DHC WG Y. Cui
Internet-Draft Q. Sun
Updates: 2131 (if approved) Tsinghua University
Intended status: Standards Track I. Farrer
Expires: August 17, 2014 Deutsche Telekom AG
Y. Lee
Comcast
Q. Sun
China Telecom
M. Boucadair
France Telecom
February 13, 2014
Dynamic Allocation of Shared IPv4 Addresses
draft-csf-dhc-dynamic-shared-v4allocation-00
Abstract
This memo describes the dynamic allocation of shared IPv4 addresses
to clients using the DHCPv4 protocol. Address sharing allows a
single IPv4 address to be allocated to multiple, active clients
simultaneously, each client being differentiated by a unique set of
L4 source ports. The changes necessary to existing DHCPv4 client and
server behaviour are described and a new DHCPv4 option for
provisioning clients with shared IPv4 addresses is included.
Due to the nature of sharing IP addresses, there are necessarily some
limitations to the applicability. This memo describes those
limitations and recommends suitable architectures and technologies
where address sharing may be utilized.
Requirements Language
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].
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on August 17, 2014.
Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Functional Overview . . . . . . . . . . . . . . . . . . . . . 4
3. Client-Server Interaction . . . . . . . . . . . . . . . . . . 4
3.1. Allocating a Shared, Dynamic IPv4 Address . . . . . . . . 5
3.2. Reusing a Previously Allocated Shared, Dynamic IPv4
address . . . . . . . . . . . . . . . . . . . . . . . . . 6
4. Server Behavior . . . . . . . . . . . . . . . . . . . . . . . 6
4.1. Leasing Shared and Non-Shared IPv4 Addresses from a
Single DHCP 4o6 Server . . . . . . . . . . . . . . . . . 7
5. Client Behavior . . . . . . . . . . . . . . . . . . . . . . . 7
5.1. Client Usage of a Shared Address . . . . . . . . . . . . 7
6. Additional Changes to RFC 2131 . . . . . . . . . . . . . . . 8
7. DHCPv4 Port Parameters Option . . . . . . . . . . . . . . . . 8
8. Security Consideration . . . . . . . . . . . . . . . . . . . 9
8.1. Denial-of-Service . . . . . . . . . . . . . . . . . . . . 9
8.2. Port Randomization . . . . . . . . . . . . . . . . . . . 9
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
11.1. Normative References . . . . . . . . . . . . . . . . . . 10
11.2. Informative References . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
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1. Introduction
Shortages of available public IPv4 addresses mean that it is not
always possible for operators to allocate a full IPv4 address to
every customer. This problem may be particularly acute whilst the
operator is in the migration phase from a native IPv4 network to a
native IPv6 network with IPv4 provided as an overlay service. This
is likely to increase the requirement on public IPv4 addresses to
provide for both existing and transition networks.
Two main types of solution have emerged to ease the problem:
1. Centralised Network Address Translation (NAT44) in the core
network
2. Distributing the same public IPv4 address to multiple clients
using non-overlapping layer 4 port sets.
The solution described in this memo is only suitable on the second
solution.
[I-D.ietf-dhc-dhcpv4-over-dhcpv6] introduces a "DHCP 4o6 Server",
which is capable of servicing both DHCPv6 [RFC3315] and DHCPv4-over-
DHCPv6 requests. This enables the provisioning of DHCPv4 based
configuration to IPv6 connected clients over IPv6 only transport
networks.
One of the benefits of the DHCPv4-over-DHCPv6 based approach is that
it allows the dynamic leasing of IPv4 addresses to clients, based on
existing mechanisms for address lease management available in DHCPv4
servers. This can make much more efficient use of remaining public
IPv4 addresses than static pre-allocation based approaches as only
IPv4 clients that are currently active need to be allocated
addresses. This memo uses the defined OPTION_PORTPARAMSV4 with
DHCPv4 over DHCPv6, achieving the dynamic leasing of the shared IPv4
addresses.
Due to the nature of address sharing in this manner, it is only
suitable for specific architectures based on the Address plus Port
Model (A+P) [RFC6346]. This model extends the unique identifier for
a client from the 32-bit IPv4 address to 48-bits by including the
16-bits of the layer 4 header. Each client is allocated a unique
block of layer 4 ports, and the client will generally utilize these
restricted source ports by implementing a NAPT44 funtion, translating
traffic from the original private IPv4 source address and
unrestricted port to the allocated shared IPv4 address and unique
restricted port range. [I-D.ietf-softwire-map] and
[I-D.ietf-softwire-lw4over6] describe two implemented examples of the
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A+P approach which may be suitable for shared, dynamic IPv4
addressing.
The use of shared addressing in other, more traditional deployment
architectures must be avoided due to the fundamental
incompatibilities of assigning a the same /32 IPv4 address to
multiple clients attached to the same layer 2 segment.
This memo also defines OPTION_PORTPARAMSV4, a DHCPv4 option for
assigning non-overlapping layer 4 port sets during the IPv4 address
allocation process.
Although DHCPv4 over DHCPv6 is used as the underlying DHCPv4
transport mechanism throughout this document, OPTION_PORTPARAMSV4 may
also be used in DHCPv4 over IPv6 [I-D.ietf-dhc-dhcpv4-over-ipv6] and
other DHCPv4 IPv4 address allocation mechanisms. The usage of
OPTION_PORTPARAMSV4 in those cases is out of scope of this document.
2. Functional Overview
Functionally, the dynamic allocation of shared IPv4 addresses by the
DHCP 4o6 Server is quite similar to the normal DHCPv4 server dynamic
allocation process described in [RFC2131]. The essential difference
is that the DHCP 4o6 Server MAY allocate the same IPv4 address to
more than one DHCP 4o6 client simultaneously, providing that each
address allocation also includes a range of layer 4 source ports
unique to that address (i.e. each PSID may only be allocated once per
/32 address).
To enable this, the DHCP 4o6 client needs to be extended to implement
OPTION_PORTPARAMSV4 (described below). This option is used to
indicate to the DHCP 4o6 server the client's support the dynamic
allocation of a shared IPv4 address and also for conveying the
allocated PSID back to the client.
The server must be extended to implement OPTION_PORTPARAMSV4 so that
it can identify clients supporting shared, dynamic address leasing.
With this option, the server can dynamically maintain shared IPv4
address leases. The server must also manage unique client leases
based on the IPv4 address and PSID tuple, instead of just IPv4
address.
3. Client-Server Interaction
Section 3 of [RFC2131] describes client-server interactions necessary
for leasing addresses. The following sections describe the changes
necessary for the client and server to implement the dynamic
allocation of a shared IPv4 address.
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3.1. Allocating a Shared, Dynamic IPv4 Address
Section 3.1 of [RFC2131] describes the client-server interaction for
allocating an IPv4 address. The process described below detail the
changes necessary for the allocation of a shared IPv4 address.
Using DHCP 4o6, the following DHCPv4 message flow is transported
within the DHCPV4-QUERY and DHCPV4-RESPONSE options, which are DHCPv6
options used for carrying DHCPv4 messages.
1. When the client constructs its DHCPv4 DHCPDISCOVER message to be
transported within the DHCPv4-query message, the DHCPDISCOVER
message MUST include the following options: A client Identifier
(constructed as per [RFC4361] and OPTION_PORTPARAMSV4 (described
below). The client MAY insert a non-zero value in the PSID-Len
field within OPTION_PORTPARAMSV4 to indicate the preferred size
of the restricted port range allocation to the DHCP 4o6 Server.
2. Each DHCP 4o6 Server that receives the DHCPDISCOVER message
within the DHCPv4-query message responds with a DHCPOFFER message
that contains an available IPv4 address in the 'yiaddr' field.
The response MUST also include OPTION_PORTPARAMSV4 containing a
restricted port-range. If the received OPTION_PORTPARAMSV4 field
contains a non-zero PSID-Len field, the DHCP 4o6 Server MAY
allocate a port set of the requested size to the client
(depending on policy). The DHCPOFFER message is included into
the DHCPv4-response message and sent to the client.
3. The client evaluates all received DHCPOFFER messages and selects
one based on the configuration parameters received, such as the
size of the offered port set. The client then sends a
DHCPREQUEST containing a server identifier and the corresponding
OPTION_PORTPARAMSV4 received in the DHCPOFFER message.
4. The server identified in the DHCPREQUEST message (via the siaddr
field) creates a binding for the client. The binding includes
the client identifier, the IPv4 address and the PSID. These
parameters are used by both the server and the client to identify
a lease referred to in any DHCP messages. The server responds
with a DHCPACK message containing the configuration parameters
for the requesting client. Optionally, the the server may also
store the IPv6 address that the client has bound the received
IPv4 paramters to.
5. The client receives the DHCPACK message with the configuration
parameters. The client MUST NOT perform a final check on the
address, such as ARPing for a duplicate allocated address.
6. If the client chooses to relinquish its lease by sending a
DHCPRELEASE message, the client MUST include the original client
identifier, the leased network address and the allocated
restricted source ports inlcuded in OPTION_PORTPARAMSV4.
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3.2. Reusing a Previously Allocated Shared, Dynamic IPv4 address
If the client remembers the previously allocated address and
restricted port range, then the process described in section 3.2 of
[RFC2131] must be followed. OPTION_PORTPARAMSV4 MUST be included in
the message flow, with the client's requested port set being included
in the DHCPDISCOVER message.
4. Server Behavior
The DHCP 4o6 Server MUST NOT reply with the OPTION_PORTPARAMSV4 until
the client has explicitly listed the option code in the Parameter
Request List (Option 55) [RFC2132].
The DHCP 4o6 Server SHOULD reply with OPTION_PORTPARAMSV4 if the
client includes the option in its Parameter Request List. In order
to achieve the dynamic management of IPv4 address and port set in the
address sharing environment, the server MUST run an address and port-
set pool that plays the same role as address pool in a regular DHCP
server. The server MUST use the combination of address and PSID as
the key to maintain the state of a lease, and look for an available
lease for assignment. The leasing database MUST include the
information of the address and PSID.
When a server receives a DHCPDISCOVER message with
OPTION_PORTPARAMSV4 in the Parameter Request List from a client, the
server chooses an IPv4 address and a port-set for the requesting
client. The logic of choosing is similar to that in Section 4.3.1 of
[RFC2131]. The difference is the server looks for the client's
binding or an available lease in the server's pool of addresses and
PSIDs. After selecting an available IPv4 address with a PSID, the
server sends a DHCPOFFER message to the requesting client.
When the server receives a DHCPREQUEST message with
OPTION_PORTPARAMSV4, the server MUST determine the client's state
according to related parameters (Section 4.3.2 of [RFC2131]) and the
value of OPTION_PORTPARAMSV4.
Upon reception of a DHCPRELEASE message with OPTION_PORTPARAMSV4, the
server looks for the lease using the address in the message and the
PSID value in the OPTION_PORTPARAMSV4, and marks it as unallocated.
The port-set assignment MUST be coupled with the address assignment
process. Therefore server MUST assign the address and port set in
the same DHCP messages. The lease information for the address is
applicable to the port-set as well.
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4.1. Leasing Shared and Non-Shared IPv4 Addresses from a Single DHCP
4o6 Server
A single DHCP 4o6 server may have clients that do not support
OPTION_PORTPARAMS as well as those that do. As the rules for the
allocation of shared addresses differ from the rules for full IPv4
address assigment, the DHCP 4o6 server MUST implement a mechanism to
ensure that clients which do not support OPTION_PORTPARAMS do not
receive shared addresses. For example two separate IPv4 addressing
pools could be used, one of which allocates IPv4 addresses and PSIDs
only to clients which have requested them.
5. Client Behavior
The DHCP client applying for a port-set MUST include the
OPTION_PORTPARAMSV4 code in the Parameter Request List (Option 55).
The client retrieves a port set using the value contained in
OPTION_PORTPARAMSV4.
When the client renews or releases the DHCP lease, it MUST put the
values of offset, PSID length and PSID into the OPTION_PORTPARAMSV4,
and send to the server within corresponding DHCPv4 messages.
In the DHCPDISCOVER message, the client MAY use a non-zero value for
the PSID-len field within OPTION_PORTPARMAS. This is used by the
client to request a specific size of port-set (i.e. the number of
source ports that it will be allocated).
5.1. Client Usage of a Shared Address
As a single IPv4 address is being shared between a number of
different clients, the allocated shared address is only suitable for
certain uses. The client MUST implement a function to ensure that
only the allocated layer 4 ports of the shared IPv4 address are used
for sourcing new connections.
The client MUST apply the following rules for any traffic to or from
the shared /32 IPv4 address:
o Only port-aware protocols or ICMP implementing [RFC5508] MUST be
used
o All connections originating from the shared IPv4 address MUST use
a source port taken from the allocated restricted port range.
o The client MUST NOT accept inbound connections on ports outside of
the allocated restricted port range.
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In order to prevent addressing conflicts which could arise from the
allocation of the same IPv4 addreses, the client MUST NOT configure
the received restricted IPv4 address on-link.
The mechanism by which a client implements these rules is outside of
the scope of this document.
In the event that the DHCPv4 over DHCPv6 configuration mechanism
fails for any reason, the client MUST NOT configure an IPv4 link-
local address [RFC3927](taken from the 169.254.0.0/16 range).
6. Additional Changes to RFC 2131
In addtion to the changes mentioned elsewhere in this document, the
following changes to the behaviour described in [RFC2131] are
necessary in order to implement dynamic allocation of a shared IPv4
address.
Section 2.2 The client MUST NOT probe a newly received IPv4 address
(e.g. with ARP) to see if it is in use by another host.
Section 3.1 Item 5. The client MUST NOT perform a final check on the
assigned IPv4 address.
7. DHCPv4 Port Parameters Option
The Port Paramaters Option for DHCPv4 specifies the restricted set of
layer 4 source ports that are necessary to dynamically allocate a
shared address. The option uses the same fields as the MAP Port
Parameters Option described in Section 4.4 of
[I-D.ietf-softwire-map-dhcp], implemented as a DHCPv4 option. This
is to maintain compatibility with existing implementations.
The construction and usage of OPTION_PORTPARAMSV4 is
0 1
2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| option-code | Length | offset | PSID-Len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PSID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: DHCPv4 Port Parameters Option
o option-code: OPTION_PORTPARAMSV4 (TBA)
o option-length: 3
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o offset: (PSID offset) 8 bits long field that specifies the numeric
value for the MAP algorithm's excluded port range/offset bits
(A-bits), as per section 5.1.1 in [I-D.ietf-softwire-map].
Allowed values are between 0 and 16, with the default value being
4 for a MAP client. This parameter is unused by a Lightweight
4over6 client and should be set to 0.
o PSID-len: Bit length value of the number of significant bits in
the PSID field (also known as 'k'). When set to 0, the PSID field
is to be ignored. After the first 'a' bits, there are k bits in
the port number representing valid of PSID. Subsequently, the
address sharing ratio would be 2^k.
o PSID: Explicit 16-bit (unsigned word) PSID value. The PSID value
algorithmically identifies a set of ports assigned to a CE. The
first k-bits on the left of this 2-octets field is the PSID value.
The remaining (16-k) bits on the right are padding zeros.
[I-D.ietf-softwire-map] (Section 5.1) provides a full description of
how the PSID is interpreted by the client.
When receiveing the Port Parameters option with an explicit PSID, the
client MUST use this explicit PSID in configuring its DHCPv4 over
DHCPv6 interface.
8. Security Consideration
8.1. Denial-of-Service
The solution is generally vulnerable to DoS when used on a shared
medium or when access network authentication is not a prerequisite to
IP address assignment. The solution SHOULD only be used on point-to-
point links, tunnels, and/or in environments where authentication at
link layer is performed before IP address assignment, and not shared
medium.
8.2. Port Randomization
Preserving port randomization [RFC6056] may be more or less difficult
depending on the address sharing ratio (i.e., the size of the port
space assigned to a CPE). The host can only randomize the ports
inside a fixed port range [RFC6269].
More discussion to improve the robustness of TCP against Blind In-
Window Attacks can be found at [RFC5961]. Other means than the
(IPv4) source port randomization to provide protection against
attacks should be used (e.g., use [I-D.vixie-dnsext-dns0x20] to
protect against DNS attacks, [RFC5961] to improve the robustness of
TCP against Blind In-Window Attacks, use IPv6).
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A proposal to preserve the entropy when selecting port is discussed
in [I-D.bajko-pripaddrassign].
9. IANA Considerations
IANA is kindly requested to allocate the following DHCPv4 option
code: TBD for OPTION_PORTPARAMSV4.
10. Acknowledgements
This document is merged from [I-D.sun-dhc-port-set-option] and
[I-D.farrer-dhc-shared-address-lease].
11. References
11.1. Normative References
[I-D.ietf-dhc-dhcpv4-over-dhcpv6]
Sun, Q., Cui, Y., Siodelski, M., Krishnan, S., and I.
Farrer, "DHCPv4 over DHCPv6 Transport", draft-ietf-dhc-
dhcpv4-over-dhcpv6-04 (work in progress), January 2014.
[I-D.ietf-softwire-map]
Troan, O., Dec, W., Li, X., Bao, C., Matsushima, S.,
Murakami, T., and T. Taylor, "Mapping of Address and Port
with Encapsulation (MAP)", draft-ietf-softwire-map-10
(work in progress), January 2014.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC
2131, March 1997.
[RFC2132] Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor
Extensions", RFC 2132, March 1997.
[RFC4361] Lemon, T. and B. Sommerfeld, "Node-specific Client
Identifiers for Dynamic Host Configuration Protocol
Version Four (DHCPv4)", RFC 4361, February 2006.
[RFC5961] Ramaiah, A., Stewart, R., and M. Dalal, "Improving TCP's
Robustness to Blind In-Window Attacks", RFC 5961, August
2010.
[RFC6056] Larsen, M. and F. Gont, "Recommendations for Transport-
Protocol Port Randomization", BCP 156, RFC 6056, January
2011.
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[RFC6269] Ford, M., Boucadair, M., Durand, A., Levis, P., and P.
Roberts, "Issues with IP Address Sharing", RFC 6269, June
2011.
11.2. Informative References
[I-D.bajko-pripaddrassign]
Bajko, G., Savolainen, T., Boucadair, M., and P. Levis,
"Port Restricted IP Address Assignment", draft-bajko-
pripaddrassign-04 (work in progress), April 2012.
[I-D.farrer-dhc-shared-address-lease]
Farrer, I., "Dynamic Allocation of Shared IPv4 Addresses
using DHCPv4 over DHCPv6", draft-farrer-dhc-shared-
address-lease-00 (work in progress), June 2013.
[I-D.ietf-dhc-dhcpv4-over-ipv6]
Cui, Y., Wu, P., Wu, J., Lemon, T., and Q. Sun, "DHCPv4
over IPv6 Transport", draft-ietf-dhc-dhcpv4-over-ipv6-08
(work in progress), October 2013.
[I-D.ietf-softwire-lw4over6]
Cui, Y., Qiong, Q., Boucadair, M., Tsou, T., Lee, Y., and
I. Farrer, "Lightweight 4over6: An Extension to the DS-
Lite Architecture", draft-ietf-softwire-lw4over6-06 (work
in progress), February 2014.
[I-D.ietf-softwire-map-dhcp]
Mrugalski, T., Troan, O., Dec, W., Bao, C.,
leaf.yeh.sdo@gmail.com, l., and X. Deng, "DHCPv6 Options
for configuration of Softwire Address and Port Mapped
Clients", draft-ietf-softwire-map-dhcp-06 (work in
progress), November 2013.
[I-D.sun-dhc-port-set-option]
Qiong, Q., Lee, Y., Sun, Q., Bajko, G., and M. Boucadair,
"Dynamic Host Configuration Protocol (DHCP) Option for
Port Set Assignment", draft-sun-dhc-port-set-option-02
(work in progress), October 2013.
[I-D.vixie-dnsext-dns0x20]
Vixie, P. and D. Dagon, "Use of Bit 0x20 in DNS Labels to
Improve Transaction Identity", draft-vixie-dnsext-
dns0x20-00 (work in progress), March 2008.
[RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
and M. Carney, "Dynamic Host Configuration Protocol for
IPv6 (DHCPv6)", RFC 3315, July 2003.
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[RFC3927] Cheshire, S., Aboba, B., and E. Guttman, "Dynamic
Configuration of IPv4 Link-Local Addresses", RFC 3927, May
2005.
[RFC5508] Srisuresh, P., Ford, B., Sivakumar, S., and S. Guha, "NAT
Behavioral Requirements for ICMP", BCP 148, RFC 5508,
April 2009.
[RFC6346] Bush, R., "The Address plus Port (A+P) Approach to the
IPv4 Address Shortage", RFC 6346, August 2011.
Authors' Addresses
Yong Cui
Tsinghua University
Beijing 100084
P.R.China
Phone: +86-10-6260-3059
Email: yong@csnet1.cs.tsinghua.edu.cn
Qi Sun
Tsinghua University
Beijing 100084
P.R.China
Phone: +86-10-6278-5822
Email: sunqi@csnet1.cs.tsinghua.edu.cn
Ian Farrer
Deutsche Telekom AG
CTO-ATI, Landgrabenweg 151
Bonn, NRW 53227
Germany
Email: ian.farrer@telekom.de
Yiu L. Lee
Comcast
One Comcast Center
Philadelphia PA 19103
USA
Email: yiu_lee@cable.comcast.com
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Qiong Sun
China Telecom
Room 708, No.118, Xizhimennei Street
Beijing 100035
P.R.China
Phone: +86-10-58552936
Email: sunqiong@ctbri.com.cn
Mohamed Boucadair
France Telecom
2330 Central Expressway
Rennes 35000
France
Email: mohamed.boucadair@orange.com
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