idnits 2.17.1 draft-templin-intarea-6706bis-21.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 (January 29, 2020) is 1539 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 1011 -- Looks like a reference, but probably isn't: '2' on line 1015 == Missing Reference: 'N' is mentioned on line 1025, but not defined == Unused Reference: 'RFC2474' is defined on line 3050, but no explicit reference was found in the text == Unused Reference: 'I-D.ietf-intarea-gue-extensions' is defined on line 3116, but no explicit reference was found in the text == Unused Reference: 'RFC2764' is defined on line 3198, but no explicit reference was found in the text == Unused Reference: 'RFC4607' is defined on line 3285, but no explicit reference was found in the text == Unused Reference: 'RFC7269' is defined on line 3372, but no explicit reference was found in the text == Unused Reference: 'RFC8086' is defined on line 3388, but no explicit reference was found in the text == Outdated reference: A later version (-15) exists of draft-ietf-dmm-distributed-mobility-anchoring-14 == Outdated reference: A later version (-13) exists of draft-ietf-intarea-tunnels-10 == Outdated reference: A later version (-26) exists of draft-ietf-rtgwg-atn-bgp-05 == Outdated reference: A later version (-11) exists of draft-templin-6man-dhcpv6-ndopt-09 == Outdated reference: A later version (-21) exists of draft-templin-atn-aero-interface-12 == 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 (~~), 15 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, January 29, 2020 5 rfc6179, rfc6706 (if 6 approved) 7 Intended status: Standards Track 8 Expires: August 1, 2020 10 Asymmetric Extended Route Optimization (AERO) 11 draft-templin-intarea-6706bis-21 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 1, 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 3.6. AERO Interface Characteristics . . . . . . . . . . . . . 21 73 3.7. AERO Interface Initialization . . . . . . . . . . . . . . 25 74 3.7.1. AERO Server/Gateway Behavior . . . . . . . . . . . . 25 75 3.7.2. AERO Proxy Behavior . . . . . . . . . . . . . . . . . 26 76 3.7.3. AERO Client Behavior . . . . . . . . . . . . . . . . 26 77 3.7.4. AERO Relay Behavior . . . . . . . . . . . . . . . . . 26 78 3.8. AERO Interface Neighbor Cache Maintenance . . . . . . . . 26 79 3.9. AERO Interface Encapsulation and Re-encapsulation . . . . 28 80 3.10. AERO Interface Decapsulation . . . . . . . . . . . . . . 29 81 3.11. AERO Interface Data Origin Authentication . . . . . . . . 30 82 3.12. AERO Interface Forwarding Algorithm . . . . . . . . . . . 30 83 3.12.1. Client Forwarding Algorithm . . . . . . . . . . . . 31 84 3.12.2. Proxy Forwarding Algorithm . . . . . . . . . . . . . 31 85 3.12.3. Server/Gateway Forwarding Algorithm . . . . . . . . 32 86 3.12.4. Relay Forwarding Algorithm . . . . . . . . . . . . . 34 87 3.13. AERO Interface MTU and Fragmentation . . . . . . . . . . 34 88 3.13.1. AERO MTU Requirements . . . . . . . . . . . . . . . 37 89 3.14. AERO Interface Error Handling . . . . . . . . . . . . . . 37 90 3.15. AERO Router Discovery, Prefix Delegation and 91 Autoconfiguration . . . . . . . . . . . . . . . . . . . . 40 92 3.15.1. AERO ND/PD Service Model . . . . . . . . . . . . . . 40 93 3.15.2. AERO Client Behavior . . . . . . . . . . . . . . . . 41 94 3.15.3. AERO Server Behavior . . . . . . . . . . . . . . . . 43 95 3.16. The AERO Proxy . . . . . . . . . . . . . . . . . . . . . 45 96 3.16.1. Detecting and Responding to Server Failures . . . . 48 97 3.17. AERO Route Optimization . . . . . . . . . . . . . . . . . 49 98 3.17.1. Route Optimization Initiation . . . . . . . . . . . 49 99 3.17.2. Relaying the NS . . . . . . . . . . . . . . . . . . 50 100 3.17.3. Processing the NS and Sending the NA . . . . . . . . 50 101 3.17.4. Relaying the NA . . . . . . . . . . . . . . . . . . 51 102 3.17.5. Processing the NA . . . . . . . . . . . . . . . . . 51 103 3.17.6. Route Optimization Maintenance . . . . . . . . . . . 51 104 3.18. Neighbor Unreachability Detection (NUD) . . . . . . . . . 52 105 3.19. Mobility Management and Quality of Service (QoS) . . . . 53 106 3.19.1. Mobility Update Messaging . . . . . . . . . . . . . 54 107 3.19.2. Announcing Link-Layer Address and/or QoS Preference 108 Changes . . . . . . . . . . . . . . . . . . . . . . 55 109 3.19.3. Bringing New Links Into Service . . . . . . . . . . 55 110 3.19.4. Removing Existing Links from Service . . . . . . . . 55 111 3.19.5. Moving to a New Server . . . . . . . . . . . . . . . 55 112 3.20. Multicast . . . . . . . . . . . . . . . . . . . . . . . . 57 113 3.20.1. Source-Specific Multicast (SSM) . . . . . . . . . . 57 114 3.20.2. Any-Source Multicast (ASM) . . . . . . . . . . . . . 58 115 3.20.3. Bi-Directional PIM (BIDIR-PIM) . . . . . . . . . . . 59 116 3.21. Operation over Multiple AERO Links (VLANs) . . . . . . . 59 117 3.22. DNS Considerations . . . . . . . . . . . . . . . . . . . 60 118 3.23. Transition Considerations . . . . . . . . . . . . . . . . 61 119 3.24. Detecting and Reacting to Server and Relay Failures . . . 61 120 4. Implementation Status . . . . . . . . . . . . . . . . . . . . 62 121 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 62 122 6. Security Considerations . . . . . . . . . . . . . . . . . . . 62 123 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 64 124 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 66 125 8.1. Normative References . . . . . . . . . . . . . . . . . . 66 126 8.2. Informative References . . . . . . . . . . . . . . . . . 67 127 Appendix A. AERO Alternate Encapsulations . . . . . . . . . . . 74 128 Appendix B. Non-Normative Considerations . . . . . . . . . . . . 75 129 B.1. Implementation Strategies for Route Optimization . . . . 76 130 B.2. Implicit Mobility Management . . . . . . . . . . . . . . 76 131 B.3. Direct Underlying Interfaces . . . . . . . . . . . . . . 77 132 B.4. AERO Clients on the Open Internetwork . . . . . . . . . . 77 133 B.5. Operation on AERO Links with /64 ASPs . . . . . . . . . . 77 134 B.6. AERO Adaptations for SEcure Neighbor Discovery (SEND) . . 78 135 B.7. AERO Critical Infrastructure Considerations . . . . . . . 78 136 B.8. AERO Server Failure Implications . . . . . . . . . . . . 79 137 B.9. AERO Client / Server Architecture . . . . . . . . . . . . 80 138 Appendix C. Change Log . . . . . . . . . . . . . . . . . . . . . 82 139 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 154 that are seen as AERO link neighbors. Each node's AERO interface 155 uses an IPv6 link-local address format (known as the AERO address) 156 that 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 form of PD known as "prefix registration" can be used 225 if the Client knows its prefix in advance and can represent it in 226 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 UDP encapsulation is used, the UDP port number is also 383 considered as part of the link-layer address. From the 384 perspective of the AERO interface, the link-layer address is 385 either an INET address for intra-segment encapsulation or a SPAN 386 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. Also, the term "IP" is used to generically 446 refer to either Internet Protocol version, i.e., IPv4 [RFC0791] or 447 IPv6 [RFC8200]. 449 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 450 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 451 "OPTIONAL" in this document are to be interpreted as described in BCP 452 14 [RFC2119][RFC8174] when, and only when, they appear in all 453 capitals, as shown here. 455 3. Asymmetric Extended Route Optimization (AERO) 457 The following sections specify the operation of IP over Asymmetric 458 Extended Route Optimization (AERO) links: 460 3.1. AERO Link Reference Model 461 +----------------+ 462 | AERO Relay R1 | 463 | Nbr: S1, S2, P1| 464 |(X1->S1; X2->S2)| 465 | MSP M1 | 466 +-+---------+--+-+ 467 +--------------+ | Secured | | +--------------+ 468 |AERO Server S1| | tunnels | | |AERO Server S2| 469 | Nbr: C1, R1 +-----+ | +-----+ Nbr: C2, R1 | 470 | default->R1 | | | default->R1 | 471 | X1->C1 | | | X2->C2 | 472 +-------+------+ | +------+-------+ 473 | AERO Link | | 474 X===+===+===================+==)===============+===+===X 475 | | | | 476 +-----+--------+ +--------+--+-----+ +--------+-----+ 477 |AERO Client C1| | AERO Proxy P1 | |AERO Client C2| 478 | Nbr: S1 | |(Proxy Nbr Cache)| | Nbr: S2 | 479 | default->S1 | +--------+--------+ | default->S2 | 480 | MNP X1 | | | MNP X2 | 481 +------+-------+ .--------+------. +-----+--------+ 482 | (- Proxyed Clients -) | 483 .-. `---------------' .-. 484 ,-( _)-. ,-( _)-. 485 .-(_ IP )-. +-------+ +-------+ .-(_ IP )-. 486 (__ EUN )--|Host H1| |Host H2|--(__ EUN ) 487 `-(______)-' +-------+ +-------+ `-(______)-' 489 Figure 1: AERO Link Reference Model 491 Figure 1 presents the AERO link reference model. In this model: 493 o the AERO link is an overlay network service configured over one or 494 more underlying INET partitions which may be managed by different 495 administrative authorities and have incompatible protocols and/or 496 addressing plans. 498 o AERO Relay R1 aggregates Mobility Service Prefix (MSP) M1, 499 discovers Mobile Network Prefixes (MNPs) X* and advertises the MSP 500 via BGP peerings over secured tunnels to Servers (S1, S2). Relays 501 use the SPAN service to bridge disjoint segments of a partitioned 502 AERO link. 504 o AERO Servers S1 and S2 configure secured tunnels with Relay R1 and 505 also act as Mobility Anchor Points (MAPs) and default routers for 506 their associated Clients C1 and C2. 508 o AERO Clients C1 and C2 associate with Servers S1 and S2, 509 respectively. They receive Mobile Network Prefix (MNP) 510 delegations X1 and X2, and also act as default routers for their 511 associated physical or internal virtual EUNs. Simple hosts H1 and 512 H2 attach to the EUNs served by Clients C1 and C2, respectively. 514 o AERO Proxy P1 configures a secured tunnel with Relay R1 and 515 provides proxy services for AERO Clients in secured enclaves that 516 cannot associate directly with other AERO link neighbors. 518 Each node on the AERO link maintains an AERO interface neighbor cache 519 and an IP forwarding table the same as for any link. Although the 520 figure shows a limited deployment, in common operational practice 521 there will normally be many additional Relays, Servers, Clients and 522 Proxys. 524 3.2. AERO Node Types 526 AERO Relays provide hybrid routing/bridging services (as well as a 527 security trust anchor) for nodes on an AERO link. Relays use 528 standard IPv6 routing to forward packets both within the same INET 529 partitions and between disjoint INET partitions based on a mid-layer 530 IPv6 encapsulation known as the SPAN header. The inner IP layer 531 experiences a virtual bridging service since the inner IP TTL/Hop 532 Limit is not decremented during forwarding. Each Relay also peers 533 with Servers and other Relays in a dynamic routing protocol instance 534 to provide a Distributed Mobility Management (DMM) service for the 535 list of active MNPs (see Section 3.3). Relays present the AERO link 536 as a set of one or more Mobility Service Prefixes (MSPs) but as link- 537 layer devices need not connect directly to the AERO link themselves 538 unless an administrative interface is desired. Relays configure 539 secured tunnels with Servers, Proxys and other Relays; they further 540 maintain IP forwarding table entries for each Mobile Network Prefix 541 (MNP) and any other reachable non-MNP prefixes. 543 AERO Servers provide default forwarding services and a Mobility 544 Anchor Point (MAP) for AERO Client Mobile Nodes (MNs). Each Server 545 also peers with Relays in a dynamic routing protocol instance to 546 advertise its list of associated MNPs (see Section 3.3). Servers 547 facilitate PD exchanges with Clients, where each delegated prefix 548 becomes an MNP taken from an MSP. Servers forward packets between 549 AERO interface neighbors and track each Client's mobility profiles. 551 AERO Clients register their MNPs through PD exchanges with AERO 552 Servers over the AERO link, and distribute the MNPs to nodes on EUNs. 553 A Client may also be co-resident on the same physical or virtual 554 platform as a Server; in that case, the Client and Server behave as a 555 single functional unit and without the need for any Client/Server 556 control messaging. 558 AERO Proxys provide a conduit for ANET AERO Clients to associate with 559 AERO Servers in external INETs. Client and Servers exchange control 560 plane messages via the Proxy acting as a bridge between the ANET/INET 561 boundary. The Proxy forwards data packets to and from Clients 562 according to forwarding information in the neighbor cache. The Proxy 563 function is specified in Section 3.16. 565 AERO Gateways are Servers that provide forwarding services between 566 the AERO interface and INET/EUN interfaces. Gateways are provisioned 567 with MNPs the same as for an AERO Client, and also run a dynamic 568 routing protocol to discover any non-MNP IP routes. The Gateway 569 advertises the MSP(s) to INETs, and distributes all of its associated 570 MNPs and non-MNP IP routes via BGP peerings with Relays. 572 AERO Relays, Servers, Proxys and Gateways are critical infrastructure 573 elements in fixed (i.e., non-mobile) INET deployments and hence have 574 permanent and unchanging INET addresses. AERO Clients are MNs that 575 connect via ANET interfaces, i.e., their ANET addresses may change 576 when the Client moves to a new ANET connection. 578 3.3. AERO Routing System 580 The AERO routing system comprises a private instance of the Border 581 Gateway Protocol (BGP) [RFC4271] that is coordinated between Relays 582 and Servers and does not interact with either the public Internet BGP 583 routing system or any underlying INET routing systems. 585 In a reference deployment, each Server is configured as an Autonomous 586 System Border Router (ASBR) for a stub Autonomous System (AS) using 587 an AS Number (ASN) that is unique within the BGP instance, and each 588 Server further uses eBGP to peer with one or more Relays but does not 589 peer with other Servers. Each INET of a multi-segment AERO link must 590 include one or more Relays, which peer with the Servers and Proxys 591 within that INET. All Relays within the same INET are members of the 592 same hub AS using a common ASN, and use iBGP to maintain a consistent 593 view of all active MNPs currently in service. The Relays of 594 different INETs peer with one another using eBGP. 596 Relays advertise the AERO link's MSPs and any non-MNP routes to each 597 of their Servers. This means that any aggregated non-MNPs (including 598 "default") are advertised to all Servers. Each Relay configures a 599 black-hole route for each of its MSPs. By black-holing the MSPs, the 600 Relay will maintain forwarding table entries only for the MNPs that 601 are currently active, and packets destined to all other MNPs will 602 correctly incur Destination Unreachable messages due to the black- 603 hole route. In this way, Servers have only partial topology 604 knowledge (i.e., they know only about the MNPs of their directly 605 associated Clients) and they forward all other packets to Relays 606 which have full topology knowledge. 608 Servers maintain a working set of associated MNPs, and dynamically 609 announce new MNPs and withdraw departed MNPs in eBGP updates to 610 Relays. Servers that are configured as Gateways also redistribute 611 non-MNP routes learned from non-AERO interfaces via their eBGP Relay 612 peerings. 614 Clients are expected to remain associated with their current Servers 615 for extended timeframes, however Servers SHOULD selectively suppress 616 updates for impatient Clients that repeatedly associate and 617 disassociate with them in order to dampen routing churn. Servers 618 that are configured as Gateways advertise the MSPs via INET/EUN 619 interfaces, and forward packets between INET/EUN interfaces and the 620 AERO interface using standard IP forwarding. 622 Scaling properties of the AERO routing system are limited by the 623 number of BGP routes that can be carried by Relays. As of 2015, the 624 global public Internet BGP routing system manages more than 500K 625 routes with linear growth and no signs of router resource exhaustion 626 [BGP]. More recent network emulation studies have also shown that a 627 single Relay can accommodate at least 1M dynamically changing BGP 628 routes even on a lightweight virtual machine, i.e., and without 629 requiring high-end dedicated router hardware. 631 Therefore, assuming each Relay can carry 1M or more routes, this 632 means that at least 1M Clients can be serviced by a single set of 633 Relays. A means of increasing scaling would be to assign a different 634 set of Relays for each set of MSPs. In that case, each Server still 635 peers with one or more Relays, but institutes route filters so that 636 BGP updates are only sent to the specific set of Relays that 637 aggregate the MSP. For example, if the MSP for the AERO link is 638 2001:db8::/32, a first set of Relays could service the MSP 639 2001:db8::/40, a second set of Relays could service 640 2001:db8:0100::/40, a third set could service 2001:db8:0200::/40, 641 etc. 643 Assuming up to 1K sets of Relays, the AERO routing system can then 644 accommodate 1B or more MNPs with no additional overhead (for example, 645 it should be possible to service 1B /64 MNPs taken from a /34 MSP and 646 even more for shorter prefixes). In this way, each set of Relays 647 services a specific set of MSPs that they advertise to the native 648 Internetwork routing system, and each Server configures MSP-specific 649 routes that list the correct set of Relays as next hops. This 650 arrangement also allows for natural incremental deployment, and can 651 support small scale initial deployments followed by dynamic 652 deployment of additional Clients, Servers and Relays without 653 disturbing the already-deployed base. 655 Server and Relays can use the Bidirectional Forwarding Detection 656 (BFD) protocol [RFC5880] to quickly detect link failures that don't 657 result in interface state changes, BGP peer failures, and 658 administrative state changes. BFD is important in environments where 659 rapid response to failures is required for routing reconvergence and, 660 hence, communications continuity. 662 A full discussion of the BGP-based routing system used by AERO is 663 found in [I-D.ietf-rtgwg-atn-bgp]. The system provides for 664 Distributed Mobility Management (DMM) per the distributed mobility 665 anchoring architecture [I-D.ietf-dmm-distributed-mobility-anchoring]. 667 3.3.1. IPv4 Compatibility Routing 669 For IPv6 MNPs, the AERO routing system includes ordinary IPv6 routes. 670 For IPv4 MNPs, the AERO routing system includes IPv6 routes based on 671 an IPv4-embedded IPv6 address format discussed in Section 3.5.1. 673 3.4. AERO Addresses 675 A Client's AERO address is an IPv6 link-local address with an 676 interface identifier based on the Client's delegated MNP. Relay, 677 Server and Proxy AERO addresses are assigned from the range fe80::/96 678 and include an administratively-provisioned value in the lower 32 679 bits. 681 For IPv6, Client AERO addresses begin with the prefix fe80::/64 and 682 include in the interface identifier (i.e., the lower 64 bits) a 683 64-bit prefix taken from one of the Client's IPv6 MNPs. For example, 684 if the AERO Client receives the IPv6 MNP: 686 2001:db8:1000:2000::/56 688 it constructs its corresponding AERO addresses as: 690 fe80::2001:db8:1000:2000 692 fe80::2001:db8:1000:2001 694 fe80::2001:db8:1000:2002 696 ... etc. ... 698 fe80::2001:db8:1000:20ff 700 For IPv4, Client AERO addresses are based on an IPv4-mapped IPv6 701 address [RFC4291] formed from an IPv4 MNP and with a Prefix Length of 702 96 plus the MNP prefix length. For example, for the IPv4 MNP 703 192.0.2.32/28 the IPv4-mapped IPv6 MNP is: 705 0:0:0:0:0:FFFF:192.0.2.16/124 (also written as 706 0:0:0:0:0:FFFF:c000:0210/124) 708 The Client then constructs its AERO addresses with the prefix 709 fe80::/64 and with the lower 64 bits of the IPv4-mapped IPv6 address 710 in the interface identifier as: 712 fe80::FFFF:192.0.2.16 714 fe80::FFFF:192.0.2.17 716 fe80::FFFF:192.0.2.18 718 ... etc. ... 720 fe80:FFFF:192.0.2.31 722 Relay, Server and Proxy AERO addresses are allocated from the range 723 fe80::/96, and MUST be managed for uniqueness. The lower 32 bits of 724 the AERO address includes a unique integer value between 1 and 725 0xfffffffe (e.g., fe80::1, fe80::2, fe80::3, etc., fe80::ffff:fffe) 726 as assigned by the administrative authority for the link. If the 727 link spans multiple SPAN segments, the AERO addresses are assigned to 728 each segment in 1x1 correspondence with SPAN addresses (see: 729 Section 3.5). The address fe80:: is the IPv6 link-local Subnet 730 Router Anycast address, and the address fe80::ffff:ffff is reserved 731 as the unspecified AERO address. 733 The lowest-numbered AERO address from a Client's MNP delegation 734 serves as the "base" AERO address (for example, for the MNP 735 2001:db8:1000:2000::/56 the base AERO address is 736 fe80::2001:db8:1000:2000). The Client then assigns the base AERO 737 address to the AERO interface and uses it for the purpose of 738 maintaining the neighbor cache entry. The Server likewise uses the 739 AERO address as its index into the neighbor cache for this Client. 741 If the Client has multiple AERO addresses (i.e., when there are 742 multiple MNPs and/or MNPs with prefix lengths shorter than /64), the 743 Client originates ND messages using the base AERO address as the 744 source address and accepts and responds to ND messages destined to 745 any of its AERO addresses as equivalent to the base AERO address. In 746 this way, the Client maintains a single neighbor cache entry that may 747 be indexed by multiple AERO addresses. 749 The Client's Subnet Router Anycast address can be statelessly 750 determined from its AERO address by simply transposing the AERO 751 address into the upper N bits of the Anycast address followed by 752 128-N bits of zeroes. For example, for the AERO address 753 fe80::2001:db8:1:2 the subnet router anycast address is 754 2001:db8:1:2::. 756 AERO addresses for mobile node Clients embed a MNP as discussed 757 above, while AERO addresses for non-MNP destinations are constructed 758 in exactly the same way. A Client AERO address therefore encodes 759 either an MNP if the prefix is reached via the SPAN or a non-MNP if 760 the prefix is reached via a Gateway. 762 3.5. Spanning Partitioned AERO Networks (SPAN) 764 An AERO link configured over a single INET appears as a single 765 unified link with a consistent underlying network addressing plan. 766 In that case, all nodes on the link can exchange packets via 767 encapsulation with INET addresses, since the underlying INET is 768 connected. In common practice, however, an AERO link may be 769 partitioned into multiple "segments", where each segment is a 770 distinct INET potentially managed under a different administrative 771 authority (e.g., as for worldwide aviation service providers such as 772 ARINC, SITA, Inmarsat, etc.). Individual INETs may themselves be 773 partitioned internally, in which case each internal partition is seen 774 as a separate segment. 776 The addressing plan of each segment is consistent internally but will 777 often bear no relation to the addressing plans of other segments. 778 Each segment is also likely to be separated from others by network 779 security devices (e.g., firewalls, proxies, packet filtering 780 gateways, etc.), and in many cases disjoint segments may not even 781 have any common physical link connections at all. Therefore, nodes 782 can only be assured of exchanging packets directly with 783 correspondents in the same segment, and not with those in other 784 segments. The only means for joining the segments therefore is 785 through inter-domain peerings between AERO Relays. 787 The same as for traditional campus LANs, multiple AERO link segments 788 can be joined into a single unified link via a virtual bridging 789 service termed the "SPAN". The SPAN performs link-layer packet 790 forwarding between segments (i.e., bridging) without decrementing the 791 network-layer TTL/Hop Limit. The SPAN model is depicted in Figure 2: 793 . . . . . . . . . . . . . . . . . . . . . . . 794 . . 795 . .-(::::::::) . 796 . .-(::::::::::::)-. +-+ . 797 . (:::: Segment A :::)--|R|---+ . 798 . `-(::::::::::::)-' +-+ | . 799 . `-(::::::)-' | . 800 . | . 801 . .-(::::::::) | . 802 . .-(::::::::::::)-. +-+ | . 803 . (:::: Segment B :::)--|R|---+ . 804 . `-(::::::::::::)-' +-+ | . 805 . `-(::::::)-' | . 806 . | . 807 . .-(::::::::) | . 808 . .-(::::::::::::)-. +-+ | . 809 . (:::: Segment C :::)--|R|---+ . 810 . `-(::::::::::::)-' +-+ | . 811 . `-(::::::)-' | . 812 . | . 813 . ..(etc).. x . 814 . . 815 . . 816 . <- AERO Link Bridged by the SPAN -> . 817 . . . . . . . . . . . . . .. . . . . . . . . 819 Figure 2: The SPAN 821 To support the SPAN, AERO links require a reserved /64 IPv6 "SPAN 822 Service Prefix (SSP)". Although any routable IPv6 prefix can be 823 used, a Unique Local Address (ULA) prefix (e.g., fd00::/64) [RFC4389] 824 is recommended since border routers are commonly configured to 825 prevent packets with ULAs from being injected into the AERO link by 826 an external IPv6 node and from leaking out of the AERO link to the 827 outside world. 829 Each segment in the SPAN assigns a unique sub-prefix of SSP::/96 830 termed a "SPAN Partition Prefix (SPP)". For example, a first segment 831 could assign fd00::1000/116, a second could assign fd00::2000/116, a 832 third could assign fd00::3000/116, etc. The administrative 833 authorities for each segment must therefore coordinate to assure 834 mutually-exclusive SPP assignments, but internal provisioning of the 835 SPP is an independent local consideration for each administrative 836 authority. 838 A "SPAN address" is an address taken from a SPP and assigned to a 839 Relay, Server or Proxy interface. SPAN addresses are formed by 840 simply replacing the upper portion of an administratively-assigned 841 AERO address with the SPP. For example, if the SPP is 842 fd00::1000/116, the SPAN address formed from the AERO address 843 fe80::1001 is simply fd00::1001. 845 An "INET address" is an address of a node's interface connection to 846 an INET. AERO/SPAN/INET address mappings are maintained as permanent 847 neighbor cache entires as discussed in Section 3.8. 849 AERO Relays serve as bridges to join multiple segments into a unified 850 AERO link over multiple diverse administrative domains. They support 851 the bridging function by first establishing forwarding table entries 852 for their SPPs either via standard BGP routing or static routes. For 853 example, if three Relays ('A', 'B' and 'C') from different segments 854 serviced the SPPs fd00::1000/116, fd00::2000/116 and fd00::3000/116 855 respectively, then the forwarding tables in each Relay are as 856 follows: 858 A: fd00::1000/116->local, fd00::2000/116->B, fd00::3000/116->C 860 B: fd00::1000/116->A, fd00::2000/116->local, fd00::3000/116->C 862 C: fd00::1000/116->A, fd00::2000/116->B, fd00::3000/116->local 864 These forwarding table entries are permanent and never change, since 865 they correspond to fixed infrastructure elements in their respective 866 segments. This provides the basis for a link-layer forwarding 867 service that cannot be disrupted by routing updates due to node 868 mobility. 870 With the SPPs in place in each Relay's forwarding table, control and 871 data packets sent between AERO nodes in different segments can 872 therefore be carried over the SPAN via encapsulation. For example, 873 when a source node in segment A forwards a packet with IPv6 address 874 2001:db8:1:2::1 to a destination node in segment C with IPv6 address 875 2001:db8:1000:2000::1, it first encapsulates the packet in a SPAN 876 header with source SPAN address taken from fd00::1000/116 (e.g., 877 fd00::1001) and destination SPAN address taken from fd00::3000/116 878 (e.g., fd00::3001). Next, it encapsulates the SPAN message in an 879 INET header with source address set to its own INET address (e.g., 880 192.0.2.100) and destination set to the INET address of a Relay 881 (e.g., 192.0.2.1). 883 SPAN encapsulation is based on Generic Packet Tunneling in IPv6 884 [RFC2473]; the encapsulation format in the above example is shown in 885 Figure 3: 887 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 888 | INET Header | 889 | src = 192.0.2.100 | 890 | dst = 192.0.2.1 | 891 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 892 | SPAN Header | 893 | src = fd00::1001 | 894 | dst = fd00::3001 | 895 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 896 | Inner IP Header | 897 | src = 2001:db8:1:2::1 | 898 | dst = 2001:db8:1000:2000::1 | 899 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 900 | | 901 ~ ~ 902 ~ Inner Packet Body ~ 903 ~ ~ 904 | | 905 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 907 Figure 3: SPAN Encapsulation 909 In this format, the inner IP header and packet body are the original 910 IP packet, the SPAN header is an IPv6 header prepared according to 911 [RFC2473], and the INET header is prepared according to Section 3.9. 912 A packet is said to be "forwarded/sent into the SPAN" when it is 913 encapsulated as described above then forwarded via a secured tunnel 914 to a neighboring Relay. 916 This gives rise to a routing system that contains both MNP routes 917 that may change dynamically due to regional node mobility and SPAN 918 routes that never change. The Relays can therefore provide link- 919 layer bridging by sending packets into the SPAN instead of network- 920 layer routing according to MNP routes. As a result, opportunities 921 for packet loss due to node mobility between different segments are 922 mitigated. 924 With reference to Figure 3, for a Client's AERO address the SPAN 925 address is simply set to the Subnet Router Anycast address. For non- 926 link-local addresses, the destination SPAN address may not be known 927 in advance for the first few packets of a flow sent via the SPAN. In 928 that case, the SPAN destination address is set to the original 929 packet's destination, and the SPAN routing system will direct the 930 packet to the correct SPAN egress node. (In the above example, the 931 SPAN destination address is simply 2001:db8:1000:2000::1.) 933 3.5.1. SPAN Compatibility Addressing 935 For IPv4 MNPs, Servers injects a "SPAN Compatibility Prefix (SCP)" 936 that embeds the MNP into the BGP routing system. The SCP begins with 937 the upper 64 bits of the SSP, followed by the constant string 938 "0000:FFFF" followed by the IPv4 MNP. For example, if the SSP is 939 fd00::/64 and the MNP is 192.0.2.0/24 then the SCP is 940 fd00::FFFF:192.0.2.0/120. 942 This allows for encapsulation of IPv4 packets in IPv6 headers with 943 "SPAN Compatibility Addresses (SCAs)". In this example, the SCA 944 corresponding to the SCP is simply fd00::FFFF:192.0.2.0, and can be 945 used as the SPAN destination address for packets forwarded via the 946 SPAN. This allows for forwarding of initial IPv4 packets over IPv6 947 SPAN routes, followed by route optimization for direct 948 communications. 950 3.6. AERO Interface Characteristics 952 AERO interfaces are virtual interfaces configured over one or more 953 underlying interfaces classified as follows: 955 o Native interfaces have global IP addresses that are reachable from 956 any INET correspondent. All Server and Relay interfaces are 957 native interfaces, as are INET-facing interfaces of Proxys. 959 o NATed interfaces connect to a private network behind a Network 960 Address Translator (NAT). The NAT does not participate in any 961 AERO control message signaling, but the Server can issue control 962 messages on behalf of the Client. Clients that are behind a NAT 963 are required to send periodic keepalive messages to keep NAT state 964 alive when there are no data packets flowing. If no other 965 periodic messaging service is available, the Client can send RS 966 messages to receive RA replies from its Server(s). 968 o VPNed interfaces use security encapsulation to a Virtual Private 969 Network (VPN) server that also acts as an AERO Server. As with 970 NATed links, the Server can issue control messages on behalf of 971 the Client, but the Client need not send periodic keepalives in 972 addition to those already used to maintain the VPN connection. 974 o Proxyed interfaces connect to an ANET that is separated from the 975 open INET by an AERO Proxy. Unlike NATed and VPNed interfaces, 976 the Proxy can actively issue control messages on behalf of the 977 Client. 979 o Direct interfaces connect a Client directly to a neighbor without 980 crossing any ANET/INET paths. An example is a line-of-sight link 981 between a remote pilot and an unmanned aircraft. 983 AERO interfaces use encapsulation (see: Section 3.9) to exchange 984 packets with AERO link neighbors over Native, NATed or VPNed 985 interfaces. AERO interfaces do not use encapsulation over Proxyed 986 and Direct underlying interfaces. 988 AERO interfaces maintain a neighbor cache for tracking per-neighbor 989 state the same as for any interface. AERO interfaces use ND messages 990 including Router Solicitation (RS), Router Advertisement (RA), 991 Neighbor Solicitation (NS) and Neighbor Advertisement (NA) for 992 neighbor cache management. 994 AERO interfaces send ND messages with an Overlay Multilink Network 995 Interface (OMNI) option formatted as specified in 996 [I-D.templin-atn-aero-interface]. The OMNI option includes prefix 997 registration information and "ifIndex-tuples" containing link quality 998 information for the AERO interface's underlying interfaces. 1000 When encapsulation is used, AERO interface ND messages MAY also 1001 include an AERO Source/Target Link-Layer Address Option (S/TLLAO) 1002 formatted as shown in Figure 4: 1004 0 1 2 3 1005 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 1006 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1007 | Type | Length | ifIndex[1] |V| Reserved[1] | 1008 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1009 ~ Link Layer Address [1] ~ 1010 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1011 | Port Number [1] | ifIndex[2] |V| Reserved[2] | 1012 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1013 ~ Link Layer Address [2] ~ 1014 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1015 | Port Number [2] | ~ 1016 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ 1017 ~ ~ 1018 ~ ... ~ 1019 ~ ~ 1020 ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1021 ~ | ifIndex[N] |V| Reserved[N] | 1022 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1023 ~ Link Layer Address [N] ~ 1024 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1025 | Port Number [N] | Trailing zero padding | 1026 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1027 | Trailing zero padding (if necessary) | 1028 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1030 Figure 4: AERO Source/Target Link-Layer Address Option (S/TLLAO) 1031 Format 1033 In this format, Type and Length are set the same as specified for S/ 1034 TLLAOs in [RFC4861], with trailing zero padding octets added as 1035 necessary to produce an integral number of 8 octet blocks. The S/ 1036 TLLAO includes N ifIndex-tuples in correspondence to ifIndex-tuples 1037 that appear in the OMNI option. Each ifIndex-tuple includes the 1038 folllowing information: 1040 o ifIndex[i] - the same value as in the corresponding ifIndex-tuple 1041 included in the OMNI option. 1043 o V[i] - a bit that identifies the IP protocol version of the 1044 address found in the Link Layer Address [i] field. The bit is set 1045 to 0 for IPv4 or 1 for IPv6. 1047 o Reserved[i] - MUST encode the value 0 on transmission, and ignored 1048 on reception. 1050 o Link Layer Address [i] - the IPv4 or IPv6 address used as the 1051 encapsulation source address. The field is 4 bytes in length for 1052 IPv4 or 16 bytes in length for IPv6. 1054 o Port Number [i] - the upper layer protocol port number used as the 1055 encapsulation source port, or 0 when no upper layer protocol 1056 encapsulation is used. The field is 2 bytes in length. 1058 If an S/TLLAO is included, the first S/TLLAO ifIndex-tuple MUST 1059 correspond to the first OMNI option ifIndex-tuple, and any additional 1060 S/TLLAO ifIndex-tuples MUST correspond to a proper subset of the 1061 remaining OMNI option ifIndex-tuples. Any S/TLLAO ifIndex-tuple 1062 having an ifIndex value that does not appear in an OMNI option 1063 ifindex-tuple is ignored. If the same ifIndex value appears in 1064 multiple ifIndex-tuples, the first tuple is consulted and the 1065 remaining tuples are ignored. Any S/TLLAO ifIndex-tuples can 1066 therefore be viewed as inter-dependent extensions to their 1067 corresponidng OMNI option ifIndex-tuples. 1069 A Client's AERO interface may be configured over multiple underlying 1070 interface connections. For example, common mobile handheld devices 1071 have both wireless local area network ("WLAN") and cellular wireless 1072 links. These links are typically used "one at a time" with low-cost 1073 WLAN preferred and highly-available cellular wireless as a standby. 1074 In a more complex example, aircraft frequently have many wireless 1075 data link types (e.g. satellite-based, cellular, terrestrial, air-to- 1076 air directional, etc.) with diverse performance and cost properties. 1078 If a Client's multiple underlying interfaces are used "one at a time" 1079 (i.e., all other interfaces are in standby mode while one interface 1080 is active), then ND message OMNI options include only a single 1081 ifIndex-tuple and set to a constant value. In that case, the Client 1082 would appear to have a single interface but with a dynamically 1083 changing link-layer address. 1085 If the Client has multiple active underlying interfaces, then from 1086 the perspective of ND it would appear to have multiple link-layer 1087 addresses. In that case, ND message OMNI options MAY include 1088 multiple ifIndex-tuples - each with a value that corresponds to a 1089 specific interface. The OMNI option MUST include a first ifIndex- 1090 tuple that corresponds to the interface over which the ND message is 1091 sent. Every ND message need not include all OMNI and/or S/TLLAO 1092 ifIndex-tuples; for any ifIndex-tuple not included, the neighbor 1093 considers the status as unchanged. 1095 Relay, Server and Proxy AERO interfaces may be configured over one or 1096 more secured tunnel interfaces. The AERO interface configures both 1097 an AERO address and its corresponding SPAN address, while the 1098 underlying secured tunnel interfaces are either unnumbered or 1099 configure the same SPAN address. The AERO interface encapsulates 1100 each IP packet in a SPAN header and presents the packet to the 1101 underlying secured tunnel interface. For Relays that do not 1102 configure an AERO interface, the secured tunnel interfaces themselves 1103 are exposed to the IP layer with each interface configuring the 1104 Relay's SPAN address. Routing protocols such as BGP therefore run 1105 directly over the Relay's secured tunnel interfaces. For nodes that 1106 configure an AERO interface, routing protocols such as BGP run over 1107 the AERO interface but do not employ SPAN encapsulation. Instead, 1108 the AERO interface presents the routing protocol messages directly to 1109 the underlying secured tunnels without applying encapsulation and 1110 while using the SPAN address as the source address. This distinction 1111 must be honored consistently according to each node's configuration 1112 so that the IP forwarding table will associate discovered IP routes 1113 with the correct interface. 1115 3.7. AERO Interface Initialization 1117 AERO Servers, Proxys and Clients configure AERO interfaces as their 1118 point of attachment to the AERO link. AERO nodes assign the MSPs for 1119 the link to their AERO interfaces (i.e., as a "route-to-interface") 1120 to ensure that packets with destination addresses covered by an MNP 1121 not explicitly assigned to a non-AERO interface are directed to the 1122 AERO interface. 1124 AERO interface initialization procedures for Servers, Proxys, Clients 1125 and Relays are discussed in the following sections. 1127 3.7.1. AERO Server/Gateway Behavior 1129 When a Server enables an AERO interface, it assigns AERO/SPAN 1130 addresses and configures permanent neighbor cache entries for 1131 neighbors in the same SPAN segment by consulting the ROS list for the 1132 segment. The Server also configures secured tunnels with one or more 1133 neighboring Relays and engages in a BGP routing protocol session with 1134 each Relay. 1136 The AERO interface provides a single interface abstraction to the IP 1137 layer, but internally comprises multiple secured tunnels as well as 1138 an NBMA nexus for sending encapsulated data packets to AERO interface 1139 neighbors. The Server further configures a service to facilitate ND/ 1140 PD exchanges with AERO Clients and manages per-Client neighbor cache 1141 entries and IP forwarding table entries based on control message 1142 exchanges. 1144 Gateways are simply Servers that run a dynamic routing protocol 1145 between the AERO interface and INET/EUN interfaces (see: 1147 Section 3.3). The Gateway provisions MNPs to networks on the INET/ 1148 EUN interfaces (i.e., the same as a Client would do) and advertises 1149 the MSP(s) for the AERO link over the INET/EUN interfaces. The 1150 Gateway further provides an attachment point of the AERO link to the 1151 non-MNP-based global topology. 1153 3.7.2. AERO Proxy Behavior 1155 When a Proxy enables an AERO interface, it assigns AERO/SPAN 1156 addresses and configures permanent neighbor cache entries the same as 1157 for Servers. The Proxy also configures secured tunnels with one or 1158 more neighboring Relays and maintains per-Client neighbor cache 1159 entries based on control message exchanges. 1161 3.7.3. AERO Client Behavior 1163 When a Client enables an AERO interface, it sends an RS message with 1164 ND/PD parameters over an ANET interface to a Server in the MAP list, 1165 which returns an RA message with corresponding PD parameters. (The 1166 RS/RA messages may pass through a Proxy in the case of a Client's 1167 Proxyed interface.) 1169 After the initial ND/PD message exchange, the Client assigns AERO 1170 addresses to the AERO interface based on the delegated prefix(es). 1171 The Client can then register additional ANET interfaces with the 1172 Server by sending an RS message over each ANET interface. 1174 3.7.4. AERO Relay Behavior 1176 AERO Relays need not connect directly to the AERO link, since they 1177 operate as link-layer forwarding devices instead of network layer 1178 routers. Configuration of AERO interfaces on Relays is therefore 1179 OPTIONAL, e.g., if an administrative interface is needed. Relays 1180 configure secured tunnels with Servers, Proxys and other Relays; they 1181 also configure AERO/SPAN addresses and permanent neighbor cache 1182 entries the same as Servers. Relays engage in a BGP routing protocol 1183 session with a subset of the Servers on the local SPAN segment, and 1184 with other Relays on the SPAN (see: Section 3.3). 1186 3.8. AERO Interface Neighbor Cache Maintenance 1188 Each AERO interface maintains a conceptual neighbor cache that 1189 includes an entry for each neighbor it communicates with on the AERO 1190 link per [RFC4861]. AERO interface neighbor cache entries are said 1191 to be one of "permanent", "symmetric", "asymmetric" or "proxy". 1193 Permanent neighbor cache entries are created through explicit 1194 administrative action; they have no timeout values and remain in 1195 place until explicitly deleted. AERO Servers and Proxys maintain 1196 permanent neighbor cache entries for all other Servers and Proxys 1197 within the same SPAN segment. Each entry maintains the mapping 1198 between the neighbor's network-layer AERO address and corresponding 1199 INET address. The list of all permanent neighbor cache entries for 1200 the SPAN segment is maintained in the segment's ROS list. 1202 Symmetric neighbor cache entries are created and maintained through 1203 RS/RA exchanges as specified in Section 3.15, and remain in place for 1204 durations bounded by ND/PD lifetimes. AERO Servers maintain 1205 symmetric neighbor cache entries for each of their associated 1206 Clients, and AERO Clients maintain symmetric neighbor cache entries 1207 for each of their associated Servers. The list of all Servers on the 1208 AERO link is maintained in the link's MAP list. 1210 Asymmetric neighbor cache entries are created or updated based on 1211 route optimization messaging as specified in Section 3.17, and are 1212 garbage-collected when keepalive timers expire. AERO route 1213 optimization sources (ROSs) maintain asymmetric neighbor cache 1214 entries for active targets with lifetimes based on ND messaging 1215 constants. Asymmetric neighbor cache entries are unidirectional 1216 since only the ROS and not the target (e.g., a Client's MAP) creates 1217 an entry. 1219 Proxy neighbor cache entries are created and maintained by AERO 1220 Proxys when they process Client/Server ND/PD exchanges, and remain in 1221 place for durations bounded by ND/PD lifetimes. AERO Proxys maintain 1222 proxy neighbor cache entries for each of their associated Clients. 1223 Proxy neighbor cache entries track the Client state and the address 1224 of the Client's associated Server. 1226 To the list of neighbor cache entry states in Section 7.3.2 of 1227 [RFC4861], Proxy and Server AERO interfaces add an additional state 1228 DEPARTED that applies to symmetric and proxy neighbor cache entries 1229 for Clients that have recently departed. The interface sets a 1230 "DepartTime" variable for the neighbor cache entry to "DEPARTTIME" 1231 seconds. DepartTime is decremented unless a new ND message causes 1232 the state to return to REACHABLE. While a neighbor cache entry is in 1233 the DEPARTED state, packets destined to the target Client are 1234 forwarded to the Client's new location instead of being dropped. 1235 When DepartTime decrements to 0, the neighbor cache entry is deleted. 1236 It is RECOMMENDED that DEPARTTIME be set to the default constant 1237 value 40 seconds to allow for packets in flight to be delivered while 1238 stale route optimization state may be present. 1240 When a target Server (acting as a Mobility Anchor Point (MAP)) 1241 receives a valid NS message used for route optimization, it searches 1242 for a symmetric neighbor cache entry for the target Client. The MAP 1243 then returns a solicited NA message without creating a neighbor cache 1244 entry for the ROS, but creates or updates a target Client "Report 1245 List" entry for the ROS and sets a "ReportTime" variable for the 1246 entry to REPORTTIME seconds. The MAP resets ReportTime when it 1247 receives a new authentic NS message, and otherwise decrements 1248 ReportTime while no NS messages have been received. It is 1249 RECOMMENDED that REPORTTIME be set to the default constant value 40 1250 seconds to allow a 10 second window so that route optimization can 1251 converge before ReportTime decrements below REACHABLETIME. 1253 When the ROS receives a solicited NA message response to its NS 1254 message, it creates or updates an asymmetric neighbor cache entry for 1255 the target network-layer and link-layer addresses. The ROS then 1256 (re)sets ReachableTime for the neighbor cache entry to REACHABLETIME 1257 seconds and uses this value to determine whether packets can be 1258 forwarded directly to the target, i.e., instead of via a default 1259 route. The ROS otherwise decrements ReachableTime while no further 1260 solicited NA messages arrive. It is RECOMMENDED that REACHABLETIME 1261 be set to the default constant value 30 seconds as specified in 1262 [RFC4861]. 1264 The ROS also uses the value MAX_UNICAST_SOLICIT to limit the number 1265 of NS keepalives sent when a correspondent may have gone unreachable, 1266 the value MAX_RTR_SOLICITATIONS to limit the number of RS messages 1267 sent without receiving an RA and the value MAX_NEIGHBOR_ADVERTISEMENT 1268 to limit the number of unsolicited NAs that can be sent based on a 1269 single event. It is RECOMMENDED that MAX_UNICAST_SOLICIT, 1270 MAX_RTR_SOLICITATIONS and MAX_NEIGHBOR_ADVERTISEMENT be set to 3 the 1271 same as specified in [RFC4861]. 1273 Different values for DEPARTTIME, REPORTTIME, REACHABLETIME, 1274 MAX_UNICAST_SOLICIT, MAX_RTR_SOLCITATIONS and 1275 MAX_NEIGHBOR_ADVERTISEMENT MAY be administratively set; however, if 1276 different values are chosen, all nodes on the link MUST consistently 1277 configure the same values. Most importantly, DEPARTTIME and 1278 REPORTTIME SHOULD be set to a value that is sufficiently longer than 1279 REACHABLETIME to avoid packet loss due to stale route optimization 1280 state. 1282 3.9. AERO Interface Encapsulation and Re-encapsulation 1284 Client AERO interfaces avoid encapsulation over Direct underlying 1285 interfaces and Proxyed underlying interfaces for which the first-hop 1286 access router is AERO-aware. Other AERO interfaces encapsulate 1287 packets according to whether they are entering the AERO interface 1288 from the network layer or if they are being re-admitted into the same 1289 AERO link they arrived on. This latter form of encapsulation is 1290 known as "re-encapsulation". 1292 For packets entering the AERO interface from the network layer, the 1293 AERO interface copies the "TTL/Hop Limit", "Type of Service/Traffic 1294 Class" [RFC2983], "Flow Label"[RFC6438] (for IPv6) and "Congestion 1295 Experienced" [RFC3168] values in the packet's IP header into the 1296 corresponding fields in the encapsulation header(s). 1298 For packets undergoing re-encapsulation, the AERO interface instead 1299 copies these values from the original encapsulation header into the 1300 new encapsulation header, i.e., the values are transferred between 1301 encapsulation headers and *not* copied from the encapsulated packet's 1302 network-layer header. (Note especially that by copying the TTL/Hop 1303 Limit between encapsulation headers the value will eventually 1304 decrement to 0 if there is a (temporary) routing loop.) For IPv4 1305 encapsulation/re-encapsulation, the AERO interface sets the DF bit as 1306 discussed in Section 3.13. 1308 AERO interfaces configured over INET underlying interfaces 1309 encapsulate each packet in a SPAN header, then encapsulate the 1310 resulting SPAN packet in an INET header according to the next hop 1311 determined in the forwarding algorithm in Section 3.12. If the next 1312 hop is reached via a secured tunnel, the AERO interface uses an INET 1313 encapsulation format specific to the secured tunnel type (see: 1314 Section 6). If the next hop is reached via an unsecured underlying 1315 interface, the AERO interface instead uses Generic UDP Encapsulation 1316 (GUE) [I-D.ietf-intarea-gue] or an alternate minimal encapsulation 1317 format Appendix A. 1319 When GUE encapsulation is used, the AERO interface next sets the UDP 1320 source port to a constant value that it will use in each successive 1321 packet it sends, and sets the UDP length field to the length of the 1322 SPAN packet plus 8 bytes for the UDP header itself plus the length of 1323 the GUE header (or 0 if GUE direct IP encapsulation is used). For 1324 packets sent to a Server or Relay, the AERO interface sets the UDP 1325 destination port to 8060, i.e., the IANA-registered port number for 1326 AERO. For packets sent to a Client, the AERO interface sets the UDP 1327 destination port to the port value stored in the neighbor cache entry 1328 for this Client. The AERO interface then either includes or omits 1329 the UDP checksum according to the GUE specification. 1331 AERO interfaces observes the packet sizing and fragmentation 1332 considerations found in Section 3.13. 1334 3.10. AERO Interface Decapsulation 1336 AERO interfaces decapsulate packets destined either to the AERO node 1337 itself or to a destination reached via an interface other than the 1338 AERO interface the packet was received on. When the encapsulated 1339 packet arrives in multiple fragments, the AERO interface reassembles 1340 as discussed in Section 3.13. Further decapsulation steps are 1341 performed according to the appropriate encapsulation format 1342 specification. 1344 3.11. AERO Interface Data Origin Authentication 1346 AERO nodes employ simple data origin authentication procedures. In 1347 particular: 1349 o AERO Relays, Servers and Proxys accept encapsulated data packets 1350 and control messages received from secured tunnels. 1352 o AERO Servers and Proxys accept encapsulated data packets and NS 1353 messages used for Neighbor Unreachability Detection (NUD) received 1354 from a source found in the ROS list. 1356 o AERO Proxys and Clients accept packets that originate from within 1357 the same secured ANET. 1359 o AERO Clients and Gateways accept packets from downstream network 1360 correspondents based on ingress filtering. 1362 AERO nodes silently drop any packets that do not satisfy the above 1363 data origin authentication procedures. Further security 1364 considerations are discussed Section 6. 1366 3.12. AERO Interface Forwarding Algorithm 1368 IP packets enter a node's AERO interface either from the network 1369 layer (i.e., from a local application or the IP forwarding system) or 1370 from the link layer (i.e., from an AERO interface neighbor). All 1371 packets entering a node's AERO interface first undergo data origin 1372 authentication as discussed in Section 3.11. Packets that satisfy 1373 data origin authentication are processed further, while all others 1374 are dropped silently. 1376 Packets that enter the AERO interface from the network layer are 1377 forwarded to an AERO interface neighbor. Packets that enter the AERO 1378 interface from the link layer are either re-admitted into the AERO 1379 link or forwarded to the network layer where they are subject to 1380 either local delivery or IP forwarding. In all cases, the AERO 1381 interface itself MUST NOT decrement the network layer TTL/Hop-count 1382 since its forwarding actions occur below the network layer. 1384 AERO interfaces may have multiple underlying interfaces and/or 1385 neighbor cache entries for neighbors with multiple ifIndex-tuple 1386 registrations (see Section 3.6). The AERO interface uses each 1387 packet's DSCP value (and/or port number) to select an outgoing 1388 underlying interface based on the node's own QoS preferences, and 1389 also to select a destination link-layer address based on the 1390 neighbor's underlying interface with the highest preference. AERO 1391 implementations SHOULD allow for QoS preference values to be modified 1392 at runtime through network management. 1394 If multiple outgoing interfaces and/or neighbor interfaces have a 1395 preference of "high", the AERO node replicates the packet and sends 1396 one copy via each of the (outgoing / neighbor) interface pairs; 1397 otherwise, the node sends a single copy of the packet via an 1398 interface with the highest preference. AERO nodes keep track of 1399 which underlying interfaces are currently "reachable" or 1400 "unreachable", and only use "reachable" interfaces for forwarding 1401 purposes. 1403 The following sections discuss the AERO interface forwarding 1404 algorithms for Clients, Proxys, Servers and Relays. In the following 1405 discussion, a packet's destination address is said to "match" if it 1406 is the same as a cached address, or if it is covered by a cached 1407 prefix (which may be encoded in an AERO address). 1409 3.12.1. Client Forwarding Algorithm 1411 When an IP packet enters a Client's AERO interface from the network 1412 layer the Client searches for an asymmetric neighbor cache entry that 1413 matches the destination. If there is a match, the Client uses one or 1414 more "reachable" neighbor interfaces in the entry for packet 1415 forwarding. If there is no asymmetric neighbor cache entry, the 1416 Client instead forwards the packet toward a Server (the packet is 1417 intercepted by a Proxy if there is a Proxy on the path). 1419 When an IP packet enters a Client's AERO interface from the link- 1420 layer, if the destination matches one of the Client's MNPs or link- 1421 local addresses the Client decapsulates the packet (if necessary) and 1422 delivers it to the network layer. Otherwise, the Client drops the 1423 packet and MAY return a network-layer ICMP Destination Unreachable 1424 message subject to rate limiting (see: Section 3.14). 1426 3.12.2. Proxy Forwarding Algorithm 1428 For control messages originating from or destined to a Client, the 1429 Proxy intercepts the message and updates its proxy neighbor cache 1430 entry for the Client. The Proxy then forwards a (proxyed) copy of 1431 the control message. (For example, the Proxy forwards a proxied 1432 version of a Client's NS/RS message to the target neighbor, and 1433 forwards a proxied version of the NA/RA reply to the Client.) 1434 When the Proxy receives a data packet from a Client within the ANET, 1435 the Proxy searches for an asymmetric neighbor cache entry that 1436 matches the destination and forwards the packet as follows: 1438 o if the destination matches an asymmetric neighbor cache entry, the 1439 Proxy uses one or more "reachable" neighbor interfaces in the 1440 entry for packet forwarding via encapsulation. If the neighbor 1441 interface is in the same SPAN segment, the Proxy forwards the 1442 packet directly to the neighbor; otherwise, it forwards the packet 1443 to a Relay. 1445 o else, the Proxy encapsulates and forwards the packet to a Relay 1446 while using the packet's destination address as the SPAN 1447 destination address. (If the destination is an AERO address, the 1448 Proxy instead uses the corresponding Subnet Router Anycast address 1449 for Client AERO addresses and the SPAN address for 1450 administratively-provisioned AERO addresses.). 1452 When the Proxy receives an encapsulated data packet from an INET 1453 neighbor or from a secured tunnel, it accepts the packet only if data 1454 origin authentication succeeds and the SPAN destination address is 1455 its own address. If the packet is a SPAN fragment, the Proxy then 1456 adds the fragment to the reassembly buffer and returns if the 1457 reassembly is still incomplete. Otherwise, the Proxy reassembles the 1458 packet (if necessary) and continues processing. 1460 Next, the Proxy searches for a proxy neighbor cache entry that 1461 matches the destination. If there is a proxy neighbor cache entry in 1462 the REACHABLE state, the Proxy decapsulates and forwards the packet 1463 to the Client. If the neighbor cache entry is in the DEPARTED state, 1464 the Proxy instead re-encapsulates the message and forwards it to a 1465 Relay. If there is no neighbor cache entry, the Proxy instead 1466 discards the packet. 1468 3.12.3. Server/Gateway Forwarding Algorithm 1470 For control messages destined to a target Client's AERO address that 1471 are received from a secured tunnel, the Server (acting as a MAP) 1472 intercepts the message and sends an appropriate response on behalf of 1473 the Client. (For example, the Server sends an NA message reply in 1474 response to an NS message directed to one of its associated Clients.) 1475 If the Client's neighbor cache entry is in the DEPARTED state, 1476 however, the Server instead forwards the packet to the Client's new 1477 Server as discussed in Section 3.19. 1479 When the Server receives an encapsulated data packet from an INET 1480 neighbor or from a secured tunnel, it accepts the packet only if data 1481 origin authentication succeeds. If the SPAN destination address is 1482 its own address, the Server reassembles if necessary and discards the 1483 SPAN header (if the reassembly is incomplete, the Server instead adds 1484 the fragment to the reassembly buffer and returns). The Server then 1485 continues processing as follows: 1487 o if the destination matches a symmetric neighbor cache entry in the 1488 REACHABLE state the Server prepares the packet for forwarding to 1489 the destination Client. If the current header is a SPAN header, 1490 the Server reassembles if necessary and discards the SPAN header. 1491 The Server then forwards the packet according to the cached link- 1492 layer information, while using SPAN encapsulation for the Client's 1493 Proxyed/Native interfaces, simple INET encapsulation for NATed/ 1494 VPNed interfaces, or no encapsulation for Direct interfaces. 1496 o else, if the destination matches a symmetric neighbor cache entry 1497 in the DEPARETED state the Server re-encapsulates the packet and 1498 forwards it using the SPAN address of the Client's new Server as 1499 the destination. 1501 o else, if the destination matches an asymmetric neighbor cache 1502 entry, the Server uses one or more "reachable" neighbor interfaces 1503 in the entry for packet forwarding via the local INET if the 1504 neighbor is in the same SPAN segment or via a Relay otherwise. 1506 o else, if the destination is an AERO address that is not assigned 1507 on the AERO interface the Server drops the packet. 1509 o else, the Server (acting as a Gateway) releases the packet to the 1510 network layer for local delivery or IP forwarding. Based on the 1511 information in the forwarding table, the network layer may return 1512 the packet to the same AERO interface in which case further 1513 processing occurs as below. (Note that this arrangement 1514 accommodates common implementations in which the IP forwarding 1515 table is not accessible from within the AERO interface. If the 1516 AERO interface can directly access the IP forwarding table, the 1517 forwarding table lookup can instead be performed internally from 1518 within the AERO interface itself.) 1520 When the Server's AERO interface receives a data packet from the 1521 network layer or from a NATed/VPNed/Direct Client, it processes the 1522 packet according to the network-layer destination address as follows: 1524 o if the destination matches a symmetric or asymmetric neighbor 1525 cache entry the Server processes the packet as above. 1527 o else, the Server encapsulates the packet and forwards it to a 1528 Relay. For administratively-assigned AERO address destinations, 1529 the Server uses the SPAN address corresponding to the destination 1530 as the SPAN destination address. For Client AERO address 1531 destinations, the Server uses the Subnet Router Anycast address 1532 corresponding to the destination as the SPAN destination address. 1533 For all others, the Server uses the packet's destination IP 1534 address as the SPAN destination address. 1536 3.12.4. Relay Forwarding Algorithm 1538 Relays forward packets over secured tunnels the same as any IP 1539 router. When the Relay receives an encapsulated packet via a secured 1540 tunnel, it removes the INET header and searches for a forwarding 1541 table entry that matches the destination address in the next header. 1542 The Relay then processes the packet as follows: 1544 o if the destination matches one of the Relay's own addresses, the 1545 Relay submits the packet for local delivery. 1547 o else, if the destination matches a forwarding table entry the 1548 Relay forwards the packet via a secured tunnel to the next hop. 1549 If the destination matches an MSP without matching an MNP, 1550 however, the Relay instead drops the packet and returns an ICMP 1551 Destination Unreachable message subject to rate limiting (see: 1552 Section 3.14). 1554 o else, the Relay drops the packet and returns an ICMP Destination 1555 Unreachable as above. 1557 As for any IP router, the Relay decrements the TTL/Hop Limit when it 1558 forwards the packet. If the packet is encapsulated in a SPAN header, 1559 only the Hop Limit in the SPAN header is decremented, and not the 1560 TTL/Hop Limit in the inner packet header. 1562 3.13. AERO Interface MTU and Fragmentation 1564 The AERO interface is the node's attachment to the AERO link. For 1565 AERO link neighbor underlying interface paths that do not require 1566 encapsulation, the AERO interface sends unencapsulated IP packets. 1567 For other paths, the AERO interface acts as a tunnel ingress when it 1568 sends packets to the neighbor and as a tunnel egress when it receives 1569 packets from the neighbor. 1571 AERO interfaces configure an MTU the same as for any IP interface, 1572 however the MTU does not reflect the physical size of any links in 1573 the path but rather determines the maximum size for reassembly. AERO 1574 interfaces observe the packet sizing considerations for tunnels 1575 discussed in [I-D.ietf-intarea-tunnels] and as specified below. 1577 The Internet Protocol expects that IP packets will either be 1578 delivered to the destination or a suitable Packet Too Big (PTB) 1579 message returned to support the process known as IP Path MTU 1580 Discovery (PMTUD) [RFC1191][RFC8201]. However, PTB messages may be 1581 crafted for malicious purposes or lost in the network [RFC2923]. 1582 This can be especially problematic for tunnels, where a condition 1583 known as a PMTUD "black hole" can result. For these reasons, AERO 1584 interfaces employ operational procedures that avoid interactions with 1585 PMTUD, including the use of fragmentation when necessary. 1587 AERO interfaces observe three different types of fragmentation. 1588 Source fragmentation occurs when the AERO interface (acting as a 1589 tunnel ingress) fragments the encapsulated packet into multiple 1590 fragments before admitting each fragment into the tunnel. Network 1591 fragmentation occurs when an encapsulated packet admitted into the 1592 tunnel by the ingress is fragmented by an IPv4 router on the path to 1593 the egress. Finally, link-layer fragmentation (aka link adaptation) 1594 occurs at a layer below IP and is coordinated between underlying data 1595 link endpoints. 1597 IPv6 specifies a minimum link Maximum Transmission Unit (MTU) of 1280 1598 bytes [RFC8200]. Although IPv4 specifies a smaller minimum link MTU 1599 of 68 bytes [RFC0791], AERO interfaces also observe the IPv6 minimum 1600 for IPv4 even if encapsulated packets may incur network 1601 fragmentation. 1603 IPv6 specifies a minimum Maximum Reassembly Unit (MRU) of 1500 bytes 1604 [RFC8200], while the minimum MRU for IPv4 is only 576 bytes [RFC1122] 1605 (but, note that many standard IPv6 over IPv4 tunnel types already 1606 assume a larger MRU than the IPv4 minimum). 1608 AERO interfaces therefore configure an MTU that MUST NOT be smaller 1609 than 1280 bytes, MUST NOT be larger than the minimum MRU among all 1610 nodes on the AERO link minus the encapsulation overhead ("ENCAPS"), 1611 and SHOULD NOT be smaller than 1500 bytes. AERO interfaces also 1612 configure a Maximum Segment Unit (MSU) as the maximum-sized 1613 encapsulated packet that the ingress can inject into the tunnel 1614 without source fragmentation. The MSU value MUST NOT be larger than 1615 1280 bytes unless there is operational assurance that a larger size 1616 can traverse the link along all paths. 1618 All AERO interfaces on the link MUST configure the same MTU value for 1619 reasons cited in [RFC3819][RFC4861]; in particular, multicast support 1620 requires a common MTU value among all nodes on the link. All AERO 1621 interfaces MUST configure an MRU large enough to reassemble packets 1622 up to (MTU+ENCAPS) bytes in length; nodes that cannot configure a 1623 large-enough MRU MUST NOT enable an AERO interface. For example, for 1624 an MTU of 1500 bytes an appropriate MRU might be 2KB. 1626 The network layer proceeds as follows when it forwards an IP packet 1627 to the AERO interface. For each IPv4 packet that is larger than the 1628 AERO interface MTU and with DF set to 0, the network layer uses IPv4 1629 fragmentation to break the packet into a minimum number of non- 1630 overlapping fragments where the first fragment is no larger than the 1631 MTU and the remaining fragments are no larger than the first. For 1632 all other IP packets, if the packet is larger than the AERO interface 1633 MTU, the network layer drops the packet and returns a PTB message to 1634 the original source. Otherwise, the network layer admits each IP 1635 packet or fragment into the AERO interface. 1637 For each IP packet admitted into AERO interface, if the neighbor is 1638 reached via an underlying interface that does not require 1639 encapsulation the AERO interface proceeds according to the underlying 1640 interface MTU. If the packet is no larger than the underlying 1641 interface MTU, the AERO interface presents the packet to the 1642 underlying interface. Otherwise, for IPv4 packets with DF set to 0 1643 the AERO interface uses IPv4 fragmentation to break the packet into 1644 fragments no larger than the underlying interface MTU. For other 1645 packets, the AERO interface either performs link adaptation or drops 1646 the packet and returns a PTB message to the original source. (If the 1647 original source corresponds to a local application, the PTB would 1648 appear to have originated from a router on the path when in fact it 1649 was locally generated from within the AERO interface.) In the same 1650 way, when a packet that has been admitted into the AERO link reaches 1651 a target neighbor but is too large to be delivered over the final-hop 1652 underlying interface, the target either performs link adaptation or 1653 drops the packet and returns a PTB. Link adaptation is preferred in 1654 both cases when possible to avoid packet loss. 1656 For underlying interfaces that require encapsulation, the AERO 1657 interface (acting as a tunnel ingress) instead encapsulates the 1658 packet and performs path MTU procedures according to the specific 1659 encapsulation format. For INET interfaces, the ingress encapsulates 1660 the packet in a SPAN header. If the SPAN packet is larger than the 1661 MSU, the ingress source fragments the SPAN packet into a minimum 1662 number of non-overlapping fragments where the first fragment is no 1663 larger than the MSU and the remaining fragments are no larger than 1664 the first. The ingress then encapsulates each SPAN packet/fragment 1665 in an INET header and admits them into the tunnel. For IPv4, the 1666 ingress sets the DF bit to 0 in the INET header in case any network 1667 fragmentation is necessary. The encapsulated packets will be 1668 delivered to the egress, which reassembles them into a whole packet 1669 if necessary. 1671 By fragmenting at the SPAN layer instead of lower layers, standard 1672 IPv6 fragmentation and reassembly [RFC8200] ensures that IPv4 issues 1673 such as data corruption due to reassembly misassociations will not 1674 occur [RFC6864][RFC4963]. The ingress sends each fragment with 1675 minimal delay so that individual fragments are unlikely to be 1676 diverted to different destinations due to routing fluctuations. 1678 Since the SPAN header and IPv6 fragment extension header reduces the 1679 room available for packet data, but the original source has no way to 1680 control its insertion, the ingress MUST include their lengths in 1681 ENCAPS even for packets in which the header is absent. 1683 3.13.1. AERO MTU Requirements 1685 In light of the above considerations, AERO interfaces SHOULD 1686 configure an MTU of 9180 bytes. This means that the AERO interface 1687 MUST be capable of reassembling original IP packets up to 9180 bytes 1688 in length. When an IP packet is admitted into an AERO interface, the 1689 interface encapsulates the packet using SPAN encapsulation and 1690 fragments the encapsulated packet into fragments that are no larger 1691 than 1280 bytes. The fragments will be reassembled by the tunnel 1692 egress that services the final destination. 1694 AERO Clients behind Proxys MAY configure an MTU smaller than 9180 1695 (but no smaller than IP minimum link MTU). If Clients configure a 1696 diversity of MTUs (e.g., 1280, 1500, 4KB, 8KB, etc.) then neighbors 1697 on the link would appear to have multiple MTUs. IPv6 Path MTU 1698 Discovery [RFC8201] accounts for this possibility since MTU discovery 1699 must be performed even between nodes that appear to be connected to 1700 the same link. 1702 Applications that cannot tolerate loss in the network due to MTU 1703 restrictions should restrict themselves to sending packets no larger 1704 than the IP minimum link MTU, i.e., even if the current path MTU 1705 would appear to support a larger size. This is due to the fact that 1706 routing changes could cause the path to traverse links with smaller 1707 MTUs at any given point in time. 1709 3.14. AERO Interface Error Handling 1711 When an AERO node admits encapsulated packets into the AERO 1712 interface, it may receive link-layer or network-layer error 1713 indications. 1715 A link-layer error indication is an ICMP error message generated by a 1716 router in the INET on the path to the neighbor or by the neighbor 1717 itself. The message includes an IP header with the address of the 1718 node that generated the error as the source address and with the 1719 link-layer address of the AERO node as the destination address. 1721 The IP header is followed by an ICMP header that includes an error 1722 Type, Code and Checksum. Valid type values include "Destination 1723 Unreachable", "Time Exceeded" and "Parameter Problem" 1724 [RFC0792][RFC4443]. (AERO interfaces ignore all link-layer IPv4 1725 "Fragmentation Needed" and IPv6 "Packet Too Big" messages since they 1726 only emit packets that are guaranteed to be no larger than the IP 1727 minimum link MTU as discussed in Section 3.13.) 1729 The ICMP header is followed by the leading portion of the packet that 1730 generated the error, also known as the "packet-in-error". For 1731 ICMPv6, [RFC4443] specifies that the packet-in-error includes: "As 1732 much of invoking packet as possible without the ICMPv6 packet 1733 exceeding the minimum IPv6 MTU" (i.e., no more than 1280 bytes). For 1734 ICMPv4, [RFC0792] specifies that the packet-in-error includes: 1735 "Internet Header + 64 bits of Original Data Datagram", however 1736 [RFC1812] Section 4.3.2.3 updates this specification by stating: "the 1737 ICMP datagram SHOULD contain as much of the original datagram as 1738 possible without the length of the ICMP datagram exceeding 576 1739 bytes". 1741 The link-layer error message format is shown in Figure 5 (where, "L2" 1742 and "L3" refer to link-layer and network-layer, respectively): 1744 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1745 ~ ~ 1746 | L2 IP Header of | 1747 | error message | 1748 ~ ~ 1749 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1750 | L2 ICMP Header | 1751 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 1752 ~ ~ P 1753 | IP and other encapsulation | a 1754 | headers of original L3 packet | c 1755 ~ ~ k 1756 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ e 1757 ~ ~ t 1758 | IP header of | 1759 | original L3 packet | i 1760 ~ ~ n 1761 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1762 ~ ~ e 1763 | Upper layer headers and | r 1764 | leading portion of body | r 1765 | of the original L3 packet | o 1766 ~ ~ r 1767 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- 1769 Figure 5: AERO Interface Link-Layer Error Message Format 1771 The AERO node rules for processing these link-layer error messages 1772 are as follows: 1774 o When an AERO node receives a link-layer Parameter Problem message, 1775 it processes the message the same as described as for ordinary 1776 ICMP errors in the normative references [RFC0792][RFC4443]. 1778 o When an AERO node receives persistent link-layer Time Exceeded 1779 messages, the IP ID field may be wrapping before earlier fragments 1780 awaiting reassembly have been processed. In that case, the node 1781 should begin including integrity checks and/or institute rate 1782 limits for subsequent packets. 1784 o When an AERO node receives persistent link-layer Destination 1785 Unreachable messages in response to encapsulated packets that it 1786 sends to one of its asymmetric neighbor correspondents, the node 1787 should process the message as an indication that a path may be 1788 failing, and optionally initiate NUD over that path. If it 1789 receives Destination Unreachable messages over multiple paths, the 1790 node should allow future packets destined to the correspondent to 1791 flow through a default route and re-initiate route optimization. 1793 o When an AERO Client receives persistent link-layer Destination 1794 Unreachable messages in response to encapsulated packets that it 1795 sends to one of its symmetric neighbor Servers, the Client should 1796 mark the path as unusable and use another path. If it receives 1797 Destination Unreachable messages on many or all paths, the Client 1798 should associate with a new Server and release its association 1799 with the old Server as specified in Section 3.19.5. 1801 o When an AERO Server receives persistent link-layer Destination 1802 Unreachable messages in response to encapsulated packets that it 1803 sends to one of its symmetric neighbor Clients, the Server should 1804 mark the underlying path as unusable and use another underlying 1805 path. 1807 o When an AERO Server or Proxy receives link-layer Destination 1808 Unreachable messages in response to an encapsulated packet that it 1809 sends to one of its permanent neighbors, it treats the messages as 1810 an indication that the path to the neighbor may be failing. 1811 However, the dynamic routing protocol should soon reconverge and 1812 correct the temporary outage. 1814 When an AERO Relay receives a packet for which the network-layer 1815 destination address is covered by an MSP, if there is no more- 1816 specific routing information for the destination the Relay drops the 1817 packet and returns a network-layer Destination Unreachable message 1818 subject to rate limiting. The Relay writes the network-layer source 1819 address of the original packet as the destination address and uses 1820 one of its non link-local addresses as the source address of the 1821 message. 1823 When an AERO node receives an encapsulated packet for which the 1824 reassembly buffer it too small, it drops the packet and returns a 1825 network-layer Packet Too Big (PTB) message. The node first writes 1826 the MRU value into the PTB message MTU field, writes the network- 1827 layer source address of the original packet as the destination 1828 address and writes one of its non link-local addresses as the source 1829 address. 1831 3.15. AERO Router Discovery, Prefix Delegation and Autoconfiguration 1833 AERO Router Discovery, Prefix Delegation and Autoconfiguration are 1834 coordinated as discussed in the following Sections. 1836 3.15.1. AERO ND/PD Service Model 1838 Each AERO Server on the link configures a PD service to facilitate 1839 Client requests. Each Server is provisioned with a database of MNP- 1840 to-Client ID mappings for all Clients enrolled in the AERO service, 1841 as well as any information necessary to authenticate each Client. 1842 The Client database is maintained by a central administrative 1843 authority for the AERO link and securely distributed to all Servers, 1844 e.g., via the Lightweight Directory Access Protocol (LDAP) [RFC4511], 1845 via static configuration, etc. Clients receive the same service 1846 regardless of the Servers they select. 1848 AERO Clients and Servers use ND messages to maintain neighbor cache 1849 entries. AERO Servers configure their AERO interfaces as advertising 1850 interfaces, and therefore send unicast RA messages with configuration 1851 information in response to a Client's RS message. Thereafter, 1852 Clients send additional RS messages to refresh prefix and/or router 1853 lifetimes. 1855 AERO Clients and Servers include PD parameters in RS/RA messages (see 1856 [I-D.templin-6man-dhcpv6-ndopt] for ND/PD alternatives). The unified 1857 ND/PD messages are exchanged between Client and Server according to 1858 the prefix management schedule required by the PD service. If the 1859 Client knows its MNP in advance, it can include its AERO address as 1860 the source address of an RS message and with an OMNI option with a 1861 valid Prefix Length for the MNP. If the Server (and Proxy) accept 1862 the Client's MNP assertion, they inject the prefix into the routing 1863 system and establish the necessary neighbor cache state. 1865 The following sections specify the Client and Server behavior. 1867 3.15.2. AERO Client Behavior 1869 AERO Clients discover the addresses of Servers in a similar manner as 1870 described in [RFC5214]. Discovery methods include static 1871 configuration (e.g., from a flat-file map of Server addresses and 1872 locations), or through an automated means such as Domain Name System 1873 (DNS) name resolution [RFC1035]. Alternatively, the Client can 1874 discover Server addresses through a layer 2 data link login exchange, 1875 or through a unicast RA response to a multicast/anycast RS as 1876 described below. In the absence of other information, the Client can 1877 resolve the DNS Fully-Qualified Domain Name (FQDN) 1878 "linkupnetworks.[domainname]" where "linkupnetworks" is a constant 1879 text string and "[domainname]" is a DNS suffix for the AERO link 1880 (e.g., "example.com"). 1882 To associate with a Server, the Client acts as a requesting router to 1883 request MNPs. The Client prepares an RS message with PD parameters 1884 and includes a Nonce and Timestamp option if the Client needs to 1885 correlate RA replies. If the Client already knows the Server's AERO 1886 address, it includes the AERO address as the network-layer 1887 destination address; otherwise, it includes all-routers multicast 1888 (ff02::2) or subnet routers anycast (fe80::) as the network-layer 1889 destination address. If the Client already knows its own AERO 1890 address, it uses the AERO address as the network-layer source 1891 address; otherwise, it uses the unspecified AERO address 1892 (fe80::ffff:ffff) as the network-layer source address. 1894 The Client next includes an OMNI option in the RS message to register 1895 its link-layer information with the Server. The first ifIndex-tuple 1896 MUST correspond to the underlying interface over which the Client 1897 will send the RS message. The Client MAY include additional ifIndex- 1898 tuples specific to other underlying interfaces. When encapsulation 1899 is used, the Client also includes an SLLAO with a single ifIndex- 1900 tuple corresponding to the first OMNI option ifIndex-tuple, then 1901 encapsulates the RS message in an ANET header with its own ANET 1902 address as the source address and the INET address of the Server as 1903 the destination. 1905 The Client then sends the RS message (either directly via Direct 1906 interfaces, via INET encapsulation for NATed interfaces, via a VPN 1907 for VPNed interfaces, via a Proxy for proxyed interfaces or via a 1908 Relay for native interfaces) and waits for an RA message reply (see 1909 Section 3.15.3). The Client retries up to MAX_RTR_SOLICITATIONS 1910 times until an RA is received. If the Client receives no RAs, or if 1911 it receives an RA with Router Lifetime set to 0, the Client SHOULD 1912 abandon this Server and try another Server. Otherwise, the Client 1913 processes the PD information found in the RA message. 1915 Next, the Client creates a symmetric neighbor cache entry with the 1916 Server's AERO address as the network-layer address and the Server's 1917 encapsulation and/or link-layer addresses as the link-layer address. 1918 The Client records the RA Router Lifetime field value in the neighbor 1919 cache entry as the time for which the Server has committed to 1920 maintaining the MNP in the routing system. The Client then 1921 autoconfigures AERO addresses for each of the delegated MNPs and 1922 assigns them to the AERO interface. The Client also caches any MSPs 1923 included in Route Information Options (RIOs) [RFC4191] as MSPs to 1924 associate with the AERO link, and assigns the MTU value in the MTU 1925 option to its AERO interface while configuring an appropriate MRU. 1927 The Client then registers additional underlying interfaces with the 1928 Server by sending RS messages via each additional interface. The RS 1929 messages include the same parameters as for the initial RS/RA 1930 exchange, but with destination address set to the Server's AERO 1931 address and with the initial OMNI option ifIndex-tuple corresponding 1932 to the underlying interface. 1934 The Client examines the P bit in the RA message flags field. If the 1935 P bit is set to 1, this indicates that the Server received an RS 1936 message with an SLLAO in which the first ifIndex-tuple addressing 1937 information did not match the information in the encapsulation 1938 headers. 1940 Following autoconfiguration, the Client sub-delegates the MNPs to its 1941 attached EUNs and/or the Client's own internal virtual interfaces as 1942 described in [I-D.templin-v6ops-pdhost] to support the Client's 1943 downstream attached "Internet of Things (IoT)". The Client 1944 subsequently maintains its MNP delegations through each of its 1945 Servers by sending additional RS messages before Router Lifetime 1946 expires. 1948 After the Client registers its underlying interfaces, it may wish to 1949 change one or more registrations, e.g., if an interface changes 1950 address or becomes unavailable, if QoS preferences change, etc. To 1951 do so, the Client prepares an RS message to send over any available 1952 underlying interface. The RS includes an OMNI option with a first 1953 ifIndex-tuple specific to the selected interface, and MAY include any 1954 additional ifIndex-tuples specific to other underlying interfaces. 1955 The Client includes fresh ifIndex-tuple values to update the Server's 1956 neighbor cache entry. When the Client receives the Server's RA 1957 response, it has assurance that the Server has been updated with the 1958 new information. 1960 If the Client wishes to discontinue use of a Server it issues an RS 1961 message over any underlying interface with an OMNI option with R set 1962 to 0. When the Server processes the message, it releases the MNP, 1963 sets the symmetric neighbor cache entry state for the Client to 1964 DEPARTED and returns an RA reply with Router Lifetime set to 0. 1965 After a short delay (e.g., 2 seconds), the Server withdraws the MNP 1966 from the routing system. 1968 3.15.3. AERO Server Behavior 1970 AERO Servers act as IP routers and support a PD service for Clients. 1971 Servers arrange to add their AERO and INET addresses to a static map 1972 of Server addresses for the link and/or the DNS resource records for 1973 the FQDN "linkupnetworks.[domainname]" before entering service. 1974 Server addresses should be geographically and/or topologically 1975 referenced, and made available for discovery by Clients on the AERO 1976 link. 1978 When a Server receives a prospective Client's RS message on its AERO 1979 interface, it SHOULD return an immediate RA reply with Router 1980 Lifetime set to 0 if it is currently too busy or otherwise unable to 1981 service the Client. Otherwise, the Server authenticates the RS 1982 message and processes the PD parameters. The Server first determines 1983 the correct MNPs to delegate to the Client by searching the Client 1984 database. When the Server delegates the MNPs, it also creates an IP 1985 forwarding table entry for each MNP so that the MNPs are propagated 1986 into the routing system (see: Section 3.3). For IPv6, the Server 1987 creates an IPv6 forwarding table entry for each MNP. For IPv4, the 1988 Server creates both an IPv4 forwarding table entry and an IPv6 1989 forwarding table entry with the SPAN Compatibility Prefix (SCP) 1990 corresponding to the IPv4 address. 1992 The Server next creates a symmetric neighbor cache entry for the 1993 Client using the base AERO address as the network-layer address and 1994 with lifetime set to no more than the smallest PD lifetime. Next, 1995 the Server updates the neighbor cache entry by recording the 1996 information in each ifIndex-tuple in the RS OMNI option. The Server 1997 also records the actual INET header source address and port number in 1998 the neighbor cache entry. If an SLLAO option was present, the Server 1999 also compares the SLLAO address information for the first ifIndex- 2000 tuple with the INET header information and sets the P bit in the 2001 flags field of the RA message if the information was different. 2003 Next, the Server prepares an RA message using its AERO address as the 2004 network-layer source address and the network-layer source address of 2005 the RS message as the network-layer destination address. The Server 2006 includes the delegated MNPs, any other PD parameters and an OMNI 2007 option with an ifIndex-tuple with ifIndex set to 0. The Server then 2008 includes one or more RIOs that encode the MSPs for the AERO link, 2009 plus an MTU option for the link MTU (see Section 3.13). The Server 2010 finally forwards the message to the Client using SPAN/INET, INET, or 2011 NULL encapsulation as necessary. 2013 After the initial RS/RA exchanges, the Server maintains a timer for 2014 the Client's symmetric neighbor cache entry set to expire after 2015 Router Lifetime seconds. If the Client (or Proxy) issues additional 2016 RS messages, the Server sends an RA response and resets the timer. 2017 If the Client (or Proxy) issues an RS with PD release indication the 2018 Server sets the Client's symmetric neighbor cache entry to the 2019 DEPARTED state and withdraws the MNP from the routing system after a 2020 short delay (e.g., 2 seconds). If the timer expires before a new RS 2021 is received, the Server deletes the neighbor cache entry and 2022 withdraws the MNP with minimal delay. 2024 The Server processes these and any other Client ND/PD messages, and 2025 returns an NA/RA reply. The Server may also issue unsolicited RA 2026 messages, e.g., with PD reconfigure parameters to cause the Client to 2027 renegotiate its PDs, with Router Lifetime set to 0 if it can no 2028 longer service this Client, etc. Finally, If the symmetric neighbor 2029 cache entry is in the DEPARTED state, the Server deletes the entry 2030 after DepartTime expires. 2032 Note: Clients SHOULD notify former Servers of their departures, but 2033 Servers are responsible for expiring neighbor cache entries and 2034 withdrawing routes even if no departure notification is received 2035 (e.g., if the Client leaves the network unexpectedly). Servers 2036 SHOULD therefore include a brief Router Lifetime (e.g., 30 seconds) 2037 in solicited RA messages to avoid persistent stale routing 2038 information in the absence of Client departure notifications. 2040 3.15.3.1. Lightweight DHCPv6 Relay Agent (LDRA) 2042 When DHCPv6 is used as the ND/PD service back end, AERO Clients and 2043 Servers are always on the same link (i.e., the AERO link) from the 2044 perspective of DHCPv6. However, in some implementations the DHCPv6 2045 server and ND function may be located in separate modules. In that 2046 case, the Server's AERO interface module can act as a Lightweight 2047 DHCPv6 Relay Agent (LDRA)[RFC6221] to relay PD messages to and from 2048 the DHCPv6 server module. 2050 When the LDRA receives an authentic RS message, it extracts the PD 2051 message parameters and uses them to construct an IPv6/UDP/DHCPv6 2052 message. It sets the IPv6 source address to the source address of 2053 the RS message, sets the IPv6 destination address to 2054 'All_DHCP_Relay_Agents_and_Servers' and sets the UDP fields to values 2055 that will be understood by the DHCPv6 server. 2057 The LDRA then wraps the message in a DHCPv6 'Relay-Forward' message 2058 header and includes an 'Interface-Id' option that includes enough 2059 information to allow the LDRA to forward the resulting Reply message 2060 back to the Client (e.g., the Client's link-layer addresses, a 2061 security association identifier, etc.). The LDRA also wraps the OMNI 2062 option and SLLAO into the Interface-Id option, then forwards the 2063 message to the DHCPv6 server. 2065 When the DHCPv6 server prepares a Reply message, it wraps the message 2066 in a 'Relay-Reply' message and echoes the Interface-Id option. The 2067 DHCPv6 server then delivers the Relay-Reply message to the LDRA, 2068 which discards the Relay-Reply wrapper and IPv6/UDP headers, then 2069 uses the DHCPv6 message to construct an RA response to the Client. 2070 The Server uses the information in the Interface-Id option to prepare 2071 the RA message and to cache the link-layer addresses taken from the 2072 OMNI option and SLLAO echoed in the Interface-Id option. 2074 3.16. The AERO Proxy 2076 Clients may connect to ANETs that require a perimeter security 2077 gateway to enable communications to Servers in outside INETs. In 2078 that case, the ANET can employ an AERO Proxy. The Proxy is located 2079 at the ANET/INET border and listens for RS messages originating from 2080 or RA messages destined to ANET Clients. The Proxy acts on these 2081 control messages as follows: 2083 o when the Proxy receives an RS message from a new ANET Client, it 2084 first authenticates the message then examines the network-layer 2085 destination address. If the destination address is a Server's 2086 AERO address, the Proxy proceeds to the next step. Otherwise, if 2087 the destination is all-routers multicast or subnet router anycast, 2088 the Proxy selects a "nearby" Server that is likely to be a good 2089 candidate to serve the Client and replaces the destination address 2090 with the Server's AERO address. Next, the Proxy creates a proxy 2091 neighbor cache entry and caches the Client and Server addresses 2092 along with any identifying information including Transaction IDs, 2093 Client Identifiers, Nonce values, etc. The Proxy then inserts an 2094 SLLAO in the RS message with a single ifIndex-tuple matching the 2095 first ifIndex-tuple in the OMNI option and with the Link Layer 2096 Address and Port Number fields set to 0. The Proxy finally 2097 encapsulates the (proxyed) RS message in a SPAN header with 2098 destination set to the Server's SPAN address then forwards the 2099 message into the SPAN. 2101 o when the Server receives the RS message, it authenticates the 2102 message then creates or updates a symmetric neighbor cache entry 2103 for the Client with the Proxy's SPAN address as the link-layer 2104 address. The Server then sends an RA message back to the Proxy 2105 via the SPAN. 2107 o when the Proxy receives the RA message, it matches the message 2108 with the RS that created the proxy neighbor cache entry. The 2109 Proxy then caches the PD route information as a mapping from the 2110 Client's MNPs to the Client's ANET address, and sets the neighbor 2111 cache entry state to REACHABLE. The Proxy then forwards the 2112 (proxyed) message to the Client. 2114 o when the Proxy forwards the (proxyed) RA message, it MAY adjust 2115 Router Lifetime to a larger value. In that case, the Proxy is 2116 responsible for performing periodic RS/RA messaging on the 2117 Client's behalf to refresh Server state lifetimes. This would 2118 allow for higher-frequency RS/RA messaging between the Proxy and 2119 Server without involving the Client, supplemented by lower- 2120 frequency RS/RA messaging between the Client and Server (via the 2121 Proxy). 2123 After the initial RS/RA exchange, the Proxy forwards any Client data 2124 packets for which there is no matching asymmetric neighbor cache 2125 entry to a Relay via the SPAN. The Proxy instead forwards any Client 2126 data destined to an asymmetric neighbor cache target directly to the 2127 target according to the link-layer information - the process of 2128 establishing asymmetric neighbor cache entries is specified in 2129 Section 3.17. 2131 While the Client is still attached to the ANET, the Proxy send RS or 2132 unsolicited NA messages to update the Server's symmetric neighbor 2133 cache entries on behalf of the Client and/or to convey QoS updates. 2134 If the Server ceases to send solicited RA responses, the Proxy marks 2135 the Server as unreachable and sends an unsolicited RA with Router 2136 Lifetime set to zero to inform Clients that this Server is no longer 2137 able to provide service. Although the Proxy engages in ND exchanges 2138 on behalf of the Client, the Client can also send ND messages on its 2139 own behalf, e.g., if it is in a better position than the Proxy to 2140 convey QoS changes, etc. For this reason, the Proxy marks any 2141 Client-originated solicitation messages (e.g., with a Nonce option) 2142 so that it can return the solicited advertisement to the Client 2143 instead of proecssing it locally. 2145 If the Client becomes unreachable, the Proxy sets the neighbor cache 2146 entry state to DEPARTED and retains the entry for DEPARTTIME seconds. 2147 While the state is DEPARTED, the Proxy forwards any packets destined 2148 to the Client to a Relay. The Relay in turn forwards the packets to 2149 the Client's current Server. When DepartTime expires, the Proxy 2150 deletes the neighbor cache entry and discards any further packets 2151 destined to this (now forgotten) Client. 2153 When a neighbor cache entry transitions to DEPARTED, some of the 2154 fragments of a multiple fragment packet may have already arrived at 2155 the Proxy while others are en route to the Client's new location. 2156 However, no special attention in the reassembly algorithm is 2157 necessary when re-routed packets are simply treated as loss. Since 2158 the fragments of a multiple-fragment packet are sent in minimal 2159 inter-packet delay bursts, such occasions will be rare. 2161 In some ANETs that employ a Proxy, the Client's MNP can be injected 2162 into the ANET routing system. In that case, the Client can send data 2163 messages without encapsulation so that the ANET native routing system 2164 transports the unencapsulated packets to the Proxy. This can be very 2165 beneficial, e.g., if the Client connects to the ANET via low-end data 2166 links such as some aviation wireless links. 2168 If the first-hop ANET access router is AERO-aware, the Client can 2169 avoid encapsulation for both its control and data messages. When the 2170 Client connects to the link, it can send an unencapsulated RS message 2171 with source address set to its AERO address and with destination 2172 address set to the AERO address of the Client's selected Server or to 2173 all-routers multicast or subnet router anycast. The Client includes 2174 an OMNI option formatted as specified in 2175 [I-D.templin-atn-aero-interface]. 2177 The Client then sends the unencapsulated RS message, which will be 2178 intercepted by the AERO-Aware access router. The access router then 2179 encapsulates the RS message in an ANET header with its own address as 2180 the source address and the address of a Proxy as the destination 2181 address. The access router further remembers the address of the 2182 Proxy so that it can encapsulate future data packets from the Client 2183 via the same Proxy. If the access router needs to change to a new 2184 Proxy, it simply sends another RS message toward the Server via the 2185 new Proxy on behalf of the Client. 2187 In some cases, the access router and Proxy may be one and the same 2188 node. In that case, the node would be located on the same physical 2189 link as the Client, but its message exchanges with the Server would 2190 need to pass through a security gateway at the ANET/INET border. The 2191 method for deploying access routers and Proxys (i.e. as a single node 2192 or multiple nodes) is an ANET-local administrative consideration. 2194 3.16.1. Detecting and Responding to Server Failures 2196 In environments where fast recovery from Server failure is required, 2197 Proxys SHOULD use proactive Neighbor Unreachability Detection (NUD) 2198 to track Server reachability in a similar fashion as for 2199 Bidirectional Forwarding Detection (BFD) [RFC5880]. Proxys can then 2200 quickly detect and react to failures so that cached information is 2201 re-established through alternate paths. The NUD control messaging is 2202 carried only over well-connected ground domain networks (i.e., and 2203 not low-end aeronautical radio links) and can therefore be tuned for 2204 rapid response. 2206 Proxys perform proactive NUD with Servers for which there are 2207 currently active ANET Clients by sending continuous NS messages in 2208 rapid succession, e.g., one message per second. The Proxy sends the 2209 NS message via the SPAN with the Proxy's AERO address as the source 2210 and the AERO address of the Server as the destination. When the 2211 Proxy is also sending RS messages to the Server on behalf of ANET 2212 Clients, the RS/RA messaging can be considered as equivalent hints of 2213 forward progress. This means that the Proxy need not also send a 2214 periodic NS if it has already sent an RS within the same period. If 2215 the Server fails (i.e., if the Proxy ceases to receive 2216 advertisements), the Proxy can quickly inform Clients by sending RA 2217 messages on the ANET interface. 2219 The Proxy sends such RA messages with source address set to the 2220 Server's address, destination address set to all-nodes multicast, and 2221 Router Lifetime set to 0. The Proxy SHOULD send 2222 MAX_FINAL_RTR_ADVERTISEMENTS RA messages separated by small delays 2223 [RFC4861]. Any Clients on the ANET that have been using the (now 2224 defunct) Server will receive the RA messages and associate with a new 2225 Server. 2227 3.17. AERO Route Optimization 2229 While data packets are flowing between a source and target node, 2230 route optimization SHOULD be used. Route optimization is initiated 2231 by the first eligible Route Optimization Source (ROS) closest to the 2232 source as follows: 2234 o For Clients on VPNed, NATed and Direct interfaces, the Server is 2235 the ROS. 2237 o For Clients on Proxyed interfaces, the Proxy is the ROS. 2239 o For Clients on native interfaces, the Client itself is the ROS. 2241 o For correspondent nodes on INET/EUN interfaces serviced by a 2242 Gateway, the Gateway is the ROS. 2244 The route optimization procedure is conducted between the ROS and the 2245 target Server/Gateway acting as a Route Optimization Responder (ROR) 2246 in the same manner as for IPv6 ND Address Resolution and using the 2247 same NS/NA messaging. The target may either be a MNP Client serviced 2248 by a Server, or a non-MNP correspondent reachable via a Gateway. 2250 The procedures are specified in the following sections. 2252 3.17.1. Route Optimization Initiation 2254 While data packets are flowing from the source node toward a target 2255 node, the ROS performs address resolution by sending an NS message to 2256 receive a solicited NA message from the ROR. 2258 When the ROS sends an NS, it includes the AERO address of the ROS as 2259 the source address (e.g., fe80::1) and the AERO address corresponding 2260 to the data packet's destination address as the destination address 2261 (e.g., if the destination address is 2001:db8:1:2::1 then the 2262 corresponding AERO address is fe80::2001:db8:1:2). The NS message 2263 includes an OMNI option with a single ifIndex-tuple with ifIndex set 2264 to 0. The message includes a Nonce and Timestamp option if the ROS 2265 needs to correlate NA replies. 2267 The ROS then encapsulates the NS message in a SPAN header with source 2268 set to its own SPAN address and destination set to the data packet's 2269 destination address, then sends the message into the SPAN without 2270 decrementing the network-layer TTL/Hop Limit field. 2272 3.17.2. Relaying the NS 2274 When the Relay receives the NS message from the ROS, it discards the 2275 INET header and determines that the ROR is the next hop by consulting 2276 its standard IPv6 forwarding table for the SPAN header destination 2277 address. The Relay then forwards the SPAN message toward the ROR the 2278 same as for any IPv6 router. The final-hop Relay in the SPAN will 2279 deliver the message via a secured tunnel to the ROR. 2281 3.17.3. Processing the NS and Sending the NA 2283 When the ROR receives the NS message, it examines the AERO 2284 destination address to determine whether it has a neighbor cache 2285 entry and/or route that matches the target. If there is no match, 2286 the ROR drops the NS message. Otherwise, the ROR continues 2287 processing as follows: 2289 o if the target belongs to an MNP Client neighbor in the DEPARTED 2290 state the ROR changes the NS message SPAN destination address to 2291 the SPAN address of the Client's new Server, forwards the message 2292 into the SPAN and returns from processing. 2294 o If the target belongs to an MNP Client neighbor in the REACHABLE 2295 state, the ROR instead adds the AERO source address to the target 2296 Client's Report List with time set to ReportTime. 2298 o If the target belongs to a non-MNP route, the ROR continues 2299 processing without adding an entry to the Report List. 2301 The ROR then prepares a solicited NA message to send back to the ROS 2302 but does not create a neighbor cache entry. The ROR sets the NA 2303 source address to the destination AERO address of the NS, and 2304 includes the Nonce value received in the NS plus the current 2305 Timestamp. 2307 If the target belongs to an MNP Client, the ROR then includes an OMNI 2308 option with prefix information set according to the MNP prefix 2309 length; otherwise, it sets it to the maximum of the non-MNP prefix 2310 length and 64. (Note that a /64 limit is imposed to avoid causing 2311 the ROS to set short prefixes (e.g., "default") that would match 2312 destinations for which the routing system includes more-specific 2313 prefixes.) 2315 The ROR next includes a first ifIndex-tuple in the OMNI option with 2316 ifIndex set to 0. If the target belongs to an MNP Client, the ROR 2317 next includes additional ifIndex-tuples in the OMNI option for the 2318 target Client's underlying interfaces with current information for 2319 each interface 2320 The ROR then includes a TLLAO option with ifIndex-tuples in one-to- 2321 one correspondence with the tuples that appear in the OMNI option. 2322 For NATed, VPNed and Direct interfaces, the link layer addresses are 2323 the SPAN address of the ROR. For Proxyed and native interfaces, the 2324 link-layer addresses are the SPAN addresses of the Proxys and the 2325 Client's native interfaces. 2327 The ROR finally encapsulates the NA message in a SPAN header with 2328 source set to its own SPAN address and destination set to the source 2329 SPAN address of the NS message, then forwards the message into the 2330 SPAN without decrementing the network-layer TTL/Hop Limit field. 2332 3.17.4. Relaying the NA 2334 When the Relay receives the NA message from the ROR, it discards the 2335 INET header and determines that the ROS is the next hop by consulting 2336 its standard IPv6 forwarding table for the SPAN header destination 2337 address. The Relay then forwards the SPAN-encapsulated NA message 2338 toward the ROS the same as for any IPv6 router. The final-hop Relay 2339 in the SPAN will deliver the message via a secured tunnel to the ROS. 2341 3.17.5. Processing the NA 2343 When the ROS receives the solicited NA message, it caches the source 2344 SPAN address then discards the INET and SPAN headers. The ROS next 2345 verifies the Nonce and Timestamp values (if present), then creates an 2346 asymmetric neighbor cache entry for the ROR and caches all 2347 information found in the solicited NA OMNI and TLLAO options. The 2348 ROS finally sets the asymmetric neighbor cache entry lifetime to 2349 ReachableTime seconds. 2351 3.17.6. Route Optimization Maintenance 2353 Following route optimization, the ROS forwards future data packets 2354 destined to the target via the addresses found in the cached link- 2355 layer information. The route optimization is shared by all sources 2356 that send packets to the target via the ROS, i.e., and not just the 2357 source on behalf of which the route optimization was initiated. 2359 While new data packets destined to the target are flowing through the 2360 ROS, it sends additional NS messages to the ROR before ReachableTime 2361 expires to receive a fresh solicited NA message the same as described 2362 in the previous sections (route optimization refreshment strategies 2363 are an implementation matter, with a non-normative example given in 2364 Appendix B.1). The ROS uses the cached SPAN address of the ROR as 2365 the NS SPAN destination address, and sends up to MAX_UNICAST_SOLICIT 2366 NS messages separated by 1 second until an NA is received. If no NA 2367 is received, the ROS assumes that the current ROR has become 2368 unreachable and deletes the neighbor cache entry. Subsequent data 2369 packets will trigger a new route optimization per Section 3.17.1 to 2370 discover a new ROR while initial data packets travel over a 2371 suboptimal route. 2373 If an NA is received, the ROS then updates the asymmetric neighbor 2374 cache entry to refresh ReachableTime, while (for MNP destinations) 2375 the ROR adds or updates the ROS address to the target Client's Report 2376 List and with time set to ReportTime. While no data packets are 2377 flowing, the ROS instead allows ReachableTime for the asymmetric 2378 neighbor cache entry to expire. When ReachableTime expires, the ROS 2379 deletes the asymmetric neighbor cache entry. Future data packets 2380 flowing through the ROS will again trigger a new route optimization. 2382 The ROS may also receive unsolicited NA messages from the ROR at any 2383 time. If there is an asymmetric neighbor cache entry for the target, 2384 the ROS updates the link-layer information but does not update 2385 ReachableTime since the receipt of an unsolicited NA does not confirm 2386 that the forward path is still working. If there is no asymmetric 2387 neighbor cache entry, the ROS simply discards the unsolicited NA. 2388 Cases in which unsolicited NA messages are generated are specified in 2389 Section 3.19. 2391 In this arrangement, the ROS holds an asymmetric neighbor cache entry 2392 for the ROR, but the ROR does not hold an asymmetric neighbor cache 2393 entry for the ROS. The route optimization neighbor relationship is 2394 therefore asymmetric and unidirectional. If the target node also has 2395 packets to send back to the source node, then a separate route 2396 optimization procedure is performed in the reverse direction. But, 2397 there is no requirement that the forward and reverse paths be 2398 symmetric. 2400 3.18. Neighbor Unreachability Detection (NUD) 2402 AERO nodes perform Neighbor Unreachability Detection (NUD) per 2403 [RFC4861]. NUD is performed either reactively in response to 2404 persistent link-layer errors (see Section 3.14) or proactively to 2405 confirm reachability. The NUD algorithm may further be seeded by ND 2406 hints of forward progress, but care must be taken to avoid inferring 2407 reachability based on spoofed information. 2409 When an ROR directs an ROS to a neighbor with one or more target 2410 link-layer addresses, the ROS can proactively test each direct path 2411 by sending an initial NS message to elicit a solicited NA response. 2412 While testing the paths, the ROS can optionally continue sending 2413 packets via the SPAN, maintain a small queue of packets until target 2414 reachability is confirmed, or (optimistically) allow packets to flow 2415 via the direct paths. In any case, the ROS should only consider the 2416 neighbor unreachable if NUD fails over multiple target link-layer 2417 address paths. 2419 When a ROS sends an NS message used for NUD, it uses its AERO 2420 addresses as the IPv6 source address and the AERO address 2421 corresponding to a target link-layer address as the destination. For 2422 each target link-layer address, the source node encapsulates the NS 2423 message in SPAN/INET headers with its own SPAN address as the source 2424 and the SPAN address of the target as the destination, If the target 2425 is located within the same SPAN segment, the source sets the INET 2426 address of the target as the destination; otherwise, it sets the INET 2427 address of a Relay as the destination. The source then forwards the 2428 message into the SPAN. 2430 Paths that pass NUD tests are marked as "reachable", while those that 2431 do not are marked as "unreachable". These markings inform the AERO 2432 interface forwarding algorithm specified in Section 3.12. 2434 Proxys can perform NUD to verify Server reachability on behalf of 2435 their proxyed Clients so that the Clients need not engage in NUD 2436 messaging themselves. 2438 3.19. Mobility Management and Quality of Service (QoS) 2440 AERO is a Distributed Mobility Management (DMM) service. Each Server 2441 is responsible for only a subset of the Clients on the AERO link, as 2442 opposed to a Centralized Mobility Management (CMM) service where 2443 there is a single network mobility collective entity for all Clients. 2444 Clients coordinate with their associated Servers via RS/RA exchanges 2445 to maintain the DMM profile, and the AERO routing system tracks all 2446 current Client/Server peering relationships. 2448 Servers provide a Mobility Anchor Point (MAP) for their dependent 2449 Clients. Clients are responsible for maintaining neighbor 2450 relationships with their Servers through periodic RS/RA exchanges, 2451 which also serves to confirm neighbor reachability. When a Client's 2452 underlying interface address and/or QoS information changes, the 2453 Client is responsible for updating the Server with this new 2454 information. Note that for Proxyed interfaces, however, the Proxy 2455 can perform the RS/RA exchanges on the Client's behalf. 2457 Mobility management considerations are specified in the following 2458 sections. 2460 3.19.1. Mobility Update Messaging 2462 Servers acting as MAPs accommodate Client mobility and/or QoS change 2463 events by sending unsolicited NA messages to each ROS in the target 2464 Client's Report List. When a MAP sends an unsolicited NA message, it 2465 sets the IPv6 source address to the Client's AERO address and sets 2466 the IPv6 destination address to all-nodes multicast (ff02::1). The 2467 MAP also includes an OMNI option with a first ifIndex-tuple with 2468 ifIndex set to 0, and with additional ifIndex-tuples for the target 2469 Client's remaining interfaces. The MAP then includes a TLLAO with 2470 corresponding ifIndex-tuples, with the link layer address of the 2471 first tuple set to the MAP's SPAN address and with link layer 2472 addresses of the remaining tuples set to the corresponding target 2473 SPAN addresses. The MAP finally encapsulates the message in a SPAN 2474 header with source set to its own SPAN address and destination set to 2475 the SPAN address of the ROS, then sends the message to a Relay. 2477 As discussed in Section 7.2.6 of [RFC4861], the transmission and 2478 reception of unsolicited NA messages is unreliable but provides a 2479 useful optimization. In well-connected Internetworks with robust 2480 data links unsolicited NA messages will be delivered with high 2481 probability, but in any case the MAP can optionally send up to 2482 MAX_NEIGHBOR_ADVERTISEMENT unsolicited NAs to each ROS to increase 2483 the likelihood that at least one will be received. 2485 When the ROS receives an unsolicited NA message, it ignores the 2486 message if there is no existing neighbor cache entry for the Client. 2487 Otherwise, it uses the included OMNI option and TLLAO information to 2488 update the neighbor cache entry, but does not reset ReachableTime 2489 since the receipt of an unsolicited NA message from the target Server 2490 does not provide confirmation that any forward paths to the target 2491 Client are working. 2493 If unsolicited NA messages are lost, the ROS may be left with stale 2494 address and/or QoS information for the Client for up to REACHABLETIME 2495 seconds. During this time, the ROS can continue sending packets 2496 according to its stale neighbor cache information. When 2497 ReachableTime is close to expiring, the ROS will re-initiate route 2498 optimization and receive fresh state information. 2500 In addition to sending unsolicited NA messages to the current set of 2501 ROSs for the Client, the MAP also sends unsolicited NAs to the former 2502 link-layer address for any ifIndex-tuple for which the link-layer 2503 address has changed. The NA messages update Proxys or Servers that 2504 cannot easily detect (e.g., without active probing) when a formerly- 2505 active Client has departed. 2507 3.19.2. Announcing Link-Layer Address and/or QoS Preference Changes 2509 When a Client needs to change its ANET addresses and/or QoS 2510 preferences (e.g., due to a mobility event), either the Client or its 2511 Proxys send RS messages to the Server via the SPAN with an OMNI 2512 option and SLLAO that include an ifIndex-tuple with the new link 2513 quality and address information. 2515 Up to MAX_RTR_SOLICITATION RS messages MAY be sent in parallel with 2516 sending actual data packets in case one or more RAs are lost. If all 2517 RAs are lost, the Client SHOULD re-associate with a new Server. 2519 When the Server receives the Client's changes, it sends unsolicited 2520 NA messages to all nodes in the Report List the same as described in 2521 the previous section. 2523 3.19.3. Bringing New Links Into Service 2525 When a Client needs to bring new underlying interfaces into service 2526 (e.g., when it activates a new data link), it sends an RS message to 2527 the Server via the underlying interface with an OMNI option with 2528 appropriate link quality values and with an SLLAO (if necessary) with 2529 link-layer address information for the new link.. 2531 3.19.4. Removing Existing Links from Service 2533 When a Client needs to remove existing underlying interfaces from 2534 service (e.g., when it de-activates an existing data link), it sends 2535 an RS message to its Server with an OMNI option with appropriate link 2536 quality values. 2538 If the Client needs to send RS messages over an underlying interface 2539 other than the one being removed from service, it MUST include an 2540 ifIndex-tuple for the sending interface as the first tuple and 2541 include additional ifIndex-tuples with appropriate link quality 2542 values for any underlying interfaces being removed from service. 2544 3.19.5. Moving to a New Server 2546 When a Client associates with a new Server, it performs the Client 2547 procedures specified in Section 3.15.2. The Client also includes a 2548 notification identifier in the RS message OMNI option per 2549 [I-D.templin-atn-aero-interface] if it wants the new Server to notify 2550 the old Server. 2552 When the new Server receives the Client's RS message, it responds by 2553 returning an RA as specified in Section 3.15.3. If the Client's RS 2554 includes a notification identifier, the new Server also prepares an 2555 RS to send to the old Server. The RS message includes the Client's 2556 AERO address as the source address, the old Server's AERO address as 2557 the destination address, and an OMNI option and SLLAO with an 2558 ifIndex-tuple with ifIndex set to 0. The OMNI option includes a 2559 release indication, and the SLLAO includes the SPAN address of the 2560 new Server. The new Server retries up to MAX_RTR_SOLICITATIONS 2561 attempts until an RA is received. (Note that the Client can 2562 alternatively send RS messages with a release indication to the old 2563 Server on its own behalf, however, this additional Client messaging 2564 may be undesirable in some environments.) 2566 When the old Server processes the RS, it changes the symmetric 2567 neighbor cache entry state to DEPARTED, sets the link-layer address 2568 of the Client to the address found in the RS SLLAO, and sets 2569 DepartTime to DEPARTTIME seconds. The old Server then returns an 2570 immediate RA message with Router Lifetime set to 0. After a short 2571 delay (e.g., 2 seconds) the old Server withdraws the Client's MNP 2572 from the routing system. After DepartTime expires, the old Server 2573 deletes the symmetric neighbor cache entry. 2575 The old Server also sends unsolicited NA messages to all ROSs in the 2576 Client's Report List with an OMNI option and TLLAO with a single 2577 ifIndex-tuple with ifIndex set to 0 and with the SPAN address of the 2578 new Server. When the ROS receives the NA, it caches the address of 2579 the new Server in the existing asymmetric neighbor cache entry and 2580 marks the entry as STALE. Subsequent data packets will then flow 2581 according to any existing cached link-layer information and trigger a 2582 new NS/NA exchange via the new Server. 2584 Clients SHOULD NOT move rapidly between Servers in order to avoid 2585 causing excessive oscillations in the AERO routing system. Examples 2586 of when a Client might wish to change to a different Server include a 2587 Server that has gone unreachable, topological movements of 2588 significant distance, movement to a new geographic region, movement 2589 to a new SPAN segment, etc. 2591 When a Client moves to a new Server, some of the fragments of a 2592 multiple fragment packet may have already arrived at the old Server 2593 while others are en route to the new Server. However, no special 2594 attention in the reassembly algorithm is necessary when re-routed 2595 fragments are simply treated as loss. Since the fragments of a 2596 multiple-fragment packet are sent with minimal inter-packet delay, 2597 such occasions will be rare. 2599 3.20. Multicast 2601 The AERO Client provides an IGMP (IPv4) [RFC2236] or MLD (IPv6) 2602 [RFC3810] proxy service for its EUNs and/or hosted applications 2603 [RFC4605]. The Client forwards IGMP/MLD messages over any of its 2604 underlying interfaces for which group membership is required. The 2605 IGMP/MLD messages may be further forwarded by a first-hop ANET access 2606 router acting as an IGMP/MLD-snooping switch [RFC4541], then 2607 ultimately delivered to an AERO Proxy/Server acting as a Protocol 2608 Independent Multicast - Sparse-Mode (PIM-SM, or simply "PIM") 2609 Designated Router (DR) [RFC7761]. AERO Gateways also act as PIM 2610 routers (i.e., the same as AERO Proxys/Servers) on behalf of nodes on 2611 INET/EUN networks. The behaviors identified in the following 2612 sections correspond to Source-Specific Multicast (SSM) and Any-Source 2613 Multicast (ASM) operational modes. 2615 3.20.1. Source-Specific Multicast (SSM) 2617 When an ROS (i.e., an AERO Proxy/Server/Gateway) "X" acting as PIM 2618 router receives a Join/Prune message from a node on its downstream 2619 interfaces containing one or more ((S)ource, (G)roup) pairs, it 2620 updates its Multicast Routing Information Base (MRIB) accordingly. 2621 For each S belonging to a prefix reachable via X's non-AERO 2622 interfaces, X then forwards the (S, G) Join/Prune to any PIM routers 2623 on those interfaces per [RFC7761]. 2625 For each S belonging to a prefix reachable via X's AERO interface, X 2626 originates a separate copy of the Join/Prune for each (S,G) in the 2627 message using its own AERO address as the source address and ALL-PIM- 2628 ROUTERS as the destination address. X then encapsulates each message 2629 in a SPAN header with source address set to the SPAN address of X and 2630 destination address set to S then forwards the message into the SPAN. 2631 The SPAN in turn forwards the message to AERO Server/Gateway "Y" that 2632 services S. At the same time, if the message was a Join, X sends a 2633 route-optimization NS message toward each S the same as discussed in 2634 Section 3.17. The resulting NAs will return the AERO address for the 2635 prefix that matches S as the network-layer source address and TLLAOs 2636 with the SPAN addresses corresponding to any ifIndex-tuples that are 2637 currently servicing S. 2639 When Y processes the Join/Prune message, if S located behind any 2640 Native, Direct, VPNed or NATed interfaces Y acts as a PIM router and 2641 updates its MRIB to list X as the next hop in the reverse path. If S 2642 is located behind any Proxys "Z"*, Y also forwards the message to 2643 each Z* over the SPAN while continuing to use the AERO address of X 2644 as the source address. Each Z* then updates its MRIB accordingly and 2645 maintains the AERO address of X as the next hop in the reverse path. 2646 Since the Relays in the SPAN do not examine network layer control 2647 messages, this means that the (reverse) multicast tree path is simply 2648 from each Z* (and/or Y) to X with no other multicast-aware routers in 2649 the path. If any Z* (and/or Y) is located on the same SPAN segment 2650 as X, the multicast data traffic sent to X directly using SPAN/INET 2651 encapsulation instead of via a Relay. 2653 Following the initial Join/Prune and NS/NA messaging, X maintains an 2654 asymmetric neighbor cache entry for each S the same as if X was 2655 sending unicast data traffic to S. In particular, X performs 2656 additional NS/NA exchanges to keep the neighbor cache entry alive for 2657 up to t_periodic seconds [RFC7761]. If no new Joins are received 2658 within t_periodic seconds, X allows the neighbor cache entry to 2659 expire. Finally, if X receives any additional Join/Prune messages 2660 for (S,G) it forwards the messages to each Y and Z* in the neighbor 2661 cache entry over the SPAN. 2663 At some later time, Client C that holds an MNP for source S may 2664 depart from a first Proxy Z1 and/or connect via a new Proxy Z2. In 2665 that case, Y sends an unsolicited NA message to X the same as 2666 specified for unicast mobility in Section 3.19. When X receives the 2667 unsolicited NA message, it updates its asymmetric neighbor cache 2668 entry for the AERO address for source S and sends new Join messages 2669 to any new Proxys Z2. There is no requirement to send any Prune 2670 messages to old Proxys Z1 since source S will no longer source any 2671 multicast data traffic via Z1. Instead, the multicast state for 2672 (S,G) in Proxy Z1 will soon time out since no new Joins will arrive. 2674 After some later time, C may move to a new Server Y2 and depart from 2675 old Sever Y1. In that case, Y1 sends Join messages for any of C's 2676 active (S,G) groups to Y2 while including its own AERO address as the 2677 source address. This causes Y2 to include Y1 in the multicast 2678 forwarding tree during the interim time that Y1's symmetric neighbor 2679 cache entry for C is in the DEPARTED state. At the same time, Y1 2680 sends an unsolicited NA message to X with an OMNI option and TLLAO 2681 with ifIndex-tuple set to 0 and a release indication to cause X to 2682 release its asymmetric neighbor cache entry. X then sends a new Join 2683 message to S via the SPAN and re-initiates route optimization the 2684 same as if it were receiving a fresh Join message from a node on a 2685 downstream link. 2687 3.20.2. Any-Source Multicast (ASM) 2689 When an ROS X acting as a PIM router receives a Join/Prune from a 2690 node on its downstream interfaces containing one or more (*,G) pairs, 2691 it updates its Multicast Routing Information Base (MRIB) accordingly. 2692 X then forwards a copy of the message to the Rendezvous Point (RP) R 2693 for each G over the SPAN. X uses its own AERO address as the source 2694 address and ALL-PIM-ROUTERS as the destination address, then 2695 encapsulates each message in a SPAN header with source address set to 2696 the SPAN address of X and destination address set to R, then sends 2697 the message into the SPAN. At the same time, if the message was a 2698 Join X initiates NS/NA route optimization the same as for the SSM 2699 case discussed in Section 3.20.1. 2701 For each source S that sends multicast traffic to group G via R, the 2702 Proxy/Server Z* for the Client that aggregates S encapsulates the 2703 packets in PIM Register messages and forwards them to R via the SPAN. 2704 R may then elect to send a PIM Join to Z* over the SPAN. This will 2705 result in an (S,G) tree rooted at Z* with R as the next hop so that R 2706 will begin to receive two copies of the packet; one native copy from 2707 the (S, G) tree and a second copy from the pre-existing (*, G) tree 2708 that still uses PIM Register encapsulation. R can then issue a PIM 2709 Register-stop message to suppress the Register-encapsulated stream. 2710 At some later time, if C moves to a new Proxy/Server Z*, it resumes 2711 sending packets via PIM Register encapsulation via the new Z*. 2713 At the same time, as multicast listeners discover individual S's for 2714 a given G, they can initiate an (S,G) Join for each S under the same 2715 procedures discussed in Section 3.20.1. Once the (S,G) tree is 2716 established, the listeners can send (S, G) Prune messages to R so 2717 that multicast packets for group G sourced by S will only be 2718 delivered via the (S, G) tree and not from the (*, G) tree rooted at 2719 R. All mobility considerations discussed for SSM apply. 2721 3.20.3. Bi-Directional PIM (BIDIR-PIM) 2723 Bi-Directional PIM (BIDIR-PIM) [RFC5015] provides an alternate 2724 approach to ASM that treats the Rendezvous Point (RP) as a Designated 2725 Forwarder (DF). Further considerations for BIDIR-PIM are out of 2726 scope. 2728 3.21. Operation over Multiple AERO Links (VLANs) 2730 An AERO Client can connect to multiple AERO links the same as for any 2731 data link service. In that case, the Client maintains a distinct 2732 AERO interface for each link, e.g., 'aero0' for the first link, 2733 'aero1' for the second, 'aero2' for the third, etc. Each AERO link 2734 would include its own distinct set of Relays, Servers and Proxys, 2735 thereby providing redundancy in case of failures. 2737 The Relays, Servers and Proxys on each AERO link can assign AERO and 2738 SPAN addresses that use the same or different numberings from those 2739 on other links. Since the links are mutually independent there is no 2740 requirement for avoiding inter-link address duplication, e.g., the 2741 same AERO address such as fe80::1000 could be used to number distinct 2742 nodes that connect to different AERO links. 2744 Each AERO link could utilize the same or different ANET connections. 2745 The links can be distinguished at the link-layer via Virtual Local 2746 Area Network (VLAN) tagging (e.g., IEEE 802.1Q) and/or through 2747 assignment of distinct sets of MSPs on each link. This gives rise to 2748 the opportunity for supporting multiple redundant networked paths, 2749 where each VLAN is distinguished by a different label (e.g., colors 2750 such as Red, Green, Blue, etc.). In particular, the Client can tag 2751 its RS messages with the appropriate label to cause the network to 2752 select the desired VLAN. 2754 Clients that connect to multiple AERO interfaces can select the 2755 outgoing interface appropriate for a given Red/Blue/Green/etc. 2756 traffic profile while (in the reverse direction) correspondent nodes 2757 must have some way of steering their packets destined to a target via 2758 the correct AERO link. 2760 In a first alternative, if each AERO link services different MSPs, 2761 then the Client can receive a distinct MNP from each of the links. 2762 IP routing will therefore assure that the correct Red/Green/Blue/etc. 2763 network is used for both outbound and inbound traffic. This can be 2764 accomplished using existing technologies and approaches, and without 2765 requiring any special supporting code in correspondent nodes or 2766 Relays. 2768 In a second alternative, if each AERO link services the same MSP(s) 2769 then each link could assign a distinct "AERO Link Anycast" address 2770 that is configured by all Relays on the link. Correspondent nodes 2771 then include a "type 4" routing header with the Anycast address for 2772 the AERO link as the IPv6 destination and with the address of the 2773 target encoded as the "next segment" in the routing header 2774 [RFC8402][I-D.ietf-6man-segment-routing-header]. Standard IP routing 2775 will then direct the packet to the nearest Relay for the correct AERO 2776 link, which will replace the destination address with the target 2777 address then forward the packet to the target. 2779 3.22. DNS Considerations 2781 AERO Client MNs and INET correspondent nodes consult the Domain Name 2782 System (DNS) the same as for any Internetworking node. When 2783 correspondent nodes and Client MNs use different IP protocol versions 2784 (e.g., IPv4 correspondents and IPv6 MNs), the INET DNS must maintain 2785 A records for IPv4 address mappings to MNs which must then be 2786 populated in Gateway NAT64 mapping caches. In that way, an IPv4 2787 correspondent node can send packets to the IPv4 address mapping of 2788 the target MN, and the Gateway will translate the IPv4 header and 2789 destination address into an IPv6 header and IPv6 destination address 2790 of the MN. 2792 When an AERO Client registers with an AERO Server, the Server can 2793 return the address(es) of DNS servers in RDNSS options [RFC6106]. 2794 The DNS server provides the IP addresses of other MNs and 2795 correspondent nodes in AAAA records for IPv6 or A records for IPv4. 2797 3.23. Transition Considerations 2799 The SPAN ensures that dissimilar INET partitions can be joined into a 2800 single unified AERO link, even though the partitions themselves may 2801 have differing protocol versions and/or incompatible addressing 2802 plans. However, a commonality can be achieved by incrementally 2803 distributing globally routable (i.e., native) IP prefixes to 2804 eventually reach all nodes (both mobile and fixed) in all SPAN 2805 segments. This can be accomplished by incrementally deploying AERO 2806 Gateways on each INET partition, with each Gateway distributing its 2807 MNPs and/or discovering non-MNP prefixes on its INET links. 2809 This gives rise to the opportunity to eventually distribute native IP 2810 addresses to all nodes, and to present a unified AERO link view 2811 (bridged by the SPAN) even if the INET partitions remain in their 2812 current protocol and addressing plans. In that way, the AERO link 2813 can serve the dual purpose of providing a mobility service and a 2814 transition service. Or, if an INET partition is transitioned to a 2815 native IP protocol version and addressing scheme that is compatible 2816 with the AERO link MNP-based addressing scheme, the partition and 2817 AERO link can be joined by Gateways. 2819 Gateways that connect INETs/EUNs with dissimilar IP protocol versions 2820 must employ a network address and protocol translation function such 2821 as NAT64[RFC6146]. 2823 3.24. Detecting and Reacting to Server and Relay Failures 2825 In environments where rapid failure recovery is required, Servers and 2826 Relays SHOULD use Bidirectional Forwarding Detection (BFD) [RFC5880]. 2827 Nodes that use BFD can quickly detect and react to failures so that 2828 cached information is re-established through alternate nodes. BFD 2829 control messaging is carried only over well-connected ground domain 2830 networks (i.e., and not low-end radio links) and can therefore be 2831 tuned for rapid response. 2833 Servers and Relays maintain BFD sessions in parallel with their BGP 2834 peerings. If a Server or Relay fails, BGP peers will quickly re- 2835 establish routes through alternate paths the same as for common BGP 2836 deployments. 2838 Proxys SHOULD use proactive NUD for Servers for which there are 2839 currently active ANET Clients in a manner that parallels BFD, i.e., 2840 by sending unicast NS messages in rapid succession to receive 2841 solicited NA messages. When the Proxy is also sending RS messages on 2842 behalf of ANET Clients, the RS/RA messaging can be considered as 2843 equivalent hints of forward progress. This means that the Proxy need 2844 not also send a periodic NS if it has already sent an RS within the 2845 same period. If a Server fails, the Proxy will cease to receive 2846 advertisements and can quickly inform Clients of the outage by 2847 sending RA messages on the ANET interface. 2849 The Proxy sends RA messages with source address set to the Server's 2850 address, destination address set to all-nodes multicast, and Router 2851 Lifetime set to 0. The Proxy SHOULD send 2852 MAX_FINAL_RTR_ADVERTISEMENTS RA messages separated by small delays 2853 [RFC4861]. Any Clients on the ANET interface that have been using 2854 the (now defunct) Server will receive the RA messages and associate 2855 with a new Server. 2857 4. Implementation Status 2859 An AERO implementation based on OpenVPN (https://openvpn.net/) was 2860 announced on the v6ops mailing list on January 10, 2018 and an 2861 initial public release of the AERO proof-of-concept source code was 2862 announced on the intarea mailing list on August 21, 2015. 2864 5. IANA Considerations 2866 The IANA has assigned a 4-octet Private Enterprise Number "45282" for 2867 AERO in the "enterprise-numbers" registry. 2869 The IANA has assigned the UDP port number "8060" for an earlier 2870 experimental version of AERO [RFC6706]. This document obsoletes 2871 [RFC6706] and claims the UDP port number "8060" for all future use. 2873 No further IANA actions are required. 2875 6. Security Considerations 2877 AERO Relays configure secured tunnels with AERO Servers and Proxys 2878 within their local SPAN segments. Applicable secured tunnel 2879 alternatives include IPsec [RFC4301], TLS/SSL [RFC8446], DTLS 2880 [RFC6347], etc. The AERO Relays of all SPAN segments in turn 2881 configure secured tunnels for their neighboring AERO Relays across 2882 the SPAN. Therefore, packets that traverse the SPAN between any pair 2883 of AERO link neighbors are already secured. 2885 AERO Servers, Gateways and Proxys targeted by a route optimization 2886 may also receive packets directly from the INET partitions instead of 2887 via the SPAN. For INET partitions that apply effective ingress 2888 filtering to defeat source address spoofing, the simple data origin 2889 authentication procedures in Section 3.11 can be applied. This 2890 implies that the ROS list must be maintained consistently by all 2891 route optimization targets within the same INET partition, and that 2892 the ROS list must be securely managed by the partition administrative 2893 authority. 2895 For INET partitions that cannot apply effective ingress filtering, 2896 the two options for securing communications include 1) disable route 2897 optimization so that all traffic is conveyed over secured tunnels via 2898 the SPAN, or 2) enable on-demand secure tunnel creation between INET 2899 partition neighbors. Option 1) would result in longer routes than 2900 necessary and traffic concentration on critical infrastructure 2901 elements. Option 2) could be coordinated by establishing a secured 2902 tunnel on-demand instead of performing an NS/NA exchange in the route 2903 optimization procedures. Procedures for establishing on-demand 2904 secured tunnels are out of scope. 2906 AERO Clients that connect to secured enclaves need not apply security 2907 to their ND messages, since the messages will be intercepted by a 2908 perimeter Proxy that applies security on its outward-facing 2909 interface. AERO Clients located outside of secured enclaves SHOULD 2910 use symmetric network and/or transport layer security services, but 2911 when there are many prospective neighbors with dynamically changing 2912 connectivity an asymmetric security service such as SEND may be 2913 needed (see: Appendix B.6). 2915 Application endpoints SHOULD use application-layer security services 2916 such as TLS/SSL, DTLS or SSH [RFC4251] to assure the same level of 2917 protection as for critical secured Internet services. AERO Clients 2918 that require host-based VPN services SHOULD use symmetric network 2919 and/or transport layer security services such as IPsec, TLS/SSL, 2920 DTLS, etc. AERO Proxys and Servers can also provide a network-based 2921 VPN service on behalf of the Client, e.g., if the Client is located 2922 within a secured enclave and cannot establish a VPN on its own 2923 behalf. 2925 AERO Servers and Relays present targets for traffic amplification 2926 Denial of Service (DoS) attacks. This concern is no different than 2927 for widely-deployed VPN security gateways in the Internet, where 2928 attackers could send spoofed packets to the gateways at high data 2929 rates. This can be mitigated by connecting Servers and Relays over 2930 dedicated links with no connections to the Internet and/or when 2931 connections to the Internet are only permitted through well-managed 2932 firewalls. Traffic amplification DoS attacks can also target an AERO 2933 Client's low data rate links. This is a concern not only for Clients 2934 located on the open Internet but also for Clients in secured 2935 enclaves. AERO Servers and Proxys can institute rate limits that 2936 protect Clients from receiving packet floods that could DoS low data 2937 rate links. 2939 AERO Gateways must implement ingress filtering to avoid a spoofing 2940 attack in which spurious SPAN messages are injected into an AERO link 2941 from an outside attacker. AERO Clients MUST ensure that their 2942 connectivity is not used by unauthorized nodes on their EUNs to gain 2943 access to a protected network, i.e., AERO Clients that act as routers 2944 MUST NOT provide routing services for unauthorized nodes. (This 2945 concern is no different than for ordinary hosts that receive an IP 2946 address delegation but then "share" the address with other nodes via 2947 some form of Internet connection sharing such as tethering.) 2949 The MAP list and ROS lists MUST be well-managed and secured from 2950 unauthorized tampering, even though the list contains only public 2951 information. The MAP list can be conveyed to the Client in a similar 2952 fashion as in [RFC5214] (e.g., through layer 2 data link login 2953 messaging, secure upload of a static file, DNS lookups, etc.). The 2954 ROS list can be conveyed to Servers and Proxys through administrative 2955 action, secured file distribution, etc. 2957 Although public domain and commercial SEND implementations exist, 2958 concerns regarding the strength of the cryptographic hash algorithm 2959 have been documented [RFC6273] [RFC4982]. 2961 Security considerations for accepting link-layer ICMP messages and 2962 reflected packets are discussed throughout the document. 2964 7. Acknowledgements 2966 Discussions in the IETF, aviation standards communities and private 2967 exchanges helped shape some of the concepts in this work. 2968 Individuals who contributed insights include Mikael Abrahamsson, Mark 2969 Andrews, Fred Baker, Bob Braden, Stewart Bryant, Brian Carpenter, 2970 Wojciech Dec, Ralph Droms, Adrian Farrel, Nick Green, Sri Gundavelli, 2971 Brian Haberman, Bernhard Haindl, Joel Halpern, Tom Herbert, Sascha 2972 Hlusiak, Lee Howard, Andre Kostur, Hubert Kuenig, Ted Lemon, Andy 2973 Malis, Satoru Matsushima, Tomek Mrugalski, Madhu Niraula, Alexandru 2974 Petrescu, Behcet Saikaya, Michal Skorepa, Joe Touch, Bernie Volz, 2975 Ryuji Wakikawa, Tony Whyman, Lloyd Wood and James Woodyatt. Members 2976 of the IESG also provided valuable input during their review process 2977 that greatly improved the document. Special thanks go to Stewart 2978 Bryant, Joel Halpern and Brian Haberman for their shepherding 2979 guidance during the publication of the AERO first edition. 2981 This work has further been encouraged and supported by Boeing 2982 colleagues including Kyle Bae, M. Wayne Benson, Dave Bernhardt, Cam 2983 Brodie, John Bush, Balaguruna Chidambaram, Irene Chin, Bruce Cornish, 2984 Claudiu Danilov, Don Dillenburg, Joe Dudkowski, Wen Fang, Samad 2985 Farooqui, Anthony Gregory, Jeff Holland, Seth Jahne, Brian Jaury, 2986 Greg Kimberly, Ed King, Madhuri Madhava Badgandi, Laurel Matthew, 2987 Gene MacLean III, Rob Muszkiewicz, Sean O'Sullivan, Vijay 2988 Rajagopalan, Greg Saccone, Rod Santiago, Kent Shuey, Brian Skeen, 2989 Mike Slane, Carrie Spiker, Katie Tran, Brendan Williams, Amelia 2990 Wilson, Julie Wulff, Yueli Yang, Eric Yeh and other members of the 2991 Boeing mobility, networking and autonomy teams. Kyle Bae, Wayne 2992 Benson, Katie Tran and Eric Yeh are especially acknowledged for 2993 implementing the AERO functions as extensions to the public domain 2994 OpenVPN distribution. 2996 Earlier works on NBMA tunneling approaches are found in 2997 [RFC2529][RFC5214][RFC5569]. 2999 Many of the constructs presented in this second edition of AERO are 3000 based on the author's earlier works, including: 3002 o The Internet Routing Overlay Network (IRON) 3003 [RFC6179][I-D.templin-ironbis] 3005 o Virtual Enterprise Traversal (VET) 3006 [RFC5558][I-D.templin-intarea-vet] 3008 o The Subnetwork Encapsulation and Adaptation Layer (SEAL) 3009 [RFC5320][I-D.templin-intarea-seal] 3011 o AERO, First Edition [RFC6706] 3013 Note that these works cite numerous earlier efforts that are not also 3014 cited here due to space limitations. The authors of those earlier 3015 works are acknowledged for their insights. 3017 This work is aligned with the NASA Safe Autonomous Systems Operation 3018 (SASO) program under NASA contract number NNA16BD84C. 3020 This work is aligned with the FAA as per the SE2025 contract number 3021 DTFAWA-15-D-00030. 3023 This work is aligned with the Boeing Commercial Airplanes (BCA) 3024 Internet of Things (IoT) and autonomy programs. 3026 This work is aligned with the Boeing Information Technology (BIT) 3027 MobileNet program. 3029 8. References 3031 8.1. Normative References 3033 [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, 3034 DOI 10.17487/RFC0791, September 1981, 3035 . 3037 [RFC0792] Postel, J., "Internet Control Message Protocol", STD 5, 3038 RFC 792, DOI 10.17487/RFC0792, September 1981, 3039 . 3041 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 3042 Requirement Levels", BCP 14, RFC 2119, 3043 DOI 10.17487/RFC2119, March 1997, 3044 . 3046 [RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in 3047 IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473, 3048 December 1998, . 3050 [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black, 3051 "Definition of the Differentiated Services Field (DS 3052 Field) in the IPv4 and IPv6 Headers", RFC 2474, 3053 DOI 10.17487/RFC2474, December 1998, 3054 . 3056 [RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander, 3057 "SEcure Neighbor Discovery (SEND)", RFC 3971, 3058 DOI 10.17487/RFC3971, March 2005, 3059 . 3061 [RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)", 3062 RFC 3972, DOI 10.17487/RFC3972, March 2005, 3063 . 3065 [RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and 3066 More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191, 3067 November 2005, . 3069 [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, 3070 "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, 3071 DOI 10.17487/RFC4861, September 2007, 3072 . 3074 [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 3075 Address Autoconfiguration", RFC 4862, 3076 DOI 10.17487/RFC4862, September 2007, 3077 . 3079 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 3080 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 3081 May 2017, . 3083 [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 3084 (IPv6) Specification", STD 86, RFC 8200, 3085 DOI 10.17487/RFC8200, July 2017, 3086 . 3088 [RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A., 3089 Richardson, M., Jiang, S., Lemon, T., and T. Winters, 3090 "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", 3091 RFC 8415, DOI 10.17487/RFC8415, November 2018, 3092 . 3094 8.2. Informative References 3096 [BGP] Huston, G., "BGP in 2015, http://potaroo.net", January 3097 2016. 3099 [I-D.ietf-6man-segment-routing-header] 3100 Filsfils, C., Dukes, D., Previdi, S., Leddy, J., 3101 Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header 3102 (SRH)", draft-ietf-6man-segment-routing-header-26 (work in 3103 progress), October 2019. 3105 [I-D.ietf-dmm-distributed-mobility-anchoring] 3106 Chan, A., Wei, X., Lee, J., Jeon, S., and C. Bernardos, 3107 "Distributed Mobility Anchoring", draft-ietf-dmm- 3108 distributed-mobility-anchoring-14 (work in progress), 3109 November 2019. 3111 [I-D.ietf-intarea-gue] 3112 Herbert, T., Yong, L., and O. Zia, "Generic UDP 3113 Encapsulation", draft-ietf-intarea-gue-09 (work in 3114 progress), October 2019. 3116 [I-D.ietf-intarea-gue-extensions] 3117 Herbert, T., Yong, L., and F. Templin, "Extensions for 3118 Generic UDP Encapsulation", draft-ietf-intarea-gue- 3119 extensions-06 (work in progress), March 2019. 3121 [I-D.ietf-intarea-tunnels] 3122 Touch, J. and M. Townsley, "IP Tunnels in the Internet 3123 Architecture", draft-ietf-intarea-tunnels-10 (work in 3124 progress), September 2019. 3126 [I-D.ietf-rtgwg-atn-bgp] 3127 Templin, F., Saccone, G., Dawra, G., Lindem, A., and V. 3128 Moreno, "A Simple BGP-based Mobile Routing System for the 3129 Aeronautical Telecommunications Network", draft-ietf- 3130 rtgwg-atn-bgp-05 (work in progress), January 2020. 3132 [I-D.templin-6man-dhcpv6-ndopt] 3133 Templin, F., "A Unified Stateful/Stateless Configuration 3134 Service for IPv6", draft-templin-6man-dhcpv6-ndopt-09 3135 (work in progress), January 2020. 3137 [I-D.templin-atn-aero-interface] 3138 Templin, F. and T. Whyman, "Transmission of IPv6 Packets 3139 over Overlay Multilink Network (OMNI) Interfaces", draft- 3140 templin-atn-aero-interface-12 (work in progress), January 3141 2020. 3143 [I-D.templin-intarea-grefrag] 3144 Templin, F., "GRE Tunnel Level Fragmentation", draft- 3145 templin-intarea-grefrag-04 (work in progress), July 2016. 3147 [I-D.templin-intarea-seal] 3148 Templin, F., "The Subnetwork Encapsulation and Adaptation 3149 Layer (SEAL)", draft-templin-intarea-seal-68 (work in 3150 progress), January 2014. 3152 [I-D.templin-intarea-vet] 3153 Templin, F., "Virtual Enterprise Traversal (VET)", draft- 3154 templin-intarea-vet-40 (work in progress), May 2013. 3156 [I-D.templin-ironbis] 3157 Templin, F., "The Interior Routing Overlay Network 3158 (IRON)", draft-templin-ironbis-16 (work in progress), 3159 March 2014. 3161 [I-D.templin-v6ops-pdhost] 3162 Templin, F., "IPv6 Prefix Delegation and Multi-Addressing 3163 Models", draft-templin-v6ops-pdhost-25 (work in progress), 3164 January 2020. 3166 [OVPN] OpenVPN, O., "http://openvpn.net", October 2016. 3168 [RFC1035] Mockapetris, P., "Domain names - implementation and 3169 specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, 3170 November 1987, . 3172 [RFC1122] Braden, R., Ed., "Requirements for Internet Hosts - 3173 Communication Layers", STD 3, RFC 1122, 3174 DOI 10.17487/RFC1122, October 1989, 3175 . 3177 [RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191, 3178 DOI 10.17487/RFC1191, November 1990, 3179 . 3181 [RFC1812] Baker, F., Ed., "Requirements for IP Version 4 Routers", 3182 RFC 1812, DOI 10.17487/RFC1812, June 1995, 3183 . 3185 [RFC2003] Perkins, C., "IP Encapsulation within IP", RFC 2003, 3186 DOI 10.17487/RFC2003, October 1996, 3187 . 3189 [RFC2236] Fenner, W., "Internet Group Management Protocol, Version 3190 2", RFC 2236, DOI 10.17487/RFC2236, November 1997, 3191 . 3193 [RFC2529] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4 3194 Domains without Explicit Tunnels", RFC 2529, 3195 DOI 10.17487/RFC2529, March 1999, 3196 . 3198 [RFC2764] Gleeson, B., Lin, A., Heinanen, J., Armitage, G., and A. 3199 Malis, "A Framework for IP Based Virtual Private 3200 Networks", RFC 2764, DOI 10.17487/RFC2764, February 2000, 3201 . 3203 [RFC2784] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P. 3204 Traina, "Generic Routing Encapsulation (GRE)", RFC 2784, 3205 DOI 10.17487/RFC2784, March 2000, 3206 . 3208 [RFC2890] Dommety, G., "Key and Sequence Number Extensions to GRE", 3209 RFC 2890, DOI 10.17487/RFC2890, September 2000, 3210 . 3212 [RFC2923] Lahey, K., "TCP Problems with Path MTU Discovery", 3213 RFC 2923, DOI 10.17487/RFC2923, September 2000, 3214 . 3216 [RFC2983] Black, D., "Differentiated Services and Tunnels", 3217 RFC 2983, DOI 10.17487/RFC2983, October 2000, 3218 . 3220 [RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition 3221 of Explicit Congestion Notification (ECN) to IP", 3222 RFC 3168, DOI 10.17487/RFC3168, September 2001, 3223 . 3225 [RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener 3226 Discovery Version 2 (MLDv2) for IPv6", RFC 3810, 3227 DOI 10.17487/RFC3810, June 2004, 3228 . 3230 [RFC3819] Karn, P., Ed., Bormann, C., Fairhurst, G., Grossman, D., 3231 Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J., and L. 3232 Wood, "Advice for Internet Subnetwork Designers", BCP 89, 3233 RFC 3819, DOI 10.17487/RFC3819, July 2004, 3234 . 3236 [RFC4213] Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms 3237 for IPv6 Hosts and Routers", RFC 4213, 3238 DOI 10.17487/RFC4213, October 2005, 3239 . 3241 [RFC4251] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH) 3242 Protocol Architecture", RFC 4251, DOI 10.17487/RFC4251, 3243 January 2006, . 3245 [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A 3246 Border Gateway Protocol 4 (BGP-4)", RFC 4271, 3247 DOI 10.17487/RFC4271, January 2006, 3248 . 3250 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing 3251 Architecture", RFC 4291, DOI 10.17487/RFC4291, February 3252 2006, . 3254 [RFC4301] Kent, S. and K. Seo, "Security Architecture for the 3255 Internet Protocol", RFC 4301, DOI 10.17487/RFC4301, 3256 December 2005, . 3258 [RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery 3259 Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April 3260 2006, . 3262 [RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet 3263 Control Message Protocol (ICMPv6) for the Internet 3264 Protocol Version 6 (IPv6) Specification", STD 89, 3265 RFC 4443, DOI 10.17487/RFC4443, March 2006, 3266 . 3268 [RFC4511] Sermersheim, J., Ed., "Lightweight Directory Access 3269 Protocol (LDAP): The Protocol", RFC 4511, 3270 DOI 10.17487/RFC4511, June 2006, 3271 . 3273 [RFC4541] Christensen, M., Kimball, K., and F. Solensky, 3274 "Considerations for Internet Group Management Protocol 3275 (IGMP) and Multicast Listener Discovery (MLD) Snooping 3276 Switches", RFC 4541, DOI 10.17487/RFC4541, May 2006, 3277 . 3279 [RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick, 3280 "Internet Group Management Protocol (IGMP) / Multicast 3281 Listener Discovery (MLD)-Based Multicast Forwarding 3282 ("IGMP/MLD Proxying")", RFC 4605, DOI 10.17487/RFC4605, 3283 August 2006, . 3285 [RFC4607] Holbrook, H. and B. Cain, "Source-Specific Multicast for 3286 IP", RFC 4607, DOI 10.17487/RFC4607, August 2006, 3287 . 3289 [RFC4963] Heffner, J., Mathis, M., and B. Chandler, "IPv4 Reassembly 3290 Errors at High Data Rates", RFC 4963, 3291 DOI 10.17487/RFC4963, July 2007, 3292 . 3294 [RFC4982] Bagnulo, M. and J. Arkko, "Support for Multiple Hash 3295 Algorithms in Cryptographically Generated Addresses 3296 (CGAs)", RFC 4982, DOI 10.17487/RFC4982, July 2007, 3297 . 3299 [RFC5015] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano, 3300 "Bidirectional Protocol Independent Multicast (BIDIR- 3301 PIM)", RFC 5015, DOI 10.17487/RFC5015, October 2007, 3302 . 3304 [RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site 3305 Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214, 3306 DOI 10.17487/RFC5214, March 2008, 3307 . 3309 [RFC5320] Templin, F., Ed., "The Subnetwork Encapsulation and 3310 Adaptation Layer (SEAL)", RFC 5320, DOI 10.17487/RFC5320, 3311 February 2010, . 3313 [RFC5522] Eddy, W., Ivancic, W., and T. Davis, "Network Mobility 3314 Route Optimization Requirements for Operational Use in 3315 Aeronautics and Space Exploration Mobile Networks", 3316 RFC 5522, DOI 10.17487/RFC5522, October 2009, 3317 . 3319 [RFC5558] Templin, F., Ed., "Virtual Enterprise Traversal (VET)", 3320 RFC 5558, DOI 10.17487/RFC5558, February 2010, 3321 . 3323 [RFC5569] Despres, R., "IPv6 Rapid Deployment on IPv4 3324 Infrastructures (6rd)", RFC 5569, DOI 10.17487/RFC5569, 3325 January 2010, . 3327 [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection 3328 (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, 3329 . 3331 [RFC6106] Jeong, J., Park, S., Beloeil, L., and S. Madanapalli, 3332 "IPv6 Router Advertisement Options for DNS Configuration", 3333 RFC 6106, DOI 10.17487/RFC6106, November 2010, 3334 . 3336 [RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful 3337 NAT64: Network Address and Protocol Translation from IPv6 3338 Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146, 3339 April 2011, . 3341 [RFC6179] Templin, F., Ed., "The Internet Routing Overlay Network 3342 (IRON)", RFC 6179, DOI 10.17487/RFC6179, March 2011, 3343 . 3345 [RFC6221] Miles, D., Ed., Ooghe, S., Dec, W., Krishnan, S., and A. 3346 Kavanagh, "Lightweight DHCPv6 Relay Agent", RFC 6221, 3347 DOI 10.17487/RFC6221, May 2011, 3348 . 3350 [RFC6273] Kukec, A., Krishnan, S., and S. Jiang, "The Secure 3351 Neighbor Discovery (SEND) Hash Threat Analysis", RFC 6273, 3352 DOI 10.17487/RFC6273, June 2011, 3353 . 3355 [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer 3356 Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, 3357 January 2012, . 3359 [RFC6438] Carpenter, B. and S. Amante, "Using the IPv6 Flow Label 3360 for Equal Cost Multipath Routing and Link Aggregation in 3361 Tunnels", RFC 6438, DOI 10.17487/RFC6438, November 2011, 3362 . 3364 [RFC6706] Templin, F., Ed., "Asymmetric Extended Route Optimization 3365 (AERO)", RFC 6706, DOI 10.17487/RFC6706, August 2012, 3366 . 3368 [RFC6864] Touch, J., "Updated Specification of the IPv4 ID Field", 3369 RFC 6864, DOI 10.17487/RFC6864, February 2013, 3370 . 3372 [RFC7269] Chen, G., Cao, Z., Xie, C., and D. Binet, "NAT64 3373 Deployment Options and Experience", RFC 7269, 3374 DOI 10.17487/RFC7269, June 2014, 3375 . 3377 [RFC7333] Chan, H., Ed., Liu, D., Seite, P., Yokota, H., and J. 3378 Korhonen, "Requirements for Distributed Mobility 3379 Management", RFC 7333, DOI 10.17487/RFC7333, August 2014, 3380 . 3382 [RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I., 3383 Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent 3384 Multicast - Sparse Mode (PIM-SM): Protocol Specification 3385 (Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March 3386 2016, . 3388 [RFC8086] Yong, L., Ed., Crabbe, E., Xu, X., and T. Herbert, "GRE- 3389 in-UDP Encapsulation", RFC 8086, DOI 10.17487/RFC8086, 3390 March 2017, . 3392 [RFC8201] McCann, J., Deering, S., Mogul, J., and R. Hinden, Ed., 3393 "Path MTU Discovery for IP version 6", STD 87, RFC 8201, 3394 DOI 10.17487/RFC8201, July 2017, 3395 . 3397 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., 3398 Decraene, B., Litkowski, S., and R. Shakir, "Segment 3399 Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, 3400 July 2018, . 3402 [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol 3403 Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, 3404 . 3406 Appendix A. AERO Alternate Encapsulations 3408 When GUE encapsulation is not needed, AERO can use common 3409 encapsulations such as IP-in-IP [RFC2003][RFC2473][RFC4213], Generic 3410 Routing Encapsulation (GRE) [RFC2784][RFC2890] and others. The 3411 encapsulation is therefore only differentiated from non-AERO tunnels 3412 through the application of AERO control messaging and not through, 3413 e.g., a well-known UDP port number. 3415 As for GUE encapsulation, alternate AERO encapsulation formats may 3416 require encapsulation layer fragmentation. For simple IP-in-IP 3417 encapsulation, an IPv6 fragment header is inserted directly between 3418 the inner and outer IP headers when needed, i.e., even if the outer 3419 header is IPv4. The IPv6 Fragment Header is identified to the outer 3420 IP layer by its IP protocol number, and the Next Header field in the 3421 IPv6 Fragment Header identifies the inner IP header version. For GRE 3422 encapsulation, a GRE fragment header is inserted within the GRE 3423 header [I-D.templin-intarea-grefrag]. 3425 Figure 6 shows the AERO IP-in-IP encapsulation format before any 3426 fragmentation is applied: 3428 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3429 | Outer IPv4 Header | | Outer IPv6 Header | 3430 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3431 |IPv6 Frag Header (optional)| |IPv6 Frag Header (optional)| 3432 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3433 | Inner IP Header | | Inner IP Header | 3434 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3435 | | | | 3436 ~ ~ ~ ~ 3437 ~ Inner Packet Body ~ ~ Inner Packet Body ~ 3438 ~ ~ ~ ~ 3439 | | | | 3440 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3442 Minimal Encapsulation in IPv4 Minimal Encapsulation in IPv6 3444 Figure 6: Minimal Encapsulation Format using IP-in-IP 3446 Figure 7 shows the AERO GRE encapsulation format before any 3447 fragmentation is applied: 3449 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3450 | Outer IP Header | 3451 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3452 | GRE Header | 3453 | (with checksum, key, etc..) | 3454 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3455 | GRE Fragment Header (optional)| 3456 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3457 | Inner IP Header | 3458 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3459 | | 3460 ~ ~ 3461 ~ Inner Packet Body ~ 3462 ~ ~ 3463 | | 3464 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 3466 Figure 7: Minimal Encapsulation Using GRE 3468 Alternate encapsulation may be preferred in environments where GUE 3469 encapsulation would add unnecessary overhead. For example, certain 3470 low-bandwidth wireless data links may benefit from a reduced 3471 encapsulation overhead. 3473 GUE encapsulation can traverse network paths that are inaccessible to 3474 non-UDP encapsulations, e.g., for crossing Network Address 3475 Translators (NATs). More and more, network middleboxes are also 3476 being configured to discard packets that include anything other than 3477 a well-known IP protocol such as UDP and TCP. It may therefore be 3478 necessary to determine the potential for middlebox filtering before 3479 enabling alternate encapsulation in a given environment. 3481 In addition to IP-in-IP, GRE and GUE, AERO can also use security 3482 encapsulations such as IPsec, TLS/SSL, DTLS, etc. In that case, AERO 3483 control messaging and route determination occur before security 3484 encapsulation is applied for outgoing packets and after security 3485 decapsulation is applied for incoming packets. 3487 AERO is especially well suited for use with VPN system encapsulations 3488 such as OpenVPN [OVPN]. 3490 Appendix B. Non-Normative Considerations 3492 AERO can be applied to a multitude of Internetworking scenarios, with 3493 each having its own adaptations. The following considerations are 3494 provided as non-normative guidance: 3496 B.1. Implementation Strategies for Route Optimization 3498 Route optimization as discussed in Section 3.17 results in the route 3499 optimization source (ROS) creating an asymmetric neighbor cache entry 3500 for the target neighbor. The neighbor cache entry is maintained for 3501 at most REACHABLETIME seconds and then deleted unless updated. In 3502 order to refresh the neighbor cache entry lifetime before the 3503 ReachableTime timer expires, the specification requires 3504 implementations to issue a new NS/NA exchange to reset ReachableTime 3505 to REACHABLETIME seconds while data packets are still flowing. 3506 However, the decision of when to initiate a new NS/NA exchange and to 3507 perpetuate the process is left as an implementation detail. 3509 One possible strategy may be to monitor the neighbor cache entry 3510 watching for data packets for (REACHABLETIME - 5) seconds. If any 3511 data packets have been sent to the neighbor within this timeframe, 3512 then send an NS to receive a new NA. If no data packets have been 3513 sent, wait for 5 additional seconds and send an immediate NS if any 3514 data packets are sent within this "expiration pending" 5 second 3515 window. If no additional data packets are sent within the 5 second 3516 window, delete the neighbor cache entry. 3518 The monitoring of the neighbor data packet traffic therefore becomes 3519 an asymmetric ongoing process during the neighbor cache entry 3520 lifetime. If the neighbor cache entry expires, future data packets 3521 will trigger a new NS/NA exchange while the packets themselves are 3522 delivered over a longer path until route optimization state is re- 3523 established. 3525 B.2. Implicit Mobility Management 3527 AERO interface neighbors MAY provide a configuration option that 3528 allows them to perform implicit mobility management in which no ND 3529 messaging is used. In that case, the Client only transmits packets 3530 over a single interface at a time, and the neighbor always observes 3531 packets arriving from the Client from the same link-layer source 3532 address. 3534 If the Client's underlying interface address changes (either due to a 3535 readdressing of the original interface or switching to a new 3536 interface) the neighbor immediately updates the neighbor cache entry 3537 for the Client and begins accepting and sending packets according to 3538 the Client's new address. This implicit mobility method applies to 3539 use cases such as cellphones with both WiFi and Cellular interfaces 3540 where only one of the interfaces is active at a given time, and the 3541 Client automatically switches over to the backup interface if the 3542 primary interface fails. 3544 B.3. Direct Underlying Interfaces 3546 When a Client's AERO interface is configured over a Direct interface, 3547 the neighbor at the other end of the Direct link can receive packets 3548 without any encapsulation. In that case, the Client sends packets 3549 over the Direct link according to QoS preferences. If the Direct 3550 interface has the highest QoS preference, then the Client's IP 3551 packets are transmitted directly to the peer without going through an 3552 ANET/INET. If other interfaces have higher QoS preferences, then the 3553 Client's IP packets are transmitted via a different interface, which 3554 may result in the inclusion of Proxys, Servers and Relays in the 3555 communications path. Direct interfaces must be tested periodically 3556 for reachability, e.g., via NUD. 3558 B.4. AERO Clients on the Open Internetwork 3560 AERO Clients that connect to the open Internetwork via either a 3561 native or NATed interface can establish a VPN to securely connect to 3562 a Server. Alternatively, the Client can exchange ND messages 3563 directly with other AERO nodes on the same SPAN segment using INET 3564 encapsulation only and without joining the SPAN. In that case, 3565 however, the Client must apply asymmetric security for ND messages to 3566 ensure routing and neighbor cache integrity (see: Section 6). 3568 B.5. Operation on AERO Links with /64 ASPs 3570 IPv6 AERO links typically have MSPs that aggregate many candidate 3571 MNPs of length /64 or shorter. However, in some cases it may be 3572 desirable to use AERO over links that have only a /64 MSP. This can 3573 be accommodated by treating all Clients on the AERO link as simple 3574 hosts that receive /128 prefix delegations. 3576 In that case, the Client sends an RS message to the Server the same 3577 as for ordinary AERO links. The Server responds with an RA message 3578 that includes one or more /128 prefixes (i.e., singleton addresses) 3579 that include the /64 MSP prefix along with an interface identifier 3580 portion to be assigned to the Client. The Client and Server then 3581 configure their AERO addresses based on the interface identifier 3582 portions of the /128s (i.e., the lower 64 bits) and not based on the 3583 /64 prefix (i.e., the upper 64 bits). 3585 For example, if the MSP for the host-only IPv6 AERO link is 3586 2001:db8:1000:2000::/64, each Client will receive one or more /128 3587 IPv6 prefix delegations such as 2001:db8:1000:2000::1/128, 3588 2001:db8:1000:2000::2/128, etc. When the Client receives the prefix 3589 delegations, it assigns the AERO addresses fe80::1, fe80::2, etc. to 3590 the AERO interface, and assigns the global IPv6 addresses (i.e., the 3591 /128s) to either the AERO interface or an internal virtual interface 3592 such as a loopback. In this arrangement, the Client conducts route 3593 optimization in the same sense as discussed in Section 3.17. 3595 This specification has applicability for nodes that act as a Client 3596 on an "upstream" AERO link, but also act as a Server on "downstream" 3597 AERO links. More specifically, if the node acts as a Client to 3598 receive a /64 prefix from the upstream AERO link it can then act as a 3599 Server to provision /128s to Clients on downstream AERO links. 3601 B.6. AERO Adaptations for SEcure Neighbor Discovery (SEND) 3603 SEcure Neighbor Discovery (SEND) [RFC3971] and Cryptographically 3604 Generated Addresses (CGAs) [RFC3972] were designed to secure IPv6 ND 3605 messaging in environments where symmetric network and/or transport- 3606 layer security services are impractical (see: Section 6). AERO nodes 3607 that use SEND/CGA employ the following adaptations. 3609 When a source AERO node prepares a SEND-protected ND message, it uses 3610 a link-local CGA as the IPv6 source address and writes the prefix 3611 embedded in its AERO address (i.e., instead of fe80::/64) in the CGA 3612 parameters Subnet Prefix field. When the neighbor receives the ND 3613 message, it first verifies the message checksum and SEND/CGA 3614 parameters while using the link-local prefix fe80::/64 (i.e., instead 3615 of the value in the Subnet Prefix field) to match against the IPv6 3616 source address of the ND message. 3618 The neighbor then derives the AERO address of the source by using the 3619 value in the Subnet Prefix field as the interface identifier of an 3620 AERO address. For example, if the Subnet Prefix field contains 3621 2001:db8:1:2, the neighbor constructs the AERO address as 3622 fe80::2001:db8:1:2. The neighbor then caches the AERO address in the 3623 neighbor cache entry it creates for the source, and uses the AERO 3624 address as the IPv6 destination address of any ND message replies. 3626 B.7. AERO Critical Infrastructure Considerations 3628 AERO Relays can be either Commercial off-the Shelf (COTS) standard IP 3629 routers or virtual machines in the cloud. Relays must be 3630 provisioned, supported and managed by the INET administrative 3631 authority, and connected to the Relays of other INETs via inter- 3632 domain peerings. Cost for purchasing, configuring and managing 3633 Relays is nominal even for very large AERO links. 3635 AERO Servers can be standard dedicated server platforms, but most 3636 often will be deployed as virtual machines in the cloud. The only 3637 requirements for Servers are that they can run the AERO user-level 3638 code and have at least one network interface connection to the INET. 3639 As with Relays, Servers must be provisioned, supported and managed by 3640 the INET administrative authority. Cost for purchasing, configuring 3641 and managing Servers is nominal especially for virtual Servers hosted 3642 in the cloud. 3644 AERO Proxys are most often standard dedicated server platforms with 3645 one network interface connected to the ANET and a second interface 3646 connected to an INET. As with Servers, the only requirements are 3647 that they can run the AERO user-level code and have at least one 3648 interface connection to the INET. Proxys must be provisioned, 3649 supported and managed by the ANET administrative authority. Cost for 3650 purchasing, configuring and managing Proxys is nominal, and borne by 3651 the ANET administrative authority. 3653 AERO Gateways can be any dedicated server or COTS router platform 3654 connected to INETs and/or EUNs. The Gateway joins the SPAN and 3655 engages in eBGP peering with one or more Relays as a stub AS. The 3656 Gateway then injects its MNPs and/or non-MNP prefixes into the BGP 3657 routing system, and provisions the prefixes to its downstream- 3658 attached networks. The Gateway can perform ROS and MAP services the 3659 same as for any Server, and can route between the MNP and non-MNP 3660 address spaces. 3662 B.8. AERO Server Failure Implications 3664 AERO Servers may appear as a single point of failure in the 3665 architecture, but such is not the case since all Servers on the link 3666 provide identical services and loss of a Server does not imply 3667 immediate and/or comprehensive communication failures. Although 3668 Clients typically associate with a single Server at a time, Server 3669 failure is quickly detected and conveyed by Bidirectional Forward 3670 Detection (BFD) and/or proactive NUD allowing Clients to migrate to 3671 new Servers. 3673 If a Server fails, ongoing packet forwarding to Clients will continue 3674 by virtue of the asymmetric neighbor cache entries that have already 3675 been established in route optimization sources (ROSs). If a Client 3676 also experiences mobility events at roughly the same time the Server 3677 fails, unsolicited NA messages may be lost but proxy neighbor cache 3678 entries in the DEPARTED state will ensure that packet forwarding to 3679 the Client's new locations will continue for up to DEPARTTIME 3680 seconds. 3682 If a Client is left without a Server for an extended timeframe (e.g., 3683 greater than REACHABLETIIME seconds) then existing asymmetric 3684 neighbor cache entries will eventually expire and both ongoing and 3685 new communications will fail. The original source will continue to 3686 retransmit until the Client has established a new Server 3687 relationship, after which time continuous communications will resume. 3689 Therefore, providing many Servers on the link with high availability 3690 profiles provides resilience against loss of individual Servers and 3691 assurance that Clients can establish new Server relationships quickly 3692 in event of a Server failure. 3694 B.9. AERO Client / Server Architecture 3696 The AERO architectural model is client / server in the control plane, 3697 with route optimization in the data plane. The same as for common 3698 Internet services, the AERO Client discovers the addresses of AERO 3699 Servers and selects one Server to connect to. The AERO service is 3700 analogous to common Internet services such as google.com, yahoo.com, 3701 cnn.com, etc. However, there is only one AERO service for the link 3702 and all Servers provide identical services. 3704 Common Internet services provide differing strategies for advertising 3705 server addresses to clients. The strategy is conveyed through the 3706 DNS resource records returned in response to name resolution queries. 3707 As of January 2020 Internet-based 'nslookup' services were used to 3708 determine the following: 3710 o When a client resolves the domainname "google.com", the DNS always 3711 returns one A record (i.e., an IPv4 address) and one AAAA record 3712 (i.e., an IPv6 address). The client receives the same addresses 3713 each time it resolves the domainname via the same DNS resolver, 3714 but may receive different addresses when it resolves the 3715 domainname via different DNS resolvers. But, in each case, 3716 exactly one A and one AAAA record are returned. 3718 o When a client resolves the domainname "ietf.org", the DNS always 3719 returns one A record and one AAAA record with the same addresses 3720 regardless of which DNS resolver is used. 3722 o When a client resolves the domainname "yahoo.com", the DNS always 3723 returns a list of 4 A records and 4 AAAA records. Each time the 3724 client resolves the domainname via the same DNS resolver, the same 3725 list of addresses are returned but in randomized order (i.e., 3726 consistent with a DNS round-robin strategy). But, interestingly, 3727 the same addresses are returned (albeit in randomized order) when 3728 the domainname is resolved via different DNS resolvers. 3730 o When a client resolves the domainname "amazon.com", the DNS always 3731 returns a list of 3 A records and no AAAA records. As with 3732 "yahoo.com", the same three A records are returned from any 3733 worldwide Internet connection point in randomized order. 3735 The above example strategies show differing approaches to Internet 3736 resilience and service distribution offered by major Internet 3737 services. The Google approach exposes only a single IPv4 and a 3738 single IPv6 address to clients. Clients can then select whichever IP 3739 protocol version offers the best response, but will always use the 3740 same IP address according to the current Internet connection point. 3741 This means that the IP address offered by the network must lead to a 3742 highly-available server and/or service distribution point. In other 3743 words, resilience is predicated on high availability within the 3744 network and with no client-initiated failovers expected (i.e., it is 3745 all-or-nothing from the client's perspective). However, Google does 3746 provide for worldwide distributed service distribution by virtue of 3747 the fact that each Internet connection point responds with a 3748 different IPv6 and IPv4 address. The IETF approach is like google 3749 (all-or-nothing from the client's perspective), but provides only a 3750 single IPv4 or IPv6 address on a worldwide basis. This means that 3751 the addresses must be made highly-available at the network level with 3752 no client failover possibility, and if there is any worldwide service 3753 distribution it would need to be conducted by a network element that 3754 is reached via the IP address acting as a service distribution point. 3756 In contrast to the Google and IETF philosophies, Yahoo and Amazon 3757 both provide clients with a (short) list of IP addresses with Yahoo 3758 providing both IP protocol versions and Amazon as IPv4-only. The 3759 order of the list is randomized with each name service query 3760 response, with the effect of round-robin load balancing for service 3761 distribution. With a short list of addresses, there is still 3762 expectation that the network will implement high availability for 3763 each address but in case any single address fails the client can 3764 switch over to using a different address. The balance then becomes 3765 one of function in the network vs function in the end system. 3767 The same implications observed for common highly-available services 3768 in the Internet apply also to the AERO client/server architecture. 3769 When an AERO Client connects to one or more ANETs, it discovers one 3770 or more AERO Server addresses through the mechanisms discussed in 3771 earlier sections. Each Server address presumably leads to a fault- 3772 tolerant clustering arrangement such as supported by Linux-HA, 3773 Extended Virtual Synchrony or Paxos. Such an arrangement has 3774 precedence in common Internet service deployments in lightweight 3775 virtual machines without requiring expensive hardware deployment. 3776 Similarly, common Internet service deployments set service IP 3777 addresses on service distribution points that may relay requests to 3778 many different servers. 3780 For AERO, the expectation is that a combination of the Google/IETF 3781 and Yahoo/Amazon philosophies would be employed. The AERO Client 3782 connects to different ANET access points and can receive 1-2 Server 3783 AERO addresses at each point. It then selects one AERO Server 3784 address, and engages in RS/RA exchanges with the same Server from all 3785 ANET connections. The Client remains with this Server unless or 3786 until the Server fails, in which case it can switch over to an 3787 alternate Server. The Client can likewise switch over to a different 3788 Server at any time if there is some reason for it to do so. So, the 3789 AERO expectation is for a balance of function in the network and end 3790 system, with fault tolerance and resilience at both levels. 3792 Appendix C. Change Log 3794 << RFC Editor - remove prior to publication >> 3796 Changes from draft-templin-intarea-6706bis-19 to draft-templin- 3797 intrea-6706bis-20: 3799 o Included new route optimization source and destination addressing 3800 strategy. Now, route optimization maintenance uses the address of 3801 the existing Server instead of the data packet destination address 3802 so that less pressure is placed on the BGP routing system 3803 convergence time and Server constancy is supported. 3805 o Included new method for releasing from old MSE without requiring 3806 Client messaging. 3808 o Included references to new OMNI interface spec (including the OMNI 3809 option). 3811 o New appendix on AERO Client/Server architecture. 3813 Changes from draft-templin-intarea-6706bis-18 to draft-templin- 3814 intrea-6706bis-19: 3816 o Changed Proxy/Server keepalives to use "proactive NUD" in a manner 3817 tha paralles BFD 3819 Changes from draft-templin-intarea-6706bis-17 to draft-templin- 3820 intrea-6706bis-18: 3822 o Discuss how AERO option is used in relation to S/TLLAOs 3824 o New text on Bidirectional Forwarding Detection (BFD) 3826 o Cleaned up usage (and non-usage) of unsolicited NAs 3828 o New appendix on Server failures 3830 Changes from draft-templin-intarea-6706bis-15 to draft-templin- 3831 intrea-6706bis-17: 3833 o S/TLLAO now includes multiple link-layer addresses within a single 3834 option instead of requiring multiple options 3836 o New unsolicited NA message to inform the old link that a Client 3837 has moved to a new link 3839 Changes from draft-templin-intarea-6706bis-14 to draft-templin- 3840 intrea-6706bis-15: 3842 o MTU and fragmentation 3844 o New details in movement to new Server 3846 Changes from draft-templin-intarea-6706bis-13 to draft-templin- 3847 intrea-6706bis-14: 3849 o Security based on secured tunnels, ingress filtering, MAP list and 3850 ROS list 3852 Changes from draft-templin-intarea-6706bis-12 to draft-templin- 3853 intrea-6706bis-13: 3855 o New paragraph in Section 3.6 on AERO interface layering over 3856 secured tunnels 3858 o Removed extraneous text in Section 3.7 3860 o Added new detail to the forwarding algorithm in Section 3.9 3862 o Clarified use of fragmentation 3864 o Route optimization now supported for both MNP and non-MNP-based 3865 prefixes 3867 o Relays are now seen as link-layer elements in the architecture. 3869 o Built out multicast section in detail. 3871 o New Appendix on implementation considerations for route 3872 optimization. 3874 Changes from draft-templin-intarea-6706bis-11 to draft-templin- 3875 intrea-6706bis-12: 3877 o Introduced Gateways as a new AERO element for connecting 3878 Correspondent Nodes on INET links 3880 o Introduced terms "Access Network (ANET)" and "Internetwork (INET)" 3881 o Changed "ASP" to "MSP", and "ACP" to "MNP" 3883 o New figure on the relation of Segments to the SPAN and AERO link 3885 o New "S" bit in S/TLLAO to indicate the "Source" S/TLLAO as opposed 3886 to additional S/TLLAOs 3888 o Changed Interface ID for Servers from 255 to 0xffff 3890 o Significant updates to Route Optimization, NUD, and Mobility 3891 Management 3893 o New Section on Multicast 3895 o New Section on AERO Clients in the open Internetwork 3897 o New Section on Operation over multiple AERO links (VLANs over the 3898 SPAN) 3900 o New Sections on DNS considerations and Transition considerations 3902 o 3904 Changes from draft-templin-intarea-6706bis-10 to draft-templin- 3905 intrea-6706bis-11: 3907 o Added The SPAN 3909 Changes from draft-templin-intarea-6706bis-09 to draft-templin- 3910 intrea-6706bis-10: 3912 o Orphaned packets in flight (e.g., when a neighbor cache entry is 3913 in the DEPARTED state) are now forwarded at the link layer instead 3914 of at the network layer. Forwarding at the network layer can 3915 result in routing loops and/or excessive delays of forwarded 3916 packets while the routing system is still reconverging. 3918 o Update route optimization to clarify the unsecured nature of the 3919 first NS used for route discovery 3921 o Many cleanups and clarifications on ND messaging parameters 3923 Changes from draft-templin-intarea-6706bis-08 to draft-templin- 3924 intrea-6706bis-09: 3926 o Changed PRL to "MAP list" 3927 o For neighbor cache entries, changed "static" to "symmetric", and 3928 "dynamic" to "asymmetric" 3930 o Specified Proxy RS/RA exchanges with Servers on behalf of Clients 3932 o Added discussion of unsolicited NAs in Section 3.16, and included 3933 forward reference to Section 3.18 3935 o Added discussion of AERO Clients used as critical infrastructure 3936 elements to connect fixed networks. 3938 o Added network-based VPN under security considerations 3940 Changes from draft-templin-intarea-6706bis-07 to draft-templin- 3941 intrea-6706bis-08: 3943 o New section on AERO-Aware Access Router 3945 Changes from draft-templin-intarea-6706bis-06 to draft-templin- 3946 intrea-6706bis-07: 3948 o Added "R" bit for release of PDs. Now have a full RS/RA service 3949 that can do PD without requiring DHCPv6 messaging over-the-air 3951 o Clarifications on solicited vs unsolicited NAs 3953 o Clarified use of MAX_NEIGHBOR_ADVERTISEMENTS for the purpose of 3954 increase reliability 3956 Changes from draft-templin-intarea-6706bis-05 to draft-templin- 3957 intrea-6706bis-06: 3959 o Major re-work and simplification of Route Optimization function 3961 o Added Distributed Mobility Management (DMM) and Mobility Anchor 3962 Point (MAP) terminology 3964 o New section on "AERO Critical Infrastructure Element 3965 Considerations" demonstrating low overall cost for the service 3967 o minor text revisions and deletions 3969 o removed extraneous appendices 3971 Changes from draft-templin-intarea-6706bis-04 to draft-templin- 3972 intrea-6706bis-05: 3974 o New Appendix E on S/TLLAO Extensions for special-purpose links. 3975 Discussed ATN/IPS as example. 3977 o New sentence in introduction to declare appendices as non- 3978 normative. 3980 Changes from draft-templin-intarea-6706bis-03 to draft-templin- 3981 intrea-6706bis-04: 3983 o Added definitions for Potential Router List (PRL) and secure 3984 enclave 3986 o Included text on mapping transport layer port numbers to network 3987 layer DSCP values 3989 o Added reference to DTLS and DMM Distributed Mobility Anchoring 3990 working group document 3992 o Reworked Security Considerations 3994 o Updated references. 3996 Changes from draft-templin-intarea-6706bis-02 to draft-templin- 3997 intrea-6706bis-03: 3999 o Added new section on SEND. 4001 o Clarifications on "AERO Address" section. 4003 o Updated references and added new reference for RFC8086. 4005 o Security considerations updates. 4007 o General text clarifications and cleanup. 4009 Changes from draft-templin-intarea-6706bis-01 to draft-templin- 4010 intrea-6706bis-02: 4012 o Note on encapsulation avoidance in Section 4. 4014 Changes from draft-templin-intarea-6706bis-00 to draft-templin- 4015 intrea-6706bis-01: 4017 o Remove DHCPv6 Server Release procedures that leveraged the old way 4018 Relays used to "route" between Server link-local addresses 4020 o Remove all text relating to Relays needing to do any AERO-specific 4021 operations 4023 o Proxy sends RS and receives RA from Server using SEND. Use CGAs 4024 as source addresses, and destination address of RA reply is to the 4025 AERO address corresponding to the Client's ACP. 4027 o Proxy uses SEND to protect RS and authenticate RA (Client does not 4028 use SEND, but rather relies on subnetwork security. When the 4029 Proxy receives an RS from the Client, it creates a new RS using 4030 its own addresses as the source and uses SEND with CGAs to send a 4031 new RS to the Server. 4033 o Emphasize distributed mobility management 4035 o AERO address-based RS injection of ACP into underlying routing 4036 system. 4038 Changes from draft-templin-aerolink-82 to draft-templin-intarea- 4039 6706bis-00: 4041 o Document use of NUD (NS/NA) for reliable link-layer address 4042 updates as an alternative to unreliable unsolicited NA. 4043 Consistent with Section 7.2.6 of RFC4861. 4045 o Server adds additional layer of encapsulation between outer and 4046 inner headers of NS/NA messages for transmission through Relays 4047 that act as vanilla IPv6 routers. The messages include the AERO 4048 Server Subnet Router Anycast address as the source and the Subnet 4049 Router Anycast address corresponding to the Client's ACP as the 4050 destination. 4052 o Clients use Subnet Router Anycast address as the encapsulation 4053 source address when the access network does not provide a 4054 topologically-fixed address. 4056 Author's Address 4058 Fred L. Templin (editor) 4059 Boeing Research & Technology 4060 P.O. Box 3707 4061 Seattle, WA 98124 4062 USA 4064 Email: fltemplin@acm.org