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Versions: 00 01

MPLS Working Group                                       C. Ramachandran
Internet-Draft                                                 V. Beeram
Intended status: Standards Track                            H. Sitaraman
Expires: July 7, 2019                                   Juniper Networks
                                                         January 3, 2019


 Node Protection for RSVP-TE tunnels on a shared MPLS forwarding plane
              draft-chandra-mpls-rsvp-shared-labels-np-01

Abstract

   Segment Routed RSVP-TE tunnels provide the ability to use a shared
   MPLS forwarding plane at every hop of the Label Switched Path (LSP).
   The shared forwarding plane is realized with the use of 'Traffic
   Engineering (TE) link labels' that get shared by LSPs traversing
   these TE links.  This paradigm helps significantly reduce the
   forwarding plane state required to support a large number of LSPs on
   a Label Switching Router (LSR).  Segment Routed RSVP-TE tunnels
   require the ingress Label Edge Router (LER) to impose a stack of
   labels.  If the ingress LER cannot impose the full label stack, it
   can use the assistance of one or more delegation hops along the path
   of the LSP to impose parts of the label stack.

   The procedures for a Point of Local Repair (PLR) to provide local
   protection against link failures using facility backup for Segment
   Routed RSVP-TE tunnels are well defined and do not require specific
   protocol extensions.  This document defines the procedures for a PLR
   to provide local protection against transit node failures using
   facility backup for these tunnels.  The procedures defined in this
   document include protection against delegation hop failures.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

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




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   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://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 7, 2019.

Copyright Notice

   Copyright (c) 2019 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
   (https://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.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Node protection specific procedures . . . . . . . . . . . . .   4
     3.1.  Applicability of this document  . . . . . . . . . . . . .   4
     3.2.  PLR procedures for protecting non-delegation next-hop LSR   4
     3.3.  PLR procedures for protecting a delegation next-hop LSR .   6
       3.3.1.  Label Allocation and Stacking . . . . . . . . . . . .   7
     3.4.  Backwards Compatibility . . . . . . . . . . . . . . . . .   8
       3.4.1.  LSR does not support node protection for Shared
               Labels  . . . . . . . . . . . . . . . . . . . . . . .   8
       3.4.2.  PLR procedures for protecting a hop not supporting
               shared Labels . . . . . . . . . . . . . . . . . . . .   9
       3.4.3.  PLR not supporting shared Labels  . . . . . . . . . .  10
   4.  Protocol Extensions . . . . . . . . . . . . . . . . . . . . .  10
     4.1.  DHLD encoding in ETLD Attributes TLV  . . . . . . . . . .  10
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  11
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
   8.  Normative References  . . . . . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12




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1.  Introduction

   With the advent of Traffic Engineering (TE) link labels and Segment
   Routed RSVP-TE Tunnels [I-D.ietf-mpls-rsvp-shared-labels],
   [I-D.ietf-mpls-rsvp-shared-labels], a shared MPLS forwarding plane
   can be realized by allowing the TE link label to be shared by MPLS
   RSVP-TE Label Switched Paths (LSPs) traversing the link.  The shared
   forwarding plane behavior helps reduce the amount of forwarding plane
   state required to support a large number of LSPs on a Label Switching
   Router (LSR).  This prevents the size of the platform specific label
   space on an LSR from being a constraint to pushing the limits of
   RSVP-TE control plane scaling on that node.

   Segment Routed RSVP-TE tunnels request the use of a shared forwarding
   plane at every hop of the LSP.  The TE link label used at each hop is
   recorded in the Record Route object (RRO) of the Resv message.  The
   ingress Label Edge Router (LER) uses this recorded information to
   construct a stack of labels that can be imposed on the packets
   steered on to the tunnel.  In the scenario where the ingress LER
   cannot impose the full label stack, it can use the assistance of one
   or more delegation hops along the path of the LSP to impose parts of
   the label stack.

   Facility backup is a local repair method [RFC4090] in which a bypass
   tunnel is used to provide protection against link or node failures
   for MPLS RSVP-TE LSPs at the Point of Local Repair (PLR).  The
   facility backup procedures that provide protection against link
   failures for Segment Routed RSVP-TE LSPs are defined in
   [I-D.ietf-mpls-rsvp-shared-labels].  This document defines the
   facility back procedures that provide protection against node
   failures for Segment Routed RSVP-TE LSPs.  These procedures include
   protection against delegation hop failures.  The document also
   discusses the procedures for handling backwards compatibility
   scenarios where a node along the path of the LSP does not support the
   protocol extensions defined in this document.

   The procedures discussed in this document do not cover protection
   against ingress/egress node failures.  They also do not apply to
   Point to Multipoint (P2MP) RSVP-TE Tunnels.

2.  Terminology

   The reader is expected to be familiar with the terminology specified
   in [RFC3209], [RFC4090] and [I-D.ietf-mpls-rsvp-shared-labels].
   Unless otherwise stated, the term LSPs in this document refer to
   Segment Routed RSVP-TE LSPs.  The following additional terms are used
   in this document:




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   Primary forwarding action:   The outbound label forwarding action
      performed at a PLR for a protected LSP before the occurrence of
      local failure.

   Backup forwarding action:   The outbound label forwarding action
      performed at a PLR for a protected LSP after the occurrence of
      local failure.

3.  Node protection specific procedures

   A set of Segment Routed RSVP-TE LSPs can share a TE link label on an
   LSR only if all the LSPs in the set share the same outbound label
   forwarding action.  For protected LSPs, having the same outbound
   label forwarding action means having the same primary forwarding
   action and the same backup forwarding action.  In the case of LSPs
   that do not request local protection or LSPs that request only link
   protection, they can use the same outbound label forwarding action if
   they reach a common next-hop LSR via a common outgoing TE link.
   However, in the case of LSPs that request node protection, they can
   use the same outbound label forwarding action only if they reach a
   common next-next-hop LSR via a common outgoing TE link and a common
   next-hop LSR.

3.1.  Applicability of this document

   The label allocation and signaling procedures defined in
   [I-D.ietf-mpls-rsvp-shared-labels] can sufficiently cater to the
   following scenarios on an LSR:

   (a)  Offer no protection to LSPs that do not request local protection

   (b)  Offer no protection or link protection to LSPs that request link
      protection

   (c)  Offer no protection or link protection to LSPs that request node
      protection

   The label allocation and signaling procedures defined in this
   document are meant to enable LSRs to offer node protection to LSPs
   that request node protection.

3.2.  PLR procedures for protecting non-delegation next-hop LSR

   If the protected next-hop LSR signals a TE link label for the LSP but
   does not set the Delegation Label flag in the RRO Label Subobject
   carried in Resv message, then the PLR SHOULD allocate multiple shared
   labels for the same TE link such that a unique label is allocated for




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   every unique next-next-hop LSR that is reachable via the protected
   next-hop LSR.

                     326     348
    +---+     +---+  321+---+345  +---+     +---+
    | A |-----| B |-----| C |-----| D |-----| E |
    +---+     +---+     +---+     +---+     +---+
      |         |         |376      |         |
      |         |         |378      |         |
      |         |         |         |         |
      |       +---+     +---+     +---+     +---+
      +-------| F |-----|G  |-----|H  |-----|I  |
              +---+     +---+     +---+     +---+

                 Figure 1: Per-nhop-nnhop label allocation

   In the example shown in Figure 1, LSR C has allocated the following
   TE link labels:

      321 for the TE link neighbor B to reach the next-next-hop LSR A
      326 for the TE link neighbor B to reach the next-next-hop LSR F
      345 for the TE link neighbor D to reach the next-next-hop LSR E
      348 for the TE link neighbor D to reach the next-next-hop LSR H
      376 for the TE link neighbor G to reach the next-next-hop LSR F
      378 for the TE link neighbor G to reach the next-next-hop LSR H

   If a LSP requesting node protection transits PLR C and if the
   protected next-hop LSR after C along the LSP path is not a delegation
   hop, then LSR C signals the respective TE link label depending on the
   next-next-hop LSR on the LSP path.

      LSP path: A -> B -> C -> D -> E : Label = 345
      LSP path: A -> B -> C -> D -> H : Label = 348
      LSP path: A -> B -> C -> G -> H : Label = 378

   In all LSP paths above, at PLR C, the protected next-hop LSRs D and G
   along the LSP paths signal TE link labels but are not delegation hops
   [I-D.ietf-mpls-rsvp-shared-labels].

   If the primary TE link is operational, LSR C will pop the TE link
   label and forward the packet to the corresponding next-hop LSR over
   that TE link.  During local repair, LSR C will pop the TE link label
   and also the label beneath the top label, and forward the packet over
   the node protecting bypass tunnel to the appropriate next-next-hop
   LSR, which is the Merge Point (MP).






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3.3.  PLR procedures for protecting a delegation next-hop LSR

   The outgoing backup label forwarding action corresponding to a label
   shared by LSPs requesting node protection MUST bypass the protected
   next-hop LSR.  The PLR MUST push the label stack on behalf of the
   delegation next-hop LSR.  Hence, the number of labels that a
   delegation hop chooses to push also depends on the number of labels
   that the upstream hop (acting as PLR) along the primary LSP can push.
   This section extends the Effective Transport Label-Stack Depth (ETLD)
   signaling procedure specified in [I-D.ietf-mpls-rsvp-shared-labels]
   for LSPs requesting node protection.

   Considering Figure 2, assume LER A and LSR B can push a maximum of 3
   labels on an MPLS packet while the remaining nodes can push a maximum
   of 5 labels.  LER A originates a Path message with an ETLD of 2 after
   reserving space for the bypass tunnel label that should be pushed for
   backup forwarding action.  In addition to setting the ETLD, LER A
   also sets the Delegation Helper Label Depth (DHLD) to 2 in the Path
   message.  The DHLD is computed as the maximum number of labels that
   the node can push after reserving space for the NNHOP bypass tunnel
   label that should be pushed for backup forwarding action.  The ETLD
   procedures dictate that each LSR add its own ETLD value before
   sending the Path message downstream.  LSRs C, E and I are
   automatically selected as delegation hops by the time the Path
   message reaches the egress LER L.  LSR C uses the DHLD signaled by
   the upstream LSR B as input when calculating the outgoing ETLD in the
   Path message.
























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             ETLD:2    ETLD:1    ETLD:2    ETLD:1    ETLD:4
             DHLD:2    DHLD:2    DHLD:4    DHLD:4    DHLD:4
             ----->    ----->    ----->    ----->    ----->
                             1300d               1500d
         +---+     +---+     +---+     +---+     +---+     +---+
         | A |-----| B |-----| C |-----| D |-----| E |-----| F |  ETLD:3
         +---+     +---+     +---+     +---+     +---+     +---+  DHLD:4
                     |         |                             |      |
                     |         |                             |      |
                     |         |       1900d                 |      |
         +---+     +---+     +---+     +---+     +---+     +---+    v
         | L |-----| K |-----| J |-----| I |-----| H |-----+ G +
         +---+     +---+     +---+     +---+     +---+     +---+

             DHLD:4    DHLD:4    DHLD:4    DHLD:4    DHLD:4
             ETLD:2    ETLD:3    ETLD:4    ETLD:1    ETLD:2
             <-----    <-----    <-----    <-----    <-----

           Notation : <Label>d - delegation label


           Figure 2: ETLD and DHLD signaling for node protection

   As shown in Figure 2, delegation hop LSR C does not set outgoing ETLD
   to 4 that it would normally have set given that LSR C can push a
   maximum of 5 labels on an outgoing packet.  Instead, LSR C sets the
   outgoing ETLD to the minimum of the ETLD that it computes and the
   DHLD value of its previous hop i.e. minimum(computed ETLD = 4,
   previous hop DHLD = 2).

   The extension for signaling the DHLD in the Path message is defined
   in Section 4.1.

3.3.1.  Label Allocation and Stacking

   An LSR that decides, based on the modified ETLD procedure, to become
   a delegation hop for one or more LSPs requesting node protection MUST
   allocate a delegation label separate from delegation label assigned
   for LSPs that are offered no protection or link protection - even
   though the delegation segments share the same hops.  In the example
   shown in Figure 2, the delegation hops LSRs C, E and I will set the
   delegation flag in the Label sub-object that they add to the Resv
   message.

   A PLR node that offers node protection to a delegation hop SHOULD be
   capable of helping the downstream delegation when the primary TE link
   to the delegation hop goes down.  In the example shown in Figure 1,
   the LSRs B, D and H act as helpers for their respective downstream



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   delegation hops.  The PLR nodes that are delegation helpers along the
   path of LSPs requesting node protection SHOULD allocate an unique
   delegation helper label for every delegation label signaled by the
   protected delegation node.

   Before primary TE link failure, the PLR playing the role of a
   delegation helper pops the incoming label and forwards the packet on
   the primary TE link.  During local repair, the delegation helper PLR
   pops the incoming label and also the label beneath it and pushes the
   label stack on behalf of the protected or next hop delegation node.

   Any LSR that creates label stack upstream of the delegation helper
   MUST include the label signaled by the delegation helper onto the
   outgoing label stack just as it uses the TE link label to construct
   outgoing label stack.

3.4.  Backwards Compatibility

3.4.1.  LSR does not support node protection for Shared Labels

   As defined in Section 3.1, any LSR along the path of an LSP
   requesting node protection may choose to instead offer no protection
   or link protection.  Hence, it must be possible to build an LSP where
   some LSRs along the path support the node protection extensions
   defined in this document whereas the rest of the LSRs support only
   [I-D.ietf-mpls-rsvp-shared-labels].  Any PLR along the LSP path that
   does not support the procedures defined in this document MUST provide
   either no protection or link protection for the LSPs requesting node
   protection.

   Any PLR along the LSP path that is protecting a delegation hop where
   both nodes support the extensions defined in this document must
   determine whether it can push the label stack on behalf of the next-
   hop delegation hop during local repair.  If the PLR cannot push the
   label stack, then it SHOULD provide link protection or no local
   protection for the next-hop LSR.















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             ETLD:2    ETLD:1    ETLD:4    ETLD:3    ETLD:2
             DHLD:2    DHLD:2       -      DHLD:4    DHLD:4
             ----->    ----->    ----->    ----->    ----->
                             1300d
         +---+     +---+     +---+     +---+     +---+     +---+
         | A |-----| B |-----| C |-----| D |-----| E |-----| F |  ETLD:1
         +---+     +---+     +---+     +---+     +---+     +---+  DHLD:4
                     |         |                             |      |
                     |         |                             |      |
                     |         |       1500d                 |      |
         +---+     +---+     +---+     +---+     +---+     +---+    v
         | L |-----| K |-----| J |-----| I |-----| H |-----+ G +
         +---+     +---+     +---+     +---+     +---+     +---+
                                                           1700d
             DHLD:4    DHLD:4    DHLD:4    DHLD:4    DHLD:4
             ETLD:4    ETLD:1    ETLD:2    ETLD:3    ETLD:4
             <-----    <-----    <-----    <-----    <-----

                Notation : <Label>d - delegation label


         Figure 3: Delegation node does not support signaling DHLD

   In Figure 3, assume LER A and LSR B can push a maximum of 3 labels to
   the MPLS packet while the remaining nodes can push a maximum of 5
   labels.  Also assume that LSR C supports the extensions defined in
   [I-D.ietf-mpls-rsvp-shared-labels] but does not support the
   extensions defined in this document.  Based on ETLD signaling
   procedure, LSR C will become a delegation hop.  However, as LSR C
   cannot understand the DHLD signaled by the previous hop LSR B, LSR C
   will set outgoing ETLD to 4.  If LSR C had supported the DHLD
   signaling, it would have set outgoing ETLD to 2 (see Section 3.3).
   When PLR B receives shared label from the protected next-hop LSR C in
   the Resv message, it must determine the number of labels it has to
   push in order to offer node protection from the RRO sub-object
   carried in Resv.  As the label stack depth of the delegation hop C is
   greater than the number of labels LSR C can push, it must either not
   provide local protection or provide only link protection for the LSP.

3.4.2.  PLR procedures for protecting a hop not supporting shared Labels

   If the ingress LER has requested label stacking to reach delegation
   hop for the LSP requesting node protection, and if the next-hop LSR
   allocates a regular label for the LSP, then the LSR MUST also
   allocate a regular label for the LSP.

   If the ingress LER has requested label stacking to reach the egress
   LER for the LSP requesting node protection, and if the next-hop LSR



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   has allocated a regular label for the LSP, then the PLR MUST become a
   delegation hop and set the RRO Label Subobject delegation label flag
   in the RRO carried in Resv message.  The PLR MUST set ETLD to 1 in
   its outgoing Path message.

3.4.3.  PLR not supporting shared Labels

   If an LSR determines that its immediate upstream LSR has not included
   an ETLD in the incoming Path message, then the LSR MUST become a
   delegation hop and set the ETLD to 1 in the outgoing Path message.
   The outgoing ETLD is set to 1 because the upstream LSR does not
   support shared labels and cannot push the label stack on behalf of
   this LSR.

4.  Protocol Extensions

   This section introduces a protocol extension to support the
   procedures in Section 3.3

4.1.  DHLD encoding in ETLD Attributes TLV

   Delegation Helper Label Depth (DHLD) is defined as the number of
   labels that an LSR has the capability to push while performing local
   repair protecting the next-hop delegation LSR.  This document updates
   the ETLD Attributes TLV defined in
   [I-D.ietf-mpls-rsvp-shared-labels].  The encoding of DHLD in the ETLD
   Attributes TLV is shown in Figure 4


       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         Reserved              |    DHLD       |     ETLD      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                     Figure 4: The ETLD Attributes TLV

   The presence of ETLD Attributes TLV in the HOP_ATTRIBUTES sub-object
   [RFC7570] of the RRO object carried in Path message indicates that
   the hop identified by the preceding IPv4 or IPv6 or Unnumbered
   Interface ID sub-object supports automatic delegation defined in
   [I-D.ietf-mpls-rsvp-shared-labels].

   An implementation that supports this document MUST set the 8 bits
   from bit number 16 to bit number 23 with its DHLD value as indicated
   in Figure 4 when signaling Path message for an LSP for which node
   protection has been requested.



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   When processing the ETLD Attributes TLV of the previous hop LSR in
   the received Path message, the LSR checks whether it has to be the
   delegation hop based on the ETLD algorithm defined in
   [I-D.ietf-mpls-rsvp-shared-labels].

   If the LSR does not become a delegation hop along the LSP path, then
   no further action is required based on the DHLD value set by the
   previous hop.

   If the LSR does become a delegation hop along the LSP path, then it
   MUST decode the 8 bit unsigned value from bit number 16 to bit number
   23 as indicated in Figure 4.  If the 8 bit value is zero, then the
   LSR MUST infer that the previous hop has not included DHLD in the
   ETLD Attributes TLV.  If the 8 bit value is non-zero, then the LSR
   MUST consider that value as the DHLD value signaled by the previous
   hop LSR and use that DHLD value for computing its own outgoing ETLD.

5.  Acknowledgements

   The authors would like to thank Raveendra Torvi for his input from
   discussions.

6.  IANA Considerations

   This document includes no requests to IANA.

7.  Security Considerations

   This document does not introduce new security issues.  The security
   considerations pertaining to the original RSVP protocol [RFC2205] and
   RSVP-TE [RFC3209] and those that are described in [RFC5920] remain
   relevant.

8.  Normative References

   [I-D.ietf-mpls-rsvp-shared-labels]
              Sitaraman, H., Beeram, V., Parikh, T., and T. Saad,
              "Signaling RSVP-TE tunnels on a shared MPLS forwarding
              plane", draft-ietf-mpls-rsvp-shared-labels-07 (work in
              progress), December 2018.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.






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   [RFC3209]  Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
              and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
              Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001,
              <https://www.rfc-editor.org/info/rfc3209>.

   [RFC4090]  Pan, P., Ed., Swallow, G., Ed., and A. Atlas, Ed., "Fast
              Reroute Extensions to RSVP-TE for LSP Tunnels", RFC 4090,
              DOI 10.17487/RFC4090, May 2005,
              <https://www.rfc-editor.org/info/rfc4090>.

   [RFC7570]  Margaria, C., Ed., Martinelli, G., Balls, S., and B.
              Wright, "Label Switched Path (LSP) Attribute in the
              Explicit Route Object (ERO)", RFC 7570,
              DOI 10.17487/RFC7570, July 2015,
              <https://www.rfc-editor.org/info/rfc7570>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

Authors' Addresses

   Chandra Ramachandran
   Juniper Networks

   Email: csekar@juniper.net


   Vishnu Pavan Beeram
   Juniper Networks
   10 Technology Park Drive
   Westford, MA  01886
   US

   Email: vbeeram@juniper.net


   Harish Sitaraman
   Juniper Networks
   1133 Innovation Way
   Sunnyvale, CA  94089
   US

   Email: hsitaraman@juniper.net







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