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Versions: (draft-raza-mpls-ldp-ip-pw-capability) 00 01 02 03 04 05 06 07 08 09 RFC 7473

MPLS Working Group                                          Kamran Raza
Internet Draft                                             Sami Boutros
Intended status: Standards Track
Expires: October 26, 2014                                 Cisco Systems

                                                         April 27, 2014


    Controlling State Advertisements Of Non-negotiated LDP Applications

                draft-ietf-mpls-ldp-ip-pw-capability-07.txt




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   document must include Simplified BSD License text as described in
   Section 4.e of the Trust Legal Provisions and are provided without
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Abstract

   There is no capability negotiation done for Label Distribution
   Protocol (LDP) applications that setup Label Switched Paths (LSPs)
   for IP prefixes or that signal Point-to-point (P2P) Pseudowires
   (PWs) for Layer 2 Virtual Private Networks (L2VPNs). When an LDP
   session comes up, an LDP speaker may unnecessarily advertise its
   local state for such LDP applications even when the peer session is
   established for some other applications like Multipoint LDP (mLDP)
   or Inter-Chassis Communication Protocol (ICCP). This document
   defines a solution by which an LDP speaker announces to its peer its
   disinterest in such non-negotiated applications, thus disabling the
   unnecessary advertisement of corresponding application state, which
   would have otherwise be advertised over the established LDP session.

Table of Contents

  1. Introduction                                                     3
  2. Conventions used in this document                                4
  3. Non-negotiated LDP applications                                  4
    3.1. Non-interesting State                                        5
  4. Controlling State Advertisement                                  5
    4.1. State Advertisement Control Capability                       5
    4.2. Capabilities Procedures                                      8
       4.2.1. State Control Capability in an Initialization message   9
       4.2.2. State Control capability in a Capability message        9
  5. Operational Examples                                             9
    5.1. Disabling Prefix-LSPs and P2P-PWs apps on an ICCP session    9
    5.2. Disabling Prefix-LSPs app on a PW Targeted LDP session      10
    5.3. Disabling Prefix-LSPs app dynamically on an LDP session     10
    5.4. Disabling Prefix-LSPs app on an mLDP-only session           11
    5.5. Disabling IPv4 or IPv6 Prefix-LSPs app on an dual-stack LSR 11
  6. Security Considerations                                         11
  7. IANA Considerations                                             12
  8. References                                                      12
    8.1. Normative References                                        12
    8.2. Informative References                                      12
  9. Acknowledgments                                                 13


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1. Introduction

  LDP Capabilities specification [RFC5561] introduced a mechanism to
  negotiate LDP capabilities for a given feature between peer Label
  Switching Routers (LSRs). The capability mechanism insures that no
  unnecessary state is exchanged between peer LSRs unless the
  corresponding feature capability is successfully negotiated between
  the peers.

  Newly defined LDP features and applications, such as Typed Wildcard
  Forwarding Equivalence Class (FEC) [RFC5918], Inter-Chassis
  Communication Protocol [ICCP], mLDP [RFC6388], and L2VPN Point-to-
  multipoint (P2MP) PW [P2MP-PW] make use of LDP capabilities framework
  for their feature negotiation. However, the earlier LDP application
  to establish LSPs for IP unicast prefixes, and application to signal
  L2VPN P2P PW [RFC4447] [RFC4762] allowed LDP speakers to exchange
  application state without any capability negotiation, thus causing
  unnecessary state advertisement when a given application is not
  enabled on one of the LDP speakers participating in a given session.
  For example, when bringing up and using an LDP peer session with a
  remote Provider Edge (PE) LSR for purely ICCP signaling reasons, an
  LDP speaker may unnecessarily advertise labels for IP (unicast)
  prefixes to this ICCP related LDP peer.

  Another example of unnecessary state advertisement can be cited when
  LDP is to be deployed in an IP dual-stack environment. For instance,
  an LSR that is locally enabled to setup LSPs for both IPv4 and IPv6
  prefixes may advertise (address and label) bindings for both IPv4 and
  IPv6 address families towards an LDP peer that is interested in IPv4
  bindings only. In this case, the advertisement of IPv6 bindings to
  the peer is unnecessary, as well as wasteful, from the point of view
  of LSR memory/CPU and network resource consumption.

  To avoid this unnecessary state advertisement and exchange, currently
  an operator is typically required to configure and define filtering
  policies on the LSR, which introduces unnecessary operational
  overhead and complexity for such deployments.

  This document defines an LDP Capabilities [RFC5561] based solution by
  which an LDP speaker may announce to its peer(s) its disinterest (or
  non-support) for state to setup IP Prefix LSPs and/or to signal L2VPN


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  P2P PW at the time of session establishment. This capability helps in
  avoiding unnecessary state advertisement for such feature
  applications. This document also states the mechanics to dynamically
  disable or enable the state advertisement for such applications
  during the session lifetime. The non-interesting state of an
  application depends on the type of application and is described later
  in section 3.1.

2. Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC-2119 [RFC2119].

   The term "IP" in this document refers to both IPv4 and IPv6 unicast
   address families.

3. Non-negotiated LDP applications

   For the applications that existed prior to the definition of LDP
   Capabilities framework [RFC5561], an LDP speaker typically
   advertises, without waiting for any capabilities exchange and
   negotiation, its corresponding application state to its peers after
   the session establishment. These early LDP applications include:

   o  IPv4/IPv6 Prefix LSPs Setup

   o  L2VPN P2P FEC128 and FEC129 PWs signaling

   This document onward uses following shorthand terms for these
   earlier LDP applications:

     o "Prefix-LSPs": Refers to an application that sets up LDP LSPs
        corresponding to IP routes/prefixes by advertising label
        bindings for Prefix FEC (as defined in RFC-5036).

     o "P2P-PWs": Refers to an application that signals FEC 128 and/or
        FEC 129 L2VPN P2P Pseudowires using LDP (as defined in
        RFC-4447).

   To disable unnecessary state exchange for such LDP applications over
   an established LDP session, a new capability is being introduced in
   this document. This new capability controls the advertisement of
   application state and enables an LDP speaker to notify its peer its
   disinterest in the state of one or more of these "Non-negotiated"
   LDP applications at the time of session establishment. Upon receipt
   of such capability, the receiving LDP speaker, if supporting the
   capability, disables the advertisement of the state related to the



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   application towards the sender of the capability. This new
   capability can also be sent later in a Capability message to either
   disable a previously enabled application's state advertisement or to
   enable a previously disabled application's state advertisement.

3.1. Non-interesting State

   A non-interesting state of a non-negotiated LDP application:

     - is the application state which is of a no interest to an LSR
        and need not be advertised to the LSR;
     - need not be advertised in any of the LDP protocol messages;
     - is dependent on application type and specified accordingly.

   For Prefix-LSPs application type, the non-interesting state refers
   to any state related to IP Prefix FEC (such as FEC label bindings,
   LDP Status). This document, however, does not classify IP address
   bindings as a non-interesting state and allows the advertisement of
   IP Address bindings to facilitate other LDP applications (such as
   mLDP) that depend on learning of peer addresses over an LDP session
   for their correct operation.

   For P2P-PWs application type, the non-interesting state refers to
   any state related to P2P PW FEC128/FEC129 (such as FEC label
   bindings, MAC [address] withdrawal, and LDP PW Status).

   From now onward in this document, the term "state" will mean to
   refer to the "non-interesting state" for an application, as defined
   in this section.

4. Controlling State Advertisement

   To control advertisement of non-interesting state related to non-
   negotiated LDP applications defined in section 3, a new capability
   TLV is defined as follows.

4.1. State Advertisement Control Capability

   The "State Advertisement Control Capability" is a new Capability
   Parameter TLV defined in accordance with section 3 of LDP
   Capabilities specification [RFC5561]. The format of this new TLV is
   as follows:







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    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |U|F| State Adv. Ctrl Cap.(IANA)|           Length              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |S|  Reserved   |                                               |
   +-+-+-+-+-+-+-+-+
   |                                                               |
   ~            State Advertisement Control Element(s)             ~
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  Figure 1: Format of an "State Advertisement Control Capability" TLV

   The value of the U-bit for the TLV MUST be set to 1 so that a
   receiver MUST silently ignore this TLV if unknown to it, and
   continue processing the rest of the message. Whereas, The value of
   F-bit MUST be set to 0. Once advertised, this capability cannot be
   withdrawn; thus S-bit MUST be set to 1 in an Initialization and
   Capability message.

   The capability data associated with this State Advertisement Control
   (SAC) Capability TLV is one or more State Advertisement Control
   Elements, where each element indicates enabling/disabling of
   advertisement of non-interesting state for a given application. The
     format of a SAC Element is defined as follows:

                              0 1 2 3 4 5 6 7
                             +-+-+-+-+-+-+-+-+
                             |D| App |Unused |
                             +-+-+-+-+-+-+-+-+

       Figure 2: Format of "State Advertisement Control Element"

   Where:

   D bit: Controls the advertisement of the state specified in "App"
    field:
       1: Disable state advertisement
       0: Enable state advertisement
      When sent in an Initialization message, D bit MUST be set to 1.

  App: Defines the application type whose state advertisement is to be



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      controlled. The value of this field is defined as follows:

       1: IPv4 Prefix-LSPs (LSPs for IPv4 prefixes)
       2: IPv6 Prefix-LSPs (LSPs for IPv6 prefixes)
       3: FEC128 P2P-PW (L2VPN PWid FEC signaling)
       4: FEC129 P2P-PW (L2VPN Generalized PWid FEC signaling)

      Any other value in this field MUST be treated as an error.

   Unused: MBZ on transmit and ignored on receipt.

   The "Length" field of SAC Capability TLV depends on the number of
   SAC Elements present in the TLV. For example, if there are two
   elements present, then the Length field is set to 3 octets. A
   receiver of this capability TLV can deduce number of elements
   present in the TLV by using the Length field.

   From now onward, this document uses the term "element" to refer to a
   SAC Element.

   As described earlier, SAC Capability TLV MAY be included by an LDP
   speaker in an Initialization message to signal to its peer LSR that
   state exchange for one or more application(s) need to be disabled on
   the given peer session. This TLV can also be sent later in a
   Capability message to selectively enable or disable these
   applications. If there are more than one elements present in a SAC
   Capability TLV, the elements MUST belong to distinct app types and
   an app type MUST NOT appear more than once. If a receiver
   receives such a malformed TLV, it SHOULD discard this TLV and
   continue processing rest of the message. If an LSR receives a
   message with a SAC capability TLV containing an element with "App"
   field set to a value other than defined above, the receiver MUST
   ignore and discard the element and continue processing the rest of
   the TLV.

   To control more than one application state, a sender LSR can either
   send a single capability TLV in a message with multiple elements
   present, or can send separate messages with capability TLV
   specifying one or more elements. A receiving LSR, however, MUST
   treat each incoming capability TLV with an element corresponding to
   a given application type as an update to its existing policy for the
   given type.

   To understand capability updates from an example, let us consider 2
   LSRs, S (LDP speaker) and P (LDP peer), both of which support all
   the non-negotiated applications listed earlier. By default, these


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   LSR will advertise state for these applications, as configured, to
   their peer as soon as an LDP session is established. Now assume that
   P receives from S a SAC capability in an Initialization message with
   "IPv6 Prefix-LSPs" and "FEC129 P2P-PW" applications disabled. This
   updates P's outbound policy towards S to advertise state related to
   only IPv4 Prefix-LSPs and FEC128 P2P-PW applications.  Later, P
   receives another capability update from S via a Capability message
   with "IPv6 Prefix-LSPs" enabled and "FEC128 P2P-PWs" disabled. This
   results in P's outbound policy towards S to advertise both IPv4 and
   IPv6 Prefix-LSPs application state, and disable both FEC128 and
   FEC129 P2P-PWs signaling. Finally, P receives another update from S
   via a Capability message that specifies to disable all four non-
   negotiated applications state, resulting in P outbound policy
   towards S to block/disable state for all these applications, and
   only advertise state for any other application, as applicable.

  4.2. Capabilities Procedures

   The SAC capability conveys the desire of an LSR to disable the
   receipt of unwanted/unnecessary state from its LDP peer. This
   capability is unilateral and unidirectional in nature, and a
   receiving LSR is not required to send a similar capability TLV in an
   Initialization or Capability message towards the sender of this
   capability. This unilateral behavior conforms to the procedures
   defined in the Section 6 of LDP Capabilities [RFC5561].

   After this capability is successfully negotiated (i.e. sent by an
   LSR and received/understood by its peer), then the receiving LSR
   MUST NOT advertise any state related to the disabled applications
   towards the capability sending LSR until and unless these
   application states are explicitly enabled again via a capability
   update. Upon receipt of a capability update to disable an enabled
   application [state] during the lifetime of a session, the receiving
   LSR MUST also withdraw from the peer any previously advertised state
   corresponding to the disabled application.

   If a receiving LDP speaker does not understand the SAC capability
   TLV, then it MUST respond to the sender with "Unsupported TLV"
   notification as described in LDP Capabilities [RFC5561]. If a
   receiving LDP speaker does not understand or does not support an
   application specified in an application control element, it SHOULD
   silently ignore/skip such an element and continue processing rest of
   the TLV.






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4.2.1. State Control Capability in an Initialization message

   LDP Capabilities [RFC5561] framework dictates that the S-bit of
   capability parameter in an Initialization message MUST be set to 1
   and SHOULD be ignored on receipt.

   An LDP speaker determines (e.g. via some local configuration or
   default policy) if it needs to disable Prefix-LSPs and/or P2P-PWs
   applications with a peer LSR. If there is a need to disable, then
     the SAC TLV needs to be included in the Initialization message with
   respective SAC elements included with their D bit set to 1.

   An LDP speaker that supports the SAC capability MUST interpret the
   capability TLV in a received Initialization message such that it
   disables the advertisement of the application state towards the
   capability sending LSR for Prefix-LSPs and/or P2P-PWs applications
   if their SAC element's D bit is set to 1.

4.2.2. State Control capability in a Capability message

   If the LDP peer supports "Dynamic Announcement Capability"
   [RFC5561], then an LDP speaker may send SAC capability in a
   Capability message towards the peer. Once advertised, these
   capabilities cannot be withdrawn and hence the S-bit of the TLV MUST
   be set to 1 when sent in a Capability message.

   An LDP speaker may decide to send this TLV towards an LDP peer if
   one or more of its Prefix-LSPs and/or P2P-PWs applications get
   disabled, or if previously disabled application gets enabled again.
   In this case, the LDP speaker constructs the TLV with appropriate
   SAC element(s) and sends the corresponding capability TLV in a
   Capability message.

   Upon receipt of this TLV in a Capability message, the receiving LDP
   speaker reacts in the same manner as it reacts upon the receipt of
   this TLV in an Initialization message. Additionally, the peer
   withdraws/advertises the application state from/to the capability
   sending LDP speaker according to the capability update.

5. Operational Examples

5.1. Disabling Prefix-LSPs and P2P-PWs applications on an ICCP session

   Consider two PE routers, LSR1 and LSR2, which understand/support SAC
   capability TLV, and have an established LDP session to exchange ICCP
   state related to dual-homed devices connected to these LSRs. Let us



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   assume that both LSRs are provisioned not to exchange any state for
   Prefix-LSPs (IPv4/IPv6) and P2P-PWs (FEC128/129) application.
     To indicate their disinterest in these applications, the LSRs will
   include a SAC capability TLV (with 4 SAC elements corresponding to
   these 4 applications with D bit set to 1 for each one) in the
   Initialization message. Upon receipt of this TLV in Initialization
   message, the receiving LSR will disable the advertisement of
   IPv4/IPv6 label bindings, as well as P2P PW FEC128/129 signaling,
   towards its peer after session establishment.

5.2. Disabling Prefix-LSPs application on a PW Targeted LDP session

   Now, consider LSR1 and LSR2 have an established Targeted LDP (T-LDP)
   session for P2P-PWs application to exchange label bindings for
   FEC 128/129. Given that there is no need to exchange IP Prefix label
   bindings amongst the PE LSRs over a PW T-LDP session in most typical
   deployments, let us assume that LSRs are provisioned to disable
   IPv4/IPv6 Prefix-LSPs application state on the given PW session.

   To indicate their disinterest in Prefix-LSPs application over a PW
   T-LDP session, the LSRs will follow/apply the same procedures as
   described in previous section. As a result, only P2P-PWs related
   state will be exchanged between these LSRs over this T-LDP session.

5.3. Disabling Prefix-LSPs application dynamically on an established
   LDP session

   Assume that LSRs from previous sections were initially provisioned
   to exchange both Prefix-LSPs and P2P-PWs state over the session
   between them, and also support "Dynamic Announcement" Capability
   [RFC5561]. Now, assume that LSR1 is dynamically provisioned to
   disable (IPv4/IPv6) Prefix-LSPs over T-LDP session with LSR2. In
   this case, LSR1 will send SAC capability TLV in a Capability message
   towards LSR2 with application control elements defined for IPv4 and
   IPv6 Prefix-LSPs with D bit set to 1. Upon receipt of this TLV, LSR2
   will disable Prefix-LSPs application state(s) towards LSR1 and
   withdraw all previously advertised application state from LSR1. To
   withdraw label bindings from its peer, LSR2 MAY use a single Prefix
   FEC Typed Wildcard Label Withdraw message [RFC5918] if the peer
   supports Typed Wildcard FEC capability.

   This dynamic disability of Prefix-LSPs application does not impact
   L2VPN P2P-PWs application on the given session, and both LSRs should
   continue to exchange PW Signaling application related state.




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5.4. Disabling Prefix-LSPs application on an mLDP-only session

   Now assume that LSR1 and LSR2 have formed an LDP session to exchange
   mLDP state only. In typical deployments, LSR1 and LSR2 also exchange
   bindings for IP (unicast) prefixes upon mLDP session, which is
   unnecessary and wasteful for an mLDP-only LSR.

   Using the procedures defined earlier, an LSR can indicate its
   disinterest in Prefix-LSPs application state to its peer upon
   session establishment time or dynamically later via LDP capabilities
   update.

   Reference to section 3.1, the peer disables the advertisement of any
   state related to IP Prefix FECs, but still advertises IP address
   bindings that are required for the correct operation of mLDP.

5.5. Disabling IPv4 or IPv6 Prefix-LSPs application on an dual-stack LSR

   In IP dual-stack scenarios, LSR2 may advertise unnecessary state
   (e.g. IPv6 prefix label bindings) towards peer LSR1 corresponding to
   IPv6 Prefix-LSPs application once a session is established mainly
   for exchanging state for IPv4. The similar scenario also applies
   when advertising IPv4 Prefix-LSPs state on a session meant for IPv6.
   The SAC capability and its procedures defined in this document can
   help to avoid such unnecessary state advertisement.

   Consider IP dual-stack environment where LSR2 is enabled for Prefix-
   LSPs application for both IPv4 and IPv6, but LSR1 is enabled for (or
   interested in) only IPv4 Prefix-LSPs. To avoid receiving unwanted
   state advertisement for IPv6 Prefix-LSPs application from LSR2, LSR1
   can send SAC capability with element for IPv6 Prefix-LSPs with D bit
   set to 1 in the Initialization message towards LSR2 at the time of
   session establishment. Upon receipt of this capability, LSR2 will
   disable all IPv6 label binding advertisement towards LSR1. If IPv6
   Prefix-LSPs application is later enabled on LSR1, LSR1 can update
   the capability by sending SAC capability in a Capability message
   towards LSR2 to enable this application dynamically.

6. Security Considerations

  The proposal introduced in this document does not introduce any new
  security considerations beyond that already apply to the base LDP
  specification [RFC5036] and [RFC5920].





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7. IANA Considerations

  This document defines a new LDP capability parameter TLV. IANA is
  requested to assign the lowest available value after 0x0500 from
  "TLV Type Name Space" in the "Label Distribution Protocol (LDP)
  Parameters" registry as the new code point for the new LDP
  capability TLV code point.

  +-----+---------------------+---------------+-----------------------+
  |Value| Description         | Reference     |Notes/Registration Date|
  +-----+---------------------+---------------+-----------------------+
  | TBA | State Advertisement | This document |                       |
  |     | Control Capability  |               |                       |
  +-----+---------------------+---------------+-----------------------+


8. References

8.1. Normative References

   [RFC5036] L. Andersson, I. Minei, and B. Thomas, "LDP
             Specification", RFC 5036, September 2007.

   [RFC5561] B. Thomas, K. Raza, S. Aggarwal, R. Aggarwal, and JL. Le
             Roux, "LDP Capabilities", RFC 5561, July 2009.

   [RFC2119] S. Bradner, "Key words for use in RFCs to Indicate
             Requirement Levels", BCP 14, RFC2119, March 1997.

8.2. Informative References

   [RFC5918] R. Asati, I. Minei, and B. Thomas, "Label Distribution
             Protocol Typed Wildcard FEC", RFC 5918, August 2010.

   [RFC4447] L. Martini, E. Rosen, El-Aawar, T. Smith, and G. Heron,
             "Pseudowire Setup and Maintenance using the Label
             Distribution Protocol", RFC 4447, April 2006.

   [RFC4762] M. Lasserre, and V. Kompella,  "Virtual Private LAN Service
             (VPLS) Using Label Distribution Protocol (LDP) Signaling",
             RFC 4762, January 2007.

   [P2MP-PW] Martini, L. et. al, "Signaling Root-Initiated Point-to-
             Multipoint Pseudowires using LDP", draft-ietf-pwe3-p2mp-pw-
             04.txt, Work in Progress, March 2012.

   [ICCP]    L. Martini, S. Salam, A. Sajassi, and S. Matsushima,
             "Inter-Chassis Communication Protocol for L2VPN PE
             Redundancy", draft-ietf-pwe3-iccp-16.txt, Work in
             Progress, March 2014.




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   [RFC6388] I. Minei, I. Wijnands, K. Kompella, and B. Thomas, "LDP
             Extensions for P2MP and MP2MP LSPs", RFC 6388, November
             2011.

   [RFC5920] L. Fang, et al., "Security Framework for MPLS and GMPLS
             Networks", RFC 5920, July 2010.

9. Acknowledgments

   The authors would like to thank Eric Rosen for his valuable input
   and comments. We also acknowledge Karthik Subramanian and IJsbrand
   Wijnands for bringing up mLDP use case.

   This document was prepared using 2-Word-v2.0.template.dot.

Authors' Addresses

  Kamran Raza
  Cisco Systems, Inc.,
  2000 Innovation Drive,
  Ottawa, ON K2K-3E8, Canada.
  E-mail: skraza@cisco.com

  Sami Boutros
  Cisco Systems, Inc.
  3750 Cisco Way,
  San Jose, CA 95134, USA.
  E-mail: sboutros@cisco.com



















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