Transmission of IPv6 Packets over Asymmetric Extended Route Optimization (AERO) Links
draft-templin-aerolink-00
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft whose latest revision state is "Replaced".
|
|
|---|---|---|---|
| Author | Fred Templin | ||
| Last updated | 2013-12-19 | ||
| Replaced by | draft-templin-intarea-6706bis, draft-templin-intarea-6706bis | ||
| RFC stream | (None) | ||
| Formats | |||
| Stream | Stream state | (No stream defined) | |
| Consensus boilerplate | Unknown | ||
| RFC Editor Note | (None) | ||
| IESG | IESG state | I-D Exists | |
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | (None) |
draft-templin-aerolink-00
Network Working Group F. Templin, Ed.
Internet-Draft Boeing Research & Technology
Obsoletes: rfc6706 (if approved) December 19, 2013
Intended status: Standards Track
Expires: June 22, 2014
Transmission of IPv6 Packets over Asymmetric Extended Route Optimization
(AERO) Links
draft-templin-aerolink-00.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)
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 June 22, 2014.
Copyright Notice
Copyright (c) 2013 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
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publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Asymmetric Extended Route Optimization (AERO) . . . . . . . . 5
3.1. AERO Interface Characteristics . . . . . . . . . . . . . . 5
3.2. AERO Node Types . . . . . . . . . . . . . . . . . . . . . 7
3.3. AERO Addresses . . . . . . . . . . . . . . . . . . . . . . 7
3.4. AERO Reference Operational Scenario . . . . . . . . . . . 8
3.5. AERO Prefix Delegation and Router Discovery . . . . . . . 9
3.5.1. AERO Client Behavior . . . . . . . . . . . . . . . . . 9
3.5.2. AERO Server Behavior . . . . . . . . . . . . . . . . . 10
3.6. AERO Neighbor Unreachability Detection . . . . . . . . . . 10
3.7. AERO Redirection . . . . . . . . . . . . . . . . . . . . . 11
3.7.1. Classical Redirection Approaches . . . . . . . . . . . 11
3.7.2. AERO Redirection Concept of Operations . . . . . . . . 12
3.7.3. AERO Redirection Message Format . . . . . . . . . . . 13
3.7.4. Sending Predirects . . . . . . . . . . . . . . . . . . 14
3.7.5. Processing Predirects and Sending Redirects . . . . . 15
3.7.6. Forwarding Redirects . . . . . . . . . . . . . . . . . 16
3.7.7. Processing Redirects . . . . . . . . . . . . . . . . . 17
3.7.8. Neighbor Reachability Considerations . . . . . . . . . 18
3.7.9. Neighbor Cache Entry Mainenance . . . . . . . . . . . 18
3.7.10. Mobility and Link-Layer Address Change
Considerations . . . . . . . . . . . . . . . . . . . . 19
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
5. Security Considerations . . . . . . . . . . . . . . . . . . . 19
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 19
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 20
7.1. Normative References . . . . . . . . . . . . . . . . . . . 20
7.2. Informative References . . . . . . . . . . . . . . . . . . 20
Appendix A. AERO Server and Relay Interworking . . . . . . . . . 21
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 23
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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.
AERO uses 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.
AERO address
an IPv6 link-local address assigned to an AERO interface and
constructed as specified in Section 3.3.
AERO node
a node that is connected to an AERO link and that participates in
IPv6 Neighbor Discovery over the link.
AERO Server ("server")
a node that configures an advertising router interface on an AERO
link over which it can provide default forwarding and redirection
services for other AERO nodes.
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AERO Client ("client")
a node that configures a non-advertising router interface on an
AERO link over which it can connect End User Networks (EUNs) to
the AERO link.
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)
a node that injects tunneled packets into an AERO link.
egress tunnel endpoint (ETE)
a node that receives tunneled packets from an AERO link.
underlying network
a connected IPv6 or IPv4 network routing region over which AERO
links tunnel IPv6 packets.
underlying interface
a node's interface point of attachment to an underlying network.
underlying address
an IPv6 or IPv4 address assigned to a node's underlying interface.
When UDP encapsulation is used, the UDP port number is also
considered as part of the link-layer address. Link-layer
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
document are to be interpreted as described in [RFC2119].
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3. Asymmetric Extended Route Optimization (AERO)
The following sections specify the operation of IPv6 over Asymmetric
Extended Route Optimization (AERO) links:
3.1. AERO Interface Characteristics
All nodes connected to an AERO link configure their AERO interfaces
as router interfaces (not host interfaces). End system applications
therefore do not bind directly to the AERO interface, but rather bind
to end user network (EUN) interfaces beyond which their packets may
be forwarded over an AERO interface.
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-IPv6 or IPv6-in-IPv4) in environments where strong
authentication and confidentiality are required.
AERO interfaces further use the Subnetwork Encapsulation and
Adaptation Layer (SEAL)[I-D.templin-intarea-seal] and can therefore
configure an unlimited Maximum Transmission Unit (MTU). This entails
the insertion of a SEAL header (i.e., an IPv6 fragment header with
the S bit set to 1) above the outer IP encapsulation header. When
NAT traversal and/or filtering middlebox traversal is necessary, a
UDP header is further inserted between the outer IP encapsulation
header and the SEAL header.
AERO interfaces maintain a neighbor cache and use an adaptation of
standard unicast IPv6 ND messaging in which Router Solicitation (RS),
Router Advertisement (RA), Neighbor Solicitation (NS) and Neighbor
Advertisement (NA) messages do not include Source/Target Link Layer
Address Options (S/TLLAO). Instead, AERO nodes discover the link-
layer addresses of neighbors by examining the encapsulation source
address of any RS/RA/NS/NA messages they receive and ignore any
S/TLLAOs included in these messages. This is vital to the operation
of AERO in environments in which AERO 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
underlying address include the full 16 bytes of the IPv6 address as
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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, 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.
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3.2. AERO Node Types
AERO Servers configure their AERO link interfaces as advertising
router interfaces (see [RFC4861], Section 6.2.2) and may therefore
send Router Advertisement (RA) messages that include non-zero Router
Lifetimes.
AERO Clients configure their AERO link interfaces as non-advertising
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 (virtual)
EUN interfaces). AERO Clients are provisioned with IPv6 Prefix
Delegations either through a DHCPv6 Prefix Delegation exchange with
an AERO Server over the AERO link or via a static delegation obtained
through an out-of-band exchange with an AERO link prefix delegation
authority.
AERO Relays relay packets between Servers 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 Server and are to be
forwarded without modification to a second AERO Server. This
relaying process can best be understood as a form of bridging.
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 64-bit
interface identifier.
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 from the Client's
delegated IPv6 prefix. 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. An AERO Client may receive
multiple IPv6 prefix delegations, in which case it would configure
multiple AERO addresses - one for each delegated prefix.
Each AERO Server configures the special AERO address fe80::1 to
support the operation of IPv6 Neighbor Discovery over the AERO link;
the address therefore has the properties of an IPv6 Anycast address.
While all Servers configure the same AERO address and therefore
cannot be distinguished from one another at the network layer,
Clients can still distinguish Servers at the link layer by examining
the Servers' link-layer addresses.
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Nodes that are configured as pure AERO Relays (i.e., and that do not
also act as Servers) do not configure an IPv6 address of any kind on
their AERO interfaces. The Relay's AERO interface is therefore used
purely for transit and does not participate in IPv6 ND message
exchanges.
3.4. 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'):
.-(::::::::)
.-(::: IPv6 :::)-. +-------------+
(:::: Internet ::::)--| Host F |
`-(::::::::::::)-' +-------------+
`-(::::::)-' 2001:db8:3::1
|
+--------------+
| AERO Server A|
| (C->B; E->D) |
+--------------+
fe80::1
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 other IPv6 routers (not
shown). Server ('A') assigns the address fe80::1 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.
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AERO Client ('B') 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 network-layer
address fe80::1 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 network-layer address 2001:
db8:0::1.
AERO Client ('D') 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 network-layer
address fe80::1 and link-layer address L2(A), then sub-delegates the
network-layer prefix 2001:db8:1::/48 to its attached EUNs. IPv6 host
('E') connects to the EUN, and configures the network-layer 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 network-
layer address 2001:db8:3::1 to its IPv6 link interface.
3.5. AERO Prefix Delegation and Router Discovery
3.5.1. AERO Client Behavior
AERO Clients observe the IPv6 router requirements defined in
[RFC6434] except that they act as "hosts" on their AERO interfaces
for the purpose of prefix delegation and router discovery in the same
fashion as for IPv6 Customer Premises Equipment (CPE) routers
[RFC6204]. 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. After discovering the link-layer
address, the Client then acts as a requesting router to obtain IPv6
prefixes through DHCPv6 Prefix Delegation [RFC3633] via the Server.
(The Client can also obtain prefixes through out-of-band means such
as static administrative configuration, etc.). After the Client
acquires prefixes, it sub-delegates them to nodes and links within
its attached EUNs. It also assigns the link-local AERO address(es)
taken from its delegated prefix(es) to the AERO interface (see:
Section 3.3).
After acquiring prefixes, the Client next prepares a unicast IPv6
Router Solicitation (RS) message using its AERO address as the
network-layer source address and fe80::1 as the network-layer
destination address. The Client then tunnels the packet to the
Server using one of its underlying addresses as the link-layer source
address and using an underlying address of the Server as the link-
layer destination address. The Server in turn returns a unicast
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Router Advertisement (RA) message, which the Client uses to create an
IPv6 neighbor cache entry for the Server on the AERO interface per
[RFC4861]. The link-layer address for the neighbor cache entry is
taken from the link-layer source address of the RA message.
After obtaining prefixes and performing an initial RS/RA exchange
with a Server, the Client continues to send periodic RS messages to
the server to obtain new RAs in order to keep neighbor cache entries
alive. 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 3.7.
3.5.2. 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 and/or provide an administrative interface for
delegation of network-layer addresses and prefixes. When the Server
delegates prefixes, it also establishes forwarding table entries that
list the AERO address of the Client as the next hop toward the
delegated IPv6 prefixes (where the AERO address is constructed as
specified in Section 3.3).
Servers respond to RS messages from Clients on their advertising AERO
interfaces by returning an RA message. When the Server receives an
RS message, it creates or updates a 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 RS 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 3.7.
3.6. AERO Neighbor Unreachability Detection
When an AERO Client forwards a packet originating from one of its
EUNs via an IPv6 route for which the next hop is reached via the AERO
interface, it first consults its neighbor cache to determine the
link-layer address of the next hop. The Client then encapsulates the
packet and uses its link-layer address as the link-layer source
address and the link-layer address of the neighbor as the link-layer
destination address. If the IPv6 route is more-specific than
"default", the Client also follows the Neighbor Unreachability
Detection (NUD) procedures in Section 7.3 of [RFC4861] to keep
neighbor cache entries alive. In particular, the Client sends NS
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messages including its AERO address as the network-layer source
address, the next hop's AERO address as the network-layer destination
address, and the same link-layer addresses used to forward the
packet. If the Client receives a solicited NA message response from
the next hop, it updates its neighbor cache entry state for the next
hop to REACHABLE, and records the link-layer source address of the NA
as the neighbor's link layer address.
When an AERO Client receives an NS message used for NUD on an AERO
interface, it either creates or updates a neighbor cache entry for
the neighbor that sent the NS including recording the link-layer
source address of the NS as the link layer address. If the Client
creates a new neighbor cache entry it sets the neighbor's state to
STALE. The Client then sends a solicited NA message back to the
source including the Client's AERO address as the network-layer
source address, the network-layer source address of the NS message as
the network-layer destination address, its own link-layer address as
the link-layer source address, and the link-layer source address of
the NS message as the link-layer destination address.
AERO Servers process NS/NA messages in the same way as AERO Clients.
However, they need not actively perform NUD if they have other means
of determining Client reachability (e.g., through RS/RA exchanges,
through reachability confirmation from the prefix delegation service,
through link-layer probing, etc.).
3.7. AERO Redirection
Section 3.4 describes the AERO reference operational scenario. We
now discuss the operation and protocol details of AERO Redirection
with respect to this reference scenario.
3.7.1. 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 forwards the packet to AERO Client ('D'), where the packet
is finally forwarded to the IPv6 destination host ('E'). When Server
('A') 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 should only occur if
there is assurance that both Client nodes are willing participants.
Consider a first alternative in which Server ('A') informs Client
('B') only and does not inform Client ('D') (i.e., "classical
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redirection"). In that case, Client ('D') has no way of knowing that
Client ('B') is authorized to forward packets from their claimed
network-layer source addresses, 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'). Finally, Client ('B') has no way
of knowing whether the final destination ('E') has moved away from
Client ('D').
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,
several conditions can occur that could result in communication
failures. First, 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 cached state to verify their source network-layer addresses.
Second, 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. Finally, timing issues
surrounding the establishment and garbage collection of neighbor
state at the two Client nodes could yield unpredictable behavior.
For example, unless the timing were carefully coordinated through
some form of synchronization loop, there would invariably be
instances in which one node has the correct neighbor state and the
other node does not resulting in non-deterministic packet loss.
Since both of these alternatives have shortcomings, a new redirection
technique (i.e., "AERO redirection") is needed.
3.7.2. 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').
Using AERO redirection, Server ('A') then 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 3.7.4. 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 to Server ('A') as
specified in Section 3.7.5. During the process, Client ('D') also
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creates or updates a neighbor cache entry for Client ('B'), and
creates an IPv6 route to be used as ingress filtering information to
accept future packets using addresses matched by Client ('B')'s
prefix.
When Server ('A') receives the Redirect message, it processes the
message and forwards it on to Client ('B') as specified in
Section 3.7.6. 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 3.7.7. During the process, Client ('B') also
creates or updates a neighbor cache entry for Client ('D'), and
creates an IPv6 route for forwarding future packets using addresses
matched by the prefixes to Client ('D').
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.
3.7.3. 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 field (the "Prefix Length" field) taken from the
Redirect message Reserved field. The Redirect/Prediect messages are
formatted as shown in Figure 4:
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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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Prefix Length | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Target Address +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Destination Address +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Options ...
+-+-+-+-+-+-+-+-+-+-+-+-
Figure 4: AERO Redirect/Predirect Message Format
3.7.4. 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::1 (i.e., the AERO
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').
3.7.5. 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 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 Preflx Length to the Interface
Identifier portion of the Target Address and records the resulting
IPv6 prefix in its IPv6 forwarding table. Client ('D') then marks
the forwarding table entry as "FILTERING", i.e., the entry is to be
used by the network layer for ingress filtering purposes only and not
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for forwarding purposes.
After processing the message, Client ('D') prepares a Redirect
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').
3.7.6. Forwarding 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].
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Following validation, Server ('A') processes the Redirect, and then
forwards a corresponding Redirect on to Client ('B') as follows.
In the reference operational scenario, Server ('A') receives the
Redirect message from Client ('D') and prepares to forward a
corresponding Redirect message to Client ('B'). Server ('A') then
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 it discards the message if
verification fails. Otherwise, Server ('A') changes the link-layer
source address of the message to 'L2(A)', changes the network-layer
source address of the message to fe80::1, and changes the link-layer
destination address to 'L2(B)' . Server ('A') finally forwards the
message to the ingress node ('B') without decrementing the network-
layer IPv6 header Hop Limit field.
While not shown in Figure 3, AERO Relays forward Redirect and
Predirect messages in exactly this same fashion described above. See
Figure 5 in Appendix A for an extension of the reference operational
scenario that includes Relays.
3.7.7. 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 creates or updates a 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 Preflx Length to the Interface Identifier portion of
the Target Address and records the resulting IPv6 prefix in its IPv6
forwarding table. Client ('B') then marks the forwarding table entry
as "FORWARDING", i.e., the entry is to be used by the network layer
for forwarding purposes only and not for ingress filtering purposes..
Now, Client ('B') has an IPv6 forwarding table entry for
Client('D')'s prefix in the "FORWARDING" state, and Client ('D') has
an IPv6 forwarding table entry for Client ('B')'s prefix in the
"FILTERING" state. Therefore, Client ('B') may forward ordinary
network-layer data packets directly to the egress node ('D') without
forwarding through Server ('A').
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To enable packet forwarding in the reverse direction, a separate AERO
redirection operation is required that is the mirror-image of the
forward operation described above but the link segments traversed in
the forward and reverse directions may be different, i.e., the
operations are asymmetric.
3.7.8. Neighbor Reachability Considerations
When Client ('B') receives a Redirect message informing it of a
direct path to Client ('D'), there is a question in point as to
whether Client ('D') can be reached directly without forwarding
through Server ('A'). On some AERO links, it may be reasonable for
Client ('B') to (optimistically) assume that reachability is
transitive, and to immediately begin forwarding data packets to
Client ('D') without testing reachability.
On AERO links in which an optimistic assumption of transitive
reachability may be unreasonable, however, Client ('B') can defer the
redirection until it tests the direct path to the egress node ('D'),
e.g., by sending an initial NS message to elicit an NA response. If
Client ('B') is unable to elicit a response after MAX_RETRY attempts,
it should consider the direct path to Client ('D') to be unusable.
In still other instances, Client ('B') may connect only to an IPvX
underlying network, while Client ('D') connects only to an IPvY
underlying network. In that case, Client ('B') has no means for
reaching Client ('D') directly (since they connect to underlying
networks of different IP protocol versions) and so must ignore any
Redirects and continue to send packets via Server ('A').
If a direct path between Client ('B') and Client ('D') can be
established, the clients can thereafter process any link-layer errors
as a hint that the direct path has either failed or has become
intermittent.
3.7.9. Neighbor Cache Entry Mainenance
While Client ('B') is actively sending packets to Client ('D'), it
should also send NS messages (subject to rate limiting) to keep
neighbor cache entries alive and to keep link-layer addresses up to
date. If Client ('B') ceases to send packets to Client ('D') for
longer than the standard neighbor discover reachability timer, it
considers Client ('D') as "unreachable". It then deletes the
neighbor cache and IPv6 routing table entries, and allows future
packets destined to Client (D')'s EUNs to once again flow through
Server ('A') (after which it may eventually receive additional
Redirects).
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3.7.10. Mobility and Link-Layer Address Change Considerations
When Client ('B') 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 Client ('D'),
which then discovers a new link-layer address.
If both Client ('B') and Client ('D') change their link-layer
addresses simultaneously, the NS/NA exchanges between the two
neighbors may fail. In that case, the Clients follow the same
neighbor unreachability procedures specified in Section 3.7.9.
4. IANA Considerations
There are no IANA actions required for this document.
5. 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 must only engage in the
AERO mechanism when it is facilitated by a trusted Server.
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] must be
used.
6. 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, and Lee Howard.
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.
Earlier works on NBMA tunneling approaches are found in
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[RFC2529][RFC5214][RFC5569].
7. References
7.1. Normative References
[I-D.templin-intarea-seal]
Templin, F., "The Subnetwork Encapsulation and Adaptation
Layer (SEAL)", draft-templin-intarea-seal-65 (work in
progress), October 2013.
[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.
[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.
7.2. Informative References
[IRON] Templin, F., "The Internet Routing Overlay Network
(IRON)", Work in Progress, June 2012.
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[RFC2529] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4
Domains without Explicit Tunnels", RFC 2529, March 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.
[RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic
Host Configuration Protocol (DHCP) version 6", RFC 3633,
December 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.
[RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site
Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214,
March 2008.
[RFC5569] Despres, R., "IPv6 Rapid Deployment on IPv4
Infrastructures (6rd)", RFC 5569, January 2010.
[RFC6204] Singh, H., Beebee, W., Donley, C., Stark, B., and O.
Troan, "Basic Requirements for IPv6 Customer Edge
Routers", RFC 6204, April 2011.
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 5.
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.-(::::::::)
.-(::: 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 5: 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
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,
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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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