Network Working Group O. Troan
Internet-Draft W. Dec
Intended status: Standards Track Cisco Systems
Expires: September 19, 2013 X. Li
C. Bao
CERNET Center/Tsinghua University
S. Matsushima
SoftBank Telecom
T. Murakami
IP Infusion
March 18, 2013
Mapping of Address and Port with Encapsulation (MAP)
draft-ietf-softwire-map-05
Abstract
This document describes a mechanism for transporting IPv4 packets
across an IPv6 network using IP encapsulation, and a generic
mechanism for mapping between IPv6 addresses and IPv4 addresses and
transport layer ports.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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Internet-Drafts are draft documents valid for a maximum of six months
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This Internet-Draft will expire on September 19, 2013.
Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Architecture . . . . . . . . . . . . . . . . . . . . . . . . . 5
5. Mapping Algorithm . . . . . . . . . . . . . . . . . . . . . . 6
5.1. Port mapping algorithm . . . . . . . . . . . . . . . . . . 8
5.2. Basic mapping rule (BMR) . . . . . . . . . . . . . . . . . 9
5.3. Forwarding mapping rule (FMR) . . . . . . . . . . . . . . 11
5.4. Destinations outside the MAP domain . . . . . . . . . . . 11
6. The IPv6 Interface Identifier . . . . . . . . . . . . . . . . 12
7. MAP Configuration . . . . . . . . . . . . . . . . . . . . . . 12
7.1. MAP CE . . . . . . . . . . . . . . . . . . . . . . . . . . 12
7.2. MAP BR . . . . . . . . . . . . . . . . . . . . . . . . . . 13
7.3. Backwards compatibility . . . . . . . . . . . . . . . . . 13
8. Forwarding Considerations . . . . . . . . . . . . . . . . . . 13
8.1. Receiving rules . . . . . . . . . . . . . . . . . . . . . 14
8.2. MAP BR . . . . . . . . . . . . . . . . . . . . . . . . . . 14
9. ICMP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
10. Fragmentation and Path MTU Discovery . . . . . . . . . . . . . 15
10.1. Fragmentation in the MAP domain . . . . . . . . . . . . . 15
10.2. Receiving IPv4 Fragments on the MAP domain borders . . . 15
10.3. Sending IPv4 fragments to the outside . . . . . . . . . . 16
11. NAT44 Considerations . . . . . . . . . . . . . . . . . . . . . 16
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
13. Security Considerations . . . . . . . . . . . . . . . . . . . 16
14. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 17
15. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 18
16. References . . . . . . . . . . . . . . . . . . . . . . . . . . 18
16.1. Normative References . . . . . . . . . . . . . . . . . . 18
16.2. Informative References . . . . . . . . . . . . . . . . . 18
Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 20
Appendix B. Alternate description of the Port mapping algorithm . 24
B.1. Bit Representation of the Algorithm . . . . . . . . . . . 25
B.2. GMA examples . . . . . . . . . . . . . . . . . . . . . . . 25
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 26
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1. Introduction
Mapping of IPv4 addresses in IPv6 addresses has been described in
numerous mechanisms dating back to 1996 [RFC1933]. The Automatic
tunneling mechanism described in RFC1933, assigned a globally unique
IPv6 address to a host by combining the host's IPv4 address with a
well-known IPv6 prefix. Given an IPv6 packet with a destination
address with an embedded IPv4 address, a node could automatically
tunnel this packet by extracting the IPv4 tunnel end-point address
from the IPv6 destination address.
There are numerous variations of this idea, described in 6over4
[RFC2529], 6to4 [RFC3056], ISATAP [RFC5214], and 6rd [RFC5969].
The commonalities of all these IPv6 over IPv4 mechanisms are:
o Automatically provisions an IPv6 address for a host or an IPv6
prefix for a site
o Algorithmic or implicit address resolution of tunnel end point
addresses. Given an IPv6 destination address, an IPv4 tunnel
endpoint address can be calculated.
o Embedding of an IPv4 address or part thereof into an IPv6 address.
In phases of IPv4 to IPv6 migration, IPv6 only networks will be
common, while there will still be a need for residual IPv4
deployment. This document describes a generic mapping of IPv4 to
IPv6, and a mechanism for encapsulating IPv4 over IPv6.
Just as the IPv6 over IPv4 mechanisms referred to above, the residual
IPv4 over IPv6 mechanism must be capable of:
o Provisioning an IPv4 prefix, an IPv4 address or a shared IPv4
address.
o Algorithmically map between an IPv4 prefix, IPv4 address or a
shared IPv4 address and an IPv6 address.
The mapping scheme described here supports encapsulation of IPv4
packets in IPv6 in both mesh and hub and spoke topologies, including
address mappings with full independence between IPv6 and IPv4
addresses.
This document describes delivery of IPv4 unicast service across an
IPv6 infrastructure. IPv4 multicast is not considered further in
this document.
The A+P (Address and Port) architecture of sharing an IPv4 address by
distributing the port space is described in [RFC6346]. Specifically
section 4 of [RFC6346] covers stateless mapping. The corresponding
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stateful solution DS-lite is described in [RFC6333]. The motivation
for the work is described in [I-D.ietf-softwire-stateless-
4v6-motivation].
A companion document defines a DHCPv6 option for provisioning of MAP
[I-D.ietf-softwire-map-dhcp]. Other means of provisioning is
possible. Deployment considerations are described in [I-D.mdt-
softwire-map-deployment].
MAP relies on IPv6 and is designed to deliver production-quality
dual-stack service while allowing IPv4 to be phased out within the SP
network. The phasing out of IPv4 within the SP network is
independent of whether the end user disables IPv4 service or not.
Further, "Greenfield"; IPv6-only networks may use MAP in order to
deliver IPv4 to sites via the IPv6 network.
2. Conventions
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].
3. Terminology
MAP domain: One or more MAP CEs and BRs connected to the
same virtual link. A service provider may
deploy a single MAP domain, or may utilize
multiple MAP domains.
MAP Rule A set of parameters describing the mapping
between an IPv4 prefix, IPv4 address or
shared IPv4 address and an IPv6 prefix or
address. Each domain uses a different
mapping rule set.
MAP node A device that implements MAP.
MAP Border Relay (BR): A MAP enabled router managed by the service
provider at the edge of a MAP domain. A
Border Relay router has at least an
IPv6-enabled interface and an IPv4 interface
connected to the native IPv4 network. A MAP
BR may also be referred to simply as a "BR"
within the context of MAP.
MAP Customer Edge (CE): A device functioning as a Customer Edge
router in a MAP deployment. A typical MAP CE
adopting MAP rules will serve a residential
site with one WAN side interface, and one or
more LAN side interfaces. A MAP CE may also
be referred to simply as a "CE" within the
context of MAP.
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Port-set: The separate part of the transport layer port
space; denoted as a port-set.
Port-set ID (PSID): Algorithmically identifies a set of ports
exclusively assigned to a CE.
Shared IPv4 address: An IPv4 address that is shared among multiple
CEs. Only ports that belong to the assigned
port-set can be used for communication. Also
known as a Port-Restricted IPv4 address.
End-user IPv6 prefix: The IPv6 prefix assigned to an End-user CE by
other means than MAP itself. E.g.
Provisioned using DHCPv6 PD [RFC3633],
assigned via SLAAC [RFC4862], or configured
manually. It is unique for each CE.
MAP IPv6 address: The IPv6 address used to reach the MAP
function of a CE from other CEs and from BRs.
Rule IPv6 prefix: An IPv6 prefix assigned by a Service Provider
for a mapping rule.
Rule IPv4 prefix: An IPv4 prefix assigned by a Service Provider
for a mapping rule.
Embedded Address (EA) bits: The IPv4 EA-bits in the IPv6 address
identify an IPv4 prefix/address (or part
thereof) or a shared IPv4 address (or part
thereof) and a port-set identifier.
4. Architecture
In accordance with the requirements stated above, the MAP mechanism
can operate with shared IPv4 addresses, full IPv4 addresses or IPv4
prefixes. Operation with shared IPv4 addresses is described here,
and the differences for full IPv4 addresses and prefixes are
described below.
The MAP mechanism uses existing standard building blocks. The
existing NAPT on the CE is used with additional support for
restricting transport protocol ports, ICMP identifiers and fragment
identifiers to the configured port set. For packets outbound from
the private IPv4 network, the CE NAPT MUST translate transport
identifiers (e.g. TCP and UDP port numbers) so that they fall within
the CE's assigned port-range.
The NAPT MUST in turn be connected to a MAP aware forwarding
function, that does encapsulation/ decapsulation of IPv4 packets in
IPv6. MAP supports the encapsulation mode specified in [RFC2473].
In addition MAP specifies an algorithm to do "address resolution"
from an IPv4 address and port to an IPv6 address. This algorithmic
mapping is specified in Section 5.
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The MAP architecture described here, restricts the use of the shared
IPv4 address to only be used as the global address (outside) of the
NAPT [RFC2663] running on the CE. A shared IPv4 address MUST NOT be
used to identify an interface. While it is theoretically possible to
make host stacks and applications port-aware, that is considered too
drastic a change to the IP model [RFC6250].
For full IPv4 addresses and IPv4 prefixes, the architecture just
described applies with two differences. First, a full IPv4 address
or IPv4 prefix can be used as it is today, e.g., for identifying an
interface or as a DHCP pool, respectively. Secondly, the NAPT is not
required to restrict the ports used on outgoing packets.
This architecture is illustrated in Figure 1.
User N
Private IPv4
| Network
|
O--+---------------O
| | MAP CE |
| +-----+--------+ |
| NAPT44| MAP | |
| +-----+ | | |\ ,-------. .------.
| +--------+ | \ ,-' `-. ,-' `-.
O------------------O / \ O---------O / Public \
/ IPv6 only \ | MAP | / IPv4 \
( Network --+ Border +- Network )
\ (MAP Domain) / | Relay | \ /
O------------------O \ / O---------O \ /
| MAP CE | /". ,-' `-. ,-'
| +-----+--------+ | / `----+--' ------'
| NAPT44| MAP | |/
| +-----+ | |
| | +--------+ |
O---.--------------O
|
User M
Private IPv4
Network
Figure 1: Network Topology
The MAP BR is responsible for connecting external IPv4 networks to
the IPv4 nodes in one or more MAP domains.
5. Mapping Algorithm
A MAP node is provisioned with one or more mapping rules.
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Mapping rules are used differently depending on their function.
Every MAP node must be provisioned with a Basic mapping rule. This
is used by the node to configure its IPv4 address, IPv4 prefix or
shared IPv4 address. This same basic rule can also be used for
forwarding, where an IPv4 destination address and optionally a
destination port is mapped into an IPv6 address. Additional mapping
rules are specified to allow for multiple different IPv4 sub-nets to
exist within the domain and optimize forwarding between them.
Traffic outside of the domain (i.e. When the destination IPv4
address does not match (using longest matching prefix) any Rule IPv4
prefix in the Rules database) is forwarded to the BR.
There are two types of mapping rules:
1. Basic Mapping Rule (BMR) - mandatory. There can only be one
Basic Mapping Rule per End-user IPv6 prefix. In combination with
the End-user IPv6 prefix, the Basic Mapping Rule is used to
derive the IPv4 prefix, address, or shared address and the PSID
assigned to the CE.
2. Forwarding Mapping Rule (FMR) - optional, used for forwarding.
The Basic Mapping Rule is also a Forwarding Mapping Rule. Each
Forwarding Mapping Rule will result in an entry in the Rules
table for the Rule IPv4 prefix. Given a destination IPv4 address
and port within the MAP domain, a MAP node can use the matching
FMR to derive the End-user IPv6 address of the interface through
which that IPv4 destination address and port combination can be
reached.
Both mapping rules share the same parameters:
o Rule IPv6 prefix (including prefix length)
o Rule IPv4 prefix (including prefix length)
o Rule EA-bits length (in bits)
A MAP node finds its Basic Mapping Rule by doing a longest match
between the End-user IPv6 prefix and the Rule IPv6 prefix in the
Mapping Rules table. The rule is then used for IPv4 prefix, address
or shared address assignment.
A MAP IPv6 address is formed from the BMR Rule IPv6 prefix. This
address MUST be assigned to an interface of the MAP node and is used
to terminate all MAP traffic being sent or received to the node.
Port-aware IPv4 entries in the Rules table are installed for all the
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Forwarding Mapping Rules and an IPv4 default route to the MAP BR.
Forwarding rules are used to allow direct communication between MAP
CEs, known as mesh mode. In hub and spoke mode, there are no
forwarding rules, all traffic MUST be forwarded directly to the BR.
5.1. Port mapping algorithm
The port mapping algorithm is used in domains whose rules allow IPv4
address sharing.
The simplest way to represent a port range is using a notation
similar to CIDR [RFC4632]. For example the first 256 ports are
represented as port prefix 0.0/8. The last 256 ports as 255.0/8. In
hexadecimal, 0x0000/8 (PSID = 0) and 0xFF00/8 (PSID = 0xFF).
To minimise dependencies between the End-user IPv6 prefix and the
resulting port set, a PSID of 0, would, in the naive representation
assign the system ports [I-D.ietf-tsvwg-iana-ports] to the user.
Instead using an infix representation, and requiring that the first
bit field (A) is greater than 0, the well known ports are excluded.
This algorithm allocates ports to a given CE as a series of
contiguous ranges.
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6
+-----------+-----------+-------+
Ports in | A | PSID | M |
the CE port set | > 0 | | |
+-----------+-----------+-------+
| a bits | k bits |m bits |
Figure 2: PSID
A For a > 0, A MUST be larger than 0. This ensures that the
algorithm excludes the system ports.
a-bits The number of offset bits. The default Offset bits (a) are 6,
this excludes the system ports (0-1023).
PSID The Port Set Identifier. Different Port-Set Identifiers (PSID)
MUST have non-overlapping port-sets.
k-bits The length in bits of the PSID field. The sharing ratio is
k^2. The number of ports assigned to the user is 2^(16-k) - 2^m
(excluded ports)
M The contiguous ports.
m bits The size contiguous ports. The number of contiguous ports is
given by 2^m.
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This algorithm allocates ports to a given CE as a series of
contiguous ranges.
5.2. Basic mapping rule (BMR)
The Basic Mapping Rule is mandatory, used by the CE to provision
itself with an IPv4 prefix, IPv4 address or shared IPv4 address.
| n bits | o bits | s bits | 128-n-o-s bits |
+--------------------+-----------+---------+-----------------------+
| Rule IPv6 prefix | EA bits |subnet ID| interface ID |
+--------------------+-----------+---------+-----------------------+
|<--- End-user IPv6 prefix --->|
Figure 3: IPv6 address format
The Rule IPv6 prefix is the part of the End-user IPv6 prefix that is
common among all CEs using the same Basic Mapping Rule within the MAP
domain. The EA bits encode the CE specific IPv4 address and port
information. The EA bits, which are unique for a given Rule IPv6
prefix, can contain a full or part of an IPv4 address and, in the
shared IPv4 address case, a Port-Set Identifier (PSID). An EA-bit
length of 0 signifies that all relevant MAP IPv4 addressing
information is passed directly in the BMR rule, and not derived from
the End-user IPv6 prefix.
The MAP IPv6 address is created by concatenating the End-user IPv6
prefix with the MAP subnet-id (if the End-user IPv6 prefix is shorter
than 64 bits) and the interface-id as specified in Section 6.
The MAP subnet ID is defined to be the first subnet (all bits set to
zero). Unless configured differently, a MAP node MUST reserve the
first IPv6 prefix in an End-user IPv6 prefix for the purpose of MAP.
The MAP IPv6 is created by combining the End-User IPv6 prefix with
the all zeros subnet-id and the MAP IPv6 interface identifier.
Shared IPv4 address:
| r bits | p bits | | q bits |
+-------------+---------------------+ +------------+
| Rule IPv4 | IPv4 Address suffix | |Port-Set ID |
+-------------+---------------------+ +------------+
| 32 bits |
Figure 4: Shared IPv4 address
Complete IPv4 address:
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| r bits | p bits |
+-------------+---------------------+
| Rule IPv4 | IPv4 Address suffix |
+-------------+---------------------+
| 32 bits |
Figure 5: Complete IPv4 address
IPv4 prefix:
| r bits | p bits |
+-------------+---------------------+
| Rule IPv4 | IPv4 Address suffix |
+-------------+---------------------+
| < 32 bits |
Figure 6: IPv4 prefix
The length of r MAY be zero, in which case the complete IPv4 address
or prefix is encoded in the EA bits. If only a part of the IPv4
address/prefix is encoded in the EA bits, the Rule IPv4 prefix is
provisioned to the CE by other means (e.g. a DHCPv6 option). To
create a complete IPv4 address (or prefix), the IPv4 address suffix
(p) from the EA bits, are concatenated with the Rule IPv4 prefix (r
bits).
The offset of the EA bits field in the IPv6 address is equal to the
BMR Rule IPv6 prefix length. The length of the EA bits field (o) is
given by the BMR Rule EA-bits length, and can be between 0 and 48. A
length of 48 means that the complete IPv4 address and port is
embedded in the End-user IPv6 prefix (a single port is assigned). A
length of 0 means that no part of the IPv4 address or port is
embedded in the address. The sum of the Rule IPv6 Prefix length and
the Rule EA-bits length MUST be less or equal than the End-user IPv6
prefix length.
If o + r < 32 (length of the IPv4 address in bits), then an IPv4
prefix is assigned.
If o + r is equal to 32, then a full IPv4 address is to be assigned.
The address is created by concatenating the Rule IPv4 prefix and the
EA-bits.
If o + r is > 32, then a shared IPv4 address is to be assigned. The
number of IPv4 address suffix bits (p) in the EA bits is given by 32
- r bits. The PSID bits are used to create a port-set. The length
of the PSID bit field within EA bits is: o - p.
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The length of r MAY be 32, with no part of the IPv4 address embedded
in the EA bits. This results in a mapping with no dependence between
the IPv4 address and the IPv6 address. In addition the length of o
MAY be zero (no EA bits embedded in the End-User IPv6 prefix),
meaning that also the PSID is provisioned using e.g. the DHCP
option.
See Appendix A for an example of the Basic Mapping Rule.
5.3. Forwarding mapping rule (FMR)
The Forwarding Mapping Rule is optional, and used in mesh mode to
merit direct CE to CE connectivity.
On adding an FMR rule, an IPv4 route is installed in the Rules table
for the Rule IPv4 prefix.
On forwarding an IPv4 packet, a best matching prefix look up is done
in the Rules table and the correct FMR is chosen.
| 32 bits | | 16 bits |
+--------------------------+ +-------------------+
| IPv4 destination address | | IPv4 dest port |
+--------------------------+ +-------------------+
: : ___/ :
| p bits | / q bits :
+----------+ +------------+
|IPv4 sufx| |Port-Set ID |
+----------+ +------------+
\ / ____/ ________/
\ : __/ _____/
\ : / /
| n bits | o bits | s bits | 128-n-o-s bits |
+--------------------+-----------+---------+------------+----------+
| Rule IPv6 prefix | EA bits |subnet ID| interface ID |
+--------------------+-----------+---------+-----------------------+
|<--- End-user IPv6 prefix --->|
Figure 7: Deriving of MAP IPv6 address
See Appendix A for an example of the Forwarding Mapping Rule.
5.4. Destinations outside the MAP domain
To reach IPv4 destinations outside of the MAP domain, traffic is sent
to the configured address of the MAP BR. On the CE, the default can
be represented as a point to point IPv4 over IPv6 tunnel [RFC2473] to
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the BR.
6. The IPv6 Interface Identifier
The Interface identifier format of a MAP node is described below.
| 128-n-o-s bits |
| 16 bits| 32 bits | 16 bits|
+--------+----------------+--------+
| 0 | IPv4 address | PSID |
+--------+----+-----------+--------+
Figure 8
In the case of an IPv4 prefix, the IPv4 address field is right-padded
with zeroes up to 32 bits. The PSID field is left-padded to create a
16 bit field. For an IPv4 prefix or a complete IPv4 address, the
PSID field is zero.
If the End-user IPv6 prefix length is larger than 64, the most
significant parts of the interface identifier is overwritten by the
prefix.
7. MAP Configuration
For a given MAP domain, the BR and CE MUST be configured with the
following MAP elements. The configured values for these elements are
identical for all CEs and BRs within a given MAP domain.
o The Basic Mapping Rule and optionally the Forwarding Mapping
Rules, including the Rule IPv6 prefix, Rule IPv4 prefix, and
Length of EA bits
o The IPv6 address of the MAP BR.
o Hub and spoke mode or Mesh mode. (If all traffic should be sent
to the BR, or if direct CE to CE traffic should be supported).
7.1. MAP CE
The MAP elements are set to values that are the same across all CEs
within a MAP domain. The values may be configured in a variety of
manners, including provisioning methods such as the Broadband Forum's
"TR-69" Residential Gateway management interface, an XML-based object
retrieved after IPv6 connectivity is established, or manual
configuration by an administrator. This document describes how to
configure the necessary parameters via a single IPv6 DHCP option. A
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CE that allows IPv6 configuration by DHCP SHOULD implement this
option. Other configuration and management methods may use the
format described by this option for consistency and convenience of
implementation on CEs that support multiple configuration methods.
The only remaining provisioning information the CE requires in order
to calculate the MAP IPv4 address and enable IPv4 connectivity is the
IPv6 prefix for the CE. The End-user IPv6 prefix is configured as
part of obtaining IPv6 Internet access.
A single MAP CE MAY be connected to more than one MAP domain, just as
any router may have more than one IPv4-enabled service provider
facing interface and more than one set of associated addresses
assigned by DHCP. Each domain a given CE operates within would
require its own set of MAP configuration elements and would generate
its own IPv4 address.
The MAP DHCP option is specified in [I-D.ietf-softwire-map-dhcp].
7.2. MAP BR
The MAP BR MUST be configured with the same MAP elements as the MAP
CEs operating within the same domain.
For increased reliability and load balancing, the BR IPv6 address MAY
be an anycast address shared across a given MAP domain. As MAP is
stateless, any BR may be used at any time. If the BR IPv6 address is
anycast the relay MUST use this anycast IPv6 address as the source
address in packets relayed to CEs.
Since MAP uses provider address space, no specific routes need to be
advertised externally for MAP to operate, neither in IPv6 nor IPv4
BGP. However, if anycast is used for the MAP IPv6 relays, the
anycast addresses must be advertised in the service provider's IGP.
7.3. Backwards compatibility
A MAP-E CE provisioned with only the IPv6 address of the BR, and with
no IPv4 address and port range configured by other means, MUST
disable its NAT44 functionality. This characteristic makes a MAP CE
compatible with DS-Lite [RFC6333] AFTRs, whose addresses are
configured as the MAP BR.
8. Forwarding Considerations
Figure 1 depicts the overall MAP architecture with IPv4 users (N and
M) networks connected to a routed IPv6 network.
MAP supports Encapsulation mode as specified in [RFC2473].
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For a shared IPv4 address, a MAP CE forwarding IPv4 packets from the
LAN performs NAT44 functions first and creates appropriate NAT44
bindings. The resulting IPv4 packets MUST contain the source IPv4
address and source transport identifiers defined by MAP. The
resulting IPv4 packet is forwarded to the CE's MAP forwarding
function. The IPv6 source and destination addresses MUST then be
derived as per Section 5 of this draft.
A MAP CE receiving an IPv6 packet to its MAP IPv6 address sends this
packet to the CE's MAP function. All other IPv6 traffic is forwarded
as per the CE's IPv6 routing rules. The resulting IPv4 packet is
then forwarded to the CE's NAT44 function where the destination port
number MUST be checked against the stateful port mapping session
table and the destination port number MUST be mapped to its original
value.
8.1. Receiving rules
The CE SHOULD check that MAP received packets' transport-layer
destination port number is in the range configured by MAP for the CE
and the CE SHOULD drop any non conforming packet and respond with an
ICMPv6 "Address Unreachable" (Type 1, Code 3).
8.2. MAP BR
A MAP BR receiving IPv6 packets selects a best matching MAP domain
rule based on a longest address match of the packets' source address
against the BR's configured MAP BMR prefix(es), as well as a match of
the packet destination address against the configured BR IPv6 address
or FMR prefix(es). The selected MAP rule allows the BR to determine
the EA-bits from the source IPv6 address. The BR MUST perform a
validation of the consistency of the source IPv6 address and source
port number for the packet using BMR. If the packets source port
number is found to be outside the range allowed for this CE and the
BMR, the BR MUST drop the packet and respond with an ICMPv6
"Destination Unreachable, Source address failed ingress/egress
policy" (Type 1, Code 5).
9. ICMP
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ICMP message should be supported in MAP domain. Hence, the NAT44 in
MAP CE must implement the behavior for ICMP message conforming to the
best current practice documented in [RFC5508].
If a MAP CE receives an ICMP message having ICMP identifier field in
ICMP header, NAT44 in the MAP CE must rewrite this field to a
specific value assigned from the port-set. BR and other CEs must
handle this field similar to the port number in the TCP/UDP header
upon receiving the ICMP message with ICMP identifier field.
If a MAP node receives an ICMP error message without the ICMP
identifier field for errors that is detected inside a IPv6 tunnel, a
node should relay the ICMP error message to the original source.
This behavior should be implemented conforming to the section 8 of
[RFC2473].
10. Fragmentation and Path MTU Discovery
Due to the different sizes of the IPv4 and IPv6 header, handling the
maximum packet size is relevant for the operation of any system
connecting the two address families. There are three mechanisms to
handle this issue: Path MTU discovery (PMTUD), fragmentation, and
transport-layer negotiation such as the TCP Maximum Segment Size
(MSS) option [RFC0897]. MAP uses all three mechanisms to deal with
different cases.
10.1. Fragmentation in the MAP domain
Encapsulating an IPv4 packet to carry it across the MAP domain will
increase its size (40 bytes). It is strongly recommended that the
MTU in the MAP domain is well managed and that the IPv6 MTU on the CE
WAN side interface is set so that no fragmentation occurs within the
boundary of the MAP domain.
Fragmentation on MAP domain entry is described in section 7.2 of
[RFC2473]
The use of an anycast source address could lead to any ICMP error
message generated on the path being sent to a different BR.
Therefore, using dynamic tunnel MTU Section 6.7 of [RFC2473] is
subject to IPv6 Path MTU black-holes. A MAP BR SHOULD NOT by default
use Path MTU discovery across the MAP domain.
Multiple BRs using the same anycast source address could send
fragmented packets to the same CE at the same time. If the
fragmented packets from different BRs happen to use the same fragment
ID, incorrect reassembly might occur. See [RFC4459] for an analysis
of the problem. Section 3.4 suggests solving the problem by
fragmenting the inner packet.
10.2. Receiving IPv4 Fragments on the MAP domain borders
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Forwarding of an IPv4 packet received from the outside of the MAP
domain requires the IPv4 destination address and the transport
protocol destination port. The transport protocol information is
only available in the first fragment received. As described in
section 5.3.3 of [RFC6346] a MAP node receiving an IPv4 fragmented
packet from outside has to reassemble the packet before sending the
packet onto the MAP link. If the first packet received contains the
transport protocol information, it is possible to optimize this
behavior by using a cache and forwarding the fragments unchanged. A
description of this algorithm is outside the scope of this document.
10.3. Sending IPv4 fragments to the outside
If two IPv4 host behind two different MAP CE's with the same IPv4
address sends fragments to an IPv4 destination host outside the
domain. Those hosts may use the same IPv4 fragmentation identifier,
resulting in incorrect reassembly of the fragments at the destination
host. Given that the IPv4 fragmentation identifier is a 16 bit
field, it could be used similarly to port ranges. A MAP CE SHOULD
rewrite the IPv4 fragmentation identifier to be within its allocated
port set.
11. NAT44 Considerations
The NAT44 implemented in the MAP CE SHOULD conform with the behavior
and best current practice documented in [RFC4787], [RFC5508], and
[RFC5382]. In MAP address sharing mode (determined by the MAP domain
/rule configuration parameters) the operation of the NAT44 MUST be
restricted to the available port numbers derived via the basic
mapping rule.
12. IANA Considerations
This specification does not require any IANA actions.
13. Security Considerations
Spoofing attacks: With consistency checks between IPv4 and IPv6
sources that are performed on IPv4/IPv6 packets received by MAP
nodes, MAP does not introduce any new opportunity for spoofing
attacks that would not already exist in IPv6.
Denial-of-service attacks: In MAP domains where IPv4 addresses are
shared, the fact that IPv4 datagram reassembly may be necessary
introduces an opportunity for DOS attacks. This is inherent to
address sharing, and is common with other address sharing
approaches such as DS-Lite and NAT64/DNS64. The best protection
against such attacks is to accelerate IPv6 deployment, so that,
where MAP is supported, it is less and less used.
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Routing-loop attacks: This attack may exist in some automatic
tunneling scenarios are documented in [RFC6324]. They cannot
exist with MAP because each BRs checks that the IPv6 source
address of a received IPv6 packet is a CE address based on
Forwarding Mapping Rule.
Attacks facilitated by restricted port set: From hosts that
are not subject to ingress filtering of [RFC2827], some attacks
are possible by an attacker injecting spoofed packets during
ongoing transport connections ([RFC4953], [RFC5961], [RFC6056].
The attacks depend on guessing which ports are currently used by
target hosts, and using an unrestricted port set is preferable,
i.e. Using native IPv6 connections that are not subject to MAP
port range restrictions. To minimize this type of attacks when
using a restricted port set, the MAP CE's NAT44 filtering behavior
SHOULD be "Address-Dependent Filtering". Furthermore, the MAP CEs
SHOULD use a DNS transport proxy function to handle DNS traffic,
and source such traffic from IPv6 interfaces not assigned to MAP.
Practicalities of these methods are discussed in Section 5.9 of
[I-D.dec-stateless-4v6].
[RFC6269] outlines general issues with IPv4 address sharing.
14. Contributors
This document is the result of the IETF Softwire MAP design team
effort and numerous previous individual contributions in this area:
Chongfeng Xie (China Telecom)
Room 708, No.118, Xizhimennei Street Beijing 100035 CN
Phone: +86-10-58552116
Email: xiechf@ctbri.com.cn
Qiong Sun (China Telecom)
Room 708, No.118, Xizhimennei Street Beijing 100035 CN
Phone: +86-10-58552936
Email: sunqiong@ctbri.com.cn
Gang Chen (China Mobile)
53A,Xibianmennei Ave. Beijing 100053 P.R.China
Email: chengang@chinamobile.com
Yu Zhai
CERNET Center/Tsinghua University
Room 225, Main Building, Tsinghua University
Beijing 100084
CN
Email: jacky.zhai@gmail.com
Wentao Shang (CERNET Center/Tsinghua University)
Room 225, Main Building, Tsinghua University Beijing 100084
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CN
Email: wentaoshang@gmail.com
Guoliang Han (CERNET Center/Tsinghua University)
Room 225, Main Building, Tsinghua University Beijing 100084
CN
Email: bupthgl@gmail.com
Rajiv Asati (Cisco Systems)
7025-6 Kit Creek Road Research Triangle Park NC 27709 USA
Email: rajiva@cisco.com
15. Acknowledgements
This document is based on the ideas of many, including Masakazu
Asama, Mohamed Boucadair, Gang Chen, Maoke Chen, Wojciech Dec,
Xiaohong Deng, Jouni Korhonen, Tomasz Mrugalski, Jacni Qin, Chunfa
Sun, Qiong Sun, and Leaf Yeh. The authors want in particular to
recognize Remi Despres, who has tirelessly worked on generalized
mechanisms for stateless address mapping.
The authors would like to thank Guillaume Gottard, Dan Wing, Jan
Zorz, Necj Scoberne, Tina Tsou, Kristian Poscic, and especially Tom
Taylor for the thorough review and comments of this document.
16. References
16.1. Normative References
[I-D.ietf-softwire-map-dhcp]
Mrugalski, T., Troan, O., Bao, C., Dec, W., and L. Yeh,
"DHCPv6 Options for Mapping of Address and Port", draft-
ietf-softwire-map-dhcp-01 (work in progress), August 2012.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in
IPv6 Specification", RFC 2473, December 1998.
16.2. Informative References
[I-D.dec-stateless-4v6]
Dec, W., Asati, R., and H. Deng, "Stateless 4Via6 Address
Sharing", draft-dec-stateless-4v6-04 (work in progress),
October 2011.
[I-D.ietf-softwire-stateless-4v6-motivation]
Boucadair, M., Matsushima, S., Lee, Y., Bonness, O.,
Borges, I., and G. Chen, "Motivations for Carrier-side
Stateless IPv4 over IPv6 Migration Solutions", draft-ietf-
softwire-stateless-4v6-motivation-05 (work in progress),
November 2012.
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[I-D.ietf-tsvwg-iana-ports]
Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S.
Cheshire, "Internet Assigned Numbers Authority (IANA)
Procedures for the Management of the Service Name and
Transport Protocol Port Number Registry", draft-ietf-
tsvwg-iana-ports-10 (work in progress), February 2011.
[RFC0897] Postel, J., "Domain name system implementation schedule",
RFC 897, February 1984.
[RFC1933] Gilligan, R. and E. Nordmark, "Transition Mechanisms for
IPv6 Hosts and Routers", RFC 1933, April 1996.
[RFC2529] Carpenter, B. and C. Jung, "Transmission of IPv6 over IPv4
Domains without Explicit Tunnels", RFC 2529, March 1999.
[RFC2663] Srisuresh, P. and M. Holdrege, "IP Network Address
Translator (NAT) Terminology and Considerations", RFC
2663, August 1999.
[RFC2827] Ferguson, P. and D. Senie, "Network Ingress Filtering:
Defeating Denial of Service Attacks which employ IP Source
Address Spoofing", BCP 38, RFC 2827, May 2000.
[RFC3056] Carpenter, B. and K. Moore, "Connection of IPv6 Domains
via IPv4 Clouds", RFC 3056, February 2001.
[RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic
Host Configuration Protocol (DHCP) version 6", RFC 3633,
December 2003.
[RFC4459] Savola, P., "MTU and Fragmentation Issues with In-the-
Network Tunneling", RFC 4459, April 2006.
[RFC4632] Fuller, V. and T. Li, "Classless Inter-domain Routing
(CIDR): The Internet Address Assignment and Aggregation
Plan", BCP 122, RFC 4632, August 2006.
[RFC4787] Audet, F. and C. Jennings, "Network Address Translation
(NAT) Behavioral Requirements for Unicast UDP", BCP 127,
RFC 4787, January 2007.
[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862, September 2007.
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[RFC4953] Touch, J., "Defending TCP Against Spoofing Attacks", RFC
4953, July 2007.
[RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site
Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214,
March 2008.
[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.
[RFC5961] Ramaiah, A., Stewart, R., and M. Dalal, "Improving TCP's
Robustness to Blind In-Window Attacks", RFC 5961, August
2010.
[RFC5969] Townsley, W. and O. Troan, "IPv6 Rapid Deployment on IPv4
Infrastructures (6rd) -- Protocol Specification", RFC
5969, August 2010.
[RFC6052] Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X.
Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052,
October 2010.
[RFC6056] Larsen, M. and F. Gont, "Recommendations for Transport-
Protocol Port Randomization", BCP 156, RFC 6056, January
2011.
[RFC6250] Thaler, D., "Evolution of the IP Model", RFC 6250, May
2011.
[RFC6269] Ford, M., Boucadair, M., Durand, A., Levis, P., and P.
Roberts, "Issues with IP Address Sharing", RFC 6269, June
2011.
[RFC6324] Nakibly, G. and F. Templin, "Routing Loop Attack Using
IPv6 Automatic Tunnels: Problem Statement and Proposed
Mitigations", RFC 6324, August 2011.
[RFC6333] Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual-
Stack Lite Broadband Deployments Following IPv4
Exhaustion", RFC 6333, August 2011.
[RFC6346] Bush, R., "The Address plus Port (A+P) Approach to the
IPv4 Address Shortage", RFC 6346, August 2011.
Appendix A. Examples
Example 1 - BMR
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Given the MAP domain information and an IPv6 address of
an endpoint:
End-user IPv6 prefix: 2001:db8:0012:3400::/56
Basic Mapping Rule: {2001:db8:0000::/40 (Rule IPv6 prefix),
192.0.2.0/24 (Rule IPv4 prefix),
16 (Rule EA-bits length)}
PSID length: (16 - (32 - 24) = 8. (Sharing ratio of 256)
PSID offset: 6
A MAP node (CE or BR) can via the BMR, or equivalent FMR,
determine the IPv4 address and port-set as shown below:
EA bits offset: 40
IPv4 suffix bits (p) Length of IPv4 address (32) -
IPv4 prefix length (24) = 8
IPv4 address: 192.0.2.18 (0xc0000212)
PSID start: 40 + p = 40 + 8 = 48
PSID length: o - p = (56 - 40) - 8 = 8
PSID: 0x34
Available ports (63 ranges) : 1232-1235, 2256-2259, ...... ,
63696-63699, 64720-64723
The BMR information allows a MAP CE also to determine (complete)
its IPv6 address within the indicated IPv6 prefix.
IPv6 address of MAP CE: 2001:db8:0012:3400:0000:c000:0212:0034
Example 2:
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Another example can be made of a hypothetical MAP BR,
configured with the following FMR when receiving a packet
with the following characteristics:
IPv4 source address: 1.2.3.4 (0x01020304)
IPv4 source port: 80
IPv4 destination address: 192.0.2.18 (0xc0000212)
IPv4 destination port: 1232
Configured Forwarding Mapping Rule: {2001:db8:0000::/40 (Rule IPv6 prefix),
192.0.2.0/24 (Rule IPv4 prefix),
16 (Rule EA-bits length)}
IPv6 address of MAP BR: 2001:db8:ffff::1
The above information allows the BR to derive as follows
the mapped destination IPv6 address for the corresponding
MAP CE, and also the mapped source IPv6 address for
the IPv4 source.
IPv4 suffix bits (p): 32 - 24 = 8 (18 (0x12))
PSID length: 8
PSID: 0x34 (1232)
The resulting IPv6 packet will have the following key fields:
IPv6 source address: 2001:db8:ffff::1
IPv6 destination address: 2001:db8:0012:3400:0000:c000:0212:0034
IPv6 source Port: 80
IPv6 destination Port: 1232
Example 3 - FMR:
An IPv4 host behind the MAP CE (addressed as per the previous
examples) corresponding with IPv4 host 1.2.3.4 will have its
packets converted into IPv6 using the IPv6 address of the BR
configured on the MAP CE as follows:
IPv6 address of BR used by MAP CE: 2001:db8:ffff::1
IPv4 source address (post NAT44 if present) 192.0.2.18
IPv4 destination address: 1.2.3.4
IPv4 source port (post NAT44 if present): 1232
IPv4 destination port: 80
IPv6 source address of MAP CE: 2001:db8:0012:3400:0000:c000:0212:0034
IPv6 destination address: 2001:db8:ffff::1
Example 4 - Rule with no embedded address bits and no address sharing
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End-User IPv6 prefix: 2001:db8:0012:3400::/56
Basic Mapping Rule: {2001:db8:0012:3400::/56 (Rule IPv6 prefix),
192.0.2.1/32 (Rule IPv4 prefix),
0 (Rule EA-bits length)}
PSID length: 0 (Sharing ratio is 1)
PSID offset: n/a
A MAP node (CE or BR) can via the BMR or equivalent FMR, determine
the IPv4 address and port-set as shown below:
EA bits offset: 0
IPv4 suffix bits (p): Length of IPv4 address (32) -
IPv4 prefix length (32) = 0
IPv4 address: 192.0.2.1 (0xc0000201)
PSID start: 0
PSID length: 0
PSID: null
The BMR information allows a MAP CE also to determine (complete)
its full IPv6 address by combining the IPv6 prefix with the MAP
interface identifier (that embeds the IPv4 address).
IPv6 address of MAP CE: 2001:db8:0012:3400:0000:c000:0201:0000
Example 5 - Rule with no embedded address bits and address sharing
(sharing ratio 256)
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End-User IPv6 prefix: 2001:db8:0012:3400::/56
Basic Mapping Rule: {2001:db8:0012:3400::/56 (Rule IPv6 prefix),
192.0.2.1/32 (Rule IPv4 prefix),
0 (Rule EA-bits length)}
PSID length: (16 - (32 - 24) = 8. (Sharing ratio of 256)
PSID offset: 6
A MAP node (CE or BR) can via the BMR or equivalent FMR determine
the IPv4 address and port-set as shown below:
EA bits offset: 0
IPv4 suffix bits (p): Length of IPv4 address (32) -
IPv4 prefix length (32) = 0
IPv4 address: 192.0.2.1 (0xc0000201)
PSID start: 0
PSID length: 8
PSID: 0x34
Available ports (63 ranges): 1232-1235, 2256-2259, ...... ,
63696-63699, 64720-64723
The BMR information allows a MAP CE also to determine (complete)
its full IPv6 address by combining the IPv6 prefix with the MAP
interface identifier (that embeds the IPv4 address and PSID).
IPv6 address of MAP CE: 2001:db8:0012:3400:0000:c000:0212:0034
Note that the IPv4 address and PSID is not derived from the IPv6
prefix assigned to the CE.
Appendix B. Alternate description of the Port mapping algorithm
The port mapping algorithm is used in domains whose rules allow IPv4
address sharing. Different Port-Set Identifiers (PSID) MUST have
non-overlapping port-sets. The two extreme cases are: (1) the port
numbers are not contiguous for each PSID, but uniformly distributed
across the port range (0-65535); (2) the port numbers are contiguous
in a single range for each PSID. The port mapping algorithm proposed
here is called the Generalized Modulus Algorithm (GMA) and supports
both these cases.
For a given sharing ratio (R) and the maximum number of contiguous
ports (M), the GMA algorithm is defined as:
1. The port number (P) of a given PSID (K) is composed of:
P = R * M * j + M * K + i
Where:
* PSID: K = 0 to R - 1
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* Port range index: j = (4096 / M) / R to ((65536 / M) / R) - 1, if
the port numbers (0 - 4095) are excluded.
* Contiguous Port index: i = 0 to M - 1
2. The PSID (K) of a given port number (P) is determined by:
K = (floor(P/M)) % R
Where:
* % is the modulus operator
* floor(arg) is a function that returns the largest integer not
greater than arg.
B.1. Bit Representation of the Algorithm
Given a sharing ratio (R=2^k), the maximum number of contiguous ports
(M=2^m), for any PSID (K) and available ports (P) can be represented
as:
0 8 15
+---------------+----------+------+-------------------+
| P |
----------------+-----------------+-------------------+
| A (j) | PSID (K) | M (i) |
+---------------+----------+------+-------------------+
|<----a bits--->|<-----k bits---->|<------m bits----->|
Figure 9: Bit representation
Where j and i are the same indexes defined in the port mapping
algorithm.
For any port number, the PSID can be obtained by bit mask operation.
For a > 0, j MUST be larger than 0. This ensures that the algorithm
excludes the system ports ([I-D.ietf-tsvwg-iana-ports]). For a = 0,
j MAY be 0 to allow for the provisioning of the system ports.
B.2. GMA examples
For example, for R = 256, PSID = 0, offset: a = 6 and PSID length: k
= 8 bits
Available ports (63 ranges) : 1024-1027, 2048-2051, ...... ,
63488-63491, 64512-64515
For example, for R = 64, PSID = 0, a = 0 (PSID offset = 0 and PSID
length = 6 bits):
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Available ports (1 range) : 0-1023
Authors' Addresses
Ole Troan
Cisco Systems
Philip Pedersens vei 1
Lysaker 1366
Norway
Email: ot@cisco.com
Wojciech Dec
Cisco Systems
Haarlerbergpark Haarlerbergweg 13-19
Amsterdam, NOORD-HOLLAND 1101 CH
Netherlands
Email: wdec@cisco.com
Xing Li
CERNET Center/Tsinghua University
Room 225, Main Building, Tsinghua University
Beijing 100084
CN
Email: xing@cernet.edu.cn
Congxiao Bao
CERNET Center/Tsinghua University
Room 225, Main Building, Tsinghua University
Beijing 100084
CN
Email: congxiao@cernet.edu.cn
Satoru Matsushima
SoftBank Telecom
1-9-1 Higashi-Shinbashi, Munato-ku
Tokyo
Japan
Email: satoru.matsushima@g.softbank.co.jp
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Tetsuya Murakami
IP Infusion
1188 East Arques Avenue
Sunnyvale
USA
Email: tetsuya@ipinfusion.com
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