Automatic Extended Route Optimization (AERO)
draft-templin-6man-aero-24
The information below is for an old version of the document.
Document | Type |
This is an older version of an Internet-Draft whose latest revision state is "Replaced".
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Author | Fred Templin | ||
Last updated | 2021-08-12 (Latest revision 2021-08-10) | ||
Replaces | draft-templin-intarea-6706bis | ||
Replaced by | draft-templin-intarea-aero | ||
RFC stream | Internet Engineering Task Force (IETF) | ||
Formats | |||
Additional resources | |||
Stream | WG state | (None) | |
Document shepherd | Eliot Lear | ||
IESG | IESG state | I-D Exists | |
Consensus boilerplate | Unknown | ||
Telechat date | (None) | ||
Responsible AD | (None) | ||
Send notices to | rfc-ise@rfc-editor.org |
draft-templin-6man-aero-24
#x27;s delegated MNP regardless of their OMNI link point of origin. These checks are necessary to prevent Clients from either accidentally or intentionally establishing endless loops that could congest Proxy/Servers and/or ANET/INET links. Note: Proxy/Servers forward secure control plane carrier packets via the SRT secured spanning tree and forward other carrier packets via the unsecured spanning tree. When a Proxy/Server receives a carrier packet from the secured spanning tree, it considers the message as authentic without having to verify upper layer authentication signatures. When a Proxy/Server receives a carrier packet from the unsecured spanning tree, it verifies any upper layer authentication signatures and/or forwards the unsecured message toward the destination which must apply data origin authentication. Note: If the Proxy/Server has multiple original IP packets to send to the same neighbor, it can concatenate them in a single OAL super- packet [I-D.templin-6man-omni]. 3.10.3. Bridge Forwarding Algorithm Bridges forward spanning tree carrier packets while decrementing the OAL header Hop Count but not the original IP header Hop Count/TTL. Bridges convey carrier packets that encapsulate critical IPv6 ND control messages or routing protocol control messages via the secured spanning tree, and may convey other carrier packets via the unsecured spanning tree or via more direct paths according to MFIB information. When the Bridge receives a carrier packet, it removes the outer *NET header and searches for an MFIB entry that matches an MFVI or an IP forwarding table entry that matches the OAL destination address. Bridges process carrier packets with OAL destinations that do not match their ADM-ULA or the SRT Subnet Router Anycast address in the same manner as for traditional IP forwarding within the OAL, i.e., nodes use IP forwarding to forward packets not explicitly addressed to themselves. Bridges process carrier packets with their ADM-ULA or the SRT Subnet Router Anycast address as the destination by first examining the packet for a CRH-32 header or a compressed OAL header. In that case, the Bridge examines the next MFVI in the carrier packet to locate the MFV entry in the MFIB for next hop forwarding (i.e., without examining IP addresses). When the Bridge forwards the carrier packet, it changes the destination address according to the Templin Expires February 13, 2022 [Page 49] Internet-Draft AERO August 2021 MFVI value for the next hop found either in the CRH-32 header or in the node's own MFIB. Bridges forward carrier packets received from a first segment via the SRT secured spanning tree to the next segment also via the secured spanning tree. Bridges forward carrier packets received from a first segment via the unsecured spanning tree to the next segment also via the unsecured spanning tree. Bridges use a single IPv6 routing table that always determines the same next hop for a given OAL destination, where the secured/unsecured spanning tree is determined through the selection of the underlying interface to be used for transmission (i.e., a secured tunnel or an open INET interface). 3.11. OMNI Interface Error Handling When an AERO node admits an original IP packet into the OMNI interface, it may receive link-layer or network-layer error indications. The AERO node may also receive OMNI link error indications in OAL-encapsulated uNA messages that include authentication signatures. A link-layer error indication is an ICMP error message generated by a router in the INET on the path to the neighbor or by the neighbor itself. The message includes an IP header with the address of the node that generated the error as the source address and with the link-layer address of the AERO node as the destination address. The IP header is followed by an ICMP header that includes an error Type, Code and Checksum. Valid type values include "Destination Unreachable", "Time Exceeded" and "Parameter Problem" [RFC0792][RFC4443]. (OMNI interfaces ignore link-layer IPv4 "Fragmentation Needed" and IPv6 "Packet Too Big" messages for carrier packets that are no larger than the minimum/path MPS as discussed in Section 3.9, however these messages may provide useful hints of probe failures during path MPS probing.) The ICMP header is followed by the leading portion of the carrier packet that generated the error, also known as the "packet-in-error". For ICMPv6, [RFC4443] specifies that the packet-in-error includes: "As much of invoking packet as possible without the ICMPv6 packet exceeding the minimum IPv6 MTU" (i.e., no more than 1280 bytes). For ICMPv4, [RFC0792] specifies that the packet-in-error includes: "Internet Header + 64 bits of Original Data Datagram", however [RFC1812] Section 4.3.2.3 updates this specification by stating: "the ICMP datagram SHOULD contain as much of the original datagram as possible without the length of the ICMP datagram exceeding 576 bytes". Templin Expires February 13, 2022 [Page 50] Internet-Draft AERO August 2021 The link-layer error message format is shown in Figure 4: +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ ~ | IP Header of link layer | | error message | ~ ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ICMP Header | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- ~ ~ P | carrier packet *NET and OAL | a | encapsulation headers | c ~ ~ k +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ e ~ ~ t | original IP packet headers | | (first-fragment only) | i ~ ~ n +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ ~ e | Portion of the body of | r | the original IP packet | r | (all fragments) | o ~ ~ r +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ --- Figure 4: OMNI Interface Link-Layer Error Message Format The AERO node rules for processing these link-layer error messages are as follows: o When an AERO node receives a link-layer Parameter Problem message, it processes the message the same as described as for ordinary ICMP errors in the normative references [RFC0792][RFC4443]. o When an AERO node receives persistent link-layer Time Exceeded messages, the IP ID field may be wrapping before earlier fragments awaiting reassembly have been processed. In that case, the node should begin including integrity checks and/or institute rate limits for subsequent packets. o When an AERO node receives persistent link-layer Destination Unreachable messages in response to carrier packets that it sends to one of its neighbor correspondents, the node should process the message as an indication that a path may be failing, and optionally initiate NUD over that path. If it receives Destination Unreachable messages over multiple paths, the node Templin Expires February 13, 2022 [Page 51] Internet-Draft AERO August 2021 should allow future carrier packets destined to the correspondent to flow through a default route and re-initiate route optimization. o When an AERO Client receives persistent link-layer Destination Unreachable messages in response to carrier packets that it sends to one of its neighbor Proxy/Servers, the Client should mark the path as unusable and use another path. If it receives Destination Unreachable messages on many or all paths, the Client should associate with a new Proxy/Server and release its association with the old Proxy/Server as specified in Section 3.16.5. o When an AERO Proxy/Server receives persistent link-layer Destination Unreachable messages in response to carrier packets that it sends to one of its neighbor Clients, the Proxy/Server should mark the underlying path as unusable and use another underlying path. o When an AERO Proxy/Server receives link-layer Destination Unreachable messages in response to a carrier packet that it sends to one of its permanent neighbors, it treats the messages as an indication that the path to the neighbor may be failing. However, the dynamic routing protocol should soon reconverge and correct the temporary outage. When an AERO Bridge receives a carrier packet for which the network- layer destination address is covered by an MSP, the Bridge drops the packet if there is no more-specific routing information for the destination and returns an OMNI interface Destination Unreachable message subject to rate limiting. When an AERO node receives a carrier packet for which reassembly is currently congested, it returns an OMNI interface Packet Too Big (PTB) message as discussed in [I-D.templin-6man-omni] (note that the PTB messages could indicate either "hard" or "soft" errors). AERO nodes include ICMPv6 error messages intended for the OAL source as sub-options in the OMNI option of secured uNA messages. When the OAL source receives the uNA message, it can extract the ICMPv6 error message enclosed in the OMNI option and either process it locally or translate it into a network-layer error to return to the original source. 3.12. AERO Router Discovery, Prefix Delegation and Autoconfiguration AERO Router Discovery, Prefix Delegation and Autoconfiguration are coordinated as discussed in the following Sections. Templin Expires February 13, 2022 [Page 52] Internet-Draft AERO August 2021 3.12.1. AERO Service Model Each AERO Proxy/Server on the OMNI link is configured to facilitate Client prefix delegation/registration requests. Each Proxy/Server is provisioned with a database of MNP-to-Client ID mappings for all Clients enrolled in the AERO service, as well as any information necessary to authenticate each Client. The Client database is maintained by a central administrative authority for the OMNI link and securely distributed to all Proxy/Servers, e.g., via the Lightweight Directory Access Protocol (LDAP) [RFC4511], via static configuration, etc. Clients receive the same service regardless of the Proxy/Servers they select. Clients associate each of their underlying interfaces with a FHS Proxy/Server. Each FHS Proxy/Server may locally service one or more of the Client's underlying interfaces, and the Client selects one among them to serve as the Hub Proxy/Server. The Hub Proxy/Server is responsible for short-term packet forwarding, for acting as a mobility anchor point and for acting as an ROR for NS(AR) messages directed to the Client. All of the Client's other FHS Proxy/Servers forward proxyed copies of RS/RA messages between the Hub Proxy/Server and Client without assuming the Hub role functions themselves. Each Client associates with a single Hub Proxy/Server at a time, while all FHS Proxy/Servers are candidates for providing the Hub role for other Clients. An FHS Proxy/Server assumes the Hub role when it receives an RS message with its own ADM-LLA or link-scoped All- Routers multicast as the destination. An FHS Proxy/Server assumes the proxy role when it receives an RS message with the ADM-LLA of another Proxy/Server as the destination. (An FHS Proxy/Server can also assume the proxy role when it receives an RS message addressed to link-scoped All-Routers multicast if it can determine the ADM-LLA of another Proxy/Server to serve as a Hub.) AERO Clients and Proxy/Servers use IPv6 ND messages to maintain neighbor cache entries. AERO Proxy/Servers configure their OMNI interfaces as advertising NBMA interfaces, and therefore send unicast RA messages with a short Router Lifetime value (e.g., ReachableTime seconds) in response to a Client's RS message. Thereafter, Clients send additional RS messages to keep Proxy/Server state alive. AERO Clients and Hub Proxy/Servers include prefix delegation and/or registration parameters in RS/RA messages (see [I-D.templin-6man-omni]). The IPv6 ND messages are exchanged between the Client and Hub Proxy/Server (via any FHS Proxy/Servers acting as proxies) according to the prefix management schedule required by the service. If the Client knows its MNP in advance, it can employ prefix registration by including its MNP-LLA as the source address of Templin Expires February 13, 2022 [Page 53] Internet-Draft AERO August 2021 an RS message and with an OMNI option with valid prefix registration information for the MNP. If the Hub Proxy/Server accepts the Client's MNP assertion, it injects the MNP into the routing system and establishes the necessary neighbor cache state. If the Client does not have a pre-assigned MNP, it can instead employ prefix delegation by including the unspecified address (::) as the source address of an RS message and with an OMNI option with prefix delegation parameters to request an MNP. The following sections specify the Client and Proxy/Server behavior. 3.12.2. AERO Client Behavior AERO Clients discover the addresses of candidate FHS Proxy/Servers by resolving the Potential Router List (PRL) in a similar manner as described in [RFC5214]. Discovery methods include static configuration (e.g., a flat-file map of Proxy/Server addresses and locations), or through an automated means such as Domain Name System (DNS) name resolution [RFC1035]. Alternatively, the Client can discover Proxy/Server addresses through a layer 2 data link login exchange, or through a unicast RA response to a multicast/anycast RS as described below. In the absence of other information, the Client can resolve the DNS Fully-Qualified Domain Name (FQDN) "linkupnetworks.[domainname]" where "linkupnetworks" is a constant text string and "[domainname]" is a DNS suffix for the OMNI link (e.g., "example.com"). To associate with a Hub Proxy/Server over a first underlying interface, the Client acts as a requesting router to request MNPs by preparing an RS message with prefix management parameters. If the Client already knows the Proxy/Server's ADM-LLA, it includes the LLA as the network-layer destination address; otherwise, the Client includes link-scoped All-Routers multicast as the network-layer destination. The Client can use its MNP-LLA as the network-layer source address and include an OMNI option with prefix registration information. If the Client does not yet have an MNP-LLA, it instead sets the network-layer source address to unspecified (::) and includes prefix delegation parameters in the OMNI option (see: [I-D.templin-6man-omni]). The Client next includes an authentication sub-option if necessary and Multilink Forwarding Parameters corresponding to the underlying interface over which it will send the RS message. Next, the Client submits the RS for OAL encapsulation and fragmentation if necessary with its own MNP-ULA and the Proxy/Server's ADM-ULA or an OMNI IPv6 anycast address as the OAL addresses while selecting an Identification value and invoking window synchronization as specified in [I-D.templin-6man-omni]. Templin Expires February 13, 2022 [Page 54] Internet-Draft AERO August 2021 The Client then sends the RS (either directly via Direct interfaces, via a VPN for VPNed interfaces, via an access router for ANET interfaces or via INET encapsulation for INET interfaces) then waits up to RetransTimer milliseconds for an RA message reply (see Section 3.12.3) (retrying up to MAX_RTR_SOLICITATIONS). If the Client receives no RAs, or if it receives an RA with Router Lifetime set to 0, the Client SHOULD abandon attempts through the first candidate Hub Proxy/Server and try another FHS Proxy/Server. Otherwise, the Client processes the prefix information found in the RA message. When the Client processes an RA, it first performs OAL reassembly and decapsulation if necessary then creates a NCE with the Hub Proxy/ Server's ADM-LLA as the network-layer address and the Hub Proxy/ Server's encapsulation and/or link-layer addresses as the link-layer address. The Client then caches the Multilink Forwarding Parameters information. The Client next records the RA Router Lifetime field value in the NCE as the time for which the Hub Proxy/Server has committed to maintaining the MNP in the routing system via this underlying interface, and caches the other RA configuration information including Cur Hop Limit, M and O flags, Reachable Time and Retrans Timer. The Client then autoconfigures MNP-LLAs for any delegated MNPs and assigns them to the OMNI interface. The Client also caches any MSPs included in Route Information Options (RIOs) [RFC4191] as MSPs to associate with the OMNI link, and assigns the MTU value in the MTU option to the underlying interface. The Client then registers its additional underlying interfaces with FHS Proxy/Servers for those interfaces discovered by sending RS messages via each additional interface but with the ADM-LLA of the Hub Proxy/Server as the destination. The additional FHS Proxy/ Servers will assume the proxy role and forward proxyed copies of the RS/RA exchanges between the Client and Hub Proxy/Server. The Client finally sub-delegates the MNPs to its attached EUNs and/or the Client's own internal virtual interfaces as described in [I-D.templin-v6ops-pdhost] to support the Client's downstream attached "Internet of Things (IoT)". The Client then sends additional RS messages over each underlying interface before the Router Lifetime received for that interface expires. After the Client registers its underlying interfaces, it may wish to change one or more registrations, e.g., if an interface changes address or becomes unavailable, if traffic selectors change, etc. To do so, the Client prepares an RS message to send over any available underlying interface as above. The RS includes an OMNI option with prefix registration/delegation information and with Multilink Forwarding Parameters specific to the selected underlying interface. When the Client receives the Hub Proxy/Server's RA response, it has Templin Expires February 13, 2022 [Page 55] Internet-Draft AERO August 2021 assurance that the Proxy/Server has been updated with the new information. If the Client wishes to discontinue use of a Hub Proxy/Server it issues an RS message over any underlying interface with an OMNI option with a prefix release indication. When the Hub Proxy/Server processes the message, it releases the MNP, sets the NCE state for the Client to DEPARTED and returns an RA reply with Router Lifetime set to 0. After a short delay (e.g., 2 seconds), the Hub Proxy/ Server withdraws the MNP from the routing system. 3.12.3. AERO Proxy/Server Behavior AERO Proxy/Servers act as both IP routers and IPv6 ND proxies, and support a prefix delegation/registration service for Clients. Proxy/ Servers arrange to add their ADM-LLAs to the PRL maintained in a static map of Proxy/Server addresses for the link, the DNS resource records for the FQDN "linkupnetworks.[domainname]", etc. before entering service. The PRL should be arranged such that Clients can discover the addresses of Proxy/Servers that are geographically and/ or topologically "close" to their underlying network connections. When an FHS Proxy/Server receives a prospective Client's RS message, it SHOULD return an immediate RA reply with Router Lifetime set to 0 if it is currently too busy or otherwise unable to service the Client. Otherwise, the Proxy/Server performs OAL reassembly if necessary, then decapsulates and authenticates the RS message. If the RS message destination is link-scoped All-Routers multicast or the Proxy/Server's own ADM-LLA, the Proxy/Server assumes the Hub role. If the RS message destination is the ADM-LLA of another node, the Proxy/Server assumes the proxy role and forwards the RS to the Hub Proxy/server via the secured spanning tree. (An FHS Proxy/Server can also assume the proxy role when it receives an RS message addressed to link-scoped All-Routers multicast if it can determine the ADM-LLA of another Proxy/Server to serve as a Hub.) The Hub Proxy/Server then determines the correct MNPs to provide to the Client by processing the MNP-LLA prefix parameters and/or the DHCPv6 OMNI sub-option. When the Hub Proxy/Server returns the MNPs, it also creates a forwarding table entry for the MNP-ULA corresponding to each MNP resulting in a BGP update (see: Section 3.2.3). For IPv6, the Hub Proxy/Server creates an IPv6 forwarding table entry for each MNP. For IPv4, the Hub Proxy/Server creates an IPv6 forwarding table entry with the IPv4-compatibility MNP-ULA prefix corresponding to the IPv4 address. The Hub Proxy/Server next creates a NCE for the Client using the base MNP-LLA as the network-layer address. Next, the Hub Proxy/Server Templin Expires February 13, 2022 [Page 56] Internet-Draft AERO August 2021 updates the NCE by recording the information in the Multilink Forwarding Parameters sub-option in the RS OMNI option. The Hub Proxy/Server also records the actual OAL/*NET addresses and RS message window synchronization parameters (if any) in the NCE. Next, the Hub Proxy/Server prepares an RA message using its ADM-LLA as the network-layer source address and the network-layer source address of the RS message as the network-layer destination address. The Hub Proxy/Server sets the Router Lifetime to the time for which it will maintain both this underlying interface individually and the NCE as a whole. The Hub Proxy/Server also sets Cur Hop Limit, M and O flags, Reachable Time and Retrans Timer to values appropriate for the OMNI link. The Hub Proxy/Server includes the MNPs, any other prefix management parameters and an OMNI option with a Multilink Forwarding Parameters sub-option with FHS addressing information filled out. The Hub Proxy/Server then includes one or more RIOs that encode the MSPs for the OMNI link, plus an MTU option (see Section 3.9). The Hub Proxy/Server finally forwards the message to the Client using OAL encapsulation/fragmentation if necessary while including an acknowledgement if the RS invoked window synchronization. After the initial RS/RA exchange, the Hub Proxy/Server maintains a ReachableTime timer for each of the Client's underlying interfaces individually (and for the Client's NCE collectively) set to expire after ReachableTime seconds. If the Client (or an FHS Proxy/Server) issues additional RS messages, the Hub Proxy/Server sends an RA response and resets ReachableTime. If the Hub Proxy/Server receives an IPv6 ND message with a prefix release indication it sets the Client's NCE to the DEPARTED state and withdraws the MNP from the routing system after a short delay (e.g., 2 seconds). If ReachableTime expires before a new RS is received on an individual underlying interface, the Hub Proxy/Server marks the interface as DOWN. If ReachableTime expires before any new RS is received on any individual underlying interface, the Hub Proxy/Server sets the NCE state to STALE and sets a 10 second timer. If the Hub Proxy/Server has not received a new RS or uNA message with a prefix release indication before the 10 second timer expires, it deletes the NCE and withdraws the MNP from the routing system. The Hub Proxy/Server processes any IPv6 ND messages pertaining to the Client and returns an NA/RA reply in response to solicitations. The Hub Proxy/Server may also issue unsolicited RA messages, e.g., with reconfigure parameters to cause the Client to renegotiate its prefix delegation/registrations, with Router Lifetime set to 0 if it can no longer service this Client, etc. Finally, If the NCE is in the DEPARTED state, the Hub Proxy/Server deletes the entry after DepartTime expires. Templin Expires February 13, 2022 [Page 57] Internet-Draft AERO August 2021 The Hub Proxy/Server may also receive carrier packets via the secured spanning tree that contain initial data packets sent while route optimization is in progress. The Hub Proxy/Server reassembles, then re-encapsulates/re-fragments and forwards the packets to the target Client. Although these fragments will have traversed the secured spanning tree, the security only assures correct reassembly and does not assure message content security. Note: Clients SHOULD notify former Hub Proxy/Servers of their departures, but Hub Proxy/Servers are responsible for expiring neighbor cache entries and withdrawing routes even if no departure notification is received (e.g., if the Client leaves the network unexpectedly). Hub Proxy/Servers SHOULD therefore set Router Lifetime to ReachableTime seconds in solicited RA messages to minimize persistent stale cache information in the absence of Client departure notifications. A short Router Lifetime also ensures that proactive RS/RA messaging between Clients and FHS Proxy/Servers will keep any NAT state alive (see above). Note: All Proxy/Servers on an OMNI link MUST advertise consistent values in the RA Cur Hop Limit, M and O flags, Reachable Time and Retrans Timer fields the same as for any link, since unpredictable behavior could result if different Proxy/Servers on the same link advertised different values. 3.12.3.1. DHCPv6-Based Prefix Registration When a Client is not pre-provisioned with an MNP-LLA, it will need for the Hub Proxy/Server to select one or more MNPs on its behalf and set up the correct state in the AERO routing service. (A Client with a pre-provisioned MNP may also request the Hub Proxy/Server to select additional MNPs.) The DHCPv6 service [RFC8415] is used to support this requirement. When a Client needs to have the Hub Proxy/Server select MNPs, it sends an RS message with source address set to the unspecified address (::) and with an OMNI option that includes a DHCPv6 message sub-option with DHCPv6 Prefix Delegation (DHCPv6-PD) parameters. When the Hub Proxy/Server receives the RS message, it extracts the DHCPv6-PD message from the OMNI option. The Hub Proxy/Server then acts as a "Proxy DHCPv6 Client" in a message exchange with the locally-resident DHCPv6 server, which delegates MNPs and returns a DHCPv6-PD Reply message. (If the Hub Proxy/Server wishes to defer creation of MN state until the DHCPv6-PD Reply is received, it can instead act as a Lightweight DHCPv6 Relay Agent per [RFC6221] by encapsulating the DHCPv6-PD message in a Templin Expires February 13, 2022 [Page 58] Internet-Draft AERO August 2021 Relay-forward/reply exchange with Relay Message and Interface ID options.) When the Hub Proxy/Server receives the DHCPv6-PD Reply, it adds a route to the routing system and creates an MNP-LLA based on the delegated MNP. The Hub Proxy/Server then sends an RA back to the Client with the (newly-created) MNP-LLA as the destination address and with the DHCPv6-PD Reply message coded in the OMNI option. When the Client receives the RA, it creates a default route, assigns the Subnet Router Anycast address and sets its MNP-LLA based on the delegated MNP. Note: See [I-D.templin-6man-omni] for an MNP delegation alternative that avoids including a DHCPv6 message sub-option in the RS. Namely, when the Client requests a single MNP it can set the RS source to the unspecified address (::) and include a Node Identification sub-option and Preflen in the OMNI option (but with no DHCPv6 message sub- option). When the Hub Proxy/Server receives the RS message, it forwards a self-generated DHCPv6 Solicit message to the DHCPv6 server on behalf of the Client. When the Hub Proxy/Server receives the DHCPv6 Reply, it prepares an RA message with an OMNI option with Preflen information (but with no DHCPv6 message sub-option), then places the (newly-created) MNP-LLA in the RA destination address and returns the message to the Client. 3.13. AERO Proxy/Server Coordination OMNI link Clients register with FHS Proxy/Servers for each underlying interface. Each of the Client's FHS Proxy/Servers must inform a single Hub Proxy/Server of all of the Client's additional underlying interfaces. For Clients on Direct and VPNed underlying interfaces, the FHS Proxy/Server for each interface is directly connected, for Clients on ANET underlying interfaces the FHS Proxy/Server is located on the ANET/INET boundary, and for Clients on INET underlying interfaces the FHS Proxy/Server is located somewhere in the connected Internetwork. When FHS Proxy/Server "A" processes a Client registration, it must either assume the Hub role or forward a proxyed registration to another FHS Proxy/Server acting as the Hub. Proxy/ Servers satisfy these requirements as follows: o when Proxy/Server "A" receives a Client RS message, it first verifies that the OAL Identification is within the window for the NCE that matches the MNP-ULA for this Client neighbor and authenticates the message. (If no NCE was found, Proxy/Server "A instead creates one in the STALE state and returns an RA message with an authentication signature if necessary and any window synchronization parameters.) Proxy/Server "A" then examines the network-layer destination address. If the destination address is Templin Expires February 13, 2022 [Page 59] Internet-Draft AERO August 2021 the ADM-LLA of a different Proxy/Server "B", Proxy/Server "A" prepares a separate proxyed version of the RS message with an OAL header with source set to its own ADM-ULA and destination set to Proxy/Server B's ADM-ULA. Proxy/Server "A" also writes its own information over the Multilink Forwarding Parameters sub-option supplied by the Client then sets the S/T-omIndex to the value for this Client underlying interface, then forwards the message into the OMNI link secured spanning tree. o when Proxy/Server "B" receives the RS, it assume the Hub role and creates or updates a NCE for the Client with FHS Proxy/Server "A"'s Multilink Forwarding Parameters as the link-layer address information for this S/T-omIndex and caches any window synchronization parameters supplied by the Client. Hub Proxy/ Server "B" then prepares an RA message with source set to its own LLA and destination set to the Client's MNP-LLA, and with any window synchronization acknowledgements. Hub Proxy/Server "B" then encapsulates the RA in an OAL header with source set to its own ADM-ULA and destination set to the ADM-ULA of FHS Proxy/Server "A, performs fragmentation if necessary, then sends the resulting carrier packets into the secured spanning tree. o when Proxy/Server "A" reassembles the RA, it locates the Client NCE based on the RA destination LLA. Proxy/Server "A" then re- encapsulates the RA message with OAL source set to its own ADM-ULA and OAL destination set to the MNP-ULA of the Client, includes an authentication signature if necessary, and echoes the Multilink Forwarding Parameters sub-option. Proxy/Server "A" sets the P flag in the RA flags field to indicate that the message has passed through a proxy [RFC4389], then fragments the RA if necessary and returns the fragments to the Client. o The Client repeats this process over each of its additional underlying interfaces while treating each FHS Proxy/Server "C", "D", "E", etc. as a proxy to facilitate RS/RA exchanges between the Hub and the Client. After the initial RS/RA exchanges each FHS Proxy/Server forwards any of the Client's carrier packets with OAL destinations for which there is no matching NCE to a Bridge using OAL encapsulation with its own ADM-ULA as the source and with destination determined by the Client. The Proxy/Server instead forwards any carrier packets destined to a neighbor cache target directly to the target according to the OAL/ link-layer information - the process of establishing neighbor cache entries is specified in Section 3.14. While the Client is still associated with each FHS Proxy/Server "A", "A" can send NS, RS and/or unsolicited NA messages to update the Templin Expires February 13, 2022 [Page 60] Internet-Draft AERO August 2021 neighbor cache entries of other AERO nodes on behalf of the Client and/or to convey Multilink Forwarding Parameter updates. This allows for higher-frequency Proxy-initiated RS/RA messaging over well- connected INET infrastructure supplemented by lower-frequency Client- initiated RS/RA messaging over constrained ANET data links. If the Hub Proxy/Server "A" ceases to send solicited RAs, Proxy/ Servers "B", "C", "D" send unsolicited RAs over the Client's underlying interface with destination set to (link-local) All-Nodes multicast and with Router Lifetime set to zero to inform Clients that the Hub Proxy/Server has failed. Although Proxy/Servers "B", "C" and "D" can engage in IPv6 ND exchanges on behalf of the Client, the Client can also send IPv6 ND messages on its own behalf, e.g., if it is in a better position to convey state changes. The IPv6 ND messages sent by the Client include the Client's MNP-LLA as the source in order to differentiate them from the IPv6 ND messages sent by Proxy/Server "A". If the Client becomes unreachable over all underlying interface it serves, the Hub Proxy/Server sets the NCE state to DEPARTED and retains the entry for DepartTime seconds. While the state is DEPARTED, the Hub Proxy/Server forwards any carrier packets destined to the Client to a Bridge via OAL encapsulation. When DepartTime expires, the Hub Proxy/Server deletes the NCE and discards any further carrier packets destined to the former Client. In some ANETs that employ a Proxy/Server, the Client's MNP can be injected into the ANET routing system. In that case, the Client can send original IP packets without invoking the OAL so that the ANET routing system transports the original IP packets to the Proxy. This can be very beneficial, e.g., if the Client connects to the ANET via low-end data links such as some aviation wireless links. If the ANET first-hop access router is on the same underlying link as the Client and recognizes the AERO/OMNI protocol, the Client can avoid OAL encapsulation for both its control and data messages. When the Client connects to the link, it can send an unencapsulated RS message with source address set to its own MNP-LLA (or to a Temporary LLA), and with destination address set to the ADM-LLA of the Client's selected Proxy/Server or to link-scoped All-Routers multicast. The Client includes an OMNI option formatted as specified in [I-D.templin-6man-omni]. The Client then sends the unencapsulated RS message, which will be intercepted by the AERO-Aware access router. The ANET access router then performs OAL encapsulation on the RS message and forwards it to a Proxy/Server at the ANET/INET boundary. When the access router and Proxy/Server are one and the same node, the Proxy/Server would share and underlying link with the Client but Templin Expires February 13, 2022 [Page 61] Internet-Draft AERO August 2021 its message exchanges with outside correspondents would need to pass through a security gateway at the ANET/INET border. The method for deploying access routers and Proxys (i.e. as a single node or multiple nodes) is an ANET-local administrative consideration. Note: When a Proxy/Server alters the IPv6 ND message contents before forwarding (e.g., such as altering the OMNI option contents), the IPv6 ND message checksum and/or authentication signature are invalidated. If the Proxy/Server forwards the message over the secured spanning tree, however, it need not re-calculate the checksum/signature since they will not be examined by the next hop. Note: When a Proxy/Server receives a secured Client NS message, it performs the same proxying procedures as for described for RS messages above. The proxying procedures for NS/NA message exchanges is specified in Section 3.14. 3.13.1. Detecting and Responding to Proxy/Server Failures In environments where fast recovery from Proxy/Server failure is required, FHS Proxy/Servers SHOULD use proactive Neighbor Unreachability Detection (NUD) to track Hub Proxy/Server reachability in a similar fashion as for Bidirectional Forwarding Detection (BFD) [RFC5880]. Each FHS Proxy/Server can then quickly detect and react to failures so that cached information is re-established through alternate paths. The NS/NA(NUD) control messaging is carried only over well-connected ground domain networks (i.e., and not low-end aeronautical radio links) and can therefore be tuned for rapid response. FHS Proxy/Servers perform continuous NS/NA(NUD) exchanges with the Hub Proxy/Server in rapid succession, e.g., one exchange per second. The FHS Proxy/Server sends the NS(NUD) message via the spanning tree with its own ADM-LLA as the source and the ADM-LLA of the Hub Proxy/ Server as the destination, and the Hub Proxy/Server responds with an NA(NUD). When the FHS Proxy/Server is also sending RS messages to a Hub Proxy/Server on behalf of Clients, the resulting RA responses can be considered as equivalent hints of forward progress. This means that the FHS Proxy/Server need not also send a periodic NS(NUD) if it has already sent an RS within the same period. If the Hub Proxy/ Server fails (i.e., if the FHS Proxy/Server ceases to receive advertisements), the FHS Proxy/Server can quickly inform Clients by sending unsolicited RA messages The FHS Proxy/Server sends unsolicited RA messages with source address set to the Hub Proxy/Server's address, destination address set to (link-local) All-Nodes multicast, and Router Lifetime set to 0. The FHS Proxy/Server SHOULD send MAX_FINAL_RTR_ADVERTISEMENTS RA Templin Expires February 13, 2022 [Page 62] Internet-Draft AERO August 2021 messages separated by small delays [RFC4861]. Any Clients that had been using the failed Hub Proxy/Server will receive the RA messages and select one of its other FHS Proxy/Servers to assume the Hub role (i.e., by sending an RS with destination set to the ADM-LLA of the new Hub). 3.14. AERO Route Optimization AERO nodes invoke route optimization when they need to forward packets to new target destinations. Route optimization is based on IPv6 ND Address Resolution messaging between a Route Optimization Source (ROS) and the target Client's current Hub Proxy/Server acting as a Route Optimization Responder (ROR). Route optimization is initiated by the first eligible ROS closest to the source as follows: o For Clients on VPNed and Direct interfaces, the Client's FHS Proxy/Server is the ROS. o For Clients on ANET interfaces, either the Client or the FHS Proxy/Server may be the ROS. o For Clients on INET interfaces, the Client itself is the ROS. o For correspondent nodes on INET/EUN interfaces serviced by a Relay, the Relay is the ROS. The route optimization procedure is conducted between the ROS and the LHS Hub Proxy/Server/Relay for the target selected by routing as the ROR. In this arrangement, the ROS is always the Client or Proxy/ Server (or Relay) nearest the source over the selected source underlying interface, while the ROR is always the target's current Hub Proxy/Server. The AERO routing system directs a route optimization request sent by the ROS to the ROR, which returns a route optimization reply which must include information that is current, consistent and authentic. The ROS is responsible for periodically refreshing the route optimization, and the ROR is responsible for quickly informing the ROS of any changes. The procedures are specified in the following sections. 3.14.1. Route Optimization Initiation When an original IP packet from a source node destined to a target node arrives, the ROS checks for a NCE with an MNP-LLA that matches the target destination. If there is a NCE in the REACHABLE state, the ROS invokes the OAL and forwards the resulting carrier packets Templin Expires February 13, 2022 [Page 63] Internet-Draft AERO August 2021 according to the cached state then returns from processing. Otherwise, if there is no NCE the ROS creates one in the INCOMPLETE state. The ROS next invokes the OAL and forwards the resulting carrier packets into the secured spanning tree, then sends an NS message for Address Resolution (NS(AR)) to receive a solicited NA(AR) message from the ROR. While route optimization is in progress, the ROS may forward additional original IP packets into the secured spanning tree but if so must impose rate limiting to minimize secured spanning tree traffic as well as ROR reassembly. The NS(AR) message must be sent securely, and includes: o the LLA of the ROS as the source address. o the MNP-LLA corresponding to the original IP packet's destination as the Target Address, e.g., for 2001:db8:1:2::10:2000 the Target Address is fe80::2001:db8:1:2. o the Solicited-Node multicast address [RFC4291] formed from the lower 24 bits of the original IP packet's destination as the destination address, e.g., for 2001:db8:1:2::10:2000 the NS(AR) destination address is ff02:0:0:0:0:1:ff10:2000. The NS(AR) message also includes an OMNI option with an authentication sub-option if necessary and with Preflen set to the prefix length associated with the NS(AR) source. The ROS then selects an Identification value and submits the NS(AR) message for OAL encapsulation with OAL source set to its own ULA and OAL destination set to the ULA corresponding to the target. (The ROS does not include any window synchronization parameters, since it will not exchange other packet types with the ROR.) The ROS then sends the resulting carrier packet into the SRT secured spanning tree without decrementing the network-layer TTL/Hop Limit field. When the ROS is an INET Client, it must instead forward the resulting carrier packet to the ADM-ULA of one of its current Proxy/Servers. The Proxy/Server then verifies the NS(AR) authentication signature, then re-encapsulates with the OAL source set to its own ADM-ULA and OAL destination set to the ULA corresponding to the target and forwards the resulting carrier packets into the secured spanning tree on behalf of the Client. Templin Expires February 13, 2022 [Page 64] Internet-Draft AERO August 2021 3.14.2. Relaying the NS(AR) *NET Packet(s) When the Bridge receives the carrier packet containing the RS from the ROS, it discards the *NET headers and determines the next hop by consulting its standard IPv6 forwarding table for the OAL header destination address. The Bridge then decrements the OAL header Hop- Limit, then re-encapsulates and forwards the carrier packet(s) via the secured spanning tree the same as for any IPv6 router, where it may traverse multiple OMNI link segments. The final-hop Bridge will deliver the carrier packet via the secured spanning tree to the ROR for the target. 3.14.3. Processing the NS(AR) and Sending the NA(AR) When the ROR for the target receives the secured carrier packet, it examines the NS(AR) target to determine whether it has a matching NCE and/or non-MNP route. If there is no match, the ROR drops the message. Otherwise, the ROR continues processing as follows: o if the NS(AR) target matches a Client NCE in the DEPARTED state, the ROR re-encapsulates while setting the OAL source to the ULA of the ROS and OAL destination address to the ADM-ULA of the Client's new Proxy/Server. The ROR then forwards the resulting carrier packet over the secured spanning tree then returns from processing. o If the NS(AR) target matches the MNP-LLA of a Client NCE in the REACHABLE state, the ROR notes whether the NS (AR) arrived from the secured spanning tree then provides route optimization information on behalf of the Client. If the message arrived via the secured spanning tree the ROR need not perform further authentication; otherwise, it must verify the message authentication signature before accepting. o If the NS(AR) target matches one of its non-MNP routes, the ROR serves as both a Relay and a route optimization target, since the Relay forwards IP packets toward the (fixed network) target at the network layer. The ROR next checks the target NCE for a Report List entry that matches the NS(AR) source LLA/ULA of the ROS. If there is a Report List entry, the ROR refreshes ReportTime for this ROR; otherwise, the ROR creates a new entry for the ROS and records both the LLA and ULA. The ROR then prepares a (solicited) NA(AR) message to return to the ROS with the source address set to its own ADM-LLA, the destination address set to the NS(AR) LLA source address and the Target Address set to the target Client's MNP-LLA. The ROR includes an OMNI option Templin Expires February 13, 2022 [Page 65] Internet-Draft AERO August 2021 with Preflen set to the prefix length associated with the NA(AR) source address, with S/T-omIndex set to the value that appeared in the NS(AR) and with Interface Attributes sub-options for all of the target's underlying interfaces with current information for each interface. For each Interface Attributes sub-option, the ROR sets the L2ADDR according to its own INET address for VPNed, Direct, ANET and NATed Client interfaces, or to the Client's INET address for native Client interfaces. The ROR then includes the lower 32 bits of its ADM-ULA as the LHS, encodes the ADM-ULA SRT prefix length in the SRT field and sets FMT as specified in Section 3.3. The ROR then sets the NA(AR) message R flag to 1 (as a router) and S flag to 1 (as a response to a solicitation) and sets the O flag to 0 (as a proxy). The ROR finally submits the NA(AR) for OAL encapsulation with source set to its own ULA and destination set to the same ULA that appeared in the NS(AR) OAL source, then performs OAL encapsulation using the same Identification value that appeared in the NS(AR) and finally forwards the resulting (*NET-encapsulated) carrier packet via the secured spanning tree without decrementing the network-layer TTL/Hop Limit field. 3.14.4. Relaying the NA(AR) When the Bridge receives NA(AR) carrier packet from the ROR, it discards the *NET header and determines the next hop by consulting its standard IPv6 forwarding table for the OAL header destination address. The Bridge then decrements the OAL header Hop-Limit, re- encapsulates the carrier packet and forwards it via the SRT secured spanning tree, where it may traverse multiple OMNI link segments. The final-hop Bridge will deliver the carrier packet via the secured spanning tree to a Proxy/Server for the ROS. 3.14.5. Processing the NA(AR) When the ROS receives the NA(AR) message, it first searches for a NCE that matches the NA(AR) target address. The ROS then processes the message the same as for standard IPv6 Address Resolution [RFC4861]. In the process, it caches all OMNI option information in the target NCE (including all Interface Attributes), and caches the NA(AR) ADM-{LLA,ULA} source addresses as the addresses of the ROR. If the ROS receives additional NA(AR) or uNA messages for this target Client with the same ADM-LLA source address but a different ADM-ULA source address, it configures the ADM-LLA corresponding to the new ADM-ULA, then caches the new ADM-{LLA,ULA} and deprecates the former ADM-{LLA,ULA}. Templin Expires February 13, 2022 [Page 66] Internet-Draft AERO August 2021 When the ROS is a Client, the SRT secured spanning tree will first deliver the solicited NA(AR) message to the local Proxy/Server, which re-encapsulates and forwards the message to the Client. If the Client is on a well-managed ANET, physical security and protected spectrum ensures security for the unmodified NA(AR); if the Client is on the open INET the Proxy/Server must instead include an authentication signature (while adjusting the OMNI option size, if necessary). The Proxy/Server uses its own ADM-ULA as the OAL source and the MNP-ULA of the Client as the OAL destination. 3.14.6. Forwarding Packets to Route Optimized Targets After the ROS receives the route optimization NA(AR) and updates the target NCE, it sends additional NS(AR) messages to the ADM-ULA of the ROR to refresh the NCE ReachableTime before expiration while it still has sustained interest in this target. While the NCE remains REACHABLE, the ROS can forward packets along paths that use best underlying interface pairs based on local preferences and target Interface Attributes. The ROS selects target underlying interfaces according to traffic selectors and/or any other traffic discriminators, but must first establish window synchronization state for each target if necessary. The ROS initiates window synchronization through a secured uncast NS/ NA(WIN) exchange as specified in Section 3.2.7. The NS/NA(WIN) exchange is conducted over a first underlying interface pair and registers only those interfaces. If the ROS and target have additional underlying interface pairs serviced by the same source/ destination LLAs, they may register new interfaces by sending additional NS/NA(WIN) messages but need not include window synchronization parameters. If the ROS and target have additional underlying interface pairs services by different source/destination LLAs, they must include window synchronization parameters when they send NS/NA(WIN) messages to establish NCE state for the new source/ destination LLAs. After window synchronization state has been established, the ROS and target Client can begin forwarding carrier packets while performing additional NS/NA(WIN) exchanges as above to update window state, register new interfaces and/or test reachability. The ROS sends carrier packets to the FHS Bridge discovered through the NS/NA(WIN) exchange which verifies the Identification is in window for the target Client. The FHS Bridge then forwards the carrier packets over the unsecured spanning tree to the LHS Bridge, which forwards them via LHS encapsulation to the LHS Proxy/Server or directly to the target Client itself. The target Client in turn sends packets to the ROS in the reverse direction while forwarding through the Bridges to minimize Proxy/Server load whenever possible. Templin Expires February 13, 2022 [Page 67] Internet-Draft AERO August 2021 While the ROS continues to actively forward packets to the target Client, it is responsible for updating window synchronization state and per-interface reachability before expiration. Window synchronization state is shared by all underlying interfaces in the ROS' NCE that use the same destination LLA so that a single NS/ NA(WIN) exchange applies for all interfaces regardless of the (single) interface used to conduct the exchange. However, the window synchronization exchange only confirms target Client reachability over the specific interface used to conduct the exchange. Reachability for other underlying interfaces that share the same window synchronization state must be determined individually using NS/NA(NUD) messages which need not be secured as long as they use in- window Identifications and do not update other state information. 3.15. Neighbor Unreachability Detection (NUD) AERO nodes perform Neighbor Unreachability Detection (NUD) per [RFC4861] either reactively in response to persistent link-layer errors (see Section 3.11) or proactively to confirm reachability. The NUD algorithm is based on periodic control message exchanges and may further be seeded by IPv6 ND hints of forward progress, but care must be taken to avoid inferring reachability based on spoofed information. For example, IPv6 ND message exchanges that include authentication codes and/or in-window Identifications may be considered as acceptable hints of forward progress, while spurious random carrier packets should be ignored. AERO nodes can perform NS/NA(NUD) exchanges over the OMNI link secured spanning tree (i.e. the same as described above for NS/ NA(WIN)) to test reachability without risk of DoS attacks from nodes pretending to be a neighbor. These NS/NA(NUD) messages use the unicast LLAs and ULAs of the parties involved in the NUD test. When only reachability information is required without updating any other NCE state, AERO nodes can instead perform NS/NA(NUD) exchanges directly between neighbors without employing the secured spanning tree as long as they include in-window Identifications and either an authentication signature or checksum. When an ROR directs an ROS to a target neighbor with one or more link-layer addresses, the ROS probes each unsecured target underlying interface either proactively or on-demand of carrier packets directed to the path by multilink forwarding to maintain the interface's state as reachable. Probing is performed through NS(NUD) messages over the SRT secured or unsecured spanning tree, or through NS(NUD) messages sent directly to an underlying interface of the target itself. While testing a target underlying interface, the ROS can optionally continue to forward carrier packets via alternate interfaces and/or Templin Expires February 13, 2022 [Page 68] Internet-Draft AERO August 2021 maintain a small queue of carrier packets until target reachability is confirmed. NS(NUD) messages are encapsulated, fragmented and transmitted as carrier packets the same as for ordinary original IP data packets, however the encapsulated destinations are the LLA of the ROS and either the ADM-LLA of the LHS Proxy/Server or the MNP-LLA of the target itself. The ROS encapsulates the NS(NUD) message the same as described in Section 3.2.7 and sets the NS(NUD) OMNI header S/ T-omIndex to identify the underlying interface used for forwarding (or to 0 if any underlying interface can be used). The ROS then fragments the OAL packet and forwards the resulting carrier packets into the unsecured spanning tree or via direct encapsulation for local segment targets. When the target receives the NS(NUD) carrier packets, it verifies that it has a NCE for this ROS and that the Identification is in- window, then submits the carrier packets for reassembly. The node then verifies the authentication signature or checksum, then searches for Interface Attributes in its NCE for the ROS that match the NS(NUD) S/T-omIndex for the NA(NUD) reply. The node then prepares the NA(NUD) with the source and destination LLAs reversed, encapsulates and sets the OAL source and destination, sets the NA(NUD) S/T-omIndex to the index of the underlying interface the NS(NUD) arrived on and sets the Target Address to the same value included in the NS(NUD). The target next sets the R flag to 1, the S flag to 1 and the O flag to 1, then selects an in-window Identification for the ROS and performs fragmentation. The node then forwards the carrier packets into the unsecured spanning tree, directly to the ROS if it is in the local segment or directly to a Bridge in the local segment. When the ROS receives the NA(NUD), it marks the target underlying interface tested as "reachable". Note that underlying interface states are maintained independently of the overall NCE REACHABLE state, and that a single NCE may have multiple target underlying interfaces in various states "reachable" and otherwise while the NCE state as a whole remains REACHABLE. Note also that the exchange of NS/NA(NUD) messages has the useful side-benefit of opening holes in NATs that may be useful for NAT traversal. For example, a Client that discovers the address of a Bridge on the local SRT segment during an NS/NA(WIN) exchange with a peer that established MFIB state can send an NS(NUD) message directly to the INET address of the Bridge while including an authentication signature. The NS(NUD) will open a hole in any NATs on the path from the Client to the Bridge, and the Bridge can verify the authentication signature before returning a direct NA(NUD) to the Templin Expires February 13, 2022 [Page 69] Internet-Draft AERO August 2021 Client's NATed L2ADDR while also including an authentication signature. Future carrier packets exchanged between the Client and peer can then be forwarded directly via the Bridge while bypassing the Client's FHS Proxy/Server. 3.16. Mobility Management and Quality of Service (QoS) AERO is a Distributed Mobility Management (DMM) service. Each Proxy/ Server is responsible for only a subset of the Clients on the OMNI link, as opposed to a Centralized Mobility Management (CMM) service where there is a single network mobility collective entity for all Clients. Clients coordinate with their associated FHS and Hub Proxy/ Servers via RS/RA exchanges to maintain the DMM profile, and the AERO routing system tracks all current Client/Proxy/Server peering relationships. Hub Proxy/Servers provide ROR, default routing and mobility anchor point services for their dependent Clients, while FHS Proxy/Servers provide a proxy conduit between the Client and the Hub. Clients are responsible for maintaining neighbor relationships with their Proxy/ Servers through periodic RS/RA exchanges, which also serves to confirm neighbor reachability. When a Client's underlying interface attributes change, the Client is responsible for updating the Hub Proxy/Server with this new information while using the FHS Proxy/ Server as a first-hop conduit. The FHS Proxy/Server can also act as a proxy to perform some IPv6 ND exchanges on the Client's behalf without consuming bandwidth on the Client underlying interface. Mobility management considerations are specified in the following sections. 3.16.1. Mobility Update Messaging RORs accommodate Client mobility and/or multilink change events by sending secured uNA messages to each ROS in the target Client's Report List. When an ROR sends a uNA message, it sets the IPv6 source address to the its own ADM-LLA, sets the destination address to the ROS LLA (i.e., an MNP-LLA if the ROS is a Client and an ADM- LLA if the ROS is a Proxy/Server) and sets the Target Address to the Client's MNP-LLA. The ROR also includes an OMNI option with Preflen set to the prefix length associated with the Client's MNP-LLA, with Interface Attributes for the target Client's underlying interfaces and with the OMNI header S/T-omIndex set to 0. The ROR then sets the uNA R flag to 1, S flag to 0 and O flag to 1, then encapsulates the message in an OAL header with source set to its own ADM-ULA and destination set to the ROS ULA (i.e., the ADM-ULA of the ROS Proxy/ Server) and sends the message into the secured spanning tree. Templin Expires February 13, 2022 [Page 70] Internet-Draft AERO August 2021 As discussed in Section 7.2.6 of [RFC4861], the transmission and reception of uNA messages is unreliable but provides a useful optimization. In well-connected Internetworks with robust data links uNA messages will be delivered with high probability, but in any case the ROR can optionally send up to MAX_NEIGHBOR_ADVERTISEMENT uNAs to each ROS to increase the likelihood that at least one will be received. Alternatively, the ROR can set the PNG flag in the uNA OMNI option header to request a solicited NA acknowledgement as specified in [I-D.templin-6man-omni]. When the ROS Proxy/Server receives a uNA message prepared as above, it ignores the message if the OAL destination is not its own ADM-ULA. If the uNA destination was its own ADM-LLA, the ROS Proxy/Server uses the included OMNI option information to update its NCE for the target but does not reset ReachableTime since the receipt of an unsolicited NA message from the ROR does not provide confirmation that any forward paths to the target Client are working. If the destination was the MNP-LLA of the ROS Client, the Proxy/Server instead re- encapsulates with the OAL source set to its own ADM-ULA, OAL destination set to the MNP-ULA of the ROS Client with an authentication signature if necessary, and with an in-window Identification for this Client. Finally, if the uNA message PNG flag was set, the ROS returns a solicited NA acknowledgement as specified in [I-D.templin-6man-omni]. In addition to sending uNA messages to the current set of ROSs for the target Client, the ROR also sends uNAs to the former Proxy/Server associated with the underlying interface for which the link-layer address has changed. These uNA messages update former Proxy/Servers that cannot easily detect (e.g., without active probing) when a formerly-active Client has departed. When the ROR sends the uNA, it sets the source address to its ADM-LLA, sets the destination address to the former Proxy/Server's ADM-LLA, and sets the Target Address to the Client's MNP-LLA. The ROR also includes an OMNI option with Preflen set to the prefix length associated with the Client's MNP- LLA, with Interface Attributes for the changed underlying interface, and with the OMNI header S/T-omIndex set to 0. The ROR then sets the uNA R flag to 1, S flag to 0 and O flag to 1, then encapsulates the message in an OAL header with source set to its own ADM-ULA and destination set to the ADM-ULA of the former Proxy/Server and sends the message into the secured spanning tree. 3.16.2. Announcing Link-Layer Address and/or QoS Preference Changes When a Client needs to change its underlying Interface Attributes (e.g., due to a mobility event), the Client sends an RS message to its Hub Proxy/Server (i.e., the ROR) via a first-hop FHS Proxy/ Server, if necessary. The RS includes an OMNI option with a Templin Expires February 13, 2022 [Page 71] Internet-Draft AERO August 2021 Multilink Forwarding Parameters sub-option with the new link quality and address information. Note that the first FHS Proxy/Server may change due to the underlying interface change; any stale state in former FHS Proxy/Servers will simply expire after ReachableTime expires with no effect on the Hub Proxy/Server. Up to MAX_RTR_SOLICITATIONS RS messages MAY be sent in parallel with sending carrier packets containing user data in case one or more RAs are lost. If all RAs are lost, the Client SHOULD re-associate with a new Proxy/Server. When the Proxy/Server receives the Client's changes, it sends uNA messages to all nodes in the Report List the same as described in the previous section. 3.16.3. Bringing New Links Into Service When a Client needs to bring new underlying interfaces into service (e.g., when it activates a new data link), it sends an RS message to the Hub Proxy/Server via a FHS Proxy/Server for the underlying interface (if necessary) with an OMNI option that includes Multilink Forwarding Parameters with appropriate link quality values and with link-layer address information for the new link. 3.16.4. Deactivating Existing Links When a Client needs to deactivate an existing underlying interface, it sends an RS message to an FHS Proxy/Server with an OMNI option with appropriate Multilink Forwarding Parameter values for the deactivated link - in particular, the link quality value 0 assures that neighbors will cease to use the link. If the Client needs to send RS messages over an underlying interface other than the one being deactivated, it MUST include Interface Attributes with appropriate link quality values for any underlying interfaces being deactivated. Note that when a Client deactivates an underlying interface, neighbors that have received the RS/uNA messages need not purge all references for the underlying interface from their neighbor cache entries. The Client may reactivate or reuse the underlying interface and/or its omIndex at a later point in time, when it will send new RS messages to an FHS Proxy/Server with fresh interface parameters to update any neighbors. Templin Expires February 13, 2022 [Page 72] Internet-Draft AERO August 2021 3.16.5. Moving Between Proxy/Servers The Client performs the procedures specified in Section 3.12.2 when it first associates with a new Hub Proxy/Server or renews its association with an existing Hub Proxy/Server. When an FHS Proxy/Server receives the Client's RS message destined to a new Hub Proxy/Server, it forwards the RS and also sends uNA messages to inform the old Hub Proxy/Server that the Client has DEPARTED. The FHS Proxy/Server sets the uNA source to the ADM-LLA of the new Hub Proxy/Server, sets the destination to the ADM-LLA of the old Hub Proxy/Server, sets the OAL source to its own ADM-ULA and sets the OAL destination to the ADM-ULA of the old Hub Proxy/Server. The FHS Proxy/Server then submits the uNA for OAL encapsulation and fragmentation, then forwards the resulting carrier packets into the secured spanning tree. When the old Hub Proxy/Server receives the uNA, it changes the Client's NCE state to DEPARTED, sets the interface attributes information for the Client to point to the new Hub Proxy/Server, and resets DepartTime. After a short delay (e.g., 2 seconds) the old Hub Proxy/Server withdraws the Client's MNP from the routing system. After DepartTime expires, the old Hub Proxy/Server deletes the Client's NCE. The old Hub Proxy/Server also iteratively sends uNA messages to each ROS in the Client's Report List with its own ADM-LLA as the source and the LLA of the ROS as the destination. The old Proxy/Server then encapsulates the uNA with OAL source address set to the ADM-ULA of the new Hub Proxy/Server and OAL destination address set to the ADM- ULA of the ROS Proxy/Server and sends the carrier packets over the secured spanning tree. When the ROS Proxy/Server receives the uNA, it forwards the message to the ROS Client if the destination is an MNP-LLA. The ROS then examines the uNA Target Address to locate the target Client's NCE and the ADM-LLA source address to identify the old Hub Proxy/Server. The ROS then caches the ULA source address as the ADM-{LLA/ULA} for the new Hub Proxy/Server for this target NCE and marks the entry as STALE. While in the STALE state, the ROS sends new NS(AR) messages using its own ULA as the OAL source and the ADM-ULA of the new Hub Proxy/Server as the OAL destination address. The new Hub Proxy/Server will then process the NS(AR) and return an NA(AR) response. Clients SHOULD NOT move rapidly between Hub Proxy/Servers in order to avoid causing excessive oscillations in the AERO routing system. Examples of when a Client might wish to change to a different Hub Proxy/Server include a Hub Proxy/Server that has gone unreachable, Templin Expires February 13, 2022 [Page 73] Internet-Draft AERO August 2021 topological movements of significant distance, movement to a new geographic region, movement to a new OMNI link segment, etc. 3.17. Multicast Clients provide an IGMP (IPv4) [RFC2236] or MLD (IPv6) [RFC3810] proxy service for its EUNs and/or hosted applications [RFC4605] and act as a Protocol Independent Multicast - Sparse-Mode (PIM-SM, or simply "PIM") Designated Router (DR) [RFC7761] on the OMNI link. Proxy/Servers act as OMNI link PIM routers for Clients on ANET, VPNed or Direct interfaces, and Relays also act as OMNI link PIM routers on behalf of nodes on other links/networks. Clients on VPNed, Direct or ANET underlying interfaces for which the ANET has deployed native multicast services forward IGMP/MLD messages into the ANET. The IGMP/MLD messages may be further forwarded by a first-hop ANET access router acting as an IGMP/MLD-snooping switch [RFC4541], then ultimately delivered to an ANET Proxy/Server. The Proxy/Server then acts as an ROS to send NS(AR) messages to an ROR. Clients on INET and ANET underlying interfaces without native multicast services instead send NS(AR) messages as an ROS to cause their Proxy/Server forward the message to an ROR. When the ROR receives an NA(AR) response, it initiates PIM protocol messaging according to the Source-Specific Multicast (SSM) and Any-Source Multicast (ASM) operational modes as discussed in the following sections. 3.17.1. Source-Specific Multicast (SSM) When an ROS "X" (i.e., either a Client or Proxy Server) acting as PIM router receives a Join/Prune message from a node on its downstream interfaces containing one or more ((S)ource, (G)roup) pairs, it updates its Multicast Routing Information Base (MRIB) accordingly. For each S belonging to a prefix reachable via X's non-OMNI interfaces, X then forwards the (S, G) Join/Prune to any PIM routers on those interfaces per [RFC7761]. For each S belonging to a prefix reachable via X's OMNI interface, X sends an NS(AR) message (see: Section 3.14) using its own LLA as the source address, the solicited node multicast address corresponding to S as the destination and the LLA of S as the target address. X then encapsulates the NS(AR) in an OAL header with source address set to its own ULA and destination address set to the ULA for S, then forwards the message into the secured spanning tree which delivers it to ROR "Y" that services S. The resulting NA(AR) will return an OMNI option with Interface Attributes for any underlying interfaces that are currently servicing S. Templin Expires February 13, 2022 [Page 74] Internet-Draft AERO August 2021 When X processes the NA(AR) it selects one or more underlying interfaces for S and performs an NS/NA(WIN) exchange over the secured spanning tree while including a PIM Join/Prune message for each multicast group of interest in the OMNI option. If S is located behind any Proxys "Z"*, each Z* then updates its MRIB accordingly and maintains the LLA of X as the next hop in the reverse path. Since Bridges forward messages not addressed to themselves without examining them, this means that the (reverse) multicast tree path is simply from each Z* (and/or S) to X with no other multicast-aware routers in the path. Following the initial combined Join/Prune and NS/NA(WIN) messaging, X maintains a NCE for each S the same as if X was sending unicast data traffic to S. In particular, X performs additional NS/NA(WIN) exchanges to keep the NCE alive for up to t_periodic seconds [RFC7761]. If no new Joins are received within t_periodic seconds, X allows the NCE to expire. Finally, if X receives any additional Join/Prune messages for (S,G) it forwards the messages over the secured spanning tree. Client C that holds an MNP for source S may later depart from a first Proxy/Server Z1 and/or connect via a new Proxy/Server Z2. In that case, Y sends a uNA message to X the same as specified for unicast mobility in Section 3.16. When X receives the uNA message, it updates its NCE for the LLA for source S and sends new Join messages in NS/NA(WIN) exchanges addressed to the new target Client underlying interface connection for S. There is no requirement to send any Prune messages to old Proxy/Server Z1 since source S will no longer source any multicast data traffic via Z1. Instead, the multicast state for (S,G) in Proxy/Server Z1 will soon expire since no new Joins will arrive. 3.17.2. Any-Source Multicast (ASM) When an ROS X acting as a PIM router receives Join/Prune messages from a node on its downstream interfaces containing one or more (*,G) pairs, it updates its Multicast Routing Information Base (MRIB) accordingly. X first performs an NS/NA(AR) exchange to receive route optimization information for Rendezvous Point (RP) R for each G. X then includes a copy of each Join/Prune message in the OMNI option of an NS(WIN) message with its own LLA as the source address and the LLA for R as the destination address, then encapsulates the NS(WIN) message in an OAL header with its own ULA as the source and the ADM- ULA of R's Proxy/Server as the destination then sends the message into the secured spanning tree. For each source S that sends multicast traffic to group G via R, Client S* that aggregates S (or its Proxy/Server) encapsulates the Templin Expires February 13, 2022 [Page 75] Internet-Draft AERO August 2021 original IP packets in PIM Register messages, includes the PIM Register messages in the OMNI options of uNA messages, performs OAL encapsulation and fragmentation then forwards the resulting carrier packets with Identification values within the receive window for Client R* that aggregates R. Client R* may then elect to send a PIM Join to S* in the OMNI option of a uNA over the secured spanning tree. This will result in an (S,G) tree rooted at S* with R as the next hop so that R will begin to receive two copies of the original IP packet; one native copy from the (S, G) tree and a second copy from the pre-existing (*, G) tree that still uses uNA PIM Register encapsulation. R can then issue a uNA PIM Register-stop message over the secured spanning tree to suppress the Register-encapsulated stream. At some later time, if Client S* moves to a new Proxy/ Server, it resumes sending original IP packets via uNA PIM Register encapsulation via the new Proxy/Server. At the same time, as multicast listeners discover individual S's for a given G, they can initiate an (S,G) Join for each S under the same procedures discussed in Section 3.17.1. Once the (S,G) tree is established, the listeners can send (S, G) Prune messages to R so that multicast original IP packets for group G sourced by S will only be delivered via the (S, G) tree and not from the (*, G) tree rooted at R. All mobility considerations discussed for SSM apply. 3.17.3. Bi-Directional PIM (BIDIR-PIM) Bi-Directional PIM (BIDIR-PIM) [RFC5015] provides an alternate approach to ASM that treats the Rendezvous Point (RP) as a Designated Forwarder (DF). Further considerations for BIDIR-PIM are out of scope. 3.18. Operation over Multiple OMNI Links An AERO Client can connect to multiple OMNI links the same as for any data link service. In that case, the Client maintains a distinct OMNI interface for each link, e.g., 'omni0' for the first link, 'omni1' for the second, 'omni2' for the third, etc. Each OMNI link would include its own distinct set of Bridges and Proxy/Servers, thereby providing redundancy in case of failures. Each OMNI link could utilize the same or different ANET connections. The links can be distinguished at the link-layer via the SRT prefix in a similar fashion as for Virtual Local Area Network (VLAN) tagging (e.g., IEEE 802.1Q) and/or through assignment of distinct sets of MSPs on each link. This gives rise to the opportunity for supporting multiple redundant networked paths (see: Section 3.2.5). Templin Expires February 13, 2022 [Page 76] Internet-Draft AERO August 2021 The Client's IP layer can select the outgoing OMNI interface appropriate for a given traffic profile while (in the reverse direction) correspondent nodes must have some way of steering their original IP packets destined to a target via the correct OMNI link. In a first alternative, if each OMNI link services different MSPs the Client can receive a distinct MNP from each of the links. IP routing will therefore assure that the correct OMNI link is used for both outbound and inbound traffic. This can be accomplished using existing technologies and approaches, and without requiring any special supporting code in correspondent nodes or Bridges. In a second alternative, if each OMNI link services the same MSP(s) then each link could assign a distinct "OMNI link Anycast" address that is configured by all Bridges on the link. Correspondent nodes can then perform Segment Routing to select the correct SRT, which will then direct the original IP packet over multiple hops to the target. 3.19. DNS Considerations AERO Client MNs and INET correspondent nodes consult the Domain Name System (DNS) the same as for any Internetworking node. When correspondent nodes and Client MNs use different IP protocol versions (e.g., IPv4 correspondents and IPv6 MNs), the INET DNS must maintain A records for IPv4 address mappings to MNs which must then be populated in Relay NAT64 mapping caches. In that way, an IPv4 correspondent node can send original IPv4 packets to the IPv4 address mapping of the target MN, and the Relay will translate the IPv4 header and destination address into an IPv6 header and IPv6 destination address of the MN. When an AERO Client registers with an AERO Proxy/Server, the Proxy/ Server can return the address(es) of DNS servers in RDNSS options [RFC6106]. The DNS server provides the IP addresses of other MNs and correspondent nodes in AAAA records for IPv6 or A records for IPv4. 3.20. Transition/Coexistence Considerations OAL encapsulation ensures that dissimilar INET partitions can be joined into a single unified OMNI link, even though the partitions themselves may have differing protocol versions and/or incompatible addressing plans. However, a commonality can be achieved by incrementally distributing globally routable (i.e., native) IP prefixes to eventually reach all nodes (both mobile and fixed) in all OMNI link segments. This can be accomplished by incrementally deploying AERO Bridges on each INET partition, with each Bridge Templin Expires February 13, 2022 [Page 77] Internet-Draft AERO August 2021 distributing its MNPs and/or discovering non-MNP IP GUA prefixes on its INET links. This gives rise to the opportunity to eventually distribute native IP addresses to all nodes, and to present a unified OMNI link view even if the INET partitions remain in their current protocol and addressing plans. In that way, the OMNI link can serve the dual purpose of providing a mobility/multilink service and a transition/ coexistence service. Or, if an INET partition is transitioned to a native IP protocol version and addressing scheme that is compatible with the OMNI link MNP-based addressing scheme, the partition and OMNI link can be joined by Bridges. Relays that connect INETs/EUNs with dissimilar IP protocol versions may need to employ a network address and protocol translation function such as NAT64 [RFC6146]. 3.21. Detecting and Reacting to Proxy/Server and Bridge Failures In environments where rapid failure recovery is required, Proxy/ Servers and Bridges SHOULD use Bidirectional Forwarding Detection (BFD) [RFC5880]. Nodes that use BFD can quickly detect and react to failures so that cached information is re-established through alternate nodes. BFD control messaging is carried only over well- connected ground domain networks (i.e., and not low-end radio links) and can therefore be tuned for rapid response. Proxy/Servers and Bridges maintain BFD sessions in parallel with their BGP peerings. If a Proxy/Server or Bridge fails, BGP peers will quickly re-establish routes through alternate paths the same as for common BGP deployments. Similarly, Proxys maintain BFD sessions with their associated Bridges even though they do not establish BGP peerings with them. 3.22. AERO Clients on the Open Internet AERO Clients that connect to the open Internet via INET interfaces can establish a VPN or direct link to securely connect to a FHS/Hub Proxy/Server in a "tethered" arrangement with all of the Client's traffic transiting the Proxy/Server which acts as a router. Alternatively, the Client can associate with an INET FHS/Hub Proxy/ Server using UDP/IP encapsulation and control message securing services as discussed in the following sections. When a Client's OMNI interface enables an INET underlying interface, it first examines the INET address. For IPv4, the Client assumes it is on the open Internet if the INET address is not a special-use IPv4 address per [RFC3330]. Similarly for IPv6, the Client assumes it is Templin Expires February 13, 2022 [Page 78] Internet-Draft AERO August 2021 on the open Internet if the INET address is a Global Unicast Address (GUA) [RFC4291]. Otherwise, the Client should assume it is behind one or several NATs. The Client then prepares an RS message with IPv6 source address set to its MNP-LLA, with IPv6 destination set to link-scoped All-Routers multicast and with an OMNI option with underlying interface attributes. If the Client believes that it is on the open Internet, it SHOULD include its IP address and UDP port number in the Multilink Forwarding Parameters sub-option corresponding to the underlying interface. If the underlying address is IPv4, the Client includes the Port Number and IPv4 address written in obfuscated form [RFC4380] as discussed in Section 3.3. If the underlying interface address is IPv6, the Client instead includes the Port Number and IPv6 address in obfuscated form. The Client finally includes an authentication signature per [I-D.templin-6man-omni] to provide message authentication, selects an Identification value and window synchronization parameters, and submits the RS for OAL encapsulation. The Client then encapsulates the OAL atomic fragment in UDP/IP headers to form a carrier packet, sets the UDP/IP source to its INET address and UDP port, sets the UDP/IP destination to the FHS Proxy/ Server's INET address and the AERO service port number (8060), then sends the carrier packet to the Proxy/Server. When the FHS Proxy/Server receives the RS, it discards the OAL encapsulation, authenticates the RS message, and examines the destination address. If the destination is the ADM-LLA of another Proxy/Server, the FHS Proxy/Server assumes the proxy role and forwards the message into the secured spanning tree. If the destination is its own ADM-LLA, the FHS Proxy/Server instead assumes the Hub role, creates a NCE and registers the Client's MNP, window synchronization state and INET interface information according to the OMNI option parameters. (If the destination is link-scoped All- Routers multicast, the FHS Proxy/Server can assume either the proxy or Hub role.) If the Multilink Forwarding Paramters sub-option includes a non-zero L2ADDR, the Hub Proxy/Server compares the encapsulation IP address and UDP port number with the (unobfuscated) values. If the values are the same, the Hub Proxy/Server caches the Client's information as an "INET" address meaning that the Client is likely to accept direct messages without requiring NAT traversal exchanges. If the values are different (or, if the OMNI option did not include an L2ADDR) the Hub Proxy/Server instead caches the Client's information as a "mapped" address meaning that NAT traversal exchanges may be necessary. Templin Expires February 13, 2022 [Page 79] Internet-Draft AERO August 2021 The Hub Proxy/Server then prepares an RA message with IPv6 source and destination set corresponding to the addresses in the RS, and with an OMNI option with an Origin Indication sub-option per [I-D.templin-6man-omni] with the mapped and obfuscated Port Number and IP address observed in the encapsulation headers. The Proxy/ Server also includes a Multilink Forwarding Parameters sub-option, an authentication signature sub-option per [I-D.templin-6man-omni] and/ or a symmetric window synchronization/acknowledgement if necessary. The Hub Proxy/Server then performs OAL encapsulation then encapsulates the carrier packet in UDP/IP headers with addresses set per the L2ADDR information in the NCE for the Client. When the Client receives the RA, it authenticates the message then process the window synchronization/acknowledgement and compares the mapped Port Number and IP address from the Multilink Forwarding Parameters sub-option with its own address. If the addresses are the same, the Client assumes the open Internet / Cone NAT principle; if the addresses are different, the Client instead assumes that further qualification procedures are necessary to detect the type of NAT and performs NAT traversal on-demand according to standard procedures [RFC6081][RFC4380]. The Client also caches the RA rest of the Multilink Forwarding Parameters information to discover the FHS Proxy/Server's local spanning tree segment. The Client finally arranges to return an explicit/implicit acknowledgement, and sends periodic RS messages to receive fresh RA messages before the Router Lifetime received on each INET interface expires. When the Client sends messages to target IP addresses, it also invokes route optimization per Section 3.14. For route optimized targets in the same OMNI link segment, if the target's L2ADDR is on the open INET, the Client forwards carrier packets directly to the target INET address. If the target is behind a NAT, the Client first establishes NAT state for the L2ADDR using the "direct bubble" and NS/NA(NUD) mechanisms discussed in Section 3.10.1. The Client continues to send carrier packets via the local Bridge discovered during window synchronization until NAT state is populated, then begins forwarding carrier packets via the direct path through the NAT to the target. For targets in different OMNI link segments, the Client forwards carrier packets to the local Bridge. The Client can send original IP packets to route-optimized neighbors in the same OMNI link segment no larger than the minimum/path MPS in one piece and with OAL encapsulation as atomic fragments. For larger original IP packets, the Client applies OAL encapsulation then fragments if necessary according to Section 3.9, with OAL header with source set to its own MNP-ULA and destination set to the MNP-ULA of the target, and with an in-window Identification value. The Client Templin Expires February 13, 2022 [Page 80] Internet-Draft AERO August 2021 then encapsulates each resulting carrier packet in UDP/IP *NET headers and sends them to the neighbor. INET Clients exchange NS/NA(WIN) messages to associate with a new peer as discussed in Section 3.2.7. The exchange establishes MFIB state in the Client, peer and all OMNI intermediate nodes in the path. After MFIB state is established, INET Clients and peers can exchange carrier packets with compressed headers that include an MFVI which is updated on a hop-by-hop basis, while employing "shortcuts" to skip any unnecessary hops. Note: The NAT traversal procedures specified in this document are applicable for Cone, Address-Restricted and Port-Restricted NATs only. While future updates to this document may specify procedures for other NAT variations (e.g., hairpinning and various forms of Symmetric NATs), it should be noted that continuous communications are always possible through Proxy/Server forwarding even for these other NAT variations. 3.23. Time-Varying MNPs In some use cases, it is desirable, beneficial and efficient for the Client to receive a constant MNP that travels with the Client wherever it moves. For example, this would allow air traffic controllers to easily track aircraft, etc. In other cases, however (e.g., intelligent transportation systems), the MN may be willing to sacrifice a modicum of efficiency in order to have time-varying MNPs that can be changed every so often to defeat adversarial tracking. The DHCPv6 service offers a way for Clients that desire time-varying MNPs to obtain short-lived prefixes (e.g., on the order of a small number of minutes). In that case, the identity of the Client would not be bound to the MNP but rather to a Node Identification value (see: [I-D.templin-6man-omni]) to be used as the Client ID seed for MNP prefix delegation. The Client would then be obligated to renumber its internal networks whenever its MNP (and therefore also its MNP-LLA) changes. This should not present a challenge for Clients with automated network renumbering services, however presents limits for the durations of ongoing sessions that would prefer to use a constant address. 4. Implementation Status An early AERO implementation based on OpenVPN (https://openvpn.net/) was announced on the v6ops mailing list on January 10, 2018 and an initial public release of the AERO proof-of-concept source code was announced on the intarea mailing list on August 21, 2015. Templin Expires February 13, 2022 [Page 81] Internet-Draft AERO August 2021 AERO Release-3.2 was tagged on March 30, 2021, and is undergoing internal testing. Additional internal releases expected within the coming months, with first public release expected end of 1H2021. Many AERO/OMNI functions are implemented and undergoing final integration. OAL fragmentation/reassembly buffer management code has been cleared for public release and will be presented at the June 2021 ICAO mobility subgroup meeting. 5. IANA Considerations The IANA has assigned the UDP port number "8060" for an earlier experimental first version of AERO [RFC6706]. This document together with [I-D.templin-6man-omni] reclaims UDP port number "8060" as the service port for UDP/IP encapsulation. This document makes no request of IANA, since [I-D.templin-6man-omni] already provides instructions. (Note: although [RFC6706] was not widely implemented or deployed, it need not be obsoleted since its messages use the invalid ICMPv6 message type number '0' which implementations of this specification can easily distinguish and ignore.) No further IANA actions are required. 6. Security Considerations AERO Bridges configure secured tunnels with AERO Proxy/Servers and Relays within their local OMNI link segments. Applicable secured tunnel alternatives include IPsec [RFC4301], TLS/SSL [RFC8446], DTLS [RFC6347], WireGuard [WG], etc. The AERO Bridges of all OMNI link segments in turn configure secured tunnels for their neighboring AERO Bridges in a secured spanning tree topology. Therefore, control messages exchanged between any pair of OMNI link neighbors over the secured spanning tree are already protected. To prevent spoofing vectors, Proxy/Servers MUST discard without responding to any unsecured NS(AR) messages. Also, Proxy/Servers MUST discard without forwarding any original IP packets received from one of their own Clients (whether directly or following OAL reassembly) with a source address that does not match the Client's MNP and/or a destination address that does match the Client's MNP. Finally, Proxy/Servers MUST discard without forwarding any carrier packets with an OAL source and destination that both match the same MNP. For INET partitions that require strong security in the data plane, two options for securing communications include 1) disable route optimization so that all traffic is conveyed over secured tunnels, or 2) enable on-demand secure tunnel creation between Client neighbors. Templin Expires February 13, 2022 [Page 82] Internet-Draft AERO August 2021 Option 1) would result in longer routes than necessary and impose traffic concentration on critical infrastructure elements. Option 2) could be coordinated between Clients using NS/NA messages with OMNI Host Identity Protocol (HIP) "Initiator/Responder" message sub- options [RFC7401][I-D.templin-6man-omni] to create a secured tunnel on-demand. AERO Clients that connect to secured ANETs need not apply security to their IPv6 ND messages, since the messages will be authenticated and forwarded by a perimeter Proxy/Server that applies security on its INET-facing interface as part of the spanning tree (see above). AERO Clients connected to the open INET can use network and/or transport layer security services such as VPNs or can by some other means establish a direct link to a Proxy/Server. When a VPN or direct link may be impractical, however, INET Clients and Proxy/Servers SHOULD include and verify authentication signatures for their IPv6 ND messages as specified in [I-D.templin-6man-omni]. Application endpoints SHOULD use transport-layer (or higher-layer) security services such as TLS/SSL, DTLS or SSH [RFC4251] to assure the same level of protection as for critical secured Internet services. AERO Clients that require host-based VPN services SHOULD use network and/or transport layer security services such as IPsec, TLS/SSL, DTLS, etc. AERO Proxys and Proxy/Servers can also provide a network-based VPN service on behalf of the Client, e.g., if the Client is located within a secured enclave and cannot establish a VPN on its own behalf. AERO Proxy/Servers and Bridges present targets for traffic amplification Denial of Service (DoS) attacks. This concern is no different than for widely-deployed VPN security gateways in the Internet, where attackers could send spoofed packets to the gateways at high data rates. This can be mitigated through the AERO/OMNI data origin authentication procedures, as well as connecting Proxy/Servers and Bridges over dedicated links with no connections to the Internet and/or when connections to the Internet are only permitted through well-managed firewalls. Traffic amplification DoS attacks can also target an AERO Client's low data rate links. This is a concern not only for Clients located on the open Internet but also for Clients in secured enclaves. AERO Proxy/Servers and Proxys can institute rate limits that protect Clients from receiving packet floods that could DoS low data rate links. AERO Relays must implement ingress filtering to avoid a spoofing attack in which spurious messages with ULA addresses are injected into an OMNI link from an outside attacker. AERO Clients MUST ensure that their connectivity is not used by unauthorized nodes on their EUNs to gain access to a protected network, i.e., AERO Clients that Templin Expires February 13, 2022 [Page 83] Internet-Draft AERO August 2021 act as routers MUST NOT provide routing services for unauthorized nodes. (This concern is no different than for ordinary hosts that receive an IP address delegation but then "share" the address with other nodes via some form of Internet connection sharing such as tethering.) The PRL MUST be well-managed and secured from unauthorized tampering, even though the list contains only public information. The PRL can be conveyed to the Client in a similar fashion as in [RFC5214] (e.g., through layer 2 data link login messaging, secure upload of a static file, DNS lookups, etc.). The AERO service for open INET Clients depends on a public key distribution service in which Client public keys and identities are maintained in a shared database accessible to all open INET Proxy/ Servers. Similarly, each Client must be able to determine the public key of each Proxy/Server, e.g. by consulting an online database. When AERO nodes register their public keys indexed by a unique Host Identity Tag (HIT) [RFC7401] in a distributed database such as the DNS, and use the HIT as an identity for applying IPv6 ND message authentication signatures, a means for determining public key attestation is available. Security considerations for IPv6 fragmentation and reassembly are discussed in [I-D.templin-6man-omni]. In environments where spoofing is considered a threat, OMNI nodes SHOULD employ Identification window synchronization and OAL destinations SHOULD configure an (end- system-based) firewall. SRH authentication facilities are specified in [RFC8754]. Security considerations for accepting link-layer ICMP messages and reflected packets are discussed throughout the document. 7. Acknowledgements Discussions in the IETF, aviation standards communities and private exchanges helped shape some of the concepts in this work. Individuals who contributed insights include Mikael Abrahamsson, Mark Andrews, Fred Baker, Bob Braden, Stewart Bryant, Scott Burleigh, Brian Carpenter, Wojciech Dec, Pavel Drasil, Ralph Droms, Adrian Farrel, Nick Green, Sri Gundavelli, Brian Haberman, Bernhard Haindl, Joel Halpern, Tom Herbert, Bob Hinden, Sascha Hlusiak, Lee Howard, Christian Huitema, Zdenek Jaron, Andre Kostur, Hubert Kuenig, Ted Lemon, Andy Malis, Satoru Matsushima, Tomek Mrugalski, Thomas Narten, Madhu Niraula, Alexandru Petrescu, Behcet Saikaya, Michal Skorepa, Dave Thaler, Joe Touch, Bernie Volz, Ryuji Wakikawa, Tony Whyman, Lloyd Wood and James Woodyatt. Members of the IESG also provided valuable input during their review process that greatly improved the Templin Expires February 13, 2022 [Page 84] Internet-Draft AERO August 2021 document. Special thanks go to Stewart Bryant, Joel Halpern and Brian Haberman for their shepherding guidance during the publication of the AERO first edition. This work has further been encouraged and supported by Boeing colleagues including Kyle Bae, M. Wayne Benson, Dave Bernhardt, Cam Brodie, John Bush, Balaguruna Chidambaram, Irene Chin, Bruce Cornish, Claudiu Danilov, Don Dillenburg, Joe Dudkowski, Wen Fang, Samad Farooqui, Anthony Gregory, Jeff Holland, Seth Jahne, Brian Jaury, Greg Kimberly, Ed King, Madhuri Madhava Badgandi, Laurel Matthew, Gene MacLean III, Kyle Mikos, Rob Muszkiewicz, Sean O'Sullivan, Vijay Rajagopalan, Greg Saccone, Rod Santiago, Kent Shuey, Brian Skeen, Mike Slane, Carrie Spiker, Katie Tran, Brendan Williams, Amelia Wilson, Julie Wulff, Yueli Yang, Eric Yeh and other members of the Boeing mobility, networking and autonomy teams. Kyle Bae, Wayne Benson, Madhuri Madhava Badgandi, Vijayasarathy Rajagopalan, Katie Tran and Eric Yeh are especially acknowledged for their work on the AERO implementation. Chuck Klabunde is honored and remembered for his early leadership, and we mourn his untimely loss. This work was inspired by the support and encouragement of countless outstanding colleagues, managers and program directors over the span of many decades. Beginning in the late 1980s,' the Digital Equipment Corporation (DEC) Ultrix Engineering and DECnet Architects groups identified early issues with fragmentation and bridging links with diverse MTUs. In the early 1990s, engagements at DEC Project Sequoia at UC Berkeley and the DEC Western Research Lab in Palo Alto included investigations into large-scale networked filesystems, ATM vs Internet and network security proxies. In the mid-1990s to early 2000s employment at the NASA Ames Research Center (Sterling Software) and SRI International supported early investigations of IPv6, ONR UAV Communications and the IETF. An employment at Nokia where important IETF documents were published gave way to a present-day engagement with The Boeing Company. The work matured at Boeing through major programs including Future Combat Systems, Advanced Airplane Program, DTN for the International Space Station, Mobility Vision Lab, CAST, Caravan, Airplane Internet of Things, the NASA UAS/CNS program, the FAA/ICAO ATN/IPS program and many others. An attempt to name all who gave support and encouragement would double the current document size and result in many unintentional omissions - but to all a humble thanks. Earlier works on NBMA tunneling approaches are found in [RFC2529][RFC5214][RFC5569]. Many of the constructs presented in this second edition of AERO are based on the author's earlier works, including: Templin Expires February 13, 2022 [Page 85] Internet-Draft AERO August 2021 o The Internet Routing Overlay Network (IRON) [RFC6179][I-D.templin-ironbis] o Virtual Enterprise Traversal (VET) [RFC5558][I-D.templin-intarea-vet] o The Subnetwork Encapsulation and Adaptation Layer (SEAL) [RFC5320][I-D.templin-intarea-seal] o AERO, First Edition [RFC6706] Note that these works cite numerous earlier efforts that are not also cited here due to space limitations. The authors of those earlier works are acknowledged for their insights. This work is aligned with the NASA Safe Autonomous Systems Operation (SASO) program under NASA contract number NNA16BD84C. This work is aligned with the FAA as per the SE2025 contract number DTFAWA-15-D-00030. This work is aligned with the Boeing Commercial Airplanes (BCA) Internet of Things (IoT) and autonomy programs. This work is aligned with the Boeing Information Technology (BIT) MobileNet program. 8. References 8.1. Normative References [I-D.templin-6man-omni] Templin, F. L. and T. Whyman, "Transmission of IP Packets over Overlay Multilink Network (OMNI) Interfaces", draft- templin-6man-omni-35 (work in progress), August 2021. [RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, DOI 10.17487/RFC0791, September 1981, <https://www.rfc-editor.org/info/rfc791>. [RFC0792] Postel, J., "Internet Control Message Protocol", STD 5, RFC 792, DOI 10.17487/RFC0792, September 1981, <https://www.rfc-editor.org/info/rfc792>. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, <https://www.rfc-editor.org/info/rfc2119>. Templin Expires February 13, 2022 [Page 86] Internet-Draft AERO August 2021 [RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473, December 1998, <https://www.rfc-editor.org/info/rfc2473>. [RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander, "SEcure Neighbor Discovery (SEND)", RFC 3971, DOI 10.17487/RFC3971, March 2005, <https://www.rfc-editor.org/info/rfc3971>. [RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)", RFC 3972, DOI 10.17487/RFC3972, March 2005, <https://www.rfc-editor.org/info/rfc3972>. [RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191, November 2005, <https://www.rfc-editor.org/info/rfc4191>. [RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005, <https://www.rfc-editor.org/info/rfc4193>. [RFC4380] Huitema, C., "Teredo: Tunneling IPv6 over UDP through Network Address Translations (NATs)", RFC 4380, DOI 10.17487/RFC4380, February 2006, <https://www.rfc-editor.org/info/rfc4380>. [RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, DOI 10.17487/RFC4861, September 2007, <https://www.rfc-editor.org/info/rfc4861>. [RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless Address Autoconfiguration", RFC 4862, DOI 10.17487/RFC4862, September 2007, <https://www.rfc-editor.org/info/rfc4862>. [RFC6081] Thaler, D., "Teredo Extensions", RFC 6081, DOI 10.17487/RFC6081, January 2011, <https://www.rfc-editor.org/info/rfc6081>. [RFC7401] Moskowitz, R., Ed., Heer, T., Jokela, P., and T. Henderson, "Host Identity Protocol Version 2 (HIPv2)", RFC 7401, DOI 10.17487/RFC7401, April 2015, <https://www.rfc-editor.org/info/rfc7401>. [RFC7739] Gont, F., "Security Implications of Predictable Fragment Identification Values", RFC 7739, DOI 10.17487/RFC7739, February 2016, <https://www.rfc-editor.org/info/rfc7739>. Templin Expires February 13, 2022 [Page 87] Internet-Draft AERO August 2021 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, <https://www.rfc-editor.org/info/rfc8174>. [RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", STD 86, RFC 8200, DOI 10.17487/RFC8200, July 2017, <https://www.rfc-editor.org/info/rfc8200>. [RFC8415] Mrugalski, T., Siodelski, M., Volz, B., Yourtchenko, A., Richardson, M., Jiang, S., Lemon, T., and T. Winters, "Dynamic Host Configuration Protocol for IPv6 (DHCPv6)", RFC 8415, DOI 10.17487/RFC8415, November 2018, <https://www.rfc-editor.org/info/rfc8415>. 8.2. Informative References [BGP] Huston, G., "BGP in 2015, http://potaroo.net", January 2016. [I-D.bonica-6man-comp-rtg-hdr] Bonica, R., Kamite, Y., Alston, A., Henriques, D., and L. Jalil, "The IPv6 Compact Routing Header (CRH)", draft- bonica-6man-comp-rtg-hdr-26 (work in progress), May 2021. [I-D.bonica-6man-crh-helper-opt] Li, X., Bao, C., Ruan, E., and R. Bonica, "Compressed Routing Header (CRH) Helper Option", draft-bonica-6man- crh-helper-opt-03 (work in progress), April 2021. [I-D.ietf-intarea-frag-fragile] Bonica, R., Baker, F., Huston, G., Hinden, R. M., Troan, O., and F. Gont, "IP Fragmentation Considered Fragile", draft-ietf-intarea-frag-fragile-17 (work in progress), September 2019. [I-D.ietf-intarea-tunnels] Touch, J. and M. Townsley, "IP Tunnels in the Internet Architecture", draft-ietf-intarea-tunnels-10 (work in progress), September 2019. [I-D.ietf-ipwave-vehicular-networking] (editor), J. (. J., "IPv6 Wireless Access in Vehicular Environments (IPWAVE): Problem Statement and Use Cases", draft-ietf-ipwave-vehicular-networking-20 (work in progress), March 2021. Templin Expires February 13, 2022 [Page 88] Internet-Draft AERO August 2021 [I-D.ietf-rtgwg-atn-bgp] Templin, F. L., Saccone, G., Dawra, G., Lindem, A., and V. Moreno, "A Simple BGP-based Mobile Routing System for the Aeronautical Telecommunications Network", draft-ietf- rtgwg-atn-bgp-11 (work in progress), July 2021. [I-D.templin-6man-dhcpv6-ndopt] Templin, F. L., "A Unified Stateful/Stateless Configuration Service for IPv6", draft-templin-6man- dhcpv6-ndopt-11 (work in progress), January 2021. [I-D.templin-intarea-seal] Templin, F. L., "The Subnetwork Encapsulation and Adaptation Layer (SEAL)", draft-templin-intarea-seal-68 (work in progress), January 2014. [I-D.templin-intarea-vet] Templin, F. L., "Virtual Enterprise Traversal (VET)", draft-templin-intarea-vet-40 (work in progress), May 2013. [I-D.templin-ipwave-uam-its] Templin, F. L., "Urban Air Mobility Implications for Intelligent Transportation Systems", draft-templin-ipwave- uam-its-04 (work in progress), January 2021. [I-D.templin-ironbis] Templin, F. L., "The Interior Routing Overlay Network (IRON)", draft-templin-ironbis-16 (work in progress), March 2014. [I-D.templin-v6ops-pdhost] Templin, F. L., "IPv6 Prefix Delegation and Multi- Addressing Models", draft-templin-v6ops-pdhost-27 (work in progress), January 2021. [OVPN] OpenVPN, O., "http://openvpn.net", October 2016. [RFC1035] Mockapetris, P., "Domain names - implementation and specification", STD 13, RFC 1035, DOI 10.17487/RFC1035, November 1987, <https://www.rfc-editor.org/info/rfc1035>. [RFC1812] Baker, F., Ed., "Requirements for IP Version 4 Routers", RFC 1812, DOI 10.17487/RFC1812, June 1995, <https://www.rfc-editor.org/info/rfc1812>. [RFC2003] Perkins, C., "IP Encapsulation within IP", RFC 2003, DOI 10.17487/RFC2003, October 1996, <https://www.rfc-editor.org/info/rfc2003>. Templin Expires February 13, 2022 [Page 89] Internet-Draft AERO August 2021 [RFC2004] Perkins, C., "Minimal Encapsulation within IP", RFC 2004, DOI 10.17487/RFC2004, October 1996, <https://www.rfc-editor.org/info/rfc2004>. [RFC2236] Fenner, W., "Internet Group Management Protocol, Version 2", RFC 2236, DOI 10.17487/RFC2236, November 1997, <https://www.rfc-editor.org/info/rfc2236>. [RFC2464] Crawford, M., "Transmission of IPv6 Packets over Ethernet Networks", RFC 2464, DOI 10.17487/RFC2464, December 1998, <https://www.rfc-editor.org/info/rfc2464>. [RFC2529] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4 Domains without Explicit Tunnels", RFC 2529, DOI 10.17487/RFC2529, March 1999, <https://www.rfc-editor.org/info/rfc2529>. [RFC2983] Black, D., "Differentiated Services and Tunnels", RFC 2983, DOI 10.17487/RFC2983, October 2000, <https://www.rfc-editor.org/info/rfc2983>. [RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition of Explicit Congestion Notification (ECN) to IP", RFC 3168, DOI 10.17487/RFC3168, September 2001, <https://www.rfc-editor.org/info/rfc3168>. [RFC3330] IANA, "Special-Use IPv4 Addresses", RFC 3330, DOI 10.17487/RFC3330, September 2002, <https://www.rfc-editor.org/info/rfc3330>. [RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener Discovery Version 2 (MLDv2) for IPv6", RFC 3810, DOI 10.17487/RFC3810, June 2004, <https://www.rfc-editor.org/info/rfc3810>. [RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally Unique IDentifier (UUID) URN Namespace", RFC 4122, DOI 10.17487/RFC4122, July 2005, <https://www.rfc-editor.org/info/rfc4122>. [RFC4251] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH) Protocol Architecture", RFC 4251, DOI 10.17487/RFC4251, January 2006, <https://www.rfc-editor.org/info/rfc4251>. [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A Border Gateway Protocol 4 (BGP-4)", RFC 4271, DOI 10.17487/RFC4271, January 2006, <https://www.rfc-editor.org/info/rfc4271>. Templin Expires February 13, 2022 [Page 90] Internet-Draft AERO August 2021 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing Architecture", RFC 4291, DOI 10.17487/RFC4291, February 2006, <https://www.rfc-editor.org/info/rfc4291>. [RFC4301] Kent, S. and K. Seo, "Security Architecture for the Internet Protocol", RFC 4301, DOI 10.17487/RFC4301, December 2005, <https://www.rfc-editor.org/info/rfc4301>. [RFC4389] Thaler, D., Talwar, M., and C. Patel, "Neighbor Discovery Proxies (ND Proxy)", RFC 4389, DOI 10.17487/RFC4389, April 2006, <https://www.rfc-editor.org/info/rfc4389>. [RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet Control Message Protocol (ICMPv6) for the Internet Protocol Version 6 (IPv6) Specification", STD 89, RFC 4443, DOI 10.17487/RFC4443, March 2006, <https://www.rfc-editor.org/info/rfc4443>. [RFC4511] Sermersheim, J., Ed., "Lightweight Directory Access Protocol (LDAP): The Protocol", RFC 4511, DOI 10.17487/RFC4511, June 2006, <https://www.rfc-editor.org/info/rfc4511>. [RFC4541] Christensen, M., Kimball, K., and F. Solensky, "Considerations for Internet Group Management Protocol (IGMP) and Multicast Listener Discovery (MLD) Snooping Switches", RFC 4541, DOI 10.17487/RFC4541, May 2006, <https://www.rfc-editor.org/info/rfc4541>. [RFC4605] Fenner, B., He, H., Haberman, B., and H. Sandick, "Internet Group Management Protocol (IGMP) / Multicast Listener Discovery (MLD)-Based Multicast Forwarding ("IGMP/MLD Proxying")", RFC 4605, DOI 10.17487/RFC4605, August 2006, <https://www.rfc-editor.org/info/rfc4605>. [RFC4982] Bagnulo, M. and J. Arkko, "Support for Multiple Hash Algorithms in Cryptographically Generated Addresses (CGAs)", RFC 4982, DOI 10.17487/RFC4982, July 2007, <https://www.rfc-editor.org/info/rfc4982>. [RFC5015] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano, "Bidirectional Protocol Independent Multicast (BIDIR- PIM)", RFC 5015, DOI 10.17487/RFC5015, October 2007, <https://www.rfc-editor.org/info/rfc5015>. Templin Expires February 13, 2022 [Page 91] Internet-Draft AERO August 2021 [RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214, DOI 10.17487/RFC5214, March 2008, <https://www.rfc-editor.org/info/rfc5214>. [RFC5320] Templin, F., Ed., "The Subnetwork Encapsulation and Adaptation Layer (SEAL)", RFC 5320, DOI 10.17487/RFC5320, February 2010, <https://www.rfc-editor.org/info/rfc5320>. [RFC5522] Eddy, W., Ivancic, W., and T. Davis, "Network Mobility Route Optimization Requirements for Operational Use in Aeronautics and Space Exploration Mobile Networks", RFC 5522, DOI 10.17487/RFC5522, October 2009, <https://www.rfc-editor.org/info/rfc5522>. [RFC5558] Templin, F., Ed., "Virtual Enterprise Traversal (VET)", RFC 5558, DOI 10.17487/RFC5558, February 2010, <https://www.rfc-editor.org/info/rfc5558>. [RFC5569] Despres, R., "IPv6 Rapid Deployment on IPv4 Infrastructures (6rd)", RFC 5569, DOI 10.17487/RFC5569, January 2010, <https://www.rfc-editor.org/info/rfc5569>. [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, <https://www.rfc-editor.org/info/rfc5880>. [RFC6106] Jeong, J., Park, S., Beloeil, L., and S. Madanapalli, "IPv6 Router Advertisement Options for DNS Configuration", RFC 6106, DOI 10.17487/RFC6106, November 2010, <https://www.rfc-editor.org/info/rfc6106>. [RFC6139] Russert, S., Ed., Fleischman, E., Ed., and F. Templin, Ed., "Routing and Addressing in Networks with Global Enterprise Recursion (RANGER) Scenarios", RFC 6139, DOI 10.17487/RFC6139, February 2011, <https://www.rfc-editor.org/info/rfc6139>. [RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful NAT64: Network Address and Protocol Translation from IPv6 Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146, April 2011, <https://www.rfc-editor.org/info/rfc6146>. [RFC6179] Templin, F., Ed., "The Internet Routing Overlay Network (IRON)", RFC 6179, DOI 10.17487/RFC6179, March 2011, <https://www.rfc-editor.org/info/rfc6179>. Templin Expires February 13, 2022 [Page 92] Internet-Draft AERO August 2021 [RFC6221] Miles, D., Ed., Ooghe, S., Dec, W., Krishnan, S., and A. Kavanagh, "Lightweight DHCPv6 Relay Agent", RFC 6221, DOI 10.17487/RFC6221, May 2011, <https://www.rfc-editor.org/info/rfc6221>. [RFC6273] Kukec, A., Krishnan, S., and S. Jiang, "The Secure Neighbor Discovery (SEND) Hash Threat Analysis", RFC 6273, DOI 10.17487/RFC6273, June 2011, <https://www.rfc-editor.org/info/rfc6273>. [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, January 2012, <https://www.rfc-editor.org/info/rfc6347>. [RFC6355] Narten, T. and J. Johnson, "Definition of the UUID-Based DHCPv6 Unique Identifier (DUID-UUID)", RFC 6355, DOI 10.17487/RFC6355, August 2011, <https://www.rfc-editor.org/info/rfc6355>. [RFC6438] Carpenter, B. and S. Amante, "Using the IPv6 Flow Label for Equal Cost Multipath Routing and Link Aggregation in Tunnels", RFC 6438, DOI 10.17487/RFC6438, November 2011, <https://www.rfc-editor.org/info/rfc6438>. [RFC6706] Templin, F., Ed., "Asymmetric Extended Route Optimization (AERO)", RFC 6706, DOI 10.17487/RFC6706, August 2012, <https://www.rfc-editor.org/info/rfc6706>. [RFC6935] Eubanks, M., Chimento, P., and M. Westerlund, "IPv6 and UDP Checksums for Tunneled Packets", RFC 6935, DOI 10.17487/RFC6935, April 2013, <https://www.rfc-editor.org/info/rfc6935>. [RFC6936] Fairhurst, G. and M. Westerlund, "Applicability Statement for the Use of IPv6 UDP Datagrams with Zero Checksums", RFC 6936, DOI 10.17487/RFC6936, April 2013, <https://www.rfc-editor.org/info/rfc6936>. [RFC7333] Chan, H., Ed., Liu, D., Seite, P., Yokota, H., and J. Korhonen, "Requirements for Distributed Mobility Management", RFC 7333, DOI 10.17487/RFC7333, August 2014, <https://www.rfc-editor.org/info/rfc7333>. [RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I., Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent Multicast - Sparse Mode (PIM-SM): Protocol Specification (Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March 2016, <https://www.rfc-editor.org/info/rfc7761>. Templin Expires February 13, 2022 [Page 93] Internet-Draft AERO August 2021 [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., Decraene, B., Litkowski, S., and R. Shakir, "Segment Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, July 2018, <https://www.rfc-editor.org/info/rfc8402>. [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, <https://www.rfc-editor.org/info/rfc8446>. [RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J., Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020, <https://www.rfc-editor.org/info/rfc8754>. [WG] Wireguard, "WireGuard, https://www.wireguard.com", August 2020. Appendix A. Non-Normative Considerations AERO can be applied to a multitude of Internetworking scenarios, with each having its own adaptations. The following considerations are provided as non-normative guidance: A.1. Implementation Strategies for Route Optimization Route optimization as discussed in Section 3.14 results in the route optimization source (ROS) creating a NCE for the target neighbor. The NCE state is set to REACHABLE for at most ReachableTime seconds. In order to refresh the NCE lifetime before the ReachableTime timer expires, the specification requires implementations to issue a new NS/NA(AR) exchange to reset ReachableTime while data packets are still flowing. However, the decision of when to initiate a new NS/ NA(AR) exchange and to perpetuate the process is left as an implementation detail. One possible strategy may be to monitor the NCE watching for data packets for (ReachableTime - 5) seconds. If any data packets have been sent to the neighbor within this timeframe, then send an NS(AR) to receive a new NA(AR). If no data packets have been sent, wait for 5 additional seconds and send an immediate NS(AR) if any data packets are sent within this "expiration pending" 5 second window. If no additional data packets are sent within the 5 second window, reset the NCE state to STALE. The monitoring of the neighbor data packet traffic therefore becomes an ongoing process during the NCE lifetime. If the NCE expires, future data packets will trigger a new NS/NA(AR) exchange while the Templin Expires February 13, 2022 [Page 94] Internet-Draft AERO August 2021 packets themselves are delivered over a longer path until route optimization state is re-established. A.2. Implicit Mobility Management OMNI interface neighbors MAY provide a configuration option that allows them to perform implicit mobility management in which no IPv6 ND messaging is used. In that case, the Client only transmits packets over a single interface at a time, and the neighbor always observes packets arriving from the Client from the same link-layer source address. If the Client's underlying interface address changes (either due to a readdressing of the original interface or switching to a new interface) the neighbor immediately updates the NCE for the Client and begins accepting and sending packets according to the Client's new address. This implicit mobility method applies to use cases such as cellphones with both WiFi and Cellular interfaces where only one of the interfaces is active at a given time, and the Client automatically switches over to the backup interface if the primary interface fails. A.3. Direct Underlying Interfaces When a Client's OMNI interface is configured over a Direct interface, the neighbor at the other end of the Direct link can receive packets without any encapsulation. In that case, the Client sends packets over the Direct link according to traffic selectors. If the Direct interface is selected, then the Client's IP packets are transmitted directly to the peer without going through an ANET/INET. If other interfaces are selected, then the Client's IP packets are transmitted via a different interface, which may result in the inclusion of Proxy/Servers and Bridges in the communications path. Direct interfaces must be tested periodically for reachability, e.g., via NUD. A.4. AERO Critical Infrastructure Considerations AERO Bridges can be either Commercial off-the Shelf (COTS) standard IP routers or virtual machines in the cloud. Bridges must be provisioned, supported and managed by the INET administrative authority, and connected to the Bridges of other INETs via inter- domain peerings. Cost for purchasing, configuring and managing Bridges is nominal even for very large OMNI links. AERO INET Proxy/Servers can be standard dedicated server platforms, but most often will be deployed as virtual machines in the cloud. The only requirements for INET Proxy/Servers are that they can run Templin Expires February 13, 2022 [Page 95] Internet-Draft AERO August 2021 the AERO/OMNI code and have at least one network interface connection to the INET. INET Proxy/Servers must be provisioned, supported and managed by the INET administrative authority. Cost for purchasing, configuring and managing cloud Proxy/Servers is nominal especially for virtual machines. AERO ANET Proxy/Servers are most often standard dedicated server platforms with one underlying interface connected to the ANET and a second interface connected to an INET. As with INET Proxy/Servers, the only requirements are that they can run the AERO/OMNI code and have at least one interface connection to the INET. ANET Proxy/ Servers must be provisioned, supported and managed by the ANET administrative authority. Cost for purchasing, configuring and managing Proxys is nominal, and borne by the ANET administrative authority. AERO Relays are simply Proxy/Servers connected to INETs and/or EUNs that provide forwarding services for non-MNP destinations. The Relay connects to the OMNI link and engages in eBGP peering with one or more Bridges as a stub AS. The Relay then injects its MNPs and/or non-MNP prefixes into the BGP routing system, and provisions the prefixes to its downstream-attached networks. The Relay can perform ROS/ROR services the same as for any Proxy/Server, and can route between the MNP and non-MNP address spaces. A.5. AERO Server Failure Implications AERO Proxy/Servers may appear as a single point of failure in the architecture, but such is not the case since all Proxy/Servers on the link provide identical services and loss of a Proxy/Server does not imply immediate and/or comprehensive communication failures. Proxy/ Server failure is quickly detected and conveyed by Bidirectional Forward Detection (BFD) and/or proactive NUD allowing Clients to migrate to new Proxy/Servers. If a Proxy/Server fails, ongoing packet forwarding to Clients will continue by virtue of the neighbor cache entries that have already been established in route optimization sources (ROSs). If a Client also experiences mobility events at roughly the same time the Proxy/ Server fails, uNA messages may be lost but neighbor cache entries in the DEPARTED state will ensure that packet forwarding to the Client's new locations will continue for up to DepartTime seconds. If a Client is left without a Proxy/Server for a considerable length of time (e.g., greater than ReachableTime seconds) then existing neighbor cache entries will eventually expire and both ongoing and new communications will fail. The original source will continue to Templin Expires February 13, 2022 [Page 96] Internet-Draft AERO August 2021 retransmit until the Client has established a new Proxy/Server relationship, after which time continuous communications will resume. Therefore, providing many Proxy/Servers on the link with high availability profiles provides resilience against loss of individual Proxy/Servers and assurance that Clients can establish new Proxy/ Server relationships quickly in event of a Proxy/Server failure. A.6. AERO Client / Server Architecture The AERO architectural model is client / server in the control plane, with route optimization in the data plane. The same as for common Internet services, the AERO Client discovers the addresses of AERO Proxy/Servers and connects to one or more of them. The AERO service is analogous to common Internet services such as google.com, yahoo.com, cnn.com, etc. However, there is only one AERO service for the link and all Proxy/Servers provide identical services. Common Internet services provide differing strategies for advertising server addresses to clients. The strategy is conveyed through the DNS resource records returned in response to name resolution queries. As of January 2020 Internet-based 'nslookup' services were used to determine the following: o When a client resolves the domainname "google.com", the DNS always returns one A record (i.e., an IPv4 address) and one AAAA record (i.e., an IPv6 address). The client receives the same addresses each time it resolves the domainname via the same DNS resolver, but may receive different addresses when it resolves the domainname via different DNS resolvers. But, in each case, exactly one A and one AAAA record are returned. o When a client resolves the domainname "ietf.org", the DNS always returns one A record and one AAAA record with the same addresses regardless of which DNS resolver is used. o When a client resolves the domainname "yahoo.com", the DNS always returns a list of 4 A records and 4 AAAA records. Each time the client resolves the domainname via the same DNS resolver, the same list of addresses are returned but in randomized order (i.e., consistent with a DNS round-robin strategy). But, interestingly, the same addresses are returned (albeit in randomized order) when the domainname is resolved via different DNS resolvers. o When a client resolves the domainname "amazon.com", the DNS always returns a list of 3 A records and no AAAA records. As with "yahoo.com", the same three A records are returned from any worldwide Internet connection point in randomized order. Templin Expires February 13, 2022 [Page 97] Internet-Draft AERO August 2021 The above example strategies show differing approaches to Internet resilience and service distribution offered by major Internet services. The Google approach exposes only a single IPv4 and a single IPv6 address to clients. Clients can then select whichever IP protocol version offers the best response, but will always use the same IP address according to the current Internet connection point. This means that the IP address offered by the network must lead to a highly-available server and/or service distribution point. In other words, resilience is predicated on high availability within the network and with no client-initiated failovers expected (i.e., it is all-or-nothing from the client's perspective). However, Google does provide for worldwide distributed service distribution by virtue of the fact that each Internet connection point responds with a different IPv6 and IPv4 address. The IETF approach is like google (all-or-nothing from the client's perspective), but provides only a single IPv4 or IPv6 address on a worldwide basis. This means that the addresses must be made highly-available at the network level with no client failover possibility, and if there is any worldwide service distribution it would need to be conducted by a network element that is reached via the IP address acting as a service distribution point. In contrast to the Google and IETF philosophies, Yahoo and Amazon both provide clients with a (short) list of IP addresses with Yahoo providing both IP protocol versions and Amazon as IPv4-only. The order of the list is randomized with each name service query response, with the effect of round-robin load balancing for service distribution. With a short list of addresses, there is still expectation that the network will implement high availability for each address but in case any single address fails the client can switch over to using a different address. The balance then becomes one of function in the network vs function in the end system. The same implications observed for common highly-available services in the Internet apply also to the AERO client/server architecture. When an AERO Client connects to one or more ANETs, it discovers one or more AERO Proxy/Server addresses through the mechanisms discussed in earlier sections. Each Proxy/Server address presumably leads to a fault-tolerant clustering arrangement such as supported by Linux-HA, Extended Virtual Synchrony or Paxos. Such an arrangement has precedence in common Internet service deployments in lightweight virtual machines without requiring expensive hardware deployment. Similarly, common Internet service deployments set service IP addresses on service distribution points that may relay requests to many different servers. For AERO, the expectation is that a combination of the Google/IETF and Yahoo/Amazon philosophies would be employed. The AERO Client connects to different ANET access points and can receive 1-2 Proxy/ Templin Expires February 13, 2022 [Page 98] Internet-Draft AERO August 2021 Server ADM-LLAs at each point. It then selects one AERO Proxy/Server address, and engages in RS/RA exchanges with the same Proxy/Server from all ANET connections. The Client remains with this Proxy/Server unless or until the Proxy/Server fails, in which case it can switch over to an alternate Proxy/Server. The Client can likewise switch over to a different Proxy/Server at any time if there is some reason for it to do so. So, the AERO expectation is for a balance of function in the network and end system, with fault tolerance and resilience at both levels. Appendix B. Change Log << RFC Editor - remove prior to publication >> Changes from draft-templin-6man-aero-21 to draft-templin-6man-aero- 22: o That's it, folks. Changes from draft-templin-6man-aero-20 to draft-templin-6man-aero- 21: o Major updates to Hub-and-Spokes Proxy/Server coordination. Changes from draft-templin-6man-aero-19 to draft-templin-6man-aero- 20: o Major updates especially in Section 3.2.7. Changes from draft-templin-6man-aero-18 to draft-templin-6man-aero- 19: o Major revision update for review. Changes from draft-templin-6man-aero-17 to draft-templin-6man-aero- 18: o Interim version with extensive new text - cleanup planned for next release. Changes from draft-templin-6man-aero-16 to draft-templin-6man-aero- 17: o Final editorial review pass resulting in multiple changes. Document now submit for final approval (with reference to rfcdiff from previous version). Templin Expires February 13, 2022 [Page 99] Internet-Draft AERO August 2021 Changes from draft-templin-6man-aero-15 to draft-templin-6man-aero- 16: o Final editorial review pass resulting in multiple changes. Document now submit for final approval (with reference to rfcdiff from previous version). Changes from draft-templin-6man-aero-14 to draft-templin-6man-aero- 15: o Final editorial review pass resulting in multiple changes. Document now submit for final approval (with reference to rfcdiff from previous version). Changes from draft-templin-6man-aero-13 to draft-templin-6man-aero- 14: o Final editorial review pass resulting in multiple changes. Document now submit for final approval (with reference to rfcdiff from previous version). Changes from draft-templin-6man-aero-12 to draft-templin-6man-aero- 13: o Final editorial review pass resulting in multiple changes. Document now submit for final approval (with reference to rfcdiff from previous version). Changes from draft-templin-6man-aero-11 to draft-templin-6man-aero- 12: o Final editorial review pass resulting in multiple changes. Document now submit for final approval (with reference to rfcdiff from previous version). Changes from draft-templin-6man-aero-10 to draft-templin-6man-aero- 11: o Final editorial review pass resulting in multiple changes. Document now submit for final approval (with reference to rfcdiff from previous version). Changes from draft-templin-6man-aero-09 to draft-templin-6man-aero- 10: o Final editorial review pass resulting in multiple changes. Document now submit for final approval (with reference to rfcdiff from previous version). Templin Expires February 13, 2022 [Page 100] Internet-Draft AERO August 2021 Changes from draft-templin-6man-aero-08 to draft-templin-6man-aero- 09: o Final editorial review pass resulting in multiple changes. Document now submit for final approval (with reference to rfcdiff from previous version). Changes from draft-templin-6man-aero-07 to draft-templin-6man-aero- 08: o Final editorial review pass resulting in multiple changes. Document now submit for final approval (with reference to rfcdiff from previous version). Changes from draft-templin-6man-aero-06 to draft-templin-6man-aero- 07: o Final editorial review pass resulting in multiple changes. Document now submit for final approval (with reference to rfcdiff from previous version). Changes from draft-templin-6man-aero-05 to draft-templin-6man-aero- 06: o Final editorial review pass resulting in multiple changes. Document now submit for final approval. Changes from draft-templin-6man-aero-04 to draft-templin-6man-aero- 05: o Changed to use traffic selectors instead of the former multilink selection strategy. Changes from draft-templin-6man-aero-03 to draft-templin-6man-aero- 04: o Removed documents from "Obsoletes" list. o Introduced the concept of "secured" and "unsecured" spanning tree. o Additional security considerations. o Additional route optimization considerations. Changes from draft-templin-6man-aero-02 to draft-templin-6man-aero- 03: Templin Expires February 13, 2022 [Page 101] Internet-Draft AERO August 2021 o Support for extended route optimization from ROR to target over target's underlying interfaces. Changes from draft-templin-6man-aero-01 to draft-templin-6man-aero- 02: o Changed reference citations to "draft-templin-6man-omni". o Several important updates to IPv6 ND cache states and route optimization message addressing. o Included introductory description of the "6M's". o Updated Multicast specification. Changes from draft-templin-6man-aero-00 to draft-templin-6man-aero- 01: o Changed category to "Informational". o Updated implementation status. Changes from earlier versions to draft-templin-6man-aero-00: o Established working baseline reference. Author's Address Fred L. Templin (editor) Boeing Research & Technology P.O. Box 3707 Seattle, WA 98124 USA Email: fltemplin@acm.org Templin Expires February 13, 2022 [Page 102]