One document matched: draft-templin-aerolink-13.xml
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<rfc category="std" docName="draft-templin-aerolink-13.txt" ipr="trust200902"
obsoletes="rfc6706">
<front>
<title abbrev="AERO">Transmission of IPv6 Packets over AERO Links</title>
<author fullname="Fred L. Templin" initials="F. L." role="editor"
surname="Templin">
<organization>Boeing Research & Technology</organization>
<address>
<postal>
<street>P.O. Box 3707</street>
<city>Seattle</city>
<region>WA</region>
<code>98124</code>
<country>USA</country>
</postal>
<email>fltemplin@acm.org</email>
</address>
</author>
<date day="2" month="April" year="2014"/>
<keyword>I-D</keyword>
<keyword>Internet-Draft</keyword>
<abstract>
<t>This document specifies the operation of IPv6 over tunnel virtual
Non-Broadcast, Multiple Access (NBMA) links using Asymmetric Extended
Route Optimization (AERO). Nodes attached to AERO links can exchange
packets via trusted intermediate routers on the link that provide
forwarding services to reach off-link destinations and/or redirection
services to inform the node of an on-link neighbor that is closer to the
final destination. Operation of the IPv6 Neighbor Discovery (ND)
protocol over AERO links is based on an IPv6 link local address format
known as the AERO address.</t>
</abstract>
</front>
<middle>
<section anchor="intro" title="Introduction">
<t>This document specifies the operation of IPv6 over tunnel virtual
Non-Broadcast, Multiple Access (NBMA) links using Asymmetric Extended
Route Optimization (AERO). Nodes attached to AERO links can exchange
packets via trusted intermediate routers on the link that provide
forwarding services to reach off-link destinations and/or redirection
services to inform the node of an on-link neighbor that is closer to the
final destination.</t>
<t>Nodes on AERO links use an IPv6 link-local address format known as
the AERO Address. This address type has properties that statelessly link
IPv6 Neighbor Discovery (ND) to IPv6 routing. The AERO link can be used
for tunneling to neighboring nodes on either IPv6 or IPv4 networks,
i.e., AERO views the IPv6 and IPv4 networks as equivalent links for
tunneling. The remainder of this document presents the AERO
specification.</t>
</section>
<section anchor="terminology" title="Terminology">
<t>The terminology in the normative references applies; the following
terms are defined within the scope of this document:</t>
<t><list style="hanging">
<t hangText="AERO link"><vspace/>a Non-Broadcast, Multiple Access
(NBMA) tunnel virtual overlay configured over a node's attached IPv6
and/or IPv4 networks. All nodes on the AERO link appear as
single-hop neighbors from the perspective of IPv6.</t>
<t hangText="AERO interface"><vspace/>a node's attachment to an AERO
link. The AERO interface Maximum Transmission Unit (MTU) is less
than or equal to the AERO link MTU.</t>
<t hangText="AERO address"><vspace/>an IPv6 link-local address
assigned to an AERO interface and constructed as specified in
Section 3.6.</t>
<t hangText="AERO node"><vspace/>a node that is connected to an AERO
link and that participates in IPv6 Neighbor Discovery over the
link.</t>
<t hangText="AERO Client ("client")"><vspace/>a node that
configures either a host interface or a router interface on an AERO
link.</t>
<t hangText="AERO Server ("server")"><vspace/>a node that
configures a router interface on an AERO link over which it can
provide default forwarding and redirection services for other AERO
nodes.</t>
<t hangText="AERO Relay ("relay")"><vspace/>a node that
relays IPv6 packets between Servers on the same AERO link, and/or
that forwards IPv6 packets between the AERO link and the IPv6
Internet. An AERO Relay may or may not also be configured as an AERO
Server.</t>
<t hangText="ingress tunnel endpoint (ITE)"><vspace/>an AERO
interface endpoint that injects tunneled packets into an AERO
link.</t>
<t hangText="egress tunnel endpoint (ETE)"><vspace/>an AERO
interface endpoint that receives tunneled packets from an AERO
link.</t>
<t hangText="underlying network"><vspace/>a connected IPv6 or IPv4
network routing region over which AERO nodes tunnel IPv6
packets.</t>
<t hangText="underlying interface"><vspace/>an AERO node's interface
point of attachment to an underlying network.</t>
<t hangText="underlying address"><vspace/>an IPv6 or IPv4 address
assigned to an AERO node's underlying interface. When UDP
encapsulation is used, the UDP port number is also considered as
part of the underlying address. Underlying addresses are used as the
source and destination addresses of the AERO encapsulation
header.</t>
<t hangText="link-layer address"><vspace/>the same as defined for
"underlying address" above.</t>
<t hangText="network layer address"><vspace/>an IPv6 address used as
the source or destination address of the inner IPv6 packet
header.</t>
<t hangText="end user network (EUN)"><vspace/>an IPv6 network
attached to a downstream interface of an AERO Client (where the AERO
interface is seen as the upstream interface).</t>
</list></t>
<t>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 <xref
target="RFC2119"/>.</t>
</section>
<section title="Asymmetric Extended Route Optimization (AERO)">
<t>The following sections specify the operation of IPv6 over Asymmetric
Extended Route Optimization (AERO) links:</t>
<section anchor="node-types" title="AERO Node Types">
<t>AERO Relays relay packets between nodes connected to the same AERO
link and also forward packets between the AERO link and the native
IPv6 network. The relaying process entails re-encapsulation of IPv6
packets that were received from a first AERO node and are to be
forwarded without modification to a second AERO node.</t>
<t>AERO Servers configure their AERO interfaces as router interfaces,
and provide default routing services to AERO Clients. AERO Servers
configure a DHCPv6 Relay or Server function and facilitate DHCPv6
Prefix Delegation (PD) exchanges. An AERO Server may also act as an
AERO Relay.</t>
<t>AERO Clients act as requesting routers to receive IPv6 prefixes
through a DHCPv6 PD exchange via an AERO Server over the AERO link.
Each AERO Client receives at least a /64 prefix delegation, and may
receive even shorter prefixes.</t>
<t>AERO Clients that act as routers configure their AERO interfaces as
router interfaces, i.e., even if the AERO Client otherwise displays
the outward characteristics of an ordinary host (for example, the
Client may internally configure both an AERO interface and (internal
virtual) End User Network (EUN) interfaces). AERO Clients that act as
routers sub-delegate portions of their received prefix delegations to
links on EUNs.</t>
<t>AERO Clients that act as ordinary hosts configure their AERO
interfaces as host interfaces and assign one or more IPv6 addresses
taken from their received prefix delegations to the AERO interface but
DO NOT assign the delegated prefix itself to the AERO interface.
Instead, the host assigns the delegated prefix to a "black hole" route
so that unused portions of the prefix are nullified.</t>
<t>End system applications on AERO hosts bind directly to the AERO
interface, while applications on AERO routers (or IPv6 hosts served by
an AERO router) bind to EUN interfaces.</t>
</section>
<section anchor="interface" title="AERO Interface Characteristics">
<t>AERO interfaces use IPv6-in-IPv6 encapsulation <xref
target="RFC2473"/> to exchange tunneled packets with AERO neighbors
attached to an underlying IPv6 network, and use IPv6-in-IPv4
encapsulation <xref target="RFC4213"/> to exchange tunneled packets
with AERO neighbors attached to an underlying IPv4 network. AERO
interfaces can also use IPsec encapsulation <xref target="RFC4301"/>
(either IPv6-in-IPsec-in-IPv6 or IPv6-in-IPsec-in-IPv4) in
environments where strong authentication and confidentiality are
required. When NAT traversal and/or filtering middlebox traversal is
necessary, a UDP header is further inserted between the outer IP
encapsulation header and the inner packet.</t>
<t>Servers assign the link-local address 'fe80::0' to their AERO
interface; this provides a handle for Clients to insert into a
neighbor cache entry for their current Server. Servers also configure
administratively-assigned link-local addresses on their AERO
interfaces to support the operation of the inter-Server/Relay routing
system (see: <xref target="IRON"/>).</t>
<t>Clients initially assign no addresses on their AERO interface, but
use 'fe80::1' as the IPv6 link-local address in the DHCPv6 PD
exchanges used to derive an AERO address. After the Client receives a
prefix delegation, it assigns the corresponding AERO address to the
AERO interface.</t>
<t>AERO interfaces maintain a neighbor cache and use a variation of
standard unicast IPv6 ND messaging. AERO interfaces use Neighbor
Solicitation (NS), Neighbor Advertisement (NA) and Redirect messages
the same as for any IPv6 link. They do not use Router Solicitation
(RS) and Router Advertisement (RA) messages for several reasons.
First, default router discovery is supported through other means more
appropriate for AERO links as described below. Second, discovery of
more-specific routes is through the receipt of Redirect messages.
Finally, AERO nodes obtain their delegated IPv6 prefixes using DHCPv6
PD; hence, there is no need for RA-based prefix discovery.</t>
<t>AERO Neighbor Solicitation (NS) and Neighbor Advertisement (NA)
messages do not include Source/Target Link Layer Address Options
(S/TLLAO). Instead, AERO nodes determine the link-layer addresses of
neighbors by examining the encapsulation IP source address and UDP
port number (when UDP encapsulation is used) of any NS/NA messages
they receive and ignore any S/TLLAOs included in these messages. This
is vital to the operation of AERO links for which neighbors are
separated by Network Address Translators (NATs) - either IPv4 or
IPv6.</t>
<t>AERO Redirect messages include a TLLAO the same as for any IPv6
link. The TLLAO includes the link-layer address of the target node,
including both the IP address and the UDP source port number used by
the target when it sends UDP-encapsulated packets over the AERO
interface (the TLLAO instead encodes the value 0 when the target does
not use UDP encapsulation). TLLAOs for target nodes that use an IPv6
underlying address include the full 16 bytes of the IPv6 address as
shown in <xref target="tllaov6"/>, while TLLAOs for target nodes that
use an IPv4 underlying address include only the 4 bytes of the IPv4
address as shown in <xref target="tllaov4"/>.</t>
<t><figure anchor="tllaov6" title="AERO TLLAO Format for IPv6">
<artwork><![CDATA[ 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 2 | Length = 3 | UDP Source Port (or 0) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+-- --+
| |
+-- IPv6 Address --+
| |
+-- --+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork>
</figure><figure anchor="tllaov4"
title="AERO TLLAO Format for IPv4">
<artwork><![CDATA[ 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 2 | Length = 1 | UDP Source Port (or 0) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork>
</figure></t>
<t>Finally, AERO interface NS/NA messages only update existing
neighbor cache entires and do not create new neighbor cache entries,
whereas Redirect messages both update and create neighbor cache
entries. This represents a departure from the normal operation of IPv6
ND over common link types, but is consistent with the spirit of IPv6
over NBMA links as discussed in <xref target="RFC4861"/>. Note however
that this restriction may be relaxed and/or redefined on AERO links
that participate in a fully distributed mobility management model
coordinated in a manner outside the scope of this document.</t>
</section>
<section anchor="aero-address" title="AERO Addresses">
<t>An AERO address is an IPv6 link-local address assigned to an AERO
interface and with an IPv6 prefix embedded within the interface
identifier. The AERO address is formatted as:</t>
<t><list style="empty">
<t>fe80::[IPv6 prefix]</t>
</list></t>
<t>Each AERO Client configures an AERO address based on the delegated
prefix it has received from the DHCPv6 server. The address begins with
the prefix fe80::/64 and includes in its interface identifier the base
/64 prefix taken from the Client's delegated IPv6 prefix. The base
prefix is determined by masking the delegated prefix with the prefix
length. For example, if an AERO Client has received the prefix
delegation:</t>
<t><list style="empty">
<t>2001:db8:1000:2000::/56</t>
</list>it would construct its AERO address as:</t>
<t><list style="empty">
<t>fe80::2001:db8:1000:2000</t>
</list>The AERO address remains stable as the Client moves between
topological locations, i.e., even if its underlying address
changes.</t>
</section>
<section title="AERO Interface Data Origin Authentication">
<t>Nodes on AERO interfaces use a simple data origin authentication
for encapsulated packets they receive from other nodes. In particular,
AERO Clients accept encapsulated packets with a link-layer source
address belonging to their current AERO Server. AERO nodes also accept
encapsulated packets with a link-layer source address that is correct
for the network-layer source address.</t>
<t>The AERO node considers the link-layer source address correct for
the network-layer source address if there is an IPv6 forwarding table
entry that matches the network-layer source address as well as a
neighbor cache entry corresponding to the next hop that includes the
link-layer address. An exception is that NS, NA and Redirect messages
may include a different link-layer address than the one currently in
the neighbor cache, and the new link-layer address updates the
neighbor cache entry.</t>
</section>
<section title="AERO Interface Conceptual Data Structures and Protocol Constants">
<t>Each AERO node maintains a per-AERO interface conceptual neighbor
cache that includes an entry for each neighbor it communicates with on
the AERO link, the same as for any IPv6 interface (see <xref
target="RFC4861"/>). Neighbor cache entries are either static or
dynamic. Static neighbor cache entries (including a Client's neighbor
cache entry for a Server or a Server's neighbor cache entry for a
Client) do not have timeout values and are retained until explicitly
deleted. Dynamic neighbor cache entries are created and maintained by
the AERO redirection procedures describe in the following
sections.</t>
<t>When an AERO node receives a valid Predirect message (See Section
3.11.5) it creates or updates a dynamic neighbor cache entry for the
Predirect target L3 and L2 addresses, and also creates an IPv6
forwarding table entry for the Predirected (source) prefix. The node
then sets an ACCEPT timer and uses this timer to validate any messages
received from the Predirected neighbor.</t>
<t>When an AERO node receives a valid Redirect message (see Section
3.11.7) it creates or updates a dynamic neighbor cache entry for the
Redirect target L3 and L2 addresses, and also creates an IPv6
forwarding table entry for the Redirected (destination) prefix. The
node then sets a FORWARD timer and uses this timer to determine
whether packets can be sent directly to the Redirected neighbor. The
node also maintains a constant value MAX_RETRY to limit the number of
keepalives sent when a neighbor has gone unreachable.</t>
<t>It is RECOMMENDED that FORWARD_TIME be set to the default constant
value 30 seconds to match the default REACHABLE_TIME value specified
for IPv6 neighbor discovery <xref target="RFC4861"/>.</t>
<t>It is RECOMMENDED that ACCEPT_TIME be set to the default constant
value 40 seconds to allow a 10 second window so that the AERO
redirection procedure can converge before the ACCEPT_TIME timer
decrements below FORWARD_TIME.</t>
<t>It is RECOMMENDED that MAX_RETRY be set to 3 the same as described
for IPv6 neighbor discovery address resolution in Section 7.3.3 of
<xref target="RFC4861"/>.</t>
<t>Different values for FORWARD_TIME, ACCEPT_TIME, and MAX_RETRY MAY
be administratively set, if necessary, to better match the AERO link's
performance characteristics; however, if different values are chosen,
all nodes on the link MUST consistently configure the same values.
ACCEPT_TIME SHOULD further be set to a value that is sufficiently
longer than FORWARD_TIME to allow the AERO redirection procedure to
converge.</t>
</section>
<section title="AERO Interface MTU Considerations">
<t>The AERO link Maximum Transmission Unit (MTU) is 64KB minus the
encapsulation overhead for IPv4 <xref target="RFC0791"/> and 4GB minus
the encapsulation overhead for IPv6 <xref target="RFC2675"/>. This is
the most that IPv4 and IPv6 (respectively) can convey within the
constraints of protocol constants, but actual sizes available for
tunneling will frequently be much smaller.</t>
<t>The base tunneling specifications for IPv4 and IPv6 typically set a
static MTU on the tunnel interface to 1500 bytes minus the
encapsulation overhead or smaller still if the tunnel is likely to
incur additional encapsulations such as IPsec on the path. This can
result in path MTU related black holes when packets that are too large
to be accommodated over the AERO link are dropped, but the resulting
ICMP Packet Too Big (PTB) messages are lost on the return path. As a
result, AERO nodes use the following MTU mitigations to accommodate
larger packets.</t>
<t>AERO nodes set their AERO interface MTU to the larger of 1500 bytes
and the underlying interface MTU minus the encapsulation overhead.
AERO nodes optionally cache other per-neighbor MTU values in the
underlying IP path MTU discovery cache initialized to the underlying
interface MTU.</t>
<t>AERO nodes admit packets that are no larger than 1280 bytes minus
the encapsulation overhead (*) as well as packets that are larger than
1500 bytes into the tunnel without fragmentation, i.e., as long as
they are no larger than the AERO interface MTU before encapsulation
and also no larger than the cached per-neighbor MTU following
encapsulation. For IPv4, the node sets the "Don't Fragment" (DF) bit
to 0 for packets no larger than 1280 bytes minus the encapsulation
overhead (*) and sets the DF bit to 1 for packets larger than 1500
bytes. If a large packet is lost in the path, the node may optionally
cache the MTU reported in the resulting PTB message or may ignore the
message, e.g., if there is a possibility that the message is
spurious.</t>
<t>For packets destined to an AERO node that are larger than 1280
bytes minus the encapsulation overhead (*) but no larger than 1500
bytes, the node uses outer IP fragmentation to fragment the packet
into two pieces (where the first fragment contains 1024 bytes of the
fragmented inner packet) then admits the fragments into the tunnel. If
the outer protocol is IPv4, the node admits the packet into the tunnel
with DF set to 0 and subject to rate limiting to avoid reassembly
errors <xref target="RFC4963"/><xref target="RFC6864"/>. For both IPv4
and IPv6, the node also sends a 1500 byte probe message (**) to the
neighbor, subject to rate limiting. To construct a probe, the node
prepares an ICMPv6 Neighbor Solicitation (NS) message with trailing
padding octets added to a length of 1500 bytes but does not include
the length of the padding in the IPv6 Payload Length field. The node
then encapsulates the NS in the outer encapsulation headers (while
including the length of the padding in the outer length fields), sets
DF to 1 (for IPv4) and sends the padded NS message to the neighbor. If
the neighbor returns an NA message, the node may then send whole
packets within this size range and (for IPv4) relax the rate limiting
requirement.</t>
<t>AERO nodes MUST be capable of reassembling packets up to 1500 bytes
plus the encapsulation overhead length. It is therefore RECOMMENDED
that AERO nodes be capable of reassembling at least 2KB.</t>
<t>(*) Note that if it is known that the minimum Path MTU to an AERO
node is MINMTU bytes (where 1280 < MINMTU < 1500) then MINMTU
can be used instead of 1280 in the fragmentation threshold
considerations listed above.</t>
<t>(**) It is RECOMMENDED that no probes smaller than 1500 bytes be
used for MTU probing purposes, since smaller probes may be fragmented
if there is a nested tunnel somewhere on the path to the neighbor.</t>
</section>
<section title="AERO Interface Encapsulation, Re-encapsulation and Decapsulation">
<t>AERO interfaces encapsulate IPv6 packets according to whether they
are entering the AERO interface for the first time or if they are
being forwarded out the same AERO interface that they arrived on. This
latter form of encapsulation is known as "re-encapsulation".</t>
<t>AERO interfaces encapsulate packets per the specifications in <xref
target="RFC2473">,</xref><xref target="RFC4213">,</xref> except that
the interface copies the "TTL/Hop Limit", "Type of Service/Traffic
Class" and "Congestion Experienced" values in the inner network layer
header into the corresponding fields in the outer IP header. For
packets undergoing re-encapsulation, the AERO interface instead copies
the "TTL/Hop Limit", "Type of Service/Traffic Class" and "Congestion
Experienced" values in the original outer IP header into the
corresponding fields in the new outer IP header (i.e., the values are
transferred between outer headers and *not* copied from the inner
network layer header).</t>
<t>When UDP encapsulation is used, the AERO interface inserts a UDP
header between the inner packet and outer IP header. If the outer
header is IPv6 and is followed by an IPv6 Fragment header, the AERO
interface inserts the UDP header between the outer IPv6 header and
IPv6 Fragment header. The AERO interface sets the UDP source port to a
constant value that it will use in each successive packet it sends,
sets the UDP checksum field to zero (see: <xref
target="RFC6935"/><xref target="RFC6936"/>) and sets the UDP length
field to the length of the inner packet plus 8 bytes for the UDP
header itself. For packets sent via a Server, the AERO interface sets
the UDP destination port to 8060 (i.e., the IANA-registerd port number
for AERO). For packets sent to a neighboring Client, the AERO
interface sets the UDP destination port to the port value stored in
the neighbor cache entry for this neighbor.</t>
<t>The AERO interface next sets the outer IP protocol number to the
appropriate value for the first protocol layer within the
encapsulation (e.g., IPv6, IPv6 Fragment Header, UDP, etc.). When IPv6
is used as the outer IP protocol, the ITE then sets the flow label
value in the outer IPv6 header the same as described in <xref
target="RFC6438"/>. When IPv4 is used as the outer IP protocol, the
AERO interface sets the DF bit as discussed in Section 3.2.</t>
<t>AERO interfaces decapsulate packets destined either to the node
itself or to a destination reached via an interface other than the
receiving AERO interface per the specifications in <xref
target="RFC2473">,</xref><xref target="RFC4213">,</xref>. When the
encapsulated packet includes a UDP header, the AERO interface examines
the first octet of data following the UDP header to determine the
inner header type. If the most significant four bits of the first
octet encode the value '0110', the inner header is an IPv6 header.
Otherwise, the interface considers the first octet as an IP protocol
type that encodes the value '44' for IPv6 fragment header, the value
'50' for Encapsulating Security Payload, the value '51' for
Authentication Header etc. (If the first octet encodes the value '0',
the interface instead discards the packet, since this is the value
reserved for experimentation under <xref target="RFC6706">,</xref>).
During the decapsulation, the AERO interface records the UDP source
port in the neighbor cache entry for this neighbor then discards the
UDP header.</t>
</section>
<section anchor="avoidance-fig"
title="AERO Reference Operational Scenario">
<t><xref target="no-onlink-prefix-fig"/> depicts the AERO reference
operational scenario. The figure shows an AERO Server('A'), two AERO
Clients ('B', 'D') and three ordinary IPv6 hosts ('C', 'E', 'F'):</t>
<figure anchor="no-onlink-prefix-fig"
title="AERO Reference Operational Scenario">
<artwork><![CDATA[ .-(::::::::)
.-(::: IPv6 :::)-. +-------------+
(:::: Internet ::::)--| Host F |
`-(::::::::::::)-' +-------------+
`-(::::::)-' 2001:db8:3::1
|
+--------------+
| AERO Server A|
| (C->B; E->D) |
+--------------+
fe80::0
L2(A)
|
X-----+-----------+-----------+--------X
| AERO Link |
L2(B) L2(D)
fe80::2001:db8:0:0 fe80::2001:db8:1:0 .-.
+--------------+ +--------------+ ,-( _)-.
| AERO Client B| | AERO Client D| .-(_ IPv6 )-.
| (default->A) | | (default->A) |--(__ EUN )
+--------------+ +--------------+ `-(______)-'
2001:DB8:0::/48 2001:DB8:1::/48 |
| 2001:db8:1::1
.-. +-------------+
,-( _)-. 2001:db8:0::1 | Host E |
.-(_ IPv6 )-. +-------------+ +-------------+
(__ EUN )--| Host C |
`-(______)-' +-------------+
]]></artwork>
</figure>
<t>In <xref target="no-onlink-prefix-fig"/>, AERO Server ('A')
connects to the AERO link and connects to the IPv6 Internet, either
directly or via an AERO Relay (not shown). Server ('A') assigns the
address fe80::0 to its AERO interface with link-layer address L2(A).
Server ('A') next arranges to add L2(A) to a published list of valid
Servers for the AERO link.</t>
<t>AERO Client ('B') registers the IPv6 prefix 2001:db8:0::/48 in a
DHCPv6 PD exchange via Server ('A') then assigns the address
fe80::2001:db8:0:0 to its AERO interface with link-layer address
L2(B). Client ('B') configures a default route via the AERO interface
with next-hop address fe80::0 and link-layer address L2(A), then
sub-delegates the prefix 2001:db8:0::/48 to its attached EUNs. IPv6
host ('C') connects to the EUN, and configures the address
2001:db8:0::1.</t>
<t>AERO Client ('D') registers the IPv6 prefix 2001:db8:1::/48 in a
DHCPv6 PD exchange via Server ('A') then assigns the address
fe80::2001:db8:1:0 to its AERO interface with link-layer address
L2(D). Client ('D') configures a default route via the AERO interface
with next-hop address fe80::0 and link-layer address L2(A), then
sub-delegates the prefix 2001:db8:1::/48 to its attached EUNs. IPv6
host ('E') connects to the EUN, and configures the address
2001:db8:1::1.</t>
<t>Finally, IPv6 host ('F') connects to an IPv6 network outside of the
AERO link domain. Host ('F') configures its IPv6 interface in a manner
specific to its attached IPv6 link, and assigns the address
2001:db8:3::1 to its IPv6 link interface.</t>
</section>
<section anchor="aeropd"
title="AERO Router Discovery and Prefix Delegation">
<section anchor="aeropd-client" title="AERO Client Behavior">
<t>AERO Clients observe the IPv6 router requirements defined in
<xref target="RFC6434"/>. AERO Clients first discover the link-layer
address of an AERO Server via static configuration, or through an
automated means such as DNS name resolution. In the absence of other
information, the Client resolves the Fully-Qualified Domain Name
(FQDN) "linkupnetworks.domainname", where "domainname" is the DNS
domain appropriate for the Client's attached underlying network. The
Client then creates a static neighbor cache entry with fe80::0 as
the network-layer address and the discovered address as the
link-layer address. The Client further creates a static default IPv6
forwarding table entry with fe80::0 as the next hop address.</t>
<t>Next, the Client acts as a requesting router to register its IPv6
prefix through DHCPv6 PD <xref target="RFC3633"/> via the Server
using fe80::1 as the IPv6 source address and fe80::0 as the IPv6
destination address. The Client further includes a DHCPv6 Unique
Identifier (DUID) based on a Universally Unique Identifier (UUID)
(also known as DUID-UUID) as described in <xref
target="RFC6355"/>.</t>
<t>After the Client registers its prefixes, it assigns the
link-local AERO address taken from its delegated prefix to the AERO
interface (see: Section 3.3) and sub-delegates the prefix to nodes
and links within its attached EUNs (the AERO link-local address
thereafter remains stable as the Client moves).</t>
<t>The Client sends periodic NS messages to the Server to obtain new
NAs in order to refresh any network state. The Client can also
forward IPv6 packets destined to networks beyond its local EUNs via
the Server as an IPv6 default router. The Server may in turn return
a Redirect message informing the Client of a neighbor on the AERO
link that is topologically closer to the final destination as
specified in <xref target="predirect"/>.</t>
</section>
<section anchor="aeropd-server" title="AERO Server Behavior">
<t>AERO Servers observe the IPv6 router requirements defined in
<xref target="RFC6434"/>. They further configure a DHCPv6
relay/server function on their AERO links. When the Server
facilitates a DHCPv6 PD exchange, it creates a temporary cache entry
referenced by the DHCPv6 request's DUID-UUID. After the PD request
is satisfied, the Server creates a static neighbor cache entry for
the Client's AERO address (see: Section 3.3) and a static IPv6
forwarding table entry that lists the Client's AERO address as the
next hop toward the delegated IPv6 prefix . The Server also injects
the Client's prefix as an IPv6 route into the inter-Server/Relay
routing system (see: <xref target="IRON"/>).</t>
<t>Servers respond to NS messages from Clients on their AERO
interfaces by returning an NA message. When the Server receives an
NS message, it updates the neighbor cache entry using the network
layer source address as the neighbor's network layer address and
using the link-layer source address of the NS message as the
neighbor's link-layer address.</t>
<t>When the Server forwards a packet via the same AERO interface on
which it arrived, it initiates an AERO route optimization procedure
as specified in <xref target="predirect"/>.</t>
</section>
</section>
<section anchor="aeronsna"
title="AERO Neighbor Solicitation and Advertisement">
<t>Each AERO node uses its delegated prefix to create an AERO address
(see: Section 3.3). It can then send unicast NS messages to elicit NA
messages from other AERO nodes the same as described for neighbor
unreachability detection in<xref target="RFC4861"> </xref> except that
the messages do not include S/TLLAOs.</t>
<t>When an AERO node sends an NS/NA message, it MUST use its AERO
address as the IPv6 source address and the AERO address of the
neighbor as the IPv6 destination address. The AERO node also includes
the AERO address of the neighbor as the NS/NA message Target address
with the exception of "terminating NS" messages as described in
Section 3.13.</t>
<t>When an AERO node receives an NS/NA message, it accepts the message
if it has a neighbor cache entry for the neighbor; otherwise, it
ignores the message.</t>
</section>
<section anchor="predirect" title="AERO Redirection">
<t><xref target="avoidance-fig"/> describes the AERO reference
operational scenario. We now discuss the operation and protocol
details of AERO Redirection with respect to this reference
scenario.</t>
<section anchor="redirect" title="Classical Redirection Approaches">
<t>With reference to <xref target="no-onlink-prefix-fig"/>, when the
IPv6 source host ('C') sends a packet to an IPv6 destination host
('E'), the packet is first forwarded via the EUN to AERO Client
('B'). Client ('B') then forwards the packet over its AERO interface
to AERO Server ('A'), which then re-encapsulates and forwards the
packet to AERO Client ('D'), where the packet is finally forwarded
to the IPv6 destination host ('E'). When Server ('A')
re-encapsulates and forwards the packet back out on its advertising
AERO interface, it must arrange to redirect Client ('B') toward
Client ('D') as a better next-hop node on the AERO link that is
closer to the final destination. However, this redirection process
applied to AERO interfaces must be more carefully orchestrated than
on ordinary links since the parties may be separated by potentially
many underlying network routing hops.</t>
<t>Consider a first alternative in which Server ('A') informs Client
('B') only and does not inform Client ('D') (i.e., "classical
redirection"). In that case, Client ('D') has no way of knowing that
Client ('B') is authorized to forward packets from the claimed
source address, and it may simply elect to drop the packets. Also,
Client ('B') has no way of knowing whether Client ('D') is
performing some form of source address filtering that would reject
packets arriving from a node other than a trusted default router,
nor whether Client ('D') is even reachable via a direct path that
does not involve Server ('A').</t>
<t>Consider a second alternative in which Server ('A') informs both
Client ('B') and Client ('D') separately, via independent
redirection control messages (i.e., "augmented redirection"). In
that case, if Client ('B') receives the redirection control message
but Client ('D') does not, subsequent packets sent by Client ('B')
could be dropped due to filtering since Client ('D') would not have
a route to verify the claimed source address. Also, if Client ('D')
receives the redirection control message but Client ('B') does not,
subsequent packets sent in the reverse direction by Client ('D')
would be lost.</t>
<t>Since both of these alternatives have shortcomings, a new
redirection technique (i.e., "AERO redirection") is needed.</t>
</section>
<section title="AERO Redirection Concept of Operations">
<t>Again, with reference to <xref target="no-onlink-prefix-fig"/>,
when source host ('C') sends a packet to destination host ('E'), the
packet is first forwarded over the source host's attached EUN to
Client ('B'), which then forwards the packet via its AERO interface
to Server ('A').</t>
<t>Server ('A') then re-encapsulates and forwards the packet out the
same AERO interface toward Client ('D') and also sends an AERO
"Predirect" message forward to Client ('D') as specified in <xref
target="sending_pre"/>. The Predirect message includes Client
('B')'s network- and link-layer addresses as well as information
that Client ('D') can use to determine the IPv6 prefix used by
Client ('B') . After Client ('D') receives the Predirect message, it
process the message and returns an AERO Redirect message destined
for Client ('B') via Server ('A') as specified in <xref
target="processing"/>. During the process, Client ('D') also creates
or updates a dynamic neighbor cache entry for Client ('B'), and
creates an IPv6 forwarding table entry for Client ('B')'s IPv6
prefix.</t>
<t>When Server ('A') receives the Redirect message, it
re-encapsulates the message and forwards it on to Client ('B') as
specified in <xref target="forwarding"/>. The message includes
Client ('D')'s network- and link-layer addresses as well as
information that Client ('B') can use to determine the IPv6 prefix
used by Client ('D'). After Client ('B') receives the Redirect
message, it processes the message as specified in <xref
target="processing_re"/>. During the process, Client ('B') also
creates or updates a dynamic neighbor cache entry for Client ('D'),
and creates an IPv6 forwarding table entry for Client ('D')'s IPv6
prefix.</t>
<t>Following the above Predirect/Redirect message exchange,
forwarding of packets from Client ('B') to Client ('D') without
involving Server ('A) as an intermediary is enabled. The mechanisms
that support this exchange are specified in the following
sections.</t>
</section>
<section anchor="rmsg" title="AERO Redirection Message Format">
<t>AERO Redirect/Predirect messages use the same format as for
ICMPv6 Redirect messages depicted in Section 4.5 of <xref
target="RFC4861"/>, but also include a new "Prefix Length" field
taken from the low-order 8 bits of the Redirect message Reserved
field (valid values for the Prefix Length field are 0 through 64).
The Redirect/Predirect messages are formatted as shown in <xref
target="aero-redirect"/>:</t>
<figure anchor="aero-redirect"
title="AERO Redirect/Predirect Message Format">
<artwork><![CDATA[ 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type (=137) | Code (=0/1) | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Prefix Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Target Address +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Destination Address +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Options ...
+-+-+-+-+-+-+-+-+-+-+-+-
]]></artwork>
</figure>
<t/>
</section>
<section anchor="sending_pre" title="Sending Predirects">
<t>When an AERO Server forwards a packet out the same AERO interface
that it arrived on, the Server sends a Predirect message forward
toward the AERO Client nearest the destination instead of sending a
Redirect message back to AERO Client nearest the source.</t>
<t>In the reference operational scenario, when Server ('A') forwards
a packet sent by Client ('B') toward Client ('D'), it also sends a
Predirect message forward toward Client ('D'), subject to rate
limiting (see Section 8.2 of <xref target="RFC4861"/>). Server ('A')
prepares the Predirect message as follows:</t>
<t><list style="symbols">
<t>the link-layer source address is set to 'L2(A)' (i.e., the
underlying address of Server ('A')).</t>
<t>the link-layer destination address is set to 'L2(D)' (i.e.,
the underlying address of Client ('D')).</t>
<t>the network-layer source address is set to fe80::0 (i.e., the
link-local address of Server ('A')).</t>
<t>the network-layer destination address is set to
fe80::2001:db8:1:0 (i.e., the AERO address of Client ('D')).</t>
<t>the Type is set to 137.</t>
<t>the Code is set to 1 to indicate "Predirect".</t>
<t>the Prefix Length is set to the length of the prefix to be
applied to Target address.</t>
<t>the Target Address is set to fe80::2001:db8:0::0 (i.e., the
AERO address of Client ('B')).</t>
<t>the Destination Address is set to the IPv6 source address of
the packet that triggered the Predirection event.</t>
<t>the message includes a TLLAO set to 'L2(B)' (i.e., the
underlying address of Client ('B')).</t>
<t>the message includes a Redirected Header Option (RHO) that
contains the originating packet truncated to ensure that at
least the network-layer header is included but the size of the
message does not exceed 1280 bytes.</t>
</list></t>
<t>Server ('A') then sends the message forward to Client ('D').</t>
</section>
<section anchor="processing"
title="Processing Predirects and Sending Redirects">
<t>When Client ('D') receives a Predirect message, it accepts the
message only if it has a link-layer source address of the Server,
i.e. 'L2(A)'. Client ('D') further accepts the message only if it is
willing to serve as a redirection target. Next, Client ('D')
validates the message according to the ICMPv6 Redirect message
validation rules in Section 8.1 of <xref target="RFC4861"/>.</t>
<t>In the reference operational scenario, when the Client ('D')
receives a valid Predirect message, it either creates or updates a
dynamic neighbor cache entry that stores the Target Address of the
message as the network-layer address of Client ('B') and stores the
link-layer address found in the TLLAO as the link-layer address of
Client ('B'). Client ('D') then applies the Prefix Length to the
Interface Identifier portion of the Target Address and records the
resulting IPv6 prefix in its IPv6 forwarding table.</t>
<t>After processing the message, Client ('D') prepares a Redirect
message response as follows:</t>
<t><list style="symbols">
<t>the link-layer source address is set to 'L2(D)' (i.e., the
link-layer address of Client ('D')).</t>
<t>the link-layer destination address is set to 'L2(A)' (i.e.,
the link-layer address of Server ('A')).</t>
<t>the network-layer source address is set to 'L3(D)' (i.e., the
AERO address of Client ('D')).</t>
<t>the network-layer destination address is set to 'L3(B)'
(i.e., the AERO address of Client ('B')).</t>
<t>the Type is set to 137.</t>
<t>the Code is set to 0 to indicate "Redirect".</t>
<t>the Prefix Length is set to the length of the prefix to be
applied to the Target and Destination address.</t>
<t>the Target Address is set to fe80::2001:db8:1::1 (i.e., the
AERO address of Client ('D')).</t>
<t>the Destination Address is set to the IPv6 destination
address of the packet that triggered the Redirection event.</t>
<t>the message includes a TLLAO set to 'L2(D)' (i.e., the
underlying address of Client ('D')).</t>
<t>the message includes as much of the RHO copied from the
corresponding AERO Predirect message as possible such that at
least the network-layer header is included but the size of the
message does not exceed 1280 bytes.</t>
</list></t>
<t>After Client ('D') prepares the Redirect message, it sends the
message to Server ('A').</t>
</section>
<section anchor="forwarding"
title="Re-encapsulating and Relaying Redirects">
<t>When Server ('A') receives a Redirect message, it accepts the
message only if it has a neighbor cache entry that associates the
message's link-layer source address with the network-layer source
address. Next, Server ('A') validates the message according to the
ICMPv6 Redirect message validation rules in Section 8.1 of <xref
target="RFC4861"/>. Following validation, Server ('A')
re-encapsulates the Redirect then relays the re-encapsulated
Redirect on to Client ('B') as follows.</t>
<t>In the reference operational scenario, Server ('A') receives the
Redirect message from Client ('D') and prepares to re-encapsulate
and forward the message to Client ('B'). Server ('A') first verifies
that Client ('D') is authorized to use the Prefix Length in the
Redirect message when applied to the AERO address in the
network-layer source of the Redirect message, and discards the
message if verification fails. Otherwise, Server ('A')
re-encapsulates the message by changing the link-layer source
address of the message to 'L2(A)', changing the network-layer source
address of the message to fe80::0, and changing the link-layer
destination address to 'L2(B)' . Server ('A') finally relays the
re-encapsulated message to the ingress node ('B') without
decrementing the network-layer IPv6 header Hop Limit field.</t>
<t>While not shown in <xref target="no-onlink-prefix-fig"/>, AERO
Relays relay Redirect and Predirect messages in exactly this same
fashion described above. See <xref target="chaining-fig"/> in
Appendix A for an extension of the reference operational scenario
that includes Relays.</t>
</section>
<section anchor="processing_re" title="Processing Redirects">
<t>When Client ('B') receives the Redirect message, it accepts the
message only if it has a link-layer source address of the Server,
i.e. 'L2(A)'. Next, Client ('B') validates the message according to
the ICMPv6 Redirect message validation rules in Section 8.1 of <xref
target="RFC4861"/>. Following validation, Client ('B') then
processes the message as follows.</t>
<t>In the reference operational scenario, when Client ('B') receives
the Redirect message, it either creates or updates a dynamic
neighbor cache entry that stores the Target Address of the message
as the network-layer address of Client ('D') and stores the
link-layer address found in the TLLAO as the link-layer address of
Client ('D'). Client ('B') then applies the Prefix Length to the
Interface Identifier portion of the Target Address and records the
resulting IPv6 prefix in its IPv6 forwarding table.</t>
<t>Now, Client ('B') has an IPv6 forwarding table entry for
Client('D')'s prefix, and Client ('D') has an IPv6 forwarding table
entry for Client ('B')'s prefix. Thereafter, the clients may
exchange ordinary network-layer data packets directly without
forwarding through Server ('A').</t>
</section>
</section>
<section anchor="reachable" title="Neighbor Reachability Maintenance">
<t>When a source Client is redirected to a target Client it MUST test
the direct path to the target by sending an initial NS message to
elicit a solicited NA response. While testing the path, the source
Client SHOULD continue sending packets via the Server until target
Client reachability has been confirmed. The source Client MUST
thereafter continue to test the direct path to the target Client (see
Section 7.3 of <xref target="RFC4861"/>) in order to keep dynamic
neighbor cache entries alive. In particular, the source Client sends
NS messages to the target Client subject to rate limiting in order to
receive solicited NA messages. If at any time the direct path appears
to be failing, the source Client can resume sending packets via the
Server which may or may not result in a new redirection event.</t>
<t>When a target Client receives an NS message from a source Client,
it resets the ACCEPT_TIME timer if a neighbor cache entry exists;
otherwise, it discards the NS message.</t>
<t>When a source Client receives a solicited NA message form a target
Client, it resets the FORWARD_TIME timer if a neighbor cache entry
exists; otherwise, it discards the NA message.</t>
<t>When both the FORWARD_TIME and ACCEPT_TIME timers on a dynamic
neighbor cache entry expire, the Client deletes both the neighbor
cache entry and the corresponding IPv6 forwarding table entry.</t>
<t>If the source Client is unable to elicit an NA response from the
target Client after MAX_RETRY attempts, it SHOULD consider the direct
path unusable for forwarding purposes. Otherwise, the source Client
may continue to send packets directly to the target Client and SHOULD
thereafter process any link-layer errors as a hint that the direct
path to the target Client has either failed or has become
intermittent.</t>
</section>
<section title="Mobility and Link-Layer Address Change Considerations">
<t>When a Client needs to change its link-layer address (e.g., due to
a mobility event, due to a change in underlying network interface,
etc.), it sends an immediate NS message forward to any of its
correspondents (including the Server and any other Clients) which then
discover the new link-layer address.</t>
<t>If two Clients change their link-layer addresses simultaneously,
the NS/NA messages may be lost. In that case, the Clients SHOULD
delete their respective dynamic neighbor cache and IPv6 forwarding
table entries, and allow packets to again flow through their Server(s)
which MAY result in a new AERO redirection exchange.</t>
<t>When a Client needs to change to a new Server, it changes the
link-layer address of the neighbor cache entry for fe80::0 to the
address of the new Server and performs a DHCPv6 PD exchange via the
new Server. After the PD exchange is satisfied, the Client sends a
"terminating NS" message to the old Server. The terminating NS message
is prepared exactly the same as for an ordinary NS message, except
that the Target Address field contains the value '0'.</t>
<t>When the Server receives the terminating NS message, it withdraws
the IPv6 route from the routing system and deletes the neighbor cache
entry and IPv6 forwarding table entry for the Client. The Server then
returns an NA message which the Client can use to verify that the
termination signal has been processed. (Note that the Server can
impose a small delay before deleting the neighbor cache and IPv6
forwarding table entries so that any packets already in the system can
still be delivered to the Client.)</t>
</section>
<section anchor="version"
title="Underlying Protocol Version Considerations">
<t>A source Client may connect only to an IPvX underlying network,
while the target Client connects only to an IPvY underlying network.
In that case, the source Client has no means for reaching the target
directly (since they connect to underlying networks of different IP
protocol versions) and so must ignore any Redirects and continue to
send packets via the Server.</t>
</section>
<section title="Multicast Considerations">
<t>When the underlying network does not support multicast, AERO nodes
map IPv6 link-scoped multicast addresses (including
"All_DHCP_Relay_Agents_and_Servers") to the underlying IP address of
the AERO Server.</t>
<t>When the underlying network supports multicast, AERO nodes use the
multicast address mapping specification found in <xref
target="RFC2529"/> for IPv4 underlying networks and use a direct
multicast mapping for IPv6 underlying networks. (In the latter case,
"direct multicast mapping" means that if the IPv6 multicast
destination address of the inner packet is "M", then the IPv6
multicast destination address of the encapsulating header is also
"M".)</t>
</section>
<section title="Operation on Server-less AERO Links">
<t>In some AERO link scenarios, there may be no Server on the link
and/or no need for Clients to use a Server as an intermediary trust
anchor. In that case, Clients can establish dynamic neighbor cache
entries and IPv6 forwarding table entries by performing direct
Client-to-Client Predirect/Redirect exchanges, and some other form of
trust basis must be applied so that each Client can verify that the
prospective neighbor is authorized to use its claimed prefix.</t>
<t>When there is no Server on the link, Clients must arrange to
receive prefix delegations and publish the delegations via a secure
prefix discovery service through some means outside the scope of this
document.</t>
</section>
<section title="Other Considerations">
<t>IPv6 hosts serviced by an AERO Client can reach IPv4-only services
via a NAT64 gateway <xref target="RFC6146"/> within the IPv6
network.</t>
<t>AERO nodes can use the Default Address Selection Policy with DHCPv6
option <xref target="RFC7078"/> the same as on any IPv6 link.</t>
<t>All other (non-multicast) functions that operate over ordinary IPv6
links operate in the same fashion over AERO links.</t>
</section>
</section>
<section anchor="implement" title="Implementation Status">
<t>An early implementation is available at:
http://linkupnetworks.com/aero/aerov2-0.1.tgz.</t>
</section>
<section anchor="iana" title="IANA Considerations">
<t>This document uses the UDP Service Port Number 8060 reserved by IANA
for AERO in <xref target="RFC6706"/>. Therefore, there are no new IANA
actions required for this document.</t>
</section>
<section anchor="secure" title="Security Considerations">
<t>AERO link security considerations are the same as for standard IPv6
Neighbor Discovery <xref target="RFC4861"/> except that AERO improves on
some aspects. In particular, AERO is dependent on a trust basis between
AERO Clients and Servers, where the Clients only engage in the AERO
mechanism when it is facilitated by a trust anchor.</t>
<t>AERO links must be protected against link-layer address spoofing
attacks in which an attacker on the link pretends to be a trusted
neighbor. Links that provide link-layer securing mechanisms (e.g., WiFi
networks) and links that provide physical security (e.g., enterprise
network LANs) provide a first line of defense that is often sufficient.
In other instances, securing mechanisms such as Secure Neighbor
Discovery (SeND) <xref target="RFC3971"/> or IPsec <xref
target="RFC4301"/> may be necessary.</t>
<t>AERO Clients MUST ensure that their connectivity is not used by
unauthorized nodes to gain access to a protected network. (This concern
is no different than for ordinary hosts that receive an IP address
delegation but then "share" the address with unauthorized nodes via an
IPv6/IPv6 NAT function.)</t>
<t>On some AERO links, establishment and maintenance of a direct path
between neighbors requires secured coordination such as through the
Internet Key Exchange (IKEv2) protocol <xref target="RFC5996"/>.</t>
</section>
<section anchor="ack" title="Acknowledgements">
<t>Discussions both on the v6ops list and in private exchanges helped
shape some of the concepts in this work. Individuals who contributed
insights include Mikael Abrahamsson, Fred Baker, Stewart Bryant, Brian
Carpenter, Brian Haberman, Joel Halpern, Sascha Hlusiak, Lee Howard and
Joe Touch. 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.</t>
<t>This work has further been encouraged and supported by Boeing
colleagues including Keith Bartley, Balaguruna Chidambaram, Jeff
Holland, Cam Brodie, Yueli Yang, Wen Fang, Ed King, Mike Slane, Kent
Shuey, Gen MacLean, and other members of the BR&T and BIT mobile
networking teams.</t>
<t>Earlier works on NBMA tunneling approaches are found in <xref
target="RFC2529"/><xref target="RFC5214"/><xref target="RFC5569"/>.</t>
</section>
</middle>
<back>
<references title="Normative References">
<?rfc include="reference.RFC.0768"?>
<?rfc include="reference.RFC.0791"?>
<?rfc include="reference.RFC.0792"?>
<?rfc include="reference.RFC.2119"?>
<?rfc include="reference.RFC.2460"?>
<?rfc include="reference.RFC.2473"?>
<?rfc include="reference.RFC.4213"?>
<?rfc include="reference.RFC.4861"?>
<?rfc include="reference.RFC.4862"?>
<?rfc include="reference.RFC.6434"?>
<?rfc include="reference.RFC.3633"?>
<?rfc include="reference.RFC.3315"?>
<?rfc include="reference.RFC.6355"?>
</references>
<references title="Informative References">
<?rfc include="reference.RFC.2675"?>
<reference anchor="IRON">
<front>
<title>The Internet Routing Overlay Network (IRON)</title>
<author fullname="Fred Templin" initials="F" surname="Templin">
<organization/>
</author>
<date day="15" month="June" year="2012"/>
<abstract>
<t>Since the Internet must continue to support escalating growth
due to increasing demand, it is clear that current routing
architectures and operational practices must be updated. This
document proposes an Internet Routing Overlay Network (IRON)
architecture that supports sustainable growth while requiring no
changes to end systems and no changes to the existing routing
system. In addition to routing scaling, IRON further addresses
other important issues including mobility management, mobile
networks, multihoming, traffic engineering, NAT traversal and
security. While business considerations are an important
determining factor for widespread adoption, they are out of scope
for this document.</t>
</abstract>
</front>
<seriesInfo name="Work in" value="Progress"/>
</reference>
<?rfc include="reference.RFC.3971"?>
<?rfc include="reference.RFC.2529"?>
<?rfc include="reference.RFC.5214"?>
<?rfc include="reference.RFC.4301"?>
<?rfc include="reference.RFC.5569"?>
<?rfc include="reference.RFC.6204"?>
<?rfc include="reference.RFC.6980"?>
<?rfc include="reference.RFC.0879"?>
<?rfc include="reference.RFC.4821"?>
<?rfc include="reference.RFC.6691"?>
<?rfc include="reference.RFC.6935"?>
<?rfc include="reference.RFC.6936"?>
<?rfc include="reference.RFC.6438"?>
<?rfc include="reference.RFC.6706"?>
<?rfc include="reference.RFC.4963"?>
<?rfc include="reference.RFC.6864"?>
<?rfc include="reference.RFC.6146"?>
<?rfc include="reference.RFC.7078"?>
<?rfc include="reference.RFC.5996"?>
</references>
<section anchor="scaling" title="AERO Server and Relay Interworking">
<t><xref target="no-onlink-prefix-fig"/> depicts a reference AERO
operational scenario with a single Server on the AERO link. In order to
support scaling to larger numbers of nodes, the AERO link can deploy
multiple Servers and Relays, e.g., as shown in <xref
target="chaining-fig"/>.</t>
<t><figure anchor="chaining-fig" title="AERO Server/Relay Interworking">
<artwork><![CDATA[ .-(::::::::)
.-(::: IPv6 :::)-.
(:: Internetwork ::)
`-(::::::::::::)-'
`-(::::::)-'
|
+--------------+ +------+-------+ +--------------+
|AERO Server C | | AERO Relay D | |AERO Server E |
| (default->D) | | (A->C; G->E) | | (default->D) |
| (A->B) | +-------+------+ | (G->F) |
+-------+------+ | +------+-------+
| | |
X---+---+-------------------+------------------+---+---X
| AERO Link |
+-----+--------+ +--------+-----+
|AERO Client B | |AERO Client F |
| (default->C) | | (default->E) |
+--------------+ +--------------+
.-. .-.
,-( _)-. ,-( _)-.
.-(_ IPv6 )-. .-(_ IPv6 )-.
(__ EUN ) (__ EUN )
`-(______)-' `-(______)-'
| |
+--------+ +--------+
| Host A | | Host G |
+--------+ +--------+
]]></artwork>
</figure>In this example, AERO Client ('B') associates with AERO
Server ('C'), while AERO Client ('F') associates with AERO Server ('E').
Furthermore, AERO Servers ('C') and ('E') do not associate with each
other directly, but rather have an association with AERO Relay ('D')
(i.e., a router that has full topology information concerning its
associated Servers and their Clients). Relay ('D') connects to the AERO
link, and also connects to the native IPv6 Internetwork.</t>
<t>When host ('A') sends a packet toward destination host ('G'), IPv6
forwarding directs the packet through the EUN to Client ('B'), which
forwards the packet to Server ('C') in absence of more-specific
forwarding information. Server ('C') forwards the packet, and it also
generates an AERO Predirect message that is then forwarded through Relay
('D') to Server ('E'). When Server ('E') receives the message, it
forwards the message to Client ('F').</t>
<t>After processing the AERO Predirect message, Client ('F') sends an
AERO Redirect message to Server ('E'). Server ('E'), in turn, forwards
the message through Relay ('D') to Server ('C'). When Server ('C')
receives the message, it forwards the message to Client ('B') informing
it that host 'G's EUN can be reached via Client ('F'), thus completing
the AERO redirection.</t>
<t>The network layer routing information shared between Servers and
Relays must be carefully coordinated in a manner outside the scope of
this document. In particular, Relays require full topology information,
while individual Servers only require partial topology information
(i.e., they only need to know the EUN prefixes associated with their
current set of Clients). See <xref target="IRON"/> for an architectural
discussion of routing coordination between Relays and Servers.</t>
</section>
</back>
</rfc>
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