Behavior Engineering for Hindrance R. Penno
Avoidance Juniper Networks
Internet-Draft T. Saxena
Intended status: Informational Cisco Systems
Expires: July 27, 2011 M. Boucadair
France Telecom
S. Sivakumar
Cisco Systems
January 23, 2011
Analysis of 64 Translation
draft-ietf-behave-64-analysis-01
Abstract
Due to specific problems, NAT-PT was deprecated by the IETF as a
mechanism to perform IPv6-IPv4 translation. Since then, new efforts
have been undertaken within IETF to standardize alternative
mechanisms to perform IPv6-IPv4 translation. This document evaluates
how the new translation mechanisms avoid the problems that caused the
IETF to deprecate NAT-PT.
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/.
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 July 27, 2011.
Copyright Notice
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Copyright (c) 2011 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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Definition . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Context . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.3. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Analysis of 64 Translation Against Concerns of RFC4966 . . . . 4
2.1. Problems Impossible to Solve . . . . . . . . . . . . . . . 5
2.2. Problems Which Can be Solved . . . . . . . . . . . . . . . 5
2.3. Problems Solved . . . . . . . . . . . . . . . . . . . . . 7
3. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 9
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
5. Security Considerations . . . . . . . . . . . . . . . . . . . 11
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
7.1. Normative References . . . . . . . . . . . . . . . . . . . 12
7.2. Informative References . . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14
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1. Introduction
1.1. Definition
This document uses 64 proposal (or 64 for short) to refer to the
mechanisms defined in the following documents:
o Stateful NAT64: Network Address and Protocol Translation from IPv6
Clients to IPv4 Servers [I-D.ietf-behave-v6v4-xlate-stateful]
o DNS64: DNS extensions for Network Address Translation from IPv6
Clients to IPv4 Servers [I-D.ietf-behave-dns64]
o IPv6 Addressing of IPv4/IPv6 Translators [RFC6052]
o Framework for IPv4/IPv6 Translation
[I-D.ietf-behave-v6v4-framework]
1.2. Context
The current 64 proposal is widely seen as a major interconnection
technique designed to enable communications between IPv6-only and
IPv4-only networks. One of the building blocks of this proposal is
decoupling the DNS functionality from the protocol translation
itself.
This approach is pragmatic in the sense that there is no dependency
on DNS implementation for the successful NAT handling. As long as
there is a function (e.g., DNS64 [I-D.ietf-behave-dns64] or other
means) that can construct an IPv6-Embedded IPv4 address with a pre-
configured IPv6 prefix, an IPv4 address and a suffix (refer to
[RFC6052]), NAT64 will work just fine.
To understand the 64 proposal, we must keep in mind that the focus of
this proposal is on the deployment and not the implementation
details. As long as a NAT64 implementation conforms to the expected
behaviour, as desired in the deployment scenario, the details are not
very important as mentioned in this excerpt from
[I-D.ietf-behave-v6v4-xlate-stateful]:
"A NAT64 MAY perform the steps in a different order, or MAY
perform different steps, but the externally visible outcome MUST
be the same as the one described in this document."
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1.3. Scope
This document provides an analysis of how the proposed set of
documents that specify stateful IPv6-only to IPv4-only translation
and replace NAT-PT [RFC2766] address the issues raised in [RFC4966].
As a reminder, it is worth mentioning the 64 proposal analysis is
limited in the sense that hosts from IPv6 networks can initiate a
communication to IPv4 network/Internet, but not vice-versa. This
corresponds to Scenario 1 and Scenario 5 described in
[I-D.ietf-behave-v6v4-framework]. Hence, the scenario of servers
moving to IPv6 while clients remaining IPv4 remains unaddressed. Of
course, IPv6 to IPv4 communications can also be supported if static
bindings are configured on the stateful NAT64.
The 64 proposal, just like any other technique under development, has
some positives and some drawbacks. The ups and downs of the proposal
must be clearly understood while going forward with its future
development.
The scope of this document does not include stateless translation.
2. Analysis of 64 Translation Against Concerns of RFC4966
Of the set of problems pointed out in [RFC4966], the 64 proposal
addresses some of them, whereas leaves others unaddressed.
Some issues mentioned in [RFC4966] were solved by [RFC4787],
[RFC5382] and [RFC5508]. At the time when NAT-PT was published these
recommendations were not in place but they are orthogonal to the
translation algorithm per se, therefore they could be implemented
with NAT-PT. On the other hand, NAT64 explicitly mentions that these
recommendations need to be followed and thus should be seen as a
complete specification.
It is also worth pointing out that the scope of the 64 proposal is
reduced when compared to NAT-PT. Following is a point by point
analysis of the problems. Issues listed in [RFC4966] are classified
into three categories:
1. Problems impossible to solve;
2. Problems which can be solved.
3. Problems solved.
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2.1. Problems Impossible to Solve
Problems discussed in [RFC4966], which are impossible to solve:
1. Inability to redirect traffic for protocols that lack de-
multiplexing capabilities or are not built on top of specific
transport-layer protocols for transport address translations
(Section 2.2 of [RFC4966]).
Analysis: This issue is not specific to 64 but to all NAT-
based solutions.
2. Loss of information due to incompatible semantics between IPv4
and IPv6 versions of headers and protocols (Section 2.4 of
[RFC4966]).
Analysis: This issue is not specific to 64 but due to the
design of IPv4 and IPv6.
3. Need for the NAT64-capable device to act as proxy for
correspondent node when IPv6 node is mobile, with consequent
restrictions on mobility (Section 2.7 of [RFC4966]).
Analysis: This is not specific to NAT64 but to all NAT
flavors. Refer to [I-D.haddad-mext-nat64-mobility-harmful]
for an early analysis on mobility complications encountered
when NAT64 is involved.
2.2. Problems Which Can be Solved
Problems discussed in [RFC4966], which can be solved:
1. Disruption of all protocols that embed IP addresses (and/or
ports) in packet payloads or apply integrity mechanisms using IP
addresses (and ports) (Section 2.1 of [RFC4966]).
Analysis: In the case of FTP [RFC0959] this problem is
addressed by the use of a FTP64 ALG [I-D.ietf-behave-ftp64]
which is a workaround solution. In the case of SIP [RFC3261],
no specific issue is induced by 64; the same techniques for
NAT traversal can be used when a NAT64 is involved in the path
(e.g., ICE [RFC5245], Hosted NAT Traversal [RFC5853], embedded
SIP ALGs, etc. ). The functioning of other protocols is left
unaddressed. Note that the traversal of NAT64 by application
embedding IP address literal is not specific to NAT64 but
generic to all NAT-based solutions.
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2. Interaction with SCTP [RFC4960] and multihoming (Section 2.6 of
[RFC4966]).
Analysis: SCTP is out of scope of 64. Only TCP and UDP
transport protocols are within the scope of 64.
3. Inability to handle multicast traffic (Section 2.8 of [RFC4966]).
Analysis: This problem is not addressed by the current 64
specifications.
4. Scalability concerns together with introduction of a single point
of failure and a security attack nexus (Section 3.2 of
[RFC4966]).
Analysis: This is not specific to NAT64 but to all stateful
NAT flavors.
5. Creation of a DoS (Denial of Service) threat relating to
exhaustion of memory and address/port pool resources on the
translator (Section 3.4 of [RFC4966]).
Analysis: This specific DoS concern on Page 6 of [RFC4966] is
under a DNS-ALG heading in that document, and refers to NAT-
PT's creation of NAT mapping state when a DNS query occurred.
With the new IPv6-IPv4 translation mechanisms, DNS queries do
not create any mapping state. Thus, this concern is fully
eliminated with the new IPv6-IPv4 translation mechanisms.
6. Restricted validity of translated DNS records: a translated
record may be forwarded to an application that cannot use it
(Section 4.2 of [RFC4966]).
Analysis: If a node on the IPv4 side forwards the address of
the other endpoint to a node which cannot reach the NAT box or
is not covered under the endpoint-independent constraint of
NAT, then the new node will not be able to initiate a
successful session.
Actually, this is not a limitation of 64 (or even NAT-PT) but
a deployment context where shared IPv4 addresses managed by
the NAT64 are not globally reachable. The same limitation can
be encountered when referrals (even without any NAT in the
path) include reachability information with limited
reachability scope (See [I-D.carpenter-behave-referral-object]
for more discussion about scope-related issues).
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7. Unless UDP encapsulation is used for IPsec [RFC3948], traffic
using IPsec AH (Authentication Header), in transport and tunnel
mode, and IPsec ESP (Encapsulating Security Payload), in
transport mode, is unable to be carried through NAT-PT without
terminating the security associations on the NAT-PT, due to their
usage of cryptographic integrity protection (Section 4.5 of
[RFC4966]).
Analysis: This is not specific to NAT64 but to all NAT
flavours.
8. Address selection issues when either the internal or external
hosts implement both IPv4 and IPv6 (Section 4.1 of [RFC4966]).
Analysis: This is out of scope of 64 since Scenarios 1 and 5
of [I-D.ietf-behave-v6v4-framework] assume IPv6-only hosts.
Therefore this issue is not resolved and mitigation techniques
outside the 64 need to be used. These techniques may allow to
offload NAT64 resources and prefer native communications which
do not involve address family translation. Avoiding NAT
devices in the path is encouraged for mobile nodes in order to
save power consumption due to keepalive messages which are
required to maintain NAT states ("always-on" services). An
in-depth discussion can be found in
[I-D.wing-behave-dns64-config].
2.3. Problems Solved
Problems, identified in [RFC4966], which are solved:
1. Constraints on network topology (as it relates to DNS-ALG; see
Section 3.1 of [RFC4966]).
Analysis: This issue has mitigated severity as the DNS is
separated from the NAT functionality. Nevertheless, a minimal
coordination may be required to ensure that the NAT64 to be
crossed (the one to which the IPv4-Converted IPv6 address
returned to a requesting host) must be in the path and has
also sufficient resources to handle received traffic.
2. Need for additional state and/or packet reconstruction in dealing
with packet fragmentation. Otherwise, implement no support for
fragments. (Section 2.5 of [RFC4966])
Analysis: This issue is not specific to 64 but to all NAT-
based solutions. [I-D.ietf-behave-v6v4-xlate-stateful]
specifies how to handle fragmentation; appropriate
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recommendations to avoid fragmentation-related DoS attacks are
proposed (e.g., limit resources to be dedicated to out of
order fragments).
3. Inappropriate translation of responses to A queries from IPv6
nodes (Section 4.3 of [RFC4966]).
Analysis: DNS64 [I-D.ietf-behave-dns64] does not resolve A
queries.
4. Address selection issues and resource consumption in a DNS-ALG
with multi-addressed nodes (Section 4.4 of [RFC4966]).
Analysis: Since the DNS-ALG is not there, there is no need to
maintain temporary states in anticipation of connections.
Note that static binding are required to allow for
communications initiated from an IPv4 client to an IPv6
server.
5. Limitations on DNS security capabilities when using a DNS-ALG
(Section 2.5 of [RFC4966]).
Analysis: A DNSSEC validating stub resolver behind a DNS64 in
server mode is not supported. Therefore if a host wants to do
its own DNSSEC validation, and it wants to use a NAT64, the
host has to also perform its own DNS64 synthesis. Refer to
Section 3 of[I-D.ietf-behave-dns64] for more details.
6. Creation of a DoS (Denial of Service) threat relating to
exhaustion of memory and address/port pool resources on the
translator (Section 3.4 of [RFC4966]).
Analysis: This specific DoS concern on Page 6 of [RFC4966] is
under a DNS-ALG heading in that document, and refers to NAT-
PT's creation of NAT mapping state when a DNS query occurred.
With the new IPv6-IPv4 translation mechanisms, DNS queries do
not create any mapping state in the NAT64. Thus, this concern
is fully eliminated in 64.
7. Requirement for applications to use keepalive mechanisms to
workaround connectivity issues caused by premature timeout for
session table and BIB entries (Section 2.3 of [RFC4966]).
Analysis: Since NAT64 follows some of the [RFC4787], [RFC5382]
and [RFC5508] requirements, there is a high lower bound for
the lifetime of sessions. In NAT-PT this was unknown and
applications needed to assume the worst case. For instance,
in NAT64, the lifetime for a TCP session is approximately 2
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hours, so not much keep-alive signalling overhead is needed.
Application clients (e.g., VPN clients) are not aware of the
timer configured in the NAT device. For unmanaged services, a
conservative approach would be adopted by applications which
issue frequent keepalive messages to be sure that an active
mapping is still be maintained by any involved NAT64 device
even if the NAT64 complies with TCP/UDP/ICMP BEHAVE WG
specifications.
Note that keepalive messages may be issued by applications to
ensure that an active entry is maintained by a firewall, with
or without a NAT in the path, which is located in the
boundaries of a local domain.
8. Lack of address mapping persistence: Some applications require
address retention between sessions. The user traffic will be
disrupted if a different mapping is used. The use of the DNS-ALG
to create address mappings with limited lifetimes means that
applications must start using the address shortly after the
mapping is created, as well as keep it alive once they start
using it. (Section 3.3 of [RFC4966])
Analysis: In the context of 64, the external IPv4 address
(representing the IPv6 host in the IPv4 network) is assigned
by the NAT64 machinery and not the DNS64 function. Address
persistence can be therefore easily ensured by the NAT64
function (which complies with BEHAVE NAT recommendations).
Address persistence should be guaranteed for both dynamic and
static bindings.
In the IPv6 side of the NAT64, the same IPv6 address is used
to represent an IPv4 host; no issue about address persistence
is raised in IPv6 network.
3. Conclusions
The above analysis of the solutions provided by the 64 proposal shows
that the majority of the problems that are not directly related to
the decoupling of NAT and DNS remain unaddressed. Some of these
problems are not specific to 64 but are generic to all NAT-based
solutions.
This points to several shortcomings of 64 proposal which must be
addressed if the future network deployments have to move reliably
towards 64 as a solution to IPv6-IPv4 interconnection.
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Some of the issues, as pointed out in [RFC4966], have possible
solutions. However these solutions will require significant updates
to the 64 proposal, increasing its complexity.
The following table summarizes the conclusions based on the analysis
of 64 proposal.
+---------------+----------+---------+----------+---------+---------+
| Issue | NAT-PT | Exists | DNS ALG | Generic | Can be |
| | Specific | in | Specific | NAT | solved? |
| | | NAT64 | | | |
+---------------+----------+---------+----------+---------+---------+
| Protocols | No | Yes | No | Yes | Yes |
| embedding | | | | | |
| addresses | | | | | |
+---------------+----------+---------+----------+---------+---------+
| Protocols | No | Yes | No | Yes | No |
| without demux | | | | | |
| capability | | | | | |
+---------------+----------+---------+----------+---------+---------+
| Binding state | No | Yes | No | Yes | -- |
| decay | | | | | |
+---------------+----------+---------+----------+---------+---------+
| Loss of | No | Yes | No | No | No |
| information | | | | | |
+---------------+----------+---------+----------+---------+---------+
| Fragmentation | No | No | No | Yes | Yes |
+---------------+----------+---------+----------+---------+---------+
| SCTP and | No | Yes | No | Yes | Yes |
| Multihoming | | | | | |
| interaction | | | | | |
+---------------+----------+---------+----------+---------+---------+
| Proxy corresp | Yes | Yes | No | Yes | ?? |
| node for | | | | | |
| MIPv6 | | | | | |
+---------------+----------+---------+----------+---------+---------+
| Multicast | No | Yes | No | Yes | Yes |
+---------------+----------+---------+----------+---------+---------+
| Topology | Yes | No | Yes | No | Yes |
| constraints | | | | | |
| with DNS-ALG | | | | | |
+---------------+----------+---------+----------+---------+---------+
| Scale and | No | Yes | No | Yes | Yes |
| Single point | | | | | |
| of failure | | | | | |
+---------------+----------+---------+----------+---------+---------+
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+---------------+----------+---------+----------+---------+---------+
| Lack of | No | Yes | No | Yes | Yes |
| address | | | | | |
| persistence | | | | | |
+---------------+----------+---------+----------+---------+---------+
| DoS attacks | No | Yes | No | Yes | Yes |
+---------------+----------+---------+----------+---------+---------+
| Address | Yes | No | Yes | No | Yes |
| selection | | | | | |
| issues with | | | | | |
| Dual stack | | | | | |
| hosts | | | | | |
+---------------+----------+---------+----------+---------+---------+
| Non-global | Yes | No | Yes | Yes | Yes |
| validity of | | | | | |
| Translated RR | | | | | |
| records | | | | | |
+---------------+----------+---------+----------+---------+---------+
| Incorrect | Yes | No | Yes | No | Yes |
| translation | | | | | |
| of A | | | | | |
| responses | | | | | |
+---------------+----------+---------+----------+---------+---------+
| DNS-ALG and | No | Yes | No | Yes | Yes |
| Multi- | | | | | |
| addressed | | | | | |
| nodes | | | | | |
+---------------+----------+---------+----------+---------+---------+
| DNSSEC | No | Yes | No | Yes | Yes |
| limitations | | | | | |
+---------------+----------+---------+----------+---------+---------+
Table 1: Summary of NAT64 analysis
4. IANA Considerations
This document makes no request of IANA.
Note to RFC Editor: this section may be removed on publication as an
RFC.
5. Security Considerations
This document does not specify any new protocol or architecture. It
only analyses how BEHAVE WG 64 documents mitigate concerns raised in
[RFC4966] and which ones are still unaddressed.
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6. Acknowledgements
Many thanks to Marcelo Bagnulo for his comments.
7. References
7.1. Normative References
[I-D.ietf-behave-dns64]
Bagnulo, M., Sullivan, A., Matthews, P., and I. Beijnum,
"DNS64: DNS extensions for Network Address Translation
from IPv6 Clients to IPv4 Servers",
draft-ietf-behave-dns64-11 (work in progress),
October 2010.
[I-D.ietf-behave-v6v4-xlate-stateful]
Bagnulo, M., Matthews, P., and I. Beijnum, "Stateful
NAT64: Network Address and Protocol Translation from IPv6
Clients to IPv4 Servers",
draft-ietf-behave-v6v4-xlate-stateful-12 (work in
progress), July 2010.
[RFC0959] Postel, J. and J. Reynolds, "File Transfer Protocol",
STD 9, RFC 959, October 1985.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4787] Audet, F. and C. Jennings, "Network Address Translation
(NAT) Behavioral Requirements for Unicast UDP", BCP 127,
RFC 4787, January 2007.
[RFC4960] Stewart, R., "Stream Control Transmission Protocol",
RFC 4960, September 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.
[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.
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[RFC6052] Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X.
Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052,
October 2010.
7.2. Informative References
[I-D.carpenter-behave-referral-object]
Carpenter, B., Boucadair, M., Halpern, J., Jiang, S., and
K. Moore, "A Generic Referral Object for Internet
Entities", draft-carpenter-behave-referral-object-01 (work
in progress), October 2009.
[I-D.haddad-mext-nat64-mobility-harmful]
Haddad, W. and C. Perkins, "A Note on NAT64 Interaction
with Mobile IPv6",
draft-haddad-mext-nat64-mobility-harmful-01 (work in
progress), April 2010.
[I-D.ietf-behave-ftp64]
Beijnum, I., "An FTP ALG for IPv6-to-IPv4 translation",
draft-ietf-behave-ftp64-06 (work in progress),
November 2010.
[I-D.ietf-behave-v6v4-framework]
Baker, F., Li, X., Bao, C., and K. Yin, "Framework for
IPv4/IPv6 Translation",
draft-ietf-behave-v6v4-framework-10 (work in progress),
August 2010.
[I-D.wing-behave-dns64-config]
Wing, D., "DNS64 Resolvers and Dual-Stack Hosts",
draft-wing-behave-dns64-config-02 (work in progress),
February 2010.
[RFC2766] Tsirtsis, G. and P. Srisuresh, "Network Address
Translation - Protocol Translation (NAT-PT)", RFC 2766,
February 2000.
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261,
June 2002.
[RFC3948] Huttunen, A., Swander, B., Volpe, V., DiBurro, L., and M.
Stenberg, "UDP Encapsulation of IPsec ESP Packets",
RFC 3948, January 2005.
[RFC5245] Rosenberg, J., "Interactive Connectivity Establishment
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(ICE): A Protocol for Network Address Translator (NAT)
Traversal for Offer/Answer Protocols", RFC 5245,
April 2010.
[RFC5853] Hautakorpi, J., Camarillo, G., Penfield, R., Hawrylyshen,
A., and M. Bhatia, "Requirements from Session Initiation
Protocol (SIP) Session Border Control (SBC) Deployments",
RFC 5853, April 2010.
Authors' Addresses
Reinaldo Penno
Juniper Networks
1194 N Mathilda Avenue
Sunnyvale, California 94089
USA
Email: rpenno@juniper.net
Tarun Saxena
Cisco Systems
Email: tasaxena@cisco.com
Mohamed Boucadair
France Telecom
Rennes 35000
France
Email: mohamed.boucadair@orange-ftgroup.com
Senthil Sivakumar
Cisco Systems
7100-8 Kit Creek Road
Research Triangle Park, North Carolina 27709
USA
Email: ssenthil@cisco.com
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