BEHAVE WG M. Bagnulo
Internet-Draft UC3M
Intended status: Standards Track P. Matthews
Expires: January 5, 2010 Alcatel-Lucent
I. van Beijnum
IMDEA Networks
July 4, 2009
NAT64: Network Address and Protocol Translation from IPv6 Clients to
IPv4 Servers
draft-ietf-behave-v6v4-xlate-stateful-00
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Abstract
NAT64 is a mechanism for translating IPv6 packets to IPv4 packets and
vice-versa. DNS64 is a mechanism for synthesizing AAAA records from
A records. These two mechanisms together enable client-server
communication between an IPv6-only client and an IPv4-only server,
without requiring any changes to either the IPv6 or the IPv4 node,
for the class of applications that work through NATs. They also
enable peer-to-peer communication between an IPv4 and an IPv6 node,
where the communication can be initiated by either end using
existing, NAT-traversing, peer-to-peer communication techniques.
This document specifies NAT64, and gives suggestions on how they
should be deployed.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Features of NAT64 . . . . . . . . . . . . . . . . . . . . 5
1.2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.2.1. NAT64 solution elements . . . . . . . . . . . . . . . 6
1.2.2. Walkthrough . . . . . . . . . . . . . . . . . . . . . 7
1.2.3. Filtering . . . . . . . . . . . . . . . . . . . . . . 10
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 10
3. NAT64 Normative Specification . . . . . . . . . . . . . . . . 11
3.1. Determining the Incoming 5-tuple . . . . . . . . . . . . . 13
3.2. Filtering and Updating Session Information . . . . . . . . 14
3.2.1. UDP Session Handling . . . . . . . . . . . . . . . . . 14
3.2.2. TCP Session Handling . . . . . . . . . . . . . . . . . 15
3.3. Computing the Outgoing 5-Tuple . . . . . . . . . . . . . . 15
3.4. Translating the Packet . . . . . . . . . . . . . . . . . . 17
3.5. Handling Hairpinning . . . . . . . . . . . . . . . . . . . 17
3.6. Path MTU discovery and fragmentation . . . . . . . . . . . 18
3.6.1. Translating whole packets and PMTUD . . . . . . . . . 18
3.6.1.1. IPv6-to-IPv4 translation . . . . . . . . . . . . . 19
3.6.1.2. IPv4-to-IPv6 . . . . . . . . . . . . . . . . . . . 20
3.6.2. Fragmentation . . . . . . . . . . . . . . . . . . . . 20
3.6.2.1. IPv4-to-IPv6 . . . . . . . . . . . . . . . . . . . 20
3.6.2.2. IPv6-to-IPv4 . . . . . . . . . . . . . . . . . . . 22
3.6.3. TCP MSS option . . . . . . . . . . . . . . . . . . . . 22
4. Application scenarios . . . . . . . . . . . . . . . . . . . . 22
4.1. Enterprise IPv6 only network . . . . . . . . . . . . . . . 22
4.2. Reaching servers in private IPv4 space . . . . . . . . . . 23
5. Security Considerations . . . . . . . . . . . . . . . . . . . 24
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26
7. Changes from Previous Draft Versions . . . . . . . . . . . . . 26
8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 26
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 26
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 26
10.1. Normative References . . . . . . . . . . . . . . . . . . . 26
10.2. Informative References . . . . . . . . . . . . . . . . . . 27
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 28
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1. Introduction
This document specifies NAT64, a mechanism for IPv6-IPv4 transition
and co-existence. Together with DNS64 [I-D.bagnulo-behave-dns64],
these two mechanisms allow a IPv6-only client to initiate
communications to an IPv4-only server, and also allow peer-to-peer
communication between IPv6-only and IPv4-only hosts.
NAT64 is a mechanism for translating IPv6 packets to IPv4 packets.
The translation is done by translating the packet headers according
to SIIT [RFC2765], translating the IPv4 server address by adding or
removing an IPv6 prefix, and translating the IPv6 client address by
installing mappings in the normal NAT manner.
DNS64 is a mechanism for synthesizing AAAA resource records (RR) from
A RR. The synthesis is done by adding a IPv6 prefix to the IPv4
address to create an IPv6 address, where the IPv6 prefix is assigned
to a NAT64 device.
Together, these two mechanisms allow a IPv6-only client to initiate
communications to an IPv4-only server.
These mechanisms are expected to play a critical role in the IPv4-
IPv6 transition and co-existence. Due to IPv4 address depletion,
it's likely that in the future, a lot of IPv6-only clients will want
to connect to IPv4-only servers. The NAT64 and DNS64 mechanisms are
easily deployable, since they require no changes to either the IPv6
client nor the IPv4 server. For basic functionality, the approach
only requires the deployment of NAT64 function in the devices
connecting an IPv6-only network to the IPv4-only network, along with
the deployment of a few DNS64-enabled name servers in the IPv6-only
network. However, some advanced features such as support for DNSSEC
validating stub resolvers or support for some IPsec modes, require
software updates to the IPv6-only hosts.
The NAT64 and DNS64 mechanisms are related to the NAT-PT mechanism
defined in [RFC2766], but significant differences exist. First,
NAT64 does not define the NATPT mechanisms used to support IPv6 only
servers to be contacted by IPv4 only clients, but only defines the
mechanisms for IPv6 clients to contact IPv4 servers and its potential
reuse to support peer to peer communications through standard NAT
traversal techniques. Second, NAT64 includes a set of features that
overcomes many of the reasons the original NAT-PT specification was
moved to historic status [RFC4966].
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1.1. Features of NAT64
The features of NAT64 and DNS64 are:
o It enables IPv6-only nodes to initiate a client-server connection
with an IPv4-only server, without needing any changes on either
IPv4 or IPv6 nodes. This works for roughly the same class of
applications that work through IPv4-to-IPv4 NATs.
o It supports peer-to-peer communication between IPv4 and IPv6
nodes, including the ability for IPv4 nodes to initiate
communication with IPv6 nodes using peer-to-peer techniques (i.e.,
using a rendezvous server and ICE). To this end, NAT64 is
compliant with the recommendations for how NATs should handle UDP
[RFC4787], TCP [RFC4787], and ICMP [RFC5508].
o Compatible with ICE.
o Supports additional features with some changes on nodes. These
features include:
* Support for DNSSEC
* Some forms of IPsec support
1.2. Overview
This section provides a non-normative introduction to the mechanisms
of NAT64.
NAT64 mechanism is implemented in an NAT64 box which has two
interfaces, an IPv4 interface connected to the the IPv4 network, and
an IPv6 interface connected to the IPv6 network. Packets generated
in the IPv6 network for a receiver located in the IPv4 network will
be routed within the IPv6 network towards the NAT64 box. The NAT64
box will translate them and forward them as IPv4 packets through the
IPv4 network to the IPv4 receiver. The reverse takes place for
packets generated in the IPv4 network for an IPv6 receiver. NAT64,
however, is not symmetric. In order to be able to perform IPv6 -
IPv4 translation NAT64 requires state, binding an IPv6 address and
port (hereafter called an IPv6 transport address) to an IPv4 address
and port (hereafter called an IPv4 transport address).
Such binding state is created when the first packet flowing from the
IPv6 network to the IPv4 network is translated. After the binding
state has been created, packets flowing in either direction on that
particular flow are translated. The result is that NAT64 only
supports communications initiated by the IPv6-only node towards an
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IPv4-only node. Some additional mechanisms, like ICE, can be used in
combination with NAT64 to provide support for communications
initiated by the IPv4-only node to the IPv6-only node. The
specification of such mechanisms, however, is out of the scope of
this document.
1.2.1. NAT64 solution elements
In this section we describe the different elements involved in the
NAT64 approach.
The main component of the proposed solution is the translator itself.
The translator has essentially two main parts, the address
translation mechanism and the protocol translation mechanism.
Protocol translation from IPv4 packet header to IPv6 packet header
and vice-versa is performed according to SIIT [RFC2765].
Address translation maps IPv6 transport addresses to IPv4 transport
addresses and vice-versa. In order to create these mappings the
NAT64 box has two pools of addresses i.e. an IPv6 address pool (to
represent IPv4 addresses in the IPv6 network) and an IPv4 address
pool (to represent IPv6 addresses in the IPv4 network). Since there
is enough IPv6 address space, it is possible to map every IPv4
address into a different IPv6 address.
NAT64 creates the required mappings by using as the IPv6 address pool
an IPv6 IPv6 prefix (hereafter called Pref64::/96). This allows each
IPv4 address to be mapped into a different IPv6 address by simply
concatenating the /96 prefix assigned as the IPv6 address pool of the
NAT64, with the IPv4 address being mapped (i.e. an IPv4 address X is
mapped into the IPv6 address Pref64:X). The NAT64 prefix Pref64::/96
is assigned by the administrator of the NAT64 box from the global
unicast IPv6 address block assigned to the site.
The IPv4 address pool is a set of IPv4 addresses, normally a small
prefix assigned by the local administrator. Since IPv4 address space
is a scarce resource, the IPv4 address pool is small and typically
not sufficient to establish permanent one-to-one mappings with IPv6
addresses. So, mappings using the IPv4 address pool will be created
and released dynamically. Moreover, because of the IPv4 address
scarcity, the usual practice for NAT64 is likely to be the mapping of
IPv6 transport addresses into IPv4 transport addresses, instead of
IPv6 addresses into IPv4 addresses directly, which enable a higher
utilization of the limited IPv4 address pool.
Because of the dynamic nature of the IPv6 to IPv4 address mapping and
the static nature of the IPv4 to IPv6 address mapping, it is easy to
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understand that it is far simpler to allow communication initiated
from the IPv6 side toward an IPv4 node, which address is permanently
mapped into an IPv6 address, than communications initiated from IPv4-
only nodes to an IPv6 node in which case IPv4 address needs to be
associated with it dynamically. For this reason NAT64 supports only
communications initiated from the IPv6 side.
An IPv6 initiator can know or derive in advance the IPv6 address
representing the IPv4 target and send packets to that address. The
packets are intercepted by the NAT64 device, which associates an IPv4
transport address of its IPv4 pool to the IPv6 transport address of
the initiator, creating binding state, so that reply packets can be
translated and forwarded back to the initiator. The binding state is
kept while packets are flowing. Once the flow stops, and based on a
timer, the IPv4 transport address is returned to the IPv4 address
pool so that it can be reused for other communications.
To allow an IPv6 initiator to do the standard DNS lookup to learn the
address of the responder, DNS64 [I-D.bagnulo-behave-dns64] is used to
synthesize an AAAA RR from the A RR (containing the real IPv4 address
of the responder). DNS64 receives the DNS queries generated by the
IPv6 initiator. If there is no AAAA record available for the target
node (which is the normal case when the target node is an IPv4-only
node), DNS64 performs a query for the A record. If an A record is
discovered, DNS64 creates a synthetic AAAA RR by adding the
Pref64::/96 of a NAT64 to the responder's IPv4 address (i.e. if the
IPv4 node has IPv4 address X, then the synthetic AAAA RR will contain
the IPv6 address formed as Pref64:X). The synthetic AAAA RR is
passed back to the IPv6 initiator, which will initiate an IPv6
communication with the IPv6 address associated to the IPv4 receiver.
The packet will be routed to the NAT64 device, which will create the
IPv6 to IPv4 address mapping as described before.
1.2.2. Walkthrough
In this example, we consider an IPv6 node located in a IPv6-only site
that initiates a communication to a IPv4 node located in the IPv4
network.
The notation used is the following: upper case letters are IPv4
addresses; upper case letters with a prime(') are IPv6 addresses;
lower case letters are ports; prefixes are indicated by "P::X", which
is a IPv6 address built from an IPv4 address X by adding the prefix
P, mappings are indicated as "(X,x) <--> (Y',y)".
The scenario for this case is depicted in the following figure:
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+---------------------------------------+ +---------------+
|IPv6 network +-------------+ | | |
| +----+ | Name server | +-------+ | IPv4 |
| | H1 | | with DNS64 | | NAT64 |----| Network |
| +----+ +-------------+ +-------+ | |
| |IP addr: Y' | | | | IP addr: X |
| --------------------------------- | | +----+ |
+---------------------------------------+ | | H2 | |
| +----+ |
+---------------+
The figure shows a IPv6 node H1 which has an IPv6 address Y' and an
IPv4 node H2 with IPv4 address X.
A NAT64 connects the IPv6 network to the IPv4 network. This NAT64
has a /96 prefix (called Pref64::/96) that it uses to represent IPv4
addresses in the IPv6 address space and an IPv4 address T assigned to
its IPv4 interface. the routing is configured in such a way, that the
IPv6 packets addressed to a destination address containing
Pref64::/96 are routed to the IPv6 interface of the NAT64 box.
Also shown is a local name server with DNS64 functionality. The
local name server needs to know the /96 prefix assigned to the local
NAT64 (Pref64::/96). For the purpose of this example, we assume it
learns this through manual configuration.
For this example, assume the typical DNS situation where IPv6 hosts
have only stub resolvers and the local name server does the recursive
lookups.
The steps by which H1 establishes communication with H2 are:
1. H1 performs a DNS query for FQDN(H2) and receives the synthetic
AAAA RR from the local name server that implements the DNS64
functionality. The AAAA record contains an IPv6 address formed
by the PRefix64::/96 associated to the NAT64 box and the IPv4
address of H2 in the lower 32 bits.
2. H1 sends a packet to H2. The packet is sent from a source
transport address of (Y',y) to a destination transport address of
(Pref64:X,x), where y and x are ports set by H1.
3. The packet is routed to the IPv6 interface of the NAT64 (since
the IPv6 routing is configured that way).
4. The NAT64 receives the packet and performs the following actions:
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* The NAT64 selects an unused port t on its IPv4 address T and
creates the mapping entry (Y',y) <--> (T,t)
* The NAT64 translates the IPv6 header into an IPv4 header using
SIIT.
* The NAT64 includes (T,t) as source transport address in the
packet and (X,x) as destination transport address in the
packet. Note that X is extracted directly from the lower 32
bits of the destination IPv6 address of the received IPv6
packet that is being translated.
5. The NAT64 sends the translated packet out its IPv4 interface and
the packet arrives at H2.
6. H2 node responds by sending a packet with destination transport
address (T,t) and source transport address (X,x).
7. The packet is routed to the NAT64 box, which will look for an
existing mapping containing (T,t). Since the mapping (Y',y) <-->
(T,t) exists, the NAT64 performs the following operations:
* The NAT64 translates the IPv4 header into an IPv6 header using
SIIT.
* The NAT64 includes (Y',y) as destination transport address in
the packet and (Pref64:X,x) as source transport address in the
packet. Note that X is extracted directly from the source
IPv4 address of the received IPv4 packet that is being
translated.
8. The translated packet is sent out the IPv6 interface to H1.
The packet exchange between H1 and H2 continues and packets are
translated in the different directions as previously described.
It is important to note that the translation still works if the IPv6
initiator H1 learns the IPv6 representation of H2's IPv4 address
(i.e. Pref64:X) through some scheme other than a DNS look-up. This
is because the DNS64 processing does NOT result in any state
installed in the NAT64 box and because the mapping of the IPv4
address into an IPv6 address is the result of concatenating the
prefix defined within the site for this purpose (called Pref64::/96
in this document) to the original IPv4 address.
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1.2.3. Filtering
A NAT64 box may do filtering, which means that it only allows a
packet in through an interface if the appropriate permission exists.
A NAT64 may do no filtering, or it may filter on its IPv4 interface.
Filtering on the IPv6 interface is not supported, as mappings are
only created by packets traveling in the IPv6 --> IPv4 direction.
If a NAT64 performs address-dependent filtering according to RFC4787
[RFC4787] on its IPv4 interface, then an incoming packet is dropped
unless a packet has been recently sent out the interface with a
source transport address equal to the destination transport address
of the incoming packet and destination IP address equal to the source
IP address of the incoming packet.
NAT64 filtering is consistent with the recommendations of RFC 4787
[RFC4787], and the ones of RFC 5382 [RFC5382]
2. Terminology
This section provides a definitive reference for all the terms used
in 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 [RFC2119].
The following terms are used in this document:
5-Tuple: The tuple (source IP address, source port, destination IP
address, destination port, transport protocol). A 5-tuple
uniquely identifies a session. When a session flows through a
NAT64, each session has two different 5-tuples: one with IPv4
addresses and one with IPv6 addresses.
BIB: Binding Information Base. A table of mappings kept by a NAT64.
Each NAT64 has two BIBs, one for TCP and one for UDP.
DNS64: A logical function that synthesizes AAAA Resource Records
(containing IPv6 addresses) from A Resource Records (containing
IPv4 addresses).
Endpoint-Independent Mapping: In NAT64, using the same mapping for
all the sessions involving a given IPv6 transport address of an
IPv6 host (irrespectively of the transport address of the IPv4
host involved in the communication). Endpoint-independent mapping
is important for peer-to-peer communication. See [RFC4787] for
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the definition of the different types of mappings in IPv4-to-IPv4
NATs.
Hairpinning: Having a packet do a "U-turn" inside a NAT and come
back out the same interface as it arrived on. Hairpinning support
is important for peer-to-peer applications, as there are cases
when two different hosts on the same side of a NAT can only
communicate using sessions that hairpin though the NAT.
Mapping: A mapping between an IPv6 transport address and a IPv4
transport address. Used to translate the addresses and ports of
packets flowing between the IPv6 host and the IPv4 host. In
NAT64, the IPv4 transport address is always a transport address
assigned to the NAT64 itself, while the IPv6 transport address
belongs to some IPv6 host.
NAT64: A device that translates IPv6 packets to IPv4 packets and
vice-versa, with the provision that the communication must be
initiated from the IPv6 side. The translation involves not only
the IP header, but also the transport header (TCP or UDP).
Session: A TCP or UDP session. In other words, the bi-directional
flow of packets between two ports on two different hosts. In
NAT64, typically one host is an IPv4 host, and the other one is an
IPv6 host.
Session table: A table of sessions kept by a NAT64. Each NAT64 has
two session tables, one for TCP and one for UDP.
Synthetic RR: A DNS Resource Record (RR) that is not contained in
any zone data file, but has been synthesized from other RRs. An
example is a synthetic AAAA record created from an A record.
Transport Address: The combination of an IPv6 or IPv4 address and a
port. Typically written as (IP address, port); e.g. (192.0.2.15,
8001).
For a detailed understanding of this document, the reader should also
be familiar with DNS terminology [RFC1035] and current NAT
terminology [RFC4787].
3. NAT64 Normative Specification
A NAT64 is a device with at least one IPv6 interface and at least one
IPv4 interface. Each NAT64 device MUST have one unicast /96 IPv6
prefix assigned to it, denoted Pref64::/96. Each NAT64 box MUST have
one or more unicast IPv4 addresses assigned to it.
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A NAT64 uses the following dynamic data structures:
o UDP Binding Information Base
o UDP Session Table
o TCP Binding Information Base
o TCP Session Table
A NAT64 has two Binding Information Bases (BIBs): one for TCP and one
for UDP. Each BIB entry specifies a mapping between an IPv6
transport address and an IPv4 transport address:
(X',x) <--> (T,t)
where X' is some IPv6 address, T is an IPv4 address, and x and t are
ports. T will always be one of the IPv4 addresses assigned to the
NAT64 A given IPv6 or IPv4 transport address can appear in at most
one entry in a BIB: for example, (2001:db8::17, 4) can appear in at
most one TCP and at most one UDP BIB entry. TCP and UDP have
separate BIBs because the port number space for TCP and UDP are
distinct.
A NAT64 also has two session tables: one for TCP sessions and one for
UDP sessions. Each entry keeps information on the state of the
corresponding session: see Section 3.2. The NAT64 uses the session
state information to determine when the session is completed, and
also uses session information for ingress filtering. A session can
be uniquely identified by either an incoming 5-tuple or an outgoing
5-tuple.
For each session, there is a corresponding BIB entry, uniquely
specified by either the source IPv6 transport address (in the IPv6
--> IPv4 direction) or the destination IPv4 transport address (in the
IPv4 --> IPv6 direction). However, a single BIB entry can have
multiple corresponding sessions. When the last corresponding session
is deleted, the BIB entry is deleted.
The processing of an incoming IP packet takes the following steps:
1. Determining the incoming 5-tuple
2. Filtering and updating session information
3. Computing the outgoing 5-tuple
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4. Translating the packet
5. Handling hairpinning
The details of these steps are specified in the following
subsections.
This breakdown of the NAT64 behavior into processing steps is done
for ease of presentation. A NAT64 MAY perform the steps in a
different order, or MAY perform different steps, as long as the
externally visible outcome is the same.
TBD: Add support for ICMP Query packets. (ICMP Error packets are
handled).
3.1. Determining the Incoming 5-tuple
This step associates a incoming 5-tuple (source IP address, source
port, destination IP address, destination port, transport protocol)
with every incoming IP packet for use in subsequent steps.
If the incoming IP packet contains a complete (un-fragmented) UDP or
TCP protocol packet, then the 5-tuple is computed by extracting the
appropriate fields from the packet.
If the incoming IP packet contains a complete (un-fragmented) ICMP
error message, then the 5-tuple is computed by extracting the
appropriate fields from the IP packet embedded inside the ICMP error
message. However, the role of source and destination is swapped when
doing this: the embedded source IP address becomes the destination IP
address in the 5-tuple, the embedded source port becomes the
destination port in the 5-tuple, etc. If it is not possible to
determine the 5-tuple (perhaps because not enough of the embedded
packet is reproduced inside the ICMP message), then the incoming IP
packet is silently discarded.
NOTE: The transport protocol is always one of TCP or UDP, even if
the IP packet contains an ICMP message.
If the incoming IP packet contains a fragment, then more processing
may be needed. This specification leaves open the exact details of
how a NAT64 handles incoming IP packets containing fragments, and
simply requires that a NAT64 handle fragments arriving out-of-order.
A NAT64 MAY elect to queue the fragments as they arrive and translate
all fragments at the same time. Alternatively, a NAT64 MAY translate
the fragments as they arrive, by storing information that allows it
to compute the 5-tuple for fragments other than the first. In the
latter case, the NAT64 will still need to handle the situation where
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subsequent fragments arrive before the first.
Implementors of NAT64 should be aware that there are a number of
well-known attacks against IP fragmentation; see [RFC1858] and
[RFC3128].
Assuming it otherwise has sufficient resources, a NAT64 MUST allow
the fragments to arrive over a time interval of at least 10 seconds.
A NAT64 MAY require that the UDP, TCP, or ICMP header be completely
contained within the first fragment.
3.2. Filtering and Updating Session Information
This step updates the per-session information stored in the
appropriate session table. This affects the lifetime of the session,
which in turn affects the lifetime of the corresponding BIB entry.
This step may also filter incoming packets, if desired.
The details of this step depend on the transport protocol (UDP or
TCP).
3.2.1. UDP Session Handling
The state information stored for a UDP session is a timer that tracks
the remaining lifetime of the UDP session. The NAT64 decrements this
timer at regular intervals. When the timer expires, the UDP session
is deleted.
The incoming packet is processed as follows:
1. If the packet arrived on the IPv4 interface and the NAT64 filters
on its IPv4 interface, then the NAT64 checks to see if the
incoming packet is allowed according to the address-dependent
filtering rule. To do this, it searches for a session table
entry with a source IPv4 transport address equal to the
destination IPv4 transport address in the incoming 5-tuple and
destination IPv4 address (in the session table entry) equal to
the source IPv4 address in the incoming 5-tuple. If such an
entry is found (there may be more than one), packet processing
continues. Otherwise, the packet is discarded. If the packet is
discarded, then an ICMP message MAY be sent to the original
sender of the packet, unless the discarded packet is itself an
ICMP message. The ICMP message, if sent, has a type of 3
(Destination Unreachable) and a code of 13 (Communication
Administratively Prohibited).
2. The NAT64 searches for the session table entry corresponding to
the incoming 5-tuple. If no such entry is found, a new entry is
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created.
3. The NAT64 sets or resets the timer in the session table entry to
maximum session lifetime. By default, the maximum session
lifetime is 5 minutes, but for specific destination ports in the
Well-Known port range (0..1023), the NAT64 MAY use a smaller
maximum lifetime.
3.2.2. TCP Session Handling
TBD: Describe the state machine required to track the state of the
TCP session. This is a simplified version of the state machine used
by the endpoints.
3.3. Computing the Outgoing 5-Tuple
This step computes the outgoing 5-tuple by translating the addresses
and ports in the incoming 5-tuple. The transport protocol in the
outgoing 5-tuple is always the same as that in the incoming 5-tuple.
In the text below, a reference to the the "BIB" means either the TCP
BIB or the UDP BIB as appropriate, as determined by the transport
protocol in the 5-tuple.
NOTE: Not all addresses are translated using the BIB. BIB entries
are used to translate IPv6 source transport addresses to IPv4
source transport addresses, and IPv4 destination transport
addresses to IPv6 destination transport addresses. They are NOT
used to translate IPv6 destination transport addresses to IPv4
destination transport addresses, nor to translate IPv4 source
transport addresses to IPv6 source transport addresses. The
latter cases are handled by adding or removing the /96 prefix.
This distinction is important; without it, hairpinning doesn't
work correctly.
When translating in the IPv6 --> IPv4 direction, let the incoming
source and destination transport addresses in the 5-tuple be (S',s)
and (D',d) respectively. The outgoing source transport address is
computed as follows:
If the BIB contains a entry (S',s) <--> (T,t), then the outgoing
source transport address is (T,t).
Otherwise, create a new BIB entry (S',s) <--> (T,t) as described
below. The outgoing source transport address is (T,t).
The outgoing destination address is computed as follows:
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If D' is composed of the NAT64's prefix followed by an IPv4
address D, then the outgoing destination transport address is
(D,d).
Otherwise, discard the packet.
If the rules specify that a new BIB entry is created for a source
transport address of (S',s), then the NAT64 allocates an IPv4
transport address for this BIB entry as follows:
If there exists some other BIB entry containing S' as the IPv6
address and mapping it to some IPv4 address T, then use T as the
IPv4 address. Otherwise, use any IPv4 address assigned to the
IPv4 interface.
If the port s is in the Well-Known port range 0..1023, then
allocate a port t from this same range. Otherwise, if the port s
is in the range 1024..65535, then allocate a port t from this
range. Furthermore, if port s is even, then t must be even, and
if port s is odd, then t must be odd.
In all cases, the allocated IPv4 transport address (T,t) MUST NOT
be in use in another entry in the same BIB, but MAY be in use in
the other BIB.
If it is not possible to allocate an appropriate IPv4 transport
address or create a BIB entry for some reason, then the packet is
discarded.
When translating in the IPv4 --> IPv6 direction, let the incoming
source and destination transport addresses in the 5-tuple be (S,s)
and (D,d) respectively. The outgoing source transport address is
computed as follows:
The outgoing source transport address is (Pref64::S,s).
The outgoing destination transport address is computed as follows:
If the BIB contains an entry (X',x) <--> (D,d), then the outgoing
destination transport address is (X',x).
Otherwise, discard the packet.
TBD: Do we delete the session entry if we cannot create a BIB entry?
[R/T] Yes, we think that the session entry should be deleted if we
cannot create a BIB entry as it wouldn't make much sense to have a
session entry without a BIB entry. Greg: I don't think you can make
a Session Table entry if you cannont create a BIB entry. You have to
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look up BIB first, to determine the correct outgoing (T,t), or to
make a new BIB entry. Only after that result can you create a
completed Session Table entry.
If the rules specify that the packet is discarded, then the NAT64 MAY
send an ICMP reply to the original sender, unless the packet being
translated contains an ICMP message. The type should be 3
(Destination Unreachable) and the code should be 0 (Network
Unreachable in IPv4, and No Route to Destination in IPv6).
3.4. Translating the Packet
This step translates the packet from IPv6 to IPv4 or vice-versa.
The translation of the packet is as specified in section 3 and
section 4 of SIIT [RFC2765], with the following modifications:
o When translating an IP header (sections 3.1 and 4.1), the source
and destination IP address fields are set to the source and
destination IP addresses from the outgoing 5-tuple.
o When the protocol following the IP header is TCP or UDP, then the
source and destination ports are modified to the source and
destination ports from the outgoing 5-tuple. In addition, the TCP
or UDP checksum must also be updated to reflect the translated
addresses and ports; note that the TCP and UDP checksum covers the
pseudo-header which contains the source and destination IP
addresses. An algorithm for efficiently updating these checksums
is described in [RFC3022].
o When the protocol following the IP header is ICMP (sections 3.4
and 4.4) and it is an ICMP error message, the source and
destination transport addresses in the embedded packet are set to
the destination and source transport addresses from the outgoing
5-tuple (note the swap of source and destination).
3.5. Handling Hairpinning
This step handles hairpinning if necessary.
If the destination IP address is an address assigned to the NAT64
itself (i.e., is one of the IPv4 addresses assigned to the IPv4
interface, or is covered by the /96 prefix assigned to the IPv6
interface), then the packet is a hairpin packet. The outgoing
5-tuple becomes the incoming 5-tuple, and the packet is treated as if
it was received on the outgoing interface. Processing of the packet
continues at step 2.
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[R/T] The reference to step 2 here was a little confusing to us. Are
you referring to Filtering and Updating Session Information (Section
3.2)? MB> I am not sure about this anymore. I mean what if the
packet that is being hairpinned is an ICMP error msge, I mean don't
we still need step 1?
TBD: Is there such a thing as a hairpin loop (likely not naturally,
but perhaps through a special-crafted attack packet with a spoofed
source address)? If so, need to drop packets that hairpin more than
once.
3.6. Path MTU discovery and fragmentation
It's the job of the network layer to adapt to different maximum
packet sizes as packets move through the network. There are three
mechanisms that handle this: transport layer negotiations such as the
TCP MSS option, path MTU discovery and fragmentation. The difference
between the IPv4 and IPv6 header sizes requires some handling in a
NAT64 translator, and there are complications because of the
differences between how IPv4 and IPv6 handle fragmentation, as well
as the issue of how to demultiplex fragmented IPv4 packets.
The vast majority of both IPv4 and IPv6 hosts use path MTU discovery
[RFC1191] [RFC1981]. With IPv4, PMTUD can be enabled on a per-packet
basis by setting the DF bit to 1. With IPv6, there is no need for
PMTUD for packets up to 1280 bytes because all IPv6 hosts are
required to be able to receive 1280-byte packets without
fragmentation. When sending larger packets, IPv6 hosts implicitly
use PMTUD.
The fragmentation behavior specified in [RFC2765] is that upon the
reception of an ICMPv6 "packet too big" message with an indicated
packet size of less than 1280 octets, IPv6 hosts will transmit 1280-
octet packets, but include a fragment header in those packets. In a
stateful translator, the identification value in this fragment header
can't be used, so the fragment header itself serves no purpose.
Additionally, the presence or absense of the fragment header isn't
enough to determine whether to set the DF bit in packets translated
to IPv4 to 0 (fragment header present) or 1 (no fragment header
present). The reason for this is that operators may decide to forego
path MTU discovery by configuring an MTU of 1280 and filtering
incoming "too big" messages. The behavior specified below is meant
to avoid PMTUD black holes in this situation
3.6.1. Translating whole packets and PMTUD
This section specifies the values in the fragmentation-related fields
in the IPv4 header when no fragmentation occurs, and how path MTU
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discovery is handled.
3.6.1.1. IPv6-to-IPv4 translation
If the NAT64 has the same MTUs on its IPv6 and IPv4 interfaces, it
will never have to generate "packet too big" messages for incoming
IPv6 packets because the translation from IPv6 to IPv4 reduces the
packet size by 20 bytes, more if the IPv6 packet has extension
headers that are removed during the translation, such as the fragment
header. If the MTU on the IPv6 side is larger than 1280 bytes and
more than 20 bytes smaller than the MTU on the IPv4 side, the NAT64
MUST generate the appropriate "packet too big" messages on the IPv6
side.
To support PMTUD, for translated packets that are larger than 1260
bytes on the IPv4 side (1280 bytes IPv6 packets with 20 byte size
reduction through the translation), the DF bit is set to 1 in the
resulting IPv4 packet.
IPv4 routers may generate "packet too big" messages indicating a
supported MTU size smaller than 1280 bytes. In those cases, the IPv6
hosts will continue to send packets larger than what the IPv4 path
MTU can support. To allow packets to be delivered successfully in
this case, the DF bit is set to 0 in all translated packets smaller
than or equal to 1260 bytes, to allow these packets to be fragmented
in the IPv4 network.
Note: it is highly recommended for IPv4 hosts running services that
may be used by IPv6 clients through a NAT64 translator to use an MTU
size of at least 1260 bytes and to properly generate "packet too big"
messages.
When a NAT64 translates "packet too big" messages from IPv6 to IPv4,
it adjusts the advertised MTU to the minimum of the original
advertised MTU + 20, the NAT64's MTU on the IPv6 side + 20 and the
NAT64's MTU on the IPv4 side.
The identification field in the IPv4 header MUST be filled with a
value generated by the NAT64 translator, similar to the way that
identification values are created for locally generated packets. It
is RECOMMENDED that a NAT64 translator keep an identification counter
for every combination of remote IPv4 destination and protocol.
In theory, IPv4 packets with DF set to 1 don't need a unique
identification value. However, it is not unheard of for operators to
configure equipment to clear the DF bit, at which time an
identification value with good uniqueness becomes necessary. As
such, it is recommended that translators include a unique
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identification value in all packets, including those with DF set to
1. However, since more packets will be sent with DF set to 1, this
will use up identification values faster. Implementations may choose
to segment the identification space and assign values from non-
overlapping pools to packets with DF set to 0 and DF set to 1 to
provide a longer period of uniqueness to fragmentable packets.
3.6.1.2. IPv4-to-IPv6
Because it may be necessary to include a fragmentation header or
other extension header, the NAT64 MUST be prepared to generate
"packet too big" messages for packets with the DF bit set to 1
received from the IPv4 side, regardless of the MTU sizes on the IPv4
and IPv6 interfaces. If the packet with DF = 1 is larger than can be
transmitted on the IPv6 side after translation, the NAT64 returns a
"packet too big" message indicating the maximum IPv4 packet size that
would be supported using the same translation as the current packet.
This can be calculated as IPv4-packet-size - 20.
When a NAT64 translates "packet too big" messages from IPv4 to IPv6,
it adjusts the advertised MTU to the minimum of the original
advertised MTU - 20, the NAT64's MTU on the IPv6 side and the NAT64's
MTU on the IPv4 side - 20. However, if the advertised MTU in "packet
too big" messages is smaller than 1260 bytes, the value put into the
translated "packet too big" message is 1280. This makes sure that
the IPv6 host will limit its packet sizes to 1280 bytes, so its
packets are subsequently translated into IPv4 packets with DF set to
0. (This deviates from [RFC2765].)
3.6.2. Fragmentation
Because NAT deviates from normal router behavior, the limitation that
IPv6 packets or IPv4 packets with DF set to 1 are not fragmented by
routers doesn't apply to a NAT64 translator. Where appropriate,
these packets are fragmented after translation as described below.
3.6.2.1. IPv4-to-IPv6
Because packets coming in on the IPv4 side may be larger than 1280
bytes after translation, a NAT64 MUST implement PMTUD on the IPv6
side. In other words, it must react to "packet too big" messages for
any IPv6 destination that it communicates with by limiting the size
of the packets that it sends to the advertised maximum.
In the case where, after translation from IPv4 to IPv6, a packet is
larger than a destination's PMTU, the NAT64 returns a "packet too
big" as outlined earlier in the case that the DF bit was set to 1 in
the IPv4 packet. If the DF bit was set to 0, the translator first
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translates the IPv4 packet, and then fragments the resulting IPv6
packets using normal IPv6 fragmentation rules. The lower 16 bits of
the IPv6 identification field are copied from the IPv4 identification
field. The upper 16 bits of the IPv6 identification field are set to
0.
Because NAT64 provides a stateful many-to-one (perhaps even many-to-
many) translation, it is necessary to recognize which session a given
packet belongs to. In the IPv4-to-IPv6 direction, the TCP or UDP
port numbers must be known to accomplish this, but the port numbers
only occur in the first fragment of a fragmented packet. There are
two possible ways to deal with this:
1. Reassemble the packet before translating it.
2. Create translation state for the fragments belonging to the same
packet so each packet can be translated.
Strategy 2 is attractive in large installations because it requires
less storage and processing. However, it may still be necessary to
buffer fragments for some time, as the fragment containing the first
part of the packet (and with that, the port numbers) may not be the
first one to arrive.
Note: based on the assumptions that hosts generate fragments in-order
and that reordering must happen through parallel network links and
that the path between these parallel links and a NAT64 supports
speeds of at least 10 Mbps, there is a very high probability that two
out-of-order fragments making up a packet will arrive at the NAT64
within 50 to 100 milliseconds. Further assuming that fragmented
traffic makes up less than 10% of all traffic, this only requires a
buffer of 6 to 12,500 fragments (50 ms at 10 Mbps to 100 ms at 10
Gbps).
In some cases, there may only be a single session matching the
fragment's source and destination addresses and protocol number. In
these cases, it would be possible to translate the fragments out-of-
order. A NAT64 translator MAY do this for TCP, however, it MUST NOT
translate UDP packets before the first fragment is available. The
reason for this is that the fragment could be part of a packet
setting up a new session. However, with TCP session establishment
packets don't carry data, so it's extremely unlikely that they are
fragmented. This is not the case with UDP, and in the IPv4-to-IPv6
direction, a UDP packet may have a zero checksum, which must be
recalculated when translating to IPv6, for which the entire packet
must be available.
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3.6.2.2. IPv6-to-IPv4
For all IPv4 packets that the NAT64 creates through translation, the
translator generates an ID value. This applies to all packets,
regardless of their size or the value of the DF field. A NAT64
translator MAY employ strategies to avoid reusing an ID value for a
certain source, destination, protocol tuple as long as possible. If
the IPv4 packets are fragments of an IPv6 packet, then state is
created that makes it possible for all the fragments to have the same
ID value on the IPv4 side.
[RFC2765] specifies copying the lower bits from the IPv6 ID field in
a fragment header (if present) to the IPv4 ID field, but this runs
the risk of two IPv6 hosts talking to the same IPv4 destination
through the NAT64 using the same ID value.
Otherwise, when translating IPv6 packets with a fragmentation header,
the fragments are translated as per [RFC2765].
In the IPv6-to-IPv4 direction, there is no need to map a fragment to
the session it belongs to in order to translate the fragment.
However, it is necessary that all the fragments have the same
identification value, so fragments may be translated individually,
but state must be kept to be able to translate subsequent fragments
of the same packet using the same identification value on the IPv4
side.
3.6.3. TCP MSS option
It is not recommended that NAT64 translators rewrite the TCP MSS
option [RFC0793]. As such, assuming the common case of all 1500-
octet MTUs, an IPv6 host will advertise a 1440-octet MSS, triggering
the IPv4 host to generate 1480-octet packets that are translated to
1500-octet IPv6 packets. IPv4 hosts will advertise a 1460-octet MSS,
which would be 1520-octet IPv6 packets. However, ethernet-connected
IPv6 hosts can only send 1500-octet packets, so in the all-ethernet
case, there is no dependency on path MTU discovery.
4. Application scenarios
In this section, we describe how to apply NAT64/DNS64 to the suitable
scenarios described in draft-arkko-townsley-coexistence.
4.1. Enterprise IPv6 only network
The Enterprise IPv6 only network basically has IPv6 hosts (those that
are currently available) and because of different reasons including
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operational simplicity, wants to run those hosts in IPv6 only mode,
while still providing access to the IPv4 Internet. The scenario is
depicted in the picture below.
+----+ +-------------+
| +------------------+IPv6 Internet+
| | +-------------+
IPv6 host-----------------+ GW |
| | +-------------+
| +------------------+IPv4 Internet+
+----+ +-------------+
|-------------------------public v6-----------------------------|
|-------public v6---------|NAT|----------public v4--------------|
The proposed NAT64/DNS64 is perfectly suitable for this particular
scenario. The deployment of the NAT64/DNS64 would be as follows: The
NAT64 function should be located in the GW device that connects the
IPv6 site to the IPv4 Internet. The DNS64 functionality can be
placed either in the local recursive DNS server or in the local
resolver in the hosts.
The proposed NAT64/DNS64 approach satisfies the requirements of this
scenario, in particular because it doesn't require any changes to
current IPv6 hosts in the site to obtain basic functionality.
4.2. Reaching servers in private IPv4 space
The scenario of servers using IPv4 private addresses and being
reached from the IPv6 Internet basically includes the cases that for
whatever reason the servers cannot be upgraded to IPv6 and they don't
have public IPv4 addresses and it would be useful to allow IPv6 nodes
in the IPv6 Internet to reach those servers. This scenario is
depicted in the figure below.
+----+
IPv6 Host(s)-------(Internet)-----+ GW +------Private IPv4 Servers
+----+
|---------public v6---------------|NAT|------private v4----------|
This scenario can again be perfectly served by the NAT64 approach.
In this case the NAT64 functionality is placed in the GW device
connecting the IPv6 Internet to the server's site. In this case, the
DNS64 functionality is not required in general since real (i.e. non
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synthetic) AAAA RRs for the IPv4 servers containing the IPv6
representation of the IPv4 address of the servers can be created.
See more discussion about this in [I-D.bagnulo-behave-dns64]
Again, this scenario is satisfied by the NAT64 since it supports the
required functionality without requiring changes in the IPv4 servers
nor in the IPv6 clients.
5. Security Considerations
Implications on end-to-end security.
Any protocol that protect IP header information are essentially
incompatible with NAT64. So, this implies that end to end IPSec
verification will fail when AH is used (both transport and tunnel
mode) and when ESP is used in transport mode. This is inherent to
any network layer translation mechanism. End-to-end IPsec protection
can be restored, using UDP encapsulation as described in [RFC3948].
Filtering.
NAT64 creates binding state using packets flowing from the IPv6 side
to the IPv4 side. In accordance with the procedures defined in this
document following the guidelines defined in RFC 4787 [RFC4787] a
NAT64 must offer "enpoint independent filtering". This means:
for any IPv6 side packet with source (S'1,s1) and destination
(Pref64::D1,d1) that creates an external mapping to (S1,s1),
(D1,d1),
for any subsequent external connection to from S'1 to (D2,d2)
within a given binding timer window,
(S1,s1) = (S2,s2) for all values of D2,d2
Implementations may also provide support for "Address-Dependent
Mapping" and "Address and Port-Dependent Mapping", as also defined in
this document and following the guidelines defined in RFC 4787
[RFC4787].
The security properties however are determined by which packets the
NAT64 filter allows in and which it does not. The security
properties are determined by the filtering behavior and filtering
configuration in the filtering portions of the NAT64, not by the
address mapping behavior. For example,
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Without filtering - When "endpoint independent filtering" is used
in NAT64, once a binding is created in the IPv6 ---> IPv4
direction, packets from any node on the IPv4 side destined to the
IPv6 transport address will traverse the NAT64 gateway and be
forwarded to the IPv6 transport address that created the binding.
However,
With filtering - When "endpoint independent filtering" is used in
NAT64, once a binding is created in the IPv6 ---> IPv4 direction,
packets from any node on the IPv4 side destined to the IPv6
transport address will first be processed against the filtering
rules. If the source IPv4 address is permitted, the packets will
be forwarded to the IPv6 transport address. If the source IPv4
address is explicitly denied -- or the default policy is to deny
all addresses not explicitly permitted -- then the packet will
discarded. A dynamic filter may be employed where by the filter
will only allow packets from the IPv4 address to which the
original packet that created the binding was sent. This means
that only the D IPv4 addresses to which the IPv6 host has
initiated connections will be able to reach the IPv6 transport
address, and no others. This essentially narrows the effective
operation of the NAT64 device to a "Address Dependent" behavior,
though not by its mapping behavior, but instead by its filtering
behavior.
Attacks to NAT64.
The NAT64 device itself is a potential victim of different type of
attacks. In particular, the NAT64 can be a victim of DoS attacks.
The NAT64 box has a limited number of resources that can be consumed
by attackers creating a DoS attack. The NAT64 has a limited number
of IPv4 addresses that it uses to create the bindings. Even though
the NAT64 performs address and port translation, it is possible for
an attacker to consume all the IPv4 transport addresses by sending
IPv6 packets with different source IPv6 transport addresses. It
should be noted that this attack can only be launched from the IPv6
side, since IPv4 packets are not used to create binding state. DoS
attacks can also affect other limited resources available in the
NAT64 such as memory or link capacity. For instance, it is possible
for an attacker to launch a DoS attack to the memory of the NAT64
device by sending fragments that the NAT64 will store for a given
period. If the number of fragments is high enough, the memory of the
NAT64 could be exhausted. NAT64 devices should implement proper
protection against such attacks, for instance allocating a limited
amount of memory for fragmented packet storage.
6. IANA Considerations
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7. Changes from Previous Draft Versions
Note to RFC Editor: Please remove this section prior to publication
of this document as an RFC.
[[This section lists the changes between the various versions of this
draft.]]
8. Contributors
George Tsirtsis
Qualcomm
tsirtsis@googlemail.com
Greg Lebovitz
Juniper
gregory.ietf@gmail.com
9. Acknowledgements
Dave Thaler, Dan Wing, Alberto Garcia-Martinez, Reinaldo Penno and
Joao Damas reviewed the document and provided useful comments to
improve it.
The content of the draft was improved thanks to discussions with Fred
Baker and Jari Arkko.
Marcelo Bagnulo and Iljitsch van Beijnum are partly funded by
Trilogy, a research project supported by the European Commission
under its Seventh Framework Program.
10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987.
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[RFC2671] Vixie, P., "Extension Mechanisms for DNS (EDNS0)",
RFC 2671, August 1999.
[RFC2765] Nordmark, E., "Stateless IP/ICMP Translation Algorithm
(SIIT)", RFC 2765, February 2000.
[RFC4787] Audet, F. and C. Jennings, "Network Address Translation
(NAT) Behavioral Requirements for Unicast UDP", BCP 127,
RFC 4787, January 2007.
[RFC3484] Draves, R., "Default Address Selection for Internet
Protocol version 6 (IPv6)", RFC 3484, February 2003.
[RFC3948] Huttunen, A., Swander, B., Volpe, V., DiBurro, L., and M.
Stenberg, "UDP Encapsulation of IPsec ESP Packets",
RFC 3948, January 2005.
[RFC5382] Guha, S., Biswas, K., Ford, B., Sivakumar, S., and P.
Srisuresh, "NAT Behavioral Requirements for TCP", BCP 142,
RFC 5382, October 2008.
[RFC5508] Srisuresh, P., Ford, B., Sivakumar, S., and S. Guha, "NAT
Behavioral Requirements for ICMP", BCP 148, RFC 5508,
April 2009.
[I-D.bagnulo-behave-dns64]
Bagnulo, M., Sullivan, A., Matthews, P., Beijnum, I., and
M. Endo, "DNS64: DNS extensions for Network Address
Translation from IPv6 Clients to IPv4 Servers",
draft-bagnulo-behave-dns64-02 (work in progress),
March 2009.
10.2. Informative References
[RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191,
November 1990.
[RFC1981] McCann, J., Deering, S., and J. Mogul, "Path MTU Discovery
for IP version 6", RFC 1981, August 1996.
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7,
RFC 793, September 1981.
[RFC2766] Tsirtsis, G. and P. Srisuresh, "Network Address
Translation - Protocol Translation (NAT-PT)", RFC 2766,
February 2000.
[RFC1858] Ziemba, G., Reed, D., and P. Traina, "Security
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Considerations for IP Fragment Filtering", RFC 1858,
October 1995.
[RFC3128] Miller, I., "Protection Against a Variant of the Tiny
Fragment Attack (RFC 1858)", RFC 3128, June 2001.
[RFC3022] Srisuresh, P. and K. Egevang, "Traditional IP Network
Address Translator (Traditional NAT)", RFC 3022,
January 2001.
[RFC4966] Aoun, C. and E. Davies, "Reasons to Move the Network
Address Translator - Protocol Translator (NAT-PT) to
Historic Status", RFC 4966, July 2007.
[I-D.ietf-mmusic-ice]
Rosenberg, J., "Interactive Connectivity Establishment
(ICE): A Protocol for Network Address Translator (NAT)
Traversal for Offer/Answer Protocols",
draft-ietf-mmusic-ice-19 (work in progress), October 2007.
[RFC3498] Kuhfeld, J., Johnson, J., and M. Thatcher, "Definitions of
Managed Objects for Synchronous Optical Network (SONET)
Linear Automatic Protection Switching (APS)
Architectures", RFC 3498, March 2003.
Authors' Addresses
Marcelo Bagnulo
UC3M
Av. Universidad 30
Leganes, Madrid 28911
Spain
Phone: +34-91-6249500
Fax:
Email: marcelo@it.uc3m.es
URI: http://www.it.uc3m.es/marcelo
Bagnulo, et al. Expires January 5, 2010 [Page 28]
Internet-Draft NAT64 July 2009
Philip Matthews
Unaffiliated
600 March Road
Ottawa, Ontario
Canada
Phone: +1 613-592-4343 x224
Fax:
Email: philip_matthews@magma.ca
URI:
Iljitsch van Beijnum
IMDEA Networks
Avda. del Mar Mediterraneo, 22
Leganes, Madrid 28918
Spain
Email: iljitsch@muada.com
Bagnulo, et al. Expires January 5, 2010 [Page 29]
