| Network Working Group | F. Templin, Ed. |
| Internet-Draft | Boeing Research & Technology |
| Obsoletes: rfc5320, rfc5558, rfc5720, | September 18, 2014 |
| rfc6179, rfc6706 (if | |
| approved) | |
| Intended status: Standards Track | |
| Expires: March 22, 2015 |
Transmission of IP Packets over AERO Links
draft-templin-aerolink-37.txt
This document specifies the operation of IP over tunnel virtual links using Asymmetric Extended Route Optimization (AERO). Nodes attached to AERO links can exchange packets via trusted intermediate routers that provide forwarding services to reach off-link destinations and redirection services for route optimization. AERO provides an IPv6 link-local address format known as the AERO address that supports operation of the IPv6 Neighbor Discovery (ND) protocol and links IPv6 ND to IP forwarding. Admission control and provisioning are supported by the Dynamic Host Configuration Protocol for IPv6 (DHCPv6), and node mobility is naturally supported through dynamic neighbor cache updates. Although DHCPv6 and IPv6 ND messaging is used in the control plane, both IPv4 and IPv6 are supported in the data plane.
This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."
This Internet-Draft will expire on March 22, 2015.
Copyright (c) 2014 IETF Trust and the persons identified as the document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.
This document specifies the operation of IP over tunnel virtual links using Asymmetric Extended Route Optimization (AERO). The AERO link can be used for tunneling to neighboring nodes over either IPv6 or IPv4 networks, i.e., AERO views the IPv6 and IPv4 networks as equivalent links for tunneling. Nodes attached to AERO links can exchange packets via trusted intermediate routers that provide forwarding services to reach off-link destinations and redirection services for route optimization that addresses the requirements outlined in [RFC5522].
AERO provides an IPv6 link-local address format known as the AERO address that supports operation of the IPv6 Neighbor Discovery (ND) [RFC4861] protocol and links IPv6 ND to IP forwarding. Admission control and provisioning are supported by the Dynamic Host Configuration Protocol for IPv6 (DHCPv6) [RFC3315], and node mobility is naturally supported through dynamic neighbor cache updates. Although DHCPv6 and IPv6 ND message signalling is used in the control plane, both IPv4 and IPv6 can be used in the data plane. The remainder of this document presents the AERO specification.
The terminology in the normative references applies; the following terms are defined within the scope of this document:
Throughout the document, the simple terms "Client", "Server" and "Relay" refer to "AERO Client", "AERO Server" and "AERO Relay", respectively. Capitalization is used to distinguish these terms from DHCPv6 client/server/relay.
Throughout the document, it is said that an address is "applied" to an AERO interface since the address is not "assigned" to the interface from the perspective of the IP layer. However, the address must at least be bound to the interface in some fashion to support the operation of DHCPv6 and the IPv6 ND protocol.
The terminology of [RFC4861] (including the names of node variables and protocol constants) applies to this document. Also throughout the document, the term "IP" is used to generically refer to either Internet Protocol version (i.e., IPv4 or IPv6).
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].
The following sections specify the operation of IP over Asymmetric Extended Route Optimization (AERO) links:
.-(::::::::)
.-(:::: IP ::::)-.
(:: Internetwork ::)
`-(::::::::::::)-'
`-(::::::)-'
|
+--------------+ +--------+-------+ +--------------+
|AERO Server S1| | AERO Relay R1 | |AERO Server S2|
| Nbr: C1; R1 | | Nbr: S1; S2 | | Nbr: C2; R1 |
| default->R1 | |(H1->S1; H2->S2)| | default->R1 |
| H1->C1 | +--------+-------+ | H2->C2 |
+-------+------+ | +------+-------+
| | |
X---+---+-------------------+------------------+---+---X
| AERO Link |
+-----+--------+ +--------+-----+
|AERO Client C1| |AERO Client C2|
| Nbr: S1 | | Nbr: S2 |
| default->S1 | | default->S2 |
+--------------+ +--------------+
.-. .-.
,-( _)-. ,-( _)-.
.-(_ IP )-. .-(_ IP )-.
(__ EUN ) (__ EUN )
`-(______)-' `-(______)-'
| |
+--------+ +--------+
| Host H1| | Host H2|
+--------+ +--------+
Figure 1: AERO Link Reference Model
Figure 1 above presents the AERO link reference model. In this model:
In common operational practice, there may be many additional Relays, Servers and Clients.
AERO Relays provide default forwarding services to AERO Servers. Relays forward packets between Servers connected to the same AERO link and also forward packets between the AERO link and the native Internetwork. Relays present the AERO link to the native Internetwork as a set of one or more AERO Service Prefixes (ASPs). Each Relay advertises the ASPs for the AERO link into the native IP Internetwork and serves as a gateway between the AERO link and the Internetwork. AERO Relays maintain an AERO interface neighbor cache entry for each AERO Server, and maintain an IP forwarding table entry for each AERO Client Prefix (ACP).
AERO Servers provide default forwarding services to AERO Clients. Each Server also peers with each Relay in a dynamic routing protocol instance to advertise its list of associated ACPs. Servers configure a DHCPv6 server function to facilitate Prefix Delegation (PD) exchanges with Clients. Each delegated prefix becomes an ACP taken from an ASP. Servers forward packets between Clients and Relays, as well as between Clients and other Clients associated with the same Server. AERO Servers maintain an AERO interface neighbor cache entry for each AERO Relay. They also maintain both a neighbor cache entry and an IP forwarding table entry for each of their associated Clients.
AERO Clients act as requesting routers to receive ACPs through DHCPv6 PD exchanges with AERO Servers over the AERO link and sub-delegate portions of their ACPs to EUN interfaces. (Each Client MAY associate with a single Server or with multiple Servers, e.g., for fault tolerance and/or load balancing.) Each IPv6 Client receives at least a /64 IPv6 ACP, and may receive even shorter prefixes. Similarly, each IPv4 Client receives at least a /32 IPv4 ACP (i.e., a singleton IPv4 address), and may receive even shorter prefixes. AERO Clients maintain an AERO interface neighbor cache entry for each of their associated Servers as well as for each of their correspondent Clients.
AERO Clients that act as hosts typically configure a TUN/TAP interface as a point-to-point linkage between the IP layer and the AERO interface. The IP layer therefore sees only the TUN/TAP interface, while the AERO interface provides an intermediate conduit between the TUN/TAP interface and the underlying interfaces. AERO Clients that act as hosts assign one or more IP addresses from their ACPs to the TUN/TAP interface.
An AERO address is an IPv6 link-local address with an embedded ACP and applied to a Client's AERO interface. The AERO address is formed as follows:
For IPv6, the AERO address begins with the prefix fe80::/64 and includes in its interface identifier the base prefix taken from the Client's IPv6 ACP. The base prefix is determined by masking the ACP with the prefix length. For example, if the AERO Client receives the IPv6 ACP:
it constructs its AERO address as:
[RFC4291] that includes the base prefix taken from the Client's IPv4 ACP. For example, if the AERO Client receives the IPv4 ACP:
For IPv4, the AERO address is formed from the lower 64 bits of an IPv4-mapped IPv6 address
it constructs its AERO address as:
The AERO address remains stable as the Client moves between topological locations, i.e., even if its link-layer addresses change.
NOTE: In some cases, prospective neighbors may not have advanced knowledge of the Client's ACP length and may therefore send initial IPv6 ND messages with an AERO destination address that matches the ACP but does not correspond to the base prefix. In that case, the Client MUST accept the address as equivalent to the base address, but then use the base address as the source address of any IPv6 ND message replies. For example, if the Client receives the IPv6 ACP 2001:db8:1000:2000::/56 then subsequently receives an IPv6 ND message with destination address fe80::2001:db8:1000:2001, it accepts the message but uses fe80::2001:db8:1000:2000 as the source address of any IPv6 ND replies.
AERO interfaces use IP-in-IPv6 encapsulation [RFC2473] to exchange tunneled packets with AERO neighbors attached to an underlying IPv6 network, and use IP-in-IPv4 encapsulation [RFC2003][RFC4213] to exchange tunneled packets with AERO neighbors attached to an underlying IPv4 network. AERO interfaces can also coordinate secured tunnel types such as IPsec [RFC4301] or TLS [RFC5246]. When Network Address Translator (NAT) traversal and/or filtering middlebox traversal may be necessary, a UDP header is further inserted immediately above the IP encapsulation header.
AERO interfaces maintain a neighbor cache, and AERO Clients and Servers use an adaptation of standard unicast IPv6 ND messaging. AERO interfaces use unicast Neighbor Solicitation (NS), Neighbor Advertisement (NA), Router Solicitation (RS) and Router Advertisement (RA) messages the same as for any IPv6 link. AERO interfaces use two redirection message types -- the first known as a Predirect message and the second being the standard Redirect message (see Section 3.9). AERO links further use link-local-only addressing; hence, AERO nodes ignore any Prefix Information Options (PIOs) they may receive in RA messages over an AERO interface.
AERO interface ND messages include one or more Target Link-Layer Address Options (TLLAOs) formatted as shown in Figure 2:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 2 | Length = 3 | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link ID | Preference | UDP Port Number (or 0) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+-- --+
| |
+-- IP Address --+
| |
+-- --+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: AERO Target Link-Layer Address Option (TLLAO) Format
In this format, Link ID is an integer value between 0 and 255 corresponding to an underlying interface of the target node, and Preference is an integer value between 0 and 255 indicating the node's preference for this underlying interface (with 255 being the highest preference, 1 being the lowest, and 0 meaning "link disabled"). UDP Port Number and IP Address are set to the addresses used by the target node when it sends encapsulated packets over the underlying interface. When no UDP encapsulation is used, UDP Port Number is set to 0. When the encapsulation IP address family is IPv4, IP Address is formed as an IPv4-mapped IPv6 address [RFC4291].
When a Relay enables an AERO interface, it applies an administratively assigned link-local address fe80::ID to the interface. Each fe80::ID address MUST be unique among all Relays and Servers on the link, and MUST NOT collide with any potential AERO addresses. The addresses are typically taken from the range fe80::/96, e.g., as fe80::1, fe80::2, fe80::3, etc. The Relay also maintains an IP forwarding table entry for each Client-Server association and maintains a neighbor cache entry for each Server on the link. Relays do not require the use of IPv6 ND messaging for reachability determination since Relays and Servers engage in a dynamic routing protocol over the AERO interface. At a minimum, however, Relays respond to NS messages by returning an NA.
When a Server enables an AERO interface, it applies the address fe80:: to the interface as a link-local Subnet Router Anycast address, and also applies an administratively assigned link-local address fe80::ID the same as for Relays. (The Server then accepts DHCPv6 and IPv6 ND solicitation messages destined to either the fe80:: or fe80::ID addresses, but always uses fe80::ID as the source address in the replies it generates.) The Server further configures a DHCPv6 server function to facilitate DHCPv6 PD exchanges with AERO Clients. The Server maintains a neighbor cache entry for each Relay on the link, and manages per-Client neighbor cache entries and IP forwarding table entries based on DHCPv6 exchanges. When the Server receives an NS/RS message on the AERO interface it returns an NA/RA message but does not update the neighbor cache. Each Server also engages in a dynamic routing protocol with all Relays on the link. Finally, the Server provides a simple conduit between Clients and Relays, or between Clients and other Clients. Therefore, packets enter the Server's AERO interface from the link layer and are forwarded back out the link layer without ever leaving the AERO interface and therefore without ever disturbing the network layer.
When a Client enables an AERO interface, it invokes DHCPv6 PD to receive an ACP from an AERO Server. Next, it applies the corresponding AERO address to the AERO interface and creates a neighbor cache entry for the Server, i.e., the PD exchange bootstraps the provisioning of a unique link-local address. The Client maintains a neighbor cache entry for each of its Servers and each of its active correspondent Clients. When the Client receives Redirect/Predirect messages on the AERO interface it updates or creates neighbor cache entries, including link-layer address information. Unsolicited NA messages update the cached link-layer addresses for correspondent Clients (e.g., following a link-layer address change due to node mobility) but do not create new neighbor cache entries. NS/NA messages used for Neighbor Unreachability Detection (NUD) update timers in existing neighbor cache entires but do not update link-layer addresses nor create new neighbor cache entries. Finally, the Client need not maintain any IP forwarding table entries for its Servers or correspondent Clients. Instead, it can set a single "route-to-interface" default route in the IP forwarding table pointing to the AERO interface, and all forwarding decisions can be made within the AERO interface based on neighbor cache entries. (On systems in which adding a default route would violate security policy, the default route could instead be installed via a "synthesized RA", e.g., as discussed in Section 3.11.2.)
AERO interfaces may be configured over multiple underlying interfaces. For example, common mobile handheld devices have both wireless local area network ("WLAN") and cellular wireless links. These links are typically used "one at a time" with low-cost WLAN preferred and highly-available cellular wireless as a standby. In a more complex example, aircraft frequently have many wireless data link types (e.g. satellite-based, terrestrial, air-to-air directional, etc.) with diverse performance and cost properties.
If a Client's multiple underlying interfaces are used "one at a time" (i.e., all other interfaces are in standby mode while one interface is active), then Redirect, Predirect and unsolicited NA messages include only a single TLLAO with Link ID set to a constant value.
If the Client has multiple active underlying interfaces, then from the perspective of IPv6 ND it would appear to have a single link-local address with multiple link-layer addresses. In that case, Redirect, Predirect and unsolicited NA messages MAY include multiple TLLAOs -- each with a different Link ID that corresponds to a specific underlying interface of the Client.
Each AERO interface maintains a conceptual neighbor cache that includes an entry for each neighbor it communicates with on the AERO link, the same as for any IPv6 interface [RFC4861]. AERO interface neighbor cache entires are said to be one of "permanent", "static" or "dynamic".
Permanent neighbor cache entries are created through explicit administrative action; they have no timeout values and remain in place until explicitly deleted. AERO Relays maintain a permanent neighbor cache entry for each Server on the link, and AERO Servers maintain a permanent neighbor cache entry for each Relay on the link.
Static neighbor cache entries are created though DHCPv6 PD exchanges and remain in place for durations bounded by prefix lifetimes. AERO Servers maintain a static neighbor cache entry for each of their associated Clients, and AERO Clients maintain a static neighbor cache for each of their associated Servers. When an AERO Server sends a DHCPv6 Reply message response to a Client's DHCPv6 Solicit/Request or Renew message, it creates or updates a static neighbor cache entry based on the Client's AERO address as the network-layer address, the prefix lifetime as the neighbor cache entry lifetime, the Client's encapsulation IP address and UDP port number as the link-layer address and the prefix length as the length to apply to the AERO address. When an AERO Client receives a DHCPv6 Reply message from a Server, it creates or updates a static neighbor cache entry based on the Reply message link-local source address as the network-layer address, the prefix lifetime as the neighbor cache entry lifetime, and the encapsulation IP source address and UDP source port number as the link-layer address.
Dynamic neighbor cache entries are created based on receipt of an IPv6 ND message, and are garbage-collected if not used within a short timescale. AERO Clients maintain dynamic neighbor cache entries for each of their active correspondent Clients with lifetimes based on IPv6 ND messaging constants. When an AERO Client receives a valid Predirect message it creates or updates a dynamic neighbor cache entry for the Predirect target network-layer and link-layer addresses plus prefix length. The node then sets an "AcceptTime" variable in the neighbor cache entry and uses this value to determine whether packets received from the correspondent can be accepted. When an AERO Client receives a valid Redirect message it creates or updates a dynamic neighbor cache entry for the Redirect target network-layer and link-layer addresses plus prefix length. The Client then sets a "ForwardTime" variable in the neighbor cache entry and uses this value to determine whether packets can be sent directly to the correspondent. The Client also maintains a "MaxRetry" variable to limit the number of keepalives sent when a correspondent may have gone unreachable.
For dynamic neighbor cache entries, when an AERO Client receives a valid NS message it (re)sets AcceptTime for the neighbor to ACCEPT_TIME. When an AERO Client receives a valid solicited NA message, it (re)sets ForwardTime for the neighbor to FORWARD_TIME and sets MaxRetry to MAX_RETRY. When an AERO Client receives a valid unsolicited NA message, it updates the correspondent's link-layer addresses but DOES NOT reset AcceptTime, ForwardTime or MaxRetry.
It is RECOMMENDED that FORWARD_TIME be set to the default constant value 30 seconds to match the default REACHABLE_TIME value specified for IPv6 ND [RFC4861].
It is RECOMMENDED that ACCEPT_TIME be set to the default constant value 40 seconds to allow a 10 second window so that the AERO redirection procedure can converge before AcceptTime decrements below FORWARD_TIME.
It is RECOMMENDED that MAX_RETRY be set to 3 the same as described for IPv6 ND address resolution in Section 7.3.3 of [RFC4861].
Different values for FORWARD_TIME, ACCEPT_TIME, and MAX_RETRY MAY be administratively set, if necessary, to better match the AERO link's performance characteristics; however, if different values are chosen, all nodes on the link MUST consistently configure the same values. Most importantly, ACCEPT_TIME SHOULD be set to a value that is sufficiently longer than FORWARD_TIME to allow the AERO redirection procedure to converge.
IP packets enter a node's AERO interface either from the network layer (i.e., from a local application or the IP forwarding system), or from the link layer (i.e., from the AERO tunnel virtual link). Packets that enter the AERO interface from the network layer are encapsulated and admitted into the AERO link (i.e., they are tunnelled to an AERO interface neighbor). Packets that enter the AERO interface from the link layer are either re-admitted into the AERO link or delivered to the network layer where they are subject to either local delivery or IP forwarding. Since each AERO node has only partial information about neighbors on the link, AERO interfaces may forward packets with link-local destination addresses at a layer below the network layer. This means that AERO nodes act as both IP routers and sub-IP layer forwarding agents. AERO interface sending considerations for Clients, Servers and Relays are given below.
When an IP packet enters a Client's AERO interface from the network layer, if the destination is covered by an ASP the Client searches for a dynamic neighbor cache entry with a non-zero ForwardTime and an AERO address that matches the packet's destination address. (The destination address may be either an address covered by the neighbor's ACP or the (link-local) AERO address itself.) If there is a match, the Client uses a link-layer address in the entry as the link-layer address for encapsulation then admits the packet into the AERO link. If there is no match, the Client instead uses the link-layer address of a neighboring Server as the link-layer address for encapsulation.
When an IP packet enters a Server's AERO interface from the link layer, if the destination is covered by an ASP the Server searches for a static neighbor cache entry with an AERO address that matches the packet's destination address. (The destination address may be either an address covered by the neighbor's ACP or the AERO address itself.) If there is a match, the Server uses a link-layer address in the entry as the link-layer address for encapsulation and re-admits the packet into the AERO link. If there is no match, the Server instead uses the link-layer address in any permanent neighbor cache entry as the link-layer address for encapsulation.
When an IP packet enters a Relay's AERO interface from the network layer, the Relay searches its IP forwarding table for an entry that is covered by an ASP and also matches the destination. If there is a match, the Relay uses the link-layer address in the neighbor cache entry for the next-hop Server as the link-layer address for encapsulation and admits the packet into the AERO link. When an IP packet enters a Relay's AERO interface from the link-layer, if the destination is not a link-local address and is not covered by an ASP the Relay removes the packet from the AERO interface and uses IP forwarding to forward the packet to the Internetwork. If the destination address is covered by an ASP, and there is a more-specific IP forwarding table entry that matches the destination, the Relay uses the link-layer address in the neighbor cache entry for the next-hop Server as the link-layer address for encapsulation and re-admits the packet into the AERO link. When an IP packet enters a Relay's AERO interface from either the network layer or link-layer, and the packet's destination address matches an ASP but there is no more-specific ACP entry, the Relay drops the packet and returns an ICMP Destination Unreachable message (see: Section 3.10).
When an AERO Server receives a packet from a Relay via the AERO interface, the Server MUST NOT forward the packet back to the same or a different Relay.
When an AERO Relay receives a packet from a Server via the AERO interface, the Relay MUST NOT forward the packet back to the same Server.
When an AERO node re-admits a packet into the AERO link without involving the network layer, the node MUST NOT decrement the network layer TTL/Hop-count.
Note that in the above that the link-layer address for encapsulation may be determined through consulting either the neighbor cache or the IP forwarding table. IP forwarding is therefore linked to IPv6 ND via the AERO address.
AERO interfaces encapsulate IP packets according to whether they are entering the AERO interface from the network layer or if they are being re-admitted into the same AERO link they arrived on. This latter form of encapsulation is known as "re-encapsulation".
AERO interfaces encapsulate packets per the base tunneling specifications (e.g., [RFC2003][RFC2473][RFC4213][RFC4301][RFC5246], etc.) except that the interface copies the "TTL/Hop Limit", "Type of Service/Traffic Class" and "Congestion Experienced" values in the packet's IP header into the corresponding fields in the encapsulation header. For packets undergoing re-encapsulation, the AERO interface instead copies the "TTL/Hop Limit", "Type of Service/Traffic Class" and "Congestion Experienced" values in the original encapsulation header into the corresponding fields in the new encapsulation header (i.e., the values are transferred between encapsulation headers and *not* copied from the encapsulated packet's network-layer header).
When AERO UDP encapsulation is used, the AERO interface encapsulates the packet per the base tunneling specification except that it inserts a UDP header between the encapsulation header and the packet's IP header. The AERO interface sets the UDP source port to a constant value that it will use in each successive packet it sends and sets the UDP length field to the length of the IP packet plus 8 bytes for the UDP header itself. For packets sent via a Server, the AERO interface sets the UDP destination port to 8060 (i.e., the IANA-registered port number for AERO) when AERO-only encapsulation is used. For packets sent to a correspondent Client, the AERO interface sets the UDP destination port to the port value stored in the neighbor cache entry for this correspondent.
The AERO interface also sets the UDP checksum field to zero (see: [RFC6935][RFC6936]) for packets that do not require assurance against reassembly errors. For packets that require reassembly checks (see Section 3.9), the AERO interface instead (re)calculates the UDP checksum and writes the resulting value in the UDP checksum field.
The AERO interface next sets the IP protocol number in the encapsulation header to the appropriate value for the first protocol layer within the encapsulation (e.g., IPv4, IPv6, UDP, IPsec, etc.). When IPv6 is used as the encapsulation protocol, the interface then sets the flow label value in the encapsulation header the same as described in [RFC6438]. When IPv4 is used as the encapsulation protocol, the AERO interface sets the DF bit as discussed in Section 3.9.
AERO interfaces decapsulate packets destined either to the node itself or to a destination reached via an interface other than the AERO interface the packet was received on. When AERO UDP encapsulation is used (i.e., when a UDP header with destination port 8060 is present) the interface first verifies the UDP checksum if the UDP checksum was non-zero, then examines the first octet of the encapsulated packet. The packet is accepted if the most significant four bits of the first octet encode the value '0110' (i.e., the version number value for IPv6) or the value '0100' (i.e., the version number value for IPv4). Otherwise, the packet is accepted if the first octet encodes a valid IP protocol number per the IANA "protocol-numbers" registry that matches a supported encapsulation type. Otherwise, the packet is discarded.
Further decapsulation then proceeds according to the appropriate base tunneling specification.
AERO nodes employ simple data origin authentication procedures for encapsulated packets they receive from other nodes on the AERO link. In particular:
Note that this simple data origin authentication only applies to environments in which link-layer addresses cannot be spoofed. Additional security mitigations may be necessary in other environments.
The AERO interface is the node's point of attachment to the AERO link. AERO links over IP networks have a maximum link MTU of 64KB minus the encapsulation overhead (i.e., "64KB-ENCAPS"), since the maximum packet size in the base IP specifications is 64KB [RFC0791][RFC2460]. AERO links over IPv6 networks have a theoretical maximum link MTU of 4GB-ENCAPS [RFC2675], however IPv6 Jumbograms are considered optional for IPv6 nodes [RFC6434] and therefore out of scope for this document.
The IP layer sees the AERO interface as an ordinary interface that configures an MTU that is no larger than the link MTU, i.e., the same as for any interface. Routers MAY set an AERO interface MTU up to the maximum link MTU. Hosts SHOULD set a more conservative MTU so that upper layer protocols will see an appropriate maximum packet size, for example when setting an initial TCP Maximum Segment Size (MSS). In all cases, routers and hosts MUST set an MTU of at least 1500 bytes.
IPv6 specifies a minimum link MTU of 1280 bytes [RFC2460]. This is the minimum packet size an AERO interface MUST be capable of forwarding without returning an ICMP Packet Too Big (PTB) message. Although IPv4 specifies a smaller minimum link MTU of 68 bytes [RFC0791], AERO interfaces also observe a 1280 byte minimum for IPv4. Additionally, the vast majority of links in the Internet configure an MTU of at least 1500 bytes. Hosts have therefore become conditioned to expect that IP packets up to 1500 bytes in length will either be delivered to the final destination or a suitable ICMP Packet Too Big (PTB) message returned, however such PTB messages are often lost [RFC2923]. Therefore, AERO interfaces MUST pass IP packets of at least 1500 bytes even if the encapsulated packet must be fragmented.
PTB messages may be generated by the IP layer of the AERO node if the packet is too large to enter the AERO interface, from within the AERO interface itself if the packet is larger than 1500 bytes and also larger than the MTU of the underlying interface to be used for tunneling minus ENCAPS, or from a router within the AERO link (i.e., the "tunnel") after the encapsulated packet has been admitted into the tunnel. The latter condition would result in a link-layer (L2) PTB message delivered to the AERO interface, while the former two conditions would result in a network-layer (L3) PTB message delivered to the original source.
For AERO links over IPv4, the IP ID field is only 16 bits in length, meaning that fragmentation at high data rates could result in dangerous reassembly misassociations [RFC6864][RFC4963]. For this reason, AERO interfaces that send fragmented IPv4-encapsulated packets MUST either institute rate limiting to ensure that the IP ID field will not wrap before all earlier fragments have been processed, or include an integrity check to detect reassembly errors.
The AERO interface therefore admits encapsulated packets into the tunnel (using fragmentation as necessary) as follows:
While sending packets according to the above specifications, the AERO interface (i.e., the tunnel ingress) MAY also send 1500 byte probe packets to the tunnel egress to determine whether the probes can traverse the tunnel without fragmentation. If the probes succeed, the tunnel ingress can begin sending packets that are larger than 1280-ENCAPS bytes but no larger than 1500 bytes without fragmentation (and for IPv4 with DF set to 1). Since the path MTU within the tunnel may fluctuate due to routing changes, the tunnel ingress SHOULD continually send additional probes subject to rate limiting in case L2 PTB messages are lost. If the path MTU within the tunnel later becomes insufficient, the tunnel ingress must resume fragmentation.
To construct a probe, the tunnel ingress prepares an NS message with a Nonce option plus trailing padding octets added to a length of 1500 bytes without including the length of the padding in the IPv6 Payload Length field. The tunnel ingress then encapsulates the padded NS message in the encapsulation headers (and for IPv4 sets DF to 1) then sends the message to the tunnel egress. If the tunnel egress returns a solicited NA message with a matching Nonce option, the tunnel ingress deems the probe successful.. Note that the tunnel ingress SHOULD NOT include the trailing padding within the Nonce option itself but rather as padding beyond the last option in the NS message; otherwise, the (large) Nonce option would be echoed back in the solicited NA message and may be lost at a link with a small MTU along the reverse path.
In light of the above fragmentation and reassembly recommendations, the tunnel egress MUST be capable of reassembling encapsulated packets up to 1500+ENCAPS bytes in length. It is therefore RECOMMENDED that the tunnel egress be capable of reassembling at least 2KB. Also, in some environments there may be operational assurance that all links within the routing region spanned by the tunnel configure sufficiently large MTUs so that fragmentation and reassembly can be avoided. In those cases, specific tunnel specifications must explain the circumstances under which the above fragmentation and reassembly recommendations need not be applied.
Of possible concern is that some network middleboxes hold the fragments of a fragmented UDP packet until all fragments have arrived before forwarding the fragments to the final destination. This means that the network middlebox must also be able to accommodate fragmented UDP packets up to 1500+ENCAPS bytes in length, i.e., and not just the IP protocol minimum reassembly size. However, network middleboxes are already capable of passing fragmented UDP datagrams up to the maximum fragmented IP packet size as evidenced through actual operational experience (see the thread "PMTUD issue discussion" in the IETF v6ops archive dated September 10, 2014). Hence, there is no need for AERO to stipulate a minimum reassembly size for such devices.
When an AERO node admits encapsulated packets into the AERO interface, it may receive link-layer (L2) or network-layer (L3) error indications.
An L2 error indication is an ICMP error message generated by a router 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. For ICMPv6 [RFC4443], the error Types include "Destination Unreachable", "Packet Too Big (PTB)", "Time Exceeded" and "Parameter Problem". For ICMPv4 [RFC0792], the error Types include "Destination Unreachable", "Fragmentation Needed" (a Destination Unreachable Code that is analogous to the ICMPv6 PTB), "Time Exceeded" and "Parameter Problem".
The ICMP header is followed by the leading portion of the 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".
The L2 error message format is shown in Figure 3:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
| L2 IP Header of |
| error message |
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| L2 ICMP Header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ---
~ ~ P
| IP and other encapsulation | a
| headers of original L3 packet | c
~ ~ k
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ e
~ ~ t
| IP header of |
| original L3 packet | i
~ ~ n
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~ e
| Upper layer headers and | r
| leading portion of body | r
| of the original L3 packet | o
~ ~ r
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ---
Figure 3: AERO Interface L2 Error Message Format
To translate an L2 PTB message to an L3 PTB message, the AERO node first caches the MTU field value of the L2 ICMP header. The node next discards the L2 IP and ICMP headers, and also discards the encapsulation headers of the original L3 packet. Next the node encapsulates the included segment of the original L3 packet in an L3 IP and ICMP header, and sets the ICMP header Type and Code values to appropriate values for the L3 IP protocol. In the process, the node writes the maximum of 1500 bytes and (L2 MTU - ENCAPS) into the MTU field of the L3 ICMP header.
The node next writes the IP source address of the original L3 packet as the destination address of the L3 PTB message and determines the next hop to the destination. If the next hop is reached via the AERO interface, the node uses the IPv6 address "::" or the IPv4 address "0.0.0.0" as the IP source address of the L3 PTB message. Otherwise, the node uses one of its non link-local addresses as the source address of the L3 PTB message. The node finally calculates the ICMP checksum over the L3 PTB message and writes the Checksum in the corresponding field of the L3 ICMP header. The L3 PTB message therefore is formatted as follows:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
| L3 IP Header of |
| error message |
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| L3 ICMP Header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ---
~ ~ p
| IP header of | k
| original L3 packet | t
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ i
~ ~ n
| Upper layer headers and |
| leading portion of body | e
| of the original L3 packet | r
~ ~ r
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ---
Figure 4: AERO Interface L3 Error Message Format
When an AERO Relay receives an L3 packet for which the destination address is covered by an ASP, if there is no more-specific routing information for the destination the Relay drops the packet and returns an L3 Destination Unreachable message. The Relay first writes the IP source address of the original L3 packet as the destination address of the L3 Destination Unreachable message and determines the next hop to the destination. If the next hop is reached via the AERO interface, the Relay uses the IPv6 address "::" or the IPv4 address "0.0.0.0" as the IP source address of the L3 Destination Unreachable message and forwards the message to the next hop within the AERO interface. Otherwise, the Relay uses one of its non link-local addresses as the source address of the L3 Destination Unreachable message and forwards the message via a link outside the AERO interface.
When an AERO node receives any L3 error message via the AERO interface, it examines the destination address in the L3 IP header of the message. If the next hop toward the destination address of the error message is via the AERO interface, the node re-encapsulates and forwards the message to the next hop within the AERO interface. Otherwise, if the source address in the L3 IP header of the message is the IPv6 address "::" or the IPv4 address "0.0.0.0", the node writes one of its non link-local addresses as the source address of the L3 message and recalculates the IP and/or ICMP checksums. The node finally forwards the message via a link outside of the AERO interface.
(*) Note that in some instances the packet-in-error field of an L2 PTB message may not include enough information for translation to an L3 PTB message. In that case, the AERO interface simply discards the L2 PTB message. It can therefore be said that translation of L2 PTB messages to L3 PTB messages can provide a useful optimization when possible, but is not critical for sources that correctly use PLPMTUD.
Each AERO Server configures a DHCPv6 server function to facilitate PD requests from Clients. Each Server is pre-configured with an identical list of ACP-to-Client ID mappings for all Clients enrolled in the AERO system, as well as any information necessary to authenticate Clients. The configuration information is maintained by a central administrative authority for the AERO link and securely propagated to all Servers whenever a new Client is enrolled or an existing Client is withdrawn.
With these identical configurations, each Server can function independently of all other Servers, including the maintenance of active leases. Therefore, no Server-to-Server DHCPv6 state synchronization is necessary, and Clients can optionally hold separate leases for the same ACP from multiple Servers.
In this way, Clients can easily associate with multiple Servers, and can receive new leases from new Servers before deprecating leases held through old Servers. This enables a graceful "make-before-break" capability.
AERO Clients discover the link-layer addresses of AERO Servers via static configuration, or through an automated means such as DNS name resolution. In the absence of other information, the Client resolves the Fully-Qualified Domain Name (FQDN) "linkupnetworks.[domainname]" where "linkupnetworks" is a constant text string and "[domainname]" is the connection-specific DNS suffix for the Client's underlying network connection (e.g., "example.com"). After discovering the link-layer addresses, the Client associates with one or more of the corresponding Servers.
To associate with a Server, the Client acts as a requesting router to request an ACP through a DHCPv6 PD exchange[RFC3315][RFC3633] in which the Client's Solicit/Request messages use the IPv6 "unspecified" address (i.e., "::") as the IPv6 source address, 'All_DHCP_Relay_Agents_and_Servers' as the IPv6 destination address and the link-layer address of the Server as the link-layer destination address. The Client also includes a Client Identifier option with a DHCP Unique Identifier (DUID) plus any necessary authentication options to identify itself to the DHCPv6 server, and includes a Client Link Layer Address Option (CLLAO) [RFC6939] with the format shown in Figure 5:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_CLIENT_LINKLAYER_ADDR | option-length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| link-layer type (16 bits) | Link ID | Preference |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: AERO Client Link-Layer Address Option (CLLAO) Format
Figure 2). If the Client is pre-provisioned with an ACP associated with the AERO service, it MAY also include the ACP in the Solicit/Request message Identity Association (IA) option to indicate its preferred ACP to the DHCPv6 server. The Client then sends the encapsulated DHCPv6 request via the underlying interface.
When the Client receives its ACP and the set of ASPs via a DHCPv6 Reply from the AERO Server, it creates a static neighbor cache entry with the Server's link-local address as the network-layer address and the Server's encapsulation address as the link-layer address. The Client then records the lifetime for the ACP in the neighbor cache entry and marks the neighbor cache entry as "default", i.e., the Client considers the Server as a default router. If the Reply message contains a Vendor-Specific Information Option (see: Section 3.10.3) the Client also caches each ASP in the option.
The Client then applies the AERO address to the AERO interface and sub-delegates the ACP to nodes and links within its attached EUNs (the AERO address thereafter remains stable as the Client moves). The Client also assigns a default IP route to the AERO interface as a route-to-interface, i.e., with no explicit next-hop. The next hop will then be determined after a packet has been submitted to the AERO interface by inspecting the neighbor cache (see above).
On some platforms (e.g., popular cell phone operating systems), the act of assigning a default IPv6 route to the AERO interface may not be permitted from a user application due to security policy. Typically, those platforms include a TUN/TAP interface that acts as a point-to-point conduit between user applications and the AERO interface. In that case, the Client can instead generate a "synthesized RA" message. The message conforms to [RFC4861] and is prepared as follows:
[RFC2131]. Note that in this method, the Client appears as a mobility proxy for applications that bind to the (point-to-point) TUN/TAP interface. The arrangement can be likened to a Proxy AERO scenario in which the mobile node and Client are located within the same physical platform (see Section 3.20 for further details on Proxy AERO).
The Client then sends the synthesized RA message via the TUN/TAP interface, where the operating system kernel will interpret it as though it were generated by an actual router. The operating system will then install a default route and use StateLess Address AutoConfiguration (SLAAC) to configure an IPv6 address on the TUN/TAP interface. Methods for similarly installing an IPv4 default route and IPv4 address on the TUN/TAP interface are based on synthesized DHCPv4 messages
The Client subsequently renews its ACP delegation through each of its Servers by performing DHCPv6 Renew/Reply exchanges with its AERO address as the IPv6 source address, 'All_DHCP_Relay_Agents_and_Servers' as the IPv6 destination address, the link-layer address of a Server as the link-layer destination address and the same Client identifier, authentication options and CLLAO option as was used in the initial PD request. Note that if the Client does not issue a DHCPv6 Renew before the Server has terminated the lease (e.g., if the Client has been out of touch with the Server for a considerable amount of time), the Server's Reply will report NoBinding and the Client must re-initiate the DHCPv6 PD procedure. If the Client sends synthesized RA and/or DHCPv4 messages (see above), it also sends a new synthesized message when issuing a DHCPv6 Renew or when re-initiating the DHCPv6 PD procedure.
Since the Client's AERO address is configured from the unique ACP delegation it receives, there is no need for Duplicate Address Detection (DAD) on AERO links. Other nodes maliciously attempting to hijack an authorized Client's AERO address will be denied access to the network by the DHCPv6 server due to an unacceptable link-layer address and/or security parameters (see: Security Considerations).
AERO Clients ignore the IP address and UDP port number in any S/TLLAO options in ND messages they receive directly from another AERO Client, but examine the Link ID and Preference values to match the message with the correct link-layer address information.
When a source Client forwards a packet to a prospective destination Client (i.e., one for which the packet's destination address is covered by an ASP), the source Client initiates an AERO route optimization procedure as specified in Section 3.13.
AERO Servers configure a DHCPv6 server function on their AERO links. AERO Servers arrange to add their encapsulation layer IP addresses (i.e., their link-layer addresses) to the DNS resource records for the FQDN "linkupnetworks.[domainname]" before entering service.
When an AERO Server receives a prospective Client's DHCPv6 PD Solicit/Request message, it first authenticates the message. If authentication succeeds, the Server determines the correct ACP to delegate to the Client by matching the Client's DUID within an online directory service (e.g., LDAP). The Server then delegates the ACP and creates a static neighbor cache entry for the Client's AERO address with lifetime set to no more than the lease lifetime and the Client's link-layer address as the link-layer address for the Link ID specified in the CLLAO option. The Server then creates an IP forwarding table entry so that the AERO routing system will propagate the ACP to all Relays (see: Section 3.12). Finally, the Server sends a DHCPv6 Reply message to the Client while using fe80::ID as the IPv6 source address, the Client's AERO address as the IPv6 destination address, and the Client's link-layer address as the destination link-layer address. The Server also includes a Server Unicast option with server-address set to fe80::ID so that all future Client/Server transactions will be link-local-only unicast over the AERO link.
When the Server sends the DHCPv6 Reply message, it also includes a DHCPv6 Vendor-Specific Information Option with 'enterprise-number' set to "TBD2" (see: IANA Considerations). The option is formatted as shown in[RFC3315] and with the AERO enterprise-specific format shown in Figure 6:
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_VENDOR_OPTS | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| enterprise-number ("TBD2") |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Prefix Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ ASP (1) +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Prefix Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ ASP (2) +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Prefix Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ ASP (3) +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. (etc.) .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: AERO Vendor-Specific Information Option
Figure 6, the option includes one or more ASP. The ASP field contains the IP prefix as it would appear in the interface identifier portion of the corresponding AERO address (see: Section 3.3). For IPv6, valid values for the Prefix Length field are 0 through 64; for IPv4, valid values are 0 through 32.
After the initial DHCPv6 PD exchange, the AERO Server maintains the neighbor cache entry for the Client as long as the lease lifetime remains current. If the Client issues a Renew/Reply exchange, the Server extends the lifetime. If the Client issues a Release/Reply exchange, or if the Client does not issue a Renew/Reply within the lease lifetime, the Server deletes the neighbor cache entry for the Client and withdraws the IP route from the AERO routing system.
Relays require full topology information of all Client/Server associations, while individual Servers only require partial topology information, i.e., they only need to know the ACPs associated with their current set of associated Clients. This is accomplished through the use of an internal instance of the Border Gateway Protocol (BGP) [RFC4271] coordinated between Servers and Relays. This internal BGP instance does not interact with the public Internet BGP instance; therefore, the AERO link is presented to the IP Internetwork as a small set of ASPs as opposed to the full set of individual ACPs.
In a reference BGP arrangement, each AERO Server is configured as an Autonomous System Border Router (ASBR) for a stub Autonomous System (AS) (possibly using a private AS Number (ASN) [RFC1930]), and each Server further peers with each Relay but does not peer with other Servers. Similarly, Relays need not peer with each other, since they will receive all updates from all Servers and will therefore have a consistent view of the AERO link ACP delegations.
Each Server maintains a working set of associated Clients, and dynamically announces new ACPs and withdraws departed ACPs in its BGP updates to Relays (this is typically accomplished via a "redistribute static" routing directive). Relays do not send BGP updates to Servers, however, such that the BGP route reporting is unidirectional from the Servers to the Relays.
The Relays therefore discover the full topology of the AERO link in terms of the working set of ACPs associated with each Server, while the Servers only discover the ACPs of their associated Clients. Since Clients are expected to remain associated with their current set of Servers for extended timeframes, the amount of BGP control messaging between Servers and Relays should be minimal. However, BGP peers SHOULD dampen any route oscillations caused by impatient Clients that repeatedly associate and disassociate with Servers.
Figure 7 depicts the AERO redirection reference operational scenario, using IPv6 addressing as the example (while not shown, a corresponding example for IPv4 addressing can be easily constructed). The figure shows an AERO Relay ('R1'), two AERO Servers ('S1', 'S2'), two AERO Clients ('C1', 'C2') and two ordinary IPv6 hosts ('H1', 'H2'):
+--------------+ +--------------+ +--------------+
| Server S1 | | Relay R1 | | Server S2 |
+--------------+ +--------------+ +--------------+
fe80::2 fe80::1 fe80::3
L2(S1) L2(R1) L2(S2)
| | |
X-----+-----+------------------+-----------------+----+----X
| AERO Link |
L2(A) L2(B)
fe80::2001:db8:0:0 fe80::2001:db8:1:0
+--------------+ +--------------+
|AERO Client C1| |AERO Client C2|
+--------------+ +--------------+
2001:DB8:0::/48 2001:DB8:1::/48
| |
.-. .-.
,-( _)-. 2001:db8:0::1 2001:db8:1::1 ,-( _)-.
.-(_ IP )-. +---------+ +---------+ .-(_ IP )-.
(__ EUN )--| Host H1 | | Host H2 |--(__ EUN )
`-(______)-' +---------+ +---------+ `-(______)-'
Figure 7: AERO Reference Operational Scenario
In Figure 7, Relay ('R1') applies the address fe80::1 to its AERO interface with link-layer address L2(R1), Server ('S1') applies the address fe80::2 with link-layer address L2(S1),and Server ('S2') applies the address fe80::3 with link-layer address L2(S2). Servers ('S1') and ('S2') next arrange to add their link-layer addresses to a published list of valid Servers for the AERO link.
AERO Client ('C1') receives the ACP 2001:db8:0::/48 in a DHCPv6 PD exchange via AERO Server ('S1') then applies the address fe80::2001:db8:0:0 to its AERO interface with link-layer address L2(C1). Client ('C1') configures a default route and neighbor cache entry via the AERO interface with next-hop address fe80::2 and link-layer address L2(S1), then sub-delegates the ACP to its attached EUNs. IPv6 host ('H1') connects to the EUN, and configures the address 2001:db8:0::1.
AERO Client ('C2') receives the ACP 2001:db8:1::/48 in a DHCPv6 PD exchange via AERO Server ('S2') then applies the address fe80::2001:db8:1:0 to its AERO interface with link-layer address L2(C2). Client ('C2') configures a default route and neighbor cache entry via the AERO interface with next-hop address fe80::3 and link-layer address L2(S2), then sub-delegates the ACP to its attached EUNs. IPv6 host ('H1') connects to the EUN, and configures the address 2001:db8:1::1.
Again, with reference to Figure 7, when source host ('H1') sends a packet to destination host ('H2'), the packet is first forwarded over the source host's attached EUN to Client ('C1'). Client ('C1') then forwards the packet via its AERO interface to Server ('S1') and also sends a Predirect message toward Client ('C2') via Server ('S1'). Server ('S1') then re-encapsulates and forwards both the packet and the Predirect message out the same AERO interface toward Client ('C2') via Relay ('R1').
When Relay ('R1') receives the packet and Predirect message, it consults its forwarding table to discover Server ('S2') as the next hop toward Client ('C2'). Relay ('R1') then forwards both the packet and the Predirect message to Server ('S2'), which then forwards them to Client ('C2').
After Client ('C2') receives the Predirect message, it process the message and returns a Redirect message toward Client ('C1') via Server ('S2'). During the process, Client ('C2') also creates or updates a dynamic neighbor cache entry for Client ('C1').
When Server ('S2') receives the Redirect message, it re-encapsulates the message and forwards it on to Relay ('R1'), which forwards the message on to Server ('S1') which forwards the message on to Client ('C1'). After Client ('C1') receives the Redirect message, it processes the message and creates or updates a dynamic neighbor cache entry for Client ('C2').
Following the above Predirect/Redirect message exchange, forwarding of packets from Client ('C1') to Client ('C2') without involving any intermediate nodes is enabled. The mechanisms that support this exchange are specified in the following sections.
AERO Redirect/Predirect messages use the same format as for ICMPv6 Redirect messages depicted in Section 4.5 of [RFC4861], but also include a new "Prefix Length" field taken from the low-order 8 bits of the Redirect message Reserved field. For IPv6, valid values for the Prefix Length field are 0 through 64; for IPv4, valid values are 0 through 32. The Redirect/Predirect messages are formatted as shown in Figure 8:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type (=137) | Code (=0/1) | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Prefix Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Target Address +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Destination Address +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Options ...
+-+-+-+-+-+-+-+-+-+-+-+-
Figure 8: AERO Redirect/Predirect Message Format
When a Client forwards a packet with a source address from one of its ACPs toward a destination address covered by an ASP (i.e., toward another AERO Client connected to the same AERO link), the source Client MAY send a Predirect message forward toward the destination Client via the Server.
In the reference operational scenario, when Client ('C1') forwards a packet toward Client ('C2'), it MAY also send a Predirect message forward toward Client ('C2'), subject to rate limiting (see Section 8.2 of [RFC4861]). Client ('C1') prepares the Predirect message as follows:
Note that the act of sending Predirect messages is cited as "MAY", since Client ('C1') may have advanced knowledge that the direct path to Client ('C2') would be unusable or otherwise undesirable. If the direct path later becomes unusable after the initial route optimization, Client ('C1') simply allows packets to again flow through Server ('S1').
When Server ('S1') receives a Predirect message from Client ('C1'), it first verifies that the TLLAOs in the Predirect are a proper subset of the Link IDs in Client ('C1')'s neighbor cache entry. If the Client's TLLAOs are not acceptable, Server ('S1') discards the message. Otherwise, Server ('S1') validates the message according to the ICMPv6 Redirect message validation rules in Section 8.1 of [RFC4861], except that the Predirect has Code=1. Server ('S1') also verifies that Client ('C1') is authorized to use the Prefix Length in the Predirect when applied to the AERO address in the network-layer source address by searching for the AERO address in the neighbor cache. If validation fails, Server ('S1') discards the Predirect; otherwise, it copies the correct UDP Port numbers and IP Addresses for Client ('C1')'s links into the (previously empty) TLLAOs.
Server ('S1') then examines the network-layer destination address of the Predirect to determine the next hop toward Client ('C2') by searching for the AERO address in the neighbor cache. Since Client ('C2') is not one of its neighbors, Server ('S1') re-encapsulates the Predirect and relays it via Relay ('R1') by changing the link-layer source address of the message to 'L2(S1)' and changing the link-layer destination address to 'L2(R1)'. Server ('S1') finally forwards the re-encapsulated message to Relay ('R1') without decrementing the network-layer TTL/Hop Limit field.
When Relay ('R1') receives the Predirect message from Server ('S1') it determines that Server ('S2') is the next hop toward Client ('C2') by consulting its forwarding table. Relay ('R1') then re-encapsulates the Predirect while changing the link-layer source address to 'L2(R1)' and changing the link-layer destination address to 'L2(S2)'. Relay ('R1') then relays the Predirect via Server ('S2').
When Server ('S2') receives the Predirect message from Relay ('R1') it determines that Client ('C2') is a neighbor by consulting its neighbor cache. Server ('S2') then re-encapsulates the Predirect while changing the link-layer source address to 'L2(S2)' and changing the link-layer destination address to 'L2(C2)'. Server ('S2') then forwards the message to Client ('C2').
When Client ('C2') receives the Predirect message, it accepts the Predirect only if the message has a link-layer source address of one of its Servers (e.g., L2(S2)). Client ('C2') further accepts the message only if it is willing to serve as a redirection target. Next, Client ('C2') validates the message according to the ICMPv6 Redirect message validation rules in Section 8.1 of [RFC4861], except that it accepts the message even though Code=1 and even though the network-layer source address is not that of it's current first-hop router.
In the reference operational scenario, when Client ('C2') receives a valid Predirect message, it either creates or updates a dynamic neighbor cache entry that stores the Target Address of the message as the network-layer address of Client ('C1') , stores the link-layer addresses found in the TLLAOs as the link-layer addresses of Client ('C1') and stores the Prefix Length as the length to be applied to the network-layer address for forwarding purposes. Client ('C2') then sets AcceptTime for the neighbor cache entry to ACCEPT_TIME.
After processing the message, Client ('C2') prepares a Redirect message response as follows:
After Client ('C2') prepares the Redirect message, it sends the message to Server ('S2').
When Server ('S2') receives a Redirect message from Client ('C2'), it first verifies that the TLLAOs in the Redirect are a proper subset of the Link IDs in Client ('C2')'s neighbor cache entry. If the Client's TLLAOs are not acceptable, Server ('S2') discards the message. Otherwise, Server ('S2') validates the message according to the ICMPv6 Redirect message validation rules in Section 8.1 of [RFC4861]. Server ('S2') also verifies that Client ('C2') is authorized to use the Prefix Length in the Redirect when applied to the AERO address in the network-layer source address by searching for the AERO address in the neighbor cache. If validation fails, Server ('S2') discards the Predirect; otherwise, it copies the correct UDP Port numbers and IP Addresses for Client ('C2')'s links into the (previously empty) TLLAOs.
Server ('S2') then examines the network-layer destination address of the Predirect to determine the next hop toward Client ('C2') by searching for the AERO address in the neighbor cache. Since Client ('C2') is not a neighbor, Server ('S2') re-encapsulates the Predirect and relays it via Relay ('R1') by changing the link-layer source address of the message to 'L2(S2)' and changing the link-layer destination address to 'L2(R1)'. Server ('S2') finally forwards the re-encapsulated message to Relay ('R1') without decrementing the network-layer TTL/Hop Limit field.
When Relay ('R1') receives the Predirect message from Server ('S2') it determines that Server ('S1') is the next hop toward Client ('C1') by consulting its forwarding table. Relay ('R1') then re-encapsulates the Predirect while changing the link-layer source address to 'L2(R1)' and changing the link-layer destination address to 'L2(S1)'. Relay ('R1') then relays the Predirect via Server ('S1').
When Server ('S1') receives the Predirect message from Relay ('R1') it determines that Client ('C1') is a neighbor by consulting its neighbor cache. Server ('S1') then re-encapsulates the Predirect while changing the link-layer source address to 'L2(S1)' and changing the link-layer destination address to 'L2(C1)'. Server ('S1') then forwards the message to Client ('C1').
When Client ('C1') receives the Redirect message, it accepts the message only if it has a link-layer source address of one of its Servers (e.g., ''L2(S1)'). Next, Client ('C1') validates the message according to the ICMPv6 Redirect message validation rules in Section 8.1 of [RFC4861], except that it accepts the message even though the network-layer source address is not that of it's current first-hop router. Following validation, Client ('C1') then processes the message as follows.
In the reference operational scenario, when Client ('C1') receives the Redirect message, it either creates or updates a dynamic neighbor cache entry that stores the Target Address of the message as the network-layer address of Client ('C2'), stores the link-layer addresses found in the TLLAOs as the link-layer addresses of Client ('C2') and stores the Prefix Length as the length to be applied to the network-layer address for forwarding purposes. Client ('C1') then sets ForwardTime for the neighbor cache entry to FORWARD_TIME.
Now, Client ('C1') has a neighbor cache entry with a valid ForwardTime value, while Client ('C2') has a neighbor cache entry with a valid AcceptTime value. Thereafter, Client ('C1') may forward ordinary network-layer data packets directly to Client ('C2') without involving any intermediate nodes, and Client ('C2') can verify that the packets came from an acceptable source. (In order for Client ('C2') to forward packets to Client ('C1'), a corresponding Predirect/Redirect message exchange is required in the reverse direction; hence, the mechanism is asymmetric.)
In some environments, the Server nearest the target Client may need to serve as the redirection target, e.g., if direct Client-to-Client communications are not possible. In that case, the Server prepares the Redirect message the same as if it were the destination Client (see: Section 3.9.6), except that it writes its own link-layer address in the TLLAO option. The Server must then maintain a neighbor cache entry for the redirected source Client.
AERO nodes perform Neighbor Unreachability Detection (NUD) by sending unicast NS messages to elicit solicited NA messages from neighbors the same as described in [RFC4861]. NUD is performed either reactively in response to persistent L2 errors (see Section 3.10) or proactively to refresh existing neighbor cache entries.
When an AERO node sends an NS/NA message, it MUST use its link-local address as the IPv6 source address and the link-local address of the neighbor as the IPv6 destination address. When an AERO node receives an NS message or a solicited NA message, it accepts the message if it has a neighbor cache entry for the neighbor; otherwise, it ignores the message.
When a source Client is redirected to a target Client it SHOULD proactively test the direct path by sending an initial NS message to elicit a solicited NA response. While testing the path, the source Client can optionally continue sending packets via the Server, maintain a small queue of packets until target reachability is confirmed, or (optimistically) allow packets to flow directly to the target. The source Client SHOULD thereafter continue to proactively test the direct path to the target Client (see Section 7.3 of [RFC4861]) periodically in order to keep dynamic neighbor cache entries alive.
In particular, while the source Client is actively sending packets to the target Client it SHOULD also send NS messages separated by RETRANS_TIMER milliseconds in order to receive solicited NA messages. If the source Client is unable to elicit a solicited NA response from the target Client after MAX_RETRY attempts, it SHOULD set ForwardTime to 0 and resume sending packets via one of its Servers. Otherwise, the source Client considers the path usable and SHOULD thereafter process any link-layer errors as a hint that the direct path to the target Client has either failed or has become intermittent.
When a target Client receives an NS message from a source Client, it resets AcceptTime to ACCEPT_TIME if a neighbor cache entry exists; otherwise, it discards the NS message. If ForwardTime is non-zero, the target Client then sends a solicited NA message to the link-layer address of the source Client; otherwise, it sends the solicited NA message to the link-layer address of one of its Servers.
When a source Client receives a solicited NA message from a target Client, it resets ForwardTime to FORWARD_TIME if a neighbor cache entry exists; otherwise, it discards the NA message.
When ForwardTime for a dynamic neighbor cache entry expires, the source Client resumes sending any subsequent packets via a Server and may (eventually) attempt to re-initiate the AERO redirection process. When AcceptTime for a dynamic neighbor cache entry expires, the target Client discards any subsequent packets received directly from the source Client. When both ForwardTime and AcceptTime for a dynamic neighbor cache entry expire, the Client deletes the neighbor cache entry.
When a Client needs to change its link-layer address, e.g., due to a mobility event, it performs an immediate DHCPv6 Rebind/Reply exchange via each of its Servers using the new link-layer address as the source and with a CLLAO that includes the correct Link ID and Preference values. If authentication succeeds, the Server then update its neighbor cache and sends a DHCPv6 Reply. Note that if the Client does not issue a DHCPv6 Rebind before the Server has terminated the lease (e.g., if the Client has been out of touch with the Server for a considerable amount of time), the Server's Reply will report NoBinding and the Client must re-initiate the DHCPv6 PD procedure.
Next, the Client sends unsolicited NA messages to each of its correspondent Client neighbors using the same procedures as specified in Section 7.2.6 of [RFC4861], except that it sends the messages as unicast to each neighbor via a Server instead of multicast. In this process, the Client should send no more than MAX_NEIGHBOR_ADVERTISEMENT messages separated by no less than RETRANS_TIMER seconds to each neighbor.
With reference to Figure 7, when Client ('C2') needs to change its link-layer address it sends unicast unsolicited NA messages to Client ('C1') via Server ('S2') as follows:
When Server ('S1') receives the NA message, it relays the message in the same way as described for relaying Redirect messages in Section 3.12.7. In particular, Server ('S1') copies the correct UDP port numbers and IP addresses into the TLLAOs, changes the link-layer source address to its own address, changes the link-layer destination address to the address of Relay ('R1'), then forwards the NA message via the relaying chain the same as for a Redirect.
When Client ('C1') receives the NA message, it accepts the message only if it already has a neighbor cache entry for Client ('C2') then updates the link-layer addresses for Client ('C2') based on the addresses in the TLLAOs. However, Client ('C1') MUST NOT update ForwardTime since Client ('C2') will not have updated AcceptTime.
Note that these unsolicited NA messages are unacknowledged; hence, Client ('C2') has no way of knowing whether Client ('C1') has received them. If the messages are somehow lost, however, Client ('C1') will soon learn of the mobility event via the NUD procedures specified in Section 3.14.
When a Client needs to bring a new underlying interface into service (e.g., when it activates a new data link), it performs an immediate Rebind/Reply exchange via each of its Servers using the new link-layer address as the source address and with a CLLAO that includes the new Link ID and Preference values. If authentication succeeds, the Server then updates its neighbor cache and sends a DHCPv6 Reply. The Client MAY then send unsolicited NA messages to each of its correspondent Clients to inform them of the new link-layer address as described in Section 3.15.1.
When a Client needs to remove an existing underlying interface from service (e.g., when it de-activates an existing data link), it performs an immediate Rebind/Reply exchange via each of its Servers over any available link with a CLLAO that includes the deprecated Link ID and a Preference value of 0. If authentication succeeds, the Server then updates its neighbor cache and sends a DHCPv6 Reply. The Client SHOULD then send unsolicited NA messages to each of its correspondent Clients to inform them of the deprecated link-layer address as described in Section 3.15.1.
When a Client associates with a new Server, it performs the Client procedures specified in Section 3.10.
When a Client disassociates with an existing Server, it sends a DHCPv6 Release message to the unicast link-local network layer address of the old Server. The Client SHOULD send the message via a new Server (i.e., by setting the link-layer destination address to the address of the new Server) in case the old Server is unreachable at the link layer, e.g., if the old Server is in a different network partition. The new Server will forward the message to a Relay, which will in turn forward the message to the old Server.
When the old Server receives the DHCPv6 Release, it first authenticates the message. If authentication succeeds, the old Server withdraws the IP route from the AERO routing system and deletes the neighbor cache entry for the Client. (The old Server MAY impose a small delay before deleting the neighbor cache entry so that any packets already in the system can still be delivered to the Client.) The old Server then returns a DHCPv6 Reply message via a Relay. The Client can then use the Reply message to verify that the termination signal has been processed, and can delete both the default route and the neighbor cache entry for the old Server. (Note that the Server's Reply to the Client's Release message may be lost, e.g., if the AERO routing system has not yet converged. Since the Client is responsible for reliability, however, it will retry until it gets an indication that the Release was successful.)
Clients SHOULD NOT move rapidly between Servers in order to avoid causing excessive oscillations in the AERO routing system. Such oscillations could result in intermittent reachability for the Client itself, while causing little harm to the network due to routing protocol dampening. Examples of when a Client might wish to change to a different Server include a Server that has gone unreachable, topological movements of significant distance, etc.
A source Client may connect only to an IPvX underlying network, while the target Client connects only to an IPvY underlying network. In that case, the target and source Clients have no means for reaching each other directly (since they connect to underlying networks of different IP protocol versions) and so must ignore any redirection messages and continue to send packets via the Server.
When the underlying network does not support multicast, AERO nodes map IPv6 link-scoped multicast addresses (including 'All_DHCP_Relay_Agents_and_Servers') to the link-layer address of a Server.
When the underlying network supports multicast, AERO nodes use the multicast address mapping specification found in [RFC2529] for IPv4 underlying networks and use a direct multicast mapping for IPv6 underlying networks. (In the latter case, "direct multicast mapping" means that if the IPv6 multicast destination address of the encapsulated packet is "M", then the IPv6 multicast destination address of the encapsulating header is also "M".)
When Servers on the AERO link do not provide DHCPv6 services, operation can still be accommodated through administrative configuration of ACPs on AERO Clients. In that case, administrative configurations of AERO interface neighbor cache entries on both the Server and Client are also necessary. However, this may interfere with the ability for Clients to dynamically change to new Servers, and can expose the AERO link to misconfigurations unless the administrative configurations are carefully coordinated.
In some AERO link scenarios, there may be no Servers on the link and/or no need for Clients to use a Server as an intermediary trust anchor. In that case, each Client acts as a Server unto itself to establish neighbor cache entries by performing direct Client-to-Client IPv6 ND message exchanges, and some other form of trust basis must be applied so that each Client can verify that the prospective neighbor is authorized to use its claimed ACP.
When there is no Server on the link, Clients must arrange to receive ACPs and publish them via a secure alternate prefix delegation authority through some means outside the scope of this document.
Proxy Mobile IPv6 (PMIPv6) [RFC5213][RFC5844] presents a localized mobility management scheme for use within an access network domain. It is typically used in cellular wireless service provider networks, and allows mobile nodes to receive and retain a stable IP address without needing to implement any special mobility protocols. In the PMIPv6 architecture, access network devices known as Mobility Access Gateways (MAGs) provide mobile nodes with an access link abstraction and receive prefixes for the mobile nodes from a Local Mobility Anchor (LMA).
The AERO Client (acting as a MAG) can similarly provide proxy services for mobile nodes that do not participate in AERO messaging. The proxy Client presents an access link abstraction to mobile nodes, and performs DHCPv6 PD exchanges over the AERO interface with an AERO Server (acting as an LMA) to receive a prefix for address provisioning of the mobile node.
When a mobile node comes onto an access link presented by a proxy Client, the Client authenticates the node and obtains a unique identifier that it can use as the DUID in its DHCPv6 PD messages to the Server. When the Server delegates a prefix, the Client creates a new AERO address for the mobile node and assigns the delegated prefix to the mobile node's access link. The Client then generates address autoconfiguration messages (e.g., IPv6 RA, DHCPv6, DHCPv4, etc.) over the access link and configures itself as a default router for the mobile node. Since the Client may serve many such mobile nodes simultaneously, it may configure multiple AERO addresses, i.e., one for each mobile node.
When two mobile nodes are associated with the same proxy Client, the Client can forward traffic between the mobiles without involving the Server since it configures the AERO addresses of each mobile and therefore also has the necessary routing information. When two mobiles are associated with different Clients, the first mobile node's Client can initiate standard AERO route optimization using the mobile's AERO address as the source for route optimization messaging. This may result in a route optimization where the first mobile node's Client discovers a direct path to the second mobile node's Client.
When a mobile node moves to a new proxy Client, the old proxy Client issues a DHCPv6 Release message and sends unsolicited NA messages to any of the mobile node's correspondents the same as specified for announcing link-layer address changes in Section 3.15.1. However, since the old Client has no way of knowing where the mobile has moved to, it sets the Code field in the NA message to 1. When the correspondent receives such an NA message, it deletes the neighbor cache entry for the departed mobile node and again allows packets to flow through its Server.
In addition to the use of DHCPv6 PD signaling, the AERO approach differs from PMIPv6 in its use of the NBMA virtual link model instead of point-to-point tunnels. This provides a more agile interface for Client-to-Server coordinations, and also facilitates simple route optimization. The AERO routing system is also arranged in such a fashion that Clients get the same service from any Server they happen to associate with. This provides a natural fault tolerance and load balancing capability such as desired for distributed mobility management. All other considerations are the same as specified in [RFC5213][RFC5844].
When an enterprise mobile device moves from a campus LAN connection to a public Internet link, it must re-enter the enterprise via a security gateway that has both an physical interface connection to the Internet and a physical interface connection to the enterprise internetwork. This most often entails the establishment of a Virtual Private Network (VPN) link over the public Internet from the mobile device to the security gateway. During this process, the mobile device supplies the security gateway with its public Internet address as the link-layer address for the VPN. The mobile device then acts as an AERO Client to negotiate with the security gateway to obtain its ACP.
In order to satisfy this need, the security gateway also operates as an AERO Server with support for AERO Client proxying. In particular, when a mobile device (i.e., the Client) connects via the security gateway (i.e., the Server), the Server provides the Client with an ACP in a DHCPv6 PD exchange the same as if it were attached to an enterprise campus access link. The Server then replaces the Client's link-layer source address with the Server's enterprise-facing link-layer address in all AERO messages the Client sends toward neighbors on the AERO link. The AERO messages are then delivered to other devices on the AERO link as if they were originated by the security gateway instead of by the AERO Client. In the reverse direction, the AERO messages sourced by devices within the enterprise network can be forwarded to the security gateway, which then replaces the link-layer destination address with the Client's link-layer address and replaces the link-layer source address with its own (Internet-facing) link-layer address.
After receiving the ACP, the Client can send IP packets that use an address taken from the ACP as the network layer source address, the Client's link-layer address as the link-layer source address, and the Server's Internet-facing link-layer address as the link-layer destination address. The Server will then rewrite the link-layer source address with the Server's own enterprise-facing link-layer address and rewrite the link-layer destination address with the target AERO node's link-layer address, and the packets will enter the enterprise network as though they were sourced from a device located within the enterprise. In the reverse direction, when a packet sourced by a node within the enterprise network uses a destination address from the Client's ACP, the packet will be delivered to the security gateway which then rewrites the link-layer destination address to the Client's link-layer address and rewrites the link-layer source address to the Server's Internet-facing link-layer address. The Server then delivers the packet across the VPN to the AERO Client. In this way, the AERO virtual link is essentially extended *through* the security gateway to the point at which the VPN link and AERO link are effectively grafted together by the link-layer address rewriting performed by the security gateway. All AERO messaging services (including route optimization and mobility signaling) are therefore extended to the Client.
In order to support this virtual link grafting, the security gateway (acting as an AERO Server) must keep static neighbor cache entries for all of its associated Clients located on the public Internet. The neighbor cache entry is keyed by the AERO Client's AERO address the same as if the Client were located within the enterprise internetwork. The neighbor cache is then managed in all ways as though the Client were an ordinary AERO Client. This includes the AERO IPv6 ND messaging signaling for Route Optimization and Neighbor Unreachability Detection.
Note that the main difference between a security gateway acting as an AERO Server and an enterprise-internal AERO Server is that the security gateway has at least one enterprise-internal physical interface and at least one public Internet physical interface. Conversely, the enterprise-internal AERO Server has only enterprise-internal physical interfaces. For this reason security gateway proxying is needed to ensure that the public Internet link-layer addressing space is kept separate from the enterprise-internal link-layer addressing space. This is afforded through a natural extension of the security association caching already performed for each VPN client by the security gateway.
An application-layer implementation is in progress.
IANA is instructed to assign a new 2-octet Hardware Type number "TBD1" for AERO in the "arp-parameters" registry per Section 2 of [RFC5494]. The number is assigned from the 2-octet Unassigned range with Hardware Type "AERO" and with this document as the reference.
IANA is instructed to assign a 4-octet Enterprise Number "TBD2" for AERO in the "enterprise-numbers" registry per [RFC3315].
AERO link security considerations are the same as for standard IPv6 Neighbor Discovery [RFC4861] except that AERO improves on some aspects. In particular, AERO uses a trust basis between Clients and Servers, where the Clients only engage in the AERO mechanism when it is facilitated by a trust anchor. Unless there is some other means of authenticating the Client's identity (e.g., link-layer security), AERO nodes SHOULD also use DHCPv6 securing services (e.g., DHCPv6 authentication, Secure DHCPv6 [I-D.ietf-dhc-sedhcpv6], etc.) for Client authentication and network admission control.
AERO Redirect, Predirect and unsolicited NA messages SHOULD include a Timestamp option (see Section 5.3 of [RFC3971]) that other AERO nodes can use to verify the message time of origin. AERO Predirect, NS and RS messages SHOULD include a Nonce option (see Section 5.3 of [RFC3971]) that recipients echo back in corresponding responses.
AERO links must be protected against link-layer address spoofing attacks in which an attacker on the link pretends to be a trusted neighbor. Links that provide link-layer securing mechanisms (e.g., IEEE 802.1X WLANs) and links that provide physical security (e.g., enterprise network wired LANs) provide a first line of defense that is often sufficient. In other instances, additional securing mechanisms such as Secure Neighbor Discovery (SeND) [RFC3971], IPsec [RFC4301] or TLS [RFC5246] may be necessary.
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 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 unauthorized nodes via a NAT function.)
On some AERO links, establishment and maintenance of a direct path between neighbors requires secured coordination such as through the Internet Key Exchange (IKEv2) protocol [RFC5996] to establish a security association.
Discussions both on IETF lists and in private exchanges helped shape some of the concepts in this work. Individuals who contributed insights include Mikael Abrahamsson, Mark Andrews, Fred Baker, Stewart Bryant, Brian Carpenter, Wojciech Dec, Ralph Droms, Sri Gundavelli, Brian Haberman, Joel Halpern, Sascha Hlusiak, Lee Howard, Andre Kostur, Ted Lemon, Joe Touch and Bernie Volz. Members of the IESG also provided valuable input during their review process that greatly improved the document. Special thanks go to Stewart Bryant, Joel Halpern and Brian Haberman for their shepherding guidance.
This work has further been encouraged and supported by Boeing colleagues including Keith Bartley, Dave Bernhardt, Cam Brodie, Balaguruna Chidambaram, Claudiu Danilov, Wen Fang, Anthony Gregory, Jeff Holland, Ed King, Gen MacLean, Kent Shuey, Brian Skeen, Mike Slane, Julie Wulff, Yueli Yang, and other members of the BR&T and BIT mobile networking teams.
Earlier works on NBMA tunneling approaches are found in [RFC2529][RFC5214][RFC5569].