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Versions: 00 01

Network Working Group                                        V. Perelman
Internet-Draft                                          J. Schoenwaelder
Intended status: Standards Track                       Jacobs University
Expires: July 21, 2012                                          M. Ersue
                                                  Nokia Siemens Networks
                                                               K. Watsen
                                                        Juniper Networks
                                                        January 18, 2012


          Network Configuration Protocol Light (NETCONF Light)
                   draft-schoenw-netconf-light-01.txt

Abstract

   This document describes a profile of the NETCONF protocol called
   NETCONF Light.  This profile modularizes the NETCONF protocol and
   allows devices to announce that they only support a subset of the
   NETCONF protocol operations.  This is useful in situations where
   devices are either too resource constrained to support all NETCONF
   operations or where devices are gradually updated from proprietary
   configuration interfaces to support NETCONF.

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 21, 2012.

Copyright Notice

   Copyright (c) 2012 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



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   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.  Motivation . . . . . . . . . . . . . . . . . . . . . . . . . .  4
     2.1.  NETCONF on Constrained Devices . . . . . . . . . . . . . .  4
     2.2.  Gradually Adding NETCONF Support . . . . . . . . . . . . .  4
   3.  NETCONF Light Overview . . . . . . . . . . . . . . . . . . . .  6
     3.1.  Reduced Protocol Operations  . . . . . . . . . . . . . . .  6
       3.1.1.  <get-config> . . . . . . . . . . . . . . . . . . . . .  6
       3.1.2.  <edit-config>  . . . . . . . . . . . . . . . . . . . .  7
       3.1.3.  <copy-config>  . . . . . . . . . . . . . . . . . . . .  7
       3.1.4.  <delete-config>  . . . . . . . . . . . . . . . . . . .  7
       3.1.5.  <lock> and <unlock>  . . . . . . . . . . . . . . . . .  7
       3.1.6.  <get>  . . . . . . . . . . . . . . . . . . . . . . . .  8
       3.1.7.  <close-session>  . . . . . . . . . . . . . . . . . . .  8
       3.1.8.  <kill-session> . . . . . . . . . . . . . . . . . . . .  8
     3.2.  Capability Negotiation . . . . . . . . . . . . . . . . . .  8
   4.  NETCONF Light YANG Module  . . . . . . . . . . . . . . . . . . 10
   5.  IANA Consideration . . . . . . . . . . . . . . . . . . . . . . 14
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 15
   7.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
     7.1.  Normative References . . . . . . . . . . . . . . . . . . . 16
     7.2.  Informative References . . . . . . . . . . . . . . . . . . 16
   Appendix A.  NETCONF Light on AVR Raven / Contiki  . . . . . . . . 17
   Appendix B.  Experience at Juniper Networks  . . . . . . . . . . . 18



















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1.  Introduction

   The Network Configuration Protocol (NETCONF) [RFC6241] provides
   mechanisms to install, manipulate, and delete the configuration of
   network devices.  This document modularizes the NETCONF protocol and
   allows devices to announce that they only support a subset of the
   NETCONF protocol operations.  This is useful in situations where
   devices are either too resource constrained to support all NETCONF
   operations or where devices are gradually updated from proprietary
   configuration interfaces to support NETCONF.

   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].





































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2.  Motivation

   This section explains the motiviation for NETCONF Light.

2.1.  NETCONF on Constrained Devices

   The original target of NETCONF were network devices such as routers
   or switches that usually have plenty of resources for running a
   NETCONF server.  However, there are a number of embedded systems
   where resources (most notably memory) are tight and hence such
   devices can only afford a subset of the NETCONF protocol operations.
   This document allows constrained devices to implement a subset of
   NETCONF and to communicate that subset to NETCONF management
   applications in an interoperable way.

   The usage of NETCONF Light on resource constrained devices is
   attractive in environments where management applications have to deal
   with a wide range of different devices, for example ranging from very
   small embedded networked sensors over more powerful data aggregation
   servers up to highly complex control networks.  Typical examples are
   Smart Grids or more general industrial control networks.

   Constrained devices can be classified according to the memory they
   have.  A recently proposed classification is the following:

   o  Class 0: too small to securely run on the Internet (too
      constrained).

   o  Class 1: about 10 KiB of data and 100 KiB of code (quite
      constrained, 10/100)

   o  Class 2: about 50 KiB of data and 250 KiB of code (not so
      constrained, 50/250)

   According to these classes, NETCONF Light should be running fine in
   "not so constrained" Class 2 devices and it may be running in "quite
   constrained" Class 1 devices, with very little resources left for
   other application code.

2.2.  Gradually Adding NETCONF Support

   While the NETCONF protocol defines a number of capabilities that may
   be optionally implemented, the base protocol remains a significant
   effort to add for existing devices.  For these devices, adding
   support for NETCONF is primarily driven by a specific integration
   target, thus the intrinsic goal is to have an initial release that
   satisfies the integration target and a subsequent release that
   implements the remainder of the NETCONF protocol.



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   Some scenarios where phasing in the imeplmentation would be helpful
   include:

   o  The device's primary goal is to implement a vendor-specific
      capability.  In this case, the device is only using NETCONF for
      its "Messages" layer (i.e.  RPC, RPC-reply, and Notification).

   o  The device's primary goal is to just support read-only access to
      its configuration.  In this case, it only needs to implement <get-
      config> initially, leaving the remaining operations for a future
      release.

   o  The device's primary goal is to enable full configuration, but it
      doesn't have the time to implement all the <edit-config>
      operations.  In this case, the device could implement just <copy-
      config>.

   o  The device's primary goal is to enable full configuration, but it
      is unable to implement <lock> or <unlock> due to its platform not
      having a locking mechanism yet.

   Each of these cases is satisfied by NETCONF Light, as the device can
   adverise the specific subset of NETCONF operations it supports.  The
   ability for development teams to incrementally implement NETCONF
   makes it a more appealing target for their short-term efforts.


























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3.  NETCONF Light Overview

   NETCONF Light uses the NETCONF message framing as defined in
   [RFC6241].  In particular, it uses the same XML encoding and XML
   namespace.

   The NETCONF specification [RFC6241] defines a set of base operations
   and a number of optional capabilities.  A NETCONF Light
   implementation may choose to not support all NETCONF base operations.
   The set of operations supported by a NETCONF Light server is
   announced to a NETCONF client as features, see the definition of the
   ietf-netconf-light YANG [RFC6020] module in Section 4.

   A NETCONF Light implementation, like any NETCONF implementation, does
   not have to support any of the optional NETCONF capabilities.  The
   normal NETCONF rules apply for the capability exchange with <hello>
   messages.

   A NETCONF Light implementation may support only a limited number of
   concurrent sessions.  On some devices, the number of concurrent
   sessions might be as low as one.  A NETCONF Light implementation
   supporting only a limited number of sessions should reject the
   establishment of a new transport, i.e., it should not even start the
   NETCONF <hello> exchange.

3.1.  Reduced Protocol Operations

   The following sections describe the changes to the NETCONF base
   protocol operations.

3.1.1.  <get-config>

   A NETCONF Light implementation MAY choose to not support the <get-
   config> operation as defined in Section 7.1 of [RFC6241].
   Furthermore, a NETCONF Light implementation MAY choose to support
   <get-config> without filtering.  An implementation not supporting the
   <get-config> operation MUST return an <rpc-error> element with an
   <error-tag> value of "operation-not-supported" when an <edit-config>
   operation is invoked.  If a <get-config> operation is invoked with a
   <filter> element and filtering is not supported, an <rpc-error>
   element MUST be returned with an <error-tag> value of "unknown-
   element".

   Note that [RFC6241] only requires to support the <running> datastore
   as source parameter.






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3.1.2.  <edit-config>

   A NETCONF Light implementation supporting only a small data model MAY
   choose to not support the <edit-config> operation defined in Section
   7.2 of [RFC6241].  An implementation not supporting the <edit-config>
   operation MUST return an <rpc-error> element with an <error-tag>
   value of "operation-not-supported" when an <edit-config> operation is
   invoked.

3.1.3.  <copy-config>

   A NETCONF Light implementation MAY choose to not support the <copy-
   config> as defined in Section 7.3 of [RFC6241].  An implementation
   not supporting the <copy-config> operation MUST return an <rpc-error>
   element with an <error-tag> value of "operation-not-supported" when a
   <copy-config> operation is invoked.

   Note that [RFC6241] only requires to support the <running> datastore
   as source parameter.  If no other capabilities are announced, the
   source parameter of the <copy-config> operation will carry the
   <config> element containing the complete configuration to copy.

3.1.4.  <delete-config>

   A NETCONF Light implementation MAY choose to not support the <delete-
   config> operation as defined in Section 7.4 of [RFC6241].  An
   implementation not supporting the <delete-config> operation MUST
   return an <rpc-error> element with an <error-tag> value of
   "operation-not-supported" when a <delete-config> operation is
   invoked.

   Note that NETCONF implementations only supporting the <running>
   datastore can trivially implement <delete-config> by always returning
   a suitable <rpc-error> since the <running> datastore cannot be
   deleted.

3.1.5.  <lock> and <unlock>

   A NETCONF Light implementation MAY choose to not support the <lock>
   and <unlock> operations as defined in Sections 7.5 and 7.6 of
   [RFC6241].  An implementation not supporting the <lock> operation or
   the <unlock> operation MUST return an <rpc-error> element with an
   <error-tag> value of "operation-not-supported" when a <lock>
   operation is invoked.







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3.1.6.  <get>

   A NETCONF Light implementations MAY choose to not support the <get>
   operation as defined in Section 7.7 of [RFC6241].  An implementation
   not supporting the <get> operation MUST return an <rpc-error> element
   with an <error-tag> value of "operation-not-supported" when a <get>
   operation is invoked.

   Some implementations MAY choose to support the <get> operation with
   the following restriction: A NETCONF Light implementation MAY choose
   to not support filtering.  If a <get> operation is invoked with a
   <filter> element and filtering is not supported, an <rpc-error>
   element MUST be returned with an <error-tag> value of "unknown-
   element".

3.1.7.  <close-session>

   A NETCONF Light implementation MAY choose to not support the <close-
   session> operation as defined in Section 7.8 of [RFC6241].  An
   implementation not supporting the <close-session> operation MUST
   return an <rpc-error> element with an <error-tag> value of
   "operation-not-supported" when a <close-session> operation is
   invoked.

3.1.8.  <kill-session>

   A NETCONF Light implementation MAY choose to not support the <kill-
   session> operation as defined in Section 7.9 of [RFC6241].  An
   implementation not supporting the <kill-session> operation MUST
   return an <rpc-error> element with an <error-tag> value of
   "operation-not-supported" when a <kill-session> operation is invoked.

3.2.  Capability Negotiation

   NETCONF advertises the capabilities during the <hello> exchange (see
   Section 8.1 of [RFC6241]).  The NETCONF base capability,
   "urn:ietf:params:netconf:base:1.1", indicates that the NETCONF peer
   supports all the base protocol operations.  Since this is not the
   case for NETCONF Light implementations, a NETCONF Light peer MUST NOT
   announce the NETCONF base capability and instead announce the NETCONF
   light capability.

   In the following example, a NETCONF Light server advertises the
   NETCONF Light capability and support for the <get-config> and <copy-
   config> operation (whitespace has been added for readability).






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      <hello xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
        <capabilities>
          <capability>
            urn:ietf:params:xml:ns:yang:ietf-netconf-light?
              module=ietf-netconf-light&amp;
              revision=2012-01-12&amp;
              features=get-config,copy-config
          </capability>
        </capabilities>
        <session-id>4</session-id>
      </hello>








































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4.  NETCONF Light YANG Module

   This section defines the ietf-netconf-light YANG [RFC6020] module.

   <CODE BEGINS> file "ietf-netconf-light@2012-01-12.yang"

   module ietf-netconf-light {

     namespace "urn:ietf:params:xml:ns:yang:ietf-netconf-light";
     prefix "ncl";

     organization
      "IETF NETCONF (Network Configuration Protocol) Working Group";

     contact
      "WG Web:   <http://tools.ietf.org/wg/netconf/>
       WG List:  <mailto:netconf@ietf.org>

       WG Chair: Bert Wijnen
                 <mailto:bertietf@bwijnen.net>

       WG Chair: Mehmet Ersue
                 <mailto:mehmet.ersue@nsn.com>

       Editor: Vladislav Perelman
               <mailto:v.perelman@jacobs-university.de>

       Editor: Juergen Schoenwaelder
               <mailto:j.schoenwaelder@jacobs-university.de>

       Editor: Mehmet Ersue
               <mailto:mehmet.ersue@nsn.com>

       Editor: Kent Watsen
               <mailto:kwatsen@juniper.net>";

     description

      "This module defines the base NETCONF protocol defined in RFC 6241
       as a suite of optionally implemented features.  The NETCONF Light
       capability is expected to be advertized in the server's <hello>
       message in lieu of the traditional base NETCONF capability.  By
       advertizing this capability, servers can indentify which parts of
       the NETCONF protocol are supported.  For the most part, NETCONF
       Light defines a one-to-one mapping between base protocol
       operations and features enabling them; exceptions include
       <get-config>, which has one feature to enable the RPC and another
       to enable subtree-filtering, and <lock>/<unlock>, which share a



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       feature called \"locking\".  Advertizing all NETCONF Light
       features is equivalent to advertizing the NETCONF base capability
       itself.

       Copyright (c) 2012 IETF Trust and the persons identified as
       authors of the code. All rights reserved.

       Redistribution and use in source and binary forms, with or
       without modification, is permitted pursuant to, and subject
       to the license terms contained in, the Simplified BSD
       License set forth in Section 4.c of the IETF Trust's
       Legal Provisions Relating to IETF Documents
       (http://trustee.ietf.org/license-info).

       This version of this YANG module is part of RFC XXXX; see
       the RFC itself for full legal notices.";
     // RFC Ed.: replace XXXX with actual RFC number and
     // remove this note

     // RFC Ed.: remove this note
     // Note: extracted from draft-schoenw-netconf-light-01.txt

     // RFC Ed.: please update the date to the date of publication

     revision 2012-01-12 {
       description "Initial version.";
       reference "RFC XXXX: Network Configuration Protocol for
                            Constrained Devices (NETCONF Light)";
     }
     // RFC Ed.: replace XXXX with actual
     // RFC number and remove this note

     feature get-config {
       description
        "This feature indicates that the server supports the
         <get-config> protocol operation, albeit without subtree
         filtering.   The server must additionally advertize
         the \"subtree-filtering\" feature to enable subtree
         filtering.  Alternatively, if the server only wants
         to support XPath filtering, it may just advertize
         the :xpath capability.";
     }

     feature subtree-filtering {
       description
        "This feature indicates that the server supports subtree
         filtering for the <get-config> operation.  This
         feature is only meaningful if the "get-config" feature



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         is advertized; if "get-config" is not also advertized,
         this feature MUST be ignored.";
     }

     feature edit-config {
       description
        "This feature indicates that the server supports the
         <edit-config> protocol operation.  If the server is
         unable to support all the <edit-config> attributes
         (merge, replace, create, delete, remove), then it
         should advertize the \"copy-config\" feature instead.";
     }

     feature copy-config {
       description
        "This feature indicates that the server supports the
         <copy-config> protocol operation.";
     }

     feature delete-config {
       description
        "This feature indicates that the server supports the
         <delete-config> protocol operation.";
     }

     feature locking {
       description
        "This feature indicates that the server supports the
         <lock> and <unlock> protocol operations.";
     }

     feature get {
       description
        "This feature indicates that the server supports the
         <get> protocol operation.";
     }

     feature close-session {
       description
        "This feature indicates that the server supports the
         <close-session> protocol operation.  When this feature
         is not advertized, clients are expected to close the
         underlying transport directly.";
     }

     feature kill-session {
       description
        "This feature indicates that the server supports the



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         <kill-session> protocol operation.";
     }
   }


   <CODE ENDS>













































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5.  IANA Consideration

   This document registers a URI in the IETF XML registry [RFC3688].
   Following the format in RFC 3688, the following registration is
   requested.

       URI: urn:ietf:params:xml:ns:yang:ietf-netconf-light

       Registrant Contact: The NETCONF WG of the IETF.

       XML: N/A, the requested URI is an XML namespace.

   This document registers a YANG module in the YANG Module Names
   registry [RFC6020].

       name:         ietf-netconf-light
       namespace:    urn:ietf:params:xml:ns:yang:ietf-netconf-light
       prefix:       ncl
       reference:    RFC XXXX
































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6.  Security Considerations

   NETCONF requires every implementation to support the SSH transport
   (Section 2.3 of [RFC6241]).  On resource constrained devices, it is
   crucial that a single security protocol can be shared between
   different application protocols.  While SSH tends to be popular for
   remote login services, it seems that TLS [RFC5246] and its datagram
   cousin DTLS [RFC4347] are enjoying much greater support on small
   embedded devices.  Hence it might be necessary to choose a different
   mandatory to implement secure transport protocol for NETCONF Light.









































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7.  References

7.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
              January 2004.

   [RFC6020]  Bjorklund, M., "YANG - A Data Modeling Language for the
              Network Configuration Protocol (NETCONF)", RFC 6020,
              October 2010.

   [RFC6241]  Enns, R., Bjorklund, M., Schoenwaelder, J., and A.
              Bierman, "Network Configuration Protocol (NETCONF)",
              RFC 6241, June 2011.

7.2.  Informative References

   [RFC4347]  Rescorla, E. and N. Modadugu, "Datagram Transport Layer
              Security", RFC 4347, April 2006.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246, August 2008.


























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Appendix A.  NETCONF Light on AVR Raven / Contiki

   An implementation of NETCONF Light on Contiki operating system has
   been created.  It is running on AVR Raven motes, which are Class 1
   devices.  The implementation is compliant with this Internet-Draft.
   It does not support filtering, <edit-config> or any other optional
   NETCONF capabilities.  NETCONF messages are currently transported
   over plain TCP connections.

   Together with the Contiki operating system (which weighs about 10 KiB
   RAM) and the System Manager application (0.4 KiB RAM), which is used
   for retrieval of the operational state of the device, NETCONF Light
   takes 13 KiB RAM out of 16 KiB RAM available.  The operating system
   together with the NETCONF Light implementation uses 78 KiB out of 128
   KiB flash memory.  This means that the current implementation of the
   protocol itself takes 2.6 KiB RAM - a value, that can be lowered by
   further code optimizations. 12 KiB out of the used 78 KiB of flash
   memory are reserved for the four files in the Coffee File System.
   These files are used for input / output manipulations in order to
   avoid using more RAM than needed.  The size of the files can be
   changed if needed, however, it is not advisable to make the files
   larger since this will constrain usage of the flash memory by other
   applications.  After installing NETCONF Light the device has 3.5 KiB
   of RAM free, which can be used by other applications.



























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Appendix B.  Experience at Juniper Networks

   Following are three case studies where NETCONF Light would have
   helped.

   As a disclaimer, please note that in accordance with the RFC, Juniper
   does not claim its devices implement NETCONF or let them listen on
   port 830 until the entire NETCONF protocol has been implemented.

   o  Juniper Networks' device management strategy depends on NETCONF
      or, more precisely, on NETCONF plus capabilities we've defined to
      support various aspects of the device (system, hardware, software,
      licenses, etc.).  In order to integrate with Juniper's NMS system,
      a device must support a number of these capabilities before the
      NMS will even attempt to configure the device.  Thus it is common
      that devices new to Juniper, either OEM'ed from a partner or
      obtained through acquisistion, to initially support just the RPCs
      needed for the most basic support by Juniper's NMS and then
      implement the rest of the NETCONF protocol in a subsequent
      release.

   o  As an extension to the previous example, it's not uncommon for a
      device to intially support configuration using its native
      configuration format, which is typically not XML.  However, since
      much of NETCONF still applies (getting/setting/locking datastores,
      etc), some NETCONF operations are extended to allow passing the
      device's native configuration format.  Specifically, the <copy-
      config> RPC and <get-config> RPC-reply are extended to support
      passing an opaque payload.  Naturally, subtree-filtering is
      disabled for the <get-config> operation.

   o  One of the devices that Juniper acquired has no notion of locking.
      The goal of the acquisition was to import the device's technology
      into Junos, but customers owning the original device wanted to
      continue using their existing hardware.  However, since it was
      deemed impossible to add NETCONF to this device (not enough
      resources), the NSM team was forced to develop a device adapter
      that could mediate between the NETCONF interface the NMS system
      requires and the CLI interface the device provided.  The adapter
      project was successful with one exception, the adapter had to
      implement the <lock>/<unlock> RPCs as null operations that blindly
      returned <ok>.









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Authors' Addresses

   Vladislav Perelman
   Jacobs University Bremen

   EMail: v.perelman@jacobs-university.de


   Juergen Schoenwaelder
   Jacobs University Bremen

   EMail: j.schoenwaelder@jacobs-university.de


   Mehmet Ersue
   Nokia Siemens Networks

   EMail: mehmet.ersue@nsn.com


   Kent Watsen
   Juniper Networks

   EMail: kwatsen@juniper.net



























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