One document matched: draft-palet-v6ops-proto41-nat-01.txt
Differences from draft-palet-v6ops-proto41-nat-00.txt
Internet Engineering Task Force
Internet Draft Jordi Palet
Document: draft-palet-v6ops-proto41-nat-01.txt Cesar Olvera
Consulintel
Category: David Fernandez
UPM
Expires: January 2004 July 2003
Forwarding Protocol 41 in NAT Boxes
draft-palet-v6ops-proto41-nat-01.txt
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026 [1].
Internet-Drafts are working documents of the Internet Engineering
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The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
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Abstract
Some NAT boxes/routers allow the establishment of IPv6 tunnels from
systems in the private LAN (using private IPv4 addresses) to routers
or tunnel servers in the public Internet.
As far as we know this is not a common way of use IPv6 tunnels; the
usual way is to finish the tunnel directly in a device with an IPv4
public address.
This behavior provides a big opportunity to rapidly deploy a huge
number of IPv6 nodes and networks, without the need of new transition
mechanism. This option is very important to facilitate the IPv6
deployment when is not possible to offer native IPv6 or 6to4.
From this point of view, this mechanism should be considered only as
a temporary solution until native IPv6 routers, or those that support
6to4, will become widely available.
This document describes this behavior and provides hints that should
be applied in the NAT boxes and tunnel brokers to facilitate it.
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Conventions used in this document
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 RFC-2119 [2].
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Table of Contents
1. Introduction...................................................4
2. Rationale for this behavior....................................6
3. Behavior of different NAT types................................6
3.1 Basic NAT..................................................6
3.2 NAPT.......................................................6
3.3 Bidirectional (or two-way) NAT.............................7
3.4 "Configurable" NAT.........................................7
4. Applicability..................................................7
5. NAT design considerations......................................8
6. Tunnel broker design considerations............................9
7. Security Considerations........................................9
8. References.....................................................9
Acknowledgments..................................................10
Author's Addresses....................ķError! Marcador no definido.
Intellectual Property Statement..................................11
Full Copyright Statement.........................................11
Acknowledgement..................................................12
1. Introduction
Some NAT boxes/routers allow the establishment of IPv6 tunnels from
systems in the private LAN (using private IPv4 addresses) to routers
or tunnel servers in the public Internet.
As far as we know [3] this is not a common way of using IPv6 tunnels;
the usual way is to finish the tunnel directly in a device with an
IPv4 public address.
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This behavior provides a big opportunity to rapidly deploy a huge
number of IPv6 nodes and networks (in the case the node behind the
NAT is an IPv6 router), without the need of new transition mechanism.
So exploring this option is very important to facilitate the IPv6
deployment, as a temporary fallback solution if neither native IPv6
nor 6to4 are available.
____
( )
( IPv6 )
(____)
|
+--------+ +--------+
| Tunnel |________| Tunnel |
| Broker | | Server |
+--------+ +--------+
\ / |
\____/ |
( ) |
( IPv4 ) |
(____) | IPv6 Tunnel
| |
Public IPv4 | |
+-----+ |
| NAT | |
| Box | |
+-----+ |
| |
Private IPv4 | |
+--------+ |
| Tunnel |------
| Client |------> (possible IPv6 or dual stack network)
+--------+
This scenario has been tested with several NAT boxes that have
successfully established IPv6 tunnels with tunnel servers from three
well known Tunnel Broker implementations (BT, Freenet6 and TILAB) as
well as with other routers (6Bone, Consulintel, Euro6IX and UPM
networks).
This can be used also without a tunnel broker, with a manual
configuration at the IPv6 router tunnel-end.
The IPv6 router side supports the establishment of this tunnel
without any additional configuration. However, in the case of some
clients under certain operating systems, the tunnel configuration
process or the tunnel broker scripts have to be modified to reflect
the private/public addressing conversion. This should be modified in
future versions of the tunnel brokers, in order to properly create
the script considering the public and private addresses.
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2. Rationale for this behavior
As described in RFC 2663 [4]:
"Address translations performed by NAT are session based and would
include translation of incoming as well as outgoing packets belonging
to that session ... a session is defined as the set of traffic that
is managed as a unit for translation. TCP/UDP sessions are uniquely
identified by the tuple of (source IP address, source TCP/UDP port,
target IP address, target TCP/UDP port). ICMP query sessions are
identified by the tuple of (source IP address, ICMP query ID, target
IP address). All other sessions are characterized by the tuple of
(source IP address, target IP address, IP protocol)."
Basically, what the router does in this case is a NAT for protocol
identifier 41 (the one used for IPv6 over IPv4 tunnels). The router
considers each tuple of the form [source IP address, target IP
address, IP protocol (41)] a different session.
3. Behavior of different NAT types
Some NAT boxes don't support creating entries for protocol 41, for
example, they may be limited to TCP, UDP and ICMP.
From now on, this NAT boxes will not be considered in this document,
until section 5.
In the case the NAT box can create a NAT entry for the protocol 41,
we can distinguish different behaviors depending on the NAT type.
3.1 Basic NAT
In Basic NATs the sessions are unidirectional. This means that, as
IPv6 tunnels are treated as any other NAT dynamic session, the tunnel
entries are only added to the table whenever an IPv6 packet is sent
from inside, but not with packets coming from the external tunnel
endpoint. Usually, an inactivity timer is started when the entry is
created, so the entry (and consequently the tunnel) is deleted if no
packets are sent for that time. The tunnel will work again if any new
packet is sent from inside the private network.
3.2 NAPT
In this case, the sessions are also unidirectional. A single shared
external address can be configured to translate different transport
identifiers (e.g., TCP and UDP port numbers, other protocol
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identifiers). At this way, different internal ports are used to
receive and forward different traffic flows/sessions (depending on
the different transport identifiers). This can also be combined with
Basic NATs.
The behavior is the same as in the case of Basic NATs.
3.3 Bidirectional (or two-way) NAT
With a Bidirectional NAT, sessions can be initiated from hosts in the
public network as well as the private network. Private network
addresses are bound to globally unique addresses, statically or
dynamically as connections are established in either direction.
In this case, the IPv6 tunnel will be working even when no internal
traffic is generated to the tunnel endpoint.
3.4 "Configurable" NAT
If the external address or pool of addresses, or different transport
identifiers, can be configured in a static way (by means of a
configuration file, http interface, CLI, etc.), then the inactivity
timer is probably not needed.
For example, in the case that one of the external addresses can be
configured to forward all the external traffic to a given internal
address then, the tunnel will work in a complete bidirectional way,
even when no internal traffic is generated, i.e. the NAT behaves as a
bidirectional NAT.
This will be also possible if the NAT can be configured to forward
all the protocol-41 packets to a given internal address.
4. Applicability
In the case of Basic NAT and NAPT, IPv6 tunnels can only be initiated
by inside-to-outside sessions. Outside-to-inside sessions only work
whenever a previous inside-to-outside session has created the proto-
41 entry in the NAT table and the inactivity timeout has not been
reached.
This fact is only a problem when IPv6 servers or services inside the
private network are needed to be accessible from outside. If the
traffic is client initiated, the session is created normally as soon
as the first packet is sent, allowing IPv6 communication.
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The only way to maintain the session permanently is to constantly
send traffic (for example, with a periodic ping from inside, a router
solicitation message, or other means). Some tunnel broker
configuration/communication protocol could be developed to extend
this support.
In the case of Bidirectional and Configurable NATs, both provide
means to support also incoming sessions, even when no outgoing
sessions had been initiated, but most probably require some type of
configuration.
This configuration can be a default one. For example a bidirectional
NAT that comes factory configured with a private address for both its
LAN interface and a pre-defined private address for the host where
all the traffic is forwarded.
In both cases, the application of this procedure allows the operation
of private IPv6 networks connected by means of non-IPv6 aware NAT
boxes to tunnel brokers or manual configured tunnels.
This document doesn't describe the local network(s) connected to the
tunnel endpoint located behind the NAT box, when, for example, it
becomes and IPv6 router. These can behave as any other IPv6 native
network, providing for example the router advertisement, DHCPv6, Home
Agent, etc.
The most usual scope of application of the behavior described in this
document seems to be SOHO and home environments, but it is not only
limited to those scenarios.
5. NAT design considerations
This document has been written following a survey with users/vendors
of different NAT boxes, and the conclusion is that most of the
manufacturers support protocol-41 forwarding. Nevertheless not all
support a bidirectional mode.
NAT boxes should tend to support native IPv6. If this is not
feasible, 6to4 should be the second option, and as a last resort,
proto-41 forwarding.
6to4 and Proto-41 forwarding can coexist in the same NAT box. At this
way, an IPv6 packet received encapsulated with proto41, will be
forwarded to the private LAN only if the IPv6 destination doesn't
belong to the local 6to4 /48 prefix, otherwise decapsulated in the
NAT box.
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New firmware/software versions of the NAT implementations should
ensure the support of protocol-41 forwarding, as a temporary
solution, while they aren't supporting native IPv6 or 6to4.
In addition, considering that the code changes needed to support a
full bidirectional NAT will be minimum, this option should also be
considered, at least as a configurable option, in an easy way by the
user (very simple http interface).
6. Tunnel broker design considerations
New releases of tunnel brokers should provide means to automatically
detect, or at least manually allow the user to input, the address of
the NAT box, if this is present.
The tunnel broker, according to the existence of the NAT box, must
properly create the script that will configure the client tunnel
endpoint.
7. Security Considerations
Note that, in the case of a tunnel, the restrictions to applications
due to NAT traversing don't apply, because NAT is made to IPv4
packets that transport IPv6 ones, not to IPv6 packets.
Besides, the protection derived from the unidirectional nature of NAT
disappears for IPv6, so some security mechanism (network or personal
firewalls) could be necessary to protect IPv6 systems in the private
network.
A possible security problem is the one related to the DoS Attack than
can be created if a host in the local network, behind the NAT sends
IPv6 packets (using protocol 41) to the tunnel endpoint, simulating
to be the original "owner" of the tunnel. The behavior of the NAT box
will define the success or failure of this attack. In any case, it
seems not reasonable that this happens in small networks (SOHO and
home environments), where the attacker can be easily identified.
8. References
1 S. Bradner, "The Internet Standards Process -- Revision 3", BCP 9,
RFC 2026, October 1996.
2 S. Bradner, "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
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3 J. Palet, C. Olvera, D. Fernandez, "IPv6 Tunnels through Routers
with NAT", Euro6IX Project,
http://www.euro6ix.org/documentation/euro6ix_co_upm-
consulintel_wp4_ipv6_tunnels_nat_v1_6.pdf, April 2003.
4 P. Srisuresh. and M. Holdrege, "IP Network Address Translator
(NAT) Terminology and Considerations", RFC 2663, August 1999.
Acknowledgments
The authors would also like to acknowledge the inputs from Tim Chown,
Miguel Angel Diaz, Alain Durand, Jun-ichiro "itojun" Hagino, Keith
Moore and the European Commission support in the co-funding of the
Euro6IX project, where this work is being developed.
Authors' Addresses
Jordi Palet Martinez
Consulintel
San Jose Artesano, 1
28108 - Alcobendas (Madrid - Spain)
Phone: +34 91 151 81 99
Fax: +34 91 151 81 98
Email: jordi.palet@consulintel.es
Cesar Olvera Morales
Consulintel
San Jose Artesano, 1
28108 - Alcobendas (Madrid - Spain)
Phone: +34 91 151 81 99
Fax: +34 91 151 81 98
Email: cesar.olvera@consulintel.es
David Fernandez
Technical University of Madrid (UPM)
Ciudad Universitaria s/n
28040 ū Madrid (Spain)
Phone: +34 91 549 57 00
Fax: +34 91 336 73 33
Email: david@dit.upm.es
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