a SPAN Partition 366 Prefix and constructed as specified in Section 3.5. SPAN 367 addresses are statelessly derived from AERO addresses, and vice- 368 versa. 370 ingress tunnel endpoint (ITE) 371 an AERO interface endpoint that injects encapsulated packets into 372 an AERO link. 374 egress tunnel endpoint (ETE) 375 an AERO interface endpoint that receives encapsulated packets from 376 an AERO link. 378 link-layer address 379 an IP address used as an encapsulation header source or 380 destination address from the perspective of the AERO interface. 382 When an upper layer protocol (e.g., UDP) is used as part of the 383 encapsulation, the port number is also considered as part of the 384 link-layer address. From the perspective of the AERO interface, 385 the link-layer address is either an INET address for intra-segment 386 encapsulation or a SPAN address for inter-segment encapsulation. 388 network layer address 389 the source or destination address of an encapsulated IP packet 390 presented to the AERO interface. 392 end user network (EUN) 393 an internal virtual or external edge IP network that an AERO 394 Client or Gateway connects to the rest of the network via the AERO 395 interface. The Client/Gateway sees each EUN as a "downstream" 396 network, and sees the AERO interface as the point of attachment to 397 the "upstream" network. 399 Mobile Node (MN) 400 an AERO Client and all of its downstream-attached networks that 401 move together as a single unit, i.e., an end system that connects 402 an Internet of Things. 404 Mobile Router (MR) 405 a MN's on-board router that forwards packets between any 406 downstream-attached networks and the AERO link. 408 Mobility Anchor Point (MAP) 409 an AERO Server that is currently tracking and reporting the 410 mobility events of its associated Mobile Node Clients. 412 Route Optimization Source (ROS) 413 the AERO node nearest the source that initiates route 414 optimization. The ROS may be a Server or Proxy acting on behalf 415 of the source Client. 417 Route Optimization responder (ROR) 418 the AERO node nearest the target destination that responds to 419 route optimization requests. The ROR may be a Server acting as a 420 MAP on behalf of a target MNP Client, or a Gateway for a non-MNP 421 destination. 423 MAP List 424 a geographically and/or topologically referenced list of AERO 425 addresses of all MAPs within the same AERO link. There is a 426 single MAP list for the entire AERO link. 428 ROS List 429 a list of AERO/SPAN-to-INET address mappings of all ROSes within 430 the same SPAN segment. There is a distinct ROS list for each 431 segment. 433 Distributed Mobility Management (DMM) 434 a BGP-based overlay routing service coordinated by Servers and 435 Relays that tracks all MAP-to-Client associations. 437 Throughout the document, the simple terms "Client", "Server", 438 "Relay", "Proxy" and "Gateway" refer to "AERO Client", "AERO Server", 439 "AERO Relay", "AERO Proxy" and "AERO Gateway", respectively. 440 Capitalization is used to distinguish these terms from other common 441 Internetworking uses in which they appear without capitalization. 443 The terminology of DHCPv6 [RFC8415] and IPv6 ND [RFC4861] (including 444 the names of node variables, messages and protocol constants) is used 445 throughout this document. The terms "All-Routers multicast", "All- 446 Nodes multicast" and "Subnet-Router anycast" are defined in [RFC4291] 447 (with Link-Local scope assumed). Also, the term "IP" is used to 448 generically refer to either Internet Protocol version, i.e., IPv4 449 [RFC0791] or IPv6 [RFC8200]. 451 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 452 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 453 "OPTIONAL" in this document are to be interpreted as described in BCP 454 14 [RFC2119][RFC8174] when, and only when, they appear in all 455 capitals, as shown here. 457 3. Asymmetric Extended Route Optimization (AERO) 459 The following sections specify the operation of IP over Asymmetric 460 Extended Route Optimization (AERO) links: 462 3.1. AERO Link Reference Model 463 +----------------+ 464 | AERO Relay R1 | 465 | Nbr: S1, S2, P1| 466 |(X1->S1; X2->S2)| 467 | MSP M1 | 468 +-+---------+--+-+ 469 +--------------+ | Secured | | +--------------+ 470 |AERO Server S1| | tunnels | | |AERO Server S2| 471 | Nbr: C1, R1 +-----+ | +-----+ Nbr: C2, R1 | 472 | default->R1 | | | default->R1 | 473 | X1->C1 | | | X2->C2 | 474 +-------+------+ | +------+-------+ 475 | AERO Link | | 476 X===+===+===================+==)===============+===+===X 477 | | | | 478 +-----+--------+ +--------+--+-----+ +--------+-----+ 479 |AERO Client C1| | AERO Proxy P1 | |AERO Client C2| 480 | Nbr: S1 | |(Proxy Nbr Cache)| | Nbr: S2 | 481 | default->S1 | +--------+--------+ | default->S2 | 482 | MNP X1 | | | MNP X2 | 483 +------+-------+ .--------+------. +-----+--------+ 484 | (- Proxyed Clients -) | 485 .-. `---------------' .-. 486 ,-( _)-. ,-( _)-. 487 .-(_ IP )-. +-------+ +-------+ .-(_ IP )-. 488 (__ EUN )--|Host H1| |Host H2|--(__ EUN ) 489 `-(______)-' +-------+ +-------+ `-(______)-' 491 Figure 1: AERO Link Reference Model 493 Figure 1 presents the AERO link reference model. In this model: 495 o the AERO link is an overlay network service configured over one or 496 more underlying INET partitions which may be managed by different 497 administrative authorities and have incompatible protocols and/or 498 addressing plans. 500 o AERO Relay R1 aggregates Mobility Service Prefix (MSP) M1, 501 discovers Mobile Network Prefixes (MNPs) X* and advertises the MSP 502 via BGP peerings over secured tunnels to Servers (S1, S2). Relays 503 use the SPAN service to bridge disjoint segments of a partitioned 504 AERO link. 506 o AERO Servers S1 and S2 configure secured tunnels with Relay R1 and 507 also act as Mobility Anchor Points (MAPs) and default routers for 508 their associated Clients C1 and C2. 510 o AERO Clients C1 and C2 associate with Servers S1 and S2, 511 respectively. They receive Mobile Network Prefix (MNP) 512 delegations X1 and X2, and also act as default routers for their 513 associated physical or internal virtual EUNs. Simple hosts H1 and 514 H2 attach to the EUNs served by Clients C1 and C2, respectively. 516 o AERO Proxy P1 configures a secured tunnel with Relay R1 and 517 provides proxy services for AERO Clients in secured enclaves that 518 cannot associate directly with other AERO link neighbors. 520 Each node on the AERO link maintains an AERO interface neighbor cache 521 and an IP forwarding table the same as for any link. Although the 522 figure shows a limited deployment, in common operational practice 523 there will normally be many additional Relays, Servers, Clients and 524 Proxys. 526 3.2. AERO Node Types 528 AERO Relays provide hybrid routing/bridging services (as well as a 529 security trust anchor) for nodes on an AERO link. Relays use 530 standard IPv6 routing to forward packets both within the same INET 531 partitions and between disjoint INET partitions based on a mid-layer 532 IPv6 encapsulation known as the SPAN header. The inner IP layer 533 experiences a virtual bridging service since the inner IP TTL/Hop 534 Limit is not decremented during forwarding. Each Relay also peers 535 with Servers and other Relays in a dynamic routing protocol instance 536 to provide a Distributed Mobility Management (DMM) service for the 537 list of active MNPs (see Section 3.3). Relays present the AERO link 538 as a set of one or more Mobility Service Prefixes (MSPs) but as link- 539 layer devices need not connect directly to the AERO link themselves 540 unless an administrative interface is desired. Relays configure 541 secured tunnels with Servers, Proxys and other Relays; they further 542 maintain IP forwarding table entries for each Mobile Network Prefix 543 (MNP) and any other reachable non-MNP prefixes. 545 AERO Servers provide default forwarding services and a Mobility 546 Anchor Point (MAP) for AERO Client Mobile Nodes (MNs). Each Server 547 also peers with Relays in a dynamic routing protocol instance to 548 advertise its list of associated MNPs (see Section 3.3). Servers 549 facilitate PD exchanges with Clients, where each delegated prefix 550 becomes an MNP taken from an MSP. Servers forward packets between 551 AERO interface neighbors and track each Client's mobility profiles. 553 AERO Clients register their MNPs through PD exchanges with AERO 554 Servers over the AERO link, and distribute the MNPs to nodes on EUNs. 555 A Client may also be co-resident on the same physical or virtual 556 platform as a Server; in that case, the Client and Server behave as a 557 single functional unit. 559 AERO Proxys provide a conduit for ANET AERO Clients to associate with 560 AERO Servers in external INETs. Client and Servers exchange control 561 plane messages via the Proxy acting as a bridge between the ANET/INET 562 boundary. The Proxy forwards data packets between Clients and the 563 AERO link according to forwarding information in the neighbor cache. 564 The Proxy function is specified in Section 3.16. 566 AERO Gateways are Servers that provide forwarding services between 567 the AERO interface and INET/EUN interfaces. Gateways are provisioned 568 with MNPs the same as for an AERO Client, and also run a dynamic 569 routing protocol to discover any non-MNP IP routes. The Gateway 570 advertises the MSP(s) to INETs, and distributes all of its associated 571 MNPs and non-MNP IP routes via BGP peerings with Relays. 573 AERO Relays, Servers, Proxys and Gateways are critical infrastructure 574 elements in fixed (i.e., non-mobile) INET deployments and hence have 575 permanent and unchanging INET addresses. AERO Clients are MNs that 576 connect via ANET interfaces, i.e., their ANET addresses may change 577 when the Client moves to a new ANET connection. 579 3.3. AERO Routing System 581 The AERO routing system comprises a private instance of the Border 582 Gateway Protocol (BGP) [RFC4271] that is coordinated between Relays 583 and Servers and does not interact with either the public Internet BGP 584 routing system or any underlying INET routing systems. 586 In a reference deployment, each Server is configured as an Autonomous 587 System Border Router (ASBR) for a stub Autonomous System (AS) using 588 an AS Number (ASN) that is unique within the BGP instance, and each 589 Server further uses eBGP to peer with one or more Relays but does not 590 peer with other Servers. Each INET of a multi-segment AERO link must 591 include one or more Relays, which peer with the Servers and Proxys 592 within that INET. All Relays within the same INET are members of the 593 same hub AS using a common ASN, and use iBGP to maintain a consistent 594 view of all active MNPs currently in service. The Relays of 595 different INETs peer with one another using eBGP. 597 Relays advertise the AERO link's MSPs and any non-MNP routes to each 598 of their Servers. This means that any aggregated non-MNPs (including 599 "default") are advertised to all Servers. Each Relay configures a 600 black-hole route for each of its MSPs. By black-holing the MSPs, the 601 Relay will maintain forwarding table entries only for the MNPs that 602 are currently active, and packets destined to all other MNPs will 603 correctly incur Destination Unreachable messages due to the black- 604 hole route. In this way, Servers have only partial topology 605 knowledge (i.e., they know only about the MNPs of their directly 606 associated Clients) and they forward all other packets to Relays 607 which have full topology knowledge. 609 Servers maintain a working set of associated MNPs, and dynamically 610 announce new MNPs and withdraw departed MNPs in eBGP updates to 611 Relays. Servers that are configured as Gateways also redistribute 612 non-MNP routes learned from non-AERO interfaces via their eBGP Relay 613 peerings. 615 Clients are expected to remain associated with their current Servers 616 for extended timeframes, however Servers SHOULD selectively suppress 617 updates for impatient Clients that repeatedly associate and 618 disassociate with them in order to dampen routing churn. Servers 619 that are configured as Gateways advertise the MSPs via INET/EUN 620 interfaces, and forward packets between INET/EUN interfaces and the 621 AERO interface using standard IP forwarding. 623 Scaling properties of the AERO routing system are limited by the 624 number of BGP routes that can be carried by Relays. As of 2015, the 625 global public Internet BGP routing system manages more than 500K 626 routes with linear growth and no signs of router resource exhaustion 627 [BGP]. More recent network emulation studies have also shown that a 628 single Relay can accommodate at least 1M dynamically changing BGP 629 routes even on a lightweight virtual machine, i.e., and without 630 requiring high-end dedicated router hardware. 632 Therefore, assuming each Relay can carry 1M or more routes, this 633 means that at least 1M Clients can be serviced by a single set of 634 Relays. A means of increasing scaling would be to assign a different 635 set of Relays for each set of MSPs. In that case, each Server still 636 peers with one or more Relays, but institutes route filters so that 637 BGP updates are only sent to the specific set of Relays that 638 aggregate the MSP. For example, if the MSP for the AERO link is 639 2001:db8::/32, a first set of Relays could service the MSP 640 2001:db8::/40, a second set of Relays could service 641 2001:db8:0100::/40, a third set could service 2001:db8:0200::/40, 642 etc. 644 Assuming up to 1K sets of Relays, the AERO routing system can then 645 accommodate 1B or more MNPs with no additional overhead (for example, 646 it should be possible to service 1B /64 MNPs taken from a /34 MSP and 647 even more for shorter prefixes). In this way, each set of Relays 648 services a specific set of MSPs that they advertise to the native 649 Internetwork routing system, and each Server configures MSP-specific 650 routes that list the correct set of Relays as next hops. This 651 arrangement also allows for natural incremental deployment, and can 652 support small scale initial deployments followed by dynamic 653 deployment of additional Clients, Servers and Relays without 654 disturbing the already-deployed base. 656 Server and Relays can use the Bidirectional Forwarding Detection 657 (BFD) protocol [RFC5880] to quickly detect link failures that don't 658 result in interface state changes, BGP peer failures, and 659 administrative state changes. BFD is important in environments where 660 rapid response to failures is required for routing reconvergence and, 661 hence, communications continuity. 663 A full discussion of the BGP-based routing system used by AERO is 664 found in [I-D.ietf-rtgwg-atn-bgp]. The system provides for 665 Distributed Mobility Management (DMM) per the distributed mobility 666 anchoring architecture [I-D.ietf-dmm-distributed-mobility-anchoring]. 668 3.3.1. IPv4 Compatibility Routing 670 For IPv6 MNPs, the AERO routing system includes ordinary IPv6 routes. 671 For IPv4 MNPs, the AERO routing system includes IPv6 routes based on 672 an IPv4-embedded IPv6 address format discussed in Section 3.5.1. 674 3.4. AERO Addresses 676 A Client's AERO address is an IPv6 link-local address with an 677 interface identifier based on the Client's delegated MNP. Relay, 678 Server and Proxy AERO addresses are assigned from the range fe80::/96 679 and include an administratively-provisioned value in the lower 32 680 bits. 682 For IPv6, Client AERO addresses begin with the prefix fe80::/64 and 683 include in the interface identifier (i.e., the lower 64 bits) a 684 64-bit prefix taken from one of the Client's IPv6 MNPs. For example, 685 if the AERO Client receives the IPv6 MNP: 687 2001:db8:1000:2000::/56 689 it constructs its corresponding AERO addresses as: 691 fe80::2001:db8:1000:2000 693 fe80::2001:db8:1000:2001 695 fe80::2001:db8:1000:2002 697 ... etc. ... 699 fe80::2001:db8:1000:20ff 701 For IPv4, Client AERO addresses are based on an IPv4-mapped IPv6 702 address [RFC4291] formed from an IPv4 MNP and with a prefix length of 703 96 plus the MNP prefix length. For example, for the IPv4 MNP 704 192.0.2.32/28 the IPv4-mapped IPv6 MNP is: 706 0:0:0:0:0:FFFF:192.0.2.16/124 (also written as 707 0:0:0:0:0:FFFF:c000:0210/124) 709 The Client then constructs its AERO addresses with the prefix 710 fe80::/64 and with the lower 64 bits of the IPv4-mapped IPv6 address 711 in the interface identifier as: 713 fe80::FFFF:192.0.2.16 715 fe80::FFFF:192.0.2.17 717 fe80::FFFF:192.0.2.18 719 ... etc. ... 721 fe80:FFFF:192.0.2.31 723 Relay, Server and Proxy AERO addresses are allocated from the range 724 fe80::/96, and MUST be managed for uniqueness. The lower 32 bits of 725 the AERO address includes a unique integer value between 1 and 726 0xfffffffe (e.g., fe80::1, fe80::2, fe80::3, etc., fe80::ffff:fffe) 727 as assigned by the administrative authority for the link. If the 728 link spans multiple SPAN segments, the AERO addresses are assigned to 729 each segment in 1x1 correspondence with SPAN addresses (see: 730 Section 3.5). The address fe80:: is the IPv6 link-local Subnet- 731 Router anycast address, and the address fe80::ffff:ffff is reserved 732 as the unspecified AERO address. 734 The lowest-numbered AERO address from a Client's MNP delegation 735 serves as the "base" AERO address (for example, for the MNP 736 2001:db8:1000:2000::/56 the base AERO address is 737 fe80::2001:db8:1000:2000). The Client then assigns the base AERO 738 address to the AERO interface and uses it for the purpose of 739 maintaining the neighbor cache entry. The Server likewise uses the 740 AERO address as its index into the neighbor cache for this Client. 742 If the Client has multiple AERO addresses (i.e., when there are 743 multiple MNPs and/or MNPs with prefix lengths shorter than /64), the 744 Client originates ND messages using the base AERO address as the 745 source address and accepts and responds to ND messages destined to 746 any of its AERO addresses as equivalent to the base AERO address. In 747 this way, the Client maintains a single neighbor cache entry that may 748 be indexed by multiple AERO addresses. 750 The Client's Subnet-Router anycast address can be statelessly 751 determined from its AERO address by simply transposing the AERO 752 address into the upper N bits of the Anycast address followed by 753 128-N bits of zeroes. For example, for the AERO address 754 fe80::2001:db8:1:2 the Subnet-Router anycast address is 755 2001:db8:1:2::. 757 AERO addresses for mobile node Clients embed a MNP as discussed 758 above, while AERO addresses for non-MNP destinations are constructed 759 in exactly the same way. A Client AERO address therefore encodes 760 either an MNP if the prefix is reached via the SPAN or a non-MNP if 761 the prefix is reached via a Gateway. 763 3.5. Spanning Partitioned AERO Networks (SPAN) 765 An AERO link configured over a single INET appears as a single 766 unified link with a consistent underlying network addressing plan. 767 In that case, all nodes on the link can exchange packets via simple 768 INET encapsulation, since the underlying INET is connected. In 769 common practice, however, an AERO link may be partitioned into 770 multiple "segments", where each segment is a distinct INET 771 potentially managed under a different administrative authority (e.g., 772 as for worldwide aviation service providers such as ARINC, SITA, 773 Inmarsat, etc.). Individual INETs may also themselves be partitioned 774 internally, in which case each internal partition is seen as a 775 separate segment. 777 The addressing plan of each segment is consistent internally but will 778 often bear no relation to the addressing plans of other segments. 779 Each segment is also likely to be separated from others by network 780 security devices (e.g., firewalls, proxies, packet filtering 781 gateways, etc.), and in many cases disjoint segments may not even 782 have any common physical link connections at all. Therefore, nodes 783 can only be assured of exchanging packets directly with 784 correspondents in the same segment, and not with those in other 785 segments. The only means for joining the segments therefore is 786 through inter-domain peerings between AERO Relays. 788 The same as for traditional campus LANs, multiple AERO link segments 789 can be joined into a single unified link via a virtual bridging 790 service termed the "SPAN". The SPAN performs link-layer packet 791 forwarding between segments (i.e., bridging) without decrementing the 792 network-layer TTL/Hop Limit. The SPAN model is depicted in Figure 2: 794 . . . . . . . . . . . . . . . . . . . . . . . 795 . . 796 . .-(::::::::) . 797 . .-(::::::::::::)-. +-+ . 798 . (:::: Segment A :::)--|R|---+ . 799 . `-(::::::::::::)-' +-+ | . 800 . `-(::::::)-' | . 801 . | . 802 . .-(::::::::) | . 803 . .-(::::::::::::)-. +-+ | . 804 . (:::: Segment B :::)--|R|---+ . 805 . `-(::::::::::::)-' +-+ | . 806 . `-(::::::)-' | . 807 . | . 808 . .-(::::::::) | . 809 . .-(::::::::::::)-. +-+ | . 810 . (:::: Segment C :::)--|R|---+ . 811 . `-(::::::::::::)-' +-+ | . 812 . `-(::::::)-' | . 813 . | . 814 . ..(etc).. x . 815 . . 816 . . 817 . <- AERO Link Bridged by the SPAN -> . 818 . . . . . . . . . . . . . .. . . . . . . . . 820 Figure 2: The SPAN 822 To support the SPAN, AERO links use the Unique Local Address (ULA) 823 prefix fd00::/10 [RFC4193] as the SPAN Service Prefix (SSP). The 824 prefix length intentionally matches the IPv6 link-local prefix 825 (fe80::/10). 827 Each segment in the SPAN assigns a unique sub-prefix of SSP::/96 828 termed a "SPAN Partition Prefix (SPP)". For example, a first segment 829 could assign fd00::1000/116, a second could assign fd00::2000/116, a 830 third could assign fd00::3000/116, etc. The administrative 831 authorities for each segment must therefore coordinate to assure 832 mutually-exclusive SPP assignments, but internal provisioning of the 833 SPP is an independent local consideration for each administrative 834 authority. 836 An administratively-assigned "SPAN address" is an address taken from 837 a SPP and assigned to a Relay, Server, Gateway or Proxy interface. 838 SPAN addresses are formed by simply replacing the upper portion of an 839 administratively-assigned AERO address with the SPP. For example, if 840 the SPP is fd00::1000/116, the SPAN address formed from the AERO 841 address fe80::1001 is simply fd00::1001. 843 An "INET address" is an address of a node's interface connection to 844 an INET. AERO/SPAN/INET address mappings are maintained as permanent 845 neighbor cache entires as discussed in Section 3.8. 847 AERO Relays serve as bridges to join multiple segments into a unified 848 AERO link over multiple diverse administrative domains. They support 849 the bridging function by first establishing forwarding table entries 850 for their SPPs either via standard BGP routing or static routes. For 851 example, if three Relays ('A', 'B' and 'C') from different segments 852 serviced the SPPs fd00::1000/116, fd00::2000/116 and fd00::3000/116 853 respectively, then the forwarding tables in each Relay are as 854 follows: 856 A: fd00::1000/116->local, fd00::2000/116->B, fd00::3000/116->C 858 B: fd00::1000/116->A, fd00::2000/116->local, fd00::3000/116->C 860 C: fd00::1000/116->A, fd00::2000/116->B, fd00::3000/116->local 862 These forwarding table entries are permanent and never change, since 863 they correspond to fixed infrastructure elements in their respective 864 segments. This provides the basis for a link-layer forwarding 865 service that cannot be disrupted by routing updates due to node 866 mobility. 868 With the SPPs in place in each Relay's forwarding table, control and 869 data packets sent between AERO nodes in different segments can 870 therefore be carried over the SPAN via encapsulation. For example, 871 when a source AERO node in segment A forwards a packet with IPv6 872 address 2001:db8:1:2::1 to a target AERO node in segment C with IPv6 873 address 2001:db8:1000:2000::1, it first encapsulates the packet in a 874 SPAN header with source SPAN address taken from fd00::1000/116 (e.g., 875 fd00::1001) and destination SPAN address taken from fd00::3000/116 876 (e.g., fd00::3001). Next, it encapsulates the SPAN message in an 877 INET header with source address set to its own INET address (e.g., 878 192.0.2.100) and destination set to the INET address of a Relay 879 (e.g., 192.0.2.1). 881 SPAN encapsulation is based on Generic Packet Tunneling in IPv6 882 [RFC2473]; the encapsulation format in the above example is shown in 883 Figure 3: 885 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 886 | INET Header | 887 | src = 192.0.2.100 | 888 | dst = 192.0.2.1 | 889 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 890 | SPAN Header | 891 | src = fd00::1001 | 892 | dst = fd00::3001 | 893 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 894 | Inner IP Header | 895 | src = 2001:db8:1:2::1 | 896 | dst = 2001:db8:1000:2000::1 | 897 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 898 | | 899 ~ ~ 900 ~ Inner Packet Body ~ 901 ~ ~ 902 | | 903 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 905 Figure 3: SPAN Encapsulation 907 In this format, the inner IP header and packet body are the original 908 IP packet, the SPAN header is an IPv6 header prepared according to 909 [RFC2473], and the INET header is prepared according to Section 3.9. 910 A packet is said to be "forwarded/sent into the SPAN" when it is 911 encapsulated as described above then forwarded via a secured tunnel 912 to a neighboring Relay. 914 This gives rise to a routing system that contains both MNP routes 915 that may change dynamically due to regional node mobility and SPAN 916 routes that never change. The Relays can therefore provide link- 917 layer bridging by sending packets into the SPAN instead of network- 918 layer routing according to MNP routes. As a result, opportunities 919 for packet loss due to node mobility between different segments are 920 mitigated. 922 With reference to Figure 3, for a Client's AERO address the SPAN 923 destination address is simply set to the Subnet-Router anycast 924 address. For non-link-local addresses, the destination SPAN address 925 may not be known in advance for the first few packets of a flow sent 926 via the SPAN. In that case, the SPAN destination address is set to 927 the original packet's destination, and the SPAN routing system will 928 direct the packet to the correct SPAN egress node. (In the above 929 example, the SPAN destination address is simply 930 2001:db8:1000:2000::1.) 932 3.5.1. SPAN Compatibility Addressing 934 For IPv4 MNPs, Servers inject a "SPAN Compatibility Prefix (SCP)" 935 that embeds the MNP into the BGP routing system. The SCP begins with 936 the upper 64 bits of the SSP, followed by the constant string 937 "0000:FFFF" followed by the IPv4 MNP. For example, if the SSP is 938 fd00::/64 and the MNP is 192.0.2.0/24 then the SCP is 939 fd00::FFFF:192.0.2.0/120. 941 This allows for encapsulation of IPv4 packets in IPv6 headers with 942 "SPAN Compatibility Addresses (SCAs)". In this example, the SCA 943 corresponding to the SCP is simply fd00::FFFF:192.0.2.0, and can be 944 used as the SPAN destination address for packets forwarded via the 945 SPAN. This allows for forwarding of initial IPv4 packets over IPv6 946 SPAN routes, followed by route optimization for direct 947 communications. 949 3.5.2. Client SPAN Addresses 951 When an AERO Client encapsulates and fragments a packet (see: 952 Section 3.12), it inserts its "Client SPAN Address" as the IPv6 953 source address of the encapsulation header. This is necessary to 954 provide reassemblers with a source address corresponding to the node 955 that actually inserted the fragment header so that the correct 956 Identification value context is provided. 958 The Client SPAN address is formed by simply replacing the upper 10 959 bits of the Client's AERO address with the most significant 10 bits 960 of fd00::/10. For example, for the Client AERO address 961 fe80::2001:db8:1:2 the corresponding Client SPAN address is 962 fd00::2001:db8:1:2. 964 Note that the Client's MNP itself (and not the Client SPAN address) 965 is injected into the routing system due to the /64 assumption in the 966 AERO address construction. Because of the /64 assumption, the most- 967 significant 64 bits of the Client's MNP are written into the least- 968 significant 64 bits of the AERO address. If MNPs longer than /64 are 969 used in the future (i.e., /65 up to /118) the least-significant bits 970 of the MNP would need to be written into bits 10 through 63 of the 971 SPAN address, which would render the address format useless for 972 longest-prefix-match. For more details, see Appendix B of 973 [I-D.templin-atn-aero-interface]. 975 3.6. AERO Interface Characteristics 977 AERO interfaces are virtual interfaces configured over one or more 978 underlying interfaces classified as follows: 980 o Native interfaces have global IP addresses that are reachable from 981 any INET correspondent. All Server, Gateway and Relay interfaces 982 are native interfaces, as are INET-facing interfaces of Proxys. 984 o NATed interfaces connect to a private network behind a Network 985 Address Translator (NAT). The NAT does not participate in any 986 AERO control message signaling, but the Server can issue control 987 messages on behalf of the Client. Clients that are behind a NAT 988 are required to send periodic keepalive messages to keep NAT state 989 alive when there are no data packets flowing. If no other 990 periodic messaging service is available, the Client can send RS 991 messages to receive RA replies from its Server(s). 993 o VPNed interfaces use security encapsulation to a Virtual Private 994 Network (VPN) server that also acts as an AERO Server. As with 995 NATed links, the Server can issue control messages on behalf of 996 the Client, but the Client need not send periodic keepalives in 997 addition to those already used to maintain the VPN connection. 999 o Proxyed interfaces connect to an ANET that is separated from the 1000 open INET by an AERO Proxy. Unlike NATed and VPNed interfaces, 1001 the Proxy can actively issue control messages on behalf of the 1002 Client. 1004 o Direct interfaces connect a Client directly to a neighbor without 1005 crossing any ANET/INET paths. An example is a line-of-sight link 1006 between a remote pilot and an unmanned aircraft. 1008 AERO interfaces use encapsulation (see: Section 3.9) to exchange 1009 packets with AERO link neighbors over Native, NATed or VPNed 1010 interfaces. AERO interfaces do not use encapsulation over Proxyed 1011 and Direct underlying interfaces. 1013 AERO interfaces maintain a neighbor cache for tracking per-neighbor 1014 state the same as for any interface. AERO interfaces use ND messages 1015 including Router Solicitation (RS), Router Advertisement (RA), 1016 Neighbor Solicitation (NS) and Neighbor Advertisement (NA) for 1017 neighbor cache management. 1019 AERO interfaces send ND messages with an Overlay Multilink Network 1020 Interface (OMNI) option formatted as specified in 1021 [I-D.templin-atn-aero-interface]. The OMNI option includes prefix 1022 registration information and "ifIndex-tuples" containing link quality 1023 information for the AERO interface's underlying interfaces. 1025 When encapsulation is used, AERO interface ND messages MAY also 1026 include an AERO Source/Target Link-Layer Address Option (S/TLLAO) 1027 formatted as shown in Figure 4: 1029 0 1 2 3 1030 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 1031 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1032 | Type | Length | ifIndex[1] |V| Reserved[1] | 1033 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1034 ~ Link Layer Address [1] ~ 1035 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1036 | Port Number [1] | ifIndex[2] |V| Reserved[2] | 1037 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1038 ~ Link Layer Address [2] ~ 1039 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1040 | Port Number [2] | ~ 1041 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ 1042 ~ ~ 1043 ~ ... ~ 1044 ~ ~ 1045 ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1046 ~ | ifIndex[N] |V| Reserved[N] | 1047 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1048 ~ Link Layer Address [N] ~ 1049 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1050 | Port Number [N] | Trailing zero padding | 1051 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1052 | Trailing zero padding (if necessary) | 1053 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1055 Figure 4: AERO Source/Target Link-Layer Address Option (S/TLLAO) 1056 Format 1058 In this format, Type and Length are set the same as specified for S/ 1059 TLLAOs in [RFC4861], with trailing zero padding octets added as 1060 necessary to produce an integral number of 8 octet blocks. The S/ 1061 TLLAO includes N ifIndex-tuples in correspondence to ifIndex-tuples 1062 that appear in the OMNI option. Each ifIndex-tuple includes the 1063 folllowing information: 1065 o ifIndex[i] - the same value as in the corresponding ifIndex-tuple 1066 included in the OMNI option. 1068 o V[i] - a bit that identifies the IP protocol version of the 1069 address found in the Link Layer Address [i] field. The bit is set 1070 to 0 for IPv4 or 1 for IPv6. 1072 o Reserved[i] - MUST encode the value 0 on transmission, and ignored 1073 on reception. 1075 o Link Layer Address [i] - the IPv4 or IPv6 address used as the 1076 encapsulation source address. The field is 4 bytes in length for 1077 IPv4 or 16 bytes in length for IPv6. 1079 o Port Number [i] - the upper layer protocol port number used as the 1080 encapsulation source port, or 0 when no upper layer protocol 1081 encapsulation is used. The field is 2 bytes in length. 1083 If an S/TLLAO is included, the first S/TLLAO ifIndex-tuple MUST 1084 correspond to the first OMNI option ifIndex-tuple, and any additional 1085 S/TLLAO ifIndex-tuples MUST correspond to a proper subset of the 1086 remaining OMNI option ifIndex-tuples. Any S/TLLAO ifIndex-tuple 1087 having an ifIndex value that does not appear in an OMNI option 1088 ifindex-tuple is ignored. If the same ifIndex value appears in 1089 multiple ifIndex-tuples, the first tuple is processed and the 1090 remaining tuples are ignored. Any S/TLLAO ifIndex-tuples can 1091 therefore be viewed as inter-dependent extensions of their 1092 corresponidng OMNI option ifIndex-tuples, i.e., the OMNI option and 1093 S/TLLAO are companion options that are interpreted in conjunction 1094 with each other. 1096 A Client's AERO interface may be configured over multiple underlying 1097 interface connections. For example, common mobile handheld devices 1098 have both wireless local area network ("WLAN") and cellular wireless 1099 links. These links are typically used "one at a time" with low-cost 1100 WLAN preferred and highly-available cellular wireless as a standby. 1101 In a more complex example, aircraft frequently have many wireless 1102 data link types (e.g. satellite-based, cellular, terrestrial, air-to- 1103 air directional, etc.) with diverse performance and cost properties. 1105 If a Client's multiple underlying interfaces are used "one at a time" 1106 (i.e., all other interfaces are in standby mode while one interface 1107 is active), then ND message OMNI options include only a single 1108 ifIndex-tuple and set to a constant value. In that case, the Client 1109 would appear to have a single interface but with a dynamically 1110 changing link-layer address. 1112 If the Client has multiple active underlying interfaces, then from 1113 the perspective of ND it would appear to have multiple link-layer 1114 addresses. In that case, ND message OMNI options MAY include 1115 multiple ifIndex-tuples - each with a value that corresponds to a 1116 specific interface. The OMNI option MUST include a first ifIndex- 1117 tuple that corresponds to the interface over which the ND message is 1118 sent. Every ND message need not include all OMNI and/or S/TLLAO 1119 ifIndex-tuples; for any ifIndex-tuple not included, the neighbor 1120 considers the status as unchanged. 1122 Relay, Server and Proxy AERO interfaces may be configured over one or 1123 more secured tunnel interfaces. The AERO interface configures both 1124 an AERO address and its corresponding SPAN address, while the 1125 underlying secured tunnel interfaces are either unnumbered or 1126 configure the same SPAN address. The AERO interface encapsulates 1127 each IP packet in a SPAN header and presents the packet to the 1128 underlying secured tunnel interface. For Relays that do not 1129 configure an AERO interface, the secured tunnel interfaces themselves 1130 are exposed to the IP layer with each interface configuring the 1131 Relay's SPAN address. Routing protocols such as BGP therefore run 1132 directly over the Relay's secured tunnel interfaces. For nodes that 1133 configure an AERO interface, routing protocols such as BGP run over 1134 the AERO interface but do not employ SPAN encapsulation. Instead, 1135 the AERO interface presents the routing protocol messages directly to 1136 the underlying secured tunnels without applying encapsulation and 1137 while using the SPAN address as the source address. This distinction 1138 must be honored consistently according to each node's configuration 1139 so that the IP forwarding table will associate discovered IP routes 1140 with the correct interface. 1142 3.7. AERO Interface Initialization 1144 AERO Servers, Proxys and Clients configure AERO interfaces as their 1145 point of attachment to the AERO link. AERO nodes assign the MSPs for 1146 the link to their AERO interfaces (i.e., as a "route-to-interface") 1147 to ensure that packets with destination addresses covered by an MNP 1148 not explicitly assigned to a non-AERO interface are directed to the 1149 AERO interface. 1151 AERO interface initialization procedures for Servers, Proxys, Clients 1152 and Relays are discussed in the following sections. 1154 3.7.1. AERO Server/Gateway Behavior 1156 When a Server enables an AERO interface, it assigns AERO/SPAN 1157 addresses and configures permanent neighbor cache entries for 1158 neighbors in the same SPAN segment by consulting the ROS list for the 1159 segment. The Server also configures secured tunnels with one or more 1160 neighboring Relays and engages in a BGP routing protocol session with 1161 each Relay. 1163 The AERO interface provides a single interface abstraction to the IP 1164 layer, but internally comprises multiple secured tunnels as well as 1165 an NBMA nexus for sending encapsulated data packets to AERO interface 1166 neighbors. The Server further configures a service to facilitate ND/ 1167 PD exchanges with AERO Clients and manages per-Client neighbor cache 1168 entries and IP forwarding table entries based on control message 1169 exchanges. 1171 Gateways are simply Servers that run a dynamic routing protocol 1172 between the AERO interface and INET/EUN interfaces (see: 1173 Section 3.3). The Gateway provisions MNPs to networks on the INET/ 1174 EUN interfaces (i.e., the same as a Client would do) and advertises 1175 the MSP(s) for the AERO link over the INET/EUN interfaces. The 1176 Gateway further provides an attachment point of the AERO link to the 1177 non-MNP-based global topology. 1179 3.7.2. AERO Proxy Behavior 1181 When a Proxy enables an AERO interface, it assigns AERO/SPAN 1182 addresses and configures permanent neighbor cache entries the same as 1183 for Servers. The Proxy also configures secured tunnels with one or 1184 more neighboring Relays and maintains per-Client neighbor cache 1185 entries based on control message exchanges. 1187 3.7.3. AERO Client Behavior 1189 When a Client enables an AERO interface, it sends an RS message with 1190 ND/PD parameters over an ANET interface to a Server in the MAP list, 1191 which returns an RA message with corresponding parameters. (The RS/ 1192 RA messages may pass through a Proxy in the case of a Client's 1193 Proxyed interface.) 1195 After the initial ND/PD message exchange, the Client assigns AERO 1196 addresses to the AERO interface based on the delegated prefix(es). 1197 The Client can then register additional ANET interfaces with the 1198 Server by sending an RS message over each ANET interface. 1200 3.7.4. AERO Relay Behavior 1202 AERO Relays need not connect directly to the AERO link, since they 1203 operate as link-layer forwarding devices instead of network layer 1204 routers. Configuration of AERO interfaces on Relays is therefore 1205 OPTIONAL, e.g., if an administrative interface is needed. Relays 1206 configure secured tunnels with Servers, Proxys and other Relays; they 1207 also configure AERO/SPAN addresses and permanent neighbor cache 1208 entries the same as Servers. Relays engage in a BGP routing protocol 1209 session with a subset of the Servers on the local SPAN segment, and 1210 with other Relays on the SPAN (see: Section 3.3). 1212 3.8. AERO Interface Neighbor Cache Maintenance 1214 Each AERO interface maintains a conceptual neighbor cache that 1215 includes an entry for each neighbor it communicates with on the AERO 1216 link per [RFC4861]. AERO interface neighbor cache entries are said 1217 to be one of "permanent", "symmetric", "asymmetric" or "proxy". 1219 Permanent neighbor cache entries are created through explicit 1220 administrative action; they have no timeout values and remain in 1221 place until explicitly deleted. AERO Servers and Proxys maintain 1222 permanent neighbor cache entries for all other Servers and Proxys 1223 within the same SPAN segment. Each entry maintains the mapping 1224 between the neighbor's network-layer AERO address and corresponding 1225 INET address. The list of all permanent neighbor cache entries for 1226 the SPAN segment is maintained in the segment's ROS list. 1228 Symmetric neighbor cache entries are created and maintained through 1229 RS/RA exchanges as specified in Section 3.15, and remain in place for 1230 durations bounded by ND/PD lifetimes. AERO Servers maintain 1231 symmetric neighbor cache entries for each of their associated 1232 Clients, and AERO Clients maintain symmetric neighbor cache entries 1233 for each of their associated Servers. The list of all Servers on the 1234 AERO link is maintained in the link's MAP list. 1236 Asymmetric neighbor cache entries are created or updated based on 1237 route optimization messaging as specified in Section 3.17, and are 1238 garbage-collected when keepalive timers expire. AERO route 1239 optimization sources (ROSs) maintain asymmetric neighbor cache 1240 entries for active targets with lifetimes based on ND messaging 1241 constants. Asymmetric neighbor cache entries are unidirectional 1242 since only the ROS and not the target (e.g., a Client's MAP) creates 1243 an entry. 1245 Proxy neighbor cache entries are created and maintained by AERO 1246 Proxys when they process Client/Server ND/PD exchanges, and remain in 1247 place for durations bounded by ND/PD lifetimes. AERO Proxys maintain 1248 proxy neighbor cache entries for each of their associated Clients. 1249 Proxy neighbor cache entries track the Client state and the address 1250 of the Client's associated Server. 1252 To the list of neighbor cache entry states in Section 7.3.2 of 1253 [RFC4861], Proxy and Server AERO interfaces add an additional state 1254 DEPARTED that applies to symmetric and proxy neighbor cache entries 1255 for Clients that have recently departed. The interface sets a 1256 "DepartTime" variable for the neighbor cache entry to "DEPARTTIME" 1257 seconds. DepartTime is decremented unless a new ND message causes 1258 the state to return to REACHABLE. While a neighbor cache entry is in 1259 the DEPARTED state, packets destined to the target Client are 1260 forwarded to the Client's new location instead of being dropped. 1261 When DepartTime decrements to 0, the neighbor cache entry is deleted. 1262 It is RECOMMENDED that DEPARTTIME be set to the default constant 1263 value REACHABLETIME plus 10 seconds (40 seconds by default) to allow 1264 a window for packets in flight to be delivered while stale route 1265 optimization state may be present. 1267 When a target Server (acting as a MAP) receives a valid NS message 1268 used for route optimization, it searches for a symmetric neighbor 1269 cache entry for the target Client. The MAP then returns a solicited 1270 NA message without creating a neighbor cache entry for the ROS, but 1271 creates or updates a target Client "Report List" entry for the ROS 1272 and sets a "ReportTime" variable for the entry to REPORTTIME seconds. 1273 The MAP resets ReportTime when it receives a new authentic NS 1274 message, and otherwise decrements ReportTime while no NS messages 1275 have been received. It is RECOMMENDED that REPORTTIME be set to the 1276 default constant value REACHABLETIME plus 10 seconds (40 seconds by 1277 default) to allow a window for route optimization to converge before 1278 ReportTime decrements below REACHABLETIME. 1280 When the ROS receives a solicited NA message response to its NS 1281 message, it creates or updates an asymmetric neighbor cache entry for 1282 the target network-layer and link-layer addresses. The ROS then 1283 (re)sets ReachableTime for the neighbor cache entry to REACHABLETIME 1284 seconds and uses this value to determine whether packets can be 1285 forwarded directly to the target, i.e., instead of via a default 1286 route. The ROS otherwise decrements ReachableTime while no further 1287 solicited NA messages arrive. It is RECOMMENDED that REACHABLETIME 1288 be set to the default constant value 30 seconds as specified in 1289 [RFC4861]. 1291 The ROS also uses the value MAX_UNICAST_SOLICIT to limit the number 1292 of NS keepalives sent when a correspondent may have gone unreachable, 1293 the value MAX_RTR_SOLICITATIONS to limit the number of RS messages 1294 sent without receiving an RA and the value MAX_NEIGHBOR_ADVERTISEMENT 1295 to limit the number of unsolicited NAs that can be sent based on a 1296 single event. It is RECOMMENDED that MAX_UNICAST_SOLICIT, 1297 MAX_RTR_SOLICITATIONS and MAX_NEIGHBOR_ADVERTISEMENT be set to 3 the 1298 same as specified in [RFC4861]. 1300 Different values for DEPARTTIME, REPORTTIME, REACHABLETIME, 1301 MAX_UNICAST_SOLICIT, MAX_RTR_SOLCITATIONS and 1302 MAX_NEIGHBOR_ADVERTISEMENT MAY be administratively set; however, if 1303 different values are chosen, all nodes on the link MUST consistently 1304 configure the same values. Most importantly, DEPARTTIME and 1305 REPORTTIME SHOULD be set to a value that is sufficiently longer than 1306 REACHABLETIME to avoid packet loss due to stale route optimization 1307 state. 1309 3.9. AERO Interface Encapsulation and Re-encapsulation 1311 Client AERO interfaces avoid encapsulation over Direct underlying 1312 interfaces and Proxyed underlying interfaces for which the first-hop 1313 access router is AERO-aware. Other AERO interfaces encapsulate 1314 packets according to whether they are entering the AERO interface 1315 from the network layer or if they are being re-admitted into the same 1316 AERO link they arrived on. This latter form of encapsulation is 1317 known as "re-encapsulation". 1319 For packets entering the AERO interface from the network layer, the 1320 AERO interface copies the "TTL/Hop Limit", "Type of Service/Traffic 1321 Class" [RFC2983], "Flow Label"[RFC6438] (for IPv6) and "Congestion 1322 Experienced" [RFC3168] values in the packet's IP header into the 1323 corresponding fields in the encapsulation header(s). 1325 For packets undergoing re-encapsulation, the AERO interface instead 1326 copies these values from the original encapsulation header into the 1327 new encapsulation header, i.e., the values are transferred between 1328 encapsulation headers and *not* copied from the encapsulated packet's 1329 network-layer header. (Note especially that by copying the TTL/Hop 1330 Limit between encapsulation headers the value will eventually 1331 decrement to 0 if there is a (temporary) routing loop.) For IPv4 1332 encapsulation/re-encapsulation, the AERO interface sets the DF bit as 1333 discussed in Section 3.12. 1335 AERO interfaces configured over INET underlying interfaces 1336 encapsulate each packet in a SPAN header, then encapsulate the 1337 resulting SPAN packet in an INET header according to the next hop 1338 determined in the forwarding algorithm in Section 3.13. If the next 1339 hop is reached via a secured tunnel, the AERO interface uses an INET 1340 encapsulation format specific to the secured tunnel type (see: 1341 Section 6). If the next hop is reached via an unsecured underlying 1342 interface, the AERO interface instead uses Generic UDP Encapsulation 1343 (GUE) [I-D.ietf-intarea-gue] or an alternate minimal encapsulation 1344 format Appendix A. 1346 When GUE encapsulation is used, the AERO interface next sets the UDP 1347 source port to a constant value that it will use in each successive 1348 packet it sends, and sets the UDP length field to the length of the 1349 SPAN packet plus 8 bytes for the UDP header itself plus the length of 1350 the GUE header (or 0 if GUE direct IP encapsulation is used). For 1351 packets sent to a Server or Relay, the AERO interface sets the UDP 1352 destination port to 8060, i.e., the IANA-registered port number for 1353 AERO. For packets sent to a Client, the AERO interface sets the UDP 1354 destination port to the port value stored in the neighbor cache entry 1355 for this Client. The AERO interface then either includes or omits 1356 the UDP checksum according to the GUE specification. 1358 AERO interfaces observes the packet sizing and fragmentation 1359 considerations found in Section 3.12. 1361 3.10. AERO Interface Decapsulation 1363 AERO interfaces decapsulate packets destined either to the AERO node 1364 itself or to a destination reached via an interface other than the 1365 AERO interface the packet was received on. When the encapsulated 1366 packet arrives in multiple fragments, the AERO interface reassembles 1367 as discussed in Section 3.12. Further decapsulation steps are 1368 performed according to the appropriate encapsulation format 1369 specification. 1371 3.11. AERO Interface Data Origin Authentication 1373 AERO nodes employ simple data origin authentication procedures. In 1374 particular: 1376 o AERO Relays, Servers and Proxys accept encapsulated data packets 1377 and control messages received from secured tunnels. 1379 o AERO Servers and Proxys accept encapsulated data packets and NS 1380 messages used for Neighbor Unreachability Detection (NUD) received 1381 from a source found in the ROS list. 1383 o AERO Proxys and Clients accept packets that originate from within 1384 the same secured ANET. 1386 o AERO Clients and Gateways accept packets from downstream network 1387 correspondents based on ingress filtering. 1389 AERO nodes silently drop any packets that do not satisfy the above 1390 data origin authentication procedures. Further security 1391 considerations are discussed Section 6. 1393 3.12. AERO Interface MTU and Fragmentation 1395 All IPv6 interfaces are REQUIRED to configure a Maximum Transmission 1396 Unit (MTU) of at least 1280 bytes [RFC8200] and MAY configure a 1397 larger MTU. IPv4 interfaces have a smaller minimum MTU [RFC1122], 1398 but SHOULD observe the IPv6 minimum MTU if possible. 1400 A Client's AERO interface configures an MTU of 9180 bytes [RFC2492]; 1401 the size is therefore not a reflection of the underlying interface 1402 MTUs, but rather determines the AERO interface Maximum Reassembly 1403 Unit (MRU). 1405 When a Client admits an IPv6 packet into the AERO interface that is 1406 larger than the MTU of the selected underlying interface, the AERO 1407 interface encapsulates the packet in a new IPv6 header per [RFC2473] 1408 with source address set to the Client's Source SPAN address and 1409 destination address set to the SPAN address of the next hop. 1411 The AERO interface then uses IPv6 fragmentation to break the 1412 encapsulated packet into fragments that are no larger than the 1413 underlying interface MTU and sends the fragments over the underlying 1414 interface to the next hop. (When encapsulation is needed for 1415 transmission over the underlying interface, an extra encapsulation 1416 header is added to each fragment, and the AERO interface needs to 1417 account for this size during fragmentation.) 1419 When a neighbor has a large packet to send to the Client it uses SPAN 1420 encapsulation and fragmentation as above. The Client then 1421 reassembles the packet and discards the encapsulation header, then 1422 forwards the whole packet to the final destination. 1424 When a Proxy, Server or Gateway forwards a Client's SPAN-encapsulated 1425 packet over the SPAN, it uses IPv6 fragmentation to break the packet 1426 into pieces no larger than 1280 bytes (i.e., the maximum size that is 1427 guaranteed to traverse all IPv6 links). When a Server or Gateway 1428 forwards a Client's SPAN-encapsulated packet to a destination outside 1429 of the AERO link, it reassembles if necessary. 1431 3.13. AERO Interface Forwarding Algorithm 1433 IP packets enter a node's AERO interface either from the network 1434 layer (i.e., from a local application or the IP forwarding system) or 1435 from the link layer (i.e., from an AERO interface neighbor). All 1436 packets entering a node's AERO interface first undergo data origin 1437 authentication as discussed in Section 3.11. Packets that satisfy 1438 data origin authentication are processed further, while all others 1439 are dropped silently. 1441 Packets that enter the AERO interface from the network layer are 1442 forwarded to an AERO interface neighbor. Packets that enter the AERO 1443 interface from the link layer are either re-admitted into the AERO 1444 link or forwarded to the network layer where they are subject to 1445 either local delivery or IP forwarding. In all cases, the AERO 1446 interface itself MUST NOT decrement the network layer TTL/Hop-count 1447 since its forwarding actions occur below the network layer. 1449 AERO interfaces may have multiple underlying interfaces and/or 1450 neighbor cache entries for neighbors with multiple ifIndex-tuple 1451 registrations (see Section 3.6). The AERO interface uses each 1452 packet's DSCP value (and/or other traffic discriminators such as port 1453 number) to select an outgoing underlying interface based on the 1454 node's own QoS preferences, and also to select a destination link- 1455 layer address based on the neighbor's underlying interface with the 1456 highest preference. AERO implementations SHOULD allow for QoS 1457 preference values to be modified at runtime through network 1458 management. 1460 If multiple outgoing interfaces and/or neighbor interfaces have a 1461 preference of "high", the AERO node replicates the packet and sends 1462 one copy via each of the (outgoing / neighbor) interface pairs; 1463 otherwise, the node sends a single copy of the packet via an 1464 interface with the highest preference. AERO nodes keep track of 1465 which underlying interfaces are currently "reachable" or 1466 "unreachable", and only use "reachable" interfaces for forwarding 1467 purposes. 1469 The following sections discuss the AERO interface forwarding 1470 algorithms for Clients, Proxys, Servers and Relays. In the following 1471 discussion, a packet's destination address is said to "match" if it 1472 is the same as a cached address, or if it is covered by a cached 1473 prefix (which may be encoded in an AERO address). 1475 3.13.1. Client Forwarding Algorithm 1477 When an IP packet enters a Client's AERO interface from the network 1478 layer the Client searches for an asymmetric neighbor cache entry that 1479 matches the destination. If there is a match, the Client uses one or 1480 more "reachable" neighbor interfaces in the entry for packet 1481 forwarding. If there is no asymmetric neighbor cache entry, the 1482 Client instead forwards the packet toward a Server (the packet is 1483 intercepted by a Proxy if there is a Proxy on the path). 1485 When an IP packet enters a Client's AERO interface from the link- 1486 layer, if the destination matches one of the Client's MNPs or link- 1487 local addresses the Client decapsulates the packet (if necessary) and 1488 delivers it to the network layer. Otherwise, the Client drops the 1489 packet and MAY return a network-layer ICMP Destination Unreachable 1490 message subject to rate limiting (see: Section 3.14). 1492 3.13.2. Proxy Forwarding Algorithm 1494 For control messages originating from or destined to a Client, the 1495 Proxy intercepts the message and updates its proxy neighbor cache 1496 entry for the Client. The Proxy then forwards a (proxyed) copy of 1497 the control message. (For example, the Proxy forwards a proxied 1498 version of a Client's NS/RS message to the target neighbor, and 1499 forwards a proxied version of the NA/RA reply to the Client.) 1501 When the Proxy receives a data packet from a Client within the ANET, 1502 the Proxy first performs (further) fragmentation per Section 3.12 if 1503 necessary. The Proxy first inserts a SPAN header if the packet does 1504 not already contain a SPAN header. The Proxy then changes the SPAN 1505 header source address to the Client's SPAN address and changes the 1506 destination address to the SPAN address of the next hop. The Proxy 1507 then fragments the SPAN packet into fragments no larger than 1280 1508 bytes if necessary, then searches for an asymmetric neighbor cache 1509 entry that matches the destination and forwards the fragments as 1510 follows: 1512 o if the destination matches an asymmetric neighbor cache entry, the 1513 Proxy uses one or more "reachable" neighbor interfaces in the 1514 entry for packet forwarding via encapsulation. If the neighbor 1515 interface is in the same SPAN segment, the Proxy forwards the 1516 packet directly to the neighbor; otherwise, it forwards the packet 1517 to a Relay. 1519 o else, the Proxy encapsulates and forwards the packet to a Relay 1520 while using the packet's destination address as the SPAN 1521 destination address. (If the destination is an AERO address, the 1522 Proxy instead uses the corresponding Subnet-Router anycast address 1523 for Client AERO addresses and the SPAN address for 1524 administratively-provisioned AERO addresses.). 1526 When the Proxy receives an encapsulated data packet from an INET 1527 neighbor or from a secured tunnel from a Relay, it accepts the packet 1528 only if data origin authentication succeeds and the SPAN destination 1529 address matches its own address. Next, the Proxy searches for a 1530 proxy neighbor cache entry that matches the inner destination. If 1531 there is a proxy neighbor cache entry in the REACHABLE state, the 1532 Proxy forwards the packet to the Client while changing the SPAN 1533 destination address to the Client's SPAN address and performing 1534 additional fragmentation if necessary. If the neighbor cache entry 1535 is in the DEPARTED state, the Proxy instead changes the SPAN 1536 destination address to the address of the new Server and forwards it 1537 to a Relay. If there is no neighbor cache entry, the Proxy instead 1538 discards the packet. 1540 Note that when the Proxy forwards an unfragmented SPAN packet to a 1541 REACHABLE Client for which the packet is no larger than the ANET MTU, 1542 it MAY decapsulate the SPAN header first and forward the 1543 (unencapsulated) packet to the Client to avoid the unnecessary 1544 overhead for carrying the SPAN header. 1546 3.13.3. Server/Gateway Forwarding Algorithm 1548 For control messages destined to a target Client's AERO address that 1549 are received from a secured tunnel, the Server (acting as a MAP) 1550 intercepts the message and sends an appropriate response on behalf of 1551 the Client. (For example, the Server sends an NA message reply in 1552 response to an NS message directed to one of its associated Clients.) 1553 If the Client's neighbor cache entry is in the DEPARTED state, 1554 however, the Server instead forwards the packet to the Client's new 1555 Server as discussed in Section 3.19. 1557 When the Server receives an encapsulated data packet from an INET 1558 neighbor or from a secured tunnel, it accepts the packet only if data 1559 origin authentication succeeds. If the SPAN destination address is 1560 its own address, the Server continues processing as follows: 1562 o if the destination matches a symmetric neighbor cache entry in the 1563 REACHABLE state the Server prepares the packet for forwarding to 1564 the destination Client. If the current header is a SPAN header, 1565 the Server sets the SPAN destination address to the Client's SPAN 1566 address then forwards the packet according to the cached link- 1567 layer information, while using SPAN encapsulation for the Client's 1568 Proxyed/Native interfaces, simple INET encapsulation for NATed/ 1569 VPNed interfaces, or no encapsulation for Direct interfaces. 1571 o else, if the destination matches a symmetric neighbor cache entry 1572 in the DEPARETED state the Server re-encapsulates the packet and 1573 forwards it using the SPAN address of the Client's new Server as 1574 the destination. 1576 o else, if the destination matches an asymmetric neighbor cache 1577 entry, the Server uses one or more "reachable" neighbor interfaces 1578 in the entry for packet forwarding via the local INET if the 1579 neighbor is in the same SPAN segment or via a Relay otherwise. 1581 o else, if the destination is an AERO address that is not assigned 1582 on the AERO interface the Server drops the packet. 1584 o else, the Server (acting as a Gateway) reassembles if necessary, 1585 decapsulates the packet and releases it to the network layer for 1586 local delivery or IP forwarding. Based on the information in the 1587 forwarding table, the network layer may return the packet to the 1588 same AERO interface in which case further processing occurs as 1589 below. (Note that this arrangement accommodates common 1590 implementations in which the IP forwarding table is not accessible 1591 from within the AERO interface. If the AERO interface can 1592 directly access the IP forwarding table (such as for in-kernel 1593 implementations) the forwarding table lookup can instead be 1594 performed internally from within the AERO interface itself.) 1596 When the Server's AERO interface receives a data packet from the 1597 network layer or from a NATed/VPNed/Direct Client, it performs SPAN 1598 encapsualtion and fragmentation if necessary, then processes the 1599 packet according to the network-layer destination address as follows: 1601 o if the destination matches a symmetric or asymmetric neighbor 1602 cache entry the Server processes the packet as above. 1604 o else, the Server encapsulates the packet and forwards it to a 1605 Relay. For administratively-assigned AERO address destinations, 1606 the Server uses the SPAN address corresponding to the destination 1607 as the SPAN destination address. For Client AERO address 1608 destinations, the Server uses the Subnet-Router anycast address 1609 corresponding to the destination as the SPAN destination address. 1610 For all others, the Server uses the packet's destination IP 1611 address as the SPAN destination address. 1613 3.13.4. Relay Forwarding Algorithm 1615 Relays forward packets over secured tunnels the same as any IP 1616 router. When the Relay receives an encapsulated packet via a secured 1617 tunnel, it removes the INET header and searches for a forwarding 1618 table entry that matches the destination address in the next header. 1619 The Relay then processes the packet as follows: 1621 o if the destination matches one of the Relay's own addresses, the 1622 Relay submits the packet for local delivery. 1624 o else, if the destination matches a forwarding table entry the 1625 Relay forwards the packet via a secured tunnel to the next hop. 1626 If the destination matches an MSP without matching an MNP, 1627 however, the Relay instead drops the packet and returns an ICMP 1628 Destination Unreachable message subject to rate limiting (see: 1629 Section 3.14). 1631 o else, the Relay drops the packet and returns an ICMP Destination 1632 Unreachable as above. 1634 As for any IP router, the Relay decrements the TTL/Hop Limit when it 1635 forwards the packet. If the packet is encapsulated in a SPAN header, 1636 only the Hop Limit in the SPAN header is decremented, and not the 1637 TTL/Hop Limit in the inner packet header. 1639 3.14. AERO Interface Error Handling 1641 When an AERO node admits a packet into the AERO interface, it may 1642 receive link-layer or network-layer error indications. 1644 A link-layer error indication is an ICMP error message generated by a 1645 router in the INET on the path to the neighbor or by the neighbor 1646 itself. The message includes an IP header with the address of the 1647 node that generated the error as the source address and with the 1648 link-layer address of the AERO node as the destination address. 1650 The IP header is followed by an ICMP header that includes an error 1651 Type, Code and Checksum. Valid type values include "Destination 1652 Unreachable", "Time Exceeded" and "Parameter Problem" 1653 [RFC0792][RFC4443]. (AERO interfaces ignore all link-layer IPv4 1654 "Fragmentation Needed" and IPv6 "Packet Too Big" messages since they 1655 only emit packets that are guaranteed to be no larger than the IP 1656 minimum link MTU as discussed in Section 3.12.) 1658 The ICMP header is followed by the leading portion of the packet that 1659 generated the error, also known as the "packet-in-error". For 1660 ICMPv6, [RFC4443] specifies that the packet-in-error includes: "As 1661 much of invoking packet as possible without the ICMPv6 packet 1662 exceeding the minimum IPv6 MTU" (i.e., no more than 1280 bytes). For 1663 ICMPv4, [RFC0792] specifies that the packet-in-error includes: 1664 "Internet Header + 64 bits of Original Data Datagram", however 1665 [RFC1812] Section 4.3.2.3 updates this specification by stating: "the 1666 ICMP datagram SHOULD contain as much of the original datagram as 1667 possible without the length of the ICMP datagram exceeding 576 1668 bytes". 1670 The link-layer error message format is shown in Figure 5 (where, "L2" 1671 and "L3" refer to link-layer and network-layer, respectively): 1673 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1674 ~ ~ 1675 | L2 IP Header of | 1676 | error message | 1677 ~ ~ 1678 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1679 | L2 ICMP Header | 1680 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 1681 ~ ~ P 1682 | IP and other encapsulation | a 1683 | headers of original L3 packet | c 1684 ~ ~ k 1685 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ e 1686 ~ ~ t 1687 | IP header of | 1688 | original L3 packet | i 1689 ~ ~ n 1690 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1691 ~ ~ e 1692 | Upper layer headers and | r 1693 | leading portion of body | r 1694 | of the original L3 packet | o 1695 ~ ~ r 1696 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 1698 Figure 5: AERO Interface Link-Layer Error Message Format 1700 The AERO node rules for processing these link-layer error messages 1701 are as follows: 1703 o When an AERO node receives a link-layer Parameter Problem message, 1704 it processes the message the same as described as for ordinary 1705 ICMP errors in the normative references [RFC0792][RFC4443]. 1707 o When an AERO node receives persistent link-layer Time Exceeded 1708 messages, the IP ID field may be wrapping before earlier fragments 1709 awaiting reassembly have been processed. In that case, the node 1710 should begin including integrity checks and/or institute rate 1711 limits for subsequent packets. 1713 o When an AERO node receives persistent link-layer Destination 1714 Unreachable messages in response to encapsulated packets that it 1715 sends to one of its asymmetric neighbor correspondents, the node 1716 should process the message as an indication that a path may be 1717 failing, and optionally initiate NUD over that path. If it 1718 receives Destination Unreachable messages over multiple paths, the 1719 node should allow future packets destined to the correspondent to 1720 flow through a default route and re-initiate route optimization. 1722 o When an AERO Client receives persistent link-layer Destination 1723 Unreachable messages in response to encapsulated packets that it 1724 sends to one of its symmetric neighbor Servers, the Client should 1725 mark the path as unusable and use another path. If it receives 1726 Destination Unreachable messages on many or all paths, the Client 1727 should associate with a new Server and release its association 1728 with the old Server as specified in Section 3.19.5. 1730 o When an AERO Server receives persistent link-layer Destination 1731 Unreachable messages in response to encapsulated packets that it 1732 sends to one of its symmetric neighbor Clients, the Server should 1733 mark the underlying path as unusable and use another underlying 1734 path. 1736 o When an AERO Server or Proxy receives link-layer Destination 1737 Unreachable messages in response to an encapsulated packet that it 1738 sends to one of its permanent neighbors, it treats the messages as 1739 an indication that the path to the neighbor may be failing. 1740 However, the dynamic routing protocol should soon reconverge and 1741 correct the temporary outage. 1743 When an AERO Relay receives a packet for which the network-layer 1744 destination address is covered by an MSP, if there is no more- 1745 specific routing information for the destination the Relay drops the 1746 packet and returns a network-layer Destination Unreachable message 1747 subject to rate limiting. The Relay writes the network-layer source 1748 address of the original packet as the destination address and uses 1749 one of its non link-local addresses as the source address of the 1750 message. 1752 When an AERO node receives an encapsulated packet for which the 1753 reassembly buffer it too small, it drops the packet and returns a 1754 network-layer Packet Too Big (PTB) message. The node first writes 1755 the MRU value into the PTB message MTU field, writes the network- 1756 layer source address of the original packet as the destination 1757 address and writes one of its non link-local addresses as the source 1758 address. 1760 3.15. AERO Router Discovery, Prefix Delegation and Autoconfiguration 1762 AERO Router Discovery, Prefix Delegation and Autoconfiguration are 1763 coordinated as discussed in the following Sections. 1765 3.15.1. AERO ND/PD Service Model 1767 Each AERO Server on the link configures a PD service to facilitate 1768 Client requests. Each Server is provisioned with a database of MNP- 1769 to-Client ID mappings for all Clients enrolled in the AERO service, 1770 as well as any information necessary to authenticate each Client. 1771 The Client database is maintained by a central administrative 1772 authority for the AERO link and securely distributed to all Servers, 1773 e.g., via the Lightweight Directory Access Protocol (LDAP) [RFC4511], 1774 via static configuration, etc. Clients receive the same service 1775 regardless of the Servers they select. 1777 AERO Clients and Servers use ND messages to maintain neighbor cache 1778 entries. AERO Servers configure their AERO interfaces as advertising 1779 interfaces, and therefore send unicast RA messages with a short 1780 Router Lifetime value (e.g., REACHABLETIME seconds) in response to a 1781 Client's RS message. Thereafter, Clients send additional RS messages 1782 to keep Server state alive. 1784 AERO Clients and Servers include PD parameters in RS/RA messages (see 1785 [I-D.templin-6man-dhcpv6-ndopt] for ND/PD alternatives). The unified 1786 ND/PD messages are exchanged between Client and Server according to 1787 the prefix management schedule required by the PD service. If the 1788 Client knows its MNP in advance, it can instead employ prefix 1789 registration by including its AERO address as the source address of 1790 an RS message and with an OMNI option with valid prefix registration 1791 information for the MNP. If the Server (and Proxy) accept the 1792 Client's MNP assertion, they inject the prefix into the routing 1793 system and establish the necessary neighbor cache state. 1795 The following sections specify the Client and Server behavior. 1797 3.15.2. AERO Client Behavior 1799 AERO Clients discover the addresses of Servers in a similar manner as 1800 described in [RFC5214]. Discovery methods include static 1801 configuration (e.g., from a flat-file map of Server addresses and 1802 locations), or through an automated means such as Domain Name System 1803 (DNS) name resolution [RFC1035]. Alternatively, the Client can 1804 discover Server addresses through a layer 2 data link login exchange, 1805 or through a unicast RA response to a multicast/anycast RS as 1806 described below. In the absence of other information, the Client can 1807 resolve the DNS Fully-Qualified Domain Name (FQDN) 1808 "linkupnetworks.[domainname]" where "linkupnetworks" is a constant 1809 text string and "[domainname]" is a DNS suffix for the AERO link 1810 (e.g., "example.com"). 1812 To associate with a Server, the Client acts as a requesting router to 1813 request MNPs. The Client prepares an RS message with PD parameters 1814 and includes a Nonce and Timestamp option if the Client needs to 1815 correlate RA replies. If the Client already knows the Server's AERO 1816 address, it includes the AERO address as the network-layer 1817 destination address; otherwise, it includes the link-scoped All- 1818 Routers multicast (ff02::2) or Subnet-Router anycast (fe80::) address 1819 as the network-layer destination. If the Client already knows its 1820 own AERO address, it uses the AERO address as the network-layer 1821 source address; otherwise, it uses the unspecified AERO address 1822 (fe80::ffff:ffff) as the network-layer source address. 1824 The Client next includes an OMNI option in the RS message to register 1825 its link-layer information with the Server. The Client sets the OMNI 1826 option prefix registration information according to the MNP, and 1827 includes a first ifIndex-tuple corresponding to the underlying 1828 interface over which the Client will send the RS message. The Client 1829 MAY include additional ifIndex-tuples specific to other underlying 1830 interfaces. The Client MAY also include an SLLAO with a single link- 1831 layer address corresponding to the first OMNI option ifIndex-tuple. 1832 The Client sets a "primary" flag in the OMNI option if it wishes to 1833 enable proxy keepalives on this underlying interface. 1835 The Client then sends the RS message (either directly via Direct 1836 interfaces, via INET encapsulation for NATed interfaces, via a VPN 1837 for VPNed interfaces, via a Proxy for proxyed interfaces or via a 1838 Relay for native interfaces) and waits for an RA message reply (see 1839 Section 3.15.3). The Client retries up to MAX_RTR_SOLICITATIONS 1840 times until an RA is received. If the Client receives no RAs, or if 1841 it receives an RA with Router Lifetime set to 0, the Client SHOULD 1842 abandon this Server and try another Server. Otherwise, the Client 1843 processes the PD information found in the RA message. 1845 Next, the Client creates a symmetric neighbor cache entry with the 1846 Server's AERO address as the network-layer address and the Server's 1847 encapsulation and/or link-layer addresses as the link-layer address. 1848 The Client records the RA Router Lifetime field value in the neighbor 1849 cache entry as the time for which the Server has committed to 1850 maintaining the MNP in the routing system, and caches the other RA 1851 configuration information including Cur Hop Limit, M and O flags, 1852 Reachable Time and Retrans Timer. The Client then autoconfigures 1853 AERO addresses for each of the delegated MNPs and assigns them to the 1854 AERO interface. The Client also caches any MSPs included in Route 1855 Information Options (RIOs) [RFC4191] as MSPs to associate with the 1856 AERO link, and assigns the MTU value in the MTU option to the 1857 underlying interface. 1859 The Client then registers additional underlying interfaces with the 1860 Server by sending RS messages via each additional interface. The RS 1861 messages include the same parameters as for the initial RS/RA 1862 exchange, but with destination address set to the Server's AERO 1863 address and with the initial OMNI option ifIndex-tuple corresponding 1864 to the underlying interface. The Client sets a "primary" flag in the 1865 OMNI option if it wishes to enable proxy keepalives on this 1866 underlying interface. 1868 Following autoconfiguration, the Client sub-delegates the MNPs to its 1869 attached EUNs and/or the Client's own internal virtual interfaces as 1870 described in [I-D.templin-v6ops-pdhost] to support the Client's 1871 downstream attached "Internet of Things (IoT)". The Client 1872 subsequently sends additional RS messages over each underlying 1873 interface before the Router Lifetime received for that interface 1874 expires. 1876 After the Client registers its underlying interfaces, it may wish to 1877 change one or more registrations, e.g., if an interface changes 1878 address or becomes unavailable, if QoS preferences change, etc. To 1879 do so, the Client prepares an RS message to send over any available 1880 underlying interface. The RS includes an OMNI option with prefix 1881 registration information specific to its MNP, with a first ifIndex- 1882 tuple specific to the selected underlying interface, and with any 1883 additional ifIndex-tuples specific to other underlying interfaces. 1884 The Client includes fresh ifIndex-tuple values to update the Server's 1885 neighbor cache entry. When the Client receives the Server's RA 1886 response, it has assurance that the Server has been updated with the 1887 new information. 1889 If the Client wishes to discontinue use of a Server it issues an RS 1890 message over any underlying interface with an OMNI option with a 1891 prefix release indication. When the Server processes the message, it 1892 releases the MNP, sets the symmetric neighbor cache entry state for 1893 the Client to DEPARTED and returns an RA reply with Router Lifetime 1894 set to 0. After a short delay (e.g., 2 seconds), the Server 1895 withdraws the MNP from the routing system. 1897 3.15.3. AERO Server Behavior 1899 AERO Servers act as IP routers and support a PD service for Clients. 1900 Servers arrange to add their AERO addresses to a static map of Server 1901 addresses for the link and/or the DNS resource records for the FQDN 1902 "linkupnetworks.[domainname]" before entering service. Server 1903 addresses should be geographically and/or topologically referenced, 1904 and made available for discovery by Clients on the AERO link. 1906 When a Server receives a prospective Client's RS message on its AERO 1907 interface, it SHOULD return an immediate RA reply with Router 1908 Lifetime set to 0 if it is currently too busy or otherwise unable to 1909 service the Client. Otherwise, the Server authenticates the RS 1910 message and processes the PD parameters. The Server first determines 1911 the correct MNPs to delegate to the Client by searching the Client 1912 database. When the Server delegates the MNPs, it also creates a 1913 forwarding table entry for each MNP so that the MNPs are propagated 1914 into the routing system (see: Section 3.3). For IPv6, the Server 1915 creates an IPv6 forwarding table entry for each MNP. For IPv4, the 1916 Server creates an IPv6 forwarding table entry with the SPAN 1917 Compatibility Prefix (SCP) corresponding to the IPv4 address. 1919 The Server next creates a symmetric neighbor cache entry for the 1920 Client using the base AERO address as the network-layer address and 1921 with lifetime set to no more than the smallest PD lifetime. Next, 1922 the Server updates the neighbor cache entry by recording the 1923 information in each ifIndex-tuple in the RS OMNI option. The Server 1924 also records the actual SPAN/INET addresses in the neighbor cache 1925 entry. If an SLLAO was present, the Server also compares the SLLAO 1926 address information for the first ifIndex-tuple with the SPAN/INET 1927 information to determine if there is a NAT on the path. 1929 Next, the Server prepares an RA message using its AERO address as the 1930 network-layer source address and the network-layer source address of 1931 the RS message as the network-layer destination address. The Server 1932 sets the Router Lifetime to the time for which it will maintain the 1933 symmetric neighbor cache entry, and sets Cur Hop Limit, M and O 1934 flags, Reachable Time and Retrans Timer to values appropriate for the 1935 AERO link. The Server includes the delegated MNPs, any other PD 1936 parameters and an OMNI option with an ifIndex-tuple with ifIndex set 1937 to 0. The Server then includes one or more RIOs that encode the MSPs 1938 for the AERO link, plus an MTU option (see Section 3.12). The Server 1939 finally forwards the message to the Client using SPAN/INET, INET, or 1940 NULL encapsulation as necessary. 1942 After the initial RS/RA exchange, the Server maintains a 1943 ReachableTime timer for the Client's symmetric neighbor cache entry 1944 set to expire after Router Lifetime seconds. If the Client (or 1945 Proxy) issues additional RS messages, the Server sends an RA response 1946 and resets ReachableTime. If the Server receives an ND message with 1947 PD release indication it sets the Client's symmetric neighbor cache 1948 entry to the DEPARTED state and withdraws the MNP from the routing 1949 system after a short delay (e.g., 2 seconds). If ReachableTime 1950 expires before a new RS is received, the Server deletes the neighbor 1951 cache entry and withdraws the MNP without delay. 1953 The Server processes any ND/PD messages pertaining to the Client and 1954 returns an NA/RA reply in response to solicitations. The Server may 1955 also issue unsolicited RA messages, e.g., with PD reconfigure 1956 parameters to cause the Client to renegotiate its PDs, with Router 1957 Lifetime set to 0 if it can no longer service this Client, etc. 1958 Finally, If the symmetric neighbor cache entry is in the DEPARTED 1959 state, the Server deletes the entry after DepartTime expires. 1961 Note: Clients SHOULD notify former Servers of their departures, but 1962 Servers are responsible for expiring neighbor cache entries and 1963 withdrawing routes even if no departure notification is received 1964 (e.g., if the Client leaves the network unexpectedly). Servers 1965 SHOULD therefore set Router Lifetime to REACHABLETIME seconds in 1966 solicited RA messages to minimize persistent stale cache information 1967 in the absence of Client departure notifications. A short Router 1968 Lifetime also ensures that proactive Client/Server RS/RA messaging 1969 will keep any NAT state alive (see above). 1971 Note: All Servers on an AERO link MUST advertise consistent values in 1972 the RA Cur Hop Limit, M and O flags, Reachable Time and Retrans Timer 1973 fields the same as for any link, since unpredictable behavior could 1974 result if different Servers on the same link advertised different 1975 values. 1977 3.15.3.1. Lightweight DHCPv6 Relay Agent (LDRA) 1979 When DHCPv6 is used as the ND/PD service back end, AERO Clients and 1980 Servers are always on the same link (i.e., the AERO link) from the 1981 perspective of DHCPv6. However, in some implementations the DHCPv6 1982 server and ND function may be located in separate modules. In that 1983 case, the Server's AERO interface module can act as a Lightweight 1984 DHCPv6 Relay Agent (LDRA)[RFC6221] to relay PD messages to and from 1985 the DHCPv6 server module. 1987 When the LDRA receives an authentic RS message, it extracts the PD 1988 message parameters and uses them to construct an IPv6/UDP/DHCPv6 1989 message. It sets the IPv6 source address to the source address of 1990 the RS message, sets the IPv6 destination address to 1991 'All_DHCP_Relay_Agents_and_Servers' and sets the UDP fields to values 1992 that will be understood by the DHCPv6 server. 1994 The LDRA then wraps the message in a DHCPv6 'Relay-Forward' message 1995 header and includes an 'Interface-Id' option that includes enough 1996 information to allow the LDRA to forward the resulting Reply message 1997 back to the Client (e.g., the Client's link-layer addresses, a 1998 security association identifier, etc.). The LDRA also wraps the OMNI 1999 option and SLLAO into the Interface-Id option, then forwards the 2000 message to the DHCPv6 server. 2002 When the DHCPv6 server prepares a Reply message, it wraps the message 2003 in a 'Relay-Reply' message and echoes the Interface-Id option. The 2004 DHCPv6 server then delivers the Relay-Reply message to the LDRA, 2005 which discards the Relay-Reply wrapper and IPv6/UDP headers, then 2006 uses the DHCPv6 message to construct an RA response to the Client. 2007 The Server uses the information in the Interface-Id option to prepare 2008 the RA message and to cache the link-layer addresses taken from the 2009 OMNI option and SLLAO echoed in the Interface-Id option. 2011 3.16. The AERO Proxy 2013 Clients may connect to ANETs that require a perimeter security 2014 gateway to enable communications to Servers in outside INETs. In 2015 that case, the ANET can employ an AERO Proxy. The Proxy is located 2016 at the ANET/INET border and listens for RS messages originating from 2017 or RA messages destined to ANET Clients. The Proxy acts on these 2018 control messages as follows: 2020 o when the Proxy receives an RS message from a new ANET Client, it 2021 first authenticates the message then examines the network-layer 2022 destination address. If the destination address is a Server's 2023 AERO address, the Proxy proceeds to the next step. Otherwise, if 2024 the destination is All-Routers multicast or Subnet-Router anycast, 2025 the Proxy selects a "nearby" Server that is likely to be a good 2026 candidate to serve the Client and replaces the destination address 2027 with the Server's AERO address. Next, the Proxy creates a proxy 2028 neighbor cache entry and caches the Client and Server link-layer 2029 addresses along with the OMNI option information and any other 2030 identifying information including Transaction IDs, Client 2031 Identifiers, Nonce values, etc. The Proxy then replaces the SLLAO 2032 in the RS message (if present) with a new SLLAO with a single 2033 ifIndex-tuple matching the first ifIndex-tuple in the OMNI option 2034 and with the Link Layer Address and Port Number fields set to the 2035 Proxy's SPAN address. The Proxy finally encapsulates the 2036 (proxyed) RS message in a SPAN header with destination set to the 2037 Server's SPAN address then forwards the message into the SPAN. 2039 o when the Server receives the RS, it authenticates the message then 2040 creates or updates a symmetric neighbor cache entry for the Client 2041 with the Proxy's SPAN address as the link-layer address. The 2042 Server then sends an RA message back to the Proxy via the SPAN. 2044 o when the Proxy receives the RA, it authenticates the message and 2045 matches it with the proxy neighbor cache entry created by the RS. 2046 The Proxy then caches the PD route information as a mapping from 2047 the Client's MNPs to the Client's ANET address, caches the 2048 Server's advertised Router Lifetime and sets the neighbor cache 2049 entry state to REACHABLE. The Proxy then replaces the RA SLLAO 2050 with an SLLAO with its own ANET address, sets the P bit in the RA 2051 flags field, sets the OMNI option "primary" flag according to the 2052 cached value from the RS, optionally rewrites the Router Lifetime 2053 and forwards the (proxyed) message to the Client. If the RA 2054 included an MTU option, the Proxy rewrites the MTU value (if 2055 necessary) to the minimum of the received MTU value and the MTU of 2056 the underlying ANET interface. 2058 After the initial RS/RA exchange, the Proxy forwards any Client data 2059 packets for which there is no matching asymmetric neighbor cache 2060 entry to a Relay via the SPAN. The Proxy instead forwards any Client 2061 data destined to an asymmetric neighbor cache target directly to the 2062 target according to the link-layer information - the process of 2063 establishing asymmetric neighbor cache entries is specified in 2064 Section 3.17. 2066 While the Client is still attached to the ANET, the Proxy sends NS, 2067 RS and/or unsolicited NA messages to update the Server's symmetric 2068 neighbor cache entries on behalf of the Client and/or to convey QoS 2069 updates. If the "primary" flag was set, the Proxy performs periodic 2070 RS/RA exchanges on the Client's behalf according to the cached Server 2071 lifetime. This allows for higher-frequency Proxy-initiated RS/RA 2072 messaging over well-connected INET infrastructure supplemented by 2073 lower-frequency Client-initiated RS/RA messaging over constrained 2074 ANET data links. 2076 If the Server ceases to send solicited advertisements, the Proxy 2077 deletes the neighbor cache entry and sends unsolicited RAs on the 2078 ANET interface with destination set to All-Nodes multicast (ff02::1) 2079 and with Router Lifetime set to zero to inform Clients that the 2080 Server has failed. Although the Proxy engages in ND exchanges on 2081 behalf of the Client, the Client can also send ND messages on its own 2082 behalf, e.g., if it is in a better position than the Proxy to convey 2083 QoS changes, etc. For this reason, the Proxy marks any Client- 2084 originated solicitation messages (e.g. by inserting a Nonce option) 2085 so that it can return the solicited advertisement to the Client 2086 instead of processsing it locally. 2088 If the Client becomes unreachable, the Proxy sets the neighbor cache 2089 entry state to DEPARTED and retains the entry for DEPARTTIME seconds. 2090 While the state is DEPARTED, the Proxy forwards any packets destined 2091 to the Client to a Relay. The Relay in turn forwards the packets to 2092 the Client's current Server. When DepartTime expires, the Proxy 2093 deletes the neighbor cache entry and discards any further packets 2094 destined to this (now forgotten) Client. 2096 In some ANETs that employ a Proxy, the Client's MNP can be injected 2097 into the ANET routing system. In that case, the Client can send data 2098 messages without encapsulation so that the ANET native routing system 2099 transports the unencapsulated packets to the Proxy. This can be very 2100 beneficial, e.g., if the Client connects to the ANET via low-end data 2101 links such as some aviation wireless links. 2103 If the first-hop ANET access router is AERO-aware, the Client can 2104 avoid encapsulation for both its control and data messages. When the 2105 Client connects to the link, it can send an unencapsulated RS message 2106 with source address set to its AERO address and with destination 2107 address set to the AERO address of the Client's selected Server or to 2108 All-Routers multicast or Subnet-Router anycast. The Client includes 2109 an OMNI option formatted as specified in 2110 [I-D.templin-atn-aero-interface]. 2112 The Client then sends the unencapsulated RS message, which will be 2113 intercepted by the AERO-Aware access router. The access router then 2114 encapsulates the RS message in an ANET header with its own address as 2115 the source address and the address of a Proxy as the destination 2116 address. The access router further remembers the address of the 2117 Proxy so that it can encapsulate future data packets from the Client 2118 via the same Proxy. If the access router needs to change to a new 2119 Proxy, it simply sends another RS message toward the Server via the 2120 new Proxy on behalf of the Client. 2122 In some cases, the access router and Proxy may be one and the same 2123 node. In that case, the node would be located on the same physical 2124 link as the Client, but its message exchanges with the Server would 2125 need to pass through a security gateway at the ANET/INET border. The 2126 method for deploying access routers and Proxys (i.e. as a single node 2127 or multiple nodes) is an ANET-local administrative consideration. 2129 3.16.1. Detecting and Responding to Server Failures 2131 In environments where fast recovery from Server failure is required, 2132 Proxys SHOULD use proactive Neighbor Unreachability Detection (NUD) 2133 to track Server reachability in a similar fashion as for 2134 Bidirectional Forwarding Detection (BFD) [RFC5880]. Proxys can then 2135 quickly detect and react to failures so that cached information is 2136 re-established through alternate paths. The NUD control messaging is 2137 carried only over well-connected ground domain networks (i.e., and 2138 not low-end aeronautical radio links) and can therefore be tuned for 2139 rapid response. 2141 Proxys perform proactive NUD with Servers for which there are 2142 currently active ANET Clients by sending continuous NS messages in 2143 rapid succession, e.g., one message per second. The Proxy sends the 2144 NS message via the SPAN with the Proxy's AERO address as the source 2145 and the AERO address of the Server as the destination. When the 2146 Proxy is also sending RS messages to the Server on behalf of ANET 2147 Clients, the resulting RA responses can be considered as equivalent 2148 hints of forward progress. This means that the Proxy need not also 2149 send a periodic NS if it has already sent an RS within the same 2150 period. If the Server fails (i.e., if the Proxy ceases to receive 2151 advertisements), the Proxy can quickly inform Clients by sending 2152 multicast RA messages on the ANET interface. 2154 The Proxy sends RA messages on the ANET interface with source address 2155 set to the Server's address, destination address set to All-Nodes 2156 multicast, and Router Lifetime set to 0. The Proxy SHOULD send 2157 MAX_FINAL_RTR_ADVERTISEMENTS RA messages separated by small delays 2158 [RFC4861]. Any Clients on the ANET that had been using the failed 2159 Server will receive the RA messages and associate with a new Server. 2161 3.17. AERO Route Optimization 2163 While data packets are flowing between a source and target node, 2164 route optimization SHOULD be used. Route optimization is initiated 2165 by the first eligible Route Optimization Source (ROS) closest to the 2166 source as follows: 2168 o For Clients on VPNed, NATed and Direct interfaces, the Server is 2169 the ROS. 2171 o For Clients on Proxyed interfaces, the Proxy is the ROS. 2173 o For Clients on native interfaces, the Client itself is the ROS. 2175 o For correspondent nodes on INET/EUN interfaces serviced by a 2176 Gateway, the Gateway is the ROS. 2178 The route optimization procedure is conducted between the ROS and the 2179 target Server/Gateway acting as a Route Optimization Responder (ROR) 2180 in the same manner as for IPv6 ND Address Resolution and using the 2181 same NS/NA messaging. The target may either be a MNP Client serviced 2182 by a Server, or a non-MNP correspondent reachable via a Gateway. 2184 The procedures are specified in the following sections. 2186 3.17.1. Route Optimization Initiation 2188 While data packets are flowing from the source node toward a target 2189 node, the ROS performs address resolution by sending an NS message to 2190 receive a solicited NA message from the ROR. 2192 When the ROS sends an NS, it includes the AERO address of the ROS as 2193 the source address (e.g., fe80::1) and the AERO address corresponding 2194 to the data packet's destination address as the destination address 2195 (e.g., if the destination address is 2001:db8:1:2::1 then the 2196 corresponding AERO address is fe80::2001:db8:1:2). The NS message 2197 includes an OMNI option with a single ifIndex-tuple with ifIndex set 2198 to 0, and an SLLAO with the SPAN address of the ROS. The message 2199 also includes a Nonce and Timestamp option if the ROS needs to 2200 correlate NA replies. 2202 The ROS then encapsulates the NS message in a SPAN header with source 2203 set to its own SPAN address and destination set to the data packet's 2204 destination address, then sends the message into the SPAN without 2205 decrementing the network-layer TTL/Hop Limit field. 2207 3.17.2. Relaying the NS 2209 When the Relay receives the NS message from the ROS, it discards the 2210 INET header and determines that the ROR is the next hop by consulting 2211 its standard IPv6 forwarding table for the SPAN header destination 2212 address. The Relay then forwards the SPAN message toward the ROR the 2213 same as for any IPv6 router. The final-hop Relay in the SPAN will 2214 deliver the message via a secured tunnel to the ROR. 2216 3.17.3. Processing the NS and Sending the NA 2218 When the ROR receives the NS message, it examines the AERO 2219 destination address to determine whether it has a neighbor cache 2220 entry and/or route that matches the target. If there is no match, 2221 the ROR drops the NS message. Otherwise, the ROR continues 2222 processing as follows: 2224 o if the target belongs to an MNP Client neighbor in the DEPARTED 2225 state the ROR changes the NS message SPAN destination address to 2226 the SPAN address of the Client's new Server, forwards the message 2227 into the SPAN and returns from processing. 2229 o If the target belongs to an MNP Client neighbor in the REACHABLE 2230 state, the ROR instead adds the AERO source address to the target 2231 Client's Report List with time set to ReportTime. 2233 o If the target belongs to a non-MNP route, the ROR continues 2234 processing without adding an entry to the Report List. 2236 The ROR then prepares a solicited NA message to send back to the ROS 2237 but does not create a neighbor cache entry. The ROR sets the NA 2238 source address to the destination AERO address of the NS, and 2239 includes the Nonce value received in the NS plus the current 2240 Timestamp. 2242 If the target belongs to an MNP Client, the ROR then includes an OMNI 2243 option with prefix registration length set to the length of the MNP; 2244 otherwise, set to the maximum of the non-MNP prefix length and 64. 2245 (Note that a /64 limit is imposed to avoid causing the ROS to set 2246 short prefixes (e.g., "default") that would match destinations for 2247 which the routing system includes more-specific prefixes.) 2249 The ROR next includes a first ifIndex-tuple in the OMNI option with 2250 ifIndex set to 0. If the target belongs to an MNP Client, the ROR 2251 next includes additional ifIndex-tuples in the OMNI option for each 2252 of the target Client's underlying interfaces with current information 2253 for each interface 2255 The ROR then includes a TLLAO option with ifIndex-tuples in one-to- 2256 one correspondence with the tuples that appear in the OMNI option. 2257 For NATed, VPNed and Direct interfaces, the link layer addresses are 2258 the SPAN address of the ROR. For Proxyed interfaces, the link-layer 2259 addresses are the SPAN addresses of the Proxy's INET interfaces. For 2260 native interfaces, the link-layer addresses are the SPAN addesses of 2261 the Client's native interfaces. 2263 The ROR finally encapsulates the NA message in a SPAN header with 2264 source set to its own SPAN address and destination set to the source 2265 SPAN address of the NS message, then forwards the message into the 2266 SPAN without decrementing the network-layer TTL/Hop Limit field. 2268 3.17.4. Relaying the NA 2270 When the Relay receives the NA message from the ROR, it discards the 2271 INET header and determines that the ROS is the next hop by consulting 2272 its standard IPv6 forwarding table for the SPAN header destination 2273 address. The Relay then forwards the SPAN-encapsulated NA message 2274 toward the ROS the same as for any IPv6 router. The final-hop Relay 2275 in the SPAN will deliver the message via a secured tunnel to the ROS. 2277 3.17.5. Processing the NA 2279 When the ROS receives the solicited NA message, it caches the source 2280 SPAN address then discards the INET and SPAN headers. The ROS next 2281 verifies the Nonce and Timestamp values (if present), then creates an 2282 asymmetric neighbor cache entry for the ROR and caches all 2283 information found in the solicited NA OMNI and TLLAO options. The 2284 ROS finally sets the asymmetric neighbor cache entry lifetime to 2285 REACHABLETIME seconds. 2287 3.17.6. Route Optimization Maintenance 2289 Following route optimization, the ROS forwards future data packets 2290 destined to the target via the addresses found in the cached link- 2291 layer information. The route optimization is shared by all sources 2292 that send packets to the target via the ROS, i.e., and not just the 2293 source on behalf of which the route optimization was initiated. 2295 While new data packets destined to the target are flowing through the 2296 ROS, it sends additional NS messages to the ROR before ReachableTime 2297 expires to receive a fresh solicited NA message the same as described 2298 in the previous sections (route optimization refreshment strategies 2299 are an implementation matter, with a non-normative example given in 2300 Appendix B.1). The ROS uses the cached SPAN address of the ROR as 2301 the NS SPAN destination address, and sends up to MAX_UNICAST_SOLICIT 2302 NS messages separated by 1 second until an NA is received. If no NA 2303 is received, the ROS assumes that the current ROR has become 2304 unreachable and deletes the neighbor cache entry. Subsequent data 2305 packets will trigger a new route optimization per Section 3.17.1 to 2306 discover a new ROR while initial data packets travel over a 2307 suboptimal route. 2309 If an NA is received, the ROS then updates the asymmetric neighbor 2310 cache entry to refresh ReachableTime, while (for MNP destinations) 2311 the ROR adds or updates the ROS address to the target Client's Report 2312 List and with time set to ReportTime. While no data packets are 2313 flowing, the ROS instead allows ReachableTime for the asymmetric 2314 neighbor cache entry to expire. When ReachableTime expires, the ROS 2315 deletes the asymmetric neighbor cache entry. Any future data packets 2316 flowing through the ROS will again trigger a new route optimization. 2318 The ROS may also receive unsolicited NA messages from the ROR at any 2319 time (see: Section 3.19). If there is an asymmetric neighbor cache 2320 entry for the target, the ROS updates the link-layer information but 2321 does not update ReachableTime since the receipt of an unsolicited NA 2322 does not confirm that the forward path is still working. If there is 2323 no asymmetric neighbor cache entry, the ROS simply discards the 2324 unsolicited NA. 2326 In this arrangement, the ROS holds an asymmetric neighbor cache entry 2327 for the ROR, but the ROR does not hold an asymmetric neighbor cache 2328 entry for the ROS. The route optimization neighbor relationship is 2329 therefore asymmetric and unidirectional. If the target node also has 2330 packets to send back to the source node, then a separate route 2331 optimization procedure is performed in the reverse direction. But, 2332 there is no requirement that the forward and reverse paths be 2333 symmetric. 2335 3.18. Neighbor Unreachability Detection (NUD) 2337 AERO nodes perform Neighbor Unreachability Detection (NUD) per 2338 [RFC4861]. NUD is performed either reactively in response to 2339 persistent link-layer errors (see Section 3.14) or proactively to 2340 confirm reachability. The NUD algorithm is based on periodic 2341 authentic NS/NA message exchanges. The algorithm may further be 2342 seeded by ND hints of forward progress, but care must be taken to 2343 avoid inferring reachability based on spoofed information. For 2344 example, authentic RS/RA exchanges may be considered as acceptable 2345 hints of forward progress, while spurious data packets should not be. 2347 When an ROR directs an ROS to a neighbor with one or more target 2348 link-layer addresses, the ROS can proactively test each direct path 2349 by sending an initial NS message to elicit a solicited NA response. 2350 While testing the paths, the ROS can optionally continue sending 2351 packets via the SPAN, maintain a small queue of packets until target 2352 reachability is confirmed, or (optimistically) allow packets to flow 2353 via the direct paths. In any case, the ROS should only consider the 2354 neighbor unreachable if NUD fails over multiple target link-layer 2355 address paths. 2357 When a ROS sends an NS message used for NUD, it uses its AERO 2358 addresses as the IPv6 source address and the AERO address 2359 corresponding to a target link-layer address as the destination. For 2360 each target link-layer address, the source node encapsulates the NS 2361 message in SPAN/INET headers with its own SPAN address as the source 2362 and the SPAN address of the target as the destination, If the target 2363 is located within the same SPAN segment, the source sets the INET 2364 address of the target as the destination; otherwise, it sets the INET 2365 address of a Relay as the destination. The source then forwards the 2366 message into the SPAN. 2368 Paths that pass NUD tests are marked as "reachable", while those that 2369 do not are marked as "unreachable". These markings inform the AERO 2370 interface forwarding algorithm specified in Section 3.13. 2372 Proxys can perform NUD to verify Server reachability on behalf of 2373 their proxyed Clients to reduce Client-initated control messaging 2374 overhead. 2376 3.19. Mobility Management and Quality of Service (QoS) 2378 AERO is a Distributed Mobility Management (DMM) service. Each Server 2379 is responsible for only a subset of the Clients on the AERO link, as 2380 opposed to a Centralized Mobility Management (CMM) service where 2381 there is a single network mobility collective entity for all Clients. 2382 Clients coordinate with their associated Servers via RS/RA exchanges 2383 to maintain the DMM profile, and the AERO routing system tracks all 2384 current Client/Server peering relationships. 2386 Servers provide a Mobility Anchor Point (MAP) for their dependent 2387 Clients. Clients are responsible for maintaining neighbor 2388 relationships with their Servers through periodic RS/RA exchanges, 2389 which also serves to confirm neighbor reachability. When a Client's 2390 underlying interface address and/or QoS information changes, the 2391 Client is responsible for updating the Server with this new 2392 information. Note that for Proxyed interfaces, however, the Proxy 2393 can perform the RS/RA exchanges on the Client's behalf. 2395 Mobility management considerations are specified in the following 2396 sections. 2398 3.19.1. Mobility Update Messaging 2400 Servers acting as MAPs accommodate Client mobility and/or QoS change 2401 events by sending unsolicited NA messages to each ROS in the target 2402 Client's Report List. When a MAP sends an unsolicited NA message, it 2403 sets the IPv6 source address to the Client's AERO address and sets 2404 the IPv6 destination address to All-Nodes multicast. The MAP also 2405 includes an OMNI option with prefix registration information, with a 2406 first ifIndex-tuple with ifIndex set to 0, and with additional 2407 ifIndex-tuples for the target Client's remaining interfaces. The MAP 2408 then includes a TLLAO with corresponding ifIndex-tuples, with the 2409 link layer address of the first tuple set to the MAP's SPAN address 2410 and with link layer addresses of the remaining tuples set to the 2411 corresponding target SPAN addresses. The MAP finally encapsulates 2412 the message in a SPAN header with source set to its own SPAN address 2413 and destination set to the SPAN address of the ROS, then sends the 2414 message to a Relay which in turn forwards it to the ROS. 2416 As discussed in Section 7.2.6 of [RFC4861], the transmission and 2417 reception of unsolicited NA messages is unreliable but provides a 2418 useful optimization. In well-connected Internetworks with robust 2419 data links unsolicited NA messages will be delivered with high 2420 probability, but in any case the MAP can optionally send up to 2421 MAX_NEIGHBOR_ADVERTISEMENT unsolicited NAs to each ROS to increase 2422 the likelihood that at least one will be received. 2424 When the ROS receives an unsolicited NA message, it ignores the 2425 message if there is no existing neighbor cache entry for the Client. 2426 Otherwise, it uses the included OMNI option and TLLAO information to 2427 update the neighbor cache entry, but does not reset ReachableTime 2428 since the receipt of an unsolicited NA message from the target Server 2429 does not provide confirmation that any forward paths to the target 2430 Client are working. 2432 If unsolicited NA messages are lost, the ROS may be left with stale 2433 address and/or QoS information for the Client for up to REACHABLETIME 2434 seconds. During this time, the ROS can continue sending packets 2435 according to its stale neighbor cache information. When 2436 ReachableTime is close to expiring, the ROS will re-initiate route 2437 optimization and receive fresh state information. 2439 In addition to sending unsolicited NA messages to the current set of 2440 ROSs for the Client, the MAP also sends unsolicited NAs to the former 2441 link-layer address for any ifIndex-tuple for which the link-layer 2442 address has changed. The NA messages update Proxys or Servers that 2443 cannot easily detect (e.g., without active probing) when a formerly- 2444 active Client has departed. 2446 3.19.2. Announcing Link-Layer Address and/or QoS Preference Changes 2448 When a Client needs to change its ANET addresses and/or QoS 2449 preferences (e.g., due to a mobility event), either the Client or its 2450 Proxys send RS messages to the Server via the SPAN with an OMNI 2451 option and SLLAO that include an ifIndex-tuple with the new link 2452 quality and address information. 2454 Up to MAX_RTR_SOLICITATION RS messages MAY be sent in parallel with 2455 sending actual data packets in case one or more RAs are lost. If all 2456 RAs are lost, the Client SHOULD re-associate with a new Server. 2458 When the Server receives the Client's changes, it sends unsolicited 2459 NA messages to all nodes in the Report List the same as described in 2460 the previous section. 2462 3.19.3. Bringing New Links Into Service 2464 When a Client needs to bring new underlying interfaces into service 2465 (e.g., when it activates a new data link), it sends an RS message to 2466 the Server via the underlying interface with an OMNI option with 2467 appropriate link quality values and with an SLLAO (if necessary) with 2468 link-layer address information for the new link.. 2470 3.19.4. Removing Existing Links from Service 2472 When a Client needs to remove existing underlying interfaces from 2473 service (e.g., when it de-activates an existing data link), it sends 2474 an RS message to its Server with an OMNI option with appropriate link 2475 quality values. 2477 If the Client needs to send RS messages over an underlying interface 2478 other than the one being removed from service, it MUST include an 2479 ifIndex-tuple for the sending interface as the first tuple and 2480 include additional ifIndex-tuples with appropriate link quality 2481 values for any underlying interfaces being removed from service. 2483 3.19.5. Moving to a New Server 2485 When a Client associates with a new Server, it performs the Client 2486 procedures specified in Section 3.15.2. The Client also includes a 2487 notification identifier in the RS message OMNI option per 2488 [I-D.templin-atn-aero-interface] if it wants the new Server to notify 2489 the old Server. 2491 When the new Server receives the Client's RS message, it responds by 2492 returning an RA as specified in Section 3.15.3. If the Client's RS 2493 includes a notification identifier, the new Server also prepares an 2494 RS or unsolicited NA message to send to the old Server. The RS/NA 2495 message includes the Client's AERO address as the source address, the 2496 old Server's AERO address as the destination address, and an OMNI 2497 option and S/TLLAO with an ifIndex-tuple with ifIndex set to 0. The 2498 OMNI option includes a prefix release indication, and the S/TLLAO 2499 includes the SPAN address of the new Server. For RS messages, the 2500 new Server retries up to MAX_RTR_SOLICITATIONS attempts until an RA 2501 is received. (Note that the Client can alternatively send RS/NA 2502 messages with a release indication to the old Server on its own 2503 behalf, however, this additional Client messaging may be undesirable 2504 in some environments. Note also that the choice of using RS or 2505 unsolicited NA is based on the need for a reliable acknowledgement; 2506 in environments where Router Lifetimes can be expected to be short, 2507 sending up to MAX_NEIGHBOR_ADVERTISEMENT unsolicited NAs may be 2508 sufficient.) 2510 When the old Server processes the RS/NA, it changes the symmetric 2511 neighbor cache entry state to DEPARTED, sets the link-layer address 2512 of the Client to the address found in the S/TLLAO, and sets 2513 DepartTime to DEPARTTIME seconds. For RS messages, the old Server 2514 then returns an immediate RA message with Router Lifetime set to 0. 2515 After a short delay (e.g., 2 seconds) the old Server withdraws the 2516 Client's MNP from the routing system. After DepartTime expires, the 2517 old Server deletes the symmetric neighbor cache entry. 2519 The old Server also sends unsolicited NA messages to all ROSs in the 2520 Client's Report List with an OMNI option with prefix release 2521 indication, with a single ifIndex-tuple with ifIndex set to 0 and 2522 with the SPAN address of the new Server in a companion TLLAO. When 2523 the ROS receives the NA, it caches the address of the new Server in 2524 the existing asymmetric neighbor cache entry and marks the entry as 2525 STALE. Subsequent data packets will then flow according to any 2526 existing cached link-layer information and trigger a new NS/NA 2527 exchange via the new Server. 2529 Clients SHOULD NOT move rapidly between Servers in order to avoid 2530 causing excessive oscillations in the AERO routing system. Examples 2531 of when a Client might wish to change to a different Server include a 2532 Server that has gone unreachable, topological movements of 2533 significant distance, movement to a new geographic region, movement 2534 to a new SPAN segment, etc. 2536 3.20. Multicast 2538 The AERO Client provides an IGMP (IPv4) [RFC2236] or MLD (IPv6) 2539 [RFC3810] proxy service for its EUNs and/or hosted applications 2540 [RFC4605]. The Client forwards IGMP/MLD messages over any of its 2541 underlying interfaces for which group membership is required. The 2542 IGMP/MLD messages may be further forwarded by a first-hop ANET access 2543 router acting as an IGMP/MLD-snooping switch [RFC4541], then 2544 ultimately delivered to an AERO Proxy/Server acting as a Protocol 2545 Independent Multicast - Sparse-Mode (PIM-SM, or simply "PIM") 2546 Designated Router (DR) [RFC7761]. AERO Gateways also act as PIM 2547 routers (i.e., the same as AERO Proxys/Servers) on behalf of nodes on 2548 INET/EUN networks. The behaviors identified in the following 2549 sections correspond to Source-Specific Multicast (SSM) and Any-Source 2550 Multicast (ASM) operational modes. 2552 3.20.1. Source-Specific Multicast (SSM) 2554 When an ROS (i.e., an AERO Proxy/Server/Gateway) "X" acting as PIM 2555 router receives a Join/Prune message from a node on its downstream 2556 interfaces containing one or more ((S)ource, (G)roup) pairs, it 2557 updates its Multicast Routing Information Base (MRIB) accordingly. 2558 For each S belonging to a prefix reachable via X's non-AERO 2559 interfaces, X then forwards the (S, G) Join/Prune to any PIM routers 2560 on those interfaces per [RFC7761]. 2562 For each S belonging to a prefix reachable via X's AERO interface, X 2563 originates a separate copy of the Join/Prune for each (S,G) in the 2564 message using its own AERO address as the source address and ALL-PIM- 2565 ROUTERS as the destination address. X then encapsulates each message 2566 in a SPAN header with source address set to the SPAN address of X and 2567 destination address set to S then forwards the message into the SPAN. 2568 The SPAN in turn forwards the message to AERO Server/Gateway "Y" that 2569 services S. At the same time, if the message was a Join, X sends a 2570 route-optimization NS message toward each S the same as discussed in 2571 Section 3.17. The resulting NAs will return the AERO address for the 2572 prefix that matches S as the network-layer source address and TLLAOs 2573 with the SPAN addresses corresponding to any ifIndex-tuples that are 2574 currently servicing S. 2576 When Y processes the Join/Prune message, if S located behind any 2577 Native, Direct, VPNed or NATed interfaces Y acts as a PIM router and 2578 updates its MRIB to list X as the next hop in the reverse path. If S 2579 is located behind any Proxys "Z"*, Y also forwards the message to 2580 each Z* over the SPAN while continuing to use the AERO address of X 2581 as the source address. Each Z* then updates its MRIB accordingly and 2582 maintains the AERO address of X as the next hop in the reverse path. 2583 Since the Relays in the SPAN do not examine network layer control 2584 messages, this means that the (reverse) multicast tree path is simply 2585 from each Z* (and/or Y) to X with no other multicast-aware routers in 2586 the path. If any Z* (and/or Y) is located on the same SPAN segment 2587 as X, the multicast data traffic sent to X directly using SPAN/INET 2588 encapsulation instead of via a Relay. 2590 Following the initial Join/Prune and NS/NA messaging, X maintains an 2591 asymmetric neighbor cache entry for each S the same as if X was 2592 sending unicast data traffic to S. In particular, X performs 2593 additional NS/NA exchanges to keep the neighbor cache entry alive for 2594 up to t_periodic seconds [RFC7761]. If no new Joins are received 2595 within t_periodic seconds, X allows the neighbor cache entry to 2596 expire. Finally, if X receives any additional Join/Prune messages 2597 for (S,G) it forwards the messages to each Y and Z* in the neighbor 2598 cache entry over the SPAN. 2600 At some later time, Client C that holds an MNP for source S may 2601 depart from a first Proxy Z1 and/or connect via a new Proxy Z2. In 2602 that case, Y sends an unsolicited NA message to X the same as 2603 specified for unicast mobility in Section 3.19. When X receives the 2604 unsolicited NA message, it updates its asymmetric neighbor cache 2605 entry for the AERO address for source S and sends new Join messages 2606 to any new Proxys Z2. There is no requirement to send any Prune 2607 messages to old Proxys Z1 since source S will no longer source any 2608 multicast data traffic via Z1. Instead, the multicast state for 2609 (S,G) in Proxy Z1 will soon time out since no new Joins will arrive. 2611 After some later time, C may move to a new Server Y2 and depart from 2612 old Sever Y1. In that case, Y1 sends Join messages for any of C's 2613 active (S,G) groups to Y2 while including its own AERO address as the 2614 source address. This causes Y2 to include Y1 in the multicast 2615 forwarding tree during the interim time that Y1's symmetric neighbor 2616 cache entry for C is in the DEPARTED state. At the same time, Y1 2617 sends an unsolicited NA message to X with an OMNI option and TLLAO 2618 with ifIndex-tuple set to 0 and a release indication to cause X to 2619 release its asymmetric neighbor cache entry. X then sends a new Join 2620 message to S via the SPAN and re-initiates route optimization the 2621 same as if it were receiving a fresh Join message from a node on a 2622 downstream link. 2624 3.20.2. Any-Source Multicast (ASM) 2626 When an ROS X acting as a PIM router receives a Join/Prune from a 2627 node on its downstream interfaces containing one or more (*,G) pairs, 2628 it updates its Multicast Routing Information Base (MRIB) accordingly. 2629 X then forwards a copy of the message to the Rendezvous Point (RP) R 2630 for each G over the SPAN. X uses its own AERO address as the source 2631 address and ALL-PIM-ROUTERS as the destination address, then 2632 encapsulates each message in a SPAN header with source address set to 2633 the SPAN address of X and destination address set to R, then sends 2634 the message into the SPAN. At the same time, if the message was a 2635 Join X initiates NS/NA route optimization the same as for the SSM 2636 case discussed in Section 3.20.1. 2638 For each source S that sends multicast traffic to group G via R, the 2639 Proxy/Server Z* for the Client that aggregates S encapsulates the 2640 packets in PIM Register messages and forwards them to R via the SPAN. 2641 R may then elect to send a PIM Join to Z* over the SPAN. This will 2642 result in an (S,G) tree rooted at Z* with R as the next hop so that R 2643 will begin to receive two copies of the packet; one native copy from 2644 the (S, G) tree and a second copy from the pre-existing (*, G) tree 2645 that still uses PIM Register encapsulation. R can then issue a PIM 2646 Register-stop message to suppress the Register-encapsulated stream. 2647 At some later time, if C moves to a new Proxy/Server Z*, it resumes 2648 sending packets via PIM Register encapsulation via the new Z*. 2650 At the same time, as multicast listeners discover individual S's for 2651 a given G, they can initiate an (S,G) Join for each S under the same 2652 procedures discussed in Section 3.20.1. Once the (S,G) tree is 2653 established, the listeners can send (S, G) Prune messages to R so 2654 that multicast packets for group G sourced by S will only be 2655 delivered via the (S, G) tree and not from the (*, G) tree rooted at 2656 R. All mobility considerations discussed for SSM apply. 2658 3.20.3. Bi-Directional PIM (BIDIR-PIM) 2660 Bi-Directional PIM (BIDIR-PIM) [RFC5015] provides an alternate 2661 approach to ASM that treats the Rendezvous Point (RP) as a Designated 2662 Forwarder (DF). Further considerations for BIDIR-PIM are out of 2663 scope. 2665 3.21. Operation over Multiple AERO Links (VLANs) 2667 An AERO Client can connect to multiple AERO links the same as for any 2668 data link service. In that case, the Client maintains a distinct 2669 AERO interface for each link, e.g., 'aero0' for the first link, 2670 'aero1' for the second, 'aero2' for the third, etc. Each AERO link 2671 would include its own distinct set of Relays, Servers and Proxys, 2672 thereby providing redundancy in case of failures. 2674 The Relays, Servers and Proxys on each AERO link can assign AERO and 2675 SPAN addresses that use the same or different numberings from those 2676 on other links. Since the links are mutually independent there is no 2677 requirement for avoiding inter-link address duplication, e.g., the 2678 same AERO address such as fe80::1000 could be used to number distinct 2679 nodes that connect to different AERO links. 2681 Each AERO link could utilize the same or different ANET connections. 2682 The links can be distinguished at the link-layer via Virtual Local 2683 Area Network (VLAN) tagging (e.g., IEEE 802.1Q) and/or through 2684 assignment of distinct sets of MSPs on each link. This gives rise to 2685 the opportunity for supporting multiple redundant networked paths, 2686 where each VLAN is distinguished by a different label (e.g., colors 2687 such as Red, Green, Blue, etc.). In particular, the Client can tag 2688 its RS messages with the appropriate label to cause the network to 2689 select the desired VLAN. 2691 Clients that connect to multiple AERO interfaces can select the 2692 outgoing interface appropriate for a given Red/Blue/Green/etc. 2693 traffic profile while (in the reverse direction) correspondent nodes 2694 must have some way of steering their packets destined to a target via 2695 the correct AERO link. 2697 In a first alternative, if each AERO link services different MSPs, 2698 then the Client can receive a distinct MNP from each of the links. 2699 IP routing will therefore assure that the correct Red/Green/Blue/etc. 2700 network is used for both outbound and inbound traffic. This can be 2701 accomplished using existing technologies and approaches, and without 2702 requiring any special supporting code in correspondent nodes or 2703 Relays. 2705 In a second alternative, if each AERO link services the same MSP(s) 2706 then each link could assign a distinct "AERO Link Anycast" address 2707 that is configured by all Relays on the link. Correspondent nodes 2708 then include a "type 4" routing header with the Anycast address for 2709 the AERO link as the IPv6 destination and with the address of the 2710 target encoded as the "next segment" in the routing header 2711 [RFC8402][I-D.ietf-6man-segment-routing-header]. Standard IP routing 2712 will then direct the packet to the nearest Relay for the correct AERO 2713 link, which will replace the destination address with the target 2714 address then forward the packet to the target. 2716 3.22. DNS Considerations 2718 AERO Client MNs and INET correspondent nodes consult the Domain Name 2719 System (DNS) the same as for any Internetworking node. When 2720 correspondent nodes and Client MNs use different IP protocol versions 2721 (e.g., IPv4 correspondents and IPv6 MNs), the INET DNS must maintain 2722 A records for IPv4 address mappings to MNs which must then be 2723 populated in Gateway NAT64 mapping caches. In that way, an IPv4 2724 correspondent node can send packets to the IPv4 address mapping of 2725 the target MN, and the Gateway will translate the IPv4 header and 2726 destination address into an IPv6 header and IPv6 destination address 2727 of the MN. 2729 When an AERO Client registers with an AERO Server, the Server can 2730 return the address(es) of DNS servers in RDNSS options [RFC6106]. 2731 The DNS server provides the IP addresses of other MNs and 2732 correspondent nodes in AAAA records for IPv6 or A records for IPv4. 2734 3.23. Transition Considerations 2736 The SPAN ensures that dissimilar INET partitions can be joined into a 2737 single unified AERO link, even though the partitions themselves may 2738 have differing protocol versions and/or incompatible addressing 2739 plans. However, a commonality can be achieved by incrementally 2740 distributing globally routable (i.e., native) IP prefixes to 2741 eventually reach all nodes (both mobile and fixed) in all SPAN 2742 segments. This can be accomplished by incrementally deploying AERO 2743 Gateways on each INET partition, with each Gateway distributing its 2744 MNPs and/or discovering non-MNP prefixes on its INET links. 2746 This gives rise to the opportunity to eventually distribute native IP 2747 addresses to all nodes, and to present a unified AERO link view 2748 (bridged by the SPAN) even if the INET partitions remain in their 2749 current protocol and addressing plans. In that way, the AERO link 2750 can serve the dual purpose of providing a mobility service and a 2751 transition service. Or, if an INET partition is transitioned to a 2752 native IP protocol version and addressing scheme that is compatible 2753 with the AERO link MNP-based addressing scheme, the partition and 2754 AERO link can be joined by Gateways. 2756 Gateways that connect INETs/EUNs with dissimilar IP protocol versions 2757 must employ a network address and protocol translation function such 2758 as NAT64[RFC6146]. 2760 3.24. Detecting and Reacting to Server and Relay Failures 2762 In environments where rapid failure recovery is required, Servers and 2763 Relays SHOULD use Bidirectional Forwarding Detection (BFD) [RFC5880]. 2764 Nodes that use BFD can quickly detect and react to failures so that 2765 cached information is re-established through alternate nodes. BFD 2766 control messaging is carried only over well-connected ground domain 2767 networks (i.e., and not low-end radio links) and can therefore be 2768 tuned for rapid response. 2770 Servers and Relays maintain BFD sessions in parallel with their BGP 2771 peerings. If a Server or Relay fails, BGP peers will quickly re- 2772 establish routes through alternate paths the same as for common BGP 2773 deployments. Similarly, Proxys maintain BFD sessions with their 2774 associated Relays even though they do not establish BGP peerings with 2775 them. 2777 Proxys SHOULD use proactive NUD for Servers for which there are 2778 currently active ANET Clients in a manner that parallels BFD, i.e., 2779 by sending unicast NS messages in rapid succession to receive 2780 solicited NA messages. When the Proxy is also sending RS messages on 2781 behalf of ANET Clients, the RS/RA messaging can be considered as 2782 equivalent hints of forward progress. This means that the Proxy need 2783 not also send a periodic NS if it has already sent an RS within the 2784 same period. If a Server fails, the Proxy will cease to receive 2785 advertisements and can quickly inform Clients of the outage by 2786 sending multicast RA messages on the ANET interface. 2788 The Proxy sends multicast RA messages with source address set to the 2789 Server's address, destination address set to All-Nodes multicast, and 2790 Router Lifetime set to 0. The Proxy SHOULD send 2791 MAX_FINAL_RTR_ADVERTISEMENTS RA messages separated by small delays 2792 [RFC4861]. Any Clients on the ANET interface that have been using 2793 the (now defunct) Server will receive the RA messages and associate 2794 with a new Server. 2796 4. Implementation Status 2798 An AERO implementation based on OpenVPN (https://openvpn.net/) was 2799 announced on the v6ops mailing list on January 10, 2018 and an 2800 initial public release of the AERO proof-of-concept source code was 2801 announced on the intarea mailing list on August 21, 2015. 2803 5. IANA Considerations 2805 The IANA has assigned a 4-octet Private Enterprise Number "45282" for 2806 AERO in the "enterprise-numbers" registry. 2808 The IANA has assigned the UDP port number "8060" for an earlier 2809 experimental version of AERO [RFC6706]. This document obsoletes 2810 [RFC6706] and claims the UDP port number "8060" for all future use. 2812 No further IANA actions are required. 2814 6. Security Considerations 2816 AERO Relays configure secured tunnels with AERO Servers and Proxys 2817 within their local SPAN segments. Applicable secured tunnel 2818 alternatives include IPsec [RFC4301], TLS/SSL [RFC8446], DTLS 2819 [RFC6347], etc. The AERO Relays of all SPAN segments in turn 2820 configure secured tunnels for their neighboring AERO Relays across 2821 the SPAN. Therefore, packets that traverse the SPAN between any pair 2822 of AERO link neighbors are already secured. 2824 AERO Servers, Gateways and Proxys targeted by a route optimization 2825 may also receive packets directly from the INET partitions instead of 2826 via the SPAN. For INET partitions that apply effective ingress 2827 filtering to defeat source address spoofing, the simple data origin 2828 authentication procedures in Section 3.11 can be applied. This 2829 implies that the ROS list must be maintained consistently by all 2830 route optimization targets within the same INET partition, and that 2831 the ROS list must be securely managed by the partition administrative 2832 authority. 2834 For INET partitions that cannot apply effective ingress filtering, 2835 the two options for securing communications include 1) disable route 2836 optimization so that all traffic is conveyed over secured tunnels via 2837 the SPAN, or 2) enable on-demand secure tunnel creation between INET 2838 partition neighbors. Option 1) would result in longer routes than 2839 necessary and traffic concentration on critical infrastructure 2840 elements. Option 2) could be coordinated by establishing a secured 2841 tunnel on-demand instead of performing an NS/NA exchange in the route 2842 optimization procedures. Procedures for establishing on-demand 2843 secured tunnels are out of scope. 2845 AERO Clients that connect to secured enclaves need not apply security 2846 to their ND messages, since the messages will be intercepted by a 2847 perimeter Proxy that applies security on its outward-facing 2848 interface. AERO Clients located outside of secured enclaves SHOULD 2849 use symmetric network and/or transport layer security services, but 2850 when there are many prospective neighbors with dynamically changing 2851 connectivity an asymmetric security service such as SEND may be 2852 needed (see: Appendix B.6). 2854 Application endpoints SHOULD use application-layer security services 2855 such as TLS/SSL, DTLS or SSH [RFC4251] to assure the same level of 2856 protection as for critical secured Internet services. AERO Clients 2857 that require host-based VPN services SHOULD use symmetric network 2858 and/or transport layer security services such as IPsec, TLS/SSL, 2859 DTLS, etc. AERO Proxys and Servers can also provide a network-based 2860 VPN service on behalf of the Client, e.g., if the Client is located 2861 within a secured enclave and cannot establish a VPN on its own 2862 behalf. 2864 AERO Servers and Relays present targets for traffic amplification 2865 Denial of Service (DoS) attacks. This concern is no different than 2866 for widely-deployed VPN security gateways in the Internet, where 2867 attackers could send spoofed packets to the gateways at high data 2868 rates. This can be mitigated by connecting Servers and Relays over 2869 dedicated links with no connections to the Internet and/or when 2870 connections to the Internet are only permitted through well-managed 2871 firewalls. Traffic amplification DoS attacks can also target an AERO 2872 Client's low data rate links. This is a concern not only for Clients 2873 located on the open Internet but also for Clients in secured 2874 enclaves. AERO Servers and Proxys can institute rate limits that 2875 protect Clients from receiving packet floods that could DoS low data 2876 rate links. 2878 AERO Gateways must implement ingress filtering to avoid a spoofing 2879 attack in which spurious SPAN messages are injected into an AERO link 2880 from an outside attacker. AERO Clients MUST ensure that their 2881 connectivity is not used by unauthorized nodes on their EUNs to gain 2882 access to a protected network, i.e., AERO Clients that act as routers 2883 MUST NOT provide routing services for unauthorized nodes. (This 2884 concern is no different than for ordinary hosts that receive an IP 2885 address delegation but then "share" the address with other nodes via 2886 some form of Internet connection sharing such as tethering.) 2888 The MAP list and ROS lists MUST be well-managed and secured from 2889 unauthorized tampering, even though the list contains only public 2890 information. The MAP list can be conveyed to the Client in a similar 2891 fashion as in [RFC5214] (e.g., through layer 2 data link login 2892 messaging, secure upload of a static file, DNS lookups, etc.). The 2893 ROS list can be conveyed to Servers and Proxys through administrative 2894 action, secured file distribution, etc. 2896 Although public domain and commercial SEND implementations exist, 2897 concerns regarding the strength of the cryptographic hash algorithm 2898 have been documented [RFC6273] [RFC4982]. 2900 Security considerations for accepting link-layer ICMP messages and 2901 reflected packets are discussed throughout the document. 2903 7. Acknowledgements 2905 Discussions in the IETF, aviation standards communities and private 2906 exchanges helped shape some of the concepts in this work. 2907 Individuals who contributed insights include Mikael Abrahamsson, Mark 2908 Andrews, Fred Baker, Bob Braden, Stewart Bryant, Brian Carpenter, 2909 Wojciech Dec, Ralph Droms, Adrian Farrel, Nick Green, Sri Gundavelli, 2910 Brian Haberman, Bernhard Haindl, Joel Halpern, Tom Herbert, Sascha 2911 Hlusiak, Lee Howard, Andre Kostur, Hubert Kuenig, Ted Lemon, Andy 2912 Malis, Satoru Matsushima, Tomek Mrugalski, Madhu Niraula, Alexandru 2913 Petrescu, Behcet Saikaya, Michal Skorepa, Joe Touch, Bernie Volz, 2914 Ryuji Wakikawa, Tony Whyman, Lloyd Wood and James Woodyatt. Members 2915 of the IESG also provided valuable input during their review process 2916 that greatly improved the document. Special thanks go to Stewart 2917 Bryant, Joel Halpern and Brian Haberman for their shepherding 2918 guidance during the publication of the AERO first edition. 2920 This work has further been encouraged and supported by Boeing 2921 colleagues including Kyle Bae, M. Wayne Benson, Dave Bernhardt, Cam 2922 Brodie, John Bush, Balaguruna Chidambaram, Irene Chin, Bruce Cornish, 2923 Claudiu Danilov, Don Dillenburg, Joe Dudkowski, Wen Fang, Samad 2924 Farooqui, Anthony Gregory, Jeff Holland, Seth Jahne, Brian Jaury, 2925 Greg Kimberly, Ed King, Madhuri Madhava Badgandi, Laurel Matthew, 2926 Gene MacLean III, Rob Muszkiewicz, Sean O'Sullivan, Vijay 2927 Rajagopalan, Greg Saccone, Rod Santiago, Kent Shuey, Brian Skeen, 2928 Mike Slane, Carrie Spiker, Katie Tran, Brendan Williams, Amelia 2929 Wilson, Julie Wulff, Yueli Yang, Eric Yeh and other members of the 2930 Boeing mobility, networking and autonomy teams. Kyle Bae, Wayne 2931 Benson, Katie Tran and Eric Yeh are especially acknowledged for 2932 implementing the AERO functions as extensions to the public domain 2933 OpenVPN distribution. 2935 Earlier works on NBMA tunneling approaches are found in 2936 [RFC2529][RFC5214][RFC5569]. 2938 Many of the constructs presented in this second edition of AERO are 2939 based on the author's earlier works, including: 2941 o The Internet Routing Overlay Network (IRON) 2942 [RFC6179][I-D.templin-ironbis] 2944 o Virtual Enterprise Traversal (VET) 2945 [RFC5558][I-D.templin-intarea-vet] 2947 o The Subnetwork Encapsulation and Adaptation Layer (SEAL) 2948 [RFC5320][I-D.templin-intarea-seal] 2950 o AERO, First Edition [RFC6706] 2951 Note that these works cite numerous earlier efforts that are not also 2952 cited here due to space limitations. The authors of those earlier 2953 works are acknowledged for their insights. 2955 This work is aligned with the NASA Safe Autonomous Systems Operation 2956 (SASO) program under NASA contract number NNA16BD84C. 2958 This work is aligned with the FAA as per the SE2025 contract number 2959 DTFAWA-15-D-00030. 2961 This work is aligned with the Boeing Commercial Airplanes (BCA) 2962 Internet of Things (IoT) and autonomy programs. 2964 This work is aligned with the Boeing Information Technology (BIT) 2965 MobileNet program. 2967 8. References 2969 8.1. Normative References 2971 [I-D.templin-atn-aero-interface] 2972 Templin, F. and T. Whyman, "Transmission of IPv6 Packets 2973 over Overlay Multilink Network (OMNI) Interfaces", draft- 2974 templin-atn-aero-interface-18 (work in progress), February 2975 2020. 2977 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, 2978 DOI 10.17487/RFC0791, September 1981, 2979 . 2981 [RFC0792] Postel, J., "Internet Control Message Protocol", STD 5, 2982 RFC 792, DOI 10.17487/RFC0792, September 1981, 2983 . 2985 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 2986 Requirement Levels", BCP 14, RFC 2119, 2987 DOI 10.17487/RFC2119, March 1997, 2988 . 2990 [RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in 2991 IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473, 2992 December 1998, . 2994 [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black, 2995 "Definition of the Differentiated Services Field (DS 2996 Field) in the IPv4 and IPv6 Headers", RFC 2474, 2997 DOI 10.17487/RFC2474, December 1998, 2998 . 3000 [RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander, 3001 "SEcure Neighbor Discovery (SEND)", RFC 3971, 3002 DOI 10.17487/RFC3971, March 2005, 3003 . 3005 [RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)", 3006 RFC 3972, DOI 10.17487/RFC3972, March 2005, 3007 . 3009 [RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and 3010 More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191, 3011 November 2005, . 3013 [RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast 3014 Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005, 3015 . 3017 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 3018 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 3019 DOI 10.17487/RFC4861, September 2007, 3020 . 3022 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 3023 Address Autoconfiguration", RFC 4862, 3024 DOI 10.17487/RFC4862, September 2007, 3025 . 3027 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 3028 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 3029 May 2017, . 3031 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 3032 (IPv6) Specification", STD 86, RFC 8200, 3033 DOI 10.17487/RFC8200, July 2017, 3034 . 3036 [RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A., 3037 Richardson, M., Jiang, S., Lemon, T., and T. Winters, 3038 "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", 3039 RFC 8415, DOI 10.17487/RFC8415, November 2018, 3040 . 3042 8.2. Informative References 3044 [BGP] Huston, G., "BGP in 2015, http://potaroo.net", January 3045 2016. 3047 [I-D.ietf-6man-segment-routing-header] 3048 Filsfils, C., Dukes, D., Previdi, S., Leddy, J., 3049 Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header 3050 (SRH)", draft-ietf-6man-segment-routing-header-26 (work in 3051 progress), October 2019. 3053 [I-D.ietf-dmm-distributed-mobility-anchoring] 3054 Chan, A., Wei, X., Lee, J., Jeon, S., and C. Bernardos, 3055 "Distributed Mobility Anchoring", draft-ietf-dmm- 3056 distributed-mobility-anchoring-14 (work in progress), 3057 November 2019. 3059 [I-D.ietf-intarea-gue] 3060 Herbert, T., Yong, L., and O. Zia, "Generic UDP 3061 Encapsulation", draft-ietf-intarea-gue-09 (work in 3062 progress), October 2019. 3064 [I-D.ietf-intarea-gue-extensions] 3065 Herbert, T., Yong, L., and F. Templin, "Extensions for 3066 Generic UDP Encapsulation", draft-ietf-intarea-gue- 3067 extensions-06 (work in progress), March 2019. 3069 [I-D.ietf-intarea-tunnels] 3070 Touch, J. and M. Townsley, "IP Tunnels in the Internet 3071 Architecture", draft-ietf-intarea-tunnels-10 (work in 3072 progress), September 2019. 3074 [I-D.ietf-rtgwg-atn-bgp] 3075 Templin, F., Saccone, G., Dawra, G., Lindem, A., and V. 3076 Moreno, "A Simple BGP-based Mobile Routing System for the 3077 Aeronautical Telecommunications Network", draft-ietf- 3078 rtgwg-atn-bgp-05 (work in progress), January 2020. 3080 [I-D.templin-6man-dhcpv6-ndopt] 3081 Templin, F., "A Unified Stateful/Stateless Configuration 3082 Service for IPv6", draft-templin-6man-dhcpv6-ndopt-09 3083 (work in progress), January 2020. 3085 [I-D.templin-intarea-grefrag] 3086 Templin, F., "GRE Tunnel Level Fragmentation", draft- 3087 templin-intarea-grefrag-04 (work in progress), July 2016. 3089 [I-D.templin-intarea-seal] 3090 Templin, F., "The Subnetwork Encapsulation and Adaptation 3091 Layer (SEAL)", draft-templin-intarea-seal-68 (work in 3092 progress), January 2014. 3094 [I-D.templin-intarea-vet] 3095 Templin, F., "Virtual Enterprise Traversal (VET)", draft- 3096 templin-intarea-vet-40 (work in progress), May 2013. 3098 [I-D.templin-ironbis] 3099 Templin, F., "The Interior Routing Overlay Network 3100 (IRON)", draft-templin-ironbis-16 (work in progress), 3101 March 2014. 3103 [I-D.templin-v6ops-pdhost] 3104 Templin, F., "IPv6 Prefix Delegation and Multi-Addressing 3105 Models", draft-templin-v6ops-pdhost-25 (work in progress), 3106 January 2020. 3108 [OVPN] OpenVPN, O., "http://openvpn.net", October 2016. 3110 [RFC1035] Mockapetris, P., "Domain names - implementation and 3111 specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, 3112 November 1987, . 3114 [RFC1122] Braden, R., Ed., "Requirements for Internet Hosts - 3115 Communication Layers", STD 3, RFC 1122, 3116 DOI 10.17487/RFC1122, October 1989, 3117 . 3119 [RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191, 3120 DOI 10.17487/RFC1191, November 1990, 3121 . 3123 [RFC1812] Baker, F., Ed., "Requirements for IP Version 4 Routers", 3124 RFC 1812, DOI 10.17487/RFC1812, June 1995, 3125 . 3127 [RFC2003] Perkins, C., "IP Encapsulation within IP", RFC 2003, 3128 DOI 10.17487/RFC2003, October 1996, 3129 . 3131 [RFC2236] Fenner, W., "Internet Group Management Protocol, Version 3132 2", RFC 2236, DOI 10.17487/RFC2236, November 1997, 3133 . 3135 [RFC2492] Armitage, G., Schulter, P., and M. Jork, "IPv6 over ATM 3136 Networks", RFC 2492, DOI 10.17487/RFC2492, January 1999, 3137 . 3139 [RFC2529] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4 3140 Domains without Explicit Tunnels", RFC 2529, 3141 DOI 10.17487/RFC2529, March 1999, 3142 . 3144 [RFC2764] Gleeson, B., Lin, A., Heinanen, J., Armitage, G., and A. 3145 Malis, "A Framework for IP Based Virtual Private 3146 Networks", RFC 2764, DOI 10.17487/RFC2764, February 2000, 3147 . 3149 [RFC2784] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P. 3150 Traina, "Generic Routing Encapsulation (GRE)", RFC 2784, 3151 DOI 10.17487/RFC2784, March 2000, 3152 . 3154 [RFC2890] Dommety, G., "Key and Sequence Number Extensions to GRE", 3155 RFC 2890, DOI 10.17487/RFC2890, September 2000, 3156 . 3158 [RFC2923] Lahey, K., "TCP Problems with Path MTU Discovery", 3159 RFC 2923, DOI 10.17487/RFC2923, September 2000, 3160 . 3162 [RFC2983] Black, D., "Differentiated Services and Tunnels", 3163 RFC 2983, DOI 10.17487/RFC2983, October 2000, 3164 . 3166 [RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition 3167 of Explicit Congestion Notification (ECN) to IP", 3168 RFC 3168, DOI 10.17487/RFC3168, September 2001, 3169 . 3171 [RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener 3172 Discovery Version 2 (MLDv2) for IPv6", RFC 3810, 3173 DOI 10.17487/RFC3810, June 2004, 3174 . 3176 [RFC3819] Karn, P., Ed., Bormann, C., Fairhurst, G., Grossman, D., 3177 Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J., and L. 3178 Wood, "Advice for Internet Subnetwork Designers", BCP 89, 3179 RFC 3819, DOI 10.17487/RFC3819, July 2004, 3180 . 3182 [RFC4213] Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms 3183 for IPv6 Hosts and Routers", RFC 4213, 3184 DOI 10.17487/RFC4213, October 2005, 3185 . 3187 [RFC4251] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH) 3188 Protocol Architecture", RFC 4251, DOI 10.17487/RFC4251, 3189 January 2006, . 3191 [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A 3192 Border Gateway Protocol 4 (BGP-4)", RFC 4271, 3193 DOI 10.17487/RFC4271, January 2006, 3194 . 3196 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 3197 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 3198 2006, . 3200 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 3201 Internet Protocol", RFC 4301, DOI 10.17487/RFC4301, 3202 December 2005, . 3204 [RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery 3205 Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April 3206 2006, . 3208 [RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet 3209 Control Message Protocol (ICMPv6) for the Internet 3210 Protocol Version 6 (IPv6) Specification", STD 89, 3211 RFC 4443, DOI 10.17487/RFC4443, March 2006, 3212 . 3214 [RFC4511] Sermersheim, J., Ed., "Lightweight Directory Access 3215 Protocol (LDAP): The Protocol", RFC 4511, 3216 DOI 10.17487/RFC4511, June 2006, 3217 . 3219 [RFC4541] Christensen, M., Kimball, K., and F. Solensky, 3220 "Considerations for Internet Group Management Protocol 3221 (IGMP) and Multicast Listener Discovery (MLD) Snooping 3222 Switches", RFC 4541, DOI 10.17487/RFC4541, May 2006, 3223 . 3225 [RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick, 3226 "Internet Group Management Protocol (IGMP) / Multicast 3227 Listener Discovery (MLD)-Based Multicast Forwarding 3228 ("IGMP/MLD Proxying")", RFC 4605, DOI 10.17487/RFC4605, 3229 August 2006, . 3231 [RFC4607] Holbrook, H. and B. Cain, "Source-Specific Multicast for 3232 IP", RFC 4607, DOI 10.17487/RFC4607, August 2006, 3233 . 3235 [RFC4963] Heffner, J., Mathis, M., and B. Chandler, "IPv4 Reassembly 3236 Errors at High Data Rates", RFC 4963, 3237 DOI 10.17487/RFC4963, July 2007, 3238 . 3240 [RFC4982] Bagnulo, M. and J. Arkko, "Support for Multiple Hash 3241 Algorithms in Cryptographically Generated Addresses 3242 (CGAs)", RFC 4982, DOI 10.17487/RFC4982, July 2007, 3243 . 3245 [RFC5015] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano, 3246 "Bidirectional Protocol Independent Multicast (BIDIR- 3247 PIM)", RFC 5015, DOI 10.17487/RFC5015, October 2007, 3248 . 3250 [RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site 3251 Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214, 3252 DOI 10.17487/RFC5214, March 2008, 3253 . 3255 [RFC5320] Templin, F., Ed., "The Subnetwork Encapsulation and 3256 Adaptation Layer (SEAL)", RFC 5320, DOI 10.17487/RFC5320, 3257 February 2010, . 3259 [RFC5522] Eddy, W., Ivancic, W., and T. Davis, "Network Mobility 3260 Route Optimization Requirements for Operational Use in 3261 Aeronautics and Space Exploration Mobile Networks", 3262 RFC 5522, DOI 10.17487/RFC5522, October 2009, 3263 . 3265 [RFC5558] Templin, F., Ed., "Virtual Enterprise Traversal (VET)", 3266 RFC 5558, DOI 10.17487/RFC5558, February 2010, 3267 . 3269 [RFC5569] Despres, R., "IPv6 Rapid Deployment on IPv4 3270 Infrastructures (6rd)", RFC 5569, DOI 10.17487/RFC5569, 3271 January 2010, . 3273 [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 3274 (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, 3275 . 3277 [RFC6106] Jeong, J., Park, S., Beloeil, L., and S. Madanapalli, 3278 "IPv6 Router Advertisement Options for DNS Configuration", 3279 RFC 6106, DOI 10.17487/RFC6106, November 2010, 3280 . 3282 [RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful 3283 NAT64: Network Address and Protocol Translation from IPv6 3284 Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146, 3285 April 2011, . 3287 [RFC6179] Templin, F., Ed., "The Internet Routing Overlay Network 3288 (IRON)", RFC 6179, DOI 10.17487/RFC6179, March 2011, 3289 . 3291 [RFC6221] Miles, D., Ed., Ooghe, S., Dec, W., Krishnan, S., and A. 3292 Kavanagh, "Lightweight DHCPv6 Relay Agent", RFC 6221, 3293 DOI 10.17487/RFC6221, May 2011, 3294 . 3296 [RFC6273] Kukec, A., Krishnan, S., and S. Jiang, "The Secure 3297 Neighbor Discovery (SEND) Hash Threat Analysis", RFC 6273, 3298 DOI 10.17487/RFC6273, June 2011, 3299 . 3301 [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer 3302 Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, 3303 January 2012, . 3305 [RFC6438] Carpenter, B. and S. Amante, "Using the IPv6 Flow Label 3306 for Equal Cost Multipath Routing and Link Aggregation in 3307 Tunnels", RFC 6438, DOI 10.17487/RFC6438, November 2011, 3308 . 3310 [RFC6706] Templin, F., Ed., "Asymmetric Extended Route Optimization 3311 (AERO)", RFC 6706, DOI 10.17487/RFC6706, August 2012, 3312 . 3314 [RFC6864] Touch, J., "Updated Specification of the IPv4 ID Field", 3315 RFC 6864, DOI 10.17487/RFC6864, February 2013, 3316 . 3318 [RFC7269] Chen, G., Cao, Z., Xie, C., and D. Binet, "NAT64 3319 Deployment Options and Experience", RFC 7269, 3320 DOI 10.17487/RFC7269, June 2014, 3321 . 3323 [RFC7333] Chan, H., Ed., Liu, D., Seite, P., Yokota, H., and J. 3324 Korhonen, "Requirements for Distributed Mobility 3325 Management", RFC 7333, DOI 10.17487/RFC7333, August 2014, 3326 . 3328 [RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I., 3329 Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent 3330 Multicast - Sparse Mode (PIM-SM): Protocol Specification 3331 (Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March 3332 2016, . 3334 [RFC8086] Yong, L., Ed., Crabbe, E., Xu, X., and T. Herbert, "GRE- 3335 in-UDP Encapsulation", RFC 8086, DOI 10.17487/RFC8086, 3336 March 2017, . 3338 [RFC8201] McCann, J., Deering, S., Mogul, J., and R. Hinden, Ed., 3339 "Path MTU Discovery for IP version 6", STD 87, RFC 8201, 3340 DOI 10.17487/RFC8201, July 2017, 3341 . 3343 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 3344 Decraene, B., Litkowski, S., and R. Shakir, "Segment 3345 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 3346 July 2018, . 3348 [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol 3349 Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, 3350 . 3352 Appendix A. AERO Alternate Encapsulations 3354 When GUE encapsulation is not needed, AERO can use common 3355 encapsulations such as IP-in-IP [RFC2003][RFC2473][RFC4213], Generic 3356 Routing Encapsulation (GRE) [RFC2784][RFC2890] and others. The 3357 encapsulation is therefore only differentiated from non-AERO tunnels 3358 through the application of AERO control messaging and not through, 3359 e.g., a well-known UDP port number. 3361 As for GUE encapsulation, alternate AERO encapsulation formats may 3362 require encapsulation layer fragmentation. For simple IP-in-IP 3363 encapsulation, an IPv6 fragment header is inserted directly between 3364 the inner and outer IP headers when needed, i.e., even if the outer 3365 header is IPv4. The IPv6 Fragment Header is identified to the outer 3366 IP layer by its IP protocol number, and the Next Header field in the 3367 IPv6 Fragment Header identifies the inner IP header version. For GRE 3368 encapsulation, a GRE fragment header is inserted within the GRE 3369 header [I-D.templin-intarea-grefrag]. 3371 Figure 6 shows the AERO IP-in-IP encapsulation format before any 3372 fragmentation is applied: 3374 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3375 | Outer IPv4 Header | | Outer IPv6 Header | 3376 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3377 |IPv6 Frag Header (optional)| |IPv6 Frag Header (optional)| 3378 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3379 | Inner IP Header | | Inner IP Header | 3380 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3381 | | | | 3382 ~ ~ ~ ~ 3383 ~ Inner Packet Body ~ ~ Inner Packet Body ~ 3384 ~ ~ ~ ~ 3385 | | | | 3386 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3388 Minimal Encapsulation in IPv4 Minimal Encapsulation in IPv6 3390 Figure 6: Minimal Encapsulation Format using IP-in-IP 3392 Figure 7 shows the AERO GRE encapsulation format before any 3393 fragmentation is applied: 3395 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3396 | Outer IP Header | 3397 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3398 | GRE Header | 3399 | (with checksum, key, etc..) | 3400 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3401 | GRE Fragment Header (optional)| 3402 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3403 | Inner IP Header | 3404 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3405 | | 3406 ~ ~ 3407 ~ Inner Packet Body ~ 3408 ~ ~ 3409 | | 3410 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3412 Figure 7: Minimal Encapsulation Using GRE 3414 Alternate encapsulation may be preferred in environments where GUE 3415 encapsulation would add unnecessary overhead. For example, certain 3416 low-bandwidth wireless data links may benefit from a reduced 3417 encapsulation overhead. 3419 GUE encapsulation can traverse network paths that are inaccessible to 3420 non-UDP encapsulations, e.g., for crossing Network Address 3421 Translators (NATs). More and more, network middleboxes are also 3422 being configured to discard packets that include anything other than 3423 a well-known IP protocol such as UDP and TCP. It may therefore be 3424 necessary to determine the potential for middlebox filtering before 3425 enabling alternate encapsulation in a given environment. 3427 In addition to IP-in-IP, GRE and GUE, AERO can also use security 3428 encapsulations such as IPsec, TLS/SSL, DTLS, etc. In that case, AERO 3429 control messaging and route determination occur before security 3430 encapsulation is applied for outgoing packets and after security 3431 decapsulation is applied for incoming packets. 3433 AERO is especially well suited for use with VPN system encapsulations 3434 such as OpenVPN [OVPN]. 3436 Appendix B. Non-Normative Considerations 3438 AERO can be applied to a multitude of Internetworking scenarios, with 3439 each having its own adaptations. The following considerations are 3440 provided as non-normative guidance: 3442 B.1. Implementation Strategies for Route Optimization 3444 Route optimization as discussed in Section 3.17 results in the route 3445 optimization source (ROS) creating an asymmetric neighbor cache entry 3446 for the target neighbor. The neighbor cache entry is maintained for 3447 at most REACHABLETIME seconds and then deleted unless updated. In 3448 order to refresh the neighbor cache entry lifetime before the 3449 ReachableTime timer expires, the specification requires 3450 implementations to issue a new NS/NA exchange to reset ReachableTime 3451 to REACHABLETIME seconds while data packets are still flowing. 3452 However, the decision of when to initiate a new NS/NA exchange and to 3453 perpetuate the process is left as an implementation detail. 3455 One possible strategy may be to monitor the neighbor cache entry 3456 watching for data packets for (REACHABLETIME - 5) seconds. If any 3457 data packets have been sent to the neighbor within this timeframe, 3458 then send an NS to receive a new NA. If no data packets have been 3459 sent, wait for 5 additional seconds and send an immediate NS if any 3460 data packets are sent within this "expiration pending" 5 second 3461 window. If no additional data packets are sent within the 5 second 3462 window, delete the neighbor cache entry. 3464 The monitoring of the neighbor data packet traffic therefore becomes 3465 an asymmetric ongoing process during the neighbor cache entry 3466 lifetime. If the neighbor cache entry expires, future data packets 3467 will trigger a new NS/NA exchange while the packets themselves are 3468 delivered over a longer path until route optimization state is re- 3469 established. 3471 B.2. Implicit Mobility Management 3473 AERO interface neighbors MAY provide a configuration option that 3474 allows them to perform implicit mobility management in which no ND 3475 messaging is used. In that case, the Client only transmits packets 3476 over a single interface at a time, and the neighbor always observes 3477 packets arriving from the Client from the same link-layer source 3478 address. 3480 If the Client's underlying interface address changes (either due to a 3481 readdressing of the original interface or switching to a new 3482 interface) the neighbor immediately updates the neighbor cache entry 3483 for the Client and begins accepting and sending packets according to 3484 the Client's new address. This implicit mobility method applies to 3485 use cases such as cellphones with both WiFi and Cellular interfaces 3486 where only one of the interfaces is active at a given time, and the 3487 Client automatically switches over to the backup interface if the 3488 primary interface fails. 3490 B.3. Direct Underlying Interfaces 3492 When a Client's AERO interface is configured over a Direct interface, 3493 the neighbor at the other end of the Direct link can receive packets 3494 without any encapsulation. In that case, the Client sends packets 3495 over the Direct link according to QoS preferences. If the Direct 3496 interface has the highest QoS preference, then the Client's IP 3497 packets are transmitted directly to the peer without going through an 3498 ANET/INET. If other interfaces have higher QoS preferences, then the 3499 Client's IP packets are transmitted via a different interface, which 3500 may result in the inclusion of Proxys, Servers and Relays in the 3501 communications path. Direct interfaces must be tested periodically 3502 for reachability, e.g., via NUD. 3504 B.4. AERO Clients on the Open Internetwork 3506 AERO Clients that connect to the open Internetwork via either a 3507 native or NATed interface can establish a VPN to securely connect to 3508 a Server. Alternatively, the Client can exchange ND messages 3509 directly with other AERO nodes on the same SPAN segment using INET 3510 encapsulation only and without joining the SPAN. In that case, 3511 however, the Client must apply asymmetric security for ND messages to 3512 ensure routing and neighbor cache integrity (see: Section 6). 3514 B.5. Operation on AERO Links with /64 ASPs 3516 IPv6 AERO links typically have MSPs that aggregate many candidate 3517 MNPs of length /64 or shorter. However, in some cases it may be 3518 desirable to use AERO over links that have only a /64 MSP. This can 3519 be accommodated by treating all Clients on the AERO link as simple 3520 hosts that receive /128 prefix delegations. 3522 In that case, the Client sends an RS message to the Server the same 3523 as for ordinary AERO links. The Server responds with an RA message 3524 that includes one or more /128 prefixes (i.e., singleton addresses) 3525 that include the /64 MSP prefix along with an interface identifier 3526 portion to be assigned to the Client. The Client and Server then 3527 configure their AERO addresses based on the interface identifier 3528 portions of the /128s (i.e., the lower 64 bits) and not based on the 3529 /64 prefix (i.e., the upper 64 bits). 3531 For example, if the MSP for the host-only IPv6 AERO link is 3532 2001:db8:1000:2000::/64, each Client will receive one or more /128 3533 IPv6 prefix delegations such as 2001:db8:1000:2000::1/128, 3534 2001:db8:1000:2000::2/128, etc. When the Client receives the prefix 3535 delegations, it assigns the AERO addresses fe80::1, fe80::2, etc. to 3536 the AERO interface, and assigns the global IPv6 addresses (i.e., the 3537 /128s) to either the AERO interface or an internal virtual interface 3538 such as a loopback. In this arrangement, the Client conducts route 3539 optimization in the same sense as discussed in Section 3.17. 3541 This specification has applicability for nodes that act as a Client 3542 on an "upstream" AERO link, but also act as a Server on "downstream" 3543 AERO links. More specifically, if the node acts as a Client to 3544 receive a /64 prefix from the upstream AERO link it can then act as a 3545 Server to provision /128s to Clients on downstream AERO links. 3547 B.6. AERO Adaptations for SEcure Neighbor Discovery (SEND) 3549 SEcure Neighbor Discovery (SEND) [RFC3971] and Cryptographically 3550 Generated Addresses (CGAs) [RFC3972] were designed to secure IPv6 ND 3551 messaging in environments where symmetric network and/or transport- 3552 layer security services are impractical (see: Section 6). AERO nodes 3553 that use SEND/CGA employ the following adaptations. 3555 When a source AERO node prepares a SEND-protected ND message, it uses 3556 a link-local CGA as the IPv6 source address and writes the prefix 3557 embedded in its AERO address (i.e., instead of fe80::/64) in the CGA 3558 parameters Subnet Prefix field. When the neighbor receives the ND 3559 message, it first verifies the message checksum and SEND/CGA 3560 parameters while using the link-local prefix fe80::/64 (i.e., instead 3561 of the value in the Subnet Prefix field) to match against the IPv6 3562 source address of the ND message. 3564 The neighbor then derives the AERO address of the source by using the 3565 value in the Subnet Prefix field as the interface identifier of an 3566 AERO address. For example, if the Subnet Prefix field contains 3567 2001:db8:1:2, the neighbor constructs the AERO address as 3568 fe80::2001:db8:1:2. The neighbor then caches the AERO address in the 3569 neighbor cache entry it creates for the source, and uses the AERO 3570 address as the IPv6 destination address of any ND message replies. 3572 B.7. AERO Critical Infrastructure Considerations 3574 AERO Relays can be either Commercial off-the Shelf (COTS) standard IP 3575 routers or virtual machines in the cloud. Relays must be 3576 provisioned, supported and managed by the INET administrative 3577 authority, and connected to the Relays of other INETs via inter- 3578 domain peerings. Cost for purchasing, configuring and managing 3579 Relays is nominal even for very large AERO links. 3581 AERO Servers can be standard dedicated server platforms, but most 3582 often will be deployed as virtual machines in the cloud. The only 3583 requirements for Servers are that they can run the AERO user-level 3584 code and have at least one network interface connection to the INET. 3585 As with Relays, Servers must be provisioned, supported and managed by 3586 the INET administrative authority. Cost for purchasing, configuring 3587 and managing Servers is nominal especially for virtual Servers hosted 3588 in the cloud. 3590 AERO Proxys are most often standard dedicated server platforms with 3591 one network interface connected to the ANET and a second interface 3592 connected to an INET. As with Servers, the only requirements are 3593 that they can run the AERO user-level code and have at least one 3594 interface connection to the INET. Proxys must be provisioned, 3595 supported and managed by the ANET administrative authority. Cost for 3596 purchasing, configuring and managing Proxys is nominal, and borne by 3597 the ANET administrative authority. 3599 AERO Gateways can be any dedicated server or COTS router platform 3600 connected to INETs and/or EUNs. The Gateway joins the SPAN and 3601 engages in eBGP peering with one or more Relays as a stub AS. The 3602 Gateway then injects its MNPs and/or non-MNP prefixes into the BGP 3603 routing system, and provisions the prefixes to its downstream- 3604 attached networks. The Gateway can perform ROS and MAP services the 3605 same as for any Server, and can route between the MNP and non-MNP 3606 address spaces. 3608 B.8. AERO Server Failure Implications 3610 AERO Servers may appear as a single point of failure in the 3611 architecture, but such is not the case since all Servers on the link 3612 provide identical services and loss of a Server does not imply 3613 immediate and/or comprehensive communication failures. Although 3614 Clients typically associate with a single Server at a time, Server 3615 failure is quickly detected and conveyed by Bidirectional Forward 3616 Detection (BFD) and/or proactive NUD allowing Clients to migrate to 3617 new Servers. 3619 If a Server fails, ongoing packet forwarding to Clients will continue 3620 by virtue of the asymmetric neighbor cache entries that have already 3621 been established in route optimization sources (ROSs). If a Client 3622 also experiences mobility events at roughly the same time the Server 3623 fails, unsolicited NA messages may be lost but proxy neighbor cache 3624 entries in the DEPARTED state will ensure that packet forwarding to 3625 the Client's new locations will continue for up to DEPARTTIME 3626 seconds. 3628 If a Client is left without a Server for an extended timeframe (e.g., 3629 greater than REACHABLETIIME seconds) then existing asymmetric 3630 neighbor cache entries will eventually expire and both ongoing and 3631 new communications will fail. The original source will continue to 3632 retransmit until the Client has established a new Server 3633 relationship, after which time continuous communications will resume. 3635 Therefore, providing many Servers on the link with high availability 3636 profiles provides resilience against loss of individual Servers and 3637 assurance that Clients can establish new Server relationships quickly 3638 in event of a Server failure. 3640 B.9. AERO Client / Server Architecture 3642 The AERO architectural model is client / server in the control plane, 3643 with route optimization in the data plane. The same as for common 3644 Internet services, the AERO Client discovers the addresses of AERO 3645 Servers and selects one Server to connect to. The AERO service is 3646 analogous to common Internet services such as google.com, yahoo.com, 3647 cnn.com, etc. However, there is only one AERO service for the link 3648 and all Servers provide identical services. 3650 Common Internet services provide differing strategies for advertising 3651 server addresses to clients. The strategy is conveyed through the 3652 DNS resource records returned in response to name resolution queries. 3653 As of January 2020 Internet-based 'nslookup' services were used to 3654 determine the following: 3656 o When a client resolves the domainname "google.com", the DNS always 3657 returns one A record (i.e., an IPv4 address) and one AAAA record 3658 (i.e., an IPv6 address). The client receives the same addresses 3659 each time it resolves the domainname via the same DNS resolver, 3660 but may receive different addresses when it resolves the 3661 domainname via different DNS resolvers. But, in each case, 3662 exactly one A and one AAAA record are returned. 3664 o When a client resolves the domainname "ietf.org", the DNS always 3665 returns one A record and one AAAA record with the same addresses 3666 regardless of which DNS resolver is used. 3668 o When a client resolves the domainname "yahoo.com", the DNS always 3669 returns a list of 4 A records and 4 AAAA records. Each time the 3670 client resolves the domainname via the same DNS resolver, the same 3671 list of addresses are returned but in randomized order (i.e., 3672 consistent with a DNS round-robin strategy). But, interestingly, 3673 the same addresses are returned (albeit in randomized order) when 3674 the domainname is resolved via different DNS resolvers. 3676 o When a client resolves the domainname "amazon.com", the DNS always 3677 returns a list of 3 A records and no AAAA records. As with 3678 "yahoo.com", the same three A records are returned from any 3679 worldwide Internet connection point in randomized order. 3681 The above example strategies show differing approaches to Internet 3682 resilience and service distribution offered by major Internet 3683 services. The Google approach exposes only a single IPv4 and a 3684 single IPv6 address to clients. Clients can then select whichever IP 3685 protocol version offers the best response, but will always use the 3686 same IP address according to the current Internet connection point. 3687 This means that the IP address offered by the network must lead to a 3688 highly-available server and/or service distribution point. In other 3689 words, resilience is predicated on high availability within the 3690 network and with no client-initiated failovers expected (i.e., it is 3691 all-or-nothing from the client's perspective). However, Google does 3692 provide for worldwide distributed service distribution by virtue of 3693 the fact that each Internet connection point responds with a 3694 different IPv6 and IPv4 address. The IETF approach is like google 3695 (all-or-nothing from the client's perspective), but provides only a 3696 single IPv4 or IPv6 address on a worldwide basis. This means that 3697 the addresses must be made highly-available at the network level with 3698 no client failover possibility, and if there is any worldwide service 3699 distribution it would need to be conducted by a network element that 3700 is reached via the IP address acting as a service distribution point. 3702 In contrast to the Google and IETF philosophies, Yahoo and Amazon 3703 both provide clients with a (short) list of IP addresses with Yahoo 3704 providing both IP protocol versions and Amazon as IPv4-only. The 3705 order of the list is randomized with each name service query 3706 response, with the effect of round-robin load balancing for service 3707 distribution. With a short list of addresses, there is still 3708 expectation that the network will implement high availability for 3709 each address but in case any single address fails the client can 3710 switch over to using a different address. The balance then becomes 3711 one of function in the network vs function in the end system. 3713 The same implications observed for common highly-available services 3714 in the Internet apply also to the AERO client/server architecture. 3715 When an AERO Client connects to one or more ANETs, it discovers one 3716 or more AERO Server addresses through the mechanisms discussed in 3717 earlier sections. Each Server address presumably leads to a fault- 3718 tolerant clustering arrangement such as supported by Linux-HA, 3719 Extended Virtual Synchrony or Paxos. Such an arrangement has 3720 precedence in common Internet service deployments in lightweight 3721 virtual machines without requiring expensive hardware deployment. 3722 Similarly, common Internet service deployments set service IP 3723 addresses on service distribution points that may relay requests to 3724 many different servers. 3726 For AERO, the expectation is that a combination of the Google/IETF 3727 and Yahoo/Amazon philosophies would be employed. The AERO Client 3728 connects to different ANET access points and can receive 1-2 Server 3729 AERO addresses at each point. It then selects one AERO Server 3730 address, and engages in RS/RA exchanges with the same Server from all 3731 ANET connections. The Client remains with this Server unless or 3732 until the Server fails, in which case it can switch over to an 3733 alternate Server. The Client can likewise switch over to a different 3734 Server at any time if there is some reason for it to do so. So, the 3735 AERO expectation is for a balance of function in the network and end 3736 system, with fault tolerance and resilience at both levels. 3738 Appendix C. Change Log 3740 << RFC Editor - remove prior to publication >> 3742 Changes from draft-templin-intarea-6706bis-25 to draft-templin- 3743 intrea-6706bis-26: 3745 o MTU and RA configuration information updated. 3747 Changes from draft-templin-intarea-6706bis-24 to draft-templin- 3748 intrea-6706bis-25: 3750 o Added concept of "primary" to allow for proxyed RS/RA over only 3751 selected underlying interfaces. 3753 o General Cleanup. 3755 Changes from draft-templin-intarea-6706bis-23 to draft-templin- 3756 intrea-6706bis-24: 3758 o OMNI interface spec now a normative reference. 3760 o Use REACHABLETIME as the nominal Router Lifetime to return in RAs. 3762 o General cleanup. 3764 Changes from draft-templin-intarea-6706bis-22 to draft-templin- 3765 intrea-6706bis-23: 3767 o Choice of using either RS/RA or unsolicited NA for old Server 3768 notification. 3770 o General cleanup. 3772 Changes from draft-templin-intarea-6706bis-21 to draft-templin- 3773 intrea-6706bis-22: 3775 o Tightened up text on Proxy. 3777 o Removed unnecessarily restrictive texts. 3779 o General cleanup. 3781 Changes from draft-templin-intarea-6706bis-20 to draft-templin- 3782 intrea-6706bis-21: 3784 o Clarified relationship between OMNI and S/TLLAO ifIndex-tuples. 3786 o Important text in Section 13.15.3 on Servers timing out Clients 3787 that have gone silent without sending a departure notification. 3789 o New text on RS/RA as "hints of forward progress" for proactive 3790 NUD. 3792 Changes from draft-templin-intarea-6706bis-19 to draft-templin- 3793 intrea-6706bis-20: 3795 o Included new route optimization source and destination addressing 3796 strategy. Now, route optimization maintenance uses the address of 3797 the existing Server instead of the data packet destination address 3798 so that less pressure is placed on the BGP routing system 3799 convergence time and Server constancy is supported. 3801 o Included new method for releasing from old MSE without requiring 3802 Client messaging. 3804 o Included references to new OMNI interface spec (including the OMNI 3805 option). 3807 o New appendix on AERO Client/Server architecture. 3809 Changes from draft-templin-intarea-6706bis-18 to draft-templin- 3810 intrea-6706bis-19: 3812 o Changed Proxy/Server keepalives to use "proactive NUD" in a manner 3813 tha paralles BFD 3815 Changes from draft-templin-intarea-6706bis-17 to draft-templin- 3816 intrea-6706bis-18: 3818 o Discuss how AERO option is used in relation to S/TLLAOs 3820 o New text on Bidirectional Forwarding Detection (BFD) 3822 o Cleaned up usage (and non-usage) of unsolicited NAs 3824 o New appendix on Server failures 3826 Changes from draft-templin-intarea-6706bis-15 to draft-templin- 3827 intrea-6706bis-17: 3829 o S/TLLAO now includes multiple link-layer addresses within a single 3830 option instead of requiring multiple options 3832 o New unsolicited NA message to inform the old link that a Client 3833 has moved to a new link 3835 Changes from draft-templin-intarea-6706bis-14 to draft-templin- 3836 intrea-6706bis-15: 3838 o MTU and fragmentation 3840 o New details in movement to new Server 3842 Changes from draft-templin-intarea-6706bis-13 to draft-templin- 3843 intrea-6706bis-14: 3845 o Security based on secured tunnels, ingress filtering, MAP list and 3846 ROS list 3848 Changes from draft-templin-intarea-6706bis-12 to draft-templin- 3849 intrea-6706bis-13: 3851 o New paragraph in Section 3.6 on AERO interface layering over 3852 secured tunnels 3854 o Removed extraneous text in Section 3.7 3856 o Added new detail to the forwarding algorithm in Section 3.9 3858 o Clarified use of fragmentation 3860 o Route optimization now supported for both MNP and non-MNP-based 3861 prefixes 3863 o Relays are now seen as link-layer elements in the architecture. 3865 o Built out multicast section in detail. 3867 o New Appendix on implementation considerations for route 3868 optimization. 3870 Changes from draft-templin-intarea-6706bis-11 to draft-templin- 3871 intrea-6706bis-12: 3873 o Introduced Gateways as a new AERO element for connecting 3874 Correspondent Nodes on INET links 3876 o Introduced terms "Access Network (ANET)" and "Internetwork (INET)" 3878 o Changed "ASP" to "MSP", and "ACP" to "MNP" 3880 o New figure on the relation of Segments to the SPAN and AERO link 3882 o New "S" bit in S/TLLAO to indicate the "Source" S/TLLAO as opposed 3883 to additional S/TLLAOs 3885 o Changed Interface ID for Servers from 255 to 0xffff 3887 o Significant updates to Route Optimization, NUD, and Mobility 3888 Management 3890 o New Section on Multicast 3892 o New Section on AERO Clients in the open Internetwork 3894 o New Section on Operation over multiple AERO links (VLANs over the 3895 SPAN) 3897 o New Sections on DNS considerations and Transition considerations 3899 o 3901 Changes from draft-templin-intarea-6706bis-10 to draft-templin- 3902 intrea-6706bis-11: 3904 o Added The SPAN 3906 Changes from draft-templin-intarea-6706bis-09 to draft-templin- 3907 intrea-6706bis-10: 3909 o Orphaned packets in flight (e.g., when a neighbor cache entry is 3910 in the DEPARTED state) are now forwarded at the link layer instead 3911 of at the network layer. Forwarding at the network layer can 3912 result in routing loops and/or excessive delays of forwarded 3913 packets while the routing system is still reconverging. 3915 o Update route optimization to clarify the unsecured nature of the 3916 first NS used for route discovery 3918 o Many cleanups and clarifications on ND messaging parameters 3920 Changes from draft-templin-intarea-6706bis-08 to draft-templin- 3921 intrea-6706bis-09: 3923 o Changed PRL to "MAP list" 3925 o For neighbor cache entries, changed "static" to "symmetric", and 3926 "dynamic" to "asymmetric" 3928 o Specified Proxy RS/RA exchanges with Servers on behalf of Clients 3930 o Added discussion of unsolicited NAs in Section 3.16, and included 3931 forward reference to Section 3.18 3933 o Added discussion of AERO Clients used as critical infrastructure 3934 elements to connect fixed networks. 3936 o Added network-based VPN under security considerations 3938 Changes from draft-templin-intarea-6706bis-07 to draft-templin- 3939 intrea-6706bis-08: 3941 o New section on AERO-Aware Access Router 3943 Changes from draft-templin-intarea-6706bis-06 to draft-templin- 3944 intrea-6706bis-07: 3946 o Added "R" bit for release of PDs. Now have a full RS/RA service 3947 that can do PD without requiring DHCPv6 messaging over-the-air 3949 o Clarifications on solicited vs unsolicited NAs 3951 o Clarified use of MAX_NEIGHBOR_ADVERTISEMENTS for the purpose of 3952 increase reliability 3954 Changes from draft-templin-intarea-6706bis-05 to draft-templin- 3955 intrea-6706bis-06: 3957 o Major re-work and simplification of Route Optimization function 3959 o Added Distributed Mobility Management (DMM) and Mobility Anchor 3960 Point (MAP) terminology 3962 o New section on "AERO Critical Infrastructure Element 3963 Considerations" demonstrating low overall cost for the service 3965 o minor text revisions and deletions 3967 o removed extraneous appendices 3969 Changes from draft-templin-intarea-6706bis-04 to draft-templin- 3970 intrea-6706bis-05: 3972 o New Appendix E on S/TLLAO Extensions for special-purpose links. 3973 Discussed ATN/IPS as example. 3975 o New sentence in introduction to declare appendices as non- 3976 normative. 3978 Changes from draft-templin-intarea-6706bis-03 to draft-templin- 3979 intrea-6706bis-04: 3981 o Added definitions for Potential Router List (PRL) and secure 3982 enclave 3984 o Included text on mapping transport layer port numbers to network 3985 layer DSCP values 3987 o Added reference to DTLS and DMM Distributed Mobility Anchoring 3988 working group document 3990 o Reworked Security Considerations 3992 o Updated references. 3994 Changes from draft-templin-intarea-6706bis-02 to draft-templin- 3995 intrea-6706bis-03: 3997 o Added new section on SEND. 3999 o Clarifications on "AERO Address" section. 4001 o Updated references and added new reference for RFC8086. 4003 o Security considerations updates. 4005 o General text clarifications and cleanup. 4007 Changes from draft-templin-intarea-6706bis-01 to draft-templin- 4008 intrea-6706bis-02: 4010 o Note on encapsulation avoidance in Section 4. 4012 Changes from draft-templin-intarea-6706bis-00 to draft-templin- 4013 intrea-6706bis-01: 4015 o Remove DHCPv6 Server Release procedures that leveraged the old way 4016 Relays used to "route" between Server link-local addresses 4018 o Remove all text relating to Relays needing to do any AERO-specific 4019 operations 4021 o Proxy sends RS and receives RA from Server using SEND. Use CGAs 4022 as source addresses, and destination address of RA reply is to the 4023 AERO address corresponding to the Client's ACP. 4025 o Proxy uses SEND to protect RS and authenticate RA (Client does not 4026 use SEND, but rather relies on subnetwork security. When the 4027 Proxy receives an RS from the Client, it creates a new RS using 4028 its own addresses as the source and uses SEND with CGAs to send a 4029 new RS to the Server. 4031 o Emphasize distributed mobility management 4033 o AERO address-based RS injection of ACP into underlying routing 4034 system. 4036 Changes from draft-templin-aerolink-82 to draft-templin-intarea- 4037 6706bis-00: 4039 o Document use of NUD (NS/NA) for reliable link-layer address 4040 updates as an alternative to unreliable unsolicited NA. 4041 Consistent with Section 7.2.6 of RFC4861. 4043 o Server adds additional layer of encapsulation between outer and 4044 inner headers of NS/NA messages for transmission through Relays 4045 that act as vanilla IPv6 routers. The messages include the AERO 4046 Server Subnet Router Anycast address as the source and the Subnet 4047 Router Anycast address corresponding to the Client's ACP as the 4048 destination. 4050 o Clients use Subnet Router Anycast address as the encapsulation 4051 source address when the access network does not provide a 4052 topologically-fixed address. 4054 Author's Address 4056 Fred L. Templin (editor) 4057 Boeing Research & Technology 4058 P.O. Box 3707 4059 Seattle, WA 98124 4060 USA 4062 Email: fltemplin@acm.org