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Versions: (draft-ietf-netconf-server-model) 00 01 02 03 04 05 06 07 08 09 10 11

NETCONF Working Group                                          K. Watsen
Internet-Draft                                          Juniper Networks
Intended status: Standards Track                                   G. Wu
Expires: January 4, 2018                                  Cisco Networks
                                                        J. Schoenwaelder
                                                Jacobs University Bremen
                                                            July 3, 2017


                    NETCONF Client and Server Models
              draft-ietf-netconf-netconf-client-server-04

Abstract

   This document defines two YANG modules, one module to configure a
   NETCONF client and the other module to configure a NETCONF server.
   Both modules support both the SSH and TLS transport protocols, and
   support both standard NETCONF and NETCONF Call Home connections.

Editorial Note (To be removed by RFC Editor)

   This draft contains many placeholder values that need to be replaced
   with finalized values at the time of publication.  This note
   summarizes all of the substitutions that are needed.  No other RFC
   Editor instructions are specified elsewhere in this document.

   This document contains references to other drafts in progress, both
   in the Normative References section, as well as in body text
   throughout.  Please update the following references to reflect their
   final RFC assignments:

   o  I-D.ietf-netconf-keystore

   o  I-D.ietf-netconf-ssh-client-server

   o  I-D.ietf-netconf-tls-client-server

   Artwork in this document contains shorthand references to drafts in
   progress.  Please apply the following replacements:

   o  "XXXX" --> the assigned RFC value for this draft

   o  "YYYY" --> the assigned RFC value for I-D.ietf-netconf-ssh-client-
      server

   o  "ZZZZ" --> the assigned RFC value for I-D.ietf-netconf-tls-client-
      server




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   Artwork in this document contains placeholder values for the date of
   publication of this draft.  Please apply the following replacement:

   o  "2017-07-03" --> the publication date of this draft

   The following Appendix section is to be removed prior to publication:

   o  Appendix A.  Change Log

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 January 4, 2018.

Copyright Notice

   Copyright (c) 2017 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
   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.











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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   4
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   4
     1.2.  Tree Diagrams . . . . . . . . . . . . . . . . . . . . . .   4
   2.  The NETCONF Client Model  . . . . . . . . . . . . . . . . . .   4
     2.1.  Tree Diagram  . . . . . . . . . . . . . . . . . . . . . .   5
     2.2.  Example Usage . . . . . . . . . . . . . . . . . . . . . .   8
     2.3.  YANG Model  . . . . . . . . . . . . . . . . . . . . . . .  10
   3.  The NETCONF Server Model  . . . . . . . . . . . . . . . . . .  20
     3.1.  Tree Diagram  . . . . . . . . . . . . . . . . . . . . . .  20
     3.2.  Example Usage . . . . . . . . . . . . . . . . . . . . . .  23
     3.3.  YANG Model  . . . . . . . . . . . . . . . . . . . . . . .  26
   4.  Design Considerations . . . . . . . . . . . . . . . . . . . .  37
     4.1.  Support all NETCONF transports  . . . . . . . . . . . . .  38
     4.2.  Enable each transport to select which keys to use . . . .  38
     4.3.  Support authenticating NETCONF clients certificates . . .  38
     4.4.  Support mapping authenticated NETCONF client certificates
           to usernames  . . . . . . . . . . . . . . . . . . . . . .  38
     4.5.  Support both listening for connections and call home  . .  38
     4.6.  For Call Home connections . . . . . . . . . . . . . . . .  39
       4.6.1.  Support more than one NETCONF client  . . . . . . . .  39
       4.6.2.  Support NETCONF clients having more than one endpoint  39
       4.6.3.  Support a reconnection strategy . . . . . . . . . . .  39
       4.6.4.  Support both persistent and periodic connections  . .  39
       4.6.5.  Reconnection strategy for periodic connections  . . .  40
       4.6.6.  Keep-alives for persistent connections  . . . . . . .  40
       4.6.7.  Customizations for periodic connections . . . . . . .  40
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  40
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  41
     6.1.  The IETF XML Registry . . . . . . . . . . . . . . . . . .  41
     6.2.  The YANG Module Names Registry  . . . . . . . . . . . . .  42
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  42
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  42
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  42
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  43
   Appendix A.  Change Log . . . . . . . . . . . . . . . . . . . . .  45
     A.1.  server-model-09 to 00 . . . . . . . . . . . . . . . . . .  45
     A.2.  00 to 01  . . . . . . . . . . . . . . . . . . . . . . . .  45
     A.3.  01 to 02  . . . . . . . . . . . . . . . . . . . . . . . .  45
     A.4.  02 to 03  . . . . . . . . . . . . . . . . . . . . . . . .  45
     A.5.  03 to 04  . . . . . . . . . . . . . . . . . . . . . . . .  45
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  46








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1.  Introduction

   This document defines two YANG [RFC7950] modules, one module to
   configure a NETCONF client and the other module to configure a
   NETCONF server.  Both modules support both the SSH and TLS transport
   protocols, and support both standard NETCONF and NETCONF Call Home
   connections.

   NETCONF is defined by [RFC6241].  SSH is defined by [RFC4252],
   [RFC4253], and [RFC4254].  TLS is defined by [RFC5246].  NETCONF Call
   Home is defined by [RFC8071]).

1.1.  Terminology

   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.

1.2.  Tree Diagrams

   A simplified graphical representation of the 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  Braces "{" and "}" enclose feature names, and indicate that the
      named feature must be present for the subtree to be present.

   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 (":").

   o  Ellipsis ("...") stands for contents of subtrees that are not
      shown.

2.  The NETCONF Client Model

   The NETCONF client model presented in this section supports both
   clients initiating connections to servers, as well as clients
   listening for connections from servers calling home.



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   This model supports both the SSH and TLS transport protocols, using
   the SSH client and TLS client groupings defined in
   [I-D.ietf-netconf-ssh-client-server] and
   [I-D.ietf-netconf-tls-client-server] respectively.

   All private keys and trusted certificates are held in the keystore
   model defined in [I-D.ietf-netconf-keystore].

   YANG feature statements are used to enable implementations to
   advertise which parts of the model the NETCONF client supports.

2.1.  Tree Diagram

   Just the container is displayed below, but there is also a grouping
   that the container is using.

   Note: all lines are folded at column 71 with no '\' character.

 module: ietf-netconf-client
     +--rw netconf-client
        +--rw initiate {initiate}?
        |  +--rw netconf-server* [name]
        |     +--rw name                  string
        |     +--rw (transport)
        |     |  +--:(ssh) {ssh-initiate}?
        |     |  |  +--rw ssh
        |     |  |     +--rw endpoints
        |     |  |     |  +--rw endpoint* [name]
        |     |  |     |     +--rw name       string
        |     |  |     |     +--rw address    inet:host
        |     |  |     |     +--rw port?      inet:port-number
        |     |  |     +--rw server-auth
        |     |  |     |  +--rw trusted-ssh-host-keys?
        |     |  |     |  |       -> /ks:keystore/trusted-host-keys/name
        |     |  |     |  +--rw trusted-ca-certs?        leafref
        |     |  |     |  |       {sshcom:ssh-x509-certs}?
        |     |  |     |  +--rw trusted-server-certs?    leafref
        |     |  |     |          {sshcom:ssh-x509-certs}?
        |     |  |     +--rw client-auth
        |     |  |     |  +--rw username?      string
        |     |  |     |  +--rw (auth-type)
        |     |  |     |     +--:(certificate)
        |     |  |     |     |  +--rw certificate?   leafref
        |     |  |     |     |          {sshcom:ssh-x509-certs}?
        |     |  |     |     +--:(public-key)
        |     |  |     |     |  +--rw public-key?
        |     |  |     |     |          -> /ks:keystore/keys/key/name
        |     |  |     |     +--:(password)



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        |     |  |     |        +--rw password?      string
        |     |  |     +--rw transport-params
        |     |  |             {ssh-client-transport-params-config}?
        |     |  |        +--rw host-key
        |     |  |        |  +--rw host-key-alg*   identityref
        |     |  |        +--rw key-exchange
        |     |  |        |  +--rw key-exchange-alg*   identityref
        |     |  |        +--rw encryption
        |     |  |        |  +--rw encryption-alg*   identityref
        |     |  |        +--rw mac
        |     |  |        |  +--rw mac-alg*   identityref
        |     |  |        +--rw compression
        |     |  |           +--rw compression-alg*   identityref
        |     |  +--:(tls) {tls-initiate}?
        |     |     +--rw tls
        |     |        +--rw endpoints
        |     |        |  +--rw endpoint* [name]
        |     |        |     +--rw name       string
        |     |        |     +--rw address    inet:host
        |     |        |     +--rw port?      inet:port-number
        |     |        +--rw server-auth
        |     |        |  +--rw trusted-ca-certs?       leafref
        |     |        |  +--rw trusted-server-certs?   leafref
        |     |        +--rw client-auth
        |     |        |  +--rw (auth-type)
        |     |        |     +--:(certificate)
        |     |        |        +--rw certificate?   leafref
        |     |        +--rw hello-params
        |     |                {tls-client-hello-params-config}?
        |     |           +--rw tls-versions
        |     |           |  +--rw tls-version*   identityref
        |     |           +--rw cipher-suites
        |     |              +--rw cipher-suite*   identityref
        |     +--rw connection-type
        |     |  +--rw (connection-type)?
        |     |     +--:(persistent-connection)
        |     |     |  +--rw persistent!
        |     |     |     +--rw idle-timeout?   uint32
        |     |     |     +--rw keep-alives
        |     |     |        +--rw max-wait?       uint16
        |     |     |        +--rw max-attempts?   uint8
        |     |     +--:(periodic-connection)
        |     |        +--rw periodic!
        |     |           +--rw idle-timeout?        uint16
        |     |           +--rw reconnect-timeout?   uint16
        |     +--rw reconnect-strategy
        |        +--rw start-with?     enumeration
        |        +--rw max-attempts?   uint8



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        +--rw listen {listen}?
           +--rw max-sessions?   uint16
           +--rw idle-timeout?   uint16
           +--rw endpoint* [name]
              +--rw name    string
              +--rw (transport)
                 +--:(ssh) {ssh-listen}?
                 |  +--rw ssh
                 |     +--rw address?            inet:ip-address
                 |     +--rw port?               inet:port-number
                 |     +--rw server-auth
                 |     |  +--rw trusted-ssh-host-keys?
                 |     |  |       -> /ks:keystore/trusted-host-keys/name
                 |     |  +--rw trusted-ca-certs?        leafref
                 |     |  |       {sshcom:ssh-x509-certs}?
                 |     |  +--rw trusted-server-certs?    leafref
                 |     |          {sshcom:ssh-x509-certs}?
                 |     +--rw client-auth
                 |     |  +--rw username?      string
                 |     |  +--rw (auth-type)
                 |     |     +--:(certificate)
                 |     |     |  +--rw certificate?   leafref
                 |     |     |          {sshcom:ssh-x509-certs}?
                 |     |     +--:(public-key)
                 |     |     |  +--rw public-key?
                 |     |     |          -> /ks:keystore/keys/key/name
                 |     |     +--:(password)
                 |     |        +--rw password?      string
                 |     +--rw transport-params
                 |             {ssh-client-transport-params-config}?
                 |        +--rw host-key
                 |        |  +--rw host-key-alg*   identityref
                 |        +--rw key-exchange
                 |        |  +--rw key-exchange-alg*   identityref
                 |        +--rw encryption
                 |        |  +--rw encryption-alg*   identityref
                 |        +--rw mac
                 |        |  +--rw mac-alg*   identityref
                 |        +--rw compression
                 |           +--rw compression-alg*   identityref
                 +--:(tls) {tls-listen}?
                    +--rw tls
                       +--rw address?        inet:ip-address
                       +--rw port?           inet:port-number
                       +--rw server-auth
                       |  +--rw trusted-ca-certs?       leafref
                       |  +--rw trusted-server-certs?   leafref
                       +--rw client-auth



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                       |  +--rw (auth-type)
                       |     +--:(certificate)
                       |        +--rw certificate?   leafref
                       +--rw hello-params
                               {tls-client-hello-params-config}?
                          +--rw tls-versions
                          |  +--rw tls-version*   identityref
                          +--rw cipher-suites
                             +--rw cipher-suite*   identityref

2.2.  Example Usage

   The following example illustrates configuring a NETCONF client to
   initiate connections, using both the SSH and TLS transport protocols,
   as well as listening for call-home connections, again using both the
   SSH and TLS transport protocols.

   This example is consistent with the examples presented in Section 2.2
   of [I-D.ietf-netconf-keystore].
































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<netconf-client
  xmlns="urn:ietf:params:xml:ns:yang:ietf-netconf-client">

  <!-- NETCONF servers to initiate connections to -->
  <initiate>
    <netconf-server>
      <name>corp-fw1</name>
      <ssh>
        <endpoints>
          <endpoint>
            <name>corp-fw1.example.com</name>
            <address>corp-fw1.example.com</address>
          </endpoint>
          <endpoint>
            <name>corp-fw2.example.com</name>
            <address>corp-fw2.example.com</address>
          </endpoint>
        </endpoints>
        <server-auth>
          <trusted-server-certs>deployment-specific-ca-certs</trusted-server-certs>
        </server-auth>
        <client-auth>
          <username>foobar</username>
          <public-key>ex-rsa-key</public-key>
        </client-auth>
      </ssh>
    </netconf-server>
  </initiate>

  <!-- endpoints to listen for NETCONF Call Home connections on -->
  <listen>
    <endpoint>
      <name>Intranet-facing listener</name>
      <ssh>
        <address>11.22.33.44</address>
        <server-auth>
          <trusted-ca-certs>deployment-specific-ca-certs</trusted-ca-certs>
          <trusted-server-certs>explicitly-trusted-server-certs</trusted-server-certs>
          <trusted-ssh-host-keys>explicitly-trusted-ssh-host-keys</trusted-ssh-host-keys>
        </server-auth>
        <client-auth>
          <username>foobar</username>
          <public-key>ex-rsa-key</public-key>
        </client-auth>
      </ssh>
    </endpoint>
  </listen>
</netconf-client>



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2.3.  YANG Model

   This YANG module imports YANG types from [RFC6991] and [RFC7407].


<CODE BEGINS> file "ietf-netconf-client@2017-07-03.yang"

module ietf-netconf-client {
  yang-version 1.1;

  namespace "urn:ietf:params:xml:ns:yang:ietf-netconf-client";
  prefix "ncc";

  import ietf-inet-types {
    prefix inet;
    reference
      "RFC 6991: Common YANG Data Types";
  }

  import ietf-ssh-client {
    prefix ss;
    revision-date 2017-06-13; // stable grouping definitions
    reference
      "RFC YYYY: SSH Client and Server Models";
  }

  import ietf-tls-client {
    prefix ts;
    revision-date 2017-06-13; // stable grouping definitions
    reference
      "RFC ZZZZ: TLS Client and Server Models";
  }

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

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

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

    Author:   Gary Wu
              <mailto:garywu@cisco.com>";


  description



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

    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.";

  revision "2017-07-03" {
    description
     "Initial version";
    reference
     "RFC XXXX: NETCONF Client and Server Models";
  }

  // Features

  feature initiate {
    description
     "The 'initiate' feature indicates that the NETCONF client
      supports initiating NETCONF connections to NETCONF servers
      using at least one transport (e.g., SSH, TLS, etc.).";
  }

  feature ssh-initiate {
    description
     "The 'ssh-initiate' feature indicates that the NETCONF client
      supports initiating SSH connections to NETCONF servers.";
    reference
     "RFC 6242: Using the NETCONF Protocol over Secure Shell (SSH)";
  }

  feature tls-initiate {
    description
     "The 'tls-initiate' feature indicates that the NETCONF client
      supports initiating TLS connections to NETCONF servers.";
    reference
     "RFC 7589: Using the NETCONF Protocol over Transport
                Layer Security (TLS) with Mutual X.509
                Authentication";



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  }

  feature listen {
    description
     "The 'listen' feature indicates that the NETCONF client
      supports opening a port to accept NETCONF server call
      home connections using at least one transport (e.g.,
      SSH, TLS, etc.).";
  }

  feature ssh-listen {
    description
     "The 'ssh-listen' feature indicates that the NETCONF client
      supports opening a port to listen for incoming NETCONF
      server call-home SSH connections.";
    reference
     "RFC 8071: NETCONF Call Home and RESTCONF Call Home";
  }

  feature tls-listen {
    description
     "The 'tls-listen' feature indicates that the NETCONF client
      supports opening a port to listen for incoming NETCONF
      server call-home TLS connections.";
    reference
     "RFC 8071: NETCONF Call Home and RESTCONF Call Home";
  }

  container netconf-client {
    uses netconf-client;
    description
      "Top-level container for NETCONF client configuration.";
  }

  grouping netconf-client {
    description
      "Top-level grouping for NETCONF client configuration.";

    container initiate {
      if-feature initiate;
      description
        "Configures client initiating underlying TCP connections.";
      list netconf-server {
        key name;
        description
          "List of NETCONF servers the NETCONF client is to initiate
           connections to.";
        leaf name {



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          type string;
          description
            "An arbitrary name for the NETCONF server.";
        }
        choice transport {
          mandatory true;
          description
            "Selects between available transports.";

          case ssh {
            if-feature ssh-initiate;
            container ssh {
              description
                "Specifies SSH-specific transport configuration.";
              uses endpoints-container {
                refine endpoints/endpoint/port {
                  default 830;
                }
              }
              uses ss:ssh-client-grouping;
            }
          } // end ssh

          case tls {
            if-feature tls-initiate;
            container tls {
              description
                "Specifies TLS-specific transport configuration.";
              uses endpoints-container {
                refine endpoints/endpoint/port {
                  default 6513;
                }
              }
              uses ts:tls-client-grouping {
                refine "client-auth/auth-type" {
                  mandatory true;
                  description
                    "NETCONF/TLS clients MUST pass some authentication
                     credentials.";
                }
              }
            }
          } // end tls

        } // end transport

        container connection-type {
          description



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           "Indicates the kind of connection to use.";
          choice connection-type {
            description
              "Selects between available connection types.";
            case persistent-connection {
              container persistent {
                presence true;
                description
                 "Maintain a persistent connection to the NETCONF
                  server. If the connection goes down, immediately
                  start trying to reconnect to it, using the
                  reconnection strategy.

                  This connection type minimizes any NETCONF server
                  to NETCONF client data-transfer delay, albeit at
                  the expense of holding resources longer.";
                leaf idle-timeout {
                  type uint32;
                  units "seconds";
                  default 86400;  // one day;
                  description
                    "Specifies the maximum number of seconds that a
                     a NETCONF session may remain idle. A NETCONF
                     session will be dropped if it is idle for an
                     interval longer than this number of seconds.
                     If set to zero, then the client will never drop
                     a session because it is idle.  Sessions that
                     have a notification subscription active are
                     never dropped.";
                }
                container keep-alives {
                  description
                    "Configures the keep-alive policy, to proactively
                     test the aliveness of the SSH/TLS server.  An
                     unresponsive SSH/TLS server will be dropped after
                     approximately max-attempts * max-wait seconds.";
                  reference
                    "RFC 8071: NETCONF Call Home and RESTCONF Call
                     Home, Section 3.1, item S6";
                  leaf max-wait {
                    type uint16 {
                      range "1..max";
                    }
                    units seconds;
                    default 30;
                    description
                     "Sets the amount of time in seconds after which
                      if no data has been received from the SSH/TLS



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                      server, a SSH/TLS-level message will be sent
                      to test the aliveness of the SSH/TLS server.";
                  }
                  leaf max-attempts {
                    type uint8;
                    default 3;
                    description
                     "Sets the maximum number of sequential keep-alive
                      messages that can fail to obtain a response from
                      the SSH/TLS server before assuming the SSH/TLS
                      server is no longer alive.";
                  }
                }
              }
            }
            case periodic-connection {
              container periodic {
                presence true;
                description
                 "Periodically connect to the NETCONF server, so that
                  the NETCONF server may deliver messages pending for
                  the NETCONF client.  The NETCONF server must close
                  the connection when it is ready to release it. Once
                  the connection has been closed, the NETCONF client
                  will restart its timer until the next connection.";
                leaf idle-timeout {
                  type uint16;
                  units "seconds";
                  default 300; // five minutes
                  description
                    "Specifies the maximum number of seconds that a
                     a NETCONF session may remain idle. A NETCONF
                     session will be dropped if it is idle for an
                     interval longer than this number of seconds.
                     If set to zero, then the server will never drop
                     a session because it is idle.  Sessions that
                     have a notification subscription active are
                     never dropped.";
                }
                leaf reconnect-timeout {
                  type uint16 {
                    range "1..max";
                  }
                  units minutes;
                  default 60;
                  description
                   "Sets the maximum amount of unconnected time the
                    NETCONF client will wait before re-establishing



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                    a connection to the NETCONF server.  The NETCONF
                    client may initiate a connection before this
                    time if desired (e.g., to set configuration).";
                }
              }
            }
          }
        }
        container reconnect-strategy {
          description
           "The reconnection strategy directs how a NETCONF client
            reconnects to a NETCONF server, after discovering its
            connection to the server has dropped, even if due to a
            reboot.  The NETCONF client starts with the specified
            endpoint and tries to connect to it max-attempts times
            before trying the next endpoint in the list (round
            robin).";
          leaf start-with {
            type enumeration {
              enum first-listed {
                description
                  "Indicates that reconnections should start with
                   the first endpoint listed.";
              }
              enum last-connected {
                description
                  "Indicates that reconnections should start with
                   the endpoint last connected to.  If no previous
                   connection has ever been established, then the
                   first endpoint configured is used.   NETCONF
                   clients SHOULD be able to remember the last
                   endpoint connected to across reboots.";
              }
            }
            default first-listed;
            description
             "Specifies which of the NETCONF server's endpoints the
              NETCONF client should start with when trying to connect
              to the NETCONF server.";
          }
          leaf max-attempts {
            type uint8 {
              range "1..max";
            }
            default 3;
            description
             "Specifies the number times the NETCONF client tries to
              connect to a specific endpoint before moving on to the



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              next endpoint in the list (round robin).";
          }
        }
      } // end netconf-server
    } // end initiate

    container listen {
      if-feature listen;
      description
        "Configures client accepting call-home TCP connections.";

      leaf max-sessions {
        type uint16;
        default 0;
        description
          "Specifies the maximum number of concurrent sessions
           that can be active at one time.  The value 0 indicates
           that no artificial session limit should be used.";
      }

      leaf idle-timeout {
        type uint16;
        units "seconds";
        default 3600; // one hour
        description
          "Specifies the maximum number of seconds that a NETCONF
           session may remain idle. A NETCONF session will be dropped
           if it is idle for an interval longer than this number of
           seconds.  If set to zero, then the server will never drop
           a session because it is idle.  Sessions that have a
           notification subscription active are never dropped.";
      }

      list endpoint {
        key name;
        description
          "List of endpoints to listen for NETCONF connections.";
        leaf name {
          type string;
          description
            "An arbitrary name for the NETCONF listen endpoint.";
        }
        choice transport {
          mandatory true;
          description
            "Selects between available transports.";
          case ssh {
            if-feature ssh-listen;



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            container ssh {
              description
                "SSH-specific listening configuration for inbound
                 connections.";
              leaf address {
                type inet:ip-address;
                description
                 "The IP address to listen for call-home connections.";
              }
              leaf port {
                type inet:port-number;
                default 4334;
                description
                 "The port number to listen for call-home connections.";
              }
              uses ss:ssh-client-grouping;
            }
          }
          case tls {
            if-feature tls-listen;
            container tls {
              description
                "TLS-specific listening configuration for inbound
                 connections.";
              leaf address {
                type inet:ip-address;
                description
                 "The IP address to listen for call-home connections.";
              }
              leaf port {
                type inet:port-number;
                default 4335;
                description
                 "The port number to listen for call-home connections.";
              }
              uses ts:tls-client-grouping {
                refine "client-auth/auth-type" {
                  mandatory true;
                  description
                    "NETCONF/TLS clients MUST pass some authentication
                     credentials.";
                }
              }
            }
          }
        } // end transport
      } // end endpoint
    } // end listen



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  } // end netconf-client


  grouping endpoints-container {
    description
      "This grouping is used to configure a set of NETCONF servers
       a NETCONF client may initiate connections to.";
    container endpoints {
      description
        "Container for the list of endpoints.";
      list endpoint {
        key name;
        unique "address port";
        min-elements 1;
        ordered-by user;
        description
          "A non-empty user-ordered list of endpoints for this NETCONF
           client to try to connect to.  Defining more than one enables
           high-availability.";
        leaf name {
          type string;
          description
            "An arbitrary name for this endpoint.";
        }
        leaf address {
          type inet:host;
          mandatory true;
          description
           "The IP address or hostname of the endpoint.  If a
            hostname is configured and the DNS resolution results
            in more than one IP address, the NETCONF client
            will process the IP addresses as if they had been
            explicitly configured in place of the hostname.";
        }
        leaf port {
          type inet:port-number;
          description
           "The IP port for this endpoint. The NETCONF client will
            use the IANA-assigned well-known port (set via a refine
            statement when uses) if no value is specified.";
        }
      }
    }
  }
}

<CODE ENDS>




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3.  The NETCONF Server Model

   The NETCONF server model presented in this section supports servers
   both listening for connections as well as initiating call-home
   connections.

   This model supports both the SSH and TLS transport protocols, using
   the SSH server and TLS server groupings defined in
   [I-D.ietf-netconf-ssh-client-server] and
   [I-D.ietf-netconf-tls-client-server] respectively.

   All private keys and trusted certificates are held in the keystore
   model defined in [I-D.ietf-netconf-keystore].

   YANG feature statements are used to enable implementations to
   advertise which parts of the model the NETCONF server supports.

3.1.  Tree Diagram

   Just the container is displayed below, but there is also a grouping
   that the container is using.

   Note: all lines are folded at column 71 with no '\' character.

module: ietf-netconf-server
    +--rw netconf-server
       +--rw session-options
       |  +--rw hello-timeout?   uint16
       +--rw listen {listen}?
       |  +--rw max-sessions?   uint16
       |  +--rw idle-timeout?   uint16
       |  +--rw endpoint* [name]
       |     +--rw name    string
       |     +--rw (transport)
       |        +--:(ssh) {ssh-listen}?
       |        |  +--rw ssh
       |        |     +--rw address?            inet:ip-address
       |        |     +--rw port?               inet:port-number
       |        |     +--rw host-keys
       |        |     |  +--rw host-key* [name]
       |        |     |     +--rw name           string
       |        |     |     +--rw (host-key-type)
       |        |     |        +--:(public-key)
       |        |     |        |  +--rw public-key?
       |        |     |        |          -> /ks:keystore/keys/key/name
       |        |     |        +--:(certificate)
       |        |     |           +--rw certificate?   leafref
       |        |     |                   {sshcom:ssh-x509-certs}?



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       |        |     +--rw client-cert-auth {sshcom:ssh-x509-certs}?
       |        |     |  +--rw trusted-ca-certs?       leafref
       |        |     |  +--rw trusted-client-certs?   leafref
       |        |     +--rw transport-params
       |        |             {ssh-server-transport-params-config}?
       |        |        +--rw host-key
       |        |        |  +--rw host-key-alg*   identityref
       |        |        +--rw key-exchange
       |        |        |  +--rw key-exchange-alg*   identityref
       |        |        +--rw encryption
       |        |        |  +--rw encryption-alg*   identityref
       |        |        +--rw mac
       |        |        |  +--rw mac-alg*   identityref
       |        |        +--rw compression
       |        |           +--rw compression-alg*   identityref
       |        +--:(tls) {tls-listen}?
       |           +--rw tls
       |              +--rw address?        inet:ip-address
       |              +--rw port?           inet:port-number
       |              +--rw certificates
       |              |  +--rw certificate* [name]
       |              |     +--rw name    leafref
       |              +--rw client-auth
       |              |  +--rw trusted-ca-certs?       leafref
       |              |  +--rw trusted-client-certs?   leafref
       |              |  +--rw cert-maps
       |              |     +--rw cert-to-name* [id]
       |              |        +--rw id             uint32
       |              |        +--rw fingerprint    x509c2n:tls-fingerprint
       |              |        +--rw map-type       identityref
       |              |        +--rw name           string
       |              +--rw hello-params
       |                      {tls-server-hello-params-config}?
       |                 +--rw tls-versions
       |                 |  +--rw tls-version*   identityref
       |                 +--rw cipher-suites
       |                    +--rw cipher-suite*   identityref
       +--rw call-home {call-home}?
          +--rw netconf-client* [name]
             +--rw name                  string
             +--rw (transport)
             |  +--:(ssh) {ssh-call-home}?
             |  |  +--rw ssh
             |  |     +--rw endpoints
             |  |     |  +--rw endpoint* [name]
             |  |     |     +--rw name       string
             |  |     |     +--rw address    inet:host
             |  |     |     +--rw port?      inet:port-number



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             |  |     +--rw host-keys
             |  |     |  +--rw host-key* [name]
             |  |     |     +--rw name           string
             |  |     |     +--rw (host-key-type)
             |  |     |        +--:(public-key)
             |  |     |        |  +--rw public-key?
             |  |     |        |          -> /ks:keystore/keys/key/name
             |  |     |        +--:(certificate)
             |  |     |           +--rw certificate?   leafref
             |  |     |                   {sshcom:ssh-x509-certs}?
             |  |     +--rw client-cert-auth {sshcom:ssh-x509-certs}?
             |  |     |  +--rw trusted-ca-certs?       leafref
             |  |     |  +--rw trusted-client-certs?   leafref
             |  |     +--rw transport-params
             |  |             {ssh-server-transport-params-config}?
             |  |        +--rw host-key
             |  |        |  +--rw host-key-alg*   identityref
             |  |        +--rw key-exchange
             |  |        |  +--rw key-exchange-alg*   identityref
             |  |        +--rw encryption
             |  |        |  +--rw encryption-alg*   identityref
             |  |        +--rw mac
             |  |        |  +--rw mac-alg*   identityref
             |  |        +--rw compression
             |  |           +--rw compression-alg*   identityref
             |  +--:(tls) {tls-call-home}?
             |     +--rw tls
             |        +--rw endpoints
             |        |  +--rw endpoint* [name]
             |        |     +--rw name       string
             |        |     +--rw address    inet:host
             |        |     +--rw port?      inet:port-number
             |        +--rw certificates
             |        |  +--rw certificate* [name]
             |        |     +--rw name    leafref
             |        +--rw client-auth
             |        |  +--rw trusted-ca-certs?       leafref
             |        |  +--rw trusted-client-certs?   leafref
             |        |  +--rw cert-maps
             |        |     +--rw cert-to-name* [id]
             |        |        +--rw id             uint32
             |        |        +--rw fingerprint    x509c2n:tls-fingerprint
             |        |        +--rw map-type       identityref
             |        |        +--rw name           string
             |        +--rw hello-params
             |                {tls-server-hello-params-config}?
             |           +--rw tls-versions
             |           |  +--rw tls-version*   identityref



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             |           +--rw cipher-suites
             |              +--rw cipher-suite*   identityref
             +--rw connection-type
             |  +--rw (connection-type)?
             |     +--:(persistent-connection)
             |     |  +--rw persistent!
             |     |     +--rw idle-timeout?   uint32
             |     |     +--rw keep-alives
             |     |        +--rw max-wait?       uint16
             |     |        +--rw max-attempts?   uint8
             |     +--:(periodic-connection)
             |        +--rw periodic!
             |           +--rw idle-timeout?        uint16
             |           +--rw reconnect-timeout?   uint16
             +--rw reconnect-strategy
                +--rw start-with?     enumeration
                +--rw max-attempts?   uint8

3.2.  Example Usage

   The following example illustrates configuring a NETCONF server to
   listen for NETCONF client connections using both the SSH and TLS
   transport protocols, as well as configuring call-home to two NETCONF
   clients, one using SSH and the other using TLS.

   This example is consistent with the examples presented in Section 2.2
   of [I-D.ietf-netconf-keystore].

<netconf-server
  xmlns="urn:ietf:params:xml:ns:yang:ietf-netconf-server"
  xmlns:x509c2n="urn:ietf:params:xml:ns:yang:ietf-x509-cert-to-name">

  <!-- listening for SSH and TLS connections -->
  <listen>
    <endpoint> <!-- listening for SSH connections -->
      <name>netconf/ssh</name>
      <ssh>
        <address>11.22.33.44</address>
        <host-keys>
          <host-key>
            <name>public-key</name>
            <public-key>ex-rsa-key</public-key>
          </host-key>
          <host-key>
            <name>certificate</name>
            <certificate>builtin-idevid-cert</certificate>
          </host-key>
        </host-keys>



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        <client-cert-auth>
          <trusted-ca-certs>deployment-specific-ca-certs</trusted-ca-certs>
          <trusted-client-certs>explicitly-trusted-client-certs</trusted-client-certs>
        </client-cert-auth>
      </ssh>
    </endpoint>
    <endpoint> <!-- listening for TLS sessions -->
      <name>netconf/tls</name>
      <tls>
        <address>11.22.33.44</address>
        <certificates>
          <certificate>
            <name>tls-ec-cert</name>
          </certificate>
        </certificates>
        <client-auth>
          <trusted-ca-certs>deployment-specific-ca-certs</trusted-ca-certs>
          <trusted-client-certs>explicitly-trusted-client-certs</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>B3:4F:A1:8C:54</fingerprint>
              <map-type>x509c2n:specified</map-type>
              <name>scooby-doo</name>
            </cert-to-name>
          </cert-maps>
        </client-auth>
      </tls>
    </endpoint>
  </listen>

  <!-- calling home to an SSH and TLS based NETCONF clients -->
  <call-home>
    <netconf-client> <!-- SSH-based client -->
      <name>config-mgr</name>
      <ssh>
        <endpoints>
          <endpoint>
            <name>east-data-center</name>
            <address>11.22.33.44</address>
          </endpoint>
          <endpoint>
            <name>west-data-center</name>



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            <address>55.66.77.88</address>
          </endpoint>
        </endpoints>
        <host-keys>
          <host-key>
            <name>certificate</name>
            <certificate>builtin-idevid-cert</certificate>
          </host-key>
        </host-keys>
        <client-cert-auth>
          <trusted-ca-certs>deployment-specific-ca-certs</trusted-ca-certs>
          <trusted-client-certs>explicitly-trusted-client-certs</trusted-client-certs>
        </client-cert-auth>
      </ssh>
      <connection-type>
        <periodic>
          <idle-timeout>300</idle-timeout>
          <reconnect-timeout>60</reconnect-timeout>
        </periodic>
      </connection-type>
      <reconnect-strategy>
        <start-with>last-connected</start-with>
        <max-attempts>3</max-attempts>
      </reconnect-strategy>
    </netconf-client>
    <netconf-client> <!-- TLS-based client -->
      <name>event-correlator</name>
      <tls>
        <endpoints>
          <endpoint>
            <name>east-data-center</name>
            <address>22.33.44.55</address>
          </endpoint>
          <endpoint>
            <name>west-data-center</name>
            <address>33.44.55.66</address>
          </endpoint>
        </endpoints>
        <certificates>
          <certificate>
            <name>tls-ec-cert</name>
          </certificate>
        </certificates>
        <client-auth>
          <trusted-ca-certs>deployment-specific-ca-certs</trusted-ca-certs>
          <trusted-client-certs>explicitly-trusted-client-certs</trusted-client-certs>
          <cert-maps>
            <cert-to-name>



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              <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>B3:4F:A1:8C:54</fingerprint>
              <map-type>x509c2n:specified</map-type>
              <name>scooby-doo</name>
            </cert-to-name>
          </cert-maps>
        </client-auth>
      </tls>
      <connection-type>
        <persistent>
          <idle-timeout>300</idle-timeout>
          <keep-alives>
            <max-wait>30</max-wait>
            <max-attempts>3</max-attempts>
          </keep-alives>
        </persistent>
      </connection-type>
      <reconnect-strategy>
        <start-with>first-listed</start-with>
        <max-attempts>3</max-attempts>
      </reconnect-strategy>
    </netconf-client>
  </call-home>
</netconf-server>

3.3.  YANG Model

   This YANG module imports YANG types from [RFC6991] and [RFC7407].


<CODE BEGINS> file "ietf-netconf-server@2017-07-03.yang"

module ietf-netconf-server {
  yang-version 1.1;

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

  import ietf-inet-types {
    prefix inet;
    reference
      "RFC 6991: Common YANG Data Types";
  }



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  import ietf-x509-cert-to-name {
    prefix x509c2n;
    reference
      "RFC 7407: A YANG Data Model for SNMP Configuration";
  }

  import ietf-ssh-server {
    prefix ss;
    revision-date 2017-06-13; // stable grouping definitions
    reference
      "RFC YYYY: SSH Client and Server Models";
  }

  import ietf-tls-server {
    prefix ts;
    revision-date 2017-06-13; // stable grouping definitions
    reference
      "RFC ZZZZ: TLS Client and Server Models";
  }

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

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

    Author:   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.";




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  revision "2017-07-03" {
    description
     "Initial version";
    reference
     "RFC XXXX: NETCONF Client and Server Models";
  }


  // Features

  feature listen {
    description
     "The 'listen' feature indicates that the NETCONF server
      supports opening a port to accept NETCONF client connections
      using at least one transport (e.g., SSH, TLS, etc.).";
  }

  feature ssh-listen {
    description
     "The 'ssh-listen' feature indicates that the NETCONF server
      supports opening a port to accept NETCONF over SSH
      client connections.";
    reference
     "RFC 6242: Using the NETCONF Protocol over Secure Shell (SSH)";
  }

  feature tls-listen {
    description
     "The 'tls-listen' feature indicates that the NETCONF server
      supports opening a port to accept NETCONF over TLS
      client connections.";
    reference
     "RFC 7589: Using the NETCONF Protocol over Transport
                Layer Security (TLS) with Mutual X.509
                Authentication";
  }

  feature call-home {
    description
     "The 'call-home' feature indicates that the NETCONF server
      supports initiating NETCONF call home connections to NETCONF
      clients using at least one transport (e.g., SSH, TLS, etc.).";
    reference
     "RFC 8071: NETCONF Call Home and RESTCONF Call Home";
  }

  feature ssh-call-home {
    description



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     "The 'ssh-call-home' feature indicates that the NETCONF
      server supports initiating a NETCONF over SSH call
      home connection to NETCONF clients.";
    reference
     "RFC 8071: NETCONF Call Home and RESTCONF Call Home";
  }

  feature tls-call-home {
    description
     "The 'tls-call-home' feature indicates that the NETCONF
      server supports initiating a NETCONF over TLS call
      home connection to NETCONF clients.";
    reference
     "RFC 8071: NETCONF Call Home and RESTCONF Call Home";
  }

  container netconf-server {
    uses netconf-server;
    description
      "Top-level container for NETCONF server configuration.";
  }

  grouping netconf-server {
    description
      "Top-level grouping for NETCONF server configuration.";

    container session-options {  // SHOULD WE REMOVE THIS ALTOGETHER?
      description
        "NETCONF session options, independent of transport
         or connection strategy.";
      leaf hello-timeout {
        type uint16;
        units "seconds";
        default 600;
        description
          "Specifies the maximum number of seconds that a SSH/TLS
           connection may wait for a hello message to be received.
           A connection will be dropped if no hello message is
           received before this number of seconds elapses.  If set
           to zero, then the server will wait forever for a hello
           message.";
      }
    }

    container listen {
      if-feature listen;
      description
        "Configures listen behavior";



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      leaf max-sessions {
        type uint16;
        default 0;
        description
          "Specifies the maximum number of concurrent sessions
           that can be active at one time.  The value 0 indicates
           that no artificial session limit should be used.";
      }
      leaf idle-timeout {
        type uint16;
        units "seconds";
        default 3600; // one hour
        description
          "Specifies the maximum number of seconds that a NETCONF
           session may remain idle. A NETCONF session will be dropped
           if it is idle for an interval longer than this number of
           seconds.  If set to zero, then the server will never drop
           a session because it is idle.  Sessions that have a
           notification subscription active are never dropped.";
      }
      list endpoint {
        key name;
        description
          "List of endpoints to listen for NETCONF connections.";
        leaf name {
          type string;
          description
            "An arbitrary name for the NETCONF listen endpoint.";
        }


        choice transport {
          mandatory true;
          description
            "Selects between available transports.";
          case ssh {
            if-feature ssh-listen;
            container ssh {
              description
                "SSH-specific listening configuration for inbound
                 connections.";
              leaf address {
                type inet:ip-address;
                description
                 "The IP address of the interface to listen on.  The
                  SSH server will listen on all interfaces if no value
                  is specified.  Please note that some addresses have
                  special meanings (e.g., '0.0.0.0' and '::').";



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              }
              leaf port {
                type inet:port-number;
                default 830;
                description
                 "The local port number on this interface the SSH server
                  listens on.";
              }
              uses ss:ssh-server-grouping;
            }
          }
          case tls {
            if-feature tls-listen;
            container tls {
              description
                "TLS-specific listening configuration for inbound
                 connections.";
              leaf address {
                type inet:ip-address;
                description
                 "The IP address of the interface to listen on.  The
                  TLS server will listen on all interfaces if no value
                  is specified.  Please note that some addresses have
                  special meanings (e.g., '0.0.0.0' and '::').";
              }
              leaf port {
                type inet:port-number;
                default 6513;
                description
                 "The local port number on this interface the TLS server
                  listens on.";
              }
              uses ts:tls-server-grouping {
                refine "client-auth" {
                  must 'trusted-ca-certs or trusted-client-certs';
                  description
                    "NETCONF/TLS servers MUST validate client
                     certiticates.";
                }
                augment "client-auth" {
                  description
                    "Augments in the cert-to-name structure.";
                  uses cert-maps-grouping;
                }
              }
            }
          }
        }



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      }
    }

    container call-home {
      if-feature call-home;
      description
        "Configures call-home behavior";
      list netconf-client {
        key name;
        description
          "List of NETCONF clients the NETCONF server is to initiate
           call-home connections to.";
        leaf name {
          type string;
          description
            "An arbitrary name for the remote NETCONF client.";
        }
        choice transport {
          mandatory true;
          description
            "Selects between available transports.";
          case ssh {
            if-feature ssh-call-home;
            container ssh {
              description
                "Specifies SSH-specific call-home transport
                 configuration.";
              uses endpoints-container {
                refine endpoints/endpoint/port {
                  default 4334;
                }
              }
              uses ss:ssh-server-grouping;
            }
          }
          case tls {
            if-feature tls-call-home;
            container tls {
              description
                "Specifies TLS-specific call-home transport
                 configuration.";
              uses endpoints-container {
                refine endpoints/endpoint/port {
                  default 4335;
                }
              }
              uses ts:tls-server-grouping {
                refine "client-auth" {



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                  must 'trusted-ca-certs or trusted-client-certs';
                  description
                    "NETCONF/TLS servers MUST validate client
                     certiticates.";
                }
                augment "client-auth" {
                  description
                    "Augments in the cert-to-name structure.";
                  uses cert-maps-grouping;
                }
              }
            }
          }
        }
        container connection-type {
          description
           "Indicates the kind of connection to use.";
          choice connection-type {
            description
              "Selects between available connection types.";
            case persistent-connection {
              container persistent {
                presence true;
                description
                 "Maintain a persistent connection to the NETCONF
                  client. If the connection goes down, immediately
                  start trying to reconnect to it, using the
                  reconnection strategy.

                  This connection type minimizes any NETCONF client
                  to NETCONF server data-transfer delay, albeit at
                  the expense of holding resources longer.";
                leaf idle-timeout {
                  type uint32;
                  units "seconds";
                  default 86400;  // one day;
                  description
                    "Specifies the maximum number of seconds that a
                     a NETCONF session may remain idle. A NETCONF
                     session will be dropped if it is idle for an
                     interval longer than this number of seconds.
                     If set to zero, then the server will never drop
                     a session because it is idle.  Sessions that
                     have a notification subscription active are
                     never dropped.";
                }
                container keep-alives {
                  description



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                    "Configures the keep-alive policy, to proactively
                     test the aliveness of the SSH/TLS client.  An
                     unresponsive SSH/TLS client will be dropped after
                     approximately max-attempts * max-wait seconds.";
                  reference
                    "RFC 8071: NETCONF Call Home and RESTCONF Call
                     Home, Section 3.1, item S6";
                  leaf max-wait {
                    type uint16 {
                      range "1..max";
                    }
                    units seconds;
                    default 30;
                    description
                     "Sets the amount of time in seconds after which
                      if no data has been received from the SSH/TLS
                      client, a SSH/TLS-level message will be sent
                      to test the aliveness of the SSH/TLS client.";
                  }
                  leaf max-attempts {
                    type uint8;
                    default 3;
                    description
                     "Sets the maximum number of sequential keep-alive
                      messages that can fail to obtain a response from
                      the SSH/TLS client before assuming the SSH/TLS
                      client is no longer alive.";
                  }
                }
              }
            }
            case periodic-connection {
              container periodic {
                presence true;
                description
                 "Periodically connect to the NETCONF client, so that
                  the NETCONF client may deliver messages pending for
                  the NETCONF server.  The NETCONF client must close
                  the connection when it is ready to release it. Once
                  the connection has been closed, the NETCONF server
                  will restart its timer until the next connection.";
                leaf idle-timeout {
                  type uint16;
                  units "seconds";
                  default 300; // five minutes
                  description
                    "Specifies the maximum number of seconds that a
                     a NETCONF session may remain idle. A NETCONF



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                     session will be dropped if it is idle for an
                     interval longer than this number of seconds.
                     If set to zero, then the server will never drop
                     a session because it is idle.  Sessions that
                     have a notification subscription active are
                     never dropped.";
                }
                leaf reconnect-timeout {
                  type uint16 {
                    range "1..max";
                  }
                  units minutes;
                  default 60;
                  description
                   "Sets the maximum amount of unconnected time the
                    NETCONF server will wait before re-establishing
                    a connection to the NETCONF client.  The NETCONF
                    server may initiate a connection before this
                    time if desired (e.g., to deliver an event
                    notification message).";
                }
              }
            }
          }
        }
        container reconnect-strategy {
          description
           "The reconnection strategy directs how a NETCONF server
            reconnects to a NETCONF client, after discovering its
            connection to the client has dropped, even if due to a
            reboot.  The NETCONF server starts with the specified
            endpoint and tries to connect to it max-attempts times
            before trying the next endpoint in the list (round
            robin).";
          leaf start-with {
            type enumeration {
              enum first-listed {
                description
                  "Indicates that reconnections should start with
                   the first endpoint listed.";
              }
              enum last-connected {
                description
                  "Indicates that reconnections should start with
                   the endpoint last connected to.  If no previous
                   connection has ever been established, then the
                   first endpoint configured is used.   NETCONF
                   servers SHOULD be able to remember the last



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                   endpoint connected to across reboots.";
              }
            }
            default first-listed;
            description
             "Specifies which of the NETCONF client's endpoints the
              NETCONF server should start with when trying to connect
              to the NETCONF client.";
          }
          leaf max-attempts {
            type uint8 {
              range "1..max";
            }
            default 3;
            description
             "Specifies the number times the NETCONF server tries to
              connect to a specific endpoint before moving on to the
              next endpoint in the list (round robin).";
          }
        }
      }
    }
  }


  grouping cert-maps-grouping {
    description
      "A grouping that defines a container around the
       cert-to-name structure defined in RFC 7407.";
    container cert-maps {
      uses x509c2n:cert-to-name;
      description
       "The cert-maps container is used by a TLS-based 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.";
      reference
        "RFC WWWW: NETCONF over TLS, Section 7";
    }
  }


  grouping endpoints-container {
    description
      "This grouping is used to configure a set of NETCONF clients
       a NETCONF server may initiate call-home connections to.";



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    container endpoints {
      description
        "Container for the list of endpoints.";
      list endpoint {
        key name;
        unique "address port";
        min-elements 1;
        ordered-by user;
        description
          "A non-empty user-ordered list of endpoints for this NETCONF
           server to try to connect to.  Defining more than one enables
           high-availability.";
        leaf name {
          type string;
          description
            "An arbitrary name for this endpoint.";
        }
        leaf address {
          type inet:host;
          mandatory true;
          description
           "The IP address or hostname of the endpoint.  If a
            hostname is configured and the DNS resolution results
            in more than one IP address, the NETCONF server
            will process the IP addresses as if they had been
            explicitly configured in place of the hostname.";
        }
        leaf port {
          type inet:port-number;
          description
           "The IP port for this endpoint. The NETCONF server will
            use the IANA-assigned well-known port (set via a refine
            statement when uses) if no value is specified.";
        }
      }
    }
  }

}


<CODE ENDS>

4.  Design Considerations

   Editorial: this section is a hold over from before, previously called
   "Objectives".  It was only written two support the "server" (not the




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   "client").  The question is if it's better to add the missing
   "client" parts, or remove this section altogether.

   The primary purpose of the YANG modules defined herein is to enable
   the configuration of the NETCONF client and servers.  This scope
   includes the following objectives:

4.1.  Support all NETCONF transports

   The YANG module should support all current NETCONF transports, namely
   NETCONF over SSH [RFC6242], NETCONF over TLS [RFC7589], and to be
   extensible to support future transports as necessary.

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

4.2.  Enable each transport to select which keys to use

   Servers may have a multiplicity of host-keys or server-certificates
   from which subsets may be selected for specific uses.  For instance,
   a NETCONF server may want to use one set of SSH host-keys when
   listening on port 830, and a different set of SSH host-keys when
   calling home.  The data models provided herein should enable
   configuration of which keys to use on a per-use basis.

4.3.  Support authenticating NETCONF clients certificates

   When a certificate is used to authenticate a NETCONF client, there is
   a need to configure the server to know how to authenticate the
   certificates.  The server should be able to authenticate the client's
   certificate either by using path-validation to a configured trust
   anchor or by matching the client-certificate to one previously
   configured.

4.4.  Support mapping authenticated NETCONF client certificates to
      usernames

   When a client certificate is used for TLS client authentication, the
   NETCONF server must be able to derive a username from the
   authenticated certificate.  Thus the modules defined herein should
   enable this mapping to be configured.

4.5.  Support both listening for connections and call home

   The NETCONF protocols were originally defined as having the server
   opening a port to listen for client connections.  More recently the
   NETCONF working group defined support for call-home ([RFC8071]),



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   enabling the server to initiate the connection to the client.  Thus
   the modules defined herein should enable configuration for both
   listening for connections and calling home.  Because implementations
   may not support both listening for connections and calling home, YANG
   "feature" statements should be used so that implementation can
   accurately advertise the connection types it supports.

4.6.  For Call Home connections

   The following objectives only pertain to call home connections.

4.6.1.  Support more than one NETCONF client

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

4.6.2.  Support NETCONF clients having more than one endpoint

   A NETCONF client managing a NETCONF server may implement a high-
   availability strategy employing a multiplicity of active and/or
   passive endpoint.  Therefore, when it is desired for a server to
   initiate call home connections, it should be able to connect to any
   of the client's endpoints.

4.6.3.  Support a reconnection strategy

   Assuming a NETCONF client has more than one endpoint, then it becomes
   necessary to configure how a NETCONF server should reconnect to the
   client should it lose its connection to one the client's endpoints.
   For instance, the NETCONF server may start with first endpoint
   defined in a user-ordered list of endpoints or with the last
   endpoints it was connected to.

4.6.4.  Support both persistent and periodic connections

   NETCONF clients may vary greatly on how frequently they need to
   interact with a NETCONF server, how responsive interactions need to
   be, and how many simultaneous connections they can support.  Some
   clients may need a persistent connection to servers to optimize real-
   time interactions, while others prefer periodic interactions in order
   to minimize resource requirements.  Therefore, when it is necessary
   for server to initiate connections, it should be configurable if the
   connection is persistent or periodic.





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4.6.5.  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.

4.6.6.  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 NETCONF
   client requirements, and therefore keep-alive settings should be
   configurable on a per-client basis.

4.6.7.  Customizations for periodic connections

   If a periodic connection is desired, it is necessary for the NETCONF
   server to know how often it should connect.  This frequency
   determines the maximum amount of time a NETCONF client may have to
   wait to send data to a server.  A server may connect to a client
   before this interval expires if desired (e.g., to send data to a
   client).

5.  Security Considerations

   A denial of service (DoS) attack MAY occur if the NETCONF server
   limits the maximum number of NETCONF sessions it will accept (i.e.
   the 'max-sessions' field in the ietf-netconf-server module is not
   zero) and either the "hello-timeout" or "idle-timeout" fields in
   ietf-netconf-server module have been set to indicate the NETCONF
   server should wait forever (i.e. set to zero).

   The YANG module defined in this document uses groupings defined in
   [I-D.ietf-netconf-ssh-client-server] and
   [I-D.ietf-netconf-tls-client-server].  Please see the Security
   Considerations section in those documents for concerns related those
   groupings.

   The YANG module defined in this document is designed to be accessed
   via YANG based management protocols, such as NETCONF [RFC6241] and
   RESTCONF [RFC8040].  Both of these protocols have mandatory-to-



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   implement secure transport layers (e.g., SSH, TLS) with mutual
   authentication.

   The NETCONF access control model (NACM) [RFC6536] provides the means
   to restrict access for particular users to a pre-configured subset of
   all available protocol operations and content.

   There are a number of data nodes defined in this YANG module that 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 operations (e.g., edit-config)
   to these data nodes without proper protection can have a negative
   effect on network operations.  These are the subtrees and data nodes
   and their sensitivity/vulnerability:

      NONE

   Some of the readable data nodes in this YANG module may be considered
   sensitive or vulnerable in some network environments.  It is thus
   important to control read access (e.g., via get, get-config, or
   notification) to these data nodes.  These are the subtrees and data
   nodes and their sensitivity/vulnerability:

      NONE

   Some of the RPC operations in this YANG module may be considered
   sensitive or vulnerable in some network environments.  It is thus
   important to control access to these operations.  These are the
   operations and their sensitivity/vulnerability:

      NONE

6.  IANA Considerations

6.1.  The IETF XML Registry

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

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




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6.2.  The YANG Module Names Registry

   This document registers two YANG modules in the YANG Module Names
   registry [RFC7950].  Following the format in [RFC7950], the the
   following registrations are requested:

      name:         ietf-netconf-client
      namespace:    urn:ietf:params:xml:ns:yang:ietf-netconf-client
      prefix:       ncc
      reference:    RFC XXXX

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

7.  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, Mehmet Ersue, Balazs Kovacs, David
   Lamparter, Alan Luchuk, Ladislav Lhotka, Radek Krejci, Tom Petch,
   Phil Shafer, Sean Turner, and Bert Wijnen.

   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.

8.  References

8.1.  Normative References

   [I-D.ietf-netconf-keystore]
              Watsen, K., "Keystore Model", draft-ietf-netconf-
              keystore-02 (work in progress), June 2017.

   [I-D.ietf-netconf-ssh-client-server]
              Watsen, K. and G. Wu, "SSH Client and Server Models",
              draft-ietf-netconf-ssh-client-server-03 (work in
              progress), June 2017.

   [I-D.ietf-netconf-tls-client-server]
              Watsen, K. and G. Wu, "TLS Client and Server Models",
              draft-ietf-netconf-tls-client-server-03 (work in
              progress), June 2017.






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

   [RFC6241]  Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
              and A. Bierman, Ed., "Network Configuration Protocol
              (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
              <http://www.rfc-editor.org/info/rfc6241>.

   [RFC6242]  Wasserman, M., "Using the NETCONF Protocol over Secure
              Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, June 2011,
              <http://www.rfc-editor.org/info/rfc6242>.

   [RFC6991]  Schoenwaelder, J., Ed., "Common YANG Data Types",
              RFC 6991, DOI 10.17487/RFC6991, July 2013,
              <http://www.rfc-editor.org/info/rfc6991>.

   [RFC7407]  Bjorklund, M. and J. Schoenwaelder, "A YANG Data Model for
              SNMP Configuration", RFC 7407, DOI 10.17487/RFC7407,
              December 2014, <http://www.rfc-editor.org/info/rfc7407>.

   [RFC7589]  Badra, M., Luchuk, A., and J. Schoenwaelder, "Using the
              NETCONF Protocol over Transport Layer Security (TLS) with
              Mutual X.509 Authentication", RFC 7589,
              DOI 10.17487/RFC7589, June 2015,
              <http://www.rfc-editor.org/info/rfc7589>.

   [RFC7950]  Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
              RFC 7950, DOI 10.17487/RFC7950, August 2016,
              <http://www.rfc-editor.org/info/rfc7950>.

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

8.2.  Informative References

   [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
              DOI 10.17487/RFC3688, January 2004,
              <http://www.rfc-editor.org/info/rfc3688>.

   [RFC4252]  Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH)
              Authentication Protocol", RFC 4252, DOI 10.17487/RFC4252,
              January 2006, <http://www.rfc-editor.org/info/rfc4252>.






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   [RFC4253]  Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH)
              Transport Layer Protocol", RFC 4253, DOI 10.17487/RFC4253,
              January 2006, <http://www.rfc-editor.org/info/rfc4253>.

   [RFC4254]  Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH)
              Connection Protocol", RFC 4254, DOI 10.17487/RFC4254,
              January 2006, <http://www.rfc-editor.org/info/rfc4254>.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246,
              DOI 10.17487/RFC5246, August 2008,
              <http://www.rfc-editor.org/info/rfc5246>.

   [RFC6536]  Bierman, A. and M. Bjorklund, "Network Configuration
              Protocol (NETCONF) Access Control Model", RFC 6536,
              DOI 10.17487/RFC6536, March 2012,
              <http://www.rfc-editor.org/info/rfc6536>.

   [RFC8040]  Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
              Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
              <http://www.rfc-editor.org/info/rfc8040>.

   [RFC8071]  Watsen, K., "NETCONF Call Home and RESTCONF Call Home",
              RFC 8071, DOI 10.17487/RFC8071, February 2017,
              <http://www.rfc-editor.org/info/rfc8071>.


























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Appendix A.  Change Log

A.1.  server-model-09 to 00

   o  This draft was split out from draft-ietf-netconf-server-model-09.

   o  Added in previously missing ietf-netconf-client module.

   o  Added in new features 'listen' and 'call-home' so future
      transports can be augmented in.

A.2.  00 to 01

   o  Renamed "keychain" to "keystore".

A.3.  01 to 02

   o  Added to ietf-netconf-client ability to connected to a cluster of
      endpoints, including a reconnection-strategy.

   o  Added to ietf-netconf-client the ability to configure connection-
      type and also keep-alive strategy.

   o  Updated both modules to accomodate new groupings in the ssh/tls
      drafts.

A.4.  02 to 03

   o  Refined use of tls-client-grouping to add a must statement
      indicating that the TLS client must specify a client-certificate.

   o  Changed 'netconf-client' to be a grouping (not a container).

A.5.  03 to 04

   o  Added RFC 8174 to Requirements Language Section.

   o  Replaced refine statement in ietf-netconf-client to add a
      mandatory true.

   o  Added refine statement in ietf-netconf-server to add a must
      statement.

   o  Now there are containers and groupings, for both the client and
      server models.






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Internet-Draft      NETCONF Client and Server Models           July 2017


Authors' Addresses

   Kent Watsen
   Juniper Networks

   EMail: kwatsen@juniper.net


   Gary Wu
   Cisco Networks

   EMail: garywu@cisco.com


   Juergen Schoenwaelder
   Jacobs University Bremen

   EMail: j.schoenwaelder@jacobs-university.de

































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