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Network Working Group F. Templin, Ed.
Internet-Draft Boeing Research & Technology
Obsoletes: rfc6706 (if approved) March 27, 2014
Intended status: Standards Track
Expires: September 28, 2014
Transmission of IPv6 Packets over AERO Links
draft-templin-aerolink-10.txt
Abstract
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.
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 http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 28, 2014.
Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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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 . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Asymmetric Extended Route Optimization (AERO) . . . . . . . . 6
3.1. AERO Node Types . . . . . . . . . . . . . . . . . . . . . 6
3.2. AERO Interface Characteristics . . . . . . . . . . . . . . 7
3.3. AERO Addresses . . . . . . . . . . . . . . . . . . . . . . 9
3.4. AERO Interface Data Origin Authentication . . . . . . . . 9
3.5. AERO Interface Conceptual Data Structures and Protocol
Constants . . . . . . . . . . . . . . . . . . . . . . . . 9
3.6. AERO Interface MTU Considerations . . . . . . . . . . . . 11
3.7. AERO Interface Encapsulation, Re-encapsulation and
Decapsulation . . . . . . . . . . . . . . . . . . . . . . 12
3.8. AERO Reference Operational Scenario . . . . . . . . . . . 13
3.9. AERO Router Discovery and Prefix Delegation . . . . . . . 15
3.9.1. AERO Client Behavior . . . . . . . . . . . . . . . . . 15
3.9.2. AERO Server Behavior . . . . . . . . . . . . . . . . . 16
3.10. AERO Neighbor Solicitation and Advertisement . . . . . . . 16
3.11. AERO Redirection . . . . . . . . . . . . . . . . . . . . . 18
3.11.1. Classical Redirection Approaches . . . . . . . . . . . 18
3.11.2. AERO Redirection Concept of Operations . . . . . . . . 19
3.11.3. AERO Redirection Message Format . . . . . . . . . . . 19
3.11.4. Sending Predirects . . . . . . . . . . . . . . . . . . 20
3.11.5. Processing Predirects and Sending Redirects . . . . . 21
3.11.6. Re-encapsulating and Relaying Redirects . . . . . . . 22
3.11.7. Processing Redirects . . . . . . . . . . . . . . . . . 23
3.12. Neighbor Reachability Maintenance . . . . . . . . . . . . 23
3.13. Mobility and Link-Layer Address Change Considerations . . 24
3.14. Underlying Protocol Version Considerations . . . . . . . . 25
3.15. Multicast Considerations . . . . . . . . . . . . . . . . . 25
3.16. Operation on Server-less AERO Links . . . . . . . . . . . 25
3.17. Other Considerations . . . . . . . . . . . . . . . . . . . 26
4. Implementation Status . . . . . . . . . . . . . . . . . . . . 26
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26
6. Security Considerations . . . . . . . . . . . . . . . . . . . 26
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 27
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 27
8.1. Normative References . . . . . . . . . . . . . . . . . . . 27
8.2. Informative References . . . . . . . . . . . . . . . . . . 28
Appendix A. AERO Server and Relay Interworking . . . . . . . . . 30
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Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 31
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1. Introduction
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.
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.
2. Terminology
The terminology in the normative references applies; the following
terms are defined within the scope of this document:
AERO link
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.
AERO interface
a node's attachment to an AERO link. The AERO interface MTU is
less than or equal to the AERO link MTU.
AERO address
an IPv6 link-local address assigned to an AERO interface and
constructed as specified in Section 3.6.
AERO node
a node that is connected to an AERO link and that participates in
IPv6 Neighbor Discovery over the link.
AERO Client ("client")
a node that configures either a host interface or a router
interface on an AERO link.
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AERO Server ("server")
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.
AERO Relay ("relay")
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.
ingress tunnel endpoint (ITE)
an AERO interface endpoint that injects tunneled packets into an
AERO link.
egress tunnel endpoint (ETE)
an AERO interface endpoint that receives tunneled packets from an
AERO link.
underlying network
a connected IPv6 or IPv4 network routing region over which AERO
nodes tunnel IPv6 packets.
underlying interface
an AERO node's interface point of attachment to an underlying
network.
underlying address
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.
link-layer address
the same as defined for "underlying address" above.
network layer address
an IPv6 address used as the source or destination address of the
inner IPv6 packet header.
end user network (EUN)
an IPv6 network attached to a downstream interface of an AERO
Client (where the AERO interface is seen as the upstream
interface).
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
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document are to be interpreted as described in [RFC2119].
3. Asymmetric Extended Route Optimization (AERO)
The following sections specify the operation of IPv6 over Asymmetric
Extended Route Optimization (AERO) links:
3.1. AERO Node Types
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.
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.
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.
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.
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.
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.
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3.2. AERO Interface Characteristics
AERO interfaces use IPv6-in-IPv6 encapsulation [RFC2473] to exchange
tunneled packets with AERO neighbors attached to an underlying IPv6
network, and use IPv6-in-IPv4 encapsulation [RFC4213] to exchange
tunneled packets with AERO neighbors attached to an underlying IPv4
network. AERO interfaces can also use IPsec encapsulation [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.
AERO interfaces assign a topology-relative link-local address of the
form 'fe80::[ID]' that is derived from their current link-layer
topology. For IPv6-in-IPv4 encapsulation, 'ID' is the IPv4 address
of the node's underlying IPv4 interface preceded by zeros per Section
3.7 of [RFC4213]. For IPv6-in-IPv6 encapsulation, 'ID' is the CRC64
calculation of the node's underlying interface IPv6 address,
beginning with the most significant bit.
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 register their delegated IPv6 prefixes using
DHCPv6 PD; hence, there is no need for RA-based prefix discovery.
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.
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
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underlying address include the full 16 bytes of the IPv6 address as
shown in Figure 1, while TLLAOs for target nodes that use an IPv4
underlying address include only the 4 bytes of the IPv4 address as
shown in Figure 2.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 2 | Length = 3 | UDP Source Port (or 0) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+-- --+
| |
+-- IPv6 Address --+
| |
+-- --+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: AERO TLLAO Format for IPv6
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: AERO TLLAO Format for IPv4
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 [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.
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3.3. AERO Addresses
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:
fe80::[IPv6 prefix]
Each AERO Client configures an AERO address based on the delegated
prefix it has received from the AERO link prefix delegation
authority. 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:
2001:db8:1000:2000::/56
it would construct its AERO address as:
fe80::2001:db8:1000:2000
Unlike the node's topology-relative link local address (i.e.,
fe80::[ID]), the AERO address remains stable as the Client moves
between topological locations.
3.4. AERO Interface Data Origin Authentication
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.
The AERO node considers the link-layer source address correct for the
network-layer source address if there is an IPv6 route 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.
3.5. AERO Interface Conceptual Data Structures and Protocol Constants
Each AERO node maintains a per-AERO interface conceptual neighbor
cache that includes an entry for each neighbor it communicates with
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on the AERO link, the same as for any IPv6 interface (see [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.
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 route
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.
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 route
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.
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 [RFC4861].
It is RECOMMENDED that ACCEPT_TIME be set to the default constant
value 40 seconds to allow a 10 second window so that the AERO
redirection procedure can converge before the ACCEPT_TIME timer
decrements below FORWARD_TIME.
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
[RFC4861].
Different values for FORWARD_TIME, ACCEPT_TIME, and MAX_RETRY MAY be
administratively set, if necessary, to better match the AERO link's
performance characteristics; however, if different values are chosen,
all nodes on the link MUST consistently configure the same values.
ACCEPT_TIME SHOULD further be set to a value that is sufficiently
longer than FORWARD_TIME to allow the AERO redirection procedure to
converge.
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3.6. AERO Interface MTU Considerations
The AERO link Maximum Transmission Unit (MTU) is 64KB minus the
encapsulation overhead for IPv4 [RFC0791] and 4GB minus the
encapsulation overhead for IPv6 [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.
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.
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.
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.
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 [RFC4963][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
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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.
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.
(*) 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.
(**) 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.
3.7. AERO Interface Encapsulation, Re-encapsulation and Decapsulation
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".
AERO interfaces encapsulate packets per the specifications in ,
[RFC2473], [RFC4213] 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).
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: [RFC6935][RFC6936]) and
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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.
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
[RFC6438]. When IPv4 is used as the outer IP protocol, the AERO
interface sets the DF bit as discussed in Section 3.2.
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 , [RFC2473],
[RFC4213]. 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 ,
[RFC6706]). During the decapsulation, the AERO interface records the
UDP source port in the neighbor cache entry for this neighbor then
discards the UDP header.
3.8. AERO Reference Operational Scenario
Figure 3 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'):
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.-(::::::::)
.-(::: IPv6 :::)-. +-------------+
(:::: Internet ::::)--| Host F |
`-(::::::::::::)-' +-------------+
`-(::::::)-' 2001:db8:3::1
|
+--------------+
| AERO Server A|
| (C->B; E->D) |
+--------------+
fe80::[ID]
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 |
`-(______)-' +-------------+
Figure 3: AERO Reference Operational Scenario
In Figure 3, 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::[ID] 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.
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::[ID] 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.
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).
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Client ('D') configures a default route via the AERO interface with
next-hop address fe80::[ID] 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.
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.
3.9. AERO Router Discovery and Prefix Delegation
3.9.1. AERO Client Behavior
AERO Clients observe the IPv6 router requirements defined in
[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 the Server's IPv6
link-local address and the discovered link-layer address as the link-
layer address. The Client further creates a static default IPv6
route with the Server's link-local address as the next hop.
Next, the Client acts as a requesting router to register its IPv6
prefix through DHCPv6 PD [RFC3633] via the Server using its current
topology-relative link-local address as the IPv6 source address.
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 therefore
becomes an additional link-local address on the interface that
remains stable as the Client moves.
After configuring a default route and registering its prefix, 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
Section 3.11.
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3.9.2. AERO Server Behavior
AERO Servers observe the IPv6 router requirements defined in
[RFC6434]. They further configure a DHCPv6 relay/server function on
their AERO links. When the Server facilitates prefix delegation, it
also 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 .
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.
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 Section 3.11.
3.10. AERO Neighbor Solicitation and Advertisement
Each AERO node uses its delegated prefix to create an AERO address
(see: Section 3.3). It can then send NS messages to elicit NA
messages from other AERO nodes. When the AERO node sends NS/NA
messages, however, it must also include the length of the prefix
corresponding to the AERO address. AERO NS/NA messages therefore
include an 8-bit "Prefix Length" field take from the low-order 8 bits
of the Reserved field as shown in Figure 4 and Figure 5.
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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 (=135) | Code | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Prefix Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Target Address +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Options ...
+-+-+-+-+-+-+-+-+-+-+-+-
Figure 4: AERO Neighbor Solicitation (NS) Message Format
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 (=136) | Code | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| R|S|O| Reserved | Prefix Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Target Address +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Options ...
+-+-+-+-+-+-+-+-+-+-+-+-
Figure 5: AERO Neighbor Advertisement (NA) Message Format
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. It MUST also include its
AERO address prefix length in the Prefix Length field.
When an AERO node receives an NS/NA message, it accepts the message
if the Prefix Length applied to the source address is correct for the
neighbor; otherwise, it ignores the message.
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3.11. AERO Redirection
Section 3.8 describes the AERO reference operational scenario. We
now discuss the operation and protocol details of AERO Redirection
with respect to this reference scenario.
3.11.1. Classical Redirection Approaches
With reference to Figure 3, 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.
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').
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.
Since both of these alternatives have shortcomings, a new redirection
technique (i.e., "AERO redirection") is needed.
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3.11.2. AERO Redirection Concept of Operations
Again, with reference to Figure 3, 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').
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
Section 3.11.4. 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 Section 3.11.5. During the
process, Client ('D') also creates or updates a dynamic neighbor
cache entry for Client ('B'), and creates an IPv6 route for Client
('B')'s IPv6 prefix.
When Server ('A') receives the Redirect message, it re-encapsulates
the message and forwards it on to Client ('B') as specified in
Section 3.11.6. 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 Section 3.11.7. During the process, Client ('B') also
creates or updates a dynamic neighbor cache entry for Client ('D'),
and creates an IPv6 route for Client ('D')'s IPv6 prefix.
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.
3.11.3. AERO Redirection Message Format
AERO Redirect/Predirect messages use the same format as for ICMPv6
Redirect messages depicted in Section 4.5 of [RFC4861], but also
include a new "Prefix Length" field taken from the low-order 8 bits
of the Redirect message Reserved field. The Redirect/Predirect
messages are formatted as shown in Figure 6:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type (=137) | Code (=0/1) | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Prefix Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Target Address +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Destination Address +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Options ...
+-+-+-+-+-+-+-+-+-+-+-+-
Figure 6: AERO Redirect/Predirect Message Format
3.11.4. Sending Predirects
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.
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 [RFC4861]). Server ('A') prepares the
Predirect message as follows:
o the link-layer source address is set to 'L2(A)' (i.e., the
underlying address of Server ('A')).
o the link-layer destination address is set to 'L2(D)' (i.e., the
underlying address of Client ('D')).
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o the network-layer source address is set to fe80::[ID] (i.e., the
link-local address of Server ('A')).
o the network-layer destination address is set to fe80::2001:db8:1:0
(i.e., the AERO address of Client ('D')).
o the Type is set to 137.
o the Code is set to 1 to indicate "Predirect".
o the Prefix Length is set to the length of the prefix to be applied
to Target address.
o the Target Address is set to fe80::2001:db8:0::0 (i.e., the AERO
address of Client ('B')).
o the Destination Address is set to the IPv6 source address of the
packet that triggered the Predirection event.
o the message includes a TLLAO set to 'L2(B)' (i.e., the underlying
address of Client ('B')).
o 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.
Server ('A') then sends the message forward to Client ('D').
3.11.5. Processing Predirects and Sending Redirects
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 [RFC4861].
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.
After processing the message, Client ('D') prepares a Redirect
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message response as follows:
o the link-layer source address is set to 'L2(D)' (i.e., the link-
layer address of Client ('D')).
o the link-layer destination address is set to 'L2(A)' (i.e., the
link-layer address of Server ('A')).
o the network-layer source address is set to 'L3(D)' (i.e., the AERO
address of Client ('D')).
o the network-layer destination address is set to 'L3(B)' (i.e., the
AERO address of Client ('B')).
o the Type is set to 137.
o the Code is set to 0 to indicate "Redirect".
o the Prefix Length is set to the length of the prefix to be applied
to the Target and Destination address.
o the Target Address is set to fe80::2001:db8:1::1 (i.e., the AERO
address of Client ('D')).
o the Destination Address is set to the IPv6 destination address of
the packet that triggered the Redirection event.
o the message includes a TLLAO set to 'L2(D)' (i.e., the underlying
address of Client ('D')).
o 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.
After Client ('D') prepares the Redirect message, it sends the
message to Server ('A').
3.11.6. Re-encapsulating and Relaying Redirects
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 [RFC4861].
Following validation, Server ('A') re-encapsulates the Redirect then
relays the re-encapsulated Redirect on to Client ('B') as follows.
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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::[ID], 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.
While not shown in Figure 3, AERO Relays relay Redirect and Predirect
messages in exactly this same fashion described above. See Figure 7
in Appendix A for an extension of the reference operational scenario
that includes Relays.
3.11.7. Processing Redirects
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
[RFC4861]. Following validation, Client ('B') then processes the
message as follows.
In the reference operational scenario, when Client ('B') receives the
Redirect message, it either cre ates 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.
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').
3.12. Neighbor Reachability Maintenance
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
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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
using Neighbor Unreachability Detection (NUD) (see Section 7.3 of
[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.
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.
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.
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 route.
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.
3.13. Mobility and Link-Layer Address Change Considerations
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.
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 entries and IPv6 routes, and
allow packets to again flow through their Server(s) which MAY result
in a new AERO redirection exchange.
When a Client needs to change to a new Server, it performs a DHCPv6
"Release" message exchange with the delegating router via the old
Server then sends a DHCPv6 "Request" message to the delegating router
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via the new Server. During this process, the Client and old Server
both delete their respective static neighbor cache entries while the
Client and new Server both create new respective static neighbor
cache entries. Note that this may result in a temporary service
outage during Server "handovers".
3.14. Underlying Protocol Version Considerations
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.
3.15. Multicast Considerations
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.
When the underlying network supports multicast, AERO nodes use the
multicast address mapping specification found in [RFC2529] for IPv4
underlying networks and use a direct multicast mapping for IPv6
underlying networks. (In the latter case, "direct multicast mapping"
means that if the IPv6 multicast destination address of the inner
packet is "M", then the IPv6 multicast destination address of the
encapsulating header is also "M".)
3.16. Operation on Server-less AERO Links
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 routes by performing direct Client-to-Client
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.
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.
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3.17. Other Considerations
IPv6 hosts serviced by an AERO Client can reach IPv4-only services
via a NAT64 gateway [RFC6146] within the IPv6 network.
AERO nodes can use the Default Address Selection Policy with DHCPv6
option [RFC7078] the same as on any IPv6 link.
All other (non-multicast) functions that operate over ordinary IPv6
links operate in the same fashion over AERO links.
4. Implementation Status
An early implementation is available at:
http://linkupnetworks.com/aero/aerov2-0.1.tgz.
5. IANA Considerations
This document uses the UDP Service Port Number 8060 reserved by IANA
for AERO in [RFC6706]. Therefore, there are no new IANA actions
required for this document.
6. Security Considerations
AERO link security considerations are the same as for standard IPv6
Neighbor Discovery [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.
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) [RFC3971] or IPsec [RFC4301] may be
necessary.
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.)
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On some AERO links, establishment and maintenance of a direct path
between neighbors requires secured coordination such as through the
Internet Key Exchange (IKEv2) protocol [RFC5996].
7. Acknowledgements
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.
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.
Earlier works on NBMA tunneling approaches are found in
[RFC2529][RFC5214][RFC5569].
8. References
8.1. Normative References
[RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768,
August 1980.
[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791,
September 1981.
[RFC0792] Postel, J., "Internet Control Message Protocol", STD 5,
RFC 792, September 1981.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, December 1998.
[RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in
IPv6 Specification", RFC 2473, December 1998.
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[RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic
Host Configuration Protocol (DHCP) version 6", RFC 3633,
December 2003.
[RFC4213] Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms
for IPv6 Hosts and Routers", RFC 4213, October 2005.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
September 2007.
[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862, September 2007.
[RFC6434] Jankiewicz, E., Loughney, J., and T. Narten, "IPv6 Node
Requirements", RFC 6434, December 2011.
8.2. Informative References
[IRON] Templin, F., "The Internet Routing Overlay Network
(IRON)", Work in Progress, June 2012.
[RFC0879] Postel, J., "TCP maximum segment size and related topics",
RFC 879, November 1983.
[RFC2529] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4
Domains without Explicit Tunnels", RFC 2529, March 1999.
[RFC2675] Borman, D., Deering, S., and R. Hinden, "IPv6 Jumbograms",
RFC 2675, August 1999.
[RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
and M. Carney, "Dynamic Host Configuration Protocol for
IPv6 (DHCPv6)", RFC 3315, July 2003.
[RFC3971] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure
Neighbor Discovery (SEND)", RFC 3971, March 2005.
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, December 2005.
[RFC4821] Mathis, M. and J. Heffner, "Packetization Layer Path MTU
Discovery", RFC 4821, March 2007.
[RFC4963] Heffner, J., Mathis, M., and B. Chandler, "IPv4 Reassembly
Errors at High Data Rates", RFC 4963, July 2007.
[RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site
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Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214,
March 2008.
[RFC5569] Despres, R., "IPv6 Rapid Deployment on IPv4
Infrastructures (6rd)", RFC 5569, January 2010.
[RFC5996] Kaufman, C., Hoffman, P., Nir, Y., and P. Eronen,
"Internet Key Exchange Protocol Version 2 (IKEv2)",
RFC 5996, September 2010.
[RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
NAT64: Network Address and Protocol Translation from IPv6
Clients to IPv4 Servers", RFC 6146, April 2011.
[RFC6204] Singh, H., Beebee, W., Donley, C., Stark, B., and O.
Troan, "Basic Requirements for IPv6 Customer Edge
Routers", RFC 6204, April 2011.
[RFC6438] Carpenter, B. and S. Amante, "Using the IPv6 Flow Label
for Equal Cost Multipath Routing and Link Aggregation in
Tunnels", RFC 6438, November 2011.
[RFC6691] Borman, D., "TCP Options and Maximum Segment Size (MSS)",
RFC 6691, July 2012.
[RFC6706] Templin, F., "Asymmetric Extended Route Optimization
(AERO)", RFC 6706, August 2012.
[RFC6864] Touch, J., "Updated Specification of the IPv4 ID Field",
RFC 6864, February 2013.
[RFC6935] Eubanks, M., Chimento, P., and M. Westerlund, "IPv6 and
UDP Checksums for Tunneled Packets", RFC 6935, April 2013.
[RFC6936] Fairhurst, G. and M. Westerlund, "Applicability Statement
for the Use of IPv6 UDP Datagrams with Zero Checksums",
RFC 6936, April 2013.
[RFC6980] Gont, F., "Security Implications of IPv6 Fragmentation
with IPv6 Neighbor Discovery", RFC 6980, August 2013.
[RFC7078] Matsumoto, A., Fujisaki, T., and T. Chown, "Distributing
Address Selection Policy Using DHCPv6", RFC 7078,
January 2014.
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Appendix A. AERO Server and Relay Interworking
Figure 3 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 Figure 7.
.-(::::::::)
.-(::: 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 |
+--------+ +--------+
Figure 7: AERO Server/Relay Interworking
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.
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
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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').
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.
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 [IRON] for an architectural
discussion of routing coordination between Relays and Servers.
Author's Address
Fred L. Templin (editor)
Boeing Research & Technology
P.O. Box 3707
Seattle, WA 98124
USA
Email: fltemplin@acm.org
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