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Versions: 00 01 02 03 04 05 06 07 08 09 draft-ietf-netconf-netconf-client-server

NETCONF Working Group                                          K. Watsen
Internet-Draft                                          Juniper Networks
Intended status: Standards Track                        J. Schoenwaelder
Expires: December 03, 2014                      Jacobs University Bremen
                                                               June 2014


                   NETCONF Server Configuration Model
                   draft-ietf-netconf-server-model-01

Abstract

   This draft defines a NETCONF server configuration data model.  This
   data model enables configuration of the NETCONF service itself,
   including which transports it supports, what ports they listen on,
   whether they support device-initiated connections, and associated
   parameters.

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 December 03, 2014.

Copyright Notice

   Copyright (c) 2014 IETF Trust and the persons identified as the
   document authors.  All rights reserved.












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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
     1.2.  Tree Diagrams . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Objectives  . . . . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Support all NETCONF Transports  . . . . . . . . . . . . .   3
     2.2.  Align Transport-Specific Configurations . . . . . . . . .   4
     2.3.  Support both Listening for Connections and Call Home  . .   4
     2.4.  For Call Home Connections . . . . . . . . . . . . . . . .   4
       2.4.1.  Support More than One Application . . . . . . . . . .   4
       2.4.2.  Support Applications Having More than One Server  . .   4
       2.4.3.  Support a Reconnection Strategy . . . . . . . . . . .   4
       2.4.4.  Support both Persistent and Periodic Connections  . .   5
       2.4.5.  Reconnection Strategy for Periodic Connections  . . .   5
       2.4.6.  Keep-Alives for Persistent Connections  . . . . . . .   5
       2.4.7.  Customizations for Periodic Connections . . . . . . .   5
   3.  Data Model  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     3.1.  Overview  . . . . . . . . . . . . . . . . . . . . . . . .   6
     3.2.  YANG Module . . . . . . . . . . . . . . . . . . . . . . .   7
   4.  Keep-Alives for SSH and TLS . . . . . . . . . . . . . . . . .  16
     4.1.  SSH . . . . . . . . . . . . . . . . . . . . . . . . . . .  16
     4.2.  TLS . . . . . . . . . . . . . . . . . . . . . . . . . . .  17
   5.  User Authentication for TLS . . . . . . . . . . . . . . . . .  17
     5.1.  Introduction  . . . . . . . . . . . . . . . . . . . . . .  17
     5.2.  Data Model Overview . . . . . . . . . . . . . . . . . . .  17
     5.3.  YANG Module . . . . . . . . . . . . . . . . . . . . . . .  18
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  23
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  24
   8.  Other Considerations  . . . . . . . . . . . . . . . . . . . .  24
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  24
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  24
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  24
     10.2.  Informative References . . . . . . . . . . . . . . . . .  26
   Appendix A.  Example: SSH Transport Configuration . . . . . . . .  26
   Appendix B.  Example: TLS Transport Configuration . . . . . . . .  27
   Appendix C.  Example: TLS Authentication Configuration  . . . . .  28
   Appendix D.  Change Log . . . . . . . . . . . . . . . . . . . . .  29



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     D.1.  I-D to 00 . . . . . . . . . . . . . . . . . . . . . . . .  29
     D.2.  00 to 01  . . . . . . . . . . . . . . . . . . . . . . . .  29
   Appendix E.  Open Issues  . . . . . . . . . . . . . . . . . . . .  29

1.  Introduction

   This draft defines a NETCONF [RFC6241] server configuration data
   model.  This data model enables configuration of the NETCONF service
   itself, including which transports are supported, what ports does the
   server listen on, whether call-home is supported, and associated
   parameters.

1.1.  Terminology

   The keywords "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].

1.2.  Tree Diagrams

   A simplified graphical representation of data models is used in this
   document.  The meaning of the symbols in these diagrams is as
   follows:

   o  Brackets "[" and "]" enclose list keys.

   o  Abbreviations before data node names: "rw" means configuration
      (read-write) and "ro" state data (read-only).

   o  Symbols after data node names: "?" means an optional node, "!"
      means a presence container, and "*" denotes a list and leaf-list.

   o  Parentheses enclose choice and case nodes, and case nodes are also
      marked with a colon (":").

2.  Objectives

   The primary purpose of the YANG module defined herein is to enable
   the configuration of the NETCONF service on the device.  This scope
   includes the following objectives:

2.1.  Support all NETCONF Transports

   The YANG module should support all current NETCONF transports, namely
   NETCONF over SSH [RFC6242] and NETCONF over TLS
   [I-D.ietf-netconf-rfc5539bis], and be extensible to support future
   transports as necessary.




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   Since implementations may not support all transports, the module
   should use YANG "feature" statements so that implementation can
   accurately advertise which transports are supported.

2.2.  Align Transport-Specific Configurations

   While each transport is unique in its protocol and may have some
   distinct configurations, there remains a significant overlap between
   them.  Thus the YANG module should use "grouping" statements so that
   the common aspects can be configured similarly.

2.3.  Support both Listening for Connections and Call Home

   NETCONF has always supported the server opening a port to listen for
   client connections.  More recently the NETCONF working group defined
   support for call-home ([I-D.ietf-netconf-rfc5539bis] and
   [draft-ieft-netconf-reverse-ssh]).  The module should configure both
   listening for connections and call-home.

   Since implementations may not support both listening for connections
   and call home, YANG "feature" statements should be used so that
   implementation can accurately advertise the connection types it
   supports.

2.4.  For Call Home Connections

   The following objectives only pertain to call home connections.

2.4.1.  Support More than One Application

   A device may be managed by more than one northbound application.  For
   instance, a deployment may have one application for provisioning and
   another for fault monitoring.  Therefore, when it is desired for a
   device to initiate call home connections, it should be able to do so
   for more than one application.

2.4.2.  Support Applications Having More than One Server

   An application managing a device may implement a high-availability
   strategy employing a multiplicity of active and/or passive servers.
   Therefore, when it is desired for a device to initiate call home
   connections, it should be able to connect to any of the applications
   servers.

2.4.3.  Support a Reconnection Strategy

   Assuming an application has more than one server, then it becomes
   necessary to configure how a device should reconnect to the



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   application should it lose its connection to the application's
   servers.  Of primary interest is if the device should start with
   first server defined in a user-ordered list of servers or with the
   last server it was connected to.  Secondary settings might specify
   the frequency of attempts and number of attempts per server.
   Therefore, a reconnection strategy should be configurable.

2.4.4.  Support both Persistent and Periodic Connections

   Applications may vary greatly on how frequently they need to interact
   with a device, how responsive interactions with devices need to be,
   and how many simultaneous connections they can support.  Some
   applications may need a persistent connection to devices to optimize
   real-time interactions, while others are satisfied with periodic
   interactions and reduced resources required.  Therefore, when it is
   necessary for devices to initiate connections, the type of connection
   desired should be configured.

2.4.5.  Reconnection Strategy for Periodic Connections

   The reconnection strategy should apply to both persistent and
   periodic connections.  How it applies to periodic connections becomes
   clear when considering that a periodic "connection" is a logical
   connection to a single server.  That is, the periods of
   unconnectedness are intentional as opposed to due to external
   reasons.  A periodic "connection" should always reconnect to the same
   server until it is no longer able to, at which time the reconnection
   strategy guides how to connect to another server.

2.4.6.  Keep-Alives for Persistent Connections

   If a persistent connection is desired, it is the responsibility of
   the connection-initiator to actively test the aliveness of the
   connection.  The connection initiator must immediately work to
   reestablish a persistent connection as soon as the connection is
   lost.  How often the connection should be tested is driven by
   applications requirements, and therefore keep-alive settings should
   be configurable on a per-application basis.

2.4.7.  Customizations for Periodic Connections

   If a periodic connection is desired, it is necessary for the device
   to know how often it should connect.  This delay essentially
   determines how long the application might have to wait to send data
   to the device.  This setting does not constrain how often the device
   must wait to send data to the application, as the device should
   immediately connect to the application whenever it has data to send
   to it.



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   A common communication pattern is that one data transmission is many
   times closely followed by another.  For instance, if the device needs
   to send a notification message, there's a high probability that it
   will send another shortly thereafter.  Likewise, the application may
   have a sequence of pending messages to send.  Thus, it should be
   possible for a device to hold a connection open until some amount of
   time of no data being transmitted as transpired.

3.  Data Model

3.1.  Overview

   To enable transports to configure listening on one or more ports in a
   common way, this grouping is defined.  This grouping defines SSH and
   TLS specific containers, each of which refines the default listening
   port appropriately.  Further, each of these transport specific
   containers use a feature statement, enabling NETCONF servers to
   accurately advertise what they support.

   module: ietf-netconf-server
      +--rw netconf-server
         +--rw listen
            +--rw ssh {ssh-listen}?
            |  +--rw (one-or-many)?
            |     +--:(one-port)
            |     |  +--rw port?        inet:port-number
            |     +--:(many-ports)
            |        +--rw interface* [address]
            |           +--rw address    inet:host
            |           +--rw port?      inet:port-number
            +--rw tls {tls-listen}?
               +--rw (one-or-many)?
                  +--:(one-port)
                  |  +--rw port?        inet:port-number
                  +--:(many-ports)
                     +--rw interface* [address]
                        +--rw address    inet:host
                        +--rw port?      inet:port-number

   To enable transports to configure initiating connections to remote
   applications in a common way, this grouping is defined.  This
   grouping configures a list of network-managers, each with some
   transport-specific configuration augmented in.  Each of the transport
   specific containers use a feature statement, enabling NETCONF servers
   to accurately advertise what they support.

   module: ietf-netconf-server
      +--rw netconf-server



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         +--rw call-home
            +--rw network-managers
               +--rw network-manager* [name]
                  +--rw name                  string
                  +--rw description?          string
                  +--rw endpoints
                  |  +--rw endpoint* [address]
                  |     +--rw address    inet:host
                  |     +--rw port?      inet:port-number
                  +--rw transport
                  |  +--rw ssh {ssh-call-home}?
                  |  |  +--rw host-keys
                  |  |     +--rw host-key* [name]
                  |  |        +--rw name    string
                  |  +--rw tls! {tls-call-home}?
                  +--rw connection-type
                  |  +--rw (connection-type)?
                  |     +--:(persistent-connection)
                  |     |  +--rw persistent
                  |     |     +--rw keep-alives
                  |     |        +--rw interval-secs?   uint8
                  |     |        +--rw count-max?       uint8
                  |     +--:(periodic-connection)
                  |        +--rw periodic
                  |           +--rw timeout-mins?   uint8
                  |           +--rw linger-secs?    uint8
                  +--rw reconnect-strategy
                     +--rw start-with?      enumeration
                     +--rw interval-secs?   uint8
                     +--rw count-max?       uint8

3.2.  YANG Module

   This YANG module imports YANG types from [RFC6991].

      RFC Ed.: update the date below with the date of RFC publication
      and remove this note.

      <CODE BEGINS> file "ietf-netconf-server.@2014-05-16.yang"

   module ietf-netconf-server {

     namespace "urn:ietf:params:xml:ns:yang:ietf-netconf-server";
     prefix "ncserver";

     import ietf-inet-types {
       prefix inet;                // RFC 6991
     }



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

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

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

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

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


     description
      "This module contains a collection of YANG definitions for
       configuring NETCONF servers.

       Copyright (c) 2014 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.: please update the date to the date of publication

     revision "2014-01-24" {
       description
        "Initial version";
       reference
        "RFC XXXX: NETCONF Server Configuration Model";
     }

     // Features

     feature ssh {



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       description
        "A NETCONF server implements this feature if it supports NETCONF
         over Secure Shell (SSH).";
       reference
        "RFC 6242: Using the NETCONF Protocol over Secure Shell (SSH)";
     }

     feature ssh-listen {
       description
        "The ssh-listen feature indicates that the NETCONF server can
         open a port to listen for incoming client connections.";
     }

     feature ssh-call-home {
       description
        "The ssh-call-home feature indicates that the NETCONF server can
         connect to a client.";
       reference
        "RFC XXXX: Reverse Secure Shell (Reverse SSH)";
     }

     feature tls {
       description
        "A NETCONF server implements this feature if it supports NETCONF
         over Transport Layer Security (TLS).";
       reference
        "RFC XXXX: NETCONF over Transport Layer Security (TLS)";
     }

     feature tls-listen {
       description
        "The tls-listen feature indicates that the NETCONF server can
         open a port to listen for incoming client connections.";
     }

     feature tls-call-home {
       description
        "The tls-call-home feature indicates that the NETCONF server can
         connect to a client.";
     }


     // Groupings

     grouping one-or-many-config {
       description
       "Provides a choice of configuring one of more ports
        to listen for incoming client connections.";



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       choice one-or-many {
        default one-port;
        case one-port {
         leaf port {
           type inet:port-number;
           description
           "The port number the NETCONF server listens on on all
            interfaces.";
         }
        }

        case many-ports {
         list interface {
           key "address";
           leaf address {
            type inet:host;
             mandatory true;
             description
              "The local IP address of the interface to listen
               on.";
            }
            leaf port {
             type inet:port-number;
             description
              "The local port number on this interface the
               NETCONF server listens on.";
             }
           }
         }
       }
     }


     grouping network-managers-config {
       container network-managers {
         description
          "A list of network managers the device initates connections
           to. The configuration for each network manager specifies
           its details, including its endpoints, the type of
           connection to maintain, and the reconnection strategy
           to use.";

         list network-manager {
           key name;
           leaf name {
             type string {
               length 1..64;  // XXX why these limits?
             }



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             mandatory true;
             description
              "An arbitrary name for the network manager the device
               is connecting to.";
           }
           leaf description {
             type string;
             description
               "An optional description for the network manager.";
           }
           container endpoints {
             description
              "An ordered listing of the network manager's
              endpoints that the device should attempt connecting
              to.  Defining more than one enables the device to
              support high-availability scenarios.";
             list endpoint {
               key address;
               min-elements 1;
               ordered-by user;
               leaf address {
                 type inet:host;
                 mandatory true;
                 description
                  "The hostname or IP address of the endpoint.
                  If a hostname is provided and DNS resolves to
                  more than one IP address, the device SHOULD
                  try all of the ones it can based on how its
                  networking stack is configured (e.g. v4, v6,
                  dual-stack).";
               }
               leaf port {
                 type inet:port-number;
                 description
                  "The IP port for this endpoint. The device will use
                   the IANA-assigned well-known port if not specified.";
               }
             }
           }
           container transport {
           }
           container connection-type {
             description
              "Indicates the network manager's preference for how the
               device's connection is maintained.";
             choice connection-type {
               default persistent-connection;




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               case persistent-connection {
                 container persistent {
                   description
                    "Maintain a persistent connection to the
                     network manager. If the connection goes down,
                     immediately start trying to reconnect to it,
                     using the reconnection strategy.

                     This connection type minimizes any
                     manager-to-device data-transfer delay,
                     albeit at the expense of holding resources
                     longer.";
                   container keep-alives {
                     leaf interval-secs {
                       type uint8;
                       units seconds;
                       default 15;
                       description
                        "Sets a timeout interval in seconds after which
                         if no data has been received from the manager's
                         endpoint, a message will be sent to request a
                         response from the endpoint.  A value of '0'
                         indicates that no keep-alive messages should
                         be sent.";
                     }
                     leaf count-max {
                       type uint8;
                       default 3;
                       description
                        "Sets the number of keep-alive messages that may
                         be sent without receiving any data from the
                         manager's endpoint before assuming the endpoint
                         is no longer alive.  If this threshold is
                         reached, the transport-level connection will be
                         disconnected (thus triggering the reconnection
                         strategy).  The interval timer is reset after
                         each transmission, thus an unresponsive
                         endpoint will be disconnected after about
                         count-max * interval-secs seconds.";
                     }
                   }
                 }
               }

               case periodic-connection {
                 container periodic {
                   description
                    "Periodically connect to network manager, using the



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                     reconnection strategy, so it can flush any pending
                     data it may be holding. This connection type
                     minimizes resources held open, albeit at the
                     expense of longer manager-to-device data-transfer
                     delay.  Note that for device-to-manager data, the
                     data should be sent immediately, connecting to
                     network manager first if not already.";
                   leaf timeout-mins {
                     type uint8;
                     units minutes;
                     default 5;
                     description
                      "The maximum amount of unconnected time the
                       device will wait until establishing a
                       connection to the network manager again. The
                       device MAY establish a connection before this
                       time if it has data it needs to send to the
                       network manager. Note: this value differs from
                       the reconnection strategy's interval-secs
                       value.";
                   }
                   leaf linger-secs {
                     type uint8;
                     units seconds;
                     default 30;
                     description
                      "The amount of time the device should wait after
                       last receiving data from or sending data to the
                       network manager's endpoint before closing its
                       connection to it.  This is an optimization to
                       prevent unnecessary connections.";
                   }
                 }
               }
             }
           }

           // XXX
           // Should we have something smarter as the reconnect
           // strategy, e.g. an exponential backoff?

           container reconnect-strategy {
             description
              "The reconnection strategy guides how a device reconnects
               to an network manager, after losing a connection to it,
               even if due to a reboot.  The device starts with the
               specified endpoint, tries to connect to it count-max
               times, waiting interval-secs between each connection



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               attempt, before trying the next endpoint in the list
               (round robin).";
             leaf start-with {
               type enumeration {
                 enum first-listed { value 1; }
                 enum last-connected { value 2; }
               }
               default first-listed;
               description
                "Specifies which of the network manager's endpoints the
                 device should start with when trying to connect to
                 the network manager.  If no previous connection has
                 ever been established, last-connected defaults to the
                 first endpoint listed.";
             }
             leaf interval-secs {
               type uint8;
               units seconds;
               default 5;
               description
                "Specifies the time delay between connection attempts
                 to the same endpoint.  Note: this value differs from
                 the periodic-connection's timeout-mins value.";
             }
             leaf count-max {
               type uint8;
               default 3;
               description
                "Specifies the number times the device tries to
                 connect to a specific endpoint before moving on to
                 the next endpoint in the list (round robin).";
             }
           }
         }
       }
     }

     grouping listen-config {
       description
         "Provides the configuration of the NETCONF server to
          open one or more ports to listen for incoming client
          connections.";
       container ssh {
         if-feature ssh-listen;
         uses one-or-many-config {
           refine one-or-many/one-port/port {
             default 830;
           }



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           refine one-or-many/many-ports/interface/port {
             default 830;
           }
         }
       }
       container tls {
         if-feature tls-listen;
         uses one-or-many-config {
           refine one-or-many/one-port/port {
             default 6513;
           }
           refine one-or-many/many-ports/interface/port {
             default 6513;
           }
         }
       }
     }


     grouping call-home-config {
       description
         "Provides the configuration of the NETCONF call-home
          clients to connect to, the overall call-home policy,
          and the reconnect strategy.";

       uses network-managers-config {
         augment network-managers/network-manager/transport {
           container ssh {
             if-feature ssh-call-home;
             container host-keys {
               description
                 "An ordered listing of the SSH host keys the
                  device should advertise to the network manager.";
               list host-key {
                 key name;
                 min-elements 1;    // requires 'ssh' element?
                 ordered-by user;
                 leaf name {
                   type string;
                   mandatory true;
                   description
                     "The name of a host key the device should
                      advertise during the SSH key exchange.";
                 }
               }
             }
           }
           container tls {



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             if-feature tls-call-home;
             presence "Enables call home using TLS when configured.";
           }
         }
       }
     }


     // Module's top-level container
     container netconf-server {
       description
         "Top-level container for NETCONF server configuration.";
       container listen {
         uses listen-config;
       }
       container call-home {
         uses call-home-config;
       }
     }


   }

      <CODE ENDS>


4.  Keep-Alives for SSH and TLS

   One the objectives listed above, Keep-Alives for Persistent
   Connections (Section 2.4.6) indicates a need for a "keep-alive"
   mechanism.  This section specifies how the NETCONF keep-alive
   mechanism is to be implemented.

   Both SSH and TLS have the ability to support keep-alives.  Using
   these mechanisms, the keep-alive messages are sent inside the
   encrypted tunnel, thus thwarting spoof attacks.

4.1.  SSH

   The SSH keep-alive solution that is expected to be used when
   configured using the data model defined in this document is
   ubiquitous in practice, though never being explicitly defined in an
   RFC.  The strategy used is to purposely send a malformed request
   message with a flag set to ensure a response.  More specifically, per
   section 4 of [RFC4253], either SSH peer can send a
   SSH_MSG_GLOBAL_REQUEST message with "want reply" set to '1' and that,
   if there is an error, will get back a SSH_MSG_REQUEST_FAILURE
   response.  Similarly, section 5 of [RFC4253] says that either SSH



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   peer can send a SSH_MSG_CHANNEL_REQUEST message with "want reply" set
   to '1' and that, if there is an error, will get back a
   SSH_MSG_CHANNEL_FAILURE response.

   To ensure that the request will fail, current implementations send an
   invalid "request name" or "request type", respectively.  Abiding to
   the extensibility guidelines specified in Section 6 of [RFC4251],
   these implementations use the "name@domain".  For instance, when
   configured to send keep-alives, OpenSSH sends the string
   "keepalive@openssh.com".  In order to remain compatible with existing
   implementations, this draft does not require a specific "request
   name" or "request type" string be used.

4.2.  TLS

   The TLS keep-alive solution is defined in [RFC6520].  This solution
   allows both peers to advertise if they can receive heartbeat request
   messages from its peer.  For standard NETCONF over TLS connections,
   devices SHOULD advertise "peer_allowed_to_send", as per [RFC6520].
   This advertisement is not a "MUST" in order to grandfather existing
   NETCONF over TLS implementations.  For NETCONF over TLS Call Home,
   the network management system MUST advertise "peer_allowed_to_send"
   per [RFC6520].  This is a "MUST" so as to ensure devices can depend
   in it always being there for call home connections, which is
   conveniently when keep-alives are needed the most.

5.  User Authentication for TLS

5.1.  Introduction

   The NETCONF Server Module defined in this draft focuses on the
   configuration the SSH and TLS transports.  This module does not
   define a means to configure User Authentication, as that is a stated
   focus for [draft-ietf-netmod-system-mgmt], however, that draft does
   not define configuration nodes for TLS client authentication.  Thus,
   this draft also includes the following YANG module to augment TLS
   client authentication into the "ietf-system" module defined in
   [draft-ietf-netmod-system-mgmt].

5.2.  Data Model Overview

   This data model augments the "ietf-system" module defined in
   [draft-ietf-netmod-system-mgmt] by adding some configuration nodes
   under its "/system/authentication" subtree.

   module: ietf-system-tls-auth
   augment /sys:system/sys:authentication:
      +--rw tls



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         +--rw trusted-ca-certs
         |  +--rw trusted-ca-cert*   binary
         +--rw trusted-client-certs
         |  +--rw trusted-client-cert*   binary
         +--rw cert-maps {tls-map-certificates}?
         |  +--rw cert-to-name* [id]
         |     +--rw id             uint32
         |     +--rw fingerprint    x509c2n:tls-fingerprint
         |     +--rw map-type       identityref
         |     +--rw name           string
         +--rw psk-maps {tls-map-pre-shared-keys}?
            +--rw psk-map* [psk-identity]
               +--rw psk-identity        string
               +--rw user-name           nacm:user-name-type
               +--rw not-valid-before?   yang:date-and-time
               +--rw not-valid-after?    yang:date-and-time
               +--rw key                 yang:hex-string

5.3.  YANG Module

   This YANG module imports YANG extensions from [RFC6536], and imports
   YANG types from [RFC6991] and a YANG grouping from
   [I-D.ietf-netmod-snmp-cfg].

        RFC Ed.: update the date below with the date of RFC publication
        and remove this note.

        <CODE BEGINS> file "ietf-system-tls-auth.@2014-05-16.yang"

   module ietf-system-tls-auth {

     namespace "urn:ietf:params:xml:ns:yang:ietf-system-tls-auth";
     prefix "system-tls-auth";

     import ietf-system {  // draft-ietf-netmod-system-mgmt
       prefix "sys";
     }
     import ietf-netconf-acm {
       prefix nacm;                // RFC 6536
     }
     import ietf-yang-types {
       prefix yang;                // RFC 6991
     }
     import ietf-x509-cert-to-name {
       prefix x509c2n;             // I-D.ietf-netconf-rfc5539bis
     }

     organization



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      "IETF NETCONF (Network Configuration) Working Group";

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

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

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

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

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


     description
      "This module augments the ietf-system module in order to
       add TLS authentication configuration nodes to the
       'authentication' container.

       Copyright (c) 2014 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.: please update the date to the date of publication

     revision "2014-05-24" {
       description
        "Initial version";
       reference
        "RFC XXXX: NETCONF Server Configuration Model";
     }




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     // Features

     feature tls-map-certificates {
       description
        "The tls-map-certificates feature indicates that the
         NETCONF server implements mapping X.509 certificates to NETCONF
         usernames.";
     }

     feature tls-map-pre-shared-keys {
       description
        "The tls-map-pre-shared-keys feature indicates that the
         NETCONF server implements mapping TLS pre-shared keys to NETCONF
         usernames.";
     }

     grouping tls-global-config {

       container trusted-ca-certs {
         description
           "A list of Certificate Authority (CA) certificates that a
            NETCONF server can use to authenticate a NETCONF client's
            certificate.  A client's certificate is authenticated if
            its Issuer matches one of the configured trusted CA
            certificates.";
         leaf-list trusted-ca-cert {
           type binary;
           ordered-by system;
           description
             "The binary certificate structure, as
              specified by RFC 5246, Section 7.4.6, i.e.,:

                opaque ASN.1Cert<1..2^24>;

             ";
           reference
             "RFC 5246: The Transport Layer Security (TLS)
                        Protocol Version 1.2";
         }
       }

       container trusted-client-certs {
         description
           "A list of client certificates that a NETCONF server can
            use to authenticate a NETCONF client's certificate.  A
            client's certificate is authenticated if it is an exact
            match to one of the configured trusted client certificates.";
         leaf-list trusted-client-cert {



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           type binary;
           ordered-by system;
           description
             "The binary certificate structure, as
              specified by RFC 5246, Section 7.4.6, i.e.,:

                opaque ASN.1Cert<1..2^24>;

             ";
           reference
             "RFC 5246: The Transport Layer Security (TLS)
                        Protocol Version 1.2";
         }
       }


       // Objects for deriving NETCONF usernames from X.509
       // certificates.
       container cert-maps {
         if-feature tls-map-certificates;
         uses x509c2n:cert-to-name;
         description
          "The cert-maps container is used by a NETCONF server to
           map the NETCONF client's presented X.509 certificate to
           a NETCONF username.

           If no matching and valid cert-to-name list entry can be
           found, then the NETCONF server MUST close the connection,
           and MUST NOT accept NETCONF messages over it.";
       }

       // Objects for deriving NETCONF usernames from TLS
       // pre-shared keys.
       container psk-maps {
         if-feature tls-map-pre-shared-keys;
         description
           "During the TLS Handshake, the client indicates which
            key to use by including a PSK identity in the TLS
            ClientKeyExchange message. On the NETCONF server side,
            this PSK identity is used to look up an entry in the psk-map
            list. If such an entry is found, and the pre-shared keys
            match, then the client is authenticated. The NETCONF
            server uses the value from the user-name leaf in the
            psk-map list as the NETCONF username.  If the NETCONF
            server cannot find an entry in the psk-map list, or if
            the pre-shared keys do not match, then the NETCONF
            server terminates the connection.";
         reference



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           "RFC 4279: Pre-Shared Key Ciphersuites for Transport Layer
                      Security (TLS)";

         list psk-map {
           key psk-identity;

           leaf psk-identity {
             type string;
             description
               "The PSK identity encoded as a UTF-8 string. For
                details how certain common PSK identity formats can
                be encoded in UTF-8, see section 5.1. of RFC 4279.";
             reference
               "RFC 4279: Pre-Shared Key Ciphersuites for Transport
                Layer Security (TLS)";
           }
           leaf user-name {
             type nacm:user-name-type;
             mandatory true;
             description
               "The NETCONF username associated with this PSK
                identity.";
           }
           leaf not-valid-before {
             type yang:date-and-time;
             description
               "This PSK identity is not valid before the given date
                and time.";
           }
           leaf not-valid-after {
             type yang:date-and-time;
             description
               "This PSK identity is not valid after the given date
                and time.";
           }
           leaf key {
             type yang:hex-string;
             mandatory true;
             nacm:default-deny-all;
             description
               "The key associated with the PSK identity";
             reference
               "RFC 4279: Pre-Shared Key Ciphersuites for Transport
                Layer Security (TLS)";
           }
         }
       }
     }



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     augment "/sys:system/sys:authentication" {
       container tls {
         uses tls-global-config;
       }
     }

   }


        <CODE ENDS>


6.  Security Considerations

   The YANG modules defined in this memo are designed to be accessed via
   the NETCONF protocol [RFC6241].  Authorization for access to specific
   portions of conceptual data and operations within this module is
   provided by the NETCONF access control model (NACM) [RFC6536].

   There are a number of data nodes defined in the "ietf-netconf-server"
   and "ietf-system-tls-auth" YANG modules which are writable/creatable/
   deletable (i.e., config true, which is the default).  These data
   nodes may be considered sensitive or vulnerable in some network
   environments.  Write and read operations to these data nodes can have
   a negative effect on network operations.  It is thus important to
   control write and read access to these data nodes.  Below are the
   data nodes and their sensitivity/vulnerability.

   ietf-netconf-server:

   o  None.

   ietf-system-tls-auth:

   o  /system/authentication/tls/psk-maps/psk-map/user-name: This leaf
      node contains a user name that some deployments may consider
      sensitive information.

   o  /system/authentication/tls/psk-maps/psk-map/key: This leaf node
      contains a shared key that remote clients use to authenticate
      themselves to the system.  This value should not be readable or
      writable by anyone by default.









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7.  IANA Considerations

   This document registers two URIs in the IETF XML registry [RFC2119].
   Following the format in [RFC3688], the following registrations are
   requested:

         URI: urn:ietf:params:xml:ns:yang:ietf-netconf-server
         Registrant Contact: The NETCONF WG of the IETF.
         XML: N/A, the requested URI is an XML namespace.

         URI: urn:ietf:params:xml:ns:yang:ietf-system-tle-auth
         Registrant Contact: The NETCONF WG of the IETF.
         XML: N/A, the requested URI is an XML namespace.

   This document registers two YANG modules in the YANG Module Names
   registry [RFC6020].

      name:         ietf-netconf-server
      namespace:    urn:ietf:params:xml:ns:yang:ietf-netconf-server
      prefix:       ncserver
      reference:    RFC XXXX

      name:         ietf-system-tls-auth
      namespace:    urn:ietf:params:xml:ns:yang:ietf-system-tls-auth
      prefix:       sys-tls-auth
      reference:    RFC XXXX

8.  Other Considerations

   The YANG module define herein does not itself support virtual routing
   and forwarding (VRF).  It is expected that external modules will
   augment in VRF designations when needed.

9.  Acknowledgements

   The authors would like to thank for following for lively discussions
   on list and in the halls (ordered by last name): Andy Bierman, Martin
   Bjorklund, Benoit Claise, David Lamparter, Alan Luchuk, Ladislav
   Lhotka, Radek Krejci, Tom Petch, and Phil Shafer.

   Juergen Schoenwaelder and was partly funded by Flamingo, a Network of
   Excellence project (ICT-318488) supported by the European Commission
   under its Seventh Framework Programme.

10.  References

10.1.  Normative References




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

   [RFC4251]  Ylonen, T. and C. Lonvick, "The Secure Shell (SSH)
              Protocol Architecture ", RFC 4251, January 2006.

   [RFC4253]  Ylonen, T. and C. Lonvick, "The Secure Shell (SSH)
              Transport Layer Protocol ", RFC 4253, January 2006.

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

   [RFC6520]  Seggelmann, R., Tuexen, M., and M. Williams, "Transport
              Layer Security (TLS) and Datagram Transport Layer Security
              (DTLS) Heartbeat Extension ", RFC 6520, February 2012.

   [RFC6536]  Bierman, A. and M. Bjorklund, "Network Configuration
              Protocol (NETCONF) Access Control Model ", RFC 6536, March
              2012.

   [RFC6991]  Schoenwaelder, J., "Common YANG Data Types", RFC 6991,
              July 2013.

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

   [RFC6242]  Wasserman, M., "Using the NETCONF Protocol over Secure
              Shell (SSH)", RFC 6242, June 2011.

   [I-D.ietf-netconf-rfc5539bis]
              Badra, M., Luchuk, A., and J. Schoenwaelder, "Using the
              NETCONF Protocol over Transport Layer Security (TLS) ",
              draft-ietf-netconf-rfc5539bis-04 (work in progress),
              October 2013.

   [I-D.ietf-netmod-snmp-cfg]
              Bjorklund, M. and J. Schoenwaelder, "A YANG Data Model for
              SNMP Configuration", draft-ietf-netmod-snmp-cfg-03 (work
              in progress), November 2013.

   [draft-ieft-netconf-reverse-ssh]
              Watsen, K., "NETCONF over SSH Call Home ", draft-ieft-
              netconf-reverse-ssh-00 (work in progress), May 2014.

   [draft-ietf-netmod-system-mgmt]




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              Bierman, A., "A YANG Data Model for System Management ",
              draft-ieft-netmod-system-mgmt-16 (work in progress), May
              2014.

10.2.  Informative References

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

Appendix A.  Example: SSH Transport Configuration

   <netconf-server xmlns="urn:ietf:params:xml:ns:yang:ietf-netconf-server">
     <listen>
       <ssh>
         <port>831</port>
       </ssh>
     </listen>
     <call-home>
       <network-managers>
         <network-manager>
           <name>config-mgr</name>
           <description>
              This entry requests the device to periodically
              connect to the network manager.
           </description>
           <endpoints>
              <endpoint>
                 <address>config-mgr1.example.com</address>
              </endpoint>
              <endpoint>
                 <address>config-mgr2.example.com</address>
              </endpoint>
           </endpoints>
           <transport>
              <ssh>
                 <host-keys>
                    <host-key>
                       <name>ssh_host_key_cert</name>
                    </host-key>
                    <host-key>
                       <name>ssh_host_key_cert2</name>
                    </host-key>
                 </host-keys>
              </ssh>
           </transport>
           <connection-type>
             <periodic>
               <timeout-mins>5</timeout-mins>



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               <linger-secs>10</linger-secs>
             </periodic>
           </connection-type>
           <reconnect-strategy>
              <start-with>last-connected</start-with>
              <interval-secs>10</interval-secs>
              <count-max>3</count-max>
           </reconnect-strategy>
         </network-manager>
       </network-managers>
     </call-home>
   </netconf-server>

Appendix B.  Example: TLS Transport Configuration

   <netconf-server xmlns="urn:ietf:params:xml:ns:yang:ietf-netconf-server">
     <listen>
       <tls>
         <interface>
           <address>192.0.2.1</address>
           <port>6514</port>
         </interface>
       </tls>
     </listen>
     <call-home>
       <network-managers>
         <network-manager>
           <name>log-monitor</name>
           <description>
              This entry requests the device to maintain a
              persistent connect to the network manager.
           </description>
           <endpoints>
              <endpoint>
                 <address>log-monitor1.example.com</address>
              </endpoint>
              <endpoint>
                 <address>log-monitor2.example.com</address>
              </endpoint>
           </endpoints>
           <transport>
             <tls/>
           </transport>
           <connection-type>
             <persistent>
               <keep-alives>
                 <interval-secs>5</interval-secs>
                 <count-max>3</count-max>



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               </keep-alives>
             </persistent>
           </connection-type>
           <reconnect-strategy>
              <start-with>first-listed</start-with>
              <interval-secs>10</interval-secs>
              <count-max>4</count-max>
           </reconnect-strategy>
         </network-manager>
       </network-managers>
     </call-home>
   </netconf-server>

Appendix C.  Example: TLS Authentication Configuration

   <system xmlns="urn:ietf:params:xml:ns:yang:ietf-system">
     <authentication>
       <tls xmlns="urn:ietf:params:xml:ns:yang:ietf-system-tls-auth">

         <trusted-ca-certs>
           <trusted-ca-cert>
             QW4gRWFzdGVyIGVnZywgZm9yIHRob3NlIHdobyBtaWdodCBsb29rICA6KQo=
           </trusted-ca-cert>
         </trusted-ca-certs>

         <trusted-client-certs>
           <trusted-client-cert>
             SSBhbSB0aGUgZWdnIG1hbiwgdGhleSBhcmUgdGhlIGVnZyBtZW4uCg==
           </trusted-client-cert>
           <trusted-client-cert>
             SSBhbSB0aGUgd2FscnVzLCBnb28gZ29vIGcnam9vYi4K
           </trusted-client-cert>
         </trusted-client-certs>

         <cert-maps>
           <cert-to-name>
             <id>1</id>
             <fingerprint>11:0A:05:11:00</fingerprint>
             <map-type>x509c2n:san-any</map-type>
           </cert-to-name>
           <cert-to-name>
             <id>2</id>
             <fingerprint>11:0A:05:11:00</fingerprint>
             <map-type>x509c2n:specified</map-type>
             <name>Joe Cool</name>
           </cert-to-name>
         </cert-maps>




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         <psk-maps>
           <psk-map>
             <psk-identity>a8gc8]klh59</psk-identity>
             <user-name>admin</user-name>
             <not-valid-before>2013-01-01T00:00:00Z</not-valid-before>
             <not-valid-after>2014-01-01T00:00:00Z</not-valid-after>
           </psk-map>
         </psk-maps>

       </tls>
     </authentication>
   </system>


Appendix D.  Change Log

D.1.  I-D to 00

   o  Changed title to "NETCONF Server Configuration Model"

   o  Mapped inbound/outbound to listen/call-home

   o  Restructured YANG module to place transport selection deeper into
      the tree, providing a more intuitive data model

   o  Added section "Keep-Alives for SSH and TLS"

   o  Updated the Security Considerations section

   o  Added text for supporting VRFs via augments

   o  Factored the TLS-AUTH config into another module augmenting the
      "ietf-system" module

D.2.  00 to 01

   o  Restructured document so it flows better

   o  Added trusted-ca-certs and trusted-client-certs objects into the
      ietf-system-tls-auth module

Appendix E.  Open Issues

   o  NETCONF implementations typically have config parameters such as
      session timeouts or hello timeouts.  Shall they be included in
      this model?





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   o  Do we need knobs to enable/disable call-home without the need to
      remove all the call-home client configuration?

Authors' Addresses

   Kent Watsen
   Juniper Networks

   EMail: kwatsen@juniper.net


   Juergen Schoenwaelder
   Jacobs University Bremen

   EMail: j.schoenwaelder@jacobs-university.de




































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