Network Working Group F. Templin, Ed.
Internet-Draft Boeing Research & Technology
Obsoletes: rfc5320, rfc5558, rfc5720, May 1, 2019
rfc6179, rfc6706 (if
approved)
Intended status: Standards Track
Expires: November 2, 2019
Asymmetric Extended Route Optimization (AERO)
draft-templin-intarea-6706bis-12.txt
Abstract
This document specifies the operation of IP over tunnel virtual links
using Asymmetric Extended Route Optimization (AERO). AERO interfaces
use an IPv6 link-local address format that supports operation of the
IPv6 Neighbor Discovery (ND) protocol and links ND to IP forwarding.
Prefix delegation services are employed to manage the routing system.
Dynamic multilink operation, mobility management, quality of service
(QoS) signaling and route optimization are naturally supported
through dynamic neighbor cache updates. Standard IP multicasting
services are also supported. AERO is a widely-applicable tunneling
solution especially well-suited to aviation services, mobile Virtual
Private Networks (VPNs) and many other applications.
Status of This Memo
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 https://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 November 2, 2019.
Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved.
Templin Expires November 2, 2019 [Page 1]
Internet-Draft AERO May 2019
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://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.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Asymmetric Extended Route Optimization (AERO) . . . . . . . . 10
3.1. AERO Link Reference Model . . . . . . . . . . . . . . . . 10
3.2. AERO Node Types . . . . . . . . . . . . . . . . . . . . . 11
3.3. AERO Routing System . . . . . . . . . . . . . . . . . . . 13
3.4. AERO Addresses . . . . . . . . . . . . . . . . . . . . . 15
3.5. Spanning Partitioned AERO Networks (SPAN) . . . . . . . . 16
3.6. AERO Interface Characteristics . . . . . . . . . . . . . 20
3.7. AERO Interface Initialization . . . . . . . . . . . . . . 24
3.7.1. AERO Relay Behavior . . . . . . . . . . . . . . . . . 24
3.7.2. AERO Server Behavior . . . . . . . . . . . . . . . . 24
3.7.3. AERO Gateway Behavior . . . . . . . . . . . . . . . . 25
3.7.4. AERO Proxy Behavior . . . . . . . . . . . . . . . . . 25
3.7.5. AERO Client Behavior . . . . . . . . . . . . . . . . 25
3.8. AERO Interface Neighbor Cache Maintenance . . . . . . . . 26
3.9. AERO Interface Forwarding Algorithm . . . . . . . . . . . 28
3.9.1. Client Forwarding Algorithm . . . . . . . . . . . . . 29
3.9.2. Proxy Forwarding Algorithm . . . . . . . . . . . . . 29
3.9.3. Server Forwarding Algorithm . . . . . . . . . . . . . 30
3.9.4. Gateway Forwarding Algorithm . . . . . . . . . . . . 31
3.9.5. Relay Forwarding Algorithm . . . . . . . . . . . . . 31
3.10. AERO Interface Encapsulation and Re-encapsulation . . . . 31
3.11. AERO Interface Decapsulation . . . . . . . . . . . . . . 32
3.12. AERO Interface Data Origin Authentication . . . . . . . . 32
3.13. AERO Interface Packet Size Issues . . . . . . . . . . . . 33
3.14. AERO Interface Error Handling . . . . . . . . . . . . . . 35
3.15. AERO Router Discovery, Prefix Delegation and
Autoconfiguration . . . . . . . . . . . . . . . . . . . . 38
3.15.1. AERO ND/PD Service Model . . . . . . . . . . . . . . 38
3.15.2. AERO Client Behavior . . . . . . . . . . . . . . . . 39
3.15.3. AERO Server Behavior . . . . . . . . . . . . . . . . 41
3.16. The AERO Proxy . . . . . . . . . . . . . . . . . . . . . 43
3.17. AERO Route Optimization . . . . . . . . . . . . . . . . . 45
3.17.1. Route Optimization Initiation . . . . . . . . . . . 46
3.17.2. Relaying the NS . . . . . . . . . . . . . . . . . . 46
Templin Expires November 2, 2019 [Page 2]
Internet-Draft AERO May 2019
3.17.3. Processing the NS and Sending the NA . . . . . . . . 46
3.17.4. Relaying the NA . . . . . . . . . . . . . . . . . . 47
3.17.5. Processing the NA . . . . . . . . . . . . . . . . . 47
3.17.6. Route Optimization Maintenance . . . . . . . . . . . 47
3.18. Neighbor Unreachability Detection (NUD) . . . . . . . . . 48
3.19. Mobility Management and Quality of Service (QoS) . . . . 49
3.19.1. Mobility Update Messaging . . . . . . . . . . . . . 50
3.19.2. Forwarding Packets on Behalf of Departed Clients . . 50
3.19.3. Announcing Link-Layer Address and/or QoS Preference
Changes . . . . . . . . . . . . . . . . . . . . . . 51
3.19.4. Bringing New Links Into Service . . . . . . . . . . 51
3.19.5. Removing Existing Links from Service . . . . . . . . 51
3.19.6. Implicit Mobility Management . . . . . . . . . . . . 52
3.19.7. Moving to a New Server . . . . . . . . . . . . . . . 52
3.20. Multicast . . . . . . . . . . . . . . . . . . . . . . . . 53
4. Direct Underlying Interfaces . . . . . . . . . . . . . . . . 54
5. AERO Clients on the Open Internetwork . . . . . . . . . . . . 54
6. Operation over Multiple AERO Links . . . . . . . . . . . . . 54
7. Operation on AERO Links with /64 ASPs . . . . . . . . . . . . 55
8. AERO Adaptations for SEcure Neighbor Discovery (SEND) . . . . 56
9. AERO Critical Infrastructure Considerations . . . . . . . . . 56
10. DNS Considerations . . . . . . . . . . . . . . . . . . . . . 57
11. Transition Considerations . . . . . . . . . . . . . . . . . . 57
12. Implementation Status . . . . . . . . . . . . . . . . . . . . 58
13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 58
14. Security Considerations . . . . . . . . . . . . . . . . . . . 58
15. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 60
16. References . . . . . . . . . . . . . . . . . . . . . . . . . 61
16.1. Normative References . . . . . . . . . . . . . . . . . . 61
16.2. Informative References . . . . . . . . . . . . . . . . . 62
Appendix A. AERO Alternate Encapsulations . . . . . . . . . . . 69
Appendix B. S/TLLAO Extensions for Special-Purpose Links . . . . 70
Appendix C. Change Log . . . . . . . . . . . . . . . . . . . . . 72
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 76
1. Introduction
Asymmetric Extended Route Optimization (AERO) fulfills the
requirements of Distributed Mobility Management (DMM) [RFC7333] and
route optimization [RFC5522] for aeronautical networking and other
network mobility use cases. AERO is based on a Non-Broadcast,
Multiple Access (NBMA) virtual link model known as the AERO link.
The AERO link is configured over one or more underlying
Internetworks, and nodes on the link can exchange IP packets via
tunneling.
AERO links provide a cloud-based service where mobile nodes may use
any Mobility Anchor Point (MAP) and fixed nodes may use any Gateway
Templin Expires November 2, 2019 [Page 3]
Internet-Draft AERO May 2019
on the link for efficient communications. Fixed nodes forward
packets destined to other AERO nodes to the nearest Gateway, which
forwards them through the cloud. A mobile node's initial packets are
forwarded through the MAP, while direct routing is supported through
route optimization once an initial session has been established.
Both unicast and multicast communications are supported, and mobile
nodes may efficiently move between locations while maintaining
continuous communications with correspondents and without changing
their IP Address.
The AERO service comprises Clients, Proxies, Servers, and Gateways
that are seen as AERO link neighbors. Each node's AERO interface
uses an IPv6 link-local address format (known as the AERO address)
that supports operation of the IPv6 Neighbor Discovery (ND) [RFC4861]
protocol and links ND to IP forwarding. A node's AERO interface can
be configured over multiple underlying interfaces, and may therefore
may appear as a single interface with multiple link-layer addresses.
Each link-layer address is subject to change due to mobility and/or
QoS fluctuations, and link-layer address changes are signaled by ND
messaging the same as for any IPv6 link.
AERO Relays are interconnected in a secured private BGP overlay
routing instance known as the "SPAN". The SPAN provides a (virtual)
layer 2 bridging service to join the underlying Internetworks of
multiple disjoint administrative domains into a single unified AERO
link. Each AERO link instance is characterized by the set of
Mobility Service Prefixes (MSPs) common to all mobile nodes. The
link should extend to the point where a Gateway/MAP is on the optimal
route from any correspondent node on the link, and provides a gateway
between the underlying Internetwork and the SPAN. To the underlying
Internetwork, the Gateway/MAP is the source of a route to its MSP,
and hence uplink traffic to the mobile node is naturally routed to
the nearest Gateway/MAP.
AERO assumes the use of PIM Sparse Mode in support of multicast
communication. In support of Source Specific Multicast (SSM) when a
Mobile Node is the source, the AERO cloud is included within the
multicast distribution tree unless and until it is optimized out by
use of AERO Direct Routing. In all other multicast scenarios there
are no AERO dependencies.
AERO is applicable to a wide variety of use cases. For example, it
can be used to coordinate the Virtual Private Network (VPN) links of
mobile nodes (e.g., cellphones, tablets, laptop computers, etc.) that
connect into a home enterprise network via public access networks
using services such as OpenVPN [OVPN]. AERO is also applicable to
aeronautical networking for both manned and unmanned aircraft where
Templin Expires November 2, 2019 [Page 4]
Internet-Draft AERO May 2019
the aircraft is treated as a mobile node that can connect an Internet
of Things (IoT). Other applicable use cases are also in scope.
The following numbered sections present the AERO specification. The
appendices at the end of the document are non-normative.
2. Terminology
The terminology in the normative references applies; the following
terms are defined within the scope of this document:
IPv6 Neighbor Discovery (ND)
an IPv6 control message service for coordinating neighbor
relationships between nodes connected to a common link. AERO
interfaces use the ND service specified in [RFC4861].
IPv6 Prefix Delegation (PD)
a networking service for delegating IPv6 prefixes to nodes on the
link. The nominal PD service is DHCPv6 [RFC8415], however
alternate services (e.g., based on ND messaging) are also in scope
[I-D.templin-v6ops-pdhost][I-D.templin-6man-dhcpv6-ndopt]. Most
notably, a form of PD known as "Prefix Assertion" can be used if
the prefix can be represented in the IPv6 source address of an ND
message.
access network (ANET)
a node's first-hop data link service network, e.g., a radio access
network, cellular service provider network, corporate enterprise
network, or the public Internet itself. For secured ANETs, link-
layer security services such as IEEE 802.1X and physical-layer
security prevent unauthorized access internally while border
network-layer security services such as firewalls and proxies
prevent unauthorized outside access. When there is no
administrative boundary established between an ANET and the
outside Internetwork, the ANET and Internetwork are one and the
same.
ANET interface
a node's attachment to a link in an ANET.
ANET address
an IP address assigned to a node's interface connection to an
ANET.
Internetwork (INET)
a connected IP network topology with a coherent routing and
addressing plan and that provides an Internetworking backbone
service for ANETs. INETs also provide an underlay service over
Templin Expires November 2, 2019 [Page 5]
Internet-Draft AERO May 2019
which the AERO virtual link is configured. Example INETs include
corporate enterprise networks, aviation networks, and the public
Internet itself.
INET interface
a node's attachment to a link in an INET.
INET address
an IP address assigned to a node's interface connection to an
INET.
AERO link
a Non-Broadcast, Multiple Access (NBMA) tunnel virtual overlay
configured over one or more underlying INETs. Nodes on the AERO
link appear as single-hop neighbors from the perspective of the
virtual overlay even though they may be separated by many
underlying INET hops.
AERO interface
a node's attachment to an AERO link. Since the addresses assigned
to an AERO interface are managed for uniqueness, AERO interfaces
do not require Duplicate Address Detection (DAD) and therefore set
the administrative variable 'DupAddrDetectTransmits' to zero
[RFC4862].
AERO address
an IPv6 link-local address assigned to an AERO interface and
constructed as specified in Section 3.4.
base AERO address
the lowest-numbered AERO address aggregated by the MNP (see
Section 3.4).
Mobility Service Prefix (MSP)
an IP prefix assigned to the AERO link and from which more-
specific Mobile Network Prefixes (MNPs) are derived.
Mobile Network Prefix (MNP)
an IP prefix derived from an MSP and delegated to an AERO Client
or Gateway.
Fixed Node (FN)
a node on an INET link serviced by an AERO Gateway.
Mobile Node (MN)
an AERO Client and all of its downstream-attached networks.
Mobile Router (MR)
Templin Expires November 2, 2019 [Page 6]
Internet-Draft AERO May 2019
a MN's on-board router that forwards packets between any
downstream-attached networks and the AERO link.
Correspondent Node (CN)
a MN or FN that is reachable over the AERO link
AERO node
a node that is connected to an AERO link.
AERO Client ("Client")
an AERO node that connects to one or more ANETs and requests MNP
PDs from one or more AERO Servers. Following PD, the Client
assigns a Client AERO address to the AERO interface for use in ND
exchanges with other AERO nodes. A Client can also be deployed on
the same platform as a Server, and a node that acts as a Client on
one AERO interface can also act as an AERO Server on a different
AERO interface.
AERO Server ("Server")
an INET node that configures an AERO interface to provide default
forwarding services and a Mobility Anchor Point (MAP) for AERO
Clients. The Server assigns an administratively-provisioned AERO
address to the AERO interface to support the operation of the ND/
PD services, and advertises all of its associated MNPs via BGP
peerings with Relays.
AERO Gateway ("Gateway")
a combined AERO Server/Client that also provides forwarding
services between CNs on the AERO link and FNs on INET links. AERO
Gateways are provisioned with MNPs used for numbering nodes and
networks on downstream-attached INET interfaces (i.e., the same as
for an AERO Client) and run a dynamic routing protocol to discover
any native INET prefixes. In both cases, the Gateway advertises
the MSP(s) to FNs in downstream-attached INET networks, and
distributes all of its associated MNPs and native INET prefixes
via BGP peerings with Relays (i.e., the same as for an AERO
Server).
AERO Relay ("Relay")
an INET node that provides both layer-3 routing and layer-2
bridging services (as well as a security trust anchor) for nodes
on an AERO link. As a router, the Relay forwards data packets
using standard IP forwarding. As a bridge, the Relay securely
forwards control messages between other AERO nodes. AERO Relays
peer with Servers and other Relays to discover the full set of
MNPs
AERO Proxy ("Proxy")
Templin Expires November 2, 2019 [Page 7]
Internet-Draft AERO May 2019
a node that provides proxying services between Clients in an ANET
and Servers in external INETs. The AERO Proxy is a conduit
between the ANET and external INETs in the same manner as for
common web proxies, and behaves in a similar fashion as for ND
proxies [RFC4389].
Spanning Partitioned AERO Networks (SPAN)
a means for bridging disjoint INETs as segments (or, partitions)
of a unified AERO link, i.e., the same as for a bridged campus
LAN. The SPAN is a mid-layer encapsulation service in the AERO
routing system that supports a unified AERO link view for all
segments. Each segment in the SPAN is a distinct INET.
SPAN Service Prefix (SSP)
a global or unique local /96 IPv6 prefix assigned to the AERO link
to support SPAN services.
SPAN Partition Prefix (SPP)
a sub-prefix of the SPAN Service Prefix uniquely assigned to a
single AERO link segment.
SPAN Address
a global or unique local IPv6 address taken from a SPAN Partition
Prefix.
ingress tunnel endpoint (ITE)
an AERO interface endpoint that injects encapsulated packets into
an AERO link.
egress tunnel endpoint (ETE)
an AERO interface endpoint that receives encapsulated packets from
an AERO link.
link-layer address
an IP address used as an encapsulation header source or
destination address from the perspective of the AERO interface.
When UDP encapsulation is used, the UDP port number is also
considered as part of the link-layer address. From the
perspective of the AERO interface, the link-layer address is
either an INET address for intra-segment encapsulation or a SPAN
address for inter-segment encapsulation.
network layer address
the source or destination address of an encapsulated IP packet
presented to the AERO interface.
end user network (EUN)
Templin Expires November 2, 2019 [Page 8]
Internet-Draft AERO May 2019
an internal virtual or external edge IP network that an AERO
Client or Gateway connects to the rest of the network via the AERO
interface. The Client/Gateway sees each EUN as a "downstream"
network, and sees the AERO interface as the point of attachment to
the "upstream" network.
Mobility Anchor Point (MAP)
an AERO Server that is currently tracking and reporting the
mobility events of its associated Clients.
Mobile Router (MR)
a router on an AERO Client that provides routing services between
the Client's EUNs and the AERO interface.
MAP List
a geographically and/or topologically referenced list of IP
addresses of Servers for the AERO link.
Distributed Mobility Management (DMM)
a BGP-based overlay routing service coordinated by Servers and
Relays that tracks all MAP-to-Client associations.
Route Optimization Source (ROS)
the AERO node nearest the source Client that initiates route
optimization. The ROS may be one of the Client's Servers, Proxies
or in some cases even the Client itself.
Route Optimization Responder (ROR)
a Server of the target Client to which a route optimization
request is directed. The ROR (acting as a MAP) returns the most
current information about the target Client's underlying interface
connections.
Throughout the document, the simple terms "Client", "Server",
"Relay", "Proxy" and "Gateway" refer to "AERO Client", "AERO Server",
"AERO Relay", "AERO Proxy" and "AERO Gateway", respectively.
Capitalization is used to distinguish these terms from DHCPv6
client/server/relay [RFC8415].
The terminology of DHCPv6 [RFC8415] and IPv6 ND [RFC4861] (including
the names of node variables, messages and protocol constants) is used
throughout this document. Also, the term "IP" is used to generically
refer to either Internet Protocol version, i.e., IPv4 [RFC0791] or
IPv6 [RFC8200].
The terms Mobility Anchor Point (MAP), Mobile Router (MR) and
Distributed Mobility Management (DMM) are used in the same sense as
standard Internetworking terminology.
Templin Expires November 2, 2019 [Page 9]
Internet-Draft AERO May 2019
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]. Lower case
uses of these words are not to be interpreted as carrying RFC2119
significance.
3. Asymmetric Extended Route Optimization (AERO)
The following sections specify the operation of IP over Asymmetric
Extended Route Optimization (AERO) links:
3.1. AERO Link Reference Model
.-(::::::::)
.-(::::::::::::)-.
(:::: Internet ::::)
`-(::::::::::::)-'
`-(::::::)-'
|
+--------------+ +--------+-------+ +--------------+
|AERO Server S1| | AERO Relay R1 | |AERO Server S2|
| Nbr: C1, R1 | | Nbr: S1, S2, P1| | Nbr: C2, R1 |
| default->R1 | |(X1->S1; X2->S2)| | default->R1 |
| X1->C1 | | MSP M1 | | X2->C2 |
+-------+------+ +--------+-------+ +------+-------+
| AERO Link | |
X---+---+-------------------+-+----------------+---+---X
| | |
+-----+--------+ +----------+------+ +--------+-----+
|AERO Client C1| | AERO Proxy P1 | |AERO Client C2|
| Nbr: S1 | |(Proxy Nbr Cache)| | Nbr: S2 |
| default->S1 | +--------+--------+ | default->S2 |
| MNP X1 | | | MNP X2 |
+------+-------+ .--------+------. +-----+--------+
| (- Proxyed Clients -) |
.-. `---------------' .-.
,-( _)-. ,-( _)-.
.-(_ IP )-. +-------+ +-------+ .-(_ IP )-.
(__ EUN )--|Host H1| |Host H2|--(__ EUN )
`-(______)-' +-------+ +-------+ `-(______)-'
Figure 1: AERO Link Reference Model
Figure 1 presents the AERO link reference model. In this model:
o the AERO link is an overlay Layer 3 service configured over one or
more underlying INETs which may be managed by different
Templin Expires November 2, 2019 [Page 10]
Internet-Draft AERO May 2019
administrative authorities and have incompatible protocols and/or
addressing plans.
o AERO Relay R1 aggregates Mobility Service Prefix (MSP) M1,
discovers Mobile Network Prefixes (MNPs) X*, acts as a default
router for its associated Servers and Proxies (S1, S2, P1), and
connects the AERO link to the external Internet. AERO Relays also
use the SPAN service to bridge disjoint segments (i.e., INETs) of
a partitioned AERO link.
o AERO Servers S1 and S2 associate with Relay R1 and also act as
Mobility Anchor Points (MAPs) and default routers for their
associated Clients C1 and C2.
o AERO Clients C1 and C2 associate with Servers S1 and S2,
respectively. They receive Mobile Network Prefix (MNP)
delegations X1 and X2, and also act as default routers for their
associated physical or internal virtual EUNs. Simple hosts H1 and
H2 attach to the EUNs served by Clients C1 and C2, respectively.
o AERO Proxy P1 provides proxy services for AERO Clients in secured
enclaves that cannot associate directly with other AERO link
neighbors.
Each node on the AERO link maintains an AERO interface neighbor cache
and an IP forwarding table the same as for any link. Although the
figure shows a limited deployment, in common operational practice
there will normally be many additional Relays, Servers, Clients and
Proxies.
3.2. AERO Node Types
AERO Relays provide both layer-3 routing and layer-2 bridging
services (as well as a security trust anchor) for nodes on an AERO
link. As a router, the Relay forwards data packets using standard IP
forwarding. As a bridge, the Relay securely forwards control
messages between Proxies and Servers both within the same INET and
between disjoint INETs. Each Relay also peers with Servers and other
Relays in a dynamic routing protocol instance to provide a
Distributed Mobility Management (DMM) service for the list of active
MNPs (see Section 3.3). Relays forward packets between neighbors
connected to the same AERO link and also forward packets between the
AERO link and the outside world. Relays present the AERO link as a
set of one or more Mobility Service Prefixes (MSPs). Relays maintain
neighbor cache entries for Servers and Proxies, and maintain an IP
forwarding table entry for each Mobile Network Prefix (MNP).
Templin Expires November 2, 2019 [Page 11]
Internet-Draft AERO May 2019
AERO Servers provide default forwarding services and a Mobility
Anchor Point (MAP) for AERO Client Mobile Nodes (MNs). Each Server
also peers with Relays in a dynamic routing protocol instance to
advertise its list of associated MNPs (see Section 3.3). Servers
facilitate PD exchanges with Clients, where each delegated prefix
becomes an MNP taken from an MSP. Servers forward packets between
AERO interface neighbors, and maintain neighbor cache entries for
Relays. They also maintain both neighbor cache entries and IP
forwarding table entries for each of their associated Clients, and
track each Client's mobility profiles.
AERO Clients act as requesting Mobile Routers (MRs) to receive MNPs
through PD exchanges with AERO Servers over the AERO link, and
distribute the MNPs to nodes on EUNs. Each Client can associate with
a single Server or with multiple Servers, e.g., for fault tolerance,
load balancing, etc. Each IPv6 Client receives at least a /64 IPv6
MNP, and may receive even shorter prefixes. Similarly, each IPv4
Client receives at least a /32 IPv4 MNP (i.e., a singleton IPv4
address), and may receive even shorter prefixes. Clients maintain an
AERO interface neighbor cache entry for each of their associated
Servers as well as for each of their correspondent Clients. A Client
may also be co-resident on the same physical or virtual platform as a
Server; in that case, the Client and Server behave as a single
functional unit and without the need for any Client/Server control
messaging.
AERO Proxies provide a conduit for AERO Clients in ANETs to associate
with AERO Servers in external INETs. The Client sends all of its
control plane messages to the Server via the Proxy, which intercepts
them before they leave the ANET. The Proxy forwards the Client's
control and data plane messages to and from the Client's current
Server(s). The Proxy may also discover a better route toward a
target destination via AERO route optimization, in which case future
outbound data packets would be forwarded via the more direct route.
Proxies maintain AERO interface neighbor cache entries for Relays,
i.e., the same as Servers. The Proxy function is specified in
Section 3.16.
AERO Gateways are combined Client/Servers that also provide
forwarding services between correspondent nodes (CNs) on the AERO
interface and fixed nodes (FNs) on INET interfaces. AERO Gateways
are provisioned with MNPs used for numbering nodes and networks on
downstream-attached INET interfaces (i.e., the same as for an AERO
Client) and may also run a dynamic routing protocol to discover any
native INET prefixes. In both cases, the Gateway advertises the
MSP(s) to correspondent nodes in downstream-attached INET networks,
and distributes all of its associated MNPs and native INET prefixes
via BGP peerings with Relays.
Templin Expires November 2, 2019 [Page 12]
Internet-Draft AERO May 2019
AERO Relays, Servers, Proxies and Gateways are critical
infrastructure elements in fixed (i.e., non-mobile) INET deployments
and hence have permanent and unchanging INET addresses. AERO Clients
are MNs that connect via ANET interfaces, i.e., their ANET addresses
may change when the Client moves to a new ANET connection.
3.3. AERO Routing System
The AERO routing system comprises a private instance of the Border
Gateway Protocol (BGP) [RFC4271] that is coordinated between Relays
and Servers and does not interact with either the public Internet BGP
routing system or any underlying INET routing systems. Relays
advertise only a small and unchanging set of MSPs to the outside
world instead of the full dynamically changing set of MNPs.
In a reference deployment, each Server is configured as an Autonomous
System Border Router (ASBR) for a stub Autonomous System (AS) using
an AS Number (ASN) that is unique within the BGP instance, and each
Server further uses eBGP to peer with one or more Relays but does not
peer with other Servers. Each INET of a multi-segment AERO link must
include one or more Relays, which peer with the Servers and Proxies
within that INET. All Relays within the same INET are members of the
same hub AS using a common ASN, and use iBGP to maintain a consistent
view of all active MNPs currently in service. The Relays of
different INETs peer with one another using eBGP.
Each Server maintains a working set of associated MNPs and native
INET prefixes, and dynamically announces new prefixes and withdraws
departed prefixes in its eBGP updates to Relays. Clients are
expected to remain associated with their current Servers for extended
timeframes, however Servers SHOULD selectively suppress updates for
impatient Clients that repeatedly associate and disassociate with
them in order to dampen routing churn. Servers that are configured
as Gateways advertise the MSP into the INET and forward packets
between INET interfaces and the AERO interface.
Each Relay configures a black-hole route for each of its MSPs. By
black-holing the MSPs, the Relay will maintain forwarding table
entries only for the MNPs that are currently active, and packets
destined to all other MNPs will correctly incur Destination
Unreachable messages due to the black hole route. Relays do not send
eBGP updates for MNPs to Servers, but instead only originate a
default route. In this way, Servers have only partial topology
knowledge (i.e., they know only about the MNPs of their directly
associated Clients) and they forward all other packets to Relays
which have full topology knowledge.
Templin Expires November 2, 2019 [Page 13]
Internet-Draft AERO May 2019
For IPv6 MNPs, the AERO routing system includes only IPv6 routes.
For IPv4 MNPs, the AERO routing system includes both IPv4 routes and
also IPv6 routes based on the IPv4-mapped IPv6 address corresponding
to the MNP and with prefix length set to 96 plus the length of the
IPv4 prefix. (For example, if the IPv4 MNP is 192.0.2.0/24 then the
IPv4-mapped prefix is 0:0:0:0:0:FFFF:192.0.2.0/120.)
Scaling properties of the AERO routing system are limited by the
number of BGP routes that can be carried by Relays. As of 2015, the
global public Internet BGP routing system manages more than 500K
routes with linear growth and no signs of router resource exhaustion
[BGP]. More recent network emulation studies have also shown that a
single Relay can accommodate at least 1M dynamically changing BGP
routes even on a lightweight virtual machine, i.e., and without
requiring high-end dedicated router hardware.
Therefore, assuming each Relay can carry 1M or more routes, this
means that at least 1M Clients can be serviced by a single set of
Relays. A means of increasing scaling would be to assign a different
set of Relays for each set of MSPs. In that case, each Server still
peers with one or more Relays, but institutes route filters so that
BGP updates are only sent to the specific set of Relays that
aggregate the MSP. For example, if the MSP for the AERO link is
2001:db8::/32, a first set of Relays could service the MSP segment
2001:db8::/40, a second set of Relays could service
2001:db8:0100::/40, a third set could service 2001:db8:0200::/40,
etc.
Assuming up to 1K sets of Relays, the AERO routing system can then
accommodate 1B or more MNPs with no additional overhead (for example,
it should be possible to service 1B /64 MNPs taken from a /34 MSP and
even more for shorter prefixes). In this way, each set of Relays
services a specific set of MSPs that they advertise to the native
Internetwork routing system, and each Server configures MSP-specific
routes that list the correct set of Relays as next hops. This
arrangement also allows for natural incremental deployment, and can
support small scale initial deployments followed by dynamic
deployment of additional Clients, Servers and Relays without
disturbing the already-deployed base.
A full discussion of the BGP-based routing system used by AERO is
found in [I-D.ietf-rtgwg-atn-bgp]. The system provides for
Distributed Mobility Management (DMM) per the distributed mobility
anchoring architecture [I-D.ietf-dmm-distributed-mobility-anchoring].
Templin Expires November 2, 2019 [Page 14]
Internet-Draft AERO May 2019
3.4. AERO Addresses
A Client's AERO address is an IPv6 link-local address with an
interface identifier based on the Client's delegated MNP. Relay,
Server and Proxy AERO addresses are assigned from the range fe80::/96
and include an administratively-provisioned value in the lower 32
bits.
For IPv6, Client AERO addresses begin with the prefix fe80::/64 and
include in the interface identifier (i.e., the lower 64 bits) a
64-bit prefix taken from one of the Client's IPv6 MNPs. For example,
if the AERO Client receives the IPv6 MNP:
2001:db8:1000:2000::/56
it constructs its corresponding AERO addresses as:
fe80::2001:db8:1000:2000
fe80::2001:db8:1000:2001
fe80::2001:db8:1000:2002
... etc. ...
fe80::2001:db8:1000:20ff
For IPv4, Client AERO addresses are based on an IPv4-mapped IPv6
address formed from an IPv4 MNP and with a Prefix Length of 96 plus
the MNP prefix length. For example, for the IPv4 MNP 192.0.2.32/28
the IPv4-mapped IPv6 MNP is:
0:0:0:0:0:FFFF:192.0.2.16/124
The Client then constructs its AERO addresses with the prefix
fe80::/64 and with the lower 64 bits of the IPv4-mapped IPv6 address
in the interface identifier as:
fe80::FFFF:192.0.2.16
fe80::FFFF:192.0.2.17
fe80::FFFF:192.0.2.18
... etc. ...
fe80:FFFF:192.0.2.31
Templin Expires November 2, 2019 [Page 15]
Internet-Draft AERO May 2019
Relay, Server and Proxy AERO addresses are allocated from the range
fe80::/96, and MUST be managed for uniqueness. The lower 32 bits of
the AERO address includes a unique integer value (e.g., fe80::1,
fe80::2, fe80::3, etc.) as assigned by the administrative authority
for the link. If the link spans multiple segments (i.e., multiple
INETs), the AERO addresses are assigned to each INET in 1x1
correspondence with SPAN addresses (see: Section 3.5). The address
fe80:: is reserved as the IPv6 link-local Subnet Router Anycast
address [RFC4291], and the address fe80::ffff:ffff is reserved as the
unspecified AERO address; hence, these values are not available
general assignment.
The lowest-numbered AERO address from a Client's MNP delegation
serves as the "base" AERO address (for example, for the MNP
2001:db8:1000:2000::/56 the base AERO address is
fe80::2001:db8:1000:2000). The Client then assigns the base AERO
address to the AERO interface and uses it for the purpose of
maintaining the neighbor cache entry. The Server likewise uses the
AERO address as its index into the neighbor cache for this Client.
If the Client has multiple AERO addresses (i.e., when there are
multiple MNPs and/or MNPs with prefix lengths shorter than /64), the
Client originates ND messages using the base AERO address as the
source address and accepts and responds to ND messages destined to
any of its AERO addresses as equivalent to the base AERO address. In
this way, the Client maintains a single neighbor cache entry that may
be indexed by multiple AERO addresses.
Client AERO addresses can be statelessly transformed into an IPv6
Subnet Router Anycast address and vice-versa. For example, for the
AERO address fe80::2001:db8:2000:3000 the corresponding Subnet Router
Anycast address is 2001:db8:2000:3000::. In the same way, for the
IPv6 Subnet Router Anycast address 2001:db8:1:2:: the corresponding
AERO address is fe80::2001:db8:1:2. In other words, the low-order 64
bits of an AERO address can be used as the high-order 64 bits of a
Subnet Router Anycast address, and vice-versa.
3.5. Spanning Partitioned AERO Networks (SPAN)
In the simplest case, an AERO link configured over a single INET
appears as a single unified link with a consistent underlying network
addressing plan. In that case, all nodes on the link can exchange
packets via encapsulation with INET addresses, since the underlying
INET is connected. In common practice, however, an AERO link may be
partitioned into multiple "segments", where each segment is a
distinct INET managed under a different administrative authority
(e.g., as for worldwide aviation service providers such as ARINC,
SITA, Inmarsat, etc.). Individual INETs may themselves be
Templin Expires November 2, 2019 [Page 16]
Internet-Draft AERO May 2019
partitioned internally, in which case each internal partition is seen
as a separate segment.
The addressing plan of each segment is consistent internally but will
often bear no relation to the addressing plans of other segments.
Each segment is also likely to be separated from others by network
security devices (e.g., firewalls, proxies, packet filtering
gateways, etc.), and in many cases disjoint segments may not even
have any common physical link connections at all. Therefore, nodes
can only be assured of exchanging packets directly with nodes in the
same segment, and not with nodes in other segments. The only means
for joining the segments therefore is through inter-domain peerings
between AERO Relays acting as bridges.
The same as for traditional campus LANs, multiple AERO link segments
can be joined into a single unified link via a bridging service
termed the "SPAN". The SPAN performs link-layer packet forwarding
between segments (i.e., bridging) without decrementing the network-
layer TTL/Hop Limit. The SPAN model is depicted in Figure 2:
. . . . . . . . . . . . . . . . . . . . . . .
. .
. .-(::::::::) .
. .-(::::::::::::)-. +-+ .
. (:::: Segment A :::)--|R|---+ .
. `-(::::::::::::)-' +-+ | .
. `-(::::::)-' | .
. | .
. .-(::::::::) | .
. .-(::::::::::::)-. +-+ | .
. (:::: Segment B :::)--|R|---+ .
. `-(::::::::::::)-' +-+ | .
. `-(::::::)-' | .
. | .
. .-(::::::::) | .
. .-(::::::::::::)-. +-+ | .
. (:::: Segment C :::)--|R|---+ .
. `-(::::::::::::)-' +-+ | .
. `-(::::::)-' | .
. | .
. ..(etc).. x .
. .
. .
. <- AERO Link Bridged by the SPAN -> .
. . . . . . . . . . . . . .. . . . . . . . .
Figure 2: The SPAN
Templin Expires November 2, 2019 [Page 17]
Internet-Draft AERO May 2019
To support the SPAN, AERO links require a reserved /96 IPv6 "SPAN
Service Prefix (SSP)". Although any routable IPv6 prefix can be
used, a Unique Local Address (ULA) prefix (e.g., fd00::/96) [RFC4389]
is preferred since border routers are commonly configured to prevent
packets with ULAs from being injected into the AERO link by an
external IPv6 node and from leaking out of the AERO link to the
outside world.
Each segment in the SPAN assigns a unique sub-prefix of the SSP
termed a "SPAN Partition Prefix (SPP)". For example, a first segment
could assign fd00::/116, a second could assign fd00::1000/116, a
third could assign fd00::2000/116, etc. The administrative
authorities for each segment must therefore coordinate to assure
mutually-exclusive SPP assignments, but internal provisioning of the
SPP is a local consideration for each administrative authority.
A "SPAN address" is an address taken from a SPP and assigned to a
Relay, Server or Proxy AERO interface. SPAN addresses are formed by
simply replacing the upper portion of an administratively-assigned
AERO address with the SPP. For example, if the SPP is fd00::/116,
the SPAN address formed from the AERO address fe80::1 is simply
fd00::1. (As with AERO addresses, the values ::0 and ::ffff:ffff are
reserved and not available for general assignment.)
An "INET address" is an address of a node's interface connection to
an INET segment. Each Relay, Server and Proxy connected to the same
segment maintains a static mapping of AERO/SPAN addresses to INET
addresses for all fixed infrastructure elements in that segment. For
example, if a Server has AERO/SPAN addresses fe80::1/fd00::1 and INET
address 192.0.2.100, then all other Relays, Servers and Proxys in
that segment keep a static mapping for those addresses. In that way,
any of the AERO/SPAN/INET addresses can be derived from a static
lookup without the need for protocol messaging.
AERO Relays serve as bridges to join multiple segments into a unified
AERO link over multiple diverse administrative domains. They support
the bridging function by first establishing forwarding table entries
for their SPPs either via standard BGP routing or static routes. For
example, if three Relays (Relays 'A', 'B' and 'C') from different
segments serviced the SPPs fd00::1000/116, fd00::2000/116 and
fd00::3000/116 respectively, then the forwarding tables in each Relay
are as follows:
A: fd00::1000/116->local, fd00::2000/116->B, fd00::3000/116->C
B: fd00::1000/116->A, fd00::2000/116->local, fd00::3000/116->C
C: fd00::1000/116->A, fd00::2000/116->B, fd00::3000/116->local
Templin Expires November 2, 2019 [Page 18]
Internet-Draft AERO May 2019
These forwarding table entries are permanent and never change, since
they correspond to fixed infrastructure elements in their respective
segments. This point is of critical importance, since it provides
the basis for a link-layer forwarding service that cannot be
disrupted by routing updates due to node mobility.
With the SPPs in place in each Relay's forwarding table, control and
data packets sent between AERO nodes in different segments can
therefore be carried over the SPAN via encapsulation. For example,
when a source node in segment A forwards a packet with IPv6 address
2001:db8:1:2::1 to a destination node in segment C with IPv6 address
2001:db8:1000:2000::1, it first encapsulates the packet in a SPAN
header with source SPAN address taken from fd00::1000/116 (e.g.,
fd00::1001) and destination SPAN address taken from fd00::3000/116
(e.g., fd00::3001). Next, it encapsulates the SPAN message in an
INET header with source address set to its own INET address (e.g.,
192.0.2.100) and destination set to the INET address of a Relay
(e.g., 192.0.2.1).
SPAN encapsulation is based on Generic Packet Tunneling in IPv6
[RFC2473]; the encapsulation format in the above example is shown
inFigure 3:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| INET Header |
| src = 192.0.2.100 |
| dst = 192.0.2.1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SPAN Header |
| src = fd00::1001 |
| dst = fd00::3001 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Inner IP Header |
| src = 2001:db8:1:2::1 |
| dst = 2001:db8:1000:2000::1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ ~
~ Inner Packet Body ~
~ ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: SPAN Encapsulation
In this format, the inner IP header and packet body are the original
IP packet, the SPAN header is an IPv6 header prepared according to
[RFC2473], and the INET header is prepared according to Section 3.10.
Templin Expires November 2, 2019 [Page 19]
Internet-Draft AERO May 2019
A packet is said to be "forwarded/sent into the SPAN" when it is
encapsulated as described above then forwarded to a neighboring
Relay. This terminology appears throughout the remainder of the
document.
This gives rise to a routing system that contains both MNP routes
that may change dynamically due to regional node mobility and SPAN
routes that never change. The Relays can therefore provide link-
layer bridging by sending packets into the SPAN instead of network-
layer routing according to MNP routes. As a result, opportunities
for packet loss due to node mobility between different segments are
mitigated.
NB: With reference to Figure 3, the destination SPAN address may not
be known in advance for the first few packets of a flow sent via the
SPAN. In that case, the SPAN destination address is set to the
subnet router anycast address corresponding to the original packet's
destination, and the SPAN routing system will direct the packet to
the correct SPAN egress node. (In the above example, the subnet
router anycast address is simply 2001:db8:1000:2000::.)
3.6. AERO Interface Characteristics
AERO interfaces use encapsulation (see: Section 3.10) to exchange
packets with neighbors attached to the AERO link.
AERO interfaces maintain a neighbor cache for tracking per-neighbor
state the same as for any interface. AERO interfaces use ND messages
including Router Solicitation (RS), Router Advertisement (RA),
Neighbor Solicitation (NS) and Neighbor Advertisement (NA) for
neighbor cache management.
AERO interface ND messages include one or more Source/Target Link-
Layer Address Options (S/TLLAOs) formatted as shown in Figure 4:
Templin Expires November 2, 2019 [Page 20]
Internet-Draft AERO May 2019
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 | Length = 5 | Prefix Length |S|R|D|X|N|Resvd|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface ID | Port Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Link Layer Address +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|P00|P01|P02|P03|P04|P05|P06|P07|P08|P09|P10|P11|P12|P13|P14|P15|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|P16|P17|P18|P19|P20|P21|P22|P23|P24|P25|P26|P27|P28|P29|P30|P31|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|P32|P33|P34|P35|P36|P37|P38|P39|P40|P41|P42|P43|P44|P45|P46|P47|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|P48|P49|P50|P51|P52|P53|P54|P55|P56|P57|P58|P59|P60|P61|P62|P63|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: AERO Source/Target Link-Layer Address Option (S/TLLAO)
Format
In this format:
o Type is set to '1' for SLLAO or '2' for TLLAO.
o Length is set to the constant value '5' (i.e., 5 units of 8
octets).
o Prefix Length is set to the MNP prefix length in an ND message for
the Client AERO address found in the source (RS), destination (RA)
or target (NA) address; otherwise set to 0 if the message is not
being used for PD or neighbor prefix discovery. If the message
contains multiple SLLAOs, only the Prefix Length value in the
SLLAO with S set to 1 is consulted and the values in other SLLAOs
are ignored.
o S (the 'Source' bit) is set to '1' in the S/TLLAO of an ND message
that corresponds to the ANET/INET interface over which the ND
message is sent, and set to 0 in all other S/TLLAOs.
o R (the "Release" bit) is set to '1' in the SLLAO of an RS message
sent for the purpose of departing from a Server; otherwise, set to
Templin Expires November 2, 2019 [Page 21]
Internet-Draft AERO May 2019
'0'. If the message contains multiple SLLAOs, only the R value in
the SLLAO with S set to 1 is consulted and the values in other
SLLAOs are ignored. The Server places the corresponding neighbor
cache entry in the DEPARTED state and releases the corresponding
PD, then returns an RA with Router Lifetime set to '0'.
o D (the "Disable" bit) is set to '1' in the S/TLLAOs of an RS/NA
message for each Interface ID that is to be disabled in the
neighbor cache entry; otherwise, set to '0'. If the message
contains an S/TLLAO with Interface ID 0xffff, the node places the
corresponding neighbor cache entry in the DEPARTED state. If the
message contains multiple S/TLLAOs the D value in each S/TLLAO is
consulted.
o X (the "proXy" bit) is set to '1' in the SLLAO of an RS/RA message
by the Proxy when there is a Proxy in the path; otherwise, set to
'0'. If the message contains multiple SLLAOs, only the X value in
the first SLLAO is consulted and the values in other SLLAOs are
ignored.
o N (the "(Network Address) Translator (NAT)" bit) is set to '1' in
the SLLAO of an RA message by the Server if there is a translator
in the path; otherwise, set to '0'. If the message contains
multiple SLLAOs, only the N value in the first SLLAO is consulted
and the values in other SLLAOs are ignored.
o Resvd is set to the value '0' on transmission and ignored on
receipt.
o Interface ID is set to a 16-bit integer value corresponding to an
AERO node's ANET/INET interface. Once the node has assigned an
Interface ID to an ANET interface, the assignment must remain
unchanged until the node fully detaches from the AERO link. The
value 0xffff is reserved as the AERO Server's INET Interface ID,
i.e., Servers MUST use Interface ID 0xffff, and Clients MUST
number their ANET Interface IDs with values in the range of
0-0xfffe.
o Port Number and Link Layer Address are set to the addresses used
by the AERO node when it sends encapsulated packets over the
specified ANET/INET interface (or to '0' when the addresses are
left unspecified). When UDP is not used as part of the
encapsulation, Port Number is set to '0'. When the encapsulation
IP address family is IPv4, IP Address is formed as an IPv4-mapped
IPv6 address as specified in Section 3.4.
o P(i) is a set of Preferences that correspond to the 64
Differentiated Service Code Point (DSCP) values [RFC2474]. Each
Templin Expires November 2, 2019 [Page 22]
Internet-Draft AERO May 2019
P(i) is set to the value '0' ("disabled"), '1' ("low"), '2'
("medium") or '3' ("high") to indicate a QoS preference level for
packet forwarding purposes.
A Client's AERO interface may be configured over multiple ANET
interface connections. 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, cellular, terrestrial, air-to-
air directional, etc.) with diverse performance and cost properties.
A Client's ANET interfaces are classified as follows:
o Native interfaces connect to the open INET, and have a global IP
address that is reachable from any INET correspondent.
o NATed interfaces connect to an ANET behind a Network Address
Translator (NAT). The NAT does not participate in any AERO
control message signaling, but the AERO Server can issue control
messages on behalf of the Client. Clients that are behind a NAT
are required to send periodic keepalive messages to keep NAT state
alive when there are no data packets flowing.
o VPNed interfaces use security encapsulation over the ANET to a
Virtual Private Network (VPN) server that also acts as an AERO
Server. As with NATed links, the AERO Server can issue control
messages on behalf of the Client, but the Client need not send
periodic keepalives in addition to those already used to maintain
the VPN connection.
o Proxyed interfaces connect to an ANET that is separated from the
open INET by an AERO Proxy. Unlike NATed and VPNed interfaces,
the AERO Proxy can actively issue control messages on behalf of
the Client.
o Direct interfaces connect the Client directly to a neighbor
without crossing any ANET/INET paths. An example is a line-of-
sight link between a remote pilot and an unmanned aircraft.
If a Client's multiple ANET interfaces are used "one at a time"
(i.e., all other interfaces are in standby mode while one interface
is active), then ND messages include only a single S/TLLAO with
Interface ID set to a constant value. In that case, the Client would
appear to have a single ANET interface but with a dynamically
changing ANET address.
Templin Expires November 2, 2019 [Page 23]
Internet-Draft AERO May 2019
If the Client has multiple active ANET interfaces, then from the
perspective of ND it would appear to have multiple link-layer
addresses. In that case, ND messages MAY include multiple S/TLLAOs
-- each with an Interface ID that corresponds to a specific ANET
interface. The S bit must be set to 1 in the S/TLLAO corresponding
to the AERO node's ANET interface used to transmit the message and
set to 0 in all other S/TLLAOs.
When the Client includes an S/TLLAO for an ANET interface for which
it is aware that there is a NAT on the path to the Server, or when a
node includes an S/TLLAO solely for the purpose of announcing new QoS
preferences, the node MAY set both Port Number and Link-Layer Address
to 0 to indicate that the addresses are unspecified at the network
layer and must instead be derived from the link-layer encapsulation
headers.
3.7. AERO Interface Initialization
3.7.1. AERO Relay Behavior
When a Relay enables an AERO interface, it first assigns an
administratively-provisioned AERO address (e.g., fe80::1) and its
companion SPAN address (e.g., fd00::1), where each address MUST be
unique among all AERO nodes on the link. The Relay also configures a
neighbor cache entry for Servers, Gateways and Proxys on the local
segment, and maintains a list of INET address mappings for all fixed
infrastructure elements on the local segment. The Relay then engages
in a BGP routing protocol session with Servers/Gateways on the local
segment and other Relays on the AERO link (see: Section 3.3). Each
Relay subsequently maintains an IP forwarding table entry for each
active MNP covered by its MSP(s) as well as for each SPAN prefix.
3.7.2. AERO Server Behavior
When a Server enables an AERO interface, it assigns AERO/SPAN
addresses and maintains a list of INET address mappings the same as
for Relays. The Server further configures a service to facilitate
ND/PD exchanges with AERO Clients, maintains neighbor cache entries
for one or more Relays on the link, and manages per-Client neighbor
cache entries and IP forwarding table entries based on control
message exchanges. The Server also engages in a BGP routing protocol
session with its neighboring Relays via the AERO interface, and also
engages in a dynamic routing protocol over its INET interfaces (see:
Section 3.3).
When the Server receives an NS/RS message on the AERO interface it
authenticates the message and returns a solicited NA/RA message.
(When the Server receives an unsolicited NA message, it likewise
Templin Expires November 2, 2019 [Page 24]
Internet-Draft AERO May 2019
authenticates the message and processes it locally.) The Server
further provides a simple link-layer conduit between AERO interface
neighbors. In particular, when a packet sent by a source CN arrives
on the Server's AERO interface and is destined to a CN belonging to a
MNP not assigned to one of the Server's INET interfaces, the Server
forwards the packet from within the AERO interface at the link layer
without ever disturbing the network layer.
3.7.3. AERO Gateway Behavior
Gateways are simply Servers that run a dynamic routing protocol
between the AERO and INET interfaces. The Gateway provisions MNPs to
networks on the downstream-attached INET interfaces (i.e., the same
as a Client would do) and advertises the MSP(s) for the AERO link
over the INET interfaces.
3.7.4. AERO Proxy Behavior
When a Proxy enables an AERO interface, it assigns AERO/SPAN
addresses and maintains a list of INET address mappings the same as
for Relays, Servers and Gateways. The Proxy further maintains
neighbor cache entires for one or more Relays, and maintains per-
Client neighbor cache entries based on control message exchanges.
Proxies forward packets between each Client and their associated
Servers and neighbors.
When the Proxy receives an RS message from a Client, it creates an
incomplete neighbor cache entry and sends a proxyed RS message to a
Server via the SPAN while using its own INET address as the source
address. When the Server returns an RA message, the Proxy completes
the proxy neighbor cache entry based on autoconfiguration information
in the RA and sends a proxyed RA to the Client while using its own
ANET address as the source address. The Client, Server and Proxy
will then have the necessary state for managing the proxy neighbor
association.
3.7.5. AERO Client Behavior
When a Client enables an AERO interface, it sends RS messages with
ND/PD parameters over an ANET interface to one or more AERO Servers,
which return RA messages with corresponding PD parameters. (The RS/
RA messages may pass through a Proxy in the case of a Client's
Proxyed interface.) See [I-D.templin-6man-dhcpv6-ndopt] for the
types of ND/PD parameters that can be included in the RS/RA message
exchanges.
After the initial ND/PD message exchange, the Client assigns AERO
addresses to the AERO interface based on the delegated prefix(es).
Templin Expires November 2, 2019 [Page 25]
Internet-Draft AERO May 2019
The Client can then register additional ANET interfaces with the
Server by sending a simple RS message (i.e., one with no PD
parameters) over each ANET interface using its base AERO address as
the source network layer address. The Server will update its
neighbor cache entry for the Client and return a simple RA message.
The Client maintains a neighbor cache entry for each of its Servers
and each of its active target Clients. When the Client receives ND
messages on the AERO interface it updates or creates neighbor cache
entries, including link-layer address and QoS preferences.
When there is a NAT on the path, the Client must send periodic
messages to keep NAT state alive. If no other periodic messaging
service is available, the Client can send RS messages to receive RA
replies from its Server(s).
A Client may be configured as a co-resident function on the same
platform as a Server. In that case, no Client/Server ND messaging is
required and the Client and Server operate as a single functional
unit. The Client function can use its MNP(s) to number downstream-
attached networks, which may connect very large numbers of nodes.
3.8. AERO Interface Neighbor Cache Maintenance
Each AERO interface maintains a conceptual neighbor cache that
includes an entry for each neighbor it communicates with on the AERO
link per [RFC4861]. AERO interface neighbor cache entries are said
to be one of "permanent", "symmetric", "asymmetric" or "proxy".
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 permanent
neighbor cache entries for their associated Relays, Servers, Gateways
and Proxys, and AERO Servers and Proxys maintain permanent neighbor
cache entries for their associated Relays. Each entry maintains the
mapping between the neighbor's network-layer AERO address and
corresponding INET address.
Symmetric neighbor cache entries are created and maintained through
ND/PD exchanges as specified in Section 3.15, and remain in place for
durations bounded by ND/PD lifetimes. AERO Servers maintain
symmetric neighbor cache entries for each of their associated
Clients, and AERO Clients maintain symmetric neighbor cache entries
for each of their associated Servers.
Asymmetric neighbor cache entries are created or updated based on
route optimization messaging as specified in Section 3.17, and are
garbage-collected when keepalive timers expire. AERO route
Templin Expires November 2, 2019 [Page 26]
Internet-Draft AERO May 2019
optimization sources (ROSs) maintain asymmetric neighbor cache
entries for each of their active target Clients with lifetimes based
on ND messaging constants. Asymmetric neighbor cache entries are
unidirectional since only the ROS (i.e., and not the route
optimization responder (ROR)) creates an entry.
Proxy neighbor cache entries are created and maintained by AERO
Proxies when they process Client/Server ND/PD exchanges, and remain
in place for durations bounded by ND/PD lifetimes. AERO Proxies
maintain proxy neighbor cache entries for each of their associated
Clients. Proxy neighbor cache entries track the Client state and the
state of each of the Client's associated Servers.
To the list of neighbor cache entry states in Section 7.3.2 of
[RFC4861], AERO interfaces add an additional state DEPARTED that
applies to symmetric and proxy neighbor cache entries for Clients
that have recently departed. The interface sets a "DepartTime"
variable for the neighbor cache entry to "DEPARTTIME" seconds.
DepartTime is decremented unless a new ND message causes the state to
return to REACHABLE. While a neighbor cache entry is in the DEPARTED
state, packets destined to the target Client are forwarded to the
Client's new location instead of being dropped. When DepartTime
decrements to 0, the neighbor cache entry is deleted. It is
RECOMMENDED that DEPARTTIME be set to the default constant value 40
seconds to allow for packets in flight to be delivered while stale
route optimization state may be present.
When a target AERO Server (acting as a Mobility Anchor Point (MAP))
receives a valid NS message used for route optimization, it searches
for a symmetric neighbor cache entry for the target Client. The
Server then acts as an ROR and returns a solicited NA message without
creating a neighbor cache entry for the ROS, but creates a target
Client "Report List" entry for the ROS and sets a "ReportTime"
variable for the entry to REPORTTIME seconds. The ROR resets
ReportTime when it receives a new authentic NS message, and otherwise
decrements ReportTime while no NS messages have been received. It is
RECOMMENDED that REPORTTIME be set to the default constant value 40
seconds to allow a 10 second window so that route optimization can
converge before ReportTime decrements below REACHABLETIME.
When the ROS receives a solicited NA message response to its NS
message, it creates or updates an asymmetric neighbor cache entry for
the target network-layer and link-layer addresses. The ROS then
(re)sets ReachableTime for the neighbor cache entry to REACHABLETIME
seconds and uses this value to determine whether packets can be
forwarded directly to the target, i.e., instead of via a default
route. The ROS otherwise decrements ReachableTime while no further
solicited NA messages arrive. It is RECOMMENDED that REACHABLETIME
Templin Expires November 2, 2019 [Page 27]
Internet-Draft AERO May 2019
be set to the default constant value 30 seconds as specified in
[RFC4861].
The ROS also uses the value MAX_UNICAST_SOLICIT to limit the number
of NS keepalives sent when a correspondent may have gone unreachable,
the value MAX_RTR_SOLICITATIONS to limit the number of RS messages
sent without receiving an RA and the value MAX_NEIGHBOR_ADVERTISEMENT
to limit the number of unsolicited NAs that can be sent based on a
single event. It is RECOMMENDED that MAX_UNICAST_SOLICIT,
MAX_RTR_SOLICITATIONS and MAX_NEIGHBOR_ADVERTISEMENT be set to 3 the
same as specified in [RFC4861].
Different values for DEPARTTIME, REPORTTIME, REACHABLETIME,
MAX_UNICAST_SOLICIT, MAX_RTR_SOLCITATIONS and
MAX_NEIGHBOR_ADVERTISEMENT MAY be administratively set; however, if
different values are chosen, all nodes on the link MUST consistently
configure the same values. Most importantly, DEPARTTIME and
REPORTTIME SHOULD be set to a value that is sufficiently longer than
REACHABLETIME to avoid packet loss due to stale route optimization
state.
3.9. AERO Interface Forwarding Algorithm
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 an AERO interface neighbor). Packets
that enter the AERO interface from the network layer are encapsulated
and forwarded into the AERO link, i.e., they are tunneled to an AERO
interface neighbor. Packets that enter the AERO interface from the
link layer are either re-admitted into the AERO link or forwarded to
the network layer where they are subject to either local delivery or
IP forwarding. In all cases, the AERO interface itself MUST NOT
decrement the network layer TTL/Hop-count since its forwarding
actions occur below the network layer.
AERO interfaces may have multiple underlying ANET/INET interfaces
and/or neighbor cache entries for neighbors with multiple Interface
ID registrations (see Section 3.6). The AERO interface uses each
packet's DSCP value (and/or port number) to select an outgoing ANET/
INET interface based on the node's own QoS preferences, and also to
select a destination link-layer address based on the neighbor's ANET/
INET interface with the highest preference. AERO implementations
SHOULD allow for QoS preference values to be modified at runtime
through network management.
If multiple outgoing interfaces and/or neighbor interfaces have a
preference of "high", the AERO node replicates the packet and sends
one copy via each of the (outgoing / neighbor) interface pairs;
Templin Expires November 2, 2019 [Page 28]
Internet-Draft AERO May 2019
otherwise, the node sends a single copy of the packet via the
interface with the highest preference. AERO nodes keep track of
which ANET/INET interfaces are currently "reachable" or
"unreachable", and only use "reachable" interfaces for forwarding
purposes.
For control messages, the source node always encapsulates the message
in SPAN/INET headers, and forwards the message into the SPAN (i.e.,
it forwards the message to a Relay). For data packets, if the
neighboring node can only be reached via the SPAN (or, if it is not
yet know that the neighboring node is within the local segment) the
source node encapsulates packets in a SPAN/INET headers and forwards
them into the SPAN. Otherwise, the source node encapsulates packets
in only an INET header for transmission within the local segment.
The following sections discuss the AERO interface forwarding
algorithms for Clients, Proxies, Servers and Relays. In the
following discussion, a packet's destination address is said to
"match" if it is a non-link-local address with a prefix covered by an
MSP/MNP, or if it is an AERO address that embeds an MNP, or if it is
the same as an administratively-provisioned AERO address.
3.9.1. Client Forwarding Algorithm
When an IP packet enters a Client's AERO interface from the network
layer the Client searches for an asymmetric neighbor cache entry that
matches the destination. If there is a match, the Client uses one or
more "reachable" underlying ANET interfaces in the entry for packet
forwarding. If there is no asymmetric neighbor cache entry, the
Client instead forwards the packets to a Server.
When an IP packet enters a Client's AERO interface from the link-
layer, if the destination matches one of the Client's MNPs or link-
local addresses the Client decapsulates the packet (if necessary) and
delivers it to the network layer. Otherwise, the Client drops the
packet and MAY return a network-layer ICMP Destination Unreachable
message subject to rate limiting (see: Section 3.14).
3.9.2. Proxy Forwarding Algorithm
For control messages originating from or destined to a Client, the
Proxy intercepts the message and updates its proxy neighbor cache
entry for the Client. The Proxy then forwards a (proxyed) copy of
the control message.
When the Proxy receives a data packet from a Client within the ANET,
the Proxy searches for an asymmetric neighbor cache entry that
matches the network-layer destination. If there is a match, the
Templin Expires November 2, 2019 [Page 29]
Internet-Draft AERO May 2019
Proxy uses one or more "reachable" neighbor interfaces in the entry
for packet forwarding. Otherwise, the Proxy uses the SPAN/INET
address in a permanent neighbor cache entry for a Relay (selected
through longest-prefix match) as the encapsulation addresses and
forwards the packet into the SPAN.
When the Proxy receives an encapsulated data packet from the INET, it
searches for a proxy neighbor cache entry that matches the
destination. If there is a proxy neighbor cache entry in the
REACHABLE state, the Proxy forwards the packet to the Client; if the
neighbor cache entry is in the DEPARTED state, the Proxy instead
forwards the packet to the Client's Server and may return an
unsolicited NA message as discussed in Section 3.19. If there is no
neighbor cache entry, the Proxy discards the packet.
3.9.3. Server Forwarding Algorithm
When an IP packet enters a Server's AERO interface from either the
network or link-layer, it decapsulates the packet (if the packet
arrived from the link-layer) then processes the packet according to
the network-layer destination address as follows:
o if the destination matches one of the Server's own addresses the
Server forwards it to the network layer for local delivery.
o else, if the destination matches a symmetric neighbor cache entry
the Server forwards the packet according to the neighbor cache
state and link-layer address information. If the neighbor cache
entry is in the REACHABLE state, the Server forwards the packet
according to the cached link-layer information. If the neighbor
cache entry is in the DEPARTED state, the Server instead continues
to forward packets to the Client's new Server as discussed in
Section 3.19. If the packet is destined to the same Client from
which it arrived, however, the Server must forward the packet via
a different "reachable" Interface ID than the one the packet
arrived on. If there are no "reachable" Interface IDs, the Server
must drop the packet.
o else, if the destination matches an asymmetric neighbor cache
entry for a target Client, the Server forwards the packet
according to the cached link-layer information.
o else, the Server uses the SPAN/INET address in a permanent
neighbor cache entry for a Relay (selected through longest-prefix
match) as the encapsulation addresses.
Templin Expires November 2, 2019 [Page 30]
Internet-Draft AERO May 2019
3.9.4. Gateway Forwarding Algorithm
Gateways perform the same forwarding procedures as for Servers, but
also forward packets between the AERO interface and any downstream-
attached INET interfaces. In particular, if the destination address
of a packet that arrives on an AERO interfaces matches a prefix
associated with a downstream-attached INET interface, the Gateway
forwards the packet to the next hop via the INET interface.
Conversely, the Gateway forwards packets that arrive on an INET
interface to the next hop via the AERO interface or another INET
interface according to longest prefix match.
3.9.5. Relay Forwarding Algorithm
Relays forward packets the same as any IP router. When the Relay
receives an encapsulated packet via the AERO link, it removes the
INET header and searches for a forwarding table entry that matches
the destination address in the SPAN header. When the Relay receives
an unencapsulated packet from a node outside the AERO link, it
searches for a forwarding table entry that matches the IP destination
address. The Relay then processes the packet as follows:
o if the destination does not match an MSP or the SSP, or if the
destination matches one of the Relay's own addresses, the Relay
submits the packet for either IP forwarding or local delivery.
o else, if the destination matches an MNP/SPP entry in the IP
forwarding table the Relay encapsulates the packet in an INET
header and forwards it to the neighbor.
o else, the Relay drops the packet and returns an ICMP Destination
Unreachable message subject to rate limiting (see: Section 3.14).
As for any IP router, the Relay decrements the TTL/Hop Count when it
forwards the packet.
3.10. AERO Interface Encapsulation and Re-encapsulation
AERO interfaces encapsulate packets in ANET/INET headers 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". Note that Clients can avoid encapsulation when the
first-hop access router is AERO-aware.
The AERO interface encapsulates the packet in an ANET/INET header per
the Generic UDP Encapsulation (GUE) procedures in
[I-D.ietf-intarea-gue][I-D.ietf-intarea-gue-extensions], or through
Templin Expires November 2, 2019 [Page 31]
Internet-Draft AERO May 2019
an alternate encapsulation format (e.g., see: Appendix A, [RFC2784],
[RFC8086], [RFC4301], etc.).
For packets entering the AERO interface from the network layer, the
AERO interface copies the "TTL/Hop Limit", "Type of Service/Traffic
Class" [RFC2983], "Flow Label"[RFC6438] (for IPv6) and "Congestion
Experienced" [RFC3168] values in the packet's IP header into the
corresponding fields in the encapsulation header(s). For packets
undergoing re-encapsulation, the AERO interface instead copies these
values from the original encapsulation header into the new
encapsulation header, i.e., the values are transferred between
encapsulation headers and *not* copied from the encapsulated packet's
network-layer header. (Note especially that by copying the TTL/Hop
Limit between encapsulation headers the value will eventually
decrement to 0 if there is a (temporary) routing loop.) For IPv4
encapsulation/re-encapsulation, the AERO interface sets the DF bit as
discussed in Section 3.13.
When GUE encapsulation is used, the AERO interface next 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
encapsulated packet plus 8 bytes for the UDP header itself plus the
length of the GUE header (or 0 if GUE direct IP encapsulation is
used). For packets sent to a Server or Relay, the AERO interface
sets the UDP destination port to 8060, i.e., the IANA-registered port
number for AERO. For packets sent to a Client, the AERO interface
sets the UDP destination port to the port value stored in the
neighbor cache entry for this Client. The AERO interface then either
includes or omits the UDP checksum according to the GUE
specification.
3.11. AERO Interface Decapsulation
AERO interfaces decapsulate packets destined either to the AERO node
itself or to a destination reached via an interface other than the
AERO interface the packet was received on. Decapsulation is per the
procedures specified for the appropriate encapsulation format.
3.12. AERO Interface Data Origin Authentication
AERO nodes employ simple data origin authentication procedures for
encapsulated packets they receive from other nodes on the AERO link.
In particular:
o AERO Relays and Servers accept encapsulated packets with a link-
layer source address that matches a permanent neighbor cache
entry.
Templin Expires November 2, 2019 [Page 32]
Internet-Draft AERO May 2019
o AERO Servers accept authentic encapsulated ND messages from
Clients (either directly or via a Proxy), and create or update a
symmetric neighbor cache entry for the Client based on the
specific message type.
o AERO Clients and Servers accept encapsulated packets if there is a
symmetric neighbor cache entry with a link-layer address that
matches the packet's link-layer source address.
o AERO Proxies accept encapsulated packets if there is a proxy
neighbor cache entry that matches the packet's network-layer
address.
Each packet should include a signature that the recipient can use to
authenticate the message origin, e.g., as for common VPN systems such
as OpenVPN [OVPN]. In some environments, however, it may be
sufficient to require signatures only for ND control plane messages
(see: Section 14) and omit signatures for data plane messages.
3.13. AERO Interface Packet Size Issues
The AERO interface is the node's attachment to the AERO link. The
AERO interface acts as a tunnel ingress when it sends a packet to an
AERO link neighbor and as a tunnel egress when it receives a packet
from an AERO link neighbor. AERO interfaces observe the packet
sizing considerations for tunnels discussed in
[I-D.ietf-intarea-tunnels] and as specified below.
The Internet Protocol expects that IP packets will either be
delivered to the destination or a suitable Packet Too Big (PTB)
message returned to support the process known as IP Path MTU
Discovery (PMTUD) [RFC1191][RFC8201]. However, PTB messages may be
crafted for malicious purposes such as denial of service, or lost in
the network [RFC2923]. This can be especially problematic for
tunnels, where a condition known as a PMTUD "black hole" can result.
For these reasons, AERO interfaces employ operational procedures that
avoid interactions with PMTUD, including the use of fragmentation
when necessary.
AERO interfaces observe two different types of fragmentation. Source
fragmentation occurs when the AERO interface (acting as a tunnel
ingress) fragments the encapsulated packet into multiple fragments
before admitting each fragment into the tunnel. Network
fragmentation occurs when an encapsulated packet admitted into the
tunnel by the ingress is fragmented by an IPv4 router on the path to
the egress. Note that an IPv4 packet that incurs source
fragmentation may also incur network fragmentation.
Templin Expires November 2, 2019 [Page 33]
Internet-Draft AERO May 2019
IPv6 specifies a minimum link Maximum Transmission Unit (MTU) of 1280
bytes [RFC8200]. Although IPv4 specifies a smaller minimum link MTU
of 68 bytes [RFC0791], AERO interfaces also observe the IPv6 minimum
for IPv4 even if encapsulated packets may incur network
fragmentation.
IPv6 specifies a minimum Maximum Reassembly Unit (MRU) of 1500 bytes
[RFC8200], while the minimum MRU for IPv4 is only 576 bytes [RFC1122]
(but, note that many standard IPv6 over IPv4 tunnel types already
assume a larger MRU than the IPv4 minimum).
AERO interfaces therefore configure an MTU that MUST NOT be smaller
than 1280 bytes, MUST NOT be larger than the minimum MRU among all
nodes on the AERO link minus the encapsulation overhead ("ENCAPS"),
and SHOULD NOT be smaller than 1500 bytes. AERO interfaces also
configure a Maximum Segment Unit (MSU) as the maximum-sized
encapsulated packet that the ingress can inject into the tunnel
without source fragmentation. The MSU value MUST NOT be larger than
(MTU+ENCAPS) and MUST NOT be larger than 1280 bytes unless there is
operational assurance that a larger size can traverse the link along
all paths.
All AERO nodes MUST configure the same MTU value for reasons cited in
[RFC3819][RFC4861]; in particular, multicast support requires a
common MTU value among all nodes on the link. All AERO nodes MUST
configure an MRU large enough to reassemble packets up to
(MTU+ENCAPS) bytes in length; nodes that cannot configure a large-
enough MRU MUST NOT enable an AERO interface.
The network layer proceeds as follow when it presents an IP packet to
the AERO interface. For each IPv4 packet that is larger than the
AERO interface MTU and with the DF bit set to 0, the network layer
uses IPv4 fragmentation to break the packet into a minimum number of
non-overlapping fragments where the first fragment is no larger than
the MTU and the remaining fragments are no larger than the first.
For all other IP packets, if the packet is larger than the AERO
interface MTU, the network layer drops the packet and returns a PTB
message to the original source. Otherwise, the network layer admits
each IP packet or fragment into the AERO interface.
For each IP packet admitted into the AERO interface, the interface
(acting as a tunnel ingress) encapsulates the packet. If the
encapsulated packet is larger than the AERO interface MSU the ingress
source-fragments the encapsulated packet into a minimum number of
non-overlapping fragments where the first fragment is no larger than
the MSU and the remaining fragments are no larger than the first.
The ingress then admits each encapsulated packet or fragment into the
tunnel, and for IPv4 sets the DF bit to 0 in the IP encapsulation
Templin Expires November 2, 2019 [Page 34]
Internet-Draft AERO May 2019
header in case any network fragmentation is necessary. The
encapsulated packets will be delivered to the egress, which
reassembles them into a whole packet if necessary.
Several factors must be considered when fragmentation is needed. 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 data
corruption due to reassembly misassociations [RFC6864][RFC4963]. In
environments where IP fragmentation issues could result in
operational problems, the ingress SHOULD employ intermediate-layer
source fragmentation (see: [RFC2764] and
[I-D.ietf-intarea-gue-extensions]) before appending the outer
encapsulation headers to each fragment. Since the encapsulation
fragment header reduces the room available for packet data, but the
original source has no way to control its insertion, the ingress MUST
include the fragment header length in the ENCAPS length even for
packets in which the header is absent.
3.14. AERO Interface Error Handling
When an AERO node admits encapsulated packets into the AERO
interface, it may receive link-layer or network-layer error
indications.
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]. (AERO interfaces ignore all link-layer IPv4
"Fragmentation Needed" and IPv6 "Packet Too Big" messages since they
only emit packets that are guaranteed to be no larger than the IP
minimum link MTU as discussed in Section 3.13.)
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
Templin Expires November 2, 2019 [Page 35]
Internet-Draft AERO May 2019
possible without the length of the ICMP datagram exceeding 576
bytes".
The link-layer error message format is shown in Figure 5 (where, "L2"
and "L3" refer to link-layer and network-layer, respectively):
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
| 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 5: AERO 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 encapsulated packets that it
Templin Expires November 2, 2019 [Page 36]
Internet-Draft AERO May 2019
sends to one of its asymmetric neighbor correspondents, the node
SHOULD process the message as an indication that a path may be
failing, and MAY initiate NUD over that path. If it receives
Destination Unreachable messages on many or all paths, the node
SHOULD set ReachableTime for the corresponding asymmetric neighbor
cache entry to 0 and allow future packets destined to the
correspondent to flow through a default route.
o When an AERO Client receives persistent link-layer Destination
Unreachable messages in response to encapsulated packets that it
sends to one of its symmetric neighbor 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 Server and release its association
with the old Server as specified in Section 3.19.7.
o When an AERO Server receives persistent link-layer Destination
Unreachable messages in response to encapsulated packets that it
sends to one of its symmetric neighbor Clients, the Server SHOULD
mark the underlying path as unusable and use another underlying
path. If it receives Destination Unreachable messages on multiple
paths, the Server should take no further actions unless it
receives an explicit ND/PD release message or if the PD lifetime
expires. In that case, the Server MUST release the Client's
delegated MNP, withdraw the MNP from the AERO routing system and
delete the neighbor cache entry.
o When an AERO Relay or Server receives link-layer Destination
Unreachable messages in response to an encapsulated 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 Relay receives a packet for which the network-layer
destination address is covered by an MSP, if there is no more-
specific routing information for the destination the Relay drops the
packet and returns a network-layer Destination Unreachable message
subject to rate limiting. The Relay writes the network-layer source
address of the original packet as the destination address and uses
one of its non link-local addresses as the source address of the
message.
When an AERO node receives an encapsulated packet for which the
reassembly buffer it too small, it drops the packet and returns a
network-layer Packet Too Big (PTB) message. The node first writes
the MRU value into the PTB message MTU field, writes the network-
layer source address of the original packet as the destination
Templin Expires November 2, 2019 [Page 37]
Internet-Draft AERO May 2019
address and writes one of its non link-local addresses as the source
address.
3.15. AERO Router Discovery, Prefix Delegation and Autoconfiguration
AERO Router Discovery, Prefix Delegation and Autoconfiguration are
coordinated as discussed in the following Sections.
3.15.1. AERO ND/PD Service Model
Each AERO Server on the link configures a PD service to facilitate
Client requests. Each 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 AERO link and securely distributed to all Servers,
e.g., via the Lightweight Directory Access Protocol (LDAP) [RFC4511],
via static configuration, etc. Therefore, no Server-to-Server PD
state synchronization is necessary, and Clients can optionally hold
separate PDs for the same MNPs from multiple Servers. Clients can
receive new PDs from new Servers before releasing PDs received from
existing Servers for service continuity. Clients receive the same
service regardless of the Servers they select, although selecting
Servers that are topologically nearby may provide better routing.
AERO Clients and Servers use ND messages to maintain neighbor cache
entries. AERO Servers configure their AERO interfaces as advertising
interfaces, and therefore send unicast RA messages with configuration
information in response to a Client's RS message. Thereafter,
Clients send additional RS messages to refresh prefix and/or router
lifetimes.
AERO Clients and Servers include PD parameters in RS/RA messages to
be used for Prefix Delegation (see [I-D.templin-6man-dhcpv6-ndopt]
for ND/PD alternatives). The unified ND/PD messages are exchanged
between Client and Server according to the prefix management schedule
required by the PD service. If the Client knows its MNP in advance,
it can include its AERO address as the source address of an RS
message and with an SLLAO with a valid Prefix Length for the MNP. If
the Server (and Proxy) accept the Client's MNP assertion, they inject
the prefix into the routing system and establish the necessary
neighbor cache state.
The following sections specify the Client and Server behavior.
Templin Expires November 2, 2019 [Page 38]
Internet-Draft AERO May 2019
3.15.2. AERO Client Behavior
AERO Clients can discover the INET and AERO addresses of AERO Servers
in the MAP list via static configuration (e.g., from a flat-file map
of Server addresses and locations), or through an automated means
such as Domain Name System (DNS) name resolution [RFC1035]. 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 Client's ANET interface (e.g., "example.com").
Alternatively, the Client can discover the Server's address through a
multicast RS as described below.
To associate with a Server, the Client acts as a requesting router to
request MNPs. The Client prepares an RS message with PD parameters
(e.g., with an SLLAO with non-zero Prefix Length). If the Client
already knows the Server's AERO address, it includes the AERO address
as the network-layer destination address; otherwise, it includes all-
routers multicast (ff02::2) as the network-layer destination address.
If the Client already knows its own AERO address, it uses the AERO
address as the network-layer source address; otherwise, it uses the
unspecified AERO address (fe80::ffff:ffff) as the network-layer
source address.
The Client next includes an SLLAO in the RS message formatted as
described in Section 3.6 to register its link-layer information with
the Server. The SLLAO corresponding to the ANET interface over which
the Client will send the RS message MUST set the S bit to 1. The
Client MAY include additional SLLAOs specific to other underlying
interfaces, but if so it MUST set their S, Port Number and Link Layer
Address fields to 0. If the Client is connected to an ANET for which
encapsulation is required, the Client finally encapsulates the RS
message in an ANET header with its own ANET address as the source
address and the INET address of the Server as the destination.
The Client then sends the RS message (either via a VPN for VPNed
interfaces, via a Proxy for proxyed interfaces or via the SPAN for
native interfaces) and waits for an RA message reply (see
Section 3.15.3) while retrying up to MAX_RTR_SOLICITATIONS times
until an RA is received. If the Client receives no RAs, or if it
receives an RA with Router Lifetime set to 0, the Client SHOULD
abandon this Server and try another Server. Otherwise, the Client
processes the PD information found in the RA message.
Next, the Client creates a symmetric neighbor cache entry with the
Server's AERO address as the network-layer address and the address in
the first SLLAO as the Server's INET address. The Client records the
RA Router Lifetime field value in the neighbor cache entry as the
Templin Expires November 2, 2019 [Page 39]
Internet-Draft AERO May 2019
time for which the Server has committed to maintaining the MNP in the
routing system. The Client then autoconfigures AERO addresses for
each of the delegated MNPs and assigns them to the AERO interface.
The Client also caches any MSPs included in Route Information Options
(RIOs) [RFC4191] as MSPs to associate with the AERO link, and assigns
the MTU value in the MTU option to its AERO interface while
configuring an appropriate MRU.
The Client then registers additional ANET interfaces with the Server
by sending additional RS messages including SLLAOs via other ANET
interfaces after the initial RS/RA exchange. The Client sends the RS
messages to the Server's AERO address but omits PD parameters since
the initial RS/RA exchange has already established PD state.
The Client examines the X and N bits in the first SLLAO of each RA
message it receives. If the X bit value is 1 the Client infers that
there is a Proxy on the path, and if the N bit value is 1 the Client
infers that there is a NAT on the path. If N is '1', the Client
SHOULD set Port Number and Link-Layer Address to 0 in the first S/
TLLAO of any subsequent ND messages it sends to the Server over that
link.
Following autoconfiguration, the Client 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
subsequently maintains its MNP delegations through each of its
Servers by sending additional RS messages with PD parameters before
Router Lifetime expires.
After the Client registers its ANET interfaces, it may wish to change
one or more registrations, e.g., if an ANET interface changes address
or becomes unavailable, if QoS preferences change, etc. To do so,
the Client prepares an RS message to send over any available ANET
interface. The RS MUST include an SLLAO specific to the selected
ANET interface as the first SLLAO and MAY include any additional
SLLAOs specific to other ANET interfaces. The Client includes fresh
'P(i)' values in each SLLAO to update the Server's neighbor cache
entry. If the Client wishes to update only the 'P(i)' values, it
sets the Port Number and Link-Layer Address fields to 0. If the
Client wishes to disable the underlying interface, it sets the D bit
to 1. When the Client receives the Server's RA response, it has
assurance that the Server has been updated with the new information.
If the Client wishes to associate with multiple Servers, it repeats
the same procedures above for each additional Server. If the Client
wishes to discontinue use of a Server it issues an RS message over
any underlying interface with the R bit set to 1 in the first SLLAO.
Templin Expires November 2, 2019 [Page 40]
Internet-Draft AERO May 2019
When the Server processes the message, it releases the MNP, sets the
symmetric neighbor cache entry state for the Client to DEPARTED,
withdraws the IP route from the routing system and returns an RA
reply with Router Lifetime set to 0.
3.15.3. AERO Server Behavior
AERO Servers act as IPv6 routers and support a PD service for
Clients. AERO Servers arrange to add their AERO and INET addresses
to a static map of Server addresses for the link and/or the DNS
resource records for the FQDN "linkupnetworks.[domainname]" before
entering service. The list of Server addresses should be
geographically and/or topologically referenced, and forms the MAP
list for the AERO link.
When an AERO Server receives a prospective Client's RS message with
PD parameters on its AERO interface, 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 Server
authenticates the RS message and processes the PD parameters. The
Server first determines the correct MNPs to delegate to the Client by
searching the Client database. When the Server delegates the MNPs,
it also creates an IP forwarding table entry for each MNP so that the
MNPs are propagated into the routing system (see: Section 3.3). For
IPv6, the Server creates a single IPv6 forwarding table entry for
each MNP. For IPv4, the Server creates both an IPv4 forwarding table
entry and an IPv6 forwarding table entry with the IPv4-mapped IPv6
address corresponding to the IPv4 address.
The Server next creates a symmetric neighbor cache entry for the
Client using the base AERO address as the network-layer address and
with lifetime set to no more than the smallest PD lifetime. Next,
the Server updates the neighbor cache entry by recording the
information in each SLLAO in the RS indexed by the Interface ID and
including the Port Number, Link Layer Address and P(i) values. For
the SLLAO with S set to 1, however, the Server records the actual
INET header source addresses instead of those that appear in the
SLLAO in case there was a NAT in the path. The Server also records
the value of the X bit to indicate whether there is a Proxy on the
path.
Next, the Server prepares an RA message using its AERO address as the
network-layer source address and the network-layer source address of
the RS message as the network-layer destination address. The Server
includes the delegated MNPs, any other PD parameters and an SLLAO
with the Link Layer Address set to the Server's SPAN address and with
Interface ID set to 0xffff. The Server then includes one or more
RIOs that encode the MSPs for the AERO link, plus an MTU option for
Templin Expires November 2, 2019 [Page 41]
Internet-Draft AERO May 2019
the link MTU (see Section 3.13). The Server finally encapsulates the
message in a SPAN header with source address set to its own SPAN
address and destination address set to the Client's (or Proxy's) SPAN
address, then forwards the message into the SPAN.
After the initial RS/RA exchange, the AERO Server maintains the
symmetric neighbor cache entry for the Client. If the Client (or
Proxy) issues additional NS/RS messages, the Server resets
ReachableTime. If the Client (or Proxy) issues an RS with PD release
parameters (e.g., by including an SLLAO with R set to 1), or if the
Client becomes unreachable, the Server sets the Client's symmetric
neighbor cache entry to the DEPARTED state and withdraws the IP
routes from the AERO routing system.
The Server processes these and any other Client ND/PD messages, and
returns an NA/RA reply. The Server may also issue an unsolicited RA
message with PD reconfigure parameters to cause the Client to
renegotiate its PDs, and may issue an unsolicited RA message with
Router Lifetime set to 0 if it can no longer service this Client.
Finally, If the symmetric neighbor cache entry is in the DEPARTED
state, the Server deletes the entry after DepartTime expires.
3.15.3.1. Lightweight DHCPv6 Relay Agent (LDRA)
When DHCPv6 is used as the ND/PD service back end, AERO Clients and
Servers are always on the same link (i.e., the AERO link) from the
perspective of DHCPv6. However, in some implementations the DHCPv6
server and ND function may be located in separate modules. In that
case, the Server's AERO interface module can act as a Lightweight
DHCPv6 Relay Agent (LDRA)[RFC6221] to relay PD messages to and from
the DHCPv6 server module.
When the LDRA receives an authentic RS message, it extracts the PD
message parameters and uses them to construct an IPv6/UDP/DHCPv6
message. It sets the IPv6 source address to the source address of
the RS message, sets the IPv6 destination address to
'All_DHCP_Relay_Agents_and_Servers' and sets the UDP fields to values
that will be understood by the DHCPv6 server.
The LDRA then wraps the message in a DHCPv6 'Relay-Forward' message
header and includes an 'Interface-Id' option that includes enough
information to allow the LDRA to forward the resulting Reply message
back to the Client (e.g., the Client's link-layer addresses, a
security association identifier, etc.). The LDRA also wraps the
information in all of the SLLAOs from the RS message into the
Interface-Id option, then forwards the message to the DHCPv6 server.
Templin Expires November 2, 2019 [Page 42]
Internet-Draft AERO May 2019
When the DHCPv6 server prepares a Reply message, it wraps the message
in a 'Relay-Reply' message and echoes the Interface-Id option. The
DHCPv6 server then delivers the Relay-Reply message to the LDRA,
which discards the Relay-Reply wrapper and IPv6/UDP headers, then
uses the DHCPv6 message to construct an RA response to the Client.
The Server uses the information in the Interface-Id option to prepare
the RA message and to cache the link-layer addresses taken from the
SLLAOs echoed in the Interface-Id option.
3.16. The AERO Proxy
Clients may connect to ANETs that do not support direct
communications to Servers in outside INETs. In that case, the ANET
can employ an AERO Proxy. The Proxy is located at the ANET/INET
border and listens for encapsulated RS messages originating from or
RA messages destined to ANET Clients. The Proxy acts on these
control messages as follows:
o when the Proxy receives an RS message from a new ANET Client, it
first authenticates the message then examines the RS message
network-layer destination address. If the destination address is
a Server's AERO address, the Proxy proceeds to the next step.
Otherwise, if the destination is all-routers multicast the Proxy
selects a "nearby" Server that is likely to be a good candidate to
serve the Client and replaces the RS destination address with the
Server's AERO address. Next, the Proxy creates a proxy neighbor
cache entry and caches the Client and Server addresses along with
any identifying information including Transaction IDs, Client
Identifiers, Nonce values, etc. The Proxy then examines the
address in the RS message SLLAO with S set to 1. If the address
is different than the Client's ANET address, the Proxy notes that
the Client is behind a NAT. The Proxy then sets the X flag in the
SLLAO to 1 and changes the address in the SLLAO to its own SPAN
address. The Proxy finally re-encapsulates the RS message in a
SPAN header using its own SPAN address as the source address and
the SPAN address of the Server as the destination address, then
forwards the message to the Server via the SPAN.
o when the Server receives the RS message, it authenticates the
message then creates or updates a symmetric neighbor cache entry
for the Client with the Proxy's SPAN address as the link-layer
address. The Server then sends an RA message with a single SLLAO
back to the Proxy via the SPAN.
o when the Proxy receives the RA message, it matches the message
with the RS that created the proxy neighbor cache entry. The
Proxy then caches the route information in the message as a
mapping from the Client's MNPs to the Client's ANET address, and
Templin Expires November 2, 2019 [Page 43]
Internet-Draft AERO May 2019
sets the neighbor cache entry state to REACHABLE. The Proxy then
changes the Link Layer Address in the SLLAO to its own ANET
address, re-encapsulates the RA message in an ANET header, sets
the X flag in the SLLAO to 1, sets the N flag in the SLLAO to 1 if
the Client is behind a NAT, and forwards the message to the
Client.
After the initial RS/RA exchange, the Proxy forwards any Client data
packets for which there is no matching asymmetric neighbor cache
entry to a Relay via the SPAN. Finally, the Proxy forwards any
Client data destined to an asymmetric neighbor cache target directly
to the target according to the link-layer information - the process
of establishing asymmetric neighbor cache entries is specified in
Section 3.17.
While the Client is still attached to the ANET, the Proxy continues
to send NS/RS messages to update each Server's symmetric neighbor
cache entries on behalf of the Client and/or to convey QoS updates.
If the Server ceases to send solicited NA/RA responses, the Proxy
marks the Server as unreachable and sends an unsolicited RA with
Router Lifetime set to zero to inform the Client that this Server is
no longer able to provide Service. If the Client becomes
unreachable, the Proxy sets the neighbor cache entry state to
DEPARTED and sends an RS message to each Server with an SLLAO with D
set to 1 and with Interface ID set to the Client's interface ID so
that the Server will de-register this Interface ID. Although the
Proxy engages in these ND exchanges on behalf of the Client, the
Client can also send ND messages on its own behalf, e.g., if it is in
a better position than the Proxy to convey QoS changes, etc.
In some ANETs that employ a Proxy, the Client's MNP can be injected
into the ANET routing system. In that case, the Client can send data
messages without encapsulation so that the ANET native routing system
transports the unencapsulated 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. This encapsulation
avoidance represents a form of "header compression", meaning that the
MTU should be sized based on the size of full encapsulated messages
even if most messages are sent unencapsulated.
If the first-hop ANET access router is AERO-aware, the Client can
avoid 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 AERO address and with destination
address set to the AERO address of the Client's selected Server or to
all-routers multicast. The Client includes an SLLAO with Interface
ID, Prefix Length and P(i) information but with Port Number and Link-
Layer Address set to 0.
Templin Expires November 2, 2019 [Page 44]
Internet-Draft AERO May 2019
The Client then sends the unencapsulated RS message, which will be
intercepted by the AERO-Aware access router. The access router then
encapsulates the RS message in an ANET header with its own address as
the source address and the address of a Proxy as the destination
address. The access router further remembers the address of the
Proxy so that it can encapsulate future data packets from the Client
via the same Proxy. If the access router needs to change to a new
Proxy, it simply sends another RS message toward the Server via the
new Proxy on behalf of the Client.
In this arrangement, the only control messages sent by the Client are
unencapsulated RS messages with its AERO address as the source
address and the AERO address of the Server as the destination
address. The Client will also receive unencapsulated RA messages
from the Server via both the Proxy and access router.
In some cases, the access router and Proxy may be one and the same
node. In that case, the node would be located on the same physical
link as the Client, but its message exchanges with the Server 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.
3.17. AERO Route Optimization
While data packets are flowing between a source and target node,
route optimization SHOULD be used. Route optimization is initiated
by the first eligible Route Optimization Source (ROS) closest to the
source as follows:
o For Clients on VPNed, NATed and Direct interfaces, the Server is
the ROS.
o For Clients on Proxyed interfaces, the Proxy is the ROS.
o For Clients on native interfaces, the Client itself is the ROS.
o For INET interfaces serviced by a Gateway, the Gateway is the ROS.
The route optimization procedure is conducted between the ROS and a
Route Optimization Responder (ROR) in the same manner as for IPv6 ND
Address Resolution, and using the same NS/NA messaging. The ROR is
the Server (MAP) for MN targets, or the Gateway for FN targets. The
procedures are specified in the following sections.
Templin Expires November 2, 2019 [Page 45]
Internet-Draft AERO May 2019
3.17.1. Route Optimization Initiation
While the data packets are flowing from the source CN toward a target
CN, the ROS also sends an NS message to receive a solicited NA
message from the ROR .
When the ROS sends an NS, it includes the AERO address of the ROS as
the source address (e.g.,fe80::1) and the AERO address corresponding
to the data packet's destination address as the destination address
(e.g., if the destination address is 2001:db8:1:2::1 then the
corresponding AERO address is fe80::2001:db8:1:2). The NS message
includes no SLLAOs, but SHOULD include a Timestamp and Nonce option.
The ROS then encapsulates the message in a SPAN header with source
set to its own SPAN address and destination set to the inner packet
destination, then sends the message into the SPAN without
decrementing the network-layer TTL/Hop Limit field.
3.17.2. Relaying the NS
When the Relay receives the (double-encapsulated) NS message from the
ROS, it discards the outer IP header and determines that the ROR is
the next hop by consulting its standard IP forwarding table for the
SPAN header destination address. The Relay then forwards the SPAN
message toward the ROR the same as for any IP router. The final-hop
Relay in the SPAN will encapsulate the message in an INET header when
it delivers the message to the ROR.
3.17.3. Processing the NS and Sending the NA
When the ROR receives the (double-encapsulated) NS message, it
examines the AERO destination address to determine whether it is the
aggregation point for the target CN; if not, it drops the NS message.
Otherwise, if the target CN is serviced by a Client in the DEPARTED
state the ROR changes the NS message SPAN destination address to the
address of the Client's new Server, re-encapsulates the message in
the appropriate SPAN/INET headers and forwards the message to new
Server. If the target CN is serviced by a Client in the REACHABLE
state the ROR adds the AERO source address to the target Client's
Report List with time set to ReportTime.
For both Servers and Gateways, the ROR next prepares a solicited NA
message to send back to the ROS but does not create a neighbor cache
entry. The ROR sets the NA source address to its own AERO address
and sets the destination address to the AERO address of the ROS. The
NA message includes the Nonce value received in the NS, the current
Timestamp, and a first TLLAO with Interface ID set to 0xffff, with
all P(i) values set to "low", with Prefix Length set to the prefix
Templin Expires November 2, 2019 [Page 46]
Internet-Draft AERO May 2019
length of the target Client's MNP and with Link Layer Address set to
the ROR's SPAN address.
The ROR next includes additional TLLAOs for all of the target
Client's Interface IDs. For NATed, VPNed and Direct interfaces, the
TLLAO Link Layer Addresses are the SPAN address of the ROR. For
Proxyed interfaces, the TLLAO Link Layer Addresses are the SPAN
addresses of the target Client's Proxies, and for native interfaces
the TLLAO Link Layer Addresses are the SPAN addresses of the target
Client.
The ROR finally encapsulates the NA message in a SPAN header with
source set to its own SPAN address and destination set to the source
SPAN address of the NS message, then sends the message into the SPAN
without decrementing the network-layer TTL/Hop Limit field.
3.17.4. Relaying the NA
When the Relay receives the (double-encapsulated) NA message from the
ROR, it discards the INET header and determines that the ROS is the
next hop by consulting its standard IP forwarding table for the SPAN
header destination address. The Relay then forwards the SPAN-
encapsulated NA message toward the ROS the same as for any IP router.
The final-hop Relay in the SPAN will encapsulate the message in an
INET header when it delivers the message to the ROS.
3.17.5. Processing the NA
When the ROS receives the (double-encapsulated) solicited NA message,
it discards the INET and SPAN headers. The ROS next verifies the
Nonce and Timestamp values, then creates an asymmetric neighbor cache
entry for the target Client or Gateway and caches all information
found in the solicited NA TLLAOs. The ROS finally sets the
asymmetric neighbor cache entry lifetime to ReachableTime seconds.
3.17.6. Route Optimization Maintenance
Following route optimization, the ROS forwards future data packets
destined to one of the target's CNs via the addresses found in the
cached link-layer information. The route optimization is shared by
all sources that send packets to the target node via the ROS, i.e.,
and not just the source on behalf of which the route optimization was
initiated.
While new data packets destined to one of the target's CNs are
flowing through the ROS, it sends additional NS messages to the ROR
before ReachableTime expires to receive a fresh solicited NA message
the same as described in the previous sections. The ROS then updates
Templin Expires November 2, 2019 [Page 47]
Internet-Draft AERO May 2019
the asymmetric neighbor cache entry to refresh ReachableTime, while
(for target Clients) the ROR adds or updates the ROS address to the
target Client's Report List and with time set to ReportTime. While
no data packets are flowing, the ROS instead allows ReachableTime for
the asymmetric neighbor cache entry to expire. When ReachableTime
expires, the ROS deletes the asymmetric neighbor cache entry. Future
data packets flowing through the ROS will again trigger a new route
optimization exchange while initial data packets travel over a
suboptimal route via Servers and/or Relays.
The ROS may also receive unsolicited NA messages from the ROR at any
time. If there is an asymmetric neighbor cache entry for the target,
the ROS updates the link-layer information but does not update
ReachableTime since the receipt of an unsolicited NA does not confirm
that the forward path is still working. If there is no asymmetric
neighbor cache entry, the route optimization source simply discards
the unsolicited NA. Cases in which unsolicited NA messages are
generated are specified in Section 3.19.
In this arrangement, the ROS holds an asymmetric neighbor cache entry
for the ROR, but the ROR does not hold an asymmetric neighbor cache
entry for the ROS. The route optimization neighbor relationship is
therefore asymmetric and unidirectional. If the target node also has
packets to send back to the source node, then a separate route
optimization procedure is required in the reverse direction. But,
there is no requirement that the forward and reverse paths be
symmetric.
3.18. Neighbor Unreachability Detection (NUD)
AERO nodes perform Neighbor Unreachability Detection (NUD) as
described in [RFC4861]. NUD is performed either reactively in
response to persistent link-layer errors (see Section 3.14) or
proactively to confirm bi-directional reachability. The NUD
algorithm may further be seeded by ND hints of forward progress, but
care must be taken to avoid inferring reachability based on spoofed
information.
When an ROR directs an ROS to one or more target link-layer
addresses, the ROS SHOULD proactively test the direct path to each
address by sending an initial NS message to elicit a solicited NA
response. While testing the path, the ROS can optionally continue
sending packets via its default router, maintain a small queue of
packets until target reachability is confirmed, or (optimistically)
allow packets to flow directly to the target.
AERO nodes may have multiple link-layer addresses for the target
neighbor. In that case, NUD SHOULD be performed over each address
Templin Expires November 2, 2019 [Page 48]
Internet-Draft AERO May 2019
individually, and the source node should only consider the neighbor
unreachable if NUD fails over multiple underlying interface paths.
When a source node sends an NS message used for NUD, it uses its AERO
addresses as the IPv6 source address and the AERO address
corresponding to each target link-layer address as the destination.
For each target link-layer address, if the address is not located
within the same AERO link segment the source node encapsulates the NS
message in a SPAN header with its own SPAN address as the source and
the SPAN address of the target as the destination, then forwards the
message into the SPAN. If the target address is located within the
same segment, however, the source node omits the SPAN header and
encapsulates the message in an INET header with is own INET address
as the source and the INET address of the target as the destination,
then sends the message directly to the target.
Paths that pass NUD tests are marked as "reachable", while those that
do not are marked as "unreachable". These markings inform the AERO
interface forwarding algorithm specified in Section 3.9.
Proxies can perform NUD to verify Server reachability on behalf of
their proxyed Clients so that the Clients need not engage in NUD
messaging themselves.
3.19. Mobility Management and Quality of Service (QoS)
AERO is a Distributed Mobility Management (DMM) service. Each Server
is responsible for only a subset of the Clients on the AERO link, as
opposed to a Centralized Mobility Management (CMM) service where
there is a single network mobility service for all Clients. Clients
coordinate with their associated Servers via RS/RA exchanges to
maintain the DMM profile, and the AERO routing system tracks all
current Client/Server peering relationships.
Servers provide a Mobility Anchor Point (MAP) for their dependent
Clients. Clients are responsible for maintaining neighbor
relationships with their Servers through periodic RS/RA exchanges,
which also serves to confirm neighbor reachability. When a Client's
underlying interface address and/or QoS information changes, the
Client is responsible for updating the Server with this new
information. Note that for Proxyed interfaces, however, the Proxy
can perform the RS/RA exchanges on the Client's behalf.
Mobility management considerations are specified in the following
sections.
Templin Expires November 2, 2019 [Page 49]
Internet-Draft AERO May 2019
3.19.1. Mobility Update Messaging
RORs (i.e., Servers acting as MAPs) accommodate mobility and/or QoS
change events by sending an unsolicited NA message to each ROS in the
target Client's Report List. When an ROR sends an unsolicited NA
message, it sets the IPv6 source address to the Client's AERO address
and sets the IPv6 destination address to all-nodes multicast
(ff02::1). The ROR also includes a TLLAO with Interface ID 0xffff
with Link Layer address set to the ROR's SPAN address, and includes
additional TLLAOs for all of the target Client's Interface IDs with
Link Layer Address set to the corresponding SPAN addresses. The ROR
finally encapsulates the message in a SPAN header with source set to
its own SPAN address and destination set to the SPAN address of the
ROS, then sends the message into the SPAN.
As for the hot-swap of interface cards discussed in Section 7.2.6 of
[RFC4861], the transmission and reception of unsolicited NA messages
is unreliable but provides a useful optimization. In well-connected
Internetworks with robust data links unsolicited NA messages will be
delivered with high probability, but in any case the ROR can
optionally send up to MAX_NEIGHBOR_ADVERTISEMENT unsolicited NAs to
each ROS to increase the likelihood that at least one will be
received.
When an ROS receives an unsolicited NA message, it ignores the
message if there is no existing neighbor cache entry for the Client.
Otherwise, it uses the included TLLAOs to update the address and QoS
information in the neighbor cache entry, but does not reset
ReachableTime since the receipt of an unsolicited NA message from the
target Server does not provide confirmation that any forward paths to
the target Client are working.
If unsolicited NA messages are lost, the ROS may be left with stale
address and/or QoS information for the Client for up to ReachableTime
seconds. During this time, the ROS can continue sending packets to
the target Client according to its current neighbor cache information
but may receive persistent unsolicited NA messages as discussed in
Section 3.19.2.
3.19.2. Forwarding Packets on Behalf of Departed Clients
When a Server receives packets with destination addresses that match
a symmetric neighbor cache entry in the DEPARTED state, it forwards
the packets to the SPAN address corresponding to the Client's new
Server. If the encapsulation source is in the Report List, the
Server also sends an unsolicited NA message via the SPAN (subject to
rate limiting) with a TLLAO with Interface ID 0xffff and with D set
to 1. The ROS will then realize that it needs to set its asymmetric
Templin Expires November 2, 2019 [Page 50]
Internet-Draft AERO May 2019
neighbor cache entry state for the target to DEPARTED, and SHOULD re-
initiate route optimization after a short delay.
When a Proxy receives packets with destination addresses that match a
proxy neighbor cache entry in the DEPARTED state, it forwards the
packets to one of the target Client's Servers. If the encapsulation
source is not one of its proxy neighbor Clients, the Proxy also
returns an unsolicited NA message via the SPAN (subject to rate
limiting) with a single TLLAO with the target Client's Interface ID
and with D set to 1. The source will then realize that it needs to
mark its neighbor cache entry Interface ID for the Proxy as
"unreachable", and SHOULD re-initiate route optimization while
continuing to forward packets according to the remaining neighbor
cache entry state.
When a Client receives packets with destination addresses that do not
match one of its MNPs, it drops the packets silently.
3.19.3. Announcing Link-Layer Address and/or QoS Preference Changes
When a Client needs to change its ANET addresses and/or QoS
preferences (e.g., due to a mobility event), either the Client or
Proxy sends RS messages to its Servers via the SPAN with SLLAOs that
include the new Client Port Number, Link Layer Address and P(i)
values. If the RS messages are sent solely for the purpose of
updating QoS preferences, S, Port Number and Link-Layer Address are
set to 0. If the RS message is not sent for the purpose of asserting
a PD, the Prefix Length is set to 0.
Up to MAX_RTR_SOLICITATION RS messages MAY be sent in parallel with
sending actual data packets in case one or more RAs are lost. If all
RAs are lost, the Client SHOULD re-associate with a new Server.
3.19.4. Bringing New Links Into Service
When a Client needs to bring new ANET interfaces into service (e.g.,
when it activates a new data link), it sends RS messages to its
Servers via the ANET interface with SLLAOs that include the new
Client Link Layer Address information. If the RS message is not sent
for the purpose of asserting a PD, the Prefix Length is set to 0.
3.19.5. Removing Existing Links from Service
When a Client needs to remove existing ANET interfaces from service
(e.g., when it de-activates an existing data link), it sends RS
messages to its Servers with SLLAOs with the D flag set to 1.
Templin Expires November 2, 2019 [Page 51]
Internet-Draft AERO May 2019
If the Client needs to send RS messages over an ANET interface other
than the one being removed from service, it MUST include a current
SLLAO for the sending interface as the first SLLAO and include SLLAOs
for any ANET interfaces being removed from service as additional
SLLAOs.
3.19.6. Implicit Mobility Management
AERO interface neighbors MAY provide a configuration option that
allows them to perform implicit mobility management in which no 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 ANET interface address changes (either due to a
readdressing of the original interface or switching to a new
interface) the neighbor immediately updates the neighbor cache entry
for the Client and begins accepting and sending packets according to
the Client's new ANET 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.
3.19.7. Moving to a New Server
When a Client associates with a new Server, it performs the Client
procedures specified in Section 3.15.2. The Client then sends an RS
message over any working ANET interface with destination set to the
old Server's AERO address, with R set to 1 in the first SLLAO and
with PD parameters to fully release itself from the old Server. The
SLLAO also includes the SPAN address of the new Server in the Link
Layer Address. If the Client does not receive an RA reply after
MAX_RTR_SOLICITATIONS attempts over multiple underlying interfaces,
the old Server may have failed and the Client should discontinue its
release attempts.
When the old Server processes the RS, it sends unsolicited NA
messages with a single TLLAO with Interface ID set to 0xffff and with
D set to 1 to all ROSs in the Client's Report List. The Server also
changes the symmetric neighbor cache entry state to DEPARTED, sets
the link-layer address of the Client to the address found in the RS
SLLAO, and sets a timer to DepartTime seconds. The Server then
returns an RA message to the Client with Router Lifetime set to 0.
After DepartTime seconds expires, the Server deletes the symmetric
neighbor cache entry.
Templin Expires November 2, 2019 [Page 52]
Internet-Draft AERO May 2019
When the Client receives the RA message with Router Lifetime set to
0, it still must inform each of its remaining Proxies that it has
released the old Server from service. To do so, it sends an RS over
each remaining proxyed ANET interface with destination set to the old
Server's AERO address and with R set to 1 in the first SLLAO but with
no PD parameters. The Proxy will mark this Server as DEAPARTED and
return an immediate RA without first performing an RS/RA exchange
with the old Server.
Clients SHOULD NOT move rapidly between 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 Server include a
Server that has gone unreachable, topological movements of
significant distance, movement to a new geographic region, movement
to a new segment, etc.
3.20. Multicast
The AERO Client serves as an IGMPv2 (IPv4) [RFC2236] or MLDv2 (IPv6)
proxy [RFC3810][RFC4605] for its EUNs and/or hosted applications.
The Client forwards IGMPv2/MLDv2 messages over any of its ANET
interfaces for which group membership is required. The IGMP/MLDv2
messages may be further forwarded by a first-hop ANET access router
acting as an IGMPv2/MLDv2-snooping switch [RFC4541], then ultimately
delivered to an AERO Proxy/Server acting as a Protocol Independent
Multicast - Sparse-Mode (PIM-SM) router [RFC7761]. AERO Gateways act
as PIM-SM routers the same as AERO Proxys/Servers, except that no
IGMPv2/MLDv2 proxying/snooping are necessary on the Gateway's
attached EUNs.
When an AERO Proxy/Server/Gateway "X" acting as a PIM-SM router
receives a Source-Specific Multicast (SSM) "Join" message for source
"S" and group "G" (i.e., (S,G)), it forwards the message to a Relay
via the SPAN. The SPAN then forwards the message to AERO Server "Y"
which forwards the message to Proxy "Z" that services "S" (note that
when "Y" is a Gateway there is no need for Proxy "Z".) Since the
Relays in the SPAN do not examine Layer 3 control messages, this
means that the (reverse) multicast tree path is simply from "S" to
"Z" to "Y" to "X" with no other Layer 3 multicast-aware routers in
the path. If "Z", "Y" and "X" are located on the same SPAN segment,
the multicast data traffic between them can be sent via simple INET
encapsulation and need not go over the SPAN. If any of "Z", "Y" and
X" are located in different SPAN segments, however, SPAN
encapsulation is necessary.
When an AERO Proxy/Server/Gateway "X" acting as a PIM-SM router
receives an Any Source Multicast (ASM) "Join" message for source "*"
and group "G" (i.e., (*,G)), it forwards the message toward the
Templin Expires November 2, 2019 [Page 53]
Internet-Draft AERO May 2019
Rendezvous Point "RP" for group "G" the same as if "RP" was the
source "S". The (reverse) multicast tree path is therefore
established in the same way as above.
After the (reverse) multicast tree path has been established via AERO
Proxy "Z", the AERO Client "C" that hosts "S" may move to a different
Proxy "Z2". In that case, the Client's multicast Server "Y" sends a
PIM-SM "Join" to the new Proxy "Z2" for each multicast group "G",
then sends a PIM-SM "Prune" to the old Proxy "Z".
After the (reverse) multicast tree path has been established, the
AERO Client "C" may move to a different Server "Y2". In that case,
the old Server "Y" must transfer its multicast tree state for all of
Client "C"'s multicast sources to the new Server "Y2", and "Y2" must
issue PIM-SM "Join" messages for each of Client "C"'s new Proxys.
4. Direct Underlying Interfaces
When a Client's AERO 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 QoS preferences. If the Direct
interface has the highest QoS preference, then the Client's IP
packets are transmitted directly to the peer without going through an
ANET/INET. If other interfaces have higher QoS preferences, then the
Client's IP packets are transmitted via a different interface, which
may result in the inclusion of Proxies, Servers and Relays in the
communications path. Direct interfaces must be tested periodically
for reachability, e.g., via NUD.
5. AERO Clients on the Open Internetwork
AERO Clients that connect to the open Internetwork via either a
native or NATed interface can establish a VPN to securely connect to
a Server. Alternatively, the Client can exchange ND messages
directly with other AERO nodes on the same Internetwork using INET
encapsulation only and without joining the SPAN. In that case,
however, the Client must apply asymmetric security for ND messages to
ensure routing and neighbor cache integrity (see: Section 14).
6. Operation over Multiple AERO Links
An AERO Client can connect to mutliple AERO links the same as for any
Layer 2 service. In that case, the Client maintains a distinct AERO
interface for each link, e.g., 'aero0' for the first link, 'aero1'
for the second, 'aero2' for the third, etc. Each AERO link would
include its own distinct set of Relays, Servers and Proxies, thereby
providing redundancy in case of failures. Each AERO link would
Templin Expires November 2, 2019 [Page 54]
Internet-Draft AERO May 2019
service a distinct MSP such that the Client would receive multiple
MNP delegations - one for each link.
The Relays, Servers and Proxies on each AERO link can assign AERO and
SPAN addresses that use the same or different numberings from those
on other links. Since the links are distinct there is no requirement
for avoiding inter-link address duplication, e.g., the same AERO
address such as fe80::1000 could be used to number distinct nodes
that connect to different links.
Each AERO link could utilize the same or different ANET connections.
The links can be distinguished at the link-layer via Virtual Local
Area Network (VLAN) tagging the same as definied in IEEE 802.1Q.
This gives rise to the opportunity for supporting multiple redundant
networked paths, where each VLAN is distinguished by a different
label (e.g., colors such as Red, Green, Blue, etc.). In particular,
the Client can tag its RS messages with the appropriate label to
cause the network to select the desired VLAN.
7. Operation on AERO Links with /64 ASPs
IPv6 AERO links typically have MSPs that cover many candidate MNPs of
length /64 or shorter. However, in some cases it may be desirable to
use AERO over links that have only a /64 MSP. This can be
accommodated by treating all Clients on the AERO link as simple hosts
that receive /128 prefix delegations.
In that case, the Client sends an RS message to the Server the same
as for ordinary AERO links. The Server responds with an RA message
that includes one or more /128 prefixes (i.e., singleton addresses)
that include the /64 MSP prefix along with an interface identifier
portion to be assigned to the Client. The Client and Server then
configure their AERO addresses based on the interface identifier
portions of the /128s (i.e., the lower 64 bits) and not based on the
/64 prefix (i.e., the upper 64 bits).
For example, if the MSP for the host-only IPv6 AERO link is
2001:db8:1000:2000::/64, each Client will receive one or more /128
IPv6 prefix delegations such as 2001:db8:1000:2000::1/128,
2001:db8:1000:2000::2/128, etc. When the Client receives the prefix
delegations, it assigns the AERO addresses fe80::1, fe80::2, etc. to
the AERO interface, and assigns the global IPv6 addresses (i.e., the
/128s) to either the AERO interface or an internal virtual interface
such as a loopback. In this arrangement, the Client conducts route
optimization in the same sense as discussed in Section 3.17.
This specification has applicability for nodes that act as a Client
on an "upstream" AERO link, but also act as a Server on "downstream"
Templin Expires November 2, 2019 [Page 55]
Internet-Draft AERO May 2019
AERO links. More specifically, if the node acts as a Client to
receive a /64 prefix from the upstream AERO link it can then act as a
Server to provision /128s to Clients on downstream AERO links.
8. AERO Adaptations for SEcure Neighbor Discovery (SEND)
SEcure Neighbor Discovery (SEND) [RFC3971] and Cryptographically
Generated Addresses (CGAs) [RFC3972] were designed to secure IPv6 ND
messaging in environments where symmetric network and/or transport-
layer security services are impractical (see: Section 14). AERO
nodes that use SEND/CGA employ the following adaptations.
When a source AERO node prepares a SEND-protected ND message, it uses
a link-local CGA as the IPv6 source address and writes the prefix
embedded in its AERO address (i.e., instead of fe80::/64) in the CGA
parameters Subnet Prefix field. When the neighbor receives the ND
message, it first verifies the message checksum and SEND/CGA
parameters while using the link-local prefix fe80::/64 (i.e., instead
of the value in the Subnet Prefix field) to match against the IPv6
source address of the ND message.
The neighbor then derives the AERO address of the source by using the
value in the Subnet Prefix field as the interface identifier of an
AERO address. For example, if the Subnet Prefix field contains
2001:db8:1:2, the neighbor constructs the AERO address as
fe80::2001:db8:1:2. The neighbor then caches the AERO address in the
neighbor cache entry it creates for the source, and uses the AERO
address as the IPv6 destination address of any ND message replies.
9. AERO Critical Infrastructure Considerations
AERO Relays can be either Commercial off-the Shelf (COTS) standard IP
routers or virtual machines in the cloud. Relays must be
provisioned, supported and managed by the INET administrative
authority, and connected to the Relays of other INETs via inter-
domain peerings. Cost for purchasing, configuring and managing
Relays is nominal even for very large AERO links.
AERO Servers can be standard dedicated server platforms, but most
often will be deployed as virtual machines in the cloud. The only
requirements for Servers are that they can run the AERO user-level
code and have at least one network interface connection to the INET.
As with Relays, Servers must be provisioned, supported and managed by
the INET administrative authority. Cost for purchasing, configuring
and managing Servers is nominal especially for virtual Servers hosted
in the cloud.
Templin Expires November 2, 2019 [Page 56]
Internet-Draft AERO May 2019
AERO Proxies are most often standard dedicated server platforms with
one network interface connected to the ANET and a second interface
connected to an INET. As with Servers, the only requirements are
that they can run the AERO user-level code and have at least one
interface connection to the INET. Proxies must be provisioned,
supported and managed by the ANET administrative authority. Cost for
purchasing, configuring and managing Proxies is nominal, and borne by
the ANET administrative authority.
AERO combined Client/Servers can be any dedicated server or COTS
router platform with one network interface connected to the INET and
a second interface connected to a downstream attached network. The
Client/Server joins the SPAN over the INET interface and engages in
eBGP peering with one or more Relays as a stub AS. The Client/Server
then injects its MNP into the BGP routing system, and provisions the
MNP to its downstream-attached networks. No Client/Server ND
messaging is necessary, and the Client/Server can perform ROS and ROR
services the same as for any Server. The combined Client/Server
construct is useful for connecting large fixed networks to the AERO
link.
10. 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 Gateway NAT64 mapping caches. In that way, an IPv4
correspondent node can send packets to the IPv4 address mapping of
the target MN, and the Gateway 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 Server, the Server returns
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.
11. Transition Considerations
The SPAN ensures that dissimilar INET segments can be joined into a
single unified AERO link, even though the INET segments themselves
may have differing protocol versions and/or incompatible addressing
plans. However, a commonality can be achieved by incrementally
distributing MNP prefixes to eventually reach all nodes (both mobile
and fixed) in all segments. This can be accomplished by
Templin Expires November 2, 2019 [Page 57]
Internet-Draft AERO May 2019
incrementally deploying AERO Gateways on each INET segment, with each
Gateway distributing its MNPs to its downstream-attached INET links.
This gives rise to the opportunity to eventually distribute MNP-based
addresses to all nodes, and to present a unified AERO link view
(bridged by the SPAN) even if the INET segments remain in their
current protocol and addressing plans. In that way, the AERO link
can serve the dual purpose of providing a mobility service and a
transition service. Or, if an INET segment is transitioned to a
protocol version and addressing scheme that is compatible with the
AERO link MNP-based addressing scheme, the NET segment and AERO link
can be joined by standard routers.
12. Implementation Status
An AERO implementation based on OpenVPN (https://openvpn.net/) was
announced on the v6ops mailing list on January 10, 2018. The latest
version is available at: http://linkupnetworks.net/aero/AERO-OpenVPN-
2.0.tgz.
An initial public release of the AERO proof-of-concept source code
was announced on the intarea mailing list on August 21, 2015. The
latest version is available at: http://linkupnetworks.net/aero/aero-
4.0.0.tgz.
A survey of public domain and commercial SEND implementations is
available at https://www.ietf.org/mail-archive/web/its/current/
msg02758.html.
13. IANA Considerations
The IANA has assigned a 4-octet Private Enterprise Number "45282" for
AERO in the "enterprise-numbers" registry.
The IANA has assigned the UDP port number "8060" for an earlier
experimental version of AERO [RFC6706]. This document obsoletes
[RFC6706] and claims the UDP port number "8060" for all future use.
No further IANA actions are required.
14. Security Considerations
AERO link security considerations include considerations for both the
data plane and the control plane.
Data plane security considerations are the same as for ordinary
Internet communications. Application endpoints in AERO Clients and
their EUNs SHOULD use application-layer security services such as
Templin Expires November 2, 2019 [Page 58]
Internet-Draft AERO May 2019
TLS/SSL [RFC8446], DTLS [RFC6347] 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 symmetric
network and/or transport layer security services such as TLS/SSL,
DTLS, IPsec [RFC4301], etc. AERO Proxies and 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.
Control plane security considerations are the same as for standard
IPv6 Neighbor Discovery [RFC4861]. As fixed infrastructure elements,
AERO Servers/Gateways and Proxies SHOULD pre-configure security
associations for one or more Relays on their SPAN segments (e.g.,
using pre-placed keys) and use symmetric network and/or transport
layer security services such as IPsec, TLS/SSL or DTLS to secure ND
messages. The AERO Relays of all SPAN segments in turn SHOULD pre-
configure security associations for their neighboring AERO Relays.
AERO Clients that connect to secured enclaves need not apply security
to their ND messages, since the messages will be intercepted by an
enclave perimeter Proxy. AERO Clients located outside of secured
enclaves SHOULD use symmetric network and/or transport layer security
to secure their ND exchanges with Servers, but when there are many
prospective neighbors with dynamically changing connectivity an
asymmetric security service such as SEND may be needed (see:
Section 8).
AERO Servers/Gateways and Relays 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 by connecting Servers/
Gateways and Relays 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 Servers/Gateways and Proxies
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 SPAN messages are injected into an AERO link
from an outside attacker. Restricting access to the link can be
achieved by having Internetwork border routers implement ingress
filtering to discard encapsulated packets injected into the link by
an outside agent.
Templin Expires November 2, 2019 [Page 59]
Internet-Draft AERO May 2019
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 other nodes via some
form of Internet connection sharing such as tethering.)
The MAP list MUST be well-managed and secured from unauthorized
tampering, even though the list contains only public information.
The MAP list can be conveyed to the Client, e.g., through secure
upload of a static file, through DNS lookups, etc.
Although public domain and commercial SEND implementations exist,
concerns regarding the strength of the cryptographic hash algorithm
have been documented [RFC6273] [RFC4982].
Security considerations for accepting link-layer ICMP messages and
reflected packets are discussed throughout the document.
15. 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, Brian Carpenter,
Wojciech Dec, Ralph Droms, Adrian Farrel, Nick Green, Sri Gundavelli,
Brian Haberman, Bernhard Haindl, Joel Halpern, Tom Herbert, Sascha
Hlusiak, Lee Howard, Andre Kostur, Hubert Kuenig, Ted Lemon, Andy
Malis, Satoru Matsushima, Tomek Mrugalski, Madhu Niraula, Alexandru
Petrescu, Behcet Saikaya, Michal Skorepa, 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 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, Balaguruna Chidambaram, Irene Chin, Bruce Cornish, Claudiu
Danilov, Wen Fang, Anthony Gregory, Jeff Holland, Seth Jahne, Ed
King, Gene MacLean III, Rob Muszkiewicz, Sean O'Sullivan, Greg
Saccone, Kent Shuey, Brian Skeen, Mike Slane, Carrie Spiker, Brendan
Williams, Julie Wulff, Yueli Yang, Eric Yeh and other members of the
BR&T and BIT mobile networking teams. Kyle Bae, Wayne Benson and
Eric Yeh are especially acknowledged for implementing the AERO
functions as extensions to the public domain OpenVPN distribution.
Templin Expires November 2, 2019 [Page 60]
Internet-Draft AERO May 2019
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:
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 Information Technology (BIT)
MobileNet program.
This work is aligned with the Boeing autonomy program.
16. References
16.1. Normative References
[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 November 2, 2019 [Page 61]
Internet-Draft AERO May 2019
[RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black,
"Definition of the Differentiated Services Field (DS
Field) in the IPv4 and IPv6 Headers", RFC 2474,
DOI 10.17487/RFC2474, December 1998,
<https://www.rfc-editor.org/info/rfc2474>.
[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>.
[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>.
[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>.
16.2. Informative References
[BGP] Huston, G., "BGP in 2015, http://potaroo.net", January
2016.
Templin Expires November 2, 2019 [Page 62]
Internet-Draft AERO May 2019
[I-D.ietf-dmm-distributed-mobility-anchoring]
Chan, A., Wei, X., Lee, J., Jeon, S., and C. Bernardos,
"Distributed Mobility Anchoring", draft-ietf-dmm-
distributed-mobility-anchoring-13 (work in progress),
March 2019.
[I-D.ietf-intarea-gue]
Herbert, T., Yong, L., and O. Zia, "Generic UDP
Encapsulation", draft-ietf-intarea-gue-07 (work in
progress), March 2019.
[I-D.ietf-intarea-gue-extensions]
Herbert, T., Yong, L., and F. Templin, "Extensions for
Generic UDP Encapsulation", draft-ietf-intarea-gue-
extensions-06 (work in progress), March 2019.
[I-D.ietf-intarea-tunnels]
Touch, J. and M. Townsley, "IP Tunnels in the Internet
Architecture", draft-ietf-intarea-tunnels-09 (work in
progress), July 2018.
[I-D.ietf-rtgwg-atn-bgp]
Templin, F., 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-01 (work in progress), January 2019.
[I-D.templin-6man-dhcpv6-ndopt]
Templin, F., "A Unified Stateful/Stateless Configuration
Service for IPv6", draft-templin-6man-dhcpv6-ndopt-07
(work in progress), December 2018.
[I-D.templin-intarea-grefrag]
Templin, F., "GRE Tunnel Level Fragmentation", draft-
templin-intarea-grefrag-04 (work in progress), July 2016.
[I-D.templin-intarea-seal]
Templin, F., "The Subnetwork Encapsulation and Adaptation
Layer (SEAL)", draft-templin-intarea-seal-68 (work in
progress), January 2014.
[I-D.templin-intarea-vet]
Templin, F., "Virtual Enterprise Traversal (VET)", draft-
templin-intarea-vet-40 (work in progress), May 2013.
Templin Expires November 2, 2019 [Page 63]
Internet-Draft AERO May 2019
[I-D.templin-ironbis]
Templin, F., "The Interior Routing Overlay Network
(IRON)", draft-templin-ironbis-16 (work in progress),
March 2014.
[I-D.templin-v6ops-pdhost]
Templin, F., "IPv6 Prefix Delegation and Multi-Addressing
Models", draft-templin-v6ops-pdhost-23 (work in progress),
December 2018.
[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>.
[RFC1122] Braden, R., Ed., "Requirements for Internet Hosts -
Communication Layers", STD 3, RFC 1122,
DOI 10.17487/RFC1122, October 1989,
<https://www.rfc-editor.org/info/rfc1122>.
[RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191,
DOI 10.17487/RFC1191, November 1990,
<https://www.rfc-editor.org/info/rfc1191>.
[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>.
[RFC2236] Fenner, W., "Internet Group Management Protocol, Version
2", RFC 2236, DOI 10.17487/RFC2236, November 1997,
<https://www.rfc-editor.org/info/rfc2236>.
[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>.
[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>.
Templin Expires November 2, 2019 [Page 64]
Internet-Draft AERO May 2019
[RFC2764] Gleeson, B., Lin, A., Heinanen, J., Armitage, G., and A.
Malis, "A Framework for IP Based Virtual Private
Networks", RFC 2764, DOI 10.17487/RFC2764, February 2000,
<https://www.rfc-editor.org/info/rfc2764>.
[RFC2784] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P.
Traina, "Generic Routing Encapsulation (GRE)", RFC 2784,
DOI 10.17487/RFC2784, March 2000,
<https://www.rfc-editor.org/info/rfc2784>.
[RFC2890] Dommety, G., "Key and Sequence Number Extensions to GRE",
RFC 2890, DOI 10.17487/RFC2890, September 2000,
<https://www.rfc-editor.org/info/rfc2890>.
[RFC2923] Lahey, K., "TCP Problems with Path MTU Discovery",
RFC 2923, DOI 10.17487/RFC2923, September 2000,
<https://www.rfc-editor.org/info/rfc2923>.
[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>.
[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>.
[RFC3819] Karn, P., Ed., Bormann, C., Fairhurst, G., Grossman, D.,
Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J., and L.
Wood, "Advice for Internet Subnetwork Designers", BCP 89,
RFC 3819, DOI 10.17487/RFC3819, July 2004,
<https://www.rfc-editor.org/info/rfc3819>.
[RFC4213] Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms
for IPv6 Hosts and Routers", RFC 4213,
DOI 10.17487/RFC4213, October 2005,
<https://www.rfc-editor.org/info/rfc4213>.
[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>.
Templin Expires November 2, 2019 [Page 65]
Internet-Draft AERO May 2019
[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>.
[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>.
[RFC4607] Holbrook, H. and B. Cain, "Source-Specific Multicast for
IP", RFC 4607, DOI 10.17487/RFC4607, August 2006,
<https://www.rfc-editor.org/info/rfc4607>.
[RFC4963] Heffner, J., Mathis, M., and B. Chandler, "IPv4 Reassembly
Errors at High Data Rates", RFC 4963,
DOI 10.17487/RFC4963, July 2007,
<https://www.rfc-editor.org/info/rfc4963>.
Templin Expires November 2, 2019 [Page 66]
Internet-Draft AERO May 2019
[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>.
[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>.
[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>.
[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>.
[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>.
Templin Expires November 2, 2019 [Page 67]
Internet-Draft AERO May 2019
[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>.
[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>.
[RFC6864] Touch, J., "Updated Specification of the IPv4 ID Field",
RFC 6864, DOI 10.17487/RFC6864, February 2013,
<https://www.rfc-editor.org/info/rfc6864>.
[RFC7269] Chen, G., Cao, Z., Xie, C., and D. Binet, "NAT64
Deployment Options and Experience", RFC 7269,
DOI 10.17487/RFC7269, June 2014,
<https://www.rfc-editor.org/info/rfc7269>.
[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>.
[RFC8086] Yong, L., Ed., Crabbe, E., Xu, X., and T. Herbert, "GRE-
in-UDP Encapsulation", RFC 8086, DOI 10.17487/RFC8086,
March 2017, <https://www.rfc-editor.org/info/rfc8086>.
[RFC8201] McCann, J., Deering, S., Mogul, J., and R. Hinden, Ed.,
"Path MTU Discovery for IP version 6", STD 87, RFC 8201,
DOI 10.17487/RFC8201, July 2017,
<https://www.rfc-editor.org/info/rfc8201>.
[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>.
Templin Expires November 2, 2019 [Page 68]
Internet-Draft AERO May 2019
Appendix A. AERO Alternate Encapsulations
When GUE encapsulation is not needed, AERO can use common
encapsulations such as IP-in-IP [RFC2003][RFC2473][RFC4213], Generic
Routing Encapsulation (GRE) [RFC2784][RFC2890] and others. The
encapsulation is therefore only differentiated from non-AERO tunnels
through the application of AERO control messaging and not through,
e.g., a well-known UDP port number.
As for GUE encapsulation, alternate AERO encapsulation formats may
require encapsulation layer fragmentation. For simple IP-in-IP
encapsulation, an IPv6 fragment header is inserted directly between
the inner and outer IP headers when needed, i.e., even if the outer
header is IPv4. The IPv6 Fragment Header is identified to the outer
IP layer by its IP protocol number, and the Next Header field in the
IPv6 Fragment Header identifies the inner IP header version. For GRE
encapsulation, a GRE fragment header is inserted within the GRE
header [I-D.templin-intarea-grefrag].
Figure 6 shows the AERO IP-in-IP encapsulation format before any
fragmentation is applied:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Outer IPv4 Header | | Outer IPv6 Header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|IPv6 Frag Header (optional)| |IPv6 Frag Header (optional)|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Inner IP Header | | Inner IP Header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | | |
~ ~ ~ ~
~ Inner Packet Body ~ ~ Inner Packet Body ~
~ ~ ~ ~
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Minimal Encapsulation in IPv4 Minimal Encapsulation in IPv6
Figure 6: Minimal Encapsulation Format using IP-in-IP
Figure 7 shows the AERO GRE encapsulation format before any
fragmentation is applied:
Templin Expires November 2, 2019 [Page 69]
Internet-Draft AERO May 2019
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Outer IP Header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| GRE Header |
| (with checksum, key, etc..) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| GRE Fragment Header (optional)|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Inner IP Header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ ~
~ Inner Packet Body ~
~ ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: Minimal Encapsulation Using GRE
Alternate encapsulation may be preferred in environments where GUE
encapsulation would add unnecessary overhead. For example, certain
low-bandwidth wireless data links may benefit from a reduced
encapsulation overhead.
GUE encapsulation can traverse network paths that are inaccessible to
non-UDP encapsulations, e.g., for crossing Network Address
Translators (NATs). More and more, network middleboxes are also
being configured to discard packets that include anything other than
a well-known IP protocol such as UDP and TCP. It may therefore be
necessary to determine the potential for middlebox filtering before
enabling alternate encapsulation in a given environment.
In addition to IP-in-IP, GRE and GUE, AERO can also use security
encapsulations such as IPsec, TLS/SSL, DTLS, etc. In that case, AERO
control messaging and route determination occur before security
encapsulation is applied for outgoing packets and after security
decapsulation is applied for incoming packets.
AERO is especially well suited for use with VPN system encapsulations
such as OpenVPN [OVPN].
Appendix B. S/TLLAO Extensions for Special-Purpose Links
The AERO S/TLLAO format specified in Section 3.6 includes a Length
value of 5 (i.e., 5 units of 8 octets). However, special-purpose
links may extend the basic format to include additional fields and a
Length value larger than 5.
Templin Expires November 2, 2019 [Page 70]
Internet-Draft AERO May 2019
For example, adaptation of AERO to the Aeronautical
Telecommunications Network with Internet Protocol Services (ATN/IPS)
includes link selection preferences based on transport port numbers
in addition to the existing DSCP-based preferences. ATN/IPS nodes
maintain a map of transport port numbers to 64 possible preference
fields, e.g., TCP port 22 maps to preference field 8, TCP port 443
maps to preference field 20, UDP port 8060 maps to preference field
34, etc. The extended S/TLLAO format for ATN/IPS is shown in
Figure 8, where the Length value is 7 and the 'Q(i)' fields provide
link preferences for the corresponding transport port number.
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 | Length = 7 | Prefix Length | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface ID | Port Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Link-Layer Address +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|P00|P01|P02|P03|P04|P05|P06|P07|P08|P09|P10|P11|P12|P13|P14|P15|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|P16|P17|P18|P19|P20|P21|P22|P23|P24|P25|P26|P27|P28|P29|P30|P31|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|P32|P33|P34|P35|P36|P37|P38|P39|P40|P41|P42|P43|P44|P45|P46|P47|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|P48|P49|P50|P51|P52|P53|P54|P55|P56|P57|P58|P59|P60|P61|P62|P63|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Q00|Q01|Q02|Q03|Q04|Q05|Q06|Q07|Q08|Q09|Q10|Q11|Q12|Q13|Q14|Q15|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Q16|Q17|Q18|Q19|Q20|Q21|Q22|Q23|Q24|Q25|Q26|Q27|Q28|Q29|Q30|Q31|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Q32|Q33|Q34|Q35|Q36|Q37|Q38|Q39|Q40|Q41|Q42|Q43|Q44|Q45|Q46|Q47|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Q48|Q49|Q50|Q51|Q52|Q53|Q54|Q55|Q56|Q57|Q58|Q59|Q60|Q61|Q62|Q63|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8: ATN/IPS Extended S/TLLAO Format
Templin Expires November 2, 2019 [Page 71]
Internet-Draft AERO May 2019
Appendix C. Change Log
<< RFC Editor - remove prior to publication >>
Changes from draft-templin-intarea-6706bis-11 to draft-templin-
intrea-6706bis-12:
o Introduced Gateways as a new AERO element for connecting
Correspondent Nodes on INET links
o Introduced terms "Access Network (ANET)" and "Internetwork (INET)"
o Changed "ASP" to "MSP", and "ACP" to "MNP"
o New figure on the relation of Segments to the SPAN and AERO link
o New "S" bit in S/TLLAO to indicate the "Source" S/TLLAO as opposed
to additional S/TLLAOs
o Changed Interface ID for Servers from 255 to 0xffff
o Significant updates to Route Optimization, NUD, and Mobility
Management
o New Section on Multicast
o New Section on AERO Clients in the open Internetwork
o New Section on Operation over multiple AERO links (VLANs over the
SPAN)
o New Sections on DNS considerations and Transition considerations
o
Changes from draft-templin-intarea-6706bis-10 to draft-templin-
intrea-6706bis-11:
o Added The SPAN
Changes from draft-templin-intarea-6706bis-09 to draft-templin-
intrea-6706bis-10:
o Orphaned packets in flight (e.g., when a neighbor cache entry is
in the DEPARTED state) are now forwarded at the link layer instead
of at the network layer. Forwarding at the network layer can
result in routing loops and/or excessive delays of forwarded
packets while the routing system is still reconverging.
Templin Expires November 2, 2019 [Page 72]
Internet-Draft AERO May 2019
o Update route optimization to clarify the unsecured nature of the
first NS used for route discovery
o Many cleanups and clarifications on ND messaging parameters
Changes from draft-templin-intarea-6706bis-08 to draft-templin-
intrea-6706bis-09:
o Changed PRL to "MAP list"
o For neighbor cache entries, changed "static" to "symmetric", and
"dynamic" to "asymmetric"
o Specified Proxy RS/RA exchanges with Servers on behalf of Clients
o Added discussion of unsolicited NAs in Section 3.16, and included
forward reference to Section 3.18
o Added discussion of AERO Clients used as critical infrastructure
elements to connect fixed networks.
o Added network-based VPN under security considerations
Changes from draft-templin-intarea-6706bis-07 to draft-templin-
intrea-6706bis-08:
o New section on AERO-Aware Access Router
Changes from draft-templin-intarea-6706bis-06 to draft-templin-
intrea-6706bis-07:
o Added "R" bit for release of PDs. Now have a full RS/RA service
that can do PD without requiring DHCPv6 messaging over-the-air
o Clarifications on solicited vs unsolicited NAs
o Clarified use of MAX_NEIGHBOR_ADVERTISEMENTS for the purpose of
increase reliability
Changes from draft-templin-intarea-6706bis-05 to draft-templin-
intrea-6706bis-06:
o Major re-work and simplification of Route Optimization function
o Added Distributed Mobility Management (DMM) and Mobility Anchor
Point (MAP) terminology
Templin Expires November 2, 2019 [Page 73]
Internet-Draft AERO May 2019
o New section on "AERO Critical Infrastructure Element
Considerations" demonstrating low overall cost for the service
o minor text revisions and deletions
o removed extraneous appendices
Changes from draft-templin-intarea-6706bis-04 to draft-templin-
intrea-6706bis-05:
o New Appendix E on S/TLLAO Extensions for special-purpose links.
Discussed ATN/IPS as example.
o New sentence in introduction to declare appendices as non-
normative.
Changes from draft-templin-intarea-6706bis-03 to draft-templin-
intrea-6706bis-04:
o Added definitions for Potential Router List (PRL) and secure
enclave
o Included text on mapping transport layer port numbers to network
layer DSCP values
o Added reference to DTLS and DMM Distributed Mobility Anchoring
working group document
o Reworked Security Considerations
o Updated references.
Changes from draft-templin-intarea-6706bis-02 to draft-templin-
intrea-6706bis-03:
o Added new section on SEND.
o Clarifications on "AERO Address" section.
o Updated references and added new reference for RFC8086.
o Security considerations updates.
o General text clarifications and cleanup.
Changes from draft-templin-intarea-6706bis-01 to draft-templin-
intrea-6706bis-02:
Templin Expires November 2, 2019 [Page 74]
Internet-Draft AERO May 2019
o Note on encapsulation avoidance in Section 4.
Changes from draft-templin-intarea-6706bis-00 to draft-templin-
intrea-6706bis-01:
o Remove DHCPv6 Server Release procedures that leveraged the old way
Relays used to "route" between Server link-local addresses
o Remove all text relating to Relays needing to do any AERO-specific
operations
o Proxy sends RS and receives RA from Server using SEND. Use CGAs
as source addresses, and destination address of RA reply is to the
AERO address corresponding to the Client's ACP.
o Proxy uses SEND to protect RS and authenticate RA (Client does not
use SEND, but rather relies on subnetwork security. When the
Proxy receives an RS from the Client, it creates a new RS using
its own addresses as the source and uses SEND with CGAs to send a
new RS to the Server.
o Emphasize distributed mobility management
o AERO address-based RS injection of ACP into underlying routing
system.
Changes from draft-templin-aerolink-82 to draft-templin-intarea-
6706bis-00:
o Document use of NUD (NS/NA) for reliable link-layer address
updates as an alternative to unreliable unsolicited NA.
Consistent with Section 7.2.6 of RFC4861.
o Server adds additional layer of encapsulation between outer and
inner headers of NS/NA messages for transmission through Relays
that act as vanilla IPv6 routers. The messages include the AERO
Server Subnet Router Anycast address as the source and the Subnet
Router Anycast address corresponding to the Client's ACP as the
destination.
o Clients use Subnet Router Anycast address as the encapsulation
source address when the access network does not provide a
topologically-fixed address.
Templin Expires November 2, 2019 [Page 75]
Internet-Draft AERO May 2019
Author's Address
Fred L. Templin (editor)
Boeing Research & Technology
P.O. Box 3707
Seattle, WA 98124
USA
Email: fltemplin@acm.org
Templin Expires November 2, 2019 [Page 76]