Network Working Group X. Li
Internet-Draft M. Chen
Intended status: Standards Track C. Bao
Expires: January 7, 2009 H. Zhang
J. Wu
CERNET Center/Tsinghua University
July 6, 2008
Prefix-specific and Stateless Address Mapping (IVI) for IPv4/IPv6
Coexistence and Transition
draft-xli-behave-ivi-00.txt
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Abstract
This document presents the concept and practice of the prefix-
specific and stateless address mapping mechanism (IVI) for IPv4/IPv6
coexistence and transition. In this scheme, subsets of the IPv4
addresses are embedded in prefix-specific IPv6 addresses and these
IPv6 addresses can therefore communicate with the global IPv6
networks directly and can communicate with the global IPv4 networks
via stateless (or almost stateless) gateways. The IVI scheme
supports the end-to-end address transparency, incremental deployment
and performance optimization in multi-homed environment. This
document is a comprehensive report on the IVI design and its
deployment in large scale public networks. Based on the IVI
scenario, the corresponding address allocation and assignment
policies are also proposed.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terms and Abbreviations . . . . . . . . . . . . . . . . . . . 6
3. The Overview of the IVI Mechanism . . . . . . . . . . . . . . 7
3.1. Address Mapping . . . . . . . . . . . . . . . . . . . . . 7
3.2. Routing and Forwarding . . . . . . . . . . . . . . . . . . 9
3.3. IVI Communication Scenarios . . . . . . . . . . . . . . . 10
4. Design Considerations . . . . . . . . . . . . . . . . . . . . 14
4.1. Address Mapping . . . . . . . . . . . . . . . . . . . . . 14
4.2. Network-layer Header Translation . . . . . . . . . . . . . 14
4.3. Transport-layer Header Translation . . . . . . . . . . . . 15
4.4. Fragmentation and MTU Handling . . . . . . . . . . . . . . 15
4.5. ICMP Handling . . . . . . . . . . . . . . . . . . . . . . 15
4.6. Application Layer Gateway . . . . . . . . . . . . . . . . 16
4.7. IPv6 Source Address Selection . . . . . . . . . . . . . . 16
4.8. IPv4 over IPv6 Support . . . . . . . . . . . . . . . . . . 16
5. DNS Configuration and Mapping . . . . . . . . . . . . . . . . 17
5.1. DNS Configuration for the IVI6(i) Addresses . . . . . . . 17
5.2. DNS Mapping for the IVIG46(i) Addresses . . . . . . . . . 17
6. Multiplexing of the Global IPv4 Addresses . . . . . . . . . . 18
6.1. Temporal Multiplexing . . . . . . . . . . . . . . . . . . 18
6.2. Port Multiplexing . . . . . . . . . . . . . . . . . . . . 18
6.3. Spatial Multiplexing . . . . . . . . . . . . . . . . . . . 19
6.4. Multiplexing using IPv4 NAT-PT . . . . . . . . . . . . . . 19
7. IVI Multicast Support . . . . . . . . . . . . . . . . . . . . 21
8. IVI Implementation and Preliminary Testing Results . . . . . . 22
9. Features of IVI . . . . . . . . . . . . . . . . . . . . . . . 23
10. Address Policy and IVI Address Evolution . . . . . . . . . . . 25
10.1. IPv6 Address Assignment Policy . . . . . . . . . . . . . . 25
10.2. IPv4 Address Allocation Policy . . . . . . . . . . . . . . 25
10.3. Evolution of the IVI Addresses and Services . . . . . . . 25
11. Security Considerations . . . . . . . . . . . . . . . . . . . 27
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 28
13. Principal Authors . . . . . . . . . . . . . . . . . . . . . . 29
14. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 30
15. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 31
16. Appendix A. The IVI gateway configuration example . . . . . . 32
17. Appendix B. The traceroute results . . . . . . . . . . . . . . 33
18. References . . . . . . . . . . . . . . . . . . . . . . . . . . 36
18.1. Normative References . . . . . . . . . . . . . . . . . . . 36
18.2. Informative References . . . . . . . . . . . . . . . . . . 37
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 39
Intellectual Property and Copyright Statements . . . . . . . . . . 41
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1. Introduction
This document presents the concept and practice of the prefix-
specific and stateless address mapping mechanism (IVI) for IPv4/IPv6
coexistence and transition.
The experiences for the IPv6 deployment in the past 10 years strongly
indicate that for a successful transition, the IPv6 hosts need to
communicate with the global IPv4 networks [JJI07]. However, the
current transition methods do not fully support this requirement
[RFC4213]. For example, dual-stack hosts can communicate with both
the IPv4 and IPv6 hosts, but the IPv4 address depletion problem makes
the dual-stack approach inapplicable [COUNT]. The tunneled
architectures can link the IPv6 islands cross IPv4 networks, but they
cannot help the communication between two address families [RFC3056]
[RFC5214] [RFC4380]. The translation architectures can relay the
communications for the hosts located in IPv4 and IPv6 networks, but
the current implementation of this kind of architecture is not
scalable and it cannot maintain the end-to-end address transparency
[RFC2766] [RFC3142] [RFC4966] [RFC2775].
However, since IPv4 and IPv6 are different protocols with different
addressing structure, the translation mechanism is still necessary
for the communication between the two address families. There are
several ways to implement the translation. One is the stateless IP/
ICMP translation algorithm (SIIT), which provides a mechanism for the
translation between IPv4 and IPv6 packet headers (including ICMP
headers) without requiring any per-connection state. But, SIIT does
not specify the address assignment and routing scheme [RFC2766]. For
example, when SIIT is used for the IPv4 mapped IPv6 addresses
[::FFFF:ipv4-addr/96] and IPv4 compatible IPv6 addresses [::ipv4-
address/96]), these addresses violate the aggregation nature of the
IPv6 routing [RFC4291]. The other translation mechanism is NAT-PT,
which has serious technical and operational difficulties and IETF has
reclassified it from proposed standard to historic status. But in
the same document, it suggested that a revised, possibly restricted
version of NAT-PT can be a suitable solution for the communication
between IPv4 and IPv6 hosts [RFC4966]. Recently, several mechanisms
are proposed in this direction, for example NAT64 translates the IPv4
server address by adding or removing a /96 prefix, and translates the
IPv6 client address by installing mappings in the normal NAT manner
[I-D.bagnulo-behave-nat64].
In this document, we follow the basic specification of SIIT, but we
define the address assignment and routing scheme (IVI). Our IVI
mechanism is related to the NAT-PT and NAT64, but differs from them
significantly. First, it is stateless (or almost stateless) in both
the IPv4-to-IPv6 mapping direction, as well as in the IPv6-to-IPv4
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mapping direction. Secondly, it supports address transparency.
Thirdly, it supports both client-server applications and the peer-to-
peer applications cross IPv4 and IPv6 address families without using
NAT-traversal techniques. Finally, it can satisfy most of the basic
and advanced requirements for the IPv4 to IPv4 transition as
specified by the Internet Drafts [I-D.v6ops-nat64-pb-statement-req].
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2. Terms and Abbreviations
The following terms and abbreviations are used in this document:
IVI: IV means 4 and VI means 6 in Roman representation, so IVI means
mapping and translation between IPv4 and IPv6.
ISP(i): A specific Internet service provider "i".
IPG4: An address set containing all IPv4 addresses, the addresses in
this set are mainly used by IPv4 hosts at the current stage.
IPS4(i): A subset of IPG4 allocated to ISP(i).
IVI4(i): A subset of IPS4(i), the addresses in this set will be
mapped to IPv6 via IVI rule and physically used by IPv6 hosts of
ISP(i).
IPG6: An address set containing all IPv6 addresses.
IPS6(i): A subset of IPG6 allocated to ISP(i).
IVIG46(i): A subset of IPS6(i), an image of IPG4 in IPv6 address
family via IVI mapping rule.
IVI6(i): A subset of IVIG46(i), an image of IVI4(i) in IPv6 address
family via IVI mapping rule.
IVI gateway: The mapping and translation gateway between IPv4 and
IPv6 based on IVI scheme.
IVI DNS: Providing IVI Domain Name Service (DNS).
The key words MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,
SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in this
document, are to be interpreted as described in [RFC2119].
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3. The Overview of the IVI Mechanism
The IVI is a prefix-specific and stateless address mapping scheme
which can be carried out by individual ISPs.
IVI mapping and translation mechanism is implemented in an IVI
gateway which connects to both IPv4 and IPv6 networks. The SIIT
stateless translation is implemented in the IVI gateway [RFC2765].
A unique, prefix-specific and stateless mapping scheme is defined
between IPv4 addresses and subsets of IPv6 addresses, so each
provider-independent IPv6 address block (usually a /32) will have a
small portion of IPv6 addresses, which is the image of the totality
of the global IPv4 addresses.
Each provider can borrow a portion of its IPv4 addresses and maps
them into IPv6 based on the above mapping rule. These special IPv6
addresses will be physically used by IPv6 hosts. The original IPv4
form of the borrowed addresses is the image of these special IPv6
addresses.
The packets generated from the global IPv4 addresses and sent to the
special IPv6 addresses are routed to the IPv4 interface of the IVI
gateway via the IPv4 routing protocol and the packets generated from
the special IPv6 addresses and sent to the global IPv4 addresses are
routed to the IPv6 interface of the IVI gateway via the IPv6 routing
protocol. The processes in both directions are symmetric. In
addition, the special IPv6 addresses can communicate with the global
IPv6 networks.
The IVI scheme related issues, for example the IVI DNS support, the
multiplexing of the public IPv4 addresses, the IVI multicast support,
etc. can be solved without involving any major change in the current
Internet protocol.
3.1. Address Mapping
The IVI address mapping is defined based on individual ISP's prefix
as shown in the following figure.
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IVI Address Mapping
| 0 |32 |40 |72 127|
------------------------------------------------------------------
| |FF | | |
------------------------------------------------------------------
|<- IPv6 prefix ->| |<- IPv4 address ->|<- zero padding ->|
Figure 1
where bit 0 to bit 31 are the prefix of ISP(i)'s /32 (e.g.
IPS6=2001:DB8::/32), bit 32 to bit 39 are all one's as the identifier
of IVI, bit 40 to bit 71 are embedded global IPv4 space (IPG4)
presented in hexadecimal format. (e.g. 2001:DB8:ff00::/40). Because
this mapping is 1-to-1 defined by the IVI mapping rule, it is
stateless and it has feature of end-to-end address transparency.
(1) The ISP(i) uses a subset of ISP4(i) defined as IVI4(i), and maps
it into IPv6 as IVI6(i). The IVI6(i) is physically used by IPv6
hosts inside ISP(i)'s IPv6 network and the IVI4(i) cannot be used by
IPv4 hosts. Therefore, IVI6(i) is the special IPv6 address block
which can communicate with both address families.
(2) Based on the above mapping rule, the ISP(i) uses a subset of
ISP6(i) defined as IVIG46(i), and maps it into IPv4 as IPG4. The
IVIG46(i) is virtually used by global IPv4 hosts and it cannot be
used by IPv6 hosts, except the portion of IVI6(i).
The mapping of the different address sets and the relations are shown
in the following figure.
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IVI Address Mapping Relation
|<-------IPG4--------------------->|
| |<----IPS4(i)----->| |
| |<-IVI4(i)->| |
| | | |
| | /\ | |
| | || | |
| | mapping | |
| | || | |
| | \/ | |
| | | |
| |<-IVI6(i)->| |
|<------IPG46(i)------------------>|
|<--------IPS6(i)------------------------------>|
|<-----------IPG6-------------------------------------------->|
Figure 2
where IVI4(i) and IVI6(i) are representing the same entities in IPv4
and IPv6 address families, respectively. Similarly, IPG4 and
IVIG46(i) are representing the same entities in IPv4 and IPv6 address
families, respectively. In addition, IVI4(i) is a subset of IPG4 and
IVI6(i) is a subset of IVIG46(i).
3.2. Routing and Forwarding
Based on the IVI address mapping rule, the routing is
straightforward, as shown in the following figure.
IVI Routing
/-----\ /-----\
(Global ) ----192.168.1.2 ------------- 2001:DB8::2---- (Global )
(IPv4 )--|R1|-------------|IVI gateway|------------|R2|---(IPv6 )
(network) ---- 192.168.1.1-------------2001:DB8::1 ---- (network)
\-----/ \-----/
Figure 3
where
(1) Router R1 has IPv4 route of IVI4(i)/k (k is the prefix length of
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IVI4(i)) with next-hop equals to 192.168.1.1 and this route is
distributed to global IPv4 networks with proper aggregation.
(2) Router R2 has IPv6 route of IVIG46(i)/40 with next-hop equals to
2001:DB8::1 and this route is distributed to global IPv6 networks
with proper aggregation.
(3) IVI gateway has IPv6 route of IVI6(i)/(40+k) with next hop equals
to 2001:DB8::2. IVI gateway also has IPv4 default route 0.0.0.0/0
with next hop equals to 192.168.1.2 .
Note that the routes described above can be learned/inserted by
dynamic routing protocols in the IVI gateway neighboring (IGP) or
peering (BGP) with R1 and R2.
The address reachability matrix of the IPv4, IVI and IPv6 is shown in
the following figure.
IVI reachability Matrix
IPG4 IVI IPG6
---------------------------
IPG4 | OK OK NO
IVI | OK OK OK
IPG6 | NO OK OK
Figure 4
Since both IVI4(i) and IVI6(i) are aggregated to IPS4(i) and IPS6(i)
in ISP(i)'s border routers respectively, there will be no affect to
the global IPv4 and IPv6 routing tables [RFC4632].
If IVI4(i) and IVI6(i) has 1-to-1 mapping relationship, then IVI is
stateless and it can support multi-homing.
Since IVI can be implemented independently in each ISP's network, it
can be incrementally deployed.
3.3. IVI Communication Scenarios
Scenario 1:
Assume that there are IPv4 address A and ISP(1) IVI-mapped IPv6
address A', an arbitrary IPv4 address B and ISP(1) IVI-mapped IPv6
address B', as well as an arbitrary IPv6 address C'. If ISP(1)
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deploys IVI, then A' is a physical IPv6 host and B is a physical IPv4
host. A' can communicate with B via the IVI gateway. Note that in
this scenario A' is actually communicating with B', an image of B,
and B is actually communicating with A, an image of A'. Since A' is
an IPv6 address inside ISP6(1), it can also communicate with
arbitrary IPv6 host C'. This can form an early stage of IPv4/IPv6
coexistence and transition.
IVI Communication Scenario 1
------------------------
/ IPv4 \
| |
| A<------->B |
\ / /
------------/-----------
| /
------ /
|IVI GW| /
------ /
| /
------/----------------------------------
/ / \
| A'<-->B' |
| |
\ IPv6 C' /
-----------------------------------------
Figure 5
Scenario 2:
Assume that there are IPv4 address A, ISP(1) IVI-mapped IPv6 address
A' and ISP(2) IVI-mapped IPv6 address A''. Similarly, assume that
there are IPv4 address B, ISP(1) IVI-mapped IPv6 address B' and
ISP(2) IVI-mapped IPv6 address B''. If both ISP(1) and ISP(2) deploy
IVI, then A' and B'' are physical IPv6 hosts. In addition, if ISP(1)
and ISP(2) do not know the IVI deployment on the other end, then A'
can still communicate with B'' through A and B via two IVI gateways.
Note that in this scenario A' is actually communicating with B', an
ISP(1)'s version image of B, and B'' is actually communicating with
A'', an ISP(2)'s version image of A. Since there are two IVI gateways
involved, the routing is not optimal.
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IVI Communication Scenario 2
------------------------
/ IPv4 \
| |
| A<--------->B |
\ \ / /
---------\-----/--------
| \ / |
------ \ / ------
|IVI GW| . |IVI GW|
------ / \ ------
| / \ |
---------/-----\-------------------------
/ / \ \
| A'<->B' \ |
| \ |
| A''<->B'' |
\ IPv6 /
-----------------------------------------
Figure 6
Scenario 3:
Assume that there are IPv4 address A and ISP(1) IVI-mapped IPv6
address A'. Similarly, assume that there are IPv4 address B and
ISP(2) IVI-mapped IPv6 address B''. If both ISP(1) and ISP(2) deploy
IVI, then A' and B'' are physical IPv6 hosts. In addition, if ISP(1)
and ISP(2) by contrast know the IVI deployment on the other end, then
A' can communicate with B'' directly. Since it is the communication
in IPv6, the routing is optimal. This can form a later stage of the
transition.
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IVI Communication Scenario 3
------------------------
/ IPv4 \
| |
| A B |
\ /
------------------------
| |
------ ------
|IVI GW| |IVI GW|
------ ------
| |
-----------------------------------------
/ \
| A'<--------->B'' |
| |
\ IPv6 /
-----------------------------------------
Figure 7
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4. Design Considerations
The components of the IVI scheme include: address mapping, network-
layer header translation, transport-layer header translation,
fragmentation/MTU handling, ICMP handling, application layer gateway,
IPv6 source address selection and IPv4 over IPv6 support.
4.1. Address Mapping
The address mapping rule is defined in Section 3.1.
In addition, depending on the implementation scope of the IVI
gateway, IVIG46(i) block can also be defined as 2001:DB8:FFFF::/48,
2001:DB8:ABCD:FF00::/56 or 2001:DB8:ABCD:FFFF::/64, etc. A special
case is to define IVIG46(i)=2001:DB8:XXXX:XXXX:XXXX:XXXX::/96, then
the mapping rule is similar to the method of translating the IPv4
server address proposed in [I-D.bagnulo-behave-nat64].
4.2. Network-layer Header Translation
IPv4 [RFC791] [RFC791] and IPv6 [RFC2460] are different protocols
with different network layer header format, the translation of the
IPv4 and IPv6 headers must be performed [MVB98] [RFC2765] as shown in
the following figures.
IPv4 to IPv6 Header translation based on IVI scheme
-------------------------------------------------------------
IPv4 Field Translated to IPv6
-------------------------------------------------------------
Version (0x4) Version (0x6)
IHL discarded
Type of Service discarded
Total Length Payload Length = Total Length -IHL * 4
Identification discarded
Flags discarded
Offset discarded
Time to Live Hop Limit
Protocol Next Header
Header Checksum discarded
Source Address IVI address mapping
Destination Address IVI address mapping
Options discarded
-------------------------------------------------------------
Figure 8
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IPv6 to IPv4 Header translation based on IVI scheme
-------------------------------------------------------------
IPv6 Field Translated to IPv4 Header
-------------------------------------------------------------
Version (0x6) Version (0x4)
Traffic Class discarded
Flow Label discarded
Payload Length Total Length = Payload Length + 20
Next Header Protocol
Hop Limit TTL
Source Address IVI address mapping
Destination Address IVI address mapping
- IHL = 5
- Header Checksum recalculated
-------------------------------------------------------------
Figure 9
4.3. Transport-layer Header Translation
Since the TCP and UDP headers [RFC793] [RFC768] consist of check sums
which include the IP header, the recalculation and updating of the
transport-layer headers must be performed [RFC2765].
4.4. Fragmentation and MTU Handling
When the packet is translated by the IVI gateway, due to the
different sizes of the IPv4 and IPv6 headers, the IVI6 packets will
be at least 20 bytes larger than the IVI4 packets, which may exceed
the MTU of the next link in the IPv6 network. Therefore, the MTU
handling and translation between IPv6 fragmentation headers and
fragmentation field in the IPv4 headers are necessary, which is
performed in the IVI gateway according to SIIT [RFC2765].
4.5. ICMP Handling
For ICMP message translation between IPv4 and IPv6, IVI follows the
ICMP/ICMPv6 message correspondence as defined in SIIT [RFC2765].
Note that the ICMP message may be generated by an intermediate router
whose IPv6 address does not belong to IVIG46(i). Since ICMP
translation is important to the path MTU discovery, the inverse
mapping for unmapped addresses is defined in this document. In the
current prototype, a pseudo IPv4 address is generated in such a way
that the first 16 bits are the IPv4 address of the IVI gateway, and
the last 16 bits are the AS number of the current domain. This
prevents translated ICMP messages from being discarded due to unknown
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or private IP source. A small IPv4 address block should be reserved
to identify the non-IVI mapped IPv6 addresses.
4.6. Application Layer Gateway
Due to the features of 1-to-1 address mapping and stateless, IVI can
support most of the existing applications, such as HTTP, SSH, Telnet
and Microsoft Remote Desktop Protocol. However, some applications
are designed such that IP addresses are used to identify application-
layer entities (e.g. FTP). In these cases, application layer
gateway (ALG) is unavoidable, but it can be integrated into the IVI
gateway. A list of applications which support the IVI scheme will be
given in a later version of this document.
4.7. IPv6 Source Address Selection
Since each IPv6 host may have multiple addresses, it is important for
the host to use an IVI6(i) address to reach the global IPv4 networks.
The short-term work around is to use IVI6(i) as the default IPv6
address of the host. The long-term solution requires that the
application be able to select the source addresses for different
services.
4.8. IPv4 over IPv6 Support
The IVI scheme can support the IPv4 over IPv6 service (NAT646), i.e.
a stub IPv4 network can be connected to an IVI gateway to reach the
IPv6 network and via another IVI gateway to reach the global IPv4
network [RFC4925]
A more interesting scenario is to integrate the functions of the
first IVI gateway into the end-system. In this case, the application
softwares are IPv4-based and there is no need to have ALG support in
the IVI gateway when it is communicating with IPv4 hosts.
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5. DNS Configuration and Mapping
The DNS [RFC1035] service is important for the IVI scheme.
5.1. DNS Configuration for the IVI6(i) Addresses
For providing authoritative DNS service for IVI4(i) and IVI6(i), each
host name will both have an A record and an AAAA record pointing to
IVI4(i) and IVI6(i), respectively. Note that the same name always
points to a unique host, which is an IVI6(i) host and it has IVI4(i)
representation via the IVI gateway.
5.2. DNS Mapping for the IVIG46(i) Addresses
For resolving the IVI IPv6-mapped global IPv4 space (IVIG46(i)), each
ISP must provide customized IVI DNS service for the IVI6(i) hosts.
The IVI DNS server is in dual stack environment. When the IVI6(i)
host queries an AAAA record for an IPv4 only domain name, the IVI DNS
server will query the A record and map it to IVIG46(i) with ISP's
IPv6 prefix and return an AAAA record to the IVI6(i) host.
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6. Multiplexing of the Global IPv4 Addresses
Since public-IPv4 address is a scarce resource, the effective use of
the IPv4 address is important for the IVI scheme. The multiplexing
techniques are temporal multiplexing, port multiplexing, spatial
multiplexing and multiplexing using IPv4 NAT-PT techniques.
6.1. Temporal Multiplexing
The IVI6 can be temporally multiplexed inside the ISP(i)'s /32. This
is to say that the ISP can dynamically assign IVI6(i) to an end
system when it requests the IPv4 communication service and release
the IVI6(i) when the communication is finished. For temporal
multiplexing, the features of stateless and end-to-end address
transparency are maintained.
6.2. Port Multiplexing
To further increase the utilization ratio of the public IPv4
addresses, the port multiplexing inside the ISP(i)'s /32 can be
deployed [RFC2766] [RFC4966]. This is to say that a single IPv4
address (IVI4(i)) can be used for multiple IVI6(i) addresses. The
mapping scheme is to use the least significant bits in the IVI6(i) to
define the multiple mapping and combine the transport-layer port
number to perform uniquely the mapping from IVI4(i) to IVI6(i).
IVI Address Mapping for Port Multiplexing
Ratio IVI6(i) range
----------------------------------------------------------------
1-to-1 2001:DB8:ffxx:xxxx:xx00:: - 2001:DB8:ffxx:xxxx:xx00::
1-to-2^1 2001:DB8:ffxx:xxxx:xx00:: - 2001:DB8:ffxx:xxxx:xx00::1
......
1-to-2^4 2001:DB8:ffxx:xxxx:xx00:: - 2001:DB8:ffxx:xxxx:xx00::15
----------------------------------------------------------------
Figure 10
Based on this method, the mapping gain can be adjusted incrementally
depending on the requirements. For example, zero bit means 1-to-1
mapping, and it is stateless. One bit means 1-to-1 mapping, and it
has two states. Four bits means 1-to-16 mapping, etc. In the case
of one-to-many mapping, when two IVI6(i)s have the same port number,
the IVI gateway will map one of the port number to an unused port
number and maintain the mapping table (IVI4(i) plus port number).
Since the one-to-many mapping loses the feature of being stateless
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and may loses the end-to-end address transparency, the proper use of
the one-to-many mapping is the balancing of tradeoffs [RFC4966].
The tradeoffs are: (1) the number of the port number (2^16); (2) the
gain of the IPv4 address utilization; (3) half association (3-tuple:
source IP address, source port, transport protocol) or full
association (5-tuple: source IP address, source port, destination IP
address, destination port, transport protocol); (4) the number of
states in the IVI gateway; (5) the average concurrent port used in an
IPv6 host and; (6) the collision ratio of the port number.
6.3. Spatial Multiplexing
The spatial multiplexing means that for different operation modes of
server and client, the different port multiplexing ratios can be
applied. There are basically three cases.
(1) Server: we suggest having 1-to-1 mapping between IVI4(i) and
IVI6(i), because it has the advantages of end-to-end address
transparency, being stateless, having multi-homing support and
providing services via well-known ports.
(2) Client with self-initiated connection: we suggest having 1-to-2^N
mapping between IVI4(i) and IVI6(i) (N is a positive integer greater
than 1), i.e. one IVI4(i) can support several IVI6(i) users to access
the IPv4 network. By adjusting N, The number of states can be
controlled. In this case, the port number is randomly generated by
the client operating system. The IVI gateway maintains the port
mapping table to avoid collision. There is no need to modify the
client operating system and/or client application.
(3) Client with peer initiated connection: we suggest having 1-to-2^M
mapping between IVI4(i) and IVI6(i) (M is a positive integer greater
than 1 and may be smaller than N), i.e. one IVI4(i) can support
several IVI6(i) users as the peer-to-peer hosts for the IPv4 network.
By adjusting M, The number of states can be controlled. In this
case, we can define "pseudo-well-known port number", which is unique
for IVI4(i) and known to the peers. However, modification of the
client operating system and/or client application may be necessary.
By combining address and pseudo-well-known port number, the feature
of end-to-end address transparency can still be maintained.
6.4. Multiplexing using IPv4 NAT-PT
If the private IPv4 address (e.g. 10.0.0.0/8) is used as the IPv4
address under the IVI scheme, combining conventional NAT-PT and NAT-
traversing techniques, the public IPv4 addresses can also be
multiplexed. The advantage of this method is that IPv4 NAT-PT
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equipments are widely available and can be deployed immediately.
Moreover, the mapped prefix-specific IPv6 addresses (IVI6(i)) are no
longer behind the NAT box in IPv6 and can be accessed by any IPv6
hosts.
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7. IVI Multicast Support
The IVI scheme can support IPv4/IPv6 communication of the protocol-
independent specific-source sparse-mode multicast (PIM SSM) [RFC3171]
[RFC3569] [RFC4607].
(1) The IVI group address mapping rule: There will be 2^24 group
addresses for IPv4 SSM. The corresponding IPv6 SSM group addresses
can be defined as shown in the following figure.
IVI Multicast Group Address Mapping
-------------------------------------------------------
IPv4 Group Address IPv6 Group Address
-------------------------------------------------------
232.0.0.0/8 ff3e:0:0:0:0:0:f000:0000/96
232.255.255.255/8 ff3e:0:0:0:0:0:f0ff:ffff/96
-------------------------------------------------------
Figure 11
(2) The IVI multicast source address selection: The source address in
IPv6 has to be IVI6(i) in order to perform reverse path forwarding
(RPF) as required by PIM-SM.
(3) The multicast protocol: The inter operation of PIM-SM for address
families IPv4 and IPv6 can either be implemented via the application
layer gateway or via the static join based on IGMPv3 and MLDv2 in
IPv4 and IPv6, respectively.
The Any Source Multicast (ASM) cannot be supported in the cross
address-family environment, since IPv6 does not support the MSDP
[RFC4611], and IPv4 does not support the embedded RP [RFC3956].
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8. IVI Implementation and Preliminary Testing Results
The IVI scheme presented in this document is implemented in the Linux
OS and the source code can be downloaded [LINUX]. The example of the
configuration is shown in Appendix A.
The IVI gateway based on the Linux implementation has been deployed
between CERNET (IPv4 and partially dual-stack) [CERNET] and CNGI-
CERNET2 (pure IPv6) [CERNET2] since March 2006. The pure IPv6 web
servers using IPv6 addresses (IVI) behand IVI gateway can be accessed
by the IPv4 hosts [IVI4], and also by the global IPv6 hosts [IVI6].
In addition, two traceroute results are presented in Appendix B to
show the address mapping of the IVI scheme.
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9. Features of IVI
The basic features of the IVI scheme are:
(1) Special IPv6 addresses can communicate with the global IPv6
network directly and can communicate with the global IPv4 network via
IVI gateways.
(2) When the mapping is 1-to-1, the IVI gateway is stateless and can
support multi-homing. When mapping is 1-to-2^N (N!=0), the IVI
gateway is stateful, but the number of state can be controlled.
(3) When the mapping is 1-to-1, the IVI scheme has the advantages of
end-to-end address transparency. When mapping is 1-to-2^M, by
introducing pseudo-well-known ports, the feature of end-to-end
address transparency can also be maintained.
(4) The IVI addresses are globally routable.
(5) The IVI scheme is incrementally deployable.
(6) Based on the multiplexing techniques, the global IPv4 addresses
can be effectively used.
The IVI scheme can satisfy most of the basic and advanced
requirements for the IPv4 to IPv4 transition as specified by the
Internet Drafts [I-D.v6ops-nat64-pb-statement-req].
For the basic requirements (MUST):
(1) No need to change the end system (IPv4 and IPv6).
(2) Support v4-initiated and v6-initiated short-lived local handle.
(3) Support interaction with dual-stack hosts.
(4) The standard IPv4 NAT can easily be integrated into the system.
(5) Do not violate standard DNS semantics.
(6) No affect to IPv6 routing.
(7) Support TCP, UDP, ICMP.
(8) Can handle fragmentation.
For the advanced requirements (SHOULD):
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(1) Support multicast (SSM).
(2) Support operational flexibility.
(3) Support central Management.
Other requirements specified by the IETF RFC or the IETF drafts will
be studied in a later version of this document.
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10. Address Policy and IVI Address Evolution
Based on the IVI scheme, we propose to modify IPv4 address-allocation
and IPv6 address-assignment policies [RFC1744] [RFC2008] for IPv4/
IPv6 coexistence and transition as follows.
10.1. IPv6 Address Assignment Policy
(1) Reserve 2001:DB8:ff00::/40 for each 2001:DB8::/32 (2001:DB8::/32
is the documentation address, which represents all /32s [RFC4291]).
(2) Encourage ISPs to deploy their IPv6 networks and to install their
IVI gateways.
(3) Encourage ISPs to use a subset (i.e. IVI4(i)) of their own IPv4
address blocks and map it into IPv6 via the IVI scheme (i.e.
IVI6(i)) for their initial deployment of IPv6. For severs using the
1-to-1 mapping, and for clients using the 1-to-2^N mapping. In this
way, the scarce IPv4 addresses can be effectively used. This special
IPv6 block can communicate with the global IPv6 networks directly and
communicate with the global IPv4 networks via IVI gateways.
(4) Encourage ISPs to increase the size of IVI4(i). When
IVI4(i)=IPS4(i), the IPv4 to IPv6 transition for ISP(i) will be
accomplished.
10.2. IPv4 Address Allocation Policy
(1) The remaining IPv4 address should be dedicated for the IVI
transition use, i.e. using these blocks for the IVI6(i) deployment.
The users using IVI6(i) can access the IPv6 networks directly and the
IPv4 networks via the IVI gateways.
(2) Based on multiplexing techniques, the global IPv4 addresses can
be used effectively. For example, with a reasonable port
multiplexing ratio (say 16), one /8 can support 268M hosts. If 10
/8s can be allocated for the IVI use, it will be 2.6 billion
addresses, possibly enough even for the unwired population in the
world. The 43.0.0.0/8 could be a good candidate for the initial
trial [APNIC].
10.3. Evolution of the IVI Addresses and Services
The IVI scheme is an effective method for transparent IPv4/IPv6
coexistence and smooth IPv4/IPv6 transition. Unlike the existing
transition techniques which treat the IPv6 addresses equally
[JSG2008], the IVI scheme suggests dividing the current IPv6
addresses into IVI6 addresses and non-IVI6 addresses. The IVI6
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addresses, due to their nature as images of IVI4, can communicate
with the global IPv4 networks via IVI gateways and they can also
communicate with the global IPv6 networks directly. Therefore, the
ISPs should use the IVI6 addresses for the initial deployment of
their IPv6 infrastructure and this should be the IPv4/IPv6
coexistence stage. When IVI4(i)=IPS4(i) for most of ISP(i), the rest
of the IPv6 addresses (non IVI6(i)) can be used for the further
development of the global Internet, as shown in the following figure.
IPv4/IPv6 Address Coexistence and Evolution
-------------------------------------------------
IPv4 area | IPv6 area
---------- --- ---------------- --------------
Service | IPv4 | | IPv6 IVI | |IPv6 non-IVI|
-------------- ---------------- --------------
| \ / | \ / |
| \ / | \ / |
| \ --- / | \/ |
| \| |/ | /\ |
Network | - --|IVI|---- | / \ |
| | |GW | | | | | |
| | /| |\ | | | | |
| | / --- \ | | | | |
| /\ | | | | /\ | | /\ | /\ |
| / \ | | | | / \ |/ / \ \ / \ |
--------------- ---------------- --------------
User | IPv4 | | IPv6 IVI | |IPv6 non-IVI|
--------------- ---------------- --------------
Coexistence => Transition
Figure 12
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11. Security Considerations
This document presents the prefix-specific and stateless address
mapping scheme (IVI) for the IPv4/IPv6 coexistence and transition.
The IPv4 security and IPv6 security issues should be addressed by
related documents of each address family and are not included in this
document.
However, the specific security issues for the IVI gateway
implementation should be studied and addressed during the development
of the IVI mechanisms.
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12. IANA Considerations
The address allocation and assignment policies discussed in this
document may have impact to IANA operation.
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13. Principal Authors
Xing Li
Maoke Chen
Congxiao Bao
Hong Zhang
Jianping Wu
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14. Contributors
The authors would like to acknowledge the following contributors in
the different phases of the IVI development: Ang Li, Yuncheng Zhu,
Junxiu Lu and Yu Zhai.
The authors would like to acknowledge the following contributors who
provided helpful inputs concerning the IVI concept: Bill Manning,
David Ward, Lixia Zhang, Jun Murai and Fred Baker.
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15. Acknowledgments
The authors thank to the funding supports of the CERNET, CNGI-
CERNET2, CNGI Research and Development, China "863" and China "973"
projects.
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16. Appendix A. The IVI gateway configuration example
IVI Configuration Example
#!/bin/bash
# open forwarding
echo 1 > /proc/sys/net/ipv6/conf/all/forwarding
echo 1 > /proc/sys/net/ipv4/conf/all/forwarding
# config route for IVI6 = 2001:da8:ffca:2661:cc00::/70,
# IVI4 = 202.38.97.204/30
# configure IPv6 route
route add -A inet6 2001:da8:ffca:2661:cc00::/70 \
gw 2001:da8:aaae::206 dev eth0
# config mapping for source-PF = 2001:da8::/32
# config mapping for destination-PF = 2001:da8::/32
# for each mapping, a unique pseudo-address (10.0.0.x/8)
# should be configured.
# ip addr add 10.0.0.1/8 dev eth0
# IPv4-to-IPv6 mapping, multiple mappings can be done via multiple
# commands.
# mroute IVI4-network IVI4-mask pseudo-address interface \
# source-PF destination-PF
/root/mroute 202.38.97.204 255.255.255.252 10.0.0.1 \
eth0 2001:da8:: 2001:da8::
# IPv6-to-IPv4 mapping
# mroute6 destination-PF destination-PF-pref-len
/root/mroute6 2001:da8:ff00:: 40
Figure 13
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17. Appendix B. The traceroute results
ivitraceroute
ivitraceroute 202.38.108.2
1 202.112.0.65 6 ms 2 ms 1 ms
2 202.112.53.73 4 ms 6 ms 12 ms
3 202.112.53.178 1 ms 1 ms 1 ms
4 202.112.61.242 1 ms 1 ms 1 ms
5 202.38.17.186 1 ms 1 ms 1 ms
202.38 AS4538
6 202.38.17.186 1 ms 1 ms 1 ms
202.38 AS4538
7 202.38.17.186 2 ms 2 ms 2 ms
202.38 AS4538
8 202.38.17.186 2 ms 2 ms 2 ms
202.38 AS4538
9 202.38.17.186 4 ms 4 ms 3 ms
202.38 AS4538
10 202.38.108.2 2 ms 3 ms 3 ms
Figure 14
Note that the non-IVI IPv6 addresses are mapped to 202.38.17.186,
which is defined in this document (the first two sections are the
IPv4 prefix of /16 of the IVI gateway interface and the last two
sections are the autonomous system number 4538).
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ivitraceroute6
ivitraceroute6 www.mit.edu
src_ivi4=202.38.97.205 src_ivi6=2001:da8:ffca:2661:cd00::
dst_host=www.mit.edu
dst_ip4=18.7.22.83 dst_ivig=2001:da8:ff12:716:5300::
traceroute to 2001:da8:ff12:716:5300:: (2001:da8:ff12:716:5300::),
30 hops max, 40 byte packets to not_ivi
1 2001:da8:ff0a:0:100:: 0.304 ms 0.262 ms 0.190 ms
10.0.0.1
2 2001:da8:ffca:7023:fe00:: 0.589 ms * *
202.112.35.254
3 2001:da8:ffca:7035:4900:: 1.660 ms 1.538 ms 1.905 ms
202.112.53.73
4 2001:da8:ffca:703d:9e00:: 0.371 ms 0.530 ms 0.459 ms
202.112.61.158
5 2001:da8:ffca:7035:1200:: 0.776 ms 0.704 ms 0.690 ms
202.112.53.18
6 2001:da8:ffcb:b5c2:7d00:: 89.382 ms 89.076 ms 89.240 ms
203.181.194.125
7 2001:da8:ffc0:cb74:9100:: 204.623 ms 204.685 ms 204.494 ms
192.203.116.145
8 2001:da8:ffcf:e7f0:8300:: 249.842 ms 249.945 ms 250.329 ms
207.231.240.131
9 2001:da8:ff40:391c:2d00:: 249.891 ms 249.936 ms 250.090 ms
64.57.28.45
10 2001:da8:ff40:391c:2a00:: 259.030 ms 259.110 ms 259.086 ms
64.57.28.42
11 2001:da8:ff40:391c:700:: 264.247 ms 264.399 ms 264.364 ms
64.57.28.7
12 2001:da8:ff40:391c:a00:: 271.014 ms 269.572 ms 269.692 ms
64.57.28.10
13 2001:da8:ffc0:559:dd00:: 274.300 ms 274.483 ms 274.316 ms
192.5.89.221
14 2001:da8:ffc0:559:ed00:: 274.534 ms 274.367 ms 274.517 ms
192.5.89.237
15 * * *
16 2001:da8:ff12:a800:1900:: 276.032 ms 275.876 ms 276.090 ms
18.168.0.25
17 2001:da8:ff12:716:5300:: 276.285 ms 276.370 ms 276.214 ms
18.7.22.83
Figure 15
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Note that all of the IPv4 addresses can be mapped to prefix-specific
IPv6 addresses (for example 18.7.22.83 is mapped to 2001:da8:ff12:
716:5300::).
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18. References
18.1. Normative References
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", RFC 1035, November 1987.
[RFC2008] Rekhter, Y. and T. Li, "Implications of Various Address
Allocation Policies for Internet Routing", RFC 2008,
October 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, March 1997.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, December 1998.
[RFC2765] Nordmark, E., "Stateless IP/ICMP Translation Algorithm
(SIIT)", RFC 2765, February 2000.
[RFC2766] Tsirtsis, G. and P. Srisuresh, "Network Address
Translation - Protocol Translation (NAT-PT)", RFC 2766,
Feb. 2000.
[RFC3056] Carpenter, B. and K. Moore, "Connection of ipv6 domains
via ipv4 clouds", RFC 3056, February 2001.
[RFC3171] Albanna, Z., Almeroth, K., Meyer, D., and M. Schipper,
"IANA Guidelines for IPv4 Multicast Address Assignments",
RFC 3171, August 2001.
[RFC3956] Savola , P. and B. Haberman , "Embedding the Rendezvous
Point (RP) Address in an IPv6 Multicast Address",
RFC 3956, November 2004.
[RFC4213] Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms
for IPv6 Hosts and Routers", RFC 4213, October 2005.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, Feb. 2006.
[RFC4380] Huitema , C., "Teredo: Tunneling ipv6 over udp through
network address translations (nats)", RFC 4380, Feb. 2006.
[RFC4607] Holbrook , H. and B. Cain , "Source-Specific Multicast for
IP", RFC 4607, August 2006.
[RFC4611] McBride, M., Meylor, J., and D. Meyer, "Multicast Source
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Discovery Protocol (MSDP) Deployment Scenarios", RFC 4611,
August 2006.
[RFC4632] Fuller, V. and T. Li, "Classless Inter-domain Routing
(CIDR): The Internet Address Assignment and Aggregation
Plan", RFC 4632, August 2006.
[RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site
Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214,
March 2008.
[RFC768] Postel , J., "User Datagram Protocol", RFC 768,
August 1981.
[RFC791] Postel, J., "Internet Protocol", RFC 791, September 1981.
[RFC793] Postel, J., "Transmission Control Protocol", RFC 793,
Semptember 1981.
18.2. Informative References
[APNIC] Ito, K., "Large IPv4 address space Usage trial for Future
IPv6 Deployment", http://www.apnic.net/meetings/25/
program/policy/ito-large-ipv4-trial.pdf .
[CERNET] "CERNET Homepage:
http://www.edu.cn/english_1369/index.shtml".
[CERNET2] "CNGI-CERNET2 Homepage:
http://www.cernet2.edu.cn/index_en.htm".
[COUNT] "IPv4 address count down: http://penrose.uk6x.com/".
[I-D.bagnulo-behave-nat64]
Bagnulo, M., Matthews, P., and I. van Beijnum, "NAT64/
DNS64: Network Address and Protocol Translation from IPv6
Clients to IPv4 Servers",
draft-bagnulo-behave-nat64-00 (work in progress),
June 2008.
[I-D.v6ops-nat64-pb-statement-req]
Bagnulo, M., Baker, F., and I. van Beijnum, "IPv4/IPv6
Coexistence and Transition: Requirements for solutions",
draft-ietf-v6ops-nat64-pb-statement-req-00 (work in
progress), May 2008.
[IVI4] "Test homepage for the IVI4(i): http://202.38.114.1/".
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[IVI6] "Test homepage for the IVI6(i):
http://[2001:250:ffca:2672:0100::0]/".
[JJI07] Joseph, D., Chuang, J., and I. Stocia, "Modeling the
Adoption of new Network Architectures", EECS Department,
University of California, Berkeley Tech. Rep. UCB/
EECS-2007-41, April 2007.
[JSG2008] "A Report of Japaness Study Group on Internet's Smooth
Transition to IPv6:
http://www.soumu.go.jp/joho_tsusin/eng/pdf/080617_1.pdf",
June 2008.
[LINUX] "Source Code of the IVI implementation for Linux:
http://linux.ivi2.org/impl/".
[MVB98] Fiuczynski, M., Lam, V., and B. Bershad , "The design and
implementation of an ipv6/ipv4 network address and
protocol translator", Proceedings of the USENIX Annual
Technical Conference (NO 98), June 1998.
[RFC1744] Huston, G., "Observations on the Management of the
Internet Address Space", RFC 1744, December 1994.
[RFC2775] Carpenter, B., "Internet Transparency", RFC 2775,
Feb. 2000.
[RFC3142] Hagino, J. and K. Yamamoto, "An IPv6-to-IPv4 Transport
Relay Translator", RFC 3142, June 2001.
[RFC3569] Bhattacharyya, S., "An Overview of Source-Specific
Multicast (SSM)", RFC 3569, July 2003.
[RFC4925] Li, X., Dawkins, S., Ward, D., and A. Durand, "Softwire
Problem Statement", RFC 4925, July 2007.
[RFC4966] Aoun, C. and E. Davies, "Reasons to Move the Network
Address Translator - Protocol Translator (NAT-PT) to
Historic Status", RFC 4966, July 2007.
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Authors' Addresses
Xing Li
CERNET Center/Tsinghua University
Room 225, Main Building, Tsinghua University
Beijing 100084
CN
Phone: +86 62785983
Email: xing@cernet.edu.cn
Maoke Chen
CERNET Center/Tsinghua University
Room 225, Main Building, Tsinghua University
Beijing 100084
CN
Phone: +86 62785983
Email: mk@cernet.edu.cn
Congxiao Bao
CERNET Center/Tsinghua University
Room 225, Main Building, Tsinghua University
Beijing 100084
CN
Phone: +86 62785983
Email: congxiao@cernet.edu.cn
Hong Zhang
CERNET Center/Tsinghua University
Room 225, Main Building, Tsinghua University
Beijing 100084
CN
Phone: +86 62785983
Email: neilzh@gmail.com
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Jianping Wu
CERNET Center/Tsinghua University
Room 225, Main Building, Tsinghua University
Beijing 100084
CN
Phone: +86 62785983
Email: jianping@cernet.edu.cn
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The IETF invites any interested party to bring to its attention any
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Li, et al. Expires January 7, 2009 [Page 41]
